source: draft-ietf-httpbis/latest/p1-messaging.xml @ 423

Last change on this file since 423 was 423, checked in by julian.reschke@…, 11 years ago

make reason phrase for 414 consistent again (related to #34)

  • Property svn:eol-style set to native
File size: 210.3 KB
Line 
1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "November">
16  <!ENTITY ID-YEAR "2008">
17  <!ENTITY caching                "<xref target='Part6' x:rel='#caching' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
18  <!ENTITY payload                "<xref target='Part3' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
19  <!ENTITY media-types            "<xref target='Part3' x:rel='#media.types' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
20  <!ENTITY content-codings        "<xref target='Part3' x:rel='#content.codings' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
21  <!ENTITY CONNECT                "<xref target='Part2' x:rel='#CONNECT' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
22  <!ENTITY content.negotiation    "<xref target='Part3' x:rel='#content.negotiation' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
23  <!ENTITY diff2045entity         "<xref target='Part3' x:rel='#differences.between.http.entities.and.rfc.2045.entities' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
24  <!ENTITY entity                 "<xref target='Part3' x:rel='#entity' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
25  <!ENTITY entity-body            "<xref target='Part3' x:rel='#entity.body' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
26  <!ENTITY entity-header-fields   "<xref target='Part3' x:rel='#entity.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
27  <!ENTITY header-accept          "<xref target='Part3' x:rel='#header.accept' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY qvalue                 "<xref target='Part3' x:rel='#quality.values' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
40  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
41]>
42<?rfc toc="yes" ?>
43<?rfc symrefs="yes" ?>
44<?rfc sortrefs="yes" ?>
45<?rfc compact="yes"?>
46<?rfc subcompact="no" ?>
47<?rfc linkmailto="no" ?>
48<?rfc editing="no" ?>
49<?rfc comments="yes"?>
50<?rfc inline="yes"?>
51<?rfc-ext allow-markup-in-artwork="yes" ?>
52<?rfc-ext include-references-in-index="yes" ?>
53<rfc obsoletes="2616" category="std" x:maturity-level="draft"
54     ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
55     xmlns:x='http://purl.org/net/xml2rfc/ext'>
56<front>
57
58  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
59
60  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
61    <organization abbrev="Day Software">Day Software</organization>
62    <address>
63      <postal>
64        <street>23 Corporate Plaza DR, Suite 280</street>
65        <city>Newport Beach</city>
66        <region>CA</region>
67        <code>92660</code>
68        <country>USA</country>
69      </postal>
70      <phone>+1-949-706-5300</phone>
71      <facsimile>+1-949-706-5305</facsimile>
72      <email>fielding@gbiv.com</email>
73      <uri>http://roy.gbiv.com/</uri>
74    </address>
75  </author>
76
77  <author initials="J." surname="Gettys" fullname="Jim Gettys">
78    <organization>One Laptop per Child</organization>
79    <address>
80      <postal>
81        <street>21 Oak Knoll Road</street>
82        <city>Carlisle</city>
83        <region>MA</region>
84        <code>01741</code>
85        <country>USA</country>
86      </postal>
87      <email>jg@laptop.org</email>
88      <uri>http://www.laptop.org/</uri>
89    </address>
90  </author>
91 
92  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
93    <organization abbrev="HP">Hewlett-Packard Company</organization>
94    <address>
95      <postal>
96        <street>HP Labs, Large Scale Systems Group</street>
97        <street>1501 Page Mill Road, MS 1177</street>
98        <city>Palo Alto</city>
99        <region>CA</region>
100        <code>94304</code>
101        <country>USA</country>
102      </postal>
103      <email>JeffMogul@acm.org</email>
104    </address>
105  </author>
106
107  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
108    <organization abbrev="Microsoft">Microsoft Corporation</organization>
109    <address>
110      <postal>
111        <street>1 Microsoft Way</street>
112        <city>Redmond</city>
113        <region>WA</region>
114        <code>98052</code>
115        <country>USA</country>
116      </postal>
117      <email>henrikn@microsoft.com</email>
118    </address>
119  </author>
120
121  <author initials="L." surname="Masinter" fullname="Larry Masinter">
122    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
123    <address>
124      <postal>
125        <street>345 Park Ave</street>
126        <city>San Jose</city>
127        <region>CA</region>
128        <code>95110</code>
129        <country>USA</country>
130      </postal>
131      <email>LMM@acm.org</email>
132      <uri>http://larry.masinter.net/</uri>
133    </address>
134  </author>
135 
136  <author initials="P." surname="Leach" fullname="Paul J. Leach">
137    <organization abbrev="Microsoft">Microsoft Corporation</organization>
138    <address>
139      <postal>
140        <street>1 Microsoft Way</street>
141        <city>Redmond</city>
142        <region>WA</region>
143        <code>98052</code>
144      </postal>
145      <email>paulle@microsoft.com</email>
146    </address>
147  </author>
148   
149  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
150    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
151    <address>
152      <postal>
153        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
154        <street>The Stata Center, Building 32</street>
155        <street>32 Vassar Street</street>
156        <city>Cambridge</city>
157        <region>MA</region>
158        <code>02139</code>
159        <country>USA</country>
160      </postal>
161      <email>timbl@w3.org</email>
162      <uri>http://www.w3.org/People/Berners-Lee/</uri>
163    </address>
164  </author>
165
166  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
167    <organization abbrev="W3C">World Wide Web Consortium</organization>
168    <address>
169      <postal>
170        <street>W3C / ERCIM</street>
171        <street>2004, rte des Lucioles</street>
172        <city>Sophia-Antipolis</city>
173        <region>AM</region>
174        <code>06902</code>
175        <country>France</country>
176      </postal>
177      <email>ylafon@w3.org</email>
178      <uri>http://www.raubacapeu.net/people/yves/</uri>
179    </address>
180  </author>
181
182  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
183    <organization abbrev="greenbytes">greenbytes GmbH</organization>
184    <address>
185      <postal>
186        <street>Hafenweg 16</street>
187        <city>Muenster</city><region>NW</region><code>48155</code>
188        <country>Germany</country>
189      </postal>
190      <phone>+49 251 2807760</phone>   
191      <facsimile>+49 251 2807761</facsimile>   
192      <email>julian.reschke@greenbytes.de</email>       
193      <uri>http://greenbytes.de/tech/webdav/</uri>     
194    </address>
195  </author>
196
197  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
198
199<abstract>
200<t>
201   The Hypertext Transfer Protocol (HTTP) is an application-level
202   protocol for distributed, collaborative, hypermedia information
203   systems. HTTP has been in use by the World Wide Web global information
204   initiative since 1990. This document is Part 1 of the seven-part specification
205   that defines the protocol referred to as "HTTP/1.1" and, taken together,
206   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
207   its associated terminology, defines the "http" and "https" Uniform
208   Resource Identifier (URI) schemes, defines the generic message syntax
209   and parsing requirements for HTTP message frames, and describes
210   general security concerns for implementations.
211</t>
212</abstract>
213
214<note title="Editorial Note (To be removed by RFC Editor)">
215  <t>
216    Discussion of this draft should take place on the HTTPBIS working group
217    mailing list (ietf-http-wg@w3.org). The current issues list is
218    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
219    and related documents (including fancy diffs) can be found at
220    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
221  </t>
222  <t>
223    The changes in this draft are summarized in <xref target="changes.since.05"/>.
224  </t>
225</note>
226</front>
227<middle>
228<section title="Introduction" anchor="introduction">
229<t>
230   The Hypertext Transfer Protocol (HTTP) is an application-level
231   request/response protocol that uses extensible semantics and MIME-like
232   message payloads for flexible interaction with network-based hypertext
233   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
234   standard <xref target="RFC3986"/> to indicate resource targets and
235   relationships between resources.
236   Messages are passed in a format similar to that used by Internet mail
237   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
238   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
239   between HTTP and MIME messages).
240</t>
241<t>
242   HTTP is a generic interface protocol for informations systems. It is
243   designed to hide the details of how a service is implemented by presenting
244   a uniform interface to clients that is independent of the types of
245   resources provided. Likewise, servers do not need to be aware of each
246   client's purpose: an HTTP request can be considered in isolation rather
247   than being associated with a specific type of client or a predetermined
248   sequence of application steps. The result is a protocol that can be used
249   effectively in many different contexts and for which implementations can
250   evolve independently over time.
251</t>
252<t>
253   HTTP is also designed for use as a generic protocol for translating
254   communication to and from other Internet information systems, such as
255   USENET news services via NNTP <xref target="RFC3977"/>,
256   file services via FTP <xref target="RFC959"/>,
257   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
258   HTTP proxies and gateways provide access to alternative information
259   services by translating their diverse protocols into a hypermedia
260   format that can be viewed and manipulated by clients in the same way
261   as HTTP services.
262</t>
263<t>
264   One consequence of HTTP flexibility is that we cannot define the protocol
265   in terms of how to implement it behind the interface. Instead, we are
266   limited to restricting the syntax of communication, defining the intent
267   of received communication, and the expected behavior of recipients. If
268   the communication is considered in isolation, then successful actions
269   should be reflected in the observable interface provided by servers.
270   However, since many clients are potentially acting in parallel and
271   perhaps at cross-purposes, it would be meaningless to require that such
272   behavior be observable.
273</t>
274<t>
275   This document is Part 1 of the seven-part specification of HTTP,
276   defining the protocol referred to as "HTTP/1.1" and obsoleting
277   <xref target="RFC2616"/>.
278   Part 1 defines the URI schemes specific to HTTP-based resources, overall
279   network operation, transport protocol connection management, and HTTP
280   message framing and forwarding requirements.
281   Our goal is to define all of the mechanisms necessary for HTTP message
282   handling that are independent of message semantics, thereby defining the
283   complete set of requirements for a message parser and transparent
284   message-forwarding intermediaries.
285</t>
286
287<section title="Requirements" anchor="intro.requirements">
288<t>
289   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
290   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
291   document are to be interpreted as described in <xref target="RFC2119"/>.
292</t>
293<t>
294   An implementation is not compliant if it fails to satisfy one or more
295   of the &MUST; or &REQUIRED; level requirements for the protocols it
296   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
297   level and all the &SHOULD; level requirements for its protocols is said
298   to be "unconditionally compliant"; one that satisfies all the &MUST;
299   level requirements but not all the &SHOULD; level requirements for its
300   protocols is said to be "conditionally compliant."
301</t>
302</section>
303
304<section title="Syntax Notation" anchor="notation">
305<iref primary="true" item="Grammar" subitem="ALPHA"/>
306<iref primary="true" item="Grammar" subitem="CR"/>
307<iref primary="true" item="Grammar" subitem="CRLF"/>
308<iref primary="true" item="Grammar" subitem="CTL"/>
309<iref primary="true" item="Grammar" subitem="DIGIT"/>
310<iref primary="true" item="Grammar" subitem="DQUOTE"/>
311<iref primary="true" item="Grammar" subitem="HEXDIG"/>
312<iref primary="true" item="Grammar" subitem="LF"/>
313<iref primary="true" item="Grammar" subitem="OCTET"/>
314<iref primary="true" item="Grammar" subitem="SP"/>
315<iref primary="true" item="Grammar" subitem="VCHAR"/>
316<iref primary="true" item="Grammar" subitem="WSP"/>
317<t anchor="core.rules">
318  <x:anchor-alias value="ALPHA"/>
319  <x:anchor-alias value="CTL"/>
320  <x:anchor-alias value="CR"/>
321  <x:anchor-alias value="CRLF"/>
322  <x:anchor-alias value="DIGIT"/>
323  <x:anchor-alias value="DQUOTE"/>
324  <x:anchor-alias value="HEXDIG"/>
325  <x:anchor-alias value="LF"/>
326  <x:anchor-alias value="OCTET"/>
327  <x:anchor-alias value="SP"/>
328  <x:anchor-alias value="VCHAR"/>
329  <x:anchor-alias value="WSP"/>
330   This specification uses the Augmented Backus-Naur Form (ABNF) notation
331   of <xref target="RFC5234"/>.  The following core rules are included by
332   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
333   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
334   DIGIT (decimal 0-9), DQUOTE (double quote),
335   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
336   OCTET (any 8-bit sequence of data), SP (space),
337   VCHAR (any visible <xref target="USASCII"/> character),
338   and WSP (whitespace).
339</t>
340
341<section title="ABNF Extension: #rule" anchor="notation.abnf">
342  <t>
343    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
344    improve readability.
345  </t>
346  <t>
347    A construct "#" is defined, similar to "*", for defining lists of
348    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
349    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
350    (",") and optional whitespace (OWS).   
351  </t>
352  <figure><preamble>
353    Thus,
354</preamble><artwork type="example">
355  1#element =&gt; element *( OWS "," OWS element )
356</artwork></figure>
357  <figure><preamble>
358    and:
359</preamble><artwork type="example">
360  #element =&gt; [ 1#element ]
361</artwork></figure>
362  <figure><preamble>
363    and for n &gt;= 1 and m &gt; 1:
364</preamble><artwork type="example">
365  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
366</artwork></figure>
367  <t>
368    For compatibility with legacy list rules, recipients &SHOULD; accept empty
369    list elements. In other words, consumers would follow the list productions:
370  </t>
371<figure><artwork type="example">
372#element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
373
3741#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
375</artwork></figure> 
376<t>
377  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
378  expanded as explained above.
379</t>
380</section>
381
382<section title="Basic Rules" anchor="basic.rules">
383<t anchor="rule.CRLF">
384  <x:anchor-alias value="CRLF"/>
385   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
386   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
387   tolerant applications). The end-of-line marker within an entity-body
388   is defined by its associated media type, as described in &media-types;.
389</t>
390<t anchor="rule.LWS">
391   This specification uses three rules to denote the use of linear
392   whitespace: OWS (optional whitespace), RWS (required whitespace), and
393   BWS ("bad" whitespace).
394</t>
395<t>
396   The OWS rule is used where zero or more linear whitespace characters may
397   appear. OWS &SHOULD; either not be produced or be produced as a single SP
398   character. Multiple OWS characters that occur within field-content &SHOULD;
399   be replaced with a single SP before interpreting the field value or
400   forwarding the message downstream.
401</t>
402<t>
403   RWS is used when at least one linear whitespace character is required to
404   separate field tokens. RWS &SHOULD; be produced as a single SP character.
405   Multiple RWS characters that occur within field-content &SHOULD; be
406   replaced with a single SP before interpreting the field value or
407   forwarding the message downstream.
408</t>
409<t>
410   BWS is used where the grammar allows optional whitespace for historical
411   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
412   recipients &MUST; accept such bad optional whitespace and remove it before
413   interpreting the field value or forwarding the message downstream.
414</t>
415<t anchor="rule.whitespace">
416  <x:anchor-alias value="BWS"/>
417  <x:anchor-alias value="OWS"/>
418  <x:anchor-alias value="RWS"/>
419  <x:anchor-alias value="obs-fold"/>
420</t>
421<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"/>
422  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
423                 ; "optional" whitespace
424  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
425                 ; "required" whitespace
426  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
427                 ; "bad" whitespace
428  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
429</artwork></figure>
430<t anchor="rule.token.separators">
431  <x:anchor-alias value="tchar"/>
432  <x:anchor-alias value="token"/>
433   Many HTTP/1.1 header field values consist of words separated by whitespace
434   or special characters. These special characters &MUST; be in a quoted
435   string to be used within a parameter value (as defined in
436   <xref target="transfer.codings"/>).
437</t>
438<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
439  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
440                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
441                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
442                 
443  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
444</artwork></figure>
445<t anchor="rule.quoted-string">
446  <x:anchor-alias value="quoted-string"/>
447  <x:anchor-alias value="qdtext"/>
448  <x:anchor-alias value="obs-text"/>
449   A string of text is parsed as a single word if it is quoted using
450   double-quote marks.
451</t>
452<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"/>
453  <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>
454  <x:ref>qdtext</x:ref>         = *( <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref> )
455  <x:ref>obs-text</x:ref>       = %x80-FF
456</artwork></figure>
457<t anchor="rule.quoted-pair">
458  <x:anchor-alias value="quoted-pair"/>
459  <x:anchor-alias value="quoted-text"/>
460   The backslash character ("\") &MAY; be used as a single-character
461   quoting mechanism only within quoted-string and comment constructs.
462</t>
463<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
464  <x:ref>quoted-text</x:ref>    = %x01-09 /
465                   %x0B-0C /
466                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
467  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
468</artwork></figure>
469</section>
470
471<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
472  <x:anchor-alias value="request-header"/>
473  <x:anchor-alias value="response-header"/>
474  <x:anchor-alias value="accept-params"/>
475  <x:anchor-alias value="entity-body"/>
476  <x:anchor-alias value="entity-header"/>
477  <x:anchor-alias value="Cache-Control"/>
478  <x:anchor-alias value="Pragma"/>
479  <x:anchor-alias value="Warning"/>
480<t>
481  The ABNF rules below are defined in other parts:
482</t>
483<figure><!-- Part2--><artwork type="abnf2616">
484  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
485  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
486</artwork></figure>
487<figure><!-- Part3--><artwork type="abnf2616">
488  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
489  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
490  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
491</artwork></figure>
492<figure><!-- Part6--><artwork type="abnf2616">
493  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
494  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
495  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
496</artwork></figure>
497</section>
498
499</section>
500</section>
501
502<section title="HTTP architecture" anchor="architecture">
503<t>
504   HTTP was created with a specific architecture in mind, the World Wide Web,
505   and has evolved over time to support the scalability needs of a worldwide
506   hypertext system. Much of that architecture is reflected in the terminology
507   and syntax productions used to define HTTP.
508</t>
509
510<section title="Uniform Resource Identifiers" anchor="uri">
511<t>
512   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
513   throughout HTTP as the means for identifying resources. URI references
514   are used to target requests, redirect responses, and define relationships.
515   HTTP does not limit what a resource may be; it merely defines an interface
516   that can be used to interact with a resource via HTTP. More information on
517   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
518</t>
519  <x:anchor-alias value="URI"/>
520  <x:anchor-alias value="URI-reference"/>
521  <x:anchor-alias value="absolute-URI"/>
522  <x:anchor-alias value="relative-part"/>
523  <x:anchor-alias value="authority"/>
524  <x:anchor-alias value="fragment"/>
525  <x:anchor-alias value="path-abempty"/>
526  <x:anchor-alias value="path-absolute"/>
527  <x:anchor-alias value="port"/>
528  <x:anchor-alias value="query"/>
529  <x:anchor-alias value="uri-host"/>
530  <x:anchor-alias value="partial-URI"/>
531<t>
532   This specification adopts the definitions of "URI-reference",
533   "absolute-URI", "relative-part", "fragment", "port", "host",
534   "path-abempty", "path-absolute", "query", and "authority" from
535   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
536   protocol elements that allow a relative URI without a fragment.
537</t>
538<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"/>
539  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
540  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
541  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
542  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
543  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
544  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
545  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
546  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
547  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
548  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
549  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
550 
551  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
552</artwork></figure>
553<t>
554   Each protocol element in HTTP that allows a URI reference will indicate in
555   its ABNF production whether the element allows only a URI in absolute form
556   (absolute-URI), any relative reference (relative-ref), or some other subset
557   of the URI-reference grammar. Unless otherwise indicated, URI references
558   are parsed relative to the request target (the default base URI for both
559   the request and its corresponding response).
560</t>
561
562<section title="http URI scheme" anchor="http.uri">
563  <x:anchor-alias value="http-URI"/>
564  <iref item="http URI scheme" primary="true"/>
565  <iref item="URI scheme" subitem="http" primary="true"/>
566<t>
567   The "http" scheme is used to locate network resources via the HTTP
568   protocol. This section defines the syntax and semantics for identifiers
569   using the http or https URI schemes.
570</t>
571<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
572  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
573</artwork></figure>
574<t>
575   If the port is empty or not given, port 80 is assumed. The semantics
576   are that the identified resource is located at the server listening
577   for TCP connections on that port of that host, and the request-target
578   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
579   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
580   the path-absolute is not present in the URL, it &MUST; be given as "/" when
581   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
582   receives a host name which is not a fully qualified domain name, it
583   &MAY; add its domain to the host name it received. If a proxy receives
584   a fully qualified domain name, the proxy &MUST-NOT; change the host
585   name.
