source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1544

Last change on this file since 1544 was 1544, checked in by fielding@…, 8 years ago

For consistency and readability, do not hyphenate "message body"
unless we are referring to the message-body ABNF rule.

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 242.2 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "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 one or more HTTP
435   <x:dfn>response</x:dfn>
436   messages, each beginning with a status line that
437   includes the protocol version, a success or error code, and textual
438   reason phrase (<xref target="status.line"/>),
439   possibly followed by MIME-like header fields containing server
440   information, resource metadata, and payload metadata
441   (<xref target="header.fields"/>),
442   an empty line to indicate the end of the header section, and finally
443   a message body containing the payload body (if any,
444   <xref target="message.body"/>).
445</t>
446<t>
447   The following example illustrates a typical message exchange for a
448   GET request on the URI "http://www.example.com/hello.txt":
449</t>
450<figure><preamble>
451client request:
452</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
453GET /hello.txt HTTP/1.1
454User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
455Host: www.example.com
456Accept: */*
457
458</artwork></figure>
459<figure><preamble>
460server response:
461</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
462HTTP/1.1 200 OK
463Date: Mon, 27 Jul 2009 12:28:53 GMT
464Server: Apache
465Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
466ETag: "34aa387-d-1568eb00"
467Accept-Ranges: bytes
468Content-Length: <x:length-of target="exbody"/>
469Vary: Accept-Encoding
470Content-Type: text/plain
471
472<x:span anchor="exbody">Hello World!
473</x:span></artwork></figure>
474</section>
475
476<section title="Connections and Transport Independence" anchor="transport-independence">
477<t>
478   HTTP messaging is independent of the underlying transport or
479   session-layer connection protocol(s).  HTTP only presumes a reliable
480   transport with in-order delivery of requests and the corresponding
481   in-order delivery of responses.  The mapping of HTTP request and
482   response structures onto the data units of the underlying transport
483   protocol is outside the scope of this specification.
484</t>
485<t>
486   The specific connection protocols to be used for an interaction
487   are determined by client configuration and the target resource's URI.
488   For example, the "http" URI scheme
489   (<xref target="http.uri"/>) indicates a default connection of TCP
490   over IP, with a default TCP port of 80, but the client might be
491   configured to use a proxy via some other connection port or protocol
492   instead of using the defaults.
493</t>
494<t>
495   A connection might be used for multiple HTTP request/response exchanges,
496   as defined in <xref target="persistent.connections"/>.
497</t>
498</section>
499
500<section title="Intermediaries" anchor="intermediaries">
501<iref primary="true" item="intermediary"/>
502<t>
503   HTTP enables the use of intermediaries to satisfy requests through
504   a chain of connections.  There are three common forms of HTTP
505   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
506   a single intermediary might act as an origin server, proxy, gateway,
507   or tunnel, switching behavior based on the nature of each request.
508</t>
509<figure><artwork type="drawing">
510         &gt;             &gt;             &gt;             &gt;
511    <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>
512               &lt;             &lt;             &lt;             &lt;
513</artwork></figure>
514<t>
515   The figure above shows three intermediaries (A, B, and C) between the
516   user agent and origin server. A request or response message that
517   travels the whole chain will pass through four separate connections.
518   Some HTTP communication options
519   might apply only to the connection with the nearest, non-tunnel
520   neighbor, only to the end-points of the chain, or to all connections
521   along the chain. Although the diagram is linear, each participant might
522   be engaged in multiple, simultaneous communications. For example, B
523   might be receiving requests from many clients other than A, and/or
524   forwarding requests to servers other than C, at the same time that it
525   is handling A's request.
526</t>
527<t>
528<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
529<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
530   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
531   to describe various requirements in relation to the directional flow of a
532   message: all messages flow from upstream to downstream.
533   Likewise, we use the terms inbound and outbound to refer to
534   directions in relation to the request path:
535   "<x:dfn>inbound</x:dfn>" means toward the origin server and
536   "<x:dfn>outbound</x:dfn>" means toward the user agent.
537</t>
538<t><iref primary="true" item="proxy"/>
539   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
540   client, usually via local configuration rules, to receive requests
541   for some type(s) of absolute URI and attempt to satisfy those
542   requests via translation through the HTTP interface.  Some translations
543   are minimal, such as for proxy requests for "http" URIs, whereas
544   other requests might require translation to and from entirely different
545   application-layer protocols. Proxies are often used to group an
546   organization's HTTP requests through a common intermediary for the
547   sake of security, annotation services, or shared caching.
548</t>
549<t>
550<iref primary="true" item="transforming proxy"/>
551<iref primary="true" item="non-transforming proxy"/>
552   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
553   or configured to modify request or response messages in a semantically
554   meaningful way (i.e., modifications, beyond those required by normal
555   HTTP processing, that change the message in a way that would be
556   significant to the original sender or potentially significant to
557   downstream recipients).  For example, a transforming proxy might be
558   acting as a shared annotation server (modifying responses to include
559   references to a local annotation database), a malware filter, a
560   format transcoder, or an intranet-to-Internet privacy filter.  Such
561   transformations are presumed to be desired by the client (or client
562   organization) that selected the proxy and are beyond the scope of
563   this specification.  However, when a proxy is not intended to transform
564   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
565   requirements that preserve HTTP message semantics. See &status-203; and
566   &header-warning; for status and warning codes related to transformations.
567</t>
568<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
569<iref primary="true" item="accelerator"/>
570   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
571   is a receiving agent that acts
572   as a layer above some other server(s) and translates the received
573   requests to the underlying server's protocol.  Gateways are often
574   used to encapsulate legacy or untrusted information services, to
575   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
576   enable partitioning or load-balancing of HTTP services across
577   multiple machines.
578</t>
579<t>
580   A gateway behaves as an origin server on its outbound connection and
581   as a user agent on its inbound connection.
582   All HTTP requirements applicable to an origin server
583   also apply to the outbound communication of a gateway.
584   A gateway communicates with inbound servers using any protocol that
585   it desires, including private extensions to HTTP that are outside
586   the scope of this specification.  However, an HTTP-to-HTTP gateway
587   that wishes to interoperate with third-party HTTP servers &MUST;
588   conform to HTTP user agent requirements on the gateway's inbound
589   connection and &MUST; implement the Connection
590   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
591   header fields for both connections.
592</t>
593<t><iref primary="true" item="tunnel"/>
594   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
595   without changing the messages. Once active, a tunnel is not
596   considered a party to the HTTP communication, though the tunnel might
597   have been initiated by an HTTP request. A tunnel ceases to exist when
598   both ends of the relayed connection are closed. Tunnels are used to
599   extend a virtual connection through an intermediary, such as when
600   transport-layer security is used to establish private communication
601   through a shared firewall proxy.
602</t>
603<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
604<iref primary="true" item="captive portal"/>
605   In addition, there may exist network intermediaries that are not
606   considered part of the HTTP communication but nevertheless act as
607   filters or redirecting agents (usually violating HTTP semantics,
608   causing security problems, and otherwise making a mess of things).
609   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
610   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
611   or "<x:dfn>captive portal</x:dfn>",
612   differs from an HTTP proxy because it has not been selected by the client.
613   Instead, the network intermediary redirects outgoing TCP port 80 packets
614   (and occasionally other common port traffic) to an internal HTTP server.
615   Interception proxies are commonly found on public network access points,
616   as a means of enforcing account subscription prior to allowing use of
617   non-local Internet services, and within corporate firewalls to enforce
618   network usage policies.
619   They are indistinguishable from a man-in-the-middle attack.
620</t>
621<t>
622   HTTP is defined as a stateless protocol, meaning that each request message
623   can be understood in isolation.  Many implementations depend on HTTP's
624   stateless design in order to reuse proxied connections or dynamically
625   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
626   assume that two requests on the same connection are from the same user
627   agent unless the connection is secured and specific to that agent.
628   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
629   been known to violate this requirement, resulting in security and
630   interoperability problems.
631</t>
632</section>
633
634<section title="Caches" anchor="caches">
635<iref primary="true" item="cache"/>
636<t>
637   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
638   subsystem that controls its message storage, retrieval, and deletion.
639   A cache stores cacheable responses in order to reduce the response
640   time and network bandwidth consumption on future, equivalent
641   requests. Any client or server &MAY; employ a cache, though a cache
642   cannot be used by a server while it is acting as a tunnel.
643</t>
644<t>
645   The effect of a cache is that the request/response chain is shortened
646   if one of the participants along the chain has a cached response
647   applicable to that request. The following illustrates the resulting
648   chain if B has a cached copy of an earlier response from O (via C)
649   for a request which has not been cached by UA or A.
650</t>
651<figure><artwork type="drawing">
652            &gt;             &gt;
653       UA =========== A =========== B - - - - - - C - - - - - - O
654                  &lt;             &lt;
655</artwork></figure>
656<t><iref primary="true" item="cacheable"/>
657   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
658   the response message for use in answering subsequent requests.
659   Even when a response is cacheable, there might be additional
660   constraints placed by the client or by the origin server on when
661   that cached response can be used for a particular request. HTTP
662   requirements for cache behavior and cacheable responses are
663   defined in &caching-overview;
664</t>
665<t>
666   There are a wide variety of architectures and configurations
667   of caches and proxies deployed across the World Wide Web and
668   inside large organizations. These systems include national hierarchies
669   of proxy caches to save transoceanic bandwidth, systems that
670   broadcast or multicast cache entries, organizations that distribute
671   subsets of cached data via optical media, and so on.
672</t>
673</section>
674
675<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
676<t>
677   This specification targets conformance criteria according to the role of
678   a participant in HTTP communication.  Hence, HTTP requirements are placed
679   on senders, recipients, clients, servers, user agents, intermediaries,
680   origin servers, proxies, gateways, or caches, depending on what behavior
681   is being constrained by the requirement.
682</t>
683<t>
684   An implementation is considered conformant if it complies with all of the
685   requirements associated with the roles it partakes in HTTP.
686</t>
687<t>
688   Senders &MUST-NOT; generate protocol elements that do not match the grammar
689   defined by the ABNF rules for those protocol elements.
690</t>
691<t>
692   Unless otherwise noted, recipients &MAY; attempt to recover a usable
693   protocol element from an invalid construct.  HTTP does not define
694   specific error handling mechanisms except when they have a direct impact
695   on security, since different applications of the protocol require
696   different error handling strategies.  For example, a Web browser might
697   wish to transparently recover from a response where the Location header
698   field doesn't parse according to the ABNF, whereas a systems control
699   client might consider any form of error recovery to be dangerous.
700</t>
701</section>
702
703<section title="Protocol Versioning" anchor="http.version">
704  <x:anchor-alias value="HTTP-Version"/>
705  <x:anchor-alias value="HTTP-Prot-Name"/>
706<t>
707   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
708   versions of the protocol. This specification defines version "1.1".
709   The protocol version as a whole indicates the sender's conformance
710   with the set of requirements laid out in that version's corresponding
711   specification of HTTP.
712</t>
713<t>
714   The version of an HTTP message is indicated by an HTTP-Version field
715   in the first line of the message. HTTP-Version is case-sensitive.
716</t>
717<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
718  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
719  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
720</artwork></figure>
721<t>
722   The HTTP version number consists of two decimal digits separated by a "."
723   (period or decimal point).  The first digit ("major version") indicates the
724   HTTP messaging syntax, whereas the second digit ("minor version") indicates
725   the highest minor version to which the sender is
726   conformant and able to understand for future communication.  The minor
727   version advertises the sender's communication capabilities even when the
728   sender is only using a backwards-compatible subset of the protocol,
729   thereby letting the recipient know that more advanced features can
730   be used in response (by servers) or in future requests (by clients).
731</t>
732<t>
733   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
734   <xref target="RFC1945"/> or a recipient whose version is unknown,
735   the HTTP/1.1 message is constructed such that it can be interpreted
736   as a valid HTTP/1.0 message if all of the newer features are ignored.
737   This specification places recipient-version requirements on some
738   new features so that a conformant sender will only use compatible
739   features until it has determined, through configuration or the
740   receipt of a message, that the recipient supports HTTP/1.1.
741</t>
742<t>
743   The interpretation of an HTTP header field does not change
744   between minor versions of the same major version, though the default
745   behavior of a recipient in the absence of such a field can change.
746   Unless specified otherwise, header fields defined in HTTP/1.1 are
747   defined for all versions of HTTP/1.x.  In particular, the Host and
748   Connection header fields ought to be implemented by all HTTP/1.x
749   implementations whether or not they advertise conformance with HTTP/1.1.
750</t>
751<t>
752   New header fields can be defined such that, when they are
753   understood by a recipient, they might override or enhance the
754   interpretation of previously defined header fields.  When an
755   implementation receives an unrecognized header field, the recipient
756   &MUST; ignore that header field for local processing regardless of
757   the message's HTTP version.  An unrecognized header field received
758   by a proxy &MUST; be forwarded downstream unless the header field's
759   field-name is listed in the message's Connection header-field
760   (see <xref target="header.connection"/>).
761   These requirements allow HTTP's functionality to be enhanced without
762   requiring prior update of deployed intermediaries.
763</t>
764<t>
765   Intermediaries that process HTTP messages (i.e., all intermediaries
766   other than those acting as tunnels) &MUST; send their own HTTP-Version
767   in forwarded messages.  In other words, they &MUST-NOT; blindly
768   forward the first line of an HTTP message without ensuring that the
769   protocol version in that message matches a version to which that
770   intermediary is conformant for both the receiving and
771   sending of messages.  Forwarding an HTTP message without rewriting
772   the HTTP-Version might result in communication errors when downstream
773   recipients use the message sender's version to determine what features
774   are safe to use for later communication with that sender.
775</t>
776<t>
777   An HTTP client &SHOULD; send a request version equal to the highest
778   version to which the client is conformant and
779   whose major version is no higher than the highest version supported
780   by the server, if this is known.  An HTTP client &MUST-NOT; send a
781   version to which it is not conformant.
782</t>
783<t>
784   An HTTP client &MAY; send a lower request version if it is known that
785   the server incorrectly implements the HTTP specification, but only
786   after the client has attempted at least one normal request and determined
787   from the response status or header fields (e.g., Server) that the
788   server improperly handles higher request versions.
789</t>
790<t>
791   An HTTP server &SHOULD; send a response version equal to the highest
792   version to which the server is conformant and
793   whose major version is less than or equal to the one received in the
794   request.  An HTTP server &MUST-NOT; send a version to which it is not
795   conformant.  A server &MAY; send a 505 (HTTP
796   Version Not Supported) response if it cannot send a response using the
797   major version used in the client's request.
798</t>
799<t>
800   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
801   if it is known or suspected that the client incorrectly implements the
802   HTTP specification and is incapable of correctly processing later
803   version responses, such as when a client fails to parse the version
804   number correctly or when an intermediary is known to blindly forward
805   the HTTP-Version even when it doesn't conform to the given minor
806   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
807   performed unless triggered by specific client attributes, such as when
808   one or more of the request header fields (e.g., User-Agent) uniquely
809   match the values sent by a client known to be in error.
810</t>
811<t>
812   The intention of HTTP's versioning design is that the major number
813   will only be incremented if an incompatible message syntax is
814   introduced, and that the minor number will only be incremented when
815   changes made to the protocol have the effect of adding to the message
816   semantics or implying additional capabilities of the sender.  However,
817   the minor version was not incremented for the changes introduced between
818   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
819   is specifically avoiding any such changes to the protocol.
820</t>
821</section>
822
823<section title="Uniform Resource Identifiers" anchor="uri">
824<iref primary="true" item="resource"/>
825<t>
826   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
827   throughout HTTP as the means for identifying resources. URI references
828   are used to target requests, indicate redirects, and define relationships.
829   HTTP does not limit what a resource might be; it merely defines an interface
830   that can be used to interact with a resource via HTTP. More information on
831   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
832</t>
833  <x:anchor-alias value="URI-reference"/>
834  <x:anchor-alias value="absolute-URI"/>
835  <x:anchor-alias value="relative-part"/>
836  <x:anchor-alias value="authority"/>
837  <x:anchor-alias value="path-abempty"/>
838  <x:anchor-alias value="path-absolute"/>
839  <x:anchor-alias value="port"/>
840  <x:anchor-alias value="query"/>
841  <x:anchor-alias value="uri-host"/>
842  <x:anchor-alias value="partial-URI"/>
843<t>
844   This specification adopts the definitions of "URI-reference",
845   "absolute-URI", "relative-part", "port", "host",
846   "path-abempty", "path-absolute", "query", and "authority" from the
847   URI generic syntax <xref target="RFC3986"/>.
848   In addition, we define a partial-URI rule for protocol elements
849   that allow a relative URI but not a fragment.
850</t>
851<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"/>
852  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
853  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
854  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
855  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
856  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
857  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
858  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
859  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
860  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
861 
862  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
863</artwork></figure>
864<t>
865   Each protocol element in HTTP that allows a URI reference will indicate
866   in its ABNF production whether the element allows any form of reference
867   (URI-reference), only a URI in absolute form (absolute-URI), only the
868   path and optional query components, or some combination of the above.
869   Unless otherwise indicated, URI references are parsed relative to the
870   effective request URI, which defines the default base URI for references
871   in both the request and its corresponding response.
872</t>
873
874<section title="http URI scheme" anchor="http.uri">
875  <x:anchor-alias value="http-URI"/>
876  <iref item="http URI scheme" primary="true"/>
877  <iref item="URI scheme" subitem="http" primary="true"/>
878<t>
879   The "http" URI scheme is hereby defined for the purpose of minting
880   identifiers according to their association with the hierarchical
881   namespace governed by a potential HTTP origin server listening for
882   TCP connections on a given port.
883</t>
884<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
885  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
886</artwork></figure>
887<t>
888   The HTTP origin server is identified by the generic syntax's
889   <x:ref>authority</x:ref> component, which includes a host identifier
890   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
891   The remainder of the URI, consisting of both the hierarchical path
892   component and optional query component, serves as an identifier for
893   a potential resource within that origin server's name space.
894</t>
895<t>
896   If the host identifier is provided as an IP literal or IPv4 address,
897   then the origin server is any listener on the indicated TCP port at
898   that IP address. If host is a registered name, then that name is
899   considered an indirect identifier and the recipient might use a name
900   resolution service, such as DNS, to find the address of a listener
901   for that host.
902   The host &MUST-NOT; be empty; if an "http" URI is received with an
903   empty host, then it &MUST; be rejected as invalid.
904   If the port subcomponent is empty or not given, then TCP port 80 is
905   assumed (the default reserved port for WWW services).
906</t>
907<t>
908   Regardless of the form of host identifier, access to that host is not
909   implied by the mere presence of its name or address. The host might or might
910   not exist and, even when it does exist, might or might not be running an
911   HTTP server or listening to the indicated port. The "http" URI scheme
912   makes use of the delegated nature of Internet names and addresses to
913   establish a naming authority (whatever entity has the ability to place
914   an HTTP server at that Internet name or address) and allows that
915   authority to determine which names are valid and how they might be used.
916</t>
917<t>
918   When an "http" URI is used within a context that calls for access to the
919   indicated resource, a client &MAY; attempt access by resolving
920   the host to an IP address, establishing a TCP connection to that address
921   on the indicated port, and sending an HTTP request message
922   (<xref target="http.message"/>) containing the URI's identifying data
923   (<xref target="message.routing"/>) to the server.
924   If the server responds to that request with a non-interim HTTP response
925   message, as described in &status-code-reasonphr;, then that response
926   is considered an authoritative answer to the client's request.
927</t>
928<t>
929   Although HTTP is independent of the transport protocol, the "http"
930   scheme is specific to TCP-based services because the name delegation
931   process depends on TCP for establishing authority.
932   An HTTP service based on some other underlying connection protocol
933   would presumably be identified using a different URI scheme, just as
934   the "https" scheme (below) is used for servers that require an SSL/TLS
935   transport layer on a connection. Other protocols might also be used to
936   provide access to "http" identified resources &mdash; it is only the
937   authoritative interface used for mapping the namespace that is
938   specific to TCP.
939</t>
940<t>
941   The URI generic syntax for authority also includes a deprecated
942   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
943   for including user authentication information in the URI.  Some
944   implementations make use of the userinfo component for internal
945   configuration of authentication information, such as within command
946   invocation options, configuration files, or bookmark lists, even
947   though such usage might expose a user identifier or password.
948   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
949   delimiter) when transmitting an "http" URI in a message.  Recipients
950   of HTTP messages that contain a URI reference &SHOULD; parse for the
951   existence of userinfo and treat its presence as an error, likely
952   indicating that the deprecated subcomponent is being used to obscure
953   the authority for the sake of phishing attacks.
954</t>
955</section>
956
957<section title="https URI scheme" anchor="https.uri">
958   <x:anchor-alias value="https-URI"/>
959   <iref item="https URI scheme"/>
960   <iref item="URI scheme" subitem="https"/>
961<t>
962   The "https" URI scheme is hereby defined for the purpose of minting
963   identifiers according to their association with the hierarchical
964   namespace governed by a potential HTTP origin server listening for
965   SSL/TLS-secured connections on a given TCP port.
966</t>
967<t>
968   All of the requirements listed above for the "http" scheme are also
969   requirements for the "https" scheme, except that a default TCP port
970   of 443 is assumed if the port subcomponent is empty or not given,
971   and the TCP connection &MUST; be secured for privacy through the
972   use of strong encryption prior to sending the first HTTP request.
973</t>
974<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
975  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
976</artwork></figure>
977<t>
978   Unlike the "http" scheme, responses to "https" identified requests
979   are never "public" and thus &MUST-NOT; be reused for shared caching.
980   They can, however, be reused in a private cache if the message is
981   cacheable by default in HTTP or specifically indicated as such by
982   the Cache-Control header field (&header-cache-control;).
983</t>
984<t>
985   Resources made available via the "https" scheme have no shared
986   identity with the "http" scheme even if their resource identifiers
987   indicate the same authority (the same host listening to the same
988   TCP port).  They are distinct name spaces and are considered to be
989   distinct origin servers.  However, an extension to HTTP that is
990   defined to apply to entire host domains, such as the Cookie protocol
991   <xref target="RFC6265"/>, can allow information
992   set by one service to impact communication with other services
993   within a matching group of host domains.
994</t>
995<t>
996   The process for authoritative access to an "https" identified
997   resource is defined in <xref target="RFC2818"/>.
