source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1535

Last change on this file since 1535 was 1535, checked in by julian.reschke@…, 8 years ago

Discourage use of chunk-extensions and deprecate definition of new ones (see #343)

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 242.8 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "February">
16  <!ENTITY ID-YEAR "2012">
17  <!ENTITY mdash "&#8212;">
18  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#response.cacheability' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-date            "<xref target='Part2' x:rel='#header.date' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-code-reasonphr  "<xref target='Part2' x:rel='#status.code.and.reason.phrase' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41  <!ENTITY status-4xx             "<xref target='Part2' x:rel='#status.4xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
42  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
43  <!ENTITY cons-new-header-fields "<xref target='Part2' x:rel='#considerations.for.creating.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
44]>
45<?rfc toc="yes" ?>
46<?rfc symrefs="yes" ?>
47<?rfc sortrefs="yes" ?>
48<?rfc compact="yes"?>
49<?rfc subcompact="no" ?>
50<?rfc linkmailto="no" ?>
51<?rfc editing="no" ?>
52<?rfc comments="yes"?>
53<?rfc inline="yes"?>
54<?rfc rfcedstyle="yes"?>
55<?rfc-ext allow-markup-in-artwork="yes" ?>
56<?rfc-ext include-references-in-index="yes" ?>
57<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="proposed"
58     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
59     xmlns:x='http://purl.org/net/xml2rfc/ext'>
60<x:link rel="next" basename="p2-semantics"/>
61<x:feedback template="mailto:ietf-http-wg@w3.org?subject={docname},%20%22{section}%22&amp;body=&lt;{ref}&gt;:"/>
62<front>
63
64  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
65
66  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
67    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
68    <address>
69      <postal>
70        <street>345 Park Ave</street>
71        <city>San Jose</city>
72        <region>CA</region>
73        <code>95110</code>
74        <country>USA</country>
75      </postal>
76      <email>fielding@gbiv.com</email>
77      <uri>http://roy.gbiv.com/</uri>
78    </address>
79  </author>
80
81  <author initials="J." surname="Gettys" fullname="Jim Gettys">
82    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
83    <address>
84      <postal>
85        <street>21 Oak Knoll Road</street>
86        <city>Carlisle</city>
87        <region>MA</region>
88        <code>01741</code>
89        <country>USA</country>
90      </postal>
91      <email>jg@freedesktop.org</email>
92      <uri>http://gettys.wordpress.com/</uri>
93    </address>
94  </author>
95 
96  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
97    <organization abbrev="HP">Hewlett-Packard Company</organization>
98    <address>
99      <postal>
100        <street>HP Labs, Large Scale Systems Group</street>
101        <street>1501 Page Mill Road, MS 1177</street>
102        <city>Palo Alto</city>
103        <region>CA</region>
104        <code>94304</code>
105        <country>USA</country>
106      </postal>
107      <email>JeffMogul@acm.org</email>
108    </address>
109  </author>
110
111  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
112    <organization abbrev="Microsoft">Microsoft Corporation</organization>
113    <address>
114      <postal>
115        <street>1 Microsoft Way</street>
116        <city>Redmond</city>
117        <region>WA</region>
118        <code>98052</code>
119        <country>USA</country>
120      </postal>
121      <email>henrikn@microsoft.com</email>
122    </address>
123  </author>
124
125  <author initials="L." surname="Masinter" fullname="Larry Masinter">
126    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
127    <address>
128      <postal>
129        <street>345 Park Ave</street>
130        <city>San Jose</city>
131        <region>CA</region>
132        <code>95110</code>
133        <country>USA</country>
134      </postal>
135      <email>LMM@acm.org</email>
136      <uri>http://larry.masinter.net/</uri>
137    </address>
138  </author>
139 
140  <author initials="P." surname="Leach" fullname="Paul J. Leach">
141    <organization abbrev="Microsoft">Microsoft Corporation</organization>
142    <address>
143      <postal>
144        <street>1 Microsoft Way</street>
145        <city>Redmond</city>
146        <region>WA</region>
147        <code>98052</code>
148      </postal>
149      <email>paulle@microsoft.com</email>
150    </address>
151  </author>
152   
153  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
154    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
155    <address>
156      <postal>
157        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
158        <street>The Stata Center, Building 32</street>
159        <street>32 Vassar Street</street>
160        <city>Cambridge</city>
161        <region>MA</region>
162        <code>02139</code>
163        <country>USA</country>
164      </postal>
165      <email>timbl@w3.org</email>
166      <uri>http://www.w3.org/People/Berners-Lee/</uri>
167    </address>
168  </author>
169
170  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
171    <organization abbrev="W3C">World Wide Web Consortium</organization>
172    <address>
173      <postal>
174        <street>W3C / ERCIM</street>
175        <street>2004, rte des Lucioles</street>
176        <city>Sophia-Antipolis</city>
177        <region>AM</region>
178        <code>06902</code>
179        <country>France</country>
180      </postal>
181      <email>ylafon@w3.org</email>
182      <uri>http://www.raubacapeu.net/people/yves/</uri>
183    </address>
184  </author>
185
186  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
187    <organization abbrev="greenbytes">greenbytes GmbH</organization>
188    <address>
189      <postal>
190        <street>Hafenweg 16</street>
191        <city>Muenster</city><region>NW</region><code>48155</code>
192        <country>Germany</country>
193      </postal>
194      <phone>+49 251 2807760</phone>
195      <facsimile>+49 251 2807761</facsimile>
196      <email>julian.reschke@greenbytes.de</email>
197      <uri>http://greenbytes.de/tech/webdav/</uri>
198    </address>
199  </author>
200
201  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
202  <workgroup>HTTPbis Working Group</workgroup>
203
204<abstract>
205<t>
206   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
207   distributed, collaborative, hypertext information systems. HTTP has been in
208   use by the World Wide Web global information initiative since 1990. This
209   document is Part 1 of the seven-part specification that defines the protocol
210   referred to as "HTTP/1.1" and, taken together, obsoletes
211   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
212   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
213   2068</xref>.
214</t>
215<t>
216   Part 1 provides an overview of HTTP and its associated terminology, defines
217   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
218   the generic message syntax and parsing requirements for HTTP message frames,
219   and describes general security concerns for implementations.
220</t>
221<t>
222   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
223   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
224   (on using CONNECT for TLS upgrades) and moves them to historic status.
225</t>
226</abstract>
227
228<note title="Editorial Note (To be removed by RFC Editor)">
229  <t>
230    Discussion of this draft should take place on the HTTPBIS working group
231    mailing list (ietf-http-wg@w3.org), which is archived at
232    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
233  </t>
234  <t>
235    The current issues list is at
236    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
237    documents (including fancy diffs) can be found at
238    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
239  </t>
240  <t>
241    The changes in this draft are summarized in <xref target="changes.since.18"/>.
242  </t>
243</note>
244</front>
245<middle>
246<section title="Introduction" anchor="introduction">
247<t>
248   The Hypertext Transfer Protocol (HTTP) is an application-level
249   request/response protocol that uses extensible semantics and MIME-like
250   message payloads for flexible interaction with network-based hypertext
251   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
252   standard <xref target="RFC3986"/> to indicate the target resource and
253   relationships between resources.
254   Messages are passed in a format similar to that used by Internet mail
255   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
256   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
257   between HTTP and MIME messages).
258</t>
259<t>
260   HTTP is a generic interface protocol for information systems. It is
261   designed to hide the details of how a service is implemented by presenting
262   a uniform interface to clients that is independent of the types of
263   resources provided. Likewise, servers do not need to be aware of each
264   client's purpose: an HTTP request can be considered in isolation rather
265   than being associated with a specific type of client or a predetermined
266   sequence of application steps. The result is a protocol that can be used
267   effectively in many different contexts and for which implementations can
268   evolve independently over time.
269</t>
270<t>
271   HTTP is also designed for use as an intermediation protocol for translating
272   communication to and from non-HTTP information systems.
273   HTTP proxies and gateways can provide access to alternative information
274   services by translating their diverse protocols into a hypertext
275   format that can be viewed and manipulated by clients in the same way
276   as HTTP services.
277</t>
278<t>
279   One consequence of HTTP flexibility is that the protocol cannot be
280   defined in terms of what occurs behind the interface. Instead, we
281   are limited to defining the syntax of communication, the intent
282   of received communication, and the expected behavior of recipients.
283   If the communication is considered in isolation, then successful
284   actions ought to be reflected in corresponding changes to the
285   observable interface provided by servers. However, since multiple
286   clients might act in parallel and perhaps at cross-purposes, we
287   cannot require that such changes be observable beyond the scope
288   of a single response.
289</t>
290<t>
291   This document is Part 1 of the seven-part specification of HTTP,
292   defining the protocol referred to as "HTTP/1.1", obsoleting
293   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
294   Part 1 describes the architectural elements that are used or
295   referred to in HTTP, defines the "http" and "https" URI schemes,
296   describes overall network operation and connection management,
297   and defines HTTP message framing and forwarding requirements.
298   Our goal is to define all of the mechanisms necessary for HTTP message
299   handling that are independent of message semantics, thereby defining the
300   complete set of requirements for message parsers and
301   message-forwarding intermediaries.
302</t>
303
304<section title="Requirement Notation" anchor="intro.requirements">
305<t>
306   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
307   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
308   document are to be interpreted as described in <xref target="RFC2119"/>.
309</t>
310</section>
311
312<section title="Syntax Notation" anchor="notation">
313<iref primary="true" item="Grammar" subitem="ALPHA"/>
314<iref primary="true" item="Grammar" subitem="CR"/>
315<iref primary="true" item="Grammar" subitem="CRLF"/>
316<iref primary="true" item="Grammar" subitem="CTL"/>
317<iref primary="true" item="Grammar" subitem="DIGIT"/>
318<iref primary="true" item="Grammar" subitem="DQUOTE"/>
319<iref primary="true" item="Grammar" subitem="HEXDIG"/>
320<iref primary="true" item="Grammar" subitem="HTAB"/>
321<iref primary="true" item="Grammar" subitem="LF"/>
322<iref primary="true" item="Grammar" subitem="OCTET"/>
323<iref primary="true" item="Grammar" subitem="SP"/>
324<iref primary="true" item="Grammar" subitem="VCHAR"/>
325<t>
326   This specification uses the Augmented Backus-Naur Form (ABNF) notation
327   of <xref target="RFC5234"/> with the list rule extension defined in
328   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
329   the collected ABNF with the list rule expanded.
330</t>
331<t anchor="core.rules">
332  <x:anchor-alias value="ALPHA"/>
333  <x:anchor-alias value="CTL"/>
334  <x:anchor-alias value="CR"/>
335  <x:anchor-alias value="CRLF"/>
336  <x:anchor-alias value="DIGIT"/>
337  <x:anchor-alias value="DQUOTE"/>
338  <x:anchor-alias value="HEXDIG"/>
339  <x:anchor-alias value="HTAB"/>
340  <x:anchor-alias value="LF"/>
341  <x:anchor-alias value="OCTET"/>
342  <x:anchor-alias value="SP"/>
343  <x:anchor-alias value="VCHAR"/>
344   The following core rules are included by
345   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
346   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
347   DIGIT (decimal 0-9), DQUOTE (double quote),
348   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
349   OCTET (any 8-bit sequence of data), SP (space), and
350   VCHAR (any visible <xref target="USASCII"/> character).
351</t>
352<t>
353   As a convention, ABNF rule names prefixed with "obs-" denote
354   "obsolete" grammar rules that appear for historical reasons.
355</t>
356</section>
357</section>
358
359<section title="Architecture" anchor="architecture">
360<t>
361   HTTP was created for the World Wide Web architecture
362   and has evolved over time to support the scalability needs of a worldwide
363   hypertext system. Much of that architecture is reflected in the terminology
364   and syntax productions used to define HTTP.
365</t>
366
367<section title="Client/Server Messaging" anchor="operation">
368<iref primary="true" item="client"/>
369<iref primary="true" item="server"/>
370<iref primary="true" item="connection"/>
371<t>
372   HTTP is a stateless request/response protocol that operates by exchanging
373   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
374   transport or session-layer
375   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
376   program that establishes a connection to a server for the purpose of
377   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
378   program that accepts connections in order to service HTTP requests by
379   sending HTTP responses.
380</t>
381<iref primary="true" item="user agent"/>
382<iref primary="true" item="origin server"/>
383<iref primary="true" item="browser"/>
384<iref primary="true" item="spider"/>
385<iref primary="true" item="sender"/>
386<iref primary="true" item="recipient"/>
387<t>
388   Note that the terms client and server refer only to the roles that
389   these programs perform for a particular connection.  The same program
390   might act as a client on some connections and a server on others.  We use
391   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
392   such as a WWW browser, editor, or spider (web-traversing robot), and
393   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
394   authoritative responses to a request.  For general requirements, we use
395   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
396   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
397   message.
398</t>
399<x:note>
400  <t>
401    <x:h>Note:</x:h> The term 'user agent' covers both those situations where
402    there is a user (human) interacting with the software agent (and for which
403    user interface or interactive suggestions might be made, e.g., warning the
404    user or given the user an option in the case of security or privacy
405    options) and also those where the software agent may act autonomously.
406  </t>
407</x:note>
408<t>
409   Most HTTP communication consists of a retrieval request (GET) for
410   a representation of some resource identified by a URI.  In the
411   simplest case, this might be accomplished via a single bidirectional
412   connection (===) between the user agent (UA) and the origin server (O).
413</t>
414<figure><artwork type="drawing">
415         request   &gt;
416    UA ======================================= O
417                                &lt;   response
418</artwork></figure>
419<iref primary="true" item="message"/>
420<iref primary="true" item="request"/>
421<iref primary="true" item="response"/>
422<t>
423   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
424   message, beginning with a request-line that includes a method, URI, and
425   protocol version (<xref target="request.line"/>),
426   followed by MIME-like header fields containing
427   request modifiers, client information, and payload metadata
428   (<xref target="header.fields"/>),
429   an empty line to indicate the end of the header section, and finally
430   a message body containing the payload body (if any,
431   <xref target="message.body"/>).
432</t>
433<t>
434   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
435   message, beginning with a status line that
436   includes the protocol version, a success or error code, and textual
437   reason phrase (<xref target="status.line"/>),
438   followed by MIME-like header fields containing server
439   information, resource metadata, and payload metadata
440   (<xref target="header.fields"/>),
441   an empty line to indicate the end of the header section, and finally
442   a message body containing the payload body (if any,
443   <xref target="message.body"/>).
444</t>
445<t>
446   Note that 1xx responses (&status-1xx;) are not final; therefore, a server
447   can send zero or more 1xx responses, followed by exactly one final response
448   (with any other status code).
449</t>
450<t>
451   The following example illustrates a typical message exchange for a
452   GET request on the URI "http://www.example.com/hello.txt":
453</t>
454<figure><preamble>
455client request:
456</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
457GET /hello.txt HTTP/1.1
458User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
459Host: www.example.com
460Accept: */*
461
462</artwork></figure>
463<figure><preamble>
464server response:
465</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
466HTTP/1.1 200 OK
467Date: Mon, 27 Jul 2009 12:28:53 GMT
468Server: Apache
469Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
470ETag: "34aa387-d-1568eb00"
471Accept-Ranges: bytes
472Content-Length: <x:length-of target="exbody"/>
473Vary: Accept-Encoding
474Content-Type: text/plain
475
476<x:span anchor="exbody">Hello World!
477</x:span></artwork></figure>
478</section>
479
480<section title="Connections and Transport Independence" anchor="transport-independence">
481<t>
482   HTTP messaging is independent of the underlying transport or
483   session-layer connection protocol(s).  HTTP only presumes a reliable
484   transport with in-order delivery of requests and the corresponding
485   in-order delivery of responses.  The mapping of HTTP request and
486   response structures onto the data units of the underlying transport
487   protocol is outside the scope of this specification.
488</t>
489<t>
490   The specific connection protocols to be used for an interaction
491   are determined by client configuration and the target resource's URI.
492   For example, the "http" URI scheme
493   (<xref target="http.uri"/>) indicates a default connection of TCP
494   over IP, with a default TCP port of 80, but the client might be
495   configured to use a proxy via some other connection port or protocol
496   instead of using the defaults.
497</t>
498<t>
499   A connection might be used for multiple HTTP request/response exchanges,
500   as defined in <xref target="persistent.connections"/>.
501</t>
502</section>
503
504<section title="Intermediaries" anchor="intermediaries">
505<iref primary="true" item="intermediary"/>
506<t>
507   HTTP enables the use of intermediaries to satisfy requests through
508   a chain of connections.  There are three common forms of HTTP
509   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
510   a single intermediary might act as an origin server, proxy, gateway,
511   or tunnel, switching behavior based on the nature of each request.
512</t>
513<figure><artwork type="drawing">
514         &gt;             &gt;             &gt;             &gt;
515    <x:highlight>UA</x:highlight> =========== <x:highlight>A</x:highlight> =========== <x:highlight>B</x:highlight> =========== <x:highlight>C</x:highlight> =========== <x:highlight>O</x:highlight>
516               &lt;             &lt;             &lt;             &lt;
517</artwork></figure>
518<t>
519   The figure above shows three intermediaries (A, B, and C) between the
520   user agent and origin server. A request or response message that
521   travels the whole chain will pass through four separate connections.
522   Some HTTP communication options
523   might apply only to the connection with the nearest, non-tunnel
524   neighbor, only to the end-points of the chain, or to all connections
525   along the chain. Although the diagram is linear, each participant might
526   be engaged in multiple, simultaneous communications. For example, B
527   might be receiving requests from many clients other than A, and/or
528   forwarding requests to servers other than C, at the same time that it
529   is handling A's request.
530</t>
531<t>
532<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
533<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
534   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
535   to describe various requirements in relation to the directional flow of a
536   message: all messages flow from upstream to downstream.
537   Likewise, we use the terms inbound and outbound to refer to
538   directions in relation to the request path:
539   "<x:dfn>inbound</x:dfn>" means toward the origin server and
540   "<x:dfn>outbound</x:dfn>" means toward the user agent.
541</t>
542<t><iref primary="true" item="proxy"/>
543   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
544   client, usually via local configuration rules, to receive requests
545   for some type(s) of absolute URI and attempt to satisfy those
546   requests via translation through the HTTP interface.  Some translations
547   are minimal, such as for proxy requests for "http" URIs, whereas
548   other requests might require translation to and from entirely different
549   application-layer protocols. Proxies are often used to group an
550   organization's HTTP requests through a common intermediary for the
551   sake of security, annotation services, or shared caching.
552</t>
553<t>
554<iref primary="true" item="transforming proxy"/>
555<iref primary="true" item="non-transforming proxy"/>
556   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
557   or configured to modify request or response messages in a semantically
558   meaningful way (i.e., modifications, beyond those required by normal
559   HTTP processing, that change the message in a way that would be
560   significant to the original sender or potentially significant to
561   downstream recipients).  For example, a transforming proxy might be
562   acting as a shared annotation server (modifying responses to include
563   references to a local annotation database), a malware filter, a
564   format transcoder, or an intranet-to-Internet privacy filter.  Such
565   transformations are presumed to be desired by the client (or client
566   organization) that selected the proxy and are beyond the scope of
567   this specification.  However, when a proxy is not intended to transform
568   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
569   requirements that preserve HTTP message semantics. See &status-203; and
570   &header-warning; for status and warning codes related to transformations.
571</t>
572<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
573<iref primary="true" item="accelerator"/>
574   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
575   is a receiving agent that acts
576   as a layer above some other server(s) and translates the received
577   requests to the underlying server's protocol.  Gateways are often
578   used to encapsulate legacy or untrusted information services, to
579   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
580   enable partitioning or load-balancing of HTTP services across
581   multiple machines.
582</t>
583<t>
584   A gateway behaves as an origin server on its outbound connection and
585   as a user agent on its inbound connection.
586   All HTTP requirements applicable to an origin server
587   also apply to the outbound communication of a gateway.
588   A gateway communicates with inbound servers using any protocol that
589   it desires, including private extensions to HTTP that are outside
590   the scope of this specification.  However, an HTTP-to-HTTP gateway
591   that wishes to interoperate with third-party HTTP servers &MUST;
592   conform to HTTP user agent requirements on the gateway's inbound
593   connection and &MUST; implement the Connection
594   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
595   header fields for both connections.
596</t>
597<t><iref primary="true" item="tunnel"/>
598   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
599   without changing the messages. Once active, a tunnel is not
600   considered a party to the HTTP communication, though the tunnel might
601   have been initiated by an HTTP request. A tunnel ceases to exist when
602   both ends of the relayed connection are closed. Tunnels are used to
603   extend a virtual connection through an intermediary, such as when
604   transport-layer security is used to establish private communication
605   through a shared firewall proxy.
606</t>
607<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
608<iref primary="true" item="captive portal"/>
609   In addition, there may exist network intermediaries that are not
610   considered part of the HTTP communication but nevertheless act as
611   filters or redirecting agents (usually violating HTTP semantics,
612   causing security problems, and otherwise making a mess of things).
613   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
614   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
615   or "<x:dfn>captive portal</x:dfn>",
616   differs from an HTTP proxy because it has not been selected by the client.
617   Instead, the network intermediary redirects outgoing TCP port 80 packets
618   (and occasionally other common port traffic) to an internal HTTP server.
619   Interception proxies are commonly found on public network access points,
620   as a means of enforcing account subscription prior to allowing use of
621   non-local Internet services, and within corporate firewalls to enforce
622   network usage policies.
623   They are indistinguishable from a man-in-the-middle attack.
624</t>
625<t>
626   HTTP is defined as a stateless protocol, meaning that each request message
627   can be understood in isolation.  Many implementations depend on HTTP's
628   stateless design in order to reuse proxied connections or dynamically
629   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
630   assume that two requests on the same connection are from the same user
631   agent unless the connection is secured and specific to that agent.
632   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
633   been known to violate this requirement, resulting in security and
634   interoperability problems.
635</t>
636</section>
637
638<section title="Caches" anchor="caches">
639<iref primary="true" item="cache"/>
640<t>
641   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
642   subsystem that controls its message storage, retrieval, and deletion.
643   A cache stores cacheable responses in order to reduce the response
644   time and network bandwidth consumption on future, equivalent
645   requests. Any client or server &MAY; employ a cache, though a cache
646   cannot be used by a server while it is acting as a tunnel.
647</t>
648<t>
649   The effect of a cache is that the request/response chain is shortened
650   if one of the participants along the chain has a cached response
651   applicable to that request. The following illustrates the resulting
652   chain if B has a cached copy of an earlier response from O (via C)
653   for a request which has not been cached by UA or A.
654</t>
655<figure><artwork type="drawing">
656            &gt;             &gt;
657       UA =========== A =========== B - - - - - - C - - - - - - O
658                  &lt;             &lt;
659</artwork></figure>
660<t><iref primary="true" item="cacheable"/>
661   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
662   the response message for use in answering subsequent requests.
663   Even when a response is cacheable, there might be additional
664   constraints placed by the client or by the origin server on when
665   that cached response can be used for a particular request. HTTP
666   requirements for cache behavior and cacheable responses are
667   defined in &caching-overview;
668</t>
669<t>
670   There are a wide variety of architectures and configurations
671   of caches and proxies deployed across the World Wide Web and
672   inside large organizations. These systems include national hierarchies
673   of proxy caches to save transoceanic bandwidth, systems that
674   broadcast or multicast cache entries, organizations that distribute
675   subsets of cached data via optical media, and so on.
676</t>
677</section>
678
679<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
680<t>
681   This specification targets conformance criteria according to the role of
682   a participant in HTTP communication.  Hence, HTTP requirements are placed
683   on senders, recipients, clients, servers, user agents, intermediaries,
684   origin servers, proxies, gateways, or caches, depending on what behavior
685   is being constrained by the requirement.
686</t>
687<t>
688   An implementation is considered conformant if it complies with all of the
689   requirements associated with the roles it partakes in HTTP.
690</t>
691<t>
692   Senders &MUST-NOT; generate protocol elements that do not match the grammar
693   defined by the ABNF rules for those protocol elements.