586</t>
587<t><list><t>
588  <iref item="https URI scheme"/>
589  <iref item="URI scheme" subitem="https"/>
590  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
591</t></list></t>
592</section>
593
594<section title="URI Comparison" anchor="uri.comparison">
595<t>
596   When comparing two URIs to decide if they match or not, a client
597   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
598   URIs, with these exceptions:
599  <list style="symbols">
600    <t>A port that is empty or not given is equivalent to the default
601        port for that URI-reference;</t>
602    <t>Comparisons of host names &MUST; be case-insensitive;</t>
603    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
604    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
605  </list>
606</t>
607<t>
608   Characters other than those in the "reserved" set (see
609   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
610   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
611</t>
612<t>
613   For example, the following three URIs are equivalent:
614</t>
615<figure><artwork type="example">
616   http://example.com:80/~smith/home.html
617   http://EXAMPLE.com/%7Esmith/home.html
618   http://EXAMPLE.com:/%7esmith/home.html
619</artwork></figure>
620</section>
621
622<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
623<t>
624</t>
625</section>
626</section>
627
628<section title="Overall Operation" anchor="intro.overall.operation">
629<t>
630   HTTP is a request/response protocol. A client sends a
631   request to the server in the form of a request method, URI, and
632   protocol version, followed by a MIME-like message containing request
633   modifiers, client information, and possible body content over a
634   connection with a server. The server responds with a status line,
635   including the message's protocol version and a success or error code,
636   followed by a MIME-like message containing server information, entity
637   metainformation, and possible entity-body content.
638</t>
639<t>
640   Most HTTP communication is initiated by a user agent and consists of
641   a request to be applied to a resource on some origin server. In the
642   simplest case, this may be accomplished via a single connection (v)
643   between the user agent (UA) and the origin server (O).
644</t>
645<figure><artwork type="drawing">
646       request chain ------------------------&gt;
647    UA -------------------v------------------- O
648       &lt;----------------------- response chain
649</artwork></figure>
650<t>
651   A more complicated situation occurs when one or more intermediaries
652   are present in the request/response chain. There are three common
653   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
654   forwarding agent, receiving requests for a URI in its absolute form,
655   rewriting all or part of the message, and forwarding the reformatted
656   request toward the server identified by the URI. A gateway is a
657   receiving agent, acting as a layer above some other server(s) and, if
658   necessary, translating the requests to the underlying server's
659   protocol. A tunnel acts as a relay point between two connections
660   without changing the messages; tunnels are used when the
661   communication needs to pass through an intermediary (such as a
662   firewall) even when the intermediary cannot understand the contents
663   of the messages.
664</t>
665<figure><artwork type="drawing">
666       request chain --------------------------------------&gt;
667    UA -----v----- A -----v----- B -----v----- C -----v----- O
668       &lt;------------------------------------- response chain
669</artwork></figure>
670<t>
671   The figure above shows three intermediaries (A, B, and C) between the
672   user agent and origin server. A request or response message that
673   travels the whole chain will pass through four separate connections.
674   This distinction is important because some HTTP communication options
675   may apply only to the connection with the nearest, non-tunnel
676   neighbor, only to the end-points of the chain, or to all connections
677   along the chain. Although the diagram is linear, each participant may
678   be engaged in multiple, simultaneous communications. For example, B
679   may be receiving requests from many clients other than A, and/or
680   forwarding requests to servers other than C, at the same time that it
681   is handling A's request.
682</t>
683<t>
684   Any party to the communication which is not acting as a tunnel may
685   employ an internal cache for handling requests. The effect of a cache
686   is that the request/response chain is shortened if one of the
687   participants along the chain has a cached response applicable to that
688   request. The following illustrates the resulting chain if B has a
689   cached copy of an earlier response from O (via C) for a request which
690   has not been cached by UA or A.
691</t>
692<figure><artwork type="drawing">
693          request chain ----------&gt;
694       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
695          &lt;--------- response chain
696</artwork></figure>
697<t>
698   Not all responses are usefully cacheable, and some requests may
699   contain modifiers which place special requirements on cache behavior.
700   HTTP requirements for cache behavior and cacheable responses are
701   defined in &caching;.
702</t>
703<t>
704   In fact, there are a wide variety of architectures and configurations
705   of caches and proxies currently being experimented with or deployed
706   across the World Wide Web. These systems include national hierarchies
707   of proxy caches to save transoceanic bandwidth, systems that
708   broadcast or multicast cache entries, organizations that distribute
709   subsets of cached data via CD-ROM, and so on. HTTP systems are used
710   in corporate intranets over high-bandwidth links, and for access via
711   PDAs with low-power radio links and intermittent connectivity. The
712   goal of HTTP/1.1 is to support the wide diversity of configurations
713   already deployed while introducing protocol constructs that meet the
714   needs of those who build web applications that require high
715   reliability and, failing that, at least reliable indications of
716   failure.
717</t>
718<t>
719   HTTP communication usually takes place over TCP/IP connections. The
720   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
721   not preclude HTTP from being implemented on top of any other protocol
722   on the Internet, or on other networks. HTTP only presumes a reliable
723   transport; any protocol that provides such guarantees can be used;
724   the mapping of the HTTP/1.1 request and response structures onto the
725   transport data units of the protocol in question is outside the scope
726   of this specification.
727</t>
728<t>
729   In HTTP/1.0, most implementations used a new connection for each
730   request/response exchange. In HTTP/1.1, a connection may be used for
731   one or more request/response exchanges, although connections may be
732   closed for a variety of reasons (see <xref target="persistent.connections"/>).
733</t>
734</section>
735
736<section title="Use of HTTP for proxy communication" anchor="http.proxy">
737<t>
738   Configured to use HTTP to proxy HTTP or other protocols.
739</t>
740</section>
741<section title="Interception of HTTP for access control" anchor="http.intercept">
742<t>
743   Interception of HTTP traffic for initiating access control.
744</t>
745</section>
746<section title="Use of HTTP by other protocols" anchor="http.others">
747<t>
748   Profiles of HTTP defined by other protocol.
749   Extensions of HTTP like WebDAV.
750</t>
751</section>
752<section title="Use of HTTP by media type specification" anchor="http.media">
753<t>
754   Instructions on composing HTTP requests via hypertext formats.
755</t>
756</section>
757</section>
758
759<section title="Protocol Parameters" anchor="protocol.parameters">
760
761<section title="HTTP Version" anchor="http.version">
762  <x:anchor-alias value="HTTP-Version"/>
763  <x:anchor-alias value="HTTP-Prot-Name"/>
764<t>
765   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
766   of the protocol. The protocol versioning policy is intended to allow
767   the sender to indicate the format of a message and its capacity for
768   understanding further HTTP communication, rather than the features
769   obtained via that communication. No change is made to the version
770   number for the addition of message components which do not affect
771   communication behavior or which only add to extensible field values.
772   The &lt;minor&gt; number is incremented when the changes made to the
773   protocol add features which do not change the general message parsing
774   algorithm, but which may add to the message semantics and imply
775   additional capabilities of the sender. The &lt;major&gt; number is
776   incremented when the format of a message within the protocol is
777   changed. See <xref target="RFC2145"/> for a fuller explanation.
778</t>
779<t>
780   The version of an HTTP message is indicated by an HTTP-Version field
781   in the first line of the message. HTTP-Version is case-sensitive.
782</t>
783<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
784  <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>
785  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
786</artwork></figure>
787<t>
788   Note that the major and minor numbers &MUST; be treated as separate
789   integers and that each &MAY; be incremented higher than a single digit.
790   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
791   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
792   &MUST-NOT; be sent.
793</t>
794<t>
795   An application that sends a request or response message that includes
796   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
797   with this specification. Applications that are at least conditionally
798   compliant with this specification &SHOULD; use an HTTP-Version of
799   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
800   not compatible with HTTP/1.0. For more details on when to send
801   specific HTTP-Version values, see <xref target="RFC2145"/>.
802</t>
803<t>
804   The HTTP version of an application is the highest HTTP version for
805   which the application is at least conditionally compliant.
806</t>
807<t>
808   Proxy and gateway applications need to be careful when forwarding
809   messages in protocol versions different from that of the application.
810   Since the protocol version indicates the protocol capability of the
811   sender, a proxy/gateway &MUST-NOT; send a message with a version
812   indicator which is greater than its actual version. If a higher
813   version request is received, the proxy/gateway &MUST; either downgrade
814   the request version, or respond with an error, or switch to tunnel
815   behavior.
816</t>
817<t>
818   Due to interoperability problems with HTTP/1.0 proxies discovered
819   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
820   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
821   they support. The proxy/gateway's response to that request &MUST; be in
822   the same major version as the request.
823</t>
824<t>
825  <list>
826    <t>
827      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
828      of header fields required or forbidden by the versions involved.
829    </t>
830  </list>
831</t>
832</section>
833
834<section title="Date/Time Formats" anchor="date.time.formats">
835<section title="Full Date" anchor="full.date">
836  <x:anchor-alias value="HTTP-date"/>
837  <x:anchor-alias value="obsolete-date"/>
838  <x:anchor-alias value="rfc1123-date"/>
839  <x:anchor-alias value="rfc850-date"/>
840  <x:anchor-alias value="asctime-date"/>
841  <x:anchor-alias value="date1"/>
842  <x:anchor-alias value="date2"/>
843  <x:anchor-alias value="date3"/>
844  <x:anchor-alias value="rfc1123-date"/>
845  <x:anchor-alias value="time"/>
846  <x:anchor-alias value="wkday"/>
847  <x:anchor-alias value="weekday"/>
848  <x:anchor-alias value="month"/>
849<t>
850   HTTP applications have historically allowed three different formats
851   for the representation of date/time stamps:
852</t>
853<figure><artwork type="example">
854   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
855   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
856   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
857</artwork></figure>
858<t>
859   The first format is preferred as an Internet standard and represents
860   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
861   other formats are described here only for
862   compatibility with obsolete implementations.
863   HTTP/1.1 clients and servers that parse the date value &MUST; accept
864   all three formats (for compatibility with HTTP/1.0), though they &MUST;
865   only generate the RFC 1123 format for representing HTTP-date values
866   in header fields. See <xref target="tolerant.applications"/> for further information.
867</t>
868<t><list><t>
869      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
870      accepting date values that may have been sent by non-HTTP
871      applications, as is sometimes the case when retrieving or posting
872      messages via proxies/gateways to SMTP or NNTP.
873</t></list></t>
874<t>
875   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
876   (GMT), without exception. For the purposes of HTTP, GMT is exactly
877   equal to UTC (Coordinated Universal Time). This is indicated in the
878   first two formats by the inclusion of "GMT" as the three-letter
879   abbreviation for time zone, and &MUST; be assumed when reading the
880   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
881   additional whitespace beyond that specifically included as SP in the
882   grammar.
883</t>
884<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="obsolete-date"/><iref primary="true" item="Grammar" subitem="rfc850-date"/><iref primary="true" item="Grammar" subitem="asctime-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><iref primary="true" item="Grammar" subitem="time"/><iref primary="true" item="Grammar" subitem="wkday"/><iref primary="true" item="Grammar" subitem="weekday"/><iref primary="true" item="Grammar" subitem="month"/>
885  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
886  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
887  <x:ref>rfc1123-date</x:ref> = <x:ref>wkday</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
888  <x:ref>rfc850-date</x:ref>  = <x:ref>weekday</x:ref> "," <x:ref>SP</x:ref> date2 <x:ref>SP</x:ref> time <x:ref>SP</x:ref> GMT
889  <x:ref>asctime-date</x:ref> = <x:ref>wkday</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
890  <x:ref>date1</x:ref>        = 2<x:ref>DIGIT</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> 4<x:ref>DIGIT</x:ref>
891                 ; day month year (e.g., 02 Jun 1982)
892  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
893                 ; day-month-year (e.g., 02-Jun-82)
894  <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> ))
895                 ; month day (e.g., Jun  2)
896  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
897                 ; 00:00:00 - 23:59:59
898  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
899               / s-Thu / s-Fri / s-Sat / s-Sun
900  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
901               / l-Thu / l-Fri / l-Sat / l-Sun
902  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
903               / s-May / s-Jun / s-Jul / s-Aug
904               / s-Sep / s-Oct / s-Nov / s-Dec
905               
906  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
907
908  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
909  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
910  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
911  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
912  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
913  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
914  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
915
916  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
917  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
918  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
919  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
920  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
921  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
922  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
923
924  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
925  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
926  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
927  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
928  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
929  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
930  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
931  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
932  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
933  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
934  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
935  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
936</artwork></figure>
937<t>
938      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
939      to their usage within the protocol stream. Clients and servers are
940      not required to use these formats for user presentation, request
941      logging, etc.
942</t>
943</section>
944</section>
945
946<section title="Transfer Codings" anchor="transfer.codings">
947  <x:anchor-alias value="parameter"/>
948  <x:anchor-alias value="transfer-coding"/>
949  <x:anchor-alias value="transfer-extension"/>
950<t>
951   Transfer-coding values are used to indicate an encoding
952   transformation that has been, can be, or may need to be applied to an
953   entity-body in order to ensure "safe transport" through the network.
954   This differs from a content coding in that the transfer-coding is a
955   property of the message, not of the original entity.
956</t>
957<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
958  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
959  <x:ref>transfer-extension</x:ref>      = <x:ref>token</x:ref> *( <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>parameter</x:ref> )
960</artwork></figure>
961<t anchor="rule.parameter">
962  <x:anchor-alias value="attribute"/>
963  <x:anchor-alias value="parameter"/>
964  <x:anchor-alias value="value"/>
965   Parameters are in  the form of attribute/value pairs.
966</t>
967<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/>
968  <x:ref>parameter</x:ref>               = <x:ref>attribute</x:ref> <x:ref>BWS</x:ref> "=" <x:ref>BWS</x:ref> <x:ref>value</x:ref>
969  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
970  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
971</artwork></figure>
972<t>
973   All transfer-coding values are case-insensitive. HTTP/1.1 uses
974   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
975   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
976</t>
977<t>
978   Whenever a transfer-coding is applied to a message-body, the set of
979   transfer-codings &MUST; include "chunked", unless the message indicates it
980   is terminated by closing the connection. When the "chunked" transfer-coding
981   is used, it &MUST; be the last transfer-coding applied to the
982   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
983   than once to a message-body. These rules allow the recipient to
984   determine the transfer-length of the message (<xref target="message.length"/>).
985</t>
986<t>
987   Transfer-codings are analogous to the Content-Transfer-Encoding
988   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
989   binary data over a 7-bit transport service. However, safe transport
990   has a different focus for an 8bit-clean transfer protocol. In HTTP,
991   the only unsafe characteristic of message-bodies is the difficulty in
992   determining the exact body length (<xref target="message.length"/>), or the desire to
993   encrypt data over a shared transport.
994</t>
995<t>
996   The Internet Assigned Numbers Authority (IANA) acts as a registry for
997   transfer-coding value tokens. Initially, the registry contains the
998   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
999   "gzip", "compress", and "deflate" (&content-codings;).
1000</t>
1001<t>
1002   New transfer-coding value tokens &SHOULD; be registered in the same way
1003   as new content-coding value tokens (&content-codings;).
1004</t>
1005<t>
1006   A server which receives an entity-body with a transfer-coding it does
1007   not understand &SHOULD; return 501 (Not Implemented), and close the
1008   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1009   client.
1010</t>
1011
1012<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1013  <x:anchor-alias value="chunk"/>
1014  <x:anchor-alias value="Chunked-Body"/>
1015  <x:anchor-alias value="chunk-data"/>
1016  <x:anchor-alias value="chunk-ext"/>
1017  <x:anchor-alias value="chunk-ext-name"/>
1018  <x:anchor-alias value="chunk-ext-val"/>
1019  <x:anchor-alias value="chunk-size"/>
1020  <x:anchor-alias value="last-chunk"/>
1021  <x:anchor-alias value="trailer-part"/>
1022<t>
1023   The chunked encoding modifies the body of a message in order to
1024   transfer it as a series of chunks, each with its own size indicator,
1025   followed by an &OPTIONAL; trailer containing entity-header fields. This
1026   allows dynamically produced content to be transferred along with the
1027   information necessary for the recipient to verify that it has
1028   received the full message.
1029</t>
1030<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"/>
1031  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1032                   <x:ref>last-chunk</x:ref>
1033                   <x:ref>trailer-part</x:ref>
1034                   <x:ref>CRLF</x:ref>
1035 
1036  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1037                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1038  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1039  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1040 
1041  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1042                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1043  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1044  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1045  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1046  <x:ref>trailer-part</x:ref>   = *(<x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref>)
1047</artwork></figure>
1048<t>
1049   The chunk-size field is a string of hex digits indicating the size of
1050   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1051   zero, followed by the trailer, which is terminated by an empty line.
1052</t>
1053<t>
1054   The trailer allows the sender to include additional HTTP header
1055   fields at the end of the message. The Trailer header field can be
1056   used to indicate which header fields are included in a trailer (see
1057   <xref target="header.trailer"/>).
1058</t>
1059<t>
1060   A server using chunked transfer-coding in a response &MUST-NOT; use the
1061   trailer for any header fields unless at least one of the following is
1062   true:
1063  <list style="numbers">
1064    <t>the request included a TE header field that indicates "trailers" is
1065     acceptable in the transfer-coding of the  response, as described in
1066     <xref target="header.te"/>; or,</t>
1067
1068    <t>the server is the origin server for the response, the trailer
1069     fields consist entirely of optional metadata, and the recipient
1070     could use the message (in a manner acceptable to the origin server)
1071     without receiving this metadata.  In other words, the origin server
1072     is willing to accept the possibility that the trailer fields might
1073     be silently discarded along the path to the client.</t>
1074  </list>
1075</t>
1076<t>
1077   This requirement prevents an interoperability failure when the
1078   message is being received by an HTTP/1.1 (or later) proxy and
1079   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1080   compliance with the protocol would have necessitated a possibly
1081   infinite buffer on the proxy.
1082</t>
1083<t>
1084   A process for decoding the "chunked" transfer-coding
1085   can be represented in pseudo-code as:
1086</t>
1087<figure><artwork type="code">
1088  length := 0
1089  read chunk-size, chunk-ext (if any) and CRLF
1090  while (chunk-size &gt; 0) {
1091     read chunk-data and CRLF
1092     append chunk-data to entity-body
1093     length := length + chunk-size
1094     read chunk-size and CRLF
1095  }
1096  read entity-header
1097  while (entity-header not empty) {
1098     append entity-header to existing header fields
1099     read entity-header
1100  }
1101  Content-Length := length
1102  Remove "chunked" from Transfer-Encoding
1103</artwork></figure>
1104<t>
1105   All HTTP/1.1 applications &MUST; be able to receive and decode the
1106   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1107   they do not understand.
1108</t>
1109</section>
1110</section>
1111
1112<section title="Product Tokens" anchor="product.tokens">
1113  <x:anchor-alias value="product"/>
1114  <x:anchor-alias value="product-version"/>
1115<t>
1116   Product tokens are used to allow communicating applications to
1117   identify themselves by software name and version. Most fields using
1118   product tokens also allow sub-products which form a significant part
1119   of the application to be listed, separated by whitespace. By
1120   convention, the products are listed in order of their significance
1121   for identifying the application.
1122</t>
1123<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1124  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1125  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1126</artwork></figure>
1127<t>
1128   Examples:
1129</t>
1130<figure><artwork type="example">
1131    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1132    Server: Apache/0.8.4
1133</artwork></figure>
1134<t>
1135   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1136   used for advertising or other non-essential information. Although any
1137   token character &MAY; appear in a product-version, this token &SHOULD;
1138   only be used for a version identifier (i.e., successive versions of
1139   the same product &SHOULD; only differ in the product-version portion of
1140   the product value).
1141</t>
1142</section>
1143
1144</section>
1145
1146<section title="HTTP Message" anchor="http.message">
1147
1148<section title="Message Types" anchor="message.types">
1149  <x:anchor-alias value="generic-message"/>
1150  <x:anchor-alias value="HTTP-message"/>
1151  <x:anchor-alias value="start-line"/>
1152<t>
1153   HTTP messages consist of requests from client to server and responses
1154   from server to client.
1155</t>
1156<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1157  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1158</artwork></figure>
1159<t>
1160   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1161   message format of <xref target="RFC5322"/> for transferring entities (the payload
1162   of the message). Both types of message consist of a start-line, zero
1163   or more header fields (also known as "headers"), an empty line (i.e.,
1164   a line with nothing preceding the CRLF) indicating the end of the
1165   header fields, and possibly a message-body.
1166</t>
1167<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1168  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1169                    *(<x:ref>message-header</x:ref> <x:ref>CRLF</x:ref>)
1170                    <x:ref>CRLF</x:ref>
1171                    [ <x:ref>message-body</x:ref> ]
1172  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1173</artwork></figure>
1174<t>
1175   In the interest of robustness, servers &SHOULD; ignore any empty
1176   line(s) received where a Request-Line is expected. In other words, if
1177   the server is reading the protocol stream at the beginning of a
1178   message and receives a CRLF first, it should ignore the CRLF.
