source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1450

Last change on this file since 1450 was 1450, checked in by julian.reschke@…, 8 years ago

fix missinh whitespace in ABNF

  • Property svn:eol-style set to native
File size: 240.8 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 "October">
16  <!ENTITY ID-YEAR "2011">
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="draft"
58     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
59     xmlns:x='http://purl.org/net/xml2rfc/ext'>
60<front>
61
62  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
63
64  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
65    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
66    <address>
67      <postal>
68        <street>345 Park Ave</street>
69        <city>San Jose</city>
70        <region>CA</region>
71        <code>95110</code>
72        <country>USA</country>
73      </postal>
74      <email>fielding@gbiv.com</email>
75      <uri>http://roy.gbiv.com/</uri>
76    </address>
77  </author>
78
79  <author initials="J." surname="Gettys" fullname="Jim Gettys">
80    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
81    <address>
82      <postal>
83        <street>21 Oak Knoll Road</street>
84        <city>Carlisle</city>
85        <region>MA</region>
86        <code>01741</code>
87        <country>USA</country>
88      </postal>
89      <email>jg@freedesktop.org</email>
90      <uri>http://gettys.wordpress.com/</uri>
91    </address>
92  </author>
93 
94  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
95    <organization abbrev="HP">Hewlett-Packard Company</organization>
96    <address>
97      <postal>
98        <street>HP Labs, Large Scale Systems Group</street>
99        <street>1501 Page Mill Road, MS 1177</street>
100        <city>Palo Alto</city>
101        <region>CA</region>
102        <code>94304</code>
103        <country>USA</country>
104      </postal>
105      <email>JeffMogul@acm.org</email>
106    </address>
107  </author>
108
109  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
110    <organization abbrev="Microsoft">Microsoft Corporation</organization>
111    <address>
112      <postal>
113        <street>1 Microsoft Way</street>
114        <city>Redmond</city>
115        <region>WA</region>
116        <code>98052</code>
117        <country>USA</country>
118      </postal>
119      <email>henrikn@microsoft.com</email>
120    </address>
121  </author>
122
123  <author initials="L." surname="Masinter" fullname="Larry Masinter">
124    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
125    <address>
126      <postal>
127        <street>345 Park Ave</street>
128        <city>San Jose</city>
129        <region>CA</region>
130        <code>95110</code>
131        <country>USA</country>
132      </postal>
133      <email>LMM@acm.org</email>
134      <uri>http://larry.masinter.net/</uri>
135    </address>
136  </author>
137 
138  <author initials="P." surname="Leach" fullname="Paul J. Leach">
139    <organization abbrev="Microsoft">Microsoft Corporation</organization>
140    <address>
141      <postal>
142        <street>1 Microsoft Way</street>
143        <city>Redmond</city>
144        <region>WA</region>
145        <code>98052</code>
146      </postal>
147      <email>paulle@microsoft.com</email>
148    </address>
149  </author>
150   
151  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
152    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
153    <address>
154      <postal>
155        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
156        <street>The Stata Center, Building 32</street>
157        <street>32 Vassar Street</street>
158        <city>Cambridge</city>
159        <region>MA</region>
160        <code>02139</code>
161        <country>USA</country>
162      </postal>
163      <email>timbl@w3.org</email>
164      <uri>http://www.w3.org/People/Berners-Lee/</uri>
165    </address>
166  </author>
167
168  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
169    <organization abbrev="W3C">World Wide Web Consortium</organization>
170    <address>
171      <postal>
172        <street>W3C / ERCIM</street>
173        <street>2004, rte des Lucioles</street>
174        <city>Sophia-Antipolis</city>
175        <region>AM</region>
176        <code>06902</code>
177        <country>France</country>
178      </postal>
179      <email>ylafon@w3.org</email>
180      <uri>http://www.raubacapeu.net/people/yves/</uri>
181    </address>
182  </author>
183
184  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
185    <organization abbrev="greenbytes">greenbytes GmbH</organization>
186    <address>
187      <postal>
188        <street>Hafenweg 16</street>
189        <city>Muenster</city><region>NW</region><code>48155</code>
190        <country>Germany</country>
191      </postal>
192      <phone>+49 251 2807760</phone>
193      <facsimile>+49 251 2807761</facsimile>
194      <email>julian.reschke@greenbytes.de</email>
195      <uri>http://greenbytes.de/tech/webdav/</uri>
196    </address>
197  </author>
198
199  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
200  <workgroup>HTTPbis Working Group</workgroup>
201
202<abstract>
203<t>
204   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
205   distributed, collaborative, hypertext information systems. HTTP has been in
206   use by the World Wide Web global information initiative since 1990. This
207   document is Part 1 of the seven-part specification that defines the protocol
208   referred to as "HTTP/1.1" and, taken together, obsoletes
209   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
210   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
211   2068</xref>.
212</t>
213<t>
214   Part 1 provides an overview of HTTP and its associated terminology, defines
215   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
216   the generic message syntax and parsing requirements for HTTP message frames,
217   and describes general security concerns for implementations.
218</t>
219<t>
220   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
221   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
222   (on using CONNECT for TLS upgrades) and moves them to historic status.
223</t>
224</abstract>
225
226<note title="Editorial Note (To be removed by RFC Editor)">
227  <t>
228    Discussion of this draft should take place on the HTTPBIS working group
229    mailing list (ietf-http-wg@w3.org), which is archived at
230    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
231  </t>
232  <t>
233    The current issues list is at
234    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
235    documents (including fancy diffs) can be found at
236    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
237  </t>
238  <t>
239    The changes in this draft are summarized in <xref target="changes.since.16"/>.
240  </t>
241</note>
242</front>
243<middle>
244<section title="Introduction" anchor="introduction">
245<t>
246   The Hypertext Transfer Protocol (HTTP) is an application-level
247   request/response protocol that uses extensible semantics and MIME-like
248   message payloads for flexible interaction with network-based hypertext
249   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
250   standard <xref target="RFC3986"/> to indicate the target resource and
251   relationships between resources.
252   Messages are passed in a format similar to that used by Internet mail
253   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
254   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
255   between HTTP and MIME messages).
256</t>
257<t>
258   HTTP is a generic interface protocol for information systems. It is
259   designed to hide the details of how a service is implemented by presenting
260   a uniform interface to clients that is independent of the types of
261   resources provided. Likewise, servers do not need to be aware of each
262   client's purpose: an HTTP request can be considered in isolation rather
263   than being associated with a specific type of client or a predetermined
264   sequence of application steps. The result is a protocol that can be used
265   effectively in many different contexts and for which implementations can
266   evolve independently over time.
267</t>
268<t>
269   HTTP is also designed for use as an intermediation protocol for translating
270   communication to and from non-HTTP information systems.
271   HTTP proxies and gateways can provide access to alternative information
272   services by translating their diverse protocols into a hypertext
273   format that can be viewed and manipulated by clients in the same way
274   as HTTP services.
275</t>
276<t>
277   One consequence of HTTP flexibility is that the protocol cannot be
278   defined in terms of what occurs behind the interface. Instead, we
279   are limited to defining the syntax of communication, the intent
280   of received communication, and the expected behavior of recipients.
281   If the communication is considered in isolation, then successful
282   actions ought to be reflected in corresponding changes to the
283   observable interface provided by servers. However, since multiple
284   clients might act in parallel and perhaps at cross-purposes, we
285   cannot require that such changes be observable beyond the scope
286   of a single response.
287</t>
288<t>
289   This document is Part 1 of the seven-part specification of HTTP,
290   defining the protocol referred to as "HTTP/1.1", obsoleting
291   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
292   Part 1 describes the architectural elements that are used or
293   referred to in HTTP, defines the "http" and "https" URI schemes,
294   describes overall network operation and connection management,
295   and defines HTTP message framing and forwarding requirements.
296   Our goal is to define all of the mechanisms necessary for HTTP message
297   handling that are independent of message semantics, thereby defining the
298   complete set of requirements for message parsers and
299   message-forwarding intermediaries.
300</t>
301
302<section title="Requirements" anchor="intro.requirements">
303<t>
304   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
305   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
306   document are to be interpreted as described in <xref target="RFC2119"/>.
307</t>
308<t>
309   An implementation is not compliant if it fails to satisfy one or more
310   of the "MUST" or "REQUIRED" level requirements for the protocols it
311   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
312   level and all the "SHOULD" level requirements for its protocols is said
313   to be "unconditionally compliant"; one that satisfies all the "MUST"
314   level requirements but not all the "SHOULD" level requirements for its
315   protocols is said to be "conditionally compliant".
316</t>
317</section>
318
319<section title="Syntax Notation" anchor="notation">
320<iref primary="true" item="Grammar" subitem="ALPHA"/>
321<iref primary="true" item="Grammar" subitem="CR"/>
322<iref primary="true" item="Grammar" subitem="CRLF"/>
323<iref primary="true" item="Grammar" subitem="CTL"/>
324<iref primary="true" item="Grammar" subitem="DIGIT"/>
325<iref primary="true" item="Grammar" subitem="DQUOTE"/>
326<iref primary="true" item="Grammar" subitem="HEXDIG"/>
327<iref primary="true" item="Grammar" subitem="HTAB"/>
328<iref primary="true" item="Grammar" subitem="LF"/>
329<iref primary="true" item="Grammar" subitem="OCTET"/>
330<iref primary="true" item="Grammar" subitem="SP"/>
331<iref primary="true" item="Grammar" subitem="VCHAR"/>
332<t>
333   This specification uses the Augmented Backus-Naur Form (ABNF) notation
334   of <xref target="RFC5234"/>.
335</t>
336<t anchor="core.rules">
337  <x:anchor-alias value="ALPHA"/>
338  <x:anchor-alias value="CTL"/>
339  <x:anchor-alias value="CR"/>
340  <x:anchor-alias value="CRLF"/>
341  <x:anchor-alias value="DIGIT"/>
342  <x:anchor-alias value="DQUOTE"/>
343  <x:anchor-alias value="HEXDIG"/>
344  <x:anchor-alias value="HTAB"/>
345  <x:anchor-alias value="LF"/>
346  <x:anchor-alias value="OCTET"/>
347  <x:anchor-alias value="SP"/>
348  <x:anchor-alias value="VCHAR"/>
349   The following core rules are included by
350   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
351   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
352   DIGIT (decimal 0-9), DQUOTE (double quote),
353   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
354   OCTET (any 8-bit sequence of data), SP (space), and
355   VCHAR (any visible <xref target="USASCII"/> character).
356</t>
357<t>
358   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
359   "obsolete" grammar rules that appear for historical reasons.
360</t>
361
362<section title="ABNF Extension: #rule" anchor="notation.abnf">
363<t>
364  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
365  improve readability.
366</t>
367<t>
368  A construct "#" is defined, similar to "*", for defining comma-delimited
369  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
370  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
371  comma (",") and optional whitespace (OWS, <xref target="basic.rules"/>).   
372</t>
373<figure><preamble>
374  Thus,
375</preamble><artwork type="example">
376  1#element =&gt; element *( OWS "," OWS element )
377</artwork></figure>
378<figure><preamble>
379  and:
380</preamble><artwork type="example">
381  #element =&gt; [ 1#element ]
382</artwork></figure>
383<figure><preamble>
384  and for n &gt;= 1 and m &gt; 1:
385</preamble><artwork type="example">
386  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
387</artwork></figure>
388<t>
389  For compatibility with legacy list rules, recipients &SHOULD; accept empty
390  list elements. In other words, consumers would follow the list productions:
391</t>
392<figure><artwork type="example">
393  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
394 
395  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
396</artwork></figure>
397<t>
398  Note that empty elements do not contribute to the count of elements present,
399  though.
400</t>
401<t>
402  For example, given these ABNF productions:
403</t>
404<figure><artwork type="example">
405  example-list      = 1#example-list-elmt
406  example-list-elmt = token ; see <xref target="field.rules"/> 
407</artwork></figure>
408<t>
409  Then these are valid values for example-list (not including the double
410  quotes, which are present for delimitation only):
411</t>
412<figure><artwork type="example">
413  "foo,bar"
414  " foo ,bar,"
415  "  foo , ,bar,charlie   "
416  "foo ,bar,   charlie "
417</artwork></figure>
418<t>
419  But these values would be invalid, as at least one non-empty element is
420  required:
421</t>
422<figure><artwork type="example">
423  ""
424  ","
425  ",   ,"
426</artwork></figure>
427<t>
428  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
429  expanded as explained above.
430</t>
431</section>
432
433<section title="Basic Rules" anchor="basic.rules">
434<t anchor="rule.LWS">
435   This specification uses three rules to denote the use of linear
436   whitespace: OWS (optional whitespace), RWS (required whitespace), and
437   BWS ("bad" whitespace).
438</t>
439<t anchor="rule.OWS">
440   The OWS rule is used where zero or more linear whitespace octets might
441   appear. OWS &SHOULD; either not be produced or be produced as a single
442   SP. Multiple OWS octets that occur within field-content &SHOULD; either
443   be replaced with a single SP or transformed to all SP octets (each
444   octet other than SP replaced with SP) before interpreting the field value
445   or forwarding the message downstream.
446</t>
447<t anchor="rule.RWS">
448   RWS is used when at least one linear whitespace octet is required to
449   separate field tokens. RWS &SHOULD; be produced as a single SP.
450   Multiple RWS octets that occur within field-content &SHOULD; either
451   be replaced with a single SP or transformed to all SP octets before
452   interpreting the field value or forwarding the message downstream.
453</t>
454<t anchor="rule.BWS">
455   BWS is used where the grammar allows optional whitespace for historical
456   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
457   recipients &MUST; accept such bad optional whitespace and remove it before
458   interpreting the field value or forwarding the message downstream.
459</t>
460<t anchor="rule.whitespace">
461  <x:anchor-alias value="BWS"/>
462  <x:anchor-alias value="OWS"/>
463  <x:anchor-alias value="RWS"/>
464  <x:anchor-alias value="obs-fold"/>
465</t>
466<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"/>
467  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
468                 ; "optional" whitespace
469  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
470                 ; "required" whitespace
471  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
472                 ; "bad" whitespace
473  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
474                 ; obsolete line folding
475                 ; see <xref target="field.parsing"/>
476</artwork></figure>
477</section>
478</section>
479</section>
480
481<section title="Architecture" anchor="architecture">
482<t>
483   HTTP was created for the World Wide Web architecture
484   and has evolved over time to support the scalability needs of a worldwide
485   hypertext system. Much of that architecture is reflected in the terminology
486   and syntax productions used to define HTTP.
487</t>
488
489<section title="Client/Server Messaging" anchor="operation">
490<iref primary="true" item="client"/>
491<iref primary="true" item="server"/>
492<iref primary="true" item="connection"/>
493<t>
494   HTTP is a stateless request/response protocol that operates by exchanging
495   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
496   transport or session-layer
497   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
498   program that establishes a connection to a server for the purpose of
499   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
500   program that accepts connections in order to service HTTP requests by
501   sending HTTP responses.
502</t>
503<iref primary="true" item="user agent"/>
504<iref primary="true" item="origin server"/>
505<iref primary="true" item="browser"/>
506<iref primary="true" item="spider"/>
507<iref primary="true" item="sender"/>
508<iref primary="true" item="recipient"/>
509<t>
510   Note that the terms client and server refer only to the roles that
511   these programs perform for a particular connection.  The same program
512   might act as a client on some connections and a server on others.  We use
513   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
514   such as a WWW browser, editor, or spider (web-traversing robot), and
515   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
516   authoritative responses to a request.  For general requirements, we use
517   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
518   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
519   message.
520</t>
521<t>
522   Most HTTP communication consists of a retrieval request (GET) for
523   a representation of some resource identified by a URI.  In the
524   simplest case, this might be accomplished via a single bidirectional
525   connection (===) between the user agent (UA) and the origin server (O).
526</t>
527<figure><artwork type="drawing">
528         request   &gt;
529    UA ======================================= O
530                                &lt;   response
531</artwork></figure>
532<iref primary="true" item="message"/>
533<iref primary="true" item="request"/>
534<iref primary="true" item="response"/>
535<t>
536   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
537   message, beginning with a request-line that includes a method, URI, and
538   protocol version (<xref target="request.line"/>),
539   followed by MIME-like header fields containing
540   request modifiers, client information, and payload metadata
541   (<xref target="header.fields"/>),
542   an empty line to indicate the end of the header section, and finally
543   a message body containing the payload body (if any,
544   <xref target="message.body"/>).
545</t>
546<t>
547   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
548   message, beginning with a status line that
549   includes the protocol version, a success or error code, and textual
550   reason phrase (<xref target="status.line"/>),
551   followed by MIME-like header fields containing server
552   information, resource metadata, and payload metadata
553   (<xref target="header.fields"/>),
554   an empty line to indicate the end of the header section, and finally
555   a message body containing the payload body (if any,
556   <xref target="message.body"/>).
557</t>
558<t>
559   The following example illustrates a typical message exchange for a
560   GET request on the URI "http://www.example.com/hello.txt":
561</t>
562<figure><preamble>
563client request:
564</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
565GET /hello.txt HTTP/1.1
566User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
567Host: www.example.com
568Accept: */*
569
570</artwork></figure>
571<figure><preamble>
572server response:
573</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
574HTTP/1.1 200 OK
575Date: Mon, 27 Jul 2009 12:28:53 GMT
576Server: Apache
577Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
578ETag: "34aa387-d-1568eb00"
579Accept-Ranges: bytes
580Content-Length: <x:length-of target="exbody"/>
581Vary: Accept-Encoding
582Content-Type: text/plain
583
584<x:span anchor="exbody">Hello World!
585</x:span></artwork></figure>
586</section>
587
588<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
589<t>
590   Fundamentally, HTTP is a message-based protocol. Although message bodies can
591   be chunked (<xref target="chunked.encoding"/>) and implementations often
592   make parts of a message available progressively, this is not required, and
593   some widely-used implementations only make a message available when it is
594   complete. Furthermore, while most proxies will progressively stream messages,
595   some amount of buffering will take place, and some proxies might buffer
596   messages to perform transformations, check content or provide other services.
597</t>
598<t>
599   Therefore, extensions to and uses of HTTP cannot rely on the availability of
600   a partial message, or assume that messages will not be buffered. There are
601   strategies that can be used to test for buffering in a given connection, but
602   it should be understood that behaviors can differ across connections, and
603   between requests and responses.
604</t>
605<t>
606   Recipients &MUST; consider every message in a connection in isolation;
607   because HTTP is a stateless protocol, it cannot be assumed that two requests
608   on the same connection are from the same client or share any other common
609   attributes. In particular, intermediaries might mix requests from different
610   clients into a single server connection. Note that some existing HTTP
611   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
612   potentially causing interoperability and security problems.
613</t>
614</section>
615
616<section title="Connections and Transport Independence" anchor="transport-independence">
617<t>
618   HTTP messaging is independent of the underlying transport or
619   session-layer connection protocol(s).  HTTP only presumes a reliable
620   transport with in-order delivery of requests and the corresponding
621   in-order delivery of responses.  The mapping of HTTP request and
622   response structures onto the data units of the underlying transport
623   protocol is outside the scope of this specification.
624</t>
625<t>
626   The specific connection protocols to be used for an interaction
627   are determined by client configuration and the target resource's URI.
628   For example, the "http" URI scheme
629   (<xref target="http.uri"/>) indicates a default connection of TCP
630   over IP, with a default TCP port of 80, but the client might be
631   configured to use a proxy via some other connection port or protocol
632   instead of using the defaults.
633</t>
634<t>
635   A connection might be used for multiple HTTP request/response exchanges,
636   as defined in <xref target="persistent.connections"/>.
637</t>
638</section>
639
640<section title="Intermediaries" anchor="intermediaries">
641<iref primary="true" item="intermediary"/>
642<t>
643   HTTP enables the use of intermediaries to satisfy requests through
644   a chain of connections.  There are three common forms of HTTP
645   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
646   a single intermediary might act as an origin server, proxy, gateway,
647   or tunnel, switching behavior based on the nature of each request.
648</t>
649<figure><artwork type="drawing">
650         &gt;             &gt;             &gt;             &gt;
651    <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>
652               &lt;             &lt;             &lt;             &lt;
653</artwork></figure>
654<t>
655   The figure above shows three intermediaries (A, B, and C) between the
656   user agent and origin server. A request or response message that
657   travels the whole chain will pass through four separate connections.
658   Some HTTP communication options
659   might apply only to the connection with the nearest, non-tunnel
660   neighbor, only to the end-points of the chain, or to all connections
661   along the chain. Although the diagram is linear, each participant might
662   be engaged in multiple, simultaneous communications. For example, B
663   might be receiving requests from many clients other than A, and/or
664   forwarding requests to servers other than C, at the same time that it
665   is handling A's request.
666</t>
667<t>
668<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
669<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
670   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
671   to describe various requirements in relation to the directional flow of a
672   message: all messages flow from upstream to downstream.
673   Likewise, we use the terms inbound and outbound to refer to
674   directions in relation to the request path:
675   "<x:dfn>inbound</x:dfn>" means toward the origin server and
676   "<x:dfn>outbound</x:dfn>" means toward the user agent.
677</t>
678<t><iref primary="true" item="proxy"/>
679   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
680   client, usually via local configuration rules, to receive requests
681   for some type(s) of absolute URI and attempt to satisfy those
682   requests via translation through the HTTP interface.  Some translations
683   are minimal, such as for proxy requests for "http" URIs, whereas
684   other requests might require translation to and from entirely different
685   application-layer protocols. Proxies are often used to group an
686   organization's HTTP requests through a common intermediary for the
687   sake of security, annotation services, or shared caching.
688</t>
689<t>
690<iref primary="true" item="transforming proxy"/>
691<iref primary="true" item="non-transforming proxy"/>
692   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
693   or configured to modify request or response messages in a semantically
694   meaningful way (i.e., modifications, beyond those required by normal
695   HTTP processing, that change the message in a way that would be
696   significant to the original sender or potentially significant to
697   downstream recipients).  For example, a transforming proxy might be
698   acting as a shared annotation server (modifying responses to include
699   references to a local annotation database), a malware filter, a
700   format transcoder, or an intranet-to-Internet privacy filter.  Such
701   transformations are presumed to be desired by the client (or client
702   organization) that selected the proxy and are beyond the scope of
703   this specification.  However, when a proxy is not intended to transform
704   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
705   requirements that preserve HTTP message semantics. See &status-203; and
706   &header-warning; for status and warning codes related to transformations.
707</t>
708<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
709<iref primary="true" item="accelerator"/>
710   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
711   is a receiving agent that acts
712   as a layer above some other server(s) and translates the received
713   requests to the underlying server's protocol.  Gateways are often
714   used to encapsulate legacy or untrusted information services, to
715   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
716   enable partitioning or load-balancing of HTTP services across
717   multiple machines.
718</t>
719<t>
720   A gateway behaves as an origin server on its outbound connection and
721   as a user agent on its inbound connection.
722   All HTTP requirements applicable to an origin server
723   also apply to the outbound communication of a gateway.
724   A gateway communicates with inbound servers using any protocol that
725   it desires, including private extensions to HTTP that are outside
726   the scope of this specification.  However, an HTTP-to-HTTP gateway
727   that wishes to interoperate with third-party HTTP servers &MUST;
728   comply with HTTP user agent requirements on the gateway's inbound
729   connection and &MUST; implement the Connection
730   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
731   header fields for both connections.
732</t>
733<t><iref primary="true" item="tunnel"/>
734   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
735   without changing the messages. Once active, a tunnel is not
736   considered a party to the HTTP communication, though the tunnel might
737   have been initiated by an HTTP request. A tunnel ceases to exist when
738   both ends of the relayed connection are closed. Tunnels are used to
739   extend a virtual connection through an intermediary, such as when
740   transport-layer security is used to establish private communication
741   through a shared firewall proxy.
