source: draft-ietf-httpbis/latest/p2-semantics.xml @ 1639

Last change on this file since 1639 was 1639, checked in by julian.reschke@…, 8 years ago

Step 1 of p2/p3-merge (see #351)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 197.3 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</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.
201</t>
202</abstract>
203
204<note title="Editorial Note (To be removed by RFC Editor)">
205  <t>
206    Discussion of this draft should take place on the HTTPBIS working group
207    mailing list (ietf-http-wg@w3.org), which is archived at
208    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
209  </t>
210  <t>
211    The current issues list is at
212    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
213    documents (including fancy diffs) can be found at
214    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
215  </t>
216  <t>
217    The changes in this draft are summarized in <xref target="changes.since.19"/>.
218  </t>
219</note>
220</front>
221<middle>
222<section title="Introduction" anchor="introduction">
223<t>
224   This document defines HTTP/1.1 request and response semantics.  Each HTTP
225   message, as defined in &messaging;, is in the form of either a request or
226   a response.  An HTTP server listens on a connection for HTTP requests and
227   responds to each request, in the order received on that connection, with
228   one or more HTTP response messages.  This document defines the commonly
229   agreed upon semantics of the HTTP uniform interface, the intentions defined
230   by each request method, and the various response messages that might be
231   expected as a result of applying that method to the target resource.
232</t>
233<t>
234   This document is currently disorganized in order to minimize the changes
235   between drafts and enable reviewers to see the smaller errata changes.
236   A future draft will reorganize the sections to better reflect the content.
237   In particular, the sections will be ordered according to the typical
238   processing of an HTTP request message (after message parsing): resource
239   mapping, methods, request modifying header fields, response status,
240   status modifying header fields, and resource metadata.  The current mess
241   reflects how widely dispersed these topics and associated requirements
242   had become in <xref target="RFC2616"/>.
243</t>
244
245<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
246<t>
247   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
248   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
249   document are to be interpreted as described in <xref target="RFC2119"/>.
250</t>
251<t>
252   This document defines conformance criteria for several roles in HTTP
253   communication, including Senders, Recipients, Clients, Servers, User-Agents,
254   Origin Servers, Intermediaries, Proxies and Gateways. See &architecture;
255   for definitions of these terms.
256</t>
257<t>
258   An implementation is considered conformant if it complies with all of the
259   requirements associated with its role(s). Note that SHOULD-level requirements
260   are relevant here, unless one of the documented exceptions is applicable.
261</t>
262<t>
263   This document also uses ABNF to define valid protocol elements
264   (<xref target="notation"/>). In addition to the prose requirements placed
265   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
266</t>
267<t>
268   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
269   protocol element from an invalid construct. However, HTTP does not define
270   specific error handling mechanisms, except in cases where it has direct
271   impact on security. This is because different uses of the protocol require
272   different error handling strategies; for example, a Web browser may wish to
273   transparently recover from a response where the Location header field
274   doesn't parse according to the ABNF, whereby in a systems control protocol
275   using HTTP, this type of error recovery could lead to dangerous consequences.
276</t>
277</section>
278
279<section title="Syntax Notation" anchor="notation">
280  <x:anchor-alias value="CR"/>
281  <x:anchor-alias value="DIGIT"/>
282  <x:anchor-alias value="LF"/>
283  <x:anchor-alias value="HTAB"/>
284  <x:anchor-alias value="VCHAR"/>
285  <x:anchor-alias value="SP"/>
286<t>
287   This specification uses the Augmented Backus-Naur Form (ABNF) notation
288   of <xref target="RFC5234"/> with the list rule extension defined in
289   &notation;<xref target="collected.abnf"/> shows the collected ABNF
290   with the list rule expanded.
291</t>
292<t>
293  The following core rules are included by
294  reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
295  ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
296  DIGIT (decimal 0-9), DQUOTE (double quote),
297  HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
298  OCTET (any 8-bit sequence of data), SP (space), and
299  VCHAR (any visible US-ASCII character).
300</t>
301
302<section title="Core Rules" anchor="core.rules">
303  <x:anchor-alias value="obs-text"/>
304  <x:anchor-alias value="quoted-string"/>
305  <x:anchor-alias value="token"/>
306  <x:anchor-alias value="BWS"/>
307  <x:anchor-alias value="OWS"/>
308  <x:anchor-alias value="RWS"/>
309<t>
310  The core rules below are defined in <xref target="Part1"/>:
311</t>
312<figure><artwork type="abnf2616">
313  <x:ref>BWS</x:ref>           = &lt;BWS, defined in &whitespace;&gt;
314  <x:ref>OWS</x:ref>           = &lt;OWS, defined in &whitespace;&gt;
315  <x:ref>RWS</x:ref>           = &lt;RWS, defined in &whitespace;&gt;
316  <x:ref>obs-text</x:ref>      = &lt;obs-text, defined in &field-components;&gt;
317  <x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in &field-components;&gt;
318  <x:ref>token</x:ref>         = &lt;token, defined in &field-components;&gt;
319</artwork></figure>
320</section>
321
322<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
323  <x:anchor-alias value="absolute-URI"/>
324  <x:anchor-alias value="comment"/>
325  <x:anchor-alias value="partial-URI"/>
326  <x:anchor-alias value="URI-reference"/>
327<t>
328  The ABNF rules below are defined in other parts:
329</t>
330<figure><!--Part1--><artwork type="abnf2616">
331  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in &uri;&gt;
332  <x:ref>comment</x:ref>       = &lt;comment, defined in &field-components;&gt;
333  <x:ref>partial-URI</x:ref>   = &lt;partial-URI, defined in &uri;&gt;
334  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in &uri;&gt;
335</artwork></figure>
336</section>
337</section>
338</section>
339
340<section title="Methods" anchor="methods">
341  <x:anchor-alias value="method"/>
342<t>
343   The method token indicates the request method to be performed on the target
344   resource (&effective-request-uri;). The method is case-sensitive.
345</t>
346<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="method"/>
347  <x:ref>method</x:ref>         = <x:ref>token</x:ref>
348</artwork></figure>
349<t>
350   The list of methods allowed by a resource can be specified in an
351   Allow header field (<xref target="header.allow"/>). The status code of the response
352   always notifies the client whether a method is currently allowed on a
353   resource, since the set of allowed methods can change dynamically. An
354   origin server &SHOULD; respond with the status code 405 (Method Not Allowed)
355   if the method is known by the origin server but not allowed for the
356   resource, and 501 (Not Implemented) if the method is
357   unrecognized or not implemented by the origin server. The methods GET
358   and HEAD &MUST; be supported by all general-purpose servers. All other
359   methods are &OPTIONAL;; however, if the above methods are implemented,
360   they &MUST; be implemented with the same semantics as those specified
361   in <xref target="method.definitions"/>.
362</t>
363
364<section title="Safe and Idempotent Methods" anchor="safe.and.idempotent">
365
366<section title="Safe Methods" anchor="safe.methods">
367<iref item="Safe Methods" primary="true"/>
368<t>
369   Implementors need to be aware that the software represents the user in
370   their interactions over the Internet, and need to allow
371   the user to be aware of any actions they take which might have an
372   unexpected significance to themselves or others.
373</t>
374<t>
375   In particular, the convention has been established that the GET, HEAD,
376   OPTIONS, and TRACE request methods &SHOULD-NOT; have the significance
377   of taking an action other than retrieval. These request methods ought
378   to be considered "<x:dfn anchor="safe">safe</x:dfn>".
379   This allows user agents to represent other methods, such as POST, PUT
380   and DELETE, in a special way, so that the user is made aware of the
381   fact that a possibly unsafe action is being requested.
382</t>
383<t>
384   Naturally, it is not possible to ensure that the server does not
385   generate side-effects as a result of performing a GET request; in
386   fact, some dynamic resources consider that a feature. The important
387   distinction here is that the user did not request the side-effects,
388   so therefore cannot be held accountable for them.
389</t>
390</section>
391
392<section title="Idempotent Methods" anchor="idempotent.methods">
393<iref item="Idempotent Methods" primary="true"/>
394<t>
395   Request methods can also have the property of "idempotence" in that,
396   aside from error or expiration issues, the intended effect of multiple
397   identical requests is the same as for a single request.
398   PUT, DELETE, and all safe request methods are idempotent.
399   It is important to note that idempotence refers only to changes
400   requested by the client: a server is free to change its state due
401   to multiple requests for the purpose of tracking those requests,
402   versioning of results, etc.
403</t>
404</section>
405</section>
406
407<section title="Method Registry" anchor="method.registry">
408<t>
409  The HTTP Method Registry defines the name space for the method token in the
410  Request line of an HTTP request.
411</t>
412<t>
413  Registrations &MUST; include the following fields:
414  <list style="symbols">
415    <t>Method Name (see <xref target="methods"/>)</t>
416    <t>Safe ("yes" or "no", see <xref target="safe.methods"/>)</t>
417    <t>Pointer to specification text</t>
418  </list>
419</t>
420<t>
421  Values to be added to this name space require IETF Review
422  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
423</t>
424<t>
425  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-methods"/>.
426</t>
427
428<section title="Considerations for New Methods" anchor="considerations.for.new.methods">
429<t>
430   When it is necessary to express new semantics for a HTTP request that
431   aren't specific to a single application or media type, and currently defined
432   methods are inadequate, it may be appropriate to register a new method.
433</t>
434<t>
435   HTTP methods are generic; that is, they are potentially applicable to any
436   resource, not just one particular media type, "type" of resource, or
437   application. As such, it is preferred that new HTTP methods be registered
438   in a document that isn't specific to a single application, so that this is
439   clear.
440</t>
441<t>
442   Due to the parsing rules defined in &message-body;, definitions of HTTP
443   methods cannot prohibit the presence of a message body on either the request
444   or the response message (with responses to HEAD requests being the single
445   exception). Definitions of new methods cannot change this rule, but they can
446   specify that only zero-length bodies (as opposed to absent bodies) are allowed.
447</t>
448<t>
449   New method definitions need to indicate whether they are safe (<xref
450   target="safe.methods"/>), what semantics (if any) the request body has,
451   and whether they are idempotent (<xref target="idempotent.methods"/>).
452   They also need to state whether they can be cached (&caching;); in
453   particular what conditions a cache may store the response, and under what
454   conditions such a stored response may be used to satisfy a subsequent
455   request.
456</t>
457</section>
458</section>
459
460<section title="Method Definitions" anchor="method.definitions">
461
462<section title="OPTIONS" anchor="OPTIONS">
463  <rdf:Description>
464    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
465  </rdf:Description>
466  <iref primary="true" item="OPTIONS method" x:for-anchor=""/>
467  <iref primary="true" item="Methods" subitem="OPTIONS" x:for-anchor=""/>
468<t>
469   The OPTIONS method requests information about the
470   communication options available on the request/response chain
471   identified by the effective request URI. This method allows a client to
472   determine the options and/or requirements associated with a resource,
473   or the capabilities of a server, without implying a resource action
474   or initiating a resource retrieval.
475</t>
476<t>
477   Responses to the OPTIONS method are not cacheable.
478</t>
479<t>
480   If the OPTIONS request includes a message body (as indicated by the
481   presence of Content-Length or Transfer-Encoding), then the media type
482   &MUST; be indicated by a Content-Type field. Although this
483   specification does not define any use for such a body, future
484   extensions to HTTP might use the OPTIONS body to make more detailed
485   queries on the server.
486</t>
487<t>
488   If the request-target (&request-target;) is an asterisk ("*"),
489   the OPTIONS request is
490   intended to apply to the server in general rather than to a specific
491   resource. Since a server's communication options typically depend on
492   the resource, the "*" request is only useful as a "ping" or "no-op"
493   type of method; it does nothing beyond allowing the client to test
494   the capabilities of the server. For example, this can be used to test
495   a proxy for HTTP/1.1 conformance (or lack thereof).
496</t>
497<t>
498   If the request-target is not an asterisk, the OPTIONS request applies
499   only to the options that are available when communicating with that
500   resource.
501</t>
502<t>
503   A 200 response &SHOULD; include any header fields that indicate
504   optional features implemented by the server and applicable to that
505   resource (e.g., Allow), possibly including extensions not defined by
506   this specification. The response body, if any, &SHOULD; also include
507   information about the communication options. The format for such a
508   body is not defined by this specification, but might be defined by
509   future extensions to HTTP. Content negotiation &MAY; be used to select
510   the appropriate response format. If no response body is included, the
511   response &MUST; include a Content-Length field with a field-value of
512   "0".
513</t>
514<t>
515   The Max-Forwards header field &MAY; be used to target a
516   specific proxy in the request chain (see <xref target="header.max-forwards"/>).
517   If no Max-Forwards field is present in the request, then the forwarded
518   request &MUST-NOT; include a Max-Forwards field.
519</t>
520</section>
521
522<section title="GET" anchor="GET">
523  <rdf:Description>
524    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
525  </rdf:Description>
526  <iref primary="true" item="GET method" x:for-anchor=""/>
527  <iref primary="true" item="Methods" subitem="GET" x:for-anchor=""/>
528<t>
529   The GET method requests transfer of a current representation of
530   the target resource.
531</t>
532<t>   
533   If the target resource is a data-producing process, it is the
534   produced data which shall be returned as the representation in the response and not
535   the source text of the process, unless that text happens to be the output of
536   the process.
537</t>
538<t>
539   The semantics of the GET method change to a "conditional GET" if the
540   request message includes an If-Modified-Since, If-Unmodified-Since,
541   If-Match, If-None-Match, or If-Range header field. A conditional GET
542   requests that the representation be transferred only under the
543   circumstances described by the conditional header field(s). The
544   conditional GET request is intended to reduce unnecessary network
545   usage by allowing cached representations to be refreshed without requiring
546   multiple requests or transferring data already held by the client.
547</t>
548<t>
549   The semantics of the GET method change to a "partial GET" if the
550   request message includes a Range header field. A partial GET requests
551   that only part of the representation be transferred, as described in &header-range;.
552   The partial GET request is intended to reduce unnecessary
553   network usage by allowing partially-retrieved representations to be
554   completed without transferring data already held by the client.
555</t>
556<t>
557   Bodies on GET requests have no defined semantics. Note that sending a body
558   on a GET request might cause some existing implementations to reject the
559   request.
560</t>
561<t>
562   The response to a GET request is cacheable and &MAY; be used to satisfy
563   subsequent GET and HEAD requests (see &caching;).
564</t>
565<t>
566   See <xref target="encoding.sensitive.information.in.uris"/> for security considerations when used for forms.
567</t>
568</section>
569
570<section title="HEAD" anchor="HEAD">
571  <rdf:Description>
572    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
573  </rdf:Description>
574  <iref primary="true" item="HEAD method" x:for-anchor=""/>
575  <iref primary="true" item="Methods" subitem="HEAD" x:for-anchor=""/>
576<t>
577   The HEAD method is identical to GET except that the server &MUST-NOT;
578   return a message body in the response. The metadata contained
579   in the HTTP header fields in response to a HEAD request &SHOULD; be identical
580   to the information sent in response to a GET request. This method can
581   be used for obtaining metadata about the representation implied by the
582   request without transferring the representation body. This method is
583   often used for testing hypertext links for validity, accessibility,
584   and recent modification.
585</t>
586<t>
587   The response to a HEAD request is cacheable and &MAY; be used to satisfy
588   a subsequent HEAD request. It also has potential side effects on
589   previously stored responses to GET; see &p6-head;.
590</t>
591<t>
592   Bodies on HEAD requests have no defined semantics. Note that sending a body
593   on a HEAD request might cause some existing implementations to reject the
594   request.
595</t>
596</section>
597
598<section title="POST" anchor="POST">
599  <iref primary="true" item="POST method" x:for-anchor=""/>
600  <iref primary="true" item="Methods" subitem="POST" x:for-anchor=""/>
601<t>
602   The POST method requests that the origin server accept the
603   representation enclosed in the request as data to be processed by the
604   target resource. POST is designed to allow a uniform method to cover the
605   following functions:
606  <list style="symbols">
607    <t>
608      Annotation of existing resources;
609    </t>
610    <t>
611        Posting a message to a bulletin board, newsgroup, mailing list,
612        or similar group of articles;
613    </t>
614    <t>
615        Providing a block of data, such as the result of submitting a
616        form, to a data-handling process;
617    </t>
618    <t>
619        Extending a database through an append operation.
620    </t>
621  </list>
622</t>
623<t>
624   The actual function performed by the POST method is determined by the
625   server and is usually dependent on the effective request URI.
626</t>
627<t>
628   The action performed by the POST method might not result in a
629   resource that can be identified by a URI. In this case, either 200
630   (OK) or 204 (No Content) is the appropriate response status code,
631   depending on whether or not the response includes a representation that
632   describes the result.
633</t>
634<t>
635   If a resource has been created on the origin server, the response
636   &SHOULD; be 201 (Created) and contain a representation which describes the
637   status of the request and refers to the new resource, and a Location
638   header field (see <xref target="header.location"/>).
639</t>
640<t>
641   Responses to POST requests are only cacheable when they
642   include explicit freshness information (see &p6-explicit;). A
643   cached POST response with a Content-Location header field
644   (see &header-content-location;) whose value is the effective
645   Request URI &MAY; be used to satisfy subsequent GET and HEAD requests.
646</t>
647<t>
648   Note that POST caching is not widely implemented.
649   However, the 303 (See Other) response can be used to direct the
650   user agent to retrieve a cacheable representation of the resource.
651</t>
652</section>
653
654<section title="PUT" anchor="PUT">
655  <iref primary="true" item="PUT method" x:for-anchor=""/>
656  <iref primary="true" item="Methods" subitem="PUT" x:for-anchor=""/>
657<t>
658   The PUT method requests that the state of the target resource
659   be created or replaced with the state defined by the representation
660   enclosed in the request message payload.  A successful PUT of a given
661   representation would suggest that a subsequent GET on that same target
662   resource will result in an equivalent representation being returned in
663   a 200 (OK) response.  However, there is no guarantee that such a state
664   change will be observable, since the target resource might be acted
665   upon by other user agents in parallel, or might be subject to dynamic
666   processing by the origin server, before any subsequent GET is received.
667   A successful response only implies that the user agent's intent was
668   achieved at the time of its processing by the origin server.
669</t>
670<t>   
671   If the target resource does not have a current representation and
672   the PUT successfully creates one, then the origin server &MUST; inform
673   the user agent by sending a 201 (Created) response.  If the target
674   resource does have a current representation and that representation is
675   successfully modified in accordance with the state of the enclosed
676   representation, then either a 200 (OK) or 204 (No Content) response
677   &SHOULD; be sent to indicate successful completion of the request.
678</t>
679<t>
680   Unrecognized header fields &SHOULD; be ignored (i.e., not saved
681   as part of the resource state).
682</t>
683<t>
684   An origin server &SHOULD; verify that the PUT representation is
685   consistent with any constraints which the server has for the target
686   resource that cannot or will not be changed by the PUT.  This is
687   particularly important when the origin server uses internal
688   configuration information related to the URI in order to set the
689   values for representation metadata on GET responses.  When a PUT
690   representation is inconsistent with the target resource, the origin
691   server &SHOULD; either make them consistent, by transforming the
692   representation or changing the resource configuration, or respond
693   with an appropriate error message containing sufficient information
694   to explain why the representation is unsuitable.  The 409 (Conflict)
695   or 415 (Unsupported Media Type) status codes are suggested, with the
696   latter being specific to constraints on Content-Type values.
697</t>
698<t>
699   For example, if the target resource is configured to always have a
700   Content-Type of "text/html" and the representation being PUT has a
701   Content-Type of "image/jpeg", then the origin server &SHOULD; do one of:
702   (a) reconfigure the target resource to reflect the new media type;
703   (b) transform the PUT representation to a format consistent with that
704   of the resource before saving it as the new resource state; or,
705   (c) reject the request with a 415 response indicating that the target
706   resource is limited to "text/html", perhaps including a link to a
707   different resource that would be a suitable target for the new
708   representation.
709</t>
710<t>
711   HTTP does not define exactly how a PUT method affects the state
712   of an origin server beyond what can be expressed by the intent of
713   the user agent request and the semantics of the origin server response.
714   It does not define what a resource might be, in any sense of that
715   word, beyond the interface provided via HTTP.  It does not define
716   how resource state is "stored", nor how such storage might change
717   as a result of a change in resource state, nor how the origin server
718   translates resource state into representations.  Generally speaking,
719   all implementation details behind the resource interface are
720   intentionally hidden by the server.
721</t>
722<t>
723   The fundamental difference between the POST and PUT methods is
724   highlighted by the different intent for the target resource.
725   The target resource in a POST request is intended to handle the
726   enclosed representation as a data-accepting process, such as for
727   a gateway to some other protocol or a document that accepts annotations.
728   In contrast, the target resource in a PUT request is intended to
729   take the enclosed representation as a new or replacement value.
730   Hence, the intent of PUT is idempotent and visible to intermediaries,
731   even though the exact effect is only known by the origin server.
732</t>
733<t>
734   Proper interpretation of a PUT request presumes that the user agent
735   knows what target resource is desired.  A service that is intended
736   to select a proper URI on behalf of the client, after receiving
737   a state-changing request, &SHOULD; be implemented using the POST
738   method rather than PUT.  If the origin server will not make the
739   requested PUT state change to the target resource and instead
740   wishes to have it applied to a different resource, such as when the
741   resource has been moved to a different URI, then the origin server
742   &MUST; send a 301 (Moved Permanently) response; the user agent &MAY;
743   then make its own decision regarding whether or not to redirect the
744   request.
