source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1479

Last change on this file since 1479 was 1479, checked in by julian.reschke@…, 8 years ago

Clarify that the query part must not be rewritten by intermediaries either (see #324)

  • Property svn:eol-style set to native
File size: 241.2 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
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="proposed"
58     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
59     xmlns:x='http://purl.org/net/xml2rfc/ext'>
60<x:link rel="next" basename="p2-semantics"/>
61<front>
62
63  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
64
65  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
66    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
67    <address>
68      <postal>
69        <street>345 Park Ave</street>
70        <city>San Jose</city>
71        <region>CA</region>
72        <code>95110</code>
73        <country>USA</country>
74      </postal>
75      <email>fielding@gbiv.com</email>
76      <uri>http://roy.gbiv.com/</uri>
77    </address>
78  </author>
79
80  <author initials="J." surname="Gettys" fullname="Jim Gettys">
81    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
82    <address>
83      <postal>
84        <street>21 Oak Knoll Road</street>
85        <city>Carlisle</city>
86        <region>MA</region>
87        <code>01741</code>
88        <country>USA</country>
89      </postal>
90      <email>jg@freedesktop.org</email>
91      <uri>http://gettys.wordpress.com/</uri>
92    </address>
93  </author>
94 
95  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
96    <organization abbrev="HP">Hewlett-Packard Company</organization>
97    <address>
98      <postal>
99        <street>HP Labs, Large Scale Systems Group</street>
100        <street>1501 Page Mill Road, MS 1177</street>
101        <city>Palo Alto</city>
102        <region>CA</region>
103        <code>94304</code>
104        <country>USA</country>
105      </postal>
106      <email>JeffMogul@acm.org</email>
107    </address>
108  </author>
109
110  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
111    <organization abbrev="Microsoft">Microsoft Corporation</organization>
112    <address>
113      <postal>
114        <street>1 Microsoft Way</street>
115        <city>Redmond</city>
116        <region>WA</region>
117        <code>98052</code>
118        <country>USA</country>
119      </postal>
120      <email>henrikn@microsoft.com</email>
121    </address>
122  </author>
123
124  <author initials="L." surname="Masinter" fullname="Larry Masinter">
125    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
126    <address>
127      <postal>
128        <street>345 Park Ave</street>
129        <city>San Jose</city>
130        <region>CA</region>
131        <code>95110</code>
132        <country>USA</country>
133      </postal>
134      <email>LMM@acm.org</email>
135      <uri>http://larry.masinter.net/</uri>
136    </address>
137  </author>
138 
139  <author initials="P." surname="Leach" fullname="Paul J. Leach">
140    <organization abbrev="Microsoft">Microsoft Corporation</organization>
141    <address>
142      <postal>
143        <street>1 Microsoft Way</street>
144        <city>Redmond</city>
145        <region>WA</region>
146        <code>98052</code>
147      </postal>
148      <email>paulle@microsoft.com</email>
149    </address>
150  </author>
151   
152  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
153    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
154    <address>
155      <postal>
156        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
157        <street>The Stata Center, Building 32</street>
158        <street>32 Vassar Street</street>
159        <city>Cambridge</city>
160        <region>MA</region>
161        <code>02139</code>
162        <country>USA</country>
163      </postal>
164      <email>timbl@w3.org</email>
165      <uri>http://www.w3.org/People/Berners-Lee/</uri>
166    </address>
167  </author>
168
169  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
170    <organization abbrev="W3C">World Wide Web Consortium</organization>
171    <address>
172      <postal>
173        <street>W3C / ERCIM</street>
174        <street>2004, rte des Lucioles</street>
175        <city>Sophia-Antipolis</city>
176        <region>AM</region>
177        <code>06902</code>
178        <country>France</country>
179      </postal>
180      <email>ylafon@w3.org</email>
181      <uri>http://www.raubacapeu.net/people/yves/</uri>
182    </address>
183  </author>
184
185  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
186    <organization abbrev="greenbytes">greenbytes GmbH</organization>
187    <address>
188      <postal>
189        <street>Hafenweg 16</street>
190        <city>Muenster</city><region>NW</region><code>48155</code>
191        <country>Germany</country>
192      </postal>
193      <phone>+49 251 2807760</phone>
194      <facsimile>+49 251 2807761</facsimile>
195      <email>julian.reschke@greenbytes.de</email>
196      <uri>http://greenbytes.de/tech/webdav/</uri>
197    </address>
198  </author>
199
200  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
201  <workgroup>HTTPbis Working Group</workgroup>
202
203<abstract>
204<t>
205   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
206   distributed, collaborative, hypertext information systems. HTTP has been in
207   use by the World Wide Web global information initiative since 1990. This
208   document is Part 1 of the seven-part specification that defines the protocol
209   referred to as "HTTP/1.1" and, taken together, obsoletes
210   <xref target="RFC2616" x:fmt="none">RFC 2616</xref> and moves it to historic
211   status, along with its predecessor <xref target="RFC2068" x:fmt="none">RFC
212   2068</xref>.
213</t>
214<t>
215   Part 1 provides an overview of HTTP and its associated terminology, defines
216   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
217   the generic message syntax and parsing requirements for HTTP message frames,
218   and describes general security concerns for implementations.
219</t>
220<t>
221   This part also obsoletes RFCs <xref target="RFC2145" x:fmt="none">2145</xref>
222   (on HTTP version numbers) and <xref target="RFC2817" x:fmt="none">2817</xref>
223   (on using CONNECT for TLS upgrades) and moves them to historic status.
224</t>
225</abstract>
226
227<note title="Editorial Note (To be removed by RFC Editor)">
228  <t>
229    Discussion of this draft should take place on the HTTPBIS working group
230    mailing list (ietf-http-wg@w3.org), which is archived at
231    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
232  </t>
233  <t>
234    The current issues list is at
235    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
236    documents (including fancy diffs) can be found at
237    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
238  </t>
239  <t>
240    The changes in this draft are summarized in <xref target="changes.since.17"/>.
241  </t>
242</note>
243</front>
244<middle>
245<section title="Introduction" anchor="introduction">
246<t>
247   The Hypertext Transfer Protocol (HTTP) is an application-level
248   request/response protocol that uses extensible semantics and MIME-like
249   message payloads for flexible interaction with network-based hypertext
250   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
251   standard <xref target="RFC3986"/> to indicate the target resource and
252   relationships between resources.
253   Messages are passed in a format similar to that used by Internet mail
254   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
255   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
256   between HTTP and MIME messages).
257</t>
258<t>
259   HTTP is a generic interface protocol for information systems. It is
260   designed to hide the details of how a service is implemented by presenting
261   a uniform interface to clients that is independent of the types of
262   resources provided. Likewise, servers do not need to be aware of each
263   client's purpose: an HTTP request can be considered in isolation rather
264   than being associated with a specific type of client or a predetermined
265   sequence of application steps. The result is a protocol that can be used
266   effectively in many different contexts and for which implementations can
267   evolve independently over time.
268</t>
269<t>
270   HTTP is also designed for use as an intermediation protocol for translating
271   communication to and from non-HTTP information systems.
272   HTTP proxies and gateways can provide access to alternative information
273   services by translating their diverse protocols into a hypertext
274   format that can be viewed and manipulated by clients in the same way
275   as HTTP services.
276</t>
277<t>
278   One consequence of HTTP flexibility is that the protocol cannot be
279   defined in terms of what occurs behind the interface. Instead, we
280   are limited to defining the syntax of communication, the intent
281   of received communication, and the expected behavior of recipients.
282   If the communication is considered in isolation, then successful
283   actions ought to be reflected in corresponding changes to the
284   observable interface provided by servers. However, since multiple
285   clients might act in parallel and perhaps at cross-purposes, we
286   cannot require that such changes be observable beyond the scope
287   of a single response.
288</t>
289<t>
290   This document is Part 1 of the seven-part specification of HTTP,
291   defining the protocol referred to as "HTTP/1.1", obsoleting
292   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
293   Part 1 describes the architectural elements that are used or
294   referred to in HTTP, defines the "http" and "https" URI schemes,
295   describes overall network operation and connection management,
296   and defines HTTP message framing and forwarding requirements.
297   Our goal is to define all of the mechanisms necessary for HTTP message
298   handling that are independent of message semantics, thereby defining the
299   complete set of requirements for message parsers and
300   message-forwarding intermediaries.
301</t>
302
303<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
304<t>
305   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
306   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
307   document are to be interpreted as described in <xref target="RFC2119"/>.
308</t>
309<t>
310   This document defines conformance criteria for several roles in HTTP
311   communication, including Senders, Recipients, Clients, Servers, User-Agents,
312   Origin Servers, Intermediaries, Proxies and Gateways. See <xref target="architecture"/>
313   for definitions of these terms.
314</t>
315<t>
316   An implementation is considered conformant if it complies with all of the
317   requirements associated with its role(s). Note that SHOULD-level requirements
318   are relevant here, unless one of the documented exceptions is applicable.
319</t>
320<t>
321   This document also uses ABNF to define valid protocol elements
322   (<xref target="notation"/>). In addition to the prose requirements placed
323   upon them, Senders &MUST-NOT; generate protocol elements that are invalid.
324</t>
325<t>
326   Unless noted otherwise, Recipients &MAY; take steps to recover a usable
327   protocol element from an invalid construct. However, HTTP does not define
328   specific error handling mechanisms, except in cases where it has direct
329   impact on security. This is because different uses of the protocol require
330   different error handling strategies; for example, a Web browser may wish to
331   transparently recover from a response where the Location header field
332   doesn't parse according to the ABNF, whereby in a systems control protocol
333   using HTTP, this type of error recovery could lead to dangerous consequences.
334</t>
335</section>
336
337<section title="Syntax Notation" anchor="notation">
338<iref primary="true" item="Grammar" subitem="ALPHA"/>
339<iref primary="true" item="Grammar" subitem="CR"/>
340<iref primary="true" item="Grammar" subitem="CRLF"/>
341<iref primary="true" item="Grammar" subitem="CTL"/>
342<iref primary="true" item="Grammar" subitem="DIGIT"/>
343<iref primary="true" item="Grammar" subitem="DQUOTE"/>
344<iref primary="true" item="Grammar" subitem="HEXDIG"/>
345<iref primary="true" item="Grammar" subitem="HTAB"/>
346<iref primary="true" item="Grammar" subitem="LF"/>
347<iref primary="true" item="Grammar" subitem="OCTET"/>
348<iref primary="true" item="Grammar" subitem="SP"/>
349<iref primary="true" item="Grammar" subitem="VCHAR"/>
350<t>
351   This specification uses the Augmented Backus-Naur Form (ABNF) notation
352   of <xref target="RFC5234"/>.
353</t>
354<t anchor="core.rules">
355  <x:anchor-alias value="ALPHA"/>
356  <x:anchor-alias value="CTL"/>
357  <x:anchor-alias value="CR"/>
358  <x:anchor-alias value="CRLF"/>
359  <x:anchor-alias value="DIGIT"/>
360  <x:anchor-alias value="DQUOTE"/>
361  <x:anchor-alias value="HEXDIG"/>
362  <x:anchor-alias value="HTAB"/>
363  <x:anchor-alias value="LF"/>
364  <x:anchor-alias value="OCTET"/>
365  <x:anchor-alias value="SP"/>
366  <x:anchor-alias value="VCHAR"/>
367   The following core rules are included by
368   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
369   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
370   DIGIT (decimal 0-9), DQUOTE (double quote),
371   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
372   OCTET (any 8-bit sequence of data), SP (space), and
373   VCHAR (any visible <xref target="USASCII"/> character).
374</t>
375<t>
376   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
377   "obsolete" grammar rules that appear for historical reasons.
378</t>
379
380<section title="ABNF Extension: #rule" anchor="notation.abnf">
381<t>
382  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
383  improve readability.
384</t>
385<t>
386  A construct "#" is defined, similar to "*", for defining comma-delimited
387  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
388  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
389  comma (",") and optional whitespace (OWS, <xref target="basic.rules"/>).   
390</t>
391<figure><preamble>
392  Thus,
393</preamble><artwork type="example">
394  1#element =&gt; element *( OWS "," OWS element )
395</artwork></figure>
396<figure><preamble>
397  and:
398</preamble><artwork type="example">
399  #element =&gt; [ 1#element ]
400</artwork></figure>
401<figure><preamble>
402  and for n &gt;= 1 and m &gt; 1:
403</preamble><artwork type="example">
404  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
405</artwork></figure>
406<t>
407  For compatibility with legacy list rules, recipients &SHOULD; accept empty
408  list elements. In other words, consumers would follow the list productions:
409</t>
410<figure><artwork type="example">
411  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
412 
413  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
414</artwork></figure>
415<t>
416  Note that empty elements do not contribute to the count of elements present,
417  though.
418</t>
419<t>
420  For example, given these ABNF productions:
421</t>
422<figure><artwork type="example">
423  example-list      = 1#example-list-elmt
424  example-list-elmt = token ; see <xref target="field.rules"/> 
425</artwork></figure>
426<t>
427  Then these are valid values for example-list (not including the double
428  quotes, which are present for delimitation only):
429</t>
430<figure><artwork type="example">
431  "foo,bar"
432  "foo ,bar,"
433  "foo , ,bar,charlie   "
434</artwork></figure>
435<t>
436  But these values would be invalid, as at least one non-empty element is
437  required:
438</t>
439<figure><artwork type="example">
440  ""
441  ","
442  ",   ,"
443</artwork></figure>
444<t>
445  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
446  expanded as explained above.
447</t>
448</section>
449
450<section title="Basic Rules" anchor="basic.rules">
451<t anchor="rule.LWS">
452   This specification uses three rules to denote the use of linear
453   whitespace: OWS (optional whitespace), RWS (required whitespace), and
454   BWS ("bad" whitespace).
455</t>
456<t anchor="rule.OWS">
457   The OWS rule is used where zero or more linear whitespace octets might
458   appear. OWS &SHOULD; either not be produced or be produced as a single
459   SP. Multiple OWS octets that occur within field-content &SHOULD; either
460   be replaced with a single SP or transformed to all SP octets (each
461   octet other than SP replaced with SP) before interpreting the field value
462   or forwarding the message downstream.
463</t>
464<t anchor="rule.RWS">
465   RWS is used when at least one linear whitespace octet is required to
466   separate field tokens. RWS &SHOULD; be produced as a single SP.
467   Multiple RWS octets that occur within field-content &SHOULD; either
468   be replaced with a single SP or transformed to all SP octets before
469   interpreting the field value or forwarding the message downstream.
470</t>
471<t anchor="rule.BWS">
472   BWS is used where the grammar allows optional whitespace for historical
473   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
474   recipients &MUST; accept such bad optional whitespace and remove it before
475   interpreting the field value or forwarding the message downstream.
476</t>
477<t anchor="rule.whitespace">
478  <x:anchor-alias value="BWS"/>
479  <x:anchor-alias value="OWS"/>
480  <x:anchor-alias value="RWS"/>
481  <x:anchor-alias value="obs-fold"/>
482</t>
483<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"/>
484  <x:ref>OWS</x:ref>            = *( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
485                 ; "optional" whitespace
486  <x:ref>RWS</x:ref>            = 1*( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> / obs-fold )
487                 ; "required" whitespace
488  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
489                 ; "bad" whitespace
490  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref> ( <x:ref>SP</x:ref> / <x:ref>HTAB</x:ref> )
491                 ; obsolete line folding
492                 ; see <xref target="field.parsing"/>
493</artwork></figure>
494</section>
495</section>
496</section>
497
498<section title="Architecture" anchor="architecture">
499<t>
500   HTTP was created for the World Wide Web architecture
501   and has evolved over time to support the scalability needs of a worldwide
502   hypertext system. Much of that architecture is reflected in the terminology
503   and syntax productions used to define HTTP.
504</t>
505
506<section title="Client/Server Messaging" anchor="operation">
507<iref primary="true" item="client"/>
508<iref primary="true" item="server"/>
509<iref primary="true" item="connection"/>
510<t>
511   HTTP is a stateless request/response protocol that operates by exchanging
512   <x:dfn>messages</x:dfn> (<xref target="http.message"/>) across a reliable
513   transport or session-layer
514   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
515   program that establishes a connection to a server for the purpose of
516   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
517   program that accepts connections in order to service HTTP requests by
518   sending HTTP responses.
519</t>
520<iref primary="true" item="user agent"/>
521<iref primary="true" item="origin server"/>
522<iref primary="true" item="browser"/>
523<iref primary="true" item="spider"/>
524<iref primary="true" item="sender"/>
525<iref primary="true" item="recipient"/>
526<t>
527   Note that the terms client and server refer only to the roles that
528   these programs perform for a particular connection.  The same program
529   might act as a client on some connections and a server on others.  We use
530   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
531   such as a WWW browser, editor, or spider (web-traversing robot), and
532   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
533   authoritative responses to a request.  For general requirements, we use
534   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
535   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
536   message.
537</t>
538<t>
539   Most HTTP communication consists of a retrieval request (GET) for
540   a representation of some resource identified by a URI.  In the
541   simplest case, this might be accomplished via a single bidirectional
542   connection (===) between the user agent (UA) and the origin server (O).
543</t>
544<figure><artwork type="drawing">
545         request   &gt;
546    UA ======================================= O
547                                &lt;   response
548</artwork></figure>
549<iref primary="true" item="message"/>
550<iref primary="true" item="request"/>
551<iref primary="true" item="response"/>
552<t>
553   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
554   message, beginning with a request-line that includes a method, URI, and
555   protocol version (<xref target="request.line"/>),
556   followed by MIME-like header fields containing
557   request modifiers, client information, and payload metadata
558   (<xref target="header.fields"/>),
559   an empty line to indicate the end of the header section, and finally
560   a message body containing the payload body (if any,
561   <xref target="message.body"/>).
562</t>
563<t>
564   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
565   message, beginning with a status line that
566   includes the protocol version, a success or error code, and textual
567   reason phrase (<xref target="status.line"/>),
568   followed by MIME-like header fields containing server
569   information, resource metadata, and payload metadata
570   (<xref target="header.fields"/>),
571   an empty line to indicate the end of the header section, and finally
572   a message body containing the payload body (if any,
573   <xref target="message.body"/>).
574</t>
575<t>
576   Note that 1xx responses (&status-1xx;) are not final; therefore, a server
577   can send zero or more 1xx responses, followed by exactly one final response
578   (with any other status code).
579</t>
580<t>
581   The following example illustrates a typical message exchange for a
582   GET request on the URI "http://www.example.com/hello.txt":
583</t>
584<figure><preamble>
585client request:
586</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
587GET /hello.txt HTTP/1.1
588User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
589Host: www.example.com
590Accept: */*
591
592</artwork></figure>
593<figure><preamble>
594server response:
595</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
596HTTP/1.1 200 OK
597Date: Mon, 27 Jul 2009 12:28:53 GMT
598Server: Apache
599Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
600ETag: "34aa387-d-1568eb00"
601Accept-Ranges: bytes
602Content-Length: <x:length-of target="exbody"/>
603Vary: Accept-Encoding
604Content-Type: text/plain
605
606<x:span anchor="exbody">Hello World!
607</x:span></artwork></figure>
608</section>
609
610<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
611<t>
612   Fundamentally, HTTP is a message-based protocol. Although message bodies can
613   be chunked (<xref target="chunked.encoding"/>) and implementations often
614   make parts of a message available progressively, this is not required, and
615   some widely-used implementations only make a message available when it is
616   complete. Furthermore, while most proxies will progressively stream messages,
617   some amount of buffering will take place, and some proxies might buffer
618   messages to perform transformations, check content or provide other services.
619</t>
620<t>
621   Therefore, extensions to and uses of HTTP cannot rely on the availability of
622   a partial message, or assume that messages will not be buffered. There are
623   strategies that can be used to test for buffering in a given connection, but
624   it should be understood that behaviors can differ across connections, and
625   between requests and responses.
626</t>
627<t>
628   Recipients &MUST; consider every message in a connection in isolation;
629   because HTTP is a stateless protocol, it cannot be assumed that two requests
630   on the same connection are from the same client or share any other common
631   attributes. In particular, intermediaries might mix requests from different
632   clients into a single server connection. Note that some existing HTTP
633   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
634   potentially causing interoperability and security problems.
635</t>
636</section>
637
638<section title="Connections and Transport Independence" anchor="transport-independence">
639<t>
640   HTTP messaging is independent of the underlying transport or
641   session-layer connection protocol(s).  HTTP only presumes a reliable
642   transport with in-order delivery of requests and the corresponding
643   in-order delivery of responses.  The mapping of HTTP request and
644   response structures onto the data units of the underlying transport
645   protocol is outside the scope of this specification.
646</t>
647<t>
648   The specific connection protocols to be used for an interaction
649   are determined by client configuration and the target resource's URI.
650   For example, the "http" URI scheme
651   (<xref target="http.uri"/>) indicates a default connection of TCP
652   over IP, with a default TCP port of 80, but the client might be
653   configured to use a proxy via some other connection port or protocol
654   instead of using the defaults.
655</t>
656<t>
657   A connection might be used for multiple HTTP request/response exchanges,
658   as defined in <xref target="persistent.connections"/>.
659</t>
660</section>
661
662<section title="Intermediaries" anchor="intermediaries">
663<iref primary="true" item="intermediary"/>
664<t>
665   HTTP enables the use of intermediaries to satisfy requests through
666   a chain of connections.  There are three common forms of HTTP
667   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
668   a single intermediary might act as an origin server, proxy, gateway,
669   or tunnel, switching behavior based on the nature of each request.
670</t>
671<figure><artwork type="drawing">
672         &gt;             &gt;             &gt;             &gt;
673    <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>
674               &lt;             &lt;             &lt;             &lt;
675</artwork></figure>
676<t>
677   The figure above shows three intermediaries (A, B, and C) between the
678   user agent and origin server. A request or response message that
679   travels the whole chain will pass through four separate connections.
680   Some HTTP communication options
681   might apply only to the connection with the nearest, non-tunnel
682   neighbor, only to the end-points of the chain, or to all connections
683   along the chain. Although the diagram is linear, each participant might
684   be engaged in multiple, simultaneous communications. For example, B
685   might be receiving requests from many clients other than A, and/or
686   forwarding requests to servers other than C, at the same time that it
687   is handling A's request.
688</t>
689<t>
690<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
691<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
692   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
693   to describe various requirements in relation to the directional flow of a
694   message: all messages flow from upstream to downstream.
695   Likewise, we use the terms inbound and outbound to refer to
696   directions in relation to the request path:
697   "<x:dfn>inbound</x:dfn>" means toward the origin server and
698   "<x:dfn>outbound</x:dfn>" means toward the user agent.
699</t>
700<t><iref primary="true" item="proxy"/>
701   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
702   client, usually via local configuration rules, to receive requests
703   for some type(s) of absolute URI and attempt to satisfy those
704   requests via translation through the HTTP interface.  Some translations
705   are minimal, such as for proxy requests for "http" URIs, whereas
706   other requests might require translation to and from entirely different
707   application-layer protocols. Proxies are often used to group an
708   organization's HTTP requests through a common intermediary for the
709   sake of security, annotation services, or shared caching.
710</t>
711<t>
712<iref primary="true" item="transforming proxy"/>
713<iref primary="true" item="non-transforming proxy"/>
714   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
715   or configured to modify request or response messages in a semantically
716   meaningful way (i.e., modifications, beyond those required by normal
717   HTTP processing, that change the message in a way that would be
718   significant to the original sender or potentially significant to
719   downstream recipients).  For example, a transforming proxy might be
720   acting as a shared annotation server (modifying responses to include
721   references to a local annotation database), a malware filter, a
722   format transcoder, or an intranet-to-Internet privacy filter.  Such
723   transformations are presumed to be desired by the client (or client
724   organization) that selected the proxy and are beyond the scope of
725   this specification.  However, when a proxy is not intended to transform
726   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
727   requirements that preserve HTTP message semantics. See &status-203; and
728   &header-warning; for status and warning codes related to transformations.