1179</t>
1180<t>
1181   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1182   after a POST request. To restate what is explicitly forbidden by the
1183   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1184   extra CRLF.
1185</t>
1186<t>
1187   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1188   header field. The presence of whitespace might be an attempt to trick a
1189   noncompliant implementation of HTTP into ignoring that field or processing
1190   the next line as a new request, either of which may result in security
1191   issues when implementations within the request chain interpret the
1192   same message differently. HTTP/1.1 servers &MUST; reject such a message
1193   with a 400 (Bad Request) response.
1194</t>
1195</section>
1196
1197<section title="Message Headers" anchor="message.headers">
1198  <x:anchor-alias value="field-content"/>
1199  <x:anchor-alias value="field-name"/>
1200  <x:anchor-alias value="field-value"/>
1201  <x:anchor-alias value="message-header"/>
1202<t>
1203   HTTP header fields follow the same general format as Internet messages in
1204   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1205   of a name followed by a colon (":"), optional whitespace, and the field
1206   value. Field names are case-insensitive.
1207</t>
1208<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-header"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/>
1209  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1210  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1211  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1212  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1213</artwork></figure>
1214<t>
1215   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1216   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1217   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1218   header field-values use only a subset of the US-ASCII charset
1219   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1220   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1221   (obs-text) octets in field-content as opaque data.
1222</t>
1223<t>
1224   No whitespace is allowed between the header field-name and colon. For
1225   security reasons, any request message received containing such whitespace
1226   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1227   whitespace in a response message &MUST; be removed.
1228</t>
1229<t>
1230   The field value &MAY; be preceded by optional whitespace; a single SP is
1231   preferred. The field-value does not include any leading or trailing white
1232   space: OWS occurring before the first non-whitespace character of the
1233   field-value or after the last non-whitespace character of the field-value
1234   is ignored and &MAY; be removed without changing the meaning of the header
1235   field.
1236</t>
1237<t>
1238   Historically, HTTP header field values could be extended over multiple
1239   lines by preceding each extra line with at least one space or horizontal
1240   tab character (line folding). This specification deprecates such line
1241   folding except within the message/http media type
1242   (<xref target="internet.media.type.message.http"/>).
1243   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1244   (i.e., that contain any field-content that matches the obs-fold rule) unless
1245   the message is intended for packaging within the message/http media type.
1246   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1247   obs-fold whitespace with a single SP prior to interpreting the field value
1248   or forwarding the message downstream.
1249</t>
1250<t anchor="rule.comment">
1251  <x:anchor-alias value="comment"/>
1252  <x:anchor-alias value="ctext"/>
1253   Comments can be included in some HTTP header fields by surrounding
1254   the comment text with parentheses. Comments are only allowed in
1255   fields containing "comment" as part of their field value definition.
1256   In all other fields, parentheses are considered part of the field
1257   value.
1258</t>
1259<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1260  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1261  <x:ref>ctext</x:ref>          = *( <x:ref>OWS</x:ref> / %x21-27 / %x2A-7E / <x:ref>obs-text</x:ref> )
1262</artwork></figure>
1263<t>
1264   The order in which header fields with differing field names are
1265   received is not significant. However, it is "good practice" to send
1266   general-header fields first, followed by request-header or response-header
1267   fields, and ending with the entity-header fields.
1268</t>
1269<t>
1270   Multiple message-header fields with the same field-name &MAY; be
1271   present in a message if and only if the entire field-value for that
1272   header field is defined as a comma-separated list [i.e., #(values)].
1273   It &MUST; be possible to combine the multiple header fields into one
1274   "field-name: field-value" pair, without changing the semantics of the
1275   message, by appending each subsequent field-value to the first, each
1276   separated by a comma. The order in which header fields with the same
1277   field-name are received is therefore significant to the
1278   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1279   change the order of these field values when a message is forwarded.
1280</t>
1281<t>
1282  <list><t>
1283   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1284   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1285   can occur multiple times, but does not use the list syntax, and thus cannot
1286   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1287   for details.) Also note that the Set-Cookie2 header specified in
1288   <xref target="RFC2965"/> does not share this problem.
1289  </t></list>
1290</t>
1291 
1292</section>
1293
1294<section title="Message Body" anchor="message.body">
1295  <x:anchor-alias value="message-body"/>
1296<t>
1297   The message-body (if any) of an HTTP message is used to carry the
1298   entity-body associated with the request or response. The message-body
1299   differs from the entity-body only when a transfer-coding has been
1300   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1301</t>
1302<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1303  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1304               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1305</artwork></figure>
1306<t>
1307   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1308   applied by an application to ensure safe and proper transfer of the
1309   message. Transfer-Encoding is a property of the message, not of the
1310   entity, and thus &MAY; be added or removed by any application along the
1311   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1312   when certain transfer-codings may be used.)
1313</t>
1314<t>
1315   The rules for when a message-body is allowed in a message differ for
1316   requests and responses.
1317</t>
1318<t>
1319   The presence of a message-body in a request is signaled by the
1320   inclusion of a Content-Length or Transfer-Encoding header field in
1321   the request's message-headers. A message-body &MUST-NOT; be included in
1322   a request if the specification of the request method (&method;)
1323   explicitly disallows an entity-body in requests.
1324   When a request message contains both a message-body of non-zero
1325   length and a method that does not define any semantics for that
1326   request message-body, then an origin server &SHOULD; either ignore
1327   the message-body or respond with an appropriate error message
1328   (e.g., 413).  A proxy or gateway, when presented the same request,
1329   &SHOULD; either forward the request inbound with the message-body or
1330   ignore the message-body when determining a response.
1331</t>
1332<t>
1333   For response messages, whether or not a message-body is included with
1334   a message is dependent on both the request method and the response
1335   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1336   &MUST-NOT; include a message-body, even though the presence of entity-header
1337   fields might lead one to believe they do. All 1xx
1338   (informational), 204 (No Content), and 304 (Not Modified) responses
1339   &MUST-NOT; include a message-body. All other responses do include a
1340   message-body, although it &MAY; be of zero length.
1341</t>
1342</section>
1343
1344<section title="Message Length" anchor="message.length">
1345<t>
1346   The transfer-length of a message is the length of the message-body as
1347   it appears in the message; that is, after any transfer-codings have
1348   been applied. When a message-body is included with a message, the
1349   transfer-length of that body is determined by one of the following
1350   (in order of precedence):
1351</t>
1352<t>
1353  <list style="numbers">
1354    <x:lt><t>
1355     Any response message which "&MUST-NOT;" include a message-body (such
1356     as the 1xx, 204, and 304 responses and any response to a HEAD
1357     request) is always terminated by the first empty line after the
1358     header fields, regardless of the entity-header fields present in
1359     the message.
1360    </t></x:lt>
1361    <x:lt><t>
1362     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1363     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1364     is used, the transfer-length is defined by the use of this transfer-coding.
1365     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1366     is not present, the transfer-length is defined by the sender closing the connection.
1367    </t></x:lt>
1368    <x:lt><t>
1369     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1370     decimal value in OCTETs represents both the entity-length and the
1371     transfer-length. The Content-Length header field &MUST-NOT; be sent
1372     if these two lengths are different (i.e., if a Transfer-Encoding
1373     header field is present). If a message is received with both a
1374     Transfer-Encoding header field and a Content-Length header field,
1375     the latter &MUST; be ignored.
1376    </t></x:lt>
1377    <x:lt><t>
1378     If the message uses the media type "multipart/byteranges", and the
1379     transfer-length is not otherwise specified, then this self-delimiting
1380     media type defines the transfer-length. This media type
1381     &MUST-NOT; be used unless the sender knows that the recipient can parse
1382     it; the presence in a request of a Range header with multiple byte-range
1383     specifiers from a 1.1 client implies that the client can parse
1384     multipart/byteranges responses.
1385    <list style="empty"><t>
1386       A range header might be forwarded by a 1.0 proxy that does not
1387       understand multipart/byteranges; in this case the server &MUST;
1388       delimit the message using methods defined in items 1, 3 or 5 of
1389       this section.
1390    </t></list>
1391    </t></x:lt>
1392    <x:lt><t>
1393     By the server closing the connection. (Closing the connection
1394     cannot be used to indicate the end of a request body, since that
1395     would leave no possibility for the server to send back a response.)
1396    </t></x:lt>
1397  </list>
1398</t>
1399<t>
1400   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1401   containing a message-body &MUST; include a valid Content-Length header
1402   field unless the server is known to be HTTP/1.1 compliant. If a
1403   request contains a message-body and a Content-Length is not given,
1404   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1405   determine the length of the message, or with 411 (Length Required) if
1406   it wishes to insist on receiving a valid Content-Length.
1407</t>
1408<t>
1409   All HTTP/1.1 applications that receive entities &MUST; accept the
1410   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1411   to be used for messages when the message length cannot be determined
1412   in advance.
1413</t>
1414<t>
1415   Messages &MUST-NOT; include both a Content-Length header field and a
1416   transfer-coding. If the message does include a
1417   transfer-coding, the Content-Length &MUST; be ignored.
1418</t>
1419<t>
1420   When a Content-Length is given in a message where a message-body is
1421   allowed, its field value &MUST; exactly match the number of OCTETs in
1422   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1423   invalid length is received and detected.
1424</t>
1425</section>
1426
1427<section title="General Header Fields" anchor="general.header.fields">
1428  <x:anchor-alias value="general-header"/>
1429<t>
1430   There are a few header fields which have general applicability for
1431   both request and response messages, but which do not apply to the
1432   entity being transferred. These header fields apply only to the
1433   message being transmitted.
1434</t>
1435<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1436  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1437                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1438                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1439                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1440                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1441                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1442                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1443                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1444                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1445</artwork></figure>
1446<t>
1447   General-header field names can be extended reliably only in
1448   combination with a change in the protocol version. However, new or
1449   experimental header fields may be given the semantics of general
1450   header fields if all parties in the communication recognize them to
1451   be general-header fields. Unrecognized header fields are treated as
1452   entity-header fields.
1453</t>
1454</section>
1455</section>
1456
1457<section title="Request" anchor="request">
1458  <x:anchor-alias value="Request"/>
1459<t>
1460   A request message from a client to a server includes, within the
1461   first line of that message, the method to be applied to the resource,
1462   the identifier of the resource, and the protocol version in use.
1463</t>
1464<!--                 Host                      ; should be moved here eventually -->
1465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1466  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1467                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1468                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1469                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1470                  <x:ref>CRLF</x:ref>
1471                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1472</artwork></figure>
1473
1474<section title="Request-Line" anchor="request-line">
1475  <x:anchor-alias value="Request-Line"/>
1476<t>
1477   The Request-Line begins with a method token, followed by the
1478   request-target and the protocol version, and ending with CRLF. The
1479   elements are separated by SP characters. No CR or LF is allowed
1480   except in the final CRLF sequence.
1481</t>
1482<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1483  <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>
1484</artwork></figure>
1485
1486<section title="Method" anchor="method">
1487  <x:anchor-alias value="Method"/>
1488<t>
1489   The Method  token indicates the method to be performed on the
1490   resource identified by the request-target. The method is case-sensitive.
1491</t>
1492<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1493  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1494</artwork></figure>
1495</section>
1496
1497<section title="request-target" anchor="request-target">
1498  <x:anchor-alias value="request-target"/>
1499<t>
1500   The request-target is a Uniform Resource Identifier (<xref target="uri"/>) and
1501   identifies the resource upon which to apply the request.
1502</t>
1503<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1504  <x:ref>request-target</x:ref> = "*"
1505                 / <x:ref>absolute-URI</x:ref>
1506                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1507                 / <x:ref>authority</x:ref>
1508</artwork></figure>
1509<t>
1510   The four options for request-target are dependent on the nature of the
1511   request. The asterisk "*" means that the request does not apply to a
1512   particular resource, but to the server itself, and is only allowed
1513   when the method used does not necessarily apply to a resource. One
1514   example would be
1515</t>
1516<figure><artwork type="example">
1517  OPTIONS * HTTP/1.1
1518</artwork></figure>
1519<t>
1520   The absolute-URI form is &REQUIRED; when the request is being made to a
1521   proxy. The proxy is requested to forward the request or service it
1522   from a valid cache, and return the response. Note that the proxy &MAY;
1523   forward the request on to another proxy or directly to the server
1524   specified by the absolute-URI. In order to avoid request loops, a
1525   proxy &MUST; be able to recognize all of its server names, including
1526   any aliases, local variations, and the numeric IP address. An example
1527   Request-Line would be:
1528</t>
1529<figure><artwork type="example">
1530  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1531</artwork></figure>
1532<t>
1533   To allow for transition to absolute-URIs in all requests in future
1534   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1535   form in requests, even though HTTP/1.1 clients will only generate
1536   them in requests to proxies.
1537</t>
1538<t>
1539   The authority form is only used by the CONNECT method (&CONNECT;).
1540</t>
1541<t>
1542   The most common form of request-target is that used to identify a
1543   resource on an origin server or gateway. In this case the absolute
1544   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1545   the request-target, and the network location of the URI (authority) &MUST;
1546   be transmitted in a Host header field. For example, a client wishing
1547   to retrieve the resource above directly from the origin server would
1548   create a TCP connection to port 80 of the host "www.example.org" and send
1549   the lines:
1550</t>
1551<figure><artwork type="example">
1552  GET /pub/WWW/TheProject.html HTTP/1.1
1553  Host: www.example.org
1554</artwork></figure>
1555<t>
1556   followed by the remainder of the Request. Note that the absolute path
1557   cannot be empty; if none is present in the original URI, it &MUST; be
1558   given as "/" (the server root).
1559</t>
1560<t>
1561   If a proxy receives a request without any path in the request-target and
1562   the method specified is capable of supporting the asterisk form of
1563   request-target, then the last proxy on the request chain &MUST; forward the
1564   request with "*" as the final request-target.
1565</t>
1566<figure><preamble>   
1567   For example, the request
1568</preamble><artwork type="example">
1569  OPTIONS http://www.example.org:8001 HTTP/1.1
1570</artwork></figure>
1571<figure><preamble>   
1572  would be forwarded by the proxy as
1573</preamble><artwork type="example">
1574  OPTIONS * HTTP/1.1
1575  Host: www.example.org:8001
1576</artwork>
1577<postamble>
1578   after connecting to port 8001 of host "www.example.org".
1579</postamble>
1580</figure>
1581<t>
1582   The request-target is transmitted in the format specified in
1583   <xref target="http.uri"/>. If the request-target is encoded using the
1584   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1585   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1586   &MUST; decode the request-target in order to
1587   properly interpret the request. Servers &SHOULD; respond to invalid
1588   request-targets with an appropriate status code.
1589</t>
1590<t>
1591   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1592   received request-target when forwarding it to the next inbound server,
1593   except as noted above to replace a null path-absolute with "/".
1594</t>
1595<t>
1596  <list><t>
1597      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1598      meaning of the request when the origin server is improperly using
1599      a non-reserved URI character for a reserved purpose.  Implementors
1600      should be aware that some pre-HTTP/1.1 proxies have been known to
1601      rewrite the request-target.
1602  </t></list>
1603</t>
1604<t>
1605   HTTP does not place a pre-defined limit on the length of a request-target.
1606   A server &MUST; be prepared to receive URIs of unbounded length and
1607   respond with the 414 (Request-target too Long) status if the received
1608   request-target would be longer than the server wishes to handle
1609   (see &status-414;).
1610</t>
1611<t>
1612   Various ad-hoc limitations on request-target length are found in practice.
1613   It is &RECOMMENDED; that all HTTP senders and recipients support
1614   request-target lengths of 8000 or more OCTETs.
1615</t>
1616</section>
1617</section>
1618
1619<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1620<t>
1621   The exact resource identified by an Internet request is determined by
1622   examining both the request-target and the Host header field.
1623</t>
1624<t>
1625   An origin server that does not allow resources to differ by the
1626   requested host &MAY; ignore the Host header field value when
1627   determining the resource identified by an HTTP/1.1 request. (But see
1628   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1629   for other requirements on Host support in HTTP/1.1.)
1630</t>
1631<t>
1632   An origin server that does differentiate resources based on the host
1633   requested (sometimes referred to as virtual hosts or vanity host
1634   names) &MUST; use the following rules for determining the requested
1635   resource on an HTTP/1.1 request:
1636  <list style="numbers">
1637    <t>If request-target is an absolute-URI, the host is part of the
1638     request-target. Any Host header field value in the request &MUST; be
1639     ignored.</t>
1640    <t>If the request-target is not an absolute-URI, and the request includes
1641     a Host header field, the host is determined by the Host header
1642     field value.</t>
1643    <t>If the host as determined by rule 1 or 2 is not a valid host on
1644     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1645  </list>
1646</t>
1647<t>
1648   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1649   attempt to use heuristics (e.g., examination of the URI path for
1650   something unique to a particular host) in order to determine what
1651   exact resource is being requested.
1652</t>
1653</section>
1654
1655</section>
1656
1657
1658<section title="Response" anchor="response">
1659  <x:anchor-alias value="Response"/>
1660<t>
1661   After receiving and interpreting a request message, a server responds
1662   with an HTTP response message.
1663</t>
1664<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1665  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1666                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1667                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1668                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref>)  ; &entity-header-fields;
1669                  <x:ref>CRLF</x:ref>
1670                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1671</artwork></figure>
1672
1673<section title="Status-Line" anchor="status-line">
1674  <x:anchor-alias value="Status-Line"/>
1675<t>
1676   The first line of a Response message is the Status-Line, consisting
1677   of the protocol version followed by a numeric status code and its
1678   associated textual phrase, with each element separated by SP
1679   characters. No CR or LF is allowed except in the final CRLF sequence.
1680</t>
1681<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1682  <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>
1683</artwork></figure>
1684
1685<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1686  <x:anchor-alias value="Reason-Phrase"/>
1687  <x:anchor-alias value="Status-Code"/>
1688<t>
1689   The Status-Code element is a 3-digit integer result code of the
1690   attempt to understand and satisfy the request. These codes are fully
1691   defined in &status-codes;.  The Reason Phrase exists for the sole
1692   purpose of providing a textual description associated with the numeric
1693   status code, out of deference to earlier Internet application protocols
1694   that were more frequently used with interactive text clients.
1695   A client &SHOULD; ignore the content of the Reason Phrase.
1696</t>
1697<t>
1698   The first digit of the Status-Code defines the class of response. The
1699   last two digits do not have any categorization role. There are 5
1700   values for the first digit:
1701  <list style="symbols">
1702    <t>
1703      1xx: Informational - Request received, continuing process
1704    </t>
1705    <t>
1706      2xx: Success - The action was successfully received,
1707        understood, and accepted
1708    </t>
1709    <t>
1710      3xx: Redirection - Further action must be taken in order to
1711        complete the request
1712    </t>
1713    <t>
1714      4xx: Client Error - The request contains bad syntax or cannot
1715        be fulfilled
1716    </t>
1717    <t>
1718      5xx: Server Error - The server failed to fulfill an apparently
1719        valid request
1720    </t>
1721  </list>
1722</t>
1723<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"/>
1724  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1725  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1726</artwork></figure>
1727</section>
1728</section>
1729
1730</section>
1731
1732
1733<section title="Connections" anchor="connections">
1734
1735<section title="Persistent Connections" anchor="persistent.connections">
1736
1737<section title="Purpose" anchor="persistent.purpose">
1738<t>
1739   Prior to persistent connections, a separate TCP connection was
1740   established to fetch each URL, increasing the load on HTTP servers
1741   and causing congestion on the Internet. The use of inline images and
1742   other associated data often require a client to make multiple
1743   requests of the same server in a short amount of time. Analysis of
1744   these performance problems and results from a prototype
1745   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1746   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1747   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1748   T/TCP <xref target="Tou1998"/>.
1749</t>
1750<t>
1751   Persistent HTTP connections have a number of advantages:
1752  <list style="symbols">
1753      <t>
1754        By opening and closing fewer TCP connections, CPU time is saved
1755        in routers and hosts (clients, servers, proxies, gateways,
1756        tunnels, or caches), and memory used for TCP protocol control
1757        blocks can be saved in hosts.
1758      </t>
1759      <t>
1760        HTTP requests and responses can be pipelined on a connection.
1761        Pipelining allows a client to make multiple requests without
1762        waiting for each response, allowing a single TCP connection to
1763        be used much more efficiently, with much lower elapsed time.
1764      </t>
1765      <t>
1766        Network congestion is reduced by reducing the number of packets
1767        caused by TCP opens, and by allowing TCP sufficient time to
1768        determine the congestion state of the network.
1769      </t>
1770      <t>
1771        Latency on subsequent requests is reduced since there is no time
1772        spent in TCP's connection opening handshake.
