source: draft-ietf-httpbis/latest/p1-messaging.xml @ 963

Last change on this file since 963 was 963, checked in by julian.reschke@…, 9 years ago

update status of issue 159 as work in progress (see #159)

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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.
1253</t>
1254<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1255  <x:ref>message-body</x:ref> = *OCTET
1256</artwork></figure>
1257<t>
1258   The message-body differs from the payload body only when a transfer-coding
1259   has been applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).  When one or more transfer-codings are
1260   applied to a payload in order to form the message-body, the
1261   Transfer-Encoding header field &MUST; contain the list of
1262   transfer-codings applied. Transfer-Encoding is a property of the message,
1263   not of the payload, and thus &MAY; be added or removed by any implementation
1264   along the request/response chain under the constraints found in
1265   <xref target="transfer.codings"/>.
1266</t>
1267<t>
1268   The rules for when a message-body is allowed in a message differ for
1269   requests and responses.
1270</t>
1271<t>
1272   The presence of a message-body in a request is signaled by the
1273   inclusion of a Content-Length or Transfer-Encoding header field in
1274   the request's header fields, even if the request method does not
1275   define any use for a message-body.  This allows the request
1276   message framing algorithm to be independent of method semantics.
1277</t>
1278<t>
1279   For response messages, whether or not a message-body is included with
1280   a message is dependent on both the request method and the response
1281   status code (<xref target="status.code.and.reason.phrase"/>).
1282   Responses to the HEAD request method never include a message-body
1283   because the associated response header fields (e.g., Transfer-Encoding,
1284   Content-Length, etc.) only indicate what their values would have been
1285   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1286   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1287   All other responses do include a message-body, although the body
1288   &MAY; be of zero length.
1289</t>
1290<t>
1291   The length of the message-body is determined by one of the following
1292   (in order of precedence):
1293</t>
1294<t>
1295  <list style="numbers">
1296    <x:lt><t>
1297     Any response to a HEAD request and any response with a status
1298     code of 100-199, 204, or 304 is always terminated by the first
1299     empty line after the header fields, regardless of the header
1300     fields present in the message, and thus cannot contain a message-body.
1301    </t></x:lt>
1302    <x:lt><t>
1303     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1304     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1305     is the final encoding, the message-body length is determined by reading
1306     and decoding the chunked data until the transfer-coding indicates the
1307     data is complete.
1308    </t>
1309    <t>
1310     If a Transfer-Encoding header field is present in a response and the
1311     "chunked" transfer-coding is not the final encoding, the message-body
1312     length is determined by reading the connection until it is closed by
1313     the server.
1314     If a Transfer-Encoding header field is present in a request and the
1315     "chunked" transfer-coding is not the final encoding, the message-body
1316     length cannot be determined reliably; the server &MUST; respond with
1317     the 400 (Bad Request) status code and then close the connection.
1318    </t>
1319    <t>
1320     If a message is received with both a Transfer-Encoding header field and a
1321     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1322     Such a message might indicate an attempt to perform request or response
1323     smuggling (bypass of security-related checks on message routing or content)
1324     and thus should be handled as an error.  The provided Content-Length &MUST;
1325     be removed, prior to forwarding the message downstream, or replaced with
1326     the real message-body length after the transfer-coding is decoded.
1327    </t></x:lt>
1328    <x:lt><t>
1329     If a message is received without Transfer-Encoding and with either
1330     multiple Content-Length header fields or a single Content-Length header
1331     field with an invalid value, then the message framing is invalid and
1332     &MUST; be treated as an error to prevent request or response smuggling.
1333     If this is a request message, the server &MUST; respond with
1334     a 400 (Bad Request) status code and then close the connection.
1335     If this is a response message received by a proxy or gateway, the proxy
1336     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1337     status code as its downstream response, and then close the connection.
1338     If this is a response message received by a user-agent, the message-body
1339     length is determined by reading the connection until it is closed;
1340     an error &SHOULD; be indicated to the user.
1341    </t></x:lt>
1342    <x:lt><t>
1343     If a valid Content-Length header field (<xref target="header.content-length"/>)
1344     is present without Transfer-Encoding, its decimal value defines the
1345     message-body length in octets.  If the actual number of octets sent in
1346     the message is less than the indicated Content-Length, the recipient
1347     &MUST; consider the message to be incomplete and treat the connection
1348     as no longer usable.
1349     If the actual number of octets sent in the message is more than the indicated
1350     Content-Length, the recipient &MUST; only process the message-body up to the
1351     field value's number of octets; the remainder of the message &MUST; either
1352     be discarded or treated as the next message in a pipeline.  For the sake of
1353     robustness, a user-agent &MAY; attempt to detect and correct such an error
1354     in message framing if it is parsing the response to the last request on
1355     on a connection and the connection has been closed by the server.
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<t>
1411   A server &MUST; read the entire request message-body or close
1412   the connection after sending its response, since otherwise the
1413   remaining data on a persistent connection would be misinterpreted
1414   as the next request.  Likewise,
1415   a client &MUST; read the entire response message-body if it intends
1416   to reuse the same connection for a subsequent request.  Pipelining
1417   multiple requests on a connection is described in <xref target="pipelining"/>.
1418</t>
1419</section>
1420
1421<section title="General Header Fields" anchor="general.header.fields">
1422  <x:anchor-alias value="general-header"/>
1423<t>
1424   There are a few header fields which have general applicability for
1425   both request and response messages, but which do not apply to the
1426   payload being transferred. These header fields apply only to the
1427   message being transmitted.
1428</t>
1429<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1430  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1431                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1432                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1433                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1434                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1435                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1436                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1437                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1438                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1439                 / <x:ref>MIME-Version</x:ref>             ; &header-mime-version;
1440</artwork></figure>
1441<t>
1442   General-header field names can be extended reliably only in
1443   combination with a change in the protocol version. However, new or
1444   experimental header fields might be given the semantics of general
1445   header fields if all parties in the communication recognize them to
1446   be general-header fields. Unrecognized header fields are treated as
1447   entity-header fields.
1448</t>
1449</section>
1450</section>
1451
1452<section title="Request" anchor="request">
1453  <x:anchor-alias value="Request"/>
1454<t>
1455   A request message from a client to a server includes, within the
1456   first line of that message, the method to be applied to the resource,
1457   the identifier of the resource, and the protocol version in use.
1458</t>
1459<!--                 Host                      ; should be moved here eventually -->
1460<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1461  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1462                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1463                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1464                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1465                  <x:ref>CRLF</x:ref>
1466                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1467</artwork></figure>
1468
1469<section title="Request-Line" anchor="request-line">
1470  <x:anchor-alias value="Request-Line"/>
1471<t>
1472   The Request-Line begins with a method token, followed by the
1473   request-target and the protocol version, and ending with CRLF. The
1474   elements are separated by SP characters. No CR or LF is allowed
1475   except in the final CRLF sequence.
1476</t>
1477<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1478  <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>
1479</artwork></figure>
1480
1481<section title="Method" anchor="method">
1482  <x:anchor-alias value="Method"/>
1483<t>
1484   The Method  token indicates the method to be performed on the
1485   resource identified by the request-target. The method is case-sensitive.
1486</t>
1487<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1488  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1489</artwork></figure>
1490</section>
1491
1492<section title="request-target" anchor="request-target">
1493  <x:anchor-alias value="request-target"/>
1494<t>
1495   The request-target
1496   identifies the resource upon which to apply the request.
1497</t>
1498<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1499  <x:ref>request-target</x:ref> = "*"
1500                 / <x:ref>absolute-URI</x:ref>
1501                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1502                 / <x:ref>authority</x:ref>
1503</artwork></figure>
1504<t>
1505   The four options for request-target are dependent on the nature of the
1506   request.
1507</t>   
1508<t>
1509   The asterisk "*" means that the request does not apply to a
1510   particular resource, but to the server itself, and is only allowed
1511   when the method used does not necessarily apply to a resource. One
1512   example would be
1513</t>
1514<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1515OPTIONS * HTTP/1.1
1516</artwork></figure>
1517<t>
1518   The absolute-URI form is &REQUIRED; when the request is being made to a
1519   proxy. The proxy is requested to forward the request or service it
1520   from a valid cache, and return the response. Note that the proxy &MAY;
1521   forward the request on to another proxy or directly to the server
1522   specified by the absolute-URI. In order to avoid request loops, a
1523   proxy &MUST; be able to recognize all of its server names, including
1524   any aliases, local variations, and the numeric IP address. An example
1525   Request-Line would be:
1526</t>
1527<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1528GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1529</artwork></figure>
1530<t>
1531   To allow for transition to absolute-URIs in all requests in future
1532   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1533   form in requests, even though HTTP/1.1 clients will only generate
1534   them in requests to proxies.
1535</t>
1536<t>
1537   The authority form is only used by the CONNECT method (&CONNECT;).
1538</t>
1539<t>
1540   The most common form of request-target is that used to identify a
1541   resource on an origin server or gateway. In this case the absolute
1542   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1543   the request-target, and the network location of the URI (authority) &MUST;
1544   be transmitted in a Host header field. For example, a client wishing
1545   to retrieve the resource above directly from the origin server would
1546   create a TCP connection to port 80 of the host "www.example.org" and send
1547   the lines:
1548</t>
1549<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1550GET /pub/WWW/TheProject.html HTTP/1.1
1551Host: www.example.org
1552</artwork></figure>
1553<t>
1554   followed by the remainder of the Request. Note that the absolute path
1555   cannot be empty; if none is present in the original URI, it &MUST; be
1556   given as "/" (the server root).
1557</t>
1558<t>
1559   If a proxy receives a request without any path in the request-target and
1560   the method specified is capable of supporting the asterisk form of
1561   request-target, then the last proxy on the request chain &MUST; forward the
1562   request with "*" as the final request-target.
1563</t>
1564<figure><preamble>   
1565   For example, the request
1566</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1567OPTIONS http://www.example.org:8001 HTTP/1.1
1568</artwork></figure>
1569<figure><preamble>   
1570  would be forwarded by the proxy as
1571</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1572OPTIONS * HTTP/1.1
1573Host: www.example.org:8001
1574</artwork>
1575<postamble>
1576   after connecting to port 8001 of host "www.example.org".
1577</postamble>
1578</figure>
1579<t>
1580   The request-target is transmitted in the format specified in
1581   <xref target="http.uri"/>. If the request-target is percent-encoded
1582   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1583   &MUST; decode the request-target in order to
1584   properly interpret the request. Servers &SHOULD; respond to invalid
1585   request-targets with an appropriate status code.
1586</t>
1587<t>
1588   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1589   received request-target when forwarding it to the next inbound server,
1590   except as noted above to replace a null path-absolute with "/" or "*".
1591</t>
1592<x:note>
1593  <t>
1594    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1595    meaning of the request when the origin server is improperly using
1596    a non-reserved URI character for a reserved purpose.  Implementors
1597    should be aware that some pre-HTTP/1.1 proxies have been known to
1598    rewrite the request-target.
1599  </t>
1600</x:note>
1601<t>
1602   HTTP does not place a pre-defined limit on the length of a request-target.
1603   A server &MUST; be prepared to receive URIs of unbounded length and
1604   respond with the 414 (URI Too Long) status code if the received
1605   request-target would be longer than the server wishes to handle
1606   (see &status-414;).
1607</t>
1608<t>
1609   Various ad-hoc limitations on request-target length are found in practice.
1610   It is &RECOMMENDED; that all HTTP senders and recipients support
1611   request-target lengths of 8000 or more octets.
1612</t>
1613<x:note>
1614  <t>
1615    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1616    are not part of the request-target and thus will not be transmitted
1617    in an HTTP request.
1618  </t>
1619</x:note>
1620</section>
1621</section>
1622
1623<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1624<t>
1625   The exact resource identified by an Internet request is determined by
1626   examining both the request-target and the Host header field.
1627</t>
1628<t>
1629   An origin server that does not allow resources to differ by the
1630   requested host &MAY; ignore the Host header field value when
1631   determining the resource identified by an HTTP/1.1 request. (But see
1632   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1633   for other requirements on Host support in HTTP/1.1.)
1634</t>
1635<t>
1636   An origin server that does differentiate resources based on the host
1637   requested (sometimes referred to as virtual hosts or vanity host
1638   names) &MUST; use the following rules for determining the requested
1639   resource on an HTTP/1.1 request:
1640  <list style="numbers">
1641    <t>If request-target is an absolute-URI, the host is part of the
1642     request-target. Any Host header field value in the request &MUST; be
1643     ignored.</t>
1644    <t>If the request-target is not an absolute-URI, and the request includes
1645     a Host header field, the host is determined by the Host header
1646     field value.</t>
1647    <t>If the host as determined by rule 1 or 2 is not a valid host on
1648     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1649  </list>
1650</t>
1651<t>
1652   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1653   attempt to use heuristics (e.g., examination of the URI path for
1654   something unique to a particular host) in order to determine what
1655   exact resource is being requested.
1656</t>
1657</section>
1658
1659<section title="Effective Request URI" anchor="effective.request.uri">
1660  <iref primary="true" item="Effective Request URI"/>
1661<t>
1662   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1663   for the resource they are intended for; instead, the value needs to be inferred from the
1664   request-target, Host header and other context. The result of this process is
1665   the "Effective Request URI".
1666</t>
1667<t>
1668   If the request-target is an absolute-URI, then the Effective Request URI is
1669   the request-target.
1670</t>
1671<t>
1672   If the request-target uses the path-absolute (plus optional query) syntax
1673   or if it is just the asterisk "*", then the Effective Request URI is
1674   constructed by concatenating
1675</t>
1676<t>
1677  <list style="symbols">
1678    <t>
1679      the scheme name: "http" if the request was received over an insecure
1680      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1681      connection,
1682    </t>
1683    <t>
1684      the character sequence "://",
1685    </t>
1686    <t>
1687      the authority component, as specified in the Host header
1688      (<xref target="header.host"/>) and determined by the rules in
1689      <xref target="the.resource.identified.by.a.request"/>,
1690      <cref anchor="effrequri-nohost" source="jre">Do we need to include the handling of missing hosts in HTTP/1.0 messages, as
1691      described in <xref target="the.resource.identified.by.a.request"/>? -- See <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/></cref>
1692      and
1693    </t>
1694    <t>
1695      the request-target obtained from the Request-Line, unless the
1696      request-target is just the asterisk "*".
1697    </t>
1698  </list>
1699</t>
1700<t>
1701   Otherwise, when request-target uses the authority form, the Effective
1702   Request URI is undefined.
1703</t>
1704<figure>
1705<preamble>
1706   Example 1: the Effective Request URI for the message
1707</preamble> 
1708<artwork type="example" x:indent-with="  ">
1709GET /pub/WWW/TheProject.html HTTP/1.1
1710Host: www.example.org:8080
1711</artwork>
1712<postamble>
1713  (received over an insecure TCP connection) is "http", plus "://", plus the
1714  authority component "www.example.org:8080", plus the request-target
1715  "/pub/WWW/TheProject.html", thus
1716  "http://www.example.org:8080/pub/WWW/TheProject.html".
1717</postamble>
1718</figure>
1719<figure>
1720<preamble>
1721   Example 2: the Effective Request URI for the message
1722</preamble> 
1723<artwork type="example" x:indent-with="  ">
1724GET * HTTP/1.1
1725Host: www.example.org
1726</artwork>
1727<postamble>
1728  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1729  authority component "www.example.org", thus "https://www.example.org".
1730</postamble>
1731</figure>
1732<t>
1733   Effective Request URIs are compared using the rules described in
1734   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1735   be treated as equivalent to an absolute path of "/".
1736</t> 
1737</section>
1738
1739</section>
1740
1741
1742<section title="Response" anchor="response">
1743  <x:anchor-alias value="Response"/>
1744<t>
1745   After receiving and interpreting a request message, a server responds
1746   with an HTTP response message.
1747</t>
1748<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1749  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1750                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1751                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1752                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1753                  <x:ref>CRLF</x:ref>
1754                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1755</artwork></figure>
1756
1757<section title="Status-Line" anchor="status-line">
1758  <x:anchor-alias value="Status-Line"/>
1759<t>
1760   The first line of a Response message is the Status-Line, consisting
1761   of the protocol version followed by a numeric status code and its
1762   associated textual phrase, with each element separated by SP
1763   characters. No CR or LF is allowed except in the final CRLF sequence.
1764</t>
1765<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1766  <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>
1767</artwork></figure>
1768
1769<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1770  <x:anchor-alias value="Reason-Phrase"/>
1771  <x:anchor-alias value="Status-Code"/>
1772<t>
1773   The Status-Code element is a 3-digit integer result code of the
1774   attempt to understand and satisfy the request. These codes are fully
1775   defined in &status-codes;.  The Reason Phrase exists for the sole
1776   purpose of providing a textual description associated with the numeric
1777   status code, out of deference to earlier Internet application protocols
1778   that were more frequently used with interactive text clients.
