source: draft-ietf-httpbis/latest/p1-messaging.xml @ 953

Last change on this file since 953 was 953, checked in by julian.reschke@…, 10 years ago

fix typo

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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 "July">
16  <!ENTITY ID-YEAR "2010">
17  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#errors.or.incomplete.response.cache.behavior' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' 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-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39]>
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="yes"?>
49<?rfc rfcedstyle="yes"?>
50<?rfc-ext allow-markup-in-artwork="yes" ?>
51<?rfc-ext include-references-in-index="yes" ?>
52<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
53     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
54     xmlns:x='http://purl.org/net/xml2rfc/ext'>
55<front>
56
57  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
58
59  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
60    <organization abbrev="Day Software">Day Software</organization>
61    <address>
62      <postal>
63        <street>23 Corporate Plaza DR, Suite 280</street>
64        <city>Newport Beach</city>
65        <region>CA</region>
66        <code>92660</code>
67        <country>USA</country>
68      </postal>
69      <phone>+1-949-706-5300</phone>
70      <facsimile>+1-949-706-5305</facsimile>
71      <email>fielding@gbiv.com</email>
72      <uri>http://roy.gbiv.com/</uri>
73    </address>
74  </author>
75
76  <author initials="J." surname="Gettys" fullname="Jim Gettys">
77    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
78    <address>
79      <postal>
80        <street>21 Oak Knoll Road</street>
81        <city>Carlisle</city>
82        <region>MA</region>
83        <code>01741</code>
84        <country>USA</country>
85      </postal>
86      <email>jg@freedesktop.org</email>
87      <uri>http://gettys.wordpress.com/</uri>
88    </address>
89  </author>
90 
91  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
92    <organization abbrev="HP">Hewlett-Packard Company</organization>
93    <address>
94      <postal>
95        <street>HP Labs, Large Scale Systems Group</street>
96        <street>1501 Page Mill Road, MS 1177</street>
97        <city>Palo Alto</city>
98        <region>CA</region>
99        <code>94304</code>
100        <country>USA</country>
101      </postal>
102      <email>JeffMogul@acm.org</email>
103    </address>
104  </author>
105
106  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
107    <organization abbrev="Microsoft">Microsoft Corporation</organization>
108    <address>
109      <postal>
110        <street>1 Microsoft Way</street>
111        <city>Redmond</city>
112        <region>WA</region>
113        <code>98052</code>
114        <country>USA</country>
115      </postal>
116      <email>henrikn@microsoft.com</email>
117    </address>
118  </author>
119
120  <author initials="L." surname="Masinter" fullname="Larry Masinter">
121    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
122    <address>
123      <postal>
124        <street>345 Park Ave</street>
125        <city>San Jose</city>
126        <region>CA</region>
127        <code>95110</code>
128        <country>USA</country>
129      </postal>
130      <email>LMM@acm.org</email>
131      <uri>http://larry.masinter.net/</uri>
132    </address>
133  </author>
134 
135  <author initials="P." surname="Leach" fullname="Paul J. Leach">
136    <organization abbrev="Microsoft">Microsoft Corporation</organization>
137    <address>
138      <postal>
139        <street>1 Microsoft Way</street>
140        <city>Redmond</city>
141        <region>WA</region>
142        <code>98052</code>
143      </postal>
144      <email>paulle@microsoft.com</email>
145    </address>
146  </author>
147   
148  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
149    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
150    <address>
151      <postal>
152        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
153        <street>The Stata Center, Building 32</street>
154        <street>32 Vassar Street</street>
155        <city>Cambridge</city>
156        <region>MA</region>
157        <code>02139</code>
158        <country>USA</country>
159      </postal>
160      <email>timbl@w3.org</email>
161      <uri>http://www.w3.org/People/Berners-Lee/</uri>
162    </address>
163  </author>
164
165  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
166    <organization abbrev="W3C">World Wide Web Consortium</organization>
167    <address>
168      <postal>
169        <street>W3C / ERCIM</street>
170        <street>2004, rte des Lucioles</street>
171        <city>Sophia-Antipolis</city>
172        <region>AM</region>
173        <code>06902</code>
174        <country>France</country>
175      </postal>
176      <email>ylafon@w3.org</email>
177      <uri>http://www.raubacapeu.net/people/yves/</uri>
178    </address>
179  </author>
180
181  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
182    <organization abbrev="greenbytes">greenbytes GmbH</organization>
183    <address>
184      <postal>
185        <street>Hafenweg 16</street>
186        <city>Muenster</city><region>NW</region><code>48155</code>
187        <country>Germany</country>
188      </postal>
189      <phone>+49 251 2807760</phone>
190      <facsimile>+49 251 2807761</facsimile>
191      <email>julian.reschke@greenbytes.de</email>
192      <uri>http://greenbytes.de/tech/webdav/</uri>
193    </address>
194  </author>
195
196  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
197  <workgroup>HTTPbis Working Group</workgroup>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypertext information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.10"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   request/response protocol that uses extensible semantics and MIME-like
232   message payloads for flexible interaction with network-based hypertext
233   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
234   standard <xref target="RFC3986"/> to indicate request targets and
235   relationships between resources.
236   Messages are passed in a format similar to that used by Internet mail
237   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
238   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
239   between HTTP and MIME messages).
240</t>
241<t>
242   HTTP is a generic interface protocol for information systems. It is
243   designed to hide the details of how a service is implemented by presenting
244   a uniform interface to clients that is independent of the types of
245   resources provided. Likewise, servers do not need to be aware of each
246   client's purpose: an HTTP request can be considered in isolation rather
247   than being associated with a specific type of client or a predetermined
248   sequence of application steps. The result is a protocol that can be used
249   effectively in many different contexts and for which implementations can
250   evolve independently over time.
251</t>
252<t>
253   HTTP is also designed for use as an intermediation protocol for translating
254   communication to and from non-HTTP information systems.
255   HTTP proxies and gateways can provide access to alternative information
256   services by translating their diverse protocols into a hypertext
257   format that can be viewed and manipulated by clients in the same way
258   as HTTP services.
259</t>
260<t>
261   One consequence of HTTP flexibility is that the protocol cannot be
262   defined in terms of what occurs behind the interface. Instead, we
263   are limited to defining the syntax of communication, the intent
264   of received communication, and the expected behavior of recipients.
265   If the communication is considered in isolation, then successful
266   actions should be reflected in corresponding changes to the
267   observable interface provided by servers. However, since multiple
268   clients might act in parallel and perhaps at cross-purposes, we
269   cannot require that such changes be observable beyond the scope
270   of a single response.
271</t>
272<t>
273   This document is Part 1 of the seven-part specification of HTTP,
274   defining the protocol referred to as "HTTP/1.1" and obsoleting
275   <xref target="RFC2616"/>.
276   Part 1 describes the architectural elements that are used or
277   referred to in HTTP, defines the "http" and "https" URI schemes,
278   describes overall network operation and connection management,
279   and defines HTTP message framing and forwarding requirements.
280   Our goal is to define all of the mechanisms necessary for HTTP message
281   handling that are independent of message semantics, thereby defining the
282   complete set of requirements for message parsers and
283   message-forwarding intermediaries.
284</t>
285
286<section title="Requirements" anchor="intro.requirements">
287<t>
288   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
289   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
290   document are to be interpreted as described in <xref target="RFC2119"/>.
291</t>
292<t>
293   An implementation is not compliant if it fails to satisfy one or more
294   of the "MUST" or "REQUIRED" level requirements for the protocols it
295   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
296   level and all the "SHOULD" level requirements for its protocols is said
297   to be "unconditionally compliant"; one that satisfies all the "MUST"
298   level requirements but not all the "SHOULD" level requirements for its
299   protocols is said to be "conditionally compliant".
300</t>
301</section>
302
303<section title="Syntax Notation" anchor="notation">
304<iref primary="true" item="Grammar" subitem="ALPHA"/>
305<iref primary="true" item="Grammar" subitem="CR"/>
306<iref primary="true" item="Grammar" subitem="CRLF"/>
307<iref primary="true" item="Grammar" subitem="CTL"/>
308<iref primary="true" item="Grammar" subitem="DIGIT"/>
309<iref primary="true" item="Grammar" subitem="DQUOTE"/>
310<iref primary="true" item="Grammar" subitem="HEXDIG"/>
311<iref primary="true" item="Grammar" subitem="LF"/>
312<iref primary="true" item="Grammar" subitem="OCTET"/>
313<iref primary="true" item="Grammar" subitem="SP"/>
314<iref primary="true" item="Grammar" subitem="VCHAR"/>
315<iref primary="true" item="Grammar" subitem="WSP"/>
316<t>
317   This specification uses the Augmented Backus-Naur Form (ABNF) notation
318   of <xref target="RFC5234"/>.
319</t>
320<t anchor="core.rules">
321  <x:anchor-alias value="ALPHA"/>
322  <x:anchor-alias value="CTL"/>
323  <x:anchor-alias value="CR"/>
324  <x:anchor-alias value="CRLF"/>
325  <x:anchor-alias value="DIGIT"/>
326  <x:anchor-alias value="DQUOTE"/>
327  <x:anchor-alias value="HEXDIG"/>
328  <x:anchor-alias value="LF"/>
329  <x:anchor-alias value="OCTET"/>
330  <x:anchor-alias value="SP"/>
331  <x:anchor-alias value="VCHAR"/>
332  <x:anchor-alias value="WSP"/>
333   The following core rules are included by
334   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
335   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
336   DIGIT (decimal 0-9), DQUOTE (double quote),
337   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
338   OCTET (any 8-bit sequence of data), SP (space),
339   VCHAR (any visible <xref target="USASCII"/> character),
340   and WSP (whitespace).
341</t>
342<t>
343   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
344   "obsolete" grammar rules that appear for historical reasons.
345</t>
346
347<section title="ABNF Extension: #rule" anchor="notation.abnf">
348<t>
349  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
350  improve readability.
351</t>
352<t>
353  A construct "#" is defined, similar to "*", for defining comma-delimited
354  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
355  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
356  comma (",") and optional whitespace (OWS,
357  <xref target="basic.rules"/>).   
358</t>
359<figure><preamble>
360  Thus,
361</preamble><artwork type="example">
362  1#element =&gt; element *( OWS "," OWS element )
363</artwork></figure>
364<figure><preamble>
365  and:
366</preamble><artwork type="example">
367  #element =&gt; [ 1#element ]
368</artwork></figure>
369<figure><preamble>
370  and for n &gt;= 1 and m &gt; 1:
371</preamble><artwork type="example">
372  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
373</artwork></figure>
374<t>
375  For compatibility with legacy list rules, recipients &SHOULD; accept empty
376  list elements. In other words, consumers would follow the list productions:
377</t>
378<figure><artwork type="example">
379  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
380 
381  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
382</artwork></figure>
383<t>
384  Note that empty elements do not contribute to the count of elements present,
385  though.
386</t>
387<t>
388  For example, given these ABNF productions:
389</t>
390<figure><artwork type="example">
391  example-list      = 1#example-list-elmt
392  example-list-elmt = token ; see <xref target="basic.rules"/> 
393</artwork></figure>
394<t>
395  Then these are valid values for example-list (not including the double
396  quotes, which are present for delimitation only):
397</t>
398<figure><artwork type="example">
399  "foo,bar"
400  " foo ,bar,"
401  "  foo , ,bar,charlie   "
402  "foo ,bar,   charlie "
403</artwork></figure>
404<t>
405  But these values would be invalid, as at least one non-empty element is
406  required:
407</t>
408<figure><artwork type="example">
409  ""
410  ","
411  ",   ,"
412</artwork></figure>
413<t>
414  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
415  expanded as explained above.
416</t>
417</section>
418
419<section title="Basic Rules" anchor="basic.rules">
420<t anchor="rule.CRLF">
421  <x:anchor-alias value="CRLF"/>
422   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
423   protocol elements other than the message-body
424   (see <xref target="tolerant.applications"/> for tolerant applications).
425</t>
426<t anchor="rule.LWS">
427   This specification uses three rules to denote the use of linear
428   whitespace: OWS (optional whitespace), RWS (required whitespace), and
429   BWS ("bad" whitespace).
430</t>
431<t>
432   The OWS rule is used where zero or more linear whitespace characters might
433   appear. OWS &SHOULD; either not be produced or be produced as a single SP
434   character. Multiple OWS characters that occur within field-content &SHOULD;
435   be replaced with a single SP before interpreting the field value or
436   forwarding the message downstream.
437</t>
438<t>
439   RWS is used when at least one linear whitespace character is required to
440   separate field tokens. RWS &SHOULD; be produced as a single SP character.
441   Multiple RWS characters that occur within field-content &SHOULD; be
442   replaced with a single SP before interpreting the field value or
443   forwarding the message downstream.
444</t>
445<t>
446   BWS is used where the grammar allows optional whitespace for historical
447   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
448   recipients &MUST; accept such bad optional whitespace and remove it before
449   interpreting the field value or forwarding the message downstream.
450</t>
451<t anchor="rule.whitespace">
452  <x:anchor-alias value="BWS"/>
453  <x:anchor-alias value="OWS"/>
454  <x:anchor-alias value="RWS"/>
455  <x:anchor-alias value="obs-fold"/>
456</t>
457<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"/>
458  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
459                 ; "optional" whitespace
460  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
461                 ; "required" whitespace
462  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
463                 ; "bad" whitespace
464  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
465                 ; see <xref target="header.fields"/>
466</artwork></figure>
467<t anchor="rule.token.separators">
468  <x:anchor-alias value="tchar"/>
469  <x:anchor-alias value="token"/>
470  <x:anchor-alias value="special"/>
471  <x:anchor-alias value="word"/>
472   Many HTTP/1.1 header field values consist of words (token or quoted-string)
473   separated by whitespace or special characters. These special characters
474   &MUST; be in a quoted string to be used within a parameter value (as defined
475   in <xref target="transfer.codings"/>).
476</t>
477<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"/>
478  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
479
480  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
481<!--
482  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
483 -->
484  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
485                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
486                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
487                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
488
489  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
490                 / ";" / ":" / "\" / DQUOTE / "/" / "["
491                 / "]" / "?" / "=" / "{" / "}"
492</artwork></figure>
493<t anchor="rule.quoted-string">
494  <x:anchor-alias value="quoted-string"/>
495  <x:anchor-alias value="qdtext"/>
496  <x:anchor-alias value="obs-text"/>
497   A string of text is parsed as a single word if it is quoted using
498   double-quote marks.
499</t>
500<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"/>
501  <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>
502  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
503                 ; <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> 
504  <x:ref>obs-text</x:ref>       = %x80-FF
505</artwork></figure>
506<t anchor="rule.quoted-pair">
507  <x:anchor-alias value="quoted-pair"/>
508   The backslash character ("\") can be used as a single-character
509   quoting mechanism within quoted-string constructs:
510</t>
511<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
512  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
513</artwork></figure>
514<t>
515   Producers &SHOULD-NOT; escape characters that do not require escaping
516   (i.e., other than DQUOTE and the backslash character).
517</t>
518</section>
519
520<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
521  <x:anchor-alias value="request-header"/>
522  <x:anchor-alias value="response-header"/>
523  <x:anchor-alias value="entity-header"/>
524  <x:anchor-alias value="Cache-Control"/>
525  <x:anchor-alias value="Pragma"/>
526  <x:anchor-alias value="Warning"/>
527  <x:anchor-alias value="MIME-Version"/>
528<t>
529  The ABNF rules below are defined in other parts:
530</t>
531<figure><!-- Part2--><artwork type="abnf2616">
532  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
533  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
534</artwork></figure>
535<figure><!-- Part3--><artwork type="abnf2616">
536  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
537  <x:ref>MIME-Version</x:ref>    = &lt;MIME-Version, defined in &header-mime-version;&gt;
538</artwork></figure>
539<figure><!-- Part6--><artwork type="abnf2616">
540  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
541  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
542  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
543</artwork></figure>
544</section>
545
546</section>
547</section>
548
549<section title="HTTP-related architecture" anchor="architecture">
550<t>
551   HTTP was created for the World Wide Web architecture
552   and has evolved over time to support the scalability needs of a worldwide
553   hypertext system. Much of that architecture is reflected in the terminology
554   and syntax productions used to define HTTP.
555</t>
556
557<section title="Client/Server Messaging" anchor="operation">
558<iref item="client"/>
559<iref item="server"/>
560<iref item="connection"/>
561<t>
562   HTTP is a stateless request/response protocol that operates by exchanging
563   messages across a reliable transport or session-layer connection. An HTTP
564   "client" is a program that establishes a connection to a server for the
565   purpose of sending one or more HTTP requests.  An HTTP "server" is a
566   program that accepts connections in order to service HTTP requests by
567   sending HTTP responses.
568</t>
569<iref item="user agent"/>
570<iref item="origin server"/>
571<t>
572   Note that the terms client and server refer only to the roles that
573   these programs perform for a particular connection.  The same program
574   might act as a client on some connections and a server on others.  We use
575   the term "user agent" to refer to the program that initiates a request,
576   such as a WWW browser, editor, or spider (web-traversing robot), and
577   the term "origin server" to refer to the program that can originate
578   authoritative responses to a request.
579</t>
580<t>
581   Most HTTP communication consists of a retrieval request (GET) for
582   a representation of some resource identified by a URI.  In the
583   simplest case, this might be accomplished via a single bidirectional
584   connection (===) between the user agent (UA) and the origin server (O).
585</t>
586<figure><artwork type="drawing">
587         request   &gt;
588    UA ======================================= O
589                                &lt;   response
590</artwork></figure>
591<iref item="message"/>
592<iref item="request"/>
593<iref item="response"/>
594<t>
595   A client sends an HTTP request to the server in the form of a request
596   message (<xref target="request"/>), beginning with a method, URI, and
597   protocol version, followed by MIME-like header fields containing
598   request modifiers, client information, and payload metadata, an empty
599   line to indicate the end of the header section, and finally the payload
600   body (if any).
601</t>
602<t>
603   A server responds to the client's request by sending an HTTP response
604   message (<xref target="response"/>), beginning with a status line that
605   includes the protocol version, a success or error code, and textual
606   reason phrase, followed by MIME-like header fields containing server
607   information, resource metadata, and payload metadata, an empty line to
608   indicate the end of the header section, and finally the payload body (if any).
609</t>
610<t>
611   The following example illustrates a typical message exchange for a
612   GET request on the URI "http://www.example.com/hello.txt":
613</t>
614<figure><preamble>
615client request:
616</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
617GET /hello.txt HTTP/1.1
618User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
619Host: www.example.com
620Accept: */*
621
622</artwork></figure>
623<figure><preamble>
624server response:
625</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
626HTTP/1.1 200 OK
627Date: Mon, 27 Jul 2009 12:28:53 GMT
628Server: Apache
629Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
630ETag: "34aa387-d-1568eb00"
631Accept-Ranges: bytes
632Content-Length: <x:length-of target="exbody"/>
633Vary: Accept-Encoding
634Content-Type: text/plain
635
636<x:span anchor="exbody">Hello World!
637</x:span></artwork></figure>
638</section>
639
640<section title="Intermediaries" anchor="intermediaries">
641<t>
642   A more complicated situation occurs when one or more intermediaries
643   are present in the request/response chain. There are three common
644   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
645   a single intermediary might act as an origin server, proxy, gateway,
646   or tunnel, switching behavior based on the nature of each request.
647</t>
648<figure><artwork type="drawing">
649         &gt;             &gt;             &gt;             &gt;
650    UA =========== A =========== B =========== C =========== O
651               &lt;             &lt;             &lt;             &lt;
652</artwork></figure>
653<t>
654   The figure above shows three intermediaries (A, B, and C) between the
655   user agent and origin server. A request or response message that
656   travels the whole chain will pass through four separate connections.
657   Some HTTP communication options
658   might apply only to the connection with the nearest, non-tunnel
659   neighbor, only to the end-points of the chain, or to all connections
660   along the chain. Although the diagram is linear, each participant might
661   be engaged in multiple, simultaneous communications. For example, B
662   might be receiving requests from many clients other than A, and/or
663   forwarding requests to servers other than C, at the same time that it
664   is handling A's request.
665</t>
666<t>
667<iref item="upstream"/><iref item="downstream"/>
668<iref item="inbound"/><iref item="outbound"/>
669   We use the terms "upstream" and "downstream" to describe various
670   requirements in relation to the directional flow of a message:
671   all messages flow from upstream to downstream.
672   Likewise, we use the terms "inbound" and "outbound" to refer to
673   directions in relation to the request path: "inbound" means toward
674   the origin server and "outbound" means toward the user agent.
675</t>
676<t><iref item="proxy"/>
677   A "proxy" is a message forwarding agent that is selected by the
678   client, usually via local configuration rules, to receive requests
679   for some type(s) of absolute URI and attempt to satisfy those
680   requests via translation through the HTTP interface.  Some translations
681   are minimal, such as for proxy requests for "http" URIs, whereas
682   other requests might require translation to and from entirely different
683   application-layer protocols. Proxies are often used to group an
684   organization's HTTP requests through a common intermediary for the
685   sake of security, annotation services, or shared caching.
686</t>
687<t><iref item="gateway"/><iref item="reverse proxy"/>
688   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
689   as a layer above some other server(s) and translates the received
690   requests to the underlying server's protocol.  Gateways are often
691   used for load balancing or partitioning HTTP services across
692   multiple machines.
693   Unlike a proxy, a gateway receives requests as if it were the
694   origin server for the requested resource; the requesting client
695   will not be aware that it is communicating with a gateway.
696   A gateway communicates with the client as if the gateway is the
697   origin server and thus is subject to all of the requirements on
698   origin servers for that connection.  A gateway communicates
699   with inbound servers using any protocol it desires, including
700   private extensions to HTTP that are outside the scope of this
701   specification.
702</t>
703<t><iref item="tunnel"/>
704   A "tunnel" acts as a blind relay between two connections
705   without changing the messages. Once active, a tunnel is not
706   considered a party to the HTTP communication, though the tunnel might
707   have been initiated by an HTTP request. A tunnel ceases to exist when
708   both ends of the relayed connection are closed. Tunnels are used to
709   extend a virtual connection through an intermediary, such as when
710   transport-layer security is used to establish private communication
711   through a shared firewall proxy.
712</t>
713</section>
714
715<section title="Caches" anchor="caches">
716<iref item="cache"/>
717<t>
718   A "cache" is a local store of previous response messages and the
719   subsystem that controls its message storage, retrieval, and deletion.