998</t>
999</section>
1000
1001<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1002<t>
1003   Since the "http" and "https" schemes conform to the URI generic syntax,
1004   such URIs are normalized and compared according to the algorithm defined
1005   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1006   described above for each scheme.
1007</t>
1008<t>
1009   If the port is equal to the default port for a scheme, the normal
1010   form is to elide the port subcomponent. Likewise, an empty path
1011   component is equivalent to an absolute path of "/", so the normal
1012   form is to provide a path of "/" instead. The scheme and host
1013   are case-insensitive and normally provided in lowercase; all
1014   other components are compared in a case-sensitive manner.
1015   Characters other than those in the "reserved" set are equivalent
1016   to their percent-encoded octets (see <xref target="RFC3986"
1017   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1018</t>
1019<t>
1020   For example, the following three URIs are equivalent:
1021</t>
1022<figure><artwork type="example">
1023   http://example.com:80/~smith/home.html
1024   http://EXAMPLE.com/%7Esmith/home.html
1025   http://EXAMPLE.com:/%7esmith/home.html
1026</artwork></figure>
1027</section>
1028</section>
1029</section>
1030
1031<section title="Message Format" anchor="http.message">
1032<x:anchor-alias value="generic-message"/>
1033<x:anchor-alias value="message.types"/>
1034<x:anchor-alias value="HTTP-message"/>
1035<x:anchor-alias value="start-line"/>
1036<iref item="header section"/>
1037<iref item="headers"/>
1038<iref item="header field"/>
1039<t>
1040   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1041   octets in a format similar to the Internet Message Format
1042   <xref target="RFC5322"/>: zero or more header fields (collectively
1043   referred to as the "headers" or the "header section"), an empty line
1044   indicating the end of the header section, and an optional message body.
1045</t>
1046<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1047  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1048                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1049                    <x:ref>CRLF</x:ref>
1050                    [ <x:ref>message-body</x:ref> ]
1051</artwork></figure>
1052<t>
1053   The normal procedure for parsing an HTTP message is to read the
1054   start-line into a structure, read each header field into a hash
1055   table by field name until the empty line, and then use the parsed
1056   data to determine if a message body is expected.  If a message body
1057   has been indicated, then it is read as a stream until an amount
1058   of octets equal to the message body length is read or the connection
1059   is closed.
1060</t>
1061<t>
1062   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1063   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1064   Parsing an HTTP message as a stream of Unicode characters, without regard
1065   for the specific encoding, creates security vulnerabilities due to the
1066   varying ways that string processing libraries handle invalid multibyte
1067   character sequences that contain the octet LF (%x0A).  String-based
1068   parsers can only be safely used within protocol elements after the element
1069   has been extracted from the message, such as within a header field-value
1070   after message parsing has delineated the individual fields.
1071</t>
1072<t>
1073   An HTTP message can be parsed as a stream for incremental processing or
1074   forwarding downstream.  However, recipients cannot rely on incremental
1075   delivery of partial messages, since some implementations will buffer or
1076   delay message forwarding for the sake of network efficiency, security
1077   checks, or payload transformations.
1078</t>
1079
1080<section title="Start Line" anchor="start.line">
1081  <x:anchor-alias value="Start-Line"/>
1082<t>
1083   An HTTP message can either be a request from client to server or a
1084   response from server to client.  Syntactically, the two types of message
1085   differ only in the start-line, which is either a Request-Line (for requests)
1086   or a Status-Line (for responses), and in the algorithm for determining
1087   the length of the message body (<xref target="message.body"/>).
1088   In theory, a client could receive requests and a server could receive
1089   responses, distinguishing them by their different start-line formats,
1090   but in practice servers are implemented to only expect a request
1091   (a response is interpreted as an unknown or invalid request method)
1092   and clients are implemented to only expect a response.
1093</t>
1094<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1095  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1096</artwork></figure>
1097<t>
1098</t>
1099<t>
1100   Implementations &MUST-NOT; send whitespace between the start-line and
1101   the first header field. The presence of such whitespace in a request
1102   might be an attempt to trick a server into ignoring that field or
1103   processing the line after it as a new request, either of which might
1104   result in a security vulnerability if other implementations within
1105   the request chain interpret the same message differently.
1106   Likewise, the presence of such whitespace in a response might be
1107   ignored by some clients or cause others to cease parsing.
1108</t>
1109
1110<section title="Request-Line" anchor="request.line">
1111  <x:anchor-alias value="Request"/>
1112  <x:anchor-alias value="Request-Line"/>
1113<t>
1114   The Request-Line begins with a method token, followed by a single
1115   space (SP), the request-target, another single space (SP), the
1116   protocol version, and ending with CRLF.
1117</t>
1118<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1119  <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>
1120</artwork></figure>
1121
1122<section title="Method" anchor="method">
1123  <x:anchor-alias value="Method"/>
1124<t>
1125   The Method token indicates the request method to be performed on the
1126   target resource. The request method is case-sensitive.
1127</t>
1128<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1129  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1130</artwork></figure>
1131<t>
1132   See &method; for further information, such as the list of methods defined
1133   by this specification, the IANA registry, and considerations for new methods.
1134</t>
1135</section>
1136
1137<section title="request-target" anchor="request-target">
1138  <x:anchor-alias value="request-target"/>
1139<t>
1140   The request-target identifies the target resource upon which to apply
1141   the request.  The four options for request-target are described in
1142   <xref target="request-target-types"/>.
1143</t>
1144<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1145  <x:ref>request-target</x:ref> = "*"
1146                 / <x:ref>absolute-URI</x:ref>
1147                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1148                 / <x:ref>authority</x:ref>
1149</artwork></figure>
1150<t>
1151   HTTP does not place a pre-defined limit on the length of a request-target.
1152   A server &MUST; be prepared to receive URIs of unbounded length and
1153   respond with the 414 (URI Too Long) status code if the received
1154   request-target would be longer than the server wishes to handle
1155   (see &status-414;).
1156</t>
1157<t>
1158   Various ad-hoc limitations on request-target length are found in practice.
1159   It is &RECOMMENDED; that all HTTP senders and recipients support
1160   request-target lengths of 8000 or more octets.
1161</t>
1162<x:note>
1163  <t>
1164    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1165    are not part of the request-target and thus will not be transmitted
1166    in an HTTP request.
1167  </t>
1168</x:note>
1169</section>
1170</section>
1171
1172<section title="Response Status-Line" anchor="status.line">
1173  <x:anchor-alias value="Response"/>
1174  <x:anchor-alias value="Status-Line"/>
1175<t>
1176   The first line of a Response message is the Status-Line, consisting
1177   of the protocol version, a space (SP), the status code, another space,
1178   a possibly-empty textual phrase describing the status code, and
1179   ending with CRLF.
1180</t>
1181<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1182  <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>
1183</artwork></figure>
1184
1185<section title="Status Code" anchor="status.code">
1186  <x:anchor-alias value="Status-Code"/>
1187<t>
1188   The Status-Code element is a 3-digit integer result code of the attempt to
1189   understand and satisfy the request. See &status-code-reasonphr; for
1190   further information, such as the list of status codes defined by this
1191   specification, the IANA registry, and considerations for new status codes.
1192</t>
1193<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/>
1194  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1195</artwork></figure>
1196</section>
1197
1198<section title="Reason Phrase" anchor="reason.phrase">
1199  <x:anchor-alias value="Reason-Phrase"/>
1200<t>   
1201   The Reason Phrase exists for the sole purpose of providing a textual
1202   description associated with the numeric status code, out of deference to
1203   earlier Internet application protocols that were more frequently used with
1204   interactive text clients. A client &SHOULD; ignore the content of the Reason
1205   Phrase.
1206</t>
1207<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1208  <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> )
1209</artwork></figure>
1210</section>
1211</section>
1212</section>
1213
1214<section title="Header Fields" anchor="header.fields">
1215  <x:anchor-alias value="header-field"/>
1216  <x:anchor-alias value="field-content"/>
1217  <x:anchor-alias value="field-name"/>
1218  <x:anchor-alias value="field-value"/>
1219  <x:anchor-alias value="OWS"/>
1220<t>
1221   Each HTTP header field consists of a case-insensitive field name
1222   followed by a colon (":"), optional whitespace, and the field value.
1223</t>
1224<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"/>
1225  <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>
1226  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1227  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1228  <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> )
1229</artwork></figure>
1230<t>
1231   The field-name token labels the corresponding field-value as having the
1232   semantics defined by that header field.  For example, the Date header field
1233   is defined in &header-date; as containing the origination
1234   timestamp for the message in which it appears.
1235</t>
1236<t>
1237   HTTP header fields are fully extensible: there is no limit on the
1238   introduction of new field names, each presumably defining new semantics,
1239   or on the number of header fields used in a given message.  Existing
1240   fields are defined in each part of this specification and in many other
1241   specifications outside the standards process.
1242   New header fields can be introduced without changing the protocol version
1243   if their defined semantics allow them to be safely ignored by recipients
1244   that do not recognize them.
1245</t>
1246<t>
1247   New HTTP header fields &SHOULD; be registered with IANA according
1248   to the procedures in &cons-new-header-fields;.
1249   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1250   field-name is listed in the Connection header field
1251   (<xref target="header.connection"/>) or the proxy is specifically
1252   configured to block or otherwise transform such fields.
1253   Unrecognized header fields &SHOULD; be ignored by other recipients.
1254</t>
1255<t>
1256   The order in which header fields with differing field names are
1257   received is not significant. However, it is "good practice" to send
1258   header fields that contain control data first, such as Host on
1259   requests and Date on responses, so that implementations can decide
1260   when not to handle a message as early as possible.  A server &MUST;
1261   wait until the entire header section is received before interpreting
1262   a request message, since later header fields might include conditionals,
1263   authentication credentials, or deliberately misleading duplicate
1264   header fields that would impact request processing.
1265</t>
1266<t>
1267   Multiple header fields with the same field name &MUST-NOT; be
1268   sent in a message unless the entire field value for that
1269   header field is defined as a comma-separated list [i.e., #(values)].
1270   Multiple header fields with the same field name can be combined into
1271   one "field-name: field-value" pair, without changing the semantics of the
1272   message, by appending each subsequent field value to the combined
1273   field value in order, separated by a comma. The order in which
1274   header fields with the same field name are received is therefore
1275   significant to the interpretation of the combined field value;
1276   a proxy &MUST-NOT; change the order of these field values when
1277   forwarding a message.
1278</t>
1279<x:note>
1280  <t>
1281   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1282   practice can occur multiple times, but does not use the list syntax, and
1283   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1284   for details.) Also note that the Set-Cookie2 header field specified in
1285   <xref target="RFC2965"/> does not share this problem.
1286  </t>
1287</x:note>
1288
1289<section title="Whitespace" anchor="whitespace">
1290<t anchor="rule.LWS">
1291   This specification uses three rules to denote the use of linear
1292   whitespace: OWS (optional whitespace), RWS (required whitespace), and
1293   BWS ("bad" whitespace).
1294</t>
1295<t anchor="rule.OWS">
1296   The OWS rule is used where zero or more linear whitespace octets might
1297   appear. OWS &SHOULD; either not be produced or be produced as a single
1298   SP. Multiple OWS octets that occur within field-content &SHOULD; either
1299   be replaced with a single SP or transformed to all SP octets (each
1300   octet other than SP replaced with SP) before interpreting the field value
1301   or forwarding the message downstream.
1302</t>
1303<t anchor="rule.RWS">
1304   RWS is used when at least one linear whitespace octet is required to
1305   separate field tokens. RWS &SHOULD; be produced as a single SP.
1306   Multiple RWS octets that occur within field-content &SHOULD; either
1307   be replaced with a single SP or transformed to all SP octets before
1308   interpreting the field value or forwarding the message downstream.
1309</t>
1310<t anchor="rule.BWS">
1311   BWS is used where the grammar allows optional whitespace for historical
1312   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
1313   recipients &MUST; accept such bad optional whitespace and remove it before
1314   interpreting the field value or forwarding the message downstream.
1315</t>
1316<t anchor="rule.whitespace">
1317  <x:anchor-alias value="BWS"/>
1318  <x:anchor-alias value="OWS"/>
1319  <x:anchor-alias value="RWS"/>
1320  <x:anchor-alias value="obs-fold"/>
1321</t>
1322<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"/>
1323  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
1324                 ; "optional" whitespace
1325  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
1326                 ; "required" whitespace
1327  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1328                 ; "bad" whitespace
1329  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1330                 ; obsolete line folding
1331                 ; see <xref target="field.parsing"/>
1332</artwork></figure>
1333</section>
1334
1335<section title="Field Parsing" anchor="field.parsing">
1336<t>
1337   No whitespace is allowed between the header field-name and colon.
1338   In the past, differences in the handling of such whitespace have led to
1339   security vulnerabilities in request routing and response handling.
1340   Any received request message that contains whitespace between a header
1341   field-name and colon &MUST; be rejected with a response code of 400
1342   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1343   message before forwarding the message downstream.
1344</t>
1345<t>
1346   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1347   preferred. The field value does not include any leading or trailing white
1348   space: OWS occurring before the first non-whitespace octet of the
1349   field value or after the last non-whitespace octet of the field value
1350   is ignored and &SHOULD; be removed before further processing (as this does
1351   not change the meaning of the header field).
1352</t>
1353<t>
1354   Historically, HTTP header field values could be extended over multiple
1355   lines by preceding each extra line with at least one space or horizontal
1356   tab (obs-fold). This specification deprecates such line
1357   folding except within the message/http media type
1358   (<xref target="internet.media.type.message.http"/>).
1359   HTTP senders &MUST-NOT; produce messages that include line folding
1360   (i.e., that contain any field-content that matches the obs-fold rule) unless
1361   the message is intended for packaging within the message/http media type.
1362   HTTP recipients &SHOULD; accept line folding and replace any embedded
1363   obs-fold whitespace with either a single SP or a matching number of SP
1364   octets (to avoid buffer copying) prior to interpreting the field value or
1365   forwarding the message downstream.
1366</t>
1367<t>
1368   Historically, HTTP has allowed field content with text in the ISO-8859-1
1369   <xref target="ISO-8859-1"/> character encoding and supported other
1370   character sets only through use of <xref target="RFC2047"/> encoding.
1371   In practice, most HTTP header field values use only a subset of the
1372   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1373   header fields &SHOULD; limit their field values to US-ASCII octets.
1374   Recipients &SHOULD; treat other (obs-text) octets in field content as
1375   opaque data.
1376</t>
1377</section>
1378
1379<section title="Field Length" anchor="field.length">
1380<t>
1381   HTTP does not place a pre-defined limit on the length of header fields,
1382   either in isolation or as a set. A server &MUST; be prepared to receive
1383   request header fields of unbounded length and respond with a 4xx status
1384   code if the received header field(s) would be longer than the server wishes
1385   to handle.
1386</t>
1387<t>
1388   A client that receives response headers that are longer than it wishes to
1389   handle can only treat it as a server error.
1390</t>
1391<t>
1392   Various ad-hoc limitations on header length are found in practice. It is
1393   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1394   combined header fields have 4000 or more octets.
1395</t>
1396</section>
1397
1398<section title="Field value components" anchor="field.components">
1399<t anchor="rule.token.separators">
1400  <x:anchor-alias value="tchar"/>
1401  <x:anchor-alias value="token"/>
1402  <x:anchor-alias value="special"/>
1403  <x:anchor-alias value="word"/>
1404   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1405   separated by whitespace or special characters. These special characters
1406   &MUST; be in a quoted string to be used within a parameter value (as defined
1407   in <xref target="transfer.codings"/>).
1408</t>
1409<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"/>
1410  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1411
1412  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1413<!--
1414  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1415 -->
1416  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1417                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1418                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1419                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1420
1421  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1422                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1423                 / "]" / "?" / "=" / "{" / "}"
1424</artwork></figure>
1425<t anchor="rule.quoted-string">
1426  <x:anchor-alias value="quoted-string"/>
1427  <x:anchor-alias value="qdtext"/>
1428  <x:anchor-alias value="obs-text"/>
1429   A string of text is parsed as a single word if it is quoted using
1430   double-quote marks.
1431</t>
1432<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"/>
1433  <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>
1434  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1435  <x:ref>obs-text</x:ref>       = %x80-FF
1436</artwork></figure>
1437<t anchor="rule.quoted-pair">
1438  <x:anchor-alias value="quoted-pair"/>
1439   The backslash octet ("\") can be used as a single-octet
1440   quoting mechanism within quoted-string constructs:
1441</t>
1442<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1443  <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> )
1444</artwork></figure>
1445<t>
1446   Recipients that process the value of the quoted-string &MUST; handle a
1447   quoted-pair as if it were replaced by the octet following the backslash.
1448</t>
1449<t>
1450   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1451   escaping (i.e., other than DQUOTE and the backslash octet).
1452</t>
1453<t anchor="rule.comment">
1454  <x:anchor-alias value="comment"/>
1455  <x:anchor-alias value="ctext"/>
1456   Comments can be included in some HTTP header fields by surrounding
1457   the comment text with parentheses. Comments are only allowed in
1458   fields containing "comment" as part of their field value definition.
1459</t>
1460<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1461  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1462  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1463</artwork></figure>
1464<t anchor="rule.quoted-cpair">
1465  <x:anchor-alias value="quoted-cpair"/>
1466   The backslash octet ("\") can be used as a single-octet
1467   quoting mechanism within comment constructs:
1468</t>
1469<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1470  <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> )
1471</artwork></figure>
1472<t>
1473   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1474   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1475</t>
1476</section>
1477
1478<section title="ABNF list extension: #rule" anchor="abnf.extension">
1479<t>
1480  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1481  improve readability in the definitions of some header field values.
1482</t>
1483<t>
1484  A construct "#" is defined, similar to "*", for defining comma-delimited
1485  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1486  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1487  comma (",") and optional whitespace (OWS).   
1488</t>
1489<figure><preamble>
1490  Thus,
1491</preamble><artwork type="example">
1492  1#element =&gt; element *( OWS "," OWS element )
1493</artwork></figure>
1494<figure><preamble>
1495  and:
1496</preamble><artwork type="example">
1497  #element =&gt; [ 1#element ]
1498</artwork></figure>
1499<figure><preamble>
1500  and for n &gt;= 1 and m &gt; 1:
1501</preamble><artwork type="example">
1502  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1503</artwork></figure>
1504<t>
1505  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1506  list elements. In other words, consumers would follow the list productions:
1507</t>
1508<figure><artwork type="example">
1509  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1510 
1511  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1512</artwork></figure>
1513<t>
1514  Note that empty elements do not contribute to the count of elements present,
1515  though.
1516</t>
1517<t>
1518  For example, given these ABNF productions:
1519</t>
1520<figure><artwork type="example">
1521  example-list      = 1#example-list-elmt
1522  example-list-elmt = token ; see <xref target="field.components"/> 
1523</artwork></figure>
1524<t>
1525  Then these are valid values for example-list (not including the double
1526  quotes, which are present for delimitation only):
1527</t>
1528<figure><artwork type="example">
1529  "foo,bar"
1530  "foo ,bar,"
1531  "foo , ,bar,charlie   "
1532</artwork></figure>
1533<t>
1534  But these values would be invalid, as at least one non-empty element is
1535  required:
1536</t>
1537<figure><artwork type="example">
1538  ""
1539  ","
1540  ",   ,"
1541</artwork></figure>
1542<t>
1543  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1544  expanded as explained above.
1545</t>
1546</section>
1547</section>
1548
1549<section title="Message Body" anchor="message.body">
1550  <x:anchor-alias value="message-body"/>
1551<t>
1552   The message body (if any) of an HTTP message is used to carry the
1553   payload body of that request or response.  The message body is
1554   identical to the payload body unless a transfer coding has been
1555   applied, as described in <xref target="header.transfer-encoding"/>.
1556</t>
1557<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1558  <x:ref>message-body</x:ref> = *OCTET
1559</artwork></figure>
1560<t>
1561   The rules for when a message body is allowed in a message differ for
1562   requests and responses.
1563</t>
1564<t>
1565   The presence of a message body in a request is signaled by a
1566   a Content-Length or Transfer-Encoding header field.
1567   Request message framing is independent of method semantics,
1568   even if the method does not define any use for a message body.
1569</t>
1570<t>
1571   The presence of a message body in a response depends on both
1572   the request method to which it is responding and the response
1573   status code (<xref target="status.code"/>).
1574   Responses to the HEAD request method never include a message body
1575   because the associated response header fields (e.g., Transfer-Encoding,
1576   Content-Length, etc.) only indicate what their values would have been
1577   if the request method had been GET.
1578   All 1xx (Informational), 204 (No Content), and 304 (Not Modified)
1579   responses &MUST-NOT; include a message body.
1580   All other responses do include a message body, although the body
1581   &MAY; be of zero length.
1582</t>
1583
1584<section title="Transfer-Encoding" anchor="header.transfer-encoding">
1585  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
1586  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
1587  <x:anchor-alias value="Transfer-Encoding"/>
1588<t>
1589   When one or more transfer encodings are applied to a payload body in order
1590   to form the message body, a Transfer-Encoding header field &MUST; be sent
1591   in the message and &MUST; contain the list of corresponding
1592   transfer-coding names in the same order that they were applied.
1593   Transfer encodings are defined in <xref target="transfer.codings"/>.
1594</t>
1595<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
1596  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
1597</artwork></figure>
1598<t>
1599   Transfer-Encoding is analogous to the Content-Transfer-Encoding field of
1600   MIME, which was designed to enable safe transport of binary data over a
1601   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1602   However, safe transport has a different focus for an 8bit-clean transfer
1603   protocol. In HTTP's case, Transfer-Encoding is primarily intended to
1604   accurately delimit a dynamically generated payload and to distinguish
1605   payload encodings that are only applied for transport efficiency or
1606   security from those that are characteristics of the target resource.
1607</t>
1608<t>
1609   The "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1610   &MUST; be implemented by all HTTP/1.1 recipients because it plays a
1611   crucial role in delimiting messages when the payload body size is not
1612   known in advance.
1613   When the "chunked" transfer-coding is used, it &MUST; be the last
1614   transfer-coding applied to form the message body and &MUST-NOT;
1615   be applied more than once in a message body.
1616   If any transfer-coding is applied to a request payload body,
1617   the final transfer-coding applied &MUST; be "chunked".
1618   If any transfer-coding is applied to a response payload body, then either
1619   the final transfer-coding applied &MUST; be "chunked" or
1620   the message &MUST; be terminated by closing the connection.
