source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1151

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Update 2109 reference (see #279)

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "March">
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 request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40]>
41<?rfc toc="yes" ?>
42<?rfc symrefs="yes" ?>
43<?rfc sortrefs="yes" ?>
44<?rfc compact="yes"?>
45<?rfc subcompact="no" ?>
46<?rfc linkmailto="no" ?>
47<?rfc editing="no" ?>
48<?rfc comments="yes"?>
49<?rfc inline="yes"?>
50<?rfc rfcedstyle="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2145,2616" updates="2817" category="std" x:maturity-level="draft"
54     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
62    <address>
63      <postal>
64        <street>345 Park Ave</street>
65        <city>San Jose</city>
66        <region>CA</region>
67        <code>95110</code>
68        <country>USA</country>
69      </postal>
70      <email>fielding@gbiv.com</email>
71      <uri>http://roy.gbiv.com/</uri>
72    </address>
73  </author>
74
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email>jg@freedesktop.org</email>
86      <uri>http://gettys.wordpress.com/</uri>
87    </address>
88  </author>
89 
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email>JeffMogul@acm.org</email>
102    </address>
103  </author>
104
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email>henrikn@microsoft.com</email>
116    </address>
117  </author>
118
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email>LMM@acm.org</email>
130      <uri>http://larry.masinter.net/</uri>
131    </address>
132  </author>
133 
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email>paulle@microsoft.com</email>
144    </address>
145  </author>
146   
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email>timbl@w3.org</email>
160      <uri>http://www.w3.org/People/Berners-Lee/</uri>
161    </address>
162  </author>
163
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email>ylafon@w3.org</email>
176      <uri>http://www.raubacapeu.net/people/yves/</uri>
177    </address>
178  </author>
179
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>
189      <facsimile>+49 251 2807761</facsimile>
190      <email>julian.reschke@greenbytes.de</email>
191      <uri>http://greenbytes.de/tech/webdav/</uri>
192    </address>
193  </author>
194
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
197
198<abstract>
199<t>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
210</t>
211</abstract>
212
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list (ietf-http-wg@w3.org). The current issues list is
217    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
218    and related documents (including fancy diffs) can be found at
219    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.12"/>.
223  </t>
224</note>
225</front>
226<middle>
227<section title="Introduction" anchor="introduction">
228<t>
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   request/response protocol that uses extensible semantics and MIME-like
231   message payloads for flexible interaction with network-based hypertext
232   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
233   standard <xref target="RFC3986"/> to indicate request targets and
234   relationships between resources.
235   Messages are passed in a format similar to that used by Internet mail
236   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
237   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
238   between HTTP and MIME messages).
239</t>
240<t>
241   HTTP is a generic interface protocol for information systems. It is
242   designed to hide the details of how a service is implemented by presenting
243   a uniform interface to clients that is independent of the types of
244   resources provided. Likewise, servers do not need to be aware of each
245   client's purpose: an HTTP request can be considered in isolation rather
246   than being associated with a specific type of client or a predetermined
247   sequence of application steps. The result is a protocol that can be used
248   effectively in many different contexts and for which implementations can
249   evolve independently over time.
250</t>
251<t>
252   HTTP is also designed for use as an intermediation protocol for translating
253   communication to and from non-HTTP information systems.
254   HTTP proxies and gateways can provide access to alternative information
255   services by translating their diverse protocols into a hypertext
256   format that can be viewed and manipulated by clients in the same way
257   as HTTP services.
258</t>
259<t>
260   One consequence of HTTP flexibility is that the protocol cannot be
261   defined in terms of what occurs behind the interface. Instead, we
262   are limited to defining the syntax of communication, the intent
263   of received communication, and the expected behavior of recipients.
264   If the communication is considered in isolation, then successful
265   actions ought to be reflected in corresponding changes to the
266   observable interface provided by servers. However, since multiple
267   clients might act in parallel and perhaps at cross-purposes, we
268   cannot require that such changes be observable beyond the scope
269   of a single response.
270</t>
271<t>
272   This document is Part 1 of the seven-part specification of HTTP,
273   defining the protocol referred to as "HTTP/1.1", obsoleting
274   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
275   Part 1 describes the architectural elements that are used or
276   referred to in HTTP, defines the "http" and "https" URI schemes,
277   describes overall network operation and connection management,
278   and defines HTTP message framing and forwarding requirements.
279   Our goal is to define all of the mechanisms necessary for HTTP message
280   handling that are independent of message semantics, thereby defining the
281   complete set of requirements for message parsers and
282   message-forwarding intermediaries.
283</t>
284
285<section title="Requirements" anchor="intro.requirements">
286<t>
287   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
288   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
289   document are to be interpreted as described in <xref target="RFC2119"/>.
290</t>
291<t>
292   An implementation is not compliant if it fails to satisfy one or more
293   of the "MUST" or "REQUIRED" level requirements for the protocols it
294   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
295   level and all the "SHOULD" level requirements for its protocols is said
296   to be "unconditionally compliant"; one that satisfies all the "MUST"
297   level requirements but not all the "SHOULD" level requirements for its
298   protocols is said to be "conditionally compliant".
299</t>
300</section>
301
302<section title="Syntax Notation" anchor="notation">
303<iref primary="true" item="Grammar" subitem="ALPHA"/>
304<iref primary="true" item="Grammar" subitem="CR"/>
305<iref primary="true" item="Grammar" subitem="CRLF"/>
306<iref primary="true" item="Grammar" subitem="CTL"/>
307<iref primary="true" item="Grammar" subitem="DIGIT"/>
308<iref primary="true" item="Grammar" subitem="DQUOTE"/>
309<iref primary="true" item="Grammar" subitem="HEXDIG"/>
310<iref primary="true" item="Grammar" subitem="LF"/>
311<iref primary="true" item="Grammar" subitem="OCTET"/>
312<iref primary="true" item="Grammar" subitem="SP"/>
313<iref primary="true" item="Grammar" subitem="VCHAR"/>
314<iref primary="true" item="Grammar" subitem="WSP"/>
315<t>
316   This specification uses the Augmented Backus-Naur Form (ABNF) notation
317   of <xref target="RFC5234"/>.
318</t>
319<t anchor="core.rules">
320  <x:anchor-alias value="ALPHA"/>
321  <x:anchor-alias value="CTL"/>
322  <x:anchor-alias value="CR"/>
323  <x:anchor-alias value="CRLF"/>
324  <x:anchor-alias value="DIGIT"/>
325  <x:anchor-alias value="DQUOTE"/>
326  <x:anchor-alias value="HEXDIG"/>
327  <x:anchor-alias value="LF"/>
328  <x:anchor-alias value="OCTET"/>
329  <x:anchor-alias value="SP"/>
330  <x:anchor-alias value="VCHAR"/>
331  <x:anchor-alias value="WSP"/>
332   The following core rules are included by
333   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335   DIGIT (decimal 0-9), DQUOTE (double quote),
336   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337   OCTET (any 8-bit sequence of data), SP (space),
338   VCHAR (any visible <xref target="USASCII"/> character),
339   and WSP (whitespace).
340</t>
341<t>
342   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
343   "obsolete" grammar rules that appear for historical reasons.
344</t>
345
346<section title="ABNF Extension: #rule" anchor="notation.abnf">
347<t>
348  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
349  improve readability.
350</t>
351<t>
352  A construct "#" is defined, similar to "*", for defining comma-delimited
353  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
354  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
355  comma (",") and optional whitespace (OWS,
356  <xref target="basic.rules"/>).   
357</t>
358<figure><preamble>
359  Thus,
360</preamble><artwork type="example">
361  1#element =&gt; element *( OWS "," OWS element )
362</artwork></figure>
363<figure><preamble>
364  and:
365</preamble><artwork type="example">
366  #element =&gt; [ 1#element ]
367</artwork></figure>
368<figure><preamble>
369  and for n &gt;= 1 and m &gt; 1:
370</preamble><artwork type="example">
371  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
372</artwork></figure>
373<t>
374  For compatibility with legacy list rules, recipients &SHOULD; accept empty
375  list elements. In other words, consumers would follow the list productions:
376</t>
377<figure><artwork type="example">
378  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
379 
380  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
381</artwork></figure>
382<t>
383  Note that empty elements do not contribute to the count of elements present,
384  though.
385</t>
386<t>
387  For example, given these ABNF productions:
388</t>
389<figure><artwork type="example">
390  example-list      = 1#example-list-elmt
391  example-list-elmt = token ; see <xref target="basic.rules"/> 
392</artwork></figure>
393<t>
394  Then these are valid values for example-list (not including the double
395  quotes, which are present for delimitation only):
396</t>
397<figure><artwork type="example">
398  "foo,bar"
399  " foo ,bar,"
400  "  foo , ,bar,charlie   "
401  "foo ,bar,   charlie "
402</artwork></figure>
403<t>
404  But these values would be invalid, as at least one non-empty element is
405  required:
406</t>
407<figure><artwork type="example">
408  ""
409  ","
410  ",   ,"
411</artwork></figure>
412<t>
413  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
414  expanded as explained above.
415</t>
416</section>
417
418<section title="Basic Rules" anchor="basic.rules">
419<t anchor="rule.CRLF">
420  <x:anchor-alias value="CRLF"/>
421   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
422   protocol elements other than the message-body
423   (see <xref target="tolerant.applications"/> for tolerant applications).
424</t>
425<t anchor="rule.LWS">
426   This specification uses three rules to denote the use of linear
427   whitespace: OWS (optional whitespace), RWS (required whitespace), and
428   BWS ("bad" whitespace).
429</t>
430<t>
431   The OWS rule is used where zero or more linear whitespace characters might
432   appear. OWS &SHOULD; either not be produced or be produced as a single SP
433   character. Multiple OWS characters that occur within field-content &SHOULD;
434   be replaced with a single SP before interpreting the field value or
435   forwarding the message downstream.
436</t>
437<t>
438   RWS is used when at least one linear whitespace character is required to
439   separate field tokens. RWS &SHOULD; be produced as a single SP character.
440   Multiple RWS characters that occur within field-content &SHOULD; be
441   replaced with a single SP before interpreting the field value or
442   forwarding the message downstream.
443</t>
444<t>
445   BWS is used where the grammar allows optional whitespace for historical
446   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
447   recipients &MUST; accept such bad optional whitespace and remove it before
448   interpreting the field value or forwarding the message downstream.
449</t>
450<t anchor="rule.whitespace">
451  <x:anchor-alias value="BWS"/>
452  <x:anchor-alias value="OWS"/>
453  <x:anchor-alias value="RWS"/>
454  <x:anchor-alias value="obs-fold"/>
455</t>
456<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"/>
457  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
458                 ; "optional" whitespace
459  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "required" whitespace
461  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
462                 ; "bad" whitespace
463  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
464                 ; see <xref target="header.fields"/>
465</artwork></figure>
466<t anchor="rule.token.separators">
467  <x:anchor-alias value="tchar"/>
468  <x:anchor-alias value="token"/>
469  <x:anchor-alias value="special"/>
470  <x:anchor-alias value="word"/>
471   Many HTTP/1.1 header field values consist of words (token or quoted-string)
472   separated by whitespace or special characters. These special characters
473   &MUST; be in a quoted string to be used within a parameter value (as defined
474   in <xref target="transfer.codings"/>).
475</t>
476<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"/>
477  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
478
479  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
480<!--
481  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
482 -->
483  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
484                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
485                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
486                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
487
488  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
489                 / ";" / ":" / "\" / DQUOTE / "/" / "["
490                 / "]" / "?" / "=" / "{" / "}"
491</artwork></figure>
492<t anchor="rule.quoted-string">
493  <x:anchor-alias value="quoted-string"/>
494  <x:anchor-alias value="qdtext"/>
495  <x:anchor-alias value="obs-text"/>
496   A string of text is parsed as a single word if it is quoted using
497   double-quote marks.
498</t>
499<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"/>
500  <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>
501  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
502                 ; <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> 
503  <x:ref>obs-text</x:ref>       = %x80-FF
504</artwork></figure>
505<t anchor="rule.quoted-pair">
506  <x:anchor-alias value="quoted-pair"/>
507   The backslash character ("\") can be used as a single-character
508   quoting mechanism within quoted-string constructs:
509</t>
510<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
511  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
512</artwork></figure>
513<t>
514   Producers &SHOULD-NOT; escape characters that do not require escaping
515   (i.e., other than DQUOTE and the backslash character).
516</t>
517</section>
518
519<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
520  <x:anchor-alias value="request-header"/>
521  <x:anchor-alias value="response-header"/>
522  <x:anchor-alias value="Cache-Control"/>
523  <x:anchor-alias value="Pragma"/>
524  <x:anchor-alias value="Warning"/>
525  <x:anchor-alias value="MIME-Version"/>
526<t>
527  The ABNF rules below are defined in other parts:
528</t>
529<figure><!-- Part2--><artwork type="abnf2616">
530  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
531  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
532</artwork></figure>
533<figure><!-- Part3--><artwork type="abnf2616">
534  <x:ref>MIME-Version</x:ref>    = &lt;MIME-Version, defined in &header-mime-version;&gt;
535</artwork></figure>
536<figure><!-- Part6--><artwork type="abnf2616">
537  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
538  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
539  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
540</artwork></figure>
541</section>
542
543</section>
544</section>
545
546<section title="HTTP-related architecture" anchor="architecture">
547<t>
548   HTTP was created for the World Wide Web architecture
549   and has evolved over time to support the scalability needs of a worldwide
550   hypertext system. Much of that architecture is reflected in the terminology
551   and syntax productions used to define HTTP.
552</t>
553
554<section title="Client/Server Messaging" anchor="operation">
555<iref primary="true" item="client"/>
556<iref primary="true" item="server"/>
557<iref primary="true" item="connection"/>
558<t>
559   HTTP is a stateless request/response protocol that operates by exchanging
560   messages across a reliable transport or session-layer connection. An HTTP
561   "client" is a program that establishes a connection to a server for the
562   purpose of sending one or more HTTP requests.  An HTTP "server" is a
563   program that accepts connections in order to service HTTP requests by
564   sending HTTP responses.
565</t>
566<iref primary="true" item="user agent"/>
567<iref primary="true" item="origin server"/>
568<iref primary="true" item="browser"/>
569<iref primary="true" item="spider"/>
570<t>
571   Note that the terms client and server refer only to the roles that
572   these programs perform for a particular connection.  The same program
573   might act as a client on some connections and a server on others.  We use
574   the term "user agent" to refer to the program that initiates a request,
575   such as a WWW browser, editor, or spider (web-traversing robot), and
576   the term "origin server" to refer to the program that can originate
577   authoritative responses to a request.  For general requirements, we use
578   the term "sender" to refer to whichever component sent a given message
579   and the term "recipient" to refer to any component that receives the
580   message.
581</t>
582<t>
583   Most HTTP communication consists of a retrieval request (GET) for
584   a representation of some resource identified by a URI.  In the
585   simplest case, this might be accomplished via a single bidirectional
586   connection (===) between the user agent (UA) and the origin server (O).
587</t>
588<figure><artwork type="drawing">
589         request   &gt;
590    UA ======================================= O
591                                &lt;   response
592</artwork></figure>
593<iref primary="true" item="message"/>
594<iref primary="true" item="request"/>
595<iref primary="true" item="response"/>
596<t>
597   A client sends an HTTP request to the server in the form of a request
598   message (<xref target="request"/>), beginning with a method, URI, and
599   protocol version, followed by MIME-like header fields containing
600   request modifiers, client information, and payload metadata, an empty
601   line to indicate the end of the header section, and finally the payload
602   body (if any).
603</t>
604<t>
605   A server responds to the client's request by sending an HTTP response
606   message (<xref target="response"/>), beginning with a status line that
607   includes the protocol version, a success or error code, and textual
608   reason phrase, followed by MIME-like header fields containing server
609   information, resource metadata, and payload metadata, an empty line to
610   indicate the end of the header section, and finally the payload body (if any).
611</t>
612<t>
613   The following example illustrates a typical message exchange for a
614   GET request on the URI "http://www.example.com/hello.txt":
615</t>
616<figure><preamble>
617client request:
618</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
619GET /hello.txt HTTP/1.1
620User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
621Host: www.example.com
622Accept: */*
623
624</artwork></figure>
625<figure><preamble>
626server response:
627</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
628HTTP/1.1 200 OK
629Date: Mon, 27 Jul 2009 12:28:53 GMT
630Server: Apache
631Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
632ETag: "34aa387-d-1568eb00"
633Accept-Ranges: bytes
634Content-Length: <x:length-of target="exbody"/>
635Vary: Accept-Encoding
636Content-Type: text/plain
637
638<x:span anchor="exbody">Hello World!
639</x:span></artwork></figure>
640</section>
641
642<section title="Connections and Transport Independence" anchor="transport-independence">
643<t>
644   HTTP messaging is independent of the underlying transport or
645   session-layer connection protocol(s).  HTTP only presumes a reliable
646   transport with in-order delivery of requests and the corresponding
647   in-order delivery of responses.  The mapping of HTTP request and
648   response structures onto the data units of the underlying transport
649   protocol is outside the scope of this specification.
650</t>
651<t>
652   The specific connection protocols to be used for an interaction
653   are determined by client configuration and the identifier (if any)
654   provided for the request target.  For example, the "http" URI scheme
655   (<xref target="http.uri"/>) indicates a default connection of TCP
656   over IP, with a default TCP port of 80, but the client might be
657   configured to use a proxy via some other connection port or protocol
658   instead of using the defaults.
659</t>
660<t>
661   A connection might be used for multiple HTTP request/response exchanges,
662   as defined in <xref target="persistent.connections"/>.
663</t>
664</section>
665
666<section title="Intermediaries" anchor="intermediaries">
667<iref primary="true" item="intermediary"/>
668<t>
669   HTTP enables the use of intermediaries to satisfy requests through
670   a chain of connections.  There are three common forms of HTTP
671   intermediary: proxy, gateway, and tunnel.  In some cases,
672   a single intermediary might act as an origin server, proxy, gateway,
673   or tunnel, switching behavior based on the nature of each request.
674</t>
675<figure><artwork type="drawing">
676         &gt;             &gt;             &gt;             &gt;
677    UA =========== A =========== B =========== C =========== O
678               &lt;             &lt;             &lt;             &lt;
679</artwork></figure>
680<t>
681   The figure above shows three intermediaries (A, B, and C) between the
682   user agent and origin server. A request or response message that
683   travels the whole chain will pass through four separate connections.
684   Some HTTP communication options
685   might apply only to the connection with the nearest, non-tunnel
686   neighbor, only to the end-points of the chain, or to all connections
687   along the chain. Although the diagram is linear, each participant might
688   be engaged in multiple, simultaneous communications. For example, B
689   might be receiving requests from many clients other than A, and/or
690   forwarding requests to servers other than C, at the same time that it
691   is handling A's request.
692</t>
693<t>
694<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
695<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
696   We use the terms "upstream" and "downstream" to describe various
697   requirements in relation to the directional flow of a message:
698   all messages flow from upstream to downstream.
699   Likewise, we use the terms "inbound" and "outbound" to refer to
700   directions in relation to the request path: "inbound" means toward
701   the origin server and "outbound" means toward the user agent.
702</t>
703<t><iref primary="true" item="proxy"/>
704   A "proxy" is a message forwarding agent that is selected by the
705   client, usually via local configuration rules, to receive requests
706   for some type(s) of absolute URI and attempt to satisfy those
707   requests via translation through the HTTP interface.  Some translations
708   are minimal, such as for proxy requests for "http" URIs, whereas
709   other requests might require translation to and from entirely different
710   application-layer protocols. Proxies are often used to group an
711   organization's HTTP requests through a common intermediary for the
712   sake of security, annotation services, or shared caching.
713</t>
714<t>
715<iref primary="true" item="transforming proxy"/>
716<iref primary="true" item="non-transforming proxy"/>
717   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
718   or configured to modify request or response messages in a semantically
719   meaningful way (i.e., modifications, beyond those required by normal
720   HTTP processing, that change the message in a way that would be
721   significant to the original sender or potentially significant to
722   downstream recipients).  For example, a transforming proxy might be
723   acting as a shared annotation server (modifying responses to include
724   references to a local annotation database), a malware filter, a
725   format transcoder, or an intranet-to-Internet privacy filter.  Such
726   transformations are presumed to be desired by the client (or client
727   organization) that selected the proxy and are beyond the scope of
728   this specification.  However, when a proxy is not intended to transform
729   a given message, we use the term "non-transforming proxy" to target
730   requirements that preserve HTTP message semantics.
731</t>
732<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
733   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
734   as a layer above some other server(s) and translates the received
735   requests to the underlying server's protocol.  Gateways are often
736   used for load balancing or partitioning HTTP services across
737   multiple machines.
738   Unlike a proxy, a gateway receives requests as if it were the
739   origin server for the target resource; the requesting client
740   will not be aware that it is communicating with a gateway.
741   A gateway communicates with the client as if the gateway is the
742   origin server and thus is subject to all of the requirements on
743   origin servers for that connection.  A gateway communicates
744   with inbound servers using any protocol it desires, including
745   private extensions to HTTP that are outside the scope of this
746   specification.
747</t>
748<t><iref primary="true" item="tunnel"/>
749   A "tunnel" acts as a blind relay between two connections
750   without changing the messages. Once active, a tunnel is not
751   considered a party to the HTTP communication, though the tunnel might
752   have been initiated by an HTTP request. A tunnel ceases to exist when
753   both ends of the relayed connection are closed. Tunnels are used to
754   extend a virtual connection through an intermediary, such as when
755   transport-layer security is used to establish private communication
756   through a shared firewall proxy.
757</t>
758<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
759   In addition, there may exist network intermediaries that are not
760   considered part of the HTTP communication but nevertheless act as
761   filters or redirecting agents (usually violating HTTP semantics,
762   causing security problems, and otherwise making a mess of things).
763   Such a network intermediary, referred to as an "interception proxy"
764   <xref target="RFC3040"/> or "transparent proxy" <xref target="RFC1919"/>,
765   differs from an HTTP proxy because it has not been selected by the client.
766   Instead, the network intermediary redirects outgoing TCP port 80 packets
767   (and occasionally other common port traffic) to an internal HTTP server.
768   Interception proxies are commonly found on public network access points
769   as a means of enforcing account subscription prior to allowing use of
770   non-local Internet services.  They are indistinguishable from a
771   man-in-the-middle attack.
772</t>
773</section>
774
775<section title="Caches" anchor="caches">
776<iref primary="true" item="cache"/>
777<t>
778   A "cache" is a local store of previous response messages and the
779   subsystem that controls its message storage, retrieval, and deletion.
780   A cache stores cacheable responses in order to reduce the response
781   time and network bandwidth consumption on future, equivalent
782   requests. Any client or server &MAY; employ a cache, though a cache
783   cannot be used by a server while it is acting as a tunnel.
784</t>
785<t>
786   The effect of a cache is that the request/response chain is shortened
787   if one of the participants along the chain has a cached response
788   applicable to that request. The following illustrates the resulting
789   chain if B has a cached copy of an earlier response from O (via C)
790   for a request which has not been cached by UA or A.
