source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1621

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY architecture               "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY agent-driven-negotiation   "<xref target='Part3' x:rel='#agent-driven.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY abnf-extension             "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY whitespace                 "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY field-components           "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY intermediaries             "<xref target='Part1' x:rel='#intermediaries' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY chunked-encoding           "<xref target='Part1' x:rel='#chunked.encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-connection          "<xref target='Part1' x:rel='#header.connection' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-content-type        "<xref target='Part3' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
64  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
65  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
66  <!ENTITY header-upgrade             "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
67  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.te' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
68  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
69  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
70  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
71  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
72  <!ENTITY media-types                "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
73  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
74  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
75  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
76  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
77  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
78  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
79  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
80  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
81  <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
82  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
83  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
84  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
85  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
86  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
87  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
88  <!ENTITY p6-head                 "<xref target='Part6' x:rel='#head.effects' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
89]>
90<?rfc toc="yes" ?>
91<?rfc symrefs="yes" ?>
92<?rfc sortrefs="yes" ?>
93<?rfc compact="yes"?>
94<?rfc subcompact="no" ?>
95<?rfc linkmailto="no" ?>
96<?rfc editing="no" ?>
97<?rfc comments="yes"?>
98<?rfc inline="yes"?>
99<?rfc rfcedstyle="yes"?>
100<?rfc-ext allow-markup-in-artwork="yes" ?>
101<?rfc-ext include-references-in-index="yes" ?>
102<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="proposed"
103     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
104     xmlns:x='http://purl.org/net/xml2rfc/ext'
105     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
106<x:link rel="prev" basename="p1-messaging"/>
107<x:link rel="next" basename="p3-payload"/>
108<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
109<front>
110
111  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics</title>
112
113  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
114    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
115    <address>
116      <postal>
117        <street>345 Park Ave</street>
118        <city>San Jose</city>
119        <region>CA</region>
120        <code>95110</code>
121        <country>USA</country>
122      </postal>
123      <email>fielding@gbiv.com</email>
124      <uri>http://roy.gbiv.com/</uri>
125    </address>
126  </author>
127
128  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
129    <organization abbrev="W3C">World Wide Web Consortium</organization>
130    <address>
131      <postal>
132        <street>W3C / ERCIM</street>
133        <street>2004, rte des Lucioles</street>
134        <city>Sophia-Antipolis</city>
135        <region>AM</region>
136        <code>06902</code>
137        <country>France</country>
138      </postal>
139      <email>ylafon@w3.org</email>
140      <uri>http://www.raubacapeu.net/people/yves/</uri>
141    </address>
142  </author>
143
144  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
145    <organization abbrev="greenbytes">greenbytes GmbH</organization>
146    <address>
147      <postal>
148        <street>Hafenweg 16</street>
149        <city>Muenster</city><region>NW</region><code>48155</code>
150        <country>Germany</country>
151      </postal>
152      <phone>+49 251 2807760</phone>
153      <facsimile>+49 251 2807761</facsimile>
154      <email>julian.reschke@greenbytes.de</email>
155      <uri>http://greenbytes.de/tech/webdav/</uri>
156    </address>
157  </author>
158
159  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
160  <workgroup>HTTPbis Working Group</workgroup>
161
162<abstract>
163<t>
164   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
165   distributed, collaborative, hypertext information systems. HTTP has been in
166   use by the World Wide Web global information initiative since 1990. This
167   document is Part 2 of the seven-part specification that defines the protocol
168   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
169</t>
170<t>
171   Part 2 defines the semantics of HTTP messages as expressed by request
172   methods, request header fields, response status codes, and response header
173   fields.
174</t>
175</abstract>
176
177<note title="Editorial Note (To be removed by RFC Editor)">
178  <t>
179    Discussion of this draft should take place on the HTTPBIS working group
180    mailing list (ietf-http-wg@w3.org), which is archived at
181    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
182  </t>
183  <t>
184    The current issues list is at
185    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
186    documents (including fancy diffs) can be found at
187    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
188  </t>
189  <t>
190    The changes in this draft are summarized in <xref target="changes.since.19"/>.
191  </t>
192</note>
193</front>
194<middle>
195<section title="Introduction" anchor="introduction">
196<t>
197   This document defines HTTP/1.1 request and response semantics.  Each HTTP
198   message, as defined in &messaging;, is in the form of either a request or
199   a response.  An HTTP server listens on a connection for HTTP requests and
200   responds to each request, in the order received on that connection, with
201   one or more HTTP response messages.  This document defines the commonly
202   agreed upon semantics of the HTTP uniform interface, the intentions defined
203   by each request method, and the various response messages that might be
204   expected as a result of applying that method to the target resource.
205</t>
206<t>
207   This document is currently disorganized in order to minimize the changes
208   between drafts and enable reviewers to see the smaller errata changes.
209   A future draft will reorganize the sections to better reflect the content.
210   In particular, the sections will be ordered according to the typical
211   processing of an HTTP request message (after message parsing): resource
212   mapping, methods, request modifying header fields, response status,
213   status modifying header fields, and resource metadata.  The current mess
214   reflects how widely dispersed these topics and associated requirements
215   had become in <xref target="RFC2616"/>.
216</t>
217
218<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
219<t>
220   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
221   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
222   document are to be interpreted as described in <xref target="RFC2119"/>.
223</t>
224<t>
225   This document defines conformance criteria for several roles in HTTP
226   communication, including Senders, Recipients, Clients, Servers, User-Agents,
227   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
228   for definitions of these terms.
229</t>
230<t>
231   An implementation is considered conformant if it complies with all of the
232   requirements associated with its role(s). Note that SHOULD-level requirements
233   are relevant here, unless one of the documented exceptions is applicable.
234</t>
235<t>
236   This document also uses ABNF to define valid protocol elements
237   (<xref target="notation"/>). In addition to the prose requirements placed
238   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
239</t>
240<t>
241   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
242   protocol element from an invalid construct. However, HTTP does not define
243   specific error handling mechanisms, except in cases where it has direct
244   impact on security. This is because different uses of the protocol require
245   different error handling strategies; for example, a Web browser may wish to
246   transparently recover from a response where the Location header field
247   doesn't parse according to the ABNF, whereby in a systems control protocol
248   using HTTP, this type of error recovery could lead to dangerous consequences.
249</t>
250</section>
251
252<section title="Syntax Notation" anchor="notation">
253  <x:anchor-alias value="CR"/>
254  <x:anchor-alias value="DIGIT"/>
255  <x:anchor-alias value="LF"/>
256  <x:anchor-alias value="HTAB"/>
257  <x:anchor-alias value="VCHAR"/>
258  <x:anchor-alias value="SP"/>
259<t>
260   This specification uses the Augmented Backus-Naur Form (ABNF) notation
261   of <xref target="RFC5234"/> with the list rule extension defined in
262   &notation;<xref target="collected.abnf"/> shows the collected ABNF
263   with the list rule expanded.
264</t>
265<t>
266  The following core rules are included by
267  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
268  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
269  DIGIT (decimal 0-9), DQUOTE (double quote),
270  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
271  OCTET (any 8-bit sequence of data), SP (space), and
272  VCHAR (any visible US-ASCII character).
273</t>
274
275<section title="Core Rules" anchor="core.rules">
276  <x:anchor-alias value="obs-text"/>
277  <x:anchor-alias value="quoted-string"/>
278  <x:anchor-alias value="token"/>
279  <x:anchor-alias value="BWS"/>
280  <x:anchor-alias value="OWS"/>
281  <x:anchor-alias value="RWS"/>
282<t>
283  The core rules below are defined in <xref target="Part1"/>:
284</t>
285<figure><artwork type="abnf2616">
286  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
287  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
288  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &whitespace;&gt;
289  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &field-components;&gt;
290  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
291  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
292</artwork></figure>
293</section>
294
295<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
296  <x:anchor-alias value="absolute-URI"/>
297  <x:anchor-alias value="comment"/>
298  <x:anchor-alias value="partial-URI"/>
299  <x:anchor-alias value="URI-reference"/>
300<t>
301  The ABNF rules below are defined in other parts:
302</t>
303<figure><!--Part1--><artwork type="abnf2616">
304  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
305  <x:ref>comment</x:ref>       = &lt;comment, defined in &field-components;&gt;
306  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
307  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
308</artwork></figure>
309</section>
310</section>
311</section>
312
313<section title="Methods" anchor="methods">
314  <x:anchor-alias value="method"/>
315<t>
316   The method token indicates the request method to be performed on the target
317   resource (&effective-request-uri;). The method is case-sensitive.
318</t>
319<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
320  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
321</artwork></figure>
322<t>
323   The list of methods allowed by a resource can be specified in an
324   Allow header field (<xref target="header.allow"/>). The status code of the response
325   always notifies the client whether a method is currently allowed on a
326   resource, since the set of allowed methods can change dynamically. An
327   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
328   if the method is known by the origin server but not allowed for the
329   resource, and 501 (Not Implemented) if the method is
330   unrecognized or not implemented by the origin server. The methods GET
331   and HEAD &MUST; be supported by all general-purpose servers. All other
332   methods are &OPTIONAL;; however, if the above methods are implemented,
333   they &MUST; be implemented with the same semantics as those specified
334   in <xref target="method.definitions"/>.
335</t>
336
337<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
338
339<section title="Safe Methods" anchor="safe.methods">
340<iref item="Safe Methods" primary="true"/>
341<t>
342   Implementors need to be aware that the software represents the user in
343   their interactions over the Internet, and need to allow
344   the user to be aware of any actions they take which might have an
345   unexpected significance to themselves or others.
346</t>
347<t>
348   In particular, the convention has been established that the GET, HEAD,
349   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
350   of taking an action other than retrieval. These request methods ought
351   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
352   This allows user agents to represent other methods, such as POST, PUT
353   and DELETE, in a special way, so that the user is made aware of the
354   fact that a possibly unsafe action is being requested.
355</t>
356<t>
357   Naturally, it is not possible to ensure that the server does not
358   generate side-effects as a result of performing a GET request; in
359   fact, some dynamic resources consider that a feature. The important
360   distinction here is that the user did not request the side-effects,
361   so therefore cannot be held accountable for them.
362</t>
363</section>
364
365<section title="Idempotent Methods" anchor="idempotent.methods">
366<iref item="Idempotent Methods" primary="true"/>
367<t>
368   Request methods can also have the property of "idempotence" in that,
369   aside from error or expiration issues, the intended effect of multiple
370   identical requests is the same as for a single request.
371   PUT, DELETE, and all safe request methods are idempotent.
372   It is important to note that idempotence refers only to changes
373   requested by the client: a server is free to change its state due
374   to multiple requests for the purpose of tracking those requests,
375   versioning of results, etc.
376</t>
377</section>
378</section>
379
380<section title="Method Registry" anchor="method.registry">
381<t>
382  The HTTP Method Registry defines the name space for the method token in the
383  Request line of an HTTP request.
384</t>
385<t>
386  Registrations &MUST; include the following fields:
387  <list style="symbols">
388    <t>Method Name (see <xref target="methods"/>)</t>
389    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
390    <t>Pointer to specification text</t>
391  </list>
392</t>
393<t>
394  Values to be added to this name space require IETF Review
395  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
396</t>
397<t>
398  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
399</t>
400
401<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
402<t>
403   When it is necessary to express new semantics for a HTTP request that
404   aren't specific to a single application or media type, and currently defined
405   methods are inadequate, it may be appropriate to register a new method.
406</t>
407<t>
408   HTTP methods are generic; that is, they are potentially applicable to any
409   resource, not just one particular media type, "type" of resource, or
410   application. As such, it is preferred that new HTTP methods be registered
411   in a document that isn't specific to a single application, so that this is
412   clear.
413</t>
414<t>
415   Due to the parsing rules defined in &message-body;, definitions of HTTP
416   methods cannot prohibit the presence of a message body on either the request
417   or the response message (with responses to HEAD requests being the single
418   exception). Definitions of new methods cannot change this rule, but they can
419   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
420</t>
421<t>
422   New method definitions need to indicate whether they are safe (<xref
423   target="safe.methods"/>), what semantics (if any) the request body has,
424   and whether they are idempotent (<xref target="idempotent.methods"/>).
425   They also need to state whether they can be cached (&caching;); in
426   particular what conditions a cache may store the response, and under what
427   conditions such a stored response may be used to satisfy a subsequent
428   request.
429</t>
430</section>
431</section>
432
433<section title="Method Definitions" anchor="method.definitions">
434
435<section title="OPTIONS" anchor="OPTIONS">
436  <rdf:Description>
437    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
438  </rdf:Description>
439  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
440  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
441<t>
442   The OPTIONS method requests information about the
443   communication options available on the request/response chain
444   identified by the effective request URI. This method allows a client to
445   determine the options and/or requirements associated with a resource,
446   or the capabilities of a server, without implying a resource action
447   or initiating a resource retrieval.
448</t>
449<t>
450   Responses to the OPTIONS method are not cacheable.
451</t>
452<t>
453   If the OPTIONS request includes a message body (as indicated by the
454   presence of Content-Length or Transfer-Encoding), then the media type
455   &MUST; be indicated by a Content-Type field. Although this
456   specification does not define any use for such a body, future
457   extensions to HTTP might use the OPTIONS body to make more detailed
458   queries on the server.
459</t>
460<t>
461   If the request-target (&request-target;) is an asterisk ("*"),
462   the OPTIONS request is
463   intended to apply to the server in general rather than to a specific
464   resource. Since a server's communication options typically depend on
465   the resource, the "*" request is only useful as a "ping" or "no-op"
466   type of method; it does nothing beyond allowing the client to test
467   the capabilities of the server. For example, this can be used to test
468   a proxy for HTTP/1.1 conformance (or lack thereof).
469</t>
470<t>
471   If the request-target is not an asterisk, the OPTIONS request applies
472   only to the options that are available when communicating with that
473   resource.
474</t>
475<t>
476   A 200 response &SHOULD; include any header fields that indicate
477   optional features implemented by the server and applicable to that
478   resource (e.g., Allow), possibly including extensions not defined by
479   this specification. The response body, if any, &SHOULD; also include
480   information about the communication options. The format for such a
481   body is not defined by this specification, but might be defined by
482   future extensions to HTTP. Content negotiation &MAY; be used to select
483   the appropriate response format. If no response body is included, the
484   response &MUST; include a Content-Length field with a field-value of
485   "0".
486</t>
487<t>
488   The Max-Forwards header field &MAY; be used to target a
489   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
490   If no Max-Forwards field is present in the request, then the forwarded
491   request &MUST-NOT; include a Max-Forwards field.
492</t>
493</section>
494
495<section title="GET" anchor="GET">
496  <rdf:Description>
497    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
498  </rdf:Description>
499  <iref primary="true" item="GET method" x:for-anchor=""/>
500  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
501<t>
502   The GET method requests transfer of a current representation of
503   the target resource.
504</t>
505<t>   
506   If the target resource is a data-producing process, it is the
507   produced data which shall be returned as the representation in the response and not
508   the source text of the process, unless that text happens to be the output of
509   the process.
510</t>
511<t>
512   The semantics of the GET method change to a "conditional GET" if the
513   request message includes an If-Modified-Since, If-Unmodified-Since,
514   If-Match, If-None-Match, or If-Range header field. A conditional GET
515   requests that the representation be transferred only under the
516   circumstances described by the conditional header field(s). The
517   conditional GET request is intended to reduce unnecessary network
518   usage by allowing cached representations to be refreshed without requiring
519   multiple requests or transferring data already held by the client.
520</t>
521<t>
522   The semantics of the GET method change to a "partial GET" if the
523   request message includes a Range header field. A partial GET requests
524   that only part of the representation be transferred, as described in &header-range;.
525   The partial GET request is intended to reduce unnecessary
526   network usage by allowing partially-retrieved representations to be
527   completed without transferring data already held by the client.
528</t>
529<t>
530   Bodies on GET requests have no defined semantics. Note that sending a body
531   on a GET request might cause some existing implementations to reject the
532   request.
533</t>
534<t>
535   The response to a GET request is cacheable and &MAY; be used to satisfy
536   subsequent GET and HEAD requests (see &caching;).
537</t>
538<t>
539   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
540</t>
541</section>
542
543<section title="HEAD" anchor="HEAD">
544  <rdf:Description>
545    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
546  </rdf:Description>
547  <iref primary="true" item="HEAD method" x:for-anchor=""/>
548  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
549<t>
550   The HEAD method is identical to GET except that the server &MUST-NOT;
551   return a message body in the response. The metadata contained
552   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
553   to the information sent in response to a GET request. This method can
554   be used for obtaining metadata about the representation implied by the
555   request without transferring the representation body. This method is
556   often used for testing hypertext links for validity, accessibility,
557   and recent modification.
558</t>
559<t>
560   The response to a HEAD request is cacheable and &MAY; be used to satisfy
561   a subsequent HEAD request. It also has potential side effects on
562   previously stored responses to GET; see &p6-head;.