1779   A client &SHOULD; ignore the content of the Reason Phrase.
1780</t>
1781<t>
1782   The first digit of the Status-Code defines the class of response. The
1783   last two digits do not have any categorization role. There are 5
1784   values for the first digit:
1785  <list style="symbols">
1786    <t>
1787      1xx: Informational - Request received, continuing process
1788    </t>
1789    <t>
1790      2xx: Success - The action was successfully received,
1791        understood, and accepted
1792    </t>
1793    <t>
1794      3xx: Redirection - Further action must be taken in order to
1795        complete the request
1796    </t>
1797    <t>
1798      4xx: Client Error - The request contains bad syntax or cannot
1799        be fulfilled
1800    </t>
1801    <t>
1802      5xx: Server Error - The server failed to fulfill an apparently
1803        valid request
1804    </t>
1805  </list>
1806</t>
1807<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"/>
1808  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1809  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1810</artwork></figure>
1811</section>
1812</section>
1813
1814</section>
1815
1816
1817<section title="Protocol Parameters" anchor="protocol.parameters">
1818
1819<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1820  <x:anchor-alias value="HTTP-date"/>
1821<t>
1822   HTTP applications have historically allowed three different formats
1823   for date/time stamps.
1824   However, the preferred format is
1825   a fixed-length subset of that defined by <xref target="RFC1123"/>:
1826</t>
1827<figure><artwork type="example" x:indent-with="  ">
1828Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1829</artwork></figure>
1830<t>
1831   The other formats are described here only for compatibility with obsolete
1832   implementations.
1833</t>
1834<figure><artwork type="example" x:indent-with="  ">
1835Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1836Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1837</artwork></figure>
1838<t>
1839   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1840   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1841   only generate the RFC 1123 format for representing HTTP-date values
1842   in header fields. See <xref target="tolerant.applications"/> for further information.
1843</t>
1844<t>
1845   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1846   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1847   equal to UTC (Coordinated Universal Time). This is indicated in the
1848   first two formats by the inclusion of "GMT" as the three-letter
1849   abbreviation for time zone, and &MUST; be assumed when reading the
1850   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1851   additional whitespace beyond that specifically included as SP in the
1852   grammar.
1853</t>
1854<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1855  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1856</artwork></figure>
1857<t anchor="preferred.date.format">
1858  <x:anchor-alias value="rfc1123-date"/>
1859  <x:anchor-alias value="time-of-day"/>
1860  <x:anchor-alias value="hour"/>
1861  <x:anchor-alias value="minute"/>
1862  <x:anchor-alias value="second"/>
1863  <x:anchor-alias value="day-name"/>
1864  <x:anchor-alias value="day"/>
1865  <x:anchor-alias value="month"/>
1866  <x:anchor-alias value="year"/>
1867  <x:anchor-alias value="GMT"/>
1868  Preferred format:
1869</t>
1870<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"/>
1871  <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>
1872
1873  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1874               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1875               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1876               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1877               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1878               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1879               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1880               
1881  <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>
1882               ; e.g., 02 Jun 1982
1883
1884  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1885  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1886               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1887               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1888               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1889               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1890               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1891               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1892               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1893               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1894               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1895               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1896               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1897  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1898
1899  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1900
1901  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1902                 ; 00:00:00 - 23:59:59
1903                 
1904  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1905  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1906  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1907</artwork></figure>
1908<t>
1909  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1910  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1911  same as those defined for the RFC 5322 constructs
1912  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1913</t>
1914<t anchor="obsolete.date.formats">
1915  <x:anchor-alias value="obs-date"/>
1916  <x:anchor-alias value="rfc850-date"/>
1917  <x:anchor-alias value="asctime-date"/>
1918  <x:anchor-alias value="date1"/>
1919  <x:anchor-alias value="date2"/>
1920  <x:anchor-alias value="date3"/>
1921  <x:anchor-alias value="rfc1123-date"/>
1922  <x:anchor-alias value="day-name-l"/>
1923  Obsolete formats:
1924</t>
1925<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1926  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1927</artwork></figure>
1928<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1929  <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>
1930  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1931                 ; day-month-year (e.g., 02-Jun-82)
1932
1933  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1934         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1935         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1936         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1937         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1938         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1939         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1940</artwork></figure>
1941<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1942  <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>
1943  <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> ))
1944                 ; month day (e.g., Jun  2)
1945</artwork></figure>
1946<x:note>
1947  <t>
1948    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1949    accepting date values that might have been sent by non-HTTP
1950    applications, as is sometimes the case when retrieving or posting
1951    messages via proxies/gateways to SMTP or NNTP.
1952  </t>
1953</x:note>
1954<x:note>
1955  <t>
1956    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1957    to their usage within the protocol stream. Clients and servers are
1958    not required to use these formats for user presentation, request
1959    logging, etc.
1960  </t>
1961</x:note>
1962</section>
1963
1964<section title="Transfer Codings" anchor="transfer.codings">
1965  <x:anchor-alias value="transfer-coding"/>
1966  <x:anchor-alias value="transfer-extension"/>
1967<t>
1968   Transfer-coding values are used to indicate an encoding
1969   transformation that has been, can be, or might need to be applied to a
1970   payload body in order to ensure "safe transport" through the network.
1971   This differs from a content coding in that the transfer-coding is a
1972   property of the message rather than a property of the representation
1973   that is being transferred.
1974</t>
1975<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1976  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1977                          / "compress" ; <xref target="compress.coding"/>
1978                          / "deflate" ; <xref target="deflate.coding"/>
1979                          / "gzip" ; <xref target="gzip.coding"/>
1980                          / <x:ref>transfer-extension</x:ref>
1981  <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> )
1982</artwork></figure>
1983<t anchor="rule.parameter">
1984  <x:anchor-alias value="attribute"/>
1985  <x:anchor-alias value="transfer-parameter"/>
1986  <x:anchor-alias value="value"/>
1987   Parameters are in the form of attribute/value pairs.
1988</t>
1989<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"/>
1990  <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>
1991  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1992  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
1993</artwork></figure>
1994<t>
1995   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1996   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1997   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1998</t>
1999<t>
2000   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2001   MIME, which were designed to enable safe transport of binary data over a
2002   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2003   However, safe transport
2004   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2005   the only unsafe characteristic of message-bodies is the difficulty in
2006   determining the exact message body length (<xref target="message.body"/>),
2007   or the desire to encrypt data over a shared transport.
2008</t>
2009<t>
2010   A server that receives a request message with a transfer-coding it does
2011   not understand &SHOULD; respond with 501 (Not Implemented) and then
2012   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2013   client.
2014</t>
2015
2016<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2017  <iref item="chunked (Coding Format)"/>
2018  <iref item="Coding Format" subitem="chunked"/>
2019  <x:anchor-alias value="chunk"/>
2020  <x:anchor-alias value="Chunked-Body"/>
2021  <x:anchor-alias value="chunk-data"/>
2022  <x:anchor-alias value="chunk-ext"/>
2023  <x:anchor-alias value="chunk-ext-name"/>
2024  <x:anchor-alias value="chunk-ext-val"/>
2025  <x:anchor-alias value="chunk-size"/>
2026  <x:anchor-alias value="last-chunk"/>
2027  <x:anchor-alias value="trailer-part"/>
2028  <x:anchor-alias value="quoted-str-nf"/>
2029  <x:anchor-alias value="qdtext-nf"/>
2030<t>
2031   The chunked encoding modifies the body of a message in order to
2032   transfer it as a series of chunks, each with its own size indicator,
2033   followed by an &OPTIONAL; trailer containing entity-header fields. This
2034   allows dynamically produced content to be transferred along with the
2035   information necessary for the recipient to verify that it has
2036   received the full message.
2037</t>
2038<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"/>
2039  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2040                   <x:ref>last-chunk</x:ref>
2041                   <x:ref>trailer-part</x:ref>
2042                   <x:ref>CRLF</x:ref>
2043 
2044  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2045                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2046  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2047  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2048 
2049  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2050                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2051  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2052  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2053  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2054  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
2055 
2056  <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>
2057                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2058  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2059                 ; <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> 
2060</artwork></figure>
2061<t>
2062   The chunk-size field is a string of hex digits indicating the size of
2063   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2064   zero, followed by the trailer, which is terminated by an empty line.
2065</t>
2066<t>
2067   The trailer allows the sender to include additional HTTP header
2068   fields at the end of the message. The Trailer header field can be
2069   used to indicate which header fields are included in a trailer (see
2070   <xref target="header.trailer"/>).
2071</t>
2072<t>
2073   A server using chunked transfer-coding in a response &MUST-NOT; use the
2074   trailer for any header fields unless at least one of the following is
2075   true:
2076  <list style="numbers">
2077    <t>the request included a TE header field that indicates "trailers" is
2078     acceptable in the transfer-coding of the  response, as described in
2079     <xref target="header.te"/>; or,</t>
2080
2081    <t>the server is the origin server for the response, the trailer
2082     fields consist entirely of optional metadata, and the recipient
2083     could use the message (in a manner acceptable to the origin server)
2084     without receiving this metadata.  In other words, the origin server
2085     is willing to accept the possibility that the trailer fields might
2086     be silently discarded along the path to the client.</t>
2087  </list>
2088</t>
2089<t>
2090   This requirement prevents an interoperability failure when the
2091   message is being received by an HTTP/1.1 (or later) proxy and
2092   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2093   compliance with the protocol would have necessitated a possibly
2094   infinite buffer on the proxy.
2095</t>
2096<t>
2097   A process for decoding the "chunked" transfer-coding
2098   can be represented in pseudo-code as:
2099</t>
2100<figure><artwork type="code">
2101  length := 0
2102  read chunk-size, chunk-ext (if any) and CRLF
2103  while (chunk-size &gt; 0) {
2104     read chunk-data and CRLF
2105     append chunk-data to decoded-body
2106     length := length + chunk-size
2107     read chunk-size and CRLF
2108  }
2109  read header-field
2110  while (header-field not empty) {
2111     append header-field to existing header fields
2112     read header-field
2113  }
2114  Content-Length := length
2115  Remove "chunked" from Transfer-Encoding
2116</artwork></figure>
2117<t>
2118   All HTTP/1.1 applications &MUST; be able to receive and decode the
2119   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2120   they do not understand.
2121</t>
2122<t>
2123   Since "chunked" is the only transfer-coding required to be understood
2124   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2125   on a persistent connection.  Whenever a transfer-coding is applied to
2126   a payload body in a request, the final transfer-coding applied &MUST;
2127   be "chunked".  If a transfer-coding is applied to a response payload
2128   body, then either the final transfer-coding applied &MUST; be "chunked"
2129   or the message &MUST; be terminated by closing the connection. When the
2130   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2131   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2132   be applied more than once in a message-body.
2133</t>
2134</section>
2135
2136<section title="Compression Codings" anchor="compression.codings">
2137<t>
2138   The codings defined below can be used to compress the payload of a
2139   message.
2140</t>
2141<x:note><t>
2142   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2143   is not desirable and is discouraged for future encodings. Their
2144   use here is representative of historical practice, not good
2145   design.
2146</t></x:note>
2147<x:note><t>
2148   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2149   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2150   equivalent to "gzip" and "compress" respectively.
2151</t></x:note>
2152
2153<section title="Compress Coding" anchor="compress.coding">
2154<iref item="compress (Coding Format)"/>
2155<iref item="Coding Format" subitem="compress"/>
2156<t>
2157   The "compress" format is produced by the common UNIX file compression
2158   program "compress". This format is an adaptive Lempel-Ziv-Welch
2159   coding (LZW).
2160</t>
2161</section>
2162
2163<section title="Deflate Coding" anchor="deflate.coding">
2164<iref item="deflate (Coding Format)"/>
2165<iref item="Coding Format" subitem="deflate"/>
2166<t>
2167   The "deflate" format is defined as the "deflate" compression mechanism
2168   (described in <xref target="RFC1951"/>) used inside the "zlib"
2169   data format (<xref target="RFC1950"/>).
2170</t>
2171<x:note>
2172  <t>
2173    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2174    compressed data without the zlib wrapper.
2175   </t>
2176</x:note>
2177</section>
2178
2179<section title="Gzip Coding" anchor="gzip.coding">
2180<iref item="gzip (Coding Format)"/>
2181<iref item="Coding Format" subitem="gzip"/>
2182<t>
2183   The "gzip" format is produced by the file compression program
2184   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2185   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2186</t>
2187</section>
2188
2189</section>
2190
2191<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2192<t>
2193   The HTTP Transfer Coding Registry defines the name space for the transfer
2194   coding names.
2195</t>
2196<t>
2197   Registrations &MUST; include the following fields:
2198   <list style="symbols">
2199     <t>Name</t>
2200     <t>Description</t>
2201     <t>Pointer to specification text</t>
2202   </list>
2203</t>
2204<t>
2205   Names of transfer codings &MUST-NOT; overlap with names of content codings
2206   (&content-codings;), unless the encoding transformation is identical (as it
2207   is the case for the compression codings defined in
2208   <xref target="compression.codings"/>).
2209</t>
2210<t>
2211   Values to be added to this name space require a specification
2212   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2213   conform to the purpose of transfer coding defined in this section.
2214</t>
2215<t>
2216   The registry itself is maintained at
2217   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2218</t>
2219</section>
2220</section>
2221
2222<section title="Product Tokens" anchor="product.tokens">
2223  <x:anchor-alias value="product"/>
2224  <x:anchor-alias value="product-version"/>
2225<t>
2226   Product tokens are used to allow communicating applications to
2227   identify themselves by software name and version. Most fields using
2228   product tokens also allow sub-products which form a significant part
2229   of the application to be listed, separated by whitespace. By
2230   convention, the products are listed in order of their significance
2231   for identifying the application.
2232</t>
2233<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2234  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2235  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2236</artwork></figure>
2237<t>
2238   Examples:
2239</t>
2240<figure><artwork type="example">
2241  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2242  Server: Apache/0.8.4
2243</artwork></figure>
2244<t>
2245   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2246   used for advertising or other non-essential information. Although any
2247   token character &MAY; appear in a product-version, this token &SHOULD;
2248   only be used for a version identifier (i.e., successive versions of
2249   the same product &SHOULD; only differ in the product-version portion of
2250   the product value).
2251</t>
2252</section>
2253
2254<section title="Quality Values" anchor="quality.values">
2255  <x:anchor-alias value="qvalue"/>
2256<t>
2257   Both transfer codings (TE request header, <xref target="header.te"/>)
2258   and content negotiation (&content.negotiation;) use short "floating point"
2259   numbers to indicate the relative importance ("weight") of various
2260   negotiable parameters.  A weight is normalized to a real number in
2261   the range 0 through 1, where 0 is the minimum and 1 the maximum
2262   value. If a parameter has a quality value of 0, then content with
2263   this parameter is "not acceptable" for the client. HTTP/1.1
2264   applications &MUST-NOT; generate more than three digits after the
2265   decimal point. User configuration of these values &SHOULD; also be
2266   limited in this fashion.
2267</t>
2268<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2269  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2270                 / ( "1" [ "." 0*3("0") ] )
2271</artwork></figure>
2272<x:note>
2273  <t>
2274     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2275     relative degradation in desired quality.
2276  </t>
2277</x:note>
2278</section>
2279
2280</section>
2281
2282<section title="Connections" anchor="connections">
2283
2284<section title="Persistent Connections" anchor="persistent.connections">
2285
2286<section title="Purpose" anchor="persistent.purpose">
2287<t>
2288   Prior to persistent connections, a separate TCP connection was
2289   established to fetch each URL, increasing the load on HTTP servers
2290   and causing congestion on the Internet. The use of inline images and
2291   other associated data often requires a client to make multiple
2292   requests of the same server in a short amount of time. Analysis of
2293   these performance problems and results from a prototype
2294   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2295   measurements of actual HTTP/1.1 implementations show good
2296   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2297   T/TCP <xref target="Tou1998"/>.
2298</t>
2299<t>
2300   Persistent HTTP connections have a number of advantages:
2301  <list style="symbols">
2302      <t>
2303        By opening and closing fewer TCP connections, CPU time is saved
2304        in routers and hosts (clients, servers, proxies, gateways,
2305        tunnels, or caches), and memory used for TCP protocol control
2306        blocks can be saved in hosts.
2307      </t>
2308      <t>
2309        HTTP requests and responses can be pipelined on a connection.
2310        Pipelining allows a client to make multiple requests without
2311        waiting for each response, allowing a single TCP connection to
2312        be used much more efficiently, with much lower elapsed time.
2313      </t>
2314      <t>
2315        Network congestion is reduced by reducing the number of packets
2316        caused by TCP opens, and by allowing TCP sufficient time to
2317        determine the congestion state of the network.
2318      </t>
2319      <t>
2320        Latency on subsequent requests is reduced since there is no time
2321        spent in TCP's connection opening handshake.