1773      </t>
1774      <t>
1775        HTTP can evolve more gracefully, since errors can be reported
1776        without the penalty of closing the TCP connection. Clients using
1777        future versions of HTTP might optimistically try a new feature,
1778        but if communicating with an older server, retry with old
1779        semantics after an error is reported.
1780      </t>
1781    </list>
1782</t>
1783<t>
1784   HTTP implementations &SHOULD; implement persistent connections.
1785</t>
1786</section>
1787
1788<section title="Overall Operation" anchor="persistent.overall">
1789<t>
1790   A significant difference between HTTP/1.1 and earlier versions of
1791   HTTP is that persistent connections are the default behavior of any
1792   HTTP connection. That is, unless otherwise indicated, the client
1793   &SHOULD; assume that the server will maintain a persistent connection,
1794   even after error responses from the server.
1795</t>
1796<t>
1797   Persistent connections provide a mechanism by which a client and a
1798   server can signal the close of a TCP connection. This signaling takes
1799   place using the Connection header field (<xref target="header.connection"/>). Once a close
1800   has been signaled, the client &MUST-NOT; send any more requests on that
1801   connection.
1802</t>
1803
1804<section title="Negotiation" anchor="persistent.negotiation">
1805<t>
1806   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1807   maintain a persistent connection unless a Connection header including
1808   the connection-token "close" was sent in the request. If the server
1809   chooses to close the connection immediately after sending the
1810   response, it &SHOULD; send a Connection header including the
1811   connection-token close.
1812</t>
1813<t>
1814   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1815   decide to keep it open based on whether the response from a server
1816   contains a Connection header with the connection-token close. In case
1817   the client does not want to maintain a connection for more than that
1818   request, it &SHOULD; send a Connection header including the
1819   connection-token close.
1820</t>
1821<t>
1822   If either the client or the server sends the close token in the
1823   Connection header, that request becomes the last one for the
1824   connection.
1825</t>
1826<t>
1827   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1828   maintained for HTTP versions less than 1.1 unless it is explicitly
1829   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1830   compatibility with HTTP/1.0 clients.
1831</t>
1832<t>
1833   In order to remain persistent, all messages on the connection &MUST;
1834   have a self-defined message length (i.e., one not defined by closure
1835   of the connection), as described in <xref target="message.length"/>.
1836</t>
1837</section>
1838
1839<section title="Pipelining" anchor="pipelining">
1840<t>
1841   A client that supports persistent connections &MAY; "pipeline" its
1842   requests (i.e., send multiple requests without waiting for each
1843   response). A server &MUST; send its responses to those requests in the
1844   same order that the requests were received.
1845</t>
1846<t>
1847   Clients which assume persistent connections and pipeline immediately
1848   after connection establishment &SHOULD; be prepared to retry their
1849   connection if the first pipelined attempt fails. If a client does
1850   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1851   persistent. Clients &MUST; also be prepared to resend their requests if
1852   the server closes the connection before sending all of the
1853   corresponding responses.
1854</t>
1855<t>
1856   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1857   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1858   premature termination of the transport connection could lead to
1859   indeterminate results. A client wishing to send a non-idempotent
1860   request &SHOULD; wait to send that request until it has received the
1861   response status for the previous request.
1862</t>
1863</section>
1864</section>
1865
1866<section title="Proxy Servers" anchor="persistent.proxy">
1867<t>
1868   It is especially important that proxies correctly implement the
1869   properties of the Connection header field as specified in <xref target="header.connection"/>.
1870</t>
1871<t>
1872   The proxy server &MUST; signal persistent connections separately with
1873   its clients and the origin servers (or other proxy servers) that it
1874   connects to. Each persistent connection applies to only one transport
1875   link.
1876</t>
1877<t>
1878   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1879   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1880   discussion of the problems with the Keep-Alive header implemented by
1881   many HTTP/1.0 clients).
1882</t>
1883</section>
1884
1885<section title="Practical Considerations" anchor="persistent.practical">
1886<t>
1887   Servers will usually have some time-out value beyond which they will
1888   no longer maintain an inactive connection. Proxy servers might make
1889   this a higher value since it is likely that the client will be making
1890   more connections through the same server. The use of persistent
1891   connections places no requirements on the length (or existence) of
1892   this time-out for either the client or the server.
1893</t>
1894<t>
1895   When a client or server wishes to time-out it &SHOULD; issue a graceful
1896   close on the transport connection. Clients and servers &SHOULD; both
1897   constantly watch for the other side of the transport close, and
1898   respond to it as appropriate. If a client or server does not detect
1899   the other side's close promptly it could cause unnecessary resource
1900   drain on the network.
1901</t>
1902<t>
1903   A client, server, or proxy &MAY; close the transport connection at any
1904   time. For example, a client might have started to send a new request
1905   at the same time that the server has decided to close the "idle"
1906   connection. From the server's point of view, the connection is being
1907   closed while it was idle, but from the client's point of view, a
1908   request is in progress.
1909</t>
1910<t>
1911   This means that clients, servers, and proxies &MUST; be able to recover
1912   from asynchronous close events. Client software &SHOULD; reopen the
1913   transport connection and retransmit the aborted sequence of requests
1914   without user interaction so long as the request sequence is
1915   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1916   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1917   human operator the choice of retrying the request(s). Confirmation by
1918   user-agent software with semantic understanding of the application
1919   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1920   be repeated if the second sequence of requests fails.
1921</t>
1922<t>
1923   Servers &SHOULD; always respond to at least one request per connection,
1924   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1925   middle of transmitting a response, unless a network or client failure
1926   is suspected.
1927</t>
1928<t>
1929   Clients that use persistent connections &SHOULD; limit the number of
1930   simultaneous connections that they maintain to a given server. A
1931   single-user client &SHOULD-NOT; maintain more than 2 connections with
1932   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1933   another server or proxy, where N is the number of simultaneously
1934   active users. These guidelines are intended to improve HTTP response
1935   times and avoid congestion.
1936</t>
1937</section>
1938</section>
1939
1940<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1941
1942<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1943<t>
1944   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1945   flow control mechanisms to resolve temporary overloads, rather than
1946   terminating connections with the expectation that clients will retry.
1947   The latter technique can exacerbate network congestion.
1948</t>
1949</section>
1950
1951<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1952<t>
1953   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1954   the network connection for an error status while it is transmitting
1955   the request. If the client sees an error status, it &SHOULD;
1956   immediately cease transmitting the body. If the body is being sent
1957   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1958   empty trailer &MAY; be used to prematurely mark the end of the message.
1959   If the body was preceded by a Content-Length header, the client &MUST;
1960   close the connection.
1961</t>
1962</section>
1963
1964<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1965<t>
1966   The purpose of the 100 (Continue) status (see &status-100;) is to
1967   allow a client that is sending a request message with a request body
1968   to determine if the origin server is willing to accept the request
1969   (based on the request headers) before the client sends the request
1970   body. In some cases, it might either be inappropriate or highly
1971   inefficient for the client to send the body if the server will reject
1972   the message without looking at the body.
1973</t>
1974<t>
1975   Requirements for HTTP/1.1 clients:
1976  <list style="symbols">
1977    <t>
1978        If a client will wait for a 100 (Continue) response before
1979        sending the request body, it &MUST; send an Expect request-header
1980        field (&header-expect;) with the "100-continue" expectation.
1981    </t>
1982    <t>
1983        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1984        with the "100-continue" expectation if it does not intend
1985        to send a request body.
1986    </t>
1987  </list>
1988</t>
1989<t>
1990   Because of the presence of older implementations, the protocol allows
1991   ambiguous situations in which a client may send "Expect: 100-continue"
1992   without receiving either a 417 (Expectation Failed) status
1993   or a 100 (Continue) status. Therefore, when a client sends this
1994   header field to an origin server (possibly via a proxy) from which it
1995   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1996   for an indefinite period before sending the request body.
1997</t>
1998<t>
1999   Requirements for HTTP/1.1 origin servers:
2000  <list style="symbols">
2001    <t> Upon receiving a request which includes an Expect request-header
2002        field with the "100-continue" expectation, an origin server &MUST;
2003        either respond with 100 (Continue) status and continue to read
2004        from the input stream, or respond with a final status code. The
2005        origin server &MUST-NOT; wait for the request body before sending
2006        the 100 (Continue) response. If it responds with a final status
2007        code, it &MAY; close the transport connection or it &MAY; continue
2008        to read and discard the rest of the request.  It &MUST-NOT;
2009        perform the requested method if it returns a final status code.
2010    </t>
2011    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2012        the request message does not include an Expect request-header
2013        field with the "100-continue" expectation, and &MUST-NOT; send a
2014        100 (Continue) response if such a request comes from an HTTP/1.0
2015        (or earlier) client. There is an exception to this rule: for
2016        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2017        status in response to an HTTP/1.1 PUT or POST request that does
2018        not include an Expect request-header field with the "100-continue"
2019        expectation. This exception, the purpose of which is
2020        to minimize any client processing delays associated with an
2021        undeclared wait for 100 (Continue) status, applies only to
2022        HTTP/1.1 requests, and not to requests with any other HTTP-version
2023        value.
2024    </t>
2025    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2026        already received some or all of the request body for the
2027        corresponding request.
2028    </t>
2029    <t> An origin server that sends a 100 (Continue) response &MUST;
2030    ultimately send a final status code, once the request body is
2031        received and processed, unless it terminates the transport
2032        connection prematurely.
2033    </t>
2034    <t> If an origin server receives a request that does not include an
2035        Expect request-header field with the "100-continue" expectation,
2036        the request includes a request body, and the server responds
2037        with a final status code before reading the entire request body
2038        from the transport connection, then the server &SHOULD-NOT;  close
2039        the transport connection until it has read the entire request,
2040        or until the client closes the connection. Otherwise, the client
2041        might not reliably receive the response message. However, this
2042        requirement is not be construed as preventing a server from
2043        defending itself against denial-of-service attacks, or from
2044        badly broken client implementations.
2045      </t>
2046    </list>
2047</t>
2048<t>
2049   Requirements for HTTP/1.1 proxies:
2050  <list style="symbols">
2051    <t> If a proxy receives a request that includes an Expect request-header
2052        field with the "100-continue" expectation, and the proxy
2053        either knows that the next-hop server complies with HTTP/1.1 or
2054        higher, or does not know the HTTP version of the next-hop
2055        server, it &MUST; forward the request, including the Expect header
2056        field.
2057    </t>
2058    <t> If the proxy knows that the version of the next-hop server is
2059        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2060        respond with a 417 (Expectation Failed) status.
2061    </t>
2062    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2063        numbers received from recently-referenced next-hop servers.
2064    </t>
2065    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2066        request message was received from an HTTP/1.0 (or earlier)
2067        client and did not include an Expect request-header field with
2068        the "100-continue" expectation. This requirement overrides the
2069        general rule for forwarding of 1xx responses (see &status-1xx;).
2070    </t>
2071  </list>
2072</t>
2073</section>
2074
2075<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2076<t>
2077   If an HTTP/1.1 client sends a request which includes a request body,
2078   but which does not include an Expect request-header field with the
2079   "100-continue" expectation, and if the client is not directly
2080   connected to an HTTP/1.1 origin server, and if the client sees the
2081   connection close before receiving any status from the server, the
2082   client &SHOULD; retry the request.  If the client does retry this
2083   request, it &MAY; use the following "binary exponential backoff"
2084   algorithm to be assured of obtaining a reliable response:
2085  <list style="numbers">
2086    <t>
2087      Initiate a new connection to the server
2088    </t>
2089    <t>
2090      Transmit the request-headers
2091    </t>
2092    <t>
2093      Initialize a variable R to the estimated round-trip time to the
2094         server (e.g., based on the time it took to establish the
2095         connection), or to a constant value of 5 seconds if the round-trip
2096         time is not available.
2097    </t>
2098    <t>
2099       Compute T = R * (2**N), where N is the number of previous
2100         retries of this request.
2101    </t>
2102    <t>
2103       Wait either for an error response from the server, or for T
2104         seconds (whichever comes first)
2105    </t>
2106    <t>
2107       If no error response is received, after T seconds transmit the
2108         body of the request.
2109    </t>
2110    <t>
2111       If client sees that the connection is closed prematurely,
2112         repeat from step 1 until the request is accepted, an error
2113         response is received, or the user becomes impatient and
2114         terminates the retry process.
2115    </t>
2116  </list>
2117</t>
2118<t>
2119   If at any point an error status is received, the client
2120  <list style="symbols">
2121      <t>&SHOULD-NOT;  continue and</t>
2122
2123      <t>&SHOULD; close the connection if it has not completed sending the
2124        request message.</t>
2125    </list>
2126</t>
2127</section>
2128</section>
2129</section>
2130
2131
2132<section title="Header Field Definitions" anchor="header.fields">
2133<t>
2134   This section defines the syntax and semantics of HTTP/1.1 header fields
2135   related to message framing and transport protocols.
2136</t>
2137<t>
2138   For entity-header fields, both sender and recipient refer to either the
2139   client or the server, depending on who sends and who receives the entity.
2140</t>
2141
2142<section title="Connection" anchor="header.connection">
2143  <iref primary="true" item="Connection header" x:for-anchor=""/>
2144  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2145  <x:anchor-alias value="Connection"/>
2146  <x:anchor-alias value="connection-token"/>
2147  <x:anchor-alias value="Connection-v"/>
2148<t>
2149   The general-header field "Connection" allows the sender to specify
2150   options that are desired for that particular connection and &MUST-NOT;
2151   be communicated by proxies over further connections.
2152</t>
2153<t>
2154   The Connection header's value has the following grammar:
2155</t>
2156<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"/>
2157  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2158  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2159  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2160</artwork></figure>
2161<t>
2162   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2163   message is forwarded and, for each connection-token in this field,
2164   remove any header field(s) from the message with the same name as the
2165   connection-token. Connection options are signaled by the presence of
2166   a connection-token in the Connection header field, not by any
2167   corresponding additional header field(s), since the additional header
2168   field may not be sent if there are no parameters associated with that
2169   connection option.
2170</t>
2171<t>
2172   Message headers listed in the Connection header &MUST-NOT; include
2173   end-to-end headers, such as Cache-Control.
2174</t>
2175<t>
2176   HTTP/1.1 defines the "close" connection option for the sender to
2177   signal that the connection will be closed after completion of the
2178   response. For example,
2179</t>
2180<figure><artwork type="example">
2181  Connection: close
2182</artwork></figure>
2183<t>
2184   in either the request or the response header fields indicates that
2185   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2186   after the current request/response is complete.
2187</t>
2188<t>
2189   An HTTP/1.1 client that does not support persistent connections &MUST;
2190   include the "close" connection option in every request message.
2191</t>
2192<t>
2193   An HTTP/1.1 server that does not support persistent connections &MUST;
2194   include the "close" connection option in every response message that
2195   does not have a 1xx (informational) status code.
2196</t>
2197<t>
2198   A system receiving an HTTP/1.0 (or lower-version) message that
2199   includes a Connection header &MUST;, for each connection-token in this
2200   field, remove and ignore any header field(s) from the message with
2201   the same name as the connection-token. This protects against mistaken
2202   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2203</t>
2204</section>
2205
2206<section title="Content-Length" anchor="header.content-length">
2207  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2208  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2209  <x:anchor-alias value="Content-Length"/>
2210  <x:anchor-alias value="Content-Length-v"/>
2211<t>
2212   The entity-header field "Content-Length" indicates the size of the
2213   entity-body, in decimal number of OCTETs, sent to the recipient or,
2214   in the case of the HEAD method, the size of the entity-body that
2215   would have been sent had the request been a GET.
2216</t>
2217<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2218  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2219  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2220</artwork></figure>
2221<t>
2222   An example is
2223</t>
2224<figure><artwork type="example">
2225  Content-Length: 3495
2226</artwork></figure>
2227<t>
2228   Applications &SHOULD; use this field to indicate the transfer-length of
2229   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2230</t>
2231<t>
2232   Any Content-Length greater than or equal to zero is a valid value.
2233   <xref target="message.length"/> describes how to determine the length of a message-body
2234   if a Content-Length is not given.
2235</t>
2236<t>
2237   Note that the meaning of this field is significantly different from
2238   the corresponding definition in MIME, where it is an optional field
2239   used within the "message/external-body" content-type. In HTTP, it
2240   &SHOULD; be sent whenever the message's length can be determined prior
2241   to being transferred, unless this is prohibited by the rules in
2242   <xref target="message.length"/>.
2243</t>
2244</section>
2245
2246<section title="Date" anchor="header.date">
2247  <iref primary="true" item="Date header" x:for-anchor=""/>
2248  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2249  <x:anchor-alias value="Date"/>
2250  <x:anchor-alias value="Date-v"/>
2251<t>
2252   The general-header field "Date" represents the date and time at which
2253   the message was originated, having the same semantics as orig-date in
2254   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2255   HTTP-date, as described in <xref target="full.date"/>;
2256   it &MUST; be sent in rfc1123-date format.
2257</t>
2258<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2259  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2260  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2261</artwork></figure>
2262<t>
2263   An example is
2264</t>
2265<figure><artwork type="example">
2266  Date: Tue, 15 Nov 1994 08:12:31 GMT
2267</artwork></figure>
2268<t>
2269   Origin servers &MUST; include a Date header field in all responses,
2270   except in these cases:
2271  <list style="numbers">
2272      <t>If the response status code is 100 (Continue) or 101 (Switching
2273         Protocols), the response &MAY; include a Date header field, at
2274         the server's option.</t>
2275
2276      <t>If the response status code conveys a server error, e.g. 500
2277         (Internal Server Error) or 503 (Service Unavailable), and it is
2278         inconvenient or impossible to generate a valid Date.</t>
2279
2280      <t>If the server does not have a clock that can provide a
2281         reasonable approximation of the current time, its responses
2282         &MUST-NOT; include a Date header field. In this case, the rules
2283         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2284  </list>
2285</t>
2286<t>
2287   A received message that does not have a Date header field &MUST; be
2288   assigned one by the recipient if the message will be cached by that
2289   recipient or gatewayed via a protocol which requires a Date. An HTTP
2290   implementation without a clock &MUST-NOT; cache responses without
2291   revalidating them on every use. An HTTP cache, especially a shared
2292   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2293   clock with a reliable external standard.
2294</t>
2295<t>
2296   Clients &SHOULD; only send a Date header field in messages that include
2297   an entity-body, as in the case of the PUT and POST requests, and even
2298   then it is optional. A client without a clock &MUST-NOT; send a Date
2299   header field in a request.
2300</t>
2301<t>
2302   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2303   time subsequent to the generation of the message. It &SHOULD; represent
2304   the best available approximation of the date and time of message
2305   generation, unless the implementation has no means of generating a
2306   reasonably accurate date and time. In theory, the date ought to
2307   represent the moment just before the entity is generated. In
2308   practice, the date can be generated at any time during the message
2309   origination without affecting its semantic value.
2310</t>
2311
2312<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2313<t>
2314   Some origin server implementations might not have a clock available.
2315   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2316   values to a response, unless these values were associated
2317   with the resource by a system or user with a reliable clock. It &MAY;
2318   assign an Expires value that is known, at or before server
2319   configuration time, to be in the past (this allows "pre-expiration"
2320   of responses without storing separate Expires values for each
2321   resource).
2322</t>
2323</section>
2324</section>
2325
2326<section title="Host" anchor="header.host">
2327  <iref primary="true" item="Host header" x:for-anchor=""/>
2328  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2329  <x:anchor-alias value="Host"/>
2330  <x:anchor-alias value="Host-v"/>
2331<t>
2332   The request-header field "Host" specifies the Internet host and port
2333   number of the resource being requested, as obtained from the original
2334   URI given by the user or referring resource (generally an http URI,
2335   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2336   the naming authority of the origin server or gateway given by the
2337   original URL. This allows the origin server or gateway to
2338   differentiate between internally-ambiguous URLs, such as the root "/"
2339   URL of a server for multiple host names on a single IP address.
2340</t>
2341<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2342  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2343  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2344</artwork></figure>
2345<t>
2346   A "host" without any trailing port information implies the default
2347   port for the service requested (e.g., "80" for an HTTP URL). For
2348   example, a request on the origin server for
2349   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2350</t>
2351<figure><artwork type="example">
2352  GET /pub/WWW/ HTTP/1.1
2353  Host: www.example.org
2354</artwork></figure>
2355<t>
2356   A client &MUST; include a Host header field in all HTTP/1.1 request
2357   messages. If the requested URI does not include an Internet host
2358   name for the service being requested, then the Host header field &MUST;
2359   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2360   request message it forwards does contain an appropriate Host header
2361   field that identifies the service being requested by the proxy. All
2362   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2363   status code to any HTTP/1.1 request message which lacks a Host header
2364   field.