720   A cache stores cacheable responses in order to reduce the response
721   time and network bandwidth consumption on future, equivalent
722   requests. Any client or server &MAY; employ a cache, though a cache
723   cannot be used by a server while it is acting as a tunnel.
724</t>
725<t>
726   The effect of a cache is that the request/response chain is shortened
727   if one of the participants along the chain has a cached response
728   applicable to that request. The following illustrates the resulting
729   chain if B has a cached copy of an earlier response from O (via C)
730   for a request which has not been cached by UA or A.
731</t>
732<figure><artwork type="drawing">
733            &gt;             &gt;
734       UA =========== A =========== B - - - - - - C - - - - - - O
735                  &lt;             &lt;
736</artwork></figure>
737<t><iref item="cacheable"/>
738   A response is "cacheable" if a cache is allowed to store a copy of
739   the response message for use in answering subsequent requests.
740   Even when a response is cacheable, there might be additional
741   constraints placed by the client or by the origin server on when
742   that cached response can be used for a particular request. HTTP
743   requirements for cache behavior and cacheable responses are
744   defined in &caching-overview;
745</t>
746<t>
747   There are a wide variety of architectures and configurations
748   of caches and proxies deployed across the World Wide Web and
749   inside large organizations. These systems include national hierarchies
750   of proxy caches to save transoceanic bandwidth, systems that
751   broadcast or multicast cache entries, organizations that distribute
752   subsets of cached data via optical media, and so on.
753</t>
754</section>
755
756<section title="Transport Independence" anchor="transport-independence">
757<t>
758  HTTP systems are used in a wide variety of environments, from
759  corporate intranets with high-bandwidth links to long-distance
760  communication over low-power radio links and intermittent connectivity.
761</t>
762<t>
763   HTTP communication usually takes place over TCP/IP connections. The
764   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
765   not preclude HTTP from being implemented on top of any other protocol
766   on the Internet, or on other networks. HTTP only presumes a reliable
767   transport; any protocol that provides such guarantees can be used;
768   the mapping of the HTTP/1.1 request and response structures onto the
769   transport data units of the protocol in question is outside the scope
770   of this specification.
771</t>
772<t>
773   In HTTP/1.0, most implementations used a new connection for each
774   request/response exchange. In HTTP/1.1, a connection might be used for
775   one or more request/response exchanges, although connections might be
776   closed for a variety of reasons (see <xref target="persistent.connections"/>).
777</t>
778</section>
779
780<section title="HTTP Version" anchor="http.version">
781  <x:anchor-alias value="HTTP-Version"/>
782  <x:anchor-alias value="HTTP-Prot-Name"/>
783<t>
784   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
785   of the protocol. The protocol versioning policy is intended to allow
786   the sender to indicate the format of a message and its capacity for
787   understanding further HTTP communication, rather than the features
788   obtained via that communication. No change is made to the version
789   number for the addition of message components which do not affect
790   communication behavior or which only add to extensible field values.
791   The &lt;minor&gt; number is incremented when the changes made to the
792   protocol add features which do not change the general message parsing
793   algorithm, but which might add to the message semantics and imply
794   additional capabilities of the sender. The &lt;major&gt; number is
795   incremented when the format of a message within the protocol is
796   changed. See <xref target="RFC2145"/> for a fuller explanation.
797</t>
798<t>
799   The version of an HTTP message is indicated by an HTTP-Version field
800   in the first line of the message. HTTP-Version is case-sensitive.
801</t>
802<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
803  <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>
804  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
805</artwork></figure>
806<t>
807   Note that the major and minor numbers &MUST; be treated as separate
808   integers and that each &MAY; be incremented higher than a single digit.
809   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
810   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
811   &MUST-NOT; be sent.
812</t>
813<t>
814   An application that sends a request or response message that includes
815   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
816   with this specification. Applications that are at least conditionally
817   compliant with this specification &SHOULD; use an HTTP-Version of
818   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
819   not compatible with HTTP/1.0. For more details on when to send
820   specific HTTP-Version values, see <xref target="RFC2145"/>.
821</t>
822<t>
823   The HTTP version of an application is the highest HTTP version for
824   which the application is at least conditionally compliant.
825</t>
826<t>
827   Proxy and gateway applications need to be careful when forwarding
828   messages in protocol versions different from that of the application.
829   Since the protocol version indicates the protocol capability of the
830   sender, a proxy/gateway &MUST-NOT; send a message with a version
831   indicator which is greater than its actual version. If a higher
832   version request is received, the proxy/gateway &MUST; either downgrade
833   the request version, or respond with an error, or switch to tunnel
834   behavior.
835</t>
836<t>
837   Due to interoperability problems with HTTP/1.0 proxies discovered
838   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
839   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
840   they support. The proxy/gateway's response to that request &MUST; be in
841   the same major version as the request.
842</t>
843<x:note>
844  <t>
845    <x:h>Note:</x:h> Converting between versions of HTTP might involve modification
846    of header fields required or forbidden by the versions involved.
847  </t>
848</x:note>
849</section>
850
851<section title="Uniform Resource Identifiers" anchor="uri">
852<iref primary="true" item="resource"/>
853<t>
854   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
855   throughout HTTP as the means for identifying resources. URI references
856   are used to target requests, indicate redirects, and define relationships.
857   HTTP does not limit what a resource might be; it merely defines an interface
858   that can be used to interact with a resource via HTTP. More information on
859   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
860</t>
861  <x:anchor-alias value="URI-reference"/>
862  <x:anchor-alias value="absolute-URI"/>
863  <x:anchor-alias value="relative-part"/>
864  <x:anchor-alias value="authority"/>
865  <x:anchor-alias value="path-abempty"/>
866  <x:anchor-alias value="path-absolute"/>
867  <x:anchor-alias value="port"/>
868  <x:anchor-alias value="query"/>
869  <x:anchor-alias value="uri-host"/>
870  <x:anchor-alias value="partial-URI"/>
871<t>
872   This specification adopts the definitions of "URI-reference",
873   "absolute-URI", "relative-part", "port", "host",
874   "path-abempty", "path-absolute", "query", and "authority" from
875   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
876   protocol elements that allow a relative URI without a fragment.
877</t>
878<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"/>
879  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
880  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
881  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
882  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
883  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
884  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
885  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
886  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
887  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
888 
889  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
890</artwork></figure>
891<t>
892   Each protocol element in HTTP that allows a URI reference will indicate in
893   its ABNF production whether the element allows only a URI in absolute form
894   (absolute-URI), any relative reference (relative-ref), or some other subset
895   of the URI-reference grammar. Unless otherwise indicated, URI references
896   are parsed relative to the request target (the default base URI for both
897   the request and its corresponding response).
898</t>
899
900<section title="http URI scheme" anchor="http.uri">
901  <x:anchor-alias value="http-URI"/>
902  <iref item="http URI scheme" primary="true"/>
903  <iref item="URI scheme" subitem="http" primary="true"/>
904<t>
905   The "http" URI scheme is hereby defined for the purpose of minting
906   identifiers according to their association with the hierarchical
907   namespace governed by a potential HTTP origin server listening for
908   TCP connections on a given port.
909   The HTTP server is identified via the generic syntax's
910   <x:ref>authority</x:ref> component, which includes a host
911   identifier and optional TCP port, and the remainder of the URI is
912   considered to be identifying data corresponding to a resource for
913   which that server might provide an HTTP interface.
914</t>
915<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
916  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
917</artwork></figure>
918<t>
919   The host identifier within an <x:ref>authority</x:ref> component is
920   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
921   provided as an IP literal or IPv4 address, then the HTTP server is any
922   listener on the indicated TCP port at that IP address. If host is a
923   registered name, then that name is considered an indirect identifier
924   and the recipient might use a name resolution service, such as DNS,
925   to find the address of a listener for that host.
926   The host &MUST-NOT; be empty; if an "http" URI is received with an
927   empty host, then it &MUST; be rejected as invalid.
928   If the port subcomponent is empty or not given, then TCP port 80 is
929   assumed (the default reserved port for WWW services).
930</t>
931<t>
932   Regardless of the form of host identifier, access to that host is not
933   implied by the mere presence of its name or address. The host might or might
934   not exist and, even when it does exist, might or might not be running an
935   HTTP server or listening to the indicated port. The "http" URI scheme
936   makes use of the delegated nature of Internet names and addresses to
937   establish a naming authority (whatever entity has the ability to place
938   an HTTP server at that Internet name or address) and allows that
939   authority to determine which names are valid and how they might be used.
940</t>
941<t>
942   When an "http" URI is used within a context that calls for access to the
943   indicated resource, a client &MAY; attempt access by resolving
944   the host to an IP address, establishing a TCP connection to that address
945   on the indicated port, and sending an HTTP request message to the server
946   containing the URI's identifying data as described in <xref target="request"/>.
947   If the server responds to that request with a non-interim HTTP response
948   message, as described in <xref target="response"/>, then that response
949   is considered an authoritative answer to the client's request.
950</t>
951<t>
952   Although HTTP is independent of the transport protocol, the "http"
953   scheme is specific to TCP-based services because the name delegation
954   process depends on TCP for establishing authority.
955   An HTTP service based on some other underlying connection protocol
956   would presumably be identified using a different URI scheme, just as
957   the "https" scheme (below) is used for servers that require an SSL/TLS
958   transport layer on a connection. Other protocols might also be used to
959   provide access to "http" identified resources --- it is only the
960   authoritative interface used for mapping the namespace that is
961   specific to TCP.
962</t>
963<t>
964   The URI generic syntax for authority also includes a deprecated
965   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
966   for including user authentication information in the URI.  The userinfo
967   subcomponent (and its "@" delimiter) &MUST-NOT; be used in an "http"
968   URI.  URI reference recipients &SHOULD; parse for the existence of
969   userinfo and treat its presence as an error, likely indicating that
970   the deprecated subcomponent is being used to obscure the authority
971   for the sake of phishing attacks.
972</t>
973</section>
974
975<section title="https URI scheme" anchor="https.uri">
976   <x:anchor-alias value="https-URI"/>
977   <iref item="https URI scheme"/>
978   <iref item="URI scheme" subitem="https"/>
979<t>
980   The "https" URI scheme is hereby defined for the purpose of minting
981   identifiers according to their association with the hierarchical
982   namespace governed by a potential HTTP origin server listening for
983   SSL/TLS-secured connections on a given TCP port.
984</t>
985<t>
986   All of the requirements listed above for the "http" scheme are also
987   requirements for the "https" scheme, except that a default TCP port
988   of 443 is assumed if the port subcomponent is empty or not given,
989   and the TCP connection &MUST; be secured for privacy through the
990   use of strong encryption prior to sending the first HTTP request.
991</t>
992<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
993  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
994</artwork></figure>
995<t>
996   Unlike the "http" scheme, responses to "https" identified requests
997   are never "public" and thus are ineligible for shared caching.
998   Their default is "private" and might be further constrained via use
999   of the Cache-Control header field.
1000</t>
1001<t>
1002   Resources made available via the "https" scheme have no shared
1003   identity with the "http" scheme even if their resource identifiers
1004   only differ by the single "s" in the scheme name.  They are
1005   different services governed by different authorities.  However,
1006   some extensions to HTTP that apply to entire host domains, such
1007   as the Cookie protocol, do allow one service to effect communication
1008   with the other services based on host domain matching.
1009</t>
1010<t>
1011   The process for authoritative access to an "https" identified
1012   resource is defined in <xref target="RFC2818"/>.
1013</t>
1014</section>
1015
1016<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1017<t>
1018   Since the "http" and "https" schemes conform to the URI generic syntax,
1019   such URIs are normalized and compared according to the algorithm defined
1020   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1021   described above for each scheme.
1022</t>
1023<t>
1024   If the port is equal to the default port for a scheme, the normal
1025   form is to elide the port subcomponent. Likewise, an empty path
1026   component is equivalent to an absolute path of "/", so the normal
1027   form is to provide a path of "/" instead. The scheme and host
1028   are case-insensitive and normally provided in lowercase; all
1029   other components are compared in a case-sensitive manner.
1030   Characters other than those in the "reserved" set are equivalent
1031   to their percent-encoded octets (see <xref target="RFC3986"
1032   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1033</t>
1034<t>
1035   For example, the following three URIs are equivalent:
1036</t>
1037<figure><artwork type="example">
1038   http://example.com:80/~smith/home.html
1039   http://EXAMPLE.com/%7Esmith/home.html
1040   http://EXAMPLE.com:/%7esmith/home.html
1041</artwork></figure>
1042<t>
1043   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1044   If path-abempty is the empty string (i.e., there is no slash "/"
1045   path separator following the authority), then the "http" URI
1046   &MUST; be given as "/" when
1047   used as a request-target (<xref target="request-target"/>). If a proxy
1048   receives a host name which is not a fully qualified domain name, it
1049   &MAY; add its domain to the host name it received. If a proxy receives
1050   a fully qualified domain name, the proxy &MUST-NOT; change the host
1051   name.
1052</t>
1053</section>
1054</section>
1055</section>
1056
1057<section title="HTTP Message" anchor="http.message">
1058<x:anchor-alias value="generic-message"/>
1059<x:anchor-alias value="message.types"/>
1060<x:anchor-alias value="HTTP-message"/>
1061<x:anchor-alias value="start-line"/>
1062<iref item="header section"/>
1063<iref item="headers"/>
1064<iref item="header field"/>
1065<t>
1066   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1067   characters in a format similar to the Internet Message Format
1068   <xref target="RFC5322"/>: zero or more header fields (collectively
1069   referred to as the "headers" or the "header section"), an empty line
1070   indicating the end of the header section, and an optional message-body.
1071</t>
1072<t>
1073   An HTTP message can either be a request from client to server or a
1074   response from server to client.  Syntactically, the two types of message
1075   differ only in the start-line, which is either a Request-Line (for requests)
1076   or a Status-Line (for responses), and in the algorithm for determining
1077   the length of the message-body (<xref target="message.body"/>).
1078   In theory, a client could receive requests and a server could receive
1079   responses, distinguishing them by their different start-line formats,
1080   but in practice servers are implemented to only expect a request
1081   (a response is interpreted as an unknown or invalid request method)
1082   and clients are implemented to only expect a response.
1083</t>
1084<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1085  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1086                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1087                    <x:ref>CRLF</x:ref>
1088                    [ <x:ref>message-body</x:ref> ]
1089  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1090</artwork></figure>
1091<t>
1092   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1093   header field. The presence of whitespace might be an attempt to trick a
1094   noncompliant implementation of HTTP into ignoring that field or processing
1095   the next line as a new request, either of which might result in security
1096   issues when implementations within the request chain interpret the
1097   same message differently. HTTP/1.1 servers &MUST; reject such a message
1098   with a 400 (Bad Request) response.
1099</t>
1100
1101<section title="Message Parsing Robustness" anchor="message.robustness">
1102<t>
1103   In the interest of robustness, servers &SHOULD; ignore at least one
1104   empty line received where a Request-Line is expected. In other words, if
1105   the server is reading the protocol stream at the beginning of a
1106   message and receives a CRLF first, it should ignore the CRLF.
1107</t>
1108<t>
1109   Some old HTTP/1.0 client implementations generate an extra CRLF
1110   after a POST request as a lame workaround for some early server
1111   applications that failed to read message-body content that was
1112   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1113   preface or follow a request with an extra CRLF.  If terminating
1114   the request message-body with a line-ending is desired, then the
1115   client &MUST; include the terminating CRLF octets as part of the
1116   message-body length.
1117</t>
1118<t>
1119   The normal procedure for parsing an HTTP message is to read the
1120   start-line into a structure, read each header field into a hash
1121   table by field name until the empty line, and then use the parsed
1122   data to determine if a message-body is expected.  If a message-body
1123   has been indicated, then it is read as a stream until an amount
1124   of octets equal to the message-body length is read or the connection
1125   is closed.  Care must be taken to parse an HTTP message as a sequence
1126   of octets in an encoding that is a superset of US-ASCII.  Attempting
1127   to parse HTTP as a stream of Unicode characters in a character encoding
1128   like UTF-16 might introduce security flaws due to the differing ways
1129   that such parsers interpret invalid characters.
1130</t>
1131</section>
1132
1133<section title="Header Fields" anchor="header.fields">
1134  <x:anchor-alias value="header-field"/>
1135  <x:anchor-alias value="field-content"/>
1136  <x:anchor-alias value="field-name"/>
1137  <x:anchor-alias value="field-value"/>
1138  <x:anchor-alias value="OWS"/>
1139<t>
1140   Each HTTP header field consists of a case-insensitive field name
1141   followed by a colon (":"), optional whitespace, and the field value.
1142</t>
1143<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"/>
1144  <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>
1145  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1146  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1147  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1148</artwork></figure>
1149<t>
1150   No whitespace is allowed between the header field name and colon. For
1151   security reasons, any request message received containing such whitespace
1152   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1153   &MUST; remove any such whitespace from a response message before
1154   forwarding the message downstream.
1155</t>
1156<t>
1157   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1158   preferred. The field value does not include any leading or trailing white
1159   space: OWS occurring before the first non-whitespace character of the
1160   field value or after the last non-whitespace character of the field value
1161   is ignored and &SHOULD; be removed before further processing (as this does
1162   not change the meaning of the header field).
1163</t>
1164<t>
1165   The order in which header fields with differing field names are
1166   received is not significant. However, it is "good practice" to send
1167   header fields that contain control data first, such as Host on
1168   requests and Date on responses, so that implementations can decide
1169   when not to handle a message as early as possible.  A server &MUST;
1170   wait until the entire header section is received before interpreting
1171   a request message, since later header fields might include conditionals,
1172   authentication credentials, or deliberately misleading duplicate
1173   header fields that would impact request processing.
1174</t>
1175<t>
1176   Multiple header fields with the same field name &MUST-NOT; be
1177   sent in a message unless the entire field value for that
1178   header field is defined as a comma-separated list [i.e., #(values)].
1179   Multiple header fields with the same field name can be combined into
1180   one "field-name: field-value" pair, without changing the semantics of the
1181   message, by appending each subsequent field value to the combined
1182   field value in order, separated by a comma. The order in which
1183   header fields with the same field name are received is therefore
1184   significant to the interpretation of the combined field value;
1185   a proxy &MUST-NOT; change the order of these field values when
1186   forwarding a message.
1187</t>
1188<x:note>
1189  <t>
1190   <x:h>Note:</x:h> The "Set-Cookie" header as implemented in
1191   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1192   can occur multiple times, but does not use the list syntax, and thus cannot
1193   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1194   for details.) Also note that the Set-Cookie2 header specified in
1195   <xref target="RFC2965"/> does not share this problem.
1196  </t>
1197</x:note>
1198<t>
1199   Historically, HTTP header field values could be extended over multiple
1200   lines by preceding each extra line with at least one space or horizontal
1201   tab character (line folding). This specification deprecates such line
1202   folding except within the message/http media type
1203   (<xref target="internet.media.type.message.http"/>).
1204   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1205   (i.e., that contain any field-content that matches the obs-fold rule) unless
1206   the message is intended for packaging within the message/http media type.
1207   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1208   obs-fold whitespace with a single SP prior to interpreting the field value
1209   or forwarding the message downstream.
1210</t>
1211<t>
1212   Historically, HTTP has allowed field content with text in the ISO-8859-1
1213   <xref target="ISO-8859-1"/> character encoding and supported other
1214   character sets only through use of <xref target="RFC2047"/> encoding.
1215   In practice, most HTTP header field values use only a subset of the
1216   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1217   header fields &SHOULD; limit their field values to US-ASCII characters.
1218   Recipients &SHOULD; treat other (obs-text) octets in field content as
1219   opaque data.
1220</t>
1221<t anchor="rule.comment">
1222  <x:anchor-alias value="comment"/>
1223  <x:anchor-alias value="ctext"/>
1224   Comments can be included in some HTTP header fields by surrounding
1225   the comment text with parentheses. Comments are only allowed in
1226   fields containing "comment" as part of their field value definition.
1227</t>
1228<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1229  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1230  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1231                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1232</artwork></figure>
1233<t anchor="rule.quoted-cpair">
1234  <x:anchor-alias value="quoted-cpair"/>
1235   The backslash character ("\") can be used as a single-character
1236   quoting mechanism within comment constructs:
1237</t>
1238<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1239  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1240</artwork></figure>
1241<t>
1242   Producers &SHOULD-NOT; escape characters that do not require escaping
1243   (i.e., other than the backslash character "\" and the parentheses "(" and
1244   ")").
1245</t>
1246</section>
1247
1248<section title="Message Body" anchor="message.body">
1249  <x:anchor-alias value="message-body"/>
1250<t>
1251   The message-body (if any) of an HTTP message is used to carry the
1252   payload body associated with the request or response. The message-body
1253   differs from the payload body only when a transfer-coding has been
1254   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1255</t>
1256<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1257  <x:ref>message-body</x:ref> = *OCTET
1258</artwork></figure>
1259<t>
1260   When one or more transfer-codings are applied to a payload body,
1261   usually for the sake of stream-delimiting or data compression, the
1262   Transfer-Encoding header field &MUST; be provided with the list of
1263   transfer-codings applied. Transfer-Encoding is a property of the message,
1264   not of the payload, and thus &MAY; be added or removed by any implementation
1265   along the request/response chain under the constraints found in
1266   <xref target="transfer.codings"/>.
1267</t>
1268<t>
1269   The rules for when a message-body is allowed in a message differ for
1270   requests and responses.
1271</t>
1272<t>
1273   The presence of a message-body in a request is signaled by the
1274   inclusion of a Content-Length or Transfer-Encoding header field in
1275   the request's header fields, even if the request method does not
1276   define any use for a message-body.  This allows the request
1277   message framing algorithm to be independent of method semantics.
1278   A server &MUST; read the entire request message-body or close
1279   the connection after sending its response.
1280</t>
1281<t>
1282   For response messages, whether or not a message-body is included with
1283   a message is dependent on both the request method and the response
1284   status code (<xref target="status.code.and.reason.phrase"/>).
1285   Responses to the HEAD request method never include a message-body
1286   because the associated response header fields (e.g., Transfer-Encoding,
1287   Content-Length, etc.) only indicate what their values would have been
1288   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1289   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1290   All other responses do include a message-body, although the body
1291   &MAY; be of zero length.
