source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1520

Last change on this file since 1520 was 1520, checked in by fielding@…, 8 years ago

Remove conditional compliance. Switch from compliance to conformance.

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 241.6 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "January">
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<front>
62
63  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
64
65  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
66    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
67    <address>
68      <postal>
69        <street>345 Park Ave</street>
70        <city>San Jose</city>
71        <region>CA</region>
72        <code>95110</code>
73        <country>USA</country>
74      </postal>
75      <email>fielding@gbiv.com</email>
76      <uri>http://roy.gbiv.com/</uri>
77    </address>
78  </author>
79
80  <author initials="J." surname="Gettys" fullname="Jim Gettys">
81    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
82    <address>
83      <postal>
84        <street>21 Oak Knoll Road</street>
85        <city>Carlisle</city>
86        <region>MA</region>
87        <code>01741</code>
88        <country>USA</country>
89      </postal>
90      <email>jg@freedesktop.org</email>
91      <uri>http://gettys.wordpress.com/</uri>
92    </address>
93  </author>
94 
95  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
96    <organization abbrev="HP">Hewlett-Packard Company</organization>
97    <address>
98      <postal>
99        <street>HP Labs, Large Scale Systems Group</street>
100        <street>1501 Page Mill Road, MS 1177</street>
101        <city>Palo Alto</city>
102        <region>CA</region>
103        <code>94304</code>
104        <country>USA</country>
105      </postal>
106      <email>JeffMogul@acm.org</email>
107    </address>
108  </author>
109
110  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
111    <organization abbrev="Microsoft">Microsoft Corporation</organization>
112    <address>
113      <postal>
114        <street>1 Microsoft Way</street>
115        <city>Redmond</city>
116        <region>WA</region>
117        <code>98052</code>
118        <country>USA</country>
119      </postal>
120      <email>henrikn@microsoft.com</email>
121    </address>
122  </author>
123
124  <author initials="L." surname="Masinter" fullname="Larry Masinter">
125    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
126    <address>
127      <postal>
128        <street>345 Park Ave</street>
129        <city>San Jose</city>
130        <region>CA</region>
131        <code>95110</code>
132        <country>USA</country>
133      </postal>
134      <email>LMM@acm.org</email>
135      <uri>http://larry.masinter.net/</uri>
136    </address>
137  </author>
138 
139  <author initials="P." surname="Leach" fullname="Paul J. Leach">
140    <organization abbrev="Microsoft">Microsoft Corporation</organization>
141    <address>
142      <postal>
143        <street>1 Microsoft Way</street>
144        <city>Redmond</city>
145        <region>WA</region>
146        <code>98052</code>
147      </postal>
148      <email>paulle@microsoft.com</email>
149    </address>
150  </author>
151   
152  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
153    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
154    <address>
155      <postal>
156        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
157        <street>The Stata Center, Building 32</street>
158        <street>32 Vassar Street</street>
159        <city>Cambridge</city>
160        <region>MA</region>
161        <code>02139</code>
162        <country>USA</country>
163      </postal>
164      <email>timbl@w3.org</email>
165      <uri>http://www.w3.org/People/Berners-Lee/</uri>
166    </address>
167  </author>
168
169  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
170    <organization abbrev="W3C">World Wide Web Consortium</organization>
171    <address>
172      <postal>
173        <street>W3C / ERCIM</street>
174        <street>2004, rte des Lucioles</street>
175        <city>Sophia-Antipolis</city>
176        <region>AM</region>
177        <code>06902</code>
178        <country>France</country>
179      </postal>
180      <email>ylafon@w3.org</email>
181      <uri>http://www.raubacapeu.net/people/yves/</uri>
182    </address>
183  </author>
184
185  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
186    <organization abbrev="greenbytes">greenbytes GmbH</organization>
187    <address>
188      <postal>
189        <street>Hafenweg 16</street>
190        <city>Muenster</city><region>NW</region><code>48155</code>
191        <country>Germany</country>
192      </postal>
193      <phone>+49 251 2807760</phone>
194      <facsimile>+49 251 2807761</facsimile>
195      <email>julian.reschke@greenbytes.de</email>
196      <uri>http://greenbytes.de/tech/webdav/</uri>
197    </address>
198  </author>
199
200  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
201  <workgroup>HTTPbis Working Group</workgroup>
202
203<abstract>
204<t>
205   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
206   distributed, collaborative, hypertext information systems. HTTP has been in
207   use by the World Wide Web global information initiative since 1990. This
208   document is Part 1 of the seven-part specification that defines the protocol
209   referred to as "HTTP/1.1" and, taken together, obsoletes
210   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
211   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
212   2068</xref>.
213</t>
214<t>
215   Part 1 provides an overview of HTTP and its associated terminology, defines
216   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
217   the generic message syntax and parsing requirements for HTTP message frames,
218   and describes general security concerns for implementations.
219</t>
220<t>
221   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
222   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
223   (on using CONNECT for TLS upgrades) and moves them to historic status.
224</t>
225</abstract>
226
227<note title="Editorial Note (To be removed by RFC Editor)">
228  <t>
229    Discussion of this draft should take place on the HTTPBIS working group
230    mailing list (ietf-http-wg@w3.org), which is archived at
231    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
232  </t>
233  <t>
234    The current issues list is at
235    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
236    documents (including fancy diffs) can be found at
237    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
238  </t>
239  <t>
240    The changes in this draft are summarized in <xref target="changes.since.18"/>.
241  </t>
242</note>
243</front>
244<middle>
245<section title="Introduction" anchor="introduction">
246<t>
247   The Hypertext Transfer Protocol (HTTP) is an application-level
248   request/response protocol that uses extensible semantics and MIME-like
249   message payloads for flexible interaction with network-based hypertext
250   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
251   standard <xref target="RFC3986"/> to indicate the target resource and
252   relationships between resources.
253   Messages are passed in a format similar to that used by Internet mail
254   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
255   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
256   between HTTP and MIME messages).
257</t>
258<t>
259   HTTP is a generic interface protocol for information systems. It is
260   designed to hide the details of how a service is implemented by presenting
261   a uniform interface to clients that is independent of the types of
262   resources provided. Likewise, servers do not need to be aware of each
263   client's purpose: an HTTP request can be considered in isolation rather
264   than being associated with a specific type of client or a predetermined
265   sequence of application steps. The result is a protocol that can be used
266   effectively in many different contexts and for which implementations can
267   evolve independently over time.
268</t>
269<t>
270   HTTP is also designed for use as an intermediation protocol for translating
271   communication to and from non-HTTP information systems.
272   HTTP proxies and gateways can provide access to alternative information
273   services by translating their diverse protocols into a hypertext
274   format that can be viewed and manipulated by clients in the same way
275   as HTTP services.
276</t>
277<t>
278   One consequence of HTTP flexibility is that the protocol cannot be
279   defined in terms of what occurs behind the interface. Instead, we
280   are limited to defining the syntax of communication, the intent
281   of received communication, and the expected behavior of recipients.
282   If the communication is considered in isolation, then successful
283   actions ought to be reflected in corresponding changes to the
284   observable interface provided by servers. However, since multiple
285   clients might act in parallel and perhaps at cross-purposes, we
286   cannot require that such changes be observable beyond the scope
287   of a single response.
288</t>
289<t>
290   This document is Part 1 of the seven-part specification of HTTP,
291   defining the protocol referred to as "HTTP/1.1", obsoleting
292   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
293   Part 1 describes the architectural elements that are used or
294   referred to in HTTP, defines the "http" and "https" URI schemes,
295   describes overall network operation and connection management,
296   and defines HTTP message framing and forwarding requirements.
297   Our goal is to define all of the mechanisms necessary for HTTP message
298   handling that are independent of message semantics, thereby defining the
299   complete set of requirements for message parsers and
300   message-forwarding intermediaries.
301</t>
302
303<section title="Requirement Notation" anchor="intro.requirements">
304<t>
305   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
306   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
307   document are to be interpreted as described in <xref target="RFC2119"/>.
308</t>
309</section>
310
311<section title="Syntax Notation" anchor="notation">
312<iref primary="true" item="Grammar" subitem="ALPHA"/>
313<iref primary="true" item="Grammar" subitem="CR"/>
314<iref primary="true" item="Grammar" subitem="CRLF"/>
315<iref primary="true" item="Grammar" subitem="CTL"/>
316<iref primary="true" item="Grammar" subitem="DIGIT"/>
317<iref primary="true" item="Grammar" subitem="DQUOTE"/>
318<iref primary="true" item="Grammar" subitem="HEXDIG"/>
319<iref primary="true" item="Grammar" subitem="HTAB"/>
320<iref primary="true" item="Grammar" subitem="LF"/>
321<iref primary="true" item="Grammar" subitem="OCTET"/>
322<iref primary="true" item="Grammar" subitem="SP"/>
323<iref primary="true" item="Grammar" subitem="VCHAR"/>
324<t>
325   This specification uses the Augmented Backus-Naur Form (ABNF) notation
326   of <xref target="RFC5234"/> with the list rule extension defined in
327   <xref target="abnf.extension"/><xref target="collected.abnf"/> shows
328   the collected ABNF with the list rule expanded.
329</t>
330<t anchor="core.rules">
331  <x:anchor-alias value="ALPHA"/>
332  <x:anchor-alias value="CTL"/>
333  <x:anchor-alias value="CR"/>
334  <x:anchor-alias value="CRLF"/>
335  <x:anchor-alias value="DIGIT"/>
336  <x:anchor-alias value="DQUOTE"/>
337  <x:anchor-alias value="HEXDIG"/>
338  <x:anchor-alias value="HTAB"/>
339  <x:anchor-alias value="LF"/>
340  <x:anchor-alias value="OCTET"/>
341  <x:anchor-alias value="SP"/>
342  <x:anchor-alias value="VCHAR"/>
343   The following core rules are included by
344   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
345   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
346   DIGIT (decimal 0-9), DQUOTE (double quote),
347   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
348   OCTET (any 8-bit sequence of data), SP (space), and
349   VCHAR (any visible <xref target="USASCII"/> character).
350</t>
351<t>
352   As a convention, ABNF rule names prefixed with "obs-" denote
353   "obsolete" grammar rules that appear for historical reasons.
354</t>
355</section>
356</section>
357
358<section title="Architecture" anchor="architecture">
359<t>
360   HTTP was created for the World Wide Web architecture
361   and has evolved over time to support the scalability needs of a worldwide
362   hypertext system. Much of that architecture is reflected in the terminology
363   and syntax productions used to define HTTP.
364</t>
365
366<section title="Client/Server Messaging" anchor="operation">
367<iref primary="true" item="client"/>
368<iref primary="true" item="server"/>
369<iref primary="true" item="connection"/>
370<t>
371   HTTP is a stateless request/response protocol that operates by exchanging
372   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
373   transport or session-layer
374   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
375   program that establishes a connection to a server for the purpose of
376   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
377   program that accepts connections in order to service HTTP requests by
378   sending HTTP responses.
379</t>
380<iref primary="true" item="user agent"/>
381<iref primary="true" item="origin server"/>
382<iref primary="true" item="browser"/>
383<iref primary="true" item="spider"/>
384<iref primary="true" item="sender"/>
385<iref primary="true" item="recipient"/>
386<t>
387   Note that the terms client and server refer only to the roles that
388   these programs perform for a particular connection.  The same program
389   might act as a client on some connections and a server on others.  We use
390   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
391   such as a WWW browser, editor, or spider (web-traversing robot), and
392   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
393   authoritative responses to a request.  For general requirements, we use
394   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
395   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
396   message.
397</t>
398<x:note>
399  <t>
400    <x:h>Note:</x:h> The term 'user agent' covers both those situations where
401    there is a user (human) interacting with the software agent (and for which
402    user interface or interactive suggestions might be made, e.g., warning the
403    user or given the user an option in the case of security or privacy
404    options) and also those where the software agent may act autonomously.
405  </t>
406</x:note>
407<t>
408   Most HTTP communication consists of a retrieval request (GET) for
409   a representation of some resource identified by a URI.  In the
410   simplest case, this might be accomplished via a single bidirectional
411   connection (===) between the user agent (UA) and the origin server (O).
412</t>
413<figure><artwork type="drawing">
414         request   &gt;
415    UA ======================================= O
416                                &lt;   response
417</artwork></figure>
418<iref primary="true" item="message"/>
419<iref primary="true" item="request"/>
420<iref primary="true" item="response"/>
421<t>
422   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
423   message, beginning with a request-line that includes a method, URI, and
424   protocol version (<xref target="request.line"/>),
425   followed by MIME-like header fields containing
426   request modifiers, client information, and payload metadata
427   (<xref target="header.fields"/>),
428   an empty line to indicate the end of the header section, and finally
429   a message body containing the payload body (if any,
430   <xref target="message.body"/>).
431</t>
432<t>
433   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
434   message, beginning with a status line that
435   includes the protocol version, a success or error code, and textual
436   reason phrase (<xref target="status.line"/>),
437   followed by MIME-like header fields containing server
438   information, resource metadata, and payload metadata
439   (<xref target="header.fields"/>),
440   an empty line to indicate the end of the header section, and finally
441   a message body containing the payload body (if any,
442   <xref target="message.body"/>).
443</t>
444<t>
445   Note that 1xx responses (&status-1xx;) are not final; therefore, a server
446   can send zero or more 1xx responses, followed by exactly one final response
447   (with any other status code).
448</t>
449<t>
450   The following example illustrates a typical message exchange for a
451   GET request on the URI "http://www.example.com/hello.txt":
452</t>
453<figure><preamble>
454client request:
455</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
456GET /hello.txt HTTP/1.1
457User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
458Host: www.example.com
459Accept: */*
460
461</artwork></figure>
462<figure><preamble>
463server response:
464</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
465HTTP/1.1 200 OK
466Date: Mon, 27 Jul 2009 12:28:53 GMT
467Server: Apache
468Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
469ETag: "34aa387-d-1568eb00"
470Accept-Ranges: bytes
471Content-Length: <x:length-of target="exbody"/>
472Vary: Accept-Encoding
473Content-Type: text/plain
474
475<x:span anchor="exbody">Hello World!
476</x:span></artwork></figure>
477</section>
478
479<section title="Connections and Transport Independence" anchor="transport-independence">
480<t>
481   HTTP messaging is independent of the underlying transport or
482   session-layer connection protocol(s).  HTTP only presumes a reliable
483   transport with in-order delivery of requests and the corresponding
484   in-order delivery of responses.  The mapping of HTTP request and
485   response structures onto the data units of the underlying transport
486   protocol is outside the scope of this specification.
487</t>
488<t>
489   The specific connection protocols to be used for an interaction
490   are determined by client configuration and the target resource's URI.
491   For example, the "http" URI scheme
492   (<xref target="http.uri"/>) indicates a default connection of TCP
493   over IP, with a default TCP port of 80, but the client might be
494   configured to use a proxy via some other connection port or protocol
495   instead of using the defaults.
496</t>
497<t>
498   A connection might be used for multiple HTTP request/response exchanges,
499   as defined in <xref target="persistent.connections"/>.
500</t>
501</section>
502
503<section title="Intermediaries" anchor="intermediaries">
504<iref primary="true" item="intermediary"/>
505<t>
506   HTTP enables the use of intermediaries to satisfy requests through
507   a chain of connections.  There are three common forms of HTTP
508   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
509   a single intermediary might act as an origin server, proxy, gateway,
510   or tunnel, switching behavior based on the nature of each request.
511</t>
512<figure><artwork type="drawing">
513         &gt;             &gt;             &gt;             &gt;
514    <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>
515               &lt;             &lt;             &lt;             &lt;
516</artwork></figure>
517<t>
518   The figure above shows three intermediaries (A, B, and C) between the
519   user agent and origin server. A request or response message that
520   travels the whole chain will pass through four separate connections.
521   Some HTTP communication options
522   might apply only to the connection with the nearest, non-tunnel
523   neighbor, only to the end-points of the chain, or to all connections
524   along the chain. Although the diagram is linear, each participant might
525   be engaged in multiple, simultaneous communications. For example, B
526   might be receiving requests from many clients other than A, and/or
527   forwarding requests to servers other than C, at the same time that it
528   is handling A's request.
529</t>
530<t>
531<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
532<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
533   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
534   to describe various requirements in relation to the directional flow of a
535   message: all messages flow from upstream to downstream.
536   Likewise, we use the terms inbound and outbound to refer to
537   directions in relation to the request path:
538   "<x:dfn>inbound</x:dfn>" means toward the origin server and
539   "<x:dfn>outbound</x:dfn>" means toward the user agent.
540</t>
541<t><iref primary="true" item="proxy"/>
542   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
543   client, usually via local configuration rules, to receive requests
544   for some type(s) of absolute URI and attempt to satisfy those
545   requests via translation through the HTTP interface.  Some translations
546   are minimal, such as for proxy requests for "http" URIs, whereas
547   other requests might require translation to and from entirely different
548   application-layer protocols. Proxies are often used to group an
549   organization's HTTP requests through a common intermediary for the
550   sake of security, annotation services, or shared caching.
551</t>
552<t>
553<iref primary="true" item="transforming proxy"/>
554<iref primary="true" item="non-transforming proxy"/>
555   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
556   or configured to modify request or response messages in a semantically
557   meaningful way (i.e., modifications, beyond those required by normal
558   HTTP processing, that change the message in a way that would be
559   significant to the original sender or potentially significant to
560   downstream recipients).  For example, a transforming proxy might be
561   acting as a shared annotation server (modifying responses to include
562   references to a local annotation database), a malware filter, a
563   format transcoder, or an intranet-to-Internet privacy filter.  Such
564   transformations are presumed to be desired by the client (or client
565   organization) that selected the proxy and are beyond the scope of
566   this specification.  However, when a proxy is not intended to transform
567   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
568   requirements that preserve HTTP message semantics. See &status-203; and
569   &header-warning; for status and warning codes related to transformations.
570</t>
571<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
572<iref primary="true" item="accelerator"/>
573   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
574   is a receiving agent that acts
575   as a layer above some other server(s) and translates the received
576   requests to the underlying server's protocol.  Gateways are often
577   used to encapsulate legacy or untrusted information services, to
578   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
579   enable partitioning or load-balancing of HTTP services across
580   multiple machines.
581</t>
582<t>
583   A gateway behaves as an origin server on its outbound connection and
584   as a user agent on its inbound connection.
585   All HTTP requirements applicable to an origin server
586   also apply to the outbound communication of a gateway.
587   A gateway communicates with inbound servers using any protocol that
588   it desires, including private extensions to HTTP that are outside
589   the scope of this specification.  However, an HTTP-to-HTTP gateway
590   that wishes to interoperate with third-party HTTP servers &MUST;
591   conform to HTTP user agent requirements on the gateway's inbound
592   connection and &MUST; implement the Connection
593   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
594   header fields for both connections.
595</t>
596<t><iref primary="true" item="tunnel"/>
597   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
598   without changing the messages. Once active, a tunnel is not
599   considered a party to the HTTP communication, though the tunnel might
600   have been initiated by an HTTP request. A tunnel ceases to exist when
601   both ends of the relayed connection are closed. Tunnels are used to
602   extend a virtual connection through an intermediary, such as when
603   transport-layer security is used to establish private communication
604   through a shared firewall proxy.
605</t>
606<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
607<iref primary="true" item="captive portal"/>
608   In addition, there may exist network intermediaries that are not
609   considered part of the HTTP communication but nevertheless act as
610   filters or redirecting agents (usually violating HTTP semantics,
611   causing security problems, and otherwise making a mess of things).
612   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
613   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
614   or "<x:dfn>captive portal</x:dfn>",
615   differs from an HTTP proxy because it has not been selected by the client.
616   Instead, the network intermediary redirects outgoing TCP port 80 packets
617   (and occasionally other common port traffic) to an internal HTTP server.
618   Interception proxies are commonly found on public network access points,
619   as a means of enforcing account subscription prior to allowing use of
620   non-local Internet services, and within corporate firewalls to enforce
621   network usage policies.
622   They are indistinguishable from a man-in-the-middle attack.
623</t>
624<t>
625   HTTP is defined as a stateless protocol, meaning that each request message
626   can be understood in isolation.  Many implementations depend on HTTP's
627   stateless design in order to reuse proxied connections or dynamically
628   load balance requests across multiple servers.  Hence, servers &MUST-NOT;
629   assume that two requests on the same connection are from the same user
630   agent unless the connection is secured and specific to that agent.
631   Some non-standard HTTP extensions (e.g., <xref target="RFC4559"/>) have
632   been known to violate this requirement, resulting in security and
633   interoperability problems.
634</t>
635</section>
636
637<section title="Caches" anchor="caches">
638<iref primary="true" item="cache"/>
639<t>
640   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
641   subsystem that controls its message storage, retrieval, and deletion.
642   A cache stores cacheable responses in order to reduce the response
643   time and network bandwidth consumption on future, equivalent
644   requests. Any client or server &MAY; employ a cache, though a cache
645   cannot be used by a server while it is acting as a tunnel.
646</t>
647<t>
648   The effect of a cache is that the request/response chain is shortened
649   if one of the participants along the chain has a cached response
650   applicable to that request. The following illustrates the resulting
651   chain if B has a cached copy of an earlier response from O (via C)
652   for a request which has not been cached by UA or A.
653</t>
654<figure><artwork type="drawing">
655            &gt;             &gt;
656       UA =========== A =========== B - - - - - - C - - - - - - O
657                  &lt;             &lt;
658</artwork></figure>
659<t><iref primary="true" item="cacheable"/>
660   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
661   the response message for use in answering subsequent requests.
662   Even when a response is cacheable, there might be additional
663   constraints placed by the client or by the origin server on when
664   that cached response can be used for a particular request. HTTP
665   requirements for cache behavior and cacheable responses are
666   defined in &caching-overview;
667</t>
668<t>
669   There are a wide variety of architectures and configurations
670   of caches and proxies deployed across the World Wide Web and
671   inside large organizations. These systems include national hierarchies
672   of proxy caches to save transoceanic bandwidth, systems that
673   broadcast or multicast cache entries, organizations that distribute
674   subsets of cached data via optical media, and so on.
675</t>
676</section>
677
678<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
679<t>
680   This specification targets conformance criteria according to the role of
681   a participant in HTTP communication.  Hence, HTTP requirements are placed
682   on senders, recipients, clients, servers, user agents, intermediaries,
683   origin servers, proxies, gateways, or caches, depending on what behavior
684   is being constrained by the requirement.
685</t>
686<t>
687   An implementation is considered conformant if it complies with all of the
688   requirements associated with the roles it partakes in HTTP.
689</t>
690<t>
691   Senders &MUST-NOT; generate protocol elements that do not match the grammar
692   defined by the ABNF rules for those protocol elements.
693</t>
694<t>
695   Unless otherwise noted, recipients &MAY; attempt to recover a usable
696   protocol element from an invalid construct.  HTTP does not define
697   specific error handling mechanisms except when they have a direct impact
698   on security, since different applications of the protocol require
699   different error handling strategies.  For example, a Web browser might
700   wish to transparently recover from a response where the Location header
701   field doesn't parse according to the ABNF, whereas a systems control
702   client might consider any form of error recovery to be dangerous.