2365</t>
2366<t>
2367   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2368   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2369   for other requirements relating to Host.
2370</t>
2371</section>
2372
2373<section title="TE" anchor="header.te">
2374  <iref primary="true" item="TE header" x:for-anchor=""/>
2375  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2376  <x:anchor-alias value="TE"/>
2377  <x:anchor-alias value="TE-v"/>
2378  <x:anchor-alias value="t-codings"/>
2379<t>
2380   The request-header field "TE" indicates what extension transfer-codings
2381   it is willing to accept in the response and whether or not it is
2382   willing to accept trailer fields in a chunked transfer-coding. Its
2383   value may consist of the keyword "trailers" and/or a comma-separated
2384   list of extension transfer-coding names with optional accept
2385   parameters (as described in <xref target="transfer.codings"/>).
2386</t>
2387<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"/>
2388  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2389  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2390  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2391</artwork></figure>
2392<t>
2393   The presence of the keyword "trailers" indicates that the client is
2394   willing to accept trailer fields in a chunked transfer-coding, as
2395   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2396   transfer-coding values even though it does not itself represent a
2397   transfer-coding.
2398</t>
2399<t>
2400   Examples of its use are:
2401</t>
2402<figure><artwork type="example">
2403  TE: deflate
2404  TE:
2405  TE: trailers, deflate;q=0.5
2406</artwork></figure>
2407<t>
2408   The TE header field only applies to the immediate connection.
2409   Therefore, the keyword &MUST; be supplied within a Connection header
2410   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2411</t>
2412<t>
2413   A server tests whether a transfer-coding is acceptable, according to
2414   a TE field, using these rules:
2415  <list style="numbers">
2416    <x:lt>
2417      <t>The "chunked" transfer-coding is always acceptable. If the
2418         keyword "trailers" is listed, the client indicates that it is
2419         willing to accept trailer fields in the chunked response on
2420         behalf of itself and any downstream clients. The implication is
2421         that, if given, the client is stating that either all
2422         downstream clients are willing to accept trailer fields in the
2423         forwarded response, or that it will attempt to buffer the
2424         response on behalf of downstream recipients.
2425      </t><t>
2426         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2427         chunked response such that a client can be assured of buffering
2428         the entire response.</t>
2429    </x:lt>
2430    <x:lt>
2431      <t>If the transfer-coding being tested is one of the transfer-codings
2432         listed in the TE field, then it is acceptable unless it
2433         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2434         qvalue of 0 means "not acceptable.")</t>
2435    </x:lt>
2436    <x:lt>
2437      <t>If multiple transfer-codings are acceptable, then the
2438         acceptable transfer-coding with the highest non-zero qvalue is
2439         preferred.  The "chunked" transfer-coding always has a qvalue
2440         of 1.</t>
2441    </x:lt>
2442  </list>
2443</t>
2444<t>
2445   If the TE field-value is empty or if no TE field is present, the only
2446   transfer-coding  is "chunked". A message with no transfer-coding is
2447   always acceptable.
2448</t>
2449</section>
2450
2451<section title="Trailer" anchor="header.trailer">
2452  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2453  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2454  <x:anchor-alias value="Trailer"/>
2455  <x:anchor-alias value="Trailer-v"/>
2456<t>
2457   The general field "Trailer" indicates that the given set of
2458   header fields is present in the trailer of a message encoded with
2459   chunked transfer-coding.
2460</t>
2461<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2462  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2463  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2464</artwork></figure>
2465<t>
2466   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2467   message using chunked transfer-coding with a non-empty trailer. Doing
2468   so allows the recipient to know which header fields to expect in the
2469   trailer.
2470</t>
2471<t>
2472   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2473   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2474   trailer fields in a "chunked" transfer-coding.
2475</t>
2476<t>
2477   Message header fields listed in the Trailer header field &MUST-NOT;
2478   include the following header fields:
2479  <list style="symbols">
2480    <t>Transfer-Encoding</t>
2481    <t>Content-Length</t>
2482    <t>Trailer</t>
2483  </list>
2484</t>
2485</section>
2486
2487<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2488  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2489  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2490  <x:anchor-alias value="Transfer-Encoding"/>
2491  <x:anchor-alias value="Transfer-Encoding-v"/>
2492<t>
2493   The general-header "Transfer-Encoding" field indicates what (if any)
2494   type of transformation has been applied to the message body in order
2495   to safely transfer it between the sender and the recipient. This
2496   differs from the content-coding in that the transfer-coding is a
2497   property of the message, not of the entity.
2498</t>
2499<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2500  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2501                        <x:ref>Transfer-Encoding-v</x:ref>
2502  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2503</artwork></figure>
2504<t>
2505   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2506</t>
2507<figure><artwork type="example">
2508  Transfer-Encoding: chunked
2509</artwork></figure>
2510<t>
2511   If multiple encodings have been applied to an entity, the transfer-codings
2512   &MUST; be listed in the order in which they were applied.
2513   Additional information about the encoding parameters &MAY; be provided
2514   by other entity-header fields not defined by this specification.
2515</t>
2516<t>
2517   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2518   header.
2519</t>
2520</section>
2521
2522<section title="Upgrade" anchor="header.upgrade">
2523  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2524  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2525  <x:anchor-alias value="Upgrade"/>
2526  <x:anchor-alias value="Upgrade-v"/>
2527<t>
2528   The general-header "Upgrade" allows the client to specify what
2529   additional communication protocols it supports and would like to use
2530   if the server finds it appropriate to switch protocols. The server
2531   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2532   response to indicate which protocol(s) are being switched.
2533</t>
2534<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2535  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2536  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2537</artwork></figure>
2538<t>
2539   For example,
2540</t>
2541<figure><artwork type="example">
2542  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2543</artwork></figure>
2544<t>
2545   The Upgrade header field is intended to provide a simple mechanism
2546   for transition from HTTP/1.1 to some other, incompatible protocol. It
2547   does so by allowing the client to advertise its desire to use another
2548   protocol, such as a later version of HTTP with a higher major version
2549   number, even though the current request has been made using HTTP/1.1.
2550   This eases the difficult transition between incompatible protocols by
2551   allowing the client to initiate a request in the more commonly
2552   supported protocol while indicating to the server that it would like
2553   to use a "better" protocol if available (where "better" is determined
2554   by the server, possibly according to the nature of the method and/or
2555   resource being requested).
2556</t>
2557<t>
2558   The Upgrade header field only applies to switching application-layer
2559   protocols upon the existing transport-layer connection. Upgrade
2560   cannot be used to insist on a protocol change; its acceptance and use
2561   by the server is optional. The capabilities and nature of the
2562   application-layer communication after the protocol change is entirely
2563   dependent upon the new protocol chosen, although the first action
2564   after changing the protocol &MUST; be a response to the initial HTTP
2565   request containing the Upgrade header field.
2566</t>
2567<t>
2568   The Upgrade header field only applies to the immediate connection.
2569   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2570   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2571   HTTP/1.1 message.
2572</t>
2573<t>
2574   The Upgrade header field cannot be used to indicate a switch to a
2575   protocol on a different connection. For that purpose, it is more
2576   appropriate to use a 301, 302, 303, or 305 redirection response.
2577</t>
2578<t>
2579   This specification only defines the protocol name "HTTP" for use by
2580   the family of Hypertext Transfer Protocols, as defined by the HTTP
2581   version rules of <xref target="http.version"/> and future updates to this
2582   specification. Any token can be used as a protocol name; however, it
2583   will only be useful if both the client and server associate the name
2584   with the same protocol.
2585</t>
2586</section>
2587
2588<section title="Via" anchor="header.via">
2589  <iref primary="true" item="Via header" x:for-anchor=""/>
2590  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2591  <x:anchor-alias value="protocol-name"/>
2592  <x:anchor-alias value="protocol-version"/>
2593  <x:anchor-alias value="pseudonym"/>
2594  <x:anchor-alias value="received-by"/>
2595  <x:anchor-alias value="received-protocol"/>
2596  <x:anchor-alias value="Via"/>
2597  <x:anchor-alias value="Via-v"/>
2598<t>
2599   The general-header field "Via" &MUST; be used by gateways and proxies to
2600   indicate the intermediate protocols and recipients between the user
2601   agent and the server on requests, and between the origin server and
2602   the client on responses. It is analogous to the "Received" field defined in
2603   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2604   avoiding request loops, and identifying the protocol capabilities of
2605   all senders along the request/response chain.
2606</t>
2607<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"/>
2608  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2609  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2610                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2611  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2612  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2613  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2614  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2615  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2616</artwork></figure>
2617<t>
2618   The received-protocol indicates the protocol version of the message
2619   received by the server or client along each segment of the
2620   request/response chain. The received-protocol version is appended to
2621   the Via field value when the message is forwarded so that information
2622   about the protocol capabilities of upstream applications remains
2623   visible to all recipients.
2624</t>
2625<t>
2626   The protocol-name is optional if and only if it would be "HTTP". The
2627   received-by field is normally the host and optional port number of a
2628   recipient server or client that subsequently forwarded the message.
2629   However, if the real host is considered to be sensitive information,
2630   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2631   be assumed to be the default port of the received-protocol.
2632</t>
2633<t>
2634   Multiple Via field values represents each proxy or gateway that has
2635   forwarded the message. Each recipient &MUST; append its information
2636   such that the end result is ordered according to the sequence of
2637   forwarding applications.
2638</t>
2639<t>
2640   Comments &MAY; be used in the Via header field to identify the software
2641   of the recipient proxy or gateway, analogous to the User-Agent and
2642   Server header fields. However, all comments in the Via field are
2643   optional and &MAY; be removed by any recipient prior to forwarding the
2644   message.
2645</t>
2646<t>
2647   For example, a request message could be sent from an HTTP/1.0 user
2648   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2649   forward the request to a public proxy at p.example.net, which completes
2650   the request by forwarding it to the origin server at www.example.com.
2651   The request received by www.example.com would then have the following
2652   Via header field:
2653</t>
2654<figure><artwork type="example">
2655  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2656</artwork></figure>
2657<t>
2658   Proxies and gateways used as a portal through a network firewall
2659   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2660   the firewall region. This information &SHOULD; only be propagated if
2661   explicitly enabled. If not enabled, the received-by host of any host
2662   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2663   for that host.
2664</t>
2665<t>
2666   For organizations that have strong privacy requirements for hiding
2667   internal structures, a proxy &MAY; combine an ordered subsequence of
2668   Via header field entries with identical received-protocol values into
2669   a single such entry. For example,
2670</t>
2671<figure><artwork type="example">
2672  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2673</artwork></figure>
2674<t>
2675        could be collapsed to
2676</t>
2677<figure><artwork type="example">
2678  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2679</artwork></figure>
2680<t>
2681   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2682   under the same organizational control and the hosts have already been
2683   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2684   have different received-protocol values.
2685</t>
2686</section>
2687
2688</section>
2689
2690<section title="IANA Considerations" anchor="IANA.considerations">
2691<section title="Message Header Registration" anchor="message.header.registration">
2692<t>
2693   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2694   with the permanent registrations below (see <xref target="RFC3864"/>):
2695</t>
2696<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2697<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2698   <ttcol>Header Field Name</ttcol>
2699   <ttcol>Protocol</ttcol>
2700   <ttcol>Status</ttcol>
2701   <ttcol>Reference</ttcol>
2702
2703   <c>Connection</c>
2704   <c>http</c>
2705   <c>standard</c>
2706   <c>
2707      <xref target="header.connection"/>
2708   </c>
2709   <c>Content-Length</c>
2710   <c>http</c>
2711   <c>standard</c>
2712   <c>
2713      <xref target="header.content-length"/>
2714   </c>
2715   <c>Date</c>
2716   <c>http</c>
2717   <c>standard</c>
2718   <c>
2719      <xref target="header.date"/>
2720   </c>
2721   <c>Host</c>
2722   <c>http</c>
2723   <c>standard</c>
2724   <c>
2725      <xref target="header.host"/>
2726   </c>
2727   <c>TE</c>
2728   <c>http</c>
2729   <c>standard</c>
2730   <c>
2731      <xref target="header.te"/>
2732   </c>
2733   <c>Trailer</c>
2734   <c>http</c>
2735   <c>standard</c>
2736   <c>
2737      <xref target="header.trailer"/>
2738   </c>
2739   <c>Transfer-Encoding</c>
2740   <c>http</c>
2741   <c>standard</c>
2742   <c>
2743      <xref target="header.transfer-encoding"/>
2744   </c>
2745   <c>Upgrade</c>
2746   <c>http</c>
2747   <c>standard</c>
2748   <c>
2749      <xref target="header.upgrade"/>
2750   </c>
2751   <c>Via</c>
2752   <c>http</c>
2753   <c>standard</c>
2754   <c>
2755      <xref target="header.via"/>
2756   </c>
2757</texttable>
2758<!--(END)-->
2759<t>
2760   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2761</t>
2762</section>
2763
2764<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2765<t>
2766   The entry for the "http" URI Scheme in the registry located at
2767   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2768   should be updated to point to <xref target="http.uri"/> of this document
2769   (see <xref target="RFC4395"/>).
2770</t>
2771</section>
2772
2773<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2774<t>
2775   This document serves as the specification for the Internet media types
2776   "message/http" and "application/http". The following is to be registered with
2777   IANA (see <xref target="RFC4288"/>).
2778</t>
2779<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2780<iref item="Media Type" subitem="message/http" primary="true"/>
2781<iref item="message/http Media Type" primary="true"/>
2782<t>
2783   The message/http type can be used to enclose a single HTTP request or
2784   response message, provided that it obeys the MIME restrictions for all
2785   "message" types regarding line length and encodings.
2786</t>
2787<t>
2788  <list style="hanging" x:indent="12em">
2789    <t hangText="Type name:">
2790      message
2791    </t>
2792    <t hangText="Subtype name:">
2793      http
2794    </t>
2795    <t hangText="Required parameters:">
2796      none
2797    </t>
2798    <t hangText="Optional parameters:">
2799      version, msgtype
2800      <list style="hanging">
2801        <t hangText="version:">
2802          The HTTP-Version number of the enclosed message
2803          (e.g., "1.1"). If not present, the version can be
2804          determined from the first line of the body.
2805        </t>
2806        <t hangText="msgtype:">
2807          The message type -- "request" or "response". If not
2808          present, the type can be determined from the first
2809          line of the body.
2810        </t>
2811      </list>
2812    </t>
2813    <t hangText="Encoding considerations:">
2814      only "7bit", "8bit", or "binary" are permitted
2815    </t>
2816    <t hangText="Security considerations:">
2817      none
2818    </t>
2819    <t hangText="Interoperability considerations:">
2820      none
2821    </t>
2822    <t hangText="Published specification:">
2823      This specification (see <xref target="internet.media.type.message.http"/>).
2824    </t>
2825    <t hangText="Applications that use this media type:">
2826    </t>
2827    <t hangText="Additional information:">
2828      <list style="hanging">
2829        <t hangText="Magic number(s):">none</t>
2830        <t hangText="File extension(s):">none</t>
2831        <t hangText="Macintosh file type code(s):">none</t>
2832      </list>
2833    </t>
2834    <t hangText="Person and email address to contact for further information:">
2835      See Authors Section.
2836    </t>
2837                <t hangText="Intended usage:">
2838                  COMMON
2839    </t>
2840                <t hangText="Restrictions on usage:">
2841                  none
2842    </t>
2843    <t hangText="Author/Change controller:">
2844      IESG
2845    </t>
2846  </list>
2847</t>
2848</section>
2849<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2850<iref item="Media Type" subitem="application/http" primary="true"/>
2851<iref item="application/http Media Type" primary="true"/>
2852<t>
2853   The application/http type can be used to enclose a pipeline of one or more
2854   HTTP request or response messages (not intermixed).
2855</t>
2856<t>
2857  <list style="hanging" x:indent="12em">
2858    <t hangText="Type name:">
2859      application
2860    </t>
2861    <t hangText="Subtype name:">
2862      http
2863    </t>
2864    <t hangText="Required parameters:">
2865      none
2866    </t>
2867    <t hangText="Optional parameters:">
2868      version, msgtype
2869      <list style="hanging">
2870        <t hangText="version:">
2871          The HTTP-Version number of the enclosed messages
2872          (e.g., "1.1"). If not present, the version can be
2873          determined from the first line of the body.
2874        </t>
2875        <t hangText="msgtype:">
2876          The message type -- "request" or "response". If not
2877          present, the type can be determined from the first
2878          line of the body.
2879        </t>
2880      </list>
2881    </t>
2882    <t hangText="Encoding considerations:">
2883      HTTP messages enclosed by this type
2884      are in "binary" format; use of an appropriate
2885      Content-Transfer-Encoding is required when
2886      transmitted via E-mail.
2887    </t>
2888    <t hangText="Security considerations:">
2889      none
2890    </t>
2891    <t hangText="Interoperability considerations:">
2892      none
2893    </t>
2894    <t hangText="Published specification:">
2895      This specification (see <xref target="internet.media.type.application.http"/>).
2896    </t>
2897    <t hangText="Applications that use this media type:">
2898    </t>
2899    <t hangText="Additional information:">
2900      <list style="hanging">
2901        <t hangText="Magic number(s):">none</t>
2902        <t hangText="File extension(s):">none</t>
2903        <t hangText="Macintosh file type code(s):">none</t>
2904      </list>
2905    </t>
2906    <t hangText="Person and email address to contact for further information:">
2907      See Authors Section.
2908    </t>
2909                <t hangText="Intended usage:">
2910                  COMMON
2911    </t>
2912                <t hangText="Restrictions on usage:">
2913                  none
2914    </t>
2915    <t hangText="Author/Change controller:">
2916      IESG
2917    </t>
2918  </list>
2919</t>
2920</section>
2921</section>
2922
2923</section>
2924
2925<section title="Security Considerations" anchor="security.considerations">
2926<t>
2927   This section is meant to inform application developers, information
2928   providers, and users of the security limitations in HTTP/1.1 as
2929   described by this document. The discussion does not include
2930   definitive solutions to the problems revealed, though it does make
2931   some suggestions for reducing security risks.
2932</t>
2933
2934<section title="Personal Information" anchor="personal.information">
2935<t>
2936   HTTP clients are often privy to large amounts of personal information
2937   (e.g. the user's name, location, mail address, passwords, encryption
2938   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2939   leakage of this information.
2940   We very strongly recommend that a convenient interface be provided
2941   for the user to control dissemination of such information, and that
2942   designers and implementors be particularly careful in this area.
2943   History shows that errors in this area often create serious security
2944   and/or privacy problems and generate highly adverse publicity for the
2945   implementor's company.
2946</t>
2947</section>
2948
2949<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2950<t>
2951   A server is in the position to save personal data about a user's
2952   requests which might identify their reading patterns or subjects of
2953   interest. This information is clearly confidential in nature and its
2954   handling can be constrained by law in certain countries. People using
2955   HTTP to provide data are responsible for ensuring that
2956   such material is not distributed without the permission of any
2957   individuals that are identifiable by the published results.
2958</t>
2959</section>
2960
2961<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2962<t>
2963   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2964   the documents returned by HTTP requests to be only those that were
2965   intended by the server administrators. If an HTTP server translates
2966   HTTP URIs directly into file system calls, the server &MUST; take
2967   special care not to serve files that were not intended to be
2968   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2969   other operating systems use ".." as a path component to indicate a
2970   directory level above the current one. On such a system, an HTTP
2971   server &MUST; disallow any such construct in the request-target if it
2972   would otherwise allow access to a resource outside those intended to
2973   be accessible via the HTTP server. Similarly, files intended for
2974   reference only internally to the server (such as access control
2975   files, configuration files, and script code) &MUST; be protected from
2976   inappropriate retrieval, since they might contain sensitive
2977   information. Experience has shown that minor bugs in such HTTP server
2978   implementations have turned into security risks.
2979</t>
2980</section>
2981
2982<section title="DNS Spoofing" anchor="dns.spoofing">
2983<t>
2984   Clients using HTTP rely heavily on the Domain Name Service, and are
2985   thus generally prone to security attacks based on the deliberate
2986   mis-association of IP addresses and DNS names. Clients need to be
2987   cautious in assuming the continuing validity of an IP number/DNS name
2988   association.
2989</t>
2990<t>
2991   In particular, HTTP clients &SHOULD; rely on their name resolver for
2992   confirmation of an IP number/DNS name association, rather than
2993   caching the result of previous host name lookups. Many platforms
2994   already can cache host name lookups locally when appropriate, and
2995   they &SHOULD; be configured to do so. It is proper for these lookups to
2996   be cached, however, only when the TTL (Time To Live) information
2997   reported by the name server makes it likely that the cached
2998   information will remain useful.
