source: draft-ietf-httpbis/latest/p1-messaging.xml @ 577

Last change on this file since 577 was 576, checked in by julian.reschke@…, 11 years ago

Make spec consistent in not stating "decimal" when it's already clear from the ABNF (related to #161)

  • Property svn:eol-style set to native
File size: 209.5 KB
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1<?xml version="1.0" encoding="utf-8"?>
2<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
3<!DOCTYPE rfc [
4  <!ENTITY MAY "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MAY</bcp14>">
5  <!ENTITY MUST "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST</bcp14>">
6  <!ENTITY MUST-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>MUST NOT</bcp14>">
7  <!ENTITY OPTIONAL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>OPTIONAL</bcp14>">
8  <!ENTITY RECOMMENDED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>RECOMMENDED</bcp14>">
9  <!ENTITY REQUIRED "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>REQUIRED</bcp14>">
10  <!ENTITY SHALL "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL</bcp14>">
11  <!ENTITY SHALL-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHALL NOT</bcp14>">
12  <!ENTITY SHOULD "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD</bcp14>">
13  <!ENTITY SHOULD-NOT "<bcp14 xmlns='http://purl.org/net/xml2rfc/ext'>SHOULD NOT</bcp14>">
14  <!ENTITY ID-VERSION "latest">
15  <!ENTITY ID-MONTH "May">
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-cache-control   "<xref target='Part6' x:rel='#header.cache-control' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
28  <!ENTITY header-expect          "<xref target='Part2' x:rel='#header.expect' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
29  <!ENTITY header-pragma          "<xref target='Part6' x:rel='#header.pragma' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
30  <!ENTITY header-warning         "<xref target='Part6' x:rel='#header.warning' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
31  <!ENTITY idempotent-methods     "<xref target='Part2' x:rel='#idempotent.methods' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
32  <!ENTITY request-header-fields  "<xref target='Part2' x:rel='#request.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
33  <!ENTITY response-header-fields "<xref target='Part2' x:rel='#response.header.fields' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
34  <!ENTITY method                 "<xref target='Part2' x:rel='#method' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
35  <!ENTITY status-codes           "<xref target='Part2' x:rel='#status.codes' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
36  <!ENTITY status-100             "<xref target='Part2' x:rel='#status.100' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
37  <!ENTITY status-1xx             "<xref target='Part2' x:rel='#status.1xx' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
38  <!ENTITY status-414             "<xref target='Part2' x:rel='#status.414' xmlns:x='http://purl.org/net/xml2rfc/ext'/>">
39]>
40<?rfc toc="yes" ?>
41<?rfc symrefs="yes" ?>
42<?rfc sortrefs="yes" ?>
43<?rfc compact="yes"?>
44<?rfc subcompact="no" ?>
45<?rfc linkmailto="no" ?>
46<?rfc editing="no" ?>
47<?rfc comments="yes"?>
48<?rfc inline="yes"?>
49<?rfc-ext allow-markup-in-artwork="yes" ?>
50<?rfc-ext include-references-in-index="yes" ?>
51<rfc obsoletes="2616" category="std" x:maturity-level="draft"
52     ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-&ID-VERSION;"
53     xmlns:x='http://purl.org/net/xml2rfc/ext'>
54<front>
55
56  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
57
58  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
59    <organization abbrev="Day Software">Day Software</organization>
60    <address>
61      <postal>
62        <street>23 Corporate Plaza DR, Suite 280</street>
63        <city>Newport Beach</city>
64        <region>CA</region>
65        <code>92660</code>
66        <country>USA</country>
67      </postal>
68      <phone>+1-949-706-5300</phone>
69      <facsimile>+1-949-706-5305</facsimile>
70      <email>fielding@gbiv.com</email>
71      <uri>http://roy.gbiv.com/</uri>
72    </address>
73  </author>
74
75  <author initials="J." surname="Gettys" fullname="Jim Gettys">
76    <organization>One Laptop per Child</organization>
77    <address>
78      <postal>
79        <street>21 Oak Knoll Road</street>
80        <city>Carlisle</city>
81        <region>MA</region>
82        <code>01741</code>
83        <country>USA</country>
84      </postal>
85      <email>jg@laptop.org</email>
86      <uri>http://www.laptop.org/</uri>
87    </address>
88  </author>
89 
90  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
91    <organization abbrev="HP">Hewlett-Packard Company</organization>
92    <address>
93      <postal>
94        <street>HP Labs, Large Scale Systems Group</street>
95        <street>1501 Page Mill Road, MS 1177</street>
96        <city>Palo Alto</city>
97        <region>CA</region>
98        <code>94304</code>
99        <country>USA</country>
100      </postal>
101      <email>JeffMogul@acm.org</email>
102    </address>
103  </author>
104
105  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
106    <organization abbrev="Microsoft">Microsoft Corporation</organization>
107    <address>
108      <postal>
109        <street>1 Microsoft Way</street>
110        <city>Redmond</city>
111        <region>WA</region>
112        <code>98052</code>
113        <country>USA</country>
114      </postal>
115      <email>henrikn@microsoft.com</email>
116    </address>
117  </author>
118
119  <author initials="L." surname="Masinter" fullname="Larry Masinter">
120    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
121    <address>
122      <postal>
123        <street>345 Park Ave</street>
124        <city>San Jose</city>
125        <region>CA</region>
126        <code>95110</code>
127        <country>USA</country>
128      </postal>
129      <email>LMM@acm.org</email>
130      <uri>http://larry.masinter.net/</uri>
131    </address>
132  </author>
133 
134  <author initials="P." surname="Leach" fullname="Paul J. Leach">
135    <organization abbrev="Microsoft">Microsoft Corporation</organization>
136    <address>
137      <postal>
138        <street>1 Microsoft Way</street>
139        <city>Redmond</city>
140        <region>WA</region>
141        <code>98052</code>
142      </postal>
143      <email>paulle@microsoft.com</email>
144    </address>
145  </author>
146   
147  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
148    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
149    <address>
150      <postal>
151        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
152        <street>The Stata Center, Building 32</street>
153        <street>32 Vassar Street</street>
154        <city>Cambridge</city>
155        <region>MA</region>
156        <code>02139</code>
157        <country>USA</country>
158      </postal>
159      <email>timbl@w3.org</email>
160      <uri>http://www.w3.org/People/Berners-Lee/</uri>
161    </address>
162  </author>
163
164  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
165    <organization abbrev="W3C">World Wide Web Consortium</organization>
166    <address>
167      <postal>
168        <street>W3C / ERCIM</street>
169        <street>2004, rte des Lucioles</street>
170        <city>Sophia-Antipolis</city>
171        <region>AM</region>
172        <code>06902</code>
173        <country>France</country>
174      </postal>
175      <email>ylafon@w3.org</email>
176      <uri>http://www.raubacapeu.net/people/yves/</uri>
177    </address>
178  </author>
179
180  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
181    <organization abbrev="greenbytes">greenbytes GmbH</organization>
182    <address>
183      <postal>
184        <street>Hafenweg 16</street>
185        <city>Muenster</city><region>NW</region><code>48155</code>
186        <country>Germany</country>
187      </postal>
188      <phone>+49 251 2807760</phone>   
189      <facsimile>+49 251 2807761</facsimile>   
190      <email>julian.reschke@greenbytes.de</email>       
191      <uri>http://greenbytes.de/tech/webdav/</uri>     
192    </address>
193  </author>
194
195  <date month="&ID-MONTH;" year="&ID-YEAR;"/>
196  <workgroup>HTTPbis Working Group</workgroup>
197
198<abstract>
199<t>
200   The Hypertext Transfer Protocol (HTTP) is an application-level
201   protocol for distributed, collaborative, hypertext information
202   systems. HTTP has been in use by the World Wide Web global information
203   initiative since 1990. This document is Part 1 of the seven-part specification
204   that defines the protocol referred to as "HTTP/1.1" and, taken together,
205   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
206   its associated terminology, defines the "http" and "https" Uniform
207   Resource Identifier (URI) schemes, defines the generic message syntax
208   and parsing requirements for HTTP message frames, and describes
209   general security concerns for implementations.
210</t>
211</abstract>
212
213<note title="Editorial Note (To be removed by RFC Editor)">
214  <t>
215    Discussion of this draft should take place on the HTTPBIS working group
216    mailing list (ietf-http-wg@w3.org). The current issues list is
217    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
218    and related documents (including fancy diffs) can be found at
219    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
220  </t>
221  <t>
222    The changes in this draft are summarized in <xref target="changes.since.06"/>.
223  </t>
224</note>
225</front>
226<middle>
227<section title="Introduction" anchor="introduction">
228<t>
229   The Hypertext Transfer Protocol (HTTP) is an application-level
230   request/response protocol that uses extensible semantics and MIME-like
231   message payloads for flexible interaction with network-based hypertext
232   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
233   standard <xref target="RFC3986"/> to indicate request targets and
234   relationships between resources.
235   Messages are passed in a format similar to that used by Internet mail
236   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
237   (MIME) <xref target="RFC2045"/> (see &diff2045entity; for the differences
238   between HTTP and MIME messages).
239</t>
240<t>
241   HTTP is a generic interface protocol for information systems. It is
242   designed to hide the details of how a service is implemented by presenting
243   a uniform interface to clients that is independent of the types of
244   resources provided. Likewise, servers do not need to be aware of each
245   client's purpose: an HTTP request can be considered in isolation rather
246   than being associated with a specific type of client or a predetermined
247   sequence of application steps. The result is a protocol that can be used
248   effectively in many different contexts and for which implementations can
249   evolve independently over time.
250</t>
251<t>
252   HTTP is also designed for use as a generic protocol for translating
253   communication to and from other Internet information systems.
254   HTTP proxies and gateways provide access to alternative information
255   services by translating their diverse protocols into a hypertext
256   format that can be viewed and manipulated by clients in the same way
257   as HTTP services.
258</t>
259<t>
260   One consequence of HTTP flexibility is that the protocol cannot be
261   defined in terms of what occurs behind the interface. Instead, we
262   are limited to defining the syntax of communication, the intent
263   of received communication, and the expected behavior of recipients.
264   If the communication is considered in isolation, then successful
265   actions should be reflected in corresponding changes to the
266   observable interface provided by servers. However, since multiple
267   clients may act in parallel and perhaps at cross-purposes, we
268   cannot require that such changes be observable beyond the scope
269   of a single response.
270</t>
271<t>
272   This document is Part 1 of the seven-part specification of HTTP,
273   defining the protocol referred to as "HTTP/1.1" and obsoleting
274   <xref target="RFC2616"/>.
275   Part 1 describes the architectural elements that are used or
276   referred to in HTTP and defines the URI schemes specific to
277   HTTP-based resources, overall network operation, connection
278   management, and HTTP message framing and forwarding requirements.
279   Our goal is to define all of the mechanisms necessary for HTTP message
280   handling that are independent of message semantics, thereby defining the
281   complete set of requirements for message parsers and
282   message-forwarding intermediaries.
283</t>
284
285<section title="Requirements" anchor="intro.requirements">
286<t>
287   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
288   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
289   document are to be interpreted as described in <xref target="RFC2119"/>.
290</t>
291<t>
292   An implementation is not compliant if it fails to satisfy one or more
293   of the &MUST; or &REQUIRED; level requirements for the protocols it
294   implements. An implementation that satisfies all the &MUST; or &REQUIRED;
295   level and all the &SHOULD; level requirements for its protocols is said
296   to be "unconditionally compliant"; one that satisfies all the &MUST;
297   level requirements but not all the &SHOULD; level requirements for its
298   protocols is said to be "conditionally compliant."
299</t>
300</section>
301
302<section title="Syntax Notation" anchor="notation">
303<iref primary="true" item="Grammar" subitem="ALPHA"/>
304<iref primary="true" item="Grammar" subitem="CR"/>
305<iref primary="true" item="Grammar" subitem="CRLF"/>
306<iref primary="true" item="Grammar" subitem="CTL"/>
307<iref primary="true" item="Grammar" subitem="DIGIT"/>
308<iref primary="true" item="Grammar" subitem="DQUOTE"/>
309<iref primary="true" item="Grammar" subitem="HEXDIG"/>
310<iref primary="true" item="Grammar" subitem="LF"/>
311<iref primary="true" item="Grammar" subitem="OCTET"/>
312<iref primary="true" item="Grammar" subitem="SP"/>
313<iref primary="true" item="Grammar" subitem="VCHAR"/>
314<iref primary="true" item="Grammar" subitem="WSP"/>
315<t>
316   This specification uses the Augmented Backus-Naur Form (ABNF) notation
317   of <xref target="RFC5234"/>.
318</t>
319<t anchor="core.rules">
320  <x:anchor-alias value="ALPHA"/>
321  <x:anchor-alias value="CTL"/>
322  <x:anchor-alias value="CR"/>
323  <x:anchor-alias value="CRLF"/>
324  <x:anchor-alias value="DIGIT"/>
325  <x:anchor-alias value="DQUOTE"/>
326  <x:anchor-alias value="HEXDIG"/>
327  <x:anchor-alias value="LF"/>
328  <x:anchor-alias value="OCTET"/>
329  <x:anchor-alias value="SP"/>
330  <x:anchor-alias value="VCHAR"/>
331  <x:anchor-alias value="WSP"/>
332   The following core rules are included by
333   reference, as defined in <xref target="RFC5234" x:fmt="," x:sec="B.1"/>:
334   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
335   DIGIT (decimal 0-9), DQUOTE (double quote),
336   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
337   OCTET (any 8-bit sequence of data), SP (space),
338   VCHAR (any visible <xref target="USASCII"/> character),
339   and WSP (whitespace).
340</t>
341
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 
375  1#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>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except <x:ref>DQUOTE</x:ref> and "\"&gt; / <x:ref>obs-text</x:ref> 
458  <x:ref>obs-text</x:ref>       = %x80-FF
459</artwork></figure>
460<t anchor="rule.quoted-pair">
461  <x:anchor-alias value="quoted-pair"/>
462  <x:anchor-alias value="quoted-text"/>
463   The backslash character ("\") &MAY; be used as a single-character
464   quoting mechanism only within quoted-string and comment constructs.
465</t>
466<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/>
467  <x:ref>quoted-text</x:ref>    = %x01-09 /
468                   %x0B-0C /
469                   %x0E-FF ; Characters excluding NUL, <x:ref>CR</x:ref> and <x:ref>LF</x:ref>
470  <x:ref>quoted-pair</x:ref>    = "\" <x:ref>quoted-text</x:ref>
471</artwork></figure>
472</section>
473
474<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
475  <x:anchor-alias value="request-header"/>
476  <x:anchor-alias value="response-header"/>
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>entity-body</x:ref>     = &lt;entity-body, defined in &entity-body;&gt;
491  <x:ref>entity-header</x:ref>   = &lt;entity-header, defined in &entity-header-fields;&gt;
492</artwork></figure>
493<figure><!-- Part6--><artwork type="abnf2616">
494  <x:ref>Cache-Control</x:ref>   = &lt;Cache-Control, defined in &header-pragma;&gt;
495  <x:ref>Pragma</x:ref>          = &lt;Pragma, defined in &header-pragma;&gt;
496  <x:ref>Warning</x:ref>         = &lt;Warning, defined in &header-warning;&gt;
497</artwork></figure>
498</section>
499
500</section>
501</section>
502
503<section title="HTTP architecture" anchor="architecture">
504<t>
505   HTTP was created with a specific architecture in mind, the World Wide Web,
506   and has evolved over time to support the scalability needs of a worldwide
507   hypertext system. Much of that architecture is reflected in the terminology
508   and syntax productions used to define HTTP.
509</t>
510
511<section title="Uniform Resource Identifiers" anchor="uri">
512<t>
513   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
514   throughout HTTP as the means for identifying resources. URI references
515   are used to target requests, redirect responses, and define relationships.
516   HTTP does not limit what a resource may be; it merely defines an interface
517   that can be used to interact with a resource via HTTP. More information on
518   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
519</t>
520  <x:anchor-alias value="URI"/>
521  <x:anchor-alias value="URI-reference"/>
522  <x:anchor-alias value="absolute-URI"/>
523  <x:anchor-alias value="relative-part"/>
524  <x:anchor-alias value="authority"/>
525  <x:anchor-alias value="fragment"/>
526  <x:anchor-alias value="path-abempty"/>
527  <x:anchor-alias value="path-absolute"/>
528  <x:anchor-alias value="port"/>
529  <x:anchor-alias value="query"/>
530  <x:anchor-alias value="uri-host"/>
531  <x:anchor-alias value="partial-URI"/>
532<t>
533   This specification adopts the definitions of "URI-reference",
534   "absolute-URI", "relative-part", "fragment", "port", "host",
535   "path-abempty", "path-absolute", "query", and "authority" from
536   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
537   protocol elements that allow a relative URI without a fragment.
538</t>
539<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"/>
540  <x:ref>URI</x:ref>           = &lt;URI, defined in <xref target="RFC3986" x:fmt="," x:sec="3"/>&gt;
541  <x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in <xref target="RFC3986" x:fmt="," x:sec="4.1"/>&gt;
542  <x:ref>absolute-URI</x:ref>  = &lt;absolute-URI, defined in <xref target="RFC3986" x:fmt="," x:sec="4.3"/>&gt;
543  <x:ref>relative-part</x:ref> = &lt;relative-part, defined in <xref target="RFC3986" x:fmt="," x:sec="4.2"/>&gt;
544  <x:ref>authority</x:ref>     = &lt;authority, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2"/>&gt;
545  <x:ref>fragment</x:ref>      = &lt;fragment, defined in <xref target="RFC3986" x:fmt="," x:sec="3.5"/>&gt;
546  <x:ref>path-abempty</x:ref>  = &lt;path-abempty, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
547  <x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in <xref target="RFC3986" x:fmt="," x:sec="3.3"/>&gt;
548  <x:ref>port</x:ref>          = &lt;port, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.3"/>&gt;
549  <x:ref>query</x:ref>         = &lt;query, defined in <xref target="RFC3986" x:fmt="," x:sec="3.4"/>&gt;
550  <x:ref>uri-host</x:ref>      = &lt;host, defined in <xref target="RFC3986" x:fmt="," x:sec="3.2.2"/>&gt;
551 
552  <x:ref>partial-URI</x:ref>   = relative-part [ "?" query ]
553</artwork></figure>
554<t>
555   Each protocol element in HTTP that allows a URI reference will indicate in
556   its ABNF production whether the element allows only a URI in absolute form
557   (absolute-URI), any relative reference (relative-ref), or some other subset
558   of the URI-reference grammar. Unless otherwise indicated, URI references
559   are parsed relative to the request target (the default base URI for both
560   the request and its corresponding response).
561</t>
562
563<section title="http URI scheme" anchor="http.uri">
564  <x:anchor-alias value="http-URI"/>
565  <iref item="http URI scheme" primary="true"/>
566  <iref item="URI scheme" subitem="http" primary="true"/>
567<t>
568   The "http" scheme is used to locate network resources via the HTTP
569   protocol.
570</t>
571<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="http-URI"/>
572  <x:ref>http-URI</x:ref> = "http:" "//" <x:ref>authority</x:ref> <x:ref>path-abempty</x:ref> [ "?" <x:ref>query</x:ref> ]
573</artwork></figure>
574<t>
575   If the port is empty or not given, port 80 is assumed. The semantics
576   are that the identified resource is located at the server listening
577   for TCP connections on that port of that host, and the request-target
578   for the resource is path-absolute (<xref target="request-target"/>). The use of IP addresses
579   in URLs &SHOULD; be avoided whenever possible (see <xref target="RFC1900"/>). If
580   the path-absolute is not present in the URL, it &MUST; be given as "/" when
581   used as a request-target for a resource (<xref target="request-target"/>). If a proxy
582   receives a host name which is not a fully qualified domain name, it
583   &MAY; add its domain to the host name it received. If a proxy receives
584   a fully qualified domain name, the proxy &MUST-NOT; change the host
585   name.
