source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1641

Last change on this file since 1641 was 1641, checked in by julian.reschke@…, 7 years ago

Step 3 of p2/p3-merge (see #351)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 198.7 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY architecture               "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY messaging                  "<xref target='Part1' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY payload                    "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY conditional                "<xref target='Part4' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY range                      "<xref target='Part5' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY caching                    "<xref target='Part6' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY auth                       "<xref target='Part7' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY content-negotiation        "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY agent-driven-negotiation   "<xref target='Part3' x:rel='#agent-driven.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY abnf-extension             "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY whitespace                 "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY field-components           "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY intermediaries             "<xref target='Part1' x:rel='#intermediaries' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY chunked-encoding           "<xref target='Part1' x:rel='#chunked.encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY http-url                   "<xref target='Part1' x:rel='#http-url' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY http-version               "<xref target='Part1' x:rel='#http.version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY use100                     "<xref target='Part1' x:rel='#use.of.the.100.status' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY qvalue                     "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY request-target             "<xref target='Part1' x:rel='#request-target' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY header-accept              "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY header-accept-charset      "<xref target='Part3' x:rel='#header.accept-charset' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY header-accept-encoding     "<xref target='Part3' x:rel='#header.accept-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44  <!ENTITY header-accept-language     "<xref target='Part3' x:rel='#header.accept-language' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
45  <!ENTITY header-accept-ranges       "<xref target='Part5' x:rel='#header.accept-ranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
46  <!ENTITY header-age                 "<xref target='Part6' x:rel='#header.age' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
47  <!ENTITY header-authorization       "<xref target='Part7' x:rel='#header.authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
48  <!ENTITY header-cache-control       "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
49  <!ENTITY header-connection          "<xref target='Part1' x:rel='#header.connection' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
50  <!ENTITY header-content-location    "<xref target='Part3' x:rel='#header.content-location' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
51  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
52  <!ENTITY header-content-type        "<xref target='Part3' x:rel='#header.content-type' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
53  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
54  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
55  <!ENTITY header-fields              "<xref target='Part1' x:rel='#header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
56  <!ENTITY header-host                "<xref target='Part1' x:rel='#header.host' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
57  <!ENTITY header-if-match            "<xref target='Part4' x:rel='#header.if-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
58  <!ENTITY header-if-modified-since   "<xref target='Part4' x:rel='#header.if-modified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
59  <!ENTITY header-if-none-match       "<xref target='Part4' x:rel='#header.if-none-match' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
60  <!ENTITY header-if-range            "<xref target='Part5' x:rel='#header.if-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
61  <!ENTITY header-if-unmodified-since "<xref target='Part4' x:rel='#header.if-unmodified-since' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
62  <!ENTITY header-pragma              "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
63  <!ENTITY header-proxy-authenticate  "<xref target='Part7' x:rel='#header.proxy-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
64  <!ENTITY header-proxy-authorization "<xref target='Part7' x:rel='#header.proxy-authorization' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
65  <!ENTITY header-range               "<xref target='Part5' x:rel='#header.range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
66  <!ENTITY header-upgrade             "<xref target='Part1' x:rel='#header.upgrade' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
67  <!ENTITY header-te                  "<xref target='Part1' x:rel='#header.te' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
68  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
69  <!ENTITY header-via                 "<xref target='Part1' x:rel='#header.via' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
70  <!ENTITY header-warning             "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
71  <!ENTITY header-www-authenticate    "<xref target='Part7' x:rel='#header.www-authenticate' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
72  <!ENTITY media-types                "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
73  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
74  <!ENTITY media-type-message-http    "<xref target='Part1' x:rel='#internet.media.type.message.http' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
75  <!ENTITY status-206                 "<xref target='Part5' x:rel='#status.206' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
76  <!ENTITY status-304                 "<xref target='Part4' x:rel='#status.304' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
77  <!ENTITY status-401                 "<xref target='Part7' x:rel='#status.401' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
78  <!ENTITY status-407                 "<xref target='Part7' x:rel='#status.407' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
79  <!ENTITY status-412                 "<xref target='Part4' x:rel='#status.412' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
80  <!ENTITY status-416                 "<xref target='Part5' x:rel='#status.416' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
81  <!ENTITY p3-header-fields           "<xref target='Part3' x:rel='#header.field.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
82  <!ENTITY p4-status-codes            "<xref target='Part4' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
83  <!ENTITY p5-status-codes            "<xref target='Part5' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
84  <!ENTITY p7-status-codes            "<xref target='Part7' x:rel='#status.code.definitions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
85  <!ENTITY p6-heuristic               "<xref target='Part6' x:rel='#heuristic.freshness' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
86  <!ENTITY p6-explicit                "<xref target='Part6' x:rel='#calculating.freshness.lifetime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
87  <!ENTITY p6-invalid                 "<xref target='Part6' x:rel='#invalidation.after.updates.or.deletions' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
88  <!ENTITY p6-head                    "<xref target='Part6' x:rel='#head.effects' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
89  <!ENTITY architecture               "<xref target='Part1' x:rel='#architecture' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
90  <!ENTITY notation                   "<xref target='Part1' x:rel='#notation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
91  <!ENTITY abnf-extension             "<xref target='Part1' x:rel='#abnf.extension' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
92  <!ENTITY acks                       "<xref target='Part1' x:rel='#acks' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
93  <!ENTITY whitespace                 "<xref target='Part1' x:rel='#whitespace' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
94  <!ENTITY field-components           "<xref target='Part1' x:rel='#field.components' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
95  <!ENTITY caching-neg-resp           "<xref target='Part6' x:rel='#caching.negotiated.responses' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
96  <!ENTITY header-transfer-encoding   "<xref target='Part1' x:rel='#header.transfer-encoding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
97  <!ENTITY header-content-length      "<xref target='Part1' x:rel='#header.content-length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
98  <!ENTITY header-content-range       "<xref target='Part5' x:rel='#header.content-range' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
99  <!ENTITY header-etag                "<xref target='Part4' x:rel='#header.etag' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
100  <!ENTITY header-expires             "<xref target='Part6' x:rel='#header.expires' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
101  <!ENTITY header-last-modified       "<xref target='Part4' x:rel='#header.last-modified' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
102  <!ENTITY header-user-agent          "<xref target='Part2' x:rel='#header.user-agent' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
103  <!ENTITY header-vary                "<xref target='Part6' x:rel='#header.vary' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
104  <!ENTITY message-body               "<xref target='Part1' x:rel='#message.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
105  <!ENTITY multipart-byteranges       "<xref target='Part5' x:rel='#internet.media.type.multipart.byteranges' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
106  <!ENTITY http-date                  "<xref target='Part2' x:rel='#http.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
107  <!ENTITY qvalue                     "<xref target='Part1' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
108  <!ENTITY uri                        "<xref target='Part1' x:rel='#uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
109  <!ENTITY effective-request-uri      "<xref target='Part1' x:rel='#effective.request.uri' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
110  <!ENTITY compression-codings        "<xref target='Part1' x:rel='#compression.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
111  <!ENTITY transfer-codings           "<xref target='Part1' x:rel='#transfer.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
112  <!ENTITY compress-coding            "<xref target='Part1' x:rel='#compress.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
113  <!ENTITY deflate-coding             "<xref target='Part1' x:rel='#deflate.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
114  <!ENTITY gzip-coding                "<xref target='Part1' x:rel='#gzip.coding' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
115  <!ENTITY response-representation    "<xref target='Part2' x:rel='#identifying.response.associated.with.representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
116]>
117<?rfc toc="yes" ?>
118<?rfc symrefs="yes" ?>
119<?rfc sortrefs="yes" ?>
120<?rfc compact="yes"?>
121<?rfc subcompact="no" ?>
122<?rfc linkmailto="no" ?>
123<?rfc editing="no" ?>
124<?rfc comments="yes"?>
125<?rfc inline="yes"?>
126<?rfc rfcedstyle="yes"?>
127<?rfc-ext allow-markup-in-artwork="yes" ?>
128<?rfc-ext include-references-in-index="yes" ?>
129<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="proposed"
130     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"
131     xmlns:x='http://purl.org/net/xml2rfc/ext'
132     xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
133<x:link rel="prev" basename="p1-messaging"/>
134<x:link rel="next" basename="p3-payload"/>
135<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
136<front>
137
138  <title abbrev="HTTP/1.1, Part 2">HTTP/1.1, part 2: Message Semantics, Payload and Content Negotiation</title>
139
140  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
141    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
142    <address>
143      <postal>
144        <street>345 Park Ave</street>
145        <city>San Jose</city>
146        <region>CA</region>
147        <code>95110</code>
148        <country>USA</country>
149      </postal>
150      <email>fielding@gbiv.com</email>
151      <uri>http://roy.gbiv.com/</uri>
152    </address>
153  </author>
154
155  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
156    <organization abbrev="W3C">World Wide Web Consortium</organization>
157    <address>
158      <postal>
159        <street>W3C / ERCIM</street>
160        <street>2004, rte des Lucioles</street>
161        <city>Sophia-Antipolis</city>
162        <region>AM</region>
163        <code>06902</code>
164        <country>France</country>
165      </postal>
166      <email>ylafon@w3.org</email>
167      <uri>http://www.raubacapeu.net/people/yves/</uri>
168    </address>
169  </author>
170
171  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
172    <organization abbrev="greenbytes">greenbytes GmbH</organization>
173    <address>
174      <postal>
175        <street>Hafenweg 16</street>
176        <city>Muenster</city><region>NW</region><code>48155</code>
177        <country>Germany</country>
178      </postal>
179      <phone>+49 251 2807760</phone>
180      <facsimile>+49 251 2807761</facsimile>
181      <email>julian.reschke@greenbytes.de</email>
182      <uri>http://greenbytes.de/tech/webdav/</uri>
183    </address>
184  </author>
185
186  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
187  <workgroup>HTTPbis Working Group</workgroup>
188
189<abstract>
190<t>
191   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
192   distributed, collaborative, hypertext information systems. HTTP has been in
193   use by the World Wide Web global information initiative since 1990. This
194   document is Part 2 of the seven-part specification that defines the protocol
195   referred to as "HTTP/1.1" and, taken together, obsoletes RFC 2616.
196</t>
197<t>
198   Part 2 defines the semantics of HTTP messages as expressed by request
199   methods, request header fields, response status codes, and response header
200   fields. Furthermore, it defines HTTP message content, metadata, and content
201   negotiation.
202   <cref>#351</cref>
203</t>
204</abstract>
205
206<note title="Editorial Note (To be removed by RFC Editor)">
207  <t>
208    Discussion of this draft should take place on the HTTPBIS working group
209    mailing list (ietf-http-wg@w3.org), which is archived at
210    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
211  </t>
212  <t>
213    The current issues list is at
214    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
215    documents (including fancy diffs) can be found at
216    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
217  </t>
218  <t>
219    The changes in this draft are summarized in <xref target="changes.since.19"/>.
220  </t>
221</note>
222</front>
223<middle>
224<section title="Introduction" anchor="introduction">
225<t>
226   This document defines HTTP/1.1 request and response semantics.  Each HTTP
227   message, as defined in &messaging;, is in the form of either a request or
228   a response.  An HTTP server listens on a connection for HTTP requests and
229   responds to each request, in the order received on that connection, with
230   one or more HTTP response messages.  This document defines the commonly
231   agreed upon semantics of the HTTP uniform interface, the intentions defined
232   by each request method, and the various response messages that might be
233   expected as a result of applying that method to the target resource.
234</t>
235<t>
236   Furthermore, it defines HTTP/1.1 message payloads (a.k.a., content), the
237   associated metadata header fields that define how the payload is intended
238   to be interpreted by a recipient, the request header fields that
239   might influence content selection, and the various selection algorithms
240   that are collectively referred to as HTTP content negotiation.
241   <cref>#351</cref>
242</t>
243<t>
244   This document is currently disorganized in order to minimize the changes
245   between drafts and enable reviewers to see the smaller errata changes.
246   A future draft will reorganize the sections to better reflect the content.
247   In particular, the sections will be ordered according to the typical
248   processing of an HTTP request message (after message parsing): resource
249   mapping, methods, request modifying header fields, response status,
250   status modifying header fields, and resource metadata.  The current mess
251   reflects how widely dispersed these topics and associated requirements
252   had become in <xref target="RFC2616"/>.
253</t>
254
255<section title="Terminology" anchor="terminology">
256<t>
257   This specification uses a number of terms to refer to the roles
258   played by participants in, and objects of, the HTTP communication.
259</t>
260<t>
261  <iref item="content negotiation"/>
262  <x:dfn>content negotiation</x:dfn>
263  <list>
264    <t>
265      The mechanism for selecting the appropriate representation when
266      servicing a request. The representation in any response
267      can be negotiated (including error responses).
268    </t>
269  </list>
270</t>
271<t>
272  <iref primary="true" item="selected representation"/>
273  <x:dfn>selected representation</x:dfn>
274  <list>
275    <t>
276      The current representation of the target resource that would have been
277      selected in a successful response if the same request had used the
278      method GET and excluded any conditional request header fields.
279    </t>
280  </list>
281</t>
282</section>
283
284<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
285<t>
286   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
287   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
288   document are to be interpreted as described in <xref target="RFC2119"/>.
289</t>
290<t>
291   This document defines conformance criteria for several roles in HTTP
292   communication, including Senders, Recipients, Clients, Servers, User-Agents,
293   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
294   for definitions of these terms.
295</t>
296<t>
297   An implementation is considered conformant if it complies with all of the
298   requirements associated with its role(s). Note that SHOULD-level requirements
299   are relevant here, unless one of the documented exceptions is applicable.
300</t>
301<t>
302   This document also uses ABNF to define valid protocol elements
303   (<xref target="notation"/>). In addition to the prose requirements placed
304   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
305</t>
306<t>
307   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
308   protocol element from an invalid construct. However, HTTP does not define
309   specific error handling mechanisms, except in cases where it has direct
310   impact on security. This is because different uses of the protocol require
311   different error handling strategies; for example, a Web browser may wish to
312   transparently recover from a response where the Location header field
313   doesn't parse according to the ABNF, whereby in a systems control protocol
314   using HTTP, this type of error recovery could lead to dangerous consequences.
315</t>
316</section>
317
318<section title="Syntax Notation" anchor="notation">
319  <x:anchor-alias value="CR"/>
320  <x:anchor-alias value="DIGIT"/>
321  <x:anchor-alias value="LF"/>
322  <x:anchor-alias value="HTAB"/>
323  <x:anchor-alias value="VCHAR"/>
324  <x:anchor-alias value="SP"/>
325<t>
326   This specification uses the Augmented Backus-Naur Form (ABNF) notation
327   of <xref target="RFC5234"/> with the list rule extension defined in
328   &notation;<xref target="collected.abnf"/> shows the collected ABNF
329   with the list rule expanded.
330</t>
331<t>
332  The following core rules are included by
333  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335  DIGIT (decimal 0-9), DQUOTE (double quote),
336  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
337  OCTET (any 8-bit sequence of data), SP (space), and
338  VCHAR (any visible US-ASCII character).
339</t>
340
341<section title="Core Rules" anchor="core.rules">
342  <x:anchor-alias value="obs-text"/>
343  <x:anchor-alias value="quoted-string"/>
344  <x:anchor-alias value="token"/>
345  <x:anchor-alias value="BWS"/>
346  <x:anchor-alias value="OWS"/>
347  <x:anchor-alias value="RWS"/>
348<t>
349  The core rules below are defined in <xref target="Part1"/>:
350</t>
351<figure><artwork type="abnf2616">
352  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
353  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
354  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &whitespace;&gt;
355  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &field-components;&gt;
356  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
357  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
358</artwork></figure>
359</section>
360
361<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
362  <x:anchor-alias value="absolute-URI"/>
363  <x:anchor-alias value="comment"/>
364  <x:anchor-alias value="partial-URI"/>
365  <x:anchor-alias value="URI-reference"/>
366<t>
367  The ABNF rules below are defined in other parts:
368</t>
369<figure><!--Part1--><artwork type="abnf2616">
370  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
371  <x:ref>comment</x:ref>       = &lt;comment, defined in &field-components;&gt;
372  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
373  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
374</artwork></figure>
375</section>
376</section>
377</section>
378
379<section title="Methods" anchor="methods">
380  <x:anchor-alias value="method"/>
381<t>
382   The method token indicates the request method to be performed on the target
383   resource (&effective-request-uri;). The method is case-sensitive.
384</t>
385<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
386  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
387</artwork></figure>
388<t>
389   The list of methods allowed by a resource can be specified in an
390   Allow header field (<xref target="header.allow"/>). The status code of the response
391   always notifies the client whether a method is currently allowed on a
392   resource, since the set of allowed methods can change dynamically. An
393   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
394   if the method is known by the origin server but not allowed for the
395   resource, and 501 (Not Implemented) if the method is
396   unrecognized or not implemented by the origin server. The methods GET
397   and HEAD &MUST; be supported by all general-purpose servers. All other
398   methods are &OPTIONAL;; however, if the above methods are implemented,
399   they &MUST; be implemented with the same semantics as those specified
400   in <xref target="method.definitions"/>.
401</t>
402
403<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
404
405<section title="Safe Methods" anchor="safe.methods">
406<iref item="Safe Methods" primary="true"/>
407<t>
408   Implementors need to be aware that the software represents the user in
409   their interactions over the Internet, and need to allow
410   the user to be aware of any actions they take which might have an
411   unexpected significance to themselves or others.
412</t>
413<t>
414   In particular, the convention has been established that the GET, HEAD,
415   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
416   of taking an action other than retrieval. These request methods ought
417   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
418   This allows user agents to represent other methods, such as POST, PUT
419   and DELETE, in a special way, so that the user is made aware of the
420   fact that a possibly unsafe action is being requested.
421</t>
422<t>
423   Naturally, it is not possible to ensure that the server does not
424   generate side-effects as a result of performing a GET request; in
425   fact, some dynamic resources consider that a feature. The important
426   distinction here is that the user did not request the side-effects,
427   so therefore cannot be held accountable for them.
428</t>
429</section>
430
431<section title="Idempotent Methods" anchor="idempotent.methods">
432<iref item="Idempotent Methods" primary="true"/>
433<t>
434   Request methods can also have the property of "idempotence" in that,
435   aside from error or expiration issues, the intended effect of multiple
436   identical requests is the same as for a single request.
437   PUT, DELETE, and all safe request methods are idempotent.
438   It is important to note that idempotence refers only to changes
439   requested by the client: a server is free to change its state due
440   to multiple requests for the purpose of tracking those requests,
441   versioning of results, etc.
442</t>
443</section>
444</section>
445
446<section title="Method Registry" anchor="method.registry">
447<t>
448  The HTTP Method Registry defines the name space for the method token in the
449  Request line of an HTTP request.
450</t>
451<t>
452  Registrations &MUST; include the following fields:
453  <list style="symbols">
454    <t>Method Name (see <xref target="methods"/>)</t>
455    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
456    <t>Pointer to specification text</t>
457  </list>
458</t>
459<t>
460  Values to be added to this name space require IETF Review
461  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
462</t>
463<t>
464  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
465</t>
466
467<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
468<t>
469   When it is necessary to express new semantics for a HTTP request that
470   aren't specific to a single application or media type, and currently defined
471   methods are inadequate, it may be appropriate to register a new method.