745</t>
746<t>
747   A PUT request applied to the target resource &MAY; have side-effects
748   on other resources.  For example, an article might have a URI for
749   identifying "the current version" (a resource) which is separate
750   from the URIs identifying each particular version (different
751   resources that at one point shared the same state as the current version
752   resource).  A successful PUT request on "the current version" URI might
753   therefore create a new version resource in addition to changing the
754   state of the target resource, and might also cause links to be added
755   between the related resources.
756</t>
757<t>
758   An origin server &SHOULD; reject any PUT request that contains a
759   Content-Range header field, since it might be misinterpreted as
760   partial content (or might be partial content that is being mistakenly
761   PUT as a full representation).  Partial content updates are
762   possible by targeting a separately identified resource with state
763   that overlaps a portion of the larger resource, or by using a
764   different method that has been specifically defined for partial
765   updates (for example, the PATCH method defined in
766   <xref target="RFC5789"/>).
767</t>
768<t>
769   Responses to the PUT method are not cacheable. If a PUT request passes
770   through a cache that has one or more stored responses for the effective
771   request URI, those stored responses will be invalidated (see
772   &p6-invalid;).
773</t>
774</section>
775
776<section title="DELETE" anchor="DELETE">
777  <iref primary="true" item="DELETE method" x:for-anchor=""/>
778  <iref primary="true" item="Methods" subitem="DELETE" x:for-anchor=""/>
779<t>
780   The DELETE method requests that the origin server delete the target
781   resource. This method &MAY; be overridden by
782   human intervention (or other means) on the origin server. The client cannot
783   be guaranteed that the operation has been carried out, even if the
784   status code returned from the origin server indicates that the action
785   has been completed successfully. However, the server &SHOULD-NOT; 
786   indicate success unless, at the time the response is given, it
787   intends to delete the resource or move it to an inaccessible
788   location.
789</t>
790<t>
791   A successful response &SHOULD; be 200 (OK) if the response includes an
792   representation describing the status, 202 (Accepted) if the action has not
793   yet been enacted, or 204 (No Content) if the action has been enacted
794   but the response does not include a representation.
795</t>
796<t>
797   Bodies on DELETE requests have no defined semantics. Note that sending a body
798   on a DELETE request might cause some existing implementations to reject the
799   request.
800</t>
801<t>
802   Responses to the DELETE method are not cacheable. If a DELETE request
803   passes through a cache that has one or more stored responses for the
804   effective request URI, those stored responses will be invalidated (see
805   &p6-invalid;).
806</t>
807</section>
808
809<section title="TRACE" anchor="TRACE">
810  <rdf:Description>
811    <safe xmlns="urn:ietf:id:draft-ietf-httpbis-p2-semantics#">yes</safe>
812  </rdf:Description>
813  <iref primary="true" item="TRACE method" x:for-anchor=""/>
814  <iref primary="true" item="Methods" subitem="TRACE" x:for-anchor=""/>
815<t>
816   The TRACE method requests a remote, application-layer loop-back
817   of the request message. The final recipient of the request
818   &SHOULD; reflect the message received back to the client as the
819   message body of a 200 (OK) response. The final recipient is either the
820   origin server or the first proxy to receive a Max-Forwards
821   value of zero (0) in the request (see <xref target="header.max-forwards"/>).
822   A TRACE request &MUST-NOT; include a message body.
823</t>
824<t>
825   TRACE allows the client to see what is being received at the other
826   end of the request chain and use that data for testing or diagnostic
827   information. The value of the Via header field (&header-via;) is of
828   particular interest, since it acts as a trace of the request chain.
829   Use of the Max-Forwards header field allows the client to limit the
830   length of the request chain, which is useful for testing a chain of
831   proxies forwarding messages in an infinite loop.
832</t>
833<t>
834   If the request is valid, the response &SHOULD; have a Content-Type of
835   "message/http" (see &media-type-message-http;) and contain a message body
836   that encloses a copy of the entire request message.
837   Responses to the TRACE method are not cacheable.
838</t>
839</section>
840
841<section title="CONNECT" anchor="CONNECT">
842  <iref primary="true" item="CONNECT method" x:for-anchor=""/>
843  <iref primary="true" item="Methods" subitem="CONNECT" x:for-anchor=""/>
844<t>
845   The CONNECT method requests that the proxy establish a tunnel
846   to the request-target and, if successful, thereafter restrict its behavior
847   to blind forwarding of packets until the connection is closed.
848</t>
849<t>
850   When using CONNECT, the request-target &MUST; use the authority form
851   (&request-target;); i.e., the request-target consists of only the
852   host name and port number of the tunnel destination, separated by a colon.
853   For example,
854</t>
855<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
856CONNECT server.example.com:80 HTTP/1.1
857Host: server.example.com:80
858
859</artwork></figure>
860<t>
861   Any successful (2xx) response to a CONNECT request indicates that the
862   proxy has established a connection to the requested host and port,
863   and has switched to tunneling the current connection to that server
864   connection.
865   The tunneled data from the server begins immediately after the blank line
866   that concludes the successful response's header block.
867   A server &SHOULD-NOT; send any Transfer-Encoding or Content-Length
868   header fields in a successful response.
869   A client &MUST; ignore any Content-Length or Transfer-Encoding header
870   fields received in a successful response.
871</t>
872<t>
873   Any response other than a successful response indicates that the tunnel
874   has not yet been formed and that the connection remains governed by HTTP.
875</t>
876<t>
877   Proxy authentication might be used to establish the
878   authority to create a tunnel:
879</t>
880<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
881CONNECT server.example.com:80 HTTP/1.1
882Host: server.example.com:80
883Proxy-Authorization: basic aGVsbG86d29ybGQ=
884
885</artwork></figure>
886<t>
887   A message body on a CONNECT request has no defined semantics. Sending a
888   body on a CONNECT request might cause existing implementations to reject
889   the request.
890</t>
891<t>
892   Similar to a pipelined HTTP/1.1 request, data to be tunneled from client
893   to server &MAY; be sent immediately after the request (before a response
894   is received). The usual caveats also apply:
895   data may be discarded if the eventual response is negative, and the
896   connection may be reset with no response if more than one TCP segment
897   is outstanding.
898</t>
899<t>
900   It may be the case that the proxy itself can only reach the requested
901   origin server through another proxy.  In this case, the first proxy
902   &SHOULD; make a CONNECT request of that next proxy, requesting a tunnel
903   to the authority.  A proxy &MUST-NOT; respond with any 2xx status code
904   unless it has either a direct or tunnel connection established to the
905   authority.
906</t>
907<t>
908   If at any point either one of the peers gets disconnected, any
909   outstanding data that came from that peer will be passed to the other
910   one, and after that also the other connection will be terminated by
911   the proxy. If there is outstanding data to that peer undelivered,
912   that data will be discarded.
913</t>
914<t>
915   An origin server which receives a CONNECT request for itself &MAY;
916   respond with a 2xx status code to indicate that a connection is
917   established.  However, most origin servers do not implement CONNECT.
918</t>
919</section>
920</section>
921
922</section>
923
924<section title="Header Fields" anchor="header.fields">
925<t>
926   Header fields are key value pairs that can be used to communicate data about
927   the message, its payload, the target resource, or about the connection
928   itself (i.e., control data).  See &header-fields; for a general definition
929   of their syntax.
930</t>
931
932<section title="Considerations for Creating Header Fields" anchor="considerations.for.creating.header.fields">
933<t>
934   New header fields are registered using the procedures described in
935   <xref target="RFC3864"/>.
936</t>
937<t>
938   The requirements for header field names are defined in
939   <xref target="RFC3864" x:fmt="of" x:sec="4.1"/>.  Authors of specifications
940   defining new fields are advised to keep the name as short as practical, and
941   not to prefix them with "X-" if they are to be registered (either
942   immediately or in the future).
943</t>
944<t>
945   New header field values typically have their syntax defined using ABNF
946   (<xref target="RFC5234"/>), using the extension defined in &abnf-extension;
947   as necessary, and are usually constrained to the range of ASCII characters.
948   Header fields needing a greater range of characters can use an encoding
949   such as the one defined in <xref target="RFC5987"/>.
950</t>
951<t>
952   Because commas (",") are used as a generic delimiter between field-values,
953   they need to be treated with care if they are allowed in the field-value's
954   payload. Typically, components that might contain a comma are protected with
955   double-quotes using the quoted-string ABNF production (&field-components;).
956</t>
957<t>
958   For example, a textual date and a URI (either of which might contain a comma)
959   could be safely carried in field-values like these:
960</t>
961<figure><artwork type="example">
962  Example-URI-Field: "http://example.com/a.html,foo",
963                     "http://without-a-comma.example.com/"
964  Example-Date-Field: "Sat, 04 May 1996", "Wed, 14 Sep 2005"
965</artwork></figure>
966<t>
967   Note that double quote delimiters almost always are used with the
968   quoted-string production; using a different syntax inside double quotes
969   will likely cause unnecessary confusion.
970</t>
971<t>
972   Many header fields use a format including (case-insensitively) named
973   parameters (for instance, Content-Type, defined in &header-content-type;).
974   Allowing both unquoted (token) and quoted (quoted-string) syntax for the
975   parameter value enables recipients to use existing parser components. When
976   allowing both forms, the meaning of a parameter value ought to be
977   independent of the syntax used for it (for an example, see the notes on
978   parameter handling for media types in &media-types;).
979</t>
980<t>
981   Authors of specifications defining new header fields are advised to consider
982   documenting:
983  <list style="symbols">
984    <x:lt>
985      <t>Whether the field is a single value, or whether it can be a list
986      (delimited by commas; see &header-fields;).</t>
987      <t>If it does not use the list syntax, document how to treat messages
988      where the header field occurs multiple times (a sensible default would
989      be to ignore the header field, but this might not always be the right
990      choice).</t>
991      <t>Note that intermediaries and software libraries might combine
992      multiple header field instances into a single one, despite the header
993      field not allowing this. A robust format enables recipients to discover
994      these situations (good example: "Content-Type", as the comma can only
995      appear inside quoted strings; bad example: "Location", as a comma can
996      occur inside a URI).</t>
997    </x:lt>
998    <x:lt><t>Under what conditions the header field can be used; e.g., only in
999    responses or requests, in all messages, only on responses to a particular
1000    request method.</t></x:lt>
1001    <x:lt><t>Whether it is appropriate to list the field-name in the Connection header
1002    (i.e., if the header is to be hop-by-hop, see &header-connection;).</t></x:lt>
1003    <x:lt><t>Under what conditions intermediaries are allowed to modify the header
1004    field's value, insert or delete it.</t></x:lt>
1005    <x:lt><t>How the header might interact with caching (see <xref target="Part6"/>).</t></x:lt>
1006    <x:lt><t>Whether the header field is useful or allowable in trailers (see
1007    &chunked-encoding;).</t></x:lt>
1008    <x:lt><t>Whether the header field should be preserved across redirects.</t></x:lt>
1009  </list>
1010</t>
1011</section>
1012
1013<section title="Request Header Fields" anchor="request.header.fields">
1014  <x:anchor-alias value="request-header"/>
1015<t>
1016   The request header fields allow the client to pass additional
1017   information about the request, and about the client itself, to the
1018   server. These fields act as request modifiers, with semantics
1019   equivalent to the parameters on a programming language method
1020   invocation.
1021</t>
1022<texttable align="left">
1023  <ttcol>Header Field Name</ttcol>
1024  <ttcol>Defined in...</ttcol>
1025
1026  <c>Accept</c> <c>&header-accept;</c>
1027  <c>Accept-Charset</c> <c>&header-accept-charset;</c>
1028  <c>Accept-Encoding</c> <c>&header-accept-encoding;</c>
1029  <c>Accept-Language</c> <c>&header-accept-language;</c>
1030  <c>Authorization</c> <c>&header-authorization;</c>
1031  <c>Expect</c> <c><xref target="header.expect"/></c>
1032  <c>From</c> <c><xref target="header.from"/></c>
1033  <c>Host</c> <c>&header-host;</c>
1034  <c>If-Match</c> <c>&header-if-match;</c>
1035  <c>If-Modified-Since</c> <c>&header-if-modified-since;</c>
1036  <c>If-None-Match</c> <c>&header-if-none-match;</c>
1037  <c>If-Range</c> <c>&header-if-range;</c>
1038  <c>If-Unmodified-Since</c> <c>&header-if-unmodified-since;</c>
1039  <c>Max-Forwards</c> <c><xref target="header.max-forwards"/></c>
1040  <c>Proxy-Authorization</c> <c>&header-proxy-authorization;</c>
1041  <c>Range</c> <c>&header-range;</c>
1042  <c>Referer</c> <c><xref target="header.referer"/></c>
1043  <c>TE</c> <c>&header-te;</c>
1044  <c>User-Agent</c> <c><xref target="header.user-agent"/></c>
1045</texttable>
1046</section>
1047
1048<section title="Response Header Fields" anchor="response.header.fields">
1049  <x:anchor-alias value="response-header"/>
1050<t>
1051   The response header fields allow the server to pass additional
1052   information about the response which cannot be placed in the status-line.
1053   These header fields give information about the server and about
1054   further access to the target resource (&effective-request-uri;).
1055</t>
1056<texttable align="left">
1057  <ttcol>Header Field Name</ttcol><ttcol>Defined in...</ttcol>
1058
1059  <c>Accept-Ranges</c> <c>&header-accept-ranges;</c>
1060  <c>Age</c> <c>&header-age;</c>
1061  <c>Allow</c> <c><xref target="header.allow"/></c>
1062  <c>Date</c> <c><xref target="header.date"/></c>
1063  <c>ETag</c> <c>&header-etag;</c>
1064  <c>Location</c> <c><xref target="header.location"/></c>
1065  <c>Proxy-Authenticate</c> <c>&header-proxy-authenticate;</c>
1066  <c>Retry-After</c> <c><xref target="header.retry-after"/></c>
1067  <c>Server</c> <c><xref target="header.server"/></c>
1068  <c>Vary</c> <c>&header-vary;</c>
1069  <c>WWW-Authenticate</c> <c>&header-www-authenticate;</c>
1070</texttable>
1071</section>
1072
1073</section>
1074
1075<section title="Status Codes" anchor="status.codes">
1076<t>
1077   The status-code element is a 3-digit integer result code of the attempt to
1078   understand and satisfy the request.
1079</t>
1080<t>
1081   HTTP status codes are extensible. HTTP applications are not required
1082   to understand the meaning of all registered status codes, though such
1083   understanding is obviously desirable. However, applications &MUST;
1084   understand the class of any status code, as indicated by the first
1085   digit, and treat any unrecognized response as being equivalent to the
1086   x00 status code of that class, with the exception that an
1087   unrecognized response &MUST-NOT; be cached. For example, if an
1088   unrecognized status code of 431 is received by the client, it can
1089   safely assume that there was something wrong with its request and
1090   treat the response as if it had received a 400 status code. In such
1091   cases, user agents &SHOULD; present to the user the representation enclosed
1092   with the response, since that representation is likely to include human-readable
1093   information which will explain the unusual status.
1094</t>
1095<t>
1096   The first digit of the status-code defines the class of response. The
1097   last two digits do not have any categorization role. There are 5
1098   values for the first digit:
1099  <list style="symbols">
1100    <t>
1101      1xx: Informational - Request received, continuing process
1102    </t>
1103    <t>
1104      2xx: Success - The action was successfully received,
1105        understood, and accepted
1106    </t>
1107    <t>
1108      3xx: Redirection - Further action needs to be taken in order to
1109        complete the request
1110    </t>
1111    <t>
1112      4xx: Client Error - The request contains bad syntax or cannot
1113        be fulfilled
1114    </t>
1115    <t>
1116      5xx: Server Error - The server failed to fulfill an apparently
1117        valid request
1118    </t>
1119  </list>
1120</t>
1121<t>
1122   For most status codes the response can carry a payload, in which case a
1123   Content-Type header field indicates the payload's media type
1124   (&header-content-type;).
1125</t>
1126
1127<section title="Overview of Status Codes" anchor="overview.of.status.codes">
1128<t> 
1129   The status codes listed below are defined in this specification,
1130   &p4-status-codes;, &p5-status-codes;, and &p7-status-codes;.
1131   The reason phrases listed here are only recommendations &mdash; they can be
1132   replaced by local equivalents without affecting the protocol.
1133</t>
1134<texttable align="left">
1135  <ttcol>status-code</ttcol>
1136  <ttcol>reason-phrase</ttcol>
1137  <ttcol>Defined in...</ttcol>
1138 
1139  <c>100</c> <c>Continue</c> <c><xref target="status.100"/></c>
1140  <c>101</c> <c>Switching Protocols</c> <c><xref target="status.101"/></c>
1141
1142  <c>200</c> <c>OK</c> <c><xref target="status.200"/></c>
1143  <c>201</c> <c>Created</c> <c><xref target="status.201"/></c>
1144  <c>202</c> <c>Accepted</c> <c><xref target="status.202"/></c>
1145  <c>203</c> <c>Non-Authoritative Information</c> <c><xref target="status.203"/></c>
1146  <c>204</c> <c>No Content</c> <c><xref target="status.204"/></c>
1147  <c>205</c> <c>Reset Content</c> <c><xref target="status.205"/></c>
1148  <c>206</c> <c>Partial Content</c> <c anchor="status.206">&status-206;</c>
1149
1150  <c>300</c> <c>Multiple Choices</c> <c><xref target="status.300"/></c>
1151  <c>301</c> <c>Moved Permanently</c> <c><xref target="status.301"/></c>
1152  <c>302</c> <c>Found</c> <c><xref target="status.302"/></c>
1153  <c>303</c> <c>See Other</c> <c><xref target="status.303"/></c>
1154  <c>304</c> <c>Not Modified</c> <c anchor="status.304">&status-304;</c>
1155  <c>305</c> <c>Use Proxy</c> <c><xref target="status.305"/></c>
1156  <c>307</c> <c>Temporary Redirect</c> <c><xref target="status.307"/></c>
1157
1158  <c>400</c> <c>Bad Request</c> <c><xref target="status.400"/></c>
1159  <c>401</c> <c>Unauthorized</c> <c anchor="status.401">&status-401;</c>
1160  <c>402</c> <c>Payment Required</c> <c><xref target="status.402"/></c>
1161  <c>403</c> <c>Forbidden</c> <c><xref target="status.403"/></c>
1162  <c>404</c> <c>Not Found</c> <c><xref target="status.404"/></c>
1163  <c>405</c> <c>Method Not Allowed</c> <c><xref target="status.405"/></c>
1164  <c>406</c> <c>Not Acceptable</c> <c><xref target="status.406"/></c>
1165  <c>407</c> <c>Proxy Authentication Required</c> <c anchor="status.407">&status-407;</c>
1166  <c>408</c> <c>Request Time-out</c> <c><xref target="status.408"/></c>
1167  <c>409</c> <c>Conflict</c> <c><xref target="status.409"/></c>
1168  <c>410</c> <c>Gone</c> <c><xref target="status.410"/></c>
1169  <c>411</c> <c>Length Required</c> <c><xref target="status.411"/></c>
1170  <c>412</c> <c>Precondition Failed</c> <c anchor="status.412">&status-412;</c>
1171  <c>413</c> <c>Request Representation Too Large</c> <c><xref target="status.413"/></c>
1172  <c>414</c> <c>URI Too Long</c> <c><xref target="status.414"/></c>
1173  <c>415</c> <c>Unsupported Media Type</c> <c><xref target="status.415"/></c>
1174  <c>416</c> <c>Requested range not satisfiable</c> <c anchor="status.416">&status-416;</c>
1175  <c>417</c> <c>Expectation Failed</c> <c><xref target="status.417"/></c>
1176  <c>426</c> <c>Upgrade Required</c> <c><xref target="status.426"/></c>
1177
1178  <c>500</c> <c>Internal Server Error</c> <c><xref target="status.500"/></c>
1179  <c>501</c> <c>Not Implemented</c> <c><xref target="status.501"/></c>
1180  <c>502</c> <c>Bad Gateway</c> <c><xref target="status.502"/></c>
1181  <c>503</c> <c>Service Unavailable</c> <c><xref target="status.503"/></c>
1182  <c>504</c> <c>Gateway Time-out</c> <c><xref target="status.504"/></c>
1183  <c>505</c> <c>HTTP Version not supported</c> <c><xref target="status.505"/></c>
1184</texttable>
1185<t>
1186   Note that this list is not exhaustive &mdash; it does not include
1187   extension status codes defined in other specifications.
1188</t>
1189</section>
1190
1191<section title="Status Code Registry" anchor="status.code.registry">
1192<t>
1193  The HTTP Status Code Registry defines the name space for the status-code
1194  token in the status-line of an HTTP response.
1195</t>
1196<t>
1197  Values to be added to this name space require IETF Review
1198  (see <xref target="RFC5226" x:fmt="," x:sec="4.1"/>).