2322      </t>
2323      <t>
2324        HTTP can evolve more gracefully, since errors can be reported
2325        without the penalty of closing the TCP connection. Clients using
2326        future versions of HTTP might optimistically try a new feature,
2327        but if communicating with an older server, retry with old
2328        semantics after an error is reported.
2329      </t>
2330    </list>
2331</t>
2332<t>
2333   HTTP implementations &SHOULD; implement persistent connections.
2334</t>
2335</section>
2336
2337<section title="Overall Operation" anchor="persistent.overall">
2338<t>
2339   A significant difference between HTTP/1.1 and earlier versions of
2340   HTTP is that persistent connections are the default behavior of any
2341   HTTP connection. That is, unless otherwise indicated, the client
2342   &SHOULD; assume that the server will maintain a persistent connection,
2343   even after error responses from the server.
2344</t>
2345<t>
2346   Persistent connections provide a mechanism by which a client and a
2347   server can signal the close of a TCP connection. This signaling takes
2348   place using the Connection header field (<xref target="header.connection"/>). Once a close
2349   has been signaled, the client &MUST-NOT; send any more requests on that
2350   connection.
2351</t>
2352
2353<section title="Negotiation" anchor="persistent.negotiation">
2354<t>
2355   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2356   maintain a persistent connection unless a Connection header including
2357   the connection-token "close" was sent in the request. If the server
2358   chooses to close the connection immediately after sending the
2359   response, it &SHOULD; send a Connection header including the
2360   connection-token "close".
2361</t>
2362<t>
2363   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2364   decide to keep it open based on whether the response from a server
2365   contains a Connection header with the connection-token close. In case
2366   the client does not want to maintain a connection for more than that
2367   request, it &SHOULD; send a Connection header including the
2368   connection-token close.
2369</t>
2370<t>
2371   If either the client or the server sends the close token in the
2372   Connection header, that request becomes the last one for the
2373   connection.
2374</t>
2375<t>
2376   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2377   maintained for HTTP versions less than 1.1 unless it is explicitly
2378   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2379   compatibility with HTTP/1.0 clients.
2380</t>
2381<t>
2382   In order to remain persistent, all messages on the connection &MUST;
2383   have a self-defined message length (i.e., one not defined by closure
2384   of the connection), as described in <xref target="message.body"/>.
2385</t>
2386</section>
2387
2388<section title="Pipelining" anchor="pipelining">
2389<t>
2390   A client that supports persistent connections &MAY; "pipeline" its
2391   requests (i.e., send multiple requests without waiting for each
2392   response). A server &MUST; send its responses to those requests in the
2393   same order that the requests were received.
2394</t>
2395<t>
2396   Clients which assume persistent connections and pipeline immediately
2397   after connection establishment &SHOULD; be prepared to retry their
2398   connection if the first pipelined attempt fails. If a client does
2399   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2400   persistent. Clients &MUST; also be prepared to resend their requests if
2401   the server closes the connection before sending all of the
2402   corresponding responses.
2403</t>
2404<t>
2405   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2406   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2407   premature termination of the transport connection could lead to
2408   indeterminate results. A client wishing to send a non-idempotent
2409   request &SHOULD; wait to send that request until it has received the
2410   response status line for the previous request.
2411</t>
2412</section>
2413</section>
2414
2415<section title="Proxy Servers" anchor="persistent.proxy">
2416<t>
2417   It is especially important that proxies correctly implement the
2418   properties of the Connection header field as specified in <xref target="header.connection"/>.
2419</t>
2420<t>
2421   The proxy server &MUST; signal persistent connections separately with
2422   its clients and the origin servers (or other proxy servers) that it
2423   connects to. Each persistent connection applies to only one transport
2424   link.
2425</t>
2426<t>
2427   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2428   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2429   for information and discussion of the problems with the Keep-Alive header
2430   implemented by many HTTP/1.0 clients).
2431</t>
2432
2433<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2434<!--<t>
2435  <cref anchor="TODO-end-to-end" source="jre">
2436    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2437    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2438  </cref>
2439</t>-->
2440<t>
2441   For the purpose of defining the behavior of caches and non-caching
2442   proxies, we divide HTTP headers into two categories:
2443  <list style="symbols">
2444      <t>End-to-end headers, which are  transmitted to the ultimate
2445        recipient of a request or response. End-to-end headers in
2446        responses MUST be stored as part of a cache entry and &MUST; be
2447        transmitted in any response formed from a cache entry.</t>
2448
2449      <t>Hop-by-hop headers, which are meaningful only for a single
2450        transport-level connection, and are not stored by caches or
2451        forwarded by proxies.</t>
2452  </list>
2453</t>
2454<t>
2455   The following HTTP/1.1 headers are hop-by-hop headers:
2456  <list style="symbols">
2457      <t>Connection</t>
2458      <t>Keep-Alive</t>
2459      <t>Proxy-Authenticate</t>
2460      <t>Proxy-Authorization</t>
2461      <t>TE</t>
2462      <t>Trailer</t>
2463      <t>Transfer-Encoding</t>
2464      <t>Upgrade</t>
2465  </list>
2466</t>
2467<t>
2468   All other headers defined by HTTP/1.1 are end-to-end headers.
2469</t>
2470<t>
2471   Other hop-by-hop headers &MUST; be listed in a Connection header
2472   (<xref target="header.connection"/>).
2473</t>
2474</section>
2475
2476<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2477<!--<t>
2478  <cref anchor="TODO-non-mod-headers" source="jre">
2479    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2480    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2481  </cref>
2482</t>-->
2483<t>
2484   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2485   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2486   modify an end-to-end header unless the definition of that header requires
2487   or specifically allows that.
2488</t>
2489<t>
2490   A transparent proxy &MUST-NOT; modify any of the following fields in a
2491   request or response, and it &MUST-NOT; add any of these fields if not
2492   already present:
2493  <list style="symbols">
2494      <t>Content-Location</t>
2495      <t>Content-MD5</t>
2496      <t>ETag</t>
2497      <t>Last-Modified</t>
2498  </list>
2499</t>
2500<t>
2501   A transparent proxy &MUST-NOT; modify any of the following fields in a
2502   response:
2503  <list style="symbols">
2504    <t>Expires</t>
2505  </list>
2506</t>
2507<t>
2508   but it &MAY; add any of these fields if not already present. If an
2509   Expires header is added, it &MUST; be given a field-value identical to
2510   that of the Date header in that response.
2511</t>
2512<t>
2513   A proxy &MUST-NOT; modify or add any of the following fields in a
2514   message that contains the no-transform cache-control directive, or in
2515   any request:
2516  <list style="symbols">
2517    <t>Content-Encoding</t>
2518    <t>Content-Range</t>
2519    <t>Content-Type</t>
2520  </list>
2521</t>
2522<t>
2523   A non-transparent proxy &MAY; modify or add these fields to a message
2524   that does not include no-transform, but if it does so, it &MUST; add a
2525   Warning 214 (Transformation applied) if one does not already appear
2526   in the message (see &header-warning;).
2527</t>
2528<x:note>
2529  <t>
2530    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2531    cause authentication failures if stronger authentication
2532    mechanisms are introduced in later versions of HTTP. Such
2533    authentication mechanisms &MAY; rely on the values of header fields
2534    not listed here.
2535  </t>
2536</x:note>
2537<t>
2538   A transparent proxy &MUST; preserve the message payload (&payload;),
2539   though it &MAY; change the message-body through application or removal
2540   of a transfer-coding (<xref target="transfer.codings"/>).
2541</t>
2542</section>
2543
2544</section>
2545
2546<section title="Practical Considerations" anchor="persistent.practical">
2547<t>
2548   Servers will usually have some time-out value beyond which they will
2549   no longer maintain an inactive connection. Proxy servers might make
2550   this a higher value since it is likely that the client will be making
2551   more connections through the same server. The use of persistent
2552   connections places no requirements on the length (or existence) of
2553   this time-out for either the client or the server.
2554</t>
2555<t>
2556   When a client or server wishes to time-out it &SHOULD; issue a graceful
2557   close on the transport connection. Clients and servers &SHOULD; both
2558   constantly watch for the other side of the transport close, and
2559   respond to it as appropriate. If a client or server does not detect
2560   the other side's close promptly it could cause unnecessary resource
2561   drain on the network.
2562</t>
2563<t>
2564   A client, server, or proxy &MAY; close the transport connection at any
2565   time. For example, a client might have started to send a new request
2566   at the same time that the server has decided to close the "idle"
2567   connection. From the server's point of view, the connection is being
2568   closed while it was idle, but from the client's point of view, a
2569   request is in progress.
2570</t>
2571<t>
2572   This means that clients, servers, and proxies &MUST; be able to recover
2573   from asynchronous close events. Client software &SHOULD; reopen the
2574   transport connection and retransmit the aborted sequence of requests
2575   without user interaction so long as the request sequence is
2576   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2577   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2578   human operator the choice of retrying the request(s). Confirmation by
2579   user-agent software with semantic understanding of the application
2580   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2581   be repeated if the second sequence of requests fails.
2582</t>
2583<t>
2584   Servers &SHOULD; always respond to at least one request per connection,
2585   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2586   middle of transmitting a response, unless a network or client failure
2587   is suspected.
2588</t>
2589<t>
2590   Clients (including proxies) &SHOULD; limit the number of simultaneous
2591   connections that they maintain to a given server (including proxies).
2592</t>
2593<t>
2594   Previous revisions of HTTP gave a specific number of connections as a
2595   ceiling, but this was found to be impractical for many applications. As a
2596   result, this specification does not mandate a particular maximum number of
2597   connections, but instead encourages clients to be conservative when opening
2598   multiple connections.
2599</t>
2600<t>
2601   In particular, while using multiple connections avoids the "head-of-line
2602   blocking" problem (whereby a request that takes significant server-side
2603   processing and/or has a large payload can block subsequent requests on the
2604   same connection), each connection used consumes server resources (sometimes
2605   significantly), and furthermore using multiple connections can cause
2606   undesirable side effects in congested networks.
2607</t>
2608<t>
2609   Note that servers might reject traffic that they deem abusive, including an
2610   excessive number of connections from a client.
2611</t>
2612</section>
2613</section>
2614
2615<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2616
2617<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2618<t>
2619   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2620   flow control mechanisms to resolve temporary overloads, rather than
2621   terminating connections with the expectation that clients will retry.
2622   The latter technique can exacerbate network congestion.
2623</t>
2624</section>
2625
2626<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2627<t>
2628   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2629   the network connection for an error status code while it is transmitting
2630   the request. If the client sees an error status code, it &SHOULD;
2631   immediately cease transmitting the body. If the body is being sent
2632   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2633   empty trailer &MAY; be used to prematurely mark the end of the message.
2634   If the body was preceded by a Content-Length header, the client &MUST;
2635   close the connection.
2636</t>
2637</section>
2638
2639<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2640<t>
2641   The purpose of the 100 (Continue) status code (see &status-100;) is to
2642   allow a client that is sending a request message with a request body
2643   to determine if the origin server is willing to accept the request
2644   (based on the request headers) before the client sends the request
2645   body. In some cases, it might either be inappropriate or highly
2646   inefficient for the client to send the body if the server will reject
2647   the message without looking at the body.
2648</t>
2649<t>
2650   Requirements for HTTP/1.1 clients:
2651  <list style="symbols">
2652    <t>
2653        If a client will wait for a 100 (Continue) response before
2654        sending the request body, it &MUST; send an Expect request-header
2655        field (&header-expect;) with the "100-continue" expectation.
2656    </t>
2657    <t>
2658        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2659        with the "100-continue" expectation if it does not intend
2660        to send a request body.
2661    </t>
2662  </list>
2663</t>
2664<t>
2665   Because of the presence of older implementations, the protocol allows
2666   ambiguous situations in which a client might send "Expect: 100-continue"
2667   without receiving either a 417 (Expectation Failed)
2668   or a 100 (Continue) status code. Therefore, when a client sends this
2669   header field to an origin server (possibly via a proxy) from which it
2670   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2671   wait for an indefinite period before sending the request body.
2672</t>
2673<t>
2674   Requirements for HTTP/1.1 origin servers:
2675  <list style="symbols">
2676    <t> Upon receiving a request which includes an Expect request-header
2677        field with the "100-continue" expectation, an origin server &MUST;
2678        either respond with 100 (Continue) status code and continue to read
2679        from the input stream, or respond with a final status code. The
2680        origin server &MUST-NOT; wait for the request body before sending
2681        the 100 (Continue) response. If it responds with a final status
2682        code, it &MAY; close the transport connection or it &MAY; continue
2683        to read and discard the rest of the request.  It &MUST-NOT;
2684        perform the requested method if it returns a final status code.
2685    </t>
2686    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2687        the request message does not include an Expect request-header
2688        field with the "100-continue" expectation, and &MUST-NOT; send a
2689        100 (Continue) response if such a request comes from an HTTP/1.0
2690        (or earlier) client. There is an exception to this rule: for
2691        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2692        status code in response to an HTTP/1.1 PUT or POST request that does
2693        not include an Expect request-header field with the "100-continue"
2694        expectation. This exception, the purpose of which is
2695        to minimize any client processing delays associated with an
2696        undeclared wait for 100 (Continue) status code, applies only to
2697        HTTP/1.1 requests, and not to requests with any other HTTP-version
2698        value.
2699    </t>
2700    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2701        already received some or all of the request body for the
2702        corresponding request.
2703    </t>
2704    <t> An origin server that sends a 100 (Continue) response &MUST;
2705    ultimately send a final status code, once the request body is
2706        received and processed, unless it terminates the transport
2707        connection prematurely.
2708    </t>
2709    <t> If an origin server receives a request that does not include an
2710        Expect request-header field with the "100-continue" expectation,
2711        the request includes a request body, and the server responds
2712        with a final status code before reading the entire request body
2713        from the transport connection, then the server &SHOULD-NOT;  close
2714        the transport connection until it has read the entire request,
2715        or until the client closes the connection. Otherwise, the client
2716        might not reliably receive the response message. However, this
2717        requirement is not be construed as preventing a server from
2718        defending itself against denial-of-service attacks, or from
2719        badly broken client implementations.
2720      </t>
2721    </list>
2722</t>
2723<t>
2724   Requirements for HTTP/1.1 proxies:
2725  <list style="symbols">
2726    <t> If a proxy receives a request that includes an Expect request-header
2727        field with the "100-continue" expectation, and the proxy
2728        either knows that the next-hop server complies with HTTP/1.1 or
2729        higher, or does not know the HTTP version of the next-hop
2730        server, it &MUST; forward the request, including the Expect header
2731        field.
2732    </t>
2733    <t> If the proxy knows that the version of the next-hop server is
2734        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2735        respond with a 417 (Expectation Failed) status code.
2736    </t>
2737    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2738        numbers received from recently-referenced next-hop servers.
2739    </t>
2740    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2741        request message was received from an HTTP/1.0 (or earlier)
2742        client and did not include an Expect request-header field with
2743        the "100-continue" expectation. This requirement overrides the
2744        general rule for forwarding of 1xx responses (see &status-1xx;).
2745    </t>
2746  </list>
2747</t>
2748</section>
2749
2750<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2751<t>
2752   If an HTTP/1.1 client sends a request which includes a request body,
2753   but which does not include an Expect request-header field with the
2754   "100-continue" expectation, and if the client is not directly
2755   connected to an HTTP/1.1 origin server, and if the client sees the
2756   connection close before receiving a status line from the server, the
2757   client &SHOULD; retry the request.  If the client does retry this
2758   request, it &MAY; use the following "binary exponential backoff"
2759   algorithm to be assured of obtaining a reliable response:
2760  <list style="numbers">
2761    <t>
2762      Initiate a new connection to the server
2763    </t>
2764    <t>
2765      Transmit the request-headers
2766    </t>
2767    <t>
2768      Initialize a variable R to the estimated round-trip time to the
2769         server (e.g., based on the time it took to establish the
2770         connection), or to a constant value of 5 seconds if the round-trip
2771         time is not available.
2772    </t>
2773    <t>
2774       Compute T = R * (2**N), where N is the number of previous
2775         retries of this request.
2776    </t>
2777    <t>
2778       Wait either for an error response from the server, or for T
2779         seconds (whichever comes first)
2780    </t>
2781    <t>
2782       If no error response is received, after T seconds transmit the
2783         body of the request.
2784    </t>
2785    <t>
2786       If client sees that the connection is closed prematurely,
2787         repeat from step 1 until the request is accepted, an error
2788         response is received, or the user becomes impatient and
2789         terminates the retry process.