694</t>
695<t>
696   Unless otherwise noted, recipients &MAY; attempt to recover a usable
697   protocol element from an invalid construct.  HTTP does not define
698   specific error handling mechanisms except when they have a direct impact
699   on security, since different applications of the protocol require
700   different error handling strategies.  For example, a Web browser might
701   wish to transparently recover from a response where the Location header
702   field doesn't parse according to the ABNF, whereas a systems control
703   client might consider any form of error recovery to be dangerous.
704</t>
705</section>
706
707<section title="Protocol Versioning" anchor="http.version">
708  <x:anchor-alias value="HTTP-Version"/>
709  <x:anchor-alias value="HTTP-Prot-Name"/>
710<t>
711   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
712   versions of the protocol. This specification defines version "1.1".
713   The protocol version as a whole indicates the sender's conformance
714   with the set of requirements laid out in that version's corresponding
715   specification of HTTP.
716</t>
717<t>
718   The version of an HTTP message is indicated by an HTTP-Version field
719   in the first line of the message. HTTP-Version is case-sensitive.
720</t>
721<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
722  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
723  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
724</artwork></figure>
725<t>
726   The HTTP version number consists of two decimal digits separated by a "."
727   (period or decimal point).  The first digit ("major version") indicates the
728   HTTP messaging syntax, whereas the second digit ("minor version") indicates
729   the highest minor version to which the sender is
730   conformant and able to understand for future communication.  The minor
731   version advertises the sender's communication capabilities even when the
732   sender is only using a backwards-compatible subset of the protocol,
733   thereby letting the recipient know that more advanced features can
734   be used in response (by servers) or in future requests (by clients).
735</t>
736<t>
737   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
738   <xref target="RFC1945"/> or a recipient whose version is unknown,
739   the HTTP/1.1 message is constructed such that it can be interpreted
740   as a valid HTTP/1.0 message if all of the newer features are ignored.
741   This specification places recipient-version requirements on some
742   new features so that a conformant sender will only use compatible
743   features until it has determined, through configuration or the
744   receipt of a message, that the recipient supports HTTP/1.1.
745</t>
746<t>
747   The interpretation of an HTTP header field does not change
748   between minor versions of the same major version, though the default
749   behavior of a recipient in the absence of such a field can change.
750   Unless specified otherwise, header fields defined in HTTP/1.1 are
751   defined for all versions of HTTP/1.x.  In particular, the Host and
752   Connection header fields ought to be implemented by all HTTP/1.x
753   implementations whether or not they advertise conformance with HTTP/1.1.
754</t>
755<t>
756   New header fields can be defined such that, when they are
757   understood by a recipient, they might override or enhance the
758   interpretation of previously defined header fields.  When an
759   implementation receives an unrecognized header field, the recipient
760   &MUST; ignore that header field for local processing regardless of
761   the message's HTTP version.  An unrecognized header field received
762   by a proxy &MUST; be forwarded downstream unless the header field's
763   field-name is listed in the message's Connection header-field
764   (see <xref target="header.connection"/>).
765   These requirements allow HTTP's functionality to be enhanced without
766   requiring prior update of deployed intermediaries.
767</t>
768<t>
769   Intermediaries that process HTTP messages (i.e., all intermediaries
770   other than those acting as tunnels) &MUST; send their own HTTP-Version
771   in forwarded messages.  In other words, they &MUST-NOT; blindly
772   forward the first line of an HTTP message without ensuring that the
773   protocol version in that message matches a version to which that
774   intermediary is conformant for both the receiving and
775   sending of messages.  Forwarding an HTTP message without rewriting
776   the HTTP-Version might result in communication errors when downstream
777   recipients use the message sender's version to determine what features
778   are safe to use for later communication with that sender.
779</t>
780<t>
781   An HTTP client &SHOULD; send a request version equal to the highest
782   version to which the client is conformant and
783   whose major version is no higher than the highest version supported
784   by the server, if this is known.  An HTTP client &MUST-NOT; send a
785   version to which it is not conformant.
786</t>
787<t>
788   An HTTP client &MAY; send a lower request version if it is known that
789   the server incorrectly implements the HTTP specification, but only
790   after the client has attempted at least one normal request and determined
791   from the response status or header fields (e.g., Server) that the
792   server improperly handles higher request versions.
793</t>
794<t>
795   An HTTP server &SHOULD; send a response version equal to the highest
796   version to which the server is conformant and
797   whose major version is less than or equal to the one received in the
798   request.  An HTTP server &MUST-NOT; send a version to which it is not
799   conformant.  A server &MAY; send a 505 (HTTP
800   Version Not Supported) response if it cannot send a response using the
801   major version used in the client's request.
802</t>
803<t>
804   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
805   if it is known or suspected that the client incorrectly implements the
806   HTTP specification and is incapable of correctly processing later
807   version responses, such as when a client fails to parse the version
808   number correctly or when an intermediary is known to blindly forward
809   the HTTP-Version even when it doesn't conform to the given minor
810   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
811   performed unless triggered by specific client attributes, such as when
812   one or more of the request header fields (e.g., User-Agent) uniquely
813   match the values sent by a client known to be in error.
814</t>
815<t>
816   The intention of HTTP's versioning design is that the major number
817   will only be incremented if an incompatible message syntax is
818   introduced, and that the minor number will only be incremented when
819   changes made to the protocol have the effect of adding to the message
820   semantics or implying additional capabilities of the sender.  However,
821   the minor version was not incremented for the changes introduced between
822   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
823   is specifically avoiding any such changes to the protocol.
824</t>
825</section>
826
827<section title="Uniform Resource Identifiers" anchor="uri">
828<iref primary="true" item="resource"/>
829<t>
830   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
831   throughout HTTP as the means for identifying resources. URI references
832   are used to target requests, indicate redirects, and define relationships.
833   HTTP does not limit what a resource might be; it merely defines an interface
834   that can be used to interact with a resource via HTTP. More information on
835   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
836</t>
837  <x:anchor-alias value="URI-reference"/>
838  <x:anchor-alias value="absolute-URI"/>
839  <x:anchor-alias value="relative-part"/>
840  <x:anchor-alias value="authority"/>
841  <x:anchor-alias value="path-abempty"/>
842  <x:anchor-alias value="path-absolute"/>
843  <x:anchor-alias value="port"/>
844  <x:anchor-alias value="query"/>
845  <x:anchor-alias value="uri-host"/>
846  <x:anchor-alias value="partial-URI"/>
847<t>
848   This specification adopts the definitions of "URI-reference",
849   "absolute-URI", "relative-part", "port", "host",
850   "path-abempty", "path-absolute", "query", and "authority" from the
851   URI generic syntax <xref target="RFC3986"/>.
852   In addition, we define a partial-URI rule for protocol elements
853   that allow a relative URI but not a fragment.
854</t>
855<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/>
856  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
857  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
858  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
859  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
860  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
861  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
862  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
863  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
864  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
865 
866  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
867</artwork></figure>
868<t>
869   Each protocol element in HTTP that allows a URI reference will indicate
870   in its ABNF production whether the element allows any form of reference
871   (URI-reference), only a URI in absolute form (absolute-URI), only the
872   path and optional query components, or some combination of the above.
873   Unless otherwise indicated, URI references are parsed relative to the
874   effective request URI, which defines the default base URI for references
875   in both the request and its corresponding response.
876</t>
877
878<section title="http URI scheme" anchor="http.uri">
879  <x:anchor-alias value="http-URI"/>
880  <iref item="http URI scheme" primary="true"/>
881  <iref item="URI scheme" subitem="http" primary="true"/>
882<t>
883   The "http" URI scheme is hereby defined for the purpose of minting
884   identifiers according to their association with the hierarchical
885   namespace governed by a potential HTTP origin server listening for
886   TCP connections on a given port.
887</t>
888<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
889  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
890</artwork></figure>
891<t>
892   The HTTP origin server is identified by the generic syntax's
893   <x:ref>authority</x:ref> component, which includes a host identifier
894   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
895   The remainder of the URI, consisting of both the hierarchical path
896   component and optional query component, serves as an identifier for
897   a potential resource within that origin server's name space.
898</t>
899<t>
900   If the host identifier is provided as an IP literal or IPv4 address,
901   then the origin server is any listener on the indicated TCP port at
902   that IP address. If host is a registered name, then that name is
903   considered an indirect identifier and the recipient might use a name
904   resolution service, such as DNS, to find the address of a listener
905   for that host.
906   The host &MUST-NOT; be empty; if an "http" URI is received with an
907   empty host, then it &MUST; be rejected as invalid.
908   If the port subcomponent is empty or not given, then TCP port 80 is
909   assumed (the default reserved port for WWW services).
910</t>
911<t>
912   Regardless of the form of host identifier, access to that host is not
913   implied by the mere presence of its name or address. The host might or might
914   not exist and, even when it does exist, might or might not be running an
915   HTTP server or listening to the indicated port. The "http" URI scheme
916   makes use of the delegated nature of Internet names and addresses to
917   establish a naming authority (whatever entity has the ability to place
918   an HTTP server at that Internet name or address) and allows that
919   authority to determine which names are valid and how they might be used.
920</t>
921<t>
922   When an "http" URI is used within a context that calls for access to the
923   indicated resource, a client &MAY; attempt access by resolving
924   the host to an IP address, establishing a TCP connection to that address
925   on the indicated port, and sending an HTTP request message
926   (<xref target="http.message"/>) containing the URI's identifying data
927   (<xref target="message.routing"/>) to the server.
928   If the server responds to that request with a non-interim HTTP response
929   message, as described in &status-code-reasonphr;, then that response
930   is considered an authoritative answer to the client's request.
931</t>
932<t>
933   Although HTTP is independent of the transport protocol, the "http"
934   scheme is specific to TCP-based services because the name delegation
935   process depends on TCP for establishing authority.
936   An HTTP service based on some other underlying connection protocol
937   would presumably be identified using a different URI scheme, just as
938   the "https" scheme (below) is used for servers that require an SSL/TLS
939   transport layer on a connection. Other protocols might also be used to
940   provide access to "http" identified resources &mdash; it is only the
941   authoritative interface used for mapping the namespace that is
942   specific to TCP.
943</t>
944<t>
945   The URI generic syntax for authority also includes a deprecated
946   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
947   for including user authentication information in the URI.  Some
948   implementations make use of the userinfo component for internal
949   configuration of authentication information, such as within command
950   invocation options, configuration files, or bookmark lists, even
951   though such usage might expose a user identifier or password.
952   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
953   delimiter) when transmitting an "http" URI in a message.  Recipients
954   of HTTP messages that contain a URI reference &SHOULD; parse for the
955   existence of userinfo and treat its presence as an error, likely
956   indicating that the deprecated subcomponent is being used to obscure
957   the authority for the sake of phishing attacks.
958</t>
959</section>
960
961<section title="https URI scheme" anchor="https.uri">
962   <x:anchor-alias value="https-URI"/>
963   <iref item="https URI scheme"/>
964   <iref item="URI scheme" subitem="https"/>
965<t>
966   The "https" URI scheme is hereby defined for the purpose of minting
967   identifiers according to their association with the hierarchical
968   namespace governed by a potential HTTP origin server listening for
969   SSL/TLS-secured connections on a given TCP port.
970</t>
971<t>
972   All of the requirements listed above for the "http" scheme are also
973   requirements for the "https" scheme, except that a default TCP port
974   of 443 is assumed if the port subcomponent is empty or not given,
975   and the TCP connection &MUST; be secured for privacy through the
976   use of strong encryption prior to sending the first HTTP request.
977</t>
978<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
979  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
980</artwork></figure>
981<t>
982   Unlike the "http" scheme, responses to "https" identified requests
983   are never "public" and thus &MUST-NOT; be reused for shared caching.
984   They can, however, be reused in a private cache if the message is
985   cacheable by default in HTTP or specifically indicated as such by
986   the Cache-Control header field (&header-cache-control;).
987</t>
988<t>
989   Resources made available via the "https" scheme have no shared
990   identity with the "http" scheme even if their resource identifiers
991   indicate the same authority (the same host listening to the same
992   TCP port).  They are distinct name spaces and are considered to be
993   distinct origin servers.  However, an extension to HTTP that is
994   defined to apply to entire host domains, such as the Cookie protocol
995   <xref target="RFC6265"/>, can allow information
996   set by one service to impact communication with other services
997   within a matching group of host domains.
998</t>
999<t>
1000   The process for authoritative access to an "https" identified
1001   resource is defined in <xref target="RFC2818"/>.
1002</t>
1003</section>
1004
1005<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1006<t>
1007   Since the "http" and "https" schemes conform to the URI generic syntax,
1008   such URIs are normalized and compared according to the algorithm defined
1009   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1010   described above for each scheme.
1011</t>
1012<t>
1013   If the port is equal to the default port for a scheme, the normal
1014   form is to elide the port subcomponent. Likewise, an empty path
1015   component is equivalent to an absolute path of "/", so the normal
1016   form is to provide a path of "/" instead. The scheme and host
1017   are case-insensitive and normally provided in lowercase; all
1018   other components are compared in a case-sensitive manner.
1019   Characters other than those in the "reserved" set are equivalent
1020   to their percent-encoded octets (see <xref target="RFC3986"
1021   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1022</t>
1023<t>
1024   For example, the following three URIs are equivalent:
1025</t>
1026<figure><artwork type="example">
1027   http://example.com:80/~smith/home.html
1028   http://EXAMPLE.com/%7Esmith/home.html
1029   http://EXAMPLE.com:/%7esmith/home.html
1030</artwork></figure>
1031</section>
1032</section>
1033</section>
1034
1035<section title="Message Format" anchor="http.message">
1036<x:anchor-alias value="generic-message"/>
1037<x:anchor-alias value="message.types"/>
1038<x:anchor-alias value="HTTP-message"/>
1039<x:anchor-alias value="start-line"/>
1040<iref item="header section"/>
1041<iref item="headers"/>
1042<iref item="header field"/>
1043<t>
1044   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1045   octets in a format similar to the Internet Message Format
1046   <xref target="RFC5322"/>: zero or more header fields (collectively
1047   referred to as the "headers" or the "header section"), an empty line
1048   indicating the end of the header section, and an optional message-body.
1049</t>
1050<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1051  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1052                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1053                    <x:ref>CRLF</x:ref>
1054                    [ <x:ref>message-body</x:ref> ]
1055</artwork></figure>
1056<t>
1057   The normal procedure for parsing an HTTP message is to read the
1058   start-line into a structure, read each header field into a hash
1059   table by field name until the empty line, and then use the parsed
1060   data to determine if a message-body is expected.  If a message-body
1061   has been indicated, then it is read as a stream until an amount
1062   of octets equal to the message-body length is read or the connection
1063   is closed.
1064</t>
1065<t>
1066   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1067   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1068   Parsing an HTTP message as a stream of Unicode characters, without regard
1069   for the specific encoding, creates security vulnerabilities due to the
1070   varying ways that string processing libraries handle invalid multibyte
1071   character sequences that contain the octet LF (%x0A).  String-based
1072   parsers can only be safely used within protocol elements after the element
1073   has been extracted from the message, such as within a header field-value
1074   after message parsing has delineated the individual fields.
1075</t>
1076<t>
1077   An HTTP message can be parsed as a stream for incremental processing or
1078   forwarding downstream.  However, recipients cannot rely on incremental
1079   delivery of partial messages, since some implementations will buffer or
1080   delay message forwarding for the sake of network efficiency, security
1081   checks, or payload transformations.
1082</t>
1083
1084<section title="Start Line" anchor="start.line">
1085  <x:anchor-alias value="Start-Line"/>
1086<t>
1087   An HTTP message can either be a request from client to server or a
1088   response from server to client.  Syntactically, the two types of message
1089   differ only in the start-line, which is either a Request-Line (for requests)
1090   or a Status-Line (for responses), and in the algorithm for determining
1091   the length of the message-body (<xref target="message.body"/>).
1092   In theory, a client could receive requests and a server could receive
1093   responses, distinguishing them by their different start-line formats,
1094   but in practice servers are implemented to only expect a request
1095   (a response is interpreted as an unknown or invalid request method)
1096   and clients are implemented to only expect a response.
1097</t>
1098<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1099  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1100</artwork></figure>
1101<t>
1102</t>
1103<t>
1104   Implementations &MUST-NOT; send whitespace between the start-line and
1105   the first header field. The presence of such whitespace in a request
1106   might be an attempt to trick a server into ignoring that field or
1107   processing the line after it as a new request, either of which might
1108   result in a security vulnerability if other implementations within
1109   the request chain interpret the same message differently.
1110   Likewise, the presence of such whitespace in a response might be
1111   ignored by some clients or cause others to cease parsing.
1112</t>
1113
1114<section title="Request-Line" anchor="request.line">
1115  <x:anchor-alias value="Request"/>
1116  <x:anchor-alias value="Request-Line"/>
1117<t>
1118   The Request-Line begins with a method token, followed by a single
1119   space (SP), the request-target, another single space (SP), the
1120   protocol version, and ending with CRLF.
1121</t>
1122<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1123  <x:ref>Request-Line</x:ref>   = <x:ref>Method</x:ref> <x:ref>SP</x:ref> <x:ref>request-target</x:ref> <x:ref>SP</x:ref> <x:ref>HTTP-Version</x:ref> <x:ref>CRLF</x:ref>
1124</artwork></figure>
1125
1126<section title="Method" anchor="method">
1127  <x:anchor-alias value="Method"/>
1128<t>
1129   The Method token indicates the request method to be performed on the
1130   target resource. The request method is case-sensitive.
1131</t>
1132<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1133  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1134</artwork></figure>
1135<t>
1136   See &method; for further information, such as the list of methods defined
1137   by this specification, the IANA registry, and considerations for new methods.
1138</t>
1139</section>
1140
1141<section title="request-target" anchor="request-target">
1142  <x:anchor-alias value="request-target"/>
1143<t>
1144   The request-target identifies the target resource upon which to apply
1145   the request.  The four options for request-target are described in
1146   <xref target="request-target-types"/>.
1147</t>
1148<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1149  <x:ref>request-target</x:ref> = "*"
1150                 / <x:ref>absolute-URI</x:ref>
1151                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1152                 / <x:ref>authority</x:ref>
1153</artwork></figure>
1154<t>
1155   HTTP does not place a pre-defined limit on the length of a request-target.
1156   A server &MUST; be prepared to receive URIs of unbounded length and
1157   respond with the 414 (URI Too Long) status code if the received
1158   request-target would be longer than the server wishes to handle
1159   (see &status-414;).
1160</t>
1161<t>
1162   Various ad-hoc limitations on request-target length are found in practice.
1163   It is &RECOMMENDED; that all HTTP senders and recipients support
1164   request-target lengths of 8000 or more octets.
1165</t>
1166<x:note>
1167  <t>
1168    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1169    are not part of the request-target and thus will not be transmitted
1170    in an HTTP request.
1171  </t>
1172</x:note>
1173</section>
1174</section>
1175
1176<section title="Response Status-Line" anchor="status.line">
1177  <x:anchor-alias value="Response"/>
1178  <x:anchor-alias value="Status-Line"/>
1179<t>
1180   The first line of a Response message is the Status-Line, consisting
1181   of the protocol version, a space (SP), the status code, another space,
1182   a possibly-empty textual phrase describing the status code, and
1183   ending with CRLF.
1184</t>
1185<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1186  <x:ref>Status-Line</x:ref> = <x:ref>HTTP-Version</x:ref> <x:ref>SP</x:ref> <x:ref>Status-Code</x:ref> <x:ref>SP</x:ref> <x:ref>Reason-Phrase</x:ref> <x:ref>CRLF</x:ref>
1187</artwork></figure>
1188
1189<section title="Status Code" anchor="status.code">
1190  <x:anchor-alias value="Status-Code"/>
1191<t>
1192   The Status-Code element is a 3-digit integer result code of the attempt to
1193   understand and satisfy the request. See &status-code-reasonphr; for
1194   further information, such as the list of status codes defined by this
1195   specification, the IANA registry, and considerations for new status codes.
1196</t>
1197<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/>
1198  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1199</artwork></figure>
1200</section>
1201
1202<section title="Reason Phrase" anchor="reason.phrase">
1203  <x:anchor-alias value="Reason-Phrase"/>
1204<t>   
1205   The Reason Phrase exists for the sole purpose of providing a textual
1206   description associated with the numeric status code, out of deference to
1207   earlier Internet application protocols that were more frequently used with
1208   interactive text clients. A client &SHOULD; ignore the content of the Reason
1209   Phrase.
1210</t>
1211<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1212  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1213</artwork></figure>
1214</section>
1215</section>
1216</section>
1217
1218<section title="Header Fields" anchor="header.fields">
1219  <x:anchor-alias value="header-field"/>
1220  <x:anchor-alias value="field-content"/>
1221  <x:anchor-alias value="field-name"/>
1222  <x:anchor-alias value="field-value"/>
1223  <x:anchor-alias value="OWS"/>
1224<t>
1225   Each HTTP header field consists of a case-insensitive field name
1226   followed by a colon (":"), optional whitespace, and the field value.
1227</t>
1228<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1229  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> <x:ref>field-value</x:ref> <x:ref>BWS</x:ref>
1230  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1231  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1232  <x:ref>field-content</x:ref>  = *( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1233</artwork></figure>
1234<t>
1235   The field-name token labels the corresponding field-value as having the
1236   semantics defined by that header field.  For example, the Date header field
1237   is defined in &header-date; as containing the origination
1238   timestamp for the message in which it appears.
1239</t>
1240<t>
1241   HTTP header fields are fully extensible: there is no limit on the
1242   introduction of new field names, each presumably defining new semantics,
1243   or on the number of header fields used in a given message.  Existing
1244   fields are defined in each part of this specification and in many other
1245   specifications outside the standards process.
1246   New header fields can be introduced without changing the protocol version
1247   if their defined semantics allow them to be safely ignored by recipients
1248   that do not recognize them.
1249</t>
1250<t>
1251   New HTTP header fields &SHOULD; be registered with IANA according
1252   to the procedures in &cons-new-header-fields;.
1253   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1254   field-name is listed in the Connection header field
1255   (<xref target="header.connection"/>) or the proxy is specifically
1256   configured to block or otherwise transform such fields.
1257   Unrecognized header fields &SHOULD; be ignored by other recipients.
1258</t>
1259<t>
1260   The order in which header fields with differing field names are
1261   received is not significant. However, it is "good practice" to send
1262   header fields that contain control data first, such as Host on
1263   requests and Date on responses, so that implementations can decide
1264   when not to handle a message as early as possible.  A server &MUST;
1265   wait until the entire header section is received before interpreting
1266   a request message, since later header fields might include conditionals,
1267   authentication credentials, or deliberately misleading duplicate
1268   header fields that would impact request processing.
1269</t>
1270<t>
1271   Multiple header fields with the same field name &MUST-NOT; be
1272   sent in a message unless the entire field value for that
1273   header field is defined as a comma-separated list [i.e., #(values)].
1274   Multiple header fields with the same field name can be combined into
1275   one "field-name: field-value" pair, without changing the semantics of the
1276   message, by appending each subsequent field value to the combined
1277   field value in order, separated by a comma. The order in which
1278   header fields with the same field name are received is therefore
1279   significant to the interpretation of the combined field value;
1280   a proxy &MUST-NOT; change the order of these field values when
1281   forwarding a message.
1282</t>
1283<x:note>
1284  <t>
1285   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1286   practice can occur multiple times, but does not use the list syntax, and
1287   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1288   for details.) Also note that the Set-Cookie2 header field specified in
1289   <xref target="RFC2965"/> does not share this problem.
1290  </t>
1291</x:note>
1292
1293<section title="Whitespace" anchor="whitespace">
1294<t anchor="rule.LWS">
1295   This specification uses three rules to denote the use of linear
1296   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1297   BWS ("bad" whitespace).
1298</t>
1299<t anchor="rule.OWS">
1300   The OWS rule is used where zero or more linear whitespace octets might
1301   appear. OWS &SHOULD; either not be produced or be produced as a single
1302   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1303   be replaced with a single SP or transformed to all SP octets (each
1304   octet other than SP replaced with SP) before interpreting the field value
1305   or forwarding the message downstream.
