source: draft-ietf-httpbis/latest/p1-messaging.xml @ 957

Last change on this file since 957 was 957, checked in by fielding@…, 9 years ago

Further clarify the message body length calculation
so that transfer-encoding always overrides content-length.
Related to changeset [852]

  • Property svn:eol-style set to native
File size: 239.9 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "July">
16  <!ENTITY ID-YEAR "2010">
17  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY cache-incomplete       "<xref target='Part6' x:rel='#errors.or.incomplete.response.cache.behavior' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY diff-mime              "<xref target='Part3' x:rel='#differences.between.http.and.mime' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY representation         "<xref target='Part3' x:rel='#representation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39]>
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="yes"?>
49<?rfc rfcedstyle="yes"?>
50<?rfc-ext allow-markup-in-artwork="yes" ?>
51<?rfc-ext include-references-in-index="yes" ?>
52<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
53     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
54     xmlns:x='http://purl.org/net/xml2rfc/ext'>
55<front>
56
57  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
58
59  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
60    <organization abbrev="Day Software">Day Software</organization>
61    <address>
62      <postal>
63        <street>23 Corporate Plaza DR, Suite 280</street>
64        <city>Newport Beach</city>
65        <region>CA</region>
66        <code>92660</code>
67        <country>USA</country>
68      </postal>
69      <phone>+1-949-706-5300</phone>
70      <facsimile>+1-949-706-5305</facsimile>
71      <email>fielding@gbiv.com</email>
72      <uri>http://roy.gbiv.com/</uri>
73    </address>
74  </author>
75
76  <author initials="J." surname="Gettys" fullname="Jim Gettys">
77    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
78    <address>
79      <postal>
80        <street>21 Oak Knoll Road</street>
81        <city>Carlisle</city>
82        <region>MA</region>
83        <code>01741</code>
84        <country>USA</country>
85      </postal>
86      <email>jg@freedesktop.org</email>
87      <uri>http://gettys.wordpress.com/</uri>
88    </address>
89  </author>
90 
91  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
92    <organization abbrev="HP">Hewlett-Packard Company</organization>
93    <address>
94      <postal>
95        <street>HP Labs, Large Scale Systems Group</street>
96        <street>1501 Page Mill Road, MS 1177</street>
97        <city>Palo Alto</city>
98        <region>CA</region>
99        <code>94304</code>
100        <country>USA</country>
101      </postal>
102      <email>JeffMogul@acm.org</email>
103    </address>
104  </author>
105
106  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
107    <organization abbrev="Microsoft">Microsoft Corporation</organization>
108    <address>
109      <postal>
110        <street>1 Microsoft Way</street>
111        <city>Redmond</city>
112        <region>WA</region>
113        <code>98052</code>
114        <country>USA</country>
115      </postal>
116      <email>henrikn@microsoft.com</email>
117    </address>
118  </author>
119
120  <author initials="L." surname="Masinter" fullname="Larry Masinter">
121    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
122    <address>
123      <postal>
124        <street>345 Park Ave</street>
125        <city>San Jose</city>
126        <region>CA</region>
127        <code>95110</code>
128        <country>USA</country>
129      </postal>
130      <email>LMM@acm.org</email>
131      <uri>http://larry.masinter.net/</uri>
132    </address>
133  </author>
134 
135  <author initials="P." surname="Leach" fullname="Paul J. Leach">
136    <organization abbrev="Microsoft">Microsoft Corporation</organization>
137    <address>
138      <postal>
139        <street>1 Microsoft Way</street>
140        <city>Redmond</city>
141        <region>WA</region>
142        <code>98052</code>
143      </postal>
144      <email>paulle@microsoft.com</email>
145    </address>
146  </author>
147   
148  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
149    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
150    <address>
151      <postal>
152        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
153        <street>The Stata Center, Building 32</street>
154        <street>32 Vassar Street</street>
155        <city>Cambridge</city>
156        <region>MA</region>
157        <code>02139</code>
158        <country>USA</country>
159      </postal>
160      <email>timbl@w3.org</email>
161      <uri>http://www.w3.org/People/Berners-Lee/</uri>
162    </address>
163  </author>
164
165  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
166    <organization abbrev="W3C">World Wide Web Consortium</organization>
167    <address>
168      <postal>
169        <street>W3C / ERCIM</street>
170        <street>2004, rte des Lucioles</street>
171        <city>Sophia-Antipolis</city>
172        <region>AM</region>
173        <code>06902</code>
174        <country>France</country>
175      </postal>
176      <email>ylafon@w3.org</email>
177      <uri>http://www.raubacapeu.net/people/yves/</uri>
178    </address>
179  </author>
180
181  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
182    <organization abbrev="greenbytes">greenbytes GmbH</organization>
183    <address>
184      <postal>
185        <street>Hafenweg 16</street>
186        <city>Muenster</city><region>NW</region><code>48155</code>
187        <country>Germany</country>
188      </postal>
189      <phone>+49 251 2807760</phone>
190      <facsimile>+49 251 2807761</facsimile>
191      <email>julian.reschke@greenbytes.de</email>
192      <uri>http://greenbytes.de/tech/webdav/</uri>
193    </address>
194  </author>
195
196  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
197  <workgroup>HTTPbis Working Group</workgroup>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypertext information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.10"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   request/response protocol that uses extensible semantics and MIME-like
232   message payloads for flexible interaction with network-based hypertext
233   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
234   standard <xref target="RFC3986"/> to indicate request targets and
235   relationships between resources.
236   Messages are passed in a format similar to that used by Internet mail
237   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
238   (MIME) <xref target="RFC2045"/> (see &diff-mime; for the differences
239   between HTTP and MIME messages).
240</t>
241<t>
242   HTTP is a generic interface protocol for information systems. It is
243   designed to hide the details of how a service is implemented by presenting
244   a uniform interface to clients that is independent of the types of
245   resources provided. Likewise, servers do not need to be aware of each
246   client's purpose: an HTTP request can be considered in isolation rather
247   than being associated with a specific type of client or a predetermined
248   sequence of application steps. The result is a protocol that can be used
249   effectively in many different contexts and for which implementations can
250   evolve independently over time.
251</t>
252<t>
253   HTTP is also designed for use as an intermediation protocol for translating
254   communication to and from non-HTTP information systems.
255   HTTP proxies and gateways can provide access to alternative information
256   services by translating their diverse protocols into a hypertext
257   format that can be viewed and manipulated by clients in the same way
258   as HTTP services.
259</t>
260<t>
261   One consequence of HTTP flexibility is that the protocol cannot be
262   defined in terms of what occurs behind the interface. Instead, we
263   are limited to defining the syntax of communication, the intent
264   of received communication, and the expected behavior of recipients.
265   If the communication is considered in isolation, then successful
266   actions should be reflected in corresponding changes to the
267   observable interface provided by servers. However, since multiple
268   clients might act in parallel and perhaps at cross-purposes, we
269   cannot require that such changes be observable beyond the scope
270   of a single response.
271</t>
272<t>
273   This document is Part 1 of the seven-part specification of HTTP,
274   defining the protocol referred to as "HTTP/1.1" and obsoleting
275   <xref target="RFC2616"/>.
276   Part 1 describes the architectural elements that are used or
277   referred to in HTTP, defines the "http" and "https" URI schemes,
278   describes overall network operation and connection management,
279   and defines HTTP message framing and forwarding requirements.
280   Our goal is to define all of the mechanisms necessary for HTTP message
281   handling that are independent of message semantics, thereby defining the
282   complete set of requirements for message parsers and
283   message-forwarding intermediaries.
284</t>
285
286<section title="Requirements" anchor="intro.requirements">
287<t>
288   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
289   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
290   document are to be interpreted as described in <xref target="RFC2119"/>.
291</t>
292<t>
293   An implementation is not compliant if it fails to satisfy one or more
294   of the "MUST" or "REQUIRED" level requirements for the protocols it
295   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
296   level and all the "SHOULD" level requirements for its protocols is said
297   to be "unconditionally compliant"; one that satisfies all the "MUST"
298   level requirements but not all the "SHOULD" level requirements for its
299   protocols is said to be "conditionally compliant".
300</t>
301</section>
302
303<section title="Syntax Notation" anchor="notation">
304<iref primary="true" item="Grammar" subitem="ALPHA"/>
305<iref primary="true" item="Grammar" subitem="CR"/>
306<iref primary="true" item="Grammar" subitem="CRLF"/>
307<iref primary="true" item="Grammar" subitem="CTL"/>
308<iref primary="true" item="Grammar" subitem="DIGIT"/>
309<iref primary="true" item="Grammar" subitem="DQUOTE"/>
310<iref primary="true" item="Grammar" subitem="HEXDIG"/>
311<iref primary="true" item="Grammar" subitem="LF"/>
312<iref primary="true" item="Grammar" subitem="OCTET"/>
313<iref primary="true" item="Grammar" subitem="SP"/>
314<iref primary="true" item="Grammar" subitem="VCHAR"/>
315<iref primary="true" item="Grammar" subitem="WSP"/>
316<t>
317   This specification uses the Augmented Backus-Naur Form (ABNF) notation
318   of <xref target="RFC5234"/>.
319</t>
320<t anchor="core.rules">
321  <x:anchor-alias value="ALPHA"/>
322  <x:anchor-alias value="CTL"/>
323  <x:anchor-alias value="CR"/>
324  <x:anchor-alias value="CRLF"/>
325  <x:anchor-alias value="DIGIT"/>
326  <x:anchor-alias value="DQUOTE"/>
327  <x:anchor-alias value="HEXDIG"/>
328  <x:anchor-alias value="LF"/>
329  <x:anchor-alias value="OCTET"/>
330  <x:anchor-alias value="SP"/>
331  <x:anchor-alias value="VCHAR"/>
332  <x:anchor-alias value="WSP"/>
333   The following core rules are included by
334   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
335   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
336   DIGIT (decimal 0-9), DQUOTE (double quote),
337   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
338   OCTET (any 8-bit sequence of data), SP (space),
339   VCHAR (any visible <xref target="USASCII"/> character),
340   and WSP (whitespace).
341</t>
342<t>
343   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
344   "obsolete" grammar rules that appear for historical reasons.
345</t>
346
347<section title="ABNF Extension: #rule" anchor="notation.abnf">
348<t>
349  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
350  improve readability.
351</t>
352<t>
353  A construct "#" is defined, similar to "*", for defining comma-delimited
354  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
355  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
356  comma (",") and optional whitespace (OWS,
357  <xref target="basic.rules"/>).   
358</t>
359<figure><preamble>
360  Thus,
361</preamble><artwork type="example">
362  1#element =&gt; element *( OWS "," OWS element )
363</artwork></figure>
364<figure><preamble>
365  and:
366</preamble><artwork type="example">
367  #element =&gt; [ 1#element ]
368</artwork></figure>
369<figure><preamble>
370  and for n &gt;= 1 and m &gt; 1:
371</preamble><artwork type="example">
372  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
373</artwork></figure>
374<t>
375  For compatibility with legacy list rules, recipients &SHOULD; accept empty
376  list elements. In other words, consumers would follow the list productions:
377</t>
378<figure><artwork type="example">
379  #element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
380 
381  1#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
382</artwork></figure>
383<t>
384  Note that empty elements do not contribute to the count of elements present,
385  though.
386</t>
387<t>
388  For example, given these ABNF productions:
389</t>
390<figure><artwork type="example">
391  example-list      = 1#example-list-elmt
392  example-list-elmt = token ; see <xref target="basic.rules"/> 
393</artwork></figure>
394<t>
395  Then these are valid values for example-list (not including the double
396  quotes, which are present for delimitation only):
397</t>
398<figure><artwork type="example">
399  "foo,bar"
400  " foo ,bar,"
401  "  foo , ,bar,charlie   "
402  "foo ,bar,   charlie "
403</artwork></figure>
404<t>
405  But these values would be invalid, as at least one non-empty element is
406  required:
407</t>
408<figure><artwork type="example">
409  ""
410  ","
411  ",   ,"
412</artwork></figure>
413<t>
414  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
415  expanded as explained above.
416</t>
417</section>
418
419<section title="Basic Rules" anchor="basic.rules">
420<t anchor="rule.CRLF">
421  <x:anchor-alias value="CRLF"/>
422   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
423   protocol elements other than the message-body
424   (see <xref target="tolerant.applications"/> for tolerant applications).
425</t>
426<t anchor="rule.LWS">
427   This specification uses three rules to denote the use of linear
428   whitespace: OWS (optional whitespace), RWS (required whitespace), and
429   BWS ("bad" whitespace).
430</t>
431<t>
432   The OWS rule is used where zero or more linear whitespace characters might
433   appear. OWS &SHOULD; either not be produced or be produced as a single SP
434   character. Multiple OWS characters that occur within field-content &SHOULD;
435   be replaced with a single SP before interpreting the field value or
436   forwarding the message downstream.
437</t>
438<t>
439   RWS is used when at least one linear whitespace character is required to
440   separate field tokens. RWS &SHOULD; be produced as a single SP character.
441   Multiple RWS characters that occur within field-content &SHOULD; be
442   replaced with a single SP before interpreting the field value or
443   forwarding the message downstream.
444</t>
445<t>
446   BWS is used where the grammar allows optional whitespace for historical
447   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
448   recipients &MUST; accept such bad optional whitespace and remove it before
449   interpreting the field value or forwarding the message downstream.
450</t>
451<t anchor="rule.whitespace">
452  <x:anchor-alias value="BWS"/>
453  <x:anchor-alias value="OWS"/>
454  <x:anchor-alias value="RWS"/>
455  <x:anchor-alias value="obs-fold"/>
456</t>
457<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/>
458  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
459                 ; "optional" whitespace
460  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
461                 ; "required" whitespace
462  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
463                 ; "bad" whitespace
464  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
465                 ; see <xref target="header.fields"/>
466</artwork></figure>
467<t anchor="rule.token.separators">
468  <x:anchor-alias value="tchar"/>
469  <x:anchor-alias value="token"/>
470  <x:anchor-alias value="special"/>
471  <x:anchor-alias value="word"/>
472   Many HTTP/1.1 header field values consist of words (token or quoted-string)
473   separated by whitespace or special characters. These special characters
474   &MUST; be in a quoted string to be used within a parameter value (as defined
475   in <xref target="transfer.codings"/>).
476</t>
477<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
478  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
479
480  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
481<!--
482  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
483 -->
484  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
485                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
486                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
487                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
488
489  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
490                 / ";" / ":" / "\" / DQUOTE / "/" / "["
491                 / "]" / "?" / "=" / "{" / "}"
492</artwork></figure>
493<t anchor="rule.quoted-string">
494  <x:anchor-alias value="quoted-string"/>
495  <x:anchor-alias value="qdtext"/>
496  <x:anchor-alias value="obs-text"/>
497   A string of text is parsed as a single word if it is quoted using
498   double-quote marks.
499</t>
500<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/>
501  <x:ref>quoted-string</x:ref>  = <x:ref>DQUOTE</x:ref> *( <x:ref>qdtext</x:ref> / <x:ref>quoted-pair</x:ref> ) <x:ref>DQUOTE</x:ref>
502  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
503                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref> 
504  <x:ref>obs-text</x:ref>       = %x80-FF
505</artwork></figure>
506<t anchor="rule.quoted-pair">
507  <x:anchor-alias value="quoted-pair"/>
508   The backslash character ("\") can be used as a single-character
509   quoting mechanism within quoted-string constructs:
510</t>
511<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
512  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
513</artwork></figure>
514<t>
515   Producers &SHOULD-NOT; escape characters that do not require escaping
516   (i.e., other than DQUOTE and the backslash character).
517</t>
518</section>
519
520<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
521  <x:anchor-alias value="request-header"/>
522  <x:anchor-alias value="response-header"/>
523  <x:anchor-alias value="entity-header"/>
524  <x:anchor-alias value="Cache-Control"/>
525  <x:anchor-alias value="Pragma"/>
526  <x:anchor-alias value="Warning"/>
527  <x:anchor-alias value="MIME-Version"/>
528<t>
529  The ABNF rules below are defined in other parts:
530</t>
531<figure><!-- Part2--><artwork type="abnf2616">
532  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
533  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
534</artwork></figure>
535<figure><!-- Part3--><artwork type="abnf2616">
536  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
537  <x:ref>MIME-Version</x:ref>    = &lt;MIME-Version, defined in &header-mime-version;&gt;
538</artwork></figure>
539<figure><!-- Part6--><artwork type="abnf2616">
540  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
541  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
542  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
543</artwork></figure>
544</section>
545
546</section>
547</section>
548
549<section title="HTTP-related architecture" anchor="architecture">
550<t>
551   HTTP was created for the World Wide Web architecture
552   and has evolved over time to support the scalability needs of a worldwide
553   hypertext system. Much of that architecture is reflected in the terminology
554   and syntax productions used to define HTTP.
555</t>
556
557<section title="Client/Server Messaging" anchor="operation">
558<iref item="client"/>
559<iref item="server"/>
560<iref item="connection"/>
561<t>
562   HTTP is a stateless request/response protocol that operates by exchanging
563   messages across a reliable transport or session-layer connection. An HTTP
564   "client" is a program that establishes a connection to a server for the
565   purpose of sending one or more HTTP requests.  An HTTP "server" is a
566   program that accepts connections in order to service HTTP requests by
567   sending HTTP responses.
568</t>
569<iref item="user agent"/>
570<iref item="origin server"/>
571<t>
572   Note that the terms client and server refer only to the roles that
573   these programs perform for a particular connection.  The same program
574   might act as a client on some connections and a server on others.  We use
575   the term "user agent" to refer to the program that initiates a request,
576   such as a WWW browser, editor, or spider (web-traversing robot), and
577   the term "origin server" to refer to the program that can originate
578   authoritative responses to a request.
579</t>
580<t>
581   Most HTTP communication consists of a retrieval request (GET) for
582   a representation of some resource identified by a URI.  In the
583   simplest case, this might be accomplished via a single bidirectional
584   connection (===) between the user agent (UA) and the origin server (O).
585</t>
586<figure><artwork type="drawing">
587         request   &gt;
588    UA ======================================= O
589                                &lt;   response
590</artwork></figure>
591<iref item="message"/>
592<iref item="request"/>
593<iref item="response"/>
594<t>
595   A client sends an HTTP request to the server in the form of a request
596   message (<xref target="request"/>), beginning with a method, URI, and
597   protocol version, followed by MIME-like header fields containing
598   request modifiers, client information, and payload metadata, an empty
599   line to indicate the end of the header section, and finally the payload
600   body (if any).
601</t>
602<t>
603   A server responds to the client's request by sending an HTTP response
604   message (<xref target="response"/>), beginning with a status line that
605   includes the protocol version, a success or error code, and textual
606   reason phrase, followed by MIME-like header fields containing server
607   information, resource metadata, and payload metadata, an empty line to
608   indicate the end of the header section, and finally the payload body (if any).
609</t>
610<t>
611   The following example illustrates a typical message exchange for a
612   GET request on the URI "http://www.example.com/hello.txt":
613</t>
614<figure><preamble>
615client request:
616</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
617GET /hello.txt HTTP/1.1
618User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
619Host: www.example.com
620Accept: */*
621
622</artwork></figure>
623<figure><preamble>
624server response:
625</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
626HTTP/1.1 200 OK
627Date: Mon, 27 Jul 2009 12:28:53 GMT
628Server: Apache
629Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
630ETag: "34aa387-d-1568eb00"
631Accept-Ranges: bytes
632Content-Length: <x:length-of target="exbody"/>
633Vary: Accept-Encoding
634Content-Type: text/plain
635
636<x:span anchor="exbody">Hello World!
637</x:span></artwork></figure>
638</section>
639
640<section title="Intermediaries" anchor="intermediaries">
641<t>
642   A more complicated situation occurs when one or more intermediaries
643   are present in the request/response chain. There are three common
644   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
645   a single intermediary might act as an origin server, proxy, gateway,
646   or tunnel, switching behavior based on the nature of each request.
647</t>
648<figure><artwork type="drawing">
649         &gt;             &gt;             &gt;             &gt;
650    UA =========== A =========== B =========== C =========== O
651               &lt;             &lt;             &lt;             &lt;
652</artwork></figure>
653<t>
654   The figure above shows three intermediaries (A, B, and C) between the
655   user agent and origin server. A request or response message that
656   travels the whole chain will pass through four separate connections.
657   Some HTTP communication options
658   might apply only to the connection with the nearest, non-tunnel
659   neighbor, only to the end-points of the chain, or to all connections
660   along the chain. Although the diagram is linear, each participant might
661   be engaged in multiple, simultaneous communications. For example, B
662   might be receiving requests from many clients other than A, and/or
663   forwarding requests to servers other than C, at the same time that it
664   is handling A's request.
665</t>
666<t>
667<iref item="upstream"/><iref item="downstream"/>
668<iref item="inbound"/><iref item="outbound"/>
669   We use the terms "upstream" and "downstream" to describe various
670   requirements in relation to the directional flow of a message:
671   all messages flow from upstream to downstream.
672   Likewise, we use the terms "inbound" and "outbound" to refer to
673   directions in relation to the request path: "inbound" means toward
674   the origin server and "outbound" means toward the user agent.
675</t>
676<t><iref item="proxy"/>
677   A "proxy" is a message forwarding agent that is selected by the
678   client, usually via local configuration rules, to receive requests
679   for some type(s) of absolute URI and attempt to satisfy those
680   requests via translation through the HTTP interface.  Some translations
681   are minimal, such as for proxy requests for "http" URIs, whereas
682   other requests might require translation to and from entirely different
683   application-layer protocols. Proxies are often used to group an
684   organization's HTTP requests through a common intermediary for the
685   sake of security, annotation services, or shared caching.
686</t>
687<t><iref item="gateway"/><iref item="reverse proxy"/>
688   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
689   as a layer above some other server(s) and translates the received
690   requests to the underlying server's protocol.  Gateways are often
691   used for load balancing or partitioning HTTP services across
692   multiple machines.
693   Unlike a proxy, a gateway receives requests as if it were the
694   origin server for the requested resource; the requesting client
695   will not be aware that it is communicating with a gateway.
696   A gateway communicates with the client as if the gateway is the
697   origin server and thus is subject to all of the requirements on
698   origin servers for that connection.  A gateway communicates
699   with inbound servers using any protocol it desires, including
700   private extensions to HTTP that are outside the scope of this
701   specification.
