source: draft-ietf-httpbis/latest/p1-messaging.xml @ 808

Last change on this file since 808 was 808, checked in by julian.reschke@…, 10 years ago

Clarify not to share coding names between the content coding and the transfer coding registry unless the encoding is the same (see #143)

  • Property svn:eol-style set to native
File size: 235.9 KB
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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 "April">
16  <!ENTITY ID-YEAR "2010">
17  <!ENTITY caching-overview       "<xref target='Part6' x:rel='#caching.overview' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY entity-length          "<xref target='Part3' x:rel='#entity.length' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39]>
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="yes"?>
49<?rfc rfcedstyle="yes"?>
50<?rfc-ext allow-markup-in-artwork="yes" ?>
51<?rfc-ext include-references-in-index="yes" ?>
52<rfc obsoletes="2616" updates="2817" category="std" x:maturity-level="draft"
53     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
54     xmlns:x='http://purl.org/net/xml2rfc/ext'>
55<front>
56
57  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
58
59  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
60    <organization abbrev="Day Software">Day Software</organization>
61    <address>
62      <postal>
63        <street>23 Corporate Plaza DR, Suite 280</street>
64        <city>Newport Beach</city>
65        <region>CA</region>
66        <code>92660</code>
67        <country>USA</country>
68      </postal>
69      <phone>+1-949-706-5300</phone>
70      <facsimile>+1-949-706-5305</facsimile>
71      <email>fielding@gbiv.com</email>
72      <uri>http://roy.gbiv.com/</uri>
73    </address>
74  </author>
75
76  <author initials="J." surname="Gettys" fullname="Jim Gettys">
77    <organization>One Laptop per Child</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@laptop.org</email>
87      <uri>http://www.laptop.org/</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/11"/>
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.09"/>.
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 &diff2045entity; 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 a generic protocol for translating
254   communication to and from other Internet information systems.
255   HTTP proxies and gateways provide access to alternative information
256   services by translating their diverse protocols into a hypertext
257   format that can be viewed and manipulated by clients in the same way
258   as HTTP services.
259</t>
260<t>
261   One consequence of HTTP flexibility is that the protocol cannot be
262   defined in terms of what occurs behind the interface. Instead, we
263   are limited to defining the syntax of communication, the intent
264   of received communication, and the expected behavior of recipients.
265   If the communication is considered in isolation, then successful
266   actions should be reflected in corresponding changes to the
267   observable interface provided by servers. However, since multiple
268   clients may 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 syntactical 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 except the entity-body (see <xref target="tolerant.applications"/> for
424   tolerant applications). The end-of-line marker within an entity-body
425   is defined by its associated media type, as described in &media-types;.
426</t>
427<t anchor="rule.LWS">
428   This specification uses three rules to denote the use of linear
429   whitespace: OWS (optional whitespace), RWS (required whitespace), and
430   BWS ("bad" whitespace).
431</t>
432<t>
433   The OWS rule is used where zero or more linear whitespace characters may
434   appear. OWS &SHOULD; either not be produced or be produced as a single SP
435   character. Multiple OWS characters that occur within field-content &SHOULD;
436   be replaced with a single SP before interpreting the field value or
437   forwarding the message downstream.
438</t>
439<t>
440   RWS is used when at least one linear whitespace character is required to
441   separate field tokens. RWS &SHOULD; be produced as a single SP character.
442   Multiple RWS characters that occur within field-content &SHOULD; be
443   replaced with a single SP before interpreting the field value or
444   forwarding the message downstream.
445</t>
446<t>
447   BWS is used where the grammar allows optional whitespace for historical
448   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
449   recipients &MUST; accept such bad optional whitespace and remove it before
450   interpreting the field value or forwarding the message downstream.
451</t>
452<t anchor="rule.whitespace">
453  <x:anchor-alias value="BWS"/>
454  <x:anchor-alias value="OWS"/>
455  <x:anchor-alias value="RWS"/>
456  <x:anchor-alias value="obs-fold"/>
457</t>
458<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"/>
459  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
460                 ; "optional" whitespace
461  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
462                 ; "required" whitespace
463  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
464                 ; "bad" whitespace
465  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
466                 ; see <xref target="header.fields"/>
467</artwork></figure>
468<t anchor="rule.token.separators">
469  <x:anchor-alias value="tchar"/>
470  <x:anchor-alias value="token"/>
471  <x:anchor-alias value="special"/>
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="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
478  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
479<!--
480  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
481 -->
482  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
483                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
484                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
485                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
486
487  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
488                 / ";" / ":" / "\" / DQUOTE / "/" / "["
489                 / "]" / "?" / "=" / "{" / "}"
490</artwork></figure>
491<t anchor="rule.quoted-string">
492  <x:anchor-alias value="quoted-string"/>
493  <x:anchor-alias value="qdtext"/>
494  <x:anchor-alias value="obs-text"/>
495   A string of text is parsed as a single word if it is quoted using
496   double-quote marks.
497</t>
498<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"/>
499  <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>
500  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
501                 ; <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> 
502  <x:ref>obs-text</x:ref>       = %x80-FF
503</artwork></figure>
504<t anchor="rule.quoted-pair">
505  <x:anchor-alias value="quoted-pair"/>
506   The backslash character ("\") can be used as a single-character
507   quoting mechanism within quoted-string constructs:
508</t>
509<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
510  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
511</artwork></figure>
512<t>
513   Producers &SHOULD-NOT; escape characters that do not require escaping
514   (i.e., other than DQUOTE and the backslash character).
515</t>
516</section>
517
518<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
519  <x:anchor-alias value="request-header"/>
520  <x:anchor-alias value="response-header"/>
521  <x:anchor-alias value="entity-body"/>
522  <x:anchor-alias value="entity-header"/>
523  <x:anchor-alias value="Cache-Control"/>
524  <x:anchor-alias value="Pragma"/>
525  <x:anchor-alias value="Warning"/>
526<t>
527  The ABNF rules below are defined in other parts:
528</t>
529<figure><!-- Part2--><artwork type="abnf2616">
530  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
531  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
532</artwork></figure>
533<figure><!-- Part3--><artwork type="abnf2616">
534  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
535  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&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 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 Operation" anchor="operation">
556<iref item="client"/>
557<iref item="server"/>
558<iref item="connection"/>
559<t>
560   HTTP is a request/response protocol that operates by exchanging messages
561   across a reliable transport or session-layer connection. An HTTP client
562   is a program that establishes a connection to a server for the purpose
563   of sending one or more HTTP requests.  An HTTP server is a program that
564   accepts connections in order to service HTTP requests by sending HTTP
565   responses.
566</t>
567<iref item="user agent"/>
568<iref item="origin server"/>
569<t>
570   Note that the terms "client" and "server" refer only to the roles that
571   these programs perform for a particular connection.  The same program
572   may act as a client on some connections and a server on others.  We use
573   the term "user agent" to refer to the program that initiates a request,
574   such as a WWW browser, editor, or spider (web-traversing robot), and
575   the term "origin server" to refer to the program that can originate
576   authoritative responses to a request.
577</t>
578<t>
579   Most HTTP communication consists of a retrieval request (GET) for
580   a representation of some resource identified by a URI.  In the
581   simplest case, this may be accomplished via a single connection (v)
582   between the user agent (UA) and the origin server (O).
583</t>
584<figure><artwork type="drawing">
585       request chain ------------------------&gt;
586    UA -------------------v------------------- O
587       &lt;----------------------- response chain
588</artwork></figure>
589<iref item="message"/>
590<iref item="request"/>
591<iref item="response"/>
592<t>
593   A client sends an HTTP request to the server in the form of a request
594   message (<xref target="request"/>), beginning with a method, URI, and
595   protocol version, followed by MIME-like header fields containing
596   request modifiers, client information, and payload metadata, an empty
597   line to indicate the end of the header section, and finally the payload
598   body (if any).
599</t>
600<t>
601   A server responds to the client's request by sending an HTTP response
602   message (<xref target="response"/>), beginning with a status line that
603   includes the protocol version, a success or error code, and textual
604   reason phrase, followed by MIME-like header fields containing server
605   information, resource metadata, and payload metadata, an empty line to
606   indicate the end of the header section, and finally the payload body (if any).
607</t>
608<t>
609   The following example illustrates a typical message exchange for a
610   GET request on the URI "http://www.example.com/hello.txt":
611</t>
612<figure><preamble>
613client request:
614</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
615GET /hello.txt HTTP/1.1
616User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
617Host: www.example.com
618Accept: */*
619
620</artwork></figure>
621<figure><preamble>
622server response:
623</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
624HTTP/1.1 200 OK
625Date: Mon, 27 Jul 2009 12:28:53 GMT
626Server: Apache
627Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
628ETag: "34aa387-d-1568eb00"
629Accept-Ranges: bytes
630Content-Length: <x:length-of target="exbody"/>
631Vary: Accept-Encoding
632Content-Type: text/plain
633
634<x:span anchor="exbody">Hello World!
635</x:span></artwork></figure>
636</section>
637
638<section title="Intermediaries" anchor="intermediaries">
639<t>
640   A more complicated situation occurs when one or more intermediaries
641   are present in the request/response chain. There are three common
642   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
643   a single intermediary may act as an origin server, proxy, gateway,
644   or tunnel, switching behavior based on the nature of each request.
645</t>
646<figure><artwork type="drawing">
647       request chain --------------------------------------&gt;
648    UA -----v----- A -----v----- B -----v----- C -----v----- O
649       &lt;------------------------------------- response chain
650</artwork></figure>
651<t>
652   The figure above shows three intermediaries (A, B, and C) between the
653   user agent and origin server. A request or response message that
654   travels the whole chain will pass through four separate connections.
655   Some HTTP communication options
656   may apply only to the connection with the nearest, non-tunnel
657   neighbor, only to the end-points of the chain, or to all connections
658   along the chain. Although the diagram is linear, each participant may
659   be engaged in multiple, simultaneous communications. For example, B
660   may be receiving requests from many clients other than A, and/or
661   forwarding requests to servers other than C, at the same time that it
662   is handling A's request.
663</t>
664<t>
665<iref item="upstream"/><iref item="downstream"/>
666<iref item="inbound"/><iref item="outbound"/>
667   We use the terms "upstream" and "downstream" to describe various
668   requirements in relation to the directional flow of a message:
669   all messages flow from upstream to downstream.
670   Likewise, we use the terms "inbound" and "outbound" to refer to
671   directions in relation to the request path: "inbound" means toward
672   the origin server and "outbound" means toward the user agent.
673</t>
674<t><iref item="proxy"/>
675   A proxy is a message forwarding agent that is selected by the
676   client, usually via local configuration rules, to receive requests
677   for some type(s) of absolute URI and attempt to satisfy those
678   requests via translation through the HTTP interface.  Some translations
679   are minimal, such as for proxy requests for "http" URIs, whereas
680   other requests may require translation to and from entirely different
681   application-layer protocols. Proxies are often used to group an
682   organization's HTTP requests through a common intermediary for the
683   sake of security, annotation services, or shared caching.
684</t>
685<t><iref item="gateway"/><iref item="reverse proxy"/>
686   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
687   as a layer above some other server(s) and translates the received
688   requests to the underlying server's protocol.  Gateways are often
689   used for load balancing or partitioning HTTP services across
690   multiple machines.
691   Unlike a proxy, a gateway receives requests as if it were the
692   origin server for the requested resource; the requesting client
693   will not be aware that it is communicating with a gateway.
694   A gateway communicates with the client as if the gateway is the
695   origin server and thus is subject to all of the requirements on
696   origin servers for that connection.  A gateway communicates
697   with inbound servers using any protocol it desires, including
698   private extensions to HTTP that are outside the scope of this
699   specification.
700</t>
701<t><iref item="tunnel"/>
702   A tunnel acts as a blind relay between two connections
703   without changing the messages. Once active, a tunnel is not
704   considered a party to the HTTP communication, though the tunnel may
705   have been initiated by an HTTP request. A tunnel ceases to exist when
706   both ends of the relayed connection are closed. Tunnels are used to
707   extend a virtual connection through an intermediary, such as when
708   transport-layer security is used to establish private communication
709   through a shared firewall proxy.
710</t>
711</section>
712
713<section title="Caches" anchor="caches">
714<iref item="cache"/>
715<t>
716   Any party to HTTP communication that is not acting as a tunnel may
717   employ an internal cache for handling requests.
718   A cache is a local store of previous response messages and the
719   subsystem that controls its message storage, retrieval, and deletion.
720   A cache stores cacheable responses in order to reduce the response
721   time and network bandwidth consumption on future, equivalent
722   requests. Any client or server may include a cache, though a cache
723   cannot be used by a server while it is acting as a tunnel.
724</t>
725<t>
726   The effect of a cache is that the request/response chain is shortened
727   if one of the participants along the chain has a cached response
728   applicable to that request. The following illustrates the resulting
729   chain if B has a cached copy of an earlier response from O (via C)
730   for a request which has not been cached by UA or A.
731</t>
732<figure><artwork type="drawing">
733          request chain ----------&gt;
734       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
735          &lt;--------- response chain
736</artwork></figure>
737<t><iref item="cacheable"/>
738   A response is cacheable if a cache is allowed to store a copy of
739   the response message for use in answering subsequent requests.
740   Even when a response is cacheable, there may be additional
741   constraints placed by the client or by the origin server on when
742   that cached response can be used for a particular request. HTTP
743   requirements for cache behavior and cacheable responses are
744   defined in &caching-overview;
745</t>
746<t>
747   There are a wide variety of architectures and configurations
748   of caches and proxies deployed across the World Wide Web and
749   inside large organizations. These systems include national hierarchies
750   of proxy caches to save transoceanic bandwidth, systems that
751   broadcast or multicast cache entries, organizations that distribute
752   subsets of cached data via optical media, and so on.
753</t>
754</section>
755
756<section title="Transport Independence" anchor="transport-independence">
757<t>
758  HTTP systems are used in a wide variety of environments, from
759  corporate intranets with high-bandwidth links to long-distance
760  communication over low-power radio links and intermittent connectivity.
761</t>
762<t>
763   HTTP communication usually takes place over TCP/IP connections. The
764   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
765   not preclude HTTP from being implemented on top of any other protocol
766   on the Internet, or on other networks. HTTP only presumes a reliable
767   transport; any protocol that provides such guarantees can be used;
768   the mapping of the HTTP/1.1 request and response structures onto the
769   transport data units of the protocol in question is outside the scope
770   of this specification.
771</t>
772<t>
773   In HTTP/1.0, most implementations used a new connection for each
774   request/response exchange. In HTTP/1.1, a connection may be used for
775   one or more request/response exchanges, although connections may be
776   closed for a variety of reasons (see <xref target="persistent.connections"/>).
777</t>
778</section>
779
780<section title="HTTP Version" anchor="http.version">
781  <x:anchor-alias value="HTTP-Version"/>
782  <x:anchor-alias value="HTTP-Prot-Name"/>
783<t>
784   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
785   of the protocol. The protocol versioning policy is intended to allow
786   the sender to indicate the format of a message and its capacity for
787   understanding further HTTP communication, rather than the features
788   obtained via that communication. No change is made to the version
789   number for the addition of message components which do not affect
790   communication behavior or which only add to extensible field values.
791   The &lt;minor&gt; number is incremented when the changes made to the
792   protocol add features which do not change the general message parsing
793   algorithm, but which may add to the message semantics and imply
794   additional capabilities of the sender. The &lt;major&gt; number is
795   incremented when the format of a message within the protocol is
796   changed. See <xref target="RFC2145"/> for a fuller explanation.
797</t>
798<t>
799   The version of an HTTP message is indicated by an HTTP-Version field
800   in the first line of the message. HTTP-Version is case-sensitive.
801</t>
802<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
803  <x:ref>HTTP-Version</x:ref>   = <x:ref>HTTP-Prot-Name</x:ref> "/" 1*<x:ref>DIGIT</x:ref> "." 1*<x:ref>DIGIT</x:ref>
804  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
805</artwork></figure>
806<t>
807   Note that the major and minor numbers &MUST; be treated as separate
808   integers and that each &MAY; be incremented higher than a single digit.
809   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
810   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
811   &MUST-NOT; be sent.
812</t>
813<t>
814   An application that sends a request or response message that includes
815   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
816   with this specification. Applications that are at least conditionally
817   compliant with this specification &SHOULD; use an HTTP-Version of
818   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
819   not compatible with HTTP/1.0. For more details on when to send
820   specific HTTP-Version values, see <xref target="RFC2145"/>.
821</t>
822<t>
823   The HTTP version of an application is the highest HTTP version for
824   which the application is at least conditionally compliant.
825</t>
826<t>
827   Proxy and gateway applications need to be careful when forwarding
828   messages in protocol versions different from that of the application.
829   Since the protocol version indicates the protocol capability of the
830   sender, a proxy/gateway &MUST-NOT; send a message with a version
831   indicator which is greater than its actual version. If a higher
832   version request is received, the proxy/gateway &MUST; either downgrade
833   the request version, or respond with an error, or switch to tunnel
834   behavior.
835</t>
836<t>
837   Due to interoperability problems with HTTP/1.0 proxies discovered
838   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
839   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
840   they support. The proxy/gateway's response to that request &MUST; be in
841   the same major version as the request.
842</t>
843<x:note>
844  <t>
845    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
846    of header fields required or forbidden by the versions involved.
847  </t>
848</x:note>
849</section>
850
851<section title="Uniform Resource Identifiers" anchor="uri">
852<iref primary="true" item="resource"/>
853<t>
854   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
855   throughout HTTP as the means for identifying resources. URI references
856   are used to target requests, indicate redirects, and define relationships.
857   HTTP does not limit what a resource may be; it merely defines an interface
858   that can be used to interact with a resource via HTTP. More information on
859   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
860</t>
861  <x:anchor-alias value="URI-reference"/>
862  <x:anchor-alias value="absolute-URI"/>
863  <x:anchor-alias value="relative-part"/>
864  <x:anchor-alias value="authority"/>
865  <x:anchor-alias value="path-abempty"/>
866  <x:anchor-alias value="path-absolute"/>
867  <x:anchor-alias value="port"/>
868  <x:anchor-alias value="query"/>
869  <x:anchor-alias value="uri-host"/>
870  <x:anchor-alias value="partial-URI"/>
871<t>
872   This specification adopts the definitions of "URI-reference",
873   "absolute-URI", "relative-part", "port", "host",
874   "path-abempty", "path-absolute", "query", and "authority" from
875   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
876   protocol elements that allow a relative URI without a fragment.
877</t>
878<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="URI-reference"/><iref primary="true" item="Grammar" subitem="absolute-URI"/><iref primary="true" item="Grammar" subitem="authority"/><iref primary="true" item="Grammar" subitem="path-absolute"/><iref primary="true" item="Grammar" subitem="port"/><iref primary="true" item="Grammar" subitem="query"/><iref primary="true" item="Grammar" subitem="uri-host"/>
879  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
880  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
881  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
882  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
883  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
884  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
885  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
886  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
887  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
888 
889  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
890</artwork></figure>
891<t>
892   Each protocol element in HTTP that allows a URI reference will indicate in
893   its ABNF production whether the element allows only a URI in absolute form
894   (absolute-URI), any relative reference (relative-ref), or some other subset
895   of the URI-reference grammar. Unless otherwise indicated, URI references
896   are parsed relative to the request target (the default base URI for both
897   the request and its corresponding response).
898</t>
899
900<section title="http URI scheme" anchor="http.uri">
901  <x:anchor-alias value="http-URI"/>
902  <iref item="http URI scheme" primary="true"/>
903  <iref item="URI scheme" subitem="http" primary="true"/>
904<t>
905   The "http" URI scheme is hereby defined for the purpose of minting
906   identifiers according to their association with the hierarchical
907   namespace governed by a potential HTTP origin server listening for
908   TCP connections on a given port.
909   The HTTP server is identified via the generic syntax's
910   <x:ref>authority</x:ref> component, which includes a host
911   identifier and optional TCP port, and the remainder of the URI is
912   considered to be identifying data corresponding to a resource for
913   which that server might provide an HTTP interface.
914</t>
915<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
916  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
917</artwork></figure>
918<t>
919   The host identifier within an <x:ref>authority</x:ref> component is
920   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
921   provided as an IP literal or IPv4 address, then the HTTP server is any
922   listener on the indicated TCP port at that IP address. If host is a
923   registered name, then that name is considered an indirect identifier
924   and the recipient might use a name resolution service, such as DNS,
925   to find the address of a listener for that host.
926   The host &MUST-NOT; be empty; if an "http" URI is received with an
927   empty host, then it &MUST; be rejected as invalid.
928   If the port subcomponent is empty or not given, then TCP port 80 is
929   assumed (the default reserved port for WWW services).
