source: draft-ietf-httpbis/latest/p1-messaging.xml @ 1099

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "January">
16  <!ENTITY ID-YEAR "2011">
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 header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-mime-version    "<xref target='Part3' x:rel='#mime-version' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-3xx             "<xref target='Part2' x:rel='#status.3xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39]>
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="yes"?>
49<?rfc rfcedstyle="yes"?>
50<?rfc-ext allow-markup-in-artwork="yes" ?>
51<?rfc-ext include-references-in-index="yes" ?>
52<rfc obsoletes="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.12"/>.
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 ought to 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="Cache-Control"/>
524  <x:anchor-alias value="Pragma"/>
525  <x:anchor-alias value="Warning"/>
526  <x:anchor-alias value="MIME-Version"/>
527<t>
528  The ABNF rules below are defined in other parts:
529</t>
530<figure><!-- Part2--><artwork type="abnf2616">
531  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
532  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
533</artwork></figure>
534<figure><!-- Part3--><artwork type="abnf2616">
535  <x:ref>MIME-Version</x:ref>    = &lt;MIME-Version, defined in &header-mime-version;&gt;
536</artwork></figure>
537<figure><!-- Part6--><artwork type="abnf2616">
538  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
539  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
540  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
541</artwork></figure>
542</section>
543
544</section>
545</section>
546
547<section title="HTTP-related architecture" anchor="architecture">
548<t>
549   HTTP was created for the World Wide Web architecture
550   and has evolved over time to support the scalability needs of a worldwide
551   hypertext system. Much of that architecture is reflected in the terminology
552   and syntax productions used to define HTTP.
553</t>
554
555<section title="Client/Server Messaging" anchor="operation">
556<iref primary="true" item="client"/>
557<iref primary="true" item="server"/>
558<iref primary="true" item="connection"/>
559<t>
560   HTTP is a stateless request/response protocol that operates by exchanging
561   messages across a reliable transport or session-layer connection. An HTTP
562   "client" is a program that establishes a connection to a server for the
563   purpose of sending one or more HTTP requests.  An HTTP "server" is a
564   program that accepts connections in order to service HTTP requests by
565   sending HTTP responses.
566</t>
567<iref primary="true" item="user agent"/>
568<iref primary="true" item="origin server"/>
569<iref primary="true" item="browser"/>
570<iref primary="true" item="spider"/>
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.  For general requirements, we use
579   the term "sender" to refer to whichever component sent a given message
580   and the term "recipient" to refer to any component that receives the
581   message.
582</t>
583<t>
584   Most HTTP communication consists of a retrieval request (GET) for
585   a representation of some resource identified by a URI.  In the
586   simplest case, this might be accomplished via a single bidirectional
587   connection (===) between the user agent (UA) and the origin server (O).
588</t>
589<figure><artwork type="drawing">
590         request   &gt;
591    UA ======================================= O
592                                &lt;   response
593</artwork></figure>
594<iref primary="true" item="message"/>
595<iref primary="true" item="request"/>
596<iref primary="true" item="response"/>
597<t>
598   A client sends an HTTP request to the server in the form of a request
599   message (<xref target="request"/>), beginning with a method, URI, and
600   protocol version, followed by MIME-like header fields containing
601   request modifiers, client information, and payload metadata, an empty
602   line to indicate the end of the header section, and finally the payload
603   body (if any).
604</t>
605<t>
606   A server responds to the client's request by sending an HTTP response
607   message (<xref target="response"/>), beginning with a status line that
608   includes the protocol version, a success or error code, and textual
609   reason phrase, followed by MIME-like header fields containing server
610   information, resource metadata, and payload metadata, an empty line to
611   indicate the end of the header section, and finally the payload body (if any).
612</t>
613<t>
614   The following example illustrates a typical message exchange for a
615   GET request on the URI "http://www.example.com/hello.txt":
616</t>
617<figure><preamble>
618client request:
619</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
620GET /hello.txt HTTP/1.1
621User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
622Host: www.example.com
623Accept: */*
624
625</artwork></figure>
626<figure><preamble>
627server response:
628</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
629HTTP/1.1 200 OK
630Date: Mon, 27 Jul 2009 12:28:53 GMT
631Server: Apache
632Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
633ETag: "34aa387-d-1568eb00"
634Accept-Ranges: bytes
635Content-Length: <x:length-of target="exbody"/>
636Vary: Accept-Encoding
637Content-Type: text/plain
638
639<x:span anchor="exbody">Hello World!
640</x:span></artwork></figure>
641</section>
642
643<section title="Intermediaries" anchor="intermediaries">
644<iref primary="true" item="intermediary"/>
645<t>
646   A more complicated situation occurs when one or more intermediaries
647   are present in the request/response chain. There are three common
648   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
649   a single intermediary might act as an origin server, proxy, gateway,
650   or tunnel, switching behavior based on the nature of each request.
651</t>
652<figure><artwork type="drawing">
653         &gt;             &gt;             &gt;             &gt;
654    UA =========== A =========== B =========== C =========== O
655               &lt;             &lt;             &lt;             &lt;
656</artwork></figure>
657<t>
658   The figure above shows three intermediaries (A, B, and C) between the
659   user agent and origin server. A request or response message that
660   travels the whole chain will pass through four separate connections.
661   Some HTTP communication options
662   might apply only to the connection with the nearest, non-tunnel
663   neighbor, only to the end-points of the chain, or to all connections
664   along the chain. Although the diagram is linear, each participant might
665   be engaged in multiple, simultaneous communications. For example, B
666   might be receiving requests from many clients other than A, and/or
667   forwarding requests to servers other than C, at the same time that it
668   is handling A's request.
669</t>
670<t>
671<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
672<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
673   We use the terms "upstream" and "downstream" to describe various
674   requirements in relation to the directional flow of a message:
675   all messages flow from upstream to downstream.
676   Likewise, we use the terms "inbound" and "outbound" to refer to
677   directions in relation to the request path: "inbound" means toward
678   the origin server and "outbound" means toward the user agent.
679</t>
680<t><iref primary="true" item="proxy"/>
681   A "proxy" is a message forwarding agent that is selected by the
682   client, usually via local configuration rules, to receive requests
683   for some type(s) of absolute URI and attempt to satisfy those
684   requests via translation through the HTTP interface.  Some translations
685   are minimal, such as for proxy requests for "http" URIs, whereas
686   other requests might require translation to and from entirely different
687   application-layer protocols. Proxies are often used to group an
688   organization's HTTP requests through a common intermediary for the
689   sake of security, annotation services, or shared caching.
690</t>
691<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
692   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
693   as a layer above some other server(s) and translates the received
694   requests to the underlying server's protocol.  Gateways are often
695   used for load balancing or partitioning HTTP services across
696   multiple machines.
697   Unlike a proxy, a gateway receives requests as if it were the
698   origin server for the target resource; the requesting client
699   will not be aware that it is communicating with a gateway.
700   A gateway communicates with the client as if the gateway is the
701   origin server and thus is subject to all of the requirements on
702   origin servers for that connection.  A gateway communicates
703   with inbound servers using any protocol it desires, including
704   private extensions to HTTP that are outside the scope of this
705   specification.
706</t>
707<t><iref primary="true" item="tunnel"/>
708   A "tunnel" acts as a blind relay between two connections
709   without changing the messages. Once active, a tunnel is not
710   considered a party to the HTTP communication, though the tunnel might
711   have been initiated by an HTTP request. A tunnel ceases to exist when
712   both ends of the relayed connection are closed. Tunnels are used to
713   extend a virtual connection through an intermediary, such as when
714   transport-layer security is used to establish private communication
715   through a shared firewall proxy.
716</t>
717</section>
718
719<section title="Caches" anchor="caches">
720<iref primary="true" item="cache"/>
721<t>
722   A "cache" is a local store of previous response messages and the
723   subsystem that controls its message storage, retrieval, and deletion.
724   A cache stores cacheable responses in order to reduce the response
725   time and network bandwidth consumption on future, equivalent
726   requests. Any client or server &MAY; employ a cache, though a cache
727   cannot be used by a server while it is acting as a tunnel.
728</t>
729<t>
730   The effect of a cache is that the request/response chain is shortened
731   if one of the participants along the chain has a cached response
732   applicable to that request. The following illustrates the resulting
733   chain if B has a cached copy of an earlier response from O (via C)
734   for a request which has not been cached by UA or A.
735</t>
736<figure><artwork type="drawing">
737            &gt;             &gt;
738       UA =========== A =========== B - - - - - - C - - - - - - O
739                  &lt;             &lt;
740</artwork></figure>
741<t><iref primary="true" item="cacheable"/>
742   A response is "cacheable" if a cache is allowed to store a copy of
743   the response message for use in answering subsequent requests.
744   Even when a response is cacheable, there might be additional
745   constraints placed by the client or by the origin server on when
746   that cached response can be used for a particular request. HTTP
747   requirements for cache behavior and cacheable responses are
748   defined in &caching-overview;
749</t>
750<t>
751   There are a wide variety of architectures and configurations
752   of caches and proxies deployed across the World Wide Web and
753   inside large organizations. These systems include national hierarchies
754   of proxy caches to save transoceanic bandwidth, systems that
755   broadcast or multicast cache entries, organizations that distribute
756   subsets of cached data via optical media, and so on.
757</t>
758</section>
759
760<section title="Transport Independence" anchor="transport-independence">
761<t>
762  HTTP systems are used in a wide variety of environments, from
763  corporate intranets with high-bandwidth links to long-distance
764  communication over low-power radio links and intermittent connectivity.
765</t>
766<t>
767   HTTP communication usually takes place over TCP/IP connections. The
768   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
769   not preclude HTTP from being implemented on top of any other protocol
770   on the Internet, or on other networks. HTTP only presumes a reliable
771   transport; any protocol that provides such guarantees can be used;
772   the mapping of the HTTP/1.1 request and response structures onto the
773   transport data units of the protocol in question is outside the scope
774   of this specification.
775</t>
776<t>
777   In HTTP/1.0, most implementations used a new connection for each
778   request/response exchange. In HTTP/1.1, a connection might be used for
779   one or more request/response exchanges, although connections might be
780   closed for a variety of reasons (see <xref target="persistent.connections"/>).
781</t>
782</section>
783
784<section title="HTTP Version" anchor="http.version">
785  <x:anchor-alias value="HTTP-Version"/>
786  <x:anchor-alias value="HTTP-Prot-Name"/>
787<t>
788   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
789   of the protocol. The protocol versioning policy is intended to allow
790   the sender to indicate the format of a message and its capacity for
791   understanding further HTTP communication, rather than the features
792   obtained via that communication. No change is made to the version
793   number for the addition of message components which do not affect
794   communication behavior or which only add to extensible field values.
795   The &lt;minor&gt; number is incremented when the changes made to the
796   protocol add features which do not change the general message parsing
797   algorithm, but which might add to the message semantics and imply
798   additional capabilities of the sender. The &lt;major&gt; number is
799   incremented when the format of a message within the protocol is
800   changed. See <xref target="RFC2145"/> for a fuller explanation.
801</t>
802<t>
803   The version of an HTTP message is indicated by an HTTP-Version field
804   in the first line of the message. HTTP-Version is case-sensitive.
805</t>
806<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
807  <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>
808  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
809</artwork></figure>
810<t>
811   Note that the major and minor numbers &MUST; be treated as separate
812   integers and that each &MAY; be incremented higher than a single digit.
813   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
814   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
815   &MUST-NOT; be sent.
816</t>
817<t>
818   An application that sends a request or response message that includes
819   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
820   with this specification. Applications that are at least conditionally
821   compliant with this specification &SHOULD; use an HTTP-Version of
822   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
823   not compatible with HTTP/1.0. For more details on when to send
824   specific HTTP-Version values, see <xref target="RFC2145"/>.
825</t>
826<t>
827   The HTTP version of an application is the highest HTTP version for
828   which the application is at least conditionally compliant.
829</t>
830<t>
831   Proxy and gateway applications need to be careful when forwarding
832   messages in protocol versions different from that of the application.
833   Since the protocol version indicates the protocol capability of the
834   sender, a proxy/gateway &MUST-NOT; send a message with a version
835   indicator which is greater than its actual version. If a higher
836   version request is received, the proxy/gateway &MUST; either downgrade
837   the request version, or respond with an error, or switch to tunnel
838   behavior.
839</t>
840<t>
841   Due to interoperability problems with HTTP/1.0 proxies discovered
842   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
843   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
844   they support. The proxy/gateway's response to that request &MUST; be in
845   the same major version as the request.
846</t>
847<x:note>
848  <t>
849    <x:h>Note:</x:h> Converting between versions of HTTP might involve modification
850    of header fields required or forbidden by the versions involved.
851  </t>
852</x:note>
853</section>
854
855<section title="Uniform Resource Identifiers" anchor="uri">
856<iref primary="true" item="resource"/>
857<t>
858   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
859   throughout HTTP as the means for identifying resources. URI references
860   are used to target requests, indicate redirects, and define relationships.
861   HTTP does not limit what a resource might be; it merely defines an interface
862   that can be used to interact with a resource via HTTP. More information on
863   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
864</t>
865  <x:anchor-alias value="URI-reference"/>
866  <x:anchor-alias value="absolute-URI"/>
867  <x:anchor-alias value="relative-part"/>
868  <x:anchor-alias value="authority"/>
869  <x:anchor-alias value="path-abempty"/>
870  <x:anchor-alias value="path-absolute"/>
871  <x:anchor-alias value="port"/>
872  <x:anchor-alias value="query"/>
873  <x:anchor-alias value="uri-host"/>
874  <x:anchor-alias value="partial-URI"/>
875<t>
876   This specification adopts the definitions of "URI-reference",
877   "absolute-URI", "relative-part", "port", "host",
878   "path-abempty", "path-absolute", "query", and "authority" from
879   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
880   protocol elements that allow a relative URI without a fragment.
881</t>
882<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"/>
883  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
884  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
885  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
886  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
887  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
888  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
889  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
890  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
891  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
892 
893  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
894</artwork></figure>
895<t>
896   Each protocol element in HTTP that allows a URI reference will indicate in
897   its ABNF production whether the element allows only a URI in absolute form
898   (absolute-URI), any relative reference (relative-ref), or some other subset
899   of the URI-reference grammar. Unless otherwise indicated, URI references
900   are parsed relative to the request target (the default base URI for both
901   the request and its corresponding response).
902</t>
903
904<section title="http URI scheme" anchor="http.uri">
905  <x:anchor-alias value="http-URI"/>
906  <iref item="http URI scheme" primary="true"/>
907  <iref item="URI scheme" subitem="http" primary="true"/>
908<t>
909   The "http" URI scheme is hereby defined for the purpose of minting
910   identifiers according to their association with the hierarchical
911   namespace governed by a potential HTTP origin server listening for
912   TCP connections on a given port.
913   The HTTP server is identified via the generic syntax's
914   <x:ref>authority</x:ref> component, which includes a host
915   identifier and optional TCP port, and the remainder of the URI is
916   considered to be identifying data corresponding to a resource for
917   which that server might provide an HTTP interface.
918</t>
919<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
920  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
921</artwork></figure>
922<t>
923   The host identifier within an <x:ref>authority</x:ref> component is
924   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
925   provided as an IP literal or IPv4 address, then the HTTP server is any
926   listener on the indicated TCP port at that IP address. If host is a
927   registered name, then that name is considered an indirect identifier
928   and the recipient might use a name resolution service, such as DNS,
929   to find the address of a listener for that host.
930   The host &MUST-NOT; be empty; if an "http" URI is received with an
931   empty host, then it &MUST; be rejected as invalid.
932   If the port subcomponent is empty or not given, then TCP port 80 is
933   assumed (the default reserved port for WWW services).
934</t>
935<t>
936   Regardless of the form of host identifier, access to that host is not
937   implied by the mere presence of its name or address. The host might or might
938   not exist and, even when it does exist, might or might not be running an
939   HTTP server or listening to the indicated port. The "http" URI scheme
940   makes use of the delegated nature of Internet names and addresses to
941   establish a naming authority (whatever entity has the ability to place
942   an HTTP server at that Internet name or address) and allows that
943   authority to determine which names are valid and how they might be used.
944</t>
945<t>
946   When an "http" URI is used within a context that calls for access to the
947   indicated resource, a client &MAY; attempt access by resolving
948   the host to an IP address, establishing a TCP connection to that address
949   on the indicated port, and sending an HTTP request message to the server
950   containing the URI's identifying data as described in <xref target="request"/>.
951   If the server responds to that request with a non-interim HTTP response
952   message, as described in <xref target="response"/>, then that response
953   is considered an authoritative answer to the client's request.
954</t>
955<t>
956   Although HTTP is independent of the transport protocol, the "http"
957   scheme is specific to TCP-based services because the name delegation
958   process depends on TCP for establishing authority.
959   An HTTP service based on some other underlying connection protocol
960   would presumably be identified using a different URI scheme, just as
961   the "https" scheme (below) is used for servers that require an SSL/TLS
962   transport layer on a connection. Other protocols might also be used to
963   provide access to "http" identified resources --- it is only the
964   authoritative interface used for mapping the namespace that is
965   specific to TCP.
966</t>
967<t>
968   The URI generic syntax for authority also includes a deprecated
969   userinfo subcomponent (<xref target="RFC3986" x:fmt="," x:sec="3.2.1"/>)
970   for including user authentication information in the URI.  The userinfo
971   subcomponent (and its "@" delimiter) &MUST-NOT; be used in an "http"
972   URI.  URI reference recipients &SHOULD; parse for the existence of
973   userinfo and treat its presence as an error, likely indicating that
974   the deprecated subcomponent is being used to obscure the authority
975   for the sake of phishing attacks.
976</t>
977</section>
978
979<section title="https URI scheme" anchor="https.uri">
980   <x:anchor-alias value="https-URI"/>
981   <iref item="https URI scheme"/>
982   <iref item="URI scheme" subitem="https"/>
983<t>
984   The "https" URI scheme is hereby defined for the purpose of minting
985   identifiers according to their association with the hierarchical
986   namespace governed by a potential HTTP origin server listening for
987   SSL/TLS-secured connections on a given TCP port.
988</t>
989<t>
990   All of the requirements listed above for the "http" scheme are also
991   requirements for the "https" scheme, except that a default TCP port
992   of 443 is assumed if the port subcomponent is empty or not given,
993   and the TCP connection &MUST; be secured for privacy through the
994   use of strong encryption prior to sending the first HTTP request.
995</t>
996<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
997  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
998</artwork></figure>
999<t>
1000   Unlike the "http" scheme, responses to "https" identified requests
1001   are never "public" and thus are ineligible for shared caching.
1002   Their default is "private" and might be further constrained via use
1003   of the Cache-Control header field.
1004</t>
1005<t>
1006   Resources made available via the "https" scheme have no shared
1007   identity with the "http" scheme even if their resource identifiers
1008   only differ by the single "s" in the scheme name.  They are
1009   different services governed by different authorities.  However,
1010   some extensions to HTTP that apply to entire host domains, such
1011   as the Cookie protocol, do allow one service to effect communication
1012   with the other services based on host domain matching.
1013</t>
1014<t>
1015   The process for authoritative access to an "https" identified
1016   resource is defined in <xref target="RFC2818"/>.
1017</t>
1018</section>
1019
1020<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1021<t>
1022   Since the "http" and "https" schemes conform to the URI generic syntax,
1023   such URIs are normalized and compared according to the algorithm defined
1024   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1025   described above for each scheme.
1026</t>
1027<t>
1028   If the port is equal to the default port for a scheme, the normal
1029   form is to elide the port subcomponent. Likewise, an empty path
1030   component is equivalent to an absolute path of "/", so the normal
1031   form is to provide a path of "/" instead. The scheme and host
1032   are case-insensitive and normally provided in lowercase; all
1033   other components are compared in a case-sensitive manner.
1034   Characters other than those in the "reserved" set are equivalent
1035   to their percent-encoded octets (see <xref target="RFC3986"
1036   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1037</t>
1038<t>
1039   For example, the following three URIs are equivalent:
1040</t>
1041<figure><artwork type="example">
1042   http://example.com:80/~smith/home.html
1043   http://EXAMPLE.com/%7Esmith/home.html
1044   http://EXAMPLE.com:/%7esmith/home.html
1045</artwork></figure>
1046<t>
1047   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1048   If path-abempty is the empty string (i.e., there is no slash "/"
1049   path separator following the authority), then the "http" URI
1050   &MUST; be given as "/" when
1051   used as a request-target (<xref target="request-target"/>). If a proxy
1052   receives a host name which is not a fully qualified domain name, it
1053   &MAY; add its domain to the host name it received. If a proxy receives
1054   a fully qualified domain name, the proxy &MUST-NOT; change the host
1055   name.
1056</t>
1057</section>
1058</section>
1059</section>
1060
1061<section title="HTTP Message" anchor="http.message">
1062<x:anchor-alias value="generic-message"/>
1063<x:anchor-alias value="message.types"/>
1064<x:anchor-alias value="HTTP-message"/>
1065<x:anchor-alias value="start-line"/>
1066<iref item="header section"/>
1067<iref item="headers"/>
1068<iref item="header field"/>
1069<t>
1070   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1071   characters in a format similar to the Internet Message Format
1072   <xref target="RFC5322"/>: zero or more header fields (collectively
1073   referred to as the "headers" or the "header section"), an empty line
1074   indicating the end of the header section, and an optional message-body.
