source: draft-ietf-httpbis/latest/p1-messaging.xml @ 810

Last change on this file since 810 was 810, checked in by julian.reschke@…, 10 years ago

Introduce "word = token / quoted-string" into ABNF and use it throughout (see #200)

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File size: 236.2 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  <x:anchor-alias value="word"/>
473   Many HTTP/1.1 header field values consist of words (token or quoted-string)
474   separated by whitespace or special characters. These special characters
475   &MUST; be in a quoted string to be used within a parameter value (as defined
476   in <xref target="transfer.codings"/>).
477</t>
478<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/>
479  <x:ref>word</x:ref>           = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
480
481  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
482<!--
483  IMPORTANT: when editing "tchar" make sure that "special" is updated accordingly!!!
484 -->
485  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
486                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
487                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
488                 ; any <x:ref>VCHAR</x:ref>, except <x:ref>special</x:ref>
489
490  <x:ref>special</x:ref>        = "(" / ")" / "&lt;" / ">" / "@" / ","
491                 / ";" / ":" / "\" / DQUOTE / "/" / "["
492                 / "]" / "?" / "=" / "{" / "}"
493</artwork></figure>
494<t anchor="rule.quoted-string">
495  <x:anchor-alias value="quoted-string"/>
496  <x:anchor-alias value="qdtext"/>
497  <x:anchor-alias value="obs-text"/>
498   A string of text is parsed as a single word if it is quoted using
499   double-quote marks.
500</t>
501<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"/>
502  <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>
503  <x:ref>qdtext</x:ref>         = <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
504                 ; <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> 
505  <x:ref>obs-text</x:ref>       = %x80-FF
506</artwork></figure>
507<t anchor="rule.quoted-pair">
508  <x:anchor-alias value="quoted-pair"/>
509   The backslash character ("\") can be used as a single-character
510   quoting mechanism within quoted-string constructs:
511</t>
512<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-pair"/>
513  <x:ref>quoted-pair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
514</artwork></figure>
515<t>
516   Producers &SHOULD-NOT; escape characters that do not require escaping
517   (i.e., other than DQUOTE and the backslash character).
518</t>
519</section>
520
521<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
522  <x:anchor-alias value="request-header"/>
523  <x:anchor-alias value="response-header"/>
524  <x:anchor-alias value="entity-body"/>
525  <x:anchor-alias value="entity-header"/>
526  <x:anchor-alias value="Cache-Control"/>
527  <x:anchor-alias value="Pragma"/>
528  <x:anchor-alias value="Warning"/>
529<t>
530  The ABNF rules below are defined in other parts:
531</t>
532<figure><!-- Part2--><artwork type="abnf2616">
533  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
534  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
535</artwork></figure>
536<figure><!-- Part3--><artwork type="abnf2616">
537  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
538  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
539</artwork></figure>
540<figure><!-- Part6--><artwork type="abnf2616">
541  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
542  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
543  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
544</artwork></figure>
545</section>
546
547</section>
548</section>
549
550<section title="HTTP architecture" anchor="architecture">
551<t>
552   HTTP was created for the World Wide Web architecture
553   and has evolved over time to support the scalability needs of a worldwide
554   hypertext system. Much of that architecture is reflected in the terminology
555   and syntax productions used to define HTTP.
556</t>
557
558<section title="Client/Server Operation" anchor="operation">
559<iref item="client"/>
560<iref item="server"/>
561<iref item="connection"/>
562<t>
563   HTTP is a request/response protocol that operates by exchanging messages
564   across a reliable transport or session-layer connection. An HTTP client
565   is a program that establishes a connection to a server for the purpose
566   of sending one or more HTTP requests.  An HTTP server is a program that
567   accepts connections in order to service HTTP requests by sending HTTP
568   responses.
569</t>
570<iref item="user agent"/>
571<iref item="origin server"/>
572<t>
573   Note that the terms "client" and "server" refer only to the roles that
574   these programs perform for a particular connection.  The same program
575   may act as a client on some connections and a server on others.  We use
576   the term "user agent" to refer to the program that initiates a request,
577   such as a WWW browser, editor, or spider (web-traversing robot), and
578   the term "origin server" to refer to the program that can originate
579   authoritative responses to a request.
580</t>
581<t>
582   Most HTTP communication consists of a retrieval request (GET) for
583   a representation of some resource identified by a URI.  In the
584   simplest case, this may be accomplished via a single connection (v)
585   between the user agent (UA) and the origin server (O).
586</t>
587<figure><artwork type="drawing">
588       request chain ------------------------&gt;
589    UA -------------------v------------------- O
590       &lt;----------------------- response chain
591</artwork></figure>
592<iref item="message"/>
593<iref item="request"/>
594<iref item="response"/>
595<t>
596   A client sends an HTTP request to the server in the form of a request
597   message (<xref target="request"/>), beginning with a method, URI, and
598   protocol version, followed by MIME-like header fields containing
599   request modifiers, client information, and payload metadata, an empty
600   line to indicate the end of the header section, and finally the payload
601   body (if any).
602</t>
603<t>
604   A server responds to the client's request by sending an HTTP response
605   message (<xref target="response"/>), beginning with a status line that
606   includes the protocol version, a success or error code, and textual
607   reason phrase, followed by MIME-like header fields containing server
608   information, resource metadata, and payload metadata, an empty line to
609   indicate the end of the header section, and finally the payload body (if any).
610</t>
611<t>
612   The following example illustrates a typical message exchange for a
613   GET request on the URI "http://www.example.com/hello.txt":
614</t>
615<figure><preamble>
616client request:
617</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
618GET /hello.txt HTTP/1.1
619User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
620Host: www.example.com
621Accept: */*
622
623</artwork></figure>
624<figure><preamble>
625server response:
626</preamble><artwork type="message/http; msgtype=&#34;response&#34;" x:indent-with="  ">
627HTTP/1.1 200 OK
628Date: Mon, 27 Jul 2009 12:28:53 GMT
629Server: Apache
630Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
631ETag: "34aa387-d-1568eb00"
632Accept-Ranges: bytes
633Content-Length: <x:length-of target="exbody"/>
634Vary: Accept-Encoding
635Content-Type: text/plain
636
637<x:span anchor="exbody">Hello World!
638</x:span></artwork></figure>
639</section>
640
641<section title="Intermediaries" anchor="intermediaries">
642<t>
643   A more complicated situation occurs when one or more intermediaries
644   are present in the request/response chain. There are three common
645   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
646   a single intermediary may act as an origin server, proxy, gateway,
647   or tunnel, switching behavior based on the nature of each request.
648</t>
649<figure><artwork type="drawing">
650       request chain --------------------------------------&gt;
651    UA -----v----- A -----v----- B -----v----- C -----v----- O
652       &lt;------------------------------------- response chain
653</artwork></figure>
654<t>
655   The figure above shows three intermediaries (A, B, and C) between the
656   user agent and origin server. A request or response message that
657   travels the whole chain will pass through four separate connections.
658   Some HTTP communication options
659   may apply only to the connection with the nearest, non-tunnel
660   neighbor, only to the end-points of the chain, or to all connections
661   along the chain. Although the diagram is linear, each participant may
662   be engaged in multiple, simultaneous communications. For example, B
663   may be receiving requests from many clients other than A, and/or
664   forwarding requests to servers other than C, at the same time that it
665   is handling A's request.
666</t>
667<t>
668<iref item="upstream"/><iref item="downstream"/>
669<iref item="inbound"/><iref item="outbound"/>
670   We use the terms "upstream" and "downstream" to describe various
671   requirements in relation to the directional flow of a message:
672   all messages flow from upstream to downstream.
673   Likewise, we use the terms "inbound" and "outbound" to refer to
674   directions in relation to the request path: "inbound" means toward
675   the origin server and "outbound" means toward the user agent.
676</t>
677<t><iref item="proxy"/>
678   A proxy is a message forwarding agent that is selected by the
679   client, usually via local configuration rules, to receive requests
680   for some type(s) of absolute URI and attempt to satisfy those
681   requests via translation through the HTTP interface.  Some translations
682   are minimal, such as for proxy requests for "http" URIs, whereas
683   other requests may require translation to and from entirely different
684   application-layer protocols. Proxies are often used to group an
685   organization's HTTP requests through a common intermediary for the
686   sake of security, annotation services, or shared caching.
687</t>
688<t><iref item="gateway"/><iref item="reverse proxy"/>
689   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
690   as a layer above some other server(s) and translates the received
691   requests to the underlying server's protocol.  Gateways are often
692   used for load balancing or partitioning HTTP services across
693   multiple machines.
694   Unlike a proxy, a gateway receives requests as if it were the
695   origin server for the requested resource; the requesting client
696   will not be aware that it is communicating with a gateway.
697   A gateway communicates with the client as if the gateway is the
698   origin server and thus is subject to all of the requirements on
699   origin servers for that connection.  A gateway communicates
700   with inbound servers using any protocol it desires, including
701   private extensions to HTTP that are outside the scope of this
702   specification.
703</t>
704<t><iref item="tunnel"/>
705   A tunnel acts as a blind relay between two connections
706   without changing the messages. Once active, a tunnel is not
707   considered a party to the HTTP communication, though the tunnel may
708   have been initiated by an HTTP request. A tunnel ceases to exist when
709   both ends of the relayed connection are closed. Tunnels are used to
710   extend a virtual connection through an intermediary, such as when
711   transport-layer security is used to establish private communication
712   through a shared firewall proxy.
713</t>
714</section>
715
716<section title="Caches" anchor="caches">
717<iref item="cache"/>
718<t>
719   Any party to HTTP communication that is not acting as a tunnel may
720   employ an internal cache for handling requests.
721   A cache is a local store of previous response messages and the
722   subsystem that controls its message storage, retrieval, and deletion.
723   A cache stores cacheable responses in order to reduce the response
724   time and network bandwidth consumption on future, equivalent
725   requests. Any client or server may include a cache, though a cache
726   cannot be used by a server while it is acting as a tunnel.
727</t>
728<t>
729   The effect of a cache is that the request/response chain is shortened
730   if one of the participants along the chain has a cached response
731   applicable to that request. The following illustrates the resulting
732   chain if B has a cached copy of an earlier response from O (via C)
733   for a request which has not been cached by UA or A.
734</t>
735<figure><artwork type="drawing">
736          request chain ----------&gt;
737       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
738          &lt;--------- response chain
739</artwork></figure>
740<t><iref item="cacheable"/>
741   A response is cacheable if a cache is allowed to store a copy of
742   the response message for use in answering subsequent requests.
743   Even when a response is cacheable, there may be additional
744   constraints placed by the client or by the origin server on when
745   that cached response can be used for a particular request. HTTP
746   requirements for cache behavior and cacheable responses are
747   defined in &caching-overview;
748</t>
749<t>
750   There are a wide variety of architectures and configurations
751   of caches and proxies deployed across the World Wide Web and
752   inside large organizations. These systems include national hierarchies
753   of proxy caches to save transoceanic bandwidth, systems that
754   broadcast or multicast cache entries, organizations that distribute
755   subsets of cached data via optical media, and so on.
756</t>
757</section>
758
759<section title="Transport Independence" anchor="transport-independence">
760<t>
761  HTTP systems are used in a wide variety of environments, from
762  corporate intranets with high-bandwidth links to long-distance
763  communication over low-power radio links and intermittent connectivity.
764</t>
765<t>
766   HTTP communication usually takes place over TCP/IP connections. The
767   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
768   not preclude HTTP from being implemented on top of any other protocol
769   on the Internet, or on other networks. HTTP only presumes a reliable
770   transport; any protocol that provides such guarantees can be used;
771   the mapping of the HTTP/1.1 request and response structures onto the
772   transport data units of the protocol in question is outside the scope
773   of this specification.
774</t>
775<t>
776   In HTTP/1.0, most implementations used a new connection for each
777   request/response exchange. In HTTP/1.1, a connection may be used for
778   one or more request/response exchanges, although connections may be
779   closed for a variety of reasons (see <xref target="persistent.connections"/>).
780</t>
781</section>
782
783<section title="HTTP Version" anchor="http.version">
784  <x:anchor-alias value="HTTP-Version"/>
785  <x:anchor-alias value="HTTP-Prot-Name"/>
786<t>
787   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
788   of the protocol. The protocol versioning policy is intended to allow
789   the sender to indicate the format of a message and its capacity for
790   understanding further HTTP communication, rather than the features
791   obtained via that communication. No change is made to the version
792   number for the addition of message components which do not affect
793   communication behavior or which only add to extensible field values.
794   The &lt;minor&gt; number is incremented when the changes made to the
795   protocol add features which do not change the general message parsing
796   algorithm, but which may add to the message semantics and imply
797   additional capabilities of the sender. The &lt;major&gt; number is
798   incremented when the format of a message within the protocol is
799   changed. See <xref target="RFC2145"/> for a fuller explanation.
800</t>
801<t>
802   The version of an HTTP message is indicated by an HTTP-Version field
803   in the first line of the message. HTTP-Version is case-sensitive.
804</t>
805<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
806  <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>
807  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
808</artwork></figure>
809<t>
810   Note that the major and minor numbers &MUST; be treated as separate
811   integers and that each &MAY; be incremented higher than a single digit.
812   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
813   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
814   &MUST-NOT; be sent.
815</t>
816<t>
817   An application that sends a request or response message that includes
818   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
819   with this specification. Applications that are at least conditionally
820   compliant with this specification &SHOULD; use an HTTP-Version of
821   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
822   not compatible with HTTP/1.0. For more details on when to send
823   specific HTTP-Version values, see <xref target="RFC2145"/>.
824</t>
825<t>
826   The HTTP version of an application is the highest HTTP version for
827   which the application is at least conditionally compliant.
828</t>
829<t>
830   Proxy and gateway applications need to be careful when forwarding
831   messages in protocol versions different from that of the application.
832   Since the protocol version indicates the protocol capability of the
833   sender, a proxy/gateway &MUST-NOT; send a message with a version
834   indicator which is greater than its actual version. If a higher
835   version request is received, the proxy/gateway &MUST; either downgrade
836   the request version, or respond with an error, or switch to tunnel
837   behavior.
838</t>
839<t>
840   Due to interoperability problems with HTTP/1.0 proxies discovered
841   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
842   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
843   they support. The proxy/gateway's response to that request &MUST; be in
844   the same major version as the request.
845</t>
846<x:note>
847  <t>
848    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
849    of header fields required or forbidden by the versions involved.
850  </t>
851</x:note>
852</section>
853
854<section title="Uniform Resource Identifiers" anchor="uri">
855<iref primary="true" item="resource"/>
856<t>
857   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
858   throughout HTTP as the means for identifying resources. URI references
859   are used to target requests, indicate redirects, and define relationships.
860   HTTP does not limit what a resource may be; it merely defines an interface
861   that can be used to interact with a resource via HTTP. More information on
862   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
863</t>
864  <x:anchor-alias value="URI-reference"/>
865  <x:anchor-alias value="absolute-URI"/>
866  <x:anchor-alias value="relative-part"/>
867  <x:anchor-alias value="authority"/>
868  <x:anchor-alias value="path-abempty"/>
869  <x:anchor-alias value="path-absolute"/>
870  <x:anchor-alias value="port"/>
871  <x:anchor-alias value="query"/>
872  <x:anchor-alias value="uri-host"/>
873  <x:anchor-alias value="partial-URI"/>
874<t>
875   This specification adopts the definitions of "URI-reference",
876   "absolute-URI", "relative-part", "port", "host",
877   "path-abempty", "path-absolute", "query", and "authority" from
878   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
879   protocol elements that allow a relative URI without a fragment.
880</t>
881<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"/>
882  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
883  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
884  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
885  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
886  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
887  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
888  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
889  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
890  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
891 
892  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
893</artwork></figure>
894<t>
895   Each protocol element in HTTP that allows a URI reference will indicate in
896   its ABNF production whether the element allows only a URI in absolute form
897   (absolute-URI), any relative reference (relative-ref), or some other subset
898   of the URI-reference grammar. Unless otherwise indicated, URI references
899   are parsed relative to the request target (the default base URI for both
900   the request and its corresponding response).
901</t>
902
903<section title="http URI scheme" anchor="http.uri">
904  <x:anchor-alias value="http-URI"/>
905  <iref item="http URI scheme" primary="true"/>
906  <iref item="URI scheme" subitem="http" primary="true"/>
907<t>
908   The "http" URI scheme is hereby defined for the purpose of minting
909   identifiers according to their association with the hierarchical
910   namespace governed by a potential HTTP origin server listening for
911   TCP connections on a given port.
912   The HTTP server is identified via the generic syntax's
913   <x:ref>authority</x:ref> component, which includes a host
914   identifier and optional TCP port, and the remainder of the URI is
915   considered to be identifying data corresponding to a resource for
916   which that server might provide an HTTP interface.
917</t>
918<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
919  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
920</artwork></figure>
921<t>
922   The host identifier within an <x:ref>authority</x:ref> component is
923   defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>.  If host is
924   provided as an IP literal or IPv4 address, then the HTTP server is any
925   listener on the indicated TCP port at that IP address. If host is a
926   registered name, then that name is considered an indirect identifier
927   and the recipient might use a name resolution service, such as DNS,
928   to find the address of a listener for that host.
929   The host &MUST-NOT; be empty; if an "http" URI is received with an
930   empty host, then it &MUST; be rejected as invalid.
931   If the port subcomponent is empty or not given, then TCP port 80 is
932   assumed (the default reserved port for WWW services).
933</t>
934<t>
935   Regardless of the form of host identifier, access to that host is not
936   implied by the mere presence of its name or address. The host may or may
937   not exist and, even when it does exist, may or may not be running an
938   HTTP server or listening to the indicated port. The "http" URI scheme
939   makes use of the delegated nature of Internet names and addresses to
940   establish a naming authority (whatever entity has the ability to place
941   an HTTP server at that Internet name or address) and allows that
942   authority to determine which names are valid and how they might be used.
943</t>
944<t>
945   When an "http" URI is used within a context that calls for access to the
946   indicated resource, a client &MAY; attempt access by resolving
947   the host to an IP address, establishing a TCP connection to that address
948   on the indicated port, and sending an HTTP request message to the server
949   containing the URI's identifying data as described in <xref target="request"/>.
950   If the server responds to that request with a non-interim HTTP response
951   message, as described in <xref target="response"/>, then that response
952   is considered an authoritative answer to the client's request.
953</t>
954<t>
955   Although HTTP is independent of the transport protocol, the "http"
956   scheme is specific to TCP-based services because the name delegation
957   process depends on TCP for establishing authority.
958   An HTTP service based on some other underlying connection protocol
959   would presumably be identified using a different URI scheme, just as
960   the "https" scheme (below) is used for servers that require an SSL/TLS
961   transport layer on a connection. Other protocols may also be used to
962   provide access to "http" identified resources --- it is only the
963   authoritative interface used for mapping the namespace that is
964   specific to TCP.
965</t>
966</section>
967
968<section title="https URI scheme" anchor="https.uri">
969   <x:anchor-alias value="https-URI"/>
970   <iref item="https URI scheme"/>
971   <iref item="URI scheme" subitem="https"/>
972<t>
973   The "https" URI scheme is hereby defined for the purpose of minting
974   identifiers according to their association with the hierarchical
975   namespace governed by a potential HTTP origin server listening for
976   SSL/TLS-secured connections on a given TCP port.
977   The host and port are determined in the same way
978   as for the "http" scheme, except that a default TCP port of 443
979   is assumed if the port subcomponent is empty or not given.
980</t>
981<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="https-URI"/>
982  <x:ref>https-URI</x:ref> = "https:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
983</artwork></figure>
984<t>
985   The primary difference between the "http" and "https" schemes is
986   that interaction with the latter is required to be secured for
987   privacy through the use of strong encryption. The URI cannot be
988   sent in a request until the connection is secure. Likewise, the
989   default for caching is that each response that would be considered
990   "public" under the "http" scheme is instead treated as "private"
991   and thus not eligible for shared caching.
992</t>
993<t>
994   The process for authoritative access to an "https" identified
995   resource is defined in <xref target="RFC2818"/>.
996</t>
997</section>
998
999<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1000<t>
1001   Since the "http" and "https" schemes conform to the URI generic syntax,
1002   such URIs are normalized and compared according to the algorithm defined
1003   in <xref target="RFC3986" x:fmt="," x:sec="6"/>, using the defaults
1004   described above for each scheme.
1005</t>
1006<t>
1007   If the port is equal to the default port for a scheme, the normal
1008   form is to elide the port subcomponent. Likewise, an empty path
1009   component is equivalent to an absolute path of "/", so the normal
1010   form is to provide a path of "/" instead. The scheme and host
1011   are case-insensitive and normally provided in lowercase; all
1012   other components are compared in a case-sensitive manner.
1013   Characters other than those in the "reserved" set are equivalent
1014   to their percent-encoded octets (see <xref target="RFC3986"
1015   x:fmt="," x:sec="2.1"/>): the normal form is to not encode them.