702</t>
703<t><iref item="tunnel"/>
704   A "tunnel" acts as a blind relay between two connections
705   without changing the messages. Once active, a tunnel is not
706   considered a party to the HTTP communication, though the tunnel might
707   have been initiated by an HTTP request. A tunnel ceases to exist when
708   both ends of the relayed connection are closed. Tunnels are used to
709   extend a virtual connection through an intermediary, such as when
710   transport-layer security is used to establish private communication
711   through a shared firewall proxy.
712</t>
713</section>
714
715<section title="Caches" anchor="caches">
716<iref item="cache"/>
717<t>
718   A "cache" is a local store of previous response messages and the
719   subsystem that controls its message storage, retrieval, and deletion.
720   A cache stores cacheable responses in order to reduce the response
721   time and network bandwidth consumption on future, equivalent
722   requests. Any client or server &MAY; employ a cache, though a cache
723   cannot be used by a server while it is acting as a tunnel.
724</t>
725<t>
726   The effect of a cache is that the request/response chain is shortened
727   if one of the participants along the chain has a cached response
728   applicable to that request. The following illustrates the resulting
729   chain if B has a cached copy of an earlier response from O (via C)
730   for a request which has not been cached by UA or A.
731</t>
732<figure><artwork type="drawing">
733            &gt;             &gt;
734       UA =========== A =========== B - - - - - - C - - - - - - O
735                  &lt;             &lt;
736</artwork></figure>
737<t><iref item="cacheable"/>
738   A response is "cacheable" if a cache is allowed to store a copy of
739   the response message for use in answering subsequent requests.
740   Even when a response is cacheable, there might be additional
741   constraints placed by the client or by the origin server on when
742   that cached response can be used for a particular request. HTTP
743   requirements for cache behavior and cacheable responses are
744   defined in &caching-overview;
745</t>
746<t>
747   There are a wide variety of architectures and configurations
748   of caches and proxies deployed across the World Wide Web and
749   inside large organizations. These systems include national hierarchies
750   of proxy caches to save transoceanic bandwidth, systems that
751   broadcast or multicast cache entries, organizations that distribute
752   subsets of cached data via optical media, and so on.
753</t>
754</section>
755
756<section title="Transport Independence" anchor="transport-independence">
757<t>
758  HTTP systems are used in a wide variety of environments, from
759  corporate intranets with high-bandwidth links to long-distance
760  communication over low-power radio links and intermittent connectivity.
761</t>
762<t>
763   HTTP communication usually takes place over TCP/IP connections. The
764   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
765   not preclude HTTP from being implemented on top of any other protocol
766   on the Internet, or on other networks. HTTP only presumes a reliable
767   transport; any protocol that provides such guarantees can be used;
768   the mapping of the HTTP/1.1 request and response structures onto the
769   transport data units of the protocol in question is outside the scope
770   of this specification.
771</t>
772<t>
773   In HTTP/1.0, most implementations used a new connection for each
774   request/response exchange. In HTTP/1.1, a connection might be used for
775   one or more request/response exchanges, although connections might be
776   closed for a variety of reasons (see <xref target="persistent.connections"/>).
777</t>
778</section>
779
780<section title="HTTP Version" anchor="http.version">
781  <x:anchor-alias value="HTTP-Version"/>
782  <x:anchor-alias value="HTTP-Prot-Name"/>
783<t>
784   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
785   of the protocol. The protocol versioning policy is intended to allow
786   the sender to indicate the format of a message and its capacity for
787   understanding further HTTP communication, rather than the features
788   obtained via that communication. No change is made to the version
789   number for the addition of message components which do not affect
790   communication behavior or which only add to extensible field values.
791   The &lt;minor&gt; number is incremented when the changes made to the
792   protocol add features which do not change the general message parsing
793   algorithm, but which might add to the message semantics and imply
794   additional capabilities of the sender. The &lt;major&gt; number is
795   incremented when the format of a message within the protocol is
796   changed. See <xref target="RFC2145"/> for a fuller explanation.
797</t>
798<t>
799   The version of an HTTP message is indicated by an HTTP-Version field
800   in the first line of the message. HTTP-Version is case-sensitive.
801</t>
802<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
803  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
804  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
805</artwork></figure>
806<t>
807   Note that the major and minor numbers &MUST; be treated as separate
808   integers and that each &MAY; be incremented higher than a single digit.
809   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
810   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
811   &MUST-NOT; be sent.
812</t>
813<t>
814   An application that sends a request or response message that includes
815   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
816   with this specification. Applications that are at least conditionally
817   compliant with this specification &SHOULD; use an HTTP-Version of
818   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
819   not compatible with HTTP/1.0. For more details on when to send
820   specific HTTP-Version values, see <xref target="RFC2145"/>.
821</t>
822<t>
823   The HTTP version of an application is the highest HTTP version for
824   which the application is at least conditionally compliant.
825</t>
826<t>
827   Proxy and gateway applications need to be careful when forwarding
828   messages in protocol versions different from that of the application.
829   Since the protocol version indicates the protocol capability of the
830   sender, a proxy/gateway &MUST-NOT; send a message with a version
831   indicator which is greater than its actual version. If a higher
832   version request is received, the proxy/gateway &MUST; either downgrade
833   the request version, or respond with an error, or switch to tunnel
834   behavior.
835</t>
836<t>
837   Due to interoperability problems with HTTP/1.0 proxies discovered
838   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
839   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
840   they support. The proxy/gateway's response to that request &MUST; be in
841   the same major version as the request.
842</t>
843<x:note>
844  <t>
845    <x:h>Note:</x:h> Converting between versions of HTTP might involve modification
846    of header fields required or forbidden by the versions involved.
847  </t>
848</x:note>
849</section>
850
851<section title="Uniform Resource Identifiers" anchor="uri">
852<iref primary="true" item="resource"/>
853<t>
854   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
855   throughout HTTP as the means for identifying resources. URI references
856   are used to target requests, indicate redirects, and define relationships.
857   HTTP does not limit what a resource might be; it merely defines an interface
858   that can be used to interact with a resource via HTTP. More information on
859   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
860</t>
861  <x:anchor-alias value="URI-reference"/>
862  <x:anchor-alias value="absolute-URI"/>
863  <x:anchor-alias value="relative-part"/>
864  <x:anchor-alias value="authority"/>
865  <x:anchor-alias value="path-abempty"/>
866  <x:anchor-alias value="path-absolute"/>
867  <x:anchor-alias value="port"/>
868  <x:anchor-alias value="query"/>
869  <x:anchor-alias value="uri-host"/>
870  <x:anchor-alias value="partial-URI"/>
871<t>
872   This specification adopts the definitions of "URI-reference",
873   "absolute-URI", "relative-part", "port", "host",
874   "path-abempty", "path-absolute", "query", and "authority" from
875   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
876   protocol elements that allow a relative URI without a fragment.
877</t>
878<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/>
879  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
880  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
881  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
882  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
883  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
884  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
885  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
886  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
887  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
888 
889  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
890</artwork></figure>
891<t>
892   Each protocol element in HTTP that allows a URI reference will indicate in
893   its ABNF production whether the element allows only a URI in absolute form
894   (absolute-URI), any relative reference (relative-ref), or some other subset
895   of the URI-reference grammar. Unless otherwise indicated, URI references
896   are parsed relative to the request target (the default base URI for both
897   the request and its corresponding response).
898</t>
899
900<section title="http URI scheme" anchor="http.uri">
901  <x:anchor-alias value="http-URI"/>
902  <iref item="http URI scheme" primary="true"/>
903  <iref item="URI scheme" subitem="http" primary="true"/>
904<t>
905   The "http" URI scheme is hereby defined for the purpose of minting
906   identifiers according to their association with the hierarchical
907   namespace governed by a potential HTTP origin server listening for
908   TCP connections on a given port.
909   The HTTP server is identified via the generic syntax's
910   <x:ref>authority</x:ref> component, which includes a host
911   identifier and optional TCP port, and the remainder of the URI is
912   considered to be identifying data corresponding to a resource for
913   which that server might provide an HTTP interface.
914</t>
915<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
916  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
917</artwork></figure>
918<t>
919   The host identifier within an <x:ref>authority</x:ref> component is
920   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
921   provided as an IP literal or IPv4 address, then the HTTP server is any
922   listener on the indicated TCP port at that IP address. If host is a
923   registered name, then that name is considered an indirect identifier
924   and the recipient might use a name resolution service, such as DNS,
925   to find the address of a listener for that host.
926   The host &MUST-NOT; be empty; if an "http" URI is received with an
927   empty host, then it &MUST; be rejected as invalid.
928   If the port subcomponent is empty or not given, then TCP port 80 is
929   assumed (the default reserved port for WWW services).
930</t>
931<t>
932   Regardless of the form of host identifier, access to that host is not
933   implied by the mere presence of its name or address. The host might or might
934   not exist and, even when it does exist, might or might not be running an
935   HTTP server or listening to the indicated port. The "http" URI scheme
936   makes use of the delegated nature of Internet names and addresses to
937   establish a naming authority (whatever entity has the ability to place
938   an HTTP server at that Internet name or address) and allows that
939   authority to determine which names are valid and how they might be used.
940</t>
941<t>
942   When an "http" URI is used within a context that calls for access to the
943   indicated resource, a client &MAY; attempt access by resolving
944   the host to an IP address, establishing a TCP connection to that address
945   on the indicated port, and sending an HTTP request message to the server
946   containing the URI's identifying data as described in <xref target="request"/>.
947   If the server responds to that request with a non-interim HTTP response
948   message, as described in <xref target="response"/>, then that response
949   is considered an authoritative answer to the client's request.
950</t>
951<t>
952   Although HTTP is independent of the transport protocol, the "http"
953   scheme is specific to TCP-based services because the name delegation
954   process depends on TCP for establishing authority.
955   An HTTP service based on some other underlying connection protocol
956   would presumably be identified using a different URI scheme, just as
957   the "https" scheme (below) is used for servers that require an SSL/TLS
958   transport layer on a connection. Other protocols might also be used to
959   provide access to "http" identified resources --- it is only the
960   authoritative interface used for mapping the namespace that is
961   specific to TCP.
962</t>
963<t>
964   The URI generic syntax for authority also includes a deprecated
965   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
966   for including user authentication information in the URI.  The userinfo
967   subcomponent (and its "@" delimiter) &MUST-NOT; be used in an "http"
968   URI.  URI reference recipients &SHOULD; parse for the existence of
969   userinfo and treat its presence as an error, likely indicating that
970   the deprecated subcomponent is being used to obscure the authority
971   for the sake of phishing attacks.
972</t>
973</section>
974
975<section title="https URI scheme" anchor="https.uri">
976   <x:anchor-alias value="https-URI"/>
977   <iref item="https URI scheme"/>
978   <iref item="URI scheme" subitem="https"/>
979<t>
980   The "https" URI scheme is hereby defined for the purpose of minting
981   identifiers according to their association with the hierarchical
982   namespace governed by a potential HTTP origin server listening for
983   SSL/TLS-secured connections on a given TCP port.
984</t>
985<t>
986   All of the requirements listed above for the "http" scheme are also
987   requirements for the "https" scheme, except that a default TCP port
988   of 443 is assumed if the port subcomponent is empty or not given,
989   and the TCP connection &MUST; be secured for privacy through the
990   use of strong encryption prior to sending the first HTTP request.
991</t>
992<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
993  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
994</artwork></figure>
995<t>
996   Unlike the "http" scheme, responses to "https" identified requests
997   are never "public" and thus are ineligible for shared caching.
998   Their default is "private" and might be further constrained via use
999   of the Cache-Control header field.
1000</t>
1001<t>
1002   Resources made available via the "https" scheme have no shared
1003   identity with the "http" scheme even if their resource identifiers
1004   only differ by the single "s" in the scheme name.  They are
1005   different services governed by different authorities.  However,
1006   some extensions to HTTP that apply to entire host domains, such
1007   as the Cookie protocol, do allow one service to effect communication
1008   with the other services based on host domain matching.
1009</t>
1010<t>
1011   The process for authoritative access to an "https" identified
1012   resource is defined in <xref target="RFC2818"/>.
1013</t>
1014</section>
1015
1016<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1017<t>
1018   Since the "http" and "https" schemes conform to the URI generic syntax,
1019   such URIs are normalized and compared according to the algorithm defined
1020   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1021   described above for each scheme.
1022</t>
1023<t>
1024   If the port is equal to the default port for a scheme, the normal
1025   form is to elide the port subcomponent. Likewise, an empty path
1026   component is equivalent to an absolute path of "/", so the normal
1027   form is to provide a path of "/" instead. The scheme and host
1028   are case-insensitive and normally provided in lowercase; all
1029   other components are compared in a case-sensitive manner.
1030   Characters other than those in the "reserved" set are equivalent
1031   to their percent-encoded octets (see <xref target="RFC3986"
1032   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1033</t>
1034<t>
1035   For example, the following three URIs are equivalent:
1036</t>
1037<figure><artwork type="example">
1038   http://example.com:80/~smith/home.html
1039   http://EXAMPLE.com/%7Esmith/home.html
1040   http://EXAMPLE.com:/%7esmith/home.html
1041</artwork></figure>
1042<t>
1043   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1044   If path-abempty is the empty string (i.e., there is no slash "/"
1045   path separator following the authority), then the "http" URI
1046   &MUST; be given as "/" when
1047   used as a request-target (<xref target="request-target"/>). If a proxy
1048   receives a host name which is not a fully qualified domain name, it
1049   &MAY; add its domain to the host name it received. If a proxy receives
1050   a fully qualified domain name, the proxy &MUST-NOT; change the host
1051   name.
1052</t>
1053</section>
1054</section>
1055</section>
1056
1057<section title="HTTP Message" anchor="http.message">
1058<x:anchor-alias value="generic-message"/>
1059<x:anchor-alias value="message.types"/>
1060<x:anchor-alias value="HTTP-message"/>
1061<x:anchor-alias value="start-line"/>
1062<iref item="header section"/>
1063<iref item="headers"/>
1064<iref item="header field"/>
1065<t>
1066   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1067   characters in a format similar to the Internet Message Format
1068   <xref target="RFC5322"/>: zero or more header fields (collectively
1069   referred to as the "headers" or the "header section"), an empty line
1070   indicating the end of the header section, and an optional message-body.
1071</t>
1072<t>
1073   An HTTP message can either be a request from client to server or a
1074   response from server to client.  Syntactically, the two types of message
1075   differ only in the start-line, which is either a Request-Line (for requests)
1076   or a Status-Line (for responses), and in the algorithm for determining
1077   the length of the message-body (<xref target="message.body"/>).
1078   In theory, a client could receive requests and a server could receive
1079   responses, distinguishing them by their different start-line formats,
1080   but in practice servers are implemented to only expect a request
1081   (a response is interpreted as an unknown or invalid request method)
1082   and clients are implemented to only expect a response.
1083</t>
1084<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1085  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1086                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1087                    <x:ref>CRLF</x:ref>
1088                    [ <x:ref>message-body</x:ref> ]
1089  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1090</artwork></figure>
1091<t>
1092   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1093   header field. The presence of whitespace might be an attempt to trick a
1094   noncompliant implementation of HTTP into ignoring that field or processing
1095   the next line as a new request, either of which might result in security
1096   issues when implementations within the request chain interpret the
1097   same message differently. HTTP/1.1 servers &MUST; reject such a message
1098   with a 400 (Bad Request) response.
1099</t>
1100
1101<section title="Message Parsing Robustness" anchor="message.robustness">
1102<t>
1103   In the interest of robustness, servers &SHOULD; ignore at least one
1104   empty line received where a Request-Line is expected. In other words, if
1105   the server is reading the protocol stream at the beginning of a
1106   message and receives a CRLF first, it should ignore the CRLF.
1107</t>
1108<t>
1109   Some old HTTP/1.0 client implementations generate an extra CRLF
1110   after a POST request as a lame workaround for some early server
1111   applications that failed to read message-body content that was
1112   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1113   preface or follow a request with an extra CRLF.  If terminating
1114   the request message-body with a line-ending is desired, then the
1115   client &MUST; include the terminating CRLF octets as part of the
1116   message-body length.
1117</t>
1118<t>
1119   The normal procedure for parsing an HTTP message is to read the
1120   start-line into a structure, read each header field into a hash
1121   table by field name until the empty line, and then use the parsed
1122   data to determine if a message-body is expected.  If a message-body
1123   has been indicated, then it is read as a stream until an amount
1124   of octets equal to the message-body length is read or the connection
1125   is closed.  Care must be taken to parse an HTTP message as a sequence
1126   of octets in an encoding that is a superset of US-ASCII.  Attempting
1127   to parse HTTP as a stream of Unicode characters in a character encoding
1128   like UTF-16 might introduce security flaws due to the differing ways
1129   that such parsers interpret invalid characters.
1130</t>
1131</section>
1132
1133<section title="Header Fields" anchor="header.fields">
1134  <x:anchor-alias value="header-field"/>
1135  <x:anchor-alias value="field-content"/>
1136  <x:anchor-alias value="field-name"/>
1137  <x:anchor-alias value="field-value"/>
1138  <x:anchor-alias value="OWS"/>
1139<t>
1140   Each HTTP header field consists of a case-insensitive field name
1141   followed by a colon (":"), optional whitespace, and the field value.
1142</t>
1143<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1144  <x:ref>header-field</x:ref>   = <x:ref>field-name</x:ref> ":" <x:ref>OWS</x:ref> [ <x:ref>field-value</x:ref> ] <x:ref>OWS</x:ref>
1145  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1146  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1147  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1148</artwork></figure>
1149<t>
1150   No whitespace is allowed between the header field name and colon. For
1151   security reasons, any request message received containing such whitespace
1152   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1153   &MUST; remove any such whitespace from a response message before
1154   forwarding the message downstream.
1155</t>
1156<t>
1157   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1158   preferred. The field value does not include any leading or trailing white
1159   space: OWS occurring before the first non-whitespace character of the
1160   field value or after the last non-whitespace character of the field value
1161   is ignored and &SHOULD; be removed before further processing (as this does
1162   not change the meaning of the header field).
1163</t>
1164<t>
1165   The order in which header fields with differing field names are
1166   received is not significant. However, it is "good practice" to send
1167   header fields that contain control data first, such as Host on
1168   requests and Date on responses, so that implementations can decide
1169   when not to handle a message as early as possible.  A server &MUST;
1170   wait until the entire header section is received before interpreting
1171   a request message, since later header fields might include conditionals,
1172   authentication credentials, or deliberately misleading duplicate
1173   header fields that would impact request processing.
1174</t>
1175<t>
1176   Multiple header fields with the same field name &MUST-NOT; be
1177   sent in a message unless the entire field value for that
1178   header field is defined as a comma-separated list [i.e., #(values)].
1179   Multiple header fields with the same field name can be combined into
1180   one "field-name: field-value" pair, without changing the semantics of the
1181   message, by appending each subsequent field value to the combined
1182   field value in order, separated by a comma. The order in which
1183   header fields with the same field name are received is therefore
1184   significant to the interpretation of the combined field value;
1185   a proxy &MUST-NOT; change the order of these field values when
1186   forwarding a message.
1187</t>
1188<x:note>
1189  <t>
1190   <x:h>Note:</x:h> The "Set-Cookie" header as implemented in
1191   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1192   can occur multiple times, but does not use the list syntax, and thus cannot
1193   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1194   for details.) Also note that the Set-Cookie2 header specified in
1195   <xref target="RFC2965"/> does not share this problem.
1196  </t>
1197</x:note>
1198<t>
1199   Historically, HTTP header field values could be extended over multiple
1200   lines by preceding each extra line with at least one space or horizontal
1201   tab character (line folding). This specification deprecates such line
1202   folding except within the message/http media type
1203   (<xref target="internet.media.type.message.http"/>).
1204   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1205   (i.e., that contain any field-content that matches the obs-fold rule) unless
1206   the message is intended for packaging within the message/http media type.
1207   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1208   obs-fold whitespace with a single SP prior to interpreting the field value
1209   or forwarding the message downstream.
1210</t>
1211<t>
1212   Historically, HTTP has allowed field content with text in the ISO-8859-1
1213   <xref target="ISO-8859-1"/> character encoding and supported other
1214   character sets only through use of <xref target="RFC2047"/> encoding.
1215   In practice, most HTTP header field values use only a subset of the
1216   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1217   header fields &SHOULD; limit their field values to US-ASCII characters.
1218   Recipients &SHOULD; treat other (obs-text) octets in field content as
1219   opaque data.
1220</t>
1221<t anchor="rule.comment">
1222  <x:anchor-alias value="comment"/>
1223  <x:anchor-alias value="ctext"/>
1224   Comments can be included in some HTTP header fields by surrounding
1225   the comment text with parentheses. Comments are only allowed in
1226   fields containing "comment" as part of their field value definition.
1227</t>
1228<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1229  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1230  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1231                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1232</artwork></figure>
1233<t anchor="rule.quoted-cpair">
1234  <x:anchor-alias value="quoted-cpair"/>
1235   The backslash character ("\") can be used as a single-character
1236   quoting mechanism within comment constructs:
1237</t>
1238<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1239  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1240</artwork></figure>
1241<t>
1242   Producers &SHOULD-NOT; escape characters that do not require escaping
1243   (i.e., other than the backslash character "\" and the parentheses "(" and
1244   ")").
1245</t>
1246</section>
1247
1248<section title="Message Body" anchor="message.body">
1249  <x:anchor-alias value="message-body"/>
1250<t>
1251   The message-body (if any) of an HTTP message is used to carry the
1252   payload body associated with the request or response. The message-body
1253   differs from the payload body only when a transfer-coding has been
1254   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1255</t>
1256<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1257  <x:ref>message-body</x:ref> = *OCTET
1258</artwork></figure>
1259<t>
1260   When one or more transfer-codings are applied to a payload body,
1261   usually for the sake of stream-delimiting or data compression, the
1262   Transfer-Encoding header field &MUST; be provided with the list of
1263   transfer-codings applied. Transfer-Encoding is a property of the message,
1264   not of the payload, and thus &MAY; be added or removed by any implementation
1265   along the request/response chain under the constraints found in
1266   <xref target="transfer.codings"/>.
1267</t>
1268<t>
1269   The rules for when a message-body is allowed in a message differ for
1270   requests and responses.
1271</t>
1272<t>
1273   The presence of a message-body in a request is signaled by the
1274   inclusion of a Content-Length or Transfer-Encoding header field in
1275   the request's header fields, even if the request method does not
1276   define any use for a message-body.  This allows the request
1277   message framing algorithm to be independent of method semantics.
1278</t>
1279<t>
1280   For response messages, whether or not a message-body is included with
1281   a message is dependent on both the request method and the response
1282   status code (<xref target="status.code.and.reason.phrase"/>).