703</t>
704</section>
705
706<section title="Protocol Versioning" anchor="http.version">
707  <x:anchor-alias value="HTTP-Version"/>
708  <x:anchor-alias value="HTTP-Prot-Name"/>
709<t>
710   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
711   versions of the protocol. This specification defines version "1.1".
712   The protocol version as a whole indicates the sender's conformance
713   with the set of requirements laid out in that version's corresponding
714   specification of HTTP.
715</t>
716<t>
717   The version of an HTTP message is indicated by an HTTP-Version field
718   in the first line of the message. HTTP-Version is case-sensitive.
719</t>
720<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
721  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
722  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
723</artwork></figure>
724<t>
725   The HTTP version number consists of two decimal digits separated by a "."
726   (period or decimal point).  The first digit ("major version") indicates the
727   HTTP messaging syntax, whereas the second digit ("minor version") indicates
728   the highest minor version to which the sender is
729   conformant and able to understand for future communication.  The minor
730   version advertises the sender's communication capabilities even when the
731   sender is only using a backwards-compatible subset of the protocol,
732   thereby letting the recipient know that more advanced features can
733   be used in response (by servers) or in future requests (by clients).
734</t>
735<t>
736   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
737   <xref target="RFC1945"/> or a recipient whose version is unknown,
738   the HTTP/1.1 message is constructed such that it can be interpreted
739   as a valid HTTP/1.0 message if all of the newer features are ignored.
740   This specification places recipient-version requirements on some
741   new features so that a conformant sender will only use compatible
742   features until it has determined, through configuration or the
743   receipt of a message, that the recipient supports HTTP/1.1.
744</t>
745<t>
746   The interpretation of an HTTP header field does not change
747   between minor versions of the same major version, though the default
748   behavior of a recipient in the absence of such a field can change.
749   Unless specified otherwise, header fields defined in HTTP/1.1 are
750   defined for all versions of HTTP/1.x.  In particular, the Host and
751   Connection header fields ought to be implemented by all HTTP/1.x
752   implementations whether or not they advertise conformance with HTTP/1.1.
753</t>
754<t>
755   New header fields can be defined such that, when they are
756   understood by a recipient, they might override or enhance the
757   interpretation of previously defined header fields.  When an
758   implementation receives an unrecognized header field, the recipient
759   &MUST; ignore that header field for local processing regardless of
760   the message's HTTP version.  An unrecognized header field received
761   by a proxy &MUST; be forwarded downstream unless the header field's
762   field-name is listed in the message's Connection header-field
763   (see <xref target="header.connection"/>).
764   These requirements allow HTTP's functionality to be enhanced without
765   requiring prior update of deployed intermediaries.
766</t>
767<t>
768   Intermediaries that process HTTP messages (i.e., all intermediaries
769   other than those acting as tunnels) &MUST; send their own HTTP-Version
770   in forwarded messages.  In other words, they &MUST-NOT; blindly
771   forward the first line of an HTTP message without ensuring that the
772   protocol version in that message matches a version to which that
773   intermediary is conformant for both the receiving and
774   sending of messages.  Forwarding an HTTP message without rewriting
775   the HTTP-Version might result in communication errors when downstream
776   recipients use the message sender's version to determine what features
777   are safe to use for later communication with that sender.
778</t>
779<t>
780   An HTTP client &SHOULD; send a request version equal to the highest
781   version to which the client is conformant and
782   whose major version is no higher than the highest version supported
783   by the server, if this is known.  An HTTP client &MUST-NOT; send a
784   version to which it is not conformant.
785</t>
786<t>
787   An HTTP client &MAY; send a lower request version if it is known that
788   the server incorrectly implements the HTTP specification, but only
789   after the client has attempted at least one normal request and determined
790   from the response status or header fields (e.g., Server) that the
791   server improperly handles higher request versions.
792</t>
793<t>
794   An HTTP server &SHOULD; send a response version equal to the highest
795   version to which the server is conformant and
796   whose major version is less than or equal to the one received in the
797   request.  An HTTP server &MUST-NOT; send a version to which it is not
798   conformant.  A server &MAY; send a 505 (HTTP
799   Version Not Supported) response if it cannot send a response using the
800   major version used in the client's request.
801</t>
802<t>
803   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
804   if it is known or suspected that the client incorrectly implements the
805   HTTP specification and is incapable of correctly processing later
806   version responses, such as when a client fails to parse the version
807   number correctly or when an intermediary is known to blindly forward
808   the HTTP-Version even when it doesn't conform to the given minor
809   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
810   performed unless triggered by specific client attributes, such as when
811   one or more of the request header fields (e.g., User-Agent) uniquely
812   match the values sent by a client known to be in error.
813</t>
814<t>
815   The intention of HTTP's versioning design is that the major number
816   will only be incremented if an incompatible message syntax is
817   introduced, and that the minor number will only be incremented when
818   changes made to the protocol have the effect of adding to the message
819   semantics or implying additional capabilities of the sender.  However,
820   the minor version was not incremented for the changes introduced between
821   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
822   is specifically avoiding any such changes to the protocol.
823</t>
824</section>
825
826<section title="Uniform Resource Identifiers" anchor="uri">
827<iref primary="true" item="resource"/>
828<t>
829   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
830   throughout HTTP as the means for identifying resources. URI references
831   are used to target requests, indicate redirects, and define relationships.
832   HTTP does not limit what a resource might be; it merely defines an interface
833   that can be used to interact with a resource via HTTP. More information on
834   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
835</t>
836  <x:anchor-alias value="URI-reference"/>
837  <x:anchor-alias value="absolute-URI"/>
838  <x:anchor-alias value="relative-part"/>
839  <x:anchor-alias value="authority"/>
840  <x:anchor-alias value="path-abempty"/>
841  <x:anchor-alias value="path-absolute"/>
842  <x:anchor-alias value="port"/>
843  <x:anchor-alias value="query"/>
844  <x:anchor-alias value="uri-host"/>
845  <x:anchor-alias value="partial-URI"/>
846<t>
847   This specification adopts the definitions of "URI-reference",
848   "absolute-URI", "relative-part", "port", "host",
849   "path-abempty", "path-absolute", "query", and "authority" from the
850   URI generic syntax <xref target="RFC3986"/>.
851   In addition, we define a partial-URI rule for protocol elements
852   that allow a relative URI but not a fragment.
853</t>
854<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"/>
855  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
856  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
857  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
858  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
859  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
860  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
861  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
862  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
863  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
864 
865  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
866</artwork></figure>
867<t>
868   Each protocol element in HTTP that allows a URI reference will indicate
869   in its ABNF production whether the element allows any form of reference
870   (URI-reference), only a URI in absolute form (absolute-URI), only the
871   path and optional query components, or some combination of the above.
872   Unless otherwise indicated, URI references are parsed relative to the
873   effective request URI, which defines the default base URI for references
874   in both the request and its corresponding response.
875</t>
876
877<section title="http URI scheme" anchor="http.uri">
878  <x:anchor-alias value="http-URI"/>
879  <iref item="http URI scheme" primary="true"/>
880  <iref item="URI scheme" subitem="http" primary="true"/>
881<t>
882   The "http" URI scheme is hereby defined for the purpose of minting
883   identifiers according to their association with the hierarchical
884   namespace governed by a potential HTTP origin server listening for
885   TCP connections on a given port.
886</t>
887<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
888  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
889</artwork></figure>
890<t>
891   The HTTP origin server is identified by the generic syntax's
892   <x:ref>authority</x:ref> component, which includes a host identifier
893   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
894   The remainder of the URI, consisting of both the hierarchical path
895   component and optional query component, serves as an identifier for
896   a potential resource within that origin server's name space.
897</t>
898<t>
899   If the host identifier is provided as an IP literal or IPv4 address,
900   then the origin server is any listener on the indicated TCP port at
901   that IP address. If host is a registered name, then that name is
902   considered an indirect identifier and the recipient might use a name
903   resolution service, such as DNS, to find the address of a listener
904   for that host.
905   The host &MUST-NOT; be empty; if an "http" URI is received with an
906   empty host, then it &MUST; be rejected as invalid.
907   If the port subcomponent is empty or not given, then TCP port 80 is
908   assumed (the default reserved port for WWW services).
909</t>
910<t>
911   Regardless of the form of host identifier, access to that host is not
912   implied by the mere presence of its name or address. The host might or might
913   not exist and, even when it does exist, might or might not be running an
914   HTTP server or listening to the indicated port. The "http" URI scheme
915   makes use of the delegated nature of Internet names and addresses to
916   establish a naming authority (whatever entity has the ability to place
917   an HTTP server at that Internet name or address) and allows that
918   authority to determine which names are valid and how they might be used.
919</t>
920<t>
921   When an "http" URI is used within a context that calls for access to the
922   indicated resource, a client &MAY; attempt access by resolving
923   the host to an IP address, establishing a TCP connection to that address
924   on the indicated port, and sending an HTTP request message
925   (<xref target="http.message"/>) containing the URI's identifying data
926   (<xref target="message.routing"/>) to the server.
927   If the server responds to that request with a non-interim HTTP response
928   message, as described in &status-code-reasonphr;, then that response
929   is considered an authoritative answer to the client's request.
930</t>
931<t>
932   Although HTTP is independent of the transport protocol, the "http"
933   scheme is specific to TCP-based services because the name delegation
934   process depends on TCP for establishing authority.
935   An HTTP service based on some other underlying connection protocol
936   would presumably be identified using a different URI scheme, just as
937   the "https" scheme (below) is used for servers that require an SSL/TLS
938   transport layer on a connection. Other protocols might also be used to
939   provide access to "http" identified resources &mdash; it is only the
940   authoritative interface used for mapping the namespace that is
941   specific to TCP.
942</t>
943<t>
944   The URI generic syntax for authority also includes a deprecated
945   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
946   for including user authentication information in the URI.  Some
947   implementations make use of the userinfo component for internal
948   configuration of authentication information, such as within command
949   invocation options, configuration files, or bookmark lists, even
950   though such usage might expose a user identifier or password.
951   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
952   delimiter) when transmitting an "http" URI in a message.  Recipients
953   of HTTP messages that contain a URI reference &SHOULD; parse for the
954   existence of userinfo and treat its presence as an error, likely
955   indicating that the deprecated subcomponent is being used to obscure
956   the authority for the sake of phishing attacks.
957</t>
958</section>
959
960<section title="https URI scheme" anchor="https.uri">
961   <x:anchor-alias value="https-URI"/>
962   <iref item="https URI scheme"/>
963   <iref item="URI scheme" subitem="https"/>
964<t>
965   The "https" URI scheme is hereby defined for the purpose of minting
966   identifiers according to their association with the hierarchical
967   namespace governed by a potential HTTP origin server listening for
968   SSL/TLS-secured connections on a given TCP port.
969</t>
970<t>
971   All of the requirements listed above for the "http" scheme are also
972   requirements for the "https" scheme, except that a default TCP port
973   of 443 is assumed if the port subcomponent is empty or not given,
974   and the TCP connection &MUST; be secured for privacy through the
975   use of strong encryption prior to sending the first HTTP request.
976</t>
977<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
978  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
979</artwork></figure>
980<t>
981   Unlike the "http" scheme, responses to "https" identified requests
982   are never "public" and thus &MUST-NOT; be reused for shared caching.
983   They can, however, be reused in a private cache if the message is
984   cacheable by default in HTTP or specifically indicated as such by
985   the Cache-Control header field (&header-cache-control;).
986</t>
987<t>
988   Resources made available via the "https" scheme have no shared
989   identity with the "http" scheme even if their resource identifiers
990   indicate the same authority (the same host listening to the same
991   TCP port).  They are distinct name spaces and are considered to be
992   distinct origin servers.  However, an extension to HTTP that is
993   defined to apply to entire host domains, such as the Cookie protocol
994   <xref target="RFC6265"/>, can allow information
995   set by one service to impact communication with other services
996   within a matching group of host domains.
997</t>
998<t>
999   The process for authoritative access to an "https" identified
1000   resource is defined in <xref target="RFC2818"/>.
1001</t>
1002</section>
1003
1004<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1005<t>
1006   Since the "http" and "https" schemes conform to the URI generic syntax,
1007   such URIs are normalized and compared according to the algorithm defined
1008   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1009   described above for each scheme.
1010</t>
1011<t>
1012   If the port is equal to the default port for a scheme, the normal
1013   form is to elide the port subcomponent. Likewise, an empty path
1014   component is equivalent to an absolute path of "/", so the normal
1015   form is to provide a path of "/" instead. The scheme and host
1016   are case-insensitive and normally provided in lowercase; all
1017   other components are compared in a case-sensitive manner.
1018   Characters other than those in the "reserved" set are equivalent
1019   to their percent-encoded octets (see <xref target="RFC3986"
1020   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1021</t>
1022<t>
1023   For example, the following three URIs are equivalent:
1024</t>
1025<figure><artwork type="example">
1026   http://example.com:80/~smith/home.html
1027   http://EXAMPLE.com/%7Esmith/home.html
1028   http://EXAMPLE.com:/%7esmith/home.html
1029</artwork></figure>
1030</section>
1031</section>
1032</section>
1033
1034<section title="Message Format" anchor="http.message">
1035<x:anchor-alias value="generic-message"/>
1036<x:anchor-alias value="message.types"/>
1037<x:anchor-alias value="HTTP-message"/>
1038<x:anchor-alias value="start-line"/>
1039<iref item="header section"/>
1040<iref item="headers"/>
1041<iref item="header field"/>
1042<t>
1043   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1044   octets in a format similar to the Internet Message Format
1045   <xref target="RFC5322"/>: zero or more header fields (collectively
1046   referred to as the "headers" or the "header section"), an empty line
1047   indicating the end of the header section, and an optional message-body.
1048</t>
1049<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1050  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1051                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1052                    <x:ref>CRLF</x:ref>
1053                    [ <x:ref>message-body</x:ref> ]
1054</artwork></figure>
1055<t>
1056   The normal procedure for parsing an HTTP message is to read the
1057   start-line into a structure, read each header field into a hash
1058   table by field name until the empty line, and then use the parsed
1059   data to determine if a message-body is expected.  If a message-body
1060   has been indicated, then it is read as a stream until an amount
1061   of octets equal to the message-body length is read or the connection
1062   is closed.
1063</t>
1064<t>
1065   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1066   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1067   Parsing an HTTP message as a stream of Unicode characters, without regard
1068   for the specific encoding, creates security vulnerabilities due to the
1069   varying ways that string processing libraries handle invalid multibyte
1070   character sequences that contain the octet LF (%x0A).  String-based
1071   parsers can only be safely used within protocol elements after the element
1072   has been extracted from the message, such as within a header field-value
1073   after message parsing has delineated the individual fields.
1074</t>
1075<t>
1076   An HTTP message can be parsed as a stream for incremental processing or
1077   forwarding downstream.  However, recipients cannot rely on incremental
1078   delivery of partial messages, since some implementations will buffer or
1079   delay message forwarding for the sake of network efficiency, security
1080   checks, or payload transformations.
1081</t>
1082
1083<section title="Start Line" anchor="start.line">
1084  <x:anchor-alias value="Start-Line"/>
1085<t>
1086   An HTTP message can either be a request from client to server or a
1087   response from server to client.  Syntactically, the two types of message
1088   differ only in the start-line, which is either a Request-Line (for requests)
1089   or a Status-Line (for responses), and in the algorithm for determining
1090   the length of the message-body (<xref target="message.body"/>).
1091   In theory, a client could receive requests and a server could receive
1092   responses, distinguishing them by their different start-line formats,
1093   but in practice servers are implemented to only expect a request
1094   (a response is interpreted as an unknown or invalid request method)
1095   and clients are implemented to only expect a response.
1096</t>
1097<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1098  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1099</artwork></figure>
1100<t>
1101</t>
1102<t>
1103   Implementations &MUST-NOT; send whitespace between the start-line and
1104   the first header field. The presence of such whitespace in a request
1105   might be an attempt to trick a server into ignoring that field or
1106   processing the line after it as a new request, either of which might
1107   result in a security vulnerability if other implementations within
1108   the request chain interpret the same message differently.
1109   Likewise, the presence of such whitespace in a response might be
1110   ignored by some clients or cause others to cease parsing.
1111</t>
1112
1113<section title="Request-Line" anchor="request.line">
1114  <x:anchor-alias value="Request"/>
1115  <x:anchor-alias value="Request-Line"/>
1116<t>
1117   The Request-Line begins with a method token, followed by a single
1118   space (SP), the request-target, another single space (SP), the
1119   protocol version, and ending with CRLF.
1120</t>
1121<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1122  <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>
1123</artwork></figure>
1124
1125<section title="Method" anchor="method">
1126  <x:anchor-alias value="Method"/>
1127<t>
1128   The Method token indicates the request method to be performed on the
1129   target resource. The request method is case-sensitive.
1130</t>
1131<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1132  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1133</artwork></figure>
1134<t>
1135   See &method; for further information, such as the list of methods defined
1136   by this specification, the IANA registry, and considerations for new methods.
1137</t>
1138</section>
1139
1140<section title="request-target" anchor="request-target">
1141  <x:anchor-alias value="request-target"/>
1142<t>
1143   The request-target identifies the target resource upon which to apply
1144   the request.  The four options for request-target are described in
1145   <xref target="request-target-types"/>.
1146</t>
1147<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1148  <x:ref>request-target</x:ref> = "*"
1149                 / <x:ref>absolute-URI</x:ref>
1150                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1151                 / <x:ref>authority</x:ref>
1152</artwork></figure>
1153<t>
1154   HTTP does not place a pre-defined limit on the length of a request-target.
1155   A server &MUST; be prepared to receive URIs of unbounded length and
1156   respond with the 414 (URI Too Long) status code if the received
1157   request-target would be longer than the server wishes to handle
1158   (see &status-414;).
1159</t>
1160<t>
1161   Various ad-hoc limitations on request-target length are found in practice.
1162   It is &RECOMMENDED; that all HTTP senders and recipients support
1163   request-target lengths of 8000 or more octets.
1164</t>
1165<x:note>
1166  <t>
1167    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1168    are not part of the request-target and thus will not be transmitted
1169    in an HTTP request.
1170  </t>
1171</x:note>
1172</section>
1173</section>
1174
1175<section title="Response Status-Line" anchor="status.line">
1176  <x:anchor-alias value="Response"/>
1177  <x:anchor-alias value="Status-Line"/>
1178<t>
1179   The first line of a Response message is the Status-Line, consisting
1180   of the protocol version, a space (SP), the status code, another space,
1181   a possibly-empty textual phrase describing the status code, and
1182   ending with CRLF.
1183</t>
1184<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1185  <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>
1186</artwork></figure>
1187
1188<section title="Status Code" anchor="status.code">
1189  <x:anchor-alias value="Status-Code"/>
1190<t>
1191   The Status-Code element is a 3-digit integer result code of the attempt to
1192   understand and satisfy the request. See &status-code-reasonphr; for
1193   further information, such as the list of status codes defined by this
1194   specification, the IANA registry, and considerations for new status codes.
1195</t>
1196<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/>
1197  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1198</artwork></figure>
1199</section>
1200
1201<section title="Reason Phrase" anchor="reason.phrase">
1202  <x:anchor-alias value="Reason-Phrase"/>
1203<t>   
1204   The Reason Phrase exists for the sole purpose of providing a textual
1205   description associated with the numeric status code, out of deference to
1206   earlier Internet application protocols that were more frequently used with
1207   interactive text clients. A client &SHOULD; ignore the content of the Reason
1208   Phrase.
1209</t>
1210<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1211  <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> )
1212</artwork></figure>
1213</section>
1214</section>
1215</section>
1216
1217<section title="Header Fields" anchor="header.fields">
1218  <x:anchor-alias value="header-field"/>
1219  <x:anchor-alias value="field-content"/>
1220  <x:anchor-alias value="field-name"/>
1221  <x:anchor-alias value="field-value"/>
1222  <x:anchor-alias value="OWS"/>
1223<t>
1224   Each HTTP header field consists of a case-insensitive field name
1225   followed by a colon (":"), optional whitespace, and the field value.
1226</t>
1227<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"/>
1228  <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>
1229  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1230  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1231  <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> )
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  <x:anchor-alias value="obs-fold"/>
1324</t>
1325<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"/>
1326  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
1327                 ; "optional" whitespace
1328  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
1329                 ; "required" whitespace
1330  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
1331                 ; "bad" whitespace
1332  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
1333                 ; obsolete line folding
1334                 ; see <xref target="field.parsing"/>
1335</artwork></figure>
1336</section>
1337
1338<section title="Field Parsing" anchor="field.parsing">
1339<t>
1340   No whitespace is allowed between the header field-name and colon.
1341   In the past, differences in the handling of such whitespace have led to
1342   security vulnerabilities in request routing and response handling.
1343   Any received request message that contains whitespace between a header
1344   field-name and colon &MUST; be rejected with a response code of 400
1345   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1346   message before forwarding the message downstream.
1347</t>
1348<t>
1349   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1350   preferred. The field value does not include any leading or trailing white
1351   space: OWS occurring before the first non-whitespace octet of the
1352   field value or after the last non-whitespace octet of the field value
1353   is ignored and &SHOULD; be removed before further processing (as this does
1354   not change the meaning of the header field).
1355</t>
1356<t>
1357   Historically, HTTP header field values could be extended over multiple
1358   lines by preceding each extra line with at least one space or horizontal
1359   tab (obs-fold). This specification deprecates such line
1360   folding except within the message/http media type
1361   (<xref target="internet.media.type.message.http"/>).
1362   HTTP senders &MUST-NOT; produce messages that include line folding
1363   (i.e., that contain any field-content that matches the obs-fold rule) unless
1364   the message is intended for packaging within the message/http media type.
1365   HTTP recipients &SHOULD; accept line folding and replace any embedded
1366   obs-fold whitespace with either a single SP or a matching number of SP
1367   octets (to avoid buffer copying) prior to interpreting the field value or
1368   forwarding the message downstream.
1369</t>
1370<t>
1371   Historically, HTTP has allowed field content with text in the ISO-8859-1
1372   <xref target="ISO-8859-1"/> character encoding and supported other
1373   character sets only through use of <xref target="RFC2047"/> encoding.
1374   In practice, most HTTP header field values use only a subset of the
1375   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1376   header fields &SHOULD; limit their field values to US-ASCII octets.
1377   Recipients &SHOULD; treat other (obs-text) octets in field content as
1378   opaque data.
1379</t>
1380</section>
1381
1382<section title="Field Length" anchor="field.length">
1383<t>
1384   HTTP does not place a pre-defined limit on the length of header fields,
1385   either in isolation or as a set. A server &MUST; be prepared to receive
1386   request header fields of unbounded length and respond with a 4xx status
1387   code if the received header field(s) would be longer than the server wishes
1388   to handle.
1389</t>
1390<t>
1391   A client that receives response headers that are longer than it wishes to
1392   handle can only treat it as a server error.