1016</t>
1017<t>
1018   For example, the following three URIs are equivalent:
1019</t>
1020<figure><artwork type="example">
1021   http://example.com:80/~smith/home.html
1022   http://EXAMPLE.com/%7Esmith/home.html
1023   http://EXAMPLE.com:/%7esmith/home.html
1024</artwork></figure>
1025<t>
1026   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1027   If path-abempty is the empty string (i.e., there is no slash "/"
1028   path separator following the authority), then the "http" URI
1029   &MUST; be given as "/" when
1030   used as a request-target (<xref target="request-target"/>). If a proxy
1031   receives a host name which is not a fully qualified domain name, it
1032   &MAY; add its domain to the host name it received. If a proxy receives
1033   a fully qualified domain name, the proxy &MUST-NOT; change the host
1034   name.
1035</t>
1036</section>
1037</section>
1038</section>
1039
1040<section title="HTTP Message" anchor="http.message">
1041<x:anchor-alias value="generic-message"/>
1042<x:anchor-alias value="message.types"/>
1043<x:anchor-alias value="HTTP-message"/>
1044<x:anchor-alias value="start-line"/>
1045<iref item="header section"/>
1046<iref item="headers"/>
1047<iref item="header field"/>
1048<t>
1049   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1050   characters in a format similar to the Internet Message Format
1051   <xref target="RFC5322"/>: zero or more header fields (collectively
1052   referred to as the "headers" or the "header section"), an empty line
1053   indicating the end of the header section, and an optional message-body.
1054</t>
1055<t>
1056   An HTTP message can either be a request from client to server or a
1057   response from server to client.  Syntactically, the two types of message
1058   differ only in the start-line, which is either a Request-Line (for requests)
1059   or a Status-Line (for responses), and in the algorithm for determining
1060   the length of the message-body (<xref target="message.length"/>).
1061   In theory, a client could receive requests and a server could receive
1062   responses, distinguishing them by their different start-line formats,
1063   but in practice servers are implemented to only expect a request
1064   (a response is interpreted as an unknown or invalid request method)
1065   and clients are implemented to only expect a response.
1066</t>
1067<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1068  <x:ref>HTTP-message</x:ref>    = <x:ref>start-line</x:ref>
1069                    *( <x:ref>header-field</x:ref> <x:ref>CRLF</x:ref> )
1070                    <x:ref>CRLF</x:ref>
1071                    [ <x:ref>message-body</x:ref> ]
1072  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1073</artwork></figure>
1074<t>
1075   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1076   header field. The presence of whitespace might be an attempt to trick a
1077   noncompliant implementation of HTTP into ignoring that field or processing
1078   the next line as a new request, either of which may result in security
1079   issues when implementations within the request chain interpret the
1080   same message differently. HTTP/1.1 servers &MUST; reject such a message
1081   with a 400 (Bad Request) response.
1082</t>
1083
1084<section title="Message Parsing Robustness" anchor="message.robustness">
1085<t>
1086   In the interest of robustness, servers &SHOULD; ignore at least one
1087   empty line received where a Request-Line is expected. In other words, if
1088   the server is reading the protocol stream at the beginning of a
1089   message and receives a CRLF first, it should ignore the CRLF.
1090</t>
1091<t>
1092   Some old HTTP/1.0 client implementations generate an extra CRLF
1093   after a POST request as a lame workaround for some early server
1094   applications that failed to read message-body content that was
1095   not terminated by a line-ending. An HTTP/1.1 client &MUST-NOT;
1096   preface or follow a request with an extra CRLF.  If terminating
1097   the request message-body with a line-ending is desired, then the
1098   client &MUST; include the terminating CRLF octets as part of the
1099   message-body length.
1100</t>
1101<t>
1102   The normal procedure for parsing an HTTP message is to read the
1103   start-line into a structure, read each header field into a hash
1104   table by field name until the empty line, and then use the parsed
1105   data to determine if a message-body is expected.  If a message-body
1106   has been indicated, then it is read as a stream until an amount
1107   of OCTETs equal to the message-length is read or the connection
1108   is closed.  Care must be taken to parse an HTTP message as a sequence
1109   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1110   to parse HTTP as a stream of Unicode characters in a character encoding
1111   like UTF-16 may introduce security flaws due to the differing ways
1112   that such parsers interpret invalid characters.
1113</t>
1114</section>
1115
1116<section title="Header Fields" anchor="header.fields">
1117  <x:anchor-alias value="header-field"/>
1118  <x:anchor-alias value="field-content"/>
1119  <x:anchor-alias value="field-name"/>
1120  <x:anchor-alias value="field-value"/>
1121  <x:anchor-alias value="OWS"/>
1122<t>
1123   Each HTTP header field consists of a case-insensitive field name
1124   followed by a colon (":"), optional whitespace, and the field value.
1125</t>
1126<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"/>
1127  <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>
1128  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1129  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1130  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1131</artwork></figure>
1132<t>
1133   No whitespace is allowed between the header field name and colon. For
1134   security reasons, any request message received containing such whitespace
1135   &MUST; be rejected with a response code of 400 (Bad Request). A proxy
1136   &MUST; remove any such whitespace from a response message before
1137   forwarding the message downstream.
1138</t>
1139<t>
1140   A field value &MAY; be preceded by optional whitespace (OWS); a single SP is
1141   preferred. The field value does not include any leading or trailing white
1142   space: OWS occurring before the first non-whitespace character of the
1143   field value or after the last non-whitespace character of the field value
1144   is ignored and &SHOULD; be removed before further processing (as this does
1145   not change the meaning of the header field).
1146</t>
1147<t>
1148   The order in which header fields with differing field names are
1149   received is not significant. However, it is "good practice" to send
1150   header fields that contain control data first, such as Host on
1151   requests and Date on responses, so that implementations can decide
1152   when not to handle a message as early as possible.  A server &MUST;
1153   wait until the entire header section is received before interpreting
1154   a request message, since later header fields might include conditionals,
1155   authentication credentials, or deliberately misleading duplicate
1156   header fields that would impact request processing.
1157</t>
1158<t>
1159   Multiple header fields with the same field name &MUST-NOT; be
1160   sent in a message unless the entire field value for that
1161   header field is defined as a comma-separated list [i.e., #(values)].
1162   Multiple header fields with the same field name can be combined into
1163   one "field-name: field-value" pair, without changing the semantics of the
1164   message, by appending each subsequent field value to the combined
1165   field value in order, separated by a comma. The order in which
1166   header fields with the same field name are received is therefore
1167   significant to the interpretation of the combined field value;
1168   a proxy &MUST-NOT; change the order of these field values when
1169   forwarding a message.
1170</t>
1171<x:note>
1172  <t>
1173   <x:h>Note:</x:h> The "Set-Cookie" header as implemented in
1174   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1175   can occur multiple times, but does not use the list syntax, and thus cannot
1176   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1177   for details.) Also note that the Set-Cookie2 header specified in
1178   <xref target="RFC2965"/> does not share this problem.
1179  </t>
1180</x:note>
1181<t>
1182   Historically, HTTP header field values could be extended over multiple
1183   lines by preceding each extra line with at least one space or horizontal
1184   tab character (line folding). This specification deprecates such line
1185   folding except within the message/http media type
1186   (<xref target="internet.media.type.message.http"/>).
1187   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1188   (i.e., that contain any field-content that matches the obs-fold rule) unless
1189   the message is intended for packaging within the message/http media type.
1190   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1191   obs-fold whitespace with a single SP prior to interpreting the field value
1192   or forwarding the message downstream.
1193</t>
1194<t>
1195   Historically, HTTP has allowed field content with text in the ISO-8859-1
1196   <xref target="ISO-8859-1"/> character encoding and supported other
1197   character sets only through use of <xref target="RFC2047"/> encoding.
1198   In practice, most HTTP header field values use only a subset of the
1199   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1200   header fields &SHOULD; limit their field values to US-ASCII characters.
1201   Recipients &SHOULD; treat other (obs-text) octets in field content as
1202   opaque data.
1203</t>
1204<t anchor="rule.comment">
1205  <x:anchor-alias value="comment"/>
1206  <x:anchor-alias value="ctext"/>
1207   Comments can be included in some HTTP header fields by surrounding
1208   the comment text with parentheses. Comments are only allowed in
1209   fields containing "comment" as part of their field value definition.
1210</t>
1211<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1212  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-cpair</x:ref> / <x:ref>comment</x:ref> ) ")"
1213  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1214                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1215</artwork></figure>
1216<t anchor="rule.quoted-cpair">
1217  <x:anchor-alias value="quoted-cpair"/>
1218   The backslash character ("\") can be used as a single-character
1219   quoting mechanism within comment constructs:
1220</t>
1221<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-cpair"/>
1222  <x:ref>quoted-cpair</x:ref>    = "\" ( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1223</artwork></figure>
1224<t>
1225   Producers &SHOULD-NOT; escape characters that do not require escaping
1226   (i.e., other than the backslash character "\" and the parentheses "(" and
1227   ")").
1228</t>
1229</section>
1230
1231<section title="Message Body" anchor="message.body">
1232  <x:anchor-alias value="message-body"/>
1233<t>
1234   The message-body (if any) of an HTTP message is used to carry the
1235   entity-body associated with the request or response. The message-body
1236   differs from the entity-body only when a transfer-coding has been
1237   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1238</t>
1239<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1240  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1241               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1242</artwork></figure>
1243<t>
1244   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1245   applied by an application to ensure safe and proper transfer of the
1246   message. Transfer-Encoding is a property of the message, not of the
1247   entity, and thus &MAY; be added or removed by any application along the
1248   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1249   when certain transfer-codings may be used.)
1250</t>
1251<t>
1252   The rules for when a message-body is allowed in a message differ for
1253   requests and responses.
1254</t>
1255<t>
1256   The presence of a message-body in a request is signaled by the
1257   inclusion of a Content-Length or Transfer-Encoding header field in
1258   the request's header fields.
1259   When a request message contains both a message-body of non-zero
1260   length and a method that does not define any semantics for that
1261   request message-body, then an origin server &SHOULD; either ignore
1262   the message-body or respond with an appropriate error message
1263   (e.g., 413).  A proxy or gateway, when presented the same request,
1264   &SHOULD; either forward the request inbound with the message-body or
1265   ignore the message-body when determining a response.
1266</t>
1267<t>
1268   For response messages, whether or not a message-body is included with
1269   a message is dependent on both the request method and the response
1270   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1271   &MUST-NOT; include a message-body, even though the presence of entity-header
1272   fields might lead one to believe they do. All 1xx
1273   (Informational), 204 (No Content), and 304 (Not Modified) responses
1274   &MUST-NOT; include a message-body. All other responses do include a
1275   message-body, although it &MAY; be of zero length.
1276</t>
1277</section>
1278
1279<section title="Message Length" anchor="message.length">
1280<t>
1281   The transfer-length of a message is the length of the message-body as
1282   it appears in the message; that is, after any transfer-codings have
1283   been applied. When a message-body is included with a message, the
1284   transfer-length of that body is determined by one of the following
1285   (in order of precedence):
1286</t>
1287<t>
1288  <list style="numbers">
1289    <x:lt><t>
1290     Any response message which "&MUST-NOT;" include a message-body (such
1291     as the 1xx, 204, and 304 responses and any response to a HEAD
1292     request) is always terminated by the first empty line after the
1293     header fields, regardless of the entity-header fields present in
1294     the message.
1295    </t></x:lt>
1296    <x:lt><t>
1297     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1298     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1299     is used, the transfer-length is defined by the use of this transfer-coding.
1300     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1301     is not present, the transfer-length is defined by the sender closing the connection.
1302    </t></x:lt>
1303    <x:lt><t>
1304     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1305     value in OCTETs represents both the entity-length and the
1306     transfer-length. The Content-Length header field &MUST-NOT; be sent
1307     if these two lengths are different (i.e., if a Transfer-Encoding
1308     header field is present). If a message is received with both a
1309     Transfer-Encoding header field and a Content-Length header field,
1310     the latter &MUST; be ignored.
1311    </t></x:lt>
1312    <x:lt><t>
1313     If the message uses the media type "multipart/byteranges", and the
1314     transfer-length is not otherwise specified, then this self-delimiting
1315     media type defines the transfer-length. This media type
1316     &MUST-NOT; be used unless the sender knows that the recipient can parse
1317     it; the presence in a request of a Range header with multiple byte-range
1318     specifiers from a HTTP/1.1 client implies that the client can parse
1319     multipart/byteranges responses.
1320    <list style="empty"><t>
1321       A range header might be forwarded by a HTTP/1.0 proxy that does not
1322       understand multipart/byteranges; in this case the server &MUST;
1323       delimit the message using methods defined in items 1, 3 or 5 of
1324       this section.
1325    </t></list>
1326    </t></x:lt>
1327    <x:lt><t>
1328     By the server closing the connection. (Closing the connection
1329     cannot be used to indicate the end of a request body, since that
1330     would leave no possibility for the server to send back a response.)
1331    </t></x:lt>
1332  </list>
1333</t>
1334<t>
1335   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1336   containing a message-body &MUST; include a valid Content-Length header
1337   field unless the server is known to be HTTP/1.1 compliant. If a
1338   request contains a message-body and a Content-Length is not given,
1339   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1340   determine the length of the message, or with 411 (Length Required) if
1341   it wishes to insist on receiving a valid Content-Length.
1342</t>
1343<t>
1344   All HTTP/1.1 applications that receive entities &MUST; accept the
1345   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1346   to be used for messages when the message length cannot be determined
1347   in advance.
1348</t>
1349<t>
1350   Messages &MUST-NOT; include both a Content-Length header field and a
1351   transfer-coding. If the message does include a
1352   transfer-coding, the Content-Length &MUST; be ignored.
1353</t>
1354<t>
1355   When a Content-Length is given in a message where a message-body is
1356   allowed, its field value &MUST; exactly match the number of OCTETs in
1357   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1358   invalid length is received and detected.
1359</t>
1360</section>
1361
1362<section title="General Header Fields" anchor="general.header.fields">
1363  <x:anchor-alias value="general-header"/>
1364<t>
1365   There are a few header fields which have general applicability for
1366   both request and response messages, but which do not apply to the
1367   entity being transferred. These header fields apply only to the
1368   message being transmitted.
1369</t>
1370<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1371  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1372                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1373                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1374                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1375                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1376                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1377                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1378                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1379                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1380</artwork></figure>
1381<t>
1382   General-header field names can be extended reliably only in
1383   combination with a change in the protocol version. However, new or
1384   experimental header fields may be given the semantics of general
1385   header fields if all parties in the communication recognize them to
1386   be general-header fields. Unrecognized header fields are treated as
1387   entity-header fields.
1388</t>
1389</section>
1390</section>
1391
1392<section title="Request" anchor="request">
1393  <x:anchor-alias value="Request"/>
1394<t>
1395   A request message from a client to a server includes, within the
1396   first line of that message, the method to be applied to the resource,
1397   the identifier of the resource, and the protocol version in use.
1398</t>
1399<!--                 Host                      ; should be moved here eventually -->
1400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1401  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1402                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1403                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1404                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1405                  <x:ref>CRLF</x:ref>
1406                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1407</artwork></figure>
1408
1409<section title="Request-Line" anchor="request-line">
1410  <x:anchor-alias value="Request-Line"/>
1411<t>
1412   The Request-Line begins with a method token, followed by the
1413   request-target and the protocol version, and ending with CRLF. The
1414   elements are separated by SP characters. No CR or LF is allowed
1415   except in the final CRLF sequence.
1416</t>
1417<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1418  <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>
1419</artwork></figure>
1420
1421<section title="Method" anchor="method">
1422  <x:anchor-alias value="Method"/>
1423<t>
1424   The Method  token indicates the method to be performed on the
1425   resource identified by the request-target. The method is case-sensitive.
1426</t>
1427<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1428  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1429</artwork></figure>
1430</section>
1431
1432<section title="request-target" anchor="request-target">
1433  <x:anchor-alias value="request-target"/>
1434<t>
1435   The request-target
1436   identifies the resource upon which to apply the request.
1437</t>
1438<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1439  <x:ref>request-target</x:ref> = "*"
1440                 / <x:ref>absolute-URI</x:ref>
1441                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1442                 / <x:ref>authority</x:ref>
1443</artwork></figure>
1444<t>
1445   The four options for request-target are dependent on the nature of the
1446   request.
1447</t>   
1448<t>
1449   The asterisk "*" means that the request does not apply to a
1450   particular resource, but to the server itself, and is only allowed
1451   when the method used does not necessarily apply to a resource. One
1452   example would be
1453</t>
1454<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1455OPTIONS * HTTP/1.1
1456</artwork></figure>
1457<t>
1458   The absolute-URI form is &REQUIRED; when the request is being made to a
1459   proxy. The proxy is requested to forward the request or service it
1460   from a valid cache, and return the response. Note that the proxy &MAY;
1461   forward the request on to another proxy or directly to the server
1462   specified by the absolute-URI. In order to avoid request loops, a
1463   proxy &MUST; be able to recognize all of its server names, including
1464   any aliases, local variations, and the numeric IP address. An example
1465   Request-Line would be:
1466</t>
1467<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1468GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1469</artwork></figure>
1470<t>
1471   To allow for transition to absolute-URIs in all requests in future
1472   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1473   form in requests, even though HTTP/1.1 clients will only generate
1474   them in requests to proxies.
1475</t>
1476<t>
1477   The authority form is only used by the CONNECT method (&CONNECT;).
1478</t>
1479<t>
1480   The most common form of request-target is that used to identify a
1481   resource on an origin server or gateway. In this case the absolute
1482   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1483   the request-target, and the network location of the URI (authority) &MUST;
1484   be transmitted in a Host header field. For example, a client wishing
1485   to retrieve the resource above directly from the origin server would
1486   create a TCP connection to port 80 of the host "www.example.org" and send
1487   the lines:
1488</t>
1489<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1490GET /pub/WWW/TheProject.html HTTP/1.1
1491Host: www.example.org
1492</artwork></figure>
1493<t>
1494   followed by the remainder of the Request. Note that the absolute path
1495   cannot be empty; if none is present in the original URI, it &MUST; be
1496   given as "/" (the server root).
1497</t>
1498<t>
1499   If a proxy receives a request without any path in the request-target and
1500   the method specified is capable of supporting the asterisk form of
1501   request-target, then the last proxy on the request chain &MUST; forward the
1502   request with "*" as the final request-target.
1503</t>
1504<figure><preamble>   
1505   For example, the request
1506</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1507OPTIONS http://www.example.org:8001 HTTP/1.1
1508</artwork></figure>
1509<figure><preamble>   
1510  would be forwarded by the proxy as
1511</preamble><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
1512OPTIONS * HTTP/1.1
1513Host: www.example.org:8001
1514</artwork>
1515<postamble>
1516   after connecting to port 8001 of host "www.example.org".
1517</postamble>
1518</figure>
1519<t>
1520   The request-target is transmitted in the format specified in
1521   <xref target="http.uri"/>. If the request-target is percent-encoded
1522   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1523   &MUST; decode the request-target in order to
1524   properly interpret the request. Servers &SHOULD; respond to invalid
1525   request-targets with an appropriate status code.
1526</t>
1527<t>
1528   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1529   received request-target when forwarding it to the next inbound server,
1530   except as noted above to replace a null path-absolute with "/".
1531</t>
1532<x:note>
1533  <t>
1534    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1535    meaning of the request when the origin server is improperly using
1536    a non-reserved URI character for a reserved purpose.  Implementors
1537    should be aware that some pre-HTTP/1.1 proxies have been known to
1538    rewrite the request-target.
1539  </t>
1540</x:note>
1541<t>
1542   HTTP does not place a pre-defined limit on the length of a request-target.
1543   A server &MUST; be prepared to receive URIs of unbounded length and
1544   respond with the 414 (URI Too Long) status if the received
1545   request-target would be longer than the server wishes to handle
1546   (see &status-414;).
1547</t>
1548<t>
1549   Various ad-hoc limitations on request-target length are found in practice.
1550   It is &RECOMMENDED; that all HTTP senders and recipients support
1551   request-target lengths of 8000 or more OCTETs.
1552</t>
1553</section>
1554</section>
1555
1556<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1557<t>
1558   The exact resource identified by an Internet request is determined by
1559   examining both the request-target and the Host header field.
1560</t>
1561<t>
1562   An origin server that does not allow resources to differ by the
1563   requested host &MAY; ignore the Host header field value when
1564   determining the resource identified by an HTTP/1.1 request. (But see
1565   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1566   for other requirements on Host support in HTTP/1.1.)