563</t>
564<t>
565   Bodies on HEAD requests have no defined semantics. Note that sending a body
566   on a HEAD request might cause some existing implementations to reject the
567   request.
568</t>
569</section>
570
571<section title="POST" anchor="POST">
572  <iref primary="true" item="POST method" x:for-anchor=""/>
573  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
574<t>
575   The POST method requests that the origin server accept the
576   representation enclosed in the request as data to be processed by the
577   target resource. POST is designed to allow a uniform method to cover the
578   following functions:
579  <list style="symbols">
580    <t>
581      Annotation of existing resources;
582    </t>
583    <t>
584        Posting a message to a bulletin board, newsgroup, mailing list,
585        or similar group of articles;
586    </t>
587    <t>
588        Providing a block of data, such as the result of submitting a
589        form, to a data-handling process;
590    </t>
591    <t>
592        Extending a database through an append operation.
593    </t>
594  </list>
595</t>
596<t>
597   The actual function performed by the POST method is determined by the
598   server and is usually dependent on the effective request URI.
599</t>
600<t>
601   The action performed by the POST method might not result in a
602   resource that can be identified by a URI. In this case, either 200
603   (OK) or 204 (No Content) is the appropriate response status code,
604   depending on whether or not the response includes a representation that
605   describes the result.
606</t>
607<t>
608   If a resource has been created on the origin server, the response
609   &SHOULD; be 201 (Created) and contain a representation which describes the
610   status of the request and refers to the new resource, and a Location
611   header field (see <xref target="header.location"/>).
612</t>
613<t>
614   Responses to POST requests are only cacheable when they
615   include explicit freshness information (see &p6-explicit;). A
616   cached POST response with a Content-Location header field
617   (see &header-content-location;) whose value is the effective
618   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
619</t>
620<t>
621   Note that POST caching is not widely implemented.
622   However, the 303 (See Other) response can be used to direct the
623   user agent to retrieve a cacheable representation of the resource.
624</t>
625</section>
626
627<section title="PUT" anchor="PUT">
628  <iref primary="true" item="PUT method" x:for-anchor=""/>
629  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
630<t>
631   The PUT method requests that the state of the target resource
632   be created or replaced with the state defined by the representation
633   enclosed in the request message payload.  A successful PUT of a given
634   representation would suggest that a subsequent GET on that same target
635   resource will result in an equivalent representation being returned in
636   a 200 (OK) response.  However, there is no guarantee that such a state
637   change will be observable, since the target resource might be acted
638   upon by other user agents in parallel, or might be subject to dynamic
639   processing by the origin server, before any subsequent GET is received.
640   A successful response only implies that the user agent's intent was
641   achieved at the time of its processing by the origin server.
642</t>
643<t>   
644   If the target resource does not have a current representation and
645   the PUT successfully creates one, then the origin server &MUST; inform
646   the user agent by sending a 201 (Created) response.  If the target
647   resource does have a current representation and that representation is
648   successfully modified in accordance with the state of the enclosed
649   representation, then either a 200 (OK) or 204 (No Content) response
650   &SHOULD; be sent to indicate successful completion of the request.
651</t>
652<t>
653   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
654   as part of the resource state).
655</t>
656<t>
657   An origin server &SHOULD; verify that the PUT representation is
658   consistent with any constraints which the server has for the target
659   resource that cannot or will not be changed by the PUT.  This is
660   particularly important when the origin server uses internal
661   configuration information related to the URI in order to set the
662   values for representation metadata on GET responses.  When a PUT
663   representation is inconsistent with the target resource, the origin
664   server &SHOULD; either make them consistent, by transforming the
665   representation or changing the resource configuration, or respond
666   with an appropriate error message containing sufficient information
667   to explain why the representation is unsuitable.  The 409 (Conflict)
668   or 415 (Unsupported Media Type) status codes are suggested, with the
669   latter being specific to constraints on Content-Type values.
670</t>
671<t>
672   For example, if the target resource is configured to always have a
673   Content-Type of "text/html" and the representation being PUT has a
674   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
675   (a) reconfigure the target resource to reflect the new media type;
676   (b) transform the PUT representation to a format consistent with that
677   of the resource before saving it as the new resource state; or,
678   (c) reject the request with a 415 response indicating that the target
679   resource is limited to "text/html", perhaps including a link to a
680   different resource that would be a suitable target for the new
681   representation.
682</t>
683<t>
684   HTTP does not define exactly how a PUT method affects the state
685   of an origin server beyond what can be expressed by the intent of
686   the user agent request and the semantics of the origin server response.
687   It does not define what a resource might be, in any sense of that
688   word, beyond the interface provided via HTTP.  It does not define
689   how resource state is "stored", nor how such storage might change
690   as a result of a change in resource state, nor how the origin server
691   translates resource state into representations.  Generally speaking,
692   all implementation details behind the resource interface are
693   intentionally hidden by the server.
694</t>
695<t>
696   The fundamental difference between the POST and PUT methods is
697   highlighted by the different intent for the target resource.
698   The target resource in a POST request is intended to handle the
699   enclosed representation as a data-accepting process, such as for
700   a gateway to some other protocol or a document that accepts annotations.
701   In contrast, the target resource in a PUT request is intended to
702   take the enclosed representation as a new or replacement value.
703   Hence, the intent of PUT is idempotent and visible to intermediaries,
704   even though the exact effect is only known by the origin server.
705</t>
706<t>
707   Proper interpretation of a PUT request presumes that the user agent
708   knows what target resource is desired.  A service that is intended
709   to select a proper URI on behalf of the client, after receiving
710   a state-changing request, &SHOULD; be implemented using the POST
711   method rather than PUT.  If the origin server will not make the
712   requested PUT state change to the target resource and instead
713   wishes to have it applied to a different resource, such as when the
714   resource has been moved to a different URI, then the origin server
715   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
716   then make its own decision regarding whether or not to redirect the
717   request.
718</t>
719<t>
720   A PUT request applied to the target resource &MAY; have side-effects
721   on other resources.  For example, an article might have a URI for
722   identifying "the current version" (a resource) which is separate
723   from the URIs identifying each particular version (different
724   resources that at one point shared the same state as the current version
725   resource).  A successful PUT request on "the current version" URI might
726   therefore create a new version resource in addition to changing the
727   state of the target resource, and might also cause links to be added
728   between the related resources.
729</t>
730<t>
731   An origin server &SHOULD; reject any PUT request that contains a
732   Content-Range header field, since it might be misinterpreted as
733   partial content (or might be partial content that is being mistakenly
734   PUT as a full representation).  Partial content updates are
735   possible by targeting a separately identified resource with state
736   that overlaps a portion of the larger resource, or by using a
737   different method that has been specifically defined for partial
738   updates (for example, the PATCH method defined in
739   <xref target="RFC5789"/>).
740</t>
741<t>
742   Responses to the PUT method are not cacheable. If a PUT request passes
743   through a cache that has one or more stored responses for the effective
744   request URI, those stored responses will be invalidated (see
745   &p6-invalid;).
746</t>
747</section>
748
749<section title="DELETE" anchor="DELETE">
750  <iref primary="true" item="DELETE method" x:for-anchor=""/>
751  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
752<t>
753   The DELETE method requests that the origin server delete the target
754   resource. This method &MAY; be overridden by
755   human intervention (or other means) on the origin server. The client cannot
756   be guaranteed that the operation has been carried out, even if the
757   status code returned from the origin server indicates that the action
758   has been completed successfully. However, the server &SHOULD-NOT; 
759   indicate success unless, at the time the response is given, it
760   intends to delete the resource or move it to an inaccessible
761   location.
762</t>
763<t>
764   A successful response &SHOULD; be 200 (OK) if the response includes an
765   representation describing the status, 202 (Accepted) if the action has not
766   yet been enacted, or 204 (No Content) if the action has been enacted
767   but the response does not include a representation.
768</t>
769<t>
770   Bodies on DELETE requests have no defined semantics. Note that sending a body
771   on a DELETE request might cause some existing implementations to reject the
772   request.
773</t>
774<t>
775   Responses to the DELETE method are not cacheable. If a DELETE request
776   passes through a cache that has one or more stored responses for the
777   effective request URI, those stored responses will be invalidated (see
778   &p6-invalid;).
779</t>
780</section>
781
782<section title="TRACE" anchor="TRACE">
783  <rdf:Description>
784    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
785  </rdf:Description>
786  <iref primary="true" item="TRACE method" x:for-anchor=""/>
787  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
788<t>
789   The TRACE method requests a remote, application-layer loop-back
790   of the request message. The final recipient of the request
791   &SHOULD; reflect the message received back to the client as the
792   message body of a 200 (OK) response. The final recipient is either the
793   origin server or the first proxy to receive a Max-Forwards
794   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
795   A TRACE request &MUST-NOT; include a message body.
796</t>
797<t>
798   TRACE allows the client to see what is being received at the other
799   end of the request chain and use that data for testing or diagnostic
800   information. The value of the Via header field (&header-via;) is of
801   particular interest, since it acts as a trace of the request chain.
802   Use of the Max-Forwards header field allows the client to limit the
803   length of the request chain, which is useful for testing a chain of
804   proxies forwarding messages in an infinite loop.
805</t>
806<t>
807   If the request is valid, the response &SHOULD; have a Content-Type of
808   "message/http" (see &media-type-message-http;) and contain a message body
809   that encloses a copy of the entire request message.
810   Responses to the TRACE method are not cacheable.
811</t>
812</section>
813
814<section title="CONNECT" anchor="CONNECT">
815  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
816  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
817<t>
818   The CONNECT method requests that the proxy establish a tunnel
819   to the request-target and, if successful, thereafter restrict its behavior
820   to blind forwarding of packets until the connection is closed.
821</t>
822<t>
823   When using CONNECT, the request-target &MUST; use the authority form
824   (&request-target;); i.e., the request-target consists of only the
825   host name and port number of the tunnel destination, separated by a colon.
826   For example,
827</t>
828<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
829CONNECT server.example.com:80 HTTP/1.1
830Host: server.example.com:80
831
832</artwork></figure>
833<t>
834   Any successful (2xx) response to a CONNECT request indicates that the
835   proxy has established a connection to the requested host and port,
836   and has switched to tunneling the current connection to that server
837   connection.
838   The tunneled data from the server begins immediately after the blank line
839   that concludes the successful response's header block.
840   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
841   header fields in a successful response.
842   A client &MUST; ignore any Content-Length or Transfer-Encoding header
843   fields received in a successful response.
844</t>
845<t>
846   Any response other than a successful response indicates that the tunnel
847   has not yet been formed and that the connection remains governed by HTTP.
848</t>
849<t>
850   Proxy authentication might be used to establish the
851   authority to create a tunnel:
852</t>
853<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
854CONNECT server.example.com:80 HTTP/1.1
855Host: server.example.com:80
856Proxy-Authorization: basic aGVsbG86d29ybGQ=
857
858</artwork></figure>
859<t>
860   A message body on a CONNECT request has no defined semantics. Sending a
861   body on a CONNECT request might cause existing implementations to reject
862   the request.
863</t>
864<t>
865   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
866   to server &MAY; be sent immediately after the request (before a response
867   is received). The usual caveats also apply:
868   data may be discarded if the eventual response is negative, and the
869   connection may be reset with no response if more than one TCP segment
870   is outstanding.
871</t>
872<t>
873   It may be the case that the proxy itself can only reach the requested
874   origin server through another proxy.  In this case, the first proxy
875   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
876   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
877   unless it has either a direct or tunnel connection established to the
878   authority.
879</t>
880<t>
881   If at any point either one of the peers gets disconnected, any
882   outstanding data that came from that peer will be passed to the other
883   one, and after that also the other connection will be terminated by
884   the proxy. If there is outstanding data to that peer undelivered,
885   that data will be discarded.
886</t>
887<t>
888   An origin server which receives a CONNECT request for itself &MAY;
889   respond with a 2xx status code to indicate that a connection is
890   established.  However, most origin servers do not implement CONNECT.
891</t>
892</section>
893</section>
894
895</section>
896
897<section title="Header Fields" anchor="header.fields">
898<t>
899   Header fields are key value pairs that can be used to communicate data about
900   the message, its payload, the target resource, or about the connection
901   itself (i.e., control data).  See &header-fields; for a general definition
902   of their syntax.
903</t>
904
905<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
906<t>
907   New header fields are registered using the procedures described in
908   <xref target="RFC3864"/>.
909</t>
910<t>
911   The requirements for header field names are defined in
912   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
913   defining new fields are advised to keep the name as short as practical, and
914   not to prefix them with "X-" if they are to be registered (either
915   immediately or in the future).
916</t>
917<t>
918   New header field values typically have their syntax defined using ABNF
919   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
920   as necessary, and are usually constrained to the range of ASCII characters.
921   Header fields needing a greater range of characters can use an encoding
922   such as the one defined in <xref target="RFC5987"/>.
923</t>
924<t>
925   Because commas (",") are used as a generic delimiter between field-values,
926   they need to be treated with care if they are allowed in the field-value's
927   payload. Typically, components that might contain a comma are protected with
928   double-quotes using the quoted-string ABNF production (&field-components;).
929</t>
930<t>
931   For example, a textual date and a URI (either of which might contain a comma)
932   could be safely carried in field-values like these:
933</t>
934<figure><artwork type="example">
935  Example-URI-Field: "http://example.com/a.html,foo",
936                     "http://without-a-comma.example.com/"
937  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
938</artwork></figure>
939<t>
940   Note that double quote delimiters almost always are used with the
941   quoted-string production; using a different syntax inside double quotes
942   will likely cause unnecessary confusion.
943</t>
944<t>
945   Many header fields use a format including (case-insensitively) named
946   parameters (for instance, Content-Type, defined in &header-content-type;).
947   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
948   parameter value enables recipients to use existing parser components. When
949   allowing both forms, the meaning of a parameter value ought to be
950   independent of the syntax used for it (for an example, see the notes on
951   parameter handling for media types in &media-types;).
952</t>
953<t>
954   Authors of specifications defining new header fields are advised to consider
955   documenting:
956  <list style="symbols">
957    <x:lt>
958      <t>Whether the field is a single value, or whether it can be a list
959      (delimited by commas; see &header-fields;).</t>
960      <t>If it does not use the list syntax, document how to treat messages
961      where the header field occurs multiple times (a sensible default would
962      be to ignore the header field, but this might not always be the right
963      choice).</t>
964      <t>Note that intermediaries and software libraries might combine
965      multiple header field instances into a single one, despite the header
966      field not allowing this. A robust format enables recipients to discover
967      these situations (good example: "Content-Type", as the comma can only
968      appear inside quoted strings; bad example: "Location", as a comma can
969      occur inside a URI).</t>
970    </x:lt>
971    <x:lt><t>Under what conditions the header field can be used; e.g., only in
972    responses or requests, in all messages, only on responses to a particular
973    request method.</t></x:lt>
974    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
975    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
976    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
977    field's value, insert or delete it.</t></x:lt>
978    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
979    <x:lt><t>Whether the header field is useful or allowable in trailers (see
980    &chunked-encoding;).</t></x:lt>
981    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
982  </list>
983</t>
984</section>
985
986<section title="Request Header Fields" anchor="request.header.fields">
987  <x:anchor-alias value="request-header"/>
988<t>
989   The request header fields allow the client to pass additional
990   information about the request, and about the client itself, to the
991   server. These fields act as request modifiers, with semantics
992   equivalent to the parameters on a programming language method
993   invocation.
994</t>
995<texttable align="left">
996  <ttcol>Header Field Name</ttcol>
997  <ttcol>Defined in...</ttcol>
998
999  <c>Accept</c> <c>&header-accept;</c>
1000  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
1001  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
1002  <c>Accept-Language</c> <c>&header-accept-language;</c>
1003  <c>Authorization</c> <c>&header-authorization;</c>
1004  <c>Expect</c> <c><xref target="header.expect"/></c>
1005  <c>From</c> <c><xref target="header.from"/></c>
1006  <c>Host</c> <c>&header-host;</c>
1007  <c>If-Match</c> <c>&header-if-match;</c>
1008  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
1009  <c>If-None-Match</c> <c>&header-if-none-match;</c>
1010  <c>If-Range</c> <c>&header-if-range;</c>
1011  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
1012  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
1013  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
1014  <c>Range</c> <c>&header-range;</c>
1015  <c>Referer</c> <c><xref target="header.referer"/></c>
1016  <c>TE</c> <c>&header-te;</c>
1017  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
1018</texttable>
1019</section>
1020
1021<section title="Response Header Fields" anchor="response.header.fields">
1022  <x:anchor-alias value="response-header"/>
1023<t>
1024   The response header fields allow the server to pass additional
1025   information about the response which cannot be placed in the status-line.
1026   These header fields give information about the server and about
1027   further access to the target resource (&effective-request-uri;).