729</t>
730<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
731<iref primary="true" item="accelerator"/>
732   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
733   is a receiving agent that acts
734   as a layer above some other server(s) and translates the received
735   requests to the underlying server's protocol.  Gateways are often
736   used to encapsulate legacy or untrusted information services, to
737   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
738   enable partitioning or load-balancing of HTTP services across
739   multiple machines.
740</t>
741<t>
742   A gateway behaves as an origin server on its outbound connection and
743   as a user agent on its inbound connection.
744   All HTTP requirements applicable to an origin server
745   also apply to the outbound communication of a gateway.
746   A gateway communicates with inbound servers using any protocol that
747   it desires, including private extensions to HTTP that are outside
748   the scope of this specification.  However, an HTTP-to-HTTP gateway
749   that wishes to interoperate with third-party HTTP servers &MUST;
750   comply with HTTP user agent requirements on the gateway's inbound
751   connection and &MUST; implement the Connection
752   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
753   header fields for both connections.
754</t>
755<t><iref primary="true" item="tunnel"/>
756   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
757   without changing the messages. Once active, a tunnel is not
758   considered a party to the HTTP communication, though the tunnel might
759   have been initiated by an HTTP request. A tunnel ceases to exist when
760   both ends of the relayed connection are closed. Tunnels are used to
761   extend a virtual connection through an intermediary, such as when
762   transport-layer security is used to establish private communication
763   through a shared firewall proxy.
764</t>
765<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
766<iref primary="true" item="captive portal"/>
767   In addition, there may exist network intermediaries that are not
768   considered part of the HTTP communication but nevertheless act as
769   filters or redirecting agents (usually violating HTTP semantics,
770   causing security problems, and otherwise making a mess of things).
771   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
772   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
773   or "<x:dfn>captive portal</x:dfn>",
774   differs from an HTTP proxy because it has not been selected by the client.
775   Instead, the network intermediary redirects outgoing TCP port 80 packets
776   (and occasionally other common port traffic) to an internal HTTP server.
777   Interception proxies are commonly found on public network access points,
778   as a means of enforcing account subscription prior to allowing use of
779   non-local Internet services, and within corporate firewalls to enforce
780   network usage policies.
781   They are indistinguishable from a man-in-the-middle attack.
782</t>
783</section>
784
785<section title="Caches" anchor="caches">
786<iref primary="true" item="cache"/>
787<t>
788   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
789   subsystem that controls its message storage, retrieval, and deletion.
790   A cache stores cacheable responses in order to reduce the response
791   time and network bandwidth consumption on future, equivalent
792   requests. Any client or server &MAY; employ a cache, though a cache
793   cannot be used by a server while it is acting as a tunnel.
794</t>
795<t>
796   The effect of a cache is that the request/response chain is shortened
797   if one of the participants along the chain has a cached response
798   applicable to that request. The following illustrates the resulting
799   chain if B has a cached copy of an earlier response from O (via C)
800   for a request which has not been cached by UA or A.
801</t>
802<figure><artwork type="drawing">
803            &gt;             &gt;
804       UA =========== A =========== B - - - - - - C - - - - - - O
805                  &lt;             &lt;
806</artwork></figure>
807<t><iref primary="true" item="cacheable"/>
808   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
809   the response message for use in answering subsequent requests.
810   Even when a response is cacheable, there might be additional
811   constraints placed by the client or by the origin server on when
812   that cached response can be used for a particular request. HTTP
813   requirements for cache behavior and cacheable responses are
814   defined in &caching-overview;
815</t>
816<t>
817   There are a wide variety of architectures and configurations
818   of caches and proxies deployed across the World Wide Web and
819   inside large organizations. These systems include national hierarchies
820   of proxy caches to save transoceanic bandwidth, systems that
821   broadcast or multicast cache entries, organizations that distribute
822   subsets of cached data via optical media, and so on.
823</t>
824</section>
825
826<section title="Protocol Versioning" anchor="http.version">
827  <x:anchor-alias value="HTTP-Version"/>
828  <x:anchor-alias value="HTTP-Prot-Name"/>
829<t>
830   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
831   versions of the protocol. This specification defines version "1.1".
832   The protocol version as a whole indicates the sender's compliance
833   with the set of requirements laid out in that version's corresponding
834   specification of HTTP.
835</t>
836<t>
837   The version of an HTTP message is indicated by an HTTP-Version field
838   in the first line of the message. HTTP-Version is case-sensitive.
839</t>
840<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
841  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
842  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
843</artwork></figure>
844<t>
845   The HTTP version number consists of two decimal digits separated by a "."
846   (period or decimal point).  The first digit ("major version") indicates the
847   HTTP messaging syntax, whereas the second digit ("minor version") indicates
848   the highest minor version to which the sender is at least conditionally
849   compliant and able to understand for future communication.  The minor
850   version advertises the sender's communication capabilities even when the
851   sender is only using a backwards-compatible subset of the protocol,
852   thereby letting the recipient know that more advanced features can
853   be used in response (by servers) or in future requests (by clients).
854</t>
855<t>
856   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
857   <xref target="RFC1945"/> or a recipient whose version is unknown,
858   the HTTP/1.1 message is constructed such that it can be interpreted
859   as a valid HTTP/1.0 message if all of the newer features are ignored.
860   This specification places recipient-version requirements on some
861   new features so that a compliant sender will only use compatible
862   features until it has determined, through configuration or the
863   receipt of a message, that the recipient supports HTTP/1.1.
864</t>
865<t>
866   The interpretation of an HTTP header field does not change
867   between minor versions of the same major version, though the default
868   behavior of a recipient in the absence of such a field can change.
869   Unless specified otherwise, header fields defined in HTTP/1.1 are
870   defined for all versions of HTTP/1.x.  In particular, the Host and
871   Connection header fields ought to be implemented by all HTTP/1.x
872   implementations whether or not they advertise compliance with HTTP/1.1.
873</t>
874<t>
875   New header fields can be defined such that, when they are
876   understood by a recipient, they might override or enhance the
877   interpretation of previously defined header fields.  When an
878   implementation receives an unrecognized header field, the recipient
879   &MUST; ignore that header field for local processing regardless of
880   the message's HTTP version.  An unrecognized header field received
881   by a proxy &MUST; be forwarded downstream unless the header field's
882   field-name is listed in the message's Connection header-field
883   (see <xref target="header.connection"/>).
884   These requirements allow HTTP's functionality to be enhanced without
885   requiring prior update of all compliant intermediaries.
886</t>
887<t>
888   Intermediaries that process HTTP messages (i.e., all intermediaries
889   other than those acting as a tunnel) &MUST; send their own HTTP-Version
890   in forwarded messages.  In other words, they &MUST-NOT; blindly
891   forward the first line of an HTTP message without ensuring that the
892   protocol version matches what the intermediary understands, and
893   is at least conditionally compliant to, for both the receiving and
894   sending of messages.  Forwarding an HTTP message without rewriting
895   the HTTP-Version might result in communication errors when downstream
896   recipients use the message sender's version to determine what features
897   are safe to use for later communication with that sender.
898</t>
899<t>
900   An HTTP client &SHOULD; send a request version equal to the highest
901   version for which the client is at least conditionally compliant and
902   whose major version is no higher than the highest version supported
903   by the server, if this is known.  An HTTP client &MUST-NOT; send a
904   version for which it is not at least conditionally compliant.
905</t>
906<t>
907   An HTTP client &MAY; send a lower request version if it is known that
908   the server incorrectly implements the HTTP specification, but only
909   after the client has attempted at least one normal request and determined
910   from the response status or header fields (e.g., Server) that the
911   server improperly handles higher request versions.
912</t>
913<t>
914   An HTTP server &SHOULD; send a response version equal to the highest
915   version for which the server is at least conditionally compliant and
916   whose major version is less than or equal to the one received in the
917   request.  An HTTP server &MUST-NOT; send a version for which it is not
918   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
919   Version Not Supported) response if it cannot send a response using the
920   major version used in the client's request.
921</t>
922<t>
923   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
924   if it is known or suspected that the client incorrectly implements the
925   HTTP specification and is incapable of correctly processing later
926   version responses, such as when a client fails to parse the version
927   number correctly or when an intermediary is known to blindly forward
928   the HTTP-Version even when it doesn't comply with the given minor
929   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
930   performed unless triggered by specific client attributes, such as when
931   one or more of the request header fields (e.g., User-Agent) uniquely
932   match the values sent by a client known to be in error.
933</t>
934<t>
935   The intention of HTTP's versioning design is that the major number
936   will only be incremented if an incompatible message syntax is
937   introduced, and that the minor number will only be incremented when
938   changes made to the protocol have the effect of adding to the message
939   semantics or implying additional capabilities of the sender.  However,
940   the minor version was not incremented for the changes introduced between
941   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
942   is specifically avoiding any such changes to the protocol.
943</t>
944</section>
945
946<section title="Uniform Resource Identifiers" anchor="uri">
947<iref primary="true" item="resource"/>
948<t>
949   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
950   throughout HTTP as the means for identifying resources. URI references
951   are used to target requests, indicate redirects, and define relationships.
952   HTTP does not limit what a resource might be; it merely defines an interface
953   that can be used to interact with a resource via HTTP. More information on
954   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
955</t>
956  <x:anchor-alias value="URI-reference"/>
957  <x:anchor-alias value="absolute-URI"/>
958  <x:anchor-alias value="relative-part"/>
959  <x:anchor-alias value="authority"/>
960  <x:anchor-alias value="path-abempty"/>
961  <x:anchor-alias value="path-absolute"/>
962  <x:anchor-alias value="port"/>
963  <x:anchor-alias value="query"/>
964  <x:anchor-alias value="uri-host"/>
965  <x:anchor-alias value="partial-URI"/>
966<t>
967   This specification adopts the definitions of "URI-reference",
968   "absolute-URI", "relative-part", "port", "host",
969   "path-abempty", "path-absolute", "query", and "authority" from the
970   URI generic syntax <xref target="RFC3986"/>.
971   In addition, we define a partial-URI rule for protocol elements
972   that allow a relative URI but not a fragment.
973</t>
974<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"/>
975  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
976  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
977  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
978  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
979  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
980  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
981  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
982  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
983  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
984 
985  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
986</artwork></figure>
987<t>
988   Each protocol element in HTTP that allows a URI reference will indicate
989   in its ABNF production whether the element allows any form of reference
990   (URI-reference), only a URI in absolute form (absolute-URI), only the
991   path and optional query components, or some combination of the above.
992   Unless otherwise indicated, URI references are parsed relative to the
993   effective request URI, which defines the default base URI for references
994   in both the request and its corresponding response.
995</t>
996
997<section title="http URI scheme" anchor="http.uri">
998  <x:anchor-alias value="http-URI"/>
999  <iref item="http URI scheme" primary="true"/>
1000  <iref item="URI scheme" subitem="http" primary="true"/>
1001<t>
1002   The "http" URI scheme is hereby defined for the purpose of minting
1003   identifiers according to their association with the hierarchical
1004   namespace governed by a potential HTTP origin server listening for
1005   TCP connections on a given port.
1006</t>
1007<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1008  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1009</artwork></figure>
1010<t>
1011   The HTTP origin server is identified by the generic syntax's
1012   <x:ref>authority</x:ref> component, which includes a host identifier
1013   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1014   The remainder of the URI, consisting of both the hierarchical path
1015   component and optional query component, serves as an identifier for
1016   a potential resource within that origin server's name space.
1017</t>
1018<t>
1019   If the host identifier is provided as an IP literal or IPv4 address,
1020   then the origin server is any listener on the indicated TCP port at
1021   that IP address. If host is a registered name, then that name is
1022   considered an indirect identifier and the recipient might use a name
1023   resolution service, such as DNS, to find the address of a listener
1024   for that host.
1025   The host &MUST-NOT; be empty; if an "http" URI is received with an
1026   empty host, then it &MUST; be rejected as invalid.
1027   If the port subcomponent is empty or not given, then TCP port 80 is
1028   assumed (the default reserved port for WWW services).
1029</t>
1030<t>
1031   Regardless of the form of host identifier, access to that host is not
1032   implied by the mere presence of its name or address. The host might or might
1033   not exist and, even when it does exist, might or might not be running an
1034   HTTP server or listening to the indicated port. The "http" URI scheme
1035   makes use of the delegated nature of Internet names and addresses to
1036   establish a naming authority (whatever entity has the ability to place
1037   an HTTP server at that Internet name or address) and allows that
1038   authority to determine which names are valid and how they might be used.
1039</t>
1040<t>
1041   When an "http" URI is used within a context that calls for access to the
1042   indicated resource, a client &MAY; attempt access by resolving
1043   the host to an IP address, establishing a TCP connection to that address
1044   on the indicated port, and sending an HTTP request message
1045   (<xref target="http.message"/>) containing the URI's identifying data
1046   (<xref target="message.routing"/>) to the server.
1047   If the server responds to that request with a non-interim HTTP response
1048   message, as described in &status-code-reasonphr;, then that response
1049   is considered an authoritative answer to the client's request.
1050</t>
1051<t>
1052   Although HTTP is independent of the transport protocol, the "http"
1053   scheme is specific to TCP-based services because the name delegation
1054   process depends on TCP for establishing authority.
1055   An HTTP service based on some other underlying connection protocol
1056   would presumably be identified using a different URI scheme, just as
1057   the "https" scheme (below) is used for servers that require an SSL/TLS
1058   transport layer on a connection. Other protocols might also be used to
1059   provide access to "http" identified resources &mdash; it is only the
1060   authoritative interface used for mapping the namespace that is
1061   specific to TCP.
1062</t>
1063<t>
1064   The URI generic syntax for authority also includes a deprecated
1065   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1066   for including user authentication information in the URI.  Some
1067   implementations make use of the userinfo component for internal
1068   configuration of authentication information, such as within command
1069   invocation options, configuration files, or bookmark lists, even
1070   though such usage might expose a user identifier or password.
1071   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1072   delimiter) when transmitting an "http" URI in a message.  Recipients
1073   of HTTP messages that contain a URI reference &SHOULD; parse for the
1074   existence of userinfo and treat its presence as an error, likely
1075   indicating that the deprecated subcomponent is being used to obscure
1076   the authority for the sake of phishing attacks.
1077</t>
1078</section>
1079
1080<section title="https URI scheme" anchor="https.uri">
1081   <x:anchor-alias value="https-URI"/>
1082   <iref item="https URI scheme"/>
1083   <iref item="URI scheme" subitem="https"/>
1084<t>
1085   The "https" URI scheme is hereby defined for the purpose of minting
1086   identifiers according to their association with the hierarchical
1087   namespace governed by a potential HTTP origin server listening for
1088   SSL/TLS-secured connections on a given TCP port.
1089</t>
1090<t>
1091   All of the requirements listed above for the "http" scheme are also
1092   requirements for the "https" scheme, except that a default TCP port
1093   of 443 is assumed if the port subcomponent is empty or not given,
1094   and the TCP connection &MUST; be secured for privacy through the
1095   use of strong encryption prior to sending the first HTTP request.
1096</t>
1097<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1098  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1099</artwork></figure>
1100<t>
1101   Unlike the "http" scheme, responses to "https" identified requests
1102   are never "public" and thus &MUST-NOT; be reused for shared caching.
1103   They can, however, be reused in a private cache if the message is
1104   cacheable by default in HTTP or specifically indicated as such by
1105   the Cache-Control header field (&header-cache-control;).
1106</t>
1107<t>
1108   Resources made available via the "https" scheme have no shared
1109   identity with the "http" scheme even if their resource identifiers
1110   indicate the same authority (the same host listening to the same
1111   TCP port).  They are distinct name spaces and are considered to be
1112   distinct origin servers.  However, an extension to HTTP that is
1113   defined to apply to entire host domains, such as the Cookie protocol
1114   <xref target="RFC6265"/>, can allow information
1115   set by one service to impact communication with other services
1116   within a matching group of host domains.
1117</t>
1118<t>
1119   The process for authoritative access to an "https" identified
1120   resource is defined in <xref target="RFC2818"/>.
1121</t>
1122</section>
1123
1124<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1125<t>
1126   Since the "http" and "https" schemes conform to the URI generic syntax,
1127   such URIs are normalized and compared according to the algorithm defined
1128   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1129   described above for each scheme.
1130</t>
1131<t>
1132   If the port is equal to the default port for a scheme, the normal
1133   form is to elide the port subcomponent. Likewise, an empty path
1134   component is equivalent to an absolute path of "/", so the normal
1135   form is to provide a path of "/" instead. The scheme and host
1136   are case-insensitive and normally provided in lowercase; all
1137   other components are compared in a case-sensitive manner.
1138   Characters other than those in the "reserved" set are equivalent
1139   to their percent-encoded octets (see <xref target="RFC3986"
1140   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1141</t>
1142<t>
1143   For example, the following three URIs are equivalent:
1144</t>
1145<figure><artwork type="example">
1146   http://example.com:80/~smith/home.html
1147   http://EXAMPLE.com/%7Esmith/home.html
1148   http://EXAMPLE.com:/%7esmith/home.html
1149</artwork></figure>
1150</section>
1151</section>
1152</section>
1153
1154<section title="Message Format" anchor="http.message">
1155<x:anchor-alias value="generic-message"/>
1156<x:anchor-alias value="message.types"/>
1157<x:anchor-alias value="HTTP-message"/>
1158<x:anchor-alias value="start-line"/>
1159<iref item="header section"/>
1160<iref item="headers"/>
1161<iref item="header field"/>
1162<t>
1163   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1164   octets in a format similar to the Internet Message Format
1165   <xref target="RFC5322"/>: zero or more header fields (collectively
1166   referred to as the "headers" or the "header section"), an empty line
1167   indicating the end of the header section, and an optional message-body.
1168</t>
1169<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1170  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1171                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1172                    <x:ref>CRLF</x:ref>
1173                    [ <x:ref>message-body</x:ref> ]
1174</artwork></figure>
1175<t>
1176   The normal procedure for parsing an HTTP message is to read the
1177   start-line into a structure, read each header field into a hash
1178   table by field name until the empty line, and then use the parsed
1179   data to determine if a message-body is expected.  If a message-body
1180   has been indicated, then it is read as a stream until an amount
1181   of octets equal to the message-body length is read or the connection
1182   is closed.
1183</t>
1184<t>
1185   Recipients &MUST; parse an HTTP message as a sequence of octets in an
1186   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1187   Parsing an HTTP message as a stream of Unicode characters, without regard
1188   for the specific encoding, creates security vulnerabilities due to the
1189   varying ways that string processing libraries handle invalid multibyte
1190   character sequences that contain the octet LF (%x0A).  String-based
1191   parsers can only be safely used within protocol elements after the element
1192   has been extracted from the message, such as within a header field-value
1193   after message parsing has delineated the individual fields.
1194</t>
1195
1196<section title="Start Line" anchor="start.line">
1197  <x:anchor-alias value="Start-Line"/>
1198<t>
1199   An HTTP message can either be a request from client to server or a
1200   response from server to client.  Syntactically, the two types of message
1201   differ only in the start-line, which is either a Request-Line (for requests)
1202   or a Status-Line (for responses), and in the algorithm for determining
1203   the length of the message-body (<xref target="message.body"/>).
1204   In theory, a client could receive requests and a server could receive
1205   responses, distinguishing them by their different start-line formats,
1206   but in practice servers are implemented to only expect a request
1207   (a response is interpreted as an unknown or invalid request method)
1208   and clients are implemented to only expect a response.
1209</t>
1210<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="start-line"/>
1211  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1212</artwork></figure>
1213<t>
1214</t>
1215<t>
1216   Implementations &MUST-NOT; send whitespace between the start-line and
1217   the first header field. The presence of such whitespace in a request
1218   might be an attempt to trick a server into ignoring that field or
1219   processing the line after it as a new request, either of which might
1220   result in a security vulnerability if other implementations within
1221   the request chain interpret the same message differently.
1222   Likewise, the presence of such whitespace in a response might be
1223   ignored by some clients or cause others to cease parsing.
1224</t>
1225
1226<section title="Request-Line" anchor="request.line">
1227  <x:anchor-alias value="Request"/>
1228  <x:anchor-alias value="Request-Line"/>
1229<t>
1230   The Request-Line begins with a method token, followed by a single
1231   space (SP), the request-target, another single space (SP), the
1232   protocol version, and ending with CRLF.
1233</t>
1234<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1235  <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>
1236</artwork></figure>
1237
1238<section title="Method" anchor="method">
1239  <x:anchor-alias value="Method"/>
1240<t>
1241   The Method token indicates the request method to be performed on the
1242   target resource. The request method is case-sensitive.
1243</t>
1244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1245  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1246</artwork></figure>
1247<t>
1248   See &method; for further information, such as the list of methods defined
1249   by this specification, the IANA registry, and considerations for new methods.
1250</t>
1251</section>
1252
1253<section title="request-target" anchor="request-target">
1254  <x:anchor-alias value="request-target"/>
1255<t>
1256   The request-target identifies the target resource upon which to apply
1257   the request.  The four options for request-target are described in
1258   <xref target="request-target-types"/>.
1259</t>
1260<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1261  <x:ref>request-target</x:ref> = "*"
1262                 / <x:ref>absolute-URI</x:ref>
1263                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1264                 / <x:ref>authority</x:ref>
1265</artwork></figure>
1266<t>
1267   HTTP does not place a pre-defined limit on the length of a request-target.
1268   A server &MUST; be prepared to receive URIs of unbounded length and
1269   respond with the 414 (URI Too Long) status code if the received
1270   request-target would be longer than the server wishes to handle
1271   (see &status-414;).
1272</t>
1273<t>
1274   Various ad-hoc limitations on request-target length are found in practice.
1275   It is &RECOMMENDED; that all HTTP senders and recipients support
1276   request-target lengths of 8000 or more octets.
1277</t>
1278<x:note>
1279  <t>
1280    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1281    are not part of the request-target and thus will not be transmitted
1282    in an HTTP request.
1283  </t>
1284</x:note>
1285</section>
1286</section>
1287
1288<section title="Response Status-Line" anchor="status.line">
1289  <x:anchor-alias value="Response"/>
1290  <x:anchor-alias value="Status-Line"/>
1291<t>
1292   The first line of a Response message is the Status-Line, consisting
1293   of the protocol version, a space (SP), the status code, another space,
1294   a possibly-empty textual phrase describing the status code, and
1295   ending with CRLF.
1296</t>
1297<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1298  <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>
1299</artwork></figure>
1300
1301<section title="Status Code" anchor="status.code">
1302  <x:anchor-alias value="Status-Code"/>
1303<t>
1304   The Status-Code element is a 3-digit integer result code of the attempt to
1305   understand and satisfy the request. See &status-code-reasonphr; for
1306   further information, such as the list of status codes defined by this
1307   specification, the IANA registry, and considerations for new status codes.
1308</t>
1309<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/>
1310  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1311</artwork></figure>
1312</section>
1313
1314<section title="Reason Phrase" anchor="reason.phrase">
1315  <x:anchor-alias value="Reason-Phrase"/>
1316<t>   
1317   The Reason Phrase exists for the sole purpose of providing a textual
1318   description associated with the numeric status code, out of deference to
1319   earlier Internet application protocols that were more frequently used with
1320   interactive text clients. A client &SHOULD; ignore the content of the Reason
1321   Phrase.
1322</t>
1323<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1324  <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> )
1325</artwork></figure>
1326</section>
1327</section>
1328
1329</section>
1330
1331<section title="Header Fields" anchor="header.fields">
1332  <x:anchor-alias value="header-field"/>
1333  <x:anchor-alias value="field-content"/>
1334  <x:anchor-alias value="field-name"/>
1335  <x:anchor-alias value="field-value"/>
1336  <x:anchor-alias value="OWS"/>
1337<t>
1338   Each HTTP header field consists of a case-insensitive field name
1339   followed by a colon (":"), optional whitespace, and the field value.