586</t>
587</section>
588
589<section title="https URI scheme" anchor="https.uri">
590   <iref item="https URI scheme"/>
591   <iref item="URI scheme" subitem="https"/>
592<t>
593   <cref>TBD: Define and explain purpose of https scheme.</cref>
594</t>
595<x:note>
596  <t>
597    <x:h>Note:</x:h> the "https" scheme is defined in <xref target="RFC2818"/>.
598  </t>
599</x:note>
600</section>
601
602<section title="URI Comparison" anchor="uri.comparison">
603<t>
604   When comparing two URIs to decide if they match or not, a client
605   &SHOULD; use a case-sensitive octet-by-octet comparison of the entire
606   URIs, with these exceptions:
607  <list style="symbols">
608    <t>A port that is empty or not given is equivalent to the default
609        port for that URI-reference;</t>
610    <t>Comparisons of host names &MUST; be case-insensitive;</t>
611    <t>Comparisons of scheme names &MUST; be case-insensitive;</t>
612    <t>An empty path-absolute is equivalent to a path-absolute of "/".</t>
613    <t>Characters other than those in the "reserved" set are equivalent to their
614       percent-encoded octets (see <xref target="RFC3986" x:fmt="," x:sec="2.1"/>).
615    </t>
616  </list>
617</t>
618<t>
619   For example, the following three URIs are equivalent:
620</t>
621<figure><artwork type="example">
622   http://example.com:80/~smith/home.html
623   http://EXAMPLE.com/%7Esmith/home.html
624   http://EXAMPLE.com:/%7esmith/home.html
625</artwork></figure>
626</section>
627
628<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
629<t>
630</t>
631</section>
632</section>
633
634<section title="Overall Operation" anchor="intro.overall.operation">
635<t>
636   HTTP is a request/response protocol. A client sends a
637   request to the server in the form of a request method, URI, and
638   protocol version, followed by a MIME-like message containing request
639   modifiers, client information, and possible body content over a
640   connection with a server. The server responds with a status line,
641   including the message's protocol version and a success or error code,
642   followed by a MIME-like message containing server information, entity
643   metainformation, and possible entity-body content.
644</t>
645<t>
646   Most HTTP communication is initiated by a user agent and consists of
647   a request to be applied to a resource on some origin server. In the
648   simplest case, this may be accomplished via a single connection (v)
649   between the user agent (UA) and the origin server (O).
650</t>
651<figure><artwork type="drawing">
652       request chain ------------------------&gt;
653    UA -------------------v------------------- O
654       &lt;----------------------- response chain
655</artwork></figure>
656<t>
657   A more complicated situation occurs when one or more intermediaries
658   are present in the request/response chain. There are three common
659   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
660   forwarding agent, receiving requests for a URI in its absolute form,
661   rewriting all or part of the message, and forwarding the reformatted
662   request toward the server identified by the URI. A gateway is a
663   receiving agent, acting as a layer above some other server(s) and, if
664   necessary, translating the requests to the underlying server's
665   protocol. A tunnel acts as a relay point between two connections
666   without changing the messages; tunnels are used when the
667   communication needs to pass through an intermediary (such as a
668   firewall) even when the intermediary cannot understand the contents
669   of the messages.
670</t>
671<figure><artwork type="drawing">
672       request chain --------------------------------------&gt;
673    UA -----v----- A -----v----- B -----v----- C -----v----- O
674       &lt;------------------------------------- response chain
675</artwork></figure>
676<t>
677   The figure above shows three intermediaries (A, B, and C) between the
678   user agent and origin server. A request or response message that
679   travels the whole chain will pass through four separate connections.
680   This distinction is important because some HTTP communication options
681   may apply only to the connection with the nearest, non-tunnel
682   neighbor, only to the end-points of the chain, or to all connections
683   along the chain. Although the diagram is linear, each participant may
684   be engaged in multiple, simultaneous communications. For example, B
685   may be receiving requests from many clients other than A, and/or
686   forwarding requests to servers other than C, at the same time that it
687   is handling A's request.
688</t>
689<t>
690   Any party to the communication which is not acting as a tunnel may
691   employ an internal cache for handling requests. The effect of a cache
692   is that the request/response chain is shortened if one of the
693   participants along the chain has a cached response applicable to that
694   request. The following illustrates the resulting chain if B has a
695   cached copy of an earlier response from O (via C) for a request which
696   has not been cached by UA or A.
697</t>
698<figure><artwork type="drawing">
699          request chain ----------&gt;
700       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
701          &lt;--------- response chain
702</artwork></figure>
703<t>
704   Not all responses are usefully cacheable, and some requests may
705   contain modifiers which place special requirements on cache behavior.
706   HTTP requirements for cache behavior and cacheable responses are
707   defined in &caching;.
708</t>
709<t>
710   In fact, there are a wide variety of architectures and configurations
711   of caches and proxies currently being experimented with or deployed
712   across the World Wide Web. These systems include national hierarchies
713   of proxy caches to save transoceanic bandwidth, systems that
714   broadcast or multicast cache entries, organizations that distribute
715   subsets of cached data via CD-ROM, and so on. HTTP systems are used
716   in corporate intranets over high-bandwidth links, and for access via
717   PDAs with low-power radio links and intermittent connectivity. The
718   goal of HTTP/1.1 is to support the wide diversity of configurations
719   already deployed while introducing protocol constructs that meet the
720   needs of those who build web applications that require high
721   reliability and, failing that, at least reliable indications of
722   failure.
723</t>
724<t>
725   HTTP communication usually takes place over TCP/IP connections. The
726   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
727   not preclude HTTP from being implemented on top of any other protocol
728   on the Internet, or on other networks. HTTP only presumes a reliable
729   transport; any protocol that provides such guarantees can be used;
730   the mapping of the HTTP/1.1 request and response structures onto the
731   transport data units of the protocol in question is outside the scope
732   of this specification.
733</t>
734<t>
735   In HTTP/1.0, most implementations used a new connection for each
736   request/response exchange. In HTTP/1.1, a connection may be used for
737   one or more request/response exchanges, although connections may be
738   closed for a variety of reasons (see <xref target="persistent.connections"/>).
739</t>
740</section>
741
742<section title="Use of HTTP for proxy communication" anchor="http.proxy">
743<t>
744   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
745</t>
746</section>
747<section title="Interception of HTTP for access control" anchor="http.intercept">
748<t>
749   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
750</t>
751</section>
752<section title="Use of HTTP by other protocols" anchor="http.others">
753<t>
754   <cref>TBD: Profiles of HTTP defined by other protocol.
755   Extensions of HTTP like WebDAV.</cref>
756</t>
757</section>
758<section title="Use of HTTP by media type specification" anchor="http.media">
759<t>
760   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
761</t>
762</section>
763</section>
764
765<section title="Protocol Parameters" anchor="protocol.parameters">
766
767<section title="HTTP Version" anchor="http.version">
768  <x:anchor-alias value="HTTP-Version"/>
769  <x:anchor-alias value="HTTP-Prot-Name"/>
770<t>
771   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
772   of the protocol. The protocol versioning policy is intended to allow
773   the sender to indicate the format of a message and its capacity for
774   understanding further HTTP communication, rather than the features
775   obtained via that communication. No change is made to the version
776   number for the addition of message components which do not affect
777   communication behavior or which only add to extensible field values.
778   The &lt;minor&gt; number is incremented when the changes made to the
779   protocol add features which do not change the general message parsing
780   algorithm, but which may add to the message semantics and imply
781   additional capabilities of the sender. The &lt;major&gt; number is
782   incremented when the format of a message within the protocol is
783   changed. See <xref target="RFC2145"/> for a fuller explanation.
784</t>
785<t>
786   The version of an HTTP message is indicated by an HTTP-Version field
787   in the first line of the message. HTTP-Version is case-sensitive.
788</t>
789<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/>
790  <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>
791  <x:ref>HTTP-Prot-Name</x:ref> = <x:abnf-char-sequence>"HTTP"</x:abnf-char-sequence> ; "HTTP", case-sensitive
792</artwork></figure>
793<t>
794   Note that the major and minor numbers &MUST; be treated as separate
795   integers and that each &MAY; be incremented higher than a single digit.
796   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
797   lower than HTTP/12.3. Leading zeros &MUST; be ignored by recipients and
798   &MUST-NOT; be sent.
799</t>
800<t>
801   An application that sends a request or response message that includes
802   HTTP-Version of "HTTP/1.1" &MUST; be at least conditionally compliant
803   with this specification. Applications that are at least conditionally
804   compliant with this specification &SHOULD; use an HTTP-Version of
805   "HTTP/1.1" in their messages, and &MUST; do so for any message that is
806   not compatible with HTTP/1.0. For more details on when to send
807   specific HTTP-Version values, see <xref target="RFC2145"/>.
808</t>
809<t>
810   The HTTP version of an application is the highest HTTP version for
811   which the application is at least conditionally compliant.
812</t>
813<t>
814   Proxy and gateway applications need to be careful when forwarding
815   messages in protocol versions different from that of the application.
816   Since the protocol version indicates the protocol capability of the
817   sender, a proxy/gateway &MUST-NOT; send a message with a version
818   indicator which is greater than its actual version. If a higher
819   version request is received, the proxy/gateway &MUST; either downgrade
820   the request version, or respond with an error, or switch to tunnel
821   behavior.
822</t>
823<t>
824   Due to interoperability problems with HTTP/1.0 proxies discovered
825   since the publication of <xref target="RFC2068"/>, caching proxies &MUST;, gateways
826   &MAY;, and tunnels &MUST-NOT; upgrade the request to the highest version
827   they support. The proxy/gateway's response to that request &MUST; be in
828   the same major version as the request.
829</t>
830<x:note>
831  <t>
832    <x:h>Note:</x:h> Converting between versions of HTTP may involve modification
833    of header fields required or forbidden by the versions involved.
834  </t>
835</x:note>
836</section>
837
838<section title="Date/Time Formats" anchor="date.time.formats">
839<section title="Full Date" anchor="full.date">
840  <x:anchor-alias value="HTTP-date"/>
841  <x:anchor-alias value="obsolete-date"/>
842  <x:anchor-alias value="rfc1123-date"/>
843  <x:anchor-alias value="rfc850-date"/>
844  <x:anchor-alias value="asctime-date"/>
845  <x:anchor-alias value="date1"/>
846  <x:anchor-alias value="date2"/>
847  <x:anchor-alias value="date3"/>
848  <x:anchor-alias value="rfc1123-date"/>
849  <x:anchor-alias value="time"/>
850  <x:anchor-alias value="wkday"/>
851  <x:anchor-alias value="weekday"/>
852  <x:anchor-alias value="month"/>
853<t>
854   HTTP applications have historically allowed three different formats
855   for the representation of date/time stamps:
856</t>
857<figure><artwork type="example">
858  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
859  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
860  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
861</artwork></figure>
862<t>
863   The first format is preferred as an Internet standard and represents
864   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
865   other formats are described here only for
866   compatibility with obsolete implementations.
867   HTTP/1.1 clients and servers that parse the date value &MUST; accept
868   all three formats (for compatibility with HTTP/1.0), though they &MUST;
869   only generate the RFC 1123 format for representing HTTP-date values
870   in header fields. See <xref target="tolerant.applications"/> for further information.
871</t>
872<x:note>
873  <t>
874    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
875    accepting date values that may have been sent by non-HTTP
876    applications, as is sometimes the case when retrieving or posting
877    messages via proxies/gateways to SMTP or NNTP.
878  </t>
879</x:note>
880<t>
881   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
882   (GMT), without exception. For the purposes of HTTP, GMT is exactly
883   equal to UTC (Coordinated Universal Time). This is indicated in the
884   first two formats by the inclusion of "GMT" as the three-letter
885   abbreviation for time zone, and &MUST; be assumed when reading the
886   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
887   additional whitespace beyond that specifically included as SP in the
888   grammar.
889</t>
890<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"/>
891  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obsolete-date</x:ref>
892  <x:ref>obsolete-date</x:ref> = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
893  <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
894  <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
895  <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>
896  <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>
897                 ; day month year (e.g., 02 Jun 1982)
898  <x:ref>date2</x:ref>        = 2<x:ref>DIGIT</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
899                 ; day-month-year (e.g., 02-Jun-82)
900  <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> ))
901                 ; month day (e.g., Jun  2)
902  <x:ref>time</x:ref>         = 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref> ":" 2<x:ref>DIGIT</x:ref>
903                 ; 00:00:00 - 23:59:59
904  <x:ref>wkday</x:ref>        = s-Mon / s-Tue / s-Wed
905               / s-Thu / s-Fri / s-Sat / s-Sun
906  <x:ref>weekday</x:ref>      = l-Mon / l-Tue / l-Wed
907               / l-Thu / l-Fri / l-Sat / l-Sun
908  <x:ref>month</x:ref>        = s-Jan / s-Feb / s-Mar / s-Apr
909               / s-May / s-Jun / s-Jul / s-Aug
910               / s-Sep / s-Oct / s-Nov / s-Dec
911               
912  GMT   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
913
914  s-Mon = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
915  s-Tue = <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
916  s-Wed = <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
917  s-Thu = <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
918  s-Fri = <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
919  s-Sat = <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
920  s-Sun = <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
921
922  l-Mon = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence>          ; "Monday", case-sensitive
923  l-Tue = <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence>       ; "Tuesday", case-sensitive
924  l-Wed = <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
925  l-Thu = <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence>    ; "Thursday", case-sensitive
926  l-Fri = <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence>          ; "Friday", case-sensitive
927  l-Sat = <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence>    ; "Saturday", case-sensitive
928  l-Sun = <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence>          ; "Sunday", case-sensitive
929
930  s-Jan = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
931  s-Feb = <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
932  s-Mar = <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
933  s-Apr = <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
934  s-May = <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
935  s-Jun = <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
936  s-Jul = <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
937  s-Aug = <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
938  s-Sep = <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
939  s-Oct = <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
940  s-Nov = <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
941  s-Dec = <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
942</artwork></figure>
943<t>
944      <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
945      to their usage within the protocol stream. Clients and servers are
946      not required to use these formats for user presentation, request
947      logging, etc.
948</t>
949</section>
950</section>
951
952<section title="Transfer Codings" anchor="transfer.codings">
953  <x:anchor-alias value="parameter"/>
954  <x:anchor-alias value="transfer-coding"/>
955  <x:anchor-alias value="transfer-extension"/>
956<t>
957   Transfer-coding values are used to indicate an encoding
958   transformation that has been, can be, or may need to be applied to an
959   entity-body in order to ensure "safe transport" through the network.
960   This differs from a content coding in that the transfer-coding is a
961   property of the message, not of the original entity.
962</t>
963<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
964  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
965  <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> )
966</artwork></figure>
967<t anchor="rule.parameter">
968  <x:anchor-alias value="attribute"/>
969  <x:anchor-alias value="parameter"/>
970  <x:anchor-alias value="value"/>
971   Parameters are in  the form of attribute/value pairs.
972</t>
973<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"/>
974  <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>
975  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
976  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
977</artwork></figure>
978<t>
979   All transfer-coding values are case-insensitive. HTTP/1.1 uses
980   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
981   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
982</t>
983<t>
984   Whenever a transfer-coding is applied to a message-body, the set of
985   transfer-codings &MUST; include "chunked", unless the message indicates it
986   is terminated by closing the connection. When the "chunked" transfer-coding
987   is used, it &MUST; be the last transfer-coding applied to the
988   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
989   than once to a message-body. These rules allow the recipient to
990   determine the transfer-length of the message (<xref target="message.length"/>).
991</t>
992<t>
993   Transfer-codings are analogous to the Content-Transfer-Encoding
994   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
995   binary data over a 7-bit transport service. However, safe transport
996   has a different focus for an 8bit-clean transfer protocol. In HTTP,
997   the only unsafe characteristic of message-bodies is the difficulty in
998   determining the exact body length (<xref target="message.length"/>), or the desire to
999   encrypt data over a shared transport.
1000</t>
1001<t>
1002   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1003   transfer-coding value tokens. Initially, the registry contains the
1004   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1005   "gzip", "compress", and "deflate" (&content-codings;).
1006</t>
1007<t>
1008   New transfer-coding value tokens &SHOULD; be registered in the same way
1009   as new content-coding value tokens (&content-codings;).
1010</t>
1011<t>
1012   A server which receives an entity-body with a transfer-coding it does
1013   not understand &SHOULD; return 501 (Not Implemented), and close the
1014   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1015   client.
1016</t>
1017
1018<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1019  <x:anchor-alias value="chunk"/>
1020  <x:anchor-alias value="Chunked-Body"/>
1021  <x:anchor-alias value="chunk-data"/>
1022  <x:anchor-alias value="chunk-ext"/>
1023  <x:anchor-alias value="chunk-ext-name"/>
1024  <x:anchor-alias value="chunk-ext-val"/>
1025  <x:anchor-alias value="chunk-size"/>
1026  <x:anchor-alias value="last-chunk"/>
1027  <x:anchor-alias value="trailer-part"/>
1028<t>
1029   The chunked encoding modifies the body of a message in order to
1030   transfer it as a series of chunks, each with its own size indicator,
1031   followed by an &OPTIONAL; trailer containing entity-header fields. This
1032   allows dynamically produced content to be transferred along with the
1033   information necessary for the recipient to verify that it has
1034   received the full message.
1035</t>
1036<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"/>
1037  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1038                   <x:ref>last-chunk</x:ref>
1039                   <x:ref>trailer-part</x:ref>
1040                   <x:ref>CRLF</x:ref>
1041 
1042  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1043                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1044  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1045  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1046 
1047  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1048                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1049  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1050  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1051  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1052  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1053</artwork></figure>
1054<t>
1055   The chunk-size field is a string of hex digits indicating the size of
1056   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1057   zero, followed by the trailer, which is terminated by an empty line.
1058</t>
1059<t>
1060   The trailer allows the sender to include additional HTTP header
1061   fields at the end of the message. The Trailer header field can be
1062   used to indicate which header fields are included in a trailer (see
1063   <xref target="header.trailer"/>).
1064</t>
1065<t>
1066   A server using chunked transfer-coding in a response &MUST-NOT; use the
1067   trailer for any header fields unless at least one of the following is
1068   true:
1069  <list style="numbers">
1070    <t>the request included a TE header field that indicates "trailers" is
1071     acceptable in the transfer-coding of the  response, as described in
1072     <xref target="header.te"/>; or,</t>
1073
1074    <t>the server is the origin server for the response, the trailer
1075     fields consist entirely of optional metadata, and the recipient
1076     could use the message (in a manner acceptable to the origin server)
1077     without receiving this metadata.  In other words, the origin server
1078     is willing to accept the possibility that the trailer fields might
1079     be silently discarded along the path to the client.</t>
1080  </list>
1081</t>
1082<t>
1083   This requirement prevents an interoperability failure when the
1084   message is being received by an HTTP/1.1 (or later) proxy and
1085   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1086   compliance with the protocol would have necessitated a possibly
1087   infinite buffer on the proxy.
1088</t>
1089<t>
1090   A process for decoding the "chunked" transfer-coding
1091   can be represented in pseudo-code as:
1092</t>
1093<figure><artwork type="code">
1094  length := 0
1095  read chunk-size, chunk-ext (if any) and CRLF
1096  while (chunk-size &gt; 0) {
1097     read chunk-data and CRLF
1098     append chunk-data to entity-body
1099     length := length + chunk-size
1100     read chunk-size and CRLF
1101  }
1102  read entity-header
1103  while (entity-header not empty) {
1104     append entity-header to existing header fields
1105     read entity-header
1106  }
1107  Content-Length := length
1108  Remove "chunked" from Transfer-Encoding
1109</artwork></figure>
1110<t>
1111   All HTTP/1.1 applications &MUST; be able to receive and decode the
1112   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1113   they do not understand.
1114</t>
1115</section>
1116</section>
1117
1118<section title="Product Tokens" anchor="product.tokens">
1119  <x:anchor-alias value="product"/>
1120  <x:anchor-alias value="product-version"/>
1121<t>
1122   Product tokens are used to allow communicating applications to
1123   identify themselves by software name and version. Most fields using
1124   product tokens also allow sub-products which form a significant part
1125   of the application to be listed, separated by whitespace. By
1126   convention, the products are listed in order of their significance
1127   for identifying the application.