1075</t>
1076<t>
1077   An HTTP message can either be a request from client to server or a
1078   response from server to client.  Syntactically, the two types of message
1079   differ only in the start-line, which is either a Request-Line (for requests)
1080   or a Status-Line (for responses), and in the algorithm for determining
1081   the length of the message-body (<xref target="message.body"/>).
1082   In theory, a client could receive requests and a server could receive
1083   responses, distinguishing them by their different start-line formats,
1084   but in practice servers are implemented to only expect a request
1085   (a response is interpreted as an unknown or invalid request method)
1086   and clients are implemented to only expect a response.
1087</t>
1088<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1089  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1090                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1091                    <x:ref>CRLF</x:ref>
1092                    [ <x:ref>message-body</x:ref> ]
1093  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1094</artwork></figure>
1095<t>
1096   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1097   header field. The presence of whitespace might be an attempt to trick a
1098   noncompliant implementation of HTTP into ignoring that field or processing
1099   the next line as a new request, either of which might result in security
1100   issues when implementations within the request chain interpret the
1101   same message differently. HTTP/1.1 servers &MUST; reject such a message
1102   with a 400 (Bad Request) response.
1103</t>
1104
1105<section title="Message Parsing Robustness" anchor="message.robustness">
1106<t>
1107   In the interest of robustness, servers &SHOULD; ignore at least one
1108   empty line received where a Request-Line is expected. In other words, if
1109   the server is reading the protocol stream at the beginning of a
1110   message and receives a CRLF first, it &SHOULD; ignore the CRLF.
1111</t>
1112<t>
1113   Some old HTTP/1.0 client implementations generate an extra CRLF
1114   after a POST request as a lame workaround for some early server
1115   applications that failed to read message-body content that was
1116   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1117   preface or follow a request with an extra CRLF.  If terminating
1118   the request message-body with a line-ending is desired, then the
1119   client &MUST; include the terminating CRLF octets as part of the
1120   message-body length.
1121</t>
1122<t>
1123   The normal procedure for parsing an HTTP message is to read the
1124   start-line into a structure, read each header field into a hash
1125   table by field name until the empty line, and then use the parsed
1126   data to determine if a message-body is expected.  If a message-body
1127   has been indicated, then it is read as a stream until an amount
1128   of octets equal to the message-body length is read or the connection
1129   is closed.  Care must be taken to parse an HTTP message as a sequence
1130   of octets in an encoding that is a superset of US-ASCII.  Attempting
1131   to parse HTTP as a stream of Unicode characters in a character encoding
1132   like UTF-16 might introduce security flaws due to the differing ways
1133   that such parsers interpret invalid characters.
1134</t>
1135<t>
1136   HTTP allows the set of defined header fields to be extended without
1137   changing the protocol version (see <xref target="header.field.registration"/>).
1138   However, such fields might not be recognized by a downstream recipient
1139   and might be stripped by non-transparent intermediaries.
1140   Unrecognized header fields &MUST; be forwarded by transparent proxies
1141   and &SHOULD; be ignored by a recipient.
1142</t>
1143</section>
1144
1145<section title="Header Fields" anchor="header.fields">
1146  <x:anchor-alias value="header-field"/>
1147  <x:anchor-alias value="field-content"/>
1148  <x:anchor-alias value="field-name"/>
1149  <x:anchor-alias value="field-value"/>
1150  <x:anchor-alias value="OWS"/>
1151<t>
1152   Each HTTP header field consists of a case-insensitive field name
1153   followed by a colon (":"), optional whitespace, and the field value.
1154</t>
1155<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"/>
1156  <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>
1157  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1158  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1159  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1160</artwork></figure>
1161<t>
1162   No whitespace is allowed between the header field name and colon. For
1163   security reasons, any request message received containing such whitespace
1164   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1165   &MUST; remove any such whitespace from a response message before
1166   forwarding the message downstream.
1167</t>
1168<t>
1169   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1170   preferred. The field value does not include any leading or trailing white
1171   space: OWS occurring before the first non-whitespace character of the
1172   field value or after the last non-whitespace character of the field value
1173   is ignored and &SHOULD; be removed before further processing (as this does
1174   not change the meaning of the header field).
1175</t>
1176<t>
1177   The order in which header fields with differing field names are
1178   received is not significant. However, it is "good practice" to send
1179   header fields that contain control data first, such as Host on
1180   requests and Date on responses, so that implementations can decide
1181   when not to handle a message as early as possible.  A server &MUST;
1182   wait until the entire header section is received before interpreting
1183   a request message, since later header fields might include conditionals,
1184   authentication credentials, or deliberately misleading duplicate
1185   header fields that would impact request processing.
1186</t>
1187<t>
1188   Multiple header fields with the same field name &MUST-NOT; be
1189   sent in a message unless the entire field value for that
1190   header field is defined as a comma-separated list [i.e., #(values)].
1191   Multiple header fields with the same field name can be combined into
1192   one "field-name: field-value" pair, without changing the semantics of the
1193   message, by appending each subsequent field value to the combined
1194   field value in order, separated by a comma. The order in which
1195   header fields with the same field name are received is therefore
1196   significant to the interpretation of the combined field value;
1197   a proxy &MUST-NOT; change the order of these field values when
1198   forwarding a message.
1199</t>
1200<x:note>
1201  <t>
1202   <x:h>Note:</x:h> The "Set-Cookie" header field as implemented in
1203   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1204   can occur multiple times, but does not use the list syntax, and thus cannot
1205   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1206   for details.) Also note that the Set-Cookie2 header field specified in
1207   <xref target="RFC2965"/> does not share this problem.
1208  </t>
1209</x:note>
1210<t>
1211   Historically, HTTP header field values could be extended over multiple
1212   lines by preceding each extra line with at least one space or horizontal
1213   tab character (line folding). This specification deprecates such line
1214   folding except within the message/http media type
1215   (<xref target="internet.media.type.message.http"/>).
1216   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1217   (i.e., that contain any field-content that matches the obs-fold rule) unless
1218   the message is intended for packaging within the message/http media type.
1219   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1220   obs-fold whitespace with a single SP prior to interpreting the field value
1221   or forwarding the message downstream.
1222</t>
1223<t>
1224   Historically, HTTP has allowed field content with text in the ISO-8859-1
1225   <xref target="ISO-8859-1"/> character encoding and supported other
1226   character sets only through use of <xref target="RFC2047"/> encoding.
1227   In practice, most HTTP header field values use only a subset of the
1228   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1229   header fields &SHOULD; limit their field values to US-ASCII characters.
1230   Recipients &SHOULD; treat other (obs-text) octets in field content as
1231   opaque data.
1232</t>
1233<t anchor="rule.comment">
1234  <x:anchor-alias value="comment"/>
1235  <x:anchor-alias value="ctext"/>
1236   Comments can be included in some HTTP header fields by surrounding
1237   the comment text with parentheses. Comments are only allowed in
1238   fields containing "comment" as part of their field value definition.
1239</t>
1240<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1241  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1242  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1243                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1244</artwork></figure>
1245<t anchor="rule.quoted-cpair">
1246  <x:anchor-alias value="quoted-cpair"/>
1247   The backslash character ("\") can be used as a single-character
1248   quoting mechanism within comment constructs:
1249</t>
1250<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1251  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1252</artwork></figure>
1253<t>
1254   Producers &SHOULD-NOT; escape characters that do not require escaping
1255   (i.e., other than the backslash character "\" and the parentheses "(" and
1256   ")").
1257</t>
1258</section>
1259
1260<section title="Message Body" anchor="message.body">
1261  <x:anchor-alias value="message-body"/>
1262<t>
1263   The message-body (if any) of an HTTP message is used to carry the
1264   payload body associated with the request or response.
1265</t>
1266<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1267  <x:ref>message-body</x:ref> = *OCTET
1268</artwork></figure>
1269<t>
1270   The message-body differs from the payload body only when a transfer-coding
1271   has been applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).  When one or more transfer-codings are
1272   applied to a payload in order to form the message-body, the
1273   Transfer-Encoding header field &MUST; contain the list of
1274   transfer-codings applied. Transfer-Encoding is a property of the message,
1275   not of the payload, and thus &MAY; be added or removed by any implementation
1276   along the request/response chain under the constraints found in
1277   <xref target="transfer.codings"/>.
1278</t>
1279<t>
1280   The rules for when a message-body is allowed in a message differ for
1281   requests and responses.
1282</t>
1283<t>
1284   The presence of a message-body in a request is signaled by the
1285   inclusion of a Content-Length or Transfer-Encoding header field in
1286   the request's header fields, even if the request method does not
1287   define any use for a message-body.  This allows the request
1288   message framing algorithm to be independent of method semantics.
1289</t>
1290<t>
1291   For response messages, whether or not a message-body is included with
1292   a message is dependent on both the request method and the response
1293   status code (<xref target="status.code.and.reason.phrase"/>).
1294   Responses to the HEAD request method never include a message-body
1295   because the associated response header fields (e.g., Transfer-Encoding,
1296   Content-Length, etc.) only indicate what their values would have been
1297   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1298   and 304 (Not Modified) responses &MUST-NOT; include a message-body.
1299   All other responses do include a message-body, although the body
1300   &MAY; be of zero length.
1301</t>
1302<t>
1303   The length of the message-body is determined by one of the following
1304   (in order of precedence):
1305</t>
1306<t>
1307  <list style="numbers">
1308    <x:lt><t>
1309     Any response to a HEAD request and any response with a status
1310     code of 100-199, 204, or 304 is always terminated by the first
1311     empty line after the header fields, regardless of the header
1312     fields present in the message, and thus cannot contain a message-body.
1313    </t></x:lt>
1314    <x:lt><t>
1315     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1316     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1317     is the final encoding, the message-body length is determined by reading
1318     and decoding the chunked data until the transfer-coding indicates the
1319     data is complete.
1320    </t>
1321    <t>
1322     If a Transfer-Encoding header field is present in a response and the
1323     "chunked" transfer-coding is not the final encoding, the message-body
1324     length is determined by reading the connection until it is closed by
1325     the server.
1326     If a Transfer-Encoding header field is present in a request and the
1327     "chunked" transfer-coding is not the final encoding, the message-body
1328     length cannot be determined reliably; the server &MUST; respond with
1329     the 400 (Bad Request) status code and then close the connection.
1330    </t>
1331    <t>
1332     If a message is received with both a Transfer-Encoding header field and a
1333     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1334     Such a message might indicate an attempt to perform request or response
1335     smuggling (bypass of security-related checks on message routing or content)
1336     and thus ought to be handled as an error.  The provided Content-Length &MUST;
1337     be removed, prior to forwarding the message downstream, or replaced with
1338     the real message-body length after the transfer-coding is decoded.
1339    </t></x:lt>
1340    <x:lt><t>
1341     If a message is received without Transfer-Encoding and with either
1342     multiple Content-Length header fields or a single Content-Length header
1343     field with an invalid value, then the message framing is invalid and
1344     &MUST; be treated as an error to prevent request or response smuggling.
1345     If this is a request message, the server &MUST; respond with
1346     a 400 (Bad Request) status code and then close the connection.
1347     If this is a response message received by a proxy or gateway, the proxy
1348     or gateway &MUST; discard the received response, send a 502 (Bad Gateway)
1349     status code as its downstream response, and then close the connection.
1350     If this is a response message received by a user-agent, it &SHOULD; be
1351     treated as an error by discarding the message and closing the connection.
1352    </t></x:lt>
1353    <x:lt><t>
1354     If a valid Content-Length header field (<xref target="header.content-length"/>)
1355     is present without Transfer-Encoding, its decimal value defines the
1356     message-body length in octets.  If the actual number of octets sent in
1357     the message is less than the indicated Content-Length, the recipient
1358     &MUST; consider the message to be incomplete and treat the connection
1359     as no longer usable.
1360     If the actual number of octets sent in the message is more than the indicated
1361     Content-Length, the recipient &MUST; only process the message-body up to the
1362     field value's number of octets; the remainder of the message &MUST; either
1363     be discarded or treated as the next message in a pipeline.  For the sake of
1364     robustness, a user-agent &MAY; attempt to detect and correct such an error
1365     in message framing if it is parsing the response to the last request on
1366     on a connection and the connection has been closed by the server.
1367    </t></x:lt>
1368    <x:lt><t>
1369     If this is a request message and none of the above are true, then the
1370     message-body length is zero (no message-body is present).
1371    </t></x:lt>
1372    <x:lt><t>
1373     Otherwise, this is a response message without a declared message-body
1374     length, so the message-body length is determined by the number of octets
1375     received prior to the server closing the connection.
1376    </t></x:lt>
1377  </list>
1378</t>
1379<t>
1380   Since there is no way to distinguish a successfully completed,
1381   close-delimited message from a partially-received message interrupted
1382   by network failure, implementations &SHOULD; use encoding or
1383   length-delimited messages whenever possible.  The close-delimiting
1384   feature exists primarily for backwards compatibility with HTTP/1.0.
1385</t>
1386<t>
1387   A server &MAY; reject a request that contains a message-body but
1388   not a Content-Length by responding with 411 (Length Required).
1389</t>
1390<t>
1391   Unless a transfer-coding other than "chunked" has been applied,
1392   a client that sends a request containing a message-body &SHOULD;
1393   use a valid Content-Length header field if the message-body length
1394   is known in advance, rather than the "chunked" encoding, since some
1395   existing services respond to "chunked" with a 411 (Length Required)
1396   status code even though they understand the chunked encoding.  This
1397   is typically because such services are implemented via a gateway that
1398   requires a content-length in advance of being called and the server
1399   is unable or unwilling to buffer the entire request before processing.
1400</t>
1401<t>
1402   A client that sends a request containing a message-body &MUST; include a
1403   valid Content-Length header field if it does not know the server will
1404   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1405   of specific user configuration or by remembering the version of a prior
1406   received response.
1407</t>
1408<t>
1409   Request messages that are prematurely terminated, possibly due to a
1410   cancelled connection or a server-imposed time-out exception, &MUST;
1411   result in closure of the connection; sending an HTTP/1.1 error response
1412   prior to closing the connection is &OPTIONAL;.
1413   Response messages that are prematurely terminated, usually by closure
1414   of the connection prior to receiving the expected number of octets or by
1415   failure to decode a transfer-encoded message-body, &MUST; be recorded
1416   as incomplete.  A user agent &MUST-NOT; render an incomplete response
1417   message-body as if it were complete (i.e., some indication must be given
1418   to the user that an error occurred).  Cache requirements for incomplete
1419   responses are defined in &cache-incomplete;.
1420</t>
1421<t>
1422   A server &MUST; read the entire request message-body or close
1423   the connection after sending its response, since otherwise the
1424   remaining data on a persistent connection would be misinterpreted
1425   as the next request.  Likewise,
1426   a client &MUST; read the entire response message-body if it intends
1427   to reuse the same connection for a subsequent request.  Pipelining
1428   multiple requests on a connection is described in <xref target="pipelining"/>.
1429</t>
1430</section>
1431
1432<section title="General Header Fields" anchor="general.header.fields">
1433  <x:anchor-alias value="general-header"/>
1434<t>
1435   There are a few header fields which have general applicability for
1436   both request and response messages, but which do not apply to the
1437   payload being transferred. These header fields apply only to the
1438   message being transmitted.
1439</t>
1440<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1441  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1442                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1443                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1444                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1445                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1446                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1447                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1448                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1449                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1450                 / <x:ref>MIME-Version</x:ref>             ; &header-mime-version;
1451</artwork></figure>
1452<t>
1453   General-header field names can be extended reliably only in
1454   combination with a change in the protocol version. However, new or
1455   experimental header fields might be given the semantics of general
1456   header fields if all parties in the communication recognize them to
1457   be general-header fields.
1458</t>
1459</section>
1460</section>
1461
1462<section title="Request" anchor="request">
1463  <x:anchor-alias value="Request"/>
1464<t>
1465   A request message from a client to a server includes, within the
1466   first line of that message, the method to be applied to the resource,
1467   the identifier of the resource, and the protocol version in use.
1468</t>
1469<!--                 Host                      ; should be moved here eventually -->
1470<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1471  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1472                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1473                  <x:ref>CRLF</x:ref>
1474                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1475</artwork></figure>
1476
1477<section title="Request-Line" anchor="request-line">
1478  <x:anchor-alias value="Request-Line"/>
1479<t>
1480   The Request-Line begins with a method token, followed by the
1481   request-target and the protocol version, and ending with CRLF. The
1482   elements are separated by SP characters. No CR or LF is allowed
1483   except in the final CRLF sequence.
1484</t>
1485<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1486  <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>
1487</artwork></figure>
1488
1489<section title="Method" anchor="method">
1490  <x:anchor-alias value="Method"/>
1491<t>
1492   The Method  token indicates the method to be performed on the
1493   resource identified by the request-target. The method is case-sensitive.
1494</t>
1495<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1496  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1497</artwork></figure>
1498</section>
1499
1500<section title="request-target" anchor="request-target">
1501  <x:anchor-alias value="request-target"/>
1502<t>
1503   The request-target identifies the resource upon which to apply the request.
1504</t>
1505<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1506  <x:ref>request-target</x:ref> = "*"
1507                 / <x:ref>absolute-URI</x:ref>
1508                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1509                 / <x:ref>authority</x:ref>
1510</artwork></figure>
1511<t>
1512   The four options for request-target are dependent on the nature of the
1513   request.
1514</t>   
1515<t><iref item="asterisk form (of request-target)"/>
1516   The asterisk "*" ("asterisk form") means that the request does not apply to a
1517   particular resource, but to the server itself. This is only allowed for the
1518   OPTIONS method. Thus, the only valid example is
1519</t>
1520<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1521OPTIONS * HTTP/1.1
1522</artwork></figure>
1523<t><iref item="absolute-URI form (of request-target)"/>
1524   The "absolute-URI" form is &REQUIRED; when the request is being made to a
1525   proxy. The proxy is requested to forward the request or service it
1526   from a valid cache, and return the response. Note that the proxy &MAY;
1527   forward the request on to another proxy or directly to the server
1528   specified by the absolute-URI. In order to avoid request loops, a
1529   proxy &MUST; be able to recognize all of its server names, including
1530   any aliases, local variations, and the numeric IP address. An example
1531   Request-Line would be:
1532</t>
1533<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1534GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1535</artwork></figure>
1536<t>
1537   To allow for transition to absolute-URIs in all requests in future
1538   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1539   form in requests, even though HTTP/1.1 clients will only generate
1540   them in requests to proxies.
1541</t>
1542<t><iref item="authority form (of request-target)"/>
1543   The "authority form" is only used by the CONNECT method (&CONNECT;).
1544</t>
1545<t><iref item="path-absolute form (of request-target)"/>
1546   The most common form of request-target is that used to identify a
1547   resource on an origin server or gateway ("path-absolute form"). In this case the absolute
1548   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1549   the request-target, and the network location of the URI (authority) &MUST;
1550   be transmitted in a Host header field. For example, a client wishing
1551   to retrieve the resource above directly from the origin server would
1552   create a TCP connection to port 80 of the host "www.example.org" and send
1553   the lines:
1554</t>
1555<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1556GET /pub/WWW/TheProject.html HTTP/1.1
1557Host: www.example.org
1558</artwork></figure>
1559<t>
1560   followed by the remainder of the Request. Note that the absolute path
1561   cannot be empty; if none is present in the original URI, it &MUST; be
1562   given as "/" (the server root).
1563</t>
1564<t>
1565   If a proxy receives a request without any path in the request-target and
1566   the method specified is capable of supporting the asterisk form of
1567   request-target, then the last proxy on the request chain &MUST; forward the
1568   request with "*" as the final request-target.
1569</t>
1570<figure><preamble>   
1571   For example, the request
1572</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1573OPTIONS http://www.example.org:8001 HTTP/1.1
1574</artwork></figure>
1575<figure><preamble>   
1576  would be forwarded by the proxy as
1577</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1578OPTIONS * HTTP/1.1
1579Host: www.example.org:8001
1580</artwork>
1581<postamble>
1582   after connecting to port 8001 of host "www.example.org".
1583</postamble>
1584</figure>
1585<t>
1586   The request-target is transmitted in the format specified in
1587   <xref target="http.uri"/>. If the request-target is percent-encoded
1588   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1589   &MUST; decode the request-target in order to
1590   properly interpret the request. Servers &SHOULD; respond to invalid
1591   request-targets with an appropriate status code.
1592</t>
1593<t>
1594   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1595   received request-target when forwarding it to the next inbound server,
1596   except as noted above to replace a null path-absolute with "/" or "*".
1597</t>
1598<x:note>
1599  <t>
1600    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1601    meaning of the request when the origin server is improperly using
1602    a non-reserved URI character for a reserved purpose.  Implementors
1603    need to be aware that some pre-HTTP/1.1 proxies have been known to
1604    rewrite the request-target.