791</t>
792<figure><artwork type="drawing">
793            &gt;             &gt;
794       UA =========== A =========== B - - - - - - C - - - - - - O
795                  &lt;             &lt;
796</artwork></figure>
797<t><iref primary="true" item="cacheable"/>
798   A response is "cacheable" if a cache is allowed to store a copy of
799   the response message for use in answering subsequent requests.
800   Even when a response is cacheable, there might be additional
801   constraints placed by the client or by the origin server on when
802   that cached response can be used for a particular request. HTTP
803   requirements for cache behavior and cacheable responses are
804   defined in &caching-overview;
805</t>
806<t>
807   There are a wide variety of architectures and configurations
808   of caches and proxies deployed across the World Wide Web and
809   inside large organizations. These systems include national hierarchies
810   of proxy caches to save transoceanic bandwidth, systems that
811   broadcast or multicast cache entries, organizations that distribute
812   subsets of cached data via optical media, and so on.
813</t>
814</section>
815
816<section title="Protocol Versioning" anchor="http.version">
817  <x:anchor-alias value="HTTP-Version"/>
818  <x:anchor-alias value="HTTP-Prot-Name"/>
819<t>
820   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
821   versions of the protocol. This specification defines version "1.1".
822   The protocol version as a whole indicates the sender's compliance
823   with the set of requirements laid out in that version's corresponding
824   specification of HTTP.
825</t>
826<t>
827   The version of an HTTP message is indicated by an HTTP-Version field
828   in the first line of the message. HTTP-Version is case-sensitive.
829</t>
830<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
831  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
832  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
833</artwork></figure>
834<t>
835   The HTTP version number consists of two non-negative decimal integers
836   separated by the "." (period or decimal point) character.  The first
837   number ("major version") indicates the HTTP messaging syntax, whereas
838   the second number ("minor version") indicates the highest minor
839   version to which the sender is at least conditionally compliant and
840   able to understand for future communication.  The minor version
841   advertises the sender's communication capabilities even when the
842   sender is only using a backwards-compatible subset of the protocol,
843   thereby letting the recipient know that more advanced features can
844   be used in response (by servers) or in future requests (by clients).
845</t>
846<t>
847   When comparing HTTP versions, the numbers &MUST; be compared
848   numerically rather than lexically.  For example, HTTP/2.4 is a lower
849   version than HTTP/2.13, which in turn is lower than HTTP/12.3.
850   Leading zeros &MUST; be ignored by recipients and &MUST-NOT; be sent.
851</t>
852<t>
853   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
854   (or a recipient whose version is unknown), the HTTP/1.1 message is
855   constructed such that it will be interpreted as a valid HTTP/1.0
856   message even if all of the provided header fields not defined in
857   the HTTP/1.0 specification <xref target="RFC1945"/> are ignored.
858   This specification excludes incompatible message constructions by
859   imposing recipient-version requirements on new HTTP/1.1 features
860   that are not safely interpreted by earlier HTTP/1.0 recipients.
861</t>
862<t>
863   The interpretation of an HTTP message header field does not change
864   between minor versions of the same major version, though the default
865   behavior of a recipient in the absence of such a field can change.
866   Unless specified otherwise, header fields defined in HTTP/1.1 are
867   defined for all versions of HTTP/1.x.  The most popular example of
868   this is the Host header field, which was introduced during the
869   standardization process of HTTP/1.1 and widely deployed for HTTP/1.0
870   requests out of necessity.
871</t>
872<t>
873   Likewise, new header fields can be defined such that, when they are
874   understood by a recipient, they might override or enhance the
875   interpretation of previously defined header fields.  When an
876   implementation receives an unrecognized header field, the recipient
877   &MUST; ignore that header field for local processing regardless of
878   the message's HTTP version.  An unrecognized header field received
879   by a proxy &MUST; be forwarded downstream unless the header field's
880   field-name is listed in the message's Connection header-field
881   (see <xref target="header.connection"/>).
882   These requirements allow HTTP's functionality to be enhanced without
883   requiring prior update of all compliant intermediaries.
884</t>
885<t>
886   Intermediaries that process HTTP messages (i.e., all intermediaries
887   other than those acting as a tunnel) &MUST; send their own HTTP-Version
888   in forwarded messages.  In other words, they &MUST-NOT; blindly
889   forward the first line of an HTTP message without ensuring that the
890   protocol version matches what the intermediary understands, and
891   is at least conditionally compliant to, for both the receiving and
892   sending of messages.  Forwarding an HTTP message without rewriting
893   the HTTP-Version might result in communication errors when downstream
894   recipients use the message sender's version to determine what features
895   are safe to use for later communication with that sender.
896</t>
897<t>
898   An HTTP client &SHOULD; send a request version equal to the highest
899   version for which the client is at least conditionally compliant and
900   whose major version is no higher than the highest version supported
901   by the server, if this is known.  An HTTP client &MUST-NOT; send a
902   version for which it is not at least conditionally compliant.
903</t>
904<t>
905   An HTTP client &MAY; send a lower request version if it is known that
906   the server incorrectly implements the HTTP specification, but only
907   after the client has attempted at least one normal request and determined
908   from the response status or header fields (e.g., Server) that the
909   server improperly handles higher request versions.
910</t>
911<t>
912   An HTTP server &SHOULD; send a response version equal to the highest
913   version for which the server is at least conditionally compliant and
914   whose major version is less than or equal to the one received in the
915   request.  An HTTP server &MUST-NOT; send a version for which it is not
916   at least conditionally compliant.  A server &MAY; send a 505 (HTTP
917   Version Not Supported) response if it cannot send a response using the
918   major version used in the client's request.
919</t>
920<t>
921   An HTTP server &MAY; send an HTTP/1.0 response to an HTTP/1.0 request
922   if it is known or suspected that the client incorrectly implements the
923   HTTP specification and is incapable of correctly processing later
924   version responses, such as when a client fails to parse the version
925   number correctly or when an intermediary is known to blindly forward
926   the HTTP-Version even when it doesn't comply with the given minor
927   version of the protocol. Such protocol downgrades &SHOULD-NOT; be
928   performed unless triggered by specific client attributes, such as when
929   one or more of the request header fields (e.g., User-Agent) uniquely
930   match the values sent by a client known to be in error.
931</t>
932<t>
933   The intention of HTTP's versioning design is that the major number
934   will only be incremented if an incompatible message syntax is
935   introduced, and that the minor number will only be incremented when
936   changes made to the protocol have the effect of adding to the message
937   semantics or implying additional capabilities of the sender.  However,
938   the minor version was not incremented for the changes introduced in
939   <xref target="RFC2616"/>, and this revision is specifically avoiding
940   any such changes to the protocol.
941</t>
942</section>
943
944<section title="Uniform Resource Identifiers" anchor="uri">
945<iref primary="true" item="resource"/>
946<t>
947   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
948   throughout HTTP as the means for identifying resources. URI references
949   are used to target requests, indicate redirects, and define relationships.
950   HTTP does not limit what a resource might be; it merely defines an interface
951   that can be used to interact with a resource via HTTP. More information on
952   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
953</t>
954  <x:anchor-alias value="URI-reference"/>
955  <x:anchor-alias value="absolute-URI"/>
956  <x:anchor-alias value="relative-part"/>
957  <x:anchor-alias value="authority"/>
958  <x:anchor-alias value="path-abempty"/>
959  <x:anchor-alias value="path-absolute"/>
960  <x:anchor-alias value="port"/>
961  <x:anchor-alias value="query"/>
962  <x:anchor-alias value="uri-host"/>
963  <x:anchor-alias value="partial-URI"/>
964<t>
965   This specification adopts the definitions of "URI-reference",
966   "absolute-URI", "relative-part", "port", "host",
967   "path-abempty", "path-absolute", "query", and "authority" from
968   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
969   protocol elements that allow a relative URI without a fragment.
970</t>
971<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"/>
972  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
973  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
974  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
975  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
976  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
977  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
978  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
979  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
980  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
981 
982  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
983</artwork></figure>
984<t>
985   Each protocol element in HTTP that allows a URI reference will indicate in
986   its ABNF production whether the element allows only a URI in absolute form
987   (absolute-URI), any relative reference (relative-ref), or some other subset
988   of the URI-reference grammar. Unless otherwise indicated, URI references
989   are parsed relative to the request target (the default base URI for both
990   the request and its corresponding response).
991</t>
992
993<section title="http URI scheme" anchor="http.uri">
994  <x:anchor-alias value="http-URI"/>
995  <iref item="http URI scheme" primary="true"/>
996  <iref item="URI scheme" subitem="http" primary="true"/>
997<t>
998   The "http" URI scheme is hereby defined for the purpose of minting
999   identifiers according to their association with the hierarchical
1000   namespace governed by a potential HTTP origin server listening for
1001   TCP connections on a given port.
1002   The HTTP server is identified via the generic syntax's
1003   <x:ref>authority</x:ref> component, which includes a host
1004   identifier and optional TCP port, and the remainder of the URI is
1005   considered to be identifying data corresponding to a resource for
1006   which that server might provide an HTTP interface.
1007</t>
1008<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
1009  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1010</artwork></figure>
1011<t>
1012   The host identifier within an <x:ref>authority</x:ref> component is
1013   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
1014   provided as an IP literal or IPv4 address, then the HTTP server is any
1015   listener on the indicated TCP port at that IP address. If host is a
1016   registered name, then that name is considered an indirect identifier
1017   and the recipient might use a name resolution service, such as DNS,
1018   to find the address of a listener for that host.
1019   The host &MUST-NOT; be empty; if an "http" URI is received with an
1020   empty host, then it &MUST; be rejected as invalid.
1021   If the port subcomponent is empty or not given, then TCP port 80 is
1022   assumed (the default reserved port for WWW services).
1023</t>
1024<t>
1025   Regardless of the form of host identifier, access to that host is not
1026   implied by the mere presence of its name or address. The host might or might
1027   not exist and, even when it does exist, might or might not be running an
1028   HTTP server or listening to the indicated port. The "http" URI scheme
1029   makes use of the delegated nature of Internet names and addresses to
1030   establish a naming authority (whatever entity has the ability to place
1031   an HTTP server at that Internet name or address) and allows that
1032   authority to determine which names are valid and how they might be used.
1033</t>
1034<t>
1035   When an "http" URI is used within a context that calls for access to the
1036   indicated resource, a client &MAY; attempt access by resolving
1037   the host to an IP address, establishing a TCP connection to that address
1038   on the indicated port, and sending an HTTP request message to the server
1039   containing the URI's identifying data as described in <xref target="request"/>.
1040   If the server responds to that request with a non-interim HTTP response
1041   message, as described in <xref target="response"/>, then that response
1042   is considered an authoritative answer to the client's request.
1043</t>
1044<t>
1045   Although HTTP is independent of the transport protocol, the "http"
1046   scheme is specific to TCP-based services because the name delegation
1047   process depends on TCP for establishing authority.
1048   An HTTP service based on some other underlying connection protocol
1049   would presumably be identified using a different URI scheme, just as
1050   the "https" scheme (below) is used for servers that require an SSL/TLS
1051   transport layer on a connection. Other protocols might also be used to
1052   provide access to "http" identified resources &mdash; it is only the
1053   authoritative interface used for mapping the namespace that is
1054   specific to TCP.
1055</t>
1056<t>
1057   The URI generic syntax for authority also includes a deprecated
1058   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
1059   for including user authentication information in the URI.  The userinfo
1060   subcomponent (and its "@" delimiter) &MUST-NOT; be used in an "http"
1061   URI.  URI reference recipients &SHOULD; parse for the existence of
1062   userinfo and treat its presence as an error, likely indicating that
1063   the deprecated subcomponent is being used to obscure the authority
1064   for the sake of phishing attacks.
1065</t>
1066</section>
1067
1068<section title="https URI scheme" anchor="https.uri">
1069   <x:anchor-alias value="https-URI"/>
1070   <iref item="https URI scheme"/>
1071   <iref item="URI scheme" subitem="https"/>
1072<t>
1073   The "https" URI scheme is hereby defined for the purpose of minting
1074   identifiers according to their association with the hierarchical
1075   namespace governed by a potential HTTP origin server listening for
1076   SSL/TLS-secured connections on a given TCP port.
1077</t>
1078<t>
1079   All of the requirements listed above for the "http" scheme are also
1080   requirements for the "https" scheme, except that a default TCP port
1081   of 443 is assumed if the port subcomponent is empty or not given,
1082   and the TCP connection &MUST; be secured for privacy through the
1083   use of strong encryption prior to sending the first HTTP request.
1084</t>
1085<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
1086  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
1087</artwork></figure>
1088<t>
1089   Unlike the "http" scheme, responses to "https" identified requests
1090   are never "public" and thus are ineligible for shared caching.
1091   Their default is "private" and might be further constrained via use
1092   of the Cache-Control header field.
1093</t>
1094<t>
1095   Resources made available via the "https" scheme have no shared
1096   identity with the "http" scheme even if their resource identifiers
1097   only differ by the single "s" in the scheme name.  They are
1098   different services governed by different authorities.  However,
1099   some extensions to HTTP that apply to entire host domains, such
1100   as the Cookie protocol, do allow one service to effect communication
1101   with the other services based on host domain matching.
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<t>
1136   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1137   If path-abempty is the empty string (i.e., there is no slash "/"
1138   path separator following the authority), then the "http" URI
1139   &MUST; be given as "/" when
1140   used as a request-target (<xref target="request-target"/>). If a proxy
1141   receives a host name which is not a fully qualified domain name, it
1142   &MAY; add its domain to the host name it received. If a proxy receives
1143   a fully qualified domain name, the proxy &MUST-NOT; change the host
1144   name.
1145</t>
1146</section>
1147</section>
1148</section>
1149
1150<section title="HTTP Message" anchor="http.message">
1151<x:anchor-alias value="generic-message"/>
1152<x:anchor-alias value="message.types"/>
1153<x:anchor-alias value="HTTP-message"/>
1154<x:anchor-alias value="start-line"/>
1155<iref item="header section"/>
1156<iref item="headers"/>
1157<iref item="header field"/>
1158<t>
1159   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1160   characters in a format similar to the Internet Message Format
1161   <xref target="RFC5322"/>: zero or more header fields (collectively
1162   referred to as the "headers" or the "header section"), an empty line
1163   indicating the end of the header section, and an optional message-body.
1164</t>
1165<t>
1166   An HTTP message can either be a request from client to server or a
1167   response from server to client.  Syntactically, the two types of message
1168   differ only in the start-line, which is either a Request-Line (for requests)
1169   or a Status-Line (for responses), and in the algorithm for determining
1170   the length of the message-body (<xref target="message.body"/>).
1171   In theory, a client could receive requests and a server could receive
1172   responses, distinguishing them by their different start-line formats,
1173   but in practice servers are implemented to only expect a request
1174   (a response is interpreted as an unknown or invalid request method)
1175   and clients are implemented to only expect a response.
1176</t>
1177<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1178  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1179                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1180                    <x:ref>CRLF</x:ref>
1181                    [ <x:ref>message-body</x:ref> ]
1182  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1183</artwork></figure>
1184<t>
1185   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1186   header field. The presence of whitespace might be an attempt to trick a
1187   noncompliant implementation of HTTP into ignoring that field or processing
1188   the next line as a new request, either of which might result in security
1189   issues when implementations within the request chain interpret the
1190   same message differently. HTTP/1.1 servers &MUST; reject such a message
1191   with a 400 (Bad Request) response.
1192</t>
1193
1194<section title="Message Parsing Robustness" anchor="message.robustness">
1195<t>
1196   In the interest of robustness, servers &SHOULD; ignore at least one
1197   empty line received where a Request-Line is expected. In other words, if
1198   the server is reading the protocol stream at the beginning of a
1199   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1200</t>
1201<t>
1202   Some old HTTP/1.0 client implementations generate an extra CRLF
1203   after a POST request as a lame workaround for some early server
1204   applications that failed to read message-body content that was
1205   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1206   preface or follow a request with an extra CRLF.  If terminating
1207   the request message-body with a line-ending is desired, then the
1208   client &MUST; include the terminating CRLF octets as part of the
1209   message-body length.
1210</t>
1211<t>
1212   The normal procedure for parsing an HTTP message is to read the
1213   start-line into a structure, read each header field into a hash
1214   table by field name until the empty line, and then use the parsed
1215   data to determine if a message-body is expected.  If a message-body
1216   has been indicated, then it is read as a stream until an amount
1217   of octets equal to the message-body length is read or the connection
1218   is closed.  Care must be taken to parse an HTTP message as a sequence
1219   of octets in an encoding that is a superset of US-ASCII.  Attempting
1220   to parse HTTP as a stream of Unicode characters in a character encoding
1221   like UTF-16 might introduce security flaws due to the differing ways
1222   that such parsers interpret invalid characters.
1223</t>
1224<t>
1225   HTTP allows the set of defined header fields to be extended without
1226   changing the protocol version (see <xref target="header.field.registration"/>).
1227   Unrecognized header fields &MUST; be forwarded by a proxy unless the
1228   proxy is specifically configured to block or otherwise transform such
1229   fields.  Unrecognized header fields &SHOULD; be ignored by other recipients.
1230</t>
1231</section>
1232
1233<section title="Header Fields" anchor="header.fields">
1234  <x:anchor-alias value="header-field"/>
1235  <x:anchor-alias value="field-content"/>
1236  <x:anchor-alias value="field-name"/>
1237  <x:anchor-alias value="field-value"/>
1238  <x:anchor-alias value="OWS"/>
1239<t>
1240   Each HTTP header field consists of a case-insensitive field name
1241   followed by a colon (":"), optional whitespace, and the field value.
1242</t>
1243<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"/>
1244  <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>
1245  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1246  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1247  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1248</artwork></figure>
1249<t>
1250   No whitespace is allowed between the header field name and colon. For
1251   security reasons, any request message received containing such whitespace
1252   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1253   &MUST; remove any such whitespace from a response message before
1254   forwarding the message downstream.
1255</t>
1256<t>
1257   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1258   preferred. The field value does not include any leading or trailing white
1259   space: OWS occurring before the first non-whitespace character of the
1260   field value or after the last non-whitespace character of the field value
1261   is ignored and &SHOULD; be removed before further processing (as this does
1262   not change the meaning of the header field).
1263</t>
1264<t>
1265   The order in which header fields with differing field names are
1266   received is not significant. However, it is "good practice" to send
1267   header fields that contain control data first, such as Host on
1268   requests and Date on responses, so that implementations can decide
1269   when not to handle a message as early as possible.  A server &MUST;
1270   wait until the entire header section is received before interpreting
1271   a request message, since later header fields might include conditionals,
1272   authentication credentials, or deliberately misleading duplicate
1273   header fields that would impact request processing.
1274</t>
1275<t>
1276   Multiple header fields with the same field name &MUST-NOT; be
1277   sent in a message unless the entire field value for that
1278   header field is defined as a comma-separated list [i.e., #(values)].
1279   Multiple header fields with the same field name can be combined into
1280   one "field-name: field-value" pair, without changing the semantics of the
1281   message, by appending each subsequent field value to the combined
1282   field value in order, separated by a comma. The order in which
1283   header fields with the same field name are received is therefore
1284   significant to the interpretation of the combined field value;
1285   a proxy &MUST-NOT; change the order of these field values when
1286   forwarding a message.
1287</t>
1288<x:note>
1289  <t>
1290   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1291   practice can occur multiple times, but does not use the list syntax, and
1292   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1293   for details.) Also note that the Set-Cookie2 header field specified in
1294   <xref target="RFC2965"/> does not share this problem.
1295  </t>
1296</x:note>
1297<t>
1298   Historically, HTTP header field values could be extended over multiple
1299   lines by preceding each extra line with at least one space or horizontal
1300   tab character (line folding). This specification deprecates such line
1301   folding except within the message/http media type
1302   (<xref target="internet.media.type.message.http"/>).
1303   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1304   (i.e., that contain any field-content that matches the obs-fold rule) unless
1305   the message is intended for packaging within the message/http media type.
1306   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1307   obs-fold whitespace with a single SP prior to interpreting the field value
1308   or forwarding the message downstream.
1309</t>
1310<t>
1311   Historically, HTTP has allowed field content with text in the ISO-8859-1
1312   <xref target="ISO-8859-1"/> character encoding and supported other
1313   character sets only through use of <xref target="RFC2047"/> encoding.
1314   In practice, most HTTP header field values use only a subset of the
1315   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1316   header fields &SHOULD; limit their field values to US-ASCII characters.
1317   Recipients &SHOULD; treat other (obs-text) octets in field content as
1318   opaque data.
1319</t>
1320<t anchor="rule.comment">
1321  <x:anchor-alias value="comment"/>
1322  <x:anchor-alias value="ctext"/>
1323   Comments can be included in some HTTP header fields by surrounding
1324   the comment text with parentheses. Comments are only allowed in
1325   fields containing "comment" as part of their field value definition.
1326</t>
1327<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1328  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1329  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1330                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1331</artwork></figure>
1332<t anchor="rule.quoted-cpair">
1333  <x:anchor-alias value="quoted-cpair"/>
1334   The backslash character ("\") can be used as a single-character
1335   quoting mechanism within comment constructs:
1336</t>
1337<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1338  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1339</artwork></figure>
1340<t>
1341   Producers &SHOULD-NOT; escape characters that do not require escaping
1342   (i.e., other than the backslash character "\" and the parentheses "(" and
1343   ")").
1344</t>
1345</section>
1346
1347<section title="Message Body" anchor="message.body">
1348  <x:anchor-alias value="message-body"/>
1349<t>
1350   The message-body (if any) of an HTTP message is used to carry the
1351   payload body associated with the request or response.
1352</t>
1353<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1354  <x:ref>message-body</x:ref> = *OCTET
1355</artwork></figure>
1356<t>
1357   The message-body differs from the payload body only when a transfer-coding
1358   has been applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).  When one or more transfer-codings are
1359   applied to a payload in order to form the message-body, the
1360   Transfer-Encoding header field &MUST; contain the list of
1361   transfer-codings applied. Transfer-Encoding is a property of the message,
1362   not of the payload, and thus &MAY; be added or removed by any implementation
1363   along the request/response chain under the constraints found in
1364   <xref target="transfer.codings"/>.
1365</t>
1366<t>
1367   The rules for when a message-body is allowed in a message differ for
1368   requests and responses.
1369</t>
1370<t>
1371   The presence of a message-body in a request is signaled by the
1372   inclusion of a Content-Length or Transfer-Encoding header field in
1373   the request's header fields, even if the request method does not
1374   define any use for a message-body.  This allows the request
1375   message framing algorithm to be independent of method semantics.
1376</t>
1377<t>
1378   For response messages, whether or not a message-body is included with
1379   a message is dependent on both the request method and the response
1380   status code (<xref target="status.code.and.reason.phrase"/>).
1381   Responses to the HEAD request method never include a message-body
1382   because the associated response header fields (e.g., Transfer-Encoding,
1383   Content-Length, etc.) only indicate what their values would have been
1384   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1385   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1386   All other responses do include a message-body, although the body
1387   &MAY; be of zero length.
1388</t>
1389<t>
1390   The length of the message-body is determined by one of the following
1391   (in order of precedence):
1392</t>
1393<t>
1394  <list style="numbers">
1395    <x:lt><t>
1396     Any response to a HEAD request and any response with a status
1397     code of 100-199, 204, or 304 is always terminated by the first
1398     empty line after the header fields, regardless of the header
1399     fields present in the message, and thus cannot contain a message-body.
