source: draft-ietf-httpbis/latest/p1-messaging.xml @ 582

Last change on this file since 582 was 582, checked in by julian.reschke@…, 11 years ago

reduce noise in date ABNF now that we use BAP's feature expanding byte sequences of printable characters into comments (related to #163)

  • Property svn:eol-style set to native
File size: 211.1 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: Full Date" anchor="date.time.formats.full.date">
839  <x:anchor-alias value="HTTP-date"/>
840<t>
841   HTTP applications have historically allowed three different formats
842   for the representation of date/time stamps:
843</t>
844<figure><artwork type="example">
845  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
846  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
847  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
848</artwork></figure>
849<t>
850   The first format is preferred as an Internet standard and represents
851   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
852   other formats are described here only for
853   compatibility with obsolete implementations.
854   HTTP/1.1 clients and servers that parse the date value &MUST; accept
855   all three formats (for compatibility with HTTP/1.0), though they &MUST;
856   only generate the RFC 1123 format for representing HTTP-date values
857   in header fields. See <xref target="tolerant.applications"/> for further information.
858</t>
859<t>
860   All HTTP date/time stamps &MUST; be represented in Greenwich Mean Time
861   (GMT), without exception. For the purposes of HTTP, GMT is exactly
862   equal to UTC (Coordinated Universal Time). This is indicated in the
863   first two formats by the inclusion of "GMT" as the three-letter
864   abbreviation for time zone, and &MUST; be assumed when reading the
865   asctime format. HTTP-date is case sensitive and &MUST-NOT; include
866   additional whitespace beyond that specifically included as SP in the
867   grammar.
868</t>
869<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-date"/>
870  <x:ref>HTTP-date</x:ref>    = <x:ref>rfc1123-date</x:ref> / <x:ref>obs-date</x:ref>
871</artwork></figure>
872<t anchor="preferred.date.format">
873  <x:anchor-alias value="rfc1123-date"/>
874  <x:anchor-alias value="time-of-day"/>
875  <x:anchor-alias value="hour"/>
876  <x:anchor-alias value="minute"/>
877  <x:anchor-alias value="second"/>
878  <x:anchor-alias value="day-name"/>
879  <x:anchor-alias value="day"/>
880  <x:anchor-alias value="month"/>
881  <x:anchor-alias value="year"/>
882  <x:anchor-alias value="GMT"/>
883  Preferred format:
884</t>
885<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/>
886  <x:ref>rfc1123-date</x:ref> = <x:ref>day-name</x:ref> "," <x:ref>SP</x:ref> date1 <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
887
888  <x:ref>day-name</x:ref>     = <x:abnf-char-sequence>"Mon"</x:abnf-char-sequence> ; "Mon", case-sensitive
889               / <x:abnf-char-sequence>"Tue"</x:abnf-char-sequence> ; "Tue", case-sensitive
890               / <x:abnf-char-sequence>"Wed"</x:abnf-char-sequence> ; "Wed", case-sensitive
891               / <x:abnf-char-sequence>"Thu"</x:abnf-char-sequence> ; "Thu", case-sensitive
892               / <x:abnf-char-sequence>"Fri"</x:abnf-char-sequence> ; "Fri", case-sensitive
893               / <x:abnf-char-sequence>"Sat"</x:abnf-char-sequence> ; "Sat", case-sensitive
894               / <x:abnf-char-sequence>"Sun"</x:abnf-char-sequence> ; "Sun", case-sensitive
895               
896  <x:ref>date1</x:ref>        = <x:ref>day</x:ref> <x:ref>SP</x:ref> <x:ref>month</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
897               ; e.g., 02 Jun 1982
898
899  <x:ref>day</x:ref>          = 2<x:ref>DIGIT</x:ref>
900  <x:ref>month</x:ref>        = <x:abnf-char-sequence>"Jan"</x:abnf-char-sequence> ; "Jan", case-sensitive
901               / <x:abnf-char-sequence>"Feb"</x:abnf-char-sequence> ; "Feb", case-sensitive
902               / <x:abnf-char-sequence>"Mar"</x:abnf-char-sequence> ; "Mar", case-sensitive
903               / <x:abnf-char-sequence>"Apr"</x:abnf-char-sequence> ; "Apr", case-sensitive
904               / <x:abnf-char-sequence>"May"</x:abnf-char-sequence> ; "May", case-sensitive
905               / <x:abnf-char-sequence>"Jun"</x:abnf-char-sequence> ; "Jun", case-sensitive
906               / <x:abnf-char-sequence>"Jul"</x:abnf-char-sequence> ; "Jul", case-sensitive
907               / <x:abnf-char-sequence>"Aug"</x:abnf-char-sequence> ; "Aug", case-sensitive
908               / <x:abnf-char-sequence>"Sep"</x:abnf-char-sequence> ; "Sep", case-sensitive
909               / <x:abnf-char-sequence>"Oct"</x:abnf-char-sequence> ; "Oct", case-sensitive
910               / <x:abnf-char-sequence>"Nov"</x:abnf-char-sequence> ; "Nov", case-sensitive
911               / <x:abnf-char-sequence>"Dec"</x:abnf-char-sequence> ; "Dec", case-sensitive
912  <x:ref>year</x:ref>         = 4<x:ref>DIGIT</x:ref>
913
914  <x:ref>GMT</x:ref>   = <x:abnf-char-sequence>"GMT"</x:abnf-char-sequence> ; "GMT", case-sensitive
915
916  <x:ref>time-of-day</x:ref>  = <x:ref>hour</x:ref> ":" <x:ref>minute</x:ref> ":" <x:ref>second</x:ref>
917                 ; 00:00:00 - 23:59:59
918                 
919  <x:ref>hour</x:ref>         = 2<x:ref>DIGIT</x:ref>               
920  <x:ref>minute</x:ref>       = 2<x:ref>DIGIT</x:ref>               
921  <x:ref>second</x:ref>       = 2<x:ref>DIGIT</x:ref>               
922</artwork></figure>
923<t>
924  The semantics of <x:ref>day-name</x:ref>, <x:ref>day</x:ref>,
925  <x:ref>month</x:ref>, <x:ref>year</x:ref>, and <x:ref>time-of-day</x:ref> are the
926  same as those defined in the RFC 5322 constructs
927  with the corresponding name (<xref target="RFC5322" x:fmt="," x:sec="3.3"/>).
928</t>
929<t anchor="obsolete.date.formats">
930  <x:anchor-alias value="obs-date"/>
931  <x:anchor-alias value="rfc850-date"/>
932  <x:anchor-alias value="asctime-date"/>
933  <x:anchor-alias value="date1"/>
934  <x:anchor-alias value="date2"/>
935  <x:anchor-alias value="date3"/>
936  <x:anchor-alias value="rfc1123-date"/>
937  <x:anchor-alias value="day-name-l"/>
938  Obsolete formats:
939</t>
940<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="obs-date"/>
941  <x:ref>obs-date</x:ref>     = <x:ref>rfc850-date</x:ref> / <x:ref>asctime-date</x:ref> 
942</artwork></figure>
943<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="rfc850-date"/>
944  <x:ref>rfc850-date</x:ref>  = <x:ref>day-name-l</x:ref> "," <x:ref>SP</x:ref> <x:ref>date2</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>GMT</x:ref>
945  <x:ref>date2</x:ref>        = <x:ref>day</x:ref> "-" <x:ref>month</x:ref> "-" 2<x:ref>DIGIT</x:ref>
946                 ; day-month-year (e.g., 02-Jun-82)
947
948  <x:ref>day-name-l</x:ref>   = <x:abnf-char-sequence>"Monday"</x:abnf-char-sequence> ; "Monday", case-sensitive
949         / <x:abnf-char-sequence>"Tuesday"</x:abnf-char-sequence> ; "Tuesday", case-sensitive
950         / <x:abnf-char-sequence>"Wednesday"</x:abnf-char-sequence> ; "Wednesday", case-sensitive
951         / <x:abnf-char-sequence>"Thursday"</x:abnf-char-sequence> ; "Thursday", case-sensitive
952         / <x:abnf-char-sequence>"Friday"</x:abnf-char-sequence> ; "Friday", case-sensitive
953         / <x:abnf-char-sequence>"Saturday"</x:abnf-char-sequence> ; "Saturday", case-sensitive
954         / <x:abnf-char-sequence>"Sunday"</x:abnf-char-sequence> ; "Sunday", case-sensitive
955</artwork></figure>
956<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="asctime-date"/>
957  <x:ref>asctime-date</x:ref> = <x:ref>day-name</x:ref> <x:ref>SP</x:ref> <x:ref>date3</x:ref> <x:ref>SP</x:ref> <x:ref>time-of-day</x:ref> <x:ref>SP</x:ref> <x:ref>year</x:ref>
958  <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> ))
959                 ; month day (e.g., Jun  2)
960</artwork></figure>
961<x:note>
962  <t>
963    <x:h>Note:</x:h> Recipients of date values are encouraged to be robust in
964    accepting date values that may have been sent by non-HTTP
965    applications, as is sometimes the case when retrieving or posting
966    messages via proxies/gateways to SMTP or NNTP.
967  </t>
968</x:note>
969<x:note>
970  <t>
971    <x:h>Note:</x:h> HTTP requirements for the date/time stamp format apply only
972    to their usage within the protocol stream. Clients and servers are
973    not required to use these formats for user presentation, request
974    logging, etc.
975  </t>
976</x:note>
977</section>
978
979<section title="Transfer Codings" anchor="transfer.codings">
980  <x:anchor-alias value="parameter"/>
981  <x:anchor-alias value="transfer-coding"/>
982  <x:anchor-alias value="transfer-extension"/>
983<t>
984   Transfer-coding values are used to indicate an encoding
985   transformation that has been, can be, or may need to be applied to an
986   entity-body in order to ensure "safe transport" through the network.
987   This differs from a content coding in that the transfer-coding is a
988   property of the message, not of the original entity.
989</t>
990<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/>
991  <x:ref>transfer-coding</x:ref>         = "chunked" / <x:ref>transfer-extension</x:ref>
992  <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> )
993</artwork></figure>
994<t anchor="rule.parameter">
995  <x:anchor-alias value="attribute"/>
996  <x:anchor-alias value="parameter"/>
997  <x:anchor-alias value="value"/>
998   Parameters are in  the form of attribute/value pairs.
999</t>
1000<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"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/>
1001  <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>
1002  <x:ref>attribute</x:ref>               = <x:ref>token</x:ref>
1003  <x:ref>value</x:ref>                   = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1004</artwork></figure>
1005<t>
1006   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1007   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1008   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1009</t>
1010<t>
1011   Whenever a transfer-coding is applied to a message-body, the set of
1012   transfer-codings &MUST; include "chunked", unless the message indicates it
1013   is terminated by closing the connection. When the "chunked" transfer-coding
1014   is used, it &MUST; be the last transfer-coding applied to the
1015   message-body. The "chunked" transfer-coding &MUST-NOT; be applied more
1016   than once to a message-body. These rules allow the recipient to
1017   determine the transfer-length of the message (<xref target="message.length"/>).
1018</t>
1019<t>
1020   Transfer-codings are analogous to the Content-Transfer-Encoding
1021   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1022   binary data over a 7-bit transport service. However, safe transport
1023   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1024   the only unsafe characteristic of message-bodies is the difficulty in
1025   determining the exact body length (<xref target="message.length"/>), or the desire to
1026   encrypt data over a shared transport.
1027</t>
1028<t>
1029   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1030   transfer-coding value tokens. Initially, the registry contains the
1031   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1032   "gzip", "compress", and "deflate" (&content-codings;).
1033</t>
1034<t>
1035   New transfer-coding value tokens &SHOULD; be registered in the same way
1036   as new content-coding value tokens (&content-codings;).
1037</t>
1038<t>
1039   A server which receives an entity-body with a transfer-coding it does
1040   not understand &SHOULD; return 501 (Not Implemented), and close the
1041   connection. A server &MUST-NOT; send transfer-codings to an HTTP/1.0
1042   client.
1043</t>
1044
1045<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1046  <x:anchor-alias value="chunk"/>
1047  <x:anchor-alias value="Chunked-Body"/>
1048  <x:anchor-alias value="chunk-data"/>
1049  <x:anchor-alias value="chunk-ext"/>
1050  <x:anchor-alias value="chunk-ext-name"/>
1051  <x:anchor-alias value="chunk-ext-val"/>
1052  <x:anchor-alias value="chunk-size"/>
1053  <x:anchor-alias value="last-chunk"/>
1054  <x:anchor-alias value="trailer-part"/>
1055<t>
1056   The chunked encoding modifies the body of a message in order to
1057   transfer it as a series of chunks, each with its own size indicator,
1058   followed by an &OPTIONAL; trailer containing entity-header fields. This
1059   allows dynamically produced content to be transferred along with the
1060   information necessary for the recipient to verify that it has
1061   received the full message.
1062</t>
1063<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"/>
1064  <x:ref>Chunked-Body</x:ref>   = *<x:ref>chunk</x:ref>
1065                   <x:ref>last-chunk</x:ref>
1066                   <x:ref>trailer-part</x:ref>
1067                   <x:ref>CRLF</x:ref>
1068 
1069  <x:ref>chunk</x:ref>          = <x:ref>chunk-size</x:ref> *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1070                   <x:ref>chunk-data</x:ref> <x:ref>CRLF</x:ref>
1071  <x:ref>chunk-size</x:ref>     = 1*<x:ref>HEXDIG</x:ref>
1072  <x:ref>last-chunk</x:ref>     = 1*("0") *WSP [ <x:ref>chunk-ext</x:ref> ] <x:ref>CRLF</x:ref>
1073 
1074  <x:ref>chunk-ext</x:ref>      = *( ";" *WSP <x:ref>chunk-ext-name</x:ref>
1075                      [ "=" <x:ref>chunk-ext-val</x:ref> ] *WSP )
1076  <x:ref>chunk-ext-name</x:ref> = <x:ref>token</x:ref>
1077  <x:ref>chunk-ext-val</x:ref>  = <x:ref>token</x:ref> / <x:ref>quoted-string</x:ref>
1078  <x:ref>chunk-data</x:ref>     = 1*<x:ref>OCTET</x:ref> ; a sequence of chunk-size octets
1079  <x:ref>trailer-part</x:ref>   = *( <x:ref>entity-header</x:ref> <x:ref>CRLF</x:ref> )
1080</artwork></figure>
1081<t>
1082   The chunk-size field is a string of hex digits indicating the size of
1083   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1084   zero, followed by the trailer, which is terminated by an empty line.
1085</t>
1086<t>
1087   The trailer allows the sender to include additional HTTP header
1088   fields at the end of the message. The Trailer header field can be
1089   used to indicate which header fields are included in a trailer (see
1090   <xref target="header.trailer"/>).
1091</t>
1092<t>
1093   A server using chunked transfer-coding in a response &MUST-NOT; use the
1094   trailer for any header fields unless at least one of the following is
1095   true:
1096  <list style="numbers">
1097    <t>the request included a TE header field that indicates "trailers" is
1098     acceptable in the transfer-coding of the  response, as described in
1099     <xref target="header.te"/>; or,</t>
1100
1101    <t>the server is the origin server for the response, the trailer
1102     fields consist entirely of optional metadata, and the recipient
1103     could use the message (in a manner acceptable to the origin server)
1104     without receiving this metadata.  In other words, the origin server
1105     is willing to accept the possibility that the trailer fields might
1106     be silently discarded along the path to the client.</t>
1107  </list>
1108</t>
1109<t>
1110   This requirement prevents an interoperability failure when the
1111   message is being received by an HTTP/1.1 (or later) proxy and
1112   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1113   compliance with the protocol would have necessitated a possibly
1114   infinite buffer on the proxy.
1115</t>
1116<t>
1117   A process for decoding the "chunked" transfer-coding
1118   can be represented in pseudo-code as:
1119</t>
1120<figure><artwork type="code">
1121  length := 0
1122  read chunk-size, chunk-ext (if any) and CRLF
1123  while (chunk-size &gt; 0) {
1124     read chunk-data and CRLF
1125     append chunk-data to entity-body
1126     length := length + chunk-size
1127     read chunk-size and CRLF
1128  }
1129  read entity-header
1130  while (entity-header not empty) {
1131     append entity-header to existing header fields
1132     read entity-header
1133  }
1134  Content-Length := length
1135  Remove "chunked" from Transfer-Encoding
1136</artwork></figure>
1137<t>
1138   All HTTP/1.1 applications &MUST; be able to receive and decode the
1139   "chunked" transfer-coding, and &MUST; ignore chunk-ext extensions
1140   they do not understand.
1141</t>
1142</section>
1143</section>
1144
1145<section title="Product Tokens" anchor="product.tokens">
1146  <x:anchor-alias value="product"/>
1147  <x:anchor-alias value="product-version"/>
1148<t>
1149   Product tokens are used to allow communicating applications to
1150   identify themselves by software name and version. Most fields using
1151   product tokens also allow sub-products which form a significant part
1152   of the application to be listed, separated by whitespace. By
1153   convention, the products are listed in order of their significance
1154   for identifying the application.
1155</t>
1156<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/>
1157  <x:ref>product</x:ref>         = <x:ref>token</x:ref> ["/" <x:ref>product-version</x:ref>]
1158  <x:ref>product-version</x:ref> = <x:ref>token</x:ref>
1159</artwork></figure>
1160<t>
1161   Examples:
1162</t>
1163<figure><artwork type="example">
1164  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1165  Server: Apache/0.8.4
1166</artwork></figure>
1167<t>
1168   Product tokens &SHOULD; be short and to the point. They &MUST-NOT; be
1169   used for advertising or other non-essential information. Although any
1170   token character &MAY; appear in a product-version, this token &SHOULD;
1171   only be used for a version identifier (i.e., successive versions of
1172   the same product &SHOULD; only differ in the product-version portion of
1173   the product value).
1174</t>
1175</section>
1176
1177<section title="Quality Values" anchor="quality.values">
1178  <x:anchor-alias value="qvalue"/>
1179<t>
1180   Both transfer codings (TE request header, <xref target="header.te"/>)
1181   and content negotiation (&content.negotiation;) use short "floating point"
1182   numbers to indicate the relative importance ("weight") of various
1183   negotiable parameters.  A weight is normalized to a real number in
1184   the range 0 through 1, where 0 is the minimum and 1 the maximum
1185   value. If a parameter has a quality value of 0, then content with
1186   this parameter is `not acceptable' for the client. HTTP/1.1
1187   applications &MUST-NOT; generate more than three digits after the
1188   decimal point. User configuration of these values &SHOULD; also be
1189   limited in this fashion.
1190</t>
1191<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="qvalue"/>
1192  <x:ref>qvalue</x:ref>         = ( "0" [ "." 0*3<x:ref>DIGIT</x:ref> ] )
1193                 / ( "1" [ "." 0*3("0") ] )
1194</artwork></figure>
1195<x:note>
1196  <t>
1197     <x:h>Note:</x:h> "Quality values" is a misnomer, since these values merely represent
1198     relative degradation in desired quality.
1199  </t>
1200</x:note>
1201</section>
1202
1203</section>
1204
1205<section title="HTTP Message" anchor="http.message">
1206
1207<section title="Message Types" anchor="message.types">
1208  <x:anchor-alias value="generic-message"/>
1209  <x:anchor-alias value="HTTP-message"/>
1210  <x:anchor-alias value="start-line"/>
1211<t>
1212   HTTP messages consist of requests from client to server and responses
1213   from server to client.
1214</t>
1215<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="HTTP-message"/>
1216  <x:ref>HTTP-message</x:ref>   = <x:ref>Request</x:ref> / <x:ref>Response</x:ref>     ; HTTP/1.1 messages
1217</artwork></figure>
1218<t>
1219   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1220   message format of <xref target="RFC5322"/> for transferring entities (the payload
1221   of the message). Both types of message consist of a start-line, zero
1222   or more header fields (also known as "headers"), an empty line (i.e.,
1223   a line with nothing preceding the CRLF) indicating the end of the
1224   header fields, and possibly a message-body.
