source: draft-ietf-httpbis/latest/p1-messaging.xml @ 440

Last change on this file since 440 was 440, checked in by julian.reschke@…, 11 years ago

update to latest version of rfc2629.xslt, add <workgroup> element throughout

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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "January">
16  <!ENTITY ID-YEAR "2009">
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  <workgroup>HTTPbis Working Group</workgroup>
199
200<abstract>
201<t>
202   The Hypertext Transfer Protocol (HTTP) is an application-level
203   protocol for distributed, collaborative, hypermedia information
204   systems. HTTP has been in use by the World Wide Web global information
205   initiative since 1990. This document is Part 1 of the seven-part specification
206   that defines the protocol referred to as "HTTP/1.1" and, taken together,
207   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
208   its associated terminology, defines the "http" and "https" Uniform
209   Resource Identifier (URI) schemes, defines the generic message syntax
210   and parsing requirements for HTTP message frames, and describes
211   general security concerns for implementations.
212</t>
213</abstract>
214
215<note title="Editorial Note (To be removed by RFC Editor)">
216  <t>
217    Discussion of this draft should take place on the HTTPBIS working group
218    mailing list (ietf-http-wg@w3.org). The current issues list is
219    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
220    and related documents (including fancy diffs) can be found at
221    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
222  </t>
223  <t>
224    The changes in this draft are summarized in <xref target="changes.since.05"/>.
225  </t>
226</note>
227</front>
228<middle>
229<section title="Introduction" anchor="introduction">
230<t>
231   The Hypertext Transfer Protocol (HTTP) is an application-level
232   request/response protocol that uses extensible semantics and MIME-like
233   message payloads for flexible interaction with network-based hypertext
234   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
235   standard <xref target="RFC3986"/> to indicate resource targets and
236   relationships between resources.
237   Messages are passed in a format similar to that used by Internet mail
238   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
239   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
240   between HTTP and MIME messages).
241</t>
242<t>
243   HTTP is a generic interface protocol for informations systems. It is
244   designed to hide the details of how a service is implemented by presenting
245   a uniform interface to clients that is independent of the types of
246   resources provided. Likewise, servers do not need to be aware of each
247   client's purpose: an HTTP request can be considered in isolation rather
248   than being associated with a specific type of client or a predetermined
249   sequence of application steps. The result is a protocol that can be used
250   effectively in many different contexts and for which implementations can
251   evolve independently over time.
252</t>
253<t>
254   HTTP is also designed for use as a generic protocol for translating
255   communication to and from other Internet information systems, such as
256   USENET news services via NNTP <xref target="RFC3977"/>,
257   file services via FTP <xref target="RFC959"/>,
258   Gopher <xref target="RFC1436"/>, and WAIS <xref target="WAIS"/>.
259   HTTP proxies and gateways provide access to alternative information
260   services by translating their diverse protocols into a hypermedia
261   format that can be viewed and manipulated by clients in the same way
262   as HTTP services.
263</t>
264<t>
265   One consequence of HTTP flexibility is that we cannot define the protocol
266   in terms of how to implement it behind the interface. Instead, we are
267   limited to restricting the syntax of communication, defining the intent
268   of received communication, and the expected behavior of recipients. If
269   the communication is considered in isolation, then successful actions
270   should be reflected in the observable interface provided by servers.
271   However, since many clients are potentially acting in parallel and
272   perhaps at cross-purposes, it would be meaningless to require that such
273   behavior be observable.
274</t>
275<t>
276   This document is Part 1 of the seven-part specification of HTTP,
277   defining the protocol referred to as "HTTP/1.1" and obsoleting
278   <xref target="RFC2616"/>.
279   Part 1 defines the URI schemes specific to HTTP-based resources, overall
280   network operation, transport protocol connection management, and HTTP
281   message framing and forwarding requirements.
282   Our goal is to define all of the mechanisms necessary for HTTP message
283   handling that are independent of message semantics, thereby defining the
284   complete set of requirements for a message parser and transparent
285   message-forwarding intermediaries.
286</t>
287
288<section title="Requirements" anchor="intro.requirements">
289<t>
290   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
291   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
292   document are to be interpreted as described in <xref target="RFC2119"/>.
293</t>
294<t>
295   An implementation is not compliant if it fails to satisfy one or more
296   of the &MUST; or &REQUIRED; level requirements for the protocols it
297   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
298   level and all the &SHOULD; level requirements for its protocols is said
299   to be "unconditionally compliant"; one that satisfies all the &MUST;
300   level requirements but not all the &SHOULD; level requirements for its
301   protocols is said to be "conditionally compliant."
302</t>
303</section>
304
305<section title="Syntax Notation" anchor="notation">
306<iref primary="true" item="Grammar" subitem="ALPHA"/>
307<iref primary="true" item="Grammar" subitem="CR"/>
308<iref primary="true" item="Grammar" subitem="CRLF"/>
309<iref primary="true" item="Grammar" subitem="CTL"/>
310<iref primary="true" item="Grammar" subitem="DIGIT"/>
311<iref primary="true" item="Grammar" subitem="DQUOTE"/>
312<iref primary="true" item="Grammar" subitem="HEXDIG"/>
313<iref primary="true" item="Grammar" subitem="LF"/>
314<iref primary="true" item="Grammar" subitem="OCTET"/>
315<iref primary="true" item="Grammar" subitem="SP"/>
316<iref primary="true" item="Grammar" subitem="VCHAR"/>
317<iref primary="true" item="Grammar" subitem="WSP"/>
318<t anchor="core.rules">
319  <x:anchor-alias value="ALPHA"/>
320  <x:anchor-alias value="CTL"/>
321  <x:anchor-alias value="CR"/>
322  <x:anchor-alias value="CRLF"/>
323  <x:anchor-alias value="DIGIT"/>
324  <x:anchor-alias value="DQUOTE"/>
325  <x:anchor-alias value="HEXDIG"/>
326  <x:anchor-alias value="LF"/>
327  <x:anchor-alias value="OCTET"/>
328  <x:anchor-alias value="SP"/>
329  <x:anchor-alias value="VCHAR"/>
330  <x:anchor-alias value="WSP"/>
331   This specification uses the Augmented Backus-Naur Form (ABNF) notation
332   of <xref target="RFC5234"/>.  The following core rules are included by
333   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335   DIGIT (decimal 0-9), DQUOTE (double quote),
336   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337   OCTET (any 8-bit sequence of data), SP (space),
338   VCHAR (any visible <xref target="USASCII"/> character),
339   and WSP (whitespace).
340</t>
341
342<section title="ABNF Extension: #rule" anchor="notation.abnf">
343  <t>
344    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
345    improve readability.
346  </t>
347  <t>
348    A construct "#" is defined, similar to "*", for defining lists of
349    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
350    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
351    (",") and optional whitespace (OWS).   
352  </t>
353  <figure><preamble>
354    Thus,
355</preamble><artwork type="example">
356  1#element =&gt; element *( OWS "," OWS element )
357</artwork></figure>
358  <figure><preamble>
359    and:
360</preamble><artwork type="example">
361  #element =&gt; [ 1#element ]
362</artwork></figure>
363  <figure><preamble>
364    and for n &gt;= 1 and m &gt; 1:
365</preamble><artwork type="example">
366  &lt;n&gt;#&lt;m&gt;element =&gt; element &lt;n-1&gt;*&lt;m-1&gt;( OWS "," OWS element )
367</artwork></figure>
368  <t>
369    For compatibility with legacy list rules, recipients &SHOULD; accept empty
370    list elements. In other words, consumers would follow the list productions:
371  </t>
372<figure><artwork type="example">
373#element =&gt; [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
374
3751#element =&gt; *( "," OWS ) element *( OWS "," [ OWS element ] )
376</artwork></figure> 
377<t>
378  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
379  expanded as explained above.
380</t>
381</section>
382
383<section title="Basic Rules" anchor="basic.rules">
384<t anchor="rule.CRLF">
385  <x:anchor-alias value="CRLF"/>
386   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
387   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
388   tolerant applications). The end-of-line marker within an entity-body
389   is defined by its associated media type, as described in &media-types;.
390</t>
391<t anchor="rule.LWS">
392   This specification uses three rules to denote the use of linear
393   whitespace: OWS (optional whitespace), RWS (required whitespace), and
394   BWS ("bad" whitespace).
395</t>
396<t>
397   The OWS rule is used where zero or more linear whitespace characters may
398   appear. OWS &SHOULD; either not be produced or be produced as a single SP
399   character. Multiple OWS characters that occur within field-content &SHOULD;
400   be replaced with a single SP before interpreting the field value or
401   forwarding the message downstream.
402</t>
403<t>
404   RWS is used when at least one linear whitespace character is required to
405   separate field tokens. RWS &SHOULD; be produced as a single SP character.
406   Multiple RWS characters that occur within field-content &SHOULD; be
407   replaced with a single SP before interpreting the field value or
408   forwarding the message downstream.
409</t>
410<t>
411   BWS is used where the grammar allows optional whitespace for historical
412   reasons but senders &SHOULD-NOT; produce it in messages. HTTP/1.1
413   recipients &MUST; accept such bad optional whitespace and remove it before
414   interpreting the field value or forwarding the message downstream.
415</t>
416<t anchor="rule.whitespace">
417  <x:anchor-alias value="BWS"/>
418  <x:anchor-alias value="OWS"/>
419  <x:anchor-alias value="RWS"/>
420  <x:anchor-alias value="obs-fold"/>
421</t>
422<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"/>
423  <x:ref>OWS</x:ref>            = *( [ obs-fold ] <x:ref>WSP</x:ref> )
424                 ; "optional" whitespace
425  <x:ref>RWS</x:ref>            = 1*( [ obs-fold ] <x:ref>WSP</x:ref> )
426                 ; "required" whitespace
427  <x:ref>BWS</x:ref>            = <x:ref>OWS</x:ref>
428                 ; "bad" whitespace
429  <x:ref>obs-fold</x:ref>       = <x:ref>CRLF</x:ref>
430                 ; see <xref target="message.headers"/>
431</artwork></figure>
432<t anchor="rule.token.separators">
433  <x:anchor-alias value="tchar"/>
434  <x:anchor-alias value="token"/>
435   Many HTTP/1.1 header field values consist of words separated by whitespace
436   or special characters. These special characters &MUST; be in a quoted
437   string to be used within a parameter value (as defined in
438   <xref target="transfer.codings"/>).
439</t>
440<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/>
441  <x:ref>tchar</x:ref>          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
442                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
443                 / <x:ref>DIGIT</x:ref> / <x:ref>ALPHA</x:ref>
444                 
445  <x:ref>token</x:ref>          = 1*<x:ref>tchar</x:ref>
446</artwork></figure>
447<t anchor="rule.quoted-string">
448  <x:anchor-alias value="quoted-string"/>
449  <x:anchor-alias value="qdtext"/>
450  <x:anchor-alias value="obs-text"/>
451   A string of text is parsed as a single word if it is quoted using
452   double-quote marks.
453</t>
454<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"/>
455  <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>
456  <x:ref>qdtext</x:ref>         = *( <x:ref>OWS</x:ref> / %x21 / %x23-5B / %x5D-7E / <x:ref>obs-text</x:ref> )
457  <x:ref>obs-text</x:ref>       = %x80-FF
458</artwork></figure>
459<t anchor="rule.quoted-pair">
460  <x:anchor-alias value="quoted-pair"/>
461  <x:anchor-alias value="quoted-text"/>
462   The backslash character ("\") &MAY; be used as a single-character
463   quoting mechanism only within quoted-string and comment constructs.
464</t>
465<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
466  <x:ref>quoted-text</x:ref>    = %x01-09 /
467                   %x0B-0C /
468                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
469  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
470</artwork></figure>
471</section>
472
473<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
474  <x:anchor-alias value="request-header"/>
475  <x:anchor-alias value="response-header"/>
476  <x:anchor-alias value="accept-params"/>
477  <x:anchor-alias value="entity-body"/>
478  <x:anchor-alias value="entity-header"/>
479  <x:anchor-alias value="Cache-Control"/>
480  <x:anchor-alias value="Pragma"/>
481  <x:anchor-alias value="Warning"/>
482<t>
483  The ABNF rules below are defined in other parts:
484</t>
485<figure><!-- Part2--><artwork type="abnf2616">
486  <x:ref>request-header</x:ref>  = &lt;request-header, defined in &request-header-fields;&gt;
487  <x:ref>response-header</x:ref> = &lt;response-header, defined in &response-header-fields;&gt;
488</artwork></figure>
489<figure><!-- Part3--><artwork type="abnf2616">
490  <x:ref>accept-params</x:ref>   = &lt;accept-params, defined in &header-accept;&gt;
491  <x:ref>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
492  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
493</artwork></figure>
494<figure><!-- Part6--><artwork type="abnf2616">
495  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
496  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
497  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
498</artwork></figure>
499</section>
500
501</section>
502</section>
503
504<section title="HTTP architecture" anchor="architecture">
505<t>
506   HTTP was created with a specific architecture in mind, the World Wide Web,
507   and has evolved over time to support the scalability needs of a worldwide
508   hypertext system. Much of that architecture is reflected in the terminology
509   and syntax productions used to define HTTP.
510</t>
511
512<section title="Uniform Resource Identifiers" anchor="uri">
513<t>
514   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
515   throughout HTTP as the means for identifying resources. URI references
516   are used to target requests, redirect responses, and define relationships.
517   HTTP does not limit what a resource may be; it merely defines an interface
518   that can be used to interact with a resource via HTTP. More information on
519   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
520</t>
521  <x:anchor-alias value="URI"/>
522  <x:anchor-alias value="URI-reference"/>
523  <x:anchor-alias value="absolute-URI"/>
524  <x:anchor-alias value="relative-part"/>
525  <x:anchor-alias value="authority"/>
526  <x:anchor-alias value="fragment"/>
527  <x:anchor-alias value="path-abempty"/>
528  <x:anchor-alias value="path-absolute"/>
529  <x:anchor-alias value="port"/>
530  <x:anchor-alias value="query"/>
531  <x:anchor-alias value="uri-host"/>
532  <x:anchor-alias value="partial-URI"/>
533<t>
534   This specification adopts the definitions of "URI-reference",
535   "absolute-URI", "relative-part", "fragment", "port", "host",
536   "path-abempty", "path-absolute", "query", and "authority" from
537   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
538   protocol elements that allow a relative URI without a fragment.
539</t>
540<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"/>
541  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
542  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
543  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
544  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
545  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
546  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
547  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
548  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
549  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
550  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
551  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
552 
553  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
554</artwork></figure>
555<t>
556   Each protocol element in HTTP that allows a URI reference will indicate in
557   its ABNF production whether the element allows only a URI in absolute form
558   (absolute-URI), any relative reference (relative-ref), or some other subset
559   of the URI-reference grammar. Unless otherwise indicated, URI references
560   are parsed relative to the request target (the default base URI for both
561   the request and its corresponding response).
562</t>
563
564<section title="http URI scheme" anchor="http.uri">
565  <x:anchor-alias value="http-URI"/>
566  <iref item="http URI scheme" primary="true"/>
567  <iref item="URI scheme" subitem="http" primary="true"/>
568<t>
569   The "http" scheme is used to locate network resources via the HTTP
570   protocol. This section defines the syntax and semantics for identifiers
571   using the http or https URI schemes.
572</t>
573<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
574  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
575</artwork></figure>
576<t>
577   If the port is empty or not given, port 80 is assumed. The semantics
578   are that the identified resource is located at the server listening
579   for TCP connections on that port of that host, and the request-target
580   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
581   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
582   the path-absolute is not present in the URL, it &MUST; be given as "/" when
583   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
584   receives a host name which is not a fully qualified domain name, it
585   &MAY; add its domain to the host name it received. If a proxy receives
586   a fully qualified domain name, the proxy &MUST-NOT; change the host
587   name.
588</t>
589<t><list><t>
590  <iref item="https URI scheme"/>
591  <iref item="URI scheme" subitem="https"/>
592  <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
593</t></list></t>
594</section>
595
596<section title="URI Comparison" anchor="uri.comparison">
597<t>
598   When comparing two URIs to decide if they match or not, a client
599   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
600   URIs, with these exceptions:
601  <list style="symbols">
602    <t>A port that is empty or not given is equivalent to the default
603        port for that URI-reference;</t>
604    <t>Comparisons of host names &MUST; be case-insensitive;</t>
605    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
606    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
607  </list>
608</t>
609<t>
610   Characters other than those in the "reserved" set (see
611   <xref target="RFC3986" x:fmt="," x:sec="2.2"/>) are equivalent to their
612   ""%" <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding.
613</t>
614<t>
615   For example, the following three URIs are equivalent:
616</t>
617<figure><artwork type="example">
618   http://example.com:80/~smith/home.html
619   http://EXAMPLE.com/%7Esmith/home.html
620   http://EXAMPLE.com:/%7esmith/home.html
621</artwork></figure>
622</section>
623
624<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
625<t>
626</t>
627</section>
628</section>
629
630<section title="Overall Operation" anchor="intro.overall.operation">
631<t>
632   HTTP is a request/response protocol. A client sends a
633   request to the server in the form of a request method, URI, and
634   protocol version, followed by a MIME-like message containing request
635   modifiers, client information, and possible body content over a
636   connection with a server. The server responds with a status line,
637   including the message's protocol version and a success or error code,
638   followed by a MIME-like message containing server information, entity
639   metainformation, and possible entity-body content.
640</t>
641<t>
642   Most HTTP communication is initiated by a user agent and consists of
643   a request to be applied to a resource on some origin server. In the
644   simplest case, this may be accomplished via a single connection (v)
645   between the user agent (UA) and the origin server (O).
646</t>
647<figure><artwork type="drawing">
648       request chain ------------------------&gt;
649    UA -------------------v------------------- O
650       &lt;----------------------- response chain
651</artwork></figure>
652<t>
653   A more complicated situation occurs when one or more intermediaries
654   are present in the request/response chain. There are three common
655   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
656   forwarding agent, receiving requests for a URI in its absolute form,
657   rewriting all or part of the message, and forwarding the reformatted
658   request toward the server identified by the URI. A gateway is a
659   receiving agent, acting as a layer above some other server(s) and, if
660   necessary, translating the requests to the underlying server's
661   protocol. A tunnel acts as a relay point between two connections
662   without changing the messages; tunnels are used when the
663   communication needs to pass through an intermediary (such as a
664   firewall) even when the intermediary cannot understand the contents
665   of the messages.
666</t>
667<figure><artwork type="drawing">
668       request chain --------------------------------------&gt;
669    UA -----v----- A -----v----- B -----v----- C -----v----- O
670       &lt;------------------------------------- response chain
671</artwork></figure>
672<t>
673   The figure above shows three intermediaries (A, B, and C) between the
674   user agent and origin server. A request or response message that
675   travels the whole chain will pass through four separate connections.
676   This distinction is important because some HTTP communication options
677   may apply only to the connection with the nearest, non-tunnel
678   neighbor, only to the end-points of the chain, or to all connections
679   along the chain. Although the diagram is linear, each participant may
680   be engaged in multiple, simultaneous communications. For example, B
681   may be receiving requests from many clients other than A, and/or
682   forwarding requests to servers other than C, at the same time that it
683   is handling A's request.
684</t>
685<t>
686   Any party to the communication which is not acting as a tunnel may
687   employ an internal cache for handling requests. The effect of a cache
688   is that the request/response chain is shortened if one of the
689   participants along the chain has a cached response applicable to that
690   request. The following illustrates the resulting chain if B has a
691   cached copy of an earlier response from O (via C) for a request which
692   has not been cached by UA or A.