1400    </t></x:lt>
1401    <x:lt><t>
1402     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1403     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1404     is the final encoding, the message-body length is determined by reading
1405     and decoding the chunked data until the transfer-coding indicates the
1406     data is complete.
1407    </t>
1408    <t>
1409     If a Transfer-Encoding header field is present in a response and the
1410     "chunked" transfer-coding is not the final encoding, the message-body
1411     length is determined by reading the connection until it is closed by
1412     the server.
1413     If a Transfer-Encoding header field is present in a request and the
1414     "chunked" transfer-coding is not the final encoding, the message-body
1415     length cannot be determined reliably; the server &MUST; respond with
1416     the 400 (Bad Request) status code and then close the connection.
1417    </t>
1418    <t>
1419     If a message is received with both a Transfer-Encoding header field and a
1420     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1421     Such a message might indicate an attempt to perform request or response
1422     smuggling (bypass of security-related checks on message routing or content)
1423     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1424     be removed, prior to forwarding the message downstream, or replaced with
1425     the real message-body length after the transfer-coding is decoded.
1426    </t></x:lt>
1427    <x:lt><t>
1428     If a message is received without Transfer-Encoding and with either
1429     multiple Content-Length header fields or a single Content-Length header
1430     field with an invalid value, then the message framing is invalid and
1431     &MUST; be treated as an error to prevent request or response smuggling.
1432     If this is a request message, the server &MUST; respond with
1433     a 400 (Bad Request) status code and then close the connection.
1434     If this is a response message received by a proxy or gateway, the proxy
1435     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1436     status code as its downstream response, and then close the connection.
1437     If this is a response message received by a user-agent, it &SHOULD; be
1438     treated as an error by discarding the message and closing the connection.
1439    </t></x:lt>
1440    <x:lt><t>
1441     If a valid Content-Length header field (<xref target="header.content-length"/>)
1442     is present without Transfer-Encoding, its decimal value defines the
1443     message-body length in octets.  If the actual number of octets sent in
1444     the message is less than the indicated Content-Length, the recipient
1445     &MUST; consider the message to be incomplete and treat the connection
1446     as no longer usable.
1447     If the actual number of octets sent in the message is more than the indicated
1448     Content-Length, the recipient &MUST; only process the message-body up to the
1449     field value's number of octets; the remainder of the message &MUST; either
1450     be discarded or treated as the next message in a pipeline.  For the sake of
1451     robustness, a user-agent &MAY; attempt to detect and correct such an error
1452     in message framing if it is parsing the response to the last request on
1453     on a connection and the connection has been closed by the server.
1454    </t></x:lt>
1455    <x:lt><t>
1456     If this is a request message and none of the above are true, then the
1457     message-body length is zero (no message-body is present).
1458    </t></x:lt>
1459    <x:lt><t>
1460     Otherwise, this is a response message without a declared message-body
1461     length, so the message-body length is determined by the number of octets
1462     received prior to the server closing the connection.
1463    </t></x:lt>
1464  </list>
1465</t>
1466<t>
1467   Since there is no way to distinguish a successfully completed,
1468   close-delimited message from a partially-received message interrupted
1469   by network failure, implementations &SHOULD; use encoding or
1470   length-delimited messages whenever possible.  The close-delimiting
1471   feature exists primarily for backwards compatibility with HTTP/1.0.
1472</t>
1473<t>
1474   A server &MAY; reject a request that contains a message-body but
1475   not a Content-Length by responding with 411 (Length Required).
1476</t>
1477<t>
1478   Unless a transfer-coding other than "chunked" has been applied,
1479   a client that sends a request containing a message-body &SHOULD;
1480   use a valid Content-Length header field if the message-body length
1481   is known in advance, rather than the "chunked" encoding, since some
1482   existing services respond to "chunked" with a 411 (Length Required)
1483   status code even though they understand the chunked encoding.  This
1484   is typically because such services are implemented via a gateway that
1485   requires a content-length in advance of being called and the server
1486   is unable or unwilling to buffer the entire request before processing.
1487</t>
1488<t>
1489   A client that sends a request containing a message-body &MUST; include a
1490   valid Content-Length header field if it does not know the server will
1491   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1492   of specific user configuration or by remembering the version of a prior
1493   received response.
1494</t>
1495<t>
1496   Request messages that are prematurely terminated, possibly due to a
1497   cancelled connection or a server-imposed time-out exception, &MUST;
1498   result in closure of the connection; sending an HTTP/1.1 error response
1499   prior to closing the connection is &OPTIONAL;.
1500   Response messages that are prematurely terminated, usually by closure
1501   of the connection prior to receiving the expected number of octets or by
1502   failure to decode a transfer-encoded message-body, &MUST; be recorded
1503   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1504   message-body as if it were complete (i.e., some indication must be given
1505   to the user that an error occurred).  Cache requirements for incomplete
1506   responses are defined in &cache-incomplete;.
1507</t>
1508<t>
1509   A server &MUST; read the entire request message-body or close
1510   the connection after sending its response, since otherwise the
1511   remaining data on a persistent connection would be misinterpreted
1512   as the next request.  Likewise,
1513   a client &MUST; read the entire response message-body if it intends
1514   to reuse the same connection for a subsequent request.  Pipelining
1515   multiple requests on a connection is described in <xref target="pipelining"/>.
1516</t>
1517</section>
1518
1519<section title="General Header Fields" anchor="general.header.fields">
1520  <x:anchor-alias value="general-header"/>
1521<t>
1522   There are a few header fields which have general applicability for
1523   both request and response messages, but which do not apply to the
1524   payload being transferred. These header fields apply only to the
1525   message being transmitted.
1526</t>
1527<texttable align="left">
1528  <ttcol>Header Field Name</ttcol>
1529  <ttcol>Defined in...</ttcol>
1530 
1531  <c>Connection</c> <c><xref target="header.connection"/></c>
1532  <c>Date</c> <c><xref target="header.date"/></c>
1533  <c>Pragma</c> <c>&header-pragma;</c>
1534  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1535  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1536  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1537  <c>Via</c> <c><xref target="header.via"/></c>
1538  <c>Warning</c> <c>&header-warning;</c>
1539  <c>MIME-Version</c> <c>&header-mime-version;</c>
1540</texttable>
1541<t>
1542   General-header field names can be extended reliably only in
1543   combination with a change in the protocol version. However, new or
1544   experimental header fields might be given the semantics of general
1545   header fields if all parties in the communication recognize them to
1546   be general-header fields.
1547</t>
1548</section>
1549</section>
1550
1551<section title="Request" anchor="request">
1552  <x:anchor-alias value="Request"/>
1553<t>
1554   A request message from a client to a server includes, within the
1555   first line of that message, the method to be applied to the resource,
1556   the identifier of the resource, and the protocol version in use.
1557</t>
1558<!--                 Host                      ; should be moved here eventually -->
1559<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1560  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1561                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1562                  <x:ref>CRLF</x:ref>
1563                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1564</artwork></figure>
1565
1566<section title="Request-Line" anchor="request-line">
1567  <x:anchor-alias value="Request-Line"/>
1568<t>
1569   The Request-Line begins with a method token, followed by the
1570   request-target and the protocol version, and ending with CRLF. The
1571   elements are separated by SP characters. No CR or LF is allowed
1572   except in the final CRLF sequence.
1573</t>
1574<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1575  <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>
1576</artwork></figure>
1577
1578<section title="Method" anchor="method">
1579  <x:anchor-alias value="Method"/>
1580<t>
1581   The Method  token indicates the method to be performed on the
1582   resource identified by the request-target. The method is case-sensitive.
1583</t>
1584<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/>
1585  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1586</artwork></figure>
1587</section>
1588
1589<section title="request-target" anchor="request-target">
1590  <x:anchor-alias value="request-target"/>
1591<t>
1592   The request-target identifies the resource upon which to apply the request.
1593</t>
1594<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1595  <x:ref>request-target</x:ref> = "*"
1596                 / <x:ref>absolute-URI</x:ref>
1597                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1598                 / <x:ref>authority</x:ref>
1599</artwork></figure>
1600<t>
1601   The four options for request-target are dependent on the nature of the
1602   request.
1603</t>   
1604<t><iref item="asterisk form (of request-target)"/>
1605   The asterisk "*" ("asterisk form") means that the request does not apply to a
1606   particular resource, but to the server itself. This is only allowed for the
1607   OPTIONS method. Thus, the only valid example is
1608</t>
1609<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1610OPTIONS * HTTP/1.1
1611</artwork></figure>
1612<t><iref item="absolute-URI form (of request-target)"/>
1613   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1614   proxy. The proxy is requested to forward the request or service it
1615   from a valid cache, and return the response. Note that the proxy &MAY;
1616   forward the request on to another proxy or directly to the server
1617   specified by the absolute-URI. In order to avoid request loops, a
1618   proxy &MUST; be able to recognize all of its server names, including
1619   any aliases, local variations, and the numeric IP address. An example
1620   Request-Line would be:
1621</t>
1622<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1623GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1624</artwork></figure>
1625<t>
1626   To allow for transition to absolute-URIs in all requests in future
1627   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1628   form in requests, even though HTTP/1.1 clients will only generate
1629   them in requests to proxies.
1630</t>
1631<t><iref item="authority form (of request-target)"/>
1632   The "authority form" is only used by the CONNECT method (&CONNECT;).
1633</t>
1634<t><iref item="path-absolute form (of request-target)"/>
1635   The most common form of request-target is that used to identify a
1636   resource on an origin server or gateway ("path-absolute form"). In this case the absolute
1637   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1638   the request-target, and the network location of the URI (authority) &MUST;
1639   be transmitted in a Host header field. For example, a client wishing
1640   to retrieve the resource above directly from the origin server would
1641   create a TCP connection to port 80 of the host "www.example.org" and send
1642   the lines:
1643</t>
1644<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1645GET /pub/WWW/TheProject.html HTTP/1.1
1646Host: www.example.org
1647</artwork></figure>
1648<t>
1649   followed by the remainder of the Request. Note that the absolute path
1650   cannot be empty; if none is present in the original URI, it &MUST; be
1651   given as "/" (the server root).
1652</t>
1653<t>
1654   If a proxy receives a request without any path in the request-target and
1655   the method specified is capable of supporting the asterisk form of
1656   request-target, then the last proxy on the request chain &MUST; forward the
1657   request with "*" as the final request-target.
1658</t>
1659<figure><preamble>   
1660   For example, the request
1661</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1662OPTIONS http://www.example.org:8001 HTTP/1.1
1663</artwork></figure>
1664<figure><preamble>   
1665  would be forwarded by the proxy as
1666</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1667OPTIONS * HTTP/1.1
1668Host: www.example.org:8001
1669</artwork>
1670<postamble>
1671   after connecting to port 8001 of host "www.example.org".
1672</postamble>
1673</figure>
1674<t>
1675   The request-target is transmitted in the format specified in
1676   <xref target="http.uri"/>. If the request-target is percent-encoded
1677   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1678   &MUST; decode the request-target in order to
1679   properly interpret the request. Servers &SHOULD; respond to invalid
1680   request-targets with an appropriate status code.
1681</t>
1682<t>
1683   A non-transforming proxy &MUST-NOT; rewrite the "path-absolute" part of the
1684   received request-target when forwarding it to the next inbound server,
1685   except as noted above to replace a null path-absolute with "/" or "*".
1686</t>
1687<x:note>
1688  <t>
1689    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1690    meaning of the request when the origin server is improperly using
1691    a non-reserved URI character for a reserved purpose.  Implementors
1692    need to be aware that some pre-HTTP/1.1 proxies have been known to
1693    rewrite the request-target.
1694  </t>
1695</x:note>
1696<t>
1697   HTTP does not place a pre-defined limit on the length of a request-target.
1698   A server &MUST; be prepared to receive URIs of unbounded length and
1699   respond with the 414 (URI Too Long) status code if the received
1700   request-target would be longer than the server wishes to handle
1701   (see &status-414;).
1702</t>
1703<t>
1704   Various ad-hoc limitations on request-target length are found in practice.
1705   It is &RECOMMENDED; that all HTTP senders and recipients support
1706   request-target lengths of 8000 or more octets.
1707</t>
1708<x:note>
1709  <t>
1710    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1711    are not part of the request-target and thus will not be transmitted
1712    in an HTTP request.
1713  </t>
1714</x:note>
1715</section>
1716</section>
1717
1718<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1719<t>
1720   The exact resource identified by an Internet request is determined by
1721   examining both the request-target and the Host header field.
1722</t>
1723<t>
1724   An origin server that does not allow resources to differ by the
1725   requested host &MAY; ignore the Host header field value when
1726   determining the resource identified by an HTTP/1.1 request. (But see
1727   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1728   for other requirements on Host support in HTTP/1.1.)
1729</t>
1730<t>
1731   An origin server that does differentiate resources based on the host
1732   requested (sometimes referred to as virtual hosts or vanity host
1733   names) &MUST; use the following rules for determining the requested
1734   resource on an HTTP/1.1 request:
1735  <list style="numbers">
1736    <t>If request-target is an absolute-URI, the host is part of the
1737     request-target. Any Host header field value in the request &MUST; be
1738     ignored.</t>
1739    <t>If the request-target is not an absolute-URI, and the request includes
1740     a Host header field, the host is determined by the Host header
1741     field value.</t>
1742    <t>If the host as determined by rule 1 or 2 is not a valid host on
1743     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1744  </list>
1745</t>
1746<t>
1747   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1748   attempt to use heuristics (e.g., examination of the URI path for
1749   something unique to a particular host) in order to determine what
1750   exact resource is being requested.
1751</t>
1752</section>
1753
1754<section title="Effective Request URI" anchor="effective.request.uri">
1755  <iref primary="true" item="effective request URI"/>
1756  <iref primary="true" item="target resource"/>
1757<t>
1758   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1759   for the target resource; instead, the URI needs to be inferred from the
1760   request-target, Host header field, and connection context. The result of
1761   this process is called the "effective request URI".  The "target resource"
1762   is the resource identified by the effective request URI.
1763</t>
1764<t>
1765   If the request-target is an absolute-URI, then the effective request URI is
1766   the request-target.
1767</t>
1768<t>
1769   If the request-target uses the path-absolute form or the asterisk form,
1770   and the Host header field is present, then the effective request URI is
1771   constructed by concatenating
1772</t>
1773<t>
1774  <list style="symbols">
1775    <t>
1776      the scheme name: "http" if the request was received over an insecure
1777      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1778      connection,
1779    </t>
1780    <t>
1781      the character sequence "://",
1782    </t>
1783    <t>
1784      the authority component, as specified in the Host header field
1785      (<xref target="header.host"/>), and
1786    </t>
1787    <t>
1788      the request-target obtained from the Request-Line, unless the
1789      request-target is just the asterisk "*".
1790    </t>
1791  </list>
1792</t>
1793<t>
1794   If the request-target uses the path-absolute form or the asterisk form,
1795   and the Host header field is not present, then the effective request URI is
1796   undefined.
1797</t>
1798<t>
1799   Otherwise, when request-target uses the authority form, the effective
1800   request URI is undefined.
1801</t>
1802<figure>
1803<preamble>
1804   Example 1: the effective request URI for the message
1805</preamble> 
1806<artwork type="example" x:indent-with="  ">
1807GET /pub/WWW/TheProject.html HTTP/1.1
1808Host: www.example.org:8080
1809</artwork>
1810<postamble>
1811  (received over an insecure TCP connection) is "http", plus "://", plus the
1812  authority component "www.example.org:8080", plus the request-target
1813  "/pub/WWW/TheProject.html", thus
1814  "http://www.example.org:8080/pub/WWW/TheProject.html".
1815</postamble>
1816</figure>
1817<figure>
1818<preamble>
1819   Example 2: the effective request URI for the message
1820</preamble> 
1821<artwork type="example" x:indent-with="  ">
1822GET * HTTP/1.1
1823Host: www.example.org
1824</artwork>
1825<postamble>
1826  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1827  authority component "www.example.org", thus "https://www.example.org".
1828</postamble>
1829</figure>
1830<t>
1831   Effective request URIs are compared using the rules described in
1832   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1833   be treated as equivalent to an absolute path of "/".
1834</t> 
1835</section>
1836
1837</section>
1838
1839
1840<section title="Response" anchor="response">
1841  <x:anchor-alias value="Response"/>
1842<t>
1843   After receiving and interpreting a request message, a server responds
1844   with an HTTP response message.
1845</t>
1846<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1847  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1848                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1849                  <x:ref>CRLF</x:ref>
1850                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1851</artwork></figure>
1852
1853<section title="Status-Line" anchor="status-line">
1854  <x:anchor-alias value="Status-Line"/>
1855<t>
1856   The first line of a Response message is the Status-Line, consisting
1857   of the protocol version followed by a numeric status code and its
1858   associated textual phrase, with each element separated by SP
1859   characters. No CR or LF is allowed except in the final CRLF sequence.
1860</t>
1861<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1862  <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>
1863</artwork></figure>
1864
1865<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1866  <x:anchor-alias value="Reason-Phrase"/>
1867  <x:anchor-alias value="Status-Code"/>
1868<t>
1869   The Status-Code element is a 3-digit integer result code of the
1870   attempt to understand and satisfy the request. These codes are fully
1871   defined in &status-codes;.  The Reason Phrase exists for the sole
1872   purpose of providing a textual description associated with the numeric
1873   status code, out of deference to earlier Internet application protocols
1874   that were more frequently used with interactive text clients.
1875   A client &SHOULD; ignore the content of the Reason Phrase.
1876</t>
1877<t>
1878   The first digit of the Status-Code defines the class of response. The
1879   last two digits do not have any categorization role. There are 5
1880   values for the first digit:
1881  <list style="symbols">
1882    <t>
1883      1xx: Informational - Request received, continuing process
1884    </t>
1885    <t>
1886      2xx: Success - The action was successfully received,
1887        understood, and accepted
1888    </t>
1889    <t>
1890      3xx: Redirection - Further action must be taken in order to
1891        complete the request
1892    </t>
1893    <t>
1894      4xx: Client Error - The request contains bad syntax or cannot
1895        be fulfilled
1896    </t>
1897    <t>
1898      5xx: Server Error - The server failed to fulfill an apparently
1899        valid request
1900    </t>
1901  </list>
1902</t>
1903<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1904  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1905  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1906</artwork></figure>
1907</section>
1908</section>
1909
1910</section>
1911
1912
1913<section title="Protocol Parameters" anchor="protocol.parameters">
1914
1915<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1916  <x:anchor-alias value="HTTP-date"/>
1917<t>
1918   HTTP applications have historically allowed three different formats
1919   for date/time stamps. However, the preferred format is a fixed-length subset
1920   of that defined by <xref target="RFC1123"/>:
1921</t>
1922<figure><artwork type="example" x:indent-with="  ">
1923Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1924</artwork></figure>
1925<t>
1926   The other formats are described here only for compatibility with obsolete
1927   implementations.
1928</t>
1929<figure><artwork type="example" x:indent-with="  ">
1930Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1931Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1932</artwork></figure>
1933<t>
1934   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1935   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1936   only generate the RFC 1123 format for representing HTTP-date values
1937   in header fields. See <xref target="tolerant.applications"/> for further information.
1938</t>
1939<t>
1940   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1941   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1942   equal to UTC (Coordinated Universal Time). This is indicated in the
1943   first two formats by the inclusion of "GMT" as the three-letter
1944   abbreviation for time zone, and &MUST; be assumed when reading the
1945   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1946   additional whitespace beyond that specifically included as SP in the
1947   grammar.
1948</t>
1949<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1950  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1951</artwork></figure>
1952<t anchor="preferred.date.format">
1953  <x:anchor-alias value="rfc1123-date"/>
1954  <x:anchor-alias value="time-of-day"/>
1955  <x:anchor-alias value="hour"/>
1956  <x:anchor-alias value="minute"/>
1957  <x:anchor-alias value="second"/>
1958  <x:anchor-alias value="day-name"/>
1959  <x:anchor-alias value="day"/>
1960  <x:anchor-alias value="month"/>
1961  <x:anchor-alias value="year"/>
1962  <x:anchor-alias value="GMT"/>
1963  Preferred format:
1964</t>
1965<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"/>
1966  <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>
1967  ; fixed length subset of the format defined in
1968  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1969 
1970  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1971               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1972               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1973               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1974               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1975               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1976               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1977               
1978  <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>
1979               ; e.g., 02 Jun 1982
1980
1981  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1982  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1983               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1984               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1985               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1986               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1987               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1988               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1989               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1990               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1991               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1992               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1993               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1994  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1995
1996  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1997
1998  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1999                 ; 00:00:00 - 23:59:59
2000                 
2001  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
2002  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2003  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
2004</artwork></figure>
2005<t>
2006  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
2007  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
2008  same as those defined for the RFC 5322 constructs
2009  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
2010</t>
2011<t anchor="obsolete.date.formats">
2012  <x:anchor-alias value="obs-date"/>
2013  <x:anchor-alias value="rfc850-date"/>
2014  <x:anchor-alias value="asctime-date"/>
2015  <x:anchor-alias value="date1"/>
2016  <x:anchor-alias value="date2"/>
2017  <x:anchor-alias value="date3"/>
2018  <x:anchor-alias value="rfc1123-date"/>
2019  <x:anchor-alias value="day-name-l"/>
2020  Obsolete formats:
2021</t>
2022<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
2023  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
2024</artwork></figure>
2025<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
2026  <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>
2027  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
2028                 ; day-month-year (e.g., 02-Jun-82)
2029
2030  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
2031         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
2032         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
2033         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
2034         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
2035         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
2036         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
2037</artwork></figure>
2038<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
2039  <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>
2040  <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> ))
2041                 ; month day (e.g., Jun  2)
2042</artwork></figure>
2043<x:note>
2044  <t>
2045    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
2046    accepting date values that might have been sent by non-HTTP
2047    applications, as is sometimes the case when retrieving or posting
2048    messages via proxies/gateways to SMTP or NNTP.
2049  </t>
2050</x:note>
2051<x:note>
2052  <t>
2053    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
2054    to their usage within the protocol stream. Clients and servers are
2055    not required to use these formats for user presentation, request
2056    logging, etc.
2057  </t>
2058</x:note>
2059</section>
2060
2061<section title="Transfer Codings" anchor="transfer.codings">
2062  <x:anchor-alias value="transfer-coding"/>
2063  <x:anchor-alias value="transfer-extension"/>
2064<t>
2065   Transfer-coding values are used to indicate an encoding
2066   transformation that has been, can be, or might need to be applied to a
2067   payload body in order to ensure "safe transport" through the network.
2068   This differs from a content coding in that the transfer-coding is a
2069   property of the message rather than a property of the representation
2070   that is being transferred.