1393</t>
1394<t>
1395   Various ad-hoc limitations on header length are found in practice. It is
1396   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1397   combined header fields have 4000 or more octets.
1398</t>
1399</section>
1400
1401<section title="Field value components" anchor="field.components">
1402<t anchor="rule.token.separators">
1403  <x:anchor-alias value="tchar"/>
1404  <x:anchor-alias value="token"/>
1405  <x:anchor-alias value="special"/>
1406  <x:anchor-alias value="word"/>
1407   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1408   separated by whitespace or special characters. These special characters
1409   &MUST; be in a quoted string to be used within a parameter value (as defined
1410   in <xref target="transfer.codings"/>).
1411</t>
1412<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"/>
1413  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1414
1415  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1416<!--
1417  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1418 -->
1419  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1420                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1421                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1422                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1423
1424  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1425                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1426                 / "]" / "?" / "=" / "{" / "}"
1427</artwork></figure>
1428<t anchor="rule.quoted-string">
1429  <x:anchor-alias value="quoted-string"/>
1430  <x:anchor-alias value="qdtext"/>
1431  <x:anchor-alias value="obs-text"/>
1432   A string of text is parsed as a single word if it is quoted using
1433   double-quote marks.
1434</t>
1435<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"/>
1436  <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>
1437  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1438  <x:ref>obs-text</x:ref>       = %x80-FF
1439</artwork></figure>
1440<t anchor="rule.quoted-pair">
1441  <x:anchor-alias value="quoted-pair"/>
1442   The backslash octet ("\") can be used as a single-octet
1443   quoting mechanism within quoted-string constructs:
1444</t>
1445<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1446  <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> )
1447</artwork></figure>
1448<t>
1449   Recipients that process the value of the quoted-string &MUST; handle a
1450   quoted-pair as if it were replaced by the octet following the backslash.
1451</t>
1452<t>
1453   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1454   escaping (i.e., other than DQUOTE and the backslash octet).
1455</t>
1456<t anchor="rule.comment">
1457  <x:anchor-alias value="comment"/>
1458  <x:anchor-alias value="ctext"/>
1459   Comments can be included in some HTTP header fields by surrounding
1460   the comment text with parentheses. Comments are only allowed in
1461   fields containing "comment" as part of their field value definition.
1462</t>
1463<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1464  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1465  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1466</artwork></figure>
1467<t anchor="rule.quoted-cpair">
1468  <x:anchor-alias value="quoted-cpair"/>
1469   The backslash octet ("\") can be used as a single-octet
1470   quoting mechanism within comment constructs:
1471</t>
1472<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1473  <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> )
1474</artwork></figure>
1475<t>
1476   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1477   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1478</t>
1479</section>
1480
1481<section title="ABNF list extension: #rule" anchor="abnf.extension">
1482<t>
1483  A #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
1484  improve readability in the definitions of some header field values.
1485</t>
1486<t>
1487  A construct "#" is defined, similar to "*", for defining comma-delimited
1488  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
1489  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
1490  comma (",") and optional whitespace (OWS).   
1491</t>
1492<figure><preamble>
1493  Thus,
1494</preamble><artwork type="example">
1495  1#element =&gt; element *( OWS "," OWS element )
1496</artwork></figure>
1497<figure><preamble>
1498  and:
1499</preamble><artwork type="example">
1500  #element =&gt; [ 1#element ]
1501</artwork></figure>
1502<figure><preamble>
1503  and for n &gt;= 1 and m &gt; 1:
1504</preamble><artwork type="example">
1505  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
1506</artwork></figure>
1507<t>
1508  For compatibility with legacy list rules, recipients &SHOULD; accept empty
1509  list elements. In other words, consumers would follow the list productions:
1510</t>
1511<figure><artwork type="example">
1512  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
1513 
1514  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
1515</artwork></figure>
1516<t>
1517  Note that empty elements do not contribute to the count of elements present,
1518  though.
1519</t>
1520<t>
1521  For example, given these ABNF productions:
1522</t>
1523<figure><artwork type="example">
1524  example-list      = 1#example-list-elmt
1525  example-list-elmt = token ; see <xref target="field.components"/> 
1526</artwork></figure>
1527<t>
1528  Then these are valid values for example-list (not including the double
1529  quotes, which are present for delimitation only):
1530</t>
1531<figure><artwork type="example">
1532  "foo,bar"
1533  "foo ,bar,"
1534  "foo , ,bar,charlie   "
1535</artwork></figure>
1536<t>
1537  But these values would be invalid, as at least one non-empty element is
1538  required:
1539</t>
1540<figure><artwork type="example">
1541  ""
1542  ","
1543  ",   ,"
1544</artwork></figure>
1545<t>
1546  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
1547  expanded as explained above.
1548</t>
1549</section>
1550</section>
1551
1552<section title="Message Body" anchor="message.body">
1553  <x:anchor-alias value="message-body"/>
1554<t>
1555   The message-body (if any) of an HTTP message is used to carry the
1556   payload body associated with the request or response.
1557</t>
1558<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1559  <x:ref>message-body</x:ref> = *OCTET
1560</artwork></figure>
1561<t>
1562   The message-body differs from the payload body only when a transfer-coding
1563   has been applied, as indicated by the Transfer-Encoding header field
1564   (<xref target="header.transfer-encoding"/>).  If more than one
1565   Transfer-Encoding header field is present in a message, the multiple
1566   field-values &MUST; be combined into one field-value, according to the
1567   algorithm defined in <xref target="header.fields"/>, before determining
1568   the message-body length.
1569</t>
1570<t>
1571   When one or more transfer-codings are applied to a payload in order to
1572   form the message-body, the Transfer-Encoding header field &MUST; contain
1573   the list of transfer-codings applied. Transfer-Encoding is a property of
1574   the message, not of the payload, and thus &MAY; be added or removed by
1575   any implementation along the request/response chain under the constraints
1576   found in <xref target="transfer.codings"/>.
1577</t>
1578<t>
1579   If a message is received that has multiple Content-Length header fields
1580   (<xref target="header.content-length"/>) with field-values consisting
1581   of the same decimal value, or a single Content-Length header field with
1582   a field value containing a list of identical decimal values (e.g.,
1583   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1584   header fields have been generated or combined by an upstream message
1585   processor, then the recipient &MUST; either reject the message as invalid
1586   or replace the duplicated field-values with a single valid Content-Length
1587   field containing that decimal value prior to determining the message-body
1588   length.
1589</t>
1590<t>
1591   The rules for when a message-body is allowed in a message differ for
1592   requests and responses.
1593</t>
1594<t>
1595   The presence of a message-body in a request is signaled by the
1596   inclusion of a Content-Length or Transfer-Encoding header field in
1597   the request's header fields, even if the request method does not
1598   define any use for a message-body.  This allows the request
1599   message framing algorithm to be independent of method semantics.
1600</t>
1601<t>
1602   For response messages, whether or not a message-body is included with
1603   a message is dependent on both the request method and the response
1604   status code (<xref target="status.code"/>).
1605   Responses to the HEAD request method never include a message-body
1606   because the associated response header fields (e.g., Transfer-Encoding,
1607   Content-Length, etc.) only indicate what their values would have been
1608   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1609   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1610   All other responses do include a message-body, although the body
1611   &MAY; be of zero length.
1612</t>
1613<t>
1614   The length of the message-body is determined by one of the following
1615   (in order of precedence):
1616</t>
1617<t>
1618  <list style="numbers">
1619    <x:lt><t>
1620     Any response to a HEAD request and any response with a status
1621     code of 100-199, 204, or 304 is always terminated by the first
1622     empty line after the header fields, regardless of the header
1623     fields present in the message, and thus cannot contain a message-body.
1624    </t></x:lt>
1625    <x:lt><t>
1626     If a Transfer-Encoding header field is present
1627     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1628     is the final encoding, the message-body length is determined by reading
1629     and decoding the chunked data until the transfer-coding indicates the
1630     data is complete.
1631    </t>
1632    <t>
1633     If a Transfer-Encoding header field is present in a response and the
1634     "chunked" transfer-coding is not the final encoding, the message-body
1635     length is determined by reading the connection until it is closed by
1636     the server.
1637     If a Transfer-Encoding header field is present in a request and the
1638     "chunked" transfer-coding is not the final encoding, the message-body
1639     length cannot be determined reliably; the server &MUST; respond with
1640     the 400 (Bad Request) status code and then close the connection.
1641    </t>
1642    <t>
1643     If a message is received with both a Transfer-Encoding header field
1644     and a Content-Length header field, the Transfer-Encoding overrides
1645     the Content-Length.
1646     Such a message might indicate an attempt to perform request or response
1647     smuggling (bypass of security-related checks on message routing or content)
1648     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1649     be removed, prior to forwarding the message downstream, or replaced with
1650     the real message-body length after the transfer-coding is decoded.
1651    </t></x:lt>
1652    <x:lt><t>
1653     If a message is received without Transfer-Encoding and with either
1654     multiple Content-Length header fields having differing field-values or
1655     a single Content-Length header field having an invalid value, then the
1656     message framing is invalid and &MUST; be treated as an error to
1657     prevent request or response smuggling.
1658     If this is a request message, the server &MUST; respond with
1659     a 400 (Bad Request) status code and then close the connection.
1660     If this is a response message received by a proxy, the proxy
1661     &MUST; discard the received response, send a 502 (Bad Gateway)
1662     status code as its downstream response, and then close the connection.
1663     If this is a response message received by a user-agent, it &MUST; be
1664     treated as an error by discarding the message and closing the connection.
1665    </t></x:lt>
1666    <x:lt><t>
1667     If a valid Content-Length header field
1668     is present without Transfer-Encoding, its decimal value defines the
1669     message-body length in octets.  If the actual number of octets sent in
1670     the message is less than the indicated Content-Length, the recipient
1671     &MUST; consider the message to be incomplete and treat the connection
1672     as no longer usable.
1673     If the actual number of octets sent in the message is more than the indicated
1674     Content-Length, the recipient &MUST; only process the message-body up to the
1675     field value's number of octets; the remainder of the message &MUST; either
1676     be discarded or treated as the next message in a pipeline.  For the sake of
1677     robustness, a user-agent &MAY; attempt to detect and correct such an error
1678     in message framing if it is parsing the response to the last request on
1679     a connection and the connection has been closed by the server.
1680    </t></x:lt>
1681    <x:lt><t>
1682     If this is a request message and none of the above are true, then the
1683     message-body length is zero (no message-body is present).
1684    </t></x:lt>
1685    <x:lt><t>
1686     Otherwise, this is a response message without a declared message-body
1687     length, so the message-body length is determined by the number of octets
1688     received prior to the server closing the connection.
1689    </t></x:lt>
1690  </list>
1691</t>
1692<t>
1693   Since there is no way to distinguish a successfully completed,
1694   close-delimited message from a partially-received message interrupted
1695   by network failure, implementations &SHOULD; use encoding or
1696   length-delimited messages whenever possible.  The close-delimiting
1697   feature exists primarily for backwards compatibility with HTTP/1.0.
1698</t>
1699<t>
1700   A server &MAY; reject a request that contains a message-body but
1701   not a Content-Length by responding with 411 (Length Required).
1702</t>
1703<t>
1704   Unless a transfer-coding other than "chunked" has been applied,
1705   a client that sends a request containing a message-body &SHOULD;
1706   use a valid Content-Length header field if the message-body length
1707   is known in advance, rather than the "chunked" encoding, since some
1708   existing services respond to "chunked" with a 411 (Length Required)
1709   status code even though they understand the chunked encoding.  This
1710   is typically because such services are implemented via a gateway that
1711   requires a content-length in advance of being called and the server
1712   is unable or unwilling to buffer the entire request before processing.
1713</t>
1714<t>
1715   A client that sends a request containing a message-body &MUST; include a
1716   valid Content-Length header field if it does not know the server will
1717   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1718   of specific user configuration or by remembering the version of a prior
1719   received response.
1720</t>
1721</section>
1722
1723<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1724<t>
1725   Request messages that are prematurely terminated, possibly due to a
1726   cancelled connection or a server-imposed time-out exception, &MUST;
1727   result in closure of the connection; sending an HTTP/1.1 error response
1728   prior to closing the connection is &OPTIONAL;.
1729</t>
1730<t>
1731   Response messages that are prematurely terminated, usually by closure
1732   of the connection prior to receiving the expected number of octets or by
1733   failure to decode a transfer-encoded message-body, &MUST; be recorded
1734   as incomplete.  A response that terminates in the middle of the header
1735   block (before the empty line is received) cannot be assumed to convey the
1736   full semantics of the response and &MUST; be treated as an error.
1737</t>
1738<t>
1739   A message-body that uses the chunked transfer encoding is
1740   incomplete if the zero-sized chunk that terminates the encoding has not
1741   been received.  A message that uses a valid Content-Length is incomplete
1742   if the size of the message-body received (in octets) is less than the
1743   value given by Content-Length.  A response that has neither chunked
1744   transfer encoding nor Content-Length is terminated by closure of the
1745   connection, and thus is considered complete regardless of the number of
1746   message-body octets received, provided that the header block was received
1747   intact.
1748</t>
1749<t>
1750   A user agent &MUST-NOT; render an incomplete response message-body as if
1751   it were complete (i.e., some indication must be given to the user that an
1752   error occurred).  Cache requirements for incomplete responses are defined
1753   in &cache-incomplete;.
1754</t>
1755<t>
1756   A server &MUST; read the entire request message-body or close
1757   the connection after sending its response, since otherwise the
1758   remaining data on a persistent connection would be misinterpreted
1759   as the next request.  Likewise,
1760   a client &MUST; read the entire response message-body if it intends
1761   to reuse the same connection for a subsequent request.  Pipelining
1762   multiple requests on a connection is described in <xref target="pipelining"/>.
1763</t>
1764</section>
1765
1766<section title="Message Parsing Robustness" anchor="message.robustness">
1767<t>
1768   Older HTTP/1.0 client implementations might send an extra CRLF
1769   after a POST request as a lame workaround for some early server
1770   applications that failed to read message-body content that was
1771   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1772   preface or follow a request with an extra CRLF.  If terminating
1773   the request message-body with a line-ending is desired, then the
1774   client &MUST; include the terminating CRLF octets as part of the
1775   message-body length.
1776</t>
1777<t>
1778   In the interest of robustness, servers &SHOULD; ignore at least one
1779   empty line received where a Request-Line is expected. In other words, if
1780   the server is reading the protocol stream at the beginning of a
1781   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1782   Likewise, although the line terminator for the start-line and header
1783   fields is the sequence CRLF, we recommend that recipients recognize a
1784   single LF as a line terminator and ignore any CR.
1785</t>
1786<t>
1787   When a server listening only for HTTP request messages, or processing
1788   what appears from the start-line to be an HTTP request message,
1789   receives a sequence of octets that does not match the HTTP-message
1790   grammar aside from the robustness exceptions listed above, the
1791   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1792</t>
1793</section>
1794</section>
1795
1796<section title="Message Routing" anchor="message.routing">
1797<t>
1798   In most cases, the user agent is provided a URI reference
1799   from which it determines an absolute URI for identifying the target
1800   resource.  When a request to the resource is initiated, all or part
1801   of that URI is used to construct the HTTP request-target.
1802</t>
1803
1804<section title="Types of Request Target" anchor="request-target-types">
1805<t>
1806   The proper format choice of the four options available to request-target
1807   depends on the method being requested and if the request is being made to
1808   a proxy.
1809</t>   
1810<t anchor="origin-form"><iref item="origin form (of request-target)"/>
1811   The most common form of request-target is that used when making
1812   a request to an origin server ("origin form") to access a resource
1813   identified by an "http" (<xref target="http.uri"/>) or
1814   "https" (<xref target="https.uri"/>) URI.
1815   In this case, the absolute path and query components of the URI
1816   &MUST; be transmitted as the request-target and the authority component
1817   (excluding any userinfo) &MUST; be transmitted in a Host header field.
1818   For example, a client wishing to retrieve a representation of the resource
1819   identified as
1820</t>
1821<figure><artwork x:indent-with="  ">
1822http://www.example.org/where?q=now
1823</artwork></figure>
1824<t>
1825   directly from the origin server would open (or reuse) a TCP connection
1826   to port 80 of the host "www.example.org" and send the lines:
1827</t>
1828<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1829GET /where?q=now HTTP/1.1
1830Host: www.example.org
1831</artwork></figure>
1832<t>
1833   followed by the remainder of the request. Note that the origin form
1834   of request-target always starts with an absolute path. If the target
1835   resource's URI path is empty, then an absolute path of "/" &MUST; be
1836   provided in the request-target.
1837</t>
1838<t>
1839   If the request-target is percent-encoded
1840   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1841   &MUST; decode the request-target in order to
1842   properly interpret the request. Servers &SHOULD; respond to invalid
1843   request-targets with an appropriate status code.
1844</t>
1845<t anchor="absolute-URI-form"><iref item="absolute-URI form (of request-target)"/>
1846   The "absolute-URI" form of request-target is &REQUIRED; when the request
1847   is being made to a proxy.  The proxy is requested to either forward the
1848   request or service it from a valid cache, and then return the response.
1849   Note that the proxy &MAY; forward the request on to another proxy or
1850   directly to the server specified by the absolute-URI.
1851   In order to avoid request loops, a proxy that forwards requests to other
1852   proxies &MUST; be able to recognize and exclude all of its own server
1853   names, including any aliases, local variations, or literal IP addresses.
1854   An example Request-Line would be:
1855</t>
1856<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1857GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1858</artwork></figure>
1859<t>
1860   To allow for transition to absolute-URIs in all requests in future
1861   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1862   form in requests, even though HTTP/1.1 clients will only generate
1863   them in requests to proxies.
1864</t>
1865<t>
1866   If a proxy receives a host name that is not a fully qualified domain
1867   name, it &MAY; add its domain to the host name it received. If a proxy
1868   receives a fully qualified domain name, the proxy &MUST-NOT; change
1869   the host name.
1870</t>
1871<t anchor="authority-form"><iref item="authority form (of request-target)"/>
1872   The "authority form" of request-target, which &MUST-NOT; be used
1873   with any request method other than CONNECT, is used to establish a
1874   tunnel through one or more proxies (&CONNECT;).  For example,
1875</t>
1876<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1877CONNECT www.example.com:80 HTTP/1.1
1878</artwork></figure>
1879<t anchor="asterix-form"><iref item="asterisk form (of request-target)"/>
1880   The asterisk ("*") form of request-target, which &MUST-NOT; be used
1881   with any request method other than OPTIONS, means that the request
1882   applies to the server as a whole (the listening process) rather than
1883   to a specific named resource at that server.  For example,
1884</t>
1885<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1886OPTIONS * HTTP/1.1
1887</artwork></figure>
1888<t>
1889   If a proxy receives an OPTIONS request with an absolute-URI form of
1890   request-target in which the URI has an empty path and no query component,
1891   then the last proxy on the request chain &MUST; use a request-target
1892   of "*" when it forwards the request to the indicated origin server.
1893</t>
1894<figure><preamble>   
1895   For example, the request
1896</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1897OPTIONS http://www.example.org:8001 HTTP/1.1
1898</artwork></figure>
1899<figure><preamble>   
1900  would be forwarded by the final proxy as
1901</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1902OPTIONS * HTTP/1.1
1903Host: www.example.org:8001
1904</artwork>
1905<postamble>
1906   after connecting to port 8001 of host "www.example.org".
1907</postamble>
1908</figure>
1909<t>
1910   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
1911   parts of the received request-target when forwarding it to the next inbound
1912   server, except as noted above to replace a null path-absolute with "/" or
1913   "*".
1914</t>
1915</section>
1916
1917<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1918<t>
1919   The exact resource identified by an Internet request is determined by
1920   examining both the request-target and the Host header field.
1921</t>
1922<t>
1923   An origin server that does not allow resources to differ by the
1924   requested host &MAY; ignore the Host header field value when
1925   determining the resource identified by an HTTP/1.1 request. (But see
1926   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1927   for other requirements on Host support in HTTP/1.1.)
1928</t>
1929<t>
1930   An origin server that does differentiate resources based on the host
1931   requested (sometimes referred to as virtual hosts or vanity host
1932   names) &MUST; use the following rules for determining the requested
1933   resource on an HTTP/1.1 request:
1934  <list style="numbers">
1935    <t>If request-target is an absolute-URI, the host is part of the
1936     request-target. Any Host header field value in the request &MUST; be
1937     ignored.</t>
1938    <t>If the request-target is not an absolute-URI, and the request includes
1939     a Host header field, the host is determined by the Host header
1940     field value.</t>
1941    <t>If the host as determined by rule 1 or 2 is not a valid host on
1942     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1943  </list>
1944</t>
1945<t>
1946   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1947   attempt to use heuristics (e.g., examination of the URI path for
1948   something unique to a particular host) in order to determine what
1949   exact resource is being requested.
1950</t>
1951</section>
1952
1953<section title="Effective Request URI" anchor="effective.request.uri">
1954  <iref primary="true" item="effective request URI"/>
1955  <iref primary="true" item="target resource"/>
1956<t>
1957   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1958   for the target resource; instead, the URI needs to be inferred from the
1959   request-target, Host header field, and connection context. The result of
1960   this process is called the "effective request URI".  The "target resource"
1961   is the resource identified by the effective request URI.
1962</t>
1963<t>
1964   If the request-target is an absolute-URI, then the effective request URI is
1965   the request-target.
1966</t>
1967<t>
1968   If the request-target uses the origin form or the asterisk form,
1969   and the Host header field is present, then the effective request URI is
1970   constructed by concatenating
1971</t>
1972<t>
1973  <list style="symbols">
1974    <t>
1975      the scheme name: "http" if the request was received over an insecure
1976      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1977      connection,
1978    </t>
1979    <t>
1980      the octet sequence "://",
1981    </t>
1982    <t>
1983      the authority component, as specified in the Host header field
1984      (<xref target="header.host"/>), and
1985    </t>
1986    <t>
1987      the request-target obtained from the Request-Line, unless the
1988      request-target is just the asterisk "*".
1989    </t>
1990  </list>
1991</t>
1992<t>
1993   If the request-target uses the origin form or the asterisk form,
1994   and the Host header field is not present, then the effective request URI is
1995   undefined.
1996</t>
1997<t>
1998   Otherwise, when request-target uses the authority form, the effective
1999   request URI is undefined.
2000</t>
2001<figure>
2002<preamble>
2003   Example 1: the effective request URI for the message
2004</preamble> 
2005<artwork type="example" x:indent-with="  ">
2006GET /pub/WWW/TheProject.html HTTP/1.1
2007Host: www.example.org:8080
2008</artwork>
2009<postamble>
2010  (received over an insecure TCP connection) is "http", plus "://", plus the
2011  authority component "www.example.org:8080", plus the request-target
2012  "/pub/WWW/TheProject.html", thus
2013  "http://www.example.org:8080/pub/WWW/TheProject.html".