742</t>
743<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
744<iref primary="true" item="captive portal"/>
745   In addition, there may exist network intermediaries that are not
746   considered part of the HTTP communication but nevertheless act as
747   filters or redirecting agents (usually violating HTTP semantics,
748   causing security problems, and otherwise making a mess of things).
749   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
750   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
751   or "<x:dfn>captive portal</x:dfn>",
752   differs from an HTTP proxy because it has not been selected by the client.
753   Instead, the network intermediary redirects outgoing TCP port 80 packets
754   (and occasionally other common port traffic) to an internal HTTP server.
755   Interception proxies are commonly found on public network access points,
756   as a means of enforcing account subscription prior to allowing use of
757   non-local Internet services, and within corporate firewalls to enforce
758   network usage policies.
759   They are indistinguishable from a man-in-the-middle attack.
760</t>
761</section>
762
763<section title="Caches" anchor="caches">
764<iref primary="true" item="cache"/>
765<t>
766   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
767   subsystem that controls its message storage, retrieval, and deletion.
768   A cache stores cacheable responses in order to reduce the response
769   time and network bandwidth consumption on future, equivalent
770   requests. Any client or server &MAY; employ a cache, though a cache
771   cannot be used by a server while it is acting as a tunnel.
772</t>
773<t>
774   The effect of a cache is that the request/response chain is shortened
775   if one of the participants along the chain has a cached response
776   applicable to that request. The following illustrates the resulting
777   chain if B has a cached copy of an earlier response from O (via C)
778   for a request which has not been cached by UA or A.
779</t>
780<figure><artwork type="drawing">
781            &gt;             &gt;
782       UA =========== A =========== B - - - - - - C - - - - - - O
783                  &lt;             &lt;
784</artwork></figure>
785<t><iref primary="true" item="cacheable"/>
786   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
787   the response message for use in answering subsequent requests.
788   Even when a response is cacheable, there might be additional
789   constraints placed by the client or by the origin server on when
790   that cached response can be used for a particular request. HTTP
791   requirements for cache behavior and cacheable responses are
792   defined in &caching-overview;
793</t>
794<t>
795   There are a wide variety of architectures and configurations
796   of caches and proxies deployed across the World Wide Web and
797   inside large organizations. These systems include national hierarchies
798   of proxy caches to save transoceanic bandwidth, systems that
799   broadcast or multicast cache entries, organizations that distribute
800   subsets of cached data via optical media, and so on.
801</t>
802</section>
803
804<section title="Protocol Versioning" anchor="http.version">
805  <x:anchor-alias value="HTTP-Version"/>
806  <x:anchor-alias value="HTTP-Prot-Name"/>
807<t>
808   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
809   versions of the protocol. This specification defines version "1.1".
810   The protocol version as a whole indicates the sender's compliance
811   with the set of requirements laid out in that version's corresponding
812   specification of HTTP.
813</t>
814<t>
815   The version of an HTTP message is indicated by an HTTP-Version field
816   in the first line of the message. HTTP-Version is case-sensitive.
817</t>
818<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
819  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
820  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
821</artwork></figure>
822<t>
823   The HTTP version number consists of two decimal digits separated by a "."
824   (period or decimal point).  The first digit ("major version") indicates the
825   HTTP messaging syntax, whereas the second digit ("minor version") indicates
826   the highest minor version to which the sender is at least conditionally
827   compliant and able to understand for future communication.  The minor
828   version advertises the sender's communication capabilities even when the
829   sender is only using a backwards-compatible subset of the protocol,
830   thereby letting the recipient know that more advanced features can
831   be used in response (by servers) or in future requests (by clients).
832</t>
833<t>
834   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
835   <xref target="RFC1945"/> or a recipient whose version is unknown,
836   the HTTP/1.1 message is constructed such that it can be interpreted
837   as a valid HTTP/1.0 message if all of the newer features are ignored.
838   This specification places recipient-version requirements on some
839   new features so that a compliant sender will only use compatible
840   features until it has determined, through configuration or the
841   receipt of a message, that the recipient supports HTTP/1.1.
842</t>
843<t>
844   The interpretation of an HTTP header field does not change
845   between minor versions of the same major version, though the default
846   behavior of a recipient in the absence of such a field can change.
847   Unless specified otherwise, header fields defined in HTTP/1.1 are
848   defined for all versions of HTTP/1.x.  In particular, the Host and
849   Connection header fields ought to be implemented by all HTTP/1.x
850   implementations whether or not they advertise compliance with HTTP/1.1.
851</t>
852<t>
853   New header fields can be defined such that, when they are
854   understood by a recipient, they might override or enhance the
855   interpretation of previously defined header fields.  When an
856   implementation receives an unrecognized header field, the recipient
857   &MUST; ignore that header field for local processing regardless of
858   the message's HTTP version.  An unrecognized header field received
859   by a proxy &MUST; be forwarded downstream unless the header field's
860   field-name is listed in the message's Connection header-field
861   (see <xref target="header.connection"/>).
862   These requirements allow HTTP's functionality to be enhanced without
863   requiring prior update of all compliant intermediaries.
864</t>
865<t>
866   Intermediaries that process HTTP messages (i.e., all intermediaries
867   other than those acting as a tunnel) &MUST; send their own HTTP-Version
868   in forwarded messages.  In other words, they &MUST-NOT; blindly
869   forward the first line of an HTTP message without ensuring that the
870   protocol version matches what the intermediary understands, and
871   is at least conditionally compliant to, for both the receiving and
872   sending of messages.  Forwarding an HTTP message without rewriting
873   the HTTP-Version might result in communication errors when downstream
874   recipients use the message sender's version to determine what features
875   are safe to use for later communication with that sender.
876</t>
877<t>
878   An HTTP client &SHOULD; send a request version equal to the highest
879   version for which the client is at least conditionally compliant and
880   whose major version is no higher than the highest version supported
881   by the server, if this is known.  An HTTP client &MUST-NOT; send a
882   version for which it is not at least conditionally compliant.
883</t>
884<t>
885   An HTTP client &MAY; send a lower request version if it is known that
886   the server incorrectly implements the HTTP specification, but only
887   after the client has attempted at least one normal request and determined
888   from the response status or header fields (e.g., Server) that the
889   server improperly handles higher request versions.
890</t>
891<t>
892   An HTTP server &SHOULD; send a response version equal to the highest
893   version for which the server is at least conditionally compliant and
894   whose major version is less than or equal to the one received in the
895   request.  An HTTP server &MUST-NOT; send a version for which it is not
896   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
897   Version Not Supported) response if it cannot send a response using the
898   major version used in the client's request.
899</t>
900<t>
901   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
902   if it is known or suspected that the client incorrectly implements the
903   HTTP specification and is incapable of correctly processing later
904   version responses, such as when a client fails to parse the version
905   number correctly or when an intermediary is known to blindly forward
906   the HTTP-Version even when it doesn't comply with the given minor
907   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
908   performed unless triggered by specific client attributes, such as when
909   one or more of the request header fields (e.g., User-Agent) uniquely
910   match the values sent by a client known to be in error.
911</t>
912<t>
913   The intention of HTTP's versioning design is that the major number
914   will only be incremented if an incompatible message syntax is
915   introduced, and that the minor number will only be incremented when
916   changes made to the protocol have the effect of adding to the message
917   semantics or implying additional capabilities of the sender.  However,
918   the minor version was not incremented for the changes introduced between
919   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
920   is specifically avoiding any such changes to the protocol.
921</t>
922</section>
923
924<section title="Uniform Resource Identifiers" anchor="uri">
925<iref primary="true" item="resource"/>
926<t>
927   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
928   throughout HTTP as the means for identifying resources. URI references
929   are used to target requests, indicate redirects, and define relationships.
930   HTTP does not limit what a resource might be; it merely defines an interface
931   that can be used to interact with a resource via HTTP. More information on
932   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
933</t>
934  <x:anchor-alias value="URI-reference"/>
935  <x:anchor-alias value="absolute-URI"/>
936  <x:anchor-alias value="relative-part"/>
937  <x:anchor-alias value="authority"/>
938  <x:anchor-alias value="path-abempty"/>
939  <x:anchor-alias value="path-absolute"/>
940  <x:anchor-alias value="port"/>
941  <x:anchor-alias value="query"/>
942  <x:anchor-alias value="uri-host"/>
943  <x:anchor-alias value="partial-URI"/>
944<t>
945   This specification adopts the definitions of "URI-reference",
946   "absolute-URI", "relative-part", "port", "host",
947   "path-abempty", "path-absolute", "query", and "authority" from the
948   URI generic syntax <xref target="RFC3986"/>.
949   In addition, we define a partial-URI rule for protocol elements
950   that allow a relative URI but not a fragment.
951</t>
952<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"/>
953  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
954  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
955  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
956  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
957  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
958  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
959  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
960  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
961  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
962 
963  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
964</artwork></figure>
965<t>
966   Each protocol element in HTTP that allows a URI reference will indicate
967   in its ABNF production whether the element allows any form of reference
968   (URI-reference), only a URI in absolute form (absolute-URI), only the
969   path and optional query components, or some combination of the above.
970   Unless otherwise indicated, URI references are parsed relative to the
971   effective request URI, which defines the default base URI for references
972   in both the request and its corresponding response.
973</t>
974
975<section title="http URI scheme" anchor="http.uri">
976  <x:anchor-alias value="http-URI"/>
977  <iref item="http URI scheme" primary="true"/>
978  <iref item="URI scheme" subitem="http" primary="true"/>
979<t>
980   The "http" URI scheme is hereby defined for the purpose of minting
981   identifiers according to their association with the hierarchical
982   namespace governed by a potential HTTP origin server listening for
983   TCP connections on a given port.
984</t>
985<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
986  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
987</artwork></figure>
988<t>
989   The HTTP origin server is identified by the generic syntax's
990   <x:ref>authority</x:ref> component, which includes a host identifier
991   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
992   The remainder of the URI, consisting of both the hierarchical path
993   component and optional query component, serves as an identifier for
994   a potential resource within that origin server's name space.
995</t>
996<t>
997   If the host identifier is provided as an IP literal or IPv4 address,
998   then the origin server is any listener on the indicated TCP port at
999   that IP address. If host is a registered name, then that name is
1000   considered an indirect identifier and the recipient might use a name
1001   resolution service, such as DNS, to find the address of a listener
1002   for that host.
1003   The host &MUST-NOT; be empty; if an "http" URI is received with an
1004   empty host, then it &MUST; be rejected as invalid.
1005   If the port subcomponent is empty or not given, then TCP port 80 is
1006   assumed (the default reserved port for WWW services).
1007</t>
1008<t>
1009   Regardless of the form of host identifier, access to that host is not
1010   implied by the mere presence of its name or address. The host might or might
1011   not exist and, even when it does exist, might or might not be running an
1012   HTTP server or listening to the indicated port. The "http" URI scheme
1013   makes use of the delegated nature of Internet names and addresses to
1014   establish a naming authority (whatever entity has the ability to place
1015   an HTTP server at that Internet name or address) and allows that
1016   authority to determine which names are valid and how they might be used.
1017</t>
1018<t>
1019   When an "http" URI is used within a context that calls for access to the
1020   indicated resource, a client &MAY; attempt access by resolving
1021   the host to an IP address, establishing a TCP connection to that address
1022   on the indicated port, and sending an HTTP request message
1023   (<xref target="http.message"/>) containing the URI's identifying data
1024   (<xref target="message.routing"/>) to the server.
1025   If the server responds to that request with a non-interim HTTP response
1026   message, as described in &status-code-reasonphr;, then that response
1027   is considered an authoritative answer to the client's request.
1028</t>
1029<t>
1030   Although HTTP is independent of the transport protocol, the "http"
1031   scheme is specific to TCP-based services because the name delegation
1032   process depends on TCP for establishing authority.
1033   An HTTP service based on some other underlying connection protocol
1034   would presumably be identified using a different URI scheme, just as
1035   the "https" scheme (below) is used for servers that require an SSL/TLS
1036   transport layer on a connection. Other protocols might also be used to
1037   provide access to "http" identified resources &mdash; it is only the
1038   authoritative interface used for mapping the namespace that is
1039   specific to TCP.
1040</t>
1041<t>
1042   The URI generic syntax for authority also includes a deprecated
1043   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1044   for including user authentication information in the URI.  Some
1045   implementations make use of the userinfo component for internal
1046   configuration of authentication information, such as within command
1047   invocation options, configuration files, or bookmark lists, even
1048   though such usage might expose a user identifier or password.
1049   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1050   delimiter) when transmitting an "http" URI in a message.  Recipients
1051   of HTTP messages that contain a URI reference &SHOULD; parse for the
1052   existence of userinfo and treat its presence as an error, likely
1053   indicating that the deprecated subcomponent is being used to obscure
1054   the authority for the sake of phishing attacks.
1055</t>
1056</section>
1057
1058<section title="https URI scheme" anchor="https.uri">
1059   <x:anchor-alias value="https-URI"/>
1060   <iref item="https URI scheme"/>
1061   <iref item="URI scheme" subitem="https"/>
1062<t>
1063   The "https" URI scheme is hereby defined for the purpose of minting
1064   identifiers according to their association with the hierarchical
1065   namespace governed by a potential HTTP origin server listening for
1066   SSL/TLS-secured connections on a given TCP port.
1067</t>
1068<t>
1069   All of the requirements listed above for the "http" scheme are also
1070   requirements for the "https" scheme, except that a default TCP port
1071   of 443 is assumed if the port subcomponent is empty or not given,
1072   and the TCP connection &MUST; be secured for privacy through the
1073   use of strong encryption prior to sending the first HTTP request.
1074</t>
1075<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1076  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1077</artwork></figure>
1078<t>
1079   Unlike the "http" scheme, responses to "https" identified requests
1080   are never "public" and thus &MUST-NOT; be reused for shared caching.
1081   They can, however, be reused in a private cache if the message is
1082   cacheable by default in HTTP or specifically indicated as such by
1083   the Cache-Control header field (&header-cache-control;).
1084</t>
1085<t>
1086   Resources made available via the "https" scheme have no shared
1087   identity with the "http" scheme even if their resource identifiers
1088   indicate the same authority (the same host listening to the same
1089   TCP port).  They are distinct name spaces and are considered to be
1090   distinct origin servers.  However, an extension to HTTP that is
1091   defined to apply to entire host domains, such as the Cookie protocol
1092   <xref target="RFC6265"/>, can allow information
1093   set by one service to impact communication with other services
1094   within a matching group of host domains.
1095</t>
1096<t>
1097   The process for authoritative access to an "https" identified
1098   resource is defined in <xref target="RFC2818"/>.
1099</t>
1100</section>
1101
1102<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1103<t>
1104   Since the "http" and "https" schemes conform to the URI generic syntax,
1105   such URIs are normalized and compared according to the algorithm defined
1106   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1107   described above for each scheme.
1108</t>
1109<t>
1110   If the port is equal to the default port for a scheme, the normal
1111   form is to elide the port subcomponent. Likewise, an empty path
1112   component is equivalent to an absolute path of "/", so the normal
1113   form is to provide a path of "/" instead. The scheme and host
1114   are case-insensitive and normally provided in lowercase; all
1115   other components are compared in a case-sensitive manner.
1116   Characters other than those in the "reserved" set are equivalent
1117   to their percent-encoded octets (see <xref target="RFC3986"
1118   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1119</t>
1120<t>
1121   For example, the following three URIs are equivalent:
1122</t>
1123<figure><artwork type="example">
1124   http://example.com:80/~smith/home.html
1125   http://EXAMPLE.com/%7Esmith/home.html
1126   http://EXAMPLE.com:/%7esmith/home.html
1127</artwork></figure>
1128</section>
1129</section>
1130</section>
1131
1132<section title="Message Format" anchor="http.message">
1133<x:anchor-alias value="generic-message"/>
1134<x:anchor-alias value="message.types"/>
1135<x:anchor-alias value="HTTP-message"/>
1136<x:anchor-alias value="start-line"/>
1137<iref item="header section"/>
1138<iref item="headers"/>
1139<iref item="header field"/>
1140<t>
1141   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1142   octets in a format similar to the Internet Message Format
1143   <xref target="RFC5322"/>: zero or more header fields (collectively
1144   referred to as the "headers" or the "header section"), an empty line
1145   indicating the end of the header section, and an optional message-body.
1146</t>
1147<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1148  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1149                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1150                    <x:ref>CRLF</x:ref>
1151                    [ <x:ref>message-body</x:ref> ]
1152</artwork></figure>
1153<t>
1154   The normal procedure for parsing an HTTP message is to read the
1155   start-line into a structure, read each header field into a hash
1156   table by field name until the empty line, and then use the parsed
1157   data to determine if a message-body is expected.  If a message-body
1158   has been indicated, then it is read as a stream until an amount
1159   of octets equal to the message-body length is read or the connection
1160   is closed.
1161</t>
1162<t>
1163   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1164   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1165   Parsing an HTTP message as a stream of Unicode characters, without regard
1166   for the specific encoding, creates security vulnerabilities due to the
1167   varying ways that string processing libraries handle invalid multibyte
1168   character sequences that contain the octet LF (%x0A).  String-based
1169   parsers can only be safely used within protocol elements after the element
1170   has been extracted from the message, such as within a header field-value
1171   after message parsing has delineated the individual fields.
1172</t>
1173
1174<section title="Start Line" anchor="start.line">
1175  <x:anchor-alias value="Start-Line"/>
1176<t>
1177   An HTTP message can either be a request from client to server or a
1178   response from server to client.  Syntactically, the two types of message
1179   differ only in the start-line, which is either a Request-Line (for requests)
1180   or a Status-Line (for responses), and in the algorithm for determining
1181   the length of the message-body (<xref target="message.body"/>).
1182   In theory, a client could receive requests and a server could receive
1183   responses, distinguishing them by their different start-line formats,
1184   but in practice servers are implemented to only expect a request
1185   (a response is interpreted as an unknown or invalid request method)
1186   and clients are implemented to only expect a response.
1187</t>
1188<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1189  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1190</artwork></figure>
1191<t>
1192</t>
1193<t>
1194   Implementations &MUST-NOT; send whitespace between the start-line and
1195   the first header field. The presence of such whitespace in a request
1196   might be an attempt to trick a server into ignoring that field or
1197   processing the line after it as a new request, either of which might
1198   result in a security vulnerability if other implementations within
1199   the request chain interpret the same message differently.
1200   Likewise, the presence of such whitespace in a response might be
1201   ignored by some clients or cause others to cease parsing.
1202</t>
1203
1204<section title="Request-Line" anchor="request.line">
1205  <x:anchor-alias value="Request"/>
1206  <x:anchor-alias value="Request-Line"/>
1207<t>
1208   The Request-Line begins with a method token, followed by a single
1209   space (SP), the request-target, another single space (SP), the
1210   protocol version, and ending with CRLF.
1211</t>
1212<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1213  <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>
1214</artwork></figure>
1215
1216<section title="Method" anchor="method">
1217  <x:anchor-alias value="Method"/>
1218<t>
1219   The Method token indicates the request method to be performed on the
1220   target resource. The request method is case-sensitive.
1221</t>
1222<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1223  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1224</artwork></figure>
1225<t>
1226   See &method; for further information, such as the list of methods defined
1227   by this specification, the IANA registry, and considerations for new methods.
1228</t>
1229</section>
1230
1231<section title="request-target" anchor="request-target">
1232  <x:anchor-alias value="request-target"/>
1233<t>
1234   The request-target identifies the target resource upon which to apply
1235   the request.  The four options for request-target are described in
1236   <xref target="request-target-types"/>.
1237</t>
1238<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1239  <x:ref>request-target</x:ref> = "*"
1240                 / <x:ref>absolute-URI</x:ref>
1241                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1242                 / <x:ref>authority</x:ref>
1243</artwork></figure>
1244<t>
1245   HTTP does not place a pre-defined limit on the length of a request-target.
1246   A server &MUST; be prepared to receive URIs of unbounded length and
1247   respond with the 414 (URI Too Long) status code if the received
1248   request-target would be longer than the server wishes to handle
1249   (see &status-414;).
1250</t>
1251<t>
1252   Various ad-hoc limitations on request-target length are found in practice.
1253   It is &RECOMMENDED; that all HTTP senders and recipients support
1254   request-target lengths of 8000 or more octets.
1255</t>
1256<x:note>
1257  <t>
1258    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1259    are not part of the request-target and thus will not be transmitted
1260    in an HTTP request.
1261  </t>
1262</x:note>
1263</section>
1264</section>
1265
1266<section title="Response Status-Line" anchor="status.line">
1267  <x:anchor-alias value="Response"/>
1268  <x:anchor-alias value="Status-Line"/>
1269<t>
1270   The first line of a Response message is the Status-Line, consisting
1271   of the protocol version, a space (SP), the status code, another space,
1272   a possibly-empty textual phrase describing the status code, and
1273   ending with CRLF.
1274</t>
1275<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1276  <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>
1277</artwork></figure>
1278
1279<section title="Status Code" anchor="status.code">
1280  <x:anchor-alias value="Status-Code"/>
1281<t>
1282   The Status-Code element is a 3-digit integer result code of the attempt to
1283   understand and satisfy the request. See &status-code-reasonphr; for
1284   further information, such as the list of status codes defined by this
1285   specification, the IANA registry, and considerations for new status codes.
1286</t>
1287<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/>
1288  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1289</artwork></figure>
1290</section>
1291
1292<section title="Reason Phrase" anchor="reason.phrase">
1293  <x:anchor-alias value="Reason-Phrase"/>
1294<t>   
1295   The Reason Phrase exists for the sole purpose of providing a textual
1296   description associated with the numeric status code, out of deference to
1297   earlier Internet application protocols that were more frequently used with
1298   interactive text clients. A client &SHOULD; ignore the content of the Reason
1299   Phrase.
1300</t>
1301<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1302  <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> )
1303</artwork></figure>
1304</section>
1305</section>
1306
1307</section>
1308
1309<section title="Header Fields" anchor="header.fields">
1310  <x:anchor-alias value="header-field"/>
1311  <x:anchor-alias value="field-content"/>
1312  <x:anchor-alias value="field-name"/>
1313  <x:anchor-alias value="field-value"/>
1314  <x:anchor-alias value="OWS"/>
1315<t>
1316   Each HTTP header field consists of a case-insensitive field name
1317   followed by a colon (":"), optional whitespace, and the field value.
1318</t>
1319<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"/>
1320  <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>
1321  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1322  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1323  <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> )
1324</artwork></figure>
1325<t>
1326   The field-name token labels the corresponding field-value as having the
1327   semantics defined by that header field.  For example, the Date header field
1328   is defined in &header-date; as containing the origination
1329   timestamp for the message in which it appears.
1330</t>
1331<t>
1332   HTTP header fields are fully extensible: there is no limit on the
1333   introduction of new field names, each presumably defining new semantics,
1334   or on the number of header fields used in a given message.  Existing
1335   fields are defined in each part of this specification and in many other
1336   specifications outside the standards process.
1337   New header fields can be introduced without changing the protocol version
1338   if their defined semantics allow them to be safely ignored by recipients
1339   that do not recognize them.
1340</t>
1341<t>
1342   New HTTP header fields &SHOULD; be registered with IANA according
1343   to the procedures in &cons-new-header-fields;.
1344   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1345   field-name is listed in the Connection header field
1346   (<xref target="header.connection"/>) or the proxy is specifically
1347   configured to block or otherwise transform such fields.