2071</t>
2072<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
2073  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
2074                          / "compress" ; <xref target="compress.coding"/>
2075                          / "deflate" ; <xref target="deflate.coding"/>
2076                          / "gzip" ; <xref target="gzip.coding"/>
2077                          / <x:ref>transfer-extension</x:ref>
2078  <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> )
2079</artwork></figure>
2080<t anchor="rule.parameter">
2081  <x:anchor-alias value="attribute"/>
2082  <x:anchor-alias value="transfer-parameter"/>
2083  <x:anchor-alias value="value"/>
2084   Parameters are in the form of attribute/value pairs.
2085</t>
2086<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"/>
2087  <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>
2088  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2089  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2090</artwork></figure>
2091<t>
2092   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2093   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2094   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2095</t>
2096<t>
2097   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2098   MIME, which were designed to enable safe transport of binary data over a
2099   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2100   However, safe transport
2101   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2102   the only unsafe characteristic of message-bodies is the difficulty in
2103   determining the exact message body length (<xref target="message.body"/>),
2104   or the desire to encrypt data over a shared transport.
2105</t>
2106<t>
2107   A server that receives a request message with a transfer-coding it does
2108   not understand &SHOULD; respond with 501 (Not Implemented) and then
2109   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2110   client.
2111</t>
2112
2113<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2114  <iref item="chunked (Coding Format)"/>
2115  <iref item="Coding Format" subitem="chunked"/>
2116  <x:anchor-alias value="chunk"/>
2117  <x:anchor-alias value="Chunked-Body"/>
2118  <x:anchor-alias value="chunk-data"/>
2119  <x:anchor-alias value="chunk-ext"/>
2120  <x:anchor-alias value="chunk-ext-name"/>
2121  <x:anchor-alias value="chunk-ext-val"/>
2122  <x:anchor-alias value="chunk-size"/>
2123  <x:anchor-alias value="last-chunk"/>
2124  <x:anchor-alias value="trailer-part"/>
2125  <x:anchor-alias value="quoted-str-nf"/>
2126  <x:anchor-alias value="qdtext-nf"/>
2127<t>
2128   The chunked encoding modifies the body of a message in order to
2129   transfer it as a series of chunks, each with its own size indicator,
2130   followed by an &OPTIONAL; trailer containing header fields. This
2131   allows dynamically produced content to be transferred along with the
2132   information necessary for the recipient to verify that it has
2133   received the full message.
2134</t>
2135<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"/>
2136  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2137                   <x:ref>last-chunk</x:ref>
2138                   <x:ref>trailer-part</x:ref>
2139                   <x:ref>CRLF</x:ref>
2140 
2141  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2142                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2143  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2144  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2145 
2146  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2147                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2148  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2149  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2150  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2151  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2152 
2153  <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>
2154                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2155  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2156                 ; <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> 
2157</artwork></figure>
2158<t>
2159   The chunk-size field is a string of hex digits indicating the size of
2160   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2161   zero, followed by the trailer, which is terminated by an empty line.
2162</t>
2163<t>
2164   The trailer allows the sender to include additional HTTP header
2165   fields at the end of the message. The Trailer header field can be
2166   used to indicate which header fields are included in a trailer (see
2167   <xref target="header.trailer"/>).
2168</t>
2169<t>
2170   A server using chunked transfer-coding in a response &MUST-NOT; use the
2171   trailer for any header fields unless at least one of the following is
2172   true:
2173  <list style="numbers">
2174    <t>the request included a TE header field that indicates "trailers" is
2175     acceptable in the transfer-coding of the  response, as described in
2176     <xref target="header.te"/>; or,</t>
2177     
2178    <t>the trailer fields consist entirely of optional metadata, and the
2179    recipient could use the message (in a manner acceptable to the server where
2180    the field originated) without receiving it. In other words, the server that
2181    generated the header (often but not always the origin server) is willing to
2182    accept the possibility that the trailer fields might be silently discarded
2183    along the path to the client.</t>
2184  </list>
2185</t>
2186<t>
2187   This requirement prevents an interoperability failure when the
2188   message is being received by an HTTP/1.1 (or later) proxy and
2189   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2190   compliance with the protocol would have necessitated a possibly
2191   infinite buffer on the proxy.
2192</t>
2193<t>
2194   A process for decoding the "chunked" transfer-coding
2195   can be represented in pseudo-code as:
2196</t>
2197<figure><artwork type="code">
2198  length := 0
2199  read chunk-size, chunk-ext (if any) and CRLF
2200  while (chunk-size &gt; 0) {
2201     read chunk-data and CRLF
2202     append chunk-data to decoded-body
2203     length := length + chunk-size
2204     read chunk-size and CRLF
2205  }
2206  read header-field
2207  while (header-field not empty) {
2208     append header-field to existing header fields
2209     read header-field
2210  }
2211  Content-Length := length
2212  Remove "chunked" from Transfer-Encoding
2213</artwork></figure>
2214<t>
2215   All HTTP/1.1 applications &MUST; be able to receive and decode the
2216   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2217   they do not understand.
2218</t>
2219<t>
2220   Since "chunked" is the only transfer-coding required to be understood
2221   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2222   on a persistent connection.  Whenever a transfer-coding is applied to
2223   a payload body in a request, the final transfer-coding applied &MUST;
2224   be "chunked".  If a transfer-coding is applied to a response payload
2225   body, then either the final transfer-coding applied &MUST; be "chunked"
2226   or the message &MUST; be terminated by closing the connection. When the
2227   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2228   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2229   be applied more than once in a message-body.
2230</t>
2231</section>
2232
2233<section title="Compression Codings" anchor="compression.codings">
2234<t>
2235   The codings defined below can be used to compress the payload of a
2236   message.
2237</t>
2238<x:note><t>
2239   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2240   is not desirable and is discouraged for future encodings. Their
2241   use here is representative of historical practice, not good
2242   design.
2243</t></x:note>
2244<x:note><t>
2245   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2246   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2247   equivalent to "gzip" and "compress" respectively.
2248</t></x:note>
2249
2250<section title="Compress Coding" anchor="compress.coding">
2251<iref item="compress (Coding Format)"/>
2252<iref item="Coding Format" subitem="compress"/>
2253<t>
2254   The "compress" format is produced by the common UNIX file compression
2255   program "compress". This format is an adaptive Lempel-Ziv-Welch
2256   coding (LZW).
2257</t>
2258</section>
2259
2260<section title="Deflate Coding" anchor="deflate.coding">
2261<iref item="deflate (Coding Format)"/>
2262<iref item="Coding Format" subitem="deflate"/>
2263<t>
2264   The "deflate" format is defined as the "deflate" compression mechanism
2265   (described in <xref target="RFC1951"/>) used inside the "zlib"
2266   data format (<xref target="RFC1950"/>).
2267</t>
2268<x:note>
2269  <t>
2270    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2271    compressed data without the zlib wrapper.
2272   </t>
2273</x:note>
2274</section>
2275
2276<section title="Gzip Coding" anchor="gzip.coding">
2277<iref item="gzip (Coding Format)"/>
2278<iref item="Coding Format" subitem="gzip"/>
2279<t>
2280   The "gzip" format is produced by the file compression program
2281   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2282   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2283</t>
2284</section>
2285
2286</section>
2287
2288<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2289<t>
2290   The HTTP Transfer Coding Registry defines the name space for the transfer
2291   coding names.
2292</t>
2293<t>
2294   Registrations &MUST; include the following fields:
2295   <list style="symbols">
2296     <t>Name</t>
2297     <t>Description</t>
2298     <t>Pointer to specification text</t>
2299   </list>
2300</t>
2301<t>
2302   Names of transfer codings &MUST-NOT; overlap with names of content codings
2303   (&content-codings;), unless the encoding transformation is identical (as it
2304   is the case for the compression codings defined in
2305   <xref target="compression.codings"/>).
2306</t>
2307<t>
2308   Values to be added to this name space require a specification
2309   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2310   conform to the purpose of transfer coding defined in this section.
2311</t>
2312<t>
2313   The registry itself is maintained at
2314   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2315</t>
2316</section>
2317</section>
2318
2319<section title="Product Tokens" anchor="product.tokens">
2320  <x:anchor-alias value="product"/>
2321  <x:anchor-alias value="product-version"/>
2322<t>
2323   Product tokens are used to allow communicating applications to
2324   identify themselves by software name and version. Most fields using
2325   product tokens also allow sub-products which form a significant part
2326   of the application to be listed, separated by whitespace. By
2327   convention, the products are listed in order of their significance
2328   for identifying the application.
2329</t>
2330<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2331  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2332  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2333</artwork></figure>
2334<t>
2335   Examples:
2336</t>
2337<figure><artwork type="example">
2338  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2339  Server: Apache/0.8.4
2340</artwork></figure>
2341<t>
2342   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2343   used for advertising or other non-essential information. Although any
2344   token character &MAY; appear in a product-version, this token &SHOULD;
2345   only be used for a version identifier (i.e., successive versions of
2346   the same product &SHOULD; only differ in the product-version portion of
2347   the product value).
2348</t>
2349</section>
2350
2351<section title="Quality Values" anchor="quality.values">
2352  <x:anchor-alias value="qvalue"/>
2353<t>
2354   Both transfer codings (TE request header field, <xref target="header.te"/>)
2355   and content negotiation (&content.negotiation;) use short "floating point"
2356   numbers to indicate the relative importance ("weight") of various
2357   negotiable parameters.  A weight is normalized to a real number in
2358   the range 0 through 1, where 0 is the minimum and 1 the maximum
2359   value. If a parameter has a quality value of 0, then content with
2360   this parameter is "not acceptable" for the client. HTTP/1.1
2361   applications &MUST-NOT; generate more than three digits after the
2362   decimal point. User configuration of these values &SHOULD; also be
2363   limited in this fashion.
2364</t>
2365<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2366  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2367                 / ( "1" [ "." 0*3("0") ] )
2368</artwork></figure>
2369<x:note>
2370  <t>
2371     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2372     relative degradation in desired quality.
2373  </t>
2374</x:note>
2375</section>
2376
2377</section>
2378
2379<section title="Connections" anchor="connections">
2380
2381<section title="Persistent Connections" anchor="persistent.connections">
2382
2383<section title="Purpose" anchor="persistent.purpose">
2384<t>
2385   Prior to persistent connections, a separate TCP connection was
2386   established to fetch each URL, increasing the load on HTTP servers
2387   and causing congestion on the Internet. The use of inline images and
2388   other associated data often requires a client to make multiple
2389   requests of the same server in a short amount of time. Analysis of
2390   these performance problems and results from a prototype
2391   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2392   measurements of actual HTTP/1.1 implementations show good
2393   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2394   T/TCP <xref target="Tou1998"/>.
2395</t>
2396<t>
2397   Persistent HTTP connections have a number of advantages:
2398  <list style="symbols">
2399      <t>
2400        By opening and closing fewer TCP connections, CPU time is saved
2401        in routers and hosts (clients, servers, proxies, gateways,
2402        tunnels, or caches), and memory used for TCP protocol control
2403        blocks can be saved in hosts.
2404      </t>
2405      <t>
2406        HTTP requests and responses can be pipelined on a connection.
2407        Pipelining allows a client to make multiple requests without
2408        waiting for each response, allowing a single TCP connection to
2409        be used much more efficiently, with much lower elapsed time.
2410      </t>
2411      <t>
2412        Network congestion is reduced by reducing the number of packets
2413        caused by TCP opens, and by allowing TCP sufficient time to
2414        determine the congestion state of the network.
2415      </t>
2416      <t>
2417        Latency on subsequent requests is reduced since there is no time
2418        spent in TCP's connection opening handshake.
2419      </t>
2420      <t>
2421        HTTP can evolve more gracefully, since errors can be reported
2422        without the penalty of closing the TCP connection. Clients using
2423        future versions of HTTP might optimistically try a new feature,
2424        but if communicating with an older server, retry with old
2425        semantics after an error is reported.
2426      </t>
2427    </list>
2428</t>
2429<t>
2430   HTTP implementations &SHOULD; implement persistent connections.
2431</t>
2432</section>
2433
2434<section title="Overall Operation" anchor="persistent.overall">
2435<t>
2436   A significant difference between HTTP/1.1 and earlier versions of
2437   HTTP is that persistent connections are the default behavior of any
2438   HTTP connection. That is, unless otherwise indicated, the client
2439   &SHOULD; assume that the server will maintain a persistent connection,
2440   even after error responses from the server.
2441</t>
2442<t>
2443   Persistent connections provide a mechanism by which a client and a
2444   server can signal the close of a TCP connection. This signaling takes
2445   place using the Connection header field (<xref target="header.connection"/>). Once a close
2446   has been signaled, the client &MUST-NOT; send any more requests on that
2447   connection.
2448</t>
2449
2450<section title="Negotiation" anchor="persistent.negotiation">
2451<t>
2452   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2453   maintain a persistent connection unless a Connection header field including
2454   the connection-token "close" was sent in the request. If the server
2455   chooses to close the connection immediately after sending the
2456   response, it &SHOULD; send a Connection header field including the
2457   connection-token "close".
2458</t>
2459<t>
2460   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2461   decide to keep it open based on whether the response from a server
2462   contains a Connection header field with the connection-token close. In case
2463   the client does not want to maintain a connection for more than that
2464   request, it &SHOULD; send a Connection header field including the
2465   connection-token close.
2466</t>
2467<t>
2468   If either the client or the server sends the close token in the
2469   Connection header field, that request becomes the last one for the
2470   connection.
2471</t>
2472<t>
2473   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2474   maintained for HTTP versions less than 1.1 unless it is explicitly
2475   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2476   compatibility with HTTP/1.0 clients.
2477</t>
2478<t>
2479   In order to remain persistent, all messages on the connection &MUST;
2480   have a self-defined message length (i.e., one not defined by closure
2481   of the connection), as described in <xref target="message.body"/>.
2482</t>
2483</section>
2484
2485<section title="Pipelining" anchor="pipelining">
2486<t>
2487   A client that supports persistent connections &MAY; "pipeline" its
2488   requests (i.e., send multiple requests without waiting for each
2489   response). A server &MUST; send its responses to those requests in the
2490   same order that the requests were received.
2491</t>
2492<t>
2493   Clients which assume persistent connections and pipeline immediately
2494   after connection establishment &SHOULD; be prepared to retry their
2495   connection if the first pipelined attempt fails. If a client does
2496   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2497   persistent. Clients &MUST; also be prepared to resend their requests if
2498   the server closes the connection before sending all of the
2499   corresponding responses.
2500</t>
2501<t>
2502   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2503   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2504   premature termination of the transport connection could lead to
2505   indeterminate results. A client wishing to send a non-idempotent
2506   request &SHOULD; wait to send that request until it has received the
2507   response status line for the previous request.
2508</t>
2509</section>
2510</section>
2511
2512<section title="Proxy Servers" anchor="persistent.proxy">
2513<t>
2514   It is especially important that proxies correctly implement the
2515   properties of the Connection header field as specified in <xref target="header.connection"/>.
2516</t>
2517<t>
2518   The proxy server &MUST; signal persistent connections separately with
2519   its clients and the origin servers (or other proxy servers) that it
2520   connects to. Each persistent connection applies to only one transport
2521   link.
2522</t>
2523<t>
2524   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2525   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2526   for information and discussion of the problems with the Keep-Alive header field
2527   implemented by many HTTP/1.0 clients).
2528</t>
2529
2530<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2531<!--<t>
2532  <cref anchor="TODO-end-to-end" source="jre">
2533    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2534    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2535  </cref>
2536</t>-->
2537<t>
2538   For the purpose of defining the behavior of caches and non-caching
2539   proxies, we divide HTTP header fields into two categories:
2540  <list style="symbols">
2541      <t>End-to-end header fields, which are  transmitted to the ultimate
2542        recipient of a request or response. End-to-end header fields in
2543        responses MUST be stored as part of a cache entry and &MUST; be
2544        transmitted in any response formed from a cache entry.</t>
2545
2546      <t>Hop-by-hop header fields, which are meaningful only for a single
2547        transport-level connection, and are not stored by caches or
2548        forwarded by proxies.</t>
2549  </list>
2550</t>
2551<t>
2552   The following HTTP/1.1 header fields are hop-by-hop header fields:
2553  <list style="symbols">
2554      <t>Connection</t>
2555      <t>Keep-Alive</t>
2556      <t>Proxy-Authenticate</t>
2557      <t>Proxy-Authorization</t>
2558      <t>TE</t>
2559      <t>Trailer</t>
2560      <t>Transfer-Encoding</t>
2561      <t>Upgrade</t>
2562  </list>
2563</t>
2564<t>
2565   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2566</t>
2567<t>
2568   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2569   (<xref target="header.connection"/>).
2570</t>
2571</section>
2572
2573<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2574<!--<t>
2575  <cref anchor="TODO-non-mod-headers" source="jre">
2576    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2577    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2578  </cref>
2579</t>-->
2580<t>
2581   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2582   value of certain end-to-end header fields. A non-transforming proxy &SHOULD-NOT;
2583   modify an end-to-end header field unless the definition of that header field requires
2584   or specifically allows that.
2585</t>
2586<t>
2587   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2588   request or response, and it &MUST-NOT; add any of these fields if not
2589   already present:
2590  <list style="symbols">
2591      <t>Content-Location</t>
2592      <t>Content-MD5</t>
2593      <t>ETag</t>
2594      <t>Last-Modified</t>
2595  </list>
2596</t>
2597<t>
2598   A non-transforming proxy &MUST-NOT; modify any of the following fields in a
2599   response:
2600  <list style="symbols">
2601    <t>Expires</t>
2602  </list>
2603</t>
2604<t>
2605   but it &MAY; add any of these fields if not already present. If an
2606   Expires header field is added, it &MUST; be given a field-value identical to
2607   that of the Date header field in that response.
2608</t>
2609<t>
2610   A proxy &MUST-NOT; modify or add any of the following fields in a
2611   message that contains the no-transform cache-control directive, or in
2612   any request:
2613  <list style="symbols">
2614    <t>Content-Encoding</t>
2615    <t>Content-Range</t>
2616    <t>Content-Type</t>
2617  </list>
2618</t>
2619<t>
2620   A transforming proxy &MAY; modify or add these fields to a message
2621   that does not include no-transform, but if it does so, it &MUST; add a
2622   Warning 214 (Transformation applied) if one does not already appear
2623   in the message (see &header-warning;).
2624</t>
2625<x:note>
2626  <t>
2627    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2628    cause authentication failures if stronger authentication
2629    mechanisms are introduced in later versions of HTTP. Such
2630    authentication mechanisms &MAY; rely on the values of header fields
2631    not listed here.
2632  </t>
2633</x:note>
2634<t>
2635   A non-transforming proxy &MUST; preserve the message payload (&payload;),
2636   though it &MAY; change the message-body through application or removal
2637   of a transfer-coding (<xref target="transfer.codings"/>).
2638</t>
2639</section>
2640
2641</section>
2642
2643<section title="Practical Considerations" anchor="persistent.practical">
2644<t>
2645   Servers will usually have some time-out value beyond which they will
2646   no longer maintain an inactive connection. Proxy servers might make
2647   this a higher value since it is likely that the client will be making
2648   more connections through the same server. The use of persistent
2649   connections places no requirements on the length (or existence) of
2650   this time-out for either the client or the server.
2651</t>
2652<t>
2653   When a client or server wishes to time-out it &SHOULD; issue a graceful
2654   close on the transport connection. Clients and servers &SHOULD; both
2655   constantly watch for the other side of the transport close, and
2656   respond to it as appropriate. If a client or server does not detect
2657   the other side's close promptly it could cause unnecessary resource
2658   drain on the network.
2659</t>
2660<t>
2661   A client, server, or proxy &MAY; close the transport connection at any
2662   time. For example, a client might have started to send a new request
2663   at the same time that the server has decided to close the "idle"
2664   connection. From the server's point of view, the connection is being
2665   closed while it was idle, but from the client's point of view, a
2666   request is in progress.
2667</t>
2668<t>
2669   This means that clients, servers, and proxies &MUST; be able to recover
2670   from asynchronous close events. Client software &SHOULD; reopen the
2671   transport connection and retransmit the aborted sequence of requests
2672   without user interaction so long as the request sequence is
2673   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2674   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2675   human operator the choice of retrying the request(s). Confirmation by
2676   user-agent software with semantic understanding of the application
2677   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2678   be repeated if the second sequence of requests fails.
2679</t>
2680<t>
2681   Servers &SHOULD; always respond to at least one request per connection,
2682   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2683   middle of transmitting a response, unless a network or client failure
2684   is suspected.
2685</t>
2686<t>
2687   Clients (including proxies) &SHOULD; limit the number of simultaneous
2688   connections that they maintain to a given server (including proxies).
2689</t>
2690<t>
2691   Previous revisions of HTTP gave a specific number of connections as a
2692   ceiling, but this was found to be impractical for many applications. As a
2693   result, this specification does not mandate a particular maximum number of
2694   connections, but instead encourages clients to be conservative when opening
2695   multiple connections.
2696</t>
2697<t>
2698   In particular, while using multiple connections avoids the "head-of-line
2699   blocking" problem (whereby a request that takes significant server-side
2700   processing and/or has a large payload can block subsequent requests on the
2701   same connection), each connection used consumes server resources (sometimes
2702   significantly), and furthermore using multiple connections can cause
2703   undesirable side effects in congested networks.
2704</t>
2705<t>
2706   Note that servers might reject traffic that they deem abusive, including an
2707   excessive number of connections from a client.
2708</t>
2709</section>
2710</section>
2711
2712<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2713
2714<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2715<t>
2716   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2717   flow control mechanisms to resolve temporary overloads, rather than
2718   terminating connections with the expectation that clients will retry.
2719   The latter technique can exacerbate network congestion.
2720</t>
2721</section>
2722
2723<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2724<t>
2725   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2726   the network connection for an error status code while it is transmitting
2727   the request. If the client sees an error status code, it &SHOULD;
2728   immediately cease transmitting the body. If the body is being sent
2729   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2730   empty trailer &MAY; be used to prematurely mark the end of the message.
2731   If the body was preceded by a Content-Length header field, the client &MUST;
2732   close the connection.
2733</t>
2734</section>
2735
2736<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2737<t>
2738   The purpose of the 100 (Continue) status code (see &status-100;) is to
2739   allow a client that is sending a request message with a request body
2740   to determine if the origin server is willing to accept the request
2741   (based on the request header fields) before the client sends the request
2742   body. In some cases, it might either be inappropriate or highly
2743   inefficient for the client to send the body if the server will reject
2744   the message without looking at the body.
2745</t>
2746<t>
2747   Requirements for HTTP/1.1 clients:
2748  <list style="symbols">
2749    <t>
2750        If a client will wait for a 100 (Continue) response before
2751        sending the request body, it &MUST; send an Expect request-header
2752        field (&header-expect;) with the "100-continue" expectation.
2753    </t>
2754    <t>
2755        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2756        with the "100-continue" expectation if it does not intend
2757        to send a request body.
2758    </t>
2759  </list>
2760</t>
2761<t>
2762   Because of the presence of older implementations, the protocol allows
2763   ambiguous situations in which a client might send "Expect: 100-continue"
2764   without receiving either a 417 (Expectation Failed)
2765   or a 100 (Continue) status code. Therefore, when a client sends this
2766   header field to an origin server (possibly via a proxy) from which it
2767   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2768   wait for an indefinite period before sending the request body.