1621</t>
1622<t>
1623   For example,
1624</t>
1625<figure><artwork type="example">
1626  Transfer-Encoding: chunked
1627</artwork></figure>
1628<t>
1629   If more than one Transfer-Encoding header field is present in a message,
1630   the multiple field-values &MUST; be combined into one field-value,
1631   according to the algorithm defined in <xref target="header.fields"/>,
1632   before determining the message body length.
1633</t>
1634<t>
1635   Unlike Content-Encoding (&content-codings;), Transfer-Encoding is a
1636   property of the message, not of the payload, and thus &MAY; be added or
1637   removed by any implementation along the request/response chain.
1638   Additional information about the encoding parameters &MAY; be provided
1639   by other header fields not defined by this specification.
1640</t>
1641<t>
1642   Transfer-Encoding was added in HTTP/1.1.  It is generally assumed that
1643   implementations advertising only HTTP/1.0 support will not understand
1644   how to process a transfer-encoded payload.
1645   A client &MUST-NOT; send a request containing Transfer-Encoding unless it
1646   knows the server will handle HTTP/1.1 (or later) requests; such knowledge
1647   might be in the form of specific user configuration or by remembering the
1648   version of a prior received response.
1649   A server &MUST-NOT; send a response containing Transfer-Encoding unless
1650   the corresponding request indicates HTTP/1.1 (or later).
1651</t>
1652<t>
1653   A server that receives a request message with a transfer-coding it does
1654   not understand &SHOULD; respond with 501 (Not Implemented) and then
1655   close the connection.
1656</t>
1657</section>
1658
1659<section title="Content-Length" anchor="header.content-length">
1660  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
1661  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
1662  <x:anchor-alias value="Content-Length"/>
1663<t>
1664   The "Content-Length" header field indicates the size of the
1665   message body, in decimal number of octets, for any message other than
1666   a response to a HEAD request or a response with a status code of 304.
1667   In the case of a response to a HEAD request, Content-Length indicates
1668   the size of the payload body (not including any potential transfer-coding)
1669   that would have been sent had the request been a GET.
1670   In the case of a 304 (Not Modified) response to a GET request,
1671   Content-Length indicates the size of the payload body (not including
1672   any potential transfer-coding) that would have been sent in a 200 (OK)
1673   response.
1674</t>
1675<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
1676  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
1677</artwork></figure>
1678<t>
1679   An example is
1680</t>
1681<figure><artwork type="example">
1682  Content-Length: 3495
1683</artwork></figure>
1684<t>
1685   Implementations &SHOULD; use this field to indicate the message body
1686   length when no transfer-coding is being applied and the
1687   payload's body length can be determined prior to being transferred.
1688   <xref target="message.body"/> describes how recipients determine the length
1689   of a message body.
1690</t>
1691<t>
1692   Any Content-Length greater than or equal to zero is a valid value.
1693</t>
1694<t>
1695   Note that the use of this field in HTTP is significantly different from
1696   the corresponding definition in MIME, where it is an optional field
1697   used within the "message/external-body" content-type.
1698</t>
1699<t>
1700   If a message is received that has multiple Content-Length header fields
1701   (<xref target="header.content-length"/>) with field-values consisting
1702   of the same decimal value, or a single Content-Length header field with
1703   a field value containing a list of identical decimal values (e.g.,
1704   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1705   header fields have been generated or combined by an upstream message
1706   processor, then the recipient &MUST; either reject the message as invalid
1707   or replace the duplicated field-values with a single valid Content-Length
1708   field containing that decimal value prior to determining the message body
1709   length.
1710</t>
1711</section>
1712
1713<section title="Message Body Length" anchor="message.body.length">
1714<t>
1715   The length of a message body is determined by one of the following
1716   (in order of precedence):
1717</t>
1718<t>
1719  <list style="numbers">
1720    <x:lt><t>
1721     Any response to a HEAD request and any response with a status
1722     code of 100-199, 204, or 304 is always terminated by the first
1723     empty line after the header fields, regardless of the header
1724     fields present in the message, and thus cannot contain a message body.
1725    </t></x:lt>
1726    <x:lt><t>
1727     If a Transfer-Encoding header field is present
1728     and the "chunked" transfer-coding (<xref target="chunked.encoding"/>)
1729     is the final encoding, the message body length is determined by reading
1730     and decoding the chunked data until the transfer-coding indicates the
1731     data is complete.
1732    </t>
1733    <t>
1734     If a Transfer-Encoding header field is present in a response and the
1735     "chunked" transfer-coding is not the final encoding, the message body
1736     length is determined by reading the connection until it is closed by
1737     the server.
1738     If a Transfer-Encoding header field is present in a request and the
1739     "chunked" transfer-coding is not the final encoding, the message body
1740     length cannot be determined reliably; the server &MUST; respond with
1741     the 400 (Bad Request) status code and then close the connection.
1742    </t>
1743    <t>
1744     If a message is received with both a Transfer-Encoding header field
1745     and a Content-Length header field, the Transfer-Encoding overrides
1746     the Content-Length.
1747     Such a message might indicate an attempt to perform request or response
1748     smuggling (bypass of security-related checks on message routing or content)
1749     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1750     be removed, prior to forwarding the message downstream, or replaced with
1751     the real message body length after the transfer-coding is decoded.
1752    </t></x:lt>
1753    <x:lt><t>
1754     If a message is received without Transfer-Encoding and with either
1755     multiple Content-Length header fields having differing field-values or
1756     a single Content-Length header field having an invalid value, then the
1757     message framing is invalid and &MUST; be treated as an error to
1758     prevent request or response smuggling.
1759     If this is a request message, the server &MUST; respond with
1760     a 400 (Bad Request) status code and then close the connection.
1761     If this is a response message received by a proxy, the proxy
1762     &MUST; discard the received response, send a 502 (Bad Gateway)
1763     status code as its downstream response, and then close the connection.
1764     If this is a response message received by a user-agent, it &MUST; be
1765     treated as an error by discarding the message and closing the connection.
1766    </t></x:lt>
1767    <x:lt><t>
1768     If a valid Content-Length header field
1769     is present without Transfer-Encoding, its decimal value defines the
1770     message body length in octets.  If the actual number of octets sent in
1771     the message is less than the indicated Content-Length, the recipient
1772     &MUST; consider the message to be incomplete and treat the connection
1773     as no longer usable.
1774     If the actual number of octets sent in the message is more than the indicated
1775     Content-Length, the recipient &MUST; only process the message body up to the
1776     field value's number of octets; the remainder of the message &MUST; either
1777     be discarded or treated as the next message in a pipeline.  For the sake of
1778     robustness, a user-agent &MAY; attempt to detect and correct such an error
1779     in message framing if it is parsing the response to the last request on
1780     a connection and the connection has been closed by the server.
1781    </t></x:lt>
1782    <x:lt><t>
1783     If this is a request message and none of the above are true, then the
1784     message body length is zero (no message body is present).
1785    </t></x:lt>
1786    <x:lt><t>
1787     Otherwise, this is a response message without a declared message body
1788     length, so the message body length is determined by the number of octets
1789     received prior to the server closing the connection.
1790    </t></x:lt>
1791  </list>
1792</t>
1793<t>
1794   Since there is no way to distinguish a successfully completed,
1795   close-delimited message from a partially-received message interrupted
1796   by network failure, implementations &SHOULD; use encoding or
1797   length-delimited messages whenever possible.  The close-delimiting
1798   feature exists primarily for backwards compatibility with HTTP/1.0.
1799</t>
1800<t>
1801   A server &MAY; reject a request that contains a message body but
1802   not a Content-Length by responding with 411 (Length Required).
1803</t>
1804<t>
1805   Unless a transfer-coding other than "chunked" has been applied,
1806   a client that sends a request containing a message body &SHOULD;
1807   use a valid Content-Length header field if the message body length
1808   is known in advance, rather than the "chunked" encoding, since some
1809   existing services respond to "chunked" with a 411 (Length Required)
1810   status code even though they understand the chunked encoding.  This
1811   is typically because such services are implemented via a gateway that
1812   requires a content-length in advance of being called and the server
1813   is unable or unwilling to buffer the entire request before processing.
1814</t>
1815<t>
1816   A client that sends a request containing a message body &MUST; include a
1817   valid Content-Length header field if it does not know the server will
1818   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1819   of specific user configuration or by remembering the version of a prior
1820   received response.
1821</t>
1822</section>
1823</section>
1824
1825<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1826<t>
1827   Request messages that are prematurely terminated, possibly due to a
1828   cancelled connection or a server-imposed time-out exception, &MUST;
1829   result in closure of the connection; sending an HTTP/1.1 error response
1830   prior to closing the connection is &OPTIONAL;.
1831</t>
1832<t>
1833   Response messages that are prematurely terminated, usually by closure
1834   of the connection prior to receiving the expected number of octets or by
1835   failure to decode a transfer-encoded message body, &MUST; be recorded
1836   as incomplete.  A response that terminates in the middle of the header
1837   block (before the empty line is received) cannot be assumed to convey the
1838   full semantics of the response and &MUST; be treated as an error.
1839</t>
1840<t>
1841   A message body that uses the chunked transfer encoding is
1842   incomplete if the zero-sized chunk that terminates the encoding has not
1843   been received.  A message that uses a valid Content-Length is incomplete
1844   if the size of the message body received (in octets) is less than the
1845   value given by Content-Length.  A response that has neither chunked
1846   transfer encoding nor Content-Length is terminated by closure of the
1847   connection, and thus is considered complete regardless of the number of
1848   message body octets received, provided that the header block was received
1849   intact.
1850</t>
1851<t>
1852   A user agent &MUST-NOT; render an incomplete response message body as if
1853   it were complete (i.e., some indication must be given to the user that an
1854   error occurred).  Cache requirements for incomplete responses are defined
1855   in &cache-incomplete;.
1856</t>
1857<t>
1858   A server &MUST; read the entire request message body or close
1859   the connection after sending its response, since otherwise the
1860   remaining data on a persistent connection would be misinterpreted
1861   as the next request.  Likewise,
1862   a client &MUST; read the entire response message body if it intends
1863   to reuse the same connection for a subsequent request.  Pipelining
1864   multiple requests on a connection is described in <xref target="pipelining"/>.
1865</t>
1866</section>
1867
1868<section title="Message Parsing Robustness" anchor="message.robustness">
1869<t>
1870   Older HTTP/1.0 client implementations might send an extra CRLF
1871   after a POST request as a lame workaround for some early server
1872   applications that failed to read message body content that was
1873   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1874   preface or follow a request with an extra CRLF.  If terminating
1875   the request message body with a line-ending is desired, then the
1876   client &MUST; include the terminating CRLF octets as part of the
1877   message body length.
1878</t>
1879<t>
1880   In the interest of robustness, servers &SHOULD; ignore at least one
1881   empty line received where a Request-Line is expected. In other words, if
1882   the server is reading the protocol stream at the beginning of a
1883   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1884   Likewise, although the line terminator for the start-line and header
1885   fields is the sequence CRLF, we recommend that recipients recognize a
1886   single LF as a line terminator and ignore any CR.
1887</t>
1888<t>
1889   When a server listening only for HTTP request messages, or processing
1890   what appears from the start-line to be an HTTP request message,
1891   receives a sequence of octets that does not match the HTTP-message
1892   grammar aside from the robustness exceptions listed above, the
1893   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1894</t>
1895</section>
1896</section>
1897
1898<section title="Message Routing" anchor="message.routing">
1899<t>
1900   In most cases, the user agent is provided a URI reference
1901   from which it determines an absolute URI for identifying the target
1902   resource.  When a request to the resource is initiated, all or part
1903   of that URI is used to construct the HTTP request-target.
1904</t>
1905
1906<section title="Types of Request Target" anchor="request-target-types">
1907<t>
1908   The proper format choice of the four options available to request-target
1909   depends on the method being requested and if the request is being made to
1910   a proxy.
1911</t>   
1912<t anchor="origin-form"><iref item="origin form (of request-target)"/>
1913   The most common form of request-target is that used when making
1914   a request to an origin server ("origin form") to access a resource
1915   identified by an "http" (<xref target="http.uri"/>) or
1916   "https" (<xref target="https.uri"/>) URI.
1917   In this case, the absolute path and query components of the URI
1918   &MUST; be transmitted as the request-target and the authority component
1919   (excluding any userinfo) &MUST; be transmitted in a Host header field.
1920   For example, a client wishing to retrieve a representation of the resource
1921   identified as
1922</t>
1923<figure><artwork x:indent-with="  ">
1924http://www.example.org/where?q=now
1925</artwork></figure>
1926<t>
1927   directly from the origin server would open (or reuse) a TCP connection
1928   to port 80 of the host "www.example.org" and send the lines:
1929</t>
1930<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1931GET /where?q=now HTTP/1.1
1932Host: www.example.org
1933</artwork></figure>
1934<t>
1935   followed by the remainder of the request. Note that the origin form
1936   of request-target always starts with an absolute path. If the target
1937   resource's URI path is empty, then an absolute path of "/" &MUST; be
1938   provided in the request-target.
1939</t>
1940<t>
1941   If the request-target is percent-encoded
1942   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1943   &MUST; decode the request-target in order to
1944   properly interpret the request. Servers &SHOULD; respond to invalid
1945   request-targets with an appropriate status code.
1946</t>
1947<t anchor="absolute-URI-form"><iref item="absolute-URI form (of request-target)"/>
1948   The "absolute-URI" form of request-target is &REQUIRED; when the request
1949   is being made to a proxy.  The proxy is requested to either forward the
1950   request or service it from a valid cache, and then return the response.
1951   Note that the proxy &MAY; forward the request on to another proxy or
1952   directly to the server specified by the absolute-URI.
1953   In order to avoid request loops, a proxy that forwards requests to other
1954   proxies &MUST; be able to recognize and exclude all of its own server
1955   names, including any aliases, local variations, or literal IP addresses.
1956   An example Request-Line would be:
1957</t>
1958<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1959GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1960</artwork></figure>
1961<t>
1962   To allow for transition to absolute-URIs in all requests in future
1963   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1964   form in requests, even though HTTP/1.1 clients will only generate
1965   them in requests to proxies.
1966</t>
1967<t>
1968   If a proxy receives a host name that is not a fully qualified domain
1969   name, it &MAY; add its domain to the host name it received. If a proxy
1970   receives a fully qualified domain name, the proxy &MUST-NOT; change
1971   the host name.
1972</t>
1973<t anchor="authority-form"><iref item="authority form (of request-target)"/>
1974   The "authority form" of request-target, which &MUST-NOT; be used
1975   with any request method other than CONNECT, is used to establish a
1976   tunnel through one or more proxies (&CONNECT;).  For example,
1977</t>
1978<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1979CONNECT www.example.com:80 HTTP/1.1
1980</artwork></figure>
1981<t anchor="asterix-form"><iref item="asterisk form (of request-target)"/>
1982   The asterisk ("*") form of request-target, which &MUST-NOT; be used
1983   with any request method other than OPTIONS, means that the request
1984   applies to the server as a whole (the listening process) rather than
1985   to a specific named resource at that server.  For example,
1986</t>
1987<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1988OPTIONS * HTTP/1.1
1989</artwork></figure>
1990<t>
1991   If a proxy receives an OPTIONS request with an absolute-URI form of
1992   request-target in which the URI has an empty path and no query component,
1993   then the last proxy on the request chain &MUST; use a request-target
1994   of "*" when it forwards the request to the indicated origin server.
1995</t>
1996<figure><preamble>   
1997   For example, the request
1998</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1999OPTIONS http://www.example.org:8001 HTTP/1.1
2000</artwork></figure>
2001<figure><preamble>   
2002  would be forwarded by the final proxy as
2003</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2004OPTIONS * HTTP/1.1
2005Host: www.example.org:8001
2006</artwork>
2007<postamble>
2008   after connecting to port 8001 of host "www.example.org".
2009</postamble>
2010</figure>
2011<t>
2012   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
2013   parts of the received request-target when forwarding it to the next inbound
2014   server, except as noted above to replace a null path-absolute with "/" or
2015   "*".
2016</t>
2017</section>
2018
2019<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
2020<t>
2021   The exact resource identified by an Internet request is determined by
2022   examining both the request-target and the Host header field.
2023</t>
2024<t>
2025   An origin server that does not allow resources to differ by the
2026   requested host &MAY; ignore the Host header field value when
2027   determining the resource identified by an HTTP/1.1 request. (But see
2028   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
2029   for other requirements on Host support in HTTP/1.1.)
2030</t>
2031<t>
2032   An origin server that does differentiate resources based on the host
2033   requested (sometimes referred to as virtual hosts or vanity host
2034   names) &MUST; use the following rules for determining the requested
2035   resource on an HTTP/1.1 request:
2036  <list style="numbers">
2037    <t>If request-target is an absolute-URI, the host is part of the
2038     request-target. Any Host header field value in the request &MUST; be
2039     ignored.</t>
2040    <t>If the request-target is not an absolute-URI, and the request includes
2041     a Host header field, the host is determined by the Host header
2042     field value.</t>
2043    <t>If the host as determined by rule 1 or 2 is not a valid host on
2044     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
2045  </list>
2046</t>
2047<t>
2048   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
2049   attempt to use heuristics (e.g., examination of the URI path for
2050   something unique to a particular host) in order to determine what
2051   exact resource is being requested.
2052</t>
2053</section>
2054
2055<section title="Effective Request URI" anchor="effective.request.uri">
2056  <iref primary="true" item="effective request URI"/>
2057  <iref primary="true" item="target resource"/>
2058<t>
2059   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
2060   for the target resource; instead, the URI needs to be inferred from the
2061   request-target, Host header field, and connection context. The result of
2062   this process is called the "effective request URI".  The "target resource"
2063   is the resource identified by the effective request URI.
2064</t>
2065<t>
2066   If the request-target is an absolute-URI, then the effective request URI is
2067   the request-target.
2068</t>
2069<t>
2070   If the request-target uses the origin form or the asterisk form,
2071   and the Host header field is present, then the effective request URI is
2072   constructed by concatenating
2073</t>
2074<t>
2075  <list style="symbols">
2076    <t>
2077      the scheme name: "http" if the request was received over an insecure
2078      TCP connection, or "https" when received over a SSL/TLS-secured TCP
2079      connection,
2080    </t>
2081    <t>
2082      the octet sequence "://",
2083    </t>
2084    <t>
2085      the authority component, as specified in the Host header field
2086      (<xref target="header.host"/>), and
2087    </t>
2088    <t>
2089      the request-target obtained from the Request-Line, unless the
2090      request-target is just the asterisk "*".
2091    </t>
2092  </list>
2093</t>
2094<t>
2095   If the request-target uses the origin form or the asterisk form,
2096   and the Host header field is not present, then the effective request URI is
2097   undefined.
2098</t>
2099<t>
2100   Otherwise, when request-target uses the authority form, the effective
2101   request URI is undefined.
2102</t>
2103<figure>
2104<preamble>
2105   Example 1: the effective request URI for the message
2106</preamble> 
2107<artwork type="example" x:indent-with="  ">
2108GET /pub/WWW/TheProject.html HTTP/1.1
2109Host: www.example.org:8080
2110</artwork>
2111<postamble>
2112  (received over an insecure TCP connection) is "http", plus "://", plus the
2113  authority component "www.example.org:8080", plus the request-target
2114  "/pub/WWW/TheProject.html", thus
2115  "http://www.example.org:8080/pub/WWW/TheProject.html".
2116</postamble>
2117</figure>
2118<figure>
2119<preamble>
2120   Example 2: the effective request URI for the message
2121</preamble> 
2122<artwork type="example" x:indent-with="  ">
2123OPTIONS * HTTP/1.1
2124Host: www.example.org
2125</artwork>
2126<postamble>
2127  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
2128  authority component "www.example.org", thus "https://www.example.org".
2129</postamble>
2130</figure>
2131<t>
2132   Effective request URIs are compared using the rules described in
2133   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
2134   be treated as equivalent to an absolute path of "/".
2135</t> 
2136</section>
2137
2138<section title="Associating a Response to a Request" anchor="associating.response.to.request">
2139<t>
2140   HTTP does not include a request identifier for associating a given
2141   request message with its corresponding one or more response messages.
2142   Hence, it relies on the order of response arrival to correspond exactly
2143   to the order in which requests are made on the same connection.
2144   More than one response message per request only occurs when one or more
2145   informational responses (1xx, see &status-1xx;) precede a final response
2146   to the same request.
2147</t>
2148<t>
2149   A client that uses persistent connections and sends more than one request
2150   per connection &MUST; maintain a list of outstanding requests in the
2151   order sent on that connection and &MUST; associate each received response
2152   message to the highest ordered request that has not yet received a final
2153   (non-1xx) response.
2154</t>
2155</section>
2156</section>
2157
2158<section title="Transfer Codings" anchor="transfer.codings">
2159  <x:anchor-alias value="transfer-coding"/>
2160  <x:anchor-alias value="transfer-extension"/>
2161<t>
2162   Transfer-coding values are used to indicate an encoding
2163   transformation that has been, can be, or might need to be applied to a
2164   payload body in order to ensure "safe transport" through the network.
2165   This differs from a content coding in that the transfer-coding is a
2166   property of the message rather than a property of the representation
2167   that is being transferred.
2168</t>
2169<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2170  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2171                          / "compress" ; <xref target="compress.coding"/>
2172                          / "deflate" ; <xref target="deflate.coding"/>
2173                          / "gzip" ; <xref target="gzip.coding"/>
2174                          / <x:ref>transfer-extension</x:ref>
2175  <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> )
2176</artwork></figure>
2177<t anchor="rule.parameter">
2178  <x:anchor-alias value="attribute"/>
2179  <x:anchor-alias value="transfer-parameter"/>
2180  <x:anchor-alias value="value"/>
2181   Parameters are in the form of attribute/value pairs.
2182</t>
2183<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"/>
2184  <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>
2185  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2186  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2187</artwork></figure>
2188<t>
2189   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2190   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2191   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2192</t>
2193
2194<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2195  <iref item="chunked (Coding Format)"/>
2196  <iref item="Coding Format" subitem="chunked"/>
2197  <x:anchor-alias value="chunk"/>
2198  <x:anchor-alias value="Chunked-Body"/>
2199  <x:anchor-alias value="chunk-data"/>
2200  <x:anchor-alias value="chunk-ext"/>
2201  <x:anchor-alias value="chunk-ext-name"/>
2202  <x:anchor-alias value="chunk-ext-val"/>
2203  <x:anchor-alias value="chunk-size"/>
2204  <x:anchor-alias value="last-chunk"/>
2205  <x:anchor-alias value="trailer-part"/>
2206  <x:anchor-alias value="quoted-str-nf"/>
2207  <x:anchor-alias value="qdtext-nf"/>
2208<t>
2209   The chunked encoding modifies the body of a message in order to
2210   transfer it as a series of chunks, each with its own size indicator,
2211   followed by an &OPTIONAL; trailer containing header fields. This
2212   allows dynamically produced content to be transferred along with the
2213   information necessary for the recipient to verify that it has
2214   received the full message.