1292</t>
1293<t>
1294   The length of the message-body is determined by one of the following
1295   (in order of precedence):
1296</t>
1297<t>
1298  <list style="numbers">
1299    <x:lt><t>
1300     Any response to a HEAD request and any response with a status
1301     code of 100-199, 204, or 304 is always terminated by the first
1302     empty line after the header fields, regardless of the header
1303     fields present in the message, and thus cannot contain a message-body.
1304    </t></x:lt>
1305    <x:lt><t>
1306     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1307     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1308     is used, the message-body length is determined by reading and decoding the
1309     chunked data until the transfer-coding indicates the data is complete.
1310    </t>
1311    <t>
1312     If a message is received with both a Transfer-Encoding header field and a
1313     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1314     Such a message might indicate an attempt to perform request or response
1315     smuggling (bypass of security-related checks on message routing or content)
1316     and thus should be handled as an error.  The provided Content-Length &MUST;
1317     be removed, prior to forwarding the message downstream, or replaced with
1318     the real message-body length after the transfer-coding is decoded.
1319    </t>
1320    <t>
1321     If a Transfer-Encoding header field is present in a response and the
1322     "chunked" transfer-coding is not present, the message-body length is
1323     determined by reading the connection until it is closed by the server.
1324     If a Transfer-Encoding header field is present in a request and the
1325     "chunked" transfer-coding is not the final encoding, the message-body
1326     length cannot be determined reliably; the server &MUST; respond with
1327     400 (Bad Request) and then close the connection.
1328    </t></x:lt>
1329    <x:lt><t>
1330     If a valid Content-Length header field (<xref target="header.content-length"/>)
1331     is present without Transfer-Encoding, its decimal value in octets defines
1332     the message-body length.  If the actual number of octets sent in the message
1333     is less than the indicated Content-Length, the recipient &MUST; consider
1334     the message to be incomplete and treat the connection as no longer usable.
1335     If the actual number of octets sent in the message is less than the indicated
1336     Content-Length, the recipient &MUST; only process the message-body up to the
1337     field value's number of octets; the remainder of the message &MUST; either
1338     be discarded or treated as the next message in a pipeline.  For the sake of
1339     robustness, a user-agent &MAY; attempt to detect and correct such an error
1340     in message framing if it is parsing the response to the last request on
1341     on a connection and the connection has been closed by the server.
1342    </t>
1343    <t>
1344     If a message is received with multiple Content-Length header fields or a
1345     Content-Length header field with an invalid value, the message framing
1346     is invalid and &MUST; be treated as an error to prevent request or
1347     response smuggling.
1348     If this is a request message, the server &MUST; respond with
1349     a 400 (Bad Request) status code and then close the connection.
1350     If this is a response message received by a proxy or gateway, the proxy
1351     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1352     status code as its downstream response, and then close the connection.
1353     If this is a response message received by a user-agent, the message-body
1354     length is determined by reading the connection until it is closed;
1355     an error &SHOULD; be indicated to the user.
1356    </t></x:lt>
1357    <x:lt><t>
1358     If this is a request message and none of the above are true, then the
1359     message-body length is zero (no message-body is present).
1360    </t></x:lt>
1361    <x:lt><t>
1362     Otherwise, this is a response message without a declared message-body
1363     length, so the message-body length is determined by the number of octets
1364     received prior to the server closing the connection.
1365    </t></x:lt>
1366  </list>
1367</t>
1368<t>
1369   Since there is no way to distinguish a successfully completed,
1370   close-delimited message from a partially-received message interrupted
1371   by network failure, implementations &SHOULD; use encoding or
1372   length-delimited messages whenever possible.  The close-delimiting
1373   feature exists primarily for backwards compatibility with HTTP/1.0.
1374</t>
1375<t>
1376   A server &MAY; reject a request that contains a message-body but
1377   not a Content-Length by responding with 411 (Length Required).
1378</t>
1379<t>
1380   Unless a transfer-coding other than "chunked" has been applied,
1381   a client that sends a request containing a message-body &SHOULD;
1382   use a valid Content-Length header field if the message-body length
1383   is known in advance, rather than the "chunked" encoding, since some
1384   existing services respond to "chunked" with a 411 (Length Required)
1385   status code even though they understand the chunked encoding.  This
1386   is typically because such services are implemented via a gateway that
1387   requires a content-length in advance of being called and the server
1388   is unable or unwilling to buffer the entire request before processing.
1389</t>
1390<t>
1391   A client that sends a request containing a message-body &MUST; include a
1392   valid Content-Length header field if it does not know the server will
1393   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1394   of specific user configuration or by remembering the version of a prior
1395   received response.
1396</t>
1397<t>
1398   Request messages that are prematurely terminated, possibly due to a
1399   cancelled connection or a server-imposed time-out exception, &MUST;
1400   result in closure of the connection; sending an HTTP/1.1 error response
1401   prior to closing the connection is &OPTIONAL;.
1402   Response messages that are prematurely terminated, usually by closure
1403   of the connection prior to receiving the expected number of octets or by
1404   failure to decode a transfer-encoded message-body, &MUST; be recorded
1405   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1406   message-body as if it were complete (i.e., some indication must be given
1407   to the user that an error occurred).  Cache requirements for incomplete
1408   responses are defined in &cache-incomplete;.
1409</t>
1410</section>
1411
1412<section title="General Header Fields" anchor="general.header.fields">
1413  <x:anchor-alias value="general-header"/>
1414<t>
1415   There are a few header fields which have general applicability for
1416   both request and response messages, but which do not apply to the
1417   payload being transferred. These header fields apply only to the
1418   message being transmitted.
1419</t>
1420<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1421  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1422                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1423                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1424                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1425                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1426                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1427                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1428                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1429                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1430                 / <x:ref>MIME-Version</x:ref>             ; &header-mime-version;
1431</artwork></figure>
1432<t>
1433   General-header field names can be extended reliably only in
1434   combination with a change in the protocol version. However, new or
1435   experimental header fields might be given the semantics of general
1436   header fields if all parties in the communication recognize them to
1437   be general-header fields. Unrecognized header fields are treated as
1438   entity-header fields.
1439</t>
1440</section>
1441</section>
1442
1443<section title="Request" anchor="request">
1444  <x:anchor-alias value="Request"/>
1445<t>
1446   A request message from a client to a server includes, within the
1447   first line of that message, the method to be applied to the resource,
1448   the identifier of the resource, and the protocol version in use.
1449</t>
1450<!--                 Host                      ; should be moved here eventually -->
1451<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1452  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1453                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1454                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1455                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1456                  <x:ref>CRLF</x:ref>
1457                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1458</artwork></figure>
1459
1460<section title="Request-Line" anchor="request-line">
1461  <x:anchor-alias value="Request-Line"/>
1462<t>
1463   The Request-Line begins with a method token, followed by the
1464   request-target and the protocol version, and ending with CRLF. The
1465   elements are separated by SP characters. No CR or LF is allowed
1466   except in the final CRLF sequence.
1467</t>
1468<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1469  <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>
1470</artwork></figure>
1471
1472<section title="Method" anchor="method">
1473  <x:anchor-alias value="Method"/>
1474<t>
1475   The Method  token indicates the method to be performed on the
1476   resource identified by the request-target. The method is case-sensitive.
1477</t>
1478<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1479  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1480</artwork></figure>
1481</section>
1482
1483<section title="request-target" anchor="request-target">
1484  <x:anchor-alias value="request-target"/>
1485<t>
1486   The request-target
1487   identifies the resource upon which to apply the request.
1488</t>
1489<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1490  <x:ref>request-target</x:ref> = "*"
1491                 / <x:ref>absolute-URI</x:ref>
1492                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1493                 / <x:ref>authority</x:ref>
1494</artwork></figure>
1495<t>
1496   The four options for request-target are dependent on the nature of the
1497   request.
1498</t>   
1499<t>
1500   The asterisk "*" means that the request does not apply to a
1501   particular resource, but to the server itself, and is only allowed
1502   when the method used does not necessarily apply to a resource. One
1503   example would be
1504</t>
1505<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1506OPTIONS * HTTP/1.1
1507</artwork></figure>
1508<t>
1509   The absolute-URI form is &REQUIRED; when the request is being made to a
1510   proxy. The proxy is requested to forward the request or service it
1511   from a valid cache, and return the response. Note that the proxy &MAY;
1512   forward the request on to another proxy or directly to the server
1513   specified by the absolute-URI. In order to avoid request loops, a
1514   proxy &MUST; be able to recognize all of its server names, including
1515   any aliases, local variations, and the numeric IP address. An example
1516   Request-Line would be:
1517</t>
1518<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1519GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1520</artwork></figure>
1521<t>
1522   To allow for transition to absolute-URIs in all requests in future
1523   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1524   form in requests, even though HTTP/1.1 clients will only generate
1525   them in requests to proxies.
1526</t>
1527<t>
1528   The authority form is only used by the CONNECT method (&CONNECT;).
1529</t>
1530<t>
1531   The most common form of request-target is that used to identify a
1532   resource on an origin server or gateway. In this case the absolute
1533   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1534   the request-target, and the network location of the URI (authority) &MUST;
1535   be transmitted in a Host header field. For example, a client wishing
1536   to retrieve the resource above directly from the origin server would
1537   create a TCP connection to port 80 of the host "www.example.org" and send
1538   the lines:
1539</t>
1540<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1541GET /pub/WWW/TheProject.html HTTP/1.1
1542Host: www.example.org
1543</artwork></figure>
1544<t>
1545   followed by the remainder of the Request. Note that the absolute path
1546   cannot be empty; if none is present in the original URI, it &MUST; be
1547   given as "/" (the server root).
1548</t>
1549<t>
1550   If a proxy receives a request without any path in the request-target and
1551   the method specified is capable of supporting the asterisk form of
1552   request-target, then the last proxy on the request chain &MUST; forward the
1553   request with "*" as the final request-target.
1554</t>
1555<figure><preamble>   
1556   For example, the request
1557</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1558OPTIONS http://www.example.org:8001 HTTP/1.1
1559</artwork></figure>
1560<figure><preamble>   
1561  would be forwarded by the proxy as
1562</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1563OPTIONS * HTTP/1.1
1564Host: www.example.org:8001
1565</artwork>
1566<postamble>
1567   after connecting to port 8001 of host "www.example.org".
1568</postamble>
1569</figure>
1570<t>
1571   The request-target is transmitted in the format specified in
1572   <xref target="http.uri"/>. If the request-target is percent-encoded
1573   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1574   &MUST; decode the request-target in order to
1575   properly interpret the request. Servers &SHOULD; respond to invalid
1576   request-targets with an appropriate status code.
1577</t>
1578<t>
1579   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1580   received request-target when forwarding it to the next inbound server,
1581   except as noted above to replace a null path-absolute with "/" or "*".
1582</t>
1583<x:note>
1584  <t>
1585    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1586    meaning of the request when the origin server is improperly using
1587    a non-reserved URI character for a reserved purpose.  Implementors
1588    should be aware that some pre-HTTP/1.1 proxies have been known to
1589    rewrite the request-target.
1590  </t>
1591</x:note>
1592<t>
1593   HTTP does not place a pre-defined limit on the length of a request-target.
1594   A server &MUST; be prepared to receive URIs of unbounded length and
1595   respond with the 414 (URI Too Long) status code if the received
1596   request-target would be longer than the server wishes to handle
1597   (see &status-414;).
1598</t>
1599<t>
1600   Various ad-hoc limitations on request-target length are found in practice.
1601   It is &RECOMMENDED; that all HTTP senders and recipients support
1602   request-target lengths of 8000 or more octets.
1603</t>
1604<x:note>
1605  <t>
1606    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1607    are not part of the request-target and thus will not be transmitted
1608    in an HTTP request.
1609  </t>
1610</x:note>
1611</section>
1612</section>
1613
1614<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1615<t>
1616   The exact resource identified by an Internet request is determined by
1617   examining both the request-target and the Host header field.
1618</t>
1619<t>
1620   An origin server that does not allow resources to differ by the
1621   requested host &MAY; ignore the Host header field value when
1622   determining the resource identified by an HTTP/1.1 request. (But see
1623   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1624   for other requirements on Host support in HTTP/1.1.)
1625</t>
1626<t>
1627   An origin server that does differentiate resources based on the host
1628   requested (sometimes referred to as virtual hosts or vanity host
1629   names) &MUST; use the following rules for determining the requested
1630   resource on an HTTP/1.1 request:
1631  <list style="numbers">
1632    <t>If request-target is an absolute-URI, the host is part of the
1633     request-target. Any Host header field value in the request &MUST; be
1634     ignored.</t>
1635    <t>If the request-target is not an absolute-URI, and the request includes
1636     a Host header field, the host is determined by the Host header
1637     field value.</t>
1638    <t>If the host as determined by rule 1 or 2 is not a valid host on
1639     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1640  </list>
1641</t>
1642<t>
1643   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1644   attempt to use heuristics (e.g., examination of the URI path for
1645   something unique to a particular host) in order to determine what
1646   exact resource is being requested.
1647</t>
1648</section>
1649
1650<section title="Effective Request URI" anchor="effective.request.uri">
1651  <iref primary="true" item="Effective Request URI"/>
1652<t>
1653   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1654   for the resource they are intended for; instead, the value needs to be inferred from the
1655   request-target, Host header and other context. The result of this process is
1656   the "Effective Request URI".
1657</t>
1658<t>
1659   If the request-target is an absolute-URI, then the Effective Request URI is
1660   the request-target.
1661</t>
1662<t>
1663   If the request-target uses the path-absolute (plus optional query) syntax
1664   or if it is just the asterisk "*", then the Effective Request URI is
1665   constructed by concatenating
1666</t>
1667<t>
1668  <list style="symbols">
1669    <t>
1670      the scheme name: "http" if the request was received over an insecure
1671      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1672      connection,
1673    </t>
1674    <t>
1675      the character sequence "://",
1676    </t>
1677    <t>
1678      the authority component, as specified in the Host header
1679      (<xref target="header.host"/>) and determined by the rules in
1680      <xref target="the.resource.identified.by.a.request"/>,
1681      <cref anchor="effrequri-nohost" source="jre">Do we need to include the handling of missing hosts in HTTP/1.0 messages, as
1682      described in <xref target="the.resource.identified.by.a.request"/>? -- See <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/></cref>
1683      and
1684    </t>
1685    <t>
1686      the request-target obtained from the Request-Line, unless the
1687      request-target is just the asterisk "*".
1688    </t>
1689  </list>
1690</t>
1691<t>
1692   Otherwise, when request-target uses the authority form, the Effective
1693   Request URI is undefined.
1694</t>
1695<figure>
1696<preamble>
1697   Example 1: the Effective Request URI for the message
1698</preamble> 
1699<artwork type="example" x:indent-with="  ">
1700GET /pub/WWW/TheProject.html HTTP/1.1
1701Host: www.example.org:8080
1702</artwork>
1703<postamble>
1704  (received over an insecure TCP connection) is "http", plus "://", plus the
1705  authority component "www.example.org:8080", plus the request-target
1706  "/pub/WWW/TheProject.html", thus
1707  "http://www.example.org:8080/pub/WWW/TheProject.html".
1708</postamble>
1709</figure>
1710<figure>
1711<preamble>
1712   Example 2: the Effective Request URI for the message
1713</preamble> 
1714<artwork type="example" x:indent-with="  ">
1715GET * HTTP/1.1
1716Host: www.example.org
1717</artwork>
1718<postamble>
1719  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1720  authority component "www.example.org", thus "https://www.example.org".
1721</postamble>
1722</figure>
1723<t>
1724   Effective Request URIs are compared using the rules described in
1725   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1726   be treated as equivalent to an absolute path of "/".
1727</t> 
1728</section>
1729
1730</section>
1731
1732
1733<section title="Response" anchor="response">
1734  <x:anchor-alias value="Response"/>
1735<t>
1736   After receiving and interpreting a request message, a server responds
1737   with an HTTP response message.
1738</t>
1739<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1740  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1741                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1742                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1743                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1744                  <x:ref>CRLF</x:ref>
1745                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1746</artwork></figure>
1747
1748<section title="Status-Line" anchor="status-line">
1749  <x:anchor-alias value="Status-Line"/>
1750<t>
1751   The first line of a Response message is the Status-Line, consisting
1752   of the protocol version followed by a numeric status code and its
1753   associated textual phrase, with each element separated by SP
1754   characters. No CR or LF is allowed except in the final CRLF sequence.
1755</t>
1756<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1757  <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>
1758</artwork></figure>
1759
1760<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1761  <x:anchor-alias value="Reason-Phrase"/>
1762  <x:anchor-alias value="Status-Code"/>
1763<t>
1764   The Status-Code element is a 3-digit integer result code of the
1765   attempt to understand and satisfy the request. These codes are fully
1766   defined in &status-codes;.  The Reason Phrase exists for the sole
1767   purpose of providing a textual description associated with the numeric
1768   status code, out of deference to earlier Internet application protocols
1769   that were more frequently used with interactive text clients.
1770   A client &SHOULD; ignore the content of the Reason Phrase.
1771</t>
1772<t>
1773   The first digit of the Status-Code defines the class of response. The
1774   last two digits do not have any categorization role. There are 5
1775   values for the first digit:
1776  <list style="symbols">
1777    <t>
1778      1xx: Informational - Request received, continuing process
1779    </t>
1780    <t>
1781      2xx: Success - The action was successfully received,
1782        understood, and accepted
1783    </t>
1784    <t>
1785      3xx: Redirection - Further action must be taken in order to
1786        complete the request
1787    </t>
1788    <t>
1789      4xx: Client Error - The request contains bad syntax or cannot
1790        be fulfilled
1791    </t>
1792    <t>
1793      5xx: Server Error - The server failed to fulfill an apparently
1794        valid request
1795    </t>
1796  </list>
1797</t>
1798<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/>
1799  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1800  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1801</artwork></figure>
1802</section>
1803</section>
1804
1805</section>
1806
1807
1808<section title="Protocol Parameters" anchor="protocol.parameters">
1809
1810<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1811  <x:anchor-alias value="HTTP-date"/>
1812<t>
1813   HTTP applications have historically allowed three different formats
1814   for date/time stamps.
1815   However, the preferred format is
1816   a fixed-length subset of that defined by <xref target="RFC1123"/>:
1817</t>
1818<figure><artwork type="example" x:indent-with="  ">
1819Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1820</artwork></figure>
1821<t>
1822   The other formats are described here only for compatibility with obsolete
1823   implementations.
1824</t>
1825<figure><artwork type="example" x:indent-with="  ">
1826Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1827Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1828</artwork></figure>
1829<t>
1830   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1831   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1832   only generate the RFC 1123 format for representing HTTP-date values
1833   in header fields. See <xref target="tolerant.applications"/> for further information.
1834</t>
1835<t>
1836   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1837   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1838   equal to UTC (Coordinated Universal Time). This is indicated in the
1839   first two formats by the inclusion of "GMT" as the three-letter
1840   abbreviation for time zone, and &MUST; be assumed when reading the
1841   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1842   additional whitespace beyond that specifically included as SP in the
1843   grammar.
1844</t>
1845<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1846  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1847</artwork></figure>
1848<t anchor="preferred.date.format">
1849  <x:anchor-alias value="rfc1123-date"/>
1850  <x:anchor-alias value="time-of-day"/>
1851  <x:anchor-alias value="hour"/>
1852  <x:anchor-alias value="minute"/>
1853  <x:anchor-alias value="second"/>
1854  <x:anchor-alias value="day-name"/>
1855  <x:anchor-alias value="day"/>
1856  <x:anchor-alias value="month"/>
1857  <x:anchor-alias value="year"/>
1858  <x:anchor-alias value="GMT"/>
1859  Preferred format:
1860</t>
1861<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"/>
1862  <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>
1863
1864  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1865               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1866               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1867               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1868               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1869               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1870               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1871               
1872  <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>
1873               ; e.g., 02 Jun 1982
1874
1875  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1876  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1877               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1878               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1879               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1880               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1881               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1882               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1883               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1884               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1885               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1886               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1887               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1888  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1889
1890  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1891
1892  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1893                 ; 00:00:00 - 23:59:59
1894                 
1895  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1896  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1897  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1898</artwork></figure>
1899<t>
1900  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1901  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1902  same as those defined for the RFC 5322 constructs
1903  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1904</t>
1905<t anchor="obsolete.date.formats">
1906  <x:anchor-alias value="obs-date"/>
1907  <x:anchor-alias value="rfc850-date"/>
1908  <x:anchor-alias value="asctime-date"/>
1909  <x:anchor-alias value="date1"/>
1910  <x:anchor-alias value="date2"/>
1911  <x:anchor-alias value="date3"/>
1912  <x:anchor-alias value="rfc1123-date"/>
1913  <x:anchor-alias value="day-name-l"/>
1914  Obsolete formats:
1915</t>
1916<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1917  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1918</artwork></figure>
1919<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1920  <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>
1921  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1922                 ; day-month-year (e.g., 02-Jun-82)
1923
1924  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1925         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1926         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1927         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1928         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1929         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1930         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1931</artwork></figure>
1932<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1933  <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>
1934  <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> ))
1935                 ; month day (e.g., Jun  2)
1936</artwork></figure>
1937<x:note>
1938  <t>
1939    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1940    accepting date values that might have been sent by non-HTTP
1941    applications, as is sometimes the case when retrieving or posting
1942    messages via proxies/gateways to SMTP or NNTP.
1943  </t>
1944</x:note>
1945<x:note>
1946  <t>
1947    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1948    to their usage within the protocol stream. Clients and servers are
1949    not required to use these formats for user presentation, request
1950    logging, etc.
1951  </t>
1952</x:note>
1953</section>
1954
1955<section title="Transfer Codings" anchor="transfer.codings">
1956  <x:anchor-alias value="transfer-coding"/>
1957  <x:anchor-alias value="transfer-extension"/>
1958<t>
1959   Transfer-coding values are used to indicate an encoding
1960   transformation that has been, can be, or might need to be applied to a
1961   payload body in order to ensure "safe transport" through the network.
1962   This differs from a content coding in that the transfer-coding is a
1963   property of the message rather than a property of the representation
1964   that is being transferred.