2769</t>
2770<t>
2771   Requirements for HTTP/1.1 origin servers:
2772  <list style="symbols">
2773    <t> Upon receiving a request which includes an Expect request-header
2774        field with the "100-continue" expectation, an origin server &MUST;
2775        either respond with 100 (Continue) status code and continue to read
2776        from the input stream, or respond with a final status code. The
2777        origin server &MUST-NOT; wait for the request body before sending
2778        the 100 (Continue) response. If it responds with a final status
2779        code, it &MAY; close the transport connection or it &MAY; continue
2780        to read and discard the rest of the request.  It &MUST-NOT;
2781        perform the requested method if it returns a final status code.
2782    </t>
2783    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2784        the request message does not include an Expect request-header
2785        field with the "100-continue" expectation, and &MUST-NOT; send a
2786        100 (Continue) response if such a request comes from an HTTP/1.0
2787        (or earlier) client. There is an exception to this rule: for
2788        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2789        status code in response to an HTTP/1.1 PUT or POST request that does
2790        not include an Expect request-header field with the "100-continue"
2791        expectation. This exception, the purpose of which is
2792        to minimize any client processing delays associated with an
2793        undeclared wait for 100 (Continue) status code, applies only to
2794        HTTP/1.1 requests, and not to requests with any other HTTP-version
2795        value.
2796    </t>
2797    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2798        already received some or all of the request body for the
2799        corresponding request.
2800    </t>
2801    <t> An origin server that sends a 100 (Continue) response &MUST;
2802    ultimately send a final status code, once the request body is
2803        received and processed, unless it terminates the transport
2804        connection prematurely.
2805    </t>
2806    <t> If an origin server receives a request that does not include an
2807        Expect request-header field with the "100-continue" expectation,
2808        the request includes a request body, and the server responds
2809        with a final status code before reading the entire request body
2810        from the transport connection, then the server &SHOULD-NOT;  close
2811        the transport connection until it has read the entire request,
2812        or until the client closes the connection. Otherwise, the client
2813        might not reliably receive the response message. However, this
2814        requirement is not be construed as preventing a server from
2815        defending itself against denial-of-service attacks, or from
2816        badly broken client implementations.
2817      </t>
2818    </list>
2819</t>
2820<t>
2821   Requirements for HTTP/1.1 proxies:
2822  <list style="symbols">
2823    <t> If a proxy receives a request that includes an Expect request-header
2824        field with the "100-continue" expectation, and the proxy
2825        either knows that the next-hop server complies with HTTP/1.1 or
2826        higher, or does not know the HTTP version of the next-hop
2827        server, it &MUST; forward the request, including the Expect header
2828        field.
2829    </t>
2830    <t> If the proxy knows that the version of the next-hop server is
2831        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2832        respond with a 417 (Expectation Failed) status code.
2833    </t>
2834    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2835        numbers received from recently-referenced next-hop servers.
2836    </t>
2837    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2838        request message was received from an HTTP/1.0 (or earlier)
2839        client and did not include an Expect request-header field with
2840        the "100-continue" expectation. This requirement overrides the
2841        general rule for forwarding of 1xx responses (see &status-1xx;).
2842    </t>
2843  </list>
2844</t>
2845</section>
2846
2847<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2848<t>
2849   If an HTTP/1.1 client sends a request which includes a request body,
2850   but which does not include an Expect request-header field with the
2851   "100-continue" expectation, and if the client is not directly
2852   connected to an HTTP/1.1 origin server, and if the client sees the
2853   connection close before receiving a status line from the server, the
2854   client &SHOULD; retry the request.  If the client does retry this
2855   request, it &MAY; use the following "binary exponential backoff"
2856   algorithm to be assured of obtaining a reliable response:
2857  <list style="numbers">
2858    <t>
2859      Initiate a new connection to the server
2860    </t>
2861    <t>
2862      Transmit the request-header fields
2863    </t>
2864    <t>
2865      Initialize a variable R to the estimated round-trip time to the
2866         server (e.g., based on the time it took to establish the
2867         connection), or to a constant value of 5 seconds if the round-trip
2868         time is not available.
2869    </t>
2870    <t>
2871       Compute T = R * (2**N), where N is the number of previous
2872         retries of this request.
2873    </t>
2874    <t>
2875       Wait either for an error response from the server, or for T
2876         seconds (whichever comes first)
2877    </t>
2878    <t>
2879       If no error response is received, after T seconds transmit the
2880         body of the request.
2881    </t>
2882    <t>
2883       If client sees that the connection is closed prematurely,
2884         repeat from step 1 until the request is accepted, an error
2885         response is received, or the user becomes impatient and
2886         terminates the retry process.
2887    </t>
2888  </list>
2889</t>
2890<t>
2891   If at any point an error status code is received, the client
2892  <list style="symbols">
2893      <t>&SHOULD-NOT;  continue and</t>
2894
2895      <t>&SHOULD; close the connection if it has not completed sending the
2896        request message.</t>
2897    </list>
2898</t>
2899</section>
2900</section>
2901</section>
2902
2903
2904<section title="Miscellaneous notes that might disappear" anchor="misc">
2905<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2906<t>
2907   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2908</t>
2909</section>
2910
2911<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2912<t>
2913   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2914</t>
2915</section>
2916
2917<section title="Interception of HTTP for access control" anchor="http.intercept">
2918<t>
2919   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2920</t>
2921</section>
2922
2923<section title="Use of HTTP by other protocols" anchor="http.others">
2924<t>
2925   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2926   Extensions of HTTP like WebDAV.</cref>
2927</t>
2928
2929</section>
2930<section title="Use of HTTP by media type specification" anchor="http.media">
2931<t>
2932   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2933</t>
2934</section>
2935</section>
2936
2937<section title="Header Field Definitions" anchor="header.field.definitions">
2938<t>
2939   This section defines the syntax and semantics of HTTP/1.1 header fields
2940   related to message framing and transport protocols.
2941</t>
2942
2943<section title="Connection" anchor="header.connection">
2944  <iref primary="true" item="Connection header field" x:for-anchor=""/>
2945  <iref primary="true" item="Header Fields" subitem="Connection" x:for-anchor=""/>
2946  <x:anchor-alias value="Connection"/>
2947  <x:anchor-alias value="connection-token"/>
2948  <x:anchor-alias value="Connection-v"/>
2949<t>
2950   The "Connection" general-header field allows the sender to specify
2951   options that are desired for that particular connection and &MUST-NOT;
2952   be communicated by proxies over further connections.
2953</t>
2954<t>
2955   The Connection header field's value has the following grammar:
2956</t>
2957<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/>
2958  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2959  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2960  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2961</artwork></figure>
2962<t>
2963   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2964   message is forwarded and, for each connection-token in this field,
2965   remove any header field(s) from the message with the same name as the
2966   connection-token. Connection options are signaled by the presence of
2967   a connection-token in the Connection header field, not by any
2968   corresponding additional header field(s), since the additional header
2969   field might not be sent if there are no parameters associated with that
2970   connection option.
2971</t>
2972<t>
2973   Message header fields listed in the Connection header field &MUST-NOT; include
2974   end-to-end header fields, such as Cache-Control.
2975</t>
2976<t>
2977   HTTP/1.1 defines the "close" connection option for the sender to
2978   signal that the connection will be closed after completion of the
2979   response. For example,
2980</t>
2981<figure><artwork type="example">
2982  Connection: close
2983</artwork></figure>
2984<t>
2985   in either the request or the response header fields indicates that
2986   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2987   after the current request/response is complete.
2988</t>
2989<t>
2990   An HTTP/1.1 client that does not support persistent connections &MUST;
2991   include the "close" connection option in every request message.
2992</t>
2993<t>
2994   An HTTP/1.1 server that does not support persistent connections &MUST;
2995   include the "close" connection option in every response message that
2996   does not have a 1xx (Informational) status code.
2997</t>
2998<t>
2999   A system receiving an HTTP/1.0 (or lower-version) message that
3000   includes a Connection header field &MUST;, for each connection-token in this
3001   field, remove and ignore any header field(s) from the message with
3002   the same name as the connection-token. This protects against mistaken
3003   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
3004</t>
3005</section>
3006
3007<section title="Content-Length" anchor="header.content-length">
3008  <iref primary="true" item="Content-Length header field" x:for-anchor=""/>
3009  <iref primary="true" item="Header Fields" subitem="Content-Length" x:for-anchor=""/>
3010  <x:anchor-alias value="Content-Length"/>
3011  <x:anchor-alias value="Content-Length-v"/>
3012<t>
3013   The "Content-Length" header field indicates the size of the
3014   message-body, in decimal number of octets, for any message other than
3015   a response to the HEAD method or a response with a status code of 304.
3016   In the case of responses to the HEAD method, it indicates the size of
3017   the payload body (not including any potential transfer-coding) that
3018   would have been sent had the request been a GET.
3019   In the case of the 304 (Not Modified) response, it indicates the size of
3020   the payload body (not including any potential transfer-coding) that
3021   would have been sent in a 200 (OK) response.
3022</t>
3023<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
3024  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
3025  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
3026</artwork></figure>
3027<t>
3028   An example is
3029</t>
3030<figure><artwork type="example">
3031  Content-Length: 3495
3032</artwork></figure>
3033<t>
3034   Implementations &SHOULD; use this field to indicate the message-body
3035   length when no transfer-coding is being applied and the
3036   payload's body length can be determined prior to being transferred.
3037   <xref target="message.body"/> describes how recipients determine the length
3038   of a message-body.
3039</t>
3040<t>
3041   Any Content-Length greater than or equal to zero is a valid value.
3042</t>
3043<t>
3044   Note that the use of this field in HTTP is significantly different from
3045   the corresponding definition in MIME, where it is an optional field
3046   used within the "message/external-body" content-type.
3047</t>
3048</section>
3049
3050<section title="Date" anchor="header.date">
3051  <iref primary="true" item="Date header field" x:for-anchor=""/>
3052  <iref primary="true" item="Header Fields" subitem="Date" x:for-anchor=""/>
3053  <x:anchor-alias value="Date"/>
3054  <x:anchor-alias value="Date-v"/>
3055<t>
3056   The "Date" general-header field represents the date and time at which
3057   the message was originated, having the same semantics as the Origination
3058   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
3059   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
3060   it &MUST; be sent in rfc1123-date format.
3061</t>
3062<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
3063  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
3064  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
3065</artwork></figure>
3066<t>
3067   An example is
3068</t>
3069<figure><artwork type="example">
3070  Date: Tue, 15 Nov 1994 08:12:31 GMT
3071</artwork></figure>
3072<t>
3073   Origin servers &MUST; include a Date header field in all responses,
3074   except in these cases:
3075  <list style="numbers">
3076      <t>If the response status code is 100 (Continue) or 101 (Switching
3077         Protocols), the response &MAY; include a Date header field, at
3078         the server's option.</t>
3079
3080      <t>If the response status code conveys a server error, e.g., 500
3081         (Internal Server Error) or 503 (Service Unavailable), and it is
3082         inconvenient or impossible to generate a valid Date.</t>
3083
3084      <t>If the server does not have a clock that can provide a
3085         reasonable approximation of the current time, its responses
3086         &MUST-NOT; include a Date header field. In this case, the rules
3087         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
3088  </list>
3089</t>
3090<t>
3091   A received message that does not have a Date header field &MUST; be
3092   assigned one by the recipient if the message will be cached by that
3093   recipient or gatewayed via a protocol which requires a Date.
3094</t>
3095<t>
3096   Clients can use the Date header field as well; in order to keep request
3097   messages small, they are advised not to include it when it doesn't convey
3098   any useful information (as it is usually the case for requests that do not
3099   contain a payload).
3100</t>
3101<t>
3102   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3103   time subsequent to the generation of the message. It &SHOULD; represent
3104   the best available approximation of the date and time of message
3105   generation, unless the implementation has no means of generating a
3106   reasonably accurate date and time. In theory, the date ought to
3107   represent the moment just before the payload is generated. In
3108   practice, the date can be generated at any time during the message
3109   origination without affecting its semantic value.
3110</t>
3111
3112<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3113<t>
3114   Some origin server implementations might not have a clock available.
3115   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3116   values to a response, unless these values were associated
3117   with the resource by a system or user with a reliable clock. It &MAY;
3118   assign an Expires value that is known, at or before server
3119   configuration time, to be in the past (this allows "pre-expiration"
3120   of responses without storing separate Expires values for each
3121   resource).
3122</t>
3123</section>
3124</section>
3125
3126<section title="Host" anchor="header.host">
3127  <iref primary="true" item="Host header field" x:for-anchor=""/>
3128  <iref primary="true" item="Header Fields" subitem="Host" x:for-anchor=""/>
3129  <x:anchor-alias value="Host"/>
3130  <x:anchor-alias value="Host-v"/>
3131<t>
3132   The "Host" request-header field specifies the Internet host and port
3133   number of the resource being requested, allowing the origin server or
3134   gateway to differentiate between internally-ambiguous URLs, such as the root
3135   "/" URL of a server for multiple host names on a single IP address.
3136</t>
3137<t>   
3138   The Host field value &MUST; represent the naming authority of the origin
3139   server or gateway given by the original URL obtained from the user or
3140   referring resource (generally an http URI, as described in
3141   <xref target="http.uri"/>).
3142</t>
3143<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3144  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3145  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3146</artwork></figure>
3147<t>
3148   A "host" without any trailing port information implies the default
3149   port for the service requested (e.g., "80" for an HTTP URL). For
3150   example, a request on the origin server for
3151   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
3152</t>
3153<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3154GET /pub/WWW/ HTTP/1.1
3155Host: www.example.org
3156</artwork></figure>
3157<t>
3158   A client &MUST; include a Host header field in all HTTP/1.1 request
3159   messages. If the requested URI does not include an Internet host
3160   name for the service being requested, then the Host header field &MUST;
3161   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3162   request message it forwards does contain an appropriate Host header
3163   field that identifies the service being requested by the proxy. All
3164   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3165   status code to any HTTP/1.1 request message which lacks a Host header
3166   field.
3167</t>
3168<t>
3169   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3170   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3171   for other requirements relating to Host.
3172</t>
3173</section>
3174
3175<section title="TE" anchor="header.te">
3176  <iref primary="true" item="TE header field" x:for-anchor=""/>
3177  <iref primary="true" item="Header Fields" subitem="TE" x:for-anchor=""/>
3178  <x:anchor-alias value="TE"/>
3179  <x:anchor-alias value="TE-v"/>
3180  <x:anchor-alias value="t-codings"/>
3181  <x:anchor-alias value="te-params"/>
3182  <x:anchor-alias value="te-ext"/>
3183<t>
3184   The "TE" request-header field indicates what extension transfer-codings
3185   it is willing to accept in the response, and whether or not it is
3186   willing to accept trailer fields in a chunked transfer-coding.
3187</t>
3188<t>
3189   Its value consists of the keyword "trailers" and/or a comma-separated
3190   list of extension transfer-coding names with optional accept
3191   parameters (as described in <xref target="transfer.codings"/>).
3192</t>
3193<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3194  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3195  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3196  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3197  <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> )
3198  <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> ]
3199</artwork></figure>
3200<t>
3201   The presence of the keyword "trailers" indicates that the client is
3202   willing to accept trailer fields in a chunked transfer-coding, as
3203   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3204   transfer-coding values even though it does not itself represent a
3205   transfer-coding.
3206</t>
3207<t>
3208   Examples of its use are:
3209</t>
3210<figure><artwork type="example">
3211  TE: deflate
3212  TE:
3213  TE: trailers, deflate;q=0.5
3214</artwork></figure>
3215<t>
3216   The TE header field only applies to the immediate connection.
3217   Therefore, the keyword &MUST; be supplied within a Connection header
3218   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3219</t>
3220<t>
3221   A server tests whether a transfer-coding is acceptable, according to
3222   a TE field, using these rules:
3223  <list style="numbers">
3224    <x:lt>
3225      <t>The "chunked" transfer-coding is always acceptable. If the
3226         keyword "trailers" is listed, the client indicates that it is
3227         willing to accept trailer fields in the chunked response on
3228         behalf of itself and any downstream clients. The implication is
3229         that, if given, the client is stating that either all
3230         downstream clients are willing to accept trailer fields in the
3231         forwarded response, or that it will attempt to buffer the
3232         response on behalf of downstream recipients.
3233      </t><t>
3234         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3235         chunked response such that a client can be assured of buffering
3236         the entire response.</t>
3237    </x:lt>
3238    <x:lt>
3239      <t>If the transfer-coding being tested is one of the transfer-codings
3240         listed in the TE field, then it is acceptable unless it
3241         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3242         qvalue of 0 means "not acceptable".)</t>
3243    </x:lt>
3244    <x:lt>
3245      <t>If multiple transfer-codings are acceptable, then the
3246         acceptable transfer-coding with the highest non-zero qvalue is
3247         preferred.  The "chunked" transfer-coding always has a qvalue
3248         of 1.</t>
3249    </x:lt>
3250  </list>
3251</t>
3252<t>
3253   If the TE field-value is empty or if no TE field is present, the only
3254   transfer-coding is "chunked". A message with no transfer-coding is
3255   always acceptable.
3256</t>
3257</section>
3258
3259<section title="Trailer" anchor="header.trailer">
3260  <iref primary="true" item="Trailer header field" x:for-anchor=""/>
3261  <iref primary="true" item="Header Fields" subitem="Trailer" x:for-anchor=""/>
3262  <x:anchor-alias value="Trailer"/>
3263  <x:anchor-alias value="Trailer-v"/>
3264<t>
3265   The "Trailer" general-header field indicates that the given set of
3266   header fields is present in the trailer of a message encoded with
3267   chunked transfer-coding.
3268</t>
3269<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3270  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3271  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3272</artwork></figure>
3273<t>
3274   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3275   message using chunked transfer-coding with a non-empty trailer. Doing
3276   so allows the recipient to know which header fields to expect in the
3277   trailer.
3278</t>
3279<t>
3280   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3281   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3282   trailer fields in a "chunked" transfer-coding.
3283</t>
3284<t>
3285   Message header fields listed in the Trailer header field &MUST-NOT;
3286   include the following header fields:
3287  <list style="symbols">
3288    <t>Transfer-Encoding</t>
3289    <t>Content-Length</t>
3290    <t>Trailer</t>
3291  </list>
3292</t>
3293</section>
3294
3295<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3296  <iref primary="true" item="Transfer-Encoding header field" x:for-anchor=""/>
3297  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding" x:for-anchor=""/>
3298  <x:anchor-alias value="Transfer-Encoding"/>
3299  <x:anchor-alias value="Transfer-Encoding-v"/>
3300<t>
3301   The "Transfer-Encoding" general-header field indicates what transfer-codings
3302   (if any) have been applied to the message body. It differs from
3303   Content-Encoding (&content-codings;) in that transfer-codings are a property
3304   of the message (and therefore are removed by intermediaries), whereas
3305   content-codings are not.
3306</t>
3307<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3308  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3309                        <x:ref>Transfer-Encoding-v</x:ref>
3310  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3311</artwork></figure>
3312<t>
3313   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3314</t>
3315<figure><artwork type="example">
3316  Transfer-Encoding: chunked
3317</artwork></figure>
3318<t>
3319   If multiple encodings have been applied to a representation, the transfer-codings
3320   &MUST; be listed in the order in which they were applied.
3321   Additional information about the encoding parameters &MAY; be provided
3322   by other header fields not defined by this specification.
3323</t>
3324<t>
3325   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3326   header field.
3327</t>
3328</section>
3329
3330<section title="Upgrade" anchor="header.upgrade">
3331  <iref primary="true" item="Upgrade header field" x:for-anchor=""/>
3332  <iref primary="true" item="Header Fields" subitem="Upgrade" x:for-anchor=""/>
3333  <x:anchor-alias value="Upgrade"/>
3334  <x:anchor-alias value="Upgrade-v"/>
3335<t>
3336   The "Upgrade" general-header field allows the client to specify what
3337   additional communication protocols it would like to use, if the server
3338   chooses to switch protocols. Servers can use it to indicate what protocols
3339   they are willing to switch to.
3340</t>
3341<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3342  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3343  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3344</artwork></figure>
3345<t>
3346   For example,
3347</t>
3348<figure><artwork type="example">
3349  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3350</artwork></figure>
3351<t>
3352   The Upgrade header field is intended to provide a simple mechanism
3353   for transition from HTTP/1.1 to some other, incompatible protocol. It
3354   does so by allowing the client to advertise its desire to use another
3355   protocol, such as a later version of HTTP with a higher major version
3356   number, even though the current request has been made using HTTP/1.1.
3357   This eases the difficult transition between incompatible protocols by
3358   allowing the client to initiate a request in the more commonly
3359   supported protocol while indicating to the server that it would like
3360   to use a "better" protocol if available (where "better" is determined
3361   by the server, possibly according to the nature of the method and/or
3362   resource being requested).
3363</t>
3364<t>
3365   The Upgrade header field only applies to switching application-layer
3366   protocols upon the existing transport-layer connection. Upgrade
3367   cannot be used to insist on a protocol change; its acceptance and use
3368   by the server is optional. The capabilities and nature of the
3369   application-layer communication after the protocol change is entirely
3370   dependent upon the new protocol chosen, although the first action
3371   after changing the protocol &MUST; be a response to the initial HTTP
3372   request containing the Upgrade header field.
3373</t>
3374<t>
3375   The Upgrade header field only applies to the immediate connection.
3376   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3377   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3378   HTTP/1.1 message.
3379</t>
3380<t>
3381   The Upgrade header field cannot be used to indicate a switch to a
3382   protocol on a different connection. For that purpose, it is more
3383   appropriate to use a 3xx redirection response (&status-3xx;).
3384</t>
3385<t>
3386   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3387   Protocols) responses to indicate which protocol(s) are being switched to,
3388   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3389   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3390   response to indicate that they are willing to upgrade to one of the
3391   specified protocols.
3392</t>
3393<t>
3394   This specification only defines the protocol name "HTTP" for use by
3395   the family of Hypertext Transfer Protocols, as defined by the HTTP
3396   version rules of <xref target="http.version"/> and future updates to this
3397   specification. Additional tokens can be registered with IANA using the
3398   registration procedure defined below. 
3399</t>
3400
3401<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3402<t>
3403   The HTTP Upgrade Token Registry defines the name space for product
3404   tokens used to identify protocols in the Upgrade header field.
3405   Each registered token is associated with contact information and
3406   an optional set of specifications that details how the connection
3407   will be processed after it has been upgraded.
3408</t>
3409<t>
3410   Registrations are allowed on a First Come First Served basis as
3411   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3412   specifications need not be IETF documents or be subject to IESG review.
3413   Registrations are subject to the following rules:
3414  <list style="numbers">
3415    <t>A token, once registered, stays registered forever.</t>
3416    <t>The registration &MUST; name a responsible party for the
3417       registration.</t>
3418    <t>The registration &MUST; name a point of contact.</t>
3419    <t>The registration &MAY; name a set of specifications associated with that
3420       token. Such specifications need not be publicly available.</t>
3421    <t>The responsible party &MAY; change the registration at any time.