2215</t>
2216<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"/>
2217  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2218                   <x:ref>last-chunk</x:ref>
2219                   <x:ref>trailer-part</x:ref>
2220                   <x:ref>CRLF</x:ref>
2221 
2222  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2223                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2224  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2225  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2226 
2227  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref>
2228                      [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2229  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2230  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2231  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2232  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2233 
2234  <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>
2235                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2236  <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>
2237</artwork></figure>
2238<t>
2239   The chunk-size field is a string of hex digits indicating the size of
2240   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2241   zero, followed by the trailer, which is terminated by an empty line.
2242</t>
2243<t>
2244   The trailer allows the sender to include additional HTTP header
2245   fields at the end of the message. The Trailer header field can be
2246   used to indicate which header fields are included in a trailer (see
2247   <xref target="header.trailer"/>).
2248</t>
2249<t>
2250   A server using chunked transfer-coding in a response &MUST-NOT; use the
2251   trailer for any header fields unless at least one of the following is
2252   true:
2253  <list style="numbers">
2254    <t>the request included a TE header field that indicates "trailers" is
2255     acceptable in the transfer-coding of the  response, as described in
2256     <xref target="header.te"/>; or,</t>
2257     
2258    <t>the trailer fields consist entirely of optional metadata, and the
2259    recipient could use the message (in a manner acceptable to the server where
2260    the field originated) without receiving it. In other words, the server that
2261    generated the header (often but not always the origin server) is willing to
2262    accept the possibility that the trailer fields might be silently discarded
2263    along the path to the client.</t>
2264  </list>
2265</t>
2266<t>
2267   This requirement prevents an interoperability failure when the
2268   message is being received by an HTTP/1.1 (or later) proxy and
2269   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2270   conformance with the protocol would have necessitated a possibly
2271   infinite buffer on the proxy.
2272</t>
2273<t>
2274   A process for decoding the "chunked" transfer-coding
2275   can be represented in pseudo-code as:
2276</t>
2277<figure><artwork type="code">
2278  length := 0
2279  read chunk-size, chunk-ext (if any) and CRLF
2280  while (chunk-size &gt; 0) {
2281     read chunk-data and CRLF
2282     append chunk-data to decoded-body
2283     length := length + chunk-size
2284     read chunk-size and CRLF
2285  }
2286  read header-field
2287  while (header-field not empty) {
2288     append header-field to existing header fields
2289     read header-field
2290  }
2291  Content-Length := length
2292  Remove "chunked" from Transfer-Encoding
2293</artwork></figure>
2294<t>
2295   All HTTP/1.1 applications &MUST; be able to receive and decode the
2296   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2297   they do not understand.
2298</t>
2299<t>
2300   Use of chunk-ext extensions by senders is deprecated; they &SHOULD-NOT; be
2301   sent and definition of new chunk-extensions is discouraged.
2302</t>
2303</section>
2304
2305<section title="Compression Codings" anchor="compression.codings">
2306<t>
2307   The codings defined below can be used to compress the payload of a
2308   message.
2309</t>
2310<x:note><t>
2311   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2312   is not desirable and is discouraged for future encodings. Their
2313   use here is representative of historical practice, not good
2314   design.
2315</t></x:note>
2316<x:note><t>
2317   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2318   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2319   equivalent to "gzip" and "compress" respectively.
2320</t></x:note>
2321
2322<section title="Compress Coding" anchor="compress.coding">
2323<iref item="compress (Coding Format)"/>
2324<iref item="Coding Format" subitem="compress"/>
2325<t>
2326   The "compress" format is produced by the common UNIX file compression
2327   program "compress". This format is an adaptive Lempel-Ziv-Welch
2328   coding (LZW).
2329</t>
2330</section>
2331
2332<section title="Deflate Coding" anchor="deflate.coding">
2333<iref item="deflate (Coding Format)"/>
2334<iref item="Coding Format" subitem="deflate"/>
2335<t>
2336   The "deflate" format is defined as the "deflate" compression mechanism
2337   (described in <xref target="RFC1951"/>) used inside the "zlib"
2338   data format (<xref target="RFC1950"/>).
2339</t>
2340<x:note>
2341  <t>
2342    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2343    compressed data without the zlib wrapper.
2344   </t>
2345</x:note>
2346</section>
2347
2348<section title="Gzip Coding" anchor="gzip.coding">
2349<iref item="gzip (Coding Format)"/>
2350<iref item="Coding Format" subitem="gzip"/>
2351<t>
2352   The "gzip" format is produced by the file compression program
2353   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2354   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2355</t>
2356</section>
2357
2358</section>
2359
2360<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2361<t>
2362   The HTTP Transfer Coding Registry defines the name space for the transfer
2363   coding names.
2364</t>
2365<t>
2366   Registrations &MUST; include the following fields:
2367   <list style="symbols">
2368     <t>Name</t>
2369     <t>Description</t>
2370     <t>Pointer to specification text</t>
2371   </list>
2372</t>
2373<t>
2374   Names of transfer codings &MUST-NOT; overlap with names of content codings
2375   (&content-codings;), unless the encoding transformation is identical (as it
2376   is the case for the compression codings defined in
2377   <xref target="compression.codings"/>).
2378</t>
2379<t>
2380   Values to be added to this name space require a specification
2381   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2382   conform to the purpose of transfer coding defined in this section.
2383</t>
2384<t>
2385   The registry itself is maintained at
2386   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2387</t>
2388</section>
2389
2390<section title="TE" anchor="header.te">
2391  <iref primary="true" item="TE header field" x:for-anchor=""/>
2392  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
2393  <x:anchor-alias value="TE"/>
2394  <x:anchor-alias value="t-codings"/>
2395  <x:anchor-alias value="te-params"/>
2396  <x:anchor-alias value="te-ext"/>
2397<t>
2398   The "TE" header field indicates what extension transfer-codings
2399   the client is willing to accept in the response, and whether or not it is
2400   willing to accept trailer fields in a chunked transfer-coding.
2401</t>
2402<t>
2403   Its value consists of the keyword "trailers" and/or a comma-separated
2404   list of extension transfer-coding names with optional accept
2405   parameters (as described in <xref target="transfer.codings"/>).
2406</t>
2407<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"/>
2408  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
2409  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2410  <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> )
2411  <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> ]
2412</artwork></figure>
2413<t>
2414   The presence of the keyword "trailers" indicates that the client is
2415   willing to accept trailer fields in a chunked transfer-coding, as
2416   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2417   transfer-coding values even though it does not itself represent a
2418   transfer-coding.
2419</t>
2420<t>
2421   Examples of its use are:
2422</t>
2423<figure><artwork type="example">
2424  TE: deflate
2425  TE:
2426  TE: trailers, deflate;q=0.5
2427</artwork></figure>
2428<t>
2429   The TE header field only applies to the immediate connection.
2430   Therefore, the keyword &MUST; be supplied within a Connection header
2431   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2432</t>
2433<t>
2434   A server tests whether a transfer-coding is acceptable, according to
2435   a TE field, using these rules:
2436  <list style="numbers">
2437    <x:lt>
2438      <t>The "chunked" transfer-coding is always acceptable. If the
2439         keyword "trailers" is listed, the client indicates that it is
2440         willing to accept trailer fields in the chunked response on
2441         behalf of itself and any downstream clients. The implication is
2442         that, if given, the client is stating that either all
2443         downstream clients are willing to accept trailer fields in the
2444         forwarded response, or that it will attempt to buffer the
2445         response on behalf of downstream recipients.
2446      </t><t>
2447         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2448         chunked response such that a client can be assured of buffering
2449         the entire response.</t>
2450    </x:lt>
2451    <x:lt>
2452      <t>If the transfer-coding being tested is one of the transfer-codings
2453         listed in the TE field, then it is acceptable unless it
2454         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2455         qvalue of 0 means "not acceptable".)</t>
2456    </x:lt>
2457    <x:lt>
2458      <t>If multiple transfer-codings are acceptable, then the
2459         acceptable transfer-coding with the highest non-zero qvalue is
2460         preferred.  The "chunked" transfer-coding always has a qvalue
2461         of 1.</t>
2462    </x:lt>
2463  </list>
2464</t>
2465<t>
2466   If the TE field-value is empty or if no TE field is present, the only
2467   acceptable transfer-coding is "chunked". A message with no transfer-coding is
2468   always acceptable.
2469</t>
2470
2471<section title="Quality Values" anchor="quality.values">
2472  <x:anchor-alias value="qvalue"/>
2473<t>
2474   Both transfer codings (TE request header field, <xref target="header.te"/>)
2475   and content negotiation (&content.negotiation;) use short "floating point"
2476   numbers to indicate the relative importance ("weight") of various
2477   negotiable parameters.  A weight is normalized to a real number in
2478   the range 0 through 1, where 0 is the minimum and 1 the maximum
2479   value. If a parameter has a quality value of 0, then content with
2480   this parameter is "not acceptable" for the client. HTTP/1.1
2481   applications &MUST-NOT; generate more than three digits after the
2482   decimal point. User configuration of these values &SHOULD; also be
2483   limited in this fashion.
2484</t>
2485<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2486  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2487                 / ( "1" [ "." 0*3("0") ] )
2488</artwork></figure>
2489<x:note>
2490  <t>
2491     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2492     relative degradation in desired quality.
2493  </t>
2494</x:note>
2495</section>
2496</section>
2497
2498<section title="Trailer" anchor="header.trailer">
2499  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
2500  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
2501  <x:anchor-alias value="Trailer"/>
2502<t>
2503   The "Trailer" header field indicates that the given set of
2504   header fields is present in the trailer of a message encoded with
2505   chunked transfer-coding.
2506</t>
2507<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
2508  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
2509</artwork></figure>
2510<t>
2511   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2512   message using chunked transfer-coding with a non-empty trailer. Doing
2513   so allows the recipient to know which header fields to expect in the
2514   trailer.
2515</t>
2516<t>
2517   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2518   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2519   trailer fields in a "chunked" transfer-coding.
2520</t>
2521<t>
2522   Message header fields listed in the Trailer header field &MUST-NOT;
2523   include the following header fields:
2524  <list style="symbols">
2525    <t>Transfer-Encoding</t>
2526    <t>Content-Length</t>
2527    <t>Trailer</t>
2528  </list>
2529</t>
2530</section>
2531</section>
2532
2533<section title="Connections" anchor="connections">
2534
2535<section title="Persistent Connections" anchor="persistent.connections">
2536
2537<section title="Purpose" anchor="persistent.purpose">
2538<t>
2539   Prior to persistent connections, a separate TCP connection was
2540   established for each request, increasing the load on HTTP servers
2541   and causing congestion on the Internet. The use of inline images and
2542   other associated data often requires a client to make multiple
2543   requests of the same server in a short amount of time. Analysis of
2544   these performance problems and results from a prototype
2545   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2546   measurements of actual HTTP/1.1 implementations show good
2547   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2548   T/TCP <xref target="Tou1998"/>.
2549</t>
2550<t>
2551   Persistent HTTP connections have a number of advantages:
2552  <list style="symbols">
2553      <t>
2554        By opening and closing fewer TCP connections, CPU time is saved
2555        in routers and hosts (clients, servers, proxies, gateways,
2556        tunnels, or caches), and memory used for TCP protocol control
2557        blocks can be saved in hosts.
2558      </t>
2559      <t>
2560        HTTP requests and responses can be pipelined on a connection.
2561        Pipelining allows a client to make multiple requests without
2562        waiting for each response, allowing a single TCP connection to
2563        be used much more efficiently, with much lower elapsed time.
2564      </t>
2565      <t>
2566        Network congestion is reduced by reducing the number of packets
2567        caused by TCP opens, and by allowing TCP sufficient time to
2568        determine the congestion state of the network.
2569      </t>
2570      <t>
2571        Latency on subsequent requests is reduced since there is no time
2572        spent in TCP's connection opening handshake.
2573      </t>
2574      <t>
2575        HTTP can evolve more gracefully, since errors can be reported
2576        without the penalty of closing the TCP connection. Clients using
2577        future versions of HTTP might optimistically try a new feature,
2578        but if communicating with an older server, retry with old
2579        semantics after an error is reported.
2580      </t>
2581    </list>
2582</t>
2583<t>
2584   HTTP implementations &SHOULD; implement persistent connections.
2585</t>
2586</section>
2587
2588<section title="Overall Operation" anchor="persistent.overall">
2589<t>
2590   A significant difference between HTTP/1.1 and earlier versions of
2591   HTTP is that persistent connections are the default behavior of any
2592   HTTP connection. That is, unless otherwise indicated, the client
2593   &SHOULD; assume that the server will maintain a persistent connection,
2594   even after error responses from the server.
2595</t>
2596<t>
2597   Persistent connections provide a mechanism by which a client and a
2598   server can signal the close of a TCP connection. This signaling takes
2599   place using the Connection header field (<xref target="header.connection"/>). Once a close
2600   has been signaled, the client &MUST-NOT; send any more requests on that
2601   connection.
2602</t>
2603
2604<section title="Negotiation" anchor="persistent.negotiation">
2605<t>
2606   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2607   maintain a persistent connection unless a Connection header field including
2608   the connection-token "close" was sent in the request. If the server
2609   chooses to close the connection immediately after sending the
2610   response, it &SHOULD; send a Connection header field including the
2611   connection-token "close".
2612</t>
2613<t>
2614   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2615   decide to keep it open based on whether the response from a server
2616   contains a Connection header field with the connection-token close. In case
2617   the client does not want to maintain a connection for more than that
2618   request, it &SHOULD; send a Connection header field including the
2619   connection-token close.
2620</t>
2621<t>
2622   If either the client or the server sends the close token in the
2623   Connection header field, that request becomes the last one for the
2624   connection.
2625</t>
2626<t>
2627   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2628   maintained for HTTP versions less than 1.1 unless it is explicitly
2629   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2630   compatibility with HTTP/1.0 clients.
2631</t>
2632<t>
2633   In order to remain persistent, all messages on the connection &MUST;
2634   have a self-defined message length (i.e., one not defined by closure
2635   of the connection), as described in <xref target="message.body"/>.
2636</t>
2637</section>
2638
2639<section title="Pipelining" anchor="pipelining">
2640<t>
2641   A client that supports persistent connections &MAY; "pipeline" its
2642   requests (i.e., send multiple requests without waiting for each
2643   response). A server &MUST; send its responses to those requests in the
2644   same order that the requests were received.
2645</t>
2646<t>
2647   Clients which assume persistent connections and pipeline immediately
2648   after connection establishment &SHOULD; be prepared to retry their
2649   connection if the first pipelined attempt fails. If a client does
2650   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2651   persistent. Clients &MUST; also be prepared to resend their requests if
2652   the server closes the connection before sending all of the
2653   corresponding responses.
2654</t>
2655<t>
2656   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2657   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2658   premature termination of the transport connection could lead to
2659   indeterminate results. A client wishing to send a non-idempotent
2660   request &SHOULD; wait to send that request until it has received the
2661   response status line for the previous request.
2662</t>
2663</section>
2664</section>
2665
2666<section title="Proxy Servers" anchor="persistent.proxy">
2667<t>
2668   It is especially important that proxies correctly implement the
2669   properties of the Connection header field as specified in <xref target="header.connection"/>.
2670</t>
2671<t>
2672   The proxy server &MUST; signal persistent connections separately with
2673   its clients and the origin servers (or other proxy servers) that it
2674   connects to. Each persistent connection applies to only one transport
2675   link.
2676</t>
2677<t>
2678   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2679   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2680   for information and discussion of the problems with the Keep-Alive header field
2681   implemented by many HTTP/1.0 clients).
2682</t>
2683
2684<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2685<!--<t>
2686  <cref anchor="TODO-end-to-end" source="jre">
2687    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2688    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2689  </cref>
2690</t>-->
2691<t>
2692   For the purpose of defining the behavior of caches and non-caching
2693   proxies, we divide HTTP header fields into two categories:
2694  <list style="symbols">
2695      <t>End-to-end header fields, which are  transmitted to the ultimate
2696        recipient of a request or response. End-to-end header fields in
2697        responses MUST be stored as part of a cache entry and &MUST; be
2698        transmitted in any response formed from a cache entry.</t>
2699
2700      <t>Hop-by-hop header fields, which are meaningful only for a single
2701        transport-level connection, and are not stored by caches or
2702        forwarded by proxies.</t>
2703  </list>
2704</t>
2705<t>
2706   The following HTTP/1.1 header fields are hop-by-hop header fields:
2707  <list style="symbols">
2708      <t>Connection</t>
2709      <t>Keep-Alive</t>
2710      <t>Proxy-Authenticate</t>
2711      <t>Proxy-Authorization</t>
2712      <t>TE</t>
2713      <t>Trailer</t>
2714      <t>Transfer-Encoding</t>
2715      <t>Upgrade</t>
2716  </list>
2717</t>
2718<t>
2719   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2720</t>
2721<t>
2722   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2723   (<xref target="header.connection"/>).
2724</t>
2725</section>
2726
2727<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2728<!--<t>
2729  <cref anchor="TODO-non-mod-headers" source="jre">
2730    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2731    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2732  </cref>
2733</t>-->
2734<t>
2735   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2736   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2737   modify an end-to-end header field unless the definition of that header field requires
2738   or specifically allows that.
2739</t>
2740<t>
2741   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2742   request or response, and it &MUST-NOT; add any of these fields if not
2743   already present:
2744  <list style="symbols">
2745    <t>Allow</t>
2746    <t>Content-Location</t>
2747    <t>Content-MD5</t>
2748    <t>ETag</t>
2749    <t>Last-Modified</t>
2750    <t>Server</t>
2751  </list>
2752</t>
2753<t>
2754   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2755   response:
2756  <list style="symbols">
2757    <t>Expires</t>
2758  </list>
2759</t>
2760<t>
2761   but it &MAY; add any of these fields if not already present. If an
2762   Expires header field is added, it &MUST; be given a field-value identical to
2763   that of the Date header field in that response.
2764</t>
2765<t>
2766   A proxy &MUST-NOT; modify or add any of the following fields in a
2767   message that contains the no-transform cache-control directive, or in
2768   any request:
2769  <list style="symbols">
2770    <t>Content-Encoding</t>
2771    <t>Content-Range</t>
2772    <t>Content-Type</t>
2773  </list>
2774</t>
2775<t>
2776   A transforming proxy &MAY; modify or add these fields to a message
2777   that does not include no-transform, but if it does so, it &MUST; add a
2778   Warning 214 (Transformation applied) if one does not already appear
2779   in the message (see &header-warning;).
2780</t>
2781<x:note>
2782  <t>
2783    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2784    cause authentication failures if stronger authentication
2785    mechanisms are introduced in later versions of HTTP. Such
2786    authentication mechanisms &MAY; rely on the values of header fields
2787    not listed here.
2788  </t>
2789</x:note>
2790<t>
2791   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2792   though it &MAY; change the message body through application or removal
2793   of a transfer-coding (<xref target="transfer.codings"/>).
2794</t>
2795</section>
2796
2797</section>
2798
2799<section title="Practical Considerations" anchor="persistent.practical">
2800<t>
2801   Servers will usually have some time-out value beyond which they will
2802   no longer maintain an inactive connection. Proxy servers might make
2803   this a higher value since it is likely that the client will be making
2804   more connections through the same server. The use of persistent
2805   connections places no requirements on the length (or existence) of
2806   this time-out for either the client or the server.
2807</t>
2808<t>
2809   When a client or server wishes to time-out it &SHOULD; issue a graceful
2810   close on the transport connection. Clients and servers &SHOULD; both
2811   constantly watch for the other side of the transport close, and
2812   respond to it as appropriate. If a client or server does not detect
2813   the other side's close promptly it could cause unnecessary resource
2814   drain on the network.
2815</t>
2816<t>
2817   A client, server, or proxy &MAY; close the transport connection at any
2818   time. For example, a client might have started to send a new request
2819   at the same time that the server has decided to close the "idle"
2820   connection. From the server's point of view, the connection is being
2821   closed while it was idle, but from the client's point of view, a
2822   request is in progress.
2823</t>
2824<t>
2825   Clients (including proxies) &SHOULD; limit the number of simultaneous
2826   connections that they maintain to a given server (including proxies).
2827</t>
2828<t>
2829   Previous revisions of HTTP gave a specific number of connections as a
2830   ceiling, but this was found to be impractical for many applications. As a
2831   result, this specification does not mandate a particular maximum number of
2832   connections, but instead encourages clients to be conservative when opening
2833   multiple connections.
2834</t>
2835<t>
2836   In particular, while using multiple connections avoids the "head-of-line
2837   blocking" problem (whereby a request that takes significant server-side
2838   processing and/or has a large payload can block subsequent requests on the
2839   same connection), each connection used consumes server resources (sometimes
2840   significantly), and furthermore using multiple connections can cause
2841   undesirable side effects in congested networks.
2842</t>
2843<t>
2844   Note that servers might reject traffic that they deem abusive, including an
2845   excessive number of connections from a client.
2846</t>
2847</section>
2848
2849<section title="Retrying Requests" anchor="persistent.retrying.requests">
2850<t>
2851   Senders can close the transport connection at any time. Therefore,
2852   clients, servers, and proxies &MUST; be able to recover
2853   from asynchronous close events. Client software &MAY; reopen the
2854   transport connection and retransmit the aborted sequence of requests
2855   without user interaction so long as the request sequence is
2856   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2857   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2858   human operator the choice of retrying the request(s). Confirmation by
2859   user-agent software with semantic understanding of the application
2860   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2861   be repeated if the second sequence of requests fails.
2862</t>
2863</section>
2864
2865</section>
2866
2867<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2868
2869<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2870<t>
2871   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2872   flow control mechanisms to resolve temporary overloads, rather than
2873   terminating connections with the expectation that clients will retry.
