source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1313

Last change on this file since 1313 was 1313, checked in by julian.reschke@…, 8 years ago

make HTTP version numbers single digits (see #273)

  • Property svn:eol-style set to native
File size: 249.3 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "June">
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='#errors.or.incomplete.response.cache.behavior' 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-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-203             "<xref target='Part2' x:rel='#status.203' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39]>
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="yes"?>
49<?rfc rfcedstyle="yes"?>
50<?rfc-ext allow-markup-in-artwork="yes" ?>
51<?rfc-ext include-references-in-index="yes" ?>
52<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="draft"
53     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
54     xmlns:x='http://purl.org/net/xml2rfc/ext'>
55<front>
56
57  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
58
59  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
60    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
61    <address>
62      <postal>
63        <street>345 Park Ave</street>
64        <city>San Jose</city>
65        <region>CA</region>
66        <code>95110</code>
67        <country>USA</country>
68      </postal>
69      <email>fielding@gbiv.com</email>
70      <uri>http://roy.gbiv.com/</uri>
71    </address>
72  </author>
73
74  <author initials="J." surname="Gettys" fullname="Jim Gettys">
75    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
76    <address>
77      <postal>
78        <street>21 Oak Knoll Road</street>
79        <city>Carlisle</city>
80        <region>MA</region>
81        <code>01741</code>
82        <country>USA</country>
83      </postal>
84      <email>jg@freedesktop.org</email>
85      <uri>http://gettys.wordpress.com/</uri>
86    </address>
87  </author>
88 
89  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
90    <organization abbrev="HP">Hewlett-Packard Company</organization>
91    <address>
92      <postal>
93        <street>HP Labs, Large Scale Systems Group</street>
94        <street>1501 Page Mill Road, MS 1177</street>
95        <city>Palo Alto</city>
96        <region>CA</region>
97        <code>94304</code>
98        <country>USA</country>
99      </postal>
100      <email>JeffMogul@acm.org</email>
101    </address>
102  </author>
103
104  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
105    <organization abbrev="Microsoft">Microsoft Corporation</organization>
106    <address>
107      <postal>
108        <street>1 Microsoft Way</street>
109        <city>Redmond</city>
110        <region>WA</region>
111        <code>98052</code>
112        <country>USA</country>
113      </postal>
114      <email>henrikn@microsoft.com</email>
115    </address>
116  </author>
117
118  <author initials="L." surname="Masinter" fullname="Larry Masinter">
119    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
120    <address>
121      <postal>
122        <street>345 Park Ave</street>
123        <city>San Jose</city>
124        <region>CA</region>
125        <code>95110</code>
126        <country>USA</country>
127      </postal>
128      <email>LMM@acm.org</email>
129      <uri>http://larry.masinter.net/</uri>
130    </address>
131  </author>
132 
133  <author initials="P." surname="Leach" fullname="Paul J. Leach">
134    <organization abbrev="Microsoft">Microsoft Corporation</organization>
135    <address>
136      <postal>
137        <street>1 Microsoft Way</street>
138        <city>Redmond</city>
139        <region>WA</region>
140        <code>98052</code>
141      </postal>
142      <email>paulle@microsoft.com</email>
143    </address>
144  </author>
145   
146  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
147    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
148    <address>
149      <postal>
150        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
151        <street>The Stata Center, Building 32</street>
152        <street>32 Vassar Street</street>
153        <city>Cambridge</city>
154        <region>MA</region>
155        <code>02139</code>
156        <country>USA</country>
157      </postal>
158      <email>timbl@w3.org</email>
159      <uri>http://www.w3.org/People/Berners-Lee/</uri>
160    </address>
161  </author>
162
163  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
164    <organization abbrev="W3C">World Wide Web Consortium</organization>
165    <address>
166      <postal>
167        <street>W3C / ERCIM</street>
168        <street>2004, rte des Lucioles</street>
169        <city>Sophia-Antipolis</city>
170        <region>AM</region>
171        <code>06902</code>
172        <country>France</country>
173      </postal>
174      <email>ylafon@w3.org</email>
175      <uri>http://www.raubacapeu.net/people/yves/</uri>
176    </address>
177  </author>
178
179  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
180    <organization abbrev="greenbytes">greenbytes GmbH</organization>
181    <address>
182      <postal>
183        <street>Hafenweg 16</street>
184        <city>Muenster</city><region>NW</region><code>48155</code>
185        <country>Germany</country>
186      </postal>
187      <phone>+49 251 2807760</phone>
188      <facsimile>+49 251 2807761</facsimile>
189      <email>julian.reschke@greenbytes.de</email>
190      <uri>http://greenbytes.de/tech/webdav/</uri>
191    </address>
192  </author>
193
194  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
195  <workgroup>HTTPbis Working Group</workgroup>
196
197<abstract>
198<t>
199   The Hypertext Transfer Protocol (HTTP) is an application-level
200   protocol for distributed, collaborative, hypertext information
201   systems. HTTP has been in use by the World Wide Web global information
202   initiative since 1990. This document is Part 1 of the seven-part specification
203   that defines the protocol referred to as "HTTP/1.1" and, taken together,
204   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
205   its associated terminology, defines the "http" and "https" Uniform
206   Resource Identifier (URI) schemes, defines the generic message syntax
207   and parsing requirements for HTTP message frames, and describes
208   general security concerns for implementations.
209</t>
210</abstract>
211
212<note title="Editorial Note (To be removed by RFC Editor)">
213  <t>
214    Discussion of this draft should take place on the HTTPBIS working group
215    mailing list (ietf-http-wg@w3.org), which is archived at
216    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
217  </t>
218  <t>
219    The current issues list is at
220    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
221    documents (including fancy diffs) can be found at
222    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
223  </t>
224  <t>
225    The changes in this draft are summarized in <xref target="changes.since.14"/>.
226  </t>
227</note>
228</front>
229<middle>
230<section title="Introduction" anchor="introduction">
231<t>
232   The Hypertext Transfer Protocol (HTTP) is an application-level
233   request/response protocol that uses extensible semantics and MIME-like
234   message payloads for flexible interaction with network-based hypertext
235   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
236   standard <xref target="RFC3986"/> to indicate the target resource and
237   relationships between resources.
238   Messages are passed in a format similar to that used by Internet mail
239   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
240   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
241   between HTTP and MIME messages).
242</t>
243<t>
244   HTTP is a generic interface protocol for information systems. It is
245   designed to hide the details of how a service is implemented by presenting
246   a uniform interface to clients that is independent of the types of
247   resources provided. Likewise, servers do not need to be aware of each
248   client's purpose: an HTTP request can be considered in isolation rather
249   than being associated with a specific type of client or a predetermined
250   sequence of application steps. The result is a protocol that can be used
251   effectively in many different contexts and for which implementations can
252   evolve independently over time.
253</t>
254<t>
255   HTTP is also designed for use as an intermediation protocol for translating
256   communication to and from non-HTTP information systems.
257   HTTP proxies and gateways can provide access to alternative information
258   services by translating their diverse protocols into a hypertext
259   format that can be viewed and manipulated by clients in the same way
260   as HTTP services.
261</t>
262<t>
263   One consequence of HTTP flexibility is that the protocol cannot be
264   defined in terms of what occurs behind the interface. Instead, we
265   are limited to defining the syntax of communication, the intent
266   of received communication, and the expected behavior of recipients.
267   If the communication is considered in isolation, then successful
268   actions ought to be reflected in corresponding changes to the
269   observable interface provided by servers. However, since multiple
270   clients might act in parallel and perhaps at cross-purposes, we
271   cannot require that such changes be observable beyond the scope
272   of a single response.
273</t>
274<t>
275   This document is Part 1 of the seven-part specification of HTTP,
276   defining the protocol referred to as "HTTP/1.1", obsoleting
277   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
278   Part 1 describes the architectural elements that are used or
279   referred to in HTTP, defines the "http" and "https" URI schemes,
280   describes overall network operation and connection management,
281   and defines HTTP message framing and forwarding requirements.
282   Our goal is to define all of the mechanisms necessary for HTTP message
283   handling that are independent of message semantics, thereby defining the
284   complete set of requirements for message parsers and
285   message-forwarding intermediaries.
286</t>
287
288<section title="Requirements" anchor="intro.requirements">
289<t>
290   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
291   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
292   document are to be interpreted as described in <xref target="RFC2119"/>.
293</t>
294<t>
295   An implementation is not compliant if it fails to satisfy one or more
296   of the "MUST" or "REQUIRED" level requirements for the protocols it
297   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
298   level and all the "SHOULD" level requirements for its protocols is said
299   to be "unconditionally compliant"; one that satisfies all the "MUST"
300   level requirements but not all the "SHOULD" level requirements for its
301   protocols is said to be "conditionally compliant".
302</t>
303</section>
304
305<section title="Syntax Notation" anchor="notation">
306<iref primary="true" item="Grammar" subitem="ALPHA"/>
307<iref primary="true" item="Grammar" subitem="CR"/>
308<iref primary="true" item="Grammar" subitem="CRLF"/>
309<iref primary="true" item="Grammar" subitem="CTL"/>
310<iref primary="true" item="Grammar" subitem="DIGIT"/>
311<iref primary="true" item="Grammar" subitem="DQUOTE"/>
312<iref primary="true" item="Grammar" subitem="HEXDIG"/>
313<iref primary="true" item="Grammar" subitem="LF"/>
314<iref primary="true" item="Grammar" subitem="OCTET"/>
315<iref primary="true" item="Grammar" subitem="SP"/>
316<iref primary="true" item="Grammar" subitem="VCHAR"/>
317<iref primary="true" item="Grammar" subitem="WSP"/>
318<t>
319   This specification uses the Augmented Backus-Naur Form (ABNF) notation
320   of <xref target="RFC5234"/>.
321</t>
322<t anchor="core.rules">
323  <x:anchor-alias value="ALPHA"/>
324  <x:anchor-alias value="CTL"/>
325  <x:anchor-alias value="CR"/>
326  <x:anchor-alias value="CRLF"/>
327  <x:anchor-alias value="DIGIT"/>
328  <x:anchor-alias value="DQUOTE"/>
329  <x:anchor-alias value="HEXDIG"/>
330  <x:anchor-alias value="LF"/>
331  <x:anchor-alias value="OCTET"/>
332  <x:anchor-alias value="SP"/>
333  <x:anchor-alias value="VCHAR"/>
334  <x:anchor-alias value="WSP"/>
335   The following core rules are included by
336   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
337   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
338   DIGIT (decimal 0-9), DQUOTE (double quote),
339   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
340   OCTET (any 8-bit sequence of data), SP (space),
341   VCHAR (any visible <xref target="USASCII"/> character),
342   and WSP (whitespace).
343</t>
344<t>
345   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
346   "obsolete" grammar rules that appear for historical reasons.
347</t>
348
349<section title="ABNF Extension: #rule" anchor="notation.abnf">
350<t>
351  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
352  improve readability.
353</t>
354<t>
355  A construct "#" is defined, similar to "*", for defining comma-delimited
356  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
357  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
358  comma (",") and optional whitespace (OWS,
359  <xref target="basic.rules"/>).   
360</t>
361<figure><preamble>
362  Thus,
363</preamble><artwork type="example">
364  1#element =&gt; element *( OWS "," OWS element )
365</artwork></figure>
366<figure><preamble>
367  and:
368</preamble><artwork type="example">
369  #element =&gt; [ 1#element ]
370</artwork></figure>
371<figure><preamble>
372  and for n &gt;= 1 and m &gt; 1:
373</preamble><artwork type="example">
374  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
375</artwork></figure>
376<t>
377  For compatibility with legacy list rules, recipients &SHOULD; accept empty
378  list elements. In other words, consumers would follow the list productions:
379</t>
380<figure><artwork type="example">
381  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
382 
383  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
384</artwork></figure>
385<t>
386  Note that empty elements do not contribute to the count of elements present,
387  though.
388</t>
389<t>
390  For example, given these ABNF productions:
391</t>
392<figure><artwork type="example">
393  example-list      = 1#example-list-elmt
394  example-list-elmt = token ; see <xref target="basic.rules"/> 
395</artwork></figure>
396<t>
397  Then these are valid values for example-list (not including the double
398  quotes, which are present for delimitation only):
399</t>
400<figure><artwork type="example">
401  "foo,bar"
402  " foo ,bar,"
403  "  foo , ,bar,charlie   "
404  "foo ,bar,   charlie "
405</artwork></figure>
406<t>
407  But these values would be invalid, as at least one non-empty element is
408  required:
409</t>
410<figure><artwork type="example">
411  ""
412  ","
413  ",   ,"
414</artwork></figure>
415<t>
416  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
417  expanded as explained above.
418</t>
419</section>
420
421<section title="Basic Rules" anchor="basic.rules">
422<t anchor="rule.CRLF">
423  <x:anchor-alias value="CRLF"/>
424   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
425   protocol elements other than the message-body
426   (see <xref target="tolerant.applications"/> for tolerant applications).
427</t>
428<t anchor="rule.LWS">
429   This specification uses three rules to denote the use of linear
430   whitespace: OWS (optional whitespace), RWS (required whitespace), and
431   BWS ("bad" whitespace).
432</t>
433<t>
434   The OWS rule is used where zero or more linear whitespace octets might
435   appear. OWS &SHOULD; either not be produced or be produced as a single
436   SP. Multiple OWS octets that occur within field-content &SHOULD;
437   be replaced with a single SP before interpreting the field value or
438   forwarding the message downstream.
439</t>
440<t>
441   RWS is used when at least one linear whitespace octet is required to
442   separate field tokens. RWS &SHOULD; be produced as a single SP.
443   Multiple RWS octets that occur within field-content &SHOULD; be
444   replaced with a single SP before interpreting the field value or
445   forwarding the message downstream.
446</t>
447<t>
448   BWS is used where the grammar allows optional whitespace for historical
449   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
450   recipients &MUST; accept such bad optional whitespace and remove it before
451   interpreting the field value or forwarding the message downstream.
452</t>
453<t anchor="rule.whitespace">
454  <x:anchor-alias value="BWS"/>
455  <x:anchor-alias value="OWS"/>
456  <x:anchor-alias value="RWS"/>
457  <x:anchor-alias value="obs-fold"/>
458</t>
459<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"/>
460  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
461                 ; "optional" whitespace
462  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
463                 ; "required" whitespace
464  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
465                 ; "bad" whitespace
466  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
467                 ; see <xref target="header.fields"/>
468</artwork></figure>
469<t anchor="rule.token.separators">
470  <x:anchor-alias value="tchar"/>
471  <x:anchor-alias value="token"/>
472  <x:anchor-alias value="special"/>
473  <x:anchor-alias value="word"/>
474   Many HTTP/1.1 header field values consist of words (token or quoted-string)
475   separated by whitespace or special characters. These special characters
476   &MUST; be in a quoted string to be used within a parameter value (as defined
477   in <xref target="transfer.codings"/>).
478</t>
479<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"/>
480  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
481
482  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
483<!--
484  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
485 -->
486  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
487                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
488                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
489                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
490
491  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
492                 / ";" / ":" / "\" / DQUOTE / "/" / "["
493                 / "]" / "?" / "=" / "{" / "}"
494</artwork></figure>
495<t anchor="rule.quoted-string">
496  <x:anchor-alias value="quoted-string"/>
497  <x:anchor-alias value="qdtext"/>
498  <x:anchor-alias value="obs-text"/>
499   A string of text is parsed as a single word if it is quoted using
500   double-quote marks.
501</t>
502<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"/>
503  <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>
504  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
505                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref> 
506  <x:ref>obs-text</x:ref>       = %x80-FF
507</artwork></figure>
508<t anchor="rule.quoted-pair">
509  <x:anchor-alias value="quoted-pair"/>
510   The backslash octet ("\") can be used as a single-octet
511   quoting mechanism within quoted-string constructs:
512</t>
513<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
514  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
515</artwork></figure>
516<t>
517   Senders &SHOULD-NOT; escape octets that do not require escaping
518   (i.e., other than DQUOTE and the backslash octet).
519</t>
520</section>
521
522</section>
523</section>
524
525<section title="HTTP-related architecture" anchor="architecture">
526<t>
527   HTTP was created for the World Wide Web architecture
528   and has evolved over time to support the scalability needs of a worldwide
529   hypertext system. Much of that architecture is reflected in the terminology
530   and syntax productions used to define HTTP.
531</t>
532
533<section title="Client/Server Messaging" anchor="operation">
534<iref primary="true" item="client"/>
535<iref primary="true" item="server"/>
536<iref primary="true" item="connection"/>
537<t>
538   HTTP is a stateless request/response protocol that operates by exchanging
539   messages across a reliable transport or session-layer
540   "<x:dfn>connection</x:dfn>". An HTTP "<x:dfn>client</x:dfn>" is a
541   program that establishes a connection to a server for the purpose of
542   sending one or more HTTP requests.  An HTTP "<x:dfn>server</x:dfn>" is a
543   program that accepts connections in order to service HTTP requests by
544   sending HTTP responses.
545</t>
546<iref primary="true" item="user agent"/>
547<iref primary="true" item="origin server"/>
548<iref primary="true" item="browser"/>
549<iref primary="true" item="spider"/>
550<iref primary="true" item="sender"/>
551<iref primary="true" item="recipient"/>
552<t>
553   Note that the terms client and server refer only to the roles that
554   these programs perform for a particular connection.  The same program
555   might act as a client on some connections and a server on others.  We use
556   the term "<x:dfn>user agent</x:dfn>" to refer to the program that initiates a request,
557   such as a WWW browser, editor, or spider (web-traversing robot), and
558   the term "<x:dfn>origin server</x:dfn>" to refer to the program that can originate
559   authoritative responses to a request.  For general requirements, we use
560   the term "<x:dfn>sender</x:dfn>" to refer to whichever component sent a given message
561   and the term "<x:dfn>recipient</x:dfn>" to refer to any component that receives the
562   message.
563</t>
564<t>
565   Most HTTP communication consists of a retrieval request (GET) for
566   a representation of some resource identified by a URI.  In the
567   simplest case, this might be accomplished via a single bidirectional
568   connection (===) between the user agent (UA) and the origin server (O).
569</t>
570<figure><artwork type="drawing">
571         request   &gt;
572    UA ======================================= O
573                                &lt;   response
574</artwork></figure>
575<iref primary="true" item="message"/>
576<iref primary="true" item="request"/>
577<iref primary="true" item="response"/>
578<t>
579   A client sends an HTTP request to the server in the form of a <x:dfn>request</x:dfn>
580   <x:dfn>message</x:dfn> (<xref target="request"/>), beginning with a method, URI, and
581   protocol version, followed by MIME-like header fields containing
582   request modifiers, client information, and payload metadata, an empty
583   line to indicate the end of the header section, and finally the payload
584   body (if any).
585</t>
586<t>
587   A server responds to the client's request by sending an HTTP <x:dfn>response</x:dfn>
588   <x:dfn>message</x:dfn> (<xref target="response"/>), beginning with a status line that
589   includes the protocol version, a success or error code, and textual
590   reason phrase, followed by MIME-like header fields containing server
591   information, resource metadata, and payload metadata, an empty line to
592   indicate the end of the header section, and finally the payload body (if any).
593</t>
594<t>
595   The following example illustrates a typical message exchange for a
596   GET request on the URI "http://www.example.com/hello.txt":
597</t>
598<figure><preamble>
599client request:
600</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
601GET /hello.txt HTTP/1.1
602User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
603Host: www.example.com
604Accept: */*
605
606</artwork></figure>
607<figure><preamble>
608server response:
609</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
610HTTP/1.1 200 OK
611Date: Mon, 27 Jul 2009 12:28:53 GMT
612Server: Apache
613Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
614ETag: "34aa387-d-1568eb00"
615Accept-Ranges: bytes
616Content-Length: <x:length-of target="exbody"/>
617Vary: Accept-Encoding
618Content-Type: text/plain
619
620<x:span anchor="exbody">Hello World!
621</x:span></artwork></figure>
622</section>
623
624<section title="Connections and Transport Independence" anchor="transport-independence">
625<t>
626   HTTP messaging is independent of the underlying transport or
627   session-layer connection protocol(s).  HTTP only presumes a reliable
628   transport with in-order delivery of requests and the corresponding
629   in-order delivery of responses.  The mapping of HTTP request and
630   response structures onto the data units of the underlying transport
631   protocol is outside the scope of this specification.
632</t>
633<t>
634   The specific connection protocols to be used for an interaction
635   are determined by client configuration and the target resource's URI.
636   For example, the "http" URI scheme
637   (<xref target="http.uri"/>) indicates a default connection of TCP
638   over IP, with a default TCP port of 80, but the client might be
639   configured to use a proxy via some other connection port or protocol
640   instead of using the defaults.
641</t>
642<t>
643   A connection might be used for multiple HTTP request/response exchanges,
644   as defined in <xref target="persistent.connections"/>.
645</t>
646</section>
647
648<section title="Intermediaries" anchor="intermediaries">
649<iref primary="true" item="intermediary"/>
650<t>
651   HTTP enables the use of intermediaries to satisfy requests through
652   a chain of connections.  There are three common forms of HTTP
653   <x:dfn>intermediary</x:dfn>: proxy, gateway, and tunnel.  In some cases,
654   a single intermediary might act as an origin server, proxy, gateway,
655   or tunnel, switching behavior based on the nature of each request.
656</t>
657<figure><artwork type="drawing">
658         &gt;             &gt;             &gt;             &gt;
659    <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>
660               &lt;             &lt;             &lt;             &lt;
661</artwork></figure>
662<t>
663   The figure above shows three intermediaries (A, B, and C) between the
664   user agent and origin server. A request or response message that
665   travels the whole chain will pass through four separate connections.
666   Some HTTP communication options
667   might apply only to the connection with the nearest, non-tunnel
668   neighbor, only to the end-points of the chain, or to all connections
669   along the chain. Although the diagram is linear, each participant might
670   be engaged in multiple, simultaneous communications. For example, B
671   might be receiving requests from many clients other than A, and/or
672   forwarding requests to servers other than C, at the same time that it
673   is handling A's request.
674</t>
675<t>
676<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
677<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
678   We use the terms "<x:dfn>upstream</x:dfn>" and "<x:dfn>downstream</x:dfn>"
679   to describe various requirements in relation to the directional flow of a
680   message: all messages flow from upstream to downstream.
681   Likewise, we use the terms inbound and outbound to refer to
682   directions in relation to the request path:
683   "<x:dfn>inbound</x:dfn>" means toward the origin server and
684   "<x:dfn>outbound</x:dfn>" means toward the user agent.
685</t>
686<t><iref primary="true" item="proxy"/>
687   A "<x:dfn>proxy</x:dfn>" is a message forwarding agent that is selected by the
688   client, usually via local configuration rules, to receive requests
689   for some type(s) of absolute URI and attempt to satisfy those
690   requests via translation through the HTTP interface.  Some translations
691   are minimal, such as for proxy requests for "http" URIs, whereas
692   other requests might require translation to and from entirely different
693   application-layer protocols. Proxies are often used to group an
694   organization's HTTP requests through a common intermediary for the
695   sake of security, annotation services, or shared caching.
696</t>
697<t>
698<iref primary="true" item="transforming proxy"/>
699<iref primary="true" item="non-transforming proxy"/>
700   An HTTP-to-HTTP proxy is called a "<x:dfn>transforming proxy</x:dfn>" if it is designed
701   or configured to modify request or response messages in a semantically
702   meaningful way (i.e., modifications, beyond those required by normal
703   HTTP processing, that change the message in a way that would be
704   significant to the original sender or potentially significant to
705   downstream recipients).  For example, a transforming proxy might be
706   acting as a shared annotation server (modifying responses to include
707   references to a local annotation database), a malware filter, a
708   format transcoder, or an intranet-to-Internet privacy filter.  Such
709   transformations are presumed to be desired by the client (or client
710   organization) that selected the proxy and are beyond the scope of
711   this specification.  However, when a proxy is not intended to transform
712   a given message, we use the term "<x:dfn>non-transforming proxy</x:dfn>" to target
713   requirements that preserve HTTP message semantics. See &status-203; and
714   &header-warning; for status and warning codes related to transformations.