693</t>
694<figure><artwork type="drawing">
695          request chain ----------&gt;
696       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
697          &lt;--------- response chain
698</artwork></figure>
699<t>
700   Not all responses are usefully cacheable, and some requests may
701   contain modifiers which place special requirements on cache behavior.
702   HTTP requirements for cache behavior and cacheable responses are
703   defined in &caching;.
704</t>
705<t>
706   In fact, there are a wide variety of architectures and configurations
707   of caches and proxies currently being experimented with or deployed
708   across the World Wide Web. These systems include national hierarchies
709   of proxy caches to save transoceanic bandwidth, systems that
710   broadcast or multicast cache entries, organizations that distribute
711   subsets of cached data via CD-ROM, and so on. HTTP systems are used
712   in corporate intranets over high-bandwidth links, and for access via
713   PDAs with low-power radio links and intermittent connectivity. The
714   goal of HTTP/1.1 is to support the wide diversity of configurations
715   already deployed while introducing protocol constructs that meet the
716   needs of those who build web applications that require high
717   reliability and, failing that, at least reliable indications of
718   failure.
719</t>
720<t>
721   HTTP communication usually takes place over TCP/IP connections. The
722   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
723   not preclude HTTP from being implemented on top of any other protocol
724   on the Internet, or on other networks. HTTP only presumes a reliable
725   transport; any protocol that provides such guarantees can be used;
726   the mapping of the HTTP/1.1 request and response structures onto the
727   transport data units of the protocol in question is outside the scope
728   of this specification.
729</t>
730<t>
731   In HTTP/1.0, most implementations used a new connection for each
732   request/response exchange. In HTTP/1.1, a connection may be used for
733   one or more request/response exchanges, although connections may be
734   closed for a variety of reasons (see <xref target="persistent.connections"/>).
735</t>
736</section>
737
738<section title="Use of HTTP for proxy communication" anchor="http.proxy">
739<t>
740   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
741</t>
742</section>
743<section title="Interception of HTTP for access control" anchor="http.intercept">
744<t>
745   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
746</t>
747</section>
748<section title="Use of HTTP by other protocols" anchor="http.others">
749<t>
750   <cref>TBD: Profiles of HTTP defined by other protocol.
751   Extensions of HTTP like WebDAV.</cref>
752</t>
753</section>
754<section title="Use of HTTP by media type specification" anchor="http.media">
755<t>
756   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
757</t>
758</section>
759</section>
760
761<section title="Protocol Parameters" anchor="protocol.parameters">
762
763<section title="HTTP Version" anchor="http.version">
764  <x:anchor-alias value="HTTP-Version"/>
765  <x:anchor-alias value="HTTP-Prot-Name"/>
766<t>
767   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
768   of the protocol. The protocol versioning policy is intended to allow
769   the sender to indicate the format of a message and its capacity for
770   understanding further HTTP communication, rather than the features
771   obtained via that communication. No change is made to the version
772   number for the addition of message components which do not affect
773   communication behavior or which only add to extensible field values.
774   The &lt;minor&gt; number is incremented when the changes made to the
775   protocol add features which do not change the general message parsing
776   algorithm, but which may add to the message semantics and imply
777   additional capabilities of the sender. The &lt;major&gt; number is
778   incremented when the format of a message within the protocol is
779   changed. See <xref target="RFC2145"/> for a fuller explanation.
780</t>
781<t>
782   The version of an HTTP message is indicated by an HTTP-Version field
783   in the first line of the message. HTTP-Version is case-sensitive.
784</t>
785<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
786  <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>
787  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
788</artwork></figure>
789<t>
790   Note that the major and minor numbers &MUST; be treated as separate
791   integers and that each &MAY; be incremented higher than a single digit.
792   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
793   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
794   &MUST-NOT; be sent.
795</t>
796<t>
797   An application that sends a request or response message that includes
798   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
799   with this specification. Applications that are at least conditionally
800   compliant with this specification &SHOULD; use an HTTP-Version of
801   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
802   not compatible with HTTP/1.0. For more details on when to send
803   specific HTTP-Version values, see <xref target="RFC2145"/>.
804</t>
805<t>
806   The HTTP version of an application is the highest HTTP version for
807   which the application is at least conditionally compliant.
808</t>
809<t>
810   Proxy and gateway applications need to be careful when forwarding
811   messages in protocol versions different from that of the application.
812   Since the protocol version indicates the protocol capability of the
813   sender, a proxy/gateway &MUST-NOT; send a message with a version
814   indicator which is greater than its actual version. If a higher
815   version request is received, the proxy/gateway &MUST; either downgrade
816   the request version, or respond with an error, or switch to tunnel
817   behavior.
818</t>
819<t>
820   Due to interoperability problems with HTTP/1.0 proxies discovered
821   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
822   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
823   they support. The proxy/gateway's response to that request &MUST; be in
824   the same major version as the request.
825</t>
826<t>
827  <list>
828    <t>
829      <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
830      of header fields required or forbidden by the versions involved.
831    </t>
832  </list>
833</t>
834</section>
835
836<section title="Date/Time Formats" anchor="date.time.formats">
837<section title="Full Date" anchor="full.date">
838  <x:anchor-alias value="HTTP-date"/>
839  <x:anchor-alias value="obsolete-date"/>
840  <x:anchor-alias value="rfc1123-date"/>
841  <x:anchor-alias value="rfc850-date"/>
842  <x:anchor-alias value="asctime-date"/>
843  <x:anchor-alias value="date1"/>
844  <x:anchor-alias value="date2"/>
845  <x:anchor-alias value="date3"/>
846  <x:anchor-alias value="rfc1123-date"/>
847  <x:anchor-alias value="time"/>
848  <x:anchor-alias value="wkday"/>
849  <x:anchor-alias value="weekday"/>
850  <x:anchor-alias value="month"/>
851<t>
852   HTTP applications have historically allowed three different formats
853   for the representation of date/time stamps:
854</t>
855<figure><artwork type="example">
856   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
857   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
858   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
859</artwork></figure>
860<t>
861   The first format is preferred as an Internet standard and represents
862   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
863   other formats are described here only for
864   compatibility with obsolete implementations.
865   HTTP/1.1 clients and servers that parse the date value &MUST; accept
866   all three formats (for compatibility with HTTP/1.0), though they &MUST;
867   only generate the RFC 1123 format for representing HTTP-date values
868   in header fields. See <xref target="tolerant.applications"/> for further information.
869</t>
870<t><list><t>
871      <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
872      accepting date values that may have been sent by non-HTTP
873      applications, as is sometimes the case when retrieving or posting
874      messages via proxies/gateways to SMTP or NNTP.
875</t></list></t>
876<t>
877   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
878   (GMT), without exception. For the purposes of HTTP, GMT is exactly
879   equal to UTC (Coordinated Universal Time). This is indicated in the
880   first two formats by the inclusion of "GMT" as the three-letter
881   abbreviation for time zone, and &MUST; be assumed when reading the
882   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
883   additional whitespace beyond that specifically included as SP in the
884   grammar.
885</t>
886<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"/>
887  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
888  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
889  <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
890  <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
891  <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>
892  <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>
893                 ; day month year (e.g., 02 Jun 1982)
894  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
895                 ; day-month-year (e.g., 02-Jun-82)
896  <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> ))
897                 ; month day (e.g., Jun  2)
898  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
899                 ; 00:00:00 - 23:59:59
900  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
901               / s-Thu / s-Fri / s-Sat / s-Sun
902  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
903               / l-Thu / l-Fri / l-Sat / l-Sun
904  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
905               / s-May / s-Jun / s-Jul / s-Aug
906               / s-Sep / s-Oct / s-Nov / s-Dec
907               
908  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
909
910  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
911  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
912  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
913  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
914  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
915  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
916  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
917
918  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
919  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
920  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
921  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
922  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
923  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
924  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
925
926  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
927  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
928  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
929  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
930  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
931  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
932  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
933  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
934  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
935  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
936  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
937  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
938</artwork></figure>
939<t>
940      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
941      to their usage within the protocol stream. Clients and servers are
942      not required to use these formats for user presentation, request
943      logging, etc.
944</t>
945</section>
946</section>
947
948<section title="Transfer Codings" anchor="transfer.codings">
949  <x:anchor-alias value="parameter"/>
950  <x:anchor-alias value="transfer-coding"/>
951  <x:anchor-alias value="transfer-extension"/>
952<t>
953   Transfer-coding values are used to indicate an encoding
954   transformation that has been, can be, or may need to be applied to an
955   entity-body in order to ensure "safe transport" through the network.
956   This differs from a content coding in that the transfer-coding is a
957   property of the message, not of the original entity.
958</t>
959<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
960  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
961  <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> )
962</artwork></figure>
963<t anchor="rule.parameter">
964  <x:anchor-alias value="attribute"/>
965  <x:anchor-alias value="parameter"/>
966  <x:anchor-alias value="value"/>
967   Parameters are in  the form of attribute/value pairs.
968</t>
969<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"/>
970  <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>
971  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
972  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
973</artwork></figure>
974<t>
975   All transfer-coding values are case-insensitive. HTTP/1.1 uses
976   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
977   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
978</t>
979<t>
980   Whenever a transfer-coding is applied to a message-body, the set of
981   transfer-codings &MUST; include "chunked", unless the message indicates it
982   is terminated by closing the connection. When the "chunked" transfer-coding
983   is used, it &MUST; be the last transfer-coding applied to the
984   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
985   than once to a message-body. These rules allow the recipient to
986   determine the transfer-length of the message (<xref target="message.length"/>).
987</t>
988<t>
989   Transfer-codings are analogous to the Content-Transfer-Encoding
990   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
991   binary data over a 7-bit transport service. However, safe transport
992   has a different focus for an 8bit-clean transfer protocol. In HTTP,
993   the only unsafe characteristic of message-bodies is the difficulty in
994   determining the exact body length (<xref target="message.length"/>), or the desire to
995   encrypt data over a shared transport.
996</t>
997<t>
998   The Internet Assigned Numbers Authority (IANA) acts as a registry for
999   transfer-coding value tokens. Initially, the registry contains the
1000   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1001   "gzip", "compress", and "deflate" (&content-codings;).
1002</t>
1003<t>
1004   New transfer-coding value tokens &SHOULD; be registered in the same way
1005   as new content-coding value tokens (&content-codings;).
1006</t>
1007<t>
1008   A server which receives an entity-body with a transfer-coding it does
1009   not understand &SHOULD; return 501 (Not Implemented), and close the
1010   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1011   client.
1012</t>
1013
1014<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1015  <x:anchor-alias value="chunk"/>
1016  <x:anchor-alias value="Chunked-Body"/>
1017  <x:anchor-alias value="chunk-data"/>
1018  <x:anchor-alias value="chunk-ext"/>
1019  <x:anchor-alias value="chunk-ext-name"/>
1020  <x:anchor-alias value="chunk-ext-val"/>
1021  <x:anchor-alias value="chunk-size"/>
1022  <x:anchor-alias value="last-chunk"/>
1023  <x:anchor-alias value="trailer-part"/>
1024<t>
1025   The chunked encoding modifies the body of a message in order to
1026   transfer it as a series of chunks, each with its own size indicator,
1027   followed by an &OPTIONAL; trailer containing entity-header fields. This
1028   allows dynamically produced content to be transferred along with the
1029   information necessary for the recipient to verify that it has
1030   received the full message.
1031</t>
1032<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"/>
1033  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1034                   <x:ref>last-chunk</x:ref>
1035                   <x:ref>trailer-part</x:ref>
1036                   <x:ref>CRLF</x:ref>
1037 
1038  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1039                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1040  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1041  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1042 
1043  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1044                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1045  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1046  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1047  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1048  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1049</artwork></figure>
1050<t>
1051   The chunk-size field is a string of hex digits indicating the size of
1052   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1053   zero, followed by the trailer, which is terminated by an empty line.
1054</t>
1055<t>
1056   The trailer allows the sender to include additional HTTP header
1057   fields at the end of the message. The Trailer header field can be
1058   used to indicate which header fields are included in a trailer (see
1059   <xref target="header.trailer"/>).
1060</t>
1061<t>
1062   A server using chunked transfer-coding in a response &MUST-NOT; use the
1063   trailer for any header fields unless at least one of the following is
1064   true:
1065  <list style="numbers">
1066    <t>the request included a TE header field that indicates "trailers" is
1067     acceptable in the transfer-coding of the  response, as described in
1068     <xref target="header.te"/>; or,</t>
1069
1070    <t>the server is the origin server for the response, the trailer
1071     fields consist entirely of optional metadata, and the recipient
1072     could use the message (in a manner acceptable to the origin server)
1073     without receiving this metadata.  In other words, the origin server
1074     is willing to accept the possibility that the trailer fields might
1075     be silently discarded along the path to the client.</t>
1076  </list>
1077</t>
1078<t>
1079   This requirement prevents an interoperability failure when the
1080   message is being received by an HTTP/1.1 (or later) proxy and
1081   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1082   compliance with the protocol would have necessitated a possibly
1083   infinite buffer on the proxy.
1084</t>
1085<t>
1086   A process for decoding the "chunked" transfer-coding
1087   can be represented in pseudo-code as:
1088</t>
1089<figure><artwork type="code">
1090  length := 0
1091  read chunk-size, chunk-ext (if any) and CRLF
1092  while (chunk-size &gt; 0) {
1093     read chunk-data and CRLF
1094     append chunk-data to entity-body
1095     length := length + chunk-size
1096     read chunk-size and CRLF
1097  }
1098  read entity-header
1099  while (entity-header not empty) {
1100     append entity-header to existing header fields
1101     read entity-header
1102  }
1103  Content-Length := length
1104  Remove "chunked" from Transfer-Encoding
1105</artwork></figure>
1106<t>
1107   All HTTP/1.1 applications &MUST; be able to receive and decode the
1108   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1109   they do not understand.
1110</t>
1111</section>
1112</section>
1113
1114<section title="Product Tokens" anchor="product.tokens">
1115  <x:anchor-alias value="product"/>
1116  <x:anchor-alias value="product-version"/>
1117<t>
1118   Product tokens are used to allow communicating applications to
1119   identify themselves by software name and version. Most fields using
1120   product tokens also allow sub-products which form a significant part
1121   of the application to be listed, separated by whitespace. By
1122   convention, the products are listed in order of their significance
1123   for identifying the application.
1124</t>
1125<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1126  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1127  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1128</artwork></figure>
1129<t>
1130   Examples:
1131</t>
1132<figure><artwork type="example">
1133    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1134    Server: Apache/0.8.4
1135</artwork></figure>
1136<t>
1137   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1138   used for advertising or other non-essential information. Although any
1139   token character &MAY; appear in a product-version, this token &SHOULD;
1140   only be used for a version identifier (i.e., successive versions of
1141   the same product &SHOULD; only differ in the product-version portion of
1142   the product value).
1143</t>
1144</section>
1145
1146</section>
1147
1148<section title="HTTP Message" anchor="http.message">
1149
1150<section title="Message Types" anchor="message.types">
1151  <x:anchor-alias value="generic-message"/>
1152  <x:anchor-alias value="HTTP-message"/>
1153  <x:anchor-alias value="start-line"/>
1154<t>
1155   HTTP messages consist of requests from client to server and responses
1156   from server to client.
1157</t>
1158<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1159  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1160</artwork></figure>
1161<t>
1162   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1163   message format of <xref target="RFC5322"/> for transferring entities (the payload
1164   of the message). Both types of message consist of a start-line, zero
1165   or more header fields (also known as "headers"), an empty line (i.e.,
1166   a line with nothing preceding the CRLF) indicating the end of the
1167   header fields, and possibly a message-body.
1168</t>
1169<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1170  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1171                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1172                    <x:ref>CRLF</x:ref>
1173                    [ <x:ref>message-body</x:ref> ]
1174  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1175</artwork></figure>
1176<t>
1177   In the interest of robustness, servers &SHOULD; ignore any empty
1178   line(s) received where a Request-Line is expected. In other words, if
1179   the server is reading the protocol stream at the beginning of a
1180   message and receives a CRLF first, it should ignore the CRLF.
1181</t>
1182<t>
1183   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1184   after a POST request. To restate what is explicitly forbidden by the
1185   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1186   extra CRLF.
1187</t>
1188<t>
1189   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1190   header field. The presence of whitespace might be an attempt to trick a
1191   noncompliant implementation of HTTP into ignoring that field or processing
1192   the next line as a new request, either of which may result in security
1193   issues when implementations within the request chain interpret the
1194   same message differently. HTTP/1.1 servers &MUST; reject such a message
1195   with a 400 (Bad Request) response.
1196</t>
1197</section>
1198
1199<section title="Message Headers" anchor="message.headers">
1200  <x:anchor-alias value="field-content"/>
1201  <x:anchor-alias value="field-name"/>
1202  <x:anchor-alias value="field-value"/>
1203  <x:anchor-alias value="message-header"/>
1204<t>
1205   HTTP header fields follow the same general format as Internet messages in
1206   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1207   of a name followed by a colon (":"), optional whitespace, and the field
1208   value. Field names are case-insensitive.
1209</t>
1210<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"/>
1211  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1212  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1213  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1214  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1215</artwork></figure>
1216<t>
1217   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1218   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1219   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1220   header field-values use only a subset of the US-ASCII charset
1221   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1222   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1223   (obs-text) octets in field-content as opaque data.
1224</t>
1225<t>
1226   No whitespace is allowed between the header field-name and colon. For
1227   security reasons, any request message received containing such whitespace
1228   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1229   whitespace in a response message &MUST; be removed.
1230</t>
1231<t>
1232   The field value &MAY; be preceded by optional whitespace; a single SP is
1233   preferred. The field-value does not include any leading or trailing white
1234   space: OWS occurring before the first non-whitespace character of the
1235   field-value or after the last non-whitespace character of the field-value
1236   is ignored and &MAY; be removed without changing the meaning of the header
1237   field.
1238</t>
1239<t>
1240   Historically, HTTP header field values could be extended over multiple
1241   lines by preceding each extra line with at least one space or horizontal
1242   tab character (line folding). This specification deprecates such line
1243   folding except within the message/http media type
1244   (<xref target="internet.media.type.message.http"/>).
1245   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1246   (i.e., that contain any field-content that matches the obs-fold rule) unless
1247   the message is intended for packaging within the message/http media type.
1248   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1249   obs-fold whitespace with a single SP prior to interpreting the field value
1250   or forwarding the message downstream.
1251</t>
1252<t anchor="rule.comment">
1253  <x:anchor-alias value="comment"/>
1254  <x:anchor-alias value="ctext"/>
1255   Comments can be included in some HTTP header fields by surrounding
1256   the comment text with parentheses. Comments are only allowed in
1257   fields containing "comment" as part of their field value definition.
1258   In all other fields, parentheses are considered part of the field
1259   value.
1260</t>
1261<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1262  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1263  <x:ref>ctext</x:ref>          = *( <x:ref>OWS</x:ref> / %x21-27 / %x2A-7E / <x:ref>obs-text</x:ref> )
1264</artwork></figure>
1265<t>
1266   The order in which header fields with differing field names are
1267   received is not significant. However, it is "good practice" to send
1268   general-header fields first, followed by request-header or response-header
1269   fields, and ending with the entity-header fields.
1270</t>
1271<t>
1272   Multiple message-header fields with the same field-name &MAY; be
1273   present in a message if and only if the entire field-value for that
1274   header field is defined as a comma-separated list [i.e., #(values)].