1199</t>
1200<t>
1201  The registry itself is maintained at <eref target="http://www.iana.org/assignments/http-status-codes"/>.
1202</t>
1203
1204<section title="Considerations for New Status Codes" anchor="considerations.for.new.status.codes">
1205<t>
1206   When it is necessary to express new semantics for a HTTP response that
1207   aren't specific to a single application or media type, and currently defined
1208   status codes are inadequate, a new status code can be registered.
1209</t>
1210<t>
1211   HTTP status codes are generic; that is, they are potentially applicable to
1212   any resource, not just one particular media type, "type" of resource, or
1213   application. As such, it is preferred that new HTTP status codes be
1214   registered in a document that isn't specific to a single application, so
1215   that this is clear.
1216</t>
1217<t>
1218   Definitions of new HTTP status codes typically explain the request
1219   conditions that produce a response containing the status code (e.g.,
1220   combinations of request headers and/or method(s)), along with any
1221   interactions with response headers (e.g., those that are required, those
1222   that modify the semantics of the response).
1223</t>
1224<t>
1225   New HTTP status codes are required to fall under one of the categories
1226   defined in <xref target="status.codes"/>. To allow existing parsers to
1227   properly handle them, new status codes cannot disallow a response body,
1228   although they can mandate a zero-length response body. They can require the
1229   presence of one or more particular HTTP response header(s).
1230</t>
1231<t>
1232   Likewise, their definitions can specify that caches are allowed to use
1233   heuristics to determine their freshness (see &caching;; by default, it is
1234   not allowed), and can define how to determine the resource which they
1235   carry a representation for (see <xref
1236   target="identifying.response.associated.with.representation"/>; by default,
1237   it is anonymous).
1238</t>
1239</section>
1240
1241</section>
1242
1243<section title="Informational 1xx" anchor="status.1xx">
1244<t>
1245   This class of status code indicates a provisional response,
1246   consisting only of the status-line and optional header fields, and is
1247   terminated by an empty line. There are no required header fields for this
1248   class of status code. Since HTTP/1.0 did not define any 1xx status
1249   codes, servers &MUST-NOT; send a 1xx response to an HTTP/1.0 client
1250   except under experimental conditions.
1251</t>
1252<t>
1253   A client &MUST; be prepared to accept one or more 1xx status responses
1254   prior to a regular response, even if the client does not expect a 100
1255   (Continue) status message. Unexpected 1xx status responses &MAY; be
1256   ignored by a user agent.
1257</t>
1258<t>
1259   Proxies &MUST; forward 1xx responses, unless the connection between the
1260   proxy and its client has been closed, or unless the proxy itself
1261   requested the generation of the 1xx response. (For example, if a
1262   proxy adds a "Expect: 100-continue" field when it forwards a request,
1263   then it need not forward the corresponding 100 (Continue)
1264   response(s).)
1265</t>
1266
1267<section title="100 Continue" anchor="status.100">
1268  <iref primary="true" item="100 Continue (status code)" x:for-anchor=""/>
1269  <iref primary="true" item="Status Codes" subitem="100 Continue" x:for-anchor=""/>
1270<t>
1271   The client &SHOULD; continue with its request. This interim response is
1272   used to inform the client that the initial part of the request has
1273   been received and has not yet been rejected by the server. The client
1274   &SHOULD; continue by sending the remainder of the request or, if the
1275   request has already been completed, ignore this response. The server
1276   &MUST; send a final response after the request has been completed. See
1277   &use100; for detailed discussion of the use and handling of this
1278   status code.
1279</t>
1280</section>
1281
1282<section title="101 Switching Protocols" anchor="status.101">
1283  <iref primary="true" item="101 Switching Protocols (status code)" x:for-anchor=""/>
1284  <iref primary="true" item="Status Codes" subitem="101 Switching Protocols" x:for-anchor=""/>
1285<t>
1286   The server understands and is willing to comply with the client's
1287   request, via the Upgrade message header field (&header-upgrade;), for a
1288   change in the application protocol being used on this connection. The
1289   server will switch protocols to those defined by the response's
1290   Upgrade header field immediately after the empty line which
1291   terminates the 101 response.
1292</t>
1293<t>
1294   The protocol &SHOULD; be switched only when it is advantageous to do
1295   so. For example, switching to a newer version of HTTP is advantageous
1296   over older versions, and switching to a real-time, synchronous
1297   protocol might be advantageous when delivering resources that use
1298   such features.
1299</t>
1300</section>
1301</section>
1302
1303<section title="Successful 2xx" anchor="status.2xx">
1304<t>
1305   This class of status code indicates that the client's request was
1306   successfully received, understood, and accepted.
1307</t>
1308
1309<section title="200 OK" anchor="status.200">
1310  <iref primary="true" item="200 OK (status code)" x:for-anchor=""/>
1311  <iref primary="true" item="Status Codes" subitem="200 OK" x:for-anchor=""/>
1312<t>
1313   The request has succeeded. The payload returned with the response
1314   is dependent on the method used in the request, for example:
1315  <list style="hanging">
1316    <t hangText="GET">
1317      a representation of the target resource is sent in the response;
1318    </t>
1319    <t hangText="HEAD">
1320      the same representation as GET, except without the message body;
1321    </t>
1322    <t hangText="POST">
1323      a representation describing or containing the result of the action;
1324    </t>
1325    <t hangText="TRACE">
1326      a representation containing the request message as received by the
1327      end server.
1328    </t>
1329  </list>
1330</t>
1331<t>
1332   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1333   freshness for 200 responses.
1334</t>
1335</section>
1336
1337<section title="201 Created" anchor="status.201">
1338  <iref primary="true" item="201 Created (status code)" x:for-anchor=""/>
1339  <iref primary="true" item="Status Codes" subitem="201 Created" x:for-anchor=""/>
1340<t>
1341   The request has been fulfilled and has resulted in a new resource being
1342   created.
1343</t>
1344<t>
1345   The newly created resource is typically linked to from the response payload,
1346   with the most relevant URI also being carried in the Location header field.
1347   If the newly created resource's URI is the same as the Effective Request URI,
1348   this information can be omitted (e.g., in the case of a response to a PUT
1349   request). 
1350</t>
1351<t>
1352   The origin server &MUST; create the resource before returning the 201 status
1353   code. If the action cannot be carried out immediately, the server &SHOULD;
1354   respond with 202 (Accepted) response instead.
1355</t>
1356<t>
1357   A 201 response &MAY; contain an ETag response header field indicating
1358   the current value of the entity-tag for the representation of the resource
1359   just created (see &header-etag;).
1360</t>
1361</section>
1362
1363<section title="202 Accepted" anchor="status.202">
1364  <iref primary="true" item="202 Accepted (status code)" x:for-anchor=""/>
1365  <iref primary="true" item="Status Codes" subitem="202 Accepted" x:for-anchor=""/>
1366<t>
1367   The request has been accepted for processing, but the processing has
1368   not been completed.  The request might or might not eventually be
1369   acted upon, as it might be disallowed when processing actually takes
1370   place. There is no facility for re-sending a status code from an
1371   asynchronous operation such as this.
1372</t>
1373<t>
1374   The 202 response is intentionally non-committal. Its purpose is to
1375   allow a server to accept a request for some other process (perhaps a
1376   batch-oriented process that is only run once per day) without
1377   requiring that the user agent's connection to the server persist
1378   until the process is completed. The representation returned with this
1379   response &SHOULD; include an indication of the request's current status
1380   and either a pointer to a status monitor or some estimate of when the
1381   user can expect the request to be fulfilled.
1382</t>
1383</section>
1384
1385<section title="203 Non-Authoritative Information" anchor="status.203">
1386  <iref primary="true" item="203 Non-Authoritative Information (status code)" x:for-anchor=""/>
1387  <iref primary="true" item="Status Codes" subitem="203 Non-Authoritative Information" x:for-anchor=""/>
1388<t>
1389   The representation in the response has been transformed or otherwise
1390   modified by a transforming proxy (&intermediaries;).  Note that the
1391   behavior of transforming intermediaries is controlled by the no-transform
1392   Cache-Control directive (&header-cache-control;).
1393</t>
1394<t>
1395   This status code is only appropriate when the response status code would
1396   have been 200 (OK) otherwise. When the status code before transformation
1397   would have been different, the 214 Transformation Applied warn-code
1398   (&header-warning;) is appropriate.
1399</t>
1400<t>
1401   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1402   freshness for 203 responses.
1403</t>
1404</section>
1405
1406<section title="204 No Content" anchor="status.204">
1407  <iref primary="true" item="204 No Content (status code)" x:for-anchor=""/>
1408  <iref primary="true" item="Status Codes" subitem="204 No Content" x:for-anchor=""/>
1409<t>
1410   The 204 (No Content) status code indicates that the server has
1411   successfully fulfilled the request and that there is no additional
1412   content to return in the response payload body.  Metadata in the
1413   response header fields refer to the target resource and its current
1414   representation after the requested action.
1415</t>
1416<t>
1417   For example, if a 204 status code is received in response to a PUT
1418   request and the response contains an ETag header field, then the PUT
1419   was successful and the ETag field-value contains the entity-tag for
1420   the new representation of that target resource.
1421</t>
1422<t>
1423   The 204 response allows a server to indicate that the action has been
1424   successfully applied to the target resource while implying that the
1425   user agent &SHOULD-NOT; traverse away from its current "document view"
1426   (if any).  The server assumes that the user agent will provide some
1427   indication of the success to its user, in accord with its own interface,
1428   and apply any new or updated metadata in the response to the active
1429   representation.
1430</t>
1431<t>
1432   For example, a 204 status code is commonly used with document editing
1433   interfaces corresponding to a "save" action, such that the document
1434   being saved remains available to the user for editing. It is also
1435   frequently used with interfaces that expect automated data transfers
1436   to be prevalent, such as within distributed version control systems.
1437</t>
1438<t>
1439   The 204 response &MUST-NOT; include a message body, and thus is always
1440   terminated by the first empty line after the header fields.
1441</t>
1442</section>
1443
1444<section title="205 Reset Content" anchor="status.205">
1445  <iref primary="true" item="205 Reset Content (status code)" x:for-anchor=""/>
1446  <iref primary="true" item="Status Codes" subitem="205 Reset Content" x:for-anchor=""/>
1447<t>
1448   The server has fulfilled the request and the user agent &SHOULD; reset
1449   the document view which caused the request to be sent. This response
1450   is primarily intended to allow input for actions to take place via
1451   user input, followed by a clearing of the form in which the input is
1452   given so that the user can easily initiate another input action.
1453</t>
1454<t>   
1455   The message body included with the response &MUST; be empty. Note that
1456   receivers still need to parse the response according to the algorithm defined
1457   in &message-body;.
1458</t>
1459</section>
1460</section>
1461
1462<section title="Redirection 3xx" anchor="status.3xx">
1463<t>
1464   This class of status code indicates that further action needs to be
1465   taken by the user agent in order to fulfill the request.  If the required
1466   action involves a subsequent HTTP request, it &MAY; be carried out by the
1467   user agent without interaction with the user if and only if the method used
1468   in the second request is known to be "safe", as defined in
1469   <xref target="safe.methods"/>.
1470</t>
1471<t>
1472   There are several types of redirects:
1473   <list style="numbers">
1474      <x:lt>
1475        <t>
1476          Redirects of the request to another URI, either temporarily or
1477          permanently. The new URI is specified in the Location header field.
1478          In this specification, the status codes 301 (Moved Permanently),
1479          302 (Found), and 307 (Temporary Redirect) fall under this category.
1480        </t>
1481      </x:lt>
1482      <x:lt>
1483        <t>
1484          Redirection to a new location that represents an indirect response to
1485          the request, such as the result of a POST operation to be retrieved
1486          with a subsequent GET request. This is status code 303 (See Other).
1487        </t>
1488      </x:lt>
1489      <x:lt>
1490        <t>
1491          Redirection offering a choice of matching resources for use by
1492          agent-driven content negotiation (&agent-driven-negotiation;). This
1493          is status code 300 (Multiple Choices).
1494        </t>
1495      </x:lt>
1496      <x:lt>
1497        <t>
1498          Other kinds of redirection, such as to a cached result (status code 304
1499          (Not Modified), see &status-304;).
1500        </t>
1501      </x:lt>
1502   </list>
1503</t>
1504<x:note>
1505  <t>
1506    <x:h>Note:</x:h> In HTTP/1.0, only the status codes 301 (Moved Permanently)
1507    and 302 (Found) were defined for the first type of redirect, and the second
1508    type did not exist at all (<xref target="RFC1945" x:fmt="," x:sec="9.3"/>).
1509    However it turned out that web forms using POST expected redirects to change
1510    the operation for the subsequent request to retrieval (GET). To address this
1511    use case, HTTP/1.1 introduced the second type of redirect with the status
1512    code 303 (See Other) (<xref target="RFC2068" x:fmt="," x:sec="10.3.4"/>).
1513    As user agents did not change their behavior to maintain backwards
1514    compatibility, the first revision of HTTP/1.1 added yet another status code,
1515    307 (Temporary Redirect), for which the backwards compatibility problems did
1516    not apply (<xref target="RFC2616" x:fmt="," x:sec="10.3.8"/>).
1517    Over 10 years later, most user agents still do method rewriting for
1518    status codes 301 and 302, therefore this specification makes that behavior
1519    conformant in case the original request was POST.
1520  </t>
1521</x:note>
1522<t>
1523   A Location header field on a 3xx response indicates that a client &MAY;
1524   automatically redirect to the URI provided; see <xref target="header.location"/>.
1525</t>
1526<t>
1527   Note that for methods not known to be "safe", as defined in <xref target="safe.methods"/>,
1528   automatic redirection needs to done with care, since the redirect might
1529   change the conditions under which the request was issued.
1530</t>
1531<t>
1532   Clients &SHOULD; detect and intervene in cyclical redirections (i.e.,
1533   "infinite" redirection loops).
1534</t>
1535<x:note>
1536  <t>
1537    <x:h>Note:</x:h> An earlier version of this specification recommended a
1538    maximum of five redirections (<xref target="RFC2068" x:fmt="," x:sec="10.3"/>).
1539    Content developers need to be aware that some clients might
1540    implement such a fixed limitation.
1541  </t>
1542</x:note>
1543
1544<section title="300 Multiple Choices" anchor="status.300">
1545  <iref primary="true" item="300 Multiple Choices (status code)" x:for-anchor=""/>
1546  <iref primary="true" item="Status Codes" subitem="300 Multiple Choices" x:for-anchor=""/>
1547<t>
1548   The target resource has more than one
1549   representation, each with its own specific location, and agent-driven
1550   negotiation information (&content-negotiation;) is being provided so that
1551   the user (or user agent) can select a preferred representation by
1552   redirecting its request to that location.
1553</t>
1554<t>
1555   Unless it was a HEAD request, the response &SHOULD; include a representation
1556   containing a list of representation metadata and location(s) from
1557   which the user or user agent can choose the one most appropriate. Depending
1558   upon the format and the capabilities of
1559   the user agent, selection of the most appropriate choice &MAY; be
1560   performed automatically. However, this specification does not define
1561   any standard for such automatic selection.
1562</t>
1563<t>
1564   If the server has a preferred choice of representation, it &SHOULD;
1565   include the specific URI for that representation in the Location
1566   field; user agents &MAY; use the Location field value for automatic
1567   redirection.
1568</t>
1569<t>
1570   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1571   freshness for 300 responses.
1572</t>
1573
1574</section>
1575
1576<section title="301 Moved Permanently" anchor="status.301">
1577  <iref primary="true" item="301 Moved Permanently (status code)" x:for-anchor=""/>
1578  <iref primary="true" item="Status Codes" subitem="301 Moved Permanently" x:for-anchor=""/>
1579<t>
1580   The target resource has been assigned a new permanent URI and any
1581   future references to this resource &SHOULD; use one of the returned
1582   URIs.  Clients with link editing capabilities ought to automatically
1583   re-link references to the effective request URI to one or more of the new
1584   references returned by the server, where possible.
1585</t>
1586<t>
1587   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine
1588   freshness for 301 responses.
1589</t>
1590<t>
1591   The new permanent URI &SHOULD; be given by the Location field in the
1592   response. A response payload can contain a short hypertext note with a
1593   hyperlink to the new URI(s).
1594</t>
1595<x:note>
1596  <t>
1597    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1598    request method from POST to GET for the subsequent request. If this
1599    behavior is undesired, status code 307 (Temporary Redirect) can be used
1600    instead.
1601  </t>
1602</x:note>
1603</section>
1604
1605<section title="302 Found" anchor="status.302">
1606  <iref primary="true" item="302 Found (status code)" x:for-anchor=""/>
1607  <iref primary="true" item="Status Codes" subitem="302 Found" x:for-anchor=""/>
1608<t>
1609   The target resource resides temporarily under a different URI.
1610   Since the redirection might be altered on occasion, the client &SHOULD;
1611   continue to use the effective request URI for future requests.
1612</t>
1613<t>
1614   The temporary URI &SHOULD; be given by the Location field in the
1615   response. A response payload can contain a short hypertext note with a
1616   hyperlink to the new URI(s).
1617</t>
1618<x:note>
1619  <t>
1620    <x:h>Note:</x:h> For historic reasons, user agents &MAY; change the
1621    request method from POST to GET for the subsequent request. If this
1622    behavior is undesired, status code 307 (Temporary Redirect) can be used
1623    instead.
1624  </t>
1625</x:note>
1626</section>
1627
1628<section title="303 See Other" anchor="status.303">
1629  <iref primary="true" item="303 See Other (status code)" x:for-anchor=""/>
1630  <iref primary="true" item="Status Codes" subitem="303 See Other" x:for-anchor=""/>
1631<t>
1632   The 303 status code indicates that the server is redirecting the
1633   user agent to a different resource, as indicated by a URI in the
1634   Location header field, that is intended to provide an indirect
1635   response to the original request.  In order to satisfy the original
1636   request, a user agent &SHOULD; perform a retrieval request using the
1637   Location URI (a GET or HEAD request if using HTTP), which
1638   may itself be redirected further, and present the eventual result as an
1639   answer to the original request.
1640   Note that the new URI in the Location header field is not considered
1641   equivalent to the effective request URI.
1642</t>
1643<t>
1644   This status code is generally applicable to any HTTP method.  It is
1645   primarily used to allow the output of a POST action to redirect
1646   the user agent to a selected resource, since doing so provides the
1647   information corresponding to the POST response in a form that
1648   can be separately identified, bookmarked, and cached independent
1649   of the original request.
1650</t>
1651<t>
1652   A 303 response to a GET request indicates that the requested
1653   resource does not have a representation of its own that can be
1654   transferred by the server over HTTP.  The Location URI indicates a
1655   resource that is descriptive of the target resource, such that the
1656   follow-on representation might be useful to recipients without
1657   implying that it adequately represents the target resource.
1658   Note that answers to the questions of what can be represented, what
1659   representations are adequate, and what might be a useful description
1660   are outside the scope of HTTP and thus entirely determined by the
1661   URI owner(s).
1662</t>
1663<t>
1664   Except for responses to a HEAD request, the representation of a 303
1665   response &SHOULD; contain a short hypertext note with a hyperlink
1666   to the Location URI.
1667</t>
1668</section>
1669
1670<section title="305 Use Proxy" anchor="status.305">
1671  <iref primary="true" item="305 Use Proxy (status code)" x:for-anchor=""/>
1672  <iref primary="true" item="Status Codes" subitem="305 Use Proxy" x:for-anchor=""/>
1673<t>
1674   The 305 status code was defined in a previous version of this specification
1675   (see <xref target="changes.from.rfc.2616"/>), and is now deprecated.
1676</t>
1677</section>
1678
1679<section title="306 (Unused)" anchor="status.306">
1680  <iref primary="true" item="306 (Unused) (status code)" x:for-anchor=""/>
1681  <iref primary="true" item="Status Codes" subitem="306 (Unused)" x:for-anchor=""/>
1682<t>
1683   The 306 status code was used in a previous version of the
1684   specification, is no longer used, and the code is reserved.
1685</t>
1686</section>
1687
1688<section title="307 Temporary Redirect" anchor="status.307">
1689  <iref primary="true" item="307 Temporary Redirect (status code)" x:for-anchor=""/>
1690  <iref primary="true" item="Status Codes" subitem="307 Temporary Redirect" x:for-anchor=""/>
1691<t>
1692   The target resource resides temporarily under a different URI.
1693   Since the redirection can change over time, the client &SHOULD;
1694   continue to use the effective request URI for future requests.
1695</t>
1696<t>
1697   The temporary URI &SHOULD; be given by the Location field in the
1698   response. A response payload can contain a short hypertext note with a
1699   hyperlink to the new URI(s).
1700</t>
1701<x:note>
1702  <t>
1703    <x:h>Note:</x:h> This status code is similar to 302 Found, except that
1704    it does not allow rewriting the request method from POST to GET. This
1705    specification defines no equivalent counterpart for 301 Moved Permanently
1706    (<xref target="draft-reschke-http-status-308"/>, however, defines the
1707    status code 308 Permanent Redirect for this purpose).
1708  </t>
1709</x:note>
1710</section>
1711</section>
1712
1713<section title="Client Error 4xx" anchor="status.4xx">
1714<t>
1715   The 4xx class of status code is intended for cases in which the
1716   client seems to have erred. Except when responding to a HEAD request,
1717   the server &SHOULD; include a representation containing an explanation of the
1718   error situation, and whether it is a temporary or permanent
1719   condition. These status codes are applicable to any request method.
