source: draft-ietf-httpbis/12/draft-ietf-httpbis-p1-messaging-12.xml @ 1515

Last change on this file since 1515 was 1500, checked in by julian.reschke@…, 8 years ago

fix mime types

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  • Property svn:mime-type set to text/xml
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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<?rfc rfcedstyle="yes"?>
17<!DOCTYPE rfc
18  PUBLIC "" "rfc2629.dtd">
19<rfc obsoletes="2616" updates="2817" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-12">
20<front>
21
22  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
23
24  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
25    <organization abbrev="Day Software">Day Software</organization>
26    <address>
27      <postal>
28        <street>23 Corporate Plaza DR, Suite 280</street>
29        <city>Newport Beach</city>
30        <region>CA</region>
31        <code>92660</code>
32        <country>USA</country>
33      </postal>
34      <phone>+1-949-706-5300</phone>
35      <facsimile>+1-949-706-5305</facsimile>
36      <email>fielding@gbiv.com</email>
37      <uri>http://roy.gbiv.com/</uri>
38    </address>
39  </author>
40
41  <author initials="J." surname="Gettys" fullname="Jim Gettys">
42    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
43    <address>
44      <postal>
45        <street>21 Oak Knoll Road</street>
46        <city>Carlisle</city>
47        <region>MA</region>
48        <code>01741</code>
49        <country>USA</country>
50      </postal>
51      <email>jg@freedesktop.org</email>
52      <uri>http://gettys.wordpress.com/</uri>
53    </address>
54  </author>
55 
56  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
57    <organization abbrev="HP">Hewlett-Packard Company</organization>
58    <address>
59      <postal>
60        <street>HP Labs, Large Scale Systems Group</street>
61        <street>1501 Page Mill Road, MS 1177</street>
62        <city>Palo Alto</city>
63        <region>CA</region>
64        <code>94304</code>
65        <country>USA</country>
66      </postal>
67      <email>JeffMogul@acm.org</email>
68    </address>
69  </author>
70
71  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
72    <organization abbrev="Microsoft">Microsoft Corporation</organization>
73    <address>
74      <postal>
75        <street>1 Microsoft Way</street>
76        <city>Redmond</city>
77        <region>WA</region>
78        <code>98052</code>
79        <country>USA</country>
80      </postal>
81      <email>henrikn@microsoft.com</email>
82    </address>
83  </author>
84
85  <author initials="L." surname="Masinter" fullname="Larry Masinter">
86    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
87    <address>
88      <postal>
89        <street>345 Park Ave</street>
90        <city>San Jose</city>
91        <region>CA</region>
92        <code>95110</code>
93        <country>USA</country>
94      </postal>
95      <email>LMM@acm.org</email>
96      <uri>http://larry.masinter.net/</uri>
97    </address>
98  </author>
99 
100  <author initials="P." surname="Leach" fullname="Paul J. Leach">
101    <organization abbrev="Microsoft">Microsoft Corporation</organization>
102    <address>
103      <postal>
104        <street>1 Microsoft Way</street>
105        <city>Redmond</city>
106        <region>WA</region>
107        <code>98052</code>
108      </postal>
109      <email>paulle@microsoft.com</email>
110    </address>
111  </author>
112   
113  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
114    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
115    <address>
116      <postal>
117        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
118        <street>The Stata Center, Building 32</street>
119        <street>32 Vassar Street</street>
120        <city>Cambridge</city>
121        <region>MA</region>
122        <code>02139</code>
123        <country>USA</country>
124      </postal>
125      <email>timbl@w3.org</email>
126      <uri>http://www.w3.org/People/Berners-Lee/</uri>
127    </address>
128  </author>
129
130  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
131    <organization abbrev="W3C">World Wide Web Consortium</organization>
132    <address>
133      <postal>
134        <street>W3C / ERCIM</street>
135        <street>2004, rte des Lucioles</street>
136        <city>Sophia-Antipolis</city>
137        <region>AM</region>
138        <code>06902</code>
139        <country>France</country>
140      </postal>
141      <email>ylafon@w3.org</email>
142      <uri>http://www.raubacapeu.net/people/yves/</uri>
143    </address>
144  </author>
145
146  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
147    <organization abbrev="greenbytes">greenbytes GmbH</organization>
148    <address>
149      <postal>
150        <street>Hafenweg 16</street>
151        <city>Muenster</city><region>NW</region><code>48155</code>
152        <country>Germany</country>
153      </postal>
154      <phone>+49 251 2807760</phone>
155      <facsimile>+49 251 2807761</facsimile>
156      <email>julian.reschke@greenbytes.de</email>
157      <uri>http://greenbytes.de/tech/webdav/</uri>
158    </address>
159  </author>
160
161  <date month="October" year="2010" day="25"/>
162  <workgroup>HTTPbis Working Group</workgroup>
163
164<abstract>
165<t>
166   The Hypertext Transfer Protocol (HTTP) is an application-level
167   protocol for distributed, collaborative, hypertext information
168   systems. HTTP has been in use by the World Wide Web global information
169   initiative since 1990. This document is Part 1 of the seven-part specification
170   that defines the protocol referred to as "HTTP/1.1" and, taken together,
171   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
172   its associated terminology, defines the "http" and "https" Uniform
173   Resource Identifier (URI) schemes, defines the generic message syntax
174   and parsing requirements for HTTP message frames, and describes
175   general security concerns for implementations.
176</t>
177</abstract>
178
179<note title="Editorial Note (To be removed by RFC Editor)">
180  <t>
181    Discussion of this draft should take place on the HTTPBIS working group
182    mailing list (ietf-http-wg@w3.org). The current issues list is
183    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
184    and related documents (including fancy diffs) can be found at
185    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
186  </t>
187  <t>
188    The changes in this draft are summarized in <xref target="changes.since.11"/>.
189  </t>
190</note>
191</front>
192<middle>
193<section title="Introduction" anchor="introduction">
194<t>
195   The Hypertext Transfer Protocol (HTTP) is an application-level
196   request/response protocol that uses extensible semantics and MIME-like
197   message payloads for flexible interaction with network-based hypertext
198   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
199   standard <xref target="RFC3986"/> to indicate request targets and
200   relationships between resources.
201   Messages are passed in a format similar to that used by Internet mail
202   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
203   (MIME) <xref target="RFC2045"/> (see Appendix A of <xref target="Part3"/> for the differences
204   between HTTP and MIME messages).
205</t>
206<t>
207   HTTP is a generic interface protocol for information systems. It is
208   designed to hide the details of how a service is implemented by presenting
209   a uniform interface to clients that is independent of the types of
210   resources provided. Likewise, servers do not need to be aware of each
211   client's purpose: an HTTP request can be considered in isolation rather
212   than being associated with a specific type of client or a predetermined
213   sequence of application steps. The result is a protocol that can be used
214   effectively in many different contexts and for which implementations can
215   evolve independently over time.
216</t>
217<t>
218   HTTP is also designed for use as an intermediation protocol for translating
219   communication to and from non-HTTP information systems.
220   HTTP proxies and gateways can provide access to alternative information
221   services by translating their diverse protocols into a hypertext
222   format that can be viewed and manipulated by clients in the same way
223   as HTTP services.
224</t>
225<t>
226   One consequence of HTTP flexibility is that the protocol cannot be
227   defined in terms of what occurs behind the interface. Instead, we
228   are limited to defining the syntax of communication, the intent
229   of received communication, and the expected behavior of recipients.
230   If the communication is considered in isolation, then successful
231   actions ought to be reflected in corresponding changes to the
232   observable interface provided by servers. However, since multiple
233   clients might act in parallel and perhaps at cross-purposes, we
234   cannot require that such changes be observable beyond the scope
235   of a single response.
236</t>
237<t>
238   This document is Part 1 of the seven-part specification of HTTP,
239   defining the protocol referred to as "HTTP/1.1" and obsoleting
240   <xref target="RFC2616"/>.
241   Part 1 describes the architectural elements that are used or
242   referred to in HTTP, defines the "http" and "https" URI schemes,
243   describes overall network operation and connection management,
244   and defines HTTP message framing and forwarding requirements.
245   Our goal is to define all of the mechanisms necessary for HTTP message
246   handling that are independent of message semantics, thereby defining the
247   complete set of requirements for message parsers and
248   message-forwarding intermediaries.
249</t>
250
251<section title="Requirements" anchor="intro.requirements">
252<t>
253   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
254   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
255   document are to be interpreted as described in <xref target="RFC2119"/>.
256</t>
257<t>
258   An implementation is not compliant if it fails to satisfy one or more
259   of the "MUST" or "REQUIRED" level requirements for the protocols it
260   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
261   level and all the "SHOULD" level requirements for its protocols is said
262   to be "unconditionally compliant"; one that satisfies all the "MUST"
263   level requirements but not all the "SHOULD" level requirements for its
264   protocols is said to be "conditionally compliant".
265</t>
266</section>
267
268<section title="Syntax Notation" anchor="notation">
269<iref primary="true" item="Grammar" subitem="ALPHA"/>
270<iref primary="true" item="Grammar" subitem="CR"/>
271<iref primary="true" item="Grammar" subitem="CRLF"/>
272<iref primary="true" item="Grammar" subitem="CTL"/>
273<iref primary="true" item="Grammar" subitem="DIGIT"/>
274<iref primary="true" item="Grammar" subitem="DQUOTE"/>
275<iref primary="true" item="Grammar" subitem="HEXDIG"/>
276<iref primary="true" item="Grammar" subitem="LF"/>
277<iref primary="true" item="Grammar" subitem="OCTET"/>
278<iref primary="true" item="Grammar" subitem="SP"/>
279<iref primary="true" item="Grammar" subitem="VCHAR"/>
280<iref primary="true" item="Grammar" subitem="WSP"/>
281<t>
282   This specification uses the Augmented Backus-Naur Form (ABNF) notation
283   of <xref target="RFC5234"/>.
284</t>
285<t anchor="core.rules">
286 
287 
288 
289 
290 
291 
292 
293 
294 
295 
296 
297 
298   The following core rules are included by
299   reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
300   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
301   DIGIT (decimal 0-9), DQUOTE (double quote),
302   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
303   OCTET (any 8-bit sequence of data), SP (space),
304   VCHAR (any visible <xref target="USASCII"/> character),
305   and WSP (whitespace).
306</t>
307<t>
308   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
309   "obsolete" grammar rules that appear for historical reasons.
310</t>
311
312<section title="ABNF Extension: #rule" anchor="notation.abnf">
313<t>
314  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
315  improve readability.
316</t>
317<t>
318  A construct "#" is defined, similar to "*", for defining comma-delimited
319  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
320  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
321  comma (",") and optional whitespace (OWS,
322  <xref target="basic.rules"/>).   
323</t>
324<figure><preamble>
325  Thus,
326</preamble><artwork type="example"><![CDATA[
327  1#element => element *( OWS "," OWS element )
328]]></artwork></figure>
329<figure><preamble>
330  and:
331</preamble><artwork type="example"><![CDATA[
332  #element => [ 1#element ]
333]]></artwork></figure>
334<figure><preamble>
335  and for n &gt;= 1 and m &gt; 1:
336</preamble><artwork type="example"><![CDATA[
337  <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
338]]></artwork></figure>
339<t>
340  For compatibility with legacy list rules, recipients SHOULD accept empty
341  list elements. In other words, consumers would follow the list productions:
342</t>
343<figure><artwork type="example"><![CDATA[
344  #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
345 
346  1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
347]]></artwork></figure>
348<t>
349  Note that empty elements do not contribute to the count of elements present,
350  though.
351</t>
352<t>
353  For example, given these ABNF productions:
354</t>
355<figure><artwork type="example"><![CDATA[
356  example-list      = 1#example-list-elmt
357  example-list-elmt = token ; see Section 1.2.2
358]]></artwork></figure>
359<t>
360  Then these are valid values for example-list (not including the double
361  quotes, which are present for delimitation only):
362</t>
363<figure><artwork type="example"><![CDATA[
364  "foo,bar"
365  " foo ,bar,"
366  "  foo , ,bar,charlie   "
367  "foo ,bar,   charlie "
368]]></artwork></figure>
369<t>
370  But these values would be invalid, as at least one non-empty element is
371  required:
372</t>
373<figure><artwork type="example"><![CDATA[
374  ""
375  ","
376  ",   ,"
377]]></artwork></figure>
378<t>
379  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
380  expanded as explained above.
381</t>
382</section>
383
384<section title="Basic Rules" anchor="basic.rules">
385<t anchor="rule.CRLF">
386 
387   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
388   protocol elements other than the message-body
389   (see <xref target="tolerant.applications"/> for tolerant applications).
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 might
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 
418 
419 
420 
421</t>
422<figure><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/><artwork type="abnf2616"><![CDATA[
423  OWS            = *( [ obs-fold ] WSP )
424                 ; "optional" whitespace
425  RWS            = 1*( [ obs-fold ] WSP )
426                 ; "required" whitespace
427  BWS            = OWS
428                 ; "bad" whitespace
429  obs-fold       = CRLF
430                 ; see Section 3.2
431]]></artwork></figure>
432<t anchor="rule.token.separators">
433 
434 
435 
436 
437   Many HTTP/1.1 header field values consist of words (token or quoted-string)
438   separated by whitespace or special characters. These special characters
439   MUST be in a quoted string to be used within a parameter value (as defined
440   in <xref target="transfer.codings"/>).
441</t>
442<figure><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/><artwork type="abnf2616"><![CDATA[
443  word           = token / quoted-string
444
445  token          = 1*tchar
446
447  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
448                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
449                 / DIGIT / ALPHA
450                 ; any VCHAR, except special
451
452  special        = "(" / ")" / "<" / ">" / "@" / ","
453                 / ";" / ":" / "\" / DQUOTE / "/" / "["
454                 / "]" / "?" / "=" / "{" / "}"
455]]></artwork></figure>
456<t anchor="rule.quoted-string">
457 
458 
459 
460   A string of text is parsed as a single word if it is quoted using
461   double-quote marks.
462</t>
463<figure><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><iref primary="true" item="Grammar" subitem="obs-text"/><artwork type="abnf2616"><![CDATA[
464  quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
465  qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
466                 ; OWS / <VCHAR except DQUOTE and "\"> / obs-text
467  obs-text       = %x80-FF
468]]></artwork></figure>
469<t anchor="rule.quoted-pair">
470 
471   The backslash character ("\") can be used as a single-character
472   quoting mechanism within quoted-string constructs:
473</t>
474<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
475  quoted-pair    = "\" ( WSP / VCHAR / obs-text )
476]]></artwork></figure>
477<t>
478   Producers SHOULD NOT escape characters that do not require escaping
479   (i.e., other than DQUOTE and the backslash character).
480</t>
481</section>
482
483<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
484 
485 
486 
487 
488 
489 
490<t>
491  The ABNF rules below are defined in other parts:
492</t>
493<figure><artwork type="abnf2616"><![CDATA[
494  request-header  = <request-header, defined in [Part2], Section 3>
495  response-header = <response-header, defined in [Part2], Section 5>
496]]></artwork></figure>
497<figure><artwork type="abnf2616"><![CDATA[
498  MIME-Version    = <MIME-Version, defined in [Part3], Appendix A.1>
499]]></artwork></figure>
500<figure><artwork type="abnf2616"><![CDATA[
501  Cache-Control   = <Cache-Control, defined in [Part6], Section 3.4>
502  Pragma          = <Pragma, defined in [Part6], Section 3.4>
503  Warning         = <Warning, defined in [Part6], Section 3.6>
504]]></artwork></figure>
505</section>
506
507</section>
508</section>
509
510<section title="HTTP-related architecture" anchor="architecture">
511<t>
512   HTTP was created for the World Wide Web architecture
513   and has evolved over time to support the scalability needs of a worldwide
514   hypertext system. Much of that architecture is reflected in the terminology
515   and syntax productions used to define HTTP.
516</t>
517
518<section title="Client/Server Messaging" anchor="operation">
519<iref primary="true" item="client"/>
520<iref primary="true" item="server"/>
521<iref primary="true" item="connection"/>
522<t>
523   HTTP is a stateless request/response protocol that operates by exchanging
524   messages across a reliable transport or session-layer connection. An HTTP
525   "client" is a program that establishes a connection to a server for the
526   purpose of sending one or more HTTP requests.  An HTTP "server" is a
527   program that accepts connections in order to service HTTP requests by
528   sending HTTP responses.
529</t>
530<iref primary="true" item="user agent"/>
531<iref primary="true" item="origin server"/>
532<iref primary="true" item="browser"/>
533<iref primary="true" item="spider"/>
534<t>
535   Note that the terms client and server refer only to the roles that
536   these programs perform for a particular connection.  The same program
537   might act as a client on some connections and a server on others.  We use
538   the term "user agent" to refer to the program that initiates a request,
539   such as a WWW browser, editor, or spider (web-traversing robot), and
540   the term "origin server" to refer to the program that can originate
541   authoritative responses to a request.  For general requirements, we use
542   the term "sender" to refer to whichever component sent a given message
543   and the term "recipient" to refer to any component that receives the
544   message.
545</t>
546<t>
547   Most HTTP communication consists of a retrieval request (GET) for
548   a representation of some resource identified by a URI.  In the
549   simplest case, this might be accomplished via a single bidirectional
550   connection (===) between the user agent (UA) and the origin server (O).
551</t>
552<figure><artwork type="drawing"><![CDATA[
553         request   >
554    UA ======================================= O
555                                <   response
556]]></artwork></figure>
557<iref primary="true" item="message"/>
558<iref primary="true" item="request"/>
559<iref primary="true" item="response"/>
560<t>
561   A client sends an HTTP request to the server in the form of a request
562   message (<xref target="request"/>), beginning with a method, URI, and
563   protocol version, followed by MIME-like header fields containing
564   request modifiers, client information, and payload metadata, an empty
565   line to indicate the end of the header section, and finally the payload
566   body (if any).
567</t>
568<t>
569   A server responds to the client's request by sending an HTTP response
570   message (<xref target="response"/>), beginning with a status line that
571   includes the protocol version, a success or error code, and textual
572   reason phrase, followed by MIME-like header fields containing server
573   information, resource metadata, and payload metadata, an empty line to
574   indicate the end of the header section, and finally the payload body (if any).
575</t>
576<t>
577   The following example illustrates a typical message exchange for a
578   GET request on the URI "http://www.example.com/hello.txt":
579</t>
580<figure><preamble>
581client request:
582</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
583  GET /hello.txt HTTP/1.1
584  User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
585  Host: www.example.com
586  Accept: */*
587 
588  ]]></artwork></figure>
589<figure><preamble>
590server response:
591</preamble><artwork type="message/http; msgtype=&#34;response&#34;"><![CDATA[
592  HTTP/1.1 200 OK
593  Date: Mon, 27 Jul 2009 12:28:53 GMT
594  Server: Apache
595  Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
596  ETag: "34aa387-d-1568eb00"
597  Accept-Ranges: bytes
598  Content-Length: 14
599  Vary: Accept-Encoding
600  Content-Type: text/plain
601 
602  Hello World!
603  ]]></artwork></figure>
604</section>
605
606<section title="Intermediaries" anchor="intermediaries">
607<iref primary="true" item="intermediary"/>
608<t>
609   A more complicated situation occurs when one or more intermediaries
610   are present in the request/response chain. There are three common
611   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
612   a single intermediary might act as an origin server, proxy, gateway,
613   or tunnel, switching behavior based on the nature of each request.
614</t>
615<figure><artwork type="drawing"><![CDATA[
616         >             >             >             >
617    UA =========== A =========== B =========== C =========== O
618               <             <             <             <
619]]></artwork></figure>
620<t>
621   The figure above shows three intermediaries (A, B, and C) between the
622   user agent and origin server. A request or response message that
623   travels the whole chain will pass through four separate connections.
624   Some HTTP communication options
625   might apply only to the connection with the nearest, non-tunnel
626   neighbor, only to the end-points of the chain, or to all connections
627   along the chain. Although the diagram is linear, each participant might
628   be engaged in multiple, simultaneous communications. For example, B
629   might be receiving requests from many clients other than A, and/or
630   forwarding requests to servers other than C, at the same time that it
631   is handling A's request.
632</t>
633<t>
634<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
635<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
636   We use the terms "upstream" and "downstream" to describe various
637   requirements in relation to the directional flow of a message:
638   all messages flow from upstream to downstream.
639   Likewise, we use the terms "inbound" and "outbound" to refer to
640   directions in relation to the request path: "inbound" means toward
641   the origin server and "outbound" means toward the user agent.
642</t>
643<t><iref primary="true" item="proxy"/>
644   A "proxy" is a message forwarding agent that is selected by the
645   client, usually via local configuration rules, to receive requests
646   for some type(s) of absolute URI and attempt to satisfy those
647   requests via translation through the HTTP interface.  Some translations
648   are minimal, such as for proxy requests for "http" URIs, whereas
649   other requests might require translation to and from entirely different
650   application-layer protocols. Proxies are often used to group an
651   organization's HTTP requests through a common intermediary for the
652   sake of security, annotation services, or shared caching.
653</t>
654<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
655   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
656   as a layer above some other server(s) and translates the received
657   requests to the underlying server's protocol.  Gateways are often
658   used for load balancing or partitioning HTTP services across
659   multiple machines.
660   Unlike a proxy, a gateway receives requests as if it were the
661   origin server for the target resource; the requesting client
662   will not be aware that it is communicating with a gateway.
663   A gateway communicates with the client as if the gateway is the
664   origin server and thus is subject to all of the requirements on
665   origin servers for that connection.  A gateway communicates
666   with inbound servers using any protocol it desires, including
667   private extensions to HTTP that are outside the scope of this
668   specification.
669</t>
670<t><iref primary="true" item="tunnel"/>
671   A "tunnel" acts as a blind relay between two connections
672   without changing the messages. Once active, a tunnel is not
673   considered a party to the HTTP communication, though the tunnel might
674   have been initiated by an HTTP request. A tunnel ceases to exist when
675   both ends of the relayed connection are closed. Tunnels are used to
676   extend a virtual connection through an intermediary, such as when
677   transport-layer security is used to establish private communication
678   through a shared firewall proxy.
679</t>
680</section>
681
682<section title="Caches" anchor="caches">
683<iref primary="true" item="cache"/>
684<t>
685   A "cache" is a local store of previous response messages and the
686   subsystem that controls its message storage, retrieval, and deletion.
687   A cache stores cacheable responses in order to reduce the response
688   time and network bandwidth consumption on future, equivalent
689   requests. Any client or server MAY employ a cache, though a cache
690   cannot be used by a server while it is acting as a tunnel.
691</t>
692<t>
693   The effect of a cache is that the request/response chain is shortened
694   if one of the participants along the chain has a cached response
695   applicable to that request. The following illustrates the resulting
696   chain if B has a cached copy of an earlier response from O (via C)
697   for a request which has not been cached by UA or A.
698</t>
699<figure><artwork type="drawing"><![CDATA[
700            >             >
701       UA =========== A =========== B - - - - - - C - - - - - - O
702                  <             <
703]]></artwork></figure>
704<t><iref primary="true" item="cacheable"/>
705   A response is "cacheable" if a cache is allowed to store a copy of
706   the response message for use in answering subsequent requests.
707   Even when a response is cacheable, there might be additional
708   constraints placed by the client or by the origin server on when
709   that cached response can be used for a particular request. HTTP
710   requirements for cache behavior and cacheable responses are
711   defined in Section 2 of <xref target="Part6"/>
712</t>
713<t>
714   There are a wide variety of architectures and configurations
715   of caches and proxies deployed across the World Wide Web and
716   inside large organizations. These systems include national hierarchies
717   of proxy caches to save transoceanic bandwidth, systems that
718   broadcast or multicast cache entries, organizations that distribute
719   subsets of cached data via optical media, and so on.
720</t>
721</section>
722
723<section title="Transport Independence" anchor="transport-independence">
724<t>
725  HTTP systems are used in a wide variety of environments, from
726  corporate intranets with high-bandwidth links to long-distance
727  communication over low-power radio links and intermittent connectivity.