1225</t>
1226<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/>
1227  <x:ref>generic-message</x:ref> = <x:ref>start-line</x:ref>
1228                    *( <x:ref>message-header</x:ref> <x:ref>CRLF</x:ref> )
1229                    <x:ref>CRLF</x:ref>
1230                    [ <x:ref>message-body</x:ref> ]
1231  <x:ref>start-line</x:ref>      = <x:ref>Request-Line</x:ref> / <x:ref>Status-Line</x:ref>
1232</artwork></figure>
1233<t>
1234   In the interest of robustness, servers &SHOULD; ignore any empty
1235   line(s) received where a Request-Line is expected. In other words, if
1236   the server is reading the protocol stream at the beginning of a
1237   message and receives a CRLF first, it should ignore the CRLF.
1238</t>
1239<t>
1240   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1241   after a POST request. To restate what is explicitly forbidden by the
1242   BNF, an HTTP/1.1 client &MUST-NOT; preface or follow a request with an
1243   extra CRLF.
1244</t>
1245<t>
1246   Whitespace (WSP) &MUST-NOT; be sent between the start-line and the first
1247   header field. The presence of whitespace might be an attempt to trick a
1248   noncompliant implementation of HTTP into ignoring that field or processing
1249   the next line as a new request, either of which may result in security
1250   issues when implementations within the request chain interpret the
1251   same message differently. HTTP/1.1 servers &MUST; reject such a message
1252   with a 400 (Bad Request) response.
1253</t>
1254</section>
1255
1256<section title="Message Headers" anchor="message.headers">
1257  <x:anchor-alias value="field-content"/>
1258  <x:anchor-alias value="field-name"/>
1259  <x:anchor-alias value="field-value"/>
1260  <x:anchor-alias value="message-header"/>
1261<t>
1262   HTTP header fields follow the same general format as Internet messages in
1263   <xref target="RFC5322" x:fmt="of" x:sec="2.1"/>. Each header field consists
1264   of a name followed by a colon (":"), optional whitespace, and the field
1265   value. Field names are case-insensitive.
1266</t>
1267<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"/>
1268  <x:ref>message-header</x:ref> = <x:ref>field-name</x:ref> ":" OWS [ <x:ref>field-value</x:ref> ] OWS
1269  <x:ref>field-name</x:ref>     = <x:ref>token</x:ref>
1270  <x:ref>field-value</x:ref>    = *( <x:ref>field-content</x:ref> / <x:ref>OWS</x:ref> )
1271  <x:ref>field-content</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1272</artwork></figure>
1273<t>
1274   Historically, HTTP has allowed field-content with text in the ISO-8859-1
1275   <xref target="ISO-8859-1"/> character encoding (allowing other character sets
1276   through use of <xref target="RFC2047"/> encoding). In practice, most HTTP
1277   header field-values use only a subset of the US-ASCII charset
1278   <xref target="USASCII"/>. Newly defined header fields &SHOULD; constrain
1279   their field-values to US-ASCII characters. Recipients &SHOULD; treat other
1280   (obs-text) octets in field-content as opaque data.
1281</t>
1282<t>
1283   No whitespace is allowed between the header field-name and colon. For
1284   security reasons, any request message received containing such whitespace
1285   &MUST; be rejected with a response code of 400 (Bad Request) and any such
1286   whitespace in a response message &MUST; be removed.
1287</t>
1288<t>
1289   The field value &MAY; be preceded by optional whitespace; a single SP is
1290   preferred. The field-value does not include any leading or trailing white
1291   space: OWS occurring before the first non-whitespace character of the
1292   field-value or after the last non-whitespace character of the field-value
1293   is ignored and &MAY; be removed without changing the meaning of the header
1294   field.
1295</t>
1296<t>
1297   Historically, HTTP header field values could be extended over multiple
1298   lines by preceding each extra line with at least one space or horizontal
1299   tab character (line folding). This specification deprecates such line
1300   folding except within the message/http media type
1301   (<xref target="internet.media.type.message.http"/>).
1302   HTTP/1.1 senders &MUST-NOT; produce messages that include line folding
1303   (i.e., that contain any field-content that matches the obs-fold rule) unless
1304   the message is intended for packaging within the message/http media type.
1305   HTTP/1.1 recipients &SHOULD; accept line folding and replace any embedded
1306   obs-fold whitespace with a single SP prior to interpreting the field value
1307   or forwarding the message downstream.
1308</t>
1309<t anchor="rule.comment">
1310  <x:anchor-alias value="comment"/>
1311  <x:anchor-alias value="ctext"/>
1312   Comments can be included in some HTTP header fields by surrounding
1313   the comment text with parentheses. Comments are only allowed in
1314   fields containing "comment" as part of their field value definition.
1315   In all other fields, parentheses are considered part of the field
1316   value.
1317</t>
1318<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/>
1319  <x:ref>comment</x:ref>        = "(" *( <x:ref>ctext</x:ref> / <x:ref>quoted-pair</x:ref> / <x:ref>comment</x:ref> ) ")"
1320  <x:ref>ctext</x:ref>          = <x:ref>OWS</x:ref> / %x21-27 / %x2A-5B / %x5D-7E / <x:ref>obs-text</x:ref>
1321                 ; <x:ref>OWS</x:ref> / &lt;<x:ref>VCHAR</x:ref> except "(", ")", and "\"&gt; / <x:ref>obs-text</x:ref>
1322</artwork></figure>
1323<t>
1324   The order in which header fields with differing field names are
1325   received is not significant. However, it is "good practice" to send
1326   general-header fields first, followed by request-header or response-header
1327   fields, and ending with the entity-header fields.
1328</t>
1329<t>
1330   Multiple message-header fields with the same field-name &MAY; be
1331   present in a message if and only if the entire field-value for that
1332   header field is defined as a comma-separated list [i.e., #(values)].
1333   It &MUST; be possible to combine the multiple header fields into one
1334   "field-name: field-value" pair, without changing the semantics of the
1335   message, by appending each subsequent field-value to the first, each
1336   separated by a comma. The order in which header fields with the same
1337   field-name are received is therefore significant to the
1338   interpretation of the combined field value, and thus a proxy &MUST-NOT;
1339   change the order of these field values when a message is forwarded.
1340</t>
1341<x:note>
1342  <t>
1343   <x:h>Note:</x:h> the "Set-Cookie" header as implemented in
1344   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1345   can occur multiple times, but does not use the list syntax, and thus cannot
1346   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1347   for details.) Also note that the Set-Cookie2 header specified in
1348   <xref target="RFC2965"/> does not share this problem.
1349  </t>
1350</x:note>
1351 
1352</section>
1353
1354<section title="Message Body" anchor="message.body">
1355  <x:anchor-alias value="message-body"/>
1356<t>
1357   The message-body (if any) of an HTTP message is used to carry the
1358   entity-body associated with the request or response. The message-body
1359   differs from the entity-body only when a transfer-coding has been
1360   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1361</t>
1362<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="message-body"/>
1363  <x:ref>message-body</x:ref> = <x:ref>entity-body</x:ref>
1364               / &lt;entity-body encoded as per <x:ref>Transfer-Encoding</x:ref>&gt;
1365</artwork></figure>
1366<t>
1367   Transfer-Encoding &MUST; be used to indicate any transfer-codings
1368   applied by an application to ensure safe and proper transfer of the
1369   message. Transfer-Encoding is a property of the message, not of the
1370   entity, and thus &MAY; be added or removed by any application along the
1371   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1372   when certain transfer-codings may be used.)
1373</t>
1374<t>
1375   The rules for when a message-body is allowed in a message differ for
1376   requests and responses.
1377</t>
1378<t>
1379   The presence of a message-body in a request is signaled by the
1380   inclusion of a Content-Length or Transfer-Encoding header field in
1381   the request's message-headers. A message-body &MUST-NOT; be included in
1382   a request if the specification of the request method (&method;)
1383   explicitly disallows an entity-body in requests.
1384   When a request message contains both a message-body of non-zero
1385   length and a method that does not define any semantics for that
1386   request message-body, then an origin server &SHOULD; either ignore
1387   the message-body or respond with an appropriate error message
1388   (e.g., 413).  A proxy or gateway, when presented the same request,
1389   &SHOULD; either forward the request inbound with the message-body or
1390   ignore the message-body when determining a response.
1391</t>
1392<t>
1393   For response messages, whether or not a message-body is included with
1394   a message is dependent on both the request method and the response
1395   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1396   &MUST-NOT; include a message-body, even though the presence of entity-header
1397   fields might lead one to believe they do. All 1xx
1398   (informational), 204 (No Content), and 304 (Not Modified) responses
1399   &MUST-NOT; include a message-body. All other responses do include a
1400   message-body, although it &MAY; be of zero length.
1401</t>
1402</section>
1403
1404<section title="Message Length" anchor="message.length">
1405<t>
1406   The transfer-length of a message is the length of the message-body as
1407   it appears in the message; that is, after any transfer-codings have
1408   been applied. When a message-body is included with a message, the
1409   transfer-length of that body is determined by one of the following
1410   (in order of precedence):
1411</t>
1412<t>
1413  <list style="numbers">
1414    <x:lt><t>
1415     Any response message which "&MUST-NOT;" include a message-body (such
1416     as the 1xx, 204, and 304 responses and any response to a HEAD
1417     request) is always terminated by the first empty line after the
1418     header fields, regardless of the entity-header fields present in
1419     the message.
1420    </t></x:lt>
1421    <x:lt><t>
1422     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1423     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1424     is used, the transfer-length is defined by the use of this transfer-coding.
1425     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1426     is not present, the transfer-length is defined by the sender closing the connection.
1427    </t></x:lt>
1428    <x:lt><t>
1429     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1430     value in OCTETs represents both the entity-length and the
1431     transfer-length. The Content-Length header field &MUST-NOT; be sent
1432     if these two lengths are different (i.e., if a Transfer-Encoding
1433     header field is present). If a message is received with both a
1434     Transfer-Encoding header field and a Content-Length header field,
1435     the latter &MUST; be ignored.
1436    </t></x:lt>
1437    <x:lt><t>
1438     If the message uses the media type "multipart/byteranges", and the
1439     transfer-length is not otherwise specified, then this self-delimiting
1440     media type defines the transfer-length. This media type
1441     &MUST-NOT; be used unless the sender knows that the recipient can parse
1442     it; the presence in a request of a Range header with multiple byte-range
1443     specifiers from a 1.1 client implies that the client can parse
1444     multipart/byteranges responses.
1445    <list style="empty"><t>
1446       A range header might be forwarded by a 1.0 proxy that does not
1447       understand multipart/byteranges; in this case the server &MUST;
1448       delimit the message using methods defined in items 1, 3 or 5 of
1449       this section.
1450    </t></list>
1451    </t></x:lt>
1452    <x:lt><t>
1453     By the server closing the connection. (Closing the connection
1454     cannot be used to indicate the end of a request body, since that
1455     would leave no possibility for the server to send back a response.)
1456    </t></x:lt>
1457  </list>
1458</t>
1459<t>
1460   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1461   containing a message-body &MUST; include a valid Content-Length header
1462   field unless the server is known to be HTTP/1.1 compliant. If a
1463   request contains a message-body and a Content-Length is not given,
1464   the server &SHOULD; respond with 400 (Bad Request) if it cannot
1465   determine the length of the message, or with 411 (Length Required) if
1466   it wishes to insist on receiving a valid Content-Length.
1467</t>
1468<t>
1469   All HTTP/1.1 applications that receive entities &MUST; accept the
1470   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1471   to be used for messages when the message length cannot be determined
1472   in advance.
1473</t>
1474<t>
1475   Messages &MUST-NOT; include both a Content-Length header field and a
1476   transfer-coding. If the message does include a
1477   transfer-coding, the Content-Length &MUST; be ignored.
1478</t>
1479<t>
1480   When a Content-Length is given in a message where a message-body is
1481   allowed, its field value &MUST; exactly match the number of OCTETs in
1482   the message-body. HTTP/1.1 user agents &MUST; notify the user when an
1483   invalid length is received and detected.
1484</t>
1485</section>
1486
1487<section title="General Header Fields" anchor="general.header.fields">
1488  <x:anchor-alias value="general-header"/>
1489<t>
1490   There are a few header fields which have general applicability for
1491   both request and response messages, but which do not apply to the
1492   entity being transferred. These header fields apply only to the
1493   message being transmitted.
1494</t>
1495<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="general-header"/>
1496  <x:ref>general-header</x:ref> = <x:ref>Cache-Control</x:ref>            ; &header-cache-control;
1497                 / <x:ref>Connection</x:ref>               ; <xref target="header.connection"/>
1498                 / <x:ref>Date</x:ref>                     ; <xref target="header.date"/>
1499                 / <x:ref>Pragma</x:ref>                   ; &header-pragma;
1500                 / <x:ref>Trailer</x:ref>                  ; <xref target="header.trailer"/>
1501                 / <x:ref>Transfer-Encoding</x:ref>        ; <xref target="header.transfer-encoding"/>
1502                 / <x:ref>Upgrade</x:ref>                  ; <xref target="header.upgrade"/>
1503                 / <x:ref>Via</x:ref>                      ; <xref target="header.via"/>
1504                 / <x:ref>Warning</x:ref>                  ; &header-warning;
1505</artwork></figure>
1506<t>
1507   General-header field names can be extended reliably only in
1508   combination with a change in the protocol version. However, new or
1509   experimental header fields may be given the semantics of general
1510   header fields if all parties in the communication recognize them to
1511   be general-header fields. Unrecognized header fields are treated as
1512   entity-header fields.
1513</t>
1514</section>
1515</section>
1516
1517<section title="Request" anchor="request">
1518  <x:anchor-alias value="Request"/>
1519<t>
1520   A request message from a client to a server includes, within the
1521   first line of that message, the method to be applied to the resource,
1522   the identifier of the resource, and the protocol version in use.
1523</t>
1524<!--                 Host                      ; should be moved here eventually -->
1525<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request"/>
1526  <x:ref>Request</x:ref>       = <x:ref>Request-Line</x:ref>              ; <xref target="request-line"/>
1527                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1528                   / <x:ref>request-header</x:ref>         ; &request-header-fields;
1529                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1530                  <x:ref>CRLF</x:ref>
1531                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1532</artwork></figure>
1533
1534<section title="Request-Line" anchor="request-line">
1535  <x:anchor-alias value="Request-Line"/>
1536<t>
1537   The Request-Line begins with a method token, followed by the
1538   request-target and the protocol version, and ending with CRLF. The
1539   elements are separated by SP characters. No CR or LF is allowed
1540   except in the final CRLF sequence.
1541</t>
1542<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Request-Line"/>
1543  <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>
1544</artwork></figure>
1545
1546<section title="Method" anchor="method">
1547  <x:anchor-alias value="Method"/>
1548<t>
1549   The Method  token indicates the method to be performed on the
1550   resource identified by the request-target. The method is case-sensitive.
1551</t>
1552<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/>
1553  <x:ref>Method</x:ref>         = <x:ref>token</x:ref>
1554</artwork></figure>
1555</section>
1556
1557<section title="request-target" anchor="request-target">
1558  <x:anchor-alias value="request-target"/>
1559<t>
1560   The request-target
1561   identifies the resource upon which to apply the request.
1562</t>
1563<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="request-target"/>
1564  <x:ref>request-target</x:ref> = "*"
1565                 / <x:ref>absolute-URI</x:ref>
1566                 / ( <x:ref>path-absolute</x:ref> [ "?" <x:ref>query</x:ref> ] )
1567                 / <x:ref>authority</x:ref>
1568</artwork></figure>
1569<t>
1570   The four options for request-target are dependent on the nature of the
1571   request. The asterisk "*" means that the request does not apply to a
1572   particular resource, but to the server itself, and is only allowed
1573   when the method used does not necessarily apply to a resource. One
1574   example would be
1575</t>
1576<figure><artwork type="example">
1577  OPTIONS * HTTP/1.1
1578</artwork></figure>
1579<t>
1580   The absolute-URI form is &REQUIRED; when the request is being made to a
1581   proxy. The proxy is requested to forward the request or service it
1582   from a valid cache, and return the response. Note that the proxy &MAY;
1583   forward the request on to another proxy or directly to the server
1584   specified by the absolute-URI. In order to avoid request loops, a
1585   proxy &MUST; be able to recognize all of its server names, including
1586   any aliases, local variations, and the numeric IP address. An example
1587   Request-Line would be:
1588</t>
1589<figure><artwork type="example">
1590  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1591</artwork></figure>
1592<t>
1593   To allow for transition to absolute-URIs in all requests in future
1594   versions of HTTP, all HTTP/1.1 servers &MUST; accept the absolute-URI
1595   form in requests, even though HTTP/1.1 clients will only generate
1596   them in requests to proxies.
1597</t>
1598<t>
1599   The authority form is only used by the CONNECT method (&CONNECT;).
1600</t>
1601<t>
1602   The most common form of request-target is that used to identify a
1603   resource on an origin server or gateway. In this case the absolute
1604   path of the URI &MUST; be transmitted (see <xref target="http.uri"/>, path-absolute) as
1605   the request-target, and the network location of the URI (authority) &MUST;
1606   be transmitted in a Host header field. For example, a client wishing
1607   to retrieve the resource above directly from the origin server would
1608   create a TCP connection to port 80 of the host "www.example.org" and send
1609   the lines:
1610</t>
1611<figure><artwork type="example">
1612  GET /pub/WWW/TheProject.html HTTP/1.1
1613  Host: www.example.org
1614</artwork></figure>
1615<t>
1616   followed by the remainder of the Request. Note that the absolute path
1617   cannot be empty; if none is present in the original URI, it &MUST; be
1618   given as "/" (the server root).
1619</t>
1620<t>
1621   If a proxy receives a request without any path in the request-target and
1622   the method specified is capable of supporting the asterisk form of
1623   request-target, then the last proxy on the request chain &MUST; forward the
1624   request with "*" as the final request-target.
1625</t>
1626<figure><preamble>   
1627   For example, the request
1628</preamble><artwork type="example">
1629  OPTIONS http://www.example.org:8001 HTTP/1.1
1630</artwork></figure>
1631<figure><preamble>   
1632  would be forwarded by the proxy as
1633</preamble><artwork type="example">
1634  OPTIONS * HTTP/1.1
1635  Host: www.example.org:8001
1636</artwork>
1637<postamble>
1638   after connecting to port 8001 of host "www.example.org".
1639</postamble>
1640</figure>
1641<t>
1642   The request-target is transmitted in the format specified in
1643   <xref target="http.uri"/>. If the request-target is percent-encoded
1644   (<xref target="RFC3986" x:fmt="," x:sec="2.1"/>), the origin server
1645   &MUST; decode the request-target in order to
1646   properly interpret the request. Servers &SHOULD; respond to invalid
1647   request-targets with an appropriate status code.
1648</t>
1649<t>
1650   A transparent proxy &MUST-NOT; rewrite the "path-absolute" part of the
1651   received request-target when forwarding it to the next inbound server,
1652   except as noted above to replace a null path-absolute with "/".
1653</t>
1654<x:note>
1655  <t>
1656    <x:h>Note:</x:h> The "no rewrite" rule prevents the proxy from changing the
1657    meaning of the request when the origin server is improperly using
1658    a non-reserved URI character for a reserved purpose.  Implementors
1659    should be aware that some pre-HTTP/1.1 proxies have been known to
1660    rewrite the request-target.
1661  </t>
1662</x:note>
1663<t>
1664   HTTP does not place a pre-defined limit on the length of a request-target.
1665   A server &MUST; be prepared to receive URIs of unbounded length and
1666   respond with the 414 (URI Too Long) status if the received
1667   request-target would be longer than the server wishes to handle
1668   (see &status-414;).