1306</t>
1307<t anchor="rule.RWS">
1308   RWS is used when at least one linear whitespace octet is required to
1309   separate field tokens. RWS &SHOULD; be produced as a single SP.
1310   Multiple RWS octets that occur within field-content &SHOULD; either
1311   be replaced with a single SP or transformed to all SP octets before
1312   interpreting the field value or forwarding the message downstream.
1313</t>
1314<t anchor="rule.BWS">
1315   BWS is used where the grammar allows optional whitespace for historical
1316   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1317   recipients &MUST; accept such bad optional whitespace and remove it before
1318   interpreting the field value or forwarding the message downstream.
1319</t>
1320<t anchor="rule.whitespace">
1321  <x:anchor-alias value="BWS"/>
1322  <x:anchor-alias value="OWS"/>
1323  <x:anchor-alias value="RWS"/>
1324  <x:anchor-alias value="obs-fold"/>
1325</t>
1326<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
1327  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
1328                 ; "optional" whitespace
1329  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
1330                 ; "required" whitespace
1331  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1332                 ; "bad" whitespace
1333  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1334                 ; obsolete line folding
1335                 ; see <xref target="field.parsing"/>
1336</artwork></figure>
1337</section>
1338
1339<section title="Field Parsing" anchor="field.parsing">
1340<t>
1341   No whitespace is allowed between the header field-name and colon.
1342   In the past, differences in the handling of such whitespace have led to
1343   security vulnerabilities in request routing and response handling.
1344   Any received request message that contains whitespace between a header
1345   field-name and colon &MUST; be rejected with a response code of 400
1346   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1347   message before forwarding the message downstream.
1348</t>
1349<t>
1350   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1351   preferred. The field value does not include any leading or trailing white
1352   space: OWS occurring before the first non-whitespace octet of the
1353   field value or after the last non-whitespace octet of the field value
1354   is ignored and &SHOULD; be removed before further processing (as this does
1355   not change the meaning of the header field).
1356</t>
1357<t>
1358   Historically, HTTP header field values could be extended over multiple
1359   lines by preceding each extra line with at least one space or horizontal
1360   tab (obs-fold). This specification deprecates such line
1361   folding except within the message/http media type
1362   (<xref target="internet.media.type.message.http"/>).
1363   HTTP senders &MUST-NOT; produce messages that include line folding
1364   (i.e., that contain any field-content that matches the obs-fold rule) unless
1365   the message is intended for packaging within the message/http media type.
1366   HTTP recipients &SHOULD; accept line folding and replace any embedded
1367   obs-fold whitespace with either a single SP or a matching number of SP
1368   octets (to avoid buffer copying) prior to interpreting the field value or
1369   forwarding the message downstream.
1370</t>
1371<t>
1372   Historically, HTTP has allowed field content with text in the ISO-8859-1
1373   <xref target="ISO-8859-1"/> character encoding and supported other
1374   character sets only through use of <xref target="RFC2047"/> encoding.
1375   In practice, most HTTP header field values use only a subset of the
1376   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1377   header fields &SHOULD; limit their field values to US-ASCII octets.
1378   Recipients &SHOULD; treat other (obs-text) octets in field content as
1379   opaque data.
1380</t>
1381</section>
1382
1383<section title="Field Length" anchor="field.length">
1384<t>
1385   HTTP does not place a pre-defined limit on the length of header fields,
1386   either in isolation or as a set. A server &MUST; be prepared to receive
1387   request header fields of unbounded length and respond with a 4xx status
1388   code if the received header field(s) would be longer than the server wishes
1389   to handle.
1390</t>
1391<t>
1392   A client that receives response headers that are longer than it wishes to
1393   handle can only treat it as a server error.
1394</t>
1395<t>
1396   Various ad-hoc limitations on header length are found in practice. It is
1397   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1398   combined header fields have 4000 or more octets.
1399</t>
1400</section>
1401
1402<section title="Field value components" anchor="field.components">
1403<t anchor="rule.token.separators">
1404  <x:anchor-alias value="tchar"/>
1405  <x:anchor-alias value="token"/>
1406  <x:anchor-alias value="special"/>
1407  <x:anchor-alias value="word"/>
1408   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1409   separated by whitespace or special characters. These special characters
1410   &MUST; be in a quoted string to be used within a parameter value (as defined
1411   in <xref target="transfer.codings"/>).
1412</t>
1413<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
1414  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1415
1416  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1417<!--
1418  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1419 -->
1420  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1421                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1422                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1423                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1424
1425  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1426                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1427                 / "]" / "?" / "=" / "{" / "}"
1428</artwork></figure>
1429<t anchor="rule.quoted-string">
1430  <x:anchor-alias value="quoted-string"/>
1431  <x:anchor-alias value="qdtext"/>
1432  <x:anchor-alias value="obs-text"/>
1433   A string of text is parsed as a single word if it is quoted using
1434   double-quote marks.
1435</t>
1436<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
1437  <x:ref>quoted-string</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
1438  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1439  <x:ref>obs-text</x:ref>       = %x80-FF
1440</artwork></figure>
1441<t anchor="rule.quoted-pair">
1442  <x:anchor-alias value="quoted-pair"/>
1443   The backslash octet ("\") can be used as a single-octet
1444   quoting mechanism within quoted-string constructs:
1445</t>
1446<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1447  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1448</artwork></figure>
1449<t>
1450   Recipients that process the value of the quoted-string &MUST; handle a
1451   quoted-pair as if it were replaced by the octet following the backslash.
1452</t>
1453<t>
1454   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1455   escaping (i.e., other than DQUOTE and the backslash octet).
1456</t>
1457<t anchor="rule.comment">
1458  <x:anchor-alias value="comment"/>
1459  <x:anchor-alias value="ctext"/>
1460   Comments can be included in some HTTP header fields by surrounding
1461   the comment text with parentheses. Comments are only allowed in
1462   fields containing "comment" as part of their field value definition.
1463</t>
1464<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1465  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1466  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1467</artwork></figure>
1468<t anchor="rule.quoted-cpair">
1469  <x:anchor-alias value="quoted-cpair"/>
1470   The backslash octet ("\") can be used as a single-octet
1471   quoting mechanism within comment constructs:
1472</t>
1473<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1474  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1475</artwork></figure>
1476<t>
1477   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1478   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1479</t>
1480</section>
1481
1482<section title="ABNF list extension: #rule" anchor="abnf.extension">
1483<t>
1484  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1485  improve readability in the definitions of some header field values.
1486</t>
1487<t>
1488  A construct "#" is defined, similar to "*", for defining comma-delimited
1489  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1490  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1491  comma (",") and optional whitespace (OWS).   
1492</t>
1493<figure><preamble>
1494  Thus,
1495</preamble><artwork type="example">
1496  1#element =&gt; element *( OWS "," OWS element )
1497</artwork></figure>
1498<figure><preamble>
1499  and:
1500</preamble><artwork type="example">
1501  #element =&gt; [ 1#element ]
1502</artwork></figure>
1503<figure><preamble>
1504  and for n &gt;= 1 and m &gt; 1:
1505</preamble><artwork type="example">
1506  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1507</artwork></figure>
1508<t>
1509  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1510  list elements. In other words, consumers would follow the list productions:
1511</t>
1512<figure><artwork type="example">
1513  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1514 
1515  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1516</artwork></figure>
1517<t>
1518  Note that empty elements do not contribute to the count of elements present,
1519  though.
1520</t>
1521<t>
1522  For example, given these ABNF productions:
1523</t>
1524<figure><artwork type="example">
1525  example-list      = 1#example-list-elmt
1526  example-list-elmt = token ; see <xref target="field.components"/> 
1527</artwork></figure>
1528<t>
1529  Then these are valid values for example-list (not including the double
1530  quotes, which are present for delimitation only):
1531</t>
1532<figure><artwork type="example">
1533  "foo,bar"
1534  "foo ,bar,"
1535  "foo , ,bar,charlie   "
1536</artwork></figure>
1537<t>
1538  But these values would be invalid, as at least one non-empty element is
1539  required:
1540</t>
1541<figure><artwork type="example">
1542  ""
1543  ","
1544  ",   ,"
1545</artwork></figure>
1546<t>
1547  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1548  expanded as explained above.
1549</t>
1550</section>
1551</section>
1552
1553<section title="Message Body" anchor="message.body">
1554  <x:anchor-alias value="message-body"/>
1555<t>
1556   The message-body (if any) of an HTTP message is used to carry the
1557   payload body associated with the request or response.
1558</t>
1559<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1560  <x:ref>message-body</x:ref> = *OCTET
1561</artwork></figure>
1562<t>
1563   The message-body differs from the payload body only when a transfer-coding
1564   has been applied, as indicated by the Transfer-Encoding header field
1565   (<xref target="header.transfer-encoding"/>).  If more than one
1566   Transfer-Encoding header field is present in a message, the multiple
1567   field-values &MUST; be combined into one field-value, according to the
1568   algorithm defined in <xref target="header.fields"/>, before determining
1569   the message-body length.
1570</t>
1571<t>
1572   When one or more transfer-codings are applied to a payload in order to
1573   form the message-body, the Transfer-Encoding header field &MUST; contain
1574   the list of transfer-codings applied. Transfer-Encoding is a property of
1575   the message, not of the payload, and thus &MAY; be added or removed by
1576   any implementation along the request/response chain under the constraints
1577   found in <xref target="transfer.codings"/>.
1578</t>
1579<t>
1580   If a message is received that has multiple Content-Length header fields
1581   (<xref target="header.content-length"/>) with field-values consisting
1582   of the same decimal value, or a single Content-Length header field with
1583   a field value containing a list of identical decimal values (e.g.,
1584   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1585   header fields have been generated or combined by an upstream message
1586   processor, then the recipient &MUST; either reject the message as invalid
1587   or replace the duplicated field-values with a single valid Content-Length
1588   field containing that decimal value prior to determining the message-body
1589   length.
1590</t>
1591<t>
1592   The rules for when a message-body is allowed in a message differ for
1593   requests and responses.
1594</t>
1595<t>
1596   The presence of a message-body in a request is signaled by the
1597   inclusion of a Content-Length or Transfer-Encoding header field in
1598   the request's header fields, even if the request method does not
1599   define any use for a message-body.  This allows the request
1600   message framing algorithm to be independent of method semantics.
1601</t>
1602<t>
1603   For response messages, whether or not a message-body is included with
1604   a message is dependent on both the request method and the response
1605   status code (<xref target="status.code"/>).
1606   Responses to the HEAD request method never include a message-body
1607   because the associated response header fields (e.g., Transfer-Encoding,
1608   Content-Length, etc.) only indicate what their values would have been
1609   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1610   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1611   All other responses do include a message-body, although the body
1612   &MAY; be of zero length.
1613</t>
1614<t>
1615   The length of the message-body is determined by one of the following
1616   (in order of precedence):
1617</t>
1618<t>
1619  <list style="numbers">
1620    <x:lt><t>
1621     Any response to a HEAD request and any response with a status
1622     code of 100-199, 204, or 304 is always terminated by the first
1623     empty line after the header fields, regardless of the header
1624     fields present in the message, and thus cannot contain a message-body.
1625    </t></x:lt>
1626    <x:lt><t>
1627     If a Transfer-Encoding header field is present
1628     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1629     is the final encoding, the message-body length is determined by reading
1630     and decoding the chunked data until the transfer-coding indicates the
1631     data is complete.
1632    </t>
1633    <t>
1634     If a Transfer-Encoding header field is present in a response and the
1635     "chunked" transfer-coding is not the final encoding, the message-body
1636     length is determined by reading the connection until it is closed by
1637     the server.
1638     If a Transfer-Encoding header field is present in a request and the
1639     "chunked" transfer-coding is not the final encoding, the message-body
1640     length cannot be determined reliably; the server &MUST; respond with
1641     the 400 (Bad Request) status code and then close the connection.
1642    </t>
1643    <t>
1644     If a message is received with both a Transfer-Encoding header field
1645     and a Content-Length header field, the Transfer-Encoding overrides
1646     the Content-Length.
1647     Such a message might indicate an attempt to perform request or response
1648     smuggling (bypass of security-related checks on message routing or content)
1649     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1650     be removed, prior to forwarding the message downstream, or replaced with
1651     the real message-body length after the transfer-coding is decoded.
1652    </t></x:lt>
1653    <x:lt><t>
1654     If a message is received without Transfer-Encoding and with either
1655     multiple Content-Length header fields having differing field-values or
1656     a single Content-Length header field having an invalid value, then the
1657     message framing is invalid and &MUST; be treated as an error to
1658     prevent request or response smuggling.
1659     If this is a request message, the server &MUST; respond with
1660     a 400 (Bad Request) status code and then close the connection.
1661     If this is a response message received by a proxy, the proxy
1662     &MUST; discard the received response, send a 502 (Bad Gateway)
1663     status code as its downstream response, and then close the connection.
1664     If this is a response message received by a user-agent, it &MUST; be
1665     treated as an error by discarding the message and closing the connection.
1666    </t></x:lt>
1667    <x:lt><t>
1668     If a valid Content-Length header field
1669     is present without Transfer-Encoding, its decimal value defines the
1670     message-body length in octets.  If the actual number of octets sent in
1671     the message is less than the indicated Content-Length, the recipient
1672     &MUST; consider the message to be incomplete and treat the connection
1673     as no longer usable.
1674     If the actual number of octets sent in the message is more than the indicated
1675     Content-Length, the recipient &MUST; only process the message-body up to the
1676     field value's number of octets; the remainder of the message &MUST; either
1677     be discarded or treated as the next message in a pipeline.  For the sake of
1678     robustness, a user-agent &MAY; attempt to detect and correct such an error
1679     in message framing if it is parsing the response to the last request on
1680     a connection and the connection has been closed by the server.
1681    </t></x:lt>
1682    <x:lt><t>
1683     If this is a request message and none of the above are true, then the
1684     message-body length is zero (no message-body is present).
1685    </t></x:lt>
1686    <x:lt><t>
1687     Otherwise, this is a response message without a declared message-body
1688     length, so the message-body length is determined by the number of octets
1689     received prior to the server closing the connection.
1690    </t></x:lt>
1691  </list>
1692</t>
1693<t>
1694   Since there is no way to distinguish a successfully completed,
1695   close-delimited message from a partially-received message interrupted
1696   by network failure, implementations &SHOULD; use encoding or
1697   length-delimited messages whenever possible.  The close-delimiting
1698   feature exists primarily for backwards compatibility with HTTP/1.0.
1699</t>
1700<t>
1701   A server &MAY; reject a request that contains a message-body but
1702   not a Content-Length by responding with 411 (Length Required).
1703</t>
1704<t>
1705   Unless a transfer-coding other than "chunked" has been applied,
1706   a client that sends a request containing a message-body &SHOULD;
1707   use a valid Content-Length header field if the message-body length
1708   is known in advance, rather than the "chunked" encoding, since some
1709   existing services respond to "chunked" with a 411 (Length Required)
1710   status code even though they understand the chunked encoding.  This
1711   is typically because such services are implemented via a gateway that
1712   requires a content-length in advance of being called and the server
1713   is unable or unwilling to buffer the entire request before processing.
1714</t>
1715<t>
1716   A client that sends a request containing a message-body &MUST; include a
1717   valid Content-Length header field if it does not know the server will
1718   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1719   of specific user configuration or by remembering the version of a prior
1720   received response.
1721</t>
1722</section>
1723
1724<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1725<t>
1726   Request messages that are prematurely terminated, possibly due to a
1727   cancelled connection or a server-imposed time-out exception, &MUST;
1728   result in closure of the connection; sending an HTTP/1.1 error response
1729   prior to closing the connection is &OPTIONAL;.
1730</t>
1731<t>
1732   Response messages that are prematurely terminated, usually by closure
1733   of the connection prior to receiving the expected number of octets or by
1734   failure to decode a transfer-encoded message-body, &MUST; be recorded
1735   as incomplete.  A response that terminates in the middle of the header
1736   block (before the empty line is received) cannot be assumed to convey the
1737   full semantics of the response and &MUST; be treated as an error.
1738</t>
1739<t>
1740   A message-body that uses the chunked transfer encoding is
1741   incomplete if the zero-sized chunk that terminates the encoding has not
1742   been received.  A message that uses a valid Content-Length is incomplete
1743   if the size of the message-body received (in octets) is less than the
1744   value given by Content-Length.  A response that has neither chunked
1745   transfer encoding nor Content-Length is terminated by closure of the
1746   connection, and thus is considered complete regardless of the number of
1747   message-body octets received, provided that the header block was received
1748   intact.
1749</t>
1750<t>
1751   A user agent &MUST-NOT; render an incomplete response message-body as if
1752   it were complete (i.e., some indication must be given to the user that an
1753   error occurred).  Cache requirements for incomplete responses are defined
1754   in &cache-incomplete;.
1755</t>
1756<t>
1757   A server &MUST; read the entire request message-body or close
1758   the connection after sending its response, since otherwise the
1759   remaining data on a persistent connection would be misinterpreted
1760   as the next request.  Likewise,
1761   a client &MUST; read the entire response message-body if it intends
1762   to reuse the same connection for a subsequent request.  Pipelining
1763   multiple requests on a connection is described in <xref target="pipelining"/>.
1764</t>
1765</section>
1766
1767<section title="Message Parsing Robustness" anchor="message.robustness">
1768<t>
1769   Older HTTP/1.0 client implementations might send an extra CRLF
1770   after a POST request as a lame workaround for some early server
1771   applications that failed to read message-body content that was
1772   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1773   preface or follow a request with an extra CRLF.  If terminating
1774   the request message-body with a line-ending is desired, then the
1775   client &MUST; include the terminating CRLF octets as part of the
1776   message-body length.
1777</t>
1778<t>
1779   In the interest of robustness, servers &SHOULD; ignore at least one
1780   empty line received where a Request-Line is expected. In other words, if
1781   the server is reading the protocol stream at the beginning of a
1782   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1783   Likewise, although the line terminator for the start-line and header
1784   fields is the sequence CRLF, we recommend that recipients recognize a
1785   single LF as a line terminator and ignore any CR.
1786</t>
1787<t>
1788   When a server listening only for HTTP request messages, or processing
1789   what appears from the start-line to be an HTTP request message,
1790   receives a sequence of octets that does not match the HTTP-message
1791   grammar aside from the robustness exceptions listed above, the
1792   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1793</t>
1794</section>
1795</section>
1796
1797<section title="Message Routing" anchor="message.routing">
1798<t>
1799   In most cases, the user agent is provided a URI reference
1800   from which it determines an absolute URI for identifying the target
1801   resource.  When a request to the resource is initiated, all or part
1802   of that URI is used to construct the HTTP request-target.
1803</t>
1804
1805<section title="Types of Request Target" anchor="request-target-types">
1806<t>
1807   The proper format choice of the four options available to request-target
1808   depends on the method being requested and if the request is being made to
1809   a proxy.
1810</t>   
1811<t anchor="origin-form"><iref item="origin form (of request-target)"/>
1812   The most common form of request-target is that used when making
1813   a request to an origin server ("origin form") to access a resource
1814   identified by an "http" (<xref target="http.uri"/>) or
1815   "https" (<xref target="https.uri"/>) URI.
1816   In this case, the absolute path and query components of the URI
1817   &MUST; be transmitted as the request-target and the authority component
1818   (excluding any userinfo) &MUST; be transmitted in a Host header field.
1819   For example, a client wishing to retrieve a representation of the resource
1820   identified as
1821</t>
1822<figure><artwork x:indent-with="  ">
1823http://www.example.org/where?q=now
1824</artwork></figure>
1825<t>
1826   directly from the origin server would open (or reuse) a TCP connection
1827   to port 80 of the host "www.example.org" and send the lines:
1828</t>
1829<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1830GET /where?q=now HTTP/1.1
1831Host: www.example.org
1832</artwork></figure>
1833<t>
1834   followed by the remainder of the request. Note that the origin form
1835   of request-target always starts with an absolute path. If the target
1836   resource's URI path is empty, then an absolute path of "/" &MUST; be
1837   provided in the request-target.
1838</t>
1839<t>
1840   If the request-target is percent-encoded
1841   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1842   &MUST; decode the request-target in order to
1843   properly interpret the request. Servers &SHOULD; respond to invalid
1844   request-targets with an appropriate status code.
1845</t>
1846<t anchor="absolute-URI-form"><iref item="absolute-URI form (of request-target)"/>
1847   The "absolute-URI" form of request-target is &REQUIRED; when the request
1848   is being made to a proxy.  The proxy is requested to either forward the
1849   request or service it from a valid cache, and then return the response.
1850   Note that the proxy &MAY; forward the request on to another proxy or
1851   directly to the server specified by the absolute-URI.
1852   In order to avoid request loops, a proxy that forwards requests to other
1853   proxies &MUST; be able to recognize and exclude all of its own server
1854   names, including any aliases, local variations, or literal IP addresses.
1855   An example Request-Line would be:
1856</t>
1857<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1858GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1859</artwork></figure>
1860<t>
1861   To allow for transition to absolute-URIs in all requests in future
1862   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1863   form in requests, even though HTTP/1.1 clients will only generate
1864   them in requests to proxies.
1865</t>
1866<t>
1867   If a proxy receives a host name that is not a fully qualified domain
1868   name, it &MAY; add its domain to the host name it received. If a proxy
1869   receives a fully qualified domain name, the proxy &MUST-NOT; change
1870   the host name.
1871</t>
1872<t anchor="authority-form"><iref item="authority form (of request-target)"/>
1873   The "authority form" of request-target, which &MUST-NOT; be used
1874   with any request method other than CONNECT, is used to establish a
1875   tunnel through one or more proxies (&CONNECT;).  For example,
1876</t>
1877<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1878CONNECT www.example.com:80 HTTP/1.1
1879</artwork></figure>
1880<t anchor="asterix-form"><iref item="asterisk form (of request-target)"/>
1881   The asterisk ("*") form of request-target, which &MUST-NOT; be used
1882   with any request method other than OPTIONS, means that the request
1883   applies to the server as a whole (the listening process) rather than
1884   to a specific named resource at that server.  For example,
1885</t>
1886<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1887OPTIONS * HTTP/1.1
1888</artwork></figure>
1889<t>
1890   If a proxy receives an OPTIONS request with an absolute-URI form of
1891   request-target in which the URI has an empty path and no query component,
1892   then the last proxy on the request chain &MUST; use a request-target
1893   of "*" when it forwards the request to the indicated origin server.
1894</t>
1895<figure><preamble>   
1896   For example, the request
1897</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1898OPTIONS http://www.example.org:8001 HTTP/1.1
1899</artwork></figure>
1900<figure><preamble>   
1901  would be forwarded by the final proxy as
1902</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1903OPTIONS * HTTP/1.1
1904Host: www.example.org:8001
1905</artwork>
1906<postamble>
1907   after connecting to port 8001 of host "www.example.org".
1908</postamble>
1909</figure>
1910<t>
1911   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
1912   parts of the received request-target when forwarding it to the next inbound
1913   server, except as noted above to replace a null path-absolute with "/" or
1914   "*".
1915</t>
1916</section>
1917
1918<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1919<t>
1920   The exact resource identified by an Internet request is determined by
1921   examining both the request-target and the Host header field.
1922</t>
1923<t>
1924   An origin server that does not allow resources to differ by the
1925   requested host &MAY; ignore the Host header field value when
1926   determining the resource identified by an HTTP/1.1 request. (But see
1927   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1928   for other requirements on Host support in HTTP/1.1.)
1929</t>
1930<t>
1931   An origin server that does differentiate resources based on the host
1932   requested (sometimes referred to as virtual hosts or vanity host
1933   names) &MUST; use the following rules for determining the requested
1934   resource on an HTTP/1.1 request:
1935  <list style="numbers">
1936    <t>If request-target is an absolute-URI, the host is part of the
1937     request-target. Any Host header field value in the request &MUST; be
1938     ignored.</t>
1939    <t>If the request-target is not an absolute-URI, and the request includes
1940     a Host header field, the host is determined by the Host header
1941     field value.</t>
1942    <t>If the host as determined by rule 1 or 2 is not a valid host on
1943     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1944  </list>
1945</t>
1946<t>
1947   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1948   attempt to use heuristics (e.g., examination of the URI path for
1949   something unique to a particular host) in order to determine what
1950   exact resource is being requested.