930</t>
931<t>
932   Regardless of the form of host identifier, access to that host is not
933   implied by the mere presence of its name or address. The host may or may
934   not exist and, even when it does exist, may or may not be running an
935   HTTP server or listening to the indicated port. The "http" URI scheme
936   makes use of the delegated nature of Internet names and addresses to
937   establish a naming authority (whatever entity has the ability to place
938   an HTTP server at that Internet name or address) and allows that
939   authority to determine which names are valid and how they might be used.
940</t>
941<t>
942   When an "http" URI is used within a context that calls for access to the
943   indicated resource, a client &MAY; attempt access by resolving
944   the host to an IP address, establishing a TCP connection to that address
945   on the indicated port, and sending an HTTP request message to the server
946   containing the URI's identifying data as described in <xref target="request"/>.
947   If the server responds to that request with a non-interim HTTP response
948   message, as described in <xref target="response"/>, then that response
949   is considered an authoritative answer to the client's request.
950</t>
951<t>
952   Although HTTP is independent of the transport protocol, the "http"
953   scheme is specific to TCP-based services because the name delegation
954   process depends on TCP for establishing authority.
955   An HTTP service based on some other underlying connection protocol
956   would presumably be identified using a different URI scheme, just as
957   the "https" scheme (below) is used for servers that require an SSL/TLS
958   transport layer on a connection. Other protocols may also be used to
959   provide access to "http" identified resources --- it is only the
960   authoritative interface used for mapping the namespace that is
961   specific to TCP.
962</t>
963</section>
964
965<section title="https URI scheme" anchor="https.uri">
966   <x:anchor-alias value="https-URI"/>
967   <iref item="https URI scheme"/>
968   <iref item="URI scheme" subitem="https"/>
969<t>
970   The "https" URI scheme is hereby defined for the purpose of minting
971   identifiers according to their association with the hierarchical
972   namespace governed by a potential HTTP origin server listening for
973   SSL/TLS-secured connections on a given TCP port.
974   The host and port are determined in the same way
975   as for the "http" scheme, except that a default TCP port of 443
976   is assumed if the port subcomponent is empty or not given.
977</t>
978<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
979  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
980</artwork></figure>
981<t>
982   The primary difference between the "http" and "https" schemes is
983   that interaction with the latter is required to be secured for
984   privacy through the use of strong encryption. The URI cannot be
985   sent in a request until the connection is secure. Likewise, the
986   default for caching is that each response that would be considered
987   "public" under the "http" scheme is instead treated as "private"
988   and thus not eligible for shared caching.
989</t>
990<t>
991   The process for authoritative access to an "https" identified
992   resource is defined in <xref target="RFC2818"/>.
993</t>
994</section>
995
996<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
997<t>
998   Since the "http" and "https" schemes conform to the URI generic syntax,
999   such URIs are normalized and compared according to the algorithm defined
1000   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1001   described above for each scheme.
1002</t>
1003<t>
1004   If the port is equal to the default port for a scheme, the normal
1005   form is to elide the port subcomponent. Likewise, an empty path
1006   component is equivalent to an absolute path of "/", so the normal
1007   form is to provide a path of "/" instead. The scheme and host
1008   are case-insensitive and normally provided in lowercase; all
1009   other components are compared in a case-sensitive manner.
1010   Characters other than those in the "reserved" set are equivalent
1011   to their percent-encoded octets (see <xref target="RFC3986"
1012   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1013</t>
1014<t>
1015   For example, the following three URIs are equivalent:
1016</t>
1017<figure><artwork type="example">
1018   http://example.com:80/~smith/home.html
1019   http://EXAMPLE.com/%7Esmith/home.html
1020   http://EXAMPLE.com:/%7esmith/home.html
1021</artwork></figure>
1022<t>
1023   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1024   If path-abempty is the empty string (i.e., there is no slash "/"
1025   path separator following the authority), then the "http" URI
1026   &MUST; be given as "/" when
1027   used as a request-target (<xref target="request-target"/>). If a proxy
1028   receives a host name which is not a fully qualified domain name, it
1029   &MAY; add its domain to the host name it received. If a proxy receives
1030   a fully qualified domain name, the proxy &MUST-NOT; change the host
1031   name.
1032</t>
1033</section>
1034</section>
1035</section>
1036
1037<section title="HTTP Message" anchor="http.message">
1038<x:anchor-alias value="generic-message"/>
1039<x:anchor-alias value="message.types"/>
1040<x:anchor-alias value="HTTP-message"/>
1041<x:anchor-alias value="start-line"/>
1042<iref item="header section"/>
1043<iref item="headers"/>
1044<iref item="header field"/>
1045<t>
1046   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1047   characters in a format similar to the Internet Message Format
1048   <xref target="RFC5322"/>: zero or more header fields (collectively
1049   referred to as the "headers" or the "header section"), an empty line
1050   indicating the end of the header section, and an optional message-body.
1051</t>
1052<t>
1053   An HTTP message can either be a request from client to server or a
1054   response from server to client.  Syntactically, the two types of message
1055   differ only in the start-line, which is either a Request-Line (for requests)
1056   or a Status-Line (for responses), and in the algorithm for determining
1057   the length of the message-body (<xref target="message.length"/>).
1058   In theory, a client could receive requests and a server could receive
1059   responses, distinguishing them by their different start-line formats,
1060   but in practice servers are implemented to only expect a request
1061   (a response is interpreted as an unknown or invalid request method)
1062   and clients are implemented to only expect a response.
1063</t>
1064<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1065  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1066                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1067                    <x:ref>CRLF</x:ref>
1068                    [ <x:ref>message-body</x:ref> ]
1069  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1070</artwork></figure>
1071<t>
1072   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1073   header field. The presence of whitespace might be an attempt to trick a
1074   noncompliant implementation of HTTP into ignoring that field or processing
1075   the next line as a new request, either of which may result in security
1076   issues when implementations within the request chain interpret the
1077   same message differently. HTTP/1.1 servers &MUST; reject such a message
1078   with a 400 (Bad Request) response.
1079</t>
1080
1081<section title="Message Parsing Robustness" anchor="message.robustness">
1082<t>
1083   In the interest of robustness, servers &SHOULD; ignore at least one
1084   empty line received where a Request-Line is expected. In other words, if
1085   the server is reading the protocol stream at the beginning of a
1086   message and receives a CRLF first, it should ignore the CRLF.
1087</t>
1088<t>
1089   Some old HTTP/1.0 client implementations generate an extra CRLF
1090   after a POST request as a lame workaround for some early server
1091   applications that failed to read message-body content that was
1092   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1093   preface or follow a request with an extra CRLF.  If terminating
1094   the request message-body with a line-ending is desired, then the
1095   client &MUST; include the terminating CRLF octets as part of the
1096   message-body length.
1097</t>
1098<t>
1099   The normal procedure for parsing an HTTP message is to read the
1100   start-line into a structure, read each header field into a hash
1101   table by field name until the empty line, and then use the parsed
1102   data to determine if a message-body is expected.  If a message-body
1103   has been indicated, then it is read as a stream until an amount
1104   of OCTETs equal to the message-length is read or the connection
1105   is closed.  Care must be taken to parse an HTTP message as a sequence
1106   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1107   to parse HTTP as a stream of Unicode characters in a character encoding
1108   like UTF-16 may introduce security flaws due to the differing ways
1109   that such parsers interpret invalid characters.
1110</t>
1111</section>
1112
1113<section title="Header Fields" anchor="header.fields">
1114  <x:anchor-alias value="header-field"/>
1115  <x:anchor-alias value="field-content"/>
1116  <x:anchor-alias value="field-name"/>
1117  <x:anchor-alias value="field-value"/>
1118  <x:anchor-alias value="OWS"/>
1119<t>
1120   Each HTTP header field consists of a case-insensitive field name
1121   followed by a colon (":"), optional whitespace, and the field value.
1122</t>
1123<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"/>
1124  <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>
1125  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1126  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1127  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1128</artwork></figure>
1129<t>
1130   No whitespace is allowed between the header field name and colon. For
1131   security reasons, any request message received containing such whitespace
1132   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1133   &MUST; remove any such whitespace from a response message before
1134   forwarding the message downstream.
1135</t>
1136<t>
1137   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1138   preferred. The field value does not include any leading or trailing white
1139   space: OWS occurring before the first non-whitespace character of the
1140   field value or after the last non-whitespace character of the field value
1141   is ignored and &SHOULD; be removed before further processing (as this does
1142   not change the meaning of the header field).
1143</t>
1144<t>
1145   The order in which header fields with differing field names are
1146   received is not significant. However, it is "good practice" to send
1147   header fields that contain control data first, such as Host on
1148   requests and Date on responses, so that implementations can decide
1149   when not to handle a message as early as possible.  A server &MUST;
1150   wait until the entire header section is received before interpreting
1151   a request message, since later header fields might include conditionals,
1152   authentication credentials, or deliberately misleading duplicate
1153   header fields that would impact request processing.
1154</t>
1155<t>
1156   Multiple header fields with the same field name &MUST-NOT; be
1157   sent in a message unless the entire field value for that
1158   header field is defined as a comma-separated list [i.e., #(values)].
1159   Multiple header fields with the same field name can be combined into
1160   one "field-name: field-value" pair, without changing the semantics of the
1161   message, by appending each subsequent field value to the combined
1162   field value in order, separated by a comma. The order in which
1163   header fields with the same field name are received is therefore
1164   significant to the interpretation of the combined field value;
1165   a proxy &MUST-NOT; change the order of these field values when
1166   forwarding a message.
1167</t>
1168<x:note>
1169  <t>
1170   <x:h>Note:</x:h> The "Set-Cookie" header as implemented in
1171   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1172   can occur multiple times, but does not use the list syntax, and thus cannot
1173   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1174   for details.) Also note that the Set-Cookie2 header specified in
1175   <xref target="RFC2965"/> does not share this problem.
1176  </t>
1177</x:note>
1178<t>
1179   Historically, HTTP header field values could be extended over multiple
1180   lines by preceding each extra line with at least one space or horizontal
1181   tab character (line folding). This specification deprecates such line
1182   folding except within the message/http media type
1183   (<xref target="internet.media.type.message.http"/>).
1184   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1185   (i.e., that contain any field-content that matches the obs-fold rule) unless
1186   the message is intended for packaging within the message/http media type.
1187   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1188   obs-fold whitespace with a single SP prior to interpreting the field value
1189   or forwarding the message downstream.
1190</t>
1191<t>
1192   Historically, HTTP has allowed field content with text in the ISO-8859-1
1193   <xref target="ISO-8859-1"/> character encoding and supported other
1194   character sets only through use of <xref target="RFC2047"/> encoding.
1195   In practice, most HTTP header field values use only a subset of the
1196   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1197   header fields &SHOULD; limit their field values to US-ASCII characters.
1198   Recipients &SHOULD; treat other (obs-text) octets in field content as
1199   opaque data.
1200</t>
1201<t anchor="rule.comment">
1202  <x:anchor-alias value="comment"/>
1203  <x:anchor-alias value="ctext"/>
1204   Comments can be included in some HTTP header fields by surrounding
1205   the comment text with parentheses. Comments are only allowed in
1206   fields containing "comment" as part of their field value definition.
1207</t>
1208<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1209  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1210  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1211                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1212</artwork></figure>
1213<t anchor="rule.quoted-cpair">
1214  <x:anchor-alias value="quoted-cpair"/>
1215   The backslash character ("\") can be used as a single-character
1216   quoting mechanism within comment constructs:
1217</t>
1218<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1219  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1220</artwork></figure>
1221<t>
1222   Producers &SHOULD-NOT; escape characters that do not require escaping
1223   (i.e., other than the backslash character "\" and the parentheses "(" and
1224   ")").
1225</t>
1226</section>
1227
1228<section title="Message Body" anchor="message.body">
1229  <x:anchor-alias value="message-body"/>
1230<t>
1231   The message-body (if any) of an HTTP message is used to carry the
1232   entity-body associated with the request or response. The message-body
1233   differs from the entity-body only when a transfer-coding has been
1234   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1235</t>
1236<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1237  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1238               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1239</artwork></figure>
1240<t>
1241   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1242   applied by an application to ensure safe and proper transfer of the
1243   message. Transfer-Encoding is a property of the message, not of the
1244   entity, and thus &MAY; be added or removed by any application along the
1245   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1246   when certain transfer-codings may be used.)
1247</t>
1248<t>
1249   The rules for when a message-body is allowed in a message differ for
1250   requests and responses.
1251</t>
1252<t>
1253   The presence of a message-body in a request is signaled by the
1254   inclusion of a Content-Length or Transfer-Encoding header field in
1255   the request's header fields.
1256   When a request message contains both a message-body of non-zero
1257   length and a method that does not define any semantics for that
1258   request message-body, then an origin server &SHOULD; either ignore
1259   the message-body or respond with an appropriate error message
1260   (e.g., 413).  A proxy or gateway, when presented the same request,
1261   &SHOULD; either forward the request inbound with the message-body or
1262   ignore the message-body when determining a response.
1263</t>
1264<t>
1265   For response messages, whether or not a message-body is included with
1266   a message is dependent on both the request method and the response
1267   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1268   &MUST-NOT; include a message-body, even though the presence of entity-header
1269   fields might lead one to believe they do. All 1xx
1270   (Informational), 204 (No Content), and 304 (Not Modified) responses
1271   &MUST-NOT; include a message-body. All other responses do include a
1272   message-body, although it &MAY; be of zero length.
1273</t>
1274</section>
1275
1276<section title="Message Length" anchor="message.length">
1277<t>
1278   The transfer-length of a message is the length of the message-body as
1279   it appears in the message; that is, after any transfer-codings have
1280   been applied. When a message-body is included with a message, the
1281   transfer-length of that body is determined by one of the following
1282   (in order of precedence):
1283</t>
1284<t>
1285  <list style="numbers">
1286    <x:lt><t>
1287     Any response message which "&MUST-NOT;" include a message-body (such
1288     as the 1xx, 204, and 304 responses and any response to a HEAD
1289     request) is always terminated by the first empty line after the
1290     header fields, regardless of the entity-header fields present in
1291     the message.
1292    </t></x:lt>
1293    <x:lt><t>
1294     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1295     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1296     is used, the transfer-length is defined by the use of this transfer-coding.
1297     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1298     is not present, the transfer-length is defined by the sender closing the connection.
1299    </t></x:lt>
1300    <x:lt><t>
1301     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1302     value in OCTETs represents both the entity-length and the
1303     transfer-length. The Content-Length header field &MUST-NOT; be sent
1304     if these two lengths are different (i.e., if a Transfer-Encoding
1305     header field is present). If a message is received with both a
1306     Transfer-Encoding header field and a Content-Length header field,
1307     the latter &MUST; be ignored.
1308    </t></x:lt>
1309    <x:lt><t>
1310     If the message uses the media type "multipart/byteranges", and the
1311     transfer-length is not otherwise specified, then this self-delimiting
1312     media type defines the transfer-length. This media type
1313     &MUST-NOT; be used unless the sender knows that the recipient can parse
1314     it; the presence in a request of a Range header with multiple byte-range
1315     specifiers from a HTTP/1.1 client implies that the client can parse
1316     multipart/byteranges responses.
1317    <list style="empty"><t>
1318       A range header might be forwarded by a HTTP/1.0 proxy that does not
1319       understand multipart/byteranges; in this case the server &MUST;
1320       delimit the message using methods defined in items 1, 3 or 5 of
1321       this section.
1322    </t></list>
1323    </t></x:lt>
1324    <x:lt><t>
1325     By the server closing the connection. (Closing the connection
1326     cannot be used to indicate the end of a request body, since that
1327     would leave no possibility for the server to send back a response.)
1328    </t></x:lt>
1329  </list>
1330</t>
1331<t>
1332   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1333   containing a message-body &MUST; include a valid Content-Length header
1334   field unless the server is known to be HTTP/1.1 compliant. If a
1335   request contains a message-body and a Content-Length is not given,
1336   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1337   determine the length of the message, or with 411 (Length Required) if
1338   it wishes to insist on receiving a valid Content-Length.
1339</t>
1340<t>
1341   All HTTP/1.1 applications that receive entities &MUST; accept the
1342   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1343   to be used for messages when the message length cannot be determined
1344   in advance.
1345</t>
1346<t>
1347   Messages &MUST-NOT; include both a Content-Length header field and a
1348   transfer-coding. If the message does include a
1349   transfer-coding, the Content-Length &MUST; be ignored.
1350</t>
1351<t>
1352   When a Content-Length is given in a message where a message-body is
1353   allowed, its field value &MUST; exactly match the number of OCTETs in
1354   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1355   invalid length is received and detected.
1356</t>
1357</section>
1358
1359<section title="General Header Fields" anchor="general.header.fields">
1360  <x:anchor-alias value="general-header"/>
1361<t>
1362   There are a few header fields which have general applicability for
1363   both request and response messages, but which do not apply to the
1364   entity being transferred. These header fields apply only to the
1365   message being transmitted.
1366</t>
1367<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1368  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1369                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1370                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1371                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1372                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1373                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1374                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1375                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1376                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1377</artwork></figure>
1378<t>
1379   General-header field names can be extended reliably only in
1380   combination with a change in the protocol version. However, new or
1381   experimental header fields may be given the semantics of general
1382   header fields if all parties in the communication recognize them to
1383   be general-header fields. Unrecognized header fields are treated as
1384   entity-header fields.
1385</t>
1386</section>
1387</section>
1388
1389<section title="Request" anchor="request">
1390  <x:anchor-alias value="Request"/>
1391<t>
1392   A request message from a client to a server includes, within the
1393   first line of that message, the method to be applied to the resource,
1394   the identifier of the resource, and the protocol version in use.
1395</t>
1396<!--                 Host                      ; should be moved here eventually -->
1397<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1398  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1399                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1400                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1401                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1402                  <x:ref>CRLF</x:ref>
1403                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1404</artwork></figure>
1405
1406<section title="Request-Line" anchor="request-line">
1407  <x:anchor-alias value="Request-Line"/>
1408<t>
1409   The Request-Line begins with a method token, followed by the
1410   request-target and the protocol version, and ending with CRLF. The
1411   elements are separated by SP characters. No CR or LF is allowed
1412   except in the final CRLF sequence.
1413</t>
1414<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1415  <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>
1416</artwork></figure>
1417
1418<section title="Method" anchor="method">
1419  <x:anchor-alias value="Method"/>
1420<t>
1421   The Method  token indicates the method to be performed on the
1422   resource identified by the request-target. The method is case-sensitive.
1423</t>
1424<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1425  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1426</artwork></figure>
1427</section>
1428
1429<section title="request-target" anchor="request-target">
1430  <x:anchor-alias value="request-target"/>
1431<t>
1432   The request-target
1433   identifies the resource upon which to apply the request.
1434</t>
1435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1436  <x:ref>request-target</x:ref> = "*"
1437                 / <x:ref>absolute-URI</x:ref>
1438                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1439                 / <x:ref>authority</x:ref>
1440</artwork></figure>
1441<t>
1442   The four options for request-target are dependent on the nature of the
1443   request. The asterisk "*" means that the request does not apply to a
1444   particular resource, but to the server itself, and is only allowed
1445   when the method used does not necessarily apply to a resource. One
1446   example would be
1447</t>
1448<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1449OPTIONS * HTTP/1.1
1450</artwork></figure>
1451<t>
1452   The absolute-URI form is &REQUIRED; when the request is being made to a
1453   proxy. The proxy is requested to forward the request or service it
1454   from a valid cache, and return the response. Note that the proxy &MAY;
1455   forward the request on to another proxy or directly to the server
1456   specified by the absolute-URI. In order to avoid request loops, a
1457   proxy &MUST; be able to recognize all of its server names, including
1458   any aliases, local variations, and the numeric IP address. An example
1459   Request-Line would be:
1460</t>
1461<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1462GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1463</artwork></figure>
1464<t>
1465   To allow for transition to absolute-URIs in all requests in future
1466   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1467   form in requests, even though HTTP/1.1 clients will only generate
1468   them in requests to proxies.
1469</t>
1470<t>
1471   The authority form is only used by the CONNECT method (&CONNECT;).
1472</t>
1473<t>
1474   The most common form of request-target is that used to identify a
1475   resource on an origin server or gateway. In this case the absolute
1476   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1477   the request-target, and the network location of the URI (authority) &MUST;
1478   be transmitted in a Host header field. For example, a client wishing
1479   to retrieve the resource above directly from the origin server would
1480   create a TCP connection to port 80 of the host "www.example.org" and send
1481   the lines:
1482</t>
1483<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1484GET /pub/WWW/TheProject.html HTTP/1.1
1485Host: www.example.org
1486</artwork></figure>
1487<t>
1488   followed by the remainder of the Request. Note that the absolute path
1489   cannot be empty; if none is present in the original URI, it &MUST; be
1490   given as "/" (the server root).