3422       The IANA will keep a record of all such changes, and make them
3423       available upon request.</t>
3424    <t>The responsible party for the first registration of a "product"
3425       token &MUST; approve later registrations of a "version" token
3426       together with that "product" token before they can be registered.</t>
3427    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3428       for a token. This will normally only be used in the case when a
3429       responsible party cannot be contacted.</t>
3430  </list>
3431</t>
3432</section>
3433
3434
3435</section>
3436
3437<section title="Via" anchor="header.via">
3438  <iref primary="true" item="Via header field" x:for-anchor=""/>
3439  <iref primary="true" item="Header Fields" subitem="Via" x:for-anchor=""/>
3440  <x:anchor-alias value="protocol-name"/>
3441  <x:anchor-alias value="protocol-version"/>
3442  <x:anchor-alias value="pseudonym"/>
3443  <x:anchor-alias value="received-by"/>
3444  <x:anchor-alias value="received-protocol"/>
3445  <x:anchor-alias value="Via"/>
3446  <x:anchor-alias value="Via-v"/>
3447<t>
3448   The "Via" general-header field &MUST; be used by gateways and proxies to
3449   indicate the intermediate protocols and recipients between the user
3450   agent and the server on requests, and between the origin server and
3451   the client on responses. It is analogous to the "Received" field defined in
3452   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3453   avoiding request loops, and identifying the protocol capabilities of
3454   all senders along the request/response chain.
3455</t>
3456<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><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"/>
3457  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3458  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3459                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3460  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3461  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3462  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3463  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3464  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3465</artwork></figure>
3466<t>
3467   The received-protocol indicates the protocol version of the message
3468   received by the server or client along each segment of the
3469   request/response chain. The received-protocol version is appended to
3470   the Via field value when the message is forwarded so that information
3471   about the protocol capabilities of upstream applications remains
3472   visible to all recipients.
3473</t>
3474<t>
3475   The protocol-name is optional if and only if it would be "HTTP". The
3476   received-by field is normally the host and optional port number of a
3477   recipient server or client that subsequently forwarded the message.
3478   However, if the real host is considered to be sensitive information,
3479   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3480   be assumed to be the default port of the received-protocol.
3481</t>
3482<t>
3483   Multiple Via field values represent each proxy or gateway that has
3484   forwarded the message. Each recipient &MUST; append its information
3485   such that the end result is ordered according to the sequence of
3486   forwarding applications.
3487</t>
3488<t>
3489   Comments &MAY; be used in the Via header field to identify the software
3490   of the recipient proxy or gateway, analogous to the User-Agent and
3491   Server header fields. However, all comments in the Via field are
3492   optional and &MAY; be removed by any recipient prior to forwarding the
3493   message.
3494</t>
3495<t>
3496   For example, a request message could be sent from an HTTP/1.0 user
3497   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3498   forward the request to a public proxy at p.example.net, which completes
3499   the request by forwarding it to the origin server at www.example.com.
3500   The request received by www.example.com would then have the following
3501   Via header field:
3502</t>
3503<figure><artwork type="example">
3504  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3505</artwork></figure>
3506<t>
3507   Proxies and gateways used as a portal through a network firewall
3508   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3509   the firewall region. This information &SHOULD; only be propagated if
3510   explicitly enabled. If not enabled, the received-by host of any host
3511   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3512   for that host.
3513</t>
3514<t>
3515   For organizations that have strong privacy requirements for hiding
3516   internal structures, a proxy &MAY; combine an ordered subsequence of
3517   Via header field entries with identical received-protocol values into
3518   a single such entry. For example,
3519</t>
3520<figure><artwork type="example">
3521  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3522</artwork></figure>
3523<t>
3524  could be collapsed to
3525</t>
3526<figure><artwork type="example">
3527  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3528</artwork></figure>
3529<t>
3530   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3531   under the same organizational control and the hosts have already been
3532   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3533   have different received-protocol values.
3534</t>
3535</section>
3536
3537</section>
3538
3539<section title="IANA Considerations" anchor="IANA.considerations">
3540
3541<section title="Header Field Registration" anchor="header.field.registration">
3542<t>
3543   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3544   with the permanent registrations below (see <xref target="RFC3864"/>):
3545</t>
3546<?BEGININC p1-messaging.iana-headers ?>
3547<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3548<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3549   <ttcol>Header Field Name</ttcol>
3550   <ttcol>Protocol</ttcol>
3551   <ttcol>Status</ttcol>
3552   <ttcol>Reference</ttcol>
3553
3554   <c>Connection</c>
3555   <c>http</c>
3556   <c>standard</c>
3557   <c>
3558      <xref target="header.connection"/>
3559   </c>
3560   <c>Content-Length</c>
3561   <c>http</c>
3562   <c>standard</c>
3563   <c>
3564      <xref target="header.content-length"/>
3565   </c>
3566   <c>Date</c>
3567   <c>http</c>
3568   <c>standard</c>
3569   <c>
3570      <xref target="header.date"/>
3571   </c>
3572   <c>Host</c>
3573   <c>http</c>
3574   <c>standard</c>
3575   <c>
3576      <xref target="header.host"/>
3577   </c>
3578   <c>TE</c>
3579   <c>http</c>
3580   <c>standard</c>
3581   <c>
3582      <xref target="header.te"/>
3583   </c>
3584   <c>Trailer</c>
3585   <c>http</c>
3586   <c>standard</c>
3587   <c>
3588      <xref target="header.trailer"/>
3589   </c>
3590   <c>Transfer-Encoding</c>
3591   <c>http</c>
3592   <c>standard</c>
3593   <c>
3594      <xref target="header.transfer-encoding"/>
3595   </c>
3596   <c>Upgrade</c>
3597   <c>http</c>
3598   <c>standard</c>
3599   <c>
3600      <xref target="header.upgrade"/>
3601   </c>
3602   <c>Via</c>
3603   <c>http</c>
3604   <c>standard</c>
3605   <c>
3606      <xref target="header.via"/>
3607   </c>
3608</texttable>
3609<!--(END)-->
3610<?ENDINC p1-messaging.iana-headers ?>
3611<t>
3612   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3613</t>
3614</section>
3615
3616<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3617<t>
3618   The entries for the "http" and "https" URI Schemes in the registry located at
3619   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3620   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3621   and <xref target="https.uri" format="counter"/> of this document
3622   (see <xref target="RFC4395"/>).
3623</t>
3624</section>
3625
3626<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3627<t>
3628   This document serves as the specification for the Internet media types
3629   "message/http" and "application/http". The following is to be registered with
3630   IANA (see <xref target="RFC4288"/>).
3631</t>
3632<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3633<iref item="Media Type" subitem="message/http" primary="true"/>
3634<iref item="message/http Media Type" primary="true"/>
3635<t>
3636   The message/http type can be used to enclose a single HTTP request or
3637   response message, provided that it obeys the MIME restrictions for all
3638   "message" types regarding line length and encodings.
3639</t>
3640<t>
3641  <list style="hanging" x:indent="12em">
3642    <t hangText="Type name:">
3643      message
3644    </t>
3645    <t hangText="Subtype name:">
3646      http
3647    </t>
3648    <t hangText="Required parameters:">
3649      none
3650    </t>
3651    <t hangText="Optional parameters:">
3652      version, msgtype
3653      <list style="hanging">
3654        <t hangText="version:">
3655          The HTTP-Version number of the enclosed message
3656          (e.g., "1.1"). If not present, the version can be
3657          determined from the first line of the body.
3658        </t>
3659        <t hangText="msgtype:">
3660          The message type &mdash; "request" or "response". If not
3661          present, the type can be determined from the first
3662          line of the body.
3663        </t>
3664      </list>
3665    </t>
3666    <t hangText="Encoding considerations:">
3667      only "7bit", "8bit", or "binary" are permitted
3668    </t>
3669    <t hangText="Security considerations:">
3670      none
3671    </t>
3672    <t hangText="Interoperability considerations:">
3673      none
3674    </t>
3675    <t hangText="Published specification:">
3676      This specification (see <xref target="internet.media.type.message.http"/>).
3677    </t>
3678    <t hangText="Applications that use this media type:">
3679    </t>
3680    <t hangText="Additional information:">
3681      <list style="hanging">
3682        <t hangText="Magic number(s):">none</t>
3683        <t hangText="File extension(s):">none</t>
3684        <t hangText="Macintosh file type code(s):">none</t>
3685      </list>
3686    </t>
3687    <t hangText="Person and email address to contact for further information:">
3688      See Authors Section.
3689    </t>
3690    <t hangText="Intended usage:">
3691      COMMON
3692    </t>
3693    <t hangText="Restrictions on usage:">
3694      none
3695    </t>
3696    <t hangText="Author/Change controller:">
3697      IESG
3698    </t>
3699  </list>
3700</t>
3701</section>
3702<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3703<iref item="Media Type" subitem="application/http" primary="true"/>
3704<iref item="application/http Media Type" primary="true"/>
3705<t>
3706   The application/http type can be used to enclose a pipeline of one or more
3707   HTTP request or response messages (not intermixed).
3708</t>
3709<t>
3710  <list style="hanging" x:indent="12em">
3711    <t hangText="Type name:">
3712      application
3713    </t>
3714    <t hangText="Subtype name:">
3715      http
3716    </t>
3717    <t hangText="Required parameters:">
3718      none
3719    </t>
3720    <t hangText="Optional parameters:">
3721      version, msgtype
3722      <list style="hanging">
3723        <t hangText="version:">
3724          The HTTP-Version number of the enclosed messages
3725          (e.g., "1.1"). If not present, the version can be
3726          determined from the first line of the body.
3727        </t>
3728        <t hangText="msgtype:">
3729          The message type &mdash; "request" or "response". If not
3730          present, the type can be determined from the first
3731          line of the body.
3732        </t>
3733      </list>
3734    </t>
3735    <t hangText="Encoding considerations:">
3736      HTTP messages enclosed by this type
3737      are in "binary" format; use of an appropriate
3738      Content-Transfer-Encoding is required when
3739      transmitted via E-mail.
3740    </t>
3741    <t hangText="Security considerations:">
3742      none
3743    </t>
3744    <t hangText="Interoperability considerations:">
3745      none
3746    </t>
3747    <t hangText="Published specification:">
3748      This specification (see <xref target="internet.media.type.application.http"/>).
3749    </t>
3750    <t hangText="Applications that use this media type:">
3751    </t>
3752    <t hangText="Additional information:">
3753      <list style="hanging">
3754        <t hangText="Magic number(s):">none</t>
3755        <t hangText="File extension(s):">none</t>
3756        <t hangText="Macintosh file type code(s):">none</t>
3757      </list>
3758    </t>
3759    <t hangText="Person and email address to contact for further information:">
3760      See Authors Section.
3761    </t>
3762    <t hangText="Intended usage:">
3763      COMMON
3764    </t>
3765    <t hangText="Restrictions on usage:">
3766      none
3767    </t>
3768    <t hangText="Author/Change controller:">
3769      IESG
3770    </t>
3771  </list>
3772</t>
3773</section>
3774</section>
3775
3776<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3777<t>
3778   The registration procedure for HTTP Transfer Codings is now defined by
3779   <xref target="transfer.coding.registry"/> of this document.
3780</t>
3781<t>
3782   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3783   shall be updated with the registrations below:
3784</t>
3785<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3786   <ttcol>Name</ttcol>
3787   <ttcol>Description</ttcol>
3788   <ttcol>Reference</ttcol>
3789   <c>chunked</c>
3790   <c>Transfer in a series of chunks</c>
3791   <c>
3792      <xref target="chunked.encoding"/>
3793   </c>
3794   <c>compress</c>
3795   <c>UNIX "compress" program method</c>
3796   <c>
3797      <xref target="compress.coding"/>
3798   </c>
3799   <c>deflate</c>
3800   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3801   the "zlib" data format (<xref target="RFC1950"/>)
3802   </c>
3803   <c>
3804      <xref target="deflate.coding"/>
3805   </c>
3806   <c>gzip</c>
3807   <c>Same as GNU zip <xref target="RFC1952"/></c>
3808   <c>
3809      <xref target="gzip.coding"/>
3810   </c>
3811</texttable>
3812</section>
3813
3814<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3815<t>
3816   The registration procedure for HTTP Upgrade Tokens &mdash; previously defined
3817   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> &mdash; is now defined
3818   by <xref target="upgrade.token.registry"/> of this document.
3819</t>
3820<t>
3821   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3822   shall be updated with the registration below:
3823</t>
3824<texttable align="left" suppress-title="true">
3825   <ttcol>Value</ttcol>
3826   <ttcol>Description</ttcol>
3827   <ttcol>Reference</ttcol>
3828
3829   <c>HTTP</c>
3830   <c>Hypertext Transfer Protocol</c> 
3831   <c><xref target="http.version"/> of this specification</c>
3832<!-- IANA should add this without our instructions; emailed on June 05, 2009
3833   <c>TLS/1.0</c>
3834   <c>Transport Layer Security</c>
3835   <c><xref target="RFC2817"/></c> -->
3836
3837</texttable>
3838</section>
3839
3840</section>
3841
3842<section title="Security Considerations" anchor="security.considerations">
3843<t>
3844   This section is meant to inform application developers, information
3845   providers, and users of the security limitations in HTTP/1.1 as
3846   described by this document. The discussion does not include
3847   definitive solutions to the problems revealed, though it does make
3848   some suggestions for reducing security risks.
3849</t>
3850
3851<section title="Personal Information" anchor="personal.information">
3852<t>
3853   HTTP clients are often privy to large amounts of personal information
3854   (e.g., the user's name, location, mail address, passwords, encryption
3855   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3856   leakage of this information.
3857   We very strongly recommend that a convenient interface be provided
3858   for the user to control dissemination of such information, and that
3859   designers and implementors be particularly careful in this area.
3860   History shows that errors in this area often create serious security
3861   and/or privacy problems and generate highly adverse publicity for the
3862   implementor's company.
3863</t>
3864</section>
3865
3866<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3867<t>
3868   A server is in the position to save personal data about a user's
3869   requests which might identify their reading patterns or subjects of
3870   interest. This information is clearly confidential in nature and its
3871   handling can be constrained by law in certain countries. People using
3872   HTTP to provide data are responsible for ensuring that
3873   such material is not distributed without the permission of any
3874   individuals that are identifiable by the published results.
3875</t>
3876</section>
3877
3878<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3879<t>
3880   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3881   the documents returned by HTTP requests to be only those that were
3882   intended by the server administrators. If an HTTP server translates
3883   HTTP URIs directly into file system calls, the server &MUST; take
3884   special care not to serve files that were not intended to be
3885   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3886   other operating systems use ".." as a path component to indicate a
3887   directory level above the current one. On such a system, an HTTP
3888   server &MUST; disallow any such construct in the request-target if it
3889   would otherwise allow access to a resource outside those intended to
3890   be accessible via the HTTP server. Similarly, files intended for
3891   reference only internally to the server (such as access control
3892   files, configuration files, and script code) &MUST; be protected from
3893   inappropriate retrieval, since they might contain sensitive
3894   information. Experience has shown that minor bugs in such HTTP server
3895   implementations have turned into security risks.
3896</t>
3897</section>
3898
3899<section title="DNS Spoofing" anchor="dns.spoofing">
3900<t>
3901   Clients using HTTP rely heavily on the Domain Name Service, and are
3902   thus generally prone to security attacks based on the deliberate
3903   mis-association of IP addresses and DNS names. Clients need to be
3904   cautious in assuming the continuing validity of an IP number/DNS name
3905   association.
3906</t>
3907<t>
3908   In particular, HTTP clients &SHOULD; rely on their name resolver for
3909   confirmation of an IP number/DNS name association, rather than
3910   caching the result of previous host name lookups. Many platforms
3911   already can cache host name lookups locally when appropriate, and
3912   they &SHOULD; be configured to do so. It is proper for these lookups to
3913   be cached, however, only when the TTL (Time To Live) information
3914   reported by the name server makes it likely that the cached
3915   information will remain useful.
3916</t>
3917<t>
3918   If HTTP clients cache the results of host name lookups in order to
3919   achieve a performance improvement, they &MUST; observe the TTL
3920   information reported by DNS.
3921</t>
3922<t>
3923   If HTTP clients do not observe this rule, they could be spoofed when
3924   a previously-accessed server's IP address changes. As network
3925   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3926   possibility of this form of attack will grow. Observing this
3927   requirement thus reduces this potential security vulnerability.
3928</t>
3929<t>
3930   This requirement also improves the load-balancing behavior of clients
3931   for replicated servers using the same DNS name and reduces the
3932   likelihood of a user's experiencing failure in accessing sites which
3933   use that strategy.
3934</t>
3935</section>
3936
3937<section title="Proxies and Caching" anchor="attack.proxies">
3938<t>
3939   By their very nature, HTTP proxies are men-in-the-middle, and
3940   represent an opportunity for man-in-the-middle attacks. Compromise of
3941   the systems on which the proxies run can result in serious security
3942   and privacy problems. Proxies have access to security-related
3943   information, personal information about individual users and
3944   organizations, and proprietary information belonging to users and
3945   content providers. A compromised proxy, or a proxy implemented or
3946   configured without regard to security and privacy considerations,
3947   might be used in the commission of a wide range of potential attacks.
3948</t>
3949<t>
3950   Proxy operators need to protect the systems on which proxies run as
3951   they would protect any system that contains or transports sensitive
3952   information. In particular, log information gathered at proxies often
3953   contains highly sensitive personal information, and/or information
3954   about organizations. Log information needs to be carefully guarded, and
3955   appropriate guidelines for use need to be developed and followed.
3956   (<xref target="abuse.of.server.log.information"/>).
3957</t>
3958<t>
3959   Proxy implementors need to consider the privacy and security
3960   implications of their design and coding decisions, and of the
3961   configuration options they provide to proxy operators (especially the
3962   default configuration).
3963</t>
3964<t>
3965   Users of a proxy need to be aware that proxies are no trustworthier than
3966   the people who run them; HTTP itself cannot solve this problem.
3967</t>
3968<t>
3969   The judicious use of cryptography, when appropriate, might suffice to
3970   protect against a broad range of security and privacy attacks. Such
3971   cryptography is beyond the scope of the HTTP/1.1 specification.
3972</t>
3973</section>
3974
3975<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3976<t>
3977   They exist. They are hard to defend against. Research continues.
3978   Beware.
3979</t>
3980</section>
3981</section>
3982
3983<section title="Acknowledgments" anchor="ack">
3984<t>
3985   HTTP has evolved considerably over the years. It has
3986   benefited from a large and active developer community &mdash; the many
3987   people who have participated on the www-talk mailing list &mdash; and it is
3988   that community which has been most responsible for the success of
3989   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3990   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3991   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3992   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3993   VanHeyningen deserve special recognition for their efforts in
3994   defining early aspects of the protocol.
3995</t>
3996<t>
3997   This document has benefited greatly from the comments of all those
3998   participating in the HTTP-WG. In addition to those already mentioned,
3999   the following individuals have contributed to this specification:
4000</t>
4001<t>
4002   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4003   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4004   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4005   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4006   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4007   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4008   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4009   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4010   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4011   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4012   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4013   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4014</t>
4015<t>
4016   Thanks to the "cave men" of Palo Alto. You know who you are.
4017</t>
4018<t>
4019   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4020   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4021   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4022   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4023   Larry Masinter for their help. And thanks go particularly to Jeff
4024   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4025</t>
4026<t>
4027   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4028   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4029   discovery of many of the problems that this document attempts to
4030   rectify.
4031</t>
4032<t>
4033   This specification makes heavy use of the augmented BNF and generic
4034   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4035   reuses many of the definitions provided by Nathaniel Borenstein and
4036   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4037   specification will help reduce past confusion over the relationship
4038   between HTTP and Internet mail message formats.
4039</t>
4040<!--
4041
4042Acknowledgements TODO list
4043
4044- Jeff Hodges ("effective request URI")
4045
4046-->
4047</section>
4048
4049</middle>
4050<back>
4051
4052<references title="Normative References">
4053
4054<reference anchor="ISO-8859-1">
4055  <front>
4056    <title>
4057     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4058    </title>
4059    <author>
4060      <organization>International Organization for Standardization</organization>
4061    </author>
4062    <date year="1998"/>
4063  </front>
4064  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4065</reference>
4066
4067<reference anchor="Part2">
4068  <front>
4069    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4070    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4071      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4072      <address><email>fielding@gbiv.com</email></address>
4073    </author>
4074    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4075      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4076      <address><email>jg@freedesktop.org</email></address>
4077    </author>
4078    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4079      <organization abbrev="HP">Hewlett-Packard Company</organization>
4080      <address><email>JeffMogul@acm.org</email></address>
4081    </author>
4082    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4083      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4084      <address><email>henrikn@microsoft.com</email></address>
4085    </author>
4086    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4087      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4088      <address><email>LMM@acm.org</email></address>
4089    </author>
4090    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4091      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4092      <address><email>paulle@microsoft.com</email></address>
4093    </author>
4094    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4095      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4096      <address><email>timbl@w3.org</email></address>
4097    </author>
4098    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4099      <organization abbrev="W3C">World Wide Web Consortium</organization>
4100      <address><email>ylafon@w3.org</email></address>
4101    </author>
4102    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4103      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4104      <address><email>julian.reschke@greenbytes.de</email></address>
4105    </author>
4106    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4107  </front>
4108  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4109  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4110</reference>
4111
4112<reference anchor="Part3">
4113  <front>
4114    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4115    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4116      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4117      <address><email>fielding@gbiv.com</email></address>
4118    </author>
4119    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4120      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4121      <address><email>jg@freedesktop.org</email></address>
4122    </author>
4123    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4124      <organization abbrev="HP">Hewlett-Packard Company</organization>
4125      <address><email>JeffMogul@acm.org</email></address>
4126    </author>
4127    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4128      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4129      <address><email>henrikn@microsoft.com</email></address>
4130    </author>
4131    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4132      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4133      <address><email>LMM@acm.org</email></address>
4134    </author>
4135    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4136      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4137      <address><email>paulle@microsoft.com</email></address>
4138    </author>
4139    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4140      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4141      <address><email>timbl@w3.org</email></address>
4142    </author>
4143    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4144      <organization abbrev="W3C">World Wide Web Consortium</organization>
4145      <address><email>ylafon@w3.org</email></address>
4146    </author>
4147    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4148      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4149      <address><email>julian.reschke@greenbytes.de</email></address>
4150    </author>
4151    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4152  </front>
4153  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4154  <x:source href="p3-payload.xml" basename="p3-payload"/>
4155</reference>
4156
4157<reference anchor="Part6">
4158  <front>
4159    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4160    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4161      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4162      <address><email>fielding@gbiv.com</email></address>
4163    </author>
4164    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4165      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4166      <address><email>jg@freedesktop.org</email></address>
4167    </author>
4168    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4169      <organization abbrev="HP">Hewlett-Packard Company</organization>
4170      <address><email>JeffMogul@acm.org</email></address>
4171    </author>
4172    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4173      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4174      <address><email>henrikn@microsoft.com</email></address>
4175    </author>
4176    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4177      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4178      <address><email>LMM@acm.org</email></address>
4179    </author>
4180    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4181      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4182      <address><email>paulle@microsoft.com</email></address>
4183    </author>
4184    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4185      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4186      <address><email>timbl@w3.org</email></address>
4187    </author>
4188    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4189      <organization abbrev="W3C">World Wide Web Consortium</organization>
4190      <address><email>ylafon@w3.org</email></address>
4191    </author>
4192    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4193      <address><email>mnot@mnot.net</email></address>
4194    </author>
4195    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4196      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4197      <address><email>julian.reschke@greenbytes.de</email></address>
4198    </author>
4199    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4200  </front>
4201  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4202  <x:source href="p6-cache.xml" basename="p6-cache"/>
4203</reference>
4204
4205<reference anchor="RFC5234">
4206  <front>
4207    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4208    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4209      <organization>Brandenburg InternetWorking</organization>
4210      <address>
4211        <email>dcrocker@bbiw.net</email>
4212      </address> 
4213    </author>
4214    <author initials="P." surname="Overell" fullname="Paul Overell">
4215      <organization>THUS plc.</organization>
4216      <address>
4217        <email>paul.overell@thus.net</email>
4218      </address>
4219    </author>
4220    <date month="January" year="2008"/>
4221  </front>
4222  <seriesInfo name="STD" value="68"/>
4223  <seriesInfo name="RFC" value="5234"/>
4224</reference>
4225
4226<reference anchor="RFC2119">
4227  <front>
4228    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4229    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4230      <organization>Harvard University</organization>
4231      <address><email>sob@harvard.edu</email></address>
4232    </author>
4233    <date month="March" year="1997"/>
4234  </front>
4235  <seriesInfo name="BCP" value="14"/>
4236  <seriesInfo name="RFC" value="2119"/>
4237</reference>
4238
4239<reference anchor="RFC3986">
4240 <front>
4241  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4242  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4243    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4244    <address>
4245       <email>timbl@w3.org</email>
4246       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4247    </address>
4248  </author>
4249  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4250    <organization abbrev="Day Software">Day Software</organization>
4251    <address>
4252      <email>fielding@gbiv.com</email>
4253      <uri>http://roy.gbiv.com/</uri>
4254    </address>
4255  </author>
4256  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4257    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4258    <address>
4259      <email>LMM@acm.org</email>
4260      <uri>http://larry.masinter.net/</uri>
4261    </address>
4262  </author>
4263  <date month='January' year='2005'></date>
4264 </front>
4265 <seriesInfo name="STD" value="66"/>
4266 <seriesInfo name="RFC" value="3986"/>
4267</reference>
4268
4269<reference anchor="USASCII">
4270  <front>
4271    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4272    <author>
4273      <organization>American National Standards Institute</organization>
4274    </author>
4275    <date year="1986"/>
4276  </front>
4277  <seriesInfo name="ANSI" value="X3.4"/>
4278</reference>
4279
4280<reference anchor="RFC1950">
4281  <front>
4282    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4283    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4284      <organization>Aladdin Enterprises</organization>
4285      <address><email>ghost@aladdin.com</email></address>
4286    </author>
4287    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4288    <date month="May" year="1996"/>
4289  </front>
4290  <seriesInfo name="RFC" value="1950"/>
4291  <annotation>
4292    RFC 1950 is an Informational RFC, thus it might be less stable than
4293    this specification. On the other hand, this downward reference was
4294    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4295    therefore it is unlikely to cause problems in practice. See also
4296    <xref target="BCP97"/>.