1275   It &MUST; be possible to combine the multiple header fields into one
1276   "field-name: field-value" pair, without changing the semantics of the
1277   message, by appending each subsequent field-value to the first, each
1278   separated by a comma. The order in which header fields with the same
1279   field-name are received is therefore significant to the
1280   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1281   change the order of these field values when a message is forwarded.
1282</t>
1283<t>
1284  <list><t>
1285   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1286   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1287   can occur multiple times, but does not use the list syntax, and thus cannot
1288   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1289   for details.) Also note that the Set-Cookie2 header specified in
1290   <xref target="RFC2965"/> does not share this problem.
1291  </t></list>
1292</t>
1293 
1294</section>
1295
1296<section title="Message Body" anchor="message.body">
1297  <x:anchor-alias value="message-body"/>
1298<t>
1299   The message-body (if any) of an HTTP message is used to carry the
1300   entity-body associated with the request or response. The message-body
1301   differs from the entity-body only when a transfer-coding has been
1302   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1303</t>
1304<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1305  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1306               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1307</artwork></figure>
1308<t>
1309   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1310   applied by an application to ensure safe and proper transfer of the
1311   message. Transfer-Encoding is a property of the message, not of the
1312   entity, and thus &MAY; be added or removed by any application along the
1313   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1314   when certain transfer-codings may be used.)
1315</t>
1316<t>
1317   The rules for when a message-body is allowed in a message differ for
1318   requests and responses.
1319</t>
1320<t>
1321   The presence of a message-body in a request is signaled by the
1322   inclusion of a Content-Length or Transfer-Encoding header field in
1323   the request's message-headers. A message-body &MUST-NOT; be included in
1324   a request if the specification of the request method (&method;)
1325   explicitly disallows an entity-body in requests.
1326   When a request message contains both a message-body of non-zero
1327   length and a method that does not define any semantics for that
1328   request message-body, then an origin server &SHOULD; either ignore
1329   the message-body or respond with an appropriate error message
1330   (e.g., 413).  A proxy or gateway, when presented the same request,
1331   &SHOULD; either forward the request inbound with the message-body or
1332   ignore the message-body when determining a response.
1333</t>
1334<t>
1335   For response messages, whether or not a message-body is included with
1336   a message is dependent on both the request method and the response
1337   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1338   &MUST-NOT; include a message-body, even though the presence of entity-header
1339   fields might lead one to believe they do. All 1xx
1340   (informational), 204 (No Content), and 304 (Not Modified) responses
1341   &MUST-NOT; include a message-body. All other responses do include a
1342   message-body, although it &MAY; be of zero length.
1343</t>
1344</section>
1345
1346<section title="Message Length" anchor="message.length">
1347<t>
1348   The transfer-length of a message is the length of the message-body as
1349   it appears in the message; that is, after any transfer-codings have
1350   been applied. When a message-body is included with a message, the
1351   transfer-length of that body is determined by one of the following
1352   (in order of precedence):
1353</t>
1354<t>
1355  <list style="numbers">
1356    <x:lt><t>
1357     Any response message which "&MUST-NOT;" include a message-body (such
1358     as the 1xx, 204, and 304 responses and any response to a HEAD
1359     request) is always terminated by the first empty line after the
1360     header fields, regardless of the entity-header fields present in
1361     the message.
1362    </t></x:lt>
1363    <x:lt><t>
1364     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1365     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1366     is used, the transfer-length is defined by the use of this transfer-coding.
1367     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1368     is not present, the transfer-length is defined by the sender closing the connection.
1369    </t></x:lt>
1370    <x:lt><t>
1371     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1372     decimal value in OCTETs represents both the entity-length and the
1373     transfer-length. The Content-Length header field &MUST-NOT; be sent
1374     if these two lengths are different (i.e., if a Transfer-Encoding
1375     header field is present). If a message is received with both a
1376     Transfer-Encoding header field and a Content-Length header field,
1377     the latter &MUST; be ignored.
1378    </t></x:lt>
1379    <x:lt><t>
1380     If the message uses the media type "multipart/byteranges", and the
1381     transfer-length is not otherwise specified, then this self-delimiting
1382     media type defines the transfer-length. This media type
1383     &MUST-NOT; be used unless the sender knows that the recipient can parse
1384     it; the presence in a request of a Range header with multiple byte-range
1385     specifiers from a 1.1 client implies that the client can parse
1386     multipart/byteranges responses.
1387    <list style="empty"><t>
1388       A range header might be forwarded by a 1.0 proxy that does not
1389       understand multipart/byteranges; in this case the server &MUST;
1390       delimit the message using methods defined in items 1, 3 or 5 of
1391       this section.
1392    </t></list>
1393    </t></x:lt>
1394    <x:lt><t>
1395     By the server closing the connection. (Closing the connection
1396     cannot be used to indicate the end of a request body, since that
1397     would leave no possibility for the server to send back a response.)
1398    </t></x:lt>
1399  </list>
1400</t>
1401<t>
1402   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1403   containing a message-body &MUST; include a valid Content-Length header
1404   field unless the server is known to be HTTP/1.1 compliant. If a
1405   request contains a message-body and a Content-Length is not given,
1406   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1407   determine the length of the message, or with 411 (Length Required) if
1408   it wishes to insist on receiving a valid Content-Length.
1409</t>
1410<t>
1411   All HTTP/1.1 applications that receive entities &MUST; accept the
1412   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1413   to be used for messages when the message length cannot be determined
1414   in advance.
1415</t>
1416<t>
1417   Messages &MUST-NOT; include both a Content-Length header field and a
1418   transfer-coding. If the message does include a
1419   transfer-coding, the Content-Length &MUST; be ignored.
1420</t>
1421<t>
1422   When a Content-Length is given in a message where a message-body is
1423   allowed, its field value &MUST; exactly match the number of OCTETs in
1424   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1425   invalid length is received and detected.
1426</t>
1427</section>
1428
1429<section title="General Header Fields" anchor="general.header.fields">
1430  <x:anchor-alias value="general-header"/>
1431<t>
1432   There are a few header fields which have general applicability for
1433   both request and response messages, but which do not apply to the
1434   entity being transferred. These header fields apply only to the
1435   message being transmitted.
1436</t>
1437<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1438  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1439                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1440                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1441                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1442                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1443                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1444                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1445                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1446                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1447</artwork></figure>
1448<t>
1449   General-header field names can be extended reliably only in
1450   combination with a change in the protocol version. However, new or
1451   experimental header fields may be given the semantics of general
1452   header fields if all parties in the communication recognize them to
1453   be general-header fields. Unrecognized header fields are treated as
1454   entity-header fields.
1455</t>
1456</section>
1457</section>
1458
1459<section title="Request" anchor="request">
1460  <x:anchor-alias value="Request"/>
1461<t>
1462   A request message from a client to a server includes, within the
1463   first line of that message, the method to be applied to the resource,
1464   the identifier of the resource, and the protocol version in use.
1465</t>
1466<!--                 Host                      ; should be moved here eventually -->
1467<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1468  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1469                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1470                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1471                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1472                  <x:ref>CRLF</x:ref>
1473                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1474</artwork></figure>
1475
1476<section title="Request-Line" anchor="request-line">
1477  <x:anchor-alias value="Request-Line"/>
1478<t>
1479   The Request-Line begins with a method token, followed by the
1480   request-target and the protocol version, and ending with CRLF. The
1481   elements are separated by SP characters. No CR or LF is allowed
1482   except in the final CRLF sequence.
1483</t>
1484<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1485  <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>
1486</artwork></figure>
1487
1488<section title="Method" anchor="method">
1489  <x:anchor-alias value="Method"/>
1490<t>
1491   The Method  token indicates the method to be performed on the
1492   resource identified by the request-target. The method is case-sensitive.
1493</t>
1494<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1495  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1496</artwork></figure>
1497</section>
1498
1499<section title="request-target" anchor="request-target">
1500  <x:anchor-alias value="request-target"/>
1501<t>
1502   The request-target is a Uniform Resource Identifier (<xref target="uri"/>) and
1503   identifies the resource upon which to apply the request.
1504</t>
1505<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1506  <x:ref>request-target</x:ref> = "*"
1507                 / <x:ref>absolute-URI</x:ref>
1508                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1509                 / <x:ref>authority</x:ref>
1510</artwork></figure>
1511<t>
1512   The four options for request-target are dependent on the nature of the
1513   request. The asterisk "*" means that the request does not apply to a
1514   particular resource, but to the server itself, and is only allowed
1515   when the method used does not necessarily apply to a resource. One
1516   example would be
1517</t>
1518<figure><artwork type="example">
1519  OPTIONS * HTTP/1.1
1520</artwork></figure>
1521<t>
1522   The absolute-URI form is &REQUIRED; when the request is being made to a
1523   proxy. The proxy is requested to forward the request or service it
1524   from a valid cache, and return the response. Note that the proxy &MAY;
1525   forward the request on to another proxy or directly to the server
1526   specified by the absolute-URI. In order to avoid request loops, a
1527   proxy &MUST; be able to recognize all of its server names, including
1528   any aliases, local variations, and the numeric IP address. An example
1529   Request-Line would be:
1530</t>
1531<figure><artwork type="example">
1532  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1533</artwork></figure>
1534<t>
1535   To allow for transition to absolute-URIs in all requests in future
1536   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1537   form in requests, even though HTTP/1.1 clients will only generate
1538   them in requests to proxies.
1539</t>
1540<t>
1541   The authority form is only used by the CONNECT method (&CONNECT;).
1542</t>
1543<t>
1544   The most common form of request-target is that used to identify a
1545   resource on an origin server or gateway. In this case the absolute
1546   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1547   the request-target, and the network location of the URI (authority) &MUST;
1548   be transmitted in a Host header field. For example, a client wishing
1549   to retrieve the resource above directly from the origin server would
1550   create a TCP connection to port 80 of the host "www.example.org" and send
1551   the lines:
1552</t>
1553<figure><artwork type="example">
1554  GET /pub/WWW/TheProject.html HTTP/1.1
1555  Host: www.example.org
1556</artwork></figure>
1557<t>
1558   followed by the remainder of the Request. Note that the absolute path
1559   cannot be empty; if none is present in the original URI, it &MUST; be
1560   given as "/" (the server root).
1561</t>
1562<t>
1563   If a proxy receives a request without any path in the request-target and
1564   the method specified is capable of supporting the asterisk form of
1565   request-target, then the last proxy on the request chain &MUST; forward the
1566   request with "*" as the final request-target.
1567</t>
1568<figure><preamble>   
1569   For example, the request
1570</preamble><artwork type="example">
1571  OPTIONS http://www.example.org:8001 HTTP/1.1
1572</artwork></figure>
1573<figure><preamble>   
1574  would be forwarded by the proxy as
1575</preamble><artwork type="example">
1576  OPTIONS * HTTP/1.1
1577  Host: www.example.org:8001
1578</artwork>
1579<postamble>
1580   after connecting to port 8001 of host "www.example.org".
1581</postamble>
1582</figure>
1583<t>
1584   The request-target is transmitted in the format specified in
1585   <xref target="http.uri"/>. If the request-target is encoded using the
1586   "% <x:ref>HEXDIG</x:ref> <x:ref>HEXDIG</x:ref>" encoding
1587   (<xref target="RFC3986" x:fmt="," x:sec="2.4"/>), the origin server
1588   &MUST; decode the request-target in order to
1589   properly interpret the request. Servers &SHOULD; respond to invalid
1590   request-targets with an appropriate status code.
1591</t>
1592<t>
1593   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1594   received request-target when forwarding it to the next inbound server,
1595   except as noted above to replace a null path-absolute with "/".
1596</t>
1597<t>
1598  <list><t>
1599      <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1600      meaning of the request when the origin server is improperly using
1601      a non-reserved URI character for a reserved purpose.  Implementors
1602      should be aware that some pre-HTTP/1.1 proxies have been known to
1603      rewrite the request-target.
1604  </t></list>
1605</t>
1606<t>
1607   HTTP does not place a pre-defined limit on the length of a request-target.
1608   A server &MUST; be prepared to receive URIs of unbounded length and
1609   respond with the 414 (Request-target too Long) status if the received
1610   request-target would be longer than the server wishes to handle
1611   (see &status-414;).
1612</t>
1613<t>
1614   Various ad-hoc limitations on request-target length are found in practice.
1615   It is &RECOMMENDED; that all HTTP senders and recipients support
1616   request-target lengths of 8000 or more OCTETs.
1617</t>
1618</section>
1619</section>
1620
1621<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1622<t>
1623   The exact resource identified by an Internet request is determined by
1624   examining both the request-target and the Host header field.
1625</t>
1626<t>
1627   An origin server that does not allow resources to differ by the
1628   requested host &MAY; ignore the Host header field value when
1629   determining the resource identified by an HTTP/1.1 request. (But see
1630   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1631   for other requirements on Host support in HTTP/1.1.)
1632</t>
1633<t>
1634   An origin server that does differentiate resources based on the host
1635   requested (sometimes referred to as virtual hosts or vanity host
1636   names) &MUST; use the following rules for determining the requested
1637   resource on an HTTP/1.1 request:
1638  <list style="numbers">
1639    <t>If request-target is an absolute-URI, the host is part of the
1640     request-target. Any Host header field value in the request &MUST; be
1641     ignored.</t>
1642    <t>If the request-target is not an absolute-URI, and the request includes
1643     a Host header field, the host is determined by the Host header
1644     field value.</t>
1645    <t>If the host as determined by rule 1 or 2 is not a valid host on
1646     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1647  </list>
1648</t>
1649<t>
1650   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1651   attempt to use heuristics (e.g., examination of the URI path for
1652   something unique to a particular host) in order to determine what
1653   exact resource is being requested.
1654</t>
1655</section>
1656
1657</section>
1658
1659
1660<section title="Response" anchor="response">
1661  <x:anchor-alias value="Response"/>
1662<t>
1663   After receiving and interpreting a request message, a server responds
1664   with an HTTP response message.
1665</t>
1666<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1667  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1668                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1669                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1670                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1671                  <x:ref>CRLF</x:ref>
1672                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1673</artwork></figure>
1674
1675<section title="Status-Line" anchor="status-line">
1676  <x:anchor-alias value="Status-Line"/>
1677<t>
1678   The first line of a Response message is the Status-Line, consisting
1679   of the protocol version followed by a numeric status code and its
1680   associated textual phrase, with each element separated by SP
1681   characters. No CR or LF is allowed except in the final CRLF sequence.
1682</t>
1683<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1684  <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>
1685</artwork></figure>
1686
1687<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1688  <x:anchor-alias value="Reason-Phrase"/>
1689  <x:anchor-alias value="Status-Code"/>
1690<t>
1691   The Status-Code element is a 3-digit integer result code of the
1692   attempt to understand and satisfy the request. These codes are fully
1693   defined in &status-codes;.  The Reason Phrase exists for the sole
1694   purpose of providing a textual description associated with the numeric
1695   status code, out of deference to earlier Internet application protocols
1696   that were more frequently used with interactive text clients.
1697   A client &SHOULD; ignore the content of the Reason Phrase.
1698</t>
1699<t>
1700   The first digit of the Status-Code defines the class of response. The
1701   last two digits do not have any categorization role. There are 5
1702   values for the first digit:
1703  <list style="symbols">
1704    <t>
1705      1xx: Informational - Request received, continuing process
1706    </t>
1707    <t>
1708      2xx: Success - The action was successfully received,
1709        understood, and accepted
1710    </t>
1711    <t>
1712      3xx: Redirection - Further action must be taken in order to
1713        complete the request
1714    </t>
1715    <t>
1716      4xx: Client Error - The request contains bad syntax or cannot
1717        be fulfilled
1718    </t>
1719    <t>
1720      5xx: Server Error - The server failed to fulfill an apparently
1721        valid request
1722    </t>
1723  </list>
1724</t>
1725<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"/>
1726  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1727  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1728</artwork></figure>
1729</section>
1730</section>
1731
1732</section>
1733
1734
1735<section title="Connections" anchor="connections">
1736
1737<section title="Persistent Connections" anchor="persistent.connections">
1738
1739<section title="Purpose" anchor="persistent.purpose">
1740<t>
1741   Prior to persistent connections, a separate TCP connection was
1742   established to fetch each URL, increasing the load on HTTP servers
1743   and causing congestion on the Internet. The use of inline images and
1744   other associated data often require a client to make multiple
1745   requests of the same server in a short amount of time. Analysis of
1746   these performance problems and results from a prototype
1747   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1748   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1749   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1750   T/TCP <xref target="Tou1998"/>.
1751</t>
1752<t>
1753   Persistent HTTP connections have a number of advantages:
1754  <list style="symbols">
1755      <t>
1756        By opening and closing fewer TCP connections, CPU time is saved
1757        in routers and hosts (clients, servers, proxies, gateways,
1758        tunnels, or caches), and memory used for TCP protocol control
1759        blocks can be saved in hosts.
1760      </t>
1761      <t>
1762        HTTP requests and responses can be pipelined on a connection.
1763        Pipelining allows a client to make multiple requests without
1764        waiting for each response, allowing a single TCP connection to
1765        be used much more efficiently, with much lower elapsed time.
1766      </t>
1767      <t>
1768        Network congestion is reduced by reducing the number of packets
1769        caused by TCP opens, and by allowing TCP sufficient time to
1770        determine the congestion state of the network.
1771      </t>
1772      <t>
1773        Latency on subsequent requests is reduced since there is no time
1774        spent in TCP's connection opening handshake.
1775      </t>
1776      <t>
1777        HTTP can evolve more gracefully, since errors can be reported
1778        without the penalty of closing the TCP connection. Clients using
1779        future versions of HTTP might optimistically try a new feature,
1780        but if communicating with an older server, retry with old
1781        semantics after an error is reported.
1782      </t>
1783    </list>
1784</t>
1785<t>
1786   HTTP implementations &SHOULD; implement persistent connections.
1787</t>
1788</section>
1789
1790<section title="Overall Operation" anchor="persistent.overall">
1791<t>
1792   A significant difference between HTTP/1.1 and earlier versions of
1793   HTTP is that persistent connections are the default behavior of any
1794   HTTP connection. That is, unless otherwise indicated, the client
1795   &SHOULD; assume that the server will maintain a persistent connection,
1796   even after error responses from the server.
1797</t>
1798<t>
1799   Persistent connections provide a mechanism by which a client and a
1800   server can signal the close of a TCP connection. This signaling takes
1801   place using the Connection header field (<xref target="header.connection"/>). Once a close
1802   has been signaled, the client &MUST-NOT; send any more requests on that
1803   connection.
1804</t>
1805
1806<section title="Negotiation" anchor="persistent.negotiation">
1807<t>
1808   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1809   maintain a persistent connection unless a Connection header including
1810   the connection-token "close" was sent in the request. If the server
1811   chooses to close the connection immediately after sending the
1812   response, it &SHOULD; send a Connection header including the
1813   connection-token close.
1814</t>
1815<t>
1816   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1817   decide to keep it open based on whether the response from a server
1818   contains a Connection header with the connection-token close. In case
1819   the client does not want to maintain a connection for more than that
1820   request, it &SHOULD; send a Connection header including the
1821   connection-token close.
1822</t>
1823<t>
1824   If either the client or the server sends the close token in the
1825   Connection header, that request becomes the last one for the
1826   connection.
1827</t>
1828<t>
1829   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1830   maintained for HTTP versions less than 1.1 unless it is explicitly
1831   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1832   compatibility with HTTP/1.0 clients.
1833</t>
1834<t>
1835   In order to remain persistent, all messages on the connection &MUST;
1836   have a self-defined message length (i.e., one not defined by closure
1837   of the connection), as described in <xref target="message.length"/>.