728</t>
729<t>
730   HTTP communication usually takes place over TCP/IP connections. The
731   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
732   not preclude HTTP from being implemented on top of any other protocol
733   on the Internet, or on other networks. HTTP only presumes a reliable
734   transport; any protocol that provides such guarantees can be used;
735   the mapping of the HTTP/1.1 request and response structures onto the
736   transport data units of the protocol in question is outside the scope
737   of this specification.
738</t>
739<t>
740   In HTTP/1.0, most implementations used a new connection for each
741   request/response exchange. In HTTP/1.1, a connection might be used for
742   one or more request/response exchanges, although connections might be
743   closed for a variety of reasons (see <xref target="persistent.connections"/>).
744</t>
745</section>
746
747<section title="HTTP Version" anchor="http.version">
748 
749 
750<t>
751   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
752   of the protocol. The protocol versioning policy is intended to allow
753   the sender to indicate the format of a message and its capacity for
754   understanding further HTTP communication, rather than the features
755   obtained via that communication. No change is made to the version
756   number for the addition of message components which do not affect
757   communication behavior or which only add to extensible field values.
758   The &lt;minor&gt; number is incremented when the changes made to the
759   protocol add features which do not change the general message parsing
760   algorithm, but which might add to the message semantics and imply
761   additional capabilities of the sender. The &lt;major&gt; number is
762   incremented when the format of a message within the protocol is
763   changed. See <xref target="RFC2145"/> for a fuller explanation.
764</t>
765<t>
766   The version of an HTTP message is indicated by an HTTP-Version field
767   in the first line of the message. HTTP-Version is case-sensitive.
768</t>
769<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
770  HTTP-Version   = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
771  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
772]]></artwork></figure>
773<t>
774   Note that the major and minor numbers MUST be treated as separate
775   integers and that each MAY be incremented higher than a single digit.
776   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
777   lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and
778   MUST NOT be sent.
779</t>
780<t>
781   An application that sends a request or response message that includes
782   HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
783   with this specification. Applications that are at least conditionally
784   compliant with this specification SHOULD use an HTTP-Version of
785   "HTTP/1.1" in their messages, and MUST do so for any message that is
786   not compatible with HTTP/1.0. For more details on when to send
787   specific HTTP-Version values, see <xref target="RFC2145"/>.
788</t>
789<t>
790   The HTTP version of an application is the highest HTTP version for
791   which the application is at least conditionally compliant.
792</t>
793<t>
794   Proxy and gateway applications need to be careful when forwarding
795   messages in protocol versions different from that of the application.
796   Since the protocol version indicates the protocol capability of the
797   sender, a proxy/gateway MUST NOT send a message with a version
798   indicator which is greater than its actual version. If a higher
799   version request is received, the proxy/gateway MUST either downgrade
800   the request version, or respond with an error, or switch to tunnel
801   behavior.
802</t>
803<t>
804   Due to interoperability problems with HTTP/1.0 proxies discovered
805   since the publication of <xref target="RFC2068"/>, caching proxies MUST, gateways
806   MAY, and tunnels MUST NOT upgrade the request to the highest version
807   they support. The proxy/gateway's response to that request MUST be in
808   the same major version as the request.
809</t>
810<t><list>
811  <t>
812    Note: Converting between versions of HTTP might involve modification
813    of header fields required or forbidden by the versions involved.
814  </t>
815</list></t>
816</section>
817
818<section title="Uniform Resource Identifiers" anchor="uri">
819<iref primary="true" item="resource"/>
820<t>
821   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
822   throughout HTTP as the means for identifying resources. URI references
823   are used to target requests, indicate redirects, and define relationships.
824   HTTP does not limit what a resource might be; it merely defines an interface
825   that can be used to interact with a resource via HTTP. More information on
826   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
827</t>
828 
829 
830 
831 
832 
833 
834 
835 
836 
837 
838<t>
839   This specification adopts the definitions of "URI-reference",
840   "absolute-URI", "relative-part", "port", "host",
841   "path-abempty", "path-absolute", "query", and "authority" from
842   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
843   protocol elements that allow a relative URI without a fragment.
844</t>
845<figure><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"/><artwork type="abnf2616"><![CDATA[
846  URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
847  absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
848  relative-part = <relative-part, defined in [RFC3986], Section 4.2>
849  authority     = <authority, defined in [RFC3986], Section 3.2>
850  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
851  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
852  port          = <port, defined in [RFC3986], Section 3.2.3>
853  query         = <query, defined in [RFC3986], Section 3.4>
854  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
855 
856  partial-URI   = relative-part [ "?" query ]
857]]></artwork></figure>
858<t>
859   Each protocol element in HTTP that allows a URI reference will indicate in
860   its ABNF production whether the element allows only a URI in absolute form
861   (absolute-URI), any relative reference (relative-ref), or some other subset
862   of the URI-reference grammar. Unless otherwise indicated, URI references
863   are parsed relative to the request target (the default base URI for both
864   the request and its corresponding response).
865</t>
866
867<section title="http URI scheme" anchor="http.uri">
868 
869  <iref item="http URI scheme" primary="true"/>
870  <iref item="URI scheme" subitem="http" primary="true"/>
871<t>
872   The "http" URI scheme is hereby defined for the purpose of minting
873   identifiers according to their association with the hierarchical
874   namespace governed by a potential HTTP origin server listening for
875   TCP connections on a given port.
876   The HTTP server is identified via the generic syntax's
877   <xref target="uri" format="none">authority</xref> component, which includes a host
878   identifier and optional TCP port, and the remainder of the URI is
879   considered to be identifying data corresponding to a resource for
880   which that server might provide an HTTP interface.
881</t>
882<figure><iref primary="true" item="Grammar" subitem="http-URI"/><artwork type="abnf2616"><![CDATA[
883  http-URI = "http:" "//" authority path-abempty [ "?" query ]
884]]></artwork></figure>
885<t>
886   The host identifier within an <xref target="uri" format="none">authority</xref> component is
887   defined in <xref target="RFC3986"/>, Section 3.2.2.  If host is
888   provided as an IP literal or IPv4 address, then the HTTP server is any
889   listener on the indicated TCP port at that IP address. If host is a
890   registered name, then that name is considered an indirect identifier
891   and the recipient might use a name resolution service, such as DNS,
892   to find the address of a listener for that host.
893   The host MUST NOT be empty; if an "http" URI is received with an
894   empty host, then it MUST be rejected as invalid.
895   If the port subcomponent is empty or not given, then TCP port 80 is
896   assumed (the default reserved port for WWW services).
897</t>
898<t>
899   Regardless of the form of host identifier, access to that host is not
900   implied by the mere presence of its name or address. The host might or might
901   not exist and, even when it does exist, might or might not be running an
902   HTTP server or listening to the indicated port. The "http" URI scheme
903   makes use of the delegated nature of Internet names and addresses to
904   establish a naming authority (whatever entity has the ability to place
905   an HTTP server at that Internet name or address) and allows that
906   authority to determine which names are valid and how they might be used.
907</t>
908<t>
909   When an "http" URI is used within a context that calls for access to the
910   indicated resource, a client MAY attempt access by resolving
911   the host to an IP address, establishing a TCP connection to that address
912   on the indicated port, and sending an HTTP request message to the server
913   containing the URI's identifying data as described in <xref target="request"/>.
914   If the server responds to that request with a non-interim HTTP response
915   message, as described in <xref target="response"/>, then that response
916   is considered an authoritative answer to the client's request.
917</t>
918<t>
919   Although HTTP is independent of the transport protocol, the "http"
920   scheme is specific to TCP-based services because the name delegation
921   process depends on TCP for establishing authority.
922   An HTTP service based on some other underlying connection protocol
923   would presumably be identified using a different URI scheme, just as
924   the "https" scheme (below) is used for servers that require an SSL/TLS
925   transport layer on a connection. Other protocols might also be used to
926   provide access to "http" identified resources --- it is only the
927   authoritative interface used for mapping the namespace that is
928   specific to TCP.
929</t>
930<t>
931   The URI generic syntax for authority also includes a deprecated
932   userinfo subcomponent (<xref target="RFC3986"/>, Section 3.2.1)
933   for including user authentication information in the URI.  The userinfo
934   subcomponent (and its "@" delimiter) MUST NOT be used in an "http"
935   URI.  URI reference recipients SHOULD parse for the existence of
936   userinfo and treat its presence as an error, likely indicating that
937   the deprecated subcomponent is being used to obscure the authority
938   for the sake of phishing attacks.
939</t>
940</section>
941
942<section title="https URI scheme" anchor="https.uri">
943   
944   <iref item="https URI scheme"/>
945   <iref item="URI scheme" subitem="https"/>
946<t>
947   The "https" URI scheme is hereby defined for the purpose of minting
948   identifiers according to their association with the hierarchical
949   namespace governed by a potential HTTP origin server listening for
950   SSL/TLS-secured connections on a given TCP port.
951</t>
952<t>
953   All of the requirements listed above for the "http" scheme are also
954   requirements for the "https" scheme, except that a default TCP port
955   of 443 is assumed if the port subcomponent is empty or not given,
956   and the TCP connection MUST be secured for privacy through the
957   use of strong encryption prior to sending the first HTTP request.
958</t>
959<figure><iref primary="true" item="Grammar" subitem="https-URI"/><artwork type="abnf2616"><![CDATA[
960  https-URI = "https:" "//" authority path-abempty [ "?" query ]
961]]></artwork></figure>
962<t>
963   Unlike the "http" scheme, responses to "https" identified requests
964   are never "public" and thus are ineligible for shared caching.
965   Their default is "private" and might be further constrained via use
966   of the Cache-Control header field.
967</t>
968<t>
969   Resources made available via the "https" scheme have no shared
970   identity with the "http" scheme even if their resource identifiers
971   only differ by the single "s" in the scheme name.  They are
972   different services governed by different authorities.  However,
973   some extensions to HTTP that apply to entire host domains, such
974   as the Cookie protocol, do allow one service to effect communication
975   with the other services based on host domain matching.
976</t>
977<t>
978   The process for authoritative access to an "https" identified
979   resource is defined in <xref target="RFC2818"/>.
980</t>
981</section>
982
983<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
984<t>
985   Since the "http" and "https" schemes conform to the URI generic syntax,
986   such URIs are normalized and compared according to the algorithm defined
987   in <xref target="RFC3986"/>, Section 6, using the defaults
988   described above for each scheme.
989</t>
990<t>
991   If the port is equal to the default port for a scheme, the normal
992   form is to elide the port subcomponent. Likewise, an empty path
993   component is equivalent to an absolute path of "/", so the normal
994   form is to provide a path of "/" instead. The scheme and host
995   are case-insensitive and normally provided in lowercase; all
996   other components are compared in a case-sensitive manner.
997   Characters other than those in the "reserved" set are equivalent
998   to their percent-encoded octets (see <xref target="RFC3986"/>, Section 2.1): the normal form is to not encode them.
999</t>
1000<t>
1001   For example, the following three URIs are equivalent:
1002</t>
1003<figure><artwork type="example"><![CDATA[
1004   http://example.com:80/~smith/home.html
1005   http://EXAMPLE.com/%7Esmith/home.html
1006   http://EXAMPLE.com:/%7esmith/home.html
1007]]></artwork></figure>
1008<t>
1009   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
1010   If path-abempty is the empty string (i.e., there is no slash "/"
1011   path separator following the authority), then the "http" URI
1012   MUST be given as "/" when
1013   used as a request-target (<xref target="request-target"/>). If a proxy
1014   receives a host name which is not a fully qualified domain name, it
1015   MAY add its domain to the host name it received. If a proxy receives
1016   a fully qualified domain name, the proxy MUST NOT change the host
1017   name.
1018</t>
1019</section>
1020</section>
1021</section>
1022
1023<section title="HTTP Message" anchor="http.message">
1024
1025
1026
1027
1028<iref item="header section"/>
1029<iref item="headers"/>
1030<iref item="header field"/>
1031<t>
1032   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1033   characters in a format similar to the Internet Message Format
1034   <xref target="RFC5322"/>: zero or more header fields (collectively
1035   referred to as the "headers" or the "header section"), an empty line
1036   indicating the end of the header section, and an optional message-body.
1037</t>
1038<t>
1039   An HTTP message can either be a request from client to server or a
1040   response from server to client.  Syntactically, the two types of message
1041   differ only in the start-line, which is either a Request-Line (for requests)
1042   or a Status-Line (for responses), and in the algorithm for determining
1043   the length of the message-body (<xref target="message.body"/>).
1044   In theory, a client could receive requests and a server could receive
1045   responses, distinguishing them by their different start-line formats,
1046   but in practice servers are implemented to only expect a request
1047   (a response is interpreted as an unknown or invalid request method)
1048   and clients are implemented to only expect a response.
1049</t>
1050<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1051  HTTP-message    = start-line
1052                    *( header-field CRLF )
1053                    CRLF
1054                    [ message-body ]
1055  start-line      = Request-Line / Status-Line
1056]]></artwork></figure>
1057<t>
1058   Whitespace (WSP) MUST NOT be sent between the start-line and the first
1059   header field. The presence of whitespace might be an attempt to trick a
1060   noncompliant implementation of HTTP into ignoring that field or processing
1061   the next line as a new request, either of which might result in security
1062   issues when implementations within the request chain interpret the
1063   same message differently. HTTP/1.1 servers MUST reject such a message
1064   with a 400 (Bad Request) response.
1065</t>
1066
1067<section title="Message Parsing Robustness" anchor="message.robustness">
1068<t>
1069   In the interest of robustness, servers SHOULD ignore at least one
1070   empty line received where a Request-Line is expected. In other words, if
1071   the server is reading the protocol stream at the beginning of a
1072   message and receives a CRLF first, it SHOULD ignore the CRLF.
1073</t>
1074<t>
1075   Some old HTTP/1.0 client implementations generate an extra CRLF
1076   after a POST request as a lame workaround for some early server
1077   applications that failed to read message-body content that was
1078   not terminated by a line-ending. An HTTP/1.1 client MUST NOT
1079   preface or follow a request with an extra CRLF.  If terminating
1080   the request message-body with a line-ending is desired, then the
1081   client MUST include the terminating CRLF octets as part of the
1082   message-body length.
1083</t>
1084<t>
1085   The normal procedure for parsing an HTTP message is to read the
1086   start-line into a structure, read each header field into a hash
1087   table by field name until the empty line, and then use the parsed
1088   data to determine if a message-body is expected.  If a message-body
1089   has been indicated, then it is read as a stream until an amount
1090   of octets equal to the message-body length is read or the connection
1091   is closed.  Care must be taken to parse an HTTP message as a sequence
1092   of octets in an encoding that is a superset of US-ASCII.  Attempting
1093   to parse HTTP as a stream of Unicode characters in a character encoding
1094   like UTF-16 might introduce security flaws due to the differing ways
1095   that such parsers interpret invalid characters.
1096</t>
1097<t>
1098   HTTP allows the set of defined header fields to be extended without
1099   changing the protocol version (see <xref target="header.field.registration"/>).
1100   However, such fields might not be recognized by a downstream recipient
1101   and might be stripped by non-transparent intermediaries.
1102   Unrecognized header fields MUST be forwarded by transparent proxies
1103   and SHOULD be ignored by a recipient.
1104</t>
1105</section>
1106
1107<section title="Header Fields" anchor="header.fields">
1108 
1109 
1110 
1111 
1112 
1113<t>
1114   Each HTTP header field consists of a case-insensitive field name
1115   followed by a colon (":"), optional whitespace, and the field value.
1116</t>
1117<figure><iref primary="true" item="Grammar" subitem="header-field"/><iref primary="true" item="Grammar" subitem="field-name"/><iref primary="true" item="Grammar" subitem="field-value"/><iref primary="true" item="Grammar" subitem="field-content"/><artwork type="abnf2616"><![CDATA[
1118  header-field   = field-name ":" OWS [ field-value ] OWS
1119  field-name     = token
1120  field-value    = *( field-content / OWS )
1121  field-content  = *( WSP / VCHAR / obs-text )
1122]]></artwork></figure>
1123<t>
1124   No whitespace is allowed between the header field name and colon. For
1125   security reasons, any request message received containing such whitespace
1126   MUST be rejected with a response code of 400 (Bad Request). A proxy
1127   MUST remove any such whitespace from a response message before
1128   forwarding the message downstream.
1129</t>
1130<t>
1131   A field value MAY be preceded by optional whitespace (OWS); a single SP is
1132   preferred. The field value does not include any leading or trailing white
1133   space: OWS occurring before the first non-whitespace character of the
1134   field value or after the last non-whitespace character of the field value
1135   is ignored and SHOULD be removed before further processing (as this does
1136   not change the meaning of the header field).
1137</t>
1138<t>
1139   The order in which header fields with differing field names are
1140   received is not significant. However, it is "good practice" to send
1141   header fields that contain control data first, such as Host on
1142   requests and Date on responses, so that implementations can decide
1143   when not to handle a message as early as possible.  A server MUST
1144   wait until the entire header section is received before interpreting
1145   a request message, since later header fields might include conditionals,
1146   authentication credentials, or deliberately misleading duplicate
1147   header fields that would impact request processing.
1148</t>
1149<t>
1150   Multiple header fields with the same field name MUST NOT be
1151   sent in a message unless the entire field value for that
1152   header field is defined as a comma-separated list [i.e., #(values)].
1153   Multiple header fields with the same field name can be combined into
1154   one "field-name: field-value" pair, without changing the semantics of the
1155   message, by appending each subsequent field value to the combined
1156   field value in order, separated by a comma. The order in which
1157   header fields with the same field name are received is therefore
1158   significant to the interpretation of the combined field value;
1159   a proxy MUST NOT change the order of these field values when
1160   forwarding a message.
1161</t>
1162<t><list>
1163  <t>
1164   Note: The "Set-Cookie" header field as implemented in
1165   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1166   can occur multiple times, but does not use the list syntax, and thus cannot
1167   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1168   for details.) Also note that the Set-Cookie2 header field specified in
1169   <xref target="RFC2965"/> does not share this problem.
1170  </t>
1171</list></t>
1172<t>
1173   Historically, HTTP header field values could be extended over multiple
1174   lines by preceding each extra line with at least one space or horizontal
1175   tab character (line folding). This specification deprecates such line
1176   folding except within the message/http media type
1177   (<xref target="internet.media.type.message.http"/>).
1178   HTTP/1.1 senders MUST NOT produce messages that include line folding
1179   (i.e., that contain any field-content that matches the obs-fold rule) unless
1180   the message is intended for packaging within the message/http media type.
1181   HTTP/1.1 recipients SHOULD accept line folding and replace any embedded
1182   obs-fold whitespace with a single SP prior to interpreting the field value
1183   or forwarding the message downstream.
1184</t>
1185<t>
1186   Historically, HTTP has allowed field content with text in the ISO-8859-1
1187   <xref target="ISO-8859-1"/> character encoding and supported other
1188   character sets only through use of <xref target="RFC2047"/> encoding.
1189   In practice, most HTTP header field values use only a subset of the
1190   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1191   header fields SHOULD limit their field values to US-ASCII characters.
1192   Recipients SHOULD treat other (obs-text) octets in field content as
1193   opaque data.
1194</t>
1195<t anchor="rule.comment">
1196 
1197 
1198   Comments can be included in some HTTP header fields by surrounding
1199   the comment text with parentheses. Comments are only allowed in
1200   fields containing "comment" as part of their field value definition.
1201</t>
1202<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
1203  comment        = "(" *( ctext / quoted-cpair / comment ) ")"
1204  ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
1205                 ; OWS / <VCHAR except "(", ")", and "\"> / obs-text
1206]]></artwork></figure>
1207<t anchor="rule.quoted-cpair">
1208 
1209   The backslash character ("\") can be used as a single-character
1210   quoting mechanism within comment constructs:
1211</t>
1212<figure><iref primary="true" item="Grammar" subitem="quoted-cpair"/><artwork type="abnf2616"><![CDATA[
1213  quoted-cpair    = "\" ( WSP / VCHAR / obs-text )
1214]]></artwork></figure>
1215<t>
1216   Producers SHOULD NOT escape characters that do not require escaping
1217   (i.e., other than the backslash character "\" and the parentheses "(" and
1218   ")").
1219</t>
1220</section>
1221
1222<section title="Message Body" anchor="message.body">
1223 
1224<t>
1225   The message-body (if any) of an HTTP message is used to carry the
1226   payload body associated with the request or response.
1227</t>
1228<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1229  message-body = *OCTET
1230]]></artwork></figure>
1231<t>
1232   The message-body differs from the payload body only when a transfer-coding
1233   has been applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).  When one or more transfer-codings are
1234   applied to a payload in order to form the message-body, the
1235   Transfer-Encoding header field MUST contain the list of
1236   transfer-codings applied. Transfer-Encoding is a property of the message,
1237   not of the payload, and thus MAY be added or removed by any implementation
1238   along the request/response chain under the constraints found in
1239   <xref target="transfer.codings"/>.
1240</t>
1241<t>
1242   The rules for when a message-body is allowed in a message differ for
1243   requests and responses.
1244</t>
1245<t>
1246   The presence of a message-body in a request is signaled by the
1247   inclusion of a Content-Length or Transfer-Encoding header field in
1248   the request's header fields, even if the request method does not
1249   define any use for a message-body.  This allows the request
1250   message framing algorithm to be independent of method semantics.
1251</t>
1252<t>
1253   For response messages, whether or not a message-body is included with
1254   a message is dependent on both the request method and the response
1255   status code (<xref target="status.code.and.reason.phrase"/>).
1256   Responses to the HEAD request method never include a message-body
1257   because the associated response header fields (e.g., Transfer-Encoding,
1258   Content-Length, etc.) only indicate what their values would have been
1259   if the method had been GET.  All 1xx (Informational), 204 (No Content),
1260   and 304 (Not Modified) responses MUST NOT include a message-body.
1261   All other responses do include a message-body, although the body
1262   MAY be of zero length.
1263</t>
1264<t>
1265   The length of the message-body is determined by one of the following
1266   (in order of precedence):
1267</t>
1268<t>
1269  <list style="numbers">
1270    <t>
1271     Any response to a HEAD request and any response with a status
1272     code of 100-199, 204, or 304 is always terminated by the first
1273     empty line after the header fields, regardless of the header
1274     fields present in the message, and thus cannot contain a message-body.
1275    </t>
1276    <t>
1277     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1278     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1279     is the final encoding, the message-body length is determined by reading
1280     and decoding the chunked data until the transfer-coding indicates the
1281     data is complete.
1282    <vspace blankLines="1"/>
1283     If a Transfer-Encoding header field is present in a response and the
1284     "chunked" transfer-coding is not the final encoding, the message-body
1285     length is determined by reading the connection until it is closed by
1286     the server.
1287     If a Transfer-Encoding header field is present in a request and the
1288     "chunked" transfer-coding is not the final encoding, the message-body
1289     length cannot be determined reliably; the server MUST respond with
1290     the 400 (Bad Request) status code and then close the connection.
1291    <vspace blankLines="1"/>
1292     If a message is received with both a Transfer-Encoding header field and a
1293     Content-Length header field, the Transfer-Encoding overrides the Content-Length.
1294     Such a message might indicate an attempt to perform request or response
1295     smuggling (bypass of security-related checks on message routing or content)
1296     and thus ought to be handled as an error.  The provided Content-Length MUST
1297     be removed, prior to forwarding the message downstream, or replaced with
1298     the real message-body length after the transfer-coding is decoded.
1299    </t>
1300    <t>
1301     If a message is received without Transfer-Encoding and with either
1302     multiple Content-Length header fields or a single Content-Length header
1303     field with an invalid value, then the message framing is invalid and
1304     MUST be treated as an error to prevent request or response smuggling.
1305     If this is a request message, the server MUST respond with
1306     a 400 (Bad Request) status code and then close the connection.
1307     If this is a response message received by a proxy or gateway, the proxy
1308     or gateway MUST discard the received response, send a 502 (Bad Gateway)
1309     status code as its downstream response, and then close the connection.
1310     If this is a response message received by a user-agent, it SHOULD be
1311     treated as an error by discarding the message and closing the connection.
1312    </t>
1313    <t>
1314     If a valid Content-Length header field (<xref target="header.content-length"/>)
1315     is present without Transfer-Encoding, its decimal value defines the
1316     message-body length in octets.  If the actual number of octets sent in
1317     the message is less than the indicated Content-Length, the recipient
1318     MUST consider the message to be incomplete and treat the connection
1319     as no longer usable.