1128</t>
1129<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1130  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1131  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1132</artwork></figure>
1133<t>
1134   Examples:
1135</t>
1136<figure><artwork type="example">
1137  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1138  Server: Apache/0.8.4
1139</artwork></figure>
1140<t>
1141   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1142   used for advertising or other non-essential information. Although any
1143   token character &MAY; appear in a product-version, this token &SHOULD;
1144   only be used for a version identifier (i.e., successive versions of
1145   the same product &SHOULD; only differ in the product-version portion of
1146   the product value).
1147</t>
1148</section>
1149
1150<section title="Quality Values" anchor="quality.values">
1151  <x:anchor-alias value="qvalue"/>
1152<t>
1153   Both transfer codings (TE request header, <xref target="header.te"/>)
1154   and content negotiation (&content.negotiation;) use short "floating point"
1155   numbers to indicate the relative importance ("weight") of various
1156   negotiable parameters.  A weight is normalized to a real number in
1157   the range 0 through 1, where 0 is the minimum and 1 the maximum
1158   value. If a parameter has a quality value of 0, then content with
1159   this parameter is `not acceptable' for the client. HTTP/1.1
1160   applications &MUST-NOT; generate more than three digits after the
1161   decimal point. User configuration of these values &SHOULD; also be
1162   limited in this fashion.
1163</t>
1164<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1165  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1166                 / ( "1" [ "." 0*3("0") ] )
1167</artwork></figure>
1168<x:note>
1169  <t>
1170     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1171     relative degradation in desired quality.
1172  </t>
1173</x:note>
1174</section>
1175
1176</section>
1177
1178<section title="HTTP Message" anchor="http.message">
1179
1180<section title="Message Types" anchor="message.types">
1181  <x:anchor-alias value="generic-message"/>
1182  <x:anchor-alias value="HTTP-message"/>
1183  <x:anchor-alias value="start-line"/>
1184<t>
1185   HTTP messages consist of requests from client to server and responses
1186   from server to client.
1187</t>
1188<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1189  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1190</artwork></figure>
1191<t>
1192   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1193   message format of <xref target="RFC5322"/> for transferring entities (the payload
1194   of the message). Both types of message consist of a start-line, zero
1195   or more header fields (also known as "headers"), an empty line (i.e.,
1196   a line with nothing preceding the CRLF) indicating the end of the
1197   header fields, and possibly a message-body.
1198</t>
1199<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1200  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1201                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1202                    <x:ref>CRLF</x:ref>
1203                    [ <x:ref>message-body</x:ref> ]
1204  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1205</artwork></figure>
1206<t>
1207   In the interest of robustness, servers &SHOULD; ignore any empty
1208   line(s) received where a Request-Line is expected. In other words, if
1209   the server is reading the protocol stream at the beginning of a
1210   message and receives a CRLF first, it should ignore the CRLF.
1211</t>
1212<t>
1213   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1214   after a POST request. To restate what is explicitly forbidden by the
1215   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1216   extra CRLF.
1217</t>
1218<t>
1219   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1220   header field. The presence of whitespace might be an attempt to trick a
1221   noncompliant implementation of HTTP into ignoring that field or processing
1222   the next line as a new request, either of which may result in security
1223   issues when implementations within the request chain interpret the
1224   same message differently. HTTP/1.1 servers &MUST; reject such a message
1225   with a 400 (Bad Request) response.
1226</t>
1227</section>
1228
1229<section title="Message Headers" anchor="message.headers">
1230  <x:anchor-alias value="field-content"/>
1231  <x:anchor-alias value="field-name"/>
1232  <x:anchor-alias value="field-value"/>
1233  <x:anchor-alias value="message-header"/>
1234<t>
1235   HTTP header fields follow the same general format as Internet messages in
1236   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1237   of a name followed by a colon (":"), optional whitespace, and the field
1238   value. Field names are case-insensitive.
1239</t>
1240<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"/>
1241  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1242  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1243  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1244  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1245</artwork></figure>
1246<t>
1247   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1248   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1249   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1250   header field-values use only a subset of the US-ASCII charset
1251   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1252   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1253   (obs-text) octets in field-content as opaque data.
1254</t>
1255<t>
1256   No whitespace is allowed between the header field-name and colon. For
1257   security reasons, any request message received containing such whitespace
1258   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1259   whitespace in a response message &MUST; be removed.
1260</t>
1261<t>
1262   The field value &MAY; be preceded by optional whitespace; a single SP is
1263   preferred. The field-value does not include any leading or trailing white
1264   space: OWS occurring before the first non-whitespace character of the
1265   field-value or after the last non-whitespace character of the field-value
1266   is ignored and &MAY; be removed without changing the meaning of the header
1267   field.
1268</t>
1269<t>
1270   Historically, HTTP header field values could be extended over multiple
1271   lines by preceding each extra line with at least one space or horizontal
1272   tab character (line folding). This specification deprecates such line
1273   folding except within the message/http media type
1274   (<xref target="internet.media.type.message.http"/>).
1275   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1276   (i.e., that contain any field-content that matches the obs-fold rule) unless
1277   the message is intended for packaging within the message/http media type.
1278   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1279   obs-fold whitespace with a single SP prior to interpreting the field value
1280   or forwarding the message downstream.
1281</t>
1282<t anchor="rule.comment">
1283  <x:anchor-alias value="comment"/>
1284  <x:anchor-alias value="ctext"/>
1285   Comments can be included in some HTTP header fields by surrounding
1286   the comment text with parentheses. Comments are only allowed in
1287   fields containing "comment" as part of their field value definition.
1288   In all other fields, parentheses are considered part of the field
1289   value.
1290</t>
1291<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1292  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1293  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1294                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1295</artwork></figure>
1296<t>
1297   The order in which header fields with differing field names are
1298   received is not significant. However, it is "good practice" to send
1299   general-header fields first, followed by request-header or response-header
1300   fields, and ending with the entity-header fields.
1301</t>
1302<t>
1303   Multiple message-header fields with the same field-name &MAY; be
1304   present in a message if and only if the entire field-value for that
1305   header field is defined as a comma-separated list [i.e., #(values)].
1306   It &MUST; be possible to combine the multiple header fields into one
1307   "field-name: field-value" pair, without changing the semantics of the
1308   message, by appending each subsequent field-value to the first, each
1309   separated by a comma. The order in which header fields with the same
1310   field-name are received is therefore significant to the
1311   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1312   change the order of these field values when a message is forwarded.
1313</t>
1314<x:note>
1315  <t>
1316   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1317   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1318   can occur multiple times, but does not use the list syntax, and thus cannot
1319   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1320   for details.) Also note that the Set-Cookie2 header specified in
1321   <xref target="RFC2965"/> does not share this problem.
1322  </t>
1323</x:note>
1324 
1325</section>
1326
1327<section title="Message Body" anchor="message.body">
1328  <x:anchor-alias value="message-body"/>
1329<t>
1330   The message-body (if any) of an HTTP message is used to carry the
1331   entity-body associated with the request or response. The message-body
1332   differs from the entity-body only when a transfer-coding has been
1333   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1334</t>
1335<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1336  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1337               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1338</artwork></figure>
1339<t>
1340   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1341   applied by an application to ensure safe and proper transfer of the
1342   message. Transfer-Encoding is a property of the message, not of the
1343   entity, and thus &MAY; be added or removed by any application along the
1344   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1345   when certain transfer-codings may be used.)
1346</t>
1347<t>
1348   The rules for when a message-body is allowed in a message differ for
1349   requests and responses.
1350</t>
1351<t>
1352   The presence of a message-body in a request is signaled by the
1353   inclusion of a Content-Length or Transfer-Encoding header field in
1354   the request's message-headers. A message-body &MUST-NOT; be included in
1355   a request if the specification of the request method (&method;)
1356   explicitly disallows an entity-body in requests.
1357   When a request message contains both a message-body of non-zero
1358   length and a method that does not define any semantics for that
1359   request message-body, then an origin server &SHOULD; either ignore
1360   the message-body or respond with an appropriate error message
1361   (e.g., 413).  A proxy or gateway, when presented the same request,
1362   &SHOULD; either forward the request inbound with the message-body or
1363   ignore the message-body when determining a response.
1364</t>
1365<t>
1366   For response messages, whether or not a message-body is included with
1367   a message is dependent on both the request method and the response
1368   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1369   &MUST-NOT; include a message-body, even though the presence of entity-header
1370   fields might lead one to believe they do. All 1xx
1371   (informational), 204 (No Content), and 304 (Not Modified) responses
1372   &MUST-NOT; include a message-body. All other responses do include a
1373   message-body, although it &MAY; be of zero length.
1374</t>
1375</section>
1376
1377<section title="Message Length" anchor="message.length">
1378<t>
1379   The transfer-length of a message is the length of the message-body as
1380   it appears in the message; that is, after any transfer-codings have
1381   been applied. When a message-body is included with a message, the
1382   transfer-length of that body is determined by one of the following
1383   (in order of precedence):
1384</t>
1385<t>
1386  <list style="numbers">
1387    <x:lt><t>
1388     Any response message which "&MUST-NOT;" include a message-body (such
1389     as the 1xx, 204, and 304 responses and any response to a HEAD
1390     request) is always terminated by the first empty line after the
1391     header fields, regardless of the entity-header fields present in
1392     the message.
1393    </t></x:lt>
1394    <x:lt><t>
1395     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1396     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1397     is used, the transfer-length is defined by the use of this transfer-coding.
1398     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1399     is not present, the transfer-length is defined by the sender closing the connection.
1400    </t></x:lt>
1401    <x:lt><t>
1402     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1403     value in OCTETs represents both the entity-length and the
1404     transfer-length. The Content-Length header field &MUST-NOT; be sent
1405     if these two lengths are different (i.e., if a Transfer-Encoding
1406     header field is present). If a message is received with both a
1407     Transfer-Encoding header field and a Content-Length header field,
1408     the latter &MUST; be ignored.
1409    </t></x:lt>
1410    <x:lt><t>
1411     If the message uses the media type "multipart/byteranges", and the
1412     transfer-length is not otherwise specified, then this self-delimiting
1413     media type defines the transfer-length. This media type
1414     &MUST-NOT; be used unless the sender knows that the recipient can parse
1415     it; the presence in a request of a Range header with multiple byte-range
1416     specifiers from a 1.1 client implies that the client can parse
1417     multipart/byteranges responses.
1418    <list style="empty"><t>
1419       A range header might be forwarded by a 1.0 proxy that does not
1420       understand multipart/byteranges; in this case the server &MUST;
1421       delimit the message using methods defined in items 1, 3 or 5 of
1422       this section.
1423    </t></list>
1424    </t></x:lt>
1425    <x:lt><t>
1426     By the server closing the connection. (Closing the connection
1427     cannot be used to indicate the end of a request body, since that
1428     would leave no possibility for the server to send back a response.)
1429    </t></x:lt>
1430  </list>
1431</t>
1432<t>
1433   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1434   containing a message-body &MUST; include a valid Content-Length header
1435   field unless the server is known to be HTTP/1.1 compliant. If a
1436   request contains a message-body and a Content-Length is not given,
1437   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1438   determine the length of the message, or with 411 (Length Required) if
1439   it wishes to insist on receiving a valid Content-Length.
1440</t>
1441<t>
1442   All HTTP/1.1 applications that receive entities &MUST; accept the
1443   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1444   to be used for messages when the message length cannot be determined
1445   in advance.
1446</t>
1447<t>
1448   Messages &MUST-NOT; include both a Content-Length header field and a
1449   transfer-coding. If the message does include a
1450   transfer-coding, the Content-Length &MUST; be ignored.
1451</t>
1452<t>
1453   When a Content-Length is given in a message where a message-body is
1454   allowed, its field value &MUST; exactly match the number of OCTETs in
1455   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1456   invalid length is received and detected.
1457</t>
1458</section>
1459
1460<section title="General Header Fields" anchor="general.header.fields">
1461  <x:anchor-alias value="general-header"/>
1462<t>
1463   There are a few header fields which have general applicability for
1464   both request and response messages, but which do not apply to the
1465   entity being transferred. These header fields apply only to the
1466   message being transmitted.
1467</t>
1468<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1469  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1470                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1471                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1472                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1473                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1474                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1475                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1476                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1477                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1478</artwork></figure>
1479<t>
1480   General-header field names can be extended reliably only in
1481   combination with a change in the protocol version. However, new or
1482   experimental header fields may be given the semantics of general
1483   header fields if all parties in the communication recognize them to
1484   be general-header fields. Unrecognized header fields are treated as
1485   entity-header fields.
1486</t>
1487</section>
1488</section>
1489
1490<section title="Request" anchor="request">
1491  <x:anchor-alias value="Request"/>
1492<t>
1493   A request message from a client to a server includes, within the
1494   first line of that message, the method to be applied to the resource,
1495   the identifier of the resource, and the protocol version in use.
1496</t>
1497<!--                 Host                      ; should be moved here eventually -->
1498<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1499  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1500                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1501                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1502                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1503                  <x:ref>CRLF</x:ref>
1504                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1505</artwork></figure>
1506
1507<section title="Request-Line" anchor="request-line">
1508  <x:anchor-alias value="Request-Line"/>
1509<t>
1510   The Request-Line begins with a method token, followed by the
1511   request-target and the protocol version, and ending with CRLF. The
1512   elements are separated by SP characters. No CR or LF is allowed
1513   except in the final CRLF sequence.
1514</t>
1515<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1516  <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>
1517</artwork></figure>
1518
1519<section title="Method" anchor="method">
1520  <x:anchor-alias value="Method"/>
1521<t>
1522   The Method  token indicates the method to be performed on the
1523   resource identified by the request-target. The method is case-sensitive.
1524</t>
1525<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1526  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1527</artwork></figure>
1528</section>
1529
1530<section title="request-target" anchor="request-target">
1531  <x:anchor-alias value="request-target"/>
1532<t>
1533   The request-target
1534   identifies the resource upon which to apply the request.
1535</t>
1536<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1537  <x:ref>request-target</x:ref> = "*"
1538                 / <x:ref>absolute-URI</x:ref>
1539                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1540                 / <x:ref>authority</x:ref>
1541</artwork></figure>
1542<t>
1543   The four options for request-target are dependent on the nature of the
1544   request. The asterisk "*" means that the request does not apply to a
1545   particular resource, but to the server itself, and is only allowed
1546   when the method used does not necessarily apply to a resource. One
1547   example would be
1548</t>
1549<figure><artwork type="example">
1550  OPTIONS * HTTP/1.1
1551</artwork></figure>
1552<t>
1553   The absolute-URI form is &REQUIRED; when the request is being made to a
1554   proxy. The proxy is requested to forward the request or service it
1555   from a valid cache, and return the response. Note that the proxy &MAY;
1556   forward the request on to another proxy or directly to the server
1557   specified by the absolute-URI. In order to avoid request loops, a
1558   proxy &MUST; be able to recognize all of its server names, including
1559   any aliases, local variations, and the numeric IP address. An example
1560   Request-Line would be:
1561</t>
1562<figure><artwork type="example">
1563  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1564</artwork></figure>
1565<t>
1566   To allow for transition to absolute-URIs in all requests in future
1567   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1568   form in requests, even though HTTP/1.1 clients will only generate
1569   them in requests to proxies.
1570</t>
1571<t>
1572   The authority form is only used by the CONNECT method (&CONNECT;).
1573</t>
1574<t>
1575   The most common form of request-target is that used to identify a
1576   resource on an origin server or gateway. In this case the absolute
1577   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1578   the request-target, and the network location of the URI (authority) &MUST;
1579   be transmitted in a Host header field. For example, a client wishing
1580   to retrieve the resource above directly from the origin server would
1581   create a TCP connection to port 80 of the host "www.example.org" and send
1582   the lines:
1583</t>
1584<figure><artwork type="example">
1585  GET /pub/WWW/TheProject.html HTTP/1.1
1586  Host: www.example.org
1587</artwork></figure>
1588<t>
1589   followed by the remainder of the Request. Note that the absolute path
1590   cannot be empty; if none is present in the original URI, it &MUST; be
1591   given as "/" (the server root).
1592</t>
1593<t>
1594   If a proxy receives a request without any path in the request-target and
1595   the method specified is capable of supporting the asterisk form of
1596   request-target, then the last proxy on the request chain &MUST; forward the
1597   request with "*" as the final request-target.
1598</t>
1599<figure><preamble>   
1600   For example, the request
1601</preamble><artwork type="example">
1602  OPTIONS http://www.example.org:8001 HTTP/1.1
1603</artwork></figure>
1604<figure><preamble>   
1605  would be forwarded by the proxy as
1606</preamble><artwork type="example">
1607  OPTIONS * HTTP/1.1
1608  Host: www.example.org:8001
1609</artwork>
1610<postamble>
1611   after connecting to port 8001 of host "www.example.org".
1612</postamble>
1613</figure>
1614<t>
1615   The request-target is transmitted in the format specified in
1616   <xref target="http.uri"/>. If the request-target is percent-encoded
1617   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1618   &MUST; decode the request-target in order to
1619   properly interpret the request. Servers &SHOULD; respond to invalid
1620   request-targets with an appropriate status code.
1621</t>
1622<t>
1623   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1624   received request-target when forwarding it to the next inbound server,
1625   except as noted above to replace a null path-absolute with "/".
1626</t>
1627<x:note>
1628  <t>
1629    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1630    meaning of the request when the origin server is improperly using
1631    a non-reserved URI character for a reserved purpose.  Implementors
1632    should be aware that some pre-HTTP/1.1 proxies have been known to
1633    rewrite the request-target.
1634  </t>
1635</x:note>
1636<t>
1637   HTTP does not place a pre-defined limit on the length of a request-target.
1638   A server &MUST; be prepared to receive URIs of unbounded length and
1639   respond with the 414 (URI Too Long) status if the received
1640   request-target would be longer than the server wishes to handle
1641   (see &status-414;).
1642</t>
1643<t>
1644   Various ad-hoc limitations on request-target length are found in practice.
1645   It is &RECOMMENDED; that all HTTP senders and recipients support
1646   request-target lengths of 8000 or more OCTETs.
1647</t>
1648</section>
1649</section>
1650
1651<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1652<t>
1653   The exact resource identified by an Internet request is determined by
1654   examining both the request-target and the Host header field.
1655</t>
1656<t>
1657   An origin server that does not allow resources to differ by the
1658   requested host &MAY; ignore the Host header field value when
1659   determining the resource identified by an HTTP/1.1 request. (But see
1660   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1661   for other requirements on Host support in HTTP/1.1.)
1662</t>
1663<t>
1664   An origin server that does differentiate resources based on the host
1665   requested (sometimes referred to as virtual hosts or vanity host
1666   names) &MUST; use the following rules for determining the requested
1667   resource on an HTTP/1.1 request:
1668  <list style="numbers">
1669    <t>If request-target is an absolute-URI, the host is part of the
1670     request-target. Any Host header field value in the request &MUST; be
1671     ignored.</t>
1672    <t>If the request-target is not an absolute-URI, and the request includes
1673     a Host header field, the host is determined by the Host header
1674     field value.</t>
1675    <t>If the host as determined by rule 1 or 2 is not a valid host on
1676     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1677  </list>
1678</t>
1679<t>
1680   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1681   attempt to use heuristics (e.g., examination of the URI path for
1682   something unique to a particular host) in order to determine what
1683   exact resource is being requested.
1684</t>
1685</section>
1686
1687</section>
1688
1689
1690<section title="Response" anchor="response">
1691  <x:anchor-alias value="Response"/>
1692<t>
1693   After receiving and interpreting a request message, a server responds
1694   with an HTTP response message.
1695</t>
1696<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1697  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1698                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1699                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1700                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1701                  <x:ref>CRLF</x:ref>
1702                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1703</artwork></figure>
1704
1705<section title="Status-Line" anchor="status-line">
1706  <x:anchor-alias value="Status-Line"/>
1707<t>
1708   The first line of a Response message is the Status-Line, consisting
1709   of the protocol version followed by a numeric status code and its
1710   associated textual phrase, with each element separated by SP
1711   characters. No CR or LF is allowed except in the final CRLF sequence.