1283   Responses to the HEAD request method never include a message-body
1284   because the associated response header fields (e.g., Transfer-Encoding,
1285   Content-Length, etc.) only indicate what their values would have been
1286   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1287   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1288   All other responses do include a message-body, although the body
1289   &MAY; be of zero length.
1290</t>
1291<t>
1292   The length of the message-body is determined by one of the following
1293   (in order of precedence):
1294</t>
1295<t>
1296  <list style="numbers">
1297    <x:lt><t>
1298     Any response to a HEAD request and any response with a status
1299     code of 100-199, 204, or 304 is always terminated by the first
1300     empty line after the header fields, regardless of the header
1301     fields present in the message, and thus cannot contain a message-body.
1302    </t></x:lt>
1303    <x:lt><t>
1304     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1305     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1306     is the final encoding, the message-body length is determined by reading
1307     and decoding the chunked data until the transfer-coding indicates the
1308     data is complete.
1309    </t>
1310    <t>
1311     If a Transfer-Encoding header field is present in a response and the
1312     "chunked" transfer-coding is not the final encoding, the message-body
1313     length is determined by reading the connection until it is closed by
1314     the server.
1315     If a Transfer-Encoding header field is present in a request and the
1316     "chunked" transfer-coding is not the final encoding, the message-body
1317     length cannot be determined reliably; the server &MUST; respond with
1318     the 400 (Bad Request) status code and then close the connection.
1319    </t>
1320    <t>
1321     If a message is received with both a Transfer-Encoding header field and a
1322     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1323     Such a message might indicate an attempt to perform request or response
1324     smuggling (bypass of security-related checks on message routing or content)
1325     and thus should be handled as an error.  The provided Content-Length &MUST;
1326     be removed, prior to forwarding the message downstream, or replaced with
1327     the real message-body length after the transfer-coding is decoded.
1328    </t></x:lt>
1329    <x:lt><t>
1330     If a message is received without Transfer-Encoding and with either
1331     multiple Content-Length header fields or a single Content-Length header
1332     field with an invalid value, then the message framing is invalid and
1333     &MUST; be treated as an error to prevent request or response smuggling.
1334     If this is a request message, the server &MUST; respond with
1335     a 400 (Bad Request) status code and then close the connection.
1336     If this is a response message received by a proxy or gateway, the proxy
1337     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1338     status code as its downstream response, and then close the connection.
1339     If this is a response message received by a user-agent, the message-body
1340     length is determined by reading the connection until it is closed;
1341     an error &SHOULD; be indicated to the user.
1342    </t></x:lt>
1343    <x:lt><t>
1344     If a valid Content-Length header field (<xref target="header.content-length"/>)
1345     is present without Transfer-Encoding, its decimal value defines the
1346     message-body length in octets.  If the actual number of octets sent in
1347     the message is less than the indicated Content-Length, the recipient
1348     &MUST; consider the message to be incomplete and treat the connection
1349     as no longer usable.
1350     If the actual number of octets sent in the message is more than the indicated
1351     Content-Length, the recipient &MUST; only process the message-body up to the
1352     field value's number of octets; the remainder of the message &MUST; either
1353     be discarded or treated as the next message in a pipeline.  For the sake of
1354     robustness, a user-agent &MAY; attempt to detect and correct such an error
1355     in message framing if it is parsing the response to the last request on
1356     on a connection and the connection has been closed by the server.
1357    </t></x:lt>
1358    <x:lt><t>
1359     If this is a request message and none of the above are true, then the
1360     message-body length is zero (no message-body is present).
1361    </t></x:lt>
1362    <x:lt><t>
1363     Otherwise, this is a response message without a declared message-body
1364     length, so the message-body length is determined by the number of octets
1365     received prior to the server closing the connection.
1366    </t></x:lt>
1367  </list>
1368</t>
1369<t>
1370   Since there is no way to distinguish a successfully completed,
1371   close-delimited message from a partially-received message interrupted
1372   by network failure, implementations &SHOULD; use encoding or
1373   length-delimited messages whenever possible.  The close-delimiting
1374   feature exists primarily for backwards compatibility with HTTP/1.0.
1375</t>
1376<t>
1377   A server &MAY; reject a request that contains a message-body but
1378   not a Content-Length by responding with 411 (Length Required).
1379</t>
1380<t>
1381   Unless a transfer-coding other than "chunked" has been applied,
1382   a client that sends a request containing a message-body &SHOULD;
1383   use a valid Content-Length header field if the message-body length
1384   is known in advance, rather than the "chunked" encoding, since some
1385   existing services respond to "chunked" with a 411 (Length Required)
1386   status code even though they understand the chunked encoding.  This
1387   is typically because such services are implemented via a gateway that
1388   requires a content-length in advance of being called and the server
1389   is unable or unwilling to buffer the entire request before processing.
1390</t>
1391<t>
1392   A client that sends a request containing a message-body &MUST; include a
1393   valid Content-Length header field if it does not know the server will
1394   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1395   of specific user configuration or by remembering the version of a prior
1396   received response.
1397</t>
1398<t>
1399   Request messages that are prematurely terminated, possibly due to a
1400   cancelled connection or a server-imposed time-out exception, &MUST;
1401   result in closure of the connection; sending an HTTP/1.1 error response
1402   prior to closing the connection is &OPTIONAL;.
1403   Response messages that are prematurely terminated, usually by closure
1404   of the connection prior to receiving the expected number of octets or by
1405   failure to decode a transfer-encoded message-body, &MUST; be recorded
1406   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1407   message-body as if it were complete (i.e., some indication must be given
1408   to the user that an error occurred).  Cache requirements for incomplete
1409   responses are defined in &cache-incomplete;.
1410</t>
1411<t>
1412   A server &MUST; read the entire request message-body or close
1413   the connection after sending its response, since otherwise the
1414   remaining data on a persistent connection would be misinterpreted
1415   as the next request.  Likewise,
1416   a client &MUST; read the entire response message-body if it intends
1417   to reuse the same connection for a subsequent request.  Pipelining
1418   multiple requests on a connection is described in <xref target="pipelining"/>.
1419</t>
1420</section>
1421
1422<section title="General Header Fields" anchor="general.header.fields">
1423  <x:anchor-alias value="general-header"/>
1424<t>
1425   There are a few header fields which have general applicability for
1426   both request and response messages, but which do not apply to the
1427   payload being transferred. These header fields apply only to the
1428   message being transmitted.
1429</t>
1430<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1431  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1432                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1433                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1434                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1435                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1436                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1437                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1438                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1439                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1440                 / <x:ref>MIME-Version</x:ref>             ; &header-mime-version;
1441</artwork></figure>
1442<t>
1443   General-header field names can be extended reliably only in
1444   combination with a change in the protocol version. However, new or
1445   experimental header fields might be given the semantics of general
1446   header fields if all parties in the communication recognize them to
1447   be general-header fields. Unrecognized header fields are treated as
1448   entity-header fields.
1449</t>
1450</section>
1451</section>
1452
1453<section title="Request" anchor="request">
1454  <x:anchor-alias value="Request"/>
1455<t>
1456   A request message from a client to a server includes, within the
1457   first line of that message, the method to be applied to the resource,
1458   the identifier of the resource, and the protocol version in use.
1459</t>
1460<!--                 Host                      ; should be moved here eventually -->
1461<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1462  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1463                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1464                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1465                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1466                  <x:ref>CRLF</x:ref>
1467                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1468</artwork></figure>
1469
1470<section title="Request-Line" anchor="request-line">
1471  <x:anchor-alias value="Request-Line"/>
1472<t>
1473   The Request-Line begins with a method token, followed by the
1474   request-target and the protocol version, and ending with CRLF. The
1475   elements are separated by SP characters. No CR or LF is allowed
1476   except in the final CRLF sequence.
1477</t>
1478<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1479  <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>
1480</artwork></figure>
1481
1482<section title="Method" anchor="method">
1483  <x:anchor-alias value="Method"/>
1484<t>
1485   The Method  token indicates the method to be performed on the
1486   resource identified by the request-target. The method is case-sensitive.
1487</t>
1488<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1489  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1490</artwork></figure>
1491</section>
1492
1493<section title="request-target" anchor="request-target">
1494  <x:anchor-alias value="request-target"/>
1495<t>
1496   The request-target
1497   identifies the resource upon which to apply the request.
1498</t>
1499<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1500  <x:ref>request-target</x:ref> = "*"
1501                 / <x:ref>absolute-URI</x:ref>
1502                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1503                 / <x:ref>authority</x:ref>
1504</artwork></figure>
1505<t>
1506   The four options for request-target are dependent on the nature of the
1507   request.
1508</t>   
1509<t>
1510   The asterisk "*" means that the request does not apply to a
1511   particular resource, but to the server itself, and is only allowed
1512   when the method used does not necessarily apply to a resource. One
1513   example would be
1514</t>
1515<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1516OPTIONS * HTTP/1.1
1517</artwork></figure>
1518<t>
1519   The absolute-URI form is &REQUIRED; when the request is being made to a
1520   proxy. The proxy is requested to forward the request or service it
1521   from a valid cache, and return the response. Note that the proxy &MAY;
1522   forward the request on to another proxy or directly to the server
1523   specified by the absolute-URI. In order to avoid request loops, a
1524   proxy &MUST; be able to recognize all of its server names, including
1525   any aliases, local variations, and the numeric IP address. An example
1526   Request-Line would be:
1527</t>
1528<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1529GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1530</artwork></figure>
1531<t>
1532   To allow for transition to absolute-URIs in all requests in future
1533   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1534   form in requests, even though HTTP/1.1 clients will only generate
1535   them in requests to proxies.
1536</t>
1537<t>
1538   The authority form is only used by the CONNECT method (&CONNECT;).
1539</t>
1540<t>
1541   The most common form of request-target is that used to identify a
1542   resource on an origin server or gateway. In this case the absolute
1543   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1544   the request-target, and the network location of the URI (authority) &MUST;
1545   be transmitted in a Host header field. For example, a client wishing
1546   to retrieve the resource above directly from the origin server would
1547   create a TCP connection to port 80 of the host "www.example.org" and send
1548   the lines:
1549</t>
1550<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1551GET /pub/WWW/TheProject.html HTTP/1.1
1552Host: www.example.org
1553</artwork></figure>
1554<t>
1555   followed by the remainder of the Request. Note that the absolute path
1556   cannot be empty; if none is present in the original URI, it &MUST; be
1557   given as "/" (the server root).
1558</t>
1559<t>
1560   If a proxy receives a request without any path in the request-target and
1561   the method specified is capable of supporting the asterisk form of
1562   request-target, then the last proxy on the request chain &MUST; forward the
1563   request with "*" as the final request-target.
1564</t>
1565<figure><preamble>   
1566   For example, the request
1567</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1568OPTIONS http://www.example.org:8001 HTTP/1.1
1569</artwork></figure>
1570<figure><preamble>   
1571  would be forwarded by the proxy as
1572</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1573OPTIONS * HTTP/1.1
1574Host: www.example.org:8001
1575</artwork>
1576<postamble>
1577   after connecting to port 8001 of host "www.example.org".
1578</postamble>
1579</figure>
1580<t>
1581   The request-target is transmitted in the format specified in
1582   <xref target="http.uri"/>. If the request-target is percent-encoded
1583   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1584   &MUST; decode the request-target in order to
1585   properly interpret the request. Servers &SHOULD; respond to invalid
1586   request-targets with an appropriate status code.
1587</t>
1588<t>
1589   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1590   received request-target when forwarding it to the next inbound server,
1591   except as noted above to replace a null path-absolute with "/" or "*".
1592</t>
1593<x:note>
1594  <t>
1595    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1596    meaning of the request when the origin server is improperly using
1597    a non-reserved URI character for a reserved purpose.  Implementors
1598    should be aware that some pre-HTTP/1.1 proxies have been known to
1599    rewrite the request-target.
1600  </t>
1601</x:note>
1602<t>
1603   HTTP does not place a pre-defined limit on the length of a request-target.
1604   A server &MUST; be prepared to receive URIs of unbounded length and
1605   respond with the 414 (URI Too Long) status code if the received
1606   request-target would be longer than the server wishes to handle
1607   (see &status-414;).
1608</t>
1609<t>
1610   Various ad-hoc limitations on request-target length are found in practice.
1611   It is &RECOMMENDED; that all HTTP senders and recipients support
1612   request-target lengths of 8000 or more octets.
1613</t>
1614<x:note>
1615  <t>
1616    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1617    are not part of the request-target and thus will not be transmitted
1618    in an HTTP request.
1619  </t>
1620</x:note>
1621</section>
1622</section>
1623
1624<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1625<t>
1626   The exact resource identified by an Internet request is determined by
1627   examining both the request-target and the Host header field.
1628</t>
1629<t>
1630   An origin server that does not allow resources to differ by the
1631   requested host &MAY; ignore the Host header field value when
1632   determining the resource identified by an HTTP/1.1 request. (But see
1633   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1634   for other requirements on Host support in HTTP/1.1.)
1635</t>
1636<t>
1637   An origin server that does differentiate resources based on the host
1638   requested (sometimes referred to as virtual hosts or vanity host
1639   names) &MUST; use the following rules for determining the requested
1640   resource on an HTTP/1.1 request:
1641  <list style="numbers">
1642    <t>If request-target is an absolute-URI, the host is part of the
1643     request-target. Any Host header field value in the request &MUST; be
1644     ignored.</t>
1645    <t>If the request-target is not an absolute-URI, and the request includes
1646     a Host header field, the host is determined by the Host header
1647     field value.</t>
1648    <t>If the host as determined by rule 1 or 2 is not a valid host on
1649     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1650  </list>
1651</t>
1652<t>
1653   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1654   attempt to use heuristics (e.g., examination of the URI path for
1655   something unique to a particular host) in order to determine what
1656   exact resource is being requested.
1657</t>
1658</section>
1659
1660<section title="Effective Request URI" anchor="effective.request.uri">
1661  <iref primary="true" item="Effective Request URI"/>
1662<t>
1663   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1664   for the resource they are intended for; instead, the value needs to be inferred from the
1665   request-target, Host header and other context. The result of this process is
1666   the "Effective Request URI".
1667</t>
1668<t>
1669   If the request-target is an absolute-URI, then the Effective Request URI is
1670   the request-target.
1671</t>
1672<t>
1673   If the request-target uses the path-absolute (plus optional query) syntax
1674   or if it is just the asterisk "*", then the Effective Request URI is
1675   constructed by concatenating
1676</t>
1677<t>
1678  <list style="symbols">
1679    <t>
1680      the scheme name: "http" if the request was received over an insecure
1681      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1682      connection,
1683    </t>
1684    <t>
1685      the character sequence "://",
1686    </t>
1687    <t>
1688      the authority component, as specified in the Host header
1689      (<xref target="header.host"/>) and determined by the rules in
1690      <xref target="the.resource.identified.by.a.request"/>,
1691      <cref anchor="effrequri-nohost" source="jre">Do we need to include the handling of missing hosts in HTTP/1.0 messages, as
1692      described in <xref target="the.resource.identified.by.a.request"/>? -- See <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/></cref>
1693      and
1694    </t>
1695    <t>
1696      the request-target obtained from the Request-Line, unless the
1697      request-target is just the asterisk "*".
1698    </t>
1699  </list>
1700</t>
1701<t>
1702   Otherwise, when request-target uses the authority form, the Effective
1703   Request URI is undefined.
1704</t>
1705<figure>
1706<preamble>
1707   Example 1: the Effective Request URI for the message
1708</preamble> 
1709<artwork type="example" x:indent-with="  ">
1710GET /pub/WWW/TheProject.html HTTP/1.1
1711Host: www.example.org:8080
1712</artwork>
1713<postamble>
1714  (received over an insecure TCP connection) is "http", plus "://", plus the
1715  authority component "www.example.org:8080", plus the request-target
1716  "/pub/WWW/TheProject.html", thus
1717  "http://www.example.org:8080/pub/WWW/TheProject.html".
1718</postamble>
1719</figure>
1720<figure>
1721<preamble>
1722   Example 2: the Effective Request URI for the message
1723</preamble> 
1724<artwork type="example" x:indent-with="  ">
1725GET * HTTP/1.1
1726Host: www.example.org
1727</artwork>
1728<postamble>
1729  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1730  authority component "www.example.org", thus "https://www.example.org".
1731</postamble>
1732</figure>
1733<t>
1734   Effective Request URIs are compared using the rules described in
1735   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1736   be treated as equivalent to an absolute path of "/".
1737</t> 
1738</section>
1739
1740</section>
1741
1742
1743<section title="Response" anchor="response">
1744  <x:anchor-alias value="Response"/>
1745<t>
1746   After receiving and interpreting a request message, a server responds
1747   with an HTTP response message.
1748</t>
1749<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1750  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1751                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1752                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1753                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1754                  <x:ref>CRLF</x:ref>
1755                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1756</artwork></figure>
1757
1758<section title="Status-Line" anchor="status-line">
1759  <x:anchor-alias value="Status-Line"/>
1760<t>
1761   The first line of a Response message is the Status-Line, consisting
1762   of the protocol version followed by a numeric status code and its
1763   associated textual phrase, with each element separated by SP
1764   characters. No CR or LF is allowed except in the final CRLF sequence.
1765</t>
1766<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1767  <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>
1768</artwork></figure>
1769
1770<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1771  <x:anchor-alias value="Reason-Phrase"/>
1772  <x:anchor-alias value="Status-Code"/>
1773<t>
1774   The Status-Code element is a 3-digit integer result code of the
1775   attempt to understand and satisfy the request. These codes are fully
1776   defined in &status-codes;.  The Reason Phrase exists for the sole
1777   purpose of providing a textual description associated with the numeric
1778   status code, out of deference to earlier Internet application protocols
1779   that were more frequently used with interactive text clients.
1780   A client &SHOULD; ignore the content of the Reason Phrase.
1781</t>
1782<t>
1783   The first digit of the Status-Code defines the class of response. The
1784   last two digits do not have any categorization role. There are 5
1785   values for the first digit:
1786  <list style="symbols">
1787    <t>
1788      1xx: Informational - Request received, continuing process
1789    </t>
1790    <t>
1791      2xx: Success - The action was successfully received,
1792        understood, and accepted
1793    </t>
1794    <t>
1795      3xx: Redirection - Further action must be taken in order to
1796        complete the request
1797    </t>
1798    <t>
1799      4xx: Client Error - The request contains bad syntax or cannot
1800        be fulfilled
1801    </t>
1802    <t>
1803      5xx: Server Error - The server failed to fulfill an apparently
1804        valid request
1805    </t>
1806  </list>
1807</t>
1808<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"/>
1809  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1810  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1811</artwork></figure>
1812</section>
1813</section>
1814
1815</section>
1816
1817
1818<section title="Protocol Parameters" anchor="protocol.parameters">
1819
1820<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1821  <x:anchor-alias value="HTTP-date"/>
1822<t>
1823   HTTP applications have historically allowed three different formats
1824   for date/time stamps.
1825   However, the preferred format is
1826   a fixed-length subset of that defined by <xref target="RFC1123"/>:
1827</t>
1828<figure><artwork type="example" x:indent-with="  ">
1829Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1830</artwork></figure>
1831<t>
1832   The other formats are described here only for compatibility with obsolete
1833   implementations.
1834</t>
1835<figure><artwork type="example" x:indent-with="  ">
1836Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1837Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1838</artwork></figure>
1839<t>
1840   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1841   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1842   only generate the RFC 1123 format for representing HTTP-date values
1843   in header fields. See <xref target="tolerant.applications"/> for further information.
1844</t>
1845<t>
1846   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1847   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1848   equal to UTC (Coordinated Universal Time). This is indicated in the
1849   first two formats by the inclusion of "GMT" as the three-letter
1850   abbreviation for time zone, and &MUST; be assumed when reading the
1851   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1852   additional whitespace beyond that specifically included as SP in the
1853   grammar.
1854</t>
1855<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1856  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1857</artwork></figure>
1858<t anchor="preferred.date.format">
1859  <x:anchor-alias value="rfc1123-date"/>
1860  <x:anchor-alias value="time-of-day"/>
1861  <x:anchor-alias value="hour"/>
1862  <x:anchor-alias value="minute"/>
1863  <x:anchor-alias value="second"/>
1864  <x:anchor-alias value="day-name"/>
1865  <x:anchor-alias value="day"/>
1866  <x:anchor-alias value="month"/>
1867  <x:anchor-alias value="year"/>
1868  <x:anchor-alias value="GMT"/>
1869  Preferred format:
1870</t>
1871<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"/>
1872  <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>
1873
1874  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1875               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1876               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1877               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1878               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1879               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1880               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1881               
1882  <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>
1883               ; e.g., 02 Jun 1982
1884
1885  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1886  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1887               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1888               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1889               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1890               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1891               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1892               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1893               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1894               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1895               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1896               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1897               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1898  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1899
1900  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1901
1902  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1903                 ; 00:00:00 - 23:59:59
1904                 
1905  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1906  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1907  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1908</artwork></figure>
1909<t>
1910  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1911  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1912  same as those defined for the RFC 5322 constructs
1913  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1914</t>
1915<t anchor="obsolete.date.formats">
1916  <x:anchor-alias value="obs-date"/>
1917  <x:anchor-alias value="rfc850-date"/>
1918  <x:anchor-alias value="asctime-date"/>
1919  <x:anchor-alias value="date1"/>
1920  <x:anchor-alias value="date2"/>
1921  <x:anchor-alias value="date3"/>
1922  <x:anchor-alias value="rfc1123-date"/>
1923  <x:anchor-alias value="day-name-l"/>
1924  Obsolete formats:
1925</t>
1926<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1927  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1928</artwork></figure>
1929<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1930  <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>
1931  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1932                 ; day-month-year (e.g., 02-Jun-82)
1933
1934  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1935         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1936         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1937         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1938         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1939         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1940         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1941</artwork></figure>
1942<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1943  <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>
1944  <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> ))
1945                 ; month day (e.g., Jun  2)
1946</artwork></figure>
1947<x:note>
1948  <t>
1949    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1950    accepting date values that might have been sent by non-HTTP
1951    applications, as is sometimes the case when retrieving or posting
1952    messages via proxies/gateways to SMTP or NNTP.
1953  </t>
1954</x:note>
1955<x:note>
1956  <t>
1957    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1958    to their usage within the protocol stream. Clients and servers are
1959    not required to use these formats for user presentation, request
1960    logging, etc.
1961  </t>
1962</x:note>
1963</section>
1964
1965<section title="Transfer Codings" anchor="transfer.codings">
1966  <x:anchor-alias value="transfer-coding"/>
1967  <x:anchor-alias value="transfer-extension"/>
1968<t>
1969   Transfer-coding values are used to indicate an encoding
1970   transformation that has been, can be, or might need to be applied to a
1971   payload body in order to ensure "safe transport" through the network.