1320     If the actual number of octets sent in the message is more than the indicated
1321     Content-Length, the recipient MUST only process the message-body up to the
1322     field value's number of octets; the remainder of the message MUST either
1323     be discarded or treated as the next message in a pipeline.  For the sake of
1324     robustness, a user-agent MAY attempt to detect and correct such an error
1325     in message framing if it is parsing the response to the last request on
1326     on a connection and the connection has been closed by the server.
1327    </t>
1328    <t>
1329     If this is a request message and none of the above are true, then the
1330     message-body length is zero (no message-body is present).
1331    </t>
1332    <t>
1333     Otherwise, this is a response message without a declared message-body
1334     length, so the message-body length is determined by the number of octets
1335     received prior to the server closing the connection.
1336    </t>
1337  </list>
1338</t>
1339<t>
1340   Since there is no way to distinguish a successfully completed,
1341   close-delimited message from a partially-received message interrupted
1342   by network failure, implementations SHOULD use encoding or
1343   length-delimited messages whenever possible.  The close-delimiting
1344   feature exists primarily for backwards compatibility with HTTP/1.0.
1345</t>
1346<t>
1347   A server MAY reject a request that contains a message-body but
1348   not a Content-Length by responding with 411 (Length Required).
1349</t>
1350<t>
1351   Unless a transfer-coding other than "chunked" has been applied,
1352   a client that sends a request containing a message-body SHOULD
1353   use a valid Content-Length header field if the message-body length
1354   is known in advance, rather than the "chunked" encoding, since some
1355   existing services respond to "chunked" with a 411 (Length Required)
1356   status code even though they understand the chunked encoding.  This
1357   is typically because such services are implemented via a gateway that
1358   requires a content-length in advance of being called and the server
1359   is unable or unwilling to buffer the entire request before processing.
1360</t>
1361<t>
1362   A client that sends a request containing a message-body MUST include a
1363   valid Content-Length header field if it does not know the server will
1364   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1365   of specific user configuration or by remembering the version of a prior
1366   received response.
1367</t>
1368<t>
1369   Request messages that are prematurely terminated, possibly due to a
1370   cancelled connection or a server-imposed time-out exception, MUST
1371   result in closure of the connection; sending an HTTP/1.1 error response
1372   prior to closing the connection is OPTIONAL.
1373   Response messages that are prematurely terminated, usually by closure
1374   of the connection prior to receiving the expected number of octets or by
1375   failure to decode a transfer-encoded message-body, MUST be recorded
1376   as incomplete.  A user agent MUST NOT render an incomplete response
1377   message-body as if it were complete (i.e., some indication must be given
1378   to the user that an error occurred).  Cache requirements for incomplete
1379   responses are defined in Section 2.1.1 of <xref target="Part6"/>.
1380</t>
1381<t>
1382   A server MUST read the entire request message-body or close
1383   the connection after sending its response, since otherwise the
1384   remaining data on a persistent connection would be misinterpreted
1385   as the next request.  Likewise,
1386   a client MUST read the entire response message-body if it intends
1387   to reuse the same connection for a subsequent request.  Pipelining
1388   multiple requests on a connection is described in <xref target="pipelining"/>.
1389</t>
1390</section>
1391
1392<section title="General Header Fields" anchor="general.header.fields">
1393 
1394<t>
1395   There are a few header fields which have general applicability for
1396   both request and response messages, but which do not apply to the
1397   payload being transferred. These header fields apply only to the
1398   message being transmitted.
1399</t>
1400<figure><iref primary="true" item="Grammar" subitem="general-header"/><artwork type="abnf2616"><![CDATA[
1401  general-header = Cache-Control            ; [Part6], Section 3.2
1402                 / Connection               ; Section 9.1
1403                 / Date                     ; Section 9.3
1404                 / Pragma                   ; [Part6], Section 3.4
1405                 / Trailer                  ; Section 9.6
1406                 / Transfer-Encoding        ; Section 9.7
1407                 / Upgrade                  ; Section 9.8
1408                 / Via                      ; Section 9.9
1409                 / Warning                  ; [Part6], Section 3.6
1410                 / MIME-Version             ; [Part3], Appendix A.1
1411]]></artwork></figure>
1412<t>
1413   General-header field names can be extended reliably only in
1414   combination with a change in the protocol version. However, new or
1415   experimental header fields might be given the semantics of general
1416   header fields if all parties in the communication recognize them to
1417   be general-header fields.
1418</t>
1419</section>
1420</section>
1421
1422<section title="Request" anchor="request">
1423 
1424<t>
1425   A request message from a client to a server includes, within the
1426   first line of that message, the method to be applied to the resource,
1427   the identifier of the resource, and the protocol version in use.
1428</t>
1429<!--                 Host                      ; should be moved here eventually -->
1430<figure><iref primary="true" item="Grammar" subitem="Request"/><artwork type="abnf2616"><![CDATA[
1431  Request       = Request-Line              ; Section 4.1
1432                  *( header-field CRLF )    ; Section 3.2
1433                  CRLF
1434                  [ message-body ]          ; Section 3.3
1435]]></artwork></figure>
1436
1437<section title="Request-Line" anchor="request-line">
1438 
1439<t>
1440   The Request-Line begins with a method token, followed by the
1441   request-target and the protocol version, and ending with CRLF. The
1442   elements are separated by SP characters. No CR or LF is allowed
1443   except in the final CRLF sequence.
1444</t>
1445<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1446  Request-Line   = Method SP request-target SP HTTP-Version CRLF
1447]]></artwork></figure>
1448
1449<section title="Method" anchor="method">
1450 
1451<t>
1452   The Method  token indicates the method to be performed on the
1453   resource identified by the request-target. The method is case-sensitive.
1454</t>
1455<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
1456  Method         = token
1457]]></artwork></figure>
1458</section>
1459
1460<section title="request-target" anchor="request-target">
1461 
1462<t>
1463   The request-target identifies the resource upon which to apply the request.
1464</t>
1465<figure><iref primary="true" item="Grammar" subitem="request-target"/><artwork type="abnf2616"><![CDATA[
1466  request-target = "*"
1467                 / absolute-URI
1468                 / ( path-absolute [ "?" query ] )
1469                 / authority
1470]]></artwork></figure>
1471<t>
1472   The four options for request-target are dependent on the nature of the
1473   request.
1474</t>   
1475<t><iref item="asterisk form (of request-target)"/>
1476   The asterisk "*" ("asterisk form") means that the request does not apply to a
1477   particular resource, but to the server itself, and is only allowed
1478   when the method used does not necessarily apply to a resource. One
1479   example would be
1480</t>
1481<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1482  OPTIONS * HTTP/1.1
1483  ]]></artwork></figure>
1484<t><iref item="absolute-URI form (of request-target)"/>
1485   The absolute-URI form is REQUIRED when the request is being made to a
1486   proxy. The proxy is requested to forward the request or service it
1487   from a valid cache, and return the response. Note that the proxy MAY
1488   forward the request on to another proxy or directly to the server
1489   specified by the absolute-URI. In order to avoid request loops, a
1490   proxy MUST be able to recognize all of its server names, including
1491   any aliases, local variations, and the numeric IP address. An example
1492   Request-Line would be:
1493</t>
1494<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1495  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1496  ]]></artwork></figure>
1497<t>
1498   To allow for transition to absolute-URIs in all requests in future
1499   versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
1500   form in requests, even though HTTP/1.1 clients will only generate
1501   them in requests to proxies.
1502</t>
1503<t><iref item="authority form (of request-target)"/>
1504   The authority form is only used by the CONNECT method (Section 7.9 of <xref target="Part2"/>).
1505</t>
1506<t><iref item="path-absolute form (of request-target)"/>
1507   The most common form of request-target is that used to identify a
1508   resource on an origin server or gateway ("path-absolute form"). In this case the absolute
1509   path of the URI MUST be transmitted (see <xref target="http.uri"/>, path-absolute) as
1510   the request-target, and the network location of the URI (authority) MUST
1511   be transmitted in a Host header field. For example, a client wishing
1512   to retrieve the resource above directly from the origin server would
1513   create a TCP connection to port 80 of the host "www.example.org" and send
1514   the lines:
1515</t>
1516<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1517  GET /pub/WWW/TheProject.html HTTP/1.1
1518  Host: www.example.org
1519  ]]></artwork></figure>
1520<t>
1521   followed by the remainder of the Request. Note that the absolute path
1522   cannot be empty; if none is present in the original URI, it MUST be
1523   given as "/" (the server root).
1524</t>
1525<t>
1526   If a proxy receives a request without any path in the request-target and
1527   the method specified is capable of supporting the asterisk form of
1528   request-target, then the last proxy on the request chain MUST forward the
1529   request with "*" as the final request-target.
1530</t>
1531<figure><preamble>   
1532   For example, the request
1533</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1534  OPTIONS http://www.example.org:8001 HTTP/1.1
1535  ]]></artwork></figure>
1536<figure><preamble>   
1537  would be forwarded by the proxy as
1538</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1539  OPTIONS * HTTP/1.1
1540  Host: www.example.org:8001
1541  ]]></artwork>
1542<postamble>
1543   after connecting to port 8001 of host "www.example.org".
1544</postamble>
1545</figure>
1546<t>
1547   The request-target is transmitted in the format specified in
1548   <xref target="http.uri"/>. If the request-target is percent-encoded
1549   (<xref target="RFC3986"/>, Section 2.1), the origin server
1550   MUST decode the request-target in order to
1551   properly interpret the request. Servers SHOULD respond to invalid
1552   request-targets with an appropriate status code.
1553</t>
1554<t>
1555   A transparent proxy MUST NOT rewrite the "path-absolute" part of the
1556   received request-target when forwarding it to the next inbound server,
1557   except as noted above to replace a null path-absolute with "/" or "*".
1558</t>
1559<t><list>
1560  <t>
1561    Note: The "no rewrite" rule prevents the proxy from changing the
1562    meaning of the request when the origin server is improperly using
1563    a non-reserved URI character for a reserved purpose.  Implementors
1564    need to be aware that some pre-HTTP/1.1 proxies have been known to
1565    rewrite the request-target.
1566  </t>
1567</list></t>
1568<t>
1569   HTTP does not place a pre-defined limit on the length of a request-target.
1570   A server MUST be prepared to receive URIs of unbounded length and
1571   respond with the 414 (URI Too Long) status code if the received
1572   request-target would be longer than the server wishes to handle
1573   (see Section 8.4.15 of <xref target="Part2"/>).
1574</t>
1575<t>
1576   Various ad-hoc limitations on request-target length are found in practice.
1577   It is RECOMMENDED that all HTTP senders and recipients support
1578   request-target lengths of 8000 or more octets.
1579</t>
1580<t><list>
1581  <t>
1582    Note: Fragments (<xref target="RFC3986"/>, Section 3.5)
1583    are not part of the request-target and thus will not be transmitted
1584    in an HTTP request.
1585  </t>
1586</list></t>
1587</section>
1588</section>
1589
1590<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1591<t>
1592   The exact resource identified by an Internet request is determined by
1593   examining both the request-target and the Host header field.
1594</t>
1595<t>
1596   An origin server that does not allow resources to differ by the
1597   requested host MAY ignore the Host header field value when
1598   determining the resource identified by an HTTP/1.1 request. (But see
1599   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1600   for other requirements on Host support in HTTP/1.1.)
1601</t>
1602<t>
1603   An origin server that does differentiate resources based on the host
1604   requested (sometimes referred to as virtual hosts or vanity host
1605   names) MUST use the following rules for determining the requested
1606   resource on an HTTP/1.1 request:
1607  <list style="numbers">
1608    <t>If request-target is an absolute-URI, the host is part of the
1609     request-target. Any Host header field value in the request MUST be
1610     ignored.</t>
1611    <t>If the request-target is not an absolute-URI, and the request includes
1612     a Host header field, the host is determined by the Host header
1613     field value.</t>
1614    <t>If the host as determined by rule 1 or 2 is not a valid host on
1615     the server, the response MUST be a 400 (Bad Request) error message.</t>
1616  </list>
1617</t>
1618<t>
1619   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1620   attempt to use heuristics (e.g., examination of the URI path for
1621   something unique to a particular host) in order to determine what
1622   exact resource is being requested.
1623</t>
1624</section>
1625
1626<section title="Effective Request URI" anchor="effective.request.uri">
1627  <iref primary="true" item="effective request URI"/>
1628  <iref primary="true" item="target resource"/>
1629<t>
1630   HTTP requests often do not carry the absolute URI (<xref target="RFC3986"/>, Section 4.3)
1631   for the target resource; instead, the URI needs to be inferred from the
1632   request-target, Host header field, and connection context. The result of
1633   this process is called the "effective request URI".  The "target resource"
1634   is the resource identified by the effective request URI.
1635</t>
1636<t>
1637   If the request-target is an absolute-URI, then the effective request URI is
1638   the request-target.
1639</t>
1640<t>
1641   If the request-target uses the path-absolute form or the asterisk form,
1642   and the Host header field is present, then the effective request URI is
1643   constructed by concatenating
1644</t>
1645<t>
1646  <list style="symbols">
1647    <t>
1648      the scheme name: "http" if the request was received over an insecure
1649      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1650      connection,
1651    </t>
1652    <t>
1653      the character sequence "://",
1654    </t>
1655    <t>
1656      the authority component, as specified in the Host header field
1657      (<xref target="header.host"/>), and
1658    </t>
1659    <t>
1660      the request-target obtained from the Request-Line, unless the
1661      request-target is just the asterisk "*".
1662    </t>
1663  </list>
1664</t>
1665<t>
1666   If the request-target uses the path-absolute form or the asterisk form,
1667   and the Host header field is not present, then the effective request URI is
1668   undefined.
1669</t>
1670<t>
1671   Otherwise, when request-target uses the authority form, the effective
1672   request URI is undefined.
1673</t>
1674<figure>
1675<preamble>
1676   Example 1: the effective request URI for the message
1677</preamble> 
1678<artwork type="example"><![CDATA[
1679  GET /pub/WWW/TheProject.html HTTP/1.1
1680  Host: www.example.org:8080
1681  ]]></artwork>
1682<postamble>
1683  (received over an insecure TCP connection) is "http", plus "://", plus the
1684  authority component "www.example.org:8080", plus the request-target
1685  "/pub/WWW/TheProject.html", thus
1686  "http://www.example.org:8080/pub/WWW/TheProject.html".
1687</postamble>
1688</figure>
1689<figure>
1690<preamble>
1691   Example 2: the effective request URI for the message
1692</preamble> 
1693<artwork type="example"><![CDATA[
1694  GET * HTTP/1.1
1695  Host: www.example.org
1696  ]]></artwork>
1697<postamble>
1698  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1699  authority component "www.example.org", thus "https://www.example.org".
1700</postamble>
1701</figure>
1702<t>
1703   Effective request URIs are compared using the rules described in
1704   <xref target="uri.comparison"/>, except that empty path components MUST NOT
1705   be treated as equivalent to an absolute path of "/".
1706</t> 
1707</section>
1708
1709</section>
1710
1711
1712<section title="Response" anchor="response">
1713 
1714<t>
1715   After receiving and interpreting a request message, a server responds
1716   with an HTTP response message.
1717</t>
1718<figure><iref primary="true" item="Grammar" subitem="Response"/><artwork type="abnf2616"><![CDATA[
1719  Response      = Status-Line               ; Section 5.1
1720                  *( header-field CRLF )    ; Section 3.2
1721                  CRLF
1722                  [ message-body ]          ; Section 3.3
1723]]></artwork></figure>
1724
1725<section title="Status-Line" anchor="status-line">
1726 
1727<t>
1728   The first line of a Response message is the Status-Line, consisting
1729   of the protocol version followed by a numeric status code and its
1730   associated textual phrase, with each element separated by SP
1731   characters. No CR or LF is allowed except in the final CRLF sequence.
1732</t>
1733<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1734  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1735]]></artwork></figure>
1736
1737<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1738 
1739 
1740<t>
1741   The Status-Code element is a 3-digit integer result code of the
1742   attempt to understand and satisfy the request. These codes are fully
1743   defined in Section 8 of <xref target="Part2"/>.  The Reason Phrase exists for the sole
1744   purpose of providing a textual description associated with the numeric
1745   status code, out of deference to earlier Internet application protocols
1746   that were more frequently used with interactive text clients.
1747   A client SHOULD ignore the content of the Reason Phrase.
1748</t>
1749<t>
1750   The first digit of the Status-Code defines the class of response. The
1751   last two digits do not have any categorization role. There are 5
1752   values for the first digit:
1753  <list style="symbols">
1754    <t>
1755      1xx: Informational - Request received, continuing process
1756    </t>
1757    <t>
1758      2xx: Success - The action was successfully received,
1759        understood, and accepted
1760    </t>
1761    <t>
1762      3xx: Redirection - Further action must be taken in order to
1763        complete the request
1764    </t>
1765    <t>
1766      4xx: Client Error - The request contains bad syntax or cannot
1767        be fulfilled
1768    </t>
1769    <t>
1770      5xx: Server Error - The server failed to fulfill an apparently
1771        valid request
1772    </t>
1773  </list>
1774</t>
1775<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
1776  Status-Code    = 3DIGIT
1777  Reason-Phrase  = *( WSP / VCHAR / obs-text )
1778]]></artwork></figure>
1779</section>
1780</section>
1781
1782</section>
1783
1784
1785<section title="Protocol Parameters" anchor="protocol.parameters">
1786
1787<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1788 
1789<t>
1790   HTTP applications have historically allowed three different formats
1791   for date/time stamps. However, the preferred format is a fixed-length subset
1792   of that defined by <xref target="RFC1123"/>:
1793</t>
1794<figure><artwork type="example"><![CDATA[
1795  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1796  ]]></artwork></figure>
1797<t>
1798   The other formats are described here only for compatibility with obsolete
1799   implementations.
1800</t>
1801<figure><artwork type="example"><![CDATA[
1802  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1803  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1804  ]]></artwork></figure>
1805<t>
1806   HTTP/1.1 clients and servers that parse a date value MUST accept
1807   all three formats (for compatibility with HTTP/1.0), though they MUST
1808   only generate the RFC 1123 format for representing HTTP-date values
1809   in header fields. See <xref target="tolerant.applications"/> for further information.
1810</t>
1811<t>
1812   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
1813   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1814   equal to UTC (Coordinated Universal Time). This is indicated in the
1815   first two formats by the inclusion of "GMT" as the three-letter
1816   abbreviation for time zone, and MUST be assumed when reading the
1817   asctime format. HTTP-date is case sensitive and MUST NOT include
1818   additional whitespace beyond that specifically included as SP in the
1819   grammar.
1820</t>
1821<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><artwork type="abnf2616"><![CDATA[
1822  HTTP-date    = rfc1123-date / obs-date
1823]]></artwork></figure>
1824<t anchor="preferred.date.format">
1825 
1826 
1827 
1828 
1829 
1830 
1831 
1832 
1833 
1834 
1835  Preferred format:
1836</t>
1837<figure><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"/><artwork type="abnf2616"><![CDATA[
1838  rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
1839  ; fixed length subset of the format defined in
1840  ; Section 5.2.14 of [RFC1123]
1841 
1842  day-name     = %x4D.6F.6E ; "Mon", case-sensitive
1843               / %x54.75.65 ; "Tue", case-sensitive
1844               / %x57.65.64 ; "Wed", case-sensitive
1845               / %x54.68.75 ; "Thu", case-sensitive
1846               / %x46.72.69 ; "Fri", case-sensitive
1847               / %x53.61.74 ; "Sat", case-sensitive
1848               / %x53.75.6E ; "Sun", case-sensitive
1849               
1850  date1        = day SP month SP year
1851               ; e.g., 02 Jun 1982
1852
1853  day          = 2DIGIT
1854  month        = %x4A.61.6E ; "Jan", case-sensitive
1855               / %x46.65.62 ; "Feb", case-sensitive
1856               / %x4D.61.72 ; "Mar", case-sensitive
1857               / %x41.70.72 ; "Apr", case-sensitive
1858               / %x4D.61.79 ; "May", case-sensitive
1859               / %x4A.75.6E ; "Jun", case-sensitive
1860               / %x4A.75.6C ; "Jul", case-sensitive
1861               / %x41.75.67 ; "Aug", case-sensitive
1862               / %x53.65.70 ; "Sep", case-sensitive
1863               / %x4F.63.74 ; "Oct", case-sensitive
1864               / %x4E.6F.76 ; "Nov", case-sensitive
1865               / %x44.65.63 ; "Dec", case-sensitive
1866  year         = 4DIGIT
1867
1868  GMT   = %x47.4D.54 ; "GMT", case-sensitive
1869
1870  time-of-day  = hour ":" minute ":" second
1871                 ; 00:00:00 - 23:59:59
1872                 
1873  hour         = 2DIGIT               
1874  minute       = 2DIGIT               
1875  second       = 2DIGIT               
1876]]></artwork></figure>
1877<t>
1878  The semantics of <xref target="preferred.date.format" format="none">day-name</xref>, <xref target="preferred.date.format" format="none">day</xref>,
1879  <xref target="preferred.date.format" format="none">month</xref>, <xref target="preferred.date.format" format="none">year</xref>, and <xref target="preferred.date.format" format="none">time-of-day</xref> are the
1880  same as those defined for the RFC 5322 constructs
1881  with the corresponding name (<xref target="RFC5322"/>, Section 3.3).
1882</t>
1883<t anchor="obsolete.date.formats">
1884 
1885 
1886 
1887 
1888 
1889 
1890 
1891 
1892  Obsolete formats:
1893</t>
1894<figure><iref primary="true" item="Grammar" subitem="obs-date"/><artwork type="abnf2616"><![CDATA[
1895  obs-date     = rfc850-date / asctime-date
1896]]></artwork></figure>
1897<figure><iref primary="true" item="Grammar" subitem="rfc850-date"/><artwork type="abnf2616"><![CDATA[
1898  rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
1899  date2        = day "-" month "-" 2DIGIT
1900                 ; day-month-year (e.g., 02-Jun-82)
1901
1902  day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
1903         / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
1904         / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
1905         / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
1906         / %x46.72.69.64.61.79 ; "Friday", case-sensitive
1907         / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
1908         / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
1909]]></artwork></figure>
1910<figure><iref primary="true" item="Grammar" subitem="asctime-date"/><artwork type="abnf2616"><![CDATA[
1911  asctime-date = day-name SP date3 SP time-of-day SP year
1912  date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
1913                 ; month day (e.g., Jun  2)
1914]]></artwork></figure>
1915<t><list>
1916  <t>
1917    Note: Recipients of date values are encouraged to be robust in
1918    accepting date values that might have been sent by non-HTTP
1919    applications, as is sometimes the case when retrieving or posting
1920    messages via proxies/gateways to SMTP or NNTP.
1921  </t>
1922</list></t>
1923<t><list>
1924  <t>
1925    Note: HTTP requirements for the date/time stamp format apply only
1926    to their usage within the protocol stream. Clients and servers are
1927    not required to use these formats for user presentation, request
1928    logging, etc.
1929  </t>
1930</list></t>
1931</section>
1932
1933<section title="Transfer Codings" anchor="transfer.codings">
1934 
1935 
1936<t>
1937   Transfer-coding values are used to indicate an encoding
1938   transformation that has been, can be, or might need to be applied to a
1939   payload body in order to ensure "safe transport" through the network.
1940   This differs from a content coding in that the transfer-coding is a
1941   property of the message rather than a property of the representation
1942   that is being transferred.
1943</t>
1944<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
1945  transfer-coding         = "chunked" ; Section 6.2.1
1946                          / "compress" ; Section 6.2.2.1
1947                          / "deflate" ; Section 6.2.2.2
1948                          / "gzip" ; Section 6.2.2.3
1949                          / transfer-extension
1950  transfer-extension      = token *( OWS ";" OWS transfer-parameter )
1951]]></artwork></figure>
1952<t anchor="rule.parameter">
1953 
1954 
1955 
1956   Parameters are in the form of attribute/value pairs.
1957</t>
1958<figure><iref primary="true" item="Grammar" subitem="transfer-parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><artwork type="abnf2616"><![CDATA[
1959  transfer-parameter      = attribute BWS "=" BWS value
1960  attribute               = token
1961  value                   = word
1962]]></artwork></figure>
1963<t>
1964   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1965   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1966   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1967</t>
1968<t>
1969   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1970   MIME, which were designed to enable safe transport of binary data over a
1971   7-bit transport service (<xref target="RFC2045"/>, Section 6).