1712</t>
1713<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1714  <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>
1715</artwork></figure>
1716
1717<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1718  <x:anchor-alias value="Reason-Phrase"/>
1719  <x:anchor-alias value="Status-Code"/>
1720<t>
1721   The Status-Code element is a 3-digit integer result code of the
1722   attempt to understand and satisfy the request. These codes are fully
1723   defined in &status-codes;.  The Reason Phrase exists for the sole
1724   purpose of providing a textual description associated with the numeric
1725   status code, out of deference to earlier Internet application protocols
1726   that were more frequently used with interactive text clients.
1727   A client &SHOULD; ignore the content of the Reason Phrase.
1728</t>
1729<t>
1730   The first digit of the Status-Code defines the class of response. The
1731   last two digits do not have any categorization role. There are 5
1732   values for the first digit:
1733  <list style="symbols">
1734    <t>
1735      1xx: Informational - Request received, continuing process
1736    </t>
1737    <t>
1738      2xx: Success - The action was successfully received,
1739        understood, and accepted
1740    </t>
1741    <t>
1742      3xx: Redirection - Further action must be taken in order to
1743        complete the request
1744    </t>
1745    <t>
1746      4xx: Client Error - The request contains bad syntax or cannot
1747        be fulfilled
1748    </t>
1749    <t>
1750      5xx: Server Error - The server failed to fulfill an apparently
1751        valid request
1752    </t>
1753  </list>
1754</t>
1755<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"/>
1756  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1757  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1758</artwork></figure>
1759</section>
1760</section>
1761
1762</section>
1763
1764
1765<section title="Connections" anchor="connections">
1766
1767<section title="Persistent Connections" anchor="persistent.connections">
1768
1769<section title="Purpose" anchor="persistent.purpose">
1770<t>
1771   Prior to persistent connections, a separate TCP connection was
1772   established to fetch each URL, increasing the load on HTTP servers
1773   and causing congestion on the Internet. The use of inline images and
1774   other associated data often require a client to make multiple
1775   requests of the same server in a short amount of time. Analysis of
1776   these performance problems and results from a prototype
1777   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1778   measurements of actual HTTP/1.1 (<xref target="RFC2068" x:fmt="none">RFC 2068</xref>) implementations show good
1779   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1780   T/TCP <xref target="Tou1998"/>.
1781</t>
1782<t>
1783   Persistent HTTP connections have a number of advantages:
1784  <list style="symbols">
1785      <t>
1786        By opening and closing fewer TCP connections, CPU time is saved
1787        in routers and hosts (clients, servers, proxies, gateways,
1788        tunnels, or caches), and memory used for TCP protocol control
1789        blocks can be saved in hosts.
1790      </t>
1791      <t>
1792        HTTP requests and responses can be pipelined on a connection.
1793        Pipelining allows a client to make multiple requests without
1794        waiting for each response, allowing a single TCP connection to
1795        be used much more efficiently, with much lower elapsed time.
1796      </t>
1797      <t>
1798        Network congestion is reduced by reducing the number of packets
1799        caused by TCP opens, and by allowing TCP sufficient time to
1800        determine the congestion state of the network.
1801      </t>
1802      <t>
1803        Latency on subsequent requests is reduced since there is no time
1804        spent in TCP's connection opening handshake.
1805      </t>
1806      <t>
1807        HTTP can evolve more gracefully, since errors can be reported
1808        without the penalty of closing the TCP connection. Clients using
1809        future versions of HTTP might optimistically try a new feature,
1810        but if communicating with an older server, retry with old
1811        semantics after an error is reported.
1812      </t>
1813    </list>
1814</t>
1815<t>
1816   HTTP implementations &SHOULD; implement persistent connections.
1817</t>
1818</section>
1819
1820<section title="Overall Operation" anchor="persistent.overall">
1821<t>
1822   A significant difference between HTTP/1.1 and earlier versions of
1823   HTTP is that persistent connections are the default behavior of any
1824   HTTP connection. That is, unless otherwise indicated, the client
1825   &SHOULD; assume that the server will maintain a persistent connection,
1826   even after error responses from the server.
1827</t>
1828<t>
1829   Persistent connections provide a mechanism by which a client and a
1830   server can signal the close of a TCP connection. This signaling takes
1831   place using the Connection header field (<xref target="header.connection"/>). Once a close
1832   has been signaled, the client &MUST-NOT; send any more requests on that
1833   connection.
1834</t>
1835
1836<section title="Negotiation" anchor="persistent.negotiation">
1837<t>
1838   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1839   maintain a persistent connection unless a Connection header including
1840   the connection-token "close" was sent in the request. If the server
1841   chooses to close the connection immediately after sending the
1842   response, it &SHOULD; send a Connection header including the
1843   connection-token close.
1844</t>
1845<t>
1846   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1847   decide to keep it open based on whether the response from a server
1848   contains a Connection header with the connection-token close. In case
1849   the client does not want to maintain a connection for more than that
1850   request, it &SHOULD; send a Connection header including the
1851   connection-token close.
1852</t>
1853<t>
1854   If either the client or the server sends the close token in the
1855   Connection header, that request becomes the last one for the
1856   connection.
1857</t>
1858<t>
1859   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1860   maintained for HTTP versions less than 1.1 unless it is explicitly
1861   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1862   compatibility with HTTP/1.0 clients.
1863</t>
1864<t>
1865   In order to remain persistent, all messages on the connection &MUST;
1866   have a self-defined message length (i.e., one not defined by closure
1867   of the connection), as described in <xref target="message.length"/>.
1868</t>
1869</section>
1870
1871<section title="Pipelining" anchor="pipelining">
1872<t>
1873   A client that supports persistent connections &MAY; "pipeline" its
1874   requests (i.e., send multiple requests without waiting for each
1875   response). A server &MUST; send its responses to those requests in the
1876   same order that the requests were received.
1877</t>
1878<t>
1879   Clients which assume persistent connections and pipeline immediately
1880   after connection establishment &SHOULD; be prepared to retry their
1881   connection if the first pipelined attempt fails. If a client does
1882   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1883   persistent. Clients &MUST; also be prepared to resend their requests if
1884   the server closes the connection before sending all of the
1885   corresponding responses.
1886</t>
1887<t>
1888   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1889   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1890   premature termination of the transport connection could lead to
1891   indeterminate results. A client wishing to send a non-idempotent
1892   request &SHOULD; wait to send that request until it has received the
1893   response status for the previous request.
1894</t>
1895</section>
1896</section>
1897
1898<section title="Proxy Servers" anchor="persistent.proxy">
1899<t>
1900   It is especially important that proxies correctly implement the
1901   properties of the Connection header field as specified in <xref target="header.connection"/>.
1902</t>
1903<t>
1904   The proxy server &MUST; signal persistent connections separately with
1905   its clients and the origin servers (or other proxy servers) that it
1906   connects to. Each persistent connection applies to only one transport
1907   link.
1908</t>
1909<t>
1910   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1911   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
1912   discussion of the problems with the Keep-Alive header implemented by
1913   many HTTP/1.0 clients).
1914</t>
1915</section>
1916
1917<section title="Practical Considerations" anchor="persistent.practical">
1918<t>
1919   Servers will usually have some time-out value beyond which they will
1920   no longer maintain an inactive connection. Proxy servers might make
1921   this a higher value since it is likely that the client will be making
1922   more connections through the same server. The use of persistent
1923   connections places no requirements on the length (or existence) of
1924   this time-out for either the client or the server.
1925</t>
1926<t>
1927   When a client or server wishes to time-out it &SHOULD; issue a graceful
1928   close on the transport connection. Clients and servers &SHOULD; both
1929   constantly watch for the other side of the transport close, and
1930   respond to it as appropriate. If a client or server does not detect
1931   the other side's close promptly it could cause unnecessary resource
1932   drain on the network.
1933</t>
1934<t>
1935   A client, server, or proxy &MAY; close the transport connection at any
1936   time. For example, a client might have started to send a new request
1937   at the same time that the server has decided to close the "idle"
1938   connection. From the server's point of view, the connection is being
1939   closed while it was idle, but from the client's point of view, a
1940   request is in progress.
1941</t>
1942<t>
1943   This means that clients, servers, and proxies &MUST; be able to recover
1944   from asynchronous close events. Client software &SHOULD; reopen the
1945   transport connection and retransmit the aborted sequence of requests
1946   without user interaction so long as the request sequence is
1947   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1948   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1949   human operator the choice of retrying the request(s). Confirmation by
1950   user-agent software with semantic understanding of the application
1951   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1952   be repeated if the second sequence of requests fails.
1953</t>
1954<t>
1955   Servers &SHOULD; always respond to at least one request per connection,
1956   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1957   middle of transmitting a response, unless a network or client failure
1958   is suspected.
1959</t>
1960<t>
1961   Clients that use persistent connections &SHOULD; limit the number of
1962   simultaneous connections that they maintain to a given server. A
1963   single-user client &SHOULD-NOT; maintain more than 2 connections with
1964   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1965   another server or proxy, where N is the number of simultaneously
1966   active users. These guidelines are intended to improve HTTP response
1967   times and avoid congestion.
1968</t>
1969</section>
1970</section>
1971
1972<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
1973
1974<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
1975<t>
1976   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
1977   flow control mechanisms to resolve temporary overloads, rather than
1978   terminating connections with the expectation that clients will retry.
1979   The latter technique can exacerbate network congestion.
1980</t>
1981</section>
1982
1983<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
1984<t>
1985   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
1986   the network connection for an error status while it is transmitting
1987   the request. If the client sees an error status, it &SHOULD;
1988   immediately cease transmitting the body. If the body is being sent
1989   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
1990   empty trailer &MAY; be used to prematurely mark the end of the message.
1991   If the body was preceded by a Content-Length header, the client &MUST;
1992   close the connection.
1993</t>
1994</section>
1995
1996<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
1997<t>
1998   The purpose of the 100 (Continue) status (see &status-100;) is to
1999   allow a client that is sending a request message with a request body
2000   to determine if the origin server is willing to accept the request
2001   (based on the request headers) before the client sends the request
2002   body. In some cases, it might either be inappropriate or highly
2003   inefficient for the client to send the body if the server will reject
2004   the message without looking at the body.
2005</t>
2006<t>
2007   Requirements for HTTP/1.1 clients:
2008  <list style="symbols">
2009    <t>
2010        If a client will wait for a 100 (Continue) response before
2011        sending the request body, it &MUST; send an Expect request-header
2012        field (&header-expect;) with the "100-continue" expectation.
2013    </t>
2014    <t>
2015        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2016        with the "100-continue" expectation if it does not intend
2017        to send a request body.
2018    </t>
2019  </list>
2020</t>
2021<t>
2022   Because of the presence of older implementations, the protocol allows
2023   ambiguous situations in which a client may send "Expect: 100-continue"
2024   without receiving either a 417 (Expectation Failed) status
2025   or a 100 (Continue) status. Therefore, when a client sends this
2026   header field to an origin server (possibly via a proxy) from which it
2027   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2028   for an indefinite period before sending the request body.
2029</t>
2030<t>
2031   Requirements for HTTP/1.1 origin servers:
2032  <list style="symbols">
2033    <t> Upon receiving a request which includes an Expect request-header
2034        field with the "100-continue" expectation, an origin server &MUST;
2035        either respond with 100 (Continue) status and continue to read
2036        from the input stream, or respond with a final status code. The
2037        origin server &MUST-NOT; wait for the request body before sending
2038        the 100 (Continue) response. If it responds with a final status
2039        code, it &MAY; close the transport connection or it &MAY; continue
2040        to read and discard the rest of the request.  It &MUST-NOT;
2041        perform the requested method if it returns a final status code.
2042    </t>
2043    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2044        the request message does not include an Expect request-header
2045        field with the "100-continue" expectation, and &MUST-NOT; send a
2046        100 (Continue) response if such a request comes from an HTTP/1.0
2047        (or earlier) client. There is an exception to this rule: for
2048        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2049        status in response to an HTTP/1.1 PUT or POST request that does
2050        not include an Expect request-header field with the "100-continue"
2051        expectation. This exception, the purpose of which is
2052        to minimize any client processing delays associated with an
2053        undeclared wait for 100 (Continue) status, applies only to
2054        HTTP/1.1 requests, and not to requests with any other HTTP-version
2055        value.
2056    </t>
2057    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2058        already received some or all of the request body for the
2059        corresponding request.
2060    </t>
2061    <t> An origin server that sends a 100 (Continue) response &MUST;
2062    ultimately send a final status code, once the request body is
2063        received and processed, unless it terminates the transport
2064        connection prematurely.
2065    </t>
2066    <t> If an origin server receives a request that does not include an
2067        Expect request-header field with the "100-continue" expectation,
2068        the request includes a request body, and the server responds
2069        with a final status code before reading the entire request body
2070        from the transport connection, then the server &SHOULD-NOT;  close
2071        the transport connection until it has read the entire request,
2072        or until the client closes the connection. Otherwise, the client
2073        might not reliably receive the response message. However, this
2074        requirement is not be construed as preventing a server from
2075        defending itself against denial-of-service attacks, or from
2076        badly broken client implementations.
2077      </t>
2078    </list>
2079</t>
2080<t>
2081   Requirements for HTTP/1.1 proxies:
2082  <list style="symbols">
2083    <t> If a proxy receives a request that includes an Expect request-header
2084        field with the "100-continue" expectation, and the proxy
2085        either knows that the next-hop server complies with HTTP/1.1 or
2086        higher, or does not know the HTTP version of the next-hop
2087        server, it &MUST; forward the request, including the Expect header
2088        field.
2089    </t>
2090    <t> If the proxy knows that the version of the next-hop server is
2091        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2092        respond with a 417 (Expectation Failed) status.
2093    </t>
2094    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2095        numbers received from recently-referenced next-hop servers.
2096    </t>
2097    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2098        request message was received from an HTTP/1.0 (or earlier)
2099        client and did not include an Expect request-header field with
2100        the "100-continue" expectation. This requirement overrides the
2101        general rule for forwarding of 1xx responses (see &status-1xx;).
2102    </t>
2103  </list>
2104</t>
2105</section>
2106
2107<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2108<t>
2109   If an HTTP/1.1 client sends a request which includes a request body,
2110   but which does not include an Expect request-header field with the
2111   "100-continue" expectation, and if the client is not directly
2112   connected to an HTTP/1.1 origin server, and if the client sees the
2113   connection close before receiving any status from the server, the
2114   client &SHOULD; retry the request.  If the client does retry this
2115   request, it &MAY; use the following "binary exponential backoff"
2116   algorithm to be assured of obtaining a reliable response:
2117  <list style="numbers">
2118    <t>
2119      Initiate a new connection to the server
2120    </t>
2121    <t>
2122      Transmit the request-headers
2123    </t>
2124    <t>
2125      Initialize a variable R to the estimated round-trip time to the
2126         server (e.g., based on the time it took to establish the
2127         connection), or to a constant value of 5 seconds if the round-trip
2128         time is not available.
2129    </t>
2130    <t>
2131       Compute T = R * (2**N), where N is the number of previous
2132         retries of this request.
2133    </t>
2134    <t>
2135       Wait either for an error response from the server, or for T
2136         seconds (whichever comes first)
2137    </t>
2138    <t>
2139       If no error response is received, after T seconds transmit the
2140         body of the request.
2141    </t>
2142    <t>
2143       If client sees that the connection is closed prematurely,
2144         repeat from step 1 until the request is accepted, an error
2145         response is received, or the user becomes impatient and
2146         terminates the retry process.
2147    </t>
2148  </list>
2149</t>
2150<t>
2151   If at any point an error status is received, the client
2152  <list style="symbols">
2153      <t>&SHOULD-NOT;  continue and</t>
2154
2155      <t>&SHOULD; close the connection if it has not completed sending the
2156        request message.</t>
2157    </list>
2158</t>
2159</section>
2160</section>
2161</section>
2162
2163
2164<section title="Header Field Definitions" anchor="header.fields">
2165<t>
2166   This section defines the syntax and semantics of HTTP/1.1 header fields
2167   related to message framing and transport protocols.
2168</t>
2169<t>
2170   For entity-header fields, both sender and recipient refer to either the
2171   client or the server, depending on who sends and who receives the entity.
2172</t>
2173
2174<section title="Connection" anchor="header.connection">
2175  <iref primary="true" item="Connection header" x:for-anchor=""/>
2176  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2177  <x:anchor-alias value="Connection"/>
2178  <x:anchor-alias value="connection-token"/>
2179  <x:anchor-alias value="Connection-v"/>
2180<t>
2181   The general-header field "Connection" allows the sender to specify
2182   options that are desired for that particular connection and &MUST-NOT;
2183   be communicated by proxies over further connections.
2184</t>
2185<t>
2186   The Connection header's value has the following grammar:
2187</t>
2188<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"/>
2189  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2190  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2191  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2192</artwork></figure>
2193<t>
2194   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2195   message is forwarded and, for each connection-token in this field,
2196   remove any header field(s) from the message with the same name as the
2197   connection-token. Connection options are signaled by the presence of
2198   a connection-token in the Connection header field, not by any
2199   corresponding additional header field(s), since the additional header
2200   field may not be sent if there are no parameters associated with that
2201   connection option.
2202</t>
2203<t>
2204   Message headers listed in the Connection header &MUST-NOT; include
2205   end-to-end headers, such as Cache-Control.
2206</t>
2207<t>
2208   HTTP/1.1 defines the "close" connection option for the sender to
2209   signal that the connection will be closed after completion of the
2210   response. For example,
2211</t>
2212<figure><artwork type="example">
2213  Connection: close
2214</artwork></figure>
2215<t>
2216   in either the request or the response header fields indicates that
2217   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2218   after the current request/response is complete.
2219</t>
2220<t>
2221   An HTTP/1.1 client that does not support persistent connections &MUST;
2222   include the "close" connection option in every request message.
2223</t>
2224<t>
2225   An HTTP/1.1 server that does not support persistent connections &MUST;
2226   include the "close" connection option in every response message that
2227   does not have a 1xx (informational) status code.
2228</t>
2229<t>
2230   A system receiving an HTTP/1.0 (or lower-version) message that
2231   includes a Connection header &MUST;, for each connection-token in this
2232   field, remove and ignore any header field(s) from the message with
2233   the same name as the connection-token. This protects against mistaken
2234   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2235</t>
2236</section>
2237
2238<section title="Content-Length" anchor="header.content-length">
2239  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2240  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2241  <x:anchor-alias value="Content-Length"/>
2242  <x:anchor-alias value="Content-Length-v"/>
2243<t>
2244   The entity-header field "Content-Length" indicates the size of the
2245   entity-body, in number of OCTETs, sent to the recipient or,
2246   in the case of the HEAD method, the size of the entity-body that
2247   would have been sent had the request been a GET.
2248</t>
2249<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2250  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2251  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2252</artwork></figure>
2253<t>
2254   An example is
2255</t>
2256<figure><artwork type="example">
2257  Content-Length: 3495
2258</artwork></figure>
2259<t>
2260   Applications &SHOULD; use this field to indicate the transfer-length of
2261   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2262</t>
2263<t>
2264   Any Content-Length greater than or equal to zero is a valid value.
2265   <xref target="message.length"/> describes how to determine the length of a message-body
2266   if a Content-Length is not given.
2267</t>
2268<t>
2269   Note that the meaning of this field is significantly different from
2270   the corresponding definition in MIME, where it is an optional field
2271   used within the "message/external-body" content-type. In HTTP, it
2272   &SHOULD; be sent whenever the message's length can be determined prior
2273   to being transferred, unless this is prohibited by the rules in
2274   <xref target="message.length"/>.
2275</t>
2276</section>
2277
2278<section title="Date" anchor="header.date">
2279  <iref primary="true" item="Date header" x:for-anchor=""/>
2280  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2281  <x:anchor-alias value="Date"/>
2282  <x:anchor-alias value="Date-v"/>
2283<t>
2284   The general-header field "Date" represents the date and time at which
2285   the message was originated, having the same semantics as orig-date in
2286   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2287   HTTP-date, as described in <xref target="full.date"/>;
2288   it &MUST; be sent in rfc1123-date format.