2014</postamble>
2015</figure>
2016<figure>
2017<preamble>
2018   Example 2: the effective request URI for the message
2019</preamble> 
2020<artwork type="example" x:indent-with="  ">
2021OPTIONS * HTTP/1.1
2022Host: www.example.org
2023</artwork>
2024<postamble>
2025  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
2026  authority component "www.example.org", thus "https://www.example.org".
2027</postamble>
2028</figure>
2029<t>
2030   Effective request URIs are compared using the rules described in
2031   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
2032   be treated as equivalent to an absolute path of "/".
2033</t> 
2034</section>
2035</section>
2036
2037
2038<section title="Protocol Parameters" anchor="protocol.parameters">
2039
2040<section title="Transfer Codings" anchor="transfer.codings">
2041  <x:anchor-alias value="transfer-coding"/>
2042  <x:anchor-alias value="transfer-extension"/>
2043<t>
2044   Transfer-coding values are used to indicate an encoding
2045   transformation that has been, can be, or might need to be applied to a
2046   payload body in order to ensure "safe transport" through the network.
2047   This differs from a content coding in that the transfer-coding is a
2048   property of the message rather than a property of the representation
2049   that is being transferred.
2050</t>
2051<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2052  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2053                          / "compress" ; <xref target="compress.coding"/>
2054                          / "deflate" ; <xref target="deflate.coding"/>
2055                          / "gzip" ; <xref target="gzip.coding"/>
2056                          / <x:ref>transfer-extension</x:ref>
2057  <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> )
2058</artwork></figure>
2059<t anchor="rule.parameter">
2060  <x:anchor-alias value="attribute"/>
2061  <x:anchor-alias value="transfer-parameter"/>
2062  <x:anchor-alias value="value"/>
2063   Parameters are in the form of attribute/value pairs.
2064</t>
2065<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"/>
2066  <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>
2067  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2068  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2069</artwork></figure>
2070<t>
2071   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2072   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2073   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2074</t>
2075<t>
2076   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2077   MIME, which were designed to enable safe transport of binary data over a
2078   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2079   However, safe transport
2080   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2081   the only unsafe characteristic of message-bodies is the difficulty in
2082   determining the exact message body length (<xref target="message.body"/>),
2083   or the desire to encrypt data over a shared transport.
2084</t>
2085<t>
2086   A server that receives a request message with a transfer-coding it does
2087   not understand &SHOULD; respond with 501 (Not Implemented) and then
2088   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2089   client.
2090</t>
2091
2092<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2093  <iref item="chunked (Coding Format)"/>
2094  <iref item="Coding Format" subitem="chunked"/>
2095  <x:anchor-alias value="chunk"/>
2096  <x:anchor-alias value="Chunked-Body"/>
2097  <x:anchor-alias value="chunk-data"/>
2098  <x:anchor-alias value="chunk-ext"/>
2099  <x:anchor-alias value="chunk-ext-name"/>
2100  <x:anchor-alias value="chunk-ext-val"/>
2101  <x:anchor-alias value="chunk-size"/>
2102  <x:anchor-alias value="last-chunk"/>
2103  <x:anchor-alias value="trailer-part"/>
2104  <x:anchor-alias value="quoted-str-nf"/>
2105  <x:anchor-alias value="qdtext-nf"/>
2106<t>
2107   The chunked encoding modifies the body of a message in order to
2108   transfer it as a series of chunks, each with its own size indicator,
2109   followed by an &OPTIONAL; trailer containing header fields. This
2110   allows dynamically produced content to be transferred along with the
2111   information necessary for the recipient to verify that it has
2112   received the full message.
2113</t>
2114<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"/>
2115  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2116                   <x:ref>last-chunk</x:ref>
2117                   <x:ref>trailer-part</x:ref>
2118                   <x:ref>CRLF</x:ref>
2119 
2120  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2121                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2122  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2123  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2124 
2125  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref>
2126                      [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2127  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2128  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2129  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2130  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2131 
2132  <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>
2133                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2134  <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>
2135</artwork></figure>
2136<t>
2137   The chunk-size field is a string of hex digits indicating the size of
2138   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2139   zero, followed by the trailer, which is terminated by an empty line.
2140</t>
2141<t>
2142   The trailer allows the sender to include additional HTTP header
2143   fields at the end of the message. The Trailer header field can be
2144   used to indicate which header fields are included in a trailer (see
2145   <xref target="header.trailer"/>).
2146</t>
2147<t>
2148   A server using chunked transfer-coding in a response &MUST-NOT; use the
2149   trailer for any header fields unless at least one of the following is
2150   true:
2151  <list style="numbers">
2152    <t>the request included a TE header field that indicates "trailers" is
2153     acceptable in the transfer-coding of the  response, as described in
2154     <xref target="header.te"/>; or,</t>
2155     
2156    <t>the trailer fields consist entirely of optional metadata, and the
2157    recipient could use the message (in a manner acceptable to the server where
2158    the field originated) without receiving it. In other words, the server that
2159    generated the header (often but not always the origin server) is willing to
2160    accept the possibility that the trailer fields might be silently discarded
2161    along the path to the client.</t>
2162  </list>
2163</t>
2164<t>
2165   This requirement prevents an interoperability failure when the
2166   message is being received by an HTTP/1.1 (or later) proxy and
2167   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2168   conformance with the protocol would have necessitated a possibly
2169   infinite buffer on the proxy.
2170</t>
2171<t>
2172   A process for decoding the "chunked" transfer-coding
2173   can be represented in pseudo-code as:
2174</t>
2175<figure><artwork type="code">
2176  length := 0
2177  read chunk-size, chunk-ext (if any) and CRLF
2178  while (chunk-size &gt; 0) {
2179     read chunk-data and CRLF
2180     append chunk-data to decoded-body
2181     length := length + chunk-size
2182     read chunk-size and CRLF
2183  }
2184  read header-field
2185  while (header-field not empty) {
2186     append header-field to existing header fields
2187     read header-field
2188  }
2189  Content-Length := length
2190  Remove "chunked" from Transfer-Encoding
2191</artwork></figure>
2192<t>
2193   All HTTP/1.1 applications &MUST; be able to receive and decode the
2194   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2195   they do not understand.
2196</t>
2197<t>
2198   Since "chunked" is the only transfer-coding required to be understood
2199   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2200   on a persistent connection.  Whenever a transfer-coding is applied to
2201   a payload body in a request, the final transfer-coding applied &MUST;
2202   be "chunked".  If a transfer-coding is applied to a response payload
2203   body, then either the final transfer-coding applied &MUST; be "chunked"
2204   or the message &MUST; be terminated by closing the connection. When the
2205   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2206   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2207   be applied more than once in a message-body.
2208</t>
2209</section>
2210
2211<section title="Compression Codings" anchor="compression.codings">
2212<t>
2213   The codings defined below can be used to compress the payload of a
2214   message.
2215</t>
2216<x:note><t>
2217   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2218   is not desirable and is discouraged for future encodings. Their
2219   use here is representative of historical practice, not good
2220   design.
2221</t></x:note>
2222<x:note><t>
2223   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2224   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2225   equivalent to "gzip" and "compress" respectively.
2226</t></x:note>
2227
2228<section title="Compress Coding" anchor="compress.coding">
2229<iref item="compress (Coding Format)"/>
2230<iref item="Coding Format" subitem="compress"/>
2231<t>
2232   The "compress" format is produced by the common UNIX file compression
2233   program "compress". This format is an adaptive Lempel-Ziv-Welch
2234   coding (LZW).
2235</t>
2236</section>
2237
2238<section title="Deflate Coding" anchor="deflate.coding">
2239<iref item="deflate (Coding Format)"/>
2240<iref item="Coding Format" subitem="deflate"/>
2241<t>
2242   The "deflate" format is defined as the "deflate" compression mechanism
2243   (described in <xref target="RFC1951"/>) used inside the "zlib"
2244   data format (<xref target="RFC1950"/>).
2245</t>
2246<x:note>
2247  <t>
2248    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2249    compressed data without the zlib wrapper.
2250   </t>
2251</x:note>
2252</section>
2253
2254<section title="Gzip Coding" anchor="gzip.coding">
2255<iref item="gzip (Coding Format)"/>
2256<iref item="Coding Format" subitem="gzip"/>
2257<t>
2258   The "gzip" format is produced by the file compression program
2259   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2260   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2261</t>
2262</section>
2263
2264</section>
2265
2266<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2267<t>
2268   The HTTP Transfer Coding Registry defines the name space for the transfer
2269   coding names.
2270</t>
2271<t>
2272   Registrations &MUST; include the following fields:
2273   <list style="symbols">
2274     <t>Name</t>
2275     <t>Description</t>
2276     <t>Pointer to specification text</t>
2277   </list>
2278</t>
2279<t>
2280   Names of transfer codings &MUST-NOT; overlap with names of content codings
2281   (&content-codings;), unless the encoding transformation is identical (as it
2282   is the case for the compression codings defined in
2283   <xref target="compression.codings"/>).
2284</t>
2285<t>
2286   Values to be added to this name space require a specification
2287   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2288   conform to the purpose of transfer coding defined in this section.
2289</t>
2290<t>
2291   The registry itself is maintained at
2292   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2293</t>
2294</section>
2295</section>
2296
2297<section title="Product Tokens" anchor="product.tokens">
2298  <x:anchor-alias value="product"/>
2299  <x:anchor-alias value="product-version"/>
2300<t>
2301   Product tokens are used to allow communicating applications to
2302   identify themselves by software name and version. Most fields using
2303   product tokens also allow sub-products which form a significant part
2304   of the application to be listed, separated by whitespace. By
2305   convention, the products are listed in order of their significance
2306   for identifying the application.
2307</t>
2308<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2309  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2310  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2311</artwork></figure>
2312<t>
2313   Examples:
2314</t>
2315<figure><artwork type="example">
2316  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2317  Server: Apache/0.8.4
2318</artwork></figure>
2319<t>
2320   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2321   used for advertising or other non-essential information. Although any
2322   token octet &MAY; appear in a product-version, this token &SHOULD;
2323   only be used for a version identifier (i.e., successive versions of
2324   the same product &SHOULD; only differ in the product-version portion of
2325   the product value).
2326</t>
2327</section>
2328
2329<section title="Quality Values" anchor="quality.values">
2330  <x:anchor-alias value="qvalue"/>
2331<t>
2332   Both transfer codings (TE request header field, <xref target="header.te"/>)
2333   and content negotiation (&content.negotiation;) use short "floating point"
2334   numbers to indicate the relative importance ("weight") of various
2335   negotiable parameters.  A weight is normalized to a real number in
2336   the range 0 through 1, where 0 is the minimum and 1 the maximum
2337   value. If a parameter has a quality value of 0, then content with
2338   this parameter is "not acceptable" for the client. HTTP/1.1
2339   applications &MUST-NOT; generate more than three digits after the
2340   decimal point. User configuration of these values &SHOULD; also be
2341   limited in this fashion.
2342</t>
2343<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2344  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2345                 / ( "1" [ "." 0*3("0") ] )
2346</artwork></figure>
2347<x:note>
2348  <t>
2349     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2350     relative degradation in desired quality.
2351  </t>
2352</x:note>
2353</section>
2354
2355</section>
2356
2357<section title="Connections" anchor="connections">
2358
2359<section title="Persistent Connections" anchor="persistent.connections">
2360
2361<section title="Purpose" anchor="persistent.purpose">
2362<t>
2363   Prior to persistent connections, a separate TCP connection was
2364   established for each request, increasing the load on HTTP servers
2365   and causing congestion on the Internet. The use of inline images and
2366   other associated data often requires a client to make multiple
2367   requests of the same server in a short amount of time. Analysis of
2368   these performance problems and results from a prototype
2369   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2370   measurements of actual HTTP/1.1 implementations show good
2371   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2372   T/TCP <xref target="Tou1998"/>.
2373</t>
2374<t>
2375   Persistent HTTP connections have a number of advantages:
2376  <list style="symbols">
2377      <t>
2378        By opening and closing fewer TCP connections, CPU time is saved
2379        in routers and hosts (clients, servers, proxies, gateways,
2380        tunnels, or caches), and memory used for TCP protocol control
2381        blocks can be saved in hosts.
2382      </t>
2383      <t>
2384        HTTP requests and responses can be pipelined on a connection.
2385        Pipelining allows a client to make multiple requests without
2386        waiting for each response, allowing a single TCP connection to
2387        be used much more efficiently, with much lower elapsed time.
2388      </t>
2389      <t>
2390        Network congestion is reduced by reducing the number of packets
2391        caused by TCP opens, and by allowing TCP sufficient time to
2392        determine the congestion state of the network.
2393      </t>
2394      <t>
2395        Latency on subsequent requests is reduced since there is no time
2396        spent in TCP's connection opening handshake.
2397      </t>
2398      <t>
2399        HTTP can evolve more gracefully, since errors can be reported
2400        without the penalty of closing the TCP connection. Clients using
2401        future versions of HTTP might optimistically try a new feature,
2402        but if communicating with an older server, retry with old
2403        semantics after an error is reported.
2404      </t>
2405    </list>
2406</t>
2407<t>
2408   HTTP implementations &SHOULD; implement persistent connections.
2409</t>
2410</section>
2411
2412<section title="Overall Operation" anchor="persistent.overall">
2413<t>
2414   A significant difference between HTTP/1.1 and earlier versions of
2415   HTTP is that persistent connections are the default behavior of any
2416   HTTP connection. That is, unless otherwise indicated, the client
2417   &SHOULD; assume that the server will maintain a persistent connection,
2418   even after error responses from the server.
2419</t>
2420<t>
2421   Persistent connections provide a mechanism by which a client and a
2422   server can signal the close of a TCP connection. This signaling takes
2423   place using the Connection header field (<xref target="header.connection"/>). Once a close
2424   has been signaled, the client &MUST-NOT; send any more requests on that
2425   connection.
2426</t>
2427
2428<section title="Negotiation" anchor="persistent.negotiation">
2429<t>
2430   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2431   maintain a persistent connection unless a Connection header field including
2432   the connection-token "close" was sent in the request. If the server
2433   chooses to close the connection immediately after sending the
2434   response, it &SHOULD; send a Connection header field including the
2435   connection-token "close".
2436</t>
2437<t>
2438   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2439   decide to keep it open based on whether the response from a server
2440   contains a Connection header field with the connection-token close. In case
2441   the client does not want to maintain a connection for more than that
2442   request, it &SHOULD; send a Connection header field including the
2443   connection-token close.
2444</t>
2445<t>
2446   If either the client or the server sends the close token in the
2447   Connection header field, that request becomes the last one for the
2448   connection.
2449</t>
2450<t>
2451   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2452   maintained for HTTP versions less than 1.1 unless it is explicitly
2453   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2454   compatibility with HTTP/1.0 clients.
2455</t>
2456<t>
2457   In order to remain persistent, all messages on the connection &MUST;
2458   have a self-defined message length (i.e., one not defined by closure
2459   of the connection), as described in <xref target="message.body"/>.
2460</t>
2461</section>
2462
2463<section title="Pipelining" anchor="pipelining">
2464<t>
2465   A client that supports persistent connections &MAY; "pipeline" its
2466   requests (i.e., send multiple requests without waiting for each
2467   response). A server &MUST; send its responses to those requests in the
2468   same order that the requests were received.
2469</t>
2470<t>
2471   Clients which assume persistent connections and pipeline immediately
2472   after connection establishment &SHOULD; be prepared to retry their
2473   connection if the first pipelined attempt fails. If a client does
2474   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2475   persistent. Clients &MUST; also be prepared to resend their requests if
2476   the server closes the connection before sending all of the
2477   corresponding responses.
2478</t>
2479<t>
2480   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2481   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2482   premature termination of the transport connection could lead to
2483   indeterminate results. A client wishing to send a non-idempotent
2484   request &SHOULD; wait to send that request until it has received the
2485   response status line for the previous request.
2486</t>
2487</section>
2488</section>
2489
2490<section title="Proxy Servers" anchor="persistent.proxy">
2491<t>
2492   It is especially important that proxies correctly implement the
2493   properties of the Connection header field as specified in <xref target="header.connection"/>.
2494</t>
2495<t>
2496   The proxy server &MUST; signal persistent connections separately with
2497   its clients and the origin servers (or other proxy servers) that it
2498   connects to. Each persistent connection applies to only one transport
2499   link.
2500</t>
2501<t>
2502   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2503   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2504   for information and discussion of the problems with the Keep-Alive header field
2505   implemented by many HTTP/1.0 clients).
2506</t>
2507
2508<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2509<!--<t>
2510  <cref anchor="TODO-end-to-end" source="jre">
2511    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2512    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2513  </cref>
2514</t>-->
2515<t>
2516   For the purpose of defining the behavior of caches and non-caching
2517   proxies, we divide HTTP header fields into two categories:
2518  <list style="symbols">
2519      <t>End-to-end header fields, which are  transmitted to the ultimate
2520        recipient of a request or response. End-to-end header fields in
2521        responses MUST be stored as part of a cache entry and &MUST; be
2522        transmitted in any response formed from a cache entry.</t>
2523
2524      <t>Hop-by-hop header fields, which are meaningful only for a single
2525        transport-level connection, and are not stored by caches or
2526        forwarded by proxies.</t>
2527  </list>
2528</t>
2529<t>
2530   The following HTTP/1.1 header fields are hop-by-hop header fields:
2531  <list style="symbols">
2532      <t>Connection</t>
2533      <t>Keep-Alive</t>
2534      <t>Proxy-Authenticate</t>
2535      <t>Proxy-Authorization</t>
2536      <t>TE</t>
2537      <t>Trailer</t>
2538      <t>Transfer-Encoding</t>
2539      <t>Upgrade</t>
2540  </list>
2541</t>
2542<t>
2543   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2544</t>
2545<t>
2546   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2547   (<xref target="header.connection"/>).
2548</t>
2549</section>
2550
2551<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2552<!--<t>
2553  <cref anchor="TODO-non-mod-headers" source="jre">
2554    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2555    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2556  </cref>
2557</t>-->
2558<t>
2559   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2560   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2561   modify an end-to-end header field unless the definition of that header field requires
2562   or specifically allows that.
2563</t>
2564<t>
2565   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2566   request or response, and it &MUST-NOT; add any of these fields if not
2567   already present:
2568  <list style="symbols">
2569    <t>Allow</t>
2570    <t>Content-Location</t>
2571    <t>Content-MD5</t>
2572    <t>ETag</t>
2573    <t>Last-Modified</t>
2574    <t>Server</t>
2575  </list>
2576</t>
2577<t>
2578   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2579   response:
2580  <list style="symbols">
2581    <t>Expires</t>
2582  </list>
2583</t>
2584<t>
2585   but it &MAY; add any of these fields if not already present. If an
2586   Expires header field is added, it &MUST; be given a field-value identical to
2587   that of the Date header field in that response.
2588</t>
2589<t>
2590   A proxy &MUST-NOT; modify or add any of the following fields in a
2591   message that contains the no-transform cache-control directive, or in
2592   any request:
2593  <list style="symbols">
2594    <t>Content-Encoding</t>
2595    <t>Content-Range</t>
2596    <t>Content-Type</t>
2597  </list>
2598</t>
2599<t>
2600   A transforming proxy &MAY; modify or add these fields to a message
2601   that does not include no-transform, but if it does so, it &MUST; add a
2602   Warning 214 (Transformation applied) if one does not already appear
2603   in the message (see &header-warning;).
2604</t>
2605<x:note>
2606  <t>
2607    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2608    cause authentication failures if stronger authentication
2609    mechanisms are introduced in later versions of HTTP. Such
2610    authentication mechanisms &MAY; rely on the values of header fields
2611    not listed here.
2612  </t>
2613</x:note>
2614<t>
2615   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2616   though it &MAY; change the message-body through application or removal
2617   of a transfer-coding (<xref target="transfer.codings"/>).
2618</t>
2619</section>
2620
2621</section>
2622
2623<section title="Practical Considerations" anchor="persistent.practical">
2624<t>
2625   Servers will usually have some time-out value beyond which they will
2626   no longer maintain an inactive connection. Proxy servers might make
2627   this a higher value since it is likely that the client will be making
2628   more connections through the same server. The use of persistent
2629   connections places no requirements on the length (or existence) of
2630   this time-out for either the client or the server.
2631</t>
2632<t>
2633   When a client or server wishes to time-out it &SHOULD; issue a graceful
2634   close on the transport connection. Clients and servers &SHOULD; both
2635   constantly watch for the other side of the transport close, and
2636   respond to it as appropriate. If a client or server does not detect
2637   the other side's close promptly it could cause unnecessary resource
2638   drain on the network.
2639</t>
2640<t>
2641   A client, server, or proxy &MAY; close the transport connection at any
2642   time. For example, a client might have started to send a new request
2643   at the same time that the server has decided to close the "idle"
2644   connection. From the server's point of view, the connection is being
2645   closed while it was idle, but from the client's point of view, a
2646   request is in progress.
2647</t>
2648<t>
2649   Clients (including proxies) &SHOULD; limit the number of simultaneous
2650   connections that they maintain to a given server (including proxies).
2651</t>
2652<t>
2653   Previous revisions of HTTP gave a specific number of connections as a
2654   ceiling, but this was found to be impractical for many applications. As a
2655   result, this specification does not mandate a particular maximum number of
2656   connections, but instead encourages clients to be conservative when opening
2657   multiple connections.
2658</t>
2659<t>
2660   In particular, while using multiple connections avoids the "head-of-line
2661   blocking" problem (whereby a request that takes significant server-side
2662   processing and/or has a large payload can block subsequent requests on the
2663   same connection), each connection used consumes server resources (sometimes
2664   significantly), and furthermore using multiple connections can cause
2665   undesirable side effects in congested networks.
2666</t>
2667<t>
2668   Note that servers might reject traffic that they deem abusive, including an
2669   excessive number of connections from a client.
2670</t>
2671</section>
2672
2673<section title="Retrying Requests" anchor="persistent.retrying.requests">
2674<t>
2675   Senders can close the transport connection at any time. Therefore,
2676   clients, servers, and proxies &MUST; be able to recover
2677   from asynchronous close events. Client software &MAY; reopen the
2678   transport connection and retransmit the aborted sequence of requests
2679   without user interaction so long as the request sequence is
2680   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2681   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2682   human operator the choice of retrying the request(s). Confirmation by
2683   user-agent software with semantic understanding of the application
2684   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2685   be repeated if the second sequence of requests fails.
2686</t>
2687</section>
2688
2689</section>
2690
2691<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2692
2693<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2694<t>
2695   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2696   flow control mechanisms to resolve temporary overloads, rather than
2697   terminating connections with the expectation that clients will retry.
2698   The latter technique can exacerbate network congestion.
2699</t>
2700</section>
2701
2702<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2703<t>
2704   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2705   the network connection for an error status code while it is transmitting
2706   the request. If the client sees an error status code, it &SHOULD;
2707   immediately cease transmitting the body. If the body is being sent
2708   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2709   empty trailer &MAY; be used to prematurely mark the end of the message.
2710   If the body was preceded by a Content-Length header field, the client &MUST;
2711   close the connection.