715</t>
716<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
717<iref primary="true" item="accelerator"/>
718   A "<x:dfn>gateway</x:dfn>" (a.k.a., "<x:dfn>reverse proxy</x:dfn>")
719   is a receiving agent that acts
720   as a layer above some other server(s) and translates the received
721   requests to the underlying server's protocol.  Gateways are often
722   used to encapsulate legacy or untrusted information services, to
723   improve server performance through "<x:dfn>accelerator</x:dfn>" caching, and to
724   enable partitioning or load-balancing of HTTP services across
725   multiple machines.
726</t>
727<t>
728   A gateway behaves as an origin server on its outbound connection and
729   as a user agent on its inbound connection.
730   All HTTP requirements applicable to an origin server
731   also apply to the outbound communication of a gateway.
732   A gateway communicates with inbound servers using any protocol that
733   it desires, including private extensions to HTTP that are outside
734   the scope of this specification.  However, an HTTP-to-HTTP gateway
735   that wishes to interoperate with third-party HTTP servers &MUST;
736   comply with HTTP user agent requirements on the gateway's inbound
737   connection and &MUST; implement the Connection
738   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
739   header fields for both connections.
740</t>
741<t><iref primary="true" item="tunnel"/>
742   A "<x:dfn>tunnel</x:dfn>" acts as a blind relay between two connections
743   without changing the messages. Once active, a tunnel is not
744   considered a party to the HTTP communication, though the tunnel might
745   have been initiated by an HTTP request. A tunnel ceases to exist when
746   both ends of the relayed connection are closed. Tunnels are used to
747   extend a virtual connection through an intermediary, such as when
748   transport-layer security is used to establish private communication
749   through a shared firewall proxy.
750</t>
751<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
752<iref primary="true" item="captive portal"/>
753   In addition, there may exist network intermediaries that are not
754   considered part of the HTTP communication but nevertheless act as
755   filters or redirecting agents (usually violating HTTP semantics,
756   causing security problems, and otherwise making a mess of things).
757   Such a network intermediary, often referred to as an "<x:dfn>interception proxy</x:dfn>"
758   <xref target="RFC3040"/>, "<x:dfn>transparent proxy</x:dfn>" <xref target="RFC1919"/>,
759   or "<x:dfn>captive portal</x:dfn>",
760   differs from an HTTP proxy because it has not been selected by the client.
761   Instead, the network intermediary redirects outgoing TCP port 80 packets
762   (and occasionally other common port traffic) to an internal HTTP server.
763   Interception proxies are commonly found on public network access points,
764   as a means of enforcing account subscription prior to allowing use of
765   non-local Internet services, and within corporate firewalls to enforce
766   network usage policies.
767   They are indistinguishable from a man-in-the-middle attack.
768</t>
769</section>
770
771<section title="Caches" anchor="caches">
772<iref primary="true" item="cache"/>
773<t>
774   A "<x:dfn>cache</x:dfn>" is a local store of previous response messages and the
775   subsystem that controls its message storage, retrieval, and deletion.
776   A cache stores cacheable responses in order to reduce the response
777   time and network bandwidth consumption on future, equivalent
778   requests. Any client or server &MAY; employ a cache, though a cache
779   cannot be used by a server while it is acting as a tunnel.
780</t>
781<t>
782   The effect of a cache is that the request/response chain is shortened
783   if one of the participants along the chain has a cached response
784   applicable to that request. The following illustrates the resulting
785   chain if B has a cached copy of an earlier response from O (via C)
786   for a request which has not been cached by UA or A.
787</t>
788<figure><artwork type="drawing">
789            &gt;             &gt;
790       UA =========== A =========== B - - - - - - C - - - - - - O
791                  &lt;             &lt;
792</artwork></figure>
793<t><iref primary="true" item="cacheable"/>
794   A response is "<x:dfn>cacheable</x:dfn>" if a cache is allowed to store a copy of
795   the response message for use in answering subsequent requests.
796   Even when a response is cacheable, there might be additional
797   constraints placed by the client or by the origin server on when
798   that cached response can be used for a particular request. HTTP
799   requirements for cache behavior and cacheable responses are
800   defined in &caching-overview;
801</t>
802<t>
803   There are a wide variety of architectures and configurations
804   of caches and proxies deployed across the World Wide Web and
805   inside large organizations. These systems include national hierarchies
806   of proxy caches to save transoceanic bandwidth, systems that
807   broadcast or multicast cache entries, organizations that distribute
808   subsets of cached data via optical media, and so on.
809</t>
810</section>
811
812<section title="Protocol Versioning" anchor="http.version">
813  <x:anchor-alias value="HTTP-Version"/>
814  <x:anchor-alias value="HTTP-Prot-Name"/>
815<t>
816   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
817   versions of the protocol. This specification defines version "1.1".
818   The protocol version as a whole indicates the sender's compliance
819   with the set of requirements laid out in that version's corresponding
820   specification of HTTP.
821</t>
822<t>
823   The version of an HTTP message is indicated by an HTTP-Version field
824   in the first line of the message. HTTP-Version is case-sensitive.
825</t>
826<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
827  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" <x:ref>DIGIT</x:ref> "." <x:ref>DIGIT</x:ref>
828  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
829</artwork></figure>
830<t>
831   The HTTP version number consists of two decimal digits separated by a "."
832   (period or decimal point).  The first digit ("major version") indicates the
833   HTTP messaging syntax, whereas the second digit ("minor version") indicates
834   the highest minor version to which the sender is at least conditionally
835   compliant and able to understand for future communication.  The minor
836   version advertises the sender's communication capabilities even when the
837   sender is only using a backwards-compatible subset of the protocol,
838   thereby letting the recipient know that more advanced features can
839   be used in response (by servers) or in future requests (by clients).
840</t>
841<t>
842   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
843   <xref target="RFC1945"/> or a recipient whose version is unknown,
844   the HTTP/1.1 message is constructed such that it can be interpreted
845   as a valid HTTP/1.0 message if all of the newer features are ignored.
846   This specification places recipient-version requirements on some
847   new features so that a compliant sender will only use compatible
848   features until it has determined, through configuration or the
849   receipt of a message, that the recipient supports HTTP/1.1.
850</t>
851<t>
852   The interpretation of an HTTP header field does not change
853   between minor versions of the same major version, though the default
854   behavior of a recipient in the absence of such a field can change.
855   Unless specified otherwise, header fields defined in HTTP/1.1 are
856   defined for all versions of HTTP/1.x.  In particular, the Host and
857   Connection header fields ought to be implemented by all HTTP/1.x
858   implementations whether or not they advertise compliance with HTTP/1.1.
859</t>
860<t>
861   New header fields can be defined such that, when they are
862   understood by a recipient, they might override or enhance the
863   interpretation of previously defined header fields.  When an
864   implementation receives an unrecognized header field, the recipient
865   &MUST; ignore that header field for local processing regardless of
866   the message's HTTP version.  An unrecognized header field received
867   by a proxy &MUST; be forwarded downstream unless the header field's
868   field-name is listed in the message's Connection header-field
869   (see <xref target="header.connection"/>).
870   These requirements allow HTTP's functionality to be enhanced without
871   requiring prior update of all compliant intermediaries.
872</t>
873<t>
874   Intermediaries that process HTTP messages (i.e., all intermediaries
875   other than those acting as a tunnel) &MUST; send their own HTTP-Version
876   in forwarded messages.  In other words, they &MUST-NOT; blindly
877   forward the first line of an HTTP message without ensuring that the
878   protocol version matches what the intermediary understands, and
879   is at least conditionally compliant to, for both the receiving and
880   sending of messages.  Forwarding an HTTP message without rewriting
881   the HTTP-Version might result in communication errors when downstream
882   recipients use the message sender's version to determine what features
883   are safe to use for later communication with that sender.
884</t>
885<t>
886   An HTTP client &SHOULD; send a request version equal to the highest
887   version for which the client is at least conditionally compliant and
888   whose major version is no higher than the highest version supported
889   by the server, if this is known.  An HTTP client &MUST-NOT; send a
890   version for which it is not at least conditionally compliant.
891</t>
892<t>
893   An HTTP client &MAY; send a lower request version if it is known that
894   the server incorrectly implements the HTTP specification, but only
895   after the client has attempted at least one normal request and determined
896   from the response status or header fields (e.g., Server) that the
897   server improperly handles higher request versions.
898</t>
899<t>
900   An HTTP server &SHOULD; send a response version equal to the highest
901   version for which the server is at least conditionally compliant and
902   whose major version is less than or equal to the one received in the
903   request.  An HTTP server &MUST-NOT; send a version for which it is not
904   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
905   Version Not Supported) response if it cannot send a response using the
906   major version used in the client's request.
907</t>
908<t>
909   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
910   if it is known or suspected that the client incorrectly implements the
911   HTTP specification and is incapable of correctly processing later
912   version responses, such as when a client fails to parse the version
913   number correctly or when an intermediary is known to blindly forward
914   the HTTP-Version even when it doesn't comply with the given minor
915   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
916   performed unless triggered by specific client attributes, such as when
917   one or more of the request header fields (e.g., User-Agent) uniquely
918   match the values sent by a client known to be in error.
919</t>
920<t>
921   The intention of HTTP's versioning design is that the major number
922   will only be incremented if an incompatible message syntax is
923   introduced, and that the minor number will only be incremented when
924   changes made to the protocol have the effect of adding to the message
925   semantics or implying additional capabilities of the sender.  However,
926   the minor version was not incremented for the changes introduced between
927   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
928   is specifically avoiding any such changes to the protocol.
929</t>
930</section>
931
932<section title="Uniform Resource Identifiers" anchor="uri">
933<iref primary="true" item="resource"/>
934<t>
935   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
936   throughout HTTP as the means for identifying resources. URI references
937   are used to target requests, indicate redirects, and define relationships.
938   HTTP does not limit what a resource might be; it merely defines an interface
939   that can be used to interact with a resource via HTTP. More information on
940   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
941</t>
942  <x:anchor-alias value="URI-reference"/>
943  <x:anchor-alias value="absolute-URI"/>
944  <x:anchor-alias value="relative-part"/>
945  <x:anchor-alias value="authority"/>
946  <x:anchor-alias value="path-abempty"/>
947  <x:anchor-alias value="path-absolute"/>
948  <x:anchor-alias value="port"/>
949  <x:anchor-alias value="query"/>
950  <x:anchor-alias value="uri-host"/>
951  <x:anchor-alias value="partial-URI"/>
952<t>
953   This specification adopts the definitions of "URI-reference",
954   "absolute-URI", "relative-part", "port", "host",
955   "path-abempty", "path-absolute", "query", and "authority" from the
956   URI generic syntax <xref target="RFC3986"/>.
957   In addition, we define a partial-URI rule for protocol elements
958   that allow a relative URI but not a fragment.
959</t>
960<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"/>
961  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
962  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
963  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
964  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
965  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
966  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
967  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
968  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
969  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
970 
971  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
972</artwork></figure>
973<t>
974   Each protocol element in HTTP that allows a URI reference will indicate
975   in its ABNF production whether the element allows any form of reference
976   (URI-reference), only a URI in absolute form (absolute-URI), only the
977   path and optional query components, or some combination of the above.
978   Unless otherwise indicated, URI references are parsed relative to the
979   effective request URI, which defines the default base URI for references
980   in both the request and its corresponding response.
981</t>
982
983<section title="http URI scheme" anchor="http.uri">
984  <x:anchor-alias value="http-URI"/>
985  <iref item="http URI scheme" primary="true"/>
986  <iref item="URI scheme" subitem="http" primary="true"/>
987<t>
988   The "http" URI scheme is hereby defined for the purpose of minting
989   identifiers according to their association with the hierarchical
990   namespace governed by a potential HTTP origin server listening for
991   TCP connections on a given port.
992</t>
993<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
994  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
995</artwork></figure>
996<t>
997   The HTTP origin server is identified by the generic syntax's
998   <x:ref>authority</x:ref> component, which includes a host identifier
999   and optional TCP port (<xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>).
1000   The remainder of the URI, consisting of both the hierarchical path
1001   component and optional query component, serves as an identifier for
1002   a potential resource within that origin server's name space.
1003</t>
1004<t>
1005   If the host identifier is provided as an IP literal or IPv4 address,
1006   then the origin server is any listener on the indicated TCP port at
1007   that IP address. If host is a registered name, then that name is
1008   considered an indirect identifier and the recipient might use a name
1009   resolution service, such as DNS, to find the address of a listener
1010   for that host.
1011   The host &MUST-NOT; be empty; if an "http" URI is received with an
1012   empty host, then it &MUST; be rejected as invalid.
1013   If the port subcomponent is empty or not given, then TCP port 80 is
1014   assumed (the default reserved port for WWW services).
1015</t>
1016<t>
1017   Regardless of the form of host identifier, access to that host is not
1018   implied by the mere presence of its name or address. The host might or might
1019   not exist and, even when it does exist, might or might not be running an
1020   HTTP server or listening to the indicated port. The "http" URI scheme
1021   makes use of the delegated nature of Internet names and addresses to
1022   establish a naming authority (whatever entity has the ability to place
1023   an HTTP server at that Internet name or address) and allows that
1024   authority to determine which names are valid and how they might be used.
1025</t>
1026<t>
1027   When an "http" URI is used within a context that calls for access to the
1028   indicated resource, a client &MAY; attempt access by resolving
1029   the host to an IP address, establishing a TCP connection to that address
1030   on the indicated port, and sending an HTTP request message to the server
1031   containing the URI's identifying data as described in <xref target="request"/>.
1032   If the server responds to that request with a non-interim HTTP response
1033   message, as described in <xref target="response"/>, then that response
1034   is considered an authoritative answer to the client's request.
1035</t>
1036<t>
1037   Although HTTP is independent of the transport protocol, the "http"
1038   scheme is specific to TCP-based services because the name delegation
1039   process depends on TCP for establishing authority.
1040   An HTTP service based on some other underlying connection protocol
1041   would presumably be identified using a different URI scheme, just as
1042   the "https" scheme (below) is used for servers that require an SSL/TLS
1043   transport layer on a connection. Other protocols might also be used to
1044   provide access to "http" identified resources &mdash; it is only the
1045   authoritative interface used for mapping the namespace that is
1046   specific to TCP.
1047</t>
1048<t>
1049   The URI generic syntax for authority also includes a deprecated
1050   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1051   for including user authentication information in the URI.  Some
1052   implementations make use of the userinfo component for internal
1053   configuration of authentication information, such as within command
1054   invocation options, configuration files, or bookmark lists, even
1055   though such usage might expose a user identifier or password.
1056   Senders &MUST-NOT; include a userinfo subcomponent (and its "@"
1057   delimiter) when transmitting an "http" URI in a message.  Recipients
1058   of HTTP messages that contain a URI reference &SHOULD; parse for the
1059   existence of userinfo and treat its presence as an error, likely
1060   indicating that the deprecated subcomponent is being used to obscure
1061   the authority for the sake of phishing attacks.
1062</t>
1063</section>
1064
1065<section title="https URI scheme" anchor="https.uri">
1066   <x:anchor-alias value="https-URI"/>
1067   <iref item="https URI scheme"/>
1068   <iref item="URI scheme" subitem="https"/>
1069<t>
1070   The "https" URI scheme is hereby defined for the purpose of minting
1071   identifiers according to their association with the hierarchical
1072   namespace governed by a potential HTTP origin server listening for
1073   SSL/TLS-secured connections on a given TCP port.
1074</t>
1075<t>
1076   All of the requirements listed above for the "http" scheme are also
1077   requirements for the "https" scheme, except that a default TCP port
1078   of 443 is assumed if the port subcomponent is empty or not given,
1079   and the TCP connection &MUST; be secured for privacy through the
1080   use of strong encryption prior to sending the first HTTP request.
1081</t>
1082<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1083  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1084</artwork></figure>
1085<t>
1086   Unlike the "http" scheme, responses to "https" identified requests
1087   are never "public" and thus &MUST-NOT; be reused for shared caching.
1088   They can, however, be reused in a private cache if the message is
1089   cacheable by default in HTTP or specifically indicated as such by
1090   the Cache-Control header field (&header-cache-control;).
1091</t>
1092<t>
1093   Resources made available via the "https" scheme have no shared
1094   identity with the "http" scheme even if their resource identifiers
1095   indicate the same authority (the same host listening to the same
1096   TCP port).  They are distinct name spaces and are considered to be
1097   distinct origin servers.  However, an extension to HTTP that is
1098   defined to apply to entire host domains, such as the Cookie protocol
1099   <xref target="RFC6265"/>, can allow information
1100   set by one service to impact communication with other services
1101   within a matching group of host domains.
1102</t>
1103<t>
1104   The process for authoritative access to an "https" identified
1105   resource is defined in <xref target="RFC2818"/>.
1106</t>
1107</section>
1108
1109<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1110<t>
1111   Since the "http" and "https" schemes conform to the URI generic syntax,
1112   such URIs are normalized and compared according to the algorithm defined
1113   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1114   described above for each scheme.
1115</t>
1116<t>
1117   If the port is equal to the default port for a scheme, the normal
1118   form is to elide the port subcomponent. Likewise, an empty path
1119   component is equivalent to an absolute path of "/", so the normal
1120   form is to provide a path of "/" instead. The scheme and host
1121   are case-insensitive and normally provided in lowercase; all
1122   other components are compared in a case-sensitive manner.
1123   Characters other than those in the "reserved" set are equivalent
1124   to their percent-encoded octets (see <xref target="RFC3986"
1125   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1126</t>
1127<t>
1128   For example, the following three URIs are equivalent:
1129</t>
1130<figure><artwork type="example">
1131   http://example.com:80/~smith/home.html
1132   http://EXAMPLE.com/%7Esmith/home.html
1133   http://EXAMPLE.com:/%7esmith/home.html
1134</artwork></figure>
1135</section>
1136</section>
1137</section>
1138
1139<section title="Message Format" anchor="http.message">
1140<x:anchor-alias value="generic-message"/>
1141<x:anchor-alias value="message.types"/>
1142<x:anchor-alias value="HTTP-message"/>
1143<x:anchor-alias value="start-line"/>
1144<iref item="header section"/>
1145<iref item="headers"/>
1146<iref item="header field"/>
1147<t>
1148   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1149   octets in a format similar to the Internet Message Format
1150   <xref target="RFC5322"/>: zero or more header fields (collectively
1151   referred to as the "headers" or the "header section"), an empty line
1152   indicating the end of the header section, and an optional message-body.
1153</t>
1154<t>
1155   An HTTP message can either be a request from client to server or a
1156   response from server to client.  Syntactically, the two types of message
1157   differ only in the start-line, which is either a Request-Line (for requests)
1158   or a Status-Line (for responses), and in the algorithm for determining
1159   the length of the message-body (<xref target="message.body"/>).
1160   In theory, a client could receive requests and a server could receive
1161   responses, distinguishing them by their different start-line formats,
1162   but in practice servers are implemented to only expect a request
1163   (a response is interpreted as an unknown or invalid request method)
1164   and clients are implemented to only expect a response.
1165</t>
1166<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1167  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1168                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1169                    <x:ref>CRLF</x:ref>
1170                    [ <x:ref>message-body</x:ref> ]
1171  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1172</artwork></figure>
1173<t>
1174   Implementations &MUST-NOT; send whitespace between the start-line and
1175   the first header field. The presence of such whitespace in a request
1176   might be an attempt to trick a server into ignoring that field or
1177   processing the line after it as a new request, either of which might
1178   result in a security vulnerability if other implementations within
1179   the request chain interpret the same message differently.
1180   Likewise, the presence of such whitespace in a response might be
1181   ignored by some clients or cause others to cease parsing.
1182</t>
1183
1184<section title="Message Parsing Robustness" anchor="message.robustness">
1185<t>
1186   In the interest of robustness, servers &SHOULD; ignore at least one
1187   empty line received where a Request-Line is expected. In other words, if
1188   the server is reading the protocol stream at the beginning of a
1189   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1190</t>
1191<t>
1192   Some old HTTP/1.0 client implementations send an extra CRLF
1193   after a POST request as a lame workaround for some early server
1194   applications that failed to read message-body content that was
1195   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1196   preface or follow a request with an extra CRLF.  If terminating
1197   the request message-body with a line-ending is desired, then the
1198   client &MUST; include the terminating CRLF octets as part of the
1199   message-body length.
1200</t>
1201<t>
1202   When a server listening only for HTTP request messages, or processing
1203   what appears from the start-line to be an HTTP request message,
1204   receives a sequence of octets that does not match the HTTP-message
1205   grammar aside from the robustness exceptions listed above, the
1206   server &MUST; respond with an HTTP/1.1 400 (Bad Request) response. 
1207</t>
1208<t>
1209   The normal procedure for parsing an HTTP message is to read the
1210   start-line into a structure, read each header field into a hash
1211   table by field name until the empty line, and then use the parsed
1212   data to determine if a message-body is expected.  If a message-body
1213   has been indicated, then it is read as a stream until an amount
1214   of octets equal to the message-body length is read or the connection
1215   is closed.  Care must be taken to parse an HTTP message as a sequence
1216   of octets in an encoding that is a superset of US-ASCII.  Attempting
1217   to parse HTTP as a stream of Unicode characters in a character encoding
1218   like UTF-16 might introduce security flaws due to the differing ways
1219   that such parsers interpret invalid characters.
1220</t>
1221<t>
1222   HTTP allows the set of defined header fields to be extended without
1223   changing the protocol version (see <xref target="header.field.registration"/>).
1224   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1225   proxy is specifically configured to block or otherwise transform such
1226   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1227</t>
1228</section>
1229
1230<section title="Header Fields" anchor="header.fields">
1231  <x:anchor-alias value="header-field"/>
1232  <x:anchor-alias value="field-content"/>
1233  <x:anchor-alias value="field-name"/>
1234  <x:anchor-alias value="field-value"/>
1235  <x:anchor-alias value="OWS"/>
1236<t>
1237   Each HTTP header field consists of a case-insensitive field name
1238   followed by a colon (":"), optional whitespace, and the field value.
1239</t>
1240<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"/>
1241  <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>OWS</x:ref>
1242  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1243  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1244  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1245</artwork></figure>
1246<t>
1247   No whitespace is allowed between the header field name and colon. For
1248   security reasons, any request message received containing such whitespace
1249   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1250   &MUST; remove any such whitespace from a response message before
1251   forwarding the message downstream.
1252</t>
1253<t>
1254   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1255   preferred. The field value does not include any leading or trailing white
1256   space: OWS occurring before the first non-whitespace octet of the
1257   field value or after the last non-whitespace octet of the field value
1258   is ignored and &SHOULD; be removed before further processing (as this does
1259   not change the meaning of the header field).
1260</t>
1261<t>
1262   The order in which header fields with differing field names are
1263   received is not significant. However, it is "good practice" to send
1264   header fields that contain control data first, such as Host on
1265   requests and Date on responses, so that implementations can decide
1266   when not to handle a message as early as possible.  A server &MUST;
1267   wait until the entire header section is received before interpreting
1268   a request message, since later header fields might include conditionals,
1269   authentication credentials, or deliberately misleading duplicate
1270   header fields that would impact request processing.
1271</t>
1272<t>
1273   Multiple header fields with the same field name &MUST-NOT; be
1274   sent in a message unless the entire field value for that
1275   header field is defined as a comma-separated list [i.e., #(values)].
1276   Multiple header fields with the same field name can be combined into
1277   one "field-name: field-value" pair, without changing the semantics of the
1278   message, by appending each subsequent field value to the combined
1279   field value in order, separated by a comma. The order in which
1280   header fields with the same field name are received is therefore
1281   significant to the interpretation of the combined field value;
1282   a proxy &MUST-NOT; change the order of these field values when
1283   forwarding a message.
1284</t>
1285<x:note>
1286  <t>
1287   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1288   practice can occur multiple times, but does not use the list syntax, and
1289   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1290   for details.) Also note that the Set-Cookie2 header field specified in
1291   <xref target="RFC2965"/> does not share this problem.
1292  </t>
1293</x:note>
1294<t>
1295   Historically, HTTP header field values could be extended over multiple
1296   lines by preceding each extra line with at least one space or horizontal
1297   tab octet (line folding). This specification deprecates such line
1298   folding except within the message/http media type
1299   (<xref target="internet.media.type.message.http"/>).