1720   User agents &SHOULD; display any included representation to the user.
1721</t>
1722
1723<section title="400 Bad Request" anchor="status.400">
1724  <iref primary="true" item="400 Bad Request (status code)" x:for-anchor=""/>
1725  <iref primary="true" item="Status Codes" subitem="400 Bad Request" x:for-anchor=""/>
1726<t>
1727   The server cannot or will not process the request, due to a client error (e.g.,
1728   malformed syntax).
1729</t>
1730</section>
1731
1732<section title="402 Payment Required" anchor="status.402">
1733  <iref primary="true" item="402 Payment Required (status code)" x:for-anchor=""/>
1734  <iref primary="true" item="Status Codes" subitem="402 Payment Required" x:for-anchor=""/>
1735<t>
1736   This code is reserved for future use.
1737</t>
1738</section>
1739
1740<section title="403 Forbidden" anchor="status.403">
1741  <iref primary="true" item="403 Forbidden (status code)" x:for-anchor=""/>
1742  <iref primary="true" item="Status Codes" subitem="403 Forbidden" x:for-anchor=""/>
1743<t>
1744   The server understood the request, but refuses to authorize it. Providing
1745   different user authentication credentials might be successful, but any
1746   credentials that were provided in the request are insufficient. The request
1747   &SHOULD-NOT; be repeated with the same credentials.
1748</t>
1749<t>
1750   If the request method was not HEAD and the server wishes to make
1751   public why the request has not been fulfilled, it &SHOULD; describe the
1752   reason for the refusal in the representation.  If the server does not wish to
1753   make this information available to the client, the status code 404
1754   (Not Found) &MAY; be used instead.
1755</t>
1756</section>
1757
1758<section title="404 Not Found" anchor="status.404">
1759  <iref primary="true" item="404 Not Found (status code)" x:for-anchor=""/>
1760  <iref primary="true" item="Status Codes" subitem="404 Not Found" x:for-anchor=""/>
1761<t>
1762   The server has not found anything matching the effective request URI. No
1763   indication is given of whether the condition is temporary or
1764   permanent. The 410 (Gone) status code &SHOULD; be used if the server
1765   knows, through some internally configurable mechanism, that an old
1766   resource is permanently unavailable and has no forwarding address.
1767   This status code is commonly used when the server does not wish to
1768   reveal exactly why the request has been refused, or when no other
1769   response is applicable.
1770</t>
1771</section>
1772
1773<section title="405 Method Not Allowed" anchor="status.405">
1774  <iref primary="true" item="405 Method Not Allowed (status code)" x:for-anchor=""/>
1775  <iref primary="true" item="Status Codes" subitem="405 Method Not Allowed" x:for-anchor=""/>
1776<t>
1777   The method specified in the request-line is not allowed for the target
1778   resource. The response &MUST; include an Allow header field containing a
1779   list of valid methods for the requested resource.
1780</t>
1781</section>
1782
1783<section title="406 Not Acceptable" anchor="status.406">
1784  <iref primary="true" item="406 Not Acceptable (status code)" x:for-anchor=""/>
1785  <iref primary="true" item="Status Codes" subitem="406 Not Acceptable" x:for-anchor=""/>
1786<t>
1787   The resource identified by the request is only capable of generating
1788   response representations which have content characteristics not acceptable
1789   according to the Accept and Accept-* header fields sent in the request
1790   (see &p3-header-fields;).
1791</t>
1792<t>
1793   Unless it was a HEAD request, the response &SHOULD; include a representation
1794   containing a list of available representation characteristics and location(s)
1795   from which the user or user agent can choose the one most
1796   appropriate. Depending upon the format and the
1797   capabilities of the user agent, selection of the most appropriate
1798   choice &MAY; be performed automatically. However, this specification
1799   does not define any standard for such automatic selection.
1800</t>
1801<x:note>
1802  <t>
1803    <x:h>Note:</x:h> HTTP/1.1 servers are allowed to return responses which are
1804    not acceptable according to the accept header fields sent in the
1805    request. In some cases, this might even be preferable to sending a
1806    406 response. User agents are encouraged to inspect the header fields of
1807    an incoming response to determine if it is acceptable.
1808  </t>
1809</x:note>
1810<t>
1811   If the response could be unacceptable, a user agent &SHOULD;
1812   temporarily stop receipt of more data and query the user for a
1813   decision on further actions.
1814</t>
1815</section>
1816
1817<section title="408 Request Timeout" anchor="status.408">
1818  <iref primary="true" item="408 Request Timeout (status code)" x:for-anchor=""/>
1819  <iref primary="true" item="Status Codes" subitem="408 Request Timeout" x:for-anchor=""/>
1820<t>
1821   The client did not produce a request within the time that the server
1822   was prepared to wait. The client &MAY; repeat the request without
1823   modifications at any later time.
1824</t>
1825</section>
1826
1827<section title="409 Conflict" anchor="status.409">
1828  <iref primary="true" item="409 Conflict (status code)" x:for-anchor=""/>
1829  <iref primary="true" item="Status Codes" subitem="409 Conflict" x:for-anchor=""/>
1830<t>
1831   The request could not be completed due to a conflict with the current
1832   state of the resource. This code is only allowed in situations where
1833   it is expected that the user might be able to resolve the conflict
1834   and resubmit the request. The response body &SHOULD; include enough
1835   information for the user to recognize the source of the conflict.
1836   Ideally, the response representation would include enough information for the
1837   user or user agent to fix the problem; however, that might not be
1838   possible and is not required.
1839</t>
1840<t>
1841   Conflicts are most likely to occur in response to a PUT request. For
1842   example, if versioning were being used and the representation being PUT
1843   included changes to a resource which conflict with those made by an
1844   earlier (third-party) request, the server might use the 409 response
1845   to indicate that it can't complete the request. In this case, the
1846   response representation would likely contain a list of the differences
1847   between the two versions.
1848</t>
1849</section>
1850
1851<section title="410 Gone" anchor="status.410">
1852  <iref primary="true" item="410 Gone (status code)" x:for-anchor=""/>
1853  <iref primary="true" item="Status Codes" subitem="410 Gone" x:for-anchor=""/>
1854<t>
1855   The target resource is no longer available at the server and no
1856   forwarding address is known. This condition is expected to be
1857   considered permanent. Clients with link editing capabilities &SHOULD;
1858   delete references to the effective request URI after user approval. If the
1859   server does not know, or has no facility to determine, whether or not
1860   the condition is permanent, the status code 404 (Not Found) &SHOULD; be
1861   used instead.
1862</t>
1863<t>
1864   The 410 response is primarily intended to assist the task of web
1865   maintenance by notifying the recipient that the resource is
1866   intentionally unavailable and that the server owners desire that
1867   remote links to that resource be removed. Such an event is common for
1868   limited-time, promotional services and for resources belonging to
1869   individuals no longer working at the server's site. It is not
1870   necessary to mark all permanently unavailable resources as "gone" or
1871   to keep the mark for any length of time &mdash; that is left to the
1872   discretion of the server owner.
1873</t>
1874<t>
1875   Caches &MAY; use a heuristic (see &p6-heuristic;) to determine freshness
1876   for 410 responses.
1877</t>
1878</section>
1879
1880<section title="411 Length Required" anchor="status.411">
1881  <iref primary="true" item="411 Length Required (status code)" x:for-anchor=""/>
1882  <iref primary="true" item="Status Codes" subitem="411 Length Required" x:for-anchor=""/>
1883<t>
1884   The server refuses to accept the request without a defined Content-Length.
1885   The client &MAY; repeat the request if it adds a valid
1886   Content-Length header field containing the length of the message body
1887   in the request message.
1888</t>
1889</section>
1890
1891<section title="413 Request Representation Too Large" anchor="status.413">
1892  <iref primary="true" item="413 Request Representation Too Large (status code)" x:for-anchor=""/>
1893  <iref primary="true" item="Status Codes" subitem="413 Request Representation Too Large" x:for-anchor=""/>
1894<t>
1895   The server is refusing to process a request because the request
1896   representation is larger than the server is willing or able to process. The
1897   server &MAY; close the connection to prevent the client from continuing
1898   the request.
1899</t>
1900<t>
1901   If the condition is temporary, the server &SHOULD; include a Retry-After
1902   header field to indicate that it is temporary and after what
1903   time the client &MAY; try again.
1904</t>
1905</section>
1906
1907<section title="414 URI Too Long" anchor="status.414">
1908  <iref primary="true" item="414 URI Too Long (status code)" x:for-anchor=""/>
1909  <iref primary="true" item="Status Codes" subitem="414 URI Too Long" x:for-anchor=""/>
1910<t>
1911   The server is refusing to service the request because the effective request URI
1912   is longer than the server is willing to interpret. This rare
1913   condition is only likely to occur when a client has improperly
1914   converted a POST request to a GET request with long query
1915   information, when the client has descended into a URI "black hole" of
1916   redirection (e.g., a redirected URI prefix that points to a suffix of
1917   itself), or when the server is under attack by a client attempting to
1918   exploit security holes present in some servers using fixed-length
1919   buffers for reading or manipulating the request-target.
1920</t>
1921</section>
1922
1923<section title="415 Unsupported Media Type" anchor="status.415">
1924  <iref primary="true" item="415 Unsupported Media Type (status code)" x:for-anchor=""/>
1925  <iref primary="true" item="Status Codes" subitem="415 Unsupported Media Type" x:for-anchor=""/>
1926<t>
1927   The server is refusing to service the request because the request
1928   payload is in a format not supported by this request method on the
1929   target resource.
1930</t>
1931</section>
1932
1933<section title="417 Expectation Failed" anchor="status.417">
1934  <iref primary="true" item="417 Expectation Failed (status code)" x:for-anchor=""/>
1935  <iref primary="true" item="Status Codes" subitem="417 Expectation Failed" x:for-anchor=""/>
1936<t>
1937   The expectation given in an Expect header field (see <xref target="header.expect"/>)
1938   could not be met by this server, or, if the server is a proxy,
1939   the server has unambiguous evidence that the request could not be met
1940   by the next-hop server.
1941</t>
1942</section>
1943
1944<section title="426 Upgrade Required" anchor="status.426">
1945  <iref primary="true" item="426 Upgrade Required (status code)" x:for-anchor=""/>
1946  <iref primary="true" item="Status Codes" subitem="426 Upgrade Required" x:for-anchor=""/>
1947<t>
1948   The request can not be completed without a prior protocol upgrade. This
1949   response &MUST; include an Upgrade header field (&header-upgrade;)
1950   specifying the required protocols.
1951</t>
1952<figure>
1953<preamble>Example:</preamble>
1954<artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
1955HTTP/1.1 426 Upgrade Required
1956Upgrade: HTTP/3.0
1957Connection: Upgrade
1958Content-Length: <x:length-of target="s426body"/>
1959Content-Type: text/plain
1960
1961<x:span anchor="s426body">This service requires use of the HTTP/3.0 protocol.
1962</x:span></artwork></figure>
1963<t>
1964   The server &SHOULD; include a message body in the 426 response which
1965   indicates in human readable form the reason for the error and describes any
1966   alternative courses which may be available to the user.
1967</t>
1968</section>
1969</section>
1970
1971<section title="Server Error 5xx" anchor="status.5xx">
1972<t>
1973   Response status codes beginning with the digit "5" indicate cases in
1974   which the server is aware that it has erred or is incapable of
1975   performing the request. Except when responding to a HEAD request, the
1976   server &SHOULD; include a representation containing an explanation of the
1977   error situation, and whether it is a temporary or permanent
1978   condition. User agents &SHOULD; display any included representation to the
1979   user. These response codes are applicable to any request method.
1980</t>
1981
1982<section title="500 Internal Server Error" anchor="status.500">
1983  <iref primary="true" item="500 Internal Server Error (status code)" x:for-anchor=""/>
1984  <iref primary="true" item="Status Codes" subitem="500 Internal Server Error" x:for-anchor=""/>
1985<t>
1986   The server encountered an unexpected condition which prevented it
1987   from fulfilling the request.
1988</t>
1989</section>
1990
1991<section title="501 Not Implemented" anchor="status.501">
1992  <iref primary="true" item="501 Not Implemented (status code)" x:for-anchor=""/>
1993  <iref primary="true" item="Status Codes" subitem="501 Not Implemented" x:for-anchor=""/>
1994<t>
1995   The server does not support the functionality required to fulfill the
1996   request. This is the appropriate response when the server does not
1997   recognize the request method and is not capable of supporting it for
1998   any resource.
1999</t>
2000</section>
2001
2002<section title="502 Bad Gateway" anchor="status.502">
2003  <iref primary="true" item="502 Bad Gateway (status code)" x:for-anchor=""/>
2004  <iref primary="true" item="Status Codes" subitem="502 Bad Gateway" x:for-anchor=""/>
2005<t>
2006   The server, while acting as a gateway or proxy, received an invalid
2007   response from the upstream server it accessed in attempting to
2008   fulfill the request.
2009</t>
2010</section>
2011
2012<section title="503 Service Unavailable" anchor="status.503">
2013  <iref primary="true" item="503 Service Unavailable (status code)" x:for-anchor=""/>
2014  <iref primary="true" item="Status Codes" subitem="503 Service Unavailable" x:for-anchor=""/>
2015<t>
2016   The server is currently unable to handle the request due to a
2017   temporary overloading or maintenance of the server.
2018</t>
2019<t>
2020   The implication is that this is a temporary condition which will be
2021   alleviated after some delay. If known, the length of the delay &MAY; be
2022   indicated in a Retry-After header field (<xref target="header.retry-after"/>).
2023   If no Retry-After is given, the client &SHOULD; handle the response as it
2024   would for a 500 response.
2025</t>
2026<x:note>
2027  <t>
2028    <x:h>Note:</x:h> The existence of the 503 status code does not imply that a
2029    server has to use it when becoming overloaded. Some servers might wish
2030    to simply refuse the connection.
2031  </t>
2032</x:note>
2033</section>
2034
2035<section title="504 Gateway Timeout" anchor="status.504">
2036  <iref primary="true" item="504 Gateway Timeout (status code)" x:for-anchor=""/>
2037  <iref primary="true" item="Status Codes" subitem="504 Gateway Timeout" x:for-anchor=""/>
2038<t>
2039   The server, while acting as a gateway or proxy, did not receive a
2040   timely response from the upstream server specified by the URI (e.g.,
2041   HTTP, FTP, LDAP) or some other auxiliary server (e.g., DNS) it needed
2042   to access in attempting to complete the request.
2043</t>
2044<x:note>
2045  <t>
2046    <x:h>Note</x:h> to implementors: some deployed proxies are known to
2047    return 400 or 500 when DNS lookups time out.
2048  </t>
2049</x:note>
2050</section>
2051
2052<section title="505 HTTP Version Not Supported" anchor="status.505">
2053  <iref primary="true" item="505 HTTP Version Not Supported (status code)" x:for-anchor=""/>
2054  <iref primary="true" item="Status Codes" subitem="505 HTTP Version Not Supported" x:for-anchor=""/>
2055<t>
2056   The server does not support, or refuses to support, the protocol
2057   version that was used in the request message. The server is
2058   indicating that it is unable or unwilling to complete the request
2059   using the same major version as the client, as described in &http-version;,
2060   other than with this error message. The response &SHOULD; contain
2061   a representation describing why that version is not supported and what other
2062   protocols are supported by that server.
2063</t>
2064
2065</section>
2066</section>
2067
2068</section>
2069
2070<section title="Representation" anchor="representation">
2071<t>
2072   Request and Response messages &MAY; transfer a representation if not otherwise
2073   restricted by the request method or response status code. A representation
2074   consists of metadata (representation header fields) and data (representation
2075   body).  When a complete or partial representation is enclosed in an HTTP message,
2076   it is referred to as the payload of the message. HTTP representations
2077   are defined in &payload;.
2078</t>
2079<t>
2080   A representation body is only present in a message when a message body is
2081   present, as described in &message-body;. The representation body is obtained
2082   from the message body by decoding any Transfer-Encoding that might
2083   have been applied to ensure safe and proper transfer of the message.
2084</t>
2085
2086<section title="Identifying the Resource Associated with a Representation" anchor="identifying.response.associated.with.representation">
2087<t>
2088   It is sometimes necessary to determine an identifier for the resource
2089   associated with a representation.
2090</t>
2091<t>
2092   An HTTP request representation, when present, is always associated with an
2093   anonymous (i.e., unidentified) resource.
2094</t>
2095<t>
2096   In the common case, an HTTP response is a representation of the target
2097   resource (see &effective-request-uri;). However, this is not always the
2098   case. To determine the URI of the resource a response is associated with,
2099   the following rules are used (with the first applicable one being selected):
2100</t>
2101<t><list style="numbers">
2102   <t>If the response status code is 200 or 203 and the request method was GET,
2103   the response payload is a representation of the target resource.</t>
2104   <t>If the response status code is 204, 206, or 304 and the request method was GET
2105   or HEAD, the response payload is a partial representation of the target
2106   resource.</t>
2107   <t>If the response has a Content-Location header field, and that URI is the same
2108   as the effective request URI, the response payload is a representation of the
2109   target resource.</t>
2110   <t>If the response has a Content-Location header field, and that URI is not the
2111   same as the effective request URI, then the response asserts that its
2112   payload is a representation of the resource identified by the
2113   Content-Location URI. However, such an assertion cannot be trusted unless
2114   it can be verified by other means (not defined by HTTP).</t>
2115   <t>Otherwise, the response is a representation of an anonymous (i.e.,
2116   unidentified) resource.</t>
2117</list></t>
2118<t>
2119  <cref anchor="TODO-req-uri">
2120   The comparison function is going to have to be defined somewhere,
2121   because we already need to compare URIs for things like cache invalidation.</cref>
2122</t>
2123</section>
2124
2125</section>
2126
2127
2128<section title="Common Protocol Parameters" anchor="common.protocol.parameters">
2129<section title="Date/Time Formats" anchor="http.date">
2130  <x:anchor-alias value="HTTP-date"/>
2131<t>
2132   HTTP applications have historically allowed three different formats
2133   for date/time stamps. However, the preferred format is a fixed-length subset
2134   of that defined by <xref target="RFC1123"/>:
2135</t>
2136<figure><artwork type="example" x:indent-with="  ">
2137Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2138</artwork></figure>
2139<t>
2140   The other formats are described here only for compatibility with obsolete
2141   implementations.
2142</t>
2143<figure><artwork type="example" x:indent-with="  ">
2144Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2145Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2146</artwork></figure>
2147<t>
2148   HTTP/1.1 clients and servers that parse a date value &MUST; accept
2149   all three formats (for compatibility with HTTP/1.0), though they &MUST;
2150   only generate the RFC 1123 format for representing HTTP-date values
2151   in header fields.
2152</t>
2153<t>
2154   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
2155   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2156   equal to UTC (Coordinated Universal Time). This is indicated in the
2157   first two formats by the inclusion of "GMT" as the three-letter
2158   abbreviation for time zone, and &MUST; be assumed when reading the
2159   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
2160   additional whitespace beyond that specifically included as SP in the
2161   grammar.
2162</t>
2163<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
2164  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
2165</artwork></figure>
2166<t anchor="preferred.date.format">
2167  <x:anchor-alias value="rfc1123-date"/>
2168  <x:anchor-alias value="time-of-day"/>
2169  <x:anchor-alias value="hour"/>
2170  <x:anchor-alias value="minute"/>
2171  <x:anchor-alias value="second"/>
2172  <x:anchor-alias value="day-name"/>
2173  <x:anchor-alias value="day"/>
2174  <x:anchor-alias value="month"/>
2175  <x:anchor-alias value="year"/>
2176  <x:anchor-alias value="GMT"/>
2177  Preferred format:
2178</t>
2179<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"/>
2180  <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>
2181  ; fixed length subset of the format defined in
2182  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
2183 
2184  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
2185               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
2186               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
2187               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
2188               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
2189               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
2190               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
2191               
2192  <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>
2193               ; e.g., 02 Jun 1982
2194
2195  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2196  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2197               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2198               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2199               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2200               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2201               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2202               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2203               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2204               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2205               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2206               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2207               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2208  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2209
2210  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2211
2212  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2213                 ; 00:00:00 - 23:59:59
2214                 
2215  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2216  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2217  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2218</artwork></figure>
2219<t>
2220  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2221  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2222  same as those defined for the RFC 5322 constructs
2223  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2224</t>
2225<t anchor="obsolete.date.formats">
2226  <x:anchor-alias value="obs-date"/>
2227  <x:anchor-alias value="rfc850-date"/>
2228  <x:anchor-alias value="asctime-date"/>
2229  <x:anchor-alias value="date1"/>
2230  <x:anchor-alias value="date2"/>
2231  <x:anchor-alias value="date3"/>
2232  <x:anchor-alias value="rfc1123-date"/>
2233  <x:anchor-alias value="day-name-l"/>
2234  Obsolete formats:
2235</t>
2236<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2237  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2238</artwork></figure>
2239<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2240  <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>
2241  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2242                 ; day-month-year (e.g., 02-Jun-82)
2243
2244  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2245         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2246         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2247         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2248         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2249         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2250         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2251</artwork></figure>
2252<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2253  <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>
2254  <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> ))
2255                 ; month day (e.g., Jun  2)
2256</artwork></figure>
2257<x:note>
2258  <t>
2259    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2260    accepting date values that might have been sent by non-HTTP
2261    applications, as is sometimes the case when retrieving or posting
2262    messages via proxies/gateways to SMTP or NNTP.