1605  </t>
1606</x:note>
1607<t>
1608   HTTP does not place a pre-defined limit on the length of a request-target.
1609   A server &MUST; be prepared to receive URIs of unbounded length and
1610   respond with the 414 (URI Too Long) status code if the received
1611   request-target would be longer than the server wishes to handle
1612   (see &status-414;).
1613</t>
1614<t>
1615   Various ad-hoc limitations on request-target length are found in practice.
1616   It is &RECOMMENDED; that all HTTP senders and recipients support
1617   request-target lengths of 8000 or more octets.
1618</t>
1619<x:note>
1620  <t>
1621    <x:h>Note:</x:h> Fragments (<xref target="RFC3986" x:fmt="," x:sec="3.5"/>)
1622    are not part of the request-target and thus will not be transmitted
1623    in an HTTP request.
1624  </t>
1625</x:note>
1626</section>
1627</section>
1628
1629<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1630<t>
1631   The exact resource identified by an Internet request is determined by
1632   examining both the request-target and the Host header field.
1633</t>
1634<t>
1635   An origin server that does not allow resources to differ by the
1636   requested host &MAY; ignore the Host header field value when
1637   determining the resource identified by an HTTP/1.1 request. (But see
1638   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1639   for other requirements on Host support in HTTP/1.1.)
1640</t>
1641<t>
1642   An origin server that does differentiate resources based on the host
1643   requested (sometimes referred to as virtual hosts or vanity host
1644   names) &MUST; use the following rules for determining the requested
1645   resource on an HTTP/1.1 request:
1646  <list style="numbers">
1647    <t>If request-target is an absolute-URI, the host is part of the
1648     request-target. Any Host header field value in the request &MUST; be
1649     ignored.</t>
1650    <t>If the request-target is not an absolute-URI, and the request includes
1651     a Host header field, the host is determined by the Host header
1652     field value.</t>
1653    <t>If the host as determined by rule 1 or 2 is not a valid host on
1654     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1655  </list>
1656</t>
1657<t>
1658   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1659   attempt to use heuristics (e.g., examination of the URI path for
1660   something unique to a particular host) in order to determine what
1661   exact resource is being requested.
1662</t>
1663</section>
1664
1665<section title="Effective Request URI" anchor="effective.request.uri">
1666  <iref primary="true" item="effective request URI"/>
1667  <iref primary="true" item="target resource"/>
1668<t>
1669   HTTP requests often do not carry the absolute URI (<xref target="RFC3986" x:fmt="," x:sec="4.3"/>)
1670   for the target resource; instead, the URI needs to be inferred from the
1671   request-target, Host header field, and connection context. The result of
1672   this process is called the "effective request URI".  The "target resource"
1673   is the resource identified by the effective request URI.
1674</t>
1675<t>
1676   If the request-target is an absolute-URI, then the effective request URI is
1677   the request-target.
1678</t>
1679<t>
1680   If the request-target uses the path-absolute form or the asterisk form,
1681   and the Host header field is present, then the effective request URI is
1682   constructed by concatenating
1683</t>
1684<t>
1685  <list style="symbols">
1686    <t>
1687      the scheme name: "http" if the request was received over an insecure
1688      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1689      connection,
1690    </t>
1691    <t>
1692      the character sequence "://",
1693    </t>
1694    <t>
1695      the authority component, as specified in the Host header field
1696      (<xref target="header.host"/>), and
1697    </t>
1698    <t>
1699      the request-target obtained from the Request-Line, unless the
1700      request-target is just the asterisk "*".
1701    </t>
1702  </list>
1703</t>
1704<t>
1705   If the request-target uses the path-absolute form or the asterisk form,
1706   and the Host header field is not present, then the effective request URI is
1707   undefined.
1708</t>
1709<t>
1710   Otherwise, when request-target uses the authority form, the effective
1711   request URI is undefined.
1712</t>
1713<figure>
1714<preamble>
1715   Example 1: the effective request URI for the message
1716</preamble> 
1717<artwork type="example" x:indent-with="  ">
1718GET /pub/WWW/TheProject.html HTTP/1.1
1719Host: www.example.org:8080
1720</artwork>
1721<postamble>
1722  (received over an insecure TCP connection) is "http", plus "://", plus the
1723  authority component "www.example.org:8080", plus the request-target
1724  "/pub/WWW/TheProject.html", thus
1725  "http://www.example.org:8080/pub/WWW/TheProject.html".
1726</postamble>
1727</figure>
1728<figure>
1729<preamble>
1730   Example 2: the effective request URI for the message
1731</preamble> 
1732<artwork type="example" x:indent-with="  ">
1733GET * HTTP/1.1
1734Host: www.example.org
1735</artwork>
1736<postamble>
1737  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1738  authority component "www.example.org", thus "https://www.example.org".
1739</postamble>
1740</figure>
1741<t>
1742   Effective request URIs are compared using the rules described in
1743   <xref target="uri.comparison"/>, except that empty path components &MUST-NOT;
1744   be treated as equivalent to an absolute path of "/".
1745</t> 
1746</section>
1747
1748</section>
1749
1750
1751<section title="Response" anchor="response">
1752  <x:anchor-alias value="Response"/>
1753<t>
1754   After receiving and interpreting a request message, a server responds
1755   with an HTTP response message.
1756</t>
1757<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1758  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1759                  *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )    ; <xref target="header.fields"/>
1760                  <x:ref>CRLF</x:ref>
1761                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1762</artwork></figure>
1763
1764<section title="Status-Line" anchor="status-line">
1765  <x:anchor-alias value="Status-Line"/>
1766<t>
1767   The first line of a Response message is the Status-Line, consisting
1768   of the protocol version followed by a numeric status code and its
1769   associated textual phrase, with each element separated by SP
1770   characters. No CR or LF is allowed except in the final CRLF sequence.
1771</t>
1772<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1773  <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>
1774</artwork></figure>
1775
1776<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1777  <x:anchor-alias value="Reason-Phrase"/>
1778  <x:anchor-alias value="Status-Code"/>
1779<t>
1780   The Status-Code element is a 3-digit integer result code of the
1781   attempt to understand and satisfy the request. These codes are fully
1782   defined in &status-codes;.  The Reason Phrase exists for the sole
1783   purpose of providing a textual description associated with the numeric
1784   status code, out of deference to earlier Internet application protocols
1785   that were more frequently used with interactive text clients.
1786   A client &SHOULD; ignore the content of the Reason Phrase.
1787</t>
1788<t>
1789   The first digit of the Status-Code defines the class of response. The
1790   last two digits do not have any categorization role. There are 5
1791   values for the first digit:
1792  <list style="symbols">
1793    <t>
1794      1xx: Informational - Request received, continuing process
1795    </t>
1796    <t>
1797      2xx: Success - The action was successfully received,
1798        understood, and accepted
1799    </t>
1800    <t>
1801      3xx: Redirection - Further action must be taken in order to
1802        complete the request
1803    </t>
1804    <t>
1805      4xx: Client Error - The request contains bad syntax or cannot
1806        be fulfilled
1807    </t>
1808    <t>
1809      5xx: Server Error - The server failed to fulfill an apparently
1810        valid request
1811    </t>
1812  </list>
1813</t>
1814<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"/>
1815  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1816  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1817</artwork></figure>
1818</section>
1819</section>
1820
1821</section>
1822
1823
1824<section title="Protocol Parameters" anchor="protocol.parameters">
1825
1826<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1827  <x:anchor-alias value="HTTP-date"/>
1828<t>
1829   HTTP applications have historically allowed three different formats
1830   for date/time stamps. However, the preferred format is a fixed-length subset
1831   of that defined by <xref target="RFC1123"/>:
1832</t>
1833<figure><artwork type="example" x:indent-with="  ">
1834Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1835</artwork></figure>
1836<t>
1837   The other formats are described here only for compatibility with obsolete
1838   implementations.
1839</t>
1840<figure><artwork type="example" x:indent-with="  ">
1841Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1842Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1843</artwork></figure>
1844<t>
1845   HTTP/1.1 clients and servers that parse a date value &MUST; accept
1846   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1847   only generate the RFC 1123 format for representing HTTP-date values
1848   in header fields. See <xref target="tolerant.applications"/> for further information.
1849</t>
1850<t>
1851   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1852   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1853   equal to UTC (Coordinated Universal Time). This is indicated in the
1854   first two formats by the inclusion of "GMT" as the three-letter
1855   abbreviation for time zone, and &MUST; be assumed when reading the
1856   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1857   additional whitespace beyond that specifically included as SP in the
1858   grammar.
1859</t>
1860<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1861  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1862</artwork></figure>
1863<t anchor="preferred.date.format">
1864  <x:anchor-alias value="rfc1123-date"/>
1865  <x:anchor-alias value="time-of-day"/>
1866  <x:anchor-alias value="hour"/>
1867  <x:anchor-alias value="minute"/>
1868  <x:anchor-alias value="second"/>
1869  <x:anchor-alias value="day-name"/>
1870  <x:anchor-alias value="day"/>
1871  <x:anchor-alias value="month"/>
1872  <x:anchor-alias value="year"/>
1873  <x:anchor-alias value="GMT"/>
1874  Preferred format:
1875</t>
1876<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"/>
1877  <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>
1878  ; fixed length subset of the format defined in
1879  ; <xref target="RFC1123" x:fmt="of" x:sec="5.2.14"/>
1880 
1881  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1882               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1883               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1884               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1885               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1886               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1887               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1888               
1889  <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>
1890               ; e.g., 02 Jun 1982
1891
1892  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1893  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1894               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1895               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1896               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1897               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1898               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1899               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1900               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1901               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1902               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1903               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1904               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1905  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1906
1907  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1908
1909  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1910                 ; 00:00:00 - 23:59:59
1911                 
1912  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1913  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1914  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1915</artwork></figure>
1916<t>
1917  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1918  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1919  same as those defined for the RFC 5322 constructs
1920  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1921</t>
1922<t anchor="obsolete.date.formats">
1923  <x:anchor-alias value="obs-date"/>
1924  <x:anchor-alias value="rfc850-date"/>
1925  <x:anchor-alias value="asctime-date"/>
1926  <x:anchor-alias value="date1"/>
1927  <x:anchor-alias value="date2"/>
1928  <x:anchor-alias value="date3"/>
1929  <x:anchor-alias value="rfc1123-date"/>
1930  <x:anchor-alias value="day-name-l"/>
1931  Obsolete formats:
1932</t>
1933<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1934  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1935</artwork></figure>
1936<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1937  <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>
1938  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1939                 ; day-month-year (e.g., 02-Jun-82)
1940
1941  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1942         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1943         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1944         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1945         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1946         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1947         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1948</artwork></figure>
1949<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1950  <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>
1951  <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> ))
1952                 ; month day (e.g., Jun  2)
1953</artwork></figure>
1954<x:note>
1955  <t>
1956    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1957    accepting date values that might have been sent by non-HTTP
1958    applications, as is sometimes the case when retrieving or posting
1959    messages via proxies/gateways to SMTP or NNTP.
1960  </t>
1961</x:note>
1962<x:note>
1963  <t>
1964    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1965    to their usage within the protocol stream. Clients and servers are
1966    not required to use these formats for user presentation, request
1967    logging, etc.
1968  </t>
1969</x:note>
1970</section>
1971
1972<section title="Transfer Codings" anchor="transfer.codings">
1973  <x:anchor-alias value="transfer-coding"/>
1974  <x:anchor-alias value="transfer-extension"/>
1975<t>
1976   Transfer-coding values are used to indicate an encoding
1977   transformation that has been, can be, or might need to be applied to a
1978   payload body in order to ensure "safe transport" through the network.
1979   This differs from a content coding in that the transfer-coding is a
1980   property of the message rather than a property of the representation
1981   that is being transferred.
1982</t>
1983<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1984  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1985                          / "compress" ; <xref target="compress.coding"/>
1986                          / "deflate" ; <xref target="deflate.coding"/>
1987                          / "gzip" ; <xref target="gzip.coding"/>
1988                          / <x:ref>transfer-extension</x:ref>
1989  <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> )
1990</artwork></figure>
1991<t anchor="rule.parameter">
1992  <x:anchor-alias value="attribute"/>
1993  <x:anchor-alias value="transfer-parameter"/>
1994  <x:anchor-alias value="value"/>
1995   Parameters are in the form of attribute/value pairs.
1996</t>
1997<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"/>
1998  <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>
1999  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
2000  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
2001</artwork></figure>
2002<t>
2003   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2004   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2005   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2006</t>
2007<t>
2008   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2009   MIME, which were designed to enable safe transport of binary data over a
2010   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
2011   However, safe transport
2012   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2013   the only unsafe characteristic of message-bodies is the difficulty in
2014   determining the exact message body length (<xref target="message.body"/>),
2015   or the desire to encrypt data over a shared transport.
2016</t>
2017<t>
2018   A server that receives a request message with a transfer-coding it does
2019   not understand &SHOULD; respond with 501 (Not Implemented) and then
2020   close the connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
2021   client.
2022</t>
2023
2024<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2025  <iref item="chunked (Coding Format)"/>
2026  <iref item="Coding Format" subitem="chunked"/>
2027  <x:anchor-alias value="chunk"/>
2028  <x:anchor-alias value="Chunked-Body"/>
2029  <x:anchor-alias value="chunk-data"/>
2030  <x:anchor-alias value="chunk-ext"/>
2031  <x:anchor-alias value="chunk-ext-name"/>
2032  <x:anchor-alias value="chunk-ext-val"/>
2033  <x:anchor-alias value="chunk-size"/>
2034  <x:anchor-alias value="last-chunk"/>
2035  <x:anchor-alias value="trailer-part"/>
2036  <x:anchor-alias value="quoted-str-nf"/>
2037  <x:anchor-alias value="qdtext-nf"/>
2038<t>
2039   The chunked encoding modifies the body of a message in order to
2040   transfer it as a series of chunks, each with its own size indicator,
2041   followed by an &OPTIONAL; trailer containing header fields. This
2042   allows dynamically produced content to be transferred along with the
2043   information necessary for the recipient to verify that it has
2044   received the full message.
2045</t>
2046<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"/>
2047  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
2048                   <x:ref>last-chunk</x:ref>
2049                   <x:ref>trailer-part</x:ref>
2050                   <x:ref>CRLF</x:ref>
2051 
2052  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2053                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
2054  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
2055  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
2056 
2057  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
2058                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
2059  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
2060  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
2061  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
2062  <x:ref>trailer-part</x:ref>   = *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
2063 
2064  <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>
2065                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
2066  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
2067                 ; <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> 
2068</artwork></figure>
2069<t>
2070   The chunk-size field is a string of hex digits indicating the size of
2071   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2072   zero, followed by the trailer, which is terminated by an empty line.
2073</t>
2074<t>
2075   The trailer allows the sender to include additional HTTP header
2076   fields at the end of the message. The Trailer header field can be
2077   used to indicate which header fields are included in a trailer (see
2078   <xref target="header.trailer"/>).
2079</t>
2080<t>
2081   A server using chunked transfer-coding in a response &MUST-NOT; use the
2082   trailer for any header fields unless at least one of the following is
2083   true:
2084  <list style="numbers">
2085    <t>the request included a TE header field that indicates "trailers" is
2086     acceptable in the transfer-coding of the  response, as described in
2087     <xref target="header.te"/>; or,</t>
2088     
2089    <t>the trailer fields consist entirely of optional metadata, and the
2090    recipient could use the message (in a manner acceptable to the server where
2091    the field originated) without receiving it. In other words, the server that
2092    generated the header (often but not always the origin server) is willing to
2093    accept the possibility that the trailer fields might be silently discarded
2094    along the path to the client.</t>
2095  </list>
2096</t>
2097<t>
2098   This requirement prevents an interoperability failure when the
2099   message is being received by an HTTP/1.1 (or later) proxy and
2100   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2101   compliance with the protocol would have necessitated a possibly
2102   infinite buffer on the proxy.
2103</t>
2104<t>
2105   A process for decoding the "chunked" transfer-coding
2106   can be represented in pseudo-code as:
2107</t>
2108<figure><artwork type="code">
2109  length := 0
2110  read chunk-size, chunk-ext (if any) and CRLF
2111  while (chunk-size &gt; 0) {
2112     read chunk-data and CRLF
2113     append chunk-data to decoded-body
2114     length := length + chunk-size
2115     read chunk-size and CRLF
2116  }
2117  read header-field
2118  while (header-field not empty) {
2119     append header-field to existing header fields
2120     read header-field
2121  }
2122  Content-Length := length
2123  Remove "chunked" from Transfer-Encoding
2124</artwork></figure>
2125<t>
2126   All HTTP/1.1 applications &MUST; be able to receive and decode the
2127   "chunked" transfer-coding and &MUST; ignore chunk-ext extensions
2128   they do not understand.
2129</t>
2130<t>
2131   Since "chunked" is the only transfer-coding required to be understood
2132   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2133   on a persistent connection.  Whenever a transfer-coding is applied to
2134   a payload body in a request, the final transfer-coding applied &MUST;
2135   be "chunked".  If a transfer-coding is applied to a response payload
2136   body, then either the final transfer-coding applied &MUST; be "chunked"
2137   or the message &MUST; be terminated by closing the connection. When the
2138   "chunked" transfer-coding is used, it &MUST; be the last transfer-coding
2139   applied to form the message-body. The "chunked" transfer-coding &MUST-NOT;
2140   be applied more than once in a message-body.
2141</t>
2142</section>
2143
2144<section title="Compression Codings" anchor="compression.codings">
2145<t>
2146   The codings defined below can be used to compress the payload of a
2147   message.
2148</t>
2149<x:note><t>
2150   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
2151   is not desirable and is discouraged for future encodings. Their
2152   use here is representative of historical practice, not good
2153   design.
2154</t></x:note>
2155<x:note><t>
2156   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2157   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2158   equivalent to "gzip" and "compress" respectively.
2159</t></x:note>
2160
2161<section title="Compress Coding" anchor="compress.coding">
2162<iref item="compress (Coding Format)"/>
2163<iref item="Coding Format" subitem="compress"/>
2164<t>
2165   The "compress" format is produced by the common UNIX file compression
2166   program "compress". This format is an adaptive Lempel-Ziv-Welch
2167   coding (LZW).
2168</t>
2169</section>
2170
2171<section title="Deflate Coding" anchor="deflate.coding">
2172<iref item="deflate (Coding Format)"/>
2173<iref item="Coding Format" subitem="deflate"/>
2174<t>
2175   The "deflate" format is defined as the "deflate" compression mechanism
2176   (described in <xref target="RFC1951"/>) used inside the "zlib"
2177   data format (<xref target="RFC1950"/>).
2178</t>
2179<x:note>
2180  <t>
2181    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2182    compressed data without the zlib wrapper.
2183   </t>
2184</x:note>
2185</section>
2186
2187<section title="Gzip Coding" anchor="gzip.coding">
2188<iref item="gzip (Coding Format)"/>
2189<iref item="Coding Format" subitem="gzip"/>
2190<t>
2191   The "gzip" format is produced by the file compression program
2192   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2193   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2194</t>
2195</section>
2196
2197</section>
2198
2199<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2200<t>
2201   The HTTP Transfer Coding Registry defines the name space for the transfer
2202   coding names.
2203</t>
2204<t>
2205   Registrations &MUST; include the following fields:
2206   <list style="symbols">
2207     <t>Name</t>
2208     <t>Description</t>
2209     <t>Pointer to specification text</t>
2210   </list>
2211</t>
2212<t>
2213   Names of transfer codings &MUST-NOT; overlap with names of content codings
2214   (&content-codings;), unless the encoding transformation is identical (as it
2215   is the case for the compression codings defined in
2216   <xref target="compression.codings"/>).
2217</t>
2218<t>
2219   Values to be added to this name space require a specification
2220   (see "Specification Required" in <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2221   conform to the purpose of transfer coding defined in this section.
2222</t>
2223<t>
2224   The registry itself is maintained at
2225   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2226</t>
2227</section>
2228</section>
2229
2230<section title="Product Tokens" anchor="product.tokens">
2231  <x:anchor-alias value="product"/>
2232  <x:anchor-alias value="product-version"/>
2233<t>
2234   Product tokens are used to allow communicating applications to
2235   identify themselves by software name and version. Most fields using
2236   product tokens also allow sub-products which form a significant part
2237   of the application to be listed, separated by whitespace. By
2238   convention, the products are listed in order of their significance
2239   for identifying the application.
2240</t>
2241<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2242  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2243  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2244</artwork></figure>
2245<t>
2246   Examples:
2247</t>
2248<figure><artwork type="example">
2249  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2250  Server: Apache/0.8.4
2251</artwork></figure>
2252<t>
2253   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2254   used for advertising or other non-essential information. Although any
2255   token character &MAY; appear in a product-version, this token &SHOULD;
2256   only be used for a version identifier (i.e., successive versions of
2257   the same product &SHOULD; only differ in the product-version portion of
2258   the product value).