472</t>
473<t>
474   HTTP methods are generic; that is, they are potentially applicable to any
475   resource, not just one particular media type, "type" of resource, or
476   application. As such, it is preferred that new HTTP methods be registered
477   in a document that isn't specific to a single application, so that this is
478   clear.
479</t>
480<t>
481   Due to the parsing rules defined in &message-body;, definitions of HTTP
482   methods cannot prohibit the presence of a message body on either the request
483   or the response message (with responses to HEAD requests being the single
484   exception). Definitions of new methods cannot change this rule, but they can
485   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
486</t>
487<t>
488   New method definitions need to indicate whether they are safe (<xref
489   target="safe.methods"/>), what semantics (if any) the request body has,
490   and whether they are idempotent (<xref target="idempotent.methods"/>).
491   They also need to state whether they can be cached (&caching;); in
492   particular what conditions a cache may store the response, and under what
493   conditions such a stored response may be used to satisfy a subsequent
494   request.
495</t>
496</section>
497</section>
498
499<section title="Method Definitions" anchor="method.definitions">
500
501<section title="OPTIONS" anchor="OPTIONS">
502  <rdf:Description>
503    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
504  </rdf:Description>
505  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
506  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
507<t>
508   The OPTIONS method requests information about the
509   communication options available on the request/response chain
510   identified by the effective request URI. This method allows a client to
511   determine the options and/or requirements associated with a resource,
512   or the capabilities of a server, without implying a resource action
513   or initiating a resource retrieval.
514</t>
515<t>
516   Responses to the OPTIONS method are not cacheable.
517</t>
518<t>
519   If the OPTIONS request includes a message body (as indicated by the
520   presence of Content-Length or Transfer-Encoding), then the media type
521   &MUST; be indicated by a Content-Type field. Although this
522   specification does not define any use for such a body, future
523   extensions to HTTP might use the OPTIONS body to make more detailed
524   queries on the server.
525</t>
526<t>
527   If the request-target (&request-target;) is an asterisk ("*"),
528   the OPTIONS request is
529   intended to apply to the server in general rather than to a specific
530   resource. Since a server's communication options typically depend on
531   the resource, the "*" request is only useful as a "ping" or "no-op"
532   type of method; it does nothing beyond allowing the client to test
533   the capabilities of the server. For example, this can be used to test
534   a proxy for HTTP/1.1 conformance (or lack thereof).
535</t>
536<t>
537   If the request-target is not an asterisk, the OPTIONS request applies
538   only to the options that are available when communicating with that
539   resource.
540</t>
541<t>
542   A 200 response &SHOULD; include any header fields that indicate
543   optional features implemented by the server and applicable to that
544   resource (e.g., Allow), possibly including extensions not defined by
545   this specification. The response body, if any, &SHOULD; also include
546   information about the communication options. The format for such a
547   body is not defined by this specification, but might be defined by
548   future extensions to HTTP. Content negotiation &MAY; be used to select
549   the appropriate response format. If no response body is included, the
550   response &MUST; include a Content-Length field with a field-value of
551   "0".
552</t>
553<t>
554   The Max-Forwards header field &MAY; be used to target a
555   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
556   If no Max-Forwards field is present in the request, then the forwarded
557   request &MUST-NOT; include a Max-Forwards field.
558</t>
559</section>
560
561<section title="GET" anchor="GET">
562  <rdf:Description>
563    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
564  </rdf:Description>
565  <iref primary="true" item="GET method" x:for-anchor=""/>
566  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
567<t>
568   The GET method requests transfer of a current representation of
569   the target resource.
570</t>
571<t>   
572   If the target resource is a data-producing process, it is the
573   produced data which shall be returned as the representation in the response and not
574   the source text of the process, unless that text happens to be the output of
575   the process.
576</t>
577<t>
578   The semantics of the GET method change to a "conditional GET" if the
579   request message includes an If-Modified-Since, If-Unmodified-Since,
580   If-Match, If-None-Match, or If-Range header field. A conditional GET
581   requests that the representation be transferred only under the
582   circumstances described by the conditional header field(s). The
583   conditional GET request is intended to reduce unnecessary network
584   usage by allowing cached representations to be refreshed without requiring
585   multiple requests or transferring data already held by the client.
586</t>
587<t>
588   The semantics of the GET method change to a "partial GET" if the
589   request message includes a Range header field. A partial GET requests
590   that only part of the representation be transferred, as described in &header-range;.
591   The partial GET request is intended to reduce unnecessary
592   network usage by allowing partially-retrieved representations to be
593   completed without transferring data already held by the client.
594</t>
595<t>
596   Bodies on GET requests have no defined semantics. Note that sending a body
597   on a GET request might cause some existing implementations to reject the
598   request.
599</t>
600<t>
601   The response to a GET request is cacheable and &MAY; be used to satisfy
602   subsequent GET and HEAD requests (see &caching;).
603</t>
604<t>
605   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
606</t>
607</section>
608
609<section title="HEAD" anchor="HEAD">
610  <rdf:Description>
611    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
612  </rdf:Description>
613  <iref primary="true" item="HEAD method" x:for-anchor=""/>
614  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
615<t>
616   The HEAD method is identical to GET except that the server &MUST-NOT;
617   return a message body in the response. The metadata contained
618   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
619   to the information sent in response to a GET request. This method can
620   be used for obtaining metadata about the representation implied by the
621   request without transferring the representation body. This method is
622   often used for testing hypertext links for validity, accessibility,
623   and recent modification.
624</t>
625<t>
626   The response to a HEAD request is cacheable and &MAY; be used to satisfy
627   a subsequent HEAD request. It also has potential side effects on
628   previously stored responses to GET; see &p6-head;.
629</t>
630<t>
631   Bodies on HEAD requests have no defined semantics. Note that sending a body
632   on a HEAD request might cause some existing implementations to reject the
633   request.
634</t>
635</section>
636
637<section title="POST" anchor="POST">
638  <iref primary="true" item="POST method" x:for-anchor=""/>
639  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
640<t>
641   The POST method requests that the origin server accept the
642   representation enclosed in the request as data to be processed by the
643   target resource. POST is designed to allow a uniform method to cover the
644   following functions:
645  <list style="symbols">
646    <t>
647      Annotation of existing resources;
648    </t>
649    <t>
650        Posting a message to a bulletin board, newsgroup, mailing list,
651        or similar group of articles;
652    </t>
653    <t>
654        Providing a block of data, such as the result of submitting a
655        form, to a data-handling process;
656    </t>
657    <t>
658        Extending a database through an append operation.
659    </t>
660  </list>
661</t>
662<t>
663   The actual function performed by the POST method is determined by the
664   server and is usually dependent on the effective request URI.
665</t>
666<t>
667   The action performed by the POST method might not result in a
668   resource that can be identified by a URI. In this case, either 200
669   (OK) or 204 (No Content) is the appropriate response status code,
670   depending on whether or not the response includes a representation that
671   describes the result.
672</t>
673<t>
674   If a resource has been created on the origin server, the response
675   &SHOULD; be 201 (Created) and contain a representation which describes the
676   status of the request and refers to the new resource, and a Location
677   header field (see <xref target="header.location"/>).
678</t>
679<t>
680   Responses to POST requests are only cacheable when they
681   include explicit freshness information (see &p6-explicit;). A
682   cached POST response with a Content-Location header field
683   (see &header-content-location;) whose value is the effective
684   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
685</t>
686<t>
687   Note that POST caching is not widely implemented.
688   However, the 303 (See Other) response can be used to direct the
689   user agent to retrieve a cacheable representation of the resource.
690</t>
691</section>
692
693<section title="PUT" anchor="PUT">
694  <iref primary="true" item="PUT method" x:for-anchor=""/>
695  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
696<t>
697   The PUT method requests that the state of the target resource
698   be created or replaced with the state defined by the representation
699   enclosed in the request message payload.  A successful PUT of a given
700   representation would suggest that a subsequent GET on that same target
701   resource will result in an equivalent representation being returned in
702   a 200 (OK) response.  However, there is no guarantee that such a state
703   change will be observable, since the target resource might be acted
704   upon by other user agents in parallel, or might be subject to dynamic
705   processing by the origin server, before any subsequent GET is received.
706   A successful response only implies that the user agent's intent was
707   achieved at the time of its processing by the origin server.
708</t>
709<t>   
710   If the target resource does not have a current representation and
711   the PUT successfully creates one, then the origin server &MUST; inform
712   the user agent by sending a 201 (Created) response.  If the target
713   resource does have a current representation and that representation is
714   successfully modified in accordance with the state of the enclosed
715   representation, then either a 200 (OK) or 204 (No Content) response
716   &SHOULD; be sent to indicate successful completion of the request.
717</t>
718<t>
719   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
720   as part of the resource state).
721</t>
722<t>
723   An origin server &SHOULD; verify that the PUT representation is
724   consistent with any constraints which the server has for the target
725   resource that cannot or will not be changed by the PUT.  This is
726   particularly important when the origin server uses internal
727   configuration information related to the URI in order to set the
728   values for representation metadata on GET responses.  When a PUT
729   representation is inconsistent with the target resource, the origin
730   server &SHOULD; either make them consistent, by transforming the
731   representation or changing the resource configuration, or respond
732   with an appropriate error message containing sufficient information
733   to explain why the representation is unsuitable.  The 409 (Conflict)
734   or 415 (Unsupported Media Type) status codes are suggested, with the
735   latter being specific to constraints on Content-Type values.
736</t>
737<t>
738   For example, if the target resource is configured to always have a
739   Content-Type of "text/html" and the representation being PUT has a
740   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
741   (a) reconfigure the target resource to reflect the new media type;
742   (b) transform the PUT representation to a format consistent with that
743   of the resource before saving it as the new resource state; or,
744   (c) reject the request with a 415 response indicating that the target
745   resource is limited to "text/html", perhaps including a link to a
746   different resource that would be a suitable target for the new
747   representation.
748</t>
749<t>
750   HTTP does not define exactly how a PUT method affects the state
751   of an origin server beyond what can be expressed by the intent of
752   the user agent request and the semantics of the origin server response.
753   It does not define what a resource might be, in any sense of that
754   word, beyond the interface provided via HTTP.  It does not define
755   how resource state is "stored", nor how such storage might change
756   as a result of a change in resource state, nor how the origin server
757   translates resource state into representations.  Generally speaking,
758   all implementation details behind the resource interface are
759   intentionally hidden by the server.
760</t>
761<t>
762   The fundamental difference between the POST and PUT methods is
763   highlighted by the different intent for the target resource.
764   The target resource in a POST request is intended to handle the
765   enclosed representation as a data-accepting process, such as for
766   a gateway to some other protocol or a document that accepts annotations.
767   In contrast, the target resource in a PUT request is intended to
768   take the enclosed representation as a new or replacement value.
769   Hence, the intent of PUT is idempotent and visible to intermediaries,
770   even though the exact effect is only known by the origin server.
771</t>
772<t>
773   Proper interpretation of a PUT request presumes that the user agent
774   knows what target resource is desired.  A service that is intended
775   to select a proper URI on behalf of the client, after receiving
776   a state-changing request, &SHOULD; be implemented using the POST
777   method rather than PUT.  If the origin server will not make the
778   requested PUT state change to the target resource and instead
779   wishes to have it applied to a different resource, such as when the
780   resource has been moved to a different URI, then the origin server
781   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
782   then make its own decision regarding whether or not to redirect the
783   request.
784</t>
785<t>
786   A PUT request applied to the target resource &MAY; have side-effects
787   on other resources.  For example, an article might have a URI for
788   identifying "the current version" (a resource) which is separate
789   from the URIs identifying each particular version (different
790   resources that at one point shared the same state as the current version
791   resource).  A successful PUT request on "the current version" URI might
792   therefore create a new version resource in addition to changing the
793   state of the target resource, and might also cause links to be added
794   between the related resources.
795</t>
796<t>
797   An origin server &SHOULD; reject any PUT request that contains a
798   Content-Range header field, since it might be misinterpreted as
799   partial content (or might be partial content that is being mistakenly
800   PUT as a full representation).  Partial content updates are
801   possible by targeting a separately identified resource with state
802   that overlaps a portion of the larger resource, or by using a
803   different method that has been specifically defined for partial
804   updates (for example, the PATCH method defined in
805   <xref target="RFC5789"/>).
806</t>
807<t>
808   Responses to the PUT method are not cacheable. If a PUT request passes
809   through a cache that has one or more stored responses for the effective
810   request URI, those stored responses will be invalidated (see
811   &p6-invalid;).
812</t>
813</section>
814
815<section title="DELETE" anchor="DELETE">
816  <iref primary="true" item="DELETE method" x:for-anchor=""/>
817  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
818<t>
819   The DELETE method requests that the origin server delete the target
820   resource. This method &MAY; be overridden by
821   human intervention (or other means) on the origin server. The client cannot
822   be guaranteed that the operation has been carried out, even if the
823   status code returned from the origin server indicates that the action
824   has been completed successfully. However, the server &SHOULD-NOT; 
825   indicate success unless, at the time the response is given, it
826   intends to delete the resource or move it to an inaccessible
827   location.
828</t>
829<t>
830   A successful response &SHOULD; be 200 (OK) if the response includes an
831   representation describing the status, 202 (Accepted) if the action has not
832   yet been enacted, or 204 (No Content) if the action has been enacted
833   but the response does not include a representation.
834</t>
835<t>
836   Bodies on DELETE requests have no defined semantics. Note that sending a body
837   on a DELETE request might cause some existing implementations to reject the
838   request.
839</t>
840<t>
841   Responses to the DELETE method are not cacheable. If a DELETE request
842   passes through a cache that has one or more stored responses for the
843   effective request URI, those stored responses will be invalidated (see
844   &p6-invalid;).
845</t>
846</section>
847
848<section title="TRACE" anchor="TRACE">
849  <rdf:Description>
850    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
851  </rdf:Description>
852  <iref primary="true" item="TRACE method" x:for-anchor=""/>
853  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
854<t>
855   The TRACE method requests a remote, application-layer loop-back
856   of the request message. The final recipient of the request
857   &SHOULD; reflect the message received back to the client as the
858   message body of a 200 (OK) response. The final recipient is either the
859   origin server or the first proxy to receive a Max-Forwards
860   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
861   A TRACE request &MUST-NOT; include a message body.
862</t>
863<t>
864   TRACE allows the client to see what is being received at the other
865   end of the request chain and use that data for testing or diagnostic
866   information. The value of the Via header field (&header-via;) is of
867   particular interest, since it acts as a trace of the request chain.
868   Use of the Max-Forwards header field allows the client to limit the
869   length of the request chain, which is useful for testing a chain of
870   proxies forwarding messages in an infinite loop.
871</t>
872<t>
873   If the request is valid, the response &SHOULD; have a Content-Type of
874   "message/http" (see &media-type-message-http;) and contain a message body
875   that encloses a copy of the entire request message.
876   Responses to the TRACE method are not cacheable.
877</t>
878</section>
879
880<section title="CONNECT" anchor="CONNECT">
881  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
882  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
883<t>
884   The CONNECT method requests that the proxy establish a tunnel
885   to the request-target and, if successful, thereafter restrict its behavior
886   to blind forwarding of packets until the connection is closed.
887</t>
888<t>
889   When using CONNECT, the request-target &MUST; use the authority form
890   (&request-target;); i.e., the request-target consists of only the
891   host name and port number of the tunnel destination, separated by a colon.
892   For example,
893</t>
894<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
895CONNECT server.example.com:80 HTTP/1.1
896Host: server.example.com:80
897
898</artwork></figure>
899<t>
900   Any successful (2xx) response to a CONNECT request indicates that the
901   proxy has established a connection to the requested host and port,
902   and has switched to tunneling the current connection to that server
903   connection.
904   The tunneled data from the server begins immediately after the blank line
905   that concludes the successful response's header block.
906   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
907   header fields in a successful response.
908   A client &MUST; ignore any Content-Length or Transfer-Encoding header
909   fields received in a successful response.
910</t>
911<t>
912   Any response other than a successful response indicates that the tunnel
913   has not yet been formed and that the connection remains governed by HTTP.
914</t>
915<t>
916   Proxy authentication might be used to establish the
917   authority to create a tunnel:
918</t>
919<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
920CONNECT server.example.com:80 HTTP/1.1
921Host: server.example.com:80
922Proxy-Authorization: basic aGVsbG86d29ybGQ=
923
924</artwork></figure>
925<t>
926   A message body on a CONNECT request has no defined semantics. Sending a
927   body on a CONNECT request might cause existing implementations to reject
928   the request.
929</t>
930<t>
931   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
932   to server &MAY; be sent immediately after the request (before a response
933   is received). The usual caveats also apply:
934   data may be discarded if the eventual response is negative, and the
935   connection may be reset with no response if more than one TCP segment
936   is outstanding.
937</t>
938<t>
939   It may be the case that the proxy itself can only reach the requested
940   origin server through another proxy.  In this case, the first proxy
941   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
942   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
943   unless it has either a direct or tunnel connection established to the
944   authority.
945</t>
946<t>
947   If at any point either one of the peers gets disconnected, any
948   outstanding data that came from that peer will be passed to the other
949   one, and after that also the other connection will be terminated by
950   the proxy. If there is outstanding data to that peer undelivered,
951   that data will be discarded.
952</t>
953<t>
954   An origin server which receives a CONNECT request for itself &MAY;
955   respond with a 2xx status code to indicate that a connection is
956   established.  However, most origin servers do not implement CONNECT.
957</t>
958</section>
959</section>
960
961</section>
962
963<section title="Header Fields" anchor="header.fields">
964<t>
965   Header fields are key value pairs that can be used to communicate data about
966   the message, its payload, the target resource, or about the connection
967   itself (i.e., control data).  See &header-fields; for a general definition
968   of their syntax.
969</t>
970
971<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
972<t>
973   New header fields are registered using the procedures described in
974   <xref target="RFC3864"/>.
975</t>
976<t>
977   The requirements for header field names are defined in
978   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
979   defining new fields are advised to keep the name as short as practical, and
980   not to prefix them with "X-" if they are to be registered (either
981   immediately or in the future).
982</t>
983<t>
984   New header field values typically have their syntax defined using ABNF
985   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
986   as necessary, and are usually constrained to the range of ASCII characters.
987   Header fields needing a greater range of characters can use an encoding
988   such as the one defined in <xref target="RFC5987"/>.
989</t>
990<t>
991   Because commas (",") are used as a generic delimiter between field-values,
992   they need to be treated with care if they are allowed in the field-value's
993   payload. Typically, components that might contain a comma are protected with
994   double-quotes using the quoted-string ABNF production (&field-components;).