1669</t>
1670<t>
1671   Various ad-hoc limitations on request-target length are found in practice.
1672   It is &RECOMMENDED; that all HTTP senders and recipients support
1673   request-target lengths of 8000 or more OCTETs.
1674</t>
1675</section>
1676</section>
1677
1678<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1679<t>
1680   The exact resource identified by an Internet request is determined by
1681   examining both the request-target and the Host header field.
1682</t>
1683<t>
1684   An origin server that does not allow resources to differ by the
1685   requested host &MAY; ignore the Host header field value when
1686   determining the resource identified by an HTTP/1.1 request. (But see
1687   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1688   for other requirements on Host support in HTTP/1.1.)
1689</t>
1690<t>
1691   An origin server that does differentiate resources based on the host
1692   requested (sometimes referred to as virtual hosts or vanity host
1693   names) &MUST; use the following rules for determining the requested
1694   resource on an HTTP/1.1 request:
1695  <list style="numbers">
1696    <t>If request-target is an absolute-URI, the host is part of the
1697     request-target. Any Host header field value in the request &MUST; be
1698     ignored.</t>
1699    <t>If the request-target is not an absolute-URI, and the request includes
1700     a Host header field, the host is determined by the Host header
1701     field value.</t>
1702    <t>If the host as determined by rule 1 or 2 is not a valid host on
1703     the server, the response &MUST; be a 400 (Bad Request) error message.</t>
1704  </list>
1705</t>
1706<t>
1707   Recipients of an HTTP/1.0 request that lacks a Host header field &MAY;
1708   attempt to use heuristics (e.g., examination of the URI path for
1709   something unique to a particular host) in order to determine what
1710   exact resource is being requested.
1711</t>
1712</section>
1713
1714</section>
1715
1716
1717<section title="Response" anchor="response">
1718  <x:anchor-alias value="Response"/>
1719<t>
1720   After receiving and interpreting a request message, a server responds
1721   with an HTTP response message.
1722</t>
1723<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Response"/>
1724  <x:ref>Response</x:ref>      = <x:ref>Status-Line</x:ref>               ; <xref target="status-line"/>
1725                  *(( <x:ref>general-header</x:ref>        ; <xref target="general.header.fields"/>
1726                   / <x:ref>response-header</x:ref>        ; &response-header-fields;
1727                   / <x:ref>entity-header</x:ref> ) <x:ref>CRLF</x:ref> )  ; &entity-header-fields;
1728                  <x:ref>CRLF</x:ref>
1729                  [ <x:ref>message-body</x:ref> ]          ; <xref target="message.body"/>
1730</artwork></figure>
1731
1732<section title="Status-Line" anchor="status-line">
1733  <x:anchor-alias value="Status-Line"/>
1734<t>
1735   The first line of a Response message is the Status-Line, consisting
1736   of the protocol version followed by a numeric status code and its
1737   associated textual phrase, with each element separated by SP
1738   characters. No CR or LF is allowed except in the final CRLF sequence.
1739</t>
1740<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Status-Line"/>
1741  <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>
1742</artwork></figure>
1743
1744<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1745  <x:anchor-alias value="Reason-Phrase"/>
1746  <x:anchor-alias value="Status-Code"/>
1747<t>
1748   The Status-Code element is a 3-digit integer result code of the
1749   attempt to understand and satisfy the request. These codes are fully
1750   defined in &status-codes;.  The Reason Phrase exists for the sole
1751   purpose of providing a textual description associated with the numeric
1752   status code, out of deference to earlier Internet application protocols
1753   that were more frequently used with interactive text clients.
1754   A client &SHOULD; ignore the content of the Reason Phrase.
1755</t>
1756<t>
1757   The first digit of the Status-Code defines the class of response. The
1758   last two digits do not have any categorization role. There are 5
1759   values for the first digit:
1760  <list style="symbols">
1761    <t>
1762      1xx: Informational - Request received, continuing process
1763    </t>
1764    <t>
1765      2xx: Success - The action was successfully received,
1766        understood, and accepted
1767    </t>
1768    <t>
1769      3xx: Redirection - Further action must be taken in order to
1770        complete the request
1771    </t>
1772    <t>
1773      4xx: Client Error - The request contains bad syntax or cannot
1774        be fulfilled
1775    </t>
1776    <t>
1777      5xx: Server Error - The server failed to fulfill an apparently
1778        valid request
1779    </t>
1780  </list>
1781</t>
1782<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"/>
1783  <x:ref>Status-Code</x:ref>    = 3<x:ref>DIGIT</x:ref>
1784  <x:ref>Reason-Phrase</x:ref>  = *( <x:ref>WSP</x:ref> / <x:ref>VCHAR</x:ref> / <x:ref>obs-text</x:ref> )
1785</artwork></figure>
1786</section>
1787</section>
1788
1789</section>
1790
1791
1792<section title="Connections" anchor="connections">
1793
1794<section title="Persistent Connections" anchor="persistent.connections">
1795
1796<section title="Purpose" anchor="persistent.purpose">
1797<t>
1798   Prior to persistent connections, a separate TCP connection was
1799   established to fetch each URL, increasing the load on HTTP servers
1800   and causing congestion on the Internet. The use of inline images and
1801   other associated data often require a client to make multiple
1802   requests of the same server in a short amount of time. Analysis of
1803   these performance problems and results from a prototype
1804   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1805   measurements of actual HTTP/1.1 implementations show good
1806   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1807   T/TCP <xref target="Tou1998"/>.
1808</t>
1809<t>
1810   Persistent HTTP connections have a number of advantages:
1811  <list style="symbols">
1812      <t>
1813        By opening and closing fewer TCP connections, CPU time is saved
1814        in routers and hosts (clients, servers, proxies, gateways,
1815        tunnels, or caches), and memory used for TCP protocol control
1816        blocks can be saved in hosts.
1817      </t>
1818      <t>
1819        HTTP requests and responses can be pipelined on a connection.
1820        Pipelining allows a client to make multiple requests without
1821        waiting for each response, allowing a single TCP connection to
1822        be used much more efficiently, with much lower elapsed time.
1823      </t>
1824      <t>
1825        Network congestion is reduced by reducing the number of packets
1826        caused by TCP opens, and by allowing TCP sufficient time to
1827        determine the congestion state of the network.
1828      </t>
1829      <t>
1830        Latency on subsequent requests is reduced since there is no time
1831        spent in TCP's connection opening handshake.
1832      </t>
1833      <t>
1834        HTTP can evolve more gracefully, since errors can be reported
1835        without the penalty of closing the TCP connection. Clients using
1836        future versions of HTTP might optimistically try a new feature,
1837        but if communicating with an older server, retry with old
1838        semantics after an error is reported.
1839      </t>
1840    </list>
1841</t>
1842<t>
1843   HTTP implementations &SHOULD; implement persistent connections.
1844</t>
1845</section>
1846
1847<section title="Overall Operation" anchor="persistent.overall">
1848<t>
1849   A significant difference between HTTP/1.1 and earlier versions of
1850   HTTP is that persistent connections are the default behavior of any
1851   HTTP connection. That is, unless otherwise indicated, the client
1852   &SHOULD; assume that the server will maintain a persistent connection,
1853   even after error responses from the server.
1854</t>
1855<t>
1856   Persistent connections provide a mechanism by which a client and a
1857   server can signal the close of a TCP connection. This signaling takes
1858   place using the Connection header field (<xref target="header.connection"/>). Once a close
1859   has been signaled, the client &MUST-NOT; send any more requests on that
1860   connection.
1861</t>
1862
1863<section title="Negotiation" anchor="persistent.negotiation">
1864<t>
1865   An HTTP/1.1 server &MAY; assume that a HTTP/1.1 client intends to
1866   maintain a persistent connection unless a Connection header including
1867   the connection-token "close" was sent in the request. If the server
1868   chooses to close the connection immediately after sending the
1869   response, it &SHOULD; send a Connection header including the
1870   connection-token close.
1871</t>
1872<t>
1873   An HTTP/1.1 client &MAY; expect a connection to remain open, but would
1874   decide to keep it open based on whether the response from a server
1875   contains a Connection header with the connection-token close. In case
1876   the client does not want to maintain a connection for more than that
1877   request, it &SHOULD; send a Connection header including the
1878   connection-token close.
1879</t>
1880<t>
1881   If either the client or the server sends the close token in the
1882   Connection header, that request becomes the last one for the
1883   connection.
1884</t>
1885<t>
1886   Clients and servers &SHOULD-NOT;  assume that a persistent connection is
1887   maintained for HTTP versions less than 1.1 unless it is explicitly
1888   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
1889   compatibility with HTTP/1.0 clients.
1890</t>
1891<t>
1892   In order to remain persistent, all messages on the connection &MUST;
1893   have a self-defined message length (i.e., one not defined by closure
1894   of the connection), as described in <xref target="message.length"/>.
1895</t>
1896</section>
1897
1898<section title="Pipelining" anchor="pipelining">
1899<t>
1900   A client that supports persistent connections &MAY; "pipeline" its
1901   requests (i.e., send multiple requests without waiting for each
1902   response). A server &MUST; send its responses to those requests in the
1903   same order that the requests were received.
1904</t>
1905<t>
1906   Clients which assume persistent connections and pipeline immediately
1907   after connection establishment &SHOULD; be prepared to retry their
1908   connection if the first pipelined attempt fails. If a client does
1909   such a retry, it &MUST-NOT; pipeline before it knows the connection is
1910   persistent. Clients &MUST; also be prepared to resend their requests if
1911   the server closes the connection before sending all of the
1912   corresponding responses.
1913</t>
1914<t>
1915   Clients &SHOULD-NOT;  pipeline requests using non-idempotent methods or
1916   non-idempotent sequences of methods (see &idempotent-methods;). Otherwise, a
1917   premature termination of the transport connection could lead to
1918   indeterminate results. A client wishing to send a non-idempotent
1919   request &SHOULD; wait to send that request until it has received the
1920   response status for the previous request.
1921</t>
1922</section>
1923</section>
1924
1925<section title="Proxy Servers" anchor="persistent.proxy">
1926<t>
1927   It is especially important that proxies correctly implement the
1928   properties of the Connection header field as specified in <xref target="header.connection"/>.
1929</t>
1930<t>
1931   The proxy server &MUST; signal persistent connections separately with
1932   its clients and the origin servers (or other proxy servers) that it
1933   connects to. Each persistent connection applies to only one transport
1934   link.
1935</t>
1936<t>
1937   A proxy server &MUST-NOT; establish a HTTP/1.1 persistent connection
1938   with an HTTP/1.0 client (but see <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>
1939   for information and discussion of the problems with the Keep-Alive header
1940   implemented by many HTTP/1.0 clients).
1941</t>
1942</section>
1943
1944<section title="Practical Considerations" anchor="persistent.practical">
1945<t>
1946   Servers will usually have some time-out value beyond which they will
1947   no longer maintain an inactive connection. Proxy servers might make
1948   this a higher value since it is likely that the client will be making
1949   more connections through the same server. The use of persistent
1950   connections places no requirements on the length (or existence) of
1951   this time-out for either the client or the server.
1952</t>
1953<t>
1954   When a client or server wishes to time-out it &SHOULD; issue a graceful
1955   close on the transport connection. Clients and servers &SHOULD; both
1956   constantly watch for the other side of the transport close, and
1957   respond to it as appropriate. If a client or server does not detect
1958   the other side's close promptly it could cause unnecessary resource
1959   drain on the network.
1960</t>
1961<t>
1962   A client, server, or proxy &MAY; close the transport connection at any
1963   time. For example, a client might have started to send a new request
1964   at the same time that the server has decided to close the "idle"
1965   connection. From the server's point of view, the connection is being
1966   closed while it was idle, but from the client's point of view, a
1967   request is in progress.
1968</t>
1969<t>
1970   This means that clients, servers, and proxies &MUST; be able to recover
1971   from asynchronous close events. Client software &SHOULD; reopen the
1972   transport connection and retransmit the aborted sequence of requests
1973   without user interaction so long as the request sequence is
1974   idempotent (see &idempotent-methods;). Non-idempotent methods or sequences
1975   &MUST-NOT; be automatically retried, although user agents &MAY; offer a
1976   human operator the choice of retrying the request(s). Confirmation by
1977   user-agent software with semantic understanding of the application
1978   &MAY; substitute for user confirmation. The automatic retry &SHOULD-NOT; 
1979   be repeated if the second sequence of requests fails.
1980</t>
1981<t>
1982   Servers &SHOULD; always respond to at least one request per connection,
1983   if at all possible. Servers &SHOULD-NOT;  close a connection in the
1984   middle of transmitting a response, unless a network or client failure
1985   is suspected.
1986</t>
1987<t>
1988   Clients that use persistent connections &SHOULD; limit the number of
1989   simultaneous connections that they maintain to a given server. A
1990   single-user client &SHOULD-NOT; maintain more than 2 connections with
1991   any server or proxy. A proxy &SHOULD; use up to 2*N connections to
1992   another server or proxy, where N is the number of simultaneously
1993   active users. These guidelines are intended to improve HTTP response
1994   times and avoid congestion.
1995</t>
1996</section>
1997</section>
1998
1999<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2000
2001<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2002<t>
2003   HTTP/1.1 servers &SHOULD; maintain persistent connections and use TCP's
2004   flow control mechanisms to resolve temporary overloads, rather than
2005   terminating connections with the expectation that clients will retry.
2006   The latter technique can exacerbate network congestion.
2007</t>
2008</section>
2009
2010<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2011<t>
2012   An HTTP/1.1 (or later) client sending a message-body &SHOULD; monitor
2013   the network connection for an error status while it is transmitting
2014   the request. If the client sees an error status, it &SHOULD;
2015   immediately cease transmitting the body. If the body is being sent
2016   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2017   empty trailer &MAY; be used to prematurely mark the end of the message.
2018   If the body was preceded by a Content-Length header, the client &MUST;
2019   close the connection.
2020</t>
2021</section>
2022
2023<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2024<t>
2025   The purpose of the 100 (Continue) status (see &status-100;) is to
2026   allow a client that is sending a request message with a request body
2027   to determine if the origin server is willing to accept the request
2028   (based on the request headers) before the client sends the request
2029   body. In some cases, it might either be inappropriate or highly
2030   inefficient for the client to send the body if the server will reject
2031   the message without looking at the body.
2032</t>
2033<t>
2034   Requirements for HTTP/1.1 clients:
2035  <list style="symbols">
2036    <t>
2037        If a client will wait for a 100 (Continue) response before
2038        sending the request body, it &MUST; send an Expect request-header
2039        field (&header-expect;) with the "100-continue" expectation.
2040    </t>
2041    <t>
2042        A client &MUST-NOT; send an Expect request-header field (&header-expect;)
2043        with the "100-continue" expectation if it does not intend
2044        to send a request body.
2045    </t>
2046  </list>
2047</t>
2048<t>
2049   Because of the presence of older implementations, the protocol allows
2050   ambiguous situations in which a client may send "Expect: 100-continue"
2051   without receiving either a 417 (Expectation Failed) status
2052   or a 100 (Continue) status. Therefore, when a client sends this
2053   header field to an origin server (possibly via a proxy) from which it
2054   has never seen a 100 (Continue) status, the client &SHOULD-NOT;  wait
2055   for an indefinite period before sending the request body.
2056</t>
2057<t>
2058   Requirements for HTTP/1.1 origin servers:
2059  <list style="symbols">
2060    <t> Upon receiving a request which includes an Expect request-header
2061        field with the "100-continue" expectation, an origin server &MUST;
2062        either respond with 100 (Continue) status and continue to read
2063        from the input stream, or respond with a final status code. The
2064        origin server &MUST-NOT; wait for the request body before sending
2065        the 100 (Continue) response. If it responds with a final status
2066        code, it &MAY; close the transport connection or it &MAY; continue
2067        to read and discard the rest of the request.  It &MUST-NOT;
2068        perform the requested method if it returns a final status code.
2069    </t>
2070    <t> An origin server &SHOULD-NOT;  send a 100 (Continue) response if
2071        the request message does not include an Expect request-header
2072        field with the "100-continue" expectation, and &MUST-NOT; send a
2073        100 (Continue) response if such a request comes from an HTTP/1.0
2074        (or earlier) client. There is an exception to this rule: for
2075        compatibility with <xref target="RFC2068"/>, a server &MAY; send a 100 (Continue)
2076        status in response to an HTTP/1.1 PUT or POST request that does
2077        not include an Expect request-header field with the "100-continue"
2078        expectation. This exception, the purpose of which is
2079        to minimize any client processing delays associated with an
2080        undeclared wait for 100 (Continue) status, applies only to
2081        HTTP/1.1 requests, and not to requests with any other HTTP-version
2082        value.
2083    </t>
2084    <t> An origin server &MAY; omit a 100 (Continue) response if it has
2085        already received some or all of the request body for the
2086        corresponding request.
2087    </t>
2088    <t> An origin server that sends a 100 (Continue) response &MUST;
2089    ultimately send a final status code, once the request body is
2090        received and processed, unless it terminates the transport
2091        connection prematurely.
2092    </t>
2093    <t> If an origin server receives a request that does not include an
2094        Expect request-header field with the "100-continue" expectation,
2095        the request includes a request body, and the server responds
2096        with a final status code before reading the entire request body
2097        from the transport connection, then the server &SHOULD-NOT;  close
2098        the transport connection until it has read the entire request,
2099        or until the client closes the connection. Otherwise, the client
2100        might not reliably receive the response message. However, this
2101        requirement is not be construed as preventing a server from
2102        defending itself against denial-of-service attacks, or from
2103        badly broken client implementations.
2104      </t>
2105    </list>
2106</t>
2107<t>
2108   Requirements for HTTP/1.1 proxies:
2109  <list style="symbols">
2110    <t> If a proxy receives a request that includes an Expect request-header
2111        field with the "100-continue" expectation, and the proxy
2112        either knows that the next-hop server complies with HTTP/1.1 or
2113        higher, or does not know the HTTP version of the next-hop
2114        server, it &MUST; forward the request, including the Expect header
2115        field.
2116    </t>
2117    <t> If the proxy knows that the version of the next-hop server is
2118        HTTP/1.0 or lower, it &MUST-NOT; forward the request, and it &MUST;
2119        respond with a 417 (Expectation Failed) status.
2120    </t>
2121    <t> Proxies &SHOULD; maintain a cache recording the HTTP version
2122        numbers received from recently-referenced next-hop servers.
2123    </t>
2124    <t> A proxy &MUST-NOT; forward a 100 (Continue) response if the
2125        request message was received from an HTTP/1.0 (or earlier)
2126        client and did not include an Expect request-header field with
2127        the "100-continue" expectation. This requirement overrides the
2128        general rule for forwarding of 1xx responses (see &status-1xx;).
2129    </t>
2130  </list>
2131</t>
2132</section>
2133
2134<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2135<t>
2136   If an HTTP/1.1 client sends a request which includes a request body,
2137   but which does not include an Expect request-header field with the
2138   "100-continue" expectation, and if the client is not directly
2139   connected to an HTTP/1.1 origin server, and if the client sees the
2140   connection close before receiving any status from the server, the
2141   client &SHOULD; retry the request.  If the client does retry this
2142   request, it &MAY; use the following "binary exponential backoff"
2143   algorithm to be assured of obtaining a reliable response:
2144  <list style="numbers">
2145    <t>
2146      Initiate a new connection to the server
2147    </t>
2148    <t>
2149      Transmit the request-headers
2150    </t>
2151    <t>
2152      Initialize a variable R to the estimated round-trip time to the
2153         server (e.g., based on the time it took to establish the
2154         connection), or to a constant value of 5 seconds if the round-trip
2155         time is not available.
2156    </t>
2157    <t>
2158       Compute T = R * (2**N), where N is the number of previous
2159         retries of this request.
2160    </t>
2161    <t>
2162       Wait either for an error response from the server, or for T
2163         seconds (whichever comes first)
2164    </t>
2165    <t>
2166       If no error response is received, after T seconds transmit the
2167         body of the request.