2874   The latter technique can exacerbate network congestion.
2875</t>
2876</section>
2877
2878<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2879<t>
2880   An HTTP/1.1 (or later) client sending a message body &SHOULD; monitor
2881   the network connection for an error status code while it is transmitting
2882   the request. If the client sees an error status code, it &SHOULD;
2883   immediately cease transmitting the body. If the body is being sent
2884   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2885   empty trailer &MAY; be used to prematurely mark the end of the message.
2886   If the body was preceded by a Content-Length header field, the client &MUST;
2887   close the connection.
2888</t>
2889</section>
2890
2891<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2892<t>
2893   The purpose of the 100 (Continue) status code (see &status-100;) is to
2894   allow a client that is sending a request message with a request body
2895   to determine if the origin server is willing to accept the request
2896   (based on the request header fields) before the client sends the request
2897   body. In some cases, it might either be inappropriate or highly
2898   inefficient for the client to send the body if the server will reject
2899   the message without looking at the body.
2900</t>
2901<t>
2902   Requirements for HTTP/1.1 clients:
2903  <list style="symbols">
2904    <t>
2905        If a client will wait for a 100 (Continue) response before
2906        sending the request body, it &MUST; send an Expect header
2907        field (&header-expect;) with the "100-continue" expectation.
2908    </t>
2909    <t>
2910        A client &MUST-NOT; send an Expect header field (&header-expect;)
2911        with the "100-continue" expectation if it does not intend
2912        to send a request body.
2913    </t>
2914  </list>
2915</t>
2916<t>
2917   Because of the presence of older implementations, the protocol allows
2918   ambiguous situations in which a client might send "Expect: 100-continue"
2919   without receiving either a 417 (Expectation Failed)
2920   or a 100 (Continue) status code. Therefore, when a client sends this
2921   header field to an origin server (possibly via a proxy) from which it
2922   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2923   wait for an indefinite period before sending the request body.
2924</t>
2925<t>
2926   Requirements for HTTP/1.1 origin servers:
2927  <list style="symbols">
2928    <t> Upon receiving a request which includes an Expect header
2929        field with the "100-continue" expectation, an origin server &MUST;
2930        either respond with 100 (Continue) status code and continue to read
2931        from the input stream, or respond with a final status code. The
2932        origin server &MUST-NOT; wait for the request body before sending
2933        the 100 (Continue) response. If it responds with a final status
2934        code, it &MAY; close the transport connection or it &MAY; continue
2935        to read and discard the rest of the request.  It &MUST-NOT;
2936        perform the request method if it returns a final status code.
2937    </t>
2938    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2939        the request message does not include an Expect header
2940        field with the "100-continue" expectation, and &MUST-NOT; send a
2941        100 (Continue) response if such a request comes from an HTTP/1.0
2942        (or earlier) client. There is an exception to this rule: for
2943        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2944        status code in response to an HTTP/1.1 PUT or POST request that does
2945        not include an Expect header field with the "100-continue"
2946        expectation. This exception, the purpose of which is
2947        to minimize any client processing delays associated with an
2948        undeclared wait for 100 (Continue) status code, applies only to
2949        HTTP/1.1 requests, and not to requests with any other HTTP-version
2950        value.
2951    </t>
2952    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2953        already received some or all of the request body for the
2954        corresponding request.
2955    </t>
2956    <t> An origin server that sends a 100 (Continue) response &MUST;
2957        ultimately send a final status code, once the request body is
2958        received and processed, unless it terminates the transport
2959        connection prematurely.
2960    </t>
2961    <t> If an origin server receives a request that does not include an
2962        Expect header field with the "100-continue" expectation,
2963        the request includes a request body, and the server responds
2964        with a final status code before reading the entire request body
2965        from the transport connection, then the server &SHOULD-NOT;  close
2966        the transport connection until it has read the entire request,
2967        or until the client closes the connection. Otherwise, the client
2968        might not reliably receive the response message. However, this
2969        requirement ought not be construed as preventing a server from
2970        defending itself against denial-of-service attacks, or from
2971        badly broken client implementations.
2972      </t>
2973    </list>
2974</t>
2975<t>
2976   Requirements for HTTP/1.1 proxies:
2977  <list style="symbols">
2978    <t> If a proxy receives a request that includes an Expect header
2979        field with the "100-continue" expectation, and the proxy
2980        either knows that the next-hop server complies with HTTP/1.1 or
2981        higher, or does not know the HTTP version of the next-hop
2982        server, it &MUST; forward the request, including the Expect header
2983        field.
2984    </t>
2985    <t> If the proxy knows that the version of the next-hop server is
2986        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2987        respond with a 417 (Expectation Failed) status code.
2988    </t>
2989    <t> Proxies &SHOULD; maintain a record of the HTTP version
2990        numbers received from recently-referenced next-hop servers.
2991    </t>
2992    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2993        request message was received from an HTTP/1.0 (or earlier)
2994        client and did not include an Expect header field with
2995        the "100-continue" expectation. This requirement overrides the
2996        general rule for forwarding of 1xx responses (see &status-1xx;).
2997    </t>
2998  </list>
2999</t>
3000</section>
3001
3002<section title="Closing Connections on Error" anchor="closing.connections.on.error">
3003<t>
3004   If the client is sending data, a server implementation using TCP
3005   &SHOULD; be careful to ensure that the client acknowledges receipt of
3006   the packet(s) containing the response, before the server closes the
3007   input connection. If the client continues sending data to the server
3008   after the close, the server's TCP stack will send a reset packet to
3009   the client, which might erase the client's unacknowledged input buffers
3010   before they can be read and interpreted by the HTTP application.
3011</t>
3012</section>
3013
3014</section>
3015</section>
3016
3017
3018<section title="Miscellaneous notes that might disappear" anchor="misc">
3019<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
3020<t>
3021   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
3022</t>
3023</section>
3024
3025<section title="Use of HTTP for proxy communication" anchor="http.proxy">
3026<t>
3027   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
3028</t>
3029</section>
3030
3031<section title="Interception of HTTP for access control" anchor="http.intercept">
3032<t>
3033   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
3034</t>
3035</section>
3036
3037<section title="Use of HTTP by other protocols" anchor="http.others">
3038<t>
3039   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
3040   Extensions of HTTP like WebDAV.</cref>
3041</t>
3042
3043</section>
3044<section title="Use of HTTP by media type specification" anchor="http.media">
3045<t>
3046   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3047</t>
3048</section>
3049</section>
3050
3051<section title="Header Field Definitions" anchor="header.field.definitions">
3052<t>
3053   This section defines the syntax and semantics of HTTP header fields
3054   related to message origination, framing, and routing.
3055</t>
3056<texttable align="left">
3057  <ttcol>Header Field Name</ttcol>
3058  <ttcol>Defined in...</ttcol>
3059 
3060  <c>Connection</c> <c><xref target="header.connection"/></c>
3061  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
3062  <c>Host</c> <c><xref target="header.host"/></c>
3063  <c>TE</c> <c><xref target="header.te"/></c>
3064  <c>Trailer</c> <c><xref target="header.trailer"/></c>
3065  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
3066  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
3067  <c>Via</c> <c><xref target="header.via"/></c>
3068</texttable>
3069
3070<section title="Connection" anchor="header.connection">
3071  <iref primary="true" item="Connection header field" x:for-anchor=""/>
3072  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
3073  <x:anchor-alias value="Connection"/>
3074  <x:anchor-alias value="connection-token"/>
3075<t>
3076   The "Connection" header field allows the sender to specify
3077   options that are desired only for that particular connection.
3078   Such connection options &MUST; be removed or replaced before the
3079   message can be forwarded downstream by a proxy or gateway.
3080   This mechanism also allows the sender to indicate which HTTP
3081   header fields used in the message are only intended for the
3082   immediate recipient ("hop-by-hop"), as opposed to all recipients
3083   on the chain ("end-to-end"), enabling the message to be
3084   self-descriptive and allowing future connection-specific extensions
3085   to be deployed in HTTP without fear that they will be blindly
3086   forwarded by previously deployed intermediaries.
3087</t>
3088<t>
3089   The Connection header field's value has the following grammar:
3090</t>
3091<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
3092  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
3093  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
3094</artwork></figure>
3095<t>
3096   A proxy or gateway &MUST; parse a received Connection
3097   header field before a message is forwarded and, for each
3098   connection-token in this field, remove any header field(s) from
3099   the message with the same name as the connection-token, and then
3100   remove the Connection header field itself or replace it with the
3101   sender's own connection options for the forwarded message.
3102</t>
3103<t>
3104   A sender &MUST-NOT; include field-names in the Connection header
3105   field-value for fields that are defined as expressing constraints
3106   for all recipients in the request or response chain, such as the
3107   Cache-Control header field (&header-cache-control;).
3108</t>
3109<t>
3110   The connection options do not have to correspond to a header field
3111   present in the message, since a connection-specific header field
3112   might not be needed if there are no parameters associated with that
3113   connection option.  Recipients that trigger certain connection
3114   behavior based on the presence of connection options &MUST; do so
3115   based on the presence of the connection-token rather than only the
3116   presence of the optional header field.  In other words, if the
3117   connection option is received as a header field but not indicated
3118   within the Connection field-value, then the recipient &MUST; ignore
3119   the connection-specific header field because it has likely been
3120   forwarded by an intermediary that is only partially conformant.
3121</t>
3122<t>
3123   When defining new connection options, specifications ought to
3124   carefully consider existing deployed header fields and ensure
3125   that the new connection-token does not share the same name as
3126   an unrelated header field that might already be deployed.
3127   Defining a new connection-token essentially reserves that potential
3128   field-name for carrying additional information related to the
3129   connection option, since it would be unwise for senders to use
3130   that field-name for anything else.
3131</t>
3132<t>
3133   HTTP/1.1 defines the "close" connection option for the sender to
3134   signal that the connection will be closed after completion of the
3135   response. For example,
3136</t>
3137<figure><artwork type="example">
3138  Connection: close
3139</artwork></figure>
3140<t>
3141   in either the request or the response header fields indicates that
3142   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3143   after the current request/response is complete.
3144</t>
3145<t>
3146   An HTTP/1.1 client that does not support persistent connections &MUST;
3147   include the "close" connection option in every request message.
3148</t>
3149<t>
3150   An HTTP/1.1 server that does not support persistent connections &MUST;
3151   include the "close" connection option in every response message that
3152   does not have a 1xx (Informational) status code.
3153</t>
3154</section>
3155
3156<section title="Host" anchor="header.host">
3157  <iref primary="true" item="Host header field" x:for-anchor=""/>
3158  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3159  <x:anchor-alias value="Host"/>
3160<t>
3161   The "Host" header field in a request provides the host and port
3162   information from the target resource's URI, enabling the origin
3163   server to distinguish between resources while servicing requests
3164   for multiple host names on a single IP address.  Since the Host
3165   field-value is critical information for handling a request, it
3166   &SHOULD; be sent as the first header field following the Request-Line.
3167</t>
3168<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3169  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3170</artwork></figure>
3171<t>
3172   A client &MUST; send a Host header field in all HTTP/1.1 request
3173   messages.  If the target resource's URI includes an authority
3174   component, then the Host field-value &MUST; be identical to that
3175   authority component after excluding any userinfo (<xref target="http.uri"/>).
3176   If the authority component is missing or undefined for the target
3177   resource's URI, then the Host header field &MUST; be sent with an
3178   empty field-value.
3179</t>
3180<t>
3181   For example, a GET request to the origin server for
3182   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3183</t>
3184<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3185GET /pub/WWW/ HTTP/1.1
3186Host: www.example.org
3187</artwork></figure>
3188<t>
3189   The Host header field &MUST; be sent in an HTTP/1.1 request even
3190   if the request-target is in the form of an absolute-URI, since this
3191   allows the Host information to be forwarded through ancient HTTP/1.0
3192   proxies that might not have implemented Host.
3193</t>
3194<t>
3195   When an HTTP/1.1 proxy receives a request with a request-target in
3196   the form of an absolute-URI, the proxy &MUST; ignore the received
3197   Host header field (if any) and instead replace it with the host
3198   information of the request-target.  When a proxy forwards a request,
3199   it &MUST; generate the Host header field based on the received
3200   absolute-URI rather than the received Host.
3201</t>
3202<t>
3203   Since the Host header field acts as an application-level routing
3204   mechanism, it is a frequent target for malware seeking to poison
3205   a shared cache or redirect a request to an unintended server.
3206   An interception proxy is particularly vulnerable if it relies on
3207   the Host header field value for redirecting requests to internal
3208   servers, or for use as a cache key in a shared cache, without
3209   first verifying that the intercepted connection is targeting a
3210   valid IP address for that host.
3211</t>
3212<t>
3213   A server &MUST; respond with a 400 (Bad Request) status code to
3214   any HTTP/1.1 request message that lacks a Host header field and
3215   to any request message that contains more than one Host header field
3216   or a Host header field with an invalid field-value.
3217</t>
3218<t>
3219   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3220   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3221   for other requirements relating to Host.
3222</t>
3223</section>
3224
3225<section title="Upgrade" anchor="header.upgrade">
3226  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3227  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3228  <x:anchor-alias value="Upgrade"/>
3229  <x:anchor-alias value="protocol"/>
3230  <x:anchor-alias value="protocol-name"/>
3231  <x:anchor-alias value="protocol-version"/>
3232<t>
3233   The "Upgrade" header field allows the client to specify what
3234   additional communication protocols it would like to use, if the server
3235   chooses to switch protocols. Servers can use it to indicate what protocols
3236   they are willing to switch to.
3237</t>
3238<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3239  <x:ref>Upgrade</x:ref>  = 1#<x:ref>protocol</x:ref>
3240
3241  <x:ref>protocol</x:ref> = <x:ref>protocol-name</x:ref> ["/" <x:ref>protocol-version</x:ref>]
3242  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3243  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3244</artwork></figure>
3245<t>
3246   For example,
3247</t>
3248<figure><artwork type="example">
3249  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3250</artwork></figure>
3251<t>
3252   The Upgrade header field is intended to provide a simple mechanism
3253   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3254   does so by allowing the client to advertise its desire to use another
3255   protocol, such as a later version of HTTP with a higher major version
3256   number, even though the current request has been made using HTTP/1.1.
3257   This eases the difficult transition between incompatible protocols by
3258   allowing the client to initiate a request in the more commonly
3259   supported protocol while indicating to the server that it would like
3260   to use a "better" protocol if available (where "better" is determined
3261   by the server, possibly according to the nature of the request method
3262   or target resource).
3263</t>
3264<t>
3265   The Upgrade header field only applies to switching application-layer
3266   protocols upon the existing transport-layer connection. Upgrade
3267   cannot be used to insist on a protocol change; its acceptance and use
3268   by the server is optional. The capabilities and nature of the
3269   application-layer communication after the protocol change is entirely
3270   dependent upon the new protocol chosen, although the first action
3271   after changing the protocol &MUST; be a response to the initial HTTP
3272   request containing the Upgrade header field.
3273</t>
3274<t>
3275   The Upgrade header field only applies to the immediate connection.
3276   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3277   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3278   HTTP/1.1 message.
3279</t>
3280<t>
3281   The Upgrade header field cannot be used to indicate a switch to a
3282   protocol on a different connection. For that purpose, it is more
3283   appropriate to use a 3xx redirection response (&status-3xx;).
3284</t>
3285<t>
3286   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3287   Protocols) responses to indicate which protocol(s) are being switched to,
3288   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3289   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3290   response to indicate that they are willing to upgrade to one of the
3291   specified protocols.
3292</t>
3293<t>
3294   This specification only defines the protocol name "HTTP" for use by
3295   the family of Hypertext Transfer Protocols, as defined by the HTTP
3296   version rules of <xref target="http.version"/> and future updates to this
3297   specification. Additional tokens can be registered with IANA using the
3298   registration procedure defined below. 
3299</t>
3300
3301<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3302<t>
3303   The HTTP Upgrade Token Registry defines the name space for protocol-name
3304   tokens used to identify protocols in the Upgrade header field.
3305   Each registered protocol-name is associated with contact information and
3306   an optional set of specifications that details how the connection
3307   will be processed after it has been upgraded.
3308</t>
3309<t>
3310   Registrations are allowed on a First Come First Served basis as
3311   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3312   specifications need not be IETF documents or be subject to IESG review.
3313   Registrations are subject to the following rules:
3314  <list style="numbers">
3315    <t>A protocol-name token, once registered, stays registered forever.</t>
3316    <t>The registration &MUST; name a responsible party for the
3317       registration.</t>
3318    <t>The registration &MUST; name a point of contact.</t>
3319    <t>The registration &MAY; name a set of specifications associated with
3320       that token. Such specifications need not be publicly available.</t>
3321    <t>The registration &SHOULD; name a set of expected "protocol-version"
3322       tokens associated with that token at the time of registration.</t>
3323    <t>The responsible party &MAY; change the registration at any time.
3324       The IANA will keep a record of all such changes, and make them
3325       available upon request.</t>
3326    <t>The IESG &MAY; reassign responsibility for a protocol token.
3327       This will normally only be used in the case when a
3328       responsible party cannot be contacted.</t>
3329  </list>
3330</t>
3331</section>
3332
3333
3334</section>
3335
3336<section title="Via" anchor="header.via">
3337  <iref primary="true" item="Via header field" x:for-anchor=""/>
3338  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3339  <x:anchor-alias value="pseudonym"/>
3340  <x:anchor-alias value="received-by"/>
3341  <x:anchor-alias value="received-protocol"/>
3342  <x:anchor-alias value="Via"/>
3343<t>
3344   The "Via" header field &MUST; be sent by a proxy or gateway to
3345   indicate the intermediate protocols and recipients between the user
3346   agent and the server on requests, and between the origin server and
3347   the client on responses. It is analogous to the "Received" field
3348   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3349   and is intended to be used for tracking message forwards,
3350   avoiding request loops, and identifying the protocol capabilities of
3351   all senders along the request/response chain.
3352</t>
3353<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"/>
3354  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3355                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3356  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3357  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3358  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3359</artwork></figure>
3360<t>
3361   The received-protocol indicates the protocol version of the message
3362   received by the server or client along each segment of the
3363   request/response chain. The received-protocol version is appended to
3364   the Via field value when the message is forwarded so that information
3365   about the protocol capabilities of upstream applications remains
3366   visible to all recipients.
3367</t>
3368<t>
3369   The protocol-name is excluded if and only if it would be "HTTP". The
3370   received-by field is normally the host and optional port number of a
3371   recipient server or client that subsequently forwarded the message.
3372   However, if the real host is considered to be sensitive information,
3373   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3374   be assumed to be the default port of the received-protocol.
3375</t>
3376<t>
3377   Multiple Via field values represent each proxy or gateway that has
3378   forwarded the message. Each recipient &MUST; append its information
3379   such that the end result is ordered according to the sequence of
3380   forwarding applications.
3381</t>
3382<t>
3383   Comments &MAY; be used in the Via header field to identify the software
3384   of each recipient, analogous to the User-Agent and Server header fields.
3385   However, all comments in the Via field are optional and &MAY; be removed
3386   by any recipient prior to forwarding the message.
3387</t>
3388<t>
3389   For example, a request message could be sent from an HTTP/1.0 user
3390   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3391   forward the request to a public proxy at p.example.net, which completes
3392   the request by forwarding it to the origin server at www.example.com.
3393   The request received by www.example.com would then have the following
3394   Via header field:
3395</t>
3396<figure><artwork type="example">
3397  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3398</artwork></figure>
3399<t>
3400   A proxy or gateway used as a portal through a network firewall
3401   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3402   region unless it is explicitly enabled to do so. If not enabled, the
3403   received-by host of any host behind the firewall &SHOULD; be replaced
3404   by an appropriate pseudonym for that host.
3405</t>
3406<t>
3407   For organizations that have strong privacy requirements for hiding
3408   internal structures, a proxy or gateway &MAY; combine an ordered
3409   subsequence of Via header field entries with identical received-protocol
3410   values into a single such entry. For example,
3411</t>
3412<figure><artwork type="example">
3413  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3414</artwork></figure>
3415<t>
3416  could be collapsed to
3417</t>
3418<figure><artwork type="example">
3419  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3420</artwork></figure>
3421<t>
3422   Senders &SHOULD-NOT; combine multiple entries unless they are all
3423   under the same organizational control and the hosts have already been
3424   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3425   have different received-protocol values.
3426</t>
3427</section>
3428
3429</section>
3430
3431<section title="IANA Considerations" anchor="IANA.considerations">
3432
3433<section title="Header Field Registration" anchor="header.field.registration">
3434<t>
3435   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3436   with the permanent registrations below (see <xref target="RFC3864"/>):
3437</t>
3438<?BEGININC p1-messaging.iana-headers ?>
3439<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3440<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3441   <ttcol>Header Field Name</ttcol>
3442   <ttcol>Protocol</ttcol>
3443   <ttcol>Status</ttcol>
3444   <ttcol>Reference</ttcol>
3445
3446   <c>Connection</c>
3447   <c>http</c>
3448   <c>standard</c>
3449   <c>
3450      <xref target="header.connection"/>
3451   </c>
3452   <c>Content-Length</c>
3453   <c>http</c>
3454   <c>standard</c>
3455   <c>
3456      <xref target="header.content-length"/>
3457   </c>
3458   <c>Host</c>
3459   <c>http</c>
3460   <c>standard</c>
3461   <c>
3462      <xref target="header.host"/>
3463   </c>
3464   <c>TE</c>
3465   <c>http</c>
3466   <c>standard</c>
3467   <c>
3468      <xref target="header.te"/>
3469   </c>
3470   <c>Trailer</c>
3471   <c>http</c>
3472   <c>standard</c>
3473   <c>
3474      <xref target="header.trailer"/>
3475   </c>
3476   <c>Transfer-Encoding</c>
3477   <c>http</c>
3478   <c>standard</c>
3479   <c>
3480      <xref target="header.transfer-encoding"/>
3481   </c>
3482   <c>Upgrade</c>
3483   <c>http</c>
3484   <c>standard</c>
3485   <c>
3486      <xref target="header.upgrade"/>
3487   </c>
3488   <c>Via</c>
3489   <c>http</c>
3490   <c>standard</c>
3491   <c>
3492      <xref target="header.via"/>
3493   </c>
3494</texttable>
3495<!--(END)-->
3496<?ENDINC p1-messaging.iana-headers ?>
3497<t>
3498   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3499   HTTP header field would be in conflict with the use of the "close" connection
3500   option for the "Connection" header field (<xref target="header.connection"/>).