995</t>
996<t>
997   For example, a textual date and a URI (either of which might contain a comma)
998   could be safely carried in field-values like these:
999</t>
1000<figure><artwork type="example">
1001  Example-URI-Field: "http://example.com/a.html,foo",
1002                     "http://without-a-comma.example.com/"
1003  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
1004</artwork></figure>
1005<t>
1006   Note that double quote delimiters almost always are used with the
1007   quoted-string production; using a different syntax inside double quotes
1008   will likely cause unnecessary confusion.
1009</t>
1010<t>
1011   Many header fields use a format including (case-insensitively) named
1012   parameters (for instance, Content-Type, defined in &header-content-type;).
1013   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
1014   parameter value enables recipients to use existing parser components. When
1015   allowing both forms, the meaning of a parameter value ought to be
1016   independent of the syntax used for it (for an example, see the notes on
1017   parameter handling for media types in &media-types;).
1018</t>
1019<t>
1020   Authors of specifications defining new header fields are advised to consider
1021   documenting:
1022  <list style="symbols">
1023    <x:lt>
1024      <t>Whether the field is a single value, or whether it can be a list
1025      (delimited by commas; see &header-fields;).</t>
1026      <t>If it does not use the list syntax, document how to treat messages
1027      where the header field occurs multiple times (a sensible default would
1028      be to ignore the header field, but this might not always be the right
1029      choice).</t>
1030      <t>Note that intermediaries and software libraries might combine
1031      multiple header field instances into a single one, despite the header
1032      field not allowing this. A robust format enables recipients to discover
1033      these situations (good example: "Content-Type", as the comma can only
1034      appear inside quoted strings; bad example: "Location", as a comma can
1035      occur inside a URI).</t>
1036    </x:lt>
1037    <x:lt><t>Under what conditions the header field can be used; e.g., only in
1038    responses or requests, in all messages, only on responses to a particular
1039    request method.</t></x:lt>
1040    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
1041    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
1042    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
1043    field's value, insert or delete it.</t></x:lt>
1044    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
1045    <x:lt><t>Whether the header field is useful or allowable in trailers (see
1046    &chunked-encoding;).</t></x:lt>
1047    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
1048  </list>
1049</t>
1050</section>
1051
1052<section title="Request Header Fields" anchor="request.header.fields">
1053  <x:anchor-alias value="request-header"/>
1054<t>
1055   The request header fields allow the client to pass additional
1056   information about the request, and about the client itself, to the
1057   server. These fields act as request modifiers, with semantics
1058   equivalent to the parameters on a programming language method
1059   invocation.
1060</t>
1061<texttable align="left">
1062  <ttcol>Header Field Name</ttcol>
1063  <ttcol>Defined in...</ttcol>
1064
1065  <c>Accept</c> <c>&header-accept;</c>
1066  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
1067  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
1068  <c>Accept-Language</c> <c>&header-accept-language;</c>
1069  <c>Authorization</c> <c>&header-authorization;</c>
1070  <c>Expect</c> <c><xref target="header.expect"/></c>
1071  <c>From</c> <c><xref target="header.from"/></c>
1072  <c>Host</c> <c>&header-host;</c>
1073  <c>If-Match</c> <c>&header-if-match;</c>
1074  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
1075  <c>If-None-Match</c> <c>&header-if-none-match;</c>
1076  <c>If-Range</c> <c>&header-if-range;</c>
1077  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
1078  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
1079  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
1080  <c>Range</c> <c>&header-range;</c>
1081  <c>Referer</c> <c><xref target="header.referer"/></c>
1082  <c>TE</c> <c>&header-te;</c>
1083  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
1084</texttable>
1085</section>
1086
1087<section title="Response Header Fields" anchor="response.header.fields">
1088  <x:anchor-alias value="response-header"/>
1089<t>
1090   The response header fields allow the server to pass additional
1091   information about the response which cannot be placed in the status-line.
1092   These header fields give information about the server and about
1093   further access to the target resource (&effective-request-uri;).
1094</t>
1095<texttable align="left">
1096  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
1097
1098  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
1099  <c>Age</c> <c>&header-age;</c>
1100  <c>Allow</c> <c><xref target="header.allow"/></c>
1101  <c>Date</c> <c><xref target="header.date"/></c>
1102  <c>ETag</c> <c>&header-etag;</c>
1103  <c>Location</c> <c><xref target="header.location"/></c>
1104  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
1105  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
1106  <c>Server</c> <c><xref target="header.server"/></c>
1107  <c>Vary</c> <c>&header-vary;</c>
1108  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
1109</texttable>
1110</section>
1111
1112</section>
1113
1114<section title="Status Codes" anchor="status.codes">
1115<t>
1116   The status-code element is a 3-digit integer result code of the attempt to
1117   understand and satisfy the request.
1118</t>
1119<t>
1120   HTTP status codes are extensible. HTTP applications are not required
1121   to understand the meaning of all registered status codes, though such
1122   understanding is obviously desirable. However, applications &MUST;
1123   understand the class of any status code, as indicated by the first
1124   digit, and treat any unrecognized response as being equivalent to the
1125   x00 status code of that class, with the exception that an
1126   unrecognized response &MUST-NOT; be cached. For example, if an
1127   unrecognized status code of 431 is received by the client, it can
1128   safely assume that there was something wrong with its request and
1129   treat the response as if it had received a 400 status code. In such
1130   cases, user agents &SHOULD; present to the user the representation enclosed
1131   with the response, since that representation is likely to include human-readable
1132   information which will explain the unusual status.
1133</t>
1134<t>
1135   The first digit of the status-code defines the class of response. The
1136   last two digits do not have any categorization role. There are 5
1137   values for the first digit:
1138  <list style="symbols">
1139    <t>
1140      1xx: Informational - Request received, continuing process
1141    </t>
1142    <t>
1143      2xx: Success - The action was successfully received,
1144        understood, and accepted
1145    </t>
1146    <t>
1147      3xx: Redirection - Further action needs to be taken in order to
1148        complete the request
1149    </t>
1150    <t>
1151      4xx: Client Error - The request contains bad syntax or cannot
1152        be fulfilled
1153    </t>
1154    <t>
1155      5xx: Server Error - The server failed to fulfill an apparently
1156        valid request
1157    </t>
1158  </list>
1159</t>
1160<t>
1161   For most status codes the response can carry a payload, in which case a
1162   Content-Type header field indicates the payload's media type
1163   (&header-content-type;).
1164</t>
1165
1166<section title="Overview of Status Codes" anchor="overview.of.status.codes">
1167<t> 
1168   The status codes listed below are defined in this specification,
1169   &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
1170   The reason phrases listed here are only recommendations &mdash; they can be
1171   replaced by local equivalents without affecting the protocol.
1172</t>
1173<texttable align="left">
1174  <ttcol>status-code</ttcol>
1175  <ttcol>reason-phrase</ttcol>
1176  <ttcol>Defined in...</ttcol>
1177 
1178  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
1179  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
1180
1181  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
1182  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
1183  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
1184  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
1185  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
1186  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
1187  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
1188
1189  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
1190  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
1191  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
1192  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
1193  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
1194  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
1195  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
1196
1197  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
1198  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
1199  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
1200  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
1201  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
1202  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
1203  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
1204  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
1205  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
1206  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
1207  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
1208  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
1209  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
1210  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
1211  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
1212  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
1213  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
1214  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
1215  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
1216
1217  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
1218  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
1219  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
1220  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
1221  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
1222  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
1223</texttable>
1224<t>
1225   Note that this list is not exhaustive &mdash; it does not include
1226   extension status codes defined in other specifications.
1227</t>
1228</section>
1229
1230<section title="Status Code Registry" anchor="status.code.registry">
1231<t>
1232  The HTTP Status Code Registry defines the name space for the status-code
1233  token in the status-line of an HTTP response.
1234</t>
1235<t>
1236  Values to be added to this name space require IETF Review
1237  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
1238</t>
1239<t>
1240  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
1241</t>
1242
1243<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
1244<t>
1245   When it is necessary to express new semantics for a HTTP response that
1246   aren't specific to a single application or media type, and currently defined
1247   status codes are inadequate, a new status code can be registered.
1248</t>
1249<t>
1250   HTTP status codes are generic; that is, they are potentially applicable to
1251   any resource, not just one particular media type, "type" of resource, or
1252   application. As such, it is preferred that new HTTP status codes be
1253   registered in a document that isn't specific to a single application, so
1254   that this is clear.
1255</t>
1256<t>
1257   Definitions of new HTTP status codes typically explain the request
1258   conditions that produce a response containing the status code (e.g.,
1259   combinations of request headers and/or method(s)), along with any
1260   interactions with response headers (e.g., those that are required, those
1261   that modify the semantics of the response).
1262</t>
1263<t>
1264   New HTTP status codes are required to fall under one of the categories
1265   defined in <xref target="status.codes"/>. To allow existing parsers to
1266   properly handle them, new status codes cannot disallow a response body,
1267   although they can mandate a zero-length response body. They can require the
1268   presence of one or more particular HTTP response header(s).
1269</t>
1270<t>
1271   Likewise, their definitions can specify that caches are allowed to use
1272   heuristics to determine their freshness (see &caching;; by default, it is
1273   not allowed), and can define how to determine the resource which they
1274   carry a representation for (see <xref
1275   target="identifying.response.associated.with.representation"/>; by default,
1276   it is anonymous).
1277</t>
1278</section>
1279
1280</section>
1281
1282<section title="Informational 1xx" anchor="status.1xx">
1283<t>
1284   This class of status code indicates a provisional response,
1285   consisting only of the status-line and optional header fields, and is
1286   terminated by an empty line. There are no required header fields for this
1287   class of status code. Since HTTP/1.0 did not define any 1xx status
1288   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1289   except under experimental conditions.
1290</t>
1291<t>
1292   A client &MUST; be prepared to accept one or more 1xx status responses
1293   prior to a regular response, even if the client does not expect a 100
1294   (Continue) status message. Unexpected 1xx status responses &MAY; be
1295   ignored by a user agent.
1296</t>
1297<t>
1298   Proxies &MUST; forward 1xx responses, unless the connection between the
1299   proxy and its client has been closed, or unless the proxy itself
1300   requested the generation of the 1xx response. (For example, if a
1301   proxy adds a "Expect: 100-continue" field when it forwards a request,
1302   then it need not forward the corresponding 100 (Continue)
1303   response(s).)
1304</t>
1305
1306<section title="100 Continue" anchor="status.100">
1307  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1308  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1309<t>
1310   The client &SHOULD; continue with its request. This interim response is
1311   used to inform the client that the initial part of the request has
1312   been received and has not yet been rejected by the server. The client
1313   &SHOULD; continue by sending the remainder of the request or, if the
1314   request has already been completed, ignore this response. The server
1315   &MUST; send a final response after the request has been completed. See
1316   &use100; for detailed discussion of the use and handling of this
1317   status code.
1318</t>
1319</section>
1320
1321<section title="101 Switching Protocols" anchor="status.101">
1322  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1323  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1324<t>
1325   The server understands and is willing to comply with the client's
1326   request, via the Upgrade message header field (&header-upgrade;), for a
1327   change in the application protocol being used on this connection. The
1328   server will switch protocols to those defined by the response's
1329   Upgrade header field immediately after the empty line which
1330   terminates the 101 response.
1331</t>
1332<t>
1333   The protocol &SHOULD; be switched only when it is advantageous to do
1334   so. For example, switching to a newer version of HTTP is advantageous
1335   over older versions, and switching to a real-time, synchronous
1336   protocol might be advantageous when delivering resources that use
1337   such features.
1338</t>
1339</section>
1340</section>
1341
1342<section title="Successful 2xx" anchor="status.2xx">
1343<t>
1344   This class of status code indicates that the client's request was
1345   successfully received, understood, and accepted.
1346</t>
1347
1348<section title="200 OK" anchor="status.200">
1349  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1350  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1351<t>
1352   The request has succeeded. The payload returned with the response
1353   is dependent on the method used in the request, for example:
1354  <list style="hanging">
1355    <t hangText="GET">
1356      a representation of the target resource is sent in the response;
1357    </t>
1358    <t hangText="HEAD">
1359      the same representation as GET, except without the message body;
1360    </t>
1361    <t hangText="POST">
1362      a representation describing or containing the result of the action;
1363    </t>
1364    <t hangText="TRACE">
1365      a representation containing the request message as received by the
1366      end server.
1367    </t>
1368  </list>
1369</t>
1370<t>
1371   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1372   freshness for 200 responses.
1373</t>
1374</section>
1375
1376<section title="201 Created" anchor="status.201">
1377  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1378  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1379<t>
1380   The request has been fulfilled and has resulted in a new resource being
1381   created.
1382</t>
1383<t>
1384   The newly created resource is typically linked to from the response payload,
1385   with the most relevant URI also being carried in the Location header field.
1386   If the newly created resource's URI is the same as the Effective Request URI,
1387   this information can be omitted (e.g., in the case of a response to a PUT
1388   request). 
1389</t>
1390<t>
1391   The origin server &MUST; create the resource before returning the 201 status
1392   code. If the action cannot be carried out immediately, the server &SHOULD;
1393   respond with 202 (Accepted) response instead.
1394</t>
1395<t>
1396   A 201 response &MAY; contain an ETag response header field indicating
1397   the current value of the entity-tag for the representation of the resource
1398   just created (see &header-etag;).
1399</t>
1400</section>
1401
1402<section title="202 Accepted" anchor="status.202">
1403  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1404  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1405<t>
1406   The request has been accepted for processing, but the processing has
1407   not been completed.  The request might or might not eventually be
1408   acted upon, as it might be disallowed when processing actually takes
1409   place. There is no facility for re-sending a status code from an
1410   asynchronous operation such as this.
1411</t>
1412<t>
1413   The 202 response is intentionally non-committal. Its purpose is to
1414   allow a server to accept a request for some other process (perhaps a
1415   batch-oriented process that is only run once per day) without
1416   requiring that the user agent's connection to the server persist
1417   until the process is completed. The representation returned with this
1418   response &SHOULD; include an indication of the request's current status
1419   and either a pointer to a status monitor or some estimate of when the
1420   user can expect the request to be fulfilled.
1421</t>
1422</section>
1423
1424<section title="203 Non-Authoritative Information" anchor="status.203">
1425  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1426  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1427<t>
1428   The representation in the response has been transformed or otherwise
1429   modified by a transforming proxy (&intermediaries;).  Note that the
1430   behavior of transforming intermediaries is controlled by the no-transform
1431   Cache-Control directive (&header-cache-control;).
1432</t>
1433<t>
1434   This status code is only appropriate when the response status code would
1435   have been 200 (OK) otherwise. When the status code before transformation
1436   would have been different, the 214 Transformation Applied warn-code
1437   (&header-warning;) is appropriate.
1438</t>
1439<t>
1440   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1441   freshness for 203 responses.
1442</t>
1443</section>
1444
1445<section title="204 No Content" anchor="status.204">
1446  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1447  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1448<t>
1449   The 204 (No Content) status code indicates that the server has
1450   successfully fulfilled the request and that there is no additional
1451   content to return in the response payload body.  Metadata in the
1452   response header fields refer to the target resource and its current
1453   representation after the requested action.
1454</t>
1455<t>
1456   For example, if a 204 status code is received in response to a PUT
1457   request and the response contains an ETag header field, then the PUT
1458   was successful and the ETag field-value contains the entity-tag for
1459   the new representation of that target resource.
1460</t>
1461<t>
1462   The 204 response allows a server to indicate that the action has been
1463   successfully applied to the target resource while implying that the
1464   user agent &SHOULD-NOT; traverse away from its current "document view"
1465   (if any).  The server assumes that the user agent will provide some
1466   indication of the success to its user, in accord with its own interface,
1467   and apply any new or updated metadata in the response to the active
1468   representation.
1469</t>
1470<t>
1471   For example, a 204 status code is commonly used with document editing
1472   interfaces corresponding to a "save" action, such that the document
1473   being saved remains available to the user for editing. It is also
1474   frequently used with interfaces that expect automated data transfers
1475   to be prevalent, such as within distributed version control systems.
1476</t>
1477<t>
1478   The 204 response &MUST-NOT; include a message body, and thus is always
1479   terminated by the first empty line after the header fields.
1480</t>
1481</section>
1482
1483<section title="205 Reset Content" anchor="status.205">
1484  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1485  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1486<t>
1487   The server has fulfilled the request and the user agent &SHOULD; reset
1488   the document view which caused the request to be sent. This response
1489   is primarily intended to allow input for actions to take place via
1490   user input, followed by a clearing of the form in which the input is
1491   given so that the user can easily initiate another input action.
1492</t>
1493<t>   
1494   The message body included with the response &MUST; be empty. Note that
1495   receivers still need to parse the response according to the algorithm defined
1496   in &message-body;.
1497</t>
1498</section>
1499</section>
1500
1501<section title="Redirection 3xx" anchor="status.3xx">
1502<t>
1503   This class of status code indicates that further action needs to be
1504   taken by the user agent in order to fulfill the request.  If the required
1505   action involves a subsequent HTTP request, it &MAY; be carried out by the
1506   user agent without interaction with the user if and only if the method used
1507   in the second request is known to be "safe", as defined in
1508   <xref target="safe.methods"/>.
1509</t>
1510<t>
1511   There are several types of redirects:
1512   <list style="numbers">
1513      <x:lt>
1514        <t>
1515          Redirects of the request to another URI, either temporarily or
1516          permanently. The new URI is specified in the Location header field.
1517          In this specification, the status codes 301 (Moved Permanently),
1518          302 (Found), and 307 (Temporary Redirect) fall under this category.
1519        </t>
1520      </x:lt>
1521      <x:lt>
1522        <t>
1523          Redirection to a new location that represents an indirect response to
1524          the request, such as the result of a POST operation to be retrieved
1525          with a subsequent GET request. This is status code 303 (See Other).
1526        </t>
1527      </x:lt>
1528      <x:lt>
1529        <t>
1530          Redirection offering a choice of matching resources for use by
1531          agent-driven content negotiation (&agent-driven-negotiation;). This
1532          is status code 300 (Multiple Choices).
1533        </t>
1534      </x:lt>
1535      <x:lt>
1536        <t>
1537          Other kinds of redirection, such as to a cached result (status code 304
1538          (Not Modified), see &status-304;).
1539        </t>
1540      </x:lt>
1541   </list>
1542</t>
1543<x:note>
1544  <t>
1545    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1546    and 302 (Found) were defined for the first type of redirect, and the second
1547    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1548    However it turned out that web forms using POST expected redirects to change
1549    the operation for the subsequent request to retrieval (GET). To address this
1550    use case, HTTP/1.1 introduced the second type of redirect with the status
1551    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1552    As user agents did not change their behavior to maintain backwards
1553    compatibility, the first revision of HTTP/1.1 added yet another status code,
1554    307 (Temporary Redirect), for which the backwards compatibility problems did
1555    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1556    Over 10 years later, most user agents still do method rewriting for
1557    status codes 301 and 302, therefore this specification makes that behavior
1558    conformant in case the original request was POST.
1559  </t>
1560</x:note>
1561<t>
1562   A Location header field on a 3xx response indicates that a client &MAY;
1563   automatically redirect to the URI provided; see <xref target="header.location"/>.