2168    </t>
2169    <t>
2170       If client sees that the connection is closed prematurely,
2171         repeat from step 1 until the request is accepted, an error
2172         response is received, or the user becomes impatient and
2173         terminates the retry process.
2174    </t>
2175  </list>
2176</t>
2177<t>
2178   If at any point an error status is received, the client
2179  <list style="symbols">
2180      <t>&SHOULD-NOT;  continue and</t>
2181
2182      <t>&SHOULD; close the connection if it has not completed sending the
2183        request message.</t>
2184    </list>
2185</t>
2186</section>
2187</section>
2188</section>
2189
2190
2191<section title="Header Field Definitions" anchor="header.fields">
2192<t>
2193   This section defines the syntax and semantics of HTTP/1.1 header fields
2194   related to message framing and transport protocols.
2195</t>
2196<t>
2197   For entity-header fields, both sender and recipient refer to either the
2198   client or the server, depending on who sends and who receives the entity.
2199</t>
2200
2201<section title="Connection" anchor="header.connection">
2202  <iref primary="true" item="Connection header" x:for-anchor=""/>
2203  <iref primary="true" item="Headers" subitem="Connection" x:for-anchor=""/>
2204  <x:anchor-alias value="Connection"/>
2205  <x:anchor-alias value="connection-token"/>
2206  <x:anchor-alias value="Connection-v"/>
2207<t>
2208   The general-header field "Connection" allows the sender to specify
2209   options that are desired for that particular connection and &MUST-NOT;
2210   be communicated by proxies over further connections.
2211</t>
2212<t>
2213   The Connection header's value has the following grammar:
2214</t>
2215<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"/>
2216  <x:ref>Connection</x:ref>       = "Connection" ":" <x:ref>OWS</x:ref> <x:ref>Connection-v</x:ref>
2217  <x:ref>Connection-v</x:ref>     = 1#<x:ref>connection-token</x:ref>
2218  <x:ref>connection-token</x:ref> = <x:ref>token</x:ref>
2219</artwork></figure>
2220<t>
2221   HTTP/1.1 proxies &MUST; parse the Connection header field before a
2222   message is forwarded and, for each connection-token in this field,
2223   remove any header field(s) from the message with the same name as the
2224   connection-token. Connection options are signaled by the presence of
2225   a connection-token in the Connection header field, not by any
2226   corresponding additional header field(s), since the additional header
2227   field may not be sent if there are no parameters associated with that
2228   connection option.
2229</t>
2230<t>
2231   Message headers listed in the Connection header &MUST-NOT; include
2232   end-to-end headers, such as Cache-Control.
2233</t>
2234<t>
2235   HTTP/1.1 defines the "close" connection option for the sender to
2236   signal that the connection will be closed after completion of the
2237   response. For example,
2238</t>
2239<figure><artwork type="example">
2240  Connection: close
2241</artwork></figure>
2242<t>
2243   in either the request or the response header fields indicates that
2244   the connection &SHOULD-NOT;  be considered `persistent' (<xref target="persistent.connections"/>)
2245   after the current request/response is complete.
2246</t>
2247<t>
2248   An HTTP/1.1 client that does not support persistent connections &MUST;
2249   include the "close" connection option in every request message.
2250</t>
2251<t>
2252   An HTTP/1.1 server that does not support persistent connections &MUST;
2253   include the "close" connection option in every response message that
2254   does not have a 1xx (informational) status code.
2255</t>
2256<t>
2257   A system receiving an HTTP/1.0 (or lower-version) message that
2258   includes a Connection header &MUST;, for each connection-token in this
2259   field, remove and ignore any header field(s) from the message with
2260   the same name as the connection-token. This protects against mistaken
2261   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2262</t>
2263</section>
2264
2265<section title="Content-Length" anchor="header.content-length">
2266  <iref primary="true" item="Content-Length header" x:for-anchor=""/>
2267  <iref primary="true" item="Headers" subitem="Content-Length" x:for-anchor=""/>
2268  <x:anchor-alias value="Content-Length"/>
2269  <x:anchor-alias value="Content-Length-v"/>
2270<t>
2271   The entity-header field "Content-Length" indicates the size of the
2272   entity-body, in number of OCTETs, sent to the recipient or,
2273   in the case of the HEAD method, the size of the entity-body that
2274   would have been sent had the request been a GET.
2275</t>
2276<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/>
2277  <x:ref>Content-Length</x:ref>   = "Content-Length" ":" <x:ref>OWS</x:ref> 1*<x:ref>Content-Length-v</x:ref>
2278  <x:ref>Content-Length-v</x:ref> = 1*<x:ref>DIGIT</x:ref>
2279</artwork></figure>
2280<t>
2281   An example is
2282</t>
2283<figure><artwork type="example">
2284  Content-Length: 3495
2285</artwork></figure>
2286<t>
2287   Applications &SHOULD; use this field to indicate the transfer-length of
2288   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2289</t>
2290<t>
2291   Any Content-Length greater than or equal to zero is a valid value.
2292   <xref target="message.length"/> describes how to determine the length of a message-body
2293   if a Content-Length is not given.
2294</t>
2295<t>
2296   Note that the meaning of this field is significantly different from
2297   the corresponding definition in MIME, where it is an optional field
2298   used within the "message/external-body" content-type. In HTTP, it
2299   &SHOULD; be sent whenever the message's length can be determined prior
2300   to being transferred, unless this is prohibited by the rules in
2301   <xref target="message.length"/>.
2302</t>
2303</section>
2304
2305<section title="Date" anchor="header.date">
2306  <iref primary="true" item="Date header" x:for-anchor=""/>
2307  <iref primary="true" item="Headers" subitem="Date" x:for-anchor=""/>
2308  <x:anchor-alias value="Date"/>
2309  <x:anchor-alias value="Date-v"/>
2310<t>
2311   The general-header field "Date" represents the date and time at which
2312   the message was originated, having the same semantics as orig-date in
2313   <xref target="RFC5322" x:fmt="of" x:sec="3.6.1"/>. The field value is an
2314   HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2315   it &MUST; be sent in rfc1123-date format.
2316</t>
2317<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/>
2318  <x:ref>Date</x:ref>   = "Date" ":" <x:ref>OWS</x:ref> <x:ref>Date-v</x:ref>
2319  <x:ref>Date-v</x:ref> = <x:ref>HTTP-date</x:ref>
2320</artwork></figure>
2321<t>
2322   An example is
2323</t>
2324<figure><artwork type="example">
2325  Date: Tue, 15 Nov 1994 08:12:31 GMT
2326</artwork></figure>
2327<t>
2328   Origin servers &MUST; include a Date header field in all responses,
2329   except in these cases:
2330  <list style="numbers">
2331      <t>If the response status code is 100 (Continue) or 101 (Switching
2332         Protocols), the response &MAY; include a Date header field, at
2333         the server's option.</t>
2334
2335      <t>If the response status code conveys a server error, e.g. 500
2336         (Internal Server Error) or 503 (Service Unavailable), and it is
2337         inconvenient or impossible to generate a valid Date.</t>
2338
2339      <t>If the server does not have a clock that can provide a
2340         reasonable approximation of the current time, its responses
2341         &MUST-NOT; include a Date header field. In this case, the rules
2342         in <xref target="clockless.origin.server.operation"/> &MUST; be followed.</t>
2343  </list>
2344</t>
2345<t>
2346   A received message that does not have a Date header field &MUST; be
2347   assigned one by the recipient if the message will be cached by that
2348   recipient or gatewayed via a protocol which requires a Date. An HTTP
2349   implementation without a clock &MUST-NOT; cache responses without
2350   revalidating them on every use. An HTTP cache, especially a shared
2351   cache, &SHOULD; use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2352   clock with a reliable external standard.
2353</t>
2354<t>
2355   Clients &SHOULD; only send a Date header field in messages that include
2356   an entity-body, as in the case of the PUT and POST requests, and even
2357   then it is optional. A client without a clock &MUST-NOT; send a Date
2358   header field in a request.
2359</t>
2360<t>
2361   The HTTP-date sent in a Date header &SHOULD-NOT;  represent a date and
2362   time subsequent to the generation of the message. It &SHOULD; represent
2363   the best available approximation of the date and time of message
2364   generation, unless the implementation has no means of generating a
2365   reasonably accurate date and time. In theory, the date ought to
2366   represent the moment just before the entity is generated. In
2367   practice, the date can be generated at any time during the message
2368   origination without affecting its semantic value.
2369</t>
2370
2371<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2372<t>
2373   Some origin server implementations might not have a clock available.
2374   An origin server without a clock &MUST-NOT; assign Expires or Last-Modified
2375   values to a response, unless these values were associated
2376   with the resource by a system or user with a reliable clock. It &MAY;
2377   assign an Expires value that is known, at or before server
2378   configuration time, to be in the past (this allows "pre-expiration"
2379   of responses without storing separate Expires values for each
2380   resource).
2381</t>
2382</section>
2383</section>
2384
2385<section title="Host" anchor="header.host">
2386  <iref primary="true" item="Host header" x:for-anchor=""/>
2387  <iref primary="true" item="Headers" subitem="Host" x:for-anchor=""/>
2388  <x:anchor-alias value="Host"/>
2389  <x:anchor-alias value="Host-v"/>
2390<t>
2391   The request-header field "Host" specifies the Internet host and port
2392   number of the resource being requested, as obtained from the original
2393   URI given by the user or referring resource (generally an http URI,
2394   as described in <xref target="http.uri"/>). The Host field value &MUST; represent
2395   the naming authority of the origin server or gateway given by the
2396   original URL. This allows the origin server or gateway to
2397   differentiate between internally-ambiguous URLs, such as the root "/"
2398   URL of a server for multiple host names on a single IP address.
2399</t>
2400<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/>
2401  <x:ref>Host</x:ref>   = "Host" ":" <x:ref>OWS</x:ref> <x:ref>Host-v</x:ref>
2402  <x:ref>Host-v</x:ref> = <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ; <xref target="http.uri"/>
2403</artwork></figure>
2404<t>
2405   A "host" without any trailing port information implies the default
2406   port for the service requested (e.g., "80" for an HTTP URL). For
2407   example, a request on the origin server for
2408   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2409</t>
2410<figure><artwork type="example">
2411  GET /pub/WWW/ HTTP/1.1
2412  Host: www.example.org
2413</artwork></figure>
2414<t>
2415   A client &MUST; include a Host header field in all HTTP/1.1 request
2416   messages. If the requested URI does not include an Internet host
2417   name for the service being requested, then the Host header field &MUST;
2418   be given with an empty value. An HTTP/1.1 proxy &MUST; ensure that any
2419   request message it forwards does contain an appropriate Host header
2420   field that identifies the service being requested by the proxy. All
2421   Internet-based HTTP/1.1 servers &MUST; respond with a 400 (Bad Request)
2422   status code to any HTTP/1.1 request message which lacks a Host header
2423   field.
2424</t>
2425<t>
2426   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2427   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2428   for other requirements relating to Host.
2429</t>
2430</section>
2431
2432<section title="TE" anchor="header.te">
2433  <iref primary="true" item="TE header" x:for-anchor=""/>
2434  <iref primary="true" item="Headers" subitem="TE" x:for-anchor=""/>
2435  <x:anchor-alias value="TE"/>
2436  <x:anchor-alias value="TE-v"/>
2437  <x:anchor-alias value="t-codings"/>
2438  <x:anchor-alias value="te-params"/>
2439  <x:anchor-alias value="te-ext"/>
2440<t>
2441   The request-header field "TE" indicates what extension transfer-codings
2442   it is willing to accept in the response and whether or not it is
2443   willing to accept trailer fields in a chunked transfer-coding. Its
2444   value may consist of the keyword "trailers" and/or a comma-separated
2445   list of extension transfer-coding names with optional accept
2446   parameters (as described in <xref target="transfer.codings"/>).
2447</t>
2448<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"/>
2449  <x:ref>TE</x:ref>        = "TE" ":" <x:ref>OWS</x:ref> <x:ref>TE-v</x:ref>
2450  <x:ref>TE-v</x:ref>      = #<x:ref>t-codings</x:ref>
2451  <x:ref>t-codings</x:ref> = "trailers" / ( <x:ref>transfer-extension</x:ref> [ <x:ref>te-params</x:ref> ] )
2452  <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> )
2453  <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> ) ]
2454</artwork></figure>
2455<t>
2456   The presence of the keyword "trailers" indicates that the client is
2457   willing to accept trailer fields in a chunked transfer-coding, as
2458   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2459   transfer-coding values even though it does not itself represent a
2460   transfer-coding.
2461</t>
2462<t>
2463   Examples of its use are:
2464</t>
2465<figure><artwork type="example">
2466  TE: deflate
2467  TE:
2468  TE: trailers, deflate;q=0.5
2469</artwork></figure>
2470<t>
2471   The TE header field only applies to the immediate connection.
2472   Therefore, the keyword &MUST; be supplied within a Connection header
2473   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2474</t>
2475<t>
2476   A server tests whether a transfer-coding is acceptable, according to
2477   a TE field, using these rules:
2478  <list style="numbers">
2479    <x:lt>
2480      <t>The "chunked" transfer-coding is always acceptable. If the
2481         keyword "trailers" is listed, the client indicates that it is
2482         willing to accept trailer fields in the chunked response on
2483         behalf of itself and any downstream clients. The implication is
2484         that, if given, the client is stating that either all
2485         downstream clients are willing to accept trailer fields in the
2486         forwarded response, or that it will attempt to buffer the
2487         response on behalf of downstream recipients.
2488      </t><t>
2489         <x:h>Note:</x:h> HTTP/1.1 does not define any means to limit the size of a
2490         chunked response such that a client can be assured of buffering
2491         the entire response.</t>
2492    </x:lt>
2493    <x:lt>
2494      <t>If the transfer-coding being tested is one of the transfer-codings
2495         listed in the TE field, then it is acceptable unless it
2496         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2497         qvalue of 0 means "not acceptable.")</t>
2498    </x:lt>
2499    <x:lt>
2500      <t>If multiple transfer-codings are acceptable, then the
2501         acceptable transfer-coding with the highest non-zero qvalue is
2502         preferred.  The "chunked" transfer-coding always has a qvalue
2503         of 1.</t>
2504    </x:lt>
2505  </list>
2506</t>
2507<t>
2508   If the TE field-value is empty or if no TE field is present, the only
2509   transfer-coding is "chunked". A message with no transfer-coding is
2510   always acceptable.
2511</t>
2512</section>
2513
2514<section title="Trailer" anchor="header.trailer">
2515  <iref primary="true" item="Trailer header" x:for-anchor=""/>
2516  <iref primary="true" item="Headers" subitem="Trailer" x:for-anchor=""/>
2517  <x:anchor-alias value="Trailer"/>
2518  <x:anchor-alias value="Trailer-v"/>
2519<t>
2520   The general field "Trailer" indicates that the given set of
2521   header fields is present in the trailer of a message encoded with
2522   chunked transfer-coding.
2523</t>
2524<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/>
2525  <x:ref>Trailer</x:ref>   = "Trailer" ":" <x:ref>OWS</x:ref> <x:ref>Trailer-v</x:ref>
2526  <x:ref>Trailer-v</x:ref> = 1#<x:ref>field-name</x:ref>
2527</artwork></figure>
2528<t>
2529   An HTTP/1.1 message &SHOULD; include a Trailer header field in a
2530   message using chunked transfer-coding with a non-empty trailer. Doing
2531   so allows the recipient to know which header fields to expect in the
2532   trailer.
2533</t>
2534<t>
2535   If no Trailer header field is present, the trailer &SHOULD-NOT;  include
2536   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2537   trailer fields in a "chunked" transfer-coding.
2538</t>
2539<t>
2540   Message header fields listed in the Trailer header field &MUST-NOT;
2541   include the following header fields:
2542  <list style="symbols">
2543    <t>Transfer-Encoding</t>
2544    <t>Content-Length</t>
2545    <t>Trailer</t>
2546  </list>
2547</t>
2548</section>
2549
2550<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2551  <iref primary="true" item="Transfer-Encoding header" x:for-anchor=""/>
2552  <iref primary="true" item="Headers" subitem="Transfer-Encoding" x:for-anchor=""/>
2553  <x:anchor-alias value="Transfer-Encoding"/>
2554  <x:anchor-alias value="Transfer-Encoding-v"/>
2555<t>
2556   The general-header "Transfer-Encoding" field indicates what (if any)
2557   type of transformation has been applied to the message body in order
2558   to safely transfer it between the sender and the recipient. This
2559   differs from the content-coding in that the transfer-coding is a
2560   property of the message, not of the entity.
2561</t>
2562<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/>
2563  <x:ref>Transfer-Encoding</x:ref>   = "Transfer-Encoding" ":" <x:ref>OWS</x:ref>
2564                        <x:ref>Transfer-Encoding-v</x:ref>
2565  <x:ref>Transfer-Encoding-v</x:ref> = 1#<x:ref>transfer-coding</x:ref>
2566</artwork></figure>
2567<t>
2568   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2569</t>
2570<figure><artwork type="example">
2571  Transfer-Encoding: chunked
2572</artwork></figure>
2573<t>
2574   If multiple encodings have been applied to an entity, the transfer-codings
2575   &MUST; be listed in the order in which they were applied.
2576   Additional information about the encoding parameters &MAY; be provided
2577   by other entity-header fields not defined by this specification.
2578</t>
2579<t>
2580   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2581   header.
2582</t>
2583</section>
2584
2585<section title="Upgrade" anchor="header.upgrade">
2586  <iref primary="true" item="Upgrade header" x:for-anchor=""/>
2587  <iref primary="true" item="Headers" subitem="Upgrade" x:for-anchor=""/>
2588  <x:anchor-alias value="Upgrade"/>
2589  <x:anchor-alias value="Upgrade-v"/>
2590<t>
2591   The general-header "Upgrade" allows the client to specify what
2592   additional communication protocols it supports and would like to use
2593   if the server finds it appropriate to switch protocols. The server
2594   &MUST; use the Upgrade header field within a 101 (Switching Protocols)
2595   response to indicate which protocol(s) are being switched.
2596</t>
2597<figure><artwork type="abnf2616"><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/>
2598  <x:ref>Upgrade</x:ref>   = "Upgrade" ":" <x:ref>OWS</x:ref> <x:ref>Upgrade-v</x:ref>
2599  <x:ref>Upgrade-v</x:ref> = 1#<x:ref>product</x:ref>
2600</artwork></figure>
2601<t>
2602   For example,
2603</t>
2604<figure><artwork type="example">
2605  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2606</artwork></figure>
2607<t>
2608   The Upgrade header field is intended to provide a simple mechanism
2609   for transition from HTTP/1.1 to some other, incompatible protocol. It
2610   does so by allowing the client to advertise its desire to use another
2611   protocol, such as a later version of HTTP with a higher major version
2612   number, even though the current request has been made using HTTP/1.1.
2613   This eases the difficult transition between incompatible protocols by
2614   allowing the client to initiate a request in the more commonly
2615   supported protocol while indicating to the server that it would like
2616   to use a "better" protocol if available (where "better" is determined
2617   by the server, possibly according to the nature of the method and/or
2618   resource being requested).
2619</t>
2620<t>
2621   The Upgrade header field only applies to switching application-layer
2622   protocols upon the existing transport-layer connection. Upgrade
2623   cannot be used to insist on a protocol change; its acceptance and use
2624   by the server is optional. The capabilities and nature of the
2625   application-layer communication after the protocol change is entirely
2626   dependent upon the new protocol chosen, although the first action
2627   after changing the protocol &MUST; be a response to the initial HTTP
2628   request containing the Upgrade header field.
2629</t>
2630<t>
2631   The Upgrade header field only applies to the immediate connection.
2632   Therefore, the upgrade keyword &MUST; be supplied within a Connection
2633   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2634   HTTP/1.1 message.