1491</t>
1492<t>
1493   If a proxy receives a request without any path in the request-target and
1494   the method specified is capable of supporting the asterisk form of
1495   request-target, then the last proxy on the request chain &MUST; forward the
1496   request with "*" as the final request-target.
1497</t>
1498<figure><preamble>   
1499   For example, the request
1500</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1501OPTIONS http://www.example.org:8001 HTTP/1.1
1502</artwork></figure>
1503<figure><preamble>   
1504  would be forwarded by the proxy as
1505</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1506OPTIONS * HTTP/1.1
1507Host: www.example.org:8001
1508</artwork>
1509<postamble>
1510   after connecting to port 8001 of host "www.example.org".
1511</postamble>
1512</figure>
1513<t>
1514   The request-target is transmitted in the format specified in
1515   <xref target="http.uri"/>. If the request-target is percent-encoded
1516   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1517   &MUST; decode the request-target in order to
1518   properly interpret the request. Servers &SHOULD; respond to invalid
1519   request-targets with an appropriate status code.
1520</t>
1521<t>
1522   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1523   received request-target when forwarding it to the next inbound server,
1524   except as noted above to replace a null path-absolute with "/".
1525</t>
1526<x:note>
1527  <t>
1528    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1529    meaning of the request when the origin server is improperly using
1530    a non-reserved URI character for a reserved purpose.  Implementors
1531    should be aware that some pre-HTTP/1.1 proxies have been known to
1532    rewrite the request-target.
1533  </t>
1534</x:note>
1535<t>
1536   HTTP does not place a pre-defined limit on the length of a request-target.
1537   A server &MUST; be prepared to receive URIs of unbounded length and
1538   respond with the 414 (URI Too Long) status if the received
1539   request-target would be longer than the server wishes to handle
1540   (see &status-414;).
1541</t>
1542<t>
1543   Various ad-hoc limitations on request-target length are found in practice.
1544   It is &RECOMMENDED; that all HTTP senders and recipients support
1545   request-target lengths of 8000 or more OCTETs.
1546</t>
1547</section>
1548</section>
1549
1550<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1551<t>
1552   The exact resource identified by an Internet request is determined by
1553   examining both the request-target and the Host header field.
1554</t>
1555<t>
1556   An origin server that does not allow resources to differ by the
1557   requested host &MAY; ignore the Host header field value when
1558   determining the resource identified by an HTTP/1.1 request. (But see
1559   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1560   for other requirements on Host support in HTTP/1.1.)
1561</t>
1562<t>
1563   An origin server that does differentiate resources based on the host
1564   requested (sometimes referred to as virtual hosts or vanity host
1565   names) &MUST; use the following rules for determining the requested
1566   resource on an HTTP/1.1 request:
1567  <list style="numbers">
1568    <t>If request-target is an absolute-URI, the host is part of the
1569     request-target. Any Host header field value in the request &MUST; be
1570     ignored.</t>
1571    <t>If the request-target is not an absolute-URI, and the request includes
1572     a Host header field, the host is determined by the Host header
1573     field value.</t>
1574    <t>If the host as determined by rule 1 or 2 is not a valid host on
1575     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1576  </list>
1577</t>
1578<t>
1579   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1580   attempt to use heuristics (e.g., examination of the URI path for
1581   something unique to a particular host) in order to determine what
1582   exact resource is being requested.
1583</t>
1584</section>
1585
1586</section>
1587
1588
1589<section title="Response" anchor="response">
1590  <x:anchor-alias value="Response"/>
1591<t>
1592   After receiving and interpreting a request message, a server responds
1593   with an HTTP response message.
1594</t>
1595<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1596  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1597                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1598                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1599                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1600                  <x:ref>CRLF</x:ref>
1601                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1602</artwork></figure>
1603
1604<section title="Status-Line" anchor="status-line">
1605  <x:anchor-alias value="Status-Line"/>
1606<t>
1607   The first line of a Response message is the Status-Line, consisting
1608   of the protocol version followed by a numeric status code and its
1609   associated textual phrase, with each element separated by SP
1610   characters. No CR or LF is allowed except in the final CRLF sequence.
1611</t>
1612<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1613  <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>
1614</artwork></figure>
1615
1616<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1617  <x:anchor-alias value="Reason-Phrase"/>
1618  <x:anchor-alias value="Status-Code"/>
1619<t>
1620   The Status-Code element is a 3-digit integer result code of the
1621   attempt to understand and satisfy the request. These codes are fully
1622   defined in &status-codes;.  The Reason Phrase exists for the sole
1623   purpose of providing a textual description associated with the numeric
1624   status code, out of deference to earlier Internet application protocols
1625   that were more frequently used with interactive text clients.
1626   A client &SHOULD; ignore the content of the Reason Phrase.
1627</t>
1628<t>
1629   The first digit of the Status-Code defines the class of response. The
1630   last two digits do not have any categorization role. There are 5
1631   values for the first digit:
1632  <list style="symbols">
1633    <t>
1634      1xx: Informational - Request received, continuing process
1635    </t>
1636    <t>
1637      2xx: Success - The action was successfully received,
1638        understood, and accepted
1639    </t>
1640    <t>
1641      3xx: Redirection - Further action must be taken in order to
1642        complete the request
1643    </t>
1644    <t>
1645      4xx: Client Error - The request contains bad syntax or cannot
1646        be fulfilled
1647    </t>
1648    <t>
1649      5xx: Server Error - The server failed to fulfill an apparently
1650        valid request
1651    </t>
1652  </list>
1653</t>
1654<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"/>
1655  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1656  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1657</artwork></figure>
1658</section>
1659</section>
1660
1661</section>
1662
1663
1664<section title="Protocol Parameters" anchor="protocol.parameters">
1665
1666<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1667  <x:anchor-alias value="HTTP-date"/>
1668<t>
1669   HTTP applications have historically allowed three different formats
1670   for the representation of date/time stamps.
1671</t>
1672<t>
1673   The first format is preferred as an Internet standard and represents
1674   a fixed-length subset of that defined by <xref target="RFC1123"/>:
1675</t>
1676<figure><artwork type="example" x:indent-with="  ">
1677Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1678</artwork></figure>
1679<t>
1680   The other formats are described here only for compatibility with obsolete
1681   implementations.
1682</t>
1683<figure><artwork type="example" x:indent-with="  ">
1684Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1685Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1686</artwork></figure>
1687<t>
1688   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1689   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1690   only generate the RFC 1123 format for representing HTTP-date values
1691   in header fields. See <xref target="tolerant.applications"/> for further information.
1692</t>
1693<t>
1694   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1695   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1696   equal to UTC (Coordinated Universal Time). This is indicated in the
1697   first two formats by the inclusion of "GMT" as the three-letter
1698   abbreviation for time zone, and &MUST; be assumed when reading the
1699   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1700   additional whitespace beyond that specifically included as SP in the
1701   grammar.
1702</t>
1703<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1704  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1705</artwork></figure>
1706<t anchor="preferred.date.format">
1707  <x:anchor-alias value="rfc1123-date"/>
1708  <x:anchor-alias value="time-of-day"/>
1709  <x:anchor-alias value="hour"/>
1710  <x:anchor-alias value="minute"/>
1711  <x:anchor-alias value="second"/>
1712  <x:anchor-alias value="day-name"/>
1713  <x:anchor-alias value="day"/>
1714  <x:anchor-alias value="month"/>
1715  <x:anchor-alias value="year"/>
1716  <x:anchor-alias value="GMT"/>
1717  Preferred format:
1718</t>
1719<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"/>
1720  <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>
1721
1722  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1723               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1724               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1725               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1726               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1727               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1728               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1729               
1730  <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>
1731               ; e.g., 02 Jun 1982
1732
1733  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1734  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1735               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1736               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1737               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1738               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1739               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1740               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1741               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1742               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1743               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1744               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1745               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1746  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1747
1748  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1749
1750  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1751                 ; 00:00:00 - 23:59:59
1752                 
1753  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1754  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1755  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1756</artwork></figure>
1757<t>
1758  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1759  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1760  same as those defined for the RFC 5322 constructs
1761  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1762</t>
1763<t anchor="obsolete.date.formats">
1764  <x:anchor-alias value="obs-date"/>
1765  <x:anchor-alias value="rfc850-date"/>
1766  <x:anchor-alias value="asctime-date"/>
1767  <x:anchor-alias value="date1"/>
1768  <x:anchor-alias value="date2"/>
1769  <x:anchor-alias value="date3"/>
1770  <x:anchor-alias value="rfc1123-date"/>
1771  <x:anchor-alias value="day-name-l"/>
1772  Obsolete formats:
1773</t>
1774<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1775  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1776</artwork></figure>
1777<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1778  <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>
1779  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1780                 ; day-month-year (e.g., 02-Jun-82)
1781
1782  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1783         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1784         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1785         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1786         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1787         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1788         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1789</artwork></figure>
1790<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1791  <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>
1792  <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> ))
1793                 ; month day (e.g., Jun  2)
1794</artwork></figure>
1795<x:note>
1796  <t>
1797    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1798    accepting date values that may have been sent by non-HTTP
1799    applications, as is sometimes the case when retrieving or posting
1800    messages via proxies/gateways to SMTP or NNTP.
1801  </t>
1802</x:note>
1803<x:note>
1804  <t>
1805    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1806    to their usage within the protocol stream. Clients and servers are
1807    not required to use these formats for user presentation, request
1808    logging, etc.
1809  </t>
1810</x:note>
1811</section>
1812
1813<section title="Transfer Codings" anchor="transfer.codings">
1814  <x:anchor-alias value="transfer-coding"/>
1815  <x:anchor-alias value="transfer-extension"/>
1816<t>
1817   Transfer-coding values are used to indicate an encoding
1818   transformation that has been, can be, or may need to be applied to an
1819   entity-body in order to ensure "safe transport" through the network.
1820   This differs from a content coding in that the transfer-coding is a
1821   property of the message, not of the original entity.
1822</t>
1823<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1824  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1825                          / "compress" ; <xref target="compress.coding"/>
1826                          / "deflate" ; <xref target="deflate.coding"/>
1827                          / "gzip" ; <xref target="gzip.coding"/>
1828                          / <x:ref>transfer-extension</x:ref>
1829  <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> )
1830</artwork></figure>
1831<t anchor="rule.parameter">
1832  <x:anchor-alias value="attribute"/>
1833  <x:anchor-alias value="transfer-parameter"/>
1834  <x:anchor-alias value="value"/>
1835   Parameters are in  the form of attribute/value pairs.
1836</t>
1837<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"/>
1838  <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>
1839  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1840  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1841</artwork></figure>
1842<t>
1843   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1844   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1845   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1846</t>
1847<t>
1848   Whenever a transfer-coding is applied to a message-body, the set of
1849   transfer-codings &MUST; include "chunked", unless the message indicates it
1850   is terminated by closing the connection. When the "chunked" transfer-coding
1851   is used, it &MUST; be the last transfer-coding applied to the
1852   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1853   than once to a message-body. These rules allow the recipient to
1854   determine the transfer-length of the message (<xref target="message.length"/>).
1855</t>
1856<t>
1857   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1858   MIME, which were designed to enable safe transport of binary data over a
1859   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1860   However, safe transport
1861   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1862   the only unsafe characteristic of message-bodies is the difficulty in
1863   determining the exact body length (<xref target="message.length"/>), or the desire to
1864   encrypt data over a shared transport.
1865</t>
1866<t>
1867   A server which receives an entity-body with a transfer-coding it does
1868   not understand &SHOULD; return 501 (Not Implemented), and close the
1869   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1870   client.
1871</t>
1872
1873<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1874  <iref item="chunked (Coding Format)"/>
1875  <iref item="Coding Format" subitem="chunked"/>
1876  <x:anchor-alias value="chunk"/>
1877  <x:anchor-alias value="Chunked-Body"/>
1878  <x:anchor-alias value="chunk-data"/>
1879  <x:anchor-alias value="chunk-ext"/>
1880  <x:anchor-alias value="chunk-ext-name"/>
1881  <x:anchor-alias value="chunk-ext-val"/>
1882  <x:anchor-alias value="chunk-size"/>
1883  <x:anchor-alias value="last-chunk"/>
1884  <x:anchor-alias value="trailer-part"/>
1885  <x:anchor-alias value="quoted-str-nf"/>
1886  <x:anchor-alias value="qdtext-nf"/>
1887<t>
1888   The chunked encoding modifies the body of a message in order to
1889   transfer it as a series of chunks, each with its own size indicator,
1890   followed by an &OPTIONAL; trailer containing entity-header fields. This
1891   allows dynamically produced content to be transferred along with the
1892   information necessary for the recipient to verify that it has
1893   received the full message.
1894</t>
1895<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"/>
1896  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1897                   <x:ref>last-chunk</x:ref>
1898                   <x:ref>trailer-part</x:ref>
1899                   <x:ref>CRLF</x:ref>
1900 
1901  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1902                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1903  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1904  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1905 
1906  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1907                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1908  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1909  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1910  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1911  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1912 
1913  <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>
1914                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1915  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1916                 ; <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> 
1917</artwork></figure>
1918<t>
1919   The chunk-size field is a string of hex digits indicating the size of
1920   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1921   zero, followed by the trailer, which is terminated by an empty line.
1922</t>
1923<t>
1924   The trailer allows the sender to include additional HTTP header
1925   fields at the end of the message. The Trailer header field can be
1926   used to indicate which header fields are included in a trailer (see
1927   <xref target="header.trailer"/>).
1928</t>
1929<t>
1930   A server using chunked transfer-coding in a response &MUST-NOT; use the
1931   trailer for any header fields unless at least one of the following is
1932   true:
1933  <list style="numbers">
1934    <t>the request included a TE header field that indicates "trailers" is
1935     acceptable in the transfer-coding of the  response, as described in
1936     <xref target="header.te"/>; or,</t>
1937
1938    <t>the server is the origin server for the response, the trailer
1939     fields consist entirely of optional metadata, and the recipient
1940     could use the message (in a manner acceptable to the origin server)
1941     without receiving this metadata.  In other words, the origin server
1942     is willing to accept the possibility that the trailer fields might
1943     be silently discarded along the path to the client.</t>
1944  </list>
1945</t>
1946<t>
1947   This requirement prevents an interoperability failure when the
1948   message is being received by an HTTP/1.1 (or later) proxy and
1949   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1950   compliance with the protocol would have necessitated a possibly
1951   infinite buffer on the proxy.
1952</t>
1953<t>
1954   A process for decoding the "chunked" transfer-coding
1955   can be represented in pseudo-code as:
1956</t>
1957<figure><artwork type="code">
1958  length := 0
1959  read chunk-size, chunk-ext (if any) and CRLF
1960  while (chunk-size &gt; 0) {
1961     read chunk-data and CRLF
1962     append chunk-data to entity-body
1963     length := length + chunk-size
1964     read chunk-size and CRLF
1965  }
1966  read entity-header
1967  while (entity-header not empty) {
1968     append entity-header to existing header fields
1969     read entity-header
1970  }
1971  Content-Length := length
1972  Remove "chunked" from Transfer-Encoding
1973</artwork></figure>
1974<t>
1975   All HTTP/1.1 applications &MUST; be able to receive and decode the
1976   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1977   they do not understand.
1978</t>
1979</section>
1980
1981<section title="Compression Codings" anchor="compression.codings">
1982<t>
1983   The codings defined below can be used to compress the payload of a
1984   message.
1985</t>
1986<x:note><t>
1987   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
1988   is not desirable and is discouraged for future encodings. Their
1989   use here is representative of historical practice, not good
1990   design.
1991</t></x:note>
1992<x:note><t>
1993   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
1994   applications &SHOULD; consider "x-gzip" and "x-compress" to be
1995   equivalent to "gzip" and "compress" respectively.
1996</t></x:note>
1997
1998<section title="Compress Coding" anchor="compress.coding">
1999<iref item="compress (Coding Format)"/>
2000<iref item="Coding Format" subitem="compress"/>
2001<t>
2002   The "compress" format is produced by the common UNIX file compression
2003   program "compress". This format is an adaptive Lempel-Ziv-Welch
2004   coding (LZW).
2005</t>
2006</section>
2007
2008<section title="Deflate Coding" anchor="deflate.coding">
2009<iref item="deflate (Coding Format)"/>
2010<iref item="Coding Format" subitem="deflate"/>
2011<t>
2012   The "deflate" format is defined as the "deflate" compression mechanism
2013   (described in <xref target="RFC1951"/>) used inside the "zlib"
2014   data format (<xref target="RFC1950"/>).
2015</t>
2016<x:note>
2017  <t>
2018    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2019    compressed data without the zlib wrapper.
2020   </t>
2021</x:note>
2022</section>
2023
2024<section title="Gzip Coding" anchor="gzip.coding">
2025<iref item="gzip (Coding Format)"/>
2026<iref item="Coding Format" subitem="gzip"/>
2027<t>
2028   The "gzip" format is produced by the file compression program
2029   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2030   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2031</t>
2032</section>
2033
2034</section>
2035
2036<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2037<t>
2038   The HTTP Transfer Coding Registry defines the name space for the transfer
2039   coding names.
2040</t>
2041<t>
2042   Registrations &MUST; include the following fields:
2043   <list style="symbols">
2044     <t>Name</t>
2045     <t>Description</t>
2046     <t>Pointer to specification text</t>
2047   </list>
2048</t>
2049<t>
2050   Names of transfer codings &MUST-NOT; overlap with names of content codings
2051   (&content-codings;), unless the encoding transformation is identical (as it
2052   is the case for the compression codings defined in
2053   <xref target="compression.codings"/>).
2054</t>
2055<t>
2056   Values to be added to this name space require expert review and a specification
2057   (see "Expert Review" and "Specification Required" in
2058   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2059   conform to the purpose of transfer coding defined in this section.
2060</t>
2061<t>
2062   The registry itself is maintained at
2063   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2064</t>
2065</section>
2066</section>
2067
2068<section title="Product Tokens" anchor="product.tokens">
2069  <x:anchor-alias value="product"/>
2070  <x:anchor-alias value="product-version"/>
2071<t>
2072   Product tokens are used to allow communicating applications to
2073   identify themselves by software name and version. Most fields using
2074   product tokens also allow sub-products which form a significant part
2075   of the application to be listed, separated by whitespace. By
2076   convention, the products are listed in order of their significance
2077   for identifying the application.
2078</t>
2079<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2080  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2081  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2082</artwork></figure>
2083<t>
2084   Examples:
2085</t>
2086<figure><artwork type="example">
2087  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2088  Server: Apache/0.8.4
2089</artwork></figure>
2090<t>
2091   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2092   used for advertising or other non-essential information. Although any
2093   token character &MAY; appear in a product-version, this token &SHOULD;
2094   only be used for a version identifier (i.e., successive versions of
2095   the same product &SHOULD; only differ in the product-version portion of
2096   the product value).
2097</t>
2098</section>
2099
2100<section title="Quality Values" anchor="quality.values">
2101  <x:anchor-alias value="qvalue"/>
2102<t>
2103   Both transfer codings (TE request header, <xref target="header.te"/>)
2104   and content negotiation (&content.negotiation;) use short "floating point"
2105   numbers to indicate the relative importance ("weight") of various
2106   negotiable parameters.  A weight is normalized to a real number in
2107   the range 0 through 1, where 0 is the minimum and 1 the maximum
2108   value. If a parameter has a quality value of 0, then content with
2109   this parameter is "not acceptable" for the client. HTTP/1.1
2110   applications &MUST-NOT; generate more than three digits after the
2111   decimal point. User configuration of these values &SHOULD; also be
2112   limited in this fashion.
2113</t>
2114<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2115  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2116                 / ( "1" [ "." 0*3("0") ] )
2117</artwork></figure>
2118<x:note>
2119  <t>
2120     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2121     relative degradation in desired quality.
2122  </t>
2123</x:note>
2124</section>
2125
2126</section>
2127
2128<section title="Connections" anchor="connections">
2129
2130<section title="Persistent Connections" anchor="persistent.connections">
2131
2132<section title="Purpose" anchor="persistent.purpose">
2133<t>
2134   Prior to persistent connections, a separate TCP connection was
2135   established to fetch each URL, increasing the load on HTTP servers
2136   and causing congestion on the Internet. The use of inline images and
2137   other associated data often requires a client to make multiple
2138   requests of the same server in a short amount of time. Analysis of
2139   these performance problems and results from a prototype
2140   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2141   measurements of actual HTTP/1.1 implementations show good
2142   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2143   T/TCP <xref target="Tou1998"/>.
2144</t>
2145<t>
2146   Persistent HTTP connections have a number of advantages:
2147  <list style="symbols">
2148      <t>
2149        By opening and closing fewer TCP connections, CPU time is saved
2150        in routers and hosts (clients, servers, proxies, gateways,
2151        tunnels, or caches), and memory used for TCP protocol control
2152        blocks can be saved in hosts.