1564</t>
1565<t>
1566   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1567   automatic redirection needs to done with care, since the redirect might
1568   change the conditions under which the request was issued.
1569</t>
1570<t>
1571   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1572   "infinite" redirection loops).
1573</t>
1574<x:note>
1575  <t>
1576    <x:h>Note:</x:h> An earlier version of this specification recommended a
1577    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1578    Content developers need to be aware that some clients might
1579    implement such a fixed limitation.
1580  </t>
1581</x:note>
1582
1583<section title="300 Multiple Choices" anchor="status.300">
1584  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1585  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1586<t>
1587   The target resource has more than one
1588   representation, each with its own specific location, and agent-driven
1589   negotiation information (&content-negotiation;) is being provided so that
1590   the user (or user agent) can select a preferred representation by
1591   redirecting its request to that location.
1592</t>
1593<t>
1594   Unless it was a HEAD request, the response &SHOULD; include a representation
1595   containing a list of representation metadata and location(s) from
1596   which the user or user agent can choose the one most appropriate. Depending
1597   upon the format and the capabilities of
1598   the user agent, selection of the most appropriate choice &MAY; be
1599   performed automatically. However, this specification does not define
1600   any standard for such automatic selection.
1601</t>
1602<t>
1603   If the server has a preferred choice of representation, it &SHOULD;
1604   include the specific URI for that representation in the Location
1605   field; user agents &MAY; use the Location field value for automatic
1606   redirection.
1607</t>
1608<t>
1609   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1610   freshness for 300 responses.
1611</t>
1612
1613</section>
1614
1615<section title="301 Moved Permanently" anchor="status.301">
1616  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1617  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1618<t>
1619   The target resource has been assigned a new permanent URI and any
1620   future references to this resource &SHOULD; use one of the returned
1621   URIs.  Clients with link editing capabilities ought to automatically
1622   re-link references to the effective request URI to one or more of the new
1623   references returned by the server, where possible.
1624</t>
1625<t>
1626   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1627   freshness for 301 responses.
1628</t>
1629<t>
1630   The new permanent URI &SHOULD; be given by the Location field in the
1631   response. A response payload can contain a short hypertext note with a
1632   hyperlink to the new URI(s).
1633</t>
1634<x:note>
1635  <t>
1636    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1637    request method from POST to GET for the subsequent request. If this
1638    behavior is undesired, status code 307 (Temporary Redirect) can be used
1639    instead.
1640  </t>
1641</x:note>
1642</section>
1643
1644<section title="302 Found" anchor="status.302">
1645  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1646  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1647<t>
1648   The target resource resides temporarily under a different URI.
1649   Since the redirection might be altered on occasion, the client &SHOULD;
1650   continue to use the effective request URI for future requests.
1651</t>
1652<t>
1653   The temporary URI &SHOULD; be given by the Location field in the
1654   response. A response payload can contain a short hypertext note with a
1655   hyperlink to the new URI(s).
1656</t>
1657<x:note>
1658  <t>
1659    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1660    request method from POST to GET for the subsequent request. If this
1661    behavior is undesired, status code 307 (Temporary Redirect) can be used
1662    instead.
1663  </t>
1664</x:note>
1665</section>
1666
1667<section title="303 See Other" anchor="status.303">
1668  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1669  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1670<t>
1671   The 303 status code indicates that the server is redirecting the
1672   user agent to a different resource, as indicated by a URI in the
1673   Location header field, that is intended to provide an indirect
1674   response to the original request.  In order to satisfy the original
1675   request, a user agent &SHOULD; perform a retrieval request using the
1676   Location URI (a GET or HEAD request if using HTTP), which
1677   may itself be redirected further, and present the eventual result as an
1678   answer to the original request.
1679   Note that the new URI in the Location header field is not considered
1680   equivalent to the effective request URI.
1681</t>
1682<t>
1683   This status code is generally applicable to any HTTP method.  It is
1684   primarily used to allow the output of a POST action to redirect
1685   the user agent to a selected resource, since doing so provides the
1686   information corresponding to the POST response in a form that
1687   can be separately identified, bookmarked, and cached independent
1688   of the original request.
1689</t>
1690<t>
1691   A 303 response to a GET request indicates that the requested
1692   resource does not have a representation of its own that can be
1693   transferred by the server over HTTP.  The Location URI indicates a
1694   resource that is descriptive of the target resource, such that the
1695   follow-on representation might be useful to recipients without
1696   implying that it adequately represents the target resource.
1697   Note that answers to the questions of what can be represented, what
1698   representations are adequate, and what might be a useful description
1699   are outside the scope of HTTP and thus entirely determined by the
1700   URI owner(s).
1701</t>
1702<t>
1703   Except for responses to a HEAD request, the representation of a 303
1704   response &SHOULD; contain a short hypertext note with a hyperlink
1705   to the Location URI.
1706</t>
1707</section>
1708
1709<section title="305 Use Proxy" anchor="status.305">
1710  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1711  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1712<t>
1713   The 305 status code was defined in a previous version of this specification
1714   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1715</t>
1716</section>
1717
1718<section title="306 (Unused)" anchor="status.306">
1719  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1720  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1721<t>
1722   The 306 status code was used in a previous version of the
1723   specification, is no longer used, and the code is reserved.
1724</t>
1725</section>
1726
1727<section title="307 Temporary Redirect" anchor="status.307">
1728  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1729  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1730<t>
1731   The target resource resides temporarily under a different URI.
1732   Since the redirection can change over time, the client &SHOULD;
1733   continue to use the effective request URI for future requests.
1734</t>
1735<t>
1736   The temporary URI &SHOULD; be given by the Location field in the
1737   response. A response payload can contain a short hypertext note with a
1738   hyperlink to the new URI(s).
1739</t>
1740<x:note>
1741  <t>
1742    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1743    it does not allow rewriting the request method from POST to GET. This
1744    specification defines no equivalent counterpart for 301 Moved Permanently
1745    (<xref target="draft-reschke-http-status-308"/>, however, defines the
1746    status code 308 Permanent Redirect for this purpose).
1747  </t>
1748</x:note>
1749</section>
1750</section>
1751
1752<section title="Client Error 4xx" anchor="status.4xx">
1753<t>
1754   The 4xx class of status code is intended for cases in which the
1755   client seems to have erred. Except when responding to a HEAD request,
1756   the server &SHOULD; include a representation containing an explanation of the
1757   error situation, and whether it is a temporary or permanent
1758   condition. These status codes are applicable to any request method.
1759   User agents &SHOULD; display any included representation to the user.
1760</t>
1761
1762<section title="400 Bad Request" anchor="status.400">
1763  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1764  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1765<t>
1766   The server cannot or will not process the request, due to a client error (e.g.,
1767   malformed syntax).
1768</t>
1769</section>
1770
1771<section title="402 Payment Required" anchor="status.402">
1772  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1773  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1774<t>
1775   This code is reserved for future use.
1776</t>
1777</section>
1778
1779<section title="403 Forbidden" anchor="status.403">
1780  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1781  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1782<t>
1783   The server understood the request, but refuses to authorize it. Providing
1784   different user authentication credentials might be successful, but any
1785   credentials that were provided in the request are insufficient. The request
1786   &SHOULD-NOT; be repeated with the same credentials.
1787</t>
1788<t>
1789   If the request method was not HEAD and the server wishes to make
1790   public why the request has not been fulfilled, it &SHOULD; describe the
1791   reason for the refusal in the representation.  If the server does not wish to
1792   make this information available to the client, the status code 404
1793   (Not Found) &MAY; be used instead.
1794</t>
1795</section>
1796
1797<section title="404 Not Found" anchor="status.404">
1798  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1799  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1800<t>
1801   The server has not found anything matching the effective request URI. No
1802   indication is given of whether the condition is temporary or
1803   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1804   knows, through some internally configurable mechanism, that an old
1805   resource is permanently unavailable and has no forwarding address.
1806   This status code is commonly used when the server does not wish to
1807   reveal exactly why the request has been refused, or when no other
1808   response is applicable.
1809</t>
1810</section>
1811
1812<section title="405 Method Not Allowed" anchor="status.405">
1813  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1814  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1815<t>
1816   The method specified in the request-line is not allowed for the target
1817   resource. The response &MUST; include an Allow header field containing a
1818   list of valid methods for the requested resource.
1819</t>
1820</section>
1821
1822<section title="406 Not Acceptable" anchor="status.406">
1823  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1824  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1825<t>
1826   The resource identified by the request is only capable of generating
1827   response representations which have content characteristics not acceptable
1828   according to the Accept and Accept-* header fields sent in the request
1829   (see &p3-header-fields;).
1830</t>
1831<t>
1832   Unless it was a HEAD request, the response &SHOULD; include a representation
1833   containing a list of available representation characteristics and location(s)
1834   from which the user or user agent can choose the one most
1835   appropriate. Depending upon the format and the
1836   capabilities of the user agent, selection of the most appropriate
1837   choice &MAY; be performed automatically. However, this specification
1838   does not define any standard for such automatic selection.
1839</t>
1840<x:note>
1841  <t>
1842    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1843    not acceptable according to the accept header fields sent in the
1844    request. In some cases, this might even be preferable to sending a
1845    406 response. User agents are encouraged to inspect the header fields of
1846    an incoming response to determine if it is acceptable.
1847  </t>
1848</x:note>
1849<t>
1850   If the response could be unacceptable, a user agent &SHOULD;
1851   temporarily stop receipt of more data and query the user for a
1852   decision on further actions.
1853</t>
1854</section>
1855
1856<section title="408 Request Timeout" anchor="status.408">
1857  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1858  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1859<t>
1860   The client did not produce a request within the time that the server
1861   was prepared to wait. The client &MAY; repeat the request without
1862   modifications at any later time.
1863</t>
1864</section>
1865
1866<section title="409 Conflict" anchor="status.409">
1867  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1868  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1869<t>
1870   The request could not be completed due to a conflict with the current
1871   state of the resource. This code is only allowed in situations where
1872   it is expected that the user might be able to resolve the conflict
1873   and resubmit the request. The response body &SHOULD; include enough
1874   information for the user to recognize the source of the conflict.
1875   Ideally, the response representation would include enough information for the
1876   user or user agent to fix the problem; however, that might not be
1877   possible and is not required.
1878</t>
1879<t>
1880   Conflicts are most likely to occur in response to a PUT request. For
1881   example, if versioning were being used and the representation being PUT
1882   included changes to a resource which conflict with those made by an
1883   earlier (third-party) request, the server might use the 409 response
1884   to indicate that it can't complete the request. In this case, the
1885   response representation would likely contain a list of the differences
1886   between the two versions.
1887</t>
1888</section>
1889
1890<section title="410 Gone" anchor="status.410">
1891  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1892  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1893<t>
1894   The target resource is no longer available at the server and no
1895   forwarding address is known. This condition is expected to be
1896   considered permanent. Clients with link editing capabilities &SHOULD;
1897   delete references to the effective request URI after user approval. If the
1898   server does not know, or has no facility to determine, whether or not
1899   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1900   used instead.
1901</t>
1902<t>
1903   The 410 response is primarily intended to assist the task of web
1904   maintenance by notifying the recipient that the resource is
1905   intentionally unavailable and that the server owners desire that
1906   remote links to that resource be removed. Such an event is common for
1907   limited-time, promotional services and for resources belonging to
1908   individuals no longer working at the server's site. It is not
1909   necessary to mark all permanently unavailable resources as "gone" or
1910   to keep the mark for any length of time &mdash; that is left to the
1911   discretion of the server owner.
1912</t>
1913<t>
1914   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1915   for 410 responses.
1916</t>
1917</section>
1918
1919<section title="411 Length Required" anchor="status.411">
1920  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1921  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1922<t>
1923   The server refuses to accept the request without a defined Content-Length.
1924   The client &MAY; repeat the request if it adds a valid
1925   Content-Length header field containing the length of the message body
1926   in the request message.
1927</t>
1928</section>
1929
1930<section title="413 Request Representation Too Large" anchor="status.413">
1931  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
1932  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
1933<t>
1934   The server is refusing to process a request because the request
1935   representation is larger than the server is willing or able to process. The
1936   server &MAY; close the connection to prevent the client from continuing
1937   the request.
1938</t>
1939<t>
1940   If the condition is temporary, the server &SHOULD; include a Retry-After
1941   header field to indicate that it is temporary and after what
1942   time the client &MAY; try again.
1943</t>
1944</section>
1945
1946<section title="414 URI Too Long" anchor="status.414">
1947  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1948  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1949<t>
1950   The server is refusing to service the request because the effective request URI
1951   is longer than the server is willing to interpret. This rare
1952   condition is only likely to occur when a client has improperly
1953   converted a POST request to a GET request with long query
1954   information, when the client has descended into a URI "black hole" of
1955   redirection (e.g., a redirected URI prefix that points to a suffix of
1956   itself), or when the server is under attack by a client attempting to
1957   exploit security holes present in some servers using fixed-length
1958   buffers for reading or manipulating the request-target.
1959</t>
1960</section>
1961
1962<section title="415 Unsupported Media Type" anchor="status.415">
1963  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1964  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1965<t>
1966   The server is refusing to service the request because the request
1967   payload is in a format not supported by this request method on the
1968   target resource.
1969</t>
1970</section>
1971
1972<section title="417 Expectation Failed" anchor="status.417">
1973  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1974  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1975<t>
1976   The expectation given in an Expect header field (see <xref target="header.expect"/>)
1977   could not be met by this server, or, if the server is a proxy,
1978   the server has unambiguous evidence that the request could not be met
1979   by the next-hop server.
1980</t>
1981</section>
1982
1983<section title="426 Upgrade Required" anchor="status.426">
1984  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
1985  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
1986<t>
1987   The request can not be completed without a prior protocol upgrade. This
1988   response &MUST; include an Upgrade header field (&header-upgrade;)
1989   specifying the required protocols.
1990</t>
1991<figure>
1992<preamble>Example:</preamble>
1993<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
1994HTTP/1.1 426 Upgrade Required
1995Upgrade: HTTP/3.0
1996Connection: Upgrade
1997Content-Length: <x:length-of target="s426body"/>
1998Content-Type: text/plain
1999
2000<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
2001</x:span></artwork></figure>
2002<t>
2003   The server &SHOULD; include a message body in the 426 response which
2004   indicates in human readable form the reason for the error and describes any
2005   alternative courses which may be available to the user.
2006</t>
2007</section>
2008</section>
2009
2010<section title="Server Error 5xx" anchor="status.5xx">
2011<t>
2012   Response status codes beginning with the digit "5" indicate cases in
2013   which the server is aware that it has erred or is incapable of
2014   performing the request. Except when responding to a HEAD request, the
2015   server &SHOULD; include a representation containing an explanation of the
2016   error situation, and whether it is a temporary or permanent
2017   condition. User agents &SHOULD; display any included representation to the
2018   user. These response codes are applicable to any request method.
2019</t>
2020
2021<section title="500 Internal Server Error" anchor="status.500">
2022  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
2023  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
2024<t>
2025   The server encountered an unexpected condition which prevented it
2026   from fulfilling the request.
2027</t>
2028</section>
2029
2030<section title="501 Not Implemented" anchor="status.501">
2031  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
2032  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
2033<t>
2034   The server does not support the functionality required to fulfill the
2035   request. This is the appropriate response when the server does not
2036   recognize the request method and is not capable of supporting it for
2037   any resource.
2038</t>
2039</section>
2040
2041<section title="502 Bad Gateway" anchor="status.502">
2042  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2043  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2044<t>
2045   The server, while acting as a gateway or proxy, received an invalid
2046   response from the upstream server it accessed in attempting to
2047   fulfill the request.
2048</t>
2049</section>
2050
2051<section title="503 Service Unavailable" anchor="status.503">
2052  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2053  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2054<t>
2055   The server is currently unable to handle the request due to a
2056   temporary overloading or maintenance of the server.
2057</t>
2058<t>
2059   The implication is that this is a temporary condition which will be
2060   alleviated after some delay. If known, the length of the delay &MAY; be
2061   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2062   If no Retry-After is given, the client &SHOULD; handle the response as it
2063   would for a 500 response.
2064</t>
2065<x:note>
2066  <t>
2067    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2068    server has to use it when becoming overloaded. Some servers might wish
2069    to simply refuse the connection.
2070  </t>
2071</x:note>
2072</section>
2073
2074<section title="504 Gateway Timeout" anchor="status.504">
2075  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2076  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2077<t>
2078   The server, while acting as a gateway or proxy, did not receive a
2079   timely response from the upstream server specified by the URI (e.g.,
2080   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2081   to access in attempting to complete the request.
2082</t>
2083<x:note>
2084  <t>
2085    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2086    return 400 or 500 when DNS lookups time out.
2087  </t>
2088</x:note>
2089</section>
2090
2091<section title="505 HTTP Version Not Supported" anchor="status.505">
2092  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2093  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2094<t>
2095   The server does not support, or refuses to support, the protocol
2096   version that was used in the request message. The server is
2097   indicating that it is unable or unwilling to complete the request
2098   using the same major version as the client, as described in &http-version;,
2099   other than with this error message. The response &SHOULD; contain
2100   a representation describing why that version is not supported and what other
2101   protocols are supported by that server.
2102</t>
2103
2104</section>
2105</section>
2106
2107</section>
2108
2109<section title="Representation" anchor="representation">
2110<t>
2111   Request and Response messages &MAY; transfer a representation if not otherwise
2112   restricted by the request method or response status code. A representation
2113   consists of metadata (representation header fields) and data (representation
2114   body).  When a complete or partial representation is enclosed in an HTTP message,
2115   it is referred to as the payload of the message. HTTP representations
2116   are defined in &payload;.
2117</t>
2118<t>
2119   A representation body is only present in a message when a message body is
2120   present, as described in &message-body;. The representation body is obtained
2121   from the message body by decoding any Transfer-Encoding that might
2122   have been applied to ensure safe and proper transfer of the message.
2123</t>
2124
2125<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
2126<t>
2127   It is sometimes necessary to determine an identifier for the resource
2128   associated with a representation.
2129</t>
2130<t>
2131   An HTTP request representation, when present, is always associated with an
2132   anonymous (i.e., unidentified) resource.