1965</t>
1966<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1967  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1968                          / "compress" ; <xref target="compress.coding"/>
1969                          / "deflate" ; <xref target="deflate.coding"/>
1970                          / "gzip" ; <xref target="gzip.coding"/>
1971                          / <x:ref>transfer-extension</x:ref>
1972  <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> )
1973</artwork></figure>
1974<t anchor="rule.parameter">
1975  <x:anchor-alias value="attribute"/>
1976  <x:anchor-alias value="transfer-parameter"/>
1977  <x:anchor-alias value="value"/>
1978   Parameters are in the form of attribute/value pairs.
1979</t>
1980<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"/>
1981  <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>
1982  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1983  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
1984</artwork></figure>
1985<t>
1986   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1987   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1988   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1989</t>
1990<t>
1991   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1992   MIME, which were designed to enable safe transport of binary data over a
1993   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1994   However, safe transport
1995   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1996   the only unsafe characteristic of message-bodies is the difficulty in
1997   determining the exact message body length (<xref target="message.body"/>),
1998   or the desire to encrypt data over a shared transport.
1999</t>
2000<t>
2001   A server that receives a request message with a transfer-coding it does
2002   not understand &SHOULD; respond with 501 (Not Implemented) and then
2003   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2004   client.
2005</t>
2006
2007<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2008  <iref item="chunked (Coding Format)"/>
2009  <iref item="Coding Format" subitem="chunked"/>
2010  <x:anchor-alias value="chunk"/>
2011  <x:anchor-alias value="Chunked-Body"/>
2012  <x:anchor-alias value="chunk-data"/>
2013  <x:anchor-alias value="chunk-ext"/>
2014  <x:anchor-alias value="chunk-ext-name"/>
2015  <x:anchor-alias value="chunk-ext-val"/>
2016  <x:anchor-alias value="chunk-size"/>
2017  <x:anchor-alias value="last-chunk"/>
2018  <x:anchor-alias value="trailer-part"/>
2019  <x:anchor-alias value="quoted-str-nf"/>
2020  <x:anchor-alias value="qdtext-nf"/>
2021<t>
2022   The chunked encoding modifies the body of a message in order to
2023   transfer it as a series of chunks, each with its own size indicator,
2024   followed by an &OPTIONAL; trailer containing entity-header fields. This
2025   allows dynamically produced content to be transferred along with the
2026   information necessary for the recipient to verify that it has
2027   received the full message.
2028</t>
2029<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"/>
2030  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2031                   <x:ref>last-chunk</x:ref>
2032                   <x:ref>trailer-part</x:ref>
2033                   <x:ref>CRLF</x:ref>
2034 
2035  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2036                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2037  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2038  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2039 
2040  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2041                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2042  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2043  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2044  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2045  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
2046 
2047  <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>
2048                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2049  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2050                 ; <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> 
2051</artwork></figure>
2052<t>
2053   The chunk-size field is a string of hex digits indicating the size of
2054   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2055   zero, followed by the trailer, which is terminated by an empty line.
2056</t>
2057<t>
2058   The trailer allows the sender to include additional HTTP header
2059   fields at the end of the message. The Trailer header field can be
2060   used to indicate which header fields are included in a trailer (see
2061   <xref target="header.trailer"/>).
2062</t>
2063<t>
2064   A server using chunked transfer-coding in a response &MUST-NOT; use the
2065   trailer for any header fields unless at least one of the following is
2066   true:
2067  <list style="numbers">
2068    <t>the request included a TE header field that indicates "trailers" is
2069     acceptable in the transfer-coding of the  response, as described in
2070     <xref target="header.te"/>; or,</t>
2071
2072    <t>the server is the origin server for the response, the trailer
2073     fields consist entirely of optional metadata, and the recipient
2074     could use the message (in a manner acceptable to the origin server)
2075     without receiving this metadata.  In other words, the origin server
2076     is willing to accept the possibility that the trailer fields might
2077     be silently discarded along the path to the client.</t>
2078  </list>
2079</t>
2080<t>
2081   This requirement prevents an interoperability failure when the
2082   message is being received by an HTTP/1.1 (or later) proxy and
2083   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2084   compliance with the protocol would have necessitated a possibly
2085   infinite buffer on the proxy.
2086</t>
2087<t>
2088   A process for decoding the "chunked" transfer-coding
2089   can be represented in pseudo-code as:
2090</t>
2091<figure><artwork type="code">
2092  length := 0
2093  read chunk-size, chunk-ext (if any) and CRLF
2094  while (chunk-size &gt; 0) {
2095     read chunk-data and CRLF
2096     append chunk-data to decoded-body
2097     length := length + chunk-size
2098     read chunk-size and CRLF
2099  }
2100  read header-field
2101  while (header-field not empty) {
2102     append header-field to existing header fields
2103     read header-field
2104  }
2105  Content-Length := length
2106  Remove "chunked" from Transfer-Encoding
2107</artwork></figure>
2108<t>
2109   All HTTP/1.1 applications &MUST; be able to receive and decode the
2110   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2111   they do not understand.
2112</t>
2113<t>
2114   Since "chunked" is the only transfer-coding required to be understood
2115   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2116   on a persistent connection.  Whenever a transfer-coding is applied to
2117   a payload body in a request, the final transfer-coding applied &MUST;
2118   be "chunked".  If a transfer-coding is applied to a response payload
2119   body, then either the final transfer-coding applied &MUST; be "chunked"
2120   or the message &MUST; be terminated by closing the connection. When the
2121   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2122   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2123   be applied more than once in a message-body.
2124</t>
2125</section>
2126
2127<section title="Compression Codings" anchor="compression.codings">
2128<t>
2129   The codings defined below can be used to compress the payload of a
2130   message.
2131</t>
2132<x:note><t>
2133   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2134   is not desirable and is discouraged for future encodings. Their
2135   use here is representative of historical practice, not good
2136   design.
2137</t></x:note>
2138<x:note><t>
2139   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2140   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2141   equivalent to "gzip" and "compress" respectively.
2142</t></x:note>
2143
2144<section title="Compress Coding" anchor="compress.coding">
2145<iref item="compress (Coding Format)"/>
2146<iref item="Coding Format" subitem="compress"/>
2147<t>
2148   The "compress" format is produced by the common UNIX file compression
2149   program "compress". This format is an adaptive Lempel-Ziv-Welch
2150   coding (LZW).
2151</t>
2152</section>
2153
2154<section title="Deflate Coding" anchor="deflate.coding">
2155<iref item="deflate (Coding Format)"/>
2156<iref item="Coding Format" subitem="deflate"/>
2157<t>
2158   The "deflate" format is defined as the "deflate" compression mechanism
2159   (described in <xref target="RFC1951"/>) used inside the "zlib"
2160   data format (<xref target="RFC1950"/>).
2161</t>
2162<x:note>
2163  <t>
2164    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2165    compressed data without the zlib wrapper.
2166   </t>
2167</x:note>
2168</section>
2169
2170<section title="Gzip Coding" anchor="gzip.coding">
2171<iref item="gzip (Coding Format)"/>
2172<iref item="Coding Format" subitem="gzip"/>
2173<t>
2174   The "gzip" format is produced by the file compression program
2175   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2176   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2177</t>
2178</section>
2179
2180</section>
2181
2182<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2183<t>
2184   The HTTP Transfer Coding Registry defines the name space for the transfer
2185   coding names.
2186</t>
2187<t>
2188   Registrations &MUST; include the following fields:
2189   <list style="symbols">
2190     <t>Name</t>
2191     <t>Description</t>
2192     <t>Pointer to specification text</t>
2193   </list>
2194</t>
2195<t>
2196   Names of transfer codings &MUST-NOT; overlap with names of content codings
2197   (&content-codings;), unless the encoding transformation is identical (as it
2198   is the case for the compression codings defined in
2199   <xref target="compression.codings"/>).
2200</t>
2201<t>
2202   Values to be added to this name space require a specification
2203   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2204   conform to the purpose of transfer coding defined in this section.
2205</t>
2206<t>
2207   The registry itself is maintained at
2208   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2209</t>
2210</section>
2211</section>
2212
2213<section title="Product Tokens" anchor="product.tokens">
2214  <x:anchor-alias value="product"/>
2215  <x:anchor-alias value="product-version"/>
2216<t>
2217   Product tokens are used to allow communicating applications to
2218   identify themselves by software name and version. Most fields using
2219   product tokens also allow sub-products which form a significant part
2220   of the application to be listed, separated by whitespace. By
2221   convention, the products are listed in order of their significance
2222   for identifying the application.
2223</t>
2224<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2225  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2226  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2227</artwork></figure>
2228<t>
2229   Examples:
2230</t>
2231<figure><artwork type="example">
2232  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2233  Server: Apache/0.8.4
2234</artwork></figure>
2235<t>
2236   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2237   used for advertising or other non-essential information. Although any
2238   token character &MAY; appear in a product-version, this token &SHOULD;
2239   only be used for a version identifier (i.e., successive versions of
2240   the same product &SHOULD; only differ in the product-version portion of
2241   the product value).
2242</t>
2243</section>
2244
2245<section title="Quality Values" anchor="quality.values">
2246  <x:anchor-alias value="qvalue"/>
2247<t>
2248   Both transfer codings (TE request header, <xref target="header.te"/>)
2249   and content negotiation (&content.negotiation;) use short "floating point"
2250   numbers to indicate the relative importance ("weight") of various
2251   negotiable parameters.  A weight is normalized to a real number in
2252   the range 0 through 1, where 0 is the minimum and 1 the maximum
2253   value. If a parameter has a quality value of 0, then content with
2254   this parameter is "not acceptable" for the client. HTTP/1.1
2255   applications &MUST-NOT; generate more than three digits after the
2256   decimal point. User configuration of these values &SHOULD; also be
2257   limited in this fashion.
2258</t>
2259<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2260  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2261                 / ( "1" [ "." 0*3("0") ] )
2262</artwork></figure>
2263<x:note>
2264  <t>
2265     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2266     relative degradation in desired quality.
2267  </t>
2268</x:note>
2269</section>
2270
2271</section>
2272
2273<section title="Connections" anchor="connections">
2274
2275<section title="Persistent Connections" anchor="persistent.connections">
2276
2277<section title="Purpose" anchor="persistent.purpose">
2278<t>
2279   Prior to persistent connections, a separate TCP connection was
2280   established to fetch each URL, increasing the load on HTTP servers
2281   and causing congestion on the Internet. The use of inline images and
2282   other associated data often requires a client to make multiple
2283   requests of the same server in a short amount of time. Analysis of
2284   these performance problems and results from a prototype
2285   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2286   measurements of actual HTTP/1.1 implementations show good
2287   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2288   T/TCP <xref target="Tou1998"/>.
2289</t>
2290<t>
2291   Persistent HTTP connections have a number of advantages:
2292  <list style="symbols">
2293      <t>
2294        By opening and closing fewer TCP connections, CPU time is saved
2295        in routers and hosts (clients, servers, proxies, gateways,
2296        tunnels, or caches), and memory used for TCP protocol control
2297        blocks can be saved in hosts.
2298      </t>
2299      <t>
2300        HTTP requests and responses can be pipelined on a connection.
2301        Pipelining allows a client to make multiple requests without
2302        waiting for each response, allowing a single TCP connection to
2303        be used much more efficiently, with much lower elapsed time.
2304      </t>
2305      <t>
2306        Network congestion is reduced by reducing the number of packets
2307        caused by TCP opens, and by allowing TCP sufficient time to
2308        determine the congestion state of the network.
2309      </t>
2310      <t>
2311        Latency on subsequent requests is reduced since there is no time
2312        spent in TCP's connection opening handshake.
2313      </t>
2314      <t>
2315        HTTP can evolve more gracefully, since errors can be reported
2316        without the penalty of closing the TCP connection. Clients using
2317        future versions of HTTP might optimistically try a new feature,
2318        but if communicating with an older server, retry with old
2319        semantics after an error is reported.
2320      </t>
2321    </list>
2322</t>
2323<t>
2324   HTTP implementations &SHOULD; implement persistent connections.
2325</t>
2326</section>
2327
2328<section title="Overall Operation" anchor="persistent.overall">
2329<t>
2330   A significant difference between HTTP/1.1 and earlier versions of
2331   HTTP is that persistent connections are the default behavior of any
2332   HTTP connection. That is, unless otherwise indicated, the client
2333   &SHOULD; assume that the server will maintain a persistent connection,
2334   even after error responses from the server.
2335</t>
2336<t>
2337   Persistent connections provide a mechanism by which a client and a
2338   server can signal the close of a TCP connection. This signaling takes
2339   place using the Connection header field (<xref target="header.connection"/>). Once a close
2340   has been signaled, the client &MUST-NOT; send any more requests on that
2341   connection.
2342</t>
2343
2344<section title="Negotiation" anchor="persistent.negotiation">
2345<t>
2346   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2347   maintain a persistent connection unless a Connection header including
2348   the connection-token "close" was sent in the request. If the server
2349   chooses to close the connection immediately after sending the
2350   response, it &SHOULD; send a Connection header including the
2351   connection-token "close".
2352</t>
2353<t>
2354   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2355   decide to keep it open based on whether the response from a server
2356   contains a Connection header with the connection-token close. In case
2357   the client does not want to maintain a connection for more than that
2358   request, it &SHOULD; send a Connection header including the
2359   connection-token close.
2360</t>
2361<t>
2362   If either the client or the server sends the close token in the
2363   Connection header, that request becomes the last one for the
2364   connection.
2365</t>
2366<t>
2367   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2368   maintained for HTTP versions less than 1.1 unless it is explicitly
2369   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2370   compatibility with HTTP/1.0 clients.
2371</t>
2372<t>
2373   In order to remain persistent, all messages on the connection &MUST;
2374   have a self-defined message length (i.e., one not defined by closure
2375   of the connection), as described in <xref target="message.body"/>.
2376</t>
2377</section>
2378
2379<section title="Pipelining" anchor="pipelining">
2380<t>
2381   A client that supports persistent connections &MAY; "pipeline" its
2382   requests (i.e., send multiple requests without waiting for each
2383   response). A server &MUST; send its responses to those requests in the
2384   same order that the requests were received.
2385</t>
2386<t>
2387   Clients which assume persistent connections and pipeline immediately
2388   after connection establishment &SHOULD; be prepared to retry their
2389   connection if the first pipelined attempt fails. If a client does
2390   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2391   persistent. Clients &MUST; also be prepared to resend their requests if
2392   the server closes the connection before sending all of the
2393   corresponding responses.
2394</t>
2395<t>
2396   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2397   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2398   premature termination of the transport connection could lead to
2399   indeterminate results. A client wishing to send a non-idempotent
2400   request &SHOULD; wait to send that request until it has received the
2401   response status line for the previous request.
2402</t>
2403</section>
2404</section>
2405
2406<section title="Proxy Servers" anchor="persistent.proxy">
2407<t>
2408   It is especially important that proxies correctly implement the
2409   properties of the Connection header field as specified in <xref target="header.connection"/>.
2410</t>
2411<t>
2412   The proxy server &MUST; signal persistent connections separately with
2413   its clients and the origin servers (or other proxy servers) that it
2414   connects to. Each persistent connection applies to only one transport
2415   link.
2416</t>
2417<t>
2418   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2419   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2420   for information and discussion of the problems with the Keep-Alive header
2421   implemented by many HTTP/1.0 clients).
2422</t>
2423
2424<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2425<!--<t>
2426  <cref anchor="TODO-end-to-end" source="jre">
2427    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2428    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2429  </cref>
2430</t>-->
2431<t>
2432   For the purpose of defining the behavior of caches and non-caching
2433   proxies, we divide HTTP headers into two categories:
2434  <list style="symbols">
2435      <t>End-to-end headers, which are  transmitted to the ultimate
2436        recipient of a request or response. End-to-end headers in
2437        responses MUST be stored as part of a cache entry and &MUST; be
2438        transmitted in any response formed from a cache entry.</t>
2439
2440      <t>Hop-by-hop headers, which are meaningful only for a single
2441        transport-level connection, and are not stored by caches or
2442        forwarded by proxies.</t>
2443  </list>
2444</t>
2445<t>
2446   The following HTTP/1.1 headers are hop-by-hop headers:
2447  <list style="symbols">
2448      <t>Connection</t>
2449      <t>Keep-Alive</t>
2450      <t>Proxy-Authenticate</t>
2451      <t>Proxy-Authorization</t>
2452      <t>TE</t>
2453      <t>Trailer</t>
2454      <t>Transfer-Encoding</t>
2455      <t>Upgrade</t>
2456  </list>
2457</t>
2458<t>
2459   All other headers defined by HTTP/1.1 are end-to-end headers.
2460</t>
2461<t>
2462   Other hop-by-hop headers &MUST; be listed in a Connection header
2463   (<xref target="header.connection"/>).
2464</t>
2465</section>
2466
2467<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2468<!--<t>
2469  <cref anchor="TODO-non-mod-headers" source="jre">
2470    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2471    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2472  </cref>
2473</t>-->
2474<t>
2475   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2476   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2477   modify an end-to-end header unless the definition of that header requires
2478   or specifically allows that.
2479</t>
2480<t>
2481   A transparent proxy &MUST-NOT; modify any of the following fields in a
2482   request or response, and it &MUST-NOT; add any of these fields if not
2483   already present:
2484  <list style="symbols">
2485      <t>Content-Location</t>
2486      <t>Content-MD5</t>
2487      <t>ETag</t>
2488      <t>Last-Modified</t>
2489  </list>
2490</t>
2491<t>
2492   A transparent proxy &MUST-NOT; modify any of the following fields in a
2493   response:
2494  <list style="symbols">
2495    <t>Expires</t>
2496  </list>
2497</t>
2498<t>
2499   but it &MAY; add any of these fields if not already present. If an
2500   Expires header is added, it &MUST; be given a field-value identical to
2501   that of the Date header in that response.
2502</t>
2503<t>
2504   A proxy &MUST-NOT; modify or add any of the following fields in a
2505   message that contains the no-transform cache-control directive, or in
2506   any request:
2507  <list style="symbols">
2508    <t>Content-Encoding</t>
2509    <t>Content-Range</t>
2510    <t>Content-Type</t>
2511  </list>
2512</t>
2513<t>
2514   A non-transparent proxy &MAY; modify or add these fields to a message
2515   that does not include no-transform, but if it does so, it &MUST; add a
2516   Warning 214 (Transformation applied) if one does not already appear
2517   in the message (see &header-warning;).
2518</t>
2519<x:note>
2520  <t>
2521    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2522    cause authentication failures if stronger authentication
2523    mechanisms are introduced in later versions of HTTP. Such
2524    authentication mechanisms &MAY; rely on the values of header fields
2525    not listed here.
2526  </t>
2527</x:note>
2528<t>
2529   A transparent proxy &MUST; preserve the message payload (&payload;),
2530   though it &MAY; change the message-body through application or removal
2531   of a transfer-coding (<xref target="transfer.codings"/>).
2532</t>
2533</section>
2534
2535</section>
2536
2537<section title="Practical Considerations" anchor="persistent.practical">
2538<t>
2539   Servers will usually have some time-out value beyond which they will
2540   no longer maintain an inactive connection. Proxy servers might make
2541   this a higher value since it is likely that the client will be making
2542   more connections through the same server. The use of persistent
2543   connections places no requirements on the length (or existence) of
2544   this time-out for either the client or the server.
2545</t>
2546<t>
2547   When a client or server wishes to time-out it &SHOULD; issue a graceful
2548   close on the transport connection. Clients and servers &SHOULD; both
2549   constantly watch for the other side of the transport close, and
2550   respond to it as appropriate. If a client or server does not detect
2551   the other side's close promptly it could cause unnecessary resource
2552   drain on the network.
2553</t>
2554<t>
2555   A client, server, or proxy &MAY; close the transport connection at any
2556   time. For example, a client might have started to send a new request
2557   at the same time that the server has decided to close the "idle"
2558   connection. From the server's point of view, the connection is being
2559   closed while it was idle, but from the client's point of view, a
2560   request is in progress.
2561</t>
2562<t>
2563   This means that clients, servers, and proxies &MUST; be able to recover
2564   from asynchronous close events. Client software &SHOULD; reopen the
2565   transport connection and retransmit the aborted sequence of requests
2566   without user interaction so long as the request sequence is
2567   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2568   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2569   human operator the choice of retrying the request(s). Confirmation by
2570   user-agent software with semantic understanding of the application
2571   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2572   be repeated if the second sequence of requests fails.
2573</t>
2574<t>
2575   Servers &SHOULD; always respond to at least one request per connection,
2576   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2577   middle of transmitting a response, unless a network or client failure
2578   is suspected.
2579</t>
2580<t>
2581   Clients (including proxies) &SHOULD; limit the number of simultaneous
2582   connections that they maintain to a given server (including proxies).
2583</t>
2584<t>
2585   Previous revisions of HTTP gave a specific number of connections as a
2586   ceiling, but this was found to be impractical for many applications. As a
2587   result, this specification does not mandate a particular maximum number of
2588   connections, but instead encourages clients to be conservative when opening
2589   multiple connections.
2590</t>
2591<t>
2592   In particular, while using multiple connections avoids the "head-of-line
2593   blocking" problem (whereby a request that takes significant server-side
2594   processing and/or has a large payload can block subsequent requests on the
2595   same connection), each connection used consumes server resources (sometimes
2596   significantly), and furthermore using multiple connections can cause
2597   undesirable side effects in congested networks.
2598</t>
2599<t>
2600   Note that servers might reject traffic that they deem abusive, including an
2601   excessive number of connections from a client.
2602</t>
2603</section>
2604</section>
2605
2606<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2607
2608<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2609<t>
2610   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2611   flow control mechanisms to resolve temporary overloads, rather than
2612   terminating connections with the expectation that clients will retry.
2613   The latter technique can exacerbate network congestion.
2614</t>
2615</section>
2616
2617<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2618<t>
2619   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2620   the network connection for an error status code while it is transmitting
2621   the request. If the client sees an error status code, it &SHOULD;
2622   immediately cease transmitting the body. If the body is being sent
2623   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2624   empty trailer &MAY; be used to prematurely mark the end of the message.
2625   If the body was preceded by a Content-Length header, the client &MUST;
2626   close the connection.
2627</t>
2628</section>
2629
2630<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2631<t>
2632   The purpose of the 100 (Continue) status code (see &status-100;) is to
2633   allow a client that is sending a request message with a request body
2634   to determine if the origin server is willing to accept the request
2635   (based on the request headers) before the client sends the request
2636   body. In some cases, it might either be inappropriate or highly
2637   inefficient for the client to send the body if the server will reject
2638   the message without looking at the body.
2639</t>
2640<t>
2641   Requirements for HTTP/1.1 clients:
2642  <list style="symbols">
2643    <t>
2644        If a client will wait for a 100 (Continue) response before
2645        sending the request body, it &MUST; send an Expect request-header
2646        field (&header-expect;) with the "100-continue" expectation.