2712</t>
2713</section>
2714
2715<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2716<t>
2717   The purpose of the 100 (Continue) status code (see &status-100;) is to
2718   allow a client that is sending a request message with a request body
2719   to determine if the origin server is willing to accept the request
2720   (based on the request header fields) before the client sends the request
2721   body. In some cases, it might either be inappropriate or highly
2722   inefficient for the client to send the body if the server will reject
2723   the message without looking at the body.
2724</t>
2725<t>
2726   Requirements for HTTP/1.1 clients:
2727  <list style="symbols">
2728    <t>
2729        If a client will wait for a 100 (Continue) response before
2730        sending the request body, it &MUST; send an Expect header
2731        field (&header-expect;) with the "100-continue" expectation.
2732    </t>
2733    <t>
2734        A client &MUST-NOT; send an Expect header field (&header-expect;)
2735        with the "100-continue" expectation if it does not intend
2736        to send a request body.
2737    </t>
2738  </list>
2739</t>
2740<t>
2741   Because of the presence of older implementations, the protocol allows
2742   ambiguous situations in which a client might send "Expect: 100-continue"
2743   without receiving either a 417 (Expectation Failed)
2744   or a 100 (Continue) status code. Therefore, when a client sends this
2745   header field to an origin server (possibly via a proxy) from which it
2746   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2747   wait for an indefinite period before sending the request body.
2748</t>
2749<t>
2750   Requirements for HTTP/1.1 origin servers:
2751  <list style="symbols">
2752    <t> Upon receiving a request which includes an Expect header
2753        field with the "100-continue" expectation, an origin server &MUST;
2754        either respond with 100 (Continue) status code and continue to read
2755        from the input stream, or respond with a final status code. The
2756        origin server &MUST-NOT; wait for the request body before sending
2757        the 100 (Continue) response. If it responds with a final status
2758        code, it &MAY; close the transport connection or it &MAY; continue
2759        to read and discard the rest of the request.  It &MUST-NOT;
2760        perform the request method if it returns a final status code.
2761    </t>
2762    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2763        the request message does not include an Expect header
2764        field with the "100-continue" expectation, and &MUST-NOT; send a
2765        100 (Continue) response if such a request comes from an HTTP/1.0
2766        (or earlier) client. There is an exception to this rule: for
2767        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2768        status code in response to an HTTP/1.1 PUT or POST request that does
2769        not include an Expect header field with the "100-continue"
2770        expectation. This exception, the purpose of which is
2771        to minimize any client processing delays associated with an
2772        undeclared wait for 100 (Continue) status code, applies only to
2773        HTTP/1.1 requests, and not to requests with any other HTTP-version
2774        value.
2775    </t>
2776    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2777        already received some or all of the request body for the
2778        corresponding request.
2779    </t>
2780    <t> An origin server that sends a 100 (Continue) response &MUST;
2781    ultimately send a final status code, once the request body is
2782        received and processed, unless it terminates the transport
2783        connection prematurely.
2784    </t>
2785    <t> If an origin server receives a request that does not include an
2786        Expect header field with the "100-continue" expectation,
2787        the request includes a request body, and the server responds
2788        with a final status code before reading the entire request body
2789        from the transport connection, then the server &SHOULD-NOT;  close
2790        the transport connection until it has read the entire request,
2791        or until the client closes the connection. Otherwise, the client
2792        might not reliably receive the response message. However, this
2793        requirement ought not be construed as preventing a server from
2794        defending itself against denial-of-service attacks, or from
2795        badly broken client implementations.
2796      </t>
2797    </list>
2798</t>
2799<t>
2800   Requirements for HTTP/1.1 proxies:
2801  <list style="symbols">
2802    <t> If a proxy receives a request that includes an Expect header
2803        field with the "100-continue" expectation, and the proxy
2804        either knows that the next-hop server complies with HTTP/1.1 or
2805        higher, or does not know the HTTP version of the next-hop
2806        server, it &MUST; forward the request, including the Expect header
2807        field.
2808    </t>
2809    <t> If the proxy knows that the version of the next-hop server is
2810        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2811        respond with a 417 (Expectation Failed) status code.
2812    </t>
2813    <t> Proxies &SHOULD; maintain a record of the HTTP version
2814        numbers received from recently-referenced next-hop servers.
2815    </t>
2816    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2817        request message was received from an HTTP/1.0 (or earlier)
2818        client and did not include an Expect header field with
2819        the "100-continue" expectation. This requirement overrides the
2820        general rule for forwarding of 1xx responses (see &status-1xx;).
2821    </t>
2822  </list>
2823</t>
2824</section>
2825
2826</section>
2827</section>
2828
2829
2830<section title="Miscellaneous notes that might disappear" anchor="misc">
2831<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2832<t>
2833   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2834</t>
2835</section>
2836
2837<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2838<t>
2839   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2840</t>
2841</section>
2842
2843<section title="Interception of HTTP for access control" anchor="http.intercept">
2844<t>
2845   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2846</t>
2847</section>
2848
2849<section title="Use of HTTP by other protocols" anchor="http.others">
2850<t>
2851   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2852   Extensions of HTTP like WebDAV.</cref>
2853</t>
2854
2855</section>
2856<section title="Use of HTTP by media type specification" anchor="http.media">
2857<t>
2858   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2859</t>
2860</section>
2861</section>
2862
2863<section title="Header Field Definitions" anchor="header.field.definitions">
2864<t>
2865   This section defines the syntax and semantics of HTTP header fields
2866   related to message origination, framing, and routing.
2867</t>
2868<texttable align="left">
2869  <ttcol>Header Field Name</ttcol>
2870  <ttcol>Defined in...</ttcol>
2871 
2872  <c>Connection</c> <c><xref target="header.connection"/></c>
2873  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
2874  <c>Host</c> <c><xref target="header.host"/></c>
2875  <c>TE</c> <c><xref target="header.te"/></c>
2876  <c>Trailer</c> <c><xref target="header.trailer"/></c>
2877  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
2878  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
2879  <c>Via</c> <c><xref target="header.via"/></c>
2880</texttable>
2881
2882<section title="Connection" anchor="header.connection">
2883  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2884  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2885  <x:anchor-alias value="Connection"/>
2886  <x:anchor-alias value="connection-token"/>
2887<t>
2888   The "Connection" header field allows the sender to specify
2889   options that are desired only for that particular connection.
2890   Such connection options &MUST; be removed or replaced before the
2891   message can be forwarded downstream by a proxy or gateway.
2892   This mechanism also allows the sender to indicate which HTTP
2893   header fields used in the message are only intended for the
2894   immediate recipient ("hop-by-hop"), as opposed to all recipients
2895   on the chain ("end-to-end"), enabling the message to be
2896   self-descriptive and allowing future connection-specific extensions
2897   to be deployed in HTTP without fear that they will be blindly
2898   forwarded by previously deployed intermediaries.
2899</t>
2900<t>
2901   The Connection header field's value has the following grammar:
2902</t>
2903<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2904  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2905  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2906</artwork></figure>
2907<t>
2908   A proxy or gateway &MUST; parse a received Connection
2909   header field before a message is forwarded and, for each
2910   connection-token in this field, remove any header field(s) from
2911   the message with the same name as the connection-token, and then
2912   remove the Connection header field itself or replace it with the
2913   sender's own connection options for the forwarded message.
2914</t>
2915<t>
2916   A sender &MUST-NOT; include field-names in the Connection header
2917   field-value for fields that are defined as expressing constraints
2918   for all recipients in the request or response chain, such as the
2919   Cache-Control header field (&header-cache-control;).
2920</t>
2921<t>
2922   The connection options do not have to correspond to a header field
2923   present in the message, since a connection-specific header field
2924   might not be needed if there are no parameters associated with that
2925   connection option.  Recipients that trigger certain connection
2926   behavior based on the presence of connection options &MUST; do so
2927   based on the presence of the connection-token rather than only the
2928   presence of the optional header field.  In other words, if the
2929   connection option is received as a header field but not indicated
2930   within the Connection field-value, then the recipient &MUST; ignore
2931   the connection-specific header field because it has likely been
2932   forwarded by an intermediary that is only partially conformant.
2933</t>
2934<t>
2935   When defining new connection options, specifications ought to
2936   carefully consider existing deployed header fields and ensure
2937   that the new connection-token does not share the same name as
2938   an unrelated header field that might already be deployed.
2939   Defining a new connection-token essentially reserves that potential
2940   field-name for carrying additional information related to the
2941   connection option, since it would be unwise for senders to use
2942   that field-name for anything else.
2943</t>
2944<t>
2945   HTTP/1.1 defines the "close" connection option for the sender to
2946   signal that the connection will be closed after completion of the
2947   response. For example,
2948</t>
2949<figure><artwork type="example">
2950  Connection: close
2951</artwork></figure>
2952<t>
2953   in either the request or the response header fields indicates that
2954   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2955   after the current request/response is complete.
2956</t>
2957<t>
2958   An HTTP/1.1 client that does not support persistent connections &MUST;
2959   include the "close" connection option in every request message.
2960</t>
2961<t>
2962   An HTTP/1.1 server that does not support persistent connections &MUST;
2963   include the "close" connection option in every response message that
2964   does not have a 1xx (Informational) status code.
2965</t>
2966</section>
2967
2968<section title="Content-Length" anchor="header.content-length">
2969  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
2970  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
2971  <x:anchor-alias value="Content-Length"/>
2972<t>
2973   The "Content-Length" header field indicates the size of the
2974   message-body, in decimal number of octets, for any message other than
2975   a response to a HEAD request or a response with a status code of 304.
2976   In the case of a response to a HEAD request, Content-Length indicates
2977   the size of the payload body (not including any potential transfer-coding)
2978   that would have been sent had the request been a GET.
2979   In the case of a 304 (Not Modified) response to a GET request,
2980   Content-Length indicates the size of the payload body (not including
2981   any potential transfer-coding) that would have been sent in a 200 (OK)
2982   response.
2983</t>
2984<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2985  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
2986</artwork></figure>
2987<t>
2988   An example is
2989</t>
2990<figure><artwork type="example">
2991  Content-Length: 3495
2992</artwork></figure>
2993<t>
2994   Implementations &SHOULD; use this field to indicate the message-body
2995   length when no transfer-coding is being applied and the
2996   payload's body length can be determined prior to being transferred.
2997   <xref target="message.body"/> describes how recipients determine the length
2998   of a message-body.
2999</t>
3000<t>
3001   Any Content-Length greater than or equal to zero is a valid value.
3002</t>
3003<t>
3004   Note that the use of this field in HTTP is significantly different from
3005   the corresponding definition in MIME, where it is an optional field
3006   used within the "message/external-body" content-type.
3007</t>
3008</section>
3009
3010<section title="Host" anchor="header.host">
3011  <iref primary="true" item="Host header field" x:for-anchor=""/>
3012  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3013  <x:anchor-alias value="Host"/>
3014<t>
3015   The "Host" header field in a request provides the host and port
3016   information from the target resource's URI, enabling the origin
3017   server to distinguish between resources while servicing requests
3018   for multiple host names on a single IP address.  Since the Host
3019   field-value is critical information for handling a request, it
3020   &SHOULD; be sent as the first header field following the Request-Line.
3021</t>
3022<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3023  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3024</artwork></figure>
3025<t>
3026   A client &MUST; send a Host header field in all HTTP/1.1 request
3027   messages.  If the target resource's URI includes an authority
3028   component, then the Host field-value &MUST; be identical to that
3029   authority component after excluding any userinfo (<xref target="http.uri"/>).
3030   If the authority component is missing or undefined for the target
3031   resource's URI, then the Host header field &MUST; be sent with an
3032   empty field-value.
3033</t>
3034<t>
3035   For example, a GET request to the origin server for
3036   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3037</t>
3038<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3039GET /pub/WWW/ HTTP/1.1
3040Host: www.example.org
3041</artwork></figure>
3042<t>
3043   The Host header field &MUST; be sent in an HTTP/1.1 request even
3044   if the request-target is in the form of an absolute-URI, since this
3045   allows the Host information to be forwarded through ancient HTTP/1.0
3046   proxies that might not have implemented Host.
3047</t>
3048<t>
3049   When an HTTP/1.1 proxy receives a request with a request-target in
3050   the form of an absolute-URI, the proxy &MUST; ignore the received
3051   Host header field (if any) and instead replace it with the host
3052   information of the request-target.  When a proxy forwards a request,
3053   it &MUST; generate the Host header field based on the received
3054   absolute-URI rather than the received Host.
3055</t>
3056<t>
3057   Since the Host header field acts as an application-level routing
3058   mechanism, it is a frequent target for malware seeking to poison
3059   a shared cache or redirect a request to an unintended server.
3060   An interception proxy is particularly vulnerable if it relies on
3061   the Host header field value for redirecting requests to internal
3062   servers, or for use as a cache key in a shared cache, without
3063   first verifying that the intercepted connection is targeting a
3064   valid IP address for that host.
3065</t>
3066<t>
3067   A server &MUST; respond with a 400 (Bad Request) status code to
3068   any HTTP/1.1 request message that lacks a Host header field and
3069   to any request message that contains more than one Host header field
3070   or a Host header field with an invalid field-value.
3071</t>
3072<t>
3073   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3074   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3075   for other requirements relating to Host.
3076</t>
3077</section>
3078
3079<section title="TE" anchor="header.te">
3080  <iref primary="true" item="TE header field" x:for-anchor=""/>
3081  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3082  <x:anchor-alias value="TE"/>
3083  <x:anchor-alias value="t-codings"/>
3084  <x:anchor-alias value="te-params"/>
3085  <x:anchor-alias value="te-ext"/>
3086<t>
3087   The "TE" header field indicates what extension transfer-codings
3088   the client is willing to accept in the response, and whether or not it is
3089   willing to accept trailer fields in a chunked transfer-coding.
3090</t>
3091<t>
3092   Its value consists of the keyword "trailers" and/or a comma-separated
3093   list of extension transfer-coding names with optional accept
3094   parameters (as described in <xref target="transfer.codings"/>).
3095</t>
3096<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"/>
3097  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3098  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3099  <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> )
3100  <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> ]
3101</artwork></figure>
3102<t>
3103   The presence of the keyword "trailers" indicates that the client is
3104   willing to accept trailer fields in a chunked transfer-coding, as
3105   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3106   transfer-coding values even though it does not itself represent a
3107   transfer-coding.
3108</t>
3109<t>
3110   Examples of its use are:
3111</t>
3112<figure><artwork type="example">
3113  TE: deflate
3114  TE:
3115  TE: trailers, deflate;q=0.5
3116</artwork></figure>
3117<t>
3118   The TE header field only applies to the immediate connection.
3119   Therefore, the keyword &MUST; be supplied within a Connection header
3120   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3121</t>
3122<t>
3123   A server tests whether a transfer-coding is acceptable, according to
3124   a TE field, using these rules:
3125  <list style="numbers">
3126    <x:lt>
3127      <t>The "chunked" transfer-coding is always acceptable. If the
3128         keyword "trailers" is listed, the client indicates that it is
3129         willing to accept trailer fields in the chunked response on
3130         behalf of itself and any downstream clients. The implication is
3131         that, if given, the client is stating that either all
3132         downstream clients are willing to accept trailer fields in the
3133         forwarded response, or that it will attempt to buffer the
3134         response on behalf of downstream recipients.
3135      </t><t>
3136         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3137         chunked response such that a client can be assured of buffering
3138         the entire response.</t>
3139    </x:lt>
3140    <x:lt>
3141      <t>If the transfer-coding being tested is one of the transfer-codings
3142         listed in the TE field, then it is acceptable unless it
3143         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3144         qvalue of 0 means "not acceptable".)</t>
3145    </x:lt>
3146    <x:lt>
3147      <t>If multiple transfer-codings are acceptable, then the
3148         acceptable transfer-coding with the highest non-zero qvalue is
3149         preferred.  The "chunked" transfer-coding always has a qvalue
3150         of 1.</t>
3151    </x:lt>
3152  </list>
3153</t>
3154<t>
3155   If the TE field-value is empty or if no TE field is present, the only
3156   acceptable transfer-coding is "chunked". A message with no transfer-coding is
3157   always acceptable.
3158</t>
3159</section>
3160
3161<section title="Trailer" anchor="header.trailer">
3162  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3163  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3164  <x:anchor-alias value="Trailer"/>
3165<t>
3166   The "Trailer" header field indicates that the given set of
3167   header fields is present in the trailer of a message encoded with
3168   chunked transfer-coding.
3169</t>
3170<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3171  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3172</artwork></figure>
3173<t>
3174   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3175   message using chunked transfer-coding with a non-empty trailer. Doing
3176   so allows the recipient to know which header fields to expect in the
3177   trailer.
3178</t>
3179<t>
3180   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3181   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3182   trailer fields in a "chunked" transfer-coding.
3183</t>
3184<t>
3185   Message header fields listed in the Trailer header field &MUST-NOT;
3186   include the following header fields:
3187  <list style="symbols">
3188    <t>Transfer-Encoding</t>
3189    <t>Content-Length</t>
3190    <t>Trailer</t>
3191  </list>
3192</t>
3193</section>
3194
3195<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3196  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3197  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3198  <x:anchor-alias value="Transfer-Encoding"/>
3199<t>
3200   The "Transfer-Encoding" header field indicates what transfer-codings
3201   (if any) have been applied to the message body. It differs from
3202   Content-Encoding (&content-codings;) in that transfer-codings are a property
3203   of the message (and therefore are removed by intermediaries), whereas
3204   content-codings are not.
3205</t>
3206<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3207  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3208</artwork></figure>
3209<t>
3210   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3211</t>
3212<figure><artwork type="example">
3213  Transfer-Encoding: chunked
3214</artwork></figure>
3215<t>
3216   If multiple encodings have been applied to a representation, the transfer-codings
3217   &MUST; be listed in the order in which they were applied.
3218   Additional information about the encoding parameters &MAY; be provided
3219   by other header fields not defined by this specification.
3220</t>
3221<t>
3222   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3223   header field.
3224</t>
3225</section>
3226
3227<section title="Upgrade" anchor="header.upgrade">
3228  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3229  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3230  <x:anchor-alias value="Upgrade"/>
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>product</x:ref>
3239</artwork></figure>
3240<t>
3241   For example,
3242</t>
3243<figure><artwork type="example">
3244  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3245</artwork></figure>
3246<t>
3247   The Upgrade header field is intended to provide a simple mechanism
3248   for transitioning from HTTP/1.1 to some other, incompatible protocol. It
3249   does so by allowing the client to advertise its desire to use another
3250   protocol, such as a later version of HTTP with a higher major version
3251   number, even though the current request has been made using HTTP/1.1.
3252   This eases the difficult transition between incompatible protocols by
3253   allowing the client to initiate a request in the more commonly
3254   supported protocol while indicating to the server that it would like
3255   to use a "better" protocol if available (where "better" is determined
3256   by the server, possibly according to the nature of the request method
3257   or target resource).
3258</t>
3259<t>
3260   The Upgrade header field only applies to switching application-layer
3261   protocols upon the existing transport-layer connection. Upgrade
3262   cannot be used to insist on a protocol change; its acceptance and use
3263   by the server is optional. The capabilities and nature of the
3264   application-layer communication after the protocol change is entirely
3265   dependent upon the new protocol chosen, although the first action
3266   after changing the protocol &MUST; be a response to the initial HTTP
3267   request containing the Upgrade header field.
3268</t>
3269<t>
3270   The Upgrade header field only applies to the immediate connection.
3271   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3272   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3273   HTTP/1.1 message.
3274</t>
3275<t>
3276   The Upgrade header field cannot be used to indicate a switch to a
3277   protocol on a different connection. For that purpose, it is more
3278   appropriate to use a 3xx redirection response (&status-3xx;).
3279</t>
3280<t>
3281   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3282   Protocols) responses to indicate which protocol(s) are being switched to,
3283   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3284   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3285   response to indicate that they are willing to upgrade to one of the
3286   specified protocols.
3287</t>
3288<t>
3289   This specification only defines the protocol name "HTTP" for use by
3290   the family of Hypertext Transfer Protocols, as defined by the HTTP
3291   version rules of <xref target="http.version"/> and future updates to this
3292   specification. Additional tokens can be registered with IANA using the
3293   registration procedure defined below. 
3294</t>
3295
3296<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3297<t>
3298   The HTTP Upgrade Token Registry defines the name space for product
3299   tokens used to identify protocols in the Upgrade header field.
3300   Each registered token is associated with contact information and
3301   an optional set of specifications that details how the connection
3302   will be processed after it has been upgraded.
3303</t>
3304<t>
3305   Registrations are allowed on a First Come First Served basis as
3306   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3307   specifications need not be IETF documents or be subject to IESG review.
3308   Registrations are subject to the following rules:
3309  <list style="numbers">
3310    <t>A token, once registered, stays registered forever.</t>
3311    <t>The registration &MUST; name a responsible party for the
3312       registration.</t>
3313    <t>The registration &MUST; name a point of contact.</t>
3314    <t>The registration &MAY; name a set of specifications associated with that
3315       token. Such specifications need not be publicly available.</t>
3316    <t>The responsible party &MAY; change the registration at any time.
3317       The IANA will keep a record of all such changes, and make them
3318       available upon request.</t>
3319    <t>The responsible party for the first registration of a "product"
3320       token &MUST; approve later registrations of a "version" token
3321       together with that "product" token before they can be registered.</t>
3322    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3323       for a token. This will normally only be used in the case when a
3324       responsible party cannot be contacted.</t>
3325  </list>
3326</t>
3327</section>
3328
3329
3330</section>
3331
3332<section title="Via" anchor="header.via">
3333  <iref primary="true" item="Via header field" x:for-anchor=""/>
3334  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3335  <x:anchor-alias value="protocol-name"/>
3336  <x:anchor-alias value="protocol-version"/>
3337  <x:anchor-alias value="pseudonym"/>
3338  <x:anchor-alias value="received-by"/>
3339  <x:anchor-alias value="received-protocol"/>
3340  <x:anchor-alias value="Via"/>
3341<t>
3342   The "Via" header field &MUST; be sent by a proxy or gateway to
3343   indicate the intermediate protocols and recipients between the user
3344   agent and the server on requests, and between the origin server and
3345   the client on responses. It is analogous to the "Received" field
3346   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3347   and is intended to be used for tracking message forwards,
3348   avoiding request loops, and identifying the protocol capabilities of
3349   all senders along the request/response chain.
3350</t>
3351<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"/>
3352  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3353                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3354  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3355  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3356  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3357  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3358  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3359</artwork></figure>
3360<t>
3361   The received-protocol indicates the protocol version of the message
3362   received by the server or client along each segment of the
3363   request/response chain. The received-protocol version is appended to
3364   the Via field value when the message is forwarded so that information
3365   about the protocol capabilities of upstream applications remains
3366   visible to all recipients.
3367</t>
3368<t>
3369   The protocol-name is excluded if and only if it would be "HTTP". The
3370   received-by field is normally the host and optional port number of a
3371   recipient server or client that subsequently forwarded the message.
3372   However, if the real host is considered to be sensitive information,
3373   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3374   be assumed to be the default port of the received-protocol.