2259</t>
2260</section>
2261
2262<section title="Quality Values" anchor="quality.values">
2263  <x:anchor-alias value="qvalue"/>
2264<t>
2265   Both transfer codings (TE request header field, <xref target="header.te"/>)
2266   and content negotiation (&content.negotiation;) use short "floating point"
2267   numbers to indicate the relative importance ("weight") of various
2268   negotiable parameters.  A weight is normalized to a real number in
2269   the range 0 through 1, where 0 is the minimum and 1 the maximum
2270   value. If a parameter has a quality value of 0, then content with
2271   this parameter is "not acceptable" for the client. HTTP/1.1
2272   applications &MUST-NOT; generate more than three digits after the
2273   decimal point. User configuration of these values &SHOULD; also be
2274   limited in this fashion.
2275</t>
2276<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2277  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2278                 / ( "1" [ "." 0*3("0") ] )
2279</artwork></figure>
2280<x:note>
2281  <t>
2282     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2283     relative degradation in desired quality.
2284  </t>
2285</x:note>
2286</section>
2287
2288</section>
2289
2290<section title="Connections" anchor="connections">
2291
2292<section title="Persistent Connections" anchor="persistent.connections">
2293
2294<section title="Purpose" anchor="persistent.purpose">
2295<t>
2296   Prior to persistent connections, a separate TCP connection was
2297   established to fetch each URL, increasing the load on HTTP servers
2298   and causing congestion on the Internet. The use of inline images and
2299   other associated data often requires a client to make multiple
2300   requests of the same server in a short amount of time. Analysis of
2301   these performance problems and results from a prototype
2302   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2303   measurements of actual HTTP/1.1 implementations show good
2304   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2305   T/TCP <xref target="Tou1998"/>.
2306</t>
2307<t>
2308   Persistent HTTP connections have a number of advantages:
2309  <list style="symbols">
2310      <t>
2311        By opening and closing fewer TCP connections, CPU time is saved
2312        in routers and hosts (clients, servers, proxies, gateways,
2313        tunnels, or caches), and memory used for TCP protocol control
2314        blocks can be saved in hosts.
2315      </t>
2316      <t>
2317        HTTP requests and responses can be pipelined on a connection.
2318        Pipelining allows a client to make multiple requests without
2319        waiting for each response, allowing a single TCP connection to
2320        be used much more efficiently, with much lower elapsed time.
2321      </t>
2322      <t>
2323        Network congestion is reduced by reducing the number of packets
2324        caused by TCP opens, and by allowing TCP sufficient time to
2325        determine the congestion state of the network.
2326      </t>
2327      <t>
2328        Latency on subsequent requests is reduced since there is no time
2329        spent in TCP's connection opening handshake.
2330      </t>
2331      <t>
2332        HTTP can evolve more gracefully, since errors can be reported
2333        without the penalty of closing the TCP connection. Clients using
2334        future versions of HTTP might optimistically try a new feature,
2335        but if communicating with an older server, retry with old
2336        semantics after an error is reported.
2337      </t>
2338    </list>
2339</t>
2340<t>
2341   HTTP implementations &SHOULD; implement persistent connections.
2342</t>
2343</section>
2344
2345<section title="Overall Operation" anchor="persistent.overall">
2346<t>
2347   A significant difference between HTTP/1.1 and earlier versions of
2348   HTTP is that persistent connections are the default behavior of any
2349   HTTP connection. That is, unless otherwise indicated, the client
2350   &SHOULD; assume that the server will maintain a persistent connection,
2351   even after error responses from the server.
2352</t>
2353<t>
2354   Persistent connections provide a mechanism by which a client and a
2355   server can signal the close of a TCP connection. This signaling takes
2356   place using the Connection header field (<xref target="header.connection"/>). Once a close
2357   has been signaled, the client &MUST-NOT; send any more requests on that
2358   connection.
2359</t>
2360
2361<section title="Negotiation" anchor="persistent.negotiation">
2362<t>
2363   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2364   maintain a persistent connection unless a Connection header field including
2365   the connection-token "close" was sent in the request. If the server
2366   chooses to close the connection immediately after sending the
2367   response, it &SHOULD; send a Connection header field including the
2368   connection-token "close".
2369</t>
2370<t>
2371   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2372   decide to keep it open based on whether the response from a server
2373   contains a Connection header field with the connection-token close. In case
2374   the client does not want to maintain a connection for more than that
2375   request, it &SHOULD; send a Connection header field including the
2376   connection-token close.
2377</t>
2378<t>
2379   If either the client or the server sends the close token in the
2380   Connection header field, that request becomes the last one for the
2381   connection.
2382</t>
2383<t>
2384   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2385   maintained for HTTP versions less than 1.1 unless it is explicitly
2386   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2387   compatibility with HTTP/1.0 clients.
2388</t>
2389<t>
2390   In order to remain persistent, all messages on the connection &MUST;
2391   have a self-defined message length (i.e., one not defined by closure
2392   of the connection), as described in <xref target="message.body"/>.
2393</t>
2394</section>
2395
2396<section title="Pipelining" anchor="pipelining">
2397<t>
2398   A client that supports persistent connections &MAY; "pipeline" its
2399   requests (i.e., send multiple requests without waiting for each
2400   response). A server &MUST; send its responses to those requests in the
2401   same order that the requests were received.
2402</t>
2403<t>
2404   Clients which assume persistent connections and pipeline immediately
2405   after connection establishment &SHOULD; be prepared to retry their
2406   connection if the first pipelined attempt fails. If a client does
2407   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2408   persistent. Clients &MUST; also be prepared to resend their requests if
2409   the server closes the connection before sending all of the
2410   corresponding responses.
2411</t>
2412<t>
2413   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2414   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2415   premature termination of the transport connection could lead to
2416   indeterminate results. A client wishing to send a non-idempotent
2417   request &SHOULD; wait to send that request until it has received the
2418   response status line for the previous request.
2419</t>
2420</section>
2421</section>
2422
2423<section title="Proxy Servers" anchor="persistent.proxy">
2424<t>
2425   It is especially important that proxies correctly implement the
2426   properties of the Connection header field as specified in <xref target="header.connection"/>.
2427</t>
2428<t>
2429   The proxy server &MUST; signal persistent connections separately with
2430   its clients and the origin servers (or other proxy servers) that it
2431   connects to. Each persistent connection applies to only one transport
2432   link.
2433</t>
2434<t>
2435   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2436   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2437   for information and discussion of the problems with the Keep-Alive header field
2438   implemented by many HTTP/1.0 clients).
2439</t>
2440
2441<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2442<!--<t>
2443  <cref anchor="TODO-end-to-end" source="jre">
2444    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2445    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2446  </cref>
2447</t>-->
2448<t>
2449   For the purpose of defining the behavior of caches and non-caching
2450   proxies, we divide HTTP header fields into two categories:
2451  <list style="symbols">
2452      <t>End-to-end header fields, which are  transmitted to the ultimate
2453        recipient of a request or response. End-to-end header fields in
2454        responses MUST be stored as part of a cache entry and &MUST; be
2455        transmitted in any response formed from a cache entry.</t>
2456
2457      <t>Hop-by-hop header fields, which are meaningful only for a single
2458        transport-level connection, and are not stored by caches or
2459        forwarded by proxies.</t>
2460  </list>
2461</t>
2462<t>
2463   The following HTTP/1.1 header fields are hop-by-hop header fields:
2464  <list style="symbols">
2465      <t>Connection</t>
2466      <t>Keep-Alive</t>
2467      <t>Proxy-Authenticate</t>
2468      <t>Proxy-Authorization</t>
2469      <t>TE</t>
2470      <t>Trailer</t>
2471      <t>Transfer-Encoding</t>
2472      <t>Upgrade</t>
2473  </list>
2474</t>
2475<t>
2476   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2477</t>
2478<t>
2479   Other hop-by-hop header fields &MUST; be listed in a Connection header field
2480   (<xref target="header.connection"/>).
2481</t>
2482</section>
2483
2484<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2485<!--<t>
2486  <cref anchor="TODO-non-mod-headers" source="jre">
2487    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2488    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2489  </cref>
2490</t>-->
2491<t>
2492   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2493   value of certain end-to-end header fields. A transparent proxy &SHOULD-NOT;
2494   modify an end-to-end header field unless the definition of that header field requires
2495   or specifically allows that.
2496</t>
2497<t>
2498   A transparent proxy &MUST-NOT; modify any of the following fields in a
2499   request or response, and it &MUST-NOT; add any of these fields if not
2500   already present:
2501  <list style="symbols">
2502      <t>Content-Location</t>
2503      <t>Content-MD5</t>
2504      <t>ETag</t>
2505      <t>Last-Modified</t>
2506  </list>
2507</t>
2508<t>
2509   A transparent proxy &MUST-NOT; modify any of the following fields in a
2510   response:
2511  <list style="symbols">
2512    <t>Expires</t>
2513  </list>
2514</t>
2515<t>
2516   but it &MAY; add any of these fields if not already present. If an
2517   Expires header field is added, it &MUST; be given a field-value identical to
2518   that of the Date header field in that response.
2519</t>
2520<t>
2521   A proxy &MUST-NOT; modify or add any of the following fields in a
2522   message that contains the no-transform cache-control directive, or in
2523   any request:
2524  <list style="symbols">
2525    <t>Content-Encoding</t>
2526    <t>Content-Range</t>
2527    <t>Content-Type</t>
2528  </list>
2529</t>
2530<t>
2531   A non-transparent proxy &MAY; modify or add these fields to a message
2532   that does not include no-transform, but if it does so, it &MUST; add a
2533   Warning 214 (Transformation applied) if one does not already appear
2534   in the message (see &header-warning;).
2535</t>
2536<x:note>
2537  <t>
2538    <x:h>Warning:</x:h> Unnecessary modification of end-to-end header fields might
2539    cause authentication failures if stronger authentication
2540    mechanisms are introduced in later versions of HTTP. Such
2541    authentication mechanisms &MAY; rely on the values of header fields
2542    not listed here.
2543  </t>
2544</x:note>
2545<t>
2546   A transparent proxy &MUST; preserve the message payload (&payload;),
2547   though it &MAY; change the message-body through application or removal
2548   of a transfer-coding (<xref target="transfer.codings"/>).
2549</t>
2550</section>
2551
2552</section>
2553
2554<section title="Practical Considerations" anchor="persistent.practical">
2555<t>
2556   Servers will usually have some time-out value beyond which they will
2557   no longer maintain an inactive connection. Proxy servers might make
2558   this a higher value since it is likely that the client will be making
2559   more connections through the same server. The use of persistent
2560   connections places no requirements on the length (or existence) of
2561   this time-out for either the client or the server.
2562</t>
2563<t>
2564   When a client or server wishes to time-out it &SHOULD; issue a graceful
2565   close on the transport connection. Clients and servers &SHOULD; both
2566   constantly watch for the other side of the transport close, and
2567   respond to it as appropriate. If a client or server does not detect
2568   the other side's close promptly it could cause unnecessary resource
2569   drain on the network.
2570</t>
2571<t>
2572   A client, server, or proxy &MAY; close the transport connection at any
2573   time. For example, a client might have started to send a new request
2574   at the same time that the server has decided to close the "idle"
2575   connection. From the server's point of view, the connection is being
2576   closed while it was idle, but from the client's point of view, a
2577   request is in progress.
2578</t>
2579<t>
2580   This means that clients, servers, and proxies &MUST; be able to recover
2581   from asynchronous close events. Client software &SHOULD; reopen the
2582   transport connection and retransmit the aborted sequence of requests
2583   without user interaction so long as the request sequence is
2584   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2585   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2586   human operator the choice of retrying the request(s). Confirmation by
2587   user-agent software with semantic understanding of the application
2588   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2589   be repeated if the second sequence of requests fails.
2590</t>
2591<t>
2592   Servers &SHOULD; always respond to at least one request per connection,
2593   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2594   middle of transmitting a response, unless a network or client failure
2595   is suspected.
2596</t>
2597<t>
2598   Clients (including proxies) &SHOULD; limit the number of simultaneous
2599   connections that they maintain to a given server (including proxies).
2600</t>
2601<t>
2602   Previous revisions of HTTP gave a specific number of connections as a
2603   ceiling, but this was found to be impractical for many applications. As a
2604   result, this specification does not mandate a particular maximum number of
2605   connections, but instead encourages clients to be conservative when opening
2606   multiple connections.
2607</t>
2608<t>
2609   In particular, while using multiple connections avoids the "head-of-line
2610   blocking" problem (whereby a request that takes significant server-side
2611   processing and/or has a large payload can block subsequent requests on the
2612   same connection), each connection used consumes server resources (sometimes
2613   significantly), and furthermore using multiple connections can cause
2614   undesirable side effects in congested networks.
2615</t>
2616<t>
2617   Note that servers might reject traffic that they deem abusive, including an
2618   excessive number of connections from a client.
2619</t>
2620</section>
2621</section>
2622
2623<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2624
2625<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2626<t>
2627   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2628   flow control mechanisms to resolve temporary overloads, rather than
2629   terminating connections with the expectation that clients will retry.
2630   The latter technique can exacerbate network congestion.
2631</t>
2632</section>
2633
2634<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2635<t>
2636   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2637   the network connection for an error status code while it is transmitting
2638   the request. If the client sees an error status code, it &SHOULD;
2639   immediately cease transmitting the body. If the body is being sent
2640   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2641   empty trailer &MAY; be used to prematurely mark the end of the message.
2642   If the body was preceded by a Content-Length header field, the client &MUST;
2643   close the connection.
2644</t>
2645</section>
2646
2647<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2648<t>
2649   The purpose of the 100 (Continue) status code (see &status-100;) is to
2650   allow a client that is sending a request message with a request body
2651   to determine if the origin server is willing to accept the request
2652   (based on the request header fields) before the client sends the request
2653   body. In some cases, it might either be inappropriate or highly
2654   inefficient for the client to send the body if the server will reject
2655   the message without looking at the body.
2656</t>
2657<t>
2658   Requirements for HTTP/1.1 clients:
2659  <list style="symbols">
2660    <t>
2661        If a client will wait for a 100 (Continue) response before
2662        sending the request body, it &MUST; send an Expect request-header
2663        field (&header-expect;) with the "100-continue" expectation.
2664    </t>
2665    <t>
2666        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2667        with the "100-continue" expectation if it does not intend
2668        to send a request body.
2669    </t>
2670  </list>
2671</t>
2672<t>
2673   Because of the presence of older implementations, the protocol allows
2674   ambiguous situations in which a client might send "Expect: 100-continue"
2675   without receiving either a 417 (Expectation Failed)
2676   or a 100 (Continue) status code. Therefore, when a client sends this
2677   header field to an origin server (possibly via a proxy) from which it
2678   has never seen a 100 (Continue) status code, the client &SHOULD-NOT; 
2679   wait for an indefinite period before sending the request body.
2680</t>
2681<t>
2682   Requirements for HTTP/1.1 origin servers:
2683  <list style="symbols">
2684    <t> Upon receiving a request which includes an Expect request-header
2685        field with the "100-continue" expectation, an origin server &MUST;
2686        either respond with 100 (Continue) status code and continue to read
2687        from the input stream, or respond with a final status code. The
2688        origin server &MUST-NOT; wait for the request body before sending
2689        the 100 (Continue) response. If it responds with a final status
2690        code, it &MAY; close the transport connection or it &MAY; continue
2691        to read and discard the rest of the request.  It &MUST-NOT;
2692        perform the requested method if it returns a final status code.
2693    </t>
2694    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2695        the request message does not include an Expect request-header
2696        field with the "100-continue" expectation, and &MUST-NOT; send a
2697        100 (Continue) response if such a request comes from an HTTP/1.0
2698        (or earlier) client. There is an exception to this rule: for
2699        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2700        status code in response to an HTTP/1.1 PUT or POST request that does
2701        not include an Expect request-header field with the "100-continue"
2702        expectation. This exception, the purpose of which is
2703        to minimize any client processing delays associated with an
2704        undeclared wait for 100 (Continue) status code, applies only to
2705        HTTP/1.1 requests, and not to requests with any other HTTP-version
2706        value.
2707    </t>
2708    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2709        already received some or all of the request body for the
2710        corresponding request.
2711    </t>
2712    <t> An origin server that sends a 100 (Continue) response &MUST;
2713    ultimately send a final status code, once the request body is
2714        received and processed, unless it terminates the transport
2715        connection prematurely.
2716    </t>
2717    <t> If an origin server receives a request that does not include an
2718        Expect request-header field with the "100-continue" expectation,
2719        the request includes a request body, and the server responds
2720        with a final status code before reading the entire request body
2721        from the transport connection, then the server &SHOULD-NOT;  close
2722        the transport connection until it has read the entire request,
2723        or until the client closes the connection. Otherwise, the client
2724        might not reliably receive the response message. However, this
2725        requirement is not be construed as preventing a server from
2726        defending itself against denial-of-service attacks, or from
2727        badly broken client implementations.
2728      </t>
2729    </list>
2730</t>
2731<t>
2732   Requirements for HTTP/1.1 proxies:
2733  <list style="symbols">
2734    <t> If a proxy receives a request that includes an Expect request-header
2735        field with the "100-continue" expectation, and the proxy
2736        either knows that the next-hop server complies with HTTP/1.1 or
2737        higher, or does not know the HTTP version of the next-hop
2738        server, it &MUST; forward the request, including the Expect header
2739        field.
2740    </t>
2741    <t> If the proxy knows that the version of the next-hop server is
2742        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2743        respond with a 417 (Expectation Failed) status code.
2744    </t>
2745    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2746        numbers received from recently-referenced next-hop servers.
2747    </t>
2748    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2749        request message was received from an HTTP/1.0 (or earlier)
2750        client and did not include an Expect request-header field with
2751        the "100-continue" expectation. This requirement overrides the
2752        general rule for forwarding of 1xx responses (see &status-1xx;).
2753    </t>
2754  </list>
2755</t>
2756</section>
2757
2758<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2759<t>
2760   If an HTTP/1.1 client sends a request which includes a request body,
2761   but which does not include an Expect request-header field with the
2762   "100-continue" expectation, and if the client is not directly
2763   connected to an HTTP/1.1 origin server, and if the client sees the
2764   connection close before receiving a status line from the server, the
2765   client &SHOULD; retry the request.  If the client does retry this
2766   request, it &MAY; use the following "binary exponential backoff"
2767   algorithm to be assured of obtaining a reliable response:
2768  <list style="numbers">
2769    <t>
2770      Initiate a new connection to the server
2771    </t>
2772    <t>
2773      Transmit the request-header fields
2774    </t>
2775    <t>
2776      Initialize a variable R to the estimated round-trip time to the
2777         server (e.g., based on the time it took to establish the
2778         connection), or to a constant value of 5 seconds if the round-trip
2779         time is not available.
2780    </t>
2781    <t>
2782       Compute T = R * (2**N), where N is the number of previous
2783         retries of this request.
2784    </t>
2785    <t>
2786       Wait either for an error response from the server, or for T
2787         seconds (whichever comes first)
2788    </t>
2789    <t>
2790       If no error response is received, after T seconds transmit the
2791         body of the request.
2792    </t>
2793    <t>
2794       If client sees that the connection is closed prematurely,
2795         repeat from step 1 until the request is accepted, an error
2796         response is received, or the user becomes impatient and
2797         terminates the retry process.
2798    </t>
2799  </list>
2800</t>
2801<t>
2802   If at any point an error status code is received, the client
2803  <list style="symbols">
2804      <t>&SHOULD-NOT;  continue and</t>
2805
2806      <t>&SHOULD; close the connection if it has not completed sending the
2807        request message.</t>
2808    </list>
2809</t>
2810</section>
2811</section>
2812</section>
2813
2814
2815<section title="Miscellaneous notes that might disappear" anchor="misc">
2816<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2817<t>
2818   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2819</t>
2820</section>
2821
2822<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2823<t>
2824   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2825</t>
2826</section>
2827
2828<section title="Interception of HTTP for access control" anchor="http.intercept">
2829<t>
2830   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2831</t>
2832</section>
2833
2834<section title="Use of HTTP by other protocols" anchor="http.others">
2835<t>
2836   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2837   Extensions of HTTP like WebDAV.</cref>
2838</t>
2839
2840</section>
2841<section title="Use of HTTP by media type specification" anchor="http.media">
2842<t>
2843   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2844</t>
2845</section>
2846</section>
2847
2848<section title="Header Field Definitions" anchor="header.field.definitions">
2849<t>
2850   This section defines the syntax and semantics of HTTP/1.1 header fields
2851   related to message framing and transport protocols.
2852</t>
2853
2854<section title="Connection" anchor="header.connection">
2855  <iref primary="true" item="Connection header" x:for-anchor=""/>
2856  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2857  <x:anchor-alias value="Connection"/>
2858  <x:anchor-alias value="connection-token"/>
2859  <x:anchor-alias value="Connection-v"/>
2860<t>
2861   The "Connection" general-header field allows the sender to specify
2862   options that are desired for that particular connection and &MUST-NOT;
2863   be communicated by proxies over further connections.
2864</t>
2865<t>
2866   The Connection header field's value has the following grammar:
2867</t>
2868<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"/>
2869  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2870  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2871  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2872</artwork></figure>
2873<t>
2874   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2875   message is forwarded and, for each connection-token in this field,
2876   remove any header field(s) from the message with the same name as the
2877   connection-token. Connection options are signaled by the presence of
2878   a connection-token in the Connection header field, not by any
2879   corresponding additional header field(s), since the additional header
2880   field might not be sent if there are no parameters associated with that
2881   connection option.