1340</t>
1341<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"/>
1342  <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>
1343  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1344  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>obs-fold</x:ref> )
1345  <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> )
1346</artwork></figure>
1347<t>
1348   The field-name token labels the corresponding field-value as having the
1349   semantics defined by that header field.  For example, the Date header field
1350   is defined in &header-date; as containing the origination
1351   timestamp for the message in which it appears.
1352</t>
1353<t>
1354   HTTP header fields are fully extensible: there is no limit on the
1355   introduction of new field names, each presumably defining new semantics,
1356   or on the number of header fields used in a given message.  Existing
1357   fields are defined in each part of this specification and in many other
1358   specifications outside the standards process.
1359   New header fields can be introduced without changing the protocol version
1360   if their defined semantics allow them to be safely ignored by recipients
1361   that do not recognize them.
1362</t>
1363<t>
1364   New HTTP header fields &SHOULD; be registered with IANA according
1365   to the procedures in &cons-new-header-fields;.
1366   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1367   field-name is listed in the Connection header field
1368   (<xref target="header.connection"/>) or the proxy is specifically
1369   configured to block or otherwise transform such fields.
1370   Unrecognized header fields &SHOULD; be ignored by other recipients.
1371</t>
1372<t>
1373   The order in which header fields with differing field names are
1374   received is not significant. However, it is "good practice" to send
1375   header fields that contain control data first, such as Host on
1376   requests and Date on responses, so that implementations can decide
1377   when not to handle a message as early as possible.  A server &MUST;
1378   wait until the entire header section is received before interpreting
1379   a request message, since later header fields might include conditionals,
1380   authentication credentials, or deliberately misleading duplicate
1381   header fields that would impact request processing.
1382</t>
1383<t>
1384   Multiple header fields with the same field name &MUST-NOT; be
1385   sent in a message unless the entire field value for that
1386   header field is defined as a comma-separated list [i.e., #(values)].
1387   Multiple header fields with the same field name can be combined into
1388   one "field-name: field-value" pair, without changing the semantics of the
1389   message, by appending each subsequent field value to the combined
1390   field value in order, separated by a comma. The order in which
1391   header fields with the same field name are received is therefore
1392   significant to the interpretation of the combined field value;
1393   a proxy &MUST-NOT; change the order of these field values when
1394   forwarding a message.
1395</t>
1396<x:note>
1397  <t>
1398   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1399   practice can occur multiple times, but does not use the list syntax, and
1400   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1401   for details.) Also note that the Set-Cookie2 header field specified in
1402   <xref target="RFC2965"/> does not share this problem.
1403  </t>
1404</x:note>
1405
1406<section title="Field Parsing" anchor="field.parsing">
1407<t>
1408   No whitespace is allowed between the header field-name and colon.
1409   In the past, differences in the handling of such whitespace have led to
1410   security vulnerabilities in request routing and response handling.
1411   Any received request message that contains whitespace between a header
1412   field-name and colon &MUST; be rejected with a response code of 400
1413   (Bad Request).  A proxy &MUST; remove any such whitespace from a response
1414   message before forwarding the message downstream.
1415</t>
1416<t>
1417   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1418   preferred. The field value does not include any leading or trailing white
1419   space: OWS occurring before the first non-whitespace octet of the
1420   field value or after the last non-whitespace octet of the field value
1421   is ignored and &SHOULD; be removed before further processing (as this does
1422   not change the meaning of the header field).
1423</t>
1424<t>
1425   Historically, HTTP header field values could be extended over multiple
1426   lines by preceding each extra line with at least one space or horizontal
1427   tab (obs-fold). This specification deprecates such line
1428   folding except within the message/http media type
1429   (<xref target="internet.media.type.message.http"/>).
1430   HTTP senders &MUST-NOT; produce messages that include line folding
1431   (i.e., that contain any field-content that matches the obs-fold rule) unless
1432   the message is intended for packaging within the message/http media type.
1433   HTTP recipients &SHOULD; accept line folding and replace any embedded
1434   obs-fold whitespace with either a single SP or a matching number of SP
1435   octets (to avoid buffer copying) prior to interpreting the field value or
1436   forwarding the message downstream.
1437</t>
1438<t>
1439   Historically, HTTP has allowed field content with text in the ISO-8859-1
1440   <xref target="ISO-8859-1"/> character encoding and supported other
1441   character sets only through use of <xref target="RFC2047"/> encoding.
1442   In practice, most HTTP header field values use only a subset of the
1443   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1444   header fields &SHOULD; limit their field values to US-ASCII octets.
1445   Recipients &SHOULD; treat other (obs-text) octets in field content as
1446   opaque data.
1447</t>
1448</section>
1449
1450<section title="Field Length" anchor="field.length">
1451<t>
1452   HTTP does not place a pre-defined limit on the length of header fields,
1453   either in isolation or as a set. A server &MUST; be prepared to receive
1454   request header fields of unbounded length and respond with a 4xx status
1455   code if the received header field(s) would be longer than the server wishes
1456   to handle.
1457</t>
1458<t>
1459   A client that receives response headers that are longer than it wishes to
1460   handle can only treat it as a server error.
1461</t>
1462<t>
1463   Various ad-hoc limitations on header length are found in practice. It is
1464   &RECOMMENDED; that all HTTP senders and recipients support messages whose
1465   combined header fields have 4000 or more octets.
1466</t>
1467</section>
1468
1469<section title="Common Field ABNF Rules" anchor="field.rules">
1470<t anchor="rule.token.separators">
1471  <x:anchor-alias value="tchar"/>
1472  <x:anchor-alias value="token"/>
1473  <x:anchor-alias value="special"/>
1474  <x:anchor-alias value="word"/>
1475   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1476   separated by whitespace or special characters. These special characters
1477   &MUST; be in a quoted string to be used within a parameter value (as defined
1478   in <xref target="transfer.codings"/>).
1479</t>
1480<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"/>
1481  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1482
1483  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
1484<!--
1485  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
1486 -->
1487  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
1488                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1489                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
1490                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
1491
1492  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
1493                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1494                 / "]" / "?" / "=" / "{" / "}"
1495</artwork></figure>
1496<t anchor="rule.quoted-string">
1497  <x:anchor-alias value="quoted-string"/>
1498  <x:anchor-alias value="qdtext"/>
1499  <x:anchor-alias value="obs-text"/>
1500   A string of text is parsed as a single word if it is quoted using
1501   double-quote marks.
1502</t>
1503<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"/>
1504  <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>
1505  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1506  <x:ref>obs-text</x:ref>       = %x80-FF
1507</artwork></figure>
1508<t anchor="rule.quoted-pair">
1509  <x:anchor-alias value="quoted-pair"/>
1510   The backslash octet ("\") can be used as a single-octet
1511   quoting mechanism within quoted-string constructs:
1512</t>
1513<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
1514  <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> )
1515</artwork></figure>
1516<t>
1517   Recipients that process the value of the quoted-string &MUST; handle a
1518   quoted-pair as if it were replaced by the octet following the backslash.
1519</t>
1520<t>
1521   Senders &SHOULD-NOT; escape octets in quoted-strings that do not require
1522   escaping (i.e., other than DQUOTE and the backslash octet).
1523</t>
1524<t anchor="rule.comment">
1525  <x:anchor-alias value="comment"/>
1526  <x:anchor-alias value="ctext"/>
1527   Comments can be included in some HTTP header fields by surrounding
1528   the comment text with parentheses. Comments are only allowed in
1529   fields containing "comment" as part of their field value definition.
1530</t>
1531<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1532  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1533  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1534</artwork></figure>
1535<t anchor="rule.quoted-cpair">
1536  <x:anchor-alias value="quoted-cpair"/>
1537   The backslash octet ("\") can be used as a single-octet
1538   quoting mechanism within comment constructs:
1539</t>
1540<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1541  <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> )
1542</artwork></figure>
1543<t>
1544   Senders &SHOULD-NOT; escape octets in comments that do not require escaping
1545   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1546</t>
1547</section>
1548</section>
1549
1550<section title="Message Body" anchor="message.body">
1551  <x:anchor-alias value="message-body"/>
1552<t>
1553   The message-body (if any) of an HTTP message is used to carry the
1554   payload body associated with the request or response.
1555</t>
1556<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1557  <x:ref>message-body</x:ref> = *OCTET
1558</artwork></figure>
1559<t>
1560   The message-body differs from the payload body only when a transfer-coding
1561   has been applied, as indicated by the Transfer-Encoding header field
1562   (<xref target="header.transfer-encoding"/>).  If more than one
1563   Transfer-Encoding header field is present in a message, the multiple
1564   field-values &MUST; be combined into one field-value, according to the
1565   algorithm defined in <xref target="header.fields"/>, before determining
1566   the message-body length.
1567</t>
1568<t>
1569   When one or more transfer-codings are applied to a payload in order to
1570   form the message-body, the Transfer-Encoding header field &MUST; contain
1571   the list of transfer-codings applied. Transfer-Encoding is a property of
1572   the message, not of the payload, and thus &MAY; be added or removed by
1573   any implementation along the request/response chain under the constraints
1574   found in <xref target="transfer.codings"/>.
1575</t>
1576<t>
1577   If a message is received that has multiple Content-Length header fields
1578   (<xref target="header.content-length"/>) with field-values consisting
1579   of the same decimal value, or a single Content-Length header field with
1580   a field value containing a list of identical decimal values (e.g.,
1581   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1582   header fields have been generated or combined by an upstream message
1583   processor, then the recipient &MUST; either reject the message as invalid
1584   or replace the duplicated field-values with a single valid Content-Length
1585   field containing that decimal value prior to determining the message-body
1586   length.
1587</t>
1588<t>
1589   The rules for when a message-body is allowed in a message differ for
1590   requests and responses.
1591</t>
1592<t>
1593   The presence of a message-body in a request is signaled by the
1594   inclusion of a Content-Length or Transfer-Encoding header field in
1595   the request's header fields, even if the request method does not
1596   define any use for a message-body.  This allows the request
1597   message framing algorithm to be independent of method semantics.
1598</t>
1599<t>
1600   For response messages, whether or not a message-body is included with
1601   a message is dependent on both the request method and the response
1602   status code (<xref target="status.code"/>).
1603   Responses to the HEAD request method never include a message-body
1604   because the associated response header fields (e.g., Transfer-Encoding,
1605   Content-Length, etc.) only indicate what their values would have been
1606   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1607   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1608   All other responses do include a message-body, although the body
1609   &MAY; be of zero length.
1610</t>
1611<t>
1612   The length of the message-body is determined by one of the following
1613   (in order of precedence):
1614</t>
1615<t>
1616  <list style="numbers">
1617    <x:lt><t>
1618     Any response to a HEAD request and any response with a status
1619     code of 100-199, 204, or 304 is always terminated by the first
1620     empty line after the header fields, regardless of the header
1621     fields present in the message, and thus cannot contain a message-body.
1622    </t></x:lt>
1623    <x:lt><t>
1624     If a Transfer-Encoding header field is present
1625     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1626     is the final encoding, the message-body length is determined by reading
1627     and decoding the chunked data until the transfer-coding indicates the
1628     data is complete.
1629    </t>
1630    <t>
1631     If a Transfer-Encoding header field is present in a response and the
1632     "chunked" transfer-coding is not the final encoding, the message-body
1633     length is determined by reading the connection until it is closed by
1634     the server.
1635     If a Transfer-Encoding header field is present in a request and the
1636     "chunked" transfer-coding is not the final encoding, the message-body
1637     length cannot be determined reliably; the server &MUST; respond with
1638     the 400 (Bad Request) status code and then close the connection.
1639    </t>
1640    <t>
1641     If a message is received with both a Transfer-Encoding header field
1642     and a Content-Length header field, the Transfer-Encoding overrides
1643     the Content-Length.
1644     Such a message might indicate an attempt to perform request or response
1645     smuggling (bypass of security-related checks on message routing or content)
1646     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1647     be removed, prior to forwarding the message downstream, or replaced with
1648     the real message-body length after the transfer-coding is decoded.
1649    </t></x:lt>
1650    <x:lt><t>
1651     If a message is received without Transfer-Encoding and with either
1652     multiple Content-Length header fields having differing field-values or
1653     a single Content-Length header field having an invalid value, then the
1654     message framing is invalid and &MUST; be treated as an error to
1655     prevent request or response smuggling.
1656     If this is a request message, the server &MUST; respond with
1657     a 400 (Bad Request) status code and then close the connection.
1658     If this is a response message received by a proxy, the proxy
1659     &MUST; discard the received response, send a 502 (Bad Gateway)
1660     status code as its downstream response, and then close the connection.
1661     If this is a response message received by a user-agent, it &MUST; be
1662     treated as an error by discarding the message and closing the connection.
1663    </t></x:lt>
1664    <x:lt><t>
1665     If a valid Content-Length header field
1666     is present without Transfer-Encoding, its decimal value defines the
1667     message-body length in octets.  If the actual number of octets sent in
1668     the message is less than the indicated Content-Length, the recipient
1669     &MUST; consider the message to be incomplete and treat the connection
1670     as no longer usable.
1671     If the actual number of octets sent in the message is more than the indicated
1672     Content-Length, the recipient &MUST; only process the message-body up to the
1673     field value's number of octets; the remainder of the message &MUST; either
1674     be discarded or treated as the next message in a pipeline.  For the sake of
1675     robustness, a user-agent &MAY; attempt to detect and correct such an error
1676     in message framing if it is parsing the response to the last request on
1677     a connection and the connection has been closed by the server.
1678    </t></x:lt>
1679    <x:lt><t>
1680     If this is a request message and none of the above are true, then the
1681     message-body length is zero (no message-body is present).
1682    </t></x:lt>
1683    <x:lt><t>
1684     Otherwise, this is a response message without a declared message-body
1685     length, so the message-body length is determined by the number of octets
1686     received prior to the server closing the connection.
1687    </t></x:lt>
1688  </list>
1689</t>
1690<t>
1691   Since there is no way to distinguish a successfully completed,
1692   close-delimited message from a partially-received message interrupted
1693   by network failure, implementations &SHOULD; use encoding or
1694   length-delimited messages whenever possible.  The close-delimiting
1695   feature exists primarily for backwards compatibility with HTTP/1.0.
1696</t>
1697<t>
1698   A server &MAY; reject a request that contains a message-body but
1699   not a Content-Length by responding with 411 (Length Required).
1700</t>
1701<t>
1702   Unless a transfer-coding other than "chunked" has been applied,
1703   a client that sends a request containing a message-body &SHOULD;
1704   use a valid Content-Length header field if the message-body length
1705   is known in advance, rather than the "chunked" encoding, since some
1706   existing services respond to "chunked" with a 411 (Length Required)
1707   status code even though they understand the chunked encoding.  This
1708   is typically because such services are implemented via a gateway that
1709   requires a content-length in advance of being called and the server
1710   is unable or unwilling to buffer the entire request before processing.
1711</t>
1712<t>
1713   A client that sends a request containing a message-body &MUST; include a
1714   valid Content-Length header field if it does not know the server will
1715   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1716   of specific user configuration or by remembering the version of a prior
1717   received response.
1718</t>
1719</section>
1720
1721<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1722<t>
1723   Request messages that are prematurely terminated, possibly due to a
1724   cancelled connection or a server-imposed time-out exception, &MUST;
1725   result in closure of the connection; sending an HTTP/1.1 error response
1726   prior to closing the connection is &OPTIONAL;.
1727</t>
1728<t>
1729   Response messages that are prematurely terminated, usually by closure
1730   of the connection prior to receiving the expected number of octets or by
1731   failure to decode a transfer-encoded message-body, &MUST; be recorded
1732   as incomplete.  A response that terminates in the middle of the header
1733   block (before the empty line is received) cannot be assumed to convey the
1734   full semantics of the response and &MUST; be treated as an error.
1735</t>
1736<t>
1737   A message-body that uses the chunked transfer encoding is
1738   incomplete if the zero-sized chunk that terminates the encoding has not
1739   been received.  A message that uses a valid Content-Length is incomplete
1740   if the size of the message-body received (in octets) is less than the
1741   value given by Content-Length.  A response that has neither chunked
1742   transfer encoding nor Content-Length is terminated by closure of the
1743   connection, and thus is considered complete regardless of the number of
1744   message-body octets received, provided that the header block was received
1745   intact.
1746</t>
1747<t>
1748   A user agent &MUST-NOT; render an incomplete response message-body as if
1749   it were complete (i.e., some indication must be given to the user that an
1750   error occurred).  Cache requirements for incomplete responses are defined
1751   in &cache-incomplete;.
1752</t>
1753<t>
1754   A server &MUST; read the entire request message-body or close
1755   the connection after sending its response, since otherwise the
1756   remaining data on a persistent connection would be misinterpreted
1757   as the next request.  Likewise,
1758   a client &MUST; read the entire response message-body if it intends
1759   to reuse the same connection for a subsequent request.  Pipelining
1760   multiple requests on a connection is described in <xref target="pipelining"/>.
1761</t>
1762</section>
1763
1764<section title="Message Parsing Robustness" anchor="message.robustness">
1765<t>
1766   Older HTTP/1.0 client implementations might send an extra CRLF
1767   after a POST request as a lame workaround for some early server
1768   applications that failed to read message-body content that was
1769   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1770   preface or follow a request with an extra CRLF.  If terminating
1771   the request message-body with a line-ending is desired, then the
1772   client &MUST; include the terminating CRLF octets as part of the
1773   message-body length.
1774</t>
1775<t>
1776   In the interest of robustness, servers &SHOULD; ignore at least one
1777   empty line received where a Request-Line is expected. In other words, if
1778   the server is reading the protocol stream at the beginning of a
1779   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1780   Likewise, although the line terminator for the start-line and header
1781   fields is the sequence CRLF, we recommend that recipients recognize a
1782   single LF as a line terminator and ignore any CR.
1783</t>
1784<t>
1785   When a server listening only for HTTP request messages, or processing
1786   what appears from the start-line to be an HTTP request message,
1787   receives a sequence of octets that does not match the HTTP-message
1788   grammar aside from the robustness exceptions listed above, the
1789   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1790</t>
1791</section>
1792</section>
1793
1794<section title="Message Routing" anchor="message.routing">
1795<t>
1796   In most cases, the user agent is provided a URI reference
1797   from which it determines an absolute URI for identifying the target
1798   resource.  When a request to the resource is initiated, all or part
1799   of that URI is used to construct the HTTP request-target.
1800</t>
1801
1802<section title="Types of Request Target" anchor="request-target-types">
1803<t>
1804   The four options for request-target are dependent on the nature of the
1805   request.
1806</t>   
1807<t><iref item="asterisk form (of request-target)"/>
1808   The asterisk "*" form of request-target, which &MUST-NOT; be used
1809   with any request method other than OPTIONS, means that the request
1810   applies to the server as a whole (the listening process) rather than
1811   to a specific named resource at that server.  For example,
1812</t>
1813<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1814OPTIONS * HTTP/1.1
1815</artwork></figure>
1816<t><iref item="absolute-URI form (of request-target)"/>
1817   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1818   proxy. The proxy is requested to either forward the request or service it
1819   from a valid cache, and then return the response. Note that the proxy &MAY;
1820   forward the request on to another proxy or directly to the server
1821   specified by the absolute-URI. In order to avoid request loops, a
1822   proxy that forwards requests to other proxies &MUST; be able to
1823   recognize and exclude all of its own server names, including
1824   any aliases, local variations, and the numeric IP address. An example
1825   Request-Line would be:
1826</t>
1827<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1828GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1829</artwork></figure>
1830<t>
1831   To allow for transition to absolute-URIs in all requests in future
1832   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1833   form in requests, even though HTTP/1.1 clients will only generate
1834   them in requests to proxies.
1835</t>
1836<t>
1837   If a proxy receives a host name that is not a fully qualified domain
1838   name, it &MAY; add its domain to the host name it received. If a proxy
1839   receives a fully qualified domain name, the proxy &MUST-NOT; change
1840   the host name.
1841</t>
1842<t><iref item="authority form (of request-target)"/>
1843   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1844</t>
1845<t><iref item="origin form (of request-target)"/>
1846   The most common form of request-target is that used when making
1847   a request to an origin server ("origin form").
1848   In this case, the absolute path and query components of the URI
1849   &MUST; be transmitted as the request-target, and the authority component
1850   &MUST; be transmitted in a Host header field. For example, a client wishing
1851   to retrieve a representation of the resource, as identified above,
1852   directly from the origin server would open (or reuse) a TCP connection
1853   to port 80 of the host "www.example.org" and send the lines:
1854</t>
1855<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1856GET /pub/WWW/TheProject.html HTTP/1.1
1857Host: www.example.org
1858</artwork></figure>
1859<t>
1860   followed by the remainder of the Request. Note that the origin form
1861   of request-target always starts with an absolute path; if the target
1862   resource's URI path is empty, then an absolute path of "/" &MUST; be
1863   provided in the request-target.
1864</t>
1865<t>
1866   If a proxy receives an OPTIONS request with an absolute-URI form of
1867   request-target in which the URI has an empty path and no query component,
1868   then the last proxy on the request chain &MUST; use a request-target
1869   of "*" when it forwards the request to the indicated origin server.
1870</t>
1871<figure><preamble>   
1872   For example, the request
1873</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1874OPTIONS http://www.example.org:8001 HTTP/1.1
1875</artwork></figure>
1876<figure><preamble>   
1877  would be forwarded by the final proxy as
1878</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1879OPTIONS * HTTP/1.1
1880Host: www.example.org:8001
1881</artwork>
1882<postamble>
1883   after connecting to port 8001 of host "www.example.org".
1884</postamble>
1885</figure>
1886<t>
1887   The request-target is transmitted in the format specified in
1888   <xref target="http.uri"/>. If the request-target is percent-encoded
1889   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1890   &MUST; decode the request-target in order to
1891   properly interpret the request. Servers &SHOULD; respond to invalid
1892   request-targets with an appropriate status code.
1893</t>
1894<t>
1895   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" and "query"
1896   parts of the received request-target when forwarding it to the next inbound
1897   server, except as noted above to replace a null path-absolute with "/" or
1898   "*".
1899</t>
1900<x:note>
1901  <t>
1902    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1903    meaning of the request when the origin server is improperly using
1904    a non-reserved URI character for a reserved purpose.  Implementors
1905    need to be aware that some pre-HTTP/1.1 proxies have been known to
1906    rewrite the request-target.
1907  </t>
1908</x:note>
1909</section>
1910
1911<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1912<t>
1913   The exact resource identified by an Internet request is determined by
1914   examining both the request-target and the Host header field.
1915</t>
1916<t>
1917   An origin server that does not allow resources to differ by the
1918   requested host &MAY; ignore the Host header field value when
1919   determining the resource identified by an HTTP/1.1 request. (But see
1920   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1921   for other requirements on Host support in HTTP/1.1.)
1922</t>
1923<t>
1924   An origin server that does differentiate resources based on the host
1925   requested (sometimes referred to as virtual hosts or vanity host
1926   names) &MUST; use the following rules for determining the requested
1927   resource on an HTTP/1.1 request:
1928  <list style="numbers">
1929    <t>If request-target is an absolute-URI, the host is part of the
1930     request-target. Any Host header field value in the request &MUST; be
1931     ignored.</t>
1932    <t>If the request-target is not an absolute-URI, and the request includes
1933     a Host header field, the host is determined by the Host header
1934     field value.</t>
1935    <t>If the host as determined by rule 1 or 2 is not a valid host on
1936     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1937  </list>
1938</t>
1939<t>
1940   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1941   attempt to use heuristics (e.g., examination of the URI path for
1942   something unique to a particular host) in order to determine what
1943   exact resource is being requested.
1944</t>
1945</section>
1946
1947<section title="Effective Request URI" anchor="effective.request.uri">
1948  <iref primary="true" item="effective request URI"/>
1949  <iref primary="true" item="target resource"/>
1950<t>
1951   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1952   for the target resource; instead, the URI needs to be inferred from the
1953   request-target, Host header field, and connection context. The result of
1954   this process is called the "effective request URI".  The "target resource"
1955   is the resource identified by the effective request URI.