1348   Unrecognized header fields &SHOULD; be ignored by other recipients.
1349</t>
1350<t>
1351   The order in which header fields with differing field names are
1352   received is not significant. However, it is "good practice" to send
1353   header fields that contain control data first, such as Host on
1354   requests and Date on responses, so that implementations can decide
1355   when not to handle a message as early as possible.  A server &MUST;
1356   wait until the entire header section is received before interpreting
1357   a request message, since later header fields might include conditionals,
1358   authentication credentials, or deliberately misleading duplicate
1359   header fields that would impact request processing.
1360</t>
1361<t>
1362   Multiple header fields with the same field name &MUST-NOT; be
1363   sent in a message unless the entire field value for that
1364   header field is defined as a comma-separated list [i.e., #(values)].
1365   Multiple header fields with the same field name can be combined into
1366   one "field-name: field-value" pair, without changing the semantics of the
1367   message, by appending each subsequent field value to the combined
1368   field value in order, separated by a comma. The order in which
1369   header fields with the same field name are received is therefore
1370   significant to the interpretation of the combined field value;
1371   a proxy &MUST-NOT; change the order of these field values when
1372   forwarding a message.
1373</t>
1374<x:note>
1375  <t>
1376   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1377   practice can occur multiple times, but does not use the list syntax, and
1378   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1379   for details.) Also note that the Set-Cookie2 header field specified in
1380   <xref target="RFC2965"/> does not share this problem.
1381  </t>
1382</x:note>
1383
1384<section title="Field Parsing" anchor="field.parsing">
1385<t>
1386   No whitespace is allowed between the header field-name and colon.
1387   In the past, differences in the handling of such whitespace have led to
1388   security vulnerabilities in request routing and response handling.
1389   Any received request message that contains whitespace between a header
1390   field-name and colon &MUST; be rejected with a response code of 400
1391   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1392   message before forwarding the message downstream.
1393</t>
1394<t>
1395   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1396   preferred. The field value does not include any leading or trailing white
1397   space: OWS occurring before the first non-whitespace octet of the
1398   field value or after the last non-whitespace octet of the field value
1399   is ignored and &SHOULD; be removed before further processing (as this does
1400   not change the meaning of the header field).
1401</t>
1402<t>
1403   Historically, HTTP header field values could be extended over multiple
1404   lines by preceding each extra line with at least one space or horizontal
1405   tab (obs-fold). This specification deprecates such line
1406   folding except within the message/http media type
1407   (<xref target="internet.media.type.message.http"/>).
1408   HTTP senders &MUST-NOT; produce messages that include line folding
1409   (i.e., that contain any field-content that matches the obs-fold rule) unless
1410   the message is intended for packaging within the message/http media type.
1411   HTTP recipients &SHOULD; accept line folding and replace any embedded
1412   obs-fold whitespace with either a single SP or a matching number of SP
1413   octets (to avoid buffer copying) prior to interpreting the field value or
1414   forwarding the message downstream.
1415</t>
1416<t>
1417   Historically, HTTP has allowed field content with text in the ISO-8859-1
1418   <xref target="ISO-8859-1"/> character encoding and supported other
1419   character sets only through use of <xref target="RFC2047"/> encoding.
1420   In practice, most HTTP header field values use only a subset of the
1421   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1422   header fields &SHOULD; limit their field values to US-ASCII octets.
1423   Recipients &SHOULD; treat other (obs-text) octets in field content as
1424   opaque data.
1425</t>
1426</section>
1427
1428<section title="Field Length" anchor="field.length">
1429<t>
1430   HTTP does not place a pre-defined limit on the length of header fields,
1431   either in isolation or as a set. A server &MUST; be prepared to receive
1432   request header fields of unbounded length and respond with a 4xx status
1433   code if the received header field(s) would be longer than the server wishes
1434   to handle.
1435</t>
1436<t>
1437   A client that receives response headers that are longer than it wishes to
1438   handle can only treat it as a server error.
1439</t>
1440<t>
1441   Various ad-hoc limitations on header length are found in practice. It is
1442   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1443   combined header fields have 4000 or more octets.
1444</t>
1445</section>
1446
1447<section title="Common Field ABNF Rules" anchor="field.rules">
1448<t anchor="rule.token.separators">
1449  <x:anchor-alias value="tchar"/>
1450  <x:anchor-alias value="token"/>
1451  <x:anchor-alias value="special"/>
1452  <x:anchor-alias value="word"/>
1453   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1454   separated by whitespace or special characters. These special characters
1455   &MUST; be in a quoted string to be used within a parameter value (as defined
1456   in <xref target="transfer.codings"/>).
1457</t>
1458<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"/>
1459  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1460
1461  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1462<!--
1463  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1464 -->
1465  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1466                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1467                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1468                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1469
1470  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1471                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1472                 / "]" / "?" / "=" / "{" / "}"
1473</artwork></figure>
1474<t anchor="rule.quoted-string">
1475  <x:anchor-alias value="quoted-string"/>
1476  <x:anchor-alias value="qdtext"/>
1477  <x:anchor-alias value="obs-text"/>
1478   A string of text is parsed as a single word if it is quoted using
1479   double-quote marks.
1480</t>
1481<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"/>
1482  <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>
1483  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1484  <x:ref>obs-text</x:ref>       = %x80-FF
1485</artwork></figure>
1486<t anchor="rule.quoted-pair">
1487  <x:anchor-alias value="quoted-pair"/>
1488   The backslash octet ("\") can be used as a single-octet
1489   quoting mechanism within quoted-string constructs:
1490</t>
1491<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1492  <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> )
1493</artwork></figure>
1494<t>
1495   Recipients that process the value of the quoted-string &MUST; handle a
1496   quoted-pair as if it were replaced by the octet following the backslash.
1497</t>
1498<t>
1499   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1500   escaping (i.e., other than DQUOTE and the backslash octet).
1501</t>
1502<t anchor="rule.comment">
1503  <x:anchor-alias value="comment"/>
1504  <x:anchor-alias value="ctext"/>
1505   Comments can be included in some HTTP header fields by surrounding
1506   the comment text with parentheses. Comments are only allowed in
1507   fields containing "comment" as part of their field value definition.
1508</t>
1509<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1510  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1511  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1512</artwork></figure>
1513<t anchor="rule.quoted-cpair">
1514  <x:anchor-alias value="quoted-cpair"/>
1515   The backslash octet ("\") can be used as a single-octet
1516   quoting mechanism within comment constructs:
1517</t>
1518<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1519  <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> )
1520</artwork></figure>
1521<t>
1522   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1523   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1524</t>
1525</section>
1526</section>
1527
1528<section title="Message Body" anchor="message.body">
1529  <x:anchor-alias value="message-body"/>
1530<t>
1531   The message-body (if any) of an HTTP message is used to carry the
1532   payload body associated with the request or response.
1533</t>
1534<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1535  <x:ref>message-body</x:ref> = *OCTET
1536</artwork></figure>
1537<t>
1538   The message-body differs from the payload body only when a transfer-coding
1539   has been applied, as indicated by the Transfer-Encoding header field
1540   (<xref target="header.transfer-encoding"/>).  If more than one
1541   Transfer-Encoding header field is present in a message, the multiple
1542   field-values &MUST; be combined into one field-value, according to the
1543   algorithm defined in <xref target="header.fields"/>, before determining
1544   the message-body length.
1545</t>
1546<t>
1547   When one or more transfer-codings are applied to a payload in order to
1548   form the message-body, the Transfer-Encoding header field &MUST; contain
1549   the list of transfer-codings applied. Transfer-Encoding is a property of
1550   the message, not of the payload, and thus &MAY; be added or removed by
1551   any implementation along the request/response chain under the constraints
1552   found in <xref target="transfer.codings"/>.
1553</t>
1554<t>
1555   If a message is received that has multiple Content-Length header fields
1556   (<xref target="header.content-length"/>) with field-values consisting
1557   of the same decimal value, or a single Content-Length header field with
1558   a field value containing a list of identical decimal values (e.g.,
1559   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1560   header fields have been generated or combined by an upstream message
1561   processor, then the recipient &MUST; either reject the message as invalid
1562   or replace the duplicated field-values with a single valid Content-Length
1563   field containing that decimal value prior to determining the message-body
1564   length.
1565</t>
1566<t>
1567   The rules for when a message-body is allowed in a message differ for
1568   requests and responses.
1569</t>
1570<t>
1571   The presence of a message-body in a request is signaled by the
1572   inclusion of a Content-Length or Transfer-Encoding header field in
1573   the request's header fields, even if the request method does not
1574   define any use for a message-body.  This allows the request
1575   message framing algorithm to be independent of method semantics.
1576</t>
1577<t>
1578   For response messages, whether or not a message-body is included with
1579   a message is dependent on both the request method and the response
1580   status code (<xref target="status.code"/>).
1581   Responses to the HEAD request method never include a message-body
1582   because the associated response header fields (e.g., Transfer-Encoding,
1583   Content-Length, etc.) only indicate what their values would have been
1584   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1585   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1586   All other responses do include a message-body, although the body
1587   &MAY; be of zero length.
1588</t>
1589<t>
1590   The length of the message-body is determined by one of the following
1591   (in order of precedence):
1592</t>
1593<t>
1594  <list style="numbers">
1595    <x:lt><t>
1596     Any response to a HEAD request and any response with a status
1597     code of 100-199, 204, or 304 is always terminated by the first
1598     empty line after the header fields, regardless of the header
1599     fields present in the message, and thus cannot contain a message-body.
1600    </t></x:lt>
1601    <x:lt><t>
1602     If a Transfer-Encoding header field is present
1603     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1604     is the final encoding, the message-body length is determined by reading
1605     and decoding the chunked data until the transfer-coding indicates the
1606     data is complete.
1607    </t>
1608    <t>
1609     If a Transfer-Encoding header field is present in a response and the
1610     "chunked" transfer-coding is not the final encoding, the message-body
1611     length is determined by reading the connection until it is closed by
1612     the server.
1613     If a Transfer-Encoding header field is present in a request and the
1614     "chunked" transfer-coding is not the final encoding, the message-body
1615     length cannot be determined reliably; the server &MUST; respond with
1616     the 400 (Bad Request) status code and then close the connection.
1617    </t>
1618    <t>
1619     If a message is received with both a Transfer-Encoding header field
1620     and a Content-Length header field, the Transfer-Encoding overrides
1621     the Content-Length.
1622     Such a message might indicate an attempt to perform request or response
1623     smuggling (bypass of security-related checks on message routing or content)
1624     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1625     be removed, prior to forwarding the message downstream, or replaced with
1626     the real message-body length after the transfer-coding is decoded.
1627    </t></x:lt>
1628    <x:lt><t>
1629     If a message is received without Transfer-Encoding and with either
1630     multiple Content-Length header fields having differing field-values or
1631     a single Content-Length header field having an invalid value, then the
1632     message framing is invalid and &MUST; be treated as an error to
1633     prevent request or response smuggling.
1634     If this is a request message, the server &MUST; respond with
1635     a 400 (Bad Request) status code and then close the connection.
1636     If this is a response message received by a proxy, the proxy
1637     &MUST; discard the received response, send a 502 (Bad Gateway)
1638     status code as its downstream response, and then close the connection.
1639     If this is a response message received by a user-agent, it &MUST; be
1640     treated as an error by discarding the message and closing the connection.
1641    </t></x:lt>
1642    <x:lt><t>
1643     If a valid Content-Length header field
1644     is present without Transfer-Encoding, its decimal value defines the
1645     message-body length in octets.  If the actual number of octets sent in
1646     the message is less than the indicated Content-Length, the recipient
1647     &MUST; consider the message to be incomplete and treat the connection
1648     as no longer usable.
1649     If the actual number of octets sent in the message is more than the indicated
1650     Content-Length, the recipient &MUST; only process the message-body up to the
1651     field value's number of octets; the remainder of the message &MUST; either
1652     be discarded or treated as the next message in a pipeline.  For the sake of
1653     robustness, a user-agent &MAY; attempt to detect and correct such an error
1654     in message framing if it is parsing the response to the last request on
1655     a connection and the connection has been closed by the server.
1656    </t></x:lt>
1657    <x:lt><t>
1658     If this is a request message and none of the above are true, then the
1659     message-body length is zero (no message-body is present).
1660    </t></x:lt>
1661    <x:lt><t>
1662     Otherwise, this is a response message without a declared message-body
1663     length, so the message-body length is determined by the number of octets
1664     received prior to the server closing the connection.
1665    </t></x:lt>
1666  </list>
1667</t>
1668<t>
1669   Since there is no way to distinguish a successfully completed,
1670   close-delimited message from a partially-received message interrupted
1671   by network failure, implementations &SHOULD; use encoding or
1672   length-delimited messages whenever possible.  The close-delimiting
1673   feature exists primarily for backwards compatibility with HTTP/1.0.
1674</t>
1675<t>
1676   A server &MAY; reject a request that contains a message-body but
1677   not a Content-Length by responding with 411 (Length Required).
1678</t>
1679<t>
1680   Unless a transfer-coding other than "chunked" has been applied,
1681   a client that sends a request containing a message-body &SHOULD;
1682   use a valid Content-Length header field if the message-body length
1683   is known in advance, rather than the "chunked" encoding, since some
1684   existing services respond to "chunked" with a 411 (Length Required)
1685   status code even though they understand the chunked encoding.  This
1686   is typically because such services are implemented via a gateway that
1687   requires a content-length in advance of being called and the server
1688   is unable or unwilling to buffer the entire request before processing.
1689</t>
1690<t>
1691   A client that sends a request containing a message-body &MUST; include a
1692   valid Content-Length header field if it does not know the server will
1693   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1694   of specific user configuration or by remembering the version of a prior
1695   received response.
1696</t>
1697</section>
1698
1699<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1700<t>
1701   Request messages that are prematurely terminated, possibly due to a
1702   cancelled connection or a server-imposed time-out exception, &MUST;
1703   result in closure of the connection; sending an HTTP/1.1 error response
1704   prior to closing the connection is &OPTIONAL;.
1705</t>
1706<t>
1707   Response messages that are prematurely terminated, usually by closure
1708   of the connection prior to receiving the expected number of octets or by
1709   failure to decode a transfer-encoded message-body, &MUST; be recorded
1710   as incomplete.  A response that terminates in the middle of the header
1711   block (before the empty line is received) cannot be assumed to convey the
1712   full semantics of the response and &MUST; be treated as an error.
1713</t>
1714<t>
1715   A message-body that uses the chunked transfer encoding is
1716   incomplete if the zero-sized chunk that terminates the encoding has not
1717   been received.  A message that uses a valid Content-Length is incomplete
1718   if the size of the message-body received (in octets) is less than the
1719   value given by Content-Length.  A response that has neither chunked
1720   transfer encoding nor Content-Length is terminated by closure of the
1721   connection, and thus is considered complete regardless of the number of
1722   message-body octets received, provided that the header block was received
1723   intact.
1724</t>
1725<t>
1726   A user agent &MUST-NOT; render an incomplete response message-body as if
1727   it were complete (i.e., some indication must be given to the user that an
1728   error occurred).  Cache requirements for incomplete responses are defined
1729   in &cache-incomplete;.
1730</t>
1731<t>
1732   A server &MUST; read the entire request message-body or close
1733   the connection after sending its response, since otherwise the
1734   remaining data on a persistent connection would be misinterpreted
1735   as the next request.  Likewise,
1736   a client &MUST; read the entire response message-body if it intends
1737   to reuse the same connection for a subsequent request.  Pipelining
1738   multiple requests on a connection is described in <xref target="pipelining"/>.
1739</t>
1740</section>
1741
1742<section title="Message Parsing Robustness" anchor="message.robustness">
1743<t>
1744   Older HTTP/1.0 client implementations might send an extra CRLF
1745   after a POST request as a lame workaround for some early server
1746   applications that failed to read message-body content that was
1747   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1748   preface or follow a request with an extra CRLF.  If terminating
1749   the request message-body with a line-ending is desired, then the
1750   client &MUST; include the terminating CRLF octets as part of the
1751   message-body length.
1752</t>
1753<t>
1754   In the interest of robustness, servers &SHOULD; ignore at least one
1755   empty line received where a Request-Line is expected. In other words, if
1756   the server is reading the protocol stream at the beginning of a
1757   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1758   Likewise, although the line terminator for the start-line and header
1759   fields is the sequence CRLF, we recommend that recipients recognize a
1760   single LF as a line terminator and ignore any CR.
1761</t>
1762<t>
1763   When a server listening only for HTTP request messages, or processing
1764   what appears from the start-line to be an HTTP request message,
1765   receives a sequence of octets that does not match the HTTP-message
1766   grammar aside from the robustness exceptions listed above, the
1767   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1768</t>
1769</section>
1770</section>
1771
1772<section title="Message Routing" anchor="message.routing">
1773<t>
1774   In most cases, the user agent is provided a URI reference
1775   from which it determines an absolute URI for identifying the target
1776   resource.  When a request to the resource is initiated, all or part
1777   of that URI is used to construct the HTTP request-target.
1778</t>
1779
1780<section title="Types of Request Target" anchor="request-target-types">
1781<t>
1782   The four options for request-target are dependent on the nature of the
1783   request.
1784</t>   
1785<t><iref item="asterisk form (of request-target)"/>
1786   The asterisk "*" form of request-target, which &MUST-NOT; be used
1787   with any request method other than OPTIONS, means that the request
1788   applies to the server as a whole (the listening process) rather than
1789   to a specific named resource at that server.  For example,
1790</t>
1791<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1792OPTIONS * HTTP/1.1
1793</artwork></figure>
1794<t><iref item="absolute-URI form (of request-target)"/>
1795   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1796   proxy. The proxy is requested to either forward the request or service it
1797   from a valid cache, and then return the response. Note that the proxy &MAY;
1798   forward the request on to another proxy or directly to the server
1799   specified by the absolute-URI. In order to avoid request loops, a
1800   proxy that forwards requests to other proxies &MUST; be able to
1801   recognize and exclude all of its own server names, including
1802   any aliases, local variations, and the numeric IP address. An example
1803   Request-Line would be:
1804</t>
1805<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1806GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1807</artwork></figure>
1808<t>
1809   To allow for transition to absolute-URIs in all requests in future
1810   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1811   form in requests, even though HTTP/1.1 clients will only generate
1812   them in requests to proxies.
1813</t>
1814<t>
1815   If a proxy receives a host name that is not a fully qualified domain
1816   name, it &MAY; add its domain to the host name it received. If a proxy
1817   receives a fully qualified domain name, the proxy &MUST-NOT; change
1818   the host name.
1819</t>
1820<t><iref item="authority form (of request-target)"/>
1821   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1822</t>
1823<t><iref item="origin form (of request-target)"/>
1824   The most common form of request-target is that used when making
1825   a request to an origin server ("origin form").
1826   In this case, the absolute path and query components of the URI
1827   &MUST; be transmitted as the request-target, and the authority component
1828   &MUST; be transmitted in a Host header field. For example, a client wishing
1829   to retrieve a representation of the resource, as identified above,
1830   directly from the origin server would open (or reuse) a TCP connection
1831   to port 80 of the host "www.example.org" and send the lines:
1832</t>
1833<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1834GET /pub/WWW/TheProject.html HTTP/1.1
1835Host: www.example.org
1836</artwork></figure>
1837<t>
1838   followed by the remainder of the Request. Note that the origin form
1839   of request-target always starts with an absolute path; if the target
1840   resource's URI path is empty, then an absolute path of "/" &MUST; be
1841   provided in the request-target.
1842</t>
1843<t>
1844   If a proxy receives an OPTIONS request with an absolute-URI form of
1845   request-target in which the URI has an empty path and no query component,
1846   then the last proxy on the request chain &MUST; use a request-target
1847   of "*" when it forwards the request to the indicated origin server.
1848</t>
1849<figure><preamble>   
1850   For example, the request
1851</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1852OPTIONS http://www.example.org:8001 HTTP/1.1
1853</artwork></figure>
1854<figure><preamble>   
1855  would be forwarded by the final proxy as
1856</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1857OPTIONS * HTTP/1.1
1858Host: www.example.org:8001
1859</artwork>
1860<postamble>
1861   after connecting to port 8001 of host "www.example.org".
1862</postamble>
1863</figure>
1864<t>
1865   The request-target is transmitted in the format specified in
1866   <xref target="http.uri"/>. If the request-target is percent-encoded
1867   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1868   &MUST; decode the request-target in order to
1869   properly interpret the request. Servers &SHOULD; respond to invalid
1870   request-targets with an appropriate status code.
1871</t>
1872<t>
1873   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1874   received request-target when forwarding it to the next inbound server,
1875   except as noted above to replace a null path-absolute with "/" or "*".
1876</t>
1877<x:note>
1878  <t>
1879    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1880    meaning of the request when the origin server is improperly using
1881    a non-reserved URI character for a reserved purpose.  Implementors
1882    need to be aware that some pre-HTTP/1.1 proxies have been known to
1883    rewrite the request-target.
1884  </t>
1885</x:note>
1886</section>
1887
1888<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1889<t>
1890   The exact resource identified by an Internet request is determined by
1891   examining both the request-target and the Host header field.
1892</t>
1893<t>
1894   An origin server that does not allow resources to differ by the
1895   requested host &MAY; ignore the Host header field value when
1896   determining the resource identified by an HTTP/1.1 request. (But see
1897   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1898   for other requirements on Host support in HTTP/1.1.)
1899</t>
1900<t>
1901   An origin server that does differentiate resources based on the host
1902   requested (sometimes referred to as virtual hosts or vanity host
1903   names) &MUST; use the following rules for determining the requested
1904   resource on an HTTP/1.1 request:
1905  <list style="numbers">
1906    <t>If request-target is an absolute-URI, the host is part of the
1907     request-target. Any Host header field value in the request &MUST; be
1908     ignored.</t>
1909    <t>If the request-target is not an absolute-URI, and the request includes
1910     a Host header field, the host is determined by the Host header
1911     field value.</t>
1912    <t>If the host as determined by rule 1 or 2 is not a valid host on
1913     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1914  </list>
1915</t>
1916<t>
1917   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1918   attempt to use heuristics (e.g., examination of the URI path for
1919   something unique to a particular host) in order to determine what
1920   exact resource is being requested.
1921</t>
1922</section>
1923
1924<section title="Effective Request URI" anchor="effective.request.uri">
1925  <iref primary="true" item="effective request URI"/>
1926  <iref primary="true" item="target resource"/>
1927<t>
1928   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1929   for the target resource; instead, the URI needs to be inferred from the
1930   request-target, Host header field, and connection context. The result of
1931   this process is called the "effective request URI".  The "target resource"
1932   is the resource identified by the effective request URI.
1933</t>
1934<t>
1935   If the request-target is an absolute-URI, then the effective request URI is
1936   the request-target.
1937</t>
1938<t>
1939   If the request-target uses the path-absolute form or the asterisk form,
1940   and the Host header field is present, then the effective request URI is
1941   constructed by concatenating
1942</t>
1943<t>
1944  <list style="symbols">
1945    <t>
1946      the scheme name: "http" if the request was received over an insecure
1947      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1948      connection,
1949    </t>
1950    <t>
1951      the octet sequence "://",
1952    </t>
1953    <t>
1954      the authority component, as specified in the Host header field
1955      (<xref target="header.host"/>), and
1956    </t>
1957    <t>
1958      the request-target obtained from the Request-Line, unless the
1959      request-target is just the asterisk "*".
1960    </t>
1961  </list>
1962</t>
1963<t>
1964   If the request-target uses the path-absolute form or the asterisk form,
1965   and the Host header field is not present, then the effective request URI is
1966   undefined.