2882</t>
2883<t>
2884   Message header fields listed in the Connection header field &MUST-NOT; include
2885   end-to-end header fields, such as Cache-Control.
2886</t>
2887<t>
2888   HTTP/1.1 defines the "close" connection option for the sender to
2889   signal that the connection will be closed after completion of the
2890   response. For example,
2891</t>
2892<figure><artwork type="example">
2893  Connection: close
2894</artwork></figure>
2895<t>
2896   in either the request or the response header fields indicates that
2897   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2898   after the current request/response is complete.
2899</t>
2900<t>
2901   An HTTP/1.1 client that does not support persistent connections &MUST;
2902   include the "close" connection option in every request message.
2903</t>
2904<t>
2905   An HTTP/1.1 server that does not support persistent connections &MUST;
2906   include the "close" connection option in every response message that
2907   does not have a 1xx (Informational) status code.
2908</t>
2909<t>
2910   A system receiving an HTTP/1.0 (or lower-version) message that
2911   includes a Connection header field &MUST;, for each connection-token in this
2912   field, remove and ignore any header field(s) from the message with
2913   the same name as the connection-token. This protects against mistaken
2914   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2915</t>
2916</section>
2917
2918<section title="Content-Length" anchor="header.content-length">
2919  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2920  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2921  <x:anchor-alias value="Content-Length"/>
2922  <x:anchor-alias value="Content-Length-v"/>
2923<t>
2924   The "Content-Length" header field indicates the size of the
2925   message-body, in decimal number of octets, for any message other than
2926   a response to the HEAD method or a response with a status code of 304.
2927   In the case of responses to the HEAD method, it indicates the size of
2928   the payload body (not including any potential transfer-coding) that
2929   would have been sent had the request been a GET.
2930   In the case of the 304 (Not Modified) response, it indicates the size of
2931   the payload body (not including any potential transfer-coding) that
2932   would have been sent in a 200 (OK) response.
2933</t>
2934<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2935  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2936  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2937</artwork></figure>
2938<t>
2939   An example is
2940</t>
2941<figure><artwork type="example">
2942  Content-Length: 3495
2943</artwork></figure>
2944<t>
2945   Implementations &SHOULD; use this field to indicate the message-body
2946   length when no transfer-coding is being applied and the
2947   payload's body length can be determined prior to being transferred.
2948   <xref target="message.body"/> describes how recipients determine the length
2949   of a message-body.
2950</t>
2951<t>
2952   Any Content-Length greater than or equal to zero is a valid value.
2953</t>
2954<t>
2955   Note that the use of this field in HTTP is significantly different from
2956   the corresponding definition in MIME, where it is an optional field
2957   used within the "message/external-body" content-type.
2958</t>
2959</section>
2960
2961<section title="Date" anchor="header.date">
2962  <iref primary="true" item="Date header" x:for-anchor=""/>
2963  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2964  <x:anchor-alias value="Date"/>
2965  <x:anchor-alias value="Date-v"/>
2966<t>
2967   The "Date" general-header field represents the date and time at which
2968   the message was originated, having the same semantics as the Origination
2969   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2970   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2971   it &MUST; be sent in rfc1123-date format.
2972</t>
2973<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2974  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2975  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2976</artwork></figure>
2977<t>
2978   An example is
2979</t>
2980<figure><artwork type="example">
2981  Date: Tue, 15 Nov 1994 08:12:31 GMT
2982</artwork></figure>
2983<t>
2984   Origin servers &MUST; include a Date header field in all responses,
2985   except in these cases:
2986  <list style="numbers">
2987      <t>If the response status code is 100 (Continue) or 101 (Switching
2988         Protocols), the response &MAY; include a Date header field, at
2989         the server's option.</t>
2990
2991      <t>If the response status code conveys a server error, e.g., 500
2992         (Internal Server Error) or 503 (Service Unavailable), and it is
2993         inconvenient or impossible to generate a valid Date.</t>
2994
2995      <t>If the server does not have a clock that can provide a
2996         reasonable approximation of the current time, its responses
2997         &MUST-NOT; include a Date header field. In this case, the rules
2998         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2999  </list>
3000</t>
3001<t>
3002   A received message that does not have a Date header field &MUST; be
3003   assigned one by the recipient if the message will be cached by that
3004   recipient or gatewayed via a protocol which requires a Date.
3005</t>
3006<t>
3007   Clients can use the Date header field as well; in order to keep request
3008   messages small, they are advised not to include it when it doesn't convey
3009   any useful information (as it is usually the case for requests that do not
3010   contain a payload).
3011</t>
3012<t>
3013   The HTTP-date sent in a Date header field &SHOULD-NOT;  represent a date and
3014   time subsequent to the generation of the message. It &SHOULD; represent
3015   the best available approximation of the date and time of message
3016   generation, unless the implementation has no means of generating a
3017   reasonably accurate date and time. In theory, the date ought to
3018   represent the moment just before the payload is generated. In
3019   practice, the date can be generated at any time during the message
3020   origination without affecting its semantic value.
3021</t>
3022
3023<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3024<t>
3025   Some origin server implementations might not have a clock available.
3026   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
3027   values to a response, unless these values were associated
3028   with the resource by a system or user with a reliable clock. It &MAY;
3029   assign an Expires value that is known, at or before server
3030   configuration time, to be in the past (this allows "pre-expiration"
3031   of responses without storing separate Expires values for each
3032   resource).
3033</t>
3034</section>
3035</section>
3036
3037<section title="Host" anchor="header.host">
3038  <iref primary="true" item="Host header" x:for-anchor=""/>
3039  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
3040  <x:anchor-alias value="Host"/>
3041  <x:anchor-alias value="Host-v"/>
3042<t>
3043   The "Host" request-header field specifies the Internet host and port
3044   number of the resource being requested, allowing the origin server or
3045   gateway to differentiate between internally-ambiguous URLs, such as the root
3046   "/" URL of a server for multiple host names on a single IP address.
3047</t>
3048<t>   
3049   The Host field value &MUST; represent the naming authority of the origin
3050   server or gateway given by the original URL obtained from the user or
3051   referring resource (generally an http URI, as described in
3052   <xref target="http.uri"/>).
3053</t>
3054<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
3055  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
3056  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
3057</artwork></figure>
3058<t>
3059   A "host" without any trailing port information implies the default
3060   port for the service requested (e.g., "80" for an HTTP URL). For
3061   example, a request on the origin server for
3062   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
3063</t>
3064<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
3065GET /pub/WWW/ HTTP/1.1
3066Host: www.example.org
3067</artwork></figure>
3068<t>
3069   A client &MUST; include a Host header field in all HTTP/1.1 request
3070   messages. If the requested URI does not include an Internet host
3071   name for the service being requested, then the Host header field &MUST;
3072   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
3073   request message it forwards does contain an appropriate Host header
3074   field that identifies the service being requested by the proxy. All
3075   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
3076   status code to any HTTP/1.1 request message which lacks a Host header
3077   field.
3078</t>
3079<t>
3080   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3081   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3082   for other requirements relating to Host.
3083</t>
3084</section>
3085
3086<section title="TE" anchor="header.te">
3087  <iref primary="true" item="TE header" x:for-anchor=""/>
3088  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
3089  <x:anchor-alias value="TE"/>
3090  <x:anchor-alias value="TE-v"/>
3091  <x:anchor-alias value="t-codings"/>
3092  <x:anchor-alias value="te-params"/>
3093  <x:anchor-alias value="te-ext"/>
3094<t>
3095   The "TE" request-header field indicates what extension transfer-codings
3096   it is willing to accept in the response, and whether or not it is
3097   willing to accept trailer fields in a chunked transfer-coding.
3098</t>
3099<t>
3100   Its value consists of the keyword "trailers" and/or a comma-separated
3101   list of extension transfer-coding names with optional accept
3102   parameters (as described in <xref target="transfer.codings"/>).
3103</t>
3104<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
3105  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
3106  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
3107  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
3108  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
3109  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
3110</artwork></figure>
3111<t>
3112   The presence of the keyword "trailers" indicates that the client is
3113   willing to accept trailer fields in a chunked transfer-coding, as
3114   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3115   transfer-coding values even though it does not itself represent a
3116   transfer-coding.
3117</t>
3118<t>
3119   Examples of its use are:
3120</t>
3121<figure><artwork type="example">
3122  TE: deflate
3123  TE:
3124  TE: trailers, deflate;q=0.5
3125</artwork></figure>
3126<t>
3127   The TE header field only applies to the immediate connection.
3128   Therefore, the keyword &MUST; be supplied within a Connection header
3129   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3130</t>
3131<t>
3132   A server tests whether a transfer-coding is acceptable, according to
3133   a TE field, using these rules:
3134  <list style="numbers">
3135    <x:lt>
3136      <t>The "chunked" transfer-coding is always acceptable. If the
3137         keyword "trailers" is listed, the client indicates that it is
3138         willing to accept trailer fields in the chunked response on
3139         behalf of itself and any downstream clients. The implication is
3140         that, if given, the client is stating that either all
3141         downstream clients are willing to accept trailer fields in the
3142         forwarded response, or that it will attempt to buffer the
3143         response on behalf of downstream recipients.
3144      </t><t>
3145         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
3146         chunked response such that a client can be assured of buffering
3147         the entire response.</t>
3148    </x:lt>
3149    <x:lt>
3150      <t>If the transfer-coding being tested is one of the transfer-codings
3151         listed in the TE field, then it is acceptable unless it
3152         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3153         qvalue of 0 means "not acceptable".)</t>
3154    </x:lt>
3155    <x:lt>
3156      <t>If multiple transfer-codings are acceptable, then the
3157         acceptable transfer-coding with the highest non-zero qvalue is
3158         preferred.  The "chunked" transfer-coding always has a qvalue
3159         of 1.</t>
3160    </x:lt>
3161  </list>
3162</t>
3163<t>
3164   If the TE field-value is empty or if no TE field is present, the only
3165   transfer-coding is "chunked". A message with no transfer-coding is
3166   always acceptable.
3167</t>
3168</section>
3169
3170<section title="Trailer" anchor="header.trailer">
3171  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3172  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3173  <x:anchor-alias value="Trailer"/>
3174  <x:anchor-alias value="Trailer-v"/>
3175<t>
3176   The "Trailer" general-header field indicates that the given set of
3177   header fields is present in the trailer of a message encoded with
3178   chunked transfer-coding.
3179</t>
3180<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3181  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3182  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3183</artwork></figure>
3184<t>
3185   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3186   message using chunked transfer-coding with a non-empty trailer. Doing
3187   so allows the recipient to know which header fields to expect in the
3188   trailer.
3189</t>
3190<t>
3191   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3192   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3193   trailer fields in a "chunked" transfer-coding.
3194</t>
3195<t>
3196   Message header fields listed in the Trailer header field &MUST-NOT;
3197   include the following header fields:
3198  <list style="symbols">
3199    <t>Transfer-Encoding</t>
3200    <t>Content-Length</t>
3201    <t>Trailer</t>
3202  </list>
3203</t>
3204</section>
3205
3206<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3207  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3208  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3209  <x:anchor-alias value="Transfer-Encoding"/>
3210  <x:anchor-alias value="Transfer-Encoding-v"/>
3211<t>
3212   The "Transfer-Encoding" general-header field indicates what transfer-codings
3213   (if any) have been applied to the message body. It differs from
3214   Content-Encoding (&content-codings;) in that transfer-codings are a property
3215   of the message (and therefore are removed by intermediaries), whereas
3216   content-codings are not.
3217</t>
3218<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3219  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3220                        <x:ref>Transfer-Encoding-v</x:ref>
3221  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3222</artwork></figure>
3223<t>
3224   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3225</t>
3226<figure><artwork type="example">
3227  Transfer-Encoding: chunked
3228</artwork></figure>
3229<t>
3230   If multiple encodings have been applied to a representation, the transfer-codings
3231   &MUST; be listed in the order in which they were applied.
3232   Additional information about the encoding parameters &MAY; be provided
3233   by other header fields not defined by this specification.
3234</t>
3235<t>
3236   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3237   header field.
3238</t>
3239</section>
3240
3241<section title="Upgrade" anchor="header.upgrade">
3242  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3243  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3244  <x:anchor-alias value="Upgrade"/>
3245  <x:anchor-alias value="Upgrade-v"/>
3246<t>
3247   The "Upgrade" general-header field allows the client to specify what
3248   additional communication protocols it would like to use, if the server
3249   chooses to switch protocols. Servers can use it to indicate what protocols
3250   they are willing to switch to.
3251</t>
3252<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3253  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3254  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3255</artwork></figure>
3256<t>
3257   For example,
3258</t>
3259<figure><artwork type="example">
3260  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3261</artwork></figure>
3262<t>
3263   The Upgrade header field is intended to provide a simple mechanism
3264   for transition from HTTP/1.1 to some other, incompatible protocol. It
3265   does so by allowing the client to advertise its desire to use another
3266   protocol, such as a later version of HTTP with a higher major version
3267   number, even though the current request has been made using HTTP/1.1.
3268   This eases the difficult transition between incompatible protocols by
3269   allowing the client to initiate a request in the more commonly
3270   supported protocol while indicating to the server that it would like
3271   to use a "better" protocol if available (where "better" is determined
3272   by the server, possibly according to the nature of the method and/or
3273   resource being requested).
3274</t>
3275<t>
3276   The Upgrade header field only applies to switching application-layer
3277   protocols upon the existing transport-layer connection. Upgrade
3278   cannot be used to insist on a protocol change; its acceptance and use
3279   by the server is optional. The capabilities and nature of the
3280   application-layer communication after the protocol change is entirely
3281   dependent upon the new protocol chosen, although the first action
3282   after changing the protocol &MUST; be a response to the initial HTTP
3283   request containing the Upgrade header field.
3284</t>
3285<t>
3286   The Upgrade header field only applies to the immediate connection.
3287   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3288   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3289   HTTP/1.1 message.
3290</t>
3291<t>
3292   The Upgrade header field cannot be used to indicate a switch to a
3293   protocol on a different connection. For that purpose, it is more
3294   appropriate to use a 3xx redirection response (&status-3xx;).
3295</t>
3296<t>
3297   Servers &MUST; include the "Upgrade" header field in 101 (Switching
3298   Protocols) responses to indicate which protocol(s) are being switched to,
3299   and &MUST; include it in 426 (Upgrade Required) responses to indicate
3300   acceptable protocols to upgrade to. Servers &MAY; include it in any other
3301   response to indicate that they are willing to upgrade to one of the
3302   specified protocols.
3303</t>
3304<t>
3305   This specification only defines the protocol name "HTTP" for use by
3306   the family of Hypertext Transfer Protocols, as defined by the HTTP
3307   version rules of <xref target="http.version"/> and future updates to this
3308   specification. Additional tokens can be registered with IANA using the
3309   registration procedure defined below. 
3310</t>
3311
3312<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3313<t>
3314   The HTTP Upgrade Token Registry defines the name space for product
3315   tokens used to identify protocols in the Upgrade header field.
3316   Each registered token is associated with contact information and
3317   an optional set of specifications that details how the connection
3318   will be processed after it has been upgraded.
3319</t>
3320<t>
3321   Registrations are allowed on a First Come First Served basis as
3322   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. The
3323   specifications need not be IETF documents or be subject to IESG review.
3324   Registrations are subject to the following rules:
3325  <list style="numbers">
3326    <t>A token, once registered, stays registered forever.</t>
3327    <t>The registration &MUST; name a responsible party for the
3328       registration.</t>
3329    <t>The registration &MUST; name a point of contact.</t>
3330    <t>The registration &MAY; name a set of specifications associated with that
3331       token. Such specifications need not be publicly available.</t>
3332    <t>The responsible party &MAY; change the registration at any time.
3333       The IANA will keep a record of all such changes, and make them
3334       available upon request.</t>
3335    <t>The responsible party for the first registration of a "product"
3336       token &MUST; approve later registrations of a "version" token
3337       together with that "product" token before they can be registered.</t>
3338    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3339       for a token. This will normally only be used in the case when a
3340       responsible party cannot be contacted.</t>
3341  </list>
3342</t>
3343</section>
3344
3345
3346</section>
3347
3348<section title="Via" anchor="header.via">
3349  <iref primary="true" item="Via header" x:for-anchor=""/>
3350  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3351  <x:anchor-alias value="protocol-name"/>
3352  <x:anchor-alias value="protocol-version"/>
3353  <x:anchor-alias value="pseudonym"/>
3354  <x:anchor-alias value="received-by"/>
3355  <x:anchor-alias value="received-protocol"/>
3356  <x:anchor-alias value="Via"/>
3357  <x:anchor-alias value="Via-v"/>
3358<t>
3359   The "Via" general-header field &MUST; be used by gateways and proxies to
3360   indicate the intermediate protocols and recipients between the user
3361   agent and the server on requests, and between the origin server and
3362   the client on responses. It is analogous to the "Received" field defined in
3363   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3364   avoiding request loops, and identifying the protocol capabilities of
3365   all senders along the request/response chain.
3366</t>
3367<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"/>
3368  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3369  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3370                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3371  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3372  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3373  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3374  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3375  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3376</artwork></figure>
3377<t>
3378   The received-protocol indicates the protocol version of the message
3379   received by the server or client along each segment of the
3380   request/response chain. The received-protocol version is appended to
3381   the Via field value when the message is forwarded so that information
3382   about the protocol capabilities of upstream applications remains
3383   visible to all recipients.
3384</t>
3385<t>
3386   The protocol-name is optional if and only if it would be "HTTP". The
3387   received-by field is normally the host and optional port number of a
3388   recipient server or client that subsequently forwarded the message.
3389   However, if the real host is considered to be sensitive information,
3390   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3391   be assumed to be the default port of the received-protocol.
3392</t>
3393<t>
3394   Multiple Via field values represent each proxy or gateway that has
3395   forwarded the message. Each recipient &MUST; append its information
3396   such that the end result is ordered according to the sequence of
3397   forwarding applications.
3398</t>
3399<t>
3400   Comments &MAY; be used in the Via header field to identify the software
3401   of the recipient proxy or gateway, analogous to the User-Agent and
3402   Server header fields. However, all comments in the Via field are
3403   optional and &MAY; be removed by any recipient prior to forwarding the
3404   message.
3405</t>
3406<t>
3407   For example, a request message could be sent from an HTTP/1.0 user
3408   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3409   forward the request to a public proxy at p.example.net, which completes
3410   the request by forwarding it to the origin server at www.example.com.
3411   The request received by www.example.com would then have the following
3412   Via header field:
3413</t>
3414<figure><artwork type="example">
3415  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3416</artwork></figure>
3417<t>
3418   Proxies and gateways used as a portal through a network firewall
3419   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3420   the firewall region. This information &SHOULD; only be propagated if
3421   explicitly enabled. If not enabled, the received-by host of any host
3422   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3423   for that host.
3424</t>
3425<t>
3426   For organizations that have strong privacy requirements for hiding
3427   internal structures, a proxy &MAY; combine an ordered subsequence of
3428   Via header field entries with identical received-protocol values into
3429   a single such entry. For example,
3430</t>
3431<figure><artwork type="example">
3432  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3433</artwork></figure>
3434<t>
3435  could be collapsed to
3436</t>
3437<figure><artwork type="example">
3438  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3439</artwork></figure>
3440<t>
3441   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3442   under the same organizational control and the hosts have already been
3443   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3444   have different received-protocol values.
3445</t>
3446</section>
3447
3448</section>
3449
3450<section title="IANA Considerations" anchor="IANA.considerations">
3451
3452<section title="Header Field Registration" anchor="header.field.registration">
3453<t>
3454   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3455   with the permanent registrations below (see <xref target="RFC3864"/>):
3456</t>
3457<?BEGININC p1-messaging.iana-headers ?>
3458<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3459<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3460   <ttcol>Header Field Name</ttcol>
3461   <ttcol>Protocol</ttcol>
3462   <ttcol>Status</ttcol>
3463   <ttcol>Reference</ttcol>
3464
3465   <c>Connection</c>
3466   <c>http</c>
3467   <c>standard</c>
3468   <c>
3469      <xref target="header.connection"/>
3470   </c>
3471   <c>Content-Length</c>
3472   <c>http</c>
3473   <c>standard</c>
3474   <c>
3475      <xref target="header.content-length"/>
3476   </c>
3477   <c>Date</c>
3478   <c>http</c>
3479   <c>standard</c>
3480   <c>
3481      <xref target="header.date"/>
3482   </c>
3483   <c>Host</c>
3484   <c>http</c>
3485   <c>standard</c>
3486   <c>
3487      <xref target="header.host"/>
3488   </c>
3489   <c>TE</c>
3490   <c>http</c>
3491   <c>standard</c>
3492   <c>
3493      <xref target="header.te"/>
3494   </c>
3495   <c>Trailer</c>
3496   <c>http</c>
3497   <c>standard</c>
3498   <c>
3499      <xref target="header.trailer"/>
3500   </c>
3501   <c>Transfer-Encoding</c>
3502   <c>http</c>
3503   <c>standard</c>
3504   <c>
3505      <xref target="header.transfer-encoding"/>
3506   </c>
3507   <c>Upgrade</c>
3508   <c>http</c>
3509   <c>standard</c>
3510   <c>
3511      <xref target="header.upgrade"/>
3512   </c>
3513   <c>Via</c>
3514   <c>http</c>
3515   <c>standard</c>
3516   <c>
3517      <xref target="header.via"/>
3518   </c>
3519</texttable>
3520<!--(END)-->
3521<?ENDINC p1-messaging.iana-headers ?>
3522<t>
3523   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3524</t>
3525</section>
3526
3527<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3528<t>
3529   The entries for the "http" and "https" URI Schemes in the registry located at
3530   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3531   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3532   and <xref target="https.uri" format="counter"/> of this document
3533   (see <xref target="RFC4395"/>).