1300   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1301   (i.e., that contain any field-content that matches the obs-fold rule) unless
1302   the message is intended for packaging within the message/http media type.
1303   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1304   obs-fold whitespace with a single SP prior to interpreting the field value
1305   or forwarding the message downstream.
1306</t>
1307<t>
1308   Historically, HTTP has allowed field content with text in the ISO-8859-1
1309   <xref target="ISO-8859-1"/> character encoding and supported other
1310   character sets only through use of <xref target="RFC2047"/> encoding.
1311   In practice, most HTTP header field values use only a subset of the
1312   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1313   header fields &SHOULD; limit their field values to US-ASCII octets.
1314   Recipients &SHOULD; treat other (obs-text) octets in field content as
1315   opaque data.
1316</t>
1317<t anchor="rule.comment">
1318  <x:anchor-alias value="comment"/>
1319  <x:anchor-alias value="ctext"/>
1320   Comments can be included in some HTTP header fields by surrounding
1321   the comment text with parentheses. Comments are only allowed in
1322   fields containing "comment" as part of their field value definition.
1323</t>
1324<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1325  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1326  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1327                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1328</artwork></figure>
1329<t anchor="rule.quoted-cpair">
1330  <x:anchor-alias value="quoted-cpair"/>
1331   The backslash octet ("\") can be used as a single-octet
1332   quoting mechanism within comment constructs:
1333</t>
1334<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1335  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1336</artwork></figure>
1337<t>
1338   Senders &SHOULD-NOT; escape octets that do not require escaping
1339   (i.e., other than the backslash octet "\" and the parentheses "(" and
1340   ")").
1341</t>
1342</section>
1343
1344<section title="Message Body" anchor="message.body">
1345  <x:anchor-alias value="message-body"/>
1346<t>
1347   The message-body (if any) of an HTTP message is used to carry the
1348   payload body associated with the request or response.
1349</t>
1350<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1351  <x:ref>message-body</x:ref> = *OCTET
1352</artwork></figure>
1353<t>
1354   The message-body differs from the payload body only when a transfer-coding
1355   has been applied, as indicated by the Transfer-Encoding header field
1356   (<xref target="header.transfer-encoding"/>).  If more than one
1357   Transfer-Encoding header field is present in a message, the multiple
1358   field-values &MUST; be combined into one field-value, according to the
1359   algorithm defined in <xref target="header.fields"/>, before determining
1360   the message-body length.
1361</t>
1362<t>
1363   When one or more transfer-codings are applied to a payload in order to
1364   form the message-body, the Transfer-Encoding header field &MUST; contain
1365   the list of transfer-codings applied. Transfer-Encoding is a property of
1366   the message, not of the payload, and thus &MAY; be added or removed by
1367   any implementation along the request/response chain under the constraints
1368   found in <xref target="transfer.codings"/>.
1369</t>
1370<t>
1371   If a message is received that has multiple Content-Length header fields
1372   (<xref target="header.content-length"/>) with field-values consisting
1373   of the same decimal value, or a single Content-Length header field with
1374   a field value containing a list of identical decimal values (e.g.,
1375   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1376   header fields have been generated or combined by an upstream message
1377   processor, then the recipient &MUST; either reject the message as invalid
1378   or replace the duplicated field-values with a single valid Content-Length
1379   field containing that decimal value prior to determining the message-body
1380   length.
1381</t>
1382<t>
1383   The rules for when a message-body is allowed in a message differ for
1384   requests and responses.
1385</t>
1386<t>
1387   The presence of a message-body in a request is signaled by the
1388   inclusion of a Content-Length or Transfer-Encoding header field in
1389   the request's header fields, even if the request method does not
1390   define any use for a message-body.  This allows the request
1391   message framing algorithm to be independent of method semantics.
1392</t>
1393<t>
1394   For response messages, whether or not a message-body is included with
1395   a message is dependent on both the request method and the response
1396   status code (<xref target="status.code.and.reason.phrase"/>).
1397   Responses to the HEAD request method never include a message-body
1398   because the associated response header fields (e.g., Transfer-Encoding,
1399   Content-Length, etc.) only indicate what their values would have been
1400   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1401   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1402   All other responses do include a message-body, although the body
1403   &MAY; be of zero length.
1404</t>
1405<t>
1406   The length of the message-body is determined by one of the following
1407   (in order of precedence):
1408</t>
1409<t>
1410  <list style="numbers">
1411    <x:lt><t>
1412     Any response to a HEAD request and any response with a status
1413     code of 100-199, 204, or 304 is always terminated by the first
1414     empty line after the header fields, regardless of the header
1415     fields present in the message, and thus cannot contain a message-body.
1416    </t></x:lt>
1417    <x:lt><t>
1418     If a Transfer-Encoding header field is present
1419     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1420     is the final encoding, the message-body length is determined by reading
1421     and decoding the chunked data until the transfer-coding indicates the
1422     data is complete.
1423    </t>
1424    <t>
1425     If a Transfer-Encoding header field is present in a response and the
1426     "chunked" transfer-coding is not the final encoding, the message-body
1427     length is determined by reading the connection until it is closed by
1428     the server.
1429     If a Transfer-Encoding header field is present in a request and the
1430     "chunked" transfer-coding is not the final encoding, the message-body
1431     length cannot be determined reliably; the server &MUST; respond with
1432     the 400 (Bad Request) status code and then close the connection.
1433    </t>
1434    <t>
1435     If a message is received with both a Transfer-Encoding header field
1436     and a Content-Length header field, the Transfer-Encoding overrides
1437     the Content-Length.
1438     Such a message might indicate an attempt to perform request or response
1439     smuggling (bypass of security-related checks on message routing or content)
1440     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1441     be removed, prior to forwarding the message downstream, or replaced with
1442     the real message-body length after the transfer-coding is decoded.
1443    </t></x:lt>
1444    <x:lt><t>
1445     If a message is received without Transfer-Encoding and with either
1446     multiple Content-Length header fields having differing field-values or
1447     a single Content-Length header field having an invalid value, then the
1448     message framing is invalid and &MUST; be treated as an error to
1449     prevent request or response smuggling.
1450     If this is a request message, the server &MUST; respond with
1451     a 400 (Bad Request) status code and then close the connection.
1452     If this is a response message received by a proxy, the proxy
1453     &MUST; discard the received response, send a 502 (Bad Gateway)
1454     status code as its downstream response, and then close the connection.
1455     If this is a response message received by a user-agent, it &MUST; be
1456     treated as an error by discarding the message and closing the connection.
1457    </t></x:lt>
1458    <x:lt><t>
1459     If a valid Content-Length header field
1460     is present without Transfer-Encoding, its decimal value defines the
1461     message-body length in octets.  If the actual number of octets sent in
1462     the message is less than the indicated Content-Length, the recipient
1463     &MUST; consider the message to be incomplete and treat the connection
1464     as no longer usable.
1465     If the actual number of octets sent in the message is more than the indicated
1466     Content-Length, the recipient &MUST; only process the message-body up to the
1467     field value's number of octets; the remainder of the message &MUST; either
1468     be discarded or treated as the next message in a pipeline.  For the sake of
1469     robustness, a user-agent &MAY; attempt to detect and correct such an error
1470     in message framing if it is parsing the response to the last request on
1471     on a connection and the connection has been closed by the server.
1472    </t></x:lt>
1473    <x:lt><t>
1474     If this is a request message and none of the above are true, then the
1475     message-body length is zero (no message-body is present).
1476    </t></x:lt>
1477    <x:lt><t>
1478     Otherwise, this is a response message without a declared message-body
1479     length, so the message-body length is determined by the number of octets
1480     received prior to the server closing the connection.
1481    </t></x:lt>
1482  </list>
1483</t>
1484<t>
1485   Since there is no way to distinguish a successfully completed,
1486   close-delimited message from a partially-received message interrupted
1487   by network failure, implementations &SHOULD; use encoding or
1488   length-delimited messages whenever possible.  The close-delimiting
1489   feature exists primarily for backwards compatibility with HTTP/1.0.
1490</t>
1491<t>
1492   A server &MAY; reject a request that contains a message-body but
1493   not a Content-Length by responding with 411 (Length Required).
1494</t>
1495<t>
1496   Unless a transfer-coding other than "chunked" has been applied,
1497   a client that sends a request containing a message-body &SHOULD;
1498   use a valid Content-Length header field if the message-body length
1499   is known in advance, rather than the "chunked" encoding, since some
1500   existing services respond to "chunked" with a 411 (Length Required)
1501   status code even though they understand the chunked encoding.  This
1502   is typically because such services are implemented via a gateway that
1503   requires a content-length in advance of being called and the server
1504   is unable or unwilling to buffer the entire request before processing.
1505</t>
1506<t>
1507   A client that sends a request containing a message-body &MUST; include a
1508   valid Content-Length header field if it does not know the server will
1509   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1510   of specific user configuration or by remembering the version of a prior
1511   received response.
1512</t>
1513<t>
1514   Request messages that are prematurely terminated, possibly due to a
1515   cancelled connection or a server-imposed time-out exception, &MUST;
1516   result in closure of the connection; sending an HTTP/1.1 error response
1517   prior to closing the connection is &OPTIONAL;.
1518   Response messages that are prematurely terminated, usually by closure
1519   of the connection prior to receiving the expected number of octets or by
1520   failure to decode a transfer-encoded message-body, &MUST; be recorded
1521   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1522   message-body as if it were complete (i.e., some indication must be given
1523   to the user that an error occurred).  Cache requirements for incomplete
1524   responses are defined in &cache-incomplete;.
1525</t>
1526<t>
1527   A server &MUST; read the entire request message-body or close
1528   the connection after sending its response, since otherwise the
1529   remaining data on a persistent connection would be misinterpreted
1530   as the next request.  Likewise,
1531   a client &MUST; read the entire response message-body if it intends
1532   to reuse the same connection for a subsequent request.  Pipelining
1533   multiple requests on a connection is described in <xref target="pipelining"/>.
1534</t>
1535</section>
1536
1537<section title="General Header Fields" anchor="general.header.fields">
1538  <x:anchor-alias value="general-header"/>
1539<t>
1540   There are a few header fields which have general applicability for
1541   both request and response messages, but which do not apply to the
1542   payload being transferred. These header fields apply only to the
1543   message being transmitted.
1544</t>
1545<texttable align="left">
1546  <ttcol>Header Field Name</ttcol>
1547  <ttcol>Defined in...</ttcol>
1548 
1549  <c>Connection</c> <c><xref target="header.connection"/></c>
1550  <c>Date</c> <c><xref target="header.date"/></c>
1551  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1552  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1553  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1554  <c>Via</c> <c><xref target="header.via"/></c>
1555</texttable>
1556</section>
1557</section>
1558
1559<section title="Request" anchor="request">
1560  <x:anchor-alias value="Request"/>
1561<t>
1562   A request message from a client to a server begins with a
1563   Request-Line, followed by zero or more header fields, an empty
1564   line signifying the end of the header block, and an optional
1565   message body.
1566</t>
1567<!--                 Host                      ; should be moved here eventually -->
1568<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1569  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1570                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1571                  <x:ref>CRLF</x:ref>
1572                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1573</artwork></figure>
1574
1575<section title="Request-Line" anchor="request-line">
1576  <x:anchor-alias value="Request-Line"/>
1577<t>
1578   The Request-Line begins with a method token, followed by a single
1579   space (SP), the request-target, another single space (SP), the
1580   protocol version, and ending with CRLF.
1581</t>
1582<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1583  <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>
1584</artwork></figure>
1585
1586<section title="Method" anchor="method">
1587  <x:anchor-alias value="Method"/>
1588<t>
1589   The Method token indicates the request method to be performed on the
1590   target resource. The request method is case-sensitive.
1591</t>
1592<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1593  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1594</artwork></figure>
1595</section>
1596
1597<section title="request-target" anchor="request-target">
1598  <x:anchor-alias value="request-target"/>
1599<t>
1600   The request-target identifies the target resource upon which to apply
1601   the request.  In most cases, the user agent is provided a URI reference
1602   from which it determines an absolute URI for identifying the target
1603   resource.  When a request to the resource is initiated, all or part
1604   of that URI is used to construct the HTTP request-target.
1605</t>
1606<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1607  <x:ref>request-target</x:ref> = "*"
1608                 / <x:ref>absolute-URI</x:ref>
1609                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1610                 / <x:ref>authority</x:ref>
1611</artwork></figure>
1612<t>
1613   The four options for request-target are dependent on the nature of the
1614   request.
1615</t>   
1616<t><iref item="asterisk form (of request-target)"/>
1617   The asterisk "*" form of request-target, which &MUST-NOT; be used
1618   with any request method other than OPTIONS, means that the request
1619   applies to the server as a whole (the listening process) rather than
1620   to a specific named resource at that server.  For example,
1621</t>
1622<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1623OPTIONS * HTTP/1.1
1624</artwork></figure>
1625<t><iref item="absolute-URI form (of request-target)"/>
1626   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1627   proxy. The proxy is requested to either forward the request or service it
1628   from a valid cache, and then return the response. Note that the proxy &MAY;
1629   forward the request on to another proxy or directly to the server
1630   specified by the absolute-URI. In order to avoid request loops, a
1631   proxy that forwards requests to other proxies &MUST; be able to
1632   recognize and exclude all of its own server names, including
1633   any aliases, local variations, and the numeric IP address. An example
1634   Request-Line would be:
1635</t>
1636<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1637GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1638</artwork></figure>
1639<t>
1640   To allow for transition to absolute-URIs in all requests in future
1641   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1642   form in requests, even though HTTP/1.1 clients will only generate
1643   them in requests to proxies.
1644</t>
1645<t>
1646   If a proxy receives a host name that is not a fully qualified domain
1647   name, it &MAY; add its domain to the host name it received. If a proxy
1648   receives a fully qualified domain name, the proxy &MUST-NOT; change
1649   the host name.
1650</t>
1651<t><iref item="authority form (of request-target)"/>
1652   The "authority form" is only used by the CONNECT request method (&CONNECT;).
1653</t>
1654<t><iref item="origin form (of request-target)"/>
1655   The most common form of request-target is that used when making
1656   a request to an origin server ("origin form").
1657   In this case, the absolute path and query components of the URI
1658   &MUST; be transmitted as the request-target, and the authority component
1659   &MUST; be transmitted in a Host header field. For example, a client wishing
1660   to retrieve a representation of the resource, as identified above,
1661   directly from the origin server would open (or reuse) a TCP connection
1662   to port 80 of the host "www.example.org" and send the lines:
1663</t>
1664<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1665GET /pub/WWW/TheProject.html HTTP/1.1
1666Host: www.example.org
1667</artwork></figure>
1668<t>
1669   followed by the remainder of the Request. Note that the origin form
1670   of request-target always starts with an absolute path; if the target
1671   resource's URI path is empty, then an absolute path of "/" &MUST; be
1672   provided in the request-target.
1673</t>
1674<t>
1675   If a proxy receives an OPTIONS request with an absolute-URI form of
1676   request-target in which the URI has an empty path and no query component,
1677   then the last proxy on the request chain &MUST; use a request-target
1678   of "*" when it forwards the request to the indicated origin server.
1679</t>
1680<figure><preamble>   
1681   For example, the request
1682</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1683OPTIONS http://www.example.org:8001 HTTP/1.1
1684</artwork></figure>
1685<figure><preamble>   
1686  would be forwarded by the final proxy as
1687</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1688OPTIONS * HTTP/1.1
1689Host: www.example.org:8001
1690</artwork>
1691<postamble>
1692   after connecting to port 8001 of host "www.example.org".
1693</postamble>
1694</figure>
1695<t>
1696   The request-target is transmitted in the format specified in
1697   <xref target="http.uri"/>. If the request-target is percent-encoded
1698   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1699   &MUST; decode the request-target in order to
1700   properly interpret the request. Servers &SHOULD; respond to invalid
1701   request-targets with an appropriate status code.
1702</t>
1703<t>
1704   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1705   received request-target when forwarding it to the next inbound server,
1706   except as noted above to replace a null path-absolute with "/" or "*".
1707</t>
1708<x:note>
1709  <t>
1710    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1711    meaning of the request when the origin server is improperly using
1712    a non-reserved URI character for a reserved purpose.  Implementors
1713    need to be aware that some pre-HTTP/1.1 proxies have been known to
1714    rewrite the request-target.
1715  </t>
1716</x:note>
1717<t>
1718   HTTP does not place a pre-defined limit on the length of a request-target.
1719   A server &MUST; be prepared to receive URIs of unbounded length and
1720   respond with the 414 (URI Too Long) status code if the received
1721   request-target would be longer than the server wishes to handle
1722   (see &status-414;).
1723</t>
1724<t>
1725   Various ad-hoc limitations on request-target length are found in practice.
1726   It is &RECOMMENDED; that all HTTP senders and recipients support
1727   request-target lengths of 8000 or more octets.
1728</t>
1729<x:note>
1730  <t>
1731    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1732    are not part of the request-target and thus will not be transmitted
1733    in an HTTP request.
1734  </t>
1735</x:note>
1736</section>
1737</section>
1738
1739<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1740<t>
1741   The exact resource identified by an Internet request is determined by
1742   examining both the request-target and the Host header field.
1743</t>
1744<t>
1745   An origin server that does not allow resources to differ by the
1746   requested host &MAY; ignore the Host header field value when
1747   determining the resource identified by an HTTP/1.1 request. (But see
1748   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1749   for other requirements on Host support in HTTP/1.1.)
1750</t>
1751<t>
1752   An origin server that does differentiate resources based on the host
1753   requested (sometimes referred to as virtual hosts or vanity host
1754   names) &MUST; use the following rules for determining the requested
1755   resource on an HTTP/1.1 request:
1756  <list style="numbers">
1757    <t>If request-target is an absolute-URI, the host is part of the
1758     request-target. Any Host header field value in the request &MUST; be
1759     ignored.</t>
1760    <t>If the request-target is not an absolute-URI, and the request includes
1761     a Host header field, the host is determined by the Host header
1762     field value.</t>
1763    <t>If the host as determined by rule 1 or 2 is not a valid host on
1764     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1765  </list>
1766</t>
1767<t>
1768   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1769   attempt to use heuristics (e.g., examination of the URI path for
1770   something unique to a particular host) in order to determine what
1771   exact resource is being requested.
1772</t>
1773</section>
1774
1775<section title="Effective Request URI" anchor="effective.request.uri">
1776  <iref primary="true" item="effective request URI"/>
1777  <iref primary="true" item="target resource"/>
1778<t>
1779   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1780   for the target resource; instead, the URI needs to be inferred from the
1781   request-target, Host header field, and connection context. The result of
1782   this process is called the "effective request URI".  The "target resource"
1783   is the resource identified by the effective request URI.
1784</t>
1785<t>
1786   If the request-target is an absolute-URI, then the effective request URI is
1787   the request-target.
1788</t>
1789<t>
1790   If the request-target uses the path-absolute form or the asterisk form,
1791   and the Host header field is present, then the effective request URI is
1792   constructed by concatenating
1793</t>
1794<t>
1795  <list style="symbols">
1796    <t>
1797      the scheme name: "http" if the request was received over an insecure
1798      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1799      connection,
1800    </t>
1801    <t>
1802      the octet sequence "://",
1803    </t>
1804    <t>
1805      the authority component, as specified in the Host header field
1806      (<xref target="header.host"/>), and
1807    </t>
1808    <t>
1809      the request-target obtained from the Request-Line, unless the
1810      request-target is just the asterisk "*".
1811    </t>
1812  </list>
1813</t>
1814<t>
1815   If the request-target uses the path-absolute form or the asterisk form,
1816   and the Host header field is not present, then the effective request URI is
1817   undefined.
1818</t>
1819<t>
1820   Otherwise, when request-target uses the authority form, the effective
1821   request URI is undefined.
1822</t>
1823<figure>
1824<preamble>
1825   Example 1: the effective request URI for the message
1826</preamble> 
1827<artwork type="example" x:indent-with="  ">
1828GET /pub/WWW/TheProject.html HTTP/1.1
1829Host: www.example.org:8080
1830</artwork>
1831<postamble>
1832  (received over an insecure TCP connection) is "http", plus "://", plus the
1833  authority component "www.example.org:8080", plus the request-target
1834  "/pub/WWW/TheProject.html", thus
1835  "http://www.example.org:8080/pub/WWW/TheProject.html".
1836</postamble>
1837</figure>
1838<figure>
1839<preamble>
1840   Example 2: the effective request URI for the message
1841</preamble> 
1842<artwork type="example" x:indent-with="  ">
1843GET * HTTP/1.1
1844Host: www.example.org
1845</artwork>
1846<postamble>
1847  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1848  authority component "www.example.org", thus "https://www.example.org".
1849</postamble>
1850</figure>
1851<t>
1852   Effective request URIs are compared using the rules described in
1853   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1854   be treated as equivalent to an absolute path of "/".
1855</t> 
1856</section>
1857
1858</section>
1859
1860
1861<section title="Response" anchor="response">
1862  <x:anchor-alias value="Response"/>
1863<t>
1864   After receiving and interpreting a request message, a server responds
1865   with an HTTP response message.
1866</t>
1867<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1868  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1869                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1870                  <x:ref>CRLF</x:ref>
1871                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1872</artwork></figure>
1873
1874<section title="Status-Line" anchor="status-line">
1875  <x:anchor-alias value="Status-Line"/>
1876<t>
1877   The first line of a Response message is the Status-Line, consisting
1878   of the protocol version, a space (SP), the status code, another space,
1879   a possibly-empty textual phrase describing the status code, and
1880   ending with CRLF.
1881</t>
1882<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1883  <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>
1884</artwork></figure>
1885
1886<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1887  <x:anchor-alias value="Reason-Phrase"/>
1888  <x:anchor-alias value="Status-Code"/>
1889<t>
1890   The Status-Code element is a 3-digit integer result code of the
1891   attempt to understand and satisfy the request. These codes are fully
1892   defined in &status-codes;.  The Reason Phrase exists for the sole
1893   purpose of providing a textual description associated with the numeric
1894   status code, out of deference to earlier Internet application protocols
1895   that were more frequently used with interactive text clients.
1896   A client &SHOULD; ignore the content of the Reason Phrase.
1897</t>
1898<t>
1899   The first digit of the Status-Code defines the class of response. The
1900   last two digits do not have any categorization role. There are 5
1901   values for the first digit:
1902  <list style="symbols">
1903    <t>
1904      1xx: Informational - Request received, continuing process
1905    </t>
1906    <t>
1907      2xx: Success - The action was successfully received,
1908        understood, and accepted
1909    </t>
1910    <t>
1911      3xx: Redirection - Further action must be taken in order to
1912        complete the request
1913    </t>
1914    <t>
1915      4xx: Client Error - The request contains bad syntax or cannot
1916        be fulfilled
1917    </t>
1918    <t>
1919      5xx: Server Error - The server failed to fulfill an apparently
1920        valid request
1921    </t>
1922  </list>
1923</t>
1924<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1925  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1926  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1927</artwork></figure>
1928</section>
1929</section>
1930
1931</section>
1932
1933
1934<section title="Protocol Parameters" anchor="protocol.parameters">
1935
1936<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1937  <x:anchor-alias value="HTTP-date"/>
1938<t>
1939   HTTP applications have historically allowed three different formats
1940   for date/time stamps. However, the preferred format is a fixed-length subset
1941   of that defined by <xref target="RFC1123"/>:
1942</t>
1943<figure><artwork type="example" x:indent-with="  ">
1944Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1945</artwork></figure>
1946<t>
1947   The other formats are described here only for compatibility with obsolete
1948   implementations.
1949</t>
1950<figure><artwork type="example" x:indent-with="  ">
1951Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1952Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1953</artwork></figure>
1954<t>
1955   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1956   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1957   only generate the RFC 1123 format for representing HTTP-date values
1958   in header fields. See <xref target="tolerant.applications"/> for further information.
1959</t>
1960<t>
1961   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1962   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1963   equal to UTC (Coordinated Universal Time). This is indicated in the
1964   first two formats by the inclusion of "GMT" as the three-letter
1965   abbreviation for time zone, and &MUST; be assumed when reading the
1966   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1967   additional whitespace beyond that specifically included as SP in the
1968   grammar.