2790    </t>
2791  </list>
2792</t>
2793<t>
2794   If at any point an error status code is received, the client
2795  <list style="symbols">
2796      <t>&SHOULD-NOT;  continue and</t>
2797
2798      <t>&SHOULD; close the connection if it has not completed sending the
2799        request message.</t>
2800    </list>
2801</t>
2802</section>
2803</section>
2804</section>
2805
2806
2807<section title="Miscellaneous notes that might disappear" anchor="misc">
2808<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2809<t>
2810   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2811</t>
2812</section>
2813
2814<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2815<t>
2816   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2817</t>
2818</section>
2819
2820<section title="Interception of HTTP for access control" anchor="http.intercept">
2821<t>
2822   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2823</t>
2824</section>
2825
2826<section title="Use of HTTP by other protocols" anchor="http.others">
2827<t>
2828   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2829   Extensions of HTTP like WebDAV.</cref>
2830</t>
2831
2832</section>
2833<section title="Use of HTTP by media type specification" anchor="http.media">
2834<t>
2835   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2836</t>
2837</section>
2838</section>
2839
2840<section title="Header Field Definitions" anchor="header.field.definitions">
2841<t>
2842   This section defines the syntax and semantics of HTTP/1.1 header fields
2843   related to message framing and transport protocols.
2844</t>
2845<t>
2846   For entity-header fields, both sender and recipient refer to either the
2847   client or the server, depending on who sends and who receives the message.
2848</t>
2849
2850<section title="Connection" anchor="header.connection">
2851  <iref primary="true" item="Connection header" x:for-anchor=""/>
2852  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2853  <x:anchor-alias value="Connection"/>
2854  <x:anchor-alias value="connection-token"/>
2855  <x:anchor-alias value="Connection-v"/>
2856<t>
2857   The "Connection" general-header field allows the sender to specify
2858   options that are desired for that particular connection and &MUST-NOT;
2859   be communicated by proxies over further connections.
2860</t>
2861<t>
2862   The Connection header's value has the following grammar:
2863</t>
2864<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"/>
2865  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2866  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2867  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2868</artwork></figure>
2869<t>
2870   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2871   message is forwarded and, for each connection-token in this field,
2872   remove any header field(s) from the message with the same name as the
2873   connection-token. Connection options are signaled by the presence of
2874   a connection-token in the Connection header field, not by any
2875   corresponding additional header field(s), since the additional header
2876   field might not be sent if there are no parameters associated with that
2877   connection option.
2878</t>
2879<t>
2880   Message headers listed in the Connection header &MUST-NOT; include
2881   end-to-end headers, such as Cache-Control.
2882</t>
2883<t>
2884   HTTP/1.1 defines the "close" connection option for the sender to
2885   signal that the connection will be closed after completion of the
2886   response. For example,
2887</t>
2888<figure><artwork type="example">
2889  Connection: close
2890</artwork></figure>
2891<t>
2892   in either the request or the response header fields indicates that
2893   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2894   after the current request/response is complete.
2895</t>
2896<t>
2897   An HTTP/1.1 client that does not support persistent connections &MUST;
2898   include the "close" connection option in every request message.
2899</t>
2900<t>
2901   An HTTP/1.1 server that does not support persistent connections &MUST;
2902   include the "close" connection option in every response message that
2903   does not have a 1xx (Informational) status code.
2904</t>
2905<t>
2906   A system receiving an HTTP/1.0 (or lower-version) message that
2907   includes a Connection header &MUST;, for each connection-token in this
2908   field, remove and ignore any header field(s) from the message with
2909   the same name as the connection-token. This protects against mistaken
2910   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2911</t>
2912</section>
2913
2914<section title="Content-Length" anchor="header.content-length">
2915  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2916  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2917  <x:anchor-alias value="Content-Length"/>
2918  <x:anchor-alias value="Content-Length-v"/>
2919<t>
2920   The "Content-Length" header field indicates the size of the
2921   message-body, in decimal number of octets, for any message other than
2922   a response to the HEAD method or a response with a status code of 304.
2923   In the case of responses to the HEAD method, it indicates the size of
2924   the payload body (not including any potential transfer-coding) that
2925   would have been sent had the request been a GET.
2926   In the case of the 304 (Not Modified) response, it indicates the size of
2927   the payload body (not including any potential transfer-coding) that
2928   would have been sent in a 200 (OK) response.
2929</t>
2930<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2931  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2932  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2933</artwork></figure>
2934<t>
2935   An example is
2936</t>
2937<figure><artwork type="example">
2938  Content-Length: 3495
2939</artwork></figure>
2940<t>
2941   Implementations &SHOULD; use this field to indicate the message-body
2942   length when no transfer-coding is being applied and the
2943   payload's body length can be determined prior to being transferred.
2944   <xref target="message.body"/> describes how recipients determine the length
2945   of a message-body.
2946</t>
2947<t>
2948   Any Content-Length greater than or equal to zero is a valid value.
2949</t>
2950<t>
2951   Note that the use of this field in HTTP is significantly different from
2952   the corresponding definition in MIME, where it is an optional field
2953   used within the "message/external-body" content-type.
2954</t>
2955</section>
2956
2957<section title="Date" anchor="header.date">
2958  <iref primary="true" item="Date header" x:for-anchor=""/>
2959  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2960  <x:anchor-alias value="Date"/>
2961  <x:anchor-alias value="Date-v"/>
2962<t>
2963   The "Date" general-header field represents the date and time at which
2964   the message was originated, having the same semantics as the Origination
2965   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2966   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2967   it &MUST; be sent in rfc1123-date format.
2968</t>
2969<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2970  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2971  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2972</artwork></figure>
2973<t>
2974   An example is
2975</t>
2976<figure><artwork type="example">
2977  Date: Tue, 15 Nov 1994 08:12:31 GMT
2978</artwork></figure>
2979<t>
2980   Origin servers &MUST; include a Date header field in all responses,
2981   except in these cases:
2982  <list style="numbers">
2983      <t>If the response status code is 100 (Continue) or 101 (Switching
2984         Protocols), the response &MAY; include a Date header field, at
2985         the server's option.</t>
2986
2987      <t>If the response status code conveys a server error, e.g., 500
2988         (Internal Server Error) or 503 (Service Unavailable), and it is
2989         inconvenient or impossible to generate a valid Date.</t>
2990
2991      <t>If the server does not have a clock that can provide a
2992         reasonable approximation of the current time, its responses
2993         &MUST-NOT; include a Date header field. In this case, the rules
2994         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2995  </list>
2996</t>
2997<t>
2998   A received message that does not have a Date header field &MUST; be
2999   assigned one by the recipient if the message will be cached by that
3000   recipient or gatewayed via a protocol which requires a Date. An HTTP
3001   implementation without a clock &MUST-NOT; cache responses without
3002   revalidating them on every use. An HTTP cache, especially a shared
3003   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
3004   clock with a reliable external standard.
3005</t>
3006<t>
3007   Clients &SHOULD; only send a Date header field in messages that include
3008   a payload, as is usually the case for PUT and POST requests, and even
3009   then it is optional. A client without a clock &MUST-NOT; send a Date
3010   header field in a request.
3011</t>
3012<t>
3013   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
3014   time subsequent to the generation of the message. It &SHOULD; represent
3015   the best available approximation of the date and time of message
3016   generation, unless the implementation has no means of generating a
3017   reasonably accurate date and time. In theory, the date ought to
3018   represent the moment just before the payload is generated. In
3019   practice, the date can be generated at any time during the message
3020   origination without affecting its semantic value.
3021</t>
3022
3023<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3024<t>
3025   Some origin server implementations might not have a clock available.
3026   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3027   values to a response, unless these values were associated
3028   with the resource by a system or user with a reliable clock. It &MAY;
3029   assign an Expires value that is known, at or before server
3030   configuration time, to be in the past (this allows "pre-expiration"
3031   of responses without storing separate Expires values for each
3032   resource).
3033</t>
3034</section>
3035</section>
3036
3037<section title="Host" anchor="header.host">
3038  <iref primary="true" item="Host header" x:for-anchor=""/>
3039  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3040  <x:anchor-alias value="Host"/>
3041  <x:anchor-alias value="Host-v"/>
3042<t>
3043   The "Host" request-header field specifies the Internet host and port
3044   number of the resource being requested, allowing the origin server or
3045   gateway to differentiate between internally-ambiguous URLs, such as the root
3046   "/" URL of a server for multiple host names on a single IP address.
3047</t>
3048<t>   
3049   The Host field value &MUST; represent the naming authority of the origin
3050   server or gateway given by the original URL obtained from the user or
3051   referring resource (generally an http URI, as described in
3052   <xref target="http.uri"/>).
3053</t>
3054<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3055  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3056  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3057</artwork></figure>
3058<t>
3059   A "host" without any trailing port information implies the default
3060   port for the service requested (e.g., "80" for an HTTP URL). For
3061   example, a request on the origin server for
3062   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
3063</t>
3064<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3065GET /pub/WWW/ HTTP/1.1
3066Host: www.example.org
3067</artwork></figure>
3068<t>
3069   A client &MUST; include a Host header field in all HTTP/1.1 request
3070   messages. If the requested URI does not include an Internet host
3071   name for the service being requested, then the Host header field &MUST;
3072   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3073   request message it forwards does contain an appropriate Host header
3074   field that identifies the service being requested by the proxy. All
3075   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3076   status code to any HTTP/1.1 request message which lacks a Host header
3077   field.
3078</t>
3079<t>
3080   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3081   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3082   for other requirements relating to Host.
3083</t>
3084</section>
3085
3086<section title="TE" anchor="header.te">
3087  <iref primary="true" item="TE header" x:for-anchor=""/>
3088  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3089  <x:anchor-alias value="TE"/>
3090  <x:anchor-alias value="TE-v"/>
3091  <x:anchor-alias value="t-codings"/>
3092  <x:anchor-alias value="te-params"/>
3093  <x:anchor-alias value="te-ext"/>
3094<t>
3095   The "TE" request-header field indicates what extension transfer-codings
3096   it is willing to accept in the response, and whether or not it is
3097   willing to accept trailer fields in a chunked transfer-coding.
3098</t>
3099<t>
3100   Its value might consist of the keyword "trailers" and/or a comma-separated
3101   list of extension transfer-coding names with optional accept
3102   parameters (as described in <xref target="transfer.codings"/>).
3103</t>
3104<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"/>
3105  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3106  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3107  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3108  <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> )
3109  <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> ]
3110</artwork></figure>
3111<t>
3112   The presence of the keyword "trailers" indicates that the client is
3113   willing to accept trailer fields in a chunked transfer-coding, as
3114   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3115   transfer-coding values even though it does not itself represent a
3116   transfer-coding.
3117</t>
3118<t>
3119   Examples of its use are:
3120</t>
3121<figure><artwork type="example">
3122  TE: deflate
3123  TE:
3124  TE: trailers, deflate;q=0.5
3125</artwork></figure>
3126<t>
3127   The TE header field only applies to the immediate connection.
3128   Therefore, the keyword &MUST; be supplied within a Connection header
3129   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3130</t>
3131<t>
3132   A server tests whether a transfer-coding is acceptable, according to
3133   a TE field, using these rules:
3134  <list style="numbers">
3135    <x:lt>
3136      <t>The "chunked" transfer-coding is always acceptable. If the
3137         keyword "trailers" is listed, the client indicates that it is
3138         willing to accept trailer fields in the chunked response on
3139         behalf of itself and any downstream clients. The implication is
3140         that, if given, the client is stating that either all
3141         downstream clients are willing to accept trailer fields in the
3142         forwarded response, or that it will attempt to buffer the
3143         response on behalf of downstream recipients.
3144      </t><t>
3145         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3146         chunked response such that a client can be assured of buffering
3147         the entire response.</t>
3148    </x:lt>
3149    <x:lt>
3150      <t>If the transfer-coding being tested is one of the transfer-codings
3151         listed in the TE field, then it is acceptable unless it
3152         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3153         qvalue of 0 means "not acceptable".)</t>
3154    </x:lt>
3155    <x:lt>
3156      <t>If multiple transfer-codings are acceptable, then the
3157         acceptable transfer-coding with the highest non-zero qvalue is
3158         preferred.  The "chunked" transfer-coding always has a qvalue
3159         of 1.</t>
3160    </x:lt>
3161  </list>
3162</t>
3163<t>
3164   If the TE field-value is empty or if no TE field is present, the only
3165   transfer-coding is "chunked". A message with no transfer-coding is
3166   always acceptable.
3167</t>
3168</section>
3169
3170<section title="Trailer" anchor="header.trailer">
3171  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3172  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3173  <x:anchor-alias value="Trailer"/>
3174  <x:anchor-alias value="Trailer-v"/>
3175<t>
3176   The "Trailer" general-header field indicates that the given set of
3177   header fields is present in the trailer of a message encoded with
3178   chunked transfer-coding.
3179</t>
3180<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3181  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3182  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3183</artwork></figure>
3184<t>
3185   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3186   message using chunked transfer-coding with a non-empty trailer. Doing
3187   so allows the recipient to know which header fields to expect in the
3188   trailer.
3189</t>
3190<t>
3191   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3192   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3193   trailer fields in a "chunked" transfer-coding.
3194</t>
3195<t>
3196   Message header fields listed in the Trailer header field &MUST-NOT;
3197   include the following header fields:
3198  <list style="symbols">
3199    <t>Transfer-Encoding</t>
3200    <t>Content-Length</t>
3201    <t>Trailer</t>
3202  </list>
3203</t>
3204</section>
3205
3206<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3207  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3208  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3209  <x:anchor-alias value="Transfer-Encoding"/>
3210  <x:anchor-alias value="Transfer-Encoding-v"/>
3211<t>
3212   The "Transfer-Encoding" general-header field indicates what transfer-codings
3213   (if any) have been applied to the message body. It differs from
3214   Content-Encoding (&content-codings;) in that transfer-codings are a property
3215   of the message (and therefore are removed by intermediaries), whereas
3216   content-codings are not.
3217</t>
3218<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3219  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3220                        <x:ref>Transfer-Encoding-v</x:ref>
3221  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3222</artwork></figure>
3223<t>
3224   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3225</t>
3226<figure><artwork type="example">
3227  Transfer-Encoding: chunked
3228</artwork></figure>
3229<t>
3230   If multiple encodings have been applied to a representation, the transfer-codings
3231   &MUST; be listed in the order in which they were applied.
3232   Additional information about the encoding parameters &MAY; be provided
3233   by other entity-header fields not defined by this specification.
3234</t>
3235<t>
3236   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3237   header.
3238</t>
3239</section>
3240
3241<section title="Upgrade" anchor="header.upgrade">
3242  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3243  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3244  <x:anchor-alias value="Upgrade"/>
3245  <x:anchor-alias value="Upgrade-v"/>
3246<t>
3247   The "Upgrade" general-header field allows the client to specify what
3248   additional communication protocols it would like to use, if the server
3249   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3250   header field within a 101 (Switching Protocols) response to indicate which
3251   protocol(s) are being switched to.
3252</t>
3253<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3254  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3255  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3256</artwork></figure>
3257<t>
3258   For example,
3259</t>
3260<figure><artwork type="example">
3261  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3262</artwork></figure>
3263<t>
3264   The Upgrade header field is intended to provide a simple mechanism
3265   for transition from HTTP/1.1 to some other, incompatible protocol. It
3266   does so by allowing the client to advertise its desire to use another
3267   protocol, such as a later version of HTTP with a higher major version
3268   number, even though the current request has been made using HTTP/1.1.
3269   This eases the difficult transition between incompatible protocols by
3270   allowing the client to initiate a request in the more commonly
3271   supported protocol while indicating to the server that it would like
3272   to use a "better" protocol if available (where "better" is determined
3273   by the server, possibly according to the nature of the method and/or
3274   resource being requested).
3275</t>
3276<t>
3277   The Upgrade header field only applies to switching application-layer
3278   protocols upon the existing transport-layer connection. Upgrade
3279   cannot be used to insist on a protocol change; its acceptance and use
3280   by the server is optional. The capabilities and nature of the
3281   application-layer communication after the protocol change is entirely
3282   dependent upon the new protocol chosen, although the first action
3283   after changing the protocol &MUST; be a response to the initial HTTP
3284   request containing the Upgrade header field.
3285</t>
3286<t>
3287   The Upgrade header field only applies to the immediate connection.
3288   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3289   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3290   HTTP/1.1 message.
3291</t>
3292<t>
3293   The Upgrade header field cannot be used to indicate a switch to a
3294   protocol on a different connection. For that purpose, it is more
3295   appropriate to use a 301, 302, 303, or 305 redirection response.
3296</t>
3297<t>
3298   This specification only defines the protocol name "HTTP" for use by
3299   the family of Hypertext Transfer Protocols, as defined by the HTTP
3300   version rules of <xref target="http.version"/> and future updates to this
3301   specification. Additional tokens can be registered with IANA using the
3302   registration procedure defined below. 
3303</t>
3304
3305<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3306<t>
3307   The HTTP Upgrade Token Registry defines the name space for product
3308   tokens used to identify protocols in the Upgrade header field.
3309   Each registered token should be associated with one or a set of
3310   specifications, and with contact information.