1028</t>
1029<texttable align="left">
1030  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
1031
1032  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
1033  <c>Age</c> <c>&header-age;</c>
1034  <c>Allow</c> <c><xref target="header.allow"/></c>
1035  <c>Date</c> <c><xref target="header.date"/></c>
1036  <c>ETag</c> <c>&header-etag;</c>
1037  <c>Location</c> <c><xref target="header.location"/></c>
1038  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
1039  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
1040  <c>Server</c> <c><xref target="header.server"/></c>
1041  <c>Vary</c> <c>&header-vary;</c>
1042  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
1043</texttable>
1044</section>
1045
1046</section>
1047
1048<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1049  <x:anchor-alias value="reason-phrase"/>
1050  <x:anchor-alias value="status-code"/>
1051  <x:anchor-alias value="extension-code"/>
1052<t>
1053   The status-code element is a 3-digit integer result code of the attempt to
1054   understand and satisfy the request.
1055</t>
1056<t>
1057   The reason-phrase is intended to give a short textual description of the
1058   status-code and is intended for a human user. The client does not need
1059   to examine or display the reason-phrase.
1060</t>
1061<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"/>
1062  <x:ref>status-code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1063  <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> )
1064</artwork></figure>
1065<t>
1066   HTTP status codes are extensible. HTTP applications are not required
1067   to understand the meaning of all registered status codes, though such
1068   understanding is obviously desirable. However, applications &MUST;
1069   understand the class of any status code, as indicated by the first
1070   digit, and treat any unrecognized response as being equivalent to the
1071   x00 status code of that class, with the exception that an
1072   unrecognized response &MUST-NOT; be cached. For example, if an
1073   unrecognized status code of 431 is received by the client, it can
1074   safely assume that there was something wrong with its request and
1075   treat the response as if it had received a 400 status code. In such
1076   cases, user agents &SHOULD; present to the user the representation enclosed
1077   with the response, since that representation is likely to include human-readable
1078   information which will explain the unusual status.
1079</t>
1080<t>
1081   The first digit of the status-code defines the class of response. The
1082   last two digits do not have any categorization role. There are 5
1083   values for the first digit:
1084  <list style="symbols">
1085    <t>
1086      1xx: Informational - Request received, continuing process
1087    </t>
1088    <t>
1089      2xx: Success - The action was successfully received,
1090        understood, and accepted
1091    </t>
1092    <t>
1093      3xx: Redirection - Further action needs to be taken in order to
1094        complete the request
1095    </t>
1096    <t>
1097      4xx: Client Error - The request contains bad syntax or cannot
1098        be fulfilled
1099    </t>
1100    <t>
1101      5xx: Server Error - The server failed to fulfill an apparently
1102        valid request
1103    </t>
1104  </list>
1105</t>
1106<t>
1107   For most status codes the response can carry a payload, in which case a
1108   Content-Type header field indicates the payload's media type
1109   (&header-content-type;).
1110</t>
1111
1112<section title="Overview of Status Codes" anchor="overview.of.status.codes">
1113<t> 
1114   The status codes listed below are defined in this specification,
1115   &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
1116   The reason phrases listed here are only recommendations &mdash; they can be
1117   replaced by local equivalents without affecting the protocol.
1118</t>
1119<texttable align="left">
1120  <ttcol>status-code</ttcol>
1121  <ttcol>reason-phrase</ttcol>
1122  <ttcol>Defined in...</ttcol>
1123 
1124  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
1125  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
1126
1127  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
1128  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
1129  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
1130  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
1131  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
1132  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
1133  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
1134
1135  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
1136  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
1137  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
1138  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
1139  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
1140  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
1141  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
1142
1143  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
1144  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
1145  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
1146  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
1147  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
1148  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
1149  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
1150  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
1151  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
1152  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
1153  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
1154  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
1155  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
1156  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
1157  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
1158  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
1159  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
1160  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
1161  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
1162
1163  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
1164  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
1165  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
1166  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
1167  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
1168  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
1169</texttable>
1170<t>
1171   Note that this list is not exhaustive &mdash; it does not include
1172   extension status codes defined in other specifications.
1173</t>
1174</section>
1175
1176<section title="Status Code Registry" anchor="status.code.registry">
1177<t>
1178  The HTTP Status Code Registry defines the name space for the status-code
1179  token in the status-line of an HTTP response.
1180</t>
1181<t>
1182  Values to be added to this name space require IETF Review
1183  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
1184</t>
1185<t>
1186  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
1187</t>
1188
1189<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
1190<t>
1191   When it is necessary to express new semantics for a HTTP response that
1192   aren't specific to a single application or media type, and currently defined
1193   status codes are inadequate, a new status code can be registered.
1194</t>
1195<t>
1196   HTTP status codes are generic; that is, they are potentially applicable to
1197   any resource, not just one particular media type, "type" of resource, or
1198   application. As such, it is preferred that new HTTP status codes be
1199   registered in a document that isn't specific to a single application, so
1200   that this is clear.
1201</t>
1202<t>
1203   Definitions of new HTTP status codes typically explain the request
1204   conditions that produce a response containing the status code (e.g.,
1205   combinations of request headers and/or method(s)), along with any
1206   interactions with response headers (e.g., those that are required, those
1207   that modify the semantics of the response).
1208</t>
1209<t>
1210   New HTTP status codes are required to fall under one of the categories
1211   defined in <xref target="status.code.and.reason.phrase"/>. To allow existing parsers to
1212   properly handle them, new status codes cannot disallow a response body,
1213   although they can mandate a zero-length response body. They can require the
1214   presence of one or more particular HTTP response header(s).
1215</t>
1216<t>
1217   Likewise, their definitions can specify that caches are allowed to use
1218   heuristics to determine their freshness (see &caching;; by default, it is
1219   not allowed), and can define how to determine the resource which they
1220   carry a representation for (see <xref
1221   target="identifying.response.associated.with.representation"/>; by default,
1222   it is anonymous).
1223</t>
1224</section>
1225
1226</section>
1227
1228<section title="Informational 1xx" anchor="status.1xx">
1229<t>
1230   This class of status code indicates a provisional response,
1231   consisting only of the status-line and optional header fields, and is
1232   terminated by an empty line. There are no required header fields for this
1233   class of status code. Since HTTP/1.0 did not define any 1xx status
1234   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1235   except under experimental conditions.
1236</t>
1237<t>
1238   A client &MUST; be prepared to accept one or more 1xx status responses
1239   prior to a regular response, even if the client does not expect a 100
1240   (Continue) status message. Unexpected 1xx status responses &MAY; be
1241   ignored by a user agent.
1242</t>
1243<t>
1244   Proxies &MUST; forward 1xx responses, unless the connection between the
1245   proxy and its client has been closed, or unless the proxy itself
1246   requested the generation of the 1xx response. (For example, if a
1247   proxy adds a "Expect: 100-continue" field when it forwards a request,
1248   then it need not forward the corresponding 100 (Continue)
1249   response(s).)
1250</t>
1251
1252<section title="100 Continue" anchor="status.100">
1253  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1254  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1255<t>
1256   The client &SHOULD; continue with its request. This interim response is
1257   used to inform the client that the initial part of the request has
1258   been received and has not yet been rejected by the server. The client
1259   &SHOULD; continue by sending the remainder of the request or, if the
1260   request has already been completed, ignore this response. The server
1261   &MUST; send a final response after the request has been completed. See
1262   &use100; for detailed discussion of the use and handling of this
1263   status code.
1264</t>
1265</section>
1266
1267<section title="101 Switching Protocols" anchor="status.101">
1268  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1269  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1270<t>
1271   The server understands and is willing to comply with the client's
1272   request, via the Upgrade message header field (&header-upgrade;), for a
1273   change in the application protocol being used on this connection. The
1274   server will switch protocols to those defined by the response's
1275   Upgrade header field immediately after the empty line which
1276   terminates the 101 response.
1277</t>
1278<t>
1279   The protocol &SHOULD; be switched only when it is advantageous to do
1280   so. For example, switching to a newer version of HTTP is advantageous
1281   over older versions, and switching to a real-time, synchronous
1282   protocol might be advantageous when delivering resources that use
1283   such features.
1284</t>
1285</section>
1286</section>
1287
1288<section title="Successful 2xx" anchor="status.2xx">
1289<t>
1290   This class of status code indicates that the client's request was
1291   successfully received, understood, and accepted.
1292</t>
1293
1294<section title="200 OK" anchor="status.200">
1295  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1296  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1297<t>
1298   The request has succeeded. The payload returned with the response
1299   is dependent on the method used in the request, for example:
1300  <list style="hanging">
1301    <t hangText="GET">
1302      a representation of the target resource is sent in the response;
1303    </t>
1304    <t hangText="HEAD">
1305      the same representation as GET, except without the message body;
1306    </t>
1307    <t hangText="POST">
1308      a representation describing or containing the result of the action;
1309    </t>
1310    <t hangText="TRACE">
1311      a representation containing the request message as received by the
1312      end server.
1313    </t>
1314  </list>
1315</t>
1316<t>
1317   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1318   freshness for 200 responses.
1319</t>
1320</section>
1321
1322<section title="201 Created" anchor="status.201">
1323  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1324  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1325<t>
1326   The request has been fulfilled and has resulted in a new resource being
1327   created.
1328</t>
1329<t>
1330   The newly created resource is typically linked to from the response payload,
1331   with the most relevant URI also being carried in the Location header field.
1332   If the newly created resource's URI is the same as the Effective Request URI,
1333   this information can be omitted (e.g., in the case of a response to a PUT
1334   request). 
1335</t>
1336<t>
1337   The origin server &MUST; create the resource before returning the 201 status
1338   code. If the action cannot be carried out immediately, the server &SHOULD;
1339   respond with 202 (Accepted) response instead.
1340</t>
1341<t>
1342   A 201 response &MAY; contain an ETag response header field indicating
1343   the current value of the entity-tag for the representation of the resource
1344   just created (see &header-etag;).
1345</t>
1346</section>
1347
1348<section title="202 Accepted" anchor="status.202">
1349  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1350  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1351<t>
1352   The request has been accepted for processing, but the processing has
1353   not been completed.  The request might or might not eventually be
1354   acted upon, as it might be disallowed when processing actually takes
1355   place. There is no facility for re-sending a status code from an
1356   asynchronous operation such as this.
1357</t>
1358<t>
1359   The 202 response is intentionally non-committal. Its purpose is to
1360   allow a server to accept a request for some other process (perhaps a
1361   batch-oriented process that is only run once per day) without
1362   requiring that the user agent's connection to the server persist
1363   until the process is completed. The representation returned with this
1364   response &SHOULD; include an indication of the request's current status
1365   and either a pointer to a status monitor or some estimate of when the
1366   user can expect the request to be fulfilled.
1367</t>
1368</section>
1369
1370<section title="203 Non-Authoritative Information" anchor="status.203">
1371  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1372  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1373<t>
1374   The representation in the response has been transformed or otherwise
1375   modified by a transforming proxy (&intermediaries;).  Note that the
1376   behavior of transforming intermediaries is controlled by the no-transform
1377   Cache-Control directive (&header-cache-control;).
1378</t>
1379<t>
1380   This status code is only appropriate when the response status code would
1381   have been 200 (OK) otherwise. When the status code before transformation
1382   would have been different, the 214 Transformation Applied warn-code
1383   (&header-warning;) is appropriate.
1384</t>
1385<t>
1386   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1387   freshness for 203 responses.
1388</t>
1389</section>
1390
1391<section title="204 No Content" anchor="status.204">
1392  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1393  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1394<t>
1395   The 204 (No Content) status code indicates that the server has
1396   successfully fulfilled the request and that there is no additional
1397   content to return in the response payload body.  Metadata in the
1398   response header fields refer to the target resource and its current
1399   representation after the requested action.
1400</t>
1401<t>
1402   For example, if a 204 status code is received in response to a PUT
1403   request and the response contains an ETag header field, then the PUT
1404   was successful and the ETag field-value contains the entity-tag for
1405   the new representation of that target resource.
1406</t>
1407<t>
1408   The 204 response allows a server to indicate that the action has been
1409   successfully applied to the target resource while implying that the
1410   user agent &SHOULD-NOT; traverse away from its current "document view"
1411   (if any).  The server assumes that the user agent will provide some
1412   indication of the success to its user, in accord with its own interface,
1413   and apply any new or updated metadata in the response to the active
1414   representation.
1415</t>
1416<t>
1417   For example, a 204 status code is commonly used with document editing
1418   interfaces corresponding to a "save" action, such that the document
1419   being saved remains available to the user for editing. It is also
1420   frequently used with interfaces that expect automated data transfers
1421   to be prevalent, such as within distributed version control systems.
1422</t>
1423<t>
1424   The 204 response &MUST-NOT; include a message body, and thus is always
1425   terminated by the first empty line after the header fields.
1426</t>
1427</section>
1428
1429<section title="205 Reset Content" anchor="status.205">
1430  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1431  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1432<t>
1433   The server has fulfilled the request and the user agent &SHOULD; reset
1434   the document view which caused the request to be sent. This response
1435   is primarily intended to allow input for actions to take place via
1436   user input, followed by a clearing of the form in which the input is
1437   given so that the user can easily initiate another input action.
1438</t>
1439<t>   
1440   The message body included with the response &MUST; be empty. Note that
1441   receivers still need to parse the response according to the algorithm defined
1442   in &message-body;.
1443</t>
1444</section>
1445</section>
1446
1447<section title="Redirection 3xx" anchor="status.3xx">
1448<t>
1449   This class of status code indicates that further action needs to be
1450   taken by the user agent in order to fulfill the request.  If the required
1451   action involves a subsequent HTTP request, it &MAY; be carried out by the
1452   user agent without interaction with the user if and only if the method used
1453   in the second request is known to be "safe", as defined in
1454   <xref target="safe.methods"/>.
1455</t>
1456<t>
1457   There are several types of redirects:
1458   <list style="numbers">
1459      <x:lt>
1460        <t>
1461          Redirects of the request to another URI, either temporarily or
1462          permanently. The new URI is specified in the Location header field.
1463          In this specification, the status codes 301 (Moved Permanently),
1464          302 (Found), and 307 (Temporary Redirect) fall under this category.
1465        </t>
1466      </x:lt>
1467      <x:lt>
1468        <t>
1469          Redirection to a new location that represents an indirect response to
1470          the request, such as the result of a POST operation to be retrieved
1471          with a subsequent GET request. This is status code 303 (See Other).
1472        </t>
1473      </x:lt>
1474      <x:lt>
1475        <t>
1476          Redirection offering a choice of matching resources for use by
1477          agent-driven content negotiation (&agent-driven-negotiation;). This
1478          is status code 300 (Multiple Choices).
1479        </t>
1480      </x:lt>
1481      <x:lt>
1482        <t>
1483          Other kinds of redirection, such as to a cached result (status code 304
1484          (Not Modified), see &status-304;).
1485        </t>
1486      </x:lt>
1487   </list>
1488</t>
1489<x:note>
1490  <t>
1491    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1492    and 302 (Found) were defined for the first type of redirect, and the second
1493    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1494    However it turned out that web forms using POST expected redirects to change
1495    the operation for the subsequent request to retrieval (GET). To address this
1496    use case, HTTP/1.1 introduced the second type of redirect with the status
1497    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1498    As user agents did not change their behavior to maintain backwards
1499    compatibility, the first revision of HTTP/1.1 added yet another status code,
1500    307 (Temporary Redirect), for which the backwards compatibility problems did
1501    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1502    Over 10 years later, most user agents still do method rewriting for
1503    status codes 301 and 302, therefore this specification makes that behavior
1504    conformant in case the original request was POST.
1505  </t>
1506</x:note>
1507<t>
1508   A Location header field on a 3xx response indicates that a client &MAY;
1509   automatically redirect to the URI provided; see <xref target="header.location"/>.
1510</t>
1511<t>
1512   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1513   automatic redirection needs to done with care, since the redirect might
1514   change the conditions under which the request was issued.
1515</t>
1516<t>
1517   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1518   "infinite" redirection loops).
1519</t>
1520<x:note>
1521  <t>
1522    <x:h>Note:</x:h> An earlier version of this specification recommended a
1523    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1524    Content developers need to be aware that some clients might
1525    implement such a fixed limitation.
1526  </t>
1527</x:note>
1528
1529<section title="300 Multiple Choices" anchor="status.300">
1530  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1531  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1532<t>
1533   The target resource has more than one
1534   representation, each with its own specific location, and agent-driven
1535   negotiation information (&content-negotiation;) is being provided so that
1536   the user (or user agent) can select a preferred representation by
1537   redirecting its request to that location.
1538</t>
1539<t>
1540   Unless it was a HEAD request, the response &SHOULD; include a representation
1541   containing a list of representation metadata and location(s) from
1542   which the user or user agent can choose the one most appropriate. Depending
1543   upon the format and the capabilities of
1544   the user agent, selection of the most appropriate choice &MAY; be
1545   performed automatically. However, this specification does not define
1546   any standard for such automatic selection.
1547</t>
1548<t>
1549   If the server has a preferred choice of representation, it &SHOULD;
1550   include the specific URI for that representation in the Location
1551   field; user agents &MAY; use the Location field value for automatic
1552   redirection.