2153      </t>
2154      <t>
2155        HTTP requests and responses can be pipelined on a connection.
2156        Pipelining allows a client to make multiple requests without
2157        waiting for each response, allowing a single TCP connection to
2158        be used much more efficiently, with much lower elapsed time.
2159      </t>
2160      <t>
2161        Network congestion is reduced by reducing the number of packets
2162        caused by TCP opens, and by allowing TCP sufficient time to
2163        determine the congestion state of the network.
2164      </t>
2165      <t>
2166        Latency on subsequent requests is reduced since there is no time
2167        spent in TCP's connection opening handshake.
2168      </t>
2169      <t>
2170        HTTP can evolve more gracefully, since errors can be reported
2171        without the penalty of closing the TCP connection. Clients using
2172        future versions of HTTP might optimistically try a new feature,
2173        but if communicating with an older server, retry with old
2174        semantics after an error is reported.
2175      </t>
2176    </list>
2177</t>
2178<t>
2179   HTTP implementations &SHOULD; implement persistent connections.
2180</t>
2181</section>
2182
2183<section title="Overall Operation" anchor="persistent.overall">
2184<t>
2185   A significant difference between HTTP/1.1 and earlier versions of
2186   HTTP is that persistent connections are the default behavior of any
2187   HTTP connection. That is, unless otherwise indicated, the client
2188   &SHOULD; assume that the server will maintain a persistent connection,
2189   even after error responses from the server.
2190</t>
2191<t>
2192   Persistent connections provide a mechanism by which a client and a
2193   server can signal the close of a TCP connection. This signaling takes
2194   place using the Connection header field (<xref target="header.connection"/>). Once a close
2195   has been signaled, the client &MUST-NOT; send any more requests on that
2196   connection.
2197</t>
2198
2199<section title="Negotiation" anchor="persistent.negotiation">
2200<t>
2201   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2202   maintain a persistent connection unless a Connection header including
2203   the connection-token "close" was sent in the request. If the server
2204   chooses to close the connection immediately after sending the
2205   response, it &SHOULD; send a Connection header including the
2206   connection-token "close".
2207</t>
2208<t>
2209   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2210   decide to keep it open based on whether the response from a server
2211   contains a Connection header with the connection-token close. In case
2212   the client does not want to maintain a connection for more than that
2213   request, it &SHOULD; send a Connection header including the
2214   connection-token close.
2215</t>
2216<t>
2217   If either the client or the server sends the close token in the
2218   Connection header, that request becomes the last one for the
2219   connection.
2220</t>
2221<t>
2222   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2223   maintained for HTTP versions less than 1.1 unless it is explicitly
2224   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2225   compatibility with HTTP/1.0 clients.
2226</t>
2227<t>
2228   In order to remain persistent, all messages on the connection &MUST;
2229   have a self-defined message length (i.e., one not defined by closure
2230   of the connection), as described in <xref target="message.length"/>.
2231</t>
2232</section>
2233
2234<section title="Pipelining" anchor="pipelining">
2235<t>
2236   A client that supports persistent connections &MAY; "pipeline" its
2237   requests (i.e., send multiple requests without waiting for each
2238   response). A server &MUST; send its responses to those requests in the
2239   same order that the requests were received.
2240</t>
2241<t>
2242   Clients which assume persistent connections and pipeline immediately
2243   after connection establishment &SHOULD; be prepared to retry their
2244   connection if the first pipelined attempt fails. If a client does
2245   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2246   persistent. Clients &MUST; also be prepared to resend their requests if
2247   the server closes the connection before sending all of the
2248   corresponding responses.
2249</t>
2250<t>
2251   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2252   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2253   premature termination of the transport connection could lead to
2254   indeterminate results. A client wishing to send a non-idempotent
2255   request &SHOULD; wait to send that request until it has received the
2256   response status for the previous request.
2257</t>
2258</section>
2259</section>
2260
2261<section title="Proxy Servers" anchor="persistent.proxy">
2262<t>
2263   It is especially important that proxies correctly implement the
2264   properties of the Connection header field as specified in <xref target="header.connection"/>.
2265</t>
2266<t>
2267   The proxy server &MUST; signal persistent connections separately with
2268   its clients and the origin servers (or other proxy servers) that it
2269   connects to. Each persistent connection applies to only one transport
2270   link.
2271</t>
2272<t>
2273   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2274   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2275   for information and discussion of the problems with the Keep-Alive header
2276   implemented by many HTTP/1.0 clients).
2277</t>
2278
2279<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2280<t>
2281  <cref anchor="TODO-end-to-end" source="jre">
2282    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2283    See also <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2284  </cref>
2285</t>
2286<t>
2287   For the purpose of defining the behavior of caches and non-caching
2288   proxies, we divide HTTP headers into two categories:
2289  <list style="symbols">
2290      <t>End-to-end headers, which are  transmitted to the ultimate
2291        recipient of a request or response. End-to-end headers in
2292        responses MUST be stored as part of a cache entry and &MUST; be
2293        transmitted in any response formed from a cache entry.</t>
2294
2295      <t>Hop-by-hop headers, which are meaningful only for a single
2296        transport-level connection, and are not stored by caches or
2297        forwarded by proxies.</t>
2298  </list>
2299</t>
2300<t>
2301   The following HTTP/1.1 headers are hop-by-hop headers:
2302  <list style="symbols">
2303      <t>Connection</t>
2304      <t>Keep-Alive</t>
2305      <t>Proxy-Authenticate</t>
2306      <t>Proxy-Authorization</t>
2307      <t>TE</t>
2308      <t>Trailer</t>
2309      <t>Transfer-Encoding</t>
2310      <t>Upgrade</t>
2311  </list>
2312</t>
2313<t>
2314   All other headers defined by HTTP/1.1 are end-to-end headers.
2315</t>
2316<t>
2317   Other hop-by-hop headers &MUST; be listed in a Connection header
2318   (<xref target="header.connection"/>).
2319</t>
2320</section>
2321
2322<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2323<t>
2324  <cref anchor="TODO-non-mod-headers" source="jre">
2325    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2326    See also <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2327  </cref>
2328</t>
2329<t>
2330   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2331   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2332   modify an end-to-end header unless the definition of that header requires
2333   or specifically allows that.
2334</t>
2335<t>
2336   A transparent proxy &MUST-NOT; modify any of the following fields in a
2337   request or response, and it &MUST-NOT; add any of these fields if not
2338   already present:
2339  <list style="symbols">
2340      <t>Content-Location</t>
2341      <t>Content-MD5</t>
2342      <t>ETag</t>
2343      <t>Last-Modified</t>
2344  </list>
2345</t>
2346<t>
2347   A transparent proxy &MUST-NOT; modify any of the following fields in a
2348   response:
2349  <list style="symbols">
2350    <t>Expires</t>
2351  </list>
2352</t>
2353<t>
2354   but it &MAY; add any of these fields if not already present. If an
2355   Expires header is added, it &MUST; be given a field-value identical to
2356   that of the Date header in that response.
2357</t>
2358<t>
2359   A proxy &MUST-NOT; modify or add any of the following fields in a
2360   message that contains the no-transform cache-control directive, or in
2361   any request:
2362  <list style="symbols">
2363    <t>Content-Encoding</t>
2364    <t>Content-Range</t>
2365    <t>Content-Type</t>
2366  </list>
2367</t>
2368<t>
2369   A non-transparent proxy &MAY; modify or add these fields to a message
2370   that does not include no-transform, but if it does so, it &MUST; add a
2371   Warning 214 (Transformation applied) if one does not already appear
2372   in the message (see &header-warning;).
2373</t>
2374<x:note>
2375  <t>
2376    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2377    cause authentication failures if stronger authentication
2378    mechanisms are introduced in later versions of HTTP. Such
2379    authentication mechanisms &MAY; rely on the values of header fields
2380    not listed here.
2381  </t>
2382</x:note>
2383<t>
2384   The Content-Length field of a request or response is added or deleted
2385   according to the rules in <xref target="message.length"/>. A transparent proxy &MUST;
2386   preserve the entity-length (&entity-length;) of the entity-body,
2387   although it &MAY; change the transfer-length (<xref target="message.length"/>).
2388</t>
2389</section>
2390
2391</section>
2392
2393<section title="Practical Considerations" anchor="persistent.practical">
2394<t>
2395   Servers will usually have some time-out value beyond which they will
2396   no longer maintain an inactive connection. Proxy servers might make
2397   this a higher value since it is likely that the client will be making
2398   more connections through the same server. The use of persistent
2399   connections places no requirements on the length (or existence) of
2400   this time-out for either the client or the server.
2401</t>
2402<t>
2403   When a client or server wishes to time-out it &SHOULD; issue a graceful
2404   close on the transport connection. Clients and servers &SHOULD; both
2405   constantly watch for the other side of the transport close, and
2406   respond to it as appropriate. If a client or server does not detect
2407   the other side's close promptly it could cause unnecessary resource
2408   drain on the network.
2409</t>
2410<t>
2411   A client, server, or proxy &MAY; close the transport connection at any
2412   time. For example, a client might have started to send a new request
2413   at the same time that the server has decided to close the "idle"
2414   connection. From the server's point of view, the connection is being
2415   closed while it was idle, but from the client's point of view, a
2416   request is in progress.
2417</t>
2418<t>
2419   This means that clients, servers, and proxies &MUST; be able to recover
2420   from asynchronous close events. Client software &SHOULD; reopen the
2421   transport connection and retransmit the aborted sequence of requests
2422   without user interaction so long as the request sequence is
2423   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2424   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2425   human operator the choice of retrying the request(s). Confirmation by
2426   user-agent software with semantic understanding of the application
2427   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2428   be repeated if the second sequence of requests fails.
2429</t>
2430<t>
2431   Servers &SHOULD; always respond to at least one request per connection,
2432   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2433   middle of transmitting a response, unless a network or client failure
2434   is suspected.
2435</t>
2436<t>
2437   Clients (including proxies) &SHOULD; limit the number of simultaneous
2438   connections that they maintain to a given server (including proxies).
2439</t>
2440<t>
2441   Previous revisions of HTTP gave a specific number of connections as a
2442   ceiling, but this was found to be impractical for many applications. As a
2443   result, this specification does not mandate a particular maximum number of
2444   connections, but instead encourages clients to be conservative when opening
2445   multiple connections.
2446</t>
2447<t>
2448   In particular, while using multiple connections avoids the "head-of-line
2449   blocking" problem (whereby a request that takes significant server-side
2450   processing and/or has a large payload can block subsequent requests on the
2451   same connection), each connection used consumes server resources (sometimes
2452   significantly), and furthermore using multiple connections can cause
2453   undesirable side effects in congested networks.
2454</t>
2455<t>
2456   Note that servers might reject traffic that they deem abusive, including an
2457   excessive number of connections from a client.
2458</t>
2459</section>
2460</section>
2461
2462<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2463
2464<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2465<t>
2466   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2467   flow control mechanisms to resolve temporary overloads, rather than
2468   terminating connections with the expectation that clients will retry.
2469   The latter technique can exacerbate network congestion.
2470</t>
2471</section>
2472
2473<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2474<t>
2475   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2476   the network connection for an error status while it is transmitting
2477   the request. If the client sees an error status, it &SHOULD;
2478   immediately cease transmitting the body. If the body is being sent
2479   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2480   empty trailer &MAY; be used to prematurely mark the end of the message.
2481   If the body was preceded by a Content-Length header, the client &MUST;
2482   close the connection.
2483</t>
2484</section>
2485
2486<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2487<t>
2488   The purpose of the 100 (Continue) status (see &status-100;) is to
2489   allow a client that is sending a request message with a request body
2490   to determine if the origin server is willing to accept the request
2491   (based on the request headers) before the client sends the request
2492   body. In some cases, it might either be inappropriate or highly
2493   inefficient for the client to send the body if the server will reject
2494   the message without looking at the body.
2495</t>
2496<t>
2497   Requirements for HTTP/1.1 clients:
2498  <list style="symbols">
2499    <t>
2500        If a client will wait for a 100 (Continue) response before
2501        sending the request body, it &MUST; send an Expect request-header
2502        field (&header-expect;) with the "100-continue" expectation.
2503    </t>
2504    <t>
2505        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2506        with the "100-continue" expectation if it does not intend
2507        to send a request body.
2508    </t>
2509  </list>
2510</t>
2511<t>
2512   Because of the presence of older implementations, the protocol allows
2513   ambiguous situations in which a client may send "Expect: 100-continue"
2514   without receiving either a 417 (Expectation Failed) status
2515   or a 100 (Continue) status. Therefore, when a client sends this
2516   header field to an origin server (possibly via a proxy) from which it
2517   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2518   for an indefinite period before sending the request body.
2519</t>
2520<t>
2521   Requirements for HTTP/1.1 origin servers:
2522  <list style="symbols">
2523    <t> Upon receiving a request which includes an Expect request-header
2524        field with the "100-continue" expectation, an origin server &MUST;
2525        either respond with 100 (Continue) status and continue to read
2526        from the input stream, or respond with a final status code. The
2527        origin server &MUST-NOT; wait for the request body before sending
2528        the 100 (Continue) response. If it responds with a final status
2529        code, it &MAY; close the transport connection or it &MAY; continue
2530        to read and discard the rest of the request.  It &MUST-NOT;
2531        perform the requested method if it returns a final status code.
2532    </t>
2533    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2534        the request message does not include an Expect request-header
2535        field with the "100-continue" expectation, and &MUST-NOT; send a
2536        100 (Continue) response if such a request comes from an HTTP/1.0
2537        (or earlier) client. There is an exception to this rule: for
2538        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2539        status in response to an HTTP/1.1 PUT or POST request that does
2540        not include an Expect request-header field with the "100-continue"
2541        expectation. This exception, the purpose of which is
2542        to minimize any client processing delays associated with an
2543        undeclared wait for 100 (Continue) status, applies only to
2544        HTTP/1.1 requests, and not to requests with any other HTTP-version
2545        value.
2546    </t>
2547    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2548        already received some or all of the request body for the
2549        corresponding request.
2550    </t>
2551    <t> An origin server that sends a 100 (Continue) response &MUST;
2552    ultimately send a final status code, once the request body is
2553        received and processed, unless it terminates the transport
2554        connection prematurely.
2555    </t>
2556    <t> If an origin server receives a request that does not include an
2557        Expect request-header field with the "100-continue" expectation,
2558        the request includes a request body, and the server responds
2559        with a final status code before reading the entire request body
2560        from the transport connection, then the server &SHOULD-NOT;  close
2561        the transport connection until it has read the entire request,
2562        or until the client closes the connection. Otherwise, the client
2563        might not reliably receive the response message. However, this
2564        requirement is not be construed as preventing a server from
2565        defending itself against denial-of-service attacks, or from
2566        badly broken client implementations.
2567      </t>
2568    </list>
2569</t>
2570<t>
2571   Requirements for HTTP/1.1 proxies:
2572  <list style="symbols">
2573    <t> If a proxy receives a request that includes an Expect request-header
2574        field with the "100-continue" expectation, and the proxy
2575        either knows that the next-hop server complies with HTTP/1.1 or
2576        higher, or does not know the HTTP version of the next-hop
2577        server, it &MUST; forward the request, including the Expect header
2578        field.
2579    </t>
2580    <t> If the proxy knows that the version of the next-hop server is
2581        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2582        respond with a 417 (Expectation Failed) status.
2583    </t>
2584    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2585        numbers received from recently-referenced next-hop servers.
2586    </t>
2587    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2588        request message was received from an HTTP/1.0 (or earlier)
2589        client and did not include an Expect request-header field with
2590        the "100-continue" expectation. This requirement overrides the
2591        general rule for forwarding of 1xx responses (see &status-1xx;).
2592    </t>
2593  </list>
2594</t>
2595</section>
2596
2597<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2598<t>
2599   If an HTTP/1.1 client sends a request which includes a request body,
2600   but which does not include an Expect request-header field with the
2601   "100-continue" expectation, and if the client is not directly
2602   connected to an HTTP/1.1 origin server, and if the client sees the
2603   connection close before receiving any status from the server, the
2604   client &SHOULD; retry the request.  If the client does retry this
2605   request, it &MAY; use the following "binary exponential backoff"
2606   algorithm to be assured of obtaining a reliable response:
2607  <list style="numbers">
2608    <t>
2609      Initiate a new connection to the server
2610    </t>
2611    <t>
2612      Transmit the request-headers
2613    </t>
2614    <t>
2615      Initialize a variable R to the estimated round-trip time to the
2616         server (e.g., based on the time it took to establish the
2617         connection), or to a constant value of 5 seconds if the round-trip
2618         time is not available.
2619    </t>
2620    <t>
2621       Compute T = R * (2**N), where N is the number of previous
2622         retries of this request.
2623    </t>
2624    <t>
2625       Wait either for an error response from the server, or for T
2626         seconds (whichever comes first)
2627    </t>
2628    <t>
2629       If no error response is received, after T seconds transmit the
2630         body of the request.
2631    </t>
2632    <t>
2633       If client sees that the connection is closed prematurely,
2634         repeat from step 1 until the request is accepted, an error
2635         response is received, or the user becomes impatient and
2636         terminates the retry process.
2637    </t>
2638  </list>
2639</t>
2640<t>
2641   If at any point an error status is received, the client
2642  <list style="symbols">
2643      <t>&SHOULD-NOT;  continue and</t>
2644
2645      <t>&SHOULD; close the connection if it has not completed sending the
2646        request message.</t>
2647    </list>
2648</t>
2649</section>
2650</section>
2651</section>
2652
2653
2654<section title="Miscellaneous notes that may disappear" anchor="misc">
2655<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2656<t>
2657   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2658</t>
2659</section>
2660
2661<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2662<t>
2663   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2664</t>
2665</section>
2666
2667<section title="Interception of HTTP for access control" anchor="http.intercept">
2668<t>
2669   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2670</t>
2671</section>
2672
2673<section title="Use of HTTP by other protocols" anchor="http.others">
2674<t>
2675   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2676   Extensions of HTTP like WebDAV.</cref>
2677</t>
2678
2679</section>
2680<section title="Use of HTTP by media type specification" anchor="http.media">
2681<t>
2682   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2683</t>
2684</section>
2685</section>
2686
2687<section title="Header Field Definitions" anchor="header.field.definitions">
2688<t>
2689   This section defines the syntax and semantics of HTTP/1.1 header fields
2690   related to message framing and transport protocols.
2691</t>
2692<t>
2693   For entity-header fields, both sender and recipient refer to either the
2694   client or the server, depending on who sends and who receives the entity.
2695</t>
2696
2697<section title="Connection" anchor="header.connection">
2698  <iref primary="true" item="Connection header" x:for-anchor=""/>
2699  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2700  <x:anchor-alias value="Connection"/>
2701  <x:anchor-alias value="connection-token"/>
2702  <x:anchor-alias value="Connection-v"/>
2703<t>
2704   The "Connection" general-header field allows the sender to specify
2705   options that are desired for that particular connection and &MUST-NOT;
2706   be communicated by proxies over further connections.
2707</t>
2708<t>
2709   The Connection header's value has the following grammar:
2710</t>
2711<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"/>
2712  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2713  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2714  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2715</artwork></figure>
2716<t>
2717   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2718   message is forwarded and, for each connection-token in this field,
2719   remove any header field(s) from the message with the same name as the
2720   connection-token. Connection options are signaled by the presence of
2721   a connection-token in the Connection header field, not by any
2722   corresponding additional header field(s), since the additional header
2723   field may not be sent if there are no parameters associated with that
2724   connection option.
2725</t>
2726<t>
2727   Message headers listed in the Connection header &MUST-NOT; include
2728   end-to-end headers, such as Cache-Control.
2729</t>
2730<t>
2731   HTTP/1.1 defines the "close" connection option for the sender to
2732   signal that the connection will be closed after completion of the
2733   response. For example,
2734</t>
2735<figure><artwork type="example">
2736  Connection: close
2737</artwork></figure>
2738<t>
2739   in either the request or the response header fields indicates that
2740   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2741   after the current request/response is complete.
2742</t>
2743<t>
2744   An HTTP/1.1 client that does not support persistent connections &MUST;
2745   include the "close" connection option in every request message.
2746</t>
2747<t>
2748   An HTTP/1.1 server that does not support persistent connections &MUST;
2749   include the "close" connection option in every response message that
2750   does not have a 1xx (Informational) status code.
2751</t>
2752<t>
2753   A system receiving an HTTP/1.0 (or lower-version) message that
2754   includes a Connection header &MUST;, for each connection-token in this
2755   field, remove and ignore any header field(s) from the message with
2756   the same name as the connection-token. This protects against mistaken
2757   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2758</t>
2759</section>
2760
2761<section title="Content-Length" anchor="header.content-length">
2762  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2763  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2764  <x:anchor-alias value="Content-Length"/>
2765  <x:anchor-alias value="Content-Length-v"/>
2766<t>
2767   The "Content-Length" entity-header field indicates the size of the
2768   entity-body, in number of OCTETs. In the case of responses to the HEAD
2769   method, it indicates the size of the entity-body that would have been sent
2770   had the request been a GET.