2263  </t>
2264</x:note>
2265<x:note>
2266  <t>
2267    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2268    to their usage within the protocol stream. Clients and servers are
2269    not required to use these formats for user presentation, request
2270    logging, etc.
2271  </t>
2272</x:note>
2273</section>
2274
2275<section title="Product Tokens" anchor="product.tokens">
2276  <x:anchor-alias value="product"/>
2277  <x:anchor-alias value="product-version"/>
2278<t>
2279   Product tokens are used to allow communicating applications to
2280   identify themselves by software name and version. Most fields using
2281   product tokens also allow sub-products which form a significant part
2282   of the application to be listed, separated by whitespace. By
2283   convention, the products are listed in order of their significance
2284   for identifying the application.
2285</t>
2286<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2287  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2288  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2289</artwork></figure>
2290<t>
2291   Examples:
2292</t>
2293<figure><artwork type="example">
2294  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2295  Server: Apache/0.8.4
2296</artwork></figure>
2297<t>
2298   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2299   used for advertising or other non-essential information. Although any
2300   token octet &MAY; appear in a product-version, this token &SHOULD;
2301   only be used for a version identifier (i.e., successive versions of
2302   the same product &SHOULD; only differ in the product-version portion of
2303   the product value).
2304</t>
2305</section>
2306</section>
2307
2308<section title="Header Field Definitions" anchor="header.field.definitions">
2309<t>
2310   This section defines the syntax and semantics of HTTP/1.1 header fields
2311   related to request and response semantics.
2312</t>
2313
2314<section title="Allow" anchor="header.allow">
2315  <iref primary="true" item="Allow header field" x:for-anchor=""/>
2316  <iref primary="true" item="Header Fields" subitem="Allow" x:for-anchor=""/>
2317  <x:anchor-alias value="Allow"/>
2318<t>
2319   The "Allow" header field lists the set of methods advertised as
2320   supported by the target resource. The purpose of this field is strictly to
2321   inform the recipient of valid request methods associated with the resource.
2322</t>
2323<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Allow"/>
2324  <x:ref>Allow</x:ref> = #<x:ref>method</x:ref>
2325</artwork></figure>
2326<t>
2327   Example of use:
2328</t>
2329<figure><artwork type="example">
2330  Allow: GET, HEAD, PUT
2331</artwork></figure>
2332<t>
2333   The actual set of allowed methods is defined by the origin server at the
2334   time of each request.
2335</t>
2336<t>
2337   A proxy &MUST-NOT; modify the Allow header field &mdash; it does not need to
2338   understand all the methods specified in order to handle them according to
2339   the generic message handling rules.
2340</t>
2341</section>
2342
2343<section title="Date" anchor="header.date">
2344  <iref primary="true" item="Date header field" x:for-anchor=""/>
2345  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
2346  <x:anchor-alias value="Date"/>
2347<t>
2348   The "Date" header field represents the date and time at which
2349   the message was originated, having the same semantics as the Origination
2350   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2351   The field value is an HTTP-date, as defined in <xref target="http.date"/>;
2352   it &MUST; be sent in rfc1123-date format.
2353</t>
2354<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
2355  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
2356</artwork></figure>
2357<t>
2358   An example is
2359</t>
2360<figure><artwork type="example">
2361  Date: Tue, 15 Nov 1994 08:12:31 GMT
2362</artwork></figure>
2363<t>
2364   Origin servers &MUST; include a Date header field in all responses,
2365   except in these cases:
2366  <list style="numbers">
2367      <t>If the response status code is 100 (Continue) or 101 (Switching
2368         Protocols), the response &MAY; include a Date header field, at
2369         the server's option.</t>
2370
2371      <t>If the response status code conveys a server error, e.g., 500
2372         (Internal Server Error) or 503 (Service Unavailable), and it is
2373         inconvenient or impossible to generate a valid Date.</t>
2374
2375      <t>If the server does not have a clock that can provide a
2376         reasonable approximation of the current time, its responses
2377         &MUST-NOT; include a Date header field.</t>
2378  </list>
2379</t>
2380<t>
2381   A received message that does not have a Date header field &MUST; be
2382   assigned one by the recipient if the message will be cached by that
2383   recipient.
2384</t>
2385<t>
2386   Clients can use the Date header field as well; in order to keep request
2387   messages small, they are advised not to include it when it doesn't convey
2388   any useful information (as is usually the case for requests that do not
2389   contain a payload).
2390</t>
2391<t>
2392   The HTTP-date sent in a Date header field &SHOULD-NOT; represent a date and
2393   time subsequent to the generation of the message. It &SHOULD; represent
2394   the best available approximation of the date and time of message
2395   generation, unless the implementation has no means of generating a
2396   reasonably accurate date and time. In theory, the date ought to
2397   represent the moment just before the payload is generated. In
2398   practice, the date can be generated at any time during the message
2399   origination without affecting its semantic value.
2400</t>
2401</section>
2402
2403<section title="Expect" anchor="header.expect">
2404  <iref primary="true" item="Expect header field" x:for-anchor=""/>
2405  <iref primary="true" item="Header Fields" subitem="Expect" x:for-anchor=""/>
2406  <x:anchor-alias value="Expect"/>
2407  <x:anchor-alias value="expectation"/>
2408  <x:anchor-alias value="expect-param"/>
2409  <x:anchor-alias value="expect-name"/>
2410  <x:anchor-alias value="expect-value"/>
2411<t>
2412   The "Expect" header field is used to indicate that particular
2413   server behaviors are required by the client.
2414</t>
2415<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"/>
2416  <x:ref>Expect</x:ref>       = 1#<x:ref>expectation</x:ref>
2417 
2418  <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> ]
2419                             *( <x:ref>OWS</x:ref> ";" [ <x:ref>OWS</x:ref> <x:ref>expect-param</x:ref> ] )
2420  <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> ]
2421 
2422  <x:ref>expect-name</x:ref>  = <x:ref>token</x:ref>
2423  <x:ref>expect-value</x:ref> = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
2424</artwork></figure>
2425<t>
2426   If all received Expect header field(s) are syntactically valid but contain
2427   an expectation that the recipient does not understand or cannot comply with,
2428   the recipient &MUST; respond with a 417 (Expectation Failed) status code. A
2429   recipient of a syntactically invalid Expectation header field &MUST; respond
2430   with a 4xx status code other than 417.
2431</t>
2432<t>
2433   The only expectation defined by this specification is:
2434</t>
2435<t><iref primary="true" item="100-continue (expect value)"/><iref primary="true" item="Expect Values" subitem="100-continue"/>
2436  100-continue
2437   <list>
2438      <t>
2439        The "100-continue" expectation is defined &use100;. It does not support
2440        any expect-params.
2441      </t>
2442   </list>
2443</t>
2444<t>
2445   Comparison is case-insensitive for names (expect-name), and case-sensitive
2446   for values (expect-value).
2447</t>
2448<t>
2449   The Expect mechanism is hop-by-hop: the above requirements apply to any
2450   server, including proxies. However, the Expect header field itself is
2451   end-to-end; it &MUST; be forwarded if the request is forwarded.
2452</t>
2453<t>
2454   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the Expect
2455   header field.
2456</t>
2457</section>
2458
2459<section title="From" anchor="header.from">
2460  <iref primary="true" item="From header field" x:for-anchor=""/>
2461  <iref primary="true" item="Header Fields" subitem="From" x:for-anchor=""/>
2462  <x:anchor-alias value="From"/>
2463  <x:anchor-alias value="mailbox"/>
2464<t>
2465   The "From" header field, if given, &SHOULD; contain an Internet
2466   e-mail address for the human user who controls the requesting user
2467   agent. The address &SHOULD; be machine-usable, as defined by "mailbox"
2468   in <xref x:sec="3.4" x:fmt="of" target="RFC5322"/>:
2469</t>
2470<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="From"/>
2471  <x:ref>From</x:ref>    = <x:ref>mailbox</x:ref>
2472 
2473  <x:ref>mailbox</x:ref> = &lt;mailbox, defined in <xref x:sec="3.4" x:fmt="," target="RFC5322"/>&gt;
2474</artwork></figure>
2475<t>
2476   An example is:
2477</t>
2478<figure><artwork type="example">
2479  From: webmaster@example.org
2480</artwork></figure>
2481<t>
2482   This header field &MAY; be used for logging purposes and as a means for
2483   identifying the source of invalid or unwanted requests. It &SHOULD-NOT; 
2484   be used as an insecure form of access protection. The interpretation
2485   of this field is that the request is being performed on behalf of the
2486   person given, who accepts responsibility for the method performed. In
2487   particular, robot agents &SHOULD; include this header field so that the
2488   person responsible for running the robot can be contacted if problems
2489   occur on the receiving end.
2490</t>
2491<t>
2492   The Internet e-mail address in this field &MAY; be separate from the
2493   Internet host which issued the request. For example, when a request
2494   is passed through a proxy the original issuer's address &SHOULD; be
2495   used.
2496</t>
2497<t>
2498   The client &SHOULD-NOT;  send the From header field without the user's
2499   approval, as it might conflict with the user's privacy interests or
2500   their site's security policy. It is strongly recommended that the
2501   user be able to disable, enable, and modify the value of this field
2502   at any time prior to a request.
2503</t>
2504</section>
2505
2506<section title="Location" anchor="header.location">
2507  <iref primary="true" item="Location header field" x:for-anchor=""/>
2508  <iref primary="true" item="Header Fields" subitem="Location" x:for-anchor=""/>
2509  <x:anchor-alias value="Location"/>
2510<t>
2511   The "Location" header field &MAY; be sent in responses to refer to
2512   a specific resource in accordance with the semantics of the status
2513   code.
2514</t>
2515<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Location"/>
2516  <x:ref>Location</x:ref> = <x:ref>URI-reference</x:ref>
2517</artwork></figure>
2518<t>
2519   For 201 (Created) responses, the Location is the URI of the new resource
2520   which was created by the request. For 3xx responses, the location &SHOULD;
2521   indicate the server's preferred URI for automatic redirection to the
2522   resource.
2523</t>
2524<t>
2525   The field value consists of a single URI-reference. When it has the form
2526   of a relative reference (<xref target="RFC3986" x:fmt="," x:sec="4.2"/>),
2527   the final value is computed by resolving it against the effective request
2528   URI (<xref target="RFC3986" x:fmt="," x:sec="5"/>). If the original URI, as
2529   navigated to by the user agent, did contain a fragment identifier, and the
2530   final value does not, then the original URI's fragment identifier is added
2531   to the final value.
2532</t>
2533<figure>
2534<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-->
2535<artwork type="example">
2536  Location: /pub/WWW/People.html#tim
2537</artwork>
2538<postamble>would result in a final value of "http://www.example.org/pub/WWW/People.html#tim"</postamble>
2539</figure>
2540<figure>
2541<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-->
2542<artwork type="example">
2543  Location: http://www.example.net/index.html
2544</artwork>
2545<postamble>would result in a final value of "http://www.example.net/index.html#larry", preserving the original fragment identifier.</postamble>
2546</figure>
2547<x:note>
2548  <t>
2549    <x:h>Note:</x:h> Some recipients attempt to recover from Location fields
2550    that are not valid URI references. This specification does not mandate or
2551    define such processing, but does allow it (see <xref target="intro.conformance.and.error.handling"/>).
2552  </t>
2553</x:note>
2554<t>
2555   There are circumstances in which a fragment identifier in a Location URI
2556   would not be appropriate. For instance, when it appears in a 201 Created
2557   response, where the Location header field specifies the URI for the entire
2558   created resource.
2559</t>
2560<x:note>
2561  <t>
2562    <x:h>Note:</x:h> The Content-Location header field (&header-content-location;) differs
2563    from Location in that the Content-Location identifies the most specific
2564    resource corresponding to the enclosed representation.
2565    It is therefore possible for a response to contain header fields for
2566    both Location and Content-Location.
2567  </t>
2568</x:note>
2569</section>
2570
2571<section title="Max-Forwards" anchor="header.max-forwards">
2572  <iref primary="true" item="Max-Forwards header field" x:for-anchor=""/>
2573  <iref primary="true" item="Header Fields" subitem="Max-Forwards" x:for-anchor=""/>
2574  <x:anchor-alias value="Max-Forwards"/>
2575<t>
2576   The "Max-Forwards" header field provides a mechanism with the
2577   TRACE (<xref target="TRACE"/>) and OPTIONS (<xref target="OPTIONS"/>)
2578   methods to limit the number of times that the request is forwarded by
2579   proxies. This can be useful when the client is attempting to
2580   trace a request which appears to be failing or looping mid-chain.
2581</t>
2582<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Max-Forwards"/>
2583  <x:ref>Max-Forwards</x:ref> = 1*<x:ref>DIGIT</x:ref>
2584</artwork></figure>
2585<t>
2586   The Max-Forwards value is a decimal integer indicating the remaining
2587   number of times this request message can be forwarded.
2588</t>
2589<t>
2590   Each recipient of a TRACE or OPTIONS request
2591   containing a Max-Forwards header field &MUST; check and update its
2592   value prior to forwarding the request. If the received value is zero
2593   (0), the recipient &MUST-NOT; forward the request; instead, it &MUST;
2594   respond as the final recipient. If the received Max-Forwards value is
2595   greater than zero, then the forwarded message &MUST; contain an updated
2596   Max-Forwards field with a value decremented by one (1).
2597</t>
2598<t>
2599   The Max-Forwards header field &MAY; be ignored for all other request
2600   methods.
2601</t>
2602</section>
2603
2604<section title="Referer" anchor="header.referer">
2605  <iref primary="true" item="Referer header field" x:for-anchor=""/>
2606  <iref primary="true" item="Header Fields" subitem="Referer" x:for-anchor=""/>
2607  <x:anchor-alias value="Referer"/>
2608<t>
2609   The "Referer" [sic] header field allows the client to specify the
2610   URI of the resource from which the target URI was obtained (the
2611   "referrer", although the header field is misspelled.).
2612</t>
2613<t>
2614   The Referer header field allows servers to generate lists of back-links to
2615   resources for interest, logging, optimized caching, etc. It also allows
2616   obsolete or mistyped links to be traced for maintenance. Some servers use
2617   Referer as a means of controlling where they allow links from (so-called
2618   "deep linking"), but legitimate requests do not always
2619   contain a Referer header field.
2620</t>
2621<t>
2622   If the target URI was obtained from a source that does not have its own
2623   URI (e.g., input from the user keyboard), the Referer field &MUST; either be
2624   sent with the value "about:blank", or not be sent at all. Note that this
2625   requirement does not apply to sources with non-HTTP URIs (e.g., FTP).
2626</t>
2627<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Referer"/>
2628  <x:ref>Referer</x:ref> = <x:ref>absolute-URI</x:ref> / <x:ref>partial-URI</x:ref>
2629</artwork></figure>
2630<t>
2631   Example:
2632</t>
2633<figure><artwork type="example">
2634  Referer: http://www.example.org/hypertext/Overview.html
2635</artwork></figure>
2636<t>
2637   If the field value is a relative URI, it &SHOULD; be interpreted
2638   relative to the effective request URI. The URI &MUST-NOT; include a fragment. See
2639   <xref target="encoding.sensitive.information.in.uris"/> for security considerations.
2640</t>
2641</section>
2642
2643<section title="Retry-After" anchor="header.retry-after">
2644  <iref primary="true" item="Retry-After header field" x:for-anchor=""/>
2645  <iref primary="true" item="Header Fields" subitem="Retry-After" x:for-anchor=""/>
2646  <x:anchor-alias value="Retry-After"/>
2647<t>
2648   The header "Retry-After" field can be used with a 503 (Service
2649   Unavailable) response to indicate how long the service is expected to
2650   be unavailable to the requesting client. This field &MAY; also be used
2651   with any 3xx (Redirection) response to indicate the minimum time the
2652   user-agent is asked to wait before issuing the redirected request.
2653</t>
2654<t>
2655   The value of this field can be either an HTTP-date or an integer number
2656   of seconds (in decimal) after the time of the response.
2657</t>
2658<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Retry-After"/>
2659  <x:ref>Retry-After</x:ref> = <x:ref>HTTP-date</x:ref> / <x:ref>delta-seconds</x:ref>
2660</artwork></figure>
2661<t anchor="rule.delta-seconds">
2662  <x:anchor-alias value="delta-seconds"/>
2663   Time spans are non-negative decimal integers, representing time in
2664   seconds.
2665</t>
2666<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="delta-seconds"/>
2667  <x:ref>delta-seconds</x:ref>  = 1*<x:ref>DIGIT</x:ref>
2668</artwork></figure>
2669<t>
2670   Two examples of its use are
2671</t>
2672<figure><artwork type="example">
2673  Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
2674  Retry-After: 120
2675</artwork></figure>
2676<t>
2677   In the latter example, the delay is 2 minutes.
2678</t>
2679</section>
2680
2681<section title="Server" anchor="header.server">
2682  <iref primary="true" item="Server header field" x:for-anchor=""/>
2683  <iref primary="true" item="Header Fields" subitem="Server" x:for-anchor=""/>
2684  <x:anchor-alias value="Server"/>
2685<t>
2686   The "Server" header field contains information about the
2687   software used by the origin server to handle the request.
2688</t>
2689<t>
2690   The field can contain multiple
2691   product tokens (<xref target="product.tokens"/>) and
2692   comments (&header-fields;) identifying the server and any significant
2693   subproducts. The product tokens are listed in order of their significance
2694   for identifying the application.
2695</t>
2696<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Server"/>
2697  <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> ) )
2698</artwork></figure>
2699<t>
2700   Example:
2701</t>
2702<figure><artwork type="example">
2703  Server: CERN/3.0 libwww/2.17
2704</artwork></figure>
2705<t>
2706   If the response is being forwarded through a proxy, the proxy
2707   application &MUST-NOT; modify the Server header field. Instead, it
2708   &MUST; include a Via field (as described in &header-via;).
2709</t>
2710<x:note>
2711  <t>
2712    <x:h>Note:</x:h> Revealing the specific software version of the server might
2713    allow the server machine to become more vulnerable to attacks
2714    against software that is known to contain security holes. Server
2715    implementors are encouraged to make this field a configurable
2716    option.
2717  </t>
2718</x:note>
2719</section>
2720
2721<section title="User-Agent" anchor="header.user-agent">
2722  <iref primary="true" item="User-Agent header field" x:for-anchor=""/>
2723  <iref primary="true" item="Header Fields" subitem="User-Agent" x:for-anchor=""/>
2724  <x:anchor-alias value="User-Agent"/>
2725<t>
2726   The "User-Agent" header field contains information about the user
2727   agent originating the request. User agents &SHOULD; include this field with
2728   requests.
2729</t>
2730<t>
2731   Typically, it is used for statistical purposes, the tracing of protocol
2732   violations, and tailoring responses to avoid particular user agent
2733   limitations.
2734</t>
2735<t>
2736   The field can contain multiple
2737   product tokens (<xref target="product.tokens"/>)
2738   and comments (&header-fields;) identifying the agent and its
2739   significant subproducts. By convention, the product tokens are listed in
2740   order of their significance for identifying the application.
2741</t>
2742<t>
2743   Because this field is usually sent on every request a user agent makes,
2744   implementations are encouraged not to include needlessly fine-grained
2745   detail, and to limit (or even prohibit) the addition of subproducts by third
2746   parties. Overly long and detailed User-Agent field values make requests
2747   larger and can also be used to identify ("fingerprint") the user against
2748   their wishes.
2749</t>
2750<t>
2751   Likewise, implementations are encouraged not to use the product tokens of
2752   other implementations in order to declare compatibility with them, as this
2753   circumvents the purpose of the field. Finally, they are encouraged not to
2754   use comments to identify products; doing so makes the field value more
2755   difficult to parse.
2756</t>
2757<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="User-Agent"/>
2758  <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> ) )
2759</artwork></figure>
2760<t>
2761   Example:
2762</t>
2763<figure><artwork type="example">
2764  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2765</artwork></figure>
2766</section>
2767
2768</section>
2769
2770<section title="IANA Considerations" anchor="IANA.considerations">
2771
2772<section title="Method Registry" anchor="method.registration">
2773<t>
2774  The registration procedure for HTTP request methods is defined by
2775  <xref target="method.registry"/> of this document.