1567</t>
1568<t>
1569   An origin server that does differentiate resources based on the host
1570   requested (sometimes referred to as virtual hosts or vanity host
1571   names) &MUST; use the following rules for determining the requested
1572   resource on an HTTP/1.1 request:
1573  <list style="numbers">
1574    <t>If request-target is an absolute-URI, the host is part of the
1575     request-target. Any Host header field value in the request &MUST; be
1576     ignored.</t>
1577    <t>If the request-target is not an absolute-URI, and the request includes
1578     a Host header field, the host is determined by the Host header
1579     field value.</t>
1580    <t>If the host as determined by rule 1 or 2 is not a valid host on
1581     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1582  </list>
1583</t>
1584<t>
1585   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1586   attempt to use heuristics (e.g., examination of the URI path for
1587   something unique to a particular host) in order to determine what
1588   exact resource is being requested.
1589</t>
1590</section>
1591
1592</section>
1593
1594
1595<section title="Response" anchor="response">
1596  <x:anchor-alias value="Response"/>
1597<t>
1598   After receiving and interpreting a request message, a server responds
1599   with an HTTP response message.
1600</t>
1601<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1602  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1603                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1604                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1605                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> ) ; &entity-header-fields;
1606                  <x:ref>CRLF</x:ref>
1607                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1608</artwork></figure>
1609
1610<section title="Status-Line" anchor="status-line">
1611  <x:anchor-alias value="Status-Line"/>
1612<t>
1613   The first line of a Response message is the Status-Line, consisting
1614   of the protocol version followed by a numeric status code and its
1615   associated textual phrase, with each element separated by SP
1616   characters. No CR or LF is allowed except in the final CRLF sequence.
1617</t>
1618<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1619  <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>
1620</artwork></figure>
1621
1622<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1623  <x:anchor-alias value="Reason-Phrase"/>
1624  <x:anchor-alias value="Status-Code"/>
1625<t>
1626   The Status-Code element is a 3-digit integer result code of the
1627   attempt to understand and satisfy the request. These codes are fully
1628   defined in &status-codes;.  The Reason Phrase exists for the sole
1629   purpose of providing a textual description associated with the numeric
1630   status code, out of deference to earlier Internet application protocols
1631   that were more frequently used with interactive text clients.
1632   A client &SHOULD; ignore the content of the Reason Phrase.
1633</t>
1634<t>
1635   The first digit of the Status-Code defines the class of response. The
1636   last two digits do not have any categorization role. There are 5
1637   values for the first digit:
1638  <list style="symbols">
1639    <t>
1640      1xx: Informational - Request received, continuing process
1641    </t>
1642    <t>
1643      2xx: Success - The action was successfully received,
1644        understood, and accepted
1645    </t>
1646    <t>
1647      3xx: Redirection - Further action must be taken in order to
1648        complete the request
1649    </t>
1650    <t>
1651      4xx: Client Error - The request contains bad syntax or cannot
1652        be fulfilled
1653    </t>
1654    <t>
1655      5xx: Server Error - The server failed to fulfill an apparently
1656        valid request
1657    </t>
1658  </list>
1659</t>
1660<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"/>
1661  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1662  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1663</artwork></figure>
1664</section>
1665</section>
1666
1667</section>
1668
1669
1670<section title="Protocol Parameters" anchor="protocol.parameters">
1671
1672<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1673  <x:anchor-alias value="HTTP-date"/>
1674<t>
1675   HTTP applications have historically allowed three different formats
1676   for the representation of date/time stamps.
1677</t>
1678<t>
1679   The first format is preferred as an Internet standard and represents
1680   a fixed-length subset of that defined by <xref target="RFC1123"/>:
1681</t>
1682<figure><artwork type="example" x:indent-with="  ">
1683Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1684</artwork></figure>
1685<t>
1686   The other formats are described here only for compatibility with obsolete
1687   implementations.
1688</t>
1689<figure><artwork type="example" x:indent-with="  ">
1690Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1691Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1692</artwork></figure>
1693<t>
1694   HTTP/1.1 clients and servers that parse the date value &MUST; accept
1695   all three formats (for compatibility with HTTP/1.0), though they &MUST;
1696   only generate the RFC 1123 format for representing HTTP-date values
1697   in header fields. See <xref target="tolerant.applications"/> for further information.
1698</t>
1699<t>
1700   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
1701   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1702   equal to UTC (Coordinated Universal Time). This is indicated in the
1703   first two formats by the inclusion of "GMT" as the three-letter
1704   abbreviation for time zone, and &MUST; be assumed when reading the
1705   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
1706   additional whitespace beyond that specifically included as SP in the
1707   grammar.
1708</t>
1709<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
1710  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
1711</artwork></figure>
1712<t anchor="preferred.date.format">
1713  <x:anchor-alias value="rfc1123-date"/>
1714  <x:anchor-alias value="time-of-day"/>
1715  <x:anchor-alias value="hour"/>
1716  <x:anchor-alias value="minute"/>
1717  <x:anchor-alias value="second"/>
1718  <x:anchor-alias value="day-name"/>
1719  <x:anchor-alias value="day"/>
1720  <x:anchor-alias value="month"/>
1721  <x:anchor-alias value="year"/>
1722  <x:anchor-alias value="GMT"/>
1723  Preferred format:
1724</t>
1725<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"/>
1726  <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>
1727
1728  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
1729               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
1730               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
1731               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
1732               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
1733               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
1734               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
1735               
1736  <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>
1737               ; e.g., 02 Jun 1982
1738
1739  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
1740  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
1741               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
1742               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
1743               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
1744               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
1745               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
1746               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
1747               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
1748               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
1749               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
1750               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
1751               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
1752  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
1753
1754  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
1755
1756  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
1757                 ; 00:00:00 - 23:59:59
1758                 
1759  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
1760  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1761  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
1762</artwork></figure>
1763<t>
1764  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
1765  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
1766  same as those defined for the RFC 5322 constructs
1767  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
1768</t>
1769<t anchor="obsolete.date.formats">
1770  <x:anchor-alias value="obs-date"/>
1771  <x:anchor-alias value="rfc850-date"/>
1772  <x:anchor-alias value="asctime-date"/>
1773  <x:anchor-alias value="date1"/>
1774  <x:anchor-alias value="date2"/>
1775  <x:anchor-alias value="date3"/>
1776  <x:anchor-alias value="rfc1123-date"/>
1777  <x:anchor-alias value="day-name-l"/>
1778  Obsolete formats:
1779</t>
1780<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
1781  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
1782</artwork></figure>
1783<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
1784  <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>
1785  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
1786                 ; day-month-year (e.g., 02-Jun-82)
1787
1788  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
1789         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
1790         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
1791         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
1792         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
1793         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
1794         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
1795</artwork></figure>
1796<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
1797  <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>
1798  <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> ))
1799                 ; month day (e.g., Jun  2)
1800</artwork></figure>
1801<x:note>
1802  <t>
1803    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
1804    accepting date values that may have been sent by non-HTTP
1805    applications, as is sometimes the case when retrieving or posting
1806    messages via proxies/gateways to SMTP or NNTP.
1807  </t>
1808</x:note>
1809<x:note>
1810  <t>
1811    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
1812    to their usage within the protocol stream. Clients and servers are
1813    not required to use these formats for user presentation, request
1814    logging, etc.
1815  </t>
1816</x:note>
1817</section>
1818
1819<section title="Transfer Codings" anchor="transfer.codings">
1820  <x:anchor-alias value="transfer-coding"/>
1821  <x:anchor-alias value="transfer-extension"/>
1822<t>
1823   Transfer-coding values are used to indicate an encoding
1824   transformation that has been, can be, or may need to be applied to an
1825   entity-body in order to ensure "safe transport" through the network.
1826   This differs from a content coding in that the transfer-coding is a
1827   property of the message, not of the original entity.
1828</t>
1829<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
1830  <x:ref>transfer-coding</x:ref>         = "chunked" ; <xref target="chunked.encoding"/>
1831                          / "compress" ; <xref target="compress.coding"/>
1832                          / "deflate" ; <xref target="deflate.coding"/>
1833                          / "gzip" ; <xref target="gzip.coding"/>
1834                          / <x:ref>transfer-extension</x:ref>
1835  <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> )
1836</artwork></figure>
1837<t anchor="rule.parameter">
1838  <x:anchor-alias value="attribute"/>
1839  <x:anchor-alias value="transfer-parameter"/>
1840  <x:anchor-alias value="value"/>
1841   Parameters are in  the form of attribute/value pairs.
1842</t>
1843<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"/>
1844  <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>
1845  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1846  <x:ref>value</x:ref>                   = <x:ref>word</x:ref>
1847</artwork></figure>
1848<t>
1849   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1850   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1851   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1852</t>
1853<t>
1854   Whenever a transfer-coding is applied to a message-body, the set of
1855   transfer-codings &MUST; include "chunked", unless the message indicates it
1856   is terminated by closing the connection. When the "chunked" transfer-coding
1857   is used, it &MUST; be the last transfer-coding applied to the
1858   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1859   than once to a message-body. These rules allow the recipient to
1860   determine the transfer-length of the message (<xref target="message.length"/>).
1861</t>
1862<t>
1863   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1864   MIME, which were designed to enable safe transport of binary data over a
1865   7-bit transport service (<xref target="RFC2045" x:fmt="," x:sec="6"/>).
1866   However, safe transport
1867   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1868   the only unsafe characteristic of message-bodies is the difficulty in
1869   determining the exact body length (<xref target="message.length"/>), or the desire to
1870   encrypt data over a shared transport.
1871</t>
1872<t>
1873   A server which receives an entity-body with a transfer-coding it does
1874   not understand &SHOULD; return 501 (Not Implemented), and close the
1875   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1876   client.
1877</t>
1878
1879<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1880  <iref item="chunked (Coding Format)"/>
1881  <iref item="Coding Format" subitem="chunked"/>
1882  <x:anchor-alias value="chunk"/>
1883  <x:anchor-alias value="Chunked-Body"/>
1884  <x:anchor-alias value="chunk-data"/>
1885  <x:anchor-alias value="chunk-ext"/>
1886  <x:anchor-alias value="chunk-ext-name"/>
1887  <x:anchor-alias value="chunk-ext-val"/>
1888  <x:anchor-alias value="chunk-size"/>
1889  <x:anchor-alias value="last-chunk"/>
1890  <x:anchor-alias value="trailer-part"/>
1891  <x:anchor-alias value="quoted-str-nf"/>
1892  <x:anchor-alias value="qdtext-nf"/>
1893<t>
1894   The chunked encoding modifies the body of a message in order to
1895   transfer it as a series of chunks, each with its own size indicator,
1896   followed by an &OPTIONAL; trailer containing entity-header fields. This
1897   allows dynamically produced content to be transferred along with the
1898   information necessary for the recipient to verify that it has
1899   received the full message.
1900</t>
1901<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"/>
1902  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1903                   <x:ref>last-chunk</x:ref>
1904                   <x:ref>trailer-part</x:ref>
1905                   <x:ref>CRLF</x:ref>
1906 
1907  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1908                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1909  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1910  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1911 
1912  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1913                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1914  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1915  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-str-nf</x:ref>
1916  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1917  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1918 
1919  <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>
1920                 ; like <x:ref>quoted-string</x:ref>, but disallowing line folding
1921  <x:ref>qdtext-nf</x:ref>      = <x:ref>WSP</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1922                 ; <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> 
1923</artwork></figure>
1924<t>
1925   The chunk-size field is a string of hex digits indicating the size of
1926   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1927   zero, followed by the trailer, which is terminated by an empty line.
1928</t>
1929<t>
1930   The trailer allows the sender to include additional HTTP header
1931   fields at the end of the message. The Trailer header field can be
1932   used to indicate which header fields are included in a trailer (see
1933   <xref target="header.trailer"/>).
1934</t>
1935<t>
1936   A server using chunked transfer-coding in a response &MUST-NOT; use the
1937   trailer for any header fields unless at least one of the following is
1938   true:
1939  <list style="numbers">
1940    <t>the request included a TE header field that indicates "trailers" is
1941     acceptable in the transfer-coding of the  response, as described in
1942     <xref target="header.te"/>; or,</t>
1943
1944    <t>the server is the origin server for the response, the trailer
1945     fields consist entirely of optional metadata, and the recipient
1946     could use the message (in a manner acceptable to the origin server)
1947     without receiving this metadata.  In other words, the origin server
1948     is willing to accept the possibility that the trailer fields might
1949     be silently discarded along the path to the client.</t>
1950  </list>
1951</t>
1952<t>
1953   This requirement prevents an interoperability failure when the
1954   message is being received by an HTTP/1.1 (or later) proxy and
1955   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1956   compliance with the protocol would have necessitated a possibly
1957   infinite buffer on the proxy.
1958</t>
1959<t>
1960   A process for decoding the "chunked" transfer-coding
1961   can be represented in pseudo-code as:
1962</t>
1963<figure><artwork type="code">
1964  length := 0
1965  read chunk-size, chunk-ext (if any) and CRLF
1966  while (chunk-size &gt; 0) {
1967     read chunk-data and CRLF
1968     append chunk-data to entity-body
1969     length := length + chunk-size
1970     read chunk-size and CRLF
1971  }
1972  read entity-header
1973  while (entity-header not empty) {
1974     append entity-header to existing header fields
1975     read entity-header
1976  }
1977  Content-Length := length
1978  Remove "chunked" from Transfer-Encoding
1979</artwork></figure>
1980<t>
1981   All HTTP/1.1 applications &MUST; be able to receive and decode the
1982   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1983   they do not understand.
1984</t>
1985</section>
1986
1987<section title="Compression Codings" anchor="compression.codings">
1988<t>
1989   The codings defined below can be used to compress the payload of a
1990   message.
1991</t>
1992<x:note><t>
1993   <x:h>Note:</x:h> Use of program names for the identification of encoding formats
1994   is not desirable and is discouraged for future encodings. Their
1995   use here is representative of historical practice, not good
1996   design.
1997</t></x:note>
1998<x:note><t>
1999   <x:h>Note:</x:h> For compatibility with previous implementations of HTTP,
2000   applications &SHOULD; consider "x-gzip" and "x-compress" to be
2001   equivalent to "gzip" and "compress" respectively.
2002</t></x:note>
2003
2004<section title="Compress Coding" anchor="compress.coding">
2005<iref item="compress (Coding Format)"/>
2006<iref item="Coding Format" subitem="compress"/>
2007<t>
2008   The "compress" format is produced by the common UNIX file compression
2009   program "compress". This format is an adaptive Lempel-Ziv-Welch
2010   coding (LZW).
2011</t>
2012</section>
2013
2014<section title="Deflate Coding" anchor="deflate.coding">
2015<iref item="deflate (Coding Format)"/>
2016<iref item="Coding Format" subitem="deflate"/>
2017<t>
2018   The "deflate" format is defined as the "deflate" compression mechanism
2019   (described in <xref target="RFC1951"/>) used inside the "zlib"
2020   data format (<xref target="RFC1950"/>).
2021</t>
2022<x:note>
2023  <t>
2024    <x:h>Note:</x:h> Some incorrect implementations send the "deflate"
2025    compressed data without the zlib wrapper.
2026   </t>
2027</x:note>
2028</section>
2029
2030<section title="Gzip Coding" anchor="gzip.coding">
2031<iref item="gzip (Coding Format)"/>
2032<iref item="Coding Format" subitem="gzip"/>
2033<t>
2034   The "gzip" format is produced by the file compression program
2035   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2036   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2037</t>
2038</section>
2039
2040</section>
2041
2042<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2043<t>
2044   The HTTP Transfer Coding Registry defines the name space for the transfer
2045   coding names.
2046</t>
2047<t>
2048   Registrations &MUST; include the following fields:
2049   <list style="symbols">
2050     <t>Name</t>
2051     <t>Description</t>
2052     <t>Pointer to specification text</t>
2053   </list>
2054</t>
2055<t>
2056   Names of transfer codings &MUST-NOT; overlap with names of content codings
2057   (&content-codings;), unless the encoding transformation is identical (as it
2058   is the case for the compression codings defined in
2059   <xref target="compression.codings"/>).
2060</t>
2061<t>
2062   Values to be added to this name space require expert review and a specification
2063   (see "Expert Review" and "Specification Required" in
2064   <xref target="RFC5226" x:fmt="of" x:sec="4.1"/>), and &MUST;
2065   conform to the purpose of transfer coding defined in this section.
2066</t>
2067<t>
2068   The registry itself is maintained at
2069   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2070</t>
2071</section>
2072</section>
2073
2074<section title="Product Tokens" anchor="product.tokens">
2075  <x:anchor-alias value="product"/>
2076  <x:anchor-alias value="product-version"/>
2077<t>
2078   Product tokens are used to allow communicating applications to
2079   identify themselves by software name and version. Most fields using
2080   product tokens also allow sub-products which form a significant part
2081   of the application to be listed, separated by whitespace. By
2082   convention, the products are listed in order of their significance
2083   for identifying the application.
2084</t>
2085<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
2086  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
2087  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
2088</artwork></figure>
2089<t>
2090   Examples:
2091</t>
2092<figure><artwork type="example">
2093  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2094  Server: Apache/0.8.4
2095</artwork></figure>
2096<t>
2097   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
2098   used for advertising or other non-essential information. Although any
2099   token character &MAY; appear in a product-version, this token &SHOULD;
2100   only be used for a version identifier (i.e., successive versions of
2101   the same product &SHOULD; only differ in the product-version portion of
2102   the product value).
2103</t>
2104</section>
2105
2106<section title="Quality Values" anchor="quality.values">
2107  <x:anchor-alias value="qvalue"/>
2108<t>
2109   Both transfer codings (TE request header, <xref target="header.te"/>)
2110   and content negotiation (&content.negotiation;) use short "floating point"
2111   numbers to indicate the relative importance ("weight") of various
2112   negotiable parameters.  A weight is normalized to a real number in
2113   the range 0 through 1, where 0 is the minimum and 1 the maximum
2114   value. If a parameter has a quality value of 0, then content with
2115   this parameter is "not acceptable" for the client. HTTP/1.1
2116   applications &MUST-NOT; generate more than three digits after the
2117   decimal point. User configuration of these values &SHOULD; also be
2118   limited in this fashion.
2119</t>
2120<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
2121  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
2122                 / ( "1" [ "." 0*3("0") ] )
2123</artwork></figure>
2124<x:note>
2125  <t>
2126     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
2127     relative degradation in desired quality.
2128  </t>
2129</x:note>
2130</section>
2131
2132</section>
2133
2134<section title="Connections" anchor="connections">
2135
2136<section title="Persistent Connections" anchor="persistent.connections">
2137
2138<section title="Purpose" anchor="persistent.purpose">
2139<t>
2140   Prior to persistent connections, a separate TCP connection was
2141   established to fetch each URL, increasing the load on HTTP servers
2142   and causing congestion on the Internet. The use of inline images and
2143   other associated data often requires a client to make multiple
2144   requests of the same server in a short amount of time. Analysis of
2145   these performance problems and results from a prototype
2146   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2147   measurements of actual HTTP/1.1 implementations show good
2148   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2149   T/TCP <xref target="Tou1998"/>.
2150</t>
2151<t>
2152   Persistent HTTP connections have a number of advantages:
2153  <list style="symbols">
2154      <t>
2155        By opening and closing fewer TCP connections, CPU time is saved
2156        in routers and hosts (clients, servers, proxies, gateways,
2157        tunnels, or caches), and memory used for TCP protocol control
2158        blocks can be saved in hosts.
2159      </t>
2160      <t>
2161        HTTP requests and responses can be pipelined on a connection.
2162        Pipelining allows a client to make multiple requests without
2163        waiting for each response, allowing a single TCP connection to
2164        be used much more efficiently, with much lower elapsed time.
2165      </t>
2166      <t>
2167        Network congestion is reduced by reducing the number of packets
2168        caused by TCP opens, and by allowing TCP sufficient time to
2169        determine the congestion state of the network.
2170      </t>
2171      <t>
2172        Latency on subsequent requests is reduced since there is no time
2173        spent in TCP's connection opening handshake.
2174      </t>
2175      <t>
2176        HTTP can evolve more gracefully, since errors can be reported
2177        without the penalty of closing the TCP connection. Clients using
2178        future versions of HTTP might optimistically try a new feature,
2179        but if communicating with an older server, retry with old
2180        semantics after an error is reported.
2181      </t>
2182    </list>
2183</t>
2184<t>
2185   HTTP implementations &SHOULD; implement persistent connections.
2186</t>
2187</section>
2188
2189<section title="Overall Operation" anchor="persistent.overall">
2190<t>
2191   A significant difference between HTTP/1.1 and earlier versions of
2192   HTTP is that persistent connections are the default behavior of any
2193   HTTP connection. That is, unless otherwise indicated, the client
2194   &SHOULD; assume that the server will maintain a persistent connection,
2195   even after error responses from the server.
2196</t>
2197<t>
2198   Persistent connections provide a mechanism by which a client and a
2199   server can signal the close of a TCP connection. This signaling takes
2200   place using the Connection header field (<xref target="header.connection"/>). Once a close
2201   has been signaled, the client &MUST-NOT; send any more requests on that
2202   connection.