1972   This differs from a content coding in that the transfer-coding is a
1973   property of the message rather than a property of the representation
1974   that is being transferred.
1975</t>
1976<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1977  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1978                          / "compress" ; <xref target="compress.coding"/>
1979                          / "deflate" ; <xref target="deflate.coding"/>
1980                          / "gzip" ; <xref target="gzip.coding"/>
1981                          / <x:ref>transfer-extension</x:ref>
1982  <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> )
1983</artwork></figure>
1984<t anchor="rule.parameter">
1985  <x:anchor-alias value="attribute"/>
1986  <x:anchor-alias value="transfer-parameter"/>
1987  <x:anchor-alias value="value"/>
1988   Parameters are in the form of attribute/value pairs.
1989</t>
1990<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"/>
1991  <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>
1992  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1993  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
1994</artwork></figure>
1995<t>
1996   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1997   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1998   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1999</t>
2000<t>
2001   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2002   MIME, which were designed to enable safe transport of binary data over a
2003   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2004   However, safe transport
2005   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2006   the only unsafe characteristic of message-bodies is the difficulty in
2007   determining the exact message body length (<xref target="message.body"/>),
2008   or the desire to encrypt data over a shared transport.
2009</t>
2010<t>
2011   A server that receives a request message with a transfer-coding it does
2012   not understand &SHOULD; respond with 501 (Not Implemented) and then
2013   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2014   client.
2015</t>
2016
2017<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2018  <iref item="chunked (Coding Format)"/>
2019  <iref item="Coding Format" subitem="chunked"/>
2020  <x:anchor-alias value="chunk"/>
2021  <x:anchor-alias value="Chunked-Body"/>
2022  <x:anchor-alias value="chunk-data"/>
2023  <x:anchor-alias value="chunk-ext"/>
2024  <x:anchor-alias value="chunk-ext-name"/>
2025  <x:anchor-alias value="chunk-ext-val"/>
2026  <x:anchor-alias value="chunk-size"/>
2027  <x:anchor-alias value="last-chunk"/>
2028  <x:anchor-alias value="trailer-part"/>
2029  <x:anchor-alias value="quoted-str-nf"/>
2030  <x:anchor-alias value="qdtext-nf"/>
2031<t>
2032   The chunked encoding modifies the body of a message in order to
2033   transfer it as a series of chunks, each with its own size indicator,
2034   followed by an &OPTIONAL; trailer containing entity-header fields. This
2035   allows dynamically produced content to be transferred along with the
2036   information necessary for the recipient to verify that it has
2037   received the full message.
2038</t>
2039<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"/>
2040  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2041                   <x:ref>last-chunk</x:ref>
2042                   <x:ref>trailer-part</x:ref>
2043                   <x:ref>CRLF</x:ref>
2044 
2045  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2046                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2047  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2048  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2049 
2050  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2051                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2052  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2053  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2054  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2055  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
2056 
2057  <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>
2058                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2059  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2060                 ; <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> 
2061</artwork></figure>
2062<t>
2063   The chunk-size field is a string of hex digits indicating the size of
2064   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2065   zero, followed by the trailer, which is terminated by an empty line.
2066</t>
2067<t>
2068   The trailer allows the sender to include additional HTTP header
2069   fields at the end of the message. The Trailer header field can be
2070   used to indicate which header fields are included in a trailer (see
2071   <xref target="header.trailer"/>).
2072</t>
2073<t>
2074   A server using chunked transfer-coding in a response &MUST-NOT; use the
2075   trailer for any header fields unless at least one of the following is
2076   true:
2077  <list style="numbers">
2078    <t>the request included a TE header field that indicates "trailers" is
2079     acceptable in the transfer-coding of the  response, as described in
2080     <xref target="header.te"/>; or,</t>
2081
2082    <t>the server is the origin server for the response, the trailer
2083     fields consist entirely of optional metadata, and the recipient
2084     could use the message (in a manner acceptable to the origin server)
2085     without receiving this metadata.  In other words, the origin server
2086     is willing to accept the possibility that the trailer fields might
2087     be silently discarded along the path to the client.</t>
2088  </list>
2089</t>
2090<t>
2091   This requirement prevents an interoperability failure when the
2092   message is being received by an HTTP/1.1 (or later) proxy and
2093   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2094   compliance with the protocol would have necessitated a possibly
2095   infinite buffer on the proxy.
2096</t>
2097<t>
2098   A process for decoding the "chunked" transfer-coding
2099   can be represented in pseudo-code as:
2100</t>
2101<figure><artwork type="code">
2102  length := 0
2103  read chunk-size, chunk-ext (if any) and CRLF
2104  while (chunk-size &gt; 0) {
2105     read chunk-data and CRLF
2106     append chunk-data to decoded-body
2107     length := length + chunk-size
2108     read chunk-size and CRLF
2109  }
2110  read header-field
2111  while (header-field not empty) {
2112     append header-field to existing header fields
2113     read header-field
2114  }
2115  Content-Length := length
2116  Remove "chunked" from Transfer-Encoding
2117</artwork></figure>
2118<t>
2119   All HTTP/1.1 applications &MUST; be able to receive and decode the
2120   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2121   they do not understand.
2122</t>
2123<t>
2124   Since "chunked" is the only transfer-coding required to be understood
2125   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2126   on a persistent connection.  Whenever a transfer-coding is applied to
2127   a payload body in a request, the final transfer-coding applied &MUST;
2128   be "chunked".  If a transfer-coding is applied to a response payload
2129   body, then either the final transfer-coding applied &MUST; be "chunked"
2130   or the message &MUST; be terminated by closing the connection. When the
2131   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2132   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2133   be applied more than once in a message-body.
2134</t>
2135</section>
2136
2137<section title="Compression Codings" anchor="compression.codings">
2138<t>
2139   The codings defined below can be used to compress the payload of a
2140   message.
2141</t>
2142<x:note><t>
2143   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2144   is not desirable and is discouraged for future encodings. Their
2145   use here is representative of historical practice, not good
2146   design.
2147</t></x:note>
2148<x:note><t>
2149   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2150   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2151   equivalent to "gzip" and "compress" respectively.
2152</t></x:note>
2153
2154<section title="Compress Coding" anchor="compress.coding">
2155<iref item="compress (Coding Format)"/>
2156<iref item="Coding Format" subitem="compress"/>
2157<t>
2158   The "compress" format is produced by the common UNIX file compression
2159   program "compress". This format is an adaptive Lempel-Ziv-Welch
2160   coding (LZW).
2161</t>
2162</section>
2163
2164<section title="Deflate Coding" anchor="deflate.coding">
2165<iref item="deflate (Coding Format)"/>
2166<iref item="Coding Format" subitem="deflate"/>
2167<t>
2168   The "deflate" format is defined as the "deflate" compression mechanism
2169   (described in <xref target="RFC1951"/>) used inside the "zlib"
2170   data format (<xref target="RFC1950"/>).
2171</t>
2172<x:note>
2173  <t>
2174    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2175    compressed data without the zlib wrapper.
2176   </t>
2177</x:note>
2178</section>
2179
2180<section title="Gzip Coding" anchor="gzip.coding">
2181<iref item="gzip (Coding Format)"/>
2182<iref item="Coding Format" subitem="gzip"/>
2183<t>
2184   The "gzip" format is produced by the file compression program
2185   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2186   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2187</t>
2188</section>
2189
2190</section>
2191
2192<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2193<t>
2194   The HTTP Transfer Coding Registry defines the name space for the transfer
2195   coding names.
2196</t>
2197<t>
2198   Registrations &MUST; include the following fields:
2199   <list style="symbols">
2200     <t>Name</t>
2201     <t>Description</t>
2202     <t>Pointer to specification text</t>
2203   </list>
2204</t>
2205<t>
2206   Names of transfer codings &MUST-NOT; overlap with names of content codings
2207   (&content-codings;), unless the encoding transformation is identical (as it
2208   is the case for the compression codings defined in
2209   <xref target="compression.codings"/>).
2210</t>
2211<t>
2212   Values to be added to this name space require a specification
2213   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2214   conform to the purpose of transfer coding defined in this section.
2215</t>
2216<t>
2217   The registry itself is maintained at
2218   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2219</t>
2220</section>
2221</section>
2222
2223<section title="Product Tokens" anchor="product.tokens">
2224  <x:anchor-alias value="product"/>
2225  <x:anchor-alias value="product-version"/>
2226<t>
2227   Product tokens are used to allow communicating applications to
2228   identify themselves by software name and version. Most fields using
2229   product tokens also allow sub-products which form a significant part
2230   of the application to be listed, separated by whitespace. By
2231   convention, the products are listed in order of their significance
2232   for identifying the application.
2233</t>
2234<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2235  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2236  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2237</artwork></figure>
2238<t>
2239   Examples:
2240</t>
2241<figure><artwork type="example">
2242  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2243  Server: Apache/0.8.4
2244</artwork></figure>
2245<t>
2246   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2247   used for advertising or other non-essential information. Although any
2248   token character &MAY; appear in a product-version, this token &SHOULD;
2249   only be used for a version identifier (i.e., successive versions of
2250   the same product &SHOULD; only differ in the product-version portion of
2251   the product value).
2252</t>
2253</section>
2254
2255<section title="Quality Values" anchor="quality.values">
2256  <x:anchor-alias value="qvalue"/>
2257<t>
2258   Both transfer codings (TE request header, <xref target="header.te"/>)
2259   and content negotiation (&content.negotiation;) use short "floating point"
2260   numbers to indicate the relative importance ("weight") of various
2261   negotiable parameters.  A weight is normalized to a real number in
2262   the range 0 through 1, where 0 is the minimum and 1 the maximum
2263   value. If a parameter has a quality value of 0, then content with
2264   this parameter is "not acceptable" for the client. HTTP/1.1
2265   applications &MUST-NOT; generate more than three digits after the
2266   decimal point. User configuration of these values &SHOULD; also be
2267   limited in this fashion.
2268</t>
2269<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2270  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2271                 / ( "1" [ "." 0*3("0") ] )
2272</artwork></figure>
2273<x:note>
2274  <t>
2275     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2276     relative degradation in desired quality.
2277  </t>
2278</x:note>
2279</section>
2280
2281</section>
2282
2283<section title="Connections" anchor="connections">
2284
2285<section title="Persistent Connections" anchor="persistent.connections">
2286
2287<section title="Purpose" anchor="persistent.purpose">
2288<t>
2289   Prior to persistent connections, a separate TCP connection was
2290   established to fetch each URL, increasing the load on HTTP servers
2291   and causing congestion on the Internet. The use of inline images and
2292   other associated data often requires a client to make multiple
2293   requests of the same server in a short amount of time. Analysis of
2294   these performance problems and results from a prototype
2295   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2296   measurements of actual HTTP/1.1 implementations show good
2297   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2298   T/TCP <xref target="Tou1998"/>.
2299</t>
2300<t>
2301   Persistent HTTP connections have a number of advantages:
2302  <list style="symbols">
2303      <t>
2304        By opening and closing fewer TCP connections, CPU time is saved
2305        in routers and hosts (clients, servers, proxies, gateways,
2306        tunnels, or caches), and memory used for TCP protocol control
2307        blocks can be saved in hosts.
2308      </t>
2309      <t>
2310        HTTP requests and responses can be pipelined on a connection.
2311        Pipelining allows a client to make multiple requests without
2312        waiting for each response, allowing a single TCP connection to
2313        be used much more efficiently, with much lower elapsed time.
2314      </t>
2315      <t>
2316        Network congestion is reduced by reducing the number of packets
2317        caused by TCP opens, and by allowing TCP sufficient time to
2318        determine the congestion state of the network.
2319      </t>
2320      <t>
2321        Latency on subsequent requests is reduced since there is no time
2322        spent in TCP's connection opening handshake.
2323      </t>
2324      <t>
2325        HTTP can evolve more gracefully, since errors can be reported
2326        without the penalty of closing the TCP connection. Clients using
2327        future versions of HTTP might optimistically try a new feature,
2328        but if communicating with an older server, retry with old
2329        semantics after an error is reported.
2330      </t>
2331    </list>
2332</t>
2333<t>
2334   HTTP implementations &SHOULD; implement persistent connections.
2335</t>
2336</section>
2337
2338<section title="Overall Operation" anchor="persistent.overall">
2339<t>
2340   A significant difference between HTTP/1.1 and earlier versions of
2341   HTTP is that persistent connections are the default behavior of any
2342   HTTP connection. That is, unless otherwise indicated, the client
2343   &SHOULD; assume that the server will maintain a persistent connection,
2344   even after error responses from the server.
2345</t>
2346<t>
2347   Persistent connections provide a mechanism by which a client and a
2348   server can signal the close of a TCP connection. This signaling takes
2349   place using the Connection header field (<xref target="header.connection"/>). Once a close
2350   has been signaled, the client &MUST-NOT; send any more requests on that
2351   connection.
2352</t>
2353
2354<section title="Negotiation" anchor="persistent.negotiation">
2355<t>
2356   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2357   maintain a persistent connection unless a Connection header including
2358   the connection-token "close" was sent in the request. If the server
2359   chooses to close the connection immediately after sending the
2360   response, it &SHOULD; send a Connection header including the
2361   connection-token "close".
2362</t>
2363<t>
2364   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2365   decide to keep it open based on whether the response from a server
2366   contains a Connection header with the connection-token close. In case
2367   the client does not want to maintain a connection for more than that
2368   request, it &SHOULD; send a Connection header including the
2369   connection-token close.
2370</t>
2371<t>
2372   If either the client or the server sends the close token in the
2373   Connection header, that request becomes the last one for the
2374   connection.
2375</t>
2376<t>
2377   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2378   maintained for HTTP versions less than 1.1 unless it is explicitly
2379   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2380   compatibility with HTTP/1.0 clients.
2381</t>
2382<t>
2383   In order to remain persistent, all messages on the connection &MUST;
2384   have a self-defined message length (i.e., one not defined by closure
2385   of the connection), as described in <xref target="message.body"/>.
2386</t>
2387</section>
2388
2389<section title="Pipelining" anchor="pipelining">
2390<t>
2391   A client that supports persistent connections &MAY; "pipeline" its
2392   requests (i.e., send multiple requests without waiting for each
2393   response). A server &MUST; send its responses to those requests in the
2394   same order that the requests were received.
2395</t>
2396<t>
2397   Clients which assume persistent connections and pipeline immediately
2398   after connection establishment &SHOULD; be prepared to retry their
2399   connection if the first pipelined attempt fails. If a client does
2400   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2401   persistent. Clients &MUST; also be prepared to resend their requests if
2402   the server closes the connection before sending all of the
2403   corresponding responses.
2404</t>
2405<t>
2406   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2407   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2408   premature termination of the transport connection could lead to
2409   indeterminate results. A client wishing to send a non-idempotent
2410   request &SHOULD; wait to send that request until it has received the
2411   response status line for the previous request.
2412</t>
2413</section>
2414</section>
2415
2416<section title="Proxy Servers" anchor="persistent.proxy">
2417<t>
2418   It is especially important that proxies correctly implement the
2419   properties of the Connection header field as specified in <xref target="header.connection"/>.
2420</t>
2421<t>
2422   The proxy server &MUST; signal persistent connections separately with
2423   its clients and the origin servers (or other proxy servers) that it
2424   connects to. Each persistent connection applies to only one transport
2425   link.
2426</t>
2427<t>
2428   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2429   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2430   for information and discussion of the problems with the Keep-Alive header
2431   implemented by many HTTP/1.0 clients).
2432</t>
2433
2434<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2435<!--<t>
2436  <cref anchor="TODO-end-to-end" source="jre">
2437    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2438    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2439  </cref>
2440</t>-->
2441<t>
2442   For the purpose of defining the behavior of caches and non-caching
2443   proxies, we divide HTTP headers into two categories:
2444  <list style="symbols">
2445      <t>End-to-end headers, which are  transmitted to the ultimate
2446        recipient of a request or response. End-to-end headers in
2447        responses MUST be stored as part of a cache entry and &MUST; be
2448        transmitted in any response formed from a cache entry.</t>
2449
2450      <t>Hop-by-hop headers, which are meaningful only for a single
2451        transport-level connection, and are not stored by caches or
2452        forwarded by proxies.</t>
2453  </list>
2454</t>
2455<t>
2456   The following HTTP/1.1 headers are hop-by-hop headers:
2457  <list style="symbols">
2458      <t>Connection</t>
2459      <t>Keep-Alive</t>
2460      <t>Proxy-Authenticate</t>
2461      <t>Proxy-Authorization</t>
2462      <t>TE</t>
2463      <t>Trailer</t>
2464      <t>Transfer-Encoding</t>
2465      <t>Upgrade</t>
2466  </list>
2467</t>
2468<t>
2469   All other headers defined by HTTP/1.1 are end-to-end headers.
2470</t>
2471<t>
2472   Other hop-by-hop headers &MUST; be listed in a Connection header
2473   (<xref target="header.connection"/>).
2474</t>
2475</section>
2476
2477<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2478<!--<t>
2479  <cref anchor="TODO-non-mod-headers" source="jre">
2480    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2481    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2482  </cref>
2483</t>-->
2484<t>
2485   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2486   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2487   modify an end-to-end header unless the definition of that header requires
2488   or specifically allows that.
2489</t>
2490<t>
2491   A transparent proxy &MUST-NOT; modify any of the following fields in a
2492   request or response, and it &MUST-NOT; add any of these fields if not
2493   already present:
2494  <list style="symbols">
2495      <t>Content-Location</t>
2496      <t>Content-MD5</t>
2497      <t>ETag</t>
2498      <t>Last-Modified</t>
2499  </list>
2500</t>
2501<t>
2502   A transparent proxy &MUST-NOT; modify any of the following fields in a
2503   response:
2504  <list style="symbols">
2505    <t>Expires</t>
2506  </list>
2507</t>
2508<t>
2509   but it &MAY; add any of these fields if not already present. If an
2510   Expires header is added, it &MUST; be given a field-value identical to
2511   that of the Date header in that response.
2512</t>
2513<t>
2514   A proxy &MUST-NOT; modify or add any of the following fields in a
2515   message that contains the no-transform cache-control directive, or in
2516   any request:
2517  <list style="symbols">
2518    <t>Content-Encoding</t>
2519    <t>Content-Range</t>
2520    <t>Content-Type</t>
2521  </list>
2522</t>
2523<t>
2524   A non-transparent proxy &MAY; modify or add these fields to a message
2525   that does not include no-transform, but if it does so, it &MUST; add a
2526   Warning 214 (Transformation applied) if one does not already appear
2527   in the message (see &header-warning;).
2528</t>
2529<x:note>
2530  <t>
2531    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2532    cause authentication failures if stronger authentication
2533    mechanisms are introduced in later versions of HTTP. Such
2534    authentication mechanisms &MAY; rely on the values of header fields
2535    not listed here.
2536  </t>
2537</x:note>
2538<t>
2539   A transparent proxy &MUST; preserve the message payload (&payload;),
2540   though it &MAY; change the message-body through application or removal
2541   of a transfer-coding (<xref target="transfer.codings"/>).
2542</t>
2543</section>
2544
2545</section>
2546
2547<section title="Practical Considerations" anchor="persistent.practical">
2548<t>
2549   Servers will usually have some time-out value beyond which they will
2550   no longer maintain an inactive connection. Proxy servers might make
2551   this a higher value since it is likely that the client will be making
2552   more connections through the same server. The use of persistent
2553   connections places no requirements on the length (or existence) of
2554   this time-out for either the client or the server.
2555</t>
2556<t>
2557   When a client or server wishes to time-out it &SHOULD; issue a graceful
2558   close on the transport connection. Clients and servers &SHOULD; both
2559   constantly watch for the other side of the transport close, and
2560   respond to it as appropriate. If a client or server does not detect
2561   the other side's close promptly it could cause unnecessary resource
2562   drain on the network.
2563</t>
2564<t>
2565   A client, server, or proxy &MAY; close the transport connection at any
2566   time. For example, a client might have started to send a new request
2567   at the same time that the server has decided to close the "idle"
2568   connection. From the server's point of view, the connection is being
2569   closed while it was idle, but from the client's point of view, a
2570   request is in progress.
2571</t>
2572<t>
2573   This means that clients, servers, and proxies &MUST; be able to recover
2574   from asynchronous close events. Client software &SHOULD; reopen the
2575   transport connection and retransmit the aborted sequence of requests
2576   without user interaction so long as the request sequence is
2577   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2578   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2579   human operator the choice of retrying the request(s). Confirmation by
2580   user-agent software with semantic understanding of the application
2581   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2582   be repeated if the second sequence of requests fails.
2583</t>
2584<t>
2585   Servers &SHOULD; always respond to at least one request per connection,
2586   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2587   middle of transmitting a response, unless a network or client failure
2588   is suspected.
2589</t>
2590<t>
2591   Clients (including proxies) &SHOULD; limit the number of simultaneous
2592   connections that they maintain to a given server (including proxies).
2593</t>
2594<t>
2595   Previous revisions of HTTP gave a specific number of connections as a
2596   ceiling, but this was found to be impractical for many applications. As a
2597   result, this specification does not mandate a particular maximum number of
2598   connections, but instead encourages clients to be conservative when opening
2599   multiple connections.
2600</t>
2601<t>
2602   In particular, while using multiple connections avoids the "head-of-line
2603   blocking" problem (whereby a request that takes significant server-side
2604   processing and/or has a large payload can block subsequent requests on the
2605   same connection), each connection used consumes server resources (sometimes
2606   significantly), and furthermore using multiple connections can cause
2607   undesirable side effects in congested networks.
2608</t>
2609<t>
2610   Note that servers might reject traffic that they deem abusive, including an
2611   excessive number of connections from a client.
2612</t>
2613</section>
2614</section>
2615
2616<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2617
2618<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2619<t>
2620   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2621   flow control mechanisms to resolve temporary overloads, rather than
2622   terminating connections with the expectation that clients will retry.
2623   The latter technique can exacerbate network congestion.
2624</t>
2625</section>
2626
2627<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2628<t>
2629   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2630   the network connection for an error status code while it is transmitting
2631   the request. If the client sees an error status code, it &SHOULD;
2632   immediately cease transmitting the body. If the body is being sent
2633   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2634   empty trailer &MAY; be used to prematurely mark the end of the message.
2635   If the body was preceded by a Content-Length header, the client &MUST;
2636   close the connection.