2289</t>
2290<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2291  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2292  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2293</artwork></figure>
2294<t>
2295   An example is
2296</t>
2297<figure><artwork type="example">
2298  Date: Tue, 15 Nov 1994 08:12:31 GMT
2299</artwork></figure>
2300<t>
2301   Origin servers &MUST; include a Date header field in all responses,
2302   except in these cases:
2303  <list style="numbers">
2304      <t>If the response status code is 100 (Continue) or 101 (Switching
2305         Protocols), the response &MAY; include a Date header field, at
2306         the server's option.</t>
2307
2308      <t>If the response status code conveys a server error, e.g. 500
2309         (Internal Server Error) or 503 (Service Unavailable), and it is
2310         inconvenient or impossible to generate a valid Date.</t>
2311
2312      <t>If the server does not have a clock that can provide a
2313         reasonable approximation of the current time, its responses
2314         &MUST-NOT; include a Date header field. In this case, the rules
2315         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2316  </list>
2317</t>
2318<t>
2319   A received message that does not have a Date header field &MUST; be
2320   assigned one by the recipient if the message will be cached by that
2321   recipient or gatewayed via a protocol which requires a Date. An HTTP
2322   implementation without a clock &MUST-NOT; cache responses without
2323   revalidating them on every use. An HTTP cache, especially a shared
2324   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2325   clock with a reliable external standard.
2326</t>
2327<t>
2328   Clients &SHOULD; only send a Date header field in messages that include
2329   an entity-body, as in the case of the PUT and POST requests, and even
2330   then it is optional. A client without a clock &MUST-NOT; send a Date
2331   header field in a request.
2332</t>
2333<t>
2334   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2335   time subsequent to the generation of the message. It &SHOULD; represent
2336   the best available approximation of the date and time of message
2337   generation, unless the implementation has no means of generating a
2338   reasonably accurate date and time. In theory, the date ought to
2339   represent the moment just before the entity is generated. In
2340   practice, the date can be generated at any time during the message
2341   origination without affecting its semantic value.
2342</t>
2343
2344<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2345<t>
2346   Some origin server implementations might not have a clock available.
2347   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2348   values to a response, unless these values were associated
2349   with the resource by a system or user with a reliable clock. It &MAY;
2350   assign an Expires value that is known, at or before server
2351   configuration time, to be in the past (this allows "pre-expiration"
2352   of responses without storing separate Expires values for each
2353   resource).
2354</t>
2355</section>
2356</section>
2357
2358<section title="Host" anchor="header.host">
2359  <iref primary="true" item="Host header" x:for-anchor=""/>
2360  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2361  <x:anchor-alias value="Host"/>
2362  <x:anchor-alias value="Host-v"/>
2363<t>
2364   The request-header field "Host" specifies the Internet host and port
2365   number of the resource being requested, as obtained from the original
2366   URI given by the user or referring resource (generally an http URI,
2367   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2368   the naming authority of the origin server or gateway given by the
2369   original URL. This allows the origin server or gateway to
2370   differentiate between internally-ambiguous URLs, such as the root "/"
2371   URL of a server for multiple host names on a single IP address.
2372</t>
2373<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2374  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2375  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2376</artwork></figure>
2377<t>
2378   A "host" without any trailing port information implies the default
2379   port for the service requested (e.g., "80" for an HTTP URL). For
2380   example, a request on the origin server for
2381   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2382</t>
2383<figure><artwork type="example">
2384  GET /pub/WWW/ HTTP/1.1
2385  Host: www.example.org
2386</artwork></figure>
2387<t>
2388   A client &MUST; include a Host header field in all HTTP/1.1 request
2389   messages. If the requested URI does not include an Internet host
2390   name for the service being requested, then the Host header field &MUST;
2391   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2392   request message it forwards does contain an appropriate Host header
2393   field that identifies the service being requested by the proxy. All
2394   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2395   status code to any HTTP/1.1 request message which lacks a Host header
2396   field.
2397</t>
2398<t>
2399   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2400   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2401   for other requirements relating to Host.
2402</t>
2403</section>
2404
2405<section title="TE" anchor="header.te">
2406  <iref primary="true" item="TE header" x:for-anchor=""/>
2407  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2408  <x:anchor-alias value="TE"/>
2409  <x:anchor-alias value="TE-v"/>
2410  <x:anchor-alias value="t-codings"/>
2411  <x:anchor-alias value="te-params"/>
2412  <x:anchor-alias value="te-ext"/>
2413<t>
2414   The request-header field "TE" indicates what extension transfer-codings
2415   it is willing to accept in the response and whether or not it is
2416   willing to accept trailer fields in a chunked transfer-coding. Its
2417   value may consist of the keyword "trailers" and/or a comma-separated
2418   list of extension transfer-coding names with optional accept
2419   parameters (as described in <xref target="transfer.codings"/>).
2420</t>
2421<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/>
2422  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2423  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2424  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2425  <x:ref>te-params</x:ref> = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> "q=" <x:ref>qvalue</x:ref> *( <x:ref>te-ext</x:ref> )
2426  <x:ref>te-ext</x:ref>    = <x:ref>OWS</x:ref> ";" <x:ref>OWS</x:ref> <x:ref>token</x:ref> [ "=" ( <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref> ) ]
2427</artwork></figure>
2428<t>
2429   The presence of the keyword "trailers" indicates that the client is
2430   willing to accept trailer fields in a chunked transfer-coding, as
2431   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2432   transfer-coding values even though it does not itself represent a
2433   transfer-coding.
2434</t>
2435<t>
2436   Examples of its use are:
2437</t>
2438<figure><artwork type="example">
2439  TE: deflate
2440  TE:
2441  TE: trailers, deflate;q=0.5
2442</artwork></figure>
2443<t>
2444   The TE header field only applies to the immediate connection.
2445   Therefore, the keyword &MUST; be supplied within a Connection header
2446   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2447</t>
2448<t>
2449   A server tests whether a transfer-coding is acceptable, according to
2450   a TE field, using these rules:
2451  <list style="numbers">
2452    <x:lt>
2453      <t>The "chunked" transfer-coding is always acceptable. If the
2454         keyword "trailers" is listed, the client indicates that it is
2455         willing to accept trailer fields in the chunked response on
2456         behalf of itself and any downstream clients. The implication is
2457         that, if given, the client is stating that either all
2458         downstream clients are willing to accept trailer fields in the
2459         forwarded response, or that it will attempt to buffer the
2460         response on behalf of downstream recipients.
2461      </t><t>
2462         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2463         chunked response such that a client can be assured of buffering
2464         the entire response.</t>
2465    </x:lt>
2466    <x:lt>
2467      <t>If the transfer-coding being tested is one of the transfer-codings
2468         listed in the TE field, then it is acceptable unless it
2469         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2470         qvalue of 0 means "not acceptable.")</t>
2471    </x:lt>
2472    <x:lt>
2473      <t>If multiple transfer-codings are acceptable, then the
2474         acceptable transfer-coding with the highest non-zero qvalue is
2475         preferred.  The "chunked" transfer-coding always has a qvalue
2476         of 1.</t>
2477    </x:lt>
2478  </list>
2479</t>
2480<t>
2481   If the TE field-value is empty or if no TE field is present, the only
2482   transfer-coding is "chunked". A message with no transfer-coding is
2483   always acceptable.
2484</t>
2485</section>
2486
2487<section title="Trailer" anchor="header.trailer">
2488  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2489  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2490  <x:anchor-alias value="Trailer"/>
2491  <x:anchor-alias value="Trailer-v"/>
2492<t>
2493   The general field "Trailer" indicates that the given set of
2494   header fields is present in the trailer of a message encoded with
2495   chunked transfer-coding.
2496</t>
2497<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2498  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2499  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2500</artwork></figure>
2501<t>
2502   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2503   message using chunked transfer-coding with a non-empty trailer. Doing
2504   so allows the recipient to know which header fields to expect in the
2505   trailer.
2506</t>
2507<t>
2508   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2509   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2510   trailer fields in a "chunked" transfer-coding.
2511</t>
2512<t>
2513   Message header fields listed in the Trailer header field &MUST-NOT;
2514   include the following header fields:
2515  <list style="symbols">
2516    <t>Transfer-Encoding</t>
2517    <t>Content-Length</t>
2518    <t>Trailer</t>
2519  </list>
2520</t>
2521</section>
2522
2523<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2524  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2525  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2526  <x:anchor-alias value="Transfer-Encoding"/>
2527  <x:anchor-alias value="Transfer-Encoding-v"/>
2528<t>
2529   The general-header "Transfer-Encoding" field indicates what (if any)
2530   type of transformation has been applied to the message body in order
2531   to safely transfer it between the sender and the recipient. This
2532   differs from the content-coding in that the transfer-coding is a
2533   property of the message, not of the entity.
2534</t>
2535<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2536  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2537                        <x:ref>Transfer-Encoding-v</x:ref>
2538  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2539</artwork></figure>
2540<t>
2541   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2542</t>
2543<figure><artwork type="example">
2544  Transfer-Encoding: chunked
2545</artwork></figure>
2546<t>
2547   If multiple encodings have been applied to an entity, the transfer-codings
2548   &MUST; be listed in the order in which they were applied.
2549   Additional information about the encoding parameters &MAY; be provided
2550   by other entity-header fields not defined by this specification.
2551</t>
2552<t>
2553   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2554   header.
2555</t>
2556</section>
2557
2558<section title="Upgrade" anchor="header.upgrade">
2559  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2560  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2561  <x:anchor-alias value="Upgrade"/>
2562  <x:anchor-alias value="Upgrade-v"/>
2563<t>
2564   The general-header "Upgrade" allows the client to specify what
2565   additional communication protocols it supports and would like to use
2566   if the server finds it appropriate to switch protocols. The server
2567   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2568   response to indicate which protocol(s) are being switched.
2569</t>
2570<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2571  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2572  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2573</artwork></figure>
2574<t>
2575   For example,
2576</t>
2577<figure><artwork type="example">
2578  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2579</artwork></figure>
2580<t>
2581   The Upgrade header field is intended to provide a simple mechanism
2582   for transition from HTTP/1.1 to some other, incompatible protocol. It
2583   does so by allowing the client to advertise its desire to use another
2584   protocol, such as a later version of HTTP with a higher major version
2585   number, even though the current request has been made using HTTP/1.1.
2586   This eases the difficult transition between incompatible protocols by
2587   allowing the client to initiate a request in the more commonly
2588   supported protocol while indicating to the server that it would like
2589   to use a "better" protocol if available (where "better" is determined
2590   by the server, possibly according to the nature of the method and/or
2591   resource being requested).
2592</t>
2593<t>
2594   The Upgrade header field only applies to switching application-layer
2595   protocols upon the existing transport-layer connection. Upgrade
2596   cannot be used to insist on a protocol change; its acceptance and use
2597   by the server is optional. The capabilities and nature of the
2598   application-layer communication after the protocol change is entirely
2599   dependent upon the new protocol chosen, although the first action
2600   after changing the protocol &MUST; be a response to the initial HTTP
2601   request containing the Upgrade header field.
2602</t>
2603<t>
2604   The Upgrade header field only applies to the immediate connection.
2605   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2606   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2607   HTTP/1.1 message.
2608</t>
2609<t>
2610   The Upgrade header field cannot be used to indicate a switch to a
2611   protocol on a different connection. For that purpose, it is more
2612   appropriate to use a 301, 302, 303, or 305 redirection response.
2613</t>
2614<t>
2615   This specification only defines the protocol name "HTTP" for use by
2616   the family of Hypertext Transfer Protocols, as defined by the HTTP
2617   version rules of <xref target="http.version"/> and future updates to this
2618   specification. Any token can be used as a protocol name; however, it
2619   will only be useful if both the client and server associate the name
2620   with the same protocol.
2621</t>
2622</section>
2623
2624<section title="Via" anchor="header.via">
2625  <iref primary="true" item="Via header" x:for-anchor=""/>
2626  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2627  <x:anchor-alias value="protocol-name"/>
2628  <x:anchor-alias value="protocol-version"/>
2629  <x:anchor-alias value="pseudonym"/>
2630  <x:anchor-alias value="received-by"/>
2631  <x:anchor-alias value="received-protocol"/>
2632  <x:anchor-alias value="Via"/>
2633  <x:anchor-alias value="Via-v"/>
2634<t>
2635   The general-header field "Via" &MUST; be used by gateways and proxies to
2636   indicate the intermediate protocols and recipients between the user
2637   agent and the server on requests, and between the origin server and
2638   the client on responses. It is analogous to the "Received" field defined in
2639   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2640   avoiding request loops, and identifying the protocol capabilities of
2641   all senders along the request/response chain.
2642</t>
2643<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"/>
2644  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2645  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2646                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2647  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2648  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2649  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2650  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2651  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2652</artwork></figure>
2653<t>
2654   The received-protocol indicates the protocol version of the message
2655   received by the server or client along each segment of the
2656   request/response chain. The received-protocol version is appended to
2657   the Via field value when the message is forwarded so that information
2658   about the protocol capabilities of upstream applications remains
2659   visible to all recipients.
2660</t>
2661<t>
2662   The protocol-name is optional if and only if it would be "HTTP". The
2663   received-by field is normally the host and optional port number of a
2664   recipient server or client that subsequently forwarded the message.
2665   However, if the real host is considered to be sensitive information,
2666   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2667   be assumed to be the default port of the received-protocol.
2668</t>
2669<t>
2670   Multiple Via field values represents each proxy or gateway that has
2671   forwarded the message. Each recipient &MUST; append its information
2672   such that the end result is ordered according to the sequence of
2673   forwarding applications.
2674</t>
2675<t>
2676   Comments &MAY; be used in the Via header field to identify the software
2677   of the recipient proxy or gateway, analogous to the User-Agent and
2678   Server header fields. However, all comments in the Via field are
2679   optional and &MAY; be removed by any recipient prior to forwarding the
2680   message.
2681</t>
2682<t>
2683   For example, a request message could be sent from an HTTP/1.0 user
2684   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2685   forward the request to a public proxy at p.example.net, which completes
2686   the request by forwarding it to the origin server at www.example.com.
2687   The request received by www.example.com would then have the following
2688   Via header field:
2689</t>
2690<figure><artwork type="example">
2691  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2692</artwork></figure>
2693<t>
2694   Proxies and gateways used as a portal through a network firewall
2695   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2696   the firewall region. This information &SHOULD; only be propagated if
2697   explicitly enabled. If not enabled, the received-by host of any host
2698   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2699   for that host.
2700</t>
2701<t>
2702   For organizations that have strong privacy requirements for hiding
2703   internal structures, a proxy &MAY; combine an ordered subsequence of
2704   Via header field entries with identical received-protocol values into
2705   a single such entry. For example,
2706</t>
2707<figure><artwork type="example">
2708  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2709</artwork></figure>
2710<t>
2711        could be collapsed to
2712</t>
2713<figure><artwork type="example">
2714  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2715</artwork></figure>
2716<t>
2717   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2718   under the same organizational control and the hosts have already been
2719   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2720   have different received-protocol values.
2721</t>
2722</section>
2723
2724</section>
2725
2726<section title="IANA Considerations" anchor="IANA.considerations">
2727<section title="Message Header Registration" anchor="message.header.registration">
2728<t>
2729   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2730   with the permanent registrations below (see <xref target="RFC3864"/>):
2731</t>
2732<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2733<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2734   <ttcol>Header Field Name</ttcol>
2735   <ttcol>Protocol</ttcol>
2736   <ttcol>Status</ttcol>
2737   <ttcol>Reference</ttcol>
2738
2739   <c>Connection</c>
2740   <c>http</c>
2741   <c>standard</c>
2742   <c>
2743      <xref target="header.connection"/>
2744   </c>
2745   <c>Content-Length</c>
2746   <c>http</c>
2747   <c>standard</c>
2748   <c>
2749      <xref target="header.content-length"/>
2750   </c>
2751   <c>Date</c>
2752   <c>http</c>
2753   <c>standard</c>
2754   <c>
2755      <xref target="header.date"/>
2756   </c>
2757   <c>Host</c>
2758   <c>http</c>
2759   <c>standard</c>
2760   <c>
2761      <xref target="header.host"/>
2762   </c>
2763   <c>TE</c>
2764   <c>http</c>
2765   <c>standard</c>
2766   <c>
2767      <xref target="header.te"/>
2768   </c>
2769   <c>Trailer</c>
2770   <c>http</c>
2771   <c>standard</c>
2772   <c>
2773      <xref target="header.trailer"/>
2774   </c>
2775   <c>Transfer-Encoding</c>
2776   <c>http</c>
2777   <c>standard</c>
2778   <c>
2779      <xref target="header.transfer-encoding"/>
2780   </c>
2781   <c>Upgrade</c>
2782   <c>http</c>
2783   <c>standard</c>
2784   <c>
2785      <xref target="header.upgrade"/>
2786   </c>
2787   <c>Via</c>
2788   <c>http</c>
2789   <c>standard</c>
2790   <c>
2791      <xref target="header.via"/>
2792   </c>
2793</texttable>
2794<!--(END)-->
2795<t>
2796   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2797</t>
2798</section>
2799
2800<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2801<t>
2802   The entry for the "http" URI Scheme in the registry located at
2803   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2804   should be updated to point to <xref target="http.uri"/> of this document
2805   (see <xref target="RFC4395"/>).
2806</t>
2807</section>
2808
2809<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2810<t>
2811   This document serves as the specification for the Internet media types
2812   "message/http" and "application/http". The following is to be registered with
2813   IANA (see <xref target="RFC4288"/>).
2814</t>
2815<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2816<iref item="Media Type" subitem="message/http" primary="true"/>
2817<iref item="message/http Media Type" primary="true"/>
2818<t>
2819   The message/http type can be used to enclose a single HTTP request or
2820   response message, provided that it obeys the MIME restrictions for all
2821   "message" types regarding line length and encodings.
2822</t>
2823<t>
2824  <list style="hanging" x:indent="12em">
2825    <t hangText="Type name:">
2826      message
2827    </t>
2828    <t hangText="Subtype name:">
2829      http
2830    </t>
2831    <t hangText="Required parameters:">
2832      none
2833    </t>
2834    <t hangText="Optional parameters:">
2835      version, msgtype
2836      <list style="hanging">
2837        <t hangText="version:">
2838          The HTTP-Version number of the enclosed message
2839          (e.g., "1.1"). If not present, the version can be
2840          determined from the first line of the body.
2841        </t>
2842        <t hangText="msgtype:">
2843          The message type -- "request" or "response". If not
2844          present, the type can be determined from the first
2845          line of the body.
2846        </t>
2847      </list>
2848    </t>
2849    <t hangText="Encoding considerations:">
2850      only "7bit", "8bit", or "binary" are permitted
2851    </t>
2852    <t hangText="Security considerations:">
2853      none
2854    </t>
2855    <t hangText="Interoperability considerations:">
2856      none
2857    </t>
2858    <t hangText="Published specification:">
2859      This specification (see <xref target="internet.media.type.message.http"/>).
2860    </t>
2861    <t hangText="Applications that use this media type:">
2862    </t>
2863    <t hangText="Additional information:">
2864      <list style="hanging">
2865        <t hangText="Magic number(s):">none</t>
2866        <t hangText="File extension(s):">none</t>
2867        <t hangText="Macintosh file type code(s):">none</t>
2868      </list>
2869    </t>
2870    <t hangText="Person and email address to contact for further information:">
2871      See Authors Section.
2872    </t>
2873                <t hangText="Intended usage:">
2874                  COMMON
2875    </t>
2876                <t hangText="Restrictions on usage:">
2877                  none
2878    </t>
2879    <t hangText="Author/Change controller:">
2880      IESG
2881    </t>
2882  </list>
2883</t>
2884</section>
2885<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2886<iref item="Media Type" subitem="application/http" primary="true"/>
2887<iref item="application/http Media Type" primary="true"/>
2888<t>
2889   The application/http type can be used to enclose a pipeline of one or more
2890   HTTP request or response messages (not intermixed).
2891</t>
2892<t>
2893  <list style="hanging" x:indent="12em">
2894    <t hangText="Type name:">
2895      application
2896    </t>
2897    <t hangText="Subtype name:">
2898      http
2899    </t>
2900    <t hangText="Required parameters:">
2901      none
2902    </t>
2903    <t hangText="Optional parameters:">
2904      version, msgtype
2905      <list style="hanging">
2906        <t hangText="version:">
2907          The HTTP-Version number of the enclosed messages
2908          (e.g., "1.1"). If not present, the version can be
2909          determined from the first line of the body.