1967</t>
1968<t>
1969   Otherwise, when request-target uses the authority form, the effective
1970   request URI is undefined.
1971</t>
1972<figure>
1973<preamble>
1974   Example 1: the effective request URI for the message
1975</preamble> 
1976<artwork type="example" x:indent-with="  ">
1977GET /pub/WWW/TheProject.html HTTP/1.1
1978Host: www.example.org:8080
1979</artwork>
1980<postamble>
1981  (received over an insecure TCP connection) is "http", plus "://", plus the
1982  authority component "www.example.org:8080", plus the request-target
1983  "/pub/WWW/TheProject.html", thus
1984  "http://www.example.org:8080/pub/WWW/TheProject.html".
1985</postamble>
1986</figure>
1987<figure>
1988<preamble>
1989   Example 2: the effective request URI for the message
1990</preamble> 
1991<artwork type="example" x:indent-with="  ">
1992OPTIONS * HTTP/1.1
1993Host: www.example.org
1994</artwork>
1995<postamble>
1996  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1997  authority component "www.example.org", thus "https://www.example.org".
1998</postamble>
1999</figure>
2000<t>
2001   Effective request URIs are compared using the rules described in
2002   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
2003   be treated as equivalent to an absolute path of "/".
2004</t> 
2005</section>
2006</section>
2007
2008
2009<section title="Protocol Parameters" anchor="protocol.parameters">
2010
2011<section title="Transfer Codings" anchor="transfer.codings">
2012  <x:anchor-alias value="transfer-coding"/>
2013  <x:anchor-alias value="transfer-extension"/>
2014<t>
2015   Transfer-coding values are used to indicate an encoding
2016   transformation that has been, can be, or might need to be applied to a
2017   payload body in order to ensure "safe transport" through the network.
2018   This differs from a content coding in that the transfer-coding is a
2019   property of the message rather than a property of the representation
2020   that is being transferred.
2021</t>
2022<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2023  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2024                          / "compress" ; <xref target="compress.coding"/>
2025                          / "deflate" ; <xref target="deflate.coding"/>
2026                          / "gzip" ; <xref target="gzip.coding"/>
2027                          / <x:ref>transfer-extension</x:ref>
2028  <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> )
2029</artwork></figure>
2030<t anchor="rule.parameter">
2031  <x:anchor-alias value="attribute"/>
2032  <x:anchor-alias value="transfer-parameter"/>
2033  <x:anchor-alias value="value"/>
2034   Parameters are in the form of attribute/value pairs.
2035</t>
2036<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"/>
2037  <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>
2038  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2039  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2040</artwork></figure>
2041<t>
2042   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2043   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2044   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2045</t>
2046<t>
2047   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2048   MIME, which were designed to enable safe transport of binary data over a
2049   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2050   However, safe transport
2051   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2052   the only unsafe characteristic of message-bodies is the difficulty in
2053   determining the exact message body length (<xref target="message.body"/>),
2054   or the desire to encrypt data over a shared transport.
2055</t>
2056<t>
2057   A server that receives a request message with a transfer-coding it does
2058   not understand &SHOULD; respond with 501 (Not Implemented) and then
2059   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2060   client.
2061</t>
2062
2063<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2064  <iref item="chunked (Coding Format)"/>
2065  <iref item="Coding Format" subitem="chunked"/>
2066  <x:anchor-alias value="chunk"/>
2067  <x:anchor-alias value="Chunked-Body"/>
2068  <x:anchor-alias value="chunk-data"/>
2069  <x:anchor-alias value="chunk-ext"/>
2070  <x:anchor-alias value="chunk-ext-name"/>
2071  <x:anchor-alias value="chunk-ext-val"/>
2072  <x:anchor-alias value="chunk-size"/>
2073  <x:anchor-alias value="last-chunk"/>
2074  <x:anchor-alias value="trailer-part"/>
2075  <x:anchor-alias value="quoted-str-nf"/>
2076  <x:anchor-alias value="qdtext-nf"/>
2077<t>
2078   The chunked encoding modifies the body of a message in order to
2079   transfer it as a series of chunks, each with its own size indicator,
2080   followed by an &OPTIONAL; trailer containing header fields. This
2081   allows dynamically produced content to be transferred along with the
2082   information necessary for the recipient to verify that it has
2083   received the full message.
2084</t>
2085<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"/>
2086  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2087                   <x:ref>last-chunk</x:ref>
2088                   <x:ref>trailer-part</x:ref>
2089                   <x:ref>CRLF</x:ref>
2090 
2091  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2092                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2093  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2094  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2095 
2096  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref>
2097                      [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2098  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2099  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2100  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2101  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2102 
2103  <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>
2104                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2105  <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>
2106</artwork></figure>
2107<t>
2108   The chunk-size field is a string of hex digits indicating the size of
2109   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2110   zero, followed by the trailer, which is terminated by an empty line.
2111</t>
2112<t>
2113   The trailer allows the sender to include additional HTTP header
2114   fields at the end of the message. The Trailer header field can be
2115   used to indicate which header fields are included in a trailer (see
2116   <xref target="header.trailer"/>).
2117</t>
2118<t>
2119   A server using chunked transfer-coding in a response &MUST-NOT; use the
2120   trailer for any header fields unless at least one of the following is
2121   true:
2122  <list style="numbers">
2123    <t>the request included a TE header field that indicates "trailers" is
2124     acceptable in the transfer-coding of the  response, as described in
2125     <xref target="header.te"/>; or,</t>
2126     
2127    <t>the trailer fields consist entirely of optional metadata, and the
2128    recipient could use the message (in a manner acceptable to the server where
2129    the field originated) without receiving it. In other words, the server that
2130    generated the header (often but not always the origin server) is willing to
2131    accept the possibility that the trailer fields might be silently discarded
2132    along the path to the client.</t>
2133  </list>
2134</t>
2135<t>
2136   This requirement prevents an interoperability failure when the
2137   message is being received by an HTTP/1.1 (or later) proxy and
2138   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2139   compliance with the protocol would have necessitated a possibly
2140   infinite buffer on the proxy.
2141</t>
2142<t>
2143   A process for decoding the "chunked" transfer-coding
2144   can be represented in pseudo-code as:
2145</t>
2146<figure><artwork type="code">
2147  length := 0
2148  read chunk-size, chunk-ext (if any) and CRLF
2149  while (chunk-size &gt; 0) {
2150     read chunk-data and CRLF
2151     append chunk-data to decoded-body
2152     length := length + chunk-size
2153     read chunk-size and CRLF
2154  }
2155  read header-field
2156  while (header-field not empty) {
2157     append header-field to existing header fields
2158     read header-field
2159  }
2160  Content-Length := length
2161  Remove "chunked" from Transfer-Encoding
2162</artwork></figure>
2163<t>
2164   All HTTP/1.1 applications &MUST; be able to receive and decode the
2165   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2166   they do not understand.
2167</t>
2168<t>
2169   Since "chunked" is the only transfer-coding required to be understood
2170   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2171   on a persistent connection.  Whenever a transfer-coding is applied to
2172   a payload body in a request, the final transfer-coding applied &MUST;
2173   be "chunked".  If a transfer-coding is applied to a response payload
2174   body, then either the final transfer-coding applied &MUST; be "chunked"
2175   or the message &MUST; be terminated by closing the connection. When the
2176   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2177   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2178   be applied more than once in a message-body.
2179</t>
2180</section>
2181
2182<section title="Compression Codings" anchor="compression.codings">
2183<t>
2184   The codings defined below can be used to compress the payload of a
2185   message.
2186</t>
2187<x:note><t>
2188   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2189   is not desirable and is discouraged for future encodings. Their
2190   use here is representative of historical practice, not good
2191   design.
2192</t></x:note>
2193<x:note><t>
2194   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2195   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2196   equivalent to "gzip" and "compress" respectively.
2197</t></x:note>
2198
2199<section title="Compress Coding" anchor="compress.coding">
2200<iref item="compress (Coding Format)"/>
2201<iref item="Coding Format" subitem="compress"/>
2202<t>
2203   The "compress" format is produced by the common UNIX file compression
2204   program "compress". This format is an adaptive Lempel-Ziv-Welch
2205   coding (LZW).
2206</t>
2207</section>
2208
2209<section title="Deflate Coding" anchor="deflate.coding">
2210<iref item="deflate (Coding Format)"/>
2211<iref item="Coding Format" subitem="deflate"/>
2212<t>
2213   The "deflate" format is defined as the "deflate" compression mechanism
2214   (described in <xref target="RFC1951"/>) used inside the "zlib"
2215   data format (<xref target="RFC1950"/>).
2216</t>
2217<x:note>
2218  <t>
2219    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2220    compressed data without the zlib wrapper.
2221   </t>
2222</x:note>
2223</section>
2224
2225<section title="Gzip Coding" anchor="gzip.coding">
2226<iref item="gzip (Coding Format)"/>
2227<iref item="Coding Format" subitem="gzip"/>
2228<t>
2229   The "gzip" format is produced by the file compression program
2230   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2231   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2232</t>
2233</section>
2234
2235</section>
2236
2237<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2238<t>
2239   The HTTP Transfer Coding Registry defines the name space for the transfer
2240   coding names.
2241</t>
2242<t>
2243   Registrations &MUST; include the following fields:
2244   <list style="symbols">
2245     <t>Name</t>
2246     <t>Description</t>
2247     <t>Pointer to specification text</t>
2248   </list>
2249</t>
2250<t>
2251   Names of transfer codings &MUST-NOT; overlap with names of content codings
2252   (&content-codings;), unless the encoding transformation is identical (as it
2253   is the case for the compression codings defined in
2254   <xref target="compression.codings"/>).
2255</t>
2256<t>
2257   Values to be added to this name space require a specification
2258   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2259   conform to the purpose of transfer coding defined in this section.
2260</t>
2261<t>
2262   The registry itself is maintained at
2263   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2264</t>
2265</section>
2266</section>
2267
2268<section title="Product Tokens" anchor="product.tokens">
2269  <x:anchor-alias value="product"/>
2270  <x:anchor-alias value="product-version"/>
2271<t>
2272   Product tokens are used to allow communicating applications to
2273   identify themselves by software name and version. Most fields using
2274   product tokens also allow sub-products which form a significant part
2275   of the application to be listed, separated by whitespace. By
2276   convention, the products are listed in order of their significance
2277   for identifying the application.
2278</t>
2279<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2280  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2281  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2282</artwork></figure>
2283<t>
2284   Examples:
2285</t>
2286<figure><artwork type="example">
2287  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2288  Server: Apache/0.8.4
2289</artwork></figure>
2290<t>
2291   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2292   used for advertising or other non-essential information. Although any
2293   token octet &MAY; appear in a product-version, this token &SHOULD;
2294   only be used for a version identifier (i.e., successive versions of
2295   the same product &SHOULD; only differ in the product-version portion of
2296   the product value).
2297</t>
2298</section>
2299
2300<section title="Quality Values" anchor="quality.values">
2301  <x:anchor-alias value="qvalue"/>
2302<t>
2303   Both transfer codings (TE request header field, <xref target="header.te"/>)
2304   and content negotiation (&content.negotiation;) use short "floating point"
2305   numbers to indicate the relative importance ("weight") of various
2306   negotiable parameters.  A weight is normalized to a real number in
2307   the range 0 through 1, where 0 is the minimum and 1 the maximum
2308   value. If a parameter has a quality value of 0, then content with
2309   this parameter is "not acceptable" for the client. HTTP/1.1
2310   applications &MUST-NOT; generate more than three digits after the
2311   decimal point. User configuration of these values &SHOULD; also be
2312   limited in this fashion.
2313</t>
2314<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2315  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2316                 / ( "1" [ "." 0*3("0") ] )
2317</artwork></figure>
2318<x:note>
2319  <t>
2320     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2321     relative degradation in desired quality.
2322  </t>
2323</x:note>
2324</section>
2325
2326</section>
2327
2328<section title="Connections" anchor="connections">
2329
2330<section title="Persistent Connections" anchor="persistent.connections">
2331
2332<section title="Purpose" anchor="persistent.purpose">
2333<t>
2334   Prior to persistent connections, a separate TCP connection was
2335   established for each request, increasing the load on HTTP servers
2336   and causing congestion on the Internet. The use of inline images and
2337   other associated data often requires a client to make multiple
2338   requests of the same server in a short amount of time. Analysis of
2339   these performance problems and results from a prototype
2340   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2341   measurements of actual HTTP/1.1 implementations show good
2342   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2343   T/TCP <xref target="Tou1998"/>.
2344</t>
2345<t>
2346   Persistent HTTP connections have a number of advantages:
2347  <list style="symbols">
2348      <t>
2349        By opening and closing fewer TCP connections, CPU time is saved
2350        in routers and hosts (clients, servers, proxies, gateways,
2351        tunnels, or caches), and memory used for TCP protocol control
2352        blocks can be saved in hosts.
2353      </t>
2354      <t>
2355        HTTP requests and responses can be pipelined on a connection.
2356        Pipelining allows a client to make multiple requests without
2357        waiting for each response, allowing a single TCP connection to
2358        be used much more efficiently, with much lower elapsed time.
2359      </t>
2360      <t>
2361        Network congestion is reduced by reducing the number of packets
2362        caused by TCP opens, and by allowing TCP sufficient time to
2363        determine the congestion state of the network.
2364      </t>
2365      <t>
2366        Latency on subsequent requests is reduced since there is no time
2367        spent in TCP's connection opening handshake.
2368      </t>
2369      <t>
2370        HTTP can evolve more gracefully, since errors can be reported
2371        without the penalty of closing the TCP connection. Clients using
2372        future versions of HTTP might optimistically try a new feature,
2373        but if communicating with an older server, retry with old
2374        semantics after an error is reported.
2375      </t>
2376    </list>
2377</t>
2378<t>
2379   HTTP implementations &SHOULD; implement persistent connections.
2380</t>
2381</section>
2382
2383<section title="Overall Operation" anchor="persistent.overall">
2384<t>
2385   A significant difference between HTTP/1.1 and earlier versions of
2386   HTTP is that persistent connections are the default behavior of any
2387   HTTP connection. That is, unless otherwise indicated, the client
2388   &SHOULD; assume that the server will maintain a persistent connection,
2389   even after error responses from the server.
2390</t>
2391<t>
2392   Persistent connections provide a mechanism by which a client and a
2393   server can signal the close of a TCP connection. This signaling takes
2394   place using the Connection header field (<xref target="header.connection"/>). Once a close
2395   has been signaled, the client &MUST-NOT; send any more requests on that
2396   connection.
2397</t>
2398
2399<section title="Negotiation" anchor="persistent.negotiation">
2400<t>
2401   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2402   maintain a persistent connection unless a Connection header field including
2403   the connection-token "close" was sent in the request. If the server
2404   chooses to close the connection immediately after sending the
2405   response, it &SHOULD; send a Connection header field including the
2406   connection-token "close".
2407</t>
2408<t>
2409   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2410   decide to keep it open based on whether the response from a server
2411   contains a Connection header field with the connection-token close. In case
2412   the client does not want to maintain a connection for more than that
2413   request, it &SHOULD; send a Connection header field including the
2414   connection-token close.
2415</t>
2416<t>
2417   If either the client or the server sends the close token in the
2418   Connection header field, that request becomes the last one for the
2419   connection.
2420</t>
2421<t>
2422   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2423   maintained for HTTP versions less than 1.1 unless it is explicitly
2424   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2425   compatibility with HTTP/1.0 clients.
2426</t>
2427<t>
2428   In order to remain persistent, all messages on the connection &MUST;
2429   have a self-defined message length (i.e., one not defined by closure
2430   of the connection), as described in <xref target="message.body"/>.
2431</t>
2432</section>
2433
2434<section title="Pipelining" anchor="pipelining">
2435<t>
2436   A client that supports persistent connections &MAY; "pipeline" its
2437   requests (i.e., send multiple requests without waiting for each
2438   response). A server &MUST; send its responses to those requests in the
2439   same order that the requests were received.
2440</t>
2441<t>
2442   Clients which assume persistent connections and pipeline immediately
2443   after connection establishment &SHOULD; be prepared to retry their
2444   connection if the first pipelined attempt fails. If a client does
2445   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2446   persistent. Clients &MUST; also be prepared to resend their requests if
2447   the server closes the connection before sending all of the
2448   corresponding responses.
2449</t>
2450<t>
2451   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2452   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2453   premature termination of the transport connection could lead to
2454   indeterminate results. A client wishing to send a non-idempotent
2455   request &SHOULD; wait to send that request until it has received the
2456   response status line for the previous request.
2457</t>
2458</section>
2459</section>
2460
2461<section title="Proxy Servers" anchor="persistent.proxy">
2462<t>
2463   It is especially important that proxies correctly implement the
2464   properties of the Connection header field as specified in <xref target="header.connection"/>.
2465</t>
2466<t>
2467   The proxy server &MUST; signal persistent connections separately with
2468   its clients and the origin servers (or other proxy servers) that it
2469   connects to. Each persistent connection applies to only one transport
2470   link.
2471</t>
2472<t>
2473   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2474   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2475   for information and discussion of the problems with the Keep-Alive header field
2476   implemented by many HTTP/1.0 clients).
2477</t>
2478
2479<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2480<!--<t>
2481  <cref anchor="TODO-end-to-end" source="jre">
2482    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2483    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2484  </cref>
2485</t>-->
2486<t>
2487   For the purpose of defining the behavior of caches and non-caching
2488   proxies, we divide HTTP header fields into two categories:
2489  <list style="symbols">
2490      <t>End-to-end header fields, which are  transmitted to the ultimate
2491        recipient of a request or response. End-to-end header fields in
2492        responses MUST be stored as part of a cache entry and &MUST; be
2493        transmitted in any response formed from a cache entry.</t>
2494
2495      <t>Hop-by-hop header fields, which are meaningful only for a single
2496        transport-level connection, and are not stored by caches or
2497        forwarded by proxies.</t>
2498  </list>
2499</t>
2500<t>
2501   The following HTTP/1.1 header fields are hop-by-hop header fields:
2502  <list style="symbols">
2503      <t>Connection</t>
2504      <t>Keep-Alive</t>
2505      <t>Proxy-Authenticate</t>
2506      <t>Proxy-Authorization</t>
2507      <t>TE</t>
2508      <t>Trailer</t>
2509      <t>Transfer-Encoding</t>
2510      <t>Upgrade</t>
2511  </list>
2512</t>
2513<t>
2514   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2515</t>
2516<t>
2517   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2518   (<xref target="header.connection"/>).
2519</t>
2520</section>
2521
2522<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2523<!--<t>
2524  <cref anchor="TODO-non-mod-headers" source="jre">
2525    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2526    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2527  </cref>
2528</t>-->
2529<t>
2530   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2531   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2532   modify an end-to-end header field unless the definition of that header field requires
2533   or specifically allows that.
2534</t>
2535<t>
2536   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2537   request or response, and it &MUST-NOT; add any of these fields if not
2538   already present:
2539  <list style="symbols">
2540    <t>Allow</t>
2541    <t>Content-Location</t>
2542    <t>Content-MD5</t>
2543    <t>ETag</t>
2544    <t>Last-Modified</t>
2545    <t>Server</t>
2546  </list>
2547</t>
2548<t>
2549   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2550   response:
2551  <list style="symbols">
2552    <t>Expires</t>
2553  </list>
2554</t>
2555<t>
2556   but it &MAY; add any of these fields if not already present. If an
2557   Expires header field is added, it &MUST; be given a field-value identical to
2558   that of the Date header field in that response.
2559</t>
2560<t>
2561   A proxy &MUST-NOT; modify or add any of the following fields in a
2562   message that contains the no-transform cache-control directive, or in
2563   any request:
2564  <list style="symbols">
2565    <t>Content-Encoding</t>
2566    <t>Content-Range</t>
2567    <t>Content-Type</t>
2568  </list>
2569</t>
2570<t>
2571   A transforming proxy &MAY; modify or add these fields to a message
2572   that does not include no-transform, but if it does so, it &MUST; add a
2573   Warning 214 (Transformation applied) if one does not already appear
2574   in the message (see &header-warning;).
2575</t>
2576<x:note>
2577  <t>
2578    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2579    cause authentication failures if stronger authentication
2580    mechanisms are introduced in later versions of HTTP. Such
2581    authentication mechanisms &MAY; rely on the values of header fields
2582    not listed here.
2583  </t>
2584</x:note>
2585<t>
2586   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2587   though it &MAY; change the message-body through application or removal
2588   of a transfer-coding (<xref target="transfer.codings"/>).
2589</t>
2590</section>
2591
2592</section>
2593
2594<section title="Practical Considerations" anchor="persistent.practical">
2595<t>
2596   Servers will usually have some time-out value beyond which they will
2597   no longer maintain an inactive connection. Proxy servers might make
2598   this a higher value since it is likely that the client will be making
2599   more connections through the same server. The use of persistent
2600   connections places no requirements on the length (or existence) of
2601   this time-out for either the client or the server.
2602</t>
2603<t>
2604   When a client or server wishes to time-out it &SHOULD; issue a graceful
2605   close on the transport connection. Clients and servers &SHOULD; both
2606   constantly watch for the other side of the transport close, and
2607   respond to it as appropriate. If a client or server does not detect
2608   the other side's close promptly it could cause unnecessary resource
2609   drain on the network.
2610</t>
2611<t>
2612   A client, server, or proxy &MAY; close the transport connection at any
2613   time. For example, a client might have started to send a new request
2614   at the same time that the server has decided to close the "idle"
2615   connection. From the server's point of view, the connection is being
2616   closed while it was idle, but from the client's point of view, a
2617   request is in progress.
2618</t>
2619<t>
2620   This means that clients, servers, and proxies &MUST; be able to recover
2621   from asynchronous close events. Client software &SHOULD; reopen the
2622   transport connection and retransmit the aborted sequence of requests
2623   without user interaction so long as the request sequence is
2624   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2625   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2626   human operator the choice of retrying the request(s). Confirmation by
2627   user-agent software with semantic understanding of the application
2628   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2629   be repeated if the second sequence of requests fails.
2630</t>
2631<t>
2632   Servers &SHOULD; always respond to at least one request per connection,
2633   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2634   middle of transmitting a response, unless a network or client failure
2635   is suspected.
2636</t>
2637<t>
2638   Clients (including proxies) &SHOULD; limit the number of simultaneous
2639   connections that they maintain to a given server (including proxies).
2640</t>
2641<t>
2642   Previous revisions of HTTP gave a specific number of connections as a
2643   ceiling, but this was found to be impractical for many applications. As a
2644   result, this specification does not mandate a particular maximum number of
2645   connections, but instead encourages clients to be conservative when opening
2646   multiple connections.
2647</t>
2648<t>
2649   In particular, while using multiple connections avoids the "head-of-line
2650   blocking" problem (whereby a request that takes significant server-side
2651   processing and/or has a large payload can block subsequent requests on the
2652   same connection), each connection used consumes server resources (sometimes
2653   significantly), and furthermore using multiple connections can cause
2654   undesirable side effects in congested networks.
2655</t>
2656<t>
2657   Note that servers might reject traffic that they deem abusive, including an
2658   excessive number of connections from a client.
2659</t>
2660</section>
2661</section>
2662
2663<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2664
2665<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2666<t>
2667   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2668   flow control mechanisms to resolve temporary overloads, rather than
2669   terminating connections with the expectation that clients will retry.
2670   The latter technique can exacerbate network congestion.
2671</t>
2672</section>
2673
2674<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2675<t>
2676   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2677   the network connection for an error status code while it is transmitting
2678   the request. If the client sees an error status code, it &SHOULD;
2679   immediately cease transmitting the body. If the body is being sent
2680   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2681   empty trailer &MAY; be used to prematurely mark the end of the message.