3501</t>
3502<texttable align="left" suppress-title="true">
3503   <ttcol>Header Field Name</ttcol>
3504   <ttcol>Protocol</ttcol>
3505   <ttcol>Status</ttcol>
3506   <ttcol>Reference</ttcol>
3507
3508   <c>Close</c>
3509   <c>http</c>
3510   <c>reserved</c>
3511   <c>
3512      <xref target="header.field.registration"/>
3513   </c>
3514</texttable>
3515<t>
3516   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3517</t>
3518</section>
3519
3520<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3521<t>
3522   The entries for the "http" and "https" URI Schemes in the registry located at
3523   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3524   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3525   and <xref target="https.uri" format="counter"/> of this document
3526   (see <xref target="RFC4395"/>).
3527</t>
3528</section>
3529
3530<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3531<t>
3532   This document serves as the specification for the Internet media types
3533   "message/http" and "application/http". The following is to be registered with
3534   IANA (see <xref target="RFC4288"/>).
3535</t>
3536<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3537<iref item="Media Type" subitem="message/http" primary="true"/>
3538<iref item="message/http Media Type" primary="true"/>
3539<t>
3540   The message/http type can be used to enclose a single HTTP request or
3541   response message, provided that it obeys the MIME restrictions for all
3542   "message" types regarding line length and encodings.
3543</t>
3544<t>
3545  <list style="hanging" x:indent="12em">
3546    <t hangText="Type name:">
3547      message
3548    </t>
3549    <t hangText="Subtype name:">
3550      http
3551    </t>
3552    <t hangText="Required parameters:">
3553      none
3554    </t>
3555    <t hangText="Optional parameters:">
3556      version, msgtype
3557      <list style="hanging">
3558        <t hangText="version:">
3559          The HTTP-Version number of the enclosed message
3560          (e.g., "1.1"). If not present, the version can be
3561          determined from the first line of the body.
3562        </t>
3563        <t hangText="msgtype:">
3564          The message type &mdash; "request" or "response". If not
3565          present, the type can be determined from the first
3566          line of the body.
3567        </t>
3568      </list>
3569    </t>
3570    <t hangText="Encoding considerations:">
3571      only "7bit", "8bit", or "binary" are permitted
3572    </t>
3573    <t hangText="Security considerations:">
3574      none
3575    </t>
3576    <t hangText="Interoperability considerations:">
3577      none
3578    </t>
3579    <t hangText="Published specification:">
3580      This specification (see <xref target="internet.media.type.message.http"/>).
3581    </t>
3582    <t hangText="Applications that use this media type:">
3583    </t>
3584    <t hangText="Additional information:">
3585      <list style="hanging">
3586        <t hangText="Magic number(s):">none</t>
3587        <t hangText="File extension(s):">none</t>
3588        <t hangText="Macintosh file type code(s):">none</t>
3589      </list>
3590    </t>
3591    <t hangText="Person and email address to contact for further information:">
3592      See Authors Section.
3593    </t>
3594    <t hangText="Intended usage:">
3595      COMMON
3596    </t>
3597    <t hangText="Restrictions on usage:">
3598      none
3599    </t>
3600    <t hangText="Author/Change controller:">
3601      IESG
3602    </t>
3603  </list>
3604</t>
3605</section>
3606<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3607<iref item="Media Type" subitem="application/http" primary="true"/>
3608<iref item="application/http Media Type" primary="true"/>
3609<t>
3610   The application/http type can be used to enclose a pipeline of one or more
3611   HTTP request or response messages (not intermixed).
3612</t>
3613<t>
3614  <list style="hanging" x:indent="12em">
3615    <t hangText="Type name:">
3616      application
3617    </t>
3618    <t hangText="Subtype name:">
3619      http
3620    </t>
3621    <t hangText="Required parameters:">
3622      none
3623    </t>
3624    <t hangText="Optional parameters:">
3625      version, msgtype
3626      <list style="hanging">
3627        <t hangText="version:">
3628          The HTTP-Version number of the enclosed messages
3629          (e.g., "1.1"). If not present, the version can be
3630          determined from the first line of the body.
3631        </t>
3632        <t hangText="msgtype:">
3633          The message type &mdash; "request" or "response". If not
3634          present, the type can be determined from the first
3635          line of the body.
3636        </t>
3637      </list>
3638    </t>
3639    <t hangText="Encoding considerations:">
3640      HTTP messages enclosed by this type
3641      are in "binary" format; use of an appropriate
3642      Content-Transfer-Encoding is required when
3643      transmitted via E-mail.
3644    </t>
3645    <t hangText="Security considerations:">
3646      none
3647    </t>
3648    <t hangText="Interoperability considerations:">
3649      none
3650    </t>
3651    <t hangText="Published specification:">
3652      This specification (see <xref target="internet.media.type.application.http"/>).
3653    </t>
3654    <t hangText="Applications that use this media type:">
3655    </t>
3656    <t hangText="Additional information:">
3657      <list style="hanging">
3658        <t hangText="Magic number(s):">none</t>
3659        <t hangText="File extension(s):">none</t>
3660        <t hangText="Macintosh file type code(s):">none</t>
3661      </list>
3662    </t>
3663    <t hangText="Person and email address to contact for further information:">
3664      See Authors Section.
3665    </t>
3666    <t hangText="Intended usage:">
3667      COMMON
3668    </t>
3669    <t hangText="Restrictions on usage:">
3670      none
3671    </t>
3672    <t hangText="Author/Change controller:">
3673      IESG
3674    </t>
3675  </list>
3676</t>
3677</section>
3678</section>
3679
3680<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3681<t>
3682   The registration procedure for HTTP Transfer Codings is now defined by
3683   <xref target="transfer.coding.registry"/> of this document.
3684</t>
3685<t>
3686   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3687   shall be updated with the registrations below:
3688</t>
3689<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3690   <ttcol>Name</ttcol>
3691   <ttcol>Description</ttcol>
3692   <ttcol>Reference</ttcol>
3693   <c>chunked</c>
3694   <c>Transfer in a series of chunks</c>
3695   <c>
3696      <xref target="chunked.encoding"/>
3697   </c>
3698   <c>compress</c>
3699   <c>UNIX "compress" program method</c>
3700   <c>
3701      <xref target="compress.coding"/>
3702   </c>
3703   <c>deflate</c>
3704   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3705   the "zlib" data format (<xref target="RFC1950"/>)
3706   </c>
3707   <c>
3708      <xref target="deflate.coding"/>
3709   </c>
3710   <c>gzip</c>
3711   <c>Same as GNU zip <xref target="RFC1952"/></c>
3712   <c>
3713      <xref target="gzip.coding"/>
3714   </c>
3715</texttable>
3716</section>
3717
3718<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3719<t>
3720   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3721   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3722   by <xref target="upgrade.token.registry"/> of this document.
3723</t>
3724<t>
3725   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3726   shall be updated with the registration below:
3727</t>
3728<texttable align="left" suppress-title="true">
3729   <ttcol>Value</ttcol>
3730   <ttcol>Description</ttcol>
3731   <ttcol>Reference</ttcol>
3732
3733   <c>HTTP</c>
3734   <c>Hypertext Transfer Protocol</c> 
3735   <c><xref target="http.version"/> of this specification</c>
3736
3737</texttable>
3738</section>
3739
3740</section>
3741
3742<section title="Security Considerations" anchor="security.considerations">
3743<t>
3744   This section is meant to inform application developers, information
3745   providers, and users of the security limitations in HTTP/1.1 as
3746   described by this document. The discussion does not include
3747   definitive solutions to the problems revealed, though it does make
3748   some suggestions for reducing security risks.
3749</t>
3750
3751<section title="Personal Information" anchor="personal.information">
3752<t>
3753   HTTP clients are often privy to large amounts of personal information
3754   (e.g., the user's name, location, mail address, passwords, encryption
3755   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3756   leakage of this information.
3757   We very strongly recommend that a convenient interface be provided
3758   for the user to control dissemination of such information, and that
3759   designers and implementors be particularly careful in this area.
3760   History shows that errors in this area often create serious security
3761   and/or privacy problems and generate highly adverse publicity for the
3762   implementor's company.
3763</t>
3764</section>
3765
3766<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3767<t>
3768   A server is in the position to save personal data about a user's
3769   requests which might identify their reading patterns or subjects of
3770   interest. This information is clearly confidential in nature and its
3771   handling can be constrained by law in certain countries. People using
3772   HTTP to provide data are responsible for ensuring that
3773   such material is not distributed without the permission of any
3774   individuals that are identifiable by the published results.
3775</t>
3776</section>
3777
3778<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3779<t>
3780   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3781   the documents returned by HTTP requests to be only those that were
3782   intended by the server administrators. If an HTTP server translates
3783   HTTP URIs directly into file system calls, the server &MUST; take
3784   special care not to serve files that were not intended to be
3785   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3786   other operating systems use ".." as a path component to indicate a
3787   directory level above the current one. On such a system, an HTTP
3788   server &MUST; disallow any such construct in the request-target if it
3789   would otherwise allow access to a resource outside those intended to
3790   be accessible via the HTTP server. Similarly, files intended for
3791   reference only internally to the server (such as access control
3792   files, configuration files, and script code) &MUST; be protected from
3793   inappropriate retrieval, since they might contain sensitive
3794   information. Experience has shown that minor bugs in such HTTP server
3795   implementations have turned into security risks.
3796</t>
3797</section>
3798
3799<section title="DNS-related Attacks" anchor="dns.related.attacks">
3800<t>
3801   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3802   generally prone to security attacks based on the deliberate misassociation
3803   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3804   cautious in assuming the validity of an IP number/DNS name association unless
3805   the response is protected by DNSSec (<xref target="RFC4033"/>).
3806</t>
3807</section>
3808
3809<section title="Proxies and Caching" anchor="attack.proxies">
3810<t>
3811   By their very nature, HTTP proxies are men-in-the-middle, and
3812   represent an opportunity for man-in-the-middle attacks. Compromise of
3813   the systems on which the proxies run can result in serious security
3814   and privacy problems. Proxies have access to security-related
3815   information, personal information about individual users and
3816   organizations, and proprietary information belonging to users and
3817   content providers. A compromised proxy, or a proxy implemented or
3818   configured without regard to security and privacy considerations,
3819   might be used in the commission of a wide range of potential attacks.
3820</t>
3821<t>
3822   Proxy operators need to protect the systems on which proxies run as
3823   they would protect any system that contains or transports sensitive
3824   information. In particular, log information gathered at proxies often
3825   contains highly sensitive personal information, and/or information
3826   about organizations. Log information needs to be carefully guarded, and
3827   appropriate guidelines for use need to be developed and followed.
3828   (<xref target="abuse.of.server.log.information"/>).
3829</t>
3830<t>
3831   Proxy implementors need to consider the privacy and security
3832   implications of their design and coding decisions, and of the
3833   configuration options they provide to proxy operators (especially the
3834   default configuration).
3835</t>
3836<t>
3837   Users of a proxy need to be aware that proxies are no more trustworthy than
3838   the people who run them; HTTP itself cannot solve this problem.
3839</t>
3840<t>
3841   The judicious use of cryptography, when appropriate, might suffice to
3842   protect against a broad range of security and privacy attacks. Such
3843   cryptography is beyond the scope of the HTTP/1.1 specification.
3844</t>
3845</section>
3846
3847<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3848<t>
3849   Because HTTP uses mostly textual, character-delimited fields, attackers can
3850   overflow buffers in implementations, and/or perform a Denial of Service
3851   against implementations that accept fields with unlimited lengths.
3852</t>
3853<t>
3854   To promote interoperability, this specification makes specific
3855   recommendations for size limits on request-targets (<xref target="request-target"/>)
3856   and blocks of header fields (<xref target="header.fields"/>). These are
3857   minimum recommendations, chosen to be supportable even by implementations
3858   with limited resources; it is expected that most implementations will choose
3859   substantially higher limits.
3860</t>
3861<t>
3862   This specification also provides a way for servers to reject messages that
3863   have request-targets that are too long (&status-414;) or request entities
3864   that are too large (&status-4xx;).
3865</t>
3866<t>
3867   Other fields (including but not limited to request methods, response status
3868   phrases, header field-names, and body chunks) &SHOULD; be limited by
3869   implementations carefully, so as to not impede interoperability.
3870</t>
3871</section>
3872
3873<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3874<t>
3875   They exist. They are hard to defend against. Research continues.
3876   Beware.
3877</t>
3878</section>
3879</section>
3880
3881<section title="Acknowledgments" anchor="acks">
3882<t>
3883   This document revision builds on the work that went into
3884   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3885   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
3886   acknowledgements.
3887</t>
3888<t>
3889   Since 1999, many contributors have helped by reporting bugs, asking
3890   smart questions, drafting and reviewing text, and discussing open issues:
3891</t>
3892<?BEGININC acks ?>
3893<t>Adam Barth,
3894Adam Roach,
3895Addison Phillips,
3896Adrian Chadd,
3897Adrien de Croy,
3898Alan Ford,
3899Alan Ruttenberg,
3900Albert Lunde,
3901Alex Rousskov,
3902Alexey Melnikov,
3903Alisha Smith,
3904Amichai Rothman,
3905Amit Klein,
3906Amos Jeffries,
3907Andreas Maier,
3908Andreas Petersson,
3909Anne van Kesteren,
3910Anthony Bryan,
3911Asbjorn Ulsberg,
3912Balachander Krishnamurthy,
3913Barry Leiba,
3914Ben Laurie,
3915Benjamin Niven-Jenkins,
3916Bil Corry,
3917Bill Burke,
3918Bjoern Hoehrmann,
3919Bob Scheifler,
3920Boris Zbarsky,
3921Brett Slatkin,
3922Brian Kell,
3923Brian McBarron,
3924Brian Pane,
3925Brian Smith,
3926Bryce Nesbitt,
3927Cameron Heavon-Jones,
3928Carl Kugler,
3929Carsten Bormann,
3930Charles Fry,
3931Chris Newman,
3932Cyrus Daboo,
3933Dale Robert Anderson,
3934Dan Winship,
3935Daniel Stenberg,
3936Dave Cridland,
3937Dave Crocker,
3938Dave Kristol,
3939David Booth,
3940David Singer,
3941David W. Morris,
3942Diwakar Shetty,
3943Dmitry Kurochkin,
3944Drummond Reed,
3945Duane Wessels,
3946Edward Lee,
3947Eliot Lear,
3948Eran Hammer-Lahav,
3949Eric D. Williams,
3950Eric J. Bowman,
3951Eric Lawrence,
3952Erik Aronesty,
3953Florian Weimer,
3954Frank Ellermann,
3955Fred Bohle,
3956Geoffrey Sneddon,
3957Gervase Markham,
3958Greg Wilkins,
3959Harald Tveit Alvestrand,
3960Harry Halpin,
3961Helge Hess,
3962Henrik Nordstrom,
3963Henry S. Thompson,
3964Henry Story,
3965Herbert van de Sompel,
3966Howard Melman,
3967Hugo Haas,
3968Ian Hickson,
3969Ingo Struck,
3970J. Ross Nicoll,
3971James H. Manger,
3972James Lacey,
3973James M. Snell,
3974Jamie Lokier,
3975Jan Algermissen,
3976Jeff Hodges (for coming up with the term 'effective Request-URI'),
3977Jeff Walden,
3978Jim Luther,
3979Joe D. Williams,
3980Joe Gregorio,
3981Joe Orton,
3982John C. Klensin,
3983John C. Mallery,
3984John Cowan,
3985John Kemp,
3986John Panzer,
3987John Schneider,
3988John Stracke,
3989Jonas Sicking,
3990Jonathan Billington,
3991Jonathan Moore,
3992Jonathan Rees,
3993Jordi Ros,
3994Joris Dobbelsteen,
3995Josh Cohen,
3996Julien Pierre,
3997Jungshik Shin,
3998Justin Chapweske,
3999Justin Erenkrantz,
4000Justin James,
4001Kalvinder Singh,
4002Karl Dubost,
4003Keith Hoffman,
4004Keith Moore,
4005Koen Holtman,
4006Konstantin Voronkov,
4007Kris Zyp,
4008Lisa Dusseault,
4009Maciej Stachowiak,
4010Marc Schneider,
4011Marc Slemko,
4012Mark Baker,
4013Mark Nottingham (Working Group chair),
4014Mark Pauley,
4015Markus Lanthaler,
4016Martin J. Duerst,
4017Martin Thomson,
4018Matt Lynch,
4019Matthew Cox,
4020Max Clark,
4021Michael Burrows,
4022Michael Hausenblas,
4023Mike Amundsen,
4024Mike Kelly,
4025Mike Schinkel,
4026Miles Sabin,
4027Mykyta Yevstifeyev,
4028Nathan Rixham,
4029Nicholas Shanks,
4030Nico Williams,
4031Nicolas Alvarez,
4032Noah Slater,
4033Pablo Castro,
4034Pat Hayes,
4035Patrick R. McManus,
4036Paul E. Jones,
4037Paul Hoffman,
4038Paul Marquess,
4039Peter Saint-Andre,
4040Peter Watkins,
4041Phil Archer,
4042Phillip Hallam-Baker,
4043Poul-Henning Kamp,
4044Preethi Natarajan,
4045Ray Polk,
4046Reto Bachmann-Gmuer,
4047Richard Cyganiak,
4048Robert Brewer,
4049Robert Collins,
4050Robert O'Callahan,
4051Robert Olofsson,
4052Robert Sayre,
4053Robert Siemer,
4054Robert de Wilde,
4055Roberto Javier Godoy,
4056Ronny Widjaja,
4057S. Mike Dierken,
4058Salvatore Loreto,
4059Sam Johnston,
4060Sam Ruby,
4061Scott Lawrence (for maintaining the original issues list),
4062Sean B. Palmer,
4063Shane McCarron,
4064Stefan Eissing,
4065Stefan Tilkov,
4066Stefanos Harhalakis,
4067Stephane Bortzmeyer,
4068Stuart Williams,
4069Subbu Allamaraju,
4070Sylvain Hellegouarch,
4071Tapan Divekar,
4072Ted Hardie,
4073Thomas Broyer,
4074Thomas Nordin,
4075Thomas Roessler,
4076Tim Morgan,
4077Tim Olsen,
4078Travis Snoozy,
4079Tyler Close,
4080Vincent Murphy,
4081Wenbo Zhu,
4082Werner Baumann,
4083Wilbur Streett,
4084Wilfredo Sanchez Vega,
4085William A. Rowe Jr.,
4086William Chan,
4087Willy Tarreau,
4088Xiaoshu Wang,
4089Yaron Goland,
4090Yngve Nysaeter Pettersen,
4091Yogesh Bang,
4092Yutaka Oiwa,
4093Zed A. Shaw, and
4094Zhong Yu.
4095</t>
4096<?ENDINC acks ?>
4097</section>
4098
4099</middle>
4100<back>
4101
4102<references title="Normative References">
4103
4104<reference anchor="ISO-8859-1">
4105  <front>
4106    <title>
4107     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4108    </title>
4109    <author>
4110      <organization>International Organization for Standardization</organization>
4111    </author>
4112    <date year="1998"/>
4113  </front>
4114  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4115</reference>
4116
4117<reference anchor="Part2">
4118  <front>
4119    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4120    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4121      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4122      <address><email>fielding@gbiv.com</email></address>
4123    </author>
4124    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4125      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4126      <address><email>jg@freedesktop.org</email></address>
4127    </author>
4128    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4129      <organization abbrev="HP">Hewlett-Packard Company</organization>
4130      <address><email>JeffMogul@acm.org</email></address>
4131    </author>
4132    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4133      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4134      <address><email>henrikn@microsoft.com</email></address>
4135    </author>
4136    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4137      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4138      <address><email>LMM@acm.org</email></address>
4139    </author>
4140    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4141      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4142      <address><email>paulle@microsoft.com</email></address>
4143    </author>
4144    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4145      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4146      <address><email>timbl@w3.org</email></address>
4147    </author>
4148    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4149      <organization abbrev="W3C">World Wide Web Consortium</organization>
4150      <address><email>ylafon@w3.org</email></address>
4151    </author>
4152    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4153      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4154      <address><email>julian.reschke@greenbytes.de</email></address>
4155    </author>
4156    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4157  </front>
4158  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4159  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4160</reference>
4161
4162<reference anchor="Part3">
4163  <front>
4164    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4165    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4166      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4167      <address><email>fielding@gbiv.com</email></address>
4168    </author>
4169    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4170      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4171      <address><email>jg@freedesktop.org</email></address>
4172    </author>
4173    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4174      <organization abbrev="HP">Hewlett-Packard Company</organization>
4175      <address><email>JeffMogul@acm.org</email></address>
4176    </author>
4177    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4178      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4179      <address><email>henrikn@microsoft.com</email></address>
4180    </author>
4181    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4182      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4183      <address><email>LMM@acm.org</email></address>
4184    </author>
4185    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4186      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4187      <address><email>paulle@microsoft.com</email></address>
4188    </author>
4189    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4190      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4191      <address><email>timbl@w3.org</email></address>
4192    </author>
4193    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4194      <organization abbrev="W3C">World Wide Web Consortium</organization>
4195      <address><email>ylafon@w3.org</email></address>
4196    </author>
4197    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4198      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4199      <address><email>julian.reschke@greenbytes.de</email></address>
4200    </author>
4201    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4202  </front>
4203  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4204  <x:source href="p3-payload.xml" basename="p3-payload"/>
4205</reference>
4206
4207<reference anchor="Part6">
4208  <front>
4209    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4210    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4211      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4212      <address><email>fielding@gbiv.com</email></address>
4213    </author>
4214    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4215      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4216      <address><email>jg@freedesktop.org</email></address>
4217    </author>
4218    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4219      <organization abbrev="HP">Hewlett-Packard Company</organization>
4220      <address><email>JeffMogul@acm.org</email></address>
4221    </author>
4222    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4223      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4224      <address><email>henrikn@microsoft.com</email></address>
4225    </author>
4226    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4227      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4228      <address><email>LMM@acm.org</email></address>
4229    </author>
4230    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4231      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4232      <address><email>paulle@microsoft.com</email></address>
4233    </author>
4234    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4235      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4236      <address><email>timbl@w3.org</email></address>
4237    </author>
4238    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4239      <organization abbrev="W3C">World Wide Web Consortium</organization>
4240      <address><email>ylafon@w3.org</email></address>
4241    </author>
4242    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4243      <organization>Rackspace</organization>
4244      <address><email>mnot@mnot.net</email></address>
4245    </author>
4246    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4247      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4248      <address><email>julian.reschke@greenbytes.de</email></address>
4249    </author>
4250    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4251  </front>
4252  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4253  <x:source href="p6-cache.xml" basename="p6-cache"/>
4254</reference>
4255
4256<reference anchor="RFC5234">
4257  <front>
4258    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4259    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4260      <organization>Brandenburg InternetWorking</organization>
4261      <address>
4262        <email>dcrocker@bbiw.net</email>
4263      </address> 
4264    </author>
4265    <author initials="P." surname="Overell" fullname="Paul Overell">
4266      <organization>THUS plc.</organization>
4267      <address>
4268        <email>paul.overell@thus.net</email>
4269      </address>
4270    </author>
4271    <date month="January" year="2008"/>
4272  </front>
4273  <seriesInfo name="STD" value="68"/>
4274  <seriesInfo name="RFC" value="5234"/>
4275</reference>
4276
4277<reference anchor="RFC2119">
4278  <front>
4279    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4280    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4281      <organization>Harvard University</organization>
4282      <address><email>sob@harvard.edu</email></address>
4283    </author>
4284    <date month="March" year="1997"/>
4285  </front>
4286  <seriesInfo name="BCP" value="14"/>
4287  <seriesInfo name="RFC" value="2119"/>
4288</reference>
4289
4290<reference anchor="RFC3986">
4291 <front>
4292  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4293  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4294    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4295    <address>
4296       <email>timbl@w3.org</email>
4297       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4298    </address>
4299  </author>
4300  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4301    <organization abbrev="Day Software">Day Software</organization>
4302    <address>
4303      <email>fielding@gbiv.com</email>
4304      <uri>http://roy.gbiv.com/</uri>
4305    </address>
4306  </author>
4307  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4308    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4309    <address>
4310      <email>LMM@acm.org</email>
4311      <uri>http://larry.masinter.net/</uri>
4312    </address>
4313  </author>
4314  <date month='January' year='2005'></date>
4315 </front>
4316 <seriesInfo name="STD" value="66"/>
4317 <seriesInfo name="RFC" value="3986"/>
4318</reference>
4319
4320<reference anchor="USASCII">
4321  <front>
4322    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4323    <author>
4324      <organization>American National Standards Institute</organization>
4325    </author>
4326    <date year="1986"/>
4327  </front>
4328  <seriesInfo name="ANSI" value="X3.4"/>
4329</reference>
4330
4331<reference anchor="RFC1950">
4332  <front>
4333    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4334    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4335      <organization>Aladdin Enterprises</organization>
4336      <address><email>ghost@aladdin.com</email></address>
4337    </author>
4338    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4339    <date month="May" year="1996"/>
4340  </front>
4341  <seriesInfo name="RFC" value="1950"/>
4342  <!--<annotation>
4343    RFC 1950 is an Informational RFC, thus it might be less stable than
4344    this specification. On the other hand, this downward reference was
4345    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4346    therefore it is unlikely to cause problems in practice. See also
4347    <xref target="BCP97"/>.