2910        </t>
2911        <t hangText="msgtype:">
2912          The message type -- "request" or "response". If not
2913          present, the type can be determined from the first
2914          line of the body.
2915        </t>
2916      </list>
2917    </t>
2918    <t hangText="Encoding considerations:">
2919      HTTP messages enclosed by this type
2920      are in "binary" format; use of an appropriate
2921      Content-Transfer-Encoding is required when
2922      transmitted via E-mail.
2923    </t>
2924    <t hangText="Security considerations:">
2925      none
2926    </t>
2927    <t hangText="Interoperability considerations:">
2928      none
2929    </t>
2930    <t hangText="Published specification:">
2931      This specification (see <xref target="internet.media.type.application.http"/>).
2932    </t>
2933    <t hangText="Applications that use this media type:">
2934    </t>
2935    <t hangText="Additional information:">
2936      <list style="hanging">
2937        <t hangText="Magic number(s):">none</t>
2938        <t hangText="File extension(s):">none</t>
2939        <t hangText="Macintosh file type code(s):">none</t>
2940      </list>
2941    </t>
2942    <t hangText="Person and email address to contact for further information:">
2943      See Authors Section.
2944    </t>
2945                <t hangText="Intended usage:">
2946                  COMMON
2947    </t>
2948                <t hangText="Restrictions on usage:">
2949                  none
2950    </t>
2951    <t hangText="Author/Change controller:">
2952      IESG
2953    </t>
2954  </list>
2955</t>
2956</section>
2957</section>
2958
2959</section>
2960
2961<section title="Security Considerations" anchor="security.considerations">
2962<t>
2963   This section is meant to inform application developers, information
2964   providers, and users of the security limitations in HTTP/1.1 as
2965   described by this document. The discussion does not include
2966   definitive solutions to the problems revealed, though it does make
2967   some suggestions for reducing security risks.
2968</t>
2969
2970<section title="Personal Information" anchor="personal.information">
2971<t>
2972   HTTP clients are often privy to large amounts of personal information
2973   (e.g. the user's name, location, mail address, passwords, encryption
2974   keys, etc.), and &SHOULD; be very careful to prevent unintentional
2975   leakage of this information.
2976   We very strongly recommend that a convenient interface be provided
2977   for the user to control dissemination of such information, and that
2978   designers and implementors be particularly careful in this area.
2979   History shows that errors in this area often create serious security
2980   and/or privacy problems and generate highly adverse publicity for the
2981   implementor's company.
2982</t>
2983</section>
2984
2985<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
2986<t>
2987   A server is in the position to save personal data about a user's
2988   requests which might identify their reading patterns or subjects of
2989   interest. This information is clearly confidential in nature and its
2990   handling can be constrained by law in certain countries. People using
2991   HTTP to provide data are responsible for ensuring that
2992   such material is not distributed without the permission of any
2993   individuals that are identifiable by the published results.
2994</t>
2995</section>
2996
2997<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
2998<t>
2999   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3000   the documents returned by HTTP requests to be only those that were
3001   intended by the server administrators. If an HTTP server translates
3002   HTTP URIs directly into file system calls, the server &MUST; take
3003   special care not to serve files that were not intended to be
3004   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3005   other operating systems use ".." as a path component to indicate a
3006   directory level above the current one. On such a system, an HTTP
3007   server &MUST; disallow any such construct in the request-target if it
3008   would otherwise allow access to a resource outside those intended to
3009   be accessible via the HTTP server. Similarly, files intended for
3010   reference only internally to the server (such as access control
3011   files, configuration files, and script code) &MUST; be protected from
3012   inappropriate retrieval, since they might contain sensitive
3013   information. Experience has shown that minor bugs in such HTTP server
3014   implementations have turned into security risks.
3015</t>
3016</section>
3017
3018<section title="DNS Spoofing" anchor="dns.spoofing">
3019<t>
3020   Clients using HTTP rely heavily on the Domain Name Service, and are
3021   thus generally prone to security attacks based on the deliberate
3022   mis-association of IP addresses and DNS names. Clients need to be
3023   cautious in assuming the continuing validity of an IP number/DNS name
3024   association.
3025</t>
3026<t>
3027   In particular, HTTP clients &SHOULD; rely on their name resolver for
3028   confirmation of an IP number/DNS name association, rather than
3029   caching the result of previous host name lookups. Many platforms
3030   already can cache host name lookups locally when appropriate, and
3031   they &SHOULD; be configured to do so. It is proper for these lookups to
3032   be cached, however, only when the TTL (Time To Live) information
3033   reported by the name server makes it likely that the cached
3034   information will remain useful.
3035</t>
3036<t>
3037   If HTTP clients cache the results of host name lookups in order to
3038   achieve a performance improvement, they &MUST; observe the TTL
3039   information reported by DNS.
3040</t>
3041<t>
3042   If HTTP clients do not observe this rule, they could be spoofed when
3043   a previously-accessed server's IP address changes. As network
3044   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3045   possibility of this form of attack will grow. Observing this
3046   requirement thus reduces this potential security vulnerability.
3047</t>
3048<t>
3049   This requirement also improves the load-balancing behavior of clients
3050   for replicated servers using the same DNS name and reduces the
3051   likelihood of a user's experiencing failure in accessing sites which
3052   use that strategy.
3053</t>
3054</section>
3055
3056<section title="Proxies and Caching" anchor="attack.proxies">
3057<t>
3058   By their very nature, HTTP proxies are men-in-the-middle, and
3059   represent an opportunity for man-in-the-middle attacks. Compromise of
3060   the systems on which the proxies run can result in serious security
3061   and privacy problems. Proxies have access to security-related
3062   information, personal information about individual users and
3063   organizations, and proprietary information belonging to users and
3064   content providers. A compromised proxy, or a proxy implemented or
3065   configured without regard to security and privacy considerations,
3066   might be used in the commission of a wide range of potential attacks.
3067</t>
3068<t>
3069   Proxy operators should protect the systems on which proxies run as
3070   they would protect any system that contains or transports sensitive
3071   information. In particular, log information gathered at proxies often
3072   contains highly sensitive personal information, and/or information
3073   about organizations. Log information should be carefully guarded, and
3074   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3075</t>
3076<t>
3077   Proxy implementors should consider the privacy and security
3078   implications of their design and coding decisions, and of the
3079   configuration options they provide to proxy operators (especially the
3080   default configuration).
3081</t>
3082<t>
3083   Users of a proxy need to be aware that they are no trustworthier than
3084   the people who run the proxy; HTTP itself cannot solve this problem.
3085</t>
3086<t>
3087   The judicious use of cryptography, when appropriate, may suffice to
3088   protect against a broad range of security and privacy attacks. Such
3089   cryptography is beyond the scope of the HTTP/1.1 specification.
3090</t>
3091</section>
3092
3093<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3094<t>
3095   They exist. They are hard to defend against. Research continues.
3096   Beware.
3097</t>
3098</section>
3099</section>
3100
3101<section title="Acknowledgments" anchor="ack">
3102<t>
3103   HTTP has evolved considerably over the years. It has
3104   benefited from a large and active developer community--the many
3105   people who have participated on the www-talk mailing list--and it is
3106   that community which has been most responsible for the success of
3107   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3108   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3109   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3110   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3111   VanHeyningen deserve special recognition for their efforts in
3112   defining early aspects of the protocol.
3113</t>
3114<t>
3115   This document has benefited greatly from the comments of all those
3116   participating in the HTTP-WG. In addition to those already mentioned,
3117   the following individuals have contributed to this specification:
3118</t>
3119<t>
3120   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3121   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3122   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3123   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3124   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3125   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3126   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3127   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3128   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3129   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3130   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3131   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3132   Josh Cohen.
3133</t>
3134<t>
3135   Thanks to the "cave men" of Palo Alto. You know who you are.
3136</t>
3137<t>
3138   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3139   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3140   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3141   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3142   Larry Masinter for their help. And thanks go particularly to Jeff
3143   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3144</t>
3145<t>
3146   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3147   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3148   discovery of many of the problems that this document attempts to
3149   rectify.
3150</t>
3151<t>
3152   This specification makes heavy use of the augmented BNF and generic
3153   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3154   reuses many of the definitions provided by Nathaniel Borenstein and
3155   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3156   specification will help reduce past confusion over the relationship
3157   between HTTP and Internet mail message formats.
3158</t>
3159</section>
3160
3161</middle>
3162<back>
3163
3164<references title="Normative References">
3165
3166<reference anchor="ISO-8859-1">
3167  <front>
3168    <title>
3169     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3170    </title>
3171    <author>
3172      <organization>International Organization for Standardization</organization>
3173    </author>
3174    <date year="1998"/>
3175  </front>
3176  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3177</reference>
3178
3179<reference anchor="Part2">
3180  <front>
3181    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3182    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3183      <organization abbrev="Day Software">Day Software</organization>
3184      <address><email>fielding@gbiv.com</email></address>
3185    </author>
3186    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3187      <organization>One Laptop per Child</organization>
3188      <address><email>jg@laptop.org</email></address>
3189    </author>
3190    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3191      <organization abbrev="HP">Hewlett-Packard Company</organization>
3192      <address><email>JeffMogul@acm.org</email></address>
3193    </author>
3194    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3195      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3196      <address><email>henrikn@microsoft.com</email></address>
3197    </author>
3198    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3199      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3200      <address><email>LMM@acm.org</email></address>
3201    </author>
3202    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3203      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3204      <address><email>paulle@microsoft.com</email></address>
3205    </author>
3206    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3207      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3208      <address><email>timbl@w3.org</email></address>
3209    </author>
3210    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3211      <organization abbrev="W3C">World Wide Web Consortium</organization>
3212      <address><email>ylafon@w3.org</email></address>
3213    </author>
3214    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3215      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3216      <address><email>julian.reschke@greenbytes.de</email></address>
3217    </author>
3218    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3219  </front>
3220  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3221  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3222</reference>
3223
3224<reference anchor="Part3">
3225  <front>
3226    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3227    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3228      <organization abbrev="Day Software">Day Software</organization>
3229      <address><email>fielding@gbiv.com</email></address>
3230    </author>
3231    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3232      <organization>One Laptop per Child</organization>
3233      <address><email>jg@laptop.org</email></address>
3234    </author>
3235    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3236      <organization abbrev="HP">Hewlett-Packard Company</organization>
3237      <address><email>JeffMogul@acm.org</email></address>
3238    </author>
3239    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3240      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3241      <address><email>henrikn@microsoft.com</email></address>
3242    </author>
3243    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3244      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3245      <address><email>LMM@acm.org</email></address>
3246    </author>
3247    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3248      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3249      <address><email>paulle@microsoft.com</email></address>
3250    </author>
3251    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3252      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3253      <address><email>timbl@w3.org</email></address>
3254    </author>
3255    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3256      <organization abbrev="W3C">World Wide Web Consortium</organization>
3257      <address><email>ylafon@w3.org</email></address>
3258    </author>
3259    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3260      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3261      <address><email>julian.reschke@greenbytes.de</email></address>
3262    </author>
3263    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3264  </front>
3265  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3266  <x:source href="p3-payload.xml" basename="p3-payload"/>
3267</reference>
3268
3269<reference anchor="Part5">
3270  <front>
3271    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3272    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3273      <organization abbrev="Day Software">Day Software</organization>
3274      <address><email>fielding@gbiv.com</email></address>
3275    </author>
3276    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3277      <organization>One Laptop per Child</organization>
3278      <address><email>jg@laptop.org</email></address>
3279    </author>
3280    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3281      <organization abbrev="HP">Hewlett-Packard Company</organization>
3282      <address><email>JeffMogul@acm.org</email></address>
3283    </author>
3284    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3285      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3286      <address><email>henrikn@microsoft.com</email></address>
3287    </author>
3288    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3289      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3290      <address><email>LMM@acm.org</email></address>
3291    </author>
3292    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3293      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3294      <address><email>paulle@microsoft.com</email></address>
3295    </author>
3296    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3297      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3298      <address><email>timbl@w3.org</email></address>
3299    </author>
3300    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3301      <organization abbrev="W3C">World Wide Web Consortium</organization>
3302      <address><email>ylafon@w3.org</email></address>
3303    </author>
3304    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3305      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3306      <address><email>julian.reschke@greenbytes.de</email></address>
3307    </author>
3308    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3309  </front>
3310  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3311  <x:source href="p5-range.xml" basename="p5-range"/>
3312</reference>
3313
3314<reference anchor="Part6">
3315  <front>
3316    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3317    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3318      <organization abbrev="Day Software">Day Software</organization>
3319      <address><email>fielding@gbiv.com</email></address>
3320    </author>
3321    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3322      <organization>One Laptop per Child</organization>
3323      <address><email>jg@laptop.org</email></address>
3324    </author>
3325    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3326      <organization abbrev="HP">Hewlett-Packard Company</organization>
3327      <address><email>JeffMogul@acm.org</email></address>
3328    </author>
3329    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3330      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3331      <address><email>henrikn@microsoft.com</email></address>
3332    </author>
3333    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3334      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3335      <address><email>LMM@acm.org</email></address>
3336    </author>
3337    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3338      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3339      <address><email>paulle@microsoft.com</email></address>
3340    </author>
3341    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3342      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3343      <address><email>timbl@w3.org</email></address>
3344    </author>
3345    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3346      <organization abbrev="W3C">World Wide Web Consortium</organization>
3347      <address><email>ylafon@w3.org</email></address>
3348    </author>
3349    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3350      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3351      <address><email>julian.reschke@greenbytes.de</email></address>
3352    </author>
3353    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3354  </front>
3355  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3356  <x:source href="p6-cache.xml" basename="p6-cache"/>
3357</reference>
3358
3359<reference anchor="RFC5234">
3360  <front>
3361    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3362    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3363      <organization>Brandenburg InternetWorking</organization>
3364      <address>
3365      <postal>
3366      <street>675 Spruce Dr.</street>
3367      <city>Sunnyvale</city>
3368      <region>CA</region>
3369      <code>94086</code>
3370      <country>US</country></postal>
3371      <phone>+1.408.246.8253</phone>
3372      <email>dcrocker@bbiw.net</email></address> 
3373    </author>
3374    <author initials="P." surname="Overell" fullname="Paul Overell">
3375      <organization>THUS plc.</organization>
3376      <address>
3377      <postal>
3378      <street>1/2 Berkeley Square</street>
3379      <street>99 Berkely Street</street>
3380      <city>Glasgow</city>
3381      <code>G3 7HR</code>
3382      <country>UK</country></postal>
3383      <email>paul.overell@thus.net</email></address>
3384    </author>
3385    <date month="January" year="2008"/>
3386  </front>
3387  <seriesInfo name="STD" value="68"/>
3388  <seriesInfo name="RFC" value="5234"/>
3389</reference>
3390
3391<reference anchor="RFC2119">
3392  <front>
3393    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3394    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3395      <organization>Harvard University</organization>
3396      <address><email>sob@harvard.edu</email></address>
3397    </author>
3398    <date month="March" year="1997"/>
3399  </front>
3400  <seriesInfo name="BCP" value="14"/>
3401  <seriesInfo name="RFC" value="2119"/>
3402</reference>
3403
3404<reference anchor="RFC3986">
3405 <front>
3406  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3407  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3408    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3409    <address>
3410       <email>timbl@w3.org</email>
3411       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3412    </address>
3413  </author>
3414  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3415    <organization abbrev="Day Software">Day Software</organization>
3416    <address>
3417      <email>fielding@gbiv.com</email>
3418      <uri>http://roy.gbiv.com/</uri>
3419    </address>
3420  </author>
3421  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3422    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3423    <address>
3424      <email>LMM@acm.org</email>
3425      <uri>http://larry.masinter.net/</uri>
3426    </address>
3427  </author>
3428  <date month='January' year='2005'></date>
3429 </front>
3430 <seriesInfo name="RFC" value="3986"/>
3431 <seriesInfo name="STD" value="66"/>
3432</reference>
3433
3434<reference anchor="USASCII">
3435  <front>
3436    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3437    <author>
3438      <organization>American National Standards Institute</organization>
3439    </author>
3440    <date year="1986"/>
3441  </front>
3442  <seriesInfo name="ANSI" value="X3.4"/>
3443</reference>
3444
3445</references>
3446
3447<references title="Informative References">
3448
3449<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3450  <front>
3451    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3452    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3453      <organization/>
3454    </author>
3455    <author initials="J." surname="Gettys" fullname="J. Gettys">
3456      <organization/>
3457    </author>
3458    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3459      <organization/>
3460    </author>
3461    <author initials="H." surname="Lie" fullname="H. Lie">
3462      <organization/>
3463    </author>
3464    <author initials="C." surname="Lilley" fullname="C. Lilley">
3465      <organization/>
3466    </author>
3467    <date year="1997" month="September"/>
3468  </front>
3469  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3470</reference>
3471
3472<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3473  <front>
3474    <title>Improving HTTP Latency</title>
3475    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3476      <organization/>
3477    </author>
3478    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3479      <organization/>
3480    </author>
3481    <date year="1995" month="December"/>
3482  </front>
3483  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3484</reference>
3485
3486<reference anchor="RFC1123">
3487  <front>
3488    <title>Requirements for Internet Hosts - Application and Support</title>
3489    <author initials="R." surname="Braden" fullname="Robert Braden">
3490      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3491      <address><email>Braden@ISI.EDU</email></address>
3492    </author>
3493    <date month="October" year="1989"/>
3494  </front>
3495  <seriesInfo name="STD" value="3"/>
3496  <seriesInfo name="RFC" value="1123"/>
3497</reference>
3498
3499<reference anchor="RFC1305">
3500  <front>
3501    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3502    <author initials="D." surname="Mills" fullname="David L. Mills">
3503      <organization>University of Delaware, Electrical Engineering Department</organization>
3504      <address><email>mills@udel.edu</email></address>
3505    </author>
3506    <date month="March" year="1992"/>
3507  </front>
3508  <seriesInfo name="RFC" value="1305"/>
3509</reference>
3510
3511<reference anchor="RFC1900">
3512  <front>
3513    <title>Renumbering Needs Work</title>
3514    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3515      <organization>CERN, Computing and Networks Division</organization>
3516      <address><email>brian@dxcoms.cern.ch</email></address>
3517    </author>
3518    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3519      <organization>cisco Systems</organization>
3520      <address><email>yakov@cisco.com</email></address>
3521    </author>
3522    <date month="February" year="1996"/>
3523  </front>
3524  <seriesInfo name="RFC" value="1900"/>
3525</reference>
3526