2637</t>
2638</section>
2639
2640<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2641<t>
2642   The purpose of the 100 (Continue) status code (see &status-100;) is to
2643   allow a client that is sending a request message with a request body
2644   to determine if the origin server is willing to accept the request
2645   (based on the request headers) before the client sends the request
2646   body. In some cases, it might either be inappropriate or highly
2647   inefficient for the client to send the body if the server will reject
2648   the message without looking at the body.
2649</t>
2650<t>
2651   Requirements for HTTP/1.1 clients:
2652  <list style="symbols">
2653    <t>
2654        If a client will wait for a 100 (Continue) response before
2655        sending the request body, it &MUST; send an Expect request-header
2656        field (&header-expect;) with the "100-continue" expectation.
2657    </t>
2658    <t>
2659        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2660        with the "100-continue" expectation if it does not intend
2661        to send a request body.
2662    </t>
2663  </list>
2664</t>
2665<t>
2666   Because of the presence of older implementations, the protocol allows
2667   ambiguous situations in which a client might send "Expect: 100-continue"
2668   without receiving either a 417 (Expectation Failed)
2669   or a 100 (Continue) status code. Therefore, when a client sends this
2670   header field to an origin server (possibly via a proxy) from which it
2671   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2672   wait for an indefinite period before sending the request body.
2673</t>
2674<t>
2675   Requirements for HTTP/1.1 origin servers:
2676  <list style="symbols">
2677    <t> Upon receiving a request which includes an Expect request-header
2678        field with the "100-continue" expectation, an origin server &MUST;
2679        either respond with 100 (Continue) status code and continue to read
2680        from the input stream, or respond with a final status code. The
2681        origin server &MUST-NOT; wait for the request body before sending
2682        the 100 (Continue) response. If it responds with a final status
2683        code, it &MAY; close the transport connection or it &MAY; continue
2684        to read and discard the rest of the request.  It &MUST-NOT;
2685        perform the requested method if it returns a final status code.
2686    </t>
2687    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2688        the request message does not include an Expect request-header
2689        field with the "100-continue" expectation, and &MUST-NOT; send a
2690        100 (Continue) response if such a request comes from an HTTP/1.0
2691        (or earlier) client. There is an exception to this rule: for
2692        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2693        status code in response to an HTTP/1.1 PUT or POST request that does
2694        not include an Expect request-header field with the "100-continue"
2695        expectation. This exception, the purpose of which is
2696        to minimize any client processing delays associated with an
2697        undeclared wait for 100 (Continue) status code, applies only to
2698        HTTP/1.1 requests, and not to requests with any other HTTP-version
2699        value.
2700    </t>
2701    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2702        already received some or all of the request body for the
2703        corresponding request.
2704    </t>
2705    <t> An origin server that sends a 100 (Continue) response &MUST;
2706    ultimately send a final status code, once the request body is
2707        received and processed, unless it terminates the transport
2708        connection prematurely.
2709    </t>
2710    <t> If an origin server receives a request that does not include an
2711        Expect request-header field with the "100-continue" expectation,
2712        the request includes a request body, and the server responds
2713        with a final status code before reading the entire request body
2714        from the transport connection, then the server &SHOULD-NOT;  close
2715        the transport connection until it has read the entire request,
2716        or until the client closes the connection. Otherwise, the client
2717        might not reliably receive the response message. However, this
2718        requirement is not be construed as preventing a server from
2719        defending itself against denial-of-service attacks, or from
2720        badly broken client implementations.
2721      </t>
2722    </list>
2723</t>
2724<t>
2725   Requirements for HTTP/1.1 proxies:
2726  <list style="symbols">
2727    <t> If a proxy receives a request that includes an Expect request-header
2728        field with the "100-continue" expectation, and the proxy
2729        either knows that the next-hop server complies with HTTP/1.1 or
2730        higher, or does not know the HTTP version of the next-hop
2731        server, it &MUST; forward the request, including the Expect header
2732        field.
2733    </t>
2734    <t> If the proxy knows that the version of the next-hop server is
2735        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2736        respond with a 417 (Expectation Failed) status code.
2737    </t>
2738    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2739        numbers received from recently-referenced next-hop servers.
2740    </t>
2741    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2742        request message was received from an HTTP/1.0 (or earlier)
2743        client and did not include an Expect request-header field with
2744        the "100-continue" expectation. This requirement overrides the
2745        general rule for forwarding of 1xx responses (see &status-1xx;).
2746    </t>
2747  </list>
2748</t>
2749</section>
2750
2751<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2752<t>
2753   If an HTTP/1.1 client sends a request which includes a request body,
2754   but which does not include an Expect request-header field with the
2755   "100-continue" expectation, and if the client is not directly
2756   connected to an HTTP/1.1 origin server, and if the client sees the
2757   connection close before receiving a status line from the server, the
2758   client &SHOULD; retry the request.  If the client does retry this
2759   request, it &MAY; use the following "binary exponential backoff"
2760   algorithm to be assured of obtaining a reliable response:
2761  <list style="numbers">
2762    <t>
2763      Initiate a new connection to the server
2764    </t>
2765    <t>
2766      Transmit the request-headers
2767    </t>
2768    <t>
2769      Initialize a variable R to the estimated round-trip time to the
2770         server (e.g., based on the time it took to establish the
2771         connection), or to a constant value of 5 seconds if the round-trip
2772         time is not available.
2773    </t>
2774    <t>
2775       Compute T = R * (2**N), where N is the number of previous
2776         retries of this request.
2777    </t>
2778    <t>
2779       Wait either for an error response from the server, or for T
2780         seconds (whichever comes first)
2781    </t>
2782    <t>
2783       If no error response is received, after T seconds transmit the
2784         body of the request.
2785    </t>
2786    <t>
2787       If client sees that the connection is closed prematurely,
2788         repeat from step 1 until the request is accepted, an error
2789         response is received, or the user becomes impatient and
2790         terminates the retry process.
2791    </t>
2792  </list>
2793</t>
2794<t>
2795   If at any point an error status code is received, the client
2796  <list style="symbols">
2797      <t>&SHOULD-NOT;  continue and</t>
2798
2799      <t>&SHOULD; close the connection if it has not completed sending the
2800        request message.</t>
2801    </list>
2802</t>
2803</section>
2804</section>
2805</section>
2806
2807
2808<section title="Miscellaneous notes that might disappear" anchor="misc">
2809<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2810<t>
2811   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2812</t>
2813</section>
2814
2815<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2816<t>
2817   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2818</t>
2819</section>
2820
2821<section title="Interception of HTTP for access control" anchor="http.intercept">
2822<t>
2823   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2824</t>
2825</section>
2826
2827<section title="Use of HTTP by other protocols" anchor="http.others">
2828<t>
2829   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2830   Extensions of HTTP like WebDAV.</cref>
2831</t>
2832
2833</section>
2834<section title="Use of HTTP by media type specification" anchor="http.media">
2835<t>
2836   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2837</t>
2838</section>
2839</section>
2840
2841<section title="Header Field Definitions" anchor="header.field.definitions">
2842<t>
2843   This section defines the syntax and semantics of HTTP/1.1 header fields
2844   related to message framing and transport protocols.
2845</t>
2846<t>
2847   For entity-header fields, both sender and recipient refer to either the
2848   client or the server, depending on who sends and who receives the message.
2849</t>
2850
2851<section title="Connection" anchor="header.connection">
2852  <iref primary="true" item="Connection header" x:for-anchor=""/>
2853  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2854  <x:anchor-alias value="Connection"/>
2855  <x:anchor-alias value="connection-token"/>
2856  <x:anchor-alias value="Connection-v"/>
2857<t>
2858   The "Connection" general-header field allows the sender to specify
2859   options that are desired for that particular connection and &MUST-NOT;
2860   be communicated by proxies over further connections.
2861</t>
2862<t>
2863   The Connection header's value has the following grammar:
2864</t>
2865<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"/>
2866  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2867  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2868  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2869</artwork></figure>
2870<t>
2871   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2872   message is forwarded and, for each connection-token in this field,
2873   remove any header field(s) from the message with the same name as the
2874   connection-token. Connection options are signaled by the presence of
2875   a connection-token in the Connection header field, not by any
2876   corresponding additional header field(s), since the additional header
2877   field might not be sent if there are no parameters associated with that
2878   connection option.
2879</t>
2880<t>
2881   Message headers listed in the Connection header &MUST-NOT; include
2882   end-to-end headers, such as Cache-Control.
2883</t>
2884<t>
2885   HTTP/1.1 defines the "close" connection option for the sender to
2886   signal that the connection will be closed after completion of the
2887   response. For example,
2888</t>
2889<figure><artwork type="example">
2890  Connection: close
2891</artwork></figure>
2892<t>
2893   in either the request or the response header fields indicates that
2894   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2895   after the current request/response is complete.
2896</t>
2897<t>
2898   An HTTP/1.1 client that does not support persistent connections &MUST;
2899   include the "close" connection option in every request message.
2900</t>
2901<t>
2902   An HTTP/1.1 server that does not support persistent connections &MUST;
2903   include the "close" connection option in every response message that
2904   does not have a 1xx (Informational) status code.
2905</t>
2906<t>
2907   A system receiving an HTTP/1.0 (or lower-version) message that
2908   includes a Connection header &MUST;, for each connection-token in this
2909   field, remove and ignore any header field(s) from the message with
2910   the same name as the connection-token. This protects against mistaken
2911   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2912</t>
2913</section>
2914
2915<section title="Content-Length" anchor="header.content-length">
2916  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2917  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2918  <x:anchor-alias value="Content-Length"/>
2919  <x:anchor-alias value="Content-Length-v"/>
2920<t>
2921   The "Content-Length" header field indicates the size of the
2922   message-body, in decimal number of octets, for any message other than
2923   a response to the HEAD method or a response with a status code of 304.
2924   In the case of responses to the HEAD method, it indicates the size of
2925   the payload body (not including any potential transfer-coding) that
2926   would have been sent had the request been a GET.
2927   In the case of the 304 (Not Modified) response, it indicates the size of
2928   the payload body (not including any potential transfer-coding) that
2929   would have been sent in a 200 (OK) response.
2930</t>
2931<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2932  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2933  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2934</artwork></figure>
2935<t>
2936   An example is
2937</t>
2938<figure><artwork type="example">
2939  Content-Length: 3495
2940</artwork></figure>
2941<t>
2942   Implementations &SHOULD; use this field to indicate the message-body
2943   length when no transfer-coding is being applied and the
2944   payload's body length can be determined prior to being transferred.
2945   <xref target="message.body"/> describes how recipients determine the length
2946   of a message-body.
2947</t>
2948<t>
2949   Any Content-Length greater than or equal to zero is a valid value.
2950</t>
2951<t>
2952   Note that the use of this field in HTTP is significantly different from
2953   the corresponding definition in MIME, where it is an optional field
2954   used within the "message/external-body" content-type.
2955</t>
2956</section>
2957
2958<section title="Date" anchor="header.date">
2959  <iref primary="true" item="Date header" x:for-anchor=""/>
2960  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2961  <x:anchor-alias value="Date"/>
2962  <x:anchor-alias value="Date-v"/>
2963<t>
2964   The "Date" general-header field represents the date and time at which
2965   the message was originated, having the same semantics as the Origination
2966   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2967   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2968   it &MUST; be sent in rfc1123-date format.
2969</t>
2970<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2971  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2972  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2973</artwork></figure>
2974<t>
2975   An example is
2976</t>
2977<figure><artwork type="example">
2978  Date: Tue, 15 Nov 1994 08:12:31 GMT
2979</artwork></figure>
2980<t>
2981   Origin servers &MUST; include a Date header field in all responses,
2982   except in these cases:
2983  <list style="numbers">
2984      <t>If the response status code is 100 (Continue) or 101 (Switching
2985         Protocols), the response &MAY; include a Date header field, at
2986         the server's option.</t>
2987
2988      <t>If the response status code conveys a server error, e.g., 500
2989         (Internal Server Error) or 503 (Service Unavailable), and it is
2990         inconvenient or impossible to generate a valid Date.</t>
2991
2992      <t>If the server does not have a clock that can provide a
2993         reasonable approximation of the current time, its responses
2994         &MUST-NOT; include a Date header field. In this case, the rules
2995         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2996  </list>
2997</t>
2998<t>
2999   A received message that does not have a Date header field &MUST; be
3000   assigned one by the recipient if the message will be cached by that
3001   recipient or gatewayed via a protocol which requires a Date. An HTTP
3002   implementation without a clock &MUST-NOT; cache responses without
3003   revalidating them on every use. An HTTP cache, especially a shared
3004   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
3005   clock with a reliable external standard.
3006</t>
3007<t>
3008   Clients &SHOULD; only send a Date header field in messages that include
3009   a payload, as is usually the case for PUT and POST requests, and even
3010   then it is optional. A client without a clock &MUST-NOT; send a Date
3011   header field in a request.
3012</t>
3013<t>
3014   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
3015   time subsequent to the generation of the message. It &SHOULD; represent
3016   the best available approximation of the date and time of message
3017   generation, unless the implementation has no means of generating a
3018   reasonably accurate date and time. In theory, the date ought to
3019   represent the moment just before the payload is generated. In
3020   practice, the date can be generated at any time during the message
3021   origination without affecting its semantic value.
3022</t>
3023
3024<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3025<t>
3026   Some origin server implementations might not have a clock available.
3027   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3028   values to a response, unless these values were associated
3029   with the resource by a system or user with a reliable clock. It &MAY;
3030   assign an Expires value that is known, at or before server
3031   configuration time, to be in the past (this allows "pre-expiration"
3032   of responses without storing separate Expires values for each
3033   resource).
3034</t>
3035</section>
3036</section>
3037
3038<section title="Host" anchor="header.host">
3039  <iref primary="true" item="Host header" x:for-anchor=""/>
3040  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3041  <x:anchor-alias value="Host"/>
3042  <x:anchor-alias value="Host-v"/>
3043<t>
3044   The "Host" request-header field specifies the Internet host and port
3045   number of the resource being requested, allowing the origin server or
3046   gateway to differentiate between internally-ambiguous URLs, such as the root
3047   "/" URL of a server for multiple host names on a single IP address.
3048</t>
3049<t>   
3050   The Host field value &MUST; represent the naming authority of the origin
3051   server or gateway given by the original URL obtained from the user or
3052   referring resource (generally an http URI, as described in
3053   <xref target="http.uri"/>).
3054</t>
3055<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3056  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3057  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3058</artwork></figure>
3059<t>
3060   A "host" without any trailing port information implies the default
3061   port for the service requested (e.g., "80" for an HTTP URL). For
3062   example, a request on the origin server for
3063   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
3064</t>
3065<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3066GET /pub/WWW/ HTTP/1.1
3067Host: www.example.org
3068</artwork></figure>
3069<t>
3070   A client &MUST; include a Host header field in all HTTP/1.1 request
3071   messages. If the requested URI does not include an Internet host
3072   name for the service being requested, then the Host header field &MUST;
3073   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3074   request message it forwards does contain an appropriate Host header
3075   field that identifies the service being requested by the proxy. All
3076   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3077   status code to any HTTP/1.1 request message which lacks a Host header
3078   field.
3079</t>
3080<t>
3081   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3082   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3083   for other requirements relating to Host.
3084</t>
3085</section>
3086
3087<section title="TE" anchor="header.te">
3088  <iref primary="true" item="TE header" x:for-anchor=""/>
3089  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3090  <x:anchor-alias value="TE"/>
3091  <x:anchor-alias value="TE-v"/>
3092  <x:anchor-alias value="t-codings"/>
3093  <x:anchor-alias value="te-params"/>
3094  <x:anchor-alias value="te-ext"/>
3095<t>
3096   The "TE" request-header field indicates what extension transfer-codings
3097   it is willing to accept in the response, and whether or not it is
3098   willing to accept trailer fields in a chunked transfer-coding.
3099</t>
3100<t>
3101   Its value might consist of the keyword "trailers" and/or a comma-separated
3102   list of extension transfer-coding names with optional accept
3103   parameters (as described in <xref target="transfer.codings"/>).
3104</t>
3105<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"/>
3106  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3107  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3108  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3109  <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> )
3110  <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> ]
3111</artwork></figure>
3112<t>
3113   The presence of the keyword "trailers" indicates that the client is
3114   willing to accept trailer fields in a chunked transfer-coding, as
3115   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3116   transfer-coding values even though it does not itself represent a
3117   transfer-coding.
3118</t>
3119<t>
3120   Examples of its use are:
3121</t>
3122<figure><artwork type="example">
3123  TE: deflate
3124  TE:
3125  TE: trailers, deflate;q=0.5
3126</artwork></figure>
3127<t>
3128   The TE header field only applies to the immediate connection.
3129   Therefore, the keyword &MUST; be supplied within a Connection header
3130   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3131</t>
3132<t>
3133   A server tests whether a transfer-coding is acceptable, according to
3134   a TE field, using these rules:
3135  <list style="numbers">
3136    <x:lt>
3137      <t>The "chunked" transfer-coding is always acceptable. If the
3138         keyword "trailers" is listed, the client indicates that it is
3139         willing to accept trailer fields in the chunked response on
3140         behalf of itself and any downstream clients. The implication is
3141         that, if given, the client is stating that either all
3142         downstream clients are willing to accept trailer fields in the
3143         forwarded response, or that it will attempt to buffer the
3144         response on behalf of downstream recipients.
3145      </t><t>
3146         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3147         chunked response such that a client can be assured of buffering
3148         the entire response.</t>
3149    </x:lt>
3150    <x:lt>
3151      <t>If the transfer-coding being tested is one of the transfer-codings
3152         listed in the TE field, then it is acceptable unless it
3153         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3154         qvalue of 0 means "not acceptable".)</t>
3155    </x:lt>
3156    <x:lt>
3157      <t>If multiple transfer-codings are acceptable, then the
3158         acceptable transfer-coding with the highest non-zero qvalue is
3159         preferred.  The "chunked" transfer-coding always has a qvalue
3160         of 1.</t>
3161    </x:lt>
3162  </list>
3163</t>
3164<t>
3165   If the TE field-value is empty or if no TE field is present, the only
3166   transfer-coding is "chunked". A message with no transfer-coding is
3167   always acceptable.
3168</t>
3169</section>
3170
3171<section title="Trailer" anchor="header.trailer">
3172  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3173  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3174  <x:anchor-alias value="Trailer"/>
3175  <x:anchor-alias value="Trailer-v"/>
3176<t>
3177   The "Trailer" general-header field indicates that the given set of
3178   header fields is present in the trailer of a message encoded with
3179   chunked transfer-coding.
3180</t>
3181<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3182  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3183  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3184</artwork></figure>
3185<t>
3186   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3187   message using chunked transfer-coding with a non-empty trailer. Doing
3188   so allows the recipient to know which header fields to expect in the
3189   trailer.
3190</t>
3191<t>
3192   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3193   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3194   trailer fields in a "chunked" transfer-coding.
3195</t>
3196<t>
3197   Message header fields listed in the Trailer header field &MUST-NOT;
3198   include the following header fields:
3199  <list style="symbols">
3200    <t>Transfer-Encoding</t>
3201    <t>Content-Length</t>
3202    <t>Trailer</t>
3203  </list>
3204</t>
3205</section>
3206
3207<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3208  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3209  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3210  <x:anchor-alias value="Transfer-Encoding"/>
3211  <x:anchor-alias value="Transfer-Encoding-v"/>
3212<t>
3213   The "Transfer-Encoding" general-header field indicates what transfer-codings
3214   (if any) have been applied to the message body. It differs from
3215   Content-Encoding (&content-codings;) in that transfer-codings are a property
3216   of the message (and therefore are removed by intermediaries), whereas
3217   content-codings are not.
3218</t>
3219<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3220  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3221                        <x:ref>Transfer-Encoding-v</x:ref>
3222  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3223</artwork></figure>
3224<t>
3225   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3226</t>
3227<figure><artwork type="example">
3228  Transfer-Encoding: chunked
3229</artwork></figure>
3230<t>
3231   If multiple encodings have been applied to a representation, the transfer-codings
3232   &MUST; be listed in the order in which they were applied.
3233   Additional information about the encoding parameters &MAY; be provided
3234   by other entity-header fields not defined by this specification.
3235</t>
3236<t>
3237   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3238   header.
3239</t>
3240</section>
3241
3242<section title="Upgrade" anchor="header.upgrade">
3243  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3244  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3245  <x:anchor-alias value="Upgrade"/>
3246  <x:anchor-alias value="Upgrade-v"/>
3247<t>
3248   The "Upgrade" general-header field allows the client to specify what
3249   additional communication protocols it would like to use, if the server
3250   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3251   header field within a 101 (Switching Protocols) response to indicate which
3252   protocol(s) are being switched to.
3253</t>
3254<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3255  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3256  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3257</artwork></figure>
3258<t>
3259   For example,
3260</t>
3261<figure><artwork type="example">
3262  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3263</artwork></figure>
3264<t>
3265   The Upgrade header field is intended to provide a simple mechanism
3266   for transition from HTTP/1.1 to some other, incompatible protocol. It
3267   does so by allowing the client to advertise its desire to use another
3268   protocol, such as a later version of HTTP with a higher major version
3269   number, even though the current request has been made using HTTP/1.1.
3270   This eases the difficult transition between incompatible protocols by
3271   allowing the client to initiate a request in the more commonly
3272   supported protocol while indicating to the server that it would like
3273   to use a "better" protocol if available (where "better" is determined
3274   by the server, possibly according to the nature of the method and/or
3275   resource being requested).
3276</t>
3277<t>
3278   The Upgrade header field only applies to switching application-layer
3279   protocols upon the existing transport-layer connection. Upgrade
3280   cannot be used to insist on a protocol change; its acceptance and use
3281   by the server is optional. The capabilities and nature of the
3282   application-layer communication after the protocol change is entirely
3283   dependent upon the new protocol chosen, although the first action
3284   after changing the protocol &MUST; be a response to the initial HTTP
3285   request containing the Upgrade header field.
3286</t>
3287<t>
3288   The Upgrade header field only applies to the immediate connection.
3289   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3290   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3291   HTTP/1.1 message.
3292</t>
3293<t>
3294   The Upgrade header field cannot be used to indicate a switch to a
3295   protocol on a different connection. For that purpose, it is more
3296   appropriate to use a 301, 302, 303, or 305 redirection response.
3297</t>
3298<t>
3299   This specification only defines the protocol name "HTTP" for use by
3300   the family of Hypertext Transfer Protocols, as defined by the HTTP
3301   version rules of <xref target="http.version"/> and future updates to this
3302   specification. Additional tokens can be registered with IANA using the
3303   registration procedure defined below. 