1553</t>
1554<t>
1555   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1556   freshness for 300 responses.
1557</t>
1558
1559</section>
1560
1561<section title="301 Moved Permanently" anchor="status.301">
1562  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1563  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1564<t>
1565   The target resource has been assigned a new permanent URI and any
1566   future references to this resource &SHOULD; use one of the returned
1567   URIs.  Clients with link editing capabilities ought to automatically
1568   re-link references to the effective request URI to one or more of the new
1569   references returned by the server, where possible.
1570</t>
1571<t>
1572   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1573   freshness for 301 responses.
1574</t>
1575<t>
1576   The new permanent URI &SHOULD; be given by the Location field in the
1577   response. A response payload can contain a short hypertext note with a
1578   hyperlink to the new URI(s).
1579</t>
1580<x:note>
1581  <t>
1582    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1583    request method from POST to GET for the subsequent request. If this
1584    behavior is undesired, status code 307 (Temporary Redirect) can be used
1585    instead.
1586  </t>
1587</x:note>
1588</section>
1589
1590<section title="302 Found" anchor="status.302">
1591  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1592  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1593<t>
1594   The target resource resides temporarily under a different URI.
1595   Since the redirection might be altered on occasion, the client &SHOULD;
1596   continue to use the effective request URI for future requests.
1597</t>
1598<t>
1599   The temporary URI &SHOULD; be given by the Location field in the
1600   response. A response payload can contain a short hypertext note with a
1601   hyperlink to the new URI(s).
1602</t>
1603<x:note>
1604  <t>
1605    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1606    request method from POST to GET for the subsequent request. If this
1607    behavior is undesired, status code 307 (Temporary Redirect) can be used
1608    instead.
1609  </t>
1610</x:note>
1611</section>
1612
1613<section title="303 See Other" anchor="status.303">
1614  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1615  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1616<t>
1617   The 303 status code indicates that the server is redirecting the
1618   user agent to a different resource, as indicated by a URI in the
1619   Location header field, that is intended to provide an indirect
1620   response to the original request.  In order to satisfy the original
1621   request, a user agent &SHOULD; perform a retrieval request using the
1622   Location URI (a GET or HEAD request if using HTTP), which
1623   may itself be redirected further, and present the eventual result as an
1624   answer to the original request.
1625   Note that the new URI in the Location header field is not considered
1626   equivalent to the effective request URI.
1627</t>
1628<t>
1629   This status code is generally applicable to any HTTP method.  It is
1630   primarily used to allow the output of a POST action to redirect
1631   the user agent to a selected resource, since doing so provides the
1632   information corresponding to the POST response in a form that
1633   can be separately identified, bookmarked, and cached independent
1634   of the original request.
1635</t>
1636<t>
1637   A 303 response to a GET request indicates that the requested
1638   resource does not have a representation of its own that can be
1639   transferred by the server over HTTP.  The Location URI indicates a
1640   resource that is descriptive of the target resource, such that the
1641   follow-on representation might be useful to recipients without
1642   implying that it adequately represents the target resource.
1643   Note that answers to the questions of what can be represented, what
1644   representations are adequate, and what might be a useful description
1645   are outside the scope of HTTP and thus entirely determined by the
1646   URI owner(s).
1647</t>
1648<t>
1649   Except for responses to a HEAD request, the representation of a 303
1650   response &SHOULD; contain a short hypertext note with a hyperlink
1651   to the Location URI.
1652</t>
1653</section>
1654
1655<section title="305 Use Proxy" anchor="status.305">
1656  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1657  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1658<t>
1659   The 305 status code was defined in a previous version of this specification
1660   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1661</t>
1662</section>
1663
1664<section title="306 (Unused)" anchor="status.306">
1665  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1666  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1667<t>
1668   The 306 status code was used in a previous version of the
1669   specification, is no longer used, and the code is reserved.
1670</t>
1671</section>
1672
1673<section title="307 Temporary Redirect" anchor="status.307">
1674  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1675  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1676<t>
1677   The target resource resides temporarily under a different URI.
1678   Since the redirection can change over time, the client &SHOULD;
1679   continue to use the effective request URI for future requests.
1680</t>
1681<t>
1682   The temporary URI &SHOULD; be given by the Location field in the
1683   response. A response payload can contain a short hypertext note with a
1684   hyperlink to the new URI(s).
1685</t>
1686<x:note>
1687  <t>
1688    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1689    it does not allow rewriting the request method from POST to GET. This
1690    specification defines no equivalent counterpart for 301 Moved Permanently
1691    (<xref target="draft-reschke-http-status-308"/>, however, defines the
1692    status code 308 Permanent Redirect for this purpose).
1693  </t>
1694</x:note>
1695</section>
1696</section>
1697
1698<section title="Client Error 4xx" anchor="status.4xx">
1699<t>
1700   The 4xx class of status code is intended for cases in which the
1701   client seems to have erred. Except when responding to a HEAD request,
1702   the server &SHOULD; include a representation containing an explanation of the
1703   error situation, and whether it is a temporary or permanent
1704   condition. These status codes are applicable to any request method.
1705   User agents &SHOULD; display any included representation to the user.
1706</t>
1707
1708<section title="400 Bad Request" anchor="status.400">
1709  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1710  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1711<t>
1712   The server cannot or will not process the request, due to a client error (e.g.,
1713   malformed syntax).
1714</t>
1715</section>
1716
1717<section title="402 Payment Required" anchor="status.402">
1718  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1719  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1720<t>
1721   This code is reserved for future use.
1722</t>
1723</section>
1724
1725<section title="403 Forbidden" anchor="status.403">
1726  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1727  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1728<t>
1729   The server understood the request, but refuses to authorize it. Providing
1730   different user authentication credentials might be successful, but any
1731   credentials that were provided in the request are insufficient. The request
1732   &SHOULD-NOT; be repeated with the same credentials.
1733</t>
1734<t>
1735   If the request method was not HEAD and the server wishes to make
1736   public why the request has not been fulfilled, it &SHOULD; describe the
1737   reason for the refusal in the representation.  If the server does not wish to
1738   make this information available to the client, the status code 404
1739   (Not Found) &MAY; be used instead.
1740</t>
1741</section>
1742
1743<section title="404 Not Found" anchor="status.404">
1744  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1745  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1746<t>
1747   The server has not found anything matching the effective request URI. No
1748   indication is given of whether the condition is temporary or
1749   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1750   knows, through some internally configurable mechanism, that an old
1751   resource is permanently unavailable and has no forwarding address.
1752   This status code is commonly used when the server does not wish to
1753   reveal exactly why the request has been refused, or when no other
1754   response is applicable.
1755</t>
1756</section>
1757
1758<section title="405 Method Not Allowed" anchor="status.405">
1759  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1760  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1761<t>
1762   The method specified in the request-line is not allowed for the target
1763   resource. The response &MUST; include an Allow header field containing a
1764   list of valid methods for the requested resource.
1765</t>
1766</section>
1767
1768<section title="406 Not Acceptable" anchor="status.406">
1769  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1770  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1771<t>
1772   The resource identified by the request is only capable of generating
1773   response representations which have content characteristics not acceptable
1774   according to the Accept and Accept-* header fields sent in the request
1775   (see &p3-header-fields;).
1776</t>
1777<t>
1778   Unless it was a HEAD request, the response &SHOULD; include a representation
1779   containing a list of available representation characteristics and location(s)
1780   from which the user or user agent can choose the one most
1781   appropriate. Depending upon the format and the
1782   capabilities of the user agent, selection of the most appropriate
1783   choice &MAY; be performed automatically. However, this specification
1784   does not define any standard for such automatic selection.
1785</t>
1786<x:note>
1787  <t>
1788    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1789    not acceptable according to the accept header fields sent in the
1790    request. In some cases, this might even be preferable to sending a
1791    406 response. User agents are encouraged to inspect the header fields of
1792    an incoming response to determine if it is acceptable.
1793  </t>
1794</x:note>
1795<t>
1796   If the response could be unacceptable, a user agent &SHOULD;
1797   temporarily stop receipt of more data and query the user for a
1798   decision on further actions.
1799</t>
1800</section>
1801
1802<section title="408 Request Timeout" anchor="status.408">
1803  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1804  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1805<t>
1806   The client did not produce a request within the time that the server
1807   was prepared to wait. The client &MAY; repeat the request without
1808   modifications at any later time.
1809</t>
1810</section>
1811
1812<section title="409 Conflict" anchor="status.409">
1813  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1814  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1815<t>
1816   The request could not be completed due to a conflict with the current
1817   state of the resource. This code is only allowed in situations where
1818   it is expected that the user might be able to resolve the conflict
1819   and resubmit the request. The response body &SHOULD; include enough
1820   information for the user to recognize the source of the conflict.
1821   Ideally, the response representation would include enough information for the
1822   user or user agent to fix the problem; however, that might not be
1823   possible and is not required.
1824</t>
1825<t>
1826   Conflicts are most likely to occur in response to a PUT request. For
1827   example, if versioning were being used and the representation being PUT
1828   included changes to a resource which conflict with those made by an
1829   earlier (third-party) request, the server might use the 409 response
1830   to indicate that it can't complete the request. In this case, the
1831   response representation would likely contain a list of the differences
1832   between the two versions.
1833</t>
1834</section>
1835
1836<section title="410 Gone" anchor="status.410">
1837  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1838  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1839<t>
1840   The target resource is no longer available at the server and no
1841   forwarding address is known. This condition is expected to be
1842   considered permanent. Clients with link editing capabilities &SHOULD;
1843   delete references to the effective request URI after user approval. If the
1844   server does not know, or has no facility to determine, whether or not
1845   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1846   used instead.
1847</t>
1848<t>
1849   The 410 response is primarily intended to assist the task of web
1850   maintenance by notifying the recipient that the resource is
1851   intentionally unavailable and that the server owners desire that
1852   remote links to that resource be removed. Such an event is common for
1853   limited-time, promotional services and for resources belonging to
1854   individuals no longer working at the server's site. It is not
1855   necessary to mark all permanently unavailable resources as "gone" or
1856   to keep the mark for any length of time &mdash; that is left to the
1857   discretion of the server owner.
1858</t>
1859<t>
1860   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1861   for 410 responses.
1862</t>
1863</section>
1864
1865<section title="411 Length Required" anchor="status.411">
1866  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1867  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1868<t>
1869   The server refuses to accept the request without a defined Content-Length.
1870   The client &MAY; repeat the request if it adds a valid
1871   Content-Length header field containing the length of the message body
1872   in the request message.
1873</t>
1874</section>
1875
1876<section title="413 Request Representation Too Large" anchor="status.413">
1877  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
1878  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
1879<t>
1880   The server is refusing to process a request because the request
1881   representation is larger than the server is willing or able to process. The
1882   server &MAY; close the connection to prevent the client from continuing
1883   the request.
1884</t>
1885<t>
1886   If the condition is temporary, the server &SHOULD; include a Retry-After
1887   header field to indicate that it is temporary and after what
1888   time the client &MAY; try again.
1889</t>
1890</section>
1891
1892<section title="414 URI Too Long" anchor="status.414">
1893  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1894  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1895<t>
1896   The server is refusing to service the request because the effective request URI
1897   is longer than the server is willing to interpret. This rare
1898   condition is only likely to occur when a client has improperly
1899   converted a POST request to a GET request with long query
1900   information, when the client has descended into a URI "black hole" of
1901   redirection (e.g., a redirected URI prefix that points to a suffix of
1902   itself), or when the server is under attack by a client attempting to
1903   exploit security holes present in some servers using fixed-length
1904   buffers for reading or manipulating the request-target.
1905</t>
1906</section>
1907
1908<section title="415 Unsupported Media Type" anchor="status.415">
1909  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1910  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1911<t>
1912   The server is refusing to service the request because the request
1913   payload is in a format not supported by this request method on the
1914   target resource.
1915</t>
1916</section>
1917
1918<section title="417 Expectation Failed" anchor="status.417">
1919  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1920  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1921<t>
1922   The expectation given in an Expect header field (see <xref target="header.expect"/>)
1923   could not be met by this server, or, if the server is a proxy,
1924   the server has unambiguous evidence that the request could not be met
1925   by the next-hop server.
1926</t>
1927</section>
1928
1929<section title="426 Upgrade Required" anchor="status.426">
1930  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
1931  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
1932<t>
1933   The request can not be completed without a prior protocol upgrade. This
1934   response &MUST; include an Upgrade header field (&header-upgrade;)
1935   specifying the required protocols.
1936</t>
1937<figure>
1938<preamble>Example:</preamble>
1939<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
1940HTTP/1.1 426 Upgrade Required
1941Upgrade: HTTP/3.0
1942Connection: Upgrade
1943Content-Length: <x:length-of target="s426body"/>
1944Content-Type: text/plain
1945
1946<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
1947</x:span></artwork></figure>
1948<t>
1949   The server &SHOULD; include a message body in the 426 response which
1950   indicates in human readable form the reason for the error and describes any
1951   alternative courses which may be available to the user.
1952</t>
1953</section>
1954</section>
1955
1956<section title="Server Error 5xx" anchor="status.5xx">
1957<t>
1958   Response status codes beginning with the digit "5" indicate cases in
1959   which the server is aware that it has erred or is incapable of
1960   performing the request. Except when responding to a HEAD request, the
1961   server &SHOULD; include a representation containing an explanation of the
1962   error situation, and whether it is a temporary or permanent
1963   condition. User agents &SHOULD; display any included representation to the
1964   user. These response codes are applicable to any request method.
1965</t>
1966
1967<section title="500 Internal Server Error" anchor="status.500">
1968  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1969  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1970<t>
1971   The server encountered an unexpected condition which prevented it
1972   from fulfilling the request.
1973</t>
1974</section>
1975
1976<section title="501 Not Implemented" anchor="status.501">
1977  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1978  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1979<t>
1980   The server does not support the functionality required to fulfill the
1981   request. This is the appropriate response when the server does not
1982   recognize the request method and is not capable of supporting it for
1983   any resource.
1984</t>
1985</section>
1986
1987<section title="502 Bad Gateway" anchor="status.502">
1988  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
1989  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
1990<t>
1991   The server, while acting as a gateway or proxy, received an invalid
1992   response from the upstream server it accessed in attempting to
1993   fulfill the request.
1994</t>
1995</section>
1996
1997<section title="503 Service Unavailable" anchor="status.503">
1998  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
1999  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2000<t>
2001   The server is currently unable to handle the request due to a
2002   temporary overloading or maintenance of the server.
2003</t>
2004<t>
2005   The implication is that this is a temporary condition which will be
2006   alleviated after some delay. If known, the length of the delay &MAY; be
2007   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2008   If no Retry-After is given, the client &SHOULD; handle the response as it
2009   would for a 500 response.
2010</t>
2011<x:note>
2012  <t>
2013    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2014    server has to use it when becoming overloaded. Some servers might wish
2015    to simply refuse the connection.
2016  </t>
2017</x:note>
2018</section>
2019
2020<section title="504 Gateway Timeout" anchor="status.504">
2021  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2022  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2023<t>
2024   The server, while acting as a gateway or proxy, did not receive a
2025   timely response from the upstream server specified by the URI (e.g.,
2026   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2027   to access in attempting to complete the request.
2028</t>
2029<x:note>
2030  <t>
2031    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2032    return 400 or 500 when DNS lookups time out.
2033  </t>
2034</x:note>
2035</section>
2036
2037<section title="505 HTTP Version Not Supported" anchor="status.505">
2038  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2039  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2040<t>
2041   The server does not support, or refuses to support, the protocol
2042   version that was used in the request message. The server is
2043   indicating that it is unable or unwilling to complete the request
2044   using the same major version as the client, as described in &http-version;,
2045   other than with this error message. The response &SHOULD; contain
2046   a representation describing why that version is not supported and what other
2047   protocols are supported by that server.
2048</t>
2049
2050</section>
2051</section>
2052
2053</section>
2054
2055<section title="Representation" anchor="representation">
2056<t>
2057   Request and Response messages &MAY; transfer a representation if not otherwise
2058   restricted by the request method or response status code. A representation
2059   consists of metadata (representation header fields) and data (representation
2060   body).  When a complete or partial representation is enclosed in an HTTP message,
2061   it is referred to as the payload of the message. HTTP representations
2062   are defined in &payload;.
2063</t>
2064<t>
2065   A representation body is only present in a message when a message body is
2066   present, as described in &message-body;. The representation body is obtained
2067   from the message body by decoding any Transfer-Encoding that might
2068   have been applied to ensure safe and proper transfer of the message.
2069</t>
2070
2071<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
2072<t>
2073   It is sometimes necessary to determine an identifier for the resource
2074   associated with a representation.
2075</t>
2076<t>
2077   An HTTP request representation, when present, is always associated with an
2078   anonymous (i.e., unidentified) resource.