1956</t>
1957<t>
1958   If the request-target is an absolute-URI, then the effective request URI is
1959   the request-target.
1960</t>
1961<t>
1962   If the request-target uses the path-absolute form or the asterisk form,
1963   and the Host header field is present, then the effective request URI is
1964   constructed by concatenating
1965</t>
1966<t>
1967  <list style="symbols">
1968    <t>
1969      the scheme name: "http" if the request was received over an insecure
1970      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1971      connection,
1972    </t>
1973    <t>
1974      the octet sequence "://",
1975    </t>
1976    <t>
1977      the authority component, as specified in the Host header field
1978      (<xref target="header.host"/>), and
1979    </t>
1980    <t>
1981      the request-target obtained from the Request-Line, unless the
1982      request-target is just the asterisk "*".
1983    </t>
1984  </list>
1985</t>
1986<t>
1987   If the request-target uses the path-absolute form or the asterisk form,
1988   and the Host header field is not present, then the effective request URI is
1989   undefined.
1990</t>
1991<t>
1992   Otherwise, when request-target uses the authority form, the effective
1993   request URI is undefined.
1994</t>
1995<figure>
1996<preamble>
1997   Example 1: the effective request URI for the message
1998</preamble> 
1999<artwork type="example" x:indent-with="  ">
2000GET /pub/WWW/TheProject.html HTTP/1.1
2001Host: www.example.org:8080
2002</artwork>
2003<postamble>
2004  (received over an insecure TCP connection) is "http", plus "://", plus the
2005  authority component "www.example.org:8080", plus the request-target
2006  "/pub/WWW/TheProject.html", thus
2007  "http://www.example.org:8080/pub/WWW/TheProject.html".
2008</postamble>
2009</figure>
2010<figure>
2011<preamble>
2012   Example 2: the effective request URI for the message
2013</preamble> 
2014<artwork type="example" x:indent-with="  ">
2015OPTIONS * HTTP/1.1
2016Host: www.example.org
2017</artwork>
2018<postamble>
2019  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
2020  authority component "www.example.org", thus "https://www.example.org".
2021</postamble>
2022</figure>
2023<t>
2024   Effective request URIs are compared using the rules described in
2025   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
2026   be treated as equivalent to an absolute path of "/".
2027</t> 
2028</section>
2029</section>
2030
2031
2032<section title="Protocol Parameters" anchor="protocol.parameters">
2033
2034<section title="Transfer Codings" anchor="transfer.codings">
2035  <x:anchor-alias value="transfer-coding"/>
2036  <x:anchor-alias value="transfer-extension"/>
2037<t>
2038   Transfer-coding values are used to indicate an encoding
2039   transformation that has been, can be, or might need to be applied to a
2040   payload body in order to ensure "safe transport" through the network.
2041   This differs from a content coding in that the transfer-coding is a
2042   property of the message rather than a property of the representation
2043   that is being transferred.
2044</t>
2045<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2046  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2047                          / "compress" ; <xref target="compress.coding"/>
2048                          / "deflate" ; <xref target="deflate.coding"/>
2049                          / "gzip" ; <xref target="gzip.coding"/>
2050                          / <x:ref>transfer-extension</x:ref>
2051  <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> )
2052</artwork></figure>
2053<t anchor="rule.parameter">
2054  <x:anchor-alias value="attribute"/>
2055  <x:anchor-alias value="transfer-parameter"/>
2056  <x:anchor-alias value="value"/>
2057   Parameters are in the form of attribute/value pairs.
2058</t>
2059<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"/>
2060  <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>
2061  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2062  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2063</artwork></figure>
2064<t>
2065   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2066   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2067   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2068</t>
2069<t>
2070   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2071   MIME, which were designed to enable safe transport of binary data over a
2072   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2073   However, safe transport
2074   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2075   the only unsafe characteristic of message-bodies is the difficulty in
2076   determining the exact message body length (<xref target="message.body"/>),
2077   or the desire to encrypt data over a shared transport.
2078</t>
2079<t>
2080   A server that receives a request message with a transfer-coding it does
2081   not understand &SHOULD; respond with 501 (Not Implemented) and then
2082   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2083   client.
2084</t>
2085
2086<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2087  <iref item="chunked (Coding Format)"/>
2088  <iref item="Coding Format" subitem="chunked"/>
2089  <x:anchor-alias value="chunk"/>
2090  <x:anchor-alias value="Chunked-Body"/>
2091  <x:anchor-alias value="chunk-data"/>
2092  <x:anchor-alias value="chunk-ext"/>
2093  <x:anchor-alias value="chunk-ext-name"/>
2094  <x:anchor-alias value="chunk-ext-val"/>
2095  <x:anchor-alias value="chunk-size"/>
2096  <x:anchor-alias value="last-chunk"/>
2097  <x:anchor-alias value="trailer-part"/>
2098  <x:anchor-alias value="quoted-str-nf"/>
2099  <x:anchor-alias value="qdtext-nf"/>
2100<t>
2101   The chunked encoding modifies the body of a message in order to
2102   transfer it as a series of chunks, each with its own size indicator,
2103   followed by an &OPTIONAL; trailer containing header fields. This
2104   allows dynamically produced content to be transferred along with the
2105   information necessary for the recipient to verify that it has
2106   received the full message.
2107</t>
2108<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"/>
2109  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2110                   <x:ref>last-chunk</x:ref>
2111                   <x:ref>trailer-part</x:ref>
2112                   <x:ref>CRLF</x:ref>
2113 
2114  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2115                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2116  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2117  <x:ref>last-chunk</x:ref>     = 1*("0") [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2118 
2119  <x:ref>chunk-ext</x:ref>      = *( ";" <x:ref>chunk-ext-name</x:ref>
2120                      [ "=" <x:ref>chunk-ext-val</x:ref> ] )
2121  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2122  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2123  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2124  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2125 
2126  <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>
2127                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2128  <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>
2129</artwork></figure>
2130<t>
2131   The chunk-size field is a string of hex digits indicating the size of
2132   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2133   zero, followed by the trailer, which is terminated by an empty line.
2134</t>
2135<t>
2136   The trailer allows the sender to include additional HTTP header
2137   fields at the end of the message. The Trailer header field can be
2138   used to indicate which header fields are included in a trailer (see
2139   <xref target="header.trailer"/>).
2140</t>
2141<t>
2142   A server using chunked transfer-coding in a response &MUST-NOT; use the
2143   trailer for any header fields unless at least one of the following is
2144   true:
2145  <list style="numbers">
2146    <t>the request included a TE header field that indicates "trailers" is
2147     acceptable in the transfer-coding of the  response, as described in
2148     <xref target="header.te"/>; or,</t>
2149     
2150    <t>the trailer fields consist entirely of optional metadata, and the
2151    recipient could use the message (in a manner acceptable to the server where
2152    the field originated) without receiving it. In other words, the server that
2153    generated the header (often but not always the origin server) is willing to
2154    accept the possibility that the trailer fields might be silently discarded
2155    along the path to the client.</t>
2156  </list>
2157</t>
2158<t>
2159   This requirement prevents an interoperability failure when the
2160   message is being received by an HTTP/1.1 (or later) proxy and
2161   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2162   compliance with the protocol would have necessitated a possibly
2163   infinite buffer on the proxy.
2164</t>
2165<t>
2166   A process for decoding the "chunked" transfer-coding
2167   can be represented in pseudo-code as:
2168</t>
2169<figure><artwork type="code">
2170  length := 0
2171  read chunk-size, chunk-ext (if any) and CRLF
2172  while (chunk-size &gt; 0) {
2173     read chunk-data and CRLF
2174     append chunk-data to decoded-body
2175     length := length + chunk-size
2176     read chunk-size and CRLF
2177  }
2178  read header-field
2179  while (header-field not empty) {
2180     append header-field to existing header fields
2181     read header-field
2182  }
2183  Content-Length := length
2184  Remove "chunked" from Transfer-Encoding
2185</artwork></figure>
2186<t>
2187   All HTTP/1.1 applications &MUST; be able to receive and decode the
2188   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2189   they do not understand.
2190</t>
2191<t>
2192   Since "chunked" is the only transfer-coding required to be understood
2193   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2194   on a persistent connection.  Whenever a transfer-coding is applied to
2195   a payload body in a request, the final transfer-coding applied &MUST;
2196   be "chunked".  If a transfer-coding is applied to a response payload
2197   body, then either the final transfer-coding applied &MUST; be "chunked"
2198   or the message &MUST; be terminated by closing the connection. When the
2199   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2200   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2201   be applied more than once in a message-body.
2202</t>
2203</section>
2204
2205<section title="Compression Codings" anchor="compression.codings">
2206<t>
2207   The codings defined below can be used to compress the payload of a
2208   message.
2209</t>
2210<x:note><t>
2211   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2212   is not desirable and is discouraged for future encodings. Their
2213   use here is representative of historical practice, not good
2214   design.
2215</t></x:note>
2216<x:note><t>
2217   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2218   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2219   equivalent to "gzip" and "compress" respectively.
2220</t></x:note>
2221
2222<section title="Compress Coding" anchor="compress.coding">
2223<iref item="compress (Coding Format)"/>
2224<iref item="Coding Format" subitem="compress"/>
2225<t>
2226   The "compress" format is produced by the common UNIX file compression
2227   program "compress". This format is an adaptive Lempel-Ziv-Welch
2228   coding (LZW).
2229</t>
2230</section>
2231
2232<section title="Deflate Coding" anchor="deflate.coding">
2233<iref item="deflate (Coding Format)"/>
2234<iref item="Coding Format" subitem="deflate"/>
2235<t>
2236   The "deflate" format is defined as the "deflate" compression mechanism
2237   (described in <xref target="RFC1951"/>) used inside the "zlib"
2238   data format (<xref target="RFC1950"/>).
2239</t>
2240<x:note>
2241  <t>
2242    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2243    compressed data without the zlib wrapper.
2244   </t>
2245</x:note>
2246</section>
2247
2248<section title="Gzip Coding" anchor="gzip.coding">
2249<iref item="gzip (Coding Format)"/>
2250<iref item="Coding Format" subitem="gzip"/>
2251<t>
2252   The "gzip" format is produced by the file compression program
2253   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2254   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2255</t>
2256</section>
2257
2258</section>
2259
2260<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2261<t>
2262   The HTTP Transfer Coding Registry defines the name space for the transfer
2263   coding names.
2264</t>
2265<t>
2266   Registrations &MUST; include the following fields:
2267   <list style="symbols">
2268     <t>Name</t>
2269     <t>Description</t>
2270     <t>Pointer to specification text</t>
2271   </list>
2272</t>
2273<t>
2274   Names of transfer codings &MUST-NOT; overlap with names of content codings
2275   (&content-codings;), unless the encoding transformation is identical (as it
2276   is the case for the compression codings defined in
2277   <xref target="compression.codings"/>).
2278</t>
2279<t>
2280   Values to be added to this name space require a specification
2281   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2282   conform to the purpose of transfer coding defined in this section.
2283</t>
2284<t>
2285   The registry itself is maintained at
2286   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2287</t>
2288</section>
2289</section>
2290
2291<section title="Product Tokens" anchor="product.tokens">
2292  <x:anchor-alias value="product"/>
2293  <x:anchor-alias value="product-version"/>
2294<t>
2295   Product tokens are used to allow communicating applications to
2296   identify themselves by software name and version. Most fields using
2297   product tokens also allow sub-products which form a significant part
2298   of the application to be listed, separated by whitespace. By
2299   convention, the products are listed in order of their significance
2300   for identifying the application.
2301</t>
2302<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2303  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2304  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2305</artwork></figure>
2306<t>
2307   Examples:
2308</t>
2309<figure><artwork type="example">
2310  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2311  Server: Apache/0.8.4
2312</artwork></figure>
2313<t>
2314   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2315   used for advertising or other non-essential information. Although any
2316   token octet &MAY; appear in a product-version, this token &SHOULD;
2317   only be used for a version identifier (i.e., successive versions of
2318   the same product &SHOULD; only differ in the product-version portion of
2319   the product value).
2320</t>
2321</section>
2322
2323<section title="Quality Values" anchor="quality.values">
2324  <x:anchor-alias value="qvalue"/>
2325<t>
2326   Both transfer codings (TE request header field, <xref target="header.te"/>)
2327   and content negotiation (&content.negotiation;) use short "floating point"
2328   numbers to indicate the relative importance ("weight") of various
2329   negotiable parameters.  A weight is normalized to a real number in
2330   the range 0 through 1, where 0 is the minimum and 1 the maximum
2331   value. If a parameter has a quality value of 0, then content with
2332   this parameter is "not acceptable" for the client. HTTP/1.1
2333   applications &MUST-NOT; generate more than three digits after the
2334   decimal point. User configuration of these values &SHOULD; also be
2335   limited in this fashion.
2336</t>
2337<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2338  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2339                 / ( "1" [ "." 0*3("0") ] )
2340</artwork></figure>
2341<x:note>
2342  <t>
2343     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2344     relative degradation in desired quality.
2345  </t>
2346</x:note>
2347</section>
2348
2349</section>
2350
2351<section title="Connections" anchor="connections">
2352
2353<section title="Persistent Connections" anchor="persistent.connections">
2354
2355<section title="Purpose" anchor="persistent.purpose">
2356<t>
2357   Prior to persistent connections, a separate TCP connection was
2358   established for each request, increasing the load on HTTP servers
2359   and causing congestion on the Internet. The use of inline images and
2360   other associated data often requires a client to make multiple
2361   requests of the same server in a short amount of time. Analysis of
2362   these performance problems and results from a prototype
2363   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2364   measurements of actual HTTP/1.1 implementations show good
2365   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2366   T/TCP <xref target="Tou1998"/>.
2367</t>
2368<t>
2369   Persistent HTTP connections have a number of advantages:
2370  <list style="symbols">
2371      <t>
2372        By opening and closing fewer TCP connections, CPU time is saved
2373        in routers and hosts (clients, servers, proxies, gateways,
2374        tunnels, or caches), and memory used for TCP protocol control
2375        blocks can be saved in hosts.
2376      </t>
2377      <t>
2378        HTTP requests and responses can be pipelined on a connection.
2379        Pipelining allows a client to make multiple requests without
2380        waiting for each response, allowing a single TCP connection to
2381        be used much more efficiently, with much lower elapsed time.
2382      </t>
2383      <t>
2384        Network congestion is reduced by reducing the number of packets
2385        caused by TCP opens, and by allowing TCP sufficient time to
2386        determine the congestion state of the network.
2387      </t>
2388      <t>
2389        Latency on subsequent requests is reduced since there is no time
2390        spent in TCP's connection opening handshake.
2391      </t>
2392      <t>
2393        HTTP can evolve more gracefully, since errors can be reported
2394        without the penalty of closing the TCP connection. Clients using
2395        future versions of HTTP might optimistically try a new feature,
2396        but if communicating with an older server, retry with old
2397        semantics after an error is reported.
2398      </t>
2399    </list>
2400</t>
2401<t>
2402   HTTP implementations &SHOULD; implement persistent connections.
2403</t>
2404</section>
2405
2406<section title="Overall Operation" anchor="persistent.overall">
2407<t>
2408   A significant difference between HTTP/1.1 and earlier versions of
2409   HTTP is that persistent connections are the default behavior of any
2410   HTTP connection. That is, unless otherwise indicated, the client
2411   &SHOULD; assume that the server will maintain a persistent connection,
2412   even after error responses from the server.
2413</t>
2414<t>
2415   Persistent connections provide a mechanism by which a client and a
2416   server can signal the close of a TCP connection. This signaling takes
2417   place using the Connection header field (<xref target="header.connection"/>). Once a close
2418   has been signaled, the client &MUST-NOT; send any more requests on that
2419   connection.
2420</t>
2421
2422<section title="Negotiation" anchor="persistent.negotiation">
2423<t>
2424   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2425   maintain a persistent connection unless a Connection header field including
2426   the connection-token "close" was sent in the request. If the server
2427   chooses to close the connection immediately after sending the
2428   response, it &SHOULD; send a Connection header field including the
2429   connection-token "close".
2430</t>
2431<t>
2432   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2433   decide to keep it open based on whether the response from a server
2434   contains a Connection header field with the connection-token close. In case
2435   the client does not want to maintain a connection for more than that
2436   request, it &SHOULD; send a Connection header field including the
2437   connection-token close.
2438</t>
2439<t>
2440   If either the client or the server sends the close token in the
2441   Connection header field, that request becomes the last one for the
2442   connection.
2443</t>
2444<t>
2445   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2446   maintained for HTTP versions less than 1.1 unless it is explicitly
2447   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2448   compatibility with HTTP/1.0 clients.
2449</t>
2450<t>
2451   In order to remain persistent, all messages on the connection &MUST;
2452   have a self-defined message length (i.e., one not defined by closure
2453   of the connection), as described in <xref target="message.body"/>.
2454</t>
2455</section>
2456
2457<section title="Pipelining" anchor="pipelining">
2458<t>
2459   A client that supports persistent connections &MAY; "pipeline" its
2460   requests (i.e., send multiple requests without waiting for each
2461   response). A server &MUST; send its responses to those requests in the
2462   same order that the requests were received.
2463</t>
2464<t>
2465   Clients which assume persistent connections and pipeline immediately
2466   after connection establishment &SHOULD; be prepared to retry their
2467   connection if the first pipelined attempt fails. If a client does
2468   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2469   persistent. Clients &MUST; also be prepared to resend their requests if
2470   the server closes the connection before sending all of the
2471   corresponding responses.
2472</t>
2473<t>
2474   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2475   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2476   premature termination of the transport connection could lead to
2477   indeterminate results. A client wishing to send a non-idempotent
2478   request &SHOULD; wait to send that request until it has received the
2479   response status line for the previous request.
2480</t>
2481</section>
2482</section>
2483
2484<section title="Proxy Servers" anchor="persistent.proxy">
2485<t>
2486   It is especially important that proxies correctly implement the
2487   properties of the Connection header field as specified in <xref target="header.connection"/>.
2488</t>
2489<t>
2490   The proxy server &MUST; signal persistent connections separately with
2491   its clients and the origin servers (or other proxy servers) that it
2492   connects to. Each persistent connection applies to only one transport
2493   link.
2494</t>
2495<t>
2496   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2497   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2498   for information and discussion of the problems with the Keep-Alive header field
2499   implemented by many HTTP/1.0 clients).
2500</t>
2501
2502<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2503<!--<t>
2504  <cref anchor="TODO-end-to-end" source="jre">
2505    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2506    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2507  </cref>
2508</t>-->
2509<t>
2510   For the purpose of defining the behavior of caches and non-caching
2511   proxies, we divide HTTP header fields into two categories:
2512  <list style="symbols">
2513      <t>End-to-end header fields, which are  transmitted to the ultimate
2514        recipient of a request or response. End-to-end header fields in
2515        responses MUST be stored as part of a cache entry and &MUST; be
2516        transmitted in any response formed from a cache entry.</t>
2517
2518      <t>Hop-by-hop header fields, which are meaningful only for a single
2519        transport-level connection, and are not stored by caches or
2520        forwarded by proxies.</t>
2521  </list>
2522</t>
2523<t>
2524   The following HTTP/1.1 header fields are hop-by-hop header fields:
2525  <list style="symbols">
2526      <t>Connection</t>
2527      <t>Keep-Alive</t>
2528      <t>Proxy-Authenticate</t>
2529      <t>Proxy-Authorization</t>
2530      <t>TE</t>
2531      <t>Trailer</t>
2532      <t>Transfer-Encoding</t>
2533      <t>Upgrade</t>
2534  </list>
2535</t>
2536<t>
2537   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2538</t>
2539<t>
2540   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2541   (<xref target="header.connection"/>).
2542</t>
2543</section>
2544
2545<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2546<!--<t>
2547  <cref anchor="TODO-non-mod-headers" source="jre">
2548    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2549    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2550  </cref>
2551</t>-->
2552<t>
2553   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2554   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2555   modify an end-to-end header field unless the definition of that header field requires
2556   or specifically allows that.
2557</t>
2558<t>
2559   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2560   request or response, and it &MUST-NOT; add any of these fields if not
2561   already present:
2562  <list style="symbols">
2563    <t>Allow</t>
2564    <t>Content-Location</t>
2565    <t>Content-MD5</t>
2566    <t>ETag</t>
2567    <t>Last-Modified</t>
2568    <t>Server</t>
2569  </list>
2570</t>
2571<t>
2572   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2573   response:
2574  <list style="symbols">
2575    <t>Expires</t>
2576  </list>
2577</t>
2578<t>
2579   but it &MAY; add any of these fields if not already present. If an
2580   Expires header field is added, it &MUST; be given a field-value identical to
2581   that of the Date header field in that response.
2582</t>
2583<t>
2584   A proxy &MUST-NOT; modify or add any of the following fields in a
2585   message that contains the no-transform cache-control directive, or in
2586   any request:
2587  <list style="symbols">
2588    <t>Content-Encoding</t>
2589    <t>Content-Range</t>
2590    <t>Content-Type</t>
2591  </list>
2592</t>
2593<t>
2594   A transforming proxy &MAY; modify or add these fields to a message
2595   that does not include no-transform, but if it does so, it &MUST; add a
2596   Warning 214 (Transformation applied) if one does not already appear
2597   in the message (see &header-warning;).
2598</t>
2599<x:note>
2600  <t>
2601    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2602    cause authentication failures if stronger authentication
2603    mechanisms are introduced in later versions of HTTP. Such
2604    authentication mechanisms &MAY; rely on the values of header fields
2605    not listed here.
2606  </t>
2607</x:note>
2608<t>
2609   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2610   though it &MAY; change the message-body through application or removal
2611   of a transfer-coding (<xref target="transfer.codings"/>).
2612</t>
2613</section>
2614
2615</section>
2616
2617<section title="Practical Considerations" anchor="persistent.practical">
2618<t>
2619   Servers will usually have some time-out value beyond which they will
2620   no longer maintain an inactive connection. Proxy servers might make
2621   this a higher value since it is likely that the client will be making
2622   more connections through the same server. The use of persistent
2623   connections places no requirements on the length (or existence) of
2624   this time-out for either the client or the server.
2625</t>
2626<t>
2627   When a client or server wishes to time-out it &SHOULD; issue a graceful
2628   close on the transport connection. Clients and servers &SHOULD; both
2629   constantly watch for the other side of the transport close, and
2630   respond to it as appropriate. If a client or server does not detect
2631   the other side's close promptly it could cause unnecessary resource
2632   drain on the network.
2633</t>
2634<t>
2635   A client, server, or proxy &MAY; close the transport connection at any
2636   time. For example, a client might have started to send a new request
2637   at the same time that the server has decided to close the "idle"
2638   connection. From the server's point of view, the connection is being
2639   closed while it was idle, but from the client's point of view, a
2640   request is in progress.
2641</t>
2642<t>
2643   Clients (including proxies) &SHOULD; limit the number of simultaneous
2644   connections that they maintain to a given server (including proxies).
2645</t>
2646<t>
2647   Previous revisions of HTTP gave a specific number of connections as a
2648   ceiling, but this was found to be impractical for many applications. As a
2649   result, this specification does not mandate a particular maximum number of
2650   connections, but instead encourages clients to be conservative when opening
2651   multiple connections.
2652</t>
2653<t>
2654   In particular, while using multiple connections avoids the "head-of-line
2655   blocking" problem (whereby a request that takes significant server-side
2656   processing and/or has a large payload can block subsequent requests on the
2657   same connection), each connection used consumes server resources (sometimes
2658   significantly), and furthermore using multiple connections can cause
2659   undesirable side effects in congested networks.
2660</t>
2661<t>
2662   Note that servers might reject traffic that they deem abusive, including an
2663   excessive number of connections from a client.