2999</t>
3000<t>
3001   If HTTP clients cache the results of host name lookups in order to
3002   achieve a performance improvement, they &MUST; observe the TTL
3003   information reported by DNS.
3004</t>
3005<t>
3006   If HTTP clients do not observe this rule, they could be spoofed when
3007   a previously-accessed server's IP address changes. As network
3008   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3009   possibility of this form of attack will grow. Observing this
3010   requirement thus reduces this potential security vulnerability.
3011</t>
3012<t>
3013   This requirement also improves the load-balancing behavior of clients
3014   for replicated servers using the same DNS name and reduces the
3015   likelihood of a user's experiencing failure in accessing sites which
3016   use that strategy.
3017</t>
3018</section>
3019
3020<section title="Proxies and Caching" anchor="attack.proxies">
3021<t>
3022   By their very nature, HTTP proxies are men-in-the-middle, and
3023   represent an opportunity for man-in-the-middle attacks. Compromise of
3024   the systems on which the proxies run can result in serious security
3025   and privacy problems. Proxies have access to security-related
3026   information, personal information about individual users and
3027   organizations, and proprietary information belonging to users and
3028   content providers. A compromised proxy, or a proxy implemented or
3029   configured without regard to security and privacy considerations,
3030   might be used in the commission of a wide range of potential attacks.
3031</t>
3032<t>
3033   Proxy operators should protect the systems on which proxies run as
3034   they would protect any system that contains or transports sensitive
3035   information. In particular, log information gathered at proxies often
3036   contains highly sensitive personal information, and/or information
3037   about organizations. Log information should be carefully guarded, and
3038   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3039</t>
3040<t>
3041   Proxy implementors should consider the privacy and security
3042   implications of their design and coding decisions, and of the
3043   configuration options they provide to proxy operators (especially the
3044   default configuration).
3045</t>
3046<t>
3047   Users of a proxy need to be aware that they are no trustworthier than
3048   the people who run the proxy; HTTP itself cannot solve this problem.
3049</t>
3050<t>
3051   The judicious use of cryptography, when appropriate, may suffice to
3052   protect against a broad range of security and privacy attacks. Such
3053   cryptography is beyond the scope of the HTTP/1.1 specification.
3054</t>
3055</section>
3056
3057<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3058<t>
3059   They exist. They are hard to defend against. Research continues.
3060   Beware.
3061</t>
3062</section>
3063</section>
3064
3065<section title="Acknowledgments" anchor="ack">
3066<t>
3067   HTTP has evolved considerably over the years. It has
3068   benefited from a large and active developer community--the many
3069   people who have participated on the www-talk mailing list--and it is
3070   that community which has been most responsible for the success of
3071   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3072   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3073   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3074   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3075   VanHeyningen deserve special recognition for their efforts in
3076   defining early aspects of the protocol.
3077</t>
3078<t>
3079   This document has benefited greatly from the comments of all those
3080   participating in the HTTP-WG. In addition to those already mentioned,
3081   the following individuals have contributed to this specification:
3082</t>
3083<t>
3084   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3085   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3086   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3087   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3088   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3089   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3090   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3091   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3092   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3093   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3094   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3095   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3096   Josh Cohen.
3097</t>
3098<t>
3099   Thanks to the "cave men" of Palo Alto. You know who you are.
3100</t>
3101<t>
3102   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3103   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3104   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3105   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3106   Larry Masinter for their help. And thanks go particularly to Jeff
3107   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3108</t>
3109<t>
3110   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3111   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3112   discovery of many of the problems that this document attempts to
3113   rectify.
3114</t>
3115<t>
3116   This specification makes heavy use of the augmented BNF and generic
3117   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3118   reuses many of the definitions provided by Nathaniel Borenstein and
3119   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3120   specification will help reduce past confusion over the relationship
3121   between HTTP and Internet mail message formats.
3122</t>
3123</section>
3124
3125</middle>
3126<back>
3127
3128<references title="Normative References">
3129
3130<reference anchor="ISO-8859-1">
3131  <front>
3132    <title>
3133     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3134    </title>
3135    <author>
3136      <organization>International Organization for Standardization</organization>
3137    </author>
3138    <date year="1998"/>
3139  </front>
3140  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3141</reference>
3142
3143<reference anchor="Part2">
3144  <front>
3145    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3146    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3147      <organization abbrev="Day Software">Day Software</organization>
3148      <address><email>fielding@gbiv.com</email></address>
3149    </author>
3150    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3151      <organization>One Laptop per Child</organization>
3152      <address><email>jg@laptop.org</email></address>
3153    </author>
3154    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3155      <organization abbrev="HP">Hewlett-Packard Company</organization>
3156      <address><email>JeffMogul@acm.org</email></address>
3157    </author>
3158    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3159      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3160      <address><email>henrikn@microsoft.com</email></address>
3161    </author>
3162    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3163      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3164      <address><email>LMM@acm.org</email></address>
3165    </author>
3166    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3167      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3168      <address><email>paulle@microsoft.com</email></address>
3169    </author>
3170    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3171      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3172      <address><email>timbl@w3.org</email></address>
3173    </author>
3174    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3175      <organization abbrev="W3C">World Wide Web Consortium</organization>
3176      <address><email>ylafon@w3.org</email></address>
3177    </author>
3178    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3179      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3180      <address><email>julian.reschke@greenbytes.de</email></address>
3181    </author>
3182    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3183  </front>
3184  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3185  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3186</reference>
3187
3188<reference anchor="Part3">
3189  <front>
3190    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3191    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3192      <organization abbrev="Day Software">Day Software</organization>
3193      <address><email>fielding@gbiv.com</email></address>
3194    </author>
3195    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3196      <organization>One Laptop per Child</organization>
3197      <address><email>jg@laptop.org</email></address>
3198    </author>
3199    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3200      <organization abbrev="HP">Hewlett-Packard Company</organization>
3201      <address><email>JeffMogul@acm.org</email></address>
3202    </author>
3203    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3204      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3205      <address><email>henrikn@microsoft.com</email></address>
3206    </author>
3207    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3208      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3209      <address><email>LMM@acm.org</email></address>
3210    </author>
3211    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3212      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3213      <address><email>paulle@microsoft.com</email></address>
3214    </author>
3215    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3216      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3217      <address><email>timbl@w3.org</email></address>
3218    </author>
3219    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3220      <organization abbrev="W3C">World Wide Web Consortium</organization>
3221      <address><email>ylafon@w3.org</email></address>
3222    </author>
3223    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3224      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3225      <address><email>julian.reschke@greenbytes.de</email></address>
3226    </author>
3227    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3228  </front>
3229  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3230  <x:source href="p3-payload.xml" basename="p3-payload"/>
3231</reference>
3232
3233<reference anchor="Part5">
3234  <front>
3235    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3236    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3237      <organization abbrev="Day Software">Day Software</organization>
3238      <address><email>fielding@gbiv.com</email></address>
3239    </author>
3240    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3241      <organization>One Laptop per Child</organization>
3242      <address><email>jg@laptop.org</email></address>
3243    </author>
3244    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3245      <organization abbrev="HP">Hewlett-Packard Company</organization>
3246      <address><email>JeffMogul@acm.org</email></address>
3247    </author>
3248    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3249      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3250      <address><email>henrikn@microsoft.com</email></address>
3251    </author>
3252    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3253      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3254      <address><email>LMM@acm.org</email></address>
3255    </author>
3256    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3257      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3258      <address><email>paulle@microsoft.com</email></address>
3259    </author>
3260    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3261      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3262      <address><email>timbl@w3.org</email></address>
3263    </author>
3264    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3265      <organization abbrev="W3C">World Wide Web Consortium</organization>
3266      <address><email>ylafon@w3.org</email></address>
3267    </author>
3268    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3269      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3270      <address><email>julian.reschke@greenbytes.de</email></address>
3271    </author>
3272    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3273  </front>
3274  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3275  <x:source href="p5-range.xml" basename="p5-range"/>
3276</reference>
3277
3278<reference anchor="Part6">
3279  <front>
3280    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3281    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3282      <organization abbrev="Day Software">Day Software</organization>
3283      <address><email>fielding@gbiv.com</email></address>
3284    </author>
3285    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3286      <organization>One Laptop per Child</organization>
3287      <address><email>jg@laptop.org</email></address>
3288    </author>
3289    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3290      <organization abbrev="HP">Hewlett-Packard Company</organization>
3291      <address><email>JeffMogul@acm.org</email></address>
3292    </author>
3293    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3294      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3295      <address><email>henrikn@microsoft.com</email></address>
3296    </author>
3297    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3298      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3299      <address><email>LMM@acm.org</email></address>
3300    </author>
3301    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3302      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3303      <address><email>paulle@microsoft.com</email></address>
3304    </author>
3305    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3306      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3307      <address><email>timbl@w3.org</email></address>
3308    </author>
3309    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3310      <organization abbrev="W3C">World Wide Web Consortium</organization>
3311      <address><email>ylafon@w3.org</email></address>
3312    </author>
3313    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3314      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3315      <address><email>julian.reschke@greenbytes.de</email></address>
3316    </author>
3317    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3318  </front>
3319  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3320  <x:source href="p6-cache.xml" basename="p6-cache"/>
3321</reference>
3322
3323<reference anchor="RFC5234">
3324  <front>
3325    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3326    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3327      <organization>Brandenburg InternetWorking</organization>
3328      <address>
3329      <postal>
3330      <street>675 Spruce Dr.</street>
3331      <city>Sunnyvale</city>
3332      <region>CA</region>
3333      <code>94086</code>
3334      <country>US</country></postal>
3335      <phone>+1.408.246.8253</phone>
3336      <email>dcrocker@bbiw.net</email></address> 
3337    </author>
3338    <author initials="P." surname="Overell" fullname="Paul Overell">
3339      <organization>THUS plc.</organization>
3340      <address>
3341      <postal>
3342      <street>1/2 Berkeley Square</street>
3343      <street>99 Berkely Street</street>
3344      <city>Glasgow</city>
3345      <code>G3 7HR</code>
3346      <country>UK</country></postal>
3347      <email>paul.overell@thus.net</email></address>
3348    </author>
3349    <date month="January" year="2008"/>
3350  </front>
3351  <seriesInfo name="STD" value="68"/>
3352  <seriesInfo name="RFC" value="5234"/>
3353</reference>
3354
3355<reference anchor="RFC2045">
3356  <front>
3357    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3358    <author initials="N." surname="Freed" fullname="Ned Freed">
3359      <organization>Innosoft International, Inc.</organization>
3360      <address><email>ned@innosoft.com</email></address>
3361    </author>
3362    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3363      <organization>First Virtual Holdings</organization>
3364      <address><email>nsb@nsb.fv.com</email></address>
3365    </author>
3366    <date month="November" year="1996"/>
3367  </front>
3368  <seriesInfo name="RFC" value="2045"/>
3369</reference>
3370
3371<reference anchor="RFC2119">
3372  <front>
3373    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3374    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3375      <organization>Harvard University</organization>
3376      <address><email>sob@harvard.edu</email></address>
3377    </author>
3378    <date month="March" year="1997"/>
3379  </front>
3380  <seriesInfo name="BCP" value="14"/>
3381  <seriesInfo name="RFC" value="2119"/>
3382</reference>
3383
3384<reference anchor="RFC3986">
3385 <front>
3386  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3387  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3388    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3389    <address>
3390       <email>timbl@w3.org</email>
3391       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3392    </address>
3393  </author>
3394  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3395    <organization abbrev="Day Software">Day Software</organization>
3396    <address>
3397      <email>fielding@gbiv.com</email>
3398      <uri>http://roy.gbiv.com/</uri>
3399    </address>
3400  </author>
3401  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3402    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3403    <address>
3404      <email>LMM@acm.org</email>
3405      <uri>http://larry.masinter.net/</uri>
3406    </address>
3407  </author>
3408  <date month='January' year='2005'></date>
3409 </front>
3410 <seriesInfo name="RFC" value="3986"/>
3411 <seriesInfo name="STD" value="66"/>
3412</reference>
3413
3414<reference anchor="USASCII">
3415  <front>
3416    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3417    <author>
3418      <organization>American National Standards Institute</organization>
3419    </author>
3420    <date year="1986"/>
3421  </front>
3422  <seriesInfo name="ANSI" value="X3.4"/>
3423</reference>
3424
3425</references>
3426
3427<references title="Informative References">
3428
3429<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3430  <front>
3431    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3432    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3433      <organization/>
3434    </author>
3435    <author initials="J." surname="Gettys" fullname="J. Gettys">
3436      <organization/>
3437    </author>
3438    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3439      <organization/>
3440    </author>
3441    <author initials="H." surname="Lie" fullname="H. Lie">
3442      <organization/>
3443    </author>
3444    <author initials="C." surname="Lilley" fullname="C. Lilley">
3445      <organization/>
3446    </author>
3447    <date year="1997" month="September"/>
3448  </front>
3449  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3450</reference>
3451
3452<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3453  <front>
3454    <title>Improving HTTP Latency</title>
3455    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3456      <organization/>
3457    </author>
3458    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3459      <organization/>
3460    </author>
3461    <date year="1995" month="December"/>
3462  </front>
3463  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3464</reference>
3465
3466<reference anchor="RFC959">
3467  <front>
3468    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3469    <author initials="J." surname="Postel" fullname="J. Postel">
3470      <organization>Information Sciences Institute (ISI)</organization>
3471    </author>
3472    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3473      <organization/>
3474    </author>
3475    <date month="October" year="1985"/>
3476  </front>
3477  <seriesInfo name="STD" value="9"/>
3478  <seriesInfo name="RFC" value="959"/>
3479</reference>
3480
3481<reference anchor="RFC1123">
3482  <front>
3483    <title>Requirements for Internet Hosts - Application and Support</title>
3484    <author initials="R." surname="Braden" fullname="Robert Braden">
3485      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3486      <address><email>Braden@ISI.EDU</email></address>
3487    </author>
3488    <date month="October" year="1989"/>
3489  </front>
3490  <seriesInfo name="STD" value="3"/>
3491  <seriesInfo name="RFC" value="1123"/>
3492</reference>
3493
3494<reference anchor="RFC1305">
3495  <front>
3496    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3497    <author initials="D." surname="Mills" fullname="David L. Mills">
3498      <organization>University of Delaware, Electrical Engineering Department</organization>
3499      <address><email>mills@udel.edu</email></address>
3500    </author>
3501    <date month="March" year="1992"/>
3502  </front>
3503  <seriesInfo name="RFC" value="1305"/>
3504</reference>
3505
3506<reference anchor="RFC1436">
3507  <front>
3508    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3509    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3510      <organization>University of Minnesota, Computer and Information Services</organization>
3511      <address><email>fxa@boombox.micro.umn.edu</email></address>
3512    </author>
3513    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3514      <organization>University of Minnesota, Computer and Information Services</organization>
3515      <address><email>mpm@boombox.micro.umn.edu</email></address>
3516    </author>
3517    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3518      <organization>University of Minnesota, Computer and Information Services</organization>
3519      <address><email>lindner@boombox.micro.umn.edu</email></address>
3520    </author>
3521    <author initials="D." surname="Johnson" fullname="David Johnson">
3522      <organization>University of Minnesota, Computer and Information Services</organization>
3523      <address><email>dmj@boombox.micro.umn.edu</email></address>
3524    </author>
3525    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3526      <organization>University of Minnesota, Computer and Information Services</organization>
3527      <address><email>daniel@boombox.micro.umn.edu</email></address>
3528    </author>
3529    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3530      <organization>University of Minnesota, Computer and Information Services</organization>
3531      <address><email>alberti@boombox.micro.umn.edu</email></address>
3532    </author>
3533    <date month="March" year="1993"/>
3534  </front>
3535  <seriesInfo name="RFC" value="1436"/>
3536</reference>
3537
3538<reference anchor="RFC1900">
3539  <front>
3540    <title>Renumbering Needs Work</title>
3541    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3542      <organization>CERN, Computing and Networks Division</organization>
3543      <address><email>brian@dxcoms.cern.ch</email></address>
3544    </author>
3545    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3546      <organization>cisco Systems</organization>
3547      <address><email>yakov@cisco.com</email></address>
3548    </author>
3549    <date month="February" year="1996"/>
3550  </front>
3551  <seriesInfo name="RFC" value="1900"/>
3552</reference>
3553
3554<reference anchor="RFC1945">
3555  <front>
3556    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3557    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3558      <organization>MIT, Laboratory for Computer Science</organization>
3559      <address><email>timbl@w3.org</email></address>
3560    </author>
3561    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3562      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3563      <address><email>fielding@ics.uci.edu</email></address>
3564    </author>
3565    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3566      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3567      <address><email>frystyk@w3.org</email></address>
3568    </author>
3569    <date month="May" year="1996"/>
3570  </front>
3571  <seriesInfo name="RFC" value="1945"/>
3572</reference>
3573
3574<reference anchor="RFC2047">
3575  <front>
3576    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3577    <author initials="K." surname="Moore" fullname="Keith Moore">
3578      <organization>University of Tennessee</organization>
3579      <address><email>moore@cs.utk.edu</email></address>
3580    </author>
3581    <date month="November" year="1996"/>
3582  </front>
3583  <seriesInfo name="RFC" value="2047"/>
3584</reference>
3585
3586<reference anchor="RFC2068">
3587  <front>
3588    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3589    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3590      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3591      <address><email>fielding@ics.uci.edu</email></address>
3592    </author>
3593    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3594      <organization>MIT Laboratory for Computer Science</organization>
3595      <address><email>jg@w3.org</email></address>
3596    </author>
3597    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3598      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3599      <address><email>mogul@wrl.dec.com</email></address>
3600    </author>
3601    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3602      <organization>MIT Laboratory for Computer Science</organization>
3603      <address><email>frystyk@w3.org</email></address>
3604    </author>
3605    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3606      <organization>MIT Laboratory for Computer Science</organization>
3607      <address><email>timbl@w3.org</email></address>
3608    </author>
3609    <date month="January" year="1997"/>
3610  </front>
3611  <seriesInfo name="RFC" value="2068"/>
3612</reference>
3613
3614<reference anchor='RFC2109'>
3615  <front>
3616    <title>HTTP State Management Mechanism</title>
3617    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3618      <organization>Bell Laboratories, Lucent Technologies</organization>
3619      <address><email>dmk@bell-labs.com</email></address>
3620    </author>
3621    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3622      <organization>Netscape Communications Corp.</organization>
3623      <address><email>montulli@netscape.com</email></address>
3624    </author>
3625    <date year='1997' month='February' />
3626  </front>
3627  <seriesInfo name='RFC' value='2109' />
3628</reference>
3629
3630<reference anchor="RFC2145">
3631  <front>