2133</t>
2134<t>
2135   In the common case, an HTTP response is a representation of the target
2136   resource (see &effective-request-uri;). However, this is not always the
2137   case. To determine the URI of the resource a response is associated with,
2138   the following rules are used (with the first applicable one being selected):
2139</t>
2140<t><list style="numbers">
2141   <t>If the response status code is 200 or 203 and the request method was GET,
2142   the response payload is a representation of the target resource.</t>
2143   <t>If the response status code is 204, 206, or 304 and the request method was GET
2144   or HEAD, the response payload is a partial representation of the target
2145   resource.</t>
2146   <t>If the response has a Content-Location header field, and that URI is the same
2147   as the effective request URI, the response payload is a representation of the
2148   target resource.</t>
2149   <t>If the response has a Content-Location header field, and that URI is not the
2150   same as the effective request URI, then the response asserts that its
2151   payload is a representation of the resource identified by the
2152   Content-Location URI. However, such an assertion cannot be trusted unless
2153   it can be verified by other means (not defined by HTTP).</t>
2154   <t>Otherwise, the response is a representation of an anonymous (i.e.,
2155   unidentified) resource.</t>
2156</list></t>
2157<t>
2158  <cref anchor="TODO-req-uri">
2159   The comparison function is going to have to be defined somewhere,
2160   because we already need to compare URIs for things like cache invalidation.</cref>
2161</t>
2162</section>
2163
2164</section>
2165
2166
2167<section title="Common Protocol Parameters" anchor="common.protocol.parameters">
2168<section title="Date/Time Formats" anchor="http.date">
2169  <x:anchor-alias value="HTTP-date"/>
2170<t>
2171   HTTP applications have historically allowed three different formats
2172   for date/time stamps. However, the preferred format is a fixed-length subset
2173   of that defined by <xref target="RFC1123"/>:
2174</t>
2175<figure><artwork type="example" x:indent-with="  ">
2176Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2177</artwork></figure>
2178<t>
2179   The other formats are described here only for compatibility with obsolete
2180   implementations.
2181</t>
2182<figure><artwork type="example" x:indent-with="  ">
2183Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2184Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2185</artwork></figure>
2186<t>
2187   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2188   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2189   only generate the RFC 1123 format for representing HTTP-date values
2190   in header fields.
2191</t>
2192<t>
2193   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2194   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2195   equal to UTC (Coordinated Universal Time). This is indicated in the
2196   first two formats by the inclusion of "GMT" as the three-letter
2197   abbreviation for time zone, and &MUST; be assumed when reading the
2198   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2199   additional whitespace beyond that specifically included as SP in the
2200   grammar.
2201</t>
2202<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2203  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2204</artwork></figure>
2205<t anchor="preferred.date.format">
2206  <x:anchor-alias value="rfc1123-date"/>
2207  <x:anchor-alias value="time-of-day"/>
2208  <x:anchor-alias value="hour"/>
2209  <x:anchor-alias value="minute"/>
2210  <x:anchor-alias value="second"/>
2211  <x:anchor-alias value="day-name"/>
2212  <x:anchor-alias value="day"/>
2213  <x:anchor-alias value="month"/>
2214  <x:anchor-alias value="year"/>
2215  <x:anchor-alias value="GMT"/>
2216  Preferred format:
2217</t>
2218<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"/>
2219  <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>
2220  ; fixed length subset of the format defined in
2221  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2222 
2223  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2224               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2225               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2226               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2227               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2228               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2229               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2230               
2231  <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>
2232               ; e.g., 02 Jun 1982
2233
2234  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2235  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2236               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2237               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2238               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2239               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2240               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2241               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2242               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2243               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2244               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2245               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2246               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2247  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2248
2249  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2250
2251  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2252                 ; 00:00:00 - 23:59:59
2253                 
2254  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2255  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2256  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2257</artwork></figure>
2258<t>
2259  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2260  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2261  same as those defined for the RFC 5322 constructs
2262  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2263</t>
2264<t anchor="obsolete.date.formats">
2265  <x:anchor-alias value="obs-date"/>
2266  <x:anchor-alias value="rfc850-date"/>
2267  <x:anchor-alias value="asctime-date"/>
2268  <x:anchor-alias value="date1"/>
2269  <x:anchor-alias value="date2"/>
2270  <x:anchor-alias value="date3"/>
2271  <x:anchor-alias value="rfc1123-date"/>
2272  <x:anchor-alias value="day-name-l"/>
2273  Obsolete formats:
2274</t>
2275<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2276  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2277</artwork></figure>
2278<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2279  <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>
2280  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2281                 ; day-month-year (e.g., 02-Jun-82)
2282
2283  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2284         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2285         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2286         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2287         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2288         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2289         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2290</artwork></figure>
2291<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2292  <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>
2293  <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> ))
2294                 ; month day (e.g., Jun  2)
2295</artwork></figure>
2296<x:note>
2297  <t>
2298    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2299    accepting date values that might have been sent by non-HTTP
2300    applications, as is sometimes the case when retrieving or posting
2301    messages via proxies/gateways to SMTP or NNTP.
2302  </t>
2303</x:note>
2304<x:note>
2305  <t>
2306    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2307    to their usage within the protocol stream. Clients and servers are
2308    not required to use these formats for user presentation, request
2309    logging, etc.
2310  </t>
2311</x:note>
2312</section>
2313
2314<section title="Product Tokens" anchor="product.tokens">
2315  <x:anchor-alias value="product"/>
2316  <x:anchor-alias value="product-version"/>
2317<t>
2318   Product tokens are used to allow communicating applications to
2319   identify themselves by software name and version. Most fields using
2320   product tokens also allow sub-products which form a significant part
2321   of the application to be listed, separated by whitespace. By
2322   convention, the products are listed in order of their significance
2323   for identifying the application.
2324</t>
2325<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2326  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2327  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2328</artwork></figure>
2329<t>
2330   Examples:
2331</t>
2332<figure><artwork type="example">
2333  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2334  Server: Apache/0.8.4
2335</artwork></figure>
2336<t>
2337   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2338   used for advertising or other non-essential information. Although any
2339   token octet &MAY; appear in a product-version, this token &SHOULD;
2340   only be used for a version identifier (i.e., successive versions of
2341   the same product &SHOULD; only differ in the product-version portion of
2342   the product value).
2343</t>
2344</section>
2345</section>
2346
2347<section title="Header Field Definitions" anchor="header.field.definitions">
2348<t>
2349   This section defines the syntax and semantics of HTTP/1.1 header fields
2350   related to request and response semantics.
2351</t>
2352
2353<section title="Allow" anchor="header.allow">
2354  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2355  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2356  <x:anchor-alias value="Allow"/>
2357<t>
2358   The "Allow" header field lists the set of methods advertised as
2359   supported by the target resource. The purpose of this field is strictly to
2360   inform the recipient of valid request methods associated with the resource.
2361</t>
2362<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2363  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2364</artwork></figure>
2365<t>
2366   Example of use:
2367</t>
2368<figure><artwork type="example">
2369  Allow: GET, HEAD, PUT
2370</artwork></figure>
2371<t>
2372   The actual set of allowed methods is defined by the origin server at the
2373   time of each request.
2374</t>
2375<t>
2376   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2377   understand all the methods specified in order to handle them according to
2378   the generic message handling rules.
2379</t>
2380</section>
2381
2382<section title="Date" anchor="header.date">
2383  <iref primary="true" item="Date header field" x:for-anchor=""/>
2384  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2385  <x:anchor-alias value="Date"/>
2386<t>
2387   The "Date" header field represents the date and time at which
2388   the message was originated, having the same semantics as the Origination
2389   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2390   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2391   it &MUST; be sent in rfc1123-date format.
2392</t>
2393<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2394  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2395</artwork></figure>
2396<t>
2397   An example is
2398</t>
2399<figure><artwork type="example">
2400  Date: Tue, 15 Nov 1994 08:12:31 GMT
2401</artwork></figure>
2402<t>
2403   Origin servers &MUST; include a Date header field in all responses,
2404   except in these cases:
2405  <list style="numbers">
2406      <t>If the response status code is 100 (Continue) or 101 (Switching
2407         Protocols), the response &MAY; include a Date header field, at
2408         the server's option.</t>
2409
2410      <t>If the response status code conveys a server error, e.g., 500
2411         (Internal Server Error) or 503 (Service Unavailable), and it is
2412         inconvenient or impossible to generate a valid Date.</t>
2413
2414      <t>If the server does not have a clock that can provide a
2415         reasonable approximation of the current time, its responses
2416         &MUST-NOT; include a Date header field.</t>
2417  </list>
2418</t>
2419<t>
2420   A received message that does not have a Date header field &MUST; be
2421   assigned one by the recipient if the message will be cached by that
2422   recipient.
2423</t>
2424<t>
2425   Clients can use the Date header field as well; in order to keep request
2426   messages small, they are advised not to include it when it doesn't convey
2427   any useful information (as is usually the case for requests that do not
2428   contain a payload).
2429</t>
2430<t>
2431   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2432   time subsequent to the generation of the message. It &SHOULD; represent
2433   the best available approximation of the date and time of message
2434   generation, unless the implementation has no means of generating a
2435   reasonably accurate date and time. In theory, the date ought to
2436   represent the moment just before the payload is generated. In
2437   practice, the date can be generated at any time during the message
2438   origination without affecting its semantic value.
2439</t>
2440</section>
2441
2442<section title="Expect" anchor="header.expect">
2443  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2444  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2445  <x:anchor-alias value="Expect"/>
2446  <x:anchor-alias value="expectation"/>
2447  <x:anchor-alias value="expect-param"/>
2448  <x:anchor-alias value="expect-name"/>
2449  <x:anchor-alias value="expect-value"/>
2450<t>
2451   The "Expect" header field is used to indicate that particular
2452   server behaviors are required by the client.
2453</t>
2454<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"/>
2455  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2456 
2457  <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> ]
2458                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2459  <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> ]
2460 
2461  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2462  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2463</artwork></figure>
2464<t>
2465   If all received Expect header field(s) are syntactically valid but contain
2466   an expectation that the recipient does not understand or cannot comply with,
2467   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2468   recipient of a syntactically invalid Expectation header field &MUST; respond
2469   with a 4xx status code other than 417.
2470</t>
2471<t>
2472   The only expectation defined by this specification is:
2473</t>
2474<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2475  100-continue
2476   <list>
2477      <t>
2478        The "100-continue" expectation is defined &use100;. It does not support
2479        any expect-params.
2480      </t>
2481   </list>
2482</t>
2483<t>
2484   Comparison is case-insensitive for names (expect-name), and case-sensitive
2485   for values (expect-value).
2486</t>
2487<t>
2488   The Expect mechanism is hop-by-hop: the above requirements apply to any
2489   server, including proxies. However, the Expect header field itself is
2490   end-to-end; it &MUST; be forwarded if the request is forwarded.
2491</t>
2492<t>
2493   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2494   header field.
2495</t>
2496</section>
2497
2498<section title="From" anchor="header.from">
2499  <iref primary="true" item="From header field" x:for-anchor=""/>
2500  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2501  <x:anchor-alias value="From"/>
2502  <x:anchor-alias value="mailbox"/>
2503<t>
2504   The "From" header field, if given, &SHOULD; contain an Internet
2505   e-mail address for the human user who controls the requesting user
2506   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2507   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2508</t>
2509<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2510  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2511 
2512  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2513</artwork></figure>
2514<t>
2515   An example is:
2516</t>
2517<figure><artwork type="example">
2518  From: webmaster@example.org
2519</artwork></figure>
2520<t>
2521   This header field &MAY; be used for logging purposes and as a means for
2522   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2523   be used as an insecure form of access protection. The interpretation
2524   of this field is that the request is being performed on behalf of the
2525   person given, who accepts responsibility for the method performed. In
2526   particular, robot agents &SHOULD; include this header field so that the
2527   person responsible for running the robot can be contacted if problems
2528   occur on the receiving end.
2529</t>
2530<t>
2531   The Internet e-mail address in this field &MAY; be separate from the
2532   Internet host which issued the request. For example, when a request
2533   is passed through a proxy the original issuer's address &SHOULD; be
2534   used.
2535</t>
2536<t>
2537   The client &SHOULD-NOT;  send the From header field without the user's
2538   approval, as it might conflict with the user's privacy interests or
2539   their site's security policy. It is strongly recommended that the
2540   user be able to disable, enable, and modify the value of this field
2541   at any time prior to a request.
2542</t>
2543</section>
2544
2545<section title="Location" anchor="header.location">
2546  <iref primary="true" item="Location header field" x:for-anchor=""/>
2547  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2548  <x:anchor-alias value="Location"/>
2549<t>
2550   The "Location" header field &MAY; be sent in responses to refer to
2551   a specific resource in accordance with the semantics of the status
2552   code.
2553</t>
2554<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2555  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2556</artwork></figure>
2557<t>
2558   For 201 (Created) responses, the Location is the URI of the new resource
2559   which was created by the request. For 3xx responses, the location &SHOULD;
2560   indicate the server's preferred URI for automatic redirection to the
2561   resource.
2562</t>
2563<t>
2564   The field value consists of a single URI-reference. When it has the form
2565   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2566   the final value is computed by resolving it against the effective request
2567   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2568   navigated to by the user agent, did contain a fragment identifier, and the
2569   final value does not, then the original URI's fragment identifier is added
2570   to the final value.
2571</t>
2572<figure>
2573<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-->
2574<artwork type="example">
2575  Location: /pub/WWW/People.html#tim
2576</artwork>
2577<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2578</figure>
2579<figure>
2580<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-->
2581<artwork type="example">
2582  Location: http://www.example.net/index.html
2583</artwork>
2584<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2585</figure>
2586<x:note>
2587  <t>
2588    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2589    that are not valid URI references. This specification does not mandate or
2590    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2591  </t>
2592</x:note>
2593<t>
2594   There are circumstances in which a fragment identifier in a Location URI
2595   would not be appropriate. For instance, when it appears in a 201 Created
2596   response, where the Location header field specifies the URI for the entire
2597   created resource.
2598</t>
2599<x:note>
2600  <t>
2601    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2602    from Location in that the Content-Location identifies the most specific
2603    resource corresponding to the enclosed representation.
2604    It is therefore possible for a response to contain header fields for
2605    both Location and Content-Location.
2606  </t>
2607</x:note>
2608</section>
2609
2610<section title="Max-Forwards" anchor="header.max-forwards">
2611  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2612  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2613  <x:anchor-alias value="Max-Forwards"/>
2614<t>
2615   The "Max-Forwards" header field provides a mechanism with the
2616   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2617   methods to limit the number of times that the request is forwarded by
2618   proxies. This can be useful when the client is attempting to
2619   trace a request which appears to be failing or looping mid-chain.
2620</t>
2621<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2622  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2623</artwork></figure>
2624<t>
2625   The Max-Forwards value is a decimal integer indicating the remaining
2626   number of times this request message can be forwarded.
2627</t>
2628<t>
2629   Each recipient of a TRACE or OPTIONS request
2630   containing a Max-Forwards header field &MUST; check and update its
2631   value prior to forwarding the request. If the received value is zero
2632   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2633   respond as the final recipient. If the received Max-Forwards value is
2634   greater than zero, then the forwarded message &MUST; contain an updated
2635   Max-Forwards field with a value decremented by one (1).
2636</t>
2637<t>
2638   The Max-Forwards header field &MAY; be ignored for all other request
2639   methods.
2640</t>
2641</section>
2642
2643<section title="Referer" anchor="header.referer">
2644  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2645  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2646  <x:anchor-alias value="Referer"/>
2647<t>
2648   The "Referer" [sic] header field allows the client to specify the
2649   URI of the resource from which the target URI was obtained (the
2650   "referrer", although the header field is misspelled.).
2651</t>
2652<t>
2653   The Referer header field allows servers to generate lists of back-links to
2654   resources for interest, logging, optimized caching, etc. It also allows
2655   obsolete or mistyped links to be traced for maintenance. Some servers use
2656   Referer as a means of controlling where they allow links from (so-called
2657   "deep linking"), but legitimate requests do not always
2658   contain a Referer header field.
2659</t>
2660<t>
2661   If the target URI was obtained from a source that does not have its own
2662   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2663   sent with the value "about:blank", or not be sent at all. Note that this
2664   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2665</t>
2666<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2667  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2668</artwork></figure>
2669<t>
2670   Example:
2671</t>
2672<figure><artwork type="example">
2673  Referer: http://www.example.org/hypertext/Overview.html
2674</artwork></figure>
2675<t>
2676   If the field value is a relative URI, it &SHOULD; be interpreted
2677   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2678   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2679</t>
2680</section>
2681
2682<section title="Retry-After" anchor="header.retry-after">
2683  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2684  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2685  <x:anchor-alias value="Retry-After"/>
2686<t>
2687   The header "Retry-After" field can be used with a 503 (Service
2688   Unavailable) response to indicate how long the service is expected to
2689   be unavailable to the requesting client. This field &MAY; also be used
2690   with any 3xx (Redirection) response to indicate the minimum time the
2691   user-agent is asked to wait before issuing the redirected request.
2692</t>
2693<t>
2694   The value of this field can be either an HTTP-date or an integer number
2695   of seconds (in decimal) after the time of the response.
2696</t>
2697<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2698  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2699</artwork></figure>
2700<t anchor="rule.delta-seconds">
2701  <x:anchor-alias value="delta-seconds"/>
2702   Time spans are non-negative decimal integers, representing time in
2703   seconds.
2704</t>
2705<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2706  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2707</artwork></figure>
2708<t>
2709   Two examples of its use are
2710</t>
2711<figure><artwork type="example">
2712  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2713  Retry-After: 120
2714</artwork></figure>
2715<t>
2716   In the latter example, the delay is 2 minutes.
2717</t>
2718</section>
2719
2720<section title="Server" anchor="header.server">
2721  <iref primary="true" item="Server header field" x:for-anchor=""/>
2722  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2723  <x:anchor-alias value="Server"/>
2724<t>
2725   The "Server" header field contains information about the
2726   software used by the origin server to handle the request.
2727</t>
2728<t>
2729   The field can contain multiple
2730   product tokens (<xref target="product.tokens"/>) and
2731   comments (&header-fields;) identifying the server and any significant
2732   subproducts. The product tokens are listed in order of their significance
2733   for identifying the application.
2734</t>
2735<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2736  <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> ) )
2737</artwork></figure>
2738<t>
2739   Example:
2740</t>
2741<figure><artwork type="example">
2742  Server: CERN/3.0 libwww/2.17
2743</artwork></figure>
2744<t>
2745   If the response is being forwarded through a proxy, the proxy
2746   application &MUST-NOT; modify the Server header field. Instead, it
2747   &MUST; include a Via field (as described in &header-via;).
2748</t>
2749<x:note>
2750  <t>
2751    <x:h>Note:</x:h> Revealing the specific software version of the server might
2752    allow the server machine to become more vulnerable to attacks
2753    against software that is known to contain security holes. Server
2754    implementors are encouraged to make this field a configurable
2755    option.
2756  </t>
2757</x:note>
2758</section>
2759
2760<section title="User-Agent" anchor="header.user-agent">
2761  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2762  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2763  <x:anchor-alias value="User-Agent"/>
2764<t>
2765   The "User-Agent" header field contains information about the user
2766   agent originating the request. User agents &SHOULD; include this field with
2767   requests.
2768</t>
2769<t>
2770   Typically, it is used for statistical purposes, the tracing of protocol
2771   violations, and tailoring responses to avoid particular user agent
2772   limitations.
2773</t>
2774<t>
2775   The field can contain multiple
2776   product tokens (<xref target="product.tokens"/>)
2777   and comments (&header-fields;) identifying the agent and its
2778   significant subproducts. By convention, the product tokens are listed in
2779   order of their significance for identifying the application.