2664</t>
2665</section>
2666
2667<section title="Retrying Requests" anchor="persistent.retrying.requests">
2668<t>
2669   Senders can close the transport connection at any time. Therefore,
2670   clients, servers, and proxies &MUST; be able to recover
2671   from asynchronous close events. Client software &MAY; reopen the
2672   transport connection and retransmit the aborted sequence of requests
2673   without user interaction so long as the request sequence is
2674   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2675   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2676   human operator the choice of retrying the request(s). Confirmation by
2677   user-agent software with semantic understanding of the application
2678   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2679   be repeated if the second sequence of requests fails.
2680</t>
2681</section>
2682
2683</section>
2684
2685<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2686
2687<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2688<t>
2689   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2690   flow control mechanisms to resolve temporary overloads, rather than
2691   terminating connections with the expectation that clients will retry.
2692   The latter technique can exacerbate network congestion.
2693</t>
2694</section>
2695
2696<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2697<t>
2698   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2699   the network connection for an error status code while it is transmitting
2700   the request. If the client sees an error status code, it &SHOULD;
2701   immediately cease transmitting the body. If the body is being sent
2702   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2703   empty trailer &MAY; be used to prematurely mark the end of the message.
2704   If the body was preceded by a Content-Length header field, the client &MUST;
2705   close the connection.
2706</t>
2707</section>
2708
2709<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2710<t>
2711   The purpose of the 100 (Continue) status code (see &status-100;) is to
2712   allow a client that is sending a request message with a request body
2713   to determine if the origin server is willing to accept the request
2714   (based on the request header fields) before the client sends the request
2715   body. In some cases, it might either be inappropriate or highly
2716   inefficient for the client to send the body if the server will reject
2717   the message without looking at the body.
2718</t>
2719<t>
2720   Requirements for HTTP/1.1 clients:
2721  <list style="symbols">
2722    <t>
2723        If a client will wait for a 100 (Continue) response before
2724        sending the request body, it &MUST; send an Expect header
2725        field (&header-expect;) with the "100-continue" expectation.
2726    </t>
2727    <t>
2728        A client &MUST-NOT; send an Expect header field (&header-expect;)
2729        with the "100-continue" expectation if it does not intend
2730        to send a request body.
2731    </t>
2732  </list>
2733</t>
2734<t>
2735   Because of the presence of older implementations, the protocol allows
2736   ambiguous situations in which a client might send "Expect: 100-continue"
2737   without receiving either a 417 (Expectation Failed)
2738   or a 100 (Continue) status code. Therefore, when a client sends this
2739   header field to an origin server (possibly via a proxy) from which it
2740   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2741   wait for an indefinite period before sending the request body.
2742</t>
2743<t>
2744   Requirements for HTTP/1.1 origin servers:
2745  <list style="symbols">
2746    <t> Upon receiving a request which includes an Expect header
2747        field with the "100-continue" expectation, an origin server &MUST;
2748        either respond with 100 (Continue) status code and continue to read
2749        from the input stream, or respond with a final status code. The
2750        origin server &MUST-NOT; wait for the request body before sending
2751        the 100 (Continue) response. If it responds with a final status
2752        code, it &MAY; close the transport connection or it &MAY; continue
2753        to read and discard the rest of the request.  It &MUST-NOT;
2754        perform the request method if it returns a final status code.
2755    </t>
2756    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2757        the request message does not include an Expect header
2758        field with the "100-continue" expectation, and &MUST-NOT; send a
2759        100 (Continue) response if such a request comes from an HTTP/1.0
2760        (or earlier) client. There is an exception to this rule: for
2761        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2762        status code in response to an HTTP/1.1 PUT or POST request that does
2763        not include an Expect header field with the "100-continue"
2764        expectation. This exception, the purpose of which is
2765        to minimize any client processing delays associated with an
2766        undeclared wait for 100 (Continue) status code, applies only to
2767        HTTP/1.1 requests, and not to requests with any other HTTP-version
2768        value.
2769    </t>
2770    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2771        already received some or all of the request body for the
2772        corresponding request.
2773    </t>
2774    <t> An origin server that sends a 100 (Continue) response &MUST;
2775    ultimately send a final status code, once the request body is
2776        received and processed, unless it terminates the transport
2777        connection prematurely.
2778    </t>
2779    <t> If an origin server receives a request that does not include an
2780        Expect header field with the "100-continue" expectation,
2781        the request includes a request body, and the server responds
2782        with a final status code before reading the entire request body
2783        from the transport connection, then the server &SHOULD-NOT;  close
2784        the transport connection until it has read the entire request,
2785        or until the client closes the connection. Otherwise, the client
2786        might not reliably receive the response message. However, this
2787        requirement is not be construed as preventing a server from
2788        defending itself against denial-of-service attacks, or from
2789        badly broken client implementations.
2790      </t>
2791    </list>
2792</t>
2793<t>
2794   Requirements for HTTP/1.1 proxies:
2795  <list style="symbols">
2796    <t> If a proxy receives a request that includes an Expect header
2797        field with the "100-continue" expectation, and the proxy
2798        either knows that the next-hop server complies with HTTP/1.1 or
2799        higher, or does not know the HTTP version of the next-hop
2800        server, it &MUST; forward the request, including the Expect header
2801        field.
2802    </t>
2803    <t> If the proxy knows that the version of the next-hop server is
2804        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2805        respond with a 417 (Expectation Failed) status code.
2806    </t>
2807    <t> Proxies &SHOULD; maintain a record of the HTTP version
2808        numbers received from recently-referenced next-hop servers.
2809    </t>
2810    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2811        request message was received from an HTTP/1.0 (or earlier)
2812        client and did not include an Expect header field with
2813        the "100-continue" expectation. This requirement overrides the
2814        general rule for forwarding of 1xx responses (see &status-1xx;).
2815    </t>
2816  </list>
2817</t>
2818</section>
2819
2820</section>
2821</section>
2822
2823
2824<section title="Miscellaneous notes that might disappear" anchor="misc">
2825<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2826<t>
2827   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2828</t>
2829</section>
2830
2831<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2832<t>
2833   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2834</t>
2835</section>
2836
2837<section title="Interception of HTTP for access control" anchor="http.intercept">
2838<t>
2839   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2840</t>
2841</section>
2842
2843<section title="Use of HTTP by other protocols" anchor="http.others">
2844<t>
2845   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2846   Extensions of HTTP like WebDAV.</cref>
2847</t>
2848
2849</section>
2850<section title="Use of HTTP by media type specification" anchor="http.media">
2851<t>
2852   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2853</t>
2854</section>
2855</section>
2856
2857<section title="Header Field Definitions" anchor="header.field.definitions">
2858<t>
2859   This section defines the syntax and semantics of HTTP header fields
2860   related to message origination, framing, and routing.
2861</t>
2862<texttable align="left">
2863  <ttcol>Header Field Name</ttcol>
2864  <ttcol>Defined in...</ttcol>
2865 
2866  <c>Connection</c> <c><xref target="header.connection"/></c>
2867  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
2868  <c>Host</c> <c><xref target="header.host"/></c>
2869  <c>TE</c> <c><xref target="header.te"/></c>
2870  <c>Trailer</c> <c><xref target="header.trailer"/></c>
2871  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
2872  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
2873  <c>Via</c> <c><xref target="header.via"/></c>
2874</texttable>
2875
2876<section title="Connection" anchor="header.connection">
2877  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2878  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2879  <x:anchor-alias value="Connection"/>
2880  <x:anchor-alias value="connection-token"/>
2881<t>
2882   The "Connection" header field allows the sender to specify
2883   options that are desired only for that particular connection.
2884   Such connection options &MUST; be removed or replaced before the
2885   message can be forwarded downstream by a proxy or gateway.
2886   This mechanism also allows the sender to indicate which HTTP
2887   header fields used in the message are only intended for the
2888   immediate recipient ("hop-by-hop"), as opposed to all recipients
2889   on the chain ("end-to-end"), enabling the message to be
2890   self-descriptive and allowing future connection-specific extensions
2891   to be deployed in HTTP without fear that they will be blindly
2892   forwarded by previously deployed intermediaries.
2893</t>
2894<t>
2895   The Connection header field's value has the following grammar:
2896</t>
2897<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2898  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2899  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2900</artwork></figure>
2901<t>
2902   A proxy or gateway &MUST; parse a received Connection
2903   header field before a message is forwarded and, for each
2904   connection-token in this field, remove any header field(s) from
2905   the message with the same name as the connection-token, and then
2906   remove the Connection header field itself or replace it with the
2907   sender's own connection options for the forwarded message.
2908</t>
2909<t>
2910   A sender &MUST-NOT; include field-names in the Connection header
2911   field-value for fields that are defined as expressing constraints
2912   for all recipients in the request or response chain, such as the
2913   Cache-Control header field (&header-cache-control;).
2914</t>
2915<t>
2916   The connection options do not have to correspond to a header field
2917   present in the message, since a connection-specific header field
2918   might not be needed if there are no parameters associated with that
2919   connection option.  Recipients that trigger certain connection
2920   behavior based on the presence of connection options &MUST; do so
2921   based on the presence of the connection-token rather than only the
2922   presence of the optional header field.  In other words, if the
2923   connection option is received as a header field but not indicated
2924   within the Connection field-value, then the recipient &MUST; ignore
2925   the connection-specific header field because it has likely been
2926   forwarded by an intermediary that is only partially compliant.
2927</t>
2928<t>
2929   When defining new connection options, specifications ought to
2930   carefully consider existing deployed header fields and ensure
2931   that the new connection-token does not share the same name as
2932   an unrelated header field that might already be deployed.
2933   Defining a new connection-token essentially reserves that potential
2934   field-name for carrying additional information related to the
2935   connection option, since it would be unwise for senders to use
2936   that field-name for anything else.
2937</t>
2938<t>
2939   HTTP/1.1 defines the "close" connection option for the sender to
2940   signal that the connection will be closed after completion of the
2941   response. For example,
2942</t>
2943<figure><artwork type="example">
2944  Connection: close
2945</artwork></figure>
2946<t>
2947   in either the request or the response header fields indicates that
2948   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2949   after the current request/response is complete.
2950</t>
2951<t>
2952   An HTTP/1.1 client that does not support persistent connections &MUST;
2953   include the "close" connection option in every request message.
2954</t>
2955<t>
2956   An HTTP/1.1 server that does not support persistent connections &MUST;
2957   include the "close" connection option in every response message that
2958   does not have a 1xx (Informational) status code.
2959</t>
2960</section>
2961
2962<section title="Content-Length" anchor="header.content-length">
2963  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
2964  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
2965  <x:anchor-alias value="Content-Length"/>
2966<t>
2967   The "Content-Length" header field indicates the size of the
2968   message-body, in decimal number of octets, for any message other than
2969   a response to a HEAD request or a response with a status code of 304.
2970   In the case of a response to a HEAD request, Content-Length indicates
2971   the size of the payload body (not including any potential transfer-coding)
2972   that would have been sent had the request been a GET.
2973   In the case of a 304 (Not Modified) response to a GET request,
2974   Content-Length indicates the size of the payload body (not including
2975   any potential transfer-coding) that would have been sent in a 200 (OK)
2976   response.
2977</t>
2978<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
2979  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
2980</artwork></figure>
2981<t>
2982   An example is
2983</t>
2984<figure><artwork type="example">
2985  Content-Length: 3495
2986</artwork></figure>
2987<t>
2988   Implementations &SHOULD; use this field to indicate the message-body
2989   length when no transfer-coding is being applied and the
2990   payload's body length can be determined prior to being transferred.
2991   <xref target="message.body"/> describes how recipients determine the length
2992   of a message-body.
2993</t>
2994<t>
2995   Any Content-Length greater than or equal to zero is a valid value.
2996</t>
2997<t>
2998   Note that the use of this field in HTTP is significantly different from
2999   the corresponding definition in MIME, where it is an optional field
3000   used within the "message/external-body" content-type.
3001</t>
3002</section>
3003
3004<section title="Host" anchor="header.host">
3005  <iref primary="true" item="Host header field" x:for-anchor=""/>
3006  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3007  <x:anchor-alias value="Host"/>
3008<t>
3009   The "Host" header field in a request provides the host and port
3010   information from the target resource's URI, enabling the origin
3011   server to distinguish between resources while servicing requests
3012   for multiple host names on a single IP address.  Since the Host
3013   field-value is critical information for handling a request, it
3014   &SHOULD; be sent as the first header field following the Request-Line.
3015</t>
3016<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3017  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3018</artwork></figure>
3019<t>
3020   A client &MUST; send a Host header field in all HTTP/1.1 request
3021   messages.  If the target resource's URI includes an authority
3022   component, then the Host field-value &MUST; be identical to that
3023   authority component after excluding any userinfo (<xref target="http.uri"/>).
3024   If the authority component is missing or undefined for the target
3025   resource's URI, then the Host header field &MUST; be sent with an
3026   empty field-value.
3027</t>
3028<t>
3029   For example, a GET request to the origin server for
3030   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3031</t>
3032<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3033GET /pub/WWW/ HTTP/1.1
3034Host: www.example.org
3035</artwork></figure>
3036<t>
3037   The Host header field &MUST; be sent in an HTTP/1.1 request even
3038   if the request-target is in the form of an absolute-URI, since this
3039   allows the Host information to be forwarded through ancient HTTP/1.0
3040   proxies that might not have implemented Host.
3041</t>
3042<t>
3043   When an HTTP/1.1 proxy receives a request with a request-target in
3044   the form of an absolute-URI, the proxy &MUST; ignore the received
3045   Host header field (if any) and instead replace it with the host
3046   information of the request-target.  When a proxy forwards a request,
3047   it &MUST; generate the Host header field based on the received
3048   absolute-URI rather than the received Host.
3049</t>
3050<t>
3051   Since the Host header field acts as an application-level routing
3052   mechanism, it is a frequent target for malware seeking to poison
3053   a shared cache or redirect a request to an unintended server.
3054   An interception proxy is particularly vulnerable if it relies on
3055   the Host header field value for redirecting requests to internal
3056   servers, or for use as a cache key in a shared cache, without
3057   first verifying that the intercepted connection is targeting a
3058   valid IP address for that host.
3059</t>
3060<t>
3061   A server &MUST; respond with a 400 (Bad Request) status code to
3062   any HTTP/1.1 request message that lacks a Host header field and
3063   to any request message that contains more than one Host header field
3064   or a Host header field with an invalid field-value.
3065</t>
3066<t>
3067   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3068   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3069   for other requirements relating to Host.
3070</t>
3071</section>
3072
3073<section title="TE" anchor="header.te">
3074  <iref primary="true" item="TE header field" x:for-anchor=""/>
3075  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3076  <x:anchor-alias value="TE"/>
3077  <x:anchor-alias value="t-codings"/>
3078  <x:anchor-alias value="te-params"/>
3079  <x:anchor-alias value="te-ext"/>
3080<t>
3081   The "TE" header field indicates what extension transfer-codings
3082   it is willing to accept in the response, and whether or not it is
3083   willing to accept trailer fields in a chunked transfer-coding.
3084</t>
3085<t>
3086   Its value consists of the keyword "trailers" and/or a comma-separated
3087   list of extension transfer-coding names with optional accept
3088   parameters (as described in <xref target="transfer.codings"/>).
3089</t>
3090<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"/>
3091  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3092  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3093  <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> )
3094  <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> ]
3095</artwork></figure>
3096<t>
3097   The presence of the keyword "trailers" indicates that the client is
3098   willing to accept trailer fields in a chunked transfer-coding, as
3099   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3100   transfer-coding values even though it does not itself represent a
3101   transfer-coding.
3102</t>
3103<t>
3104   Examples of its use are:
3105</t>
3106<figure><artwork type="example">
3107  TE: deflate
3108  TE:
3109  TE: trailers, deflate;q=0.5
3110</artwork></figure>
3111<t>
3112   The TE header field only applies to the immediate connection.
3113   Therefore, the keyword &MUST; be supplied within a Connection header
3114   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3115</t>
3116<t>
3117   A server tests whether a transfer-coding is acceptable, according to
3118   a TE field, using these rules:
3119  <list style="numbers">
3120    <x:lt>
3121      <t>The "chunked" transfer-coding is always acceptable. If the
3122         keyword "trailers" is listed, the client indicates that it is
3123         willing to accept trailer fields in the chunked response on
3124         behalf of itself and any downstream clients. The implication is
3125         that, if given, the client is stating that either all
3126         downstream clients are willing to accept trailer fields in the
3127         forwarded response, or that it will attempt to buffer the
3128         response on behalf of downstream recipients.
3129      </t><t>
3130         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3131         chunked response such that a client can be assured of buffering
3132         the entire response.</t>
3133    </x:lt>
3134    <x:lt>
3135      <t>If the transfer-coding being tested is one of the transfer-codings
3136         listed in the TE field, then it is acceptable unless it
3137         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3138         qvalue of 0 means "not acceptable".)</t>
3139    </x:lt>
3140    <x:lt>
3141      <t>If multiple transfer-codings are acceptable, then the
3142         acceptable transfer-coding with the highest non-zero qvalue is
3143         preferred.  The "chunked" transfer-coding always has a qvalue
3144         of 1.</t>
3145    </x:lt>
3146  </list>
3147</t>
3148<t>
3149   If the TE field-value is empty or if no TE field is present, the only
3150   transfer-coding is "chunked". A message with no transfer-coding is
3151   always acceptable.
3152</t>
3153</section>
3154
3155<section title="Trailer" anchor="header.trailer">
3156  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3157  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3158  <x:anchor-alias value="Trailer"/>
3159<t>
3160   The "Trailer" header field indicates that the given set of
3161   header fields is present in the trailer of a message encoded with
3162   chunked transfer-coding.
3163</t>
3164<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3165  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3166</artwork></figure>
3167<t>
3168   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3169   message using chunked transfer-coding with a non-empty trailer. Doing
3170   so allows the recipient to know which header fields to expect in the
3171   trailer.
3172</t>
3173<t>
3174   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3175   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3176   trailer fields in a "chunked" transfer-coding.
3177</t>
3178<t>
3179   Message header fields listed in the Trailer header field &MUST-NOT;
3180   include the following header fields:
3181  <list style="symbols">
3182    <t>Transfer-Encoding</t>
3183    <t>Content-Length</t>
3184    <t>Trailer</t>
3185  </list>
3186</t>
3187</section>
3188
3189<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3190  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3191  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3192  <x:anchor-alias value="Transfer-Encoding"/>
3193<t>
3194   The "Transfer-Encoding" header field indicates what transfer-codings
3195   (if any) have been applied to the message body. It differs from
3196   Content-Encoding (&content-codings;) in that transfer-codings are a property
3197   of the message (and therefore are removed by intermediaries), whereas
3198   content-codings are not.
3199</t>
3200<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3201  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3202</artwork></figure>
3203<t>
3204   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3205</t>
3206<figure><artwork type="example">
3207  Transfer-Encoding: chunked
3208</artwork></figure>
3209<t>
3210   If multiple encodings have been applied to a representation, the transfer-codings
3211   &MUST; be listed in the order in which they were applied.
3212   Additional information about the encoding parameters &MAY; be provided
3213   by other header fields not defined by this specification.
3214</t>
3215<t>
3216   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3217   header field.
3218</t>
3219</section>
3220
3221<section title="Upgrade" anchor="header.upgrade">
3222  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3223  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3224  <x:anchor-alias value="Upgrade"/>
3225<t>
3226   The "Upgrade" header field allows the client to specify what
3227   additional communication protocols it would like to use, if the server
3228   chooses to switch protocols. Servers can use it to indicate what protocols
3229   they are willing to switch to.
3230</t>
3231<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3232  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3233</artwork></figure>
3234<t>
3235   For example,
3236</t>
3237<figure><artwork type="example">
3238  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3239</artwork></figure>
3240<t>
3241   The Upgrade header field is intended to provide a simple mechanism
3242   for transition from HTTP/1.1 to some other, incompatible protocol. It
3243   does so by allowing the client to advertise its desire to use another
3244   protocol, such as a later version of HTTP with a higher major version
3245   number, even though the current request has been made using HTTP/1.1.
3246   This eases the difficult transition between incompatible protocols by
3247   allowing the client to initiate a request in the more commonly
3248   supported protocol while indicating to the server that it would like
3249   to use a "better" protocol if available (where "better" is determined
3250   by the server, possibly according to the nature of the request method
3251   or target resource).
3252</t>
3253<t>
3254   The Upgrade header field only applies to switching application-layer
3255   protocols upon the existing transport-layer connection. Upgrade
3256   cannot be used to insist on a protocol change; its acceptance and use
3257   by the server is optional. The capabilities and nature of the
3258   application-layer communication after the protocol change is entirely
3259   dependent upon the new protocol chosen, although the first action
3260   after changing the protocol &MUST; be a response to the initial HTTP
3261   request containing the Upgrade header field.
3262</t>
3263<t>
3264   The Upgrade header field only applies to the immediate connection.
3265   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3266   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3267   HTTP/1.1 message.
3268</t>
3269<t>
3270   The Upgrade header field cannot be used to indicate a switch to a
3271   protocol on a different connection. For that purpose, it is more
3272   appropriate to use a 3xx redirection response (&status-3xx;).
3273</t>
3274<t>
3275   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3276   Protocols) responses to indicate which protocol(s) are being switched to,
3277   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3278   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3279   response to indicate that they are willing to upgrade to one of the
3280   specified protocols.
3281</t>
3282<t>
3283   This specification only defines the protocol name "HTTP" for use by
3284   the family of Hypertext Transfer Protocols, as defined by the HTTP
3285   version rules of <xref target="http.version"/> and future updates to this
3286   specification. Additional tokens can be registered with IANA using the
3287   registration procedure defined below. 
3288</t>
3289
3290<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3291<t>
3292   The HTTP Upgrade Token Registry defines the name space for product
3293   tokens used to identify protocols in the Upgrade header field.
3294   Each registered token is associated with contact information and
3295   an optional set of specifications that details how the connection
3296   will be processed after it has been upgraded.
3297</t>
3298<t>
3299   Registrations are allowed on a First Come First Served basis as
3300   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3301   specifications need not be IETF documents or be subject to IESG review.
3302   Registrations are subject to the following rules:
3303  <list style="numbers">
3304    <t>A token, once registered, stays registered forever.</t>
3305    <t>The registration &MUST; name a responsible party for the
3306       registration.</t>
3307    <t>The registration &MUST; name a point of contact.</t>
3308    <t>The registration &MAY; name a set of specifications associated with that
3309       token. Such specifications need not be publicly available.</t>
3310    <t>The responsible party &MAY; change the registration at any time.
3311       The IANA will keep a record of all such changes, and make them
3312       available upon request.</t>
3313    <t>The responsible party for the first registration of a "product"
3314       token &MUST; approve later registrations of a "version" token
3315       together with that "product" token before they can be registered.</t>
3316    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3317       for a token. This will normally only be used in the case when a
3318       responsible party cannot be contacted.</t>
3319  </list>
3320</t>
3321</section>
3322
3323
3324</section>
3325
3326<section title="Via" anchor="header.via">
3327  <iref primary="true" item="Via header field" x:for-anchor=""/>
3328  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3329  <x:anchor-alias value="protocol-name"/>
3330  <x:anchor-alias value="protocol-version"/>
3331  <x:anchor-alias value="pseudonym"/>
3332  <x:anchor-alias value="received-by"/>
3333  <x:anchor-alias value="received-protocol"/>
3334  <x:anchor-alias value="Via"/>
3335<t>
3336   The "Via" header field &MUST; be sent by a proxy or gateway to
3337   indicate the intermediate protocols and recipients between the user
3338   agent and the server on requests, and between the origin server and
3339   the client on responses. It is analogous to the "Received" field
3340   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3341   and is intended to be used for tracking message forwards,
3342   avoiding request loops, and identifying the protocol capabilities of
3343   all senders along the request/response chain.