1951</t>
1952</section>
1953
1954<section title="Effective Request URI" anchor="effective.request.uri">
1955  <iref primary="true" item="effective request URI"/>
1956  <iref primary="true" item="target resource"/>
1957<t>
1958   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1959   for the target resource; instead, the URI needs to be inferred from the
1960   request-target, Host header field, and connection context. The result of
1961   this process is called the "effective request URI".  The "target resource"
1962   is the resource identified by the effective request URI.
1963</t>
1964<t>
1965   If the request-target is an absolute-URI, then the effective request URI is
1966   the request-target.
1967</t>
1968<t>
1969   If the request-target uses the origin form or the asterisk form,
1970   and the Host header field is present, then the effective request URI is
1971   constructed by concatenating
1972</t>
1973<t>
1974  <list style="symbols">
1975    <t>
1976      the scheme name: "http" if the request was received over an insecure
1977      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1978      connection,
1979    </t>
1980    <t>
1981      the octet sequence "://",
1982    </t>
1983    <t>
1984      the authority component, as specified in the Host header field
1985      (<xref target="header.host"/>), and
1986    </t>
1987    <t>
1988      the request-target obtained from the Request-Line, unless the
1989      request-target is just the asterisk "*".
1990    </t>
1991  </list>
1992</t>
1993<t>
1994   If the request-target uses the origin form or the asterisk form,
1995   and the Host header field is not present, then the effective request URI is
1996   undefined.
1997</t>
1998<t>
1999   Otherwise, when request-target uses the authority form, the effective
2000   request URI is undefined.
2001</t>
2002<figure>
2003<preamble>
2004   Example 1: the effective request URI for the message
2005</preamble> 
2006<artwork type="example" x:indent-with="  ">
2007GET /pub/WWW/TheProject.html HTTP/1.1
2008Host: www.example.org:8080
2009</artwork>
2010<postamble>
2011  (received over an insecure TCP connection) is "http", plus "://", plus the
2012  authority component "www.example.org:8080", plus the request-target
2013  "/pub/WWW/TheProject.html", thus
2014  "http://www.example.org:8080/pub/WWW/TheProject.html".
2015</postamble>
2016</figure>
2017<figure>
2018<preamble>
2019   Example 2: the effective request URI for the message
2020</preamble> 
2021<artwork type="example" x:indent-with="  ">
2022OPTIONS * HTTP/1.1
2023Host: www.example.org
2024</artwork>
2025<postamble>
2026  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
2027  authority component "www.example.org", thus "https://www.example.org".
2028</postamble>
2029</figure>
2030<t>
2031   Effective request URIs are compared using the rules described in
2032   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
2033   be treated as equivalent to an absolute path of "/".
2034</t> 
2035</section>
2036</section>
2037
2038
2039<section title="Protocol Parameters" anchor="protocol.parameters">
2040
2041<section title="Transfer Codings" anchor="transfer.codings">
2042  <x:anchor-alias value="transfer-coding"/>
2043  <x:anchor-alias value="transfer-extension"/>
2044<t>
2045   Transfer-coding values are used to indicate an encoding
2046   transformation that has been, can be, or might need to be applied to a
2047   payload body in order to ensure "safe transport" through the network.
2048   This differs from a content coding in that the transfer-coding is a
2049   property of the message rather than a property of the representation
2050   that is being transferred.
2051</t>
2052<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2053  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2054                          / "compress" ; <xref target="compress.coding"/>
2055                          / "deflate" ; <xref target="deflate.coding"/>
2056                          / "gzip" ; <xref target="gzip.coding"/>
2057                          / <x:ref>transfer-extension</x:ref>
2058  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>transfer-parameter</x:ref> )
2059</artwork></figure>
2060<t anchor="rule.parameter">
2061  <x:anchor-alias value="attribute"/>
2062  <x:anchor-alias value="transfer-parameter"/>
2063  <x:anchor-alias value="value"/>
2064   Parameters are in the form of attribute/value pairs.
2065</t>
2066<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
2067  <x:ref>transfer-parameter</x:ref>      = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
2068  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2069  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2070</artwork></figure>
2071<t>
2072   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2073   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2074   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2075</t>
2076<t>
2077   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2078   MIME, which were designed to enable safe transport of binary data over a
2079   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2080   However, safe transport
2081   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2082   the only unsafe characteristic of message-bodies is the difficulty in
2083   determining the exact message body length (<xref target="message.body"/>),
2084   or the desire to encrypt data over a shared transport.
2085</t>
2086<t>
2087   A server that receives a request message with a transfer-coding it does
2088   not understand &SHOULD; respond with 501 (Not Implemented) and then
2089   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2090   client.
2091</t>
2092
2093<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2094  <iref item="chunked (Coding Format)"/>
2095  <iref item="Coding Format" subitem="chunked"/>
2096  <x:anchor-alias value="chunk"/>
2097  <x:anchor-alias value="Chunked-Body"/>
2098  <x:anchor-alias value="chunk-data"/>
2099  <x:anchor-alias value="chunk-ext"/>
2100  <x:anchor-alias value="chunk-ext-name"/>
2101  <x:anchor-alias value="chunk-ext-val"/>
2102  <x:anchor-alias value="chunk-size"/>
2103  <x:anchor-alias value="last-chunk"/>
2104  <x:anchor-alias value="trailer-part"/>
2105  <x:anchor-alias value="quoted-str-nf"/>
2106  <x:anchor-alias value="qdtext-nf"/>
2107<t>
2108   The chunked encoding modifies the body of a message in order to
2109   transfer it as a series of chunks, each with its own size indicator,
2110   followed by an &OPTIONAL; trailer containing header fields. This
2111   allows dynamically produced content to be transferred along with the
2112   information necessary for the recipient to verify that it has
2113   received the full message.
2114</t>
2115<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Chunked-Body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/>
2116  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2117                   <x:ref>last-chunk</x:ref>
2118                   <x:ref>trailer-part</x:ref>
2119                   <x:ref>CRLF</x:ref>
2120 
2121  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2122                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2123  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2124  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2125 
2126  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref>
2127                      [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2128  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2129  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2130  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2131  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2132 
2133  <x:ref>quoted-str-nf</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext-nf</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
2134                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2135  <x:ref>qdtext-nf</x:ref>      = <x:ref>HTAB</x:ref> / <x:ref>SP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2136</artwork></figure>
2137<t>
2138   The chunk-size field is a string of hex digits indicating the size of
2139   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2140   zero, followed by the trailer, which is terminated by an empty line.
2141</t>
2142<t>
2143   The trailer allows the sender to include additional HTTP header
2144   fields at the end of the message. The Trailer header field can be
2145   used to indicate which header fields are included in a trailer (see
2146   <xref target="header.trailer"/>).
2147</t>
2148<t>
2149   A server using chunked transfer-coding in a response &MUST-NOT; use the
2150   trailer for any header fields unless at least one of the following is
2151   true:
2152  <list style="numbers">
2153    <t>the request included a TE header field that indicates "trailers" is
2154     acceptable in the transfer-coding of the  response, as described in
2155     <xref target="header.te"/>; or,</t>
2156     
2157    <t>the trailer fields consist entirely of optional metadata, and the
2158    recipient could use the message (in a manner acceptable to the server where
2159    the field originated) without receiving it. In other words, the server that
2160    generated the header (often but not always the origin server) is willing to
2161    accept the possibility that the trailer fields might be silently discarded
2162    along the path to the client.</t>
2163  </list>
2164</t>
2165<t>
2166   This requirement prevents an interoperability failure when the
2167   message is being received by an HTTP/1.1 (or later) proxy and
2168   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2169   conformance with the protocol would have necessitated a possibly
2170   infinite buffer on the proxy.
2171</t>
2172<t>
2173   A process for decoding the "chunked" transfer-coding
2174   can be represented in pseudo-code as:
2175</t>
2176<figure><artwork type="code">
2177  length := 0
2178  read chunk-size, chunk-ext (if any) and CRLF
2179  while (chunk-size &gt; 0) {
2180     read chunk-data and CRLF
2181     append chunk-data to decoded-body
2182     length := length + chunk-size
2183     read chunk-size and CRLF
2184  }
2185  read header-field
2186  while (header-field not empty) {
2187     append header-field to existing header fields
2188     read header-field
2189  }
2190  Content-Length := length
2191  Remove "chunked" from Transfer-Encoding
2192</artwork></figure>
2193<t>
2194   All HTTP/1.1 applications &MUST; be able to receive and decode the
2195   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2196   they do not understand.
2197</t>
2198<t>
2199   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
2200   sent and definition of new chunk-extensions is discouraged.
2201</t>
2202<t>
2203   Since "chunked" is the only transfer-coding required to be understood
2204   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2205   on a persistent connection.  Whenever a transfer-coding is applied to
2206   a payload body in a request, the final transfer-coding applied &MUST;
2207   be "chunked".  If a transfer-coding is applied to a response payload
2208   body, then either the final transfer-coding applied &MUST; be "chunked"
2209   or the message &MUST; be terminated by closing the connection. When the
2210   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2211   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2212   be applied more than once in a message-body.
2213</t>
2214</section>
2215
2216<section title="Compression Codings" anchor="compression.codings">
2217<t>
2218   The codings defined below can be used to compress the payload of a
2219   message.
2220</t>
2221<x:note><t>
2222   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2223   is not desirable and is discouraged for future encodings. Their
2224   use here is representative of historical practice, not good
2225   design.
2226</t></x:note>
2227<x:note><t>
2228   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2229   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2230   equivalent to "gzip" and "compress" respectively.
2231</t></x:note>
2232
2233<section title="Compress Coding" anchor="compress.coding">
2234<iref item="compress (Coding Format)"/>
2235<iref item="Coding Format" subitem="compress"/>
2236<t>
2237   The "compress" format is produced by the common UNIX file compression
2238   program "compress". This format is an adaptive Lempel-Ziv-Welch
2239   coding (LZW).
2240</t>
2241</section>
2242
2243<section title="Deflate Coding" anchor="deflate.coding">
2244<iref item="deflate (Coding Format)"/>
2245<iref item="Coding Format" subitem="deflate"/>
2246<t>
2247   The "deflate" format is defined as the "deflate" compression mechanism
2248   (described in <xref target="RFC1951"/>) used inside the "zlib"
2249   data format (<xref target="RFC1950"/>).
2250</t>
2251<x:note>
2252  <t>
2253    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2254    compressed data without the zlib wrapper.
2255   </t>
2256</x:note>
2257</section>
2258
2259<section title="Gzip Coding" anchor="gzip.coding">
2260<iref item="gzip (Coding Format)"/>
2261<iref item="Coding Format" subitem="gzip"/>
2262<t>
2263   The "gzip" format is produced by the file compression program
2264   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2265   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2266</t>
2267</section>
2268
2269</section>
2270
2271<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2272<t>
2273   The HTTP Transfer Coding Registry defines the name space for the transfer
2274   coding names.
2275</t>
2276<t>
2277   Registrations &MUST; include the following fields:
2278   <list style="symbols">
2279     <t>Name</t>
2280     <t>Description</t>
2281     <t>Pointer to specification text</t>
2282   </list>
2283</t>
2284<t>
2285   Names of transfer codings &MUST-NOT; overlap with names of content codings
2286   (&content-codings;), unless the encoding transformation is identical (as it
2287   is the case for the compression codings defined in
2288   <xref target="compression.codings"/>).
2289</t>
2290<t>
2291   Values to be added to this name space require a specification
2292   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2293   conform to the purpose of transfer coding defined in this section.
2294</t>
2295<t>
2296   The registry itself is maintained at
2297   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2298</t>
2299</section>
2300</section>
2301
2302<section title="Product Tokens" anchor="product.tokens">
2303  <x:anchor-alias value="product"/>
2304  <x:anchor-alias value="product-version"/>
2305<t>
2306   Product tokens are used to allow communicating applications to
2307   identify themselves by software name and version. Most fields using
2308   product tokens also allow sub-products which form a significant part
2309   of the application to be listed, separated by whitespace. By
2310   convention, the products are listed in order of their significance
2311   for identifying the application.
2312</t>
2313<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2314  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2315  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2316</artwork></figure>
2317<t>
2318   Examples:
2319</t>
2320<figure><artwork type="example">
2321  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2322  Server: Apache/0.8.4
2323</artwork></figure>
2324<t>
2325   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2326   used for advertising or other non-essential information. Although any
2327   token octet &MAY; appear in a product-version, this token &SHOULD;
2328   only be used for a version identifier (i.e., successive versions of
2329   the same product &SHOULD; only differ in the product-version portion of
2330   the product value).
2331</t>
2332</section>
2333
2334<section title="Quality Values" anchor="quality.values">
2335  <x:anchor-alias value="qvalue"/>
2336<t>
2337   Both transfer codings (TE request header field, <xref target="header.te"/>)
2338   and content negotiation (&content.negotiation;) use short "floating point"
2339   numbers to indicate the relative importance ("weight") of various
2340   negotiable parameters.  A weight is normalized to a real number in
2341   the range 0 through 1, where 0 is the minimum and 1 the maximum
2342   value. If a parameter has a quality value of 0, then content with
2343   this parameter is "not acceptable" for the client. HTTP/1.1
2344   applications &MUST-NOT; generate more than three digits after the
2345   decimal point. User configuration of these values &SHOULD; also be
2346   limited in this fashion.
2347</t>
2348<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2349  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2350                 / ( "1" [ "." 0*3("0") ] )
2351</artwork></figure>
2352<x:note>
2353  <t>
2354     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2355     relative degradation in desired quality.
2356  </t>
2357</x:note>
2358</section>
2359
2360</section>
2361
2362<section title="Connections" anchor="connections">
2363
2364<section title="Persistent Connections" anchor="persistent.connections">
2365
2366<section title="Purpose" anchor="persistent.purpose">
2367<t>
2368   Prior to persistent connections, a separate TCP connection was
2369   established for each request, increasing the load on HTTP servers
2370   and causing congestion on the Internet. The use of inline images and
2371   other associated data often requires a client to make multiple
2372   requests of the same server in a short amount of time. Analysis of
2373   these performance problems and results from a prototype
2374   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2375   measurements of actual HTTP/1.1 implementations show good
2376   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2377   T/TCP <xref target="Tou1998"/>.
2378</t>
2379<t>
2380   Persistent HTTP connections have a number of advantages:
2381  <list style="symbols">
2382      <t>
2383        By opening and closing fewer TCP connections, CPU time is saved
2384        in routers and hosts (clients, servers, proxies, gateways,
2385        tunnels, or caches), and memory used for TCP protocol control
2386        blocks can be saved in hosts.
2387      </t>
2388      <t>
2389        HTTP requests and responses can be pipelined on a connection.
2390        Pipelining allows a client to make multiple requests without
2391        waiting for each response, allowing a single TCP connection to
2392        be used much more efficiently, with much lower elapsed time.
2393      </t>
2394      <t>
2395        Network congestion is reduced by reducing the number of packets
2396        caused by TCP opens, and by allowing TCP sufficient time to
2397        determine the congestion state of the network.
2398      </t>
2399      <t>
2400        Latency on subsequent requests is reduced since there is no time
2401        spent in TCP's connection opening handshake.
2402      </t>
2403      <t>
2404        HTTP can evolve more gracefully, since errors can be reported
2405        without the penalty of closing the TCP connection. Clients using
2406        future versions of HTTP might optimistically try a new feature,
2407        but if communicating with an older server, retry with old
2408        semantics after an error is reported.
2409      </t>
2410    </list>
2411</t>
2412<t>
2413   HTTP implementations &SHOULD; implement persistent connections.
2414</t>
2415</section>
2416
2417<section title="Overall Operation" anchor="persistent.overall">
2418<t>
2419   A significant difference between HTTP/1.1 and earlier versions of
2420   HTTP is that persistent connections are the default behavior of any
2421   HTTP connection. That is, unless otherwise indicated, the client
2422   &SHOULD; assume that the server will maintain a persistent connection,
2423   even after error responses from the server.
2424</t>
2425<t>
2426   Persistent connections provide a mechanism by which a client and a
2427   server can signal the close of a TCP connection. This signaling takes
2428   place using the Connection header field (<xref target="header.connection"/>). Once a close
2429   has been signaled, the client &MUST-NOT; send any more requests on that
2430   connection.
2431</t>
2432
2433<section title="Negotiation" anchor="persistent.negotiation">
2434<t>
2435   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2436   maintain a persistent connection unless a Connection header field including
2437   the connection-token "close" was sent in the request. If the server
2438   chooses to close the connection immediately after sending the
2439   response, it &SHOULD; send a Connection header field including the
2440   connection-token "close".
2441</t>
2442<t>
2443   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2444   decide to keep it open based on whether the response from a server
2445   contains a Connection header field with the connection-token close. In case
2446   the client does not want to maintain a connection for more than that
2447   request, it &SHOULD; send a Connection header field including the
2448   connection-token close.
2449</t>
2450<t>
2451   If either the client or the server sends the close token in the
2452   Connection header field, that request becomes the last one for the
2453   connection.
2454</t>
2455<t>
2456   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2457   maintained for HTTP versions less than 1.1 unless it is explicitly
2458   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2459   compatibility with HTTP/1.0 clients.
2460</t>
2461<t>
2462   In order to remain persistent, all messages on the connection &MUST;
2463   have a self-defined message length (i.e., one not defined by closure
2464   of the connection), as described in <xref target="message.body"/>.
2465</t>
2466</section>
2467
2468<section title="Pipelining" anchor="pipelining">
2469<t>
2470   A client that supports persistent connections &MAY; "pipeline" its
2471   requests (i.e., send multiple requests without waiting for each
2472   response). A server &MUST; send its responses to those requests in the
2473   same order that the requests were received.
2474</t>
2475<t>
2476   Clients which assume persistent connections and pipeline immediately
2477   after connection establishment &SHOULD; be prepared to retry their
2478   connection if the first pipelined attempt fails. If a client does
2479   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2480   persistent. Clients &MUST; also be prepared to resend their requests if
2481   the server closes the connection before sending all of the
2482   corresponding responses.
2483</t>
2484<t>
2485   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2486   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2487   premature termination of the transport connection could lead to
2488   indeterminate results. A client wishing to send a non-idempotent
2489   request &SHOULD; wait to send that request until it has received the
2490   response status line for the previous request.
2491</t>
2492</section>
2493</section>
2494
2495<section title="Proxy Servers" anchor="persistent.proxy">
2496<t>
2497   It is especially important that proxies correctly implement the
2498   properties of the Connection header field as specified in <xref target="header.connection"/>.
2499</t>
2500<t>
2501   The proxy server &MUST; signal persistent connections separately with
2502   its clients and the origin servers (or other proxy servers) that it
2503   connects to. Each persistent connection applies to only one transport
2504   link.
2505</t>
2506<t>
2507   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2508   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2509   for information and discussion of the problems with the Keep-Alive header field
2510   implemented by many HTTP/1.0 clients).
2511</t>
2512
2513<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2514<!--<t>
2515  <cref anchor="TODO-end-to-end" source="jre">
2516    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2517    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2518  </cref>
2519</t>-->
2520<t>
2521   For the purpose of defining the behavior of caches and non-caching
2522   proxies, we divide HTTP header fields into two categories:
2523  <list style="symbols">
2524      <t>End-to-end header fields, which are  transmitted to the ultimate
2525        recipient of a request or response. End-to-end header fields in
2526        responses MUST be stored as part of a cache entry and &MUST; be
2527        transmitted in any response formed from a cache entry.</t>
2528
2529      <t>Hop-by-hop header fields, which are meaningful only for a single
2530        transport-level connection, and are not stored by caches or
2531        forwarded by proxies.</t>
2532  </list>
2533</t>
2534<t>
2535   The following HTTP/1.1 header fields are hop-by-hop header fields:
2536  <list style="symbols">
2537      <t>Connection</t>
2538      <t>Keep-Alive</t>
2539      <t>Proxy-Authenticate</t>
2540      <t>Proxy-Authorization</t>
2541      <t>TE</t>
2542      <t>Trailer</t>
2543      <t>Transfer-Encoding</t>
2544      <t>Upgrade</t>
2545  </list>
2546</t>
2547<t>
2548   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2549</t>
2550<t>
2551   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2552   (<xref target="header.connection"/>).
2553</t>
2554</section>
2555
2556<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2557<!--<t>
2558  <cref anchor="TODO-non-mod-headers" source="jre">
2559    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2560    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2561  </cref>
2562</t>-->
2563<t>
2564   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2565   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2566   modify an end-to-end header field unless the definition of that header field requires
2567   or specifically allows that.
2568</t>
2569<t>
2570   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2571   request or response, and it &MUST-NOT; add any of these fields if not
2572   already present:
2573  <list style="symbols">
2574    <t>Allow</t>
2575    <t>Content-Location</t>
2576    <t>Content-MD5</t>
2577    <t>ETag</t>
2578    <t>Last-Modified</t>
2579    <t>Server</t>
2580  </list>
2581</t>
2582<t>
2583   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2584   response:
2585  <list style="symbols">
2586    <t>Expires</t>
2587  </list>
2588</t>
2589<t>
2590   but it &MAY; add any of these fields if not already present. If an
2591   Expires header field is added, it &MUST; be given a field-value identical to
2592   that of the Date header field in that response.
2593</t>
2594<t>
2595   A proxy &MUST-NOT; modify or add any of the following fields in a
2596   message that contains the no-transform cache-control directive, or in
2597   any request:
2598  <list style="symbols">
2599    <t>Content-Encoding</t>
2600    <t>Content-Range</t>
2601    <t>Content-Type</t>
2602  </list>
2603</t>
2604<t>
2605   A transforming proxy &MAY; modify or add these fields to a message
2606   that does not include no-transform, but if it does so, it &MUST; add a
2607   Warning 214 (Transformation applied) if one does not already appear
2608   in the message (see &header-warning;).
2609</t>
2610<x:note>
2611  <t>
2612    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2613    cause authentication failures if stronger authentication
2614    mechanisms are introduced in later versions of HTTP. Such
2615    authentication mechanisms &MAY; rely on the values of header fields
2616    not listed here.
2617  </t>
2618</x:note>
2619<t>
2620   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2621   though it &MAY; change the message-body through application or removal
2622   of a transfer-coding (<xref target="transfer.codings"/>).
2623</t>
2624</section>
2625
2626</section>
2627
2628<section title="Practical Considerations" anchor="persistent.practical">
2629<t>
2630   Servers will usually have some time-out value beyond which they will
2631   no longer maintain an inactive connection. Proxy servers might make
2632   this a higher value since it is likely that the client will be making
2633   more connections through the same server. The use of persistent
2634   connections places no requirements on the length (or existence) of
2635   this time-out for either the client or the server.
2636</t>
2637<t>
2638   When a client or server wishes to time-out it &SHOULD; issue a graceful
2639   close on the transport connection. Clients and servers &SHOULD; both
2640   constantly watch for the other side of the transport close, and
2641   respond to it as appropriate. If a client or server does not detect
2642   the other side's close promptly it could cause unnecessary resource
2643   drain on the network.
2644</t>
2645<t>
2646   A client, server, or proxy &MAY; close the transport connection at any
2647   time. For example, a client might have started to send a new request
2648   at the same time that the server has decided to close the "idle"
2649   connection. From the server's point of view, the connection is being
2650   closed while it was idle, but from the client's point of view, a
2651   request is in progress.
2652</t>
2653<t>
2654   Clients (including proxies) &SHOULD; limit the number of simultaneous
2655   connections that they maintain to a given server (including proxies).
2656</t>
2657<t>
2658   Previous revisions of HTTP gave a specific number of connections as a
2659   ceiling, but this was found to be impractical for many applications. As a
2660   result, this specification does not mandate a particular maximum number of
2661   connections, but instead encourages clients to be conservative when opening
2662   multiple connections.