1969</t>
1970<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1971  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1972</artwork></figure>
1973<t anchor="preferred.date.format">
1974  <x:anchor-alias value="rfc1123-date"/>
1975  <x:anchor-alias value="time-of-day"/>
1976  <x:anchor-alias value="hour"/>
1977  <x:anchor-alias value="minute"/>
1978  <x:anchor-alias value="second"/>
1979  <x:anchor-alias value="day-name"/>
1980  <x:anchor-alias value="day"/>
1981  <x:anchor-alias value="month"/>
1982  <x:anchor-alias value="year"/>
1983  <x:anchor-alias value="GMT"/>
1984  Preferred format:
1985</t>
1986<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
1987  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
1988  ; fixed length subset of the format defined in
1989  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1990 
1991  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1992               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1993               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1994               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1995               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1996               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1997               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1998               
1999  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2000               ; e.g., 02 Jun 1982
2001
2002  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
2003  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
2004               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
2005               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
2006               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
2007               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
2008               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
2009               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
2010               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
2011               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
2012               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
2013               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
2014               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
2015  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
2016
2017  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
2018
2019  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
2020                 ; 00:00:00 - 23:59:59
2021                 
2022  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2023  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2024  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2025</artwork></figure>
2026<t>
2027  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2028  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2029  same as those defined for the RFC 5322 constructs
2030  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2031</t>
2032<t anchor="obsolete.date.formats">
2033  <x:anchor-alias value="obs-date"/>
2034  <x:anchor-alias value="rfc850-date"/>
2035  <x:anchor-alias value="asctime-date"/>
2036  <x:anchor-alias value="date1"/>
2037  <x:anchor-alias value="date2"/>
2038  <x:anchor-alias value="date3"/>
2039  <x:anchor-alias value="rfc1123-date"/>
2040  <x:anchor-alias value="day-name-l"/>
2041  Obsolete formats:
2042</t>
2043<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2044  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2045</artwork></figure>
2046<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2047  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
2048  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2049                 ; day-month-year (e.g., 02-Jun-82)
2050
2051  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2052         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2053         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2054         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2055         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2056         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2057         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2058</artwork></figure>
2059<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2060  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
2061  <x:ref>date3</x:ref>        = <x:ref>month</x:ref> <x:ref>SP</x:ref> ( 2<x:ref>DIGIT</x:ref> / ( <x:ref>SP</x:ref> 1<x:ref>DIGIT</x:ref> ))
2062                 ; month day (e.g., Jun  2)
2063</artwork></figure>
2064<x:note>
2065  <t>
2066    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2067    accepting date values that might have been sent by non-HTTP
2068    applications, as is sometimes the case when retrieving or posting
2069    messages via proxies/gateways to SMTP or NNTP.
2070  </t>
2071</x:note>
2072<x:note>
2073  <t>
2074    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2075    to their usage within the protocol stream. Clients and servers are
2076    not required to use these formats for user presentation, request
2077    logging, etc.
2078  </t>
2079</x:note>
2080</section>
2081
2082<section title="Transfer Codings" anchor="transfer.codings">
2083  <x:anchor-alias value="transfer-coding"/>
2084  <x:anchor-alias value="transfer-extension"/>
2085<t>
2086   Transfer-coding values are used to indicate an encoding
2087   transformation that has been, can be, or might need to be applied to a
2088   payload body in order to ensure "safe transport" through the network.
2089   This differs from a content coding in that the transfer-coding is a
2090   property of the message rather than a property of the representation
2091   that is being transferred.
2092</t>
2093<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2094  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2095                          / "compress" ; <xref target="compress.coding"/>
2096                          / "deflate" ; <xref target="deflate.coding"/>
2097                          / "gzip" ; <xref target="gzip.coding"/>
2098                          / <x:ref>transfer-extension</x:ref>
2099  <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> )
2100</artwork></figure>
2101<t anchor="rule.parameter">
2102  <x:anchor-alias value="attribute"/>
2103  <x:anchor-alias value="transfer-parameter"/>
2104  <x:anchor-alias value="value"/>
2105   Parameters are in the form of attribute/value pairs.
2106</t>
2107<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"/>
2108  <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>
2109  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2110  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2111</artwork></figure>
2112<t>
2113   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2114   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2115   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2116</t>
2117<t>
2118   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2119   MIME, which were designed to enable safe transport of binary data over a
2120   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2121   However, safe transport
2122   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2123   the only unsafe characteristic of message-bodies is the difficulty in
2124   determining the exact message body length (<xref target="message.body"/>),
2125   or the desire to encrypt data over a shared transport.
2126</t>
2127<t>
2128   A server that receives a request message with a transfer-coding it does
2129   not understand &SHOULD; respond with 501 (Not Implemented) and then
2130   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2131   client.
2132</t>
2133
2134<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2135  <iref item="chunked (Coding Format)"/>
2136  <iref item="Coding Format" subitem="chunked"/>
2137  <x:anchor-alias value="chunk"/>
2138  <x:anchor-alias value="Chunked-Body"/>
2139  <x:anchor-alias value="chunk-data"/>
2140  <x:anchor-alias value="chunk-ext"/>
2141  <x:anchor-alias value="chunk-ext-name"/>
2142  <x:anchor-alias value="chunk-ext-val"/>
2143  <x:anchor-alias value="chunk-size"/>
2144  <x:anchor-alias value="last-chunk"/>
2145  <x:anchor-alias value="trailer-part"/>
2146  <x:anchor-alias value="quoted-str-nf"/>
2147  <x:anchor-alias value="qdtext-nf"/>
2148<t>
2149   The chunked encoding modifies the body of a message in order to
2150   transfer it as a series of chunks, each with its own size indicator,
2151   followed by an &OPTIONAL; trailer containing header fields. This
2152   allows dynamically produced content to be transferred along with the
2153   information necessary for the recipient to verify that it has
2154   received the full message.
2155</t>
2156<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"/>
2157  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2158                   <x:ref>last-chunk</x:ref>
2159                   <x:ref>trailer-part</x:ref>
2160                   <x:ref>CRLF</x:ref>
2161 
2162  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2163                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2164  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2165  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2166 
2167  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2168                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2169  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2170  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2171  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2172  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2173 
2174  <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>
2175                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2176  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2177                 ; <x:ref>WSP</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref> 
2178</artwork></figure>
2179<t>
2180   The chunk-size field is a string of hex digits indicating the size of
2181   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2182   zero, followed by the trailer, which is terminated by an empty line.
2183</t>
2184<t>
2185   The trailer allows the sender to include additional HTTP header
2186   fields at the end of the message. The Trailer header field can be
2187   used to indicate which header fields are included in a trailer (see
2188   <xref target="header.trailer"/>).
2189</t>
2190<t>
2191   A server using chunked transfer-coding in a response &MUST-NOT; use the
2192   trailer for any header fields unless at least one of the following is
2193   true:
2194  <list style="numbers">
2195    <t>the request included a TE header field that indicates "trailers" is
2196     acceptable in the transfer-coding of the  response, as described in
2197     <xref target="header.te"/>; or,</t>
2198     
2199    <t>the trailer fields consist entirely of optional metadata, and the
2200    recipient could use the message (in a manner acceptable to the server where
2201    the field originated) without receiving it. In other words, the server that
2202    generated the header (often but not always the origin server) is willing to
2203    accept the possibility that the trailer fields might be silently discarded
2204    along the path to the client.</t>
2205  </list>
2206</t>
2207<t>
2208   This requirement prevents an interoperability failure when the
2209   message is being received by an HTTP/1.1 (or later) proxy and
2210   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2211   compliance with the protocol would have necessitated a possibly
2212   infinite buffer on the proxy.
2213</t>
2214<t>
2215   A process for decoding the "chunked" transfer-coding
2216   can be represented in pseudo-code as:
2217</t>
2218<figure><artwork type="code">
2219  length := 0
2220  read chunk-size, chunk-ext (if any) and CRLF
2221  while (chunk-size &gt; 0) {
2222     read chunk-data and CRLF
2223     append chunk-data to decoded-body
2224     length := length + chunk-size
2225     read chunk-size and CRLF
2226  }
2227  read header-field
2228  while (header-field not empty) {
2229     append header-field to existing header fields
2230     read header-field
2231  }
2232  Content-Length := length
2233  Remove "chunked" from Transfer-Encoding
2234</artwork></figure>
2235<t>
2236   All HTTP/1.1 applications &MUST; be able to receive and decode the
2237   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2238   they do not understand.
2239</t>
2240<t>
2241   Since "chunked" is the only transfer-coding required to be understood
2242   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2243   on a persistent connection.  Whenever a transfer-coding is applied to
2244   a payload body in a request, the final transfer-coding applied &MUST;
2245   be "chunked".  If a transfer-coding is applied to a response payload
2246   body, then either the final transfer-coding applied &MUST; be "chunked"
2247   or the message &MUST; be terminated by closing the connection. When the
2248   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2249   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2250   be applied more than once in a message-body.
2251</t>
2252</section>
2253
2254<section title="Compression Codings" anchor="compression.codings">
2255<t>
2256   The codings defined below can be used to compress the payload of a
2257   message.
2258</t>
2259<x:note><t>
2260   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2261   is not desirable and is discouraged for future encodings. Their
2262   use here is representative of historical practice, not good
2263   design.
2264</t></x:note>
2265<x:note><t>
2266   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2267   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2268   equivalent to "gzip" and "compress" respectively.
2269</t></x:note>
2270
2271<section title="Compress Coding" anchor="compress.coding">
2272<iref item="compress (Coding Format)"/>
2273<iref item="Coding Format" subitem="compress"/>
2274<t>
2275   The "compress" format is produced by the common UNIX file compression
2276   program "compress". This format is an adaptive Lempel-Ziv-Welch
2277   coding (LZW).
2278</t>
2279</section>
2280
2281<section title="Deflate Coding" anchor="deflate.coding">
2282<iref item="deflate (Coding Format)"/>
2283<iref item="Coding Format" subitem="deflate"/>
2284<t>
2285   The "deflate" format is defined as the "deflate" compression mechanism
2286   (described in <xref target="RFC1951"/>) used inside the "zlib"
2287   data format (<xref target="RFC1950"/>).
2288</t>
2289<x:note>
2290  <t>
2291    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2292    compressed data without the zlib wrapper.
2293   </t>
2294</x:note>
2295</section>
2296
2297<section title="Gzip Coding" anchor="gzip.coding">
2298<iref item="gzip (Coding Format)"/>
2299<iref item="Coding Format" subitem="gzip"/>
2300<t>
2301   The "gzip" format is produced by the file compression program
2302   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2303   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2304</t>
2305</section>
2306
2307</section>
2308
2309<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2310<t>
2311   The HTTP Transfer Coding Registry defines the name space for the transfer
2312   coding names.
2313</t>
2314<t>
2315   Registrations &MUST; include the following fields:
2316   <list style="symbols">
2317     <t>Name</t>
2318     <t>Description</t>
2319     <t>Pointer to specification text</t>
2320   </list>
2321</t>
2322<t>
2323   Names of transfer codings &MUST-NOT; overlap with names of content codings
2324   (&content-codings;), unless the encoding transformation is identical (as it
2325   is the case for the compression codings defined in
2326   <xref target="compression.codings"/>).
2327</t>
2328<t>
2329   Values to be added to this name space require a specification
2330   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2331   conform to the purpose of transfer coding defined in this section.
2332</t>
2333<t>
2334   The registry itself is maintained at
2335   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2336</t>
2337</section>
2338</section>
2339
2340<section title="Product Tokens" anchor="product.tokens">
2341  <x:anchor-alias value="product"/>
2342  <x:anchor-alias value="product-version"/>
2343<t>
2344   Product tokens are used to allow communicating applications to
2345   identify themselves by software name and version. Most fields using
2346   product tokens also allow sub-products which form a significant part
2347   of the application to be listed, separated by whitespace. By
2348   convention, the products are listed in order of their significance
2349   for identifying the application.
2350</t>
2351<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2352  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2353  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2354</artwork></figure>
2355<t>
2356   Examples:
2357</t>
2358<figure><artwork type="example">
2359  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2360  Server: Apache/0.8.4
2361</artwork></figure>
2362<t>
2363   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2364   used for advertising or other non-essential information. Although any
2365   token octet &MAY; appear in a product-version, this token &SHOULD;
2366   only be used for a version identifier (i.e., successive versions of
2367   the same product &SHOULD; only differ in the product-version portion of
2368   the product value).
2369</t>
2370</section>
2371
2372<section title="Quality Values" anchor="quality.values">
2373  <x:anchor-alias value="qvalue"/>
2374<t>
2375   Both transfer codings (TE request header field, <xref target="header.te"/>)
2376   and content negotiation (&content.negotiation;) use short "floating point"
2377   numbers to indicate the relative importance ("weight") of various
2378   negotiable parameters.  A weight is normalized to a real number in
2379   the range 0 through 1, where 0 is the minimum and 1 the maximum
2380   value. If a parameter has a quality value of 0, then content with
2381   this parameter is "not acceptable" for the client. HTTP/1.1
2382   applications &MUST-NOT; generate more than three digits after the
2383   decimal point. User configuration of these values &SHOULD; also be
2384   limited in this fashion.
2385</t>
2386<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2387  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2388                 / ( "1" [ "." 0*3("0") ] )
2389</artwork></figure>
2390<x:note>
2391  <t>
2392     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2393     relative degradation in desired quality.
2394  </t>
2395</x:note>
2396</section>
2397
2398</section>
2399
2400<section title="Connections" anchor="connections">
2401
2402<section title="Persistent Connections" anchor="persistent.connections">
2403
2404<section title="Purpose" anchor="persistent.purpose">
2405<t>
2406   Prior to persistent connections, a separate TCP connection was
2407   established for each request, increasing the load on HTTP servers
2408   and causing congestion on the Internet. The use of inline images and
2409   other associated data often requires a client to make multiple
2410   requests of the same server in a short amount of time. Analysis of
2411   these performance problems and results from a prototype
2412   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2413   measurements of actual HTTP/1.1 implementations show good
2414   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2415   T/TCP <xref target="Tou1998"/>.
2416</t>
2417<t>
2418   Persistent HTTP connections have a number of advantages:
2419  <list style="symbols">
2420      <t>
2421        By opening and closing fewer TCP connections, CPU time is saved
2422        in routers and hosts (clients, servers, proxies, gateways,
2423        tunnels, or caches), and memory used for TCP protocol control
2424        blocks can be saved in hosts.
2425      </t>
2426      <t>
2427        HTTP requests and responses can be pipelined on a connection.
2428        Pipelining allows a client to make multiple requests without
2429        waiting for each response, allowing a single TCP connection to
2430        be used much more efficiently, with much lower elapsed time.
2431      </t>
2432      <t>
2433        Network congestion is reduced by reducing the number of packets
2434        caused by TCP opens, and by allowing TCP sufficient time to
2435        determine the congestion state of the network.
2436      </t>
2437      <t>
2438        Latency on subsequent requests is reduced since there is no time
2439        spent in TCP's connection opening handshake.
2440      </t>
2441      <t>
2442        HTTP can evolve more gracefully, since errors can be reported
2443        without the penalty of closing the TCP connection. Clients using
2444        future versions of HTTP might optimistically try a new feature,
2445        but if communicating with an older server, retry with old
2446        semantics after an error is reported.
2447      </t>
2448    </list>
2449</t>
2450<t>
2451   HTTP implementations &SHOULD; implement persistent connections.
2452</t>
2453</section>
2454
2455<section title="Overall Operation" anchor="persistent.overall">
2456<t>
2457   A significant difference between HTTP/1.1 and earlier versions of
2458   HTTP is that persistent connections are the default behavior of any
2459   HTTP connection. That is, unless otherwise indicated, the client
2460   &SHOULD; assume that the server will maintain a persistent connection,
2461   even after error responses from the server.
2462</t>
2463<t>
2464   Persistent connections provide a mechanism by which a client and a
2465   server can signal the close of a TCP connection. This signaling takes
2466   place using the Connection header field (<xref target="header.connection"/>). Once a close
2467   has been signaled, the client &MUST-NOT; send any more requests on that
2468   connection.
2469</t>
2470
2471<section title="Negotiation" anchor="persistent.negotiation">
2472<t>
2473   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2474   maintain a persistent connection unless a Connection header field including
2475   the connection-token "close" was sent in the request. If the server
2476   chooses to close the connection immediately after sending the
2477   response, it &SHOULD; send a Connection header field including the
2478   connection-token "close".
2479</t>
2480<t>
2481   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2482   decide to keep it open based on whether the response from a server
2483   contains a Connection header field with the connection-token close. In case
2484   the client does not want to maintain a connection for more than that
2485   request, it &SHOULD; send a Connection header field including the
2486   connection-token close.
2487</t>
2488<t>
2489   If either the client or the server sends the close token in the
2490   Connection header field, that request becomes the last one for the
2491   connection.
2492</t>
2493<t>
2494   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2495   maintained for HTTP versions less than 1.1 unless it is explicitly
2496   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2497   compatibility with HTTP/1.0 clients.
2498</t>
2499<t>
2500   In order to remain persistent, all messages on the connection &MUST;
2501   have a self-defined message length (i.e., one not defined by closure
2502   of the connection), as described in <xref target="message.body"/>.
2503</t>
2504</section>
2505
2506<section title="Pipelining" anchor="pipelining">
2507<t>
2508   A client that supports persistent connections &MAY; "pipeline" its
2509   requests (i.e., send multiple requests without waiting for each
2510   response). A server &MUST; send its responses to those requests in the
2511   same order that the requests were received.
2512</t>
2513<t>
2514   Clients which assume persistent connections and pipeline immediately
2515   after connection establishment &SHOULD; be prepared to retry their
2516   connection if the first pipelined attempt fails. If a client does
2517   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2518   persistent. Clients &MUST; also be prepared to resend their requests if
2519   the server closes the connection before sending all of the
2520   corresponding responses.
2521</t>
2522<t>
2523   Clients &SHOULD-NOT; pipeline requests using non-idempotent request methods or
2524   non-idempotent sequences of request methods (see &idempotent-methods;). Otherwise, a
2525   premature termination of the transport connection could lead to
2526   indeterminate results. A client wishing to send a non-idempotent
2527   request &SHOULD; wait to send that request until it has received the
2528   response status line for the previous request.
2529</t>
2530</section>
2531</section>
2532
2533<section title="Proxy Servers" anchor="persistent.proxy">
2534<t>
2535   It is especially important that proxies correctly implement the
2536   properties of the Connection header field as specified in <xref target="header.connection"/>.
2537</t>
2538<t>
2539   The proxy server &MUST; signal persistent connections separately with
2540   its clients and the origin servers (or other proxy servers) that it
2541   connects to. Each persistent connection applies to only one transport
2542   link.
2543</t>
2544<t>
2545   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2546   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2547   for information and discussion of the problems with the Keep-Alive header field
2548   implemented by many HTTP/1.0 clients).
2549</t>
2550
2551<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2552<!--<t>
2553  <cref anchor="TODO-end-to-end" source="jre">
2554    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2555    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2556  </cref>
2557</t>-->
2558<t>
2559   For the purpose of defining the behavior of caches and non-caching
2560   proxies, we divide HTTP header fields into two categories:
2561  <list style="symbols">
2562      <t>End-to-end header fields, which are  transmitted to the ultimate
2563        recipient of a request or response. End-to-end header fields in
2564        responses MUST be stored as part of a cache entry and &MUST; be
2565        transmitted in any response formed from a cache entry.</t>
2566
2567      <t>Hop-by-hop header fields, which are meaningful only for a single
2568        transport-level connection, and are not stored by caches or
2569        forwarded by proxies.</t>
2570  </list>
2571</t>
2572<t>
2573   The following HTTP/1.1 header fields are hop-by-hop header fields:
2574  <list style="symbols">
2575      <t>Connection</t>
2576      <t>Keep-Alive</t>
2577      <t>Proxy-Authenticate</t>
2578      <t>Proxy-Authorization</t>
2579      <t>TE</t>
2580      <t>Trailer</t>
2581      <t>Transfer-Encoding</t>
2582      <t>Upgrade</t>
2583  </list>
2584</t>
2585<t>
2586   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2587</t>
2588<t>
2589   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2590   (<xref target="header.connection"/>).
2591</t>
2592</section>
2593
2594<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2595<!--<t>
2596  <cref anchor="TODO-non-mod-headers" source="jre">
2597    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2598    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2599  </cref>
2600</t>-->
2601<t>
2602   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2603   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2604   modify an end-to-end header field unless the definition of that header field requires
2605   or specifically allows that.
2606</t>
2607<t>
2608   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2609   request or response, and it &MUST-NOT; add any of these fields if not
2610   already present:
2611  <list style="symbols">
2612    <t>Allow</t>
2613    <t>Content-Location</t>
2614    <t>Content-MD5</t>
2615    <t>ETag</t>
2616    <t>Last-Modified</t>
2617    <t>Server</t>
2618  </list>
2619</t>
2620<t>
2621   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2622   response:
2623  <list style="symbols">
2624    <t>Expires</t>
2625  </list>
2626</t>
2627<t>
2628   but it &MAY; add any of these fields if not already present. If an
2629   Expires header field is added, it &MUST; be given a field-value identical to
2630   that of the Date header field in that response.
2631</t>
2632<t>
2633   A proxy &MUST-NOT; modify or add any of the following fields in a
2634   message that contains the no-transform cache-control directive, or in
2635   any request:
2636  <list style="symbols">
2637    <t>Content-Encoding</t>
2638    <t>Content-Range</t>
2639    <t>Content-Type</t>
2640  </list>
2641</t>
2642<t>
2643   A transforming proxy &MAY; modify or add these fields to a message
2644   that does not include no-transform, but if it does so, it &MUST; add a
2645   Warning 214 (Transformation applied) if one does not already appear
2646   in the message (see &header-warning;).
2647</t>
2648<x:note>
2649  <t>
2650    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2651    cause authentication failures if stronger authentication
2652    mechanisms are introduced in later versions of HTTP. Such
2653    authentication mechanisms &MAY; rely on the values of header fields
2654    not listed here.
2655  </t>
2656</x:note>
2657<t>
2658   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2659   though it &MAY; change the message-body through application or removal
2660   of a transfer-coding (<xref target="transfer.codings"/>).
2661</t>
2662</section>
2663
2664</section>
2665
2666<section title="Practical Considerations" anchor="persistent.practical">
2667<t>
2668   Servers will usually have some time-out value beyond which they will
2669   no longer maintain an inactive connection. Proxy servers might make
2670   this a higher value since it is likely that the client will be making
2671   more connections through the same server. The use of persistent
2672   connections places no requirements on the length (or existence) of
2673   this time-out for either the client or the server.
2674</t>
2675<t>
2676   When a client or server wishes to time-out it &SHOULD; issue a graceful
2677   close on the transport connection. Clients and servers &SHOULD; both
2678   constantly watch for the other side of the transport close, and
2679   respond to it as appropriate. If a client or server does not detect
2680   the other side's close promptly it could cause unnecessary resource
2681   drain on the network.
2682</t>
2683<t>
2684   A client, server, or proxy &MAY; close the transport connection at any
2685   time. For example, a client might have started to send a new request
2686   at the same time that the server has decided to close the "idle"
2687   connection. From the server's point of view, the connection is being
2688   closed while it was idle, but from the client's point of view, a
2689   request is in progress.
2690</t>
2691<t>
2692   This means that clients, servers, and proxies &MUST; be able to recover
2693   from asynchronous close events. Client software &SHOULD; reopen the
2694   transport connection and retransmit the aborted sequence of requests
2695   without user interaction so long as the request sequence is
2696   idempotent (see &idempotent-methods;). Non-idempotent request methods or sequences
2697   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2698   human operator the choice of retrying the request(s). Confirmation by
2699   user-agent software with semantic understanding of the application
2700   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2701   be repeated if the second sequence of requests fails.
2702</t>
2703<t>
2704   Servers &SHOULD; always respond to at least one request per connection,
2705   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2706   middle of transmitting a response, unless a network or client failure
2707   is suspected.
