source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1547

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