2635</t>
2636<t>
2637   The Upgrade header field cannot be used to indicate a switch to a
2638   protocol on a different connection. For that purpose, it is more
2639   appropriate to use a 301, 302, 303, or 305 redirection response.
2640</t>
2641<t>
2642   This specification only defines the protocol name "HTTP" for use by
2643   the family of Hypertext Transfer Protocols, as defined by the HTTP
2644   version rules of <xref target="http.version"/> and future updates to this
2645   specification. Any token can be used as a protocol name; however, it
2646   will only be useful if both the client and server associate the name
2647   with the same protocol.
2648</t>
2649</section>
2650
2651<section title="Via" anchor="header.via">
2652  <iref primary="true" item="Via header" x:for-anchor=""/>
2653  <iref primary="true" item="Headers" subitem="Via" x:for-anchor=""/>
2654  <x:anchor-alias value="protocol-name"/>
2655  <x:anchor-alias value="protocol-version"/>
2656  <x:anchor-alias value="pseudonym"/>
2657  <x:anchor-alias value="received-by"/>
2658  <x:anchor-alias value="received-protocol"/>
2659  <x:anchor-alias value="Via"/>
2660  <x:anchor-alias value="Via-v"/>
2661<t>
2662   The general-header field "Via" &MUST; be used by gateways and proxies to
2663   indicate the intermediate protocols and recipients between the user
2664   agent and the server on requests, and between the origin server and
2665   the client on responses. It is analogous to the "Received" field defined in
2666   <xref target="RFC5322" x:fmt="of" x:sec="3.6.7"/> and is intended to be used for tracking message forwards,
2667   avoiding request loops, and identifying the protocol capabilities of
2668   all senders along the request/response chain.
2669</t>
2670<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"/>
2671  <x:ref>Via</x:ref>               = "Via" ":" <x:ref>OWS</x:ref> <x:ref>Via-v</x:ref>
2672  <x:ref>Via-v</x:ref>             = 1#( <x:ref>received-protocol</x:ref> <x:ref>RWS</x:ref> <x:ref>received-by</x:ref>
2673                          [ <x:ref>RWS</x:ref> <x:ref>comment</x:ref> ] )
2674  <x:ref>received-protocol</x:ref> = [ <x:ref>protocol-name</x:ref> "/" ] <x:ref>protocol-version</x:ref>
2675  <x:ref>protocol-name</x:ref>     = <x:ref>token</x:ref>
2676  <x:ref>protocol-version</x:ref>  = <x:ref>token</x:ref>
2677  <x:ref>received-by</x:ref>       = ( <x:ref>uri-host</x:ref> [ ":" <x:ref>port</x:ref> ] ) / <x:ref>pseudonym</x:ref>
2678  <x:ref>pseudonym</x:ref>         = <x:ref>token</x:ref>
2679</artwork></figure>
2680<t>
2681   The received-protocol indicates the protocol version of the message
2682   received by the server or client along each segment of the
2683   request/response chain. The received-protocol version is appended to
2684   the Via field value when the message is forwarded so that information
2685   about the protocol capabilities of upstream applications remains
2686   visible to all recipients.
2687</t>
2688<t>
2689   The protocol-name is optional if and only if it would be "HTTP". The
2690   received-by field is normally the host and optional port number of a
2691   recipient server or client that subsequently forwarded the message.
2692   However, if the real host is considered to be sensitive information,
2693   it &MAY; be replaced by a pseudonym. If the port is not given, it &MAY;
2694   be assumed to be the default port of the received-protocol.
2695</t>
2696<t>
2697   Multiple Via field values represents each proxy or gateway that has
2698   forwarded the message. Each recipient &MUST; append its information
2699   such that the end result is ordered according to the sequence of
2700   forwarding applications.
2701</t>
2702<t>
2703   Comments &MAY; be used in the Via header field to identify the software
2704   of the recipient proxy or gateway, analogous to the User-Agent and
2705   Server header fields. However, all comments in the Via field are
2706   optional and &MAY; be removed by any recipient prior to forwarding the
2707   message.
2708</t>
2709<t>
2710   For example, a request message could be sent from an HTTP/1.0 user
2711   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2712   forward the request to a public proxy at p.example.net, which completes
2713   the request by forwarding it to the origin server at www.example.com.
2714   The request received by www.example.com would then have the following
2715   Via header field:
2716</t>
2717<figure><artwork type="example">
2718  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2719</artwork></figure>
2720<t>
2721   Proxies and gateways used as a portal through a network firewall
2722   &SHOULD-NOT;, by default, forward the names and ports of hosts within
2723   the firewall region. This information &SHOULD; only be propagated if
2724   explicitly enabled. If not enabled, the received-by host of any host
2725   behind the firewall &SHOULD; be replaced by an appropriate pseudonym
2726   for that host.
2727</t>
2728<t>
2729   For organizations that have strong privacy requirements for hiding
2730   internal structures, a proxy &MAY; combine an ordered subsequence of
2731   Via header field entries with identical received-protocol values into
2732   a single such entry. For example,
2733</t>
2734<figure><artwork type="example">
2735  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2736</artwork></figure>
2737<t>
2738        could be collapsed to
2739</t>
2740<figure><artwork type="example">
2741  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2742</artwork></figure>
2743<t>
2744   Applications &SHOULD-NOT;  combine multiple entries unless they are all
2745   under the same organizational control and the hosts have already been
2746   replaced by pseudonyms. Applications &MUST-NOT; combine entries which
2747   have different received-protocol values.
2748</t>
2749</section>
2750
2751</section>
2752
2753<section title="IANA Considerations" anchor="IANA.considerations">
2754<section title="Message Header Registration" anchor="message.header.registration">
2755<t>
2756   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2757   with the permanent registrations below (see <xref target="RFC3864"/>):
2758</t>
2759<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2760<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2761   <ttcol>Header Field Name</ttcol>
2762   <ttcol>Protocol</ttcol>
2763   <ttcol>Status</ttcol>
2764   <ttcol>Reference</ttcol>
2765
2766   <c>Connection</c>
2767   <c>http</c>
2768   <c>standard</c>
2769   <c>
2770      <xref target="header.connection"/>
2771   </c>
2772   <c>Content-Length</c>
2773   <c>http</c>
2774   <c>standard</c>
2775   <c>
2776      <xref target="header.content-length"/>
2777   </c>
2778   <c>Date</c>
2779   <c>http</c>
2780   <c>standard</c>
2781   <c>
2782      <xref target="header.date"/>
2783   </c>
2784   <c>Host</c>
2785   <c>http</c>
2786   <c>standard</c>
2787   <c>
2788      <xref target="header.host"/>
2789   </c>
2790   <c>TE</c>
2791   <c>http</c>
2792   <c>standard</c>
2793   <c>
2794      <xref target="header.te"/>
2795   </c>
2796   <c>Trailer</c>
2797   <c>http</c>
2798   <c>standard</c>
2799   <c>
2800      <xref target="header.trailer"/>
2801   </c>
2802   <c>Transfer-Encoding</c>
2803   <c>http</c>
2804   <c>standard</c>
2805   <c>
2806      <xref target="header.transfer-encoding"/>
2807   </c>
2808   <c>Upgrade</c>
2809   <c>http</c>
2810   <c>standard</c>
2811   <c>
2812      <xref target="header.upgrade"/>
2813   </c>
2814   <c>Via</c>
2815   <c>http</c>
2816   <c>standard</c>
2817   <c>
2818      <xref target="header.via"/>
2819   </c>
2820</texttable>
2821<!--(END)-->
2822<t>
2823   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2824</t>
2825</section>
2826
2827<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2828<t>
2829   The entry for the "http" URI Scheme in the registry located at
2830   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2831   should be updated to point to <xref target="http.uri"/> of this document
2832   (see <xref target="RFC4395"/>).
2833</t>
2834</section>
2835
2836<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2837<t>
2838   This document serves as the specification for the Internet media types
2839   "message/http" and "application/http". The following is to be registered with
2840   IANA (see <xref target="RFC4288"/>).
2841</t>
2842<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2843<iref item="Media Type" subitem="message/http" primary="true"/>
2844<iref item="message/http Media Type" primary="true"/>
2845<t>
2846   The message/http type can be used to enclose a single HTTP request or
2847   response message, provided that it obeys the MIME restrictions for all
2848   "message" types regarding line length and encodings.
2849</t>
2850<t>
2851  <list style="hanging" x:indent="12em">
2852    <t hangText="Type name:">
2853      message
2854    </t>
2855    <t hangText="Subtype name:">
2856      http
2857    </t>
2858    <t hangText="Required parameters:">
2859      none
2860    </t>
2861    <t hangText="Optional parameters:">
2862      version, msgtype
2863      <list style="hanging">
2864        <t hangText="version:">
2865          The HTTP-Version number of the enclosed message
2866          (e.g., "1.1"). If not present, the version can be
2867          determined from the first line of the body.
2868        </t>
2869        <t hangText="msgtype:">
2870          The message type -- "request" or "response". If not
2871          present, the type can be determined from the first
2872          line of the body.
2873        </t>
2874      </list>
2875    </t>
2876    <t hangText="Encoding considerations:">
2877      only "7bit", "8bit", or "binary" are permitted
2878    </t>
2879    <t hangText="Security considerations:">
2880      none
2881    </t>
2882    <t hangText="Interoperability considerations:">
2883      none
2884    </t>
2885    <t hangText="Published specification:">
2886      This specification (see <xref target="internet.media.type.message.http"/>).
2887    </t>
2888    <t hangText="Applications that use this media type:">
2889    </t>
2890    <t hangText="Additional information:">
2891      <list style="hanging">
2892        <t hangText="Magic number(s):">none</t>
2893        <t hangText="File extension(s):">none</t>
2894        <t hangText="Macintosh file type code(s):">none</t>
2895      </list>
2896    </t>
2897    <t hangText="Person and email address to contact for further information:">
2898      See Authors Section.
2899    </t>
2900                <t hangText="Intended usage:">
2901                  COMMON
2902    </t>
2903                <t hangText="Restrictions on usage:">
2904                  none
2905    </t>
2906    <t hangText="Author/Change controller:">
2907      IESG
2908    </t>
2909  </list>
2910</t>
2911</section>
2912<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
2913<iref item="Media Type" subitem="application/http" primary="true"/>
2914<iref item="application/http Media Type" primary="true"/>
2915<t>
2916   The application/http type can be used to enclose a pipeline of one or more
2917   HTTP request or response messages (not intermixed).
2918</t>
2919<t>
2920  <list style="hanging" x:indent="12em">
2921    <t hangText="Type name:">
2922      application
2923    </t>
2924    <t hangText="Subtype name:">
2925      http
2926    </t>
2927    <t hangText="Required parameters:">
2928      none
2929    </t>
2930    <t hangText="Optional parameters:">
2931      version, msgtype
2932      <list style="hanging">
2933        <t hangText="version:">
2934          The HTTP-Version number of the enclosed messages
2935          (e.g., "1.1"). If not present, the version can be
2936          determined from the first line of the body.
2937        </t>
2938        <t hangText="msgtype:">
2939          The message type -- "request" or "response". If not
2940          present, the type can be determined from the first
2941          line of the body.
2942        </t>
2943      </list>
2944    </t>
2945    <t hangText="Encoding considerations:">
2946      HTTP messages enclosed by this type
2947      are in "binary" format; use of an appropriate
2948      Content-Transfer-Encoding is required when
2949      transmitted via E-mail.
2950    </t>
2951    <t hangText="Security considerations:">
2952      none
2953    </t>
2954    <t hangText="Interoperability considerations:">
2955      none
2956    </t>
2957    <t hangText="Published specification:">
2958      This specification (see <xref target="internet.media.type.application.http"/>).
2959    </t>
2960    <t hangText="Applications that use this media type:">
2961    </t>
2962    <t hangText="Additional information:">
2963      <list style="hanging">
2964        <t hangText="Magic number(s):">none</t>
2965        <t hangText="File extension(s):">none</t>
2966        <t hangText="Macintosh file type code(s):">none</t>
2967      </list>
2968    </t>
2969    <t hangText="Person and email address to contact for further information:">
2970      See Authors Section.
2971    </t>
2972                <t hangText="Intended usage:">
2973                  COMMON
2974    </t>
2975                <t hangText="Restrictions on usage:">
2976                  none
2977    </t>
2978    <t hangText="Author/Change controller:">
2979      IESG
2980    </t>
2981  </list>
2982</t>
2983</section>
2984</section>
2985
2986</section>
2987
2988<section title="Security Considerations" anchor="security.considerations">
2989<t>
2990   This section is meant to inform application developers, information
2991   providers, and users of the security limitations in HTTP/1.1 as
2992   described by this document. The discussion does not include
2993   definitive solutions to the problems revealed, though it does make
2994   some suggestions for reducing security risks.
2995</t>
2996
2997<section title="Personal Information" anchor="personal.information">
2998<t>
2999   HTTP clients are often privy to large amounts of personal information
3000   (e.g. the user's name, location, mail address, passwords, encryption
3001   keys, etc.), and &SHOULD; be very careful to prevent unintentional
3002   leakage of this information.
3003   We very strongly recommend that a convenient interface be provided
3004   for the user to control dissemination of such information, and that
3005   designers and implementors be particularly careful in this area.
3006   History shows that errors in this area often create serious security
3007   and/or privacy problems and generate highly adverse publicity for the
3008   implementor's company.
3009</t>
3010</section>
3011
3012<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3013<t>
3014   A server is in the position to save personal data about a user's
3015   requests which might identify their reading patterns or subjects of
3016   interest. This information is clearly confidential in nature and its
3017   handling can be constrained by law in certain countries. People using
3018   HTTP to provide data are responsible for ensuring that
3019   such material is not distributed without the permission of any
3020   individuals that are identifiable by the published results.
3021</t>
3022</section>
3023
3024<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3025<t>
3026   Implementations of HTTP origin servers &SHOULD; be careful to restrict
3027   the documents returned by HTTP requests to be only those that were
3028   intended by the server administrators. If an HTTP server translates
3029   HTTP URIs directly into file system calls, the server &MUST; take
3030   special care not to serve files that were not intended to be
3031   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3032   other operating systems use ".." as a path component to indicate a
3033   directory level above the current one. On such a system, an HTTP
3034   server &MUST; disallow any such construct in the request-target if it
3035   would otherwise allow access to a resource outside those intended to
3036   be accessible via the HTTP server. Similarly, files intended for
3037   reference only internally to the server (such as access control
3038   files, configuration files, and script code) &MUST; be protected from
3039   inappropriate retrieval, since they might contain sensitive
3040   information. Experience has shown that minor bugs in such HTTP server
3041   implementations have turned into security risks.
3042</t>
3043</section>
3044
3045<section title="DNS Spoofing" anchor="dns.spoofing">
3046<t>
3047   Clients using HTTP rely heavily on the Domain Name Service, and are
3048   thus generally prone to security attacks based on the deliberate
3049   mis-association of IP addresses and DNS names. Clients need to be
3050   cautious in assuming the continuing validity of an IP number/DNS name
3051   association.
3052</t>
3053<t>
3054   In particular, HTTP clients &SHOULD; rely on their name resolver for
3055   confirmation of an IP number/DNS name association, rather than
3056   caching the result of previous host name lookups. Many platforms
3057   already can cache host name lookups locally when appropriate, and
3058   they &SHOULD; be configured to do so. It is proper for these lookups to
3059   be cached, however, only when the TTL (Time To Live) information
3060   reported by the name server makes it likely that the cached
3061   information will remain useful.
3062</t>
3063<t>
3064   If HTTP clients cache the results of host name lookups in order to
3065   achieve a performance improvement, they &MUST; observe the TTL
3066   information reported by DNS.
3067</t>
3068<t>
3069   If HTTP clients do not observe this rule, they could be spoofed when
3070   a previously-accessed server's IP address changes. As network
3071   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3072   possibility of this form of attack will grow. Observing this
3073   requirement thus reduces this potential security vulnerability.
3074</t>
3075<t>
3076   This requirement also improves the load-balancing behavior of clients
3077   for replicated servers using the same DNS name and reduces the
3078   likelihood of a user's experiencing failure in accessing sites which
3079   use that strategy.
3080</t>
3081</section>
3082
3083<section title="Proxies and Caching" anchor="attack.proxies">
3084<t>
3085   By their very nature, HTTP proxies are men-in-the-middle, and
3086   represent an opportunity for man-in-the-middle attacks. Compromise of
3087   the systems on which the proxies run can result in serious security
3088   and privacy problems. Proxies have access to security-related
3089   information, personal information about individual users and
3090   organizations, and proprietary information belonging to users and
3091   content providers. A compromised proxy, or a proxy implemented or
3092   configured without regard to security and privacy considerations,
3093   might be used in the commission of a wide range of potential attacks.
3094</t>
3095<t>
3096   Proxy operators should protect the systems on which proxies run as
3097   they would protect any system that contains or transports sensitive
3098   information. In particular, log information gathered at proxies often
3099   contains highly sensitive personal information, and/or information
3100   about organizations. Log information should be carefully guarded, and
3101   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3102</t>
3103<t>
3104   Proxy implementors should consider the privacy and security
3105   implications of their design and coding decisions, and of the
3106   configuration options they provide to proxy operators (especially the
3107   default configuration).
3108</t>
3109<t>
3110   Users of a proxy need to be aware that they are no trustworthier than
3111   the people who run the proxy; HTTP itself cannot solve this problem.
3112</t>
3113<t>
3114   The judicious use of cryptography, when appropriate, may suffice to
3115   protect against a broad range of security and privacy attacks. Such
3116   cryptography is beyond the scope of the HTTP/1.1 specification.
3117</t>
3118</section>
3119
3120<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3121<t>
3122   They exist. They are hard to defend against. Research continues.
3123   Beware.
3124</t>
3125</section>
3126</section>
3127
3128<section title="Acknowledgments" anchor="ack">
3129<t>
3130   HTTP has evolved considerably over the years. It has
3131   benefited from a large and active developer community--the many
3132   people who have participated on the www-talk mailing list--and it is
3133   that community which has been most responsible for the success of
3134   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3135   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3136   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3137   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3138   VanHeyningen deserve special recognition for their efforts in
3139   defining early aspects of the protocol.
3140</t>
3141<t>
3142   This document has benefited greatly from the comments of all those
3143   participating in the HTTP-WG. In addition to those already mentioned,
3144   the following individuals have contributed to this specification:
3145</t>
3146<t>
3147   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3148   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3149   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3150   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3151   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3152   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3153   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3154   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3155   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3156   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3157   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3158   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3159   Josh Cohen.
3160</t>
3161<t>
3162   Thanks to the "cave men" of Palo Alto. You know who you are.
3163</t>
3164<t>
3165   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3166   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3167   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3168   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3169   Larry Masinter for their help. And thanks go particularly to Jeff
3170   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3171</t>
3172<t>
3173   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3174   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3175   discovery of many of the problems that this document attempts to
3176   rectify.
3177</t>
3178<t>
3179   This specification makes heavy use of the augmented BNF and generic
3180   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3181   reuses many of the definitions provided by Nathaniel Borenstein and
3182   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3183   specification will help reduce past confusion over the relationship
3184   between HTTP and Internet mail message formats.