2708</t>
2709<t>
2710   Clients (including proxies) &SHOULD; limit the number of simultaneous
2711   connections that they maintain to a given server (including proxies).
2712</t>
2713<t>
2714   Previous revisions of HTTP gave a specific number of connections as a
2715   ceiling, but this was found to be impractical for many applications. As a
2716   result, this specification does not mandate a particular maximum number of
2717   connections, but instead encourages clients to be conservative when opening
2718   multiple connections.
2719</t>
2720<t>
2721   In particular, while using multiple connections avoids the "head-of-line
2722   blocking" problem (whereby a request that takes significant server-side
2723   processing and/or has a large payload can block subsequent requests on the
2724   same connection), each connection used consumes server resources (sometimes
2725   significantly), and furthermore using multiple connections can cause
2726   undesirable side effects in congested networks.
2727</t>
2728<t>
2729   Note that servers might reject traffic that they deem abusive, including an
2730   excessive number of connections from a client.
2731</t>
2732</section>
2733</section>
2734
2735<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2736
2737<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2738<t>
2739   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2740   flow control mechanisms to resolve temporary overloads, rather than
2741   terminating connections with the expectation that clients will retry.
2742   The latter technique can exacerbate network congestion.
2743</t>
2744</section>
2745
2746<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2747<t>
2748   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2749   the network connection for an error status code while it is transmitting
2750   the request. If the client sees an error status code, it &SHOULD;
2751   immediately cease transmitting the body. If the body is being sent
2752   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2753   empty trailer &MAY; be used to prematurely mark the end of the message.
2754   If the body was preceded by a Content-Length header field, the client &MUST;
2755   close the connection.
2756</t>
2757</section>
2758
2759<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2760<t>
2761   The purpose of the 100 (Continue) status code (see &status-100;) is to
2762   allow a client that is sending a request message with a request body
2763   to determine if the origin server is willing to accept the request
2764   (based on the request header fields) before the client sends the request
2765   body. In some cases, it might either be inappropriate or highly
2766   inefficient for the client to send the body if the server will reject
2767   the message without looking at the body.
2768</t>
2769<t>
2770   Requirements for HTTP/1.1 clients:
2771  <list style="symbols">
2772    <t>
2773        If a client will wait for a 100 (Continue) response before
2774        sending the request body, it &MUST; send an Expect header
2775        field (&header-expect;) with the "100-continue" expectation.
2776    </t>
2777    <t>
2778        A client &MUST-NOT; send an Expect header field (&header-expect;)
2779        with the "100-continue" expectation if it does not intend
2780        to send a request body.
2781    </t>
2782  </list>
2783</t>
2784<t>
2785   Because of the presence of older implementations, the protocol allows
2786   ambiguous situations in which a client might send "Expect: 100-continue"
2787   without receiving either a 417 (Expectation Failed)
2788   or a 100 (Continue) status code. Therefore, when a client sends this
2789   header field to an origin server (possibly via a proxy) from which it
2790   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2791   wait for an indefinite period before sending the request body.
2792</t>
2793<t>
2794   Requirements for HTTP/1.1 origin servers:
2795  <list style="symbols">
2796    <t> Upon receiving a request which includes an Expect header
2797        field with the "100-continue" expectation, an origin server &MUST;
2798        either respond with 100 (Continue) status code and continue to read
2799        from the input stream, or respond with a final status code. The
2800        origin server &MUST-NOT; wait for the request body before sending
2801        the 100 (Continue) response. If it responds with a final status
2802        code, it &MAY; close the transport connection or it &MAY; continue
2803        to read and discard the rest of the request.  It &MUST-NOT;
2804        perform the request method if it returns a final status code.
2805    </t>
2806    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2807        the request message does not include an Expect header
2808        field with the "100-continue" expectation, and &MUST-NOT; send a
2809        100 (Continue) response if such a request comes from an HTTP/1.0
2810        (or earlier) client. There is an exception to this rule: for
2811        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2812        status code in response to an HTTP/1.1 PUT or POST request that does
2813        not include an Expect header field with the "100-continue"
2814        expectation. This exception, the purpose of which is
2815        to minimize any client processing delays associated with an
2816        undeclared wait for 100 (Continue) status code, applies only to
2817        HTTP/1.1 requests, and not to requests with any other HTTP-version
2818        value.
2819    </t>
2820    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2821        already received some or all of the request body for the
2822        corresponding request.
2823    </t>
2824    <t> An origin server that sends a 100 (Continue) response &MUST;
2825    ultimately send a final status code, once the request body is
2826        received and processed, unless it terminates the transport
2827        connection prematurely.
2828    </t>
2829    <t> If an origin server receives a request that does not include an
2830        Expect header field with the "100-continue" expectation,
2831        the request includes a request body, and the server responds
2832        with a final status code before reading the entire request body
2833        from the transport connection, then the server &SHOULD-NOT;  close
2834        the transport connection until it has read the entire request,
2835        or until the client closes the connection. Otherwise, the client
2836        might not reliably receive the response message. However, this
2837        requirement is not be construed as preventing a server from
2838        defending itself against denial-of-service attacks, or from
2839        badly broken client implementations.
2840      </t>
2841    </list>
2842</t>
2843<t>
2844   Requirements for HTTP/1.1 proxies:
2845  <list style="symbols">
2846    <t> If a proxy receives a request that includes an Expect header
2847        field with the "100-continue" expectation, and the proxy
2848        either knows that the next-hop server complies with HTTP/1.1 or
2849        higher, or does not know the HTTP version of the next-hop
2850        server, it &MUST; forward the request, including the Expect header
2851        field.
2852    </t>
2853    <t> If the proxy knows that the version of the next-hop server is
2854        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2855        respond with a 417 (Expectation Failed) status code.
2856    </t>
2857    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2858        numbers received from recently-referenced next-hop servers.
2859    </t>
2860    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2861        request message was received from an HTTP/1.0 (or earlier)
2862        client and did not include an Expect header field with
2863        the "100-continue" expectation. This requirement overrides the
2864        general rule for forwarding of 1xx responses (see &status-1xx;).
2865    </t>
2866  </list>
2867</t>
2868</section>
2869
2870<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2871<t>
2872   If an HTTP/1.1 client sends a request which includes a request body,
2873   but which does not include an Expect header field with the
2874   "100-continue" expectation, and if the client is not directly
2875   connected to an HTTP/1.1 origin server, and if the client sees the
2876   connection close before receiving a status line from the server, the
2877   client &SHOULD; retry the request.  If the client does retry this
2878   request, it &MAY; use the following "binary exponential backoff"
2879   algorithm to be assured of obtaining a reliable response:
2880  <list style="numbers">
2881    <t>
2882      Initiate a new connection to the server
2883    </t>
2884    <t>
2885      Transmit the request-line, header fields, and the CRLF that
2886      indicates the end of header fields.
2887    </t>
2888    <t>
2889      Initialize a variable R to the estimated round-trip time to the
2890         server (e.g., based on the time it took to establish the
2891         connection), or to a constant value of 5 seconds if the round-trip
2892         time is not available.
2893    </t>
2894    <t>
2895       Compute T = R * (2**N), where N is the number of previous
2896         retries of this request.
2897    </t>
2898    <t>
2899       Wait either for an error response from the server, or for T
2900         seconds (whichever comes first)
2901    </t>
2902    <t>
2903       If no error response is received, after T seconds transmit the
2904         body of the request.
2905    </t>
2906    <t>
2907       If client sees that the connection is closed prematurely,
2908         repeat from step 1 until the request is accepted, an error
2909         response is received, or the user becomes impatient and
2910         terminates the retry process.
2911    </t>
2912  </list>
2913</t>
2914<t>
2915   If at any point an error status code is received, the client
2916  <list style="symbols">
2917      <t>&SHOULD-NOT;  continue and</t>
2918
2919      <t>&SHOULD; close the connection if it has not completed sending the
2920        request message.</t>
2921    </list>
2922</t>
2923</section>
2924</section>
2925</section>
2926
2927
2928<section title="Miscellaneous notes that might disappear" anchor="misc">
2929<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2930<t>
2931   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2932</t>
2933</section>
2934
2935<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2936<t>
2937   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2938</t>
2939</section>
2940
2941<section title="Interception of HTTP for access control" anchor="http.intercept">
2942<t>
2943   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2944</t>
2945</section>
2946
2947<section title="Use of HTTP by other protocols" anchor="http.others">
2948<t>
2949   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2950   Extensions of HTTP like WebDAV.</cref>
2951</t>
2952
2953</section>
2954<section title="Use of HTTP by media type specification" anchor="http.media">
2955<t>
2956   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2957</t>
2958</section>
2959</section>
2960
2961<section title="Header Field Definitions" anchor="header.field.definitions">
2962<t>
2963   This section defines the syntax and semantics of HTTP header fields
2964   related to message framing and transport protocols.
2965</t>
2966
2967<section title="Connection" anchor="header.connection">
2968  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2969  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2970  <x:anchor-alias value="Connection"/>
2971  <x:anchor-alias value="connection-token"/>
2972<t>
2973   The "Connection" header field allows the sender to specify
2974   options that are desired only for that particular connection.
2975   Such connection options &MUST; be removed or replaced before the
2976   message can be forwarded downstream by a proxy or gateway.
2977   This mechanism also allows the sender to indicate which HTTP
2978   header fields used in the message are only intended for the
2979   immediate recipient ("hop-by-hop"), as opposed to all recipients
2980   on the chain ("end-to-end"), enabling the message to be
2981   self-descriptive and allowing future connection-specific extensions
2982   to be deployed in HTTP without fear that they will be blindly
2983   forwarded by previously deployed intermediaries.
2984</t>
2985<t>
2986   The Connection header field's value has the following grammar:
2987</t>
2988<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2989  <x:ref>Connection</x:ref>       = 1#<x:ref>connection-token</x:ref>
2990  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2991</artwork></figure>
2992<t>
2993   A proxy or gateway &MUST; parse a received Connection
2994   header field before a message is forwarded and, for each
2995   connection-token in this field, remove any header field(s) from
2996   the message with the same name as the connection-token, and then
2997   remove the Connection header field itself or replace it with the
2998   sender's own connection options for the forwarded message.
2999</t>
3000<t>
3001   A sender &MUST-NOT; include field-names in the Connection header
3002   field-value for fields that are defined as expressing constraints
3003   for all recipients in the request or response chain, such as the
3004   Cache-Control header field (&header-cache-control;).
3005</t>
3006<t>
3007   The connection options do not have to correspond to a header field
3008   present in the message, since a connection-specific header field
3009   might not be needed if there are no parameters associated with that
3010   connection option.  Recipients that trigger certain connection
3011   behavior based on the presence of connection options &MUST; do so
3012   based on the presence of the connection-token rather than only the
3013   presence of the optional header field.  In other words, if the
3014   connection option is received as a header field but not indicated
3015   within the Connection field-value, then the recipient &MUST; ignore
3016   the connection-specific header field because it has likely been
3017   forwarded by an intermediary that is only partially compliant.
3018</t>
3019<t>
3020   When defining new connection options, specifications ought to
3021   carefully consider existing deployed header fields and ensure
3022   that the new connection-token does not share the same name as
3023   an unrelated header field that might already be deployed.
3024   Defining a new connection-token essentially reserves that potential
3025   field-name for carrying additional information related to the
3026   connection option, since it would be unwise for senders to use
3027   that field-name for anything else.
3028</t>
3029<t>
3030   HTTP/1.1 defines the "close" connection option for the sender to
3031   signal that the connection will be closed after completion of the
3032   response. For example,
3033</t>
3034<figure><artwork type="example">
3035  Connection: close
3036</artwork></figure>
3037<t>
3038   in either the request or the response header fields indicates that
3039   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
3040   after the current request/response is complete.
3041</t>
3042<t>
3043   An HTTP/1.1 client that does not support persistent connections &MUST;
3044   include the "close" connection option in every request message.
3045</t>
3046<t>
3047   An HTTP/1.1 server that does not support persistent connections &MUST;
3048   include the "close" connection option in every response message that
3049   does not have a 1xx (Informational) status code.
3050</t>
3051</section>
3052
3053<section title="Content-Length" anchor="header.content-length">
3054  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3055  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3056  <x:anchor-alias value="Content-Length"/>
3057<t>
3058   The "Content-Length" header field indicates the size of the
3059   message-body, in decimal number of octets, for any message other than
3060   a response to a HEAD request or a response with a status code of 304.
3061   In the case of a response to a HEAD request, Content-Length indicates
3062   the size of the payload body (not including any potential transfer-coding)
3063   that would have been sent had the request been a GET.
3064   In the case of a 304 (Not Modified) response to a GET request,
3065   Content-Length indicates the size of the payload body (not including
3066   any potential transfer-coding) that would have been sent in a 200 (OK)
3067   response.
3068</t>
3069<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/>
3070  <x:ref>Content-Length</x:ref> = 1*<x:ref>DIGIT</x:ref>
3071</artwork></figure>
3072<t>
3073   An example is
3074</t>
3075<figure><artwork type="example">
3076  Content-Length: 3495
3077</artwork></figure>
3078<t>
3079   Implementations &SHOULD; use this field to indicate the message-body
3080   length when no transfer-coding is being applied and the
3081   payload's body length can be determined prior to being transferred.
3082   <xref target="message.body"/> describes how recipients determine the length
3083   of a message-body.
3084</t>
3085<t>
3086   Any Content-Length greater than or equal to zero is a valid value.
3087</t>
3088<t>
3089   Note that the use of this field in HTTP is significantly different from
3090   the corresponding definition in MIME, where it is an optional field
3091   used within the "message/external-body" content-type.
3092</t>
3093</section>
3094
3095<section title="Date" anchor="header.date">
3096  <iref primary="true" item="Date header field" x:for-anchor=""/>
3097  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3098  <x:anchor-alias value="Date"/>
3099<t>
3100   The "Date" header field represents the date and time at which
3101   the message was originated, having the same semantics as the Origination
3102   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3103   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
3104   it &MUST; be sent in rfc1123-date format.
3105</t>
3106<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/>
3107  <x:ref>Date</x:ref> = <x:ref>HTTP-date</x:ref>
3108</artwork></figure>
3109<t>
3110   An example is
3111</t>
3112<figure><artwork type="example">
3113  Date: Tue, 15 Nov 1994 08:12:31 GMT
3114</artwork></figure>
3115<t>
3116   Origin servers &MUST; include a Date header field in all responses,
3117   except in these cases:
3118  <list style="numbers">
3119      <t>If the response status code is 100 (Continue) or 101 (Switching
3120         Protocols), the response &MAY; include a Date header field, at
3121         the server's option.</t>
3122
3123      <t>If the response status code conveys a server error, e.g., 500
3124         (Internal Server Error) or 503 (Service Unavailable), and it is
3125         inconvenient or impossible to generate a valid Date.</t>
3126
3127      <t>If the server does not have a clock that can provide a
3128         reasonable approximation of the current time, its responses
3129         &MUST-NOT; include a Date header field. In this case, the rules
3130         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3131  </list>
3132</t>
3133<t>
3134   A received message that does not have a Date header field &MUST; be
3135   assigned one by the recipient if the message will be cached by that
3136   recipient.
3137</t>
3138<t>
3139   Clients can use the Date header field as well; in order to keep request
3140   messages small, they are advised not to include it when it doesn't convey
3141   any useful information (as it is usually the case for requests that do not
3142   contain a payload).
3143</t>
3144<t>
3145   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3146   time subsequent to the generation of the message. It &SHOULD; represent
3147   the best available approximation of the date and time of message
3148   generation, unless the implementation has no means of generating a
3149   reasonably accurate date and time. In theory, the date ought to
3150   represent the moment just before the payload is generated. In
3151   practice, the date can be generated at any time during the message
3152   origination without affecting its semantic value.
3153</t>
3154
3155<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3156<t>
3157   Some origin server implementations might not have a clock available.
3158   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3159   values to a response, unless these values were associated
3160   with the resource by a system or user with a reliable clock. It &MAY;
3161   assign an Expires value that is known, at or before server
3162   configuration time, to be in the past (this allows "pre-expiration"
3163   of responses without storing separate Expires values for each
3164   resource).
3165</t>
3166</section>
3167</section>
3168
3169<section title="Host" anchor="header.host">
3170  <iref primary="true" item="Host header field" x:for-anchor=""/>
3171  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3172  <x:anchor-alias value="Host"/>
3173<t>
3174   The "Host" header field in a request provides the host and port
3175   information from the target resource's URI, enabling the origin
3176   server to distinguish between resources while servicing requests
3177   for multiple host names on a single IP address.  Since the Host
3178   field-value is critical information for handling a request, it
3179   &SHOULD; be sent as the first header field following the Request-Line.
3180</t>
3181<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/>
3182  <x:ref>Host</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3183</artwork></figure>
3184<t>
3185   A client &MUST; send a Host header field in all HTTP/1.1 request
3186   messages.  If the target resource's URI includes an authority
3187   component, then the Host field-value &MUST; be identical to that
3188   authority component after excluding any userinfo (<xref target="http.uri"/>).
3189   If the authority component is missing or undefined for the target
3190   resource's URI, then the Host header field &MUST; be sent with an
3191   empty field-value.
3192</t>
3193<t>
3194   For example, a GET request to the origin server for
3195   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3196</t>
3197<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3198GET /pub/WWW/ HTTP/1.1
3199Host: www.example.org
3200</artwork></figure>
3201<t>
3202   The Host header field &MUST; be sent in an HTTP/1.1 request even
3203   if the request-target is in the form of an absolute-URI, since this
3204   allows the Host information to be forwarded through ancient HTTP/1.0
3205   proxies that might not have implemented Host.
3206</t>
3207<t>
3208   When an HTTP/1.1 proxy receives a request with a request-target in
3209   the form of an absolute-URI, the proxy &MUST; ignore the received
3210   Host header field (if any) and instead replace it with the host
3211   information of the request-target.  When a proxy forwards a request,
3212   it &MUST; generate the Host header field based on the received
3213   absolute-URI rather than the received Host.
3214</t>
3215<t>
3216   Since the Host header field acts as an application-level routing
3217   mechanism, it is a frequent target for malware seeking to poison
3218   a shared cache or redirect a request to an unintended server.
3219   An interception proxy is particularly vulnerable if it relies on
3220   the Host header field value for redirecting requests to internal
3221   servers, or for use as a cache key in a shared cache, without
3222   first verifying that the intercepted connection is targeting a
3223   valid IP address for that host.
3224</t>
3225<t>
3226   A server &MUST; respond with a 400 (Bad Request) status code to
3227   any HTTP/1.1 request message that lacks a Host header field and
3228   to any request message that contains more than one Host header field
3229   or a Host header field with an invalid field-value.
3230</t>
3231<t>
3232   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3233   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3234   for other requirements relating to Host.
3235</t>
3236</section>
3237
3238<section title="TE" anchor="header.te">
3239  <iref primary="true" item="TE header field" x:for-anchor=""/>
3240  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3241  <x:anchor-alias value="TE"/>
3242  <x:anchor-alias value="t-codings"/>
3243  <x:anchor-alias value="te-params"/>
3244  <x:anchor-alias value="te-ext"/>
3245<t>
3246   The "TE" header field indicates what extension transfer-codings
3247   it is willing to accept in the response, and whether or not it is
3248   willing to accept trailer fields in a chunked transfer-coding.
3249</t>
3250<t>
3251   Its value consists of the keyword "trailers" and/or a comma-separated
3252   list of extension transfer-coding names with optional accept
3253   parameters (as described in <xref target="transfer.codings"/>).
3254</t>
3255<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"/>
3256  <x:ref>TE</x:ref>        = #<x:ref>t-codings</x:ref>
3257  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3258  <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> )
3259  <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> ]
3260</artwork></figure>
3261<t>
3262   The presence of the keyword "trailers" indicates that the client is
3263   willing to accept trailer fields in a chunked transfer-coding, as
3264   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3265   transfer-coding values even though it does not itself represent a
3266   transfer-coding.
3267</t>
3268<t>
3269   Examples of its use are:
3270</t>
3271<figure><artwork type="example">
3272  TE: deflate
3273  TE:
3274  TE: trailers, deflate;q=0.5
3275</artwork></figure>
3276<t>
3277   The TE header field only applies to the immediate connection.
3278   Therefore, the keyword &MUST; be supplied within a Connection header
3279   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3280</t>
3281<t>
3282   A server tests whether a transfer-coding is acceptable, according to
3283   a TE field, using these rules:
3284  <list style="numbers">
3285    <x:lt>
3286      <t>The "chunked" transfer-coding is always acceptable. If the
3287         keyword "trailers" is listed, the client indicates that it is
3288         willing to accept trailer fields in the chunked response on
3289         behalf of itself and any downstream clients. The implication is
3290         that, if given, the client is stating that either all
3291         downstream clients are willing to accept trailer fields in the
3292         forwarded response, or that it will attempt to buffer the
3293         response on behalf of downstream recipients.
3294      </t><t>
3295         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3296         chunked response such that a client can be assured of buffering
3297         the entire response.</t>
3298    </x:lt>
3299    <x:lt>
3300      <t>If the transfer-coding being tested is one of the transfer-codings
3301         listed in the TE field, then it is acceptable unless it
3302         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3303         qvalue of 0 means "not acceptable".)</t>
3304    </x:lt>
3305    <x:lt>
3306      <t>If multiple transfer-codings are acceptable, then the
3307         acceptable transfer-coding with the highest non-zero qvalue is
3308         preferred.  The "chunked" transfer-coding always has a qvalue
3309         of 1.</t>
3310    </x:lt>
3311  </list>
3312</t>
3313<t>
3314   If the TE field-value is empty or if no TE field is present, the only
3315   transfer-coding is "chunked". A message with no transfer-coding is
3316   always acceptable.
3317</t>
3318</section>
3319
3320<section title="Trailer" anchor="header.trailer">
3321  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3322  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3323  <x:anchor-alias value="Trailer"/>
3324<t>
3325   The "Trailer" header field indicates that the given set of
3326   header fields is present in the trailer of a message encoded with
3327   chunked transfer-coding.
3328</t>
3329<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/>
3330  <x:ref>Trailer</x:ref> = 1#<x:ref>field-name</x:ref>
3331</artwork></figure>
3332<t>
3333   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3334   message using chunked transfer-coding with a non-empty trailer. Doing
3335   so allows the recipient to know which header fields to expect in the
3336   trailer.
3337</t>
3338<t>
3339   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3340   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3341   trailer fields in a "chunked" transfer-coding.
3342</t>
3343<t>
3344   Message header fields listed in the Trailer header field &MUST-NOT;
3345   include the following header fields:
3346  <list style="symbols">
3347    <t>Transfer-Encoding</t>
3348    <t>Content-Length</t>
3349    <t>Trailer</t>
3350  </list>
3351</t>
3352</section>
3353
3354<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3355  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3356  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3357  <x:anchor-alias value="Transfer-Encoding"/>
3358<t>
3359   The "Transfer-Encoding" header field indicates what transfer-codings
3360   (if any) have been applied to the message body. It differs from
3361   Content-Encoding (&content-codings;) in that transfer-codings are a property
3362   of the message (and therefore are removed by intermediaries), whereas
3363   content-codings are not.
3364</t>
3365<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/>
3366  <x:ref>Transfer-Encoding</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3367</artwork></figure>
3368<t>
3369   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3370</t>
3371<figure><artwork type="example">
3372  Transfer-Encoding: chunked
3373</artwork></figure>
3374<t>
3375   If multiple encodings have been applied to a representation, the transfer-codings
3376   &MUST; be listed in the order in which they were applied.
3377   Additional information about the encoding parameters &MAY; be provided
3378   by other header fields not defined by this specification.
3379</t>
3380<t>
3381   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3382   header field.
3383</t>
3384</section>
3385
3386<section title="Upgrade" anchor="header.upgrade">
3387  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3388  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3389  <x:anchor-alias value="Upgrade"/>
3390<t>
3391   The "Upgrade" header field allows the client to specify what
3392   additional communication protocols it would like to use, if the server
3393   chooses to switch protocols. Servers can use it to indicate what protocols
3394   they are willing to switch to.
