source: draft-ietf-httpbis/latest/p1-messaging.xml @ 922

Last change on this file since 922 was 922, checked in by julian.reschke@…, 9 years ago

remove unused reference

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