2780</t>
2781<t>
2782   Because this field is usually sent on every request a user agent makes,
2783   implementations are encouraged not to include needlessly fine-grained
2784   detail, and to limit (or even prohibit) the addition of subproducts by third
2785   parties. Overly long and detailed User-Agent field values make requests
2786   larger and can also be used to identify ("fingerprint") the user against
2787   their wishes.
2788</t>
2789<t>
2790   Likewise, implementations are encouraged not to use the product tokens of
2791   other implementations in order to declare compatibility with them, as this
2792   circumvents the purpose of the field. Finally, they are encouraged not to
2793   use comments to identify products; doing so makes the field value more
2794   difficult to parse.
2795</t>
2796<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2797  <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> ) )
2798</artwork></figure>
2799<t>
2800   Example:
2801</t>
2802<figure><artwork type="example">
2803  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2804</artwork></figure>
2805</section>
2806
2807</section>
2808
2809<section title="IANA Considerations" anchor="IANA.considerations">
2810
2811<section title="Method Registry" anchor="method.registration">
2812<t>
2813  The registration procedure for HTTP request methods is defined by
2814  <xref target="method.registry"/> of this document.
2815</t>
2816<t>
2817   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2818   and be populated with the registrations below:
2819</t>
2820<?BEGININC p2-semantics.iana-methods ?>
2821<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2822<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2823   <ttcol>Method</ttcol>
2824   <ttcol>Safe</ttcol>
2825   <ttcol>Reference</ttcol>
2826   <c>CONNECT</c>
2827   <c>no</c>
2828   <c>
2829      <xref target="CONNECT"/>
2830   </c>
2831   <c>DELETE</c>
2832   <c>no</c>
2833   <c>
2834      <xref target="DELETE"/>
2835   </c>
2836   <c>GET</c>
2837   <c>yes</c>
2838   <c>
2839      <xref target="GET"/>
2840   </c>
2841   <c>HEAD</c>
2842   <c>yes</c>
2843   <c>
2844      <xref target="HEAD"/>
2845   </c>
2846   <c>OPTIONS</c>
2847   <c>yes</c>
2848   <c>
2849      <xref target="OPTIONS"/>
2850   </c>
2851   <c>POST</c>
2852   <c>no</c>
2853   <c>
2854      <xref target="POST"/>
2855   </c>
2856   <c>PUT</c>
2857   <c>no</c>
2858   <c>
2859      <xref target="PUT"/>
2860   </c>
2861   <c>TRACE</c>
2862   <c>yes</c>
2863   <c>
2864      <xref target="TRACE"/>
2865   </c>
2866</texttable>
2867<!--(END)-->
2868<?ENDINC p2-semantics.iana-methods ?>
2869</section>
2870
2871<section title="Status Code Registry" anchor="status.code.registration">
2872<t>
2873   The registration procedure for HTTP Status Codes &mdash; previously defined
2874   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2875   by <xref target="status.code.registry"/> of this document.
2876</t>
2877<t>
2878   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2879   shall be updated with the registrations below:
2880</t>
2881<?BEGININC p2-semantics.iana-status-codes ?>
2882<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2883<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2884   <ttcol>Value</ttcol>
2885   <ttcol>Description</ttcol>
2886   <ttcol>Reference</ttcol>
2887   <c>100</c>
2888   <c>Continue</c>
2889   <c>
2890      <xref target="status.100"/>
2891   </c>
2892   <c>101</c>
2893   <c>Switching Protocols</c>
2894   <c>
2895      <xref target="status.101"/>
2896   </c>
2897   <c>200</c>
2898   <c>OK</c>
2899   <c>
2900      <xref target="status.200"/>
2901   </c>
2902   <c>201</c>
2903   <c>Created</c>
2904   <c>
2905      <xref target="status.201"/>
2906   </c>
2907   <c>202</c>
2908   <c>Accepted</c>
2909   <c>
2910      <xref target="status.202"/>
2911   </c>
2912   <c>203</c>
2913   <c>Non-Authoritative Information</c>
2914   <c>
2915      <xref target="status.203"/>
2916   </c>
2917   <c>204</c>
2918   <c>No Content</c>
2919   <c>
2920      <xref target="status.204"/>
2921   </c>
2922   <c>205</c>
2923   <c>Reset Content</c>
2924   <c>
2925      <xref target="status.205"/>
2926   </c>
2927   <c>300</c>
2928   <c>Multiple Choices</c>
2929   <c>
2930      <xref target="status.300"/>
2931   </c>
2932   <c>301</c>
2933   <c>Moved Permanently</c>
2934   <c>
2935      <xref target="status.301"/>
2936   </c>
2937   <c>302</c>
2938   <c>Found</c>
2939   <c>
2940      <xref target="status.302"/>
2941   </c>
2942   <c>303</c>
2943   <c>See Other</c>
2944   <c>
2945      <xref target="status.303"/>
2946   </c>
2947   <c>305</c>
2948   <c>Use Proxy</c>
2949   <c>
2950      <xref target="status.305"/>
2951   </c>
2952   <c>306</c>
2953   <c>(Unused)</c>
2954   <c>
2955      <xref target="status.306"/>
2956   </c>
2957   <c>307</c>
2958   <c>Temporary Redirect</c>
2959   <c>
2960      <xref target="status.307"/>
2961   </c>
2962   <c>400</c>
2963   <c>Bad Request</c>
2964   <c>
2965      <xref target="status.400"/>
2966   </c>
2967   <c>402</c>
2968   <c>Payment Required</c>
2969   <c>
2970      <xref target="status.402"/>
2971   </c>
2972   <c>403</c>
2973   <c>Forbidden</c>
2974   <c>
2975      <xref target="status.403"/>
2976   </c>
2977   <c>404</c>
2978   <c>Not Found</c>
2979   <c>
2980      <xref target="status.404"/>
2981   </c>
2982   <c>405</c>
2983   <c>Method Not Allowed</c>
2984   <c>
2985      <xref target="status.405"/>
2986   </c>
2987   <c>406</c>
2988   <c>Not Acceptable</c>
2989   <c>
2990      <xref target="status.406"/>
2991   </c>
2992   <c>408</c>
2993   <c>Request Timeout</c>
2994   <c>
2995      <xref target="status.408"/>
2996   </c>
2997   <c>409</c>
2998   <c>Conflict</c>
2999   <c>
3000      <xref target="status.409"/>
3001   </c>
3002   <c>410</c>
3003   <c>Gone</c>
3004   <c>
3005      <xref target="status.410"/>
3006   </c>
3007   <c>411</c>
3008   <c>Length Required</c>
3009   <c>
3010      <xref target="status.411"/>
3011   </c>
3012   <c>413</c>
3013   <c>Request Representation Too Large</c>
3014   <c>
3015      <xref target="status.413"/>
3016   </c>
3017   <c>414</c>
3018   <c>URI Too Long</c>
3019   <c>
3020      <xref target="status.414"/>
3021   </c>
3022   <c>415</c>
3023   <c>Unsupported Media Type</c>
3024   <c>
3025      <xref target="status.415"/>
3026   </c>
3027   <c>417</c>
3028   <c>Expectation Failed</c>
3029   <c>
3030      <xref target="status.417"/>
3031   </c>
3032   <c>426</c>
3033   <c>Upgrade Required</c>
3034   <c>
3035      <xref target="status.426"/>
3036   </c>
3037   <c>500</c>
3038   <c>Internal Server Error</c>
3039   <c>
3040      <xref target="status.500"/>
3041   </c>
3042   <c>501</c>
3043   <c>Not Implemented</c>
3044   <c>
3045      <xref target="status.501"/>
3046   </c>
3047   <c>502</c>
3048   <c>Bad Gateway</c>
3049   <c>
3050      <xref target="status.502"/>
3051   </c>
3052   <c>503</c>
3053   <c>Service Unavailable</c>
3054   <c>
3055      <xref target="status.503"/>
3056   </c>
3057   <c>504</c>
3058   <c>Gateway Timeout</c>
3059   <c>
3060      <xref target="status.504"/>
3061   </c>
3062   <c>505</c>
3063   <c>HTTP Version Not Supported</c>
3064   <c>
3065      <xref target="status.505"/>
3066   </c>
3067</texttable>
3068<!--(END)-->
3069<?ENDINC p2-semantics.iana-status-codes ?>
3070</section>
3071<section title="Header Field Registration" anchor="header.field.registration">
3072<t>
3073   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3074   with the permanent registrations below (see <xref target="RFC3864"/>):
3075</t>
3076<?BEGININC p2-semantics.iana-headers ?>
3077<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3078<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3079   <ttcol>Header Field Name</ttcol>
3080   <ttcol>Protocol</ttcol>
3081   <ttcol>Status</ttcol>
3082   <ttcol>Reference</ttcol>
3083
3084   <c>Allow</c>
3085   <c>http</c>
3086   <c>standard</c>
3087   <c>
3088      <xref target="header.allow"/>
3089   </c>
3090   <c>Date</c>
3091   <c>http</c>
3092   <c>standard</c>
3093   <c>
3094      <xref target="header.date"/>
3095   </c>
3096   <c>Expect</c>
3097   <c>http</c>
3098   <c>standard</c>
3099   <c>
3100      <xref target="header.expect"/>
3101   </c>
3102   <c>From</c>
3103   <c>http</c>
3104   <c>standard</c>
3105   <c>
3106      <xref target="header.from"/>
3107   </c>
3108   <c>Location</c>
3109   <c>http</c>
3110   <c>standard</c>
3111   <c>
3112      <xref target="header.location"/>
3113   </c>
3114   <c>Max-Forwards</c>
3115   <c>http</c>
3116   <c>standard</c>
3117   <c>
3118      <xref target="header.max-forwards"/>
3119   </c>
3120   <c>Referer</c>
3121   <c>http</c>
3122   <c>standard</c>
3123   <c>
3124      <xref target="header.referer"/>
3125   </c>
3126   <c>Retry-After</c>
3127   <c>http</c>
3128   <c>standard</c>
3129   <c>
3130      <xref target="header.retry-after"/>
3131   </c>
3132   <c>Server</c>
3133   <c>http</c>
3134   <c>standard</c>
3135   <c>
3136      <xref target="header.server"/>
3137   </c>
3138   <c>User-Agent</c>
3139   <c>http</c>
3140   <c>standard</c>
3141   <c>
3142      <xref target="header.user-agent"/>
3143   </c>
3144</texttable>
3145<!--(END)-->
3146<?ENDINC p2-semantics.iana-headers ?>
3147<t>
3148   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3149</t>
3150</section>
3151</section>
3152
3153<section title="Security Considerations" anchor="security.considerations">
3154<t>
3155   This section is meant to inform application developers, information
3156   providers, and users of the security limitations in HTTP/1.1 as
3157   described by this document. The discussion does not include
3158   definitive solutions to the problems revealed, though it does make
3159   some suggestions for reducing security risks.
3160</t>
3161
3162<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3163<t>
3164   Like any generic data transfer protocol, HTTP cannot regulate the
3165   content of the data that is transferred, nor is there any a priori
3166   method of determining the sensitivity of any particular piece of
3167   information within the context of any given request. Therefore,
3168   applications &SHOULD; supply as much control over this information as
3169   possible to the provider of that information. Four header fields are
3170   worth special mention in this context: Server, Via, Referer and From.
3171</t>
3172<t>
3173   Revealing the specific software version of the server might allow the
3174   server machine to become more vulnerable to attacks against software
3175   that is known to contain security holes. Implementors &SHOULD; make the
3176   Server header field a configurable option.
3177</t>
3178<t>
3179   Proxies which serve as a portal through a network firewall &SHOULD;
3180   take special precautions regarding the transfer of header information
3181   that identifies the hosts behind the firewall. In particular, they
3182   &SHOULD; remove, or replace with sanitized versions, any Via fields
3183   generated behind the firewall.
3184</t>
3185<t>
3186   The Referer header field allows reading patterns to be studied and reverse
3187   links drawn. Although it can be very useful, its power can be abused
3188   if user details are not separated from the information contained in
3189   the Referer. Even when the personal information has been removed, the
3190   Referer header field might indicate a private document's URI whose
3191   publication would be inappropriate.
3192</t>
3193<t>
3194   The information sent in the From field might conflict with the user's
3195   privacy interests or their site's security policy, and hence it
3196   &SHOULD-NOT;  be transmitted without the user being able to disable,
3197   enable, and modify the contents of the field. The user &MUST; be able
3198   to set the contents of this field within a user preference or
3199   application defaults configuration.
3200</t>
3201<t>
3202   We suggest, though do not require, that a convenient toggle interface
3203   be provided for the user to enable or disable the sending of From and
3204   Referer information.
3205</t>
3206<t>
3207   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3208   target="header.server"/>) header fields can sometimes be used to determine
3209   that a specific client or server has a particular security hole which might
3210   be exploited. Unfortunately, this same information is often used for other
3211   valuable purposes for which HTTP currently has no better mechanism.
3212</t>
3213<t>
3214   Furthermore, the User-Agent header field may contain enough entropy to be
3215   used, possibly in conjunction with other material, to uniquely identify the
3216   user.
3217</t>
3218<t>
3219   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3220   that was sent in request header fields within the body of their response.
3221   Clients &SHOULD; be careful with sensitive information, like Cookies,
3222   Authorization credentials, and other header fields that might be used to
3223   collect data from the client.
3224</t> 
3225</section>
3226
3227<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3228<t>
3229   Because the source of a link might be private information or might
3230   reveal an otherwise private information source, it is strongly
3231   recommended that the user be able to select whether or not the
3232   Referer field is sent. For example, a browser client could have a
3233   toggle switch for browsing openly/anonymously, which would
3234   respectively enable/disable the sending of Referer and From
3235   information.
3236</t>
3237<t>
3238   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3239   HTTP request if the referring page was transferred with a secure
3240   protocol.
3241</t>
3242<t>
3243   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3244   sensitive data because that data will be placed in the request-target. Many
3245   existing servers, proxies, and user agents log or display the request-target
3246   in places where it might be visible to third parties. Such services can
3247   use POST-based form submission instead.
3248</t>
3249</section>
3250
3251<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3252<t>
3253   If a single server supports multiple organizations that do not trust
3254   one another, then it &MUST; check the values of Location and Content-Location
3255   header fields in responses that are generated under control of
3256   said organizations to make sure that they do not attempt to
3257   invalidate resources over which they have no authority.
3258</t>
3259<t>
3260   Furthermore, appending the fragment identifier from one URI to another
3261   one obtained from a Location header field might leak confidential
3262   information to the target server &mdash; although the fragment identifier is
3263   not transmitted in the final request, it might be visible to the user agent
3264   through other means, such as scripting.
3265</t>
3266</section>
3267
3268<section title="Security Considerations for CONNECT">
3269<t>
3270   Since tunneled data is opaque to the proxy, there are additional
3271   risks to tunneling to other well-known or reserved ports.
3272   A HTTP client CONNECTing to port 25 could relay spam
3273   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3274   access to a small number of known ports.
3275</t>
3276</section>
3277
3278</section>
3279
3280<section title="Acknowledgments" anchor="acks">
3281<t>
3282  See &acks;.
3283</t>
3284</section>
3285</middle>
3286<back>
3287
3288<references title="Normative References">
3289
3290<reference anchor="Part1">
3291  <front>
3292    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3293    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3294      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3295      <address><email>fielding@gbiv.com</email></address>
3296    </author>
3297    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3298      <organization abbrev="W3C">World Wide Web Consortium</organization>
3299      <address><email>ylafon@w3.org</email></address>
3300    </author>
3301    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3302      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3303      <address><email>julian.reschke@greenbytes.de</email></address>
3304    </author>
3305    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3306  </front>
3307  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3308  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3309</reference>
3310
3311<reference anchor="Part3">
3312  <front>
3313    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3314    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3315      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3316      <address><email>fielding@gbiv.com</email></address>
3317    </author>
3318    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3319      <organization abbrev="W3C">World Wide Web Consortium</organization>
3320      <address><email>ylafon@w3.org</email></address>
3321    </author>
3322    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3323      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3324      <address><email>julian.reschke@greenbytes.de</email></address>
3325    </author>
3326    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3327  </front>
3328  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3329  <x:source href="p3-payload.xml" basename="p3-payload"/>
3330</reference>
3331
3332<reference anchor="Part4">
3333  <front>
3334    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3335    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3336      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3337      <address><email>fielding@gbiv.com</email></address>
3338    </author>
3339    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3340      <organization abbrev="W3C">World Wide Web Consortium</organization>
3341      <address><email>ylafon@w3.org</email></address>
3342    </author>
3343    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3344      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3345      <address><email>julian.reschke@greenbytes.de</email></address>
3346    </author>
3347    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3348  </front>
3349  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3350  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3351</reference>
3352
3353<reference anchor="Part5">
3354  <front>
3355    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3356    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3357      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3358      <address><email>fielding@gbiv.com</email></address>
3359    </author>
3360    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3361      <organization abbrev="W3C">World Wide Web Consortium</organization>
3362      <address><email>ylafon@w3.org</email></address>
3363    </author>
3364    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3365      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3366      <address><email>julian.reschke@greenbytes.de</email></address>
3367    </author>
3368    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3369  </front>
3370  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3371  <x:source href="p5-range.xml" basename="p5-range"/>
3372</reference>
3373
3374<reference anchor="Part6">
3375  <front>
3376    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3377    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3378      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3379      <address><email>fielding@gbiv.com</email></address>
3380    </author>
3381    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3382      <organization abbrev="W3C">World Wide Web Consortium</organization>
3383      <address><email>ylafon@w3.org</email></address>
3384    </author>
3385    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3386      <organization>Rackspace</organization>
3387      <address><email>mnot@mnot.net</email></address>
3388    </author>
3389    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3390      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3391      <address><email>julian.reschke@greenbytes.de</email></address>
3392    </author>
3393    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3394  </front>
3395  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3396  <x:source href="p6-cache.xml" basename="p6-cache"/>
3397</reference>
3398
3399<reference anchor="Part7">
3400  <front>
3401    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3402    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3403      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3404      <address><email>fielding@gbiv.com</email></address>
3405    </author>
3406    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3407      <organization abbrev="W3C">World Wide Web Consortium</organization>
3408      <address><email>ylafon@w3.org</email></address>
3409    </author>
3410    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3411      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3412      <address><email>julian.reschke@greenbytes.de</email></address>
3413    </author>
3414    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3415  </front>
3416  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3417  <x:source href="p7-auth.xml" basename="p7-auth"/>
3418</reference>
3419
3420<reference anchor="RFC1950">
3421  <front>
3422    <title>ZLIB Compressed Data Format Specification version 3.3</title>
3423    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3424      <organization>Aladdin Enterprises</organization>
3425      <address><email>ghost@aladdin.com</email></address>
3426    </author>
3427    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
3428    <date month="May" year="1996"/>
3429  </front>
3430  <seriesInfo name="RFC" value="1950"/>
3431  <!--<annotation>
3432    RFC 1950 is an Informational RFC, thus it might be less stable than
3433    this specification. On the other hand, this downward reference was
3434    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3435    therefore it is unlikely to cause problems in practice. See also
3436    <xref target="BCP97"/>.