3344</t>
3345<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"/>
3346  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3347                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3348  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3349  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3350  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3351  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3352  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3353</artwork></figure>
3354<t>
3355   The received-protocol indicates the protocol version of the message
3356   received by the server or client along each segment of the
3357   request/response chain. The received-protocol version is appended to
3358   the Via field value when the message is forwarded so that information
3359   about the protocol capabilities of upstream applications remains
3360   visible to all recipients.
3361</t>
3362<t>
3363   The protocol-name is excluded if and only if it would be "HTTP". The
3364   received-by field is normally the host and optional port number of a
3365   recipient server or client that subsequently forwarded the message.
3366   However, if the real host is considered to be sensitive information,
3367   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3368   be assumed to be the default port of the received-protocol.
3369</t>
3370<t>
3371   Multiple Via field values represent each proxy or gateway that has
3372   forwarded the message. Each recipient &MUST; append its information
3373   such that the end result is ordered according to the sequence of
3374   forwarding applications.
3375</t>
3376<t>
3377   Comments &MAY; be used in the Via header field to identify the software
3378   of each recipient, analogous to the User-Agent and Server header fields.
3379   However, all comments in the Via field are optional and &MAY; be removed
3380   by any recipient prior to forwarding the message.
3381</t>
3382<t>
3383   For example, a request message could be sent from an HTTP/1.0 user
3384   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3385   forward the request to a public proxy at p.example.net, which completes
3386   the request by forwarding it to the origin server at www.example.com.
3387   The request received by www.example.com would then have the following
3388   Via header field:
3389</t>
3390<figure><artwork type="example">
3391  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3392</artwork></figure>
3393<t>
3394   A proxy or gateway used as a portal through a network firewall
3395   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3396   region unless it is explicitly enabled to do so. If not enabled, the
3397   received-by host of any host behind the firewall &SHOULD; be replaced
3398   by an appropriate pseudonym for that host.
3399</t>
3400<t>
3401   For organizations that have strong privacy requirements for hiding
3402   internal structures, a proxy or gateway &MAY; combine an ordered
3403   subsequence of Via header field entries with identical received-protocol
3404   values into a single such entry. For example,
3405</t>
3406<figure><artwork type="example">
3407  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3408</artwork></figure>
3409<t>
3410  could be collapsed to
3411</t>
3412<figure><artwork type="example">
3413  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3414</artwork></figure>
3415<t>
3416   Senders &SHOULD-NOT; combine multiple entries unless they are all
3417   under the same organizational control and the hosts have already been
3418   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3419   have different received-protocol values.
3420</t>
3421</section>
3422
3423</section>
3424
3425<section title="IANA Considerations" anchor="IANA.considerations">
3426
3427<section title="Header Field Registration" anchor="header.field.registration">
3428<t>
3429   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3430   with the permanent registrations below (see <xref target="RFC3864"/>):
3431</t>
3432<?BEGININC p1-messaging.iana-headers ?>
3433<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3434<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3435   <ttcol>Header Field Name</ttcol>
3436   <ttcol>Protocol</ttcol>
3437   <ttcol>Status</ttcol>
3438   <ttcol>Reference</ttcol>
3439
3440   <c>Connection</c>
3441   <c>http</c>
3442   <c>standard</c>
3443   <c>
3444      <xref target="header.connection"/>
3445   </c>
3446   <c>Content-Length</c>
3447   <c>http</c>
3448   <c>standard</c>
3449   <c>
3450      <xref target="header.content-length"/>
3451   </c>
3452   <c>Host</c>
3453   <c>http</c>
3454   <c>standard</c>
3455   <c>
3456      <xref target="header.host"/>
3457   </c>
3458   <c>TE</c>
3459   <c>http</c>
3460   <c>standard</c>
3461   <c>
3462      <xref target="header.te"/>
3463   </c>
3464   <c>Trailer</c>
3465   <c>http</c>
3466   <c>standard</c>
3467   <c>
3468      <xref target="header.trailer"/>
3469   </c>
3470   <c>Transfer-Encoding</c>
3471   <c>http</c>
3472   <c>standard</c>
3473   <c>
3474      <xref target="header.transfer-encoding"/>
3475   </c>
3476   <c>Upgrade</c>
3477   <c>http</c>
3478   <c>standard</c>
3479   <c>
3480      <xref target="header.upgrade"/>
3481   </c>
3482   <c>Via</c>
3483   <c>http</c>
3484   <c>standard</c>
3485   <c>
3486      <xref target="header.via"/>
3487   </c>
3488</texttable>
3489<!--(END)-->
3490<?ENDINC p1-messaging.iana-headers ?>
3491<t>
3492   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3493   HTTP header field would be in conflict with the use of the "close" connection
3494   option for the "Connection" header field (<xref target="header.connection"/>).
3495</t>
3496<texttable align="left" suppress-title="true">
3497   <ttcol>Header Field Name</ttcol>
3498   <ttcol>Protocol</ttcol>
3499   <ttcol>Status</ttcol>
3500   <ttcol>Reference</ttcol>
3501
3502   <c>Close</c>
3503   <c>http</c>
3504   <c>reserved</c>
3505   <c>
3506      <xref target="header.field.registration"/>
3507   </c>
3508</texttable>
3509<t>
3510   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3511</t>
3512</section>
3513
3514<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3515<t>
3516   The entries for the "http" and "https" URI Schemes in the registry located at
3517   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3518   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3519   and <xref target="https.uri" format="counter"/> of this document
3520   (see <xref target="RFC4395"/>).
3521</t>
3522</section>
3523
3524<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3525<t>
3526   This document serves as the specification for the Internet media types
3527   "message/http" and "application/http". The following is to be registered with
3528   IANA (see <xref target="RFC4288"/>).
3529</t>
3530<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3531<iref item="Media Type" subitem="message/http" primary="true"/>
3532<iref item="message/http Media Type" primary="true"/>
3533<t>
3534   The message/http type can be used to enclose a single HTTP request or
3535   response message, provided that it obeys the MIME restrictions for all
3536   "message" types regarding line length and encodings.
3537</t>
3538<t>
3539  <list style="hanging" x:indent="12em">
3540    <t hangText="Type name:">
3541      message
3542    </t>
3543    <t hangText="Subtype name:">
3544      http
3545    </t>
3546    <t hangText="Required parameters:">
3547      none
3548    </t>
3549    <t hangText="Optional parameters:">
3550      version, msgtype
3551      <list style="hanging">
3552        <t hangText="version:">
3553          The HTTP-Version number of the enclosed message
3554          (e.g., "1.1"). If not present, the version can be
3555          determined from the first line of the body.
3556        </t>
3557        <t hangText="msgtype:">
3558          The message type &mdash; "request" or "response". If not
3559          present, the type can be determined from the first
3560          line of the body.
3561        </t>
3562      </list>
3563    </t>
3564    <t hangText="Encoding considerations:">
3565      only "7bit", "8bit", or "binary" are permitted
3566    </t>
3567    <t hangText="Security considerations:">
3568      none
3569    </t>
3570    <t hangText="Interoperability considerations:">
3571      none
3572    </t>
3573    <t hangText="Published specification:">
3574      This specification (see <xref target="internet.media.type.message.http"/>).
3575    </t>
3576    <t hangText="Applications that use this media type:">
3577    </t>
3578    <t hangText="Additional information:">
3579      <list style="hanging">
3580        <t hangText="Magic number(s):">none</t>
3581        <t hangText="File extension(s):">none</t>
3582        <t hangText="Macintosh file type code(s):">none</t>
3583      </list>
3584    </t>
3585    <t hangText="Person and email address to contact for further information:">
3586      See Authors Section.
3587    </t>
3588    <t hangText="Intended usage:">
3589      COMMON
3590    </t>
3591    <t hangText="Restrictions on usage:">
3592      none
3593    </t>
3594    <t hangText="Author/Change controller:">
3595      IESG
3596    </t>
3597  </list>
3598</t>
3599</section>
3600<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3601<iref item="Media Type" subitem="application/http" primary="true"/>
3602<iref item="application/http Media Type" primary="true"/>
3603<t>
3604   The application/http type can be used to enclose a pipeline of one or more
3605   HTTP request or response messages (not intermixed).
3606</t>
3607<t>
3608  <list style="hanging" x:indent="12em">
3609    <t hangText="Type name:">
3610      application
3611    </t>
3612    <t hangText="Subtype name:">
3613      http
3614    </t>
3615    <t hangText="Required parameters:">
3616      none
3617    </t>
3618    <t hangText="Optional parameters:">
3619      version, msgtype
3620      <list style="hanging">
3621        <t hangText="version:">
3622          The HTTP-Version number of the enclosed messages
3623          (e.g., "1.1"). If not present, the version can be
3624          determined from the first line of the body.
3625        </t>
3626        <t hangText="msgtype:">
3627          The message type &mdash; "request" or "response". If not
3628          present, the type can be determined from the first
3629          line of the body.
3630        </t>
3631      </list>
3632    </t>
3633    <t hangText="Encoding considerations:">
3634      HTTP messages enclosed by this type
3635      are in "binary" format; use of an appropriate
3636      Content-Transfer-Encoding is required when
3637      transmitted via E-mail.
3638    </t>
3639    <t hangText="Security considerations:">
3640      none
3641    </t>
3642    <t hangText="Interoperability considerations:">
3643      none
3644    </t>
3645    <t hangText="Published specification:">
3646      This specification (see <xref target="internet.media.type.application.http"/>).
3647    </t>
3648    <t hangText="Applications that use this media type:">
3649    </t>
3650    <t hangText="Additional information:">
3651      <list style="hanging">
3652        <t hangText="Magic number(s):">none</t>
3653        <t hangText="File extension(s):">none</t>
3654        <t hangText="Macintosh file type code(s):">none</t>
3655      </list>
3656    </t>
3657    <t hangText="Person and email address to contact for further information:">
3658      See Authors Section.
3659    </t>
3660    <t hangText="Intended usage:">
3661      COMMON
3662    </t>
3663    <t hangText="Restrictions on usage:">
3664      none
3665    </t>
3666    <t hangText="Author/Change controller:">
3667      IESG
3668    </t>
3669  </list>
3670</t>
3671</section>
3672</section>
3673
3674<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3675<t>
3676   The registration procedure for HTTP Transfer Codings is now defined by
3677   <xref target="transfer.coding.registry"/> of this document.
3678</t>
3679<t>
3680   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3681   shall be updated with the registrations below:
3682</t>
3683<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3684   <ttcol>Name</ttcol>
3685   <ttcol>Description</ttcol>
3686   <ttcol>Reference</ttcol>
3687   <c>chunked</c>
3688   <c>Transfer in a series of chunks</c>
3689   <c>
3690      <xref target="chunked.encoding"/>
3691   </c>
3692   <c>compress</c>
3693   <c>UNIX "compress" program method</c>
3694   <c>
3695      <xref target="compress.coding"/>
3696   </c>
3697   <c>deflate</c>
3698   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3699   the "zlib" data format (<xref target="RFC1950"/>)
3700   </c>
3701   <c>
3702      <xref target="deflate.coding"/>
3703   </c>
3704   <c>gzip</c>
3705   <c>Same as GNU zip <xref target="RFC1952"/></c>
3706   <c>
3707      <xref target="gzip.coding"/>
3708   </c>
3709</texttable>
3710</section>
3711
3712<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3713<t>
3714   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3715   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3716   by <xref target="upgrade.token.registry"/> of this document.
3717</t>
3718<t>
3719   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3720   shall be updated with the registration below:
3721</t>
3722<texttable align="left" suppress-title="true">
3723   <ttcol>Value</ttcol>
3724   <ttcol>Description</ttcol>
3725   <ttcol>Reference</ttcol>
3726
3727   <c>HTTP</c>
3728   <c>Hypertext Transfer Protocol</c> 
3729   <c><xref target="http.version"/> of this specification</c>
3730
3731</texttable>
3732</section>
3733
3734</section>
3735
3736<section title="Security Considerations" anchor="security.considerations">
3737<t>
3738   This section is meant to inform application developers, information
3739   providers, and users of the security limitations in HTTP/1.1 as
3740   described by this document. The discussion does not include
3741   definitive solutions to the problems revealed, though it does make
3742   some suggestions for reducing security risks.
3743</t>
3744
3745<section title="Personal Information" anchor="personal.information">
3746<t>
3747   HTTP clients are often privy to large amounts of personal information
3748   (e.g., the user's name, location, mail address, passwords, encryption
3749   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3750   leakage of this information.
3751   We very strongly recommend that a convenient interface be provided
3752   for the user to control dissemination of such information, and that
3753   designers and implementors be particularly careful in this area.
3754   History shows that errors in this area often create serious security
3755   and/or privacy problems and generate highly adverse publicity for the
3756   implementor's company.
3757</t>
3758</section>
3759
3760<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3761<t>
3762   A server is in the position to save personal data about a user's
3763   requests which might identify their reading patterns or subjects of
3764   interest. This information is clearly confidential in nature and its
3765   handling can be constrained by law in certain countries. People using
3766   HTTP to provide data are responsible for ensuring that
3767   such material is not distributed without the permission of any
3768   individuals that are identifiable by the published results.
3769</t>
3770</section>
3771
3772<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3773<t>
3774   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3775   the documents returned by HTTP requests to be only those that were
3776   intended by the server administrators. If an HTTP server translates
3777   HTTP URIs directly into file system calls, the server &MUST; take
3778   special care not to serve files that were not intended to be
3779   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3780   other operating systems use ".." as a path component to indicate a
3781   directory level above the current one. On such a system, an HTTP
3782   server &MUST; disallow any such construct in the request-target if it
3783   would otherwise allow access to a resource outside those intended to
3784   be accessible via the HTTP server. Similarly, files intended for
3785   reference only internally to the server (such as access control
3786   files, configuration files, and script code) &MUST; be protected from
3787   inappropriate retrieval, since they might contain sensitive
3788   information. Experience has shown that minor bugs in such HTTP server
3789   implementations have turned into security risks.
3790</t>
3791</section>
3792
3793<section title="DNS-related Attacks" anchor="dns.related.attacks">
3794<t>
3795   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3796   generally prone to security attacks based on the deliberate misassociation
3797   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3798   cautious in assuming the validity of an IP number/DNS name association unless
3799   the response is protected by DNSSec (<xref target="RFC4033"/>).
3800</t>
3801</section>
3802
3803<section title="Proxies and Caching" anchor="attack.proxies">
3804<t>
3805   By their very nature, HTTP proxies are men-in-the-middle, and
3806   represent an opportunity for man-in-the-middle attacks. Compromise of
3807   the systems on which the proxies run can result in serious security
3808   and privacy problems. Proxies have access to security-related
3809   information, personal information about individual users and
3810   organizations, and proprietary information belonging to users and
3811   content providers. A compromised proxy, or a proxy implemented or
3812   configured without regard to security and privacy considerations,
3813   might be used in the commission of a wide range of potential attacks.
3814</t>
3815<t>
3816   Proxy operators need to protect the systems on which proxies run as
3817   they would protect any system that contains or transports sensitive
3818   information. In particular, log information gathered at proxies often
3819   contains highly sensitive personal information, and/or information
3820   about organizations. Log information needs to be carefully guarded, and
3821   appropriate guidelines for use need to be developed and followed.
3822   (<xref target="abuse.of.server.log.information"/>).
3823</t>
3824<t>
3825   Proxy implementors need to consider the privacy and security
3826   implications of their design and coding decisions, and of the
3827   configuration options they provide to proxy operators (especially the
3828   default configuration).
3829</t>
3830<t>
3831   Users of a proxy need to be aware that proxies are no trustworthier than
3832   the people who run them; HTTP itself cannot solve this problem.
3833</t>
3834<t>
3835   The judicious use of cryptography, when appropriate, might suffice to
3836   protect against a broad range of security and privacy attacks. Such
3837   cryptography is beyond the scope of the HTTP/1.1 specification.
3838</t>
3839</section>
3840
3841<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3842<t>
3843   Because HTTP uses mostly textual, character-delimited fields, attackers can
3844   overflow buffers in implementations, and/or perform a Denial of Service
3845   against implementations that accept fields with unlimited lengths.
3846</t>
3847<t>
3848   To promote interoperability, this specification makes specific
3849   recommendations for size limits on request-targets (<xref target="request-target"/>)
3850   and blocks of header fields (<xref target="header.fields"/>). These are
3851   minimum recommendations, chosen to be supportable even by implementations
3852   with limited resources; it is expected that most implementations will choose
3853   substantially higher limits.
3854</t>
3855<t>
3856   This specification also provides a way for servers to reject messages that
3857   have request-targets that are too long (&status-414;) or request entities
3858   that are too large (&status-4xx;).
3859</t>
3860<t>
3861   Other fields (including but not limited to request methods, response status
3862   phrases, header field-names, and body chunks) &SHOULD; be limited by
3863   implementations carefully, so as to not impede interoperability.
3864</t>
3865</section>
3866
3867<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3868<t>
3869   They exist. They are hard to defend against. Research continues.
3870   Beware.
3871</t>
3872</section>
3873</section>
3874
3875<section title="Acknowledgments" anchor="acks">
3876<t>
3877   This document revision builds on the work that went into
3878   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3879   See <xref target="RFC2616" x:fmt="of" x:sec="16"/> for detailed
3880   acknowledgements.
3881</t>
3882<t>
3883   Since 1999, many contributors have helped by reporting bugs, asking
3884   smart questions, drafting and reviewing text, and discussing open issues:
3885</t>
3886<?BEGININC acks ?>
3887<t>Adam Barth,
3888Adam Roach,
3889Addison Phillips,
3890Adrian Chadd,
3891Adrien de Croy,
3892Alan Ford,
3893Alan Ruttenberg,
3894Albert Lunde,
3895Alex Rousskov,
3896Alexey Melnikov,
3897Alisha Smith,
3898Amichai Rothman,
3899Amit Klein,
3900Amos Jeffries,
3901Andreas Maier,
3902Andreas Petersson,
3903Anne van Kesteren,
3904Anthony Bryan,
3905Asbjorn Ulsberg,
3906Balachander Krishnamurthy,
3907Barry Leiba,
3908Ben Laurie,
3909Benjamin Niven-Jenkins,
3910Bil Corry,
3911Bill Burke,
3912Bjoern Hoehrmann,
3913Bob Scheifler,
3914Boris Zbarsky,
3915Brett Slatkin,
3916Brian Kell,
3917Brian McBarron,
3918Brian Pane,
3919Brian Smith,
3920Bryce Nesbitt,
3921Carl Kugler,
3922Charles Fry,
3923Chris Newman,
3924Cyrus Daboo,
3925Dale Robert Anderson,
3926Dan Winship,
3927Daniel Stenberg,
3928Dave Cridland,
3929Dave Crocker,
3930Dave Kristol,
3931David Booth,
3932David Singer,
3933David W. Morris,
3934Diwakar Shetty,
3935Dmitry Kurochkin,
3936Drummond Reed,
3937Duane Wessels,
3938Edward Lee,
3939Eliot Lear,
3940Eran Hammer-Lahav,
3941Eric D. Williams,
3942Eric J. Bowman,
3943Eric Lawrence,
3944Erik Aronesty,
3945Florian Weimer,
3946Frank Ellermann,
3947Fred Bohle,
3948Geoffrey Sneddon,
3949Gervase Markham,
3950Greg Wilkins,
3951Harald Tveit Alvestrand,
3952Harry Halpin,
3953Helge Hess,
3954Henrik Nordstrom,
3955Henry S. Thompson,
3956Henry Story,
3957Howard Melman,
3958Hugo Haas,
3959Ian Hickson,
3960Ingo Struck,
3961J. Ross Nicoll,
3962James H. Manger,
3963James Lacey,
3964James M. Snell,
3965Jamie Lokier,
3966Jan Algermissen,
3967Jeff Hodges (for coming up with the term 'effective Request-URI'),
3968Jeff Walden,
3969Jim Luther,
3970Joe D. Williams,
3971Joe Gregorio,
3972Joe Orton,
3973John C. Klensin,
3974John C. Mallery,
3975John Cowan,
3976John Kemp,
3977John Panzer,
3978John Schneider,
3979John Stracke,
3980Jonas Sicking,
3981Jonathan Moore,
3982Jonathan Rees,
3983Jordi Ros,
3984Joris Dobbelsteen,
3985Josh Cohen,
3986Julien Pierre,
3987Jungshik Shin,
3988Justin Chapweske,
3989Justin Erenkrantz,
3990Justin James,
3991Kalvinder Singh,
3992Karl Dubost,
3993Keith Hoffman,
3994Keith Moore,
3995Koen Holtman,
3996Konstantin Voronkov,
3997Kris Zyp,
3998Lisa Dusseault,
3999Maciej Stachowiak,
4000Marc Schneider,
4001Marc Slemko,
4002Mark Baker,
4003Mark Nottingham (Working Group chair),
4004Mark Pauley,
4005Martin J. Duerst,
4006Martin Thomson,
4007Matt Lynch,
4008Matthew Cox,
4009Max Clark,
4010Michael Burrows,
4011Michael Hausenblas,
4012Mike Amundsen,
4013Mike Kelly,
4014Mike Schinkel,
4015Miles Sabin,
4016Mykyta Yevstifeyev,
4017Nathan Rixham,
4018Nicholas Shanks,
4019Nico Williams,
4020Nicolas Alvarez,
4021Noah Slater,
4022Pablo Castro,
4023Pat Hayes,
4024Patrick R. McManus,
4025Paul E. Jones,
4026Paul Hoffman,
4027Paul Marquess,
4028Peter Saint-Andre,
4029Peter Watkins,
4030Phil Archer,
4031Phillip Hallam-Baker,
4032Poul-Henning Kamp,
4033Preethi Natarajan,
4034Reto Bachmann-Gmuer,
4035Richard Cyganiak,
4036Robert Brewer,
4037Robert Collins,
4038Robert O'Callahan,
4039Robert Olofsson,
4040Robert Sayre,
4041Robert Siemer,
4042Robert de Wilde,
4043Roberto Javier Godoy,
4044Ronny Widjaja,
4045S. Mike Dierken,
4046Salvatore Loreto,
4047Sam Johnston,
4048Sam Ruby,
4049Scott Lawrence (for maintaining the original issues list),
4050Sean B. Palmer,
4051Shane McCarron,
4052Stefan Eissing,
4053Stefan Tilkov,
4054Stefanos Harhalakis,
4055Stephane Bortzmeyer,
4056Stuart Williams,
4057Subbu Allamaraju,
4058Sylvain Hellegouarch,
4059Tapan Divekar,
4060Thomas Broyer,
4061Thomas Nordin,
4062Thomas Roessler,
4063Tim Morgan,
4064Tim Olsen,
4065Travis Snoozy,
4066Tyler Close,
4067Vincent Murphy,
4068Wenbo Zhu,
4069Werner Baumann,
4070Wilbur Streett,
4071Wilfredo Sanchez Vega,
4072William A. Rowe Jr.,
4073William Chan,
4074Willy Tarreau,
4075Xiaoshu Wang,
4076Yaron Goland,
4077Yngve Nysaeter Pettersen,
4078Yogesh Bang,
4079Yutaka Oiwa, and
4080Zed A. Shaw.