2771</t>
2772<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2773  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2774  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2775</artwork></figure>
2776<t>
2777   An example is
2778</t>
2779<figure><artwork type="example">
2780  Content-Length: 3495
2781</artwork></figure>
2782<t>
2783   Applications &SHOULD; use this field to indicate the transfer-length of
2784   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2785</t>
2786<t>
2787   Any Content-Length greater than or equal to zero is a valid value.
2788   <xref target="message.length"/> describes how to determine the length of a message-body
2789   if a Content-Length is not given.
2790</t>
2791<t>
2792   Note that the meaning of this field is significantly different from
2793   the corresponding definition in MIME, where it is an optional field
2794   used within the "message/external-body" content-type. In HTTP, it
2795   &SHOULD; be sent whenever the message's length can be determined prior
2796   to being transferred, unless this is prohibited by the rules in
2797   <xref target="message.length"/>.
2798</t>
2799</section>
2800
2801<section title="Date" anchor="header.date">
2802  <iref primary="true" item="Date header" x:for-anchor=""/>
2803  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2804  <x:anchor-alias value="Date"/>
2805  <x:anchor-alias value="Date-v"/>
2806<t>
2807   The "Date" general-header field represents the date and time at which
2808   the message was originated, having the same semantics as the Origination
2809   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2810   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2811   it &MUST; be sent in rfc1123-date format.
2812</t>
2813<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2814  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2815  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2816</artwork></figure>
2817<t>
2818   An example is
2819</t>
2820<figure><artwork type="example">
2821  Date: Tue, 15 Nov 1994 08:12:31 GMT
2822</artwork></figure>
2823<t>
2824   Origin servers &MUST; include a Date header field in all responses,
2825   except in these cases:
2826  <list style="numbers">
2827      <t>If the response status code is 100 (Continue) or 101 (Switching
2828         Protocols), the response &MAY; include a Date header field, at
2829         the server's option.</t>
2830
2831      <t>If the response status code conveys a server error, e.g., 500
2832         (Internal Server Error) or 503 (Service Unavailable), and it is
2833         inconvenient or impossible to generate a valid Date.</t>
2834
2835      <t>If the server does not have a clock that can provide a
2836         reasonable approximation of the current time, its responses
2837         &MUST-NOT; include a Date header field. In this case, the rules
2838         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2839  </list>
2840</t>
2841<t>
2842   A received message that does not have a Date header field &MUST; be
2843   assigned one by the recipient if the message will be cached by that
2844   recipient or gatewayed via a protocol which requires a Date. An HTTP
2845   implementation without a clock &MUST-NOT; cache responses without
2846   revalidating them on every use. An HTTP cache, especially a shared
2847   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2848   clock with a reliable external standard.
2849</t>
2850<t>
2851   Clients &SHOULD; only send a Date header field in messages that include
2852   an entity-body, as in the case of the PUT and POST requests, and even
2853   then it is optional. A client without a clock &MUST-NOT; send a Date
2854   header field in a request.
2855</t>
2856<t>
2857   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2858   time subsequent to the generation of the message. It &SHOULD; represent
2859   the best available approximation of the date and time of message
2860   generation, unless the implementation has no means of generating a
2861   reasonably accurate date and time. In theory, the date ought to
2862   represent the moment just before the entity is generated. In
2863   practice, the date can be generated at any time during the message
2864   origination without affecting its semantic value.
2865</t>
2866
2867<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2868<t>
2869   Some origin server implementations might not have a clock available.
2870   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2871   values to a response, unless these values were associated
2872   with the resource by a system or user with a reliable clock. It &MAY;
2873   assign an Expires value that is known, at or before server
2874   configuration time, to be in the past (this allows "pre-expiration"
2875   of responses without storing separate Expires values for each
2876   resource).
2877</t>
2878</section>
2879</section>
2880
2881<section title="Host" anchor="header.host">
2882  <iref primary="true" item="Host header" x:for-anchor=""/>
2883  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2884  <x:anchor-alias value="Host"/>
2885  <x:anchor-alias value="Host-v"/>
2886<t>
2887   The "Host" request-header field specifies the Internet host and port
2888   number of the resource being requested, allowing the origin server or
2889   gateway to differentiate between internally-ambiguous URLs, such as the root
2890   "/" URL of a server for multiple host names on a single IP address.
2891</t>
2892<t>   
2893   The Host field value &MUST; represent the naming authority of the origin
2894   server or gateway given by the original URL obtained from the user or
2895   referring resource (generally an http URI, as described in
2896   <xref target="http.uri"/>).
2897</t>
2898<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2899  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2900  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2901</artwork></figure>
2902<t>
2903   A "host" without any trailing port information implies the default
2904   port for the service requested (e.g., "80" for an HTTP URL). For
2905   example, a request on the origin server for
2906   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2907</t>
2908<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2909GET /pub/WWW/ HTTP/1.1
2910Host: www.example.org
2911</artwork></figure>
2912<t>
2913   A client &MUST; include a Host header field in all HTTP/1.1 request
2914   messages. If the requested URI does not include an Internet host
2915   name for the service being requested, then the Host header field &MUST;
2916   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2917   request message it forwards does contain an appropriate Host header
2918   field that identifies the service being requested by the proxy. All
2919   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2920   status code to any HTTP/1.1 request message which lacks a Host header
2921   field.
2922</t>
2923<t>
2924   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2925   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2926   for other requirements relating to Host.
2927</t>
2928</section>
2929
2930<section title="TE" anchor="header.te">
2931  <iref primary="true" item="TE header" x:for-anchor=""/>
2932  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2933  <x:anchor-alias value="TE"/>
2934  <x:anchor-alias value="TE-v"/>
2935  <x:anchor-alias value="t-codings"/>
2936  <x:anchor-alias value="te-params"/>
2937  <x:anchor-alias value="te-ext"/>
2938<t>
2939   The "TE" request-header field indicates what extension transfer-codings
2940   it is willing to accept in the response, and whether or not it is
2941   willing to accept trailer fields in a chunked transfer-coding.
2942</t>
2943<t>
2944   Its value may consist of the keyword "trailers" and/or a comma-separated
2945   list of extension transfer-coding names with optional accept
2946   parameters (as described in <xref target="transfer.codings"/>).
2947</t>
2948<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"/>
2949  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2950  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2951  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2952  <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> )
2953  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2954</artwork></figure>
2955<t>
2956   The presence of the keyword "trailers" indicates that the client is
2957   willing to accept trailer fields in a chunked transfer-coding, as
2958   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2959   transfer-coding values even though it does not itself represent a
2960   transfer-coding.
2961</t>
2962<t>
2963   Examples of its use are:
2964</t>
2965<figure><artwork type="example">
2966  TE: deflate
2967  TE:
2968  TE: trailers, deflate;q=0.5
2969</artwork></figure>
2970<t>
2971   The TE header field only applies to the immediate connection.
2972   Therefore, the keyword &MUST; be supplied within a Connection header
2973   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2974</t>
2975<t>
2976   A server tests whether a transfer-coding is acceptable, according to
2977   a TE field, using these rules:
2978  <list style="numbers">
2979    <x:lt>
2980      <t>The "chunked" transfer-coding is always acceptable. If the
2981         keyword "trailers" is listed, the client indicates that it is
2982         willing to accept trailer fields in the chunked response on
2983         behalf of itself and any downstream clients. The implication is
2984         that, if given, the client is stating that either all
2985         downstream clients are willing to accept trailer fields in the
2986         forwarded response, or that it will attempt to buffer the
2987         response on behalf of downstream recipients.
2988      </t><t>
2989         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2990         chunked response such that a client can be assured of buffering
2991         the entire response.</t>
2992    </x:lt>
2993    <x:lt>
2994      <t>If the transfer-coding being tested is one of the transfer-codings
2995         listed in the TE field, then it is acceptable unless it
2996         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2997         qvalue of 0 means "not acceptable.")</t>
2998    </x:lt>
2999    <x:lt>
3000      <t>If multiple transfer-codings are acceptable, then the
3001         acceptable transfer-coding with the highest non-zero qvalue is
3002         preferred.  The "chunked" transfer-coding always has a qvalue
3003         of 1.</t>
3004    </x:lt>
3005  </list>
3006</t>
3007<t>
3008   If the TE field-value is empty or if no TE field is present, the only
3009   transfer-coding is "chunked". A message with no transfer-coding is
3010   always acceptable.
3011</t>
3012</section>
3013
3014<section title="Trailer" anchor="header.trailer">
3015  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3016  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3017  <x:anchor-alias value="Trailer"/>
3018  <x:anchor-alias value="Trailer-v"/>
3019<t>
3020   The "Trailer" general-header field indicates that the given set of
3021   header fields is present in the trailer of a message encoded with
3022   chunked transfer-coding.
3023</t>
3024<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3025  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3026  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3027</artwork></figure>
3028<t>
3029   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3030   message using chunked transfer-coding with a non-empty trailer. Doing
3031   so allows the recipient to know which header fields to expect in the
3032   trailer.
3033</t>
3034<t>
3035   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3036   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3037   trailer fields in a "chunked" transfer-coding.
3038</t>
3039<t>
3040   Message header fields listed in the Trailer header field &MUST-NOT;
3041   include the following header fields:
3042  <list style="symbols">
3043    <t>Transfer-Encoding</t>
3044    <t>Content-Length</t>
3045    <t>Trailer</t>
3046  </list>
3047</t>
3048</section>
3049
3050<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3051  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3052  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3053  <x:anchor-alias value="Transfer-Encoding"/>
3054  <x:anchor-alias value="Transfer-Encoding-v"/>
3055<t>
3056   The "Transfer-Encoding" general-header field indicates what transfer-codings
3057   (if any) have been applied to the message body. It differs from
3058   Content-Encoding (&content-codings;) in that transfer-codings are a property
3059   of the message (and therefore are removed by intermediaries), whereas
3060   content-codings are not.
3061</t>
3062<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3063  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3064                        <x:ref>Transfer-Encoding-v</x:ref>
3065  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3066</artwork></figure>
3067<t>
3068   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3069</t>
3070<figure><artwork type="example">
3071  Transfer-Encoding: chunked
3072</artwork></figure>
3073<t>
3074   If multiple encodings have been applied to an entity, the transfer-codings
3075   &MUST; be listed in the order in which they were applied.
3076   Additional information about the encoding parameters &MAY; be provided
3077   by other entity-header fields not defined by this specification.
3078</t>
3079<t>
3080   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3081   header.
3082</t>
3083</section>
3084
3085<section title="Upgrade" anchor="header.upgrade">
3086  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3087  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3088  <x:anchor-alias value="Upgrade"/>
3089  <x:anchor-alias value="Upgrade-v"/>
3090<t>
3091   The "Upgrade" general-header field allows the client to specify what
3092   additional communication protocols it would like to use, if the server
3093   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3094   header field within a 101 (Switching Protocols) response to indicate which
3095   protocol(s) are being switched to.
3096</t>
3097<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3098  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3099  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3100</artwork></figure>
3101<t>
3102   For example,
3103</t>
3104<figure><artwork type="example">
3105  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3106</artwork></figure>
3107<t>
3108   The Upgrade header field is intended to provide a simple mechanism
3109   for transition from HTTP/1.1 to some other, incompatible protocol. It
3110   does so by allowing the client to advertise its desire to use another
3111   protocol, such as a later version of HTTP with a higher major version
3112   number, even though the current request has been made using HTTP/1.1.
3113   This eases the difficult transition between incompatible protocols by
3114   allowing the client to initiate a request in the more commonly
3115   supported protocol while indicating to the server that it would like
3116   to use a "better" protocol if available (where "better" is determined
3117   by the server, possibly according to the nature of the method and/or
3118   resource being requested).
3119</t>
3120<t>
3121   The Upgrade header field only applies to switching application-layer
3122   protocols upon the existing transport-layer connection. Upgrade
3123   cannot be used to insist on a protocol change; its acceptance and use
3124   by the server is optional. The capabilities and nature of the
3125   application-layer communication after the protocol change is entirely
3126   dependent upon the new protocol chosen, although the first action
3127   after changing the protocol &MUST; be a response to the initial HTTP
3128   request containing the Upgrade header field.
3129</t>
3130<t>
3131   The Upgrade header field only applies to the immediate connection.
3132   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3133   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3134   HTTP/1.1 message.
3135</t>
3136<t>
3137   The Upgrade header field cannot be used to indicate a switch to a
3138   protocol on a different connection. For that purpose, it is more
3139   appropriate to use a 301, 302, 303, or 305 redirection response.
3140</t>
3141<t>
3142   This specification only defines the protocol name "HTTP" for use by
3143   the family of Hypertext Transfer Protocols, as defined by the HTTP
3144   version rules of <xref target="http.version"/> and future updates to this
3145   specification. Additional tokens can be registered with IANA using the
3146   registration procedure defined below. 
3147</t>
3148
3149<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3150<t>
3151   The HTTP Upgrade Token Registry defines the name space for product
3152   tokens used to identify protocols in the Upgrade header field.
3153   Each registered token should be associated with one or a set of
3154   specifications, and with contact information.
3155</t>
3156<t>
3157   Registrations should be allowed on a First Come First Served basis as
3158   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
3159   specifications need not be IETF documents or be subject to IESG review, but
3160   should obey the following rules:
3161  <list style="numbers">
3162    <t>A token, once registered, stays registered forever.</t>
3163    <t>The registration &MUST; name a responsible party for the
3164       registration.</t>
3165    <t>The registration &MUST; name a point of contact.</t>
3166    <t>The registration &MAY; name the documentation required for the
3167       token.</t>
3168    <t>The responsible party &MAY; change the registration at any time.
3169       The IANA will keep a record of all such changes, and make them
3170       available upon request.</t>
3171    <t>The responsible party for the first registration of a "product"
3172       token &MUST; approve later registrations of a "version" token
3173       together with that "product" token before they can be registered.</t>
3174    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3175       for a token. This will normally only be used in the case when a
3176       responsible party cannot be contacted.</t>
3177  </list>
3178</t>
3179<t>
3180   It is not required that specifications for upgrade tokens be made
3181   publicly available, but the contact information for the registration
3182   should be.
3183</t>
3184</section>
3185
3186
3187</section>
3188
3189<section title="Via" anchor="header.via">
3190  <iref primary="true" item="Via header" x:for-anchor=""/>
3191  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3192  <x:anchor-alias value="protocol-name"/>
3193  <x:anchor-alias value="protocol-version"/>
3194  <x:anchor-alias value="pseudonym"/>
3195  <x:anchor-alias value="received-by"/>
3196  <x:anchor-alias value="received-protocol"/>
3197  <x:anchor-alias value="Via"/>
3198  <x:anchor-alias value="Via-v"/>
3199<t>
3200   The "Via" general-header field &MUST; be used by gateways and proxies to
3201   indicate the intermediate protocols and recipients between the user
3202   agent and the server on requests, and between the origin server and
3203   the client on responses. It is analogous to the "Received" field defined in
3204   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3205   avoiding request loops, and identifying the protocol capabilities of
3206   all senders along the request/response chain.
3207</t>
3208<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"/>
3209  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3210  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3211                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3212  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3213  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3214  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3215  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3216  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3217</artwork></figure>
3218<t>
3219   The received-protocol indicates the protocol version of the message
3220   received by the server or client along each segment of the
3221   request/response chain. The received-protocol version is appended to
3222   the Via field value when the message is forwarded so that information
3223   about the protocol capabilities of upstream applications remains
3224   visible to all recipients.
3225</t>
3226<t>
3227   The protocol-name is optional if and only if it would be "HTTP". The
3228   received-by field is normally the host and optional port number of a
3229   recipient server or client that subsequently forwarded the message.
3230   However, if the real host is considered to be sensitive information,
3231   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3232   be assumed to be the default port of the received-protocol.
3233</t>
3234<t>
3235   Multiple Via field values represent each proxy or gateway that has
3236   forwarded the message. Each recipient &MUST; append its information
3237   such that the end result is ordered according to the sequence of
3238   forwarding applications.
3239</t>
3240<t>
3241   Comments &MAY; be used in the Via header field to identify the software
3242   of the recipient proxy or gateway, analogous to the User-Agent and
3243   Server header fields. However, all comments in the Via field are
3244   optional and &MAY; be removed by any recipient prior to forwarding the
3245   message.
3246</t>
3247<t>
3248   For example, a request message could be sent from an HTTP/1.0 user
3249   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3250   forward the request to a public proxy at p.example.net, which completes
3251   the request by forwarding it to the origin server at www.example.com.
3252   The request received by www.example.com would then have the following
3253   Via header field:
3254</t>
3255<figure><artwork type="example">
3256  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3257</artwork></figure>
3258<t>
3259   Proxies and gateways used as a portal through a network firewall
3260   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3261   the firewall region. This information &SHOULD; only be propagated if
3262   explicitly enabled. If not enabled, the received-by host of any host
3263   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3264   for that host.
3265</t>
3266<t>
3267   For organizations that have strong privacy requirements for hiding
3268   internal structures, a proxy &MAY; combine an ordered subsequence of
3269   Via header field entries with identical received-protocol values into
3270   a single such entry. For example,
3271</t>
3272<figure><artwork type="example">
3273  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3274</artwork></figure>
3275<t>
3276  could be collapsed to
3277</t>
3278<figure><artwork type="example">
3279  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3280</artwork></figure>
3281<t>
3282   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3283   under the same organizational control and the hosts have already been
3284   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3285   have different received-protocol values.
3286</t>
3287</section>
3288
3289</section>
3290
3291<section title="IANA Considerations" anchor="IANA.considerations">
3292
3293<section title="Message Header Registration" anchor="message.header.registration">
3294<t>
3295   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3296   with the permanent registrations below (see <xref target="RFC3864"/>):
3297</t>
3298<?BEGININC p1-messaging.iana-headers ?>
3299<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3300<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3301   <ttcol>Header Field Name</ttcol>
3302   <ttcol>Protocol</ttcol>
3303   <ttcol>Status</ttcol>
3304   <ttcol>Reference</ttcol>
3305
3306   <c>Connection</c>
3307   <c>http</c>
3308   <c>standard</c>
3309   <c>
3310      <xref target="header.connection"/>
3311   </c>
3312   <c>Content-Length</c>
3313   <c>http</c>
3314   <c>standard</c>
3315   <c>
3316      <xref target="header.content-length"/>
3317   </c>
3318   <c>Date</c>
3319   <c>http</c>
3320   <c>standard</c>
3321   <c>
3322      <xref target="header.date"/>
3323   </c>
3324   <c>Host</c>
3325   <c>http</c>
3326   <c>standard</c>
3327   <c>
3328      <xref target="header.host"/>
3329   </c>
3330   <c>TE</c>
3331   <c>http</c>
3332   <c>standard</c>
3333   <c>
3334      <xref target="header.te"/>
3335   </c>
3336   <c>Trailer</c>
3337   <c>http</c>
3338   <c>standard</c>
3339   <c>
3340      <xref target="header.trailer"/>
3341   </c>
3342   <c>Transfer-Encoding</c>
3343   <c>http</c>
3344   <c>standard</c>
3345   <c>
3346      <xref target="header.transfer-encoding"/>
3347   </c>
3348   <c>Upgrade</c>
3349   <c>http</c>
3350   <c>standard</c>
3351   <c>
3352      <xref target="header.upgrade"/>
3353   </c>
3354   <c>Via</c>
3355   <c>http</c>
3356   <c>standard</c>
3357   <c>
3358      <xref target="header.via"/>
3359   </c>
3360</texttable>
3361<!--(END)-->
3362<?ENDINC p1-messaging.iana-headers ?>
3363<t>
3364   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3365</t>
3366</section>
3367
3368<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3369<t>
3370   The entries for the "http" and "https" URI Schemes in the registry located at
3371   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3372   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3373   and <xref target="https.uri" format="counter"/> of this document
3374   (see <xref target="RFC4395"/>).
3375</t>
3376</section>
3377
3378<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3379<t>
3380   This document serves as the specification for the Internet media types
3381   "message/http" and "application/http". The following is to be registered with
3382   IANA (see <xref target="RFC4288"/>).
3383</t>
3384<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3385<iref item="Media Type" subitem="message/http" primary="true"/>
3386<iref item="message/http Media Type" primary="true"/>
3387<t>
3388   The message/http type can be used to enclose a single HTTP request or
3389   response message, provided that it obeys the MIME restrictions for all
3390   "message" types regarding line length and encodings.