3304</t>
3305
3306<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3307<t>
3308   The HTTP Upgrade Token Registry defines the name space for product
3309   tokens used to identify protocols in the Upgrade header field.
3310   Each registered token should be associated with one or a set of
3311   specifications, and with contact information.
3312</t>
3313<t>
3314   Registrations should be allowed on a First Come First Served basis as
3315   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
3316   specifications need not be IETF documents or be subject to IESG review, but
3317   should obey the following rules:
3318  <list style="numbers">
3319    <t>A token, once registered, stays registered forever.</t>
3320    <t>The registration &MUST; name a responsible party for the
3321       registration.</t>
3322    <t>The registration &MUST; name a point of contact.</t>
3323    <t>The registration &MAY; name the documentation required for the
3324       token.</t>
3325    <t>The responsible party &MAY; change the registration at any time.
3326       The IANA will keep a record of all such changes, and make them
3327       available upon request.</t>
3328    <t>The responsible party for the first registration of a "product"
3329       token &MUST; approve later registrations of a "version" token
3330       together with that "product" token before they can be registered.</t>
3331    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3332       for a token. This will normally only be used in the case when a
3333       responsible party cannot be contacted.</t>
3334  </list>
3335</t>
3336<t>
3337   It is not required that specifications for upgrade tokens be made
3338   publicly available, but the contact information for the registration
3339   should be.
3340</t>
3341</section>
3342
3343
3344</section>
3345
3346<section title="Via" anchor="header.via">
3347  <iref primary="true" item="Via header" x:for-anchor=""/>
3348  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3349  <x:anchor-alias value="protocol-name"/>
3350  <x:anchor-alias value="protocol-version"/>
3351  <x:anchor-alias value="pseudonym"/>
3352  <x:anchor-alias value="received-by"/>
3353  <x:anchor-alias value="received-protocol"/>
3354  <x:anchor-alias value="Via"/>
3355  <x:anchor-alias value="Via-v"/>
3356<t>
3357   The "Via" general-header field &MUST; be used by gateways and proxies to
3358   indicate the intermediate protocols and recipients between the user
3359   agent and the server on requests, and between the origin server and
3360   the client on responses. It is analogous to the "Received" field defined in
3361   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3362   avoiding request loops, and identifying the protocol capabilities of
3363   all senders along the request/response chain.
3364</t>
3365<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"/>
3366  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3367  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3368                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3369  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3370  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3371  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3372  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3373  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3374</artwork></figure>
3375<t>
3376   The received-protocol indicates the protocol version of the message
3377   received by the server or client along each segment of the
3378   request/response chain. The received-protocol version is appended to
3379   the Via field value when the message is forwarded so that information
3380   about the protocol capabilities of upstream applications remains
3381   visible to all recipients.
3382</t>
3383<t>
3384   The protocol-name is optional if and only if it would be "HTTP". The
3385   received-by field is normally the host and optional port number of a
3386   recipient server or client that subsequently forwarded the message.
3387   However, if the real host is considered to be sensitive information,
3388   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3389   be assumed to be the default port of the received-protocol.
3390</t>
3391<t>
3392   Multiple Via field values represent each proxy or gateway that has
3393   forwarded the message. Each recipient &MUST; append its information
3394   such that the end result is ordered according to the sequence of
3395   forwarding applications.
3396</t>
3397<t>
3398   Comments &MAY; be used in the Via header field to identify the software
3399   of the recipient proxy or gateway, analogous to the User-Agent and
3400   Server header fields. However, all comments in the Via field are
3401   optional and &MAY; be removed by any recipient prior to forwarding the
3402   message.
3403</t>
3404<t>
3405   For example, a request message could be sent from an HTTP/1.0 user
3406   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3407   forward the request to a public proxy at p.example.net, which completes
3408   the request by forwarding it to the origin server at www.example.com.
3409   The request received by www.example.com would then have the following
3410   Via header field:
3411</t>
3412<figure><artwork type="example">
3413  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3414</artwork></figure>
3415<t>
3416   Proxies and gateways used as a portal through a network firewall
3417   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3418   the firewall region. This information &SHOULD; only be propagated if
3419   explicitly enabled. If not enabled, the received-by host of any host
3420   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3421   for that host.
3422</t>
3423<t>
3424   For organizations that have strong privacy requirements for hiding
3425   internal structures, a proxy &MAY; combine an ordered subsequence of
3426   Via header field entries with identical received-protocol values into
3427   a single such entry. For example,
3428</t>
3429<figure><artwork type="example">
3430  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3431</artwork></figure>
3432<t>
3433  could be collapsed to
3434</t>
3435<figure><artwork type="example">
3436  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3437</artwork></figure>
3438<t>
3439   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3440   under the same organizational control and the hosts have already been
3441   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3442   have different received-protocol values.
3443</t>
3444</section>
3445
3446</section>
3447
3448<section title="IANA Considerations" anchor="IANA.considerations">
3449
3450<section title="Header Field Registration" anchor="header.field.registration">
3451<t>
3452   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3453   with the permanent registrations below (see <xref target="RFC3864"/>):
3454</t>
3455<?BEGININC p1-messaging.iana-headers ?>
3456<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3457<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3458   <ttcol>Header Field Name</ttcol>
3459   <ttcol>Protocol</ttcol>
3460   <ttcol>Status</ttcol>
3461   <ttcol>Reference</ttcol>
3462
3463   <c>Connection</c>
3464   <c>http</c>
3465   <c>standard</c>
3466   <c>
3467      <xref target="header.connection"/>
3468   </c>
3469   <c>Content-Length</c>
3470   <c>http</c>
3471   <c>standard</c>
3472   <c>
3473      <xref target="header.content-length"/>
3474   </c>
3475   <c>Date</c>
3476   <c>http</c>
3477   <c>standard</c>
3478   <c>
3479      <xref target="header.date"/>
3480   </c>
3481   <c>Host</c>
3482   <c>http</c>
3483   <c>standard</c>
3484   <c>
3485      <xref target="header.host"/>
3486   </c>
3487   <c>TE</c>
3488   <c>http</c>
3489   <c>standard</c>
3490   <c>
3491      <xref target="header.te"/>
3492   </c>
3493   <c>Trailer</c>
3494   <c>http</c>
3495   <c>standard</c>
3496   <c>
3497      <xref target="header.trailer"/>
3498   </c>
3499   <c>Transfer-Encoding</c>
3500   <c>http</c>
3501   <c>standard</c>
3502   <c>
3503      <xref target="header.transfer-encoding"/>
3504   </c>
3505   <c>Upgrade</c>
3506   <c>http</c>
3507   <c>standard</c>
3508   <c>
3509      <xref target="header.upgrade"/>
3510   </c>
3511   <c>Via</c>
3512   <c>http</c>
3513   <c>standard</c>
3514   <c>
3515      <xref target="header.via"/>
3516   </c>
3517</texttable>
3518<!--(END)-->
3519<?ENDINC p1-messaging.iana-headers ?>
3520<t>
3521   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3522</t>
3523</section>
3524
3525<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3526<t>
3527   The entries for the "http" and "https" URI Schemes in the registry located at
3528   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3529   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3530   and <xref target="https.uri" format="counter"/> of this document
3531   (see <xref target="RFC4395"/>).
3532</t>
3533</section>
3534
3535<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3536<t>
3537   This document serves as the specification for the Internet media types
3538   "message/http" and "application/http". The following is to be registered with
3539   IANA (see <xref target="RFC4288"/>).
3540</t>
3541<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3542<iref item="Media Type" subitem="message/http" primary="true"/>
3543<iref item="message/http Media Type" primary="true"/>
3544<t>
3545   The message/http type can be used to enclose a single HTTP request or
3546   response message, provided that it obeys the MIME restrictions for all
3547   "message" types regarding line length and encodings.
3548</t>
3549<t>
3550  <list style="hanging" x:indent="12em">
3551    <t hangText="Type name:">
3552      message
3553    </t>
3554    <t hangText="Subtype name:">
3555      http
3556    </t>
3557    <t hangText="Required parameters:">
3558      none
3559    </t>
3560    <t hangText="Optional parameters:">
3561      version, msgtype
3562      <list style="hanging">
3563        <t hangText="version:">
3564          The HTTP-Version number of the enclosed message
3565          (e.g., "1.1"). If not present, the version can be
3566          determined from the first line of the body.
3567        </t>
3568        <t hangText="msgtype:">
3569          The message type -- "request" or "response". If not
3570          present, the type can be determined from the first
3571          line of the body.
3572        </t>
3573      </list>
3574    </t>
3575    <t hangText="Encoding considerations:">
3576      only "7bit", "8bit", or "binary" are permitted
3577    </t>
3578    <t hangText="Security considerations:">
3579      none
3580    </t>
3581    <t hangText="Interoperability considerations:">
3582      none
3583    </t>
3584    <t hangText="Published specification:">
3585      This specification (see <xref target="internet.media.type.message.http"/>).
3586    </t>
3587    <t hangText="Applications that use this media type:">
3588    </t>
3589    <t hangText="Additional information:">
3590      <list style="hanging">
3591        <t hangText="Magic number(s):">none</t>
3592        <t hangText="File extension(s):">none</t>
3593        <t hangText="Macintosh file type code(s):">none</t>
3594      </list>
3595    </t>
3596    <t hangText="Person and email address to contact for further information:">
3597      See Authors Section.
3598    </t>
3599    <t hangText="Intended usage:">
3600      COMMON
3601    </t>
3602    <t hangText="Restrictions on usage:">
3603      none
3604    </t>
3605    <t hangText="Author/Change controller:">
3606      IESG
3607    </t>
3608  </list>
3609</t>
3610</section>
3611<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3612<iref item="Media Type" subitem="application/http" primary="true"/>
3613<iref item="application/http Media Type" primary="true"/>
3614<t>
3615   The application/http type can be used to enclose a pipeline of one or more
3616   HTTP request or response messages (not intermixed).
3617</t>
3618<t>
3619  <list style="hanging" x:indent="12em">
3620    <t hangText="Type name:">
3621      application
3622    </t>
3623    <t hangText="Subtype name:">
3624      http
3625    </t>
3626    <t hangText="Required parameters:">
3627      none
3628    </t>
3629    <t hangText="Optional parameters:">
3630      version, msgtype
3631      <list style="hanging">
3632        <t hangText="version:">
3633          The HTTP-Version number of the enclosed messages
3634          (e.g., "1.1"). If not present, the version can be
3635          determined from the first line of the body.
3636        </t>
3637        <t hangText="msgtype:">
3638          The message type -- "request" or "response". If not
3639          present, the type can be determined from the first
3640          line of the body.
3641        </t>
3642      </list>
3643    </t>
3644    <t hangText="Encoding considerations:">
3645      HTTP messages enclosed by this type
3646      are in "binary" format; use of an appropriate
3647      Content-Transfer-Encoding is required when
3648      transmitted via E-mail.
3649    </t>
3650    <t hangText="Security considerations:">
3651      none
3652    </t>
3653    <t hangText="Interoperability considerations:">
3654      none
3655    </t>
3656    <t hangText="Published specification:">
3657      This specification (see <xref target="internet.media.type.application.http"/>).
3658    </t>
3659    <t hangText="Applications that use this media type:">
3660    </t>
3661    <t hangText="Additional information:">
3662      <list style="hanging">
3663        <t hangText="Magic number(s):">none</t>
3664        <t hangText="File extension(s):">none</t>
3665        <t hangText="Macintosh file type code(s):">none</t>
3666      </list>
3667    </t>
3668    <t hangText="Person and email address to contact for further information:">
3669      See Authors Section.
3670    </t>
3671    <t hangText="Intended usage:">
3672      COMMON
3673    </t>
3674    <t hangText="Restrictions on usage:">
3675      none
3676    </t>
3677    <t hangText="Author/Change controller:">
3678      IESG
3679    </t>
3680  </list>
3681</t>
3682</section>
3683</section>
3684
3685<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3686<t>
3687   The registration procedure for HTTP Transfer Codings is now defined by
3688   <xref target="transfer.coding.registry"/> of this document.
3689</t>
3690<t>
3691   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3692   should be updated with the registrations below:
3693</t>
3694<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3695   <ttcol>Name</ttcol>
3696   <ttcol>Description</ttcol>
3697   <ttcol>Reference</ttcol>
3698   <c>chunked</c>
3699   <c>Transfer in a series of chunks</c>
3700   <c>
3701      <xref target="chunked.encoding"/>
3702   </c>
3703   <c>compress</c>
3704   <c>UNIX "compress" program method</c>
3705   <c>
3706      <xref target="compress.coding"/>
3707   </c>
3708   <c>deflate</c>
3709   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3710   the "zlib" data format (<xref target="RFC1950"/>)
3711   </c>
3712   <c>
3713      <xref target="deflate.coding"/>
3714   </c>
3715   <c>gzip</c>
3716   <c>Same as GNU zip <xref target="RFC1952"/></c>
3717   <c>
3718      <xref target="gzip.coding"/>
3719   </c>
3720</texttable>
3721</section>
3722
3723<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3724<t>
3725   The registration procedure for HTTP Upgrade Tokens -- previously defined
3726   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3727   by <xref target="upgrade.token.registry"/> of this document.
3728</t>
3729<t>
3730   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3731   should be updated with the registration below:
3732</t>
3733<texttable align="left" suppress-title="true">
3734   <ttcol>Value</ttcol>
3735   <ttcol>Description</ttcol>
3736   <ttcol>Reference</ttcol>
3737
3738   <c>HTTP</c>
3739   <c>Hypertext Transfer Protocol</c> 
3740   <c><xref target="http.version"/> of this specification</c>
3741<!-- IANA should add this without our instructions; emailed on June 05, 2009
3742   <c>TLS/1.0</c>
3743   <c>Transport Layer Security</c>
3744   <c><xref target="RFC2817"/></c> -->
3745
3746</texttable>
3747</section>
3748
3749</section>
3750
3751<section title="Security Considerations" anchor="security.considerations">
3752<t>
3753   This section is meant to inform application developers, information
3754   providers, and users of the security limitations in HTTP/1.1 as
3755   described by this document. The discussion does not include
3756   definitive solutions to the problems revealed, though it does make
3757   some suggestions for reducing security risks.
3758</t>
3759
3760<section title="Personal Information" anchor="personal.information">
3761<t>
3762   HTTP clients are often privy to large amounts of personal information
3763   (e.g., the user's name, location, mail address, passwords, encryption
3764   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3765   leakage of this information.
3766   We very strongly recommend that a convenient interface be provided
3767   for the user to control dissemination of such information, and that
3768   designers and implementors be particularly careful in this area.
3769   History shows that errors in this area often create serious security
3770   and/or privacy problems and generate highly adverse publicity for the
3771   implementor's company.
3772</t>
3773</section>
3774
3775<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3776<t>
3777   A server is in the position to save personal data about a user's
3778   requests which might identify their reading patterns or subjects of
3779   interest. This information is clearly confidential in nature and its
3780   handling can be constrained by law in certain countries. People using
3781   HTTP to provide data are responsible for ensuring that
3782   such material is not distributed without the permission of any
3783   individuals that are identifiable by the published results.
3784</t>
3785</section>
3786
3787<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3788<t>
3789   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3790   the documents returned by HTTP requests to be only those that were
3791   intended by the server administrators. If an HTTP server translates
3792   HTTP URIs directly into file system calls, the server &MUST; take
3793   special care not to serve files that were not intended to be
3794   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3795   other operating systems use ".." as a path component to indicate a
3796   directory level above the current one. On such a system, an HTTP
3797   server &MUST; disallow any such construct in the request-target if it
3798   would otherwise allow access to a resource outside those intended to
3799   be accessible via the HTTP server. Similarly, files intended for
3800   reference only internally to the server (such as access control
3801   files, configuration files, and script code) &MUST; be protected from
3802   inappropriate retrieval, since they might contain sensitive
3803   information. Experience has shown that minor bugs in such HTTP server
3804   implementations have turned into security risks.
3805</t>
3806</section>
3807
3808<section title="DNS Spoofing" anchor="dns.spoofing">
3809<t>
3810   Clients using HTTP rely heavily on the Domain Name Service, and are
3811   thus generally prone to security attacks based on the deliberate
3812   mis-association of IP addresses and DNS names. Clients need to be
3813   cautious in assuming the continuing validity of an IP number/DNS name
3814   association.
3815</t>
3816<t>
3817   In particular, HTTP clients &SHOULD; rely on their name resolver for
3818   confirmation of an IP number/DNS name association, rather than
3819   caching the result of previous host name lookups. Many platforms
3820   already can cache host name lookups locally when appropriate, and
3821   they &SHOULD; be configured to do so. It is proper for these lookups to
3822   be cached, however, only when the TTL (Time To Live) information
3823   reported by the name server makes it likely that the cached
3824   information will remain useful.
3825</t>
3826<t>
3827   If HTTP clients cache the results of host name lookups in order to
3828   achieve a performance improvement, they &MUST; observe the TTL
3829   information reported by DNS.
3830</t>
3831<t>
3832   If HTTP clients do not observe this rule, they could be spoofed when
3833   a previously-accessed server's IP address changes. As network
3834   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3835   possibility of this form of attack will grow. Observing this
3836   requirement thus reduces this potential security vulnerability.
3837</t>
3838<t>
3839   This requirement also improves the load-balancing behavior of clients
3840   for replicated servers using the same DNS name and reduces the
3841   likelihood of a user's experiencing failure in accessing sites which
3842   use that strategy.
3843</t>
3844</section>
3845
3846<section title="Proxies and Caching" anchor="attack.proxies">
3847<t>
3848   By their very nature, HTTP proxies are men-in-the-middle, and
3849   represent an opportunity for man-in-the-middle attacks. Compromise of
3850   the systems on which the proxies run can result in serious security
3851   and privacy problems. Proxies have access to security-related
3852   information, personal information about individual users and
3853   organizations, and proprietary information belonging to users and
3854   content providers. A compromised proxy, or a proxy implemented or
3855   configured without regard to security and privacy considerations,
3856   might be used in the commission of a wide range of potential attacks.
3857</t>
3858<t>
3859   Proxy operators should protect the systems on which proxies run as
3860   they would protect any system that contains or transports sensitive
3861   information. In particular, log information gathered at proxies often
3862   contains highly sensitive personal information, and/or information
3863   about organizations. Log information should be carefully guarded, and
3864   appropriate guidelines for use should be developed and followed.
3865   (<xref target="abuse.of.server.log.information"/>).
3866</t>
3867<t>
3868   Proxy implementors should consider the privacy and security
3869   implications of their design and coding decisions, and of the
3870   configuration options they provide to proxy operators (especially the
3871   default configuration).
3872</t>
3873<t>
3874   Users of a proxy need to be aware that proxies are no trustworthier than
3875   the people who run them; HTTP itself cannot solve this problem.
3876</t>
3877<t>
3878   The judicious use of cryptography, when appropriate, might suffice to
3879   protect against a broad range of security and privacy attacks. Such
3880   cryptography is beyond the scope of the HTTP/1.1 specification.
3881</t>
3882</section>
3883
3884<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3885<t>
3886   They exist. They are hard to defend against. Research continues.
3887   Beware.
3888</t>
3889</section>
3890</section>
3891
3892<section title="Acknowledgments" anchor="ack">
3893<t>
3894   HTTP has evolved considerably over the years. It has
3895   benefited from a large and active developer community--the many
3896   people who have participated on the www-talk mailing list--and it is
3897   that community which has been most responsible for the success of
3898   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3899   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3900   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3901   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3902   VanHeyningen deserve special recognition for their efforts in
3903   defining early aspects of the protocol.
3904</t>
3905<t>
3906   This document has benefited greatly from the comments of all those
3907   participating in the HTTP-WG. In addition to those already mentioned,
3908   the following individuals have contributed to this specification:
3909</t>
3910<t>
3911   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3912   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3913   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3914   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3915   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3916   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3917   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3918   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3919   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3920   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3921   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3922   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3923</t>
3924<t>
3925   Thanks to the "cave men" of Palo Alto. You know who you are.
3926</t>
3927<t>
3928   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3929   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3930   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3931   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3932   Larry Masinter for their help. And thanks go particularly to Jeff
3933   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3934</t>
3935<t>
3936   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3937   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3938   discovery of many of the problems that this document attempts to
3939   rectify.
3940</t>
3941<t>
3942   This specification makes heavy use of the augmented BNF and generic
3943   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3944   reuses many of the definitions provided by Nathaniel Borenstein and
3945   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3946   specification will help reduce past confusion over the relationship
3947   between HTTP and Internet mail message formats.
