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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-10">
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="July" year="2010" day="12"/>
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.09"/>.
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 a generic protocol for translating
219   communication to and from other Internet information systems.
220   HTTP proxies and gateways 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 should be reflected in corresponding changes to the
232   observable interface provided by servers. However, since multiple
233   clients may 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 syntactical 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 except the entity-body (see <xref target="tolerant.applications"/> for
389   tolerant applications). The end-of-line marker within an entity-body
390   is defined by its associated media type, as described in Section 2.3 of <xref target="Part3"/>.
391</t>
392<t anchor="rule.LWS">
393   This specification uses three rules to denote the use of linear
394   whitespace: OWS (optional whitespace), RWS (required whitespace), and
395   BWS ("bad" whitespace).
396</t>
397<t>
398   The OWS rule is used where zero or more linear whitespace characters may
399   appear. OWS SHOULD either not be produced or be produced as a single SP
400   character. Multiple OWS characters that occur within field-content SHOULD
401   be replaced with a single SP before interpreting the field value or
402   forwarding the message downstream.
403</t>
404<t>
405   RWS is used when at least one linear whitespace character is required to
406   separate field tokens. RWS SHOULD be produced as a single SP character.
407   Multiple RWS characters that occur within field-content SHOULD be
408   replaced with a single SP before interpreting the field value or
409   forwarding the message downstream.
410</t>
411<t>
412   BWS is used where the grammar allows optional whitespace for historical
413   reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
414   recipients MUST accept such bad optional whitespace and remove it before
415   interpreting the field value or forwarding the message downstream.
416</t>
417<t anchor="rule.whitespace">
418 
419 
420 
421 
422</t>
423<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[
424  OWS            = *( [ obs-fold ] WSP )
425                 ; "optional" whitespace
426  RWS            = 1*( [ obs-fold ] WSP )
427                 ; "required" whitespace
428  BWS            = OWS
429                 ; "bad" whitespace
430  obs-fold       = CRLF
431                 ; see Section 3.2
432]]></artwork></figure>
433<t anchor="rule.token.separators">
434 
435 
436 
437 
438   Many HTTP/1.1 header field values consist of words (token or quoted-string)
439   separated by whitespace or special characters. These special characters
440   MUST be in a quoted string to be used within a parameter value (as defined
441   in <xref target="transfer.codings"/>).
442</t>
443<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[
444  word           = token / quoted-string
445
446  token          = 1*tchar
447
448  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
449                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
450                 / DIGIT / ALPHA
451                 ; any VCHAR, except special
452
453  special        = "(" / ")" / "<" / ">" / "@" / ","
454                 / ";" / ":" / "\" / DQUOTE / "/" / "["
455                 / "]" / "?" / "=" / "{" / "}"
456]]></artwork></figure>
457<t anchor="rule.quoted-string">
458 
459 
460 
461   A string of text is parsed as a single word if it is quoted using
462   double-quote marks.
463</t>
464<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[
465  quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
466  qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
467                 ; OWS / <VCHAR except DQUOTE and "\"> / obs-text
468  obs-text       = %x80-FF
469]]></artwork></figure>
470<t anchor="rule.quoted-pair">
471 
472   The backslash character ("\") can be used as a single-character
473   quoting mechanism within quoted-string constructs:
474</t>
475<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
476  quoted-pair    = "\" ( WSP / VCHAR / obs-text )
477]]></artwork></figure>
478<t>
479   Producers SHOULD NOT escape characters that do not require escaping
480   (i.e., other than DQUOTE and the backslash character).
481</t>
482</section>
483
484<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
485 
486 
487 
488 
489 
490 
491 
492<t>
493  The ABNF rules below are defined in other parts:
494</t>
495<figure><artwork type="abnf2616"><![CDATA[
496  request-header  = <request-header, defined in [Part2], Section 3>
497  response-header = <response-header, defined in [Part2], Section 5>
498]]></artwork></figure>
499<figure><artwork type="abnf2616"><![CDATA[
500  entity-body     = <entity-body, defined in [Part3], Section 3.2>
501  entity-header   = <entity-header, defined in [Part3], Section 3.1>
502]]></artwork></figure>
503<figure><artwork type="abnf2616"><![CDATA[
504  Cache-Control   = <Cache-Control, defined in [Part6], Section 3.4>
505  Pragma          = <Pragma, defined in [Part6], Section 3.4>
506  Warning         = <Warning, defined in [Part6], Section 3.6>
507]]></artwork></figure>
508</section>
509
510</section>
511</section>
512
513<section title="HTTP architecture" anchor="architecture">
514<t>
515   HTTP was created for the World Wide Web architecture
516   and has evolved over time to support the scalability needs of a worldwide
517   hypertext system. Much of that architecture is reflected in the terminology
518   and syntax productions used to define HTTP.
519</t>
520
521<section title="Client/Server Operation" anchor="operation">
522<iref item="client"/>
523<iref item="server"/>
524<iref item="connection"/>
525<t>
526   HTTP is a request/response protocol that operates by exchanging messages
527   across a reliable transport or session-layer connection. An HTTP client
528   is a program that establishes a connection to a server for the purpose
529   of sending one or more HTTP requests.  An HTTP server is a program that
530   accepts connections in order to service HTTP requests by sending HTTP
531   responses.
532</t>
533<iref item="user agent"/>
534<iref item="origin server"/>
535<t>
536   Note that the terms "client" and "server" refer only to the roles that
537   these programs perform for a particular connection.  The same program
538   may act as a client on some connections and a server on others.  We use
539   the term "user agent" to refer to the program that initiates a request,
540   such as a WWW browser, editor, or spider (web-traversing robot), and
541   the term "origin server" to refer to the program that can originate
542   authoritative responses to a request.
543</t>
544<t>
545   Most HTTP communication consists of a retrieval request (GET) for
546   a representation of some resource identified by a URI.  In the
547   simplest case, this may be accomplished via a single connection (v)
548   between the user agent (UA) and the origin server (O).
549</t>
550<figure><artwork type="drawing"><![CDATA[
551       request chain ------------------------>
552    UA -------------------v------------------- O
553       <----------------------- response chain
554]]></artwork></figure>
555<iref item="message"/>
556<iref item="request"/>
557<iref item="response"/>
558<t>
559   A client sends an HTTP request to the server in the form of a request
560   message (<xref target="request"/>), beginning with a method, URI, and
561   protocol version, followed by MIME-like header fields containing
562   request modifiers, client information, and payload metadata, an empty
563   line to indicate the end of the header section, and finally the payload
564   body (if any).
565</t>
566<t>
567   A server responds to the client's request by sending an HTTP response
568   message (<xref target="response"/>), beginning with a status line that
569   includes the protocol version, a success or error code, and textual
570   reason phrase, followed by MIME-like header fields containing server
571   information, resource metadata, and payload metadata, an empty line to
572   indicate the end of the header section, and finally the payload body (if any).
573</t>
574<t>
575   The following example illustrates a typical message exchange for a
576   GET request on the URI "http://www.example.com/hello.txt":
577</t>
578<figure><preamble>
579client request:
580</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
581  GET /hello.txt HTTP/1.1
582  User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
583  Host: www.example.com
584  Accept: */*
585 
586  ]]></artwork></figure>
587<figure><preamble>
588server response:
589</preamble><artwork type="message/http; msgtype=&#34;response&#34;"><![CDATA[
590  HTTP/1.1 200 OK
591  Date: Mon, 27 Jul 2009 12:28:53 GMT
592  Server: Apache
593  Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
594  ETag: "34aa387-d-1568eb00"
595  Accept-Ranges: bytes
596  Content-Length: 14
597  Vary: Accept-Encoding
598  Content-Type: text/plain
599 
600  Hello World!
601  ]]></artwork></figure>
602</section>
603
604<section title="Intermediaries" anchor="intermediaries">
605<t>
606   A more complicated situation occurs when one or more intermediaries
607   are present in the request/response chain. There are three common
608   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
609   a single intermediary may act as an origin server, proxy, gateway,
610   or tunnel, switching behavior based on the nature of each request.
611</t>
612<figure><artwork type="drawing"><![CDATA[
613       request chain -------------------------------------->
614    UA -----v----- A -----v----- B -----v----- C -----v----- O
615       <------------------------------------- response chain
616]]></artwork></figure>
617<t>
618   The figure above shows three intermediaries (A, B, and C) between the
619   user agent and origin server. A request or response message that
620   travels the whole chain will pass through four separate connections.
621   Some HTTP communication options
622   may apply only to the connection with the nearest, non-tunnel
623   neighbor, only to the end-points of the chain, or to all connections
624   along the chain. Although the diagram is linear, each participant may
625   be engaged in multiple, simultaneous communications. For example, B
626   may be receiving requests from many clients other than A, and/or
627   forwarding requests to servers other than C, at the same time that it
628   is handling A's request.
629</t>
630<t>
631<iref item="upstream"/><iref item="downstream"/>
632<iref item="inbound"/><iref item="outbound"/>
633   We use the terms "upstream" and "downstream" to describe various
634   requirements in relation to the directional flow of a message:
635   all messages flow from upstream to downstream.
636   Likewise, we use the terms "inbound" and "outbound" to refer to
637   directions in relation to the request path: "inbound" means toward
638   the origin server and "outbound" means toward the user agent.
639</t>
640<t><iref item="proxy"/>
641   A proxy is a message forwarding agent that is selected by the
642   client, usually via local configuration rules, to receive requests
643   for some type(s) of absolute URI and attempt to satisfy those
644   requests via translation through the HTTP interface.  Some translations
645   are minimal, such as for proxy requests for "http" URIs, whereas
646   other requests may require translation to and from entirely different
647   application-layer protocols. Proxies are often used to group an
648   organization's HTTP requests through a common intermediary for the
649   sake of security, annotation services, or shared caching.
650</t>
651<t><iref item="gateway"/><iref item="reverse proxy"/>
652   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
653   as a layer above some other server(s) and translates the received
654   requests to the underlying server's protocol.  Gateways are often
655   used for load balancing or partitioning HTTP services across
656   multiple machines.
657   Unlike a proxy, a gateway receives requests as if it were the
658   origin server for the requested resource; the requesting client
659   will not be aware that it is communicating with a gateway.
660   A gateway communicates with the client as if the gateway is the
661   origin server and thus is subject to all of the requirements on
662   origin servers for that connection.  A gateway communicates
663   with inbound servers using any protocol it desires, including
664   private extensions to HTTP that are outside the scope of this
665   specification.
666</t>
667<t><iref item="tunnel"/>
668   A tunnel acts as a blind relay between two connections
669   without changing the messages. Once active, a tunnel is not
670   considered a party to the HTTP communication, though the tunnel may
671   have been initiated by an HTTP request. A tunnel ceases to exist when
672   both ends of the relayed connection are closed. Tunnels are used to
673   extend a virtual connection through an intermediary, such as when
674   transport-layer security is used to establish private communication
675   through a shared firewall proxy.
676</t>
677</section>
678
679<section title="Caches" anchor="caches">
680<iref item="cache"/>
681<t>
682   Any party to HTTP communication that is not acting as a tunnel may
683   employ an internal cache for handling requests.
684   A cache is a local store of previous response messages and the
685   subsystem that controls its message storage, retrieval, and deletion.
686   A cache stores cacheable responses in order to reduce the response
687   time and network bandwidth consumption on future, equivalent
688   requests. Any client or server may include a cache, though a cache
689   cannot be used by a server while it is acting as a tunnel.
690</t>
691<t>
692   The effect of a cache is that the request/response chain is shortened
693   if one of the participants along the chain has a cached response
694   applicable to that request. The following illustrates the resulting
695   chain if B has a cached copy of an earlier response from O (via C)
696   for a request which has not been cached by UA or A.
697</t>
698<figure><artwork type="drawing"><![CDATA[
699          request chain ---------->
700       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
701          <--------- response chain
702]]></artwork></figure>
703<t><iref item="cacheable"/>
704   A response is cacheable if a cache is allowed to store a copy of
705   the response message for use in answering subsequent requests.
706   Even when a response is cacheable, there may be additional
707   constraints placed by the client or by the origin server on when
708   that cached response can be used for a particular request. HTTP
709   requirements for cache behavior and cacheable responses are
710   defined in Section 2 of <xref target="Part6"/>
711</t>
712<t>
713   There are a wide variety of architectures and configurations
714   of caches and proxies deployed across the World Wide Web and
715   inside large organizations. These systems include national hierarchies
716   of proxy caches to save transoceanic bandwidth, systems that
717   broadcast or multicast cache entries, organizations that distribute
718   subsets of cached data via optical media, and so on.
719</t>
720</section>
721
722<section title="Transport Independence" anchor="transport-independence">
723<t>
724  HTTP systems are used in a wide variety of environments, from
725  corporate intranets with high-bandwidth links to long-distance
726  communication over low-power radio links and intermittent connectivity.
727</t>
728<t>
729   HTTP communication usually takes place over TCP/IP connections. The
730   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
731   not preclude HTTP from being implemented on top of any other protocol
732   on the Internet, or on other networks. HTTP only presumes a reliable
733   transport; any protocol that provides such guarantees can be used;
734   the mapping of the HTTP/1.1 request and response structures onto the
735   transport data units of the protocol in question is outside the scope
736   of this specification.
737</t>
738<t>
739   In HTTP/1.0, most implementations used a new connection for each
740   request/response exchange. In HTTP/1.1, a connection may be used for
741   one or more request/response exchanges, although connections may be
742   closed for a variety of reasons (see <xref target="persistent.connections"/>).
743</t>
744</section>
745
746<section title="HTTP Version" anchor="http.version">
747 
748 
749<t>
750   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
751   of the protocol. The protocol versioning policy is intended to allow
752   the sender to indicate the format of a message and its capacity for
753   understanding further HTTP communication, rather than the features
754   obtained via that communication. No change is made to the version
755   number for the addition of message components which do not affect
756   communication behavior or which only add to extensible field values.
757   The &lt;minor&gt; number is incremented when the changes made to the
758   protocol add features which do not change the general message parsing
759   algorithm, but which may add to the message semantics and imply
760   additional capabilities of the sender. The &lt;major&gt; number is
761   incremented when the format of a message within the protocol is
762   changed. See <xref target="RFC2145"/> for a fuller explanation.
763</t>
764<t>
765   The version of an HTTP message is indicated by an HTTP-Version field
766   in the first line of the message. HTTP-Version is case-sensitive.
767</t>
768<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
769  HTTP-Version   = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
770  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
771]]></artwork></figure>
772<t>
773   Note that the major and minor numbers MUST be treated as separate
774   integers and that each MAY be incremented higher than a single digit.
775   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
776   lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and
777   MUST NOT be sent.
778</t>
779<t>
780   An application that sends a request or response message that includes
781   HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
782   with this specification. Applications that are at least conditionally
783   compliant with this specification SHOULD use an HTTP-Version of
784   "HTTP/1.1" in their messages, and MUST do so for any message that is
785   not compatible with HTTP/1.0. For more details on when to send
786   specific HTTP-Version values, see <xref target="RFC2145"/>.
787</t>
788<t>
789   The HTTP version of an application is the highest HTTP version for
790   which the application is at least conditionally compliant.
791</t>
792<t>
793   Proxy and gateway applications need to be careful when forwarding
794   messages in protocol versions different from that of the application.
795   Since the protocol version indicates the protocol capability of the
796   sender, a proxy/gateway MUST NOT send a message with a version
797   indicator which is greater than its actual version. If a higher
798   version request is received, the proxy/gateway MUST either downgrade
799   the request version, or respond with an error, or switch to tunnel
800   behavior.
801</t>
802<t>
803   Due to interoperability problems with HTTP/1.0 proxies discovered
804   since the publication of <xref target="RFC2068"/>, caching proxies MUST, gateways
805   MAY, and tunnels MUST NOT upgrade the request to the highest version
806   they support. The proxy/gateway's response to that request MUST be in
807   the same major version as the request.
808</t>
809<t><list>
810  <t>
811    Note: Converting between versions of HTTP may involve modification
812    of header fields required or forbidden by the versions involved.
813  </t>
814</list></t>
815</section>
816
817<section title="Uniform Resource Identifiers" anchor="uri">
818<iref primary="true" item="resource"/>
819<t>
820   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
821   throughout HTTP as the means for identifying resources. URI references
822   are used to target requests, indicate redirects, and define relationships.
823   HTTP does not limit what a resource may be; it merely defines an interface
824   that can be used to interact with a resource via HTTP. More information on
825   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
826</t>
827 
828 
829 
830 
831 
832 
833 
834 
835 
836 
837<t>
838   This specification adopts the definitions of "URI-reference",
839   "absolute-URI", "relative-part", "port", "host",
840   "path-abempty", "path-absolute", "query", and "authority" from
841   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
842   protocol elements that allow a relative URI without a fragment.
843</t>
844<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[
845  URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
846  absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
847  relative-part = <relative-part, defined in [RFC3986], Section 4.2>
848  authority     = <authority, defined in [RFC3986], Section 3.2>
849  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
850  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
851  port          = <port, defined in [RFC3986], Section 3.2.3>
852  query         = <query, defined in [RFC3986], Section 3.4>
853  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
854 
855  partial-URI   = relative-part [ "?" query ]
856]]></artwork></figure>
857<t>
858   Each protocol element in HTTP that allows a URI reference will indicate in
859   its ABNF production whether the element allows only a URI in absolute form
860   (absolute-URI), any relative reference (relative-ref), or some other subset
861   of the URI-reference grammar. Unless otherwise indicated, URI references
862   are parsed relative to the request target (the default base URI for both
863   the request and its corresponding response).
864</t>
865
866<section title="http URI scheme" anchor="http.uri">
867 
868  <iref item="http URI scheme" primary="true"/>
869  <iref item="URI scheme" subitem="http" primary="true"/>
870<t>
871   The "http" URI scheme is hereby defined for the purpose of minting
872   identifiers according to their association with the hierarchical
873   namespace governed by a potential HTTP origin server listening for
874   TCP connections on a given port.
875   The HTTP server is identified via the generic syntax's
876   <xref target="uri" format="none">authority</xref> component, which includes a host
877   identifier and optional TCP port, and the remainder of the URI is
878   considered to be identifying data corresponding to a resource for
879   which that server might provide an HTTP interface.
880</t>
881<figure><iref primary="true" item="Grammar" subitem="http-URI"/><artwork type="abnf2616"><![CDATA[
882  http-URI = "http:" "//" authority path-abempty [ "?" query ]
883]]></artwork></figure>
884<t>
885   The host identifier within an <xref target="uri" format="none">authority</xref> component is
886   defined in <xref target="RFC3986"/>, Section 3.2.2.  If host is
887   provided as an IP literal or IPv4 address, then the HTTP server is any
888   listener on the indicated TCP port at that IP address. If host is a
889   registered name, then that name is considered an indirect identifier
890   and the recipient might use a name resolution service, such as DNS,
891   to find the address of a listener for that host.
892   The host MUST NOT be empty; if an "http" URI is received with an
893   empty host, then it MUST be rejected as invalid.
894   If the port subcomponent is empty or not given, then TCP port 80 is
895   assumed (the default reserved port for WWW services).
896</t>
897<t>
898   Regardless of the form of host identifier, access to that host is not
899   implied by the mere presence of its name or address. The host may or may
900   not exist and, even when it does exist, may or may not be running an
901   HTTP server or listening to the indicated port. The "http" URI scheme
902   makes use of the delegated nature of Internet names and addresses to
903   establish a naming authority (whatever entity has the ability to place
904   an HTTP server at that Internet name or address) and allows that
905   authority to determine which names are valid and how they might be used.
906</t>
907<t>
908   When an "http" URI is used within a context that calls for access to the
909   indicated resource, a client MAY attempt access by resolving
910   the host to an IP address, establishing a TCP connection to that address
911   on the indicated port, and sending an HTTP request message to the server
912   containing the URI's identifying data as described in <xref target="request"/>.