1972   However, safe transport
1973   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1974   the only unsafe characteristic of message-bodies is the difficulty in
1975   determining the exact message body length (<xref target="message.body"/>),
1976   or the desire to encrypt data over a shared transport.
1977</t>
1978<t>
1979   A server that receives a request message with a transfer-coding it does
1980   not understand SHOULD respond with 501 (Not Implemented) and then
1981   close the connection. A server MUST NOT send transfer-codings to an HTTP/1.0
1982   client.
1983</t>
1984
1985<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1986  <iref item="chunked (Coding Format)"/>
1987  <iref item="Coding Format" subitem="chunked"/>
1988 
1989 
1990 
1991 
1992 
1993 
1994 
1995 
1996 
1997 
1998 
1999<t>
2000   The chunked encoding modifies the body of a message in order to
2001   transfer it as a series of chunks, each with its own size indicator,
2002   followed by an OPTIONAL trailer containing header fields. This
2003   allows dynamically produced content to be transferred along with the
2004   information necessary for the recipient to verify that it has
2005   received the full message.
2006</t>
2007<figure><iref primary="true" item="Grammar" subitem="Chunked-Body"/><iref primary="true" item="Grammar" subitem="chunk"/><iref primary="true" item="Grammar" subitem="chunk-size"/><iref primary="true" item="Grammar" subitem="last-chunk"/><iref primary="true" item="Grammar" subitem="chunk-ext"/><iref primary="true" item="Grammar" subitem="chunk-ext-name"/><iref primary="true" item="Grammar" subitem="chunk-ext-val"/><iref primary="true" item="Grammar" subitem="chunk-data"/><iref primary="true" item="Grammar" subitem="trailer-part"/><iref primary="true" item="Grammar" subitem="quoted-str-nf"/><iref primary="true" item="Grammar" subitem="qdtext-nf"/><artwork type="abnf2616"><![CDATA[
2008  Chunked-Body   = *chunk
2009                   last-chunk
2010                   trailer-part
2011                   CRLF
2012 
2013  chunk          = chunk-size *WSP [ chunk-ext ] CRLF
2014                   chunk-data CRLF
2015  chunk-size     = 1*HEXDIG
2016  last-chunk     = 1*("0") *WSP [ chunk-ext ] CRLF
2017 
2018  chunk-ext      = *( ";" *WSP chunk-ext-name
2019                      [ "=" chunk-ext-val ] *WSP )
2020  chunk-ext-name = token
2021  chunk-ext-val  = token / quoted-str-nf
2022  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
2023  trailer-part   = *( header-field CRLF )
2024 
2025  quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
2026                 ; like quoted-string, but disallowing line folding
2027  qdtext-nf      = WSP / %x21 / %x23-5B / %x5D-7E / obs-text
2028                 ; WSP / <VCHAR except DQUOTE and "\"> / obs-text
2029]]></artwork></figure>
2030<t>
2031   The chunk-size field is a string of hex digits indicating the size of
2032   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2033   zero, followed by the trailer, which is terminated by an empty line.
2034</t>
2035<t>
2036   The trailer allows the sender to include additional HTTP header
2037   fields at the end of the message. The Trailer header field can be
2038   used to indicate which header fields are included in a trailer (see
2039   <xref target="header.trailer"/>).
2040</t>
2041<t>
2042   A server using chunked transfer-coding in a response MUST NOT use the
2043   trailer for any header fields unless at least one of the following is
2044   true:
2045  <list style="numbers">
2046    <t>the request included a TE header field that indicates "trailers" is
2047     acceptable in the transfer-coding of the  response, as described in
2048     <xref target="header.te"/>; or,</t>
2049     
2050    <t>the trailer fields consist entirely of optional metadata, and the
2051    recipient could use the message (in a manner acceptable to the server where
2052    the field originated) without receiving it. In other words, the server that
2053    generated the header (often but not always the origin server) is willing to
2054    accept the possibility that the trailer fields might be silently discarded
2055    along the path to the client.</t>
2056  </list>
2057</t>
2058<t>
2059   This requirement prevents an interoperability failure when the
2060   message is being received by an HTTP/1.1 (or later) proxy and
2061   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2062   compliance with the protocol would have necessitated a possibly
2063   infinite buffer on the proxy.
2064</t>
2065<t>
2066   A process for decoding the "chunked" transfer-coding
2067   can be represented in pseudo-code as:
2068</t>
2069<figure><artwork type="code"><![CDATA[
2070  length := 0
2071  read chunk-size, chunk-ext (if any) and CRLF
2072  while (chunk-size > 0) {
2073     read chunk-data and CRLF
2074     append chunk-data to decoded-body
2075     length := length + chunk-size
2076     read chunk-size and CRLF
2077  }
2078  read header-field
2079  while (header-field not empty) {
2080     append header-field to existing header fields
2081     read header-field
2082  }
2083  Content-Length := length
2084  Remove "chunked" from Transfer-Encoding
2085]]></artwork></figure>
2086<t>
2087   All HTTP/1.1 applications MUST be able to receive and decode the
2088   "chunked" transfer-coding and MUST ignore chunk-ext extensions
2089   they do not understand.
2090</t>
2091<t>
2092   Since "chunked" is the only transfer-coding required to be understood
2093   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2094   on a persistent connection.  Whenever a transfer-coding is applied to
2095   a payload body in a request, the final transfer-coding applied MUST
2096   be "chunked".  If a transfer-coding is applied to a response payload
2097   body, then either the final transfer-coding applied MUST be "chunked"
2098   or the message MUST be terminated by closing the connection. When the
2099   "chunked" transfer-coding is used, it MUST be the last transfer-coding
2100   applied to form the message-body. The "chunked" transfer-coding MUST NOT
2101   be applied more than once in a message-body.
2102</t>
2103</section>
2104
2105<section title="Compression Codings" anchor="compression.codings">
2106<t>
2107   The codings defined below can be used to compress the payload of a
2108   message.
2109</t>
2110<t><list><t>
2111   Note: Use of program names for the identification of encoding formats
2112   is not desirable and is discouraged for future encodings. Their
2113   use here is representative of historical practice, not good
2114   design.
2115</t></list></t>
2116<t><list><t>
2117   Note: For compatibility with previous implementations of HTTP,
2118   applications SHOULD consider "x-gzip" and "x-compress" to be
2119   equivalent to "gzip" and "compress" respectively.
2120</t></list></t>
2121
2122<section title="Compress Coding" anchor="compress.coding">
2123<iref item="compress (Coding Format)"/>
2124<iref item="Coding Format" subitem="compress"/>
2125<t>
2126   The "compress" format is produced by the common UNIX file compression
2127   program "compress". This format is an adaptive Lempel-Ziv-Welch
2128   coding (LZW).
2129</t>
2130</section>
2131
2132<section title="Deflate Coding" anchor="deflate.coding">
2133<iref item="deflate (Coding Format)"/>
2134<iref item="Coding Format" subitem="deflate"/>
2135<t>
2136   The "deflate" format is defined as the "deflate" compression mechanism
2137   (described in <xref target="RFC1951"/>) used inside the "zlib"
2138   data format (<xref target="RFC1950"/>).
2139</t>
2140<t><list>
2141  <t>
2142    Note: Some incorrect implementations send the "deflate"
2143    compressed data without the zlib wrapper.
2144   </t>
2145</list></t>
2146</section>
2147
2148<section title="Gzip Coding" anchor="gzip.coding">
2149<iref item="gzip (Coding Format)"/>
2150<iref item="Coding Format" subitem="gzip"/>
2151<t>
2152   The "gzip" format is produced by the file compression program
2153   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2154   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2155</t>
2156</section>
2157
2158</section>
2159
2160<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2161<t>
2162   The HTTP Transfer Coding Registry defines the name space for the transfer
2163   coding names.
2164</t>
2165<t>
2166   Registrations MUST include the following fields:
2167   <list style="symbols">
2168     <t>Name</t>
2169     <t>Description</t>
2170     <t>Pointer to specification text</t>
2171   </list>
2172</t>
2173<t>
2174   Names of transfer codings MUST NOT overlap with names of content codings
2175   (Section 2.2 of <xref target="Part3"/>), unless the encoding transformation is identical (as it
2176   is the case for the compression codings defined in
2177   <xref target="compression.codings"/>).
2178</t>
2179<t>
2180   Values to be added to this name space require a specification
2181   (see "Specification Required" in Section 4.1 of <xref target="RFC5226"/>), and MUST
2182   conform to the purpose of transfer coding defined in this section.
2183</t>
2184<t>
2185   The registry itself is maintained at
2186   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2187</t>
2188</section>
2189</section>
2190
2191<section title="Product Tokens" anchor="product.tokens">
2192 
2193 
2194<t>
2195   Product tokens are used to allow communicating applications to
2196   identify themselves by software name and version. Most fields using
2197   product tokens also allow sub-products which form a significant part
2198   of the application to be listed, separated by whitespace. By
2199   convention, the products are listed in order of their significance
2200   for identifying the application.
2201</t>
2202<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
2203  product         = token ["/" product-version]
2204  product-version = token
2205]]></artwork></figure>
2206<t>
2207   Examples:
2208</t>
2209<figure><artwork type="example"><![CDATA[
2210  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2211  Server: Apache/0.8.4
2212]]></artwork></figure>
2213<t>
2214   Product tokens SHOULD be short and to the point. They MUST NOT be
2215   used for advertising or other non-essential information. Although any
2216   token character MAY appear in a product-version, this token SHOULD
2217   only be used for a version identifier (i.e., successive versions of
2218   the same product SHOULD only differ in the product-version portion of
2219   the product value).
2220</t>
2221</section>
2222
2223<section title="Quality Values" anchor="quality.values">
2224 
2225<t>
2226   Both transfer codings (TE request header field, <xref target="header.te"/>)
2227   and content negotiation (Section 5 of <xref target="Part3"/>) use short "floating point"
2228   numbers to indicate the relative importance ("weight") of various
2229   negotiable parameters.  A weight is normalized to a real number in
2230   the range 0 through 1, where 0 is the minimum and 1 the maximum
2231   value. If a parameter has a quality value of 0, then content with
2232   this parameter is "not acceptable" for the client. HTTP/1.1
2233   applications MUST NOT generate more than three digits after the
2234   decimal point. User configuration of these values SHOULD also be
2235   limited in this fashion.
2236</t>
2237<figure><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
2238  qvalue         = ( "0" [ "." 0*3DIGIT ] )
2239                 / ( "1" [ "." 0*3("0") ] )
2240]]></artwork></figure>
2241<t><list>
2242  <t>
2243     Note: "Quality values" is a misnomer, since these values merely represent
2244     relative degradation in desired quality.
2245  </t>
2246</list></t>
2247</section>
2248
2249</section>
2250
2251<section title="Connections" anchor="connections">
2252
2253<section title="Persistent Connections" anchor="persistent.connections">
2254
2255<section title="Purpose" anchor="persistent.purpose">
2256<t>
2257   Prior to persistent connections, a separate TCP connection was
2258   established to fetch each URL, increasing the load on HTTP servers
2259   and causing congestion on the Internet. The use of inline images and
2260   other associated data often requires a client to make multiple
2261   requests of the same server in a short amount of time. Analysis of
2262   these performance problems and results from a prototype
2263   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2264   measurements of actual HTTP/1.1 implementations show good
2265   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2266   T/TCP <xref target="Tou1998"/>.
2267</t>
2268<t>
2269   Persistent HTTP connections have a number of advantages:
2270  <list style="symbols">
2271      <t>
2272        By opening and closing fewer TCP connections, CPU time is saved
2273        in routers and hosts (clients, servers, proxies, gateways,
2274        tunnels, or caches), and memory used for TCP protocol control
2275        blocks can be saved in hosts.
2276      </t>
2277      <t>
2278        HTTP requests and responses can be pipelined on a connection.
2279        Pipelining allows a client to make multiple requests without
2280        waiting for each response, allowing a single TCP connection to
2281        be used much more efficiently, with much lower elapsed time.
2282      </t>
2283      <t>
2284        Network congestion is reduced by reducing the number of packets
2285        caused by TCP opens, and by allowing TCP sufficient time to
2286        determine the congestion state of the network.
2287      </t>
2288      <t>
2289        Latency on subsequent requests is reduced since there is no time
2290        spent in TCP's connection opening handshake.
2291      </t>
2292      <t>
2293        HTTP can evolve more gracefully, since errors can be reported
2294        without the penalty of closing the TCP connection. Clients using
2295        future versions of HTTP might optimistically try a new feature,
2296        but if communicating with an older server, retry with old
2297        semantics after an error is reported.
2298      </t>
2299    </list>
2300</t>
2301<t>
2302   HTTP implementations SHOULD implement persistent connections.
2303</t>
2304</section>
2305
2306<section title="Overall Operation" anchor="persistent.overall">
2307<t>
2308   A significant difference between HTTP/1.1 and earlier versions of
2309   HTTP is that persistent connections are the default behavior of any
2310   HTTP connection. That is, unless otherwise indicated, the client
2311   SHOULD assume that the server will maintain a persistent connection,
2312   even after error responses from the server.
2313</t>
2314<t>
2315   Persistent connections provide a mechanism by which a client and a
2316   server can signal the close of a TCP connection. This signaling takes
2317   place using the Connection header field (<xref target="header.connection"/>). Once a close
2318   has been signaled, the client MUST NOT send any more requests on that
2319   connection.
2320</t>
2321
2322<section title="Negotiation" anchor="persistent.negotiation">
2323<t>
2324   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
2325   maintain a persistent connection unless a Connection header field including
2326   the connection-token "close" was sent in the request. If the server
2327   chooses to close the connection immediately after sending the
2328   response, it SHOULD send a Connection header field including the
2329   connection-token "close".
2330</t>
2331<t>
2332   An HTTP/1.1 client MAY expect a connection to remain open, but would
2333   decide to keep it open based on whether the response from a server
2334   contains a Connection header field with the connection-token close. In case
2335   the client does not want to maintain a connection for more than that
2336   request, it SHOULD send a Connection header field including the
2337   connection-token close.
2338</t>
2339<t>
2340   If either the client or the server sends the close token in the
2341   Connection header field, that request becomes the last one for the
2342   connection.
2343</t>
2344<t>
2345   Clients and servers SHOULD NOT  assume that a persistent connection is
2346   maintained for HTTP versions less than 1.1 unless it is explicitly
2347   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2348   compatibility with HTTP/1.0 clients.
2349</t>
2350<t>
2351   In order to remain persistent, all messages on the connection MUST
2352   have a self-defined message length (i.e., one not defined by closure
2353   of the connection), as described in <xref target="message.body"/>.
2354</t>
2355</section>
2356
2357<section title="Pipelining" anchor="pipelining">
2358<t>
2359   A client that supports persistent connections MAY "pipeline" its
2360   requests (i.e., send multiple requests without waiting for each
2361   response). A server MUST send its responses to those requests in the
2362   same order that the requests were received.
2363</t>
2364<t>
2365   Clients which assume persistent connections and pipeline immediately
2366   after connection establishment SHOULD be prepared to retry their
2367   connection if the first pipelined attempt fails. If a client does
2368   such a retry, it MUST NOT pipeline before it knows the connection is
2369   persistent. Clients MUST also be prepared to resend their requests if
2370   the server closes the connection before sending all of the
2371   corresponding responses.
2372</t>
2373<t>
2374   Clients SHOULD NOT  pipeline requests using non-idempotent methods or
2375   non-idempotent sequences of methods (see Section 7.1.2 of <xref target="Part2"/>). Otherwise, a
2376   premature termination of the transport connection could lead to
2377   indeterminate results. A client wishing to send a non-idempotent
2378   request SHOULD wait to send that request until it has received the
2379   response status line for the previous request.
2380</t>
2381</section>
2382</section>
2383
2384<section title="Proxy Servers" anchor="persistent.proxy">
2385<t>
2386   It is especially important that proxies correctly implement the
2387   properties of the Connection header field as specified in <xref target="header.connection"/>.
2388</t>
2389<t>
2390   The proxy server MUST signal persistent connections separately with
2391   its clients and the origin servers (or other proxy servers) that it
2392   connects to. Each persistent connection applies to only one transport
2393   link.
2394</t>
2395<t>
2396   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
2397   with an HTTP/1.0 client (but see Section 19.7.1 of <xref target="RFC2068"/>
2398   for information and discussion of the problems with the Keep-Alive header field
2399   implemented by many HTTP/1.0 clients).
2400</t>
2401
2402<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2403<!--<t>
2404  <cref anchor="TODO-end-to-end" source="jre">
2405    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2406    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2407  </cref>
2408</t>-->
2409<t>
2410   For the purpose of defining the behavior of caches and non-caching
2411   proxies, we divide HTTP header fields into two categories:
2412  <list style="symbols">
2413      <t>End-to-end header fields, which are  transmitted to the ultimate
2414        recipient of a request or response. End-to-end header fields in
2415        responses MUST be stored as part of a cache entry and MUST be
2416        transmitted in any response formed from a cache entry.</t>
2417
2418      <t>Hop-by-hop header fields, which are meaningful only for a single
2419        transport-level connection, and are not stored by caches or
2420        forwarded by proxies.</t>
2421  </list>
2422</t>
2423<t>
2424   The following HTTP/1.1 header fields are hop-by-hop header fields:
2425  <list style="symbols">
2426      <t>Connection</t>
2427      <t>Keep-Alive</t>
2428      <t>Proxy-Authenticate</t>
2429      <t>Proxy-Authorization</t>
2430      <t>TE</t>
2431      <t>Trailer</t>
2432      <t>Transfer-Encoding</t>
2433      <t>Upgrade</t>
2434  </list>
2435</t>
2436<t>
2437   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2438</t>
2439<t>
2440   Other hop-by-hop header fields MUST be listed in a Connection header field
2441   (<xref target="header.connection"/>).
2442</t>
2443</section>
2444
2445<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2446<!--<t>
2447  <cref anchor="TODO-non-mod-headers" source="jre">
2448    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2449    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2450  </cref>
2451</t>-->
2452<t>
2453   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2454   value of certain end-to-end header fields. A transparent proxy SHOULD NOT
2455   modify an end-to-end header field unless the definition of that header field requires
2456   or specifically allows that.
2457</t>
2458<t>
2459   A transparent proxy MUST NOT modify any of the following fields in a
2460   request or response, and it MUST NOT add any of these fields if not
2461   already present:
2462  <list style="symbols">
2463      <t>Content-Location</t>
2464      <t>Content-MD5</t>
2465      <t>ETag</t>
2466      <t>Last-Modified</t>
2467  </list>
2468</t>
2469<t>
2470   A transparent proxy MUST NOT modify any of the following fields in a
2471   response:
2472  <list style="symbols">
2473    <t>Expires</t>
2474  </list>
2475</t>
2476<t>
2477   but it MAY add any of these fields if not already present. If an
2478   Expires header field is added, it MUST be given a field-value identical to
2479   that of the Date header field in that response.
2480</t>
2481<t>
2482   A proxy MUST NOT modify or add any of the following fields in a
2483   message that contains the no-transform cache-control directive, or in
2484   any request:
2485  <list style="symbols">
2486    <t>Content-Encoding</t>
2487    <t>Content-Range</t>
2488    <t>Content-Type</t>
2489  </list>
2490</t>
2491<t>
2492   A non-transparent proxy MAY modify or add these fields to a message
2493   that does not include no-transform, but if it does so, it MUST add a
2494   Warning 214 (Transformation applied) if one does not already appear
2495   in the message (see Section 3.6 of <xref target="Part6"/>).
2496</t>
2497<t><list>
2498  <t>
2499    Warning: Unnecessary modification of end-to-end header fields might
2500    cause authentication failures if stronger authentication
2501    mechanisms are introduced in later versions of HTTP. Such
2502    authentication mechanisms MAY rely on the values of header fields
2503    not listed here.
2504  </t>
2505</list></t>
2506<t>
2507   A transparent proxy MUST preserve the message payload (<xref target="Part3"/>),
2508   though it MAY change the message-body through application or removal
2509   of a transfer-coding (<xref target="transfer.codings"/>).
2510</t>
2511</section>
2512
2513</section>
2514
2515<section title="Practical Considerations" anchor="persistent.practical">
2516<t>
2517   Servers will usually have some time-out value beyond which they will
2518   no longer maintain an inactive connection. Proxy servers might make
2519   this a higher value since it is likely that the client will be making
2520   more connections through the same server. The use of persistent
2521   connections places no requirements on the length (or existence) of
2522   this time-out for either the client or the server.
2523</t>
2524<t>
2525   When a client or server wishes to time-out it SHOULD issue a graceful
2526   close on the transport connection. Clients and servers SHOULD both
2527   constantly watch for the other side of the transport close, and
2528   respond to it as appropriate. If a client or server does not detect
2529   the other side's close promptly it could cause unnecessary resource
2530   drain on the network.
2531</t>
2532<t>
2533   A client, server, or proxy MAY close the transport connection at any
2534   time. For example, a client might have started to send a new request
2535   at the same time that the server has decided to close the "idle"
2536   connection. From the server's point of view, the connection is being
2537   closed while it was idle, but from the client's point of view, a
2538   request is in progress.
2539</t>
2540<t>
2541   This means that clients, servers, and proxies MUST be able to recover
2542   from asynchronous close events. Client software SHOULD reopen the
2543   transport connection and retransmit the aborted sequence of requests
2544   without user interaction so long as the request sequence is
2545   idempotent (see Section 7.1.2 of <xref target="Part2"/>). Non-idempotent methods or sequences
2546   MUST NOT be automatically retried, although user agents MAY offer a
2547   human operator the choice of retrying the request(s). Confirmation by
2548   user-agent software with semantic understanding of the application
2549   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2550   be repeated if the second sequence of requests fails.
2551</t>
2552<t>
2553   Servers SHOULD always respond to at least one request per connection,
2554   if at all possible. Servers SHOULD NOT  close a connection in the
2555   middle of transmitting a response, unless a network or client failure
2556   is suspected.
2557</t>
2558<t>
2559   Clients (including proxies) SHOULD limit the number of simultaneous
2560   connections that they maintain to a given server (including proxies).
2561</t>
2562<t>
2563   Previous revisions of HTTP gave a specific number of connections as a
2564   ceiling, but this was found to be impractical for many applications. As a
2565   result, this specification does not mandate a particular maximum number of
2566   connections, but instead encourages clients to be conservative when opening
2567   multiple connections.
2568</t>
2569<t>
2570   In particular, while using multiple connections avoids the "head-of-line
2571   blocking" problem (whereby a request that takes significant server-side
2572   processing and/or has a large payload can block subsequent requests on the
2573   same connection), each connection used consumes server resources (sometimes
2574   significantly), and furthermore using multiple connections can cause
2575   undesirable side effects in congested networks.
2576</t>
2577<t>
2578   Note that servers might reject traffic that they deem abusive, including an
2579   excessive number of connections from a client.
2580</t>
2581</section>
2582</section>
2583
2584<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2585
2586<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2587<t>
2588   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2589   flow control mechanisms to resolve temporary overloads, rather than
2590   terminating connections with the expectation that clients will retry.
2591   The latter technique can exacerbate network congestion.
2592</t>
2593</section>
2594
2595<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2596<t>
2597   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2598   the network connection for an error status code while it is transmitting
2599   the request. If the client sees an error status code, it SHOULD
2600   immediately cease transmitting the body. If the body is being sent
2601   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2602   empty trailer MAY be used to prematurely mark the end of the message.
2603   If the body was preceded by a Content-Length header field, the client MUST
2604   close the connection.