3375</t>
3376<t>
3377   Multiple Via field values represent each proxy or gateway that has
3378   forwarded the message. Each recipient &MUST; append its information
3379   such that the end result is ordered according to the sequence of
3380   forwarding applications.
3381</t>
3382<t>
3383   Comments &MAY; be used in the Via header field to identify the software
3384   of each recipient, analogous to the User-Agent and Server header fields.
3385   However, all comments in the Via field are optional and &MAY; be removed
3386   by any recipient prior to forwarding the message.
3387</t>
3388<t>
3389   For example, a request message could be sent from an HTTP/1.0 user
3390   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3391   forward the request to a public proxy at p.example.net, which completes
3392   the request by forwarding it to the origin server at www.example.com.
3393   The request received by www.example.com would then have the following
3394   Via header field:
3395</t>
3396<figure><artwork type="example">
3397  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3398</artwork></figure>
3399<t>
3400   A proxy or gateway used as a portal through a network firewall
3401   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3402   region unless it is explicitly enabled to do so. If not enabled, the
3403   received-by host of any host behind the firewall &SHOULD; be replaced
3404   by an appropriate pseudonym for that host.
3405</t>
3406<t>
3407   For organizations that have strong privacy requirements for hiding
3408   internal structures, a proxy or gateway &MAY; combine an ordered
3409   subsequence of Via header field entries with identical received-protocol
3410   values into a single such entry. For example,
3411</t>
3412<figure><artwork type="example">
3413  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3414</artwork></figure>
3415<t>
3416  could be collapsed to
3417</t>
3418<figure><artwork type="example">
3419  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3420</artwork></figure>
3421<t>
3422   Senders &SHOULD-NOT; combine multiple entries unless they are all
3423   under the same organizational control and the hosts have already been
3424   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3425   have different received-protocol values.
3426</t>
3427</section>
3428
3429</section>
3430
3431<section title="IANA Considerations" anchor="IANA.considerations">
3432
3433<section title="Header Field Registration" anchor="header.field.registration">
3434<t>
3435   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3436   with the permanent registrations below (see <xref target="RFC3864"/>):
3437</t>
3438<?BEGININC p1-messaging.iana-headers ?>
3439<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3440<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3441   <ttcol>Header Field Name</ttcol>
3442   <ttcol>Protocol</ttcol>
3443   <ttcol>Status</ttcol>
3444   <ttcol>Reference</ttcol>
3445
3446   <c>Connection</c>
3447   <c>http</c>
3448   <c>standard</c>
3449   <c>
3450      <xref target="header.connection"/>
3451   </c>
3452   <c>Content-Length</c>
3453   <c>http</c>
3454   <c>standard</c>
3455   <c>
3456      <xref target="header.content-length"/>
3457   </c>
3458   <c>Host</c>
3459   <c>http</c>
3460   <c>standard</c>
3461   <c>
3462      <xref target="header.host"/>
3463   </c>
3464   <c>TE</c>
3465   <c>http</c>
3466   <c>standard</c>
3467   <c>
3468      <xref target="header.te"/>
3469   </c>
3470   <c>Trailer</c>
3471   <c>http</c>
3472   <c>standard</c>
3473   <c>
3474      <xref target="header.trailer"/>
3475   </c>
3476   <c>Transfer-Encoding</c>
3477   <c>http</c>
3478   <c>standard</c>
3479   <c>
3480      <xref target="header.transfer-encoding"/>
3481   </c>
3482   <c>Upgrade</c>
3483   <c>http</c>
3484   <c>standard</c>
3485   <c>
3486      <xref target="header.upgrade"/>
3487   </c>
3488   <c>Via</c>
3489   <c>http</c>
3490   <c>standard</c>
3491   <c>
3492      <xref target="header.via"/>
3493   </c>
3494</texttable>
3495<!--(END)-->
3496<?ENDINC p1-messaging.iana-headers ?>
3497<t>
3498   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3499   HTTP header field would be in conflict with the use of the "close" connection
3500   option for the "Connection" header field (<xref target="header.connection"/>).
3501</t>
3502<texttable align="left" suppress-title="true">
3503   <ttcol>Header Field Name</ttcol>
3504   <ttcol>Protocol</ttcol>
3505   <ttcol>Status</ttcol>
3506   <ttcol>Reference</ttcol>
3507
3508   <c>Close</c>
3509   <c>http</c>
3510   <c>reserved</c>
3511   <c>
3512      <xref target="header.field.registration"/>
3513   </c>
3514</texttable>
3515<t>
3516   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3517</t>
3518</section>
3519
3520<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3521<t>
3522   The entries for the "http" and "https" URI Schemes in the registry located at
3523   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3524   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3525   and <xref target="https.uri" format="counter"/> of this document
3526   (see <xref target="RFC4395"/>).
3527</t>
3528</section>
3529
3530<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3531<t>
3532   This document serves as the specification for the Internet media types
3533   "message/http" and "application/http". The following is to be registered with
3534   IANA (see <xref target="RFC4288"/>).
3535</t>
3536<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3537<iref item="Media Type" subitem="message/http" primary="true"/>
3538<iref item="message/http Media Type" primary="true"/>
3539<t>
3540   The message/http type can be used to enclose a single HTTP request or
3541   response message, provided that it obeys the MIME restrictions for all
3542   "message" types regarding line length and encodings.
3543</t>
3544<t>
3545  <list style="hanging" x:indent="12em">
3546    <t hangText="Type name:">
3547      message
3548    </t>
3549    <t hangText="Subtype name:">
3550      http
3551    </t>
3552    <t hangText="Required parameters:">
3553      none
3554    </t>
3555    <t hangText="Optional parameters:">
3556      version, msgtype
3557      <list style="hanging">
3558        <t hangText="version:">
3559          The HTTP-Version number of the enclosed message
3560          (e.g., "1.1"). If not present, the version can be
3561          determined from the first line of the body.
3562        </t>
3563        <t hangText="msgtype:">
3564          The message type &mdash; "request" or "response". If not
3565          present, the type can be determined from the first
3566          line of the body.
3567        </t>
3568      </list>
3569    </t>
3570    <t hangText="Encoding considerations:">
3571      only "7bit", "8bit", or "binary" are permitted
3572    </t>
3573    <t hangText="Security considerations:">
3574      none
3575    </t>
3576    <t hangText="Interoperability considerations:">
3577      none
3578    </t>
3579    <t hangText="Published specification:">
3580      This specification (see <xref target="internet.media.type.message.http"/>).
3581    </t>
3582    <t hangText="Applications that use this media type:">
3583    </t>
3584    <t hangText="Additional information:">
3585      <list style="hanging">
3586        <t hangText="Magic number(s):">none</t>
3587        <t hangText="File extension(s):">none</t>
3588        <t hangText="Macintosh file type code(s):">none</t>
3589      </list>
3590    </t>
3591    <t hangText="Person and email address to contact for further information:">
3592      See Authors Section.
3593    </t>
3594    <t hangText="Intended usage:">
3595      COMMON
3596    </t>
3597    <t hangText="Restrictions on usage:">
3598      none
3599    </t>
3600    <t hangText="Author/Change controller:">
3601      IESG
3602    </t>
3603  </list>
3604</t>
3605</section>
3606<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3607<iref item="Media Type" subitem="application/http" primary="true"/>
3608<iref item="application/http Media Type" primary="true"/>
3609<t>
3610   The application/http type can be used to enclose a pipeline of one or more
3611   HTTP request or response messages (not intermixed).
3612</t>
3613<t>
3614  <list style="hanging" x:indent="12em">
3615    <t hangText="Type name:">
3616      application
3617    </t>
3618    <t hangText="Subtype name:">
3619      http
3620    </t>
3621    <t hangText="Required parameters:">
3622      none
3623    </t>
3624    <t hangText="Optional parameters:">
3625      version, msgtype
3626      <list style="hanging">
3627        <t hangText="version:">
3628          The HTTP-Version number of the enclosed messages
3629          (e.g., "1.1"). If not present, the version can be
3630          determined from the first line of the body.
3631        </t>
3632        <t hangText="msgtype:">
3633          The message type &mdash; "request" or "response". If not
3634          present, the type can be determined from the first
3635          line of the body.
3636        </t>
3637      </list>
3638    </t>
3639    <t hangText="Encoding considerations:">
3640      HTTP messages enclosed by this type
3641      are in "binary" format; use of an appropriate
3642      Content-Transfer-Encoding is required when
3643      transmitted via E-mail.
3644    </t>
3645    <t hangText="Security considerations:">
3646      none
3647    </t>
3648    <t hangText="Interoperability considerations:">
3649      none
3650    </t>
3651    <t hangText="Published specification:">
3652      This specification (see <xref target="internet.media.type.application.http"/>).
3653    </t>
3654    <t hangText="Applications that use this media type:">
3655    </t>
3656    <t hangText="Additional information:">
3657      <list style="hanging">
3658        <t hangText="Magic number(s):">none</t>
3659        <t hangText="File extension(s):">none</t>
3660        <t hangText="Macintosh file type code(s):">none</t>
3661      </list>
3662    </t>
3663    <t hangText="Person and email address to contact for further information:">
3664      See Authors Section.
3665    </t>
3666    <t hangText="Intended usage:">
3667      COMMON
3668    </t>
3669    <t hangText="Restrictions on usage:">
3670      none
3671    </t>
3672    <t hangText="Author/Change controller:">
3673      IESG
3674    </t>
3675  </list>
3676</t>
3677</section>
3678</section>
3679
3680<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3681<t>
3682   The registration procedure for HTTP Transfer Codings is now defined by
3683   <xref target="transfer.coding.registry"/> of this document.
3684</t>
3685<t>
3686   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3687   shall be updated with the registrations below:
3688</t>
3689<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3690   <ttcol>Name</ttcol>
3691   <ttcol>Description</ttcol>
3692   <ttcol>Reference</ttcol>
3693   <c>chunked</c>
3694   <c>Transfer in a series of chunks</c>
3695   <c>
3696      <xref target="chunked.encoding"/>
3697   </c>
3698   <c>compress</c>
3699   <c>UNIX "compress" program method</c>
3700   <c>
3701      <xref target="compress.coding"/>
3702   </c>
3703   <c>deflate</c>
3704   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3705   the "zlib" data format (<xref target="RFC1950"/>)
3706   </c>
3707   <c>
3708      <xref target="deflate.coding"/>
3709   </c>
3710   <c>gzip</c>
3711   <c>Same as GNU zip <xref target="RFC1952"/></c>
3712   <c>
3713      <xref target="gzip.coding"/>
3714   </c>
3715</texttable>
3716</section>
3717
3718<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3719<t>
3720   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3721   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3722   by <xref target="upgrade.token.registry"/> of this document.
3723</t>
3724<t>
3725   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3726   shall be updated with the registration below:
3727</t>
3728<texttable align="left" suppress-title="true">
3729   <ttcol>Value</ttcol>
3730   <ttcol>Description</ttcol>
3731   <ttcol>Reference</ttcol>
3732
3733   <c>HTTP</c>
3734   <c>Hypertext Transfer Protocol</c> 
3735   <c><xref target="http.version"/> of this specification</c>
3736
3737</texttable>
3738</section>
3739
3740</section>
3741
3742<section title="Security Considerations" anchor="security.considerations">
3743<t>
3744   This section is meant to inform application developers, information
3745   providers, and users of the security limitations in HTTP/1.1 as
3746   described by this document. The discussion does not include
3747   definitive solutions to the problems revealed, though it does make
3748   some suggestions for reducing security risks.
3749</t>
3750
3751<section title="Personal Information" anchor="personal.information">
3752<t>
3753   HTTP clients are often privy to large amounts of personal information
3754   (e.g., the user's name, location, mail address, passwords, encryption
3755   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3756   leakage of this information.
3757   We very strongly recommend that a convenient interface be provided
3758   for the user to control dissemination of such information, and that
3759   designers and implementors be particularly careful in this area.
3760   History shows that errors in this area often create serious security
3761   and/or privacy problems and generate highly adverse publicity for the
3762   implementor's company.
3763</t>
3764</section>
3765
3766<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3767<t>
3768   A server is in the position to save personal data about a user's
3769   requests which might identify their reading patterns or subjects of
3770   interest. This information is clearly confidential in nature and its
3771   handling can be constrained by law in certain countries. People using
3772   HTTP to provide data are responsible for ensuring that
3773   such material is not distributed without the permission of any
3774   individuals that are identifiable by the published results.
3775</t>
3776</section>
3777
3778<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3779<t>
3780   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3781   the documents returned by HTTP requests to be only those that were
3782   intended by the server administrators. If an HTTP server translates
3783   HTTP URIs directly into file system calls, the server &MUST; take
3784   special care not to serve files that were not intended to be
3785   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3786   other operating systems use ".." as a path component to indicate a
3787   directory level above the current one. On such a system, an HTTP
3788   server &MUST; disallow any such construct in the request-target if it
3789   would otherwise allow access to a resource outside those intended to
3790   be accessible via the HTTP server. Similarly, files intended for
3791   reference only internally to the server (such as access control
3792   files, configuration files, and script code) &MUST; be protected from
3793   inappropriate retrieval, since they might contain sensitive
3794   information. Experience has shown that minor bugs in such HTTP server
3795   implementations have turned into security risks.
3796</t>
3797</section>
3798
3799<section title="DNS-related Attacks" anchor="dns.related.attacks">
3800<t>
3801   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3802   generally prone to security attacks based on the deliberate misassociation
3803   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3804   cautious in assuming the validity of an IP number/DNS name association unless
3805   the response is protected by DNSSec (<xref target="RFC4033"/>).
3806</t>
3807</section>
3808
3809<section title="Proxies and Caching" anchor="attack.proxies">
3810<t>
3811   By their very nature, HTTP proxies are men-in-the-middle, and
3812   represent an opportunity for man-in-the-middle attacks. Compromise of
3813   the systems on which the proxies run can result in serious security
3814   and privacy problems. Proxies have access to security-related
3815   information, personal information about individual users and
3816   organizations, and proprietary information belonging to users and
3817   content providers. A compromised proxy, or a proxy implemented or
3818   configured without regard to security and privacy considerations,
3819   might be used in the commission of a wide range of potential attacks.
3820</t>
3821<t>
3822   Proxy operators need to protect the systems on which proxies run as
3823   they would protect any system that contains or transports sensitive
3824   information. In particular, log information gathered at proxies often
3825   contains highly sensitive personal information, and/or information
3826   about organizations. Log information needs to be carefully guarded, and
3827   appropriate guidelines for use need to be developed and followed.
3828   (<xref target="abuse.of.server.log.information"/>).
3829</t>
3830<t>
3831   Proxy implementors need to consider the privacy and security
3832   implications of their design and coding decisions, and of the
3833   configuration options they provide to proxy operators (especially the
3834   default configuration).
3835</t>
3836<t>
3837   Users of a proxy need to be aware that proxies are no more trustworthy than
3838   the people who run them; HTTP itself cannot solve this problem.
3839</t>
3840<t>
3841   The judicious use of cryptography, when appropriate, might suffice to
3842   protect against a broad range of security and privacy attacks. Such
3843   cryptography is beyond the scope of the HTTP/1.1 specification.
3844</t>
3845</section>
3846
3847<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3848<t>
3849   Because HTTP uses mostly textual, character-delimited fields, attackers can
3850   overflow buffers in implementations, and/or perform a Denial of Service
3851   against implementations that accept fields with unlimited lengths.
3852</t>
3853<t>
3854   To promote interoperability, this specification makes specific
3855   recommendations for size limits on request-targets (<xref target="request-target"/>)
3856   and blocks of header fields (<xref target="header.fields"/>). These are
3857   minimum recommendations, chosen to be supportable even by implementations
3858   with limited resources; it is expected that most implementations will choose
3859   substantially higher limits.
3860</t>
3861<t>
3862   This specification also provides a way for servers to reject messages that
3863   have request-targets that are too long (&status-414;) or request entities
3864   that are too large (&status-4xx;).
3865</t>
3866<t>
3867   Other fields (including but not limited to request methods, response status
3868   phrases, header field-names, and body chunks) &SHOULD; be limited by
3869   implementations carefully, so as to not impede interoperability.
3870</t>
3871</section>
3872
3873<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3874<t>
3875   They exist. They are hard to defend against. Research continues.
3876   Beware.
3877</t>
3878</section>
3879</section>
3880
3881<section title="Acknowledgments" anchor="acks">
3882<t>
3883   This document revision builds on the work that went into
3884   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3885   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
3886   acknowledgements.
3887</t>
3888<t>
3889   Since 1999, many contributors have helped by reporting bugs, asking
3890   smart questions, drafting and reviewing text, and discussing open issues:
3891</t>
3892<?BEGININC acks ?>
3893<t>Adam Barth,
3894Adam Roach,
3895Addison Phillips,
3896Adrian Chadd,
3897Adrien de Croy,
3898Alan Ford,
3899Alan Ruttenberg,
3900Albert Lunde,
3901Alex Rousskov,
3902Alexey Melnikov,
3903Alisha Smith,
3904Amichai Rothman,
3905Amit Klein,
3906Amos Jeffries,
3907Andreas Maier,
3908Andreas Petersson,
3909Anne van Kesteren,
3910Anthony Bryan,
3911Asbjorn Ulsberg,
3912Balachander Krishnamurthy,
3913Barry Leiba,
3914Ben Laurie,
3915Benjamin Niven-Jenkins,
3916Bil Corry,
3917Bill Burke,
3918Bjoern Hoehrmann,
3919Bob Scheifler,
3920Boris Zbarsky,
3921Brett Slatkin,
3922Brian Kell,
3923Brian McBarron,
3924Brian Pane,
3925Brian Smith,
3926Bryce Nesbitt,
3927Cameron Heavon-Jones,
3928Carl Kugler,
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 Moore,
3990Jonathan Rees,
3991Jordi Ros,
3992Joris Dobbelsteen,
3993Josh Cohen,
3994Julien Pierre,
3995Jungshik Shin,
3996Justin Chapweske,
3997Justin Erenkrantz,
3998Justin James,
3999Kalvinder Singh,
4000Karl Dubost,
4001Keith Hoffman,
4002Keith Moore,
4003Koen Holtman,
4004Konstantin Voronkov,
4005Kris Zyp,
4006Lisa Dusseault,
4007Maciej Stachowiak,
4008Marc Schneider,
4009Marc Slemko,
4010Mark Baker,
4011Mark Nottingham (Working Group chair),
4012Mark Pauley,
4013Markus Lanthaler,
4014Martin J. Duerst,
4015Martin Thomson,
4016Matt Lynch,
4017Matthew Cox,
4018Max Clark,
4019Michael Burrows,
4020Michael Hausenblas,
4021Mike Amundsen,
4022Mike Kelly,
4023Mike Schinkel,
4024Miles Sabin,
4025Mykyta Yevstifeyev,
4026Nathan Rixham,
4027Nicholas Shanks,
4028Nico Williams,
4029Nicolas Alvarez,
4030Noah Slater,
4031Pablo Castro,
4032Pat Hayes,
4033Patrick R. McManus,
4034Paul E. Jones,
4035Paul Hoffman,
4036Paul Marquess,
4037Peter Saint-Andre,
4038Peter Watkins,
4039Phil Archer,
4040Phillip Hallam-Baker,
4041Poul-Henning Kamp,
4042Preethi Natarajan,
4043Ray Polk,
4044Reto Bachmann-Gmuer,
4045Richard Cyganiak,
4046Robert Brewer,
4047Robert Collins,
4048Robert O'Callahan,
4049Robert Olofsson,
4050Robert Sayre,
4051Robert Siemer,
4052Robert de Wilde,
4053Roberto Javier Godoy,
4054Ronny Widjaja,
4055S. Mike Dierken,
4056Salvatore Loreto,
4057Sam Johnston,
4058Sam Ruby,
4059Scott Lawrence (for maintaining the original issues list),
4060Sean B. Palmer,
4061Shane McCarron,
4062Stefan Eissing,
4063Stefan Tilkov,
4064Stefanos Harhalakis,
4065Stephane Bortzmeyer,
4066Stuart Williams,
4067Subbu Allamaraju,
4068Sylvain Hellegouarch,
4069Tapan Divekar,
4070Thomas Broyer,
4071Thomas Nordin,
4072Thomas Roessler,
4073Tim Morgan,
4074Tim Olsen,
4075Travis Snoozy,
4076Tyler Close,
4077Vincent Murphy,
4078Wenbo Zhu,
4079Werner Baumann,
4080Wilbur Streett,
4081Wilfredo Sanchez Vega,
4082William A. Rowe Jr.,
4083William Chan,
4084Willy Tarreau,
4085Xiaoshu Wang,
4086Yaron Goland,
4087Yngve Nysaeter Pettersen,
4088Yogesh Bang,
4089Yutaka Oiwa,
4090Zed A. Shaw, and
4091Zhong Yu.