2663</t>
2664<t>
2665   In particular, while using multiple connections avoids the "head-of-line
2666   blocking" problem (whereby a request that takes significant server-side
2667   processing and/or has a large payload can block subsequent requests on the
2668   same connection), each connection used consumes server resources (sometimes
2669   significantly), and furthermore using multiple connections can cause
2670   undesirable side effects in congested networks.
2671</t>
2672<t>
2673   Note that servers might reject traffic that they deem abusive, including an
2674   excessive number of connections from a client.
2675</t>
2676</section>
2677
2678<section title="Retrying Requests" anchor="persistent.retrying.requests">
2679<t>
2680   Senders can close the transport connection at any time. Therefore,
2681   clients, servers, and proxies &MUST; be able to recover
2682   from asynchronous close events. Client software &MAY; reopen the
2683   transport connection and retransmit the aborted sequence of requests
2684   without user interaction so long as the request sequence is
2685   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2686   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2687   human operator the choice of retrying the request(s). Confirmation by
2688   user-agent software with semantic understanding of the application
2689   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2690   be repeated if the second sequence of requests fails.
2691</t>
2692</section>
2693
2694</section>
2695
2696<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2697
2698<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2699<t>
2700   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2701   flow control mechanisms to resolve temporary overloads, rather than
2702   terminating connections with the expectation that clients will retry.
2703   The latter technique can exacerbate network congestion.
2704</t>
2705</section>
2706
2707<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2708<t>
2709   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2710   the network connection for an error status code while it is transmitting
2711   the request. If the client sees an error status code, it &SHOULD;
2712   immediately cease transmitting the body. If the body is being sent
2713   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2714   empty trailer &MAY; be used to prematurely mark the end of the message.
2715   If the body was preceded by a Content-Length header field, the client &MUST;
2716   close the connection.
2717</t>
2718</section>
2719
2720<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2721<t>
2722   The purpose of the 100 (Continue) status code (see &status-100;) is to
2723   allow a client that is sending a request message with a request body
2724   to determine if the origin server is willing to accept the request
2725   (based on the request header fields) before the client sends the request
2726   body. In some cases, it might either be inappropriate or highly
2727   inefficient for the client to send the body if the server will reject
2728   the message without looking at the body.
2729</t>
2730<t>
2731   Requirements for HTTP/1.1 clients:
2732  <list style="symbols">
2733    <t>
2734        If a client will wait for a 100 (Continue) response before
2735        sending the request body, it &MUST; send an Expect header
2736        field (&header-expect;) with the "100-continue" expectation.
2737    </t>
2738    <t>
2739        A client &MUST-NOT; send an Expect header field (&header-expect;)
2740        with the "100-continue" expectation if it does not intend
2741        to send a request body.
2742    </t>
2743  </list>
2744</t>
2745<t>
2746   Because of the presence of older implementations, the protocol allows
2747   ambiguous situations in which a client might send "Expect: 100-continue"
2748   without receiving either a 417 (Expectation Failed)
2749   or a 100 (Continue) status code. Therefore, when a client sends this
2750   header field to an origin server (possibly via a proxy) from which it
2751   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2752   wait for an indefinite period before sending the request body.
2753</t>
2754<t>
2755   Requirements for HTTP/1.1 origin servers:
2756  <list style="symbols">
2757    <t> Upon receiving a request which includes an Expect header
2758        field with the "100-continue" expectation, an origin server &MUST;
2759        either respond with 100 (Continue) status code and continue to read
2760        from the input stream, or respond with a final status code. The
2761        origin server &MUST-NOT; wait for the request body before sending
2762        the 100 (Continue) response. If it responds with a final status
2763        code, it &MAY; close the transport connection or it &MAY; continue
2764        to read and discard the rest of the request.  It &MUST-NOT;
2765        perform the request method if it returns a final status code.
2766    </t>
2767    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2768        the request message does not include an Expect header
2769        field with the "100-continue" expectation, and &MUST-NOT; send a
2770        100 (Continue) response if such a request comes from an HTTP/1.0
2771        (or earlier) client. There is an exception to this rule: for
2772        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2773        status code in response to an HTTP/1.1 PUT or POST request that does
2774        not include an Expect header field with the "100-continue"
2775        expectation. This exception, the purpose of which is
2776        to minimize any client processing delays associated with an
2777        undeclared wait for 100 (Continue) status code, applies only to
2778        HTTP/1.1 requests, and not to requests with any other HTTP-version
2779        value.
2780    </t>
2781    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2782        already received some or all of the request body for the
2783        corresponding request.
2784    </t>
2785    <t> An origin server that sends a 100 (Continue) response &MUST;
2786        ultimately send a final status code, once the request body is
2787        received and processed, unless it terminates the transport
2788        connection prematurely.
2789    </t>
2790    <t> If an origin server receives a request that does not include an
2791        Expect header field with the "100-continue" expectation,
2792        the request includes a request body, and the server responds
2793        with a final status code before reading the entire request body
2794        from the transport connection, then the server &SHOULD-NOT;  close
2795        the transport connection until it has read the entire request,
2796        or until the client closes the connection. Otherwise, the client
2797        might not reliably receive the response message. However, this
2798        requirement ought not be construed as preventing a server from
2799        defending itself against denial-of-service attacks, or from
2800        badly broken client implementations.
2801      </t>
2802    </list>
2803</t>
2804<t>
2805   Requirements for HTTP/1.1 proxies:
2806  <list style="symbols">
2807    <t> If a proxy receives a request that includes an Expect header
2808        field with the "100-continue" expectation, and the proxy
2809        either knows that the next-hop server complies with HTTP/1.1 or
2810        higher, or does not know the HTTP version of the next-hop
2811        server, it &MUST; forward the request, including the Expect header
2812        field.
2813    </t>
2814    <t> If the proxy knows that the version of the next-hop server is
2815        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2816        respond with a 417 (Expectation Failed) status code.
2817    </t>
2818    <t> Proxies &SHOULD; maintain a record of the HTTP version
2819        numbers received from recently-referenced next-hop servers.
2820    </t>
2821    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2822        request message was received from an HTTP/1.0 (or earlier)
2823        client and did not include an Expect header field with
2824        the "100-continue" expectation. This requirement overrides the
2825        general rule for forwarding of 1xx responses (see &status-1xx;).
2826    </t>
2827  </list>
2828</t>
2829</section>
2830
2831<section title="Closing Connections on Error" anchor="closing.connections.on.error">
2832<t>
2833   If the client is sending data, a server implementation using TCP
2834   &SHOULD; be careful to ensure that the client acknowledges receipt of
2835   the packet(s) containing the response, before the server closes the
2836   input connection. If the client continues sending data to the server
2837   after the close, the server's TCP stack will send a reset packet to
2838   the client, which might erase the client's unacknowledged input buffers
2839   before they can be read and interpreted by the HTTP application.
2840</t>
2841</section>
2842
2843</section>
2844</section>
2845
2846
2847<section title="Miscellaneous notes that might disappear" anchor="misc">
2848<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2849<t>
2850   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2851</t>
2852</section>
2853
2854<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2855<t>
2856   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2857</t>
2858</section>
2859
2860<section title="Interception of HTTP for access control" anchor="http.intercept">
2861<t>
2862   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2863</t>
2864</section>
2865
2866<section title="Use of HTTP by other protocols" anchor="http.others">
2867<t>
2868   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2869   Extensions of HTTP like WebDAV.</cref>
2870</t>
2871
2872</section>
2873<section title="Use of HTTP by media type specification" anchor="http.media">
2874<t>
2875   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2876</t>
2877</section>
2878</section>
2879
2880<section title="Header Field Definitions" anchor="header.field.definitions">
2881<t>
2882   This section defines the syntax and semantics of HTTP header fields
2883   related to message origination, framing, and routing.
2884</t>
2885<texttable align="left">
2886  <ttcol>Header Field Name</ttcol>
2887  <ttcol>Defined in...</ttcol>
2888 
2889  <c>Connection</c> <c><xref target="header.connection"/></c>
2890  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
2891  <c>Host</c> <c><xref target="header.host"/></c>
2892  <c>TE</c> <c><xref target="header.te"/></c>
2893  <c>Trailer</c> <c><xref target="header.trailer"/></c>
2894  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
2895  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
2896  <c>Via</c> <c><xref target="header.via"/></c>
2897</texttable>
2898
2899<section title="Connection" anchor="header.connection">
2900  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2901  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2902  <x:anchor-alias value="Connection"/>
2903  <x:anchor-alias value="connection-token"/>
2904<t>
2905   The "Connection" header field allows the sender to specify
2906   options that are desired only for that particular connection.
2907   Such connection options &MUST; be removed or replaced before the
2908   message can be forwarded downstream by a proxy or gateway.
2909   This mechanism also allows the sender to indicate which HTTP
2910   header fields used in the message are only intended for the
2911   immediate recipient ("hop-by-hop"), as opposed to all recipients
2912   on the chain ("end-to-end"), enabling the message to be
2913   self-descriptive and allowing future connection-specific extensions
2914   to be deployed in HTTP without fear that they will be blindly
2915   forwarded by previously deployed intermediaries.
2916</t>
2917<t>
2918   The Connection header field's value has the following grammar:
2919</t>
2920<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2921  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2922  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2923</artwork></figure>
2924<t>
2925   A proxy or gateway &MUST; parse a received Connection
2926   header field before a message is forwarded and, for each
2927   connection-token in this field, remove any header field(s) from
2928   the message with the same name as the connection-token, and then
2929   remove the Connection header field itself or replace it with the
2930   sender's own connection options for the forwarded message.
2931</t>
2932<t>
2933   A sender &MUST-NOT; include field-names in the Connection header
2934   field-value for fields that are defined as expressing constraints
2935   for all recipients in the request or response chain, such as the
2936   Cache-Control header field (&header-cache-control;).
2937</t>
2938<t>
2939   The connection options do not have to correspond to a header field
2940   present in the message, since a connection-specific header field
2941   might not be needed if there are no parameters associated with that
2942   connection option.  Recipients that trigger certain connection
2943   behavior based on the presence of connection options &MUST; do so
2944   based on the presence of the connection-token rather than only the
2945   presence of the optional header field.  In other words, if the
2946   connection option is received as a header field but not indicated
2947   within the Connection field-value, then the recipient &MUST; ignore
2948   the connection-specific header field because it has likely been
2949   forwarded by an intermediary that is only partially conformant.
2950</t>
2951<t>
2952   When defining new connection options, specifications ought to
2953   carefully consider existing deployed header fields and ensure
2954   that the new connection-token does not share the same name as
2955   an unrelated header field that might already be deployed.
2956   Defining a new connection-token essentially reserves that potential
2957   field-name for carrying additional information related to the
2958   connection option, since it would be unwise for senders to use
2959   that field-name for anything else.
2960</t>
2961<t>
2962   HTTP/1.1 defines the "close" connection option for the sender to
2963   signal that the connection will be closed after completion of the
2964   response. For example,
2965</t>
2966<figure><artwork type="example">
2967  Connection: close
2968</artwork></figure>
2969<t>
2970   in either the request or the response header fields indicates that
2971   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2972   after the current request/response is complete.
2973</t>
2974<t>
2975   An HTTP/1.1 client that does not support persistent connections &MUST;
2976   include the "close" connection option in every request message.
2977</t>
2978<t>
2979   An HTTP/1.1 server that does not support persistent connections &MUST;
2980   include the "close" connection option in every response message that
2981   does not have a 1xx (Informational) status code.
2982</t>
2983</section>
2984
2985<section title="Content-Length" anchor="header.content-length">
2986  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
2987  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
2988  <x:anchor-alias value="Content-Length"/>
2989<t>
2990   The "Content-Length" header field indicates the size of the
2991   message-body, in decimal number of octets, for any message other than
2992   a response to a HEAD request or a response with a status code of 304.
2993   In the case of a response to a HEAD request, Content-Length indicates
2994   the size of the payload body (not including any potential transfer-coding)
2995   that would have been sent had the request been a GET.
2996   In the case of a 304 (Not Modified) response to a GET request,
2997   Content-Length indicates the size of the payload body (not including
2998   any potential transfer-coding) that would have been sent in a 200 (OK)
2999   response.
3000</t>
3001<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3002  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3003</artwork></figure>
3004<t>
3005   An example is
3006</t>
3007<figure><artwork type="example">
3008  Content-Length: 3495
3009</artwork></figure>
3010<t>
3011   Implementations &SHOULD; use this field to indicate the message-body
3012   length when no transfer-coding is being applied and the
3013   payload's body length can be determined prior to being transferred.
3014   <xref target="message.body"/> describes how recipients determine the length
3015   of a message-body.
3016</t>
3017<t>
3018   Any Content-Length greater than or equal to zero is a valid value.
3019</t>
3020<t>
3021   Note that the use of this field in HTTP is significantly different from
3022   the corresponding definition in MIME, where it is an optional field
3023   used within the "message/external-body" content-type.
3024</t>
3025</section>
3026
3027<section title="Host" anchor="header.host">
3028  <iref primary="true" item="Host header field" x:for-anchor=""/>
3029  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3030  <x:anchor-alias value="Host"/>
3031<t>
3032   The "Host" header field in a request provides the host and port
3033   information from the target resource's URI, enabling the origin
3034   server to distinguish between resources while servicing requests
3035   for multiple host names on a single IP address.  Since the Host
3036   field-value is critical information for handling a request, it
3037   &SHOULD; be sent as the first header field following the Request-Line.
3038</t>
3039<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3040  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3041</artwork></figure>
3042<t>
3043   A client &MUST; send a Host header field in all HTTP/1.1 request
3044   messages.  If the target resource's URI includes an authority
3045   component, then the Host field-value &MUST; be identical to that
3046   authority component after excluding any userinfo (<xref target="http.uri"/>).
3047   If the authority component is missing or undefined for the target
3048   resource's URI, then the Host header field &MUST; be sent with an
3049   empty field-value.
3050</t>
3051<t>
3052   For example, a GET request to the origin server for
3053   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3054</t>
3055<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3056GET /pub/WWW/ HTTP/1.1
3057Host: www.example.org
3058</artwork></figure>
3059<t>
3060   The Host header field &MUST; be sent in an HTTP/1.1 request even
3061   if the request-target is in the form of an absolute-URI, since this
3062   allows the Host information to be forwarded through ancient HTTP/1.0
3063   proxies that might not have implemented Host.
3064</t>
3065<t>
3066   When an HTTP/1.1 proxy receives a request with a request-target in
3067   the form of an absolute-URI, the proxy &MUST; ignore the received
3068   Host header field (if any) and instead replace it with the host
3069   information of the request-target.  When a proxy forwards a request,
3070   it &MUST; generate the Host header field based on the received
3071   absolute-URI rather than the received Host.
3072</t>
3073<t>
3074   Since the Host header field acts as an application-level routing
3075   mechanism, it is a frequent target for malware seeking to poison
3076   a shared cache or redirect a request to an unintended server.
3077   An interception proxy is particularly vulnerable if it relies on
3078   the Host header field value for redirecting requests to internal
3079   servers, or for use as a cache key in a shared cache, without
3080   first verifying that the intercepted connection is targeting a
3081   valid IP address for that host.
3082</t>
3083<t>
3084   A server &MUST; respond with a 400 (Bad Request) status code to
3085   any HTTP/1.1 request message that lacks a Host header field and
3086   to any request message that contains more than one Host header field
3087   or a Host header field with an invalid field-value.
3088</t>
3089<t>
3090   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3091   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3092   for other requirements relating to Host.
3093</t>
3094</section>
3095
3096<section title="TE" anchor="header.te">
3097  <iref primary="true" item="TE header field" x:for-anchor=""/>
3098  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3099  <x:anchor-alias value="TE"/>
3100  <x:anchor-alias value="t-codings"/>
3101  <x:anchor-alias value="te-params"/>
3102  <x:anchor-alias value="te-ext"/>
3103<t>
3104   The "TE" header field indicates what extension transfer-codings
3105   the client is willing to accept in the response, and whether or not it is
3106   willing to accept trailer fields in a chunked transfer-coding.
3107</t>
3108<t>
3109   Its value consists of the keyword "trailers" and/or a comma-separated
3110   list of extension transfer-coding names with optional accept
3111   parameters (as described in <xref target="transfer.codings"/>).
3112</t>
3113<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3114  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3115  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3116  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
3117  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
3118</artwork></figure>
3119<t>
3120   The presence of the keyword "trailers" indicates that the client is
3121   willing to accept trailer fields in a chunked transfer-coding, as
3122   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3123   transfer-coding values even though it does not itself represent a
3124   transfer-coding.
3125</t>
3126<t>
3127   Examples of its use are:
3128</t>
3129<figure><artwork type="example">
3130  TE: deflate
3131  TE:
3132  TE: trailers, deflate;q=0.5
3133</artwork></figure>
3134<t>
3135   The TE header field only applies to the immediate connection.
3136   Therefore, the keyword &MUST; be supplied within a Connection header
3137   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3138</t>
3139<t>
3140   A server tests whether a transfer-coding is acceptable, according to
3141   a TE field, using these rules:
3142  <list style="numbers">
3143    <x:lt>
3144      <t>The "chunked" transfer-coding is always acceptable. If the
3145         keyword "trailers" is listed, the client indicates that it is
3146         willing to accept trailer fields in the chunked response on
3147         behalf of itself and any downstream clients. The implication is
3148         that, if given, the client is stating that either all
3149         downstream clients are willing to accept trailer fields in the
3150         forwarded response, or that it will attempt to buffer the
3151         response on behalf of downstream recipients.
3152      </t><t>
3153         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3154         chunked response such that a client can be assured of buffering
3155         the entire response.</t>
3156    </x:lt>
3157    <x:lt>
3158      <t>If the transfer-coding being tested is one of the transfer-codings
3159         listed in the TE field, then it is acceptable unless it
3160         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3161         qvalue of 0 means "not acceptable".)</t>
3162    </x:lt>
3163    <x:lt>
3164      <t>If multiple transfer-codings are acceptable, then the
3165         acceptable transfer-coding with the highest non-zero qvalue is
3166         preferred.  The "chunked" transfer-coding always has a qvalue
3167         of 1.</t>
3168    </x:lt>
3169  </list>
3170</t>
3171<t>
3172   If the TE field-value is empty or if no TE field is present, the only
3173   acceptable transfer-coding is "chunked". A message with no transfer-coding is
3174   always acceptable.
3175</t>
3176</section>
3177
3178<section title="Trailer" anchor="header.trailer">
3179  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3180  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3181  <x:anchor-alias value="Trailer"/>
3182<t>
3183   The "Trailer" header field indicates that the given set of
3184   header fields is present in the trailer of a message encoded with
3185   chunked transfer-coding.
3186</t>
3187<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3188  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3189</artwork></figure>
3190<t>
3191   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3192   message using chunked transfer-coding with a non-empty trailer. Doing
3193   so allows the recipient to know which header fields to expect in the
3194   trailer.
3195</t>
3196<t>
3197   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3198   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3199   trailer fields in a "chunked" transfer-coding.
3200</t>
3201<t>
3202   Message header fields listed in the Trailer header field &MUST-NOT;
3203   include the following header fields:
3204  <list style="symbols">
3205    <t>Transfer-Encoding</t>
3206    <t>Content-Length</t>
3207    <t>Trailer</t>
3208  </list>
3209</t>
3210</section>
3211
3212<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3213  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3214  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3215  <x:anchor-alias value="Transfer-Encoding"/>
3216<t>
3217   The "Transfer-Encoding" header field indicates what transfer-codings
3218   (if any) have been applied to the message body. It differs from
3219   Content-Encoding (&content-codings;) in that transfer-codings are a property
3220   of the message (and therefore are removed by intermediaries), whereas
3221   content-codings are not.
3222</t>
3223<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3224  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3225</artwork></figure>
3226<t>
3227   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3228</t>
3229<figure><artwork type="example">
3230  Transfer-Encoding: chunked
3231</artwork></figure>
3232<t>
3233   If multiple encodings have been applied to a representation, the transfer-codings
3234   &MUST; be listed in the order in which they were applied.
3235   Additional information about the encoding parameters &MAY; be provided
3236   by other header fields not defined by this specification.
3237</t>
3238<t>
3239   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3240   header field.
3241</t>
3242</section>
3243
3244<section title="Upgrade" anchor="header.upgrade">
3245  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3246  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3247  <x:anchor-alias value="Upgrade"/>
3248<t>
3249   The "Upgrade" header field allows the client to specify what
3250   additional communication protocols it would like to use, if the server
3251   chooses to switch protocols. Servers can use it to indicate what protocols
3252   they are willing to switch to.
3253</t>
3254<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3255  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3256</artwork></figure>
3257<t>
3258   For example,
3259</t>
3260<figure><artwork type="example">
3261  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3262</artwork></figure>
3263<t>
3264   The Upgrade header field is intended to provide a simple mechanism
3265   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3266   does so by allowing the client to advertise its desire to use another
3267   protocol, such as a later version of HTTP with a higher major version
3268   number, even though the current request has been made using HTTP/1.1.
3269   This eases the difficult transition between incompatible protocols by
3270   allowing the client to initiate a request in the more commonly
3271   supported protocol while indicating to the server that it would like
3272   to use a "better" protocol if available (where "better" is determined
3273   by the server, possibly according to the nature of the request method
3274   or target resource).
3275</t>
3276<t>
3277   The Upgrade header field only applies to switching application-layer
3278   protocols upon the existing transport-layer connection. Upgrade
3279   cannot be used to insist on a protocol change; its acceptance and use
3280   by the server is optional. The capabilities and nature of the
3281   application-layer communication after the protocol change is entirely
3282   dependent upon the new protocol chosen, although the first action
3283   after changing the protocol &MUST; be a response to the initial HTTP
3284   request containing the Upgrade header field.
3285</t>
3286<t>
3287   The Upgrade header field only applies to the immediate connection.
3288   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3289   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3290   HTTP/1.1 message.
3291</t>
3292<t>
3293   The Upgrade header field cannot be used to indicate a switch to a
3294   protocol on a different connection. For that purpose, it is more
3295   appropriate to use a 3xx redirection response (&status-3xx;).
3296</t>
3297<t>
3298   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3299   Protocols) responses to indicate which protocol(s) are being switched to,
3300   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3301   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3302   response to indicate that they are willing to upgrade to one of the
3303   specified protocols.
3304</t>
3305<t>
3306   This specification only defines the protocol name "HTTP" for use by
3307   the family of Hypertext Transfer Protocols, as defined by the HTTP
3308   version rules of <xref target="http.version"/> and future updates to this
3309   specification. Additional tokens can be registered with IANA using the
3310   registration procedure defined below. 
3311</t>
3312
3313<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3314<t>
3315   The HTTP Upgrade Token Registry defines the name space for product
3316   tokens used to identify protocols in the Upgrade header field.
3317   Each registered token is associated with contact information and
3318   an optional set of specifications that details how the connection
3319   will be processed after it has been upgraded.
3320</t>
3321<t>
3322   Registrations are allowed on a First Come First Served basis as
3323   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3324   specifications need not be IETF documents or be subject to IESG review.
3325   Registrations are subject to the following rules:
3326  <list style="numbers">
3327    <t>A token, once registered, stays registered forever.</t>
3328    <t>The registration &MUST; name a responsible party for the
3329       registration.</t>
3330    <t>The registration &MUST; name a point of contact.</t>
3331    <t>The registration &MAY; name a set of specifications associated with that
3332       token. Such specifications need not be publicly available.</t>
3333    <t>The responsible party &MAY; change the registration at any time.