3527<reference anchor="RFC1945">
3528  <front>
3529    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3530    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3531      <organization>MIT, Laboratory for Computer Science</organization>
3532      <address><email>timbl@w3.org</email></address>
3533    </author>
3534    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3535      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3536      <address><email>fielding@ics.uci.edu</email></address>
3537    </author>
3538    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3539      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3540      <address><email>frystyk@w3.org</email></address>
3541    </author>
3542    <date month="May" year="1996"/>
3543  </front>
3544  <seriesInfo name="RFC" value="1945"/>
3545</reference>
3546
3547<reference anchor="RFC2045">
3548  <front>
3549    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3550    <author initials="N." surname="Freed" fullname="Ned Freed">
3551      <organization>Innosoft International, Inc.</organization>
3552      <address><email>ned@innosoft.com</email></address>
3553    </author>
3554    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3555      <organization>First Virtual Holdings</organization>
3556      <address><email>nsb@nsb.fv.com</email></address>
3557    </author>
3558    <date month="November" year="1996"/>
3559  </front>
3560  <seriesInfo name="RFC" value="2045"/>
3561</reference>
3562
3563<reference anchor="RFC2047">
3564  <front>
3565    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3566    <author initials="K." surname="Moore" fullname="Keith Moore">
3567      <organization>University of Tennessee</organization>
3568      <address><email>moore@cs.utk.edu</email></address>
3569    </author>
3570    <date month="November" year="1996"/>
3571  </front>
3572  <seriesInfo name="RFC" value="2047"/>
3573</reference>
3574
3575<reference anchor="RFC2068">
3576  <front>
3577    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3578    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3579      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3580      <address><email>fielding@ics.uci.edu</email></address>
3581    </author>
3582    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3583      <organization>MIT Laboratory for Computer Science</organization>
3584      <address><email>jg@w3.org</email></address>
3585    </author>
3586    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3587      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3588      <address><email>mogul@wrl.dec.com</email></address>
3589    </author>
3590    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3591      <organization>MIT Laboratory for Computer Science</organization>
3592      <address><email>frystyk@w3.org</email></address>
3593    </author>
3594    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3595      <organization>MIT Laboratory for Computer Science</organization>
3596      <address><email>timbl@w3.org</email></address>
3597    </author>
3598    <date month="January" year="1997"/>
3599  </front>
3600  <seriesInfo name="RFC" value="2068"/>
3601</reference>
3602
3603<reference anchor='RFC2109'>
3604  <front>
3605    <title>HTTP State Management Mechanism</title>
3606    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3607      <organization>Bell Laboratories, Lucent Technologies</organization>
3608      <address><email>dmk@bell-labs.com</email></address>
3609    </author>
3610    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3611      <organization>Netscape Communications Corp.</organization>
3612      <address><email>montulli@netscape.com</email></address>
3613    </author>
3614    <date year='1997' month='February' />
3615  </front>
3616  <seriesInfo name='RFC' value='2109' />
3617</reference>
3618
3619<reference anchor="RFC2145">
3620  <front>
3621    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3622    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3623      <organization>Western Research Laboratory</organization>
3624      <address><email>mogul@wrl.dec.com</email></address>
3625    </author>
3626    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3627      <organization>Department of Information and Computer Science</organization>
3628      <address><email>fielding@ics.uci.edu</email></address>
3629    </author>
3630    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3631      <organization>MIT Laboratory for Computer Science</organization>
3632      <address><email>jg@w3.org</email></address>
3633    </author>
3634    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3635      <organization>W3 Consortium</organization>
3636      <address><email>frystyk@w3.org</email></address>
3637    </author>
3638    <date month="May" year="1997"/>
3639  </front>
3640  <seriesInfo name="RFC" value="2145"/>
3641</reference>
3642
3643<reference anchor="RFC2616">
3644  <front>
3645    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3646    <author initials="R." surname="Fielding" fullname="R. Fielding">
3647      <organization>University of California, Irvine</organization>
3648      <address><email>fielding@ics.uci.edu</email></address>
3649    </author>
3650    <author initials="J." surname="Gettys" fullname="J. Gettys">
3651      <organization>W3C</organization>
3652      <address><email>jg@w3.org</email></address>
3653    </author>
3654    <author initials="J." surname="Mogul" fullname="J. Mogul">
3655      <organization>Compaq Computer Corporation</organization>
3656      <address><email>mogul@wrl.dec.com</email></address>
3657    </author>
3658    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3659      <organization>MIT Laboratory for Computer Science</organization>
3660      <address><email>frystyk@w3.org</email></address>
3661    </author>
3662    <author initials="L." surname="Masinter" fullname="L. Masinter">
3663      <organization>Xerox Corporation</organization>
3664      <address><email>masinter@parc.xerox.com</email></address>
3665    </author>
3666    <author initials="P." surname="Leach" fullname="P. Leach">
3667      <organization>Microsoft Corporation</organization>
3668      <address><email>paulle@microsoft.com</email></address>
3669    </author>
3670    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3671      <organization>W3C</organization>
3672      <address><email>timbl@w3.org</email></address>
3673    </author>
3674    <date month="June" year="1999"/>
3675  </front>
3676  <seriesInfo name="RFC" value="2616"/>
3677</reference>
3678
3679<reference anchor='RFC2818'>
3680  <front>
3681    <title>HTTP Over TLS</title>
3682    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3683      <organization>RTFM, Inc.</organization>
3684      <address><email>ekr@rtfm.com</email></address>
3685    </author>
3686    <date year='2000' month='May' />
3687  </front>
3688  <seriesInfo name='RFC' value='2818' />
3689</reference>
3690
3691<reference anchor='RFC2965'>
3692  <front>
3693    <title>HTTP State Management Mechanism</title>
3694    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3695      <organization>Bell Laboratories, Lucent Technologies</organization>
3696      <address><email>dmk@bell-labs.com</email></address>
3697    </author>
3698    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3699      <organization>Epinions.com, Inc.</organization>
3700      <address><email>lou@montulli.org</email></address>
3701    </author>
3702    <date year='2000' month='October' />
3703  </front>
3704  <seriesInfo name='RFC' value='2965' />
3705</reference>
3706
3707<reference anchor='RFC3864'>
3708  <front>
3709    <title>Registration Procedures for Message Header Fields</title>
3710    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3711      <organization>Nine by Nine</organization>
3712      <address><email>GK-IETF@ninebynine.org</email></address>
3713    </author>
3714    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3715      <organization>BEA Systems</organization>
3716      <address><email>mnot@pobox.com</email></address>
3717    </author>
3718    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3719      <organization>HP Labs</organization>
3720      <address><email>JeffMogul@acm.org</email></address>
3721    </author>
3722    <date year='2004' month='September' />
3723  </front>
3724  <seriesInfo name='BCP' value='90' />
3725  <seriesInfo name='RFC' value='3864' />
3726</reference>
3727
3728<reference anchor="RFC4288">
3729  <front>
3730    <title>Media Type Specifications and Registration Procedures</title>
3731    <author initials="N." surname="Freed" fullname="N. Freed">
3732      <organization>Sun Microsystems</organization>
3733      <address>
3734        <email>ned.freed@mrochek.com</email>
3735      </address>
3736    </author>
3737    <author initials="J." surname="Klensin" fullname="J. Klensin">
3738      <organization/>
3739      <address>
3740        <email>klensin+ietf@jck.com</email>
3741      </address>
3742    </author>
3743    <date year="2005" month="December"/>
3744  </front>
3745  <seriesInfo name="BCP" value="13"/>
3746  <seriesInfo name="RFC" value="4288"/>
3747</reference>
3748
3749<reference anchor='RFC4395'>
3750  <front>
3751    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3752    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3753      <organization>AT&amp;T Laboratories</organization>
3754      <address>
3755        <email>tony+urireg@maillennium.att.com</email>
3756      </address>
3757    </author>
3758    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3759      <organization>Qualcomm, Inc.</organization>
3760      <address>
3761        <email>hardie@qualcomm.com</email>
3762      </address>
3763    </author>
3764    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3765      <organization>Adobe Systems</organization>
3766      <address>
3767        <email>LMM@acm.org</email>
3768      </address>
3769    </author>
3770    <date year='2006' month='February' />
3771  </front>
3772  <seriesInfo name='BCP' value='115' />
3773  <seriesInfo name='RFC' value='4395' />
3774</reference>
3775
3776<reference anchor="RFC5322">
3777  <front>
3778    <title>Internet Message Format</title>
3779    <author initials="P." surname="Resnick" fullname="P. Resnick">
3780      <organization>Qualcomm Incorporated</organization>
3781    </author>
3782    <date year="2008" month="October"/>
3783  </front> 
3784  <seriesInfo name="RFC" value="5322"/>
3785</reference>
3786
3787<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3788  <front>
3789    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3790    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3791      <organization/>
3792    </author>
3793    <date year="2001" month="November"/>
3794  </front>
3795  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3796</reference>
3797
3798<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3799  <front>
3800  <title>Analysis of HTTP Performance Problems</title>
3801  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3802    <organization/>
3803  </author>
3804  <date/>
3805  </front>
3806</reference>
3807
3808<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3809  <front>
3810  <title>Analysis of HTTP Performance</title>
3811  <author initials="J." surname="Touch" fullname="Joe Touch">
3812    <organization>USC/Information Sciences Institute</organization>
3813    <address><email>touch@isi.edu</email></address>
3814  </author>
3815  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3816    <organization>USC/Information Sciences Institute</organization>
3817    <address><email>johnh@isi.edu</email></address>
3818  </author>
3819  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3820    <organization>USC/Information Sciences Institute</organization>
3821    <address><email>katia@isi.edu</email></address>
3822  </author>
3823  <date year="1998" month="Aug"/>
3824  </front>
3825  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3826  <annotation>(original report dated Aug. 1996)</annotation>
3827</reference>
3828
3829</references>
3830
3831
3832<section title="Tolerant Applications" anchor="tolerant.applications">
3833<t>
3834   Although this document specifies the requirements for the generation
3835   of HTTP/1.1 messages, not all applications will be correct in their
3836   implementation. We therefore recommend that operational applications
3837   be tolerant of deviations whenever those deviations can be
3838   interpreted unambiguously.
3839</t>
3840<t>
3841   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3842   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3843   accept any amount of WSP characters between fields, even though
3844   only a single SP is required.
3845</t>
3846<t>
3847   The line terminator for message-header fields is the sequence CRLF.
3848   However, we recommend that applications, when parsing such headers,
3849   recognize a single LF as a line terminator and ignore the leading CR.
3850</t>
3851<t>
3852   The character set of an entity-body &SHOULD; be labeled as the lowest
3853   common denominator of the character codes used within that body, with
3854   the exception that not labeling the entity is preferred over labeling
3855   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3856</t>
3857<t>
3858   Additional rules for requirements on parsing and encoding of dates
3859   and other potential problems with date encodings include:
3860</t>
3861<t>
3862  <list style="symbols">
3863     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3864        which appears to be more than 50 years in the future is in fact
3865        in the past (this helps solve the "year 2000" problem).</t>
3866
3867     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3868        Expires date as earlier than the proper value, but &MUST-NOT;
3869        internally represent a parsed Expires date as later than the
3870        proper value.</t>
3871
3872     <t>All expiration-related calculations &MUST; be done in GMT. The
3873        local time zone &MUST-NOT; influence the calculation or comparison
3874        of an age or expiration time.</t>
3875
3876     <t>If an HTTP header incorrectly carries a date value with a time
3877        zone other than GMT, it &MUST; be converted into GMT using the
3878        most conservative possible conversion.</t>
3879  </list>
3880</t>
3881</section>
3882
3883<section title="Compatibility with Previous Versions" anchor="compatibility">
3884<t>
3885   HTTP has been in use by the World-Wide Web global information initiative
3886   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3887   was a simple protocol for hypertext data transfer across the Internet
3888   with only a single method and no metadata.
3889   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3890   methods and MIME-like messaging that could include metadata about the data
3891   transferred and modifiers on the request/response semantics. However,
3892   HTTP/1.0 did not sufficiently take into consideration the effects of
3893   hierarchical proxies, caching, the need for persistent connections, or
3894   name-based virtual hosts. The proliferation of incompletely-implemented
3895   applications calling themselves "HTTP/1.0" further necessitated a
3896   protocol version change in order for two communicating applications
3897   to determine each other's true capabilities.
3898</t>
3899<t>
3900   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3901   requirements that enable reliable implementations, adding only
3902   those new features that will either be safely ignored by an HTTP/1.0
3903   recipient or only sent when communicating with a party advertising
3904   compliance with HTTP/1.1.
3905</t>
3906<t>
3907   It is beyond the scope of a protocol specification to mandate
3908   compliance with previous versions. HTTP/1.1 was deliberately
3909   designed, however, to make supporting previous versions easy. It is
3910   worth noting that, at the time of composing this specification
3911   (1996), we would expect commercial HTTP/1.1 servers to:
3912  <list style="symbols">
3913     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3914        1.1 requests;</t>
3915
3916     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3917        1.1;</t>
3918
3919     <t>respond appropriately with a message in the same major version
3920        used by the client.</t>
3921  </list>
3922</t>
3923<t>
3924   And we would expect HTTP/1.1 clients to:
3925  <list style="symbols">
3926     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3927        responses;</t>
3928
3929     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3930        1.1.</t>
3931  </list>
3932</t>
3933<t>
3934   For most implementations of HTTP/1.0, each connection is established
3935   by the client prior to the request and closed by the server after
3936   sending the response. Some implementations implement the Keep-Alive
3937   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3938</t>
3939
3940<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3941<t>
3942   This section summarizes major differences between versions HTTP/1.0
3943   and HTTP/1.1.
3944</t>
3945
3946<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">
3947<t>
3948   The requirements that clients and servers support the Host request-header,
3949   report an error if the Host request-header (<xref target="header.host"/>) is
3950   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3951   are among the most important changes defined by this
3952   specification.
3953</t>
3954<t>
3955   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3956   addresses and servers; there was no other established mechanism for
3957   distinguishing the intended server of a request than the IP address
3958   to which that request was directed. The changes outlined above will
3959   allow the Internet, once older HTTP clients are no longer common, to
3960   support multiple Web sites from a single IP address, greatly
3961   simplifying large operational Web servers, where allocation of many
3962   IP addresses to a single host has created serious problems. The
3963   Internet will also be able to recover the IP addresses that have been
3964   allocated for the sole purpose of allowing special-purpose domain
3965   names to be used in root-level HTTP URLs. Given the rate of growth of
3966   the Web, and the number of servers already deployed, it is extremely
3967   important that all implementations of HTTP (including updates to
3968   existing HTTP/1.0 applications) correctly implement these
3969   requirements:
3970  <list style="symbols">
3971     <t>Both clients and servers &MUST; support the Host request-header.</t>
3972
3973     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
3974
3975     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
3976        request does not include a Host request-header.</t>
3977
3978     <t>Servers &MUST; accept absolute URIs.</t>
3979  </list>
3980</t>
3981</section>
3982</section>
3983
3984<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
3985<t>
3986   Some clients and servers might wish to be compatible with some
3987   previous implementations of persistent connections in HTTP/1.0
3988   clients and servers. Persistent connections in HTTP/1.0 are
3989   explicitly negotiated as they are not the default behavior. HTTP/1.0
3990   experimental implementations of persistent connections are faulty,
3991   and the new facilities in HTTP/1.1 are designed to rectify these
3992   problems. The problem was that some existing 1.0 clients may be
3993   sending Keep-Alive to a proxy server that doesn't understand
3994   Connection, which would then erroneously forward it to the next
3995   inbound server, which would establish the Keep-Alive connection and
3996   result in a hung HTTP/1.0 proxy waiting for the close on the
3997   response. The result is that HTTP/1.0 clients must be prevented from
3998   using Keep-Alive when talking to proxies.
3999</t>
4000<t>
4001   However, talking to proxies is the most important use of persistent
4002   connections, so that prohibition is clearly unacceptable. Therefore,
4003   we need some other mechanism for indicating a persistent connection
4004   is desired, which is safe to use even when talking to an old proxy
4005   that ignores Connection. Persistent connections are the default for
4006   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4007   declaring non-persistence. See <xref target="header.connection"/>.
4008</t>
4009<t>
4010   The original HTTP/1.0 form of persistent connections (the Connection:
4011   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4012</t>
4013</section>
4014
4015<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4016<t>
4017   This specification has been carefully audited to correct and
4018   disambiguate key word usage; RFC 2068 had many problems in respect to
4019   the conventions laid out in <xref target="RFC2119"/>.
4020</t>
4021<t>
4022   Transfer-coding and message lengths all interact in ways that
4023   required fixing exactly when chunked encoding is used (to allow for
4024   transfer encoding that may not be self delimiting); it was important
4025   to straighten out exactly how message lengths are computed. (Sections
4026   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4027   <xref target="header.content-length" format="counter"/>,
4028   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4029</t>
4030<t>
4031   The use and interpretation of HTTP version numbers has been clarified
4032   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4033   version they support to deal with problems discovered in HTTP/1.0
4034   implementations (<xref target="http.version"/>)
4035</t>
4036<t>
4037   Quality Values of zero should indicate that "I don't want something"
4038   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4039</t>
4040<t>
4041   Transfer-coding had significant problems, particularly with
4042   interactions with chunked encoding. The solution is that transfer-codings
4043   become as full fledged as content-codings. This involves
4044   adding an IANA registry for transfer-codings (separate from content
4045   codings), a new header field (TE) and enabling trailer headers in the
4046   future. Transfer encoding is a major performance benefit, so it was
4047   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4048   interoperability problem that could have occurred due to interactions
4049   between authentication trailers, chunked encoding and HTTP/1.0
4050   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4051   and <xref target="header.te" format="counter"/>)
4052</t>
4053</section>
4054
4055<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4056<t>
4057  Empty list elements in list productions have been deprecated.
4058  (<xref target="notation.abnf"/>)
4059</t>
4060<t>
4061  Rules about implicit linear whitespace between certain grammar productions
4062  have been removed; now it's only allowed when specifically pointed out
4063  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4064  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4065  Non-ASCII content in header fields and reason phrase has been obsoleted and
4066  made opaque (the TEXT rule was removed)
4067  (<xref target="basic.rules"/>)
4068</t>
4069<t>
4070  Clarify that HTTP-Version is case sensitive.
4071  (<xref target="http.version"/>)
4072</t>
4073<t>
4074  Remove reference to non-existant identity transfer-coding value tokens.
4075  (Sections <xref format="counter" target="transfer.codings"/> and
4076  <xref format="counter" target="message.length"/>)
4077</t>
4078<t>
4079  Clarification that the chunk length does not include
4080  the count of the octets in the chunk header and trailer.
4081  (<xref target="chunked.transfer.encoding"/>)
4082</t>
4083<t>
4084  Require that invalid whitespace around field-names be rejected.
4085  (<xref target="message.headers"/>)
4086</t>
4087<t>
4088  Update use of abs_path production from RFC1808 to the path-absolute + query
4089  components of RFC3986.
4090  (<xref target="request-target"/>)
4091</t>
4092<t>
4093  Clarify exactly when close connection options must be sent.
4094  (<xref target="header.connection"/>)
4095</t>
4096</section>
4097</section>
4098
4099<section title="Terminology" anchor="terminology">
4100<t>
4101   This specification uses a number of terms to refer to the roles
4102   played by participants in, and objects of, the HTTP communication.
4103</t>
4104<t>
4105  <iref item="cache"/>
4106  <x:dfn>cache</x:dfn>
4107  <list>
4108    <t>
4109      A program's local store of response messages and the subsystem
4110      that controls its message storage, retrieval, and deletion. A
4111      cache stores cacheable responses in order to reduce the response
4112      time and network bandwidth consumption on future, equivalent
4113      requests. Any client or server may include a cache, though a cache
4114      cannot be used by a server that is acting as a tunnel.
4115    </t>
4116  </list>
4117</t>
4118<t>
4119  <iref item="cacheable"/>
4120  <x:dfn>cacheable</x:dfn>
4121  <list>
4122    <t>
4123      A response is cacheable if a cache is allowed to store a copy of
4124      the response message for use in answering subsequent requests. The
4125      rules for determining the cacheability of HTTP responses are
4126      defined in &caching;. Even if a resource is cacheable, there may
4127      be additional constraints on whether a cache can use the cached
4128      copy for a particular request.
4129    </t>
4130  </list>
4131</t>
4132<t>
4133  <iref item="client"/>
4134  <x:dfn>client</x:dfn>
4135  <list>
4136    <t>
4137      A program that establishes connections for the purpose of sending
4138      requests.
4139    </t>
4140  </list>
4141</t>
4142<t>
4143  <iref item="connection"/>
4144  <x:dfn>connection</x:dfn>
4145  <list>
4146    <t>
4147      A transport layer virtual circuit established between two programs
4148      for the purpose of communication.
4149    </t>
4150  </list>
4151</t>
4152<t>
4153  <iref item="content negotiation"/>
4154  <x:dfn>content negotiation</x:dfn>
4155  <list>
4156    <t>
4157      The mechanism for selecting the appropriate representation when
4158      servicing a request, as described in &content.negotiation;. The
4159      representation of entities in any response can be negotiated
4160      (including error responses).