4348  </annotation>-->
4349</reference>
4350
4351<reference anchor="RFC1951">
4352  <front>
4353    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4354    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4355      <organization>Aladdin Enterprises</organization>
4356      <address><email>ghost@aladdin.com</email></address>
4357    </author>
4358    <date month="May" year="1996"/>
4359  </front>
4360  <seriesInfo name="RFC" value="1951"/>
4361  <!--<annotation>
4362    RFC 1951 is an Informational RFC, thus it might be less stable than
4363    this specification. On the other hand, this downward reference was
4364    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4365    therefore it is unlikely to cause problems in practice. See also
4366    <xref target="BCP97"/>.
4367  </annotation>-->
4368</reference>
4369
4370<reference anchor="RFC1952">
4371  <front>
4372    <title>GZIP file format specification version 4.3</title>
4373    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4374      <organization>Aladdin Enterprises</organization>
4375      <address><email>ghost@aladdin.com</email></address>
4376    </author>
4377    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4378      <address><email>gzip@prep.ai.mit.edu</email></address>
4379    </author>
4380    <author initials="M." surname="Adler" fullname="Mark Adler">
4381      <address><email>madler@alumni.caltech.edu</email></address>
4382    </author>
4383    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4384      <address><email>ghost@aladdin.com</email></address>
4385    </author>
4386    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4387      <address><email>randeg@alumni.rpi.edu</email></address>
4388    </author>
4389    <date month="May" year="1996"/>
4390  </front>
4391  <seriesInfo name="RFC" value="1952"/>
4392  <!--<annotation>
4393    RFC 1952 is an Informational RFC, thus it might be less stable than
4394    this specification. On the other hand, this downward reference was
4395    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4396    therefore it is unlikely to cause problems in practice. See also
4397    <xref target="BCP97"/>.
4398  </annotation>-->
4399</reference>
4400
4401</references>
4402
4403<references title="Informative References">
4404
4405<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4406  <front>
4407    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4408    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4409    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4410    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4411    <author initials="H." surname="Lie" fullname="H. Lie"/>
4412    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4413    <date year="1997" month="September"/>
4414  </front>
4415  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4416</reference>
4417
4418<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4419  <front>
4420    <title>Improving HTTP Latency</title>
4421    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4422    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4423    <date year="1995" month="December"/>
4424  </front>
4425  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4426</reference>
4427
4428<reference anchor='RFC1919'>
4429  <front>
4430    <title>Classical versus Transparent IP Proxies</title>
4431    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4432      <address><email>mchatel@pax.eunet.ch</email></address>
4433    </author>
4434    <date year='1996' month='March' />
4435  </front>
4436  <seriesInfo name='RFC' value='1919' />
4437</reference>
4438
4439<reference anchor="RFC1945">
4440  <front>
4441    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4442    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4443      <organization>MIT, Laboratory for Computer Science</organization>
4444      <address><email>timbl@w3.org</email></address>
4445    </author>
4446    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4447      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4448      <address><email>fielding@ics.uci.edu</email></address>
4449    </author>
4450    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4451      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4452      <address><email>frystyk@w3.org</email></address>
4453    </author>
4454    <date month="May" year="1996"/>
4455  </front>
4456  <seriesInfo name="RFC" value="1945"/>
4457</reference>
4458
4459<reference anchor="RFC2045">
4460  <front>
4461    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4462    <author initials="N." surname="Freed" fullname="Ned Freed">
4463      <organization>Innosoft International, Inc.</organization>
4464      <address><email>ned@innosoft.com</email></address>
4465    </author>
4466    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4467      <organization>First Virtual Holdings</organization>
4468      <address><email>nsb@nsb.fv.com</email></address>
4469    </author>
4470    <date month="November" year="1996"/>
4471  </front>
4472  <seriesInfo name="RFC" value="2045"/>
4473</reference>
4474
4475<reference anchor="RFC2047">
4476  <front>
4477    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4478    <author initials="K." surname="Moore" fullname="Keith Moore">
4479      <organization>University of Tennessee</organization>
4480      <address><email>moore@cs.utk.edu</email></address>
4481    </author>
4482    <date month="November" year="1996"/>
4483  </front>
4484  <seriesInfo name="RFC" value="2047"/>
4485</reference>
4486
4487<reference anchor="RFC2068">
4488  <front>
4489    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4490    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4491      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4492      <address><email>fielding@ics.uci.edu</email></address>
4493    </author>
4494    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4495      <organization>MIT Laboratory for Computer Science</organization>
4496      <address><email>jg@w3.org</email></address>
4497    </author>
4498    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4499      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4500      <address><email>mogul@wrl.dec.com</email></address>
4501    </author>
4502    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4503      <organization>MIT Laboratory for Computer Science</organization>
4504      <address><email>frystyk@w3.org</email></address>
4505    </author>
4506    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4507      <organization>MIT Laboratory for Computer Science</organization>
4508      <address><email>timbl@w3.org</email></address>
4509    </author>
4510    <date month="January" year="1997"/>
4511  </front>
4512  <seriesInfo name="RFC" value="2068"/>
4513</reference>
4514
4515<reference anchor="RFC2145">
4516  <front>
4517    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4518    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4519      <organization>Western Research Laboratory</organization>
4520      <address><email>mogul@wrl.dec.com</email></address>
4521    </author>
4522    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4523      <organization>Department of Information and Computer Science</organization>
4524      <address><email>fielding@ics.uci.edu</email></address>
4525    </author>
4526    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4527      <organization>MIT Laboratory for Computer Science</organization>
4528      <address><email>jg@w3.org</email></address>
4529    </author>
4530    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4531      <organization>W3 Consortium</organization>
4532      <address><email>frystyk@w3.org</email></address>
4533    </author>
4534    <date month="May" year="1997"/>
4535  </front>
4536  <seriesInfo name="RFC" value="2145"/>
4537</reference>
4538
4539<reference anchor="RFC2616">
4540  <front>
4541    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4542    <author initials="R." surname="Fielding" fullname="R. Fielding">
4543      <organization>University of California, Irvine</organization>
4544      <address><email>fielding@ics.uci.edu</email></address>
4545    </author>
4546    <author initials="J." surname="Gettys" fullname="J. Gettys">
4547      <organization>W3C</organization>
4548      <address><email>jg@w3.org</email></address>
4549    </author>
4550    <author initials="J." surname="Mogul" fullname="J. Mogul">
4551      <organization>Compaq Computer Corporation</organization>
4552      <address><email>mogul@wrl.dec.com</email></address>
4553    </author>
4554    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4555      <organization>MIT Laboratory for Computer Science</organization>
4556      <address><email>frystyk@w3.org</email></address>
4557    </author>
4558    <author initials="L." surname="Masinter" fullname="L. Masinter">
4559      <organization>Xerox Corporation</organization>
4560      <address><email>masinter@parc.xerox.com</email></address>
4561    </author>
4562    <author initials="P." surname="Leach" fullname="P. Leach">
4563      <organization>Microsoft Corporation</organization>
4564      <address><email>paulle@microsoft.com</email></address>
4565    </author>
4566    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4567      <organization>W3C</organization>
4568      <address><email>timbl@w3.org</email></address>
4569    </author>
4570    <date month="June" year="1999"/>
4571  </front>
4572  <seriesInfo name="RFC" value="2616"/>
4573</reference>
4574
4575<reference anchor='RFC2817'>
4576  <front>
4577    <title>Upgrading to TLS Within HTTP/1.1</title>
4578    <author initials='R.' surname='Khare' fullname='R. Khare'>
4579      <organization>4K Associates / UC Irvine</organization>
4580      <address><email>rohit@4K-associates.com</email></address>
4581    </author>
4582    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4583      <organization>Agranat Systems, Inc.</organization>
4584      <address><email>lawrence@agranat.com</email></address>
4585    </author>
4586    <date year='2000' month='May' />
4587  </front>
4588  <seriesInfo name='RFC' value='2817' />
4589</reference>
4590
4591<reference anchor='RFC2818'>
4592  <front>
4593    <title>HTTP Over TLS</title>
4594    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4595      <organization>RTFM, Inc.</organization>
4596      <address><email>ekr@rtfm.com</email></address>
4597    </author>
4598    <date year='2000' month='May' />
4599  </front>
4600  <seriesInfo name='RFC' value='2818' />
4601</reference>
4602
4603<reference anchor='RFC2965'>
4604  <front>
4605    <title>HTTP State Management Mechanism</title>
4606    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4607      <organization>Bell Laboratories, Lucent Technologies</organization>
4608      <address><email>dmk@bell-labs.com</email></address>
4609    </author>
4610    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4611      <organization>Epinions.com, Inc.</organization>
4612      <address><email>lou@montulli.org</email></address>
4613    </author>
4614    <date year='2000' month='October' />
4615  </front>
4616  <seriesInfo name='RFC' value='2965' />
4617</reference>
4618
4619<reference anchor='RFC3040'>
4620  <front>
4621    <title>Internet Web Replication and Caching Taxonomy</title>
4622    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4623      <organization>Equinix, Inc.</organization>
4624    </author>
4625    <author initials='I.' surname='Melve' fullname='I. Melve'>
4626      <organization>UNINETT</organization>
4627    </author>
4628    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4629      <organization>CacheFlow Inc.</organization>
4630    </author>
4631    <date year='2001' month='January' />
4632  </front>
4633  <seriesInfo name='RFC' value='3040' />
4634</reference>
4635
4636<reference anchor='RFC3864'>
4637  <front>
4638    <title>Registration Procedures for Message Header Fields</title>
4639    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4640      <organization>Nine by Nine</organization>
4641      <address><email>GK-IETF@ninebynine.org</email></address>
4642    </author>
4643    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4644      <organization>BEA Systems</organization>
4645      <address><email>mnot@pobox.com</email></address>
4646    </author>
4647    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4648      <organization>HP Labs</organization>
4649      <address><email>JeffMogul@acm.org</email></address>
4650    </author>
4651    <date year='2004' month='September' />
4652  </front>
4653  <seriesInfo name='BCP' value='90' />
4654  <seriesInfo name='RFC' value='3864' />
4655</reference>
4656
4657<reference anchor='RFC4033'>
4658  <front>
4659    <title>DNS Security Introduction and Requirements</title>
4660    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4661    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4662    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4663    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4664    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4665    <date year='2005' month='March' />
4666  </front>
4667  <seriesInfo name='RFC' value='4033' />
4668</reference>
4669
4670<reference anchor="RFC4288">
4671  <front>
4672    <title>Media Type Specifications and Registration Procedures</title>
4673    <author initials="N." surname="Freed" fullname="N. Freed">
4674      <organization>Sun Microsystems</organization>
4675      <address>
4676        <email>ned.freed@mrochek.com</email>
4677      </address>
4678    </author>
4679    <author initials="J." surname="Klensin" fullname="J. Klensin">
4680      <address>
4681        <email>klensin+ietf@jck.com</email>
4682      </address>
4683    </author>
4684    <date year="2005" month="December"/>
4685  </front>
4686  <seriesInfo name="BCP" value="13"/>
4687  <seriesInfo name="RFC" value="4288"/>
4688</reference>
4689
4690<reference anchor='RFC4395'>
4691  <front>
4692    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4693    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4694      <organization>AT&amp;T Laboratories</organization>
4695      <address>
4696        <email>tony+urireg@maillennium.att.com</email>
4697      </address>
4698    </author>
4699    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4700      <organization>Qualcomm, Inc.</organization>
4701      <address>
4702        <email>hardie@qualcomm.com</email>
4703      </address>
4704    </author>
4705    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4706      <organization>Adobe Systems</organization>
4707      <address>
4708        <email>LMM@acm.org</email>
4709      </address>
4710    </author>
4711    <date year='2006' month='February' />
4712  </front>
4713  <seriesInfo name='BCP' value='115' />
4714  <seriesInfo name='RFC' value='4395' />
4715</reference>
4716
4717<reference anchor='RFC4559'>
4718  <front>
4719    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4720    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4721    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4722    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4723    <date year='2006' month='June' />
4724  </front>
4725  <seriesInfo name='RFC' value='4559' />
4726</reference>
4727
4728<reference anchor='RFC5226'>
4729  <front>
4730    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4731    <author initials='T.' surname='Narten' fullname='T. Narten'>
4732      <organization>IBM</organization>
4733      <address><email>narten@us.ibm.com</email></address>
4734    </author>
4735    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4736      <organization>Google</organization>
4737      <address><email>Harald@Alvestrand.no</email></address>
4738    </author>
4739    <date year='2008' month='May' />
4740  </front>
4741  <seriesInfo name='BCP' value='26' />
4742  <seriesInfo name='RFC' value='5226' />
4743</reference>
4744
4745<reference anchor="RFC5322">
4746  <front>
4747    <title>Internet Message Format</title>
4748    <author initials="P." surname="Resnick" fullname="P. Resnick">
4749      <organization>Qualcomm Incorporated</organization>
4750    </author>
4751    <date year="2008" month="October"/>
4752  </front> 
4753  <seriesInfo name="RFC" value="5322"/>
4754</reference>
4755
4756<reference anchor="RFC6265">
4757  <front>
4758    <title>HTTP State Management Mechanism</title>
4759    <author initials="A." surname="Barth" fullname="Adam Barth">
4760      <organization abbrev="U.C. Berkeley">
4761        University of California, Berkeley
4762      </organization>
4763      <address><email>abarth@eecs.berkeley.edu</email></address>
4764    </author>
4765    <date year="2011" month="April" />
4766  </front>
4767  <seriesInfo name="RFC" value="6265"/>
4768</reference>
4769
4770<!--<reference anchor='BCP97'>
4771  <front>
4772    <title>Handling Normative References to Standards-Track Documents</title>
4773    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4774      <address>
4775        <email>klensin+ietf@jck.com</email>
4776      </address>
4777    </author>
4778    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4779      <organization>MIT</organization>
4780      <address>
4781        <email>hartmans-ietf@mit.edu</email>
4782      </address>
4783    </author>
4784    <date year='2007' month='June' />
4785  </front>
4786  <seriesInfo name='BCP' value='97' />
4787  <seriesInfo name='RFC' value='4897' />
4788</reference>-->
4789
4790<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4791  <front>
4792    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4793    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4794    <date year="2001" month="November"/>
4795  </front>
4796  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4797</reference>
4798
4799<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4800  <front>
4801    <title>Analysis of HTTP Performance Problems</title>
4802    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4803    <date/>
4804  </front>
4805</reference>
4806
4807<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4808  <front>
4809  <title>Analysis of HTTP Performance</title>
4810  <author initials="J." surname="Touch" fullname="Joe Touch">
4811    <organization>USC/Information Sciences Institute</organization>
4812    <address><email>touch@isi.edu</email></address>
4813  </author>
4814  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4815    <organization>USC/Information Sciences Institute</organization>
4816    <address><email>johnh@isi.edu</email></address>
4817  </author>
4818  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4819    <organization>USC/Information Sciences Institute</organization>
4820    <address><email>katia@isi.edu</email></address>
4821  </author>
4822  <date year="1998" month="Aug"/>
4823  </front>
4824  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4825  <annotation>(original report dated Aug. 1996)</annotation>
4826</reference>
4827
4828</references>
4829
4830
4831<section title="HTTP Version History" anchor="compatibility">
4832<t>
4833   HTTP has been in use by the World-Wide Web global information initiative
4834   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4835   was a simple protocol for hypertext data transfer across the Internet
4836   with only a single request method (GET) and no metadata.
4837   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4838   methods and MIME-like messaging that could include metadata about the data
4839   transferred and modifiers on the request/response semantics. However,
4840   HTTP/1.0 did not sufficiently take into consideration the effects of
4841   hierarchical proxies, caching, the need for persistent connections, or
4842   name-based virtual hosts. The proliferation of incompletely-implemented
4843   applications calling themselves "HTTP/1.0" further necessitated a
4844   protocol version change in order for two communicating applications
4845   to determine each other's true capabilities.
4846</t>
4847<t>
4848   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4849   requirements that enable reliable implementations, adding only
4850   those new features that will either be safely ignored by an HTTP/1.0
4851   recipient or only sent when communicating with a party advertising
4852   conformance with HTTP/1.1.
4853</t>
4854<t>
4855   It is beyond the scope of a protocol specification to mandate
4856   conformance with previous versions. HTTP/1.1 was deliberately
4857   designed, however, to make supporting previous versions easy.
4858   We would expect a general-purpose HTTP/1.1 server to understand
4859   any valid request in the format of HTTP/1.0 and respond appropriately
4860   with an HTTP/1.1 message that only uses features understood (or
4861   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4862   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4863</t>
4864<t>
4865   Since HTTP/0.9 did not support header fields in a request,
4866   there is no mechanism for it to support name-based virtual
4867   hosts (selection of resource by inspection of the Host header
4868   field).  Any server that implements name-based virtual hosts
4869   ought to disable support for HTTP/0.9.  Most requests that
4870   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4871   requests wherein a buggy client failed to properly encode
4872   linear whitespace found in a URI reference and placed in
4873   the request-target.
4874</t>
4875
4876<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4877<t>
4878   This section summarizes major differences between versions HTTP/1.0
4879   and HTTP/1.1.
4880</t>
4881
4882<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4883<t>
4884   The requirements that clients and servers support the Host header
4885   field (<xref target="header.host"/>), report an error if it is
4886   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4887   are among the most important changes defined by HTTP/1.1.
4888</t>
4889<t>
4890   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4891   addresses and servers; there was no other established mechanism for
4892   distinguishing the intended server of a request than the IP address
4893   to which that request was directed. The Host header field was
4894   introduced during the development of HTTP/1.1 and, though it was
4895   quickly implemented by most HTTP/1.0 browsers, additional requirements
4896   were placed on all HTTP/1.1 requests in order to ensure complete
4897   adoption.  At the time of this writing, most HTTP-based services
4898   are dependent upon the Host header field for targeting requests.
4899</t>
4900</section>
4901
4902<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4903<t>
4904   In HTTP/1.0, each connection is established by the client prior to the
4905   request and closed by the server after sending the response. However, some
4906   implementations implement the explicitly negotiated ("Keep-Alive") version
4907   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4908   target="RFC2068"/>.
4909</t>
4910<t>
4911   Some clients and servers might wish to be compatible with these previous
4912   approaches to persistent connections, by explicitly negotiating for them
4913   with a "Connection: keep-alive" request header field. However, some
4914   experimental implementations of HTTP/1.0 persistent connections are faulty;
4915   for example, if a HTTP/1.0 proxy server doesn't understand Connection, it
4916   will erroneously forward that header to the next inbound server, which
4917   would result in a hung connection.
4918</t>
4919<t>
4920   One attempted solution was the introduction of a Proxy-Connection header,
4921   targeted specifically at proxies. In practice, this was also unworkable,
4922   because proxies are often deployed in multiple layers, bringing about the
4923   same problem discussed above.
4924</t>
4925<t>
4926   As a result, clients are encouraged not to send the Proxy-Connection header
4927   in any requests.
4928</t>
4929<t>
4930   Clients are also encouraged to consider the use of Connection: keep-alive
4931   in requests carefully; while they can enable persistent connections with
4932   HTTP/1.0 servers, clients using them need will need to monitor the
4933   connection for "hung" requests (which indicate that the client ought stop
4934   sending the header), and this mechanism ought not be used by clients at all
4935   when a proxy is being used.