2605</t>
2606</section>
2607
2608<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2609<t>
2610   The purpose of the 100 (Continue) status code (see Section 8.1.1 of <xref target="Part2"/>) is to
2611   allow a client that is sending a request message with a request body
2612   to determine if the origin server is willing to accept the request
2613   (based on the request header fields) before the client sends the request
2614   body. In some cases, it might either be inappropriate or highly
2615   inefficient for the client to send the body if the server will reject
2616   the message without looking at the body.
2617</t>
2618<t>
2619   Requirements for HTTP/1.1 clients:
2620  <list style="symbols">
2621    <t>
2622        If a client will wait for a 100 (Continue) response before
2623        sending the request body, it MUST send an Expect request-header
2624        field (Section 9.2 of <xref target="Part2"/>) with the "100-continue" expectation.
2625    </t>
2626    <t>
2627        A client MUST NOT send an Expect request-header field (Section 9.2 of <xref target="Part2"/>)
2628        with the "100-continue" expectation if it does not intend
2629        to send a request body.
2630    </t>
2631  </list>
2632</t>
2633<t>
2634   Because of the presence of older implementations, the protocol allows
2635   ambiguous situations in which a client might send "Expect: 100-continue"
2636   without receiving either a 417 (Expectation Failed)
2637   or a 100 (Continue) status code. Therefore, when a client sends this
2638   header field to an origin server (possibly via a proxy) from which it
2639   has never seen a 100 (Continue) status code, the client SHOULD NOT 
2640   wait for an indefinite period before sending the request body.
2641</t>
2642<t>
2643   Requirements for HTTP/1.1 origin servers:
2644  <list style="symbols">
2645    <t> Upon receiving a request which includes an Expect request-header
2646        field with the "100-continue" expectation, an origin server MUST
2647        either respond with 100 (Continue) status code and continue to read
2648        from the input stream, or respond with a final status code. The
2649        origin server MUST NOT wait for the request body before sending
2650        the 100 (Continue) response. If it responds with a final status
2651        code, it MAY close the transport connection or it MAY continue
2652        to read and discard the rest of the request.  It MUST NOT
2653        perform the requested method if it returns a final status code.
2654    </t>
2655    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2656        the request message does not include an Expect request-header
2657        field with the "100-continue" expectation, and MUST NOT send a
2658        100 (Continue) response if such a request comes from an HTTP/1.0
2659        (or earlier) client. There is an exception to this rule: for
2660        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2661        status code in response to an HTTP/1.1 PUT or POST request that does
2662        not include an Expect request-header field with the "100-continue"
2663        expectation. This exception, the purpose of which is
2664        to minimize any client processing delays associated with an
2665        undeclared wait for 100 (Continue) status code, applies only to
2666        HTTP/1.1 requests, and not to requests with any other HTTP-version
2667        value.
2668    </t>
2669    <t> An origin server MAY omit a 100 (Continue) response if it has
2670        already received some or all of the request body for the
2671        corresponding request.
2672    </t>
2673    <t> An origin server that sends a 100 (Continue) response MUST
2674    ultimately send a final status code, once the request body is
2675        received and processed, unless it terminates the transport
2676        connection prematurely.
2677    </t>
2678    <t> If an origin server receives a request that does not include an
2679        Expect request-header field with the "100-continue" expectation,
2680        the request includes a request body, and the server responds
2681        with a final status code before reading the entire request body
2682        from the transport connection, then the server SHOULD NOT  close
2683        the transport connection until it has read the entire request,
2684        or until the client closes the connection. Otherwise, the client
2685        might not reliably receive the response message. However, this
2686        requirement is not be construed as preventing a server from
2687        defending itself against denial-of-service attacks, or from
2688        badly broken client implementations.
2689      </t>
2690    </list>
2691</t>
2692<t>
2693   Requirements for HTTP/1.1 proxies:
2694  <list style="symbols">
2695    <t> If a proxy receives a request that includes an Expect request-header
2696        field with the "100-continue" expectation, and the proxy
2697        either knows that the next-hop server complies with HTTP/1.1 or
2698        higher, or does not know the HTTP version of the next-hop
2699        server, it MUST forward the request, including the Expect header
2700        field.
2701    </t>
2702    <t> If the proxy knows that the version of the next-hop server is
2703        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2704        respond with a 417 (Expectation Failed) status code.
2705    </t>
2706    <t> Proxies SHOULD maintain a cache recording the HTTP version
2707        numbers received from recently-referenced next-hop servers.
2708    </t>
2709    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2710        request message was received from an HTTP/1.0 (or earlier)
2711        client and did not include an Expect request-header field with
2712        the "100-continue" expectation. This requirement overrides the
2713        general rule for forwarding of 1xx responses (see Section 8.1 of <xref target="Part2"/>).
2714    </t>
2715  </list>
2716</t>
2717</section>
2718
2719<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2720<t>
2721   If an HTTP/1.1 client sends a request which includes a request body,
2722   but which does not include an Expect request-header field with the
2723   "100-continue" expectation, and if the client is not directly
2724   connected to an HTTP/1.1 origin server, and if the client sees the
2725   connection close before receiving a status line from the server, the
2726   client SHOULD retry the request.  If the client does retry this
2727   request, it MAY use the following "binary exponential backoff"
2728   algorithm to be assured of obtaining a reliable response:
2729  <list style="numbers">
2730    <t>
2731      Initiate a new connection to the server
2732    </t>
2733    <t>
2734      Transmit the request-header fields
2735    </t>
2736    <t>
2737      Initialize a variable R to the estimated round-trip time to the
2738         server (e.g., based on the time it took to establish the
2739         connection), or to a constant value of 5 seconds if the round-trip
2740         time is not available.
2741    </t>
2742    <t>
2743       Compute T = R * (2**N), where N is the number of previous
2744         retries of this request.
2745    </t>
2746    <t>
2747       Wait either for an error response from the server, or for T
2748         seconds (whichever comes first)
2749    </t>
2750    <t>
2751       If no error response is received, after T seconds transmit the
2752         body of the request.
2753    </t>
2754    <t>
2755       If client sees that the connection is closed prematurely,
2756         repeat from step 1 until the request is accepted, an error
2757         response is received, or the user becomes impatient and
2758         terminates the retry process.
2759    </t>
2760  </list>
2761</t>
2762<t>
2763   If at any point an error status code is received, the client
2764  <list style="symbols">
2765      <t>SHOULD NOT  continue and</t>
2766
2767      <t>SHOULD close the connection if it has not completed sending the
2768        request message.</t>
2769    </list>
2770</t>
2771</section>
2772</section>
2773</section>
2774
2775
2776<section title="Miscellaneous notes that might disappear" anchor="misc">
2777<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2778<t>
2779   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2780</t>
2781</section>
2782
2783<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2784<t>
2785   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2786</t>
2787</section>
2788
2789<section title="Interception of HTTP for access control" anchor="http.intercept">
2790<t>
2791   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2792</t>
2793</section>
2794
2795<section title="Use of HTTP by other protocols" anchor="http.others">
2796<t>
2797   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2798   Extensions of HTTP like WebDAV.</cref>
2799</t>
2800
2801</section>
2802<section title="Use of HTTP by media type specification" anchor="http.media">
2803<t>
2804   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2805</t>
2806</section>
2807</section>
2808
2809<section title="Header Field Definitions" anchor="header.field.definitions">
2810<t>
2811   This section defines the syntax and semantics of HTTP/1.1 header fields
2812   related to message framing and transport protocols.
2813</t>
2814
2815<section title="Connection" anchor="header.connection">
2816  <iref primary="true" item="Connection header"/>
2817  <iref primary="true" item="Headers" subitem="Connection"/>
2818 
2819 
2820 
2821<t>
2822   The "Connection" general-header field allows the sender to specify
2823   options that are desired for that particular connection and MUST NOT
2824   be communicated by proxies over further connections.
2825</t>
2826<t>
2827   The Connection header field's value has the following grammar:
2828</t>
2829<figure><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/><artwork type="abnf2616"><![CDATA[
2830  Connection       = "Connection" ":" OWS Connection-v
2831  Connection-v     = 1#connection-token
2832  connection-token = token
2833]]></artwork></figure>
2834<t>
2835   HTTP/1.1 proxies MUST parse the Connection header field before a
2836   message is forwarded and, for each connection-token in this field,
2837   remove any header field(s) from the message with the same name as the
2838   connection-token. Connection options are signaled by the presence of
2839   a connection-token in the Connection header field, not by any
2840   corresponding additional header field(s), since the additional header
2841   field might not be sent if there are no parameters associated with that
2842   connection option.
2843</t>
2844<t>
2845   Message header fields listed in the Connection header field MUST NOT include
2846   end-to-end header fields, such as Cache-Control.
2847</t>
2848<t>
2849   HTTP/1.1 defines the "close" connection option for the sender to
2850   signal that the connection will be closed after completion of the
2851   response. For example,
2852</t>
2853<figure><artwork type="example"><![CDATA[
2854  Connection: close
2855]]></artwork></figure>
2856<t>
2857   in either the request or the response header fields indicates that
2858   the connection SHOULD NOT  be considered "persistent" (<xref target="persistent.connections"/>)
2859   after the current request/response is complete.
2860</t>
2861<t>
2862   An HTTP/1.1 client that does not support persistent connections MUST
2863   include the "close" connection option in every request message.
2864</t>
2865<t>
2866   An HTTP/1.1 server that does not support persistent connections MUST
2867   include the "close" connection option in every response message that
2868   does not have a 1xx (Informational) status code.
2869</t>
2870<t>
2871   A system receiving an HTTP/1.0 (or lower-version) message that
2872   includes a Connection header field MUST, for each connection-token in this
2873   field, remove and ignore any header field(s) from the message with
2874   the same name as the connection-token. This protects against mistaken
2875   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2876</t>
2877</section>
2878
2879<section title="Content-Length" anchor="header.content-length">
2880  <iref primary="true" item="Content-Length header"/>
2881  <iref primary="true" item="Headers" subitem="Content-Length"/>
2882 
2883 
2884<t>
2885   The "Content-Length" header field indicates the size of the
2886   message-body, in decimal number of octets, for any message other than
2887   a response to the HEAD method or a response with a status code of 304.
2888   In the case of responses to the HEAD method, it indicates the size of
2889   the payload body (not including any potential transfer-coding) that
2890   would have been sent had the request been a GET.
2891   In the case of the 304 (Not Modified) response, it indicates the size of
2892   the payload body (not including any potential transfer-coding) that
2893   would have been sent in a 200 (OK) response.
2894</t>
2895<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/><artwork type="abnf2616"><![CDATA[
2896  Content-Length   = "Content-Length" ":" OWS 1*Content-Length-v
2897  Content-Length-v = 1*DIGIT
2898]]></artwork></figure>
2899<t>
2900   An example is
2901</t>
2902<figure><artwork type="example"><![CDATA[
2903  Content-Length: 3495
2904]]></artwork></figure>
2905<t>
2906   Implementations SHOULD use this field to indicate the message-body
2907   length when no transfer-coding is being applied and the
2908   payload's body length can be determined prior to being transferred.
2909   <xref target="message.body"/> describes how recipients determine the length
2910   of a message-body.
2911</t>
2912<t>
2913   Any Content-Length greater than or equal to zero is a valid value.
2914</t>
2915<t>
2916   Note that the use of this field in HTTP is significantly different from
2917   the corresponding definition in MIME, where it is an optional field
2918   used within the "message/external-body" content-type.
2919</t>
2920</section>
2921
2922<section title="Date" anchor="header.date">
2923  <iref primary="true" item="Date header"/>
2924  <iref primary="true" item="Headers" subitem="Date"/>
2925 
2926 
2927<t>
2928   The "Date" general-header field represents the date and time at which
2929   the message was originated, having the same semantics as the Origination
2930   Date Field (orig-date) defined in Section 3.6.1 of <xref target="RFC5322"/>.
2931   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2932   it MUST be sent in rfc1123-date format.
2933</t>
2934<figure><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/><artwork type="abnf2616"><![CDATA[
2935  Date   = "Date" ":" OWS Date-v
2936  Date-v = HTTP-date
2937]]></artwork></figure>
2938<t>
2939   An example is
2940</t>
2941<figure><artwork type="example"><![CDATA[
2942  Date: Tue, 15 Nov 1994 08:12:31 GMT
2943]]></artwork></figure>
2944<t>
2945   Origin servers MUST include a Date header field in all responses,
2946   except in these cases:
2947  <list style="numbers">
2948      <t>If the response status code is 100 (Continue) or 101 (Switching
2949         Protocols), the response MAY include a Date header field, at
2950         the server's option.</t>
2951
2952      <t>If the response status code conveys a server error, e.g., 500
2953         (Internal Server Error) or 503 (Service Unavailable), and it is
2954         inconvenient or impossible to generate a valid Date.</t>
2955
2956      <t>If the server does not have a clock that can provide a
2957         reasonable approximation of the current time, its responses
2958         MUST NOT include a Date header field. In this case, the rules
2959         in <xref target="clockless.origin.server.operation"/> MUST be followed.</t>
2960  </list>
2961</t>
2962<t>
2963   A received message that does not have a Date header field MUST be
2964   assigned one by the recipient if the message will be cached by that
2965   recipient or gatewayed via a protocol which requires a Date.
2966</t>
2967<t>
2968   Clients can use the Date header field as well; in order to keep request
2969   messages small, they are advised not to include it when it doesn't convey
2970   any useful information (as it is usually the case for requests that do not
2971   contain a payload).
2972</t>
2973<t>
2974   The HTTP-date sent in a Date header field SHOULD NOT  represent a date and
2975   time subsequent to the generation of the message. It SHOULD represent
2976   the best available approximation of the date and time of message
2977   generation, unless the implementation has no means of generating a
2978   reasonably accurate date and time. In theory, the date ought to
2979   represent the moment just before the payload is generated. In
2980   practice, the date can be generated at any time during the message
2981   origination without affecting its semantic value.
2982</t>
2983
2984<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2985<t>
2986   Some origin server implementations might not have a clock available.
2987   An origin server without a clock MUST NOT assign Expires or Last-Modified
2988   values to a response, unless these values were associated
2989   with the resource by a system or user with a reliable clock. It MAY
2990   assign an Expires value that is known, at or before server
2991   configuration time, to be in the past (this allows "pre-expiration"
2992   of responses without storing separate Expires values for each
2993   resource).
2994</t>
2995</section>
2996</section>
2997
2998<section title="Host" anchor="header.host">
2999  <iref primary="true" item="Host header"/>
3000  <iref primary="true" item="Headers" subitem="Host"/>
3001 
3002 
3003<t>
3004   The "Host" request-header field specifies the Internet host and port
3005   number of the resource being requested, allowing the origin server or
3006   gateway to differentiate between internally-ambiguous URLs, such as the root
3007   "/" URL of a server for multiple host names on a single IP address.
3008</t>
3009<t>   
3010   The Host field value MUST represent the naming authority of the origin
3011   server or gateway given by the original URL obtained from the user or
3012   referring resource (generally an http URI, as described in
3013   <xref target="http.uri"/>).
3014</t>
3015<figure><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/><artwork type="abnf2616"><![CDATA[
3016  Host   = "Host" ":" OWS Host-v
3017  Host-v = uri-host [ ":" port ] ; Section 2.6.1
3018]]></artwork></figure>
3019<t>
3020   A "host" without any trailing port information implies the default
3021   port for the service requested (e.g., "80" for an HTTP URL). For
3022   example, a request on the origin server for
3023   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
3024</t>
3025<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
3026  GET /pub/WWW/ HTTP/1.1
3027  Host: www.example.org
3028  ]]></artwork></figure>
3029<t>
3030   A client MUST include a Host header field in all HTTP/1.1 request
3031   messages. If the requested URI does not include an Internet host
3032   name for the service being requested, then the Host header field MUST
3033   be given with an empty value. An HTTP/1.1 proxy MUST ensure that any
3034   request message it forwards does contain an appropriate Host header
3035   field that identifies the service being requested by the proxy. All
3036   Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
3037   status code to any HTTP/1.1 request message which lacks a Host header
3038   field.
3039</t>
3040<t>
3041   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3042   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3043   for other requirements relating to Host.
3044</t>
3045</section>
3046
3047<section title="TE" anchor="header.te">
3048  <iref primary="true" item="TE header"/>
3049  <iref primary="true" item="Headers" subitem="TE"/>
3050 
3051 
3052 
3053 
3054 
3055<t>
3056   The "TE" request-header field indicates what extension transfer-codings
3057   it is willing to accept in the response, and whether or not it is
3058   willing to accept trailer fields in a chunked transfer-coding.
3059</t>
3060<t>
3061   Its value consists of the keyword "trailers" and/or a comma-separated
3062   list of extension transfer-coding names with optional accept
3063   parameters (as described in <xref target="transfer.codings"/>).
3064</t>
3065<figure><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"/><artwork type="abnf2616"><![CDATA[
3066  TE        = "TE" ":" OWS TE-v
3067  TE-v      = #t-codings
3068  t-codings = "trailers" / ( transfer-extension [ te-params ] )
3069  te-params = OWS ";" OWS "q=" qvalue *( te-ext )
3070  te-ext    = OWS ";" OWS token [ "=" word ]
3071]]></artwork></figure>
3072<t>
3073   The presence of the keyword "trailers" indicates that the client is
3074   willing to accept trailer fields in a chunked transfer-coding, as
3075   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3076   transfer-coding values even though it does not itself represent a
3077   transfer-coding.
3078</t>
3079<t>
3080   Examples of its use are:
3081</t>
3082<figure><artwork type="example"><![CDATA[
3083  TE: deflate
3084  TE:
3085  TE: trailers, deflate;q=0.5
3086]]></artwork></figure>
3087<t>
3088   The TE header field only applies to the immediate connection.
3089   Therefore, the keyword MUST be supplied within a Connection header
3090   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3091</t>
3092<t>
3093   A server tests whether a transfer-coding is acceptable, according to
3094   a TE field, using these rules:
3095  <list style="numbers">
3096    <t>The "chunked" transfer-coding is always acceptable. If the
3097         keyword "trailers" is listed, the client indicates that it is
3098         willing to accept trailer fields in the chunked response on
3099         behalf of itself and any downstream clients. The implication is
3100         that, if given, the client is stating that either all
3101         downstream clients are willing to accept trailer fields in the
3102         forwarded response, or that it will attempt to buffer the
3103         response on behalf of downstream recipients.
3104      <vspace blankLines="1"/>
3105         Note: HTTP/1.1 does not define any means to limit the size of a
3106         chunked response such that a client can be assured of buffering
3107         the entire response.</t>
3108    <t>If the transfer-coding being tested is one of the transfer-codings
3109         listed in the TE field, then it is acceptable unless it
3110         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3111         qvalue of 0 means "not acceptable".)</t>
3112    <t>If multiple transfer-codings are acceptable, then the
3113         acceptable transfer-coding with the highest non-zero qvalue is
3114         preferred.  The "chunked" transfer-coding always has a qvalue
3115         of 1.</t>
3116  </list>
3117</t>
3118<t>
3119   If the TE field-value is empty or if no TE field is present, the only
3120   transfer-coding is "chunked". A message with no transfer-coding is
3121   always acceptable.
3122</t>
3123</section>
3124
3125<section title="Trailer" anchor="header.trailer">
3126  <iref primary="true" item="Trailer header"/>
3127  <iref primary="true" item="Headers" subitem="Trailer"/>
3128 
3129 
3130<t>
3131   The "Trailer" general-header field indicates that the given set of
3132   header fields is present in the trailer of a message encoded with
3133   chunked transfer-coding.
3134</t>
3135<figure><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/><artwork type="abnf2616"><![CDATA[
3136  Trailer   = "Trailer" ":" OWS Trailer-v
3137  Trailer-v = 1#field-name
3138]]></artwork></figure>
3139<t>
3140   An HTTP/1.1 message SHOULD include a Trailer header field in a
3141   message using chunked transfer-coding with a non-empty trailer. Doing
3142   so allows the recipient to know which header fields to expect in the
3143   trailer.
3144</t>
3145<t>
3146   If no Trailer header field is present, the trailer SHOULD NOT  include
3147   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3148   trailer fields in a "chunked" transfer-coding.
3149</t>
3150<t>
3151   Message header fields listed in the Trailer header field MUST NOT
3152   include the following header fields:
3153  <list style="symbols">
3154    <t>Transfer-Encoding</t>
3155    <t>Content-Length</t>
3156    <t>Trailer</t>
3157  </list>
3158</t>
3159</section>
3160
3161<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3162  <iref primary="true" item="Transfer-Encoding header"/>
3163  <iref primary="true" item="Headers" subitem="Transfer-Encoding"/>
3164 
3165 
3166<t>
3167   The "Transfer-Encoding" general-header field indicates what transfer-codings
3168   (if any) have been applied to the message body. It differs from
3169   Content-Encoding (Section 2.2 of <xref target="Part3"/>) in that transfer-codings are a property
3170   of the message (and therefore are removed by intermediaries), whereas
3171   content-codings are not.
3172</t>
3173<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/><artwork type="abnf2616"><![CDATA[
3174  Transfer-Encoding   = "Transfer-Encoding" ":" OWS
3175                        Transfer-Encoding-v
3176  Transfer-Encoding-v = 1#transfer-coding
3177]]></artwork></figure>
3178<t>
3179   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3180</t>
3181<figure><artwork type="example"><![CDATA[
3182  Transfer-Encoding: chunked
3183]]></artwork></figure>
3184<t>
3185   If multiple encodings have been applied to a representation, the transfer-codings
3186   MUST be listed in the order in which they were applied.
3187   Additional information about the encoding parameters MAY be provided
3188   by other header fields not defined by this specification.
3189</t>
3190<t>
3191   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3192   header field.
3193</t>
3194</section>
3195
3196<section title="Upgrade" anchor="header.upgrade">
3197  <iref primary="true" item="Upgrade header"/>
3198  <iref primary="true" item="Headers" subitem="Upgrade"/>
3199 
3200 
3201<t>
3202   The "Upgrade" general-header field allows the client to specify what
3203   additional communication protocols it would like to use, if the server
3204   chooses to switch protocols. Additionally, the server MUST use the Upgrade
3205   header field within a 101 (Switching Protocols) response to indicate which
3206   protocol(s) are being switched to.
3207</t>
3208<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/><artwork type="abnf2616"><![CDATA[
3209  Upgrade   = "Upgrade" ":" OWS Upgrade-v
3210  Upgrade-v = 1#product
3211]]></artwork></figure>
3212<t>
3213   For example,
3214</t>
3215<figure><artwork type="example"><![CDATA[
3216  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3217]]></artwork></figure>
3218<t>
3219   The Upgrade header field is intended to provide a simple mechanism
3220   for transition from HTTP/1.1 to some other, incompatible protocol. It
3221   does so by allowing the client to advertise its desire to use another
3222   protocol, such as a later version of HTTP with a higher major version
3223   number, even though the current request has been made using HTTP/1.1.
3224   This eases the difficult transition between incompatible protocols by
3225   allowing the client to initiate a request in the more commonly
3226   supported protocol while indicating to the server that it would like
3227   to use a "better" protocol if available (where "better" is determined
3228   by the server, possibly according to the nature of the method and/or
3229   resource being requested).
3230</t>
3231<t>
3232   The Upgrade header field only applies to switching application-layer
3233   protocols upon the existing transport-layer connection. Upgrade
3234   cannot be used to insist on a protocol change; its acceptance and use
3235   by the server is optional. The capabilities and nature of the
3236   application-layer communication after the protocol change is entirely
3237   dependent upon the new protocol chosen, although the first action
3238   after changing the protocol MUST be a response to the initial HTTP
3239   request containing the Upgrade header field.
3240</t>
3241<t>
3242   The Upgrade header field only applies to the immediate connection.
3243   Therefore, the upgrade keyword MUST be supplied within a Connection
3244   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3245   HTTP/1.1 message.
3246</t>
3247<t>
3248   The Upgrade header field cannot be used to indicate a switch to a
3249   protocol on a different connection. For that purpose, it is more
3250   appropriate to use a 301, 302, 303, or 305 redirection response.
3251</t>
3252<t>
3253   This specification only defines the protocol name "HTTP" for use by
3254   the family of Hypertext Transfer Protocols, as defined by the HTTP
3255   version rules of <xref target="http.version"/> and future updates to this
3256   specification. Additional tokens can be registered with IANA using the
3257   registration procedure defined below. 