2079</t>
2080<t>
2081   In the common case, an HTTP response is a representation of the target
2082   resource (see &effective-request-uri;). However, this is not always the
2083   case. To determine the URI of the resource a response is associated with,
2084   the following rules are used (with the first applicable one being selected):
2085</t>
2086<t><list style="numbers">
2087   <t>If the response status code is 200 or 203 and the request method was GET,
2088   the response payload is a representation of the target resource.</t>
2089   <t>If the response status code is 204, 206, or 304 and the request method was GET
2090   or HEAD, the response payload is a partial representation of the target
2091   resource.</t>
2092   <t>If the response has a Content-Location header field, and that URI is the same
2093   as the effective request URI, the response payload is a representation of the
2094   target resource.</t>
2095   <t>If the response has a Content-Location header field, and that URI is not the
2096   same as the effective request URI, then the response asserts that its
2097   payload is a representation of the resource identified by the
2098   Content-Location URI. However, such an assertion cannot be trusted unless
2099   it can be verified by other means (not defined by HTTP).</t>
2100   <t>Otherwise, the response is a representation of an anonymous (i.e.,
2101   unidentified) resource.</t>
2102</list></t>
2103<t>
2104  <cref anchor="TODO-req-uri">
2105   The comparison function is going to have to be defined somewhere,
2106   because we already need to compare URIs for things like cache invalidation.</cref>
2107</t>
2108</section>
2109
2110</section>
2111
2112
2113<section title="Common Protocol Parameters" anchor="common.protocol.parameters">
2114<section title="Date/Time Formats" anchor="http.date">
2115  <x:anchor-alias value="HTTP-date"/>
2116<t>
2117   HTTP applications have historically allowed three different formats
2118   for date/time stamps. However, the preferred format is a fixed-length subset
2119   of that defined by <xref target="RFC1123"/>:
2120</t>
2121<figure><artwork type="example" x:indent-with="  ">
2122Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2123</artwork></figure>
2124<t>
2125   The other formats are described here only for compatibility with obsolete
2126   implementations.
2127</t>
2128<figure><artwork type="example" x:indent-with="  ">
2129Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2130Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2131</artwork></figure>
2132<t>
2133   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2134   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2135   only generate the RFC 1123 format for representing HTTP-date values
2136   in header fields.
2137</t>
2138<t>
2139   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2140   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2141   equal to UTC (Coordinated Universal Time). This is indicated in the
2142   first two formats by the inclusion of "GMT" as the three-letter
2143   abbreviation for time zone, and &MUST; be assumed when reading the
2144   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2145   additional whitespace beyond that specifically included as SP in the
2146   grammar.
2147</t>
2148<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2149  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2150</artwork></figure>
2151<t anchor="preferred.date.format">
2152  <x:anchor-alias value="rfc1123-date"/>
2153  <x:anchor-alias value="time-of-day"/>
2154  <x:anchor-alias value="hour"/>
2155  <x:anchor-alias value="minute"/>
2156  <x:anchor-alias value="second"/>
2157  <x:anchor-alias value="day-name"/>
2158  <x:anchor-alias value="day"/>
2159  <x:anchor-alias value="month"/>
2160  <x:anchor-alias value="year"/>
2161  <x:anchor-alias value="GMT"/>
2162  Preferred format:
2163</t>
2164<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"/>
2165  <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>
2166  ; fixed length subset of the format defined in
2167  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2168 
2169  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2170               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2171               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2172               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2173               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2174               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2175               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2176               
2177  <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>
2178               ; e.g., 02 Jun 1982
2179
2180  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2181  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2182               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2183               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2184               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2185               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2186               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2187               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2188               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2189               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2190               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2191               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2192               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2193  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2194
2195  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2196
2197  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2198                 ; 00:00:00 - 23:59:59
2199                 
2200  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2201  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2202  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2203</artwork></figure>
2204<t>
2205  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2206  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2207  same as those defined for the RFC 5322 constructs
2208  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2209</t>
2210<t anchor="obsolete.date.formats">
2211  <x:anchor-alias value="obs-date"/>
2212  <x:anchor-alias value="rfc850-date"/>
2213  <x:anchor-alias value="asctime-date"/>
2214  <x:anchor-alias value="date1"/>
2215  <x:anchor-alias value="date2"/>
2216  <x:anchor-alias value="date3"/>
2217  <x:anchor-alias value="rfc1123-date"/>
2218  <x:anchor-alias value="day-name-l"/>
2219  Obsolete formats:
2220</t>
2221<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2222  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2223</artwork></figure>
2224<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2225  <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>
2226  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2227                 ; day-month-year (e.g., 02-Jun-82)
2228
2229  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2230         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2231         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2232         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2233         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2234         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2235         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2236</artwork></figure>
2237<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2238  <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>
2239  <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> ))
2240                 ; month day (e.g., Jun  2)
2241</artwork></figure>
2242<x:note>
2243  <t>
2244    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2245    accepting date values that might have been sent by non-HTTP
2246    applications, as is sometimes the case when retrieving or posting
2247    messages via proxies/gateways to SMTP or NNTP.
2248  </t>
2249</x:note>
2250<x:note>
2251  <t>
2252    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2253    to their usage within the protocol stream. Clients and servers are
2254    not required to use these formats for user presentation, request
2255    logging, etc.
2256  </t>
2257</x:note>
2258</section>
2259
2260<section title="Product Tokens" anchor="product.tokens">
2261  <x:anchor-alias value="product"/>
2262  <x:anchor-alias value="product-version"/>
2263<t>
2264   Product tokens are used to allow communicating applications to
2265   identify themselves by software name and version. Most fields using
2266   product tokens also allow sub-products which form a significant part
2267   of the application to be listed, separated by whitespace. By
2268   convention, the products are listed in order of their significance
2269   for identifying the application.
2270</t>
2271<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2272  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2273  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2274</artwork></figure>
2275<t>
2276   Examples:
2277</t>
2278<figure><artwork type="example">
2279  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2280  Server: Apache/0.8.4
2281</artwork></figure>
2282<t>
2283   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2284   used for advertising or other non-essential information. Although any
2285   token octet &MAY; appear in a product-version, this token &SHOULD;
2286   only be used for a version identifier (i.e., successive versions of
2287   the same product &SHOULD; only differ in the product-version portion of
2288   the product value).
2289</t>
2290</section>
2291</section>
2292
2293<section title="Header Field Definitions" anchor="header.field.definitions">
2294<t>
2295   This section defines the syntax and semantics of HTTP/1.1 header fields
2296   related to request and response semantics.
2297</t>
2298
2299<section title="Allow" anchor="header.allow">
2300  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2301  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2302  <x:anchor-alias value="Allow"/>
2303<t>
2304   The "Allow" header field lists the set of methods advertised as
2305   supported by the target resource. The purpose of this field is strictly to
2306   inform the recipient of valid request methods associated with the resource.
2307</t>
2308<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2309  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2310</artwork></figure>
2311<t>
2312   Example of use:
2313</t>
2314<figure><artwork type="example">
2315  Allow: GET, HEAD, PUT
2316</artwork></figure>
2317<t>
2318   The actual set of allowed methods is defined by the origin server at the
2319   time of each request.
2320</t>
2321<t>
2322   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2323   understand all the methods specified in order to handle them according to
2324   the generic message handling rules.
2325</t>
2326</section>
2327
2328<section title="Date" anchor="header.date">
2329  <iref primary="true" item="Date header field" x:for-anchor=""/>
2330  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2331  <x:anchor-alias value="Date"/>
2332<t>
2333   The "Date" header field represents the date and time at which
2334   the message was originated, having the same semantics as the Origination
2335   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2336   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2337   it &MUST; be sent in rfc1123-date format.
2338</t>
2339<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2340  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2341</artwork></figure>
2342<t>
2343   An example is
2344</t>
2345<figure><artwork type="example">
2346  Date: Tue, 15 Nov 1994 08:12:31 GMT
2347</artwork></figure>
2348<t>
2349   Origin servers &MUST; include a Date header field in all responses,
2350   except in these cases:
2351  <list style="numbers">
2352      <t>If the response status code is 100 (Continue) or 101 (Switching
2353         Protocols), the response &MAY; include a Date header field, at
2354         the server's option.</t>
2355
2356      <t>If the response status code conveys a server error, e.g., 500
2357         (Internal Server Error) or 503 (Service Unavailable), and it is
2358         inconvenient or impossible to generate a valid Date.</t>
2359
2360      <t>If the server does not have a clock that can provide a
2361         reasonable approximation of the current time, its responses
2362         &MUST-NOT; include a Date header field.</t>
2363  </list>
2364</t>
2365<t>
2366   A received message that does not have a Date header field &MUST; be
2367   assigned one by the recipient if the message will be cached by that
2368   recipient.
2369</t>
2370<t>
2371   Clients can use the Date header field as well; in order to keep request
2372   messages small, they are advised not to include it when it doesn't convey
2373   any useful information (as is usually the case for requests that do not
2374   contain a payload).
2375</t>
2376<t>
2377   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2378   time subsequent to the generation of the message. It &SHOULD; represent
2379   the best available approximation of the date and time of message
2380   generation, unless the implementation has no means of generating a
2381   reasonably accurate date and time. In theory, the date ought to
2382   represent the moment just before the payload is generated. In
2383   practice, the date can be generated at any time during the message
2384   origination without affecting its semantic value.
2385</t>
2386</section>
2387
2388<section title="Expect" anchor="header.expect">
2389  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2390  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2391  <x:anchor-alias value="Expect"/>
2392  <x:anchor-alias value="expectation"/>
2393  <x:anchor-alias value="expect-param"/>
2394  <x:anchor-alias value="expect-name"/>
2395  <x:anchor-alias value="expect-value"/>
2396<t>
2397   The "Expect" header field is used to indicate that particular
2398   server behaviors are required by the client.
2399</t>
2400<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"/>
2401  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2402 
2403  <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> ]
2404                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2405  <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> ]
2406 
2407  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2408  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2409</artwork></figure>
2410<t>
2411   If all received Expect header field(s) are syntactically valid but contain
2412   an expectation that the recipient does not understand or cannot comply with,
2413   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2414   recipient of a syntactically invalid Expectation header field &MUST; respond
2415   with a 4xx status code other than 417.
2416</t>
2417<t>
2418   The only expectation defined by this specification is:
2419</t>
2420<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2421  100-continue
2422   <list>
2423      <t>
2424        The "100-continue" expectation is defined &use100;. It does not support
2425        any expect-params.
2426      </t>
2427   </list>
2428</t>
2429<t>
2430   Comparison is case-insensitive for names (expect-name), and case-sensitive
2431   for values (expect-value).
2432</t>
2433<t>
2434   The Expect mechanism is hop-by-hop: the above requirements apply to any
2435   server, including proxies. However, the Expect header field itself is
2436   end-to-end; it &MUST; be forwarded if the request is forwarded.
2437</t>
2438<t>
2439   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2440   header field.
2441</t>
2442</section>
2443
2444<section title="From" anchor="header.from">
2445  <iref primary="true" item="From header field" x:for-anchor=""/>
2446  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2447  <x:anchor-alias value="From"/>
2448  <x:anchor-alias value="mailbox"/>
2449<t>
2450   The "From" header field, if given, &SHOULD; contain an Internet
2451   e-mail address for the human user who controls the requesting user
2452   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2453   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2454</t>
2455<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2456  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2457 
2458  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2459</artwork></figure>
2460<t>
2461   An example is:
2462</t>
2463<figure><artwork type="example">
2464  From: webmaster@example.org
2465</artwork></figure>
2466<t>
2467   This header field &MAY; be used for logging purposes and as a means for
2468   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2469   be used as an insecure form of access protection. The interpretation
2470   of this field is that the request is being performed on behalf of the
2471   person given, who accepts responsibility for the method performed. In
2472   particular, robot agents &SHOULD; include this header field so that the
2473   person responsible for running the robot can be contacted if problems
2474   occur on the receiving end.
2475</t>
2476<t>
2477   The Internet e-mail address in this field &MAY; be separate from the
2478   Internet host which issued the request. For example, when a request
2479   is passed through a proxy the original issuer's address &SHOULD; be
2480   used.
2481</t>
2482<t>
2483   The client &SHOULD-NOT;  send the From header field without the user's
2484   approval, as it might conflict with the user's privacy interests or
2485   their site's security policy. It is strongly recommended that the
2486   user be able to disable, enable, and modify the value of this field
2487   at any time prior to a request.
2488</t>
2489</section>
2490
2491<section title="Location" anchor="header.location">
2492  <iref primary="true" item="Location header field" x:for-anchor=""/>
2493  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2494  <x:anchor-alias value="Location"/>
2495<t>
2496   The "Location" header field &MAY; be sent in responses to refer to
2497   a specific resource in accordance with the semantics of the status
2498   code.
2499</t>
2500<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2501  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2502</artwork></figure>
2503<t>
2504   For 201 (Created) responses, the Location is the URI of the new resource
2505   which was created by the request. For 3xx responses, the location &SHOULD;
2506   indicate the server's preferred URI for automatic redirection to the
2507   resource.
2508</t>
2509<t>
2510   The field value consists of a single URI-reference. When it has the form
2511   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2512   the final value is computed by resolving it against the effective request
2513   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2514   navigated to by the user agent, did contain a fragment identifier, and the
2515   final value does not, then the original URI's fragment identifier is added
2516   to the final value.
2517</t>
2518<figure>
2519<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-->
2520<artwork type="example">
2521  Location: /pub/WWW/People.html#tim
2522</artwork>
2523<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2524</figure>
2525<figure>
2526<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-->
2527<artwork type="example">
2528  Location: http://www.example.net/index.html
2529</artwork>
2530<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2531</figure>
2532<x:note>
2533  <t>
2534    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2535    that are not valid URI references. This specification does not mandate or
2536    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2537  </t>
2538</x:note>
2539<t>
2540   There are circumstances in which a fragment identifier in a Location URI
2541   would not be appropriate. For instance, when it appears in a 201 Created
2542   response, where the Location header field specifies the URI for the entire
2543   created resource.
2544</t>
2545<x:note>
2546  <t>
2547    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2548    from Location in that the Content-Location identifies the most specific
2549    resource corresponding to the enclosed representation.
2550    It is therefore possible for a response to contain header fields for
2551    both Location and Content-Location.
2552  </t>
2553</x:note>
2554</section>
2555
2556<section title="Max-Forwards" anchor="header.max-forwards">
2557  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2558  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2559  <x:anchor-alias value="Max-Forwards"/>
2560<t>
2561   The "Max-Forwards" header field provides a mechanism with the
2562   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2563   methods to limit the number of times that the request is forwarded by
2564   proxies. This can be useful when the client is attempting to
2565   trace a request which appears to be failing or looping mid-chain.
2566</t>
2567<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2568  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2569</artwork></figure>
2570<t>
2571   The Max-Forwards value is a decimal integer indicating the remaining
2572   number of times this request message can be forwarded.
2573</t>
2574<t>
2575   Each recipient of a TRACE or OPTIONS request
2576   containing a Max-Forwards header field &MUST; check and update its
2577   value prior to forwarding the request. If the received value is zero
2578   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2579   respond as the final recipient. If the received Max-Forwards value is
2580   greater than zero, then the forwarded message &MUST; contain an updated
2581   Max-Forwards field with a value decremented by one (1).
2582</t>
2583<t>
2584   The Max-Forwards header field &MAY; be ignored for all other request
2585   methods.
2586</t>
2587</section>
2588
2589<section title="Referer" anchor="header.referer">
2590  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2591  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2592  <x:anchor-alias value="Referer"/>
2593<t>
2594   The "Referer" [sic] header field allows the client to specify the
2595   URI of the resource from which the target URI was obtained (the
2596   "referrer", although the header field is misspelled.).
2597</t>
2598<t>
2599   The Referer header field allows servers to generate lists of back-links to
2600   resources for interest, logging, optimized caching, etc. It also allows
2601   obsolete or mistyped links to be traced for maintenance. Some servers use
2602   Referer as a means of controlling where they allow links from (so-called
2603   "deep linking"), but legitimate requests do not always
2604   contain a Referer header field.
2605</t>
2606<t>
2607   If the target URI was obtained from a source that does not have its own
2608   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2609   sent with the value "about:blank", or not be sent at all. Note that this
2610   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2611</t>
2612<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2613  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2614</artwork></figure>
2615<t>
2616   Example:
2617</t>
2618<figure><artwork type="example">
2619  Referer: http://www.example.org/hypertext/Overview.html
2620</artwork></figure>
2621<t>
2622   If the field value is a relative URI, it &SHOULD; be interpreted
2623   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2624   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2625</t>
2626</section>
2627
2628<section title="Retry-After" anchor="header.retry-after">
2629  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2630  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2631  <x:anchor-alias value="Retry-After"/>
2632<t>
2633   The header "Retry-After" field can be used with a 503 (Service
2634   Unavailable) response to indicate how long the service is expected to
2635   be unavailable to the requesting client. This field &MAY; also be used
2636   with any 3xx (Redirection) response to indicate the minimum time the
2637   user-agent is asked to wait before issuing the redirected request.