3391</t>
3392<t>
3393  <list style="hanging" x:indent="12em">
3394    <t hangText="Type name:">
3395      message
3396    </t>
3397    <t hangText="Subtype name:">
3398      http
3399    </t>
3400    <t hangText="Required parameters:">
3401      none
3402    </t>
3403    <t hangText="Optional parameters:">
3404      version, msgtype
3405      <list style="hanging">
3406        <t hangText="version:">
3407          The HTTP-Version number of the enclosed message
3408          (e.g., "1.1"). If not present, the version can be
3409          determined from the first line of the body.
3410        </t>
3411        <t hangText="msgtype:">
3412          The message type -- "request" or "response". If not
3413          present, the type can be determined from the first
3414          line of the body.
3415        </t>
3416      </list>
3417    </t>
3418    <t hangText="Encoding considerations:">
3419      only "7bit", "8bit", or "binary" are permitted
3420    </t>
3421    <t hangText="Security considerations:">
3422      none
3423    </t>
3424    <t hangText="Interoperability considerations:">
3425      none
3426    </t>
3427    <t hangText="Published specification:">
3428      This specification (see <xref target="internet.media.type.message.http"/>).
3429    </t>
3430    <t hangText="Applications that use this media type:">
3431    </t>
3432    <t hangText="Additional information:">
3433      <list style="hanging">
3434        <t hangText="Magic number(s):">none</t>
3435        <t hangText="File extension(s):">none</t>
3436        <t hangText="Macintosh file type code(s):">none</t>
3437      </list>
3438    </t>
3439    <t hangText="Person and email address to contact for further information:">
3440      See Authors Section.
3441    </t>
3442    <t hangText="Intended usage:">
3443      COMMON
3444    </t>
3445    <t hangText="Restrictions on usage:">
3446      none
3447    </t>
3448    <t hangText="Author/Change controller:">
3449      IESG
3450    </t>
3451  </list>
3452</t>
3453</section>
3454<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3455<iref item="Media Type" subitem="application/http" primary="true"/>
3456<iref item="application/http Media Type" primary="true"/>
3457<t>
3458   The application/http type can be used to enclose a pipeline of one or more
3459   HTTP request or response messages (not intermixed).
3460</t>
3461<t>
3462  <list style="hanging" x:indent="12em">
3463    <t hangText="Type name:">
3464      application
3465    </t>
3466    <t hangText="Subtype name:">
3467      http
3468    </t>
3469    <t hangText="Required parameters:">
3470      none
3471    </t>
3472    <t hangText="Optional parameters:">
3473      version, msgtype
3474      <list style="hanging">
3475        <t hangText="version:">
3476          The HTTP-Version number of the enclosed messages
3477          (e.g., "1.1"). If not present, the version can be
3478          determined from the first line of the body.
3479        </t>
3480        <t hangText="msgtype:">
3481          The message type -- "request" or "response". If not
3482          present, the type can be determined from the first
3483          line of the body.
3484        </t>
3485      </list>
3486    </t>
3487    <t hangText="Encoding considerations:">
3488      HTTP messages enclosed by this type
3489      are in "binary" format; use of an appropriate
3490      Content-Transfer-Encoding is required when
3491      transmitted via E-mail.
3492    </t>
3493    <t hangText="Security considerations:">
3494      none
3495    </t>
3496    <t hangText="Interoperability considerations:">
3497      none
3498    </t>
3499    <t hangText="Published specification:">
3500      This specification (see <xref target="internet.media.type.application.http"/>).
3501    </t>
3502    <t hangText="Applications that use this media type:">
3503    </t>
3504    <t hangText="Additional information:">
3505      <list style="hanging">
3506        <t hangText="Magic number(s):">none</t>
3507        <t hangText="File extension(s):">none</t>
3508        <t hangText="Macintosh file type code(s):">none</t>
3509      </list>
3510    </t>
3511    <t hangText="Person and email address to contact for further information:">
3512      See Authors Section.
3513    </t>
3514    <t hangText="Intended usage:">
3515      COMMON
3516    </t>
3517    <t hangText="Restrictions on usage:">
3518      none
3519    </t>
3520    <t hangText="Author/Change controller:">
3521      IESG
3522    </t>
3523  </list>
3524</t>
3525</section>
3526</section>
3527
3528<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3529<t>
3530   The registration procedure for HTTP Transfer Codings is now defined by
3531   <xref target="transfer.coding.registry"/> of this document.
3532</t>
3533<t>
3534   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3535   should be updated with the registrations below:
3536</t>
3537<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3538   <ttcol>Name</ttcol>
3539   <ttcol>Description</ttcol>
3540   <ttcol>Reference</ttcol>
3541   <c>chunked</c>
3542   <c>Transfer in a series of chunks</c>
3543   <c>
3544      <xref target="chunked.encoding"/>
3545   </c>
3546   <c>compress</c>
3547   <c>UNIX "compress" program method</c>
3548   <c>
3549      <xref target="compress.coding"/>
3550   </c>
3551   <c>deflate</c>
3552   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3553   the "zlib" data format (<xref target="RFC1950"/>)
3554   </c>
3555   <c>
3556      <xref target="deflate.coding"/>
3557   </c>
3558   <c>gzip</c>
3559   <c>Same as GNU zip <xref target="RFC1952"/></c>
3560   <c>
3561      <xref target="gzip.coding"/>
3562   </c>
3563</texttable>
3564</section>
3565
3566<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3567<t>
3568   The registration procedure for HTTP Upgrade Tokens -- previously defined
3569   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3570   by <xref target="upgrade.token.registry"/> of this document.
3571</t>
3572<t>
3573   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3574   should be updated with the registration below:
3575</t>
3576<texttable align="left" suppress-title="true">
3577   <ttcol>Value</ttcol>
3578   <ttcol>Description</ttcol>
3579   <ttcol>Reference</ttcol>
3580
3581   <c>HTTP</c>
3582   <c>Hypertext Transfer Protocol</c> 
3583   <c><xref target="http.version"/> of this specification</c>
3584<!-- IANA should add this without our instructions; emailed on June 05, 2009
3585   <c>TLS/1.0</c>
3586   <c>Transport Layer Security</c>
3587   <c><xref target="RFC2817"/></c> -->
3588
3589</texttable>
3590</section>
3591
3592</section>
3593
3594<section title="Security Considerations" anchor="security.considerations">
3595<t>
3596   This section is meant to inform application developers, information
3597   providers, and users of the security limitations in HTTP/1.1 as
3598   described by this document. The discussion does not include
3599   definitive solutions to the problems revealed, though it does make
3600   some suggestions for reducing security risks.
3601</t>
3602
3603<section title="Personal Information" anchor="personal.information">
3604<t>
3605   HTTP clients are often privy to large amounts of personal information
3606   (e.g., the user's name, location, mail address, passwords, encryption
3607   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3608   leakage of this information.
3609   We very strongly recommend that a convenient interface be provided
3610   for the user to control dissemination of such information, and that
3611   designers and implementors be particularly careful in this area.
3612   History shows that errors in this area often create serious security
3613   and/or privacy problems and generate highly adverse publicity for the
3614   implementor's company.
3615</t>
3616</section>
3617
3618<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3619<t>
3620   A server is in the position to save personal data about a user's
3621   requests which might identify their reading patterns or subjects of
3622   interest. This information is clearly confidential in nature and its
3623   handling can be constrained by law in certain countries. People using
3624   HTTP to provide data are responsible for ensuring that
3625   such material is not distributed without the permission of any
3626   individuals that are identifiable by the published results.
3627</t>
3628</section>
3629
3630<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3631<t>
3632   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3633   the documents returned by HTTP requests to be only those that were
3634   intended by the server administrators. If an HTTP server translates
3635   HTTP URIs directly into file system calls, the server &MUST; take
3636   special care not to serve files that were not intended to be
3637   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3638   other operating systems use ".." as a path component to indicate a
3639   directory level above the current one. On such a system, an HTTP
3640   server &MUST; disallow any such construct in the request-target if it
3641   would otherwise allow access to a resource outside those intended to
3642   be accessible via the HTTP server. Similarly, files intended for
3643   reference only internally to the server (such as access control
3644   files, configuration files, and script code) &MUST; be protected from
3645   inappropriate retrieval, since they might contain sensitive
3646   information. Experience has shown that minor bugs in such HTTP server
3647   implementations have turned into security risks.
3648</t>
3649</section>
3650
3651<section title="DNS Spoofing" anchor="dns.spoofing">
3652<t>
3653   Clients using HTTP rely heavily on the Domain Name Service, and are
3654   thus generally prone to security attacks based on the deliberate
3655   mis-association of IP addresses and DNS names. Clients need to be
3656   cautious in assuming the continuing validity of an IP number/DNS name
3657   association.
3658</t>
3659<t>
3660   In particular, HTTP clients &SHOULD; rely on their name resolver for
3661   confirmation of an IP number/DNS name association, rather than
3662   caching the result of previous host name lookups. Many platforms
3663   already can cache host name lookups locally when appropriate, and
3664   they &SHOULD; be configured to do so. It is proper for these lookups to
3665   be cached, however, only when the TTL (Time To Live) information
3666   reported by the name server makes it likely that the cached
3667   information will remain useful.
3668</t>
3669<t>
3670   If HTTP clients cache the results of host name lookups in order to
3671   achieve a performance improvement, they &MUST; observe the TTL
3672   information reported by DNS.
3673</t>
3674<t>
3675   If HTTP clients do not observe this rule, they could be spoofed when
3676   a previously-accessed server's IP address changes. As network
3677   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3678   possibility of this form of attack will grow. Observing this
3679   requirement thus reduces this potential security vulnerability.
3680</t>
3681<t>
3682   This requirement also improves the load-balancing behavior of clients
3683   for replicated servers using the same DNS name and reduces the
3684   likelihood of a user's experiencing failure in accessing sites which
3685   use that strategy.
3686</t>
3687</section>
3688
3689<section title="Proxies and Caching" anchor="attack.proxies">
3690<t>
3691   By their very nature, HTTP proxies are men-in-the-middle, and
3692   represent an opportunity for man-in-the-middle attacks. Compromise of
3693   the systems on which the proxies run can result in serious security
3694   and privacy problems. Proxies have access to security-related
3695   information, personal information about individual users and
3696   organizations, and proprietary information belonging to users and
3697   content providers. A compromised proxy, or a proxy implemented or
3698   configured without regard to security and privacy considerations,
3699   might be used in the commission of a wide range of potential attacks.
3700</t>
3701<t>
3702   Proxy operators should protect the systems on which proxies run as
3703   they would protect any system that contains or transports sensitive
3704   information. In particular, log information gathered at proxies often
3705   contains highly sensitive personal information, and/or information
3706   about organizations. Log information should be carefully guarded, and
3707   appropriate guidelines for use should be developed and followed.
3708   (<xref target="abuse.of.server.log.information"/>).
3709</t>
3710<t>
3711   Proxy implementors should consider the privacy and security
3712   implications of their design and coding decisions, and of the
3713   configuration options they provide to proxy operators (especially the
3714   default configuration).
3715</t>
3716<t>
3717   Users of a proxy need to be aware that proxies are no trustworthier than
3718   the people who run them; HTTP itself cannot solve this problem.
3719</t>
3720<t>
3721   The judicious use of cryptography, when appropriate, may suffice to
3722   protect against a broad range of security and privacy attacks. Such
3723   cryptography is beyond the scope of the HTTP/1.1 specification.
3724</t>
3725</section>
3726
3727<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3728<t>
3729   They exist. They are hard to defend against. Research continues.
3730   Beware.
3731</t>
3732</section>
3733</section>
3734
3735<section title="Acknowledgments" anchor="ack">
3736<t>
3737   HTTP has evolved considerably over the years. It has
3738   benefited from a large and active developer community--the many
3739   people who have participated on the www-talk mailing list--and it is
3740   that community which has been most responsible for the success of
3741   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3742   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3743   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3744   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3745   VanHeyningen deserve special recognition for their efforts in
3746   defining early aspects of the protocol.
3747</t>
3748<t>
3749   This document has benefited greatly from the comments of all those
3750   participating in the HTTP-WG. In addition to those already mentioned,
3751   the following individuals have contributed to this specification:
3752</t>
3753<t>
3754   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3755   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3756   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3757   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3758   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3759   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3760   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3761   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3762   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3763   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3764   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3765   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3766   Josh Cohen.
3767</t>
3768<t>
3769   Thanks to the "cave men" of Palo Alto. You know who you are.
3770</t>
3771<t>
3772   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3773   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3774   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3775   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3776   Larry Masinter for their help. And thanks go particularly to Jeff
3777   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3778</t>
3779<t>
3780   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3781   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3782   discovery of many of the problems that this document attempts to
3783   rectify.
3784</t>
3785<t>
3786   This specification makes heavy use of the augmented BNF and generic
3787   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3788   reuses many of the definitions provided by Nathaniel Borenstein and
3789   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3790   specification will help reduce past confusion over the relationship
3791   between HTTP and Internet mail message formats.
3792</t>
3793</section>
3794
3795</middle>
3796<back>
3797
3798<references title="Normative References">
3799
3800<reference anchor="ISO-8859-1">
3801  <front>
3802    <title>
3803     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3804    </title>
3805    <author>
3806      <organization>International Organization for Standardization</organization>
3807    </author>
3808    <date year="1998"/>
3809  </front>
3810  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3811</reference>
3812
3813<reference anchor="Part2">
3814  <front>
3815    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3816    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3817      <organization abbrev="Day Software">Day Software</organization>
3818      <address><email>fielding@gbiv.com</email></address>
3819    </author>
3820    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3821      <organization>One Laptop per Child</organization>
3822      <address><email>jg@laptop.org</email></address>
3823    </author>
3824    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3825      <organization abbrev="HP">Hewlett-Packard Company</organization>
3826      <address><email>JeffMogul@acm.org</email></address>
3827    </author>
3828    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3829      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3830      <address><email>henrikn@microsoft.com</email></address>
3831    </author>
3832    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3833      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3834      <address><email>LMM@acm.org</email></address>
3835    </author>
3836    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3837      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3838      <address><email>paulle@microsoft.com</email></address>
3839    </author>
3840    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3841      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3842      <address><email>timbl@w3.org</email></address>
3843    </author>
3844    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3845      <organization abbrev="W3C">World Wide Web Consortium</organization>
3846      <address><email>ylafon@w3.org</email></address>
3847    </author>
3848    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3849      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3850      <address><email>julian.reschke@greenbytes.de</email></address>
3851    </author>
3852    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3853  </front>
3854  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3855  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3856</reference>
3857
3858<reference anchor="Part3">
3859  <front>
3860    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3861    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3862      <organization abbrev="Day Software">Day Software</organization>
3863      <address><email>fielding@gbiv.com</email></address>
3864    </author>
3865    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3866      <organization>One Laptop per Child</organization>
3867      <address><email>jg@laptop.org</email></address>
3868    </author>
3869    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3870      <organization abbrev="HP">Hewlett-Packard Company</organization>
3871      <address><email>JeffMogul@acm.org</email></address>
3872    </author>
3873    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3874      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3875      <address><email>henrikn@microsoft.com</email></address>
3876    </author>
3877    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3878      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3879      <address><email>LMM@acm.org</email></address>
3880    </author>
3881    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3882      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3883      <address><email>paulle@microsoft.com</email></address>
3884    </author>
3885    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3886      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3887      <address><email>timbl@w3.org</email></address>
3888    </author>
3889    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3890      <organization abbrev="W3C">World Wide Web Consortium</organization>
3891      <address><email>ylafon@w3.org</email></address>
3892    </author>
3893    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3894      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3895      <address><email>julian.reschke@greenbytes.de</email></address>
3896    </author>
3897    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3898  </front>
3899  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3900  <x:source href="p3-payload.xml" basename="p3-payload"/>
3901</reference>
3902
3903<reference anchor="Part5">
3904  <front>
3905    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3906    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3907      <organization abbrev="Day Software">Day Software</organization>
3908      <address><email>fielding@gbiv.com</email></address>
3909    </author>
3910    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3911      <organization>One Laptop per Child</organization>
3912      <address><email>jg@laptop.org</email></address>
3913    </author>
3914    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3915      <organization abbrev="HP">Hewlett-Packard Company</organization>
3916      <address><email>JeffMogul@acm.org</email></address>
3917    </author>
3918    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3919      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3920      <address><email>henrikn@microsoft.com</email></address>
3921    </author>
3922    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3923      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3924      <address><email>LMM@acm.org</email></address>
3925    </author>
3926    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3927      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3928      <address><email>paulle@microsoft.com</email></address>
3929    </author>
3930    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3931      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3932      <address><email>timbl@w3.org</email></address>
3933    </author>
3934    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3935      <organization abbrev="W3C">World Wide Web Consortium</organization>
3936      <address><email>ylafon@w3.org</email></address>
3937    </author>
3938    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3939      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3940      <address><email>julian.reschke@greenbytes.de</email></address>
3941    </author>
3942    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3943  </front>
3944  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3945  <x:source href="p5-range.xml" basename="p5-range"/>
3946</reference>
3947
3948<reference anchor="Part6">
3949  <front>
3950    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3951    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3952      <organization abbrev="Day Software">Day Software</organization>
3953      <address><email>fielding@gbiv.com</email></address>
3954    </author>
3955    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3956      <organization>One Laptop per Child</organization>
3957      <address><email>jg@laptop.org</email></address>
3958    </author>
3959    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3960      <organization abbrev="HP">Hewlett-Packard Company</organization>
3961      <address><email>JeffMogul@acm.org</email></address>
3962    </author>
3963    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3964      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3965      <address><email>henrikn@microsoft.com</email></address>
3966    </author>
3967    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3968      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3969      <address><email>LMM@acm.org</email></address>
3970    </author>
3971    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3972      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3973      <address><email>paulle@microsoft.com</email></address>
3974    </author>
3975    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3976      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3977      <address><email>timbl@w3.org</email></address>
3978    </author>
3979    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3980      <organization abbrev="W3C">World Wide Web Consortium</organization>
3981      <address><email>ylafon@w3.org</email></address>
3982    </author>
3983    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3984      <address><email>mnot@mnot.net</email></address>
3985    </author>
3986    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3987      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3988      <address><email>julian.reschke@greenbytes.de</email></address>
3989    </author>
3990    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3991  </front>
3992  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3993  <x:source href="p6-cache.xml" basename="p6-cache"/>
3994</reference>
3995
3996<reference anchor="RFC5234">
3997  <front>
3998    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3999    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4000      <organization>Brandenburg InternetWorking</organization>
4001      <address>
4002        <email>dcrocker@bbiw.net</email>
4003      </address> 
4004    </author>
4005    <author initials="P." surname="Overell" fullname="Paul Overell">
4006      <organization>THUS plc.</organization>
4007      <address>
4008        <email>paul.overell@thus.net</email>
4009      </address>
4010    </author>
4011    <date month="January" year="2008"/>
4012  </front>
4013  <seriesInfo name="STD" value="68"/>
4014  <seriesInfo name="RFC" value="5234"/>
4015</reference>
4016
4017<reference anchor="RFC2119">
4018  <front>
4019    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4020    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4021      <organization>Harvard University</organization>
4022      <address><email>sob@harvard.edu</email></address>
4023    </author>
4024    <date month="March" year="1997"/>
4025  </front>
4026  <seriesInfo name="BCP" value="14"/>
4027  <seriesInfo name="RFC" value="2119"/>
4028</reference>
4029
4030<reference anchor="RFC3986">
4031 <front>
4032  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4033  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4034    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4035    <address>
4036       <email>timbl@w3.org</email>
4037       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4038    </address>
4039  </author>
4040  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4041    <organization abbrev="Day Software">Day Software</organization>
4042    <address>
4043      <email>fielding@gbiv.com</email>
4044      <uri>http://roy.gbiv.com/</uri>
4045    </address>
4046  </author>
4047  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4048    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4049    <address>
4050      <email>LMM@acm.org</email>
4051      <uri>http://larry.masinter.net/</uri>
4052    </address>
4053  </author>
4054  <date month='January' year='2005'></date>
4055 </front>
4056 <seriesInfo name="RFC" value="3986"/>
4057 <seriesInfo name="STD" value="66"/>
4058</reference>
4059
4060<reference anchor="USASCII">
4061  <front>
4062    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4063    <author>
4064      <organization>American National Standards Institute</organization>
4065    </author>
4066    <date year="1986"/>
4067  </front>
4068  <seriesInfo name="ANSI" value="X3.4"/>
4069</reference>
4070
4071<reference anchor="RFC1950">
4072  <front>
4073    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4074    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4075      <organization>Aladdin Enterprises</organization>
4076      <address><email>ghost@aladdin.com</email></address>
4077    </author>
4078    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4079    <date month="May" year="1996"/>
4080  </front>
4081  <seriesInfo name="RFC" value="1950"/>
4082  <annotation>
4083    RFC 1950 is an Informational RFC, thus it may be less stable than
4084    this specification. On the other hand, this downward reference was
4085    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4086    therefore it is unlikely to cause problems in practice. See also
4087    <xref target="BCP97"/>.