2203</t>
2204
2205<section title="Negotiation" anchor="persistent.negotiation">
2206<t>
2207   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
2208   maintain a persistent connection unless a Connection header including
2209   the connection-token "close" was sent in the request. If the server
2210   chooses to close the connection immediately after sending the
2211   response, it &SHOULD; send a Connection header including the
2212   connection-token "close".
2213</t>
2214<t>
2215   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
2216   decide to keep it open based on whether the response from a server
2217   contains a Connection header with the connection-token close. In case
2218   the client does not want to maintain a connection for more than that
2219   request, it &SHOULD; send a Connection header including the
2220   connection-token close.
2221</t>
2222<t>
2223   If either the client or the server sends the close token in the
2224   Connection header, that request becomes the last one for the
2225   connection.
2226</t>
2227<t>
2228   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
2229   maintained for HTTP versions less than 1.1 unless it is explicitly
2230   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2231   compatibility with HTTP/1.0 clients.
2232</t>
2233<t>
2234   In order to remain persistent, all messages on the connection &MUST;
2235   have a self-defined message length (i.e., one not defined by closure
2236   of the connection), as described in <xref target="message.length"/>.
2237</t>
2238</section>
2239
2240<section title="Pipelining" anchor="pipelining">
2241<t>
2242   A client that supports persistent connections &MAY; "pipeline" its
2243   requests (i.e., send multiple requests without waiting for each
2244   response). A server &MUST; send its responses to those requests in the
2245   same order that the requests were received.
2246</t>
2247<t>
2248   Clients which assume persistent connections and pipeline immediately
2249   after connection establishment &SHOULD; be prepared to retry their
2250   connection if the first pipelined attempt fails. If a client does
2251   such a retry, it &MUST-NOT; pipeline before it knows the connection is
2252   persistent. Clients &MUST; also be prepared to resend their requests if
2253   the server closes the connection before sending all of the
2254   corresponding responses.
2255</t>
2256<t>
2257   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
2258   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
2259   premature termination of the transport connection could lead to
2260   indeterminate results. A client wishing to send a non-idempotent
2261   request &SHOULD; wait to send that request until it has received the
2262   response status for the previous request.
2263</t>
2264</section>
2265</section>
2266
2267<section title="Proxy Servers" anchor="persistent.proxy">
2268<t>
2269   It is especially important that proxies correctly implement the
2270   properties of the Connection header field as specified in <xref target="header.connection"/>.
2271</t>
2272<t>
2273   The proxy server &MUST; signal persistent connections separately with
2274   its clients and the origin servers (or other proxy servers) that it
2275   connects to. Each persistent connection applies to only one transport
2276   link.
2277</t>
2278<t>
2279   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
2280   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
2281   for information and discussion of the problems with the Keep-Alive header
2282   implemented by many HTTP/1.0 clients).
2283</t>
2284
2285<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2286<t>
2287  <cref anchor="TODO-end-to-end" source="jre">
2288    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2289    See also <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2290  </cref>
2291</t>
2292<t>
2293   For the purpose of defining the behavior of caches and non-caching
2294   proxies, we divide HTTP headers into two categories:
2295  <list style="symbols">
2296      <t>End-to-end headers, which are  transmitted to the ultimate
2297        recipient of a request or response. End-to-end headers in
2298        responses MUST be stored as part of a cache entry and &MUST; be
2299        transmitted in any response formed from a cache entry.</t>
2300
2301      <t>Hop-by-hop headers, which are meaningful only for a single
2302        transport-level connection, and are not stored by caches or
2303        forwarded by proxies.</t>
2304  </list>
2305</t>
2306<t>
2307   The following HTTP/1.1 headers are hop-by-hop headers:
2308  <list style="symbols">
2309      <t>Connection</t>
2310      <t>Keep-Alive</t>
2311      <t>Proxy-Authenticate</t>
2312      <t>Proxy-Authorization</t>
2313      <t>TE</t>
2314      <t>Trailer</t>
2315      <t>Transfer-Encoding</t>
2316      <t>Upgrade</t>
2317  </list>
2318</t>
2319<t>
2320   All other headers defined by HTTP/1.1 are end-to-end headers.
2321</t>
2322<t>
2323   Other hop-by-hop headers &MUST; be listed in a Connection header
2324   (<xref target="header.connection"/>).
2325</t>
2326</section>
2327
2328<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2329<t>
2330  <cref anchor="TODO-non-mod-headers" source="jre">
2331    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2332    See also <eref target="http://trac.tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2333  </cref>
2334</t>
2335<t>
2336   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2337   value of certain end-to-end headers. A transparent proxy &SHOULD-NOT;
2338   modify an end-to-end header unless the definition of that header requires
2339   or specifically allows that.
2340</t>
2341<t>
2342   A transparent proxy &MUST-NOT; modify any of the following fields in a
2343   request or response, and it &MUST-NOT; add any of these fields if not
2344   already present:
2345  <list style="symbols">
2346      <t>Content-Location</t>
2347      <t>Content-MD5</t>
2348      <t>ETag</t>
2349      <t>Last-Modified</t>
2350  </list>
2351</t>
2352<t>
2353   A transparent proxy &MUST-NOT; modify any of the following fields in a
2354   response:
2355  <list style="symbols">
2356    <t>Expires</t>
2357  </list>
2358</t>
2359<t>
2360   but it &MAY; add any of these fields if not already present. If an
2361   Expires header is added, it &MUST; be given a field-value identical to
2362   that of the Date header in that response.
2363</t>
2364<t>
2365   A proxy &MUST-NOT; modify or add any of the following fields in a
2366   message that contains the no-transform cache-control directive, or in
2367   any request:
2368  <list style="symbols">
2369    <t>Content-Encoding</t>
2370    <t>Content-Range</t>
2371    <t>Content-Type</t>
2372  </list>
2373</t>
2374<t>
2375   A non-transparent proxy &MAY; modify or add these fields to a message
2376   that does not include no-transform, but if it does so, it &MUST; add a
2377   Warning 214 (Transformation applied) if one does not already appear
2378   in the message (see &header-warning;).
2379</t>
2380<x:note>
2381  <t>
2382    <x:h>Warning:</x:h> Unnecessary modification of end-to-end headers might
2383    cause authentication failures if stronger authentication
2384    mechanisms are introduced in later versions of HTTP. Such
2385    authentication mechanisms &MAY; rely on the values of header fields
2386    not listed here.
2387  </t>
2388</x:note>
2389<t>
2390   The Content-Length field of a request or response is added or deleted
2391   according to the rules in <xref target="message.length"/>. A transparent proxy &MUST;
2392   preserve the entity-length (&entity-length;) of the entity-body,
2393   although it &MAY; change the transfer-length (<xref target="message.length"/>).
2394</t>
2395</section>
2396
2397</section>
2398
2399<section title="Practical Considerations" anchor="persistent.practical">
2400<t>
2401   Servers will usually have some time-out value beyond which they will
2402   no longer maintain an inactive connection. Proxy servers might make
2403   this a higher value since it is likely that the client will be making
2404   more connections through the same server. The use of persistent
2405   connections places no requirements on the length (or existence) of
2406   this time-out for either the client or the server.
2407</t>
2408<t>
2409   When a client or server wishes to time-out it &SHOULD; issue a graceful
2410   close on the transport connection. Clients and servers &SHOULD; both
2411   constantly watch for the other side of the transport close, and
2412   respond to it as appropriate. If a client or server does not detect
2413   the other side's close promptly it could cause unnecessary resource
2414   drain on the network.
2415</t>
2416<t>
2417   A client, server, or proxy &MAY; close the transport connection at any
2418   time. For example, a client might have started to send a new request
2419   at the same time that the server has decided to close the "idle"
2420   connection. From the server's point of view, the connection is being
2421   closed while it was idle, but from the client's point of view, a
2422   request is in progress.
2423</t>
2424<t>
2425   This means that clients, servers, and proxies &MUST; be able to recover
2426   from asynchronous close events. Client software &SHOULD; reopen the
2427   transport connection and retransmit the aborted sequence of requests
2428   without user interaction so long as the request sequence is
2429   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
2430   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
2431   human operator the choice of retrying the request(s). Confirmation by
2432   user-agent software with semantic understanding of the application
2433   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
2434   be repeated if the second sequence of requests fails.
2435</t>
2436<t>
2437   Servers &SHOULD; always respond to at least one request per connection,
2438   if at all possible. Servers &SHOULD-NOT;  close a connection in the
2439   middle of transmitting a response, unless a network or client failure
2440   is suspected.
2441</t>
2442<t>
2443   Clients (including proxies) &SHOULD; limit the number of simultaneous
2444   connections that they maintain to a given server (including proxies).
2445</t>
2446<t>
2447   Previous revisions of HTTP gave a specific number of connections as a
2448   ceiling, but this was found to be impractical for many applications. As a
2449   result, this specification does not mandate a particular maximum number of
2450   connections, but instead encourages clients to be conservative when opening
2451   multiple connections.
2452</t>
2453<t>
2454   In particular, while using multiple connections avoids the "head-of-line
2455   blocking" problem (whereby a request that takes significant server-side
2456   processing and/or has a large payload can block subsequent requests on the
2457   same connection), each connection used consumes server resources (sometimes
2458   significantly), and furthermore using multiple connections can cause
2459   undesirable side effects in congested networks.
2460</t>
2461<t>
2462   Note that servers might reject traffic that they deem abusive, including an
2463   excessive number of connections from a client.
2464</t>
2465</section>
2466</section>
2467
2468<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2469
2470<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2471<t>
2472   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2473   flow control mechanisms to resolve temporary overloads, rather than
2474   terminating connections with the expectation that clients will retry.
2475   The latter technique can exacerbate network congestion.
2476</t>
2477</section>
2478
2479<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2480<t>
2481   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2482   the network connection for an error status while it is transmitting
2483   the request. If the client sees an error status, it &SHOULD;
2484   immediately cease transmitting the body. If the body is being sent
2485   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2486   empty trailer &MAY; be used to prematurely mark the end of the message.
2487   If the body was preceded by a Content-Length header, the client &MUST;
2488   close the connection.
2489</t>
2490</section>
2491
2492<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2493<t>
2494   The purpose of the 100 (Continue) status (see &status-100;) is to
2495   allow a client that is sending a request message with a request body
2496   to determine if the origin server is willing to accept the request
2497   (based on the request headers) before the client sends the request
2498   body. In some cases, it might either be inappropriate or highly
2499   inefficient for the client to send the body if the server will reject
2500   the message without looking at the body.
2501</t>
2502<t>
2503   Requirements for HTTP/1.1 clients:
2504  <list style="symbols">
2505    <t>
2506        If a client will wait for a 100 (Continue) response before
2507        sending the request body, it &MUST; send an Expect request-header
2508        field (&header-expect;) with the "100-continue" expectation.
2509    </t>
2510    <t>
2511        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2512        with the "100-continue" expectation if it does not intend
2513        to send a request body.
2514    </t>
2515  </list>
2516</t>
2517<t>
2518   Because of the presence of older implementations, the protocol allows
2519   ambiguous situations in which a client may send "Expect: 100-continue"
2520   without receiving either a 417 (Expectation Failed) status
2521   or a 100 (Continue) status. Therefore, when a client sends this
2522   header field to an origin server (possibly via a proxy) from which it
2523   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2524   for an indefinite period before sending the request body.
2525</t>
2526<t>
2527   Requirements for HTTP/1.1 origin servers:
2528  <list style="symbols">
2529    <t> Upon receiving a request which includes an Expect request-header
2530        field with the "100-continue" expectation, an origin server &MUST;
2531        either respond with 100 (Continue) status and continue to read
2532        from the input stream, or respond with a final status code. The
2533        origin server &MUST-NOT; wait for the request body before sending
2534        the 100 (Continue) response. If it responds with a final status
2535        code, it &MAY; close the transport connection or it &MAY; continue
2536        to read and discard the rest of the request.  It &MUST-NOT;
2537        perform the requested method if it returns a final status code.
2538    </t>
2539    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2540        the request message does not include an Expect request-header
2541        field with the "100-continue" expectation, and &MUST-NOT; send a
2542        100 (Continue) response if such a request comes from an HTTP/1.0
2543        (or earlier) client. There is an exception to this rule: for
2544        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2545        status in response to an HTTP/1.1 PUT or POST request that does
2546        not include an Expect request-header field with the "100-continue"
2547        expectation. This exception, the purpose of which is
2548        to minimize any client processing delays associated with an
2549        undeclared wait for 100 (Continue) status, applies only to
2550        HTTP/1.1 requests, and not to requests with any other HTTP-version
2551        value.
2552    </t>
2553    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2554        already received some or all of the request body for the
2555        corresponding request.
2556    </t>
2557    <t> An origin server that sends a 100 (Continue) response &MUST;
2558    ultimately send a final status code, once the request body is
2559        received and processed, unless it terminates the transport
2560        connection prematurely.
2561    </t>
2562    <t> If an origin server receives a request that does not include an
2563        Expect request-header field with the "100-continue" expectation,
2564        the request includes a request body, and the server responds
2565        with a final status code before reading the entire request body
2566        from the transport connection, then the server &SHOULD-NOT;  close
2567        the transport connection until it has read the entire request,
2568        or until the client closes the connection. Otherwise, the client
2569        might not reliably receive the response message. However, this
2570        requirement is not be construed as preventing a server from
2571        defending itself against denial-of-service attacks, or from
2572        badly broken client implementations.
2573      </t>
2574    </list>
2575</t>
2576<t>
2577   Requirements for HTTP/1.1 proxies:
2578  <list style="symbols">
2579    <t> If a proxy receives a request that includes an Expect request-header
2580        field with the "100-continue" expectation, and the proxy
2581        either knows that the next-hop server complies with HTTP/1.1 or
2582        higher, or does not know the HTTP version of the next-hop
2583        server, it &MUST; forward the request, including the Expect header
2584        field.
2585    </t>
2586    <t> If the proxy knows that the version of the next-hop server is
2587        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2588        respond with a 417 (Expectation Failed) status.
2589    </t>
2590    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2591        numbers received from recently-referenced next-hop servers.
2592    </t>
2593    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2594        request message was received from an HTTP/1.0 (or earlier)
2595        client and did not include an Expect request-header field with
2596        the "100-continue" expectation. This requirement overrides the
2597        general rule for forwarding of 1xx responses (see &status-1xx;).
2598    </t>
2599  </list>
2600</t>
2601</section>
2602
2603<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2604<t>
2605   If an HTTP/1.1 client sends a request which includes a request body,
2606   but which does not include an Expect request-header field with the
2607   "100-continue" expectation, and if the client is not directly
2608   connected to an HTTP/1.1 origin server, and if the client sees the
2609   connection close before receiving any status from the server, the
2610   client &SHOULD; retry the request.  If the client does retry this
2611   request, it &MAY; use the following "binary exponential backoff"
2612   algorithm to be assured of obtaining a reliable response:
2613  <list style="numbers">
2614    <t>
2615      Initiate a new connection to the server
2616    </t>
2617    <t>
2618      Transmit the request-headers
2619    </t>
2620    <t>
2621      Initialize a variable R to the estimated round-trip time to the
2622         server (e.g., based on the time it took to establish the
2623         connection), or to a constant value of 5 seconds if the round-trip
2624         time is not available.
2625    </t>
2626    <t>
2627       Compute T = R * (2**N), where N is the number of previous
2628         retries of this request.
2629    </t>
2630    <t>
2631       Wait either for an error response from the server, or for T
2632         seconds (whichever comes first)
2633    </t>
2634    <t>
2635       If no error response is received, after T seconds transmit the
2636         body of the request.
2637    </t>
2638    <t>
2639       If client sees that the connection is closed prematurely,
2640         repeat from step 1 until the request is accepted, an error
2641         response is received, or the user becomes impatient and
2642         terminates the retry process.
2643    </t>
2644  </list>
2645</t>
2646<t>
2647   If at any point an error status is received, the client
2648  <list style="symbols">
2649      <t>&SHOULD-NOT;  continue and</t>
2650
2651      <t>&SHOULD; close the connection if it has not completed sending the
2652        request message.</t>
2653    </list>
2654</t>
2655</section>
2656</section>
2657</section>
2658
2659
2660<section title="Miscellaneous notes that may disappear" anchor="misc">
2661<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2662<t>
2663   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2664</t>
2665</section>
2666
2667<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2668<t>
2669   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2670</t>
2671</section>
2672
2673<section title="Interception of HTTP for access control" anchor="http.intercept">
2674<t>
2675   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2676</t>
2677</section>
2678
2679<section title="Use of HTTP by other protocols" anchor="http.others">
2680<t>
2681   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2682   Extensions of HTTP like WebDAV.</cref>
2683</t>
2684
2685</section>
2686<section title="Use of HTTP by media type specification" anchor="http.media">
2687<t>
2688   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2689</t>
2690</section>
2691</section>
2692
2693<section title="Header Field Definitions" anchor="header.field.definitions">
2694<t>
2695   This section defines the syntax and semantics of HTTP/1.1 header fields
2696   related to message framing and transport protocols.
2697</t>
2698<t>
2699   For entity-header fields, both sender and recipient refer to either the
2700   client or the server, depending on who sends and who receives the entity.
2701</t>
2702
2703<section title="Connection" anchor="header.connection">
2704  <iref primary="true" item="Connection header" x:for-anchor=""/>
2705  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2706  <x:anchor-alias value="Connection"/>
2707  <x:anchor-alias value="connection-token"/>
2708  <x:anchor-alias value="Connection-v"/>
2709<t>
2710   The "Connection" general-header field allows the sender to specify
2711   options that are desired for that particular connection and &MUST-NOT;
2712   be communicated by proxies over further connections.
2713</t>
2714<t>
2715   The Connection header's value has the following grammar:
2716</t>
2717<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"/>
2718  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2719  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2720  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2721</artwork></figure>
2722<t>
2723   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2724   message is forwarded and, for each connection-token in this field,
2725   remove any header field(s) from the message with the same name as the
2726   connection-token. Connection options are signaled by the presence of
2727   a connection-token in the Connection header field, not by any
2728   corresponding additional header field(s), since the additional header
2729   field may not be sent if there are no parameters associated with that
2730   connection option.
2731</t>
2732<t>
2733   Message headers listed in the Connection header &MUST-NOT; include
2734   end-to-end headers, such as Cache-Control.
2735</t>
2736<t>
2737   HTTP/1.1 defines the "close" connection option for the sender to
2738   signal that the connection will be closed after completion of the
2739   response. For example,
2740</t>
2741<figure><artwork type="example">
2742  Connection: close
2743</artwork></figure>
2744<t>
2745   in either the request or the response header fields indicates that
2746   the connection &SHOULD-NOT;  be considered "persistent" (<xref target="persistent.connections"/>)
2747   after the current request/response is complete.
2748</t>
2749<t>
2750   An HTTP/1.1 client that does not support persistent connections &MUST;
2751   include the "close" connection option in every request message.
2752</t>
2753<t>
2754   An HTTP/1.1 server that does not support persistent connections &MUST;
2755   include the "close" connection option in every response message that
2756   does not have a 1xx (Informational) status code.
2757</t>
2758<t>
2759   A system receiving an HTTP/1.0 (or lower-version) message that
2760   includes a Connection header &MUST;, for each connection-token in this
2761   field, remove and ignore any header field(s) from the message with
2762   the same name as the connection-token. This protects against mistaken
2763   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2764</t>
2765</section>
2766
2767<section title="Content-Length" anchor="header.content-length">
2768  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2769  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2770  <x:anchor-alias value="Content-Length"/>
2771  <x:anchor-alias value="Content-Length-v"/>
2772<t>
2773   The "Content-Length" entity-header field indicates the size of the
2774   entity-body, in number of OCTETs. In the case of responses to the HEAD
2775   method, it indicates the size of the entity-body that would have been sent
2776   had the request been a GET.
2777</t>
2778<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2779  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2780  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2781</artwork></figure>
2782<t>
2783   An example is
2784</t>
2785<figure><artwork type="example">
2786  Content-Length: 3495
2787</artwork></figure>
2788<t>
2789   Applications &SHOULD; use this field to indicate the transfer-length of
2790   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2791</t>
2792<t>
2793   Any Content-Length greater than or equal to zero is a valid value.
2794   <xref target="message.length"/> describes how to determine the length of a message-body
2795   if a Content-Length is not given.
2796</t>
2797<t>
2798   Note that the meaning of this field is significantly different from
2799   the corresponding definition in MIME, where it is an optional field
2800   used within the "message/external-body" content-type. In HTTP, it
2801   &SHOULD; be sent whenever the message's length can be determined prior
2802   to being transferred, unless this is prohibited by the rules in
2803   <xref target="message.length"/>.
2804</t>
2805</section>
2806
2807<section title="Date" anchor="header.date">
2808  <iref primary="true" item="Date header" x:for-anchor=""/>
2809  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2810  <x:anchor-alias value="Date"/>
2811  <x:anchor-alias value="Date-v"/>
2812<t>
2813   The "Date" general-header field represents the date and time at which
2814   the message was originated, having the same semantics as the Origination
2815   Date Field (orig-date) defined in <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>.
2816   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2817   it &MUST; be sent in rfc1123-date format.