3534</t>
3535</section>
3536
3537<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3538<t>
3539   This document serves as the specification for the Internet media types
3540   "message/http" and "application/http". The following is to be registered with
3541   IANA (see <xref target="RFC4288"/>).
3542</t>
3543<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3544<iref item="Media Type" subitem="message/http" primary="true"/>
3545<iref item="message/http Media Type" primary="true"/>
3546<t>
3547   The message/http type can be used to enclose a single HTTP request or
3548   response message, provided that it obeys the MIME restrictions for all
3549   "message" types regarding line length and encodings.
3550</t>
3551<t>
3552  <list style="hanging" x:indent="12em">
3553    <t hangText="Type name:">
3554      message
3555    </t>
3556    <t hangText="Subtype name:">
3557      http
3558    </t>
3559    <t hangText="Required parameters:">
3560      none
3561    </t>
3562    <t hangText="Optional parameters:">
3563      version, msgtype
3564      <list style="hanging">
3565        <t hangText="version:">
3566          The HTTP-Version number of the enclosed message
3567          (e.g., "1.1"). If not present, the version can be
3568          determined from the first line of the body.
3569        </t>
3570        <t hangText="msgtype:">
3571          The message type -- "request" or "response". If not
3572          present, the type can be determined from the first
3573          line of the body.
3574        </t>
3575      </list>
3576    </t>
3577    <t hangText="Encoding considerations:">
3578      only "7bit", "8bit", or "binary" are permitted
3579    </t>
3580    <t hangText="Security considerations:">
3581      none
3582    </t>
3583    <t hangText="Interoperability considerations:">
3584      none
3585    </t>
3586    <t hangText="Published specification:">
3587      This specification (see <xref target="internet.media.type.message.http"/>).
3588    </t>
3589    <t hangText="Applications that use this media type:">
3590    </t>
3591    <t hangText="Additional information:">
3592      <list style="hanging">
3593        <t hangText="Magic number(s):">none</t>
3594        <t hangText="File extension(s):">none</t>
3595        <t hangText="Macintosh file type code(s):">none</t>
3596      </list>
3597    </t>
3598    <t hangText="Person and email address to contact for further information:">
3599      See Authors Section.
3600    </t>
3601    <t hangText="Intended usage:">
3602      COMMON
3603    </t>
3604    <t hangText="Restrictions on usage:">
3605      none
3606    </t>
3607    <t hangText="Author/Change controller:">
3608      IESG
3609    </t>
3610  </list>
3611</t>
3612</section>
3613<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3614<iref item="Media Type" subitem="application/http" primary="true"/>
3615<iref item="application/http Media Type" primary="true"/>
3616<t>
3617   The application/http type can be used to enclose a pipeline of one or more
3618   HTTP request or response messages (not intermixed).
3619</t>
3620<t>
3621  <list style="hanging" x:indent="12em">
3622    <t hangText="Type name:">
3623      application
3624    </t>
3625    <t hangText="Subtype name:">
3626      http
3627    </t>
3628    <t hangText="Required parameters:">
3629      none
3630    </t>
3631    <t hangText="Optional parameters:">
3632      version, msgtype
3633      <list style="hanging">
3634        <t hangText="version:">
3635          The HTTP-Version number of the enclosed messages
3636          (e.g., "1.1"). If not present, the version can be
3637          determined from the first line of the body.
3638        </t>
3639        <t hangText="msgtype:">
3640          The message type -- "request" or "response". If not
3641          present, the type can be determined from the first
3642          line of the body.
3643        </t>
3644      </list>
3645    </t>
3646    <t hangText="Encoding considerations:">
3647      HTTP messages enclosed by this type
3648      are in "binary" format; use of an appropriate
3649      Content-Transfer-Encoding is required when
3650      transmitted via E-mail.
3651    </t>
3652    <t hangText="Security considerations:">
3653      none
3654    </t>
3655    <t hangText="Interoperability considerations:">
3656      none
3657    </t>
3658    <t hangText="Published specification:">
3659      This specification (see <xref target="internet.media.type.application.http"/>).
3660    </t>
3661    <t hangText="Applications that use this media type:">
3662    </t>
3663    <t hangText="Additional information:">
3664      <list style="hanging">
3665        <t hangText="Magic number(s):">none</t>
3666        <t hangText="File extension(s):">none</t>
3667        <t hangText="Macintosh file type code(s):">none</t>
3668      </list>
3669    </t>
3670    <t hangText="Person and email address to contact for further information:">
3671      See Authors Section.
3672    </t>
3673    <t hangText="Intended usage:">
3674      COMMON
3675    </t>
3676    <t hangText="Restrictions on usage:">
3677      none
3678    </t>
3679    <t hangText="Author/Change controller:">
3680      IESG
3681    </t>
3682  </list>
3683</t>
3684</section>
3685</section>
3686
3687<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3688<t>
3689   The registration procedure for HTTP Transfer Codings is now defined by
3690   <xref target="transfer.coding.registry"/> of this document.
3691</t>
3692<t>
3693   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3694   shall be updated with the registrations below:
3695</t>
3696<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3697   <ttcol>Name</ttcol>
3698   <ttcol>Description</ttcol>
3699   <ttcol>Reference</ttcol>
3700   <c>chunked</c>
3701   <c>Transfer in a series of chunks</c>
3702   <c>
3703      <xref target="chunked.encoding"/>
3704   </c>
3705   <c>compress</c>
3706   <c>UNIX "compress" program method</c>
3707   <c>
3708      <xref target="compress.coding"/>
3709   </c>
3710   <c>deflate</c>
3711   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3712   the "zlib" data format (<xref target="RFC1950"/>)
3713   </c>
3714   <c>
3715      <xref target="deflate.coding"/>
3716   </c>
3717   <c>gzip</c>
3718   <c>Same as GNU zip <xref target="RFC1952"/></c>
3719   <c>
3720      <xref target="gzip.coding"/>
3721   </c>
3722</texttable>
3723</section>
3724
3725<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3726<t>
3727   The registration procedure for HTTP Upgrade Tokens -- previously defined
3728   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3729   by <xref target="upgrade.token.registry"/> of this document.
3730</t>
3731<t>
3732   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3733   shall be updated with the registration below:
3734</t>
3735<texttable align="left" suppress-title="true">
3736   <ttcol>Value</ttcol>
3737   <ttcol>Description</ttcol>
3738   <ttcol>Reference</ttcol>
3739
3740   <c>HTTP</c>
3741   <c>Hypertext Transfer Protocol</c> 
3742   <c><xref target="http.version"/> of this specification</c>
3743<!-- IANA should add this without our instructions; emailed on June 05, 2009
3744   <c>TLS/1.0</c>
3745   <c>Transport Layer Security</c>
3746   <c><xref target="RFC2817"/></c> -->
3747
3748</texttable>
3749</section>
3750
3751</section>
3752
3753<section title="Security Considerations" anchor="security.considerations">
3754<t>
3755   This section is meant to inform application developers, information
3756   providers, and users of the security limitations in HTTP/1.1 as
3757   described by this document. The discussion does not include
3758   definitive solutions to the problems revealed, though it does make
3759   some suggestions for reducing security risks.
3760</t>
3761
3762<section title="Personal Information" anchor="personal.information">
3763<t>
3764   HTTP clients are often privy to large amounts of personal information
3765   (e.g., the user's name, location, mail address, passwords, encryption
3766   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3767   leakage of this information.
3768   We very strongly recommend that a convenient interface be provided
3769   for the user to control dissemination of such information, and that
3770   designers and implementors be particularly careful in this area.
3771   History shows that errors in this area often create serious security
3772   and/or privacy problems and generate highly adverse publicity for the
3773   implementor's company.
3774</t>
3775</section>
3776
3777<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3778<t>
3779   A server is in the position to save personal data about a user's
3780   requests which might identify their reading patterns or subjects of
3781   interest. This information is clearly confidential in nature and its
3782   handling can be constrained by law in certain countries. People using
3783   HTTP to provide data are responsible for ensuring that
3784   such material is not distributed without the permission of any
3785   individuals that are identifiable by the published results.
3786</t>
3787</section>
3788
3789<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3790<t>
3791   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3792   the documents returned by HTTP requests to be only those that were
3793   intended by the server administrators. If an HTTP server translates
3794   HTTP URIs directly into file system calls, the server &MUST; take
3795   special care not to serve files that were not intended to be
3796   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3797   other operating systems use ".." as a path component to indicate a
3798   directory level above the current one. On such a system, an HTTP
3799   server &MUST; disallow any such construct in the request-target if it
3800   would otherwise allow access to a resource outside those intended to
3801   be accessible via the HTTP server. Similarly, files intended for
3802   reference only internally to the server (such as access control
3803   files, configuration files, and script code) &MUST; be protected from
3804   inappropriate retrieval, since they might contain sensitive
3805   information. Experience has shown that minor bugs in such HTTP server
3806   implementations have turned into security risks.
3807</t>
3808</section>
3809
3810<section title="DNS Spoofing" anchor="dns.spoofing">
3811<t>
3812   Clients using HTTP rely heavily on the Domain Name Service, and are
3813   thus generally prone to security attacks based on the deliberate
3814   mis-association of IP addresses and DNS names. Clients need to be
3815   cautious in assuming the continuing validity of an IP number/DNS name
3816   association.
3817</t>
3818<t>
3819   In particular, HTTP clients &SHOULD; rely on their name resolver for
3820   confirmation of an IP number/DNS name association, rather than
3821   caching the result of previous host name lookups. Many platforms
3822   already can cache host name lookups locally when appropriate, and
3823   they &SHOULD; be configured to do so. It is proper for these lookups to
3824   be cached, however, only when the TTL (Time To Live) information
3825   reported by the name server makes it likely that the cached
3826   information will remain useful.
3827</t>
3828<t>
3829   If HTTP clients cache the results of host name lookups in order to
3830   achieve a performance improvement, they &MUST; observe the TTL
3831   information reported by DNS.
3832</t>
3833<t>
3834   If HTTP clients do not observe this rule, they could be spoofed when
3835   a previously-accessed server's IP address changes. As network
3836   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3837   possibility of this form of attack will grow. Observing this
3838   requirement thus reduces this potential security vulnerability.
3839</t>
3840<t>
3841   This requirement also improves the load-balancing behavior of clients
3842   for replicated servers using the same DNS name and reduces the
3843   likelihood of a user's experiencing failure in accessing sites which
3844   use that strategy.
3845</t>
3846</section>
3847
3848<section title="Proxies and Caching" anchor="attack.proxies">
3849<t>
3850   By their very nature, HTTP proxies are men-in-the-middle, and
3851   represent an opportunity for man-in-the-middle attacks. Compromise of
3852   the systems on which the proxies run can result in serious security
3853   and privacy problems. Proxies have access to security-related
3854   information, personal information about individual users and
3855   organizations, and proprietary information belonging to users and
3856   content providers. A compromised proxy, or a proxy implemented or
3857   configured without regard to security and privacy considerations,
3858   might be used in the commission of a wide range of potential attacks.
3859</t>
3860<t>
3861   Proxy operators need to protect the systems on which proxies run as
3862   they would protect any system that contains or transports sensitive
3863   information. In particular, log information gathered at proxies often
3864   contains highly sensitive personal information, and/or information
3865   about organizations. Log information needs to be carefully guarded, and
3866   appropriate guidelines for use need to be developed and followed.
3867   (<xref target="abuse.of.server.log.information"/>).
3868</t>
3869<t>
3870   Proxy implementors need to consider the privacy and security
3871   implications of their design and coding decisions, and of the
3872   configuration options they provide to proxy operators (especially the
3873   default configuration).
3874</t>
3875<t>
3876   Users of a proxy need to be aware that proxies are no trustworthier than
3877   the people who run them; HTTP itself cannot solve this problem.
3878</t>
3879<t>
3880   The judicious use of cryptography, when appropriate, might suffice to
3881   protect against a broad range of security and privacy attacks. Such
3882   cryptography is beyond the scope of the HTTP/1.1 specification.
3883</t>
3884</section>
3885
3886<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3887<t>
3888   They exist. They are hard to defend against. Research continues.
3889   Beware.
3890</t>
3891</section>
3892</section>
3893
3894<section title="Acknowledgments" anchor="ack">
3895<t>
3896   HTTP has evolved considerably over the years. It has
3897   benefited from a large and active developer community--the many
3898   people who have participated on the www-talk mailing list--and it is
3899   that community which has been most responsible for the success of
3900   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3901   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3902   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3903   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3904   VanHeyningen deserve special recognition for their efforts in
3905   defining early aspects of the protocol.
3906</t>
3907<t>
3908   This document has benefited greatly from the comments of all those
3909   participating in the HTTP-WG. In addition to those already mentioned,
3910   the following individuals have contributed to this specification:
3911</t>
3912<t>
3913   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3914   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3915   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3916   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3917   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3918   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3919   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3920   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3921   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3922   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3923   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3924   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3925</t>
3926<t>
3927   Thanks to the "cave men" of Palo Alto. You know who you are.
3928</t>
3929<t>
3930   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3931   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3932   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3933   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3934   Larry Masinter for their help. And thanks go particularly to Jeff
3935   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3936</t>
3937<t>
3938   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3939   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3940   discovery of many of the problems that this document attempts to
3941   rectify.
3942</t>
3943<t>
3944   This specification makes heavy use of the augmented BNF and generic
3945   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3946   reuses many of the definitions provided by Nathaniel Borenstein and
3947   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3948   specification will help reduce past confusion over the relationship
3949   between HTTP and Internet mail message formats.
3950</t>
3951<!--
3952
3953Acknowledgements TODO list
3954
3955- Jeff Hodges ("effective request URI")
3956
3957-->
3958</section>
3959
3960</middle>
3961<back>
3962
3963<references title="Normative References">
3964
3965<reference anchor="ISO-8859-1">
3966  <front>
3967    <title>
3968     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3969    </title>
3970    <author>
3971      <organization>International Organization for Standardization</organization>
3972    </author>
3973    <date year="1998"/>
3974  </front>
3975  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3976</reference>
3977
3978<reference anchor="Part2">
3979  <front>
3980    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3981    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3982      <organization abbrev="Day Software">Day Software</organization>
3983      <address><email>fielding@gbiv.com</email></address>
3984    </author>
3985    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3986      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3987      <address><email>jg@freedesktop.org</email></address>
3988    </author>
3989    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3990      <organization abbrev="HP">Hewlett-Packard Company</organization>
3991      <address><email>JeffMogul@acm.org</email></address>
3992    </author>
3993    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3994      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3995      <address><email>henrikn@microsoft.com</email></address>
3996    </author>
3997    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3998      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3999      <address><email>LMM@acm.org</email></address>
4000    </author>
4001    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4002      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4003      <address><email>paulle@microsoft.com</email></address>
4004    </author>
4005    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4006      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4007      <address><email>timbl@w3.org</email></address>
4008    </author>
4009    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4010      <organization abbrev="W3C">World Wide Web Consortium</organization>
4011      <address><email>ylafon@w3.org</email></address>
4012    </author>
4013    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4014      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4015      <address><email>julian.reschke@greenbytes.de</email></address>
4016    </author>
4017    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4018  </front>
4019  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
4020  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
4021</reference>
4022
4023<reference anchor="Part3">
4024  <front>
4025    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4026    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4027      <organization abbrev="Day Software">Day Software</organization>
4028      <address><email>fielding@gbiv.com</email></address>
4029    </author>
4030    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4031      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4032      <address><email>jg@freedesktop.org</email></address>
4033    </author>
4034    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4035      <organization abbrev="HP">Hewlett-Packard Company</organization>
4036      <address><email>JeffMogul@acm.org</email></address>
4037    </author>
4038    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4039      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4040      <address><email>henrikn@microsoft.com</email></address>
4041    </author>
4042    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4043      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4044      <address><email>LMM@acm.org</email></address>
4045    </author>
4046    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4047      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4048      <address><email>paulle@microsoft.com</email></address>
4049    </author>
4050    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4051      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4052      <address><email>timbl@w3.org</email></address>
4053    </author>
4054    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4055      <organization abbrev="W3C">World Wide Web Consortium</organization>
4056      <address><email>ylafon@w3.org</email></address>
4057    </author>
4058    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4059      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4060      <address><email>julian.reschke@greenbytes.de</email></address>
4061    </author>
4062    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4063  </front>
4064  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
4065  <x:source href="p3-payload.xml" basename="p3-payload"/>
4066</reference>
4067
4068<reference anchor="Part6">
4069  <front>
4070    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4071    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4072      <organization abbrev="Day Software">Day Software</organization>
4073      <address><email>fielding@gbiv.com</email></address>
4074    </author>
4075    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4076      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4077      <address><email>jg@freedesktop.org</email></address>
4078    </author>
4079    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4080      <organization abbrev="HP">Hewlett-Packard Company</organization>
4081      <address><email>JeffMogul@acm.org</email></address>
4082    </author>
4083    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4084      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4085      <address><email>henrikn@microsoft.com</email></address>
4086    </author>
4087    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4088      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4089      <address><email>LMM@acm.org</email></address>
4090    </author>
4091    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4092      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4093      <address><email>paulle@microsoft.com</email></address>
4094    </author>
4095    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4096      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4097      <address><email>timbl@w3.org</email></address>
4098    </author>
4099    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4100      <organization abbrev="W3C">World Wide Web Consortium</organization>
4101      <address><email>ylafon@w3.org</email></address>
4102    </author>
4103    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4104      <address><email>mnot@mnot.net</email></address>
4105    </author>
4106    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4107      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4108      <address><email>julian.reschke@greenbytes.de</email></address>
4109    </author>
4110    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
4111  </front>
4112  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
4113  <x:source href="p6-cache.xml" basename="p6-cache"/>
4114</reference>
4115
4116<reference anchor="RFC5234">
4117  <front>
4118    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4119    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4120      <organization>Brandenburg InternetWorking</organization>
4121      <address>
4122        <email>dcrocker@bbiw.net</email>
4123      </address> 
4124    </author>
4125    <author initials="P." surname="Overell" fullname="Paul Overell">
4126      <organization>THUS plc.</organization>
4127      <address>
4128        <email>paul.overell@thus.net</email>
4129      </address>
4130    </author>
4131    <date month="January" year="2008"/>
4132  </front>
4133  <seriesInfo name="STD" value="68"/>
4134  <seriesInfo name="RFC" value="5234"/>
4135</reference>
4136
4137<reference anchor="RFC2119">
4138  <front>
4139    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4140    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4141      <organization>Harvard University</organization>
4142      <address><email>sob@harvard.edu</email></address>
4143    </author>
4144    <date month="March" year="1997"/>
4145  </front>
4146  <seriesInfo name="BCP" value="14"/>
4147  <seriesInfo name="RFC" value="2119"/>
4148</reference>
4149
4150<reference anchor="RFC3986">
4151 <front>
4152  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4153  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4154    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4155    <address>
4156       <email>timbl@w3.org</email>
4157       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4158    </address>
4159  </author>
4160  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4161    <organization abbrev="Day Software">Day Software</organization>
4162    <address>
4163      <email>fielding@gbiv.com</email>
4164      <uri>http://roy.gbiv.com/</uri>
4165    </address>
4166  </author>
4167  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4168    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4169    <address>
4170      <email>LMM@acm.org</email>
4171      <uri>http://larry.masinter.net/</uri>
4172    </address>
4173  </author>
4174  <date month='January' year='2005'></date>
4175 </front>
4176 <seriesInfo name="STD" value="66"/>
4177 <seriesInfo name="RFC" value="3986"/>
4178</reference>
4179
4180<reference anchor="USASCII">
4181  <front>
4182    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4183    <author>
4184      <organization>American National Standards Institute</organization>
4185    </author>
4186    <date year="1986"/>
4187  </front>
4188  <seriesInfo name="ANSI" value="X3.4"/>
4189</reference>
4190
4191<reference anchor="RFC1950">
4192  <front>
4193    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4194    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4195      <organization>Aladdin Enterprises</organization>
4196      <address><email>ghost@aladdin.com</email></address>
4197    </author>
4198    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4199    <date month="May" year="1996"/>
4200  </front>
4201  <seriesInfo name="RFC" value="1950"/>
4202  <annotation>
4203    RFC 1950 is an Informational RFC, thus it might be less stable than
4204    this specification. On the other hand, this downward reference was
4205    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4206    therefore it is unlikely to cause problems in practice. See also
4207    <xref target="BCP97"/>.