3311</t>
3312<t>
3313   Registrations should be allowed on a First Come First Served basis as
3314   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
3315   specifications need not be IETF documents or be subject to IESG review, but
3316   should obey the following rules:
3317  <list style="numbers">
3318    <t>A token, once registered, stays registered forever.</t>
3319    <t>The registration &MUST; name a responsible party for the
3320       registration.</t>
3321    <t>The registration &MUST; name a point of contact.</t>
3322    <t>The registration &MAY; name the documentation required for the
3323       token.</t>
3324    <t>The responsible party &MAY; change the registration at any time.
3325       The IANA will keep a record of all such changes, and make them
3326       available upon request.</t>
3327    <t>The responsible party for the first registration of a "product"
3328       token &MUST; approve later registrations of a "version" token
3329       together with that "product" token before they can be registered.</t>
3330    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3331       for a token. This will normally only be used in the case when a
3332       responsible party cannot be contacted.</t>
3333  </list>
3334</t>
3335<t>
3336   It is not required that specifications for upgrade tokens be made
3337   publicly available, but the contact information for the registration
3338   should be.
3339</t>
3340</section>
3341
3342
3343</section>
3344
3345<section title="Via" anchor="header.via">
3346  <iref primary="true" item="Via header" x:for-anchor=""/>
3347  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3348  <x:anchor-alias value="protocol-name"/>
3349  <x:anchor-alias value="protocol-version"/>
3350  <x:anchor-alias value="pseudonym"/>
3351  <x:anchor-alias value="received-by"/>
3352  <x:anchor-alias value="received-protocol"/>
3353  <x:anchor-alias value="Via"/>
3354  <x:anchor-alias value="Via-v"/>
3355<t>
3356   The "Via" general-header field &MUST; be used by gateways and proxies to
3357   indicate the intermediate protocols and recipients between the user
3358   agent and the server on requests, and between the origin server and
3359   the client on responses. It is analogous to the "Received" field defined in
3360   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3361   avoiding request loops, and identifying the protocol capabilities of
3362   all senders along the request/response chain.
3363</t>
3364<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"/>
3365  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3366  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3367                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3368  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3369  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3370  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3371  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3372  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3373</artwork></figure>
3374<t>
3375   The received-protocol indicates the protocol version of the message
3376   received by the server or client along each segment of the
3377   request/response chain. The received-protocol version is appended to
3378   the Via field value when the message is forwarded so that information
3379   about the protocol capabilities of upstream applications remains
3380   visible to all recipients.
3381</t>
3382<t>
3383   The protocol-name is optional if and only if it would be "HTTP". The
3384   received-by field is normally the host and optional port number of a
3385   recipient server or client that subsequently forwarded the message.
3386   However, if the real host is considered to be sensitive information,
3387   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3388   be assumed to be the default port of the received-protocol.
3389</t>
3390<t>
3391   Multiple Via field values represent each proxy or gateway that has
3392   forwarded the message. Each recipient &MUST; append its information
3393   such that the end result is ordered according to the sequence of
3394   forwarding applications.
3395</t>
3396<t>
3397   Comments &MAY; be used in the Via header field to identify the software
3398   of the recipient proxy or gateway, analogous to the User-Agent and
3399   Server header fields. However, all comments in the Via field are
3400   optional and &MAY; be removed by any recipient prior to forwarding the
3401   message.
3402</t>
3403<t>
3404   For example, a request message could be sent from an HTTP/1.0 user
3405   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3406   forward the request to a public proxy at p.example.net, which completes
3407   the request by forwarding it to the origin server at www.example.com.
3408   The request received by www.example.com would then have the following
3409   Via header field:
3410</t>
3411<figure><artwork type="example">
3412  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3413</artwork></figure>
3414<t>
3415   Proxies and gateways used as a portal through a network firewall
3416   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3417   the firewall region. This information &SHOULD; only be propagated if
3418   explicitly enabled. If not enabled, the received-by host of any host
3419   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3420   for that host.
3421</t>
3422<t>
3423   For organizations that have strong privacy requirements for hiding
3424   internal structures, a proxy &MAY; combine an ordered subsequence of
3425   Via header field entries with identical received-protocol values into
3426   a single such entry. For example,
3427</t>
3428<figure><artwork type="example">
3429  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3430</artwork></figure>
3431<t>
3432  could be collapsed to
3433</t>
3434<figure><artwork type="example">
3435  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3436</artwork></figure>
3437<t>
3438   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3439   under the same organizational control and the hosts have already been
3440   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3441   have different received-protocol values.
3442</t>
3443</section>
3444
3445</section>
3446
3447<section title="IANA Considerations" anchor="IANA.considerations">
3448
3449<section title="Header Field Registration" anchor="header.field.registration">
3450<t>
3451   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3452   with the permanent registrations below (see <xref target="RFC3864"/>):
3453</t>
3454<?BEGININC p1-messaging.iana-headers ?>
3455<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3456<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3457   <ttcol>Header Field Name</ttcol>
3458   <ttcol>Protocol</ttcol>
3459   <ttcol>Status</ttcol>
3460   <ttcol>Reference</ttcol>
3461
3462   <c>Connection</c>
3463   <c>http</c>
3464   <c>standard</c>
3465   <c>
3466      <xref target="header.connection"/>
3467   </c>
3468   <c>Content-Length</c>
3469   <c>http</c>
3470   <c>standard</c>
3471   <c>
3472      <xref target="header.content-length"/>
3473   </c>
3474   <c>Date</c>
3475   <c>http</c>
3476   <c>standard</c>
3477   <c>
3478      <xref target="header.date"/>
3479   </c>
3480   <c>Host</c>
3481   <c>http</c>
3482   <c>standard</c>
3483   <c>
3484      <xref target="header.host"/>
3485   </c>
3486   <c>TE</c>
3487   <c>http</c>
3488   <c>standard</c>
3489   <c>
3490      <xref target="header.te"/>
3491   </c>
3492   <c>Trailer</c>
3493   <c>http</c>
3494   <c>standard</c>
3495   <c>
3496      <xref target="header.trailer"/>
3497   </c>
3498   <c>Transfer-Encoding</c>
3499   <c>http</c>
3500   <c>standard</c>
3501   <c>
3502      <xref target="header.transfer-encoding"/>
3503   </c>
3504   <c>Upgrade</c>
3505   <c>http</c>
3506   <c>standard</c>
3507   <c>
3508      <xref target="header.upgrade"/>
3509   </c>
3510   <c>Via</c>
3511   <c>http</c>
3512   <c>standard</c>
3513   <c>
3514      <xref target="header.via"/>
3515   </c>
3516</texttable>
3517<!--(END)-->
3518<?ENDINC p1-messaging.iana-headers ?>
3519<t>
3520   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3521</t>
3522</section>
3523
3524<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3525<t>
3526   The entries for the "http" and "https" URI Schemes in the registry located at
3527   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3528   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3529   and <xref target="https.uri" format="counter"/> of this document
3530   (see <xref target="RFC4395"/>).
3531</t>
3532</section>
3533
3534<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3535<t>
3536   This document serves as the specification for the Internet media types
3537   "message/http" and "application/http". The following is to be registered with
3538   IANA (see <xref target="RFC4288"/>).
3539</t>
3540<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3541<iref item="Media Type" subitem="message/http" primary="true"/>
3542<iref item="message/http Media Type" primary="true"/>
3543<t>
3544   The message/http type can be used to enclose a single HTTP request or
3545   response message, provided that it obeys the MIME restrictions for all
3546   "message" types regarding line length and encodings.
3547</t>
3548<t>
3549  <list style="hanging" x:indent="12em">
3550    <t hangText="Type name:">
3551      message
3552    </t>
3553    <t hangText="Subtype name:">
3554      http
3555    </t>
3556    <t hangText="Required parameters:">
3557      none
3558    </t>
3559    <t hangText="Optional parameters:">
3560      version, msgtype
3561      <list style="hanging">
3562        <t hangText="version:">
3563          The HTTP-Version number of the enclosed message
3564          (e.g., "1.1"). If not present, the version can be
3565          determined from the first line of the body.
3566        </t>
3567        <t hangText="msgtype:">
3568          The message type -- "request" or "response". If not
3569          present, the type can be determined from the first
3570          line of the body.
3571        </t>
3572      </list>
3573    </t>
3574    <t hangText="Encoding considerations:">
3575      only "7bit", "8bit", or "binary" are permitted
3576    </t>
3577    <t hangText="Security considerations:">
3578      none
3579    </t>
3580    <t hangText="Interoperability considerations:">
3581      none
3582    </t>
3583    <t hangText="Published specification:">
3584      This specification (see <xref target="internet.media.type.message.http"/>).
3585    </t>
3586    <t hangText="Applications that use this media type:">
3587    </t>
3588    <t hangText="Additional information:">
3589      <list style="hanging">
3590        <t hangText="Magic number(s):">none</t>
3591        <t hangText="File extension(s):">none</t>
3592        <t hangText="Macintosh file type code(s):">none</t>
3593      </list>
3594    </t>
3595    <t hangText="Person and email address to contact for further information:">
3596      See Authors Section.
3597    </t>
3598    <t hangText="Intended usage:">
3599      COMMON
3600    </t>
3601    <t hangText="Restrictions on usage:">
3602      none
3603    </t>
3604    <t hangText="Author/Change controller:">
3605      IESG
3606    </t>
3607  </list>
3608</t>
3609</section>
3610<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3611<iref item="Media Type" subitem="application/http" primary="true"/>
3612<iref item="application/http Media Type" primary="true"/>
3613<t>
3614   The application/http type can be used to enclose a pipeline of one or more
3615   HTTP request or response messages (not intermixed).
3616</t>
3617<t>
3618  <list style="hanging" x:indent="12em">
3619    <t hangText="Type name:">
3620      application
3621    </t>
3622    <t hangText="Subtype name:">
3623      http
3624    </t>
3625    <t hangText="Required parameters:">
3626      none
3627    </t>
3628    <t hangText="Optional parameters:">
3629      version, msgtype
3630      <list style="hanging">
3631        <t hangText="version:">
3632          The HTTP-Version number of the enclosed messages
3633          (e.g., "1.1"). If not present, the version can be
3634          determined from the first line of the body.
3635        </t>
3636        <t hangText="msgtype:">
3637          The message type -- "request" or "response". If not
3638          present, the type can be determined from the first
3639          line of the body.
3640        </t>
3641      </list>
3642    </t>
3643    <t hangText="Encoding considerations:">
3644      HTTP messages enclosed by this type
3645      are in "binary" format; use of an appropriate
3646      Content-Transfer-Encoding is required when
3647      transmitted via E-mail.
3648    </t>
3649    <t hangText="Security considerations:">
3650      none
3651    </t>
3652    <t hangText="Interoperability considerations:">
3653      none
3654    </t>
3655    <t hangText="Published specification:">
3656      This specification (see <xref target="internet.media.type.application.http"/>).
3657    </t>
3658    <t hangText="Applications that use this media type:">
3659    </t>
3660    <t hangText="Additional information:">
3661      <list style="hanging">
3662        <t hangText="Magic number(s):">none</t>
3663        <t hangText="File extension(s):">none</t>
3664        <t hangText="Macintosh file type code(s):">none</t>
3665      </list>
3666    </t>
3667    <t hangText="Person and email address to contact for further information:">
3668      See Authors Section.
3669    </t>
3670    <t hangText="Intended usage:">
3671      COMMON
3672    </t>
3673    <t hangText="Restrictions on usage:">
3674      none
3675    </t>
3676    <t hangText="Author/Change controller:">
3677      IESG
3678    </t>
3679  </list>
3680</t>
3681</section>
3682</section>
3683
3684<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3685<t>
3686   The registration procedure for HTTP Transfer Codings is now defined by
3687   <xref target="transfer.coding.registry"/> of this document.
3688</t>
3689<t>
3690   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3691   should be updated with the registrations below:
3692</t>
3693<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3694   <ttcol>Name</ttcol>
3695   <ttcol>Description</ttcol>
3696   <ttcol>Reference</ttcol>
3697   <c>chunked</c>
3698   <c>Transfer in a series of chunks</c>
3699   <c>
3700      <xref target="chunked.encoding"/>
3701   </c>
3702   <c>compress</c>
3703   <c>UNIX "compress" program method</c>
3704   <c>
3705      <xref target="compress.coding"/>
3706   </c>
3707   <c>deflate</c>
3708   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3709   the "zlib" data format (<xref target="RFC1950"/>)
3710   </c>
3711   <c>
3712      <xref target="deflate.coding"/>
3713   </c>
3714   <c>gzip</c>
3715   <c>Same as GNU zip <xref target="RFC1952"/></c>
3716   <c>
3717      <xref target="gzip.coding"/>
3718   </c>
3719</texttable>
3720</section>
3721
3722<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3723<t>
3724   The registration procedure for HTTP Upgrade Tokens -- previously defined
3725   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3726   by <xref target="upgrade.token.registry"/> of this document.
3727</t>
3728<t>
3729   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3730   should be updated with the registration below:
3731</t>
3732<texttable align="left" suppress-title="true">
3733   <ttcol>Value</ttcol>
3734   <ttcol>Description</ttcol>
3735   <ttcol>Reference</ttcol>
3736
3737   <c>HTTP</c>
3738   <c>Hypertext Transfer Protocol</c> 
3739   <c><xref target="http.version"/> of this specification</c>
3740<!-- IANA should add this without our instructions; emailed on June 05, 2009
3741   <c>TLS/1.0</c>
3742   <c>Transport Layer Security</c>
3743   <c><xref target="RFC2817"/></c> -->
3744
3745</texttable>
3746</section>
3747
3748</section>
3749
3750<section title="Security Considerations" anchor="security.considerations">
3751<t>
3752   This section is meant to inform application developers, information
3753   providers, and users of the security limitations in HTTP/1.1 as
3754   described by this document. The discussion does not include
3755   definitive solutions to the problems revealed, though it does make
3756   some suggestions for reducing security risks.
3757</t>
3758
3759<section title="Personal Information" anchor="personal.information">
3760<t>
3761   HTTP clients are often privy to large amounts of personal information
3762   (e.g., the user's name, location, mail address, passwords, encryption
3763   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3764   leakage of this information.
3765   We very strongly recommend that a convenient interface be provided
3766   for the user to control dissemination of such information, and that
3767   designers and implementors be particularly careful in this area.
3768   History shows that errors in this area often create serious security
3769   and/or privacy problems and generate highly adverse publicity for the
3770   implementor's company.
3771</t>
3772</section>
3773
3774<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3775<t>
3776   A server is in the position to save personal data about a user's
3777   requests which might identify their reading patterns or subjects of
3778   interest. This information is clearly confidential in nature and its
3779   handling can be constrained by law in certain countries. People using
3780   HTTP to provide data are responsible for ensuring that
3781   such material is not distributed without the permission of any
3782   individuals that are identifiable by the published results.
3783</t>
3784</section>
3785
3786<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3787<t>
3788   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3789   the documents returned by HTTP requests to be only those that were
3790   intended by the server administrators. If an HTTP server translates
3791   HTTP URIs directly into file system calls, the server &MUST; take
3792   special care not to serve files that were not intended to be
3793   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3794   other operating systems use ".." as a path component to indicate a
3795   directory level above the current one. On such a system, an HTTP
3796   server &MUST; disallow any such construct in the request-target if it
3797   would otherwise allow access to a resource outside those intended to
3798   be accessible via the HTTP server. Similarly, files intended for
3799   reference only internally to the server (such as access control
3800   files, configuration files, and script code) &MUST; be protected from
3801   inappropriate retrieval, since they might contain sensitive
3802   information. Experience has shown that minor bugs in such HTTP server
3803   implementations have turned into security risks.
3804</t>
3805</section>
3806
3807<section title="DNS Spoofing" anchor="dns.spoofing">
3808<t>
3809   Clients using HTTP rely heavily on the Domain Name Service, and are
3810   thus generally prone to security attacks based on the deliberate
3811   mis-association of IP addresses and DNS names. Clients need to be
3812   cautious in assuming the continuing validity of an IP number/DNS name
3813   association.
3814</t>
3815<t>
3816   In particular, HTTP clients &SHOULD; rely on their name resolver for
3817   confirmation of an IP number/DNS name association, rather than
3818   caching the result of previous host name lookups. Many platforms
3819   already can cache host name lookups locally when appropriate, and
3820   they &SHOULD; be configured to do so. It is proper for these lookups to
3821   be cached, however, only when the TTL (Time To Live) information
3822   reported by the name server makes it likely that the cached
3823   information will remain useful.
3824</t>
3825<t>
3826   If HTTP clients cache the results of host name lookups in order to
3827   achieve a performance improvement, they &MUST; observe the TTL
3828   information reported by DNS.
3829</t>
3830<t>
3831   If HTTP clients do not observe this rule, they could be spoofed when
3832   a previously-accessed server's IP address changes. As network
3833   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3834   possibility of this form of attack will grow. Observing this
3835   requirement thus reduces this potential security vulnerability.
3836</t>
3837<t>
3838   This requirement also improves the load-balancing behavior of clients
3839   for replicated servers using the same DNS name and reduces the
3840   likelihood of a user's experiencing failure in accessing sites which
3841   use that strategy.