2647    </t>
2648    <t>
2649        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2650        with the "100-continue" expectation if it does not intend
2651        to send a request body.
2652    </t>
2653  </list>
2654</t>
2655<t>
2656   Because of the presence of older implementations, the protocol allows
2657   ambiguous situations in which a client might send "Expect: 100-continue"
2658   without receiving either a 417 (Expectation Failed)
2659   or a 100 (Continue) status code. Therefore, when a client sends this
2660   header field to an origin server (possibly via a proxy) from which it
2661   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2662   wait for an indefinite period before sending the request body.
2663</t>
2664<t>
2665   Requirements for HTTP/1.1 origin servers:
2666  <list style="symbols">
2667    <t> Upon receiving a request which includes an Expect request-header
2668        field with the "100-continue" expectation, an origin server &MUST;
2669        either respond with 100 (Continue) status code and continue to read
2670        from the input stream, or respond with a final status code. The
2671        origin server &MUST-NOT; wait for the request body before sending
2672        the 100 (Continue) response. If it responds with a final status
2673        code, it &MAY; close the transport connection or it &MAY; continue
2674        to read and discard the rest of the request.  It &MUST-NOT;
2675        perform the requested method if it returns a final status code.
2676    </t>
2677    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2678        the request message does not include an Expect request-header
2679        field with the "100-continue" expectation, and &MUST-NOT; send a
2680        100 (Continue) response if such a request comes from an HTTP/1.0
2681        (or earlier) client. There is an exception to this rule: for
2682        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2683        status code in response to an HTTP/1.1 PUT or POST request that does
2684        not include an Expect request-header field with the "100-continue"
2685        expectation. This exception, the purpose of which is
2686        to minimize any client processing delays associated with an
2687        undeclared wait for 100 (Continue) status code, applies only to
2688        HTTP/1.1 requests, and not to requests with any other HTTP-version
2689        value.
2690    </t>
2691    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2692        already received some or all of the request body for the
2693        corresponding request.
2694    </t>
2695    <t> An origin server that sends a 100 (Continue) response &MUST;
2696    ultimately send a final status code, once the request body is
2697        received and processed, unless it terminates the transport
2698        connection prematurely.
2699    </t>
2700    <t> If an origin server receives a request that does not include an
2701        Expect request-header field with the "100-continue" expectation,
2702        the request includes a request body, and the server responds
2703        with a final status code before reading the entire request body
2704        from the transport connection, then the server &SHOULD-NOT;  close
2705        the transport connection until it has read the entire request,
2706        or until the client closes the connection. Otherwise, the client
2707        might not reliably receive the response message. However, this
2708        requirement is not be construed as preventing a server from
2709        defending itself against denial-of-service attacks, or from
2710        badly broken client implementations.
2711      </t>
2712    </list>
2713</t>
2714<t>
2715   Requirements for HTTP/1.1 proxies:
2716  <list style="symbols">
2717    <t> If a proxy receives a request that includes an Expect request-header
2718        field with the "100-continue" expectation, and the proxy
2719        either knows that the next-hop server complies with HTTP/1.1 or
2720        higher, or does not know the HTTP version of the next-hop
2721        server, it &MUST; forward the request, including the Expect header
2722        field.
2723    </t>
2724    <t> If the proxy knows that the version of the next-hop server is
2725        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2726        respond with a 417 (Expectation Failed) status code.
2727    </t>
2728    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2729        numbers received from recently-referenced next-hop servers.
2730    </t>
2731    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2732        request message was received from an HTTP/1.0 (or earlier)
2733        client and did not include an Expect request-header field with
2734        the "100-continue" expectation. This requirement overrides the
2735        general rule for forwarding of 1xx responses (see &status-1xx;).
2736    </t>
2737  </list>
2738</t>
2739</section>
2740
2741<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2742<t>
2743   If an HTTP/1.1 client sends a request which includes a request body,
2744   but which does not include an Expect request-header field with the
2745   "100-continue" expectation, and if the client is not directly
2746   connected to an HTTP/1.1 origin server, and if the client sees the
2747   connection close before receiving a status line from the server, the
2748   client &SHOULD; retry the request.  If the client does retry this
2749   request, it &MAY; use the following "binary exponential backoff"
2750   algorithm to be assured of obtaining a reliable response:
2751  <list style="numbers">
2752    <t>
2753      Initiate a new connection to the server
2754    </t>
2755    <t>
2756      Transmit the request-headers
2757    </t>
2758    <t>
2759      Initialize a variable R to the estimated round-trip time to the
2760         server (e.g., based on the time it took to establish the
2761         connection), or to a constant value of 5 seconds if the round-trip
2762         time is not available.
2763    </t>
2764    <t>
2765       Compute T = R * (2**N), where N is the number of previous
2766         retries of this request.
2767    </t>
2768    <t>
2769       Wait either for an error response from the server, or for T
2770         seconds (whichever comes first)
2771    </t>
2772    <t>
2773       If no error response is received, after T seconds transmit the
2774         body of the request.
2775    </t>
2776    <t>
2777       If client sees that the connection is closed prematurely,
2778         repeat from step 1 until the request is accepted, an error
2779         response is received, or the user becomes impatient and
2780         terminates the retry process.
2781    </t>
2782  </list>
2783</t>
2784<t>
2785   If at any point an error status code is received, the client
2786  <list style="symbols">
2787      <t>&SHOULD-NOT;  continue and</t>
2788
2789      <t>&SHOULD; close the connection if it has not completed sending the
2790        request message.</t>
2791    </list>
2792</t>
2793</section>
2794</section>
2795</section>
2796
2797
2798<section title="Miscellaneous notes that might disappear" anchor="misc">
2799<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2800<t>
2801   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2802</t>
2803</section>
2804
2805<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2806<t>
2807   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2808</t>
2809</section>
2810
2811<section title="Interception of HTTP for access control" anchor="http.intercept">
2812<t>
2813   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2814</t>
2815</section>
2816
2817<section title="Use of HTTP by other protocols" anchor="http.others">
2818<t>
2819   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2820   Extensions of HTTP like WebDAV.</cref>
2821</t>
2822
2823</section>
2824<section title="Use of HTTP by media type specification" anchor="http.media">
2825<t>
2826   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2827</t>
2828</section>
2829</section>
2830
2831<section title="Header Field Definitions" anchor="header.field.definitions">
2832<t>
2833   This section defines the syntax and semantics of HTTP/1.1 header fields
2834   related to message framing and transport protocols.
2835</t>
2836<t>
2837   For entity-header fields, both sender and recipient refer to either the
2838   client or the server, depending on who sends and who receives the message.
2839</t>
2840
2841<section title="Connection" anchor="header.connection">
2842  <iref primary="true" item="Connection header" x:for-anchor=""/>
2843  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2844  <x:anchor-alias value="Connection"/>
2845  <x:anchor-alias value="connection-token"/>
2846  <x:anchor-alias value="Connection-v"/>
2847<t>
2848   The "Connection" general-header field allows the sender to specify
2849   options that are desired for that particular connection and &MUST-NOT;
2850   be communicated by proxies over further connections.
2851</t>
2852<t>
2853   The Connection header's value has the following grammar:
2854</t>
2855<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"/>
2856  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2857  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2858  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2859</artwork></figure>
2860<t>
2861   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2862   message is forwarded and, for each connection-token in this field,
2863   remove any header field(s) from the message with the same name as the
2864   connection-token. Connection options are signaled by the presence of
2865   a connection-token in the Connection header field, not by any
2866   corresponding additional header field(s), since the additional header
2867   field might not be sent if there are no parameters associated with that
2868   connection option.
2869</t>
2870<t>
2871   Message headers listed in the Connection header &MUST-NOT; include
2872   end-to-end headers, such as Cache-Control.
2873</t>
2874<t>
2875   HTTP/1.1 defines the "close" connection option for the sender to
2876   signal that the connection will be closed after completion of the
2877   response. For example,
2878</t>
2879<figure><artwork type="example">
2880  Connection: close
2881</artwork></figure>
2882<t>
2883   in either the request or the response header fields indicates that
2884   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2885   after the current request/response is complete.
2886</t>
2887<t>
2888   An HTTP/1.1 client that does not support persistent connections &MUST;
2889   include the "close" connection option in every request message.
2890</t>
2891<t>
2892   An HTTP/1.1 server that does not support persistent connections &MUST;
2893   include the "close" connection option in every response message that
2894   does not have a 1xx (Informational) status code.
2895</t>
2896<t>
2897   A system receiving an HTTP/1.0 (or lower-version) message that
2898   includes a Connection header &MUST;, for each connection-token in this
2899   field, remove and ignore any header field(s) from the message with
2900   the same name as the connection-token. This protects against mistaken
2901   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2902</t>
2903</section>
2904
2905<section title="Content-Length" anchor="header.content-length">
2906  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2907  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2908  <x:anchor-alias value="Content-Length"/>
2909  <x:anchor-alias value="Content-Length-v"/>
2910<t>
2911   The "Content-Length" header field indicates the size of the
2912   message-body, in decimal number of octets, for any message other than
2913   a response to the HEAD method or a response with a status code of 304.
2914   In the case of responses to the HEAD method, it indicates the size of
2915   the payload body (not including any potential transfer-coding) that
2916   would have been sent had the request been a GET.
2917   In the case of the 304 (Not Modified) response, it indicates the size of
2918   the payload body (not including any potential transfer-coding) that
2919   would have been sent in a 200 (OK) response.
2920</t>
2921<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2922  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2923  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2924</artwork></figure>
2925<t>
2926   An example is
2927</t>
2928<figure><artwork type="example">
2929  Content-Length: 3495
2930</artwork></figure>
2931<t>
2932   Implementations &SHOULD; use this field to indicate the message-body
2933   length when no transfer-coding is being applied and the
2934   payload's body length can be determined prior to being transferred.
2935   <xref target="message.body"/> describes how recipients determine the length
2936   of a message-body.
2937</t>
2938<t>
2939   Any Content-Length greater than or equal to zero is a valid value.
2940</t>
2941<t>
2942   Note that the use of this field in HTTP is significantly different from
2943   the corresponding definition in MIME, where it is an optional field
2944   used within the "message/external-body" content-type.
2945</t>
2946</section>
2947
2948<section title="Date" anchor="header.date">
2949  <iref primary="true" item="Date header" x:for-anchor=""/>
2950  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2951  <x:anchor-alias value="Date"/>
2952  <x:anchor-alias value="Date-v"/>
2953<t>
2954   The "Date" general-header field represents the date and time at which
2955   the message was originated, having the same semantics as the Origination
2956   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2957   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2958   it &MUST; be sent in rfc1123-date format.
2959</t>
2960<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2961  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2962  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2963</artwork></figure>
2964<t>
2965   An example is
2966</t>
2967<figure><artwork type="example">
2968  Date: Tue, 15 Nov 1994 08:12:31 GMT
2969</artwork></figure>
2970<t>
2971   Origin servers &MUST; include a Date header field in all responses,
2972   except in these cases:
2973  <list style="numbers">
2974      <t>If the response status code is 100 (Continue) or 101 (Switching
2975         Protocols), the response &MAY; include a Date header field, at
2976         the server's option.</t>
2977
2978      <t>If the response status code conveys a server error, e.g., 500
2979         (Internal Server Error) or 503 (Service Unavailable), and it is
2980         inconvenient or impossible to generate a valid Date.</t>
2981
2982      <t>If the server does not have a clock that can provide a
2983         reasonable approximation of the current time, its responses
2984         &MUST-NOT; include a Date header field. In this case, the rules
2985         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2986  </list>
2987</t>
2988<t>
2989   A received message that does not have a Date header field &MUST; be
2990   assigned one by the recipient if the message will be cached by that
2991   recipient or gatewayed via a protocol which requires a Date. An HTTP
2992   implementation without a clock &MUST-NOT; cache responses without
2993   revalidating them on every use. An HTTP cache, especially a shared
2994   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2995   clock with a reliable external standard.
2996</t>
2997<t>
2998   Clients &SHOULD; only send a Date header field in messages that include
2999   a payload, as is usually the case for PUT and POST requests, and even
3000   then it is optional. A client without a clock &MUST-NOT; send a Date
3001   header field in a request.
3002</t>
3003<t>
3004   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
3005   time subsequent to the generation of the message. It &SHOULD; represent
3006   the best available approximation of the date and time of message
3007   generation, unless the implementation has no means of generating a
3008   reasonably accurate date and time. In theory, the date ought to
3009   represent the moment just before the payload is generated. In
3010   practice, the date can be generated at any time during the message
3011   origination without affecting its semantic value.
3012</t>
3013
3014<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3015<t>
3016   Some origin server implementations might not have a clock available.
3017   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3018   values to a response, unless these values were associated
3019   with the resource by a system or user with a reliable clock. It &MAY;
3020   assign an Expires value that is known, at or before server
3021   configuration time, to be in the past (this allows "pre-expiration"
3022   of responses without storing separate Expires values for each
3023   resource).
3024</t>
3025</section>
3026</section>
3027
3028<section title="Host" anchor="header.host">
3029  <iref primary="true" item="Host header" x:for-anchor=""/>
3030  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3031  <x:anchor-alias value="Host"/>
3032  <x:anchor-alias value="Host-v"/>
3033<t>
3034   The "Host" request-header field specifies the Internet host and port
3035   number of the resource being requested, allowing the origin server or
3036   gateway to differentiate between internally-ambiguous URLs, such as the root
3037   "/" URL of a server for multiple host names on a single IP address.
3038</t>
3039<t>   
3040   The Host field value &MUST; represent the naming authority of the origin
3041   server or gateway given by the original URL obtained from the user or
3042   referring resource (generally an http URI, as described in
3043   <xref target="http.uri"/>).
3044</t>
3045<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3046  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3047  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3048</artwork></figure>
3049<t>
3050   A "host" without any trailing port information implies the default
3051   port for the service requested (e.g., "80" for an HTTP URL). For
3052   example, a request on the origin server for
3053   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
3054</t>
3055<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3056GET /pub/WWW/ HTTP/1.1
3057Host: www.example.org
3058</artwork></figure>
3059<t>
3060   A client &MUST; include a Host header field in all HTTP/1.1 request
3061   messages. If the requested URI does not include an Internet host
3062   name for the service being requested, then the Host header field &MUST;
3063   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3064   request message it forwards does contain an appropriate Host header
3065   field that identifies the service being requested by the proxy. All
3066   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3067   status code to any HTTP/1.1 request message which lacks a Host header
3068   field.
3069</t>
3070<t>
3071   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3072   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3073   for other requirements relating to Host.
3074</t>
3075</section>
3076
3077<section title="TE" anchor="header.te">
3078  <iref primary="true" item="TE header" x:for-anchor=""/>
3079  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3080  <x:anchor-alias value="TE"/>
3081  <x:anchor-alias value="TE-v"/>
3082  <x:anchor-alias value="t-codings"/>
3083  <x:anchor-alias value="te-params"/>
3084  <x:anchor-alias value="te-ext"/>
3085<t>
3086   The "TE" request-header field indicates what extension transfer-codings
3087   it is willing to accept in the response, and whether or not it is
3088   willing to accept trailer fields in a chunked transfer-coding.
3089</t>
3090<t>
3091   Its value might consist of the keyword "trailers" and/or a comma-separated
3092   list of extension transfer-coding names with optional accept
3093   parameters (as described in <xref target="transfer.codings"/>).
3094</t>
3095<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"/>
3096  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3097  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3098  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3099  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
3100  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
3101</artwork></figure>
3102<t>
3103   The presence of the keyword "trailers" indicates that the client is
3104   willing to accept trailer fields in a chunked transfer-coding, as
3105   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3106   transfer-coding values even though it does not itself represent a
3107   transfer-coding.
3108</t>
3109<t>
3110   Examples of its use are:
3111</t>
3112<figure><artwork type="example">
3113  TE: deflate
3114  TE:
3115  TE: trailers, deflate;q=0.5
3116</artwork></figure>
3117<t>
3118   The TE header field only applies to the immediate connection.
3119   Therefore, the keyword &MUST; be supplied within a Connection header
3120   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3121</t>
3122<t>
3123   A server tests whether a transfer-coding is acceptable, according to
3124   a TE field, using these rules:
3125  <list style="numbers">
3126    <x:lt>
3127      <t>The "chunked" transfer-coding is always acceptable. If the
3128         keyword "trailers" is listed, the client indicates that it is
3129         willing to accept trailer fields in the chunked response on
3130         behalf of itself and any downstream clients. The implication is
3131         that, if given, the client is stating that either all
3132         downstream clients are willing to accept trailer fields in the
3133         forwarded response, or that it will attempt to buffer the
3134         response on behalf of downstream recipients.
3135      </t><t>
3136         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3137         chunked response such that a client can be assured of buffering
3138         the entire response.</t>
3139    </x:lt>
3140    <x:lt>
3141      <t>If the transfer-coding being tested is one of the transfer-codings
3142         listed in the TE field, then it is acceptable unless it
3143         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3144         qvalue of 0 means "not acceptable".)</t>
3145    </x:lt>
3146    <x:lt>
3147      <t>If multiple transfer-codings are acceptable, then the
3148         acceptable transfer-coding with the highest non-zero qvalue is
3149         preferred.  The "chunked" transfer-coding always has a qvalue
3150         of 1.</t>
3151    </x:lt>
3152  </list>
3153</t>
3154<t>
3155   If the TE field-value is empty or if no TE field is present, the only
3156   transfer-coding is "chunked". A message with no transfer-coding is
3157   always acceptable.
3158</t>
3159</section>
3160
3161<section title="Trailer" anchor="header.trailer">
3162  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3163  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3164  <x:anchor-alias value="Trailer"/>
3165  <x:anchor-alias value="Trailer-v"/>
3166<t>
3167   The "Trailer" general-header field indicates that the given set of
3168   header fields is present in the trailer of a message encoded with
3169   chunked transfer-coding.
3170</t>
3171<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3172  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3173  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3174</artwork></figure>
3175<t>
3176   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3177   message using chunked transfer-coding with a non-empty trailer. Doing
3178   so allows the recipient to know which header fields to expect in the
3179   trailer.
3180</t>
3181<t>
3182   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3183   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3184   trailer fields in a "chunked" transfer-coding.
3185</t>
3186<t>
3187   Message header fields listed in the Trailer header field &MUST-NOT;
3188   include the following header fields:
3189  <list style="symbols">
3190    <t>Transfer-Encoding</t>
3191    <t>Content-Length</t>
3192    <t>Trailer</t>
3193  </list>
3194</t>
3195</section>
3196
3197<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3198  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3199  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3200  <x:anchor-alias value="Transfer-Encoding"/>
3201  <x:anchor-alias value="Transfer-Encoding-v"/>
3202<t>
3203   The "Transfer-Encoding" general-header field indicates what transfer-codings
3204   (if any) have been applied to the message body. It differs from
3205   Content-Encoding (&content-codings;) in that transfer-codings are a property
3206   of the message (and therefore are removed by intermediaries), whereas
3207   content-codings are not.
3208</t>
3209<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3210  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3211                        <x:ref>Transfer-Encoding-v</x:ref>
3212  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3213</artwork></figure>
3214<t>
3215   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3216</t>
3217<figure><artwork type="example">
3218  Transfer-Encoding: chunked
3219</artwork></figure>
3220<t>
3221   If multiple encodings have been applied to a representation, the transfer-codings
3222   &MUST; be listed in the order in which they were applied.
3223   Additional information about the encoding parameters &MAY; be provided
3224   by other entity-header fields not defined by this specification.
3225</t>
3226<t>
3227   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3228   header.
3229</t>
3230</section>
3231
3232<section title="Upgrade" anchor="header.upgrade">
3233  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3234  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3235  <x:anchor-alias value="Upgrade"/>
3236  <x:anchor-alias value="Upgrade-v"/>
3237<t>
3238   The "Upgrade" general-header field allows the client to specify what
3239   additional communication protocols it would like to use, if the server
3240   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3241   header field within a 101 (Switching Protocols) response to indicate which
3242   protocol(s) are being switched to.
3243</t>
3244<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3245  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3246  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3247</artwork></figure>
3248<t>
3249   For example,
3250</t>
3251<figure><artwork type="example">
3252  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3253</artwork></figure>
3254<t>
3255   The Upgrade header field is intended to provide a simple mechanism
3256   for transition from HTTP/1.1 to some other, incompatible protocol. It
3257   does so by allowing the client to advertise its desire to use another
3258   protocol, such as a later version of HTTP with a higher major version
3259   number, even though the current request has been made using HTTP/1.1.
3260   This eases the difficult transition between incompatible protocols by
3261   allowing the client to initiate a request in the more commonly
3262   supported protocol while indicating to the server that it would like
3263   to use a "better" protocol if available (where "better" is determined
3264   by the server, possibly according to the nature of the method and/or
3265   resource being requested).
3266</t>
3267<t>
3268   The Upgrade header field only applies to switching application-layer
3269   protocols upon the existing transport-layer connection. Upgrade
3270   cannot be used to insist on a protocol change; its acceptance and use
3271   by the server is optional. The capabilities and nature of the
3272   application-layer communication after the protocol change is entirely
3273   dependent upon the new protocol chosen, although the first action
3274   after changing the protocol &MUST; be a response to the initial HTTP
3275   request containing the Upgrade header field.
3276</t>
3277<t>
3278   The Upgrade header field only applies to the immediate connection.
3279   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3280   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3281   HTTP/1.1 message.
3282</t>
3283<t>
3284   The Upgrade header field cannot be used to indicate a switch to a
3285   protocol on a different connection. For that purpose, it is more
3286   appropriate to use a 301, 302, 303, or 305 redirection response.
3287</t>
3288<t>
3289   This specification only defines the protocol name "HTTP" for use by
3290   the family of Hypertext Transfer Protocols, as defined by the HTTP
3291   version rules of <xref target="http.version"/> and future updates to this
3292   specification. Additional tokens can be registered with IANA using the
3293   registration procedure defined below. 
3294</t>
3295
3296<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3297<t>
3298   The HTTP Upgrade Token Registry defines the name space for product
3299   tokens used to identify protocols in the Upgrade header field.
3300   Each registered token should be associated with one or a set of
3301   specifications, and with contact information.