913   If the server responds to that request with a non-interim HTTP response
914   message, as described in <xref target="response"/>, then that response
915   is considered an authoritative answer to the client's request.
916</t>
917<t>
918   Although HTTP is independent of the transport protocol, the "http"
919   scheme is specific to TCP-based services because the name delegation
920   process depends on TCP for establishing authority.
921   An HTTP service based on some other underlying connection protocol
922   would presumably be identified using a different URI scheme, just as
923   the "https" scheme (below) is used for servers that require an SSL/TLS
924   transport layer on a connection. Other protocols may also be used to
925   provide access to "http" identified resources --- it is only the
926   authoritative interface used for mapping the namespace that is
927   specific to TCP.
928</t>
929</section>
930
931<section title="https URI scheme" anchor="https.uri">
932   
933   <iref item="https URI scheme"/>
934   <iref item="URI scheme" subitem="https"/>
935<t>
936   The "https" URI scheme is hereby defined for the purpose of minting
937   identifiers according to their association with the hierarchical
938   namespace governed by a potential HTTP origin server listening for
939   SSL/TLS-secured connections on a given TCP port.
940   The host and port are determined in the same way
941   as for the "http" scheme, except that a default TCP port of 443
942   is assumed if the port subcomponent is empty or not given.
943</t>
944<figure><iref primary="true" item="Grammar" subitem="https-URI"/><artwork type="abnf2616"><![CDATA[
945  https-URI = "https:" "//" authority path-abempty [ "?" query ]
946]]></artwork></figure>
947<t>
948   The primary difference between the "http" and "https" schemes is
949   that interaction with the latter is required to be secured for
950   privacy through the use of strong encryption. The URI cannot be
951   sent in a request until the connection is secure. Likewise, the
952   default for caching is that each response that would be considered
953   "public" under the "http" scheme is instead treated as "private"
954   and thus not eligible for shared caching.
955</t>
956<t>
957   The process for authoritative access to an "https" identified
958   resource is defined in <xref target="RFC2818"/>.
959</t>
960</section>
961
962<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
963<t>
964   Since the "http" and "https" schemes conform to the URI generic syntax,
965   such URIs are normalized and compared according to the algorithm defined
966   in <xref target="RFC3986"/>, Section 6, using the defaults
967   described above for each scheme.
968</t>
969<t>
970   If the port is equal to the default port for a scheme, the normal
971   form is to elide the port subcomponent. Likewise, an empty path
972   component is equivalent to an absolute path of "/", so the normal
973   form is to provide a path of "/" instead. The scheme and host
974   are case-insensitive and normally provided in lowercase; all
975   other components are compared in a case-sensitive manner.
976   Characters other than those in the "reserved" set are equivalent
977   to their percent-encoded octets (see <xref target="RFC3986"/>, Section 2.1): the normal form is to not encode them.
978</t>
979<t>
980   For example, the following three URIs are equivalent:
981</t>
982<figure><artwork type="example"><![CDATA[
983   http://example.com:80/~smith/home.html
984   http://EXAMPLE.com/%7Esmith/home.html
985   http://EXAMPLE.com:/%7esmith/home.html
986]]></artwork></figure>
987<t>
988   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
989   If path-abempty is the empty string (i.e., there is no slash "/"
990   path separator following the authority), then the "http" URI
991   MUST be given as "/" when
992   used as a request-target (<xref target="request-target"/>). If a proxy
993   receives a host name which is not a fully qualified domain name, it
994   MAY add its domain to the host name it received. If a proxy receives
995   a fully qualified domain name, the proxy MUST NOT change the host
996   name.
997</t>
998</section>
999</section>
1000</section>
1001
1002<section title="HTTP Message" anchor="http.message">
1003
1004
1005
1006
1007<iref item="header section"/>
1008<iref item="headers"/>
1009<iref item="header field"/>
1010<t>
1011   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1012   characters in a format similar to the Internet Message Format
1013   <xref target="RFC5322"/>: zero or more header fields (collectively
1014   referred to as the "headers" or the "header section"), an empty line
1015   indicating the end of the header section, and an optional message-body.
1016</t>
1017<t>
1018   An HTTP message can either be a request from client to server or a
1019   response from server to client.  Syntactically, the two types of message
1020   differ only in the start-line, which is either a Request-Line (for requests)
1021   or a Status-Line (for responses), and in the algorithm for determining
1022   the length of the message-body (<xref target="message.length"/>).
1023   In theory, a client could receive requests and a server could receive
1024   responses, distinguishing them by their different start-line formats,
1025   but in practice servers are implemented to only expect a request
1026   (a response is interpreted as an unknown or invalid request method)
1027   and clients are implemented to only expect a response.
1028</t>
1029<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1030  HTTP-message    = start-line
1031                    *( header-field CRLF )
1032                    CRLF
1033                    [ message-body ]
1034  start-line      = Request-Line / Status-Line
1035]]></artwork></figure>
1036<t>
1037   Whitespace (WSP) MUST NOT be sent between the start-line and the first
1038   header field. The presence of whitespace might be an attempt to trick a
1039   noncompliant implementation of HTTP into ignoring that field or processing
1040   the next line as a new request, either of which may result in security
1041   issues when implementations within the request chain interpret the
1042   same message differently. HTTP/1.1 servers MUST reject such a message
1043   with a 400 (Bad Request) response.
1044</t>
1045
1046<section title="Message Parsing Robustness" anchor="message.robustness">
1047<t>
1048   In the interest of robustness, servers SHOULD ignore at least one
1049   empty line received where a Request-Line is expected. In other words, if
1050   the server is reading the protocol stream at the beginning of a
1051   message and receives a CRLF first, it should ignore the CRLF.
1052</t>
1053<t>
1054   Some old HTTP/1.0 client implementations generate an extra CRLF
1055   after a POST request as a lame workaround for some early server
1056   applications that failed to read message-body content that was
1057   not terminated by a line-ending. An HTTP/1.1 client MUST NOT
1058   preface or follow a request with an extra CRLF.  If terminating
1059   the request message-body with a line-ending is desired, then the
1060   client MUST include the terminating CRLF octets as part of the
1061   message-body length.
1062</t>
1063<t>
1064   The normal procedure for parsing an HTTP message is to read the
1065   start-line into a structure, read each header field into a hash
1066   table by field name until the empty line, and then use the parsed
1067   data to determine if a message-body is expected.  If a message-body
1068   has been indicated, then it is read as a stream until an amount
1069   of OCTETs equal to the message-length is read or the connection
1070   is closed.  Care must be taken to parse an HTTP message as a sequence
1071   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1072   to parse HTTP as a stream of Unicode characters in a character encoding
1073   like UTF-16 may introduce security flaws due to the differing ways
1074   that such parsers interpret invalid characters.
1075</t>
1076</section>
1077
1078<section title="Header Fields" anchor="header.fields">
1079 
1080 
1081 
1082 
1083 
1084<t>
1085   Each HTTP header field consists of a case-insensitive field name
1086   followed by a colon (":"), optional whitespace, and the field value.
1087</t>
1088<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[
1089  header-field   = field-name ":" OWS [ field-value ] OWS
1090  field-name     = token
1091  field-value    = *( field-content / OWS )
1092  field-content  = *( WSP / VCHAR / obs-text )
1093]]></artwork></figure>
1094<t>
1095   No whitespace is allowed between the header field name and colon. For
1096   security reasons, any request message received containing such whitespace
1097   MUST be rejected with a response code of 400 (Bad Request). A proxy
1098   MUST remove any such whitespace from a response message before
1099   forwarding the message downstream.
1100</t>
1101<t>
1102   A field value MAY be preceded by optional whitespace (OWS); a single SP is
1103   preferred. The field value does not include any leading or trailing white
1104   space: OWS occurring before the first non-whitespace character of the
1105   field value or after the last non-whitespace character of the field value
1106   is ignored and SHOULD be removed before further processing (as this does
1107   not change the meaning of the header field).
1108</t>
1109<t>
1110   The order in which header fields with differing field names are
1111   received is not significant. However, it is "good practice" to send
1112   header fields that contain control data first, such as Host on
1113   requests and Date on responses, so that implementations can decide
1114   when not to handle a message as early as possible.  A server MUST
1115   wait until the entire header section is received before interpreting
1116   a request message, since later header fields might include conditionals,
1117   authentication credentials, or deliberately misleading duplicate
1118   header fields that would impact request processing.
1119</t>
1120<t>
1121   Multiple header fields with the same field name MUST NOT be
1122   sent in a message unless the entire field value for that
1123   header field is defined as a comma-separated list [i.e., #(values)].
1124   Multiple header fields with the same field name can be combined into
1125   one "field-name: field-value" pair, without changing the semantics of the
1126   message, by appending each subsequent field value to the combined
1127   field value in order, separated by a comma. The order in which
1128   header fields with the same field name are received is therefore
1129   significant to the interpretation of the combined field value;
1130   a proxy MUST NOT change the order of these field values when
1131   forwarding a message.
1132</t>
1133<t><list>
1134  <t>
1135   Note: The "Set-Cookie" header as implemented in
1136   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1137   can occur multiple times, but does not use the list syntax, and thus cannot
1138   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1139   for details.) Also note that the Set-Cookie2 header specified in
1140   <xref target="RFC2965"/> does not share this problem.
1141  </t>
1142</list></t>
1143<t>
1144   Historically, HTTP header field values could be extended over multiple
1145   lines by preceding each extra line with at least one space or horizontal
1146   tab character (line folding). This specification deprecates such line
1147   folding except within the message/http media type
1148   (<xref target="internet.media.type.message.http"/>).
1149   HTTP/1.1 senders MUST NOT produce messages that include line folding
1150   (i.e., that contain any field-content that matches the obs-fold rule) unless
1151   the message is intended for packaging within the message/http media type.
1152   HTTP/1.1 recipients SHOULD accept line folding and replace any embedded
1153   obs-fold whitespace with a single SP prior to interpreting the field value
1154   or forwarding the message downstream.
1155</t>
1156<t>
1157   Historically, HTTP has allowed field content with text in the ISO-8859-1
1158   <xref target="ISO-8859-1"/> character encoding and supported other
1159   character sets only through use of <xref target="RFC2047"/> encoding.
1160   In practice, most HTTP header field values use only a subset of the
1161   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1162   header fields SHOULD limit their field values to US-ASCII characters.
1163   Recipients SHOULD treat other (obs-text) octets in field content as
1164   opaque data.
1165</t>
1166<t anchor="rule.comment">
1167 
1168 
1169   Comments can be included in some HTTP header fields by surrounding
1170   the comment text with parentheses. Comments are only allowed in
1171   fields containing "comment" as part of their field value definition.
1172</t>
1173<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
1174  comment        = "(" *( ctext / quoted-cpair / comment ) ")"
1175  ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
1176                 ; OWS / <VCHAR except "(", ")", and "\"> / obs-text
1177]]></artwork></figure>
1178<t anchor="rule.quoted-cpair">
1179 
1180   The backslash character ("\") can be used as a single-character
1181   quoting mechanism within comment constructs:
1182</t>
1183<figure><iref primary="true" item="Grammar" subitem="quoted-cpair"/><artwork type="abnf2616"><![CDATA[
1184  quoted-cpair    = "\" ( WSP / VCHAR / obs-text )
1185]]></artwork></figure>
1186<t>
1187   Producers SHOULD NOT escape characters that do not require escaping
1188   (i.e., other than the backslash character "\" and the parentheses "(" and
1189   ")").
1190</t>
1191</section>
1192
1193<section title="Message Body" anchor="message.body">
1194 
1195<t>
1196   The message-body (if any) of an HTTP message is used to carry the
1197   entity-body associated with the request or response. The message-body
1198   differs from the entity-body only when a transfer-coding has been
1199   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1200</t>
1201<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1202  message-body = entity-body
1203               / <entity-body encoded as per Transfer-Encoding>
1204]]></artwork></figure>
1205<t>
1206   Transfer-Encoding MUST be used to indicate any transfer-codings
1207   applied by an application to ensure safe and proper transfer of the
1208   message. Transfer-Encoding is a property of the message, not of the
1209   entity, and thus MAY be added or removed by any application along the
1210   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1211   when certain transfer-codings may be used.)
1212</t>
1213<t>
1214   The rules for when a message-body is allowed in a message differ for
1215   requests and responses.
1216</t>
1217<t>
1218   The presence of a message-body in a request is signaled by the
1219   inclusion of a Content-Length or Transfer-Encoding header field in
1220   the request's header fields.
1221   When a request message contains both a message-body of non-zero
1222   length and a method that does not define any semantics for that
1223   request message-body, then an origin server SHOULD either ignore
1224   the message-body or respond with an appropriate error message
1225   (e.g., 413).  A proxy or gateway, when presented the same request,
1226   SHOULD either forward the request inbound with the message-body or
1227   ignore the message-body when determining a response.
1228</t>
1229<t>
1230   For response messages, whether or not a message-body is included with
1231   a message is dependent on both the request method and the response
1232   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1233   MUST NOT include a message-body, even though the presence of entity-header
1234   fields might lead one to believe they do. All 1xx
1235   (Informational), 204 (No Content), and 304 (Not Modified) responses
1236   MUST NOT include a message-body. All other responses do include a
1237   message-body, although it MAY be of zero length.
1238</t>
1239</section>
1240
1241<section title="Message Length" anchor="message.length">
1242<t>
1243   The transfer-length of a message is the length of the message-body as
1244   it appears in the message; that is, after any transfer-codings have
1245   been applied. When a message-body is included with a message, the
1246   transfer-length of that body is determined by one of the following
1247   (in order of precedence):
1248</t>
1249<t>
1250  <list style="numbers">
1251    <t>
1252     Any response message which "MUST NOT" include a message-body (such
1253     as the 1xx, 204, and 304 responses and any response to a HEAD
1254     request) is always terminated by the first empty line after the
1255     header fields, regardless of the entity-header fields present in
1256     the message.
1257    </t>
1258    <t>
1259     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1260     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1261     is used, the transfer-length is defined by the use of this transfer-coding.
1262     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1263     is not present, the transfer-length is defined by the sender closing the connection.
1264    </t>
1265    <t>
1266     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1267     value in OCTETs represents both the entity-length and the
1268     transfer-length. The Content-Length header field MUST NOT be sent
1269     if these two lengths are different (i.e., if a Transfer-Encoding
1270     header field is present). If a message is received with both a
1271     Transfer-Encoding header field and a Content-Length header field,
1272     the latter MUST be ignored.
1273    </t>
1274    <t>
1275     If the message uses the media type "multipart/byteranges", and the
1276     transfer-length is not otherwise specified, then this self-delimiting
1277     media type defines the transfer-length. This media type
1278     MUST NOT be used unless the sender knows that the recipient can parse
1279     it; the presence in a request of a Range header with multiple byte-range
1280     specifiers from a HTTP/1.1 client implies that the client can parse
1281     multipart/byteranges responses.
1282    <list style="empty"><t>
1283       A range header might be forwarded by a HTTP/1.0 proxy that does not
1284       understand multipart/byteranges; in this case the server MUST
1285       delimit the message using methods defined in items 1, 3 or 5 of
1286       this section.
1287    </t></list>
1288    </t>
1289    <t>
1290     By the server closing the connection. (Closing the connection
1291     cannot be used to indicate the end of a request body, since that
1292     would leave no possibility for the server to send back a response.)
1293    </t>
1294  </list>
1295</t>
1296<t>
1297   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1298   containing a message-body MUST include a valid Content-Length header
1299   field unless the server is known to be HTTP/1.1 compliant. If a
1300   request contains a message-body and a Content-Length is not given,
1301   the server SHOULD respond with 400 (Bad Request) if it cannot
1302   determine the length of the message, or with 411 (Length Required) if
1303   it wishes to insist on receiving a valid Content-Length.
1304</t>
1305<t>
1306   All HTTP/1.1 applications that receive entities MUST accept the
1307   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1308   to be used for messages when the message length cannot be determined
1309   in advance.
1310</t>
1311<t>
1312   Messages MUST NOT include both a Content-Length header field and a
1313   transfer-coding. If the message does include a
1314   transfer-coding, the Content-Length MUST be ignored.
1315</t>
1316<t>
1317   When a Content-Length is given in a message where a message-body is
1318   allowed, its field value MUST exactly match the number of OCTETs in
1319   the message-body. HTTP/1.1 user agents MUST notify the user when an
1320   invalid length is received and detected.
1321</t>
1322</section>
1323
1324<section title="General Header Fields" anchor="general.header.fields">
1325 
1326<t>
1327   There are a few header fields which have general applicability for
1328   both request and response messages, but which do not apply to the
1329   entity being transferred. These header fields apply only to the
1330   message being transmitted.
1331</t>
1332<figure><iref primary="true" item="Grammar" subitem="general-header"/><artwork type="abnf2616"><![CDATA[
1333  general-header = Cache-Control            ; [Part6], Section 3.2
1334                 / Connection               ; Section 9.1
1335                 / Date                     ; Section 9.3
1336                 / Pragma                   ; [Part6], Section 3.4
1337                 / Trailer                  ; Section 9.6
1338                 / Transfer-Encoding        ; Section 9.7
1339                 / Upgrade                  ; Section 9.8
1340                 / Via                      ; Section 9.9
1341                 / Warning                  ; [Part6], Section 3.6
1342]]></artwork></figure>
1343<t>
1344   General-header field names can be extended reliably only in
1345   combination with a change in the protocol version. However, new or
1346   experimental header fields may be given the semantics of general
1347   header fields if all parties in the communication recognize them to
1348   be general-header fields. Unrecognized header fields are treated as
1349   entity-header fields.
1350</t>
1351</section>
1352</section>
1353
1354<section title="Request" anchor="request">
1355 
1356<t>
1357   A request message from a client to a server includes, within the
1358   first line of that message, the method to be applied to the resource,
1359   the identifier of the resource, and the protocol version in use.
1360</t>
1361<!--                 Host                      ; should be moved here eventually -->
1362<figure><iref primary="true" item="Grammar" subitem="Request"/><artwork type="abnf2616"><![CDATA[
1363  Request       = Request-Line              ; Section 4.1
1364                  *(( general-header        ; Section 3.5
1365                   / request-header         ; [Part2], Section 3
1366                   / entity-header ) CRLF ) ; [Part3], Section 3.1
1367                  CRLF
1368                  [ message-body ]          ; Section 3.3
1369]]></artwork></figure>
1370
1371<section title="Request-Line" anchor="request-line">
1372 
1373<t>
1374   The Request-Line begins with a method token, followed by the
1375   request-target and the protocol version, and ending with CRLF. The
1376   elements are separated by SP characters. No CR or LF is allowed
1377   except in the final CRLF sequence.
1378</t>
1379<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1380  Request-Line   = Method SP request-target SP HTTP-Version CRLF
1381]]></artwork></figure>
1382
1383<section title="Method" anchor="method">
1384 
1385<t>
1386   The Method  token indicates the method to be performed on the
1387   resource identified by the request-target. The method is case-sensitive.
1388</t>
1389<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
1390  Method         = token
1391]]></artwork></figure>
1392</section>
1393
1394<section title="request-target" anchor="request-target">
1395 
1396<t>
1397   The request-target
1398   identifies the resource upon which to apply the request.
1399</t>
1400<figure><iref primary="true" item="Grammar" subitem="request-target"/><artwork type="abnf2616"><![CDATA[
1401  request-target = "*"
1402                 / absolute-URI
1403                 / ( path-absolute [ "?" query ] )
1404                 / authority
1405]]></artwork></figure>
1406<t>
1407   The four options for request-target are dependent on the nature of the
1408   request.