4081</t>
4082<?ENDINC acks ?>
4083</section>
4084
4085</middle>
4086<back>
4087
4088<references title="Normative References">
4089
4090<reference anchor="ISO-8859-1">
4091  <front>
4092    <title>
4093     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4094    </title>
4095    <author>
4096      <organization>International Organization for Standardization</organization>
4097    </author>
4098    <date year="1998"/>
4099  </front>
4100  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4101</reference>
4102
4103<reference anchor="Part2">
4104  <front>
4105    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4106    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4107      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4108      <address><email>fielding@gbiv.com</email></address>
4109    </author>
4110    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4111      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4112      <address><email>jg@freedesktop.org</email></address>
4113    </author>
4114    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4115      <organization abbrev="HP">Hewlett-Packard Company</organization>
4116      <address><email>JeffMogul@acm.org</email></address>
4117    </author>
4118    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4119      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4120      <address><email>henrikn@microsoft.com</email></address>
4121    </author>
4122    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4123      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4124      <address><email>LMM@acm.org</email></address>
4125    </author>
4126    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4127      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4128      <address><email>paulle@microsoft.com</email></address>
4129    </author>
4130    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4131      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4132      <address><email>timbl@w3.org</email></address>
4133    </author>
4134    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4135      <organization abbrev="W3C">World Wide Web Consortium</organization>
4136      <address><email>ylafon@w3.org</email></address>
4137    </author>
4138    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4139      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4140      <address><email>julian.reschke@greenbytes.de</email></address>
4141    </author>
4142    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4143  </front>
4144  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4145  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4146</reference>
4147
4148<reference anchor="Part3">
4149  <front>
4150    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4151    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4152      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4153      <address><email>fielding@gbiv.com</email></address>
4154    </author>
4155    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4156      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4157      <address><email>jg@freedesktop.org</email></address>
4158    </author>
4159    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4160      <organization abbrev="HP">Hewlett-Packard Company</organization>
4161      <address><email>JeffMogul@acm.org</email></address>
4162    </author>
4163    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4164      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4165      <address><email>henrikn@microsoft.com</email></address>
4166    </author>
4167    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4168      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4169      <address><email>LMM@acm.org</email></address>
4170    </author>
4171    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4172      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4173      <address><email>paulle@microsoft.com</email></address>
4174    </author>
4175    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4176      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4177      <address><email>timbl@w3.org</email></address>
4178    </author>
4179    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4180      <organization abbrev="W3C">World Wide Web Consortium</organization>
4181      <address><email>ylafon@w3.org</email></address>
4182    </author>
4183    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4184      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4185      <address><email>julian.reschke@greenbytes.de</email></address>
4186    </author>
4187    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4188  </front>
4189  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4190  <x:source href="p3-payload.xml" basename="p3-payload"/>
4191</reference>
4192
4193<reference anchor="Part6">
4194  <front>
4195    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4196    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4197      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4198      <address><email>fielding@gbiv.com</email></address>
4199    </author>
4200    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4201      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4202      <address><email>jg@freedesktop.org</email></address>
4203    </author>
4204    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4205      <organization abbrev="HP">Hewlett-Packard Company</organization>
4206      <address><email>JeffMogul@acm.org</email></address>
4207    </author>
4208    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4209      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4210      <address><email>henrikn@microsoft.com</email></address>
4211    </author>
4212    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4213      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4214      <address><email>LMM@acm.org</email></address>
4215    </author>
4216    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4217      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4218      <address><email>paulle@microsoft.com</email></address>
4219    </author>
4220    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4221      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4222      <address><email>timbl@w3.org</email></address>
4223    </author>
4224    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4225      <organization abbrev="W3C">World Wide Web Consortium</organization>
4226      <address><email>ylafon@w3.org</email></address>
4227    </author>
4228    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4229      <organization>Rackspace</organization>
4230      <address><email>mnot@mnot.net</email></address>
4231    </author>
4232    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4233      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4234      <address><email>julian.reschke@greenbytes.de</email></address>
4235    </author>
4236    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4237  </front>
4238  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4239  <x:source href="p6-cache.xml" basename="p6-cache"/>
4240</reference>
4241
4242<reference anchor="RFC5234">
4243  <front>
4244    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4245    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4246      <organization>Brandenburg InternetWorking</organization>
4247      <address>
4248        <email>dcrocker@bbiw.net</email>
4249      </address> 
4250    </author>
4251    <author initials="P." surname="Overell" fullname="Paul Overell">
4252      <organization>THUS plc.</organization>
4253      <address>
4254        <email>paul.overell@thus.net</email>
4255      </address>
4256    </author>
4257    <date month="January" year="2008"/>
4258  </front>
4259  <seriesInfo name="STD" value="68"/>
4260  <seriesInfo name="RFC" value="5234"/>
4261</reference>
4262
4263<reference anchor="RFC2119">
4264  <front>
4265    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4266    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4267      <organization>Harvard University</organization>
4268      <address><email>sob@harvard.edu</email></address>
4269    </author>
4270    <date month="March" year="1997"/>
4271  </front>
4272  <seriesInfo name="BCP" value="14"/>
4273  <seriesInfo name="RFC" value="2119"/>
4274</reference>
4275
4276<reference anchor="RFC3986">
4277 <front>
4278  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4279  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4280    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4281    <address>
4282       <email>timbl@w3.org</email>
4283       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4284    </address>
4285  </author>
4286  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4287    <organization abbrev="Day Software">Day Software</organization>
4288    <address>
4289      <email>fielding@gbiv.com</email>
4290      <uri>http://roy.gbiv.com/</uri>
4291    </address>
4292  </author>
4293  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4294    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4295    <address>
4296      <email>LMM@acm.org</email>
4297      <uri>http://larry.masinter.net/</uri>
4298    </address>
4299  </author>
4300  <date month='January' year='2005'></date>
4301 </front>
4302 <seriesInfo name="STD" value="66"/>
4303 <seriesInfo name="RFC" value="3986"/>
4304</reference>
4305
4306<reference anchor="USASCII">
4307  <front>
4308    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4309    <author>
4310      <organization>American National Standards Institute</organization>
4311    </author>
4312    <date year="1986"/>
4313  </front>
4314  <seriesInfo name="ANSI" value="X3.4"/>
4315</reference>
4316
4317<reference anchor="RFC1950">
4318  <front>
4319    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4320    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4321      <organization>Aladdin Enterprises</organization>
4322      <address><email>ghost@aladdin.com</email></address>
4323    </author>
4324    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4325    <date month="May" year="1996"/>
4326  </front>
4327  <seriesInfo name="RFC" value="1950"/>
4328  <!--<annotation>
4329    RFC 1950 is an Informational RFC, thus it might be less stable than
4330    this specification. On the other hand, this downward reference was
4331    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4332    therefore it is unlikely to cause problems in practice. See also
4333    <xref target="BCP97"/>.
4334  </annotation>-->
4335</reference>
4336
4337<reference anchor="RFC1951">
4338  <front>
4339    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4340    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4341      <organization>Aladdin Enterprises</organization>
4342      <address><email>ghost@aladdin.com</email></address>
4343    </author>
4344    <date month="May" year="1996"/>
4345  </front>
4346  <seriesInfo name="RFC" value="1951"/>
4347  <!--<annotation>
4348    RFC 1951 is an Informational RFC, thus it might be less stable than
4349    this specification. On the other hand, this downward reference was
4350    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4351    therefore it is unlikely to cause problems in practice. See also
4352    <xref target="BCP97"/>.
4353  </annotation>-->
4354</reference>
4355
4356<reference anchor="RFC1952">
4357  <front>
4358    <title>GZIP file format specification version 4.3</title>
4359    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4360      <organization>Aladdin Enterprises</organization>
4361      <address><email>ghost@aladdin.com</email></address>
4362    </author>
4363    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4364      <address><email>gzip@prep.ai.mit.edu</email></address>
4365    </author>
4366    <author initials="M." surname="Adler" fullname="Mark Adler">
4367      <address><email>madler@alumni.caltech.edu</email></address>
4368    </author>
4369    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4370      <address><email>ghost@aladdin.com</email></address>
4371    </author>
4372    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4373      <address><email>randeg@alumni.rpi.edu</email></address>
4374    </author>
4375    <date month="May" year="1996"/>
4376  </front>
4377  <seriesInfo name="RFC" value="1952"/>
4378  <!--<annotation>
4379    RFC 1952 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</references>
4388
4389<references title="Informative References">
4390
4391<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4392  <front>
4393    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4394    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4395    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4396    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4397    <author initials="H." surname="Lie" fullname="H. Lie"/>
4398    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4399    <date year="1997" month="September"/>
4400  </front>
4401  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4402</reference>
4403
4404<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4405  <front>
4406    <title>Improving HTTP Latency</title>
4407    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4408    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4409    <date year="1995" month="December"/>
4410  </front>
4411  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4412</reference>
4413
4414<reference anchor='RFC1919'>
4415  <front>
4416    <title>Classical versus Transparent IP Proxies</title>
4417    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4418      <address><email>mchatel@pax.eunet.ch</email></address>
4419    </author>
4420    <date year='1996' month='March' />
4421  </front>
4422  <seriesInfo name='RFC' value='1919' />
4423</reference>
4424
4425<reference anchor="RFC1945">
4426  <front>
4427    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4428    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4429      <organization>MIT, Laboratory for Computer Science</organization>
4430      <address><email>timbl@w3.org</email></address>
4431    </author>
4432    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4433      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4434      <address><email>fielding@ics.uci.edu</email></address>
4435    </author>
4436    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4437      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4438      <address><email>frystyk@w3.org</email></address>
4439    </author>
4440    <date month="May" year="1996"/>
4441  </front>
4442  <seriesInfo name="RFC" value="1945"/>
4443</reference>
4444
4445<reference anchor="RFC2045">
4446  <front>
4447    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4448    <author initials="N." surname="Freed" fullname="Ned Freed">
4449      <organization>Innosoft International, Inc.</organization>
4450      <address><email>ned@innosoft.com</email></address>
4451    </author>
4452    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4453      <organization>First Virtual Holdings</organization>
4454      <address><email>nsb@nsb.fv.com</email></address>
4455    </author>
4456    <date month="November" year="1996"/>
4457  </front>
4458  <seriesInfo name="RFC" value="2045"/>
4459</reference>
4460
4461<reference anchor="RFC2047">
4462  <front>
4463    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4464    <author initials="K." surname="Moore" fullname="Keith Moore">
4465      <organization>University of Tennessee</organization>
4466      <address><email>moore@cs.utk.edu</email></address>
4467    </author>
4468    <date month="November" year="1996"/>
4469  </front>
4470  <seriesInfo name="RFC" value="2047"/>
4471</reference>
4472
4473<reference anchor="RFC2068">
4474  <front>
4475    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4476    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4477      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4478      <address><email>fielding@ics.uci.edu</email></address>
4479    </author>
4480    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4481      <organization>MIT Laboratory for Computer Science</organization>
4482      <address><email>jg@w3.org</email></address>
4483    </author>
4484    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4485      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4486      <address><email>mogul@wrl.dec.com</email></address>
4487    </author>
4488    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4489      <organization>MIT Laboratory for Computer Science</organization>
4490      <address><email>frystyk@w3.org</email></address>
4491    </author>
4492    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4493      <organization>MIT Laboratory for Computer Science</organization>
4494      <address><email>timbl@w3.org</email></address>
4495    </author>
4496    <date month="January" year="1997"/>
4497  </front>
4498  <seriesInfo name="RFC" value="2068"/>
4499</reference>
4500
4501<reference anchor="RFC2145">
4502  <front>
4503    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4504    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4505      <organization>Western Research Laboratory</organization>
4506      <address><email>mogul@wrl.dec.com</email></address>
4507    </author>
4508    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4509      <organization>Department of Information and Computer Science</organization>
4510      <address><email>fielding@ics.uci.edu</email></address>
4511    </author>
4512    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4513      <organization>MIT Laboratory for Computer Science</organization>
4514      <address><email>jg@w3.org</email></address>
4515    </author>
4516    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4517      <organization>W3 Consortium</organization>
4518      <address><email>frystyk@w3.org</email></address>
4519    </author>
4520    <date month="May" year="1997"/>
4521  </front>
4522  <seriesInfo name="RFC" value="2145"/>
4523</reference>
4524
4525<reference anchor="RFC2616">
4526  <front>
4527    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4528    <author initials="R." surname="Fielding" fullname="R. Fielding">
4529      <organization>University of California, Irvine</organization>
4530      <address><email>fielding@ics.uci.edu</email></address>
4531    </author>
4532    <author initials="J." surname="Gettys" fullname="J. Gettys">
4533      <organization>W3C</organization>
4534      <address><email>jg@w3.org</email></address>
4535    </author>
4536    <author initials="J." surname="Mogul" fullname="J. Mogul">
4537      <organization>Compaq Computer Corporation</organization>
4538      <address><email>mogul@wrl.dec.com</email></address>
4539    </author>
4540    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4541      <organization>MIT Laboratory for Computer Science</organization>
4542      <address><email>frystyk@w3.org</email></address>
4543    </author>
4544    <author initials="L." surname="Masinter" fullname="L. Masinter">
4545      <organization>Xerox Corporation</organization>
4546      <address><email>masinter@parc.xerox.com</email></address>
4547    </author>
4548    <author initials="P." surname="Leach" fullname="P. Leach">
4549      <organization>Microsoft Corporation</organization>
4550      <address><email>paulle@microsoft.com</email></address>
4551    </author>
4552    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4553      <organization>W3C</organization>
4554      <address><email>timbl@w3.org</email></address>
4555    </author>
4556    <date month="June" year="1999"/>
4557  </front>
4558  <seriesInfo name="RFC" value="2616"/>
4559</reference>
4560
4561<reference anchor='RFC2817'>
4562  <front>
4563    <title>Upgrading to TLS Within HTTP/1.1</title>
4564    <author initials='R.' surname='Khare' fullname='R. Khare'>
4565      <organization>4K Associates / UC Irvine</organization>
4566      <address><email>rohit@4K-associates.com</email></address>
4567    </author>
4568    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4569      <organization>Agranat Systems, Inc.</organization>
4570      <address><email>lawrence@agranat.com</email></address>
4571    </author>
4572    <date year='2000' month='May' />
4573  </front>
4574  <seriesInfo name='RFC' value='2817' />
4575</reference>
4576
4577<reference anchor='RFC2818'>
4578  <front>
4579    <title>HTTP Over TLS</title>
4580    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4581      <organization>RTFM, Inc.</organization>
4582      <address><email>ekr@rtfm.com</email></address>
4583    </author>
4584    <date year='2000' month='May' />
4585  </front>
4586  <seriesInfo name='RFC' value='2818' />
4587</reference>
4588
4589<reference anchor='RFC2965'>
4590  <front>
4591    <title>HTTP State Management Mechanism</title>
4592    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4593      <organization>Bell Laboratories, Lucent Technologies</organization>
4594      <address><email>dmk@bell-labs.com</email></address>
4595    </author>
4596    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4597      <organization>Epinions.com, Inc.</organization>
4598      <address><email>lou@montulli.org</email></address>
4599    </author>
4600    <date year='2000' month='October' />
4601  </front>
4602  <seriesInfo name='RFC' value='2965' />
4603</reference>
4604
4605<reference anchor='RFC3040'>
4606  <front>
4607    <title>Internet Web Replication and Caching Taxonomy</title>
4608    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4609      <organization>Equinix, Inc.</organization>
4610    </author>
4611    <author initials='I.' surname='Melve' fullname='I. Melve'>
4612      <organization>UNINETT</organization>
4613    </author>
4614    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4615      <organization>CacheFlow Inc.</organization>
4616    </author>
4617    <date year='2001' month='January' />
4618  </front>
4619  <seriesInfo name='RFC' value='3040' />
4620</reference>
4621
4622<reference anchor='RFC3864'>
4623  <front>
4624    <title>Registration Procedures for Message Header Fields</title>
4625    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4626      <organization>Nine by Nine</organization>
4627      <address><email>GK-IETF@ninebynine.org</email></address>
4628    </author>
4629    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4630      <organization>BEA Systems</organization>
4631      <address><email>mnot@pobox.com</email></address>
4632    </author>
4633    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4634      <organization>HP Labs</organization>
4635      <address><email>JeffMogul@acm.org</email></address>
4636    </author>
4637    <date year='2004' month='September' />
4638  </front>
4639  <seriesInfo name='BCP' value='90' />
4640  <seriesInfo name='RFC' value='3864' />
4641</reference>
4642
4643<reference anchor='RFC4033'>
4644  <front>
4645    <title>DNS Security Introduction and Requirements</title>
4646    <author initials='R.' surname='Arends' fullname='R. Arends'/>
4647    <author initials='R.' surname='Austein' fullname='R. Austein'/>
4648    <author initials='M.' surname='Larson' fullname='M. Larson'/>
4649    <author initials='D.' surname='Massey' fullname='D. Massey'/>
4650    <author initials='S.' surname='Rose' fullname='S. Rose'/>
4651    <date year='2005' month='March' />
4652  </front>
4653  <seriesInfo name='RFC' value='4033' />
4654</reference>
4655
4656<reference anchor="RFC4288">
4657  <front>
4658    <title>Media Type Specifications and Registration Procedures</title>
4659    <author initials="N." surname="Freed" fullname="N. Freed">
4660      <organization>Sun Microsystems</organization>
4661      <address>
4662        <email>ned.freed@mrochek.com</email>
4663      </address>
4664    </author>
4665    <author initials="J." surname="Klensin" fullname="J. Klensin">
4666      <address>
4667        <email>klensin+ietf@jck.com</email>
4668      </address>
4669    </author>
4670    <date year="2005" month="December"/>
4671  </front>
4672  <seriesInfo name="BCP" value="13"/>
4673  <seriesInfo name="RFC" value="4288"/>
4674</reference>
4675
4676<reference anchor='RFC4395'>
4677  <front>
4678    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4679    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4680      <organization>AT&amp;T Laboratories</organization>
4681      <address>
4682        <email>tony+urireg@maillennium.att.com</email>
4683      </address>
4684    </author>
4685    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4686      <organization>Qualcomm, Inc.</organization>
4687      <address>
4688        <email>hardie@qualcomm.com</email>
4689      </address>
4690    </author>
4691    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4692      <organization>Adobe Systems</organization>
4693      <address>
4694        <email>LMM@acm.org</email>
4695      </address>
4696    </author>
4697    <date year='2006' month='February' />
4698  </front>
4699  <seriesInfo name='BCP' value='115' />
4700  <seriesInfo name='RFC' value='4395' />
4701</reference>
4702
4703<reference anchor='RFC4559'>
4704  <front>
4705    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4706    <author initials='K.' surname='Jaganathan' fullname='K. Jaganathan'/>
4707    <author initials='L.' surname='Zhu' fullname='L. Zhu'/>
4708    <author initials='J.' surname='Brezak' fullname='J. Brezak'/>
4709    <date year='2006' month='June' />
4710  </front>
4711  <seriesInfo name='RFC' value='4559' />
4712</reference>
4713
4714<reference anchor='RFC5226'>
4715  <front>
4716    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4717    <author initials='T.' surname='Narten' fullname='T. Narten'>
4718      <organization>IBM</organization>
4719      <address><email>narten@us.ibm.com</email></address>
4720    </author>
4721    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4722      <organization>Google</organization>
4723      <address><email>Harald@Alvestrand.no</email></address>
4724    </author>
4725    <date year='2008' month='May' />
4726  </front>
4727  <seriesInfo name='BCP' value='26' />
4728  <seriesInfo name='RFC' value='5226' />
4729</reference>
4730
4731<reference anchor="RFC5322">
4732  <front>
4733    <title>Internet Message Format</title>
4734    <author initials="P." surname="Resnick" fullname="P. Resnick">
4735      <organization>Qualcomm Incorporated</organization>
4736    </author>
4737    <date year="2008" month="October"/>
4738  </front> 
4739  <seriesInfo name="RFC" value="5322"/>
4740</reference>
4741
4742<reference anchor="RFC6265">
4743  <front>
4744    <title>HTTP State Management Mechanism</title>
4745    <author initials="A." surname="Barth" fullname="Adam Barth">
4746      <organization abbrev="U.C. Berkeley">
4747        University of California, Berkeley
4748      </organization>
4749      <address><email>abarth@eecs.berkeley.edu</email></address>
4750    </author>
4751    <date year="2011" month="April" />
4752  </front>
4753  <seriesInfo name="RFC" value="6265"/>
4754</reference>
4755
4756<!--<reference anchor='BCP97'>
4757  <front>
4758    <title>Handling Normative References to Standards-Track Documents</title>
4759    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4760      <address>
4761        <email>klensin+ietf@jck.com</email>
4762      </address>
4763    </author>
4764    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4765      <organization>MIT</organization>
4766      <address>
4767        <email>hartmans-ietf@mit.edu</email>
4768      </address>
4769    </author>
4770    <date year='2007' month='June' />
4771  </front>
4772  <seriesInfo name='BCP' value='97' />
4773  <seriesInfo name='RFC' value='4897' />
4774</reference>-->
4775
4776<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4777  <front>
4778    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4779    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4780    <date year="2001" month="November"/>
4781  </front>
4782  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4783</reference>
4784
4785<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4786  <front>
4787    <title>Analysis of HTTP Performance Problems</title>
4788    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4789    <date/>
4790  </front>
4791</reference>
4792
4793<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4794  <front>
4795  <title>Analysis of HTTP Performance</title>
4796  <author initials="J." surname="Touch" fullname="Joe Touch">
4797    <organization>USC/Information Sciences Institute</organization>
4798    <address><email>touch@isi.edu</email></address>
4799  </author>
4800  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4801    <organization>USC/Information Sciences Institute</organization>
4802    <address><email>johnh@isi.edu</email></address>
4803  </author>
4804  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4805    <organization>USC/Information Sciences Institute</organization>
4806    <address><email>katia@isi.edu</email></address>
4807  </author>
4808  <date year="1998" month="Aug"/>
4809  </front>
4810  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4811  <annotation>(original report dated Aug. 1996)</annotation>
4812</reference>
4813
4814</references>
4815
4816
4817<section title="HTTP Version History" anchor="compatibility">
4818<t>
4819   HTTP has been in use by the World-Wide Web global information initiative
4820   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4821   was a simple protocol for hypertext data transfer across the Internet
4822   with only a single request method (GET) and no metadata.
4823   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4824   methods and MIME-like messaging that could include metadata about the data
4825   transferred and modifiers on the request/response semantics. However,
4826   HTTP/1.0 did not sufficiently take into consideration the effects of
4827   hierarchical proxies, caching, the need for persistent connections, or
4828   name-based virtual hosts. The proliferation of incompletely-implemented
4829   applications calling themselves "HTTP/1.0" further necessitated a
4830   protocol version change in order for two communicating applications
4831   to determine each other's true capabilities.
4832</t>
4833<t>
4834   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4835   requirements that enable reliable implementations, adding only
4836   those new features that will either be safely ignored by an HTTP/1.0
4837   recipient or only sent when communicating with a party advertising
4838   compliance with HTTP/1.1.
4839</t>
4840<t>
4841   It is beyond the scope of a protocol specification to mandate
4842   compliance with previous versions. HTTP/1.1 was deliberately
4843   designed, however, to make supporting previous versions easy.
4844   We would expect a general-purpose HTTP/1.1 server to understand
4845   any valid request in the format of HTTP/1.0 and respond appropriately
4846   with an HTTP/1.1 message that only uses features understood (or
4847   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4848   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4849</t>
4850<t>
4851   Since HTTP/0.9 did not support header fields in a request,
4852   there is no mechanism for it to support name-based virtual
4853   hosts (selection of resource by inspection of the Host header
4854   field).  Any server that implements name-based virtual hosts
4855   ought to disable support for HTTP/0.9.  Most requests that
4856   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4857   requests wherein a buggy client failed to properly encode
4858   linear whitespace found in a URI reference and placed in
4859   the request-target.
4860</t>
4861
4862<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4863<t>
4864   This section summarizes major differences between versions HTTP/1.0
4865   and HTTP/1.1.
4866</t>
4867
4868<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4869<t>
4870   The requirements that clients and servers support the Host header
4871   field (<xref target="header.host"/>), report an error if it is
4872   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4873   are among the most important changes defined by HTTP/1.1.
4874</t>
4875<t>
4876   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4877   addresses and servers; there was no other established mechanism for
4878   distinguishing the intended server of a request than the IP address
4879   to which that request was directed. The Host header field was
4880   introduced during the development of HTTP/1.1 and, though it was
4881   quickly implemented by most HTTP/1.0 browsers, additional requirements
4882   were placed on all HTTP/1.1 requests in order to ensure complete
4883   adoption.  At the time of this writing, most HTTP-based services
4884   are dependent upon the Host header field for targeting requests.