2638</t>
2639<t>
2640   The value of this field can be either an HTTP-date or an integer number
2641   of seconds (in decimal) after the time of the response.
2642</t>
2643<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2644  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2645</artwork></figure>
2646<t anchor="rule.delta-seconds">
2647  <x:anchor-alias value="delta-seconds"/>
2648   Time spans are non-negative decimal integers, representing time in
2649   seconds.
2650</t>
2651<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2652  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2653</artwork></figure>
2654<t>
2655   Two examples of its use are
2656</t>
2657<figure><artwork type="example">
2658  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2659  Retry-After: 120
2660</artwork></figure>
2661<t>
2662   In the latter example, the delay is 2 minutes.
2663</t>
2664</section>
2665
2666<section title="Server" anchor="header.server">
2667  <iref primary="true" item="Server header field" x:for-anchor=""/>
2668  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2669  <x:anchor-alias value="Server"/>
2670<t>
2671   The "Server" header field contains information about the
2672   software used by the origin server to handle the request.
2673</t>
2674<t>
2675   The field can contain multiple
2676   product tokens (<xref target="product.tokens"/>) and
2677   comments (&header-fields;) identifying the server and any significant
2678   subproducts. The product tokens are listed in order of their significance
2679   for identifying the application.
2680</t>
2681<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2682  <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> ) )
2683</artwork></figure>
2684<t>
2685   Example:
2686</t>
2687<figure><artwork type="example">
2688  Server: CERN/3.0 libwww/2.17
2689</artwork></figure>
2690<t>
2691   If the response is being forwarded through a proxy, the proxy
2692   application &MUST-NOT; modify the Server header field. Instead, it
2693   &MUST; include a Via field (as described in &header-via;).
2694</t>
2695<x:note>
2696  <t>
2697    <x:h>Note:</x:h> Revealing the specific software version of the server might
2698    allow the server machine to become more vulnerable to attacks
2699    against software that is known to contain security holes. Server
2700    implementors are encouraged to make this field a configurable
2701    option.
2702  </t>
2703</x:note>
2704</section>
2705
2706<section title="User-Agent" anchor="header.user-agent">
2707  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2708  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2709  <x:anchor-alias value="User-Agent"/>
2710<t>
2711   The "User-Agent" header field contains information about the user
2712   agent originating the request. User agents &SHOULD; include this field with
2713   requests.
2714</t>
2715<t>
2716   Typically, it is used for statistical purposes, the tracing of protocol
2717   violations, and tailoring responses to avoid particular user agent
2718   limitations.
2719</t>
2720<t>
2721   The field can contain multiple
2722   product tokens (<xref target="product.tokens"/>)
2723   and comments (&header-fields;) identifying the agent and its
2724   significant subproducts. By convention, the product tokens are listed in
2725   order of their significance for identifying the application.
2726</t>
2727<t>
2728   Because this field is usually sent on every request a user agent makes,
2729   implementations are encouraged not to include needlessly fine-grained
2730   detail, and to limit (or even prohibit) the addition of subproducts by third
2731   parties. Overly long and detailed User-Agent field values make requests
2732   larger and can also be used to identify ("fingerprint") the user against
2733   their wishes.
2734</t>
2735<t>
2736   Likewise, implementations are encouraged not to use the product tokens of
2737   other implementations in order to declare compatibility with them, as this
2738   circumvents the purpose of the field. Finally, they are encouraged not to
2739   use comments to identify products; doing so makes the field value more
2740   difficult to parse.
2741</t>
2742<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2743  <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> ) )
2744</artwork></figure>
2745<t>
2746   Example:
2747</t>
2748<figure><artwork type="example">
2749  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2750</artwork></figure>
2751</section>
2752
2753</section>
2754
2755<section title="IANA Considerations" anchor="IANA.considerations">
2756
2757<section title="Method Registry" anchor="method.registration">
2758<t>
2759  The registration procedure for HTTP request methods is defined by
2760  <xref target="method.registry"/> of this document.
2761</t>
2762<t>
2763   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2764   and be populated with the registrations below:
2765</t>
2766<?BEGININC p2-semantics.iana-methods ?>
2767<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2768<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2769   <ttcol>Method</ttcol>
2770   <ttcol>Safe</ttcol>
2771   <ttcol>Reference</ttcol>
2772   <c>CONNECT</c>
2773   <c>no</c>
2774   <c>
2775      <xref target="CONNECT"/>
2776   </c>
2777   <c>DELETE</c>
2778   <c>no</c>
2779   <c>
2780      <xref target="DELETE"/>
2781   </c>
2782   <c>GET</c>
2783   <c>yes</c>
2784   <c>
2785      <xref target="GET"/>
2786   </c>
2787   <c>HEAD</c>
2788   <c>yes</c>
2789   <c>
2790      <xref target="HEAD"/>
2791   </c>
2792   <c>OPTIONS</c>
2793   <c>yes</c>
2794   <c>
2795      <xref target="OPTIONS"/>
2796   </c>
2797   <c>POST</c>
2798   <c>no</c>
2799   <c>
2800      <xref target="POST"/>
2801   </c>
2802   <c>PUT</c>
2803   <c>no</c>
2804   <c>
2805      <xref target="PUT"/>
2806   </c>
2807   <c>TRACE</c>
2808   <c>yes</c>
2809   <c>
2810      <xref target="TRACE"/>
2811   </c>
2812</texttable>
2813<!--(END)-->
2814<?ENDINC p2-semantics.iana-methods ?>
2815</section>
2816
2817<section title="Status Code Registry" anchor="status.code.registration">
2818<t>
2819   The registration procedure for HTTP Status Codes &mdash; previously defined
2820   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2821   by <xref target="status.code.registry"/> of this document.
2822</t>
2823<t>
2824   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2825   shall be updated with the registrations below:
2826</t>
2827<?BEGININC p2-semantics.iana-status-codes ?>
2828<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2829<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2830   <ttcol>Value</ttcol>
2831   <ttcol>Description</ttcol>
2832   <ttcol>Reference</ttcol>
2833   <c>100</c>
2834   <c>Continue</c>
2835   <c>
2836      <xref target="status.100"/>
2837   </c>
2838   <c>101</c>
2839   <c>Switching Protocols</c>
2840   <c>
2841      <xref target="status.101"/>
2842   </c>
2843   <c>200</c>
2844   <c>OK</c>
2845   <c>
2846      <xref target="status.200"/>
2847   </c>
2848   <c>201</c>
2849   <c>Created</c>
2850   <c>
2851      <xref target="status.201"/>
2852   </c>
2853   <c>202</c>
2854   <c>Accepted</c>
2855   <c>
2856      <xref target="status.202"/>
2857   </c>
2858   <c>203</c>
2859   <c>Non-Authoritative Information</c>
2860   <c>
2861      <xref target="status.203"/>
2862   </c>
2863   <c>204</c>
2864   <c>No Content</c>
2865   <c>
2866      <xref target="status.204"/>
2867   </c>
2868   <c>205</c>
2869   <c>Reset Content</c>
2870   <c>
2871      <xref target="status.205"/>
2872   </c>
2873   <c>300</c>
2874   <c>Multiple Choices</c>
2875   <c>
2876      <xref target="status.300"/>
2877   </c>
2878   <c>301</c>
2879   <c>Moved Permanently</c>
2880   <c>
2881      <xref target="status.301"/>
2882   </c>
2883   <c>302</c>
2884   <c>Found</c>
2885   <c>
2886      <xref target="status.302"/>
2887   </c>
2888   <c>303</c>
2889   <c>See Other</c>
2890   <c>
2891      <xref target="status.303"/>
2892   </c>
2893   <c>305</c>
2894   <c>Use Proxy</c>
2895   <c>
2896      <xref target="status.305"/>
2897   </c>
2898   <c>306</c>
2899   <c>(Unused)</c>
2900   <c>
2901      <xref target="status.306"/>
2902   </c>
2903   <c>307</c>
2904   <c>Temporary Redirect</c>
2905   <c>
2906      <xref target="status.307"/>
2907   </c>
2908   <c>400</c>
2909   <c>Bad Request</c>
2910   <c>
2911      <xref target="status.400"/>
2912   </c>
2913   <c>402</c>
2914   <c>Payment Required</c>
2915   <c>
2916      <xref target="status.402"/>
2917   </c>
2918   <c>403</c>
2919   <c>Forbidden</c>
2920   <c>
2921      <xref target="status.403"/>
2922   </c>
2923   <c>404</c>
2924   <c>Not Found</c>
2925   <c>
2926      <xref target="status.404"/>
2927   </c>
2928   <c>405</c>
2929   <c>Method Not Allowed</c>
2930   <c>
2931      <xref target="status.405"/>
2932   </c>
2933   <c>406</c>
2934   <c>Not Acceptable</c>
2935   <c>
2936      <xref target="status.406"/>
2937   </c>
2938   <c>408</c>
2939   <c>Request Timeout</c>
2940   <c>
2941      <xref target="status.408"/>
2942   </c>
2943   <c>409</c>
2944   <c>Conflict</c>
2945   <c>
2946      <xref target="status.409"/>
2947   </c>
2948   <c>410</c>
2949   <c>Gone</c>
2950   <c>
2951      <xref target="status.410"/>
2952   </c>
2953   <c>411</c>
2954   <c>Length Required</c>
2955   <c>
2956      <xref target="status.411"/>
2957   </c>
2958   <c>413</c>
2959   <c>Request Representation Too Large</c>
2960   <c>
2961      <xref target="status.413"/>
2962   </c>
2963   <c>414</c>
2964   <c>URI Too Long</c>
2965   <c>
2966      <xref target="status.414"/>
2967   </c>
2968   <c>415</c>
2969   <c>Unsupported Media Type</c>
2970   <c>
2971      <xref target="status.415"/>
2972   </c>
2973   <c>417</c>
2974   <c>Expectation Failed</c>
2975   <c>
2976      <xref target="status.417"/>
2977   </c>
2978   <c>426</c>
2979   <c>Upgrade Required</c>
2980   <c>
2981      <xref target="status.426"/>
2982   </c>
2983   <c>500</c>
2984   <c>Internal Server Error</c>
2985   <c>
2986      <xref target="status.500"/>
2987   </c>
2988   <c>501</c>
2989   <c>Not Implemented</c>
2990   <c>
2991      <xref target="status.501"/>
2992   </c>
2993   <c>502</c>
2994   <c>Bad Gateway</c>
2995   <c>
2996      <xref target="status.502"/>
2997   </c>
2998   <c>503</c>
2999   <c>Service Unavailable</c>
3000   <c>
3001      <xref target="status.503"/>
3002   </c>
3003   <c>504</c>
3004   <c>Gateway Timeout</c>
3005   <c>
3006      <xref target="status.504"/>
3007   </c>
3008   <c>505</c>
3009   <c>HTTP Version Not Supported</c>
3010   <c>
3011      <xref target="status.505"/>
3012   </c>
3013</texttable>
3014<!--(END)-->
3015<?ENDINC p2-semantics.iana-status-codes ?>
3016</section>
3017<section title="Header Field Registration" anchor="header.field.registration">
3018<t>
3019   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3020   with the permanent registrations below (see <xref target="RFC3864"/>):
3021</t>
3022<?BEGININC p2-semantics.iana-headers ?>
3023<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3024<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3025   <ttcol>Header Field Name</ttcol>
3026   <ttcol>Protocol</ttcol>
3027   <ttcol>Status</ttcol>
3028   <ttcol>Reference</ttcol>
3029
3030   <c>Allow</c>
3031   <c>http</c>
3032   <c>standard</c>
3033   <c>
3034      <xref target="header.allow"/>
3035   </c>
3036   <c>Date</c>
3037   <c>http</c>
3038   <c>standard</c>
3039   <c>
3040      <xref target="header.date"/>
3041   </c>
3042   <c>Expect</c>
3043   <c>http</c>
3044   <c>standard</c>
3045   <c>
3046      <xref target="header.expect"/>
3047   </c>
3048   <c>From</c>
3049   <c>http</c>
3050   <c>standard</c>
3051   <c>
3052      <xref target="header.from"/>
3053   </c>
3054   <c>Location</c>
3055   <c>http</c>
3056   <c>standard</c>
3057   <c>
3058      <xref target="header.location"/>
3059   </c>
3060   <c>Max-Forwards</c>
3061   <c>http</c>
3062   <c>standard</c>
3063   <c>
3064      <xref target="header.max-forwards"/>
3065   </c>
3066   <c>Referer</c>
3067   <c>http</c>
3068   <c>standard</c>
3069   <c>
3070      <xref target="header.referer"/>
3071   </c>
3072   <c>Retry-After</c>
3073   <c>http</c>
3074   <c>standard</c>
3075   <c>
3076      <xref target="header.retry-after"/>
3077   </c>
3078   <c>Server</c>
3079   <c>http</c>
3080   <c>standard</c>
3081   <c>
3082      <xref target="header.server"/>
3083   </c>
3084   <c>User-Agent</c>
3085   <c>http</c>
3086   <c>standard</c>
3087   <c>
3088      <xref target="header.user-agent"/>
3089   </c>
3090</texttable>
3091<!--(END)-->
3092<?ENDINC p2-semantics.iana-headers ?>
3093<t>
3094   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3095</t>
3096</section>
3097</section>
3098
3099<section title="Security Considerations" anchor="security.considerations">
3100<t>
3101   This section is meant to inform application developers, information
3102   providers, and users of the security limitations in HTTP/1.1 as
3103   described by this document. The discussion does not include
3104   definitive solutions to the problems revealed, though it does make
3105   some suggestions for reducing security risks.
3106</t>
3107
3108<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3109<t>
3110   Like any generic data transfer protocol, HTTP cannot regulate the
3111   content of the data that is transferred, nor is there any a priori
3112   method of determining the sensitivity of any particular piece of
3113   information within the context of any given request. Therefore,
3114   applications &SHOULD; supply as much control over this information as
3115   possible to the provider of that information. Four header fields are
3116   worth special mention in this context: Server, Via, Referer and From.
3117</t>
3118<t>
3119   Revealing the specific software version of the server might allow the
3120   server machine to become more vulnerable to attacks against software
3121   that is known to contain security holes. Implementors &SHOULD; make the
3122   Server header field a configurable option.
3123</t>
3124<t>
3125   Proxies which serve as a portal through a network firewall &SHOULD;
3126   take special precautions regarding the transfer of header information
3127   that identifies the hosts behind the firewall. In particular, they
3128   &SHOULD; remove, or replace with sanitized versions, any Via fields
3129   generated behind the firewall.
3130</t>
3131<t>
3132   The Referer header field allows reading patterns to be studied and reverse
3133   links drawn. Although it can be very useful, its power can be abused
3134   if user details are not separated from the information contained in
3135   the Referer. Even when the personal information has been removed, the
3136   Referer header field might indicate a private document's URI whose
3137   publication would be inappropriate.
3138</t>
3139<t>
3140   The information sent in the From field might conflict with the user's
3141   privacy interests or their site's security policy, and hence it
3142   &SHOULD-NOT;  be transmitted without the user being able to disable,
3143   enable, and modify the contents of the field. The user &MUST; be able
3144   to set the contents of this field within a user preference or
3145   application defaults configuration.
3146</t>
3147<t>
3148   We suggest, though do not require, that a convenient toggle interface
3149   be provided for the user to enable or disable the sending of From and
3150   Referer information.
3151</t>
3152<t>
3153   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3154   target="header.server"/>) header fields can sometimes be used to determine
3155   that a specific client or server has a particular security hole which might
3156   be exploited. Unfortunately, this same information is often used for other
3157   valuable purposes for which HTTP currently has no better mechanism.
3158</t>
3159<t>
3160   Furthermore, the User-Agent header field may contain enough entropy to be
3161   used, possibly in conjunction with other material, to uniquely identify the
3162   user.
3163</t>
3164<t>
3165   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3166   that was sent in request header fields within the body of their response.
3167   Clients &SHOULD; be careful with sensitive information, like Cookies,
3168   Authorization credentials, and other header fields that might be used to
3169   collect data from the client.
3170</t> 
3171</section>
3172
3173<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3174<t>
3175   Because the source of a link might be private information or might
3176   reveal an otherwise private information source, it is strongly
3177   recommended that the user be able to select whether or not the
3178   Referer field is sent. For example, a browser client could have a
3179   toggle switch for browsing openly/anonymously, which would
3180   respectively enable/disable the sending of Referer and From
3181   information.
3182</t>
3183<t>
3184   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3185   HTTP request if the referring page was transferred with a secure
3186   protocol.
3187</t>
3188<t>
3189   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3190   sensitive data because that data will be placed in the request-target. Many
3191   existing servers, proxies, and user agents log or display the request-target
3192   in places where it might be visible to third parties. Such services can
3193   use POST-based form submission instead.
3194</t>
3195</section>
3196
3197<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3198<t>
3199   If a single server supports multiple organizations that do not trust
3200   one another, then it &MUST; check the values of Location and Content-Location
3201   header fields in responses that are generated under control of
3202   said organizations to make sure that they do not attempt to
3203   invalidate resources over which they have no authority.