1409</t>   
1410<t>
1411   The asterisk "*" means that the request does not apply to a
1412   particular resource, but to the server itself, and is only allowed
1413   when the method used does not necessarily apply to a resource. One
1414   example would be
1415</t>
1416<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1417  OPTIONS * HTTP/1.1
1418  ]]></artwork></figure>
1419<t>
1420   The absolute-URI form is REQUIRED when the request is being made to a
1421   proxy. The proxy is requested to forward the request or service it
1422   from a valid cache, and return the response. Note that the proxy MAY
1423   forward the request on to another proxy or directly to the server
1424   specified by the absolute-URI. In order to avoid request loops, a
1425   proxy MUST be able to recognize all of its server names, including
1426   any aliases, local variations, and the numeric IP address. An example
1427   Request-Line would be:
1428</t>
1429<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1430  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1431  ]]></artwork></figure>
1432<t>
1433   To allow for transition to absolute-URIs in all requests in future
1434   versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
1435   form in requests, even though HTTP/1.1 clients will only generate
1436   them in requests to proxies.
1437</t>
1438<t>
1439   The authority form is only used by the CONNECT method (Section 7.9 of <xref target="Part2"/>).
1440</t>
1441<t>
1442   The most common form of request-target is that used to identify a
1443   resource on an origin server or gateway. In this case the absolute
1444   path of the URI MUST be transmitted (see <xref target="http.uri"/>, path-absolute) as
1445   the request-target, and the network location of the URI (authority) MUST
1446   be transmitted in a Host header field. For example, a client wishing
1447   to retrieve the resource above directly from the origin server would
1448   create a TCP connection to port 80 of the host "www.example.org" and send
1449   the lines:
1450</t>
1451<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1452  GET /pub/WWW/TheProject.html HTTP/1.1
1453  Host: www.example.org
1454  ]]></artwork></figure>
1455<t>
1456   followed by the remainder of the Request. Note that the absolute path
1457   cannot be empty; if none is present in the original URI, it MUST be
1458   given as "/" (the server root).
1459</t>
1460<t>
1461   If a proxy receives a request without any path in the request-target and
1462   the method specified is capable of supporting the asterisk form of
1463   request-target, then the last proxy on the request chain MUST forward the
1464   request with "*" as the final request-target.
1465</t>
1466<figure><preamble>   
1467   For example, the request
1468</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1469  OPTIONS http://www.example.org:8001 HTTP/1.1
1470  ]]></artwork></figure>
1471<figure><preamble>   
1472  would be forwarded by the proxy as
1473</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1474  OPTIONS * HTTP/1.1
1475  Host: www.example.org:8001
1476  ]]></artwork>
1477<postamble>
1478   after connecting to port 8001 of host "www.example.org".
1479</postamble>
1480</figure>
1481<t>
1482   The request-target is transmitted in the format specified in
1483   <xref target="http.uri"/>. If the request-target is percent-encoded
1484   (<xref target="RFC3986"/>, Section 2.1), the origin server
1485   MUST decode the request-target in order to
1486   properly interpret the request. Servers SHOULD respond to invalid
1487   request-targets with an appropriate status code.
1488</t>
1489<t>
1490   A transparent proxy MUST NOT rewrite the "path-absolute" part of the
1491   received request-target when forwarding it to the next inbound server,
1492   except as noted above to replace a null path-absolute with "/" or "*".
1493</t>
1494<t><list>
1495  <t>
1496    Note: The "no rewrite" rule prevents the proxy from changing the
1497    meaning of the request when the origin server is improperly using
1498    a non-reserved URI character for a reserved purpose.  Implementors
1499    should be aware that some pre-HTTP/1.1 proxies have been known to
1500    rewrite the request-target.
1501  </t>
1502</list></t>
1503<t>
1504   HTTP does not place a pre-defined limit on the length of a request-target.
1505   A server MUST be prepared to receive URIs of unbounded length and
1506   respond with the 414 (URI Too Long) status if the received
1507   request-target would be longer than the server wishes to handle
1508   (see Section 8.4.15 of <xref target="Part2"/>).
1509</t>
1510<t>
1511   Various ad-hoc limitations on request-target length are found in practice.
1512   It is RECOMMENDED that all HTTP senders and recipients support
1513   request-target lengths of 8000 or more OCTETs.
1514</t>
1515<t><list>
1516  <t>
1517    Note: Fragments (<xref target="RFC3986"/>, Section 3.5)
1518    are not part of the request-target and thus will not be transmitted
1519    in an HTTP request.
1520  </t>
1521</list></t>
1522</section>
1523</section>
1524
1525<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1526<t>
1527   The exact resource identified by an Internet request is determined by
1528   examining both the request-target and the Host header field.
1529</t>
1530<t>
1531   An origin server that does not allow resources to differ by the
1532   requested host MAY ignore the Host header field value when
1533   determining the resource identified by an HTTP/1.1 request. (But see
1534   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1535   for other requirements on Host support in HTTP/1.1.)
1536</t>
1537<t>
1538   An origin server that does differentiate resources based on the host
1539   requested (sometimes referred to as virtual hosts or vanity host
1540   names) MUST use the following rules for determining the requested
1541   resource on an HTTP/1.1 request:
1542  <list style="numbers">
1543    <t>If request-target is an absolute-URI, the host is part of the
1544     request-target. Any Host header field value in the request MUST be
1545     ignored.</t>
1546    <t>If the request-target is not an absolute-URI, and the request includes
1547     a Host header field, the host is determined by the Host header
1548     field value.</t>
1549    <t>If the host as determined by rule 1 or 2 is not a valid host on
1550     the server, the response MUST be a 400 (Bad Request) error message.</t>
1551  </list>
1552</t>
1553<t>
1554   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1555   attempt to use heuristics (e.g., examination of the URI path for
1556   something unique to a particular host) in order to determine what
1557   exact resource is being requested.
1558</t>
1559</section>
1560
1561<section title="Effective Request URI" anchor="effective.request.uri">
1562  <iref primary="true" item="Effective Request URI"/>
1563<t>
1564   HTTP requests often do not carry the absolute URI (<xref target="RFC3986"/>, Section 4.3)
1565   for the resource they are intended for; instead, the value needs to be inferred from the
1566   request-target, Host header and other context. The result of this process is
1567   the "Effective Request URI".
1568</t>
1569<t>
1570   If the request-target is an absolute-URI, then the Effective Request URI is
1571   the request-target.
1572</t>
1573<t>
1574   If the request-target uses the path-absolute (plus optional query) syntax
1575   or if it is just the asterisk "*", then the Effective Request URI is
1576   constructed by concatenating
1577</t>
1578<t>
1579  <list style="symbols">
1580    <t>
1581      the scheme name: "http" if the request was received over an insecure
1582      TCP connection, or "https" when received over SSL/TLS-secured TCP
1583      connection,
1584    </t>
1585    <t>
1586      the character sequence "://",
1587    </t>
1588    <t>
1589      the authority component, as specified in the Host header
1590      (<xref target="header.host"/>) and determined by the rules in
1591      <xref target="the.resource.identified.by.a.request"/>,
1592      <cref anchor="effrequri-nohost" source="jre">Do we need to include the handling of missing hosts in HTTP/1.0 messages, as
1593      described in Section 4.2?</cref>
1594      and
1595    </t>
1596    <t>
1597      the request-target obtained from the Request-Line, unless the
1598      request-target is just the asterisk "*".
1599    </t>
1600  </list>
1601</t>
1602<t>
1603   Otherwise, when request-target uses the authority form, the Effective
1604   Request URI is undefined.
1605</t>
1606<figure>
1607<preamble>
1608   Example 1: the Effective Request URI for the message
1609</preamble> 
1610<artwork type="example"><![CDATA[
1611  GET /pub/WWW/TheProject.html HTTP/1.1
1612  Host: www.example.org:8080
1613  ]]></artwork>
1614<postamble>
1615  (received over an insecure TCP connection) is "http", plus "://", plus the
1616  authority component "www.example.org:8080", plus the request-target
1617  "/pub/WWW/TheProject.html", thus
1618  "http://www.example.org:8080/pub/WWW/TheProject.html".
1619</postamble>
1620</figure>
1621<figure>
1622<preamble>
1623   Example 2: the Effective Request URI for the message
1624</preamble> 
1625<artwork type="example"><![CDATA[
1626  GET * HTTP/1.1
1627  Host: www.example.org
1628  ]]></artwork>
1629<postamble>
1630  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1631  authority component "www.example.org", thus "https://www.example.org".
1632</postamble>
1633</figure>
1634<t>
1635   Effective Request URIs are compared using the rules described in
1636   <xref target="uri.comparison"/>, except that empty path components MUST NOT
1637   be treated as equivalent to an absolute path of "/".
1638</t> 
1639</section>
1640
1641</section>
1642
1643
1644<section title="Response" anchor="response">
1645 
1646<t>
1647   After receiving and interpreting a request message, a server responds
1648   with an HTTP response message.
1649</t>
1650<figure><iref primary="true" item="Grammar" subitem="Response"/><artwork type="abnf2616"><![CDATA[
1651  Response      = Status-Line               ; Section 5.1
1652                  *(( general-header        ; Section 3.5
1653                   / response-header        ; [Part2], Section 5
1654                   / entity-header ) CRLF ) ; [Part3], Section 3.1
1655                  CRLF
1656                  [ message-body ]          ; Section 3.3
1657]]></artwork></figure>
1658
1659<section title="Status-Line" anchor="status-line">
1660 
1661<t>
1662   The first line of a Response message is the Status-Line, consisting
1663   of the protocol version followed by a numeric status code and its
1664   associated textual phrase, with each element separated by SP
1665   characters. No CR or LF is allowed except in the final CRLF sequence.
1666</t>
1667<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1668  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1669]]></artwork></figure>
1670
1671<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1672 
1673 
1674<t>
1675   The Status-Code element is a 3-digit integer result code of the
1676   attempt to understand and satisfy the request. These codes are fully
1677   defined in Section 8 of <xref target="Part2"/>.  The Reason Phrase exists for the sole
1678   purpose of providing a textual description associated with the numeric
1679   status code, out of deference to earlier Internet application protocols
1680   that were more frequently used with interactive text clients.
1681   A client SHOULD ignore the content of the Reason Phrase.
1682</t>
1683<t>
1684   The first digit of the Status-Code defines the class of response. The
1685   last two digits do not have any categorization role. There are 5
1686   values for the first digit:
1687  <list style="symbols">
1688    <t>
1689      1xx: Informational - Request received, continuing process
1690    </t>
1691    <t>
1692      2xx: Success - The action was successfully received,
1693        understood, and accepted
1694    </t>
1695    <t>
1696      3xx: Redirection - Further action must be taken in order to
1697        complete the request
1698    </t>
1699    <t>
1700      4xx: Client Error - The request contains bad syntax or cannot
1701        be fulfilled
1702    </t>
1703    <t>
1704      5xx: Server Error - The server failed to fulfill an apparently
1705        valid request
1706    </t>
1707  </list>
1708</t>
1709<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[
1710  Status-Code    = 3DIGIT
1711  Reason-Phrase  = *( WSP / VCHAR / obs-text )
1712]]></artwork></figure>
1713</section>
1714</section>
1715
1716</section>
1717
1718
1719<section title="Protocol Parameters" anchor="protocol.parameters">
1720
1721<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1722 
1723<t>
1724   HTTP applications have historically allowed three different formats
1725   for the representation of date/time stamps.
1726</t>
1727<t>
1728   The first format is preferred as an Internet standard and represents
1729   a fixed-length subset of that defined by <xref target="RFC1123"/>:
1730</t>
1731<figure><artwork type="example"><![CDATA[
1732  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1733  ]]></artwork></figure>
1734<t>
1735   The other formats are described here only for compatibility with obsolete
1736   implementations.
1737</t>
1738<figure><artwork type="example"><![CDATA[
1739  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1740  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1741  ]]></artwork></figure>
1742<t>
1743   HTTP/1.1 clients and servers that parse the date value MUST accept
1744   all three formats (for compatibility with HTTP/1.0), though they MUST
1745   only generate the RFC 1123 format for representing HTTP-date values
1746   in header fields. See <xref target="tolerant.applications"/> for further information.
1747</t>
1748<t>
1749   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
1750   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1751   equal to UTC (Coordinated Universal Time). This is indicated in the
1752   first two formats by the inclusion of "GMT" as the three-letter
1753   abbreviation for time zone, and MUST be assumed when reading the
1754   asctime format. HTTP-date is case sensitive and MUST NOT include
1755   additional whitespace beyond that specifically included as SP in the
1756   grammar.
1757</t>
1758<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><artwork type="abnf2616"><![CDATA[
1759  HTTP-date    = rfc1123-date / obs-date
1760]]></artwork></figure>
1761<t anchor="preferred.date.format">
1762 
1763 
1764 
1765 
1766 
1767 
1768 
1769 
1770 
1771 
1772  Preferred format:
1773</t>
1774<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[
1775  rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
1776
1777  day-name     = %x4D.6F.6E ; "Mon", case-sensitive
1778               / %x54.75.65 ; "Tue", case-sensitive
1779               / %x57.65.64 ; "Wed", case-sensitive
1780               / %x54.68.75 ; "Thu", case-sensitive
1781               / %x46.72.69 ; "Fri", case-sensitive
1782               / %x53.61.74 ; "Sat", case-sensitive
1783               / %x53.75.6E ; "Sun", case-sensitive
1784               
1785  date1        = day SP month SP year
1786               ; e.g., 02 Jun 1982
1787
1788  day          = 2DIGIT
1789  month        = %x4A.61.6E ; "Jan", case-sensitive
1790               / %x46.65.62 ; "Feb", case-sensitive
1791               / %x4D.61.72 ; "Mar", case-sensitive
1792               / %x41.70.72 ; "Apr", case-sensitive
1793               / %x4D.61.79 ; "May", case-sensitive
1794               / %x4A.75.6E ; "Jun", case-sensitive
1795               / %x4A.75.6C ; "Jul", case-sensitive
1796               / %x41.75.67 ; "Aug", case-sensitive
1797               / %x53.65.70 ; "Sep", case-sensitive
1798               / %x4F.63.74 ; "Oct", case-sensitive
1799               / %x4E.6F.76 ; "Nov", case-sensitive
1800               / %x44.65.63 ; "Dec", case-sensitive
1801  year         = 4DIGIT
1802
1803  GMT   = %x47.4D.54 ; "GMT", case-sensitive
1804
1805  time-of-day  = hour ":" minute ":" second
1806                 ; 00:00:00 - 23:59:59
1807                 
1808  hour         = 2DIGIT               
1809  minute       = 2DIGIT               
1810  second       = 2DIGIT               
1811]]></artwork></figure>
1812<t>
1813  The semantics of <xref target="preferred.date.format" format="none">day-name</xref>, <xref target="preferred.date.format" format="none">day</xref>,
1814  <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
1815  same as those defined for the RFC 5322 constructs
1816  with the corresponding name (<xref target="RFC5322"/>, Section 3.3).
1817</t>
1818<t anchor="obsolete.date.formats">
1819 
1820 
1821 
1822 
1823 
1824 
1825 
1826 
1827  Obsolete formats:
1828</t>
1829<figure><iref primary="true" item="Grammar" subitem="obs-date"/><artwork type="abnf2616"><![CDATA[
1830  obs-date     = rfc850-date / asctime-date
1831]]></artwork></figure>
1832<figure><iref primary="true" item="Grammar" subitem="rfc850-date"/><artwork type="abnf2616"><![CDATA[
1833  rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
1834  date2        = day "-" month "-" 2DIGIT
1835                 ; day-month-year (e.g., 02-Jun-82)
1836
1837  day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
1838         / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
1839         / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
1840         / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
1841         / %x46.72.69.64.61.79 ; "Friday", case-sensitive
1842         / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
1843         / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
1844]]></artwork></figure>
1845<figure><iref primary="true" item="Grammar" subitem="asctime-date"/><artwork type="abnf2616"><![CDATA[
1846  asctime-date = day-name SP date3 SP time-of-day SP year
1847  date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
1848                 ; month day (e.g., Jun  2)
1849]]></artwork></figure>
1850<t><list>
1851  <t>
1852    Note: Recipients of date values are encouraged to be robust in
1853    accepting date values that may have been sent by non-HTTP
1854    applications, as is sometimes the case when retrieving or posting
1855    messages via proxies/gateways to SMTP or NNTP.
1856  </t>
1857</list></t>
1858<t><list>
1859  <t>
1860    Note: HTTP requirements for the date/time stamp format apply only
1861    to their usage within the protocol stream. Clients and servers are
1862    not required to use these formats for user presentation, request
1863    logging, etc.
1864  </t>
1865</list></t>
1866</section>
1867
1868<section title="Transfer Codings" anchor="transfer.codings">
1869 
1870 
1871<t>
1872   Transfer-coding values are used to indicate an encoding
1873   transformation that has been, can be, or may need to be applied to an
1874   entity-body in order to ensure "safe transport" through the network.
1875   This differs from a content coding in that the transfer-coding is a
1876   property of the message, not of the original entity.
1877</t>
1878<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
1879  transfer-coding         = "chunked" ; Section 6.2.1
1880                          / "compress" ; Section 6.2.2.1
1881                          / "deflate" ; Section 6.2.2.2
1882                          / "gzip" ; Section 6.2.2.3
1883                          / transfer-extension
1884  transfer-extension      = token *( OWS ";" OWS transfer-parameter )
1885]]></artwork></figure>
1886<t anchor="rule.parameter">
1887 
1888 
1889 
1890   Parameters are in  the form of attribute/value pairs.
1891</t>
1892<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[
1893  transfer-parameter      = attribute BWS "=" BWS value
1894  attribute               = token
1895  value                   = word
1896]]></artwork></figure>
1897<t>
1898   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1899   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1900   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1901</t>
1902<t>
1903   Whenever a transfer-coding is applied to a message-body, the set of
1904   transfer-codings MUST include "chunked", unless the message indicates it
1905   is terminated by closing the connection. When the "chunked" transfer-coding
1906   is used, it MUST be the last transfer-coding applied to the
1907   message-body. The "chunked" transfer-coding MUST NOT be applied more
1908   than once to a message-body. These rules allow the recipient to
1909   determine the transfer-length of the message (<xref target="message.length"/>).
1910</t>
1911<t>
1912   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1913   MIME, which were designed to enable safe transport of binary data over a
1914   7-bit transport service (<xref target="RFC2045"/>, Section 6).
1915   However, safe transport
1916   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1917   the only unsafe characteristic of message-bodies is the difficulty in
1918   determining the exact body length (<xref target="message.length"/>), or the desire to
1919   encrypt data over a shared transport.
1920</t>
1921<t>
1922   A server which receives an entity-body with a transfer-coding it does
1923   not understand SHOULD return 501 (Not Implemented), and close the
1924   connection. A server MUST NOT send transfer-codings to an HTTP/1.0
1925   client.
1926</t>
1927
1928<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1929  <iref item="chunked (Coding Format)"/>
1930  <iref item="Coding Format" subitem="chunked"/>
1931 
1932 
1933 
1934 
1935 
1936 
1937 
1938 
1939 
1940 
1941 
1942<t>
1943   The chunked encoding modifies the body of a message in order to
1944   transfer it as a series of chunks, each with its own size indicator,
1945   followed by an OPTIONAL trailer containing entity-header fields. This
1946   allows dynamically produced content to be transferred along with the
1947   information necessary for the recipient to verify that it has
1948   received the full message.
1949</t>
1950<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[
1951  Chunked-Body   = *chunk
1952                   last-chunk
1953                   trailer-part
1954                   CRLF
1955 
1956  chunk          = chunk-size *WSP [ chunk-ext ] CRLF
1957                   chunk-data CRLF
1958  chunk-size     = 1*HEXDIG
1959  last-chunk     = 1*("0") *WSP [ chunk-ext ] CRLF
1960 
1961  chunk-ext      = *( ";" *WSP chunk-ext-name
1962                      [ "=" chunk-ext-val ] *WSP )
1963  chunk-ext-name = token
1964  chunk-ext-val  = token / quoted-str-nf
1965  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
1966  trailer-part   = *( entity-header CRLF )
1967 
1968  quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
1969                 ; like quoted-string, but disallowing line folding
1970  qdtext-nf      = WSP / %x21 / %x23-5B / %x5D-7E / obs-text
1971                 ; WSP / <VCHAR except DQUOTE and "\"> / obs-text
1972]]></artwork></figure>
1973<t>
1974   The chunk-size field is a string of hex digits indicating the size of
1975   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1976   zero, followed by the trailer, which is terminated by an empty line.