3258</t>
3259
3260<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3261<t>
3262   The HTTP Upgrade Token Registry defines the name space for product
3263   tokens used to identify protocols in the Upgrade header field.
3264   Each registered token is associated with contact information and
3265   an optional set of specifications that details how the connection
3266   will be processed after it has been upgraded.
3267</t>
3268<t>
3269   Registrations are allowed on a First Come First Served basis as
3270   described in Section 4.1 of <xref target="RFC5226"/>. The
3271   specifications need not be IETF documents or be subject to IESG review.
3272   Registrations are subject to the following rules:
3273  <list style="numbers">
3274    <t>A token, once registered, stays registered forever.</t>
3275    <t>The registration MUST name a responsible party for the
3276       registration.</t>
3277    <t>The registration MUST name a point of contact.</t>
3278    <t>The registration MAY name a set of specifications associated with that
3279       token. Such specifications need not be publicly available.</t>
3280    <t>The responsible party MAY change the registration at any time.
3281       The IANA will keep a record of all such changes, and make them
3282       available upon request.</t>
3283    <t>The responsible party for the first registration of a "product"
3284       token MUST approve later registrations of a "version" token
3285       together with that "product" token before they can be registered.</t>
3286    <t>If absolutely required, the IESG MAY reassign the responsibility
3287       for a token. This will normally only be used in the case when a
3288       responsible party cannot be contacted.</t>
3289  </list>
3290</t>
3291</section>
3292
3293
3294</section>
3295
3296<section title="Via" anchor="header.via">
3297  <iref primary="true" item="Via header"/>
3298  <iref primary="true" item="Headers" subitem="Via"/>
3299 
3300 
3301 
3302 
3303 
3304 
3305 
3306<t>
3307   The "Via" general-header field MUST be used by gateways and proxies to
3308   indicate the intermediate protocols and recipients between the user
3309   agent and the server on requests, and between the origin server and
3310   the client on responses. It is analogous to the "Received" field defined in
3311   Section 3.6.7 of <xref target="RFC5322"/> and is intended to be used for tracking message forwards,
3312   avoiding request loops, and identifying the protocol capabilities of
3313   all senders along the request/response chain.
3314</t>
3315<figure><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"/><artwork type="abnf2616"><![CDATA[
3316  Via               = "Via" ":" OWS Via-v
3317  Via-v             = 1#( received-protocol RWS received-by
3318                          [ RWS comment ] )
3319  received-protocol = [ protocol-name "/" ] protocol-version
3320  protocol-name     = token
3321  protocol-version  = token
3322  received-by       = ( uri-host [ ":" port ] ) / pseudonym
3323  pseudonym         = token
3324]]></artwork></figure>
3325<t>
3326   The received-protocol indicates the protocol version of the message
3327   received by the server or client along each segment of the
3328   request/response chain. The received-protocol version is appended to
3329   the Via field value when the message is forwarded so that information
3330   about the protocol capabilities of upstream applications remains
3331   visible to all recipients.
3332</t>
3333<t>
3334   The protocol-name is optional if and only if it would be "HTTP". The
3335   received-by field is normally the host and optional port number of a
3336   recipient server or client that subsequently forwarded the message.
3337   However, if the real host is considered to be sensitive information,
3338   it MAY be replaced by a pseudonym. If the port is not given, it MAY
3339   be assumed to be the default port of the received-protocol.
3340</t>
3341<t>
3342   Multiple Via field values represent each proxy or gateway that has
3343   forwarded the message. Each recipient MUST append its information
3344   such that the end result is ordered according to the sequence of
3345   forwarding applications.
3346</t>
3347<t>
3348   Comments MAY be used in the Via header field to identify the software
3349   of the recipient proxy or gateway, analogous to the User-Agent and
3350   Server header fields. However, all comments in the Via field are
3351   optional and MAY be removed by any recipient prior to forwarding the
3352   message.
3353</t>
3354<t>
3355   For example, a request message could be sent from an HTTP/1.0 user
3356   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3357   forward the request to a public proxy at p.example.net, which completes
3358   the request by forwarding it to the origin server at www.example.com.
3359   The request received by www.example.com would then have the following
3360   Via header field:
3361</t>
3362<figure><artwork type="example"><![CDATA[
3363  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3364]]></artwork></figure>
3365<t>
3366   Proxies and gateways used as a portal through a network firewall
3367   SHOULD NOT, by default, forward the names and ports of hosts within
3368   the firewall region. This information SHOULD only be propagated if
3369   explicitly enabled. If not enabled, the received-by host of any host
3370   behind the firewall SHOULD be replaced by an appropriate pseudonym
3371   for that host.
3372</t>
3373<t>
3374   For organizations that have strong privacy requirements for hiding
3375   internal structures, a proxy MAY combine an ordered subsequence of
3376   Via header field entries with identical received-protocol values into
3377   a single such entry. For example,
3378</t>
3379<figure><artwork type="example"><![CDATA[
3380  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3381]]></artwork></figure>
3382<t>
3383  could be collapsed to
3384</t>
3385<figure><artwork type="example"><![CDATA[
3386  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3387]]></artwork></figure>
3388<t>
3389   Applications SHOULD NOT  combine multiple entries unless they are all
3390   under the same organizational control and the hosts have already been
3391   replaced by pseudonyms. Applications MUST NOT combine entries which
3392   have different received-protocol values.
3393</t>
3394</section>
3395
3396</section>
3397
3398<section title="IANA Considerations" anchor="IANA.considerations">
3399
3400<section title="Header Field Registration" anchor="header.field.registration">
3401<t>
3402   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3403   with the permanent registrations below (see <xref target="RFC3864"/>):
3404</t>
3405
3406<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3407<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3408   <ttcol>Header Field Name</ttcol>
3409   <ttcol>Protocol</ttcol>
3410   <ttcol>Status</ttcol>
3411   <ttcol>Reference</ttcol>
3412
3413   <c>Connection</c>
3414   <c>http</c>
3415   <c>standard</c>
3416   <c>
3417      <xref target="header.connection"/>
3418   </c>
3419   <c>Content-Length</c>
3420   <c>http</c>
3421   <c>standard</c>
3422   <c>
3423      <xref target="header.content-length"/>
3424   </c>
3425   <c>Date</c>
3426   <c>http</c>
3427   <c>standard</c>
3428   <c>
3429      <xref target="header.date"/>
3430   </c>
3431   <c>Host</c>
3432   <c>http</c>
3433   <c>standard</c>
3434   <c>
3435      <xref target="header.host"/>
3436   </c>
3437   <c>TE</c>
3438   <c>http</c>
3439   <c>standard</c>
3440   <c>
3441      <xref target="header.te"/>
3442   </c>
3443   <c>Trailer</c>
3444   <c>http</c>
3445   <c>standard</c>
3446   <c>
3447      <xref target="header.trailer"/>
3448   </c>
3449   <c>Transfer-Encoding</c>
3450   <c>http</c>
3451   <c>standard</c>
3452   <c>
3453      <xref target="header.transfer-encoding"/>
3454   </c>
3455   <c>Upgrade</c>
3456   <c>http</c>
3457   <c>standard</c>
3458   <c>
3459      <xref target="header.upgrade"/>
3460   </c>
3461   <c>Via</c>
3462   <c>http</c>
3463   <c>standard</c>
3464   <c>
3465      <xref target="header.via"/>
3466   </c>
3467</texttable>
3468<!--(END)-->
3469
3470<t>
3471   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3472</t>
3473</section>
3474
3475<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3476<t>
3477   The entries for the "http" and "https" URI Schemes in the registry located at
3478   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3479   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3480   and <xref target="https.uri" format="counter"/> of this document
3481   (see <xref target="RFC4395"/>).
3482</t>
3483</section>
3484
3485<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3486<t>
3487   This document serves as the specification for the Internet media types
3488   "message/http" and "application/http". The following is to be registered with
3489   IANA (see <xref target="RFC4288"/>).
3490</t>
3491<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3492<iref item="Media Type" subitem="message/http" primary="true"/>
3493<iref item="message/http Media Type" primary="true"/>
3494<t>
3495   The message/http type can be used to enclose a single HTTP request or
3496   response message, provided that it obeys the MIME restrictions for all
3497   "message" types regarding line length and encodings.
3498</t>
3499<t>
3500  <list style="hanging">
3501    <t hangText="Type name:">
3502      message
3503    </t>
3504    <t hangText="Subtype name:">
3505      http
3506    </t>
3507    <t hangText="Required parameters:">
3508      none
3509    </t>
3510    <t hangText="Optional parameters:">
3511      version, msgtype
3512      <list style="hanging">
3513        <t hangText="version:">
3514          The HTTP-Version number of the enclosed message
3515          (e.g., "1.1"). If not present, the version can be
3516          determined from the first line of the body.
3517        </t>
3518        <t hangText="msgtype:">
3519          The message type -- "request" or "response". If not
3520          present, the type can be determined from the first
3521          line of the body.
3522        </t>
3523      </list>
3524    </t>
3525    <t hangText="Encoding considerations:">
3526      only "7bit", "8bit", or "binary" are permitted
3527    </t>
3528    <t hangText="Security considerations:">
3529      none
3530    </t>
3531    <t hangText="Interoperability considerations:">
3532      none
3533    </t>
3534    <t hangText="Published specification:">
3535      This specification (see <xref target="internet.media.type.message.http"/>).
3536    </t>
3537    <t hangText="Applications that use this media type:">
3538    </t>
3539    <t hangText="Additional information:">
3540      <list style="hanging">
3541        <t hangText="Magic number(s):">none</t>
3542        <t hangText="File extension(s):">none</t>
3543        <t hangText="Macintosh file type code(s):">none</t>
3544      </list>
3545    </t>
3546    <t hangText="Person and email address to contact for further information:">
3547      See Authors Section.
3548    </t>
3549    <t hangText="Intended usage:">
3550      COMMON
3551    </t>
3552    <t hangText="Restrictions on usage:">
3553      none
3554    </t>
3555    <t hangText="Author/Change controller:">
3556      IESG
3557    </t>
3558  </list>
3559</t>
3560</section>
3561<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3562<iref item="Media Type" subitem="application/http" primary="true"/>
3563<iref item="application/http Media Type" primary="true"/>
3564<t>
3565   The application/http type can be used to enclose a pipeline of one or more
3566   HTTP request or response messages (not intermixed).
3567</t>
3568<t>
3569  <list style="hanging">
3570    <t hangText="Type name:">
3571      application
3572    </t>
3573    <t hangText="Subtype name:">
3574      http
3575    </t>
3576    <t hangText="Required parameters:">
3577      none
3578    </t>
3579    <t hangText="Optional parameters:">
3580      version, msgtype
3581      <list style="hanging">
3582        <t hangText="version:">
3583          The HTTP-Version number of the enclosed messages
3584          (e.g., "1.1"). If not present, the version can be
3585          determined from the first line of the body.
3586        </t>
3587        <t hangText="msgtype:">
3588          The message type -- "request" or "response". If not
3589          present, the type can be determined from the first
3590          line of the body.
3591        </t>
3592      </list>
3593    </t>
3594    <t hangText="Encoding considerations:">
3595      HTTP messages enclosed by this type
3596      are in "binary" format; use of an appropriate
3597      Content-Transfer-Encoding is required when
3598      transmitted via E-mail.
3599    </t>
3600    <t hangText="Security considerations:">
3601      none
3602    </t>
3603    <t hangText="Interoperability considerations:">
3604      none
3605    </t>
3606    <t hangText="Published specification:">
3607      This specification (see <xref target="internet.media.type.application.http"/>).
3608    </t>
3609    <t hangText="Applications that use this media type:">
3610    </t>
3611    <t hangText="Additional information:">
3612      <list style="hanging">
3613        <t hangText="Magic number(s):">none</t>
3614        <t hangText="File extension(s):">none</t>
3615        <t hangText="Macintosh file type code(s):">none</t>
3616      </list>
3617    </t>
3618    <t hangText="Person and email address to contact for further information:">
3619      See Authors Section.
3620    </t>
3621    <t hangText="Intended usage:">
3622      COMMON
3623    </t>
3624    <t hangText="Restrictions on usage:">
3625      none
3626    </t>
3627    <t hangText="Author/Change controller:">
3628      IESG
3629    </t>
3630  </list>
3631</t>
3632</section>
3633</section>
3634
3635<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3636<t>
3637   The registration procedure for HTTP Transfer Codings is now defined by
3638   <xref target="transfer.coding.registry"/> of this document.
3639</t>
3640<t>
3641   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3642   shall be updated with the registrations below:
3643</t>
3644<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3645   <ttcol>Name</ttcol>
3646   <ttcol>Description</ttcol>
3647   <ttcol>Reference</ttcol>
3648   <c>chunked</c>
3649   <c>Transfer in a series of chunks</c>
3650   <c>
3651      <xref target="chunked.encoding"/>
3652   </c>
3653   <c>compress</c>
3654   <c>UNIX "compress" program method</c>
3655   <c>
3656      <xref target="compress.coding"/>
3657   </c>
3658   <c>deflate</c>
3659   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3660   the "zlib" data format (<xref target="RFC1950"/>)
3661   </c>
3662   <c>
3663      <xref target="deflate.coding"/>
3664   </c>
3665   <c>gzip</c>
3666   <c>Same as GNU zip <xref target="RFC1952"/></c>
3667   <c>
3668      <xref target="gzip.coding"/>
3669   </c>
3670</texttable>
3671</section>
3672
3673<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3674<t>
3675   The registration procedure for HTTP Upgrade Tokens -- previously defined
3676   in Section 7.2 of <xref target="RFC2817"/> -- is now defined
3677   by <xref target="upgrade.token.registry"/> of this document.
3678</t>
3679<t>
3680   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3681   shall be updated with the registration below:
3682</t>
3683<texttable align="left" suppress-title="true">
3684   <ttcol>Value</ttcol>
3685   <ttcol>Description</ttcol>
3686   <ttcol>Reference</ttcol>
3687
3688   <c>HTTP</c>
3689   <c>Hypertext Transfer Protocol</c> 
3690   <c><xref target="http.version"/> of this specification</c>
3691<!-- IANA should add this without our instructions; emailed on June 05, 2009
3692   <c>TLS/1.0</c>
3693   <c>Transport Layer Security</c>
3694   <c><xref target="RFC2817"/></c> -->
3695
3696</texttable>
3697</section>
3698
3699</section>
3700
3701<section title="Security Considerations" anchor="security.considerations">
3702<t>
3703   This section is meant to inform application developers, information
3704   providers, and users of the security limitations in HTTP/1.1 as
3705   described by this document. The discussion does not include
3706   definitive solutions to the problems revealed, though it does make
3707   some suggestions for reducing security risks.
3708</t>
3709
3710<section title="Personal Information" anchor="personal.information">
3711<t>
3712   HTTP clients are often privy to large amounts of personal information
3713   (e.g., the user's name, location, mail address, passwords, encryption
3714   keys, etc.), and SHOULD be very careful to prevent unintentional
3715   leakage of this information.
3716   We very strongly recommend that a convenient interface be provided
3717   for the user to control dissemination of such information, and that
3718   designers and implementors be particularly careful in this area.
3719   History shows that errors in this area often create serious security
3720   and/or privacy problems and generate highly adverse publicity for the
3721   implementor's company.
3722</t>
3723</section>
3724
3725<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3726<t>
3727   A server is in the position to save personal data about a user's
3728   requests which might identify their reading patterns or subjects of
3729   interest. This information is clearly confidential in nature and its
3730   handling can be constrained by law in certain countries. People using
3731   HTTP to provide data are responsible for ensuring that
3732   such material is not distributed without the permission of any
3733   individuals that are identifiable by the published results.
3734</t>
3735</section>
3736
3737<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3738<t>
3739   Implementations of HTTP origin servers SHOULD be careful to restrict
3740   the documents returned by HTTP requests to be only those that were
3741   intended by the server administrators. If an HTTP server translates
3742   HTTP URIs directly into file system calls, the server MUST take
3743   special care not to serve files that were not intended to be
3744   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3745   other operating systems use ".." as a path component to indicate a
3746   directory level above the current one. On such a system, an HTTP
3747   server MUST disallow any such construct in the request-target if it
3748   would otherwise allow access to a resource outside those intended to
3749   be accessible via the HTTP server. Similarly, files intended for
3750   reference only internally to the server (such as access control
3751   files, configuration files, and script code) MUST be protected from
3752   inappropriate retrieval, since they might contain sensitive
3753   information. Experience has shown that minor bugs in such HTTP server
3754   implementations have turned into security risks.
3755</t>
3756</section>
3757
3758<section title="DNS Spoofing" anchor="dns.spoofing">
3759<t>
3760   Clients using HTTP rely heavily on the Domain Name Service, and are
3761   thus generally prone to security attacks based on the deliberate
3762   mis-association of IP addresses and DNS names. Clients need to be
3763   cautious in assuming the continuing validity of an IP number/DNS name
3764   association.
3765</t>
3766<t>
3767   In particular, HTTP clients SHOULD rely on their name resolver for
3768   confirmation of an IP number/DNS name association, rather than
3769   caching the result of previous host name lookups. Many platforms
3770   already can cache host name lookups locally when appropriate, and
3771   they SHOULD be configured to do so. It is proper for these lookups to
3772   be cached, however, only when the TTL (Time To Live) information
3773   reported by the name server makes it likely that the cached
3774   information will remain useful.
3775</t>
3776<t>
3777   If HTTP clients cache the results of host name lookups in order to
3778   achieve a performance improvement, they MUST observe the TTL
3779   information reported by DNS.
3780</t>
3781<t>
3782   If HTTP clients do not observe this rule, they could be spoofed when
3783   a previously-accessed server's IP address changes. As network
3784   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3785   possibility of this form of attack will grow. Observing this
3786   requirement thus reduces this potential security vulnerability.
3787</t>
3788<t>
3789   This requirement also improves the load-balancing behavior of clients
3790   for replicated servers using the same DNS name and reduces the
3791   likelihood of a user's experiencing failure in accessing sites which
3792   use that strategy.
3793</t>
3794</section>
3795
3796<section title="Proxies and Caching" anchor="attack.proxies">
3797<t>
3798   By their very nature, HTTP proxies are men-in-the-middle, and
3799   represent an opportunity for man-in-the-middle attacks. Compromise of
3800   the systems on which the proxies run can result in serious security
3801   and privacy problems. Proxies have access to security-related
3802   information, personal information about individual users and
3803   organizations, and proprietary information belonging to users and
3804   content providers. A compromised proxy, or a proxy implemented or
3805   configured without regard to security and privacy considerations,
3806   might be used in the commission of a wide range of potential attacks.
3807</t>
3808<t>
3809   Proxy operators need to protect the systems on which proxies run as
3810   they would protect any system that contains or transports sensitive
3811   information. In particular, log information gathered at proxies often
3812   contains highly sensitive personal information, and/or information
3813   about organizations. Log information needs to be carefully guarded, and
3814   appropriate guidelines for use need to be developed and followed.
3815   (<xref target="abuse.of.server.log.information"/>).
3816</t>
3817<t>
3818   Proxy implementors need to consider the privacy and security
3819   implications of their design and coding decisions, and of the
3820   configuration options they provide to proxy operators (especially the
3821   default configuration).
3822</t>
3823<t>
3824   Users of a proxy need to be aware that proxies are no trustworthier than
3825   the people who run them; HTTP itself cannot solve this problem.
3826</t>
3827<t>
3828   The judicious use of cryptography, when appropriate, might suffice to
3829   protect against a broad range of security and privacy attacks. Such
3830   cryptography is beyond the scope of the HTTP/1.1 specification.
3831</t>
3832</section>
3833
3834<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3835<t>
3836   They exist. They are hard to defend against. Research continues.
3837   Beware.
3838</t>
3839</section>
3840</section>
3841
3842<section title="Acknowledgments" anchor="ack">
3843<t>
3844   HTTP has evolved considerably over the years. It has
3845   benefited from a large and active developer community--the many
3846   people who have participated on the www-talk mailing list--and it is
3847   that community which has been most responsible for the success of
3848   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3849   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3850   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3851   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3852   VanHeyningen deserve special recognition for their efforts in
3853   defining early aspects of the protocol.
3854</t>
3855<t>
3856   This document has benefited greatly from the comments of all those
3857   participating in the HTTP-WG. In addition to those already mentioned,
3858   the following individuals have contributed to this specification:
3859</t>
3860<t>
3861   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3862   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3863   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3864   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3865   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3866   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3867   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3868   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3869   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3870   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3871   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3872   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3873</t>
3874<t>
3875   Thanks to the "cave men" of Palo Alto. You know who you are.
3876</t>
3877<t>
3878   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3879   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3880   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3881   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3882   Larry Masinter for their help. And thanks go particularly to Jeff
3883   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3884</t>
3885<t>
3886   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3887   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3888   discovery of many of the problems that this document attempts to
3889   rectify.
3890</t>
3891<t>
3892   This specification makes heavy use of the augmented BNF and generic
3893   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3894   reuses many of the definitions provided by Nathaniel Borenstein and
3895   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3896   specification will help reduce past confusion over the relationship
3897   between HTTP and Internet mail message formats.