2818</t>
2819<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2820  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2821  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2822</artwork></figure>
2823<t>
2824   An example is
2825</t>
2826<figure><artwork type="example">
2827  Date: Tue, 15 Nov 1994 08:12:31 GMT
2828</artwork></figure>
2829<t>
2830   Origin servers &MUST; include a Date header field in all responses,
2831   except in these cases:
2832  <list style="numbers">
2833      <t>If the response status code is 100 (Continue) or 101 (Switching
2834         Protocols), the response &MAY; include a Date header field, at
2835         the server's option.</t>
2836
2837      <t>If the response status code conveys a server error, e.g., 500
2838         (Internal Server Error) or 503 (Service Unavailable), and it is
2839         inconvenient or impossible to generate a valid Date.</t>
2840
2841      <t>If the server does not have a clock that can provide a
2842         reasonable approximation of the current time, its responses
2843         &MUST-NOT; include a Date header field. In this case, the rules
2844         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2845  </list>
2846</t>
2847<t>
2848   A received message that does not have a Date header field &MUST; be
2849   assigned one by the recipient if the message will be cached by that
2850   recipient or gatewayed via a protocol which requires a Date. An HTTP
2851   implementation without a clock &MUST-NOT; cache responses without
2852   revalidating them on every use. An HTTP cache, especially a shared
2853   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2854   clock with a reliable external standard.
2855</t>
2856<t>
2857   Clients &SHOULD; only send a Date header field in messages that include
2858   an entity-body, as in the case of the PUT and POST requests, and even
2859   then it is optional. A client without a clock &MUST-NOT; send a Date
2860   header field in a request.
2861</t>
2862<t>
2863   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2864   time subsequent to the generation of the message. It &SHOULD; represent
2865   the best available approximation of the date and time of message
2866   generation, unless the implementation has no means of generating a
2867   reasonably accurate date and time. In theory, the date ought to
2868   represent the moment just before the entity is generated. In
2869   practice, the date can be generated at any time during the message
2870   origination without affecting its semantic value.
2871</t>
2872
2873<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2874<t>
2875   Some origin server implementations might not have a clock available.
2876   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2877   values to a response, unless these values were associated
2878   with the resource by a system or user with a reliable clock. It &MAY;
2879   assign an Expires value that is known, at or before server
2880   configuration time, to be in the past (this allows "pre-expiration"
2881   of responses without storing separate Expires values for each
2882   resource).
2883</t>
2884</section>
2885</section>
2886
2887<section title="Host" anchor="header.host">
2888  <iref primary="true" item="Host header" x:for-anchor=""/>
2889  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2890  <x:anchor-alias value="Host"/>
2891  <x:anchor-alias value="Host-v"/>
2892<t>
2893   The "Host" request-header field specifies the Internet host and port
2894   number of the resource being requested, allowing the origin server or
2895   gateway to differentiate between internally-ambiguous URLs, such as the root
2896   "/" URL of a server for multiple host names on a single IP address.
2897</t>
2898<t>   
2899   The Host field value &MUST; represent the naming authority of the origin
2900   server or gateway given by the original URL obtained from the user or
2901   referring resource (generally an http URI, as described in
2902   <xref target="http.uri"/>).
2903</t>
2904<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2905  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2906  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2907</artwork></figure>
2908<t>
2909   A "host" without any trailing port information implies the default
2910   port for the service requested (e.g., "80" for an HTTP URL). For
2911   example, a request on the origin server for
2912   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2913</t>
2914<figure><artwork type="message/http; msgtype=&#34;request&#34;" x:indent-with="  ">
2915GET /pub/WWW/ HTTP/1.1
2916Host: www.example.org
2917</artwork></figure>
2918<t>
2919   A client &MUST; include a Host header field in all HTTP/1.1 request
2920   messages. If the requested URI does not include an Internet host
2921   name for the service being requested, then the Host header field &MUST;
2922   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2923   request message it forwards does contain an appropriate Host header
2924   field that identifies the service being requested by the proxy. All
2925   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2926   status code to any HTTP/1.1 request message which lacks a Host header
2927   field.
2928</t>
2929<t>
2930   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2931   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2932   for other requirements relating to Host.
2933</t>
2934</section>
2935
2936<section title="TE" anchor="header.te">
2937  <iref primary="true" item="TE header" x:for-anchor=""/>
2938  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2939  <x:anchor-alias value="TE"/>
2940  <x:anchor-alias value="TE-v"/>
2941  <x:anchor-alias value="t-codings"/>
2942  <x:anchor-alias value="te-params"/>
2943  <x:anchor-alias value="te-ext"/>
2944<t>
2945   The "TE" request-header field indicates what extension transfer-codings
2946   it is willing to accept in the response, and whether or not it is
2947   willing to accept trailer fields in a chunked transfer-coding.
2948</t>
2949<t>
2950   Its value may consist of the keyword "trailers" and/or a comma-separated
2951   list of extension transfer-coding names with optional accept
2952   parameters (as described in <xref target="transfer.codings"/>).
2953</t>
2954<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"/>
2955  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2956  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2957  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2958  <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> )
2959  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" <x:ref>word</x:ref> ]
2960</artwork></figure>
2961<t>
2962   The presence of the keyword "trailers" indicates that the client is
2963   willing to accept trailer fields in a chunked transfer-coding, as
2964   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2965   transfer-coding values even though it does not itself represent a
2966   transfer-coding.
2967</t>
2968<t>
2969   Examples of its use are:
2970</t>
2971<figure><artwork type="example">
2972  TE: deflate
2973  TE:
2974  TE: trailers, deflate;q=0.5
2975</artwork></figure>
2976<t>
2977   The TE header field only applies to the immediate connection.
2978   Therefore, the keyword &MUST; be supplied within a Connection header
2979   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2980</t>
2981<t>
2982   A server tests whether a transfer-coding is acceptable, according to
2983   a TE field, using these rules:
2984  <list style="numbers">
2985    <x:lt>
2986      <t>The "chunked" transfer-coding is always acceptable. If the
2987         keyword "trailers" is listed, the client indicates that it is
2988         willing to accept trailer fields in the chunked response on
2989         behalf of itself and any downstream clients. The implication is
2990         that, if given, the client is stating that either all
2991         downstream clients are willing to accept trailer fields in the
2992         forwarded response, or that it will attempt to buffer the
2993         response on behalf of downstream recipients.
2994      </t><t>
2995         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2996         chunked response such that a client can be assured of buffering
2997         the entire response.</t>
2998    </x:lt>
2999    <x:lt>
3000      <t>If the transfer-coding being tested is one of the transfer-codings
3001         listed in the TE field, then it is acceptable unless it
3002         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3003         qvalue of 0 means "not acceptable.")</t>
3004    </x:lt>
3005    <x:lt>
3006      <t>If multiple transfer-codings are acceptable, then the
3007         acceptable transfer-coding with the highest non-zero qvalue is
3008         preferred.  The "chunked" transfer-coding always has a qvalue
3009         of 1.</t>
3010    </x:lt>
3011  </list>
3012</t>
3013<t>
3014   If the TE field-value is empty or if no TE field is present, the only
3015   transfer-coding is "chunked". A message with no transfer-coding is
3016   always acceptable.
3017</t>
3018</section>
3019
3020<section title="Trailer" anchor="header.trailer">
3021  <iref primary="true" item="Trailer header" x:for-anchor=""/>
3022  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
3023  <x:anchor-alias value="Trailer"/>
3024  <x:anchor-alias value="Trailer-v"/>
3025<t>
3026   The "Trailer" general-header field indicates that the given set of
3027   header fields is present in the trailer of a message encoded with
3028   chunked transfer-coding.
3029</t>
3030<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
3031  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
3032  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
3033</artwork></figure>
3034<t>
3035   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
3036   message using chunked transfer-coding with a non-empty trailer. Doing
3037   so allows the recipient to know which header fields to expect in the
3038   trailer.
3039</t>
3040<t>
3041   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
3042   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3043   trailer fields in a "chunked" transfer-coding.
3044</t>
3045<t>
3046   Message header fields listed in the Trailer header field &MUST-NOT;
3047   include the following header fields:
3048  <list style="symbols">
3049    <t>Transfer-Encoding</t>
3050    <t>Content-Length</t>
3051    <t>Trailer</t>
3052  </list>
3053</t>
3054</section>
3055
3056<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3057  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
3058  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
3059  <x:anchor-alias value="Transfer-Encoding"/>
3060  <x:anchor-alias value="Transfer-Encoding-v"/>
3061<t>
3062   The "Transfer-Encoding" general-header field indicates what transfer-codings
3063   (if any) have been applied to the message body. It differs from
3064   Content-Encoding (&content-codings;) in that transfer-codings are a property
3065   of the message (and therefore are removed by intermediaries), whereas
3066   content-codings are not.
3067</t>
3068<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
3069  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
3070                        <x:ref>Transfer-Encoding-v</x:ref>
3071  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
3072</artwork></figure>
3073<t>
3074   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3075</t>
3076<figure><artwork type="example">
3077  Transfer-Encoding: chunked
3078</artwork></figure>
3079<t>
3080   If multiple encodings have been applied to an entity, the transfer-codings
3081   &MUST; be listed in the order in which they were applied.
3082   Additional information about the encoding parameters &MAY; be provided
3083   by other entity-header fields not defined by this specification.
3084</t>
3085<t>
3086   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3087   header.
3088</t>
3089</section>
3090
3091<section title="Upgrade" anchor="header.upgrade">
3092  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
3093  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
3094  <x:anchor-alias value="Upgrade"/>
3095  <x:anchor-alias value="Upgrade-v"/>
3096<t>
3097   The "Upgrade" general-header field allows the client to specify what
3098   additional communication protocols it would like to use, if the server
3099   chooses to switch protocols. Additionally, the server &MUST; use the Upgrade
3100   header field within a 101 (Switching Protocols) response to indicate which
3101   protocol(s) are being switched to.
3102</t>
3103<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
3104  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
3105  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
3106</artwork></figure>
3107<t>
3108   For example,
3109</t>
3110<figure><artwork type="example">
3111  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3112</artwork></figure>
3113<t>
3114   The Upgrade header field is intended to provide a simple mechanism
3115   for transition from HTTP/1.1 to some other, incompatible protocol. It
3116   does so by allowing the client to advertise its desire to use another
3117   protocol, such as a later version of HTTP with a higher major version
3118   number, even though the current request has been made using HTTP/1.1.
3119   This eases the difficult transition between incompatible protocols by
3120   allowing the client to initiate a request in the more commonly
3121   supported protocol while indicating to the server that it would like
3122   to use a "better" protocol if available (where "better" is determined
3123   by the server, possibly according to the nature of the method and/or
3124   resource being requested).
3125</t>
3126<t>
3127   The Upgrade header field only applies to switching application-layer
3128   protocols upon the existing transport-layer connection. Upgrade
3129   cannot be used to insist on a protocol change; its acceptance and use
3130   by the server is optional. The capabilities and nature of the
3131   application-layer communication after the protocol change is entirely
3132   dependent upon the new protocol chosen, although the first action
3133   after changing the protocol &MUST; be a response to the initial HTTP
3134   request containing the Upgrade header field.
3135</t>
3136<t>
3137   The Upgrade header field only applies to the immediate connection.
3138   Therefore, the upgrade keyword &MUST; be supplied within a Connection
3139   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3140   HTTP/1.1 message.
3141</t>
3142<t>
3143   The Upgrade header field cannot be used to indicate a switch to a
3144   protocol on a different connection. For that purpose, it is more
3145   appropriate to use a 301, 302, 303, or 305 redirection response.
3146</t>
3147<t>
3148   This specification only defines the protocol name "HTTP" for use by
3149   the family of Hypertext Transfer Protocols, as defined by the HTTP
3150   version rules of <xref target="http.version"/> and future updates to this
3151   specification. Additional tokens can be registered with IANA using the
3152   registration procedure defined below. 
3153</t>
3154
3155<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3156<t>
3157   The HTTP Upgrade Token Registry defines the name space for product
3158   tokens used to identify protocols in the Upgrade header field.
3159   Each registered token should be associated with one or a set of
3160   specifications, and with contact information.
3161</t>
3162<t>
3163   Registrations should be allowed on a First Come First Served basis as
3164   described in <xref target="RFC5226" x:sec="4.1" x:fmt="of"/>. These
3165   specifications need not be IETF documents or be subject to IESG review, but
3166   should obey the following rules:
3167  <list style="numbers">
3168    <t>A token, once registered, stays registered forever.</t>
3169    <t>The registration &MUST; name a responsible party for the
3170       registration.</t>
3171    <t>The registration &MUST; name a point of contact.</t>
3172    <t>The registration &MAY; name the documentation required for the
3173       token.</t>
3174    <t>The responsible party &MAY; change the registration at any time.
3175       The IANA will keep a record of all such changes, and make them
3176       available upon request.</t>
3177    <t>The responsible party for the first registration of a "product"
3178       token &MUST; approve later registrations of a "version" token
3179       together with that "product" token before they can be registered.</t>
3180    <t>If absolutely required, the IESG &MAY; reassign the responsibility
3181       for a token. This will normally only be used in the case when a
3182       responsible party cannot be contacted.</t>
3183  </list>
3184</t>
3185<t>
3186   It is not required that specifications for upgrade tokens be made
3187   publicly available, but the contact information for the registration
3188   should be.
3189</t>
3190</section>
3191
3192
3193</section>
3194
3195<section title="Via" anchor="header.via">
3196  <iref primary="true" item="Via header" x:for-anchor=""/>
3197  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
3198  <x:anchor-alias value="protocol-name"/>
3199  <x:anchor-alias value="protocol-version"/>
3200  <x:anchor-alias value="pseudonym"/>
3201  <x:anchor-alias value="received-by"/>
3202  <x:anchor-alias value="received-protocol"/>
3203  <x:anchor-alias value="Via"/>
3204  <x:anchor-alias value="Via-v"/>
3205<t>
3206   The "Via" general-header field &MUST; be used by gateways and proxies to
3207   indicate the intermediate protocols and recipients between the user
3208   agent and the server on requests, and between the origin server and
3209   the client on responses. It is analogous to the "Received" field defined in
3210   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
3211   avoiding request loops, and identifying the protocol capabilities of
3212   all senders along the request/response chain.
3213</t>
3214<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"/>
3215  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
3216  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
3217                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
3218  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
3219  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
3220  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
3221  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
3222  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
3223</artwork></figure>
3224<t>
3225   The received-protocol indicates the protocol version of the message
3226   received by the server or client along each segment of the
3227   request/response chain. The received-protocol version is appended to
3228   the Via field value when the message is forwarded so that information
3229   about the protocol capabilities of upstream applications remains
3230   visible to all recipients.
3231</t>
3232<t>
3233   The protocol-name is optional if and only if it would be "HTTP". The
3234   received-by field is normally the host and optional port number of a
3235   recipient server or client that subsequently forwarded the message.
3236   However, if the real host is considered to be sensitive information,
3237   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
3238   be assumed to be the default port of the received-protocol.
3239</t>
3240<t>
3241   Multiple Via field values represent each proxy or gateway that has
3242   forwarded the message. Each recipient &MUST; append its information
3243   such that the end result is ordered according to the sequence of
3244   forwarding applications.
3245</t>
3246<t>
3247   Comments &MAY; be used in the Via header field to identify the software
3248   of the recipient proxy or gateway, analogous to the User-Agent and
3249   Server header fields. However, all comments in the Via field are
3250   optional and &MAY; be removed by any recipient prior to forwarding the
3251   message.
3252</t>
3253<t>
3254   For example, a request message could be sent from an HTTP/1.0 user
3255   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3256   forward the request to a public proxy at p.example.net, which completes
3257   the request by forwarding it to the origin server at www.example.com.
3258   The request received by www.example.com would then have the following
3259   Via header field:
3260</t>
3261<figure><artwork type="example">
3262  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3263</artwork></figure>
3264<t>
3265   Proxies and gateways used as a portal through a network firewall
3266   &SHOULD-NOT;, by default, forward the names and ports of hosts within
3267   the firewall region. This information &SHOULD; only be propagated if
3268   explicitly enabled. If not enabled, the received-by host of any host
3269   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
3270   for that host.
3271</t>
3272<t>
3273   For organizations that have strong privacy requirements for hiding
3274   internal structures, a proxy &MAY; combine an ordered subsequence of
3275   Via header field entries with identical received-protocol values into
3276   a single such entry. For example,
3277</t>
3278<figure><artwork type="example">
3279  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3280</artwork></figure>
3281<t>
3282  could be collapsed to
3283</t>
3284<figure><artwork type="example">
3285  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3286</artwork></figure>
3287<t>
3288   Applications &SHOULD-NOT;  combine multiple entries unless they are all
3289   under the same organizational control and the hosts have already been
3290   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
3291   have different received-protocol values.
3292</t>
3293</section>
3294
3295</section>
3296
3297<section title="IANA Considerations" anchor="IANA.considerations">
3298
3299<section title="Message Header Registration" anchor="message.header.registration">
3300<t>
3301   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3302   with the permanent registrations below (see <xref target="RFC3864"/>):
3303</t>
3304<?BEGININC p1-messaging.iana-headers ?>
3305<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3306<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3307   <ttcol>Header Field Name</ttcol>
3308   <ttcol>Protocol</ttcol>
3309   <ttcol>Status</ttcol>
3310   <ttcol>Reference</ttcol>
3311
3312   <c>Connection</c>
3313   <c>http</c>
3314   <c>standard</c>
3315   <c>
3316      <xref target="header.connection"/>
3317   </c>
3318   <c>Content-Length</c>
3319   <c>http</c>
3320   <c>standard</c>
3321   <c>
3322      <xref target="header.content-length"/>
3323   </c>
3324   <c>Date</c>
3325   <c>http</c>
3326   <c>standard</c>
3327   <c>
3328      <xref target="header.date"/>
3329   </c>
3330   <c>Host</c>
3331   <c>http</c>
3332   <c>standard</c>
3333   <c>
3334      <xref target="header.host"/>
3335   </c>
3336   <c>TE</c>
3337   <c>http</c>
3338   <c>standard</c>
3339   <c>
3340      <xref target="header.te"/>
3341   </c>
3342   <c>Trailer</c>
3343   <c>http</c>
3344   <c>standard</c>
3345   <c>
3346      <xref target="header.trailer"/>
3347   </c>
3348   <c>Transfer-Encoding</c>
3349   <c>http</c>
3350   <c>standard</c>
3351   <c>
3352      <xref target="header.transfer-encoding"/>
3353   </c>
3354   <c>Upgrade</c>
3355   <c>http</c>
3356   <c>standard</c>
3357   <c>
3358      <xref target="header.upgrade"/>
3359   </c>
3360   <c>Via</c>
3361   <c>http</c>
3362   <c>standard</c>
3363   <c>
3364      <xref target="header.via"/>
3365   </c>
3366</texttable>
3367<!--(END)-->
3368<?ENDINC p1-messaging.iana-headers ?>
3369<t>
3370   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3371</t>
3372</section>
3373
3374<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3375<t>
3376   The entries for the "http" and "https" URI Schemes in the registry located at
3377   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3378   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3379   and <xref target="https.uri" format="counter"/> of this document
3380   (see <xref target="RFC4395"/>).
3381</t>
3382</section>
3383
3384<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3385<t>
3386   This document serves as the specification for the Internet media types
3387   "message/http" and "application/http". The following is to be registered with
3388   IANA (see <xref target="RFC4288"/>).
3389</t>
3390<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3391<iref item="Media Type" subitem="message/http" primary="true"/>
3392<iref item="message/http Media Type" primary="true"/>
3393<t>
3394   The message/http type can be used to enclose a single HTTP request or
3395   response message, provided that it obeys the MIME restrictions for all
3396   "message" types regarding line length and encodings.
3397</t>
3398<t>
3399  <list style="hanging" x:indent="12em">
3400    <t hangText="Type name:">
3401      message
3402    </t>
3403    <t hangText="Subtype name:">
3404      http
3405    </t>
3406    <t hangText="Required parameters:">
3407      none
3408    </t>
3409    <t hangText="Optional parameters:">
3410      version, msgtype
3411      <list style="hanging">
3412        <t hangText="version:">
3413          The HTTP-Version number of the enclosed message
3414          (e.g., "1.1"). If not present, the version can be
3415          determined from the first line of the body.
3416        </t>
3417        <t hangText="msgtype:">
3418          The message type -- "request" or "response". If not
3419          present, the type can be determined from the first
3420          line of the body.