3302</t>
3303<t>
3304   Registrations should be allowed on a First Come First Served basis as
3305   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
3306   specifications need not be IETF documents or be subject to IESG review, but
3307   should obey the following rules:
3308  <list style="numbers">
3309    <t>A token, once registered, stays registered forever.</t>
3310    <t>The registration &MUST; name a responsible party for the
3311       registration.</t>
3312    <t>The registration &MUST; name a point of contact.</t>
3313    <t>The registration &MAY; name the documentation required for the
3314       token.</t>
3315    <t>The responsible party &MAY; change the registration at any time.
3316       The IANA will keep a record of all such changes, and make them
3317       available upon request.</t>
3318    <t>The responsible party for the first registration of a "product"
3319       token &MUST; approve later registrations of a "version" token
3320       together with that "product" token before they can be registered.</t>
3321    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3322       for a token. This will normally only be used in the case when a
3323       responsible party cannot be contacted.</t>
3324  </list>
3325</t>
3326<t>
3327   It is not required that specifications for upgrade tokens be made
3328   publicly available, but the contact information for the registration
3329   should be.
3330</t>
3331</section>
3332
3333
3334</section>
3335
3336<section title="Via" anchor="header.via">
3337  <iref primary="true" item="Via header" x:for-anchor=""/>
3338  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3339  <x:anchor-alias value="protocol-name"/>
3340  <x:anchor-alias value="protocol-version"/>
3341  <x:anchor-alias value="pseudonym"/>
3342  <x:anchor-alias value="received-by"/>
3343  <x:anchor-alias value="received-protocol"/>
3344  <x:anchor-alias value="Via"/>
3345  <x:anchor-alias value="Via-v"/>
3346<t>
3347   The "Via" general-header field &MUST; be used by gateways and proxies to
3348   indicate the intermediate protocols and recipients between the user
3349   agent and the server on requests, and between the origin server and
3350   the client on responses. It is analogous to the "Received" field defined in
3351   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3352   avoiding request loops, and identifying the protocol capabilities of
3353   all senders along the request/response chain.
3354</t>
3355<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"/>
3356  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3357  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3358                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3359  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3360  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3361  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3362  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3363  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3364</artwork></figure>
3365<t>
3366   The received-protocol indicates the protocol version of the message
3367   received by the server or client along each segment of the
3368   request/response chain. The received-protocol version is appended to
3369   the Via field value when the message is forwarded so that information
3370   about the protocol capabilities of upstream applications remains
3371   visible to all recipients.
3372</t>
3373<t>
3374   The protocol-name is optional if and only if it would be "HTTP". The
3375   received-by field is normally the host and optional port number of a
3376   recipient server or client that subsequently forwarded the message.
3377   However, if the real host is considered to be sensitive information,
3378   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3379   be assumed to be the default port of the received-protocol.
3380</t>
3381<t>
3382   Multiple Via field values represent each proxy or gateway that has
3383   forwarded the message. Each recipient &MUST; append its information
3384   such that the end result is ordered according to the sequence of
3385   forwarding applications.
3386</t>
3387<t>
3388   Comments &MAY; be used in the Via header field to identify the software
3389   of the recipient proxy or gateway, analogous to the User-Agent and
3390   Server header fields. However, all comments in the Via field are
3391   optional and &MAY; be removed by any recipient prior to forwarding the
3392   message.
3393</t>
3394<t>
3395   For example, a request message could be sent from an HTTP/1.0 user
3396   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3397   forward the request to a public proxy at p.example.net, which completes
3398   the request by forwarding it to the origin server at www.example.com.
3399   The request received by www.example.com would then have the following
3400   Via header field:
3401</t>
3402<figure><artwork type="example">
3403  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3404</artwork></figure>
3405<t>
3406   Proxies and gateways used as a portal through a network firewall
3407   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3408   the firewall region. This information &SHOULD; only be propagated if
3409   explicitly enabled. If not enabled, the received-by host of any host
3410   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3411   for that host.
3412</t>
3413<t>
3414   For organizations that have strong privacy requirements for hiding
3415   internal structures, a proxy &MAY; combine an ordered subsequence of
3416   Via header field entries with identical received-protocol values into
3417   a single such entry. For example,
3418</t>
3419<figure><artwork type="example">
3420  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3421</artwork></figure>
3422<t>
3423  could be collapsed to
3424</t>
3425<figure><artwork type="example">
3426  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3427</artwork></figure>
3428<t>
3429   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3430   under the same organizational control and the hosts have already been
3431   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3432   have different received-protocol values.
3433</t>
3434</section>
3435
3436</section>
3437
3438<section title="IANA Considerations" anchor="IANA.considerations">
3439
3440<section title="Header Field Registration" anchor="header.field.registration">
3441<t>
3442   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3443   with the permanent registrations below (see <xref target="RFC3864"/>):
3444</t>
3445<?BEGININC p1-messaging.iana-headers ?>
3446<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3447<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3448   <ttcol>Header Field Name</ttcol>
3449   <ttcol>Protocol</ttcol>
3450   <ttcol>Status</ttcol>
3451   <ttcol>Reference</ttcol>
3452
3453   <c>Connection</c>
3454   <c>http</c>
3455   <c>standard</c>
3456   <c>
3457      <xref target="header.connection"/>
3458   </c>
3459   <c>Content-Length</c>
3460   <c>http</c>
3461   <c>standard</c>
3462   <c>
3463      <xref target="header.content-length"/>
3464   </c>
3465   <c>Date</c>
3466   <c>http</c>
3467   <c>standard</c>
3468   <c>
3469      <xref target="header.date"/>
3470   </c>
3471   <c>Host</c>
3472   <c>http</c>
3473   <c>standard</c>
3474   <c>
3475      <xref target="header.host"/>
3476   </c>
3477   <c>TE</c>
3478   <c>http</c>
3479   <c>standard</c>
3480   <c>
3481      <xref target="header.te"/>
3482   </c>
3483   <c>Trailer</c>
3484   <c>http</c>
3485   <c>standard</c>
3486   <c>
3487      <xref target="header.trailer"/>
3488   </c>
3489   <c>Transfer-Encoding</c>
3490   <c>http</c>
3491   <c>standard</c>
3492   <c>
3493      <xref target="header.transfer-encoding"/>
3494   </c>
3495   <c>Upgrade</c>
3496   <c>http</c>
3497   <c>standard</c>
3498   <c>
3499      <xref target="header.upgrade"/>
3500   </c>
3501   <c>Via</c>
3502   <c>http</c>
3503   <c>standard</c>
3504   <c>
3505      <xref target="header.via"/>
3506   </c>
3507</texttable>
3508<!--(END)-->
3509<?ENDINC p1-messaging.iana-headers ?>
3510<t>
3511   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3512</t>
3513</section>
3514
3515<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3516<t>
3517   The entries for the "http" and "https" URI Schemes in the registry located at
3518   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3519   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3520   and <xref target="https.uri" format="counter"/> of this document
3521   (see <xref target="RFC4395"/>).
3522</t>
3523</section>
3524
3525<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3526<t>
3527   This document serves as the specification for the Internet media types
3528   "message/http" and "application/http". The following is to be registered with
3529   IANA (see <xref target="RFC4288"/>).
3530</t>
3531<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3532<iref item="Media Type" subitem="message/http" primary="true"/>
3533<iref item="message/http Media Type" primary="true"/>
3534<t>
3535   The message/http type can be used to enclose a single HTTP request or
3536   response message, provided that it obeys the MIME restrictions for all
3537   "message" types regarding line length and encodings.
3538</t>
3539<t>
3540  <list style="hanging" x:indent="12em">
3541    <t hangText="Type name:">
3542      message
3543    </t>
3544    <t hangText="Subtype name:">
3545      http
3546    </t>
3547    <t hangText="Required parameters:">
3548      none
3549    </t>
3550    <t hangText="Optional parameters:">
3551      version, msgtype
3552      <list style="hanging">
3553        <t hangText="version:">
3554          The HTTP-Version number of the enclosed message
3555          (e.g., "1.1"). If not present, the version can be
3556          determined from the first line of the body.
3557        </t>
3558        <t hangText="msgtype:">
3559          The message type -- "request" or "response". If not
3560          present, the type can be determined from the first
3561          line of the body.
3562        </t>
3563      </list>
3564    </t>
3565    <t hangText="Encoding considerations:">
3566      only "7bit", "8bit", or "binary" are permitted
3567    </t>
3568    <t hangText="Security considerations:">
3569      none
3570    </t>
3571    <t hangText="Interoperability considerations:">
3572      none
3573    </t>
3574    <t hangText="Published specification:">
3575      This specification (see <xref target="internet.media.type.message.http"/>).
3576    </t>
3577    <t hangText="Applications that use this media type:">
3578    </t>
3579    <t hangText="Additional information:">
3580      <list style="hanging">
3581        <t hangText="Magic number(s):">none</t>
3582        <t hangText="File extension(s):">none</t>
3583        <t hangText="Macintosh file type code(s):">none</t>
3584      </list>
3585    </t>
3586    <t hangText="Person and email address to contact for further information:">
3587      See Authors Section.
3588    </t>
3589    <t hangText="Intended usage:">
3590      COMMON
3591    </t>
3592    <t hangText="Restrictions on usage:">
3593      none
3594    </t>
3595    <t hangText="Author/Change controller:">
3596      IESG
3597    </t>
3598  </list>
3599</t>
3600</section>
3601<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3602<iref item="Media Type" subitem="application/http" primary="true"/>
3603<iref item="application/http Media Type" primary="true"/>
3604<t>
3605   The application/http type can be used to enclose a pipeline of one or more
3606   HTTP request or response messages (not intermixed).
3607</t>
3608<t>
3609  <list style="hanging" x:indent="12em">
3610    <t hangText="Type name:">
3611      application
3612    </t>
3613    <t hangText="Subtype name:">
3614      http
3615    </t>
3616    <t hangText="Required parameters:">
3617      none
3618    </t>
3619    <t hangText="Optional parameters:">
3620      version, msgtype
3621      <list style="hanging">
3622        <t hangText="version:">
3623          The HTTP-Version number of the enclosed messages
3624          (e.g., "1.1"). If not present, the version can be
3625          determined from the first line of the body.
3626        </t>
3627        <t hangText="msgtype:">
3628          The message type -- "request" or "response". If not
3629          present, the type can be determined from the first
3630          line of the body.
3631        </t>
3632      </list>
3633    </t>
3634    <t hangText="Encoding considerations:">
3635      HTTP messages enclosed by this type
3636      are in "binary" format; use of an appropriate
3637      Content-Transfer-Encoding is required when
3638      transmitted via E-mail.
3639    </t>
3640    <t hangText="Security considerations:">
3641      none
3642    </t>
3643    <t hangText="Interoperability considerations:">
3644      none
3645    </t>
3646    <t hangText="Published specification:">
3647      This specification (see <xref target="internet.media.type.application.http"/>).
3648    </t>
3649    <t hangText="Applications that use this media type:">
3650    </t>
3651    <t hangText="Additional information:">
3652      <list style="hanging">
3653        <t hangText="Magic number(s):">none</t>
3654        <t hangText="File extension(s):">none</t>
3655        <t hangText="Macintosh file type code(s):">none</t>
3656      </list>
3657    </t>
3658    <t hangText="Person and email address to contact for further information:">
3659      See Authors Section.
3660    </t>
3661    <t hangText="Intended usage:">
3662      COMMON
3663    </t>
3664    <t hangText="Restrictions on usage:">
3665      none
3666    </t>
3667    <t hangText="Author/Change controller:">
3668      IESG
3669    </t>
3670  </list>
3671</t>
3672</section>
3673</section>
3674
3675<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3676<t>
3677   The registration procedure for HTTP Transfer Codings is now defined by
3678   <xref target="transfer.coding.registry"/> of this document.
3679</t>
3680<t>
3681   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3682   should be updated with the registrations below:
3683</t>
3684<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3685   <ttcol>Name</ttcol>
3686   <ttcol>Description</ttcol>
3687   <ttcol>Reference</ttcol>
3688   <c>chunked</c>
3689   <c>Transfer in a series of chunks</c>
3690   <c>
3691      <xref target="chunked.encoding"/>
3692   </c>
3693   <c>compress</c>
3694   <c>UNIX "compress" program method</c>
3695   <c>
3696      <xref target="compress.coding"/>
3697   </c>
3698   <c>deflate</c>
3699   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3700   the "zlib" data format (<xref target="RFC1950"/>)
3701   </c>
3702   <c>
3703      <xref target="deflate.coding"/>
3704   </c>
3705   <c>gzip</c>
3706   <c>Same as GNU zip <xref target="RFC1952"/></c>
3707   <c>
3708      <xref target="gzip.coding"/>
3709   </c>
3710</texttable>
3711</section>
3712
3713<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3714<t>
3715   The registration procedure for HTTP Upgrade Tokens -- previously defined
3716   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3717   by <xref target="upgrade.token.registry"/> of this document.
3718</t>
3719<t>
3720   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3721   should be updated with the registration below:
3722</t>
3723<texttable align="left" suppress-title="true">
3724   <ttcol>Value</ttcol>
3725   <ttcol>Description</ttcol>
3726   <ttcol>Reference</ttcol>
3727
3728   <c>HTTP</c>
3729   <c>Hypertext Transfer Protocol</c> 
3730   <c><xref target="http.version"/> of this specification</c>
3731<!-- IANA should add this without our instructions; emailed on June 05, 2009
3732   <c>TLS/1.0</c>
3733   <c>Transport Layer Security</c>
3734   <c><xref target="RFC2817"/></c> -->
3735
3736</texttable>
3737</section>
3738
3739</section>
3740
3741<section title="Security Considerations" anchor="security.considerations">
3742<t>
3743   This section is meant to inform application developers, information
3744   providers, and users of the security limitations in HTTP/1.1 as
3745   described by this document. The discussion does not include
3746   definitive solutions to the problems revealed, though it does make
3747   some suggestions for reducing security risks.
3748</t>
3749
3750<section title="Personal Information" anchor="personal.information">
3751<t>
3752   HTTP clients are often privy to large amounts of personal information
3753   (e.g., the user's name, location, mail address, passwords, encryption
3754   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3755   leakage of this information.
3756   We very strongly recommend that a convenient interface be provided
3757   for the user to control dissemination of such information, and that
3758   designers and implementors be particularly careful in this area.
3759   History shows that errors in this area often create serious security
3760   and/or privacy problems and generate highly adverse publicity for the
3761   implementor's company.
3762</t>
3763</section>
3764
3765<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3766<t>
3767   A server is in the position to save personal data about a user's
3768   requests which might identify their reading patterns or subjects of
3769   interest. This information is clearly confidential in nature and its
3770   handling can be constrained by law in certain countries. People using
3771   HTTP to provide data are responsible for ensuring that
3772   such material is not distributed without the permission of any
3773   individuals that are identifiable by the published results.
3774</t>
3775</section>
3776
3777<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3778<t>
3779   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3780   the documents returned by HTTP requests to be only those that were
3781   intended by the server administrators. If an HTTP server translates
3782   HTTP URIs directly into file system calls, the server &MUST; take
3783   special care not to serve files that were not intended to be
3784   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3785   other operating systems use ".." as a path component to indicate a
3786   directory level above the current one. On such a system, an HTTP
3787   server &MUST; disallow any such construct in the request-target if it
3788   would otherwise allow access to a resource outside those intended to
3789   be accessible via the HTTP server. Similarly, files intended for
3790   reference only internally to the server (such as access control
3791   files, configuration files, and script code) &MUST; be protected from
3792   inappropriate retrieval, since they might contain sensitive
3793   information. Experience has shown that minor bugs in such HTTP server
3794   implementations have turned into security risks.
3795</t>
3796</section>
3797
3798<section title="DNS Spoofing" anchor="dns.spoofing">
3799<t>
3800   Clients using HTTP rely heavily on the Domain Name Service, and are
3801   thus generally prone to security attacks based on the deliberate
3802   mis-association of IP addresses and DNS names. Clients need to be
3803   cautious in assuming the continuing validity of an IP number/DNS name
3804   association.
3805</t>
3806<t>
3807   In particular, HTTP clients &SHOULD; rely on their name resolver for
3808   confirmation of an IP number/DNS name association, rather than
3809   caching the result of previous host name lookups. Many platforms
3810   already can cache host name lookups locally when appropriate, and
3811   they &SHOULD; be configured to do so. It is proper for these lookups to
3812   be cached, however, only when the TTL (Time To Live) information
3813   reported by the name server makes it likely that the cached
3814   information will remain useful.
3815</t>
3816<t>
3817   If HTTP clients cache the results of host name lookups in order to
3818   achieve a performance improvement, they &MUST; observe the TTL
3819   information reported by DNS.
3820</t>
3821<t>
3822   If HTTP clients do not observe this rule, they could be spoofed when
3823   a previously-accessed server's IP address changes. As network
3824   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3825   possibility of this form of attack will grow. Observing this
3826   requirement thus reduces this potential security vulnerability.
3827</t>
3828<t>
3829   This requirement also improves the load-balancing behavior of clients
3830   for replicated servers using the same DNS name and reduces the
3831   likelihood of a user's experiencing failure in accessing sites which
3832   use that strategy.
3833</t>
3834</section>
3835
3836<section title="Proxies and Caching" anchor="attack.proxies">
3837<t>
3838   By their very nature, HTTP proxies are men-in-the-middle, and
3839   represent an opportunity for man-in-the-middle attacks. Compromise of
3840   the systems on which the proxies run can result in serious security
3841   and privacy problems. Proxies have access to security-related
3842   information, personal information about individual users and
3843   organizations, and proprietary information belonging to users and
3844   content providers. A compromised proxy, or a proxy implemented or
3845   configured without regard to security and privacy considerations,
3846   might be used in the commission of a wide range of potential attacks.
3847</t>
3848<t>
3849   Proxy operators should protect the systems on which proxies run as
3850   they would protect any system that contains or transports sensitive
3851   information. In particular, log information gathered at proxies often
3852   contains highly sensitive personal information, and/or information
3853   about organizations. Log information should be carefully guarded, and
3854   appropriate guidelines for use should be developed and followed.
3855   (<xref target="abuse.of.server.log.information"/>).
3856</t>
3857<t>
3858   Proxy implementors should consider the privacy and security
3859   implications of their design and coding decisions, and of the
3860   configuration options they provide to proxy operators (especially the
3861   default configuration).
3862</t>
3863<t>
3864   Users of a proxy need to be aware that proxies are no trustworthier than
3865   the people who run them; HTTP itself cannot solve this problem.
3866</t>
3867<t>
3868   The judicious use of cryptography, when appropriate, might suffice to
3869   protect against a broad range of security and privacy attacks. Such
3870   cryptography is beyond the scope of the HTTP/1.1 specification.
3871</t>
3872</section>
3873
3874<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3875<t>
3876   They exist. They are hard to defend against. Research continues.
3877   Beware.
3878</t>
3879</section>
3880</section>
3881
3882<section title="Acknowledgments" anchor="ack">
3883<t>
3884   HTTP has evolved considerably over the years. It has
3885   benefited from a large and active developer community--the many
3886   people who have participated on the www-talk mailing list--and it is
3887   that community which has been most responsible for the success of
3888   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3889   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3890   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3891   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3892   VanHeyningen deserve special recognition for their efforts in
3893   defining early aspects of the protocol.
3894</t>
3895<t>
3896   This document has benefited greatly from the comments of all those
3897   participating in the HTTP-WG. In addition to those already mentioned,
3898   the following individuals have contributed to this specification:
3899</t>
3900<t>
3901   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3902   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3903   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3904   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3905   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3906   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3907   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3908   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3909   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3910   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3911   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3912   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3913</t>
3914<t>
3915   Thanks to the "cave men" of Palo Alto. You know who you are.
3916</t>
3917<t>
3918   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3919   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3920   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3921   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3922   Larry Masinter for their help. And thanks go particularly to Jeff
3923   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3924</t>
3925<t>
3926   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3927   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3928   discovery of many of the problems that this document attempts to
3929   rectify.
3930</t>
3931<t>
3932   This specification makes heavy use of the augmented BNF and generic
3933   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3934   reuses many of the definitions provided by Nathaniel Borenstein and
3935   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3936   specification will help reduce past confusion over the relationship
3937   between HTTP and Internet mail message formats.