3204</t>
3205<t>
3206   Furthermore, appending the fragment identifier from one URI to another
3207   one obtained from a Location header field might leak confidential
3208   information to the target server &mdash; although the fragment identifier is
3209   not transmitted in the final request, it might be visible to the user agent
3210   through other means, such as scripting.
3211</t>
3212</section>
3213
3214<section title="Security Considerations for CONNECT">
3215<t>
3216   Since tunneled data is opaque to the proxy, there are additional
3217   risks to tunneling to other well-known or reserved ports.
3218   A HTTP client CONNECTing to port 25 could relay spam
3219   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3220   access to a small number of known ports.
3221</t>
3222</section>
3223
3224</section>
3225
3226<section title="Acknowledgments" anchor="acks">
3227<t>
3228  See &acks;.
3229</t>
3230</section>
3231</middle>
3232<back>
3233
3234<references title="Normative References">
3235
3236<reference anchor="Part1">
3237  <front>
3238    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3239    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3240      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3241      <address><email>fielding@gbiv.com</email></address>
3242    </author>
3243    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3244      <organization abbrev="W3C">World Wide Web Consortium</organization>
3245      <address><email>ylafon@w3.org</email></address>
3246    </author>
3247    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3248      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3249      <address><email>julian.reschke@greenbytes.de</email></address>
3250    </author>
3251    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3252  </front>
3253  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3254  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3255</reference>
3256
3257<reference anchor="Part3">
3258  <front>
3259    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3260    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3261      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3262      <address><email>fielding@gbiv.com</email></address>
3263    </author>
3264    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3265      <organization abbrev="W3C">World Wide Web Consortium</organization>
3266      <address><email>ylafon@w3.org</email></address>
3267    </author>
3268    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3269      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3270      <address><email>julian.reschke@greenbytes.de</email></address>
3271    </author>
3272    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3273  </front>
3274  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3275  <x:source href="p3-payload.xml" basename="p3-payload"/>
3276</reference>
3277
3278<reference anchor="Part4">
3279  <front>
3280    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3281    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3282      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3283      <address><email>fielding@gbiv.com</email></address>
3284    </author>
3285    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3286      <organization abbrev="W3C">World Wide Web Consortium</organization>
3287      <address><email>ylafon@w3.org</email></address>
3288    </author>
3289    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3290      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3291      <address><email>julian.reschke@greenbytes.de</email></address>
3292    </author>
3293    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3294  </front>
3295  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3296  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3297</reference>
3298
3299<reference anchor="Part5">
3300  <front>
3301    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3302    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3303      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3304      <address><email>fielding@gbiv.com</email></address>
3305    </author>
3306    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3307      <organization abbrev="W3C">World Wide Web Consortium</organization>
3308      <address><email>ylafon@w3.org</email></address>
3309    </author>
3310    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3311      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3312      <address><email>julian.reschke@greenbytes.de</email></address>
3313    </author>
3314    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3315  </front>
3316  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3317  <x:source href="p5-range.xml" basename="p5-range"/>
3318</reference>
3319
3320<reference anchor="Part6">
3321  <front>
3322    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3323    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3324      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3325      <address><email>fielding@gbiv.com</email></address>
3326    </author>
3327    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3328      <organization abbrev="W3C">World Wide Web Consortium</organization>
3329      <address><email>ylafon@w3.org</email></address>
3330    </author>
3331    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3332      <organization>Rackspace</organization>
3333      <address><email>mnot@mnot.net</email></address>
3334    </author>
3335    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3336      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3337      <address><email>julian.reschke@greenbytes.de</email></address>
3338    </author>
3339    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3340  </front>
3341  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3342  <x:source href="p6-cache.xml" basename="p6-cache"/>
3343</reference>
3344
3345<reference anchor="Part7">
3346  <front>
3347    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3348    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3349      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3350      <address><email>fielding@gbiv.com</email></address>
3351    </author>
3352    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3353      <organization abbrev="W3C">World Wide Web Consortium</organization>
3354      <address><email>ylafon@w3.org</email></address>
3355    </author>
3356    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3357      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3358      <address><email>julian.reschke@greenbytes.de</email></address>
3359    </author>
3360    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3361  </front>
3362  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3363  <x:source href="p7-auth.xml" basename="p7-auth"/>
3364</reference>
3365
3366<reference anchor="RFC2119">
3367  <front>
3368    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3369    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3370      <organization>Harvard University</organization>
3371      <address><email>sob@harvard.edu</email></address>
3372    </author>
3373    <date month="March" year="1997"/>
3374  </front>
3375  <seriesInfo name="BCP" value="14"/>
3376  <seriesInfo name="RFC" value="2119"/>
3377</reference>
3378
3379<reference anchor="RFC3986">
3380 <front>
3381  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3382  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3383    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3384    <address>
3385       <email>timbl@w3.org</email>
3386       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3387    </address>
3388  </author>
3389  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3390    <organization abbrev="Day Software">Day Software</organization>
3391    <address>
3392      <email>fielding@gbiv.com</email>
3393      <uri>http://roy.gbiv.com/</uri>
3394    </address>
3395  </author>
3396  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3397    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3398    <address>
3399      <email>LMM@acm.org</email>
3400      <uri>http://larry.masinter.net/</uri>
3401    </address>
3402  </author>
3403  <date month='January' year='2005'></date>
3404 </front>
3405 <seriesInfo name="STD" value="66"/>
3406 <seriesInfo name="RFC" value="3986"/>
3407</reference>
3408
3409<reference anchor="RFC5234">
3410  <front>
3411    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3412    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3413      <organization>Brandenburg InternetWorking</organization>
3414      <address>
3415        <email>dcrocker@bbiw.net</email>
3416      </address> 
3417    </author>
3418    <author initials="P." surname="Overell" fullname="Paul Overell">
3419      <organization>THUS plc.</organization>
3420      <address>
3421        <email>paul.overell@thus.net</email>
3422      </address>
3423    </author>
3424    <date month="January" year="2008"/>
3425  </front>
3426  <seriesInfo name="STD" value="68"/>
3427  <seriesInfo name="RFC" value="5234"/>
3428</reference>
3429
3430</references>
3431
3432<references title="Informative References">
3433
3434<reference anchor="RFC1123">
3435  <front>
3436    <title>Requirements for Internet Hosts - Application and Support</title>
3437    <author initials="R." surname="Braden" fullname="Robert Braden">
3438      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3439      <address><email>Braden@ISI.EDU</email></address>
3440    </author>
3441    <date month="October" year="1989"/>
3442  </front>
3443  <seriesInfo name="STD" value="3"/>
3444  <seriesInfo name="RFC" value="1123"/>
3445</reference>
3446
3447<reference anchor="RFC1945">
3448  <front>
3449    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3450    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3451      <organization>MIT, Laboratory for Computer Science</organization>
3452      <address><email>timbl@w3.org</email></address>
3453    </author>
3454    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3455      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3456      <address><email>fielding@ics.uci.edu</email></address>
3457    </author>
3458    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3459      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3460      <address><email>frystyk@w3.org</email></address>
3461    </author>
3462    <date month="May" year="1996"/>
3463  </front>
3464  <seriesInfo name="RFC" value="1945"/>
3465</reference>
3466
3467<reference anchor="RFC2068">
3468  <front>
3469    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3470    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3471      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3472      <address><email>fielding@ics.uci.edu</email></address>
3473    </author>
3474    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3475      <organization>MIT Laboratory for Computer Science</organization>
3476      <address><email>jg@w3.org</email></address>
3477    </author>
3478    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3479      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3480      <address><email>mogul@wrl.dec.com</email></address>
3481    </author>
3482    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3483      <organization>MIT Laboratory for Computer Science</organization>
3484      <address><email>frystyk@w3.org</email></address>
3485    </author>
3486    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3487      <organization>MIT Laboratory for Computer Science</organization>
3488      <address><email>timbl@w3.org</email></address>
3489    </author>
3490    <date month="January" year="1997"/>
3491  </front>
3492  <seriesInfo name="RFC" value="2068"/>
3493</reference>
3494
3495<reference anchor="RFC2616">
3496  <front>
3497    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3498    <author initials="R." surname="Fielding" fullname="R. Fielding">
3499      <organization>University of California, Irvine</organization>
3500      <address><email>fielding@ics.uci.edu</email></address>
3501    </author>
3502    <author initials="J." surname="Gettys" fullname="J. Gettys">
3503      <organization>W3C</organization>
3504      <address><email>jg@w3.org</email></address>
3505    </author>
3506    <author initials="J." surname="Mogul" fullname="J. Mogul">
3507      <organization>Compaq Computer Corporation</organization>
3508      <address><email>mogul@wrl.dec.com</email></address>
3509    </author>
3510    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3511      <organization>MIT Laboratory for Computer Science</organization>
3512      <address><email>frystyk@w3.org</email></address>
3513    </author>
3514    <author initials="L." surname="Masinter" fullname="L. Masinter">
3515      <organization>Xerox Corporation</organization>
3516      <address><email>masinter@parc.xerox.com</email></address>
3517    </author>
3518    <author initials="P." surname="Leach" fullname="P. Leach">
3519      <organization>Microsoft Corporation</organization>
3520      <address><email>paulle@microsoft.com</email></address>
3521    </author>
3522    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3523      <organization>W3C</organization>
3524      <address><email>timbl@w3.org</email></address>
3525    </author>
3526    <date month="June" year="1999"/>
3527  </front>
3528  <seriesInfo name="RFC" value="2616"/>
3529</reference>
3530
3531<reference anchor='RFC2817'>
3532  <front>
3533    <title>Upgrading to TLS Within HTTP/1.1</title>
3534    <author initials='R.' surname='Khare' fullname='R. Khare'>
3535      <organization>4K Associates / UC Irvine</organization>
3536      <address><email>rohit@4K-associates.com</email></address>
3537    </author>
3538    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3539      <organization>Agranat Systems, Inc.</organization>
3540      <address><email>lawrence@agranat.com</email></address>
3541    </author>
3542    <date year='2000' month='May' />
3543  </front>
3544  <seriesInfo name='RFC' value='2817' />
3545</reference>
3546
3547<reference anchor='RFC3864'>
3548  <front>
3549    <title>Registration Procedures for Message Header Fields</title>
3550    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3551      <organization>Nine by Nine</organization>
3552      <address><email>GK-IETF@ninebynine.org</email></address>
3553    </author>
3554    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3555      <organization>BEA Systems</organization>
3556      <address><email>mnot@pobox.com</email></address>
3557    </author>
3558    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3559      <organization>HP Labs</organization>
3560      <address><email>JeffMogul@acm.org</email></address>
3561    </author>
3562    <date year='2004' month='September' />
3563  </front>
3564  <seriesInfo name='BCP' value='90' />
3565  <seriesInfo name='RFC' value='3864' />
3566</reference>
3567
3568<reference anchor='RFC5226'>
3569  <front>
3570    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3571    <author initials='T.' surname='Narten' fullname='T. Narten'>
3572      <organization>IBM</organization>
3573      <address><email>narten@us.ibm.com</email></address>
3574    </author>
3575    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3576      <organization>Google</organization>
3577      <address><email>Harald@Alvestrand.no</email></address>
3578    </author>
3579    <date year='2008' month='May' />
3580  </front>
3581  <seriesInfo name='BCP' value='26' />
3582  <seriesInfo name='RFC' value='5226' />
3583</reference>
3584
3585<reference anchor="RFC5322">
3586  <front>
3587    <title>Internet Message Format</title>
3588    <author initials="P." surname="Resnick" fullname="P. Resnick">
3589      <organization>Qualcomm Incorporated</organization>
3590    </author>
3591    <date year="2008" month="October"/>
3592  </front> 
3593  <seriesInfo name="RFC" value="5322"/>
3594</reference>
3595
3596<reference anchor='RFC5789'>
3597  <front>
3598    <title>PATCH Method for HTTP</title>
3599    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3600      <organization>Linden Lab</organization>
3601    </author>
3602    <author initials='J.' surname='Snell' fullname='J. Snell' />
3603    <date year='2010' month='March' />
3604  </front>
3605  <seriesInfo name='RFC' value='5789' />
3606</reference>
3607
3608<reference anchor="RFC5987">
3609        <front>
3610    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3611    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3612      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3613      <address>
3614        <postal>
3615          <street>Hafenweg 16</street>
3616          <city>Muenster</city><region>NW</region><code>48155</code>
3617          <country>Germany</country>
3618        </postal>
3619        <email>julian.reschke@greenbytes.de</email>     
3620        <uri>http://greenbytes.de/tech/webdav/</uri>   
3621      </address>
3622    </author>
3623    <date month="August" year="2010"/>
3624  </front>
3625  <seriesInfo name="RFC" value="5987"/>
3626</reference>
3627
3628<reference anchor="draft-reschke-http-status-308">
3629        <front>
3630    <title abbrev="HTTP Status Code 308">The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)</title>
3631    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3632      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3633      <address>
3634        <email>julian.reschke@greenbytes.de</email>     
3635      </address>
3636    </author>
3637    <date month="March" year="2012"/>
3638  </front>
3639  <seriesInfo name="Internet-Draft" value="draft-reschke-http-status-308-07"/>
3640</reference>
3641
3642</references>
3643
3644<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3645<t>
3646  Clarify definition of POST.
3647  (<xref target="POST"/>)
3648</t>
3649<t>
3650  Remove requirement to handle all Content-* header fields; ban use of
3651  Content-Range with PUT.
3652  (<xref target="PUT"/>)
3653</t>
3654<t>
3655  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3656  (<xref target="CONNECT"/>)
3657</t>
3658<t>
3659  This document takes over the Status Code Registry, previously defined
3660  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3661  (<xref target="status.code.registry"/>)
3662</t>
3663<t>
3664  Broadened the definition of 203 (Non-Authoritative Information) to include
3665  cases of payload transformations as well.
3666  (<xref target="status.203"/>)
3667</t>
3668<t>
3669  Status codes 301, 302, and 307: removed the normative requirements on both
3670  response payloads and user interaction.
3671  (<xref target="status.3xx"/>)
3672</t>
3673<t>
3674  Failed to consider that there are many other request methods that are safe
3675  to automatically redirect, and further that the user agent is able to make
3676  that determination based on the request method semantics.
3677  Furthermore, allow user agents to rewrite the method from POST to GET
3678  for status codes 301 and 302.
3679  (Sections <xref format="counter" target="status.301"/>,
3680  <xref format="counter" target="status.302"/> and
3681  <xref format="counter" target="status.307"/>)
3682</t>
3683<t>
3684  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3685  It used to indicate that the target resource needs to be accessed through the
3686  proxy given by the Location field. The Location field gave the URI of the
3687  proxy. The recipient was expected to repeat this single request via the proxy.
3688  (<xref target="status.305"/>)
3689</t>
3690<t>
3691  Define status 426 (Upgrade Required) (this was incorporated from
3692  <xref target="RFC2817"/>).
3693  (<xref target="status.426"/>)
3694</t>
3695<t>
3696  Change ABNF productions for header fields to only define the field value.
3697  (<xref target="header.field.definitions"/>)
3698</t>
3699<t>
3700  Reclassify "Allow" as response header field, removing the option to
3701  specify it in a PUT request.
3702  Relax the server requirement on the contents of the Allow header field and
3703  remove requirement on clients to always trust the header field value.
3704  (<xref target="header.allow"/>)
3705</t>
3706<t>
3707  The ABNF for the Expect header field has been both fixed (allowing parameters
3708  for value-less expectations as well) and simplified (allowing trailing
3709  semicolons after "100-continue" when they were invalid before).
3710  (<xref target="header.expect"/>)
3711</t>
3712<t>
3713  Correct syntax of Location header field to allow URI references (including
3714  relative references and fragments), as referred symbol "absoluteURI" wasn't
3715  what was expected, and add some clarifications as to when use of fragments
3716  would not be appropriate.
3717  (<xref target="header.location"/>)
3718</t>
3719<t>
3720  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
3721  extension methods could have used it as well).
3722  (<xref target="header.max-forwards"/>)
3723</t>
3724<t>
3725  Allow Referer field value of "about:blank" as alternative to not specifying it.
3726  (<xref target="header.referer"/>)
3727</t>
3728<t>
3729  In the description of the Server header field, the Via field
3730  was described as a SHOULD. The requirement was and is stated
3731  correctly in the description of the Via header field in &header-via;.