1977</t>
1978<t>
1979   The trailer allows the sender to include additional HTTP header
1980   fields at the end of the message. The Trailer header field can be
1981   used to indicate which header fields are included in a trailer (see
1982   <xref target="header.trailer"/>).
1983</t>
1984<t>
1985   A server using chunked transfer-coding in a response MUST NOT use the
1986   trailer for any header fields unless at least one of the following is
1987   true:
1988  <list style="numbers">
1989    <t>the request included a TE header field that indicates "trailers" is
1990     acceptable in the transfer-coding of the  response, as described in
1991     <xref target="header.te"/>; or,</t>
1992
1993    <t>the server is the origin server for the response, the trailer
1994     fields consist entirely of optional metadata, and the recipient
1995     could use the message (in a manner acceptable to the origin server)
1996     without receiving this metadata.  In other words, the origin server
1997     is willing to accept the possibility that the trailer fields might
1998     be silently discarded along the path to the client.</t>
1999  </list>
2000</t>
2001<t>
2002   This requirement prevents an interoperability failure when the
2003   message is being received by an HTTP/1.1 (or later) proxy and
2004   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2005   compliance with the protocol would have necessitated a possibly
2006   infinite buffer on the proxy.
2007</t>
2008<t>
2009   A process for decoding the "chunked" transfer-coding
2010   can be represented in pseudo-code as:
2011</t>
2012<figure><artwork type="code"><![CDATA[
2013  length := 0
2014  read chunk-size, chunk-ext (if any) and CRLF
2015  while (chunk-size > 0) {
2016     read chunk-data and CRLF
2017     append chunk-data to entity-body
2018     length := length + chunk-size
2019     read chunk-size and CRLF
2020  }
2021  read entity-header
2022  while (entity-header not empty) {
2023     append entity-header to existing header fields
2024     read entity-header
2025  }
2026  Content-Length := length
2027  Remove "chunked" from Transfer-Encoding
2028]]></artwork></figure>
2029<t>
2030   All HTTP/1.1 applications MUST be able to receive and decode the
2031   "chunked" transfer-coding, and MUST ignore chunk-ext extensions
2032   they do not understand.
2033</t>
2034</section>
2035
2036<section title="Compression Codings" anchor="compression.codings">
2037<t>
2038   The codings defined below can be used to compress the payload of a
2039   message.
2040</t>
2041<t><list><t>
2042   Note: Use of program names for the identification of encoding formats
2043   is not desirable and is discouraged for future encodings. Their
2044   use here is representative of historical practice, not good
2045   design.
2046</t></list></t>
2047<t><list><t>
2048   Note: For compatibility with previous implementations of HTTP,
2049   applications SHOULD consider "x-gzip" and "x-compress" to be
2050   equivalent to "gzip" and "compress" respectively.
2051</t></list></t>
2052
2053<section title="Compress Coding" anchor="compress.coding">
2054<iref item="compress (Coding Format)"/>
2055<iref item="Coding Format" subitem="compress"/>
2056<t>
2057   The "compress" format is produced by the common UNIX file compression
2058   program "compress". This format is an adaptive Lempel-Ziv-Welch
2059   coding (LZW).
2060</t>
2061</section>
2062
2063<section title="Deflate Coding" anchor="deflate.coding">
2064<iref item="deflate (Coding Format)"/>
2065<iref item="Coding Format" subitem="deflate"/>
2066<t>
2067   The "deflate" format is defined as the "deflate" compression mechanism
2068   (described in <xref target="RFC1951"/>) used inside the "zlib"
2069   data format (<xref target="RFC1950"/>).
2070</t>
2071<t><list>
2072  <t>
2073    Note: Some incorrect implementations send the "deflate"
2074    compressed data without the zlib wrapper.
2075   </t>
2076</list></t>
2077</section>
2078
2079<section title="Gzip Coding" anchor="gzip.coding">
2080<iref item="gzip (Coding Format)"/>
2081<iref item="Coding Format" subitem="gzip"/>
2082<t>
2083   The "gzip" format is produced by the file compression program
2084   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2085   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2086</t>
2087</section>
2088
2089</section>
2090
2091<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2092<t>
2093   The HTTP Transfer Coding Registry defines the name space for the transfer
2094   coding names.
2095</t>
2096<t>
2097   Registrations MUST include the following fields:
2098   <list style="symbols">
2099     <t>Name</t>
2100     <t>Description</t>
2101     <t>Pointer to specification text</t>
2102   </list>
2103</t>
2104<t>
2105   Names of transfer codings MUST NOT overlap with names of content codings
2106   (Section 2.2 of <xref target="Part3"/>), unless the encoding transformation is identical (as it
2107   is the case for the compression codings defined in
2108   <xref target="compression.codings"/>).
2109</t>
2110<t>
2111   Values to be added to this name space require expert review and a specification
2112   (see "Expert Review" and "Specification Required" in
2113   Section 4.1 of <xref target="RFC5226"/>), and MUST
2114   conform to the purpose of transfer coding defined in this section.
2115</t>
2116<t>
2117   The registry itself is maintained at
2118   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2119</t>
2120</section>
2121</section>
2122
2123<section title="Product Tokens" anchor="product.tokens">
2124 
2125 
2126<t>
2127   Product tokens are used to allow communicating applications to
2128   identify themselves by software name and version. Most fields using
2129   product tokens also allow sub-products which form a significant part
2130   of the application to be listed, separated by whitespace. By
2131   convention, the products are listed in order of their significance
2132   for identifying the application.
2133</t>
2134<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
2135  product         = token ["/" product-version]
2136  product-version = token
2137]]></artwork></figure>
2138<t>
2139   Examples:
2140</t>
2141<figure><artwork type="example"><![CDATA[
2142  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2143  Server: Apache/0.8.4
2144]]></artwork></figure>
2145<t>
2146   Product tokens SHOULD be short and to the point. They MUST NOT be
2147   used for advertising or other non-essential information. Although any
2148   token character MAY appear in a product-version, this token SHOULD
2149   only be used for a version identifier (i.e., successive versions of
2150   the same product SHOULD only differ in the product-version portion of
2151   the product value).
2152</t>
2153</section>
2154
2155<section title="Quality Values" anchor="quality.values">
2156 
2157<t>
2158   Both transfer codings (TE request header, <xref target="header.te"/>)
2159   and content negotiation (Section 4 of <xref target="Part3"/>) use short "floating point"
2160   numbers to indicate the relative importance ("weight") of various
2161   negotiable parameters.  A weight is normalized to a real number in
2162   the range 0 through 1, where 0 is the minimum and 1 the maximum
2163   value. If a parameter has a quality value of 0, then content with
2164   this parameter is "not acceptable" for the client. HTTP/1.1
2165   applications MUST NOT generate more than three digits after the
2166   decimal point. User configuration of these values SHOULD also be
2167   limited in this fashion.
2168</t>
2169<figure><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
2170  qvalue         = ( "0" [ "." 0*3DIGIT ] )
2171                 / ( "1" [ "." 0*3("0") ] )
2172]]></artwork></figure>
2173<t><list>
2174  <t>
2175     Note: "Quality values" is a misnomer, since these values merely represent
2176     relative degradation in desired quality.
2177  </t>
2178</list></t>
2179</section>
2180
2181</section>
2182
2183<section title="Connections" anchor="connections">
2184
2185<section title="Persistent Connections" anchor="persistent.connections">
2186
2187<section title="Purpose" anchor="persistent.purpose">
2188<t>
2189   Prior to persistent connections, a separate TCP connection was
2190   established to fetch each URL, increasing the load on HTTP servers
2191   and causing congestion on the Internet. The use of inline images and
2192   other associated data often requires a client to make multiple
2193   requests of the same server in a short amount of time. Analysis of
2194   these performance problems and results from a prototype
2195   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2196   measurements of actual HTTP/1.1 implementations show good
2197   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2198   T/TCP <xref target="Tou1998"/>.
2199</t>
2200<t>
2201   Persistent HTTP connections have a number of advantages:
2202  <list style="symbols">
2203      <t>
2204        By opening and closing fewer TCP connections, CPU time is saved
2205        in routers and hosts (clients, servers, proxies, gateways,
2206        tunnels, or caches), and memory used for TCP protocol control
2207        blocks can be saved in hosts.
2208      </t>
2209      <t>
2210        HTTP requests and responses can be pipelined on a connection.
2211        Pipelining allows a client to make multiple requests without
2212        waiting for each response, allowing a single TCP connection to
2213        be used much more efficiently, with much lower elapsed time.
2214      </t>
2215      <t>
2216        Network congestion is reduced by reducing the number of packets
2217        caused by TCP opens, and by allowing TCP sufficient time to
2218        determine the congestion state of the network.
2219      </t>
2220      <t>
2221        Latency on subsequent requests is reduced since there is no time
2222        spent in TCP's connection opening handshake.
2223      </t>
2224      <t>
2225        HTTP can evolve more gracefully, since errors can be reported
2226        without the penalty of closing the TCP connection. Clients using
2227        future versions of HTTP might optimistically try a new feature,
2228        but if communicating with an older server, retry with old
2229        semantics after an error is reported.
2230      </t>
2231    </list>
2232</t>
2233<t>
2234   HTTP implementations SHOULD implement persistent connections.
2235</t>
2236</section>
2237
2238<section title="Overall Operation" anchor="persistent.overall">
2239<t>
2240   A significant difference between HTTP/1.1 and earlier versions of
2241   HTTP is that persistent connections are the default behavior of any
2242   HTTP connection. That is, unless otherwise indicated, the client
2243   SHOULD assume that the server will maintain a persistent connection,
2244   even after error responses from the server.
2245</t>
2246<t>
2247   Persistent connections provide a mechanism by which a client and a
2248   server can signal the close of a TCP connection. This signaling takes
2249   place using the Connection header field (<xref target="header.connection"/>). Once a close
2250   has been signaled, the client MUST NOT send any more requests on that
2251   connection.
2252</t>
2253
2254<section title="Negotiation" anchor="persistent.negotiation">
2255<t>
2256   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
2257   maintain a persistent connection unless a Connection header including
2258   the connection-token "close" was sent in the request. If the server
2259   chooses to close the connection immediately after sending the
2260   response, it SHOULD send a Connection header including the
2261   connection-token "close".
2262</t>
2263<t>
2264   An HTTP/1.1 client MAY expect a connection to remain open, but would
2265   decide to keep it open based on whether the response from a server
2266   contains a Connection header with the connection-token close. In case
2267   the client does not want to maintain a connection for more than that
2268   request, it SHOULD send a Connection header including the
2269   connection-token close.
2270</t>
2271<t>
2272   If either the client or the server sends the close token in the
2273   Connection header, that request becomes the last one for the
2274   connection.
2275</t>
2276<t>
2277   Clients and servers SHOULD NOT  assume that a persistent connection is
2278   maintained for HTTP versions less than 1.1 unless it is explicitly
2279   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2280   compatibility with HTTP/1.0 clients.
2281</t>
2282<t>
2283   In order to remain persistent, all messages on the connection MUST
2284   have a self-defined message length (i.e., one not defined by closure
2285   of the connection), as described in <xref target="message.length"/>.
2286</t>
2287</section>
2288
2289<section title="Pipelining" anchor="pipelining">
2290<t>
2291   A client that supports persistent connections MAY "pipeline" its
2292   requests (i.e., send multiple requests without waiting for each
2293   response). A server MUST send its responses to those requests in the
2294   same order that the requests were received.
2295</t>
2296<t>
2297   Clients which assume persistent connections and pipeline immediately
2298   after connection establishment SHOULD be prepared to retry their
2299   connection if the first pipelined attempt fails. If a client does
2300   such a retry, it MUST NOT pipeline before it knows the connection is
2301   persistent. Clients MUST also be prepared to resend their requests if
2302   the server closes the connection before sending all of the
2303   corresponding responses.
2304</t>
2305<t>
2306   Clients SHOULD NOT  pipeline requests using non-idempotent methods or
2307   non-idempotent sequences of methods (see Section 7.1.2 of <xref target="Part2"/>). Otherwise, a
2308   premature termination of the transport connection could lead to
2309   indeterminate results. A client wishing to send a non-idempotent
2310   request SHOULD wait to send that request until it has received the
2311   response status for the previous request.
2312</t>
2313</section>
2314</section>
2315
2316<section title="Proxy Servers" anchor="persistent.proxy">
2317<t>
2318   It is especially important that proxies correctly implement the
2319   properties of the Connection header field as specified in <xref target="header.connection"/>.
2320</t>
2321<t>
2322   The proxy server MUST signal persistent connections separately with
2323   its clients and the origin servers (or other proxy servers) that it
2324   connects to. Each persistent connection applies to only one transport
2325   link.
2326</t>
2327<t>
2328   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
2329   with an HTTP/1.0 client (but see Section 19.7.1 of <xref target="RFC2068"/>
2330   for information and discussion of the problems with the Keep-Alive header
2331   implemented by many HTTP/1.0 clients).
2332</t>
2333
2334<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2335<!--<t>
2336  <cref anchor="TODO-end-to-end" source="jre">
2337    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2338    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2339  </cref>
2340</t>-->
2341<t>
2342   For the purpose of defining the behavior of caches and non-caching
2343   proxies, we divide HTTP headers into two categories:
2344  <list style="symbols">
2345      <t>End-to-end headers, which are  transmitted to the ultimate
2346        recipient of a request or response. End-to-end headers in
2347        responses MUST be stored as part of a cache entry and MUST be
2348        transmitted in any response formed from a cache entry.</t>
2349
2350      <t>Hop-by-hop headers, which are meaningful only for a single
2351        transport-level connection, and are not stored by caches or
2352        forwarded by proxies.</t>
2353  </list>
2354</t>
2355<t>
2356   The following HTTP/1.1 headers are hop-by-hop headers:
2357  <list style="symbols">
2358      <t>Connection</t>
2359      <t>Keep-Alive</t>
2360      <t>Proxy-Authenticate</t>
2361      <t>Proxy-Authorization</t>
2362      <t>TE</t>
2363      <t>Trailer</t>
2364      <t>Transfer-Encoding</t>
2365      <t>Upgrade</t>
2366  </list>
2367</t>
2368<t>
2369   All other headers defined by HTTP/1.1 are end-to-end headers.
2370</t>
2371<t>
2372   Other hop-by-hop headers MUST be listed in a Connection header
2373   (<xref target="header.connection"/>).
2374</t>
2375</section>
2376
2377<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2378<!--<t>
2379  <cref anchor="TODO-non-mod-headers" source="jre">
2380    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2381    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2382  </cref>
2383</t>-->
2384<t>
2385   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2386   value of certain end-to-end headers. A transparent proxy SHOULD NOT
2387   modify an end-to-end header unless the definition of that header requires
2388   or specifically allows that.
2389</t>
2390<t>
2391   A transparent proxy MUST NOT modify any of the following fields in a
2392   request or response, and it MUST NOT add any of these fields if not
2393   already present:
2394  <list style="symbols">
2395      <t>Content-Location</t>
2396      <t>Content-MD5</t>
2397      <t>ETag</t>
2398      <t>Last-Modified</t>
2399  </list>
2400</t>
2401<t>
2402   A transparent proxy MUST NOT modify any of the following fields in a
2403   response:
2404  <list style="symbols">
2405    <t>Expires</t>
2406  </list>
2407</t>
2408<t>
2409   but it MAY add any of these fields if not already present. If an
2410   Expires header is added, it MUST be given a field-value identical to
2411   that of the Date header in that response.
2412</t>
2413<t>
2414   A proxy MUST NOT modify or add any of the following fields in a
2415   message that contains the no-transform cache-control directive, or in
2416   any request:
2417  <list style="symbols">
2418    <t>Content-Encoding</t>
2419    <t>Content-Range</t>
2420    <t>Content-Type</t>
2421  </list>
2422</t>
2423<t>
2424   A non-transparent proxy MAY modify or add these fields to a message
2425   that does not include no-transform, but if it does so, it MUST add a
2426   Warning 214 (Transformation applied) if one does not already appear
2427   in the message (see Section 3.6 of <xref target="Part6"/>).
2428</t>
2429<t><list>
2430  <t>
2431    Warning: Unnecessary modification of end-to-end headers might
2432    cause authentication failures if stronger authentication
2433    mechanisms are introduced in later versions of HTTP. Such
2434    authentication mechanisms MAY rely on the values of header fields
2435    not listed here.
2436  </t>
2437</list></t>
2438<t>
2439   The Content-Length field of a request or response is added or deleted
2440   according to the rules in <xref target="message.length"/>. A transparent proxy MUST
2441   preserve the entity-length (Section 3.2.2 of <xref target="Part3"/>) of the entity-body,
2442   although it MAY change the transfer-length (<xref target="message.length"/>).
2443</t>
2444</section>
2445
2446</section>
2447
2448<section title="Practical Considerations" anchor="persistent.practical">
2449<t>
2450   Servers will usually have some time-out value beyond which they will
2451   no longer maintain an inactive connection. Proxy servers might make
2452   this a higher value since it is likely that the client will be making
2453   more connections through the same server. The use of persistent
2454   connections places no requirements on the length (or existence) of
2455   this time-out for either the client or the server.
2456</t>
2457<t>
2458   When a client or server wishes to time-out it SHOULD issue a graceful
2459   close on the transport connection. Clients and servers SHOULD both
2460   constantly watch for the other side of the transport close, and
2461   respond to it as appropriate. If a client or server does not detect
2462   the other side's close promptly it could cause unnecessary resource
2463   drain on the network.
2464</t>
2465<t>
2466   A client, server, or proxy MAY close the transport connection at any
2467   time. For example, a client might have started to send a new request
2468   at the same time that the server has decided to close the "idle"
2469   connection. From the server's point of view, the connection is being
2470   closed while it was idle, but from the client's point of view, a
2471   request is in progress.
2472</t>
2473<t>
2474   This means that clients, servers, and proxies MUST be able to recover
2475   from asynchronous close events. Client software SHOULD reopen the
2476   transport connection and retransmit the aborted sequence of requests
2477   without user interaction so long as the request sequence is
2478   idempotent (see Section 7.1.2 of <xref target="Part2"/>). Non-idempotent methods or sequences
2479   MUST NOT be automatically retried, although user agents MAY offer a
2480   human operator the choice of retrying the request(s). Confirmation by
2481   user-agent software with semantic understanding of the application
2482   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2483   be repeated if the second sequence of requests fails.
2484</t>
2485<t>
2486   Servers SHOULD always respond to at least one request per connection,
2487   if at all possible. Servers SHOULD NOT  close a connection in the
2488   middle of transmitting a response, unless a network or client failure
2489   is suspected.
2490</t>
2491<t>
2492   Clients (including proxies) SHOULD limit the number of simultaneous
2493   connections that they maintain to a given server (including proxies).
2494</t>
2495<t>
2496   Previous revisions of HTTP gave a specific number of connections as a
2497   ceiling, but this was found to be impractical for many applications. As a
2498   result, this specification does not mandate a particular maximum number of
2499   connections, but instead encourages clients to be conservative when opening
2500   multiple connections.
2501</t>
2502<t>
2503   In particular, while using multiple connections avoids the "head-of-line
2504   blocking" problem (whereby a request that takes significant server-side
2505   processing and/or has a large payload can block subsequent requests on the
2506   same connection), each connection used consumes server resources (sometimes
2507   significantly), and furthermore using multiple connections can cause
2508   undesirable side effects in congested networks.