3948</t>
3949</section>
3950
3951</middle>
3952<back>
3953
3954<references title="Normative References">
3955
3956<reference anchor="ISO-8859-1">
3957  <front>
3958    <title>
3959     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3960    </title>
3961    <author>
3962      <organization>International Organization for Standardization</organization>
3963    </author>
3964    <date year="1998"/>
3965  </front>
3966  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3967</reference>
3968
3969<reference anchor="Part2">
3970  <front>
3971    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3972    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3973      <organization abbrev="Day Software">Day Software</organization>
3974      <address><email>fielding@gbiv.com</email></address>
3975    </author>
3976    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3977      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3978      <address><email>jg@freedesktop.org</email></address>
3979    </author>
3980    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3981      <organization abbrev="HP">Hewlett-Packard Company</organization>
3982      <address><email>JeffMogul@acm.org</email></address>
3983    </author>
3984    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3985      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3986      <address><email>henrikn@microsoft.com</email></address>
3987    </author>
3988    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3989      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3990      <address><email>LMM@acm.org</email></address>
3991    </author>
3992    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3993      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3994      <address><email>paulle@microsoft.com</email></address>
3995    </author>
3996    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3997      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3998      <address><email>timbl@w3.org</email></address>
3999    </author>
4000    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4001      <organization abbrev="W3C">World Wide Web Consortium</organization>
4002      <address><email>ylafon@w3.org</email></address>
4003    </author>
4004    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4005      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4006      <address><email>julian.reschke@greenbytes.de</email></address>
4007    </author>
4008    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4009  </front>
4010  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4011  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4012</reference>
4013
4014<reference anchor="Part3">
4015  <front>
4016    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4017    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4018      <organization abbrev="Day Software">Day Software</organization>
4019      <address><email>fielding@gbiv.com</email></address>
4020    </author>
4021    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4022      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4023      <address><email>jg@freedesktop.org</email></address>
4024    </author>
4025    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4026      <organization abbrev="HP">Hewlett-Packard Company</organization>
4027      <address><email>JeffMogul@acm.org</email></address>
4028    </author>
4029    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4030      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4031      <address><email>henrikn@microsoft.com</email></address>
4032    </author>
4033    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4034      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4035      <address><email>LMM@acm.org</email></address>
4036    </author>
4037    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4038      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4039      <address><email>paulle@microsoft.com</email></address>
4040    </author>
4041    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4042      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4043      <address><email>timbl@w3.org</email></address>
4044    </author>
4045    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4046      <organization abbrev="W3C">World Wide Web Consortium</organization>
4047      <address><email>ylafon@w3.org</email></address>
4048    </author>
4049    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4050      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4051      <address><email>julian.reschke@greenbytes.de</email></address>
4052    </author>
4053    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4054  </front>
4055  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4056  <x:source href="p3-payload.xml" basename="p3-payload"/>
4057</reference>
4058
4059<reference anchor="Part6">
4060  <front>
4061    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4062    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4063      <organization abbrev="Day Software">Day Software</organization>
4064      <address><email>fielding@gbiv.com</email></address>
4065    </author>
4066    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4067      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4068      <address><email>jg@freedesktop.org</email></address>
4069    </author>
4070    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4071      <organization abbrev="HP">Hewlett-Packard Company</organization>
4072      <address><email>JeffMogul@acm.org</email></address>
4073    </author>
4074    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4075      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4076      <address><email>henrikn@microsoft.com</email></address>
4077    </author>
4078    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4079      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4080      <address><email>LMM@acm.org</email></address>
4081    </author>
4082    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4083      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4084      <address><email>paulle@microsoft.com</email></address>
4085    </author>
4086    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4087      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4088      <address><email>timbl@w3.org</email></address>
4089    </author>
4090    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4091      <organization abbrev="W3C">World Wide Web Consortium</organization>
4092      <address><email>ylafon@w3.org</email></address>
4093    </author>
4094    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4095      <address><email>mnot@mnot.net</email></address>
4096    </author>
4097    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4098      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4099      <address><email>julian.reschke@greenbytes.de</email></address>
4100    </author>
4101    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4102  </front>
4103  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4104  <x:source href="p6-cache.xml" basename="p6-cache"/>
4105</reference>
4106
4107<reference anchor="RFC5234">
4108  <front>
4109    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4110    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4111      <organization>Brandenburg InternetWorking</organization>
4112      <address>
4113        <email>dcrocker@bbiw.net</email>
4114      </address> 
4115    </author>
4116    <author initials="P." surname="Overell" fullname="Paul Overell">
4117      <organization>THUS plc.</organization>
4118      <address>
4119        <email>paul.overell@thus.net</email>
4120      </address>
4121    </author>
4122    <date month="January" year="2008"/>
4123  </front>
4124  <seriesInfo name="STD" value="68"/>
4125  <seriesInfo name="RFC" value="5234"/>
4126</reference>
4127
4128<reference anchor="RFC2119">
4129  <front>
4130    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4131    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4132      <organization>Harvard University</organization>
4133      <address><email>sob@harvard.edu</email></address>
4134    </author>
4135    <date month="March" year="1997"/>
4136  </front>
4137  <seriesInfo name="BCP" value="14"/>
4138  <seriesInfo name="RFC" value="2119"/>
4139</reference>
4140
4141<reference anchor="RFC3986">
4142 <front>
4143  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4144  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4145    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4146    <address>
4147       <email>timbl@w3.org</email>
4148       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4149    </address>
4150  </author>
4151  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4152    <organization abbrev="Day Software">Day Software</organization>
4153    <address>
4154      <email>fielding@gbiv.com</email>
4155      <uri>http://roy.gbiv.com/</uri>
4156    </address>
4157  </author>
4158  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4159    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4160    <address>
4161      <email>LMM@acm.org</email>
4162      <uri>http://larry.masinter.net/</uri>
4163    </address>
4164  </author>
4165  <date month='January' year='2005'></date>
4166 </front>
4167 <seriesInfo name="RFC" value="3986"/>
4168 <seriesInfo name="STD" value="66"/>
4169</reference>
4170
4171<reference anchor="USASCII">
4172  <front>
4173    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4174    <author>
4175      <organization>American National Standards Institute</organization>
4176    </author>
4177    <date year="1986"/>
4178  </front>
4179  <seriesInfo name="ANSI" value="X3.4"/>
4180</reference>
4181
4182<reference anchor="RFC1950">
4183  <front>
4184    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4185    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4186      <organization>Aladdin Enterprises</organization>
4187      <address><email>ghost@aladdin.com</email></address>
4188    </author>
4189    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4190    <date month="May" year="1996"/>
4191  </front>
4192  <seriesInfo name="RFC" value="1950"/>
4193  <annotation>
4194    RFC 1950 is an Informational RFC, thus it might be less stable than
4195    this specification. On the other hand, this downward reference was
4196    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4197    therefore it is unlikely to cause problems in practice. See also
4198    <xref target="BCP97"/>.
4199  </annotation>
4200</reference>
4201
4202<reference anchor="RFC1951">
4203  <front>
4204    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4205    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4206      <organization>Aladdin Enterprises</organization>
4207      <address><email>ghost@aladdin.com</email></address>
4208    </author>
4209    <date month="May" year="1996"/>
4210  </front>
4211  <seriesInfo name="RFC" value="1951"/>
4212  <annotation>
4213    RFC 1951 is an Informational RFC, thus it might be less stable than
4214    this specification. On the other hand, this downward reference was
4215    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4216    therefore it is unlikely to cause problems in practice. See also
4217    <xref target="BCP97"/>.
4218  </annotation>
4219</reference>
4220
4221<reference anchor="RFC1952">
4222  <front>
4223    <title>GZIP file format specification version 4.3</title>
4224    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4225      <organization>Aladdin Enterprises</organization>
4226      <address><email>ghost@aladdin.com</email></address>
4227    </author>
4228    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4229      <address><email>gzip@prep.ai.mit.edu</email></address>
4230    </author>
4231    <author initials="M." surname="Adler" fullname="Mark Adler">
4232      <address><email>madler@alumni.caltech.edu</email></address>
4233    </author>
4234    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4235      <address><email>ghost@aladdin.com</email></address>
4236    </author>
4237    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4238      <address><email>randeg@alumni.rpi.edu</email></address>
4239    </author>
4240    <date month="May" year="1996"/>
4241  </front>
4242  <seriesInfo name="RFC" value="1952"/>
4243  <annotation>
4244    RFC 1952 is an Informational RFC, thus it might be less stable than
4245    this specification. On the other hand, this downward reference was
4246    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4247    therefore it is unlikely to cause problems in practice. See also
4248    <xref target="BCP97"/>.
4249  </annotation>
4250</reference>
4251
4252</references>
4253
4254<references title="Informative References">
4255
4256<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4257  <front>
4258    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4259    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4260    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4261    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4262    <author initials="H." surname="Lie" fullname="H. Lie"/>
4263    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4264    <date year="1997" month="September"/>
4265  </front>
4266  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4267</reference>
4268
4269<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4270  <front>
4271    <title>Improving HTTP Latency</title>
4272    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4273    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4274    <date year="1995" month="December"/>
4275  </front>
4276  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4277</reference>
4278
4279<reference anchor="RFC1123">
4280  <front>
4281    <title>Requirements for Internet Hosts - Application and Support</title>
4282    <author initials="R." surname="Braden" fullname="Robert Braden">
4283      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4284      <address><email>Braden@ISI.EDU</email></address>
4285    </author>
4286    <date month="October" year="1989"/>
4287  </front>
4288  <seriesInfo name="STD" value="3"/>
4289  <seriesInfo name="RFC" value="1123"/>
4290</reference>
4291
4292<reference anchor="RFC1305">
4293  <front>
4294    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4295    <author initials="D." surname="Mills" fullname="David L. Mills">
4296      <organization>University of Delaware, Electrical Engineering Department</organization>
4297      <address><email>mills@udel.edu</email></address>
4298    </author>
4299    <date month="March" year="1992"/>
4300  </front>
4301  <seriesInfo name="RFC" value="1305"/>
4302</reference>
4303
4304<reference anchor="RFC1900">
4305  <front>
4306    <title>Renumbering Needs Work</title>
4307    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4308      <organization>CERN, Computing and Networks Division</organization>
4309      <address><email>brian@dxcoms.cern.ch</email></address>
4310    </author>
4311    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4312      <organization>cisco Systems</organization>
4313      <address><email>yakov@cisco.com</email></address>
4314    </author>
4315    <date month="February" year="1996"/>
4316  </front>
4317  <seriesInfo name="RFC" value="1900"/>
4318</reference>
4319
4320<reference anchor="RFC1945">
4321  <front>
4322    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4323    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4324      <organization>MIT, Laboratory for Computer Science</organization>
4325      <address><email>timbl@w3.org</email></address>
4326    </author>
4327    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4328      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4329      <address><email>fielding@ics.uci.edu</email></address>
4330    </author>
4331    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4332      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4333      <address><email>frystyk@w3.org</email></address>
4334    </author>
4335    <date month="May" year="1996"/>
4336  </front>
4337  <seriesInfo name="RFC" value="1945"/>
4338</reference>
4339
4340<reference anchor="RFC2045">
4341  <front>
4342    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4343    <author initials="N." surname="Freed" fullname="Ned Freed">
4344      <organization>Innosoft International, Inc.</organization>
4345      <address><email>ned@innosoft.com</email></address>
4346    </author>
4347    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4348      <organization>First Virtual Holdings</organization>
4349      <address><email>nsb@nsb.fv.com</email></address>
4350    </author>
4351    <date month="November" year="1996"/>
4352  </front>
4353  <seriesInfo name="RFC" value="2045"/>
4354</reference>
4355
4356<reference anchor="RFC2047">
4357  <front>
4358    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4359    <author initials="K." surname="Moore" fullname="Keith Moore">
4360      <organization>University of Tennessee</organization>
4361      <address><email>moore@cs.utk.edu</email></address>
4362    </author>
4363    <date month="November" year="1996"/>
4364  </front>
4365  <seriesInfo name="RFC" value="2047"/>
4366</reference>
4367
4368<reference anchor="RFC2068">
4369  <front>
4370    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4371    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4372      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4373      <address><email>fielding@ics.uci.edu</email></address>
4374    </author>
4375    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4376      <organization>MIT Laboratory for Computer Science</organization>
4377      <address><email>jg@w3.org</email></address>
4378    </author>
4379    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4380      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4381      <address><email>mogul@wrl.dec.com</email></address>
4382    </author>
4383    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4384      <organization>MIT Laboratory for Computer Science</organization>
4385      <address><email>frystyk@w3.org</email></address>
4386    </author>
4387    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4388      <organization>MIT Laboratory for Computer Science</organization>
4389      <address><email>timbl@w3.org</email></address>
4390    </author>
4391    <date month="January" year="1997"/>
4392  </front>
4393  <seriesInfo name="RFC" value="2068"/>
4394</reference>
4395
4396<reference anchor='RFC2109'>
4397  <front>
4398    <title>HTTP State Management Mechanism</title>
4399    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4400      <organization>Bell Laboratories, Lucent Technologies</organization>
4401      <address><email>dmk@bell-labs.com</email></address>
4402    </author>
4403    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4404      <organization>Netscape Communications Corp.</organization>
4405      <address><email>montulli@netscape.com</email></address>
4406    </author>
4407    <date year='1997' month='February' />
4408  </front>
4409  <seriesInfo name='RFC' value='2109' />
4410</reference>
4411
4412<reference anchor="RFC2145">
4413  <front>
4414    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4415    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4416      <organization>Western Research Laboratory</organization>
4417      <address><email>mogul@wrl.dec.com</email></address>
4418    </author>
4419    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4420      <organization>Department of Information and Computer Science</organization>
4421      <address><email>fielding@ics.uci.edu</email></address>
4422    </author>
4423    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4424      <organization>MIT Laboratory for Computer Science</organization>
4425      <address><email>jg@w3.org</email></address>
4426    </author>
4427    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4428      <organization>W3 Consortium</organization>
4429      <address><email>frystyk@w3.org</email></address>
4430    </author>
4431    <date month="May" year="1997"/>
4432  </front>
4433  <seriesInfo name="RFC" value="2145"/>
4434</reference>
4435
4436<reference anchor="RFC2616">
4437  <front>
4438    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4439    <author initials="R." surname="Fielding" fullname="R. Fielding">
4440      <organization>University of California, Irvine</organization>
4441      <address><email>fielding@ics.uci.edu</email></address>
4442    </author>
4443    <author initials="J." surname="Gettys" fullname="J. Gettys">
4444      <organization>W3C</organization>
4445      <address><email>jg@w3.org</email></address>
4446    </author>
4447    <author initials="J." surname="Mogul" fullname="J. Mogul">
4448      <organization>Compaq Computer Corporation</organization>
4449      <address><email>mogul@wrl.dec.com</email></address>
4450    </author>
4451    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4452      <organization>MIT Laboratory for Computer Science</organization>
4453      <address><email>frystyk@w3.org</email></address>
4454    </author>
4455    <author initials="L." surname="Masinter" fullname="L. Masinter">
4456      <organization>Xerox Corporation</organization>
4457      <address><email>masinter@parc.xerox.com</email></address>
4458    </author>
4459    <author initials="P." surname="Leach" fullname="P. Leach">
4460      <organization>Microsoft Corporation</organization>
4461      <address><email>paulle@microsoft.com</email></address>
4462    </author>
4463    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4464      <organization>W3C</organization>
4465      <address><email>timbl@w3.org</email></address>
4466    </author>
4467    <date month="June" year="1999"/>
4468  </front>
4469  <seriesInfo name="RFC" value="2616"/>
4470</reference>
4471
4472<reference anchor='RFC2817'>
4473  <front>
4474    <title>Upgrading to TLS Within HTTP/1.1</title>
4475    <author initials='R.' surname='Khare' fullname='R. Khare'>
4476      <organization>4K Associates / UC Irvine</organization>
4477      <address><email>rohit@4K-associates.com</email></address>
4478    </author>
4479    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4480      <organization>Agranat Systems, Inc.</organization>
4481      <address><email>lawrence@agranat.com</email></address>
4482    </author>
4483    <date year='2000' month='May' />
4484  </front>
4485  <seriesInfo name='RFC' value='2817' />
4486</reference>
4487
4488<reference anchor='RFC2818'>
4489  <front>
4490    <title>HTTP Over TLS</title>
4491    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4492      <organization>RTFM, Inc.</organization>
4493      <address><email>ekr@rtfm.com</email></address>
4494    </author>
4495    <date year='2000' month='May' />
4496  </front>
4497  <seriesInfo name='RFC' value='2818' />
4498</reference>
4499
4500<reference anchor='RFC2965'>
4501  <front>
4502    <title>HTTP State Management Mechanism</title>
4503    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4504      <organization>Bell Laboratories, Lucent Technologies</organization>
4505      <address><email>dmk@bell-labs.com</email></address>
4506    </author>
4507    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4508      <organization>Epinions.com, Inc.</organization>
4509      <address><email>lou@montulli.org</email></address>
4510    </author>
4511    <date year='2000' month='October' />
4512  </front>
4513  <seriesInfo name='RFC' value='2965' />
4514</reference>
4515
4516<reference anchor='RFC3864'>
4517  <front>
4518    <title>Registration Procedures for Message Header Fields</title>
4519    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4520      <organization>Nine by Nine</organization>
4521      <address><email>GK-IETF@ninebynine.org</email></address>
4522    </author>
4523    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4524      <organization>BEA Systems</organization>
4525      <address><email>mnot@pobox.com</email></address>
4526    </author>
4527    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4528      <organization>HP Labs</organization>
4529      <address><email>JeffMogul@acm.org</email></address>
4530    </author>
4531    <date year='2004' month='September' />
4532  </front>
4533  <seriesInfo name='BCP' value='90' />
4534  <seriesInfo name='RFC' value='3864' />
4535</reference>
4536
4537<reference anchor="RFC4288">
4538  <front>
4539    <title>Media Type Specifications and Registration Procedures</title>
4540    <author initials="N." surname="Freed" fullname="N. Freed">
4541      <organization>Sun Microsystems</organization>
4542      <address>
4543        <email>ned.freed@mrochek.com</email>
4544      </address>
4545    </author>
4546    <author initials="J." surname="Klensin" fullname="J. Klensin">
4547      <address>
4548        <email>klensin+ietf@jck.com</email>
4549      </address>
4550    </author>
4551    <date year="2005" month="December"/>
4552  </front>
4553  <seriesInfo name="BCP" value="13"/>
4554  <seriesInfo name="RFC" value="4288"/>
4555</reference>
4556
4557<reference anchor='RFC4395'>
4558  <front>
4559    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4560    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4561      <organization>AT&amp;T Laboratories</organization>
4562      <address>
4563        <email>tony+urireg@maillennium.att.com</email>
4564      </address>
4565    </author>
4566    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4567      <organization>Qualcomm, Inc.</organization>
4568      <address>
4569        <email>hardie@qualcomm.com</email>
4570      </address>
4571    </author>
4572    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4573      <organization>Adobe Systems</organization>
4574      <address>
4575        <email>LMM@acm.org</email>
4576      </address>
4577    </author>
4578    <date year='2006' month='February' />
4579  </front>
4580  <seriesInfo name='BCP' value='115' />
4581  <seriesInfo name='RFC' value='4395' />
4582</reference>
4583
4584<reference anchor='RFC5226'>
4585  <front>
4586    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4587    <author initials='T.' surname='Narten' fullname='T. Narten'>
4588      <organization>IBM</organization>
4589      <address><email>narten@us.ibm.com</email></address>
4590    </author>
4591    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4592      <organization>Google</organization>
4593      <address><email>Harald@Alvestrand.no</email></address>
4594    </author>
4595    <date year='2008' month='May' />
4596  </front>
4597  <seriesInfo name='BCP' value='26' />
4598  <seriesInfo name='RFC' value='5226' />
4599</reference>
4600
4601<reference anchor="RFC5322">
4602  <front>
4603    <title>Internet Message Format</title>
4604    <author initials="P." surname="Resnick" fullname="P. Resnick">
4605      <organization>Qualcomm Incorporated</organization>
4606    </author>
4607    <date year="2008" month="October"/>
4608  </front> 
4609  <seriesInfo name="RFC" value="5322"/>
4610</reference>
4611
4612<reference anchor='BCP97'>
4613  <front>
4614    <title>Handling Normative References to Standards-Track Documents</title>
4615    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4616      <address>
4617        <email>klensin+ietf@jck.com</email>
4618      </address>
4619    </author>
4620    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4621      <organization>MIT</organization>
4622      <address>
4623        <email>hartmans-ietf@mit.edu</email>
4624      </address>
4625    </author>
4626    <date year='2007' month='June' />
4627  </front>
4628  <seriesInfo name='BCP' value='97' />
4629  <seriesInfo name='RFC' value='4897' />
4630</reference>
4631
4632<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4633  <front>
4634    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4635    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4636    <date year="2001" month="November"/>
4637  </front>
4638  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4639</reference>
4640
4641<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4642  <front>
4643    <title>Analysis of HTTP Performance Problems</title>
4644    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4645    <date/>
4646  </front>
4647</reference>
4648
4649<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4650  <front>
4651  <title>Analysis of HTTP Performance</title>
4652  <author initials="J." surname="Touch" fullname="Joe Touch">
4653    <organization>USC/Information Sciences Institute</organization>
4654    <address><email>touch@isi.edu</email></address>
4655  </author>
4656  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4657    <organization>USC/Information Sciences Institute</organization>
4658    <address><email>johnh@isi.edu</email></address>
4659  </author>
4660  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4661    <organization>USC/Information Sciences Institute</organization>
4662    <address><email>katia@isi.edu</email></address>
4663  </author>
4664  <date year="1998" month="Aug"/>
4665  </front>
4666  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4667  <annotation>(original report dated Aug. 1996)</annotation>
4668</reference>
4669
4670</references>
4671
4672
4673<section title="Tolerant Applications" anchor="tolerant.applications">
4674<t>
4675   Although this document specifies the requirements for the generation
4676   of HTTP/1.1 messages, not all applications will be correct in their
4677   implementation. We therefore recommend that operational applications
4678   be tolerant of deviations whenever those deviations can be
4679   interpreted unambiguously.
4680</t>
4681<t>
4682   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4683   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4684   &SHOULD; accept any amount of WSP characters between fields, even though
4685   only a single SP is required.
4686</t>
4687<t>
4688   The line terminator for header fields is the sequence CRLF.
4689   However, we recommend that applications, when parsing such headers,
4690   recognize a single LF as a line terminator and ignore the leading CR.
4691</t>
4692<t>
4693   The character set of a representation &SHOULD; be labeled as the lowest
4694   common denominator of the character codes used within that representation, with
4695   the exception that not labeling the representation is preferred over labeling
4696   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4697</t>
4698<t>
4699   Additional rules for requirements on parsing and encoding of dates
4700   and other potential problems with date encodings include:
4701</t>
4702<t>
4703  <list style="symbols">
4704     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4705        which appears to be more than 50 years in the future is in fact
4706        in the past (this helps solve the "year 2000" problem).</t>
4707
4708     <t>Although all date formats are specified to be case-sensitive,
4709        recipients &SHOULD; match day, week and timezone names
4710        case-insensitively.</t>
4711             
4712     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4713        Expires date as earlier than the proper value, but &MUST-NOT;
4714        internally represent a parsed Expires date as later than the
4715        proper value.</t>
4716
4717     <t>All expiration-related calculations &MUST; be done in GMT. The
4718        local time zone &MUST-NOT; influence the calculation or comparison
4719        of an age or expiration time.</t>
4720
4721     <t>If an HTTP header incorrectly carries a date value with a time
4722        zone other than GMT, it &MUST; be converted into GMT using the
4723        most conservative possible conversion.</t>
4724  </list>
4725</t>
4726</section>
4727
4728<section title="Compatibility with Previous Versions" anchor="compatibility">
4729<t>
4730   HTTP has been in use by the World-Wide Web global information initiative
4731   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4732   was a simple protocol for hypertext data transfer across the Internet
4733   with only a single method and no metadata.
4734   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4735   methods and MIME-like messaging that could include metadata about the data
4736   transferred and modifiers on the request/response semantics. However,
4737   HTTP/1.0 did not sufficiently take into consideration the effects of
4738   hierarchical proxies, caching, the need for persistent connections, or
4739   name-based virtual hosts. The proliferation of incompletely-implemented
4740   applications calling themselves "HTTP/1.0" further necessitated a
4741   protocol version change in order for two communicating applications
4742   to determine each other's true capabilities.