3185</t>
3186</section>
3187
3188</middle>
3189<back>
3190
3191<references title="Normative References">
3192
3193<reference anchor="ISO-8859-1">
3194  <front>
3195    <title>
3196     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3197    </title>
3198    <author>
3199      <organization>International Organization for Standardization</organization>
3200    </author>
3201    <date year="1998"/>
3202  </front>
3203  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3204</reference>
3205
3206<reference anchor="Part2">
3207  <front>
3208    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3209    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3210      <organization abbrev="Day Software">Day Software</organization>
3211      <address><email>fielding@gbiv.com</email></address>
3212    </author>
3213    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3214      <organization>One Laptop per Child</organization>
3215      <address><email>jg@laptop.org</email></address>
3216    </author>
3217    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3218      <organization abbrev="HP">Hewlett-Packard Company</organization>
3219      <address><email>JeffMogul@acm.org</email></address>
3220    </author>
3221    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3222      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3223      <address><email>henrikn@microsoft.com</email></address>
3224    </author>
3225    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3226      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3227      <address><email>LMM@acm.org</email></address>
3228    </author>
3229    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3230      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3231      <address><email>paulle@microsoft.com</email></address>
3232    </author>
3233    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3234      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3235      <address><email>timbl@w3.org</email></address>
3236    </author>
3237    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3238      <organization abbrev="W3C">World Wide Web Consortium</organization>
3239      <address><email>ylafon@w3.org</email></address>
3240    </author>
3241    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3242      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3243      <address><email>julian.reschke@greenbytes.de</email></address>
3244    </author>
3245    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3246  </front>
3247  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-&ID-VERSION;"/>
3248  <x:source href="p2-semantics.xml" basename="p2-semantics"/>
3249</reference>
3250
3251<reference anchor="Part3">
3252  <front>
3253    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3254    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3255      <organization abbrev="Day Software">Day Software</organization>
3256      <address><email>fielding@gbiv.com</email></address>
3257    </author>
3258    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3259      <organization>One Laptop per Child</organization>
3260      <address><email>jg@laptop.org</email></address>
3261    </author>
3262    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3263      <organization abbrev="HP">Hewlett-Packard Company</organization>
3264      <address><email>JeffMogul@acm.org</email></address>
3265    </author>
3266    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3267      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3268      <address><email>henrikn@microsoft.com</email></address>
3269    </author>
3270    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3271      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3272      <address><email>LMM@acm.org</email></address>
3273    </author>
3274    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3275      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3276      <address><email>paulle@microsoft.com</email></address>
3277    </author>
3278    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3279      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3280      <address><email>timbl@w3.org</email></address>
3281    </author>
3282    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3283      <organization abbrev="W3C">World Wide Web Consortium</organization>
3284      <address><email>ylafon@w3.org</email></address>
3285    </author>
3286    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3287      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3288      <address><email>julian.reschke@greenbytes.de</email></address>
3289    </author>
3290    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3291  </front>
3292  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-&ID-VERSION;"/>
3293  <x:source href="p3-payload.xml" basename="p3-payload"/>
3294</reference>
3295
3296<reference anchor="Part5">
3297  <front>
3298    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3299    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3300      <organization abbrev="Day Software">Day Software</organization>
3301      <address><email>fielding@gbiv.com</email></address>
3302    </author>
3303    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3304      <organization>One Laptop per Child</organization>
3305      <address><email>jg@laptop.org</email></address>
3306    </author>
3307    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3308      <organization abbrev="HP">Hewlett-Packard Company</organization>
3309      <address><email>JeffMogul@acm.org</email></address>
3310    </author>
3311    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3312      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3313      <address><email>henrikn@microsoft.com</email></address>
3314    </author>
3315    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3316      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3317      <address><email>LMM@acm.org</email></address>
3318    </author>
3319    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3320      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3321      <address><email>paulle@microsoft.com</email></address>
3322    </author>
3323    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3324      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3325      <address><email>timbl@w3.org</email></address>
3326    </author>
3327    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3328      <organization abbrev="W3C">World Wide Web Consortium</organization>
3329      <address><email>ylafon@w3.org</email></address>
3330    </author>
3331    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3332      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3333      <address><email>julian.reschke@greenbytes.de</email></address>
3334    </author>
3335    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3336  </front>
3337  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-&ID-VERSION;"/>
3338  <x:source href="p5-range.xml" basename="p5-range"/>
3339</reference>
3340
3341<reference anchor="Part6">
3342  <front>
3343    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3344    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3345      <organization abbrev="Day Software">Day Software</organization>
3346      <address><email>fielding@gbiv.com</email></address>
3347    </author>
3348    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3349      <organization>One Laptop per Child</organization>
3350      <address><email>jg@laptop.org</email></address>
3351    </author>
3352    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3353      <organization abbrev="HP">Hewlett-Packard Company</organization>
3354      <address><email>JeffMogul@acm.org</email></address>
3355    </author>
3356    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3357      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3358      <address><email>henrikn@microsoft.com</email></address>
3359    </author>
3360    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3361      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3362      <address><email>LMM@acm.org</email></address>
3363    </author>
3364    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3365      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3366      <address><email>paulle@microsoft.com</email></address>
3367    </author>
3368    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3369      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3370      <address><email>timbl@w3.org</email></address>
3371    </author>
3372    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3373      <organization abbrev="W3C">World Wide Web Consortium</organization>
3374      <address><email>ylafon@w3.org</email></address>
3375    </author>
3376    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3377      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3378      <address><email>julian.reschke@greenbytes.de</email></address>
3379    </author>
3380    <date month="&ID-MONTH;" year="&ID-YEAR;"/>
3381  </front>
3382  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-&ID-VERSION;"/>
3383  <x:source href="p6-cache.xml" basename="p6-cache"/>
3384</reference>
3385
3386<reference anchor="RFC5234">
3387  <front>
3388    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3389    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3390      <organization>Brandenburg InternetWorking</organization>
3391      <address>
3392      <postal>
3393      <street>675 Spruce Dr.</street>
3394      <city>Sunnyvale</city>
3395      <region>CA</region>
3396      <code>94086</code>
3397      <country>US</country></postal>
3398      <phone>+1.408.246.8253</phone>
3399      <email>dcrocker@bbiw.net</email></address> 
3400    </author>
3401    <author initials="P." surname="Overell" fullname="Paul Overell">
3402      <organization>THUS plc.</organization>
3403      <address>
3404      <postal>
3405      <street>1/2 Berkeley Square</street>
3406      <street>99 Berkely Street</street>
3407      <city>Glasgow</city>
3408      <code>G3 7HR</code>
3409      <country>UK</country></postal>
3410      <email>paul.overell@thus.net</email></address>
3411    </author>
3412    <date month="January" year="2008"/>
3413  </front>
3414  <seriesInfo name="STD" value="68"/>
3415  <seriesInfo name="RFC" value="5234"/>
3416</reference>
3417
3418<reference anchor="RFC2119">
3419  <front>
3420    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3421    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3422      <organization>Harvard University</organization>
3423      <address><email>sob@harvard.edu</email></address>
3424    </author>
3425    <date month="March" year="1997"/>
3426  </front>
3427  <seriesInfo name="BCP" value="14"/>
3428  <seriesInfo name="RFC" value="2119"/>
3429</reference>
3430
3431<reference anchor="RFC3986">
3432 <front>
3433  <title abbrev='URI Generic Syntax'>Uniform Resource Identifier (URI): Generic Syntax</title>
3434  <author initials='T.' surname='Berners-Lee' fullname='Tim Berners-Lee'>
3435    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3436    <address>
3437       <email>timbl@w3.org</email>
3438       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3439    </address>
3440  </author>
3441  <author initials='R.' surname='Fielding' fullname='Roy T. Fielding'>
3442    <organization abbrev="Day Software">Day Software</organization>
3443    <address>
3444      <email>fielding@gbiv.com</email>
3445      <uri>http://roy.gbiv.com/</uri>
3446    </address>
3447  </author>
3448  <author initials='L.' surname='Masinter' fullname='Larry Masinter'>
3449    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3450    <address>
3451      <email>LMM@acm.org</email>
3452      <uri>http://larry.masinter.net/</uri>
3453    </address>
3454  </author>
3455  <date month='January' year='2005'></date>
3456 </front>
3457 <seriesInfo name="RFC" value="3986"/>
3458 <seriesInfo name="STD" value="66"/>
3459</reference>
3460
3461<reference anchor="USASCII">
3462  <front>
3463    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3464    <author>
3465      <organization>American National Standards Institute</organization>
3466    </author>
3467    <date year="1986"/>
3468  </front>
3469  <seriesInfo name="ANSI" value="X3.4"/>
3470</reference>
3471
3472</references>
3473
3474<references title="Informative References">
3475
3476<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3477  <front>
3478    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3479    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3480      <organization/>
3481    </author>
3482    <author initials="J." surname="Gettys" fullname="J. Gettys">
3483      <organization/>
3484    </author>
3485    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3486      <organization/>
3487    </author>
3488    <author initials="H." surname="Lie" fullname="H. Lie">
3489      <organization/>
3490    </author>
3491    <author initials="C." surname="Lilley" fullname="C. Lilley">
3492      <organization/>
3493    </author>
3494    <date year="1997" month="September"/>
3495  </front>
3496  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3497</reference>
3498
3499<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3500  <front>
3501    <title>Improving HTTP Latency</title>
3502    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3503      <organization/>
3504    </author>
3505    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3506      <organization/>
3507    </author>
3508    <date year="1995" month="December"/>
3509  </front>
3510  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3511</reference>
3512
3513<reference anchor="RFC1123">
3514  <front>
3515    <title>Requirements for Internet Hosts - Application and Support</title>
3516    <author initials="R." surname="Braden" fullname="Robert Braden">
3517      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3518      <address><email>Braden@ISI.EDU</email></address>
3519    </author>
3520    <date month="October" year="1989"/>
3521  </front>
3522  <seriesInfo name="STD" value="3"/>
3523  <seriesInfo name="RFC" value="1123"/>
3524</reference>
3525
3526<reference anchor="RFC1305">
3527  <front>
3528    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3529    <author initials="D." surname="Mills" fullname="David L. Mills">
3530      <organization>University of Delaware, Electrical Engineering Department</organization>
3531      <address><email>mills@udel.edu</email></address>
3532    </author>
3533    <date month="March" year="1992"/>
3534  </front>
3535  <seriesInfo name="RFC" value="1305"/>
3536</reference>
3537
3538<reference anchor="RFC1900">
3539  <front>
3540    <title>Renumbering Needs Work</title>
3541    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3542      <organization>CERN, Computing and Networks Division</organization>
3543      <address><email>brian@dxcoms.cern.ch</email></address>
3544    </author>
3545    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3546      <organization>cisco Systems</organization>
3547      <address><email>yakov@cisco.com</email></address>
3548    </author>
3549    <date month="February" year="1996"/>
3550  </front>
3551  <seriesInfo name="RFC" value="1900"/>
3552</reference>
3553
3554<reference anchor="RFC1945">
3555  <front>
3556    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3557    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3558      <organization>MIT, Laboratory for Computer Science</organization>
3559      <address><email>timbl@w3.org</email></address>
3560    </author>
3561    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3562      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3563      <address><email>fielding@ics.uci.edu</email></address>
3564    </author>
3565    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3566      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3567      <address><email>frystyk@w3.org</email></address>
3568    </author>
3569    <date month="May" year="1996"/>
3570  </front>
3571  <seriesInfo name="RFC" value="1945"/>
3572</reference>
3573
3574<reference anchor="RFC2045">
3575  <front>
3576    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3577    <author initials="N." surname="Freed" fullname="Ned Freed">
3578      <organization>Innosoft International, Inc.</organization>
3579      <address><email>ned@innosoft.com</email></address>
3580    </author>
3581    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3582      <organization>First Virtual Holdings</organization>
3583      <address><email>nsb@nsb.fv.com</email></address>
3584    </author>
3585    <date month="November" year="1996"/>
3586  </front>
3587  <seriesInfo name="RFC" value="2045"/>
3588</reference>
3589
3590<reference anchor="RFC2047">
3591  <front>
3592    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3593    <author initials="K." surname="Moore" fullname="Keith Moore">
3594      <organization>University of Tennessee</organization>
3595      <address><email>moore@cs.utk.edu</email></address>
3596    </author>
3597    <date month="November" year="1996"/>
3598  </front>
3599  <seriesInfo name="RFC" value="2047"/>
3600</reference>
3601
3602<reference anchor="RFC2068">
3603  <front>
3604    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3605    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3606      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3607      <address><email>fielding@ics.uci.edu</email></address>
3608    </author>
3609    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3610      <organization>MIT Laboratory for Computer Science</organization>
3611      <address><email>jg@w3.org</email></address>
3612    </author>
3613    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3614      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3615      <address><email>mogul@wrl.dec.com</email></address>
3616    </author>
3617    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3618      <organization>MIT Laboratory for Computer Science</organization>
3619      <address><email>frystyk@w3.org</email></address>
3620    </author>
3621    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3622      <organization>MIT Laboratory for Computer Science</organization>
3623      <address><email>timbl@w3.org</email></address>
3624    </author>
3625    <date month="January" year="1997"/>
3626  </front>
3627  <seriesInfo name="RFC" value="2068"/>
3628</reference>
3629
3630<reference anchor='RFC2109'>
3631  <front>
3632    <title>HTTP State Management Mechanism</title>
3633    <author initials='D.M.' surname='Kristol' fullname='David M. Kristol'>
3634      <organization>Bell Laboratories, Lucent Technologies</organization>
3635      <address><email>dmk@bell-labs.com</email></address>
3636    </author>
3637    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3638      <organization>Netscape Communications Corp.</organization>
3639      <address><email>montulli@netscape.com</email></address>
3640    </author>
3641    <date year='1997' month='February' />
3642  </front>
3643  <seriesInfo name='RFC' value='2109' />
3644</reference>
3645
3646<reference anchor="RFC2145">
3647  <front>
3648    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3649    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3650      <organization>Western Research Laboratory</organization>
3651      <address><email>mogul@wrl.dec.com</email></address>
3652    </author>
3653    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3654      <organization>Department of Information and Computer Science</organization>
3655      <address><email>fielding@ics.uci.edu</email></address>
3656    </author>
3657    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3658      <organization>MIT Laboratory for Computer Science</organization>
3659      <address><email>jg@w3.org</email></address>
3660    </author>
3661    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3662      <organization>W3 Consortium</organization>
3663      <address><email>frystyk@w3.org</email></address>
3664    </author>
3665    <date month="May" year="1997"/>
3666  </front>
3667  <seriesInfo name="RFC" value="2145"/>
3668</reference>
3669
3670<reference anchor="RFC2616">
3671  <front>
3672    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3673    <author initials="R." surname="Fielding" fullname="R. Fielding">
3674      <organization>University of California, Irvine</organization>
3675      <address><email>fielding@ics.uci.edu</email></address>
3676    </author>
3677    <author initials="J." surname="Gettys" fullname="J. Gettys">
3678      <organization>W3C</organization>
3679      <address><email>jg@w3.org</email></address>
3680    </author>
3681    <author initials="J." surname="Mogul" fullname="J. Mogul">
3682      <organization>Compaq Computer Corporation</organization>
3683      <address><email>mogul@wrl.dec.com</email></address>
3684    </author>
3685    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3686      <organization>MIT Laboratory for Computer Science</organization>
3687      <address><email>frystyk@w3.org</email></address>
3688    </author>
3689    <author initials="L." surname="Masinter" fullname="L. Masinter">
3690      <organization>Xerox Corporation</organization>
3691      <address><email>masinter@parc.xerox.com</email></address>
3692    </author>
3693    <author initials="P." surname="Leach" fullname="P. Leach">
3694      <organization>Microsoft Corporation</organization>
3695      <address><email>paulle@microsoft.com</email></address>
3696    </author>
3697    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3698      <organization>W3C</organization>
3699      <address><email>timbl@w3.org</email></address>
3700    </author>
3701    <date month="June" year="1999"/>
3702  </front>
3703  <seriesInfo name="RFC" value="2616"/>
3704</reference>
3705
3706<reference anchor='RFC2818'>
3707  <front>
3708    <title>HTTP Over TLS</title>
3709    <author initials='E.' surname='Rescorla' fullname='Eric Rescorla'>
3710      <organization>RTFM, Inc.</organization>
3711      <address><email>ekr@rtfm.com</email></address>
3712    </author>
3713    <date year='2000' month='May' />
3714  </front>
3715  <seriesInfo name='RFC' value='2818' />
3716</reference>
3717
3718<reference anchor='RFC2965'>
3719  <front>
3720    <title>HTTP State Management Mechanism</title>
3721    <author initials='D. M.' surname='Kristol' fullname='David M. Kristol'>
3722      <organization>Bell Laboratories, Lucent Technologies</organization>
3723      <address><email>dmk@bell-labs.com</email></address>
3724    </author>
3725    <author initials='L.' surname='Montulli' fullname='Lou Montulli'>
3726      <organization>Epinions.com, Inc.</organization>
3727      <address><email>lou@montulli.org</email></address>
3728    </author>
3729    <date year='2000' month='October' />
3730  </front>
3731  <seriesInfo name='RFC' value='2965' />
3732</reference>
3733
3734<reference anchor='RFC3864'>
3735  <front>
3736    <title>Registration Procedures for Message Header Fields</title>
3737    <author initials='G.' surname='Klyne' fullname='G. Klyne'>
3738      <organization>Nine by Nine</organization>
3739      <address><email>GK-IETF@ninebynine.org</email></address>
3740    </author>
3741    <author initials='M.' surname='Nottingham' fullname='M. Nottingham'>
3742      <organization>BEA Systems</organization>
3743      <address><email>mnot@pobox.com</email></address>
3744    </author>
3745    <author initials='J.' surname='Mogul' fullname='J. Mogul'>
3746      <organization>HP Labs</organization>
3747      <address><email>JeffMogul@acm.org</email></address>
3748    </author>
3749    <date year='2004' month='September' />
3750  </front>
3751  <seriesInfo name='BCP' value='90' />
3752  <seriesInfo name='RFC' value='3864' />
3753</reference>
3754
3755<reference anchor="RFC4288">
3756  <front>
3757    <title>Media Type Specifications and Registration Procedures</title>
3758    <author initials="N." surname="Freed" fullname="N. Freed">
3759      <organization>Sun Microsystems</organization>
3760      <address>
3761        <email>ned.freed@mrochek.com</email>
3762      </address>
3763    </author>
3764    <author initials="J." surname="Klensin" fullname="J. Klensin">
3765      <organization/>
3766      <address>
3767        <email>klensin+ietf@jck.com</email>
3768      </address>
3769    </author>
3770    <date year="2005" month="December"/>
3771  </front>
3772  <seriesInfo name="BCP" value="13"/>
3773  <seriesInfo name="RFC" value="4288"/>
3774</reference>
3775
3776<reference anchor='RFC4395'>
3777  <front>
3778    <title>Guidelines and Registration Procedures for New URI Schemes</title>
3779    <author initials='T.' surname='Hansen' fullname='T. Hansen'>
3780      <organization>AT&amp;T Laboratories</organization>
3781      <address>
3782        <email>tony+urireg@maillennium.att.com</email>
3783      </address>
3784    </author>
3785    <author initials='T.' surname='Hardie' fullname='T. Hardie'>
3786      <organization>Qualcomm, Inc.</organization>
3787      <address>
3788        <email>hardie@qualcomm.com</email>
3789      </address>
3790    </author>
3791    <author initials='L.' surname='Masinter' fullname='L. Masinter'>
3792      <organization>Adobe Systems</organization>
3793      <address>
3794        <email>LMM@acm.org</email>
3795      </address>
3796    </author>
3797    <date year='2006' month='February' />
3798  </front>
3799  <seriesInfo name='BCP' value='115' />
3800  <seriesInfo name='RFC' value='4395' />
3801</reference>
3802
3803<reference anchor="RFC5322">
3804  <front>
3805    <title>Internet Message Format</title>
3806    <author initials="P." surname="Resnick" fullname="P. Resnick">
3807      <organization>Qualcomm Incorporated</organization>
3808    </author>
3809    <date year="2008" month="October"/>
3810  </front> 
3811  <seriesInfo name="RFC" value="5322"/>
3812</reference>
3813
3814<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
3815  <front>
3816    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
3817    <author initials="D." surname="Kristol" fullname="David M. Kristol">
3818      <organization/>
3819    </author>
3820    <date year="2001" month="November"/>
3821  </front>
3822  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
3823</reference>
3824
3825<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
3826  <front>
3827  <title>Analysis of HTTP Performance Problems</title>
3828  <author initials="S." surname="Spero" fullname="Simon E. Spero">
3829    <organization/>
3830  </author>
3831  <date/>
3832  </front>
3833</reference>
3834
3835<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
3836  <front>
3837  <title>Analysis of HTTP Performance</title>
3838  <author initials="J." surname="Touch" fullname="Joe Touch">
3839    <organization>USC/Information Sciences Institute</organization>
3840    <address><email>touch@isi.edu</email></address>
3841  </author>
3842  <author initials="J." surname="Heidemann" fullname="John Heidemann">
3843    <organization>USC/Information Sciences Institute</organization>
3844    <address><email>johnh@isi.edu</email></address>
3845  </author>
3846  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
3847    <organization>USC/Information Sciences Institute</organization>
3848    <address><email>katia@isi.edu</email></address>
3849  </author>
3850  <date year="1998" month="Aug"/>
3851  </front>
3852  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
3853  <annotation>(original report dated Aug. 1996)</annotation>
3854</reference>
3855
3856</references>
3857
3858
3859<section title="Tolerant Applications" anchor="tolerant.applications">
3860<t>
3861   Although this document specifies the requirements for the generation
3862   of HTTP/1.1 messages, not all applications will be correct in their
3863   implementation. We therefore recommend that operational applications
3864   be tolerant of deviations whenever those deviations can be
3865   interpreted unambiguously.