2509</t>
2510<t>
2511   Note that servers might reject traffic that they deem abusive, including an
2512   excessive number of connections from a client.
2513</t>
2514</section>
2515</section>
2516
2517<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2518
2519<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2520<t>
2521   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2522   flow control mechanisms to resolve temporary overloads, rather than
2523   terminating connections with the expectation that clients will retry.
2524   The latter technique can exacerbate network congestion.
2525</t>
2526</section>
2527
2528<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2529<t>
2530   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2531   the network connection for an error status while it is transmitting
2532   the request. If the client sees an error status, it SHOULD
2533   immediately cease transmitting the body. If the body is being sent
2534   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2535   empty trailer MAY be used to prematurely mark the end of the message.
2536   If the body was preceded by a Content-Length header, the client MUST
2537   close the connection.
2538</t>
2539</section>
2540
2541<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2542<t>
2543   The purpose of the 100 (Continue) status (see Section 8.1.1 of <xref target="Part2"/>) is to
2544   allow a client that is sending a request message with a request body
2545   to determine if the origin server is willing to accept the request
2546   (based on the request headers) before the client sends the request
2547   body. In some cases, it might either be inappropriate or highly
2548   inefficient for the client to send the body if the server will reject
2549   the message without looking at the body.
2550</t>
2551<t>
2552   Requirements for HTTP/1.1 clients:
2553  <list style="symbols">
2554    <t>
2555        If a client will wait for a 100 (Continue) response before
2556        sending the request body, it MUST send an Expect request-header
2557        field (Section 9.2 of <xref target="Part2"/>) with the "100-continue" expectation.
2558    </t>
2559    <t>
2560        A client MUST NOT send an Expect request-header field (Section 9.2 of <xref target="Part2"/>)
2561        with the "100-continue" expectation if it does not intend
2562        to send a request body.
2563    </t>
2564  </list>
2565</t>
2566<t>
2567   Because of the presence of older implementations, the protocol allows
2568   ambiguous situations in which a client may send "Expect: 100-continue"
2569   without receiving either a 417 (Expectation Failed) status
2570   or a 100 (Continue) status. Therefore, when a client sends this
2571   header field to an origin server (possibly via a proxy) from which it
2572   has never seen a 100 (Continue) status, the client SHOULD NOT  wait
2573   for an indefinite period before sending the request body.
2574</t>
2575<t>
2576   Requirements for HTTP/1.1 origin servers:
2577  <list style="symbols">
2578    <t> Upon receiving a request which includes an Expect request-header
2579        field with the "100-continue" expectation, an origin server MUST
2580        either respond with 100 (Continue) status and continue to read
2581        from the input stream, or respond with a final status code. The
2582        origin server MUST NOT wait for the request body before sending
2583        the 100 (Continue) response. If it responds with a final status
2584        code, it MAY close the transport connection or it MAY continue
2585        to read and discard the rest of the request.  It MUST NOT
2586        perform the requested method if it returns a final status code.
2587    </t>
2588    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2589        the request message does not include an Expect request-header
2590        field with the "100-continue" expectation, and MUST NOT send a
2591        100 (Continue) response if such a request comes from an HTTP/1.0
2592        (or earlier) client. There is an exception to this rule: for
2593        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2594        status in response to an HTTP/1.1 PUT or POST request that does
2595        not include an Expect request-header field with the "100-continue"
2596        expectation. This exception, the purpose of which is
2597        to minimize any client processing delays associated with an
2598        undeclared wait for 100 (Continue) status, applies only to
2599        HTTP/1.1 requests, and not to requests with any other HTTP-version
2600        value.
2601    </t>
2602    <t> An origin server MAY omit a 100 (Continue) response if it has
2603        already received some or all of the request body for the
2604        corresponding request.
2605    </t>
2606    <t> An origin server that sends a 100 (Continue) response MUST
2607    ultimately send a final status code, once the request body is
2608        received and processed, unless it terminates the transport
2609        connection prematurely.
2610    </t>
2611    <t> If an origin server receives a request that does not include an
2612        Expect request-header field with the "100-continue" expectation,
2613        the request includes a request body, and the server responds
2614        with a final status code before reading the entire request body
2615        from the transport connection, then the server SHOULD NOT  close
2616        the transport connection until it has read the entire request,
2617        or until the client closes the connection. Otherwise, the client
2618        might not reliably receive the response message. However, this
2619        requirement is not be construed as preventing a server from
2620        defending itself against denial-of-service attacks, or from
2621        badly broken client implementations.
2622      </t>
2623    </list>
2624</t>
2625<t>
2626   Requirements for HTTP/1.1 proxies:
2627  <list style="symbols">
2628    <t> If a proxy receives a request that includes an Expect request-header
2629        field with the "100-continue" expectation, and the proxy
2630        either knows that the next-hop server complies with HTTP/1.1 or
2631        higher, or does not know the HTTP version of the next-hop
2632        server, it MUST forward the request, including the Expect header
2633        field.
2634    </t>
2635    <t> If the proxy knows that the version of the next-hop server is
2636        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2637        respond with a 417 (Expectation Failed) status.
2638    </t>
2639    <t> Proxies SHOULD maintain a cache recording the HTTP version
2640        numbers received from recently-referenced next-hop servers.
2641    </t>
2642    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2643        request message was received from an HTTP/1.0 (or earlier)
2644        client and did not include an Expect request-header field with
2645        the "100-continue" expectation. This requirement overrides the
2646        general rule for forwarding of 1xx responses (see Section 8.1 of <xref target="Part2"/>).
2647    </t>
2648  </list>
2649</t>
2650</section>
2651
2652<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2653<t>
2654   If an HTTP/1.1 client sends a request which includes a request body,
2655   but which does not include an Expect request-header field with the
2656   "100-continue" expectation, and if the client is not directly
2657   connected to an HTTP/1.1 origin server, and if the client sees the
2658   connection close before receiving any status from the server, the
2659   client SHOULD retry the request.  If the client does retry this
2660   request, it MAY use the following "binary exponential backoff"
2661   algorithm to be assured of obtaining a reliable response:
2662  <list style="numbers">
2663    <t>
2664      Initiate a new connection to the server
2665    </t>
2666    <t>
2667      Transmit the request-headers
2668    </t>
2669    <t>
2670      Initialize a variable R to the estimated round-trip time to the
2671         server (e.g., based on the time it took to establish the
2672         connection), or to a constant value of 5 seconds if the round-trip
2673         time is not available.
2674    </t>
2675    <t>
2676       Compute T = R * (2**N), where N is the number of previous
2677         retries of this request.
2678    </t>
2679    <t>
2680       Wait either for an error response from the server, or for T
2681         seconds (whichever comes first)
2682    </t>
2683    <t>
2684       If no error response is received, after T seconds transmit the
2685         body of the request.
2686    </t>
2687    <t>
2688       If client sees that the connection is closed prematurely,
2689         repeat from step 1 until the request is accepted, an error
2690         response is received, or the user becomes impatient and
2691         terminates the retry process.
2692    </t>
2693  </list>
2694</t>
2695<t>
2696   If at any point an error status is received, the client
2697  <list style="symbols">
2698      <t>SHOULD NOT  continue and</t>
2699
2700      <t>SHOULD close the connection if it has not completed sending the
2701        request message.</t>
2702    </list>
2703</t>
2704</section>
2705</section>
2706</section>
2707
2708
2709<section title="Miscellaneous notes that may disappear" anchor="misc">
2710<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2711<t>
2712   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2713</t>
2714</section>
2715
2716<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2717<t>
2718   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2719</t>
2720</section>
2721
2722<section title="Interception of HTTP for access control" anchor="http.intercept">
2723<t>
2724   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2725</t>
2726</section>
2727
2728<section title="Use of HTTP by other protocols" anchor="http.others">
2729<t>
2730   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2731   Extensions of HTTP like WebDAV.</cref>
2732</t>
2733
2734</section>
2735<section title="Use of HTTP by media type specification" anchor="http.media">
2736<t>
2737   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2738</t>
2739</section>
2740</section>
2741
2742<section title="Header Field Definitions" anchor="header.field.definitions">
2743<t>
2744   This section defines the syntax and semantics of HTTP/1.1 header fields
2745   related to message framing and transport protocols.
2746</t>
2747<t>
2748   For entity-header fields, both sender and recipient refer to either the
2749   client or the server, depending on who sends and who receives the entity.
2750</t>
2751
2752<section title="Connection" anchor="header.connection">
2753  <iref primary="true" item="Connection header"/>
2754  <iref primary="true" item="Headers" subitem="Connection"/>
2755 
2756 
2757 
2758<t>
2759   The "Connection" general-header field allows the sender to specify
2760   options that are desired for that particular connection and MUST NOT
2761   be communicated by proxies over further connections.
2762</t>
2763<t>
2764   The Connection header's value has the following grammar:
2765</t>
2766<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[
2767  Connection       = "Connection" ":" OWS Connection-v
2768  Connection-v     = 1#connection-token
2769  connection-token = token
2770]]></artwork></figure>
2771<t>
2772   HTTP/1.1 proxies MUST parse the Connection header field before a
2773   message is forwarded and, for each connection-token in this field,
2774   remove any header field(s) from the message with the same name as the
2775   connection-token. Connection options are signaled by the presence of
2776   a connection-token in the Connection header field, not by any
2777   corresponding additional header field(s), since the additional header
2778   field may not be sent if there are no parameters associated with that
2779   connection option.
2780</t>
2781<t>
2782   Message headers listed in the Connection header MUST NOT include
2783   end-to-end headers, such as Cache-Control.
2784</t>
2785<t>
2786   HTTP/1.1 defines the "close" connection option for the sender to
2787   signal that the connection will be closed after completion of the
2788   response. For example,
2789</t>
2790<figure><artwork type="example"><![CDATA[
2791  Connection: close
2792]]></artwork></figure>
2793<t>
2794   in either the request or the response header fields indicates that
2795   the connection SHOULD NOT  be considered "persistent" (<xref target="persistent.connections"/>)
2796   after the current request/response is complete.
2797</t>
2798<t>
2799   An HTTP/1.1 client that does not support persistent connections MUST
2800   include the "close" connection option in every request message.
2801</t>
2802<t>
2803   An HTTP/1.1 server that does not support persistent connections MUST
2804   include the "close" connection option in every response message that
2805   does not have a 1xx (Informational) status code.
2806</t>
2807<t>
2808   A system receiving an HTTP/1.0 (or lower-version) message that
2809   includes a Connection header MUST, for each connection-token in this
2810   field, remove and ignore any header field(s) from the message with
2811   the same name as the connection-token. This protects against mistaken
2812   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2813</t>
2814</section>
2815
2816<section title="Content-Length" anchor="header.content-length">
2817  <iref primary="true" item="Content-Length header"/>
2818  <iref primary="true" item="Headers" subitem="Content-Length"/>
2819 
2820 
2821<t>
2822   The "Content-Length" entity-header field indicates the size of the
2823   entity-body, in number of OCTETs. In the case of responses to the HEAD
2824   method, it indicates the size of the entity-body that would have been sent
2825   had the request been a GET.
2826</t>
2827<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/><artwork type="abnf2616"><![CDATA[
2828  Content-Length   = "Content-Length" ":" OWS 1*Content-Length-v
2829  Content-Length-v = 1*DIGIT
2830]]></artwork></figure>
2831<t>
2832   An example is
2833</t>
2834<figure><artwork type="example"><![CDATA[
2835  Content-Length: 3495
2836]]></artwork></figure>
2837<t>
2838   Applications SHOULD use this field to indicate the transfer-length of
2839   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2840</t>
2841<t>
2842   Any Content-Length greater than or equal to zero is a valid value.
2843   <xref target="message.length"/> describes how to determine the length of a message-body
2844   if a Content-Length is not given.
2845</t>
2846<t>
2847   Note that the meaning of this field is significantly different from
2848   the corresponding definition in MIME, where it is an optional field
2849   used within the "message/external-body" content-type. In HTTP, it
2850   SHOULD be sent whenever the message's length can be determined prior
2851   to being transferred, unless this is prohibited by the rules in
2852   <xref target="message.length"/>.
2853</t>
2854</section>
2855
2856<section title="Date" anchor="header.date">
2857  <iref primary="true" item="Date header"/>
2858  <iref primary="true" item="Headers" subitem="Date"/>
2859 
2860 
2861<t>
2862   The "Date" general-header field represents the date and time at which
2863   the message was originated, having the same semantics as the Origination
2864   Date Field (orig-date) defined in Section 3.6.1 of <xref target="RFC5322"/>.
2865   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2866   it MUST be sent in rfc1123-date format.
2867</t>
2868<figure><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/><artwork type="abnf2616"><![CDATA[
2869  Date   = "Date" ":" OWS Date-v
2870  Date-v = HTTP-date
2871]]></artwork></figure>
2872<t>
2873   An example is
2874</t>
2875<figure><artwork type="example"><![CDATA[
2876  Date: Tue, 15 Nov 1994 08:12:31 GMT
2877]]></artwork></figure>
2878<t>
2879   Origin servers MUST include a Date header field in all responses,
2880   except in these cases:
2881  <list style="numbers">
2882      <t>If the response status code is 100 (Continue) or 101 (Switching
2883         Protocols), the response MAY include a Date header field, at
2884         the server's option.</t>
2885
2886      <t>If the response status code conveys a server error, e.g., 500
2887         (Internal Server Error) or 503 (Service Unavailable), and it is
2888         inconvenient or impossible to generate a valid Date.</t>
2889
2890      <t>If the server does not have a clock that can provide a
2891         reasonable approximation of the current time, its responses
2892         MUST NOT include a Date header field. In this case, the rules
2893         in <xref target="clockless.origin.server.operation"/> MUST be followed.</t>
2894  </list>
2895</t>
2896<t>
2897   A received message that does not have a Date header field MUST be
2898   assigned one by the recipient if the message will be cached by that
2899   recipient or gatewayed via a protocol which requires a Date. An HTTP
2900   implementation without a clock MUST NOT cache responses without
2901   revalidating them on every use. An HTTP cache, especially a shared
2902   cache, SHOULD use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2903   clock with a reliable external standard.
2904</t>
2905<t>
2906   Clients SHOULD only send a Date header field in messages that include
2907   an entity-body, as in the case of the PUT and POST requests, and even
2908   then it is optional. A client without a clock MUST NOT send a Date
2909   header field in a request.
2910</t>
2911<t>
2912   The HTTP-date sent in a Date header SHOULD NOT  represent a date and
2913   time subsequent to the generation of the message. It SHOULD represent
2914   the best available approximation of the date and time of message
2915   generation, unless the implementation has no means of generating a
2916   reasonably accurate date and time. In theory, the date ought to
2917   represent the moment just before the entity is generated. In
2918   practice, the date can be generated at any time during the message
2919   origination without affecting its semantic value.
2920</t>
2921
2922<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2923<t>
2924   Some origin server implementations might not have a clock available.
2925   An origin server without a clock MUST NOT assign Expires or Last-Modified
2926   values to a response, unless these values were associated
2927   with the resource by a system or user with a reliable clock. It MAY
2928   assign an Expires value that is known, at or before server
2929   configuration time, to be in the past (this allows "pre-expiration"
2930   of responses without storing separate Expires values for each
2931   resource).
2932</t>
2933</section>
2934</section>
2935
2936<section title="Host" anchor="header.host">
2937  <iref primary="true" item="Host header"/>
2938  <iref primary="true" item="Headers" subitem="Host"/>
2939 
2940 
2941<t>
2942   The "Host" request-header field specifies the Internet host and port
2943   number of the resource being requested, allowing the origin server or
2944   gateway to differentiate between internally-ambiguous URLs, such as the root
2945   "/" URL of a server for multiple host names on a single IP address.
2946</t>
2947<t>   
2948   The Host field value MUST represent the naming authority of the origin
2949   server or gateway given by the original URL obtained from the user or
2950   referring resource (generally an http URI, as described in
2951   <xref target="http.uri"/>).
2952</t>
2953<figure><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/><artwork type="abnf2616"><![CDATA[
2954  Host   = "Host" ":" OWS Host-v
2955  Host-v = uri-host [ ":" port ] ; Section 2.6.1
2956]]></artwork></figure>
2957<t>
2958   A "host" without any trailing port information implies the default
2959   port for the service requested (e.g., "80" for an HTTP URL). For
2960   example, a request on the origin server for
2961   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2962</t>
2963<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
2964  GET /pub/WWW/ HTTP/1.1
2965  Host: www.example.org
2966  ]]></artwork></figure>
2967<t>
2968   A client MUST include a Host header field in all HTTP/1.1 request
2969   messages. If the requested URI does not include an Internet host
2970   name for the service being requested, then the Host header field MUST
2971   be given with an empty value. An HTTP/1.1 proxy MUST ensure that any
2972   request message it forwards does contain an appropriate Host header
2973   field that identifies the service being requested by the proxy. All
2974   Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
2975   status code to any HTTP/1.1 request message which lacks a Host header
2976   field.
2977</t>
2978<t>
2979   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2980   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2981   for other requirements relating to Host.
2982</t>
2983</section>
2984
2985<section title="TE" anchor="header.te">
2986  <iref primary="true" item="TE header"/>
2987  <iref primary="true" item="Headers" subitem="TE"/>
2988 
2989 
2990 
2991 
2992 
2993<t>
2994   The "TE" request-header field indicates what extension transfer-codings
2995   it is willing to accept in the response, and whether or not it is
2996   willing to accept trailer fields in a chunked transfer-coding.
2997</t>
2998<t>
2999   Its value may consist of the keyword "trailers" and/or a comma-separated
3000   list of extension transfer-coding names with optional accept
3001   parameters (as described in <xref target="transfer.codings"/>).
3002</t>
3003<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[
3004  TE        = "TE" ":" OWS TE-v
3005  TE-v      = #t-codings
3006  t-codings = "trailers" / ( transfer-extension [ te-params ] )
3007  te-params = OWS ";" OWS "q=" qvalue *( te-ext )
3008  te-ext    = OWS ";" OWS token [ "=" word ]
3009]]></artwork></figure>
3010<t>
3011   The presence of the keyword "trailers" indicates that the client is
3012   willing to accept trailer fields in a chunked transfer-coding, as
3013   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3014   transfer-coding values even though it does not itself represent a
3015   transfer-coding.
3016</t>
3017<t>
3018   Examples of its use are:
3019</t>
3020<figure><artwork type="example"><![CDATA[
3021  TE: deflate
3022  TE:
3023  TE: trailers, deflate;q=0.5
3024]]></artwork></figure>
3025<t>
3026   The TE header field only applies to the immediate connection.
3027   Therefore, the keyword MUST be supplied within a Connection header
3028   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3029</t>
3030<t>
3031   A server tests whether a transfer-coding is acceptable, according to
3032   a TE field, using these rules:
3033  <list style="numbers">
3034    <t>The "chunked" transfer-coding is always acceptable. If the
3035         keyword "trailers" is listed, the client indicates that it is
3036         willing to accept trailer fields in the chunked response on
3037         behalf of itself and any downstream clients. The implication is
3038         that, if given, the client is stating that either all
3039         downstream clients are willing to accept trailer fields in the
3040         forwarded response, or that it will attempt to buffer the
3041         response on behalf of downstream recipients.
3042      <vspace blankLines="1"/>
3043         Note: HTTP/1.1 does not define any means to limit the size of a
3044         chunked response such that a client can be assured of buffering
3045         the entire response.</t>
3046    <t>If the transfer-coding being tested is one of the transfer-codings
3047         listed in the TE field, then it is acceptable unless it
3048         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3049         qvalue of 0 means "not acceptable.")</t>
3050    <t>If multiple transfer-codings are acceptable, then the
3051         acceptable transfer-coding with the highest non-zero qvalue is
3052         preferred.  The "chunked" transfer-coding always has a qvalue
3053         of 1.</t>
3054  </list>
3055</t>
3056<t>
3057   If the TE field-value is empty or if no TE field is present, the only
3058   transfer-coding is "chunked". A message with no transfer-coding is
3059   always acceptable.