4092</t>
4093<?ENDINC acks ?>
4094</section>
4095
4096</middle>
4097<back>
4098
4099<references title="Normative References">
4100
4101<reference anchor="ISO-8859-1">
4102  <front>
4103    <title>
4104     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4105    </title>
4106    <author>
4107      <organization>International Organization for Standardization</organization>
4108    </author>
4109    <date year="1998"/>
4110  </front>
4111  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4112</reference>
4113
4114<reference anchor="Part2">
4115  <front>
4116    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4117    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4118      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4119      <address><email>fielding@gbiv.com</email></address>
4120    </author>
4121    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4122      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4123      <address><email>jg@freedesktop.org</email></address>
4124    </author>
4125    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4126      <organization abbrev="HP">Hewlett-Packard Company</organization>
4127      <address><email>JeffMogul@acm.org</email></address>
4128    </author>
4129    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4130      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4131      <address><email>henrikn@microsoft.com</email></address>
4132    </author>
4133    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4134      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4135      <address><email>LMM@acm.org</email></address>
4136    </author>
4137    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4138      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4139      <address><email>paulle@microsoft.com</email></address>
4140    </author>
4141    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4142      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4143      <address><email>timbl@w3.org</email></address>
4144    </author>
4145    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4146      <organization abbrev="W3C">World Wide Web Consortium</organization>
4147      <address><email>ylafon@w3.org</email></address>
4148    </author>
4149    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4150      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4151      <address><email>julian.reschke@greenbytes.de</email></address>
4152    </author>
4153    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4154  </front>
4155  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4156  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4157</reference>
4158
4159<reference anchor="Part3">
4160  <front>
4161    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4162    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4163      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4164      <address><email>fielding@gbiv.com</email></address>
4165    </author>
4166    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4167      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4168      <address><email>jg@freedesktop.org</email></address>
4169    </author>
4170    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4171      <organization abbrev="HP">Hewlett-Packard Company</organization>
4172      <address><email>JeffMogul@acm.org</email></address>
4173    </author>
4174    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4175      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4176      <address><email>henrikn@microsoft.com</email></address>
4177    </author>
4178    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4179      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4180      <address><email>LMM@acm.org</email></address>
4181    </author>
4182    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4183      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4184      <address><email>paulle@microsoft.com</email></address>
4185    </author>
4186    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4187      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4188      <address><email>timbl@w3.org</email></address>
4189    </author>
4190    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4191      <organization abbrev="W3C">World Wide Web Consortium</organization>
4192      <address><email>ylafon@w3.org</email></address>
4193    </author>
4194    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4195      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4196      <address><email>julian.reschke@greenbytes.de</email></address>
4197    </author>
4198    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4199  </front>
4200  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4201  <x:source href="p3-payload.xml" basename="p3-payload"/>
4202</reference>
4203
4204<reference anchor="Part6">
4205  <front>
4206    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4207    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4208      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4209      <address><email>fielding@gbiv.com</email></address>
4210    </author>
4211    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4212      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4213      <address><email>jg@freedesktop.org</email></address>
4214    </author>
4215    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4216      <organization abbrev="HP">Hewlett-Packard Company</organization>
4217      <address><email>JeffMogul@acm.org</email></address>
4218    </author>
4219    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4220      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4221      <address><email>henrikn@microsoft.com</email></address>
4222    </author>
4223    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4224      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4225      <address><email>LMM@acm.org</email></address>
4226    </author>
4227    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4228      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4229      <address><email>paulle@microsoft.com</email></address>
4230    </author>
4231    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4232      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4233      <address><email>timbl@w3.org</email></address>
4234    </author>
4235    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4236      <organization abbrev="W3C">World Wide Web Consortium</organization>
4237      <address><email>ylafon@w3.org</email></address>
4238    </author>
4239    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4240      <organization>Rackspace</organization>
4241      <address><email>mnot@mnot.net</email></address>
4242    </author>
4243    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4244      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4245      <address><email>julian.reschke@greenbytes.de</email></address>
4246    </author>
4247    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4248  </front>
4249  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4250  <x:source href="p6-cache.xml" basename="p6-cache"/>
4251</reference>
4252
4253<reference anchor="RFC5234">
4254  <front>
4255    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4256    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4257      <organization>Brandenburg InternetWorking</organization>
4258      <address>
4259        <email>dcrocker@bbiw.net</email>
4260      </address> 
4261    </author>
4262    <author initials="P." surname="Overell" fullname="Paul Overell">
4263      <organization>THUS plc.</organization>
4264      <address>
4265        <email>paul.overell@thus.net</email>
4266      </address>
4267    </author>
4268    <date month="January" year="2008"/>
4269  </front>
4270  <seriesInfo name="STD" value="68"/>
4271  <seriesInfo name="RFC" value="5234"/>
4272</reference>
4273
4274<reference anchor="RFC2119">
4275  <front>
4276    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4277    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4278      <organization>Harvard University</organization>
4279      <address><email>sob@harvard.edu</email></address>
4280    </author>
4281    <date month="March" year="1997"/>
4282  </front>
4283  <seriesInfo name="BCP" value="14"/>
4284  <seriesInfo name="RFC" value="2119"/>
4285</reference>
4286
4287<reference anchor="RFC3986">
4288 <front>
4289  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4290  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4291    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4292    <address>
4293       <email>timbl@w3.org</email>
4294       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4295    </address>
4296  </author>
4297  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4298    <organization abbrev="Day Software">Day Software</organization>
4299    <address>
4300      <email>fielding@gbiv.com</email>
4301      <uri>http://roy.gbiv.com/</uri>
4302    </address>
4303  </author>
4304  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4305    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4306    <address>
4307      <email>LMM@acm.org</email>
4308      <uri>http://larry.masinter.net/</uri>
4309    </address>
4310  </author>
4311  <date month='January' year='2005'></date>
4312 </front>
4313 <seriesInfo name="STD" value="66"/>
4314 <seriesInfo name="RFC" value="3986"/>
4315</reference>
4316
4317<reference anchor="USASCII">
4318  <front>
4319    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4320    <author>
4321      <organization>American National Standards Institute</organization>
4322    </author>
4323    <date year="1986"/>
4324  </front>
4325  <seriesInfo name="ANSI" value="X3.4"/>
4326</reference>
4327
4328<reference anchor="RFC1950">
4329  <front>
4330    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4331    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4332      <organization>Aladdin Enterprises</organization>
4333      <address><email>ghost@aladdin.com</email></address>
4334    </author>
4335    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4336    <date month="May" year="1996"/>
4337  </front>
4338  <seriesInfo name="RFC" value="1950"/>
4339  <!--<annotation>
4340    RFC 1950 is an Informational RFC, thus it might be less stable than
4341    this specification. On the other hand, this downward reference was
4342    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4343    therefore it is unlikely to cause problems in practice. See also
4344    <xref target="BCP97"/>.
4345  </annotation>-->
4346</reference>
4347
4348<reference anchor="RFC1951">
4349  <front>
4350    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4351    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4352      <organization>Aladdin Enterprises</organization>
4353      <address><email>ghost@aladdin.com</email></address>
4354    </author>
4355    <date month="May" year="1996"/>
4356  </front>
4357  <seriesInfo name="RFC" value="1951"/>
4358  <!--<annotation>
4359    RFC 1951 is an Informational RFC, thus it might be less stable than
4360    this specification. On the other hand, this downward reference was
4361    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4362    therefore it is unlikely to cause problems in practice. See also
4363    <xref target="BCP97"/>.
4364  </annotation>-->
4365</reference>
4366
4367<reference anchor="RFC1952">
4368  <front>
4369    <title>GZIP file format specification version 4.3</title>
4370    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4371      <organization>Aladdin Enterprises</organization>
4372      <address><email>ghost@aladdin.com</email></address>
4373    </author>
4374    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4375      <address><email>gzip@prep.ai.mit.edu</email></address>
4376    </author>
4377    <author initials="M." surname="Adler" fullname="Mark Adler">
4378      <address><email>madler@alumni.caltech.edu</email></address>
4379    </author>
4380    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4381      <address><email>ghost@aladdin.com</email></address>
4382    </author>
4383    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4384      <address><email>randeg@alumni.rpi.edu</email></address>
4385    </author>
4386    <date month="May" year="1996"/>
4387  </front>
4388  <seriesInfo name="RFC" value="1952"/>
4389  <!--<annotation>
4390    RFC 1952 is an Informational RFC, thus it might be less stable than
4391    this specification. On the other hand, this downward reference was
4392    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4393    therefore it is unlikely to cause problems in practice. See also
4394    <xref target="BCP97"/>.
4395  </annotation>-->
4396</reference>
4397
4398</references>
4399
4400<references title="Informative References">
4401
4402<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4403  <front>
4404    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4405    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4406    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4407    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4408    <author initials="H." surname="Lie" fullname="H. Lie"/>
4409    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4410    <date year="1997" month="September"/>
4411  </front>
4412  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4413</reference>
4414
4415<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4416  <front>
4417    <title>Improving HTTP Latency</title>
4418    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4419    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4420    <date year="1995" month="December"/>
4421  </front>
4422  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4423</reference>
4424
4425<reference anchor='RFC1919'>
4426  <front>
4427    <title>Classical versus Transparent IP Proxies</title>
4428    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4429      <address><email>mchatel@pax.eunet.ch</email></address>
4430    </author>
4431    <date year='1996' month='March' />
4432  </front>
4433  <seriesInfo name='RFC' value='1919' />
4434</reference>
4435
4436<reference anchor="RFC1945">
4437  <front>
4438    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4439    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4440      <organization>MIT, Laboratory for Computer Science</organization>
4441      <address><email>timbl@w3.org</email></address>
4442    </author>
4443    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4444      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4445      <address><email>fielding@ics.uci.edu</email></address>
4446    </author>
4447    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4448      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4449      <address><email>frystyk@w3.org</email></address>
4450    </author>
4451    <date month="May" year="1996"/>
4452  </front>
4453  <seriesInfo name="RFC" value="1945"/>
4454</reference>
4455
4456<reference anchor="RFC2045">
4457  <front>
4458    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4459    <author initials="N." surname="Freed" fullname="Ned Freed">
4460      <organization>Innosoft International, Inc.</organization>
4461      <address><email>ned@innosoft.com</email></address>
4462    </author>
4463    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4464      <organization>First Virtual Holdings</organization>
4465      <address><email>nsb@nsb.fv.com</email></address>
4466    </author>
4467    <date month="November" year="1996"/>
4468  </front>
4469  <seriesInfo name="RFC" value="2045"/>
4470</reference>
4471
4472<reference anchor="RFC2047">
4473  <front>
4474    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4475    <author initials="K." surname="Moore" fullname="Keith Moore">
4476      <organization>University of Tennessee</organization>
4477      <address><email>moore@cs.utk.edu</email></address>
4478    </author>
4479    <date month="November" year="1996"/>
4480  </front>
4481  <seriesInfo name="RFC" value="2047"/>
4482</reference>
4483
4484<reference anchor="RFC2068">
4485  <front>
4486    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4487    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4488      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4489      <address><email>fielding@ics.uci.edu</email></address>
4490    </author>
4491    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4492      <organization>MIT Laboratory for Computer Science</organization>
4493      <address><email>jg@w3.org</email></address>
4494    </author>
4495    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4496      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4497      <address><email>mogul@wrl.dec.com</email></address>
4498    </author>
4499    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4500      <organization>MIT Laboratory for Computer Science</organization>
4501      <address><email>frystyk@w3.org</email></address>
4502    </author>
4503    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4504      <organization>MIT Laboratory for Computer Science</organization>
4505      <address><email>timbl@w3.org</email></address>
4506    </author>
4507    <date month="January" year="1997"/>
4508  </front>
4509  <seriesInfo name="RFC" value="2068"/>
4510</reference>
4511
4512<reference anchor="RFC2145">
4513  <front>
4514    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4515    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4516      <organization>Western Research Laboratory</organization>
4517      <address><email>mogul@wrl.dec.com</email></address>
4518    </author>
4519    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4520      <organization>Department of Information and Computer Science</organization>
4521      <address><email>fielding@ics.uci.edu</email></address>
4522    </author>
4523    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4524      <organization>MIT Laboratory for Computer Science</organization>
4525      <address><email>jg@w3.org</email></address>
4526    </author>
4527    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4528      <organization>W3 Consortium</organization>
4529      <address><email>frystyk@w3.org</email></address>
4530    </author>
4531    <date month="May" year="1997"/>
4532  </front>
4533  <seriesInfo name="RFC" value="2145"/>
4534</reference>
4535
4536<reference anchor="RFC2616">
4537  <front>
4538    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4539    <author initials="R." surname="Fielding" fullname="R. Fielding">
4540      <organization>University of California, Irvine</organization>
4541      <address><email>fielding@ics.uci.edu</email></address>
4542    </author>
4543    <author initials="J." surname="Gettys" fullname="J. Gettys">
4544      <organization>W3C</organization>
4545      <address><email>jg@w3.org</email></address>
4546    </author>
4547    <author initials="J." surname="Mogul" fullname="J. Mogul">
4548      <organization>Compaq Computer Corporation</organization>
4549      <address><email>mogul@wrl.dec.com</email></address>
4550    </author>
4551    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4552      <organization>MIT Laboratory for Computer Science</organization>
4553      <address><email>frystyk@w3.org</email></address>
4554    </author>
4555    <author initials="L." surname="Masinter" fullname="L. Masinter">
4556      <organization>Xerox Corporation</organization>
4557      <address><email>masinter@parc.xerox.com</email></address>
4558    </author>
4559    <author initials="P." surname="Leach" fullname="P. Leach">
4560      <organization>Microsoft Corporation</organization>
4561      <address><email>paulle@microsoft.com</email></address>
4562    </author>
4563    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4564      <organization>W3C</organization>
4565      <address><email>timbl@w3.org</email></address>
4566    </author>
4567    <date month="June" year="1999"/>
4568  </front>
4569  <seriesInfo name="RFC" value="2616"/>
4570</reference>
4571
4572<reference anchor='RFC2817'>
4573  <front>
4574    <title>Upgrading to TLS Within HTTP/1.1</title>
4575    <author initials='R.' surname='Khare' fullname='R. Khare'>
4576      <organization>4K Associates / UC Irvine</organization>
4577      <address><email>rohit@4K-associates.com</email></address>
4578    </author>
4579    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4580      <organization>Agranat Systems, Inc.</organization>
4581      <address><email>lawrence@agranat.com</email></address>
4582    </author>
4583    <date year='2000' month='May' />
4584  </front>
4585  <seriesInfo name='RFC' value='2817' />
4586</reference>
4587
4588<reference anchor='RFC2818'>
4589  <front>
4590    <title>HTTP Over TLS</title>
4591    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4592      <organization>RTFM, Inc.</organization>
4593      <address><email>ekr@rtfm.com</email></address>
4594    </author>
4595    <date year='2000' month='May' />
4596  </front>
4597  <seriesInfo name='RFC' value='2818' />
4598</reference>
4599
4600<reference anchor='RFC2965'>
4601  <front>
4602    <title>HTTP State Management Mechanism</title>
4603    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4604      <organization>Bell Laboratories, Lucent Technologies</organization>
4605      <address><email>dmk@bell-labs.com</email></address>
4606    </author>
4607    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4608      <organization>Epinions.com, Inc.</organization>
4609      <address><email>lou@montulli.org</email></address>
4610    </author>
4611    <date year='2000' month='October' />
4612  </front>
4613  <seriesInfo name='RFC' value='2965' />
4614</reference>
4615
4616<reference anchor='RFC3040'>
4617  <front>
4618    <title>Internet Web Replication and Caching Taxonomy</title>
4619    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4620      <organization>Equinix, Inc.</organization>
4621    </author>
4622    <author initials='I.' surname='Melve' fullname='I. Melve'>
4623      <organization>UNINETT</organization>
4624    </author>
4625    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4626      <organization>CacheFlow Inc.</organization>
4627    </author>
4628    <date year='2001' month='January' />
4629  </front>
4630  <seriesInfo name='RFC' value='3040' />
4631</reference>
4632
4633<reference anchor='RFC3864'>
4634  <front>
4635    <title>Registration Procedures for Message Header Fields</title>
4636    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4637      <organization>Nine by Nine</organization>
4638      <address><email>GK-IETF@ninebynine.org</email></address>
4639    </author>
4640    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4641      <organization>BEA Systems</organization>
4642      <address><email>mnot@pobox.com</email></address>
4643    </author>
4644    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4645      <organization>HP Labs</organization>
4646      <address><email>JeffMogul@acm.org</email></address>
4647    </author>
4648    <date year='2004' month='September' />
4649  </front>
4650  <seriesInfo name='BCP' value='90' />
4651  <seriesInfo name='RFC' value='3864' />
4652</reference>
4653
4654<reference anchor='RFC4033'>
4655  <front>
4656    <title>DNS Security Introduction and Requirements</title>
4657    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4658    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4659    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4660    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4661    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4662    <date year='2005' month='March' />
4663  </front>
4664  <seriesInfo name='RFC' value='4033' />
4665</reference>
4666
4667<reference anchor="RFC4288">
4668  <front>
4669    <title>Media Type Specifications and Registration Procedures</title>
4670    <author initials="N." surname="Freed" fullname="N. Freed">
4671      <organization>Sun Microsystems</organization>
4672      <address>
4673        <email>ned.freed@mrochek.com</email>
4674      </address>
4675    </author>
4676    <author initials="J." surname="Klensin" fullname="J. Klensin">
4677      <address>
4678        <email>klensin+ietf@jck.com</email>
4679      </address>
4680    </author>
4681    <date year="2005" month="December"/>
4682  </front>
4683  <seriesInfo name="BCP" value="13"/>
4684  <seriesInfo name="RFC" value="4288"/>
4685</reference>
4686
4687<reference anchor='RFC4395'>
4688  <front>
4689    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4690    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4691      <organization>AT&amp;T Laboratories</organization>
4692      <address>
4693        <email>tony+urireg@maillennium.att.com</email>
4694      </address>
4695    </author>
4696    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4697      <organization>Qualcomm, Inc.</organization>
4698      <address>
4699        <email>hardie@qualcomm.com</email>
4700      </address>
4701    </author>
4702    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4703      <organization>Adobe Systems</organization>
4704      <address>
4705        <email>LMM@acm.org</email>
4706      </address>
4707    </author>
4708    <date year='2006' month='February' />
4709  </front>
4710  <seriesInfo name='BCP' value='115' />
4711  <seriesInfo name='RFC' value='4395' />
4712</reference>
4713
4714<reference anchor='RFC4559'>
4715  <front>
4716    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4717    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4718    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4719    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4720    <date year='2006' month='June' />
4721  </front>
4722  <seriesInfo name='RFC' value='4559' />
4723</reference>
4724
4725<reference anchor='RFC5226'>
4726  <front>
4727    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4728    <author initials='T.' surname='Narten' fullname='T. Narten'>
4729      <organization>IBM</organization>
4730      <address><email>narten@us.ibm.com</email></address>
4731    </author>
4732    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4733      <organization>Google</organization>
4734      <address><email>Harald@Alvestrand.no</email></address>
4735    </author>
4736    <date year='2008' month='May' />
4737  </front>
4738  <seriesInfo name='BCP' value='26' />
4739  <seriesInfo name='RFC' value='5226' />
4740</reference>
4741
4742<reference anchor="RFC5322">
4743  <front>
4744    <title>Internet Message Format</title>
4745    <author initials="P." surname="Resnick" fullname="P. Resnick">
4746      <organization>Qualcomm Incorporated</organization>
4747    </author>
4748    <date year="2008" month="October"/>
4749  </front> 
4750  <seriesInfo name="RFC" value="5322"/>
4751</reference>
4752
4753<reference anchor="RFC6265">
4754  <front>
4755    <title>HTTP State Management Mechanism</title>
4756    <author initials="A." surname="Barth" fullname="Adam Barth">
4757      <organization abbrev="U.C. Berkeley">
4758        University of California, Berkeley
4759      </organization>
4760      <address><email>abarth@eecs.berkeley.edu</email></address>
4761    </author>
4762    <date year="2011" month="April" />
4763  </front>
4764  <seriesInfo name="RFC" value="6265"/>
4765</reference>
4766
4767<!--<reference anchor='BCP97'>
4768  <front>
4769    <title>Handling Normative References to Standards-Track Documents</title>
4770    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4771      <address>
4772        <email>klensin+ietf@jck.com</email>
4773      </address>
4774    </author>
4775    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4776      <organization>MIT</organization>
4777      <address>
4778        <email>hartmans-ietf@mit.edu</email>
4779      </address>
4780    </author>
4781    <date year='2007' month='June' />
4782  </front>
4783  <seriesInfo name='BCP' value='97' />
4784  <seriesInfo name='RFC' value='4897' />
4785</reference>-->
4786
4787<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4788  <front>
4789    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4790    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4791    <date year="2001" month="November"/>
4792  </front>
4793  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4794</reference>
4795
4796<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4797  <front>
4798    <title>Analysis of HTTP Performance Problems</title>
4799    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4800    <date/>
4801  </front>
4802</reference>
4803
4804<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4805  <front>
4806  <title>Analysis of HTTP Performance</title>
4807  <author initials="J." surname="Touch" fullname="Joe Touch">
4808    <organization>USC/Information Sciences Institute</organization>
4809    <address><email>touch@isi.edu</email></address>
4810  </author>
4811  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4812    <organization>USC/Information Sciences Institute</organization>
4813    <address><email>johnh@isi.edu</email></address>
4814  </author>
4815  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4816    <organization>USC/Information Sciences Institute</organization>
4817    <address><email>katia@isi.edu</email></address>
4818  </author>
4819  <date year="1998" month="Aug"/>
4820  </front>
4821  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4822  <annotation>(original report dated Aug. 1996)</annotation>
4823</reference>
4824
4825</references>
4826
4827
4828<section title="HTTP Version History" anchor="compatibility">
4829<t>
4830   HTTP has been in use by the World-Wide Web global information initiative
4831   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4832   was a simple protocol for hypertext data transfer across the Internet
4833   with only a single request method (GET) and no metadata.
4834   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4835   methods and MIME-like messaging that could include metadata about the data
4836   transferred and modifiers on the request/response semantics. However,
4837   HTTP/1.0 did not sufficiently take into consideration the effects of
4838   hierarchical proxies, caching, the need for persistent connections, or
4839   name-based virtual hosts. The proliferation of incompletely-implemented
4840   applications calling themselves "HTTP/1.0" further necessitated a
4841   protocol version change in order for two communicating applications
4842   to determine each other's true capabilities.
4843</t>
4844<t>
4845   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4846   requirements that enable reliable implementations, adding only
4847   those new features that will either be safely ignored by an HTTP/1.0
4848   recipient or only sent when communicating with a party advertising
4849   conformance with HTTP/1.1.
4850</t>
4851<t>
4852   It is beyond the scope of a protocol specification to mandate
4853   conformance with previous versions. HTTP/1.1 was deliberately
4854   designed, however, to make supporting previous versions easy.
4855   We would expect a general-purpose HTTP/1.1 server to understand
4856   any valid request in the format of HTTP/1.0 and respond appropriately
4857   with an HTTP/1.1 message that only uses features understood (or
4858   safely ignored) by HTTP/1.0 clients.  Likewise, we would expect
4859   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4860</t>
4861<t>
4862   Since HTTP/0.9 did not support header fields in a request,
4863   there is no mechanism for it to support name-based virtual
4864   hosts (selection of resource by inspection of the Host header
4865   field).  Any server that implements name-based virtual hosts
4866   ought to disable support for HTTP/0.9.  Most requests that
4867   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4868   requests wherein a buggy client failed to properly encode
4869   linear whitespace found in a URI reference and placed in
4870   the request-target.
4871</t>
4872
4873<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4874<t>
4875   This section summarizes major differences between versions HTTP/1.0
4876   and HTTP/1.1.
4877</t>
4878
4879<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4880<t>
4881   The requirements that clients and servers support the Host header
4882   field (<xref target="header.host"/>), report an error if it is
4883   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4884   are among the most important changes defined by HTTP/1.1.
4885</t>
4886<t>
4887   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4888   addresses and servers; there was no other established mechanism for
4889   distinguishing the intended server of a request than the IP address
4890   to which that request was directed. The Host header field was
4891   introduced during the development of HTTP/1.1 and, though it was
4892   quickly implemented by most HTTP/1.0 browsers, additional requirements
4893   were placed on all HTTP/1.1 requests in order to ensure complete
4894   adoption.  At the time of this writing, most HTTP-based services
4895   are dependent upon the Host header field for targeting requests.
4896</t>
4897</section>
4898
4899<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4900<t>
4901   In HTTP/1.0, each connection is established by the client prior to the
4902   request and closed by the server after sending the response. However, some
4903   implementations implement the explicitly negotiated ("Keep-Alive") version
4904   of persistent connections described in <xref x:sec="19.7.1" x:fmt="of"
4905   target="RFC2068"/>.
4906</t>
4907<t>
4908   Some clients and servers might wish to be compatible with these previous
4909   approaches to persistent connections, by explicitly negotiating for them
4910   with a "Connection: keep-alive" request header field. However, some
4911   experimental implementations of HTTP/1.0 persistent connections are faulty;
4912   for example, if a HTTP/1.0 proxy server doesn't understand Connection, it
4913   will erroneously forward that header to the next inbound server, which
4914   would result in a hung connection.