3334       The IANA will keep a record of all such changes, and make them
3335       available upon request.</t>
3336    <t>The responsible party for the first registration of a "product"
3337       token &MUST; approve later registrations of a "version" token
3338       together with that "product" token before they can be registered.</t>
3339    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3340       for a token. This will normally only be used in the case when a
3341       responsible party cannot be contacted.</t>
3342  </list>
3343</t>
3344</section>
3345
3346
3347</section>
3348
3349<section title="Via" anchor="header.via">
3350  <iref primary="true" item="Via header field" x:for-anchor=""/>
3351  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3352  <x:anchor-alias value="protocol-name"/>
3353  <x:anchor-alias value="protocol-version"/>
3354  <x:anchor-alias value="pseudonym"/>
3355  <x:anchor-alias value="received-by"/>
3356  <x:anchor-alias value="received-protocol"/>
3357  <x:anchor-alias value="Via"/>
3358<t>
3359   The "Via" header field &MUST; be sent by a proxy or gateway to
3360   indicate the intermediate protocols and recipients between the user
3361   agent and the server on requests, and between the origin server and
3362   the client on responses. It is analogous to the "Received" field
3363   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3364   and is intended to be used for tracking message forwards,
3365   avoiding request loops, and identifying the protocol capabilities of
3366   all senders along the request/response chain.
3367</t>
3368<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/>
3369  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3370                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3371  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3372  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3373  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3374  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3375  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3376</artwork></figure>
3377<t>
3378   The received-protocol indicates the protocol version of the message
3379   received by the server or client along each segment of the
3380   request/response chain. The received-protocol version is appended to
3381   the Via field value when the message is forwarded so that information
3382   about the protocol capabilities of upstream applications remains
3383   visible to all recipients.
3384</t>
3385<t>
3386   The protocol-name is excluded if and only if it would be "HTTP". The
3387   received-by field is normally the host and optional port number of a
3388   recipient server or client that subsequently forwarded the message.
3389   However, if the real host is considered to be sensitive information,
3390   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3391   be assumed to be the default port of the received-protocol.
3392</t>
3393<t>
3394   Multiple Via field values represent each proxy or gateway that has
3395   forwarded the message. Each recipient &MUST; append its information
3396   such that the end result is ordered according to the sequence of
3397   forwarding applications.
3398</t>
3399<t>
3400   Comments &MAY; be used in the Via header field to identify the software
3401   of each recipient, analogous to the User-Agent and Server header fields.
3402   However, all comments in the Via field are optional and &MAY; be removed
3403   by any recipient prior to forwarding the message.
3404</t>
3405<t>
3406   For example, a request message could be sent from an HTTP/1.0 user
3407   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3408   forward the request to a public proxy at p.example.net, which completes
3409   the request by forwarding it to the origin server at www.example.com.
3410   The request received by www.example.com would then have the following
3411   Via header field:
3412</t>
3413<figure><artwork type="example">
3414  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3415</artwork></figure>
3416<t>
3417   A proxy or gateway used as a portal through a network firewall
3418   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3419   region unless it is explicitly enabled to do so. If not enabled, the
3420   received-by host of any host behind the firewall &SHOULD; be replaced
3421   by an appropriate pseudonym for that host.
3422</t>
3423<t>
3424   For organizations that have strong privacy requirements for hiding
3425   internal structures, a proxy or gateway &MAY; combine an ordered
3426   subsequence of Via header field entries with identical received-protocol
3427   values into a single such entry. For example,
3428</t>
3429<figure><artwork type="example">
3430  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3431</artwork></figure>
3432<t>
3433  could be collapsed to
3434</t>
3435<figure><artwork type="example">
3436  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3437</artwork></figure>
3438<t>
3439   Senders &SHOULD-NOT; combine multiple entries unless they are all
3440   under the same organizational control and the hosts have already been
3441   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3442   have different received-protocol values.
3443</t>
3444</section>
3445
3446</section>
3447
3448<section title="IANA Considerations" anchor="IANA.considerations">
3449
3450<section title="Header Field Registration" anchor="header.field.registration">
3451<t>
3452   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3453   with the permanent registrations below (see <xref target="RFC3864"/>):
3454</t>
3455<?BEGININC p1-messaging.iana-headers ?>
3456<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3457<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3458   <ttcol>Header Field Name</ttcol>
3459   <ttcol>Protocol</ttcol>
3460   <ttcol>Status</ttcol>
3461   <ttcol>Reference</ttcol>
3462
3463   <c>Connection</c>
3464   <c>http</c>
3465   <c>standard</c>
3466   <c>
3467      <xref target="header.connection"/>
3468   </c>
3469   <c>Content-Length</c>
3470   <c>http</c>
3471   <c>standard</c>
3472   <c>
3473      <xref target="header.content-length"/>
3474   </c>
3475   <c>Host</c>
3476   <c>http</c>
3477   <c>standard</c>
3478   <c>
3479      <xref target="header.host"/>
3480   </c>
3481   <c>TE</c>
3482   <c>http</c>
3483   <c>standard</c>
3484   <c>
3485      <xref target="header.te"/>
3486   </c>
3487   <c>Trailer</c>
3488   <c>http</c>
3489   <c>standard</c>
3490   <c>
3491      <xref target="header.trailer"/>
3492   </c>
3493   <c>Transfer-Encoding</c>
3494   <c>http</c>
3495   <c>standard</c>
3496   <c>
3497      <xref target="header.transfer-encoding"/>
3498   </c>
3499   <c>Upgrade</c>
3500   <c>http</c>
3501   <c>standard</c>
3502   <c>
3503      <xref target="header.upgrade"/>
3504   </c>
3505   <c>Via</c>
3506   <c>http</c>
3507   <c>standard</c>
3508   <c>
3509      <xref target="header.via"/>
3510   </c>
3511</texttable>
3512<!--(END)-->
3513<?ENDINC p1-messaging.iana-headers ?>
3514<t>
3515   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3516   HTTP header field would be in conflict with the use of the "close" connection
3517   option for the "Connection" header field (<xref target="header.connection"/>).
3518</t>
3519<texttable align="left" suppress-title="true">
3520   <ttcol>Header Field Name</ttcol>
3521   <ttcol>Protocol</ttcol>
3522   <ttcol>Status</ttcol>
3523   <ttcol>Reference</ttcol>
3524
3525   <c>Close</c>
3526   <c>http</c>
3527   <c>reserved</c>
3528   <c>
3529      <xref target="header.field.registration"/>
3530   </c>
3531</texttable>
3532<t>
3533   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3534</t>
3535</section>
3536
3537<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3538<t>
3539   The entries for the "http" and "https" URI Schemes in the registry located at
3540   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3541   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3542   and <xref target="https.uri" format="counter"/> of this document
3543   (see <xref target="RFC4395"/>).
3544</t>
3545</section>
3546
3547<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3548<t>
3549   This document serves as the specification for the Internet media types
3550   "message/http" and "application/http". The following is to be registered with
3551   IANA (see <xref target="RFC4288"/>).
3552</t>
3553<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3554<iref item="Media Type" subitem="message/http" primary="true"/>
3555<iref item="message/http Media Type" primary="true"/>
3556<t>
3557   The message/http type can be used to enclose a single HTTP request or
3558   response message, provided that it obeys the MIME restrictions for all
3559   "message" types regarding line length and encodings.
3560</t>
3561<t>
3562  <list style="hanging" x:indent="12em">
3563    <t hangText="Type name:">
3564      message
3565    </t>
3566    <t hangText="Subtype name:">
3567      http
3568    </t>
3569    <t hangText="Required parameters:">
3570      none
3571    </t>
3572    <t hangText="Optional parameters:">
3573      version, msgtype
3574      <list style="hanging">
3575        <t hangText="version:">
3576          The HTTP-Version number of the enclosed message
3577          (e.g., "1.1"). If not present, the version can be
3578          determined from the first line of the body.
3579        </t>
3580        <t hangText="msgtype:">
3581          The message type &mdash; "request" or "response". If not
3582          present, the type can be determined from the first
3583          line of the body.
3584        </t>
3585      </list>
3586    </t>
3587    <t hangText="Encoding considerations:">
3588      only "7bit", "8bit", or "binary" are permitted
3589    </t>
3590    <t hangText="Security considerations:">
3591      none
3592    </t>
3593    <t hangText="Interoperability considerations:">
3594      none
3595    </t>
3596    <t hangText="Published specification:">
3597      This specification (see <xref target="internet.media.type.message.http"/>).
3598    </t>
3599    <t hangText="Applications that use this media type:">
3600    </t>
3601    <t hangText="Additional information:">
3602      <list style="hanging">
3603        <t hangText="Magic number(s):">none</t>
3604        <t hangText="File extension(s):">none</t>
3605        <t hangText="Macintosh file type code(s):">none</t>
3606      </list>
3607    </t>
3608    <t hangText="Person and email address to contact for further information:">
3609      See Authors Section.
3610    </t>
3611    <t hangText="Intended usage:">
3612      COMMON
3613    </t>
3614    <t hangText="Restrictions on usage:">
3615      none
3616    </t>
3617    <t hangText="Author/Change controller:">
3618      IESG
3619    </t>
3620  </list>
3621</t>
3622</section>
3623<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3624<iref item="Media Type" subitem="application/http" primary="true"/>
3625<iref item="application/http Media Type" primary="true"/>
3626<t>
3627   The application/http type can be used to enclose a pipeline of one or more
3628   HTTP request or response messages (not intermixed).
3629</t>
3630<t>
3631  <list style="hanging" x:indent="12em">
3632    <t hangText="Type name:">
3633      application
3634    </t>
3635    <t hangText="Subtype name:">
3636      http
3637    </t>
3638    <t hangText="Required parameters:">
3639      none
3640    </t>
3641    <t hangText="Optional parameters:">
3642      version, msgtype
3643      <list style="hanging">
3644        <t hangText="version:">
3645          The HTTP-Version number of the enclosed messages
3646          (e.g., "1.1"). If not present, the version can be
3647          determined from the first line of the body.
3648        </t>
3649        <t hangText="msgtype:">
3650          The message type &mdash; "request" or "response". If not
3651          present, the type can be determined from the first
3652          line of the body.
3653        </t>
3654      </list>
3655    </t>
3656    <t hangText="Encoding considerations:">
3657      HTTP messages enclosed by this type
3658      are in "binary" format; use of an appropriate
3659      Content-Transfer-Encoding is required when
3660      transmitted via E-mail.
3661    </t>
3662    <t hangText="Security considerations:">
3663      none
3664    </t>
3665    <t hangText="Interoperability considerations:">
3666      none
3667    </t>
3668    <t hangText="Published specification:">
3669      This specification (see <xref target="internet.media.type.application.http"/>).
3670    </t>
3671    <t hangText="Applications that use this media type:">
3672    </t>
3673    <t hangText="Additional information:">
3674      <list style="hanging">
3675        <t hangText="Magic number(s):">none</t>
3676        <t hangText="File extension(s):">none</t>
3677        <t hangText="Macintosh file type code(s):">none</t>
3678      </list>
3679    </t>
3680    <t hangText="Person and email address to contact for further information:">
3681      See Authors Section.
3682    </t>
3683    <t hangText="Intended usage:">
3684      COMMON
3685    </t>
3686    <t hangText="Restrictions on usage:">
3687      none
3688    </t>
3689    <t hangText="Author/Change controller:">
3690      IESG
3691    </t>
3692  </list>
3693</t>
3694</section>
3695</section>
3696
3697<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3698<t>
3699   The registration procedure for HTTP Transfer Codings is now defined by
3700   <xref target="transfer.coding.registry"/> of this document.
3701</t>
3702<t>
3703   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3704   shall be updated with the registrations below:
3705</t>
3706<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3707   <ttcol>Name</ttcol>
3708   <ttcol>Description</ttcol>
3709   <ttcol>Reference</ttcol>
3710   <c>chunked</c>
3711   <c>Transfer in a series of chunks</c>
3712   <c>
3713      <xref target="chunked.encoding"/>
3714   </c>
3715   <c>compress</c>
3716   <c>UNIX "compress" program method</c>
3717   <c>
3718      <xref target="compress.coding"/>
3719   </c>
3720   <c>deflate</c>
3721   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3722   the "zlib" data format (<xref target="RFC1950"/>)
3723   </c>
3724   <c>
3725      <xref target="deflate.coding"/>
3726   </c>
3727   <c>gzip</c>
3728   <c>Same as GNU zip <xref target="RFC1952"/></c>
3729   <c>
3730      <xref target="gzip.coding"/>
3731   </c>
3732</texttable>
3733</section>
3734
3735<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3736<t>
3737   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3738   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3739   by <xref target="upgrade.token.registry"/> of this document.
3740</t>
3741<t>
3742   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3743   shall be updated with the registration below:
3744</t>
3745<texttable align="left" suppress-title="true">
3746   <ttcol>Value</ttcol>
3747   <ttcol>Description</ttcol>
3748   <ttcol>Reference</ttcol>
3749
3750   <c>HTTP</c>
3751   <c>Hypertext Transfer Protocol</c> 
3752   <c><xref target="http.version"/> of this specification</c>
3753
3754</texttable>
3755</section>
3756
3757</section>
3758
3759<section title="Security Considerations" anchor="security.considerations">
3760<t>
3761   This section is meant to inform application developers, information
3762   providers, and users of the security limitations in HTTP/1.1 as
3763   described by this document. The discussion does not include
3764   definitive solutions to the problems revealed, though it does make
3765   some suggestions for reducing security risks.
3766</t>
3767
3768<section title="Personal Information" anchor="personal.information">
3769<t>
3770   HTTP clients are often privy to large amounts of personal information
3771   (e.g., the user's name, location, mail address, passwords, encryption
3772   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3773   leakage of this information.
3774   We very strongly recommend that a convenient interface be provided
3775   for the user to control dissemination of such information, and that
3776   designers and implementors be particularly careful in this area.
3777   History shows that errors in this area often create serious security
3778   and/or privacy problems and generate highly adverse publicity for the
3779   implementor's company.
3780</t>
3781</section>
3782
3783<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3784<t>
3785   A server is in the position to save personal data about a user's
3786   requests which might identify their reading patterns or subjects of
3787   interest. This information is clearly confidential in nature and its
3788   handling can be constrained by law in certain countries. People using
3789   HTTP to provide data are responsible for ensuring that
3790   such material is not distributed without the permission of any
3791   individuals that are identifiable by the published results.
3792</t>
3793</section>
3794
3795<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3796<t>
3797   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3798   the documents returned by HTTP requests to be only those that were
3799   intended by the server administrators. If an HTTP server translates
3800   HTTP URIs directly into file system calls, the server &MUST; take
3801   special care not to serve files that were not intended to be
3802   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3803   other operating systems use ".." as a path component to indicate a
3804   directory level above the current one. On such a system, an HTTP
3805   server &MUST; disallow any such construct in the request-target if it
3806   would otherwise allow access to a resource outside those intended to
3807   be accessible via the HTTP server. Similarly, files intended for
3808   reference only internally to the server (such as access control
3809   files, configuration files, and script code) &MUST; be protected from
3810   inappropriate retrieval, since they might contain sensitive
3811   information. Experience has shown that minor bugs in such HTTP server
3812   implementations have turned into security risks.
3813</t>
3814</section>
3815
3816<section title="DNS-related Attacks" anchor="dns.related.attacks">
3817<t>
3818   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3819   generally prone to security attacks based on the deliberate misassociation
3820   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3821   cautious in assuming the validity of an IP number/DNS name association unless
3822   the response is protected by DNSSec (<xref target="RFC4033"/>).
3823</t>
3824</section>
3825
3826<section title="Proxies and Caching" anchor="attack.proxies">
3827<t>
3828   By their very nature, HTTP proxies are men-in-the-middle, and
3829   represent an opportunity for man-in-the-middle attacks. Compromise of
3830   the systems on which the proxies run can result in serious security
3831   and privacy problems. Proxies have access to security-related
3832   information, personal information about individual users and
3833   organizations, and proprietary information belonging to users and
3834   content providers. A compromised proxy, or a proxy implemented or
3835   configured without regard to security and privacy considerations,
3836   might be used in the commission of a wide range of potential attacks.
3837</t>
3838<t>
3839   Proxy operators need to protect the systems on which proxies run as
3840   they would protect any system that contains or transports sensitive
3841   information. In particular, log information gathered at proxies often
3842   contains highly sensitive personal information, and/or information
3843   about organizations. Log information needs to be carefully guarded, and
3844   appropriate guidelines for use need to be developed and followed.
3845   (<xref target="abuse.of.server.log.information"/>).
3846</t>
3847<t>
3848   Proxy implementors need to consider the privacy and security
3849   implications of their design and coding decisions, and of the
3850   configuration options they provide to proxy operators (especially the
3851   default configuration).
3852</t>
3853<t>
3854   Users of a proxy need to be aware that proxies are no more trustworthy than
3855   the people who run them; HTTP itself cannot solve this problem.
3856</t>
3857<t>
3858   The judicious use of cryptography, when appropriate, might suffice to
3859   protect against a broad range of security and privacy attacks. Such
3860   cryptography is beyond the scope of the HTTP/1.1 specification.
3861</t>
3862</section>
3863
3864<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3865<t>
3866   Because HTTP uses mostly textual, character-delimited fields, attackers can
3867   overflow buffers in implementations, and/or perform a Denial of Service
3868   against implementations that accept fields with unlimited lengths.
3869</t>
3870<t>
3871   To promote interoperability, this specification makes specific
3872   recommendations for size limits on request-targets (<xref target="request-target"/>)
3873   and blocks of header fields (<xref target="header.fields"/>). These are
3874   minimum recommendations, chosen to be supportable even by implementations
3875   with limited resources; it is expected that most implementations will choose
3876   substantially higher limits.
3877</t>
3878<t>
3879   This specification also provides a way for servers to reject messages that
3880   have request-targets that are too long (&status-414;) or request entities
3881   that are too large (&status-4xx;).
3882</t>
3883<t>
3884   Other fields (including but not limited to request methods, response status
3885   phrases, header field-names, and body chunks) &SHOULD; be limited by
3886   implementations carefully, so as to not impede interoperability.
3887</t>
3888</section>
3889
3890<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3891<t>
3892   They exist. They are hard to defend against. Research continues.
3893   Beware.
3894</t>
3895</section>
3896</section>
3897
3898<section title="Acknowledgments" anchor="acks">
3899<t>
3900   This document revision builds on the work that went into
3901   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3902   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
3903   acknowledgements.
3904</t>
3905<t>
3906   Since 1999, many contributors have helped by reporting bugs, asking
3907   smart questions, drafting and reviewing text, and discussing open issues:
3908</t>
3909<?BEGININC acks ?>
3910<t>Adam Barth,
3911Adam Roach,
3912Addison Phillips,
3913Adrian Chadd,
3914Adrien de Croy,
3915Alan Ford,
3916Alan Ruttenberg,
3917Albert Lunde,
3918Alex Rousskov,
3919Alexey Melnikov,
3920Alisha Smith,
3921Amichai Rothman,
3922Amit Klein,
3923Amos Jeffries,
3924Andreas Maier,
3925Andreas Petersson,
3926Anne van Kesteren,
3927Anthony Bryan,
3928Asbjorn Ulsberg,
3929Balachander Krishnamurthy,
3930Barry Leiba,
3931Ben Laurie,
3932Benjamin Niven-Jenkins,
3933Bil Corry,
3934Bill Burke,
3935Bjoern Hoehrmann,
3936Bob Scheifler,
3937Boris Zbarsky,
3938Brett Slatkin,
3939Brian Kell,
3940Brian McBarron,
3941Brian Pane,
3942Brian Smith,
3943Bryce Nesbitt,
3944Cameron Heavon-Jones,
3945Carl Kugler,
3946Carsten Bormann,
3947Charles Fry,
3948Chris Newman,
3949Cyrus Daboo,
3950Dale Robert Anderson,
3951Dan Winship,
3952Daniel Stenberg,
3953Dave Cridland,
3954Dave Crocker,
3955Dave Kristol,
3956David Booth,
3957David Singer,
3958David W. Morris,
3959Diwakar Shetty,
3960Dmitry Kurochkin,
3961Drummond Reed,
3962Duane Wessels,
3963Edward Lee,
3964Eliot Lear,
3965Eran Hammer-Lahav,
3966Eric D. Williams,
3967Eric J. Bowman,
3968Eric Lawrence,
3969Erik Aronesty,
3970Florian Weimer,
3971Frank Ellermann,
3972Fred Bohle,
3973Geoffrey Sneddon,
3974Gervase Markham,
3975Greg Wilkins,
3976Harald Tveit Alvestrand,
3977Harry Halpin,
3978Helge Hess,
3979Henrik Nordstrom,
3980Henry S. Thompson,
3981Henry Story,
3982Herbert van de Sompel,
3983Howard Melman,
3984Hugo Haas,
3985Ian Hickson,
3986Ingo Struck,
3987J. Ross Nicoll,
3988James H. Manger,
3989James Lacey,
3990James M. Snell,
3991Jamie Lokier,
3992Jan Algermissen,
3993Jeff Hodges (for coming up with the term 'effective Request-URI'),
3994Jeff Walden,
3995Jim Luther,
3996Joe D. Williams,
3997Joe Gregorio,
3998Joe Orton,
3999John C. Klensin,
4000John C. Mallery,
4001John Cowan,
4002John Kemp,
4003John Panzer,
4004John Schneider,
4005John Stracke,
4006Jonas Sicking,
4007Jonathan Billington,
4008Jonathan Moore,
4009Jonathan Rees,
4010Jordi Ros,
4011Joris Dobbelsteen,
4012Josh Cohen,
4013Julien Pierre,
4014Jungshik Shin,
4015Justin Chapweske,
4016Justin Erenkrantz,
4017Justin James,
4018Kalvinder Singh,
4019Karl Dubost,
4020Keith Hoffman,
4021Keith Moore,
4022Koen Holtman,
4023Konstantin Voronkov,
4024Kris Zyp,
4025Lisa Dusseault,
4026Maciej Stachowiak,
4027Marc Schneider,
4028Marc Slemko,
4029Mark Baker,
4030Mark Nottingham (Working Group chair),
4031Mark Pauley,
4032Markus Lanthaler,
4033Martin J. Duerst,
4034Martin Thomson,
4035Matt Lynch,
4036Matthew Cox,
4037Max Clark,
4038Michael Burrows,
4039Michael Hausenblas,
4040Mike Amundsen,
4041Mike Kelly,
4042Mike Schinkel,
4043Miles Sabin,
4044Mykyta Yevstifeyev,
4045Nathan Rixham,
4046Nicholas Shanks,
4047Nico Williams,
4048Nicolas Alvarez,
4049Noah Slater,
4050Pablo Castro,
4051Pat Hayes,
4052Patrick R. McManus,
4053Paul E. Jones,
4054Paul Hoffman,
4055Paul Marquess,
4056Peter Saint-Andre,
4057Peter Watkins,
4058Phil Archer,
4059Phillip Hallam-Baker,
4060Poul-Henning Kamp,
4061Preethi Natarajan,
4062Ray Polk,
4063Reto Bachmann-Gmuer,
4064Richard Cyganiak,
4065Robert Brewer,
4066Robert Collins,
4067Robert O'Callahan,
4068Robert Olofsson,
4069Robert Sayre,
4070Robert Siemer,
4071Robert de Wilde,
4072Roberto Javier Godoy,
4073Ronny Widjaja,
4074S. Mike Dierken,
4075Salvatore Loreto,
4076Sam Johnston,
4077Sam Ruby,
4078Scott Lawrence (for maintaining the original issues list),
4079Sean B. Palmer,
4080Shane McCarron,
4081Stefan Eissing,
4082Stefan Tilkov,
4083Stefanos Harhalakis,
4084Stephane Bortzmeyer,
4085Stuart Williams,
4086Subbu Allamaraju,
4087Sylvain Hellegouarch,
4088Tapan Divekar,
4089Ted Hardie,
4090Thomas Broyer,
4091Thomas Nordin,
4092Thomas Roessler,
4093Tim Morgan,
4094Tim Olsen,
4095Travis Snoozy,
4096Tyler Close,
4097Vincent Murphy,
4098Wenbo Zhu,
4099Werner Baumann,
4100Wilbur Streett,
4101Wilfredo Sanchez Vega,
4102William A. Rowe Jr.,
4103William Chan,
4104Willy Tarreau,
4105Xiaoshu Wang,
4106Yaron Goland,
4107Yngve Nysaeter Pettersen,
4108Yogesh Bang,
4109Yutaka Oiwa,
4110Zed A. Shaw, and
4111Zhong Yu.