4297  </annotation>
4298</reference>
4299
4300<reference anchor="RFC1951">
4301  <front>
4302    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4303    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4304      <organization>Aladdin Enterprises</organization>
4305      <address><email>ghost@aladdin.com</email></address>
4306    </author>
4307    <date month="May" year="1996"/>
4308  </front>
4309  <seriesInfo name="RFC" value="1951"/>
4310  <annotation>
4311    RFC 1951 is an Informational RFC, thus it might be less stable than
4312    this specification. On the other hand, this downward reference was
4313    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4314    therefore it is unlikely to cause problems in practice. See also
4315    <xref target="BCP97"/>.
4316  </annotation>
4317</reference>
4318
4319<reference anchor="RFC1952">
4320  <front>
4321    <title>GZIP file format specification version 4.3</title>
4322    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4323      <organization>Aladdin Enterprises</organization>
4324      <address><email>ghost@aladdin.com</email></address>
4325    </author>
4326    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4327      <address><email>gzip@prep.ai.mit.edu</email></address>
4328    </author>
4329    <author initials="M." surname="Adler" fullname="Mark Adler">
4330      <address><email>madler@alumni.caltech.edu</email></address>
4331    </author>
4332    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4333      <address><email>ghost@aladdin.com</email></address>
4334    </author>
4335    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4336      <address><email>randeg@alumni.rpi.edu</email></address>
4337    </author>
4338    <date month="May" year="1996"/>
4339  </front>
4340  <seriesInfo name="RFC" value="1952"/>
4341  <annotation>
4342    RFC 1952 is an Informational RFC, thus it might be less stable than
4343    this specification. On the other hand, this downward reference was
4344    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4345    therefore it is unlikely to cause problems in practice. See also
4346    <xref target="BCP97"/>.
4347  </annotation>
4348</reference>
4349
4350</references>
4351
4352<references title="Informative References">
4353
4354<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4355  <front>
4356    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4357    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4358    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4359    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4360    <author initials="H." surname="Lie" fullname="H. Lie"/>
4361    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4362    <date year="1997" month="September"/>
4363  </front>
4364  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4365</reference>
4366
4367<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4368  <front>
4369    <title>Improving HTTP Latency</title>
4370    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4371    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4372    <date year="1995" month="December"/>
4373  </front>
4374  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4375</reference>
4376
4377<reference anchor="RFC1123">
4378  <front>
4379    <title>Requirements for Internet Hosts - Application and Support</title>
4380    <author initials="R." surname="Braden" fullname="Robert Braden">
4381      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4382      <address><email>Braden@ISI.EDU</email></address>
4383    </author>
4384    <date month="October" year="1989"/>
4385  </front>
4386  <seriesInfo name="STD" value="3"/>
4387  <seriesInfo name="RFC" value="1123"/>
4388</reference>
4389
4390<reference anchor="RFC1900">
4391  <front>
4392    <title>Renumbering Needs Work</title>
4393    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4394      <organization>CERN, Computing and Networks Division</organization>
4395      <address><email>brian@dxcoms.cern.ch</email></address>
4396    </author>
4397    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4398      <organization>cisco Systems</organization>
4399      <address><email>yakov@cisco.com</email></address>
4400    </author>
4401    <date month="February" year="1996"/>
4402  </front>
4403  <seriesInfo name="RFC" value="1900"/>
4404</reference>
4405
4406<reference anchor='RFC1919'>
4407  <front>
4408    <title>Classical versus Transparent IP Proxies</title>
4409    <author initials='M.' surname='Chatel' fullname='Marc Chatel'>
4410      <address><email>mchatel@pax.eunet.ch</email></address>
4411    </author>
4412    <date year='1996' month='March' />
4413  </front>
4414  <seriesInfo name='RFC' value='1919' />
4415</reference>
4416
4417<reference anchor="RFC1945">
4418  <front>
4419    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4420    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4421      <organization>MIT, Laboratory for Computer Science</organization>
4422      <address><email>timbl@w3.org</email></address>
4423    </author>
4424    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4425      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4426      <address><email>fielding@ics.uci.edu</email></address>
4427    </author>
4428    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4429      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4430      <address><email>frystyk@w3.org</email></address>
4431    </author>
4432    <date month="May" year="1996"/>
4433  </front>
4434  <seriesInfo name="RFC" value="1945"/>
4435</reference>
4436
4437<reference anchor="RFC2045">
4438  <front>
4439    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4440    <author initials="N." surname="Freed" fullname="Ned Freed">
4441      <organization>Innosoft International, Inc.</organization>
4442      <address><email>ned@innosoft.com</email></address>
4443    </author>
4444    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4445      <organization>First Virtual Holdings</organization>
4446      <address><email>nsb@nsb.fv.com</email></address>
4447    </author>
4448    <date month="November" year="1996"/>
4449  </front>
4450  <seriesInfo name="RFC" value="2045"/>
4451</reference>
4452
4453<reference anchor="RFC2047">
4454  <front>
4455    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4456    <author initials="K." surname="Moore" fullname="Keith Moore">
4457      <organization>University of Tennessee</organization>
4458      <address><email>moore@cs.utk.edu</email></address>
4459    </author>
4460    <date month="November" year="1996"/>
4461  </front>
4462  <seriesInfo name="RFC" value="2047"/>
4463</reference>
4464
4465<reference anchor="RFC2068">
4466  <front>
4467    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4468    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4469      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4470      <address><email>fielding@ics.uci.edu</email></address>
4471    </author>
4472    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4473      <organization>MIT Laboratory for Computer Science</organization>
4474      <address><email>jg@w3.org</email></address>
4475    </author>
4476    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4477      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4478      <address><email>mogul@wrl.dec.com</email></address>
4479    </author>
4480    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4481      <organization>MIT Laboratory for Computer Science</organization>
4482      <address><email>frystyk@w3.org</email></address>
4483    </author>
4484    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4485      <organization>MIT Laboratory for Computer Science</organization>
4486      <address><email>timbl@w3.org</email></address>
4487    </author>
4488    <date month="January" year="1997"/>
4489  </front>
4490  <seriesInfo name="RFC" value="2068"/>
4491</reference>
4492
4493<reference anchor="RFC2145">
4494  <front>
4495    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4496    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4497      <organization>Western Research Laboratory</organization>
4498      <address><email>mogul@wrl.dec.com</email></address>
4499    </author>
4500    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4501      <organization>Department of Information and Computer Science</organization>
4502      <address><email>fielding@ics.uci.edu</email></address>
4503    </author>
4504    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4505      <organization>MIT Laboratory for Computer Science</organization>
4506      <address><email>jg@w3.org</email></address>
4507    </author>
4508    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4509      <organization>W3 Consortium</organization>
4510      <address><email>frystyk@w3.org</email></address>
4511    </author>
4512    <date month="May" year="1997"/>
4513  </front>
4514  <seriesInfo name="RFC" value="2145"/>
4515</reference>
4516
4517<reference anchor="RFC2616">
4518  <front>
4519    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4520    <author initials="R." surname="Fielding" fullname="R. Fielding">
4521      <organization>University of California, Irvine</organization>
4522      <address><email>fielding@ics.uci.edu</email></address>
4523    </author>
4524    <author initials="J." surname="Gettys" fullname="J. Gettys">
4525      <organization>W3C</organization>
4526      <address><email>jg@w3.org</email></address>
4527    </author>
4528    <author initials="J." surname="Mogul" fullname="J. Mogul">
4529      <organization>Compaq Computer Corporation</organization>
4530      <address><email>mogul@wrl.dec.com</email></address>
4531    </author>
4532    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4533      <organization>MIT Laboratory for Computer Science</organization>
4534      <address><email>frystyk@w3.org</email></address>
4535    </author>
4536    <author initials="L." surname="Masinter" fullname="L. Masinter">
4537      <organization>Xerox Corporation</organization>
4538      <address><email>masinter@parc.xerox.com</email></address>
4539    </author>
4540    <author initials="P." surname="Leach" fullname="P. Leach">
4541      <organization>Microsoft Corporation</organization>
4542      <address><email>paulle@microsoft.com</email></address>
4543    </author>
4544    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4545      <organization>W3C</organization>
4546      <address><email>timbl@w3.org</email></address>
4547    </author>
4548    <date month="June" year="1999"/>
4549  </front>
4550  <seriesInfo name="RFC" value="2616"/>
4551</reference>
4552
4553<reference anchor='RFC2817'>
4554  <front>
4555    <title>Upgrading to TLS Within HTTP/1.1</title>
4556    <author initials='R.' surname='Khare' fullname='R. Khare'>
4557      <organization>4K Associates / UC Irvine</organization>
4558      <address><email>rohit@4K-associates.com</email></address>
4559    </author>
4560    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4561      <organization>Agranat Systems, Inc.</organization>
4562      <address><email>lawrence@agranat.com</email></address>
4563    </author>
4564    <date year='2000' month='May' />
4565  </front>
4566  <seriesInfo name='RFC' value='2817' />
4567</reference>
4568
4569<reference anchor='RFC2818'>
4570  <front>
4571    <title>HTTP Over TLS</title>
4572    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4573      <organization>RTFM, Inc.</organization>
4574      <address><email>ekr@rtfm.com</email></address>
4575    </author>
4576    <date year='2000' month='May' />
4577  </front>
4578  <seriesInfo name='RFC' value='2818' />
4579</reference>
4580
4581<reference anchor='RFC2965'>
4582  <front>
4583    <title>HTTP State Management Mechanism</title>
4584    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4585      <organization>Bell Laboratories, Lucent Technologies</organization>
4586      <address><email>dmk@bell-labs.com</email></address>
4587    </author>
4588    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4589      <organization>Epinions.com, Inc.</organization>
4590      <address><email>lou@montulli.org</email></address>
4591    </author>
4592    <date year='2000' month='October' />
4593  </front>
4594  <seriesInfo name='RFC' value='2965' />
4595</reference>
4596
4597<reference anchor='RFC3040'>
4598  <front>
4599    <title>Internet Web Replication and Caching Taxonomy</title>
4600    <author initials='I.' surname='Cooper' fullname='I. Cooper'>
4601      <organization>Equinix, Inc.</organization>
4602    </author>
4603    <author initials='I.' surname='Melve' fullname='I. Melve'>
4604      <organization>UNINETT</organization>
4605    </author>
4606    <author initials='G.' surname='Tomlinson' fullname='G. Tomlinson'>
4607      <organization>CacheFlow Inc.</organization>
4608    </author>
4609    <date year='2001' month='January' />
4610  </front>
4611  <seriesInfo name='RFC' value='3040' />
4612</reference>
4613
4614<reference anchor='RFC3864'>
4615  <front>
4616    <title>Registration Procedures for Message Header Fields</title>
4617    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4618      <organization>Nine by Nine</organization>
4619      <address><email>GK-IETF@ninebynine.org</email></address>
4620    </author>
4621    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4622      <organization>BEA Systems</organization>
4623      <address><email>mnot@pobox.com</email></address>
4624    </author>
4625    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4626      <organization>HP Labs</organization>
4627      <address><email>JeffMogul@acm.org</email></address>
4628    </author>
4629    <date year='2004' month='September' />
4630  </front>
4631  <seriesInfo name='BCP' value='90' />
4632  <seriesInfo name='RFC' value='3864' />
4633</reference>
4634
4635<reference anchor="RFC4288">
4636  <front>
4637    <title>Media Type Specifications and Registration Procedures</title>
4638    <author initials="N." surname="Freed" fullname="N. Freed">
4639      <organization>Sun Microsystems</organization>
4640      <address>
4641        <email>ned.freed@mrochek.com</email>
4642      </address>
4643    </author>
4644    <author initials="J." surname="Klensin" fullname="J. Klensin">
4645      <address>
4646        <email>klensin+ietf@jck.com</email>
4647      </address>
4648    </author>
4649    <date year="2005" month="December"/>
4650  </front>
4651  <seriesInfo name="BCP" value="13"/>
4652  <seriesInfo name="RFC" value="4288"/>
4653</reference>
4654
4655<reference anchor='RFC4395'>
4656  <front>
4657    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4658    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4659      <organization>AT&amp;T Laboratories</organization>
4660      <address>
4661        <email>tony+urireg@maillennium.att.com</email>
4662      </address>
4663    </author>
4664    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4665      <organization>Qualcomm, Inc.</organization>
4666      <address>
4667        <email>hardie@qualcomm.com</email>
4668      </address>
4669    </author>
4670    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4671      <organization>Adobe Systems</organization>
4672      <address>
4673        <email>LMM@acm.org</email>
4674      </address>
4675    </author>
4676    <date year='2006' month='February' />
4677  </front>
4678  <seriesInfo name='BCP' value='115' />
4679  <seriesInfo name='RFC' value='4395' />
4680</reference>
4681
4682<reference anchor='RFC5226'>
4683  <front>
4684    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4685    <author initials='T.' surname='Narten' fullname='T. Narten'>
4686      <organization>IBM</organization>
4687      <address><email>narten@us.ibm.com</email></address>
4688    </author>
4689    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4690      <organization>Google</organization>
4691      <address><email>Harald@Alvestrand.no</email></address>
4692    </author>
4693    <date year='2008' month='May' />
4694  </front>
4695  <seriesInfo name='BCP' value='26' />
4696  <seriesInfo name='RFC' value='5226' />
4697</reference>
4698
4699<reference anchor="RFC5322">
4700  <front>
4701    <title>Internet Message Format</title>
4702    <author initials="P." surname="Resnick" fullname="P. Resnick">
4703      <organization>Qualcomm Incorporated</organization>
4704    </author>
4705    <date year="2008" month="October"/>
4706  </front> 
4707  <seriesInfo name="RFC" value="5322"/>
4708</reference>
4709
4710<reference anchor='draft-ietf-httpstate-cookie'>
4711  <front>
4712    <title>HTTP State Management Mechanism</title>
4713    <author initials="A." surname="Barth" fullname="Adam Barth">
4714      <organization abbrev="U.C. Berkeley">
4715        University of California, Berkeley
4716      </organization>
4717      <address><email>abarth@eecs.berkeley.edu</email></address>
4718    </author>
4719    <date year='2011' month='March' />
4720  </front>
4721  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4722</reference>
4723
4724<reference anchor='BCP97'>
4725  <front>
4726    <title>Handling Normative References to Standards-Track Documents</title>
4727    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4728      <address>
4729        <email>klensin+ietf@jck.com</email>
4730      </address>
4731    </author>
4732    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4733      <organization>MIT</organization>
4734      <address>
4735        <email>hartmans-ietf@mit.edu</email>
4736      </address>
4737    </author>
4738    <date year='2007' month='June' />
4739  </front>
4740  <seriesInfo name='BCP' value='97' />
4741  <seriesInfo name='RFC' value='4897' />
4742</reference>
4743
4744<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4745  <front>
4746    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4747    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4748    <date year="2001" month="November"/>
4749  </front>
4750  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4751</reference>
4752
4753<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4754  <front>
4755    <title>Analysis of HTTP Performance Problems</title>
4756    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4757    <date/>
4758  </front>
4759</reference>
4760
4761<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4762  <front>
4763  <title>Analysis of HTTP Performance</title>
4764  <author initials="J." surname="Touch" fullname="Joe Touch">
4765    <organization>USC/Information Sciences Institute</organization>
4766    <address><email>touch@isi.edu</email></address>
4767  </author>
4768  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4769    <organization>USC/Information Sciences Institute</organization>
4770    <address><email>johnh@isi.edu</email></address>
4771  </author>
4772  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4773    <organization>USC/Information Sciences Institute</organization>
4774    <address><email>katia@isi.edu</email></address>
4775  </author>
4776  <date year="1998" month="Aug"/>
4777  </front>
4778  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4779  <annotation>(original report dated Aug. 1996)</annotation>
4780</reference>
4781
4782</references>
4783
4784
4785<section title="Tolerant Applications" anchor="tolerant.applications">
4786<t>
4787   Although this document specifies the requirements for the generation
4788   of HTTP/1.1 messages, not all applications will be correct in their
4789   implementation. We therefore recommend that operational applications
4790   be tolerant of deviations whenever those deviations can be
4791   interpreted unambiguously.
4792</t>
4793<t>
4794   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4795   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4796   &SHOULD; accept any amount of WSP characters between fields, even though
4797   only a single SP is required.
4798</t>
4799<t>
4800   The line terminator for header fields is the sequence CRLF.
4801   However, we recommend that applications, when parsing such headers fields,
4802   recognize a single LF as a line terminator and ignore the leading CR.
4803</t>
4804<t>
4805   The character set of a representation &SHOULD; be labeled as the lowest
4806   common denominator of the character codes used within that representation, with
4807   the exception that not labeling the representation is preferred over labeling
4808   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4809</t>
4810<t>
4811   Additional rules for requirements on parsing and encoding of dates
4812   and other potential problems with date encodings include:
4813</t>
4814<t>
4815  <list style="symbols">
4816     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4817        which appears to be more than 50 years in the future is in fact
4818        in the past (this helps solve the "year 2000" problem).</t>
4819
4820     <t>Although all date formats are specified to be case-sensitive,
4821        recipients &SHOULD; match day, week and timezone names
4822        case-insensitively.</t>
4823             
4824     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4825        Expires date as earlier than the proper value, but &MUST-NOT;
4826        internally represent a parsed Expires date as later than the
4827        proper value.</t>
4828
4829     <t>All expiration-related calculations &MUST; be done in GMT. The
4830        local time zone &MUST-NOT; influence the calculation or comparison
4831        of an age or expiration time.</t>
4832
4833     <t>If an HTTP header field incorrectly carries a date value with a time
4834        zone other than GMT, it &MUST; be converted into GMT using the
4835        most conservative possible conversion.</t>
4836  </list>
4837</t>
4838</section>
4839
4840<section title="Compatibility with Previous Versions" anchor="compatibility">
4841<t>
4842   HTTP has been in use by the World-Wide Web global information initiative
4843   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4844   was a simple protocol for hypertext data transfer across the Internet
4845   with only a single method and no metadata.
4846   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4847   methods and MIME-like messaging that could include metadata about the data
4848   transferred and modifiers on the request/response semantics. However,
4849   HTTP/1.0 did not sufficiently take into consideration the effects of
4850   hierarchical proxies, caching, the need for persistent connections, or
4851   name-based virtual hosts. The proliferation of incompletely-implemented
4852   applications calling themselves "HTTP/1.0" further necessitated a
4853   protocol version change in order for two communicating applications
4854   to determine each other's true capabilities.
4855</t>
4856<t>
4857   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4858   requirements that enable reliable implementations, adding only
4859   those new features that will either be safely ignored by an HTTP/1.0
4860   recipient or only sent when communicating with a party advertising
4861   compliance with HTTP/1.1.
4862</t>
4863<t>
4864   It is beyond the scope of a protocol specification to mandate
4865   compliance with previous versions. HTTP/1.1 was deliberately
4866   designed, however, to make supporting previous versions easy. It is
4867   worth noting that, at the time of composing this specification, we would
4868   expect general-purpose HTTP/1.1 servers to:
4869  <list style="symbols">
4870     <t>understand any valid request in the format of HTTP/1.0 and
4871        1.1;</t>
4872
4873     <t>respond appropriately with a message in the same major version
4874        used by the client.</t>
4875  </list>
4876</t>
4877<t>
4878   And we would expect HTTP/1.1 clients to:
4879  <list style="symbols">
4880     <t>understand any valid response in the format of HTTP/1.0 or
4881        1.1.</t>
4882  </list>
4883</t>
4884<t>
4885   For most implementations of HTTP/1.0, each connection is established
4886   by the client prior to the request and closed by the server after
4887   sending the response. Some implementations implement the Keep-Alive
4888   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4889</t>
4890
4891<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4892<t>
4893   This section summarizes major differences between versions HTTP/1.0
4894   and HTTP/1.1.
4895</t>
4896
4897<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4898<t>
4899   The requirements that clients and servers support the Host request-header
4900   field (<xref target="header.host"/>), report an error if it is
4901   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4902   are among the most important changes defined by this
4903   specification.