3866</t>
3867<t>
3868   Clients &SHOULD; be tolerant in parsing the Status-Line and servers
3869   tolerant when parsing the Request-Line. In particular, they &SHOULD;
3870   accept any amount of WSP characters between fields, even though
3871   only a single SP is required.
3872</t>
3873<t>
3874   The line terminator for message-header fields is the sequence CRLF.
3875   However, we recommend that applications, when parsing such headers,
3876   recognize a single LF as a line terminator and ignore the leading CR.
3877</t>
3878<t>
3879   The character set of an entity-body &SHOULD; be labeled as the lowest
3880   common denominator of the character codes used within that body, with
3881   the exception that not labeling the entity is preferred over labeling
3882   the entity with the labels US-ASCII or ISO-8859-1. See &payload;.
3883</t>
3884<t>
3885   Additional rules for requirements on parsing and encoding of dates
3886   and other potential problems with date encodings include:
3887</t>
3888<t>
3889  <list style="symbols">
3890     <t>HTTP/1.1 clients and caches &SHOULD; assume that an RFC-850 date
3891        which appears to be more than 50 years in the future is in fact
3892        in the past (this helps solve the "year 2000" problem).</t>
3893
3894     <t>An HTTP/1.1 implementation &MAY; internally represent a parsed
3895        Expires date as earlier than the proper value, but &MUST-NOT;
3896        internally represent a parsed Expires date as later than the
3897        proper value.</t>
3898
3899     <t>All expiration-related calculations &MUST; be done in GMT. The
3900        local time zone &MUST-NOT; influence the calculation or comparison
3901        of an age or expiration time.</t>
3902
3903     <t>If an HTTP header incorrectly carries a date value with a time
3904        zone other than GMT, it &MUST; be converted into GMT using the
3905        most conservative possible conversion.</t>
3906  </list>
3907</t>
3908</section>
3909
3910<section title="Compatibility with Previous Versions" anchor="compatibility">
3911<t>
3912   HTTP has been in use by the World-Wide Web global information initiative
3913   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
3914   was a simple protocol for hypertext data transfer across the Internet
3915   with only a single method and no metadata.
3916   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
3917   methods and MIME-like messaging that could include metadata about the data
3918   transferred and modifiers on the request/response semantics. However,
3919   HTTP/1.0 did not sufficiently take into consideration the effects of
3920   hierarchical proxies, caching, the need for persistent connections, or
3921   name-based virtual hosts. The proliferation of incompletely-implemented
3922   applications calling themselves "HTTP/1.0" further necessitated a
3923   protocol version change in order for two communicating applications
3924   to determine each other's true capabilities.
3925</t>
3926<t>
3927   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
3928   requirements that enable reliable implementations, adding only
3929   those new features that will either be safely ignored by an HTTP/1.0
3930   recipient or only sent when communicating with a party advertising
3931   compliance with HTTP/1.1.
3932</t>
3933<t>
3934   It is beyond the scope of a protocol specification to mandate
3935   compliance with previous versions. HTTP/1.1 was deliberately
3936   designed, however, to make supporting previous versions easy. It is
3937   worth noting that, at the time of composing this specification
3938   (1996), we would expect commercial HTTP/1.1 servers to:
3939  <list style="symbols">
3940     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
3941        1.1 requests;</t>
3942
3943     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
3944        1.1;</t>
3945
3946     <t>respond appropriately with a message in the same major version
3947        used by the client.</t>
3948  </list>
3949</t>
3950<t>
3951   And we would expect HTTP/1.1 clients to:
3952  <list style="symbols">
3953     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
3954        responses;</t>
3955
3956     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
3957        1.1.</t>
3958  </list>
3959</t>
3960<t>
3961   For most implementations of HTTP/1.0, each connection is established
3962   by the client prior to the request and closed by the server after
3963   sending the response. Some implementations implement the Keep-Alive
3964   version of persistent connections described in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
3965</t>
3966
3967<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
3968<t>
3969   This section summarizes major differences between versions HTTP/1.0
3970   and HTTP/1.1.
3971</t>
3972
3973<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">
3974<t>
3975   The requirements that clients and servers support the Host request-header,
3976   report an error if the Host request-header (<xref target="header.host"/>) is
3977   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
3978   are among the most important changes defined by this
3979   specification.
3980</t>
3981<t>
3982   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
3983   addresses and servers; there was no other established mechanism for
3984   distinguishing the intended server of a request than the IP address
3985   to which that request was directed. The changes outlined above will
3986   allow the Internet, once older HTTP clients are no longer common, to
3987   support multiple Web sites from a single IP address, greatly
3988   simplifying large operational Web servers, where allocation of many
3989   IP addresses to a single host has created serious problems. The
3990   Internet will also be able to recover the IP addresses that have been
3991   allocated for the sole purpose of allowing special-purpose domain
3992   names to be used in root-level HTTP URLs. Given the rate of growth of
3993   the Web, and the number of servers already deployed, it is extremely
3994   important that all implementations of HTTP (including updates to
3995   existing HTTP/1.0 applications) correctly implement these
3996   requirements:
3997  <list style="symbols">
3998     <t>Both clients and servers &MUST; support the Host request-header.</t>
3999
4000     <t>A client that sends an HTTP/1.1 request &MUST; send a Host header.</t>
4001
4002     <t>Servers &MUST; report a 400 (Bad Request) error if an HTTP/1.1
4003        request does not include a Host request-header.</t>
4004
4005     <t>Servers &MUST; accept absolute URIs.</t>
4006  </list>
4007</t>
4008</section>
4009</section>
4010
4011<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4012<t>
4013   Some clients and servers might wish to be compatible with some
4014   previous implementations of persistent connections in HTTP/1.0
4015   clients and servers. Persistent connections in HTTP/1.0 are
4016   explicitly negotiated as they are not the default behavior. HTTP/1.0
4017   experimental implementations of persistent connections are faulty,
4018   and the new facilities in HTTP/1.1 are designed to rectify these
4019   problems. The problem was that some existing 1.0 clients may be
4020   sending Keep-Alive to a proxy server that doesn't understand
4021   Connection, which would then erroneously forward it to the next
4022   inbound server, which would establish the Keep-Alive connection and
4023   result in a hung HTTP/1.0 proxy waiting for the close on the
4024   response. The result is that HTTP/1.0 clients must be prevented from
4025   using Keep-Alive when talking to proxies.
4026</t>
4027<t>
4028   However, talking to proxies is the most important use of persistent
4029   connections, so that prohibition is clearly unacceptable. Therefore,
4030   we need some other mechanism for indicating a persistent connection
4031   is desired, which is safe to use even when talking to an old proxy
4032   that ignores Connection. Persistent connections are the default for
4033   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4034   declaring non-persistence. See <xref target="header.connection"/>.
4035</t>
4036<t>
4037   The original HTTP/1.0 form of persistent connections (the Connection:
4038   Keep-Alive and Keep-Alive header) is documented in <xref x:sec="19.7.1" x:fmt="of" target="RFC2068"/>.
4039</t>
4040</section>
4041
4042<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4043<t>
4044   This specification has been carefully audited to correct and
4045   disambiguate key word usage; RFC 2068 had many problems in respect to
4046   the conventions laid out in <xref target="RFC2119"/>.
4047</t>
4048<t>
4049   Transfer-coding and message lengths all interact in ways that
4050   required fixing exactly when chunked encoding is used (to allow for
4051   transfer encoding that may not be self delimiting); it was important
4052   to straighten out exactly how message lengths are computed. (Sections
4053   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4054   <xref target="header.content-length" format="counter"/>,
4055   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4056</t>
4057<t>
4058   The use and interpretation of HTTP version numbers has been clarified
4059   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4060   version they support to deal with problems discovered in HTTP/1.0
4061   implementations (<xref target="http.version"/>)
4062</t>
4063<t>
4064   Quality Values of zero should indicate that "I don't want something"
4065   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4066</t>
4067<t>
4068   Transfer-coding had significant problems, particularly with
4069   interactions with chunked encoding. The solution is that transfer-codings
4070   become as full fledged as content-codings. This involves
4071   adding an IANA registry for transfer-codings (separate from content
4072   codings), a new header field (TE) and enabling trailer headers in the
4073   future. Transfer encoding is a major performance benefit, so it was
4074   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4075   interoperability problem that could have occurred due to interactions
4076   between authentication trailers, chunked encoding and HTTP/1.0
4077   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4078   and <xref target="header.te" format="counter"/>)
4079</t>
4080</section>
4081
4082<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4083<t>
4084  Empty list elements in list productions have been deprecated.
4085  (<xref target="notation.abnf"/>)
4086</t>
4087<t>
4088  Rules about implicit linear whitespace between certain grammar productions
4089  have been removed; now it's only allowed when specifically pointed out
4090  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4091  text. The quoted-pair rule no longer allows escaping NUL, CR or LF.
4092  Non-ASCII content in header fields and reason phrase has been obsoleted and
4093  made opaque (the TEXT rule was removed)
4094  (<xref target="basic.rules"/>)
4095</t>
4096<t>
4097  Clarify that HTTP-Version is case sensitive.
4098  (<xref target="http.version"/>)
4099</t>
4100<t>
4101  Remove reference to non-existant identity transfer-coding value tokens.
4102  (Sections <xref format="counter" target="transfer.codings"/> and
4103  <xref format="counter" target="message.length"/>)
4104</t>
4105<t>
4106  Clarification that the chunk length does not include
4107  the count of the octets in the chunk header and trailer.
4108  (<xref target="chunked.transfer.encoding"/>)
4109</t>
4110<t>
4111  Require that invalid whitespace around field-names be rejected.
4112  (<xref target="message.headers"/>)
4113</t>
4114<t>
4115  Update use of abs_path production from RFC1808 to the path-absolute + query
4116  components of RFC3986.
4117  (<xref target="request-target"/>)
4118</t>
4119<t>
4120  Clarify exactly when close connection options must be sent.
4121  (<xref target="header.connection"/>)
4122</t>
4123</section>
4124</section>
4125
4126<section title="Terminology" anchor="terminology">
4127<t>
4128   This specification uses a number of terms to refer to the roles
4129   played by participants in, and objects of, the HTTP communication.
4130</t>
4131<t>
4132  <iref item="cache"/>
4133  <x:dfn>cache</x:dfn>
4134  <list>
4135    <t>
4136      A program's local store of response messages and the subsystem
4137      that controls its message storage, retrieval, and deletion. A
4138      cache stores cacheable responses in order to reduce the response
4139      time and network bandwidth consumption on future, equivalent
4140      requests. Any client or server may include a cache, though a cache
4141      cannot be used by a server that is acting as a tunnel.
4142    </t>
4143  </list>
4144</t>
4145<t>
4146  <iref item="cacheable"/>
4147  <x:dfn>cacheable</x:dfn>
4148  <list>
4149    <t>
4150      A response is cacheable if a cache is allowed to store a copy of
4151      the response message for use in answering subsequent requests. The
4152      rules for determining the cacheability of HTTP responses are
4153      defined in &caching;. Even if a resource is cacheable, there may
4154      be additional constraints on whether a cache can use the cached
4155      copy for a particular request.
4156    </t>
4157  </list>
4158</t>
4159<t>
4160  <iref item="client"/>
4161  <x:dfn>client</x:dfn>
4162  <list>
4163    <t>
4164      A program that establishes connections for the purpose of sending
4165      requests.
4166    </t>
4167  </list>
4168</t>
4169<t>
4170  <iref item="connection"/>
4171  <x:dfn>connection</x:dfn>
4172  <list>
4173    <t>
4174      A transport layer virtual circuit established between two programs
4175      for the purpose of communication.
4176    </t>
4177  </list>
4178</t>
4179<t>
4180  <iref item="content negotiation"/>
4181  <x:dfn>content negotiation</x:dfn>
4182  <list>
4183    <t>
4184      The mechanism for selecting the appropriate representation when
4185      servicing a request, as described in &content.negotiation;. The
4186      representation of entities in any response can be negotiated
4187      (including error responses).
4188    </t>
4189  </list>
4190</t>
4191<t>
4192  <iref item="entity"/>
4193  <x:dfn>entity</x:dfn>
4194  <list>
4195    <t>
4196      The information transferred as the payload of a request or
4197      response. An entity consists of metainformation in the form of
4198      entity-header fields and content in the form of an entity-body, as
4199      described in &entity;.
4200    </t>
4201  </list>
4202</t>
4203<t>
4204  <iref item="gateway"/>
4205  <x:dfn>gateway</x:dfn>
4206  <list>
4207    <t>
4208      A server which acts as an intermediary for some other server.
4209      Unlike a proxy, a gateway receives requests as if it were the
4210      origin server for the requested resource; the requesting client
4211      may not be aware that it is communicating with a gateway.
4212    </t>
4213  </list>
4214</t>
4215<t>
4216  <iref item="inbound"/>
4217  <iref item="outbound"/>
4218  <x:dfn>inbound</x:dfn>/<x:dfn>outbound</x:dfn>
4219  <list>
4220    <t>
4221      Inbound and outbound refer to the request and response paths for
4222      messages: "inbound" means "traveling toward the origin server",
4223      and "outbound" means "traveling toward the user agent"
4224    </t>
4225  </list>
4226</t>
4227<t>
4228  <iref item="message"/>
4229  <x:dfn>message</x:dfn>
4230  <list>
4231    <t>
4232      The basic unit of HTTP communication, consisting of a structured
4233      sequence of octets matching the syntax defined in <xref target="http.message"/> and
4234      transmitted via the connection.
4235    </t>
4236  </list>
4237</t>
4238<t>
4239  <iref item="origin server"/>
4240  <x:dfn>origin server</x:dfn>
4241  <list>
4242    <t>
4243      The server on which a given resource resides or is to be created.
4244    </t>
4245  </list>
4246</t>
4247<t>
4248  <iref item="proxy"/>
4249  <x:dfn>proxy</x:dfn>
4250  <list>
4251    <t>
4252      An intermediary program which acts as both a server and a client
4253      for the purpose of making requests on behalf of other clients.
4254      Requests are serviced internally or by passing them on, with
4255      possible translation, to other servers. A proxy &MUST; implement
4256      both the client and server requirements of this specification. A
4257      "transparent proxy" is a proxy that does not modify the request or
4258      response beyond what is required for proxy authentication and
4259      identification. A "non-transparent proxy" is a proxy that modifies
4260      the request or response in order to provide some added service to
4261      the user agent, such as group annotation services, media type
4262      transformation, protocol reduction, or anonymity filtering. Except
4263      where either transparent or non-transparent behavior is explicitly
4264      stated, the HTTP proxy requirements apply to both types of
4265      proxies.
4266    </t>
4267  </list>
4268</t>
4269<t>
4270  <iref item="request"/>
4271  <x:dfn>request</x:dfn>
4272  <list>
4273    <t>
4274      An HTTP request message, as defined in <xref target="request"/>.
4275    </t>
4276  </list>
4277</t>
4278<t>
4279  <iref item="resource"/>
4280  <x:dfn>resource</x:dfn>
4281  <list>
4282    <t>
4283      A network data object or service that can be identified by a URI,
4284      as defined in <xref target="uri"/>. Resources may be available in multiple
4285      representations (e.g. multiple languages, data formats, size, and
4286      resolutions) or vary in other ways.
4287    </t>
4288  </list>
4289</t>
4290<t>
4291  <iref item="response"/>
4292  <x:dfn>response</x:dfn>
4293  <list>
4294    <t>
4295      An HTTP response message, as defined in <xref target="response"/>.
4296    </t>
4297  </list>
4298</t>
4299<t>
4300  <iref item="representation"/>
4301  <x:dfn>representation</x:dfn>
4302  <list>
4303    <t>
4304      An entity included with a response that is subject to content
4305      negotiation, as described in &content.negotiation;. There may exist multiple
4306      representations associated with a particular response status.
4307    </t>
4308  </list>
4309</t>
4310<t>
4311  <iref item="server"/>
4312  <x:dfn>server</x:dfn>
4313  <list>
4314    <t>
4315      An application program that accepts connections in order to
4316      service requests by sending back responses. Any given program may
4317      be capable of being both a client and a server; our use of these
4318      terms refers only to the role being performed by the program for a
4319      particular connection, rather than to the program's capabilities
4320      in general. Likewise, any server may act as an origin server,
4321      proxy, gateway, or tunnel, switching behavior based on the nature
4322      of each request.
4323    </t>
4324  </list>
4325</t>
4326<t>
4327  <iref item="tunnel"/>
4328  <x:dfn>tunnel</x:dfn>
4329  <list>
4330    <t>
4331      An intermediary program which is acting as a blind relay between
4332      two connections. Once active, a tunnel is not considered a party
4333      to the HTTP communication, though the tunnel may have been
4334      initiated by an HTTP request. The tunnel ceases to exist when both
4335      ends of the relayed connections are closed.
4336    </t>
4337  </list>
4338</t>
4339<t>
4340  <iref item="upstream"/>
4341  <iref item="downstream"/>
4342  <x:dfn>upstream</x:dfn>/<x:dfn>downstream</x:dfn>
4343  <list>
4344    <t>
4345      Upstream and downstream describe the flow of a message: all
4346      messages flow from upstream to downstream.
4347    </t>
4348  </list>
4349</t>
4350<t>
4351  <iref item="user agent"/>
4352  <x:dfn>user agent</x:dfn>
4353  <list>
4354    <t>
4355      The client which initiates a request. These are often browsers,
4356      editors, spiders (web-traversing robots), or other end user tools.
4357    </t>
4358  </list>
4359</t>
4360<t>
4361  <iref item="variant"/>
4362  <x:dfn>variant</x:dfn>
4363  <list>
4364    <t>
4365      A resource may have one, or more than one, representation(s)
4366      associated with it at any given instant. Each of these
4367      representations is termed a `variant'.  Use of the term `variant'
4368      does not necessarily imply that the resource is subject to content
4369      negotiation.