3421        </t>
3422      </list>
3423    </t>
3424    <t hangText="Encoding considerations:">
3425      only "7bit", "8bit", or "binary" are permitted
3426    </t>
3427    <t hangText="Security considerations:">
3428      none
3429    </t>
3430    <t hangText="Interoperability considerations:">
3431      none
3432    </t>
3433    <t hangText="Published specification:">
3434      This specification (see <xref target="internet.media.type.message.http"/>).
3435    </t>
3436    <t hangText="Applications that use this media type:">
3437    </t>
3438    <t hangText="Additional information:">
3439      <list style="hanging">
3440        <t hangText="Magic number(s):">none</t>
3441        <t hangText="File extension(s):">none</t>
3442        <t hangText="Macintosh file type code(s):">none</t>
3443      </list>
3444    </t>
3445    <t hangText="Person and email address to contact for further information:">
3446      See Authors Section.
3447    </t>
3448    <t hangText="Intended usage:">
3449      COMMON
3450    </t>
3451    <t hangText="Restrictions on usage:">
3452      none
3453    </t>
3454    <t hangText="Author/Change controller:">
3455      IESG
3456    </t>
3457  </list>
3458</t>
3459</section>
3460<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3461<iref item="Media Type" subitem="application/http" primary="true"/>
3462<iref item="application/http Media Type" primary="true"/>
3463<t>
3464   The application/http type can be used to enclose a pipeline of one or more
3465   HTTP request or response messages (not intermixed).
3466</t>
3467<t>
3468  <list style="hanging" x:indent="12em">
3469    <t hangText="Type name:">
3470      application
3471    </t>
3472    <t hangText="Subtype name:">
3473      http
3474    </t>
3475    <t hangText="Required parameters:">
3476      none
3477    </t>
3478    <t hangText="Optional parameters:">
3479      version, msgtype
3480      <list style="hanging">
3481        <t hangText="version:">
3482          The HTTP-Version number of the enclosed messages
3483          (e.g., "1.1"). If not present, the version can be
3484          determined from the first line of the body.
3485        </t>
3486        <t hangText="msgtype:">
3487          The message type -- "request" or "response". If not
3488          present, the type can be determined from the first
3489          line of the body.
3490        </t>
3491      </list>
3492    </t>
3493    <t hangText="Encoding considerations:">
3494      HTTP messages enclosed by this type
3495      are in "binary" format; use of an appropriate
3496      Content-Transfer-Encoding is required when
3497      transmitted via E-mail.
3498    </t>
3499    <t hangText="Security considerations:">
3500      none
3501    </t>
3502    <t hangText="Interoperability considerations:">
3503      none
3504    </t>
3505    <t hangText="Published specification:">
3506      This specification (see <xref target="internet.media.type.application.http"/>).
3507    </t>
3508    <t hangText="Applications that use this media type:">
3509    </t>
3510    <t hangText="Additional information:">
3511      <list style="hanging">
3512        <t hangText="Magic number(s):">none</t>
3513        <t hangText="File extension(s):">none</t>
3514        <t hangText="Macintosh file type code(s):">none</t>
3515      </list>
3516    </t>
3517    <t hangText="Person and email address to contact for further information:">
3518      See Authors Section.
3519    </t>
3520    <t hangText="Intended usage:">
3521      COMMON
3522    </t>
3523    <t hangText="Restrictions on usage:">
3524      none
3525    </t>
3526    <t hangText="Author/Change controller:">
3527      IESG
3528    </t>
3529  </list>
3530</t>
3531</section>
3532</section>
3533
3534<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3535<t>
3536   The registration procedure for HTTP Transfer Codings is now defined by
3537   <xref target="transfer.coding.registry"/> of this document.
3538</t>
3539<t>
3540   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3541   should be updated with the registrations below:
3542</t>
3543<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3544   <ttcol>Name</ttcol>
3545   <ttcol>Description</ttcol>
3546   <ttcol>Reference</ttcol>
3547   <c>chunked</c>
3548   <c>Transfer in a series of chunks</c>
3549   <c>
3550      <xref target="chunked.encoding"/>
3551   </c>
3552   <c>compress</c>
3553   <c>UNIX "compress" program method</c>
3554   <c>
3555      <xref target="compress.coding"/>
3556   </c>
3557   <c>deflate</c>
3558   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3559   the "zlib" data format (<xref target="RFC1950"/>)
3560   </c>
3561   <c>
3562      <xref target="deflate.coding"/>
3563   </c>
3564   <c>gzip</c>
3565   <c>Same as GNU zip <xref target="RFC1952"/></c>
3566   <c>
3567      <xref target="gzip.coding"/>
3568   </c>
3569</texttable>
3570</section>
3571
3572<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3573<t>
3574   The registration procedure for HTTP Upgrade Tokens -- previously defined
3575   in <xref target="RFC2817" x:fmt="of" x:sec="7.2"/> -- is now defined
3576   by <xref target="upgrade.token.registry"/> of this document.
3577</t>
3578<t>
3579   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3580   should be updated with the registration below:
3581</t>
3582<texttable align="left" suppress-title="true">
3583   <ttcol>Value</ttcol>
3584   <ttcol>Description</ttcol>
3585   <ttcol>Reference</ttcol>
3586
3587   <c>HTTP</c>
3588   <c>Hypertext Transfer Protocol</c> 
3589   <c><xref target="http.version"/> of this specification</c>
3590<!-- IANA should add this without our instructions; emailed on June 05, 2009
3591   <c>TLS/1.0</c>
3592   <c>Transport Layer Security</c>
3593   <c><xref target="RFC2817"/></c> -->
3594
3595</texttable>
3596</section>
3597
3598</section>
3599
3600<section title="Security Considerations" anchor="security.considerations">
3601<t>
3602   This section is meant to inform application developers, information
3603   providers, and users of the security limitations in HTTP/1.1 as
3604   described by this document. The discussion does not include
3605   definitive solutions to the problems revealed, though it does make
3606   some suggestions for reducing security risks.
3607</t>
3608
3609<section title="Personal Information" anchor="personal.information">
3610<t>
3611   HTTP clients are often privy to large amounts of personal information
3612   (e.g., the user's name, location, mail address, passwords, encryption
3613   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3614   leakage of this information.
3615   We very strongly recommend that a convenient interface be provided
3616   for the user to control dissemination of such information, and that
3617   designers and implementors be particularly careful in this area.
3618   History shows that errors in this area often create serious security
3619   and/or privacy problems and generate highly adverse publicity for the
3620   implementor's company.
3621</t>
3622</section>
3623
3624<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3625<t>
3626   A server is in the position to save personal data about a user's
3627   requests which might identify their reading patterns or subjects of
3628   interest. This information is clearly confidential in nature and its
3629   handling can be constrained by law in certain countries. People using
3630   HTTP to provide data are responsible for ensuring that
3631   such material is not distributed without the permission of any
3632   individuals that are identifiable by the published results.
3633</t>
3634</section>
3635
3636<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3637<t>
3638   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3639   the documents returned by HTTP requests to be only those that were
3640   intended by the server administrators. If an HTTP server translates
3641   HTTP URIs directly into file system calls, the server &MUST; take
3642   special care not to serve files that were not intended to be
3643   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3644   other operating systems use ".." as a path component to indicate a
3645   directory level above the current one. On such a system, an HTTP
3646   server &MUST; disallow any such construct in the request-target if it
3647   would otherwise allow access to a resource outside those intended to
3648   be accessible via the HTTP server. Similarly, files intended for
3649   reference only internally to the server (such as access control
3650   files, configuration files, and script code) &MUST; be protected from
3651   inappropriate retrieval, since they might contain sensitive
3652   information. Experience has shown that minor bugs in such HTTP server
3653   implementations have turned into security risks.
3654</t>
3655</section>
3656
3657<section title="DNS Spoofing" anchor="dns.spoofing">
3658<t>
3659   Clients using HTTP rely heavily on the Domain Name Service, and are
3660   thus generally prone to security attacks based on the deliberate
3661   mis-association of IP addresses and DNS names. Clients need to be
3662   cautious in assuming the continuing validity of an IP number/DNS name
3663   association.
3664</t>
3665<t>
3666   In particular, HTTP clients &SHOULD; rely on their name resolver for
3667   confirmation of an IP number/DNS name association, rather than
3668   caching the result of previous host name lookups. Many platforms
3669   already can cache host name lookups locally when appropriate, and
3670   they &SHOULD; be configured to do so. It is proper for these lookups to
3671   be cached, however, only when the TTL (Time To Live) information
3672   reported by the name server makes it likely that the cached
3673   information will remain useful.
3674</t>
3675<t>
3676   If HTTP clients cache the results of host name lookups in order to
3677   achieve a performance improvement, they &MUST; observe the TTL
3678   information reported by DNS.
3679</t>
3680<t>
3681   If HTTP clients do not observe this rule, they could be spoofed when
3682   a previously-accessed server's IP address changes. As network
3683   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3684   possibility of this form of attack will grow. Observing this
3685   requirement thus reduces this potential security vulnerability.
3686</t>
3687<t>
3688   This requirement also improves the load-balancing behavior of clients
3689   for replicated servers using the same DNS name and reduces the
3690   likelihood of a user's experiencing failure in accessing sites which
3691   use that strategy.
3692</t>
3693</section>
3694
3695<section title="Proxies and Caching" anchor="attack.proxies">
3696<t>
3697   By their very nature, HTTP proxies are men-in-the-middle, and
3698   represent an opportunity for man-in-the-middle attacks. Compromise of
3699   the systems on which the proxies run can result in serious security
3700   and privacy problems. Proxies have access to security-related
3701   information, personal information about individual users and
3702   organizations, and proprietary information belonging to users and
3703   content providers. A compromised proxy, or a proxy implemented or
3704   configured without regard to security and privacy considerations,
3705   might be used in the commission of a wide range of potential attacks.
3706</t>
3707<t>
3708   Proxy operators should protect the systems on which proxies run as
3709   they would protect any system that contains or transports sensitive
3710   information. In particular, log information gathered at proxies often
3711   contains highly sensitive personal information, and/or information
3712   about organizations. Log information should be carefully guarded, and
3713   appropriate guidelines for use should be developed and followed.
3714   (<xref target="abuse.of.server.log.information"/>).
3715</t>
3716<t>
3717   Proxy implementors should consider the privacy and security
3718   implications of their design and coding decisions, and of the
3719   configuration options they provide to proxy operators (especially the
3720   default configuration).
3721</t>
3722<t>
3723   Users of a proxy need to be aware that proxies are no trustworthier than
3724   the people who run them; HTTP itself cannot solve this problem.
3725</t>
3726<t>
3727   The judicious use of cryptography, when appropriate, may suffice to
3728   protect against a broad range of security and privacy attacks. Such
3729   cryptography is beyond the scope of the HTTP/1.1 specification.
3730</t>
3731</section>
3732
3733<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3734<t>
3735   They exist. They are hard to defend against. Research continues.
3736   Beware.
3737</t>
3738</section>
3739</section>
3740
3741<section title="Acknowledgments" anchor="ack">
3742<t>
3743   HTTP has evolved considerably over the years. It has
3744   benefited from a large and active developer community--the many
3745   people who have participated on the www-talk mailing list--and it is
3746   that community which has been most responsible for the success of
3747   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3748   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3749   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3750   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3751   VanHeyningen deserve special recognition for their efforts in
3752   defining early aspects of the protocol.
3753</t>
3754<t>
3755   This document has benefited greatly from the comments of all those
3756   participating in the HTTP-WG. In addition to those already mentioned,
3757   the following individuals have contributed to this specification:
3758</t>
3759<t>
3760   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3761   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3762   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3763   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3764   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3765   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3766   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3767   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3768   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3769   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3770   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3771   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3772   Josh Cohen.
3773</t>
3774<t>
3775   Thanks to the "cave men" of Palo Alto. You know who you are.
3776</t>
3777<t>
3778   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3779   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3780   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3781   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3782   Larry Masinter for their help. And thanks go particularly to Jeff
3783   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3784</t>
3785<t>
3786   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3787   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3788   discovery of many of the problems that this document attempts to
3789   rectify.
3790</t>
3791<t>
3792   This specification makes heavy use of the augmented BNF and generic
3793   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3794   reuses many of the definitions provided by Nathaniel Borenstein and
3795   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3796   specification will help reduce past confusion over the relationship
3797   between HTTP and Internet mail message formats.
3798</t>
3799</section>
3800
3801</middle>
3802<back>
3803
3804<references title="Normative References">
3805
3806<reference anchor="ISO-8859-1">
3807  <front>
3808    <title>
3809     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3810    </title>
3811    <author>
3812      <organization>International Organization for Standardization</organization>
3813    </author>
3814    <date year="1998"/>
3815  </front>
3816  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3817</reference>
3818
3819<reference anchor="Part2">
3820  <front>
3821    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3822    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3823      <organization abbrev="Day Software">Day Software</organization>
3824      <address><email>fielding@gbiv.com</email></address>
3825    </author>
3826    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3827      <organization>One Laptop per Child</organization>
3828      <address><email>jg@laptop.org</email></address>
3829    </author>
3830    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3831      <organization abbrev="HP">Hewlett-Packard Company</organization>
3832      <address><email>JeffMogul@acm.org</email></address>
3833    </author>
3834    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3835      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3836      <address><email>henrikn@microsoft.com</email></address>
3837    </author>
3838    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3839      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3840      <address><email>LMM@acm.org</email></address>
3841    </author>
3842    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3843      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3844      <address><email>paulle@microsoft.com</email></address>
3845    </author>
3846    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3847      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3848      <address><email>timbl@w3.org</email></address>
3849    </author>
3850    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3851      <organization abbrev="W3C">World Wide Web Consortium</organization>
3852      <address><email>ylafon@w3.org</email></address>
3853    </author>
3854    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3855      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3856      <address><email>julian.reschke@greenbytes.de</email></address>
3857    </author>
3858    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3859  </front>
3860  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3861  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3862</reference>
3863
3864<reference anchor="Part3">
3865  <front>
3866    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3867    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3868      <organization abbrev="Day Software">Day Software</organization>
3869      <address><email>fielding@gbiv.com</email></address>
3870    </author>
3871    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3872      <organization>One Laptop per Child</organization>
3873      <address><email>jg@laptop.org</email></address>
3874    </author>
3875    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3876      <organization abbrev="HP">Hewlett-Packard Company</organization>
3877      <address><email>JeffMogul@acm.org</email></address>
3878    </author>
3879    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3880      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3881      <address><email>henrikn@microsoft.com</email></address>
3882    </author>
3883    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3884      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3885      <address><email>LMM@acm.org</email></address>
3886    </author>
3887    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3888      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3889      <address><email>paulle@microsoft.com</email></address>
3890    </author>
3891    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3892      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3893      <address><email>timbl@w3.org</email></address>
3894    </author>
3895    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3896      <organization abbrev="W3C">World Wide Web Consortium</organization>
3897      <address><email>ylafon@w3.org</email></address>
3898    </author>
3899    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3900      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3901      <address><email>julian.reschke@greenbytes.de</email></address>
3902    </author>
3903    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3904  </front>
3905  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3906  <x:source href="p3-payload.xml" basename="p3-payload"/>
3907</reference>
3908
3909<reference anchor="Part5">
3910  <front>
3911    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3912    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3913      <organization abbrev="Day Software">Day Software</organization>
3914      <address><email>fielding@gbiv.com</email></address>
3915    </author>
3916    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3917      <organization>One Laptop per Child</organization>
3918      <address><email>jg@laptop.org</email></address>
3919    </author>
3920    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3921      <organization abbrev="HP">Hewlett-Packard Company</organization>
3922      <address><email>JeffMogul@acm.org</email></address>
3923    </author>
3924    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3925      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3926      <address><email>henrikn@microsoft.com</email></address>
3927    </author>
3928    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3929      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3930      <address><email>LMM@acm.org</email></address>
3931    </author>
3932    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3933      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3934      <address><email>paulle@microsoft.com</email></address>
3935    </author>
3936    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3937      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3938      <address><email>timbl@w3.org</email></address>
3939    </author>
3940    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3941      <organization abbrev="W3C">World Wide Web Consortium</organization>
3942      <address><email>ylafon@w3.org</email></address>
3943    </author>
3944    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3945      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3946      <address><email>julian.reschke@greenbytes.de</email></address>
3947    </author>
3948    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3949  </front>
3950  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3951  <x:source href="p5-range.xml" basename="p5-range"/>
3952</reference>
3953
3954<reference anchor="Part6">
3955  <front>
3956    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3957    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3958      <organization abbrev="Day Software">Day Software</organization>
3959      <address><email>fielding@gbiv.com</email></address>
3960    </author>
3961    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3962      <organization>One Laptop per Child</organization>
3963      <address><email>jg@laptop.org</email></address>
3964    </author>
3965    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3966      <organization abbrev="HP">Hewlett-Packard Company</organization>
3967      <address><email>JeffMogul@acm.org</email></address>
3968    </author>
3969    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3970      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3971      <address><email>henrikn@microsoft.com</email></address>
3972    </author>
3973    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3974      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3975      <address><email>LMM@acm.org</email></address>
3976    </author>
3977    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3978      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3979      <address><email>paulle@microsoft.com</email></address>
3980    </author>
3981    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3982      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3983      <address><email>timbl@w3.org</email></address>
3984    </author>
3985    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3986      <organization abbrev="W3C">World Wide Web Consortium</organization>
3987      <address><email>ylafon@w3.org</email></address>
3988    </author>
3989    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3990      <address><email>mnot@mnot.net</email></address>
3991    </author>
3992    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3993      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3994      <address><email>julian.reschke@greenbytes.de</email></address>
3995    </author>
3996    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3997  </front>
3998  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3999  <x:source href="p6-cache.xml" basename="p6-cache"/>
4000</reference>
4001
4002<reference anchor="RFC5234">
4003  <front>
4004    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4005    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4006      <organization>Brandenburg InternetWorking</organization>
4007      <address>
4008        <email>dcrocker@bbiw.net</email>
4009      </address> 
4010    </author>
4011    <author initials="P." surname="Overell" fullname="Paul Overell">
4012      <organization>THUS plc.</organization>
4013      <address>
4014        <email>paul.overell@thus.net</email>
4015      </address>
4016    </author>
4017    <date month="January" year="2008"/>
4018  </front>
4019  <seriesInfo name="STD" value="68"/>
4020  <seriesInfo name="RFC" value="5234"/>
4021</reference>
4022
4023<reference anchor="RFC2119">
4024  <front>
4025    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4026    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4027      <organization>Harvard University</organization>
4028      <address><email>sob@harvard.edu</email></address>
4029    </author>
4030    <date month="March" year="1997"/>
4031  </front>
4032  <seriesInfo name="BCP" value="14"/>
4033  <seriesInfo name="RFC" value="2119"/>
4034</reference>
4035
4036<reference anchor="RFC3986">
4037 <front>
4038  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
4039  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
4040    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4041    <address>
4042       <email>timbl@w3.org</email>
4043       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4044    </address>
4045  </author>
4046  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
4047    <organization abbrev="Day Software">Day Software</organization>
4048    <address>
4049      <email>fielding@gbiv.com</email>
4050      <uri>http://roy.gbiv.com/</uri>
4051    </address>
4052  </author>
4053  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
4054    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4055    <address>
4056      <email>LMM@acm.org</email>
4057      <uri>http://larry.masinter.net/</uri>
4058    </address>
4059  </author>
4060  <date month='January' year='2005'></date>
4061 </front>
4062 <seriesInfo name="RFC" value="3986"/>
4063 <seriesInfo name="STD" value="66"/>
4064</reference>
4065
4066<reference anchor="USASCII">
4067  <front>
4068    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4069    <author>
4070      <organization>American National Standards Institute</organization>
4071    </author>
4072    <date year="1986"/>
4073  </front>
4074  <seriesInfo name="ANSI" value="X3.4"/>
4075</reference>
4076
4077<reference anchor="RFC1950">
4078  <front>
4079    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4080    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4081      <organization>Aladdin Enterprises</organization>
4082      <address><email>ghost@aladdin.com</email></address>
4083    </author>
4084    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4085    <date month="May" year="1996"/>
4086  </front>
4087  <seriesInfo name="RFC" value="1950"/>
4088  <annotation>
4089    RFC 1950 is an Informational RFC, thus it may be less stable than
4090    this specification. On the other hand, this downward reference was
4091    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4092    therefore it is unlikely to cause problems in practice. See also
4093    <xref target="BCP97"/>.
4094  </annotation>
4095</reference>
4096
4097<reference anchor="RFC1951">
4098  <front>
4099    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4100    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4101      <organization>Aladdin Enterprises</organization>
4102      <address><email>ghost@aladdin.com</email></address>
4103    </author>
4104    <date month="May" year="1996"/>
4105  </front>
4106  <seriesInfo name="RFC" value="1951"/>
4107  <annotation>
4108    RFC 1951 is an Informational RFC, thus it may be less stable than
4109    this specification. On the other hand, this downward reference was
4110    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4111    therefore it is unlikely to cause problems in practice. See also
4112    <xref target="BCP97"/>.