3437  </annotation>-->
3438</reference>
3439
3440<reference anchor="RFC1951">
3441  <front>
3442    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
3443    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3444      <organization>Aladdin Enterprises</organization>
3445      <address><email>ghost@aladdin.com</email></address>
3446    </author>
3447    <date month="May" year="1996"/>
3448  </front>
3449  <seriesInfo name="RFC" value="1951"/>
3450  <!--<annotation>
3451    RFC 1951 is an Informational RFC, thus it might be less stable than
3452    this specification. On the other hand, this downward reference was
3453    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3454    therefore it is unlikely to cause problems in practice. See also
3455    <xref target="BCP97"/>.
3456  </annotation>-->
3457</reference>
3458
3459<reference anchor="RFC1952">
3460  <front>
3461    <title>GZIP file format specification version 4.3</title>
3462    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3463      <organization>Aladdin Enterprises</organization>
3464      <address><email>ghost@aladdin.com</email></address>
3465    </author>
3466    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
3467      <address><email>gzip@prep.ai.mit.edu</email></address>
3468    </author>
3469    <author initials="M." surname="Adler" fullname="Mark Adler">
3470      <address><email>madler@alumni.caltech.edu</email></address>
3471    </author>
3472    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3473      <address><email>ghost@aladdin.com</email></address>
3474    </author>
3475    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
3476      <address><email>randeg@alumni.rpi.edu</email></address>
3477    </author>
3478    <date month="May" year="1996"/>
3479  </front>
3480  <seriesInfo name="RFC" value="1952"/>
3481  <!--<annotation>
3482    RFC 1952 is an Informational RFC, thus it might be less stable than
3483    this specification. On the other hand, this downward reference was
3484    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3485    therefore it is unlikely to cause problems in practice. See also
3486    <xref target="BCP97"/>.
3487  </annotation>-->
3488</reference>
3489
3490<reference anchor="RFC2045">
3491  <front>
3492    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3493    <author initials="N." surname="Freed" fullname="Ned Freed">
3494      <organization>Innosoft International, Inc.</organization>
3495      <address><email>ned@innosoft.com</email></address>
3496    </author>
3497    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3498      <organization>First Virtual Holdings</organization>
3499      <address><email>nsb@nsb.fv.com</email></address>
3500    </author>
3501    <date month="November" year="1996"/>
3502  </front>
3503  <seriesInfo name="RFC" value="2045"/>
3504</reference>
3505
3506<reference anchor="RFC2046">
3507  <front>
3508    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
3509    <author initials="N." surname="Freed" fullname="Ned Freed">
3510      <organization>Innosoft International, Inc.</organization>
3511      <address><email>ned@innosoft.com</email></address>
3512    </author>
3513    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3514      <organization>First Virtual Holdings</organization>
3515      <address><email>nsb@nsb.fv.com</email></address>
3516    </author>
3517    <date month="November" year="1996"/>
3518  </front>
3519  <seriesInfo name="RFC" value="2046"/>
3520</reference>
3521
3522<reference anchor="RFC2119">
3523  <front>
3524    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3525    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3526      <organization>Harvard University</organization>
3527      <address><email>sob@harvard.edu</email></address>
3528    </author>
3529    <date month="March" year="1997"/>
3530  </front>
3531  <seriesInfo name="BCP" value="14"/>
3532  <seriesInfo name="RFC" value="2119"/>
3533</reference>
3534
3535<reference anchor="RFC3986">
3536 <front>
3537  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3538  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3539    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3540    <address>
3541       <email>timbl@w3.org</email>
3542       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3543    </address>
3544  </author>
3545  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3546    <organization abbrev="Day Software">Day Software</organization>
3547    <address>
3548      <email>fielding@gbiv.com</email>
3549      <uri>http://roy.gbiv.com/</uri>
3550    </address>
3551  </author>
3552  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3553    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3554    <address>
3555      <email>LMM@acm.org</email>
3556      <uri>http://larry.masinter.net/</uri>
3557    </address>
3558  </author>
3559  <date month='January' year='2005'></date>
3560 </front>
3561 <seriesInfo name="STD" value="66"/>
3562 <seriesInfo name="RFC" value="3986"/>
3563</reference>
3564
3565<reference anchor='RFC4647'>
3566  <front>
3567    <title>Matching of Language Tags</title>
3568    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
3569      <organization>Yahoo! Inc.</organization>
3570      <address><email>addison@inter-locale.com</email></address>
3571    </author>
3572    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
3573      <organization>Google</organization>
3574      <address><email>mark.davis@macchiato.com</email></address>
3575    </author>
3576    <date year='2006' month='September' />
3577  </front>
3578  <seriesInfo name='BCP' value='47' />
3579  <seriesInfo name='RFC' value='4647' />
3580</reference>
3581
3582<reference anchor="RFC5234">
3583  <front>
3584    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3585    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3586      <organization>Brandenburg InternetWorking</organization>
3587      <address>
3588        <email>dcrocker@bbiw.net</email>
3589      </address> 
3590    </author>
3591    <author initials="P." surname="Overell" fullname="Paul Overell">
3592      <organization>THUS plc.</organization>
3593      <address>
3594        <email>paul.overell@thus.net</email>
3595      </address>
3596    </author>
3597    <date month="January" year="2008"/>
3598  </front>
3599  <seriesInfo name="STD" value="68"/>
3600  <seriesInfo name="RFC" value="5234"/>
3601</reference>
3602
3603<reference anchor='RFC5646'>
3604  <front>
3605    <title>Tags for Identifying Languages</title>
3606    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
3607      <organization>Lab126</organization>
3608      <address><email>addison@inter-locale.com</email></address>
3609    </author>
3610    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
3611      <organization>Google</organization>
3612      <address><email>mark.davis@google.com</email></address>
3613    </author>
3614    <date month='September' year='2009' />
3615  </front>
3616  <seriesInfo name='BCP' value='47' />
3617  <seriesInfo name='RFC' value='5646' />
3618</reference>
3619
3620</references>
3621
3622<references title="Informative References">
3623
3624<reference anchor="RFC1123">
3625  <front>
3626    <title>Requirements for Internet Hosts - Application and Support</title>
3627    <author initials="R." surname="Braden" fullname="Robert Braden">
3628      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3629      <address><email>Braden@ISI.EDU</email></address>
3630    </author>
3631    <date month="October" year="1989"/>
3632  </front>
3633  <seriesInfo name="STD" value="3"/>
3634  <seriesInfo name="RFC" value="1123"/>
3635</reference>
3636
3637<reference anchor="RFC1945">
3638  <front>
3639    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3640    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3641      <organization>MIT, Laboratory for Computer Science</organization>
3642      <address><email>timbl@w3.org</email></address>
3643    </author>
3644    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3645      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3646      <address><email>fielding@ics.uci.edu</email></address>
3647    </author>
3648    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3649      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3650      <address><email>frystyk@w3.org</email></address>
3651    </author>
3652    <date month="May" year="1996"/>
3653  </front>
3654  <seriesInfo name="RFC" value="1945"/>
3655</reference>
3656
3657<reference anchor="RFC2049">
3658  <front>
3659    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
3660    <author initials="N." surname="Freed" fullname="Ned Freed">
3661      <organization>Innosoft International, Inc.</organization>
3662      <address><email>ned@innosoft.com</email></address>
3663    </author>
3664    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3665      <organization>First Virtual Holdings</organization>
3666      <address><email>nsb@nsb.fv.com</email></address>
3667    </author>
3668    <date month="November" year="1996"/>
3669  </front>
3670  <seriesInfo name="RFC" value="2049"/>
3671</reference>
3672
3673<reference anchor="RFC2068">
3674  <front>
3675    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3676    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3677      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3678      <address><email>fielding@ics.uci.edu</email></address>
3679    </author>
3680    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3681      <organization>MIT Laboratory for Computer Science</organization>
3682      <address><email>jg@w3.org</email></address>
3683    </author>
3684    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3685      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3686      <address><email>mogul@wrl.dec.com</email></address>
3687    </author>
3688    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3689      <organization>MIT Laboratory for Computer Science</organization>
3690      <address><email>frystyk@w3.org</email></address>
3691    </author>
3692    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3693      <organization>MIT Laboratory for Computer Science</organization>
3694      <address><email>timbl@w3.org</email></address>
3695    </author>
3696    <date month="January" year="1997"/>
3697  </front>
3698  <seriesInfo name="RFC" value="2068"/>
3699</reference>
3700
3701<reference anchor="RFC2076">
3702  <front>
3703    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
3704    <author initials="J." surname="Palme" fullname="Jacob Palme">
3705      <organization>Stockholm University/KTH</organization>
3706      <address><email>jpalme@dsv.su.se</email></address>
3707    </author>
3708    <date month="February" year="1997"/>
3709  </front>
3710  <seriesInfo name="RFC" value="2076"/>
3711</reference>
3712
3713<reference anchor="RFC2277">
3714  <front>
3715    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
3716    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
3717      <organization>UNINETT</organization>
3718      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
3719    </author>
3720    <date month="January" year="1998"/>
3721  </front>
3722  <seriesInfo name="BCP" value="18"/>
3723  <seriesInfo name="RFC" value="2277"/>
3724</reference>
3725
3726<reference anchor='RFC2295'>
3727  <front>
3728    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
3729    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
3730      <organization>Technische Universiteit Eindhoven</organization>
3731      <address>
3732        <email>koen@win.tue.nl</email>
3733      </address>
3734    </author>
3735    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
3736      <organization>Hewlett-Packard Company</organization>
3737      <address>
3738        <email>mutz@hpl.hp.com</email>
3739      </address>
3740    </author>
3741    <date year='1998' month='March'/>
3742  </front>
3743  <seriesInfo name='RFC' value='2295'/>
3744</reference>
3745
3746<reference anchor="RFC2388">
3747  <front>
3748    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
3749    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3750      <organization>Xerox Palo Alto Research Center</organization>
3751      <address><email>masinter@parc.xerox.com</email></address>
3752    </author>
3753    <date year="1998" month="August"/>
3754  </front>
3755  <seriesInfo name="RFC" value="2388"/>
3756</reference>
3757
3758<reference anchor="RFC2557">
3759  <front>
3760    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
3761    <author initials="F." surname="Palme" fullname="Jacob Palme">
3762      <organization>Stockholm University and KTH</organization>
3763      <address><email>jpalme@dsv.su.se</email></address>
3764    </author>
3765    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
3766      <organization>Microsoft Corporation</organization>
3767      <address><email>alexhop@microsoft.com</email></address>
3768    </author>
3769    <author initials="N." surname="Shelness" fullname="Nick Shelness">
3770      <organization>Lotus Development Corporation</organization>
3771      <address><email>Shelness@lotus.com</email></address>
3772    </author>
3773    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
3774      <address><email>stef@nma.com</email></address>
3775    </author>
3776    <date year="1999" month="March"/>
3777  </front>
3778  <seriesInfo name="RFC" value="2557"/>
3779</reference>
3780
3781<reference anchor="RFC2616">
3782  <front>
3783    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3784    <author initials="R." surname="Fielding" fullname="R. Fielding">
3785      <organization>University of California, Irvine</organization>
3786      <address><email>fielding@ics.uci.edu</email></address>
3787    </author>
3788    <author initials="J." surname="Gettys" fullname="J. Gettys">
3789      <organization>W3C</organization>
3790      <address><email>jg@w3.org</email></address>
3791    </author>
3792    <author initials="J." surname="Mogul" fullname="J. Mogul">
3793      <organization>Compaq Computer Corporation</organization>
3794      <address><email>mogul@wrl.dec.com</email></address>
3795    </author>
3796    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3797      <organization>MIT Laboratory for Computer Science</organization>
3798      <address><email>frystyk@w3.org</email></address>
3799    </author>
3800    <author initials="L." surname="Masinter" fullname="L. Masinter">
3801      <organization>Xerox Corporation</organization>
3802      <address><email>masinter@parc.xerox.com</email></address>
3803    </author>
3804    <author initials="P." surname="Leach" fullname="P. Leach">
3805      <organization>Microsoft Corporation</organization>
3806      <address><email>paulle@microsoft.com</email></address>
3807    </author>
3808    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3809      <organization>W3C</organization>
3810      <address><email>timbl@w3.org</email></address>
3811    </author>
3812    <date month="June" year="1999"/>
3813  </front>
3814  <seriesInfo name="RFC" value="2616"/>
3815</reference>
3816
3817<reference anchor='RFC2817'>
3818  <front>
3819    <title>Upgrading to TLS Within HTTP/1.1</title>
3820    <author initials='R.' surname='Khare' fullname='R. Khare'>
3821      <organization>4K Associates / UC Irvine</organization>
3822      <address><email>rohit@4K-associates.com</email></address>
3823    </author>
3824    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3825      <organization>Agranat Systems, Inc.</organization>
3826      <address><email>lawrence@agranat.com</email></address>
3827    </author>
3828    <date year='2000' month='May' />
3829  </front>
3830  <seriesInfo name='RFC' value='2817' />
3831</reference>
3832
3833<reference anchor="RFC3629">
3834  <front>
3835    <title>UTF-8, a transformation format of ISO 10646</title>
3836    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
3837      <organization>Alis Technologies</organization>
3838      <address><email>fyergeau@alis.com</email></address>
3839    </author>
3840    <date month="November" year="2003"/>
3841  </front>
3842  <seriesInfo name="STD" value="63"/>
3843  <seriesInfo name="RFC" value="3629"/>
3844</reference>
3845
3846<reference anchor='RFC3864'>
3847  <front>
3848    <title>Registration Procedures for Message Header Fields</title>
3849    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3850      <organization>Nine by Nine</organization>
3851      <address><email>GK-IETF@ninebynine.org</email></address>
3852    </author>
3853    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3854      <organization>BEA Systems</organization>
3855      <address><email>mnot@pobox.com</email></address>
3856    </author>
3857    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3858      <organization>HP Labs</organization>
3859      <address><email>JeffMogul@acm.org</email></address>
3860    </author>
3861    <date year='2004' month='September' />
3862  </front>
3863  <seriesInfo name='BCP' value='90' />
3864  <seriesInfo name='RFC' value='3864' />
3865</reference>
3866
3867<reference anchor="RFC4288">
3868  <front>
3869    <title>Media Type Specifications and Registration Procedures</title>
3870    <author initials="N." surname="Freed" fullname="N. Freed">
3871      <organization>Sun Microsystems</organization>
3872      <address>
3873        <email>ned.freed@mrochek.com</email>
3874      </address>
3875    </author>
3876    <author initials="J." surname="Klensin" fullname="J. Klensin">
3877      <address>
3878        <email>klensin+ietf@jck.com</email>
3879      </address>
3880    </author>
3881    <date year="2005" month="December"/>
3882  </front>
3883  <seriesInfo name="BCP" value="13"/>
3884  <seriesInfo name="RFC" value="4288"/>
3885</reference>
3886
3887<reference anchor='RFC5226'>
3888  <front>
3889    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3890    <author initials='T.' surname='Narten' fullname='T. Narten'>
3891      <organization>IBM</organization>
3892      <address><email>narten@us.ibm.com</email></address>
3893    </author>
3894    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3895      <organization>Google</organization>
3896      <address><email>Harald@Alvestrand.no</email></address>
3897    </author>
3898    <date year='2008' month='May' />
3899  </front>
3900  <seriesInfo name='BCP' value='26' />
3901  <seriesInfo name='RFC' value='5226' />
3902</reference>
3903
3904<reference anchor="RFC5322">
3905  <front>
3906    <title>Internet Message Format</title>
3907    <author initials="P." surname="Resnick" fullname="P. Resnick">
3908      <organization>Qualcomm Incorporated</organization>
3909    </author>
3910    <date year="2008" month="October"/>
3911  </front> 
3912  <seriesInfo name="RFC" value="5322"/>
3913</reference>
3914
3915<reference anchor='RFC5789'>
3916  <front>
3917    <title>PATCH Method for HTTP</title>
3918    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3919      <organization>Linden Lab</organization>
3920    </author>
3921    <author initials='J.' surname='Snell' fullname='J. Snell' />
3922    <date year='2010' month='March' />
3923  </front>
3924  <seriesInfo name='RFC' value='5789' />
3925</reference>
3926
3927<reference anchor="RFC5987">
3928        <front>
3929    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3930    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3931      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3932      <address>
3933        <postal>
3934          <street>Hafenweg 16</street>
3935          <city>Muenster</city><region>NW</region><code>48155</code>
3936          <country>Germany</country>
3937        </postal>
3938        <email>julian.reschke@greenbytes.de</email>     
3939        <uri>http://greenbytes.de/tech/webdav/</uri>   
3940      </address>
3941    </author>
3942    <date month="August" year="2010"/>
3943  </front>
3944  <seriesInfo name="RFC" value="5987"/>
3945</reference>
3946
3947<reference anchor="RFC6151">
3948  <front>
3949    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
3950    <author initials="S." surname="Turner" fullname="S. Turner"/>
3951    <author initials="L." surname="Chen" fullname="L. Chen"/>
3952    <date year="2011" month="March" />
3953  </front>
3954  <seriesInfo name="RFC" value="6151" />
3955</reference>
3956
3957<reference anchor="RFC6266">
3958  <front>
3959    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
3960    in the Hypertext Transfer Protocol (HTTP)</title>
3961    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3962      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3963      <address>
3964        <email>julian.reschke@greenbytes.de</email>
3965      </address>
3966    </author>
3967    <date month="June" year="2011"/>
3968  </front>
3969  <seriesInfo name='RFC' value='6266' />
3970</reference>
3971
3972<reference anchor="draft-reschke-http-status-308">
3973        <front>
3974    <title abbrev="HTTP Status Code 308">The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)</title>
3975    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3976      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3977      <address>
3978        <email>julian.reschke@greenbytes.de</email>     
3979      </address>
3980    </author>
3981    <date month="March" year="2012"/>
3982  </front>
3983  <seriesInfo name="Internet-Draft" value="draft-reschke-http-status-308-07"/>
3984</reference>
3985
3986</references>
3987
3988<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3989<t>
3990  Clarify definition of POST.
3991  (<xref target="POST"/>)
3992</t>
3993<t>
3994  Remove requirement to handle all Content-* header fields; ban use of
3995  Content-Range with PUT.
3996  (<xref target="PUT"/>)
3997</t>
3998<t>
3999  Take over definition of CONNECT method from <xref target="RFC2817"/>.
4000  (<xref target="CONNECT"/>)
4001</t>
4002<t>
4003  This document takes over the Status Code Registry, previously defined
4004  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
4005  (<xref target="status.code.registry"/>)
4006</t>
4007<t>
4008  Broadened the definition of 203 (Non-Authoritative Information) to include
4009  cases of payload transformations as well.
4010  (<xref target="status.203"/>)
4011</t>
4012<t>
4013  Status codes 301, 302, and 307: removed the normative requirements on both
4014  response payloads and user interaction.
4015  (<xref target="status.3xx"/>)
4016</t>
4017<t>
4018  Failed to consider that there are many other request methods that are safe
4019  to automatically redirect, and further that the user agent is able to make
4020  that determination based on the request method semantics.