3632    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3633    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3634      <organization>Western Research Laboratory</organization>
3635      <address><email>mogul@wrl.dec.com</email></address>
3636    </author>
3637    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3638      <organization>Department of Information and Computer Science</organization>
3639      <address><email>fielding@ics.uci.edu</email></address>
3640    </author>
3641    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3642      <organization>MIT Laboratory for Computer Science</organization>
3643      <address><email>jg@w3.org</email></address>
3644    </author>
3645    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3646      <organization>W3 Consortium</organization>
3647      <address><email>frystyk@w3.org</email></address>
3648    </author>
3649    <date month="May" year="1997"/>
3650  </front>
3651  <seriesInfo name="RFC" value="2145"/>
3652</reference>
3653
3654<reference anchor="RFC2616">
3655  <front>
3656    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3657    <author initials="R." surname="Fielding" fullname="R. Fielding">
3658      <organization>University of California, Irvine</organization>
3659      <address><email>fielding@ics.uci.edu</email></address>
3660    </author>
3661    <author initials="J." surname="Gettys" fullname="J. Gettys">
3662      <organization>W3C</organization>
3663      <address><email>jg@w3.org</email></address>
3664    </author>
3665    <author initials="J." surname="Mogul" fullname="J. Mogul">
3666      <organization>Compaq Computer Corporation</organization>
3667      <address><email>mogul@wrl.dec.com</email></address>
3668    </author>
3669    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3670      <organization>MIT Laboratory for Computer Science</organization>
3671      <address><email>frystyk@w3.org</email></address>
3672    </author>
3673    <author initials="L." surname="Masinter" fullname="L. Masinter">
3674      <organization>Xerox Corporation</organization>
3675      <address><email>masinter@parc.xerox.com</email></address>
3676    </author>
3677    <author initials="P." surname="Leach" fullname="P. Leach">
3678      <organization>Microsoft Corporation</organization>
3679      <address><email>paulle@microsoft.com</email></address>
3680    </author>
3681    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3682      <organization>W3C</organization>
3683      <address><email>timbl@w3.org</email></address>
3684    </author>
3685    <date month="June" year="1999"/>
3686  </front>
3687  <seriesInfo name="RFC" value="2616"/>
3688</reference>
3689
3690<reference anchor='RFC2818'>
3691  <front>
3692    <title>HTTP Over TLS</title>
3693    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3694      <organization>RTFM, Inc.</organization>
3695      <address><email>ekr@rtfm.com</email></address>
3696    </author>
3697    <date year='2000' month='May' />
3698  </front>
3699  <seriesInfo name='RFC' value='2818' />
3700</reference>
3701
3702<reference anchor='RFC2965'>
3703  <front>
3704    <title>HTTP State Management Mechanism</title>
3705    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3706      <organization>Bell Laboratories, Lucent Technologies</organization>
3707      <address><email>dmk@bell-labs.com</email></address>
3708    </author>
3709    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3710      <organization>Epinions.com, Inc.</organization>
3711      <address><email>lou@montulli.org</email></address>
3712    </author>
3713    <date year='2000' month='October' />
3714  </front>
3715  <seriesInfo name='RFC' value='2965' />
3716</reference>
3717
3718<reference anchor='RFC3864'>
3719  <front>
3720    <title>Registration Procedures for Message Header Fields</title>
3721    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3722      <organization>Nine by Nine</organization>
3723      <address><email>GK-IETF@ninebynine.org</email></address>
3724    </author>
3725    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3726      <organization>BEA Systems</organization>
3727      <address><email>mnot@pobox.com</email></address>
3728    </author>
3729    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3730      <organization>HP Labs</organization>
3731      <address><email>JeffMogul@acm.org</email></address>
3732    </author>
3733    <date year='2004' month='September' />
3734  </front>
3735  <seriesInfo name='BCP' value='90' />
3736  <seriesInfo name='RFC' value='3864' />
3737</reference>
3738
3739<reference anchor='RFC3977'>
3740  <front>
3741    <title>Network News Transfer Protocol (NNTP)</title>
3742    <author initials='C.' surname='Feather' fullname='C. Feather'>
3743      <organization>THUS plc</organization>
3744      <address><email>clive@demon.net</email></address>
3745    </author>
3746    <date year='2006' month='October' />
3747  </front>
3748  <seriesInfo name="RFC" value="3977"/>
3749</reference>
3750
3751<reference anchor="RFC4288">
3752  <front>
3753    <title>Media Type Specifications and Registration Procedures</title>
3754    <author initials="N." surname="Freed" fullname="N. Freed">
3755      <organization>Sun Microsystems</organization>
3756      <address>
3757        <email>ned.freed@mrochek.com</email>
3758      </address>
3759    </author>
3760    <author initials="J." surname="Klensin" fullname="J. Klensin">
3761      <organization/>
3762      <address>
3763        <email>klensin+ietf@jck.com</email>
3764      </address>
3765    </author>
3766    <date year="2005" month="December"/>
3767  </front>
3768  <seriesInfo name="BCP" value="13"/>
3769  <seriesInfo name="RFC" value="4288"/>
3770</reference>
3771
3772<reference anchor='RFC4395'>
3773  <front>
3774    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3775    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3776      <organization>AT&amp;T Laboratories</organization>
3777      <address>
3778        <email>tony+urireg@maillennium.att.com</email>
3779      </address>
3780    </author>
3781    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3782      <organization>Qualcomm, Inc.</organization>
3783      <address>
3784        <email>hardie@qualcomm.com</email>
3785      </address>
3786    </author>
3787    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3788      <organization>Adobe Systems</organization>
3789      <address>
3790        <email>LMM@acm.org</email>
3791      </address>
3792    </author>
3793    <date year='2006' month='February' />
3794  </front>
3795  <seriesInfo name='BCP' value='115' />
3796  <seriesInfo name='RFC' value='4395' />
3797</reference>
3798
3799<reference anchor="RFC5322">
3800  <front>
3801    <title>Internet Message Format</title>
3802    <author initials="P." surname="Resnick" fullname="P. Resnick">
3803      <organization>Qualcomm Incorporated</organization>
3804    </author>
3805    <date year="2008" month="October"/>
3806  </front> 
3807  <seriesInfo name="RFC" value="5322"/>
3808</reference>
3809
3810<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3811  <front>
3812    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3813    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3814      <organization/>
3815    </author>
3816    <date year="2001" month="November"/>
3817  </front>
3818  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3819</reference>
3820
3821<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3822  <front>
3823  <title>Analysis of HTTP Performance Problems</title>
3824  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3825    <organization/>
3826  </author>
3827  <date/>
3828  </front>
3829</reference>
3830
3831<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3832  <front>
3833  <title>Analysis of HTTP Performance</title>
3834  <author initials="J." surname="Touch" fullname="Joe Touch">
3835    <organization>USC/Information Sciences Institute</organization>
3836    <address><email>touch@isi.edu</email></address>
3837  </author>
3838  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3839    <organization>USC/Information Sciences Institute</organization>
3840    <address><email>johnh@isi.edu</email></address>
3841  </author>
3842  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3843    <organization>USC/Information Sciences Institute</organization>
3844    <address><email>katia@isi.edu</email></address>
3845  </author>
3846  <date year="1998" month="Aug"/>
3847  </front>
3848  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3849  <annotation>(original report dated Aug. 1996)</annotation>
3850</reference>
3851
3852<reference anchor="WAIS">
3853  <front>
3854    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3855    <author initials="F." surname="Davis" fullname="F. Davis">
3856      <organization>Thinking Machines Corporation</organization>
3857    </author>
3858    <author initials="B." surname="Kahle" fullname="B. Kahle">
3859      <organization>Thinking Machines Corporation</organization>
3860    </author>
3861    <author initials="H." surname="Morris" fullname="H. Morris">
3862      <organization>Thinking Machines Corporation</organization>
3863    </author>
3864    <author initials="J." surname="Salem" fullname="J. Salem">
3865      <organization>Thinking Machines Corporation</organization>
3866    </author>
3867    <author initials="T." surname="Shen" fullname="T. Shen">
3868      <organization>Thinking Machines Corporation</organization>
3869    </author>
3870    <author initials="R." surname="Wang" fullname="R. Wang">
3871      <organization>Thinking Machines Corporation</organization>
3872    </author>
3873    <author initials="J." surname="Sui" fullname="J. Sui">
3874      <organization>Thinking Machines Corporation</organization>
3875    </author>
3876    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3877      <organization>Thinking Machines Corporation</organization>
3878    </author>
3879    <date month="April" year="1990"/>
3880  </front>
3881  <seriesInfo name="Thinking Machines Corporation" value=""/>
3882</reference>
3883
3884</references>
3885
3886
3887<section title="Tolerant Applications" anchor="tolerant.applications">
3888<t>
3889   Although this document specifies the requirements for the generation
3890   of HTTP/1.1 messages, not all applications will be correct in their
3891   implementation. We therefore recommend that operational applications
3892   be tolerant of deviations whenever those deviations can be
3893   interpreted unambiguously.
3894</t>
3895<t>
3896   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3897   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3898   accept any amount of WSP characters between fields, even though
3899   only a single SP is required.
3900</t>
3901<t>
3902   The line terminator for message-header fields is the sequence CRLF.
3903   However, we recommend that applications, when parsing such headers,
3904   recognize a single LF as a line terminator and ignore the leading CR.
3905</t>
3906<t>
3907   The character set of an entity-body &SHOULD; be labeled as the lowest
3908   common denominator of the character codes used within that body, with
3909   the exception that not labeling the entity is preferred over labeling
3910   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3911</t>
3912<t>
3913   Additional rules for requirements on parsing and encoding of dates
3914   and other potential problems with date encodings include:
3915</t>
3916<t>
3917  <list style="symbols">
3918     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3919        which appears to be more than 50 years in the future is in fact
3920        in the past (this helps solve the "year 2000" problem).</t>
3921
3922     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3923        Expires date as earlier than the proper value, but &MUST-NOT;
3924        internally represent a parsed Expires date as later than the
3925        proper value.</t>
3926
3927     <t>All expiration-related calculations &MUST; be done in GMT. The
3928        local time zone &MUST-NOT; influence the calculation or comparison
3929        of an age or expiration time.</t>
3930
3931     <t>If an HTTP header incorrectly carries a date value with a time
3932        zone other than GMT, it &MUST; be converted into GMT using the
3933        most conservative possible conversion.</t>
3934  </list>
3935</t>
3936</section>
3937
3938<section title="Compatibility with Previous Versions" anchor="compatibility">
3939<t>
3940   HTTP has been in use by the World-Wide Web global information initiative
3941   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3942   was a simple protocol for hypertext data transfer across the Internet
3943   with only a single method and no metadata.
3944   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3945   methods and MIME-like messaging that could include metadata about the data
3946   transferred and modifiers on the request/response semantics. However,
3947   HTTP/1.0 did not sufficiently take into consideration the effects of
3948   hierarchical proxies, caching, the need for persistent connections, or
3949   name-based virtual hosts. The proliferation of incompletely-implemented
3950   applications calling themselves "HTTP/1.0" further necessitated a
3951   protocol version change in order for two communicating applications
3952   to determine each other's true capabilities.
3953</t>
3954<t>
3955   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3956   requirements that enable reliable implementations, adding only
3957   those new features that will either be safely ignored by an HTTP/1.0
3958   recipient or only sent when communicating with a party advertising
3959   compliance with HTTP/1.1.
3960</t>
3961<t>
3962   It is beyond the scope of a protocol specification to mandate
3963   compliance with previous versions. HTTP/1.1 was deliberately
3964   designed, however, to make supporting previous versions easy. It is
3965   worth noting that, at the time of composing this specification
3966   (1996), we would expect commercial HTTP/1.1 servers to:
3967  <list style="symbols">
3968     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3969        1.1 requests;</t>
3970
3971     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3972        1.1;</t>
3973
3974     <t>respond appropriately with a message in the same major version
3975        used by the client.</t>
3976  </list>
3977</t>
3978<t>
3979   And we would expect HTTP/1.1 clients to:
3980  <list style="symbols">
3981     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3982        responses;</t>
3983
3984     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3985        1.1.</t>
3986  </list>
3987</t>
3988<t>
3989   For most implementations of HTTP/1.0, each connection is established
3990   by the client prior to the request and closed by the server after
3991   sending the response. Some implementations implement the Keep-Alive
3992   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3993</t>
3994
3995<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3996<t>
3997   This section summarizes major differences between versions HTTP/1.0
3998   and HTTP/1.1.
3999</t>
4000
4001<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">
4002<t>
4003   The requirements that clients and servers support the Host request-header,
4004   report an error if the Host request-header (<xref target="header.host"/>) is
4005   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4006   are among the most important changes defined by this
4007   specification.
4008</t>
4009<t>
4010   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4011   addresses and servers; there was no other established mechanism for
4012   distinguishing the intended server of a request than the IP address
4013   to which that request was directed. The changes outlined above will
4014   allow the Internet, once older HTTP clients are no longer common, to
4015   support multiple Web sites from a single IP address, greatly
4016   simplifying large operational Web servers, where allocation of many
4017   IP addresses to a single host has created serious problems. The
4018   Internet will also be able to recover the IP addresses that have been
4019   allocated for the sole purpose of allowing special-purpose domain
4020   names to be used in root-level HTTP URLs. Given the rate of growth of
4021   the Web, and the number of servers already deployed, it is extremely
4022   important that all implementations of HTTP (including updates to
4023   existing HTTP/1.0 applications) correctly implement these
4024   requirements:
4025  <list style="symbols">
4026     <t>Both clients and servers &MUST; support the Host request-header.</t>
4027
4028     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4029
4030     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4031        request does not include a Host request-header.</t>
4032
4033     <t>Servers &MUST; accept absolute URIs.</t>
4034  </list>
4035</t>
4036</section>
4037</section>
4038
4039<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4040<t>
4041   Some clients and servers might wish to be compatible with some
4042   previous implementations of persistent connections in HTTP/1.0
4043   clients and servers. Persistent connections in HTTP/1.0 are
4044   explicitly negotiated as they are not the default behavior. HTTP/1.0
4045   experimental implementations of persistent connections are faulty,
4046   and the new facilities in HTTP/1.1 are designed to rectify these
4047   problems. The problem was that some existing 1.0 clients may be
4048   sending Keep-Alive to a proxy server that doesn't understand
4049   Connection, which would then erroneously forward it to the next
4050   inbound server, which would establish the Keep-Alive connection and
4051   result in a hung HTTP/1.0 proxy waiting for the close on the
4052   response. The result is that HTTP/1.0 clients must be prevented from
4053   using Keep-Alive when talking to proxies.
4054</t>
4055<t>
4056   However, talking to proxies is the most important use of persistent
4057   connections, so that prohibition is clearly unacceptable. Therefore,
4058   we need some other mechanism for indicating a persistent connection
4059   is desired, which is safe to use even when talking to an old proxy
4060   that ignores Connection. Persistent connections are the default for
4061   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4062   declaring non-persistence. See <xref target="header.connection"/>.
4063</t>
4064<t>
4065   The original HTTP/1.0 form of persistent connections (the Connection:
4066   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4067</t>
4068</section>
4069
4070<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4071<t>
4072   This specification has been carefully audited to correct and
4073   disambiguate key word usage; RFC 2068 had many problems in respect to
4074   the conventions laid out in <xref target="RFC2119"/>.
4075</t>
4076<t>
4077   Transfer-coding and message lengths all interact in ways that
4078   required fixing exactly when chunked encoding is used (to allow for
4079   transfer encoding that may not be self delimiting); it was important
4080   to straighten out exactly how message lengths are computed. (Sections
4081   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4082   <xref target="header.content-length" format="counter"/>,
4083   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4084</t>
4085<t>
4086   The use and interpretation of HTTP version numbers has been clarified
4087   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4088   version they support to deal with problems discovered in HTTP/1.0
4089   implementations (<xref target="http.version"/>)
4090</t>
4091<t>
4092   Transfer-coding had significant problems, particularly with
4093   interactions with chunked encoding. The solution is that transfer-codings
4094   become as full fledged as content-codings. This involves
4095   adding an IANA registry for transfer-codings (separate from content
4096   codings), a new header field (TE) and enabling trailer headers in the
4097   future. Transfer encoding is a major performance benefit, so it was
4098   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4099   interoperability problem that could have occurred due to interactions
4100   between authentication trailers, chunked encoding and HTTP/1.0
4101   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4102   and <xref target="header.te" format="counter"/>)
4103</t>
4104</section>
4105
4106<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4107<t>
4108  Empty list elements in list productions have been deprecated.
4109  (<xref target="notation.abnf"/>)
4110</t>
4111<t>
4112  Rules about implicit linear whitespace between certain grammar productions
4113  have been removed; now it's only allowed when specifically pointed out
4114  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4115  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4116  Non-ASCII content in header fields and reason phrase has been obsoleted and
4117  made opaque (the TEXT rule was removed)
4118  (<xref target="basic.rules"/>)
4119</t>
4120<t>
4121  Clarify that HTTP-Version is case sensitive.
4122  (<xref target="http.version"/>)
4123</t>
4124<t>
4125  Remove reference to non-existant identity transfer-coding value tokens.
4126  (Sections <xref format="counter" target="transfer.codings"/> and
4127  <xref format="counter" target="message.length"/>)
4128</t>
4129<t>
4130  Clarification that the chunk length does not include
4131  the count of the octets in the chunk header and trailer.
4132  (<xref target="chunked.transfer.encoding"/>)
4133</t>
4134<t>
4135  Require that invalid whitespace around field-names be rejected.
4136  (<xref target="message.headers"/>)
4137</t>
4138<t>
4139  Update use of abs_path production from RFC1808 to the path-absolute + query
4140  components of RFC3986.
4141  (<xref target="request-target"/>)
4142</t>
4143<t>
4144  Clarify exactly when close connection options must be sent.
4145  (<xref target="header.connection"/>)
4146</t>
4147</section>
4148</section>
4149
4150<section title="Terminology" anchor="terminology">
4151<t>
4152   This specification uses a number of terms to refer to the roles
4153   played by participants in, and objects of, the HTTP communication.
4154</t>
4155<t>
4156  <iref item="cache"/>
4157  <x:dfn>cache</x:dfn>
4158  <list>
4159    <t>
4160      A program's local store of response messages and the subsystem
4161      that controls its message storage, retrieval, and deletion. A
4162      cache stores cacheable responses in order to reduce the response
4163      time and network bandwidth consumption on future, equivalent
4164      requests. Any client or server may include a cache, though a cache
4165      cannot be used by a server that is acting as a tunnel.
4166    </t>
4167  </list>
4168</t>
4169<t>
4170  <iref item="cacheable"/>
4171  <x:dfn>cacheable</x:dfn>
4172  <list>
4173    <t>
4174      A response is cacheable if a cache is allowed to store a copy of
4175      the response message for use in answering subsequent requests. The
4176      rules for determining the cacheability of HTTP responses are
4177      defined in &caching;. Even if a resource is cacheable, there may
4178      be additional constraints on whether a cache can use the cached
4179      copy for a particular request.
4180    </t>
4181  </list>
4182</t>
4183<t>
4184  <iref item="client"/>
4185  <x:dfn>client</x:dfn>
4186  <list>
4187    <t>
4188      A program that establishes connections for the purpose of sending
4189      requests.
4190    </t>
4191  </list>
4192</t>
4193<t>
4194  <iref item="connection"/>
4195  <x:dfn>connection</x:dfn>
4196  <list>
4197    <t>
4198      A transport layer virtual circuit established between two programs
4199      for the purpose of communication.
4200    </t>
4201  </list>
4202</t>
4203<t>
4204  <iref item="content negotiation"/>
4205  <x:dfn>content negotiation</x:dfn>
4206  <list>
4207    <t>
4208      The mechanism for selecting the appropriate representation when
4209      servicing a request, as described in &content.negotiation;. The
4210      representation of entities in any response can be negotiated
4211      (including error responses).
4212    </t>
4213  </list>
4214</t>
4215<t>
4216  <iref item="entity"/>
4217  <x:dfn>entity</x:dfn>
4218  <list>
4219    <t>
4220      The information transferred as the payload of a request or
4221      response. An entity consists of metainformation in the form of
4222      entity-header fields and content in the form of an entity-body, as
4223      described in &entity;.
4224    </t>
4225  </list>
4226</t>
4227<t>
4228  <iref item="gateway"/>
4229  <x:dfn>gateway</x:dfn>
4230  <list>
4231    <t>
4232      A server which acts as an intermediary for some other server.
4233      Unlike a proxy, a gateway receives requests as if it were the
4234      origin server for the requested resource; the requesting client
4235      may not be aware that it is communicating with a gateway.
4236    </t>
4237  </list>
4238</t>
4239<t>
4240  <iref item="inbound"/>
4241  <iref item="outbound"/>
4242  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4243  <list>
4244    <t>
4245      Inbound and outbound refer to the request and response paths for
4246      messages: "inbound" means "traveling toward the origin server",
4247      and "outbound" means "traveling toward the user agent"
4248    </t>
4249  </list>
4250</t>
4251<t>
4252  <iref item="message"/>
4253  <x:dfn>message</x:dfn>
4254  <list>
4255    <t>
4256      The basic unit of HTTP communication, consisting of a structured
4257      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4258      transmitted via the connection.
4259    </t>
4260  </list>
4261</t>
4262<t>
4263  <iref item="origin server"/>
4264  <x:dfn>origin server</x:dfn>
4265  <list>
4266    <t>
4267      The server on which a given resource resides or is to be created.
4268    </t>
4269  </list>
4270</t>
4271<t>
4272  <iref item="proxy"/>
4273  <x:dfn>proxy</x:dfn>
4274  <list>
4275    <t>
4276      An intermediary program which acts as both a server and a client
4277      for the purpose of making requests on behalf of other clients.
4278      Requests are serviced internally or by passing them on, with
4279      possible translation, to other servers. A proxy &MUST; implement
4280      both the client and server requirements of this specification. A
4281      "transparent proxy" is a proxy that does not modify the request or
4282      response beyond what is required for proxy authentication and
4283      identification. A "non-transparent proxy" is a proxy that modifies
4284      the request or response in order to provide some added service to
4285      the user agent, such as group annotation services, media type
4286      transformation, protocol reduction, or anonymity filtering. Except
4287      where either transparent or non-transparent behavior is explicitly
4288      stated, the HTTP proxy requirements apply to both types of
4289      proxies.