1838</t>
1839</section>
1840
1841<section title="Pipelining" anchor="pipelining">
1842<t>
1843   A client that supports persistent connections &MAY; "pipeline" its
1844   requests (i.e., send multiple requests without waiting for each
1845   response). A server &MUST; send its responses to those requests in the
1846   same order that the requests were received.
1847</t>
1848<t>
1849   Clients which assume persistent connections and pipeline immediately
1850   after connection establishment &SHOULD; be prepared to retry their
1851   connection if the first pipelined attempt fails. If a client does
1852   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1853   persistent. Clients &MUST; also be prepared to resend their requests if
1854   the server closes the connection before sending all of the
1855   corresponding responses.
1856</t>
1857<t>
1858   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1859   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1860   premature termination of the transport connection could lead to
1861   indeterminate results. A client wishing to send a non-idempotent
1862   request &SHOULD; wait to send that request until it has received the
1863   response status for the previous request.
1864</t>
1865</section>
1866</section>
1867
1868<section title="Proxy Servers" anchor="persistent.proxy">
1869<t>
1870   It is especially important that proxies correctly implement the
1871   properties of the Connection header field as specified in <xref target="header.connection"/>.
1872</t>
1873<t>
1874   The proxy server &MUST; signal persistent connections separately with
1875   its clients and the origin servers (or other proxy servers) that it
1876   connects to. Each persistent connection applies to only one transport
1877   link.
1878</t>
1879<t>
1880   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1881   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1882   discussion of the problems with the Keep-Alive header implemented by
1883   many HTTP/1.0 clients).
1884</t>
1885</section>
1886
1887<section title="Practical Considerations" anchor="persistent.practical">
1888<t>
1889   Servers will usually have some time-out value beyond which they will
1890   no longer maintain an inactive connection. Proxy servers might make
1891   this a higher value since it is likely that the client will be making
1892   more connections through the same server. The use of persistent
1893   connections places no requirements on the length (or existence) of
1894   this time-out for either the client or the server.
1895</t>
1896<t>
1897   When a client or server wishes to time-out it &SHOULD; issue a graceful
1898   close on the transport connection. Clients and servers &SHOULD; both
1899   constantly watch for the other side of the transport close, and
1900   respond to it as appropriate. If a client or server does not detect
1901   the other side's close promptly it could cause unnecessary resource
1902   drain on the network.
1903</t>
1904<t>
1905   A client, server, or proxy &MAY; close the transport connection at any
1906   time. For example, a client might have started to send a new request
1907   at the same time that the server has decided to close the "idle"
1908   connection. From the server's point of view, the connection is being
1909   closed while it was idle, but from the client's point of view, a
1910   request is in progress.
1911</t>
1912<t>
1913   This means that clients, servers, and proxies &MUST; be able to recover
1914   from asynchronous close events. Client software &SHOULD; reopen the
1915   transport connection and retransmit the aborted sequence of requests
1916   without user interaction so long as the request sequence is
1917   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1918   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1919   human operator the choice of retrying the request(s). Confirmation by
1920   user-agent software with semantic understanding of the application
1921   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1922   be repeated if the second sequence of requests fails.
1923</t>
1924<t>
1925   Servers &SHOULD; always respond to at least one request per connection,
1926   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1927   middle of transmitting a response, unless a network or client failure
1928   is suspected.
1929</t>
1930<t>
1931   Clients that use persistent connections &SHOULD; limit the number of
1932   simultaneous connections that they maintain to a given server. A
1933   single-user client &SHOULD-NOT; maintain more than 2 connections with
1934   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1935   another server or proxy, where N is the number of simultaneously
1936   active users. These guidelines are intended to improve HTTP response
1937   times and avoid congestion.
1938</t>
1939</section>
1940</section>
1941
1942<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1943
1944<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1945<t>
1946   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1947   flow control mechanisms to resolve temporary overloads, rather than
1948   terminating connections with the expectation that clients will retry.
1949   The latter technique can exacerbate network congestion.
1950</t>
1951</section>
1952
1953<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1954<t>
1955   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1956   the network connection for an error status while it is transmitting
1957   the request. If the client sees an error status, it &SHOULD;
1958   immediately cease transmitting the body. If the body is being sent
1959   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1960   empty trailer &MAY; be used to prematurely mark the end of the message.
1961   If the body was preceded by a Content-Length header, the client &MUST;
1962   close the connection.
1963</t>
1964</section>
1965
1966<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1967<t>
1968   The purpose of the 100 (Continue) status (see &status-100;) is to
1969   allow a client that is sending a request message with a request body
1970   to determine if the origin server is willing to accept the request
1971   (based on the request headers) before the client sends the request
1972   body. In some cases, it might either be inappropriate or highly
1973   inefficient for the client to send the body if the server will reject
1974   the message without looking at the body.
1975</t>
1976<t>
1977   Requirements for HTTP/1.1 clients:
1978  <list style="symbols">
1979    <t>
1980        If a client will wait for a 100 (Continue) response before
1981        sending the request body, it &MUST; send an Expect request-header
1982        field (&header-expect;) with the "100-continue" expectation.
1983    </t>
1984    <t>
1985        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
1986        with the "100-continue" expectation if it does not intend
1987        to send a request body.
1988    </t>
1989  </list>
1990</t>
1991<t>
1992   Because of the presence of older implementations, the protocol allows
1993   ambiguous situations in which a client may send "Expect: 100-continue"
1994   without receiving either a 417 (Expectation Failed) status
1995   or a 100 (Continue) status. Therefore, when a client sends this
1996   header field to an origin server (possibly via a proxy) from which it
1997   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
1998   for an indefinite period before sending the request body.
1999</t>
2000<t>
2001   Requirements for HTTP/1.1 origin servers:
2002  <list style="symbols">
2003    <t> Upon receiving a request which includes an Expect request-header
2004        field with the "100-continue" expectation, an origin server &MUST;
2005        either respond with 100 (Continue) status and continue to read
2006        from the input stream, or respond with a final status code. The
2007        origin server &MUST-NOT; wait for the request body before sending
2008        the 100 (Continue) response. If it responds with a final status
2009        code, it &MAY; close the transport connection or it &MAY; continue
2010        to read and discard the rest of the request.  It &MUST-NOT;
2011        perform the requested method if it returns a final status code.
2012    </t>
2013    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2014        the request message does not include an Expect request-header
2015        field with the "100-continue" expectation, and &MUST-NOT; send a
2016        100 (Continue) response if such a request comes from an HTTP/1.0
2017        (or earlier) client. There is an exception to this rule: for
2018        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2019        status in response to an HTTP/1.1 PUT or POST request that does
2020        not include an Expect request-header field with the "100-continue"
2021        expectation. This exception, the purpose of which is
2022        to minimize any client processing delays associated with an
2023        undeclared wait for 100 (Continue) status, applies only to
2024        HTTP/1.1 requests, and not to requests with any other HTTP-version
2025        value.
2026    </t>
2027    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2028        already received some or all of the request body for the
2029        corresponding request.
2030    </t>
2031    <t> An origin server that sends a 100 (Continue) response &MUST;
2032    ultimately send a final status code, once the request body is
2033        received and processed, unless it terminates the transport
2034        connection prematurely.
2035    </t>
2036    <t> If an origin server receives a request that does not include an
2037        Expect request-header field with the "100-continue" expectation,
2038        the request includes a request body, and the server responds
2039        with a final status code before reading the entire request body
2040        from the transport connection, then the server &SHOULD-NOT;  close
2041        the transport connection until it has read the entire request,
2042        or until the client closes the connection. Otherwise, the client
2043        might not reliably receive the response message. However, this
2044        requirement is not be construed as preventing a server from
2045        defending itself against denial-of-service attacks, or from
2046        badly broken client implementations.
2047      </t>
2048    </list>
2049</t>
2050<t>
2051   Requirements for HTTP/1.1 proxies:
2052  <list style="symbols">
2053    <t> If a proxy receives a request that includes an Expect request-header
2054        field with the "100-continue" expectation, and the proxy
2055        either knows that the next-hop server complies with HTTP/1.1 or
2056        higher, or does not know the HTTP version of the next-hop
2057        server, it &MUST; forward the request, including the Expect header
2058        field.
2059    </t>
2060    <t> If the proxy knows that the version of the next-hop server is
2061        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2062        respond with a 417 (Expectation Failed) status.
2063    </t>
2064    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2065        numbers received from recently-referenced next-hop servers.
2066    </t>
2067    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2068        request message was received from an HTTP/1.0 (or earlier)
2069        client and did not include an Expect request-header field with
2070        the "100-continue" expectation. This requirement overrides the
2071        general rule for forwarding of 1xx responses (see &status-1xx;).
2072    </t>
2073  </list>
2074</t>
2075</section>
2076
2077<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2078<t>
2079   If an HTTP/1.1 client sends a request which includes a request body,
2080   but which does not include an Expect request-header field with the
2081   "100-continue" expectation, and if the client is not directly
2082   connected to an HTTP/1.1 origin server, and if the client sees the
2083   connection close before receiving any status from the server, the
2084   client &SHOULD; retry the request.  If the client does retry this
2085   request, it &MAY; use the following "binary exponential backoff"
2086   algorithm to be assured of obtaining a reliable response:
2087  <list style="numbers">
2088    <t>
2089      Initiate a new connection to the server
2090    </t>
2091    <t>
2092      Transmit the request-headers
2093    </t>
2094    <t>
2095      Initialize a variable R to the estimated round-trip time to the
2096         server (e.g., based on the time it took to establish the
2097         connection), or to a constant value of 5 seconds if the round-trip
2098         time is not available.
2099    </t>
2100    <t>
2101       Compute T = R * (2**N), where N is the number of previous
2102         retries of this request.
2103    </t>
2104    <t>
2105       Wait either for an error response from the server, or for T
2106         seconds (whichever comes first)
2107    </t>
2108    <t>
2109       If no error response is received, after T seconds transmit the
2110         body of the request.
2111    </t>
2112    <t>
2113       If client sees that the connection is closed prematurely,
2114         repeat from step 1 until the request is accepted, an error
2115         response is received, or the user becomes impatient and
2116         terminates the retry process.
2117    </t>
2118  </list>
2119</t>
2120<t>
2121   If at any point an error status is received, the client
2122  <list style="symbols">
2123      <t>&SHOULD-NOT;  continue and</t>
2124
2125      <t>&SHOULD; close the connection if it has not completed sending the
2126        request message.</t>
2127    </list>
2128</t>
2129</section>
2130</section>
2131</section>
2132
2133
2134<section title="Header Field Definitions" anchor="header.fields">
2135<t>
2136   This section defines the syntax and semantics of HTTP/1.1 header fields
2137   related to message framing and transport protocols.
2138</t>
2139<t>
2140   For entity-header fields, both sender and recipient refer to either the
2141   client or the server, depending on who sends and who receives the entity.
2142</t>
2143
2144<section title="Connection" anchor="header.connection">
2145  <iref primary="true" item="Connection header" x:for-anchor=""/>
2146  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2147  <x:anchor-alias value="Connection"/>
2148  <x:anchor-alias value="connection-token"/>
2149  <x:anchor-alias value="Connection-v"/>
2150<t>
2151   The general-header field "Connection" allows the sender to specify
2152   options that are desired for that particular connection and &MUST-NOT;
2153   be communicated by proxies over further connections.
2154</t>
2155<t>
2156   The Connection header's value has the following grammar:
2157</t>
2158<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"/>
2159  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2160  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2161  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2162</artwork></figure>
2163<t>
2164   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2165   message is forwarded and, for each connection-token in this field,
2166   remove any header field(s) from the message with the same name as the
2167   connection-token. Connection options are signaled by the presence of
2168   a connection-token in the Connection header field, not by any
2169   corresponding additional header field(s), since the additional header
2170   field may not be sent if there are no parameters associated with that
2171   connection option.
2172</t>
2173<t>
2174   Message headers listed in the Connection header &MUST-NOT; include
2175   end-to-end headers, such as Cache-Control.
2176</t>
2177<t>
2178   HTTP/1.1 defines the "close" connection option for the sender to
2179   signal that the connection will be closed after completion of the
2180   response. For example,
2181</t>
2182<figure><artwork type="example">
2183  Connection: close
2184</artwork></figure>
2185<t>
2186   in either the request or the response header fields indicates that
2187   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2188   after the current request/response is complete.
2189</t>
2190<t>
2191   An HTTP/1.1 client that does not support persistent connections &MUST;
2192   include the "close" connection option in every request message.
2193</t>
2194<t>
2195   An HTTP/1.1 server that does not support persistent connections &MUST;
2196   include the "close" connection option in every response message that
2197   does not have a 1xx (informational) status code.
2198</t>
2199<t>
2200   A system receiving an HTTP/1.0 (or lower-version) message that
2201   includes a Connection header &MUST;, for each connection-token in this
2202   field, remove and ignore any header field(s) from the message with
2203   the same name as the connection-token. This protects against mistaken
2204   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2205</t>
2206</section>
2207
2208<section title="Content-Length" anchor="header.content-length">
2209  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2210  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2211  <x:anchor-alias value="Content-Length"/>
2212  <x:anchor-alias value="Content-Length-v"/>
2213<t>
2214   The entity-header field "Content-Length" indicates the size of the
2215   entity-body, in decimal number of OCTETs, sent to the recipient or,
2216   in the case of the HEAD method, the size of the entity-body that
2217   would have been sent had the request been a GET.
2218</t>
2219<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2220  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2221  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2222</artwork></figure>
2223<t>
2224   An example is
2225</t>
2226<figure><artwork type="example">
2227  Content-Length: 3495
2228</artwork></figure>
2229<t>
2230   Applications &SHOULD; use this field to indicate the transfer-length of
2231   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2232</t>
2233<t>
2234   Any Content-Length greater than or equal to zero is a valid value.
2235   <xref target="message.length"/> describes how to determine the length of a message-body
2236   if a Content-Length is not given.
2237</t>
2238<t>
2239   Note that the meaning of this field is significantly different from
2240   the corresponding definition in MIME, where it is an optional field
2241   used within the "message/external-body" content-type. In HTTP, it
2242   &SHOULD; be sent whenever the message's length can be determined prior
2243   to being transferred, unless this is prohibited by the rules in
2244   <xref target="message.length"/>.
2245</t>
2246</section>
2247
2248<section title="Date" anchor="header.date">
2249  <iref primary="true" item="Date header" x:for-anchor=""/>
2250  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2251  <x:anchor-alias value="Date"/>
2252  <x:anchor-alias value="Date-v"/>
2253<t>
2254   The general-header field "Date" represents the date and time at which
2255   the message was originated, having the same semantics as orig-date in
2256   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2257   HTTP-date, as described in <xref target="full.date"/>;
2258   it &MUST; be sent in rfc1123-date format.
2259</t>
2260<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2261  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2262  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2263</artwork></figure>
2264<t>
2265   An example is
2266</t>
2267<figure><artwork type="example">
2268  Date: Tue, 15 Nov 1994 08:12:31 GMT
2269</artwork></figure>
2270<t>
2271   Origin servers &MUST; include a Date header field in all responses,
2272   except in these cases:
2273  <list style="numbers">
2274      <t>If the response status code is 100 (Continue) or 101 (Switching
2275         Protocols), the response &MAY; include a Date header field, at
2276         the server's option.</t>
2277
2278      <t>If the response status code conveys a server error, e.g. 500
2279         (Internal Server Error) or 503 (Service Unavailable), and it is
2280         inconvenient or impossible to generate a valid Date.</t>
2281
2282      <t>If the server does not have a clock that can provide a
2283         reasonable approximation of the current time, its responses
2284         &MUST-NOT; include a Date header field. In this case, the rules
2285         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2286  </list>
2287</t>
2288<t>
2289   A received message that does not have a Date header field &MUST; be
2290   assigned one by the recipient if the message will be cached by that
2291   recipient or gatewayed via a protocol which requires a Date. An HTTP
2292   implementation without a clock &MUST-NOT; cache responses without
2293   revalidating them on every use. An HTTP cache, especially a shared
2294   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2295   clock with a reliable external standard.
2296</t>
2297<t>
2298   Clients &SHOULD; only send a Date header field in messages that include
2299   an entity-body, as in the case of the PUT and POST requests, and even
2300   then it is optional. A client without a clock &MUST-NOT; send a Date
2301   header field in a request.
2302</t>
2303<t>
2304   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2305   time subsequent to the generation of the message. It &SHOULD; represent
2306   the best available approximation of the date and time of message
2307   generation, unless the implementation has no means of generating a
2308   reasonably accurate date and time. In theory, the date ought to
2309   represent the moment just before the entity is generated. In
2310   practice, the date can be generated at any time during the message
2311   origination without affecting its semantic value.
2312</t>
2313
2314<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2315<t>
2316   Some origin server implementations might not have a clock available.
2317   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2318   values to a response, unless these values were associated
2319   with the resource by a system or user with a reliable clock. It &MAY;
2320   assign an Expires value that is known, at or before server
2321   configuration time, to be in the past (this allows "pre-expiration"
2322   of responses without storing separate Expires values for each
2323   resource).
2324</t>
2325</section>
2326</section>
2327
2328<section title="Host" anchor="header.host">
2329  <iref primary="true" item="Host header" x:for-anchor=""/>
2330  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2331  <x:anchor-alias value="Host"/>
2332  <x:anchor-alias value="Host-v"/>
2333<t>
2334   The request-header field "Host" specifies the Internet host and port
2335   number of the resource being requested, as obtained from the original
2336   URI given by the user or referring resource (generally an http URI,
2337   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2338   the naming authority of the origin server or gateway given by the
2339   original URL. This allows the origin server or gateway to
2340   differentiate between internally-ambiguous URLs, such as the root "/"
2341   URL of a server for multiple host names on a single IP address.
2342</t>
2343<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2344  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2345  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2346</artwork></figure>
2347<t>
2348   A "host" without any trailing port information implies the default
2349   port for the service requested (e.g., "80" for an HTTP URL). For
2350   example, a request on the origin server for
2351   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2352</t>
2353<figure><artwork type="example">
2354  GET /pub/WWW/ HTTP/1.1
2355  Host: www.example.org
2356</artwork></figure>
2357<t>
2358   A client &MUST; include a Host header field in all HTTP/1.1 request
2359   messages. If the requested URI does not include an Internet host
2360   name for the service being requested, then the Host header field &MUST;
2361   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2362   request message it forwards does contain an appropriate Host header
2363   field that identifies the service being requested by the proxy. All
2364   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2365   status code to any HTTP/1.1 request message which lacks a Host header
2366   field.
2367</t>
2368<t>
2369   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2370   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2371   for other requirements relating to Host.
2372</t>
2373</section>
2374
2375<section title="TE" anchor="header.te">
2376  <iref primary="true" item="TE header" x:for-anchor=""/>
2377  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2378  <x:anchor-alias value="TE"/>
2379  <x:anchor-alias value="TE-v"/>
2380  <x:anchor-alias value="t-codings"/>
2381<t>
2382   The request-header field "TE" indicates what extension transfer-codings
2383   it is willing to accept in the response and whether or not it is
2384   willing to accept trailer fields in a chunked transfer-coding. Its
2385   value may consist of the keyword "trailers" and/or a comma-separated
2386   list of extension transfer-coding names with optional accept
2387   parameters (as described in <xref target="transfer.codings"/>).
2388</t>
2389<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"/>
2390  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2391  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2392  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>accept-params</x:ref> ] )
2393</artwork></figure>
2394<t>
2395   The presence of the keyword "trailers" indicates that the client is
2396   willing to accept trailer fields in a chunked transfer-coding, as
2397   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2398   transfer-coding values even though it does not itself represent a
2399   transfer-coding.