4208  </annotation>
4209</reference>
4210
4211<reference anchor="RFC1951">
4212  <front>
4213    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4214    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4215      <organization>Aladdin Enterprises</organization>
4216      <address><email>ghost@aladdin.com</email></address>
4217    </author>
4218    <date month="May" year="1996"/>
4219  </front>
4220  <seriesInfo name="RFC" value="1951"/>
4221  <annotation>
4222    RFC 1951 is an Informational RFC, thus it might be less stable than
4223    this specification. On the other hand, this downward reference was
4224    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4225    therefore it is unlikely to cause problems in practice. See also
4226    <xref target="BCP97"/>.
4227  </annotation>
4228</reference>
4229
4230<reference anchor="RFC1952">
4231  <front>
4232    <title>GZIP file format specification version 4.3</title>
4233    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4234      <organization>Aladdin Enterprises</organization>
4235      <address><email>ghost@aladdin.com</email></address>
4236    </author>
4237    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4238      <address><email>gzip@prep.ai.mit.edu</email></address>
4239    </author>
4240    <author initials="M." surname="Adler" fullname="Mark Adler">
4241      <address><email>madler@alumni.caltech.edu</email></address>
4242    </author>
4243    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4244      <address><email>ghost@aladdin.com</email></address>
4245    </author>
4246    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4247      <address><email>randeg@alumni.rpi.edu</email></address>
4248    </author>
4249    <date month="May" year="1996"/>
4250  </front>
4251  <seriesInfo name="RFC" value="1952"/>
4252  <annotation>
4253    RFC 1952 is an Informational RFC, thus it might be less stable than
4254    this specification. On the other hand, this downward reference was
4255    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4256    therefore it is unlikely to cause problems in practice. See also
4257    <xref target="BCP97"/>.
4258  </annotation>
4259</reference>
4260
4261</references>
4262
4263<references title="Informative References">
4264
4265<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4266  <front>
4267    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4268    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4269    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4270    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4271    <author initials="H." surname="Lie" fullname="H. Lie"/>
4272    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4273    <date year="1997" month="September"/>
4274  </front>
4275  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4276</reference>
4277
4278<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4279  <front>
4280    <title>Improving HTTP Latency</title>
4281    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4282    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4283    <date year="1995" month="December"/>
4284  </front>
4285  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4286</reference>
4287
4288<reference anchor="RFC1123">
4289  <front>
4290    <title>Requirements for Internet Hosts - Application and Support</title>
4291    <author initials="R." surname="Braden" fullname="Robert Braden">
4292      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4293      <address><email>Braden@ISI.EDU</email></address>
4294    </author>
4295    <date month="October" year="1989"/>
4296  </front>
4297  <seriesInfo name="STD" value="3"/>
4298  <seriesInfo name="RFC" value="1123"/>
4299</reference>
4300
4301<reference anchor="RFC1900">
4302  <front>
4303    <title>Renumbering Needs Work</title>
4304    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4305      <organization>CERN, Computing and Networks Division</organization>
4306      <address><email>brian@dxcoms.cern.ch</email></address>
4307    </author>
4308    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4309      <organization>cisco Systems</organization>
4310      <address><email>yakov@cisco.com</email></address>
4311    </author>
4312    <date month="February" year="1996"/>
4313  </front>
4314  <seriesInfo name="RFC" value="1900"/>
4315</reference>
4316
4317<reference anchor="RFC1945">
4318  <front>
4319    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4320    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4321      <organization>MIT, Laboratory for Computer Science</organization>
4322      <address><email>timbl@w3.org</email></address>
4323    </author>
4324    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4325      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4326      <address><email>fielding@ics.uci.edu</email></address>
4327    </author>
4328    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4329      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4330      <address><email>frystyk@w3.org</email></address>
4331    </author>
4332    <date month="May" year="1996"/>
4333  </front>
4334  <seriesInfo name="RFC" value="1945"/>
4335</reference>
4336
4337<reference anchor="RFC2045">
4338  <front>
4339    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4340    <author initials="N." surname="Freed" fullname="Ned Freed">
4341      <organization>Innosoft International, Inc.</organization>
4342      <address><email>ned@innosoft.com</email></address>
4343    </author>
4344    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4345      <organization>First Virtual Holdings</organization>
4346      <address><email>nsb@nsb.fv.com</email></address>
4347    </author>
4348    <date month="November" year="1996"/>
4349  </front>
4350  <seriesInfo name="RFC" value="2045"/>
4351</reference>
4352
4353<reference anchor="RFC2047">
4354  <front>
4355    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4356    <author initials="K." surname="Moore" fullname="Keith Moore">
4357      <organization>University of Tennessee</organization>
4358      <address><email>moore@cs.utk.edu</email></address>
4359    </author>
4360    <date month="November" year="1996"/>
4361  </front>
4362  <seriesInfo name="RFC" value="2047"/>
4363</reference>
4364
4365<reference anchor="RFC2068">
4366  <front>
4367    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4368    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4369      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4370      <address><email>fielding@ics.uci.edu</email></address>
4371    </author>
4372    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4373      <organization>MIT Laboratory for Computer Science</organization>
4374      <address><email>jg@w3.org</email></address>
4375    </author>
4376    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4377      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4378      <address><email>mogul@wrl.dec.com</email></address>
4379    </author>
4380    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4381      <organization>MIT Laboratory for Computer Science</organization>
4382      <address><email>frystyk@w3.org</email></address>
4383    </author>
4384    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4385      <organization>MIT Laboratory for Computer Science</organization>
4386      <address><email>timbl@w3.org</email></address>
4387    </author>
4388    <date month="January" year="1997"/>
4389  </front>
4390  <seriesInfo name="RFC" value="2068"/>
4391</reference>
4392
4393<reference anchor='RFC2109'>
4394  <front>
4395    <title>HTTP State Management Mechanism</title>
4396    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4397      <organization>Bell Laboratories, Lucent Technologies</organization>
4398      <address><email>dmk@bell-labs.com</email></address>
4399    </author>
4400    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4401      <organization>Netscape Communications Corp.</organization>
4402      <address><email>montulli@netscape.com</email></address>
4403    </author>
4404    <date year='1997' month='February' />
4405  </front>
4406  <seriesInfo name='RFC' value='2109' />
4407</reference>
4408
4409<reference anchor="RFC2145">
4410  <front>
4411    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4412    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4413      <organization>Western Research Laboratory</organization>
4414      <address><email>mogul@wrl.dec.com</email></address>
4415    </author>
4416    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4417      <organization>Department of Information and Computer Science</organization>
4418      <address><email>fielding@ics.uci.edu</email></address>
4419    </author>
4420    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4421      <organization>MIT Laboratory for Computer Science</organization>
4422      <address><email>jg@w3.org</email></address>
4423    </author>
4424    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4425      <organization>W3 Consortium</organization>
4426      <address><email>frystyk@w3.org</email></address>
4427    </author>
4428    <date month="May" year="1997"/>
4429  </front>
4430  <seriesInfo name="RFC" value="2145"/>
4431</reference>
4432
4433<reference anchor="RFC2616">
4434  <front>
4435    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4436    <author initials="R." surname="Fielding" fullname="R. Fielding">
4437      <organization>University of California, Irvine</organization>
4438      <address><email>fielding@ics.uci.edu</email></address>
4439    </author>
4440    <author initials="J." surname="Gettys" fullname="J. Gettys">
4441      <organization>W3C</organization>
4442      <address><email>jg@w3.org</email></address>
4443    </author>
4444    <author initials="J." surname="Mogul" fullname="J. Mogul">
4445      <organization>Compaq Computer Corporation</organization>
4446      <address><email>mogul@wrl.dec.com</email></address>
4447    </author>
4448    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4449      <organization>MIT Laboratory for Computer Science</organization>
4450      <address><email>frystyk@w3.org</email></address>
4451    </author>
4452    <author initials="L." surname="Masinter" fullname="L. Masinter">
4453      <organization>Xerox Corporation</organization>
4454      <address><email>masinter@parc.xerox.com</email></address>
4455    </author>
4456    <author initials="P." surname="Leach" fullname="P. Leach">
4457      <organization>Microsoft Corporation</organization>
4458      <address><email>paulle@microsoft.com</email></address>
4459    </author>
4460    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4461      <organization>W3C</organization>
4462      <address><email>timbl@w3.org</email></address>
4463    </author>
4464    <date month="June" year="1999"/>
4465  </front>
4466  <seriesInfo name="RFC" value="2616"/>
4467</reference>
4468
4469<reference anchor='RFC2817'>
4470  <front>
4471    <title>Upgrading to TLS Within HTTP/1.1</title>
4472    <author initials='R.' surname='Khare' fullname='R. Khare'>
4473      <organization>4K Associates / UC Irvine</organization>
4474      <address><email>rohit@4K-associates.com</email></address>
4475    </author>
4476    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4477      <organization>Agranat Systems, Inc.</organization>
4478      <address><email>lawrence@agranat.com</email></address>
4479    </author>
4480    <date year='2000' month='May' />
4481  </front>
4482  <seriesInfo name='RFC' value='2817' />
4483</reference>
4484
4485<reference anchor='RFC2818'>
4486  <front>
4487    <title>HTTP Over TLS</title>
4488    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4489      <organization>RTFM, Inc.</organization>
4490      <address><email>ekr@rtfm.com</email></address>
4491    </author>
4492    <date year='2000' month='May' />
4493  </front>
4494  <seriesInfo name='RFC' value='2818' />
4495</reference>
4496
4497<reference anchor='RFC2965'>
4498  <front>
4499    <title>HTTP State Management Mechanism</title>
4500    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4501      <organization>Bell Laboratories, Lucent Technologies</organization>
4502      <address><email>dmk@bell-labs.com</email></address>
4503    </author>
4504    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4505      <organization>Epinions.com, Inc.</organization>
4506      <address><email>lou@montulli.org</email></address>
4507    </author>
4508    <date year='2000' month='October' />
4509  </front>
4510  <seriesInfo name='RFC' value='2965' />
4511</reference>
4512
4513<reference anchor='RFC3864'>
4514  <front>
4515    <title>Registration Procedures for Message Header Fields</title>
4516    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4517      <organization>Nine by Nine</organization>
4518      <address><email>GK-IETF@ninebynine.org</email></address>
4519    </author>
4520    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4521      <organization>BEA Systems</organization>
4522      <address><email>mnot@pobox.com</email></address>
4523    </author>
4524    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4525      <organization>HP Labs</organization>
4526      <address><email>JeffMogul@acm.org</email></address>
4527    </author>
4528    <date year='2004' month='September' />
4529  </front>
4530  <seriesInfo name='BCP' value='90' />
4531  <seriesInfo name='RFC' value='3864' />
4532</reference>
4533
4534<reference anchor="RFC4288">
4535  <front>
4536    <title>Media Type Specifications and Registration Procedures</title>
4537    <author initials="N." surname="Freed" fullname="N. Freed">
4538      <organization>Sun Microsystems</organization>
4539      <address>
4540        <email>ned.freed@mrochek.com</email>
4541      </address>
4542    </author>
4543    <author initials="J." surname="Klensin" fullname="J. Klensin">
4544      <address>
4545        <email>klensin+ietf@jck.com</email>
4546      </address>
4547    </author>
4548    <date year="2005" month="December"/>
4549  </front>
4550  <seriesInfo name="BCP" value="13"/>
4551  <seriesInfo name="RFC" value="4288"/>
4552</reference>
4553
4554<reference anchor='RFC4395'>
4555  <front>
4556    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4557    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4558      <organization>AT&amp;T Laboratories</organization>
4559      <address>
4560        <email>tony+urireg@maillennium.att.com</email>
4561      </address>
4562    </author>
4563    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4564      <organization>Qualcomm, Inc.</organization>
4565      <address>
4566        <email>hardie@qualcomm.com</email>
4567      </address>
4568    </author>
4569    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4570      <organization>Adobe Systems</organization>
4571      <address>
4572        <email>LMM@acm.org</email>
4573      </address>
4574    </author>
4575    <date year='2006' month='February' />
4576  </front>
4577  <seriesInfo name='BCP' value='115' />
4578  <seriesInfo name='RFC' value='4395' />
4579</reference>
4580
4581<reference anchor='RFC5226'>
4582  <front>
4583    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4584    <author initials='T.' surname='Narten' fullname='T. Narten'>
4585      <organization>IBM</organization>
4586      <address><email>narten@us.ibm.com</email></address>
4587    </author>
4588    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4589      <organization>Google</organization>
4590      <address><email>Harald@Alvestrand.no</email></address>
4591    </author>
4592    <date year='2008' month='May' />
4593  </front>
4594  <seriesInfo name='BCP' value='26' />
4595  <seriesInfo name='RFC' value='5226' />
4596</reference>
4597
4598<reference anchor="RFC5322">
4599  <front>
4600    <title>Internet Message Format</title>
4601    <author initials="P." surname="Resnick" fullname="P. Resnick">
4602      <organization>Qualcomm Incorporated</organization>
4603    </author>
4604    <date year="2008" month="October"/>
4605  </front> 
4606  <seriesInfo name="RFC" value="5322"/>
4607</reference>
4608
4609<reference anchor='BCP97'>
4610  <front>
4611    <title>Handling Normative References to Standards-Track Documents</title>
4612    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4613      <address>
4614        <email>klensin+ietf@jck.com</email>
4615      </address>
4616    </author>
4617    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4618      <organization>MIT</organization>
4619      <address>
4620        <email>hartmans-ietf@mit.edu</email>
4621      </address>
4622    </author>
4623    <date year='2007' month='June' />
4624  </front>
4625  <seriesInfo name='BCP' value='97' />
4626  <seriesInfo name='RFC' value='4897' />
4627</reference>
4628
4629<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4630  <front>
4631    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4632    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4633    <date year="2001" month="November"/>
4634  </front>
4635  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4636</reference>
4637
4638<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4639  <front>
4640    <title>Analysis of HTTP Performance Problems</title>
4641    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4642    <date/>
4643  </front>
4644</reference>
4645
4646<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4647  <front>
4648  <title>Analysis of HTTP Performance</title>
4649  <author initials="J." surname="Touch" fullname="Joe Touch">
4650    <organization>USC/Information Sciences Institute</organization>
4651    <address><email>touch@isi.edu</email></address>
4652  </author>
4653  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4654    <organization>USC/Information Sciences Institute</organization>
4655    <address><email>johnh@isi.edu</email></address>
4656  </author>
4657  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4658    <organization>USC/Information Sciences Institute</organization>
4659    <address><email>katia@isi.edu</email></address>
4660  </author>
4661  <date year="1998" month="Aug"/>
4662  </front>
4663  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4664  <annotation>(original report dated Aug. 1996)</annotation>
4665</reference>
4666
4667</references>
4668
4669
4670<section title="Tolerant Applications" anchor="tolerant.applications">
4671<t>
4672   Although this document specifies the requirements for the generation
4673   of HTTP/1.1 messages, not all applications will be correct in their
4674   implementation. We therefore recommend that operational applications
4675   be tolerant of deviations whenever those deviations can be
4676   interpreted unambiguously.
4677</t>
4678<t>
4679   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4680   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4681   &SHOULD; accept any amount of WSP characters between fields, even though
4682   only a single SP is required.
4683</t>
4684<t>
4685   The line terminator for header fields is the sequence CRLF.
4686   However, we recommend that applications, when parsing such headers fields,
4687   recognize a single LF as a line terminator and ignore the leading CR.
4688</t>
4689<t>
4690   The character set of a representation &SHOULD; be labeled as the lowest
4691   common denominator of the character codes used within that representation, with
4692   the exception that not labeling the representation is preferred over labeling
4693   the representation with the labels US-ASCII or ISO-8859-1. See &payload;.
4694</t>
4695<t>
4696   Additional rules for requirements on parsing and encoding of dates
4697   and other potential problems with date encodings include:
4698</t>
4699<t>
4700  <list style="symbols">
4701     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4702        which appears to be more than 50 years in the future is in fact
4703        in the past (this helps solve the "year 2000" problem).</t>
4704
4705     <t>Although all date formats are specified to be case-sensitive,
4706        recipients &SHOULD; match day, week and timezone names
4707        case-insensitively.</t>
4708             
4709     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4710        Expires date as earlier than the proper value, but &MUST-NOT;
4711        internally represent a parsed Expires date as later than the
4712        proper value.</t>
4713
4714     <t>All expiration-related calculations &MUST; be done in GMT. The
4715        local time zone &MUST-NOT; influence the calculation or comparison
4716        of an age or expiration time.</t>
4717
4718     <t>If an HTTP header field incorrectly carries a date value with a time
4719        zone other than GMT, it &MUST; be converted into GMT using the
4720        most conservative possible conversion.</t>
4721  </list>
4722</t>
4723</section>
4724
4725<section title="Compatibility with Previous Versions" anchor="compatibility">
4726<t>
4727   HTTP has been in use by the World-Wide Web global information initiative
4728   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4729   was a simple protocol for hypertext data transfer across the Internet
4730   with only a single method and no metadata.
4731   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4732   methods and MIME-like messaging that could include metadata about the data
4733   transferred and modifiers on the request/response semantics. However,
4734   HTTP/1.0 did not sufficiently take into consideration the effects of
4735   hierarchical proxies, caching, the need for persistent connections, or
4736   name-based virtual hosts. The proliferation of incompletely-implemented
4737   applications calling themselves "HTTP/1.0" further necessitated a
4738   protocol version change in order for two communicating applications
4739   to determine each other's true capabilities.
4740</t>
4741<t>
4742   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4743   requirements that enable reliable implementations, adding only
4744   those new features that will either be safely ignored by an HTTP/1.0
4745   recipient or only sent when communicating with a party advertising
4746   compliance with HTTP/1.1.
4747</t>
4748<t>
4749   It is beyond the scope of a protocol specification to mandate
4750   compliance with previous versions. HTTP/1.1 was deliberately
4751   designed, however, to make supporting previous versions easy. It is
4752   worth noting that, at the time of composing this specification, we would
4753   expect general-purpose HTTP/1.1 servers to:
4754  <list style="symbols">
4755     <t>understand any valid request in the format of HTTP/1.0 and
4756        1.1;</t>
4757
4758     <t>respond appropriately with a message in the same major version
4759        used by the client.</t>
4760  </list>
4761</t>
4762<t>
4763   And we would expect HTTP/1.1 clients to:
4764  <list style="symbols">
4765     <t>understand any valid response in the format of HTTP/1.0 or
4766        1.1.</t>
4767  </list>
4768</t>
4769<t>
4770   For most implementations of HTTP/1.0, each connection is established
4771   by the client prior to the request and closed by the server after
4772   sending the response. Some implementations implement the Keep-Alive
4773   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4774</t>
4775
4776<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4777<t>
4778   This section summarizes major differences between versions HTTP/1.0
4779   and HTTP/1.1.
4780</t>
4781
4782<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">
4783<t>
4784   The requirements that clients and servers support the Host request-header
4785   field (<xref target="header.host"/>), report an error if it is
4786   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4787   are among the most important changes defined by this
4788   specification.
4789</t>
4790<t>
4791   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4792   addresses and servers; there was no other established mechanism for
4793   distinguishing the intended server of a request than the IP address
4794   to which that request was directed. The changes outlined above will
4795   allow the Internet, once older HTTP clients are no longer common, to
4796   support multiple Web sites from a single IP address, greatly
4797   simplifying large operational Web servers, where allocation of many
4798   IP addresses to a single host has created serious problems. The
4799   Internet will also be able to recover the IP addresses that have been
4800   allocated for the sole purpose of allowing special-purpose domain
4801   names to be used in root-level HTTP URLs. Given the rate of growth of
4802   the Web, and the number of servers already deployed, it is extremely
4803   important that all implementations of HTTP (including updates to
4804   existing HTTP/1.0 applications) correctly implement these
4805   requirements:
4806  <list style="symbols">
4807     <t>Both clients and servers &MUST; support the Host request-header field.</t>
4808
4809     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header field.</t>
4810
4811     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4812        request does not include a Host request-header field.</t>
4813
4814     <t>Servers &MUST; accept absolute URIs.</t>
4815  </list>
4816</t>
4817</section>
4818</section>
4819
4820<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4821<t>
4822   Some clients and servers might wish to be compatible with some
4823   previous implementations of persistent connections in HTTP/1.0
4824   clients and servers. Persistent connections in HTTP/1.0 are
4825   explicitly negotiated as they are not the default behavior. HTTP/1.0
4826   experimental implementations of persistent connections are faulty,
4827   and the new facilities in HTTP/1.1 are designed to rectify these
4828   problems. The problem was that some existing HTTP/1.0 clients might
4829   send Keep-Alive to a proxy server that doesn't understand
4830   Connection, which would then erroneously forward it to the next
4831   inbound server, which would establish the Keep-Alive connection and
4832   result in a hung HTTP/1.0 proxy waiting for the close on the
4833   response. The result is that HTTP/1.0 clients must be prevented from
4834   using Keep-Alive when talking to proxies.