4290    </t>
4291  </list>
4292</t>
4293<t>
4294  <iref item="request"/>
4295  <x:dfn>request</x:dfn>
4296  <list>
4297    <t>
4298      An HTTP request message, as defined in <xref target="request"/>.
4299    </t>
4300  </list>
4301</t>
4302<t>
4303  <iref item="resource"/>
4304  <x:dfn>resource</x:dfn>
4305  <list>
4306    <t>
4307      A network data object or service that can be identified by a URI,
4308      as defined in <xref target="uri"/>. Resources may be available in multiple
4309      representations (e.g. multiple languages, data formats, size, and
4310      resolutions) or vary in other ways.
4311    </t>
4312  </list>
4313</t>
4314<t>
4315  <iref item="response"/>
4316  <x:dfn>response</x:dfn>
4317  <list>
4318    <t>
4319      An HTTP response message, as defined in <xref target="response"/>.
4320    </t>
4321  </list>
4322</t>
4323<t>
4324  <iref item="representation"/>
4325  <x:dfn>representation</x:dfn>
4326  <list>
4327    <t>
4328      An entity included with a response that is subject to content
4329      negotiation, as described in &content.negotiation;. There may exist multiple
4330      representations associated with a particular response status.
4331    </t>
4332  </list>
4333</t>
4334<t>
4335  <iref item="server"/>
4336  <x:dfn>server</x:dfn>
4337  <list>
4338    <t>
4339      An application program that accepts connections in order to
4340      service requests by sending back responses. Any given program may
4341      be capable of being both a client and a server; our use of these
4342      terms refers only to the role being performed by the program for a
4343      particular connection, rather than to the program's capabilities
4344      in general. Likewise, any server may act as an origin server,
4345      proxy, gateway, or tunnel, switching behavior based on the nature
4346      of each request.
4347    </t>
4348  </list>
4349</t>
4350<t>
4351  <iref item="tunnel"/>
4352  <x:dfn>tunnel</x:dfn>
4353  <list>
4354    <t>
4355      An intermediary program which is acting as a blind relay between
4356      two connections. Once active, a tunnel is not considered a party
4357      to the HTTP communication, though the tunnel may have been
4358      initiated by an HTTP request. The tunnel ceases to exist when both
4359      ends of the relayed connections are closed.
4360    </t>
4361  </list>
4362</t>
4363<t>
4364  <iref item="upstream"/>
4365  <iref item="downstream"/>
4366  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4367  <list>
4368    <t>
4369      Upstream and downstream describe the flow of a message: all
4370      messages flow from upstream to downstream.
4371    </t>
4372  </list>
4373</t>
4374<t>
4375  <iref item="user agent"/>
4376  <x:dfn>user agent</x:dfn>
4377  <list>
4378    <t>
4379      The client which initiates a request. These are often browsers,
4380      editors, spiders (web-traversing robots), or other end user tools.
4381    </t>
4382  </list>
4383</t>
4384<t>
4385  <iref item="variant"/>
4386  <x:dfn>variant</x:dfn>
4387  <list>
4388    <t>
4389      A resource may have one, or more than one, representation(s)
4390      associated with it at any given instant. Each of these
4391      representations is termed a `variant'.  Use of the term `variant'
4392      does not necessarily imply that the resource is subject to content
4393      negotiation.
4394    </t>
4395  </list>
4396</t>
4397</section>
4398
4399<section title="Collected ABNF" anchor="collected.abnf">
4400   <figure>
4401      <artwork type="abnf" name="p1-messaging.parsed-abnf">BWS = OWS&#xD;
4402Cache-Control = &lt;Cache-Control, defined in [Part6], Section 16.4&gt;&#xD;
4403Chunked-Body = *chunk last-chunk trailer-part CRLF&#xD;
4404Connection = "Connection:" OWS Connection-v&#xD;
4405Connection-v = *( "," OWS ) connection-token *( OWS "," [ OWS&#xD;
4406 connection-token ] )&#xD;
4407Content-Length = "Content-Length:" OWS 1*Content-Length-v&#xD;
4408Content-Length-v = 1*DIGIT&#xD;
4409Date = "Date:" OWS Date-v&#xD;
4410Date-v = HTTP-date&#xD;
4411GMT = %x47.4D.54&#xD;
4412HTTP-Prot-Name = %x48.54.54.50&#xD;
4413HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT&#xD;
4414HTTP-date = rfc1123-date / obsolete-date&#xD;
4415HTTP-message = Request / Response&#xD;
4416Host = "Host:" OWS Host-v&#xD;
4417Host-v = uri-host [ ":" port ]&#xD;
4418Method = token&#xD;
4419OWS = *( [ obs-fold ] WSP )&#xD;
4420Pragma = &lt;Pragma, defined in [Part6], Section 16.4&gt;&#xD;
4421RWS = 1*( [ obs-fold ] WSP )&#xD;
4422Reason-Phrase = *( WSP / VCHAR / obs-text )&#xD;
4423Request = Request-Line *( ( general-header / request-header /&#xD;
4424 entity-header ) CRLF ) CRLF [ message-body ]&#xD;
4425Request-Line = Method SP request-target SP HTTP-Version CRLF&#xD;
4426Response = Status-Line *( ( general-header / response-header /&#xD;
4427 entity-header ) CRLF ) CRLF [ message-body ]&#xD;
4428Status-Code = 3DIGIT&#xD;
4429Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF&#xD;
4430TE = "TE:" OWS TE-v&#xD;
4431TE-v = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]&#xD;
4432Trailer = "Trailer:" OWS Trailer-v&#xD;
4433Trailer-v = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )&#xD;
4434Transfer-Encoding = "Transfer-Encoding:" OWS Transfer-Encoding-v&#xD;
4435Transfer-Encoding-v = *( "," OWS ) transfer-coding *( OWS "," [ OWS&#xD;
4436 transfer-coding ] )&#xD;
4437URI = &lt;URI, defined in [RFC3986], Section 3&gt;&#xD;
4438URI-reference = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;&#xD;
4439Upgrade = "Upgrade:" OWS Upgrade-v&#xD;
4440Upgrade-v = *( "," OWS ) product *( OWS "," [ OWS product ] )&#xD;
4441Via = "Via:" OWS Via-v&#xD;
4442Via-v = *( "," OWS ) received-protocol RWS received-by [ RWS comment&#xD;
4443 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]&#xD;
4444 ] )&#xD;
4445Warning = &lt;Warning, defined in [Part6], Section 16.6&gt;&#xD;
4446absolute-URI = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;&#xD;
4447accept-params = &lt;accept-params, defined in [Part3], Section 6.1&gt;&#xD;
4448asctime-date = wkday SP date3 SP time SP 4DIGIT&#xD;
4449attribute = token&#xD;
4450authority = &lt;authority, defined in [RFC3986], Section 3.2&gt;&#xD;
4451chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF&#xD;
4452chunk-data = 1*OCTET&#xD;
4453chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )&#xD;
4454chunk-ext-name = token&#xD;
4455chunk-ext-val = token / quoted-string&#xD;
4456chunk-size = 1*HEXDIG&#xD;
4457comment = "(" *( ctext / quoted-pair / comment ) ")"&#xD;
4458connection-token = token&#xD;
4459ctext = *( OWS / %x21-27 / %x2A-7E / obs-text )&#xD;
4460date1 = 2DIGIT SP month SP 4DIGIT&#xD;
4461date2 = 2DIGIT "-" month "-" 2DIGIT&#xD;
4462date3 = month SP ( 2DIGIT / ( SP DIGIT ) )&#xD;
4463entity-body = &lt;entity-body, defined in [Part3], Section 4.2&gt;&#xD;
4464entity-header = &lt;entity-header, defined in [Part3], Section 4.1&gt;&#xD;
4465field-content = *( WSP / VCHAR / obs-text )&#xD;
4466field-name = token&#xD;
4467field-value = *( field-content / OWS )&#xD;
4468fragment = &lt;fragment, defined in [RFC3986], Section 3.5&gt;&#xD;
4469general-header = Cache-Control / Connection / Date / Pragma / Trailer&#xD;
4470 / Transfer-Encoding / Upgrade / Via / Warning&#xD;
4471generic-message = start-line *( message-header CRLF ) CRLF [&#xD;
4472 message-body ]&#xD;
4473http-URI = "http://" authority path-abempty [ "?" query ]&#xD;
4474l-Fri = %x46.72.69.64.61.79&#xD;
4475l-Mon = %x4D.6F.6E.64.61.79&#xD;
4476l-Sat = %x53.61.74.75.72.64.61.79&#xD;
4477l-Sun = %x53.75.6E.64.61.79&#xD;
4478l-Thu = %x54.68.75.72.73.64.61.79&#xD;
4479l-Tue = %x54.75.65.73.64.61.79&#xD;
4480l-Wed = %x57.65.64.6E.65.73.64.61.79&#xD;
4481last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF&#xD;
4482message-body = entity-body / &lt;entity-body encoded as per&#xD;
4483 Transfer-Encoding&gt;&#xD;
4484message-header = field-name ":" OWS [ field-value ] OWS&#xD;
4485month = s-Jan / s-Feb / s-Mar / s-Apr / s-May / s-Jun / s-Jul / s-Aug&#xD;
4486 / s-Sep / s-Oct / s-Nov / s-Dec&#xD;
4487obs-fold = CRLF&#xD;
4488obs-text = %x80-FF&#xD;
4489obsolete-date = rfc850-date / asctime-date&#xD;
4490parameter = attribute BWS "=" BWS value&#xD;
4491partial-URI = relative-part [ "?" query ]&#xD;
4492path-abempty = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;&#xD;
4493path-absolute = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;&#xD;
4494port = &lt;port, defined in [RFC3986], Section 3.2.3&gt;&#xD;
4495product = token [ "/" product-version ]&#xD;
4496product-version = token&#xD;
4497protocol-name = token&#xD;
4498protocol-version = token&#xD;
4499pseudonym = token&#xD;
4500qdtext = *( OWS / "!" / %x23-5B / %x5D-7E / obs-text )&#xD;
4501query = &lt;query, defined in [RFC3986], Section 3.4&gt;&#xD;
4502quoted-pair = "\" quoted-text&#xD;
4503quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE&#xD;
4504quoted-text = %x01-09 / %x0B-0C / %x0E-FF&#xD;
4505received-by = ( uri-host [ ":" port ] ) / pseudonym&#xD;
4506received-protocol = [ protocol-name "/" ] protocol-version&#xD;
4507relative-part = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;&#xD;
4508request-header = &lt;request-header, defined in [Part2], Section 4&gt;&#xD;
4509request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )&#xD;
4510 / authority&#xD;
4511response-header = &lt;response-header, defined in [Part2], Section 6&gt;&#xD;
4512rfc1123-date = wkday "," SP date1 SP time SP GMT&#xD;
4513rfc850-date = weekday "," SP date2 SP time SP GMT&#xD;
4514s-Apr = %x41.70.72&#xD;
4515s-Aug = %x41.75.67&#xD;
4516s-Dec = %x44.65.63&#xD;
4517s-Feb = %x46.65.62&#xD;
4518s-Fri = %x46.72.69&#xD;
4519s-Jan = %x4A.61.6E&#xD;
4520s-Jul = %x4A.75.6C&#xD;
4521s-Jun = %x4A.75.6E&#xD;
4522s-Mar = %x4D.61.72&#xD;
4523s-May = %x4D.61.79&#xD;
4524s-Mon = %x4D.6F.6E&#xD;
4525s-Nov = %x4E.6F.76&#xD;
4526s-Oct = %x4F.63.74&#xD;
4527s-Sat = %x53.61.74&#xD;
4528s-Sep = %x53.65.70&#xD;
4529s-Sun = %x53.75.6E&#xD;
4530s-Thu = %x54.68.75&#xD;
4531s-Tue = %x54.75.65&#xD;
4532s-Wed = %x57.65.64&#xD;
4533start-line = Request-Line / Status-Line&#xD;
4534t-codings = "trailers" / ( transfer-extension [ accept-params ] )&#xD;
4535tchar = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /&#xD;
4536 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA&#xD;
4537time = 2DIGIT ":" 2DIGIT ":" 2DIGIT&#xD;
4538token = 1*tchar&#xD;
4539trailer-part = *( entity-header CRLF )&#xD;
4540transfer-coding = "chunked" / transfer-extension&#xD;
4541transfer-extension = token *( OWS ";" OWS parameter )&#xD;
4542uri-host = &lt;host, defined in [RFC3986], Section 3.2.2&gt;&#xD;
4543value = token / quoted-string&#xD;
4544weekday = l-Mon / l-Tue / l-Wed / l-Thu / l-Fri / l-Sat / l-Sun&#xD;
4545wkday = s-Mon / s-Tue / s-Wed / s-Thu / s-Fri / s-Sat / s-Sun&#xD;
4546; Chunked-Body defined but not used&#xD;
4547; Content-Length defined but not used&#xD;
4548; HTTP-message defined but not used&#xD;
4549; Host defined but not used&#xD;
4550; TE defined but not used&#xD;
4551; URI defined but not used&#xD;
4552; URI-reference defined but not used&#xD;
4553; fragment defined but not used&#xD;
4554; generic-message defined but not used&#xD;
4555; http-URI defined but not used&#xD;
4556; partial-URI defined but not used&#xD;
4557</artwork>
4558   </figure>
4559</section>
4560
4561<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4562
4563<section title="Since RFC2616">
4564<t>
4565  Extracted relevant partitions from <xref target="RFC2616"/>.
4566</t>
4567</section>
4568
4569<section title="Since draft-ietf-httpbis-p1-messaging-00">
4570<t>
4571  Closed issues:
4572  <list style="symbols"> 
4573    <t>
4574      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4575      "HTTP Version should be case sensitive"
4576      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4577    </t>
4578    <t>
4579      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4580      "'unsafe' characters"
4581      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4582    </t>
4583    <t>
4584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4585      "Chunk Size Definition"
4586      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4587    </t>
4588    <t>
4589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4590      "Message Length"
4591      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4592    </t>
4593    <t>
4594      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4595      "Media Type Registrations"
4596      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4597    </t>
4598    <t>
4599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4600      "URI includes query"
4601      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4602    </t>
4603    <t>
4604      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4605      "No close on 1xx responses"
4606      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4607    </t>
4608    <t>
4609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4610      "Remove 'identity' token references"
4611      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4612    </t>
4613    <t>
4614      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4615      "Import query BNF"
4616    </t>
4617    <t>
4618      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4619      "qdtext BNF"
4620    </t>
4621    <t>
4622      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4623      "Normative and Informative references"
4624    </t>
4625    <t>
4626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4627      "RFC2606 Compliance"
4628    </t>
4629    <t>
4630      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4631      "RFC977 reference"
4632    </t>
4633    <t>
4634      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4635      "RFC1700 references"
4636    </t>
4637    <t>
4638      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4639      "inconsistency in date format explanation"
4640    </t>
4641    <t>
4642      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4643      "Date reference typo"
4644    </t>
4645    <t>
4646      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4647      "Informative references"
4648    </t>
4649    <t>
4650      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4651      "ISO-8859-1 Reference"
4652    </t>
4653    <t>
4654      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4655      "Normative up-to-date references"
4656    </t>
4657  </list>
4658</t>
4659<t>
4660  Other changes:
4661  <list style="symbols"> 
4662    <t>
4663      Update media type registrations to use RFC4288 template.
4664    </t>
4665    <t>
4666      Use names of RFC4234 core rules DQUOTE and WSP,
4667      fix broken ABNF for chunk-data
4668      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4669    </t>
4670  </list>
4671</t>
4672</section>
4673
4674<section title="Since draft-ietf-httpbis-p1-messaging-01">
4675<t>
4676  Closed issues:
4677  <list style="symbols"> 
4678    <t>
4679      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4680      "Bodies on GET (and other) requests"
4681    </t>
4682    <t>
4683      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4684      "Updating to RFC4288"
4685    </t>
4686    <t>
4687      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4688      "Status Code and Reason Phrase"
4689    </t>
4690    <t>
4691      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4692      "rel_path not used"
4693    </t>
4694  </list>
4695</t>
4696<t>
4697  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4698  <list style="symbols"> 
4699    <t>
4700      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4701      "trailer-part").
4702    </t>
4703    <t>
4704      Avoid underscore character in rule names ("http_URL" ->
4705      "http-URL", "abs_path" -> "path-absolute").
4706    </t>
4707    <t>
4708      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4709      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4710      have to be updated when switching over to RFC3986.
4711    </t>
4712    <t>
4713      Synchronize core rules with RFC5234.
4714    </t>
4715    <t>
4716      Get rid of prose rules that span multiple lines.
4717    </t>
4718    <t>
4719      Get rid of unused rules LOALPHA and UPALPHA.
4720    </t>
4721    <t>
4722      Move "Product Tokens" section (back) into Part 1, as "token" is used
4723      in the definition of the Upgrade header.
4724    </t>
4725    <t>
4726      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4727    </t>
4728    <t>
4729      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4730    </t>
4731  </list>
4732</t>
4733</section>
4734
4735<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4736<t>
4737  Closed issues:
4738  <list style="symbols"> 
4739    <t>
4740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4741      "HTTP-date vs. rfc1123-date"
4742    </t>
4743    <t>
4744      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4745      "WS in quoted-pair"
4746    </t>
4747  </list>
4748</t>
4749<t>
4750  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4751  <list style="symbols"> 
4752    <t>
4753      Reference RFC 3984, and update header registrations for headers defined
4754      in this document.
4755    </t>
4756  </list>
4757</t>
4758<t>
4759  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4760  <list style="symbols"> 
4761    <t>
4762      Replace string literals when the string really is case-sensitive (HTTP-Version).
4763    </t>
4764  </list>
4765</t>
4766</section>
4767
4768<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4769<t>
4770  Closed issues:
4771  <list style="symbols"> 
4772    <t>
4773      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4774      "Connection closing"
4775    </t>
4776    <t>
4777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4778      "Move registrations and registry information to IANA Considerations"
4779    </t>
4780    <t>
4781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4782      "need new URL for PAD1995 reference"
4783    </t>
4784    <t>
4785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4786      "IANA Considerations: update HTTP URI scheme registration"
4787    </t>
4788    <t>
4789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4790      "Cite HTTPS URI scheme definition"
4791    </t>
4792    <t>
4793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4794      "List-type headers vs Set-Cookie"
4795    </t>
4796  </list>
4797</t>
4798<t>
4799  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4800  <list style="symbols"> 
4801    <t>
4802      Replace string literals when the string really is case-sensitive (HTTP-Date).
4803    </t>
4804    <t>
4805      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4806    </t>
4807  </list>
4808</t>
4809</section>
4810
4811<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4812<t>
4813  Closed issues:
4814  <list style="symbols"> 
4815    <t>
4816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4817      "Out-of-date reference for URIs"
4818    </t>
4819    <t>
4820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4821      "RFC 2822 is updated by RFC 5322"
4822    </t>
4823  </list>
4824</t>
4825<t>
4826  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4827  <list style="symbols"> 
4828    <t>
4829      Use "/" instead of "|" for alternatives.
4830    </t>
4831    <t>
4832      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4833    </t>
4834    <t>
4835      Only reference RFC 5234's core rules.
4836    </t>
4837    <t>
4838      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4839      whitespace ("OWS") and required whitespace ("RWS").
4840    </t>
4841    <t>
4842      Rewrite ABNFs to spell out whitespace rules, factor out
4843      header value format definitions.
4844    </t>
4845  </list>
4846</t>
4847</section>
4848
4849<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4850<t>
4851  Closed issues:
4852  <list style="symbols"> 
4853    <t>
4854      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
4855      "Header LWS"
4856    </t>
4857    <t>
4858      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
4859      "Sort 1.3 Terminology"
4860    </t>
4861    <t>
4862      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
4863      "RFC2047 encoded words"
4864    </t>
4865    <t>
4866      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
4867      "Character Encodings in TEXT"
4868    </t>
4869    <t>
4870      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
4871      "Line Folding"
4872    </t>
4873    <t>
4874      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
4875      "OPTIONS * and proxies"
4876    </t>
4877    <t>
4878      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4879      "Reason-Phrase BNF"
4880    </t>
4881    <t>
4882      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
4883      "Use of TEXT"
4884    </t>
4885    <t>
4886      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4887      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4888    </t>
4889    <t>
4890      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4891      "RFC822 reference left in discussion of date formats"
4892    </t>
4893  </list>
4894</t>
4895<t>
4896  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4897  <list style="symbols"> 
4898    <t>
4899      Rewrite definition of list rules, deprecate empty list elements.
4900    </t>
4901    <t>
4902      Add appendix containing collected and expanded ABNF.
4903    </t>
4904  </list>
4905</t>
4906<t>
4907  Other changes:
4908  <list style="symbols"> 
4909    <t>
4910      Rewrite introduction; add mostly new Architecture Section.
4911    </t>
4912  </list>
4913</t>
4914</section>
4915
4916</section>
4917
4918</back>
4919</rfc>
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