2400</t>
2401<t>
2402   Examples of its use are:
2403</t>
2404<figure><artwork type="example">
2405  TE: deflate
2406  TE:
2407  TE: trailers, deflate;q=0.5
2408</artwork></figure>
2409<t>
2410   The TE header field only applies to the immediate connection.
2411   Therefore, the keyword &MUST; be supplied within a Connection header
2412   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2413</t>
2414<t>
2415   A server tests whether a transfer-coding is acceptable, according to
2416   a TE field, using these rules:
2417  <list style="numbers">
2418    <x:lt>
2419      <t>The "chunked" transfer-coding is always acceptable. If the
2420         keyword "trailers" is listed, the client indicates that it is
2421         willing to accept trailer fields in the chunked response on
2422         behalf of itself and any downstream clients. The implication is
2423         that, if given, the client is stating that either all
2424         downstream clients are willing to accept trailer fields in the
2425         forwarded response, or that it will attempt to buffer the
2426         response on behalf of downstream recipients.
2427      </t><t>
2428         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2429         chunked response such that a client can be assured of buffering
2430         the entire response.</t>
2431    </x:lt>
2432    <x:lt>
2433      <t>If the transfer-coding being tested is one of the transfer-codings
2434         listed in the TE field, then it is acceptable unless it
2435         is accompanied by a qvalue of 0. (As defined in &qvalue;, a
2436         qvalue of 0 means "not acceptable.")</t>
2437    </x:lt>
2438    <x:lt>
2439      <t>If multiple transfer-codings are acceptable, then the
2440         acceptable transfer-coding with the highest non-zero qvalue is
2441         preferred.  The "chunked" transfer-coding always has a qvalue
2442         of 1.</t>
2443    </x:lt>
2444  </list>
2445</t>
2446<t>
2447   If the TE field-value is empty or if no TE field is present, the only
2448   transfer-coding  is "chunked". A message with no transfer-coding is
2449   always acceptable.
2450</t>
2451</section>
2452
2453<section title="Trailer" anchor="header.trailer">
2454  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2455  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2456  <x:anchor-alias value="Trailer"/>
2457  <x:anchor-alias value="Trailer-v"/>
2458<t>
2459   The general field "Trailer" indicates that the given set of
2460   header fields is present in the trailer of a message encoded with
2461   chunked transfer-coding.
2462</t>
2463<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2464  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2465  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2466</artwork></figure>
2467<t>
2468   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2469   message using chunked transfer-coding with a non-empty trailer. Doing
2470   so allows the recipient to know which header fields to expect in the
2471   trailer.
2472</t>
2473<t>
2474   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2475   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2476   trailer fields in a "chunked" transfer-coding.
2477</t>
2478<t>
2479   Message header fields listed in the Trailer header field &MUST-NOT;
2480   include the following header fields:
2481  <list style="symbols">
2482    <t>Transfer-Encoding</t>
2483    <t>Content-Length</t>
2484    <t>Trailer</t>
2485  </list>
2486</t>
2487</section>
2488
2489<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2490  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2491  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2492  <x:anchor-alias value="Transfer-Encoding"/>
2493  <x:anchor-alias value="Transfer-Encoding-v"/>
2494<t>
2495   The general-header "Transfer-Encoding" field indicates what (if any)
2496   type of transformation has been applied to the message body in order
2497   to safely transfer it between the sender and the recipient. This
2498   differs from the content-coding in that the transfer-coding is a
2499   property of the message, not of the entity.
2500</t>
2501<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2502  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2503                        <x:ref>Transfer-Encoding-v</x:ref>
2504  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2505</artwork></figure>
2506<t>
2507   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2508</t>
2509<figure><artwork type="example">
2510  Transfer-Encoding: chunked
2511</artwork></figure>
2512<t>
2513   If multiple encodings have been applied to an entity, the transfer-codings
2514   &MUST; be listed in the order in which they were applied.
2515   Additional information about the encoding parameters &MAY; be provided
2516   by other entity-header fields not defined by this specification.
2517</t>
2518<t>
2519   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2520   header.
2521</t>
2522</section>
2523
2524<section title="Upgrade" anchor="header.upgrade">
2525  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2526  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2527  <x:anchor-alias value="Upgrade"/>
2528  <x:anchor-alias value="Upgrade-v"/>
2529<t>
2530   The general-header "Upgrade" allows the client to specify what
2531   additional communication protocols it supports and would like to use
2532   if the server finds it appropriate to switch protocols. The server
2533   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2534   response to indicate which protocol(s) are being switched.
2535</t>
2536<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2537  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2538  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2539</artwork></figure>
2540<t>
2541   For example,
2542</t>
2543<figure><artwork type="example">
2544  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2545</artwork></figure>
2546<t>
2547   The Upgrade header field is intended to provide a simple mechanism
2548   for transition from HTTP/1.1 to some other, incompatible protocol. It
2549   does so by allowing the client to advertise its desire to use another
2550   protocol, such as a later version of HTTP with a higher major version
2551   number, even though the current request has been made using HTTP/1.1.
2552   This eases the difficult transition between incompatible protocols by
2553   allowing the client to initiate a request in the more commonly
2554   supported protocol while indicating to the server that it would like
2555   to use a "better" protocol if available (where "better" is determined
2556   by the server, possibly according to the nature of the method and/or
2557   resource being requested).
2558</t>
2559<t>
2560   The Upgrade header field only applies to switching application-layer
2561   protocols upon the existing transport-layer connection. Upgrade
2562   cannot be used to insist on a protocol change; its acceptance and use
2563   by the server is optional. The capabilities and nature of the
2564   application-layer communication after the protocol change is entirely
2565   dependent upon the new protocol chosen, although the first action
2566   after changing the protocol &MUST; be a response to the initial HTTP
2567   request containing the Upgrade header field.
2568</t>
2569<t>
2570   The Upgrade header field only applies to the immediate connection.
2571   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2572   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2573   HTTP/1.1 message.
2574</t>
2575<t>
2576   The Upgrade header field cannot be used to indicate a switch to a
2577   protocol on a different connection. For that purpose, it is more
2578   appropriate to use a 301, 302, 303, or 305 redirection response.
2579</t>
2580<t>
2581   This specification only defines the protocol name "HTTP" for use by
2582   the family of Hypertext Transfer Protocols, as defined by the HTTP
2583   version rules of <xref target="http.version"/> and future updates to this
2584   specification. Any token can be used as a protocol name; however, it
2585   will only be useful if both the client and server associate the name
2586   with the same protocol.
2587</t>
2588</section>
2589
2590<section title="Via" anchor="header.via">
2591  <iref primary="true" item="Via header" x:for-anchor=""/>
2592  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2593  <x:anchor-alias value="protocol-name"/>
2594  <x:anchor-alias value="protocol-version"/>
2595  <x:anchor-alias value="pseudonym"/>
2596  <x:anchor-alias value="received-by"/>
2597  <x:anchor-alias value="received-protocol"/>
2598  <x:anchor-alias value="Via"/>
2599  <x:anchor-alias value="Via-v"/>
2600<t>
2601   The general-header field "Via" &MUST; be used by gateways and proxies to
2602   indicate the intermediate protocols and recipients between the user
2603   agent and the server on requests, and between the origin server and
2604   the client on responses. It is analogous to the "Received" field defined in
2605   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2606   avoiding request loops, and identifying the protocol capabilities of
2607   all senders along the request/response chain.
2608</t>
2609<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"/>
2610  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2611  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2612                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2613  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2614  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2615  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2616  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2617  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2618</artwork></figure>
2619<t>
2620   The received-protocol indicates the protocol version of the message
2621   received by the server or client along each segment of the
2622   request/response chain. The received-protocol version is appended to
2623   the Via field value when the message is forwarded so that information
2624   about the protocol capabilities of upstream applications remains
2625   visible to all recipients.
2626</t>
2627<t>
2628   The protocol-name is optional if and only if it would be "HTTP". The
2629   received-by field is normally the host and optional port number of a
2630   recipient server or client that subsequently forwarded the message.
2631   However, if the real host is considered to be sensitive information,
2632   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2633   be assumed to be the default port of the received-protocol.
2634</t>
2635<t>
2636   Multiple Via field values represents each proxy or gateway that has
2637   forwarded the message. Each recipient &MUST; append its information
2638   such that the end result is ordered according to the sequence of
2639   forwarding applications.
2640</t>
2641<t>
2642   Comments &MAY; be used in the Via header field to identify the software
2643   of the recipient proxy or gateway, analogous to the User-Agent and
2644   Server header fields. However, all comments in the Via field are
2645   optional and &MAY; be removed by any recipient prior to forwarding the
2646   message.
2647</t>
2648<t>
2649   For example, a request message could be sent from an HTTP/1.0 user
2650   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2651   forward the request to a public proxy at p.example.net, which completes
2652   the request by forwarding it to the origin server at www.example.com.
2653   The request received by www.example.com would then have the following
2654   Via header field:
2655</t>
2656<figure><artwork type="example">
2657  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2658</artwork></figure>
2659<t>
2660   Proxies and gateways used as a portal through a network firewall
2661   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2662   the firewall region. This information &SHOULD; only be propagated if
2663   explicitly enabled. If not enabled, the received-by host of any host
2664   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2665   for that host.
2666</t>
2667<t>
2668   For organizations that have strong privacy requirements for hiding
2669   internal structures, a proxy &MAY; combine an ordered subsequence of
2670   Via header field entries with identical received-protocol values into
2671   a single such entry. For example,
2672</t>
2673<figure><artwork type="example">
2674  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2675</artwork></figure>
2676<t>
2677        could be collapsed to
2678</t>
2679<figure><artwork type="example">
2680  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2681</artwork></figure>
2682<t>
2683   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2684   under the same organizational control and the hosts have already been
2685   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2686   have different received-protocol values.
2687</t>
2688</section>
2689
2690</section>
2691
2692<section title="IANA Considerations" anchor="IANA.considerations">
2693<section title="Message Header Registration" anchor="message.header.registration">
2694<t>
2695   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2696   with the permanent registrations below (see <xref target="RFC3864"/>):
2697</t>
2698<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2699<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2700   <ttcol>Header Field Name</ttcol>
2701   <ttcol>Protocol</ttcol>
2702   <ttcol>Status</ttcol>
2703   <ttcol>Reference</ttcol>
2704
2705   <c>Connection</c>
2706   <c>http</c>
2707   <c>standard</c>
2708   <c>
2709      <xref target="header.connection"/>
2710   </c>
2711   <c>Content-Length</c>
2712   <c>http</c>
2713   <c>standard</c>
2714   <c>
2715      <xref target="header.content-length"/>
2716   </c>
2717   <c>Date</c>
2718   <c>http</c>
2719   <c>standard</c>
2720   <c>
2721      <xref target="header.date"/>
2722   </c>
2723   <c>Host</c>
2724   <c>http</c>
2725   <c>standard</c>
2726   <c>
2727      <xref target="header.host"/>
2728   </c>
2729   <c>TE</c>
2730   <c>http</c>
2731   <c>standard</c>
2732   <c>
2733      <xref target="header.te"/>
2734   </c>
2735   <c>Trailer</c>
2736   <c>http</c>
2737   <c>standard</c>
2738   <c>
2739      <xref target="header.trailer"/>
2740   </c>
2741   <c>Transfer-Encoding</c>
2742   <c>http</c>
2743   <c>standard</c>
2744   <c>
2745      <xref target="header.transfer-encoding"/>
2746   </c>
2747   <c>Upgrade</c>
2748   <c>http</c>
2749   <c>standard</c>
2750   <c>
2751      <xref target="header.upgrade"/>
2752   </c>
2753   <c>Via</c>
2754   <c>http</c>
2755   <c>standard</c>
2756   <c>
2757      <xref target="header.via"/>
2758   </c>
2759</texttable>
2760<!--(END)-->
2761<t>
2762   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2763</t>
2764</section>
2765
2766<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2767<t>
2768   The entry for the "http" URI Scheme in the registry located at
2769   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2770   should be updated to point to <xref target="http.uri"/> of this document
2771   (see <xref target="RFC4395"/>).
2772</t>
2773</section>
2774
2775<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2776<t>
2777   This document serves as the specification for the Internet media types
2778   "message/http" and "application/http". The following is to be registered with
2779   IANA (see <xref target="RFC4288"/>).
2780</t>
2781<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2782<iref item="Media Type" subitem="message/http" primary="true"/>
2783<iref item="message/http Media Type" primary="true"/>
2784<t>
2785   The message/http type can be used to enclose a single HTTP request or
2786   response message, provided that it obeys the MIME restrictions for all
2787   "message" types regarding line length and encodings.
2788</t>
2789<t>
2790  <list style="hanging" x:indent="12em">
2791    <t hangText="Type name:">
2792      message
2793    </t>
2794    <t hangText="Subtype name:">
2795      http
2796    </t>
2797    <t hangText="Required parameters:">
2798      none
2799    </t>
2800    <t hangText="Optional parameters:">
2801      version, msgtype
2802      <list style="hanging">
2803        <t hangText="version:">
2804          The HTTP-Version number of the enclosed message
2805          (e.g., "1.1"). If not present, the version can be
2806          determined from the first line of the body.
2807        </t>
2808        <t hangText="msgtype:">
2809          The message type -- "request" or "response". If not
2810          present, the type can be determined from the first
2811          line of the body.
2812        </t>
2813      </list>
2814    </t>
2815    <t hangText="Encoding considerations:">
2816      only "7bit", "8bit", or "binary" are permitted
2817    </t>
2818    <t hangText="Security considerations:">
2819      none
2820    </t>
2821    <t hangText="Interoperability considerations:">
2822      none
2823    </t>
2824    <t hangText="Published specification:">
2825      This specification (see <xref target="internet.media.type.message.http"/>).
2826    </t>
2827    <t hangText="Applications that use this media type:">
2828    </t>
2829    <t hangText="Additional information:">
2830      <list style="hanging">
2831        <t hangText="Magic number(s):">none</t>
2832        <t hangText="File extension(s):">none</t>
2833        <t hangText="Macintosh file type code(s):">none</t>
2834      </list>
2835    </t>
2836    <t hangText="Person and email address to contact for further information:">
2837      See Authors Section.
2838    </t>
2839                <t hangText="Intended usage:">
2840                  COMMON
2841    </t>
2842                <t hangText="Restrictions on usage:">
2843                  none
2844    </t>
2845    <t hangText="Author/Change controller:">
2846      IESG
2847    </t>
2848  </list>
2849</t>
2850</section>
2851<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2852<iref item="Media Type" subitem="application/http" primary="true"/>
2853<iref item="application/http Media Type" primary="true"/>
2854<t>
2855   The application/http type can be used to enclose a pipeline of one or more
2856   HTTP request or response messages (not intermixed).
2857</t>
2858<t>
2859  <list style="hanging" x:indent="12em">
2860    <t hangText="Type name:">
2861      application
2862    </t>
2863    <t hangText="Subtype name:">
2864      http
2865    </t>
2866    <t hangText="Required parameters:">
2867      none
2868    </t>
2869    <t hangText="Optional parameters:">
2870      version, msgtype
2871      <list style="hanging">
2872        <t hangText="version:">
2873          The HTTP-Version number of the enclosed messages
2874          (e.g., "1.1"). If not present, the version can be
2875          determined from the first line of the body.
2876        </t>
2877        <t hangText="msgtype:">
2878          The message type -- "request" or "response". If not
2879          present, the type can be determined from the first
2880          line of the body.
2881        </t>
2882      </list>
2883    </t>
2884    <t hangText="Encoding considerations:">
2885      HTTP messages enclosed by this type
2886      are in "binary" format; use of an appropriate
2887      Content-Transfer-Encoding is required when
2888      transmitted via E-mail.
2889    </t>
2890    <t hangText="Security considerations:">
2891      none
2892    </t>
2893    <t hangText="Interoperability considerations:">
2894      none
2895    </t>
2896    <t hangText="Published specification:">
2897      This specification (see <xref target="internet.media.type.application.http"/>).
2898    </t>
2899    <t hangText="Applications that use this media type:">
2900    </t>
2901    <t hangText="Additional information:">
2902      <list style="hanging">
2903        <t hangText="Magic number(s):">none</t>
2904        <t hangText="File extension(s):">none</t>
2905        <t hangText="Macintosh file type code(s):">none</t>
2906      </list>
2907    </t>
2908    <t hangText="Person and email address to contact for further information:">
2909      See Authors Section.
2910    </t>
2911                <t hangText="Intended usage:">
2912                  COMMON
2913    </t>
2914                <t hangText="Restrictions on usage:">
2915                  none
2916    </t>
2917    <t hangText="Author/Change controller:">
2918      IESG
2919    </t>
2920  </list>
2921</t>
2922</section>
2923</section>
2924
2925</section>
2926
2927<section title="Security Considerations" anchor="security.considerations">
2928<t>
2929   This section is meant to inform application developers, information
2930   providers, and users of the security limitations in HTTP/1.1 as
2931   described by this document. The discussion does not include
2932   definitive solutions to the problems revealed, though it does make
2933   some suggestions for reducing security risks.
2934</t>
2935
2936<section title="Personal Information" anchor="personal.information">
2937<t>
2938   HTTP clients are often privy to large amounts of personal information
2939   (e.g. the user's name, location, mail address, passwords, encryption
2940   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2941   leakage of this information.
2942   We very strongly recommend that a convenient interface be provided
2943   for the user to control dissemination of such information, and that
2944   designers and implementors be particularly careful in this area.
2945   History shows that errors in this area often create serious security
2946   and/or privacy problems and generate highly adverse publicity for the
2947   implementor's company.
2948</t>
2949</section>
2950
2951<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2952<t>
2953   A server is in the position to save personal data about a user's
2954   requests which might identify their reading patterns or subjects of
2955   interest. This information is clearly confidential in nature and its
2956   handling can be constrained by law in certain countries. People using
2957   HTTP to provide data are responsible for ensuring that
2958   such material is not distributed without the permission of any
2959   individuals that are identifiable by the published results.
2960</t>
2961</section>
2962
2963<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2964<t>
2965   Implementations of HTTP origin servers &SHOULD; be careful to restrict
2966   the documents returned by HTTP requests to be only those that were
2967   intended by the server administrators. If an HTTP server translates
2968   HTTP URIs directly into file system calls, the server &MUST; take
2969   special care not to serve files that were not intended to be
2970   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
2971   other operating systems use ".." as a path component to indicate a
2972   directory level above the current one. On such a system, an HTTP
2973   server &MUST; disallow any such construct in the request-target if it
2974   would otherwise allow access to a resource outside those intended to
2975   be accessible via the HTTP server. Similarly, files intended for
2976   reference only internally to the server (such as access control
2977   files, configuration files, and script code) &MUST; be protected from
2978   inappropriate retrieval, since they might contain sensitive
2979   information. Experience has shown that minor bugs in such HTTP server
2980   implementations have turned into security risks.
2981</t>
2982</section>
2983
2984<section title="DNS Spoofing" anchor="dns.spoofing">
2985<t>
2986   Clients using HTTP rely heavily on the Domain Name Service, and are
2987   thus generally prone to security attacks based on the deliberate
2988   mis-association of IP addresses and DNS names. Clients need to be
2989   cautious in assuming the continuing validity of an IP number/DNS name
2990   association.
2991</t>
2992<t>
2993   In particular, HTTP clients &SHOULD; rely on their name resolver for
2994   confirmation of an IP number/DNS name association, rather than
2995   caching the result of previous host name lookups. Many platforms
2996   already can cache host name lookups locally when appropriate, and
2997   they &SHOULD; be configured to do so. It is proper for these lookups to
2998   be cached, however, only when the TTL (Time To Live) information
2999   reported by the name server makes it likely that the cached
3000   information will remain useful.