3060</t>
3061</section>
3062
3063<section title="Trailer" anchor="header.trailer">
3064  <iref primary="true" item="Trailer header"/>
3065  <iref primary="true" item="Headers" subitem="Trailer"/>
3066 
3067 
3068<t>
3069   The "Trailer" general-header field indicates that the given set of
3070   header fields is present in the trailer of a message encoded with
3071   chunked transfer-coding.
3072</t>
3073<figure><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/><artwork type="abnf2616"><![CDATA[
3074  Trailer   = "Trailer" ":" OWS Trailer-v
3075  Trailer-v = 1#field-name
3076]]></artwork></figure>
3077<t>
3078   An HTTP/1.1 message SHOULD include a Trailer header field in a
3079   message using chunked transfer-coding with a non-empty trailer. Doing
3080   so allows the recipient to know which header fields to expect in the
3081   trailer.
3082</t>
3083<t>
3084   If no Trailer header field is present, the trailer SHOULD NOT  include
3085   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3086   trailer fields in a "chunked" transfer-coding.
3087</t>
3088<t>
3089   Message header fields listed in the Trailer header field MUST NOT
3090   include the following header fields:
3091  <list style="symbols">
3092    <t>Transfer-Encoding</t>
3093    <t>Content-Length</t>
3094    <t>Trailer</t>
3095  </list>
3096</t>
3097</section>
3098
3099<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3100  <iref primary="true" item="Transfer-Encoding header"/>
3101  <iref primary="true" item="Headers" subitem="Transfer-Encoding"/>
3102 
3103 
3104<t>
3105   The "Transfer-Encoding" general-header field indicates what transfer-codings
3106   (if any) have been applied to the message body. It differs from
3107   Content-Encoding (Section 2.2 of <xref target="Part3"/>) in that transfer-codings are a property
3108   of the message (and therefore are removed by intermediaries), whereas
3109   content-codings are not.
3110</t>
3111<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/><artwork type="abnf2616"><![CDATA[
3112  Transfer-Encoding   = "Transfer-Encoding" ":" OWS
3113                        Transfer-Encoding-v
3114  Transfer-Encoding-v = 1#transfer-coding
3115]]></artwork></figure>
3116<t>
3117   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3118</t>
3119<figure><artwork type="example"><![CDATA[
3120  Transfer-Encoding: chunked
3121]]></artwork></figure>
3122<t>
3123   If multiple encodings have been applied to an entity, the transfer-codings
3124   MUST be listed in the order in which they were applied.
3125   Additional information about the encoding parameters MAY be provided
3126   by other entity-header fields not defined by this specification.
3127</t>
3128<t>
3129   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3130   header.
3131</t>
3132</section>
3133
3134<section title="Upgrade" anchor="header.upgrade">
3135  <iref primary="true" item="Upgrade header"/>
3136  <iref primary="true" item="Headers" subitem="Upgrade"/>
3137 
3138 
3139<t>
3140   The "Upgrade" general-header field allows the client to specify what
3141   additional communication protocols it would like to use, if the server
3142   chooses to switch protocols. Additionally, the server MUST use the Upgrade
3143   header field within a 101 (Switching Protocols) response to indicate which
3144   protocol(s) are being switched to.
3145</t>
3146<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/><artwork type="abnf2616"><![CDATA[
3147  Upgrade   = "Upgrade" ":" OWS Upgrade-v
3148  Upgrade-v = 1#product
3149]]></artwork></figure>
3150<t>
3151   For example,
3152</t>
3153<figure><artwork type="example"><![CDATA[
3154  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3155]]></artwork></figure>
3156<t>
3157   The Upgrade header field is intended to provide a simple mechanism
3158   for transition from HTTP/1.1 to some other, incompatible protocol. It
3159   does so by allowing the client to advertise its desire to use another
3160   protocol, such as a later version of HTTP with a higher major version
3161   number, even though the current request has been made using HTTP/1.1.
3162   This eases the difficult transition between incompatible protocols by
3163   allowing the client to initiate a request in the more commonly
3164   supported protocol while indicating to the server that it would like
3165   to use a "better" protocol if available (where "better" is determined
3166   by the server, possibly according to the nature of the method and/or
3167   resource being requested).
3168</t>
3169<t>
3170   The Upgrade header field only applies to switching application-layer
3171   protocols upon the existing transport-layer connection. Upgrade
3172   cannot be used to insist on a protocol change; its acceptance and use
3173   by the server is optional. The capabilities and nature of the
3174   application-layer communication after the protocol change is entirely
3175   dependent upon the new protocol chosen, although the first action
3176   after changing the protocol MUST be a response to the initial HTTP
3177   request containing the Upgrade header field.
3178</t>
3179<t>
3180   The Upgrade header field only applies to the immediate connection.
3181   Therefore, the upgrade keyword MUST be supplied within a Connection
3182   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3183   HTTP/1.1 message.
3184</t>
3185<t>
3186   The Upgrade header field cannot be used to indicate a switch to a
3187   protocol on a different connection. For that purpose, it is more
3188   appropriate to use a 301, 302, 303, or 305 redirection response.
3189</t>
3190<t>
3191   This specification only defines the protocol name "HTTP" for use by
3192   the family of Hypertext Transfer Protocols, as defined by the HTTP
3193   version rules of <xref target="http.version"/> and future updates to this
3194   specification. Additional tokens can be registered with IANA using the
3195   registration procedure defined below. 
3196</t>
3197
3198<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3199<t>
3200   The HTTP Upgrade Token Registry defines the name space for product
3201   tokens used to identify protocols in the Upgrade header field.
3202   Each registered token should be associated with one or a set of
3203   specifications, and with contact information.
3204</t>
3205<t>
3206   Registrations should be allowed on a First Come First Served basis as
3207   described in Section 4.1 of <xref target="RFC5226"/>. These
3208   specifications need not be IETF documents or be subject to IESG review, but
3209   should obey the following rules:
3210  <list style="numbers">
3211    <t>A token, once registered, stays registered forever.</t>
3212    <t>The registration MUST name a responsible party for the
3213       registration.</t>
3214    <t>The registration MUST name a point of contact.</t>
3215    <t>The registration MAY name the documentation required for the
3216       token.</t>
3217    <t>The responsible party MAY change the registration at any time.
3218       The IANA will keep a record of all such changes, and make them
3219       available upon request.</t>
3220    <t>The responsible party for the first registration of a "product"
3221       token MUST approve later registrations of a "version" token
3222       together with that "product" token before they can be registered.</t>
3223    <t>If absolutely required, the IESG MAY reassign the responsibility
3224       for a token. This will normally only be used in the case when a
3225       responsible party cannot be contacted.</t>
3226  </list>
3227</t>
3228<t>
3229   It is not required that specifications for upgrade tokens be made
3230   publicly available, but the contact information for the registration
3231   should be.
3232</t>
3233</section>
3234
3235
3236</section>
3237
3238<section title="Via" anchor="header.via">
3239  <iref primary="true" item="Via header"/>
3240  <iref primary="true" item="Headers" subitem="Via"/>
3241 
3242 
3243 
3244 
3245 
3246 
3247 
3248<t>
3249   The "Via" general-header field MUST be used by gateways and proxies to
3250   indicate the intermediate protocols and recipients between the user
3251   agent and the server on requests, and between the origin server and
3252   the client on responses. It is analogous to the "Received" field defined in
3253   Section 3.6.7 of <xref target="RFC5322"/> and is intended to be used for tracking message forwards,
3254   avoiding request loops, and identifying the protocol capabilities of
3255   all senders along the request/response chain.
3256</t>
3257<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[
3258  Via               = "Via" ":" OWS Via-v
3259  Via-v             = 1#( received-protocol RWS received-by
3260                          [ RWS comment ] )
3261  received-protocol = [ protocol-name "/" ] protocol-version
3262  protocol-name     = token
3263  protocol-version  = token
3264  received-by       = ( uri-host [ ":" port ] ) / pseudonym
3265  pseudonym         = token
3266]]></artwork></figure>
3267<t>
3268   The received-protocol indicates the protocol version of the message
3269   received by the server or client along each segment of the
3270   request/response chain. The received-protocol version is appended to
3271   the Via field value when the message is forwarded so that information
3272   about the protocol capabilities of upstream applications remains
3273   visible to all recipients.
3274</t>
3275<t>
3276   The protocol-name is optional if and only if it would be "HTTP". The
3277   received-by field is normally the host and optional port number of a
3278   recipient server or client that subsequently forwarded the message.
3279   However, if the real host is considered to be sensitive information,
3280   it MAY be replaced by a pseudonym. If the port is not given, it MAY
3281   be assumed to be the default port of the received-protocol.
3282</t>
3283<t>
3284   Multiple Via field values represent each proxy or gateway that has
3285   forwarded the message. Each recipient MUST append its information
3286   such that the end result is ordered according to the sequence of
3287   forwarding applications.
3288</t>
3289<t>
3290   Comments MAY be used in the Via header field to identify the software
3291   of the recipient proxy or gateway, analogous to the User-Agent and
3292   Server header fields. However, all comments in the Via field are
3293   optional and MAY be removed by any recipient prior to forwarding the
3294   message.
3295</t>
3296<t>
3297   For example, a request message could be sent from an HTTP/1.0 user
3298   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3299   forward the request to a public proxy at p.example.net, which completes
3300   the request by forwarding it to the origin server at www.example.com.
3301   The request received by www.example.com would then have the following
3302   Via header field:
3303</t>
3304<figure><artwork type="example"><![CDATA[
3305  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3306]]></artwork></figure>
3307<t>
3308   Proxies and gateways used as a portal through a network firewall
3309   SHOULD NOT, by default, forward the names and ports of hosts within
3310   the firewall region. This information SHOULD only be propagated if
3311   explicitly enabled. If not enabled, the received-by host of any host
3312   behind the firewall SHOULD be replaced by an appropriate pseudonym
3313   for that host.
3314</t>
3315<t>
3316   For organizations that have strong privacy requirements for hiding
3317   internal structures, a proxy MAY combine an ordered subsequence of
3318   Via header field entries with identical received-protocol values into
3319   a single such entry. For example,
3320</t>
3321<figure><artwork type="example"><![CDATA[
3322  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3323]]></artwork></figure>
3324<t>
3325  could be collapsed to
3326</t>
3327<figure><artwork type="example"><![CDATA[
3328  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3329]]></artwork></figure>
3330<t>
3331   Applications SHOULD NOT  combine multiple entries unless they are all
3332   under the same organizational control and the hosts have already been
3333   replaced by pseudonyms. Applications MUST NOT combine entries which
3334   have different received-protocol values.
3335</t>
3336</section>
3337
3338</section>
3339
3340<section title="IANA Considerations" anchor="IANA.considerations">
3341
3342<section title="Message Header Registration" anchor="message.header.registration">
3343<t>
3344   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3345   with the permanent registrations below (see <xref target="RFC3864"/>):
3346</t>
3347
3348<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3349<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3350   <ttcol>Header Field Name</ttcol>
3351   <ttcol>Protocol</ttcol>
3352   <ttcol>Status</ttcol>
3353   <ttcol>Reference</ttcol>
3354
3355   <c>Connection</c>
3356   <c>http</c>
3357   <c>standard</c>
3358   <c>
3359      <xref target="header.connection"/>
3360   </c>
3361   <c>Content-Length</c>
3362   <c>http</c>
3363   <c>standard</c>
3364   <c>
3365      <xref target="header.content-length"/>
3366   </c>
3367   <c>Date</c>
3368   <c>http</c>
3369   <c>standard</c>
3370   <c>
3371      <xref target="header.date"/>
3372   </c>
3373   <c>Host</c>
3374   <c>http</c>
3375   <c>standard</c>
3376   <c>
3377      <xref target="header.host"/>
3378   </c>
3379   <c>TE</c>
3380   <c>http</c>
3381   <c>standard</c>
3382   <c>
3383      <xref target="header.te"/>
3384   </c>
3385   <c>Trailer</c>
3386   <c>http</c>
3387   <c>standard</c>
3388   <c>
3389      <xref target="header.trailer"/>
3390   </c>
3391   <c>Transfer-Encoding</c>
3392   <c>http</c>
3393   <c>standard</c>
3394   <c>
3395      <xref target="header.transfer-encoding"/>
3396   </c>
3397   <c>Upgrade</c>
3398   <c>http</c>
3399   <c>standard</c>
3400   <c>
3401      <xref target="header.upgrade"/>
3402   </c>
3403   <c>Via</c>
3404   <c>http</c>
3405   <c>standard</c>
3406   <c>
3407      <xref target="header.via"/>
3408   </c>
3409</texttable>
3410<!--(END)-->
3411
3412<t>
3413   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3414</t>
3415</section>
3416
3417<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3418<t>
3419   The entries for the "http" and "https" URI Schemes in the registry located at
3420   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3421   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3422   and <xref target="https.uri" format="counter"/> of this document
3423   (see <xref target="RFC4395"/>).
3424</t>
3425</section>
3426
3427<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3428<t>
3429   This document serves as the specification for the Internet media types
3430   "message/http" and "application/http". The following is to be registered with
3431   IANA (see <xref target="RFC4288"/>).
3432</t>
3433<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3434<iref item="Media Type" subitem="message/http" primary="true"/>
3435<iref item="message/http Media Type" primary="true"/>
3436<t>
3437   The message/http type can be used to enclose a single HTTP request or
3438   response message, provided that it obeys the MIME restrictions for all
3439   "message" types regarding line length and encodings.
3440</t>
3441<t>
3442  <list style="hanging">
3443    <t hangText="Type name:">
3444      message
3445    </t>
3446    <t hangText="Subtype name:">
3447      http
3448    </t>
3449    <t hangText="Required parameters:">
3450      none
3451    </t>
3452    <t hangText="Optional parameters:">
3453      version, msgtype
3454      <list style="hanging">
3455        <t hangText="version:">
3456          The HTTP-Version number of the enclosed message
3457          (e.g., "1.1"). If not present, the version can be
3458          determined from the first line of the body.
3459        </t>
3460        <t hangText="msgtype:">
3461          The message type -- "request" or "response". If not
3462          present, the type can be determined from the first
3463          line of the body.
3464        </t>
3465      </list>
3466    </t>
3467    <t hangText="Encoding considerations:">
3468      only "7bit", "8bit", or "binary" are permitted
3469    </t>
3470    <t hangText="Security considerations:">
3471      none
3472    </t>
3473    <t hangText="Interoperability considerations:">
3474      none
3475    </t>
3476    <t hangText="Published specification:">
3477      This specification (see <xref target="internet.media.type.message.http"/>).
3478    </t>
3479    <t hangText="Applications that use this media type:">
3480    </t>
3481    <t hangText="Additional information:">
3482      <list style="hanging">
3483        <t hangText="Magic number(s):">none</t>
3484        <t hangText="File extension(s):">none</t>
3485        <t hangText="Macintosh file type code(s):">none</t>
3486      </list>
3487    </t>
3488    <t hangText="Person and email address to contact for further information:">
3489      See Authors Section.
3490    </t>
3491    <t hangText="Intended usage:">
3492      COMMON
3493    </t>
3494    <t hangText="Restrictions on usage:">
3495      none
3496    </t>
3497    <t hangText="Author/Change controller:">
3498      IESG
3499    </t>
3500  </list>
3501</t>
3502</section>
3503<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3504<iref item="Media Type" subitem="application/http" primary="true"/>
3505<iref item="application/http Media Type" primary="true"/>
3506<t>
3507   The application/http type can be used to enclose a pipeline of one or more
3508   HTTP request or response messages (not intermixed).
3509</t>
3510<t>
3511  <list style="hanging">
3512    <t hangText="Type name:">
3513      application
3514    </t>
3515    <t hangText="Subtype name:">
3516      http
3517    </t>
3518    <t hangText="Required parameters:">
3519      none
3520    </t>
3521    <t hangText="Optional parameters:">
3522      version, msgtype
3523      <list style="hanging">
3524        <t hangText="version:">
3525          The HTTP-Version number of the enclosed messages
3526          (e.g., "1.1"). If not present, the version can be
3527          determined from the first line of the body.
3528        </t>
3529        <t hangText="msgtype:">
3530          The message type -- "request" or "response". If not
3531          present, the type can be determined from the first
3532          line of the body.
3533        </t>
3534      </list>
3535    </t>
3536    <t hangText="Encoding considerations:">
3537      HTTP messages enclosed by this type
3538      are in "binary" format; use of an appropriate
3539      Content-Transfer-Encoding is required when
3540      transmitted via E-mail.
3541    </t>
3542    <t hangText="Security considerations:">
3543      none
3544    </t>
3545    <t hangText="Interoperability considerations:">
3546      none
3547    </t>
3548    <t hangText="Published specification:">
3549      This specification (see <xref target="internet.media.type.application.http"/>).
3550    </t>
3551    <t hangText="Applications that use this media type:">
3552    </t>
3553    <t hangText="Additional information:">
3554      <list style="hanging">
3555        <t hangText="Magic number(s):">none</t>
3556        <t hangText="File extension(s):">none</t>
3557        <t hangText="Macintosh file type code(s):">none</t>
3558      </list>
3559    </t>
3560    <t hangText="Person and email address to contact for further information:">
3561      See Authors Section.
3562    </t>
3563    <t hangText="Intended usage:">
3564      COMMON
3565    </t>
3566    <t hangText="Restrictions on usage:">
3567      none
3568    </t>
3569    <t hangText="Author/Change controller:">
3570      IESG
3571    </t>
3572  </list>
3573</t>
3574</section>
3575</section>
3576
3577<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3578<t>
3579   The registration procedure for HTTP Transfer Codings is now defined by
3580   <xref target="transfer.coding.registry"/> of this document.
3581</t>
3582<t>
3583   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3584   should be updated with the registrations below:
3585</t>
3586<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3587   <ttcol>Name</ttcol>
3588   <ttcol>Description</ttcol>
3589   <ttcol>Reference</ttcol>
3590   <c>chunked</c>
3591   <c>Transfer in a series of chunks</c>
3592   <c>
3593      <xref target="chunked.encoding"/>
3594   </c>
3595   <c>compress</c>
3596   <c>UNIX "compress" program method</c>
3597   <c>
3598      <xref target="compress.coding"/>
3599   </c>
3600   <c>deflate</c>
3601   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3602   the "zlib" data format (<xref target="RFC1950"/>)
3603   </c>
3604   <c>
3605      <xref target="deflate.coding"/>
3606   </c>
3607   <c>gzip</c>
3608   <c>Same as GNU zip <xref target="RFC1952"/></c>
3609   <c>
3610      <xref target="gzip.coding"/>
3611   </c>
3612</texttable>
3613</section>
3614
3615<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3616<t>
3617   The registration procedure for HTTP Upgrade Tokens -- previously defined
3618   in Section 7.2 of <xref target="RFC2817"/> -- is now defined
3619   by <xref target="upgrade.token.registry"/> of this document.
3620</t>
3621<t>
3622   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3623   should be updated with the registration below:
3624</t>
3625<texttable align="left" suppress-title="true">
3626   <ttcol>Value</ttcol>
3627   <ttcol>Description</ttcol>
3628   <ttcol>Reference</ttcol>
3629
3630   <c>HTTP</c>
3631   <c>Hypertext Transfer Protocol</c> 
3632   <c><xref target="http.version"/> of this specification</c>
3633<!-- IANA should add this without our instructions; emailed on June 05, 2009
3634   <c>TLS/1.0</c>
3635   <c>Transport Layer Security</c>
3636   <c><xref target="RFC2817"/></c> -->
3637
3638</texttable>
3639</section>
3640
3641</section>
3642
3643<section title="Security Considerations" anchor="security.considerations">
3644<t>
3645   This section is meant to inform application developers, information
3646   providers, and users of the security limitations in HTTP/1.1 as
3647   described by this document. The discussion does not include
3648   definitive solutions to the problems revealed, though it does make
3649   some suggestions for reducing security risks.