4088  </annotation>
4089</reference>
4090
4091<reference anchor="RFC1951">
4092  <front>
4093    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4094    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4095      <organization>Aladdin Enterprises</organization>
4096      <address><email>ghost@aladdin.com</email></address>
4097    </author>
4098    <date month="May" year="1996"/>
4099  </front>
4100  <seriesInfo name="RFC" value="1951"/>
4101  <annotation>
4102    RFC 1951 is an Informational RFC, thus it may be less stable than
4103    this specification. On the other hand, this downward reference was
4104    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4105    therefore it is unlikely to cause problems in practice. See also
4106    <xref target="BCP97"/>.
4107  </annotation>
4108</reference>
4109
4110<reference anchor="RFC1952">
4111  <front>
4112    <title>GZIP file format specification version 4.3</title>
4113    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4114      <organization>Aladdin Enterprises</organization>
4115      <address><email>ghost@aladdin.com</email></address>
4116    </author>
4117    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4118      <address><email>gzip@prep.ai.mit.edu</email></address>
4119    </author>
4120    <author initials="M." surname="Adler" fullname="Mark Adler">
4121      <address><email>madler@alumni.caltech.edu</email></address>
4122    </author>
4123    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4124      <address><email>ghost@aladdin.com</email></address>
4125    </author>
4126    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4127      <address><email>randeg@alumni.rpi.edu</email></address>
4128    </author>
4129    <date month="May" year="1996"/>
4130  </front>
4131  <seriesInfo name="RFC" value="1952"/>
4132  <annotation>
4133    RFC 1952 is an Informational RFC, thus it may be less stable than
4134    this specification. On the other hand, this downward reference was
4135    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4136    therefore it is unlikely to cause problems in practice. See also
4137    <xref target="BCP97"/>.
4138  </annotation>
4139</reference>
4140
4141</references>
4142
4143<references title="Informative References">
4144
4145<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4146  <front>
4147    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4148    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen"/>
4149    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4150    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4151    <author initials="H." surname="Lie" fullname="H. Lie"/>
4152    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4153    <date year="1997" month="September"/>
4154  </front>
4155  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4156</reference>
4157
4158<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4159  <front>
4160    <title>Improving HTTP Latency</title>
4161    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4162    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4163    <date year="1995" month="December"/>
4164  </front>
4165  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4166</reference>
4167
4168<reference anchor="RFC1123">
4169  <front>
4170    <title>Requirements for Internet Hosts - Application and Support</title>
4171    <author initials="R." surname="Braden" fullname="Robert Braden">
4172      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4173      <address><email>Braden@ISI.EDU</email></address>
4174    </author>
4175    <date month="October" year="1989"/>
4176  </front>
4177  <seriesInfo name="STD" value="3"/>
4178  <seriesInfo name="RFC" value="1123"/>
4179</reference>
4180
4181<reference anchor="RFC1305">
4182  <front>
4183    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4184    <author initials="D." surname="Mills" fullname="David L. Mills">
4185      <organization>University of Delaware, Electrical Engineering Department</organization>
4186      <address><email>mills@udel.edu</email></address>
4187    </author>
4188    <date month="March" year="1992"/>
4189  </front>
4190  <seriesInfo name="RFC" value="1305"/>
4191</reference>
4192
4193<reference anchor="RFC1900">
4194  <front>
4195    <title>Renumbering Needs Work</title>
4196    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4197      <organization>CERN, Computing and Networks Division</organization>
4198      <address><email>brian@dxcoms.cern.ch</email></address>
4199    </author>
4200    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4201      <organization>cisco Systems</organization>
4202      <address><email>yakov@cisco.com</email></address>
4203    </author>
4204    <date month="February" year="1996"/>
4205  </front>
4206  <seriesInfo name="RFC" value="1900"/>
4207</reference>
4208
4209<reference anchor="RFC1945">
4210  <front>
4211    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4212    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4213      <organization>MIT, Laboratory for Computer Science</organization>
4214      <address><email>timbl@w3.org</email></address>
4215    </author>
4216    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4217      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4218      <address><email>fielding@ics.uci.edu</email></address>
4219    </author>
4220    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4221      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4222      <address><email>frystyk@w3.org</email></address>
4223    </author>
4224    <date month="May" year="1996"/>
4225  </front>
4226  <seriesInfo name="RFC" value="1945"/>
4227</reference>
4228
4229<reference anchor="RFC2045">
4230  <front>
4231    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4232    <author initials="N." surname="Freed" fullname="Ned Freed">
4233      <organization>Innosoft International, Inc.</organization>
4234      <address><email>ned@innosoft.com</email></address>
4235    </author>
4236    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4237      <organization>First Virtual Holdings</organization>
4238      <address><email>nsb@nsb.fv.com</email></address>
4239    </author>
4240    <date month="November" year="1996"/>
4241  </front>
4242  <seriesInfo name="RFC" value="2045"/>
4243</reference>
4244
4245<reference anchor="RFC2047">
4246  <front>
4247    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4248    <author initials="K." surname="Moore" fullname="Keith Moore">
4249      <organization>University of Tennessee</organization>
4250      <address><email>moore@cs.utk.edu</email></address>
4251    </author>
4252    <date month="November" year="1996"/>
4253  </front>
4254  <seriesInfo name="RFC" value="2047"/>
4255</reference>
4256
4257<reference anchor="RFC2068">
4258  <front>
4259    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4260    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4261      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4262      <address><email>fielding@ics.uci.edu</email></address>
4263    </author>
4264    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4265      <organization>MIT Laboratory for Computer Science</organization>
4266      <address><email>jg@w3.org</email></address>
4267    </author>
4268    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4269      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4270      <address><email>mogul@wrl.dec.com</email></address>
4271    </author>
4272    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4273      <organization>MIT Laboratory for Computer Science</organization>
4274      <address><email>frystyk@w3.org</email></address>
4275    </author>
4276    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4277      <organization>MIT Laboratory for Computer Science</organization>
4278      <address><email>timbl@w3.org</email></address>
4279    </author>
4280    <date month="January" year="1997"/>
4281  </front>
4282  <seriesInfo name="RFC" value="2068"/>
4283</reference>
4284
4285<reference anchor='RFC2109'>
4286  <front>
4287    <title>HTTP State Management Mechanism</title>
4288    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4289      <organization>Bell Laboratories, Lucent Technologies</organization>
4290      <address><email>dmk@bell-labs.com</email></address>
4291    </author>
4292    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4293      <organization>Netscape Communications Corp.</organization>
4294      <address><email>montulli@netscape.com</email></address>
4295    </author>
4296    <date year='1997' month='February' />
4297  </front>
4298  <seriesInfo name='RFC' value='2109' />
4299</reference>
4300
4301<reference anchor="RFC2145">
4302  <front>
4303    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4304    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4305      <organization>Western Research Laboratory</organization>
4306      <address><email>mogul@wrl.dec.com</email></address>
4307    </author>
4308    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4309      <organization>Department of Information and Computer Science</organization>
4310      <address><email>fielding@ics.uci.edu</email></address>
4311    </author>
4312    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4313      <organization>MIT Laboratory for Computer Science</organization>
4314      <address><email>jg@w3.org</email></address>
4315    </author>
4316    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4317      <organization>W3 Consortium</organization>
4318      <address><email>frystyk@w3.org</email></address>
4319    </author>
4320    <date month="May" year="1997"/>
4321  </front>
4322  <seriesInfo name="RFC" value="2145"/>
4323</reference>
4324
4325<reference anchor="RFC2616">
4326  <front>
4327    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4328    <author initials="R." surname="Fielding" fullname="R. Fielding">
4329      <organization>University of California, Irvine</organization>
4330      <address><email>fielding@ics.uci.edu</email></address>
4331    </author>
4332    <author initials="J." surname="Gettys" fullname="J. Gettys">
4333      <organization>W3C</organization>
4334      <address><email>jg@w3.org</email></address>
4335    </author>
4336    <author initials="J." surname="Mogul" fullname="J. Mogul">
4337      <organization>Compaq Computer Corporation</organization>
4338      <address><email>mogul@wrl.dec.com</email></address>
4339    </author>
4340    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4341      <organization>MIT Laboratory for Computer Science</organization>
4342      <address><email>frystyk@w3.org</email></address>
4343    </author>
4344    <author initials="L." surname="Masinter" fullname="L. Masinter">
4345      <organization>Xerox Corporation</organization>
4346      <address><email>masinter@parc.xerox.com</email></address>
4347    </author>
4348    <author initials="P." surname="Leach" fullname="P. Leach">
4349      <organization>Microsoft Corporation</organization>
4350      <address><email>paulle@microsoft.com</email></address>
4351    </author>
4352    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4353      <organization>W3C</organization>
4354      <address><email>timbl@w3.org</email></address>
4355    </author>
4356    <date month="June" year="1999"/>
4357  </front>
4358  <seriesInfo name="RFC" value="2616"/>
4359</reference>
4360
4361<reference anchor='RFC2817'>
4362  <front>
4363    <title>Upgrading to TLS Within HTTP/1.1</title>
4364    <author initials='R.' surname='Khare' fullname='R. Khare'>
4365      <organization>4K Associates / UC Irvine</organization>
4366      <address><email>rohit@4K-associates.com</email></address>
4367    </author>
4368    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4369      <organization>Agranat Systems, Inc.</organization>
4370      <address><email>lawrence@agranat.com</email></address>
4371    </author>
4372    <date year='2000' month='May' />
4373  </front>
4374  <seriesInfo name='RFC' value='2817' />
4375</reference>
4376
4377<reference anchor='RFC2818'>
4378  <front>
4379    <title>HTTP Over TLS</title>
4380    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4381      <organization>RTFM, Inc.</organization>
4382      <address><email>ekr@rtfm.com</email></address>
4383    </author>
4384    <date year='2000' month='May' />
4385  </front>
4386  <seriesInfo name='RFC' value='2818' />
4387</reference>
4388
4389<reference anchor='RFC2965'>
4390  <front>
4391    <title>HTTP State Management Mechanism</title>
4392    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4393      <organization>Bell Laboratories, Lucent Technologies</organization>
4394      <address><email>dmk@bell-labs.com</email></address>
4395    </author>
4396    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4397      <organization>Epinions.com, Inc.</organization>
4398      <address><email>lou@montulli.org</email></address>
4399    </author>
4400    <date year='2000' month='October' />
4401  </front>
4402  <seriesInfo name='RFC' value='2965' />
4403</reference>
4404
4405<reference anchor='RFC3864'>
4406  <front>
4407    <title>Registration Procedures for Message Header Fields</title>
4408    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4409      <organization>Nine by Nine</organization>
4410      <address><email>GK-IETF@ninebynine.org</email></address>
4411    </author>
4412    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4413      <organization>BEA Systems</organization>
4414      <address><email>mnot@pobox.com</email></address>
4415    </author>
4416    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4417      <organization>HP Labs</organization>
4418      <address><email>JeffMogul@acm.org</email></address>
4419    </author>
4420    <date year='2004' month='September' />
4421  </front>
4422  <seriesInfo name='BCP' value='90' />
4423  <seriesInfo name='RFC' value='3864' />
4424</reference>
4425
4426<reference anchor="RFC4288">
4427  <front>
4428    <title>Media Type Specifications and Registration Procedures</title>
4429    <author initials="N." surname="Freed" fullname="N. Freed">
4430      <organization>Sun Microsystems</organization>
4431      <address>
4432        <email>ned.freed@mrochek.com</email>
4433      </address>
4434    </author>
4435    <author initials="J." surname="Klensin" fullname="J. Klensin">
4436      <address>
4437        <email>klensin+ietf@jck.com</email>
4438      </address>
4439    </author>
4440    <date year="2005" month="December"/>
4441  </front>
4442  <seriesInfo name="BCP" value="13"/>
4443  <seriesInfo name="RFC" value="4288"/>
4444</reference>
4445
4446<reference anchor='RFC4395'>
4447  <front>
4448    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4449    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4450      <organization>AT&amp;T Laboratories</organization>
4451      <address>
4452        <email>tony+urireg@maillennium.att.com</email>
4453      </address>
4454    </author>
4455    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4456      <organization>Qualcomm, Inc.</organization>
4457      <address>
4458        <email>hardie@qualcomm.com</email>
4459      </address>
4460    </author>
4461    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4462      <organization>Adobe Systems</organization>
4463      <address>
4464        <email>LMM@acm.org</email>
4465      </address>
4466    </author>
4467    <date year='2006' month='February' />
4468  </front>
4469  <seriesInfo name='BCP' value='115' />
4470  <seriesInfo name='RFC' value='4395' />
4471</reference>
4472
4473<reference anchor='RFC5226'>
4474  <front>
4475    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4476    <author initials='T.' surname='Narten' fullname='T. Narten'>
4477      <organization>IBM</organization>
4478      <address><email>narten@us.ibm.com</email></address>
4479    </author>
4480    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4481      <organization>Google</organization>
4482      <address><email>Harald@Alvestrand.no</email></address>
4483    </author>
4484    <date year='2008' month='May' />
4485  </front>
4486  <seriesInfo name='BCP' value='26' />
4487  <seriesInfo name='RFC' value='5226' />
4488</reference>
4489
4490<reference anchor="RFC5322">
4491  <front>
4492    <title>Internet Message Format</title>
4493    <author initials="P." surname="Resnick" fullname="P. Resnick">
4494      <organization>Qualcomm Incorporated</organization>
4495    </author>
4496    <date year="2008" month="October"/>
4497  </front> 
4498  <seriesInfo name="RFC" value="5322"/>
4499</reference>
4500
4501<reference anchor='BCP97'>
4502  <front>
4503    <title>Handling Normative References to Standards-Track Documents</title>
4504    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4505      <address>
4506        <email>klensin+ietf@jck.com</email>
4507      </address>
4508    </author>
4509    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4510      <organization>MIT</organization>
4511      <address>
4512        <email>hartmans-ietf@mit.edu</email>
4513      </address>
4514    </author>
4515    <date year='2007' month='June' />
4516  </front>
4517  <seriesInfo name='BCP' value='97' />
4518  <seriesInfo name='RFC' value='4897' />
4519</reference>
4520
4521<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4522  <front>
4523    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4524    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4525    <date year="2001" month="November"/>
4526  </front>
4527  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4528</reference>
4529
4530<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4531  <front>
4532    <title>Analysis of HTTP Performance Problems</title>
4533    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4534    <date/>
4535  </front>
4536</reference>
4537
4538<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4539  <front>
4540  <title>Analysis of HTTP Performance</title>
4541  <author initials="J." surname="Touch" fullname="Joe Touch">
4542    <organization>USC/Information Sciences Institute</organization>
4543    <address><email>touch@isi.edu</email></address>
4544  </author>
4545  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4546    <organization>USC/Information Sciences Institute</organization>
4547    <address><email>johnh@isi.edu</email></address>
4548  </author>
4549  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4550    <organization>USC/Information Sciences Institute</organization>
4551    <address><email>katia@isi.edu</email></address>
4552  </author>
4553  <date year="1998" month="Aug"/>
4554  </front>
4555  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4556  <annotation>(original report dated Aug. 1996)</annotation>
4557</reference>
4558
4559</references>
4560
4561
4562<section title="Tolerant Applications" anchor="tolerant.applications">
4563<t>
4564   Although this document specifies the requirements for the generation
4565   of HTTP/1.1 messages, not all applications will be correct in their
4566   implementation. We therefore recommend that operational applications
4567   be tolerant of deviations whenever those deviations can be
4568   interpreted unambiguously.
4569</t>
4570<t>
4571   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4572   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4573   &SHOULD; accept any amount of WSP characters between fields, even though
4574   only a single SP is required.
4575</t>
4576<t>
4577   The line terminator for header fields is the sequence CRLF.
4578   However, we recommend that applications, when parsing such headers,
4579   recognize a single LF as a line terminator and ignore the leading CR.
4580</t>
4581<t>
4582   The character set of an entity-body &SHOULD; be labeled as the lowest
4583   common denominator of the character codes used within that body, with
4584   the exception that not labeling the entity is preferred over labeling
4585   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4586</t>
4587<t>
4588   Additional rules for requirements on parsing and encoding of dates
4589   and other potential problems with date encodings include:
4590</t>
4591<t>
4592  <list style="symbols">
4593     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4594        which appears to be more than 50 years in the future is in fact
4595        in the past (this helps solve the "year 2000" problem).</t>
4596
4597     <t>Although all date formats are specified to be case-sensitive,
4598        recipients &SHOULD; match day, week and timezone names
4599        case-insensitively.</t>
4600             
4601     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4602        Expires date as earlier than the proper value, but &MUST-NOT;
4603        internally represent a parsed Expires date as later than the
4604        proper value.</t>
4605
4606     <t>All expiration-related calculations &MUST; be done in GMT. The
4607        local time zone &MUST-NOT; influence the calculation or comparison
4608        of an age or expiration time.</t>
4609
4610     <t>If an HTTP header incorrectly carries a date value with a time
4611        zone other than GMT, it &MUST; be converted into GMT using the
4612        most conservative possible conversion.</t>
4613  </list>
4614</t>
4615</section>
4616
4617<section title="Compatibility with Previous Versions" anchor="compatibility">
4618<t>
4619   HTTP has been in use by the World-Wide Web global information initiative
4620   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4621   was a simple protocol for hypertext data transfer across the Internet
4622   with only a single method and no metadata.
4623   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4624   methods and MIME-like messaging that could include metadata about the data
4625   transferred and modifiers on the request/response semantics. However,
4626   HTTP/1.0 did not sufficiently take into consideration the effects of
4627   hierarchical proxies, caching, the need for persistent connections, or
4628   name-based virtual hosts. The proliferation of incompletely-implemented
4629   applications calling themselves "HTTP/1.0" further necessitated a
4630   protocol version change in order for two communicating applications
4631   to determine each other's true capabilities.
4632</t>
4633<t>
4634   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4635   requirements that enable reliable implementations, adding only
4636   those new features that will either be safely ignored by an HTTP/1.0
4637   recipient or only sent when communicating with a party advertising
4638   compliance with HTTP/1.1.
4639</t>
4640<t>
4641   It is beyond the scope of a protocol specification to mandate
4642   compliance with previous versions. HTTP/1.1 was deliberately
4643   designed, however, to make supporting previous versions easy. It is
4644   worth noting that, at the time of composing this specification, we would
4645   expect general-purpose HTTP/1.1 servers to:
4646  <list style="symbols">
4647     <t>understand any valid request in the format of HTTP/1.0 and
4648        1.1;</t>
4649
4650     <t>respond appropriately with a message in the same major version
4651        used by the client.</t>
4652  </list>
4653</t>
4654<t>
4655   And we would expect HTTP/1.1 clients to:
4656  <list style="symbols">
4657     <t>understand any valid response in the format of HTTP/1.0 or
4658        1.1.</t>
4659  </list>
4660</t>
4661<t>
4662   For most implementations of HTTP/1.0, each connection is established
4663   by the client prior to the request and closed by the server after
4664   sending the response. Some implementations implement the Keep-Alive
4665   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4666</t>
4667
4668<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4669<t>
4670   This section summarizes major differences between versions HTTP/1.0
4671   and HTTP/1.1.
4672</t>
4673
4674<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">
4675<t>
4676   The requirements that clients and servers support the Host request-header,
4677   report an error if the Host request-header (<xref target="header.host"/>) is
4678   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4679   are among the most important changes defined by this
4680   specification.
4681</t>
4682<t>
4683   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4684   addresses and servers; there was no other established mechanism for
4685   distinguishing the intended server of a request than the IP address
4686   to which that request was directed. The changes outlined above will
4687   allow the Internet, once older HTTP clients are no longer common, to
4688   support multiple Web sites from a single IP address, greatly
4689   simplifying large operational Web servers, where allocation of many
4690   IP addresses to a single host has created serious problems. The
4691   Internet will also be able to recover the IP addresses that have been
4692   allocated for the sole purpose of allowing special-purpose domain
4693   names to be used in root-level HTTP URLs. Given the rate of growth of
4694   the Web, and the number of servers already deployed, it is extremely
4695   important that all implementations of HTTP (including updates to
4696   existing HTTP/1.0 applications) correctly implement these
4697   requirements:
4698  <list style="symbols">
4699     <t>Both clients and servers &MUST; support the Host request-header.</t>
4700
4701     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4702
4703     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4704        request does not include a Host request-header.</t>
4705
4706     <t>Servers &MUST; accept absolute URIs.</t>
4707  </list>
4708</t>
4709</section>
4710</section>
4711
4712<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4713<t>
4714   Some clients and servers might wish to be compatible with some
4715   previous implementations of persistent connections in HTTP/1.0
4716   clients and servers. Persistent connections in HTTP/1.0 are
4717   explicitly negotiated as they are not the default behavior. HTTP/1.0
4718   experimental implementations of persistent connections are faulty,
4719   and the new facilities in HTTP/1.1 are designed to rectify these
4720   problems. The problem was that some existing HTTP/1.0 clients may be
4721   sending Keep-Alive to a proxy server that doesn't understand
4722   Connection, which would then erroneously forward it to the next
4723   inbound server, which would establish the Keep-Alive connection and
4724   result in a hung HTTP/1.0 proxy waiting for the close on the
4725   response. The result is that HTTP/1.0 clients must be prevented from
4726   using Keep-Alive when talking to proxies.