4370    </t>
4371  </list>
4372</t>
4373</section>
4374
4375<section xmlns:x="http://purl.org/net/xml2rfc/ext" title="Collected ABNF" anchor="collected.abnf">
4376<figure>
4377<artwork type="abnf" name="p1-messaging.parsed-abnf">
4378<x:ref>BWS</x:ref> = OWS
4379
4380<x:ref>Cache-Control</x:ref> = &lt;Cache-Control, defined in [Part6], Section 3.4&gt;
4381<x:ref>Chunked-Body</x:ref> = *chunk last-chunk trailer-part CRLF
4382<x:ref>Connection</x:ref> = "Connection:" OWS Connection-v
4383<x:ref>Connection-v</x:ref> = *( "," OWS ) connection-token *( OWS "," [ OWS
4384 connection-token ] )
4385<x:ref>Content-Length</x:ref> = "Content-Length:" OWS 1*Content-Length-v
4386<x:ref>Content-Length-v</x:ref> = 1*DIGIT
4387
4388<x:ref>Date</x:ref> = "Date:" OWS Date-v
4389<x:ref>Date-v</x:ref> = HTTP-date
4390
4391<x:ref>GMT</x:ref> = %x47.4D.54 ; GMT
4392
4393<x:ref>HTTP-Prot-Name</x:ref> = %x48.54.54.50 ; HTTP
4394<x:ref>HTTP-Version</x:ref> = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4395<x:ref>HTTP-date</x:ref> = rfc1123-date / obs-date
4396<x:ref>HTTP-message</x:ref> = Request / Response
4397<x:ref>Host</x:ref> = "Host:" OWS Host-v
4398<x:ref>Host-v</x:ref> = uri-host [ ":" port ]
4399
4400<x:ref>Method</x:ref> = token
4401
4402<x:ref>OWS</x:ref> = *( [ obs-fold ] WSP )
4403
4404<x:ref>Pragma</x:ref> = &lt;Pragma, defined in [Part6], Section 3.4&gt;
4405
4406<x:ref>RWS</x:ref> = 1*( [ obs-fold ] WSP )
4407<x:ref>Reason-Phrase</x:ref> = *( WSP / VCHAR / obs-text )
4408<x:ref>Request</x:ref> = Request-Line *( ( general-header / request-header /
4409 entity-header ) CRLF ) CRLF [ message-body ]
4410<x:ref>Request-Line</x:ref> = Method SP request-target SP HTTP-Version CRLF
4411<x:ref>Response</x:ref> = Status-Line *( ( general-header / response-header /
4412 entity-header ) CRLF ) CRLF [ message-body ]
4413
4414<x:ref>Status-Code</x:ref> = 3DIGIT
4415<x:ref>Status-Line</x:ref> = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4416
4417<x:ref>TE</x:ref> = "TE:" OWS TE-v
4418<x:ref>TE-v</x:ref> = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4419<x:ref>Trailer</x:ref> = "Trailer:" OWS Trailer-v
4420<x:ref>Trailer-v</x:ref> = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4421<x:ref>Transfer-Encoding</x:ref> = "Transfer-Encoding:" OWS Transfer-Encoding-v
4422<x:ref>Transfer-Encoding-v</x:ref> = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4423 transfer-coding ] )
4424
4425<x:ref>URI</x:ref> = &lt;URI, defined in [RFC3986], Section 3&gt;
4426<x:ref>URI-reference</x:ref> = &lt;URI-reference, defined in [RFC3986], Section 4.1&gt;
4427<x:ref>Upgrade</x:ref> = "Upgrade:" OWS Upgrade-v
4428<x:ref>Upgrade-v</x:ref> = *( "," OWS ) product *( OWS "," [ OWS product ] )
4429
4430<x:ref>Via</x:ref> = "Via:" OWS Via-v
4431<x:ref>Via-v</x:ref> = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4432 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4433 ] )
4434
4435<x:ref>Warning</x:ref> = &lt;Warning, defined in [Part6], Section 3.6&gt;
4436
4437<x:ref>absolute-URI</x:ref> = &lt;absolute-URI, defined in [RFC3986], Section 4.3&gt;
4438<x:ref>asctime-date</x:ref> = day-name SP date3 SP time-of-day SP year
4439<x:ref>attribute</x:ref> = token
4440<x:ref>authority</x:ref> = &lt;authority, defined in [RFC3986], Section 3.2&gt;
4441
4442<x:ref>chunk</x:ref> = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4443<x:ref>chunk-data</x:ref> = 1*OCTET
4444<x:ref>chunk-ext</x:ref> = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4445<x:ref>chunk-ext-name</x:ref> = token
4446<x:ref>chunk-ext-val</x:ref> = token / quoted-string
4447<x:ref>chunk-size</x:ref> = 1*HEXDIG
4448<x:ref>comment</x:ref> = "(" *( ctext / quoted-pair / comment ) ")"
4449<x:ref>connection-token</x:ref> = token
4450<x:ref>ctext</x:ref> = OWS / %x21-27 ; '!'-'''
4451 / %x2A-5B ; '*'-'['
4452 / %x5D-7E ; ']'-'~'
4453 / obs-text
4454
4455<x:ref>date1</x:ref> = day SP month SP year
4456<x:ref>date2</x:ref> = day "-" month "-" 2DIGIT
4457<x:ref>date3</x:ref> = month SP ( 2DIGIT / ( SP DIGIT ) )
4458<x:ref>day</x:ref> = 2DIGIT
4459<x:ref>day-name</x:ref> = %x4D.6F.6E ; Mon
4460 / %x54.75.65 ; Tue
4461 / %x57.65.64 ; Wed
4462 / %x54.68.75 ; Thu
4463 / %x46.72.69 ; Fri
4464 / %x53.61.74 ; Sat
4465 / %x53.75.6E ; Sun
4466<x:ref>day-name-l</x:ref> = %x4D.6F.6E.64.61.79 ; Monday
4467 / %x54.75.65.73.64.61.79 ; Tuesday
4468 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4469 / %x54.68.75.72.73.64.61.79 ; Thursday
4470 / %x46.72.69.64.61.79 ; Friday
4471 / %x53.61.74.75.72.64.61.79 ; Saturday
4472 / %x53.75.6E.64.61.79 ; Sunday
4473
4474<x:ref>entity-body</x:ref> = &lt;entity-body, defined in [Part3], Section 3.2&gt;
4475<x:ref>entity-header</x:ref> = &lt;entity-header, defined in [Part3], Section 3.1&gt;
4476
4477<x:ref>field-content</x:ref> = *( WSP / VCHAR / obs-text )
4478<x:ref>field-name</x:ref> = token
4479<x:ref>field-value</x:ref> = *( field-content / OWS )
4480<x:ref>fragment</x:ref> = &lt;fragment, defined in [RFC3986], Section 3.5&gt;
4481
4482<x:ref>general-header</x:ref> = Cache-Control / Connection / Date / Pragma / Trailer
4483 / Transfer-Encoding / Upgrade / Via / Warning
4484<x:ref>generic-message</x:ref> = start-line *( message-header CRLF ) CRLF [
4485 message-body ]
4486
4487<x:ref>hour</x:ref> = 2DIGIT
4488<x:ref>http-URI</x:ref> = "http://" authority path-abempty [ "?" query ]
4489
4490<x:ref>last-chunk</x:ref> = 1*"0" *WSP [ chunk-ext ] CRLF
4491
4492<x:ref>message-body</x:ref> = entity-body /
4493 &lt;entity-body encoded as per Transfer-Encoding&gt;
4494<x:ref>message-header</x:ref> = field-name ":" OWS [ field-value ] OWS
4495<x:ref>minute</x:ref> = 2DIGIT
4496<x:ref>month</x:ref> = %x4A.61.6E ; Jan
4497 / %x46.65.62 ; Feb
4498 / %x4D.61.72 ; Mar
4499 / %x41.70.72 ; Apr
4500 / %x4D.61.79 ; May
4501 / %x4A.75.6E ; Jun
4502 / %x4A.75.6C ; Jul
4503 / %x41.75.67 ; Aug
4504 / %x53.65.70 ; Sep
4505 / %x4F.63.74 ; Oct
4506 / %x4E.6F.76 ; Nov
4507 / %x44.65.63 ; Dec
4508
4509<x:ref>obs-date</x:ref> = rfc850-date / asctime-date
4510<x:ref>obs-fold</x:ref> = CRLF
4511<x:ref>obs-text</x:ref> = %x80-FF
4512
4513<x:ref>parameter</x:ref> = attribute BWS "=" BWS value
4514<x:ref>partial-URI</x:ref> = relative-part [ "?" query ]
4515<x:ref>path-abempty</x:ref> = &lt;path-abempty, defined in [RFC3986], Section 3.3&gt;
4516<x:ref>path-absolute</x:ref> = &lt;path-absolute, defined in [RFC3986], Section 3.3&gt;
4517<x:ref>port</x:ref> = &lt;port, defined in [RFC3986], Section 3.2.3&gt;
4518<x:ref>product</x:ref> = token [ "/" product-version ]
4519<x:ref>product-version</x:ref> = token
4520<x:ref>protocol-name</x:ref> = token
4521<x:ref>protocol-version</x:ref> = token
4522<x:ref>pseudonym</x:ref> = token
4523
4524<x:ref>qdtext</x:ref> = OWS / "!" / %x23-5B ; '#'-'['
4525 / %x5D-7E ; ']'-'~'
4526 / obs-text
4527<x:ref>query</x:ref> = &lt;query, defined in [RFC3986], Section 3.4&gt;
4528<x:ref>quoted-pair</x:ref> = "\" quoted-text
4529<x:ref>quoted-string</x:ref> = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4530<x:ref>quoted-text</x:ref> = %x01-09 / %x0B-0C / %x0E-FF
4531<x:ref>qvalue</x:ref> = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4532
4533<x:ref>received-by</x:ref> = ( uri-host [ ":" port ] ) / pseudonym
4534<x:ref>received-protocol</x:ref> = [ protocol-name "/" ] protocol-version
4535<x:ref>relative-part</x:ref> = &lt;relative-part, defined in [RFC3986], Section 4.2&gt;
4536<x:ref>request-header</x:ref> = &lt;request-header, defined in [Part2], Section 3&gt;
4537<x:ref>request-target</x:ref> = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4538 / authority
4539<x:ref>response-header</x:ref> = &lt;response-header, defined in [Part2], Section 5&gt;
4540<x:ref>rfc1123-date</x:ref> = day-name "," SP date1 SP time-of-day SP GMT
4541<x:ref>rfc850-date</x:ref> = day-name-l "," SP date2 SP time-of-day SP GMT
4542
4543<x:ref>second</x:ref> = 2DIGIT
4544<x:ref>start-line</x:ref> = Request-Line / Status-Line
4545
4546<x:ref>t-codings</x:ref> = "trailers" / ( transfer-extension [ te-params ] )
4547<x:ref>tchar</x:ref> = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*" / "+" / "-" / "." /
4548 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4549<x:ref>te-ext</x:ref> = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4550<x:ref>te-params</x:ref> = OWS ";" OWS "q=" qvalue *te-ext
4551<x:ref>time-of-day</x:ref> = hour ":" minute ":" second
4552<x:ref>token</x:ref> = 1*tchar
4553<x:ref>trailer-part</x:ref> = *( entity-header CRLF )
4554<x:ref>transfer-coding</x:ref> = "chunked" / transfer-extension
4555<x:ref>transfer-extension</x:ref> = token *( OWS ";" OWS parameter )
4556
4557<x:ref>uri-host</x:ref> = &lt;host, defined in [RFC3986], Section 3.2.2&gt;
4558
4559<x:ref>value</x:ref> = token / quoted-string
4560
4561<x:ref>year</x:ref> = 4DIGIT
4562</artwork>
4563</figure>
4564<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline">
4565; Chunked-Body defined but not used
4566; Content-Length defined but not used
4567; HTTP-message defined but not used
4568; Host defined but not used
4569; TE defined but not used
4570; URI defined but not used
4571; URI-reference defined but not used
4572; fragment defined but not used
4573; generic-message defined but not used
4574; http-URI defined but not used
4575; partial-URI defined but not used
4576</artwork></figure></section>
4577
4578<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4579
4580<section title="Since RFC2616">
4581<t>
4582  Extracted relevant partitions from <xref target="RFC2616"/>.
4583</t>
4584</section>
4585
4586<section title="Since draft-ietf-httpbis-p1-messaging-00">
4587<t>
4588  Closed issues:
4589  <list style="symbols"> 
4590    <t>
4591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4592      "HTTP Version should be case sensitive"
4593      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4594    </t>
4595    <t>
4596      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4597      "'unsafe' characters"
4598      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4599    </t>
4600    <t>
4601      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4602      "Chunk Size Definition"
4603      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4604    </t>
4605    <t>
4606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4607      "Message Length"
4608      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4609    </t>
4610    <t>
4611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4612      "Media Type Registrations"
4613      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4614    </t>
4615    <t>
4616      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4617      "URI includes query"
4618      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4619    </t>
4620    <t>
4621      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4622      "No close on 1xx responses"
4623      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4624    </t>
4625    <t>
4626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4627      "Remove 'identity' token references"
4628      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4629    </t>
4630    <t>
4631      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4632      "Import query BNF"
4633    </t>
4634    <t>
4635      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4636      "qdtext BNF"
4637    </t>
4638    <t>
4639      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4640      "Normative and Informative references"
4641    </t>
4642    <t>
4643      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4644      "RFC2606 Compliance"
4645    </t>
4646    <t>
4647      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4648      "RFC977 reference"
4649    </t>
4650    <t>
4651      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4652      "RFC1700 references"
4653    </t>
4654    <t>
4655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4656      "inconsistency in date format explanation"
4657    </t>
4658    <t>
4659      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4660      "Date reference typo"
4661    </t>
4662    <t>
4663      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4664      "Informative references"
4665    </t>
4666    <t>
4667      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4668      "ISO-8859-1 Reference"
4669    </t>
4670    <t>
4671      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4672      "Normative up-to-date references"
4673    </t>
4674  </list>
4675</t>
4676<t>
4677  Other changes:
4678  <list style="symbols"> 
4679    <t>
4680      Update media type registrations to use RFC4288 template.
4681    </t>
4682    <t>
4683      Use names of RFC4234 core rules DQUOTE and WSP,
4684      fix broken ABNF for chunk-data
4685      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4686    </t>
4687  </list>
4688</t>
4689</section>
4690
4691<section title="Since draft-ietf-httpbis-p1-messaging-01">
4692<t>
4693  Closed issues:
4694  <list style="symbols"> 
4695    <t>
4696      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4697      "Bodies on GET (and other) requests"
4698    </t>
4699    <t>
4700      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4701      "Updating to RFC4288"
4702    </t>
4703    <t>
4704      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4705      "Status Code and Reason Phrase"
4706    </t>
4707    <t>
4708      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4709      "rel_path not used"
4710    </t>
4711  </list>
4712</t>
4713<t>
4714  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4715  <list style="symbols"> 
4716    <t>
4717      Get rid of duplicate BNF rule names ("host" -> "uri-host", "trailer" ->
4718      "trailer-part").
4719    </t>
4720    <t>
4721      Avoid underscore character in rule names ("http_URL" ->
4722      "http-URL", "abs_path" -> "path-absolute").
4723    </t>
4724    <t>
4725      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4726      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4727      have to be updated when switching over to RFC3986.
4728    </t>
4729    <t>
4730      Synchronize core rules with RFC5234.
4731    </t>
4732    <t>
4733      Get rid of prose rules that span multiple lines.
4734    </t>
4735    <t>
4736      Get rid of unused rules LOALPHA and UPALPHA.
4737    </t>
4738    <t>
4739      Move "Product Tokens" section (back) into Part 1, as "token" is used
4740      in the definition of the Upgrade header.
4741    </t>
4742    <t>
4743      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4744    </t>
4745    <t>
4746      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4747    </t>
4748  </list>
4749</t>
4750</section>
4751
4752<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4753<t>
4754  Closed issues:
4755  <list style="symbols"> 
4756    <t>
4757      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4758      "HTTP-date vs. rfc1123-date"
4759    </t>
4760    <t>
4761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4762      "WS in quoted-pair"
4763    </t>
4764  </list>
4765</t>
4766<t>
4767  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4768  <list style="symbols"> 
4769    <t>
4770      Reference RFC 3984, and update header registrations for headers defined
4771      in this document.
4772    </t>
4773  </list>
4774</t>
4775<t>
4776  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4777  <list style="symbols"> 
4778    <t>
4779      Replace string literals when the string really is case-sensitive (HTTP-Version).
4780    </t>
4781  </list>
4782</t>
4783</section>
4784
4785<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4786<t>
4787  Closed issues:
4788  <list style="symbols"> 
4789    <t>
4790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4791      "Connection closing"
4792    </t>
4793    <t>
4794      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4795      "Move registrations and registry information to IANA Considerations"
4796    </t>
4797    <t>
4798      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4799      "need new URL for PAD1995 reference"
4800    </t>
4801    <t>
4802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4803      "IANA Considerations: update HTTP URI scheme registration"
4804    </t>
4805    <t>
4806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4807      "Cite HTTPS URI scheme definition"
4808    </t>
4809    <t>
4810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4811      "List-type headers vs Set-Cookie"
4812    </t>
4813  </list>
4814</t>
4815<t>
4816  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4817  <list style="symbols"> 
4818    <t>
4819      Replace string literals when the string really is case-sensitive (HTTP-Date).
4820    </t>
4821    <t>
4822      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4823    </t>
4824  </list>
4825</t>
4826</section>
4827
4828<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
4829<t>
4830  Closed issues:
4831  <list style="symbols"> 
4832    <t>
4833      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
4834      "Out-of-date reference for URIs"
4835    </t>
4836    <t>
4837      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
4838      "RFC 2822 is updated by RFC 5322"
4839    </t>
4840  </list>
4841</t>
4842<t>
4843  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4844  <list style="symbols"> 
4845    <t>
4846      Use "/" instead of "|" for alternatives.
4847    </t>
4848    <t>
4849      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
4850    </t>
4851    <t>
4852      Only reference RFC 5234's core rules.
4853    </t>
4854    <t>
4855      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
4856      whitespace ("OWS") and required whitespace ("RWS").
4857    </t>
4858    <t>
4859      Rewrite ABNFs to spell out whitespace rules, factor out
4860      header value format definitions.
4861    </t>
4862  </list>
4863</t>
4864</section>
4865
4866<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
4867<t>
4868  Closed issues:
4869  <list style="symbols"> 
4870    <t>
4871      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
4872      "Header LWS"
4873    </t>
4874    <t>
4875      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
4876      "Sort 1.3 Terminology"
4877    </t>
4878    <t>
4879      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
4880      "RFC2047 encoded words"
4881    </t>
4882    <t>
4883      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
4884      "Character Encodings in TEXT"
4885    </t>
4886    <t>
4887      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
4888      "Line Folding"
4889    </t>
4890    <t>
4891      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
4892      "OPTIONS * and proxies"
4893    </t>
4894    <t>
4895      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
4896      "Reason-Phrase BNF"
4897    </t>
4898    <t>
4899      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
4900      "Use of TEXT"
4901    </t>
4902    <t>
4903      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
4904      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
4905    </t>
4906    <t>
4907      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
4908      "RFC822 reference left in discussion of date formats"
4909    </t>
4910  </list>
4911</t>
4912<t>
4913  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4914  <list style="symbols"> 
4915    <t>
4916      Rewrite definition of list rules, deprecate empty list elements.
4917    </t>
4918    <t>
4919      Add appendix containing collected and expanded ABNF.
4920    </t>
4921  </list>
4922</t>
4923<t>
4924  Other changes:
4925  <list style="symbols"> 
4926    <t>
4927      Rewrite introduction; add mostly new Architecture Section.
4928    </t>
4929    <t>
4930      Move definition of quality values from Part 3 into Part 1;
4931      make TE request header grammar independent of accept-params (defined in Part 3).
4932    </t>
4933  </list>
4934</t>
4935</section>
4936
4937<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
4938<t>
4939  Closed issues:
4940  <list style="symbols"> 
4941    <t>
4942      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
4943      "base for numeric protocol elements"
4944    </t>
4945    <t>
4946      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
4947      "comment ABNF"
4948    </t>
4949  </list>
4950</t>
4951<t>
4952  Partly resolved issues:
4953  <list style="symbols"> 
4954    <t>
4955      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
4956      "editorial improvements around HTTP-date"
4957    </t>
4958  </list>
4959</t>
4960</section>
4961
4962</section>
4963
4964</back>
4965</rfc>
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