3395</t>
3396<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/>
3397  <x:ref>Upgrade</x:ref> = 1#<x:ref>product</x:ref>
3398</artwork></figure>
3399<t>
3400   For example,
3401</t>
3402<figure><artwork type="example">
3403  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3404</artwork></figure>
3405<t>
3406   The Upgrade header field is intended to provide a simple mechanism
3407   for transition from HTTP/1.1 to some other, incompatible protocol. It
3408   does so by allowing the client to advertise its desire to use another
3409   protocol, such as a later version of HTTP with a higher major version
3410   number, even though the current request has been made using HTTP/1.1.
3411   This eases the difficult transition between incompatible protocols by
3412   allowing the client to initiate a request in the more commonly
3413   supported protocol while indicating to the server that it would like
3414   to use a "better" protocol if available (where "better" is determined
3415   by the server, possibly according to the nature of the request method
3416   or target resource).
3417</t>
3418<t>
3419   The Upgrade header field only applies to switching application-layer
3420   protocols upon the existing transport-layer connection. Upgrade
3421   cannot be used to insist on a protocol change; its acceptance and use
3422   by the server is optional. The capabilities and nature of the
3423   application-layer communication after the protocol change is entirely
3424   dependent upon the new protocol chosen, although the first action
3425   after changing the protocol &MUST; be a response to the initial HTTP
3426   request containing the Upgrade header field.
3427</t>
3428<t>
3429   The Upgrade header field only applies to the immediate connection.
3430   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3431   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3432   HTTP/1.1 message.
3433</t>
3434<t>
3435   The Upgrade header field cannot be used to indicate a switch to a
3436   protocol on a different connection. For that purpose, it is more
3437   appropriate to use a 3xx redirection response (&status-3xx;).
3438</t>
3439<t>
3440   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3441   Protocols) responses to indicate which protocol(s) are being switched to,
3442   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3443   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3444   response to indicate that they are willing to upgrade to one of the
3445   specified protocols.
3446</t>
3447<t>
3448   This specification only defines the protocol name "HTTP" for use by
3449   the family of Hypertext Transfer Protocols, as defined by the HTTP
3450   version rules of <xref target="http.version"/> and future updates to this
3451   specification. Additional tokens can be registered with IANA using the
3452   registration procedure defined below. 
3453</t>
3454
3455<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3456<t>
3457   The HTTP Upgrade Token Registry defines the name space for product
3458   tokens used to identify protocols in the Upgrade header field.
3459   Each registered token is associated with contact information and
3460   an optional set of specifications that details how the connection
3461   will be processed after it has been upgraded.
3462</t>
3463<t>
3464   Registrations are allowed on a First Come First Served basis as
3465   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3466   specifications need not be IETF documents or be subject to IESG review.
3467   Registrations are subject to the following rules:
3468  <list style="numbers">
3469    <t>A token, once registered, stays registered forever.</t>
3470    <t>The registration &MUST; name a responsible party for the
3471       registration.</t>
3472    <t>The registration &MUST; name a point of contact.</t>
3473    <t>The registration &MAY; name a set of specifications associated with that
3474       token. Such specifications need not be publicly available.</t>
3475    <t>The responsible party &MAY; change the registration at any time.
3476       The IANA will keep a record of all such changes, and make them
3477       available upon request.</t>
3478    <t>The responsible party for the first registration of a "product"
3479       token &MUST; approve later registrations of a "version" token
3480       together with that "product" token before they can be registered.</t>
3481    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3482       for a token. This will normally only be used in the case when a
3483       responsible party cannot be contacted.</t>
3484  </list>
3485</t>
3486</section>
3487
3488
3489</section>
3490
3491<section title="Via" anchor="header.via">
3492  <iref primary="true" item="Via header field" x:for-anchor=""/>
3493  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3494  <x:anchor-alias value="protocol-name"/>
3495  <x:anchor-alias value="protocol-version"/>
3496  <x:anchor-alias value="pseudonym"/>
3497  <x:anchor-alias value="received-by"/>
3498  <x:anchor-alias value="received-protocol"/>
3499  <x:anchor-alias value="Via"/>
3500<t>
3501   The "Via" header field &MUST; be sent by a proxy or gateway to
3502   indicate the intermediate protocols and recipients between the user
3503   agent and the server on requests, and between the origin server and
3504   the client on responses. It is analogous to the "Received" field
3505   used by email systems (<xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/>)
3506   and is intended to be used for tracking message forwards,
3507   avoiding request loops, and identifying the protocol capabilities of
3508   all senders along the request/response chain.
3509</t>
3510<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"/>
3511  <x:ref>Via</x:ref>               = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3512                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3513  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3514  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3515  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3516  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3517  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3518</artwork></figure>
3519<t>
3520   The received-protocol indicates the protocol version of the message
3521   received by the server or client along each segment of the
3522   request/response chain. The received-protocol version is appended to
3523   the Via field value when the message is forwarded so that information
3524   about the protocol capabilities of upstream applications remains
3525   visible to all recipients.
3526</t>
3527<t>
3528   The protocol-name is excluded if and only if it would be "HTTP". The
3529   received-by field is normally the host and optional port number of a
3530   recipient server or client that subsequently forwarded the message.
3531   However, if the real host is considered to be sensitive information,
3532   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3533   be assumed to be the default port of the received-protocol.
3534</t>
3535<t>
3536   Multiple Via field values represent each proxy or gateway that has
3537   forwarded the message. Each recipient &MUST; append its information
3538   such that the end result is ordered according to the sequence of
3539   forwarding applications.
3540</t>
3541<t>
3542   Comments &MAY; be used in the Via header field to identify the software
3543   of each recipient, analogous to the User-Agent and Server header fields.
3544   However, all comments in the Via field are optional and &MAY; be removed
3545   by any recipient prior to forwarding the message.
3546</t>
3547<t>
3548   For example, a request message could be sent from an HTTP/1.0 user
3549   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3550   forward the request to a public proxy at p.example.net, which completes
3551   the request by forwarding it to the origin server at www.example.com.
3552   The request received by www.example.com would then have the following
3553   Via header field:
3554</t>
3555<figure><artwork type="example">
3556  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3557</artwork></figure>
3558<t>
3559   A proxy or gateway used as a portal through a network firewall
3560   &SHOULD-NOT; forward the names and ports of hosts within the firewall
3561   region unless it is explicitly enabled to do so. If not enabled, the
3562   received-by host of any host behind the firewall &SHOULD; be replaced
3563   by an appropriate pseudonym for that host.
3564</t>
3565<t>
3566   For organizations that have strong privacy requirements for hiding
3567   internal structures, a proxy or gateway &MAY; combine an ordered
3568   subsequence of Via header field entries with identical received-protocol
3569   values into a single such entry. For example,
3570</t>
3571<figure><artwork type="example">
3572  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3573</artwork></figure>
3574<t>
3575  could be collapsed to
3576</t>
3577<figure><artwork type="example">
3578  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3579</artwork></figure>
3580<t>
3581   Senders &SHOULD-NOT; combine multiple entries unless they are all
3582   under the same organizational control and the hosts have already been
3583   replaced by pseudonyms. Senders &MUST-NOT; combine entries which
3584   have different received-protocol values.
3585</t>
3586</section>
3587
3588</section>
3589
3590<section title="IANA Considerations" anchor="IANA.considerations">
3591
3592<section title="Header Field Registration" anchor="header.field.registration">
3593<t>
3594   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3595   with the permanent registrations below (see <xref target="RFC3864"/>):
3596</t>
3597<?BEGININC p1-messaging.iana-headers ?>
3598<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3599<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3600   <ttcol>Header Field Name</ttcol>
3601   <ttcol>Protocol</ttcol>
3602   <ttcol>Status</ttcol>
3603   <ttcol>Reference</ttcol>
3604
3605   <c>Connection</c>
3606   <c>http</c>
3607   <c>standard</c>
3608   <c>
3609      <xref target="header.connection"/>
3610   </c>
3611   <c>Content-Length</c>
3612   <c>http</c>
3613   <c>standard</c>
3614   <c>
3615      <xref target="header.content-length"/>
3616   </c>
3617   <c>Date</c>
3618   <c>http</c>
3619   <c>standard</c>
3620   <c>
3621      <xref target="header.date"/>
3622   </c>
3623   <c>Host</c>
3624   <c>http</c>
3625   <c>standard</c>
3626   <c>
3627      <xref target="header.host"/>
3628   </c>
3629   <c>TE</c>
3630   <c>http</c>
3631   <c>standard</c>
3632   <c>
3633      <xref target="header.te"/>
3634   </c>
3635   <c>Trailer</c>
3636   <c>http</c>
3637   <c>standard</c>
3638   <c>
3639      <xref target="header.trailer"/>
3640   </c>
3641   <c>Transfer-Encoding</c>
3642   <c>http</c>
3643   <c>standard</c>
3644   <c>
3645      <xref target="header.transfer-encoding"/>
3646   </c>
3647   <c>Upgrade</c>
3648   <c>http</c>
3649   <c>standard</c>
3650   <c>
3651      <xref target="header.upgrade"/>
3652   </c>
3653   <c>Via</c>
3654   <c>http</c>
3655   <c>standard</c>
3656   <c>
3657      <xref target="header.via"/>
3658   </c>
3659</texttable>
3660<!--(END)-->
3661<?ENDINC p1-messaging.iana-headers ?>
3662<t>
3663   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3664</t>
3665</section>
3666
3667<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3668<t>
3669   The entries for the "http" and "https" URI Schemes in the registry located at
3670   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3671   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3672   and <xref target="https.uri" format="counter"/> of this document
3673   (see <xref target="RFC4395"/>).
3674</t>
3675</section>
3676
3677<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3678<t>
3679   This document serves as the specification for the Internet media types
3680   "message/http" and "application/http". The following is to be registered with
3681   IANA (see <xref target="RFC4288"/>).
3682</t>
3683<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3684<iref item="Media Type" subitem="message/http" primary="true"/>
3685<iref item="message/http Media Type" primary="true"/>
3686<t>
3687   The message/http type can be used to enclose a single HTTP request or
3688   response message, provided that it obeys the MIME restrictions for all
3689   "message" types regarding line length and encodings.
3690</t>
3691<t>
3692  <list style="hanging" x:indent="12em">
3693    <t hangText="Type name:">
3694      message
3695    </t>
3696    <t hangText="Subtype name:">
3697      http
3698    </t>
3699    <t hangText="Required parameters:">
3700      none
3701    </t>
3702    <t hangText="Optional parameters:">
3703      version, msgtype
3704      <list style="hanging">
3705        <t hangText="version:">
3706          The HTTP-Version number of the enclosed message
3707          (e.g., "1.1"). If not present, the version can be
3708          determined from the first line of the body.
3709        </t>
3710        <t hangText="msgtype:">
3711          The message type &mdash; "request" or "response". If not
3712          present, the type can be determined from the first
3713          line of the body.
3714        </t>
3715      </list>
3716    </t>
3717    <t hangText="Encoding considerations:">
3718      only "7bit", "8bit", or "binary" are permitted
3719    </t>
3720    <t hangText="Security considerations:">
3721      none
3722    </t>
3723    <t hangText="Interoperability considerations:">
3724      none
3725    </t>
3726    <t hangText="Published specification:">
3727      This specification (see <xref target="internet.media.type.message.http"/>).
3728    </t>
3729    <t hangText="Applications that use this media type:">
3730    </t>
3731    <t hangText="Additional information:">
3732      <list style="hanging">
3733        <t hangText="Magic number(s):">none</t>
3734        <t hangText="File extension(s):">none</t>
3735        <t hangText="Macintosh file type code(s):">none</t>
3736      </list>
3737    </t>
3738    <t hangText="Person and email address to contact for further information:">
3739      See Authors Section.
3740    </t>
3741    <t hangText="Intended usage:">
3742      COMMON
3743    </t>
3744    <t hangText="Restrictions on usage:">
3745      none
3746    </t>
3747    <t hangText="Author/Change controller:">
3748      IESG
3749    </t>
3750  </list>
3751</t>
3752</section>
3753<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3754<iref item="Media Type" subitem="application/http" primary="true"/>
3755<iref item="application/http Media Type" primary="true"/>
3756<t>
3757   The application/http type can be used to enclose a pipeline of one or more
3758   HTTP request or response messages (not intermixed).
3759</t>
3760<t>
3761  <list style="hanging" x:indent="12em">
3762    <t hangText="Type name:">
3763      application
3764    </t>
3765    <t hangText="Subtype name:">
3766      http
3767    </t>
3768    <t hangText="Required parameters:">
3769      none
3770    </t>
3771    <t hangText="Optional parameters:">
3772      version, msgtype
3773      <list style="hanging">
3774        <t hangText="version:">
3775          The HTTP-Version number of the enclosed messages
3776          (e.g., "1.1"). If not present, the version can be
3777          determined from the first line of the body.
3778        </t>
3779        <t hangText="msgtype:">
3780          The message type &mdash; "request" or "response". If not
3781          present, the type can be determined from the first
3782          line of the body.
3783        </t>
3784      </list>
3785    </t>
3786    <t hangText="Encoding considerations:">
3787      HTTP messages enclosed by this type
3788      are in "binary" format; use of an appropriate
3789      Content-Transfer-Encoding is required when
3790      transmitted via E-mail.
3791    </t>
3792    <t hangText="Security considerations:">
3793      none
3794    </t>
3795    <t hangText="Interoperability considerations:">
3796      none
3797    </t>
3798    <t hangText="Published specification:">
3799      This specification (see <xref target="internet.media.type.application.http"/>).
3800    </t>
3801    <t hangText="Applications that use this media type:">
3802    </t>
3803    <t hangText="Additional information:">
3804      <list style="hanging">
3805        <t hangText="Magic number(s):">none</t>
3806        <t hangText="File extension(s):">none</t>
3807        <t hangText="Macintosh file type code(s):">none</t>
3808      </list>
3809    </t>
3810    <t hangText="Person and email address to contact for further information:">
3811      See Authors Section.
3812    </t>
3813    <t hangText="Intended usage:">
3814      COMMON
3815    </t>
3816    <t hangText="Restrictions on usage:">
3817      none
3818    </t>
3819    <t hangText="Author/Change controller:">
3820      IESG
3821    </t>
3822  </list>
3823</t>
3824</section>
3825</section>
3826
3827<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3828<t>
3829   The registration procedure for HTTP Transfer Codings is now defined by
3830   <xref target="transfer.coding.registry"/> of this document.
3831</t>
3832<t>
3833   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3834   shall be updated with the registrations below:
3835</t>
3836<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3837   <ttcol>Name</ttcol>
3838   <ttcol>Description</ttcol>
3839   <ttcol>Reference</ttcol>
3840   <c>chunked</c>
3841   <c>Transfer in a series of chunks</c>
3842   <c>
3843      <xref target="chunked.encoding"/>
3844   </c>
3845   <c>compress</c>
3846   <c>UNIX "compress" program method</c>
3847   <c>
3848      <xref target="compress.coding"/>
3849   </c>
3850   <c>deflate</c>
3851   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3852   the "zlib" data format (<xref target="RFC1950"/>)
3853   </c>
3854   <c>
3855      <xref target="deflate.coding"/>
3856   </c>
3857   <c>gzip</c>
3858   <c>Same as GNU zip <xref target="RFC1952"/></c>
3859   <c>
3860      <xref target="gzip.coding"/>
3861   </c>
3862</texttable>
3863</section>
3864
3865<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3866<t>
3867   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3868   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3869   by <xref target="upgrade.token.registry"/> of this document.
3870</t>
3871<t>
3872   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3873   shall be updated with the registration below:
3874</t>
3875<texttable align="left" suppress-title="true">
3876   <ttcol>Value</ttcol>
3877   <ttcol>Description</ttcol>
3878   <ttcol>Reference</ttcol>
3879
3880   <c>HTTP</c>
3881   <c>Hypertext Transfer Protocol</c> 
3882   <c><xref target="http.version"/> of this specification</c>
3883<!-- IANA should add this without our instructions; emailed on June 05, 2009
3884   <c>TLS/1.0</c>
3885   <c>Transport Layer Security</c>
3886   <c><xref target="RFC2817"/></c> -->
3887
3888</texttable>
3889</section>
3890
3891</section>
3892
3893<section title="Security Considerations" anchor="security.considerations">
3894<t>
3895   This section is meant to inform application developers, information
3896   providers, and users of the security limitations in HTTP/1.1 as
3897   described by this document. The discussion does not include
3898   definitive solutions to the problems revealed, though it does make
3899   some suggestions for reducing security risks.
3900</t>
3901
3902<section title="Personal Information" anchor="personal.information">
3903<t>
3904   HTTP clients are often privy to large amounts of personal information
3905   (e.g., the user's name, location, mail address, passwords, encryption
3906   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3907   leakage of this information.
3908   We very strongly recommend that a convenient interface be provided
3909   for the user to control dissemination of such information, and that
3910   designers and implementors be particularly careful in this area.
3911   History shows that errors in this area often create serious security
3912   and/or privacy problems and generate highly adverse publicity for the
3913   implementor's company.
3914</t>
3915</section>
3916
3917<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3918<t>
3919   A server is in the position to save personal data about a user's
3920   requests which might identify their reading patterns or subjects of
3921   interest. This information is clearly confidential in nature and its
3922   handling can be constrained by law in certain countries. People using
3923   HTTP to provide data are responsible for ensuring that
3924   such material is not distributed without the permission of any
3925   individuals that are identifiable by the published results.
3926</t>
3927</section>
3928
3929<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3930<t>
3931   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3932   the documents returned by HTTP requests to be only those that were
3933   intended by the server administrators. If an HTTP server translates
3934   HTTP URIs directly into file system calls, the server &MUST; take
3935   special care not to serve files that were not intended to be
3936   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3937   other operating systems use ".." as a path component to indicate a
3938   directory level above the current one. On such a system, an HTTP
3939   server &MUST; disallow any such construct in the request-target if it
3940   would otherwise allow access to a resource outside those intended to
3941   be accessible via the HTTP server. Similarly, files intended for
3942   reference only internally to the server (such as access control
3943   files, configuration files, and script code) &MUST; be protected from
3944   inappropriate retrieval, since they might contain sensitive
3945   information. Experience has shown that minor bugs in such HTTP server
3946   implementations have turned into security risks.
3947</t>
3948</section>
3949
3950<section title="DNS Spoofing" anchor="dns.spoofing">
3951<t>
3952   Clients using HTTP rely heavily on the Domain Name Service, and are
3953   thus generally prone to security attacks based on the deliberate
3954   mis-association of IP addresses and DNS names. Clients need to be
3955   cautious in assuming the continuing validity of an IP number/DNS name
3956   association.
3957</t>
3958<t>
3959   In particular, HTTP clients &SHOULD; rely on their name resolver for
3960   confirmation of an IP number/DNS name association, rather than
3961   caching the result of previous host name lookups. Many platforms
3962   already can cache host name lookups locally when appropriate, and
3963   they &SHOULD; be configured to do so. It is proper for these lookups to
3964   be cached, however, only when the TTL (Time To Live) information
3965   reported by the name server makes it likely that the cached
3966   information will remain useful.
3967</t>
3968<t>
3969   If HTTP clients cache the results of host name lookups in order to
3970   achieve a performance improvement, they &MUST; observe the TTL
3971   information reported by DNS.
3972</t>
3973<t>
3974   If HTTP clients do not observe this rule, they could be spoofed when
3975   a previously-accessed server's IP address changes. As network
3976   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3977   possibility of this form of attack will grow. Observing this
3978   requirement thus reduces this potential security vulnerability.
3979</t>
3980<t>
3981   This requirement also improves the load-balancing behavior of clients
3982   for replicated servers using the same DNS name and reduces the
3983   likelihood of a user's experiencing failure in accessing sites which
3984   use that strategy.
3985</t>
3986</section>
3987
3988<section title="Proxies and Caching" anchor="attack.proxies">
3989<t>
3990   By their very nature, HTTP proxies are men-in-the-middle, and
3991   represent an opportunity for man-in-the-middle attacks. Compromise of
3992   the systems on which the proxies run can result in serious security
3993   and privacy problems. Proxies have access to security-related
3994   information, personal information about individual users and
3995   organizations, and proprietary information belonging to users and
3996   content providers. A compromised proxy, or a proxy implemented or
3997   configured without regard to security and privacy considerations,
3998   might be used in the commission of a wide range of potential attacks.
3999</t>
4000<t>
4001   Proxy operators need to protect the systems on which proxies run as
4002   they would protect any system that contains or transports sensitive
4003   information. In particular, log information gathered at proxies often
4004   contains highly sensitive personal information, and/or information
4005   about organizations. Log information needs to be carefully guarded, and
4006   appropriate guidelines for use need to be developed and followed.
4007   (<xref target="abuse.of.server.log.information"/>).
4008</t>
4009<t>
4010   Proxy implementors need to consider the privacy and security
4011   implications of their design and coding decisions, and of the
4012   configuration options they provide to proxy operators (especially the
4013   default configuration).
4014</t>
4015<t>
4016   Users of a proxy need to be aware that proxies are no trustworthier than
4017   the people who run them; HTTP itself cannot solve this problem.
4018</t>
4019<t>
4020   The judicious use of cryptography, when appropriate, might suffice to
4021   protect against a broad range of security and privacy attacks. Such
4022   cryptography is beyond the scope of the HTTP/1.1 specification.
4023</t>
4024</section>
4025
4026<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4027<t>
4028   They exist. They are hard to defend against. Research continues.
4029   Beware.
4030</t>
4031</section>
4032</section>
4033
4034<section title="Acknowledgments" anchor="ack">
4035<t>
4036   HTTP has evolved considerably over the years. It has
4037   benefited from a large and active developer community &mdash; the many
4038   people who have participated on the www-talk mailing list &mdash; and it is
4039   that community which has been most responsible for the success of
4040   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4041   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4042   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4043   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4044   VanHeyningen deserve special recognition for their efforts in
4045   defining early aspects of the protocol.
4046</t>
4047<t>
4048   This document has benefited greatly from the comments of all those
4049   participating in the HTTP-WG. In addition to those already mentioned,
4050   the following individuals have contributed to this specification:
4051</t>
4052<t>
4053   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4054   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4055   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4056   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4057   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4058   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4059   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4060   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4061   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4062   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4063   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4064   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4065</t>
4066<t>
4067   Thanks to the "cave men" of Palo Alto. You know who you are.
4068</t>
4069<t>
4070   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4071   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4072   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4073   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4074   Larry Masinter for their help. And thanks go particularly to Jeff
4075   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4076</t>
4077<t>
4078   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4079   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4080   discovery of many of the problems that this document attempts to
4081   rectify.
4082</t>
4083<t>
4084   This specification makes heavy use of the augmented BNF and generic
4085   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4086   reuses many of the definitions provided by Nathaniel Borenstein and
4087   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4088   specification will help reduce past confusion over the relationship
4089   between HTTP and Internet mail message formats.