4936</t>
4937</section>
4938</section>
4939
4940<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4941<t>
4942  Empty list elements in list productions have been deprecated.
4943  (<xref target="abnf.extension"/>)
4944</t>
4945<t>
4946  Rules about implicit linear whitespace between certain grammar productions
4947  have been removed; now whitespace is only allowed where specifically
4948  defined in the ABNF.
4949  (<xref target="whitespace"/>)
4950</t>
4951<t>
4952  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4953  sensitive. Restrict the version numbers to be single digits due to the fact
4954  that implementations are known to handle multi-digit version numbers
4955  incorrectly.
4956  (<xref target="http.version"/>)
4957</t>
4958<t>
4959  Require that invalid whitespace around field-names be rejected.
4960  (<xref target="header.fields"/>)
4961</t>
4962<t> 
4963  The NUL octet is no longer allowed in comment and quoted-string
4964  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4965  Non-ASCII content in header fields and reason phrase has been obsoleted and
4966  made opaque (the TEXT rule was removed).
4967  (<xref target="field.components"/>)
4968</t>
4969<t>
4970  Require recipients to handle bogus Content-Length header fields as errors.
4971  (<xref target="message.body"/>)
4972</t>
4973<t>
4974  Remove reference to non-existent identity transfer-coding value tokens.
4975  (Sections <xref format="counter" target="message.body"/> and
4976  <xref format="counter" target="transfer.codings"/>)
4977</t>
4978<t>
4979  Update use of abs_path production from RFC 1808 to the path-absolute + query
4980  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4981  request method only.
4982  (<xref target="request-target"/>)
4983</t>
4984<t>
4985  Clarification that the chunk length does not include the count of the octets
4986  in the chunk header and trailer. Furthermore disallowed line folding
4987  in chunk extensions, and deprecate their use.
4988  (<xref target="chunked.encoding"/>)
4989</t>
4990<t>
4991  Remove hard limit of two connections per server.
4992  Remove requirement to retry a sequence of requests as long it was idempotent.
4993  Remove requirements about when servers are allowed to close connections
4994  prematurely.
4995  (<xref target="persistent.practical"/>)
4996</t>
4997<t>
4998  Remove requirement to retry requests under certain cirumstances when the
4999  server prematurely closes the connection.
5000  (<xref target="message.transmission.requirements"/>)
5001</t>
5002<t>
5003  Change ABNF productions for header fields to only define the field value.
5004  (<xref target="header.field.definitions"/>)
5005</t>
5006<t>
5007  Clarify exactly when close connection options must be sent.
5008  (<xref target="header.connection"/>)
5009</t>
5010<t>
5011  Define the semantics of the "Upgrade" header field in responses other than
5012  101 (this was incorporated from <xref target="RFC2817"/>).
5013  (<xref target="header.upgrade"/>)
5014</t>
5015</section>
5016</section>
5017
5018<?BEGININC p1-messaging.abnf-appendix ?>
5019<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5020<figure>
5021<artwork type="abnf" name="p1-messaging.parsed-abnf">
5022<x:ref>BWS</x:ref> = OWS
5023
5024<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5025<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5026 connection-token ] )
5027<x:ref>Content-Length</x:ref> = 1*DIGIT
5028
5029<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5030<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5031<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5032 ]
5033<x:ref>Host</x:ref> = uri-host [ ":" port ]
5034
5035<x:ref>Method</x:ref> = token
5036
5037<x:ref>OWS</x:ref> = *( SP / HTAB / obs-fold )
5038
5039<x:ref>RWS</x:ref> = 1*( SP / HTAB / obs-fold )
5040<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5041<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5042
5043<x:ref>Status-Code</x:ref> = 3DIGIT
5044<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5045
5046<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5047<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5048<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5049 transfer-coding ] )
5050
5051<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5052<x:ref>Upgrade</x:ref> = *( "," OWS ) protocol *( OWS "," [ OWS protocol ] )
5053
5054<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5055 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5056 )
5057
5058<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5059<x:ref>attribute</x:ref> = token
5060<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5061
5062<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5063<x:ref>chunk-data</x:ref> = 1*OCTET
5064<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5065<x:ref>chunk-ext-name</x:ref> = token
5066<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5067<x:ref>chunk-size</x:ref> = 1*HEXDIG
5068<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5069<x:ref>connection-token</x:ref> = token
5070<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5071 / %x2A-5B ; '*'-'['
5072 / %x5D-7E ; ']'-'~'
5073 / obs-text
5074
5075<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5076<x:ref>field-name</x:ref> = token
5077<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5078
5079<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5080<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5081<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5082
5083<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5084
5085<x:ref>message-body</x:ref> = *OCTET
5086
5087<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5088<x:ref>obs-text</x:ref> = %x80-FF
5089
5090<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5091<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5092<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5093<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5094<x:ref>protocol</x:ref> = protocol-name [ "/" protocol-version ]
5095<x:ref>protocol-name</x:ref> = token
5096<x:ref>protocol-version</x:ref> = token
5097<x:ref>pseudonym</x:ref> = token
5098
5099<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5100 / %x5D-7E ; ']'-'~'
5101 / obs-text
5102<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5103 / %x5D-7E ; ']'-'~'
5104 / obs-text
5105<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5106<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5107<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5108<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5109<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5110<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5111
5112<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5113<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5114<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5115<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5116 / authority
5117
5118<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5119 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5120<x:ref>start-line</x:ref> = Request-Line / Status-Line
5121
5122<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5123<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5124 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5125<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5126<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5127<x:ref>token</x:ref> = 1*tchar
5128<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5129<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5130 transfer-extension
5131<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5132<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5133
5134<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5135
5136<x:ref>value</x:ref> = word
5137
5138<x:ref>word</x:ref> = token / quoted-string
5139</artwork>
5140</figure>
5141<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5142; Chunked-Body defined but not used
5143; Connection defined but not used
5144; Content-Length defined but not used
5145; HTTP-message defined but not used
5146; Host defined but not used
5147; TE defined but not used
5148; Trailer defined but not used
5149; Transfer-Encoding defined but not used
5150; URI-reference defined but not used
5151; Upgrade defined but not used
5152; Via defined but not used
5153; http-URI defined but not used
5154; https-URI defined but not used
5155; partial-URI defined but not used
5156; special defined but not used
5157</artwork></figure></section>
5158<?ENDINC p1-messaging.abnf-appendix ?>
5159
5160<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5161
5162<section title="Since RFC 2616">
5163<t>
5164  Extracted relevant partitions from <xref target="RFC2616"/>.
5165</t>
5166</section>
5167
5168<section title="Since draft-ietf-httpbis-p1-messaging-00">
5169<t>
5170  Closed issues:
5171  <list style="symbols"> 
5172    <t>
5173      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5174      "HTTP Version should be case sensitive"
5175      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5176    </t>
5177    <t>
5178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5179      "'unsafe' characters"
5180      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5181    </t>
5182    <t>
5183      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5184      "Chunk Size Definition"
5185      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5186    </t>
5187    <t>
5188      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5189      "Message Length"
5190      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5191    </t>
5192    <t>
5193      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5194      "Media Type Registrations"
5195      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5196    </t>
5197    <t>
5198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5199      "URI includes query"
5200      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5201    </t>
5202    <t>
5203      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5204      "No close on 1xx responses"
5205      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5206    </t>
5207    <t>
5208      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5209      "Remove 'identity' token references"
5210      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5211    </t>
5212    <t>
5213      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5214      "Import query BNF"
5215    </t>
5216    <t>
5217      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5218      "qdtext BNF"
5219    </t>
5220    <t>
5221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5222      "Normative and Informative references"
5223    </t>
5224    <t>
5225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5226      "RFC2606 Compliance"
5227    </t>
5228    <t>
5229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5230      "RFC977 reference"
5231    </t>
5232    <t>
5233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5234      "RFC1700 references"
5235    </t>
5236    <t>
5237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5238      "inconsistency in date format explanation"
5239    </t>
5240    <t>
5241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5242      "Date reference typo"
5243    </t>
5244    <t>
5245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5246      "Informative references"
5247    </t>
5248    <t>
5249      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5250      "ISO-8859-1 Reference"
5251    </t>
5252    <t>
5253      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5254      "Normative up-to-date references"
5255    </t>
5256  </list>
5257</t>
5258<t>
5259  Other changes:
5260  <list style="symbols"> 
5261    <t>
5262      Update media type registrations to use RFC4288 template.
5263    </t>
5264    <t>
5265      Use names of RFC4234 core rules DQUOTE and HTAB,
5266      fix broken ABNF for chunk-data
5267      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5268    </t>
5269  </list>
5270</t>
5271</section>
5272
5273<section title="Since draft-ietf-httpbis-p1-messaging-01">
5274<t>
5275  Closed issues:
5276  <list style="symbols"> 
5277    <t>
5278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5279      "Bodies on GET (and other) requests"
5280    </t>
5281    <t>
5282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5283      "Updating to RFC4288"
5284    </t>
5285    <t>
5286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5287      "Status Code and Reason Phrase"
5288    </t>
5289    <t>
5290      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5291      "rel_path not used"
5292    </t>
5293  </list>
5294</t>
5295<t>
5296  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5297  <list style="symbols"> 
5298    <t>
5299      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5300      "trailer-part").
5301    </t>
5302    <t>
5303      Avoid underscore character in rule names ("http_URL" ->
5304      "http-URL", "abs_path" -> "path-absolute").
5305    </t>
5306    <t>
5307      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5308      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5309      have to be updated when switching over to RFC3986.
5310    </t>
5311    <t>
5312      Synchronize core rules with RFC5234.
5313    </t>
5314    <t>
5315      Get rid of prose rules that span multiple lines.
5316    </t>
5317    <t>
5318      Get rid of unused rules LOALPHA and UPALPHA.
5319    </t>
5320    <t>
5321      Move "Product Tokens" section (back) into Part 1, as "token" is used
5322      in the definition of the Upgrade header field.
5323    </t>
5324    <t>
5325      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5326    </t>
5327    <t>
5328      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5329    </t>
5330  </list>
5331</t>
5332</section>
5333
5334<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5335<t>
5336  Closed issues:
5337  <list style="symbols"> 
5338    <t>
5339      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5340      "HTTP-date vs. rfc1123-date"
5341    </t>
5342    <t>
5343      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5344      "WS in quoted-pair"
5345    </t>
5346  </list>
5347</t>
5348<t>
5349  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5350  <list style="symbols"> 
5351    <t>
5352      Reference RFC 3984, and update header field registrations for headers defined
5353      in this document.
5354    </t>
5355  </list>
5356</t>
5357<t>
5358  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5359  <list style="symbols"> 
5360    <t>
5361      Replace string literals when the string really is case-sensitive (HTTP-Version).
5362    </t>
5363  </list>
5364</t>
5365</section>
5366
5367<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5368<t>
5369  Closed issues:
5370  <list style="symbols"> 
5371    <t>
5372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5373      "Connection closing"
5374    </t>
5375    <t>
5376      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5377      "Move registrations and registry information to IANA Considerations"
5378    </t>
5379    <t>
5380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5381      "need new URL for PAD1995 reference"
5382    </t>
5383    <t>
5384      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5385      "IANA Considerations: update HTTP URI scheme registration"
5386    </t>
5387    <t>
5388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5389      "Cite HTTPS URI scheme definition"
5390    </t>
5391    <t>
5392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5393      "List-type headers vs Set-Cookie"
5394    </t>
5395  </list>
5396</t>
5397<t>
5398  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5399  <list style="symbols"> 
5400    <t>
5401      Replace string literals when the string really is case-sensitive (HTTP-Date).
5402    </t>
5403    <t>
5404      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5405    </t>
5406  </list>
5407</t>
5408</section>
5409
5410<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5411<t>
5412  Closed issues:
5413  <list style="symbols"> 
5414    <t>
5415      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5416      "Out-of-date reference for URIs"
5417    </t>
5418    <t>
5419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5420      "RFC 2822 is updated by RFC 5322"
5421    </t>
5422  </list>
5423</t>
5424<t>
5425  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5426  <list style="symbols"> 
5427    <t>
5428      Use "/" instead of "|" for alternatives.
5429    </t>
5430    <t>
5431      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5432    </t>
5433    <t>
5434      Only reference RFC 5234's core rules.
5435    </t>
5436    <t>
5437      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5438      whitespace ("OWS") and required whitespace ("RWS").
5439    </t>
5440    <t>
5441      Rewrite ABNFs to spell out whitespace rules, factor out
5442      header field value format definitions.
5443    </t>
5444  </list>
5445</t>
5446</section>
5447
5448<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5449<t>
5450  Closed issues:
5451  <list style="symbols"> 
5452    <t>
5453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5454      "Header LWS"
5455    </t>
5456    <t>
5457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5458      "Sort 1.3 Terminology"
5459    </t>
5460    <t>
5461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5462      "RFC2047 encoded words"
5463    </t>
5464    <t>
5465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5466      "Character Encodings in TEXT"
5467    </t>
5468    <t>
5469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5470      "Line Folding"
5471    </t>
5472    <t>
5473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5474      "OPTIONS * and proxies"
5475    </t>
5476    <t>
5477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5478      "Reason-Phrase BNF"
5479    </t>
5480    <t>
5481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5482      "Use of TEXT"
5483    </t>
5484    <t>
5485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5486      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5487    </t>
5488    <t>
5489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5490      "RFC822 reference left in discussion of date formats"
5491    </t>
5492  </list>
5493</t>
5494<t>
5495  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5496  <list style="symbols"> 
5497    <t>
5498      Rewrite definition of list rules, deprecate empty list elements.
5499    </t>
5500    <t>
5501      Add appendix containing collected and expanded ABNF.
5502    </t>
5503  </list>
5504</t>
5505<t>
5506  Other changes:
5507  <list style="symbols"> 
5508    <t>
5509      Rewrite introduction; add mostly new Architecture Section.
5510    </t>
5511    <t>
5512      Move definition of quality values from Part 3 into Part 1;
5513      make TE request header field grammar independent of accept-params (defined in Part 3).
5514    </t>
5515  </list>
5516</t>
5517</section>
5518
5519<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5520<t>
5521  Closed issues:
5522  <list style="symbols"> 
5523    <t>
5524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5525      "base for numeric protocol elements"
5526    </t>
5527    <t>
5528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5529      "comment ABNF"
5530    </t>
5531  </list>
5532</t>
5533<t>
5534  Partly resolved issues:
5535  <list style="symbols"> 
5536    <t>
5537      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5538      "205 Bodies" (took out language that implied that there might be
5539      methods for which a request body MUST NOT be included)
5540    </t>
5541    <t>
5542      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5543      "editorial improvements around HTTP-date"
5544    </t>
5545  </list>
5546</t>
5547</section>
5548
5549<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5550<t>
5551  Closed issues:
5552  <list style="symbols"> 
5553    <t>
5554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5555      "Repeating single-value headers"
5556    </t>
5557    <t>
5558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5559      "increase connection limit"
5560    </t>
5561    <t>
5562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5563      "IP addresses in URLs"
5564    </t>
5565    <t>
5566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5567      "take over HTTP Upgrade Token Registry"
5568    </t>
5569    <t>
5570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5571      "CR and LF in chunk extension values"
5572    </t>
5573    <t>
5574      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5575      "HTTP/0.9 support"
5576    </t>
5577    <t>
5578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5579      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5580    </t>
5581    <t>
5582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5583      "move definitions of gzip/deflate/compress to part 1"
5584    </t>
5585    <t>
5586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5587      "disallow control characters in quoted-pair"
5588    </t>
5589  </list>
5590</t>
5591<t>
5592  Partly resolved issues:
5593  <list style="symbols"> 
5594    <t>
5595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5596      "update IANA requirements wrt Transfer-Coding values" (add the
5597      IANA Considerations subsection)
5598    </t>
5599  </list>
5600</t>
5601</section>
5602
5603<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5604<t>
5605  Closed issues:
5606  <list style="symbols"> 
5607    <t>
5608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5609      "header parsing, treatment of leading and trailing OWS"
5610    </t>
5611  </list>
5612</t>
5613<t>
5614  Partly resolved issues:
5615  <list style="symbols"> 
5616    <t>
5617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5618      "Placement of 13.5.1 and 13.5.2"
5619    </t>
5620    <t>
5621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5622      "use of term "word" when talking about header structure"
5623    </t>
5624  </list>
5625</t>
5626</section>
5627
5628<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5629<t>
5630  Closed issues:
5631  <list style="symbols"> 
5632    <t>
5633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5634      "Clarification of the term 'deflate'"
5635    </t>
5636    <t>
5637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5638      "OPTIONS * and proxies"
5639    </t>
5640    <t>
5641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5642      "MIME-Version not listed in P1, general header fields"
5643    </t>
5644    <t>
5645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5646      "IANA registry for content/transfer encodings"
5647    </t>
5648    <t>
5649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5650      "Case-sensitivity of HTTP-date"
5651    </t>
5652    <t>
5653      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5654      "use of term "word" when talking about header structure"
5655    </t>
5656  </list>
5657</t>
5658<t>
5659  Partly resolved issues:
5660  <list style="symbols"> 
5661    <t>
5662      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5663      "Term for the requested resource's URI"
5664    </t>
5665  </list>
5666</t>
5667</section>
5668
5669<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5670<t>
5671  Closed issues:
5672  <list style="symbols">
5673    <t>
5674      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5675      "Connection Closing"
5676    </t>
5677    <t>
5678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5679      "Delimiting messages with multipart/byteranges"
5680    </t>
5681    <t>
5682      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5683      "Handling multiple Content-Length headers"
5684    </t>
5685    <t>
5686      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5687      "Clarify entity / representation / variant terminology"
5688    </t>
5689    <t>
5690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5691      "consider removing the 'changes from 2068' sections"
5692    </t>
5693  </list>
5694</t>
5695<t>
5696  Partly resolved issues:
5697  <list style="symbols"> 
5698    <t>
5699      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5700      "HTTP(s) URI scheme definitions"
5701    </t>
5702  </list>
5703</t>
5704</section>
5705
5706<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5707<t>
5708  Closed issues:
5709  <list style="symbols">
5710    <t>
5711      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5712      "Trailer requirements"
5713    </t>
5714    <t>
5715      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5716      "Text about clock requirement for caches belongs in p6"
5717    </t>
5718    <t>
5719      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5720      "effective request URI: handling of missing host in HTTP/1.0"
5721    </t>
5722    <t>
5723      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5724      "confusing Date requirements for clients"
5725    </t>
5726  </list>
5727</t>
5728<t>
5729  Partly resolved issues:
5730  <list style="symbols"> 
5731    <t>
5732      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5733      "Handling multiple Content-Length headers"
5734    </t>
5735  </list>
5736</t>
5737</section>
5738
5739<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5740<t>
5741  Closed issues:
5742  <list style="symbols">
5743    <t>
5744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5745      "RFC2145 Normative"
5746    </t>
5747    <t>
5748      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5749      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5750    </t>
5751    <t>
5752      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5753      "define 'transparent' proxy"
5754    </t>
5755    <t>
5756      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5757      "Header Classification"
5758    </t>
5759    <t>
5760      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5761      "Is * usable as a request-uri for new methods?"
5762    </t>
5763    <t>
5764      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5765      "Migrate Upgrade details from RFC2817"
5766    </t>
5767    <t>
5768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5769      "untangle ABNFs for header fields"
5770    </t>
5771    <t>
5772      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5773      "update RFC 2109 reference"
5774    </t>
5775  </list>
5776</t>
5777</section>
5778
5779<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5780<t>
5781  Closed issues:
5782  <list style="symbols">
5783    <t>
5784      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5785      "Allow is not in 13.5.2"
5786    </t>
5787    <t>
5788      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5789      "Handling multiple Content-Length headers"
5790    </t>
5791    <t>
5792      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5793      "untangle ABNFs for header fields"
5794    </t>
5795    <t>
5796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5797      "Content-Length ABNF broken"
5798    </t>
5799  </list>
5800</t>
5801</section>
5802
5803<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5804<t>
5805  Closed issues:
5806  <list style="symbols">
5807    <t>
5808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5809      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5810    </t>
5811    <t>
5812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5813      "Recommend minimum sizes for protocol elements"
5814    </t>
5815    <t>
5816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5817      "Set expectations around buffering"
5818    </t>
5819    <t>
5820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5821      "Considering messages in isolation"
5822    </t>
5823  </list>
5824</t>
5825</section>
5826
5827<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5828<t>
5829  Closed issues:
5830  <list style="symbols">
5831    <t>
5832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5833      "DNS Spoofing / DNS Binding advice"
5834    </t>
5835    <t>
5836      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5837      "move RFCs 2145, 2616, 2817 to Historic status"
5838    </t>
5839    <t>
5840      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5841      "\-escaping in quoted strings"
5842    </t>
5843    <t>
5844      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5845      "'Close' should be reserved in the HTTP header field registry"
5846    </t>
5847  </list>
5848</t>
5849</section>
5850
5851<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5852<t>
5853  Closed issues:
5854  <list style="symbols">
5855    <t>
5856      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5857      "Document HTTP's error-handling philosophy"
5858    </t>
5859    <t>
5860      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5861      "Explain header registration"
5862    </t>
5863    <t>
5864      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5865      "Revise Acknowledgements Sections"
5866    </t>
5867    <t>
5868      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5869      "Retrying Requests"
5870    </t>
5871    <t>
5872      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5873      "Closing the connection on server error"
5874    </t>
5875  </list>
5876</t>
5877</section>
5878
5879<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5880<t>
5881  Closed issues:
5882  <list style="symbols">
5883    <t>
5884      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5885      "Clarify 'User Agent'"
5886    </t>
5887    <t>
5888      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5889      "Define non-final responses"
5890    </t>
5891    <t>
5892      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5893      "intended maturity level vs normative references"
5894    </t>
5895    <t>
5896      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5897      "Intermediary rewriting of queries"
5898    </t>
5899    <t>
5900      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5901      "Proxy-Connection and Keep-Alive"
5902    </t>
5903  </list>
5904</t>
5905</section>
5906
5907<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5908<t>
5909  Closed issues:
5910  <list style="symbols">
5911    <t>
5912      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/302"/>:
5913      "Misplaced text on connection handling in p2"
5914    </t>
5915    <t>
5916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/343"/>:
5917      "chunk-extensions"
5918    </t>
5919  </list>
5920</t>
5921</section>
5922
5923</section>
5924
5925</back>
5926</rfc>
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