3001</t>
3002<t>
3003   If HTTP clients cache the results of host name lookups in order to
3004   achieve a performance improvement, they &MUST; observe the TTL
3005   information reported by DNS.
3006</t>
3007<t>
3008   If HTTP clients do not observe this rule, they could be spoofed when
3009   a previously-accessed server's IP address changes. As network
3010   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3011   possibility of this form of attack will grow. Observing this
3012   requirement thus reduces this potential security vulnerability.
3013</t>
3014<t>
3015   This requirement also improves the load-balancing behavior of clients
3016   for replicated servers using the same DNS name and reduces the
3017   likelihood of a user's experiencing failure in accessing sites which
3018   use that strategy.
3019</t>
3020</section>
3021
3022<section title="Proxies and Caching" anchor="attack.proxies">
3023<t>
3024   By their very nature, HTTP proxies are men-in-the-middle, and
3025   represent an opportunity for man-in-the-middle attacks. Compromise of
3026   the systems on which the proxies run can result in serious security
3027   and privacy problems. Proxies have access to security-related
3028   information, personal information about individual users and
3029   organizations, and proprietary information belonging to users and
3030   content providers. A compromised proxy, or a proxy implemented or
3031   configured without regard to security and privacy considerations,
3032   might be used in the commission of a wide range of potential attacks.
3033</t>
3034<t>
3035   Proxy operators should protect the systems on which proxies run as
3036   they would protect any system that contains or transports sensitive
3037   information. In particular, log information gathered at proxies often
3038   contains highly sensitive personal information, and/or information
3039   about organizations. Log information should be carefully guarded, and
3040   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3041</t>
3042<t>
3043   Proxy implementors should consider the privacy and security
3044   implications of their design and coding decisions, and of the
3045   configuration options they provide to proxy operators (especially the
3046   default configuration).
3047</t>
3048<t>
3049   Users of a proxy need to be aware that they are no trustworthier than
3050   the people who run the proxy; HTTP itself cannot solve this problem.
3051</t>
3052<t>
3053   The judicious use of cryptography, when appropriate, may suffice to
3054   protect against a broad range of security and privacy attacks. Such
3055   cryptography is beyond the scope of the HTTP/1.1 specification.
3056</t>
3057</section>
3058
3059<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3060<t>
3061   They exist. They are hard to defend against. Research continues.
3062   Beware.
3063</t>
3064</section>
3065</section>
3066
3067<section title="Acknowledgments" anchor="ack">
3068<t>
3069   HTTP has evolved considerably over the years. It has
3070   benefited from a large and active developer community--the many
3071   people who have participated on the www-talk mailing list--and it is
3072   that community which has been most responsible for the success of
3073   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3074   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3075   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3076   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3077   VanHeyningen deserve special recognition for their efforts in
3078   defining early aspects of the protocol.
3079</t>
3080<t>
3081   This document has benefited greatly from the comments of all those
3082   participating in the HTTP-WG. In addition to those already mentioned,
3083   the following individuals have contributed to this specification:
3084</t>
3085<t>
3086   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3087   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3088   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3089   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3090   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3091   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3092   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3093   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3094   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3095   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3096   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3097   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3098   Josh Cohen.
3099</t>
3100<t>
3101   Thanks to the "cave men" of Palo Alto. You know who you are.
3102</t>
3103<t>
3104   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3105   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3106   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3107   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3108   Larry Masinter for their help. And thanks go particularly to Jeff
3109   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3110</t>
3111<t>
3112   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3113   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3114   discovery of many of the problems that this document attempts to
3115   rectify.
3116</t>
3117<t>
3118   This specification makes heavy use of the augmented BNF and generic
3119   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3120   reuses many of the definitions provided by Nathaniel Borenstein and
3121   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3122   specification will help reduce past confusion over the relationship
3123   between HTTP and Internet mail message formats.
3124</t>
3125</section>
3126
3127</middle>
3128<back>
3129
3130<references title="Normative References">
3131
3132<reference anchor="ISO-8859-1">
3133  <front>
3134    <title>
3135     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3136    </title>
3137    <author>
3138      <organization>International Organization for Standardization</organization>
3139    </author>
3140    <date year="1998"/>
3141  </front>
3142  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3143</reference>
3144
3145<reference anchor="Part2">
3146  <front>
3147    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3148    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3149      <organization abbrev="Day Software">Day Software</organization>
3150      <address><email>fielding@gbiv.com</email></address>
3151    </author>
3152    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3153      <organization>One Laptop per Child</organization>
3154      <address><email>jg@laptop.org</email></address>
3155    </author>
3156    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3157      <organization abbrev="HP">Hewlett-Packard Company</organization>
3158      <address><email>JeffMogul@acm.org</email></address>
3159    </author>
3160    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3161      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3162      <address><email>henrikn@microsoft.com</email></address>
3163    </author>
3164    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3165      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3166      <address><email>LMM@acm.org</email></address>
3167    </author>
3168    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3169      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3170      <address><email>paulle@microsoft.com</email></address>
3171    </author>
3172    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3173      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3174      <address><email>timbl@w3.org</email></address>
3175    </author>
3176    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3177      <organization abbrev="W3C">World Wide Web Consortium</organization>
3178      <address><email>ylafon@w3.org</email></address>
3179    </author>
3180    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3181      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3182      <address><email>julian.reschke@greenbytes.de</email></address>
3183    </author>
3184    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3185  </front>
3186  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3187  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3188</reference>
3189
3190<reference anchor="Part3">
3191  <front>
3192    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3193    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3194      <organization abbrev="Day Software">Day Software</organization>
3195      <address><email>fielding@gbiv.com</email></address>
3196    </author>
3197    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3198      <organization>One Laptop per Child</organization>
3199      <address><email>jg@laptop.org</email></address>
3200    </author>
3201    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3202      <organization abbrev="HP">Hewlett-Packard Company</organization>
3203      <address><email>JeffMogul@acm.org</email></address>
3204    </author>
3205    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3206      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3207      <address><email>henrikn@microsoft.com</email></address>
3208    </author>
3209    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3210      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3211      <address><email>LMM@acm.org</email></address>
3212    </author>
3213    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3214      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3215      <address><email>paulle@microsoft.com</email></address>
3216    </author>
3217    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3218      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3219      <address><email>timbl@w3.org</email></address>
3220    </author>
3221    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3222      <organization abbrev="W3C">World Wide Web Consortium</organization>
3223      <address><email>ylafon@w3.org</email></address>
3224    </author>
3225    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3226      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3227      <address><email>julian.reschke@greenbytes.de</email></address>
3228    </author>
3229    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3230  </front>
3231  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3232  <x:source href="p3-payload.xml" basename="p3-payload"/>
3233</reference>
3234
3235<reference anchor="Part5">
3236  <front>
3237    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3238    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3239      <organization abbrev="Day Software">Day Software</organization>
3240      <address><email>fielding@gbiv.com</email></address>
3241    </author>
3242    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3243      <organization>One Laptop per Child</organization>
3244      <address><email>jg@laptop.org</email></address>
3245    </author>
3246    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3247      <organization abbrev="HP">Hewlett-Packard Company</organization>
3248      <address><email>JeffMogul@acm.org</email></address>
3249    </author>
3250    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3251      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3252      <address><email>henrikn@microsoft.com</email></address>
3253    </author>
3254    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3255      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3256      <address><email>LMM@acm.org</email></address>
3257    </author>
3258    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3259      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3260      <address><email>paulle@microsoft.com</email></address>
3261    </author>
3262    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3263      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3264      <address><email>timbl@w3.org</email></address>
3265    </author>
3266    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3267      <organization abbrev="W3C">World Wide Web Consortium</organization>
3268      <address><email>ylafon@w3.org</email></address>
3269    </author>
3270    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3271      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3272      <address><email>julian.reschke@greenbytes.de</email></address>
3273    </author>
3274    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3275  </front>
3276  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3277  <x:source href="p5-range.xml" basename="p5-range"/>
3278</reference>
3279
3280<reference anchor="Part6">
3281  <front>
3282    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3283    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3284      <organization abbrev="Day Software">Day Software</organization>
3285      <address><email>fielding@gbiv.com</email></address>
3286    </author>
3287    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3288      <organization>One Laptop per Child</organization>
3289      <address><email>jg@laptop.org</email></address>
3290    </author>
3291    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3292      <organization abbrev="HP">Hewlett-Packard Company</organization>
3293      <address><email>JeffMogul@acm.org</email></address>
3294    </author>
3295    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3296      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3297      <address><email>henrikn@microsoft.com</email></address>
3298    </author>
3299    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3300      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3301      <address><email>LMM@acm.org</email></address>
3302    </author>
3303    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3304      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3305      <address><email>paulle@microsoft.com</email></address>
3306    </author>
3307    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3308      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3309      <address><email>timbl@w3.org</email></address>
3310    </author>
3311    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3312      <organization abbrev="W3C">World Wide Web Consortium</organization>
3313      <address><email>ylafon@w3.org</email></address>
3314    </author>
3315    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3316      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3317      <address><email>julian.reschke@greenbytes.de</email></address>
3318    </author>
3319    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3320  </front>
3321  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3322  <x:source href="p6-cache.xml" basename="p6-cache"/>
3323</reference>
3324
3325<reference anchor="RFC5234">
3326  <front>
3327    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3328    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3329      <organization>Brandenburg InternetWorking</organization>
3330      <address>
3331      <postal>
3332      <street>675 Spruce Dr.</street>
3333      <city>Sunnyvale</city>
3334      <region>CA</region>
3335      <code>94086</code>
3336      <country>US</country></postal>
3337      <phone>+1.408.246.8253</phone>
3338      <email>dcrocker@bbiw.net</email></address> 
3339    </author>
3340    <author initials="P." surname="Overell" fullname="Paul Overell">
3341      <organization>THUS plc.</organization>
3342      <address>
3343      <postal>
3344      <street>1/2 Berkeley Square</street>
3345      <street>99 Berkely Street</street>
3346      <city>Glasgow</city>
3347      <code>G3 7HR</code>
3348      <country>UK</country></postal>
3349      <email>paul.overell@thus.net</email></address>
3350    </author>
3351    <date month="January" year="2008"/>
3352  </front>
3353  <seriesInfo name="STD" value="68"/>
3354  <seriesInfo name="RFC" value="5234"/>
3355</reference>
3356
3357<reference anchor="RFC2045">
3358  <front>
3359    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3360    <author initials="N." surname="Freed" fullname="Ned Freed">
3361      <organization>Innosoft International, Inc.</organization>
3362      <address><email>ned@innosoft.com</email></address>
3363    </author>
3364    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3365      <organization>First Virtual Holdings</organization>
3366      <address><email>nsb@nsb.fv.com</email></address>
3367    </author>
3368    <date month="November" year="1996"/>
3369  </front>
3370  <seriesInfo name="RFC" value="2045"/>
3371</reference>
3372
3373<reference anchor="RFC2119">
3374  <front>
3375    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3376    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3377      <organization>Harvard University</organization>
3378      <address><email>sob@harvard.edu</email></address>
3379    </author>
3380    <date month="March" year="1997"/>
3381  </front>
3382  <seriesInfo name="BCP" value="14"/>
3383  <seriesInfo name="RFC" value="2119"/>
3384</reference>
3385
3386<reference anchor="RFC3986">
3387 <front>
3388  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3389  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3390    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3391    <address>
3392       <email>timbl@w3.org</email>
3393       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3394    </address>
3395  </author>
3396  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3397    <organization abbrev="Day Software">Day Software</organization>
3398    <address>
3399      <email>fielding@gbiv.com</email>
3400      <uri>http://roy.gbiv.com/</uri>
3401    </address>
3402  </author>
3403  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3404    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3405    <address>
3406      <email>LMM@acm.org</email>
3407      <uri>http://larry.masinter.net/</uri>
3408    </address>
3409  </author>
3410  <date month='January' year='2005'></date>
3411 </front>
3412 <seriesInfo name="RFC" value="3986"/>
3413 <seriesInfo name="STD" value="66"/>
3414</reference>
3415
3416<reference anchor="USASCII">
3417  <front>
3418    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3419    <author>
3420      <organization>American National Standards Institute</organization>
3421    </author>
3422    <date year="1986"/>
3423  </front>
3424  <seriesInfo name="ANSI" value="X3.4"/>
3425</reference>
3426
3427</references>
3428
3429<references title="Informative References">
3430
3431<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3432  <front>
3433    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3434    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3435      <organization/>
3436    </author>
3437    <author initials="J." surname="Gettys" fullname="J. Gettys">
3438      <organization/>
3439    </author>
3440    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3441      <organization/>
3442    </author>
3443    <author initials="H." surname="Lie" fullname="H. Lie">
3444      <organization/>
3445    </author>
3446    <author initials="C." surname="Lilley" fullname="C. Lilley">
3447      <organization/>
3448    </author>
3449    <date year="1997" month="September"/>
3450  </front>
3451  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3452</reference>
3453
3454<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3455  <front>
3456    <title>Improving HTTP Latency</title>
3457    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3458      <organization/>
3459    </author>
3460    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3461      <organization/>
3462    </author>
3463    <date year="1995" month="December"/>
3464  </front>
3465  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3466</reference>
3467
3468<reference anchor="RFC959">
3469  <front>
3470    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3471    <author initials="J." surname="Postel" fullname="J. Postel">
3472      <organization>Information Sciences Institute (ISI)</organization>
3473    </author>
3474    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3475      <organization/>
3476    </author>
3477    <date month="October" year="1985"/>
3478  </front>
3479  <seriesInfo name="STD" value="9"/>
3480  <seriesInfo name="RFC" value="959"/>
3481</reference>
3482
3483<reference anchor="RFC1123">
3484  <front>
3485    <title>Requirements for Internet Hosts - Application and Support</title>
3486    <author initials="R." surname="Braden" fullname="Robert Braden">
3487      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3488      <address><email>Braden@ISI.EDU</email></address>
3489    </author>
3490    <date month="October" year="1989"/>
3491  </front>
3492  <seriesInfo name="STD" value="3"/>
3493  <seriesInfo name="RFC" value="1123"/>
3494</reference>
3495
3496<reference anchor="RFC1305">
3497  <front>
3498    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3499    <author initials="D." surname="Mills" fullname="David L. Mills">
3500      <organization>University of Delaware, Electrical Engineering Department</organization>
3501      <address><email>mills@udel.edu</email></address>
3502    </author>
3503    <date month="March" year="1992"/>
3504  </front>
3505  <seriesInfo name="RFC" value="1305"/>
3506</reference>
3507
3508<reference anchor="RFC1436">
3509  <front>
3510    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3511    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3512      <organization>University of Minnesota, Computer and Information Services</organization>
3513      <address><email>fxa@boombox.micro.umn.edu</email></address>
3514    </author>
3515    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3516      <organization>University of Minnesota, Computer and Information Services</organization>
3517      <address><email>mpm@boombox.micro.umn.edu</email></address>
3518    </author>
3519    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3520      <organization>University of Minnesota, Computer and Information Services</organization>
3521      <address><email>lindner@boombox.micro.umn.edu</email></address>
3522    </author>
3523    <author initials="D." surname="Johnson" fullname="David Johnson">
3524      <organization>University of Minnesota, Computer and Information Services</organization>
3525      <address><email>dmj@boombox.micro.umn.edu</email></address>
3526    </author>
3527    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3528      <organization>University of Minnesota, Computer and Information Services</organization>
3529      <address><email>daniel@boombox.micro.umn.edu</email></address>
3530    </author>
3531    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3532      <organization>University of Minnesota, Computer and Information Services</organization>
3533      <address><email>alberti@boombox.micro.umn.edu</email></address>
3534    </author>
3535    <date month="March" year="1993"/>
3536  </front>
3537  <seriesInfo name="RFC" value="1436"/>
3538</reference>
3539
3540<reference anchor="RFC1900">
3541  <front>
3542    <title>Renumbering Needs Work</title>
3543    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3544      <organization>CERN, Computing and Networks Division</organization>
3545      <address><email>brian@dxcoms.cern.ch</email></address>
3546    </author>
3547    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3548      <organization>cisco Systems</organization>
3549      <address><email>yakov@cisco.com</email></address>
3550    </author>
3551    <date month="February" year="1996"/>
3552  </front>
3553  <seriesInfo name="RFC" value="1900"/>
3554</reference>
3555
3556<reference anchor="RFC1945">
3557  <front>
3558    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3559    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3560      <organization>MIT, Laboratory for Computer Science</organization>
3561      <address><email>timbl@w3.org</email></address>
3562    </author>
3563    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3564      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3565      <address><email>fielding@ics.uci.edu</email></address>
3566    </author>
3567    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3568      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3569      <address><email>frystyk@w3.org</email></address>
3570    </author>
3571    <date month="May" year="1996"/>
3572  </front>
3573  <seriesInfo name="RFC" value="1945"/>
3574</reference>
3575
3576<reference anchor="RFC2047">
3577  <front>
3578    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3579    <author initials="K." surname="Moore" fullname="Keith Moore">
3580      <organization>University of Tennessee</organization>
3581      <address><email>moore@cs.utk.edu</email></address>
3582    </author>
3583    <date month="November" year="1996"/>
3584  </front>
3585  <seriesInfo name="RFC" value="2047"/>
3586</reference>
3587
3588<reference anchor="RFC2068">
3589  <front>
3590    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3591    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3592      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3593      <address><email>fielding@ics.uci.edu</email></address>
3594    </author>
3595    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3596      <organization>MIT Laboratory for Computer Science</organization>
3597      <address><email>jg@w3.org</email></address>
3598    </author>
3599    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3600      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3601      <address><email>mogul@wrl.dec.com</email></address>
3602    </author>
3603    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3604      <organization>MIT Laboratory for Computer Science</organization>