4113  </annotation>
4114</reference>
4115
4116<reference anchor="RFC1952">
4117  <front>
4118    <title>GZIP file format specification version 4.3</title>
4119    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4120      <organization>Aladdin Enterprises</organization>
4121      <address><email>ghost@aladdin.com</email></address>
4122    </author>
4123    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4124      <address><email>gzip@prep.ai.mit.edu</email></address>
4125    </author>
4126    <author initials="M." surname="Adler" fullname="Mark Adler">
4127      <address><email>madler@alumni.caltech.edu</email></address>
4128    </author>
4129    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4130      <address><email>ghost@aladdin.com</email></address>
4131    </author>
4132    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4133      <address><email>randeg@alumni.rpi.edu</email></address>
4134    </author>
4135    <date month="May" year="1996"/>
4136  </front>
4137  <seriesInfo name="RFC" value="1952"/>
4138  <annotation>
4139    RFC 1952 is an Informational RFC, thus it may be less stable than
4140    this specification. On the other hand, this downward reference was
4141    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4142    therefore it is unlikely to cause problems in practice. See also
4143    <xref target="BCP97"/>.
4144  </annotation>
4145</reference>
4146
4147</references>
4148
4149<references title="Informative References">
4150
4151<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4152  <front>
4153    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4154    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen"/>
4155    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4156    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4157    <author initials="H." surname="Lie" fullname="H. Lie"/>
4158    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4159    <date year="1997" month="September"/>
4160  </front>
4161  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4162</reference>
4163
4164<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4165  <front>
4166    <title>Improving HTTP Latency</title>
4167    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4168    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4169    <date year="1995" month="December"/>
4170  </front>
4171  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4172</reference>
4173
4174<reference anchor="RFC1123">
4175  <front>
4176    <title>Requirements for Internet Hosts - Application and Support</title>
4177    <author initials="R." surname="Braden" fullname="Robert Braden">
4178      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4179      <address><email>Braden@ISI.EDU</email></address>
4180    </author>
4181    <date month="October" year="1989"/>
4182  </front>
4183  <seriesInfo name="STD" value="3"/>
4184  <seriesInfo name="RFC" value="1123"/>
4185</reference>
4186
4187<reference anchor="RFC1305">
4188  <front>
4189    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4190    <author initials="D." surname="Mills" fullname="David L. Mills">
4191      <organization>University of Delaware, Electrical Engineering Department</organization>
4192      <address><email>mills@udel.edu</email></address>
4193    </author>
4194    <date month="March" year="1992"/>
4195  </front>
4196  <seriesInfo name="RFC" value="1305"/>
4197</reference>
4198
4199<reference anchor="RFC1900">
4200  <front>
4201    <title>Renumbering Needs Work</title>
4202    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4203      <organization>CERN, Computing and Networks Division</organization>
4204      <address><email>brian@dxcoms.cern.ch</email></address>
4205    </author>
4206    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4207      <organization>cisco Systems</organization>
4208      <address><email>yakov@cisco.com</email></address>
4209    </author>
4210    <date month="February" year="1996"/>
4211  </front>
4212  <seriesInfo name="RFC" value="1900"/>
4213</reference>
4214
4215<reference anchor="RFC1945">
4216  <front>
4217    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4218    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4219      <organization>MIT, Laboratory for Computer Science</organization>
4220      <address><email>timbl@w3.org</email></address>
4221    </author>
4222    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4223      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4224      <address><email>fielding@ics.uci.edu</email></address>
4225    </author>
4226    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4227      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4228      <address><email>frystyk@w3.org</email></address>
4229    </author>
4230    <date month="May" year="1996"/>
4231  </front>
4232  <seriesInfo name="RFC" value="1945"/>
4233</reference>
4234
4235<reference anchor="RFC2045">
4236  <front>
4237    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4238    <author initials="N." surname="Freed" fullname="Ned Freed">
4239      <organization>Innosoft International, Inc.</organization>
4240      <address><email>ned@innosoft.com</email></address>
4241    </author>
4242    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4243      <organization>First Virtual Holdings</organization>
4244      <address><email>nsb@nsb.fv.com</email></address>
4245    </author>
4246    <date month="November" year="1996"/>
4247  </front>
4248  <seriesInfo name="RFC" value="2045"/>
4249</reference>
4250
4251<reference anchor="RFC2047">
4252  <front>
4253    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4254    <author initials="K." surname="Moore" fullname="Keith Moore">
4255      <organization>University of Tennessee</organization>
4256      <address><email>moore@cs.utk.edu</email></address>
4257    </author>
4258    <date month="November" year="1996"/>
4259  </front>
4260  <seriesInfo name="RFC" value="2047"/>
4261</reference>
4262
4263<reference anchor="RFC2068">
4264  <front>
4265    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4266    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4267      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4268      <address><email>fielding@ics.uci.edu</email></address>
4269    </author>
4270    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4271      <organization>MIT Laboratory for Computer Science</organization>
4272      <address><email>jg@w3.org</email></address>
4273    </author>
4274    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4275      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4276      <address><email>mogul@wrl.dec.com</email></address>
4277    </author>
4278    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4279      <organization>MIT Laboratory for Computer Science</organization>
4280      <address><email>frystyk@w3.org</email></address>
4281    </author>
4282    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4283      <organization>MIT Laboratory for Computer Science</organization>
4284      <address><email>timbl@w3.org</email></address>
4285    </author>
4286    <date month="January" year="1997"/>
4287  </front>
4288  <seriesInfo name="RFC" value="2068"/>
4289</reference>
4290
4291<reference anchor='RFC2109'>
4292  <front>
4293    <title>HTTP State Management Mechanism</title>
4294    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
4295      <organization>Bell Laboratories, Lucent Technologies</organization>
4296      <address><email>dmk@bell-labs.com</email></address>
4297    </author>
4298    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4299      <organization>Netscape Communications Corp.</organization>
4300      <address><email>montulli@netscape.com</email></address>
4301    </author>
4302    <date year='1997' month='February' />
4303  </front>
4304  <seriesInfo name='RFC' value='2109' />
4305</reference>
4306
4307<reference anchor="RFC2145">
4308  <front>
4309    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4310    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4311      <organization>Western Research Laboratory</organization>
4312      <address><email>mogul@wrl.dec.com</email></address>
4313    </author>
4314    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4315      <organization>Department of Information and Computer Science</organization>
4316      <address><email>fielding@ics.uci.edu</email></address>
4317    </author>
4318    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4319      <organization>MIT Laboratory for Computer Science</organization>
4320      <address><email>jg@w3.org</email></address>
4321    </author>
4322    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4323      <organization>W3 Consortium</organization>
4324      <address><email>frystyk@w3.org</email></address>
4325    </author>
4326    <date month="May" year="1997"/>
4327  </front>
4328  <seriesInfo name="RFC" value="2145"/>
4329</reference>
4330
4331<reference anchor="RFC2616">
4332  <front>
4333    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4334    <author initials="R." surname="Fielding" fullname="R. Fielding">
4335      <organization>University of California, Irvine</organization>
4336      <address><email>fielding@ics.uci.edu</email></address>
4337    </author>
4338    <author initials="J." surname="Gettys" fullname="J. Gettys">
4339      <organization>W3C</organization>
4340      <address><email>jg@w3.org</email></address>
4341    </author>
4342    <author initials="J." surname="Mogul" fullname="J. Mogul">
4343      <organization>Compaq Computer Corporation</organization>
4344      <address><email>mogul@wrl.dec.com</email></address>
4345    </author>
4346    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4347      <organization>MIT Laboratory for Computer Science</organization>
4348      <address><email>frystyk@w3.org</email></address>
4349    </author>
4350    <author initials="L." surname="Masinter" fullname="L. Masinter">
4351      <organization>Xerox Corporation</organization>
4352      <address><email>masinter@parc.xerox.com</email></address>
4353    </author>
4354    <author initials="P." surname="Leach" fullname="P. Leach">
4355      <organization>Microsoft Corporation</organization>
4356      <address><email>paulle@microsoft.com</email></address>
4357    </author>
4358    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4359      <organization>W3C</organization>
4360      <address><email>timbl@w3.org</email></address>
4361    </author>
4362    <date month="June" year="1999"/>
4363  </front>
4364  <seriesInfo name="RFC" value="2616"/>
4365</reference>
4366
4367<reference anchor='RFC2817'>
4368  <front>
4369    <title>Upgrading to TLS Within HTTP/1.1</title>
4370    <author initials='R.' surname='Khare' fullname='R. Khare'>
4371      <organization>4K Associates / UC Irvine</organization>
4372      <address><email>rohit@4K-associates.com</email></address>
4373    </author>
4374    <author initials='S.' surname='Lawrence' fullname='S. Lawrence'>
4375      <organization>Agranat Systems, Inc.</organization>
4376      <address><email>lawrence@agranat.com</email></address>
4377    </author>
4378    <date year='2000' month='May' />
4379  </front>
4380  <seriesInfo name='RFC' value='2817' />
4381</reference>
4382
4383<reference anchor='RFC2818'>
4384  <front>
4385    <title>HTTP Over TLS</title>
4386    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
4387      <organization>RTFM, Inc.</organization>
4388      <address><email>ekr@rtfm.com</email></address>
4389    </author>
4390    <date year='2000' month='May' />
4391  </front>
4392  <seriesInfo name='RFC' value='2818' />
4393</reference>
4394
4395<reference anchor='RFC2965'>
4396  <front>
4397    <title>HTTP State Management Mechanism</title>
4398    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
4399      <organization>Bell Laboratories, Lucent Technologies</organization>
4400      <address><email>dmk@bell-labs.com</email></address>
4401    </author>
4402    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
4403      <organization>Epinions.com, Inc.</organization>
4404      <address><email>lou@montulli.org</email></address>
4405    </author>
4406    <date year='2000' month='October' />
4407  </front>
4408  <seriesInfo name='RFC' value='2965' />
4409</reference>
4410
4411<reference anchor='RFC3864'>
4412  <front>
4413    <title>Registration Procedures for Message Header Fields</title>
4414    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
4415      <organization>Nine by Nine</organization>
4416      <address><email>GK-IETF@ninebynine.org</email></address>
4417    </author>
4418    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
4419      <organization>BEA Systems</organization>
4420      <address><email>mnot@pobox.com</email></address>
4421    </author>
4422    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
4423      <organization>HP Labs</organization>
4424      <address><email>JeffMogul@acm.org</email></address>
4425    </author>
4426    <date year='2004' month='September' />
4427  </front>
4428  <seriesInfo name='BCP' value='90' />
4429  <seriesInfo name='RFC' value='3864' />
4430</reference>
4431
4432<reference anchor="RFC4288">
4433  <front>
4434    <title>Media Type Specifications and Registration Procedures</title>
4435    <author initials="N." surname="Freed" fullname="N. Freed">
4436      <organization>Sun Microsystems</organization>
4437      <address>
4438        <email>ned.freed@mrochek.com</email>
4439      </address>
4440    </author>
4441    <author initials="J." surname="Klensin" fullname="J. Klensin">
4442      <address>
4443        <email>klensin+ietf@jck.com</email>
4444      </address>
4445    </author>
4446    <date year="2005" month="December"/>
4447  </front>
4448  <seriesInfo name="BCP" value="13"/>
4449  <seriesInfo name="RFC" value="4288"/>
4450</reference>
4451
4452<reference anchor='RFC4395'>
4453  <front>
4454    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4455    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
4456      <organization>AT&amp;T Laboratories</organization>
4457      <address>
4458        <email>tony+urireg@maillennium.att.com</email>
4459      </address>
4460    </author>
4461    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
4462      <organization>Qualcomm, Inc.</organization>
4463      <address>
4464        <email>hardie@qualcomm.com</email>
4465      </address>
4466    </author>
4467    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
4468      <organization>Adobe Systems</organization>
4469      <address>
4470        <email>LMM@acm.org</email>
4471      </address>
4472    </author>
4473    <date year='2006' month='February' />
4474  </front>
4475  <seriesInfo name='BCP' value='115' />
4476  <seriesInfo name='RFC' value='4395' />
4477</reference>
4478
4479<reference anchor='RFC5226'>
4480  <front>
4481    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4482    <author initials='T.' surname='Narten' fullname='T. Narten'>
4483      <organization>IBM</organization>
4484      <address><email>narten@us.ibm.com</email></address>
4485    </author>
4486    <author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'>
4487      <organization>Google</organization>
4488      <address><email>Harald@Alvestrand.no</email></address>
4489    </author>
4490    <date year='2008' month='May' />
4491  </front>
4492  <seriesInfo name='BCP' value='26' />
4493  <seriesInfo name='RFC' value='5226' />
4494</reference>
4495
4496<reference anchor="RFC5322">
4497  <front>
4498    <title>Internet Message Format</title>
4499    <author initials="P." surname="Resnick" fullname="P. Resnick">
4500      <organization>Qualcomm Incorporated</organization>
4501    </author>
4502    <date year="2008" month="October"/>
4503  </front> 
4504  <seriesInfo name="RFC" value="5322"/>
4505</reference>
4506
4507<reference anchor='BCP97'>
4508  <front>
4509    <title>Handling Normative References to Standards-Track Documents</title>
4510    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4511      <address>
4512        <email>klensin+ietf@jck.com</email>
4513      </address>
4514    </author>
4515    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4516      <organization>MIT</organization>
4517      <address>
4518        <email>hartmans-ietf@mit.edu</email>
4519      </address>
4520    </author>
4521    <date year='2007' month='June' />
4522  </front>
4523  <seriesInfo name='BCP' value='97' />
4524  <seriesInfo name='RFC' value='4897' />
4525</reference>
4526
4527<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4528  <front>
4529    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4530    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4531    <date year="2001" month="November"/>
4532  </front>
4533  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4534</reference>
4535
4536<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4537  <front>
4538    <title>Analysis of HTTP Performance Problems</title>
4539    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4540    <date/>
4541  </front>
4542</reference>
4543
4544<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4545  <front>
4546  <title>Analysis of HTTP Performance</title>
4547  <author initials="J." surname="Touch" fullname="Joe Touch">
4548    <organization>USC/Information Sciences Institute</organization>
4549    <address><email>touch@isi.edu</email></address>
4550  </author>
4551  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4552    <organization>USC/Information Sciences Institute</organization>
4553    <address><email>johnh@isi.edu</email></address>
4554  </author>
4555  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4556    <organization>USC/Information Sciences Institute</organization>
4557    <address><email>katia@isi.edu</email></address>
4558  </author>
4559  <date year="1998" month="Aug"/>
4560  </front>
4561  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4562  <annotation>(original report dated Aug. 1996)</annotation>
4563</reference>
4564
4565</references>
4566
4567
4568<section title="Tolerant Applications" anchor="tolerant.applications">
4569<t>
4570   Although this document specifies the requirements for the generation
4571   of HTTP/1.1 messages, not all applications will be correct in their
4572   implementation. We therefore recommend that operational applications
4573   be tolerant of deviations whenever those deviations can be
4574   interpreted unambiguously.
4575</t>
4576<t>
4577   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
4578   &SHOULD; be tolerant when parsing the Request-Line. In particular, they
4579   &SHOULD; accept any amount of WSP characters between fields, even though
4580   only a single SP is required.
4581</t>
4582<t>
4583   The line terminator for header fields is the sequence CRLF.
4584   However, we recommend that applications, when parsing such headers,
4585   recognize a single LF as a line terminator and ignore the leading CR.
4586</t>
4587<t>
4588   The character set of an entity-body &SHOULD; be labeled as the lowest
4589   common denominator of the character codes used within that body, with
4590   the exception that not labeling the entity is preferred over labeling
4591   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
4592</t>
4593<t>
4594   Additional rules for requirements on parsing and encoding of dates
4595   and other potential problems with date encodings include:
4596</t>
4597<t>
4598  <list style="symbols">
4599     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
4600        which appears to be more than 50 years in the future is in fact
4601        in the past (this helps solve the "year 2000" problem).</t>
4602
4603     <t>Although all date formats are specified to be case-sensitive,
4604        recipients &SHOULD; match day, week and timezone names
4605        case-insensitively.</t>
4606             
4607     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
4608        Expires date as earlier than the proper value, but &MUST-NOT;
4609        internally represent a parsed Expires date as later than the
4610        proper value.</t>
4611
4612     <t>All expiration-related calculations &MUST; be done in GMT. The
4613        local time zone &MUST-NOT; influence the calculation or comparison
4614        of an age or expiration time.</t>
4615
4616     <t>If an HTTP header incorrectly carries a date value with a time
4617        zone other than GMT, it &MUST; be converted into GMT using the
4618        most conservative possible conversion.</t>
4619  </list>
4620</t>
4621</section>
4622
4623<section title="Compatibility with Previous Versions" anchor="compatibility">
4624<t>
4625   HTTP has been in use by the World-Wide Web global information initiative
4626   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4627   was a simple protocol for hypertext data transfer across the Internet
4628   with only a single method and no metadata.
4629   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4630   methods and MIME-like messaging that could include metadata about the data
4631   transferred and modifiers on the request/response semantics. However,
4632   HTTP/1.0 did not sufficiently take into consideration the effects of
4633   hierarchical proxies, caching, the need for persistent connections, or
4634   name-based virtual hosts. The proliferation of incompletely-implemented
4635   applications calling themselves "HTTP/1.0" further necessitated a
4636   protocol version change in order for two communicating applications
4637   to determine each other's true capabilities.
4638</t>
4639<t>
4640   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4641   requirements that enable reliable implementations, adding only
4642   those new features that will either be safely ignored by an HTTP/1.0
4643   recipient or only sent when communicating with a party advertising
4644   compliance with HTTP/1.1.
4645</t>
4646<t>
4647   It is beyond the scope of a protocol specification to mandate
4648   compliance with previous versions. HTTP/1.1 was deliberately
4649   designed, however, to make supporting previous versions easy. It is
4650   worth noting that, at the time of composing this specification, we would
4651   expect general-purpose HTTP/1.1 servers to:
4652  <list style="symbols">
4653     <t>understand any valid request in the format of HTTP/1.0 and
4654        1.1;</t>
4655
4656     <t>respond appropriately with a message in the same major version
4657        used by the client.</t>
4658  </list>
4659</t>
4660<t>
4661   And we would expect HTTP/1.1 clients to:
4662  <list style="symbols">
4663     <t>understand any valid response in the format of HTTP/1.0 or
4664        1.1.</t>
4665  </list>
4666</t>
4667<t>
4668   For most implementations of HTTP/1.0, each connection is established
4669   by the client prior to the request and closed by the server after
4670   sending the response. Some implementations implement the Keep-Alive
4671   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4672</t>
4673
4674<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4675<t>
4676   This section summarizes major differences between versions HTTP/1.0
4677   and HTTP/1.1.
4678</t>
4679
4680<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">
4681<t>
4682   The requirements that clients and servers support the Host request-header,
4683   report an error if the Host request-header (<xref target="header.host"/>) is
4684   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4685   are among the most important changes defined by this
4686   specification.
4687</t>
4688<t>
4689   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4690   addresses and servers; there was no other established mechanism for
4691   distinguishing the intended server of a request than the IP address
4692   to which that request was directed. The changes outlined above will
4693   allow the Internet, once older HTTP clients are no longer common, to
4694   support multiple Web sites from a single IP address, greatly
4695   simplifying large operational Web servers, where allocation of many
4696   IP addresses to a single host has created serious problems. The
4697   Internet will also be able to recover the IP addresses that have been
4698   allocated for the sole purpose of allowing special-purpose domain
4699   names to be used in root-level HTTP URLs. Given the rate of growth of
4700   the Web, and the number of servers already deployed, it is extremely
4701   important that all implementations of HTTP (including updates to
4702   existing HTTP/1.0 applications) correctly implement these
4703   requirements:
4704  <list style="symbols">
4705     <t>Both clients and servers &MUST; support the Host request-header.</t>
4706
4707     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4708
4709     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4710        request does not include a Host request-header.</t>
4711
4712     <t>Servers &MUST; accept absolute URIs.</t>
4713  </list>
4714</t>
4715</section>
4716</section>
4717
4718<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4719<t>
4720   Some clients and servers might wish to be compatible with some
4721   previous implementations of persistent connections in HTTP/1.0
4722   clients and servers. Persistent connections in HTTP/1.0 are
4723   explicitly negotiated as they are not the default behavior. HTTP/1.0
4724   experimental implementations of persistent connections are faulty,
4725   and the new facilities in HTTP/1.1 are designed to rectify these
4726   problems. The problem was that some existing HTTP/1.0 clients may be
4727   sending Keep-Alive to a proxy server that doesn't understand
4728   Connection, which would then erroneously forward it to the next
4729   inbound server, which would establish the Keep-Alive connection and
4730   result in a hung HTTP/1.0 proxy waiting for the close on the
4731   response. The result is that HTTP/1.0 clients must be prevented from
4732   using Keep-Alive when talking to proxies.
4733</t>
4734<t>
4735   However, talking to proxies is the most important use of persistent
4736   connections, so that prohibition is clearly unacceptable. Therefore,
4737   we need some other mechanism for indicating a persistent connection
4738   is desired, which is safe to use even when talking to an old proxy
4739   that ignores Connection. Persistent connections are the default for
4740   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4741   declaring non-persistence. See <xref target="header.connection"/>.