4727</t>
4728<t>
4729   However, talking to proxies is the most important use of persistent
4730   connections, so that prohibition is clearly unacceptable. Therefore,
4731   we need some other mechanism for indicating a persistent connection
4732   is desired, which is safe to use even when talking to an old proxy
4733   that ignores Connection. Persistent connections are the default for
4734   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4735   declaring non-persistence. See <xref target="header.connection"/>.
4736</t>
4737<t>
4738   The original HTTP/1.0 form of persistent connections (the Connection:
4739   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4740</t>
4741</section>
4742
4743<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4744<t>
4745   This specification has been carefully audited to correct and
4746   disambiguate key word usage; RFC 2068 had many problems in respect to
4747   the conventions laid out in <xref target="RFC2119"/>.
4748</t>
4749<t>
4750   Transfer-coding and message lengths all interact in ways that
4751   required fixing exactly when chunked encoding is used (to allow for
4752   transfer encoding that may not be self delimiting); it was important
4753   to straighten out exactly how message lengths are computed. (Sections
4754   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4755   <xref target="header.content-length" format="counter"/>,
4756   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4757</t>
4758<t>
4759   The use and interpretation of HTTP version numbers has been clarified
4760   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4761   version they support to deal with problems discovered in HTTP/1.0
4762   implementations (<xref target="http.version"/>)
4763</t>
4764<t>
4765   Quality Values of zero should indicate that "I don't want something"
4766   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4767</t>
4768<t>
4769   Transfer-coding had significant problems, particularly with
4770   interactions with chunked encoding. The solution is that transfer-codings
4771   become as full fledged as content-codings. This involves
4772   adding an IANA registry for transfer-codings (separate from content
4773   codings), a new header field (TE) and enabling trailer headers in the
4774   future. Transfer encoding is a major performance benefit, so it was
4775   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4776   interoperability problem that could have occurred due to interactions
4777   between authentication trailers, chunked encoding and HTTP/1.0
4778   clients.(Section
4779   <xref target="transfer.codings" format="counter"/>,
4780   <xref target="chunked.encoding" format="counter"/>,
4781   <xref target="non-modifiable.headers" format="counter"/>,
4782   and <xref target="header.te" format="counter"/>)
4783</t>
4784<t>
4785  Proxies should be able to add Content-Length when appropriate.
4786  (<xref target="non-modifiable.headers"/>)
4787</t>
4788</section>
4789
4790<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4791<t>
4792  Empty list elements in list productions have been deprecated.
4793  (<xref target="notation.abnf"/>)
4794</t>
4795<t>
4796  Rules about implicit linear whitespace between certain grammar productions
4797  have been removed; now it's only allowed when specifically pointed out
4798  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4799  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4800  Non-ASCII content in header fields and reason phrase has been obsoleted and
4801  made opaque (the TEXT rule was removed)
4802  (<xref target="basic.rules"/>)
4803</t>
4804<t>
4805  Clarify that HTTP-Version is case sensitive.
4806  (<xref target="http.version"/>)
4807</t>
4808<t>
4809  Remove reference to non-existent identity transfer-coding value tokens.
4810  (Sections <xref format="counter" target="transfer.codings"/> and
4811  <xref format="counter" target="message.length"/>)
4812</t>
4813<t>
4814  Require that invalid whitespace around field-names be rejected.
4815  (<xref target="header.fields"/>)
4816</t>
4817<t>
4818  Update use of abs_path production from RFC1808 to the path-absolute + query
4819  components of RFC3986.
4820  (<xref target="request-target"/>)
4821</t>
4822<t>
4823  Clarification that the chunk length does not include the count of the octets
4824  in the chunk header and trailer. Furthermore disallowed line folding
4825  in chunk extensions.
4826  (<xref target="chunked.encoding"/>)
4827</t>
4828<t>
4829  Remove hard limit of two connections per server.
4830  (<xref target="persistent.practical"/>)
4831</t>
4832<t>
4833  Clarify exactly when close connection options must be sent.
4834  (<xref target="header.connection"/>)
4835</t>
4836</section>
4837</section>
4838
4839<?BEGININC p1-messaging.abnf-appendix ?>
4840<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4841<figure>
4842<artwork type="abnf" name="p1-messaging.parsed-abnf">
4843<x:ref>BWS</x:ref> = OWS
4844
4845<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4846<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4847<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4848<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4849 connection-token ] )
4850<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4851<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4852
4853<x:ref>Date</x:ref> = "Date:" OWS Date-v
4854<x:ref>Date-v</x:ref> = HTTP-date
4855
4856<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4857
4858<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4859<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4860<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4861<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4862 ]
4863<x:ref>Host</x:ref> = "Host:" OWS Host-v
4864<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4865
4866<x:ref>Method</x:ref> = token
4867
4868<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4869
4870<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4871
4872<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4873<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4874<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4875 entity-header ) CRLF ) CRLF [ message-body ]
4876<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4877<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4878 entity-header ) CRLF ) CRLF [ message-body ]
4879
4880<x:ref>Status-Code</x:ref> = 3DIGIT
4881<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4882
4883<x:ref>TE</x:ref> = "TE:" OWS TE-v
4884<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4885<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4886<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4887<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4888<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4889 transfer-coding ] )
4890
4891<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4892<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4893<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4894
4895<x:ref>Via</x:ref> = "Via:" OWS Via-v
4896<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4897 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4898 ] )
4899
4900<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4901
4902<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4903<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4904<x:ref>attribute</x:ref> = token
4905<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4906
4907<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4908<x:ref>chunk-data</x:ref> = 1*OCTET
4909<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4910<x:ref>chunk-ext-name</x:ref> = token
4911<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4912<x:ref>chunk-size</x:ref> = 1*HEXDIG
4913<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4914<x:ref>connection-token</x:ref> = token
4915<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4916 / %x2A-5B ; '*'-'['
4917 / %x5D-7E ; ']'-'~'
4918 / obs-text
4919
4920<x:ref>date1</x:ref> = day SP month SP year
4921<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4922<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4923<x:ref>day</x:ref> = 2DIGIT
4924<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4925 / %x54.75.65 ; Tue
4926 / %x57.65.64 ; Wed
4927 / %x54.68.75 ; Thu
4928 / %x46.72.69 ; Fri
4929 / %x53.61.74 ; Sat
4930 / %x53.75.6E ; Sun
4931<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4932 / %x54.75.65.73.64.61.79 ; Tuesday
4933 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4934 / %x54.68.75.72.73.64.61.79 ; Thursday
4935 / %x46.72.69.64.61.79 ; Friday
4936 / %x53.61.74.75.72.64.61.79 ; Saturday
4937 / %x53.75.6E.64.61.79 ; Sunday
4938
4939<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4940<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4941
4942<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4943<x:ref>field-name</x:ref> = token
4944<x:ref>field-value</x:ref> = *( field-content / OWS )
4945
4946<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4947 / Transfer-Encoding / Upgrade / Via / Warning
4948
4949<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
4950<x:ref>hour</x:ref> = 2DIGIT
4951<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4952<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4953
4954<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4955
4956<x:ref>message-body</x:ref> = entity-body /
4957 &lt;entity-body encoded as per Transfer-Encoding&gt;
4958<x:ref>minute</x:ref> = 2DIGIT
4959<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4960 / %x46.65.62 ; Feb
4961 / %x4D.61.72 ; Mar
4962 / %x41.70.72 ; Apr
4963 / %x4D.61.79 ; May
4964 / %x4A.75.6E ; Jun
4965 / %x4A.75.6C ; Jul
4966 / %x41.75.67 ; Aug
4967 / %x53.65.70 ; Sep
4968 / %x4F.63.74 ; Oct
4969 / %x4E.6F.76 ; Nov
4970 / %x44.65.63 ; Dec
4971
4972<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4973<x:ref>obs-fold</x:ref> = CRLF
4974<x:ref>obs-text</x:ref> = %x80-FF
4975
4976<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4977<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4978<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4979<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4980<x:ref>product</x:ref> = token [ "/" product-version ]
4981<x:ref>product-version</x:ref> = token
4982<x:ref>protocol-name</x:ref> = token
4983<x:ref>protocol-version</x:ref> = token
4984<x:ref>pseudonym</x:ref> = token
4985
4986<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4987 / %x5D-7E ; ']'-'~'
4988 / obs-text
4989<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
4990 / %x5D-7E ; ']'-'~'
4991 / obs-text
4992<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4993<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
4994<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
4995<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4996<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4997<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4998
4999<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5000<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5001<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5002<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5003<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5004 / authority
5005<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5006<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5007<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5008
5009<x:ref>second</x:ref> = 2DIGIT
5010<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5011 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5012<x:ref>start-line</x:ref> = Request-Line / Status-Line
5013
5014<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5015<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5016 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5017<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
5018<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5019<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5020<x:ref>token</x:ref> = 1*tchar
5021<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
5022<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5023 transfer-extension
5024<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5025<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5026
5027<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5028
5029<x:ref>value</x:ref> = token / quoted-string
5030
5031<x:ref>year</x:ref> = 4DIGIT
5032</artwork>
5033</figure>
5034<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5035; Chunked-Body defined but not used
5036; Content-Length defined but not used
5037; HTTP-message defined but not used
5038; Host defined but not used
5039; Request defined but not used
5040; Response defined but not used
5041; TE defined but not used
5042; URI-reference defined but not used
5043; http-URI defined but not used
5044; https-URI defined but not used
5045; partial-URI defined but not used
5046; special defined but not used
5047</artwork></figure></section>
5048<?ENDINC p1-messaging.abnf-appendix ?>
5049
5050<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5051
5052<section title="Since RFC2616">
5053<t>
5054  Extracted relevant partitions from <xref target="RFC2616"/>.
5055</t>
5056</section>
5057
5058<section title="Since draft-ietf-httpbis-p1-messaging-00">
5059<t>
5060  Closed issues:
5061  <list style="symbols"> 
5062    <t>
5063      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5064      "HTTP Version should be case sensitive"
5065      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5066    </t>
5067    <t>
5068      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5069      "'unsafe' characters"
5070      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5071    </t>
5072    <t>
5073      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5074      "Chunk Size Definition"
5075      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5076    </t>
5077    <t>
5078      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5079      "Message Length"
5080      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5081    </t>
5082    <t>
5083      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5084      "Media Type Registrations"
5085      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5086    </t>
5087    <t>
5088      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5089      "URI includes query"
5090      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5091    </t>
5092    <t>
5093      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5094      "No close on 1xx responses"
5095      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5096    </t>
5097    <t>
5098      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5099      "Remove 'identity' token references"
5100      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5101    </t>
5102    <t>
5103      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5104      "Import query BNF"
5105    </t>
5106    <t>
5107      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5108      "qdtext BNF"
5109    </t>
5110    <t>
5111      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5112      "Normative and Informative references"
5113    </t>
5114    <t>
5115      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5116      "RFC2606 Compliance"
5117    </t>
5118    <t>
5119      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5120      "RFC977 reference"
5121    </t>
5122    <t>
5123      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5124      "RFC1700 references"
5125    </t>
5126    <t>
5127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5128      "inconsistency in date format explanation"
5129    </t>
5130    <t>
5131      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5132      "Date reference typo"
5133    </t>
5134    <t>
5135      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5136      "Informative references"
5137    </t>
5138    <t>
5139      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5140      "ISO-8859-1 Reference"
5141    </t>
5142    <t>
5143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5144      "Normative up-to-date references"
5145    </t>
5146  </list>
5147</t>
5148<t>
5149  Other changes:
5150  <list style="symbols"> 
5151    <t>
5152      Update media type registrations to use RFC4288 template.
5153    </t>
5154    <t>
5155      Use names of RFC4234 core rules DQUOTE and WSP,
5156      fix broken ABNF for chunk-data
5157      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5158    </t>
5159  </list>
5160</t>
5161</section>
5162
5163<section title="Since draft-ietf-httpbis-p1-messaging-01">
5164<t>
5165  Closed issues:
5166  <list style="symbols"> 
5167    <t>
5168      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5169      "Bodies on GET (and other) requests"
5170    </t>
5171    <t>
5172      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5173      "Updating to RFC4288"
5174    </t>
5175    <t>
5176      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5177      "Status Code and Reason Phrase"
5178    </t>
5179    <t>
5180      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5181      "rel_path not used"
5182    </t>
5183  </list>
5184</t>
5185<t>
5186  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5187  <list style="symbols"> 
5188    <t>
5189      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5190      "trailer-part").
5191    </t>
5192    <t>
5193      Avoid underscore character in rule names ("http_URL" ->
5194      "http-URL", "abs_path" -> "path-absolute").
5195    </t>
5196    <t>
5197      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5198      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5199      have to be updated when switching over to RFC3986.
5200    </t>
5201    <t>
5202      Synchronize core rules with RFC5234.
5203    </t>
5204    <t>
5205      Get rid of prose rules that span multiple lines.
5206    </t>
5207    <t>
5208      Get rid of unused rules LOALPHA and UPALPHA.
5209    </t>
5210    <t>
5211      Move "Product Tokens" section (back) into Part 1, as "token" is used
5212      in the definition of the Upgrade header.
5213    </t>
5214    <t>
5215      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5216    </t>
5217    <t>
5218      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5219    </t>
5220  </list>
5221</t>
5222</section>
5223
5224<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5225<t>
5226  Closed issues:
5227  <list style="symbols"> 
5228    <t>
5229      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5230      "HTTP-date vs. rfc1123-date"
5231    </t>
5232    <t>
5233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5234      "WS in quoted-pair"
5235    </t>
5236  </list>
5237</t>
5238<t>
5239  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5240  <list style="symbols"> 
5241    <t>
5242      Reference RFC 3984, and update header registrations for headers defined
5243      in this document.
5244    </t>
5245  </list>
5246</t>
5247<t>
5248  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5249  <list style="symbols"> 
5250    <t>
5251      Replace string literals when the string really is case-sensitive (HTTP-Version).
5252    </t>
5253  </list>
5254</t>
5255</section>
5256
5257<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5258<t>
5259  Closed issues:
5260  <list style="symbols"> 
5261    <t>
5262      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5263      "Connection closing"
5264    </t>
5265    <t>
5266      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5267      "Move registrations and registry information to IANA Considerations"
5268    </t>
5269    <t>
5270      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5271      "need new URL for PAD1995 reference"
5272    </t>
5273    <t>
5274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5275      "IANA Considerations: update HTTP URI scheme registration"
5276    </t>
5277    <t>
5278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5279      "Cite HTTPS URI scheme definition"
5280    </t>
5281    <t>
5282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5283      "List-type headers vs Set-Cookie"
5284    </t>
5285  </list>
5286</t>
5287<t>
5288  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5289  <list style="symbols"> 
5290    <t>
5291      Replace string literals when the string really is case-sensitive (HTTP-Date).
5292    </t>
5293    <t>
5294      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5295    </t>
5296  </list>
5297</t>
5298</section>
5299
5300<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5301<t>
5302  Closed issues:
5303  <list style="symbols"> 
5304    <t>
5305      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5306      "Out-of-date reference for URIs"
5307    </t>
5308    <t>
5309      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5310      "RFC 2822 is updated by RFC 5322"
5311    </t>
5312  </list>
5313</t>
5314<t>
5315  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5316  <list style="symbols"> 
5317    <t>
5318      Use "/" instead of "|" for alternatives.
5319    </t>
5320    <t>
5321      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5322    </t>
5323    <t>
5324      Only reference RFC 5234's core rules.
5325    </t>
5326    <t>
5327      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5328      whitespace ("OWS") and required whitespace ("RWS").
5329    </t>
5330    <t>
5331      Rewrite ABNFs to spell out whitespace rules, factor out
5332      header value format definitions.
5333    </t>
5334  </list>
5335</t>
5336</section>
5337
5338<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5339<t>
5340  Closed issues:
5341  <list style="symbols"> 
5342    <t>
5343      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5344      "Header LWS"
5345    </t>
5346    <t>
5347      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5348      "Sort 1.3 Terminology"
5349    </t>
5350    <t>
5351      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5352      "RFC2047 encoded words"
5353    </t>
5354    <t>
5355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5356      "Character Encodings in TEXT"
5357    </t>
5358    <t>
5359      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5360      "Line Folding"
5361    </t>
5362    <t>
5363      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5364      "OPTIONS * and proxies"
5365    </t>
5366    <t>
5367      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5368      "Reason-Phrase BNF"
5369    </t>
5370    <t>
5371      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5372      "Use of TEXT"
5373    </t>
5374    <t>
5375      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5376      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5377    </t>
5378    <t>
5379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5380      "RFC822 reference left in discussion of date formats"
5381    </t>
5382  </list>
5383</t>
5384<t>
5385  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5386  <list style="symbols"> 
5387    <t>
5388      Rewrite definition of list rules, deprecate empty list elements.
5389    </t>
5390    <t>
5391      Add appendix containing collected and expanded ABNF.
5392    </t>
5393  </list>
5394</t>
5395<t>
5396  Other changes:
5397  <list style="symbols"> 
5398    <t>
5399      Rewrite introduction; add mostly new Architecture Section.
5400    </t>
5401    <t>
5402      Move definition of quality values from Part 3 into Part 1;
5403      make TE request header grammar independent of accept-params (defined in Part 3).
5404    </t>
5405  </list>
5406</t>
5407</section>
5408
5409<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5410<t>
5411  Closed issues:
5412  <list style="symbols"> 
5413    <t>
5414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5415      "base for numeric protocol elements"
5416    </t>
5417    <t>
5418      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5419      "comment ABNF"
5420    </t>
5421  </list>
5422</t>
5423<t>
5424  Partly resolved issues:
5425  <list style="symbols"> 
5426    <t>
5427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5428      "205 Bodies" (took out language that implied that there may be
5429      methods for which a request body MUST NOT be included)
5430    </t>
5431    <t>
5432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5433      "editorial improvements around HTTP-date"
5434    </t>
5435  </list>
5436</t>
5437</section>
5438
5439<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5440<t>
5441  Closed issues:
5442  <list style="symbols"> 
5443    <t>
5444      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5445      "Repeating single-value headers"
5446    </t>
5447    <t>
5448      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5449      "increase connection limit"
5450    </t>
5451    <t>
5452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5453      "IP addresses in URLs"
5454    </t>
5455    <t>
5456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5457      "take over HTTP Upgrade Token Registry"
5458    </t>
5459    <t>
5460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5461      "CR and LF in chunk extension values"
5462    </t>
5463    <t>
5464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5465      "HTTP/0.9 support"
5466    </t>
5467    <t>
5468      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5469      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5470    </t>
5471    <t>
5472      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5473      "move definitions of gzip/deflate/compress to part 1"
5474    </t>
5475    <t>
5476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5477      "disallow control characters in quoted-pair"
5478    </t>
5479  </list>
5480</t>
5481<t>
5482  Partly resolved issues:
5483  <list style="symbols"> 
5484    <t>
5485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5486      "update IANA requirements wrt Transfer-Coding values" (add the
5487      IANA Considerations subsection)
5488    </t>
5489  </list>
5490</t>
5491</section>
5492
5493<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5494<t>
5495  Closed issues:
5496  <list style="symbols"> 
5497    <t>
5498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5499      "header parsing, treatment of leading and trailing OWS"
5500    </t>
5501  </list>
5502</t>
5503<t>
5504  Partly resolved issues:
5505  <list style="symbols"> 
5506    <t>
5507      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5508      "Placement of 13.5.1 and 13.5.2"
5509    </t>
5510    <t>
5511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5512      "use of term "word" when talking about header structure"
5513    </t>
5514  </list>
5515</t>
5516</section>
5517
5518<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5519<t>
5520  Closed issues:
5521  <list style="symbols"> 
5522    <t>
5523      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5524      "Clarification of the term 'deflate'"
5525    </t>
5526    <t>
5527      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5528      "IANA registry for content/transfer encodings"
5529    </t>
5530    <t>
5531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5532      "Case-sensitivity of HTTP-date"
5533    </t>
5534  </list>
5535</t>
5536</section>
5537
5538</section>
5539
5540</back>
5541</rfc>
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