4112</t>
4113<?ENDINC acks ?>
4114</section>
4115
4116</middle>
4117<back>
4118
4119<references title="Normative References">
4120
4121<reference anchor="ISO-8859-1">
4122  <front>
4123    <title>
4124     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4125    </title>
4126    <author>
4127      <organization>International Organization for Standardization</organization>
4128    </author>
4129    <date year="1998"/>
4130  </front>
4131  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4132</reference>
4133
4134<reference anchor="Part2">
4135  <front>
4136    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4137    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4138      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4139      <address><email>fielding@gbiv.com</email></address>
4140    </author>
4141    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4142      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4143      <address><email>jg@freedesktop.org</email></address>
4144    </author>
4145    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4146      <organization abbrev="HP">Hewlett-Packard Company</organization>
4147      <address><email>JeffMogul@acm.org</email></address>
4148    </author>
4149    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4150      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4151      <address><email>henrikn@microsoft.com</email></address>
4152    </author>
4153    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4154      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4155      <address><email>LMM@acm.org</email></address>
4156    </author>
4157    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4158      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4159      <address><email>paulle@microsoft.com</email></address>
4160    </author>
4161    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4162      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4163      <address><email>timbl@w3.org</email></address>
4164    </author>
4165    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4166      <organization abbrev="W3C">World Wide Web Consortium</organization>
4167      <address><email>ylafon@w3.org</email></address>
4168    </author>
4169    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4170      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4171      <address><email>julian.reschke@greenbytes.de</email></address>
4172    </author>
4173    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4174  </front>
4175  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4176  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4177</reference>
4178
4179<reference anchor="Part3">
4180  <front>
4181    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4182    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4183      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4184      <address><email>fielding@gbiv.com</email></address>
4185    </author>
4186    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4187      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4188      <address><email>jg@freedesktop.org</email></address>
4189    </author>
4190    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4191      <organization abbrev="HP">Hewlett-Packard Company</organization>
4192      <address><email>JeffMogul@acm.org</email></address>
4193    </author>
4194    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4195      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4196      <address><email>henrikn@microsoft.com</email></address>
4197    </author>
4198    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4199      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4200      <address><email>LMM@acm.org</email></address>
4201    </author>
4202    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4203      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4204      <address><email>paulle@microsoft.com</email></address>
4205    </author>
4206    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4207      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4208      <address><email>timbl@w3.org</email></address>
4209    </author>
4210    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4211      <organization abbrev="W3C">World Wide Web Consortium</organization>
4212      <address><email>ylafon@w3.org</email></address>
4213    </author>
4214    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4215      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4216      <address><email>julian.reschke@greenbytes.de</email></address>
4217    </author>
4218    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4219  </front>
4220  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4221  <x:source href="p3-payload.xml" basename="p3-payload"/>
4222</reference>
4223
4224<reference anchor="Part6">
4225  <front>
4226    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4227    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4228      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4229      <address><email>fielding@gbiv.com</email></address>
4230    </author>
4231    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4232      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4233      <address><email>jg@freedesktop.org</email></address>
4234    </author>
4235    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4236      <organization abbrev="HP">Hewlett-Packard Company</organization>
4237      <address><email>JeffMogul@acm.org</email></address>
4238    </author>
4239    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4240      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4241      <address><email>henrikn@microsoft.com</email></address>
4242    </author>
4243    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4244      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4245      <address><email>LMM@acm.org</email></address>
4246    </author>
4247    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4248      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4249      <address><email>paulle@microsoft.com</email></address>
4250    </author>
4251    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4252      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4253      <address><email>timbl@w3.org</email></address>
4254    </author>
4255    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4256      <organization abbrev="W3C">World Wide Web Consortium</organization>
4257      <address><email>ylafon@w3.org</email></address>
4258    </author>
4259    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4260      <organization>Rackspace</organization>
4261      <address><email>mnot@mnot.net</email></address>
4262    </author>
4263    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4264      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4265      <address><email>julian.reschke@greenbytes.de</email></address>
4266    </author>
4267    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4268  </front>
4269  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4270  <x:source href="p6-cache.xml" basename="p6-cache"/>
4271</reference>
4272
4273<reference anchor="RFC5234">
4274  <front>
4275    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4276    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4277      <organization>Brandenburg InternetWorking</organization>
4278      <address>
4279        <email>dcrocker@bbiw.net</email>
4280      </address> 
4281    </author>
4282    <author initials="P." surname="Overell" fullname="Paul Overell">
4283      <organization>THUS plc.</organization>
4284      <address>
4285        <email>paul.overell@thus.net</email>
4286      </address>
4287    </author>
4288    <date month="January" year="2008"/>
4289  </front>
4290  <seriesInfo name="STD" value="68"/>
4291  <seriesInfo name="RFC" value="5234"/>
4292</reference>
4293
4294<reference anchor="RFC2119">
4295  <front>
4296    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4297    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4298      <organization>Harvard University</organization>
4299      <address><email>sob@harvard.edu</email></address>
4300    </author>
4301    <date month="March" year="1997"/>
4302  </front>
4303  <seriesInfo name="BCP" value="14"/>
4304  <seriesInfo name="RFC" value="2119"/>
4305</reference>
4306
4307<reference anchor="RFC3986">
4308 <front>
4309  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4310  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4311    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4312    <address>
4313       <email>timbl@w3.org</email>
4314       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4315    </address>
4316  </author>
4317  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4318    <organization abbrev="Day Software">Day Software</organization>
4319    <address>
4320      <email>fielding@gbiv.com</email>
4321      <uri>http://roy.gbiv.com/</uri>
4322    </address>
4323  </author>
4324  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4325    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4326    <address>
4327      <email>LMM@acm.org</email>
4328      <uri>http://larry.masinter.net/</uri>
4329    </address>
4330  </author>
4331  <date month='January' year='2005'></date>
4332 </front>
4333 <seriesInfo name="STD" value="66"/>
4334 <seriesInfo name="RFC" value="3986"/>
4335</reference>
4336
4337<reference anchor="USASCII">
4338  <front>
4339    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4340    <author>
4341      <organization>American National Standards Institute</organization>
4342    </author>
4343    <date year="1986"/>
4344  </front>
4345  <seriesInfo name="ANSI" value="X3.4"/>
4346</reference>
4347
4348<reference anchor="RFC1950">
4349  <front>
4350    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4351    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4352      <organization>Aladdin Enterprises</organization>
4353      <address><email>ghost@aladdin.com</email></address>
4354    </author>
4355    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4356    <date month="May" year="1996"/>
4357  </front>
4358  <seriesInfo name="RFC" value="1950"/>
4359  <!--<annotation>
4360    RFC 1950 is an Informational RFC, thus it might be less stable than
4361    this specification. On the other hand, this downward reference was
4362    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4363    therefore it is unlikely to cause problems in practice. See also
4364    <xref target="BCP97"/>.
4365  </annotation>-->
4366</reference>
4367
4368<reference anchor="RFC1951">
4369  <front>
4370    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4371    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4372      <organization>Aladdin Enterprises</organization>
4373      <address><email>ghost@aladdin.com</email></address>
4374    </author>
4375    <date month="May" year="1996"/>
4376  </front>
4377  <seriesInfo name="RFC" value="1951"/>
4378  <!--<annotation>
4379    RFC 1951 is an Informational RFC, thus it might be less stable than
4380    this specification. On the other hand, this downward reference was
4381    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4382    therefore it is unlikely to cause problems in practice. See also
4383    <xref target="BCP97"/>.
4384  </annotation>-->
4385</reference>
4386
4387<reference anchor="RFC1952">
4388  <front>
4389    <title>GZIP file format specification version 4.3</title>
4390    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4391      <organization>Aladdin Enterprises</organization>
4392      <address><email>ghost@aladdin.com</email></address>
4393    </author>
4394    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4395      <address><email>gzip@prep.ai.mit.edu</email></address>
4396    </author>
4397    <author initials="M." surname="Adler" fullname="Mark Adler">
4398      <address><email>madler@alumni.caltech.edu</email></address>
4399    </author>
4400    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4401      <address><email>ghost@aladdin.com</email></address>
4402    </author>
4403    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4404      <address><email>randeg@alumni.rpi.edu</email></address>
4405    </author>
4406    <date month="May" year="1996"/>
4407  </front>
4408  <seriesInfo name="RFC" value="1952"/>
4409  <!--<annotation>
4410    RFC 1952 is an Informational RFC, thus it might be less stable than
4411    this specification. On the other hand, this downward reference was
4412    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4413    therefore it is unlikely to cause problems in practice. See also
4414    <xref target="BCP97"/>.
4415  </annotation>-->
4416</reference>
4417
4418</references>
4419
4420<references title="Informative References">
4421
4422<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4423  <front>
4424    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4425    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4426    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4427    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4428    <author initials="H." surname="Lie" fullname="H. Lie"/>
4429    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4430    <date year="1997" month="September"/>
4431  </front>
4432  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4433</reference>
4434
4435<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4436  <front>
4437    <title>Improving HTTP Latency</title>
4438    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4439    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4440    <date year="1995" month="December"/>
4441  </front>
4442  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4443</reference>
4444
4445<reference anchor='RFC1919'>
4446  <front>
4447    <title>Classical versus Transparent IP Proxies</title>
4448    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4449      <address><email>mchatel@pax.eunet.ch</email></address>
4450    </author>
4451    <date year='1996' month='March' />
4452  </front>
4453  <seriesInfo name='RFC' value='1919' />
4454</reference>
4455
4456<reference anchor="RFC1945">
4457  <front>
4458    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4459    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4460      <organization>MIT, Laboratory for Computer Science</organization>
4461      <address><email>timbl@w3.org</email></address>
4462    </author>
4463    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4464      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4465      <address><email>fielding@ics.uci.edu</email></address>
4466    </author>
4467    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4468      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4469      <address><email>frystyk@w3.org</email></address>
4470    </author>
4471    <date month="May" year="1996"/>
4472  </front>
4473  <seriesInfo name="RFC" value="1945"/>
4474</reference>
4475
4476<reference anchor="RFC2045">
4477  <front>
4478    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4479    <author initials="N." surname="Freed" fullname="Ned Freed">
4480      <organization>Innosoft International, Inc.</organization>
4481      <address><email>ned@innosoft.com</email></address>
4482    </author>
4483    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4484      <organization>First Virtual Holdings</organization>
4485      <address><email>nsb@nsb.fv.com</email></address>
4486    </author>
4487    <date month="November" year="1996"/>
4488  </front>
4489  <seriesInfo name="RFC" value="2045"/>
4490</reference>
4491
4492<reference anchor="RFC2047">
4493  <front>
4494    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4495    <author initials="K." surname="Moore" fullname="Keith Moore">
4496      <organization>University of Tennessee</organization>
4497      <address><email>moore@cs.utk.edu</email></address>
4498    </author>
4499    <date month="November" year="1996"/>
4500  </front>
4501  <seriesInfo name="RFC" value="2047"/>
4502</reference>
4503
4504<reference anchor="RFC2068">
4505  <front>
4506    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4507    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4508      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4509      <address><email>fielding@ics.uci.edu</email></address>
4510    </author>
4511    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4512      <organization>MIT Laboratory for Computer Science</organization>
4513      <address><email>jg@w3.org</email></address>
4514    </author>
4515    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4516      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4517      <address><email>mogul@wrl.dec.com</email></address>
4518    </author>
4519    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4520      <organization>MIT Laboratory for Computer Science</organization>
4521      <address><email>frystyk@w3.org</email></address>
4522    </author>
4523    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4524      <organization>MIT Laboratory for Computer Science</organization>
4525      <address><email>timbl@w3.org</email></address>
4526    </author>
4527    <date month="January" year="1997"/>
4528  </front>
4529  <seriesInfo name="RFC" value="2068"/>
4530</reference>
4531
4532<reference anchor="RFC2145">
4533  <front>
4534    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4535    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4536      <organization>Western Research Laboratory</organization>
4537      <address><email>mogul@wrl.dec.com</email></address>
4538    </author>
4539    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4540      <organization>Department of Information and Computer Science</organization>
4541      <address><email>fielding@ics.uci.edu</email></address>
4542    </author>
4543    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4544      <organization>MIT Laboratory for Computer Science</organization>
4545      <address><email>jg@w3.org</email></address>
4546    </author>
4547    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4548      <organization>W3 Consortium</organization>
4549      <address><email>frystyk@w3.org</email></address>
4550    </author>
4551    <date month="May" year="1997"/>
4552  </front>
4553  <seriesInfo name="RFC" value="2145"/>
4554</reference>
4555
4556<reference anchor="RFC2616">
4557  <front>
4558    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4559    <author initials="R." surname="Fielding" fullname="R. Fielding">
4560      <organization>University of California, Irvine</organization>
4561      <address><email>fielding@ics.uci.edu</email></address>
4562    </author>
4563    <author initials="J." surname="Gettys" fullname="J. Gettys">
4564      <organization>W3C</organization>
4565      <address><email>jg@w3.org</email></address>
4566    </author>
4567    <author initials="J." surname="Mogul" fullname="J. Mogul">
4568      <organization>Compaq Computer Corporation</organization>
4569      <address><email>mogul@wrl.dec.com</email></address>
4570    </author>
4571    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4572      <organization>MIT Laboratory for Computer Science</organization>
4573      <address><email>frystyk@w3.org</email></address>
4574    </author>
4575    <author initials="L." surname="Masinter" fullname="L. Masinter">
4576      <organization>Xerox Corporation</organization>
4577      <address><email>masinter@parc.xerox.com</email></address>
4578    </author>
4579    <author initials="P." surname="Leach" fullname="P. Leach">
4580      <organization>Microsoft Corporation</organization>
4581      <address><email>paulle@microsoft.com</email></address>
4582    </author>
4583    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4584      <organization>W3C</organization>
4585      <address><email>timbl@w3.org</email></address>
4586    </author>
4587    <date month="June" year="1999"/>
4588  </front>
4589  <seriesInfo name="RFC" value="2616"/>
4590</reference>
4591
4592<reference anchor='RFC2817'>
4593  <front>
4594    <title>Upgrading to TLS Within HTTP/1.1</title>
4595    <author initials='R.' surname='Khare' fullname='R. Khare'>
4596      <organization>4K Associates / UC Irvine</organization>
4597      <address><email>rohit@4K-associates.com</email></address>
4598    </author>
4599    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4600      <organization>Agranat Systems, Inc.</organization>
4601      <address><email>lawrence@agranat.com</email></address>
4602    </author>
4603    <date year='2000' month='May' />
4604  </front>
4605  <seriesInfo name='RFC' value='2817' />
4606</reference>
4607
4608<reference anchor='RFC2818'>
4609  <front>
4610    <title>HTTP Over TLS</title>
4611    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4612      <organization>RTFM, Inc.</organization>
4613      <address><email>ekr@rtfm.com</email></address>
4614    </author>
4615    <date year='2000' month='May' />
4616  </front>
4617  <seriesInfo name='RFC' value='2818' />
4618</reference>
4619
4620<reference anchor='RFC2965'>
4621  <front>
4622    <title>HTTP State Management Mechanism</title>
4623    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4624      <organization>Bell Laboratories, Lucent Technologies</organization>
4625      <address><email>dmk@bell-labs.com</email></address>
4626    </author>
4627    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4628      <organization>Epinions.com, Inc.</organization>
4629      <address><email>lou@montulli.org</email></address>
4630    </author>
4631    <date year='2000' month='October' />
4632  </front>
4633  <seriesInfo name='RFC' value='2965' />
4634</reference>
4635
4636<reference anchor='RFC3040'>
4637  <front>
4638    <title>Internet Web Replication and Caching Taxonomy</title>
4639    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4640      <organization>Equinix, Inc.</organization>
4641    </author>
4642    <author initials='I.' surname='Melve' fullname='I. Melve'>
4643      <organization>UNINETT</organization>
4644    </author>
4645    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4646      <organization>CacheFlow Inc.</organization>
4647    </author>
4648    <date year='2001' month='January' />
4649  </front>
4650  <seriesInfo name='RFC' value='3040' />
4651</reference>
4652
4653<reference anchor='RFC3864'>
4654  <front>
4655    <title>Registration Procedures for Message Header Fields</title>
4656    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4657      <organization>Nine by Nine</organization>
4658      <address><email>GK-IETF@ninebynine.org</email></address>
4659    </author>
4660    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4661      <organization>BEA Systems</organization>
4662      <address><email>mnot@pobox.com</email></address>
4663    </author>
4664    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4665      <organization>HP Labs</organization>
4666      <address><email>JeffMogul@acm.org</email></address>
4667    </author>
4668    <date year='2004' month='September' />
4669  </front>
4670  <seriesInfo name='BCP' value='90' />
4671  <seriesInfo name='RFC' value='3864' />
4672</reference>
4673
4674<reference anchor='RFC4033'>
4675  <front>
4676    <title>DNS Security Introduction and Requirements</title>
4677    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4678    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4679    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4680    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4681    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4682    <date year='2005' month='March' />
4683  </front>
4684  <seriesInfo name='RFC' value='4033' />
4685</reference>
4686
4687<reference anchor="RFC4288">
4688  <front>
4689    <title>Media Type Specifications and Registration Procedures</title>
4690    <author initials="N." surname="Freed" fullname="N. Freed">
4691      <organization>Sun Microsystems</organization>
4692      <address>
4693        <email>ned.freed@mrochek.com</email>
4694      </address>
4695    </author>
4696    <author initials="J." surname="Klensin" fullname="J. Klensin">
4697      <address>
4698        <email>klensin+ietf@jck.com</email>
4699      </address>
4700    </author>
4701    <date year="2005" month="December"/>
4702  </front>
4703  <seriesInfo name="BCP" value="13"/>
4704  <seriesInfo name="RFC" value="4288"/>
4705</reference>
4706
4707<reference anchor='RFC4395'>
4708  <front>
4709    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4710    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4711      <organization>AT&amp;T Laboratories</organization>
4712      <address>
4713        <email>tony+urireg@maillennium.att.com</email>
4714      </address>
4715    </author>
4716    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4717      <organization>Qualcomm, Inc.</organization>
4718      <address>
4719        <email>hardie@qualcomm.com</email>
4720      </address>
4721    </author>
4722    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4723      <organization>Adobe Systems</organization>
4724      <address>
4725        <email>LMM@acm.org</email>
4726      </address>
4727    </author>
4728    <date year='2006' month='February' />
4729  </front>
4730  <seriesInfo name='BCP' value='115' />
4731  <seriesInfo name='RFC' value='4395' />
4732</reference>
4733
4734<reference anchor='RFC4559'>
4735  <front>
4736    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4737    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4738    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4739    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4740    <date year='2006' month='June' />
4741  </front>
4742  <seriesInfo name='RFC' value='4559' />
4743</reference>
4744
4745<reference anchor='RFC5226'>
4746  <front>
4747    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4748    <author initials='T.' surname='Narten' fullname='T. Narten'>
4749      <organization>IBM</organization>
4750      <address><email>narten@us.ibm.com</email></address>
4751    </author>
4752    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4753      <organization>Google</organization>
4754      <address><email>Harald@Alvestrand.no</email></address>
4755    </author>
4756    <date year='2008' month='May' />
4757  </front>
4758  <seriesInfo name='BCP' value='26' />
4759  <seriesInfo name='RFC' value='5226' />
4760</reference>
4761
4762<reference anchor="RFC5322">
4763  <front>
4764    <title>Internet Message Format</title>
4765    <author initials="P." surname="Resnick" fullname="P. Resnick">
4766      <organization>Qualcomm Incorporated</organization>
4767    </author>
4768    <date year="2008" month="October"/>
4769  </front> 
4770  <seriesInfo name="RFC" value="5322"/>
4771</reference>
4772
4773<reference anchor="RFC6265">
4774  <front>
4775    <title>HTTP State Management Mechanism</title>
4776    <author initials="A." surname="Barth" fullname="Adam Barth">
4777      <organization abbrev="U.C. Berkeley">
4778        University of California, Berkeley
4779      </organization>
4780      <address><email>abarth@eecs.berkeley.edu</email></address>
4781    </author>
4782    <date year="2011" month="April" />
4783  </front>
4784  <seriesInfo name="RFC" value="6265"/>
4785</reference>
4786
4787<!--<reference anchor='BCP97'>
4788  <front>
4789    <title>Handling Normative References to Standards-Track Documents</title>
4790    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4791      <address>
4792        <email>klensin+ietf@jck.com</email>
4793      </address>
4794    </author>
4795    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4796      <organization>MIT</organization>
4797      <address>
4798        <email>hartmans-ietf@mit.edu</email>
4799      </address>
4800    </author>
4801    <date year='2007' month='June' />
4802  </front>
4803  <seriesInfo name='BCP' value='97' />
4804  <seriesInfo name='RFC' value='4897' />
4805</reference>-->
4806
4807<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4808  <front>
4809    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4810    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4811    <date year="2001" month="November"/>
4812  </front>
4813  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4814</reference>
4815
4816<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4817  <front>
4818    <title>Analysis of HTTP Performance Problems</title>
4819    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4820    <date/>
4821  </front>
4822</reference>
4823
4824<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4825  <front>
4826  <title>Analysis of HTTP Performance</title>
4827  <author initials="J." surname="Touch" fullname="Joe Touch">
4828    <organization>USC/Information Sciences Institute</organization>
4829    <address><email>touch@isi.edu</email></address>
4830  </author>
4831  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4832    <organization>USC/Information Sciences Institute</organization>
4833    <address><email>johnh@isi.edu</email></address>
4834  </author>
4835  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4836    <organization>USC/Information Sciences Institute</organization>
4837    <address><email>katia@isi.edu</email></address>
4838  </author>
4839  <date year="1998" month="Aug"/>
4840  </front>
4841  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4842  <annotation>(original report dated Aug. 1996)</annotation>
4843</reference>
4844
4845</references>
4846
4847
4848<section title="HTTP Version History" anchor="compatibility">
4849<t>
4850   HTTP has been in use by the World-Wide Web global information initiative
4851   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4852   was a simple protocol for hypertext data transfer across the Internet
4853   with only a single request method (GET) and no metadata.
4854   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4855   methods and MIME-like messaging that could include metadata about the data
4856   transferred and modifiers on the request/response semantics. However,
4857   HTTP/1.0 did not sufficiently take into consideration the effects of
4858   hierarchical proxies, caching, the need for persistent connections, or
4859   name-based virtual hosts. The proliferation of incompletely-implemented
4860   applications calling themselves "HTTP/1.0" further necessitated a
4861   protocol version change in order for two communicating applications
4862   to determine each other's true capabilities.
4863</t>
4864<t>
4865   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4866   requirements that enable reliable implementations, adding only
4867   those new features that will either be safely ignored by an HTTP/1.0
4868   recipient or only sent when communicating with a party advertising
4869   conformance with HTTP/1.1.
4870</t>
4871<t>
4872   It is beyond the scope of a protocol specification to mandate
4873   conformance with previous versions. HTTP/1.1 was deliberately
4874   designed, however, to make supporting previous versions easy.
4875   We would expect a general-purpose HTTP/1.1 server to understand
4876   any valid request in the format of HTTP/1.0 and respond appropriately
4877   with an HTTP/1.1 message that only uses features understood (or
4878   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4879   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4880</t>
4881<t>
4882   Since HTTP/0.9 did not support header fields in a request,
4883   there is no mechanism for it to support name-based virtual
4884   hosts (selection of resource by inspection of the Host header
4885   field).  Any server that implements name-based virtual hosts
4886   ought to disable support for HTTP/0.9.  Most requests that
4887   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4888   requests wherein a buggy client failed to properly encode
4889   linear whitespace found in a URI reference and placed in
4890   the request-target.
4891</t>
4892
4893<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4894<t>
4895   This section summarizes major differences between versions HTTP/1.0
4896   and HTTP/1.1.
4897</t>
4898
4899<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4900<t>
4901   The requirements that clients and servers support the Host header
4902   field (<xref target="header.host"/>), report an error if it is
4903   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4904   are among the most important changes defined by HTTP/1.1.