3842</t>
3843</section>
3844
3845<section title="Proxies and Caching" anchor="attack.proxies">
3846<t>
3847   By their very nature, HTTP proxies are men-in-the-middle, and
3848   represent an opportunity for man-in-the-middle attacks. Compromise of
3849   the systems on which the proxies run can result in serious security
3850   and privacy problems. Proxies have access to security-related
3851   information, personal information about individual users and
3852   organizations, and proprietary information belonging to users and
3853   content providers. A compromised proxy, or a proxy implemented or
3854   configured without regard to security and privacy considerations,
3855   might be used in the commission of a wide range of potential attacks.
3856</t>
3857<t>
3858   Proxy operators should protect the systems on which proxies run as
3859   they would protect any system that contains or transports sensitive
3860   information. In particular, log information gathered at proxies often
3861   contains highly sensitive personal information, and/or information
3862   about organizations. Log information should be carefully guarded, and
3863   appropriate guidelines for use should be developed and followed.
3864   (<xref target="abuse.of.server.log.information"/>).
3865</t>
3866<t>
3867   Proxy implementors should consider the privacy and security
3868   implications of their design and coding decisions, and of the
3869   configuration options they provide to proxy operators (especially the
3870   default configuration).
3871</t>
3872<t>
3873   Users of a proxy need to be aware that proxies are no trustworthier than
3874   the people who run them; HTTP itself cannot solve this problem.
3875</t>
3876<t>
3877   The judicious use of cryptography, when appropriate, might suffice to
3878   protect against a broad range of security and privacy attacks. Such
3879   cryptography is beyond the scope of the HTTP/1.1 specification.
3880</t>
3881</section>
3882
3883<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3884<t>
3885   They exist. They are hard to defend against. Research continues.
3886   Beware.
3887</t>
3888</section>
3889</section>
3890
3891<section title="Acknowledgments" anchor="ack">
3892<t>
3893   HTTP has evolved considerably over the years. It has
3894   benefited from a large and active developer community--the many
3895   people who have participated on the www-talk mailing list--and it is
3896   that community which has been most responsible for the success of
3897   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3898   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3899   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3900   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3901   VanHeyningen deserve special recognition for their efforts in
3902   defining early aspects of the protocol.
3903</t>
3904<t>
3905   This document has benefited greatly from the comments of all those
3906   participating in the HTTP-WG. In addition to those already mentioned,
3907   the following individuals have contributed to this specification:
3908</t>
3909<t>
3910   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3911   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3912   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3913   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3914   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3915   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3916   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3917   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3918   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3919   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3920   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3921   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3922</t>
3923<t>
3924   Thanks to the "cave men" of Palo Alto. You know who you are.
3925</t>
3926<t>
3927   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3928   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3929   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3930   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3931   Larry Masinter for their help. And thanks go particularly to Jeff
3932   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3933</t>
3934<t>
3935   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3936   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3937   discovery of many of the problems that this document attempts to
3938   rectify.
3939</t>
3940<t>
3941   This specification makes heavy use of the augmented BNF and generic
3942   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3943   reuses many of the definitions provided by Nathaniel Borenstein and
3944   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3945   specification will help reduce past confusion over the relationship
3946   between HTTP and Internet mail message formats.
3947</t>
3948</section>
3949
3950</middle>
3951<back>
3952
3953<references title="Normative References">
3954
3955<reference anchor="ISO-8859-1">
3956  <front>
3957    <title>
3958     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3959    </title>
3960    <author>
3961      <organization>International Organization for Standardization</organization>
3962    </author>
3963    <date year="1998"/>
3964  </front>
3965  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3966</reference>
3967
3968<reference anchor="Part2">
3969  <front>
3970    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3971    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3972      <organization abbrev="Day Software">Day Software</organization>
3973      <address><email>fielding@gbiv.com</email></address>
3974    </author>
3975    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3976      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3977      <address><email>jg@freedesktop.org</email></address>
3978    </author>
3979    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3980      <organization abbrev="HP">Hewlett-Packard Company</organization>
3981      <address><email>JeffMogul@acm.org</email></address>
3982    </author>
3983    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3984      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3985      <address><email>henrikn@microsoft.com</email></address>
3986    </author>
3987    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3988      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3989      <address><email>LMM@acm.org</email></address>
3990    </author>
3991    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3992      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3993      <address><email>paulle@microsoft.com</email></address>
3994    </author>
3995    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3996      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3997      <address><email>timbl@w3.org</email></address>
3998    </author>
3999    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4000      <organization abbrev="W3C">World Wide Web Consortium</organization>
4001      <address><email>ylafon@w3.org</email></address>
4002    </author>
4003    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4004      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4005      <address><email>julian.reschke@greenbytes.de</email></address>
4006    </author>
4007    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4008  </front>
4009  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4010  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4011</reference>
4012
4013<reference anchor="Part3">
4014  <front>
4015    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4016    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4017      <organization abbrev="Day Software">Day Software</organization>
4018      <address><email>fielding@gbiv.com</email></address>
4019    </author>
4020    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4021      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4022      <address><email>jg@freedesktop.org</email></address>
4023    </author>
4024    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4025      <organization abbrev="HP">Hewlett-Packard Company</organization>
4026      <address><email>JeffMogul@acm.org</email></address>
4027    </author>
4028    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4029      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4030      <address><email>henrikn@microsoft.com</email></address>
4031    </author>
4032    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4033      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4034      <address><email>LMM@acm.org</email></address>
4035    </author>
4036    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4037      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4038      <address><email>paulle@microsoft.com</email></address>
4039    </author>
4040    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4041      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4042      <address><email>timbl@w3.org</email></address>
4043    </author>
4044    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4045      <organization abbrev="W3C">World Wide Web Consortium</organization>
4046      <address><email>ylafon@w3.org</email></address>
4047    </author>
4048    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4049      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4050      <address><email>julian.reschke@greenbytes.de</email></address>
4051    </author>
4052    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4053  </front>
4054  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4055  <x:source href="p3-payload.xml" basename="p3-payload"/>
4056</reference>
4057
4058<reference anchor="Part6">
4059  <front>
4060    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4061    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4062      <organization abbrev="Day Software">Day Software</organization>
4063      <address><email>fielding@gbiv.com</email></address>
4064    </author>
4065    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4066      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4067      <address><email>jg@freedesktop.org</email></address>
4068    </author>
4069    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4070      <organization abbrev="HP">Hewlett-Packard Company</organization>
4071      <address><email>JeffMogul@acm.org</email></address>
4072    </author>
4073    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4074      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4075      <address><email>henrikn@microsoft.com</email></address>
4076    </author>
4077    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4078      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4079      <address><email>LMM@acm.org</email></address>
4080    </author>
4081    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4082      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4083      <address><email>paulle@microsoft.com</email></address>
4084    </author>
4085    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4086      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4087      <address><email>timbl@w3.org</email></address>
4088    </author>
4089    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4090      <organization abbrev="W3C">World Wide Web Consortium</organization>
4091      <address><email>ylafon@w3.org</email></address>
4092    </author>
4093    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4094      <address><email>mnot@mnot.net</email></address>
4095    </author>
4096    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4097      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4098      <address><email>julian.reschke@greenbytes.de</email></address>
4099    </author>
4100    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4101  </front>
4102  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4103  <x:source href="p6-cache.xml" basename="p6-cache"/>
4104</reference>
4105
4106<reference anchor="RFC5234">
4107  <front>
4108    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4109    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4110      <organization>Brandenburg InternetWorking</organization>
4111      <address>
4112        <email>dcrocker@bbiw.net</email>
4113      </address> 
4114    </author>
4115    <author initials="P." surname="Overell" fullname="Paul Overell">
4116      <organization>THUS plc.</organization>
4117      <address>
4118        <email>paul.overell@thus.net</email>
4119      </address>
4120    </author>
4121    <date month="January" year="2008"/>
4122  </front>
4123  <seriesInfo name="STD" value="68"/>
4124  <seriesInfo name="RFC" value="5234"/>
4125</reference>
4126
4127<reference anchor="RFC2119">
4128  <front>
4129    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4130    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4131      <organization>Harvard University</organization>
4132      <address><email>sob@harvard.edu</email></address>
4133    </author>
4134    <date month="March" year="1997"/>
4135  </front>
4136  <seriesInfo name="BCP" value="14"/>
4137  <seriesInfo name="RFC" value="2119"/>
4138</reference>
4139
4140<reference anchor="RFC3986">
4141 <front>
4142  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4143  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4144    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4145    <address>
4146       <email>timbl@w3.org</email>
4147       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4148    </address>
4149  </author>
4150  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4151    <organization abbrev="Day Software">Day Software</organization>
4152    <address>
4153      <email>fielding@gbiv.com</email>
4154      <uri>http://roy.gbiv.com/</uri>
4155    </address>
4156  </author>
4157  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4158    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4159    <address>
4160      <email>LMM@acm.org</email>
4161      <uri>http://larry.masinter.net/</uri>
4162    </address>
4163  </author>
4164  <date month='January' year='2005'></date>
4165 </front>
4166 <seriesInfo name="RFC" value="3986"/>
4167 <seriesInfo name="STD" value="66"/>
4168</reference>
4169
4170<reference anchor="USASCII">
4171  <front>
4172    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4173    <author>
4174      <organization>American National Standards Institute</organization>
4175    </author>
4176    <date year="1986"/>
4177  </front>
4178  <seriesInfo name="ANSI" value="X3.4"/>
4179</reference>
4180
4181<reference anchor="RFC1950">
4182  <front>
4183    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4184    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4185      <organization>Aladdin Enterprises</organization>
4186      <address><email>ghost@aladdin.com</email></address>
4187    </author>
4188    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4189    <date month="May" year="1996"/>
4190  </front>
4191  <seriesInfo name="RFC" value="1950"/>
4192  <annotation>
4193    RFC 1950 is an Informational RFC, thus it might be less stable than
4194    this specification. On the other hand, this downward reference was
4195    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4196    therefore it is unlikely to cause problems in practice. See also
4197    <xref target="BCP97"/>.
4198  </annotation>
4199</reference>
4200
4201<reference anchor="RFC1951">
4202  <front>
4203    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4204    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4205      <organization>Aladdin Enterprises</organization>
4206      <address><email>ghost@aladdin.com</email></address>
4207    </author>
4208    <date month="May" year="1996"/>
4209  </front>
4210  <seriesInfo name="RFC" value="1951"/>
4211  <annotation>
4212    RFC 1951 is an Informational RFC, thus it might be less stable than
4213    this specification. On the other hand, this downward reference was
4214    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4215    therefore it is unlikely to cause problems in practice. See also
4216    <xref target="BCP97"/>.
4217  </annotation>
4218</reference>
4219
4220<reference anchor="RFC1952">
4221  <front>
4222    <title>GZIP file format specification version 4.3</title>
4223    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4224      <organization>Aladdin Enterprises</organization>
4225      <address><email>ghost@aladdin.com</email></address>
4226    </author>
4227    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4228      <address><email>gzip@prep.ai.mit.edu</email></address>
4229    </author>
4230    <author initials="M." surname="Adler" fullname="Mark Adler">
4231      <address><email>madler@alumni.caltech.edu</email></address>
4232    </author>
4233    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4234      <address><email>ghost@aladdin.com</email></address>
4235    </author>
4236    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4237      <address><email>randeg@alumni.rpi.edu</email></address>
4238    </author>
4239    <date month="May" year="1996"/>
4240  </front>
4241  <seriesInfo name="RFC" value="1952"/>
4242  <annotation>
4243    RFC 1952 is an Informational RFC, thus it might be less stable than
4244    this specification. On the other hand, this downward reference was
4245    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4246    therefore it is unlikely to cause problems in practice. See also
4247    <xref target="BCP97"/>.
4248  </annotation>
4249</reference>
4250
4251</references>
4252
4253<references title="Informative References">
4254
4255<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4256  <front>
4257    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4258    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4259    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4260    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4261    <author initials="H." surname="Lie" fullname="H. Lie"/>
4262    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4263    <date year="1997" month="September"/>
4264  </front>
4265  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4266</reference>
4267
4268<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4269  <front>
4270    <title>Improving HTTP Latency</title>
4271    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4272    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4273    <date year="1995" month="December"/>
4274  </front>
4275  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4276</reference>
4277
4278<reference anchor="RFC1123">
4279  <front>
4280    <title>Requirements for Internet Hosts - Application and Support</title>
4281    <author initials="R." surname="Braden" fullname="Robert Braden">
4282      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4283      <address><email>Braden@ISI.EDU</email></address>
4284    </author>
4285    <date month="October" year="1989"/>
4286  </front>
4287  <seriesInfo name="STD" value="3"/>
4288  <seriesInfo name="RFC" value="1123"/>
4289</reference>
4290
4291<reference anchor="RFC1305">
4292  <front>
4293    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4294    <author initials="D." surname="Mills" fullname="David L. Mills">
4295      <organization>University of Delaware, Electrical Engineering Department</organization>
4296      <address><email>mills@udel.edu</email></address>
4297    </author>
4298    <date month="March" year="1992"/>
4299  </front>
4300  <seriesInfo name="RFC" value="1305"/>
4301</reference>
4302
4303<reference anchor="RFC1900">
4304  <front>
4305    <title>Renumbering Needs Work</title>
4306    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4307      <organization>CERN, Computing and Networks Division</organization>
4308      <address><email>brian@dxcoms.cern.ch</email></address>
4309    </author>
4310    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4311      <organization>cisco Systems</organization>
4312      <address><email>yakov@cisco.com</email></address>
4313    </author>
4314    <date month="February" year="1996"/>
4315  </front>
4316  <seriesInfo name="RFC" value="1900"/>
4317</reference>
4318
4319<reference anchor="RFC1945">
4320  <front>
4321    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4322    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4323      <organization>MIT, Laboratory for Computer Science</organization>
4324      <address><email>timbl@w3.org</email></address>
4325    </author>
4326    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4327      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4328      <address><email>fielding@ics.uci.edu</email></address>
4329    </author>
4330    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4331      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4332      <address><email>frystyk@w3.org</email></address>
4333    </author>
4334    <date month="May" year="1996"/>
4335  </front>
4336  <seriesInfo name="RFC" value="1945"/>
4337</reference>
4338
4339<reference anchor="RFC2045">
4340  <front>
4341    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4342    <author initials="N." surname="Freed" fullname="Ned Freed">
4343      <organization>Innosoft International, Inc.</organization>
4344      <address><email>ned@innosoft.com</email></address>
4345    </author>
4346    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4347      <organization>First Virtual Holdings</organization>
4348      <address><email>nsb@nsb.fv.com</email></address>
4349    </author>
4350    <date month="November" year="1996"/>
4351  </front>
4352  <seriesInfo name="RFC" value="2045"/>
4353</reference>
4354
4355<reference anchor="RFC2047">
4356  <front>
4357    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4358    <author initials="K." surname="Moore" fullname="Keith Moore">
4359      <organization>University of Tennessee</organization>
4360      <address><email>moore@cs.utk.edu</email></address>
4361    </author>
4362    <date month="November" year="1996"/>
4363  </front>