2776</t>
2777<t>
2778   The HTTP Method Registry shall be created at <eref target="http://www.iana.org/assignments/http-methods"/>
2779   and be populated with the registrations below:
2780</t>
2781<?BEGININC p2-semantics.iana-methods ?>
2782<!--AUTOGENERATED FROM extract-method-defs.xslt, do not edit manually-->
2783<texttable align="left" suppress-title="true" anchor="iana.method.registration.table">
2784   <ttcol>Method</ttcol>
2785   <ttcol>Safe</ttcol>
2786   <ttcol>Reference</ttcol>
2787   <c>CONNECT</c>
2788   <c>no</c>
2789   <c>
2790      <xref target="CONNECT"/>
2791   </c>
2792   <c>DELETE</c>
2793   <c>no</c>
2794   <c>
2795      <xref target="DELETE"/>
2796   </c>
2797   <c>GET</c>
2798   <c>yes</c>
2799   <c>
2800      <xref target="GET"/>
2801   </c>
2802   <c>HEAD</c>
2803   <c>yes</c>
2804   <c>
2805      <xref target="HEAD"/>
2806   </c>
2807   <c>OPTIONS</c>
2808   <c>yes</c>
2809   <c>
2810      <xref target="OPTIONS"/>
2811   </c>
2812   <c>POST</c>
2813   <c>no</c>
2814   <c>
2815      <xref target="POST"/>
2816   </c>
2817   <c>PUT</c>
2818   <c>no</c>
2819   <c>
2820      <xref target="PUT"/>
2821   </c>
2822   <c>TRACE</c>
2823   <c>yes</c>
2824   <c>
2825      <xref target="TRACE"/>
2826   </c>
2827</texttable>
2828<!--(END)-->
2829<?ENDINC p2-semantics.iana-methods ?>
2830</section>
2831
2832<section title="Status Code Registry" anchor="status.code.registration">
2833<t>
2834   The registration procedure for HTTP Status Codes &mdash; previously defined
2835   in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/> &mdash; is now defined
2836   by <xref target="status.code.registry"/> of this document.
2837</t>
2838<t>
2839   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-status-codes"/>
2840   shall be updated with the registrations below:
2841</t>
2842<?BEGININC p2-semantics.iana-status-codes ?>
2843<!--AUTOGENERATED FROM extract-status-code-defs.xslt, do not edit manually-->
2844<texttable align="left" suppress-title="true" anchor="iana.status.code.registration.table">
2845   <ttcol>Value</ttcol>
2846   <ttcol>Description</ttcol>
2847   <ttcol>Reference</ttcol>
2848   <c>100</c>
2849   <c>Continue</c>
2850   <c>
2851      <xref target="status.100"/>
2852   </c>
2853   <c>101</c>
2854   <c>Switching Protocols</c>
2855   <c>
2856      <xref target="status.101"/>
2857   </c>
2858   <c>200</c>
2859   <c>OK</c>
2860   <c>
2861      <xref target="status.200"/>
2862   </c>
2863   <c>201</c>
2864   <c>Created</c>
2865   <c>
2866      <xref target="status.201"/>
2867   </c>
2868   <c>202</c>
2869   <c>Accepted</c>
2870   <c>
2871      <xref target="status.202"/>
2872   </c>
2873   <c>203</c>
2874   <c>Non-Authoritative Information</c>
2875   <c>
2876      <xref target="status.203"/>
2877   </c>
2878   <c>204</c>
2879   <c>No Content</c>
2880   <c>
2881      <xref target="status.204"/>
2882   </c>
2883   <c>205</c>
2884   <c>Reset Content</c>
2885   <c>
2886      <xref target="status.205"/>
2887   </c>
2888   <c>300</c>
2889   <c>Multiple Choices</c>
2890   <c>
2891      <xref target="status.300"/>
2892   </c>
2893   <c>301</c>
2894   <c>Moved Permanently</c>
2895   <c>
2896      <xref target="status.301"/>
2897   </c>
2898   <c>302</c>
2899   <c>Found</c>
2900   <c>
2901      <xref target="status.302"/>
2902   </c>
2903   <c>303</c>
2904   <c>See Other</c>
2905   <c>
2906      <xref target="status.303"/>
2907   </c>
2908   <c>305</c>
2909   <c>Use Proxy</c>
2910   <c>
2911      <xref target="status.305"/>
2912   </c>
2913   <c>306</c>
2914   <c>(Unused)</c>
2915   <c>
2916      <xref target="status.306"/>
2917   </c>
2918   <c>307</c>
2919   <c>Temporary Redirect</c>
2920   <c>
2921      <xref target="status.307"/>
2922   </c>
2923   <c>400</c>
2924   <c>Bad Request</c>
2925   <c>
2926      <xref target="status.400"/>
2927   </c>
2928   <c>402</c>
2929   <c>Payment Required</c>
2930   <c>
2931      <xref target="status.402"/>
2932   </c>
2933   <c>403</c>
2934   <c>Forbidden</c>
2935   <c>
2936      <xref target="status.403"/>
2937   </c>
2938   <c>404</c>
2939   <c>Not Found</c>
2940   <c>
2941      <xref target="status.404"/>
2942   </c>
2943   <c>405</c>
2944   <c>Method Not Allowed</c>
2945   <c>
2946      <xref target="status.405"/>
2947   </c>
2948   <c>406</c>
2949   <c>Not Acceptable</c>
2950   <c>
2951      <xref target="status.406"/>
2952   </c>
2953   <c>408</c>
2954   <c>Request Timeout</c>
2955   <c>
2956      <xref target="status.408"/>
2957   </c>
2958   <c>409</c>
2959   <c>Conflict</c>
2960   <c>
2961      <xref target="status.409"/>
2962   </c>
2963   <c>410</c>
2964   <c>Gone</c>
2965   <c>
2966      <xref target="status.410"/>
2967   </c>
2968   <c>411</c>
2969   <c>Length Required</c>
2970   <c>
2971      <xref target="status.411"/>
2972   </c>
2973   <c>413</c>
2974   <c>Request Representation Too Large</c>
2975   <c>
2976      <xref target="status.413"/>
2977   </c>
2978   <c>414</c>
2979   <c>URI Too Long</c>
2980   <c>
2981      <xref target="status.414"/>
2982   </c>
2983   <c>415</c>
2984   <c>Unsupported Media Type</c>
2985   <c>
2986      <xref target="status.415"/>
2987   </c>
2988   <c>417</c>
2989   <c>Expectation Failed</c>
2990   <c>
2991      <xref target="status.417"/>
2992   </c>
2993   <c>426</c>
2994   <c>Upgrade Required</c>
2995   <c>
2996      <xref target="status.426"/>
2997   </c>
2998   <c>500</c>
2999   <c>Internal Server Error</c>
3000   <c>
3001      <xref target="status.500"/>
3002   </c>
3003   <c>501</c>
3004   <c>Not Implemented</c>
3005   <c>
3006      <xref target="status.501"/>
3007   </c>
3008   <c>502</c>
3009   <c>Bad Gateway</c>
3010   <c>
3011      <xref target="status.502"/>
3012   </c>
3013   <c>503</c>
3014   <c>Service Unavailable</c>
3015   <c>
3016      <xref target="status.503"/>
3017   </c>
3018   <c>504</c>
3019   <c>Gateway Timeout</c>
3020   <c>
3021      <xref target="status.504"/>
3022   </c>
3023   <c>505</c>
3024   <c>HTTP Version Not Supported</c>
3025   <c>
3026      <xref target="status.505"/>
3027   </c>
3028</texttable>
3029<!--(END)-->
3030<?ENDINC p2-semantics.iana-status-codes ?>
3031</section>
3032<section title="Header Field Registration" anchor="header.field.registration">
3033<t>
3034   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3035   with the permanent registrations below (see <xref target="RFC3864"/>):
3036</t>
3037<?BEGININC p2-semantics.iana-headers ?>
3038<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3039<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3040   <ttcol>Header Field Name</ttcol>
3041   <ttcol>Protocol</ttcol>
3042   <ttcol>Status</ttcol>
3043   <ttcol>Reference</ttcol>
3044
3045   <c>Allow</c>
3046   <c>http</c>
3047   <c>standard</c>
3048   <c>
3049      <xref target="header.allow"/>
3050   </c>
3051   <c>Date</c>
3052   <c>http</c>
3053   <c>standard</c>
3054   <c>
3055      <xref target="header.date"/>
3056   </c>
3057   <c>Expect</c>
3058   <c>http</c>
3059   <c>standard</c>
3060   <c>
3061      <xref target="header.expect"/>
3062   </c>
3063   <c>From</c>
3064   <c>http</c>
3065   <c>standard</c>
3066   <c>
3067      <xref target="header.from"/>
3068   </c>
3069   <c>Location</c>
3070   <c>http</c>
3071   <c>standard</c>
3072   <c>
3073      <xref target="header.location"/>
3074   </c>
3075   <c>Max-Forwards</c>
3076   <c>http</c>
3077   <c>standard</c>
3078   <c>
3079      <xref target="header.max-forwards"/>
3080   </c>
3081   <c>Referer</c>
3082   <c>http</c>
3083   <c>standard</c>
3084   <c>
3085      <xref target="header.referer"/>
3086   </c>
3087   <c>Retry-After</c>
3088   <c>http</c>
3089   <c>standard</c>
3090   <c>
3091      <xref target="header.retry-after"/>
3092   </c>
3093   <c>Server</c>
3094   <c>http</c>
3095   <c>standard</c>
3096   <c>
3097      <xref target="header.server"/>
3098   </c>
3099   <c>User-Agent</c>
3100   <c>http</c>
3101   <c>standard</c>
3102   <c>
3103      <xref target="header.user-agent"/>
3104   </c>
3105</texttable>
3106<!--(END)-->
3107<?ENDINC p2-semantics.iana-headers ?>
3108<t>
3109   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3110</t>
3111</section>
3112</section>
3113
3114<section title="Security Considerations" anchor="security.considerations">
3115<t>
3116   This section is meant to inform application developers, information
3117   providers, and users of the security limitations in HTTP/1.1 as
3118   described by this document. The discussion does not include
3119   definitive solutions to the problems revealed, though it does make
3120   some suggestions for reducing security risks.
3121</t>
3122
3123<section title="Transfer of Sensitive Information" anchor="security.sensitive">
3124<t>
3125   Like any generic data transfer protocol, HTTP cannot regulate the
3126   content of the data that is transferred, nor is there any a priori
3127   method of determining the sensitivity of any particular piece of
3128   information within the context of any given request. Therefore,
3129   applications &SHOULD; supply as much control over this information as
3130   possible to the provider of that information. Four header fields are
3131   worth special mention in this context: Server, Via, Referer and From.
3132</t>
3133<t>
3134   Revealing the specific software version of the server might allow the
3135   server machine to become more vulnerable to attacks against software
3136   that is known to contain security holes. Implementors &SHOULD; make the
3137   Server header field a configurable option.
3138</t>
3139<t>
3140   Proxies which serve as a portal through a network firewall &SHOULD;
3141   take special precautions regarding the transfer of header information
3142   that identifies the hosts behind the firewall. In particular, they
3143   &SHOULD; remove, or replace with sanitized versions, any Via fields
3144   generated behind the firewall.
3145</t>
3146<t>
3147   The Referer header field allows reading patterns to be studied and reverse
3148   links drawn. Although it can be very useful, its power can be abused
3149   if user details are not separated from the information contained in
3150   the Referer. Even when the personal information has been removed, the
3151   Referer header field might indicate a private document's URI whose
3152   publication would be inappropriate.
3153</t>
3154<t>
3155   The information sent in the From field might conflict with the user's
3156   privacy interests or their site's security policy, and hence it
3157   &SHOULD-NOT;  be transmitted without the user being able to disable,
3158   enable, and modify the contents of the field. The user &MUST; be able
3159   to set the contents of this field within a user preference or
3160   application defaults configuration.
3161</t>
3162<t>
3163   We suggest, though do not require, that a convenient toggle interface
3164   be provided for the user to enable or disable the sending of From and
3165   Referer information.
3166</t>
3167<t>
3168   The User-Agent (<xref target="header.user-agent"/>) or Server (<xref
3169   target="header.server"/>) header fields can sometimes be used to determine
3170   that a specific client or server has a particular security hole which might
3171   be exploited. Unfortunately, this same information is often used for other
3172   valuable purposes for which HTTP currently has no better mechanism.
3173</t>
3174<t>
3175   Furthermore, the User-Agent header field may contain enough entropy to be
3176   used, possibly in conjunction with other material, to uniquely identify the
3177   user.
3178</t>
3179<t>
3180   Some request methods, like TRACE (<xref target="TRACE"/>), expose information
3181   that was sent in request header fields within the body of their response.
3182   Clients &SHOULD; be careful with sensitive information, like Cookies,
3183   Authorization credentials, and other header fields that might be used to
3184   collect data from the client.
3185</t> 
3186</section>
3187
3188<section title="Encoding Sensitive Information in URIs" anchor="encoding.sensitive.information.in.uris">
3189<t>
3190   Because the source of a link might be private information or might
3191   reveal an otherwise private information source, it is strongly
3192   recommended that the user be able to select whether or not the
3193   Referer field is sent. For example, a browser client could have a
3194   toggle switch for browsing openly/anonymously, which would
3195   respectively enable/disable the sending of Referer and From
3196   information.
3197</t>
3198<t>
3199   Clients &SHOULD-NOT; include a Referer header field in a (non-secure)
3200   HTTP request if the referring page was transferred with a secure
3201   protocol.
3202</t>
3203<t>
3204   Authors of services &SHOULD-NOT; use GET-based forms for the submission of
3205   sensitive data because that data will be placed in the request-target. Many
3206   existing servers, proxies, and user agents log or display the request-target
3207   in places where it might be visible to third parties. Such services can
3208   use POST-based form submission instead.
3209</t>
3210</section>
3211
3212<section title="Location Header Fields: Spoofing and Information Leakage" anchor="location.spoofing-leakage">
3213<t>
3214   If a single server supports multiple organizations that do not trust
3215   one another, then it &MUST; check the values of Location and Content-Location
3216   header fields in responses that are generated under control of
3217   said organizations to make sure that they do not attempt to
3218   invalidate resources over which they have no authority.
3219</t>
3220<t>
3221   Furthermore, appending the fragment identifier from one URI to another
3222   one obtained from a Location header field might leak confidential
3223   information to the target server &mdash; although the fragment identifier is
3224   not transmitted in the final request, it might be visible to the user agent
3225   through other means, such as scripting.
3226</t>
3227</section>
3228
3229<section title="Security Considerations for CONNECT">
3230<t>
3231   Since tunneled data is opaque to the proxy, there are additional
3232   risks to tunneling to other well-known or reserved ports.
3233   A HTTP client CONNECTing to port 25 could relay spam
3234   via SMTP, for example. As such, proxies &SHOULD; restrict CONNECT
3235   access to a small number of known ports.
3236</t>
3237</section>
3238
3239</section>
3240
3241<section title="Acknowledgments" anchor="acks">
3242<t>
3243  See &acks;.
3244</t>
3245</section>
3246</middle>
3247<back>
3248
3249<references title="Normative References">
3250
3251<reference anchor="Part1">
3252  <front>
3253    <title abbrev="HTTP/1.1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
3254    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3255      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3256      <address><email>fielding@gbiv.com</email></address>
3257    </author>
3258    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3259      <organization abbrev="W3C">World Wide Web Consortium</organization>
3260      <address><email>ylafon@w3.org</email></address>
3261    </author>
3262    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3263      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3264      <address><email>julian.reschke@greenbytes.de</email></address>
3265    </author>
3266    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3267  </front>
3268  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"/>
3269  <x:source href="p1-messaging.xml" basename="p1-messaging"/>
3270</reference>
3271
3272<reference anchor="Part3">
3273  <front>
3274    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3275    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3276      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3277      <address><email>fielding@gbiv.com</email></address>
3278    </author>
3279    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3280      <organization abbrev="W3C">World Wide Web Consortium</organization>
3281      <address><email>ylafon@w3.org</email></address>
3282    </author>
3283    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3284      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3285      <address><email>julian.reschke@greenbytes.de</email></address>
3286    </author>
3287    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3288  </front>
3289  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3290  <x:source href="p3-payload.xml" basename="p3-payload"/>
3291</reference>
3292
3293<reference anchor="Part4">
3294  <front>
3295    <title abbrev="HTTP/1.1">HTTP/1.1, part 4: Conditional Requests</title>
3296    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3297      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3298      <address><email>fielding@gbiv.com</email></address>
3299    </author>
3300    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3301      <organization abbrev="W3C">World Wide Web Consortium</organization>
3302      <address><email>ylafon@w3.org</email></address>
3303    </author>
3304    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3305      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3306      <address><email>julian.reschke@greenbytes.de</email></address>
3307    </author>
3308    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3309  </front>
3310  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p4-conditional-&ID-VERSION;"/>
3311  <x:source href="p4-conditional.xml" basename="p4-conditional"/>
3312</reference>
3313
3314<reference anchor="Part5">
3315  <front>
3316    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3317    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3318      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3319      <address><email>fielding@gbiv.com</email></address>
3320    </author>
3321    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3322      <organization abbrev="W3C">World Wide Web Consortium</organization>
3323      <address><email>ylafon@w3.org</email></address>
3324    </author>
3325    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3326      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3327      <address><email>julian.reschke@greenbytes.de</email></address>
3328    </author>
3329    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3330  </front>
3331  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3332  <x:source href="p5-range.xml" basename="p5-range"/>
3333</reference>
3334
3335<reference anchor="Part6">
3336  <front>
3337    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3338    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3339      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3340      <address><email>fielding@gbiv.com</email></address>
3341    </author>
3342    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3343      <organization abbrev="W3C">World Wide Web Consortium</organization>
3344      <address><email>ylafon@w3.org</email></address>
3345    </author>
3346    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3347      <organization>Rackspace</organization>
3348      <address><email>mnot@mnot.net</email></address>
3349    </author>
3350    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3351      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3352      <address><email>julian.reschke@greenbytes.de</email></address>
3353    </author>
3354    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3355  </front>
3356  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3357  <x:source href="p6-cache.xml" basename="p6-cache"/>
3358</reference>
3359
3360<reference anchor="Part7">
3361  <front>
3362    <title abbrev="HTTP/1.1">HTTP/1.1, part 7: Authentication</title>
3363    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3364      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
3365      <address><email>fielding@gbiv.com</email></address>
3366    </author>
3367    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3368      <organization abbrev="W3C">World Wide Web Consortium</organization>
3369      <address><email>ylafon@w3.org</email></address>
3370    </author>
3371    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3372      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3373      <address><email>julian.reschke@greenbytes.de</email></address>
3374    </author>
3375    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3376  </front>
3377  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p7-auth-&ID-VERSION;"/>
3378  <x:source href="p7-auth.xml" basename="p7-auth"/>
3379</reference>
3380
3381<reference anchor="RFC1950">
3382  <front>
3383    <title>ZLIB Compressed Data Format Specification version 3.3</title>
3384    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3385      <organization>Aladdin Enterprises</organization>
3386      <address><email>ghost@aladdin.com</email></address>
3387    </author>
3388    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
3389    <date month="May" year="1996"/>
3390  </front>
3391  <seriesInfo name="RFC" value="1950"/>
3392  <!--<annotation>
3393    RFC 1950 is an Informational RFC, thus it might be less stable than
3394    this specification. On the other hand, this downward reference was
3395    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3396    therefore it is unlikely to cause problems in practice. See also
3397    <xref target="BCP97"/>.
3398  </annotation>-->
3399</reference>
3400
3401<reference anchor="RFC1951">
3402  <front>
3403    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
3404    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3405      <organization>Aladdin Enterprises</organization>
3406      <address><email>ghost@aladdin.com</email></address>
3407    </author>
3408    <date month="May" year="1996"/>
3409  </front>
3410  <seriesInfo name="RFC" value="1951"/>
3411  <!--<annotation>
3412    RFC 1951 is an Informational RFC, thus it might be less stable than
3413    this specification. On the other hand, this downward reference was
3414    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3415    therefore it is unlikely to cause problems in practice. See also
3416    <xref target="BCP97"/>.
3417  </annotation>-->
3418</reference>
3419
3420<reference anchor="RFC1952">
3421  <front>
3422    <title>GZIP file format specification version 4.3</title>
3423    <author initials="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      <address><email>gzip@prep.ai.mit.edu</email></address>
3429    </author>
3430    <author initials="M." surname="Adler" fullname="Mark Adler">
3431      <address><email>madler@alumni.caltech.edu</email></address>
3432    </author>
3433    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3434      <address><email>ghost@aladdin.com</email></address>
3435    </author>
3436    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
3437      <address><email>randeg@alumni.rpi.edu</email></address>
3438    </author>
3439    <date month="May" year="1996"/>
3440  </front>
3441  <seriesInfo name="RFC" value="1952"/>
3442  <!--<annotation>
3443    RFC 1952 is an Informational RFC, thus it might be less stable than
3444    this specification. On the other hand, this downward reference was
3445    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
3446    therefore it is unlikely to cause problems in practice. See also
3447    <xref target="BCP97"/>.