3650</t>
3651
3652<section title="Personal Information" anchor="personal.information">
3653<t>
3654   HTTP clients are often privy to large amounts of personal information
3655   (e.g., the user's name, location, mail address, passwords, encryption
3656   keys, etc.), and SHOULD be very careful to prevent unintentional
3657   leakage of this information.
3658   We very strongly recommend that a convenient interface be provided
3659   for the user to control dissemination of such information, and that
3660   designers and implementors be particularly careful in this area.
3661   History shows that errors in this area often create serious security
3662   and/or privacy problems and generate highly adverse publicity for the
3663   implementor's company.
3664</t>
3665</section>
3666
3667<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3668<t>
3669   A server is in the position to save personal data about a user's
3670   requests which might identify their reading patterns or subjects of
3671   interest. This information is clearly confidential in nature and its
3672   handling can be constrained by law in certain countries. People using
3673   HTTP to provide data are responsible for ensuring that
3674   such material is not distributed without the permission of any
3675   individuals that are identifiable by the published results.
3676</t>
3677</section>
3678
3679<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3680<t>
3681   Implementations of HTTP origin servers SHOULD be careful to restrict
3682   the documents returned by HTTP requests to be only those that were
3683   intended by the server administrators. If an HTTP server translates
3684   HTTP URIs directly into file system calls, the server MUST take
3685   special care not to serve files that were not intended to be
3686   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3687   other operating systems use ".." as a path component to indicate a
3688   directory level above the current one. On such a system, an HTTP
3689   server MUST disallow any such construct in the request-target if it
3690   would otherwise allow access to a resource outside those intended to
3691   be accessible via the HTTP server. Similarly, files intended for
3692   reference only internally to the server (such as access control
3693   files, configuration files, and script code) MUST be protected from
3694   inappropriate retrieval, since they might contain sensitive
3695   information. Experience has shown that minor bugs in such HTTP server
3696   implementations have turned into security risks.
3697</t>
3698</section>
3699
3700<section title="DNS Spoofing" anchor="dns.spoofing">
3701<t>
3702   Clients using HTTP rely heavily on the Domain Name Service, and are
3703   thus generally prone to security attacks based on the deliberate
3704   mis-association of IP addresses and DNS names. Clients need to be
3705   cautious in assuming the continuing validity of an IP number/DNS name
3706   association.
3707</t>
3708<t>
3709   In particular, HTTP clients SHOULD rely on their name resolver for
3710   confirmation of an IP number/DNS name association, rather than
3711   caching the result of previous host name lookups. Many platforms
3712   already can cache host name lookups locally when appropriate, and
3713   they SHOULD be configured to do so. It is proper for these lookups to
3714   be cached, however, only when the TTL (Time To Live) information
3715   reported by the name server makes it likely that the cached
3716   information will remain useful.
3717</t>
3718<t>
3719   If HTTP clients cache the results of host name lookups in order to
3720   achieve a performance improvement, they MUST observe the TTL
3721   information reported by DNS.
3722</t>
3723<t>
3724   If HTTP clients do not observe this rule, they could be spoofed when
3725   a previously-accessed server's IP address changes. As network
3726   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3727   possibility of this form of attack will grow. Observing this
3728   requirement thus reduces this potential security vulnerability.
3729</t>
3730<t>
3731   This requirement also improves the load-balancing behavior of clients
3732   for replicated servers using the same DNS name and reduces the
3733   likelihood of a user's experiencing failure in accessing sites which
3734   use that strategy.
3735</t>
3736</section>
3737
3738<section title="Proxies and Caching" anchor="attack.proxies">
3739<t>
3740   By their very nature, HTTP proxies are men-in-the-middle, and
3741   represent an opportunity for man-in-the-middle attacks. Compromise of
3742   the systems on which the proxies run can result in serious security
3743   and privacy problems. Proxies have access to security-related
3744   information, personal information about individual users and
3745   organizations, and proprietary information belonging to users and
3746   content providers. A compromised proxy, or a proxy implemented or
3747   configured without regard to security and privacy considerations,
3748   might be used in the commission of a wide range of potential attacks.
3749</t>
3750<t>
3751   Proxy operators should protect the systems on which proxies run as
3752   they would protect any system that contains or transports sensitive
3753   information. In particular, log information gathered at proxies often
3754   contains highly sensitive personal information, and/or information
3755   about organizations. Log information should be carefully guarded, and
3756   appropriate guidelines for use should be developed and followed.
3757   (<xref target="abuse.of.server.log.information"/>).
3758</t>
3759<t>
3760   Proxy implementors should consider the privacy and security
3761   implications of their design and coding decisions, and of the
3762   configuration options they provide to proxy operators (especially the
3763   default configuration).
3764</t>
3765<t>
3766   Users of a proxy need to be aware that proxies are no trustworthier than
3767   the people who run them; HTTP itself cannot solve this problem.
3768</t>
3769<t>
3770   The judicious use of cryptography, when appropriate, may suffice to
3771   protect against a broad range of security and privacy attacks. Such
3772   cryptography is beyond the scope of the HTTP/1.1 specification.
3773</t>
3774</section>
3775
3776<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3777<t>
3778   They exist. They are hard to defend against. Research continues.
3779   Beware.
3780</t>
3781</section>
3782</section>
3783
3784<section title="Acknowledgments" anchor="ack">
3785<t>
3786   HTTP has evolved considerably over the years. It has
3787   benefited from a large and active developer community--the many
3788   people who have participated on the www-talk mailing list--and it is
3789   that community which has been most responsible for the success of
3790   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3791   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3792   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3793   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3794   VanHeyningen deserve special recognition for their efforts in
3795   defining early aspects of the protocol.
3796</t>
3797<t>
3798   This document has benefited greatly from the comments of all those
3799   participating in the HTTP-WG. In addition to those already mentioned,
3800   the following individuals have contributed to this specification:
3801</t>
3802<t>
3803   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3804   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
3805   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3806   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3807   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3808   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3809   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3810   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3811   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3812   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3813   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3814   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
3815</t>
3816<t>
3817   Thanks to the "cave men" of Palo Alto. You know who you are.
3818</t>
3819<t>
3820   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3821   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3822   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3823   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3824   Larry Masinter for their help. And thanks go particularly to Jeff
3825   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3826</t>
3827<t>
3828   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3829   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3830   discovery of many of the problems that this document attempts to
3831   rectify.
3832</t>
3833<t>
3834   This specification makes heavy use of the augmented BNF and generic
3835   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3836   reuses many of the definitions provided by Nathaniel Borenstein and
3837   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3838   specification will help reduce past confusion over the relationship
3839   between HTTP and Internet mail message formats.
3840</t>
3841</section>
3842
3843</middle>
3844<back>
3845
3846<references title="Normative References">
3847
3848<reference anchor="ISO-8859-1">
3849  <front>
3850    <title>
3851     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3852    </title>
3853    <author>
3854      <organization>International Organization for Standardization</organization>
3855    </author>
3856    <date year="1998"/>
3857  </front>
3858  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3859</reference>
3860
3861<reference anchor="Part2">
3862  <front>
3863    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3864    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3865      <organization abbrev="Day Software">Day Software</organization>
3866      <address><email>fielding@gbiv.com</email></address>
3867    </author>
3868    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3869      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3870      <address><email>jg@freedesktop.org</email></address>
3871    </author>
3872    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3873      <organization abbrev="HP">Hewlett-Packard Company</organization>
3874      <address><email>JeffMogul@acm.org</email></address>
3875    </author>
3876    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3877      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3878      <address><email>henrikn@microsoft.com</email></address>
3879    </author>
3880    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3881      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3882      <address><email>LMM@acm.org</email></address>
3883    </author>
3884    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3885      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3886      <address><email>paulle@microsoft.com</email></address>
3887    </author>
3888    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3889      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3890      <address><email>timbl@w3.org</email></address>
3891    </author>
3892    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3893      <organization abbrev="W3C">World Wide Web Consortium</organization>
3894      <address><email>ylafon@w3.org</email></address>
3895    </author>
3896    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3897      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3898      <address><email>julian.reschke@greenbytes.de</email></address>
3899    </author>
3900    <date month="July" year="2010"/>
3901  </front>
3902  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-10"/>
3903 
3904</reference>
3905
3906<reference anchor="Part3">
3907  <front>
3908    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3909    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3910      <organization abbrev="Day Software">Day Software</organization>
3911      <address><email>fielding@gbiv.com</email></address>
3912    </author>
3913    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3914      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3915      <address><email>jg@freedesktop.org</email></address>
3916    </author>
3917    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3918      <organization abbrev="HP">Hewlett-Packard Company</organization>
3919      <address><email>JeffMogul@acm.org</email></address>
3920    </author>
3921    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3922      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3923      <address><email>henrikn@microsoft.com</email></address>
3924    </author>
3925    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3926      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3927      <address><email>LMM@acm.org</email></address>
3928    </author>
3929    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3930      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3931      <address><email>paulle@microsoft.com</email></address>
3932    </author>
3933    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3934      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3935      <address><email>timbl@w3.org</email></address>
3936    </author>
3937    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3938      <organization abbrev="W3C">World Wide Web Consortium</organization>
3939      <address><email>ylafon@w3.org</email></address>
3940    </author>
3941    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3942      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3943      <address><email>julian.reschke@greenbytes.de</email></address>
3944    </author>
3945    <date month="July" year="2010"/>
3946  </front>
3947  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-10"/>
3948 
3949</reference>
3950
3951<reference anchor="Part5">
3952  <front>
3953    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3954    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3955      <organization abbrev="Day Software">Day Software</organization>
3956      <address><email>fielding@gbiv.com</email></address>
3957    </author>
3958    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3959      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
3960      <address><email>jg@freedesktop.org</email></address>
3961    </author>
3962    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3963      <organization abbrev="HP">Hewlett-Packard Company</organization>
3964      <address><email>JeffMogul@acm.org</email></address>
3965    </author>
3966    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3967      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3968      <address><email>henrikn@microsoft.com</email></address>
3969    </author>
3970    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3971      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3972      <address><email>LMM@acm.org</email></address>
3973    </author>
3974    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3975      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3976      <address><email>paulle@microsoft.com</email></address>
3977    </author>
3978    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3979      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3980      <address><email>timbl@w3.org</email></address>
3981    </author>
3982    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3983      <organization abbrev="W3C">World Wide Web Consortium</organization>
3984      <address><email>ylafon@w3.org</email></address>
3985    </author>
3986    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3987      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3988      <address><email>julian.reschke@greenbytes.de</email></address>
3989    </author>
3990    <date month="July" year="2010"/>
3991  </front>
3992  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-10"/>
3993 
3994</reference>
3995
3996<reference anchor="Part6">
3997  <front>
3998    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3999    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4000      <organization abbrev="Day Software">Day Software</organization>
4001      <address><email>fielding@gbiv.com</email></address>
4002    </author>
4003    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4004      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4005      <address><email>jg@freedesktop.org</email></address>
4006    </author>
4007    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4008      <organization abbrev="HP">Hewlett-Packard Company</organization>
4009      <address><email>JeffMogul@acm.org</email></address>
4010    </author>
4011    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4012      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4013      <address><email>henrikn@microsoft.com</email></address>
4014    </author>
4015    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4016      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
4017      <address><email>LMM@acm.org</email></address>
4018    </author>
4019    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4020      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4021      <address><email>paulle@microsoft.com</email></address>
4022    </author>
4023    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4024      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4025      <address><email>timbl@w3.org</email></address>
4026    </author>
4027    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4028      <organization abbrev="W3C">World Wide Web Consortium</organization>
4029      <address><email>ylafon@w3.org</email></address>
4030    </author>
4031    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4032      <address><email>mnot@mnot.net</email></address>
4033    </author>
4034    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4035      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4036      <address><email>julian.reschke@greenbytes.de</email></address>
4037    </author>
4038    <date month="July" year="2010"/>
4039  </front>
4040  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-10"/>
4041 
4042</reference>
4043
4044<reference anchor="RFC5234">
4045  <front>
4046    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4047    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4048      <organization>Brandenburg InternetWorking</organization>
4049      <address>
4050        <email>dcrocker@bbiw.net</email>
4051      </address> 
4052    </author>
4053    <author initials="P." surname="Overell" fullname="Paul Overell">
4054      <organization>THUS plc.</organization>
4055      <address>
4056        <email>paul.overell@thus.net</email>
4057      </address>
4058    </author>
4059    <date month="January" year="2008"/>
4060  </front>
4061  <seriesInfo name="STD" value="68"/>
4062  <seriesInfo name="RFC" value="5234"/>
4063</reference>
4064
4065<reference anchor="RFC2119">
4066  <front>
4067    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4068    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4069      <organization>Harvard University</organization>
4070      <address><email>sob@harvard.edu</email></address>
4071    </author>
4072    <date month="March" year="1997"/>
4073  </front>
4074  <seriesInfo name="BCP" value="14"/>
4075  <seriesInfo name="RFC" value="2119"/>
4076</reference>
4077
4078<reference anchor="RFC3986">
4079 <front>
4080  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
4081  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4082    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4083    <address>
4084       <email>timbl@w3.org</email>
4085       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4086    </address>
4087  </author>
4088  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4089    <organization abbrev="Day Software">Day Software</organization>
4090    <address>
4091      <email>fielding@gbiv.com</email>
4092      <uri>http://roy.gbiv.com/</uri>
4093    </address>
4094  </author>
4095  <author initials="L." surname="Masinter" fullname="Larry Masinter">
4096    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4097    <address>
4098      <email>LMM@acm.org</email>
4099      <uri>http://larry.masinter.net/</uri>
4100    </address>
4101  </author>
4102  <date month="January" year="2005"/>
4103 </front>
4104 <seriesInfo name="RFC" value="3986"/>
4105 <seriesInfo name="STD" value="66"/>
4106</reference>
4107
4108<reference anchor="USASCII">
4109  <front>
4110    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4111    <author>
4112      <organization>American National Standards Institute</organization>
4113    </author>
4114    <date year="1986"/>
4115  </front>
4116  <seriesInfo name="ANSI" value="X3.4"/>
4117</reference>
4118
4119<reference anchor="RFC1950">
4120  <front>
4121    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4122    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4123      <organization>Aladdin Enterprises</organization>
4124      <address><email>ghost@aladdin.com</email></address>
4125    </author>
4126    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4127    <date month="May" year="1996"/>
4128  </front>
4129  <seriesInfo name="RFC" value="1950"/>
4130  <annotation>
4131    RFC 1950 is an Informational RFC, thus it may be less stable than
4132    this specification. On the other hand, this downward reference was
4133    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4134    therefore it is unlikely to cause problems in practice. See also
4135    <xref target="BCP97"/>.
4136  </annotation>
4137</reference>
4138
4139<reference anchor="RFC1951">
4140  <front>
4141    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4142    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4143      <organization>Aladdin Enterprises</organization>
4144      <address><email>ghost@aladdin.com</email></address>
4145    </author>
4146    <date month="May" year="1996"/>
4147  </front>
4148  <seriesInfo name="RFC" value="1951"/>
4149  <annotation>
4150    RFC 1951 is an Informational RFC, thus it may be less stable than
4151    this specification. On the other hand, this downward reference was
4152    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4153    therefore it is unlikely to cause problems in practice. See also
4154    <xref target="BCP97"/>.
4155  </annotation>
4156</reference>
4157
4158<reference anchor="RFC1952">
4159  <front>
4160    <title>GZIP file format specification version 4.3</title>
4161    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4162      <organization>Aladdin Enterprises</organization>
4163      <address><email>ghost@aladdin.com</email></address>
4164    </author>
4165    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4166      <address><email>gzip@prep.ai.mit.edu</email></address>
4167    </author>
4168    <author initials="M." surname="Adler" fullname="Mark Adler">
4169      <address><email>madler@alumni.caltech.edu</email></address>
4170    </author>
4171    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4172      <address><email>ghost@aladdin.com</email></address>
4173    </author>
4174    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4175      <address><email>randeg@alumni.rpi.edu</email></address>
4176    </author>
4177    <date month="May" year="1996"/>
4178  </front>
4179  <seriesInfo name="RFC" value="1952"/>
4180  <annotation>
4181    RFC 1952 is an Informational RFC, thus it may be less stable than
4182    this specification. On the other hand, this downward reference was
4183    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4184    therefore it is unlikely to cause problems in practice. See also
4185    <xref target="BCP97"/>.