4364  <seriesInfo name="RFC" value="2047"/>
4365</reference>
4366
4367<reference anchor="RFC2068">
4368  <front>
4369    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4370    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4371      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4372      <address><email>fielding@ics.uci.edu</email></address>
4373    </author>
4374    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4375      <organization>MIT Laboratory for Computer Science</organization>
4376      <address><email>jg@w3.org</email></address>
4377    </author>
4378    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4379      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4380      <address><email>mogul@wrl.dec.com</email></address>
4381    </author>
4382    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4383      <organization>MIT Laboratory for Computer Science</organization>
4384      <address><email>frystyk@w3.org</email></address>
4385    </author>
4386    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4387      <organization>MIT Laboratory for Computer Science</organization>
4388      <address><email>timbl@w3.org</email></address>
4389    </author>
4390    <date month="January" year="1997"/>
4391  </front>
4392  <seriesInfo name="RFC" value="2068"/>
4393</reference>
4394
4395<reference anchor='RFC2109'>
4396  <front>
4397    <title>HTTP State Management Mechanism</title>
4398    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4399      <organization>Bell Laboratories, Lucent Technologies</organization>
4400      <address><email>dmk@bell-labs.com</email></address>
4401    </author>
4402    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4403      <organization>Netscape Communications Corp.</organization>
4404      <address><email>montulli@netscape.com</email></address>
4405    </author>
4406    <date year='1997' month='February' />
4407  </front>
4408  <seriesInfo name='RFC' value='2109' />
4409</reference>
4410
4411<reference anchor="RFC2145">
4412  <front>
4413    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4414    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4415      <organization>Western Research Laboratory</organization>
4416      <address><email>mogul@wrl.dec.com</email></address>
4417    </author>
4418    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4419      <organization>Department of Information and Computer Science</organization>
4420      <address><email>fielding@ics.uci.edu</email></address>
4421    </author>
4422    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4423      <organization>MIT Laboratory for Computer Science</organization>
4424      <address><email>jg@w3.org</email></address>
4425    </author>
4426    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4427      <organization>W3 Consortium</organization>
4428      <address><email>frystyk@w3.org</email></address>
4429    </author>
4430    <date month="May" year="1997"/>
4431  </front>
4432  <seriesInfo name="RFC" value="2145"/>
4433</reference>
4434
4435<reference anchor="RFC2616">
4436  <front>
4437    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4438    <author initials="R." surname="Fielding" fullname="R. Fielding">
4439      <organization>University of California, Irvine</organization>
4440      <address><email>fielding@ics.uci.edu</email></address>
4441    </author>
4442    <author initials="J." surname="Gettys" fullname="J. Gettys">
4443      <organization>W3C</organization>
4444      <address><email>jg@w3.org</email></address>
4445    </author>
4446    <author initials="J." surname="Mogul" fullname="J. Mogul">
4447      <organization>Compaq Computer Corporation</organization>
4448      <address><email>mogul@wrl.dec.com</email></address>
4449    </author>
4450    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4451      <organization>MIT Laboratory for Computer Science</organization>
4452      <address><email>frystyk@w3.org</email></address>
4453    </author>
4454    <author initials="L." surname="Masinter" fullname="L. Masinter">
4455      <organization>Xerox Corporation</organization>
4456      <address><email>masinter@parc.xerox.com</email></address>
4457    </author>
4458    <author initials="P." surname="Leach" fullname="P. Leach">
4459      <organization>Microsoft Corporation</organization>
4460      <address><email>paulle@microsoft.com</email></address>
4461    </author>
4462    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4463      <organization>W3C</organization>
4464      <address><email>timbl@w3.org</email></address>
4465    </author>
4466    <date month="June" year="1999"/>
4467  </front>
4468  <seriesInfo name="RFC" value="2616"/>
4469</reference>
4470
4471<reference anchor='RFC2817'>
4472  <front>
4473    <title>Upgrading to TLS Within HTTP/1.1</title>
4474    <author initials='R.' surname='Khare' fullname='R. Khare'>
4475      <organization>4K Associates / UC Irvine</organization>
4476      <address><email>rohit@4K-associates.com</email></address>
4477    </author>
4478    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4479      <organization>Agranat Systems, Inc.</organization>
4480      <address><email>lawrence@agranat.com</email></address>
4481    </author>
4482    <date year='2000' month='May' />
4483  </front>
4484  <seriesInfo name='RFC' value='2817' />
4485</reference>
4486
4487<reference anchor='RFC2818'>
4488  <front>
4489    <title>HTTP Over TLS</title>
4490    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4491      <organization>RTFM, Inc.</organization>
4492      <address><email>ekr@rtfm.com</email></address>
4493    </author>
4494    <date year='2000' month='May' />
4495  </front>
4496  <seriesInfo name='RFC' value='2818' />
4497</reference>
4498
4499<reference anchor='RFC2965'>
4500  <front>
4501    <title>HTTP State Management Mechanism</title>
4502    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4503      <organization>Bell Laboratories, Lucent Technologies</organization>
4504      <address><email>dmk@bell-labs.com</email></address>
4505    </author>
4506    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4507      <organization>Epinions.com, Inc.</organization>
4508      <address><email>lou@montulli.org</email></address>
4509    </author>
4510    <date year='2000' month='October' />
4511  </front>
4512  <seriesInfo name='RFC' value='2965' />
4513</reference>
4514
4515<reference anchor='RFC3864'>
4516  <front>
4517    <title>Registration Procedures for Message Header Fields</title>
4518    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4519      <organization>Nine by Nine</organization>
4520      <address><email>GK-IETF@ninebynine.org</email></address>
4521    </author>
4522    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4523      <organization>BEA Systems</organization>
4524      <address><email>mnot@pobox.com</email></address>
4525    </author>
4526    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4527      <organization>HP Labs</organization>
4528      <address><email>JeffMogul@acm.org</email></address>
4529    </author>
4530    <date year='2004' month='September' />
4531  </front>
4532  <seriesInfo name='BCP' value='90' />
4533  <seriesInfo name='RFC' value='3864' />
4534</reference>
4535
4536<reference anchor="RFC4288">
4537  <front>
4538    <title>Media Type Specifications and Registration Procedures</title>
4539    <author initials="N." surname="Freed" fullname="N. Freed">
4540      <organization>Sun Microsystems</organization>
4541      <address>
4542        <email>ned.freed@mrochek.com</email>
4543      </address>
4544    </author>
4545    <author initials="J." surname="Klensin" fullname="J. Klensin">
4546      <address>
4547        <email>klensin+ietf@jck.com</email>
4548      </address>
4549    </author>
4550    <date year="2005" month="December"/>
4551  </front>
4552  <seriesInfo name="BCP" value="13"/>
4553  <seriesInfo name="RFC" value="4288"/>
4554</reference>
4555
4556<reference anchor='RFC4395'>
4557  <front>
4558    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4559    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4560      <organization>AT&amp;T Laboratories</organization>
4561      <address>
4562        <email>tony+urireg@maillennium.att.com</email>
4563      </address>
4564    </author>
4565    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4566      <organization>Qualcomm, Inc.</organization>
4567      <address>
4568        <email>hardie@qualcomm.com</email>
4569      </address>
4570    </author>
4571    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4572      <organization>Adobe Systems</organization>
4573      <address>
4574        <email>LMM@acm.org</email>
4575      </address>
4576    </author>
4577    <date year='2006' month='February' />
4578  </front>
4579  <seriesInfo name='BCP' value='115' />
4580  <seriesInfo name='RFC' value='4395' />
4581</reference>
4582
4583<reference anchor='RFC5226'>
4584  <front>
4585    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4586    <author initials='T.' surname='Narten' fullname='T. Narten'>
4587      <organization>IBM</organization>
4588      <address><email>narten@us.ibm.com</email></address>
4589    </author>
4590    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4591      <organization>Google</organization>
4592      <address><email>Harald@Alvestrand.no</email></address>
4593    </author>
4594    <date year='2008' month='May' />
4595  </front>
4596  <seriesInfo name='BCP' value='26' />
4597  <seriesInfo name='RFC' value='5226' />
4598</reference>
4599
4600<reference anchor="RFC5322">
4601  <front>
4602    <title>Internet Message Format</title>
4603    <author initials="P." surname="Resnick" fullname="P. Resnick">
4604      <organization>Qualcomm Incorporated</organization>
4605    </author>
4606    <date year="2008" month="October"/>
4607  </front> 
4608  <seriesInfo name="RFC" value="5322"/>
4609</reference>
4610
4611<reference anchor='BCP97'>
4612  <front>
4613    <title>Handling Normative References to Standards-Track Documents</title>
4614    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4615      <address>
4616        <email>klensin+ietf@jck.com</email>
4617      </address>
4618    </author>
4619    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4620      <organization>MIT</organization>
4621      <address>
4622        <email>hartmans-ietf@mit.edu</email>
4623      </address>
4624    </author>
4625    <date year='2007' month='June' />
4626  </front>
4627  <seriesInfo name='BCP' value='97' />
4628  <seriesInfo name='RFC' value='4897' />
4629</reference>
4630
4631<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4632  <front>
4633    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4634    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4635    <date year="2001" month="November"/>
4636  </front>
4637  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4638</reference>
4639
4640<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4641  <front>
4642    <title>Analysis of HTTP Performance Problems</title>
4643    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4644    <date/>
4645  </front>
4646</reference>
4647
4648<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4649  <front>
4650  <title>Analysis of HTTP Performance</title>
4651  <author initials="J." surname="Touch" fullname="Joe Touch">
4652    <organization>USC/Information Sciences Institute</organization>
4653    <address><email>touch@isi.edu</email></address>
4654  </author>
4655  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4656    <organization>USC/Information Sciences Institute</organization>
4657    <address><email>johnh@isi.edu</email></address>
4658  </author>
4659  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4660    <organization>USC/Information Sciences Institute</organization>
4661    <address><email>katia@isi.edu</email></address>
4662  </author>
4663  <date year="1998" month="Aug"/>
4664  </front>
4665  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4666  <annotation>(original report dated Aug. 1996)</annotation>
4667</reference>
4668
4669</references>
4670
4671
4672<section title="Tolerant Applications" anchor="tolerant.applications">
4673<t>
4674   Although this document specifies the requirements for the generation
4675   of HTTP/1.1 messages, not all applications will be correct in their
4676   implementation. We therefore recommend that operational applications
4677   be tolerant of deviations whenever those deviations can be
4678   interpreted unambiguously.
4679</t>
4680<t>
4681   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4682   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4683   &SHOULD; accept any amount of WSP characters between fields, even though
4684   only a single SP is required.
4685</t>
4686<t>
4687   The line terminator for header fields is the sequence CRLF.
4688   However, we recommend that applications, when parsing such headers,
4689   recognize a single LF as a line terminator and ignore the leading CR.
4690</t>
4691<t>
4692   The character set of a representation &SHOULD; be labeled as the lowest
4693   common denominator of the character codes used within that representation, with
4694   the exception that not labeling the representation is preferred over labeling
4695   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4696</t>
4697<t>
4698   Additional rules for requirements on parsing and encoding of dates
4699   and other potential problems with date encodings include:
4700</t>
4701<t>
4702  <list style="symbols">
4703     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4704        which appears to be more than 50 years in the future is in fact
4705        in the past (this helps solve the "year 2000" problem).</t>
4706
4707     <t>Although all date formats are specified to be case-sensitive,
4708        recipients &SHOULD; match day, week and timezone names
4709        case-insensitively.</t>
4710             
4711     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4712        Expires date as earlier than the proper value, but &MUST-NOT;
4713        internally represent a parsed Expires date as later than the
4714        proper value.</t>
4715
4716     <t>All expiration-related calculations &MUST; be done in GMT. The
4717        local time zone &MUST-NOT; influence the calculation or comparison
4718        of an age or expiration time.</t>
4719
4720     <t>If an HTTP header incorrectly carries a date value with a time
4721        zone other than GMT, it &MUST; be converted into GMT using the
4722        most conservative possible conversion.</t>
4723  </list>
4724</t>
4725</section>
4726
4727<section title="Compatibility with Previous Versions" anchor="compatibility">
4728<t>
4729   HTTP has been in use by the World-Wide Web global information initiative
4730   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4731   was a simple protocol for hypertext data transfer across the Internet
4732   with only a single method and no metadata.
4733   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4734   methods and MIME-like messaging that could include metadata about the data
4735   transferred and modifiers on the request/response semantics. However,
4736   HTTP/1.0 did not sufficiently take into consideration the effects of
4737   hierarchical proxies, caching, the need for persistent connections, or
4738   name-based virtual hosts. The proliferation of incompletely-implemented
4739   applications calling themselves "HTTP/1.0" further necessitated a
4740   protocol version change in order for two communicating applications
4741   to determine each other's true capabilities.
4742</t>
4743<t>
4744   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4745   requirements that enable reliable implementations, adding only
4746   those new features that will either be safely ignored by an HTTP/1.0
4747   recipient or only sent when communicating with a party advertising
4748   compliance with HTTP/1.1.
4749</t>
4750<t>
4751   It is beyond the scope of a protocol specification to mandate
4752   compliance with previous versions. HTTP/1.1 was deliberately
4753   designed, however, to make supporting previous versions easy. It is
4754   worth noting that, at the time of composing this specification, we would
4755   expect general-purpose HTTP/1.1 servers to:
4756  <list style="symbols">
4757     <t>understand any valid request in the format of HTTP/1.0 and
4758        1.1;</t>
4759
4760     <t>respond appropriately with a message in the same major version
4761        used by the client.</t>
4762  </list>
4763</t>
4764<t>
4765   And we would expect HTTP/1.1 clients to:
4766  <list style="symbols">
4767     <t>understand any valid response in the format of HTTP/1.0 or
4768        1.1.</t>
4769  </list>
4770</t>
4771<t>
4772   For most implementations of HTTP/1.0, each connection is established
4773   by the client prior to the request and closed by the server after
4774   sending the response. Some implementations implement the Keep-Alive
4775   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4776</t>
4777
4778<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4779<t>
4780   This section summarizes major differences between versions HTTP/1.0
4781   and HTTP/1.1.
4782</t>
4783
4784<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">
4785<t>
4786   The requirements that clients and servers support the Host request-header,
4787   report an error if the Host request-header (<xref target="header.host"/>) is
4788   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4789   are among the most important changes defined by this
4790   specification.
4791</t>
4792<t>
4793   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4794   addresses and servers; there was no other established mechanism for
4795   distinguishing the intended server of a request than the IP address
4796   to which that request was directed. The changes outlined above will
4797   allow the Internet, once older HTTP clients are no longer common, to
4798   support multiple Web sites from a single IP address, greatly
4799   simplifying large operational Web servers, where allocation of many
4800   IP addresses to a single host has created serious problems. The
4801   Internet will also be able to recover the IP addresses that have been
4802   allocated for the sole purpose of allowing special-purpose domain
4803   names to be used in root-level HTTP URLs. Given the rate of growth of
4804   the Web, and the number of servers already deployed, it is extremely
4805   important that all implementations of HTTP (including updates to
4806   existing HTTP/1.0 applications) correctly implement these
4807   requirements:
4808  <list style="symbols">
4809     <t>Both clients and servers &MUST; support the Host request-header.</t>
4810
4811     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4812
4813     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4814        request does not include a Host request-header.</t>
4815
4816     <t>Servers &MUST; accept absolute URIs.</t>
4817  </list>
4818</t>
4819</section>
4820</section>
4821
4822<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4823<t>
4824   Some clients and servers might wish to be compatible with some
4825   previous implementations of persistent connections in HTTP/1.0
4826   clients and servers. Persistent connections in HTTP/1.0 are
4827   explicitly negotiated as they are not the default behavior. HTTP/1.0
4828   experimental implementations of persistent connections are faulty,
4829   and the new facilities in HTTP/1.1 are designed to rectify these
4830   problems. The problem was that some existing HTTP/1.0 clients might
4831   send Keep-Alive to a proxy server that doesn't understand
4832   Connection, which would then erroneously forward it to the next
4833   inbound server, which would establish the Keep-Alive connection and
4834   result in a hung HTTP/1.0 proxy waiting for the close on the
4835   response. The result is that HTTP/1.0 clients must be prevented from
4836   using Keep-Alive when talking to proxies.
4837</t>
4838<t>
4839   However, talking to proxies is the most important use of persistent
4840   connections, so that prohibition is clearly unacceptable. Therefore,
4841   we need some other mechanism for indicating a persistent connection
4842   is desired, which is safe to use even when talking to an old proxy
4843   that ignores Connection. Persistent connections are the default for
4844   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4845   declaring non-persistence. See <xref target="header.connection"/>.
4846</t>
4847<t>
4848   The original HTTP/1.0 form of persistent connections (the Connection:
4849   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4850</t>
4851</section>
4852
4853<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4854<t>
4855  Empty list elements in list productions have been deprecated.
4856  (<xref target="notation.abnf"/>)
4857</t>
4858<t>
4859  Rules about implicit linear whitespace between certain grammar productions
4860  have been removed; now it's only allowed when specifically pointed out
4861  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4862  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4863  Non-ASCII content in header fields and reason phrase has been obsoleted and
4864  made opaque (the TEXT rule was removed)
4865  (<xref target="basic.rules"/>)
4866</t>
4867<t>
4868  Clarify that HTTP-Version is case sensitive.
4869  (<xref target="http.version"/>)
4870</t>
4871<t>
4872  Remove reference to non-existent identity transfer-coding value tokens.
4873  (Sections <xref format="counter" target="transfer.codings"/> and
4874  <xref format="counter" target="message.body"/>)
4875</t>
4876<t>
4877  Require that invalid whitespace around field-names be rejected.
4878  (<xref target="header.fields"/>)
4879</t>
4880<t>
4881  Update use of abs_path production from RFC1808 to the path-absolute + query
4882  components of RFC3986.
4883  (<xref target="request-target"/>)
4884</t>
4885<t>
4886  Clarification that the chunk length does not include the count of the octets
4887  in the chunk header and trailer. Furthermore disallowed line folding
4888  in chunk extensions.