4885</t>
4886</section>
4887
4888<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4889<t>
4890   For most implementations of HTTP/1.0, each connection is established
4891   by the client prior to the request and closed by the server after
4892   sending the response. However, some implementations implement the
4893   Keep-Alive version of persistent connections described in
4894   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4895</t>
4896<t>
4897   Some clients and servers might wish to be compatible with some
4898   previous implementations of persistent connections in HTTP/1.0
4899   clients and servers. Persistent connections in HTTP/1.0 are
4900   explicitly negotiated as they are not the default behavior. HTTP/1.0
4901   experimental implementations of persistent connections are faulty,
4902   and the new facilities in HTTP/1.1 are designed to rectify these
4903   problems. The problem was that some existing HTTP/1.0 clients might
4904   send Keep-Alive to a proxy server that doesn't understand
4905   Connection, which would then erroneously forward it to the next
4906   inbound server, which would establish the Keep-Alive connection and
4907   result in a hung HTTP/1.0 proxy waiting for the close on the
4908   response. The result is that HTTP/1.0 clients must be prevented from
4909   using Keep-Alive when talking to proxies.
4910</t>
4911<t>
4912   However, talking to proxies is the most important use of persistent
4913   connections, so that prohibition is clearly unacceptable. Therefore,
4914   we need some other mechanism for indicating a persistent connection
4915   is desired, which is safe to use even when talking to an old proxy
4916   that ignores Connection. Persistent connections are the default for
4917   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4918   declaring non-persistence. See <xref target="header.connection"/>.
4919</t>
4920</section>
4921</section>
4922
4923<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4924<t>
4925  Empty list elements in list productions have been deprecated.
4926  (<xref target="notation.abnf"/>)
4927</t>
4928<t>
4929  Rules about implicit linear whitespace between certain grammar productions
4930  have been removed; now it's only allowed when specifically pointed out
4931  in the ABNF.
4932  (<xref target="basic.rules"/>)
4933</t>
4934<t>
4935  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4936  sensitive. Restrict the version numbers to be single digits due to the fact
4937  that implementations are known to handle multi-digit version numbers
4938  incorrectly.
4939  (<xref target="http.version"/>)
4940</t>
4941<t>
4942  Require that invalid whitespace around field-names be rejected.
4943  (<xref target="header.fields"/>)
4944</t>
4945<t> 
4946  The NUL octet is no longer allowed in comment and quoted-string
4947  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4948  Non-ASCII content in header fields and reason phrase has been obsoleted and
4949  made opaque (the TEXT rule was removed).
4950  (<xref target="field.rules"/>)
4951</t>
4952<t>
4953  Require recipients to handle bogus Content-Length header fields as errors.
4954  (<xref target="message.body"/>)
4955</t>
4956<t>
4957  Remove reference to non-existent identity transfer-coding value tokens.
4958  (Sections <xref format="counter" target="message.body"/> and
4959  <xref format="counter" target="transfer.codings"/>)
4960</t>
4961<t>
4962  Update use of abs_path production from RFC 1808 to the path-absolute + query
4963  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4964  request method only.
4965  (<xref target="request-target"/>)
4966</t>
4967<t>
4968  Clarification that the chunk length does not include the count of the octets
4969  in the chunk header and trailer. Furthermore disallowed line folding
4970  in chunk extensions.
4971  (<xref target="chunked.encoding"/>)
4972</t>
4973<t>
4974  Remove hard limit of two connections per server.
4975  Remove requirement to retry a sequence of requests as long it was idempotent.
4976  Remove requirements about when servers are allowed to close connections
4977  prematurely.
4978  (<xref target="persistent.practical"/>)
4979</t>
4980<t>
4981  Remove requirement to retry requests under certain cirumstances when the
4982  server prematurely closes the connection.
4983  (<xref target="message.transmission.requirements"/>)
4984</t>
4985<t>
4986  Change ABNF productions for header fields to only define the field value.
4987  (<xref target="header.field.definitions"/>)
4988</t>
4989<t>
4990  Clarify exactly when close connection options must be sent.
4991  (<xref target="header.connection"/>)
4992</t>
4993<t>
4994  Define the semantics of the "Upgrade" header field in responses other than
4995  101 (this was incorporated from <xref target="RFC2817"/>).
4996  (<xref target="header.upgrade"/>)
4997</t>
4998</section>
4999</section>
5000
5001<?BEGININC p1-messaging.abnf-appendix ?>
5002<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5003<figure>
5004<artwork type="abnf" name="p1-messaging.parsed-abnf">
5005<x:ref>BWS</x:ref> = OWS
5006
5007<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5008<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5009 connection-token ] )
5010<x:ref>Content-Length</x:ref> = 1*DIGIT
5011
5012<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5013<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5014<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5015 ]
5016<x:ref>Host</x:ref> = uri-host [ ":" port ]
5017
5018<x:ref>Method</x:ref> = token
5019
5020<x:ref>OWS</x:ref> = *( SP / HTAB / obs-fold )
5021
5022<x:ref>RWS</x:ref> = 1*( SP / HTAB / obs-fold )
5023<x:ref>Reason-Phrase</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5024<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5025
5026<x:ref>Status-Code</x:ref> = 3DIGIT
5027<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5028
5029<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5030<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5031<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5032 transfer-coding ] )
5033
5034<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5035<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5036
5037<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5038 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5039 )
5040
5041<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5042<x:ref>attribute</x:ref> = token
5043<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5044
5045<x:ref>chunk</x:ref> = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5046<x:ref>chunk-data</x:ref> = 1*OCTET
5047<x:ref>chunk-ext</x:ref> = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5048<x:ref>chunk-ext-name</x:ref> = token
5049<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5050<x:ref>chunk-size</x:ref> = 1*HEXDIG
5051<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5052<x:ref>connection-token</x:ref> = token
5053<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5054 / %x2A-5B ; '*'-'['
5055 / %x5D-7E ; ']'-'~'
5056 / obs-text
5057
5058<x:ref>field-content</x:ref> = *( HTAB / SP / VCHAR / obs-text )
5059<x:ref>field-name</x:ref> = token
5060<x:ref>field-value</x:ref> = *( field-content / obs-fold )
5061
5062<x:ref>header-field</x:ref> = field-name ":" OWS field-value BWS
5063<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5064<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5065
5066<x:ref>last-chunk</x:ref> = 1*"0" [ chunk-ext ] CRLF
5067
5068<x:ref>message-body</x:ref> = *OCTET
5069
5070<x:ref>obs-fold</x:ref> = CRLF ( SP / HTAB )
5071<x:ref>obs-text</x:ref> = %x80-FF
5072
5073<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5074<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5075<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5076<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5077<x:ref>product</x:ref> = token [ "/" product-version ]
5078<x:ref>product-version</x:ref> = token
5079<x:ref>protocol-name</x:ref> = token
5080<x:ref>protocol-version</x:ref> = token
5081<x:ref>pseudonym</x:ref> = token
5082
5083<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5084 / %x5D-7E ; ']'-'~'
5085 / obs-text
5086<x:ref>qdtext-nf</x:ref> = HTAB / SP / "!" / %x23-5B ; '#'-'['
5087 / %x5D-7E ; ']'-'~'
5088 / obs-text
5089<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5090<x:ref>quoted-cpair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5091<x:ref>quoted-pair</x:ref> = "\" ( HTAB / SP / VCHAR / obs-text )
5092<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5093<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5094<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5095
5096<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5097<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5098<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5099<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5100 / authority
5101
5102<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5103 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5104<x:ref>start-line</x:ref> = Request-Line / Status-Line
5105
5106<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5107<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5108 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5109<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5110<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5111<x:ref>token</x:ref> = 1*tchar
5112<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5113<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5114 transfer-extension
5115<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5116<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5117
5118<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5119
5120<x:ref>value</x:ref> = word
5121
5122<x:ref>word</x:ref> = token / quoted-string
5123</artwork>
5124</figure>
5125<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5126; Chunked-Body defined but not used
5127; Connection defined but not used
5128; Content-Length defined but not used
5129; HTTP-message defined but not used
5130; Host defined but not used
5131; TE defined but not used
5132; Trailer defined but not used
5133; Transfer-Encoding defined but not used
5134; URI-reference defined but not used
5135; Upgrade defined but not used
5136; Via defined but not used
5137; http-URI defined but not used
5138; https-URI defined but not used
5139; partial-URI defined but not used
5140; special defined but not used
5141</artwork></figure></section>
5142<?ENDINC p1-messaging.abnf-appendix ?>
5143
5144<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5145
5146<section title="Since RFC 2616">
5147<t>
5148  Extracted relevant partitions from <xref target="RFC2616"/>.
5149</t>
5150</section>
5151
5152<section title="Since draft-ietf-httpbis-p1-messaging-00">
5153<t>
5154  Closed issues:
5155  <list style="symbols"> 
5156    <t>
5157      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5158      "HTTP Version should be case sensitive"
5159      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5160    </t>
5161    <t>
5162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5163      "'unsafe' characters"
5164      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5165    </t>
5166    <t>
5167      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5168      "Chunk Size Definition"
5169      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5170    </t>
5171    <t>
5172      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5173      "Message Length"
5174      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5175    </t>
5176    <t>
5177      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5178      "Media Type Registrations"
5179      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5180    </t>
5181    <t>
5182      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5183      "URI includes query"
5184      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5185    </t>
5186    <t>
5187      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5188      "No close on 1xx responses"
5189      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5190    </t>
5191    <t>
5192      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5193      "Remove 'identity' token references"
5194      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5195    </t>
5196    <t>
5197      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5198      "Import query BNF"
5199    </t>
5200    <t>
5201      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5202      "qdtext BNF"
5203    </t>
5204    <t>
5205      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5206      "Normative and Informative references"
5207    </t>
5208    <t>
5209      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5210      "RFC2606 Compliance"
5211    </t>
5212    <t>
5213      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5214      "RFC977 reference"
5215    </t>
5216    <t>
5217      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5218      "RFC1700 references"
5219    </t>
5220    <t>
5221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5222      "inconsistency in date format explanation"
5223    </t>
5224    <t>
5225      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5226      "Date reference typo"
5227    </t>
5228    <t>
5229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5230      "Informative references"
5231    </t>
5232    <t>
5233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5234      "ISO-8859-1 Reference"
5235    </t>
5236    <t>
5237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5238      "Normative up-to-date references"
5239    </t>
5240  </list>
5241</t>
5242<t>
5243  Other changes:
5244  <list style="symbols"> 
5245    <t>
5246      Update media type registrations to use RFC4288 template.
5247    </t>
5248    <t>
5249      Use names of RFC4234 core rules DQUOTE and HTAB,
5250      fix broken ABNF for chunk-data
5251      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5252    </t>
5253  </list>
5254</t>
5255</section>
5256
5257<section title="Since draft-ietf-httpbis-p1-messaging-01">
5258<t>
5259  Closed issues:
5260  <list style="symbols"> 
5261    <t>
5262      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5263      "Bodies on GET (and other) requests"
5264    </t>
5265    <t>
5266      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5267      "Updating to RFC4288"
5268    </t>
5269    <t>
5270      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5271      "Status Code and Reason Phrase"
5272    </t>
5273    <t>
5274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5275      "rel_path not used"
5276    </t>
5277  </list>
5278</t>
5279<t>
5280  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5281  <list style="symbols"> 
5282    <t>
5283      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5284      "trailer-part").
5285    </t>
5286    <t>
5287      Avoid underscore character in rule names ("http_URL" ->
5288      "http-URL", "abs_path" -> "path-absolute").
5289    </t>
5290    <t>
5291      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5292      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5293      have to be updated when switching over to RFC3986.
5294    </t>
5295    <t>
5296      Synchronize core rules with RFC5234.
5297    </t>
5298    <t>
5299      Get rid of prose rules that span multiple lines.
5300    </t>
5301    <t>
5302      Get rid of unused rules LOALPHA and UPALPHA.
5303    </t>
5304    <t>
5305      Move "Product Tokens" section (back) into Part 1, as "token" is used
5306      in the definition of the Upgrade header field.
5307    </t>
5308    <t>
5309      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5310    </t>
5311    <t>
5312      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5313    </t>
5314  </list>
5315</t>
5316</section>
5317
5318<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5319<t>
5320  Closed issues:
5321  <list style="symbols"> 
5322    <t>
5323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5324      "HTTP-date vs. rfc1123-date"
5325    </t>
5326    <t>
5327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5328      "WS in quoted-pair"
5329    </t>
5330  </list>
5331</t>
5332<t>
5333  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5334  <list style="symbols"> 
5335    <t>
5336      Reference RFC 3984, and update header field registrations for headers defined
5337      in this document.
5338    </t>
5339  </list>
5340</t>
5341<t>
5342  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5343  <list style="symbols"> 
5344    <t>
5345      Replace string literals when the string really is case-sensitive (HTTP-Version).
5346    </t>
5347  </list>
5348</t>
5349</section>
5350
5351<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5352<t>
5353  Closed issues:
5354  <list style="symbols"> 
5355    <t>
5356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5357      "Connection closing"
5358    </t>
5359    <t>
5360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5361      "Move registrations and registry information to IANA Considerations"
5362    </t>
5363    <t>
5364      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5365      "need new URL for PAD1995 reference"
5366    </t>
5367    <t>
5368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5369      "IANA Considerations: update HTTP URI scheme registration"
5370    </t>
5371    <t>
5372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5373      "Cite HTTPS URI scheme definition"
5374    </t>
5375    <t>
5376      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5377      "List-type headers vs Set-Cookie"
5378    </t>
5379  </list>
5380</t>
5381<t>
5382  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5383  <list style="symbols"> 
5384    <t>
5385      Replace string literals when the string really is case-sensitive (HTTP-Date).
5386    </t>
5387    <t>
5388      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5389    </t>
5390  </list>
5391</t>
5392</section>
5393
5394<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5395<t>
5396  Closed issues:
5397  <list style="symbols"> 
5398    <t>
5399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5400      "Out-of-date reference for URIs"
5401    </t>
5402    <t>
5403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5404      "RFC 2822 is updated by RFC 5322"
5405    </t>
5406  </list>
5407</t>
5408<t>
5409  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5410  <list style="symbols"> 
5411    <t>
5412      Use "/" instead of "|" for alternatives.
5413    </t>
5414    <t>
5415      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5416    </t>
5417    <t>
5418      Only reference RFC 5234's core rules.
5419    </t>
5420    <t>
5421      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5422      whitespace ("OWS") and required whitespace ("RWS").
5423    </t>
5424    <t>
5425      Rewrite ABNFs to spell out whitespace rules, factor out
5426      header field value format definitions.
5427    </t>
5428  </list>
5429</t>
5430</section>
5431
5432<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5433<t>
5434  Closed issues:
5435  <list style="symbols"> 
5436    <t>
5437      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5438      "Header LWS"
5439    </t>
5440    <t>
5441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5442      "Sort 1.3 Terminology"
5443    </t>
5444    <t>
5445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5446      "RFC2047 encoded words"
5447    </t>
5448    <t>
5449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5450      "Character Encodings in TEXT"
5451    </t>
5452    <t>
5453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5454      "Line Folding"
5455    </t>
5456    <t>
5457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5458      "OPTIONS * and proxies"
5459    </t>
5460    <t>
5461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5462      "Reason-Phrase BNF"
5463    </t>
5464    <t>
5465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5466      "Use of TEXT"
5467    </t>
5468    <t>
5469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5470      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5471    </t>
5472    <t>
5473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5474      "RFC822 reference left in discussion of date formats"
5475    </t>
5476  </list>
5477</t>
5478<t>
5479  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5480  <list style="symbols"> 
5481    <t>
5482      Rewrite definition of list rules, deprecate empty list elements.
5483    </t>
5484    <t>
5485      Add appendix containing collected and expanded ABNF.
5486    </t>
5487  </list>
5488</t>
5489<t>
5490  Other changes:
5491  <list style="symbols"> 
5492    <t>
5493      Rewrite introduction; add mostly new Architecture Section.
5494    </t>
5495    <t>
5496      Move definition of quality values from Part 3 into Part 1;
5497      make TE request header field grammar independent of accept-params (defined in Part 3).
5498    </t>
5499  </list>
5500</t>
5501</section>
5502
5503<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5504<t>
5505  Closed issues:
5506  <list style="symbols"> 
5507    <t>
5508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5509      "base for numeric protocol elements"
5510    </t>
5511    <t>
5512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5513      "comment ABNF"
5514    </t>
5515  </list>
5516</t>
5517<t>
5518  Partly resolved issues:
5519  <list style="symbols"> 
5520    <t>
5521      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5522      "205 Bodies" (took out language that implied that there might be
5523      methods for which a request body MUST NOT be included)
5524    </t>
5525    <t>
5526      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5527      "editorial improvements around HTTP-date"
5528    </t>
5529  </list>
5530</t>
5531</section>
5532
5533<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5534<t>
5535  Closed issues:
5536  <list style="symbols"> 
5537    <t>
5538      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5539      "Repeating single-value headers"
5540    </t>
5541    <t>
5542      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5543      "increase connection limit"
5544    </t>
5545    <t>
5546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5547      "IP addresses in URLs"
5548    </t>
5549    <t>
5550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5551      "take over HTTP Upgrade Token Registry"
5552    </t>
5553    <t>
5554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5555      "CR and LF in chunk extension values"
5556    </t>
5557    <t>
5558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5559      "HTTP/0.9 support"
5560    </t>
5561    <t>
5562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5563      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5564    </t>
5565    <t>
5566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5567      "move definitions of gzip/deflate/compress to part 1"
5568    </t>
5569    <t>
5570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5571      "disallow control characters in quoted-pair"
5572    </t>
5573  </list>
5574</t>
5575<t>
5576  Partly resolved issues:
5577  <list style="symbols"> 
5578    <t>
5579      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5580      "update IANA requirements wrt Transfer-Coding values" (add the
5581      IANA Considerations subsection)
5582    </t>
5583  </list>
5584</t>
5585</section>
5586
5587<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5588<t>
5589  Closed issues:
5590  <list style="symbols"> 
5591    <t>
5592      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5593      "header parsing, treatment of leading and trailing OWS"
5594    </t>
5595  </list>
5596</t>
5597<t>
5598  Partly resolved issues:
5599  <list style="symbols"> 
5600    <t>
5601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5602      "Placement of 13.5.1 and 13.5.2"
5603    </t>
5604    <t>
5605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5606      "use of term "word" when talking about header structure"
5607    </t>
5608  </list>
5609</t>
5610</section>
5611
5612<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5613<t>
5614  Closed issues:
5615  <list style="symbols"> 
5616    <t>
5617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5618      "Clarification of the term 'deflate'"
5619    </t>
5620    <t>
5621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5622      "OPTIONS * and proxies"
5623    </t>
5624    <t>
5625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5626      "MIME-Version not listed in P1, general header fields"
5627    </t>
5628    <t>
5629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5630      "IANA registry for content/transfer encodings"
5631    </t>
5632    <t>
5633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5634      "Case-sensitivity of HTTP-date"
5635    </t>
5636    <t>
5637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5638      "use of term "word" when talking about header structure"
5639    </t>
5640  </list>
5641</t>
5642<t>
5643  Partly resolved issues:
5644  <list style="symbols"> 
5645    <t>
5646      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5647      "Term for the requested resource's URI"
5648    </t>
5649  </list>
5650</t>
5651</section>
5652
5653<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5654<t>
5655  Closed issues:
5656  <list style="symbols">
5657    <t>
5658      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5659      "Connection Closing"
5660    </t>
5661    <t>
5662      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5663      "Delimiting messages with multipart/byteranges"
5664    </t>
5665    <t>
5666      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5667      "Handling multiple Content-Length headers"
5668    </t>
5669    <t>
5670      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5671      "Clarify entity / representation / variant terminology"
5672    </t>
5673    <t>
5674      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5675      "consider removing the 'changes from 2068' sections"
5676    </t>
5677  </list>
5678</t>
5679<t>
5680  Partly resolved issues:
5681  <list style="symbols"> 
5682    <t>
5683      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5684      "HTTP(s) URI scheme definitions"
5685    </t>
5686  </list>
5687</t>
5688</section>
5689
5690<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5691<t>
5692  Closed issues:
5693  <list style="symbols">
5694    <t>
5695      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5696      "Trailer requirements"
5697    </t>
5698    <t>
5699      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5700      "Text about clock requirement for caches belongs in p6"
5701    </t>
5702    <t>
5703      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5704      "effective request URI: handling of missing host in HTTP/1.0"
5705    </t>
5706    <t>
5707      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5708      "confusing Date requirements for clients"
5709    </t>
5710  </list>
5711</t>
5712<t>
5713  Partly resolved issues:
5714  <list style="symbols"> 
5715    <t>
5716      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5717      "Handling multiple Content-Length headers"
5718    </t>
5719  </list>
5720</t>
5721</section>
5722
5723<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5724<t>
5725  Closed issues:
5726  <list style="symbols">
5727    <t>
5728      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5729      "RFC2145 Normative"
5730    </t>
5731    <t>
5732      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5733      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5734    </t>
5735    <t>
5736      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5737      "define 'transparent' proxy"
5738    </t>
5739    <t>
5740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5741      "Header Classification"
5742    </t>
5743    <t>
5744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5745      "Is * usable as a request-uri for new methods?"
5746    </t>
5747    <t>
5748      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5749      "Migrate Upgrade details from RFC2817"
5750    </t>
5751    <t>
5752      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5753      "untangle ABNFs for header fields"
5754    </t>
5755    <t>
5756      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5757      "update RFC 2109 reference"
5758    </t>
5759  </list>
5760</t>
5761</section>
5762
5763<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5764<t>
5765  Closed issues:
5766  <list style="symbols">
5767    <t>
5768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5769      "Allow is not in 13.5.2"
5770    </t>
5771    <t>
5772      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5773      "Handling multiple Content-Length headers"
5774    </t>
5775    <t>
5776      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5777      "untangle ABNFs for header fields"
5778    </t>
5779    <t>
5780      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5781      "Content-Length ABNF broken"
5782    </t>
5783  </list>
5784</t>
5785</section>
5786
5787<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5788<t>
5789  Closed issues:
5790  <list style="symbols">
5791    <t>
5792      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5793      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5794    </t>
5795    <t>
5796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5797      "Recommend minimum sizes for protocol elements"
5798    </t>
5799    <t>
5800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5801      "Set expectations around buffering"
5802    </t>
5803    <t>
5804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5805      "Considering messages in isolation"
5806    </t>
5807  </list>
5808</t>
5809</section>
5810
5811<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5812<t>
5813  Closed issues:
5814  <list style="symbols">
5815    <t>
5816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5817      "DNS Spoofing / DNS Binding advice"
5818    </t>
5819    <t>
5820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5821      "move RFCs 2145, 2616, 2817 to Historic status"
5822    </t>
5823    <t>
5824      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5825      "\-escaping in quoted strings"
5826    </t>
5827    <t>
5828      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5829      "'Close' should be reserved in the HTTP header field registry"
5830    </t>
5831  </list>
5832</t>
5833</section>
5834
5835<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5836<t>
5837  Closed issues:
5838  <list style="symbols">
5839    <t>
5840      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5841      "Document HTTP's error-handling philosophy"
5842    </t>
5843    <t>
5844      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5845      "Explain header registration"
5846    </t>
5847    <t>
5848      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5849      "Revise Acknowledgements Sections"
5850    </t>
5851    <t>
5852      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5853      "Retrying Requests"
5854    </t>
5855    <t>
5856      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5857      "Closing the connection on server error"
5858    </t>
5859  </list>
5860</t>
5861</section>
5862
5863<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5864<t>
5865  Closed issues:
5866  <list style="symbols">
5867    <t>
5868      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5869      "Define non-final responses"
5870    </t>
5871    <t>
5872      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5873      "intended maturity level vs normative references"
5874    </t>
5875    <t>
5876      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5877      "Intermediary rewriting of queries"
5878    </t>
5879  </list>
5880</t>
5881</section>
5882
5883</section>
5884
5885</back>
5886</rfc>
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