2682   If the body was preceded by a Content-Length header field, the client &MUST;
2683   close the connection.
2684</t>
2685</section>
2686
2687<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2688<t>
2689   The purpose of the 100 (Continue) status code (see &status-100;) is to
2690   allow a client that is sending a request message with a request body
2691   to determine if the origin server is willing to accept the request
2692   (based on the request header fields) before the client sends the request
2693   body. In some cases, it might either be inappropriate or highly
2694   inefficient for the client to send the body if the server will reject
2695   the message without looking at the body.
2696</t>
2697<t>
2698   Requirements for HTTP/1.1 clients:
2699  <list style="symbols">
2700    <t>
2701        If a client will wait for a 100 (Continue) response before
2702        sending the request body, it &MUST; send an Expect header
2703        field (&header-expect;) with the "100-continue" expectation.
2704    </t>
2705    <t>
2706        A client &MUST-NOT; send an Expect header field (&header-expect;)
2707        with the "100-continue" expectation if it does not intend
2708        to send a request body.
2709    </t>
2710  </list>
2711</t>
2712<t>
2713   Because of the presence of older implementations, the protocol allows
2714   ambiguous situations in which a client might send "Expect: 100-continue"
2715   without receiving either a 417 (Expectation Failed)
2716   or a 100 (Continue) status code. Therefore, when a client sends this
2717   header field to an origin server (possibly via a proxy) from which it
2718   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2719   wait for an indefinite period before sending the request body.
2720</t>
2721<t>
2722   Requirements for HTTP/1.1 origin servers:
2723  <list style="symbols">
2724    <t> Upon receiving a request which includes an Expect header
2725        field with the "100-continue" expectation, an origin server &MUST;
2726        either respond with 100 (Continue) status code and continue to read
2727        from the input stream, or respond with a final status code. The
2728        origin server &MUST-NOT; wait for the request body before sending
2729        the 100 (Continue) response. If it responds with a final status
2730        code, it &MAY; close the transport connection or it &MAY; continue
2731        to read and discard the rest of the request.  It &MUST-NOT;
2732        perform the request method if it returns a final status code.
2733    </t>
2734    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2735        the request message does not include an Expect header
2736        field with the "100-continue" expectation, and &MUST-NOT; send a
2737        100 (Continue) response if such a request comes from an HTTP/1.0
2738        (or earlier) client. There is an exception to this rule: for
2739        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2740        status code in response to an HTTP/1.1 PUT or POST request that does
2741        not include an Expect header field with the "100-continue"
2742        expectation. This exception, the purpose of which is
2743        to minimize any client processing delays associated with an
2744        undeclared wait for 100 (Continue) status code, applies only to
2745        HTTP/1.1 requests, and not to requests with any other HTTP-version
2746        value.
2747    </t>
2748    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2749        already received some or all of the request body for the
2750        corresponding request.
2751    </t>
2752    <t> An origin server that sends a 100 (Continue) response &MUST;
2753    ultimately send a final status code, once the request body is
2754        received and processed, unless it terminates the transport
2755        connection prematurely.
2756    </t>
2757    <t> If an origin server receives a request that does not include an
2758        Expect header field with the "100-continue" expectation,
2759        the request includes a request body, and the server responds
2760        with a final status code before reading the entire request body
2761        from the transport connection, then the server &SHOULD-NOT;  close
2762        the transport connection until it has read the entire request,
2763        or until the client closes the connection. Otherwise, the client
2764        might not reliably receive the response message. However, this
2765        requirement is not be construed as preventing a server from
2766        defending itself against denial-of-service attacks, or from
2767        badly broken client implementations.
2768      </t>
2769    </list>
2770</t>
2771<t>
2772   Requirements for HTTP/1.1 proxies:
2773  <list style="symbols">
2774    <t> If a proxy receives a request that includes an Expect header
2775        field with the "100-continue" expectation, and the proxy
2776        either knows that the next-hop server complies with HTTP/1.1 or
2777        higher, or does not know the HTTP version of the next-hop
2778        server, it &MUST; forward the request, including the Expect header
2779        field.
2780    </t>
2781    <t> If the proxy knows that the version of the next-hop server is
2782        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2783        respond with a 417 (Expectation Failed) status code.
2784    </t>
2785    <t> Proxies &SHOULD; maintain a record of the HTTP version
2786        numbers received from recently-referenced next-hop servers.
2787    </t>
2788    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2789        request message was received from an HTTP/1.0 (or earlier)
2790        client and did not include an Expect header field with
2791        the "100-continue" expectation. This requirement overrides the
2792        general rule for forwarding of 1xx responses (see &status-1xx;).
2793    </t>
2794  </list>
2795</t>
2796</section>
2797
2798<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2799<t>
2800   If an HTTP/1.1 client sends a request which includes a request body,
2801   but which does not include an Expect header field with the
2802   "100-continue" expectation, and if the client is not directly
2803   connected to an HTTP/1.1 origin server, and if the client sees the
2804   connection close before receiving a status line from the server, the
2805   client &SHOULD; retry the request.  If the client does retry this
2806   request, it &MAY; use the following "binary exponential backoff"
2807   algorithm to be assured of obtaining a reliable response:
2808  <list style="numbers">
2809    <t>
2810      Initiate a new connection to the server
2811    </t>
2812    <t>
2813      Transmit the request-line, header fields, and the CRLF that
2814      indicates the end of header fields.
2815    </t>
2816    <t>
2817      Initialize a variable R to the estimated round-trip time to the
2818         server (e.g., based on the time it took to establish the
2819         connection), or to a constant value of 5 seconds if the round-trip
2820         time is not available.
2821    </t>
2822    <t>
2823       Compute T = R * (2**N), where N is the number of previous
2824         retries of this request.
2825    </t>
2826    <t>
2827       Wait either for an error response from the server, or for T
2828         seconds (whichever comes first)
2829    </t>
2830    <t>
2831       If no error response is received, after T seconds transmit the
2832         body of the request.
2833    </t>
2834    <t>
2835       If client sees that the connection is closed prematurely,
2836         repeat from step 1 until the request is accepted, an error
2837         response is received, or the user becomes impatient and
2838         terminates the retry process.
2839    </t>
2840  </list>
2841</t>
2842<t>
2843   If at any point an error status code is received, the client
2844  <list style="symbols">
2845      <t>&SHOULD-NOT;  continue and</t>
2846
2847      <t>&SHOULD; close the connection if it has not completed sending the
2848        request message.</t>
2849    </list>
2850</t>
2851</section>
2852</section>
2853</section>
2854
2855
2856<section title="Miscellaneous notes that might disappear" anchor="misc">
2857<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2858<t>
2859   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2860</t>
2861</section>
2862
2863<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2864<t>
2865   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2866</t>
2867</section>
2868
2869<section title="Interception of HTTP for access control" anchor="http.intercept">
2870<t>
2871   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2872</t>
2873</section>
2874
2875<section title="Use of HTTP by other protocols" anchor="http.others">
2876<t>
2877   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2878   Extensions of HTTP like WebDAV.</cref>
2879</t>
2880
2881</section>
2882<section title="Use of HTTP by media type specification" anchor="http.media">
2883<t>
2884   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2885</t>
2886</section>
2887</section>
2888
2889<section title="Header Field Definitions" anchor="header.field.definitions">
2890<t>
2891   This section defines the syntax and semantics of HTTP header fields
2892   related to message origination, framing, and routing.
2893</t>
2894<texttable align="left">
2895  <ttcol>Header Field Name</ttcol>
2896  <ttcol>Defined in...</ttcol>
2897 
2898  <c>Connection</c> <c><xref target="header.connection"/></c>
2899  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
2900  <c>Host</c> <c><xref target="header.host"/></c>
2901  <c>TE</c> <c><xref target="header.te"/></c>
2902  <c>Trailer</c> <c><xref target="header.trailer"/></c>
2903  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
2904  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
2905  <c>Via</c> <c><xref target="header.via"/></c>
2906</texttable>
2907
2908<section title="Connection" anchor="header.connection">
2909  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2910  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2911  <x:anchor-alias value="Connection"/>
2912  <x:anchor-alias value="connection-token"/>
2913<t>
2914   The "Connection" header field allows the sender to specify
2915   options that are desired only for that particular connection.
2916   Such connection options &MUST; be removed or replaced before the
2917   message can be forwarded downstream by a proxy or gateway.
2918   This mechanism also allows the sender to indicate which HTTP
2919   header fields used in the message are only intended for the
2920   immediate recipient ("hop-by-hop"), as opposed to all recipients
2921   on the chain ("end-to-end"), enabling the message to be
2922   self-descriptive and allowing future connection-specific extensions
2923   to be deployed in HTTP without fear that they will be blindly
2924   forwarded by previously deployed intermediaries.
2925</t>
2926<t>
2927   The Connection header field's value has the following grammar:
2928</t>
2929<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2930  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2931  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2932</artwork></figure>
2933<t>
2934   A proxy or gateway &MUST; parse a received Connection
2935   header field before a message is forwarded and, for each
2936   connection-token in this field, remove any header field(s) from
2937   the message with the same name as the connection-token, and then
2938   remove the Connection header field itself or replace it with the
2939   sender's own connection options for the forwarded message.
2940</t>
2941<t>
2942   A sender &MUST-NOT; include field-names in the Connection header
2943   field-value for fields that are defined as expressing constraints
2944   for all recipients in the request or response chain, such as the
2945   Cache-Control header field (&header-cache-control;).
2946</t>
2947<t>
2948   The connection options do not have to correspond to a header field
2949   present in the message, since a connection-specific header field
2950   might not be needed if there are no parameters associated with that
2951   connection option.  Recipients that trigger certain connection
2952   behavior based on the presence of connection options &MUST; do so
2953   based on the presence of the connection-token rather than only the
2954   presence of the optional header field.  In other words, if the
2955   connection option is received as a header field but not indicated
2956   within the Connection field-value, then the recipient &MUST; ignore
2957   the connection-specific header field because it has likely been
2958   forwarded by an intermediary that is only partially compliant.
2959</t>
2960<t>
2961   When defining new connection options, specifications ought to
2962   carefully consider existing deployed header fields and ensure
2963   that the new connection-token does not share the same name as
2964   an unrelated header field that might already be deployed.
2965   Defining a new connection-token essentially reserves that potential
2966   field-name for carrying additional information related to the
2967   connection option, since it would be unwise for senders to use
2968   that field-name for anything else.
2969</t>
2970<t>
2971   HTTP/1.1 defines the "close" connection option for the sender to
2972   signal that the connection will be closed after completion of the
2973   response. For example,
2974</t>
2975<figure><artwork type="example">
2976  Connection: close
2977</artwork></figure>
2978<t>
2979   in either the request or the response header fields indicates that
2980   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2981   after the current request/response is complete.
2982</t>
2983<t>
2984   An HTTP/1.1 client that does not support persistent connections &MUST;
2985   include the "close" connection option in every request message.
2986</t>
2987<t>
2988   An HTTP/1.1 server that does not support persistent connections &MUST;
2989   include the "close" connection option in every response message that
2990   does not have a 1xx (Informational) status code.
2991</t>
2992</section>
2993
2994<section title="Content-Length" anchor="header.content-length">
2995  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
2996  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
2997  <x:anchor-alias value="Content-Length"/>
2998<t>
2999   The "Content-Length" header field indicates the size of the
3000   message-body, in decimal number of octets, for any message other than
3001   a response to a HEAD request or a response with a status code of 304.
3002   In the case of a response to a HEAD request, Content-Length indicates
3003   the size of the payload body (not including any potential transfer-coding)
3004   that would have been sent had the request been a GET.
3005   In the case of a 304 (Not Modified) response to a GET request,
3006   Content-Length indicates the size of the payload body (not including
3007   any potential transfer-coding) that would have been sent in a 200 (OK)
3008   response.
3009</t>
3010<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3011  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3012</artwork></figure>
3013<t>
3014   An example is
3015</t>
3016<figure><artwork type="example">
3017  Content-Length: 3495
3018</artwork></figure>
3019<t>
3020   Implementations &SHOULD; use this field to indicate the message-body
3021   length when no transfer-coding is being applied and the
3022   payload's body length can be determined prior to being transferred.
3023   <xref target="message.body"/> describes how recipients determine the length
3024   of a message-body.
3025</t>
3026<t>
3027   Any Content-Length greater than or equal to zero is a valid value.
3028</t>
3029<t>
3030   Note that the use of this field in HTTP is significantly different from
3031   the corresponding definition in MIME, where it is an optional field
3032   used within the "message/external-body" content-type.
3033</t>
3034</section>
3035
3036<section title="Host" anchor="header.host">
3037  <iref primary="true" item="Host header field" x:for-anchor=""/>
3038  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3039  <x:anchor-alias value="Host"/>
3040<t>
3041   The "Host" header field in a request provides the host and port
3042   information from the target resource's URI, enabling the origin
3043   server to distinguish between resources while servicing requests
3044   for multiple host names on a single IP address.  Since the Host
3045   field-value is critical information for handling a request, it
3046   &SHOULD; be sent as the first header field following the Request-Line.
3047</t>
3048<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3049  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3050</artwork></figure>
3051<t>
3052   A client &MUST; send a Host header field in all HTTP/1.1 request
3053   messages.  If the target resource's URI includes an authority
3054   component, then the Host field-value &MUST; be identical to that
3055   authority component after excluding any userinfo (<xref target="http.uri"/>).
3056   If the authority component is missing or undefined for the target
3057   resource's URI, then the Host header field &MUST; be sent with an
3058   empty field-value.
3059</t>
3060<t>
3061   For example, a GET request to the origin server for
3062   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3063</t>
3064<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3065GET /pub/WWW/ HTTP/1.1
3066Host: www.example.org
3067</artwork></figure>
3068<t>
3069   The Host header field &MUST; be sent in an HTTP/1.1 request even
3070   if the request-target is in the form of an absolute-URI, since this
3071   allows the Host information to be forwarded through ancient HTTP/1.0
3072   proxies that might not have implemented Host.
3073</t>
3074<t>
3075   When an HTTP/1.1 proxy receives a request with a request-target in
3076   the form of an absolute-URI, the proxy &MUST; ignore the received
3077   Host header field (if any) and instead replace it with the host
3078   information of the request-target.  When a proxy forwards a request,
3079   it &MUST; generate the Host header field based on the received
3080   absolute-URI rather than the received Host.
3081</t>
3082<t>
3083   Since the Host header field acts as an application-level routing
3084   mechanism, it is a frequent target for malware seeking to poison
3085   a shared cache or redirect a request to an unintended server.
3086   An interception proxy is particularly vulnerable if it relies on
3087   the Host header field value for redirecting requests to internal
3088   servers, or for use as a cache key in a shared cache, without
3089   first verifying that the intercepted connection is targeting a
3090   valid IP address for that host.
3091</t>
3092<t>
3093   A server &MUST; respond with a 400 (Bad Request) status code to
3094   any HTTP/1.1 request message that lacks a Host header field and
3095   to any request message that contains more than one Host header field
3096   or a Host header field with an invalid field-value.
3097</t>
3098<t>
3099   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3100   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3101   for other requirements relating to Host.
3102</t>
3103</section>
3104
3105<section title="TE" anchor="header.te">
3106  <iref primary="true" item="TE header field" x:for-anchor=""/>
3107  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3108  <x:anchor-alias value="TE"/>
3109  <x:anchor-alias value="t-codings"/>
3110  <x:anchor-alias value="te-params"/>
3111  <x:anchor-alias value="te-ext"/>
3112<t>
3113   The "TE" header field indicates what extension transfer-codings
3114   it is willing to accept in the response, and whether or not it is
3115   willing to accept trailer fields in a chunked transfer-coding.
3116</t>
3117<t>
3118   Its value consists of the keyword "trailers" and/or a comma-separated
3119   list of extension transfer-coding names with optional accept
3120   parameters (as described in <xref target="transfer.codings"/>).
3121</t>
3122<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"/>
3123  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3124  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3125  <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> )
3126  <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> ]
3127</artwork></figure>
3128<t>
3129   The presence of the keyword "trailers" indicates that the client is
3130   willing to accept trailer fields in a chunked transfer-coding, as
3131   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3132   transfer-coding values even though it does not itself represent a
3133   transfer-coding.
3134</t>
3135<t>
3136   Examples of its use are:
3137</t>
3138<figure><artwork type="example">
3139  TE: deflate
3140  TE:
3141  TE: trailers, deflate;q=0.5
3142</artwork></figure>
3143<t>
3144   The TE header field only applies to the immediate connection.
3145   Therefore, the keyword &MUST; be supplied within a Connection header
3146   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3147</t>
3148<t>
3149   A server tests whether a transfer-coding is acceptable, according to
3150   a TE field, using these rules:
3151  <list style="numbers">
3152    <x:lt>
3153      <t>The "chunked" transfer-coding is always acceptable. If the
3154         keyword "trailers" is listed, the client indicates that it is
3155         willing to accept trailer fields in the chunked response on
3156         behalf of itself and any downstream clients. The implication is
3157         that, if given, the client is stating that either all
3158         downstream clients are willing to accept trailer fields in the
3159         forwarded response, or that it will attempt to buffer the
3160         response on behalf of downstream recipients.
3161      </t><t>
3162         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3163         chunked response such that a client can be assured of buffering
3164         the entire response.</t>
3165    </x:lt>
3166    <x:lt>
3167      <t>If the transfer-coding being tested is one of the transfer-codings
3168         listed in the TE field, then it is acceptable unless it
3169         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3170         qvalue of 0 means "not acceptable".)</t>
3171    </x:lt>
3172    <x:lt>
3173      <t>If multiple transfer-codings are acceptable, then the
3174         acceptable transfer-coding with the highest non-zero qvalue is
3175         preferred.  The "chunked" transfer-coding always has a qvalue
3176         of 1.</t>
3177    </x:lt>
3178  </list>
3179</t>
3180<t>
3181   If the TE field-value is empty or if no TE field is present, the only
3182   transfer-coding is "chunked". A message with no transfer-coding is
3183   always acceptable.
3184</t>
3185</section>
3186
3187<section title="Trailer" anchor="header.trailer">
3188  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3189  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3190  <x:anchor-alias value="Trailer"/>
3191<t>
3192   The "Trailer" header field indicates that the given set of
3193   header fields is present in the trailer of a message encoded with
3194   chunked transfer-coding.
3195</t>
3196<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3197  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3198</artwork></figure>
3199<t>
3200   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3201   message using chunked transfer-coding with a non-empty trailer. Doing
3202   so allows the recipient to know which header fields to expect in the
3203   trailer.
3204</t>
3205<t>
3206   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3207   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3208   trailer fields in a "chunked" transfer-coding.
3209</t>
3210<t>
3211   Message header fields listed in the Trailer header field &MUST-NOT;
3212   include the following header fields:
3213  <list style="symbols">
3214    <t>Transfer-Encoding</t>
3215    <t>Content-Length</t>
3216    <t>Trailer</t>
3217  </list>
3218</t>
3219</section>
3220
3221<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3222  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3223  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3224  <x:anchor-alias value="Transfer-Encoding"/>
3225<t>
3226   The "Transfer-Encoding" header field indicates what transfer-codings
3227   (if any) have been applied to the message body. It differs from
3228   Content-Encoding (&content-codings;) in that transfer-codings are a property
3229   of the message (and therefore are removed by intermediaries), whereas
3230   content-codings are not.
3231</t>
3232<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3233  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3234</artwork></figure>
3235<t>
3236   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3237</t>
3238<figure><artwork type="example">
3239  Transfer-Encoding: chunked
3240</artwork></figure>
3241<t>
3242   If multiple encodings have been applied to a representation, the transfer-codings
3243   &MUST; be listed in the order in which they were applied.
3244   Additional information about the encoding parameters &MAY; be provided
3245   by other header fields not defined by this specification.
3246</t>
3247<t>
3248   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3249   header field.
3250</t>
3251</section>
3252
3253<section title="Upgrade" anchor="header.upgrade">
3254  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3255  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3256  <x:anchor-alias value="Upgrade"/>
3257<t>
3258   The "Upgrade" header field allows the client to specify what
3259   additional communication protocols it would like to use, if the server
3260   chooses to switch protocols. Servers can use it to indicate what protocols
3261   they are willing to switch to.
3262</t>
3263<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3264  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3265</artwork></figure>
3266<t>
3267   For example,
3268</t>
3269<figure><artwork type="example">
3270  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3271</artwork></figure>
3272<t>
3273   The Upgrade header field is intended to provide a simple mechanism
3274   for transition from HTTP/1.1 to some other, incompatible protocol. It
3275   does so by allowing the client to advertise its desire to use another
3276   protocol, such as a later version of HTTP with a higher major version
3277   number, even though the current request has been made using HTTP/1.1.
3278   This eases the difficult transition between incompatible protocols by
3279   allowing the client to initiate a request in the more commonly
3280   supported protocol while indicating to the server that it would like
3281   to use a "better" protocol if available (where "better" is determined
3282   by the server, possibly according to the nature of the request method
3283   or target resource).
3284</t>
3285<t>
3286   The Upgrade header field only applies to switching application-layer
3287   protocols upon the existing transport-layer connection. Upgrade
3288   cannot be used to insist on a protocol change; its acceptance and use
3289   by the server is optional. The capabilities and nature of the
3290   application-layer communication after the protocol change is entirely
3291   dependent upon the new protocol chosen, although the first action
3292   after changing the protocol &MUST; be a response to the initial HTTP
3293   request containing the Upgrade header field.
3294</t>
3295<t>
3296   The Upgrade header field only applies to the immediate connection.
3297   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3298   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3299   HTTP/1.1 message.
3300</t>
3301<t>
3302   The Upgrade header field cannot be used to indicate a switch to a
3303   protocol on a different connection. For that purpose, it is more
3304   appropriate to use a 3xx redirection response (&status-3xx;).
3305</t>
3306<t>
3307   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3308   Protocols) responses to indicate which protocol(s) are being switched to,
3309   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3310   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3311   response to indicate that they are willing to upgrade to one of the
3312   specified protocols.
3313</t>
3314<t>
3315   This specification only defines the protocol name "HTTP" for use by
3316   the family of Hypertext Transfer Protocols, as defined by the HTTP
3317   version rules of <xref target="http.version"/> and future updates to this
3318   specification. Additional tokens can be registered with IANA using the
3319   registration procedure defined below. 
3320</t>
3321
3322<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3323<t>
3324   The HTTP Upgrade Token Registry defines the name space for product
3325   tokens used to identify protocols in the Upgrade header field.
3326   Each registered token is associated with contact information and
3327   an optional set of specifications that details how the connection
3328   will be processed after it has been upgraded.
3329</t>
3330<t>
3331   Registrations are allowed on a First Come First Served basis as
3332   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3333   specifications need not be IETF documents or be subject to IESG review.
3334   Registrations are subject to the following rules:
3335  <list style="numbers">
3336    <t>A token, once registered, stays registered forever.</t>
3337    <t>The registration &MUST; name a responsible party for the
3338       registration.</t>
3339    <t>The registration &MUST; name a point of contact.</t>
3340    <t>The registration &MAY; name a set of specifications associated with that
3341       token. Such specifications need not be publicly available.</t>
3342    <t>The responsible party &MAY; change the registration at any time.