3732  (<xref target="header.server"/>)
3733</t>
3734</section>
3735
3736<?BEGININC p2-semantics.abnf-appendix ?>
3737<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
3738<figure>
3739<artwork type="abnf" name="p2-semantics.parsed-abnf">
3740<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
3741
3742<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
3743
3744<x:ref>Date</x:ref> = HTTP-date
3745
3746<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
3747
3748<x:ref>From</x:ref> = mailbox
3749
3750<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
3751
3752<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
3753
3754<x:ref>Location</x:ref> = URI-reference
3755
3756<x:ref>Max-Forwards</x:ref> = 1*DIGIT
3757
3758<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
3759
3760<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
3761<x:ref>Referer</x:ref> = absolute-URI / partial-URI
3762<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
3763
3764<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
3765
3766<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
3767<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
3768
3769<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
3770<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
3771
3772<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
3773
3774<x:ref>date1</x:ref> = day SP month SP year
3775<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
3776<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
3777<x:ref>day</x:ref> = 2DIGIT
3778<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
3779 / %x54.75.65 ; Tue
3780 / %x57.65.64 ; Wed
3781 / %x54.68.75 ; Thu
3782 / %x46.72.69 ; Fri
3783 / %x53.61.74 ; Sat
3784 / %x53.75.6E ; Sun
3785<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
3786 / %x54.75.65.73.64.61.79 ; Tuesday
3787 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
3788 / %x54.68.75.72.73.64.61.79 ; Thursday
3789 / %x46.72.69.64.61.79 ; Friday
3790 / %x53.61.74.75.72.64.61.79 ; Saturday
3791 / %x53.75.6E.64.61.79 ; Sunday
3792<x:ref>delta-seconds</x:ref> = 1*DIGIT
3793
3794<x:ref>expect-name</x:ref> = token
3795<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
3796<x:ref>expect-value</x:ref> = token / quoted-string
3797<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
3798 OWS expect-param ] )
3799
3800<x:ref>hour</x:ref> = 2DIGIT
3801
3802<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
3803<x:ref>method</x:ref> = token
3804<x:ref>minute</x:ref> = 2DIGIT
3805<x:ref>month</x:ref> = %x4A.61.6E ; Jan
3806 / %x46.65.62 ; Feb
3807 / %x4D.61.72 ; Mar
3808 / %x41.70.72 ; Apr
3809 / %x4D.61.79 ; May
3810 / %x4A.75.6E ; Jun
3811 / %x4A.75.6C ; Jul
3812 / %x41.75.67 ; Aug
3813 / %x53.65.70 ; Sep
3814 / %x4F.63.74 ; Oct
3815 / %x4E.6F.76 ; Nov
3816 / %x44.65.63 ; Dec
3817
3818<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
3819<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
3820
3821<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
3822<x:ref>product</x:ref> = token [ "/" product-version ]
3823<x:ref>product-version</x:ref> = token
3824
3825<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
3826
3827<x:ref>reason-phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
3828<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
3829<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
3830
3831<x:ref>second</x:ref> = 2DIGIT
3832<x:ref>status-code</x:ref> = 3DIGIT
3833
3834<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
3835<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
3836
3837<x:ref>year</x:ref> = 4DIGIT
3838</artwork>
3839</figure>
3840<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
3841; Allow defined but not used
3842; Date defined but not used
3843; Expect defined but not used
3844; From defined but not used
3845; Location defined but not used
3846; Max-Forwards defined but not used
3847; Referer defined but not used
3848; Retry-After defined but not used
3849; Server defined but not used
3850; User-Agent defined but not used
3851; reason-phrase defined but not used
3852; status-code defined but not used
3853</artwork></figure></section>
3854<?ENDINC p2-semantics.abnf-appendix ?>
3855
3856<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
3857
3858<section title="Since RFC 2616">
3859<t>
3860  Extracted relevant partitions from <xref target="RFC2616"/>.
3861</t>
3862</section>
3863
3864<section title="Since draft-ietf-httpbis-p2-semantics-00">
3865<t>
3866  Closed issues:
3867  <list style="symbols"> 
3868    <t>
3869      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
3870      "Via is a MUST"
3871      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
3872    </t>
3873    <t>
3874      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
3875      "Fragments allowed in Location"
3876      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
3877    </t>
3878    <t>
3879      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
3880      "Safe Methods vs Redirection"
3881      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
3882    </t>
3883    <t>
3884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
3885      "Revise description of the POST method"
3886      (<eref target="http://purl.org/NET/http-errata#post"/>)
3887    </t>
3888    <t>
3889      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
3890      "Normative and Informative references"
3891    </t>
3892    <t>
3893      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
3894      "RFC2606 Compliance"
3895    </t>
3896    <t>
3897      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
3898      "Informative references"
3899    </t>
3900    <t>
3901      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
3902      "Redundant cross-references"
3903    </t>
3904  </list>
3905</t>
3906<t>
3907  Other changes:
3908  <list style="symbols"> 
3909    <t>
3910      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
3911    </t>
3912  </list>
3913</t>
3914</section>
3915
3916<section title="Since draft-ietf-httpbis-p2-semantics-01">
3917<t>
3918  Closed issues:
3919  <list style="symbols"> 
3920    <t>
3921      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
3922      "PUT side effects"
3923    </t>
3924    <t>
3925      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
3926      "Duplicate Host header requirements"
3927    </t>
3928  </list>
3929</t>
3930<t>
3931  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3932  <list style="symbols"> 
3933    <t>
3934      Move "Product Tokens" section (back) into Part 1, as "token" is used
3935      in the definition of the Upgrade header field.
3936    </t>
3937    <t>
3938      Add explicit references to BNF syntax and rules imported from other parts of the specification.
3939    </t>
3940    <t>
3941      Copy definition of delta-seconds from Part6 instead of referencing it.
3942    </t>
3943  </list>
3944</t>
3945</section>
3946
3947<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
3948<t>
3949  Closed issues:
3950  <list style="symbols"> 
3951    <t>
3952      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
3953      "Requiring Allow in 405 responses"
3954    </t>
3955    <t>
3956      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
3957      "Status Code Registry"
3958    </t>
3959    <t>
3960      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
3961      "Redirection vs. Location"
3962    </t>
3963    <t>
3964      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
3965      "Cacheability of 303 response"
3966    </t>
3967    <t>
3968      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
3969      "305 Use Proxy"
3970    </t>
3971    <t>
3972      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
3973      "Classification for Allow header"
3974    </t>
3975    <t>
3976      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
3977      "PUT - 'store under' vs 'store at'"
3978    </t>
3979  </list>
3980</t>
3981<t>
3982  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
3983  <list style="symbols"> 
3984    <t>
3985      Reference RFC 3984, and update header field registrations for headers defined
3986      in this document.
3987    </t>
3988  </list>
3989</t>
3990<t>
3991  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
3992  <list style="symbols"> 
3993    <t>
3994      Replace string literals when the string really is case-sensitive (method).
3995    </t>
3996  </list>
3997</t>
3998</section>
3999
4000<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4001<t>
4002  Closed issues:
4003  <list style="symbols"> 
4004    <t>
4005      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4006      "OPTIONS request bodies"
4007    </t>
4008    <t>
4009      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4010      "Description of CONNECT should refer to RFC2817"
4011    </t>
4012    <t>
4013      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4014      "Location Content-Location reference request/response mixup"
4015    </t>
4016  </list>
4017</t>
4018<t>
4019  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4020  <list style="symbols"> 
4021    <t>
4022      Added initial proposal for registration process, plus initial
4023      content (non-HTTP/1.1 methods to be added by a separate specification).
4024    </t>
4025  </list>
4026</t>
4027</section>
4028
4029<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4030<t>
4031  Closed issues:
4032  <list style="symbols"> 
4033    <t>
4034      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4035      "Content-*"
4036    </t>
4037    <t>
4038      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4039      "RFC 2822 is updated by RFC 5322"
4040    </t>
4041  </list>
4042</t>
4043<t>
4044  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4045  <list style="symbols"> 
4046    <t>
4047      Use "/" instead of "|" for alternatives.
4048    </t>
4049    <t>
4050      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4051      whitespace ("OWS") and required whitespace ("RWS").
4052    </t>
4053    <t>
4054      Rewrite ABNFs to spell out whitespace rules, factor out
4055      header field value format definitions.
4056    </t>
4057  </list>
4058</t>
4059</section>
4060
4061<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4062<t>
4063  Closed issues:
4064  <list style="symbols"> 
4065    <t>
4066      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4067      "reason-phrase BNF"
4068    </t>
4069  </list>
4070</t>
4071<t>
4072  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4073  <list style="symbols"> 
4074    <t>
4075      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4076    </t>
4077  </list>
4078</t>
4079</section>
4080
4081<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4082<t>
4083  Closed issues:
4084  <list style="symbols"> 
4085    <t>
4086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4087      "Clarify when Referer is sent"
4088    </t>
4089    <t>
4090      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4091      "status codes vs methods"
4092    </t>
4093    <t>
4094      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4095      "Do not require "updates" relation for specs that register status codes or method names"
4096    </t>
4097  </list>
4098</t>
4099</section>
4100
4101<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4102<t>
4103  Closed issues:
4104  <list style="symbols"> 
4105    <t>
4106      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4107      "Idempotency"
4108    </t>
4109    <t>
4110      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4111      "TRACE security considerations"
4112    </t>
4113    <t>
4114      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4115      "Clarify rules for determining what entities a response carries"
4116    </t>
4117    <t>
4118      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4119      "update note citing RFC 1945 and 2068"
4120    </t>
4121    <t>
4122      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4123      "update note about redirect limit"
4124    </t>
4125    <t>
4126      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4127      "Location header ABNF should use 'URI'"
4128    </t>
4129    <t>
4130      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4131      "fragments in Location vs status 303"
4132    </t>
4133    <t>
4134      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4135      "move IANA registrations for optional status codes"
4136    </t>
4137  </list>
4138</t>
4139<t>
4140  Partly resolved issues:
4141  <list style="symbols"> 
4142    <t>
4143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4144      "Are OPTIONS and TRACE safe?"
4145    </t>
4146  </list>
4147</t>
4148</section>
4149
4150<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4151<t>
4152  Closed issues:
4153  <list style="symbols"> 
4154    <t>
4155      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4156      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4157      status codes when fixing this previously)
4158    </t>
4159  </list>
4160</t>
4161</section>
4162
4163<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4164<t>
4165  Closed issues:
4166  <list style="symbols"> 
4167    <t>
4168      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4169      "Fragment combination / precedence during redirects"
4170    </t>
4171  </list>
4172</t>
4173<t>
4174  Partly resolved issues:
4175  <list style="symbols"> 
4176    <t>
4177      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4178      "Location header payload handling"
4179    </t>
4180    <t>
4181      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4182      "Term for the requested resource's URI"
4183    </t>
4184  </list>
4185</t>
4186</section>
4187
4188<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4189<t>
4190  Closed issues:
4191  <list style="symbols"> 
4192    <t>
4193      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4194      "Clarify 'Requested Variant'"
4195    </t>
4196    <t>
4197      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4198      "Clarify entity / representation / variant terminology"
4199    </t>
4200    <t>
4201      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4202      "Methods and Caching"
4203    </t>
4204    <t>
4205      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4206      "OPTIONS vs Max-Forwards"
4207    </t>
4208    <t>
4209      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4210      "Status codes and caching"
4211    </t>
4212    <t>
4213      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4214      "consider removing the 'changes from 2068' sections"
4215    </t>
4216  </list>
4217</t>
4218</section>
4219
4220<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4221<t>
4222  Closed issues:
4223  <list style="symbols"> 
4224    <t>
4225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4226      "Considerations for new status codes"
4227    </t>
4228    <t>
4229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4230      "Considerations for new methods"
4231    </t>
4232    <t>
4233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4234      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4235    </t>
4236  </list>
4237</t>
4238</section>
4239
4240<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4241<t>
4242  Closed issues:
4243  <list style="symbols"> 
4244    <t>
4245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4246      "Fragment combination / precedence during redirects" (added warning
4247      about having a fragid on the redirect may cause inconvenience in
4248      some cases)
4249    </t>
4250    <t>
4251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4252      "Content-* vs. PUT"
4253    </t>
4254    <t>
4255      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4256      "205 Bodies"
4257    </t>
4258    <t>
4259      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4260      "Understanding Content-* on non-PUT requests"
4261    </t>
4262    <t>
4263      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4264      "Content-*"
4265    </t>
4266    <t>
4267      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4268      "Header type defaulting"
4269    </t>
4270    <t>
4271      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4272      "PUT - 'store under' vs 'store at'"
4273    </t>
4274    <t>
4275      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4276      "duplicate ABNF for reason-phrase"
4277    </t>
4278    <t>
4279      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4280      "Note special status of Content-* prefix in header registration procedures"
4281    </t>
4282    <t>
4283      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4284      "Max-Forwards vs extension methods"
4285    </t>
4286    <t>
4287      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4288      "What is the value space of HTTP status codes?" (actually fixed in
4289      draft-ietf-httpbis-p2-semantics-11)
4290    </t>
4291    <t>
4292      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4293      "Header Classification"
4294    </t>
4295    <t>
4296      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4297      "PUT side effect: invalidation or just stale?"
4298    </t>
4299    <t>
4300      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4301      "proxies not supporting certain methods"
4302    </t>
4303    <t>
4304      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4305      "Migrate CONNECT from RFC2817 to p2"
4306    </t>
4307    <t>
4308      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4309      "Migrate Upgrade details from RFC2817"
4310    </t>
4311    <t>
4312      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4313      "clarify PUT semantics'"
4314    </t>
4315    <t>
4316      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4317      "duplicate ABNF for 'Method'"
4318    </t>
4319    <t>
4320      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4321      "untangle ABNFs for header fields"
4322    </t>
4323  </list>
4324</t>
4325</section>
4326
4327<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4328<t>
4329  Closed issues:
4330  <list style="symbols"> 
4331    <t>
4332      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4333      "untangle ABNFs for header fields"
4334    </t>
4335    <t>
4336      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4337      "message body in CONNECT request"
4338    </t>
4339  </list>
4340</t>
4341</section>
4342
4343<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4344<t>
4345  Closed issues:
4346  <list style="symbols"> 
4347    <t>
4348      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4349      "Clarify status code for rate limiting"
4350    </t>
4351    <t>
4352      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4353      "clarify 403 forbidden"
4354    </t>
4355    <t>
4356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4357      "Clarify 203 Non-Authoritative Information"
4358    </t>
4359    <t>
4360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4361      "update default reason phrase for 413"
4362    </t>
4363  </list>
4364</t>
4365</section>
4366
4367<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4368<t>
4369  Closed issues:
4370  <list style="symbols"> 
4371    <t>
4372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4373      "Strength of requirements on Accept re: 406"
4374    </t>
4375    <t>
4376      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4377      "400 response isn't generic"
4378    </t>
4379  </list>
4380</t>
4381</section>
4382
4383<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4384<t>
4385  Closed issues:
4386  <list style="symbols"> 
4387    <t>
4388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4389      "Redirects and non-GET methods"
4390    </t>
4391    <t>
4392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4393      "Document HTTP's error-handling philosophy"
4394    </t>
4395    <t>
4396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4397      "Considerations for new headers"
4398    </t>
4399    <t>
4400      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4401      "clarify 303 redirect on HEAD"
4402    </t>
4403  </list>
4404</t>
4405</section>
4406
4407<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4408<t>
4409  Closed issues:
4410  <list style="symbols"> 
4411    <t>
4412      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4413      "Location header payload handling"
4414    </t>
4415    <t>
4416      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4417      "Clarify status code for rate limiting" (change backed out because
4418      a new status code is being defined for this purpose)
4419    </t>
4420    <t>
4421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4422      "should there be a permanent variant of 307"
4423    </t>
4424    <t>
4425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4426      "When are Location's semantics triggered?"
4427    </t>
4428    <t>
4429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4430      "'expect' grammar missing OWS"
4431    </t>
4432    <t>
4433      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4434      "header field considerations: quoted-string vs use of double quotes"
4435    </t>
4436  </list>
4437</t>
4438</section>
4439
4440<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4441<t>
4442  Closed issues:
4443  <list style="symbols"> 
4444    <t>
4445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4446      "Combining HEAD responses"
4447    </t>
4448    <t>
4449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4450      "Requirements for user intervention during redirects"
4451    </t>
4452    <t>
4453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4454      "message-body in CONNECT response"
4455    </t>
4456    <t>
4457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4458      "Applying original fragment to 'plain' redirected URI"
4459    </t>
4460    <t>
4461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4462      "Misplaced text on connection handling in p2"
4463    </t>
4464    <t>
4465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4466      "clarify that 201 doesn't require Location header fields"
4467    </t>
4468    <t>
4469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4470      "relax requirements on hypertext in 3/4/5xx error responses"
4471    </t>
4472    <t>
4473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4474      "example for 426 response should have a payload"
4475    </t>
4476    <t>
4477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4478      "drop indirection entries for status codes"
4479    </t>
4480  </list>
4481</t>
4482</section>
4483
4484<section title="Since draft-ietf-httpbis-p2-semantics-19" anchor="changes.since.19">
4485<t>
4486  Closed issues:
4487  <list style="symbols"> 
4488    <t>
4489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4490      "should there be a permanent variant of 307"
4491    </t>
4492  </list>
4493</t>
4494</section>
4495
4496</section>
4497
4498</back>
4499</rfc>
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