4915</t>
4916<t>
4917   One attempted solution was the introduction of a Proxy-Connection header,
4918   targeted specifically at proxies. In practice, this was also unworkable,
4919   because proxies are often deployed in multiple layers, bringing about the
4920   same problem discussed above.
4921</t>
4922<t>
4923   As a result, clients are encouraged not to send the Proxy-Connection header
4924   in any requests.
4925</t>
4926<t>
4927   Clients are also encouraged to consider the use of Connection: keep-alive
4928   in requests carefully; while they can enable persistent connections with
4929   HTTP/1.0 servers, clients using them need will need to monitor the
4930   connection for "hung" requests (which indicate that the client ought stop
4931   sending the header), and this mechanism ought not be used by clients at all
4932   when a proxy is being used.
4933</t>
4934</section>
4935</section>
4936
4937<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4938<t>
4939  Empty list elements in list productions have been deprecated.
4940  (<xref target="abnf.extension"/>)
4941</t>
4942<t>
4943  Rules about implicit linear whitespace between certain grammar productions
4944  have been removed; now whitespace is only allowed where specifically
4945  defined in the ABNF.
4946  (<xref target="whitespace"/>)
4947</t>
4948<t>
4949  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4950  sensitive. Restrict the version numbers to be single digits due to the fact
4951  that implementations are known to handle multi-digit version numbers
4952  incorrectly.
4953  (<xref target="http.version"/>)
4954</t>
4955<t>
4956  Require that invalid whitespace around field-names be rejected.
4957  (<xref target="header.fields"/>)
4958</t>
4959<t> 
4960  The NUL octet is no longer allowed in comment and quoted-string
4961  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4962  Non-ASCII content in header fields and reason phrase has been obsoleted and
4963  made opaque (the TEXT rule was removed).
4964  (<xref target="field.components"/>)
4965</t>
4966<t>
4967  Require recipients to handle bogus Content-Length header fields as errors.
4968  (<xref target="message.body"/>)
4969</t>
4970<t>
4971  Remove reference to non-existent identity transfer-coding value tokens.
4972  (Sections <xref format="counter" target="message.body"/> and
4973  <xref format="counter" target="transfer.codings"/>)
4974</t>
4975<t>
4976  Update use of abs_path production from RFC 1808 to the path-absolute + query
4977  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4978  request method only.
4979  (<xref target="request-target"/>)
4980</t>
4981<t>
4982  Clarification that the chunk length does not include the count of the octets
4983  in the chunk header and trailer. Furthermore disallowed line folding
4984  in chunk extensions.
4985  (<xref target="chunked.encoding"/>)
4986</t>
4987<t>
4988  Remove hard limit of two connections per server.
4989  Remove requirement to retry a sequence of requests as long it was idempotent.
4990  Remove requirements about when servers are allowed to close connections
4991  prematurely.
4992  (<xref target="persistent.practical"/>)
4993</t>
4994<t>
4995  Remove requirement to retry requests under certain cirumstances when the
4996  server prematurely closes the connection.
4997  (<xref target="message.transmission.requirements"/>)
4998</t>
4999<t>
5000  Change ABNF productions for header fields to only define the field value.
5001  (<xref target="header.field.definitions"/>)
5002</t>
5003<t>
5004  Clarify exactly when close connection options must be sent.
5005  (<xref target="header.connection"/>)
5006</t>
5007<t>
5008  Define the semantics of the "Upgrade" header field in responses other than
5009  101 (this was incorporated from <xref target="RFC2817"/>).
5010  (<xref target="header.upgrade"/>)
5011</t>
5012</section>
5013</section>
5014
5015<?BEGININC p1-messaging.abnf-appendix ?>
5016<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5017<figure>
5018<artwork type="abnf" name="p1-messaging.parsed-abnf">
5019<x:ref>BWS</x:ref> = OWS
5020
5021<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5022<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5023 connection-token ] )
5024<x:ref>Content-Length</x:ref> = 1*DIGIT
5025
5026<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5027<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5028<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5029 ]
5030<x:ref>Host</x:ref> = uri-host [ ":" port ]
5031
5032<x:ref>Method</x:ref> = token
5033
5034<x:ref>OWS</x:ref> = *( SP / HTAB / obs-fold )
5035
5036<x:ref>RWS</x:ref> = 1*( SP / HTAB / obs-fold )
5037<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5038<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5039
5040<x:ref>Status-Code</x:ref> = 3DIGIT
5041<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5042
5043<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5044<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5045<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5046 transfer-coding ] )
5047
5048<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5049<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5050
5051<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5052 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5053 )
5054
5055<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5056<x:ref>attribute</x:ref> = token
5057<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5058
5059<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5060<x:ref>chunk-data</x:ref> = 1*OCTET
5061<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5062<x:ref>chunk-ext-name</x:ref> = token
5063<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5064<x:ref>chunk-size</x:ref> = 1*HEXDIG
5065<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5066<x:ref>connection-token</x:ref> = token
5067<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5068 / %x2A-5B ; '*'-'['
5069 / %x5D-7E ; ']'-'~'
5070 / obs-text
5071
5072<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5073<x:ref>field-name</x:ref> = token
5074<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5075
5076<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5077<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5078<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5079
5080<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5081
5082<x:ref>message-body</x:ref> = *OCTET
5083
5084<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5085<x:ref>obs-text</x:ref> = %x80-FF
5086
5087<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5088<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5089<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5090<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5091<x:ref>product</x:ref> = token [ "/" product-version ]
5092<x:ref>product-version</x:ref> = token
5093<x:ref>protocol-name</x:ref> = token
5094<x:ref>protocol-version</x:ref> = token
5095<x:ref>pseudonym</x:ref> = token
5096
5097<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5098 / %x5D-7E ; ']'-'~'
5099 / obs-text
5100<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5101 / %x5D-7E ; ']'-'~'
5102 / obs-text
5103<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5104<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5105<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5106<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5107<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5108<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5109
5110<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5111<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5112<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5113<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5114 / authority
5115
5116<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5117 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5118<x:ref>start-line</x:ref> = Request-Line / Status-Line
5119
5120<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5121<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5122 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5123<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5124<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5125<x:ref>token</x:ref> = 1*tchar
5126<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5127<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5128 transfer-extension
5129<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5130<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5131
5132<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5133
5134<x:ref>value</x:ref> = word
5135
5136<x:ref>word</x:ref> = token / quoted-string
5137</artwork>
5138</figure>
5139<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5140; Chunked-Body defined but not used
5141; Connection defined but not used
5142; Content-Length defined but not used
5143; HTTP-message defined but not used
5144; Host defined but not used
5145; TE defined but not used
5146; Trailer defined but not used
5147; Transfer-Encoding defined but not used
5148; URI-reference defined but not used
5149; Upgrade defined but not used
5150; Via defined but not used
5151; http-URI defined but not used
5152; https-URI defined but not used
5153; partial-URI defined but not used
5154; special defined but not used
5155</artwork></figure></section>
5156<?ENDINC p1-messaging.abnf-appendix ?>
5157
5158<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5159
5160<section title="Since RFC 2616">
5161<t>
5162  Extracted relevant partitions from <xref target="RFC2616"/>.
5163</t>
5164</section>
5165
5166<section title="Since draft-ietf-httpbis-p1-messaging-00">
5167<t>
5168  Closed issues:
5169  <list style="symbols"> 
5170    <t>
5171      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5172      "HTTP Version should be case sensitive"
5173      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5174    </t>
5175    <t>
5176      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5177      "'unsafe' characters"
5178      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5179    </t>
5180    <t>
5181      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5182      "Chunk Size Definition"
5183      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5184    </t>
5185    <t>
5186      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5187      "Message Length"
5188      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5189    </t>
5190    <t>
5191      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5192      "Media Type Registrations"
5193      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5194    </t>
5195    <t>
5196      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5197      "URI includes query"
5198      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5199    </t>
5200    <t>
5201      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5202      "No close on 1xx responses"
5203      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5204    </t>
5205    <t>
5206      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5207      "Remove 'identity' token references"
5208      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5209    </t>
5210    <t>
5211      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5212      "Import query BNF"
5213    </t>
5214    <t>
5215      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5216      "qdtext BNF"
5217    </t>
5218    <t>
5219      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5220      "Normative and Informative references"
5221    </t>
5222    <t>
5223      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5224      "RFC2606 Compliance"
5225    </t>
5226    <t>
5227      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5228      "RFC977 reference"
5229    </t>
5230    <t>
5231      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5232      "RFC1700 references"
5233    </t>
5234    <t>
5235      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5236      "inconsistency in date format explanation"
5237    </t>
5238    <t>
5239      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5240      "Date reference typo"
5241    </t>
5242    <t>
5243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5244      "Informative references"
5245    </t>
5246    <t>
5247      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5248      "ISO-8859-1 Reference"
5249    </t>
5250    <t>
5251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5252      "Normative up-to-date references"
5253    </t>
5254  </list>
5255</t>
5256<t>
5257  Other changes:
5258  <list style="symbols"> 
5259    <t>
5260      Update media type registrations to use RFC4288 template.
5261    </t>
5262    <t>
5263      Use names of RFC4234 core rules DQUOTE and HTAB,
5264      fix broken ABNF for chunk-data
5265      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5266    </t>
5267  </list>
5268</t>
5269</section>
5270
5271<section title="Since draft-ietf-httpbis-p1-messaging-01">
5272<t>
5273  Closed issues:
5274  <list style="symbols"> 
5275    <t>
5276      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5277      "Bodies on GET (and other) requests"
5278    </t>
5279    <t>
5280      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5281      "Updating to RFC4288"
5282    </t>
5283    <t>
5284      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5285      "Status Code and Reason Phrase"
5286    </t>
5287    <t>
5288      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5289      "rel_path not used"
5290    </t>
5291  </list>
5292</t>
5293<t>
5294  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5295  <list style="symbols"> 
5296    <t>
5297      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5298      "trailer-part").
5299    </t>
5300    <t>
5301      Avoid underscore character in rule names ("http_URL" ->
5302      "http-URL", "abs_path" -> "path-absolute").
5303    </t>
5304    <t>
5305      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5306      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5307      have to be updated when switching over to RFC3986.
5308    </t>
5309    <t>
5310      Synchronize core rules with RFC5234.
5311    </t>
5312    <t>
5313      Get rid of prose rules that span multiple lines.
5314    </t>
5315    <t>
5316      Get rid of unused rules LOALPHA and UPALPHA.
5317    </t>
5318    <t>
5319      Move "Product Tokens" section (back) into Part 1, as "token" is used
5320      in the definition of the Upgrade header field.
5321    </t>
5322    <t>
5323      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5324    </t>
5325    <t>
5326      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5327    </t>
5328  </list>
5329</t>
5330</section>
5331
5332<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5333<t>
5334  Closed issues:
5335  <list style="symbols"> 
5336    <t>
5337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5338      "HTTP-date vs. rfc1123-date"
5339    </t>
5340    <t>
5341      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5342      "WS in quoted-pair"
5343    </t>
5344  </list>
5345</t>
5346<t>
5347  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5348  <list style="symbols"> 
5349    <t>
5350      Reference RFC 3984, and update header field registrations for headers defined
5351      in this document.
5352    </t>
5353  </list>
5354</t>
5355<t>
5356  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5357  <list style="symbols"> 
5358    <t>
5359      Replace string literals when the string really is case-sensitive (HTTP-Version).
5360    </t>
5361  </list>
5362</t>
5363</section>
5364
5365<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5366<t>
5367  Closed issues:
5368  <list style="symbols"> 
5369    <t>
5370      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5371      "Connection closing"
5372    </t>
5373    <t>
5374      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5375      "Move registrations and registry information to IANA Considerations"
5376    </t>
5377    <t>
5378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5379      "need new URL for PAD1995 reference"
5380    </t>
5381    <t>
5382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5383      "IANA Considerations: update HTTP URI scheme registration"
5384    </t>
5385    <t>
5386      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5387      "Cite HTTPS URI scheme definition"
5388    </t>
5389    <t>
5390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5391      "List-type headers vs Set-Cookie"
5392    </t>
5393  </list>
5394</t>
5395<t>
5396  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5397  <list style="symbols"> 
5398    <t>
5399      Replace string literals when the string really is case-sensitive (HTTP-Date).
5400    </t>
5401    <t>
5402      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5403    </t>
5404  </list>
5405</t>
5406</section>
5407
5408<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5409<t>
5410  Closed issues:
5411  <list style="symbols"> 
5412    <t>
5413      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5414      "Out-of-date reference for URIs"
5415    </t>
5416    <t>
5417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5418      "RFC 2822 is updated by RFC 5322"
5419    </t>
5420  </list>
5421</t>
5422<t>
5423  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5424  <list style="symbols"> 
5425    <t>
5426      Use "/" instead of "|" for alternatives.
5427    </t>
5428    <t>
5429      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5430    </t>
5431    <t>
5432      Only reference RFC 5234's core rules.
5433    </t>
5434    <t>
5435      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5436      whitespace ("OWS") and required whitespace ("RWS").
5437    </t>
5438    <t>
5439      Rewrite ABNFs to spell out whitespace rules, factor out
5440      header field value format definitions.
5441    </t>
5442  </list>
5443</t>
5444</section>
5445
5446<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5447<t>
5448  Closed issues:
5449  <list style="symbols"> 
5450    <t>
5451      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5452      "Header LWS"
5453    </t>
5454    <t>
5455      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5456      "Sort 1.3 Terminology"
5457    </t>
5458    <t>
5459      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5460      "RFC2047 encoded words"
5461    </t>
5462    <t>
5463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5464      "Character Encodings in TEXT"
5465    </t>
5466    <t>
5467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5468      "Line Folding"
5469    </t>
5470    <t>
5471      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5472      "OPTIONS * and proxies"
5473    </t>
5474    <t>
5475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5476      "Reason-Phrase BNF"
5477    </t>
5478    <t>
5479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5480      "Use of TEXT"
5481    </t>
5482    <t>
5483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5484      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5485    </t>
5486    <t>
5487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5488      "RFC822 reference left in discussion of date formats"
5489    </t>
5490  </list>
5491</t>
5492<t>
5493  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5494  <list style="symbols"> 
5495    <t>
5496      Rewrite definition of list rules, deprecate empty list elements.
5497    </t>
5498    <t>
5499      Add appendix containing collected and expanded ABNF.
5500    </t>
5501  </list>
5502</t>
5503<t>
5504  Other changes:
5505  <list style="symbols"> 
5506    <t>
5507      Rewrite introduction; add mostly new Architecture Section.
5508    </t>
5509    <t>
5510      Move definition of quality values from Part 3 into Part 1;
5511      make TE request header field grammar independent of accept-params (defined in Part 3).
5512    </t>
5513  </list>
5514</t>
5515</section>
5516
5517<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5518<t>
5519  Closed issues:
5520  <list style="symbols"> 
5521    <t>
5522      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5523      "base for numeric protocol elements"
5524    </t>
5525    <t>
5526      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5527      "comment ABNF"
5528    </t>
5529  </list>
5530</t>
5531<t>
5532  Partly resolved issues:
5533  <list style="symbols"> 
5534    <t>
5535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5536      "205 Bodies" (took out language that implied that there might be
5537      methods for which a request body MUST NOT be included)
5538    </t>
5539    <t>
5540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5541      "editorial improvements around HTTP-date"
5542    </t>
5543  </list>
5544</t>
5545</section>
5546
5547<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5548<t>
5549  Closed issues:
5550  <list style="symbols"> 
5551    <t>
5552      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5553      "Repeating single-value headers"
5554    </t>
5555    <t>
5556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5557      "increase connection limit"
5558    </t>
5559    <t>
5560      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5561      "IP addresses in URLs"
5562    </t>
5563    <t>
5564      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5565      "take over HTTP Upgrade Token Registry"
5566    </t>
5567    <t>
5568      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5569      "CR and LF in chunk extension values"
5570    </t>
5571    <t>
5572      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5573      "HTTP/0.9 support"
5574    </t>
5575    <t>
5576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5577      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5578    </t>
5579    <t>
5580      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5581      "move definitions of gzip/deflate/compress to part 1"
5582    </t>
5583    <t>
5584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5585      "disallow control characters in quoted-pair"
5586    </t>
5587  </list>
5588</t>
5589<t>
5590  Partly resolved issues:
5591  <list style="symbols"> 
5592    <t>
5593      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5594      "update IANA requirements wrt Transfer-Coding values" (add the
5595      IANA Considerations subsection)
5596    </t>
5597  </list>
5598</t>
5599</section>
5600
5601<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5602<t>
5603  Closed issues:
5604  <list style="symbols"> 
5605    <t>
5606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5607      "header parsing, treatment of leading and trailing OWS"
5608    </t>
5609  </list>
5610</t>
5611<t>
5612  Partly resolved issues:
5613  <list style="symbols"> 
5614    <t>
5615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5616      "Placement of 13.5.1 and 13.5.2"
5617    </t>
5618    <t>
5619      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5620      "use of term "word" when talking about header structure"
5621    </t>
5622  </list>
5623</t>
5624</section>
5625
5626<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5627<t>
5628  Closed issues:
5629  <list style="symbols"> 
5630    <t>
5631      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5632      "Clarification of the term 'deflate'"
5633    </t>
5634    <t>
5635      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5636      "OPTIONS * and proxies"
5637    </t>
5638    <t>
5639      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5640      "MIME-Version not listed in P1, general header fields"
5641    </t>
5642    <t>
5643      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5644      "IANA registry for content/transfer encodings"
5645    </t>
5646    <t>
5647      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5648      "Case-sensitivity of HTTP-date"
5649    </t>
5650    <t>
5651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5652      "use of term "word" when talking about header structure"
5653    </t>
5654  </list>
5655</t>
5656<t>
5657  Partly resolved issues:
5658  <list style="symbols"> 
5659    <t>
5660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5661      "Term for the requested resource's URI"
5662    </t>
5663  </list>
5664</t>
5665</section>
5666
5667<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5668<t>
5669  Closed issues:
5670  <list style="symbols">
5671    <t>
5672      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5673      "Connection Closing"
5674    </t>
5675    <t>
5676      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5677      "Delimiting messages with multipart/byteranges"
5678    </t>
5679    <t>
5680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5681      "Handling multiple Content-Length headers"
5682    </t>
5683    <t>
5684      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5685      "Clarify entity / representation / variant terminology"
5686    </t>
5687    <t>
5688      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5689      "consider removing the 'changes from 2068' sections"
5690    </t>
5691  </list>
5692</t>
5693<t>
5694  Partly resolved issues:
5695  <list style="symbols"> 
5696    <t>
5697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5698      "HTTP(s) URI scheme definitions"
5699    </t>
5700  </list>
5701</t>
5702</section>
5703
5704<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5705<t>
5706  Closed issues:
5707  <list style="symbols">
5708    <t>
5709      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5710      "Trailer requirements"
5711    </t>
5712    <t>
5713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5714      "Text about clock requirement for caches belongs in p6"
5715    </t>
5716    <t>
5717      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5718      "effective request URI: handling of missing host in HTTP/1.0"
5719    </t>
5720    <t>
5721      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5722      "confusing Date requirements for clients"
5723    </t>
5724  </list>
5725</t>
5726<t>
5727  Partly resolved issues:
5728  <list style="symbols"> 
5729    <t>
5730      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5731      "Handling multiple Content-Length headers"
5732    </t>
5733  </list>
5734</t>
5735</section>
5736
5737<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5738<t>
5739  Closed issues:
5740  <list style="symbols">
5741    <t>
5742      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5743      "RFC2145 Normative"
5744    </t>
5745    <t>
5746      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5747      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5748    </t>
5749    <t>
5750      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5751      "define 'transparent' proxy"
5752    </t>
5753    <t>
5754      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5755      "Header Classification"
5756    </t>
5757    <t>
5758      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5759      "Is * usable as a request-uri for new methods?"
5760    </t>
5761    <t>
5762      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5763      "Migrate Upgrade details from RFC2817"
5764    </t>
5765    <t>
5766      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5767      "untangle ABNFs for header fields"
5768    </t>
5769    <t>
5770      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5771      "update RFC 2109 reference"
5772    </t>
5773  </list>
5774</t>
5775</section>
5776
5777<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5778<t>
5779  Closed issues:
5780  <list style="symbols">
5781    <t>
5782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5783      "Allow is not in 13.5.2"
5784    </t>
5785    <t>
5786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5787      "Handling multiple Content-Length headers"
5788    </t>
5789    <t>
5790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5791      "untangle ABNFs for header fields"
5792    </t>
5793    <t>
5794      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5795      "Content-Length ABNF broken"
5796    </t>
5797  </list>
5798</t>
5799</section>
5800
5801<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5802<t>
5803  Closed issues:
5804  <list style="symbols">
5805    <t>
5806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5807      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5808    </t>
5809    <t>
5810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5811      "Recommend minimum sizes for protocol elements"
5812    </t>
5813    <t>
5814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5815      "Set expectations around buffering"
5816    </t>
5817    <t>
5818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5819      "Considering messages in isolation"
5820    </t>
5821  </list>
5822</t>
5823</section>
5824
5825<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5826<t>
5827  Closed issues:
5828  <list style="symbols">
5829    <t>
5830      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5831      "DNS Spoofing / DNS Binding advice"
5832    </t>
5833    <t>
5834      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5835      "move RFCs 2145, 2616, 2817 to Historic status"
5836    </t>
5837    <t>
5838      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5839      "\-escaping in quoted strings"
5840    </t>
5841    <t>
5842      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5843      "'Close' should be reserved in the HTTP header field registry"
5844    </t>
5845  </list>
5846</t>
5847</section>
5848
5849<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5850<t>
5851  Closed issues:
5852  <list style="symbols">
5853    <t>
5854      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5855      "Document HTTP's error-handling philosophy"
5856    </t>
5857    <t>
5858      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5859      "Explain header registration"
5860    </t>
5861    <t>
5862      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5863      "Revise Acknowledgements Sections"
5864    </t>
5865    <t>
5866      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5867      "Retrying Requests"
5868    </t>
5869    <t>
5870      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5871      "Closing the connection on server error"
5872    </t>
5873  </list>
5874</t>
5875</section>
5876
5877<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5878<t>
5879  Closed issues:
5880  <list style="symbols">
5881    <t>
5882      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5883      "Clarify 'User Agent'"
5884    </t>
5885    <t>
5886      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5887      "Define non-final responses"
5888    </t>
5889    <t>
5890      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5891      "intended maturity level vs normative references"
5892    </t>
5893    <t>
5894      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5895      "Intermediary rewriting of queries"
5896    </t>
5897    <t>
5898      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5899      "Proxy-Connection and Keep-Alive"
5900    </t>
5901  </list>
5902</t>
5903</section>
5904
5905<section title="Since draft-ietf-httpbis-p1-messaging-18" anchor="changes.since.18">
5906<t>
5907  None yet.
5908</t>
5909</section>
5910
5911</section>
5912
5913</back>
5914</rfc>
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