4889  (<xref target="chunked.encoding"/>)
4890</t>
4891<t>
4892  Remove hard limit of two connections per server.
4893  (<xref target="persistent.practical"/>)
4894</t>
4895<t>
4896  Clarify exactly when close connection options must be sent.
4897  (<xref target="header.connection"/>)
4898</t>
4899</section>
4900</section>
4901
4902<?BEGININC p1-messaging.abnf-appendix ?>
4903<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4904<figure>
4905<artwork type="abnf" name="p1-messaging.parsed-abnf">
4906<x:ref>BWS</x:ref> = OWS
4907
4908<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4909<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4910<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4911<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4912 connection-token ] )
4913<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4914<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4915
4916<x:ref>Date</x:ref> = "Date:" OWS Date-v
4917<x:ref>Date-v</x:ref> = HTTP-date
4918
4919<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4920
4921<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4922<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4923<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4924<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4925 ]
4926<x:ref>Host</x:ref> = "Host:" OWS Host-v
4927<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4928
4929<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
4930<x:ref>Method</x:ref> = token
4931
4932<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4933
4934<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4935
4936<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4937<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4938<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4939 entity-header ) CRLF ) CRLF [ message-body ]
4940<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4941<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4942 entity-header ) CRLF ) CRLF [ message-body ]
4943
4944<x:ref>Status-Code</x:ref> = 3DIGIT
4945<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4946
4947<x:ref>TE</x:ref> = "TE:" OWS TE-v
4948<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4949<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4950<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4951<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4952<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4953 transfer-coding ] )
4954
4955<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4956<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4957<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4958
4959<x:ref>Via</x:ref> = "Via:" OWS Via-v
4960<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4961 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4962 ] )
4963
4964<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4965
4966<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4967<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4968<x:ref>attribute</x:ref> = token
4969<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4970
4971<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4972<x:ref>chunk-data</x:ref> = 1*OCTET
4973<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4974<x:ref>chunk-ext-name</x:ref> = token
4975<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4976<x:ref>chunk-size</x:ref> = 1*HEXDIG
4977<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4978<x:ref>connection-token</x:ref> = token
4979<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4980 / %x2A-5B ; '*'-'['
4981 / %x5D-7E ; ']'-'~'
4982 / obs-text
4983
4984<x:ref>date1</x:ref> = day SP month SP year
4985<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4986<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4987<x:ref>day</x:ref> = 2DIGIT
4988<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4989 / %x54.75.65 ; Tue
4990 / %x57.65.64 ; Wed
4991 / %x54.68.75 ; Thu
4992 / %x46.72.69 ; Fri
4993 / %x53.61.74 ; Sat
4994 / %x53.75.6E ; Sun
4995<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4996 / %x54.75.65.73.64.61.79 ; Tuesday
4997 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4998 / %x54.68.75.72.73.64.61.79 ; Thursday
4999 / %x46.72.69.64.61.79 ; Friday
5000 / %x53.61.74.75.72.64.61.79 ; Saturday
5001 / %x53.75.6E.64.61.79 ; Sunday
5002
5003<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
5004
5005<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5006<x:ref>field-name</x:ref> = token
5007<x:ref>field-value</x:ref> = *( field-content / OWS )
5008
5009<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5010 / Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
5011
5012<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5013<x:ref>hour</x:ref> = 2DIGIT
5014<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5015<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5016
5017<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5018
5019<x:ref>message-body</x:ref> = *OCTET
5020<x:ref>minute</x:ref> = 2DIGIT
5021<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5022 / %x46.65.62 ; Feb
5023 / %x4D.61.72 ; Mar
5024 / %x41.70.72 ; Apr
5025 / %x4D.61.79 ; May
5026 / %x4A.75.6E ; Jun
5027 / %x4A.75.6C ; Jul
5028 / %x41.75.67 ; Aug
5029 / %x53.65.70 ; Sep
5030 / %x4F.63.74 ; Oct
5031 / %x4E.6F.76 ; Nov
5032 / %x44.65.63 ; Dec
5033
5034<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5035<x:ref>obs-fold</x:ref> = CRLF
5036<x:ref>obs-text</x:ref> = %x80-FF
5037
5038<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5039<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5040<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5041<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5042<x:ref>product</x:ref> = token [ "/" product-version ]
5043<x:ref>product-version</x:ref> = token
5044<x:ref>protocol-name</x:ref> = token
5045<x:ref>protocol-version</x:ref> = token
5046<x:ref>pseudonym</x:ref> = token
5047
5048<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5049 / %x5D-7E ; ']'-'~'
5050 / obs-text
5051<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5052 / %x5D-7E ; ']'-'~'
5053 / obs-text
5054<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5055<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5056<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5057<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5058<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5059<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5060
5061<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5062<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5063<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5064<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5065<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5066 / authority
5067<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5068<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5069<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5070
5071<x:ref>second</x:ref> = 2DIGIT
5072<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5073 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5074<x:ref>start-line</x:ref> = Request-Line / Status-Line
5075
5076<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5077<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5078 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5079<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5080<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5081<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5082<x:ref>token</x:ref> = 1*tchar
5083<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
5084<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5085 transfer-extension
5086<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5087<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5088
5089<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5090
5091<x:ref>value</x:ref> = word
5092
5093<x:ref>word</x:ref> = token / quoted-string
5094
5095<x:ref>year</x:ref> = 4DIGIT
5096</artwork>
5097</figure>
5098<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5099; Chunked-Body defined but not used
5100; Content-Length defined but not used
5101; HTTP-message defined but not used
5102; Host defined but not used
5103; Request defined but not used
5104; Response defined but not used
5105; TE defined but not used
5106; URI-reference defined but not used
5107; http-URI defined but not used
5108; https-URI defined but not used
5109; partial-URI defined but not used
5110; special defined but not used
5111</artwork></figure></section>
5112<?ENDINC p1-messaging.abnf-appendix ?>
5113
5114<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5115
5116<section title="Since RFC2616">
5117<t>
5118  Extracted relevant partitions from <xref target="RFC2616"/>.
5119</t>
5120</section>
5121
5122<section title="Since draft-ietf-httpbis-p1-messaging-00">
5123<t>
5124  Closed issues:
5125  <list style="symbols"> 
5126    <t>
5127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5128      "HTTP Version should be case sensitive"
5129      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5130    </t>
5131    <t>
5132      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5133      "'unsafe' characters"
5134      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5135    </t>
5136    <t>
5137      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5138      "Chunk Size Definition"
5139      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5140    </t>
5141    <t>
5142      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5143      "Message Length"
5144      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5145    </t>
5146    <t>
5147      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5148      "Media Type Registrations"
5149      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5150    </t>
5151    <t>
5152      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5153      "URI includes query"
5154      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5155    </t>
5156    <t>
5157      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5158      "No close on 1xx responses"
5159      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5160    </t>
5161    <t>
5162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5163      "Remove 'identity' token references"
5164      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5165    </t>
5166    <t>
5167      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5168      "Import query BNF"
5169    </t>
5170    <t>
5171      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5172      "qdtext BNF"
5173    </t>
5174    <t>
5175      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5176      "Normative and Informative references"
5177    </t>
5178    <t>
5179      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5180      "RFC2606 Compliance"
5181    </t>
5182    <t>
5183      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5184      "RFC977 reference"
5185    </t>
5186    <t>
5187      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5188      "RFC1700 references"
5189    </t>
5190    <t>
5191      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5192      "inconsistency in date format explanation"
5193    </t>
5194    <t>
5195      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5196      "Date reference typo"
5197    </t>
5198    <t>
5199      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5200      "Informative references"
5201    </t>
5202    <t>
5203      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5204      "ISO-8859-1 Reference"
5205    </t>
5206    <t>
5207      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5208      "Normative up-to-date references"
5209    </t>
5210  </list>
5211</t>
5212<t>
5213  Other changes:
5214  <list style="symbols"> 
5215    <t>
5216      Update media type registrations to use RFC4288 template.
5217    </t>
5218    <t>
5219      Use names of RFC4234 core rules DQUOTE and WSP,
5220      fix broken ABNF for chunk-data
5221      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5222    </t>
5223  </list>
5224</t>
5225</section>
5226
5227<section title="Since draft-ietf-httpbis-p1-messaging-01">
5228<t>
5229  Closed issues:
5230  <list style="symbols"> 
5231    <t>
5232      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5233      "Bodies on GET (and other) requests"
5234    </t>
5235    <t>
5236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5237      "Updating to RFC4288"
5238    </t>
5239    <t>
5240      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5241      "Status Code and Reason Phrase"
5242    </t>
5243    <t>
5244      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5245      "rel_path not used"
5246    </t>
5247  </list>
5248</t>
5249<t>
5250  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5251  <list style="symbols"> 
5252    <t>
5253      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5254      "trailer-part").
5255    </t>
5256    <t>
5257      Avoid underscore character in rule names ("http_URL" ->
5258      "http-URL", "abs_path" -> "path-absolute").
5259    </t>
5260    <t>
5261      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5262      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5263      have to be updated when switching over to RFC3986.
5264    </t>
5265    <t>
5266      Synchronize core rules with RFC5234.
5267    </t>
5268    <t>
5269      Get rid of prose rules that span multiple lines.
5270    </t>
5271    <t>
5272      Get rid of unused rules LOALPHA and UPALPHA.
5273    </t>
5274    <t>
5275      Move "Product Tokens" section (back) into Part 1, as "token" is used
5276      in the definition of the Upgrade header.
5277    </t>
5278    <t>
5279      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5280    </t>
5281    <t>
5282      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5283    </t>
5284  </list>
5285</t>
5286</section>
5287
5288<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5289<t>
5290  Closed issues:
5291  <list style="symbols"> 
5292    <t>
5293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5294      "HTTP-date vs. rfc1123-date"
5295    </t>
5296    <t>
5297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5298      "WS in quoted-pair"
5299    </t>
5300  </list>
5301</t>
5302<t>
5303  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5304  <list style="symbols"> 
5305    <t>
5306      Reference RFC 3984, and update header registrations for headers defined
5307      in this document.
5308    </t>
5309  </list>
5310</t>
5311<t>
5312  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5313  <list style="symbols"> 
5314    <t>
5315      Replace string literals when the string really is case-sensitive (HTTP-Version).
5316    </t>
5317  </list>
5318</t>
5319</section>
5320
5321<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5322<t>
5323  Closed issues:
5324  <list style="symbols"> 
5325    <t>
5326      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5327      "Connection closing"
5328    </t>
5329    <t>
5330      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5331      "Move registrations and registry information to IANA Considerations"
5332    </t>
5333    <t>
5334      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5335      "need new URL for PAD1995 reference"
5336    </t>
5337    <t>
5338      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5339      "IANA Considerations: update HTTP URI scheme registration"
5340    </t>
5341    <t>
5342      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5343      "Cite HTTPS URI scheme definition"
5344    </t>
5345    <t>
5346      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5347      "List-type headers vs Set-Cookie"
5348    </t>
5349  </list>
5350</t>
5351<t>
5352  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5353  <list style="symbols"> 
5354    <t>
5355      Replace string literals when the string really is case-sensitive (HTTP-Date).
5356    </t>
5357    <t>
5358      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5359    </t>
5360  </list>
5361</t>
5362</section>
5363
5364<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5365<t>
5366  Closed issues:
5367  <list style="symbols"> 
5368    <t>
5369      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5370      "Out-of-date reference for URIs"
5371    </t>
5372    <t>
5373      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5374      "RFC 2822 is updated by RFC 5322"
5375    </t>
5376  </list>
5377</t>
5378<t>
5379  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5380  <list style="symbols"> 
5381    <t>
5382      Use "/" instead of "|" for alternatives.
5383    </t>
5384    <t>
5385      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5386    </t>
5387    <t>
5388      Only reference RFC 5234's core rules.
5389    </t>
5390    <t>
5391      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5392      whitespace ("OWS") and required whitespace ("RWS").
5393    </t>
5394    <t>
5395      Rewrite ABNFs to spell out whitespace rules, factor out
5396      header value format definitions.
5397    </t>
5398  </list>
5399</t>
5400</section>
5401
5402<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5403<t>
5404  Closed issues:
5405  <list style="symbols"> 
5406    <t>
5407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5408      "Header LWS"
5409    </t>
5410    <t>
5411      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5412      "Sort 1.3 Terminology"
5413    </t>
5414    <t>
5415      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5416      "RFC2047 encoded words"
5417    </t>
5418    <t>
5419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5420      "Character Encodings in TEXT"
5421    </t>
5422    <t>
5423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5424      "Line Folding"
5425    </t>
5426    <t>
5427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5428      "OPTIONS * and proxies"
5429    </t>
5430    <t>
5431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5432      "Reason-Phrase BNF"
5433    </t>
5434    <t>
5435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5436      "Use of TEXT"
5437    </t>
5438    <t>
5439      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5440      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5441    </t>
5442    <t>
5443      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5444      "RFC822 reference left in discussion of date formats"
5445    </t>
5446  </list>
5447</t>
5448<t>
5449  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5450  <list style="symbols"> 
5451    <t>
5452      Rewrite definition of list rules, deprecate empty list elements.
5453    </t>
5454    <t>
5455      Add appendix containing collected and expanded ABNF.
5456    </t>
5457  </list>
5458</t>
5459<t>
5460  Other changes:
5461  <list style="symbols"> 
5462    <t>
5463      Rewrite introduction; add mostly new Architecture Section.
5464    </t>
5465    <t>
5466      Move definition of quality values from Part 3 into Part 1;
5467      make TE request header grammar independent of accept-params (defined in Part 3).
5468    </t>
5469  </list>
5470</t>
5471</section>
5472
5473<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5474<t>
5475  Closed issues:
5476  <list style="symbols"> 
5477    <t>
5478      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5479      "base for numeric protocol elements"
5480    </t>
5481    <t>
5482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5483      "comment ABNF"
5484    </t>
5485  </list>
5486</t>
5487<t>
5488  Partly resolved issues:
5489  <list style="symbols"> 
5490    <t>
5491      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5492      "205 Bodies" (took out language that implied that there might be
5493      methods for which a request body MUST NOT be included)
5494    </t>
5495    <t>
5496      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5497      "editorial improvements around HTTP-date"
5498    </t>
5499  </list>
5500</t>
5501</section>
5502
5503<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5504<t>
5505  Closed issues:
5506  <list style="symbols"> 
5507    <t>
5508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5509      "Repeating single-value headers"
5510    </t>
5511    <t>
5512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5513      "increase connection limit"
5514    </t>
5515    <t>
5516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5517      "IP addresses in URLs"
5518    </t>
5519    <t>
5520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5521      "take over HTTP Upgrade Token Registry"
5522    </t>
5523    <t>
5524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5525      "CR and LF in chunk extension values"
5526    </t>
5527    <t>
5528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5529      "HTTP/0.9 support"
5530    </t>
5531    <t>
5532      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5533      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5534    </t>
5535    <t>
5536      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5537      "move definitions of gzip/deflate/compress to part 1"
5538    </t>
5539    <t>
5540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5541      "disallow control characters in quoted-pair"
5542    </t>
5543  </list>
5544</t>
5545<t>
5546  Partly resolved issues:
5547  <list style="symbols"> 
5548    <t>
5549      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5550      "update IANA requirements wrt Transfer-Coding values" (add the
5551      IANA Considerations subsection)
5552    </t>
5553  </list>
5554</t>
5555</section>
5556
5557<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5558<t>
5559  Closed issues:
5560  <list style="symbols"> 
5561    <t>
5562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5563      "header parsing, treatment of leading and trailing OWS"
5564    </t>
5565  </list>
5566</t>
5567<t>
5568  Partly resolved issues:
5569  <list style="symbols"> 
5570    <t>
5571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5572      "Placement of 13.5.1 and 13.5.2"
5573    </t>
5574    <t>
5575      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5576      "use of term "word" when talking about header structure"
5577    </t>
5578  </list>
5579</t>
5580</section>
5581
5582<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5583<t>
5584  Closed issues:
5585  <list style="symbols"> 
5586    <t>
5587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5588      "Clarification of the term 'deflate'"
5589    </t>
5590    <t>
5591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5592      "OPTIONS * and proxies"
5593    </t>
5594    <t>
5595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5596      "MIME-Version not listed in P1, general header fields"
5597    </t>
5598    <t>
5599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5600      "IANA registry for content/transfer encodings"
5601    </t>
5602    <t>
5603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5604      "Case-sensitivity of HTTP-date"
5605    </t>
5606    <t>
5607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5608      "use of term "word" when talking about header structure"
5609    </t>
5610  </list>
5611</t>
5612<t>
5613  Partly resolved issues:
5614  <list style="symbols"> 
5615    <t>
5616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5617      "Term for the requested resource's URI"
5618    </t>
5619  </list>
5620</t>
5621</section>
5622
5623<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5624<t>
5625  Closed issues:
5626  <list style="symbols">
5627    <t>
5628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5629      "Connection Closing"
5630    </t>
5631    <t>
5632      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5633      "Delimiting messages with multipart/byteranges"
5634    </t>
5635    <t>
5636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5637      "Handling multiple Content-Length headers"
5638    </t>
5639    <t>
5640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5641      "consider removing the 'changes from 2068' sections"
5642    </t>
5643  </list>
5644</t>
5645<t>
5646  Partly resolved issues:
5647  <list style="symbols"> 
5648    <t>
5649      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5650      "HTTP(s) URI scheme definitions"
5651    </t>
5652  </list>
5653</t>
5654</section>
5655
5656</section>
5657
5658</back>
5659</rfc>
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