4905</t>
4906<t>
4907   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4908   addresses and servers; there was no other established mechanism for
4909   distinguishing the intended server of a request than the IP address
4910   to which that request was directed. The Host header field was
4911   introduced during the development of HTTP/1.1 and, though it was
4912   quickly implemented by most HTTP/1.0 browsers, additional requirements
4913   were placed on all HTTP/1.1 requests in order to ensure complete
4914   adoption.  At the time of this writing, most HTTP-based services
4915   are dependent upon the Host header field for targeting requests.
4916</t>
4917</section>
4918
4919<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4920<t>
4921   In HTTP/1.0, each connection is established by the client prior to the
4922   request and closed by the server after sending the response. However, some
4923   implementations implement the explicitly negotiated ("Keep-Alive") version
4924   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4925   target="RFC2068"/>.
4926</t>
4927<t>
4928   Some clients and servers might wish to be compatible with these previous
4929   approaches to persistent connections, by explicitly negotiating for them
4930   with a "Connection: keep-alive" request header field. However, some
4931   experimental implementations of HTTP/1.0 persistent connections are faulty;
4932   for example, if a HTTP/1.0 proxy server doesn't understand Connection, it
4933   will erroneously forward that header to the next inbound server, which
4934   would result in a hung connection.
4935</t>
4936<t>
4937   One attempted solution was the introduction of a Proxy-Connection header,
4938   targeted specifically at proxies. In practice, this was also unworkable,
4939   because proxies are often deployed in multiple layers, bringing about the
4940   same problem discussed above.
4941</t>
4942<t>
4943   As a result, clients are encouraged not to send the Proxy-Connection header
4944   in any requests.
4945</t>
4946<t>
4947   Clients are also encouraged to consider the use of Connection: keep-alive
4948   in requests carefully; while they can enable persistent connections with
4949   HTTP/1.0 servers, clients using them need will need to monitor the
4950   connection for "hung" requests (which indicate that the client ought stop
4951   sending the header), and this mechanism ought not be used by clients at all
4952   when a proxy is being used.
4953</t>
4954</section>
4955</section>
4956
4957<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4958<t>
4959  Empty list elements in list productions have been deprecated.
4960  (<xref target="abnf.extension"/>)
4961</t>
4962<t>
4963  Rules about implicit linear whitespace between certain grammar productions
4964  have been removed; now whitespace is only allowed where specifically
4965  defined in the ABNF.
4966  (<xref target="whitespace"/>)
4967</t>
4968<t>
4969  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4970  sensitive. Restrict the version numbers to be single digits due to the fact
4971  that implementations are known to handle multi-digit version numbers
4972  incorrectly.
4973  (<xref target="http.version"/>)
4974</t>
4975<t>
4976  Require that invalid whitespace around field-names be rejected.
4977  (<xref target="header.fields"/>)
4978</t>
4979<t> 
4980  The NUL octet is no longer allowed in comment and quoted-string
4981  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4982  Non-ASCII content in header fields and reason phrase has been obsoleted and
4983  made opaque (the TEXT rule was removed).
4984  (<xref target="field.components"/>)
4985</t>
4986<t>
4987  Require recipients to handle bogus Content-Length header fields as errors.
4988  (<xref target="message.body"/>)
4989</t>
4990<t>
4991  Remove reference to non-existent identity transfer-coding value tokens.
4992  (Sections <xref format="counter" target="message.body"/> and
4993  <xref format="counter" target="transfer.codings"/>)
4994</t>
4995<t>
4996  Update use of abs_path production from RFC 1808 to the path-absolute + query
4997  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4998  request method only.
4999  (<xref target="request-target"/>)
5000</t>
5001<t>
5002  Clarification that the chunk length does not include the count of the octets
5003  in the chunk header and trailer. Furthermore disallowed line folding
5004  in chunk extensions, and deprecate their use.
5005  (<xref target="chunked.encoding"/>)
5006</t>
5007<t>
5008  Remove hard limit of two connections per server.
5009  Remove requirement to retry a sequence of requests as long it was idempotent.
5010  Remove requirements about when servers are allowed to close connections
5011  prematurely.
5012  (<xref target="persistent.practical"/>)
5013</t>
5014<t>
5015  Remove requirement to retry requests under certain cirumstances when the
5016  server prematurely closes the connection.
5017  (<xref target="message.transmission.requirements"/>)
5018</t>
5019<t>
5020  Change ABNF productions for header fields to only define the field value.
5021  (<xref target="header.field.definitions"/>)
5022</t>
5023<t>
5024  Clarify exactly when close connection options must be sent.
5025  (<xref target="header.connection"/>)
5026</t>
5027<t>
5028  Define the semantics of the "Upgrade" header field in responses other than
5029  101 (this was incorporated from <xref target="RFC2817"/>).
5030  (<xref target="header.upgrade"/>)
5031</t>
5032</section>
5033</section>
5034
5035<?BEGININC p1-messaging.abnf-appendix ?>
5036<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5037<figure>
5038<artwork type="abnf" name="p1-messaging.parsed-abnf">
5039<x:ref>BWS</x:ref> = OWS
5040
5041<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5042<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5043 connection-token ] )
5044<x:ref>Content-Length</x:ref> = 1*DIGIT
5045
5046<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5047<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5048<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5049 ]
5050<x:ref>Host</x:ref> = uri-host [ ":" port ]
5051
5052<x:ref>Method</x:ref> = token
5053
5054<x:ref>OWS</x:ref> = *( SP / HTAB / obs-fold )
5055
5056<x:ref>RWS</x:ref> = 1*( SP / HTAB / obs-fold )
5057<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5058<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5059
5060<x:ref>Status-Code</x:ref> = 3DIGIT
5061<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5062
5063<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5064<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5065<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5066 transfer-coding ] )
5067
5068<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5069<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5070
5071<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5072 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5073 )
5074
5075<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5076<x:ref>attribute</x:ref> = token
5077<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5078
5079<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5080<x:ref>chunk-data</x:ref> = 1*OCTET
5081<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5082<x:ref>chunk-ext-name</x:ref> = token
5083<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5084<x:ref>chunk-size</x:ref> = 1*HEXDIG
5085<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5086<x:ref>connection-token</x:ref> = token
5087<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5088 / %x2A-5B ; '*'-'['
5089 / %x5D-7E ; ']'-'~'
5090 / obs-text
5091
5092<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5093<x:ref>field-name</x:ref> = token
5094<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5095
5096<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5097<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5098<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5099
5100<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5101
5102<x:ref>message-body</x:ref> = *OCTET
5103
5104<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5105<x:ref>obs-text</x:ref> = %x80-FF
5106
5107<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5108<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5109<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5110<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5111<x:ref>product</x:ref> = token [ "/" product-version ]
5112<x:ref>product-version</x:ref> = token
5113<x:ref>protocol-name</x:ref> = token
5114<x:ref>protocol-version</x:ref> = token
5115<x:ref>pseudonym</x:ref> = token
5116
5117<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5118 / %x5D-7E ; ']'-'~'
5119 / obs-text
5120<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5121 / %x5D-7E ; ']'-'~'
5122 / obs-text
5123<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5124<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5125<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5126<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5127<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5128<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5129
5130<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5131<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5132<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5133<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5134 / authority
5135
5136<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5137 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5138<x:ref>start-line</x:ref> = Request-Line / Status-Line
5139
5140<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5141<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5142 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5143<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5144<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5145<x:ref>token</x:ref> = 1*tchar
5146<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5147<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5148 transfer-extension
5149<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5150<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5151
5152<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5153
5154<x:ref>value</x:ref> = word
5155
5156<x:ref>word</x:ref> = token / quoted-string
5157</artwork>
5158</figure>
5159<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5160; Chunked-Body defined but not used
5161; Connection defined but not used
5162; Content-Length defined but not used
5163; HTTP-message defined but not used
5164; Host defined but not used
5165; TE defined but not used
5166; Trailer defined but not used
5167; Transfer-Encoding defined but not used
5168; URI-reference defined but not used
5169; Upgrade defined but not used
5170; Via defined but not used
5171; http-URI defined but not used
5172; https-URI defined but not used
5173; partial-URI defined but not used
5174; special defined but not used
5175</artwork></figure></section>
5176<?ENDINC p1-messaging.abnf-appendix ?>
5177
5178<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5179
5180<section title="Since RFC 2616">
5181<t>
5182  Extracted relevant partitions from <xref target="RFC2616"/>.
5183</t>
5184</section>
5185
5186<section title="Since draft-ietf-httpbis-p1-messaging-00">
5187<t>
5188  Closed issues:
5189  <list style="symbols"> 
5190    <t>
5191      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5192      "HTTP Version should be case sensitive"
5193      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5194    </t>
5195    <t>
5196      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5197      "'unsafe' characters"
5198      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5199    </t>
5200    <t>
5201      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5202      "Chunk Size Definition"
5203      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5204    </t>
5205    <t>
5206      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5207      "Message Length"
5208      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5209    </t>
5210    <t>
5211      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5212      "Media Type Registrations"
5213      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5214    </t>
5215    <t>
5216      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5217      "URI includes query"
5218      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5219    </t>
5220    <t>
5221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5222      "No close on 1xx responses"
5223      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5224    </t>
5225    <t>
5226      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5227      "Remove 'identity' token references"
5228      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5229    </t>
5230    <t>
5231      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5232      "Import query BNF"
5233    </t>
5234    <t>
5235      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5236      "qdtext BNF"
5237    </t>
5238    <t>
5239      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5240      "Normative and Informative references"
5241    </t>
5242    <t>
5243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5244      "RFC2606 Compliance"
5245    </t>
5246    <t>
5247      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5248      "RFC977 reference"
5249    </t>
5250    <t>
5251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5252      "RFC1700 references"
5253    </t>
5254    <t>
5255      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5256      "inconsistency in date format explanation"
5257    </t>
5258    <t>
5259      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5260      "Date reference typo"
5261    </t>
5262    <t>
5263      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5264      "Informative references"
5265    </t>
5266    <t>
5267      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5268      "ISO-8859-1 Reference"
5269    </t>
5270    <t>
5271      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5272      "Normative up-to-date references"
5273    </t>
5274  </list>
5275</t>
5276<t>
5277  Other changes:
5278  <list style="symbols"> 
5279    <t>
5280      Update media type registrations to use RFC4288 template.
5281    </t>
5282    <t>
5283      Use names of RFC4234 core rules DQUOTE and HTAB,
5284      fix broken ABNF for chunk-data
5285      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5286    </t>
5287  </list>
5288</t>
5289</section>
5290
5291<section title="Since draft-ietf-httpbis-p1-messaging-01">
5292<t>
5293  Closed issues:
5294  <list style="symbols"> 
5295    <t>
5296      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5297      "Bodies on GET (and other) requests"
5298    </t>
5299    <t>
5300      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5301      "Updating to RFC4288"
5302    </t>
5303    <t>
5304      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5305      "Status Code and Reason Phrase"
5306    </t>
5307    <t>
5308      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5309      "rel_path not used"
5310    </t>
5311  </list>
5312</t>
5313<t>
5314  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5315  <list style="symbols"> 
5316    <t>
5317      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5318      "trailer-part").
5319    </t>
5320    <t>
5321      Avoid underscore character in rule names ("http_URL" ->
5322      "http-URL", "abs_path" -> "path-absolute").
5323    </t>
5324    <t>
5325      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5326      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5327      have to be updated when switching over to RFC3986.
5328    </t>
5329    <t>
5330      Synchronize core rules with RFC5234.
5331    </t>
5332    <t>
5333      Get rid of prose rules that span multiple lines.
5334    </t>
5335    <t>
5336      Get rid of unused rules LOALPHA and UPALPHA.
5337    </t>
5338    <t>
5339      Move "Product Tokens" section (back) into Part 1, as "token" is used
5340      in the definition of the Upgrade header field.
5341    </t>
5342    <t>
5343      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5344    </t>
5345    <t>
5346      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5347    </t>
5348  </list>
5349</t>
5350</section>
5351
5352<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5353<t>
5354  Closed issues:
5355  <list style="symbols"> 
5356    <t>
5357      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5358      "HTTP-date vs. rfc1123-date"
5359    </t>
5360    <t>
5361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5362      "WS in quoted-pair"
5363    </t>
5364  </list>
5365</t>
5366<t>
5367  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5368  <list style="symbols"> 
5369    <t>
5370      Reference RFC 3984, and update header field registrations for headers defined
5371      in this document.
5372    </t>
5373  </list>
5374</t>
5375<t>
5376  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5377  <list style="symbols"> 
5378    <t>
5379      Replace string literals when the string really is case-sensitive (HTTP-Version).
5380    </t>
5381  </list>
5382</t>
5383</section>
5384
5385<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5386<t>
5387  Closed issues:
5388  <list style="symbols"> 
5389    <t>
5390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5391      "Connection closing"
5392    </t>
5393    <t>
5394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5395      "Move registrations and registry information to IANA Considerations"
5396    </t>
5397    <t>
5398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5399      "need new URL for PAD1995 reference"
5400    </t>
5401    <t>
5402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5403      "IANA Considerations: update HTTP URI scheme registration"
5404    </t>
5405    <t>
5406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5407      "Cite HTTPS URI scheme definition"
5408    </t>
5409    <t>
5410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5411      "List-type headers vs Set-Cookie"
5412    </t>
5413  </list>
5414</t>
5415<t>
5416  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5417  <list style="symbols"> 
5418    <t>
5419      Replace string literals when the string really is case-sensitive (HTTP-Date).
5420    </t>
5421    <t>
5422      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5423    </t>
5424  </list>
5425</t>
5426</section>
5427
5428<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5429<t>
5430  Closed issues:
5431  <list style="symbols"> 
5432    <t>
5433      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5434      "Out-of-date reference for URIs"
5435    </t>
5436    <t>
5437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5438      "RFC 2822 is updated by RFC 5322"
5439    </t>
5440  </list>
5441</t>
5442<t>
5443  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5444  <list style="symbols"> 
5445    <t>
5446      Use "/" instead of "|" for alternatives.
5447    </t>
5448    <t>
5449      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5450    </t>
5451    <t>
5452      Only reference RFC 5234's core rules.
5453    </t>
5454    <t>
5455      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5456      whitespace ("OWS") and required whitespace ("RWS").
5457    </t>
5458    <t>
5459      Rewrite ABNFs to spell out whitespace rules, factor out
5460      header field value format definitions.
5461    </t>
5462  </list>
5463</t>
5464</section>
5465
5466<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5467<t>
5468  Closed issues:
5469  <list style="symbols"> 
5470    <t>
5471      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5472      "Header LWS"
5473    </t>
5474    <t>
5475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5476      "Sort 1.3 Terminology"
5477    </t>
5478    <t>
5479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5480      "RFC2047 encoded words"
5481    </t>
5482    <t>
5483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5484      "Character Encodings in TEXT"
5485    </t>
5486    <t>
5487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5488      "Line Folding"
5489    </t>
5490    <t>
5491      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5492      "OPTIONS * and proxies"
5493    </t>
5494    <t>
5495      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5496      "Reason-Phrase BNF"
5497    </t>
5498    <t>
5499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5500      "Use of TEXT"
5501    </t>
5502    <t>
5503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5504      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5505    </t>
5506    <t>
5507      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5508      "RFC822 reference left in discussion of date formats"
5509    </t>
5510  </list>
5511</t>
5512<t>
5513  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5514  <list style="symbols"> 
5515    <t>
5516      Rewrite definition of list rules, deprecate empty list elements.
5517    </t>
5518    <t>
5519      Add appendix containing collected and expanded ABNF.
5520    </t>
5521  </list>
5522</t>
5523<t>
5524  Other changes:
5525  <list style="symbols"> 
5526    <t>
5527      Rewrite introduction; add mostly new Architecture Section.
5528    </t>
5529    <t>
5530      Move definition of quality values from Part 3 into Part 1;
5531      make TE request header field grammar independent of accept-params (defined in Part 3).
5532    </t>
5533  </list>
5534</t>
5535</section>
5536
5537<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5538<t>
5539  Closed issues:
5540  <list style="symbols"> 
5541    <t>
5542      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5543      "base for numeric protocol elements"
5544    </t>
5545    <t>
5546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5547      "comment ABNF"
5548    </t>
5549  </list>
5550</t>
5551<t>
5552  Partly resolved issues:
5553  <list style="symbols"> 
5554    <t>
5555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5556      "205 Bodies" (took out language that implied that there might be
5557      methods for which a request body MUST NOT be included)
5558    </t>
5559    <t>
5560      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5561      "editorial improvements around HTTP-date"
5562    </t>
5563  </list>
5564</t>
5565</section>
5566
5567<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5568<t>
5569  Closed issues:
5570  <list style="symbols"> 
5571    <t>
5572      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5573      "Repeating single-value headers"
5574    </t>
5575    <t>
5576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5577      "increase connection limit"
5578    </t>
5579    <t>
5580      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5581      "IP addresses in URLs"
5582    </t>
5583    <t>
5584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5585      "take over HTTP Upgrade Token Registry"
5586    </t>
5587    <t>
5588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5589      "CR and LF in chunk extension values"
5590    </t>
5591    <t>
5592      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5593      "HTTP/0.9 support"
5594    </t>
5595    <t>
5596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5597      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5598    </t>
5599    <t>
5600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5601      "move definitions of gzip/deflate/compress to part 1"
5602    </t>
5603    <t>
5604      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5605      "disallow control characters in quoted-pair"
5606    </t>
5607  </list>
5608</t>
5609<t>
5610  Partly resolved issues:
5611  <list style="symbols"> 
5612    <t>
5613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5614      "update IANA requirements wrt Transfer-Coding values" (add the
5615      IANA Considerations subsection)
5616    </t>
5617  </list>
5618</t>
5619</section>
5620
5621<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5622<t>
5623  Closed issues:
5624  <list style="symbols"> 
5625    <t>
5626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5627      "header parsing, treatment of leading and trailing OWS"
5628    </t>
5629  </list>
5630</t>
5631<t>
5632  Partly resolved issues:
5633  <list style="symbols"> 
5634    <t>
5635      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5636      "Placement of 13.5.1 and 13.5.2"
5637    </t>
5638    <t>
5639      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5640      "use of term "word" when talking about header structure"
5641    </t>
5642  </list>
5643</t>
5644</section>
5645
5646<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5647<t>
5648  Closed issues:
5649  <list style="symbols"> 
5650    <t>
5651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5652      "Clarification of the term 'deflate'"
5653    </t>
5654    <t>
5655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5656      "OPTIONS * and proxies"
5657    </t>
5658    <t>
5659      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5660      "MIME-Version not listed in P1, general header fields"
5661    </t>
5662    <t>
5663      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5664      "IANA registry for content/transfer encodings"
5665    </t>
5666    <t>
5667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5668      "Case-sensitivity of HTTP-date"
5669    </t>
5670    <t>
5671      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5672      "use of term "word" when talking about header structure"
5673    </t>
5674  </list>
5675</t>
5676<t>
5677  Partly resolved issues:
5678  <list style="symbols"> 
5679    <t>
5680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5681      "Term for the requested resource's URI"
5682    </t>
5683  </list>
5684</t>
5685</section>
5686
5687<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5688<t>
5689  Closed issues:
5690  <list style="symbols">
5691    <t>
5692      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5693      "Connection Closing"
5694    </t>
5695    <t>
5696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5697      "Delimiting messages with multipart/byteranges"
5698    </t>
5699    <t>
5700      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5701      "Handling multiple Content-Length headers"
5702    </t>
5703    <t>
5704      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5705      "Clarify entity / representation / variant terminology"
5706    </t>
5707    <t>
5708      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5709      "consider removing the 'changes from 2068' sections"
5710    </t>
5711  </list>
5712</t>
5713<t>
5714  Partly resolved issues:
5715  <list style="symbols"> 
5716    <t>
5717      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5718      "HTTP(s) URI scheme definitions"
5719    </t>
5720  </list>
5721</t>
5722</section>
5723
5724<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5725<t>
5726  Closed issues:
5727  <list style="symbols">
5728    <t>
5729      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5730      "Trailer requirements"
5731    </t>
5732    <t>
5733      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5734      "Text about clock requirement for caches belongs in p6"
5735    </t>
5736    <t>
5737      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5738      "effective request URI: handling of missing host in HTTP/1.0"
5739    </t>
5740    <t>
5741      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5742      "confusing Date requirements for clients"
5743    </t>
5744  </list>
5745</t>
5746<t>
5747  Partly resolved issues:
5748  <list style="symbols"> 
5749    <t>
5750      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5751      "Handling multiple Content-Length headers"
5752    </t>
5753  </list>
5754</t>
5755</section>
5756
5757<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5758<t>
5759  Closed issues:
5760  <list style="symbols">
5761    <t>
5762      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5763      "RFC2145 Normative"
5764    </t>
5765    <t>
5766      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5767      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5768    </t>
5769    <t>
5770      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5771      "define 'transparent' proxy"
5772    </t>
5773    <t>
5774      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5775      "Header Classification"
5776    </t>
5777    <t>
5778      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5779      "Is * usable as a request-uri for new methods?"
5780    </t>
5781    <t>
5782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5783      "Migrate Upgrade details from RFC2817"
5784    </t>
5785    <t>
5786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5787      "untangle ABNFs for header fields"
5788    </t>
5789    <t>
5790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5791      "update RFC 2109 reference"
5792    </t>
5793  </list>
5794</t>
5795</section>
5796
5797<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5798<t>
5799  Closed issues:
5800  <list style="symbols">
5801    <t>
5802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5803      "Allow is not in 13.5.2"
5804    </t>
5805    <t>
5806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5807      "Handling multiple Content-Length headers"
5808    </t>
5809    <t>
5810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5811      "untangle ABNFs for header fields"
5812    </t>
5813    <t>
5814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5815      "Content-Length ABNF broken"
5816    </t>
5817  </list>
5818</t>
5819</section>
5820
5821<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5822<t>
5823  Closed issues:
5824  <list style="symbols">
5825    <t>
5826      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5827      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5828    </t>
5829    <t>
5830      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5831      "Recommend minimum sizes for protocol elements"
5832    </t>
5833    <t>
5834      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5835      "Set expectations around buffering"
5836    </t>
5837    <t>
5838      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5839      "Considering messages in isolation"
5840    </t>
5841  </list>
5842</t>
5843</section>
5844
5845<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5846<t>
5847  Closed issues:
5848  <list style="symbols">
5849    <t>
5850      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5851      "DNS Spoofing / DNS Binding advice"
5852    </t>
5853    <t>
5854      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5855      "move RFCs 2145, 2616, 2817 to Historic status"
5856    </t>
5857    <t>
5858      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5859      "\-escaping in quoted strings"
5860    </t>
5861    <t>
5862      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5863      "'Close' should be reserved in the HTTP header field registry"
5864    </t>
5865  </list>
5866</t>
5867</section>
5868
5869<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5870<t>
5871  Closed issues:
5872  <list style="symbols">
5873    <t>
5874      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5875      "Document HTTP's error-handling philosophy"
5876    </t>
5877    <t>
5878      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5879      "Explain header registration"
5880    </t>
5881    <t>
5882      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5883      "Revise Acknowledgements Sections"
5884    </t>
5885    <t>
5886      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5887      "Retrying Requests"
5888    </t>
5889    <t>
5890      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5891      "Closing the connection on server error"
5892    </t>
5893  </list>
5894</t>
5895</section>
5896
5897<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5898<t>
5899  Closed issues:
5900  <list style="symbols">
5901    <t>
5902      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5903      "Clarify 'User Agent'"
5904    </t>
5905    <t>
5906      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5907      "Define non-final responses"
5908    </t>
5909    <t>
5910      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5911      "intended maturity level vs normative references"
5912    </t>
5913    <t>
5914      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5915      "Intermediary rewriting of queries"
5916    </t>
5917    <t>
5918      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5919      "Proxy-Connection and Keep-Alive"
5920    </t>
5921  </list>
5922</t>
5923</section>
5924
5925<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5926<t>
5927  Closed issues:
5928  <list style="symbols">
5929    <t>
5930      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5931      "Misplaced text on connection handling in p2"
5932    </t>
5933    <t>
5934      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5935      "chunk-extensions"
5936    </t>
5937  </list>
5938</t>
5939</section>
5940
5941</section>
5942
5943</back>
5944</rfc>
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