4161    </t>
4162  </list>
4163</t>
4164<t>
4165  <iref item="entity"/>
4166  <x:dfn>entity</x:dfn>
4167  <list>
4168    <t>
4169      The information transferred as the payload of a request or
4170      response. An entity consists of metainformation in the form of
4171      entity-header fields and content in the form of an entity-body, as
4172      described in &entity;.
4173    </t>
4174  </list>
4175</t>
4176<t>
4177  <iref item="gateway"/>
4178  <x:dfn>gateway</x:dfn>
4179  <list>
4180    <t>
4181      A server which acts as an intermediary for some other server.
4182      Unlike a proxy, a gateway receives requests as if it were the
4183      origin server for the requested resource; the requesting client
4184      may not be aware that it is communicating with a gateway.
4185    </t>
4186  </list>
4187</t>
4188<t>
4189  <iref item="inbound"/>
4190  <iref item="outbound"/>
4191  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4192  <list>
4193    <t>
4194      Inbound and outbound refer to the request and response paths for
4195      messages: "inbound" means "traveling toward the origin server",
4196      and "outbound" means "traveling toward the user agent"
4197    </t>
4198  </list>
4199</t>
4200<t>
4201  <iref item="message"/>
4202  <x:dfn>message</x:dfn>
4203  <list>
4204    <t>
4205      The basic unit of HTTP communication, consisting of a structured
4206      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4207      transmitted via the connection.
4208    </t>
4209  </list>
4210</t>
4211<t>
4212  <iref item="origin server"/>
4213  <x:dfn>origin server</x:dfn>
4214  <list>
4215    <t>
4216      The server on which a given resource resides or is to be created.
4217    </t>
4218  </list>
4219</t>
4220<t>
4221  <iref item="proxy"/>
4222  <x:dfn>proxy</x:dfn>
4223  <list>
4224    <t>
4225      An intermediary program which acts as both a server and a client
4226      for the purpose of making requests on behalf of other clients.
4227      Requests are serviced internally or by passing them on, with
4228      possible translation, to other servers. A proxy &MUST; implement
4229      both the client and server requirements of this specification. A
4230      "transparent proxy" is a proxy that does not modify the request or
4231      response beyond what is required for proxy authentication and
4232      identification. A "non-transparent proxy" is a proxy that modifies
4233      the request or response in order to provide some added service to
4234      the user agent, such as group annotation services, media type
4235      transformation, protocol reduction, or anonymity filtering. Except
4236      where either transparent or non-transparent behavior is explicitly
4237      stated, the HTTP proxy requirements apply to both types of
4238      proxies.
4239    </t>
4240  </list>
4241</t>
4242<t>
4243  <iref item="request"/>
4244  <x:dfn>request</x:dfn>
4245  <list>
4246    <t>
4247      An HTTP request message, as defined in <xref target="request"/>.
4248    </t>
4249  </list>
4250</t>
4251<t>
4252  <iref item="resource"/>
4253  <x:dfn>resource</x:dfn>
4254  <list>
4255    <t>
4256      A network data object or service that can be identified by a URI,
4257      as defined in <xref target="uri"/>. Resources may be available in multiple
4258      representations (e.g. multiple languages, data formats, size, and
4259      resolutions) or vary in other ways.
4260    </t>
4261  </list>
4262</t>
4263<t>
4264  <iref item="response"/>
4265  <x:dfn>response</x:dfn>
4266  <list>
4267    <t>
4268      An HTTP response message, as defined in <xref target="response"/>.
4269    </t>
4270  </list>
4271</t>
4272<t>
4273  <iref item="representation"/>
4274  <x:dfn>representation</x:dfn>
4275  <list>
4276    <t>
4277      An entity included with a response that is subject to content
4278      negotiation, as described in &content.negotiation;. There may exist multiple
4279      representations associated with a particular response status.
4280    </t>
4281  </list>
4282</t>
4283<t>
4284  <iref item="server"/>
4285  <x:dfn>server</x:dfn>
4286  <list>
4287    <t>
4288      An application program that accepts connections in order to
4289      service requests by sending back responses. Any given program may
4290      be capable of being both a client and a server; our use of these
4291      terms refers only to the role being performed by the program for a
4292      particular connection, rather than to the program's capabilities
4293      in general. Likewise, any server may act as an origin server,
4294      proxy, gateway, or tunnel, switching behavior based on the nature
4295      of each request.
4296    </t>
4297  </list>
4298</t>
4299<t>
4300  <iref item="tunnel"/>
4301  <x:dfn>tunnel</x:dfn>
4302  <list>
4303    <t>
4304      An intermediary program which is acting as a blind relay between
4305      two connections. Once active, a tunnel is not considered a party
4306      to the HTTP communication, though the tunnel may have been
4307      initiated by an HTTP request. The tunnel ceases to exist when both
4308      ends of the relayed connections are closed.
4309    </t>
4310  </list>
4311</t>
4312<t>
4313  <iref item="upstream"/>
4314  <iref item="downstream"/>
4315  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4316  <list>
4317    <t>
4318      Upstream and downstream describe the flow of a message: all
4319      messages flow from upstream to downstream.
4320    </t>
4321  </list>
4322</t>
4323<t>
4324  <iref item="user agent"/>
4325  <x:dfn>user agent</x:dfn>
4326  <list>
4327    <t>
4328      The client which initiates a request. These are often browsers,
4329      editors, spiders (web-traversing robots), or other end user tools.
4330    </t>
4331  </list>
4332</t>
4333<t>
4334  <iref item="variant"/>
4335  <x:dfn>variant</x:dfn>
4336  <list>
4337    <t>
4338      A resource may have one, or more than one, representation(s)
4339      associated with it at any given instant. Each of these
4340      representations is termed a `variant'.  Use of the term `variant'
4341      does not necessarily imply that the resource is subject to content
4342      negotiation.
4343    </t>
4344  </list>
4345</t>
4346</section>
4347
4348<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4349<figure>
4350<artwork type="abnf" name="p1-messaging.parsed-abnf">
4351<x:ref>BWS</x:ref> = OWS
4352
4353<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4354<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4355<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4356<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4357 connection-token ] )
4358<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4359<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4360
4361<x:ref>Date</x:ref> = "Date:" OWS Date-v
4362<x:ref>Date-v</x:ref> = HTTP-date
4363
4364GMT = %x47.4D.54
4365
4366<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50
4367<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4368<x:ref>HTTP-date</x:ref> = rfc1123-date / obsolete-date
4369<x:ref>HTTP-message</x:ref> = Request / Response
4370<x:ref>Host</x:ref> = "Host:" OWS Host-v
4371<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4372
4373<x:ref>Method</x:ref> = token
4374
4375<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4376
4377<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4378
4379<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4380<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4381<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4382 entity-header ) CRLF ) CRLF [ message-body ]
4383<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4384<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4385 entity-header ) CRLF ) CRLF [ message-body ]
4386
4387<x:ref>Status-Code</x:ref> = 3DIGIT
4388<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4389
4390<x:ref>TE</x:ref> = "TE:" OWS TE-v
4391<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4392<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4393<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4394<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4395<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4396 transfer-coding ] )
4397
4398<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4399<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4400<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4401<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4402
4403<x:ref>Via</x:ref> = "Via:" OWS Via-v
4404<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4405 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4406 ] )
4407
4408<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4409
4410<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4411<x:ref>asctime-date</x:ref> = wkday SP date3 SP time SP 4DIGIT
4412<x:ref>attribute</x:ref> = token
4413<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4414
4415<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4416<x:ref>chunk-data</x:ref> = 1*OCTET
4417<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4418<x:ref>chunk-ext-name</x:ref> = token
4419<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4420<x:ref>chunk-size</x:ref> = 1*HEXDIG
4421<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4422<x:ref>connection-token</x:ref> = token
4423<x:ref>ctext</x:ref> = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
4424
4425<x:ref>date1</x:ref> = 2DIGIT SP month SP 4DIGIT
4426<x:ref>date2</x:ref> = 2DIGIT "-" month "-" 2DIGIT
4427<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4428
4429<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4430<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4431
4432<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4433<x:ref>field-name</x:ref> = token
4434<x:ref>field-value</x:ref> = *( field-content / OWS )
4435<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4436
4437<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4438 / Transfer-Encoding / Upgrade / Via / Warning
4439<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4440 message-body ]
4441
4442<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4443
4444l-Fri = %x46.72.69.64.61.79
4445l-Mon = %x4D.6F.6E.64.61.79
4446l-Sat = %x53.61.74.75.72.64.61.79
4447l-Sun = %x53.75.6E.64.61.79
4448l-Thu = %x54.68.75.72.73.64.61.79
4449l-Tue = %x54.75.65.73.64.61.79
4450l-Wed = %x57.65.64.6E.65.73.64.61.79
4451<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4452
4453<x:ref>message-body</x:ref> = entity-body /
4454 &lt;entity-body encoded as per Transfer-Encoding&gt;
4455<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4456<x:ref>month</x:ref> = s-Jan / s-Feb / s-Mar / s-Apr / s-May / s-Jun / s-Jul / s-Aug
4457 / s-Sep / s-Oct / s-Nov / s-Dec
4458
4459<x:ref>obs-fold</x:ref> = CRLF
4460<x:ref>obs-text</x:ref> = %x80-FF
4461<x:ref>obsolete-date</x:ref> = rfc850-date / asctime-date
4462
4463<x:ref>parameter</x:ref> = attribute BWS "=" BWS value
4464<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4465<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4466<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4467<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4468<x:ref>product</x:ref> = token [ "/" product-version ]
4469<x:ref>product-version</x:ref> = token
4470<x:ref>protocol-name</x:ref> = token
4471<x:ref>protocol-version</x:ref> = token
4472<x:ref>pseudonym</x:ref> = token
4473
4474<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B / %x5D-7E / obs-text
4475<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4476<x:ref>quoted-pair</x:ref> = "\" quoted-text
4477<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4478<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4479<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4480
4481<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4482<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4483<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4484<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4485<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4486 / authority
4487<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4488<x:ref>rfc1123-date</x:ref> = wkday "," SP date1 SP time SP GMT
4489<x:ref>rfc850-date</x:ref> = weekday "," SP date2 SP time SP GMT
4490
4491s-Apr = %x41.70.72
4492s-Aug = %x41.75.67
4493s-Dec = %x44.65.63
4494s-Feb = %x46.65.62
4495s-Fri = %x46.72.69
4496s-Jan = %x4A.61.6E
4497s-Jul = %x4A.75.6C
4498s-Jun = %x4A.75.6E
4499s-Mar = %x4D.61.72
4500s-May = %x4D.61.79
4501s-Mon = %x4D.6F.6E
4502s-Nov = %x4E.6F.76
4503s-Oct = %x4F.63.74
4504s-Sat = %x53.61.74
4505s-Sep = %x53.65.70
4506s-Sun = %x53.75.6E
4507s-Thu = %x54.68.75
4508s-Tue = %x54.75.65
4509s-Wed = %x57.65.64
4510<x:ref>start-line</x:ref> = Request-Line / Status-Line
4511
4512<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4513<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4514 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4515<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4516<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4517<x:ref>time</x:ref> = 2DIGIT ":" 2DIGIT ":" 2DIGIT
4518<x:ref>token</x:ref> = 1*tchar
4519<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4520<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4521<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS parameter )
4522
4523<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4524
4525<x:ref>value</x:ref> = token / quoted-string
4526
4527<x:ref>weekday</x:ref> = l-Mon / l-Tue / l-Wed / l-Thu / l-Fri / l-Sat / l-Sun
4528<x:ref>wkday</x:ref> = s-Mon / s-Tue / s-Wed / s-Thu / s-Fri / s-Sat / s-Sun
4529
4530
4531</artwork>
4532</figure>
4533<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4534; Chunked-Body defined but not used
4535; Content-Length defined but not used
4536; HTTP-message defined but not used
4537; Host defined but not used
4538; TE defined but not used
4539; URI defined but not used
4540; URI-reference defined but not used
4541; fragment defined but not used
4542; generic-message defined but not used
4543; http-URI defined but not used
4544; partial-URI defined but not used
4545</artwork></figure></section>
4546
4547
4548<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4549
4550<section title="Since RFC2616">
4551<t>
4552  Extracted relevant partitions from <xref target="RFC2616"/>.
4553</t>
4554</section>
4555
4556<section title="Since draft-ietf-httpbis-p1-messaging-00">
4557<t>
4558  Closed issues:
4559  <list style="symbols"> 
4560    <t>
4561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4562      "HTTP Version should be case sensitive"
4563      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4564    </t>
4565    <t>
4566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4567      "'unsafe' characters"
4568      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4569    </t>
4570    <t>
4571      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4572      "Chunk Size Definition"
4573      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4574    </t>
4575    <t>
4576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4577      "Message Length"
4578      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4579    </t>
4580    <t>
4581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4582      "Media Type Registrations"
4583      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4584    </t>
4585    <t>
4586      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4587      "URI includes query"
4588      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4589    </t>
4590    <t>
4591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4592      "No close on 1xx responses"
4593      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4594    </t>
4595    <t>
4596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4597      "Remove 'identity' token references"
4598      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4599    </t>
4600    <t>
4601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4602      "Import query BNF"
4603    </t>
4604    <t>
4605      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4606      "qdtext BNF"
4607    </t>
4608    <t>
4609      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4610      "Normative and Informative references"
4611    </t>
4612    <t>
4613      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4614      "RFC2606 Compliance"
4615    </t>
4616    <t>
4617      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4618      "RFC977 reference"
4619    </t>
4620    <t>
4621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4622      "RFC1700 references"
4623    </t>
4624    <t>
4625      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4626      "inconsistency in date format explanation"
4627    </t>
4628    <t>
4629      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4630      "Date reference typo"
4631    </t>
4632    <t>
4633      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4634      "Informative references"
4635    </t>
4636    <t>
4637      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4638      "ISO-8859-1 Reference"
4639    </t>
4640    <t>
4641      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4642      "Normative up-to-date references"
4643    </t>
4644  </list>
4645</t>
4646<t>
4647  Other changes:
4648  <list style="symbols"> 
4649    <t>
4650      Update media type registrations to use RFC4288 template.
4651    </t>
4652    <t>
4653      Use names of RFC4234 core rules DQUOTE and WSP,
4654      fix broken ABNF for chunk-data
4655      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4656    </t>
4657  </list>
4658</t>
4659</section>
4660
4661<section title="Since draft-ietf-httpbis-p1-messaging-01">
4662<t>
4663  Closed issues:
4664  <list style="symbols"> 
4665    <t>
4666      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4667      "Bodies on GET (and other) requests"
4668    </t>
4669    <t>
4670      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4671      "Updating to RFC4288"
4672    </t>
4673    <t>
4674      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4675      "Status Code and Reason Phrase"
4676    </t>
4677    <t>
4678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4679      "rel_path not used"
4680    </t>
4681  </list>
4682</t>
4683<t>
4684  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4685  <list style="symbols"> 
4686    <t>
4687      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4688      "trailer-part").
4689    </t>
4690    <t>
4691      Avoid underscore character in rule names ("http_URL" ->
4692      "http-URL", "abs_path" -> "path-absolute").
4693    </t>
4694    <t>
4695      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4696      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4697      have to be updated when switching over to RFC3986.
4698    </t>
4699    <t>
4700      Synchronize core rules with RFC5234.
4701    </t>
4702    <t>
4703      Get rid of prose rules that span multiple lines.
4704    </t>
4705    <t>
4706      Get rid of unused rules LOALPHA and UPALPHA.
4707    </t>
4708    <t>
4709      Move "Product Tokens" section (back) into Part 1, as "token" is used
4710      in the definition of the Upgrade header.
4711    </t>
4712    <t>
4713      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4714    </t>
4715    <t>
4716      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4717    </t>
4718  </list>
4719</t>
4720</section>
4721
4722<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4723<t>
4724  Closed issues:
4725  <list style="symbols"> 
4726    <t>
4727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4728      "HTTP-date vs. rfc1123-date"
4729    </t>
4730    <t>
4731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4732      "WS in quoted-pair"
4733    </t>
4734  </list>
4735</t>
4736<t>
4737  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4738  <list style="symbols"> 
4739    <t>
4740      Reference RFC 3984, and update header registrations for headers defined
4741      in this document.
4742    </t>
4743  </list>
4744</t>
4745<t>
4746  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4747  <list style="symbols"> 
4748    <t>
4749      Replace string literals when the string really is case-sensitive (HTTP-Version).
4750    </t>
4751  </list>
4752</t>
4753</section>
4754
4755<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4756<t>
4757  Closed issues:
4758  <list style="symbols"> 
4759    <t>
4760      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4761      "Connection closing"
4762    </t>
4763    <t>
4764      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4765      "Move registrations and registry information to IANA Considerations"
4766    </t>
4767    <t>
4768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4769      "need new URL for PAD1995 reference"
4770    </t>
4771    <t>
4772      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4773      "IANA Considerations: update HTTP URI scheme registration"
4774    </t>
4775    <t>
4776      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4777      "Cite HTTPS URI scheme definition"
4778    </t>
4779    <t>
4780      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4781      "List-type headers vs Set-Cookie"
4782    </t>
4783  </list>
4784</t>
4785<t>
4786  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4787  <list style="symbols"> 
4788    <t>
4789      Replace string literals when the string really is case-sensitive (HTTP-Date).
4790    </t>
4791    <t>
4792      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4793    </t>
4794  </list>
4795</t>
4796</section>
4797
4798<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4799<t>
4800  Closed issues:
4801  <list style="symbols"> 
4802    <t>
4803      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4804      "Out-of-date reference for URIs"
4805    </t>
4806    <t>
4807      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4808      "RFC 2822 is updated by RFC 5322"
4809    </t>
4810  </list>
4811</t>
4812<t>
4813  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4814  <list style="symbols"> 
4815    <t>
4816      Use "/" instead of "|" for alternatives.
4817    </t>
4818    <t>
4819      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4820    </t>
4821    <t>
4822      Only reference RFC 5234's core rules.
4823    </t>
4824    <t>
4825      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4826      whitespace ("OWS") and required whitespace ("RWS").
4827    </t>
4828    <t>
4829      Rewrite ABNFs to spell out whitespace rules, factor out
4830      header value format definitions.
4831    </t>
4832  </list>
4833</t>
4834</section>
4835
4836<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4837<t>
4838  Closed issues:
4839  <list style="symbols"> 
4840    <t>
4841      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
4842      "Header LWS"
4843    </t>
4844    <t>
4845      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
4846      "Sort 1.3 Terminology"
4847    </t>
4848    <t>
4849      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
4850      "RFC2047 encoded words"
4851    </t>
4852    <t>
4853      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
4854      "Character Encodings in TEXT"
4855    </t>
4856    <t>
4857      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
4858      "Line Folding"
4859    </t>
4860    <t>
4861      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
4862      "OPTIONS * and proxies"
4863    </t>
4864    <t>
4865      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4866      "Reason-Phrase BNF"
4867    </t>
4868    <t>
4869      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
4870      "Use of TEXT"
4871    </t>
4872    <t>
4873      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4874      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4875    </t>
4876    <t>
4877      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4878      "RFC822 reference left in discussion of date formats"
4879    </t>
4880  </list>
4881</t>
4882<t>
4883  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4884  <list style="symbols"> 
4885    <t>
4886      Rewrite definition of list rules, deprecate empty list elements.
4887    </t>
4888    <t>
4889      Add appendix containing collected and expanded ABNF.
4890    </t>
4891  </list>
4892</t>
4893<t>
4894  Other changes:
4895  <list style="symbols"> 
4896    <t>
4897      Rewrite introduction; add mostly new Architecture Section.
4898    </t>
4899    <t>
4900      Move definition of quality values from Part 3 into Part 1;
4901      make TE request header grammar independent of accept-params (defined in Part 3).
4902    </t>
4903  </list>
4904</t>
4905</section>
4906
4907<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
4908<t>
4909  Closed issues:
4910  <list style="symbols"> 
4911    <t>
4912      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
4913      "base for numeric protocol elements"
4914    </t>
4915    <t>
4916      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
4917      "comment ABNF"
4918    </t>
4919  </list>
4920</t>
4921</section>
4922
4923</section>
4924
4925</back>
4926</rfc>
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