4742</t>
4743<t>
4744   The original HTTP/1.0 form of persistent connections (the Connection:
4745   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4746</t>
4747</section>
4748
4749<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4750<t>
4751   This specification has been carefully audited to correct and
4752   disambiguate key word usage; RFC 2068 had many problems in respect to
4753   the conventions laid out in <xref target="RFC2119"/>.
4754</t>
4755<t>
4756   Transfer-coding and message lengths all interact in ways that
4757   required fixing exactly when chunked encoding is used (to allow for
4758   transfer encoding that may not be self delimiting); it was important
4759   to straighten out exactly how message lengths are computed. (Sections
4760   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4761   <xref target="header.content-length" format="counter"/>,
4762   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4763</t>
4764<t>
4765   The use and interpretation of HTTP version numbers has been clarified
4766   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4767   version they support to deal with problems discovered in HTTP/1.0
4768   implementations (<xref target="http.version"/>)
4769</t>
4770<t>
4771   Quality Values of zero should indicate that "I don't want something"
4772   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4773</t>
4774<t>
4775   Transfer-coding had significant problems, particularly with
4776   interactions with chunked encoding. The solution is that transfer-codings
4777   become as full fledged as content-codings. This involves
4778   adding an IANA registry for transfer-codings (separate from content
4779   codings), a new header field (TE) and enabling trailer headers in the
4780   future. Transfer encoding is a major performance benefit, so it was
4781   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4782   interoperability problem that could have occurred due to interactions
4783   between authentication trailers, chunked encoding and HTTP/1.0
4784   clients.(Section
4785   <xref target="transfer.codings" format="counter"/>,
4786   <xref target="chunked.encoding" format="counter"/>,
4787   <xref target="non-modifiable.headers" format="counter"/>,
4788   and <xref target="header.te" format="counter"/>)
4789</t>
4790<t>
4791  Proxies should be able to add Content-Length when appropriate.
4792  (<xref target="non-modifiable.headers"/>)
4793</t>
4794</section>
4795
4796<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4797<t>
4798  Empty list elements in list productions have been deprecated.
4799  (<xref target="notation.abnf"/>)
4800</t>
4801<t>
4802  Rules about implicit linear whitespace between certain grammar productions
4803  have been removed; now it's only allowed when specifically pointed out
4804  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4805  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4806  Non-ASCII content in header fields and reason phrase has been obsoleted and
4807  made opaque (the TEXT rule was removed)
4808  (<xref target="basic.rules"/>)
4809</t>
4810<t>
4811  Clarify that HTTP-Version is case sensitive.
4812  (<xref target="http.version"/>)
4813</t>
4814<t>
4815  Remove reference to non-existent identity transfer-coding value tokens.
4816  (Sections <xref format="counter" target="transfer.codings"/> and
4817  <xref format="counter" target="message.length"/>)
4818</t>
4819<t>
4820  Require that invalid whitespace around field-names be rejected.
4821  (<xref target="header.fields"/>)
4822</t>
4823<t>
4824  Update use of abs_path production from RFC1808 to the path-absolute + query
4825  components of RFC3986.
4826  (<xref target="request-target"/>)
4827</t>
4828<t>
4829  Clarification that the chunk length does not include the count of the octets
4830  in the chunk header and trailer. Furthermore disallowed line folding
4831  in chunk extensions.
4832  (<xref target="chunked.encoding"/>)
4833</t>
4834<t>
4835  Remove hard limit of two connections per server.
4836  (<xref target="persistent.practical"/>)
4837</t>
4838<t>
4839  Clarify exactly when close connection options must be sent.
4840  (<xref target="header.connection"/>)
4841</t>
4842</section>
4843</section>
4844
4845<?BEGININC p1-messaging.abnf-appendix ?>
4846<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4847<figure>
4848<artwork type="abnf" name="p1-messaging.parsed-abnf">
4849<x:ref>BWS</x:ref> = OWS
4850
4851<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4852<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4853<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4854<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4855 connection-token ] )
4856<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4857<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4858
4859<x:ref>Date</x:ref> = "Date:" OWS Date-v
4860<x:ref>Date-v</x:ref> = HTTP-date
4861
4862<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4863
4864<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4865<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4866<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4867<x:ref>HTTP-message</x:ref> = start-line *( header-field CRLF ) CRLF [ message-body
4868 ]
4869<x:ref>Host</x:ref> = "Host:" OWS Host-v
4870<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4871
4872<x:ref>Method</x:ref> = token
4873
4874<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4875
4876<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4877
4878<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4879<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4880<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4881 entity-header ) CRLF ) CRLF [ message-body ]
4882<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4883<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4884 entity-header ) CRLF ) CRLF [ message-body ]
4885
4886<x:ref>Status-Code</x:ref> = 3DIGIT
4887<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4888
4889<x:ref>TE</x:ref> = "TE:" OWS TE-v
4890<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4891<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4892<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4893<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4894<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4895 transfer-coding ] )
4896
4897<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4898<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4899<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4900
4901<x:ref>Via</x:ref> = "Via:" OWS Via-v
4902<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4903 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4904 ] )
4905
4906<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4907
4908<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4909<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4910<x:ref>attribute</x:ref> = token
4911<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4912
4913<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4914<x:ref>chunk-data</x:ref> = 1*OCTET
4915<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4916<x:ref>chunk-ext-name</x:ref> = token
4917<x:ref>chunk-ext-val</x:ref> = token / quoted-str-nf
4918<x:ref>chunk-size</x:ref> = 1*HEXDIG
4919<x:ref>comment</x:ref> = "(" *( ctext / quoted-cpair / comment ) ")"
4920<x:ref>connection-token</x:ref> = token
4921<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4922 / %x2A-5B ; '*'-'['
4923 / %x5D-7E ; ']'-'~'
4924 / obs-text
4925
4926<x:ref>date1</x:ref> = day SP month SP year
4927<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4928<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4929<x:ref>day</x:ref> = 2DIGIT
4930<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4931 / %x54.75.65 ; Tue
4932 / %x57.65.64 ; Wed
4933 / %x54.68.75 ; Thu
4934 / %x46.72.69 ; Fri
4935 / %x53.61.74 ; Sat
4936 / %x53.75.6E ; Sun
4937<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4938 / %x54.75.65.73.64.61.79 ; Tuesday
4939 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4940 / %x54.68.75.72.73.64.61.79 ; Thursday
4941 / %x46.72.69.64.61.79 ; Friday
4942 / %x53.61.74.75.72.64.61.79 ; Saturday
4943 / %x53.75.6E.64.61.79 ; Sunday
4944
4945<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4946<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4947
4948<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4949<x:ref>field-name</x:ref> = token
4950<x:ref>field-value</x:ref> = *( field-content / OWS )
4951
4952<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4953 / Transfer-Encoding / Upgrade / Via / Warning
4954
4955<x:ref>header-field</x:ref> = field-name ":" OWS [ field-value ] OWS
4956<x:ref>hour</x:ref> = 2DIGIT
4957<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4958<x:ref>https-URI</x:ref> = "https://" authority path-abempty [ "?" query ]
4959
4960<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4961
4962<x:ref>message-body</x:ref> = entity-body /
4963 &lt;entity-body encoded as per Transfer-Encoding&gt;
4964<x:ref>minute</x:ref> = 2DIGIT
4965<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4966 / %x46.65.62 ; Feb
4967 / %x4D.61.72 ; Mar
4968 / %x41.70.72 ; Apr
4969 / %x4D.61.79 ; May
4970 / %x4A.75.6E ; Jun
4971 / %x4A.75.6C ; Jul
4972 / %x41.75.67 ; Aug
4973 / %x53.65.70 ; Sep
4974 / %x4F.63.74 ; Oct
4975 / %x4E.6F.76 ; Nov
4976 / %x44.65.63 ; Dec
4977
4978<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4979<x:ref>obs-fold</x:ref> = CRLF
4980<x:ref>obs-text</x:ref> = %x80-FF
4981
4982<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4983<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4984<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4985<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4986<x:ref>product</x:ref> = token [ "/" product-version ]
4987<x:ref>product-version</x:ref> = token
4988<x:ref>protocol-name</x:ref> = token
4989<x:ref>protocol-version</x:ref> = token
4990<x:ref>pseudonym</x:ref> = token
4991
4992<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4993 / %x5D-7E ; ']'-'~'
4994 / obs-text
4995<x:ref>qdtext-nf</x:ref> = WSP / "!" / %x23-5B ; '#'-'['
4996 / %x5D-7E ; ']'-'~'
4997 / obs-text
4998<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4999<x:ref>quoted-cpair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5000<x:ref>quoted-pair</x:ref> = "\" ( WSP / VCHAR / obs-text )
5001<x:ref>quoted-str-nf</x:ref> = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5002<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5003<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5004
5005<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
5006<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
5007<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
5008<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
5009<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5010 / authority
5011<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
5012<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
5013<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
5014
5015<x:ref>second</x:ref> = 2DIGIT
5016<x:ref>special</x:ref> = "(" / ")" / "&lt;" / "&gt;" / "@" / "," / ";" / ":" / "\" /
5017 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5018<x:ref>start-line</x:ref> = Request-Line / Status-Line
5019
5020<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
5021<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
5022 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5023<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" word ]
5024<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
5025<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
5026<x:ref>token</x:ref> = 1*tchar
5027<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
5028<x:ref>transfer-coding</x:ref> = "chunked" / "compress" / "deflate" / "gzip" /
5029 transfer-extension
5030<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS transfer-parameter )
5031<x:ref>transfer-parameter</x:ref> = attribute BWS "=" BWS value
5032
5033<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
5034
5035<x:ref>value</x:ref> = word
5036
5037<x:ref>word</x:ref> = token / quoted-string
5038
5039<x:ref>year</x:ref> = 4DIGIT
5040</artwork>
5041</figure>
5042<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
5043; Chunked-Body defined but not used
5044; Content-Length defined but not used
5045; HTTP-message defined but not used
5046; Host defined but not used
5047; Request defined but not used
5048; Response defined but not used
5049; TE defined but not used
5050; URI-reference defined but not used
5051; http-URI defined but not used
5052; https-URI defined but not used
5053; partial-URI defined but not used
5054; special defined but not used
5055</artwork></figure></section>
5056<?ENDINC p1-messaging.abnf-appendix ?>
5057
5058<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5059
5060<section title="Since RFC2616">
5061<t>
5062  Extracted relevant partitions from <xref target="RFC2616"/>.
5063</t>
5064</section>
5065
5066<section title="Since draft-ietf-httpbis-p1-messaging-00">
5067<t>
5068  Closed issues:
5069  <list style="symbols"> 
5070    <t>
5071      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5072      "HTTP Version should be case sensitive"
5073      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5074    </t>
5075    <t>
5076      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5077      "'unsafe' characters"
5078      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5079    </t>
5080    <t>
5081      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5082      "Chunk Size Definition"
5083      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5084    </t>
5085    <t>
5086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5087      "Message Length"
5088      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5089    </t>
5090    <t>
5091      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5092      "Media Type Registrations"
5093      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5094    </t>
5095    <t>
5096      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5097      "URI includes query"
5098      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5099    </t>
5100    <t>
5101      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5102      "No close on 1xx responses"
5103      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5104    </t>
5105    <t>
5106      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5107      "Remove 'identity' token references"
5108      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5109    </t>
5110    <t>
5111      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5112      "Import query BNF"
5113    </t>
5114    <t>
5115      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5116      "qdtext BNF"
5117    </t>
5118    <t>
5119      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5120      "Normative and Informative references"
5121    </t>
5122    <t>
5123      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5124      "RFC2606 Compliance"
5125    </t>
5126    <t>
5127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5128      "RFC977 reference"
5129    </t>
5130    <t>
5131      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5132      "RFC1700 references"
5133    </t>
5134    <t>
5135      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5136      "inconsistency in date format explanation"
5137    </t>
5138    <t>
5139      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5140      "Date reference typo"
5141    </t>
5142    <t>
5143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5144      "Informative references"
5145    </t>
5146    <t>
5147      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5148      "ISO-8859-1 Reference"
5149    </t>
5150    <t>
5151      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5152      "Normative up-to-date references"
5153    </t>
5154  </list>
5155</t>
5156<t>
5157  Other changes:
5158  <list style="symbols"> 
5159    <t>
5160      Update media type registrations to use RFC4288 template.
5161    </t>
5162    <t>
5163      Use names of RFC4234 core rules DQUOTE and WSP,
5164      fix broken ABNF for chunk-data
5165      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5166    </t>
5167  </list>
5168</t>
5169</section>
5170
5171<section title="Since draft-ietf-httpbis-p1-messaging-01">
5172<t>
5173  Closed issues:
5174  <list style="symbols"> 
5175    <t>
5176      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5177      "Bodies on GET (and other) requests"
5178    </t>
5179    <t>
5180      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5181      "Updating to RFC4288"
5182    </t>
5183    <t>
5184      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5185      "Status Code and Reason Phrase"
5186    </t>
5187    <t>
5188      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5189      "rel_path not used"
5190    </t>
5191  </list>
5192</t>
5193<t>
5194  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5195  <list style="symbols"> 
5196    <t>
5197      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
5198      "trailer-part").
5199    </t>
5200    <t>
5201      Avoid underscore character in rule names ("http_URL" ->
5202      "http-URL", "abs_path" -> "path-absolute").
5203    </t>
5204    <t>
5205      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5206      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5207      have to be updated when switching over to RFC3986.
5208    </t>
5209    <t>
5210      Synchronize core rules with RFC5234.
5211    </t>
5212    <t>
5213      Get rid of prose rules that span multiple lines.
5214    </t>
5215    <t>
5216      Get rid of unused rules LOALPHA and UPALPHA.
5217    </t>
5218    <t>
5219      Move "Product Tokens" section (back) into Part 1, as "token" is used
5220      in the definition of the Upgrade header.
5221    </t>
5222    <t>
5223      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5224    </t>
5225    <t>
5226      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5227    </t>
5228  </list>
5229</t>
5230</section>
5231
5232<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5233<t>
5234  Closed issues:
5235  <list style="symbols"> 
5236    <t>
5237      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5238      "HTTP-date vs. rfc1123-date"
5239    </t>
5240    <t>
5241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5242      "WS in quoted-pair"
5243    </t>
5244  </list>
5245</t>
5246<t>
5247  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5248  <list style="symbols"> 
5249    <t>
5250      Reference RFC 3984, and update header registrations for headers defined
5251      in this document.
5252    </t>
5253  </list>
5254</t>
5255<t>
5256  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5257  <list style="symbols"> 
5258    <t>
5259      Replace string literals when the string really is case-sensitive (HTTP-Version).
5260    </t>
5261  </list>
5262</t>
5263</section>
5264
5265<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5266<t>
5267  Closed issues:
5268  <list style="symbols"> 
5269    <t>
5270      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5271      "Connection closing"
5272    </t>
5273    <t>
5274      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5275      "Move registrations and registry information to IANA Considerations"
5276    </t>
5277    <t>
5278      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5279      "need new URL for PAD1995 reference"
5280    </t>
5281    <t>
5282      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5283      "IANA Considerations: update HTTP URI scheme registration"
5284    </t>
5285    <t>
5286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5287      "Cite HTTPS URI scheme definition"
5288    </t>
5289    <t>
5290      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5291      "List-type headers vs Set-Cookie"
5292    </t>
5293  </list>
5294</t>
5295<t>
5296  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5297  <list style="symbols"> 
5298    <t>
5299      Replace string literals when the string really is case-sensitive (HTTP-Date).
5300    </t>
5301    <t>
5302      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5303    </t>
5304  </list>
5305</t>
5306</section>
5307
5308<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5309<t>
5310  Closed issues:
5311  <list style="symbols"> 
5312    <t>
5313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5314      "Out-of-date reference for URIs"
5315    </t>
5316    <t>
5317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5318      "RFC 2822 is updated by RFC 5322"
5319    </t>
5320  </list>
5321</t>
5322<t>
5323  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5324  <list style="symbols"> 
5325    <t>
5326      Use "/" instead of "|" for alternatives.
5327    </t>
5328    <t>
5329      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5330    </t>
5331    <t>
5332      Only reference RFC 5234's core rules.
5333    </t>
5334    <t>
5335      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5336      whitespace ("OWS") and required whitespace ("RWS").
5337    </t>
5338    <t>
5339      Rewrite ABNFs to spell out whitespace rules, factor out
5340      header value format definitions.
5341    </t>
5342  </list>
5343</t>
5344</section>
5345
5346<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5347<t>
5348  Closed issues:
5349  <list style="symbols"> 
5350    <t>
5351      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5352      "Header LWS"
5353    </t>
5354    <t>
5355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5356      "Sort 1.3 Terminology"
5357    </t>
5358    <t>
5359      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5360      "RFC2047 encoded words"
5361    </t>
5362    <t>
5363      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5364      "Character Encodings in TEXT"
5365    </t>
5366    <t>
5367      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5368      "Line Folding"
5369    </t>
5370    <t>
5371      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5372      "OPTIONS * and proxies"
5373    </t>
5374    <t>
5375      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5376      "Reason-Phrase BNF"
5377    </t>
5378    <t>
5379      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5380      "Use of TEXT"
5381    </t>
5382    <t>
5383      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5384      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5385    </t>
5386    <t>
5387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5388      "RFC822 reference left in discussion of date formats"
5389    </t>
5390  </list>
5391</t>
5392<t>
5393  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5394  <list style="symbols"> 
5395    <t>
5396      Rewrite definition of list rules, deprecate empty list elements.
5397    </t>
5398    <t>
5399      Add appendix containing collected and expanded ABNF.
5400    </t>
5401  </list>
5402</t>
5403<t>
5404  Other changes:
5405  <list style="symbols"> 
5406    <t>
5407      Rewrite introduction; add mostly new Architecture Section.
5408    </t>
5409    <t>
5410      Move definition of quality values from Part 3 into Part 1;
5411      make TE request header grammar independent of accept-params (defined in Part 3).
5412    </t>
5413  </list>
5414</t>
5415</section>
5416
5417<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5418<t>
5419  Closed issues:
5420  <list style="symbols"> 
5421    <t>
5422      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5423      "base for numeric protocol elements"
5424    </t>
5425    <t>
5426      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5427      "comment ABNF"
5428    </t>
5429  </list>
5430</t>
5431<t>
5432  Partly resolved issues:
5433  <list style="symbols"> 
5434    <t>
5435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5436      "205 Bodies" (took out language that implied that there may be
5437      methods for which a request body MUST NOT be included)
5438    </t>
5439    <t>
5440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5441      "editorial improvements around HTTP-date"
5442    </t>
5443  </list>
5444</t>
5445</section>
5446
5447<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5448<t>
5449  Closed issues:
5450  <list style="symbols"> 
5451    <t>
5452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5453      "Repeating single-value headers"
5454    </t>
5455    <t>
5456      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5457      "increase connection limit"
5458    </t>
5459    <t>
5460      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5461      "IP addresses in URLs"
5462    </t>
5463    <t>
5464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5465      "take over HTTP Upgrade Token Registry"
5466    </t>
5467    <t>
5468      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5469      "CR and LF in chunk extension values"
5470    </t>
5471    <t>
5472      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5473      "HTTP/0.9 support"
5474    </t>
5475    <t>
5476      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5477      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5478    </t>
5479    <t>
5480      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5481      "move definitions of gzip/deflate/compress to part 1"
5482    </t>
5483    <t>
5484      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5485      "disallow control characters in quoted-pair"
5486    </t>
5487  </list>
5488</t>
5489<t>
5490  Partly resolved issues:
5491  <list style="symbols"> 
5492    <t>
5493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5494      "update IANA requirements wrt Transfer-Coding values" (add the
5495      IANA Considerations subsection)
5496    </t>
5497  </list>
5498</t>
5499</section>
5500
5501<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5502<t>
5503  Closed issues:
5504  <list style="symbols"> 
5505    <t>
5506      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5507      "header parsing, treatment of leading and trailing OWS"
5508    </t>
5509  </list>
5510</t>
5511<t>
5512  Partly resolved issues:
5513  <list style="symbols"> 
5514    <t>
5515      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5516      "Placement of 13.5.1 and 13.5.2"
5517    </t>
5518    <t>
5519      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5520      "use of term "word" when talking about header structure"
5521    </t>
5522  </list>
5523</t>
5524</section>
5525
5526<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5527<t>
5528  Closed issues:
5529  <list style="symbols"> 
5530    <t>
5531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5532      "Clarification of the term 'deflate'"
5533    </t>
5534    <t>
5535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5536      "IANA registry for content/transfer encodings"
5537    </t>
5538    <t>
5539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5540      "Case-sensitivity of HTTP-date"
5541    </t>
5542    <t>
5543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5544      "use of term "word" when talking about header structure"
5545    </t>
5546  </list>
5547</t>
5548</section>
5549
5550</section>
5551
5552</back>
5553</rfc>
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