3898</t>
3899<!--
3900
3901Acknowledgements TODO list
3902
3903- Jeff Hodges ("effective request URI")
3904
3905-->
3906</section>
3907
3908</middle>
3909<back>
3910
3911<references title="Normative References">
3912
3913<reference anchor="ISO-8859-1">
3914  <front>
3915    <title>
3916     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3917    </title>
3918    <author>
3919      <organization>International Organization for Standardization</organization>
3920    </author>
3921    <date year="1998"/>
3922  </front>
3923  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3924</reference>
3925
3926<reference anchor="Part2">
3927  <front>
3928    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3929    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3930      <organization abbrev="Day Software">Day Software</organization>
3931      <address><email>fielding@gbiv.com</email></address>
3932    </author>
3933    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3934      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3935      <address><email>jg@freedesktop.org</email></address>
3936    </author>
3937    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3938      <organization abbrev="HP">Hewlett-Packard Company</organization>
3939      <address><email>JeffMogul@acm.org</email></address>
3940    </author>
3941    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3942      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3943      <address><email>henrikn@microsoft.com</email></address>
3944    </author>
3945    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3946      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3947      <address><email>LMM@acm.org</email></address>
3948    </author>
3949    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3950      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3951      <address><email>paulle@microsoft.com</email></address>
3952    </author>
3953    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3954      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3955      <address><email>timbl@w3.org</email></address>
3956    </author>
3957    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3958      <organization abbrev="W3C">World Wide Web Consortium</organization>
3959      <address><email>ylafon@w3.org</email></address>
3960    </author>
3961    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3962      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3963      <address><email>julian.reschke@greenbytes.de</email></address>
3964    </author>
3965    <date month="October" year="2010"/>
3966  </front>
3967  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-12"/>
3968 
3969</reference>
3970
3971<reference anchor="Part3">
3972  <front>
3973    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3974    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3975      <organization abbrev="Day Software">Day Software</organization>
3976      <address><email>fielding@gbiv.com</email></address>
3977    </author>
3978    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3979      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3980      <address><email>jg@freedesktop.org</email></address>
3981    </author>
3982    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3983      <organization abbrev="HP">Hewlett-Packard Company</organization>
3984      <address><email>JeffMogul@acm.org</email></address>
3985    </author>
3986    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3987      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3988      <address><email>henrikn@microsoft.com</email></address>
3989    </author>
3990    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3991      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3992      <address><email>LMM@acm.org</email></address>
3993    </author>
3994    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3995      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3996      <address><email>paulle@microsoft.com</email></address>
3997    </author>
3998    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3999      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4000      <address><email>timbl@w3.org</email></address>
4001    </author>
4002    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4003      <organization abbrev="W3C">World Wide Web Consortium</organization>
4004      <address><email>ylafon@w3.org</email></address>
4005    </author>
4006    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4007      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4008      <address><email>julian.reschke@greenbytes.de</email></address>
4009    </author>
4010    <date month="October" year="2010"/>
4011  </front>
4012  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-12"/>
4013 
4014</reference>
4015
4016<reference anchor="Part6">
4017  <front>
4018    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4019    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4020      <organization abbrev="Day Software">Day Software</organization>
4021      <address><email>fielding@gbiv.com</email></address>
4022    </author>
4023    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4024      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4025      <address><email>jg@freedesktop.org</email></address>
4026    </author>
4027    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4028      <organization abbrev="HP">Hewlett-Packard Company</organization>
4029      <address><email>JeffMogul@acm.org</email></address>
4030    </author>
4031    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4032      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4033      <address><email>henrikn@microsoft.com</email></address>
4034    </author>
4035    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4036      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4037      <address><email>LMM@acm.org</email></address>
4038    </author>
4039    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4040      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4041      <address><email>paulle@microsoft.com</email></address>
4042    </author>
4043    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4044      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4045      <address><email>timbl@w3.org</email></address>
4046    </author>
4047    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4048      <organization abbrev="W3C">World Wide Web Consortium</organization>
4049      <address><email>ylafon@w3.org</email></address>
4050    </author>
4051    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4052      <address><email>mnot@mnot.net</email></address>
4053    </author>
4054    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4055      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4056      <address><email>julian.reschke@greenbytes.de</email></address>
4057    </author>
4058    <date month="October" year="2010"/>
4059  </front>
4060  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-12"/>
4061 
4062</reference>
4063
4064<reference anchor="RFC5234">
4065  <front>
4066    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4067    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4068      <organization>Brandenburg InternetWorking</organization>
4069      <address>
4070        <email>dcrocker@bbiw.net</email>
4071      </address> 
4072    </author>
4073    <author initials="P." surname="Overell" fullname="Paul Overell">
4074      <organization>THUS plc.</organization>
4075      <address>
4076        <email>paul.overell@thus.net</email>
4077      </address>
4078    </author>
4079    <date month="January" year="2008"/>
4080  </front>
4081  <seriesInfo name="STD" value="68"/>
4082  <seriesInfo name="RFC" value="5234"/>
4083</reference>
4084
4085<reference anchor="RFC2119">
4086  <front>
4087    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4088    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4089      <organization>Harvard University</organization>
4090      <address><email>sob@harvard.edu</email></address>
4091    </author>
4092    <date month="March" year="1997"/>
4093  </front>
4094  <seriesInfo name="BCP" value="14"/>
4095  <seriesInfo name="RFC" value="2119"/>
4096</reference>
4097
4098<reference anchor="RFC3986">
4099 <front>
4100  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
4101  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4102    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4103    <address>
4104       <email>timbl@w3.org</email>
4105       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4106    </address>
4107  </author>
4108  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4109    <organization abbrev="Day Software">Day Software</organization>
4110    <address>
4111      <email>fielding@gbiv.com</email>
4112      <uri>http://roy.gbiv.com/</uri>
4113    </address>
4114  </author>
4115  <author initials="L." surname="Masinter" fullname="Larry Masinter">
4116    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4117    <address>
4118      <email>LMM@acm.org</email>
4119      <uri>http://larry.masinter.net/</uri>
4120    </address>
4121  </author>
4122  <date month="January" year="2005"/>
4123 </front>
4124 <seriesInfo name="STD" value="66"/>
4125 <seriesInfo name="RFC" value="3986"/>
4126</reference>
4127
4128<reference anchor="USASCII">
4129  <front>
4130    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4131    <author>
4132      <organization>American National Standards Institute</organization>
4133    </author>
4134    <date year="1986"/>
4135  </front>
4136  <seriesInfo name="ANSI" value="X3.4"/>
4137</reference>
4138
4139<reference anchor="RFC1950">
4140  <front>
4141    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4142    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4143      <organization>Aladdin Enterprises</organization>
4144      <address><email>ghost@aladdin.com</email></address>
4145    </author>
4146    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4147    <date month="May" year="1996"/>
4148  </front>
4149  <seriesInfo name="RFC" value="1950"/>
4150  <annotation>
4151    RFC 1950 is an Informational RFC, thus it might be less stable than
4152    this specification. On the other hand, this downward reference was
4153    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4154    therefore it is unlikely to cause problems in practice. See also
4155    <xref target="BCP97"/>.
4156  </annotation>
4157</reference>
4158
4159<reference anchor="RFC1951">
4160  <front>
4161    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4162    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4163      <organization>Aladdin Enterprises</organization>
4164      <address><email>ghost@aladdin.com</email></address>
4165    </author>
4166    <date month="May" year="1996"/>
4167  </front>
4168  <seriesInfo name="RFC" value="1951"/>
4169  <annotation>
4170    RFC 1951 is an Informational RFC, thus it might be less stable than
4171    this specification. On the other hand, this downward reference was
4172    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4173    therefore it is unlikely to cause problems in practice. See also
4174    <xref target="BCP97"/>.
4175  </annotation>
4176</reference>
4177
4178<reference anchor="RFC1952">
4179  <front>
4180    <title>GZIP file format specification version 4.3</title>
4181    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4182      <organization>Aladdin Enterprises</organization>
4183      <address><email>ghost@aladdin.com</email></address>
4184    </author>
4185    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4186      <address><email>gzip@prep.ai.mit.edu</email></address>
4187    </author>
4188    <author initials="M." surname="Adler" fullname="Mark Adler">
4189      <address><email>madler@alumni.caltech.edu</email></address>
4190    </author>
4191    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4192      <address><email>ghost@aladdin.com</email></address>
4193    </author>
4194    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4195      <address><email>randeg@alumni.rpi.edu</email></address>
4196    </author>
4197    <date month="May" year="1996"/>
4198  </front>
4199  <seriesInfo name="RFC" value="1952"/>
4200  <annotation>
4201    RFC 1952 is an Informational RFC, thus it might be less stable than
4202    this specification. On the other hand, this downward reference was
4203    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4204    therefore it is unlikely to cause problems in practice. See also
4205    <xref target="BCP97"/>.
4206  </annotation>
4207</reference>
4208
4209</references>
4210
4211<references title="Informative References">
4212
4213<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4214  <front>
4215    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4216    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4217    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4218    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4219    <author initials="H." surname="Lie" fullname="H. Lie"/>
4220    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4221    <date year="1997" month="September"/>
4222  </front>
4223  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4224</reference>
4225
4226<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4227  <front>
4228    <title>Improving HTTP Latency</title>
4229    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4230    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4231    <date year="1995" month="December"/>
4232  </front>
4233  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4234</reference>
4235
4236<reference anchor="RFC1123">
4237  <front>
4238    <title>Requirements for Internet Hosts - Application and Support</title>
4239    <author initials="R." surname="Braden" fullname="Robert Braden">
4240      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4241      <address><email>Braden@ISI.EDU</email></address>
4242    </author>
4243    <date month="October" year="1989"/>
4244  </front>
4245  <seriesInfo name="STD" value="3"/>
4246  <seriesInfo name="RFC" value="1123"/>
4247</reference>
4248
4249<reference anchor="RFC1900">
4250  <front>
4251    <title>Renumbering Needs Work</title>
4252    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4253      <organization>CERN, Computing and Networks Division</organization>
4254      <address><email>brian@dxcoms.cern.ch</email></address>
4255    </author>
4256    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4257      <organization>cisco Systems</organization>
4258      <address><email>yakov@cisco.com</email></address>
4259    </author>
4260    <date month="February" year="1996"/>
4261  </front>
4262  <seriesInfo name="RFC" value="1900"/>
4263</reference>
4264
4265<reference anchor="RFC1945">
4266  <front>
4267    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4268    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4269      <organization>MIT, Laboratory for Computer Science</organization>
4270      <address><email>timbl@w3.org</email></address>
4271    </author>
4272    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4273      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4274      <address><email>fielding@ics.uci.edu</email></address>
4275    </author>
4276    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4277      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4278      <address><email>frystyk@w3.org</email></address>
4279    </author>
4280    <date month="May" year="1996"/>
4281  </front>
4282  <seriesInfo name="RFC" value="1945"/>
4283</reference>
4284
4285<reference anchor="RFC2045">
4286  <front>
4287    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4288    <author initials="N." surname="Freed" fullname="Ned Freed">
4289      <organization>Innosoft International, Inc.</organization>
4290      <address><email>ned@innosoft.com</email></address>
4291    </author>
4292    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4293      <organization>First Virtual Holdings</organization>
4294      <address><email>nsb@nsb.fv.com</email></address>
4295    </author>
4296    <date month="November" year="1996"/>
4297  </front>
4298  <seriesInfo name="RFC" value="2045"/>
4299</reference>
4300
4301<reference anchor="RFC2047">
4302  <front>
4303    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4304    <author initials="K." surname="Moore" fullname="Keith Moore">
4305      <organization>University of Tennessee</organization>
4306      <address><email>moore@cs.utk.edu</email></address>
4307    </author>
4308    <date month="November" year="1996"/>
4309  </front>
4310  <seriesInfo name="RFC" value="2047"/>
4311</reference>
4312
4313<reference anchor="RFC2068">
4314  <front>
4315    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4316    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4317      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4318      <address><email>fielding@ics.uci.edu</email></address>
4319    </author>
4320    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4321      <organization>MIT Laboratory for Computer Science</organization>
4322      <address><email>jg@w3.org</email></address>
4323    </author>
4324    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4325      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4326      <address><email>mogul@wrl.dec.com</email></address>
4327    </author>
4328    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4329      <organization>MIT Laboratory for Computer Science</organization>
4330      <address><email>frystyk@w3.org</email></address>
4331    </author>
4332    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4333      <organization>MIT Laboratory for Computer Science</organization>
4334      <address><email>timbl@w3.org</email></address>
4335    </author>
4336    <date month="January" year="1997"/>
4337  </front>
4338  <seriesInfo name="RFC" value="2068"/>
4339</reference>
4340
4341<reference anchor="RFC2109">
4342  <front>
4343    <title>HTTP State Management Mechanism</title>
4344    <author initials="D.M." surname="Kristol" fullname="David M. Kristol">
4345      <organization>Bell Laboratories, Lucent Technologies</organization>
4346      <address><email>dmk@bell-labs.com</email></address>
4347    </author>
4348    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4349      <organization>Netscape Communications Corp.</organization>
4350      <address><email>montulli@netscape.com</email></address>
4351    </author>
4352    <date year="1997" month="February"/>
4353  </front>
4354  <seriesInfo name="RFC" value="2109"/>
4355</reference>
4356
4357<reference anchor="RFC2145">
4358  <front>
4359    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4360    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4361      <organization>Western Research Laboratory</organization>
4362      <address><email>mogul@wrl.dec.com</email></address>
4363    </author>
4364    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4365      <organization>Department of Information and Computer Science</organization>
4366      <address><email>fielding@ics.uci.edu</email></address>
4367    </author>
4368    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4369      <organization>MIT Laboratory for Computer Science</organization>
4370      <address><email>jg@w3.org</email></address>
4371    </author>
4372    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4373      <organization>W3 Consortium</organization>
4374      <address><email>frystyk@w3.org</email></address>
4375    </author>
4376    <date month="May" year="1997"/>
4377  </front>
4378  <seriesInfo name="RFC" value="2145"/>
4379</reference>
4380
4381<reference anchor="RFC2616">
4382  <front>
4383    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4384    <author initials="R." surname="Fielding" fullname="R. Fielding">
4385      <organization>University of California, Irvine</organization>
4386      <address><email>fielding@ics.uci.edu</email></address>
4387    </author>
4388    <author initials="J." surname="Gettys" fullname="J. Gettys">
4389      <organization>W3C</organization>
4390      <address><email>jg@w3.org</email></address>
4391    </author>
4392    <author initials="J." surname="Mogul" fullname="J. Mogul">
4393      <organization>Compaq Computer Corporation</organization>
4394      <address><email>mogul@wrl.dec.com</email></address>
4395    </author>
4396    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4397      <organization>MIT Laboratory for Computer Science</organization>
4398      <address><email>frystyk@w3.org</email></address>
4399    </author>
4400    <author initials="L." surname="Masinter" fullname="L. Masinter">
4401      <organization>Xerox Corporation</organization>
4402      <address><email>masinter@parc.xerox.com</email></address>
4403    </author>
4404    <author initials="P." surname="Leach" fullname="P. Leach">
4405      <organization>Microsoft Corporation</organization>
4406      <address><email>paulle@microsoft.com</email></address>
4407    </author>
4408    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4409      <organization>W3C</organization>
4410      <address><email>timbl@w3.org</email></address>
4411    </author>
4412    <date month="June" year="1999"/>
4413  </front>
4414  <seriesInfo name="RFC" value="2616"/>
4415</reference>
4416
4417<reference anchor="RFC2817">
4418  <front>
4419    <title>Upgrading to TLS Within HTTP/1.1</title>
4420    <author initials="R." surname="Khare" fullname="R. Khare">
4421      <organization>4K Associates / UC Irvine</organization>
4422      <address><email>rohit@4K-associates.com</email></address>
4423    </author>
4424    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
4425      <organization>Agranat Systems, Inc.</organization>
4426      <address><email>lawrence@agranat.com</email></address>
4427    </author>
4428    <date year="2000" month="May"/>
4429  </front>
4430  <seriesInfo name="RFC" value="2817"/>
4431</reference>
4432
4433<reference anchor="RFC2818">
4434  <front>
4435    <title>HTTP Over TLS</title>
4436    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
4437      <organization>RTFM, Inc.</organization>
4438      <address><email>ekr@rtfm.com</email></address>
4439    </author>
4440    <date year="2000" month="May"/>
4441  </front>
4442  <seriesInfo name="RFC" value="2818"/>
4443</reference>
4444
4445<reference anchor="RFC2965">
4446  <front>
4447    <title>HTTP State Management Mechanism</title>
4448    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
4449      <organization>Bell Laboratories, Lucent Technologies</organization>
4450      <address><email>dmk@bell-labs.com</email></address>
4451    </author>
4452    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4453      <organization>Epinions.com, Inc.</organization>
4454      <address><email>lou@montulli.org</email></address>
4455    </author>
4456    <date year="2000" month="October"/>
4457  </front>
4458  <seriesInfo name="RFC" value="2965"/>
4459</reference>
4460
4461<reference anchor="RFC3864">
4462  <front>
4463    <title>Registration Procedures for Message Header Fields</title>
4464    <author initials="G." surname="Klyne" fullname="G. Klyne">
4465      <organization>Nine by Nine</organization>
4466      <address><email>GK-IETF@ninebynine.org</email></address>
4467    </author>
4468    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
4469      <organization>BEA Systems</organization>
4470      <address><email>mnot@pobox.com</email></address>
4471    </author>
4472    <author initials="J." surname="Mogul" fullname="J. Mogul">
4473      <organization>HP Labs</organization>
4474      <address><email>JeffMogul@acm.org</email></address>
4475    </author>
4476    <date year="2004" month="September"/>
4477  </front>
4478  <seriesInfo name="BCP" value="90"/>
4479  <seriesInfo name="RFC" value="3864"/>
4480</reference>
4481
4482<reference anchor="RFC4288">
4483  <front>
4484    <title>Media Type Specifications and Registration Procedures</title>
4485    <author initials="N." surname="Freed" fullname="N. Freed">
4486      <organization>Sun Microsystems</organization>
4487      <address>
4488        <email>ned.freed@mrochek.com</email>
4489      </address>
4490    </author>
4491    <author initials="J." surname="Klensin" fullname="J. Klensin">
4492      <address>
4493        <email>klensin+ietf@jck.com</email>
4494      </address>
4495    </author>
4496    <date year="2005" month="December"/>
4497  </front>
4498  <seriesInfo name="BCP" value="13"/>
4499  <seriesInfo name="RFC" value="4288"/>
4500</reference>
4501
4502<reference anchor="RFC4395">
4503  <front>
4504    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4505    <author initials="T." surname="Hansen" fullname="T. Hansen">
4506      <organization>AT&amp;T Laboratories</organization>
4507      <address>
4508        <email>tony+urireg@maillennium.att.com</email>
4509      </address>
4510    </author>
4511    <author initials="T." surname="Hardie" fullname="T. Hardie">
4512      <organization>Qualcomm, Inc.</organization>
4513      <address>
4514        <email>hardie@qualcomm.com</email>
4515      </address>
4516    </author>
4517    <author initials="L." surname="Masinter" fullname="L. Masinter">
4518      <organization>Adobe Systems</organization>
4519      <address>
4520        <email>LMM@acm.org</email>
4521      </address>
4522    </author>
4523    <date year="2006" month="February"/>
4524  </front>
4525  <seriesInfo name="BCP" value="115"/>
4526  <seriesInfo name="RFC" value="4395"/>
4527</reference>
4528
4529<reference anchor="RFC5226">
4530  <front>
4531    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4532    <author initials="T." surname="Narten" fullname="T. Narten">
4533      <organization>IBM</organization>
4534      <address><email>narten@us.ibm.com</email></address>
4535    </author>
4536    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
4537      <organization>Google</organization>
4538      <address><email>Harald@Alvestrand.no</email></address>
4539    </author>
4540    <date year="2008" month="May"/>
4541  </front>
4542  <seriesInfo name="BCP" value="26"/>
4543  <seriesInfo name="RFC" value="5226"/>
4544</reference>
4545
4546<reference anchor="RFC5322">
4547  <front>
4548    <title>Internet Message Format</title>
4549    <author initials="P." surname="Resnick" fullname="P. Resnick">
4550      <organization>Qualcomm Incorporated</organization>
4551    </author>
4552    <date year="2008" month="October"/>
4553  </front> 
4554  <seriesInfo name="RFC" value="5322"/>
4555</reference>
4556
4557<reference anchor="BCP97">
4558  <front>
4559    <title>Handling Normative References to Standards-Track Documents</title>
4560    <author initials="J." surname="Klensin" fullname="J. Klensin">
4561      <address>
4562        <email>klensin+ietf@jck.com</email>
4563      </address>
4564    </author>
4565    <author initials="S." surname="Hartman" fullname="S. Hartman">
4566      <organization>MIT</organization>
4567      <address>
4568        <email>hartmans-ietf@mit.edu</email>
4569      </address>
4570    </author>
4571    <date year="2007" month="June"/>
4572  </front>
4573  <seriesInfo name="BCP" value="97"/>
4574  <seriesInfo name="RFC" value="4897"/>
4575</reference>
4576
4577<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4578  <front>
4579    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4580    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4581    <date year="2001" month="November"/>
4582  </front>
4583  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4584</reference>
4585
4586<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4587  <front>
4588    <title>Analysis of HTTP Performance Problems</title>
4589    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4590    <date/>
4591  </front>
4592</reference>
4593
4594<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4595  <front>
4596  <title>Analysis of HTTP Performance</title>
4597  <author initials="J." surname="Touch" fullname="Joe Touch">
4598    <organization>USC/Information Sciences Institute</organization>
4599    <address><email>touch@isi.edu</email></address>
4600  </author>
4601  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4602    <organization>USC/Information Sciences Institute</organization>
4603    <address><email>johnh@isi.edu</email></address>
4604  </author>
4605  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4606    <organization>USC/Information Sciences Institute</organization>
4607    <address><email>katia@isi.edu</email></address>
4608  </author>
4609  <date year="1998" month="Aug"/>
4610  </front>
4611  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4612  <annotation>(original report dated Aug. 1996)</annotation>
4613</reference>
4614
4615</references>
4616
4617
4618<section title="Tolerant Applications" anchor="tolerant.applications">
4619<t>
4620   Although this document specifies the requirements for the generation
4621   of HTTP/1.1 messages, not all applications will be correct in their
4622   implementation. We therefore recommend that operational applications
4623   be tolerant of deviations whenever those deviations can be
4624   interpreted unambiguously.
4625</t>
4626<t>
4627   Clients SHOULD be tolerant in parsing the Status-Line and servers
4628   SHOULD be tolerant when parsing the Request-Line. In particular, they
4629   SHOULD accept any amount of WSP characters between fields, even though
4630   only a single SP is required.
4631</t>
4632<t>
4633   The line terminator for header fields is the sequence CRLF.
4634   However, we recommend that applications, when parsing such headers fields,
4635   recognize a single LF as a line terminator and ignore the leading CR.
4636</t>
4637<t>
4638   The character set of a representation SHOULD be labeled as the lowest
4639   common denominator of the character codes used within that representation, with
4640   the exception that not labeling the representation is preferred over labeling
4641   the representation with the labels US-ASCII or ISO-8859-1. See <xref target="Part3"/>.
4642</t>
4643<t>
4644   Additional rules for requirements on parsing and encoding of dates
4645   and other potential problems with date encodings include:
4646</t>
4647<t>
4648  <list style="symbols">
4649     <t>HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
4650        which appears to be more than 50 years in the future is in fact
4651        in the past (this helps solve the "year 2000" problem).</t>
4652
4653     <t>Although all date formats are specified to be case-sensitive,
4654        recipients SHOULD match day, week and timezone names
4655        case-insensitively.</t>
4656             
4657     <t>An HTTP/1.1 implementation MAY internally represent a parsed
4658        Expires date as earlier than the proper value, but MUST NOT
4659        internally represent a parsed Expires date as later than the
4660        proper value.</t>
4661
4662     <t>All expiration-related calculations MUST be done in GMT. The
4663        local time zone MUST NOT influence the calculation or comparison
4664        of an age or expiration time.</t>
4665
4666     <t>If an HTTP header field incorrectly carries a date value with a time
4667        zone other than GMT, it MUST be converted into GMT using the
4668        most conservative possible conversion.</t>
4669  </list>
4670</t>
4671</section>
4672
4673<section title="Compatibility with Previous Versions" anchor="compatibility">
4674<t>
4675   HTTP has been in use by the World-Wide Web global information initiative
4676   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4677   was a simple protocol for hypertext data transfer across the Internet
4678   with only a single method and no metadata.
4679   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4680   methods and MIME-like messaging that could include metadata about the data
4681   transferred and modifiers on the request/response semantics. However,
4682   HTTP/1.0 did not sufficiently take into consideration the effects of
4683   hierarchical proxies, caching, the need for persistent connections, or
4684   name-based virtual hosts. The proliferation of incompletely-implemented
4685   applications calling themselves "HTTP/1.0" further necessitated a
4686   protocol version change in order for two communicating applications
4687   to determine each other's true capabilities.
4688</t>
4689<t>
4690   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4691   requirements that enable reliable implementations, adding only
4692   those new features that will either be safely ignored by an HTTP/1.0
4693   recipient or only sent when communicating with a party advertising
4694   compliance with HTTP/1.1.
4695</t>
4696<t>
4697   It is beyond the scope of a protocol specification to mandate
4698   compliance with previous versions. HTTP/1.1 was deliberately
4699   designed, however, to make supporting previous versions easy. It is
4700   worth noting that, at the time of composing this specification, we would
4701   expect general-purpose HTTP/1.1 servers to:
4702  <list style="symbols">
4703     <t>understand any valid request in the format of HTTP/1.0 and
4704        1.1;</t>
4705
4706     <t>respond appropriately with a message in the same major version
4707        used by the client.</t>
4708  </list>
4709</t>
4710<t>
4711   And we would expect HTTP/1.1 clients to:
4712  <list style="symbols">
4713     <t>understand any valid response in the format of HTTP/1.0 or
4714        1.1.</t>
4715  </list>
4716</t>
4717<t>
4718   For most implementations of HTTP/1.0, each connection is established
4719   by the client prior to the request and closed by the server after
4720   sending the response. Some implementations implement the Keep-Alive
4721   version of persistent connections described in Section 19.7.1 of <xref target="RFC2068"/>.
4722</t>
4723
4724<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4725<t>
4726   This section summarizes major differences between versions HTTP/1.0
4727   and HTTP/1.1.
4728</t>
4729
4730<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">
4731<t>
4732   The requirements that clients and servers support the Host request-header
4733   field (<xref target="header.host"/>), report an error if it is
4734   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4735   are among the most important changes defined by this
4736   specification.