3448  </annotation>-->
3449</reference>
3450
3451<reference anchor="RFC2045">
3452  <front>
3453    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3454    <author initials="N." surname="Freed" fullname="Ned Freed">
3455      <organization>Innosoft International, Inc.</organization>
3456      <address><email>ned@innosoft.com</email></address>
3457    </author>
3458    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3459      <organization>First Virtual Holdings</organization>
3460      <address><email>nsb@nsb.fv.com</email></address>
3461    </author>
3462    <date month="November" year="1996"/>
3463  </front>
3464  <seriesInfo name="RFC" value="2045"/>
3465</reference>
3466
3467<reference anchor="RFC2046">
3468  <front>
3469    <title abbrev="Media Types">Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types</title>
3470    <author initials="N." surname="Freed" fullname="Ned Freed">
3471      <organization>Innosoft International, Inc.</organization>
3472      <address><email>ned@innosoft.com</email></address>
3473    </author>
3474    <author initials="N." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3475      <organization>First Virtual Holdings</organization>
3476      <address><email>nsb@nsb.fv.com</email></address>
3477    </author>
3478    <date month="November" year="1996"/>
3479  </front>
3480  <seriesInfo name="RFC" value="2046"/>
3481</reference>
3482
3483<reference anchor="RFC2119">
3484  <front>
3485    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3486    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3487      <organization>Harvard University</organization>
3488      <address><email>sob@harvard.edu</email></address>
3489    </author>
3490    <date month="March" year="1997"/>
3491  </front>
3492  <seriesInfo name="BCP" value="14"/>
3493  <seriesInfo name="RFC" value="2119"/>
3494</reference>
3495
3496<reference anchor="RFC3986">
3497 <front>
3498  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3499  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3500    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3501    <address>
3502       <email>timbl@w3.org</email>
3503       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3504    </address>
3505  </author>
3506  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3507    <organization abbrev="Day Software">Day Software</organization>
3508    <address>
3509      <email>fielding@gbiv.com</email>
3510      <uri>http://roy.gbiv.com/</uri>
3511    </address>
3512  </author>
3513  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3514    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3515    <address>
3516      <email>LMM@acm.org</email>
3517      <uri>http://larry.masinter.net/</uri>
3518    </address>
3519  </author>
3520  <date month='January' year='2005'></date>
3521 </front>
3522 <seriesInfo name="STD" value="66"/>
3523 <seriesInfo name="RFC" value="3986"/>
3524</reference>
3525
3526<reference anchor='RFC4647'>
3527  <front>
3528    <title>Matching of Language Tags</title>
3529    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role="editor">
3530      <organization>Yahoo! Inc.</organization>
3531      <address><email>addison@inter-locale.com</email></address>
3532    </author>
3533    <author initials='M.' surname='Davis' fullname='Mark Davis' role="editor">
3534      <organization>Google</organization>
3535      <address><email>mark.davis@macchiato.com</email></address>
3536    </author>
3537    <date year='2006' month='September' />
3538  </front>
3539  <seriesInfo name='BCP' value='47' />
3540  <seriesInfo name='RFC' value='4647' />
3541</reference>
3542
3543<reference anchor="RFC5234">
3544  <front>
3545    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3546    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3547      <organization>Brandenburg InternetWorking</organization>
3548      <address>
3549        <email>dcrocker@bbiw.net</email>
3550      </address> 
3551    </author>
3552    <author initials="P." surname="Overell" fullname="Paul Overell">
3553      <organization>THUS plc.</organization>
3554      <address>
3555        <email>paul.overell@thus.net</email>
3556      </address>
3557    </author>
3558    <date month="January" year="2008"/>
3559  </front>
3560  <seriesInfo name="STD" value="68"/>
3561  <seriesInfo name="RFC" value="5234"/>
3562</reference>
3563
3564<reference anchor='RFC5646'>
3565  <front>
3566    <title>Tags for Identifying Languages</title>
3567    <author initials='A.' surname='Phillips' fullname='Addison Phillips' role='editor'>
3568      <organization>Lab126</organization>
3569      <address><email>addison@inter-locale.com</email></address>
3570    </author>
3571    <author initials='M.' surname='Davis' fullname='Mark Davis' role='editor'>
3572      <organization>Google</organization>
3573      <address><email>mark.davis@google.com</email></address>
3574    </author>
3575    <date month='September' year='2009' />
3576  </front>
3577  <seriesInfo name='BCP' value='47' />
3578  <seriesInfo name='RFC' value='5646' />
3579</reference>
3580
3581</references>
3582
3583<references title="Informative References">
3584
3585<reference anchor="RFC1123">
3586  <front>
3587    <title>Requirements for Internet Hosts - Application and Support</title>
3588    <author initials="R." surname="Braden" fullname="Robert Braden">
3589      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3590      <address><email>Braden@ISI.EDU</email></address>
3591    </author>
3592    <date month="October" year="1989"/>
3593  </front>
3594  <seriesInfo name="STD" value="3"/>
3595  <seriesInfo name="RFC" value="1123"/>
3596</reference>
3597
3598<reference anchor="RFC1945">
3599  <front>
3600    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3601    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3602      <organization>MIT, Laboratory for Computer Science</organization>
3603      <address><email>timbl@w3.org</email></address>
3604    </author>
3605    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3606      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3607      <address><email>fielding@ics.uci.edu</email></address>
3608    </author>
3609    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3610      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3611      <address><email>frystyk@w3.org</email></address>
3612    </author>
3613    <date month="May" year="1996"/>
3614  </front>
3615  <seriesInfo name="RFC" value="1945"/>
3616</reference>
3617
3618<reference anchor="RFC2049">
3619  <front>
3620    <title abbrev="MIME Conformance">Multipurpose Internet Mail Extensions (MIME) Part Five: Conformance Criteria and Examples</title>
3621    <author initials="N." surname="Freed" fullname="Ned Freed">
3622      <organization>Innosoft International, Inc.</organization>
3623      <address><email>ned@innosoft.com</email></address>
3624    </author>
3625    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3626      <organization>First Virtual Holdings</organization>
3627      <address><email>nsb@nsb.fv.com</email></address>
3628    </author>
3629    <date month="November" year="1996"/>
3630  </front>
3631  <seriesInfo name="RFC" value="2049"/>
3632</reference>
3633
3634<reference anchor="RFC2068">
3635  <front>
3636    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3637    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3638      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3639      <address><email>fielding@ics.uci.edu</email></address>
3640    </author>
3641    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3642      <organization>MIT Laboratory for Computer Science</organization>
3643      <address><email>jg@w3.org</email></address>
3644    </author>
3645    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3646      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3647      <address><email>mogul@wrl.dec.com</email></address>
3648    </author>
3649    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3650      <organization>MIT Laboratory for Computer Science</organization>
3651      <address><email>frystyk@w3.org</email></address>
3652    </author>
3653    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3654      <organization>MIT Laboratory for Computer Science</organization>
3655      <address><email>timbl@w3.org</email></address>
3656    </author>
3657    <date month="January" year="1997"/>
3658  </front>
3659  <seriesInfo name="RFC" value="2068"/>
3660</reference>
3661
3662<reference anchor="RFC2076">
3663  <front>
3664    <title abbrev="Internet Message Headers">Common Internet Message Headers</title>
3665    <author initials="J." surname="Palme" fullname="Jacob Palme">
3666      <organization>Stockholm University/KTH</organization>
3667      <address><email>jpalme@dsv.su.se</email></address>
3668    </author>
3669    <date month="February" year="1997"/>
3670  </front>
3671  <seriesInfo name="RFC" value="2076"/>
3672</reference>
3673
3674<reference anchor="RFC2277">
3675  <front>
3676    <title abbrev="Charset Policy">IETF Policy on Character Sets and Languages</title>
3677    <author initials="H.T." surname="Alvestrand" fullname="Harald Tveit Alvestrand">
3678      <organization>UNINETT</organization>
3679      <address><email>Harald.T.Alvestrand@uninett.no</email></address>
3680    </author>
3681    <date month="January" year="1998"/>
3682  </front>
3683  <seriesInfo name="BCP" value="18"/>
3684  <seriesInfo name="RFC" value="2277"/>
3685</reference>
3686
3687<reference anchor='RFC2295'>
3688  <front>
3689    <title abbrev='HTTP Content Negotiation'>Transparent Content Negotiation in HTTP</title>
3690    <author initials='K.' surname='Holtman' fullname='Koen Holtman'>
3691      <organization>Technische Universiteit Eindhoven</organization>
3692      <address>
3693        <email>koen@win.tue.nl</email>
3694      </address>
3695    </author>
3696    <author initials='A.H.' surname='Mutz' fullname='Andrew H. Mutz'>
3697      <organization>Hewlett-Packard Company</organization>
3698      <address>
3699        <email>mutz@hpl.hp.com</email>
3700      </address>
3701    </author>
3702    <date year='1998' month='March'/>
3703  </front>
3704  <seriesInfo name='RFC' value='2295'/>
3705</reference>
3706
3707<reference anchor="RFC2388">
3708  <front>
3709    <title abbrev="multipart/form-data">Returning Values from Forms:  multipart/form-data</title>
3710    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3711      <organization>Xerox Palo Alto Research Center</organization>
3712      <address><email>masinter@parc.xerox.com</email></address>
3713    </author>
3714    <date year="1998" month="August"/>
3715  </front>
3716  <seriesInfo name="RFC" value="2388"/>
3717</reference>
3718
3719<reference anchor="RFC2557">
3720  <front>
3721    <title abbrev="MIME Encapsulation of Aggregate Documents">MIME Encapsulation of Aggregate Documents, such as HTML (MHTML)</title>
3722    <author initials="F." surname="Palme" fullname="Jacob Palme">
3723      <organization>Stockholm University and KTH</organization>
3724      <address><email>jpalme@dsv.su.se</email></address>
3725    </author>
3726    <author initials="A." surname="Hopmann" fullname="Alex Hopmann">
3727      <organization>Microsoft Corporation</organization>
3728      <address><email>alexhop@microsoft.com</email></address>
3729    </author>
3730    <author initials="N." surname="Shelness" fullname="Nick Shelness">
3731      <organization>Lotus Development Corporation</organization>
3732      <address><email>Shelness@lotus.com</email></address>
3733    </author>
3734    <author initials="E." surname="Stefferud" fullname="Einar Stefferud">
3735      <address><email>stef@nma.com</email></address>
3736    </author>
3737    <date year="1999" month="March"/>
3738  </front>
3739  <seriesInfo name="RFC" value="2557"/>
3740</reference>
3741
3742<reference anchor="RFC2616">
3743  <front>
3744    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3745    <author initials="R." surname="Fielding" fullname="R. Fielding">
3746      <organization>University of California, Irvine</organization>
3747      <address><email>fielding@ics.uci.edu</email></address>
3748    </author>
3749    <author initials="J." surname="Gettys" fullname="J. Gettys">
3750      <organization>W3C</organization>
3751      <address><email>jg@w3.org</email></address>
3752    </author>
3753    <author initials="J." surname="Mogul" fullname="J. Mogul">
3754      <organization>Compaq Computer Corporation</organization>
3755      <address><email>mogul@wrl.dec.com</email></address>
3756    </author>
3757    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3758      <organization>MIT Laboratory for Computer Science</organization>
3759      <address><email>frystyk@w3.org</email></address>
3760    </author>
3761    <author initials="L." surname="Masinter" fullname="L. Masinter">
3762      <organization>Xerox Corporation</organization>
3763      <address><email>masinter@parc.xerox.com</email></address>
3764    </author>
3765    <author initials="P." surname="Leach" fullname="P. Leach">
3766      <organization>Microsoft Corporation</organization>
3767      <address><email>paulle@microsoft.com</email></address>
3768    </author>
3769    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3770      <organization>W3C</organization>
3771      <address><email>timbl@w3.org</email></address>
3772    </author>
3773    <date month="June" year="1999"/>
3774  </front>
3775  <seriesInfo name="RFC" value="2616"/>
3776</reference>
3777
3778<reference anchor='RFC2817'>
3779  <front>
3780    <title>Upgrading to TLS Within HTTP/1.1</title>
3781    <author initials='R.' surname='Khare' fullname='R. Khare'>
3782      <organization>4K Associates / UC Irvine</organization>
3783      <address><email>rohit@4K-associates.com</email></address>
3784    </author>
3785    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
3786      <organization>Agranat Systems, Inc.</organization>
3787      <address><email>lawrence@agranat.com</email></address>
3788    </author>
3789    <date year='2000' month='May' />
3790  </front>
3791  <seriesInfo name='RFC' value='2817' />
3792</reference>
3793
3794<reference anchor="RFC3629">
3795  <front>
3796    <title>UTF-8, a transformation format of ISO 10646</title>
3797    <author initials="F." surname="Yergeau" fullname="F. Yergeau">
3798      <organization>Alis Technologies</organization>
3799      <address><email>fyergeau@alis.com</email></address>
3800    </author>
3801    <date month="November" year="2003"/>
3802  </front>
3803  <seriesInfo name="STD" value="63"/>
3804  <seriesInfo name="RFC" value="3629"/>
3805</reference>
3806
3807<reference anchor='RFC3864'>
3808  <front>
3809    <title>Registration Procedures for Message Header Fields</title>
3810    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3811      <organization>Nine by Nine</organization>
3812      <address><email>GK-IETF@ninebynine.org</email></address>
3813    </author>
3814    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3815      <organization>BEA Systems</organization>
3816      <address><email>mnot@pobox.com</email></address>
3817    </author>
3818    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3819      <organization>HP Labs</organization>
3820      <address><email>JeffMogul@acm.org</email></address>
3821    </author>
3822    <date year='2004' month='September' />
3823  </front>
3824  <seriesInfo name='BCP' value='90' />
3825  <seriesInfo name='RFC' value='3864' />
3826</reference>
3827
3828<reference anchor="RFC4288">
3829  <front>
3830    <title>Media Type Specifications and Registration Procedures</title>
3831    <author initials="N." surname="Freed" fullname="N. Freed">
3832      <organization>Sun Microsystems</organization>
3833      <address>
3834        <email>ned.freed@mrochek.com</email>
3835      </address>
3836    </author>
3837    <author initials="J." surname="Klensin" fullname="J. Klensin">
3838      <address>
3839        <email>klensin+ietf@jck.com</email>
3840      </address>
3841    </author>
3842    <date year="2005" month="December"/>
3843  </front>
3844  <seriesInfo name="BCP" value="13"/>
3845  <seriesInfo name="RFC" value="4288"/>
3846</reference>
3847
3848<reference anchor='RFC5226'>
3849  <front>
3850    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
3851    <author initials='T.' surname='Narten' fullname='T. Narten'>
3852      <organization>IBM</organization>
3853      <address><email>narten@us.ibm.com</email></address>
3854    </author>
3855    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
3856      <organization>Google</organization>
3857      <address><email>Harald@Alvestrand.no</email></address>
3858    </author>
3859    <date year='2008' month='May' />
3860  </front>
3861  <seriesInfo name='BCP' value='26' />
3862  <seriesInfo name='RFC' value='5226' />
3863</reference>
3864
3865<reference anchor="RFC5322">
3866  <front>
3867    <title>Internet Message Format</title>
3868    <author initials="P." surname="Resnick" fullname="P. Resnick">
3869      <organization>Qualcomm Incorporated</organization>
3870    </author>
3871    <date year="2008" month="October"/>
3872  </front> 
3873  <seriesInfo name="RFC" value="5322"/>
3874</reference>
3875
3876<reference anchor='RFC5789'>
3877  <front>
3878    <title>PATCH Method for HTTP</title>
3879    <author initials='L.' surname='Dusseault' fullname='L. Dusseault'>
3880      <organization>Linden Lab</organization>
3881    </author>
3882    <author initials='J.' surname='Snell' fullname='J. Snell' />
3883    <date year='2010' month='March' />
3884  </front>
3885  <seriesInfo name='RFC' value='5789' />
3886</reference>
3887
3888<reference anchor="RFC5987">
3889        <front>
3890    <title>Character Set and Language Encoding for Hypertext Transfer Protocol (HTTP) Header Field Parameters</title>
3891    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3892      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3893      <address>
3894        <postal>
3895          <street>Hafenweg 16</street>
3896          <city>Muenster</city><region>NW</region><code>48155</code>
3897          <country>Germany</country>
3898        </postal>
3899        <email>julian.reschke@greenbytes.de</email>     
3900        <uri>http://greenbytes.de/tech/webdav/</uri>   
3901      </address>
3902    </author>
3903    <date month="August" year="2010"/>
3904  </front>
3905  <seriesInfo name="RFC" value="5987"/>
3906</reference>
3907
3908<reference anchor="RFC6151">
3909  <front>
3910    <title>Updated Security Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithms</title>
3911    <author initials="S." surname="Turner" fullname="S. Turner"/>
3912    <author initials="L." surname="Chen" fullname="L. Chen"/>
3913    <date year="2011" month="March" />
3914  </front>
3915  <seriesInfo name="RFC" value="6151" />
3916</reference>
3917
3918<reference anchor="RFC6266">
3919  <front>
3920    <title abbrev="Content-Disposition in HTTP">Use of the Content-Disposition Header Field
3921    in the Hypertext Transfer Protocol (HTTP)</title>
3922    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3923      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3924      <address>
3925        <email>julian.reschke@greenbytes.de</email>
3926      </address>
3927    </author>
3928    <date month="June" year="2011"/>
3929  </front>
3930  <seriesInfo name='RFC' value='6266' />
3931</reference>
3932
3933<reference anchor="draft-reschke-http-status-308">
3934        <front>
3935    <title abbrev="HTTP Status Code 308">The Hypertext Transfer Protocol (HTTP) Status Code 308 (Permanent Redirect)</title>
3936    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke">
3937      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3938      <address>
3939        <email>julian.reschke@greenbytes.de</email>     
3940      </address>
3941    </author>
3942    <date month="March" year="2012"/>
3943  </front>
3944  <seriesInfo name="Internet-Draft" value="draft-reschke-http-status-308-07"/>
3945</reference>
3946
3947</references>
3948
3949<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
3950<t>
3951  Clarify definition of POST.
3952  (<xref target="POST"/>)
3953</t>
3954<t>
3955  Remove requirement to handle all Content-* header fields; ban use of
3956  Content-Range with PUT.
3957  (<xref target="PUT"/>)
3958</t>
3959<t>
3960  Take over definition of CONNECT method from <xref target="RFC2817"/>.
3961  (<xref target="CONNECT"/>)
3962</t>
3963<t>
3964  This document takes over the Status Code Registry, previously defined
3965  in <xref target="RFC2817" x:fmt="of" x:sec="7.1"/>.
3966  (<xref target="status.code.registry"/>)
3967</t>
3968<t>
3969  Broadened the definition of 203 (Non-Authoritative Information) to include
3970  cases of payload transformations as well.
3971  (<xref target="status.203"/>)
3972</t>
3973<t>
3974  Status codes 301, 302, and 307: removed the normative requirements on both
3975  response payloads and user interaction.
3976  (<xref target="status.3xx"/>)
3977</t>
3978<t>
3979  Failed to consider that there are many other request methods that are safe
3980  to automatically redirect, and further that the user agent is able to make
3981  that determination based on the request method semantics.
3982  Furthermore, allow user agents to rewrite the method from POST to GET
3983  for status codes 301 and 302.
3984  (Sections <xref format="counter" target="status.301"/>,
3985  <xref format="counter" target="status.302"/> and
3986  <xref format="counter" target="status.307"/>)
3987</t>
3988<t>
3989  Deprecate 305 Use Proxy status code, because user agents did not implement it.
3990  It used to indicate that the target resource needs to be accessed through the
3991  proxy given by the Location field. The Location field gave the URI of the
3992  proxy. The recipient was expected to repeat this single request via the proxy.
3993  (<xref target="status.305"/>)
3994</t>
3995<t>
3996  Define status 426 (Upgrade Required) (this was incorporated from
3997  <xref target="RFC2817"/>).
3998  (<xref target="status.426"/>)
3999</t>
4000<t>
4001  Change ABNF productions for header fields to only define the field value.
4002  (<xref target="header.field.definitions"/>)
4003</t>
4004<t>
4005  Reclassify "Allow" as response header field, removing the option to
4006  specify it in a PUT request.
4007  Relax the server requirement on the contents of the Allow header field and
4008  remove requirement on clients to always trust the header field value.
4009  (<xref target="header.allow"/>)
4010</t>
4011<t>
4012  The ABNF for the Expect header field has been both fixed (allowing parameters
4013  for value-less expectations as well) and simplified (allowing trailing
4014  semicolons after "100-continue" when they were invalid before).
4015  (<xref target="header.expect"/>)
4016</t>
4017<t>
4018  Correct syntax of Location header field to allow URI references (including
4019  relative references and fragments), as referred symbol "absoluteURI" wasn't
4020  what was expected, and add some clarifications as to when use of fragments
4021  would not be appropriate.
4022  (<xref target="header.location"/>)
4023</t>
4024<t>
4025  Restrict Max-Forwards header field to OPTIONS and TRACE (previously,
4026  extension methods could have used it as well).
4027  (<xref target="header.max-forwards"/>)
4028</t>
4029<t>
4030  Allow Referer field value of "about:blank" as alternative to not specifying it.
4031  (<xref target="header.referer"/>)
4032</t>
4033<t>
4034  In the description of the Server header field, the Via field
4035  was described as a SHOULD. The requirement was and is stated
4036  correctly in the description of the Via header field in &header-via;.