3343       The IANA will keep a record of all such changes, and make them
3344       available upon request.</t>
3345    <t>The responsible party for the first registration of a "product"
3346       token &MUST; approve later registrations of a "version" token
3347       together with that "product" token before they can be registered.</t>
3348    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3349       for a token. This will normally only be used in the case when a
3350       responsible party cannot be contacted.</t>
3351  </list>
3352</t>
3353</section>
3354
3355
3356</section>
3357
3358<section title="Via" anchor="header.via">
3359  <iref primary="true" item="Via header field" x:for-anchor=""/>
3360  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3361  <x:anchor-alias value="protocol-name"/>
3362  <x:anchor-alias value="protocol-version"/>
3363  <x:anchor-alias value="pseudonym"/>
3364  <x:anchor-alias value="received-by"/>
3365  <x:anchor-alias value="received-protocol"/>
3366  <x:anchor-alias value="Via"/>
3367<t>
3368   The "Via" header field &MUST; be sent by a proxy or gateway to
3369   indicate the intermediate protocols and recipients between the user
3370   agent and the server on requests, and between the origin server and
3371   the client on responses. It is analogous to the "Received" field
3372   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3373   and is intended to be used for tracking message forwards,
3374   avoiding request loops, and identifying the protocol capabilities of
3375   all senders along the request/response chain.
3376</t>
3377<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"/>
3378  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3379                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3380  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3381  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3382  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3383  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3384  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3385</artwork></figure>
3386<t>
3387   The received-protocol indicates the protocol version of the message
3388   received by the server or client along each segment of the
3389   request/response chain. The received-protocol version is appended to
3390   the Via field value when the message is forwarded so that information
3391   about the protocol capabilities of upstream applications remains
3392   visible to all recipients.
3393</t>
3394<t>
3395   The protocol-name is excluded if and only if it would be "HTTP". The
3396   received-by field is normally the host and optional port number of a
3397   recipient server or client that subsequently forwarded the message.
3398   However, if the real host is considered to be sensitive information,
3399   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3400   be assumed to be the default port of the received-protocol.
3401</t>
3402<t>
3403   Multiple Via field values represent each proxy or gateway that has
3404   forwarded the message. Each recipient &MUST; append its information
3405   such that the end result is ordered according to the sequence of
3406   forwarding applications.
3407</t>
3408<t>
3409   Comments &MAY; be used in the Via header field to identify the software
3410   of each recipient, analogous to the User-Agent and Server header fields.
3411   However, all comments in the Via field are optional and &MAY; be removed
3412   by any recipient prior to forwarding the message.
3413</t>
3414<t>
3415   For example, a request message could be sent from an HTTP/1.0 user
3416   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3417   forward the request to a public proxy at p.example.net, which completes
3418   the request by forwarding it to the origin server at www.example.com.
3419   The request received by www.example.com would then have the following
3420   Via header field:
3421</t>
3422<figure><artwork type="example">
3423  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3424</artwork></figure>
3425<t>
3426   A proxy or gateway used as a portal through a network firewall
3427   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3428   region unless it is explicitly enabled to do so. If not enabled, the
3429   received-by host of any host behind the firewall &SHOULD; be replaced
3430   by an appropriate pseudonym for that host.
3431</t>
3432<t>
3433   For organizations that have strong privacy requirements for hiding
3434   internal structures, a proxy or gateway &MAY; combine an ordered
3435   subsequence of Via header field entries with identical received-protocol
3436   values into a single such entry. For example,
3437</t>
3438<figure><artwork type="example">
3439  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3440</artwork></figure>
3441<t>
3442  could be collapsed to
3443</t>
3444<figure><artwork type="example">
3445  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3446</artwork></figure>
3447<t>
3448   Senders &SHOULD-NOT; combine multiple entries unless they are all
3449   under the same organizational control and the hosts have already been
3450   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3451   have different received-protocol values.
3452</t>
3453</section>
3454
3455</section>
3456
3457<section title="IANA Considerations" anchor="IANA.considerations">
3458
3459<section title="Header Field Registration" anchor="header.field.registration">
3460<t>
3461   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3462   with the permanent registrations below (see <xref target="RFC3864"/>):
3463</t>
3464<?BEGININC p1-messaging.iana-headers ?>
3465<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3466<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3467   <ttcol>Header Field Name</ttcol>
3468   <ttcol>Protocol</ttcol>
3469   <ttcol>Status</ttcol>
3470   <ttcol>Reference</ttcol>
3471
3472   <c>Connection</c>
3473   <c>http</c>
3474   <c>standard</c>
3475   <c>
3476      <xref target="header.connection"/>
3477   </c>
3478   <c>Content-Length</c>
3479   <c>http</c>
3480   <c>standard</c>
3481   <c>
3482      <xref target="header.content-length"/>
3483   </c>
3484   <c>Host</c>
3485   <c>http</c>
3486   <c>standard</c>
3487   <c>
3488      <xref target="header.host"/>
3489   </c>
3490   <c>TE</c>
3491   <c>http</c>
3492   <c>standard</c>
3493   <c>
3494      <xref target="header.te"/>
3495   </c>
3496   <c>Trailer</c>
3497   <c>http</c>
3498   <c>standard</c>
3499   <c>
3500      <xref target="header.trailer"/>
3501   </c>
3502   <c>Transfer-Encoding</c>
3503   <c>http</c>
3504   <c>standard</c>
3505   <c>
3506      <xref target="header.transfer-encoding"/>
3507   </c>
3508   <c>Upgrade</c>
3509   <c>http</c>
3510   <c>standard</c>
3511   <c>
3512      <xref target="header.upgrade"/>
3513   </c>
3514   <c>Via</c>
3515   <c>http</c>
3516   <c>standard</c>
3517   <c>
3518      <xref target="header.via"/>
3519   </c>
3520</texttable>
3521<!--(END)-->
3522<?ENDINC p1-messaging.iana-headers ?>
3523<t>
3524   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3525   HTTP header field would be in conflict with the use of the "close" connection
3526   option for the "Connection" header field (<xref target="header.connection"/>).
3527</t>
3528<texttable align="left" suppress-title="true">
3529   <ttcol>Header Field Name</ttcol>
3530   <ttcol>Protocol</ttcol>
3531   <ttcol>Status</ttcol>
3532   <ttcol>Reference</ttcol>
3533
3534   <c>Close</c>
3535   <c>http</c>
3536   <c>reserved</c>
3537   <c>
3538      <xref target="header.field.registration"/>
3539   </c>
3540</texttable>
3541<t>
3542   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3543</t>
3544</section>
3545
3546<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3547<t>
3548   The entries for the "http" and "https" URI Schemes in the registry located at
3549   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3550   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3551   and <xref target="https.uri" format="counter"/> of this document
3552   (see <xref target="RFC4395"/>).
3553</t>
3554</section>
3555
3556<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3557<t>
3558   This document serves as the specification for the Internet media types
3559   "message/http" and "application/http". The following is to be registered with
3560   IANA (see <xref target="RFC4288"/>).
3561</t>
3562<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3563<iref item="Media Type" subitem="message/http" primary="true"/>
3564<iref item="message/http Media Type" primary="true"/>
3565<t>
3566   The message/http type can be used to enclose a single HTTP request or
3567   response message, provided that it obeys the MIME restrictions for all
3568   "message" types regarding line length and encodings.
3569</t>
3570<t>
3571  <list style="hanging" x:indent="12em">
3572    <t hangText="Type name:">
3573      message
3574    </t>
3575    <t hangText="Subtype name:">
3576      http
3577    </t>
3578    <t hangText="Required parameters:">
3579      none
3580    </t>
3581    <t hangText="Optional parameters:">
3582      version, msgtype
3583      <list style="hanging">
3584        <t hangText="version:">
3585          The HTTP-Version number of the enclosed message
3586          (e.g., "1.1"). If not present, the version can be
3587          determined from the first line of the body.
3588        </t>
3589        <t hangText="msgtype:">
3590          The message type &mdash; "request" or "response". If not
3591          present, the type can be determined from the first
3592          line of the body.
3593        </t>
3594      </list>
3595    </t>
3596    <t hangText="Encoding considerations:">
3597      only "7bit", "8bit", or "binary" are permitted
3598    </t>
3599    <t hangText="Security considerations:">
3600      none
3601    </t>
3602    <t hangText="Interoperability considerations:">
3603      none
3604    </t>
3605    <t hangText="Published specification:">
3606      This specification (see <xref target="internet.media.type.message.http"/>).
3607    </t>
3608    <t hangText="Applications that use this media type:">
3609    </t>
3610    <t hangText="Additional information:">
3611      <list style="hanging">
3612        <t hangText="Magic number(s):">none</t>
3613        <t hangText="File extension(s):">none</t>
3614        <t hangText="Macintosh file type code(s):">none</t>
3615      </list>
3616    </t>
3617    <t hangText="Person and email address to contact for further information:">
3618      See Authors Section.
3619    </t>
3620    <t hangText="Intended usage:">
3621      COMMON
3622    </t>
3623    <t hangText="Restrictions on usage:">
3624      none
3625    </t>
3626    <t hangText="Author/Change controller:">
3627      IESG
3628    </t>
3629  </list>
3630</t>
3631</section>
3632<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3633<iref item="Media Type" subitem="application/http" primary="true"/>
3634<iref item="application/http Media Type" primary="true"/>
3635<t>
3636   The application/http type can be used to enclose a pipeline of one or more
3637   HTTP request or response messages (not intermixed).
3638</t>
3639<t>
3640  <list style="hanging" x:indent="12em">
3641    <t hangText="Type name:">
3642      application
3643    </t>
3644    <t hangText="Subtype name:">
3645      http
3646    </t>
3647    <t hangText="Required parameters:">
3648      none
3649    </t>
3650    <t hangText="Optional parameters:">
3651      version, msgtype
3652      <list style="hanging">
3653        <t hangText="version:">
3654          The HTTP-Version number of the enclosed messages
3655          (e.g., "1.1"). If not present, the version can be
3656          determined from the first line of the body.
3657        </t>
3658        <t hangText="msgtype:">
3659          The message type &mdash; "request" or "response". If not
3660          present, the type can be determined from the first
3661          line of the body.
3662        </t>
3663      </list>
3664    </t>
3665    <t hangText="Encoding considerations:">
3666      HTTP messages enclosed by this type
3667      are in "binary" format; use of an appropriate
3668      Content-Transfer-Encoding is required when
3669      transmitted via E-mail.
3670    </t>
3671    <t hangText="Security considerations:">
3672      none
3673    </t>
3674    <t hangText="Interoperability considerations:">
3675      none
3676    </t>
3677    <t hangText="Published specification:">
3678      This specification (see <xref target="internet.media.type.application.http"/>).
3679    </t>
3680    <t hangText="Applications that use this media type:">
3681    </t>
3682    <t hangText="Additional information:">
3683      <list style="hanging">
3684        <t hangText="Magic number(s):">none</t>
3685        <t hangText="File extension(s):">none</t>
3686        <t hangText="Macintosh file type code(s):">none</t>
3687      </list>
3688    </t>
3689    <t hangText="Person and email address to contact for further information:">
3690      See Authors Section.
3691    </t>
3692    <t hangText="Intended usage:">
3693      COMMON
3694    </t>
3695    <t hangText="Restrictions on usage:">
3696      none
3697    </t>
3698    <t hangText="Author/Change controller:">
3699      IESG
3700    </t>
3701  </list>
3702</t>
3703</section>
3704</section>
3705
3706<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3707<t>
3708   The registration procedure for HTTP Transfer Codings is now defined by
3709   <xref target="transfer.coding.registry"/> of this document.
3710</t>
3711<t>
3712   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3713   shall be updated with the registrations below:
3714</t>
3715<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3716   <ttcol>Name</ttcol>
3717   <ttcol>Description</ttcol>
3718   <ttcol>Reference</ttcol>
3719   <c>chunked</c>
3720   <c>Transfer in a series of chunks</c>
3721   <c>
3722      <xref target="chunked.encoding"/>
3723   </c>
3724   <c>compress</c>
3725   <c>UNIX "compress" program method</c>
3726   <c>
3727      <xref target="compress.coding"/>
3728   </c>
3729   <c>deflate</c>
3730   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3731   the "zlib" data format (<xref target="RFC1950"/>)
3732   </c>
3733   <c>
3734      <xref target="deflate.coding"/>
3735   </c>
3736   <c>gzip</c>
3737   <c>Same as GNU zip <xref target="RFC1952"/></c>
3738   <c>
3739      <xref target="gzip.coding"/>
3740   </c>
3741</texttable>
3742</section>
3743
3744<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3745<t>
3746   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3747   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3748   by <xref target="upgrade.token.registry"/> of this document.
3749</t>
3750<t>
3751   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3752   shall be updated with the registration below:
3753</t>
3754<texttable align="left" suppress-title="true">
3755   <ttcol>Value</ttcol>
3756   <ttcol>Description</ttcol>
3757   <ttcol>Reference</ttcol>
3758
3759   <c>HTTP</c>
3760   <c>Hypertext Transfer Protocol</c> 
3761   <c><xref target="http.version"/> of this specification</c>
3762
3763</texttable>
3764</section>
3765
3766</section>
3767
3768<section title="Security Considerations" anchor="security.considerations">
3769<t>
3770   This section is meant to inform application developers, information
3771   providers, and users of the security limitations in HTTP/1.1 as
3772   described by this document. The discussion does not include
3773   definitive solutions to the problems revealed, though it does make
3774   some suggestions for reducing security risks.
3775</t>
3776
3777<section title="Personal Information" anchor="personal.information">
3778<t>
3779   HTTP clients are often privy to large amounts of personal information
3780   (e.g., the user's name, location, mail address, passwords, encryption
3781   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3782   leakage of this information.
3783   We very strongly recommend that a convenient interface be provided
3784   for the user to control dissemination of such information, and that
3785   designers and implementors be particularly careful in this area.
3786   History shows that errors in this area often create serious security
3787   and/or privacy problems and generate highly adverse publicity for the
3788   implementor's company.
3789</t>
3790</section>
3791
3792<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3793<t>
3794   A server is in the position to save personal data about a user's
3795   requests which might identify their reading patterns or subjects of
3796   interest. This information is clearly confidential in nature and its
3797   handling can be constrained by law in certain countries. People using
3798   HTTP to provide data are responsible for ensuring that
3799   such material is not distributed without the permission of any
3800   individuals that are identifiable by the published results.
3801</t>
3802</section>
3803
3804<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3805<t>
3806   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3807   the documents returned by HTTP requests to be only those that were
3808   intended by the server administrators. If an HTTP server translates
3809   HTTP URIs directly into file system calls, the server &MUST; take
3810   special care not to serve files that were not intended to be
3811   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3812   other operating systems use ".." as a path component to indicate a
3813   directory level above the current one. On such a system, an HTTP
3814   server &MUST; disallow any such construct in the request-target if it
3815   would otherwise allow access to a resource outside those intended to
3816   be accessible via the HTTP server. Similarly, files intended for
3817   reference only internally to the server (such as access control
3818   files, configuration files, and script code) &MUST; be protected from
3819   inappropriate retrieval, since they might contain sensitive
3820   information. Experience has shown that minor bugs in such HTTP server
3821   implementations have turned into security risks.
3822</t>
3823</section>
3824
3825<section title="DNS-related Attacks" anchor="dns.related.attacks">
3826<t>
3827   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3828   generally prone to security attacks based on the deliberate misassociation
3829   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3830   cautious in assuming the validity of an IP number/DNS name association unless
3831   the response is protected by DNSSec (<xref target="RFC4033"/>).
3832</t>
3833</section>
3834
3835<section title="Proxies and Caching" anchor="attack.proxies">
3836<t>
3837   By their very nature, HTTP proxies are men-in-the-middle, and
3838   represent an opportunity for man-in-the-middle attacks. Compromise of
3839   the systems on which the proxies run can result in serious security
3840   and privacy problems. Proxies have access to security-related
3841   information, personal information about individual users and
3842   organizations, and proprietary information belonging to users and
3843   content providers. A compromised proxy, or a proxy implemented or
3844   configured without regard to security and privacy considerations,
3845   might be used in the commission of a wide range of potential attacks.
3846</t>
3847<t>
3848   Proxy operators need to protect the systems on which proxies run as
3849   they would protect any system that contains or transports sensitive
3850   information. In particular, log information gathered at proxies often
3851   contains highly sensitive personal information, and/or information
3852   about organizations. Log information needs to be carefully guarded, and
3853   appropriate guidelines for use need to be developed and followed.
3854   (<xref target="abuse.of.server.log.information"/>).
3855</t>
3856<t>
3857   Proxy implementors need to consider the privacy and security
3858   implications of their design and coding decisions, and of the
3859   configuration options they provide to proxy operators (especially the
3860   default configuration).
3861</t>
3862<t>
3863   Users of a proxy need to be aware that proxies are no trustworthier than
3864   the people who run them; HTTP itself cannot solve this problem.
3865</t>
3866<t>
3867   The judicious use of cryptography, when appropriate, might suffice to
3868   protect against a broad range of security and privacy attacks. Such
3869   cryptography is beyond the scope of the HTTP/1.1 specification.
3870</t>
3871</section>
3872
3873<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3874<t>
3875   Because HTTP uses mostly textual, character-delimited fields, attackers can
3876   overflow buffers in implementations, and/or perform a Denial of Service
3877   against implementations that accept fields with unlimited lengths.
3878</t>
3879<t>
3880   To promote interoperability, this specification makes specific
3881   recommendations for size limits on request-targets (<xref target="request-target"/>)
3882   and blocks of header fields (<xref target="header.fields"/>). These are
3883   minimum recommendations, chosen to be supportable even by implementations
3884   with limited resources; it is expected that most implementations will choose
3885   substantially higher limits.
3886</t>
3887<t>
3888   This specification also provides a way for servers to reject messages that
3889   have request-targets that are too long (&status-414;) or request entities
3890   that are too large (&status-4xx;).
3891</t>
3892<t>
3893   Other fields (including but not limited to request methods, response status
3894   phrases, header field-names, and body chunks) &SHOULD; be limited by
3895   implementations carefully, so as to not impede interoperability.
3896</t>
3897</section>
3898
3899<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3900<t>
3901   They exist. They are hard to defend against. Research continues.
3902   Beware.
3903</t>
3904</section>
3905</section>
3906
3907<section title="Acknowledgments" anchor="acks">
3908<t>
3909   This document revision builds on the work that went into
3910   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3911   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
3912   acknowledgements.
3913</t>
3914<t>
3915   Since 1999, many contributors have helped by reporting bugs, asking
3916   smart questions, drafting and reviewing text, and discussing open issues:
3917</t>
3918<?BEGININC acks ?>
3919<t>Adam Barth,
3920Adam Roach,
3921Addison Phillips,
3922Adrian Chadd,
3923Adrien de Croy,
3924Alan Ford,
3925Alan Ruttenberg,
3926Albert Lunde,
3927Alex Rousskov,
3928Alexey Melnikov,
3929Alisha Smith,
3930Amichai Rothman,
3931Amit Klein,
3932Amos Jeffries,
3933Andreas Maier,
3934Andreas Petersson,
3935Anne van Kesteren,
3936Anthony Bryan,
3937Asbjorn Ulsberg,
3938Balachander Krishnamurthy,
3939Barry Leiba,
3940Ben Laurie,
3941Benjamin Niven-Jenkins,
3942Bil Corry,
3943Bill Burke,
3944Bjoern Hoehrmann,
3945Bob Scheifler,
3946Boris Zbarsky,
3947Brett Slatkin,
3948Brian Kell,
3949Brian McBarron,
3950Brian Pane,
3951Brian Smith,
3952Bryce Nesbitt,
3953Carl Kugler,
3954Charles Fry,
3955Chris Newman,
3956Cyrus Daboo,
3957Dale Robert Anderson,
3958Dan Winship,
3959Daniel Stenberg,
3960Dave Cridland,
3961Dave Crocker,
3962Dave Kristol,
3963David Booth,
3964David Singer,
3965David W. Morris,
3966Diwakar Shetty,
3967Drummond Reed,
3968Duane Wessels,
3969Edward Lee,
3970Eliot Lear,
3971Eran Hammer-Lahav,
3972Eric D. Williams,
3973Eric J. Bowman,
3974Eric Lawrence,
3975Erik Aronesty,
3976Florian Weimer,
3977Frank Ellermann,
3978Fred Bohle,
3979Geoffrey Sneddon,
3980Gervase Markham,
3981Greg Wilkins,
3982Harald Tveit Alvestrand,
3983Harry Halpin,
3984Helge Hess,
3985Henrik Nordstrom,
3986Henry S. Thompson,
3987Henry Story,
3988Howard Melman,
3989Hugo Haas,
3990Ian Hickson,
3991Ingo Struck,
3992J. Ross Nicoll,
3993James H. Manger,
3994James Lacey,
3995James M. Snell,
3996Jamie Lokier,
3997Jan Algermissen,
3998Jeff Hodges (for coming up with the term 'effective Request-URI'),
3999Jeff Walden,
4000Jim Luther,
4001Joe D. Williams,
4002Joe Gregorio,
4003Joe Orton,
4004John C. Klensin,
4005John C. Mallery,
4006John Cowan,
4007John Kemp,
4008John Panzer,
4009John Schneider,
4010John Stracke,
4011Jonas Sicking,
4012Jonathan Moore,
4013Jonathan Rees,
4014Jordi Ros,
4015Joris Dobbelsteen,
4016Josh Cohen,
4017Julien Pierre,
4018Jungshik Shin,
4019Justin Chapweske,
4020Justin Erenkrantz,
4021Justin James,
4022Kalvinder Singh,
4023Karl Dubost,
4024Keith Hoffman,
4025Keith Moore,
4026Koen Holtman,
4027Konstantin Voronkov,
4028Kris Zyp,
4029Lisa Dusseault,
4030Maciej Stachowiak,
4031Marc Schneider,
4032Marc Slemko,
4033Mark Baker,
4034Mark Nottingham (Working Group chair),
4035Mark Pauley,
4036Martin J. Duerst,
4037Martin Thomson,
4038Matt Lynch,
4039Matthew Cox,
4040Max Clark,
4041Michael Burrows,
4042Michael Hausenblas,
4043Mike Amundsen,
4044Mike Kelly,
4045Mike Schinkel,
4046Miles Sabin,
4047Mykyta Yevstifeyev,
4048Nathan Rixham,
4049Nicholas Shanks,
4050Nico Williams,
4051Nicolas Alvarez,
4052Noah Slater,
4053Pablo Castro,
4054Pat Hayes,
4055Patrick R. McManus,
4056Paul E. Jones,
4057Paul Hoffman,
4058Paul Marquess,
4059Peter Saint-Andre,
4060Peter Watkins,
4061Phil Archer,
4062Phillip Hallam-Baker,
4063Poul-Henning Kamp,
4064Preethi Natarajan,
4065Reto Bachmann-Gmuer,
4066Richard Cyganiak,
4067Robert Brewer,
4068Robert Collins,
4069Robert O'Callahan,
4070Robert Olofsson,
4071Robert Sayre,
4072Robert Siemer,
4073Robert de Wilde,
4074Roberto Javier Godoy,
4075Ronny Widjaja,
4076S. Mike Dierken,
4077Salvatore Loreto,
4078Sam Johnston,
4079Sam Ruby,
4080Scott Lawrence (for maintaining the original issues list),
4081Sean B. Palmer,
4082Shane McCarron,
4083Stefan Eissing,
4084Stefan Tilkov,
4085Stefanos Harhalakis,
4086Stephane Bortzmeyer,
4087Stuart Williams,
4088Subbu Allamaraju,
4089Sylvain Hellegouarch,
4090Tapan Divekar,
4091Thomas Broyer,
4092Thomas Nordin,
4093Thomas Roessler,
4094Tim Morgan,
4095Tim Olsen,
4096Travis Snoozy,
4097Tyler Close,
4098Vincent Murphy,
4099Wenbo Zhu,
4100Werner Baumann,
4101Wilbur Streett,
4102Wilfredo Sanchez Vega,
4103William A. Rowe Jr.,
4104William Chan,
4105Willy Tarreau,
4106Xiaoshu Wang,
4107Yaron Goland,
4108Yngve Nysaeter Pettersen,
4109Yogesh Bang,
4110Yutaka Oiwa, and
4111Zed A. Shaw.