4090</t>
4091<!--
4092
4093Acknowledgements TODO list
4094
4095- Jeff Hodges ("effective request URI")
4096
4097-->
4098</section>
4099
4100</middle>
4101<back>
4102
4103<references title="Normative References">
4104
4105<reference anchor="ISO-8859-1">
4106  <front>
4107    <title>
4108     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4109    </title>
4110    <author>
4111      <organization>International Organization for Standardization</organization>
4112    </author>
4113    <date year="1998"/>
4114  </front>
4115  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4116</reference>
4117
4118<reference anchor="Part2">
4119  <front>
4120    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4121    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4122      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4123      <address><email>fielding@gbiv.com</email></address>
4124    </author>
4125    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4126      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4127      <address><email>jg@freedesktop.org</email></address>
4128    </author>
4129    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4130      <organization abbrev="HP">Hewlett-Packard Company</organization>
4131      <address><email>JeffMogul@acm.org</email></address>
4132    </author>
4133    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4134      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4135      <address><email>henrikn@microsoft.com</email></address>
4136    </author>
4137    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4138      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4139      <address><email>LMM@acm.org</email></address>
4140    </author>
4141    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4142      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4143      <address><email>paulle@microsoft.com</email></address>
4144    </author>
4145    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4146      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4147      <address><email>timbl@w3.org</email></address>
4148    </author>
4149    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4150      <organization abbrev="W3C">World Wide Web Consortium</organization>
4151      <address><email>ylafon@w3.org</email></address>
4152    </author>
4153    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4154      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4155      <address><email>julian.reschke@greenbytes.de</email></address>
4156    </author>
4157    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4158  </front>
4159  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4160  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4161</reference>
4162
4163<reference anchor="Part3">
4164  <front>
4165    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4166    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4167      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4168      <address><email>fielding@gbiv.com</email></address>
4169    </author>
4170    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4171      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4172      <address><email>jg@freedesktop.org</email></address>
4173    </author>
4174    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4175      <organization abbrev="HP">Hewlett-Packard Company</organization>
4176      <address><email>JeffMogul@acm.org</email></address>
4177    </author>
4178    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4179      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4180      <address><email>henrikn@microsoft.com</email></address>
4181    </author>
4182    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4183      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4184      <address><email>LMM@acm.org</email></address>
4185    </author>
4186    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4187      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4188      <address><email>paulle@microsoft.com</email></address>
4189    </author>
4190    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4191      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4192      <address><email>timbl@w3.org</email></address>
4193    </author>
4194    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4195      <organization abbrev="W3C">World Wide Web Consortium</organization>
4196      <address><email>ylafon@w3.org</email></address>
4197    </author>
4198    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4199      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4200      <address><email>julian.reschke@greenbytes.de</email></address>
4201    </author>
4202    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4203  </front>
4204  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4205  <x:source href="p3-payload.xml" basename="p3-payload"/>
4206</reference>
4207
4208<reference anchor="Part6">
4209  <front>
4210    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4211    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4212      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4213      <address><email>fielding@gbiv.com</email></address>
4214    </author>
4215    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4216      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4217      <address><email>jg@freedesktop.org</email></address>
4218    </author>
4219    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4220      <organization abbrev="HP">Hewlett-Packard Company</organization>
4221      <address><email>JeffMogul@acm.org</email></address>
4222    </author>
4223    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4224      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4225      <address><email>henrikn@microsoft.com</email></address>
4226    </author>
4227    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4228      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4229      <address><email>LMM@acm.org</email></address>
4230    </author>
4231    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4232      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4233      <address><email>paulle@microsoft.com</email></address>
4234    </author>
4235    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4236      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4237      <address><email>timbl@w3.org</email></address>
4238    </author>
4239    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4240      <organization abbrev="W3C">World Wide Web Consortium</organization>
4241      <address><email>ylafon@w3.org</email></address>
4242    </author>
4243    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4244      <address><email>mnot@mnot.net</email></address>
4245    </author>
4246    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4247      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4248      <address><email>julian.reschke@greenbytes.de</email></address>
4249    </author>
4250    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4251  </front>
4252  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4253  <x:source href="p6-cache.xml" basename="p6-cache"/>
4254</reference>
4255
4256<reference anchor="RFC5234">
4257  <front>
4258    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4259    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4260      <organization>Brandenburg InternetWorking</organization>
4261      <address>
4262        <email>dcrocker@bbiw.net</email>
4263      </address> 
4264    </author>
4265    <author initials="P." surname="Overell" fullname="Paul Overell">
4266      <organization>THUS plc.</organization>
4267      <address>
4268        <email>paul.overell@thus.net</email>
4269      </address>
4270    </author>
4271    <date month="January" year="2008"/>
4272  </front>
4273  <seriesInfo name="STD" value="68"/>
4274  <seriesInfo name="RFC" value="5234"/>
4275</reference>
4276
4277<reference anchor="RFC2119">
4278  <front>
4279    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4280    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4281      <organization>Harvard University</organization>
4282      <address><email>sob@harvard.edu</email></address>
4283    </author>
4284    <date month="March" year="1997"/>
4285  </front>
4286  <seriesInfo name="BCP" value="14"/>
4287  <seriesInfo name="RFC" value="2119"/>
4288</reference>
4289
4290<reference anchor="RFC3986">
4291 <front>
4292  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4293  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4294    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4295    <address>
4296       <email>timbl@w3.org</email>
4297       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4298    </address>
4299  </author>
4300  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4301    <organization abbrev="Day Software">Day Software</organization>
4302    <address>
4303      <email>fielding@gbiv.com</email>
4304      <uri>http://roy.gbiv.com/</uri>
4305    </address>
4306  </author>
4307  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4308    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4309    <address>
4310      <email>LMM@acm.org</email>
4311      <uri>http://larry.masinter.net/</uri>
4312    </address>
4313  </author>
4314  <date month='January' year='2005'></date>
4315 </front>
4316 <seriesInfo name="STD" value="66"/>
4317 <seriesInfo name="RFC" value="3986"/>
4318</reference>
4319
4320<reference anchor="USASCII">
4321  <front>
4322    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4323    <author>
4324      <organization>American National Standards Institute</organization>
4325    </author>
4326    <date year="1986"/>
4327  </front>
4328  <seriesInfo name="ANSI" value="X3.4"/>
4329</reference>
4330
4331<reference anchor="RFC1950">
4332  <front>
4333    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4334    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4335      <organization>Aladdin Enterprises</organization>
4336      <address><email>ghost@aladdin.com</email></address>
4337    </author>
4338    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4339    <date month="May" year="1996"/>
4340  </front>
4341  <seriesInfo name="RFC" value="1950"/>
4342  <annotation>
4343    RFC 1950 is an Informational RFC, thus it might be less stable than
4344    this specification. On the other hand, this downward reference was
4345    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4346    therefore it is unlikely to cause problems in practice. See also
4347    <xref target="BCP97"/>.
4348  </annotation>
4349</reference>
4350
4351<reference anchor="RFC1951">
4352  <front>
4353    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4354    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4355      <organization>Aladdin Enterprises</organization>
4356      <address><email>ghost@aladdin.com</email></address>
4357    </author>
4358    <date month="May" year="1996"/>
4359  </front>
4360  <seriesInfo name="RFC" value="1951"/>
4361  <annotation>
4362    RFC 1951 is an Informational RFC, thus it might be less stable than
4363    this specification. On the other hand, this downward reference was
4364    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4365    therefore it is unlikely to cause problems in practice. See also
4366    <xref target="BCP97"/>.
4367  </annotation>
4368</reference>
4369
4370<reference anchor="RFC1952">
4371  <front>
4372    <title>GZIP file format specification version 4.3</title>
4373    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4374      <organization>Aladdin Enterprises</organization>
4375      <address><email>ghost@aladdin.com</email></address>
4376    </author>
4377    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4378      <address><email>gzip@prep.ai.mit.edu</email></address>
4379    </author>
4380    <author initials="M." surname="Adler" fullname="Mark Adler">
4381      <address><email>madler@alumni.caltech.edu</email></address>
4382    </author>
4383    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4384      <address><email>ghost@aladdin.com</email></address>
4385    </author>
4386    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4387      <address><email>randeg@alumni.rpi.edu</email></address>
4388    </author>
4389    <date month="May" year="1996"/>
4390  </front>
4391  <seriesInfo name="RFC" value="1952"/>
4392  <annotation>
4393    RFC 1952 is an Informational RFC, thus it might be less stable than
4394    this specification. On the other hand, this downward reference was
4395    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4396    therefore it is unlikely to cause problems in practice. See also
4397    <xref target="BCP97"/>.
4398  </annotation>
4399</reference>
4400
4401</references>
4402
4403<references title="Informative References">
4404
4405<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4406  <front>
4407    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4408    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4409    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4410    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4411    <author initials="H." surname="Lie" fullname="H. Lie"/>
4412    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4413    <date year="1997" month="September"/>
4414  </front>
4415  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4416</reference>
4417
4418<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4419  <front>
4420    <title>Improving HTTP Latency</title>
4421    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4422    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4423    <date year="1995" month="December"/>
4424  </front>
4425  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4426</reference>
4427
4428<reference anchor="RFC1123">
4429  <front>
4430    <title>Requirements for Internet Hosts - Application and Support</title>
4431    <author initials="R." surname="Braden" fullname="Robert Braden">
4432      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4433      <address><email>Braden@ISI.EDU</email></address>
4434    </author>
4435    <date month="October" year="1989"/>
4436  </front>
4437  <seriesInfo name="STD" value="3"/>
4438  <seriesInfo name="RFC" value="1123"/>
4439</reference>
4440
4441<reference anchor="RFC1900">
4442  <front>
4443    <title>Renumbering Needs Work</title>
4444    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4445      <organization>CERN, Computing and Networks Division</organization>
4446      <address><email>brian@dxcoms.cern.ch</email></address>
4447    </author>
4448    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4449      <organization>cisco Systems</organization>
4450      <address><email>yakov@cisco.com</email></address>
4451    </author>
4452    <date month="February" year="1996"/>
4453  </front>
4454  <seriesInfo name="RFC" value="1900"/>
4455</reference>
4456
4457<reference anchor='RFC1919'>
4458  <front>
4459    <title>Classical versus Transparent IP Proxies</title>
4460    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4461      <address><email>mchatel@pax.eunet.ch</email></address>
4462    </author>
4463    <date year='1996' month='March' />
4464  </front>
4465  <seriesInfo name='RFC' value='1919' />
4466</reference>
4467
4468<reference anchor="RFC1945">
4469  <front>
4470    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4471    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4472      <organization>MIT, Laboratory for Computer Science</organization>
4473      <address><email>timbl@w3.org</email></address>
4474    </author>
4475    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4476      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4477      <address><email>fielding@ics.uci.edu</email></address>
4478    </author>
4479    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4480      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4481      <address><email>frystyk@w3.org</email></address>
4482    </author>
4483    <date month="May" year="1996"/>
4484  </front>
4485  <seriesInfo name="RFC" value="1945"/>
4486</reference>
4487
4488<reference anchor="RFC2045">
4489  <front>
4490    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4491    <author initials="N." surname="Freed" fullname="Ned Freed">
4492      <organization>Innosoft International, Inc.</organization>
4493      <address><email>ned@innosoft.com</email></address>
4494    </author>
4495    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4496      <organization>First Virtual Holdings</organization>
4497      <address><email>nsb@nsb.fv.com</email></address>
4498    </author>
4499    <date month="November" year="1996"/>
4500  </front>
4501  <seriesInfo name="RFC" value="2045"/>
4502</reference>
4503
4504<reference anchor="RFC2047">
4505  <front>
4506    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4507    <author initials="K." surname="Moore" fullname="Keith Moore">
4508      <organization>University of Tennessee</organization>
4509      <address><email>moore@cs.utk.edu</email></address>
4510    </author>
4511    <date month="November" year="1996"/>
4512  </front>
4513  <seriesInfo name="RFC" value="2047"/>
4514</reference>
4515
4516<reference anchor="RFC2068">
4517  <front>
4518    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4519    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4520      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4521      <address><email>fielding@ics.uci.edu</email></address>
4522    </author>
4523    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4524      <organization>MIT Laboratory for Computer Science</organization>
4525      <address><email>jg@w3.org</email></address>
4526    </author>
4527    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4528      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4529      <address><email>mogul@wrl.dec.com</email></address>
4530    </author>
4531    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4532      <organization>MIT Laboratory for Computer Science</organization>
4533      <address><email>frystyk@w3.org</email></address>
4534    </author>
4535    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4536      <organization>MIT Laboratory for Computer Science</organization>
4537      <address><email>timbl@w3.org</email></address>
4538    </author>
4539    <date month="January" year="1997"/>
4540  </front>
4541  <seriesInfo name="RFC" value="2068"/>
4542</reference>
4543
4544<reference anchor="RFC2145">
4545  <front>
4546    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4547    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4548      <organization>Western Research Laboratory</organization>
4549      <address><email>mogul@wrl.dec.com</email></address>
4550    </author>
4551    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4552      <organization>Department of Information and Computer Science</organization>
4553      <address><email>fielding@ics.uci.edu</email></address>
4554    </author>
4555    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4556      <organization>MIT Laboratory for Computer Science</organization>
4557      <address><email>jg@w3.org</email></address>
4558    </author>
4559    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4560      <organization>W3 Consortium</organization>
4561      <address><email>frystyk@w3.org</email></address>
4562    </author>
4563    <date month="May" year="1997"/>
4564  </front>
4565  <seriesInfo name="RFC" value="2145"/>
4566</reference>
4567
4568<reference anchor="RFC2616">
4569  <front>
4570    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4571    <author initials="R." surname="Fielding" fullname="R. Fielding">
4572      <organization>University of California, Irvine</organization>
4573      <address><email>fielding@ics.uci.edu</email></address>
4574    </author>
4575    <author initials="J." surname="Gettys" fullname="J. Gettys">
4576      <organization>W3C</organization>
4577      <address><email>jg@w3.org</email></address>
4578    </author>
4579    <author initials="J." surname="Mogul" fullname="J. Mogul">
4580      <organization>Compaq Computer Corporation</organization>
4581      <address><email>mogul@wrl.dec.com</email></address>
4582    </author>
4583    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4584      <organization>MIT Laboratory for Computer Science</organization>
4585      <address><email>frystyk@w3.org</email></address>
4586    </author>
4587    <author initials="L." surname="Masinter" fullname="L. Masinter">
4588      <organization>Xerox Corporation</organization>
4589      <address><email>masinter@parc.xerox.com</email></address>
4590    </author>
4591    <author initials="P." surname="Leach" fullname="P. Leach">
4592      <organization>Microsoft Corporation</organization>
4593      <address><email>paulle@microsoft.com</email></address>
4594    </author>
4595    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4596      <organization>W3C</organization>
4597      <address><email>timbl@w3.org</email></address>
4598    </author>
4599    <date month="June" year="1999"/>
4600  </front>
4601  <seriesInfo name="RFC" value="2616"/>
4602</reference>
4603
4604<reference anchor='RFC2817'>
4605  <front>
4606    <title>Upgrading to TLS Within HTTP/1.1</title>
4607    <author initials='R.' surname='Khare' fullname='R. Khare'>
4608      <organization>4K Associates / UC Irvine</organization>
4609      <address><email>rohit@4K-associates.com</email></address>
4610    </author>
4611    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4612      <organization>Agranat Systems, Inc.</organization>
4613      <address><email>lawrence@agranat.com</email></address>
4614    </author>
4615    <date year='2000' month='May' />
4616  </front>
4617  <seriesInfo name='RFC' value='2817' />
4618</reference>
4619
4620<reference anchor='RFC2818'>
4621  <front>
4622    <title>HTTP Over TLS</title>
4623    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4624      <organization>RTFM, Inc.</organization>
4625      <address><email>ekr@rtfm.com</email></address>
4626    </author>
4627    <date year='2000' month='May' />
4628  </front>
4629  <seriesInfo name='RFC' value='2818' />
4630</reference>
4631
4632<reference anchor='RFC2965'>
4633  <front>
4634    <title>HTTP State Management Mechanism</title>
4635    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4636      <organization>Bell Laboratories, Lucent Technologies</organization>
4637      <address><email>dmk@bell-labs.com</email></address>
4638    </author>
4639    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4640      <organization>Epinions.com, Inc.</organization>
4641      <address><email>lou@montulli.org</email></address>
4642    </author>
4643    <date year='2000' month='October' />
4644  </front>
4645  <seriesInfo name='RFC' value='2965' />
4646</reference>
4647
4648<reference anchor='RFC3040'>
4649  <front>
4650    <title>Internet Web Replication and Caching Taxonomy</title>
4651    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4652      <organization>Equinix, Inc.</organization>
4653    </author>
4654    <author initials='I.' surname='Melve' fullname='I. Melve'>
4655      <organization>UNINETT</organization>
4656    </author>
4657    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4658      <organization>CacheFlow Inc.</organization>
4659    </author>
4660    <date year='2001' month='January' />
4661  </front>
4662  <seriesInfo name='RFC' value='3040' />
4663</reference>
4664
4665<reference anchor='RFC3864'>
4666  <front>
4667    <title>Registration Procedures for Message Header Fields</title>
4668    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4669      <organization>Nine by Nine</organization>
4670      <address><email>GK-IETF@ninebynine.org</email></address>
4671    </author>
4672    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4673      <organization>BEA Systems</organization>
4674      <address><email>mnot@pobox.com</email></address>
4675    </author>
4676    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4677      <organization>HP Labs</organization>
4678      <address><email>JeffMogul@acm.org</email></address>
4679    </author>
4680    <date year='2004' month='September' />
4681  </front>
4682  <seriesInfo name='BCP' value='90' />
4683  <seriesInfo name='RFC' value='3864' />
4684</reference>
4685
4686<reference anchor="RFC4288">
4687  <front>
4688    <title>Media Type Specifications and Registration Procedures</title>
4689    <author initials="N." surname="Freed" fullname="N. Freed">
4690      <organization>Sun Microsystems</organization>
4691      <address>
4692        <email>ned.freed@mrochek.com</email>
4693      </address>
4694    </author>
4695    <author initials="J." surname="Klensin" fullname="J. Klensin">
4696      <address>
4697        <email>klensin+ietf@jck.com</email>
4698      </address>
4699    </author>
4700    <date year="2005" month="December"/>
4701  </front>
4702  <seriesInfo name="BCP" value="13"/>
4703  <seriesInfo name="RFC" value="4288"/>
4704</reference>
4705
4706<reference anchor='RFC4395'>
4707  <front>
4708    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4709    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4710      <organization>AT&amp;T Laboratories</organization>
4711      <address>
4712        <email>tony+urireg@maillennium.att.com</email>
4713      </address>
4714    </author>
4715    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4716      <organization>Qualcomm, Inc.</organization>
4717      <address>
4718        <email>hardie@qualcomm.com</email>
4719      </address>
4720    </author>
4721    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4722      <organization>Adobe Systems</organization>
4723      <address>
4724        <email>LMM@acm.org</email>
4725      </address>
4726    </author>
4727    <date year='2006' month='February' />
4728  </front>
4729  <seriesInfo name='BCP' value='115' />
4730  <seriesInfo name='RFC' value='4395' />
4731</reference>
4732
4733<reference anchor='RFC5226'>
4734  <front>
4735    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4736    <author initials='T.' surname='Narten' fullname='T. Narten'>
4737      <organization>IBM</organization>
4738      <address><email>narten@us.ibm.com</email></address>
4739    </author>
4740    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4741      <organization>Google</organization>
4742      <address><email>Harald@Alvestrand.no</email></address>
4743    </author>
4744    <date year='2008' month='May' />
4745  </front>
4746  <seriesInfo name='BCP' value='26' />
4747  <seriesInfo name='RFC' value='5226' />
4748</reference>
4749
4750<reference anchor="RFC5322">
4751  <front>
4752    <title>Internet Message Format</title>
4753    <author initials="P." surname="Resnick" fullname="P. Resnick">
4754      <organization>Qualcomm Incorporated</organization>
4755    </author>
4756    <date year="2008" month="October"/>
4757  </front> 
4758  <seriesInfo name="RFC" value="5322"/>
4759</reference>
4760
4761<reference anchor="RFC6265">
4762  <front>
4763    <title>HTTP State Management Mechanism</title>
4764    <author initials="A." surname="Barth" fullname="Adam Barth">
4765      <organization abbrev="U.C. Berkeley">
4766        University of California, Berkeley
4767      </organization>
4768      <address><email>abarth@eecs.berkeley.edu</email></address>
4769    </author>
4770    <date year="2011" month="April" />
4771  </front>
4772  <seriesInfo name="RFC" value="6265"/>
4773</reference>
4774
4775<reference anchor='BCP97'>
4776  <front>
4777    <title>Handling Normative References to Standards-Track Documents</title>
4778    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4779      <address>
4780        <email>klensin+ietf@jck.com</email>
4781      </address>
4782    </author>
4783    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4784      <organization>MIT</organization>
4785      <address>
4786        <email>hartmans-ietf@mit.edu</email>
4787      </address>
4788    </author>
4789    <date year='2007' month='June' />
4790  </front>
4791  <seriesInfo name='BCP' value='97' />
4792  <seriesInfo name='RFC' value='4897' />
4793</reference>
4794
4795<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4796  <front>
4797    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4798    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4799    <date year="2001" month="November"/>
4800  </front>
4801  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4802</reference>
4803
4804<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4805  <front>
4806    <title>Analysis of HTTP Performance Problems</title>
4807    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4808    <date/>
4809  </front>
4810</reference>
4811
4812<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4813  <front>
4814  <title>Analysis of HTTP Performance</title>
4815  <author initials="J." surname="Touch" fullname="Joe Touch">
4816    <organization>USC/Information Sciences Institute</organization>
4817    <address><email>touch@isi.edu</email></address>
4818  </author>
4819  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4820    <organization>USC/Information Sciences Institute</organization>
4821    <address><email>johnh@isi.edu</email></address>
4822  </author>
4823  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4824    <organization>USC/Information Sciences Institute</organization>
4825    <address><email>katia@isi.edu</email></address>
4826  </author>
4827  <date year="1998" month="Aug"/>
4828  </front>
4829  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4830  <annotation>(original report dated Aug. 1996)</annotation>
4831</reference>
4832
4833</references>
4834
4835
4836<section title="Tolerant Applications" anchor="tolerant.applications">
4837<t>
4838   Although this document specifies the requirements for the generation
4839   of HTTP/1.1 messages, not all applications will be correct in their
4840   implementation. We therefore recommend that operational applications
4841   be tolerant of deviations whenever those deviations can be
4842   interpreted unambiguously.
4843</t>
4844<t>
4845   The line terminator for header fields is the sequence CRLF.
4846   However, we recommend that applications, when parsing such headers fields,
4847   recognize a single LF as a line terminator and ignore the leading CR.
4848</t>
4849<t>
4850   The character encoding of a representation &SHOULD; be labeled as the lowest
4851   common denominator of the character codes used within that representation, with
4852   the exception that not labeling the representation is preferred over labeling
4853   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4854</t>
4855<t>
4856   Additional rules for requirements on parsing and encoding of dates
4857   and other potential problems with date encodings include:
4858</t>
4859<t>
4860  <list style="symbols">
4861     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4862        which appears to be more than 50 years in the future is in fact
4863        in the past (this helps solve the "year 2000" problem).</t>
4864
4865     <t>Although all date formats are specified to be case-sensitive,
4866        recipients &SHOULD; match day, week and timezone names
4867        case-insensitively.</t>
4868             
4869     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4870        Expires date as earlier than the proper value, but &MUST-NOT;
4871        internally represent a parsed Expires date as later than the
4872        proper value.</t>
4873
4874     <t>All expiration-related calculations &MUST; be done in GMT. The
4875        local time zone &MUST-NOT; influence the calculation or comparison
4876        of an age or expiration time.</t>
4877
4878     <t>If an HTTP header field incorrectly carries a date value with a time
4879        zone other than GMT, it &MUST; be converted into GMT using the
4880        most conservative possible conversion.</t>
4881  </list>
4882</t>
4883</section>
4884
4885<section title="HTTP Version History" anchor="compatibility">
4886<t>
4887   HTTP has been in use by the World-Wide Web global information initiative
4888   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4889   was a simple protocol for hypertext data transfer across the Internet
4890   with only a single request method (GET) and no metadata.
4891   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4892   methods and MIME-like messaging that could include metadata about the data
4893   transferred and modifiers on the request/response semantics. However,
4894   HTTP/1.0 did not sufficiently take into consideration the effects of
4895   hierarchical proxies, caching, the need for persistent connections, or
4896   name-based virtual hosts. The proliferation of incompletely-implemented
4897   applications calling themselves "HTTP/1.0" further necessitated a
4898   protocol version change in order for two communicating applications
4899   to determine each other's true capabilities.
4900</t>
4901<t>
4902   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4903   requirements that enable reliable implementations, adding only
4904   those new features that will either be safely ignored by an HTTP/1.0
4905   recipient or only sent when communicating with a party advertising
4906   compliance with HTTP/1.1.
4907</t>
4908<t>
4909   It is beyond the scope of a protocol specification to mandate
4910   compliance with previous versions. HTTP/1.1 was deliberately
4911   designed, however, to make supporting previous versions easy.