3605      <address><email>frystyk@w3.org</email></address>
3606    </author>
3607    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3608      <organization>MIT Laboratory for Computer Science</organization>
3609      <address><email>timbl@w3.org</email></address>
3610    </author>
3611    <date month="January" year="1997"/>
3612  </front>
3613  <seriesInfo name="RFC" value="2068"/>
3614</reference>
3615
3616<reference anchor='RFC2109'>
3617  <front>
3618    <title>HTTP State Management Mechanism</title>
3619    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3620      <organization>Bell Laboratories, Lucent Technologies</organization>
3621      <address><email>dmk@bell-labs.com</email></address>
3622    </author>
3623    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3624      <organization>Netscape Communications Corp.</organization>
3625      <address><email>montulli@netscape.com</email></address>
3626    </author>
3627    <date year='1997' month='February' />
3628  </front>
3629  <seriesInfo name='RFC' value='2109' />
3630</reference>
3631
3632<reference anchor="RFC2145">
3633  <front>
3634    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3635    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3636      <organization>Western Research Laboratory</organization>
3637      <address><email>mogul@wrl.dec.com</email></address>
3638    </author>
3639    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3640      <organization>Department of Information and Computer Science</organization>
3641      <address><email>fielding@ics.uci.edu</email></address>
3642    </author>
3643    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3644      <organization>MIT Laboratory for Computer Science</organization>
3645      <address><email>jg@w3.org</email></address>
3646    </author>
3647    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3648      <organization>W3 Consortium</organization>
3649      <address><email>frystyk@w3.org</email></address>
3650    </author>
3651    <date month="May" year="1997"/>
3652  </front>
3653  <seriesInfo name="RFC" value="2145"/>
3654</reference>
3655
3656<reference anchor="RFC2616">
3657  <front>
3658    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3659    <author initials="R." surname="Fielding" fullname="R. Fielding">
3660      <organization>University of California, Irvine</organization>
3661      <address><email>fielding@ics.uci.edu</email></address>
3662    </author>
3663    <author initials="J." surname="Gettys" fullname="J. Gettys">
3664      <organization>W3C</organization>
3665      <address><email>jg@w3.org</email></address>
3666    </author>
3667    <author initials="J." surname="Mogul" fullname="J. Mogul">
3668      <organization>Compaq Computer Corporation</organization>
3669      <address><email>mogul@wrl.dec.com</email></address>
3670    </author>
3671    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3672      <organization>MIT Laboratory for Computer Science</organization>
3673      <address><email>frystyk@w3.org</email></address>
3674    </author>
3675    <author initials="L." surname="Masinter" fullname="L. Masinter">
3676      <organization>Xerox Corporation</organization>
3677      <address><email>masinter@parc.xerox.com</email></address>
3678    </author>
3679    <author initials="P." surname="Leach" fullname="P. Leach">
3680      <organization>Microsoft Corporation</organization>
3681      <address><email>paulle@microsoft.com</email></address>
3682    </author>
3683    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3684      <organization>W3C</organization>
3685      <address><email>timbl@w3.org</email></address>
3686    </author>
3687    <date month="June" year="1999"/>
3688  </front>
3689  <seriesInfo name="RFC" value="2616"/>
3690</reference>
3691
3692<reference anchor='RFC2818'>
3693  <front>
3694    <title>HTTP Over TLS</title>
3695    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3696      <organization>RTFM, Inc.</organization>
3697      <address><email>ekr@rtfm.com</email></address>
3698    </author>
3699    <date year='2000' month='May' />
3700  </front>
3701  <seriesInfo name='RFC' value='2818' />
3702</reference>
3703
3704<reference anchor='RFC2965'>
3705  <front>
3706    <title>HTTP State Management Mechanism</title>
3707    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3708      <organization>Bell Laboratories, Lucent Technologies</organization>
3709      <address><email>dmk@bell-labs.com</email></address>
3710    </author>
3711    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3712      <organization>Epinions.com, Inc.</organization>
3713      <address><email>lou@montulli.org</email></address>
3714    </author>
3715    <date year='2000' month='October' />
3716  </front>
3717  <seriesInfo name='RFC' value='2965' />
3718</reference>
3719
3720<reference anchor='RFC3864'>
3721  <front>
3722    <title>Registration Procedures for Message Header Fields</title>
3723    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3724      <organization>Nine by Nine</organization>
3725      <address><email>GK-IETF@ninebynine.org</email></address>
3726    </author>
3727    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3728      <organization>BEA Systems</organization>
3729      <address><email>mnot@pobox.com</email></address>
3730    </author>
3731    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3732      <organization>HP Labs</organization>
3733      <address><email>JeffMogul@acm.org</email></address>
3734    </author>
3735    <date year='2004' month='September' />
3736  </front>
3737  <seriesInfo name='BCP' value='90' />
3738  <seriesInfo name='RFC' value='3864' />
3739</reference>
3740
3741<reference anchor='RFC3977'>
3742  <front>
3743    <title>Network News Transfer Protocol (NNTP)</title>
3744    <author initials='C.' surname='Feather' fullname='C. Feather'>
3745      <organization>THUS plc</organization>
3746      <address><email>clive@demon.net</email></address>
3747    </author>
3748    <date year='2006' month='October' />
3749  </front>
3750  <seriesInfo name="RFC" value="3977"/>
3751</reference>
3752
3753<reference anchor="RFC4288">
3754  <front>
3755    <title>Media Type Specifications and Registration Procedures</title>
3756    <author initials="N." surname="Freed" fullname="N. Freed">
3757      <organization>Sun Microsystems</organization>
3758      <address>
3759        <email>ned.freed@mrochek.com</email>
3760      </address>
3761    </author>
3762    <author initials="J." surname="Klensin" fullname="J. Klensin">
3763      <organization/>
3764      <address>
3765        <email>klensin+ietf@jck.com</email>
3766      </address>
3767    </author>
3768    <date year="2005" month="December"/>
3769  </front>
3770  <seriesInfo name="BCP" value="13"/>
3771  <seriesInfo name="RFC" value="4288"/>
3772</reference>
3773
3774<reference anchor='RFC4395'>
3775  <front>
3776    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3777    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3778      <organization>AT&amp;T Laboratories</organization>
3779      <address>
3780        <email>tony+urireg@maillennium.att.com</email>
3781      </address>
3782    </author>
3783    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3784      <organization>Qualcomm, Inc.</organization>
3785      <address>
3786        <email>hardie@qualcomm.com</email>
3787      </address>
3788    </author>
3789    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3790      <organization>Adobe Systems</organization>
3791      <address>
3792        <email>LMM@acm.org</email>
3793      </address>
3794    </author>
3795    <date year='2006' month='February' />
3796  </front>
3797  <seriesInfo name='BCP' value='115' />
3798  <seriesInfo name='RFC' value='4395' />
3799</reference>
3800
3801<reference anchor="RFC5322">
3802  <front>
3803    <title>Internet Message Format</title>
3804    <author initials="P." surname="Resnick" fullname="P. Resnick">
3805      <organization>Qualcomm Incorporated</organization>
3806    </author>
3807    <date year="2008" month="October"/>
3808  </front> 
3809  <seriesInfo name="RFC" value="5322"/>
3810</reference>
3811
3812<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3813  <front>
3814    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3815    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3816      <organization/>
3817    </author>
3818    <date year="2001" month="November"/>
3819  </front>
3820  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3821</reference>
3822
3823<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3824  <front>
3825  <title>Analysis of HTTP Performance Problems</title>
3826  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3827    <organization/>
3828  </author>
3829  <date/>
3830  </front>
3831</reference>
3832
3833<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3834  <front>
3835  <title>Analysis of HTTP Performance</title>
3836  <author initials="J." surname="Touch" fullname="Joe Touch">
3837    <organization>USC/Information Sciences Institute</organization>
3838    <address><email>touch@isi.edu</email></address>
3839  </author>
3840  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3841    <organization>USC/Information Sciences Institute</organization>
3842    <address><email>johnh@isi.edu</email></address>
3843  </author>
3844  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3845    <organization>USC/Information Sciences Institute</organization>
3846    <address><email>katia@isi.edu</email></address>
3847  </author>
3848  <date year="1998" month="Aug"/>
3849  </front>
3850  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3851  <annotation>(original report dated Aug. 1996)</annotation>
3852</reference>
3853
3854<reference anchor="WAIS">
3855  <front>
3856    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
3857    <author initials="F." surname="Davis" fullname="F. Davis">
3858      <organization>Thinking Machines Corporation</organization>
3859    </author>
3860    <author initials="B." surname="Kahle" fullname="B. Kahle">
3861      <organization>Thinking Machines Corporation</organization>
3862    </author>
3863    <author initials="H." surname="Morris" fullname="H. Morris">
3864      <organization>Thinking Machines Corporation</organization>
3865    </author>
3866    <author initials="J." surname="Salem" fullname="J. Salem">
3867      <organization>Thinking Machines Corporation</organization>
3868    </author>
3869    <author initials="T." surname="Shen" fullname="T. Shen">
3870      <organization>Thinking Machines Corporation</organization>
3871    </author>
3872    <author initials="R." surname="Wang" fullname="R. Wang">
3873      <organization>Thinking Machines Corporation</organization>
3874    </author>
3875    <author initials="J." surname="Sui" fullname="J. Sui">
3876      <organization>Thinking Machines Corporation</organization>
3877    </author>
3878    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
3879      <organization>Thinking Machines Corporation</organization>
3880    </author>
3881    <date month="April" year="1990"/>
3882  </front>
3883  <seriesInfo name="Thinking Machines Corporation" value=""/>
3884</reference>
3885
3886</references>
3887
3888
3889<section title="Tolerant Applications" anchor="tolerant.applications">
3890<t>
3891   Although this document specifies the requirements for the generation
3892   of HTTP/1.1 messages, not all applications will be correct in their
3893   implementation. We therefore recommend that operational applications
3894   be tolerant of deviations whenever those deviations can be
3895   interpreted unambiguously.
3896</t>
3897<t>
3898   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3899   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3900   accept any amount of WSP characters between fields, even though
3901   only a single SP is required.
3902</t>
3903<t>
3904   The line terminator for message-header fields is the sequence CRLF.
3905   However, we recommend that applications, when parsing such headers,
3906   recognize a single LF as a line terminator and ignore the leading CR.
3907</t>
3908<t>
3909   The character set of an entity-body &SHOULD; be labeled as the lowest
3910   common denominator of the character codes used within that body, with
3911   the exception that not labeling the entity is preferred over labeling
3912   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3913</t>
3914<t>
3915   Additional rules for requirements on parsing and encoding of dates
3916   and other potential problems with date encodings include:
3917</t>
3918<t>
3919  <list style="symbols">
3920     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3921        which appears to be more than 50 years in the future is in fact
3922        in the past (this helps solve the "year 2000" problem).</t>
3923
3924     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3925        Expires date as earlier than the proper value, but &MUST-NOT;
3926        internally represent a parsed Expires date as later than the
3927        proper value.</t>
3928
3929     <t>All expiration-related calculations &MUST; be done in GMT. The
3930        local time zone &MUST-NOT; influence the calculation or comparison
3931        of an age or expiration time.</t>
3932
3933     <t>If an HTTP header incorrectly carries a date value with a time
3934        zone other than GMT, it &MUST; be converted into GMT using the
3935        most conservative possible conversion.</t>
3936  </list>
3937</t>
3938</section>
3939
3940<section title="Compatibility with Previous Versions" anchor="compatibility">
3941<t>
3942   HTTP has been in use by the World-Wide Web global information initiative
3943   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3944   was a simple protocol for hypertext data transfer across the Internet
3945   with only a single method and no metadata.
3946   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3947   methods and MIME-like messaging that could include metadata about the data
3948   transferred and modifiers on the request/response semantics. However,
3949   HTTP/1.0 did not sufficiently take into consideration the effects of
3950   hierarchical proxies, caching, the need for persistent connections, or
3951   name-based virtual hosts. The proliferation of incompletely-implemented
3952   applications calling themselves "HTTP/1.0" further necessitated a
3953   protocol version change in order for two communicating applications
3954   to determine each other's true capabilities.
3955</t>
3956<t>
3957   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3958   requirements that enable reliable implementations, adding only
3959   those new features that will either be safely ignored by an HTTP/1.0
3960   recipient or only sent when communicating with a party advertising
3961   compliance with HTTP/1.1.
3962</t>
3963<t>
3964   It is beyond the scope of a protocol specification to mandate
3965   compliance with previous versions. HTTP/1.1 was deliberately
3966   designed, however, to make supporting previous versions easy. It is
3967   worth noting that, at the time of composing this specification
3968   (1996), we would expect commercial HTTP/1.1 servers to:
3969  <list style="symbols">
3970     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3971        1.1 requests;</t>
3972
3973     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3974        1.1;</t>
3975
3976     <t>respond appropriately with a message in the same major version
3977        used by the client.</t>
3978  </list>
3979</t>
3980<t>
3981   And we would expect HTTP/1.1 clients to:
3982  <list style="symbols">
3983     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3984        responses;</t>
3985
3986     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3987        1.1.</t>
3988  </list>
3989</t>
3990<t>
3991   For most implementations of HTTP/1.0, each connection is established
3992   by the client prior to the request and closed by the server after
3993   sending the response. Some implementations implement the Keep-Alive
3994   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3995</t>
3996
3997<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3998<t>
3999   This section summarizes major differences between versions HTTP/1.0
4000   and HTTP/1.1.
4001</t>
4002
4003<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">
4004<t>
4005   The requirements that clients and servers support the Host request-header,
4006   report an error if the Host request-header (<xref target="header.host"/>) is
4007   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4008   are among the most important changes defined by this
4009   specification.
4010</t>
4011<t>
4012   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4013   addresses and servers; there was no other established mechanism for
4014   distinguishing the intended server of a request than the IP address
4015   to which that request was directed. The changes outlined above will
4016   allow the Internet, once older HTTP clients are no longer common, to
4017   support multiple Web sites from a single IP address, greatly
4018   simplifying large operational Web servers, where allocation of many
4019   IP addresses to a single host has created serious problems. The
4020   Internet will also be able to recover the IP addresses that have been
4021   allocated for the sole purpose of allowing special-purpose domain
4022   names to be used in root-level HTTP URLs. Given the rate of growth of
4023   the Web, and the number of servers already deployed, it is extremely
4024   important that all implementations of HTTP (including updates to
4025   existing HTTP/1.0 applications) correctly implement these
4026   requirements:
4027  <list style="symbols">
4028     <t>Both clients and servers &MUST; support the Host request-header.</t>
4029
4030     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4031
4032     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4033        request does not include a Host request-header.</t>
4034
4035     <t>Servers &MUST; accept absolute URIs.</t>
4036  </list>
4037</t>
4038</section>
4039</section>
4040
4041<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4042<t>
4043   Some clients and servers might wish to be compatible with some
4044   previous implementations of persistent connections in HTTP/1.0
4045   clients and servers. Persistent connections in HTTP/1.0 are
4046   explicitly negotiated as they are not the default behavior. HTTP/1.0
4047   experimental implementations of persistent connections are faulty,
4048   and the new facilities in HTTP/1.1 are designed to rectify these
4049   problems. The problem was that some existing 1.0 clients may be
4050   sending Keep-Alive to a proxy server that doesn't understand
4051   Connection, which would then erroneously forward it to the next
4052   inbound server, which would establish the Keep-Alive connection and
4053   result in a hung HTTP/1.0 proxy waiting for the close on the
4054   response. The result is that HTTP/1.0 clients must be prevented from
4055   using Keep-Alive when talking to proxies.
4056</t>
4057<t>
4058   However, talking to proxies is the most important use of persistent
4059   connections, so that prohibition is clearly unacceptable. Therefore,
4060   we need some other mechanism for indicating a persistent connection
4061   is desired, which is safe to use even when talking to an old proxy
4062   that ignores Connection. Persistent connections are the default for
4063   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4064   declaring non-persistence. See <xref target="header.connection"/>.
4065</t>
4066<t>
4067   The original HTTP/1.0 form of persistent connections (the Connection:
4068   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4069</t>
4070</section>
4071
4072<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4073<t>
4074   This specification has been carefully audited to correct and
4075   disambiguate key word usage; RFC 2068 had many problems in respect to
4076   the conventions laid out in <xref target="RFC2119"/>.
4077</t>
4078<t>
4079   Transfer-coding and message lengths all interact in ways that
4080   required fixing exactly when chunked encoding is used (to allow for
4081   transfer encoding that may not be self delimiting); it was important
4082   to straighten out exactly how message lengths are computed. (Sections
4083   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4084   <xref target="header.content-length" format="counter"/>,
4085   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4086</t>
4087<t>
4088   The use and interpretation of HTTP version numbers has been clarified
4089   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4090   version they support to deal with problems discovered in HTTP/1.0
4091   implementations (<xref target="http.version"/>)
4092</t>
4093<t>
4094   Transfer-coding had significant problems, particularly with
4095   interactions with chunked encoding. The solution is that transfer-codings
4096   become as full fledged as content-codings. This involves
4097   adding an IANA registry for transfer-codings (separate from content
4098   codings), a new header field (TE) and enabling trailer headers in the
4099   future. Transfer encoding is a major performance benefit, so it was
4100   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4101   interoperability problem that could have occurred due to interactions
4102   between authentication trailers, chunked encoding and HTTP/1.0
4103   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4104   and <xref target="header.te" format="counter"/>)
4105</t>
4106</section>
4107
4108<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4109<t>
4110  Empty list elements in list productions have been deprecated.
4111  (<xref target="notation.abnf"/>)
4112</t>
4113<t>
4114  Rules about implicit linear whitespace between certain grammar productions
4115  have been removed; now it's only allowed when specifically pointed out
4116  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4117  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4118  Non-ASCII content in header fields and reason phrase has been obsoleted and
4119  made opaque (the TEXT rule was removed)
4120  (<xref target="basic.rules"/>)
4121</t>
4122<t>
4123  Clarify that HTTP-Version is case sensitive.
4124  (<xref target="http.version"/>)
4125</t>
4126<t>
4127  Remove reference to non-existant identity transfer-coding value tokens.
4128  (Sections <xref format="counter" target="transfer.codings"/> and
4129  <xref format="counter" target="message.length"/>)
4130</t>
4131<t>
4132  Clarification that the chunk length does not include
4133  the count of the octets in the chunk header and trailer.
4134  (<xref target="chunked.transfer.encoding"/>)
4135</t>
4136<t>
4137  Require that invalid whitespace around field-names be rejected.
4138  (<xref target="message.headers"/>)
4139</t>
4140<t>
4141  Update use of abs_path production from RFC1808 to the path-absolute + query
4142  components of RFC3986.
4143  (<xref target="request-target"/>)
4144</t>
4145<t>
4146  Clarify exactly when close connection options must be sent.
4147  (<xref target="header.connection"/>)
4148</t>
4149</section>
4150</section>
4151
4152<section title="Terminology" anchor="terminology">
4153<t>
4154   This specification uses a number of terms to refer to the roles
4155   played by participants in, and objects of, the HTTP communication.
4156</t>
4157<t>
4158  <iref item="cache"/>
4159  <x:dfn>cache</x:dfn>
4160  <list>
4161    <t>
4162      A program's local store of response messages and the subsystem
4163      that controls its message storage, retrieval, and deletion. A
4164      cache stores cacheable responses in order to reduce the response
4165      time and network bandwidth consumption on future, equivalent
4166      requests. Any client or server may include a cache, though a cache
4167      cannot be used by a server that is acting as a tunnel.
4168    </t>
4169  </list>
4170</t>
4171<t>
4172  <iref item="cacheable"/>
4173  <x:dfn>cacheable</x:dfn>
4174  <list>
4175    <t>
4176      A response is cacheable if a cache is allowed to store a copy of
4177      the response message for use in answering subsequent requests. The
4178      rules for determining the cacheability of HTTP responses are
4179      defined in &caching;. Even if a resource is cacheable, there may
4180      be additional constraints on whether a cache can use the cached
4181      copy for a particular request.
4182    </t>
4183  </list>
4184</t>
4185<t>
4186  <iref item="client"/>
4187  <x:dfn>client</x:dfn>
4188  <list>
4189    <t>
4190      A program that establishes connections for the purpose of sending
4191      requests.
4192    </t>
4193  </list>
4194</t>
4195<t>
4196  <iref item="connection"/>
4197  <x:dfn>connection</x:dfn>
4198  <list>
4199    <t>
4200      A transport layer virtual circuit established between two programs
4201      for the purpose of communication.
4202    </t>
4203  </list>
4204</t>
4205<t>
4206  <iref item="content negotiation"/>
4207  <x:dfn>content negotiation</x:dfn>
4208  <list>
4209    <t>
4210      The mechanism for selecting the appropriate representation when
4211      servicing a request, as described in &content.negotiation;. The
4212      representation of entities in any response can be negotiated
4213      (including error responses).
4214    </t>
4215  </list>
4216</t>
4217<t>
4218  <iref item="entity"/>
4219  <x:dfn>entity</x:dfn>
4220  <list>
4221    <t>
4222      The information transferred as the payload of a request or
4223      response. An entity consists of metainformation in the form of
4224      entity-header fields and content in the form of an entity-body, as
4225      described in &entity;.