3938</t>
3939</section>
3940
3941</middle>
3942<back>
3943
3944<references title="Normative References">
3945
3946<reference anchor="ISO-8859-1">
3947  <front>
3948    <title>
3949     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3950    </title>
3951    <author>
3952      <organization>International Organization for Standardization</organization>
3953    </author>
3954    <date year="1998"/>
3955  </front>
3956  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3957</reference>
3958
3959<reference anchor="Part2">
3960  <front>
3961    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3962    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3963      <organization abbrev="Day Software">Day Software</organization>
3964      <address><email>fielding@gbiv.com</email></address>
3965    </author>
3966    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3967      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3968      <address><email>jg@freedesktop.org</email></address>
3969    </author>
3970    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3971      <organization abbrev="HP">Hewlett-Packard Company</organization>
3972      <address><email>JeffMogul@acm.org</email></address>
3973    </author>
3974    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3975      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3976      <address><email>henrikn@microsoft.com</email></address>
3977    </author>
3978    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3979      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3980      <address><email>LMM@acm.org</email></address>
3981    </author>
3982    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3983      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3984      <address><email>paulle@microsoft.com</email></address>
3985    </author>
3986    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3987      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3988      <address><email>timbl@w3.org</email></address>
3989    </author>
3990    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3991      <organization abbrev="W3C">World Wide Web Consortium</organization>
3992      <address><email>ylafon@w3.org</email></address>
3993    </author>
3994    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3995      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3996      <address><email>julian.reschke@greenbytes.de</email></address>
3997    </author>
3998    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3999  </front>
4000  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4001  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4002</reference>
4003
4004<reference anchor="Part3">
4005  <front>
4006    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4007    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4008      <organization abbrev="Day Software">Day Software</organization>
4009      <address><email>fielding@gbiv.com</email></address>
4010    </author>
4011    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4012      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4013      <address><email>jg@freedesktop.org</email></address>
4014    </author>
4015    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4016      <organization abbrev="HP">Hewlett-Packard Company</organization>
4017      <address><email>JeffMogul@acm.org</email></address>
4018    </author>
4019    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4020      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4021      <address><email>henrikn@microsoft.com</email></address>
4022    </author>
4023    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4024      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4025      <address><email>LMM@acm.org</email></address>
4026    </author>
4027    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4028      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4029      <address><email>paulle@microsoft.com</email></address>
4030    </author>
4031    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4032      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4033      <address><email>timbl@w3.org</email></address>
4034    </author>
4035    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4036      <organization abbrev="W3C">World Wide Web Consortium</organization>
4037      <address><email>ylafon@w3.org</email></address>
4038    </author>
4039    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4040      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4041      <address><email>julian.reschke@greenbytes.de</email></address>
4042    </author>
4043    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4044  </front>
4045  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4046  <x:source href="p3-payload.xml" basename="p3-payload"/>
4047</reference>
4048
4049<reference anchor="Part6">
4050  <front>
4051    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4052    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4053      <organization abbrev="Day Software">Day Software</organization>
4054      <address><email>fielding@gbiv.com</email></address>
4055    </author>
4056    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4057      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4058      <address><email>jg@freedesktop.org</email></address>
4059    </author>
4060    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4061      <organization abbrev="HP">Hewlett-Packard Company</organization>
4062      <address><email>JeffMogul@acm.org</email></address>
4063    </author>
4064    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4065      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4066      <address><email>henrikn@microsoft.com</email></address>
4067    </author>
4068    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4069      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4070      <address><email>LMM@acm.org</email></address>
4071    </author>
4072    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4073      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4074      <address><email>paulle@microsoft.com</email></address>
4075    </author>
4076    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4077      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4078      <address><email>timbl@w3.org</email></address>
4079    </author>
4080    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4081      <organization abbrev="W3C">World Wide Web Consortium</organization>
4082      <address><email>ylafon@w3.org</email></address>
4083    </author>
4084    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4085      <address><email>mnot@mnot.net</email></address>
4086    </author>
4087    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4088      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4089      <address><email>julian.reschke@greenbytes.de</email></address>
4090    </author>
4091    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4092  </front>
4093  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4094  <x:source href="p6-cache.xml" basename="p6-cache"/>
4095</reference>
4096
4097<reference anchor="RFC5234">
4098  <front>
4099    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4100    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4101      <organization>Brandenburg InternetWorking</organization>
4102      <address>
4103        <email>dcrocker@bbiw.net</email>
4104      </address> 
4105    </author>
4106    <author initials="P." surname="Overell" fullname="Paul Overell">
4107      <organization>THUS plc.</organization>
4108      <address>
4109        <email>paul.overell@thus.net</email>
4110      </address>
4111    </author>
4112    <date month="January" year="2008"/>
4113  </front>
4114  <seriesInfo name="STD" value="68"/>
4115  <seriesInfo name="RFC" value="5234"/>
4116</reference>
4117
4118<reference anchor="RFC2119">
4119  <front>
4120    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4121    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4122      <organization>Harvard University</organization>
4123      <address><email>sob@harvard.edu</email></address>
4124    </author>
4125    <date month="March" year="1997"/>
4126  </front>
4127  <seriesInfo name="BCP" value="14"/>
4128  <seriesInfo name="RFC" value="2119"/>
4129</reference>
4130
4131<reference anchor="RFC3986">
4132 <front>
4133  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4134  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4135    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4136    <address>
4137       <email>timbl@w3.org</email>
4138       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4139    </address>
4140  </author>
4141  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4142    <organization abbrev="Day Software">Day Software</organization>
4143    <address>
4144      <email>fielding@gbiv.com</email>
4145      <uri>http://roy.gbiv.com/</uri>
4146    </address>
4147  </author>
4148  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4149    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4150    <address>
4151      <email>LMM@acm.org</email>
4152      <uri>http://larry.masinter.net/</uri>
4153    </address>
4154  </author>
4155  <date month='January' year='2005'></date>
4156 </front>
4157 <seriesInfo name="RFC" value="3986"/>
4158 <seriesInfo name="STD" value="66"/>
4159</reference>
4160
4161<reference anchor="USASCII">
4162  <front>
4163    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4164    <author>
4165      <organization>American National Standards Institute</organization>
4166    </author>
4167    <date year="1986"/>
4168  </front>
4169  <seriesInfo name="ANSI" value="X3.4"/>
4170</reference>
4171
4172<reference anchor="RFC1950">
4173  <front>
4174    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4175    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4176      <organization>Aladdin Enterprises</organization>
4177      <address><email>ghost@aladdin.com</email></address>
4178    </author>
4179    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4180    <date month="May" year="1996"/>
4181  </front>
4182  <seriesInfo name="RFC" value="1950"/>
4183  <annotation>
4184    RFC 1950 is an Informational RFC, thus it might be less stable than
4185    this specification. On the other hand, this downward reference was
4186    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4187    therefore it is unlikely to cause problems in practice. See also
4188    <xref target="BCP97"/>.
4189  </annotation>
4190</reference>
4191
4192<reference anchor="RFC1951">
4193  <front>
4194    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4195    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4196      <organization>Aladdin Enterprises</organization>
4197      <address><email>ghost@aladdin.com</email></address>
4198    </author>
4199    <date month="May" year="1996"/>
4200  </front>
4201  <seriesInfo name="RFC" value="1951"/>
4202  <annotation>
4203    RFC 1951 is an Informational RFC, thus it might be less stable than
4204    this specification. On the other hand, this downward reference was
4205    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4206    therefore it is unlikely to cause problems in practice. See also
4207    <xref target="BCP97"/>.
4208  </annotation>
4209</reference>
4210
4211<reference anchor="RFC1952">
4212  <front>
4213    <title>GZIP file format specification version 4.3</title>
4214    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4215      <organization>Aladdin Enterprises</organization>
4216      <address><email>ghost@aladdin.com</email></address>
4217    </author>
4218    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4219      <address><email>gzip@prep.ai.mit.edu</email></address>
4220    </author>
4221    <author initials="M." surname="Adler" fullname="Mark Adler">
4222      <address><email>madler@alumni.caltech.edu</email></address>
4223    </author>
4224    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4225      <address><email>ghost@aladdin.com</email></address>
4226    </author>
4227    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4228      <address><email>randeg@alumni.rpi.edu</email></address>
4229    </author>
4230    <date month="May" year="1996"/>
4231  </front>
4232  <seriesInfo name="RFC" value="1952"/>
4233  <annotation>
4234    RFC 1952 is an Informational RFC, thus it might be less stable than
4235    this specification. On the other hand, this downward reference was
4236    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4237    therefore it is unlikely to cause problems in practice. See also
4238    <xref target="BCP97"/>.
4239  </annotation>
4240</reference>
4241
4242</references>
4243
4244<references title="Informative References">
4245
4246<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4247  <front>
4248    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4249    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4250    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4251    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4252    <author initials="H." surname="Lie" fullname="H. Lie"/>
4253    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4254    <date year="1997" month="September"/>
4255  </front>
4256  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4257</reference>
4258
4259<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4260  <front>
4261    <title>Improving HTTP Latency</title>
4262    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4263    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4264    <date year="1995" month="December"/>
4265  </front>
4266  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4267</reference>
4268
4269<reference anchor="RFC1123">
4270  <front>
4271    <title>Requirements for Internet Hosts - Application and Support</title>
4272    <author initials="R." surname="Braden" fullname="Robert Braden">
4273      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4274      <address><email>Braden@ISI.EDU</email></address>
4275    </author>
4276    <date month="October" year="1989"/>
4277  </front>
4278  <seriesInfo name="STD" value="3"/>
4279  <seriesInfo name="RFC" value="1123"/>
4280</reference>
4281
4282<reference anchor="RFC1305">
4283  <front>
4284    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4285    <author initials="D." surname="Mills" fullname="David L. Mills">
4286      <organization>University of Delaware, Electrical Engineering Department</organization>
4287      <address><email>mills@udel.edu</email></address>
4288    </author>
4289    <date month="March" year="1992"/>
4290  </front>
4291  <seriesInfo name="RFC" value="1305"/>
4292</reference>
4293
4294<reference anchor="RFC1900">
4295  <front>
4296    <title>Renumbering Needs Work</title>
4297    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4298      <organization>CERN, Computing and Networks Division</organization>
4299      <address><email>brian@dxcoms.cern.ch</email></address>
4300    </author>
4301    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4302      <organization>cisco Systems</organization>
4303      <address><email>yakov@cisco.com</email></address>
4304    </author>
4305    <date month="February" year="1996"/>
4306  </front>
4307  <seriesInfo name="RFC" value="1900"/>
4308</reference>
4309
4310<reference anchor="RFC1945">
4311  <front>
4312    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4313    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4314      <organization>MIT, Laboratory for Computer Science</organization>
4315      <address><email>timbl@w3.org</email></address>
4316    </author>
4317    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4318      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4319      <address><email>fielding@ics.uci.edu</email></address>
4320    </author>
4321    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4322      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4323      <address><email>frystyk@w3.org</email></address>
4324    </author>
4325    <date month="May" year="1996"/>
4326  </front>
4327  <seriesInfo name="RFC" value="1945"/>
4328</reference>
4329
4330<reference anchor="RFC2045">
4331  <front>
4332    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4333    <author initials="N." surname="Freed" fullname="Ned Freed">
4334      <organization>Innosoft International, Inc.</organization>
4335      <address><email>ned@innosoft.com</email></address>
4336    </author>
4337    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4338      <organization>First Virtual Holdings</organization>
4339      <address><email>nsb@nsb.fv.com</email></address>
4340    </author>
4341    <date month="November" year="1996"/>
4342  </front>
4343  <seriesInfo name="RFC" value="2045"/>
4344</reference>
4345
4346<reference anchor="RFC2047">
4347  <front>
4348    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4349    <author initials="K." surname="Moore" fullname="Keith Moore">
4350      <organization>University of Tennessee</organization>
4351      <address><email>moore@cs.utk.edu</email></address>
4352    </author>
4353    <date month="November" year="1996"/>
4354  </front>
4355  <seriesInfo name="RFC" value="2047"/>
4356</reference>
4357
4358<reference anchor="RFC2068">
4359  <front>
4360    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4361    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4362      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4363      <address><email>fielding@ics.uci.edu</email></address>
4364    </author>
4365    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4366      <organization>MIT Laboratory for Computer Science</organization>
4367      <address><email>jg@w3.org</email></address>
4368    </author>
4369    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4370      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4371      <address><email>mogul@wrl.dec.com</email></address>
4372    </author>
4373    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4374      <organization>MIT Laboratory for Computer Science</organization>
4375      <address><email>frystyk@w3.org</email></address>
4376    </author>
4377    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4378      <organization>MIT Laboratory for Computer Science</organization>
4379      <address><email>timbl@w3.org</email></address>
4380    </author>
4381    <date month="January" year="1997"/>
4382  </front>
4383  <seriesInfo name="RFC" value="2068"/>
4384</reference>
4385
4386<reference anchor='RFC2109'>
4387  <front>
4388    <title>HTTP State Management Mechanism</title>
4389    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4390      <organization>Bell Laboratories, Lucent Technologies</organization>
4391      <address><email>dmk@bell-labs.com</email></address>
4392    </author>
4393    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4394      <organization>Netscape Communications Corp.</organization>
4395      <address><email>montulli@netscape.com</email></address>
4396    </author>
4397    <date year='1997' month='February' />
4398  </front>
4399  <seriesInfo name='RFC' value='2109' />
4400</reference>
4401
4402<reference anchor="RFC2145">
4403  <front>
4404    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4405    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4406      <organization>Western Research Laboratory</organization>
4407      <address><email>mogul@wrl.dec.com</email></address>
4408    </author>
4409    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4410      <organization>Department of Information and Computer Science</organization>
4411      <address><email>fielding@ics.uci.edu</email></address>
4412    </author>
4413    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4414      <organization>MIT Laboratory for Computer Science</organization>
4415      <address><email>jg@w3.org</email></address>
4416    </author>
4417    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4418      <organization>W3 Consortium</organization>
4419      <address><email>frystyk@w3.org</email></address>
4420    </author>
4421    <date month="May" year="1997"/>
4422  </front>
4423  <seriesInfo name="RFC" value="2145"/>
4424</reference>
4425
4426<reference anchor="RFC2616">
4427  <front>
4428    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4429    <author initials="R." surname="Fielding" fullname="R. Fielding">
4430      <organization>University of California, Irvine</organization>
4431      <address><email>fielding@ics.uci.edu</email></address>
4432    </author>
4433    <author initials="J." surname="Gettys" fullname="J. Gettys">
4434      <organization>W3C</organization>
4435      <address><email>jg@w3.org</email></address>
4436    </author>
4437    <author initials="J." surname="Mogul" fullname="J. Mogul">
4438      <organization>Compaq Computer Corporation</organization>
4439      <address><email>mogul@wrl.dec.com</email></address>
4440    </author>
4441    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4442      <organization>MIT Laboratory for Computer Science</organization>
4443      <address><email>frystyk@w3.org</email></address>
4444    </author>
4445    <author initials="L." surname="Masinter" fullname="L. Masinter">
4446      <organization>Xerox Corporation</organization>
4447      <address><email>masinter@parc.xerox.com</email></address>
4448    </author>
4449    <author initials="P." surname="Leach" fullname="P. Leach">
4450      <organization>Microsoft Corporation</organization>
4451      <address><email>paulle@microsoft.com</email></address>
4452    </author>
4453    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4454      <organization>W3C</organization>
4455      <address><email>timbl@w3.org</email></address>
4456    </author>
4457    <date month="June" year="1999"/>
4458  </front>
4459  <seriesInfo name="RFC" value="2616"/>
4460</reference>
4461
4462<reference anchor='RFC2817'>
4463  <front>
4464    <title>Upgrading to TLS Within HTTP/1.1</title>
4465    <author initials='R.' surname='Khare' fullname='R. Khare'>
4466      <organization>4K Associates / UC Irvine</organization>
4467      <address><email>rohit@4K-associates.com</email></address>
4468    </author>
4469    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4470      <organization>Agranat Systems, Inc.</organization>
4471      <address><email>lawrence@agranat.com</email></address>
4472    </author>
4473    <date year='2000' month='May' />
4474  </front>
4475  <seriesInfo name='RFC' value='2817' />
4476</reference>
4477
4478<reference anchor='RFC2818'>
4479  <front>
4480    <title>HTTP Over TLS</title>
4481    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4482      <organization>RTFM, Inc.</organization>
4483      <address><email>ekr@rtfm.com</email></address>
4484    </author>
4485    <date year='2000' month='May' />
4486  </front>
4487  <seriesInfo name='RFC' value='2818' />
4488</reference>
4489
4490<reference anchor='RFC2965'>
4491  <front>
4492    <title>HTTP State Management Mechanism</title>
4493    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4494      <organization>Bell Laboratories, Lucent Technologies</organization>
4495      <address><email>dmk@bell-labs.com</email></address>
4496    </author>
4497    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4498      <organization>Epinions.com, Inc.</organization>
4499      <address><email>lou@montulli.org</email></address>
4500    </author>
4501    <date year='2000' month='October' />
4502  </front>
4503  <seriesInfo name='RFC' value='2965' />
4504</reference>
4505
4506<reference anchor='RFC3864'>
4507  <front>
4508    <title>Registration Procedures for Message Header Fields</title>
4509    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4510      <organization>Nine by Nine</organization>
4511      <address><email>GK-IETF@ninebynine.org</email></address>
4512    </author>
4513    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4514      <organization>BEA Systems</organization>
4515      <address><email>mnot@pobox.com</email></address>
4516    </author>
4517    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4518      <organization>HP Labs</organization>
4519      <address><email>JeffMogul@acm.org</email></address>
4520    </author>
4521    <date year='2004' month='September' />
4522  </front>
4523  <seriesInfo name='BCP' value='90' />
4524  <seriesInfo name='RFC' value='3864' />
4525</reference>
4526
4527<reference anchor="RFC4288">
4528  <front>
4529    <title>Media Type Specifications and Registration Procedures</title>
4530    <author initials="N." surname="Freed" fullname="N. Freed">
4531      <organization>Sun Microsystems</organization>
4532      <address>
4533        <email>ned.freed@mrochek.com</email>
4534      </address>
4535    </author>
4536    <author initials="J." surname="Klensin" fullname="J. Klensin">
4537      <address>
4538        <email>klensin+ietf@jck.com</email>
4539      </address>
4540    </author>
4541    <date year="2005" month="December"/>
4542  </front>
4543  <seriesInfo name="BCP" value="13"/>
4544  <seriesInfo name="RFC" value="4288"/>
4545</reference>
4546
4547<reference anchor='RFC4395'>
4548  <front>
4549    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4550    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4551      <organization>AT&amp;T Laboratories</organization>
4552      <address>
4553        <email>tony+urireg@maillennium.att.com</email>
4554      </address>
4555    </author>
4556    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4557      <organization>Qualcomm, Inc.</organization>
4558      <address>
4559        <email>hardie@qualcomm.com</email>
4560      </address>
4561    </author>
4562    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4563      <organization>Adobe Systems</organization>
4564      <address>
4565        <email>LMM@acm.org</email>
4566      </address>
4567    </author>
4568    <date year='2006' month='February' />
4569  </front>
4570  <seriesInfo name='BCP' value='115' />
4571  <seriesInfo name='RFC' value='4395' />
4572</reference>
4573
4574<reference anchor='RFC5226'>
4575  <front>
4576    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4577    <author initials='T.' surname='Narten' fullname='T. Narten'>
4578      <organization>IBM</organization>
4579      <address><email>narten@us.ibm.com</email></address>
4580    </author>
4581    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4582      <organization>Google</organization>
4583      <address><email>Harald@Alvestrand.no</email></address>
4584    </author>
4585    <date year='2008' month='May' />
4586  </front>
4587  <seriesInfo name='BCP' value='26' />
4588  <seriesInfo name='RFC' value='5226' />
4589</reference>
4590
4591<reference anchor="RFC5322">
4592  <front>
4593    <title>Internet Message Format</title>
4594    <author initials="P." surname="Resnick" fullname="P. Resnick">
4595      <organization>Qualcomm Incorporated</organization>
4596    </author>
4597    <date year="2008" month="October"/>
4598  </front> 
4599  <seriesInfo name="RFC" value="5322"/>
4600</reference>
4601
4602<reference anchor='BCP97'>
4603  <front>
4604    <title>Handling Normative References to Standards-Track Documents</title>
4605    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4606      <address>
4607        <email>klensin+ietf@jck.com</email>
4608      </address>
4609    </author>
4610    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4611      <organization>MIT</organization>
4612      <address>
4613        <email>hartmans-ietf@mit.edu</email>
4614      </address>
4615    </author>
4616    <date year='2007' month='June' />
4617  </front>
4618  <seriesInfo name='BCP' value='97' />
4619  <seriesInfo name='RFC' value='4897' />
4620</reference>
4621
4622<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4623  <front>
4624    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4625    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4626    <date year="2001" month="November"/>
4627  </front>
4628  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4629</reference>
4630
4631<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4632  <front>
4633    <title>Analysis of HTTP Performance Problems</title>
4634    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4635    <date/>
4636  </front>
4637</reference>
4638
4639<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4640  <front>
4641  <title>Analysis of HTTP Performance</title>
4642  <author initials="J." surname="Touch" fullname="Joe Touch">
4643    <organization>USC/Information Sciences Institute</organization>
4644    <address><email>touch@isi.edu</email></address>
4645  </author>
4646  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4647    <organization>USC/Information Sciences Institute</organization>
4648    <address><email>johnh@isi.edu</email></address>
4649  </author>
4650  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4651    <organization>USC/Information Sciences Institute</organization>
4652    <address><email>katia@isi.edu</email></address>
4653  </author>
4654  <date year="1998" month="Aug"/>
4655  </front>
4656  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4657  <annotation>(original report dated Aug. 1996)</annotation>
4658</reference>
4659
4660</references>
4661
4662
4663<section title="Tolerant Applications" anchor="tolerant.applications">
4664<t>
4665   Although this document specifies the requirements for the generation
4666   of HTTP/1.1 messages, not all applications will be correct in their
4667   implementation. We therefore recommend that operational applications
4668   be tolerant of deviations whenever those deviations can be
4669   interpreted unambiguously.
4670</t>
4671<t>
4672   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4673   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4674   &SHOULD; accept any amount of WSP characters between fields, even though
4675   only a single SP is required.
4676</t>
4677<t>
4678   The line terminator for header fields is the sequence CRLF.
4679   However, we recommend that applications, when parsing such headers,
4680   recognize a single LF as a line terminator and ignore the leading CR.
4681</t>
4682<t>
4683   The character set of a representation &SHOULD; be labeled as the lowest
4684   common denominator of the character codes used within that representation, with
4685   the exception that not labeling the representation is preferred over labeling
4686   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4687</t>
4688<t>
4689   Additional rules for requirements on parsing and encoding of dates
4690   and other potential problems with date encodings include:
4691</t>
4692<t>
4693  <list style="symbols">
4694     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4695        which appears to be more than 50 years in the future is in fact
4696        in the past (this helps solve the "year 2000" problem).</t>
4697
4698     <t>Although all date formats are specified to be case-sensitive,
4699        recipients &SHOULD; match day, week and timezone names
4700        case-insensitively.</t>
4701             
4702     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4703        Expires date as earlier than the proper value, but &MUST-NOT;
4704        internally represent a parsed Expires date as later than the
4705        proper value.</t>
4706
4707     <t>All expiration-related calculations &MUST; be done in GMT. The
4708        local time zone &MUST-NOT; influence the calculation or comparison
4709        of an age or expiration time.</t>
4710
4711     <t>If an HTTP header incorrectly carries a date value with a time
4712        zone other than GMT, it &MUST; be converted into GMT using the
4713        most conservative possible conversion.</t>
4714  </list>
4715</t>
4716</section>
4717
4718<section title="Compatibility with Previous Versions" anchor="compatibility">
4719<t>
4720   HTTP has been in use by the World-Wide Web global information initiative
4721   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4722   was a simple protocol for hypertext data transfer across the Internet
4723   with only a single method and no metadata.
4724   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4725   methods and MIME-like messaging that could include metadata about the data
4726   transferred and modifiers on the request/response semantics. However,
4727   HTTP/1.0 did not sufficiently take into consideration the effects of
4728   hierarchical proxies, caching, the need for persistent connections, or
4729   name-based virtual hosts. The proliferation of incompletely-implemented
4730   applications calling themselves "HTTP/1.0" further necessitated a
4731   protocol version change in order for two communicating applications
4732   to determine each other's true capabilities.
4733</t>
4734<t>
4735   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4736   requirements that enable reliable implementations, adding only
4737   those new features that will either be safely ignored by an HTTP/1.0
4738   recipient or only sent when communicating with a party advertising
4739   compliance with HTTP/1.1.