4112</t>
4113<?ENDINC acks ?>
4114</section>
4115
4116</middle>
4117<back>
4118
4119<references title="Normative References">
4120
4121<reference anchor="ISO-8859-1">
4122  <front>
4123    <title>
4124     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4125    </title>
4126    <author>
4127      <organization>International Organization for Standardization</organization>
4128    </author>
4129    <date year="1998"/>
4130  </front>
4131  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4132</reference>
4133
4134<reference anchor="Part2">
4135  <front>
4136    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4137    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4138      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4139      <address><email>fielding@gbiv.com</email></address>
4140    </author>
4141    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4142      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4143      <address><email>jg@freedesktop.org</email></address>
4144    </author>
4145    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4146      <organization abbrev="HP">Hewlett-Packard Company</organization>
4147      <address><email>JeffMogul@acm.org</email></address>
4148    </author>
4149    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4150      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4151      <address><email>henrikn@microsoft.com</email></address>
4152    </author>
4153    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4154      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4155      <address><email>LMM@acm.org</email></address>
4156    </author>
4157    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4158      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4159      <address><email>paulle@microsoft.com</email></address>
4160    </author>
4161    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4162      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4163      <address><email>timbl@w3.org</email></address>
4164    </author>
4165    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4166      <organization abbrev="W3C">World Wide Web Consortium</organization>
4167      <address><email>ylafon@w3.org</email></address>
4168    </author>
4169    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4170      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4171      <address><email>julian.reschke@greenbytes.de</email></address>
4172    </author>
4173    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4174  </front>
4175  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4176  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4177</reference>
4178
4179<reference anchor="Part3">
4180  <front>
4181    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4182    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4183      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4184      <address><email>fielding@gbiv.com</email></address>
4185    </author>
4186    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4187      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4188      <address><email>jg@freedesktop.org</email></address>
4189    </author>
4190    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4191      <organization abbrev="HP">Hewlett-Packard Company</organization>
4192      <address><email>JeffMogul@acm.org</email></address>
4193    </author>
4194    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4195      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4196      <address><email>henrikn@microsoft.com</email></address>
4197    </author>
4198    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4199      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4200      <address><email>LMM@acm.org</email></address>
4201    </author>
4202    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4203      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4204      <address><email>paulle@microsoft.com</email></address>
4205    </author>
4206    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4207      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4208      <address><email>timbl@w3.org</email></address>
4209    </author>
4210    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4211      <organization abbrev="W3C">World Wide Web Consortium</organization>
4212      <address><email>ylafon@w3.org</email></address>
4213    </author>
4214    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4215      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4216      <address><email>julian.reschke@greenbytes.de</email></address>
4217    </author>
4218    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4219  </front>
4220  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4221  <x:source href="p3-payload.xml" basename="p3-payload"/>
4222</reference>
4223
4224<reference anchor="Part6">
4225  <front>
4226    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4227    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4228      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4229      <address><email>fielding@gbiv.com</email></address>
4230    </author>
4231    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4232      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4233      <address><email>jg@freedesktop.org</email></address>
4234    </author>
4235    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4236      <organization abbrev="HP">Hewlett-Packard Company</organization>
4237      <address><email>JeffMogul@acm.org</email></address>
4238    </author>
4239    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4240      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4241      <address><email>henrikn@microsoft.com</email></address>
4242    </author>
4243    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4244      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4245      <address><email>LMM@acm.org</email></address>
4246    </author>
4247    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4248      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4249      <address><email>paulle@microsoft.com</email></address>
4250    </author>
4251    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4252      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4253      <address><email>timbl@w3.org</email></address>
4254    </author>
4255    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4256      <organization abbrev="W3C">World Wide Web Consortium</organization>
4257      <address><email>ylafon@w3.org</email></address>
4258    </author>
4259    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4260      <organization>Rackspace</organization>
4261      <address><email>mnot@mnot.net</email></address>
4262    </author>
4263    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4264      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4265      <address><email>julian.reschke@greenbytes.de</email></address>
4266    </author>
4267    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4268  </front>
4269  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4270  <x:source href="p6-cache.xml" basename="p6-cache"/>
4271</reference>
4272
4273<reference anchor="RFC5234">
4274  <front>
4275    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4276    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4277      <organization>Brandenburg InternetWorking</organization>
4278      <address>
4279        <email>dcrocker@bbiw.net</email>
4280      </address> 
4281    </author>
4282    <author initials="P." surname="Overell" fullname="Paul Overell">
4283      <organization>THUS plc.</organization>
4284      <address>
4285        <email>paul.overell@thus.net</email>
4286      </address>
4287    </author>
4288    <date month="January" year="2008"/>
4289  </front>
4290  <seriesInfo name="STD" value="68"/>
4291  <seriesInfo name="RFC" value="5234"/>
4292</reference>
4293
4294<reference anchor="RFC2119">
4295  <front>
4296    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4297    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4298      <organization>Harvard University</organization>
4299      <address><email>sob@harvard.edu</email></address>
4300    </author>
4301    <date month="March" year="1997"/>
4302  </front>
4303  <seriesInfo name="BCP" value="14"/>
4304  <seriesInfo name="RFC" value="2119"/>
4305</reference>
4306
4307<reference anchor="RFC3986">
4308 <front>
4309  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4310  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4311    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4312    <address>
4313       <email>timbl@w3.org</email>
4314       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4315    </address>
4316  </author>
4317  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4318    <organization abbrev="Day Software">Day Software</organization>
4319    <address>
4320      <email>fielding@gbiv.com</email>
4321      <uri>http://roy.gbiv.com/</uri>
4322    </address>
4323  </author>
4324  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4325    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4326    <address>
4327      <email>LMM@acm.org</email>
4328      <uri>http://larry.masinter.net/</uri>
4329    </address>
4330  </author>
4331  <date month='January' year='2005'></date>
4332 </front>
4333 <seriesInfo name="STD" value="66"/>
4334 <seriesInfo name="RFC" value="3986"/>
4335</reference>
4336
4337<reference anchor="USASCII">
4338  <front>
4339    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4340    <author>
4341      <organization>American National Standards Institute</organization>
4342    </author>
4343    <date year="1986"/>
4344  </front>
4345  <seriesInfo name="ANSI" value="X3.4"/>
4346</reference>
4347
4348<reference anchor="RFC1950">
4349  <front>
4350    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4351    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4352      <organization>Aladdin Enterprises</organization>
4353      <address><email>ghost@aladdin.com</email></address>
4354    </author>
4355    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4356    <date month="May" year="1996"/>
4357  </front>
4358  <seriesInfo name="RFC" value="1950"/>
4359  <annotation>
4360    RFC 1950 is an Informational RFC, thus it might be less stable than
4361    this specification. On the other hand, this downward reference was
4362    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4363    therefore it is unlikely to cause problems in practice. See also
4364    <xref target="BCP97"/>.
4365  </annotation>
4366</reference>
4367
4368<reference anchor="RFC1951">
4369  <front>
4370    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4371    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4372      <organization>Aladdin Enterprises</organization>
4373      <address><email>ghost@aladdin.com</email></address>
4374    </author>
4375    <date month="May" year="1996"/>
4376  </front>
4377  <seriesInfo name="RFC" value="1951"/>
4378  <annotation>
4379    RFC 1951 is an Informational RFC, thus it might be less stable than
4380    this specification. On the other hand, this downward reference was
4381    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4382    therefore it is unlikely to cause problems in practice. See also
4383    <xref target="BCP97"/>.
4384  </annotation>
4385</reference>
4386
4387<reference anchor="RFC1952">
4388  <front>
4389    <title>GZIP file format specification version 4.3</title>
4390    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4391      <organization>Aladdin Enterprises</organization>
4392      <address><email>ghost@aladdin.com</email></address>
4393    </author>
4394    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4395      <address><email>gzip@prep.ai.mit.edu</email></address>
4396    </author>
4397    <author initials="M." surname="Adler" fullname="Mark Adler">
4398      <address><email>madler@alumni.caltech.edu</email></address>
4399    </author>
4400    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4401      <address><email>ghost@aladdin.com</email></address>
4402    </author>
4403    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4404      <address><email>randeg@alumni.rpi.edu</email></address>
4405    </author>
4406    <date month="May" year="1996"/>
4407  </front>
4408  <seriesInfo name="RFC" value="1952"/>
4409  <annotation>
4410    RFC 1952 is an Informational RFC, thus it might be less stable than
4411    this specification. On the other hand, this downward reference was
4412    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4413    therefore it is unlikely to cause problems in practice. See also
4414    <xref target="BCP97"/>.
4415  </annotation>
4416</reference>
4417
4418</references>
4419
4420<references title="Informative References">
4421
4422<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4423  <front>
4424    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4425    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4426    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4427    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4428    <author initials="H." surname="Lie" fullname="H. Lie"/>
4429    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4430    <date year="1997" month="September"/>
4431  </front>
4432  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4433</reference>
4434
4435<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4436  <front>
4437    <title>Improving HTTP Latency</title>
4438    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4439    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4440    <date year="1995" month="December"/>
4441  </front>
4442  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4443</reference>
4444
4445<reference anchor='RFC1919'>
4446  <front>
4447    <title>Classical versus Transparent IP Proxies</title>
4448    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4449      <address><email>mchatel@pax.eunet.ch</email></address>
4450    </author>
4451    <date year='1996' month='March' />
4452  </front>
4453  <seriesInfo name='RFC' value='1919' />
4454</reference>
4455
4456<reference anchor="RFC1945">
4457  <front>
4458    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4459    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4460      <organization>MIT, Laboratory for Computer Science</organization>
4461      <address><email>timbl@w3.org</email></address>
4462    </author>
4463    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4464      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4465      <address><email>fielding@ics.uci.edu</email></address>
4466    </author>
4467    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4468      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4469      <address><email>frystyk@w3.org</email></address>
4470    </author>
4471    <date month="May" year="1996"/>
4472  </front>
4473  <seriesInfo name="RFC" value="1945"/>
4474</reference>
4475
4476<reference anchor="RFC2045">
4477  <front>
4478    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4479    <author initials="N." surname="Freed" fullname="Ned Freed">
4480      <organization>Innosoft International, Inc.</organization>
4481      <address><email>ned@innosoft.com</email></address>
4482    </author>
4483    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4484      <organization>First Virtual Holdings</organization>
4485      <address><email>nsb@nsb.fv.com</email></address>
4486    </author>
4487    <date month="November" year="1996"/>
4488  </front>
4489  <seriesInfo name="RFC" value="2045"/>
4490</reference>
4491
4492<reference anchor="RFC2047">
4493  <front>
4494    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4495    <author initials="K." surname="Moore" fullname="Keith Moore">
4496      <organization>University of Tennessee</organization>
4497      <address><email>moore@cs.utk.edu</email></address>
4498    </author>
4499    <date month="November" year="1996"/>
4500  </front>
4501  <seriesInfo name="RFC" value="2047"/>
4502</reference>
4503
4504<reference anchor="RFC2068">
4505  <front>
4506    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4507    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4508      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4509      <address><email>fielding@ics.uci.edu</email></address>
4510    </author>
4511    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4512      <organization>MIT Laboratory for Computer Science</organization>
4513      <address><email>jg@w3.org</email></address>
4514    </author>
4515    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4516      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4517      <address><email>mogul@wrl.dec.com</email></address>
4518    </author>
4519    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4520      <organization>MIT Laboratory for Computer Science</organization>
4521      <address><email>frystyk@w3.org</email></address>
4522    </author>
4523    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4524      <organization>MIT Laboratory for Computer Science</organization>
4525      <address><email>timbl@w3.org</email></address>
4526    </author>
4527    <date month="January" year="1997"/>
4528  </front>
4529  <seriesInfo name="RFC" value="2068"/>
4530</reference>
4531
4532<reference anchor="RFC2145">
4533  <front>
4534    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4535    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4536      <organization>Western Research Laboratory</organization>
4537      <address><email>mogul@wrl.dec.com</email></address>
4538    </author>
4539    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4540      <organization>Department of Information and Computer Science</organization>
4541      <address><email>fielding@ics.uci.edu</email></address>
4542    </author>
4543    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4544      <organization>MIT Laboratory for Computer Science</organization>
4545      <address><email>jg@w3.org</email></address>
4546    </author>
4547    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4548      <organization>W3 Consortium</organization>
4549      <address><email>frystyk@w3.org</email></address>
4550    </author>
4551    <date month="May" year="1997"/>
4552  </front>
4553  <seriesInfo name="RFC" value="2145"/>
4554</reference>
4555
4556<reference anchor="RFC2616">
4557  <front>
4558    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4559    <author initials="R." surname="Fielding" fullname="R. Fielding">
4560      <organization>University of California, Irvine</organization>
4561      <address><email>fielding@ics.uci.edu</email></address>
4562    </author>
4563    <author initials="J." surname="Gettys" fullname="J. Gettys">
4564      <organization>W3C</organization>
4565      <address><email>jg@w3.org</email></address>
4566    </author>
4567    <author initials="J." surname="Mogul" fullname="J. Mogul">
4568      <organization>Compaq Computer Corporation</organization>
4569      <address><email>mogul@wrl.dec.com</email></address>
4570    </author>
4571    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4572      <organization>MIT Laboratory for Computer Science</organization>
4573      <address><email>frystyk@w3.org</email></address>
4574    </author>
4575    <author initials="L." surname="Masinter" fullname="L. Masinter">
4576      <organization>Xerox Corporation</organization>
4577      <address><email>masinter@parc.xerox.com</email></address>
4578    </author>
4579    <author initials="P." surname="Leach" fullname="P. Leach">
4580      <organization>Microsoft Corporation</organization>
4581      <address><email>paulle@microsoft.com</email></address>
4582    </author>
4583    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4584      <organization>W3C</organization>
4585      <address><email>timbl@w3.org</email></address>
4586    </author>
4587    <date month="June" year="1999"/>
4588  </front>
4589  <seriesInfo name="RFC" value="2616"/>
4590</reference>
4591
4592<reference anchor='RFC2817'>
4593  <front>
4594    <title>Upgrading to TLS Within HTTP/1.1</title>
4595    <author initials='R.' surname='Khare' fullname='R. Khare'>
4596      <organization>4K Associates / UC Irvine</organization>
4597      <address><email>rohit@4K-associates.com</email></address>
4598    </author>
4599    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4600      <organization>Agranat Systems, Inc.</organization>
4601      <address><email>lawrence@agranat.com</email></address>
4602    </author>
4603    <date year='2000' month='May' />
4604  </front>
4605  <seriesInfo name='RFC' value='2817' />
4606</reference>
4607
4608<reference anchor='RFC2818'>
4609  <front>
4610    <title>HTTP Over TLS</title>
4611    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4612      <organization>RTFM, Inc.</organization>
4613      <address><email>ekr@rtfm.com</email></address>
4614    </author>
4615    <date year='2000' month='May' />
4616  </front>
4617  <seriesInfo name='RFC' value='2818' />
4618</reference>
4619
4620<reference anchor='RFC2965'>
4621  <front>
4622    <title>HTTP State Management Mechanism</title>
4623    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4624      <organization>Bell Laboratories, Lucent Technologies</organization>
4625      <address><email>dmk@bell-labs.com</email></address>
4626    </author>
4627    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4628      <organization>Epinions.com, Inc.</organization>
4629      <address><email>lou@montulli.org</email></address>
4630    </author>
4631    <date year='2000' month='October' />
4632  </front>
4633  <seriesInfo name='RFC' value='2965' />
4634</reference>
4635
4636<reference anchor='RFC3040'>
4637  <front>
4638    <title>Internet Web Replication and Caching Taxonomy</title>
4639    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4640      <organization>Equinix, Inc.</organization>
4641    </author>
4642    <author initials='I.' surname='Melve' fullname='I. Melve'>
4643      <organization>UNINETT</organization>
4644    </author>
4645    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4646      <organization>CacheFlow Inc.</organization>
4647    </author>
4648    <date year='2001' month='January' />
4649  </front>
4650  <seriesInfo name='RFC' value='3040' />
4651</reference>
4652
4653<reference anchor='RFC3864'>
4654  <front>
4655    <title>Registration Procedures for Message Header Fields</title>
4656    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4657      <organization>Nine by Nine</organization>
4658      <address><email>GK-IETF@ninebynine.org</email></address>
4659    </author>
4660    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4661      <organization>BEA Systems</organization>
4662      <address><email>mnot@pobox.com</email></address>
4663    </author>
4664    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4665      <organization>HP Labs</organization>
4666      <address><email>JeffMogul@acm.org</email></address>
4667    </author>
4668    <date year='2004' month='September' />
4669  </front>
4670  <seriesInfo name='BCP' value='90' />
4671  <seriesInfo name='RFC' value='3864' />
4672</reference>
4673
4674<reference anchor='RFC4033'>
4675  <front>
4676    <title>DNS Security Introduction and Requirements</title>
4677    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4678    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4679    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4680    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4681    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4682    <date year='2005' month='March' />
4683  </front>
4684  <seriesInfo name='RFC' value='4033' />
4685</reference>
4686
4687<reference anchor="RFC4288">
4688  <front>
4689    <title>Media Type Specifications and Registration Procedures</title>
4690    <author initials="N." surname="Freed" fullname="N. Freed">
4691      <organization>Sun Microsystems</organization>
4692      <address>
4693        <email>ned.freed@mrochek.com</email>
4694      </address>
4695    </author>
4696    <author initials="J." surname="Klensin" fullname="J. Klensin">
4697      <address>
4698        <email>klensin+ietf@jck.com</email>
4699      </address>
4700    </author>
4701    <date year="2005" month="December"/>
4702  </front>
4703  <seriesInfo name="BCP" value="13"/>
4704  <seriesInfo name="RFC" value="4288"/>
4705</reference>
4706
4707<reference anchor='RFC4395'>
4708  <front>
4709    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4710    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4711      <organization>AT&amp;T Laboratories</organization>
4712      <address>
4713        <email>tony+urireg@maillennium.att.com</email>
4714      </address>
4715    </author>
4716    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4717      <organization>Qualcomm, Inc.</organization>
4718      <address>
4719        <email>hardie@qualcomm.com</email>
4720      </address>
4721    </author>
4722    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4723      <organization>Adobe Systems</organization>
4724      <address>
4725        <email>LMM@acm.org</email>
4726      </address>
4727    </author>
4728    <date year='2006' month='February' />
4729  </front>
4730  <seriesInfo name='BCP' value='115' />
4731  <seriesInfo name='RFC' value='4395' />
4732</reference>
4733
4734<reference anchor='RFC4559'>
4735  <front>
4736    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4737    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4738    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4739    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4740    <date year='2006' month='June' />
4741  </front>
4742  <seriesInfo name='RFC' value='4559' />
4743</reference>
4744
4745<reference anchor='RFC5226'>
4746  <front>
4747    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4748    <author initials='T.' surname='Narten' fullname='T. Narten'>
4749      <organization>IBM</organization>
4750      <address><email>narten@us.ibm.com</email></address>
4751    </author>
4752    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4753      <organization>Google</organization>
4754      <address><email>Harald@Alvestrand.no</email></address>
4755    </author>
4756    <date year='2008' month='May' />
4757  </front>
4758  <seriesInfo name='BCP' value='26' />
4759  <seriesInfo name='RFC' value='5226' />
4760</reference>
4761
4762<reference anchor="RFC5322">
4763  <front>
4764    <title>Internet Message Format</title>
4765    <author initials="P." surname="Resnick" fullname="P. Resnick">
4766      <organization>Qualcomm Incorporated</organization>
4767    </author>
4768    <date year="2008" month="October"/>
4769  </front> 
4770  <seriesInfo name="RFC" value="5322"/>
4771</reference>
4772
4773<reference anchor="RFC6265">
4774  <front>
4775    <title>HTTP State Management Mechanism</title>
4776    <author initials="A." surname="Barth" fullname="Adam Barth">
4777      <organization abbrev="U.C. Berkeley">
4778        University of California, Berkeley
4779      </organization>
4780      <address><email>abarth@eecs.berkeley.edu</email></address>
4781    </author>
4782    <date year="2011" month="April" />
4783  </front>
4784  <seriesInfo name="RFC" value="6265"/>
4785</reference>
4786
4787<reference anchor='BCP97'>
4788  <front>
4789    <title>Handling Normative References to Standards-Track Documents</title>
4790    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4791      <address>
4792        <email>klensin+ietf@jck.com</email>
4793      </address>
4794    </author>
4795    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4796      <organization>MIT</organization>
4797      <address>
4798        <email>hartmans-ietf@mit.edu</email>
4799      </address>
4800    </author>
4801    <date year='2007' month='June' />
4802  </front>
4803  <seriesInfo name='BCP' value='97' />
4804  <seriesInfo name='RFC' value='4897' />
4805</reference>
4806
4807<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4808  <front>
4809    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4810    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4811    <date year="2001" month="November"/>
4812  </front>
4813  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4814</reference>
4815
4816<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4817  <front>
4818    <title>Analysis of HTTP Performance Problems</title>
4819    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4820    <date/>
4821  </front>
4822</reference>
4823
4824<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4825  <front>
4826  <title>Analysis of HTTP Performance</title>
4827  <author initials="J." surname="Touch" fullname="Joe Touch">
4828    <organization>USC/Information Sciences Institute</organization>
4829    <address><email>touch@isi.edu</email></address>
4830  </author>
4831  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4832    <organization>USC/Information Sciences Institute</organization>
4833    <address><email>johnh@isi.edu</email></address>
4834  </author>
4835  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4836    <organization>USC/Information Sciences Institute</organization>
4837    <address><email>katia@isi.edu</email></address>
4838  </author>
4839  <date year="1998" month="Aug"/>
4840  </front>
4841  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4842  <annotation>(original report dated Aug. 1996)</annotation>
4843</reference>
4844
4845</references>
4846
4847
4848<section title="HTTP Version History" anchor="compatibility">
4849<t>
4850   HTTP has been in use by the World-Wide Web global information initiative
4851   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4852   was a simple protocol for hypertext data transfer across the Internet
4853   with only a single request method (GET) and no metadata.
4854   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4855   methods and MIME-like messaging that could include metadata about the data
4856   transferred and modifiers on the request/response semantics. However,
4857   HTTP/1.0 did not sufficiently take into consideration the effects of
4858   hierarchical proxies, caching, the need for persistent connections, or
4859   name-based virtual hosts. The proliferation of incompletely-implemented
4860   applications calling themselves "HTTP/1.0" further necessitated a
4861   protocol version change in order for two communicating applications
4862   to determine each other's true capabilities.
4863</t>
4864<t>
4865   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4866   requirements that enable reliable implementations, adding only
4867   those new features that will either be safely ignored by an HTTP/1.0
4868   recipient or only sent when communicating with a party advertising
4869   compliance with HTTP/1.1.
4870</t>
4871<t>
4872   It is beyond the scope of a protocol specification to mandate
4873   compliance with previous versions. HTTP/1.1 was deliberately
4874   designed, however, to make supporting previous versions easy.