4912   We would expect a general-purpose HTTP/1.1 server to understand
4913   any valid request in the format of HTTP/1.0 and respond appropriately
4914   with an HTTP/1.1 message that only uses features understood (or
4915   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4916   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4917</t>
4918<t>
4919   Since HTTP/0.9 did not support header fields in a request,
4920   there is no mechanism for it to support name-based virtual
4921   hosts (selection of resource by inspection of the Host header
4922   field).  Any server that implements name-based virtual hosts
4923   ought to disable support for HTTP/0.9.  Most requests that
4924   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4925   requests wherein a buggy client failed to properly encode
4926   linear whitespace found in a URI reference and placed in
4927   the request-target.
4928</t>
4929
4930<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4931<t>
4932   This section summarizes major differences between versions HTTP/1.0
4933   and HTTP/1.1.
4934</t>
4935
4936<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4937<t>
4938   The requirements that clients and servers support the Host header
4939   field (<xref target="header.host"/>), report an error if it is
4940   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4941   are among the most important changes defined by HTTP/1.1.
4942</t>
4943<t>
4944   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4945   addresses and servers; there was no other established mechanism for
4946   distinguishing the intended server of a request than the IP address
4947   to which that request was directed. The Host header field was
4948   introduced during the development of HTTP/1.1 and, though it was
4949   quickly implemented by most HTTP/1.0 browsers, additional requirements
4950   were placed on all HTTP/1.1 requests in order to ensure complete
4951   adoption.  At the time of this writing, most HTTP-based services
4952   are dependent upon the Host header field for targeting requests.
4953</t>
4954</section>
4955
4956<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4957<t>
4958   For most implementations of HTTP/1.0, each connection is established
4959   by the client prior to the request and closed by the server after
4960   sending the response. However, some implementations implement the
4961   Keep-Alive version of persistent connections described in
4962   <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4963</t>
4964<t>
4965   Some clients and servers might wish to be compatible with some
4966   previous implementations of persistent connections in HTTP/1.0
4967   clients and servers. Persistent connections in HTTP/1.0 are
4968   explicitly negotiated as they are not the default behavior. HTTP/1.0
4969   experimental implementations of persistent connections are faulty,
4970   and the new facilities in HTTP/1.1 are designed to rectify these
4971   problems. The problem was that some existing HTTP/1.0 clients might
4972   send Keep-Alive to a proxy server that doesn't understand
4973   Connection, which would then erroneously forward it to the next
4974   inbound server, which would establish the Keep-Alive connection and
4975   result in a hung HTTP/1.0 proxy waiting for the close on the
4976   response. The result is that HTTP/1.0 clients must be prevented from
4977   using Keep-Alive when talking to proxies.
4978</t>
4979<t>
4980   However, talking to proxies is the most important use of persistent
4981   connections, so that prohibition is clearly unacceptable. Therefore,
4982   we need some other mechanism for indicating a persistent connection
4983   is desired, which is safe to use even when talking to an old proxy
4984   that ignores Connection. Persistent connections are the default for
4985   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4986   declaring non-persistence. See <xref target="header.connection"/>.
4987</t>
4988</section>
4989</section>
4990
4991<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4992<t>
4993  Empty list elements in list productions have been deprecated.
4994  (<xref target="notation.abnf"/>)
4995</t>
4996<t>
4997  Rules about implicit linear whitespace between certain grammar productions
4998  have been removed; now it's only allowed when specifically pointed out
4999  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
5000  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
5001  Non-ASCII content in header fields and reason phrase has been obsoleted and
5002  made opaque (the TEXT rule was removed)
5003  (<xref target="basic.rules"/>)
5004</t>
5005<t>
5006  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
5007  sensitive. Restrict the version numbers to be single digits due to the fact
5008  that implementations are known to handle multi-digit version numbers
5009  incorrectly.
5010  (<xref target="http.version"/>)
5011</t>
5012<t>
5013  Require that invalid whitespace around field-names be rejected.
5014  (<xref target="header.fields"/>)
5015</t>
5016<t>
5017  Require recipients to handle bogus Content-Length header fields as errors.
5018  (<xref target="message.body"/>)
5019</t>
5020<t>
5021  Remove reference to non-existent identity transfer-coding value tokens.
5022  (Sections <xref format="counter" target="message.body"/> and
5023  <xref format="counter" target="transfer.codings"/>)
5024</t>
5025<t>
5026  Update use of abs_path production from RFC 1808 to the path-absolute + query
5027  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5028  request method only.
5029  (<xref target="request-target"/>)
5030</t>
5031<t>
5032  Clarification that the chunk length does not include the count of the octets
5033  in the chunk header and trailer. Furthermore disallowed line folding
5034  in chunk extensions.
5035  (<xref target="chunked.encoding"/>)
5036</t>
5037<t>
5038  Remove hard limit of two connections per server.
5039  (<xref target="persistent.practical"/>)
5040</t>
5041<t>
5042  Change ABNF productions for header fields to only define the field value.
5043  (<xref target="header.field.definitions"/>)
5044</t>
5045<t>
5046  Clarify exactly when close connection options must be sent.
5047  (<xref target="header.connection"/>)
5048</t>
5049<t>
5050  Define the semantics of the "Upgrade" header field in responses other than
5051  101 (this was incorporated from <xref target="RFC2817"/>).
5052  (<xref target="header.upgrade"/>)
5053</t>
5054</section>
5055</section>
5056
5057<?BEGININC p1-messaging.abnf-appendix ?>
5058<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5059<figure>
5060<artwork type="abnf" name="p1-messaging.parsed-abnf">
5061<x:ref>BWS</x:ref> = OWS
5062
5063<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5064<x:ref>Connection</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5065 connection-token ] )
5066<x:ref>Content-Length</x:ref> = 1*DIGIT
5067
5068<x:ref>Date</x:ref> = HTTP-date
5069
5070<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5071
5072<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5073<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" DIGIT "." DIGIT
5074<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5075<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5076 ]
5077<x:ref>Host</x:ref> = uri-host [ ":" port ]
5078
5079<x:ref>Method</x:ref> = token
5080
5081<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5082
5083<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5084<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5085<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5086<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5087<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5088
5089<x:ref>Status-Code</x:ref> = 3DIGIT
5090<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5091
5092<x:ref>TE</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5093<x:ref>Trailer</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5094<x:ref>Transfer-Encoding</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5095 transfer-coding ] )
5096
5097<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5098<x:ref>Upgrade</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5099
5100<x:ref>Via</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5101 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5102 )
5103
5104<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5105<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5106<x:ref>attribute</x:ref> = token
5107<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5108
5109<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5110<x:ref>chunk-data</x:ref> = 1*OCTET
5111<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5112<x:ref>chunk-ext-name</x:ref> = token
5113<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5114<x:ref>chunk-size</x:ref> = 1*HEXDIG
5115<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5116<x:ref>connection-token</x:ref> = token
5117<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5118 / %x2A-5B ; '*'-'['
5119 / %x5D-7E ; ']'-'~'
5120 / obs-text
5121
5122<x:ref>date1</x:ref> = day SP month SP year
5123<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5124<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5125<x:ref>day</x:ref> = 2DIGIT
5126<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5127 / %x54.75.65 ; Tue
5128 / %x57.65.64 ; Wed
5129 / %x54.68.75 ; Thu
5130 / %x46.72.69 ; Fri
5131 / %x53.61.74 ; Sat
5132 / %x53.75.6E ; Sun
5133<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5134 / %x54.75.65.73.64.61.79 ; Tuesday
5135 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
5136 / %x54.68.75.72.73.64.61.79 ; Thursday
5137 / %x46.72.69.64.61.79 ; Friday
5138 / %x53.61.74.75.72.64.61.79 ; Saturday
5139 / %x53.75.6E.64.61.79 ; Sunday
5140
5141<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5142<x:ref>field-name</x:ref> = token
5143<x:ref>field-value</x:ref> = *( field-content / OWS )
5144
5145<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5146<x:ref>hour</x:ref> = 2DIGIT
5147<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5148<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5149
5150<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5151
5152<x:ref>message-body</x:ref> = *OCTET
5153<x:ref>minute</x:ref> = 2DIGIT
5154<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5155 / %x46.65.62 ; Feb
5156 / %x4D.61.72 ; Mar
5157 / %x41.70.72 ; Apr
5158 / %x4D.61.79 ; May
5159 / %x4A.75.6E ; Jun
5160 / %x4A.75.6C ; Jul
5161 / %x41.75.67 ; Aug
5162 / %x53.65.70 ; Sep
5163 / %x4F.63.74 ; Oct
5164 / %x4E.6F.76 ; Nov
5165 / %x44.65.63 ; Dec
5166
5167<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5168<x:ref>obs-fold</x:ref> = CRLF
5169<x:ref>obs-text</x:ref> = %x80-FF
5170
5171<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5172<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5173<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5174<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5175<x:ref>product</x:ref> = token [ "/" product-version ]
5176<x:ref>product-version</x:ref> = token
5177<x:ref>protocol-name</x:ref> = token
5178<x:ref>protocol-version</x:ref> = token
5179<x:ref>pseudonym</x:ref> = token
5180
5181<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5182 / %x5D-7E ; ']'-'~'
5183 / obs-text
5184<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5185 / %x5D-7E ; ']'-'~'
5186 / obs-text
5187<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5188<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5189<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5190<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5191<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5192<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5193
5194<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5195<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5196<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5197<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5198 / authority
5199<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5200<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5201
5202<x:ref>second</x:ref> = 2DIGIT
5203<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5204 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5205<x:ref>start-line</x:ref> = Request-Line / Status-Line
5206
5207<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5208<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5209 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5210<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5211<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5212<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5213<x:ref>token</x:ref> = 1*tchar
5214<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5215<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5216 transfer-extension
5217<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5218<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5219
5220<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5221
5222<x:ref>value</x:ref> = word
5223
5224<x:ref>word</x:ref> = token / quoted-string
5225
5226<x:ref>year</x:ref> = 4DIGIT
5227</artwork>
5228</figure>
5229<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5230; Chunked-Body defined but not used
5231; Connection defined but not used
5232; Content-Length defined but not used
5233; Date defined but not used
5234; HTTP-message defined but not used
5235; Host defined but not used
5236; Request defined but not used
5237; Response defined but not used
5238; TE defined but not used
5239; Trailer defined but not used
5240; Transfer-Encoding defined but not used
5241; URI-reference defined but not used
5242; Upgrade defined but not used
5243; Via defined but not used
5244; http-URI defined but not used
5245; https-URI defined but not used
5246; partial-URI defined but not used
5247; special defined but not used
5248</artwork></figure></section>
5249<?ENDINC p1-messaging.abnf-appendix ?>
5250
5251<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5252
5253<section title="Since RFC 2616">
5254<t>
5255  Extracted relevant partitions from <xref target="RFC2616"/>.
5256</t>
5257</section>
5258
5259<section title="Since draft-ietf-httpbis-p1-messaging-00">
5260<t>
5261  Closed issues:
5262  <list style="symbols"> 
5263    <t>
5264      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5265      "HTTP Version should be case sensitive"
5266      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5267    </t>
5268    <t>
5269      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5270      "'unsafe' characters"
5271      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5272    </t>
5273    <t>
5274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5275      "Chunk Size Definition"
5276      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5277    </t>
5278    <t>
5279      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5280      "Message Length"
5281      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5282    </t>
5283    <t>
5284      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5285      "Media Type Registrations"
5286      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5287    </t>
5288    <t>
5289      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5290      "URI includes query"
5291      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5292    </t>
5293    <t>
5294      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5295      "No close on 1xx responses"
5296      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5297    </t>
5298    <t>
5299      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5300      "Remove 'identity' token references"
5301      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5302    </t>
5303    <t>
5304      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5305      "Import query BNF"
5306    </t>
5307    <t>
5308      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5309      "qdtext BNF"
5310    </t>
5311    <t>
5312      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5313      "Normative and Informative references"
5314    </t>
5315    <t>
5316      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5317      "RFC2606 Compliance"
5318    </t>
5319    <t>
5320      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5321      "RFC977 reference"
5322    </t>
5323    <t>
5324      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5325      "RFC1700 references"
5326    </t>
5327    <t>
5328      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5329      "inconsistency in date format explanation"
5330    </t>
5331    <t>
5332      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5333      "Date reference typo"
5334    </t>
5335    <t>
5336      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5337      "Informative references"
5338    </t>
5339    <t>
5340      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5341      "ISO-8859-1 Reference"
5342    </t>
5343    <t>
5344      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5345      "Normative up-to-date references"
5346    </t>
5347  </list>
5348</t>
5349<t>
5350  Other changes:
5351  <list style="symbols"> 
5352    <t>
5353      Update media type registrations to use RFC4288 template.
5354    </t>
5355    <t>
5356      Use names of RFC4234 core rules DQUOTE and WSP,
5357      fix broken ABNF for chunk-data
5358      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5359    </t>
5360  </list>
5361</t>
5362</section>
5363
5364<section title="Since draft-ietf-httpbis-p1-messaging-01">
5365<t>
5366  Closed issues:
5367  <list style="symbols"> 
5368    <t>
5369      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5370      "Bodies on GET (and other) requests"
5371    </t>
5372    <t>
5373      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5374      "Updating to RFC4288"
5375    </t>
5376    <t>
5377      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5378      "Status Code and Reason Phrase"
5379    </t>
5380    <t>
5381      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5382      "rel_path not used"
5383    </t>
5384  </list>
5385</t>
5386<t>
5387  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5388  <list style="symbols"> 
5389    <t>
5390      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5391      "trailer-part").
5392    </t>
5393    <t>
5394      Avoid underscore character in rule names ("http_URL" ->
5395      "http-URL", "abs_path" -> "path-absolute").
5396    </t>
5397    <t>
5398      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5399      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5400      have to be updated when switching over to RFC3986.
5401    </t>
5402    <t>
5403      Synchronize core rules with RFC5234.
5404    </t>
5405    <t>
5406      Get rid of prose rules that span multiple lines.
5407    </t>
5408    <t>
5409      Get rid of unused rules LOALPHA and UPALPHA.
5410    </t>
5411    <t>
5412      Move "Product Tokens" section (back) into Part 1, as "token" is used
5413      in the definition of the Upgrade header field.
5414    </t>
5415    <t>
5416      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5417    </t>
5418    <t>
5419      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5420    </t>
5421  </list>
5422</t>
5423</section>
5424
5425<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5426<t>
5427  Closed issues:
5428  <list style="symbols"> 
5429    <t>
5430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5431      "HTTP-date vs. rfc1123-date"
5432    </t>
5433    <t>
5434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5435      "WS in quoted-pair"
5436    </t>
5437  </list>
5438</t>
5439<t>
5440  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5441  <list style="symbols"> 
5442    <t>
5443      Reference RFC 3984, and update header field registrations for headers defined
5444      in this document.
5445    </t>
5446  </list>
5447</t>
5448<t>
5449  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5450  <list style="symbols"> 
5451    <t>
5452      Replace string literals when the string really is case-sensitive (HTTP-Version).
5453    </t>
5454  </list>
5455</t>
5456</section>
5457
5458<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5459<t>
5460  Closed issues:
5461  <list style="symbols"> 
5462    <t>
5463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5464      "Connection closing"
5465    </t>
5466    <t>
5467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5468      "Move registrations and registry information to IANA Considerations"
5469    </t>
5470    <t>
5471      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5472      "need new URL for PAD1995 reference"
5473    </t>
5474    <t>
5475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5476      "IANA Considerations: update HTTP URI scheme registration"
5477    </t>
5478    <t>
5479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5480      "Cite HTTPS URI scheme definition"
5481    </t>
5482    <t>
5483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5484      "List-type headers vs Set-Cookie"
5485    </t>
5486  </list>
5487</t>
5488<t>
5489  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5490  <list style="symbols"> 
5491    <t>
5492      Replace string literals when the string really is case-sensitive (HTTP-Date).
5493    </t>
5494    <t>
5495      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5496    </t>
5497  </list>
5498</t>
5499</section>
5500
5501<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5502<t>
5503  Closed issues:
5504  <list style="symbols"> 
5505    <t>
5506      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5507      "Out-of-date reference for URIs"
5508    </t>
5509    <t>
5510      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5511      "RFC 2822 is updated by RFC 5322"
5512    </t>
5513  </list>
5514</t>
5515<t>
5516  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5517  <list style="symbols"> 
5518    <t>
5519      Use "/" instead of "|" for alternatives.
5520    </t>
5521    <t>
5522      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5523    </t>
5524    <t>
5525      Only reference RFC 5234's core rules.
5526    </t>
5527    <t>
5528      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5529      whitespace ("OWS") and required whitespace ("RWS").
5530    </t>
5531    <t>
5532      Rewrite ABNFs to spell out whitespace rules, factor out
5533      header field value format definitions.
5534    </t>
5535  </list>
5536</t>
5537</section>
5538
5539<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5540<t>
5541  Closed issues:
5542  <list style="symbols"> 
5543    <t>
5544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5545      "Header LWS"
5546    </t>
5547    <t>
5548      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5549      "Sort 1.3 Terminology"
5550    </t>
5551    <t>
5552      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5553      "RFC2047 encoded words"
5554    </t>
5555    <t>
5556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5557      "Character Encodings in TEXT"
5558    </t>
5559    <t>
5560      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5561      "Line Folding"
5562    </t>
5563    <t>
5564      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5565      "OPTIONS * and proxies"
5566    </t>
5567    <t>
5568      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5569      "Reason-Phrase BNF"
5570    </t>
5571    <t>
5572      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5573      "Use of TEXT"
5574    </t>
5575    <t>
5576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5577      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5578    </t>
5579    <t>
5580      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5581      "RFC822 reference left in discussion of date formats"
5582    </t>
5583  </list>
5584</t>
5585<t>
5586  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5587  <list style="symbols"> 
5588    <t>
5589      Rewrite definition of list rules, deprecate empty list elements.
5590    </t>
5591    <t>
5592      Add appendix containing collected and expanded ABNF.
5593    </t>
5594  </list>
5595</t>
5596<t>
5597  Other changes:
5598  <list style="symbols"> 
5599    <t>
5600      Rewrite introduction; add mostly new Architecture Section.
5601    </t>
5602    <t>
5603      Move definition of quality values from Part 3 into Part 1;
5604      make TE request header field grammar independent of accept-params (defined in Part 3).
5605    </t>
5606  </list>
5607</t>
5608</section>
5609
5610<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5611<t>
5612  Closed issues:
5613  <list style="symbols"> 
5614    <t>
5615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5616      "base for numeric protocol elements"
5617    </t>
5618    <t>
5619      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5620      "comment ABNF"
5621    </t>
5622  </list>
5623</t>
5624<t>
5625  Partly resolved issues:
5626  <list style="symbols"> 
5627    <t>
5628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5629      "205 Bodies" (took out language that implied that there might be
5630      methods for which a request body MUST NOT be included)
5631    </t>
5632    <t>
5633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5634      "editorial improvements around HTTP-date"
5635    </t>
5636  </list>
5637</t>
5638</section>
5639
5640<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5641<t>
5642  Closed issues:
5643  <list style="symbols"> 
5644    <t>
5645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5646      "Repeating single-value headers"
5647    </t>
5648    <t>
5649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5650      "increase connection limit"
5651    </t>
5652    <t>
5653      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5654      "IP addresses in URLs"
5655    </t>
5656    <t>
5657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5658      "take over HTTP Upgrade Token Registry"
5659    </t>
5660    <t>
5661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5662      "CR and LF in chunk extension values"
5663    </t>
5664    <t>
5665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5666      "HTTP/0.9 support"
5667    </t>
5668    <t>
5669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5670      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5671    </t>
5672    <t>
5673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5674      "move definitions of gzip/deflate/compress to part 1"
5675    </t>
5676    <t>
5677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5678      "disallow control characters in quoted-pair"
5679    </t>
5680  </list>
5681</t>
5682<t>
5683  Partly resolved issues:
5684  <list style="symbols"> 
5685    <t>
5686      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5687      "update IANA requirements wrt Transfer-Coding values" (add the
5688      IANA Considerations subsection)
5689    </t>
5690  </list>
5691</t>
5692</section>
5693
5694<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5695<t>
5696  Closed issues:
5697  <list style="symbols"> 
5698    <t>
5699      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5700      "header parsing, treatment of leading and trailing OWS"
5701    </t>
5702  </list>
5703</t>
5704<t>
5705  Partly resolved issues:
5706  <list style="symbols"> 
5707    <t>
5708      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5709      "Placement of 13.5.1 and 13.5.2"
5710    </t>
5711    <t>
5712      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5713      "use of term "word" when talking about header structure"
5714    </t>
5715  </list>
5716</t>
5717</section>
5718
5719<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5720<t>
5721  Closed issues:
5722  <list style="symbols"> 
5723    <t>
5724      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5725      "Clarification of the term 'deflate'"
5726    </t>
5727    <t>
5728      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5729      "OPTIONS * and proxies"
5730    </t>
5731    <t>
5732      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5733      "MIME-Version not listed in P1, general header fields"
5734    </t>
5735    <t>
5736      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5737      "IANA registry for content/transfer encodings"
5738    </t>
5739    <t>
5740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5741      "Case-sensitivity of HTTP-date"
5742    </t>
5743    <t>
5744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5745      "use of term "word" when talking about header structure"
5746    </t>
5747  </list>
5748</t>
5749<t>
5750  Partly resolved issues:
5751  <list style="symbols"> 
5752    <t>
5753      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5754      "Term for the requested resource's URI"
5755    </t>
5756  </list>
5757</t>
5758</section>
5759
5760<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5761<t>
5762  Closed issues:
5763  <list style="symbols">
5764    <t>
5765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5766      "Connection Closing"
5767    </t>
5768    <t>
5769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5770      "Delimiting messages with multipart/byteranges"
5771    </t>
5772    <t>
5773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5774      "Handling multiple Content-Length headers"
5775    </t>
5776    <t>
5777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5778      "Clarify entity / representation / variant terminology"
5779    </t>
5780    <t>
5781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5782      "consider removing the 'changes from 2068' sections"
5783    </t>
5784  </list>
5785</t>
5786<t>
5787  Partly resolved issues:
5788  <list style="symbols"> 
5789    <t>
5790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5791      "HTTP(s) URI scheme definitions"
5792    </t>
5793  </list>
5794</t>
5795</section>
5796
5797<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5798<t>
5799  Closed issues:
5800  <list style="symbols">
5801    <t>
5802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5803      "Trailer requirements"
5804    </t>
5805    <t>
5806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5807      "Text about clock requirement for caches belongs in p6"
5808    </t>
5809    <t>
5810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5811      "effective request URI: handling of missing host in HTTP/1.0"
5812    </t>
5813    <t>
5814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5815      "confusing Date requirements for clients"
5816    </t>
5817  </list>
5818</t>
5819<t>
5820  Partly resolved issues:
5821  <list style="symbols"> 
5822    <t>
5823      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5824      "Handling multiple Content-Length headers"
5825    </t>
5826  </list>
5827</t>
5828</section>
5829
5830<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5831<t>
5832  Closed issues:
5833  <list style="symbols">
5834    <t>
5835      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5836      "RFC2145 Normative"
5837    </t>
5838    <t>
5839      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5840      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5841    </t>
5842    <t>
5843      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5844      "define 'transparent' proxy"
5845    </t>
5846    <t>
5847      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5848      "Header Classification"
5849    </t>
5850    <t>
5851      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5852      "Is * usable as a request-uri for new methods?"
5853    </t>
5854    <t>
5855      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5856      "Migrate Upgrade details from RFC2817"
5857    </t>
5858    <t>
5859      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5860      "untangle ABNFs for header fields"
5861    </t>
5862    <t>
5863      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5864      "update RFC 2109 reference"
5865    </t>
5866  </list>
5867</t>
5868</section>
5869
5870<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5871<t>
5872  Closed issues:
5873  <list style="symbols">
5874    <t>
5875      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5876      "Allow is not in 13.5.2"
5877    </t>
5878    <t>
5879      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5880      "untangle ABNFs for header fields"
5881    </t>
5882    <t>
5883      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5884      "Content-Length ABNF broken"
5885    </t>
5886  </list>
5887</t>
5888</section>
5889
5890<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5891<t>
5892  Closed issues:
5893  <list style="symbols">
5894    <t>
5895      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5896      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5897    </t>
5898  </list>
5899</t>
5900</section>
5901
5902</section>
5903
5904</back>
5905</rfc>
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