4037  (<xref target="header.server"/>)
4038</t>
4039</section>
4040
4041<?BEGININC p2-semantics.abnf-appendix ?>
4042<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4043<figure>
4044<artwork type="abnf" name="p2-semantics.parsed-abnf">
4045<x:ref>Allow</x:ref> = [ ( "," / method ) *( OWS "," [ OWS method ] ) ]
4046
4047<x:ref>BWS</x:ref> = &lt;BWS, defined in [Part1], Section 3.2.1&gt;
4048
4049<x:ref>Date</x:ref> = HTTP-date
4050
4051<x:ref>Expect</x:ref> = *( "," OWS ) expectation *( OWS "," [ OWS expectation ] )
4052
4053<x:ref>From</x:ref> = mailbox
4054
4055<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4056
4057<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4058
4059<x:ref>Location</x:ref> = URI-reference
4060
4061<x:ref>Max-Forwards</x:ref> = 1*DIGIT
4062
4063<x:ref>OWS</x:ref> = &lt;OWS, defined in [Part1], Section 3.2.1&gt;
4064
4065<x:ref>RWS</x:ref> = &lt;RWS, defined in [Part1], Section 3.2.1&gt;
4066<x:ref>Referer</x:ref> = absolute-URI / partial-URI
4067<x:ref>Retry-After</x:ref> = HTTP-date / delta-seconds
4068
4069<x:ref>Server</x:ref> = product *( RWS ( product / comment ) )
4070
4071<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [Part1], Section 2.7&gt;
4072<x:ref>User-Agent</x:ref> = product *( RWS ( product / comment ) )
4073
4074<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [Part1], Section 2.7&gt;
4075<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4076
4077<x:ref>comment</x:ref> = &lt;comment, defined in [Part1], Section 3.2.4&gt;
4078
4079<x:ref>date1</x:ref> = day SP month SP year
4080<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4081<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4082<x:ref>day</x:ref> = 2DIGIT
4083<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4084 / %x54.75.65 ; Tue
4085 / %x57.65.64 ; Wed
4086 / %x54.68.75 ; Thu
4087 / %x46.72.69 ; Fri
4088 / %x53.61.74 ; Sat
4089 / %x53.75.6E ; Sun
4090<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4091 / %x54.75.65.73.64.61.79 ; Tuesday
4092 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4093 / %x54.68.75.72.73.64.61.79 ; Thursday
4094 / %x46.72.69.64.61.79 ; Friday
4095 / %x53.61.74.75.72.64.61.79 ; Saturday
4096 / %x53.75.6E.64.61.79 ; Sunday
4097<x:ref>delta-seconds</x:ref> = 1*DIGIT
4098
4099<x:ref>expect-name</x:ref> = token
4100<x:ref>expect-param</x:ref> = expect-name [ BWS "=" BWS expect-value ]
4101<x:ref>expect-value</x:ref> = token / quoted-string
4102<x:ref>expectation</x:ref> = expect-name [ BWS "=" BWS expect-value ] *( OWS ";" [
4103 OWS expect-param ] )
4104
4105<x:ref>hour</x:ref> = 2DIGIT
4106
4107<x:ref>mailbox</x:ref> = &lt;mailbox, defined in [RFC5322], Section 3.4&gt;
4108<x:ref>method</x:ref> = token
4109<x:ref>minute</x:ref> = 2DIGIT
4110<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4111 / %x46.65.62 ; Feb
4112 / %x4D.61.72 ; Mar
4113 / %x41.70.72 ; Apr
4114 / %x4D.61.79 ; May
4115 / %x4A.75.6E ; Jun
4116 / %x4A.75.6C ; Jul
4117 / %x41.75.67 ; Aug
4118 / %x53.65.70 ; Sep
4119 / %x4F.63.74 ; Oct
4120 / %x4E.6F.76 ; Nov
4121 / %x44.65.63 ; Dec
4122
4123<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4124<x:ref>obs-text</x:ref> = &lt;obs-text, defined in [Part1], Section 3.2.4&gt;
4125
4126<x:ref>partial-URI</x:ref> = &lt;partial-URI, defined in [Part1], Section 2.7&gt;
4127<x:ref>product</x:ref> = token [ "/" product-version ]
4128<x:ref>product-version</x:ref> = token
4129
4130<x:ref>quoted-string</x:ref> = &lt;quoted-string, defined in [Part1], Section 3.2.4&gt;
4131
4132<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4133<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4134
4135<x:ref>second</x:ref> = 2DIGIT
4136
4137<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4138<x:ref>token</x:ref> = &lt;token, defined in [Part1], Section 3.2.4&gt;
4139
4140<x:ref>year</x:ref> = 4DIGIT
4141</artwork>
4142</figure>
4143<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4144; Allow defined but not used
4145; Date defined but not used
4146; Expect defined but not used
4147; From defined but not used
4148; Location defined but not used
4149; Max-Forwards defined but not used
4150; Referer defined but not used
4151; Retry-After defined but not used
4152; Server defined but not used
4153; User-Agent defined but not used
4154; obs-text defined but not used
4155</artwork></figure></section>
4156<?ENDINC p2-semantics.abnf-appendix ?>
4157
4158<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4159
4160<section title="Since RFC 2616">
4161<t>
4162  Extracted relevant partitions from <xref target="RFC2616"/>.
4163</t>
4164</section>
4165
4166<section title="Since draft-ietf-httpbis-p2-semantics-00">
4167<t>
4168  Closed issues:
4169  <list style="symbols"> 
4170    <t>
4171      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/5"/>:
4172      "Via is a MUST"
4173      (<eref target="http://purl.org/NET/http-errata#via-must"/>)
4174    </t>
4175    <t>
4176      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/6"/>:
4177      "Fragments allowed in Location"
4178      (<eref target="http://purl.org/NET/http-errata#location-fragments"/>)
4179    </t>
4180    <t>
4181      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4182      "Safe Methods vs Redirection"
4183      (<eref target="http://purl.org/NET/http-errata#saferedirect"/>)
4184    </t>
4185    <t>
4186      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/17"/>:
4187      "Revise description of the POST method"
4188      (<eref target="http://purl.org/NET/http-errata#post"/>)
4189    </t>
4190    <t>
4191      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4192      "Normative and Informative references"
4193    </t>
4194    <t>
4195      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4196      "RFC2606 Compliance"
4197    </t>
4198    <t>
4199      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4200      "Informative references"
4201    </t>
4202    <t>
4203      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/84"/>:
4204      "Redundant cross-references"
4205    </t>
4206  </list>
4207</t>
4208<t>
4209  Other changes:
4210  <list style="symbols"> 
4211    <t>
4212      Move definitions of 304 and 412 condition codes to <xref target="Part4"/>
4213    </t>
4214  </list>
4215</t>
4216</section>
4217
4218<section title="Since draft-ietf-httpbis-p2-semantics-01">
4219<t>
4220  Closed issues:
4221  <list style="symbols"> 
4222    <t>
4223      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/21"/>:
4224      "PUT side effects"
4225    </t>
4226    <t>
4227      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/91"/>:
4228      "Duplicate Host header requirements"
4229    </t>
4230  </list>
4231</t>
4232<t>
4233  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4234  <list style="symbols"> 
4235    <t>
4236      Move "Product Tokens" section (back) into Part 1, as "token" is used
4237      in the definition of the Upgrade header field.
4238    </t>
4239    <t>
4240      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4241    </t>
4242    <t>
4243      Copy definition of delta-seconds from Part6 instead of referencing it.
4244    </t>
4245  </list>
4246</t>
4247</section>
4248
4249<section title="Since draft-ietf-httpbis-p2-semantics-02" anchor="changes.since.02">
4250<t>
4251  Closed issues:
4252  <list style="symbols"> 
4253    <t>
4254      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/24"/>:
4255      "Requiring Allow in 405 responses"
4256    </t>
4257    <t>
4258      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/59"/>:
4259      "Status Code Registry"
4260    </t>
4261    <t>
4262      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/61"/>:
4263      "Redirection vs. Location"
4264    </t>
4265    <t>
4266      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/70"/>:
4267      "Cacheability of 303 response"
4268    </t>
4269    <t>
4270      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/76"/>:
4271      "305 Use Proxy"
4272    </t>
4273    <t>
4274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/105"/>:
4275      "Classification for Allow header"
4276    </t>
4277    <t>
4278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4279      "PUT - 'store under' vs 'store at'"
4280    </t>
4281  </list>
4282</t>
4283<t>
4284  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4285  <list style="symbols"> 
4286    <t>
4287      Reference RFC 3984, and update header field registrations for headers defined
4288      in this document.
4289    </t>
4290  </list>
4291</t>
4292<t>
4293  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4294  <list style="symbols"> 
4295    <t>
4296      Replace string literals when the string really is case-sensitive (method).
4297    </t>
4298  </list>
4299</t>
4300</section>
4301
4302<section title="Since draft-ietf-httpbis-p2-semantics-03" anchor="changes.since.03">
4303<t>
4304  Closed issues:
4305  <list style="symbols"> 
4306    <t>
4307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/98"/>:
4308      "OPTIONS request bodies"
4309    </t>
4310    <t>
4311      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/119"/>:
4312      "Description of CONNECT should refer to RFC2817"
4313    </t>
4314    <t>
4315      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/125"/>:
4316      "Location Content-Location reference request/response mixup"
4317    </t>
4318  </list>
4319</t>
4320<t>
4321  Ongoing work on Method Registry (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/72"/>):
4322  <list style="symbols"> 
4323    <t>
4324      Added initial proposal for registration process, plus initial
4325      content (non-HTTP/1.1 methods to be added by a separate specification).
4326    </t>
4327  </list>
4328</t>
4329</section>
4330
4331<section title="Since draft-ietf-httpbis-p2-semantics-04" anchor="changes.since.04">
4332<t>
4333  Closed issues:
4334  <list style="symbols"> 
4335    <t>
4336      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4337      "Content-*"
4338    </t>
4339    <t>
4340      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4341      "RFC 2822 is updated by RFC 5322"
4342    </t>
4343  </list>
4344</t>
4345<t>
4346  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4347  <list style="symbols"> 
4348    <t>
4349      Use "/" instead of "|" for alternatives.
4350    </t>
4351    <t>
4352      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4353      whitespace ("OWS") and required whitespace ("RWS").
4354    </t>
4355    <t>
4356      Rewrite ABNFs to spell out whitespace rules, factor out
4357      header field value format definitions.
4358    </t>
4359  </list>
4360</t>
4361</section>
4362
4363<section title="Since draft-ietf-httpbis-p2-semantics-05" anchor="changes.since.05">
4364<t>
4365  Closed issues:
4366  <list style="symbols"> 
4367    <t>
4368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4369      "reason-phrase BNF"
4370    </t>
4371  </list>
4372</t>
4373<t>
4374  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4375  <list style="symbols"> 
4376    <t>
4377      Add appendix containing collected and expanded ABNF, reorganize ABNF introduction.
4378    </t>
4379  </list>
4380</t>
4381</section>
4382
4383<section title="Since draft-ietf-httpbis-p2-semantics-06" anchor="changes.since.06">
4384<t>
4385  Closed issues:
4386  <list style="symbols"> 
4387    <t>
4388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/144"/>:
4389      "Clarify when Referer is sent"
4390    </t>
4391    <t>
4392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/164"/>:
4393      "status codes vs methods"
4394    </t>
4395    <t>
4396      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/170"/>:
4397      "Do not require "updates" relation for specs that register status codes or method names"
4398    </t>
4399  </list>
4400</t>
4401</section>
4402
4403<section title="Since draft-ietf-httpbis-p2-semantics-07" anchor="changes.since.07">
4404<t>
4405  Closed issues:
4406  <list style="symbols"> 
4407    <t>
4408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/27"/>:
4409      "Idempotency"
4410    </t>
4411    <t>
4412      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/33"/>:
4413      "TRACE security considerations"
4414    </t>
4415    <t>
4416      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/110"/>:
4417      "Clarify rules for determining what entities a response carries"
4418    </t>
4419    <t>
4420      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/140"/>:
4421      "update note citing RFC 1945 and 2068"
4422    </t>
4423    <t>
4424      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/182"/>:
4425      "update note about redirect limit"
4426    </t>
4427    <t>
4428      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/191"/>:
4429      "Location header ABNF should use 'URI'"
4430    </t>
4431    <t>
4432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/192"/>:
4433      "fragments in Location vs status 303"
4434    </t>
4435    <t>
4436      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/198"/>:
4437      "move IANA registrations for optional status codes"
4438    </t>
4439  </list>
4440</t>
4441<t>
4442  Partly resolved issues:
4443  <list style="symbols"> 
4444    <t>
4445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/171"/>:
4446      "Are OPTIONS and TRACE safe?"
4447    </t>
4448  </list>
4449</t>
4450</section>
4451
4452<section title="Since draft-ietf-httpbis-p2-semantics-08" anchor="changes.since.08">
4453<t>
4454  Closed issues:
4455  <list style="symbols"> 
4456    <t>
4457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/10"/>:
4458      "Safe Methods vs Redirection" (we missed the introduction to the 3xx
4459      status codes when fixing this previously)
4460    </t>
4461  </list>
4462</t>
4463</section>
4464
4465<section title="Since draft-ietf-httpbis-p2-semantics-09" anchor="changes.since.09">
4466<t>
4467  Closed issues:
4468  <list style="symbols"> 
4469    <t>
4470      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4471      "Fragment combination / precedence during redirects"
4472    </t>
4473  </list>
4474</t>
4475<t>
4476  Partly resolved issues:
4477  <list style="symbols"> 
4478    <t>
4479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4480      "Location header payload handling"
4481    </t>
4482    <t>
4483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
4484      "Term for the requested resource's URI"
4485    </t>
4486  </list>
4487</t>
4488</section>
4489
4490<section title="Since draft-ietf-httpbis-p2-semantics-10" anchor="changes.since.10">
4491<t>
4492  Closed issues:
4493  <list style="symbols"> 
4494    <t>
4495      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/69"/>:
4496      "Clarify 'Requested Variant'"
4497    </t>
4498    <t>
4499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
4500      "Clarify entity / representation / variant terminology"
4501    </t>
4502    <t>
4503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/139"/>:
4504      "Methods and Caching"
4505    </t>
4506    <t>
4507      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/190"/>:
4508      "OPTIONS vs Max-Forwards"
4509    </t>
4510    <t>
4511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/199"/>:
4512      "Status codes and caching"
4513    </t>
4514    <t>
4515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
4516      "consider removing the 'changes from 2068' sections"
4517    </t>
4518  </list>
4519</t>
4520</section>
4521
4522<section title="Since draft-ietf-httpbis-p2-semantics-11" anchor="changes.since.11">
4523<t>
4524  Closed issues:
4525  <list style="symbols"> 
4526    <t>
4527      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/229"/>:
4528      "Considerations for new status codes"
4529    </t>
4530    <t>
4531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/230"/>:
4532      "Considerations for new methods"
4533    </t>
4534    <t>
4535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/232"/>:
4536      "User-Agent guidelines" (relating to the 'User-Agent' header field)
4537    </t>
4538  </list>
4539</t>
4540</section>
4541
4542<section title="Since draft-ietf-httpbis-p2-semantics-12" anchor="changes.since.12">
4543<t>
4544  Closed issues:
4545  <list style="symbols"> 
4546    <t>
4547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/43"/>:
4548      "Fragment combination / precedence during redirects" (added warning
4549      about having a fragid on the redirect may cause inconvenience in
4550      some cases)
4551    </t>
4552    <t>
4553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/79"/>:
4554      "Content-* vs. PUT"
4555    </t>
4556    <t>
4557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
4558      "205 Bodies"
4559    </t>
4560    <t>
4561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/102"/>:
4562      "Understanding Content-* on non-PUT requests"
4563    </t>
4564    <t>
4565      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/103"/>:
4566      "Content-*"
4567    </t>
4568    <t>
4569      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/104"/>:
4570      "Header type defaulting"
4571    </t>
4572    <t>
4573      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/112"/>:
4574      "PUT - 'store under' vs 'store at'"
4575    </t>
4576    <t>
4577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/137"/>:
4578      "duplicate ABNF for reason-phrase"
4579    </t>
4580    <t>
4581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/180"/>:
4582      "Note special status of Content-* prefix in header registration procedures"
4583    </t>
4584    <t>
4585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/203"/>:
4586      "Max-Forwards vs extension methods"
4587    </t>
4588    <t>
4589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/213"/>:
4590      "What is the value space of HTTP status codes?" (actually fixed in
4591      draft-ietf-httpbis-p2-semantics-11)
4592    </t>
4593    <t>
4594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
4595      "Header Classification"
4596    </t>
4597    <t>
4598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/225"/>:
4599      "PUT side effect: invalidation or just stale?"
4600    </t>
4601    <t>
4602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/226"/>:
4603      "proxies not supporting certain methods"
4604    </t>
4605    <t>
4606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/239"/>:
4607      "Migrate CONNECT from RFC2817 to p2"
4608    </t>
4609    <t>
4610      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
4611      "Migrate Upgrade details from RFC2817"
4612    </t>
4613    <t>
4614      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/267"/>:
4615      "clarify PUT semantics'"
4616    </t>
4617    <t>
4618      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/275"/>:
4619      "duplicate ABNF for 'Method'"
4620    </t>
4621    <t>
4622      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4623      "untangle ABNFs for header fields"
4624    </t>
4625  </list>
4626</t>
4627</section>
4628
4629<section title="Since draft-ietf-httpbis-p2-semantics-13" anchor="changes.since.13">
4630<t>
4631  Closed issues:
4632  <list style="symbols"> 
4633    <t>
4634      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
4635      "untangle ABNFs for header fields"
4636    </t>
4637    <t>
4638      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/251"/>:
4639      "message body in CONNECT request"
4640    </t>
4641  </list>
4642</t>
4643</section>
4644
4645<section title="Since draft-ietf-httpbis-p2-semantics-14" anchor="changes.since.14">
4646<t>
4647  Closed issues:
4648  <list style="symbols"> 
4649    <t>
4650      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4651      "Clarify status code for rate limiting"
4652    </t>
4653    <t>
4654      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/294"/>:
4655      "clarify 403 forbidden"
4656    </t>
4657    <t>
4658      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/296"/>:
4659      "Clarify 203 Non-Authoritative Information"
4660    </t>
4661    <t>
4662      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/298"/>:
4663      "update default reason phrase for 413"
4664    </t>
4665  </list>
4666</t>
4667</section>
4668
4669<section title="Since draft-ietf-httpbis-p2-semantics-15" anchor="changes.since.15">
4670<t>
4671  Closed issues:
4672  <list style="symbols"> 
4673    <t>
4674      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/285"/>:
4675      "Strength of requirements on Accept re: 406"
4676    </t>
4677    <t>
4678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/303"/>:
4679      "400 response isn't generic"
4680    </t>
4681  </list>
4682</t>
4683</section>
4684
4685<section title="Since draft-ietf-httpbis-p2-semantics-16" anchor="changes.since.16">
4686<t>
4687  Closed issues:
4688  <list style="symbols"> 
4689    <t>
4690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/160"/>:
4691      "Redirects and non-GET methods"
4692    </t>
4693    <t>
4694      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
4695      "Document HTTP's error-handling philosophy"
4696    </t>
4697    <t>
4698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/231"/>:
4699      "Considerations for new headers"
4700    </t>
4701    <t>
4702      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/310"/>:
4703      "clarify 303 redirect on HEAD"
4704    </t>
4705  </list>
4706</t>
4707</section>
4708
4709<section title="Since draft-ietf-httpbis-p2-semantics-17" anchor="changes.since.17">
4710<t>
4711  Closed issues:
4712  <list style="symbols"> 
4713    <t>
4714      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/185"/>:
4715      "Location header payload handling"
4716    </t>
4717    <t>
4718      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/255"/>:
4719      "Clarify status code for rate limiting" (change backed out because
4720      a new status code is being defined for this purpose)
4721    </t>
4722    <t>
4723      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4724      "should there be a permanent variant of 307"
4725    </t>
4726    <t>
4727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/325"/>:
4728      "When are Location's semantics triggered?"
4729    </t>
4730    <t>
4731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/327"/>:
4732      "'expect' grammar missing OWS"
4733    </t>
4734    <t>
4735      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/329"/>:
4736      "header field considerations: quoted-string vs use of double quotes"
4737    </t>
4738  </list>
4739</t>
4740</section>
4741
4742<section title="Since draft-ietf-httpbis-p2-semantics-18" anchor="changes.since.18">
4743<t>
4744  Closed issues:
4745  <list style="symbols"> 
4746    <t>
4747      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/227"/>:
4748      "Combining HEAD responses"
4749    </t>
4750    <t>
4751      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/238"/>:
4752      "Requirements for user intervention during redirects"
4753    </t>
4754    <t>
4755      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/250"/>:
4756      "message-body in CONNECT response"
4757    </t>
4758    <t>
4759      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/295"/>:
4760      "Applying original fragment to 'plain' redirected URI"
4761    </t>
4762    <t>
4763      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
4764      "Misplaced text on connection handling in p2"
4765    </t>
4766    <t>
4767      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/331"/>:
4768      "clarify that 201 doesn't require Location header fields"
4769    </t>
4770    <t>
4771      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/332"/>:
4772      "relax requirements on hypertext in 3/4/5xx error responses"
4773    </t>
4774    <t>
4775      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/333"/>:
4776      "example for 426 response should have a payload"
4777    </t>
4778    <t>
4779      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/336"/>:
4780      "drop indirection entries for status codes"
4781    </t>
4782  </list>
4783</t>
4784</section>
4785
4786<section title="Since draft-ietf-httpbis-p2-semantics-19" anchor="changes.since.19">
4787<t>
4788  Closed issues:
4789  <list style="symbols"> 
4790    <t>
4791      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/312"/>:
4792      "should there be a permanent variant of 307"
4793    </t>
4794  </list>
4795</t>
4796</section>
4797
4798</section>
4799
4800</back>
4801</rfc>
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