4875   We would expect a general-purpose HTTP/1.1 server to understand
4876   any valid request in the format of HTTP/1.0 and respond appropriately
4877   with an HTTP/1.1 message that only uses features understood (or
4878   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4879   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4880</t>
4881<t>
4882   Since HTTP/0.9 did not support header fields in a request,
4883   there is no mechanism for it to support name-based virtual
4884   hosts (selection of resource by inspection of the Host header
4885   field).  Any server that implements name-based virtual hosts
4886   ought to disable support for HTTP/0.9.  Most requests that
4887   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4888   requests wherein a buggy client failed to properly encode
4889   linear whitespace found in a URI reference and placed in
4890   the request-target.
4891</t>
4892
4893<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4894<t>
4895   This section summarizes major differences between versions HTTP/1.0
4896   and HTTP/1.1.
4897</t>
4898
4899<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4900<t>
4901   The requirements that clients and servers support the Host header
4902   field (<xref target="header.host"/>), report an error if it is
4903   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4904   are among the most important changes defined by HTTP/1.1.
4905</t>
4906<t>
4907   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4908   addresses and servers; there was no other established mechanism for
4909   distinguishing the intended server of a request than the IP address
4910   to which that request was directed. The Host header field was
4911   introduced during the development of HTTP/1.1 and, though it was
4912   quickly implemented by most HTTP/1.0 browsers, additional requirements
4913   were placed on all HTTP/1.1 requests in order to ensure complete
4914   adoption.  At the time of this writing, most HTTP-based services
4915   are dependent upon the Host header field for targeting requests.
4916</t>
4917</section>
4918
4919<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4920<t>
4921   For most implementations of HTTP/1.0, each connection is established
4922   by the client prior to the request and closed by the server after
4923   sending the response. However, some implementations implement the
4924   Keep-Alive version of persistent connections described in
4925   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4926</t>
4927<t>
4928   Some clients and servers might wish to be compatible with some
4929   previous implementations of persistent connections in HTTP/1.0
4930   clients and servers. Persistent connections in HTTP/1.0 are
4931   explicitly negotiated as they are not the default behavior. HTTP/1.0
4932   experimental implementations of persistent connections are faulty,
4933   and the new facilities in HTTP/1.1 are designed to rectify these
4934   problems. The problem was that some existing HTTP/1.0 clients might
4935   send Keep-Alive to a proxy server that doesn't understand
4936   Connection, which would then erroneously forward it to the next
4937   inbound server, which would establish the Keep-Alive connection and
4938   result in a hung HTTP/1.0 proxy waiting for the close on the
4939   response. The result is that HTTP/1.0 clients must be prevented from
4940   using Keep-Alive when talking to proxies.
4941</t>
4942<t>
4943   However, talking to proxies is the most important use of persistent
4944   connections, so that prohibition is clearly unacceptable. Therefore,
4945   we need some other mechanism for indicating a persistent connection
4946   is desired, which is safe to use even when talking to an old proxy
4947   that ignores Connection. Persistent connections are the default for
4948   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4949   declaring non-persistence. See <xref target="header.connection"/>.
4950</t>
4951</section>
4952</section>
4953
4954<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4955<t>
4956  Empty list elements in list productions have been deprecated.
4957  (<xref target="notation.abnf"/>)
4958</t>
4959<t>
4960  Rules about implicit linear whitespace between certain grammar productions
4961  have been removed; now it's only allowed when specifically pointed out
4962  in the ABNF.
4963  (<xref target="basic.rules"/>)
4964</t>
4965<t>
4966  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4967  sensitive. Restrict the version numbers to be single digits due to the fact
4968  that implementations are known to handle multi-digit version numbers
4969  incorrectly.
4970  (<xref target="http.version"/>)
4971</t>
4972<t>
4973  Require that invalid whitespace around field-names be rejected.
4974  (<xref target="header.fields"/>)
4975</t>
4976<t> 
4977  The NUL octet is no longer allowed in comment and quoted-string
4978  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4979  Non-ASCII content in header fields and reason phrase has been obsoleted and
4980  made opaque (the TEXT rule was removed).
4981  (<xref target="field.rules"/>)
4982</t>
4983<t>
4984  Require recipients to handle bogus Content-Length header fields as errors.
4985  (<xref target="message.body"/>)
4986</t>
4987<t>
4988  Remove reference to non-existent identity transfer-coding value tokens.
4989  (Sections <xref format="counter" target="message.body"/> and
4990  <xref format="counter" target="transfer.codings"/>)
4991</t>
4992<t>
4993  Update use of abs_path production from RFC 1808 to the path-absolute + query
4994  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4995  request method only.
4996  (<xref target="request-target"/>)
4997</t>
4998<t>
4999  Clarification that the chunk length does not include the count of the octets
5000  in the chunk header and trailer. Furthermore disallowed line folding
5001  in chunk extensions.
5002  (<xref target="chunked.encoding"/>)
5003</t>
5004<t>
5005  Remove hard limit of two connections per server.
5006  (<xref target="persistent.practical"/>)
5007</t>
5008<t>
5009  Change ABNF productions for header fields to only define the field value.
5010  (<xref target="header.field.definitions"/>)
5011</t>
5012<t>
5013  Clarify exactly when close connection options must be sent.
5014  (<xref target="header.connection"/>)
5015</t>
5016<t>
5017  Define the semantics of the "Upgrade" header field in responses other than
5018  101 (this was incorporated from <xref target="RFC2817"/>).
5019  (<xref target="header.upgrade"/>)
5020</t>
5021</section>
5022</section>
5023
5024<?BEGININC p1-messaging.abnf-appendix ?>
5025<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5026<figure>
5027<artwork type="abnf" name="p1-messaging.parsed-abnf">
5028<x:ref>BWS</x:ref> = OWS
5029
5030<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5031<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5032 connection-token ] )
5033<x:ref>Content-Length</x:ref> = 1*DIGIT
5034
5035<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5036<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5037<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5038 ]
5039<x:ref>Host</x:ref> = uri-host [ ":" port ]
5040
5041<x:ref>Method</x:ref> = token
5042
5043<x:ref>OWS</x:ref> = *( SP / HTAB / obs-fold )
5044
5045<x:ref>RWS</x:ref> = 1*( SP / HTAB / obs-fold )
5046<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5047<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5048
5049<x:ref>Status-Code</x:ref> = 3DIGIT
5050<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5051
5052<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5053<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5054<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5055 transfer-coding ] )
5056
5057<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5058<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5059
5060<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5061 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5062 )
5063
5064<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5065<x:ref>attribute</x:ref> = token
5066<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5067
5068<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5069<x:ref>chunk-data</x:ref> = 1*OCTET
5070<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5071<x:ref>chunk-ext-name</x:ref> = token
5072<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5073<x:ref>chunk-size</x:ref> = 1*HEXDIG
5074<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5075<x:ref>connection-token</x:ref> = token
5076<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5077 / %x2A-5B ; '*'-'['
5078 / %x5D-7E ; ']'-'~'
5079 / obs-text
5080
5081<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5082<x:ref>field-name</x:ref> = token
5083<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5084
5085<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5086<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5087<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5088
5089<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5090
5091<x:ref>message-body</x:ref> = *OCTET
5092
5093<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5094<x:ref>obs-text</x:ref> = %x80-FF
5095
5096<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5097<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5098<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5099<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5100<x:ref>product</x:ref> = token [ "/" product-version ]
5101<x:ref>product-version</x:ref> = token
5102<x:ref>protocol-name</x:ref> = token
5103<x:ref>protocol-version</x:ref> = token
5104<x:ref>pseudonym</x:ref> = token
5105
5106<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5107 / %x5D-7E ; ']'-'~'
5108 / obs-text
5109<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5110 / %x5D-7E ; ']'-'~'
5111 / obs-text
5112<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5113<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5114<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5115<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5116<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5117<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5118
5119<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5120<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5121<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5122<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5123 / authority
5124
5125<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5126 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5127<x:ref>start-line</x:ref> = Request-Line / Status-Line
5128
5129<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5130<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5131 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5132<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5133<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5134<x:ref>token</x:ref> = 1*tchar
5135<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5136<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5137 transfer-extension
5138<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5139<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5140
5141<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5142
5143<x:ref>value</x:ref> = word
5144
5145<x:ref>word</x:ref> = token / quoted-string
5146</artwork>
5147</figure>
5148<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5149; Chunked-Body defined but not used
5150; Connection defined but not used
5151; Content-Length defined but not used
5152; HTTP-message defined but not used
5153; Host defined but not used
5154; TE defined but not used
5155; Trailer defined but not used
5156; Transfer-Encoding defined but not used
5157; URI-reference defined but not used
5158; Upgrade defined but not used
5159; Via defined but not used
5160; http-URI defined but not used
5161; https-URI defined but not used
5162; partial-URI defined but not used
5163; special defined but not used
5164</artwork></figure></section>
5165<?ENDINC p1-messaging.abnf-appendix ?>
5166
5167<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5168
5169<section title="Since RFC 2616">
5170<t>
5171  Extracted relevant partitions from <xref target="RFC2616"/>.
5172</t>
5173</section>
5174
5175<section title="Since draft-ietf-httpbis-p1-messaging-00">
5176<t>
5177  Closed issues:
5178  <list style="symbols"> 
5179    <t>
5180      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5181      "HTTP Version should be case sensitive"
5182      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5183    </t>
5184    <t>
5185      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5186      "'unsafe' characters"
5187      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5188    </t>
5189    <t>
5190      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5191      "Chunk Size Definition"
5192      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5193    </t>
5194    <t>
5195      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5196      "Message Length"
5197      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5198    </t>
5199    <t>
5200      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5201      "Media Type Registrations"
5202      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5203    </t>
5204    <t>
5205      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5206      "URI includes query"
5207      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5208    </t>
5209    <t>
5210      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5211      "No close on 1xx responses"
5212      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5213    </t>
5214    <t>
5215      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5216      "Remove 'identity' token references"
5217      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5218    </t>
5219    <t>
5220      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5221      "Import query BNF"
5222    </t>
5223    <t>
5224      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5225      "qdtext BNF"
5226    </t>
5227    <t>
5228      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5229      "Normative and Informative references"
5230    </t>
5231    <t>
5232      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5233      "RFC2606 Compliance"
5234    </t>
5235    <t>
5236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5237      "RFC977 reference"
5238    </t>
5239    <t>
5240      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5241      "RFC1700 references"
5242    </t>
5243    <t>
5244      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5245      "inconsistency in date format explanation"
5246    </t>
5247    <t>
5248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5249      "Date reference typo"
5250    </t>
5251    <t>
5252      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5253      "Informative references"
5254    </t>
5255    <t>
5256      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5257      "ISO-8859-1 Reference"
5258    </t>
5259    <t>
5260      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5261      "Normative up-to-date references"
5262    </t>
5263  </list>
5264</t>
5265<t>
5266  Other changes:
5267  <list style="symbols"> 
5268    <t>
5269      Update media type registrations to use RFC4288 template.
5270    </t>
5271    <t>
5272      Use names of RFC4234 core rules DQUOTE and HTAB,
5273      fix broken ABNF for chunk-data
5274      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5275    </t>
5276  </list>
5277</t>
5278</section>
5279
5280<section title="Since draft-ietf-httpbis-p1-messaging-01">
5281<t>
5282  Closed issues:
5283  <list style="symbols"> 
5284    <t>
5285      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5286      "Bodies on GET (and other) requests"
5287    </t>
5288    <t>
5289      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5290      "Updating to RFC4288"
5291    </t>
5292    <t>
5293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5294      "Status Code and Reason Phrase"
5295    </t>
5296    <t>
5297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5298      "rel_path not used"
5299    </t>
5300  </list>
5301</t>
5302<t>
5303  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5304  <list style="symbols"> 
5305    <t>
5306      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5307      "trailer-part").
5308    </t>
5309    <t>
5310      Avoid underscore character in rule names ("http_URL" ->
5311      "http-URL", "abs_path" -> "path-absolute").
5312    </t>
5313    <t>
5314      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5315      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5316      have to be updated when switching over to RFC3986.
5317    </t>
5318    <t>
5319      Synchronize core rules with RFC5234.
5320    </t>
5321    <t>
5322      Get rid of prose rules that span multiple lines.
5323    </t>
5324    <t>
5325      Get rid of unused rules LOALPHA and UPALPHA.
5326    </t>
5327    <t>
5328      Move "Product Tokens" section (back) into Part 1, as "token" is used
5329      in the definition of the Upgrade header field.
5330    </t>
5331    <t>
5332      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5333    </t>
5334    <t>
5335      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5336    </t>
5337  </list>
5338</t>
5339</section>
5340
5341<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5342<t>
5343  Closed issues:
5344  <list style="symbols"> 
5345    <t>
5346      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5347      "HTTP-date vs. rfc1123-date"
5348    </t>
5349    <t>
5350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5351      "WS in quoted-pair"
5352    </t>
5353  </list>
5354</t>
5355<t>
5356  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5357  <list style="symbols"> 
5358    <t>
5359      Reference RFC 3984, and update header field registrations for headers defined
5360      in this document.
5361    </t>
5362  </list>
5363</t>
5364<t>
5365  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5366  <list style="symbols"> 
5367    <t>
5368      Replace string literals when the string really is case-sensitive (HTTP-Version).
5369    </t>
5370  </list>
5371</t>
5372</section>
5373
5374<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5375<t>
5376  Closed issues:
5377  <list style="symbols"> 
5378    <t>
5379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5380      "Connection closing"
5381    </t>
5382    <t>
5383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5384      "Move registrations and registry information to IANA Considerations"
5385    </t>
5386    <t>
5387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5388      "need new URL for PAD1995 reference"
5389    </t>
5390    <t>
5391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5392      "IANA Considerations: update HTTP URI scheme registration"
5393    </t>
5394    <t>
5395      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5396      "Cite HTTPS URI scheme definition"
5397    </t>
5398    <t>
5399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5400      "List-type headers vs Set-Cookie"
5401    </t>
5402  </list>
5403</t>
5404<t>
5405  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5406  <list style="symbols"> 
5407    <t>
5408      Replace string literals when the string really is case-sensitive (HTTP-Date).
5409    </t>
5410    <t>
5411      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5412    </t>
5413  </list>
5414</t>
5415</section>
5416
5417<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5418<t>
5419  Closed issues:
5420  <list style="symbols"> 
5421    <t>
5422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5423      "Out-of-date reference for URIs"
5424    </t>
5425    <t>
5426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5427      "RFC 2822 is updated by RFC 5322"
5428    </t>
5429  </list>
5430</t>
5431<t>
5432  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5433  <list style="symbols"> 
5434    <t>
5435      Use "/" instead of "|" for alternatives.
5436    </t>
5437    <t>
5438      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5439    </t>
5440    <t>
5441      Only reference RFC 5234's core rules.
5442    </t>
5443    <t>
5444      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5445      whitespace ("OWS") and required whitespace ("RWS").
5446    </t>
5447    <t>
5448      Rewrite ABNFs to spell out whitespace rules, factor out
5449      header field value format definitions.
5450    </t>
5451  </list>
5452</t>
5453</section>
5454
5455<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5456<t>
5457  Closed issues:
5458  <list style="symbols"> 
5459    <t>
5460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5461      "Header LWS"
5462    </t>
5463    <t>
5464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5465      "Sort 1.3 Terminology"
5466    </t>
5467    <t>
5468      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5469      "RFC2047 encoded words"
5470    </t>
5471    <t>
5472      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5473      "Character Encodings in TEXT"
5474    </t>
5475    <t>
5476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5477      "Line Folding"
5478    </t>
5479    <t>
5480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5481      "OPTIONS * and proxies"
5482    </t>
5483    <t>
5484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5485      "Reason-Phrase BNF"
5486    </t>
5487    <t>
5488      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5489      "Use of TEXT"
5490    </t>
5491    <t>
5492      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5493      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5494    </t>
5495    <t>
5496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5497      "RFC822 reference left in discussion of date formats"
5498    </t>
5499  </list>
5500</t>
5501<t>
5502  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5503  <list style="symbols"> 
5504    <t>
5505      Rewrite definition of list rules, deprecate empty list elements.
5506    </t>
5507    <t>
5508      Add appendix containing collected and expanded ABNF.
5509    </t>
5510  </list>
5511</t>
5512<t>
5513  Other changes:
5514  <list style="symbols"> 
5515    <t>
5516      Rewrite introduction; add mostly new Architecture Section.
5517    </t>
5518    <t>
5519      Move definition of quality values from Part 3 into Part 1;
5520      make TE request header field grammar independent of accept-params (defined in Part 3).
5521    </t>
5522  </list>
5523</t>
5524</section>
5525
5526<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5527<t>
5528  Closed issues:
5529  <list style="symbols"> 
5530    <t>
5531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5532      "base for numeric protocol elements"
5533    </t>
5534    <t>
5535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5536      "comment ABNF"
5537    </t>
5538  </list>
5539</t>
5540<t>
5541  Partly resolved issues:
5542  <list style="symbols"> 
5543    <t>
5544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5545      "205 Bodies" (took out language that implied that there might be
5546      methods for which a request body MUST NOT be included)
5547    </t>
5548    <t>
5549      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5550      "editorial improvements around HTTP-date"
5551    </t>
5552  </list>
5553</t>
5554</section>
5555
5556<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5557<t>
5558  Closed issues:
5559  <list style="symbols"> 
5560    <t>
5561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5562      "Repeating single-value headers"
5563    </t>
5564    <t>
5565      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5566      "increase connection limit"
5567    </t>
5568    <t>
5569      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5570      "IP addresses in URLs"
5571    </t>
5572    <t>
5573      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5574      "take over HTTP Upgrade Token Registry"
5575    </t>
5576    <t>
5577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5578      "CR and LF in chunk extension values"
5579    </t>
5580    <t>
5581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5582      "HTTP/0.9 support"
5583    </t>
5584    <t>
5585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5586      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5587    </t>
5588    <t>
5589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5590      "move definitions of gzip/deflate/compress to part 1"
5591    </t>
5592    <t>
5593      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5594      "disallow control characters in quoted-pair"
5595    </t>
5596  </list>
5597</t>
5598<t>
5599  Partly resolved issues:
5600  <list style="symbols"> 
5601    <t>
5602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5603      "update IANA requirements wrt Transfer-Coding values" (add the
5604      IANA Considerations subsection)
5605    </t>
5606  </list>
5607</t>
5608</section>
5609
5610<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5611<t>
5612  Closed issues:
5613  <list style="symbols"> 
5614    <t>
5615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5616      "header parsing, treatment of leading and trailing OWS"
5617    </t>
5618  </list>
5619</t>
5620<t>
5621  Partly resolved issues:
5622  <list style="symbols"> 
5623    <t>
5624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5625      "Placement of 13.5.1 and 13.5.2"
5626    </t>
5627    <t>
5628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5629      "use of term "word" when talking about header structure"
5630    </t>
5631  </list>
5632</t>
5633</section>
5634
5635<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5636<t>
5637  Closed issues:
5638  <list style="symbols"> 
5639    <t>
5640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5641      "Clarification of the term 'deflate'"
5642    </t>
5643    <t>
5644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5645      "OPTIONS * and proxies"
5646    </t>
5647    <t>
5648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5649      "MIME-Version not listed in P1, general header fields"
5650    </t>
5651    <t>
5652      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5653      "IANA registry for content/transfer encodings"
5654    </t>
5655    <t>
5656      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5657      "Case-sensitivity of HTTP-date"
5658    </t>
5659    <t>
5660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5661      "use of term "word" when talking about header structure"
5662    </t>
5663  </list>
5664</t>
5665<t>
5666  Partly resolved issues:
5667  <list style="symbols"> 
5668    <t>
5669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5670      "Term for the requested resource's URI"
5671    </t>
5672  </list>
5673</t>
5674</section>
5675
5676<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5677<t>
5678  Closed issues:
5679  <list style="symbols">
5680    <t>
5681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5682      "Connection Closing"
5683    </t>
5684    <t>
5685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5686      "Delimiting messages with multipart/byteranges"
5687    </t>
5688    <t>
5689      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5690      "Handling multiple Content-Length headers"
5691    </t>
5692    <t>
5693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5694      "Clarify entity / representation / variant terminology"
5695    </t>
5696    <t>
5697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5698      "consider removing the 'changes from 2068' sections"
5699    </t>
5700  </list>
5701</t>
5702<t>
5703  Partly resolved issues:
5704  <list style="symbols"> 
5705    <t>
5706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5707      "HTTP(s) URI scheme definitions"
5708    </t>
5709  </list>
5710</t>
5711</section>
5712
5713<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5714<t>
5715  Closed issues:
5716  <list style="symbols">
5717    <t>
5718      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5719      "Trailer requirements"
5720    </t>
5721    <t>
5722      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5723      "Text about clock requirement for caches belongs in p6"
5724    </t>
5725    <t>
5726      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5727      "effective request URI: handling of missing host in HTTP/1.0"
5728    </t>
5729    <t>
5730      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5731      "confusing Date requirements for clients"
5732    </t>
5733  </list>
5734</t>
5735<t>
5736  Partly resolved issues:
5737  <list style="symbols"> 
5738    <t>
5739      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5740      "Handling multiple Content-Length headers"
5741    </t>
5742  </list>
5743</t>
5744</section>
5745
5746<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5747<t>
5748  Closed issues:
5749  <list style="symbols">
5750    <t>
5751      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5752      "RFC2145 Normative"
5753    </t>
5754    <t>
5755      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5756      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5757    </t>
5758    <t>
5759      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5760      "define 'transparent' proxy"
5761    </t>
5762    <t>
5763      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5764      "Header Classification"
5765    </t>
5766    <t>
5767      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5768      "Is * usable as a request-uri for new methods?"
5769    </t>
5770    <t>
5771      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5772      "Migrate Upgrade details from RFC2817"
5773    </t>
5774    <t>
5775      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5776      "untangle ABNFs for header fields"
5777    </t>
5778    <t>
5779      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5780      "update RFC 2109 reference"
5781    </t>
5782  </list>
5783</t>
5784</section>
5785
5786<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5787<t>
5788  Closed issues:
5789  <list style="symbols">
5790    <t>
5791      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5792      "Allow is not in 13.5.2"
5793    </t>
5794    <t>
5795      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5796      "Handling multiple Content-Length headers"
5797    </t>
5798    <t>
5799      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5800      "untangle ABNFs for header fields"
5801    </t>
5802    <t>
5803      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5804      "Content-Length ABNF broken"
5805    </t>
5806  </list>
5807</t>
5808</section>
5809
5810<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5811<t>
5812  Closed issues:
5813  <list style="symbols">
5814    <t>
5815      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5816      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5817    </t>
5818    <t>
5819      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5820      "Recommend minimum sizes for protocol elements"
5821    </t>
5822    <t>
5823      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5824      "Set expectations around buffering"
5825    </t>
5826    <t>
5827      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5828      "Considering messages in isolation"
5829    </t>
5830  </list>
5831</t>
5832</section>
5833
5834<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5835<t>
5836  Closed issues:
5837  <list style="symbols">
5838    <t>
5839      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5840      "DNS Spoofing / DNS Binding advice"
5841    </t>
5842    <t>
5843      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5844      "move RFCs 2145, 2616, 2817 to Historic status"
5845    </t>
5846    <t>
5847      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5848      "\-escaping in quoted strings"
5849    </t>
5850    <t>
5851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5852      "'Close' should be reserved in the HTTP header field registry"
5853    </t>
5854  </list>
5855</t>
5856</section>
5857
5858<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5859<t>
5860  Closed issues:
5861  <list style="symbols">
5862    <t>
5863      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5864      "Explain header registration"
5865    </t>
5866    <t>
5867      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5868      "Revise Acknowledgements Sections"
5869    </t>
5870  </list>
5871</t>
5872</section>
5873
5874</section>
5875
5876</back>
5877</rfc>
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