4740</t>
4741<t>
4742   It is beyond the scope of a protocol specification to mandate
4743   compliance with previous versions. HTTP/1.1 was deliberately
4744   designed, however, to make supporting previous versions easy. It is
4745   worth noting that, at the time of composing this specification, we would
4746   expect general-purpose HTTP/1.1 servers to:
4747  <list style="symbols">
4748     <t>understand any valid request in the format of HTTP/1.0 and
4749        1.1;</t>
4750
4751     <t>respond appropriately with a message in the same major version
4752        used by the client.</t>
4753  </list>
4754</t>
4755<t>
4756   And we would expect HTTP/1.1 clients to:
4757  <list style="symbols">
4758     <t>understand any valid response in the format of HTTP/1.0 or
4759        1.1.</t>
4760  </list>
4761</t>
4762<t>
4763   For most implementations of HTTP/1.0, each connection is established
4764   by the client prior to the request and closed by the server after
4765   sending the response. Some implementations implement the Keep-Alive
4766   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4767</t>
4768
4769<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4770<t>
4771   This section summarizes major differences between versions HTTP/1.0
4772   and HTTP/1.1.
4773</t>
4774
4775<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">
4776<t>
4777   The requirements that clients and servers support the Host request-header,
4778   report an error if the Host request-header (<xref target="header.host"/>) is
4779   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4780   are among the most important changes defined by this
4781   specification.
4782</t>
4783<t>
4784   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4785   addresses and servers; there was no other established mechanism for
4786   distinguishing the intended server of a request than the IP address
4787   to which that request was directed. The changes outlined above will
4788   allow the Internet, once older HTTP clients are no longer common, to
4789   support multiple Web sites from a single IP address, greatly
4790   simplifying large operational Web servers, where allocation of many
4791   IP addresses to a single host has created serious problems. The
4792   Internet will also be able to recover the IP addresses that have been
4793   allocated for the sole purpose of allowing special-purpose domain
4794   names to be used in root-level HTTP URLs. Given the rate of growth of
4795   the Web, and the number of servers already deployed, it is extremely
4796   important that all implementations of HTTP (including updates to
4797   existing HTTP/1.0 applications) correctly implement these
4798   requirements:
4799  <list style="symbols">
4800     <t>Both clients and servers &MUST; support the Host request-header.</t>
4801
4802     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4803
4804     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4805        request does not include a Host request-header.</t>
4806
4807     <t>Servers &MUST; accept absolute URIs.</t>
4808  </list>
4809</t>
4810</section>
4811</section>
4812
4813<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4814<t>
4815   Some clients and servers might wish to be compatible with some
4816   previous implementations of persistent connections in HTTP/1.0
4817   clients and servers. Persistent connections in HTTP/1.0 are
4818   explicitly negotiated as they are not the default behavior. HTTP/1.0
4819   experimental implementations of persistent connections are faulty,
4820   and the new facilities in HTTP/1.1 are designed to rectify these
4821   problems. The problem was that some existing HTTP/1.0 clients might
4822   send Keep-Alive to a proxy server that doesn't understand
4823   Connection, which would then erroneously forward it to the next
4824   inbound server, which would establish the Keep-Alive connection and
4825   result in a hung HTTP/1.0 proxy waiting for the close on the
4826   response. The result is that HTTP/1.0 clients must be prevented from
4827   using Keep-Alive when talking to proxies.
4828</t>
4829<t>
4830   However, talking to proxies is the most important use of persistent
4831   connections, so that prohibition is clearly unacceptable. Therefore,
4832   we need some other mechanism for indicating a persistent connection
4833   is desired, which is safe to use even when talking to an old proxy
4834   that ignores Connection. Persistent connections are the default for
4835   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4836   declaring non-persistence. See <xref target="header.connection"/>.
4837</t>
4838<t>
4839   The original HTTP/1.0 form of persistent connections (the Connection:
4840   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4841</t>
4842</section>
4843
4844<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4845<t>
4846  Empty list elements in list productions have been deprecated.
4847  (<xref target="notation.abnf"/>)
4848</t>
4849<t>
4850  Rules about implicit linear whitespace between certain grammar productions
4851  have been removed; now it's only allowed when specifically pointed out
4852  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4853  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4854  Non-ASCII content in header fields and reason phrase has been obsoleted and
4855  made opaque (the TEXT rule was removed)
4856  (<xref target="basic.rules"/>)
4857</t>
4858<t>
4859  Clarify that HTTP-Version is case sensitive.
4860  (<xref target="http.version"/>)
4861</t>
4862<t>
4863  Remove reference to non-existent identity transfer-coding value tokens.
4864  (Sections <xref format="counter" target="transfer.codings"/> and
4865  <xref format="counter" target="message.body"/>)
4866</t>
4867<t>
4868  Require that invalid whitespace around field-names be rejected.
4869  (<xref target="header.fields"/>)
4870</t>
4871<t>
4872  Update use of abs_path production from RFC1808 to the path-absolute + query
4873  components of RFC3986.
4874  (<xref target="request-target"/>)
4875</t>
4876<t>
4877  Clarification that the chunk length does not include the count of the octets
4878  in the chunk header and trailer. Furthermore disallowed line folding
4879  in chunk extensions.
4880  (<xref target="chunked.encoding"/>)
4881</t>
4882<t>
4883  Remove hard limit of two connections per server.
4884  (<xref target="persistent.practical"/>)
4885</t>
4886<t>
4887  Clarify exactly when close connection options must be sent.
4888  (<xref target="header.connection"/>)
4889</t>
4890</section>
4891</section>
4892
4893<?BEGININC p1-messaging.abnf-appendix ?>
4894<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4895<figure>
4896<artwork type="abnf" name="p1-messaging.parsed-abnf">
4897<x:ref>BWS</x:ref> = OWS
4898
4899<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4900<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4901<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4902<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4903 connection-token ] )
4904<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4905<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4906
4907<x:ref>Date</x:ref> = "Date:" OWS Date-v
4908<x:ref>Date-v</x:ref> = HTTP-date
4909
4910<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4911
4912<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4913<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4914<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4915<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4916 ]
4917<x:ref>Host</x:ref> = "Host:" OWS Host-v
4918<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4919
4920<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
4921<x:ref>Method</x:ref> = token
4922
4923<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4924
4925<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4926
4927<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4928<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4929<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4930 entity-header ) CRLF ) CRLF [ message-body ]
4931<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4932<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4933 entity-header ) CRLF ) CRLF [ message-body ]
4934
4935<x:ref>Status-Code</x:ref> = 3DIGIT
4936<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4937
4938<x:ref>TE</x:ref> = "TE:" OWS TE-v
4939<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4940<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4941<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4942<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4943<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4944 transfer-coding ] )
4945
4946<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4947<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4948<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4949
4950<x:ref>Via</x:ref> = "Via:" OWS Via-v
4951<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4952 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4953 ] )
4954
4955<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4956
4957<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4958<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4959<x:ref>attribute</x:ref> = token
4960<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4961
4962<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4963<x:ref>chunk-data</x:ref> = 1*OCTET
4964<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4965<x:ref>chunk-ext-name</x:ref> = token
4966<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4967<x:ref>chunk-size</x:ref> = 1*HEXDIG
4968<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4969<x:ref>connection-token</x:ref> = token
4970<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4971 / %x2A-5B ; '*'-'['
4972 / %x5D-7E ; ']'-'~'
4973 / obs-text
4974
4975<x:ref>date1</x:ref> = day SP month SP year
4976<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4977<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4978<x:ref>day</x:ref> = 2DIGIT
4979<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4980 / %x54.75.65 ; Tue
4981 / %x57.65.64 ; Wed
4982 / %x54.68.75 ; Thu
4983 / %x46.72.69 ; Fri
4984 / %x53.61.74 ; Sat
4985 / %x53.75.6E ; Sun
4986<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4987 / %x54.75.65.73.64.61.79 ; Tuesday
4988 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4989 / %x54.68.75.72.73.64.61.79 ; Thursday
4990 / %x46.72.69.64.61.79 ; Friday
4991 / %x53.61.74.75.72.64.61.79 ; Saturday
4992 / %x53.75.6E.64.61.79 ; Sunday
4993
4994<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4995
4996<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4997<x:ref>field-name</x:ref> = token
4998<x:ref>field-value</x:ref> = *( field-content / OWS )
4999
5000<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5001 / Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
5002
5003<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5004<x:ref>hour</x:ref> = 2DIGIT
5005<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5006<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5007
5008<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5009
5010<x:ref>message-body</x:ref> = *OCTET
5011<x:ref>minute</x:ref> = 2DIGIT
5012<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5013 / %x46.65.62 ; Feb
5014 / %x4D.61.72 ; Mar
5015 / %x41.70.72 ; Apr
5016 / %x4D.61.79 ; May
5017 / %x4A.75.6E ; Jun
5018 / %x4A.75.6C ; Jul
5019 / %x41.75.67 ; Aug
5020 / %x53.65.70 ; Sep
5021 / %x4F.63.74 ; Oct
5022 / %x4E.6F.76 ; Nov
5023 / %x44.65.63 ; Dec
5024
5025<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5026<x:ref>obs-fold</x:ref> = CRLF
5027<x:ref>obs-text</x:ref> = %x80-FF
5028
5029<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5030<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5031<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5032<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5033<x:ref>product</x:ref> = token [ "/" product-version ]
5034<x:ref>product-version</x:ref> = token
5035<x:ref>protocol-name</x:ref> = token
5036<x:ref>protocol-version</x:ref> = token
5037<x:ref>pseudonym</x:ref> = token
5038
5039<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5040 / %x5D-7E ; ']'-'~'
5041 / obs-text
5042<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5043 / %x5D-7E ; ']'-'~'
5044 / obs-text
5045<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5046<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5047<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5048<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5049<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5050<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5051
5052<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5053<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5054<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5055<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5056<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5057 / authority
5058<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5059<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5060<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5061
5062<x:ref>second</x:ref> = 2DIGIT
5063<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5064 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5065<x:ref>start-line</x:ref> = Request-Line / Status-Line
5066
5067<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5068<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5069 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5070<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5071<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5072<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5073<x:ref>token</x:ref> = 1*tchar
5074<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
5075<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5076 transfer-extension
5077<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5078<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5079
5080<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5081
5082<x:ref>value</x:ref> = word
5083
5084<x:ref>word</x:ref> = token / quoted-string
5085
5086<x:ref>year</x:ref> = 4DIGIT
5087</artwork>
5088</figure>
5089<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5090; Chunked-Body defined but not used
5091; Content-Length defined but not used
5092; HTTP-message defined but not used
5093; Host defined but not used
5094; Request defined but not used
5095; Response defined but not used
5096; TE defined but not used
5097; URI-reference defined but not used
5098; http-URI defined but not used
5099; https-URI defined but not used
5100; partial-URI defined but not used
5101; special defined but not used
5102</artwork></figure></section>
5103<?ENDINC p1-messaging.abnf-appendix ?>
5104
5105<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5106
5107<section title="Since RFC2616">
5108<t>
5109  Extracted relevant partitions from <xref target="RFC2616"/>.
5110</t>
5111</section>
5112
5113<section title="Since draft-ietf-httpbis-p1-messaging-00">
5114<t>
5115  Closed issues:
5116  <list style="symbols"> 
5117    <t>
5118      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5119      "HTTP Version should be case sensitive"
5120      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5121    </t>
5122    <t>
5123      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5124      "'unsafe' characters"
5125      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5126    </t>
5127    <t>
5128      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5129      "Chunk Size Definition"
5130      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5131    </t>
5132    <t>
5133      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5134      "Message Length"
5135      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5136    </t>
5137    <t>
5138      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5139      "Media Type Registrations"
5140      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5141    </t>
5142    <t>
5143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5144      "URI includes query"
5145      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5146    </t>
5147    <t>
5148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5149      "No close on 1xx responses"
5150      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5151    </t>
5152    <t>
5153      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5154      "Remove 'identity' token references"
5155      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5156    </t>
5157    <t>
5158      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5159      "Import query BNF"
5160    </t>
5161    <t>
5162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5163      "qdtext BNF"
5164    </t>
5165    <t>
5166      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5167      "Normative and Informative references"
5168    </t>
5169    <t>
5170      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5171      "RFC2606 Compliance"
5172    </t>
5173    <t>
5174      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5175      "RFC977 reference"
5176    </t>
5177    <t>
5178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5179      "RFC1700 references"
5180    </t>
5181    <t>
5182      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5183      "inconsistency in date format explanation"
5184    </t>
5185    <t>
5186      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5187      "Date reference typo"
5188    </t>
5189    <t>
5190      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5191      "Informative references"
5192    </t>
5193    <t>
5194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5195      "ISO-8859-1 Reference"
5196    </t>
5197    <t>
5198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5199      "Normative up-to-date references"
5200    </t>
5201  </list>
5202</t>
5203<t>
5204  Other changes:
5205  <list style="symbols"> 
5206    <t>
5207      Update media type registrations to use RFC4288 template.
5208    </t>
5209    <t>
5210      Use names of RFC4234 core rules DQUOTE and WSP,
5211      fix broken ABNF for chunk-data
5212      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5213    </t>
5214  </list>
5215</t>
5216</section>
5217
5218<section title="Since draft-ietf-httpbis-p1-messaging-01">
5219<t>
5220  Closed issues:
5221  <list style="symbols"> 
5222    <t>
5223      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5224      "Bodies on GET (and other) requests"
5225    </t>
5226    <t>
5227      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5228      "Updating to RFC4288"
5229    </t>
5230    <t>
5231      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5232      "Status Code and Reason Phrase"
5233    </t>
5234    <t>
5235      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5236      "rel_path not used"
5237    </t>
5238  </list>
5239</t>
5240<t>
5241  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5242  <list style="symbols"> 
5243    <t>
5244      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5245      "trailer-part").
5246    </t>
5247    <t>
5248      Avoid underscore character in rule names ("http_URL" ->
5249      "http-URL", "abs_path" -> "path-absolute").
5250    </t>
5251    <t>
5252      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5253      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5254      have to be updated when switching over to RFC3986.
5255    </t>
5256    <t>
5257      Synchronize core rules with RFC5234.
5258    </t>
5259    <t>
5260      Get rid of prose rules that span multiple lines.
5261    </t>
5262    <t>
5263      Get rid of unused rules LOALPHA and UPALPHA.
5264    </t>
5265    <t>
5266      Move "Product Tokens" section (back) into Part 1, as "token" is used
5267      in the definition of the Upgrade header.
5268    </t>
5269    <t>
5270      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5271    </t>
5272    <t>
5273      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5274    </t>
5275  </list>
5276</t>
5277</section>
5278
5279<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5280<t>
5281  Closed issues:
5282  <list style="symbols"> 
5283    <t>
5284      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5285      "HTTP-date vs. rfc1123-date"
5286    </t>
5287    <t>
5288      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5289      "WS in quoted-pair"
5290    </t>
5291  </list>
5292</t>
5293<t>
5294  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5295  <list style="symbols"> 
5296    <t>
5297      Reference RFC 3984, and update header registrations for headers defined
5298      in this document.
5299    </t>
5300  </list>
5301</t>
5302<t>
5303  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5304  <list style="symbols"> 
5305    <t>
5306      Replace string literals when the string really is case-sensitive (HTTP-Version).
5307    </t>
5308  </list>
5309</t>
5310</section>
5311
5312<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5313<t>
5314  Closed issues:
5315  <list style="symbols"> 
5316    <t>
5317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5318      "Connection closing"
5319    </t>
5320    <t>
5321      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5322      "Move registrations and registry information to IANA Considerations"
5323    </t>
5324    <t>
5325      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5326      "need new URL for PAD1995 reference"
5327    </t>
5328    <t>
5329      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5330      "IANA Considerations: update HTTP URI scheme registration"
5331    </t>
5332    <t>
5333      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5334      "Cite HTTPS URI scheme definition"
5335    </t>
5336    <t>
5337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5338      "List-type headers vs Set-Cookie"
5339    </t>
5340  </list>
5341</t>
5342<t>
5343  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5344  <list style="symbols"> 
5345    <t>
5346      Replace string literals when the string really is case-sensitive (HTTP-Date).
5347    </t>
5348    <t>
5349      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5350    </t>
5351  </list>
5352</t>
5353</section>
5354
5355<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5356<t>
5357  Closed issues:
5358  <list style="symbols"> 
5359    <t>
5360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5361      "Out-of-date reference for URIs"
5362    </t>
5363    <t>
5364      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5365      "RFC 2822 is updated by RFC 5322"
5366    </t>
5367  </list>
5368</t>
5369<t>
5370  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5371  <list style="symbols"> 
5372    <t>
5373      Use "/" instead of "|" for alternatives.
5374    </t>
5375    <t>
5376      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5377    </t>
5378    <t>
5379      Only reference RFC 5234's core rules.
5380    </t>
5381    <t>
5382      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5383      whitespace ("OWS") and required whitespace ("RWS").
5384    </t>
5385    <t>
5386      Rewrite ABNFs to spell out whitespace rules, factor out
5387      header value format definitions.
5388    </t>
5389  </list>
5390</t>
5391</section>
5392
5393<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5394<t>
5395  Closed issues:
5396  <list style="symbols"> 
5397    <t>
5398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5399      "Header LWS"
5400    </t>
5401    <t>
5402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5403      "Sort 1.3 Terminology"
5404    </t>
5405    <t>
5406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5407      "RFC2047 encoded words"
5408    </t>
5409    <t>
5410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5411      "Character Encodings in TEXT"
5412    </t>
5413    <t>
5414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5415      "Line Folding"
5416    </t>
5417    <t>
5418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5419      "OPTIONS * and proxies"
5420    </t>
5421    <t>
5422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5423      "Reason-Phrase BNF"
5424    </t>
5425    <t>
5426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5427      "Use of TEXT"
5428    </t>
5429    <t>
5430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5431      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5432    </t>
5433    <t>
5434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5435      "RFC822 reference left in discussion of date formats"
5436    </t>
5437  </list>
5438</t>
5439<t>
5440  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5441  <list style="symbols"> 
5442    <t>
5443      Rewrite definition of list rules, deprecate empty list elements.
5444    </t>
5445    <t>
5446      Add appendix containing collected and expanded ABNF.
5447    </t>
5448  </list>
5449</t>
5450<t>
5451  Other changes:
5452  <list style="symbols"> 
5453    <t>
5454      Rewrite introduction; add mostly new Architecture Section.
5455    </t>
5456    <t>
5457      Move definition of quality values from Part 3 into Part 1;
5458      make TE request header grammar independent of accept-params (defined in Part 3).
5459    </t>
5460  </list>
5461</t>
5462</section>
5463
5464<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5465<t>
5466  Closed issues:
5467  <list style="symbols"> 
5468    <t>
5469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5470      "base for numeric protocol elements"
5471    </t>
5472    <t>
5473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5474      "comment ABNF"
5475    </t>
5476  </list>
5477</t>
5478<t>
5479  Partly resolved issues:
5480  <list style="symbols"> 
5481    <t>
5482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5483      "205 Bodies" (took out language that implied that there might be
5484      methods for which a request body MUST NOT be included)
5485    </t>
5486    <t>
5487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5488      "editorial improvements around HTTP-date"
5489    </t>
5490  </list>
5491</t>
5492</section>
5493
5494<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5495<t>
5496  Closed issues:
5497  <list style="symbols"> 
5498    <t>
5499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5500      "Repeating single-value headers"
5501    </t>
5502    <t>
5503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5504      "increase connection limit"
5505    </t>
5506    <t>
5507      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5508      "IP addresses in URLs"
5509    </t>
5510    <t>
5511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5512      "take over HTTP Upgrade Token Registry"
5513    </t>
5514    <t>
5515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5516      "CR and LF in chunk extension values"
5517    </t>
5518    <t>
5519      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5520      "HTTP/0.9 support"
5521    </t>
5522    <t>
5523      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5524      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5525    </t>
5526    <t>
5527      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5528      "move definitions of gzip/deflate/compress to part 1"
5529    </t>
5530    <t>
5531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5532      "disallow control characters in quoted-pair"
5533    </t>
5534  </list>
5535</t>
5536<t>
5537  Partly resolved issues:
5538  <list style="symbols"> 
5539    <t>
5540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5541      "update IANA requirements wrt Transfer-Coding values" (add the
5542      IANA Considerations subsection)
5543    </t>
5544  </list>
5545</t>
5546</section>
5547
5548<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5549<t>
5550  Closed issues:
5551  <list style="symbols"> 
5552    <t>
5553      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5554      "header parsing, treatment of leading and trailing OWS"
5555    </t>
5556  </list>
5557</t>
5558<t>
5559  Partly resolved issues:
5560  <list style="symbols"> 
5561    <t>
5562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5563      "Placement of 13.5.1 and 13.5.2"
5564    </t>
5565    <t>
5566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5567      "use of term "word" when talking about header structure"
5568    </t>
5569  </list>
5570</t>
5571</section>
5572
5573<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5574<t>
5575  Closed issues:
5576  <list style="symbols"> 
5577    <t>
5578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5579      "Clarification of the term 'deflate'"
5580    </t>
5581    <t>
5582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5583      "OPTIONS * and proxies"
5584    </t>
5585    <t>
5586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5587      "MIME-Version not listed in P1, general header fields"
5588    </t>
5589    <t>
5590      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5591      "IANA registry for content/transfer encodings"
5592    </t>
5593    <t>
5594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5595      "Case-sensitivity of HTTP-date"
5596    </t>
5597    <t>
5598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5599      "use of term "word" when talking about header structure"
5600    </t>
5601  </list>
5602</t>
5603<t>
5604  Partly resolved issues:
5605  <list style="symbols"> 
5606    <t>
5607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5608      "Term for the requested resource's URI"
5609    </t>
5610  </list>
5611</t>
5612</section>
5613
5614<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5615<t>
5616  Closed issues:
5617  <list style="symbols">
5618    <t>
5619      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5620      "Connection Closing"
5621    </t>
5622    <t>
5623      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5624      "Delimiting messages with multipart/byteranges"
5625    </t>
5626    <t>
5627      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5628      "Handling multiple Content-Length headers"
5629    </t>
5630    <t>
5631      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5632      "HTTP(s) URI scheme definitions"
5633    </t>
5634    <t>
5635      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5636      "consider removing the 'changes from 2068' sections"
5637    </t>
5638  </list>
5639</t>
5640</section>
5641
5642</section>
5643
5644</back>
5645</rfc>
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