4226    </t>
4227  </list>
4228</t>
4229<t>
4230  <iref item="gateway"/>
4231  <x:dfn>gateway</x:dfn>
4232  <list>
4233    <t>
4234      A server which acts as an intermediary for some other server.
4235      Unlike a proxy, a gateway receives requests as if it were the
4236      origin server for the requested resource; the requesting client
4237      may not be aware that it is communicating with a gateway.
4238    </t>
4239  </list>
4240</t>
4241<t>
4242  <iref item="inbound"/>
4243  <iref item="outbound"/>
4244  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4245  <list>
4246    <t>
4247      Inbound and outbound refer to the request and response paths for
4248      messages: "inbound" means "traveling toward the origin server",
4249      and "outbound" means "traveling toward the user agent"
4250    </t>
4251  </list>
4252</t>
4253<t>
4254  <iref item="message"/>
4255  <x:dfn>message</x:dfn>
4256  <list>
4257    <t>
4258      The basic unit of HTTP communication, consisting of a structured
4259      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4260      transmitted via the connection.
4261    </t>
4262  </list>
4263</t>
4264<t>
4265  <iref item="origin server"/>
4266  <x:dfn>origin server</x:dfn>
4267  <list>
4268    <t>
4269      The server on which a given resource resides or is to be created.
4270    </t>
4271  </list>
4272</t>
4273<t>
4274  <iref item="proxy"/>
4275  <x:dfn>proxy</x:dfn>
4276  <list>
4277    <t>
4278      An intermediary program which acts as both a server and a client
4279      for the purpose of making requests on behalf of other clients.
4280      Requests are serviced internally or by passing them on, with
4281      possible translation, to other servers. A proxy &MUST; implement
4282      both the client and server requirements of this specification. A
4283      "transparent proxy" is a proxy that does not modify the request or
4284      response beyond what is required for proxy authentication and
4285      identification. A "non-transparent proxy" is a proxy that modifies
4286      the request or response in order to provide some added service to
4287      the user agent, such as group annotation services, media type
4288      transformation, protocol reduction, or anonymity filtering. Except
4289      where either transparent or non-transparent behavior is explicitly
4290      stated, the HTTP proxy requirements apply to both types of
4291      proxies.
4292    </t>
4293  </list>
4294</t>
4295<t>
4296  <iref item="request"/>
4297  <x:dfn>request</x:dfn>
4298  <list>
4299    <t>
4300      An HTTP request message, as defined in <xref target="request"/>.
4301    </t>
4302  </list>
4303</t>
4304<t>
4305  <iref item="resource"/>
4306  <x:dfn>resource</x:dfn>
4307  <list>
4308    <t>
4309      A network data object or service that can be identified by a URI,
4310      as defined in <xref target="uri"/>. Resources may be available in multiple
4311      representations (e.g. multiple languages, data formats, size, and
4312      resolutions) or vary in other ways.
4313    </t>
4314  </list>
4315</t>
4316<t>
4317  <iref item="response"/>
4318  <x:dfn>response</x:dfn>
4319  <list>
4320    <t>
4321      An HTTP response message, as defined in <xref target="response"/>.
4322    </t>
4323  </list>
4324</t>
4325<t>
4326  <iref item="representation"/>
4327  <x:dfn>representation</x:dfn>
4328  <list>
4329    <t>
4330      An entity included with a response that is subject to content
4331      negotiation, as described in &content.negotiation;. There may exist multiple
4332      representations associated with a particular response status.
4333    </t>
4334  </list>
4335</t>
4336<t>
4337  <iref item="server"/>
4338  <x:dfn>server</x:dfn>
4339  <list>
4340    <t>
4341      An application program that accepts connections in order to
4342      service requests by sending back responses. Any given program may
4343      be capable of being both a client and a server; our use of these
4344      terms refers only to the role being performed by the program for a
4345      particular connection, rather than to the program's capabilities
4346      in general. Likewise, any server may act as an origin server,
4347      proxy, gateway, or tunnel, switching behavior based on the nature
4348      of each request.
4349    </t>
4350  </list>
4351</t>
4352<t>
4353  <iref item="tunnel"/>
4354  <x:dfn>tunnel</x:dfn>
4355  <list>
4356    <t>
4357      An intermediary program which is acting as a blind relay between
4358      two connections. Once active, a tunnel is not considered a party
4359      to the HTTP communication, though the tunnel may have been
4360      initiated by an HTTP request. The tunnel ceases to exist when both
4361      ends of the relayed connections are closed.
4362    </t>
4363  </list>
4364</t>
4365<t>
4366  <iref item="upstream"/>
4367  <iref item="downstream"/>
4368  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4369  <list>
4370    <t>
4371      Upstream and downstream describe the flow of a message: all
4372      messages flow from upstream to downstream.
4373    </t>
4374  </list>
4375</t>
4376<t>
4377  <iref item="user agent"/>
4378  <x:dfn>user agent</x:dfn>
4379  <list>
4380    <t>
4381      The client which initiates a request. These are often browsers,
4382      editors, spiders (web-traversing robots), or other end user tools.
4383    </t>
4384  </list>
4385</t>
4386<t>
4387  <iref item="variant"/>
4388  <x:dfn>variant</x:dfn>
4389  <list>
4390    <t>
4391      A resource may have one, or more than one, representation(s)
4392      associated with it at any given instant. Each of these
4393      representations is termed a `variant'.  Use of the term `variant'
4394      does not necessarily imply that the resource is subject to content
4395      negotiation.
4396    </t>
4397  </list>
4398</t>
4399</section>
4400
4401<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4402<figure>
4403<artwork type="abnf" name="p1-messaging.parsed-abnf">
4404<x:ref>BWS</x:ref> = OWS
4405
4406<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 15.4&gt;
4407<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4408<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4409<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4410 connection-token ] )
4411<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4412<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4413
4414<x:ref>Date</x:ref> = "Date:" OWS Date-v
4415<x:ref>Date-v</x:ref> = HTTP-date
4416
4417GMT = %x47.4D.54
4418
4419<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50
4420<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4421<x:ref>HTTP-date</x:ref> = rfc1123-date / obsolete-date
4422<x:ref>HTTP-message</x:ref> = Request / Response
4423<x:ref>Host</x:ref> = "Host:" OWS Host-v
4424<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4425
4426<x:ref>Method</x:ref> = token
4427
4428<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4429
4430<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 15.4&gt;
4431
4432<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4433<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4434<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4435 entity-header ) CRLF ) CRLF [ message-body ]
4436<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4437<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4438 entity-header ) CRLF ) CRLF [ message-body ]
4439
4440<x:ref>Status-Code</x:ref> = 3DIGIT
4441<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4442
4443<x:ref>TE</x:ref> = "TE:" OWS TE-v
4444<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4445<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4446<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4447<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4448<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4449 transfer-coding ] )
4450
4451<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4452<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4453<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4454<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4455
4456<x:ref>Via</x:ref> = "Via:" OWS Via-v
4457<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4458 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4459 ] )
4460
4461<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 15.6&gt;
4462
4463<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4464<x:ref>accept-params</x:ref> = &lt;accept-params, defined in [Part3], Section 5.1&gt;
4465<x:ref>asctime-date</x:ref> = wkday SP date3 SP time SP 4DIGIT
4466<x:ref>attribute</x:ref> = token
4467<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4468
4469<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4470<x:ref>chunk-data</x:ref> = 1*OCTET
4471<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4472<x:ref>chunk-ext-name</x:ref> = token
4473<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4474<x:ref>chunk-size</x:ref> = 1*HEXDIG
4475<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4476<x:ref>connection-token</x:ref> = token
4477<x:ref>ctext</x:ref> = *( OWS / %x21-27 / %x2A-7E / obs-text )
4478
4479<x:ref>date1</x:ref> = 2DIGIT SP month SP 4DIGIT
4480<x:ref>date2</x:ref> = 2DIGIT "-" month "-" 2DIGIT
4481<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4482
4483<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4484<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4485
4486<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4487<x:ref>field-name</x:ref> = token
4488<x:ref>field-value</x:ref> = *( field-content / OWS )
4489<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4490
4491<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4492 / Transfer-Encoding / Upgrade / Via / Warning
4493<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4494 message-body ]
4495
4496<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4497
4498l-Fri = %x46.72.69.64.61.79
4499l-Mon = %x4D.6F.6E.64.61.79
4500l-Sat = %x53.61.74.75.72.64.61.79
4501l-Sun = %x53.75.6E.64.61.79
4502l-Thu = %x54.68.75.72.73.64.61.79
4503l-Tue = %x54.75.65.73.64.61.79
4504l-Wed = %x57.65.64.6E.65.73.64.61.79
4505<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4506
4507<x:ref>message-body</x:ref> = entity-body / &lt;entity-body encoded as per
4508 Transfer-Encoding&gt;
4509<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4510<x:ref>month</x:ref> = s-Jan / s-Feb / s-Mar / s-Apr / s-May / s-Jun / s-Jul / s-Aug
4511 / s-Sep / s-Oct / s-Nov / s-Dec
4512
4513<x:ref>obs-fold</x:ref> = CRLF
4514<x:ref>obs-text</x:ref> = %x80-FF
4515<x:ref>obsolete-date</x:ref> = rfc850-date / asctime-date
4516
4517<x:ref>parameter</x:ref> = attribute BWS "=" BWS value
4518<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4519<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4520<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4521<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4522<x:ref>product</x:ref> = token [ "/" product-version ]
4523<x:ref>product-version</x:ref> = token
4524<x:ref>protocol-name</x:ref> = token
4525<x:ref>protocol-version</x:ref> = token
4526<x:ref>pseudonym</x:ref> = token
4527
4528<x:ref>qdtext</x:ref> = *( OWS / "!" / %x23-5B / %x5D-7E / obs-text )
4529<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4530<x:ref>quoted-pair</x:ref> = "\" quoted-text
4531<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4532<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4533
4534<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4535<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4536<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4537<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4538<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4539 / authority
4540<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4541<x:ref>rfc1123-date</x:ref> = wkday "," SP date1 SP time SP GMT
4542<x:ref>rfc850-date</x:ref> = weekday "," SP date2 SP time SP GMT
4543
4544s-Apr = %x41.70.72
4545s-Aug = %x41.75.67
4546s-Dec = %x44.65.63
4547s-Feb = %x46.65.62
4548s-Fri = %x46.72.69
4549s-Jan = %x4A.61.6E
4550s-Jul = %x4A.75.6C
4551s-Jun = %x4A.75.6E
4552s-Mar = %x4D.61.72
4553s-May = %x4D.61.79
4554s-Mon = %x4D.6F.6E
4555s-Nov = %x4E.6F.76
4556s-Oct = %x4F.63.74
4557s-Sat = %x53.61.74
4558s-Sep = %x53.65.70
4559s-Sun = %x53.75.6E
4560s-Thu = %x54.68.75
4561s-Tue = %x54.75.65
4562s-Wed = %x57.65.64
4563<x:ref>start-line</x:ref> = Request-Line / Status-Line
4564
4565<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ accept-params ] )
4566<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4567 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4568<x:ref>time</x:ref> = 2DIGIT ":" 2DIGIT ":" 2DIGIT
4569<x:ref>token</x:ref> = 1*tchar
4570<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4571<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4572<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS parameter )
4573
4574<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4575
4576<x:ref>value</x:ref> = token / quoted-string
4577
4578<x:ref>weekday</x:ref> = l-Mon / l-Tue / l-Wed / l-Thu / l-Fri / l-Sat / l-Sun
4579<x:ref>wkday</x:ref> = s-Mon / s-Tue / s-Wed / s-Thu / s-Fri / s-Sat / s-Sun
4580
4581; Chunked-Body defined but not used
4582; Content-Length defined but not used
4583; HTTP-message defined but not used
4584; Host defined but not used
4585; TE defined but not used
4586; URI defined but not used
4587; URI-reference defined but not used
4588; fragment defined but not used
4589; generic-message defined but not used
4590; http-URI defined but not used
4591; partial-URI defined but not used
4592
4593
4594</artwork>
4595</figure>
4596</section>
4597
4598<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4599
4600<section title="Since RFC2616">
4601<t>
4602  Extracted relevant partitions from <xref target="RFC2616"/>.
4603</t>
4604</section>
4605
4606<section title="Since draft-ietf-httpbis-p1-messaging-00">
4607<t>
4608  Closed issues:
4609  <list style="symbols"> 
4610    <t>
4611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4612      "HTTP Version should be case sensitive"
4613      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4614    </t>
4615    <t>
4616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4617      "'unsafe' characters"
4618      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4619    </t>
4620    <t>
4621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4622      "Chunk Size Definition"
4623      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4624    </t>
4625    <t>
4626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4627      "Message Length"
4628      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4629    </t>
4630    <t>
4631      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4632      "Media Type Registrations"
4633      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4634    </t>
4635    <t>
4636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4637      "URI includes query"
4638      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4639    </t>
4640    <t>
4641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4642      "No close on 1xx responses"
4643      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4644    </t>
4645    <t>
4646      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4647      "Remove 'identity' token references"
4648      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4649    </t>
4650    <t>
4651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4652      "Import query BNF"
4653    </t>
4654    <t>
4655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4656      "qdtext BNF"
4657    </t>
4658    <t>
4659      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4660      "Normative and Informative references"
4661    </t>
4662    <t>
4663      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4664      "RFC2606 Compliance"
4665    </t>
4666    <t>
4667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4668      "RFC977 reference"
4669    </t>
4670    <t>
4671      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4672      "RFC1700 references"
4673    </t>
4674    <t>
4675      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4676      "inconsistency in date format explanation"
4677    </t>
4678    <t>
4679      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4680      "Date reference typo"
4681    </t>
4682    <t>
4683      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4684      "Informative references"
4685    </t>
4686    <t>
4687      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4688      "ISO-8859-1 Reference"
4689    </t>
4690    <t>
4691      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4692      "Normative up-to-date references"
4693    </t>
4694  </list>
4695</t>
4696<t>
4697  Other changes:
4698  <list style="symbols"> 
4699    <t>
4700      Update media type registrations to use RFC4288 template.
4701    </t>
4702    <t>
4703      Use names of RFC4234 core rules DQUOTE and WSP,
4704      fix broken ABNF for chunk-data
4705      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4706    </t>
4707  </list>
4708</t>
4709</section>
4710
4711<section title="Since draft-ietf-httpbis-p1-messaging-01">
4712<t>
4713  Closed issues:
4714  <list style="symbols"> 
4715    <t>
4716      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4717      "Bodies on GET (and other) requests"
4718    </t>
4719    <t>
4720      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4721      "Updating to RFC4288"
4722    </t>
4723    <t>
4724      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4725      "Status Code and Reason Phrase"
4726    </t>
4727    <t>
4728      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4729      "rel_path not used"
4730    </t>
4731  </list>
4732</t>
4733<t>
4734  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4735  <list style="symbols"> 
4736    <t>
4737      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4738      "trailer-part").
4739    </t>
4740    <t>
4741      Avoid underscore character in rule names ("http_URL" ->
4742      "http-URL", "abs_path" -> "path-absolute").
4743    </t>
4744    <t>
4745      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4746      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4747      have to be updated when switching over to RFC3986.
4748    </t>
4749    <t>
4750      Synchronize core rules with RFC5234.
4751    </t>
4752    <t>
4753      Get rid of prose rules that span multiple lines.
4754    </t>
4755    <t>
4756      Get rid of unused rules LOALPHA and UPALPHA.
4757    </t>
4758    <t>
4759      Move "Product Tokens" section (back) into Part 1, as "token" is used
4760      in the definition of the Upgrade header.
4761    </t>
4762    <t>
4763      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4764    </t>
4765    <t>
4766      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4767    </t>
4768  </list>
4769</t>
4770</section>
4771
4772<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4773<t>
4774  Closed issues:
4775  <list style="symbols"> 
4776    <t>
4777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4778      "HTTP-date vs. rfc1123-date"
4779    </t>
4780    <t>
4781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4782      "WS in quoted-pair"
4783    </t>
4784  </list>
4785</t>
4786<t>
4787  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4788  <list style="symbols"> 
4789    <t>
4790      Reference RFC 3984, and update header registrations for headers defined
4791      in this document.
4792    </t>
4793  </list>
4794</t>
4795<t>
4796  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4797  <list style="symbols"> 
4798    <t>
4799      Replace string literals when the string really is case-sensitive (HTTP-Version).
4800    </t>
4801  </list>
4802</t>
4803</section>
4804
4805<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4806<t>
4807  Closed issues:
4808  <list style="symbols"> 
4809    <t>
4810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4811      "Connection closing"
4812    </t>
4813    <t>
4814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4815      "Move registrations and registry information to IANA Considerations"
4816    </t>
4817    <t>
4818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4819      "need new URL for PAD1995 reference"
4820    </t>
4821    <t>
4822      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4823      "IANA Considerations: update HTTP URI scheme registration"
4824    </t>
4825    <t>
4826      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4827      "Cite HTTPS URI scheme definition"
4828    </t>
4829    <t>
4830      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4831      "List-type headers vs Set-Cookie"
4832    </t>
4833  </list>
4834</t>
4835<t>
4836  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4837  <list style="symbols"> 
4838    <t>
4839      Replace string literals when the string really is case-sensitive (HTTP-Date).
4840    </t>
4841    <t>
4842      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4843    </t>
4844  </list>
4845</t>
4846</section>
4847
4848<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4849<t>
4850  Closed issues:
4851  <list style="symbols"> 
4852    <t>
4853      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4854      "Out-of-date reference for URIs"
4855    </t>
4856    <t>
4857      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4858      "RFC 2822 is updated by RFC 5322"
4859    </t>
4860  </list>
4861</t>
4862<t>
4863  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4864  <list style="symbols"> 
4865    <t>
4866      Use "/" instead of "|" for alternatives.
4867    </t>
4868    <t>
4869      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4870    </t>
4871    <t>
4872      Only reference RFC 5234's core rules.
4873    </t>
4874    <t>
4875      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4876      whitespace ("OWS") and required whitespace ("RWS").
4877    </t>
4878    <t>
4879      Rewrite ABNFs to spell out whitespace rules, factor out
4880      header value format definitions.
4881    </t>
4882  </list>
4883</t>
4884</section>
4885
4886<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4887<t>
4888  Closed issues:
4889  <list style="symbols"> 
4890    <t>
4891      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
4892      "Header LWS"
4893    </t>
4894    <t>
4895      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
4896      "Sort 1.3 Terminology"
4897    </t>
4898    <t>
4899      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
4900      "RFC2047 encoded words"
4901    </t>
4902    <t>
4903      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
4904      "Character Encodings in TEXT"
4905    </t>
4906    <t>
4907      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
4908      "Line Folding"
4909    </t>
4910    <t>
4911      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
4912      "OPTIONS * and proxies"
4913    </t>
4914    <t>
4915      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4916      "Reason-Phrase BNF"
4917    </t>
4918    <t>
4919      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
4920      "Use of TEXT"
4921    </t>
4922    <t>
4923      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4924      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4925    </t>
4926    <t>
4927      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4928      "RFC822 reference left in discussion of date formats"
4929    </t>
4930  </list>
4931</t>
4932<t>
4933  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4934  <list style="symbols"> 
4935    <t>
4936      Rewrite definition of list rules, deprecate empty list elements.
4937    </t>
4938    <t>
4939      Add appendix containing collected and expanded ABNF.
4940    </t>
4941  </list>
4942</t>
4943<t>
4944  Other changes:
4945  <list style="symbols"> 
4946    <t>
4947      Rewrite introduction; add mostly new Architecture Section.
4948    </t>
4949  </list>
4950</t>
4951</section>
4952
4953</section>
4954
4955</back>
4956</rfc>
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