4021  Furthermore, allow user agents to rewrite the method from POST to GET
4022  for status codes 301 and 302.
4023  (Sections <xref format="counter" target="status.301"/>,
4024  <xref format="counter" target="status.302"/> and
4025  <xref format="counter" target="status.307"/>)
4026</t>
4027<t>
4028  Deprecate 305 Use Proxy status code, because user agents did not implement it.
4029  It used to indicate that the target resource needs to be accessed through the
4030  proxy given by the Location field. The Location field gave the URI of the
4031  proxy. The recipient was expected to repeat this single request via the proxy.
4032  (<xref target="status.305"/>)
4033</t>
4034<t>
4035  Define status 426 (Upgrade Required) (this was incorporated from
4036  <xref target="RFC2817"/>).
4037  (<xref target="status.426"/>)
4038</t>
4039<t>
4040  Change ABNF productions for header fields to only define the field value.
4041  (<xref target="header.field.definitions"/>)
4042</t>
4043<t>
4044  Reclassify "Allow" as response header field, removing the option to
4045  specify it in a PUT request.
4046  Relax the server requirement on the contents of the Allow header field and
4047  remove requirement on clients to always trust the header field value.
4048  (<xref target="header.allow"/>)
4049</t>
4050<t>
4051  The ABNF for the Expect header field has been both fixed (allowing parameters
4052  for value-less expectations as well) and simplified (allowing trailing
4053  semicolons after "100-continue" when they were invalid before).
4054  (<xref target="header.expect"/>)
4055</t>
4056<t>
4057  Correct syntax of Location header field to allow URI references (including
4058  relative references and fragments), as referred symbol "absoluteURI" wasn't
4059  what was expected, and add some clarifications as to when use of fragments
4060  would not be appropriate.
4061  (<xref target="header.location"/>)
4062</t>
4063<t>
4064  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
4065  extension methods could have used it as well).
4066  (<xref target="header.max-forwards"/>)
4067</t>
4068<t>
4069  Allow Referer field value of "about:blank" as alternative to not specifying it.
4070  (<xref target="header.referer"/>)
4071</t>
4072<t>
4073  In the description of the Server header field, the Via field
4074  was described as a SHOULD. The requirement was and is stated
4075  correctly in the description of the Via header field in &header-via;.
4076  (<xref target="header.server"/>)
4077</t>
4078</section>
4079
4080<?BEGININC p2-semantics.abnf-appendix ?>
4081<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4082<figure>
4083<artwork type="abnf" name="p2-semantics.parsed-abnf">
4084<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
4085
4086<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
4087
4088<x:ref>Date</x:ref> = HTTP-date
4089
4090<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
4091
4092<x:ref>From</x:ref> = mailbox
4093
4094<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4095
4096<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4097
4098<x:ref>Location</x:ref> = URI-reference
4099
4100<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4101
4102<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
4103
4104<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
4105<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4106<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4107
4108<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4109
4110<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4111<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4112
4113<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4114<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4115
4116<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
4117
4118<x:ref>date1</x:ref> = day SP month SP year
4119<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4120<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4121<x:ref>day</x:ref> = 2DIGIT
4122<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4123 / %x54.75.65 ; Tue
4124 / %x57.65.64 ; Wed
4125 / %x54.68.75 ; Thu
4126 / %x46.72.69 ; Fri
4127 / %x53.61.74 ; Sat
4128 / %x53.75.6E ; Sun
4129<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4130 / %x54.75.65.73.64.61.79 ; Tuesday
4131 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4132 / %x54.68.75.72.73.64.61.79 ; Thursday
4133 / %x46.72.69.64.61.79 ; Friday
4134 / %x53.61.74.75.72.64.61.79 ; Saturday
4135 / %x53.75.6E.64.61.79 ; Sunday
4136<x:ref>delta-seconds</x:ref> = 1*DIGIT
4137
4138<x:ref>expect-name</x:ref> = token
4139<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
4140<x:ref>expect-value</x:ref> = token / quoted-string
4141<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
4142 OWS expect-param ] )
4143
4144<x:ref>hour</x:ref> = 2DIGIT
4145
4146<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4147<x:ref>method</x:ref> = token
4148<x:ref>minute</x:ref> = 2DIGIT
4149<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4150 / %x46.65.62 ; Feb
4151 / %x4D.61.72 ; Mar
4152 / %x41.70.72 ; Apr
4153 / %x4D.61.79 ; May
4154 / %x4A.75.6E ; Jun
4155 / %x4A.75.6C ; Jul
4156 / %x41.75.67 ; Aug
4157 / %x53.65.70 ; Sep
4158 / %x4F.63.74 ; Oct
4159 / %x4E.6F.76 ; Nov
4160 / %x44.65.63 ; Dec
4161
4162<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4163<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
4164
4165<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4166<x:ref>product</x:ref> = token [ "/" product-version ]
4167<x:ref>product-version</x:ref> = token
4168
4169<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
4170
4171<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4172<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4173
4174<x:ref>second</x:ref> = 2DIGIT
4175
4176<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4177<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
4178
4179<x:ref>year</x:ref> = 4DIGIT
4180</artwork>
4181</figure>
4182<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4183; Allow defined but not used
4184; Date defined but not used
4185; Expect defined but not used
4186; From defined but not used
4187; Location defined but not used
4188; Max-Forwards defined but not used
4189; Referer defined but not used
4190; Retry-After defined but not used
4191; Server defined but not used
4192; User-Agent defined but not used
4193; obs-text defined but not used
4194</artwork></figure></section>
4195<?ENDINC p2-semantics.abnf-appendix ?>
4196
4197<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4198
4199<section title="Since RFC 2616">
4200<t>
4201  Extracted relevant partitions from <xref target="RFC2616"/>.
4202</t>
4203</section>
4204
4205<section title="Since draft-ietf-httpbis-p2-semantics-00">
4206<t>
4207  Closed issues:
4208  <list style="symbols"> 
4209    <t>
4210      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4211      "Via is a MUST"
4212      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4213    </t>
4214    <t>
4215      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4216      "Fragments allowed in Location"
4217      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4218    </t>
4219    <t>
4220      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4221      "Safe Methods vs Redirection"
4222      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4223    </t>
4224    <t>
4225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4226      "Revise description of the POST method"
4227      (<eref target="http://purl.org/NET/http-errata#post"/>)
4228    </t>
4229    <t>
4230      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4231      "Normative and Informative references"
4232    </t>
4233    <t>
4234      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4235      "RFC2606 Compliance"
4236    </t>
4237    <t>
4238      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4239      "Informative references"
4240    </t>
4241    <t>
4242      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4243      "Redundant cross-references"
4244    </t>
4245  </list>
4246</t>
4247<t>
4248  Other changes:
4249  <list style="symbols"> 
4250    <t>
4251      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4252    </t>
4253  </list>
4254</t>
4255</section>
4256
4257<section title="Since draft-ietf-httpbis-p2-semantics-01">
4258<t>
4259  Closed issues:
4260  <list style="symbols"> 
4261    <t>
4262      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4263      "PUT side effects"
4264    </t>
4265    <t>
4266      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4267      "Duplicate Host header requirements"
4268    </t>
4269  </list>
4270</t>
4271<t>
4272  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4273  <list style="symbols"> 
4274    <t>
4275      Move "Product Tokens" section (back) into Part 1, as "token" is used
4276      in the definition of the Upgrade header field.
4277    </t>
4278    <t>
4279      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4280    </t>
4281    <t>
4282      Copy definition of delta-seconds from Part6 instead of referencing it.
4283    </t>
4284  </list>
4285</t>
4286</section>
4287
4288<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4289<t>
4290  Closed issues:
4291  <list style="symbols"> 
4292    <t>
4293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4294      "Requiring Allow in 405 responses"
4295    </t>
4296    <t>
4297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4298      "Status Code Registry"
4299    </t>
4300    <t>
4301      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4302      "Redirection vs. Location"
4303    </t>
4304    <t>
4305      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4306      "Cacheability of 303 response"
4307    </t>
4308    <t>
4309      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4310      "305 Use Proxy"
4311    </t>
4312    <t>
4313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4314      "Classification for Allow header"
4315    </t>
4316    <t>
4317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4318      "PUT - 'store under' vs 'store at'"
4319    </t>
4320  </list>
4321</t>
4322<t>
4323  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4324  <list style="symbols"> 
4325    <t>
4326      Reference RFC 3984, and update header field registrations for headers defined
4327      in this document.
4328    </t>
4329  </list>
4330</t>
4331<t>
4332  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4333  <list style="symbols"> 
4334    <t>
4335      Replace string literals when the string really is case-sensitive (method).
4336    </t>
4337  </list>
4338</t>
4339</section>
4340
4341<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4342<t>
4343  Closed issues:
4344  <list style="symbols"> 
4345    <t>
4346      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4347      "OPTIONS request bodies"
4348    </t>
4349    <t>
4350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4351      "Description of CONNECT should refer to RFC2817"
4352    </t>
4353    <t>
4354      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4355      "Location Content-Location reference request/response mixup"
4356    </t>
4357  </list>
4358</t>
4359<t>
4360  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4361  <list style="symbols"> 
4362    <t>
4363      Added initial proposal for registration process, plus initial
4364      content (non-HTTP/1.1 methods to be added by a separate specification).
4365    </t>
4366  </list>
4367</t>
4368</section>
4369
4370<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4371<t>
4372  Closed issues:
4373  <list style="symbols"> 
4374    <t>
4375      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4376      "Content-*"
4377    </t>
4378    <t>
4379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4380      "RFC 2822 is updated by RFC 5322"
4381    </t>
4382  </list>
4383</t>
4384<t>
4385  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4386  <list style="symbols"> 
4387    <t>
4388      Use "/" instead of "|" for alternatives.
4389    </t>
4390    <t>
4391      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4392      whitespace ("OWS") and required whitespace ("RWS").
4393    </t>
4394    <t>
4395      Rewrite ABNFs to spell out whitespace rules, factor out
4396      header field value format definitions.
4397    </t>
4398  </list>
4399</t>
4400</section>
4401
4402<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4403<t>
4404  Closed issues:
4405  <list style="symbols"> 
4406    <t>
4407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4408      "reason-phrase BNF"
4409    </t>
4410  </list>
4411</t>
4412<t>
4413  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4414  <list style="symbols"> 
4415    <t>
4416      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4417    </t>
4418  </list>
4419</t>
4420</section>
4421
4422<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4423<t>
4424  Closed issues:
4425  <list style="symbols"> 
4426    <t>
4427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4428      "Clarify when Referer is sent"
4429    </t>
4430    <t>
4431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4432      "status codes vs methods"
4433    </t>
4434    <t>
4435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4436      "Do not require "updates" relation for specs that register status codes or method names"
4437    </t>
4438  </list>
4439</t>
4440</section>
4441
4442<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4443<t>
4444  Closed issues:
4445  <list style="symbols"> 
4446    <t>
4447      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4448      "Idempotency"
4449    </t>
4450    <t>
4451      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4452      "TRACE security considerations"
4453    </t>
4454    <t>
4455      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4456      "Clarify rules for determining what entities a response carries"
4457    </t>
4458    <t>
4459      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4460      "update note citing RFC 1945 and 2068"
4461    </t>
4462    <t>
4463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4464      "update note about redirect limit"
4465    </t>
4466    <t>
4467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4468      "Location header ABNF should use 'URI'"
4469    </t>
4470    <t>
4471      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4472      "fragments in Location vs status 303"
4473    </t>
4474    <t>
4475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4476      "move IANA registrations for optional status codes"
4477    </t>
4478  </list>
4479</t>
4480<t>
4481  Partly resolved issues:
4482  <list style="symbols"> 
4483    <t>
4484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4485      "Are OPTIONS and TRACE safe?"
4486    </t>
4487  </list>
4488</t>
4489</section>
4490
4491<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4492<t>
4493  Closed issues:
4494  <list style="symbols"> 
4495    <t>
4496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4497      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4498      status codes when fixing this previously)
4499    </t>
4500  </list>
4501</t>
4502</section>
4503
4504<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4505<t>
4506  Closed issues:
4507  <list style="symbols"> 
4508    <t>
4509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4510      "Fragment combination / precedence during redirects"
4511    </t>
4512  </list>
4513</t>
4514<t>
4515  Partly resolved issues:
4516  <list style="symbols"> 
4517    <t>
4518      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4519      "Location header payload handling"
4520    </t>
4521    <t>
4522      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4523      "Term for the requested resource's URI"
4524    </t>
4525  </list>
4526</t>
4527</section>
4528
4529<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4530<t>
4531  Closed issues:
4532  <list style="symbols"> 
4533    <t>
4534      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4535      "Clarify 'Requested Variant'"
4536    </t>
4537    <t>
4538      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4539      "Clarify entity / representation / variant terminology"
4540    </t>
4541    <t>
4542      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4543      "Methods and Caching"
4544    </t>
4545    <t>
4546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4547      "OPTIONS vs Max-Forwards"
4548    </t>
4549    <t>
4550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4551      "Status codes and caching"
4552    </t>
4553    <t>
4554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4555      "consider removing the 'changes from 2068' sections"
4556    </t>
4557  </list>
4558</t>
4559</section>
4560
4561<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4562<t>
4563  Closed issues:
4564  <list style="symbols"> 
4565    <t>
4566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4567      "Considerations for new status codes"
4568    </t>
4569    <t>
4570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4571      "Considerations for new methods"
4572    </t>
4573    <t>
4574      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4575      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4576    </t>
4577  </list>
4578</t>
4579</section>
4580
4581<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4582<t>
4583  Closed issues:
4584  <list style="symbols"> 
4585    <t>
4586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4587      "Fragment combination / precedence during redirects" (added warning
4588      about having a fragid on the redirect may cause inconvenience in
4589      some cases)
4590    </t>
4591    <t>
4592      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4593      "Content-* vs. PUT"
4594    </t>
4595    <t>
4596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4597      "205 Bodies"
4598    </t>
4599    <t>
4600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4601      "Understanding Content-* on non-PUT requests"
4602    </t>
4603    <t>
4604      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4605      "Content-*"
4606    </t>
4607    <t>
4608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4609      "Header type defaulting"
4610    </t>
4611    <t>
4612      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4613      "PUT - 'store under' vs 'store at'"
4614    </t>
4615    <t>
4616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4617      "duplicate ABNF for reason-phrase"
4618    </t>
4619    <t>
4620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4621      "Note special status of Content-* prefix in header registration procedures"
4622    </t>
4623    <t>
4624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4625      "Max-Forwards vs extension methods"
4626    </t>
4627    <t>
4628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4629      "What is the value space of HTTP status codes?" (actually fixed in
4630      draft-ietf-httpbis-p2-semantics-11)
4631    </t>
4632    <t>
4633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4634      "Header Classification"
4635    </t>
4636    <t>
4637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4638      "PUT side effect: invalidation or just stale?"
4639    </t>
4640    <t>
4641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4642      "proxies not supporting certain methods"
4643    </t>
4644    <t>
4645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4646      "Migrate CONNECT from RFC2817 to p2"
4647    </t>
4648    <t>
4649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4650      "Migrate Upgrade details from RFC2817"
4651    </t>
4652    <t>
4653      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4654      "clarify PUT semantics'"
4655    </t>
4656    <t>
4657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4658      "duplicate ABNF for 'Method'"
4659    </t>
4660    <t>
4661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4662      "untangle ABNFs for header fields"
4663    </t>
4664  </list>
4665</t>
4666</section>
4667
4668<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4669<t>
4670  Closed issues:
4671  <list style="symbols"> 
4672    <t>
4673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4674      "untangle ABNFs for header fields"
4675    </t>
4676    <t>
4677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4678      "message body in CONNECT request"
4679    </t>
4680  </list>
4681</t>
4682</section>
4683
4684<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4685<t>
4686  Closed issues:
4687  <list style="symbols"> 
4688    <t>
4689      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4690      "Clarify status code for rate limiting"
4691    </t>
4692    <t>
4693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4694      "clarify 403 forbidden"
4695    </t>
4696    <t>
4697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4698      "Clarify 203 Non-Authoritative Information"
4699    </t>
4700    <t>
4701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4702      "update default reason phrase for 413"
4703    </t>
4704  </list>
4705</t>
4706</section>
4707
4708<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4709<t>
4710  Closed issues:
4711  <list style="symbols"> 
4712    <t>
4713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4714      "Strength of requirements on Accept re: 406"
4715    </t>
4716    <t>
4717      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4718      "400 response isn't generic"
4719    </t>
4720  </list>
4721</t>
4722</section>
4723
4724<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4725<t>
4726  Closed issues:
4727  <list style="symbols"> 
4728    <t>
4729      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4730      "Redirects and non-GET methods"
4731    </t>
4732    <t>
4733      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4734      "Document HTTP's error-handling philosophy"
4735    </t>
4736    <t>
4737      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4738      "Considerations for new headers"
4739    </t>
4740    <t>
4741      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4742      "clarify 303 redirect on HEAD"
4743    </t>
4744  </list>
4745</t>
4746</section>
4747
4748<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4749<t>
4750  Closed issues:
4751  <list style="symbols"> 
4752    <t>
4753      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4754      "Location header payload handling"
4755    </t>
4756    <t>
4757      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4758      "Clarify status code for rate limiting" (change backed out because
4759      a new status code is being defined for this purpose)
4760    </t>
4761    <t>
4762      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4763      "should there be a permanent variant of 307"
4764    </t>
4765    <t>
4766      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4767      "When are Location's semantics triggered?"
4768    </t>
4769    <t>
4770      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4771      "'expect' grammar missing OWS"
4772    </t>
4773    <t>
4774      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4775      "header field considerations: quoted-string vs use of double quotes"
4776    </t>
4777  </list>
4778</t>
4779</section>
4780
4781<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4782<t>
4783  Closed issues:
4784  <list style="symbols"> 
4785    <t>
4786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4787      "Combining HEAD responses"
4788    </t>
4789    <t>
4790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4791      "Requirements for user intervention during redirects"
4792    </t>
4793    <t>
4794      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4795      "message-body in CONNECT response"
4796    </t>
4797    <t>
4798      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4799      "Applying original fragment to 'plain' redirected URI"
4800    </t>
4801    <t>
4802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4803      "Misplaced text on connection handling in p2"
4804    </t>
4805    <t>
4806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4807      "clarify that 201 doesn't require Location header fields"
4808    </t>
4809    <t>
4810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4811      "relax requirements on hypertext in 3/4/5xx error responses"
4812    </t>
4813    <t>
4814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4815      "example for 426 response should have a payload"
4816    </t>
4817    <t>
4818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4819      "drop indirection entries for status codes"
4820    </t>
4821  </list>
4822</t>
4823</section>
4824
4825<section title="Since draft-ietf-httpbis-p2-semantics-19" anchor="changes.since.19">
4826<t>
4827  Closed issues:
4828  <list style="symbols"> 
4829    <t>
4830      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4831      "should there be a permanent variant of 307"
4832    </t>
4833  </list>
4834</t>
4835</section>
4836
4837</section>
4838
4839</back>
4840</rfc>
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