4737</t>
4738<t>
4739   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4740   addresses and servers; there was no other established mechanism for
4741   distinguishing the intended server of a request than the IP address
4742   to which that request was directed. The changes outlined above will
4743   allow the Internet, once older HTTP clients are no longer common, to
4744   support multiple Web sites from a single IP address, greatly
4745   simplifying large operational Web servers, where allocation of many
4746   IP addresses to a single host has created serious problems. The
4747   Internet will also be able to recover the IP addresses that have been
4748   allocated for the sole purpose of allowing special-purpose domain
4749   names to be used in root-level HTTP URLs. Given the rate of growth of
4750   the Web, and the number of servers already deployed, it is extremely
4751   important that all implementations of HTTP (including updates to
4752   existing HTTP/1.0 applications) correctly implement these
4753   requirements:
4754  <list style="symbols">
4755     <t>Both clients and servers MUST support the Host request-header field.</t>
4756
4757     <t>A client that sends an HTTP/1.1 request MUST send a Host header field.</t>
4758
4759     <t>Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
4760        request does not include a Host request-header field.</t>
4761
4762     <t>Servers MUST accept absolute URIs.</t>
4763  </list>
4764</t>
4765</section>
4766</section>
4767
4768<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4769<t>
4770   Some clients and servers might wish to be compatible with some
4771   previous implementations of persistent connections in HTTP/1.0
4772   clients and servers. Persistent connections in HTTP/1.0 are
4773   explicitly negotiated as they are not the default behavior. HTTP/1.0
4774   experimental implementations of persistent connections are faulty,
4775   and the new facilities in HTTP/1.1 are designed to rectify these
4776   problems. The problem was that some existing HTTP/1.0 clients might
4777   send Keep-Alive to a proxy server that doesn't understand
4778   Connection, which would then erroneously forward it to the next
4779   inbound server, which would establish the Keep-Alive connection and
4780   result in a hung HTTP/1.0 proxy waiting for the close on the
4781   response. The result is that HTTP/1.0 clients must be prevented from
4782   using Keep-Alive when talking to proxies.
4783</t>
4784<t>
4785   However, talking to proxies is the most important use of persistent
4786   connections, so that prohibition is clearly unacceptable. Therefore,
4787   we need some other mechanism for indicating a persistent connection
4788   is desired, which is safe to use even when talking to an old proxy
4789   that ignores Connection. Persistent connections are the default for
4790   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4791   declaring non-persistence. See <xref target="header.connection"/>.
4792</t>
4793<t>
4794   The original HTTP/1.0 form of persistent connections (the Connection:
4795   Keep-Alive and Keep-Alive header field) is documented in Section 19.7.1 of <xref target="RFC2068"/>.
4796</t>
4797</section>
4798
4799<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4800<t>
4801  Empty list elements in list productions have been deprecated.
4802  (<xref target="notation.abnf"/>)
4803</t>
4804<t>
4805  Rules about implicit linear whitespace between certain grammar productions
4806  have been removed; now it's only allowed when specifically pointed out
4807  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4808  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4809  Non-ASCII content in header fields and reason phrase has been obsoleted and
4810  made opaque (the TEXT rule was removed)
4811  (<xref target="basic.rules"/>)
4812</t>
4813<t>
4814  Clarify that HTTP-Version is case sensitive.
4815  (<xref target="http.version"/>)
4816</t>
4817<t>
4818  Require that invalid whitespace around field-names be rejected.
4819  (<xref target="header.fields"/>)
4820</t>
4821<t>
4822  Require recipients to handle bogus Content-Length header fields as errors.
4823  (<xref target="message.body"/>)
4824</t>
4825<t>
4826  Remove reference to non-existent identity transfer-coding value tokens.
4827  (Sections <xref format="counter" target="message.body"/> and
4828  <xref format="counter" target="transfer.codings"/>)
4829</t>
4830<t>
4831  Update use of abs_path production from RFC 1808 to the path-absolute + query
4832  components of RFC 3986.
4833  (<xref target="request-target"/>)
4834</t>
4835<t>
4836  Clarification that the chunk length does not include the count of the octets
4837  in the chunk header and trailer. Furthermore disallowed line folding
4838  in chunk extensions.
4839  (<xref target="chunked.encoding"/>)
4840</t>
4841<t>
4842  Remove hard limit of two connections per server.
4843  (<xref target="persistent.practical"/>)
4844</t>
4845<t>
4846  Clarify exactly when close connection options must be sent.
4847  (<xref target="header.connection"/>)
4848</t>
4849</section>
4850</section>
4851
4852
4853<section title="Collected ABNF" anchor="collected.abnf">
4854<figure>
4855<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
4856BWS = OWS
4857
4858Cache-Control = <Cache-Control, defined in [Part6], Section 3.4>
4859Chunked-Body = *chunk last-chunk trailer-part CRLF
4860Connection = "Connection:" OWS Connection-v
4861Connection-v = *( "," OWS ) connection-token *( OWS "," [ OWS
4862 connection-token ] )
4863Content-Length = "Content-Length:" OWS 1*Content-Length-v
4864Content-Length-v = 1*DIGIT
4865
4866Date = "Date:" OWS Date-v
4867Date-v = HTTP-date
4868
4869GMT = %x47.4D.54 ; GMT
4870
4871HTTP-Prot-Name = %x48.54.54.50 ; HTTP
4872HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4873HTTP-date = rfc1123-date / obs-date
4874HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
4875 ]
4876Host = "Host:" OWS Host-v
4877Host-v = uri-host [ ":" port ]
4878
4879MIME-Version = <MIME-Version, defined in [Part3], Appendix A.1>
4880Method = token
4881
4882OWS = *( [ obs-fold ] WSP )
4883
4884Pragma = <Pragma, defined in [Part6], Section 3.4>
4885
4886RWS = 1*( [ obs-fold ] WSP )
4887Reason-Phrase = *( WSP / VCHAR / obs-text )
4888Request = Request-Line *( header-field CRLF ) CRLF [ message-body ]
4889Request-Line = Method SP request-target SP HTTP-Version CRLF
4890Response = Status-Line *( header-field CRLF ) CRLF [ message-body ]
4891
4892Status-Code = 3DIGIT
4893Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4894
4895TE = "TE:" OWS TE-v
4896TE-v = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4897Trailer = "Trailer:" OWS Trailer-v
4898Trailer-v = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4899Transfer-Encoding = "Transfer-Encoding:" OWS Transfer-Encoding-v
4900Transfer-Encoding-v = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4901 transfer-coding ] )
4902
4903URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
4904Upgrade = "Upgrade:" OWS Upgrade-v
4905Upgrade-v = *( "," OWS ) product *( OWS "," [ OWS product ] )
4906
4907Via = "Via:" OWS Via-v
4908Via-v = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4909 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4910 ] )
4911
4912Warning = <Warning, defined in [Part6], Section 3.6>
4913
4914absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
4915asctime-date = day-name SP date3 SP time-of-day SP year
4916attribute = token
4917authority = <authority, defined in [RFC3986], Section 3.2>
4918
4919chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4920chunk-data = 1*OCTET
4921chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4922chunk-ext-name = token
4923chunk-ext-val = token / quoted-str-nf
4924chunk-size = 1*HEXDIG
4925comment = "(" *( ctext / quoted-cpair / comment ) ")"
4926connection-token = token
4927ctext = OWS / %x21-27 ; '!'-'''
4928 / %x2A-5B ; '*'-'['
4929 / %x5D-7E ; ']'-'~'
4930 / obs-text
4931
4932date1 = day SP month SP year
4933date2 = day "-" month "-" 2DIGIT
4934date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
4935day = 2DIGIT
4936day-name = %x4D.6F.6E ; Mon
4937 / %x54.75.65 ; Tue
4938 / %x57.65.64 ; Wed
4939 / %x54.68.75 ; Thu
4940 / %x46.72.69 ; Fri
4941 / %x53.61.74 ; Sat
4942 / %x53.75.6E ; Sun
4943day-name-l = %x4D.6F.6E.64.61.79 ; Monday
4944 / %x54.75.65.73.64.61.79 ; Tuesday
4945 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4946 / %x54.68.75.72.73.64.61.79 ; Thursday
4947 / %x46.72.69.64.61.79 ; Friday
4948 / %x53.61.74.75.72.64.61.79 ; Saturday
4949 / %x53.75.6E.64.61.79 ; Sunday
4950
4951field-content = *( WSP / VCHAR / obs-text )
4952field-name = token
4953field-value = *( field-content / OWS )
4954
4955general-header = Cache-Control / Connection / Date / Pragma / Trailer
4956 / Transfer-Encoding / Upgrade / Via / Warning / MIME-Version
4957
4958header-field = field-name ":" OWS [ field-value ] OWS
4959hour = 2DIGIT
4960http-URI = "http://" authority path-abempty [ "?" query ]
4961https-URI = "https://" authority path-abempty [ "?" query ]
4962
4963last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF
4964
4965message-body = *OCTET
4966minute = 2DIGIT
4967month = %x4A.61.6E ; Jan
4968 / %x46.65.62 ; Feb
4969 / %x4D.61.72 ; Mar
4970 / %x41.70.72 ; Apr
4971 / %x4D.61.79 ; May
4972 / %x4A.75.6E ; Jun
4973 / %x4A.75.6C ; Jul
4974 / %x41.75.67 ; Aug
4975 / %x53.65.70 ; Sep
4976 / %x4F.63.74 ; Oct
4977 / %x4E.6F.76 ; Nov
4978 / %x44.65.63 ; Dec
4979
4980obs-date = rfc850-date / asctime-date
4981obs-fold = CRLF
4982obs-text = %x80-FF
4983
4984partial-URI = relative-part [ "?" query ]
4985path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
4986path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
4987port = <port, defined in [RFC3986], Section 3.2.3>
4988product = token [ "/" product-version ]
4989product-version = token
4990protocol-name = token
4991protocol-version = token
4992pseudonym = token
4993
4994qdtext = OWS / "!" / %x23-5B ; '#'-'['
4995 / %x5D-7E ; ']'-'~'
4996 / obs-text
4997qdtext-nf = WSP / "!" / %x23-5B ; '#'-'['
4998 / %x5D-7E ; ']'-'~'
4999 / obs-text
5000query = <query, defined in [RFC3986], Section 3.4>
5001quoted-cpair = "\" ( WSP / VCHAR / obs-text )
5002quoted-pair = "\" ( WSP / VCHAR / obs-text )
5003quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5004quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5005qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5006
5007received-by = ( uri-host [ ":" port ] ) / pseudonym
5008received-protocol = [ protocol-name "/" ] protocol-version
5009relative-part = <relative-part, defined in [RFC3986], Section 4.2>
5010request-header = <request-header, defined in [Part2], Section 3>
5011request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5012 / authority
5013response-header = <response-header, defined in [Part2], Section 5>
5014rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
5015rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
5016
5017second = 2DIGIT
5018special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
5019 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5020start-line = Request-Line / Status-Line
5021
5022t-codings = "trailers" / ( transfer-extension [ te-params ] )
5023tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
5024 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5025te-ext = OWS ";" OWS token [ "=" word ]
5026te-params = OWS ";" OWS "q=" qvalue *te-ext
5027time-of-day = hour ":" minute ":" second
5028token = 1*tchar
5029trailer-part = *( header-field CRLF )
5030transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
5031 transfer-extension
5032transfer-extension = token *( OWS ";" OWS transfer-parameter )
5033transfer-parameter = attribute BWS "=" BWS value
5034
5035uri-host = <host, defined in [RFC3986], Section 3.2.2>
5036
5037value = word
5038
5039word = token / quoted-string
5040
5041year = 4DIGIT
5042]]></artwork>
5043</figure>
5044<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
5045; Chunked-Body defined but not used
5046; Content-Length defined but not used
5047; HTTP-message defined but not used
5048; Host defined but not used
5049; Request defined but not used
5050; Response defined but not used
5051; TE defined but not used
5052; URI-reference defined but not used
5053; general-header defined but not used
5054; http-URI defined but not used
5055; https-URI defined but not used
5056; partial-URI defined but not used
5057; request-header defined but not used
5058; response-header defined but not used
5059; special defined but not used
5060]]></artwork></figure></section>
5061
5062
5063<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5064
5065<section title="Since RFC 2616">
5066<t>
5067  Extracted relevant partitions from <xref target="RFC2616"/>.
5068</t>
5069</section>
5070
5071<section title="Since draft-ietf-httpbis-p1-messaging-00">
5072<t>
5073  Closed issues:
5074  <list style="symbols"> 
5075    <t>
5076      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5077      "HTTP Version should be case sensitive"
5078      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5079    </t>
5080    <t>
5081      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5082      "'unsafe' characters"
5083      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5084    </t>
5085    <t>
5086      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5087      "Chunk Size Definition"
5088      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5089    </t>
5090    <t>
5091      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5092      "Message Length"
5093      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5094    </t>
5095    <t>
5096      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5097      "Media Type Registrations"
5098      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5099    </t>
5100    <t>
5101      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5102      "URI includes query"
5103      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5104    </t>
5105    <t>
5106      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5107      "No close on 1xx responses"
5108      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5109    </t>
5110    <t>
5111      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5112      "Remove 'identity' token references"
5113      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5114    </t>
5115    <t>
5116      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5117      "Import query BNF"
5118    </t>
5119    <t>
5120      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5121      "qdtext BNF"
5122    </t>
5123    <t>
5124      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5125      "Normative and Informative references"
5126    </t>
5127    <t>
5128      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5129      "RFC2606 Compliance"
5130    </t>
5131    <t>
5132      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5133      "RFC977 reference"
5134    </t>
5135    <t>
5136      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5137      "RFC1700 references"
5138    </t>
5139    <t>
5140      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5141      "inconsistency in date format explanation"
5142    </t>
5143    <t>
5144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5145      "Date reference typo"
5146    </t>
5147    <t>
5148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5149      "Informative references"
5150    </t>
5151    <t>
5152      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5153      "ISO-8859-1 Reference"
5154    </t>
5155    <t>
5156      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5157      "Normative up-to-date references"
5158    </t>
5159  </list>
5160</t>
5161<t>
5162  Other changes:
5163  <list style="symbols"> 
5164    <t>
5165      Update media type registrations to use RFC4288 template.
5166    </t>
5167    <t>
5168      Use names of RFC4234 core rules DQUOTE and WSP,
5169      fix broken ABNF for chunk-data
5170      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5171    </t>
5172  </list>
5173</t>
5174</section>
5175
5176<section title="Since draft-ietf-httpbis-p1-messaging-01">
5177<t>
5178  Closed issues:
5179  <list style="symbols"> 
5180    <t>
5181      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5182      "Bodies on GET (and other) requests"
5183    </t>
5184    <t>
5185      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5186      "Updating to RFC4288"
5187    </t>
5188    <t>
5189      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5190      "Status Code and Reason Phrase"
5191    </t>
5192    <t>
5193      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5194      "rel_path not used"
5195    </t>
5196  </list>
5197</t>
5198<t>
5199  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5200  <list style="symbols"> 
5201    <t>
5202      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
5203      "trailer-part").
5204    </t>
5205    <t>
5206      Avoid underscore character in rule names ("http_URL" -&gt;
5207      "http-URL", "abs_path" -&gt; "path-absolute").
5208    </t>
5209    <t>
5210      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5211      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5212      have to be updated when switching over to RFC3986.
5213    </t>
5214    <t>
5215      Synchronize core rules with RFC5234.
5216    </t>
5217    <t>
5218      Get rid of prose rules that span multiple lines.
5219    </t>
5220    <t>
5221      Get rid of unused rules LOALPHA and UPALPHA.
5222    </t>
5223    <t>
5224      Move "Product Tokens" section (back) into Part 1, as "token" is used
5225      in the definition of the Upgrade header field.
5226    </t>
5227    <t>
5228      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5229    </t>
5230    <t>
5231      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5232    </t>
5233  </list>
5234</t>
5235</section>
5236
5237<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5238<t>
5239  Closed issues:
5240  <list style="symbols"> 
5241    <t>
5242      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5243      "HTTP-date vs. rfc1123-date"
5244    </t>
5245    <t>
5246      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5247      "WS in quoted-pair"
5248    </t>
5249  </list>
5250</t>
5251<t>
5252  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5253  <list style="symbols"> 
5254    <t>
5255      Reference RFC 3984, and update header field registrations for headers defined
5256      in this document.
5257    </t>
5258  </list>
5259</t>
5260<t>
5261  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5262  <list style="symbols"> 
5263    <t>
5264      Replace string literals when the string really is case-sensitive (HTTP-Version).
5265    </t>
5266  </list>
5267</t>
5268</section>
5269
5270<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5271<t>
5272  Closed issues:
5273  <list style="symbols"> 
5274    <t>
5275      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5276      "Connection closing"
5277    </t>
5278    <t>
5279      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5280      "Move registrations and registry information to IANA Considerations"
5281    </t>
5282    <t>
5283      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5284      "need new URL for PAD1995 reference"
5285    </t>
5286    <t>
5287      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5288      "IANA Considerations: update HTTP URI scheme registration"
5289    </t>
5290    <t>
5291      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5292      "Cite HTTPS URI scheme definition"
5293    </t>
5294    <t>
5295      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5296      "List-type headers vs Set-Cookie"
5297    </t>
5298  </list>
5299</t>
5300<t>
5301  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5302  <list style="symbols"> 
5303    <t>
5304      Replace string literals when the string really is case-sensitive (HTTP-Date).
5305    </t>
5306    <t>
5307      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5308    </t>
5309  </list>
5310</t>
5311</section>
5312
5313<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5314<t>
5315  Closed issues:
5316  <list style="symbols"> 
5317    <t>
5318      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5319      "Out-of-date reference for URIs"
5320    </t>
5321    <t>
5322      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5323      "RFC 2822 is updated by RFC 5322"
5324    </t>
5325  </list>
5326</t>
5327<t>
5328  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5329  <list style="symbols"> 
5330    <t>
5331      Use "/" instead of "|" for alternatives.
5332    </t>
5333    <t>
5334      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5335    </t>
5336    <t>
5337      Only reference RFC 5234's core rules.
5338    </t>
5339    <t>
5340      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5341      whitespace ("OWS") and required whitespace ("RWS").
5342    </t>
5343    <t>
5344      Rewrite ABNFs to spell out whitespace rules, factor out
5345      header field value format definitions.
5346    </t>
5347  </list>
5348</t>
5349</section>
5350
5351<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5352<t>
5353  Closed issues:
5354  <list style="symbols"> 
5355    <t>
5356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5357      "Header LWS"
5358    </t>
5359    <t>
5360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5361      "Sort 1.3 Terminology"
5362    </t>
5363    <t>
5364      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5365      "RFC2047 encoded words"
5366    </t>
5367    <t>
5368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5369      "Character Encodings in TEXT"
5370    </t>
5371    <t>
5372      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5373      "Line Folding"
5374    </t>
5375    <t>
5376      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5377      "OPTIONS * and proxies"
5378    </t>
5379    <t>
5380      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5381      "Reason-Phrase BNF"
5382    </t>
5383    <t>
5384      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5385      "Use of TEXT"
5386    </t>
5387    <t>
5388      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5389      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5390    </t>
5391    <t>
5392      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5393      "RFC822 reference left in discussion of date formats"
5394    </t>
5395  </list>
5396</t>
5397<t>
5398  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5399  <list style="symbols"> 
5400    <t>
5401      Rewrite definition of list rules, deprecate empty list elements.
5402    </t>
5403    <t>
5404      Add appendix containing collected and expanded ABNF.
5405    </t>
5406  </list>
5407</t>
5408<t>
5409  Other changes:
5410  <list style="symbols"> 
5411    <t>
5412      Rewrite introduction; add mostly new Architecture Section.
5413    </t>
5414    <t>
5415      Move definition of quality values from Part 3 into Part 1;
5416      make TE request header field grammar independent of accept-params (defined in Part 3).
5417    </t>
5418  </list>
5419</t>
5420</section>
5421
5422<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5423<t>
5424  Closed issues:
5425  <list style="symbols"> 
5426    <t>
5427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5428      "base for numeric protocol elements"
5429    </t>
5430    <t>
5431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5432      "comment ABNF"
5433    </t>
5434  </list>
5435</t>
5436<t>
5437  Partly resolved issues:
5438  <list style="symbols"> 
5439    <t>
5440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5441      "205 Bodies" (took out language that implied that there might be
5442      methods for which a request body MUST NOT be included)
5443    </t>
5444    <t>
5445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5446      "editorial improvements around HTTP-date"
5447    </t>
5448  </list>
5449</t>
5450</section>
5451
5452<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5453<t>
5454  Closed issues:
5455  <list style="symbols"> 
5456    <t>
5457      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5458      "Repeating single-value headers"
5459    </t>
5460    <t>
5461      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5462      "increase connection limit"
5463    </t>
5464    <t>
5465      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5466      "IP addresses in URLs"
5467    </t>
5468    <t>
5469      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5470      "take over HTTP Upgrade Token Registry"
5471    </t>
5472    <t>
5473      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5474      "CR and LF in chunk extension values"
5475    </t>
5476    <t>
5477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5478      "HTTP/0.9 support"
5479    </t>
5480    <t>
5481      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5482      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5483    </t>
5484    <t>
5485      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5486      "move definitions of gzip/deflate/compress to part 1"
5487    </t>
5488    <t>
5489      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5490      "disallow control characters in quoted-pair"
5491    </t>
5492  </list>
5493</t>
5494<t>
5495  Partly resolved issues:
5496  <list style="symbols"> 
5497    <t>
5498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5499      "update IANA requirements wrt Transfer-Coding values" (add the
5500      IANA Considerations subsection)
5501    </t>
5502  </list>
5503</t>
5504</section>
5505
5506<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5507<t>
5508  Closed issues:
5509  <list style="symbols"> 
5510    <t>
5511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5512      "header parsing, treatment of leading and trailing OWS"
5513    </t>
5514  </list>
5515</t>
5516<t>
5517  Partly resolved issues:
5518  <list style="symbols"> 
5519    <t>
5520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5521      "Placement of 13.5.1 and 13.5.2"
5522    </t>
5523    <t>
5524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5525      "use of term "word" when talking about header structure"
5526    </t>
5527  </list>
5528</t>
5529</section>
5530
5531<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5532<t>
5533  Closed issues:
5534  <list style="symbols"> 
5535    <t>
5536      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5537      "Clarification of the term 'deflate'"
5538    </t>
5539    <t>
5540      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5541      "OPTIONS * and proxies"
5542    </t>
5543    <t>
5544      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5545      "MIME-Version not listed in P1, general header fields"
5546    </t>
5547    <t>
5548      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5549      "IANA registry for content/transfer encodings"
5550    </t>
5551    <t>
5552      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5553      "Case-sensitivity of HTTP-date"
5554    </t>
5555    <t>
5556      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5557      "use of term "word" when talking about header structure"
5558    </t>
5559  </list>
5560</t>
5561<t>
5562  Partly resolved issues:
5563  <list style="symbols"> 
5564    <t>
5565      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5566      "Term for the requested resource's URI"
5567    </t>
5568  </list>
5569</t>
5570</section>
5571
5572<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5573<t>
5574  Closed issues:
5575  <list style="symbols">
5576    <t>
5577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5578      "Connection Closing"
5579    </t>
5580    <t>
5581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5582      "Delimiting messages with multipart/byteranges"
5583    </t>
5584    <t>
5585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5586      "Handling multiple Content-Length headers"
5587    </t>
5588    <t>
5589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5590      "Clarify entity / representation / variant terminology"
5591    </t>
5592    <t>
5593      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5594      "consider removing the 'changes from 2068' sections"
5595    </t>
5596  </list>
5597</t>
5598<t>
5599  Partly resolved issues:
5600  <list style="symbols"> 
5601    <t>
5602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5603      "HTTP(s) URI scheme definitions"
5604    </t>
5605  </list>
5606</t>
5607</section>
5608
5609<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5610<t>
5611  Closed issues:
5612  <list style="symbols">
5613    <t>
5614      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5615      "Trailer requirements"
5616    </t>
5617    <t>
5618      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5619      "Text about clock requirement for caches belongs in p6"
5620    </t>
5621    <t>
5622      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5623      "effective request URI: handling of missing host in HTTP/1.0"
5624    </t>
5625    <t>
5626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5627      "confusing Date requirements for clients"
5628    </t>
5629  </list>
5630</t>
5631<t>
5632  Partly resolved issues:
5633  <list style="symbols"> 
5634    <t>
5635      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5636      "Handling multiple Content-Length headers"
5637    </t>
5638  </list>
5639</t>
5640</section>
5641
5642</section>
5643
5644</back>
5645</rfc>
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