4904</t>
4905<t>
4906   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4907   addresses and servers; there was no other established mechanism for
4908   distinguishing the intended server of a request than the IP address
4909   to which that request was directed. The changes outlined above will
4910   allow the Internet, once older HTTP clients are no longer common, to
4911   support multiple Web sites from a single IP address, greatly
4912   simplifying large operational Web servers, where allocation of many
4913   IP addresses to a single host has created serious problems. The
4914   Internet will also be able to recover the IP addresses that have been
4915   allocated for the sole purpose of allowing special-purpose domain
4916   names to be used in root-level HTTP URLs. Given the rate of growth of
4917   the Web, and the number of servers already deployed, it is extremely
4918   important that all implementations of HTTP (including updates to
4919   existing HTTP/1.0 applications) correctly implement these
4920   requirements:
4921  <list style="symbols">
4922     <t>Both clients and servers &MUST; support the Host request-header field.</t>
4923
4924     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4925
4926     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4927        request does not include a Host request-header field.</t>
4928
4929     <t>Servers &MUST; accept absolute URIs.</t>
4930  </list>
4931</t>
4932</section>
4933</section>
4934
4935<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4936<t>
4937   Some clients and servers might wish to be compatible with some
4938   previous implementations of persistent connections in HTTP/1.0
4939   clients and servers. Persistent connections in HTTP/1.0 are
4940   explicitly negotiated as they are not the default behavior. HTTP/1.0
4941   experimental implementations of persistent connections are faulty,
4942   and the new facilities in HTTP/1.1 are designed to rectify these
4943   problems. The problem was that some existing HTTP/1.0 clients might
4944   send Keep-Alive to a proxy server that doesn't understand
4945   Connection, which would then erroneously forward it to the next
4946   inbound server, which would establish the Keep-Alive connection and
4947   result in a hung HTTP/1.0 proxy waiting for the close on the
4948   response. The result is that HTTP/1.0 clients must be prevented from
4949   using Keep-Alive when talking to proxies.
4950</t>
4951<t>
4952   However, talking to proxies is the most important use of persistent
4953   connections, so that prohibition is clearly unacceptable. Therefore,
4954   we need some other mechanism for indicating a persistent connection
4955   is desired, which is safe to use even when talking to an old proxy
4956   that ignores Connection. Persistent connections are the default for
4957   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4958   declaring non-persistence. See <xref target="header.connection"/>.
4959</t>
4960<t>
4961   The original HTTP/1.0 form of persistent connections (the Connection:
4962   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4963</t>
4964</section>
4965
4966<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4967<t>
4968  Empty list elements in list productions have been deprecated.
4969  (<xref target="notation.abnf"/>)
4970</t>
4971<t>
4972  Rules about implicit linear whitespace between certain grammar productions
4973  have been removed; now it's only allowed when specifically pointed out
4974  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4975  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4976  Non-ASCII content in header fields and reason phrase has been obsoleted and
4977  made opaque (the TEXT rule was removed)
4978  (<xref target="basic.rules"/>)
4979</t>
4980<t>
4981  Clarify that HTTP-Version is case sensitive.
4982  (<xref target="http.version"/>)
4983</t>
4984<t>
4985  Require that invalid whitespace around field-names be rejected.
4986  (<xref target="header.fields"/>)
4987</t>
4988<t>
4989  Require recipients to handle bogus Content-Length header fields as errors.
4990  (<xref target="message.body"/>)
4991</t>
4992<t>
4993  Remove reference to non-existent identity transfer-coding value tokens.
4994  (Sections <xref format="counter" target="message.body"/> and
4995  <xref format="counter" target="transfer.codings"/>)
4996</t>
4997<t>
4998  Update use of abs_path production from RFC 1808 to the path-absolute + query
4999  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5000  method only.
5001  (<xref target="request-target"/>)
5002</t>
5003<t>
5004  Clarification that the chunk length does not include the count of the octets
5005  in the chunk header and trailer. Furthermore disallowed line folding
5006  in chunk extensions.
5007  (<xref target="chunked.encoding"/>)
5008</t>
5009<t>
5010  Remove hard limit of two connections per server.
5011  (<xref target="persistent.practical"/>)
5012</t>
5013<t>
5014  Clarify exactly when close connection options must be sent.
5015  (<xref target="header.connection"/>)
5016</t>
5017<t>
5018  Define the semantics of the "Upgrade" header field in responses other than
5019  101 (this was incorporated from <xref target="RFC2817"/>).
5020  (<xref target="header.upgrade"/>)
5021</t>
5022</section>
5023</section>
5024
5025<?BEGININC p1-messaging.abnf-appendix ?>
5026<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
5027<figure>
5028<artwork type="abnf" name="p1-messaging.parsed-abnf">
5029<x:ref>BWS</x:ref> = OWS
5030
5031<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
5032<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
5033<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
5034<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
5035 connection-token ] )
5036<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
5037<x:ref>Content-Length-v</x:ref> = 1*DIGIT
5038
5039<x:ref>Date</x:ref> = "Date:" OWS Date-v
5040<x:ref>Date-v</x:ref> = HTTP-date
5041
5042<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
5043
5044<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
5045<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5046<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
5047<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
5048 ]
5049<x:ref>Host</x:ref> = "Host:" OWS Host-v
5050<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
5051
5052<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
5053<x:ref>Method</x:ref> = token
5054
5055<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
5056
5057<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
5058
5059<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
5060<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
5061<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5062<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
5063<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5064
5065<x:ref>Status-Code</x:ref> = 3DIGIT
5066<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5067
5068<x:ref>TE</x:ref> = "TE:" OWS TE-v
5069<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5070<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
5071<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5072<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
5073<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5074 transfer-coding ] )
5075
5076<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
5077<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
5078<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
5079
5080<x:ref>Via</x:ref> = "Via:" OWS Via-v
5081<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5082 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5083 ] )
5084
5085<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
5086
5087<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
5088<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
5089<x:ref>attribute</x:ref> = token
5090<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
5091
5092<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5093<x:ref>chunk-data</x:ref> = 1*OCTET
5094<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5095<x:ref>chunk-ext-name</x:ref> = token
5096<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
5097<x:ref>chunk-size</x:ref> = 1*HEXDIG
5098<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
5099<x:ref>connection-token</x:ref> = token
5100<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
5101 / %x2A-5B ; '*'-'['
5102 / %x5D-7E ; ']'-'~'
5103 / obs-text
5104
5105<x:ref>date1</x:ref> = day SP month SP year
5106<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
5107<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
5108<x:ref>day</x:ref> = 2DIGIT
5109<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
5110 / %x54.75.65 ; Tue
5111 / %x57.65.64 ; Wed
5112 / %x54.68.75 ; Thu
5113 / %x46.72.69 ; Fri
5114 / %x53.61.74 ; Sat
5115 / %x53.75.6E ; Sun
5116<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5117 / %x54.75.65.73.64.61.79 ; Tuesday
5118 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
5119 / %x54.68.75.72.73.64.61.79 ; Thursday
5120 / %x46.72.69.64.61.79 ; Friday
5121 / %x53.61.74.75.72.64.61.79 ; Saturday
5122 / %x53.75.6E.64.61.79 ; Sunday
5123
5124<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5125<x:ref>field-name</x:ref> = token
5126<x:ref>field-value</x:ref> = *( field-content / OWS )
5127
5128<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5129<x:ref>hour</x:ref> = 2DIGIT
5130<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5131<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5132
5133<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5134
5135<x:ref>message-body</x:ref> = *OCTET
5136<x:ref>minute</x:ref> = 2DIGIT
5137<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5138 / %x46.65.62 ; Feb
5139 / %x4D.61.72 ; Mar
5140 / %x41.70.72 ; Apr
5141 / %x4D.61.79 ; May
5142 / %x4A.75.6E ; Jun
5143 / %x4A.75.6C ; Jul
5144 / %x41.75.67 ; Aug
5145 / %x53.65.70 ; Sep
5146 / %x4F.63.74 ; Oct
5147 / %x4E.6F.76 ; Nov
5148 / %x44.65.63 ; Dec
5149
5150<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5151<x:ref>obs-fold</x:ref> = CRLF
5152<x:ref>obs-text</x:ref> = %x80-FF
5153
5154<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5155<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5156<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5157<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5158<x:ref>product</x:ref> = token [ "/" product-version ]
5159<x:ref>product-version</x:ref> = token
5160<x:ref>protocol-name</x:ref> = token
5161<x:ref>protocol-version</x:ref> = token
5162<x:ref>pseudonym</x:ref> = token
5163
5164<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5165 / %x5D-7E ; ']'-'~'
5166 / obs-text
5167<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5168 / %x5D-7E ; ']'-'~'
5169 / obs-text
5170<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5171<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5172<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5173<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5174<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5175<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5176
5177<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5178<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5179<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5180<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5181<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5182 / authority
5183<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5184<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5185<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5186
5187<x:ref>second</x:ref> = 2DIGIT
5188<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5189 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5190<x:ref>start-line</x:ref> = Request-Line / Status-Line
5191
5192<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5193<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5194 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5195<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5196<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5197<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5198<x:ref>token</x:ref> = 1*tchar
5199<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5200<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5201 transfer-extension
5202<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5203<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5204
5205<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5206
5207<x:ref>value</x:ref> = word
5208
5209<x:ref>word</x:ref> = token / quoted-string
5210
5211<x:ref>year</x:ref> = 4DIGIT
5212</artwork>
5213</figure>
5214<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5215; Cache-Control defined but not used
5216; Chunked-Body defined but not used
5217; Connection defined but not used
5218; Content-Length defined but not used
5219; Date defined but not used
5220; HTTP-message defined but not used
5221; Host defined but not used
5222; MIME-Version defined but not used
5223; Pragma defined but not used
5224; Request defined but not used
5225; Response defined but not used
5226; TE defined but not used
5227; Trailer defined but not used
5228; Transfer-Encoding defined but not used
5229; URI-reference defined but not used
5230; Upgrade defined but not used
5231; Via defined but not used
5232; Warning defined but not used
5233; http-URI defined but not used
5234; https-URI defined but not used
5235; partial-URI defined but not used
5236; request-header defined but not used
5237; response-header defined but not used
5238; special defined but not used
5239</artwork></figure></section>
5240<?ENDINC p1-messaging.abnf-appendix ?>
5241
5242<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5243
5244<section title="Since RFC 2616">
5245<t>
5246  Extracted relevant partitions from <xref target="RFC2616"/>.
5247</t>
5248</section>
5249
5250<section title="Since draft-ietf-httpbis-p1-messaging-00">
5251<t>
5252  Closed issues:
5253  <list style="symbols"> 
5254    <t>
5255      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5256      "HTTP Version should be case sensitive"
5257      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5258    </t>
5259    <t>
5260      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5261      "'unsafe' characters"
5262      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5263    </t>
5264    <t>
5265      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5266      "Chunk Size Definition"
5267      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5268    </t>
5269    <t>
5270      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5271      "Message Length"
5272      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5273    </t>
5274    <t>
5275      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5276      "Media Type Registrations"
5277      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5278    </t>
5279    <t>
5280      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5281      "URI includes query"
5282      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5283    </t>
5284    <t>
5285      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5286      "No close on 1xx responses"
5287      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5288    </t>
5289    <t>
5290      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5291      "Remove 'identity' token references"
5292      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5293    </t>
5294    <t>
5295      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5296      "Import query BNF"
5297    </t>
5298    <t>
5299      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5300      "qdtext BNF"
5301    </t>
5302    <t>
5303      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5304      "Normative and Informative references"
5305    </t>
5306    <t>
5307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5308      "RFC2606 Compliance"
5309    </t>
5310    <t>
5311      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5312      "RFC977 reference"
5313    </t>
5314    <t>
5315      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5316      "RFC1700 references"
5317    </t>
5318    <t>
5319      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5320      "inconsistency in date format explanation"
5321    </t>
5322    <t>
5323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5324      "Date reference typo"
5325    </t>
5326    <t>
5327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5328      "Informative references"
5329    </t>
5330    <t>
5331      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5332      "ISO-8859-1 Reference"
5333    </t>
5334    <t>
5335      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5336      "Normative up-to-date references"
5337    </t>
5338  </list>
5339</t>
5340<t>
5341  Other changes:
5342  <list style="symbols"> 
5343    <t>
5344      Update media type registrations to use RFC4288 template.
5345    </t>
5346    <t>
5347      Use names of RFC4234 core rules DQUOTE and WSP,
5348      fix broken ABNF for chunk-data
5349      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5350    </t>
5351  </list>
5352</t>
5353</section>
5354
5355<section title="Since draft-ietf-httpbis-p1-messaging-01">
5356<t>
5357  Closed issues:
5358  <list style="symbols"> 
5359    <t>
5360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5361      "Bodies on GET (and other) requests"
5362    </t>
5363    <t>
5364      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5365      "Updating to RFC4288"
5366    </t>
5367    <t>
5368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5369      "Status Code and Reason Phrase"
5370    </t>
5371    <t>
5372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5373      "rel_path not used"
5374    </t>
5375  </list>
5376</t>
5377<t>
5378  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5379  <list style="symbols"> 
5380    <t>
5381      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5382      "trailer-part").
5383    </t>
5384    <t>
5385      Avoid underscore character in rule names ("http_URL" ->
5386      "http-URL", "abs_path" -> "path-absolute").
5387    </t>
5388    <t>
5389      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5390      "path-absolute", "port", "query", "relativeURI", "host) &mdash; these will
5391      have to be updated when switching over to RFC3986.
5392    </t>
5393    <t>
5394      Synchronize core rules with RFC5234.
5395    </t>
5396    <t>
5397      Get rid of prose rules that span multiple lines.
5398    </t>
5399    <t>
5400      Get rid of unused rules LOALPHA and UPALPHA.
5401    </t>
5402    <t>
5403      Move "Product Tokens" section (back) into Part 1, as "token" is used
5404      in the definition of the Upgrade header field.
5405    </t>
5406    <t>
5407      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5408    </t>
5409    <t>
5410      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5411    </t>
5412  </list>
5413</t>
5414</section>
5415
5416<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5417<t>
5418  Closed issues:
5419  <list style="symbols"> 
5420    <t>
5421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5422      "HTTP-date vs. rfc1123-date"
5423    </t>
5424    <t>
5425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5426      "WS in quoted-pair"
5427    </t>
5428  </list>
5429</t>
5430<t>
5431  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5432  <list style="symbols"> 
5433    <t>
5434      Reference RFC 3984, and update header field registrations for headers defined
5435      in this document.
5436    </t>
5437  </list>
5438</t>
5439<t>
5440  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5441  <list style="symbols"> 
5442    <t>
5443      Replace string literals when the string really is case-sensitive (HTTP-Version).
5444    </t>
5445  </list>
5446</t>
5447</section>
5448
5449<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5450<t>
5451  Closed issues:
5452  <list style="symbols"> 
5453    <t>
5454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5455      "Connection closing"
5456    </t>
5457    <t>
5458      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5459      "Move registrations and registry information to IANA Considerations"
5460    </t>
5461    <t>
5462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5463      "need new URL for PAD1995 reference"
5464    </t>
5465    <t>
5466      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5467      "IANA Considerations: update HTTP URI scheme registration"
5468    </t>
5469    <t>
5470      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5471      "Cite HTTPS URI scheme definition"
5472    </t>
5473    <t>
5474      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5475      "List-type headers vs Set-Cookie"
5476    </t>
5477  </list>
5478</t>
5479<t>
5480  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5481  <list style="symbols"> 
5482    <t>
5483      Replace string literals when the string really is case-sensitive (HTTP-Date).
5484    </t>
5485    <t>
5486      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5487    </t>
5488  </list>
5489</t>
5490</section>
5491
5492<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5493<t>
5494  Closed issues:
5495  <list style="symbols"> 
5496    <t>
5497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5498      "Out-of-date reference for URIs"
5499    </t>
5500    <t>
5501      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5502      "RFC 2822 is updated by RFC 5322"
5503    </t>
5504  </list>
5505</t>
5506<t>
5507  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5508  <list style="symbols"> 
5509    <t>
5510      Use "/" instead of "|" for alternatives.
5511    </t>
5512    <t>
5513      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5514    </t>
5515    <t>
5516      Only reference RFC 5234's core rules.
5517    </t>
5518    <t>
5519      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5520      whitespace ("OWS") and required whitespace ("RWS").
5521    </t>
5522    <t>
5523      Rewrite ABNFs to spell out whitespace rules, factor out
5524      header field value format definitions.
5525    </t>
5526  </list>
5527</t>
5528</section>
5529
5530<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5531<t>
5532  Closed issues:
5533  <list style="symbols"> 
5534    <t>
5535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5536      "Header LWS"
5537    </t>
5538    <t>
5539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5540      "Sort 1.3 Terminology"
5541    </t>
5542    <t>
5543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5544      "RFC2047 encoded words"
5545    </t>
5546    <t>
5547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5548      "Character Encodings in TEXT"
5549    </t>
5550    <t>
5551      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5552      "Line Folding"
5553    </t>
5554    <t>
5555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5556      "OPTIONS * and proxies"
5557    </t>
5558    <t>
5559      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5560      "Reason-Phrase BNF"
5561    </t>
5562    <t>
5563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5564      "Use of TEXT"
5565    </t>
5566    <t>
5567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5568      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5569    </t>
5570    <t>
5571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5572      "RFC822 reference left in discussion of date formats"
5573    </t>
5574  </list>
5575</t>
5576<t>
5577  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5578  <list style="symbols"> 
5579    <t>
5580      Rewrite definition of list rules, deprecate empty list elements.
5581    </t>
5582    <t>
5583      Add appendix containing collected and expanded ABNF.
5584    </t>
5585  </list>
5586</t>
5587<t>
5588  Other changes:
5589  <list style="symbols"> 
5590    <t>
5591      Rewrite introduction; add mostly new Architecture Section.
5592    </t>
5593    <t>
5594      Move definition of quality values from Part 3 into Part 1;
5595      make TE request header field grammar independent of accept-params (defined in Part 3).
5596    </t>
5597  </list>
5598</t>
5599</section>
5600
5601<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5602<t>
5603  Closed issues:
5604  <list style="symbols"> 
5605    <t>
5606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5607      "base for numeric protocol elements"
5608    </t>
5609    <t>
5610      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5611      "comment ABNF"
5612    </t>
5613  </list>
5614</t>
5615<t>
5616  Partly resolved issues:
5617  <list style="symbols"> 
5618    <t>
5619      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5620      "205 Bodies" (took out language that implied that there might be
5621      methods for which a request body MUST NOT be included)
5622    </t>
5623    <t>
5624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5625      "editorial improvements around HTTP-date"
5626    </t>
5627  </list>
5628</t>
5629</section>
5630
5631<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5632<t>
5633  Closed issues:
5634  <list style="symbols"> 
5635    <t>
5636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5637      "Repeating single-value headers"
5638    </t>
5639    <t>
5640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5641      "increase connection limit"
5642    </t>
5643    <t>
5644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5645      "IP addresses in URLs"
5646    </t>
5647    <t>
5648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5649      "take over HTTP Upgrade Token Registry"
5650    </t>
5651    <t>
5652      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5653      "CR and LF in chunk extension values"
5654    </t>
5655    <t>
5656      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5657      "HTTP/0.9 support"
5658    </t>
5659    <t>
5660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5661      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5662    </t>
5663    <t>
5664      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5665      "move definitions of gzip/deflate/compress to part 1"
5666    </t>
5667    <t>
5668      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5669      "disallow control characters in quoted-pair"
5670    </t>
5671  </list>
5672</t>
5673<t>
5674  Partly resolved issues:
5675  <list style="symbols"> 
5676    <t>
5677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5678      "update IANA requirements wrt Transfer-Coding values" (add the
5679      IANA Considerations subsection)
5680    </t>
5681  </list>
5682</t>
5683</section>
5684
5685<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5686<t>
5687  Closed issues:
5688  <list style="symbols"> 
5689    <t>
5690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5691      "header parsing, treatment of leading and trailing OWS"
5692    </t>
5693  </list>
5694</t>
5695<t>
5696  Partly resolved issues:
5697  <list style="symbols"> 
5698    <t>
5699      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5700      "Placement of 13.5.1 and 13.5.2"
5701    </t>
5702    <t>
5703      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5704      "use of term "word" when talking about header structure"
5705    </t>
5706  </list>
5707</t>
5708</section>
5709
5710<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5711<t>
5712  Closed issues:
5713  <list style="symbols"> 
5714    <t>
5715      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5716      "Clarification of the term 'deflate'"
5717    </t>
5718    <t>
5719      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5720      "OPTIONS * and proxies"
5721    </t>
5722    <t>
5723      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5724      "MIME-Version not listed in P1, general header fields"
5725    </t>
5726    <t>
5727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5728      "IANA registry for content/transfer encodings"
5729    </t>
5730    <t>
5731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5732      "Case-sensitivity of HTTP-date"
5733    </t>
5734    <t>
5735      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5736      "use of term "word" when talking about header structure"
5737    </t>
5738  </list>
5739</t>
5740<t>
5741  Partly resolved issues:
5742  <list style="symbols"> 
5743    <t>
5744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5745      "Term for the requested resource's URI"
5746    </t>
5747  </list>
5748</t>
5749</section>
5750
5751<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5752<t>
5753  Closed issues:
5754  <list style="symbols">
5755    <t>
5756      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5757      "Connection Closing"
5758    </t>
5759    <t>
5760      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5761      "Delimiting messages with multipart/byteranges"
5762    </t>
5763    <t>
5764      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5765      "Handling multiple Content-Length headers"
5766    </t>
5767    <t>
5768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5769      "Clarify entity / representation / variant terminology"
5770    </t>
5771    <t>
5772      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5773      "consider removing the 'changes from 2068' sections"
5774    </t>
5775  </list>
5776</t>
5777<t>
5778  Partly resolved issues:
5779  <list style="symbols"> 
5780    <t>
5781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5782      "HTTP(s) URI scheme definitions"
5783    </t>
5784  </list>
5785</t>
5786</section>
5787
5788<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5789<t>
5790  Closed issues:
5791  <list style="symbols">
5792    <t>
5793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5794      "Trailer requirements"
5795    </t>
5796    <t>
5797      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5798      "Text about clock requirement for caches belongs in p6"
5799    </t>
5800    <t>
5801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5802      "effective request URI: handling of missing host in HTTP/1.0"
5803    </t>
5804    <t>
5805      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5806      "confusing Date requirements for clients"
5807    </t>
5808  </list>
5809</t>
5810<t>
5811  Partly resolved issues:
5812  <list style="symbols"> 
5813    <t>
5814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5815      "Handling multiple Content-Length headers"
5816    </t>
5817  </list>
5818</t>
5819</section>
5820
5821<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5822<t>
5823  Closed issues:
5824  <list style="symbols">
5825    <t>
5826      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5827      "RFC2145 Normative"
5828    </t>
5829    <t>
5830      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5831      "define 'transparent' proxy"
5832    </t>
5833    <t>
5834      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5835      "Is * usable as a request-uri for new methods?"
5836    </t>
5837    <t>
5838      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5839      "Migrate Upgrade details from RFC2817"
5840    </t>
5841    <t>
5842      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5843      "untangle ABNFs for header fields"
5844    </t>
5845    <t>
5846      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5847      "update RFC 2109 reference"
5848    </t>
5849  </list>
5850</t>
5851</section>
5852
5853</section>
5854
5855</back>
5856</rfc>
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