4835</t>
4836<t>
4837   However, talking to proxies is the most important use of persistent
4838   connections, so that prohibition is clearly unacceptable. Therefore,
4839   we need some other mechanism for indicating a persistent connection
4840   is desired, which is safe to use even when talking to an old proxy
4841   that ignores Connection. Persistent connections are the default for
4842   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4843   declaring non-persistence. See <xref target="header.connection"/>.
4844</t>
4845<t>
4846   The original HTTP/1.0 form of persistent connections (the Connection:
4847   Keep-Alive and Keep-Alive header field) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4848</t>
4849</section>
4850
4851<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4852<t>
4853  Empty list elements in list productions have been deprecated.
4854  (<xref target="notation.abnf"/>)
4855</t>
4856<t>
4857  Rules about implicit linear whitespace between certain grammar productions
4858  have been removed; now it's only allowed when specifically pointed out
4859  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4860  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4861  Non-ASCII content in header fields and reason phrase has been obsoleted and
4862  made opaque (the TEXT rule was removed)
4863  (<xref target="basic.rules"/>)
4864</t>
4865<t>
4866  Clarify that HTTP-Version is case sensitive.
4867  (<xref target="http.version"/>)
4868</t>
4869<t>
4870  Require that invalid whitespace around field-names be rejected.
4871  (<xref target="header.fields"/>)
4872</t>
4873<t>
4874  Require recipients to handle bogus Content-Length header fields as errors.
4875  (<xref target="message.body"/>)
4876</t>
4877<t>
4878  Remove reference to non-existent identity transfer-coding value tokens.
4879  (Sections <xref format="counter" target="message.body"/> and
4880  <xref format="counter" target="transfer.codings"/>)
4881</t>
4882<t>
4883  Update use of abs_path production from RFC 1808 to the path-absolute + query
4884  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4885  method only.
4886  (<xref target="request-target"/>)
4887</t>
4888<t>
4889  Clarification that the chunk length does not include the count of the octets
4890  in the chunk header and trailer. Furthermore disallowed line folding
4891  in chunk extensions.
4892  (<xref target="chunked.encoding"/>)
4893</t>
4894<t>
4895  Remove hard limit of two connections per server.
4896  (<xref target="persistent.practical"/>)
4897</t>
4898<t>
4899  Clarify exactly when close connection options must be sent.
4900  (<xref target="header.connection"/>)
4901</t>
4902<t>
4903  Define the semantics of the "Upgrade" header field in responses other than
4904  101 (this was incorporated from <xref target="RFC2817"/>).
4905  (<xref target="header.upgrade"/>)
4906</t>
4907</section>
4908</section>
4909
4910<?BEGININC p1-messaging.abnf-appendix ?>
4911<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4912<figure>
4913<artwork type="abnf" name="p1-messaging.parsed-abnf">
4914<x:ref>BWS</x:ref> = OWS
4915
4916<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4917<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4918<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4919<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4920 connection-token ] )
4921<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4922<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4923
4924<x:ref>Date</x:ref> = "Date:" OWS Date-v
4925<x:ref>Date-v</x:ref> = HTTP-date
4926
4927<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4928
4929<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4930<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4931<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4932<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4933 ]
4934<x:ref>Host</x:ref> = "Host:" OWS Host-v
4935<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4936
4937<x:ref>MIME-Version</x:ref> = &lt;MIME-Version, defined in [Part3], Appendix A.1&gt;
4938<x:ref>Method</x:ref> = token
4939
4940<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4941
4942<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4943
4944<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4945<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4946<x:ref>Request</x:ref> = Request-Line *( header-field CRLF ) CRLF [ message-body ]
4947<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4948<x:ref>Response</x:ref> = Status-Line *( header-field CRLF ) CRLF [ message-body ]
4949
4950<x:ref>Status-Code</x:ref> = 3DIGIT
4951<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4952
4953<x:ref>TE</x:ref> = "TE:" OWS TE-v
4954<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4955<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4956<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4957<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4958<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4959 transfer-coding ] )
4960
4961<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4962<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4963<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4964
4965<x:ref>Via</x:ref> = "Via:" OWS Via-v
4966<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4967 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4968 ] )
4969
4970<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4971
4972<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4973<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4974<x:ref>attribute</x:ref> = token
4975<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4976
4977<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4978<x:ref>chunk-data</x:ref> = 1*OCTET
4979<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4980<x:ref>chunk-ext-name</x:ref> = token
4981<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4982<x:ref>chunk-size</x:ref> = 1*HEXDIG
4983<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4984<x:ref>connection-token</x:ref> = token
4985<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4986 / %x2A-5B ; '*'-'['
4987 / %x5D-7E ; ']'-'~'
4988 / obs-text
4989
4990<x:ref>date1</x:ref> = day SP month SP year
4991<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4992<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4993<x:ref>day</x:ref> = 2DIGIT
4994<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4995 / %x54.75.65 ; Tue
4996 / %x57.65.64 ; Wed
4997 / %x54.68.75 ; Thu
4998 / %x46.72.69 ; Fri
4999 / %x53.61.74 ; Sat
5000 / %x53.75.6E ; Sun
5001<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
5002 / %x54.75.65.73.64.61.79 ; Tuesday
5003 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
5004 / %x54.68.75.72.73.64.61.79 ; Thursday
5005 / %x46.72.69.64.61.79 ; Friday
5006 / %x53.61.74.75.72.64.61.79 ; Saturday
5007 / %x53.75.6E.64.61.79 ; Sunday
5008
5009<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
5010<x:ref>field-name</x:ref> = token
5011<x:ref>field-value</x:ref> = *( field-content / OWS )
5012
5013<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
5014 / Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
5015
5016<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
5017<x:ref>hour</x:ref> = 2DIGIT
5018<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
5019<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
5020
5021<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
5022
5023<x:ref>message-body</x:ref> = *OCTET
5024<x:ref>minute</x:ref> = 2DIGIT
5025<x:ref>month</x:ref> = %x4A.61.6E ; Jan
5026 / %x46.65.62 ; Feb
5027 / %x4D.61.72 ; Mar
5028 / %x41.70.72 ; Apr
5029 / %x4D.61.79 ; May
5030 / %x4A.75.6E ; Jun
5031 / %x4A.75.6C ; Jul
5032 / %x41.75.67 ; Aug
5033 / %x53.65.70 ; Sep
5034 / %x4F.63.74 ; Oct
5035 / %x4E.6F.76 ; Nov
5036 / %x44.65.63 ; Dec
5037
5038<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
5039<x:ref>obs-fold</x:ref> = CRLF
5040<x:ref>obs-text</x:ref> = %x80-FF
5041
5042<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
5043<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
5044<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
5045<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
5046<x:ref>product</x:ref> = token [ "/" product-version ]
5047<x:ref>product-version</x:ref> = token
5048<x:ref>protocol-name</x:ref> = token
5049<x:ref>protocol-version</x:ref> = token
5050<x:ref>pseudonym</x:ref> = token
5051
5052<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
5053 / %x5D-7E ; ']'-'~'
5054 / obs-text
5055<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
5056 / %x5D-7E ; ']'-'~'
5057 / obs-text
5058<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
5059<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5060<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5061<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5062<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5063<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5064
5065<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5066<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5067<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5068<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5069<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5070 / authority
5071<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5072<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5073<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5074
5075<x:ref>second</x:ref> = 2DIGIT
5076<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5077 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5078<x:ref>start-line</x:ref> = Request-Line / Status-Line
5079
5080<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5081<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5082 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5083<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5084<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5085<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5086<x:ref>token</x:ref> = 1*tchar
5087<x:ref>trailer-part</x:ref> = *( header-field CRLF )
5088<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5089 transfer-extension
5090<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5091<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5092
5093<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5094
5095<x:ref>value</x:ref> = word
5096
5097<x:ref>word</x:ref> = token / quoted-string
5098
5099<x:ref>year</x:ref> = 4DIGIT
5100</artwork>
5101</figure>
5102<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5103; Chunked-Body defined but not used
5104; Content-Length defined but not used
5105; HTTP-message defined but not used
5106; Host defined but not used
5107; Request defined but not used
5108; Response defined but not used
5109; TE defined but not used
5110; URI-reference defined but not used
5111; general-header defined but not used
5112; http-URI defined but not used
5113; https-URI defined but not used
5114; partial-URI defined but not used
5115; request-header defined but not used
5116; response-header defined but not used
5117; special defined but not used
5118</artwork></figure></section>
5119<?ENDINC p1-messaging.abnf-appendix ?>
5120
5121<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5122
5123<section title="Since RFC 2616">
5124<t>
5125  Extracted relevant partitions from <xref target="RFC2616"/>.
5126</t>
5127</section>
5128
5129<section title="Since draft-ietf-httpbis-p1-messaging-00">
5130<t>
5131  Closed issues:
5132  <list style="symbols"> 
5133    <t>
5134      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5135      "HTTP Version should be case sensitive"
5136      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5137    </t>
5138    <t>
5139      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5140      "'unsafe' characters"
5141      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5142    </t>
5143    <t>
5144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5145      "Chunk Size Definition"
5146      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5147    </t>
5148    <t>
5149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5150      "Message Length"
5151      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5152    </t>
5153    <t>
5154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5155      "Media Type Registrations"
5156      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5157    </t>
5158    <t>
5159      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5160      "URI includes query"
5161      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5162    </t>
5163    <t>
5164      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5165      "No close on 1xx responses"
5166      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5167    </t>
5168    <t>
5169      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5170      "Remove 'identity' token references"
5171      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5172    </t>
5173    <t>
5174      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5175      "Import query BNF"
5176    </t>
5177    <t>
5178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5179      "qdtext BNF"
5180    </t>
5181    <t>
5182      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5183      "Normative and Informative references"
5184    </t>
5185    <t>
5186      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5187      "RFC2606 Compliance"
5188    </t>
5189    <t>
5190      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5191      "RFC977 reference"
5192    </t>
5193    <t>
5194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5195      "RFC1700 references"
5196    </t>
5197    <t>
5198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5199      "inconsistency in date format explanation"
5200    </t>
5201    <t>
5202      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5203      "Date reference typo"
5204    </t>
5205    <t>
5206      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5207      "Informative references"
5208    </t>
5209    <t>
5210      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5211      "ISO-8859-1 Reference"
5212    </t>
5213    <t>
5214      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5215      "Normative up-to-date references"
5216    </t>
5217  </list>
5218</t>
5219<t>
5220  Other changes:
5221  <list style="symbols"> 
5222    <t>
5223      Update media type registrations to use RFC4288 template.
5224    </t>
5225    <t>
5226      Use names of RFC4234 core rules DQUOTE and WSP,
5227      fix broken ABNF for chunk-data
5228      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5229    </t>
5230  </list>
5231</t>
5232</section>
5233
5234<section title="Since draft-ietf-httpbis-p1-messaging-01">
5235<t>
5236  Closed issues:
5237  <list style="symbols"> 
5238    <t>
5239      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5240      "Bodies on GET (and other) requests"
5241    </t>
5242    <t>
5243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5244      "Updating to RFC4288"
5245    </t>
5246    <t>
5247      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5248      "Status Code and Reason Phrase"
5249    </t>
5250    <t>
5251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5252      "rel_path not used"
5253    </t>
5254  </list>
5255</t>
5256<t>
5257  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5258  <list style="symbols"> 
5259    <t>
5260      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5261      "trailer-part").
5262    </t>
5263    <t>
5264      Avoid underscore character in rule names ("http_URL" ->
5265      "http-URL", "abs_path" -> "path-absolute").
5266    </t>
5267    <t>
5268      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5269      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5270      have to be updated when switching over to RFC3986.
5271    </t>
5272    <t>
5273      Synchronize core rules with RFC5234.
5274    </t>
5275    <t>
5276      Get rid of prose rules that span multiple lines.
5277    </t>
5278    <t>
5279      Get rid of unused rules LOALPHA and UPALPHA.
5280    </t>
5281    <t>
5282      Move "Product Tokens" section (back) into Part 1, as "token" is used
5283      in the definition of the Upgrade header field.
5284    </t>
5285    <t>
5286      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5287    </t>
5288    <t>
5289      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5290    </t>
5291  </list>
5292</t>
5293</section>
5294
5295<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5296<t>
5297  Closed issues:
5298  <list style="symbols"> 
5299    <t>
5300      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5301      "HTTP-date vs. rfc1123-date"
5302    </t>
5303    <t>
5304      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5305      "WS in quoted-pair"
5306    </t>
5307  </list>
5308</t>
5309<t>
5310  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5311  <list style="symbols"> 
5312    <t>
5313      Reference RFC 3984, and update header field registrations for headers defined
5314      in this document.
5315    </t>
5316  </list>
5317</t>
5318<t>
5319  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5320  <list style="symbols"> 
5321    <t>
5322      Replace string literals when the string really is case-sensitive (HTTP-Version).
5323    </t>
5324  </list>
5325</t>
5326</section>
5327
5328<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5329<t>
5330  Closed issues:
5331  <list style="symbols"> 
5332    <t>
5333      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5334      "Connection closing"
5335    </t>
5336    <t>
5337      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5338      "Move registrations and registry information to IANA Considerations"
5339    </t>
5340    <t>
5341      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5342      "need new URL for PAD1995 reference"
5343    </t>
5344    <t>
5345      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5346      "IANA Considerations: update HTTP URI scheme registration"
5347    </t>
5348    <t>
5349      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5350      "Cite HTTPS URI scheme definition"
5351    </t>
5352    <t>
5353      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5354      "List-type headers vs Set-Cookie"
5355    </t>
5356  </list>
5357</t>
5358<t>
5359  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5360  <list style="symbols"> 
5361    <t>
5362      Replace string literals when the string really is case-sensitive (HTTP-Date).
5363    </t>
5364    <t>
5365      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5366    </t>
5367  </list>
5368</t>
5369</section>
5370
5371<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5372<t>
5373  Closed issues:
5374  <list style="symbols"> 
5375    <t>
5376      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5377      "Out-of-date reference for URIs"
5378    </t>
5379    <t>
5380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5381      "RFC 2822 is updated by RFC 5322"
5382    </t>
5383  </list>
5384</t>
5385<t>
5386  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5387  <list style="symbols"> 
5388    <t>
5389      Use "/" instead of "|" for alternatives.
5390    </t>
5391    <t>
5392      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5393    </t>
5394    <t>
5395      Only reference RFC 5234's core rules.
5396    </t>
5397    <t>
5398      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5399      whitespace ("OWS") and required whitespace ("RWS").
5400    </t>
5401    <t>
5402      Rewrite ABNFs to spell out whitespace rules, factor out
5403      header field value format definitions.
5404    </t>
5405  </list>
5406</t>
5407</section>
5408
5409<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5410<t>
5411  Closed issues:
5412  <list style="symbols"> 
5413    <t>
5414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5415      "Header LWS"
5416    </t>
5417    <t>
5418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5419      "Sort 1.3 Terminology"
5420    </t>
5421    <t>
5422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5423      "RFC2047 encoded words"
5424    </t>
5425    <t>
5426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5427      "Character Encodings in TEXT"
5428    </t>
5429    <t>
5430      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5431      "Line Folding"
5432    </t>
5433    <t>
5434      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5435      "OPTIONS * and proxies"
5436    </t>
5437    <t>
5438      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5439      "Reason-Phrase BNF"
5440    </t>
5441    <t>
5442      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5443      "Use of TEXT"
5444    </t>
5445    <t>
5446      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5447      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5448    </t>
5449    <t>
5450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5451      "RFC822 reference left in discussion of date formats"
5452    </t>
5453  </list>
5454</t>
5455<t>
5456  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5457  <list style="symbols"> 
5458    <t>
5459      Rewrite definition of list rules, deprecate empty list elements.
5460    </t>
5461    <t>
5462      Add appendix containing collected and expanded ABNF.
5463    </t>
5464  </list>
5465</t>
5466<t>
5467  Other changes:
5468  <list style="symbols"> 
5469    <t>
5470      Rewrite introduction; add mostly new Architecture Section.
5471    </t>
5472    <t>
5473      Move definition of quality values from Part 3 into Part 1;
5474      make TE request header field grammar independent of accept-params (defined in Part 3).
5475    </t>
5476  </list>
5477</t>
5478</section>
5479
5480<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5481<t>
5482  Closed issues:
5483  <list style="symbols"> 
5484    <t>
5485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5486      "base for numeric protocol elements"
5487    </t>
5488    <t>
5489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5490      "comment ABNF"
5491    </t>
5492  </list>
5493</t>
5494<t>
5495  Partly resolved issues:
5496  <list style="symbols"> 
5497    <t>
5498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5499      "205 Bodies" (took out language that implied that there might be
5500      methods for which a request body MUST NOT be included)
5501    </t>
5502    <t>
5503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5504      "editorial improvements around HTTP-date"
5505    </t>
5506  </list>
5507</t>
5508</section>
5509
5510<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5511<t>
5512  Closed issues:
5513  <list style="symbols"> 
5514    <t>
5515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5516      "Repeating single-value headers"
5517    </t>
5518    <t>
5519      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5520      "increase connection limit"
5521    </t>
5522    <t>
5523      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5524      "IP addresses in URLs"
5525    </t>
5526    <t>
5527      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5528      "take over HTTP Upgrade Token Registry"
5529    </t>
5530    <t>
5531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5532      "CR and LF in chunk extension values"
5533    </t>
5534    <t>
5535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5536      "HTTP/0.9 support"
5537    </t>
5538    <t>
5539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5540      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5541    </t>
5542    <t>
5543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5544      "move definitions of gzip/deflate/compress to part 1"
5545    </t>
5546    <t>
5547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5548      "disallow control characters in quoted-pair"
5549    </t>
5550  </list>
5551</t>
5552<t>
5553  Partly resolved issues:
5554  <list style="symbols"> 
5555    <t>
5556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5557      "update IANA requirements wrt Transfer-Coding values" (add the
5558      IANA Considerations subsection)
5559    </t>
5560  </list>
5561</t>
5562</section>
5563
5564<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5565<t>
5566  Closed issues:
5567  <list style="symbols"> 
5568    <t>
5569      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5570      "header parsing, treatment of leading and trailing OWS"
5571    </t>
5572  </list>
5573</t>
5574<t>
5575  Partly resolved issues:
5576  <list style="symbols"> 
5577    <t>
5578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5579      "Placement of 13.5.1 and 13.5.2"
5580    </t>
5581    <t>
5582      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5583      "use of term "word" when talking about header structure"
5584    </t>
5585  </list>
5586</t>
5587</section>
5588
5589<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5590<t>
5591  Closed issues:
5592  <list style="symbols"> 
5593    <t>
5594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5595      "Clarification of the term 'deflate'"
5596    </t>
5597    <t>
5598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5599      "OPTIONS * and proxies"
5600    </t>
5601    <t>
5602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5603      "MIME-Version not listed in P1, general header fields"
5604    </t>
5605    <t>
5606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5607      "IANA registry for content/transfer encodings"
5608    </t>
5609    <t>
5610      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5611      "Case-sensitivity of HTTP-date"
5612    </t>
5613    <t>
5614      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5615      "use of term "word" when talking about header structure"
5616    </t>
5617  </list>
5618</t>
5619<t>
5620  Partly resolved issues:
5621  <list style="symbols"> 
5622    <t>
5623      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5624      "Term for the requested resource's URI"
5625    </t>
5626  </list>
5627</t>
5628</section>
5629
5630<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5631<t>
5632  Closed issues:
5633  <list style="symbols">
5634    <t>
5635      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5636      "Connection Closing"
5637    </t>
5638    <t>
5639      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5640      "Delimiting messages with multipart/byteranges"
5641    </t>
5642    <t>
5643      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5644      "Handling multiple Content-Length headers"
5645    </t>
5646    <t>
5647      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5648      "Clarify entity / representation / variant terminology"
5649    </t>
5650    <t>
5651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5652      "consider removing the 'changes from 2068' sections"
5653    </t>
5654  </list>
5655</t>
5656<t>
5657  Partly resolved issues:
5658  <list style="symbols"> 
5659    <t>
5660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5661      "HTTP(s) URI scheme definitions"
5662    </t>
5663  </list>
5664</t>
5665</section>
5666
5667<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5668<t>
5669  Closed issues:
5670  <list style="symbols">
5671    <t>
5672      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5673      "Trailer requirements"
5674    </t>
5675    <t>
5676      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5677      "Text about clock requirement for caches belongs in p6"
5678    </t>
5679    <t>
5680      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5681      "effective request URI: handling of missing host in HTTP/1.0"
5682    </t>
5683    <t>
5684      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5685      "confusing Date requirements for clients"
5686    </t>
5687  </list>
5688</t>
5689<t>
5690  Partly resolved issues:
5691  <list style="symbols"> 
5692    <t>
5693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5694      "Handling multiple Content-Length headers"
5695    </t>
5696  </list>
5697</t>
5698</section>
5699
5700<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5701<t>
5702  Closed issues:
5703  <list style="symbols">
5704    <t>
5705      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5706      "Is * usable as a request-uri for new methods?"
5707    </t>
5708    <t>
5709      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5710      "Migrate Upgrade details from RFC2817"
5711    </t>
5712  </list>
5713</t>
5714</section>
5715
5716</section>
5717
5718</back>
5719</rfc>
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