4743</t>
4744<t>
4745   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4746   requirements that enable reliable implementations, adding only
4747   those new features that will either be safely ignored by an HTTP/1.0
4748   recipient or only sent when communicating with a party advertising
4749   compliance with HTTP/1.1.
4750</t>
4751<t>
4752   It is beyond the scope of a protocol specification to mandate
4753   compliance with previous versions. HTTP/1.1 was deliberately
4754   designed, however, to make supporting previous versions easy. It is
4755   worth noting that, at the time of composing this specification, we would
4756   expect general-purpose HTTP/1.1 servers to:
4757  <list style="symbols">
4758     <t>understand any valid request in the format of HTTP/1.0 and
4759        1.1;</t>
4760
4761     <t>respond appropriately with a message in the same major version
4762        used by the client.</t>
4763  </list>
4764</t>
4765<t>
4766   And we would expect HTTP/1.1 clients to:
4767  <list style="symbols">
4768     <t>understand any valid response in the format of HTTP/1.0 or
4769        1.1.</t>
4770  </list>
4771</t>
4772<t>
4773   For most implementations of HTTP/1.0, each connection is established
4774   by the client prior to the request and closed by the server after
4775   sending the response. Some implementations implement the Keep-Alive
4776   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4777</t>
4778
4779<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4780<t>
4781   This section summarizes major differences between versions HTTP/1.0
4782   and HTTP/1.1.
4783</t>
4784
4785<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">
4786<t>
4787   The requirements that clients and servers support the Host request-header,
4788   report an error if the Host request-header (<xref target="header.host"/>) is
4789   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4790   are among the most important changes defined by this
4791   specification.
4792</t>
4793<t>
4794   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4795   addresses and servers; there was no other established mechanism for
4796   distinguishing the intended server of a request than the IP address
4797   to which that request was directed. The changes outlined above will
4798   allow the Internet, once older HTTP clients are no longer common, to
4799   support multiple Web sites from a single IP address, greatly
4800   simplifying large operational Web servers, where allocation of many
4801   IP addresses to a single host has created serious problems. The
4802   Internet will also be able to recover the IP addresses that have been
4803   allocated for the sole purpose of allowing special-purpose domain
4804   names to be used in root-level HTTP URLs. Given the rate of growth of
4805   the Web, and the number of servers already deployed, it is extremely
4806   important that all implementations of HTTP (including updates to
4807   existing HTTP/1.0 applications) correctly implement these
4808   requirements:
4809  <list style="symbols">
4810     <t>Both clients and servers &MUST; support the Host request-header.</t>
4811
4812     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4813
4814     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4815        request does not include a Host request-header.</t>
4816
4817     <t>Servers &MUST; accept absolute URIs.</t>
4818  </list>
4819</t>
4820</section>
4821</section>
4822
4823<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4824<t>
4825   Some clients and servers might wish to be compatible with some
4826   previous implementations of persistent connections in HTTP/1.0
4827   clients and servers. Persistent connections in HTTP/1.0 are
4828   explicitly negotiated as they are not the default behavior. HTTP/1.0
4829   experimental implementations of persistent connections are faulty,
4830   and the new facilities in HTTP/1.1 are designed to rectify these
4831   problems. The problem was that some existing HTTP/1.0 clients might
4832   send Keep-Alive to a proxy server that doesn't understand
4833   Connection, which would then erroneously forward it to the next
4834   inbound server, which would establish the Keep-Alive connection and
4835   result in a hung HTTP/1.0 proxy waiting for the close on the
4836   response. The result is that HTTP/1.0 clients must be prevented from
4837   using Keep-Alive when talking to proxies.
4838</t>
4839<t>
4840   However, talking to proxies is the most important use of persistent
4841   connections, so that prohibition is clearly unacceptable. Therefore,
4842   we need some other mechanism for indicating a persistent connection
4843   is desired, which is safe to use even when talking to an old proxy
4844   that ignores Connection. Persistent connections are the default for
4845   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4846   declaring non-persistence. See <xref target="header.connection"/>.
4847</t>
4848<t>
4849   The original HTTP/1.0 form of persistent connections (the Connection:
4850   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4851</t>
4852</section>
4853
4854<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4855<t>
4856  Empty list elements in list productions have been deprecated.
4857  (<xref target="notation.abnf"/>)
4858</t>
4859<t>
4860  Rules about implicit linear whitespace between certain grammar productions
4861  have been removed; now it's only allowed when specifically pointed out
4862  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4863  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4864  Non-ASCII content in header fields and reason phrase has been obsoleted and
4865  made opaque (the TEXT rule was removed)
4866  (<xref target="basic.rules"/>)
4867</t>
4868<t>
4869  Clarify that HTTP-Version is case sensitive.
4870  (<xref target="http.version"/>)
4871</t>
4872<t>
4873  Remove reference to non-existent identity transfer-coding value tokens.
4874  (Sections <xref format="counter" target="transfer.codings"/> and
4875  <xref format="counter" target="message.body"/>)
4876</t>
4877<t>
4878  Require that invalid whitespace around field-names be rejected.
4879  (<xref target="header.fields"/>)
4880</t>
4881<t>
4882  Update use of abs_path production from RFC1808 to the path-absolute + query
4883  components of RFC3986.
4884  (<xref target="request-target"/>)
4885</t>
4886<t>
4887  Clarification that the chunk length does not include the count of the octets
4888  in the chunk header and trailer. Furthermore disallowed line folding
4889  in chunk extensions.
4890  (<xref target="chunked.encoding"/>)
4891</t>
4892<t>
4893  Remove hard limit of two connections per server.
4894  (<xref target="persistent.practical"/>)
4895</t>
4896<t>
4897  Clarify exactly when close connection options must be sent.
4898  (<xref target="header.connection"/>)
4899</t>
4900</section>
4901</section>
4902
4903<?BEGININC p1-messaging.abnf-appendix ?>
4904<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4905<figure>
4906<artwork type="abnf" name="p1-messaging.parsed-abnf">
4907<x:ref>BWS</x:ref> = OWS
4908
4909<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4910<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4911<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4912<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4913 connection-token ] )
4914<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4915<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4916
4917<x:ref>Date</x:ref> = "Date:" OWS Date-v
4918<x:ref>Date-v</x:ref> = HTTP-date
4919
4920<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4921
4922<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4923<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4924<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4925<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4926 ]
4927<x:ref>Host</x:ref> = "Host:" OWS Host-v
4928<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4929
4930<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
4931<x:ref>Method</x:ref> = token
4932
4933<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4934
4935<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4936
4937<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4938<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4939<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4940 entity-header ) CRLF ) CRLF [ message-body ]
4941<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4942<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4943 entity-header ) CRLF ) CRLF [ message-body ]
4944
4945<x:ref>Status-Code</x:ref> = 3DIGIT
4946<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4947
4948<x:ref>TE</x:ref> = "TE:" OWS TE-v
4949<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4950<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4951<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4952<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4953<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4954 transfer-coding ] )
4955
4956<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4957<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4958<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4959
4960<x:ref>Via</x:ref> = "Via:" OWS Via-v
4961<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4962 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4963 ] )
4964
4965<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4966
4967<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4968<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4969<x:ref>attribute</x:ref> = token
4970<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4971
4972<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4973<x:ref>chunk-data</x:ref> = 1*OCTET
4974<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4975<x:ref>chunk-ext-name</x:ref> = token
4976<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4977<x:ref>chunk-size</x:ref> = 1*HEXDIG
4978<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4979<x:ref>connection-token</x:ref> = token
4980<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4981 / %x2A-5B ; '*'-'['
4982 / %x5D-7E ; ']'-'~'
4983 / obs-text
4984
4985<x:ref>date1</x:ref> = day SP month SP year
4986<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4987<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4988<x:ref>day</x:ref> = 2DIGIT
4989<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4990 / %x54.75.65 ; Tue
4991 / %x57.65.64 ; Wed
4992 / %x54.68.75 ; Thu
4993 / %x46.72.69 ; Fri
4994 / %x53.61.74 ; Sat
4995 / %x53.75.6E ; Sun
4996<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4997 / %x54.75.65.73.64.61.79 ; Tuesday
4998 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4999 / %x54.68.75.72.73.64.61.79 ; Thursday
5000 / %x46.72.69.64.61.79 ; Friday
5001 / %x53.61.74.75.72.64.61.79 ; Saturday
5002 / %x53.75.6E.64.61.79 ; Sunday
5003
5004<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
5005
5006<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5007<x:ref>field-name</x:ref> = token
5008<x:ref>field-value</x:ref> = *( field-content / OWS )
5009
5010<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5011 / Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
5012
5013<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5014<x:ref>hour</x:ref> = 2DIGIT
5015<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5016<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5017
5018<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5019
5020<x:ref>message-body</x:ref> = *OCTET
5021<x:ref>minute</x:ref> = 2DIGIT
5022<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5023 / %x46.65.62 ; Feb
5024 / %x4D.61.72 ; Mar
5025 / %x41.70.72 ; Apr
5026 / %x4D.61.79 ; May
5027 / %x4A.75.6E ; Jun
5028 / %x4A.75.6C ; Jul
5029 / %x41.75.67 ; Aug
5030 / %x53.65.70 ; Sep
5031 / %x4F.63.74 ; Oct
5032 / %x4E.6F.76 ; Nov
5033 / %x44.65.63 ; Dec
5034
5035<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5036<x:ref>obs-fold</x:ref> = CRLF
5037<x:ref>obs-text</x:ref> = %x80-FF
5038
5039<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5040<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5041<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5042<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5043<x:ref>product</x:ref> = token [ "/" product-version ]
5044<x:ref>product-version</x:ref> = token
5045<x:ref>protocol-name</x:ref> = token
5046<x:ref>protocol-version</x:ref> = token
5047<x:ref>pseudonym</x:ref> = token
5048
5049<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5050 / %x5D-7E ; ']'-'~'
5051 / obs-text
5052<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5053 / %x5D-7E ; ']'-'~'
5054 / obs-text
5055<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5056<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5057<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5058<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5059<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5060<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5061
5062<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5063<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5064<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5065<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5066<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5067 / authority
5068<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5069<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5070<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5071
5072<x:ref>second</x:ref> = 2DIGIT
5073<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5074 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5075<x:ref>start-line</x:ref> = Request-Line / Status-Line
5076
5077<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5078<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5079 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5080<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5081<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5082<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5083<x:ref>token</x:ref> = 1*tchar
5084<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
5085<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5086 transfer-extension
5087<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5088<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5089
5090<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5091
5092<x:ref>value</x:ref> = word
5093
5094<x:ref>word</x:ref> = token / quoted-string
5095
5096<x:ref>year</x:ref> = 4DIGIT
5097</artwork>
5098</figure>
5099<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5100; Chunked-Body defined but not used
5101; Content-Length defined but not used
5102; HTTP-message defined but not used
5103; Host defined but not used
5104; Request defined but not used
5105; Response defined but not used
5106; TE defined but not used
5107; URI-reference defined but not used
5108; http-URI defined but not used
5109; https-URI defined but not used
5110; partial-URI defined but not used
5111; special defined but not used
5112</artwork></figure></section>
5113<?ENDINC p1-messaging.abnf-appendix ?>
5114
5115<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5116
5117<section title="Since RFC2616">
5118<t>
5119  Extracted relevant partitions from <xref target="RFC2616"/>.
5120</t>
5121</section>
5122
5123<section title="Since draft-ietf-httpbis-p1-messaging-00">
5124<t>
5125  Closed issues:
5126  <list style="symbols"> 
5127    <t>
5128      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5129      "HTTP Version should be case sensitive"
5130      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5131    </t>
5132    <t>
5133      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5134      "'unsafe' characters"
5135      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5136    </t>
5137    <t>
5138      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5139      "Chunk Size Definition"
5140      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5141    </t>
5142    <t>
5143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5144      "Message Length"
5145      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5146    </t>
5147    <t>
5148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5149      "Media Type Registrations"
5150      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5151    </t>
5152    <t>
5153      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5154      "URI includes query"
5155      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5156    </t>
5157    <t>
5158      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5159      "No close on 1xx responses"
5160      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5161    </t>
5162    <t>
5163      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5164      "Remove 'identity' token references"
5165      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5166    </t>
5167    <t>
5168      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5169      "Import query BNF"
5170    </t>
5171    <t>
5172      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5173      "qdtext BNF"
5174    </t>
5175    <t>
5176      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5177      "Normative and Informative references"
5178    </t>
5179    <t>
5180      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5181      "RFC2606 Compliance"
5182    </t>
5183    <t>
5184      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5185      "RFC977 reference"
5186    </t>
5187    <t>
5188      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5189      "RFC1700 references"
5190    </t>
5191    <t>
5192      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5193      "inconsistency in date format explanation"
5194    </t>
5195    <t>
5196      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5197      "Date reference typo"
5198    </t>
5199    <t>
5200      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5201      "Informative references"
5202    </t>
5203    <t>
5204      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5205      "ISO-8859-1 Reference"
5206    </t>
5207    <t>
5208      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5209      "Normative up-to-date references"
5210    </t>
5211  </list>
5212</t>
5213<t>
5214  Other changes:
5215  <list style="symbols"> 
5216    <t>
5217      Update media type registrations to use RFC4288 template.
5218    </t>
5219    <t>
5220      Use names of RFC4234 core rules DQUOTE and WSP,
5221      fix broken ABNF for chunk-data
5222      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5223    </t>
5224  </list>
5225</t>
5226</section>
5227
5228<section title="Since draft-ietf-httpbis-p1-messaging-01">
5229<t>
5230  Closed issues:
5231  <list style="symbols"> 
5232    <t>
5233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5234      "Bodies on GET (and other) requests"
5235    </t>
5236    <t>
5237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5238      "Updating to RFC4288"
5239    </t>
5240    <t>
5241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5242      "Status Code and Reason Phrase"
5243    </t>
5244    <t>
5245      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5246      "rel_path not used"
5247    </t>
5248  </list>
5249</t>
5250<t>
5251  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5252  <list style="symbols"> 
5253    <t>
5254      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5255      "trailer-part").
5256    </t>
5257    <t>
5258      Avoid underscore character in rule names ("http_URL" ->
5259      "http-URL", "abs_path" -> "path-absolute").
5260    </t>
5261    <t>
5262      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5263      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5264      have to be updated when switching over to RFC3986.
5265    </t>
5266    <t>
5267      Synchronize core rules with RFC5234.
5268    </t>
5269    <t>
5270      Get rid of prose rules that span multiple lines.
5271    </t>
5272    <t>
5273      Get rid of unused rules LOALPHA and UPALPHA.
5274    </t>
5275    <t>
5276      Move "Product Tokens" section (back) into Part 1, as "token" is used
5277      in the definition of the Upgrade header.
5278    </t>
5279    <t>
5280      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5281    </t>
5282    <t>
5283      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5284    </t>
5285  </list>
5286</t>
5287</section>
5288
5289<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5290<t>
5291  Closed issues:
5292  <list style="symbols"> 
5293    <t>
5294      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5295      "HTTP-date vs. rfc1123-date"
5296    </t>
5297    <t>
5298      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5299      "WS in quoted-pair"
5300    </t>
5301  </list>
5302</t>
5303<t>
5304  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5305  <list style="symbols"> 
5306    <t>
5307      Reference RFC 3984, and update header registrations for headers defined
5308      in this document.
5309    </t>
5310  </list>
5311</t>
5312<t>
5313  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5314  <list style="symbols"> 
5315    <t>
5316      Replace string literals when the string really is case-sensitive (HTTP-Version).
5317    </t>
5318  </list>
5319</t>
5320</section>
5321
5322<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5323<t>
5324  Closed issues:
5325  <list style="symbols"> 
5326    <t>
5327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5328      "Connection closing"
5329    </t>
5330    <t>
5331      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5332      "Move registrations and registry information to IANA Considerations"
5333    </t>
5334    <t>
5335      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5336      "need new URL for PAD1995 reference"
5337    </t>
5338    <t>
5339      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5340      "IANA Considerations: update HTTP URI scheme registration"
5341    </t>
5342    <t>
5343      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5344      "Cite HTTPS URI scheme definition"
5345    </t>
5346    <t>
5347      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5348      "List-type headers vs Set-Cookie"
5349    </t>
5350  </list>
5351</t>
5352<t>
5353  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5354  <list style="symbols"> 
5355    <t>
5356      Replace string literals when the string really is case-sensitive (HTTP-Date).
5357    </t>
5358    <t>
5359      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5360    </t>
5361  </list>
5362</t>
5363</section>
5364
5365<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5366<t>
5367  Closed issues:
5368  <list style="symbols"> 
5369    <t>
5370      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5371      "Out-of-date reference for URIs"
5372    </t>
5373    <t>
5374      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5375      "RFC 2822 is updated by RFC 5322"
5376    </t>
5377  </list>
5378</t>
5379<t>
5380  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5381  <list style="symbols"> 
5382    <t>
5383      Use "/" instead of "|" for alternatives.
5384    </t>
5385    <t>
5386      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5387    </t>
5388    <t>
5389      Only reference RFC 5234's core rules.
5390    </t>
5391    <t>
5392      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5393      whitespace ("OWS") and required whitespace ("RWS").
5394    </t>
5395    <t>
5396      Rewrite ABNFs to spell out whitespace rules, factor out
5397      header value format definitions.
5398    </t>
5399  </list>
5400</t>
5401</section>
5402
5403<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5404<t>
5405  Closed issues:
5406  <list style="symbols"> 
5407    <t>
5408      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5409      "Header LWS"
5410    </t>
5411    <t>
5412      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5413      "Sort 1.3 Terminology"
5414    </t>
5415    <t>
5416      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5417      "RFC2047 encoded words"
5418    </t>
5419    <t>
5420      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5421      "Character Encodings in TEXT"
5422    </t>
5423    <t>
5424      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5425      "Line Folding"
5426    </t>
5427    <t>
5428      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5429      "OPTIONS * and proxies"
5430    </t>
5431    <t>
5432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5433      "Reason-Phrase BNF"
5434    </t>
5435    <t>
5436      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5437      "Use of TEXT"
5438    </t>
5439    <t>
5440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5441      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5442    </t>
5443    <t>
5444      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5445      "RFC822 reference left in discussion of date formats"
5446    </t>
5447  </list>
5448</t>
5449<t>
5450  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5451  <list style="symbols"> 
5452    <t>
5453      Rewrite definition of list rules, deprecate empty list elements.
5454    </t>
5455    <t>
5456      Add appendix containing collected and expanded ABNF.
5457    </t>
5458  </list>
5459</t>
5460<t>
5461  Other changes:
5462  <list style="symbols"> 
5463    <t>
5464      Rewrite introduction; add mostly new Architecture Section.
5465    </t>
5466    <t>
5467      Move definition of quality values from Part 3 into Part 1;
5468      make TE request header grammar independent of accept-params (defined in Part 3).
5469    </t>
5470  </list>
5471</t>
5472</section>
5473
5474<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5475<t>
5476  Closed issues:
5477  <list style="symbols"> 
5478    <t>
5479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5480      "base for numeric protocol elements"
5481    </t>
5482    <t>
5483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5484      "comment ABNF"
5485    </t>
5486  </list>
5487</t>
5488<t>
5489  Partly resolved issues:
5490  <list style="symbols"> 
5491    <t>
5492      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5493      "205 Bodies" (took out language that implied that there might be
5494      methods for which a request body MUST NOT be included)
5495    </t>
5496    <t>
5497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5498      "editorial improvements around HTTP-date"
5499    </t>
5500  </list>
5501</t>
5502</section>
5503
5504<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5505<t>
5506  Closed issues:
5507  <list style="symbols"> 
5508    <t>
5509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5510      "Repeating single-value headers"
5511    </t>
5512    <t>
5513      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5514      "increase connection limit"
5515    </t>
5516    <t>
5517      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5518      "IP addresses in URLs"
5519    </t>
5520    <t>
5521      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5522      "take over HTTP Upgrade Token Registry"
5523    </t>
5524    <t>
5525      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5526      "CR and LF in chunk extension values"
5527    </t>
5528    <t>
5529      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5530      "HTTP/0.9 support"
5531    </t>
5532    <t>
5533      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5534      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5535    </t>
5536    <t>
5537      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5538      "move definitions of gzip/deflate/compress to part 1"
5539    </t>
5540    <t>
5541      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5542      "disallow control characters in quoted-pair"
5543    </t>
5544  </list>
5545</t>
5546<t>
5547  Partly resolved issues:
5548  <list style="symbols"> 
5549    <t>
5550      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5551      "update IANA requirements wrt Transfer-Coding values" (add the
5552      IANA Considerations subsection)
5553    </t>
5554  </list>
5555</t>
5556</section>
5557
5558<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5559<t>
5560  Closed issues:
5561  <list style="symbols"> 
5562    <t>
5563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5564      "header parsing, treatment of leading and trailing OWS"
5565    </t>
5566  </list>
5567</t>
5568<t>
5569  Partly resolved issues:
5570  <list style="symbols"> 
5571    <t>
5572      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5573      "Placement of 13.5.1 and 13.5.2"
5574    </t>
5575    <t>
5576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5577      "use of term "word" when talking about header structure"
5578    </t>
5579  </list>
5580</t>
5581</section>
5582
5583<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5584<t>
5585  Closed issues:
5586  <list style="symbols"> 
5587    <t>
5588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5589      "Clarification of the term 'deflate'"
5590    </t>
5591    <t>
5592      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5593      "OPTIONS * and proxies"
5594    </t>
5595    <t>
5596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5597      "MIME-Version not listed in P1, general header fields"
5598    </t>
5599    <t>
5600      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5601      "IANA registry for content/transfer encodings"
5602    </t>
5603    <t>
5604      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5605      "Case-sensitivity of HTTP-date"
5606    </t>
5607    <t>
5608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5609      "use of term "word" when talking about header structure"
5610    </t>
5611  </list>
5612</t>
5613<t>
5614  Partly resolved issues:
5615  <list style="symbols"> 
5616    <t>
5617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5618      "Term for the requested resource's URI"
5619    </t>
5620  </list>
5621</t>
5622</section>
5623
5624<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5625<t>
5626  Closed issues:
5627  <list style="symbols">
5628    <t>
5629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5630      "Connection Closing"
5631    </t>
5632    <t>
5633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5634      "Delimiting messages with multipart/byteranges"
5635    </t>
5636    <t>
5637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5638      "Handling multiple Content-Length headers"
5639    </t>
5640    <t>
5641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5642      "HTTP(s) URI scheme definitions"
5643    </t>
5644    <t>
5645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5646      "consider removing the 'changes from 2068' sections"
5647    </t>
5648  </list>
5649</t>
5650</section>
5651
5652</section>
5653
5654</back>
5655</rfc>
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