4186  </annotation>
4187</reference>
4188
4189</references>
4190
4191<references title="Informative References">
4192
4193<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4194  <front>
4195    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4196    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4197    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4198    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4199    <author initials="H." surname="Lie" fullname="H. Lie"/>
4200    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4201    <date year="1997" month="September"/>
4202  </front>
4203  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4204</reference>
4205
4206<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4207  <front>
4208    <title>Improving HTTP Latency</title>
4209    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4210    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4211    <date year="1995" month="December"/>
4212  </front>
4213  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4214</reference>
4215
4216<reference anchor="RFC1123">
4217  <front>
4218    <title>Requirements for Internet Hosts - Application and Support</title>
4219    <author initials="R." surname="Braden" fullname="Robert Braden">
4220      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4221      <address><email>Braden@ISI.EDU</email></address>
4222    </author>
4223    <date month="October" year="1989"/>
4224  </front>
4225  <seriesInfo name="STD" value="3"/>
4226  <seriesInfo name="RFC" value="1123"/>
4227</reference>
4228
4229<reference anchor="RFC1305">
4230  <front>
4231    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4232    <author initials="D." surname="Mills" fullname="David L. Mills">
4233      <organization>University of Delaware, Electrical Engineering Department</organization>
4234      <address><email>mills@udel.edu</email></address>
4235    </author>
4236    <date month="March" year="1992"/>
4237  </front>
4238  <seriesInfo name="RFC" value="1305"/>
4239</reference>
4240
4241<reference anchor="RFC1900">
4242  <front>
4243    <title>Renumbering Needs Work</title>
4244    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4245      <organization>CERN, Computing and Networks Division</organization>
4246      <address><email>brian@dxcoms.cern.ch</email></address>
4247    </author>
4248    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4249      <organization>cisco Systems</organization>
4250      <address><email>yakov@cisco.com</email></address>
4251    </author>
4252    <date month="February" year="1996"/>
4253  </front>
4254  <seriesInfo name="RFC" value="1900"/>
4255</reference>
4256
4257<reference anchor="RFC1945">
4258  <front>
4259    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4260    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4261      <organization>MIT, Laboratory for Computer Science</organization>
4262      <address><email>timbl@w3.org</email></address>
4263    </author>
4264    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4265      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4266      <address><email>fielding@ics.uci.edu</email></address>
4267    </author>
4268    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4269      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4270      <address><email>frystyk@w3.org</email></address>
4271    </author>
4272    <date month="May" year="1996"/>
4273  </front>
4274  <seriesInfo name="RFC" value="1945"/>
4275</reference>
4276
4277<reference anchor="RFC2045">
4278  <front>
4279    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4280    <author initials="N." surname="Freed" fullname="Ned Freed">
4281      <organization>Innosoft International, Inc.</organization>
4282      <address><email>ned@innosoft.com</email></address>
4283    </author>
4284    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4285      <organization>First Virtual Holdings</organization>
4286      <address><email>nsb@nsb.fv.com</email></address>
4287    </author>
4288    <date month="November" year="1996"/>
4289  </front>
4290  <seriesInfo name="RFC" value="2045"/>
4291</reference>
4292
4293<reference anchor="RFC2047">
4294  <front>
4295    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4296    <author initials="K." surname="Moore" fullname="Keith Moore">
4297      <organization>University of Tennessee</organization>
4298      <address><email>moore@cs.utk.edu</email></address>
4299    </author>
4300    <date month="November" year="1996"/>
4301  </front>
4302  <seriesInfo name="RFC" value="2047"/>
4303</reference>
4304
4305<reference anchor="RFC2068">
4306  <front>
4307    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4308    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4309      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4310      <address><email>fielding@ics.uci.edu</email></address>
4311    </author>
4312    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4313      <organization>MIT Laboratory for Computer Science</organization>
4314      <address><email>jg@w3.org</email></address>
4315    </author>
4316    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4317      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4318      <address><email>mogul@wrl.dec.com</email></address>
4319    </author>
4320    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4321      <organization>MIT Laboratory for Computer Science</organization>
4322      <address><email>frystyk@w3.org</email></address>
4323    </author>
4324    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4325      <organization>MIT Laboratory for Computer Science</organization>
4326      <address><email>timbl@w3.org</email></address>
4327    </author>
4328    <date month="January" year="1997"/>
4329  </front>
4330  <seriesInfo name="RFC" value="2068"/>
4331</reference>
4332
4333<reference anchor="RFC2109">
4334  <front>
4335    <title>HTTP State Management Mechanism</title>
4336    <author initials="D.M." surname="Kristol" fullname="David M. Kristol">
4337      <organization>Bell Laboratories, Lucent Technologies</organization>
4338      <address><email>dmk@bell-labs.com</email></address>
4339    </author>
4340    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4341      <organization>Netscape Communications Corp.</organization>
4342      <address><email>montulli@netscape.com</email></address>
4343    </author>
4344    <date year="1997" month="February"/>
4345  </front>
4346  <seriesInfo name="RFC" value="2109"/>
4347</reference>
4348
4349<reference anchor="RFC2145">
4350  <front>
4351    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4352    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4353      <organization>Western Research Laboratory</organization>
4354      <address><email>mogul@wrl.dec.com</email></address>
4355    </author>
4356    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4357      <organization>Department of Information and Computer Science</organization>
4358      <address><email>fielding@ics.uci.edu</email></address>
4359    </author>
4360    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4361      <organization>MIT Laboratory for Computer Science</organization>
4362      <address><email>jg@w3.org</email></address>
4363    </author>
4364    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4365      <organization>W3 Consortium</organization>
4366      <address><email>frystyk@w3.org</email></address>
4367    </author>
4368    <date month="May" year="1997"/>
4369  </front>
4370  <seriesInfo name="RFC" value="2145"/>
4371</reference>
4372
4373<reference anchor="RFC2616">
4374  <front>
4375    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4376    <author initials="R." surname="Fielding" fullname="R. Fielding">
4377      <organization>University of California, Irvine</organization>
4378      <address><email>fielding@ics.uci.edu</email></address>
4379    </author>
4380    <author initials="J." surname="Gettys" fullname="J. Gettys">
4381      <organization>W3C</organization>
4382      <address><email>jg@w3.org</email></address>
4383    </author>
4384    <author initials="J." surname="Mogul" fullname="J. Mogul">
4385      <organization>Compaq Computer Corporation</organization>
4386      <address><email>mogul@wrl.dec.com</email></address>
4387    </author>
4388    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4389      <organization>MIT Laboratory for Computer Science</organization>
4390      <address><email>frystyk@w3.org</email></address>
4391    </author>
4392    <author initials="L." surname="Masinter" fullname="L. Masinter">
4393      <organization>Xerox Corporation</organization>
4394      <address><email>masinter@parc.xerox.com</email></address>
4395    </author>
4396    <author initials="P." surname="Leach" fullname="P. Leach">
4397      <organization>Microsoft Corporation</organization>
4398      <address><email>paulle@microsoft.com</email></address>
4399    </author>
4400    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4401      <organization>W3C</organization>
4402      <address><email>timbl@w3.org</email></address>
4403    </author>
4404    <date month="June" year="1999"/>
4405  </front>
4406  <seriesInfo name="RFC" value="2616"/>
4407</reference>
4408
4409<reference anchor="RFC2817">
4410  <front>
4411    <title>Upgrading to TLS Within HTTP/1.1</title>
4412    <author initials="R." surname="Khare" fullname="R. Khare">
4413      <organization>4K Associates / UC Irvine</organization>
4414      <address><email>rohit@4K-associates.com</email></address>
4415    </author>
4416    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
4417      <organization>Agranat Systems, Inc.</organization>
4418      <address><email>lawrence@agranat.com</email></address>
4419    </author>
4420    <date year="2000" month="May"/>
4421  </front>
4422  <seriesInfo name="RFC" value="2817"/>
4423</reference>
4424
4425<reference anchor="RFC2818">
4426  <front>
4427    <title>HTTP Over TLS</title>
4428    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
4429      <organization>RTFM, Inc.</organization>
4430      <address><email>ekr@rtfm.com</email></address>
4431    </author>
4432    <date year="2000" month="May"/>
4433  </front>
4434  <seriesInfo name="RFC" value="2818"/>
4435</reference>
4436
4437<reference anchor="RFC2965">
4438  <front>
4439    <title>HTTP State Management Mechanism</title>
4440    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
4441      <organization>Bell Laboratories, Lucent Technologies</organization>
4442      <address><email>dmk@bell-labs.com</email></address>
4443    </author>
4444    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4445      <organization>Epinions.com, Inc.</organization>
4446      <address><email>lou@montulli.org</email></address>
4447    </author>
4448    <date year="2000" month="October"/>
4449  </front>
4450  <seriesInfo name="RFC" value="2965"/>
4451</reference>
4452
4453<reference anchor="RFC3864">
4454  <front>
4455    <title>Registration Procedures for Message Header Fields</title>
4456    <author initials="G." surname="Klyne" fullname="G. Klyne">
4457      <organization>Nine by Nine</organization>
4458      <address><email>GK-IETF@ninebynine.org</email></address>
4459    </author>
4460    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
4461      <organization>BEA Systems</organization>
4462      <address><email>mnot@pobox.com</email></address>
4463    </author>
4464    <author initials="J." surname="Mogul" fullname="J. Mogul">
4465      <organization>HP Labs</organization>
4466      <address><email>JeffMogul@acm.org</email></address>
4467    </author>
4468    <date year="2004" month="September"/>
4469  </front>
4470  <seriesInfo name="BCP" value="90"/>
4471  <seriesInfo name="RFC" value="3864"/>
4472</reference>
4473
4474<reference anchor="RFC4288">
4475  <front>
4476    <title>Media Type Specifications and Registration Procedures</title>
4477    <author initials="N." surname="Freed" fullname="N. Freed">
4478      <organization>Sun Microsystems</organization>
4479      <address>
4480        <email>ned.freed@mrochek.com</email>
4481      </address>
4482    </author>
4483    <author initials="J." surname="Klensin" fullname="J. Klensin">
4484      <address>
4485        <email>klensin+ietf@jck.com</email>
4486      </address>
4487    </author>
4488    <date year="2005" month="December"/>
4489  </front>
4490  <seriesInfo name="BCP" value="13"/>
4491  <seriesInfo name="RFC" value="4288"/>
4492</reference>
4493
4494<reference anchor="RFC4395">
4495  <front>
4496    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4497    <author initials="T." surname="Hansen" fullname="T. Hansen">
4498      <organization>AT&amp;T Laboratories</organization>
4499      <address>
4500        <email>tony+urireg@maillennium.att.com</email>
4501      </address>
4502    </author>
4503    <author initials="T." surname="Hardie" fullname="T. Hardie">
4504      <organization>Qualcomm, Inc.</organization>
4505      <address>
4506        <email>hardie@qualcomm.com</email>
4507      </address>
4508    </author>
4509    <author initials="L." surname="Masinter" fullname="L. Masinter">
4510      <organization>Adobe Systems</organization>
4511      <address>
4512        <email>LMM@acm.org</email>
4513      </address>
4514    </author>
4515    <date year="2006" month="February"/>
4516  </front>
4517  <seriesInfo name="BCP" value="115"/>
4518  <seriesInfo name="RFC" value="4395"/>
4519</reference>
4520
4521<reference anchor="RFC5226">
4522  <front>
4523    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4524    <author initials="T." surname="Narten" fullname="T. Narten">
4525      <organization>IBM</organization>
4526      <address><email>narten@us.ibm.com</email></address>
4527    </author>
4528    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
4529      <organization>Google</organization>
4530      <address><email>Harald@Alvestrand.no</email></address>
4531    </author>
4532    <date year="2008" month="May"/>
4533  </front>
4534  <seriesInfo name="BCP" value="26"/>
4535  <seriesInfo name="RFC" value="5226"/>
4536</reference>
4537
4538<reference anchor="RFC5322">
4539  <front>
4540    <title>Internet Message Format</title>
4541    <author initials="P." surname="Resnick" fullname="P. Resnick">
4542      <organization>Qualcomm Incorporated</organization>
4543    </author>
4544    <date year="2008" month="October"/>
4545  </front> 
4546  <seriesInfo name="RFC" value="5322"/>
4547</reference>
4548
4549<reference anchor="BCP97">
4550  <front>
4551    <title>Handling Normative References to Standards-Track Documents</title>
4552    <author initials="J." surname="Klensin" fullname="J. Klensin">
4553      <address>
4554        <email>klensin+ietf@jck.com</email>
4555      </address>
4556    </author>
4557    <author initials="S." surname="Hartman" fullname="S. Hartman">
4558      <organization>MIT</organization>
4559      <address>
4560        <email>hartmans-ietf@mit.edu</email>
4561      </address>
4562    </author>
4563    <date year="2007" month="June"/>
4564  </front>
4565  <seriesInfo name="BCP" value="97"/>
4566  <seriesInfo name="RFC" value="4897"/>
4567</reference>
4568
4569<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4570  <front>
4571    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4572    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4573    <date year="2001" month="November"/>
4574  </front>
4575  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4576</reference>
4577
4578<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4579  <front>
4580    <title>Analysis of HTTP Performance Problems</title>
4581    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4582    <date/>
4583  </front>
4584</reference>
4585
4586<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4587  <front>
4588  <title>Analysis of HTTP Performance</title>
4589  <author initials="J." surname="Touch" fullname="Joe Touch">
4590    <organization>USC/Information Sciences Institute</organization>
4591    <address><email>touch@isi.edu</email></address>
4592  </author>
4593  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4594    <organization>USC/Information Sciences Institute</organization>
4595    <address><email>johnh@isi.edu</email></address>
4596  </author>
4597  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4598    <organization>USC/Information Sciences Institute</organization>
4599    <address><email>katia@isi.edu</email></address>
4600  </author>
4601  <date year="1998" month="Aug"/>
4602  </front>
4603  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4604  <annotation>(original report dated Aug. 1996)</annotation>
4605</reference>
4606
4607</references>
4608
4609
4610<section title="Tolerant Applications" anchor="tolerant.applications">
4611<t>
4612   Although this document specifies the requirements for the generation
4613   of HTTP/1.1 messages, not all applications will be correct in their
4614   implementation. We therefore recommend that operational applications
4615   be tolerant of deviations whenever those deviations can be
4616   interpreted unambiguously.
4617</t>
4618<t>
4619   Clients SHOULD be tolerant in parsing the Status-Line and servers
4620   SHOULD be tolerant when parsing the Request-Line. In particular, they
4621   SHOULD accept any amount of WSP characters between fields, even though
4622   only a single SP is required.
4623</t>
4624<t>
4625   The line terminator for header fields is the sequence CRLF.
4626   However, we recommend that applications, when parsing such headers,
4627   recognize a single LF as a line terminator and ignore the leading CR.
4628</t>
4629<t>
4630   The character set of an entity-body SHOULD be labeled as the lowest
4631   common denominator of the character codes used within that body, with
4632   the exception that not labeling the entity is preferred over labeling
4633   the entity with the labels US-ASCII or ISO-8859-1. See <xref target="Part3"/>.
4634</t>
4635<t>
4636   Additional rules for requirements on parsing and encoding of dates
4637   and other potential problems with date encodings include:
4638</t>
4639<t>
4640  <list style="symbols">
4641     <t>HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
4642        which appears to be more than 50 years in the future is in fact
4643        in the past (this helps solve the "year 2000" problem).</t>
4644
4645     <t>Although all date formats are specified to be case-sensitive,
4646        recipients SHOULD match day, week and timezone names
4647        case-insensitively.</t>
4648             
4649     <t>An HTTP/1.1 implementation MAY internally represent a parsed
4650        Expires date as earlier than the proper value, but MUST NOT
4651        internally represent a parsed Expires date as later than the
4652        proper value.</t>
4653
4654     <t>All expiration-related calculations MUST be done in GMT. The
4655        local time zone MUST NOT influence the calculation or comparison
4656        of an age or expiration time.</t>
4657
4658     <t>If an HTTP header incorrectly carries a date value with a time
4659        zone other than GMT, it MUST be converted into GMT using the
4660        most conservative possible conversion.</t>
4661  </list>
4662</t>
4663</section>
4664
4665<section title="Compatibility with Previous Versions" anchor="compatibility">
4666<t>
4667   HTTP has been in use by the World-Wide Web global information initiative
4668   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4669   was a simple protocol for hypertext data transfer across the Internet
4670   with only a single method and no metadata.
4671   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4672   methods and MIME-like messaging that could include metadata about the data
4673   transferred and modifiers on the request/response semantics. However,
4674   HTTP/1.0 did not sufficiently take into consideration the effects of
4675   hierarchical proxies, caching, the need for persistent connections, or
4676   name-based virtual hosts. The proliferation of incompletely-implemented
4677   applications calling themselves "HTTP/1.0" further necessitated a
4678   protocol version change in order for two communicating applications
4679   to determine each other's true capabilities.
4680</t>
4681<t>
4682   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4683   requirements that enable reliable implementations, adding only
4684   those new features that will either be safely ignored by an HTTP/1.0
4685   recipient or only sent when communicating with a party advertising
4686   compliance with HTTP/1.1.
4687</t>
4688<t>
4689   It is beyond the scope of a protocol specification to mandate
4690   compliance with previous versions. HTTP/1.1 was deliberately
4691   designed, however, to make supporting previous versions easy. It is
4692   worth noting that, at the time of composing this specification, we would
4693   expect general-purpose HTTP/1.1 servers to:
4694  <list style="symbols">
4695     <t>understand any valid request in the format of HTTP/1.0 and
4696        1.1;</t>
4697
4698     <t>respond appropriately with a message in the same major version
4699        used by the client.</t>
4700  </list>
4701</t>
4702<t>
4703   And we would expect HTTP/1.1 clients to:
4704  <list style="symbols">
4705     <t>understand any valid response in the format of HTTP/1.0 or
4706        1.1.</t>
4707  </list>
4708</t>
4709<t>
4710   For most implementations of HTTP/1.0, each connection is established
4711   by the client prior to the request and closed by the server after
4712   sending the response. Some implementations implement the Keep-Alive
4713   version of persistent connections described in Section 19.7.1 of <xref target="RFC2068"/>.
4714</t>
4715
4716<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4717<t>
4718   This section summarizes major differences between versions HTTP/1.0
4719   and HTTP/1.1.
4720</t>
4721
4722<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">
4723<t>
4724   The requirements that clients and servers support the Host request-header,
4725   report an error if the Host request-header (<xref target="header.host"/>) is
4726   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4727   are among the most important changes defined by this
4728   specification.
4729</t>
4730<t>
4731   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4732   addresses and servers; there was no other established mechanism for
4733   distinguishing the intended server of a request than the IP address
4734   to which that request was directed. The changes outlined above will
4735   allow the Internet, once older HTTP clients are no longer common, to
4736   support multiple Web sites from a single IP address, greatly
4737   simplifying large operational Web servers, where allocation of many
4738   IP addresses to a single host has created serious problems. The
4739   Internet will also be able to recover the IP addresses that have been
4740   allocated for the sole purpose of allowing special-purpose domain
4741   names to be used in root-level HTTP URLs. Given the rate of growth of
4742   the Web, and the number of servers already deployed, it is extremely
4743   important that all implementations of HTTP (including updates to
4744   existing HTTP/1.0 applications) correctly implement these
4745   requirements:
4746  <list style="symbols">
4747     <t>Both clients and servers MUST support the Host request-header.</t>
4748
4749     <t>A client that sends an HTTP/1.1 request MUST send a Host header.</t>
4750
4751     <t>Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
4752        request does not include a Host request-header.</t>
4753
4754     <t>Servers MUST accept absolute URIs.</t>
4755  </list>
4756</t>
4757</section>
4758</section>
4759
4760<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4761<t>
4762   Some clients and servers might wish to be compatible with some
4763   previous implementations of persistent connections in HTTP/1.0
4764   clients and servers. Persistent connections in HTTP/1.0 are
4765   explicitly negotiated as they are not the default behavior. HTTP/1.0
4766   experimental implementations of persistent connections are faulty,
4767   and the new facilities in HTTP/1.1 are designed to rectify these
4768   problems. The problem was that some existing HTTP/1.0 clients may be
4769   sending Keep-Alive to a proxy server that doesn't understand
4770   Connection, which would then erroneously forward it to the next
4771   inbound server, which would establish the Keep-Alive connection and
4772   result in a hung HTTP/1.0 proxy waiting for the close on the
4773   response. The result is that HTTP/1.0 clients must be prevented from
4774   using Keep-Alive when talking to proxies.
4775</t>
4776<t>
4777   However, talking to proxies is the most important use of persistent
4778   connections, so that prohibition is clearly unacceptable. Therefore,
4779   we need some other mechanism for indicating a persistent connection
4780   is desired, which is safe to use even when talking to an old proxy
4781   that ignores Connection. Persistent connections are the default for
4782   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4783   declaring non-persistence. See <xref target="header.connection"/>.
4784</t>
4785<t>
4786   The original HTTP/1.0 form of persistent connections (the Connection:
4787   Keep-Alive and Keep-Alive header) is documented in Section 19.7.1 of <xref target="RFC2068"/>.
4788</t>
4789</section>
4790
4791<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4792<t>
4793   This specification has been carefully audited to correct and
4794   disambiguate key word usage; RFC 2068 had many problems in respect to
4795   the conventions laid out in <xref target="RFC2119"/>.
4796</t>
4797<t>
4798   Transfer-coding and message lengths all interact in ways that
4799   required fixing exactly when chunked encoding is used (to allow for
4800   transfer encoding that may not be self delimiting); it was important
4801   to straighten out exactly how message lengths are computed. (Sections
4802   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4803   <xref target="header.content-length" format="counter"/>,
4804   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4805</t>
4806<t>
4807   The use and interpretation of HTTP version numbers has been clarified
4808   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4809   version they support to deal with problems discovered in HTTP/1.0
4810   implementations (<xref target="http.version"/>)
4811</t>
4812<t>
4813   Quality Values of zero should indicate that "I don't want something"
4814   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4815</t>
4816<t>
4817   Transfer-coding had significant problems, particularly with
4818   interactions with chunked encoding. The solution is that transfer-codings
4819   become as full fledged as content-codings. This involves
4820   adding an IANA registry for transfer-codings (separate from content
4821   codings), a new header field (TE) and enabling trailer headers in the
4822   future. Transfer encoding is a major performance benefit, so it was
4823   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4824   interoperability problem that could have occurred due to interactions
4825   between authentication trailers, chunked encoding and HTTP/1.0
4826   clients.(Section
4827   <xref target="transfer.codings" format="counter"/>,
4828   <xref target="chunked.encoding" format="counter"/>,
4829   <xref target="non-modifiable.headers" format="counter"/>,
4830   and <xref target="header.te" format="counter"/>)
4831</t>
4832<t>
4833  Proxies should be able to add Content-Length when appropriate.
4834  (<xref target="non-modifiable.headers"/>)
4835</t>
4836</section>
4837
4838<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4839<t>
4840  Empty list elements in list productions have been deprecated.
4841  (<xref target="notation.abnf"/>)
4842</t>
4843<t>
4844  Rules about implicit linear whitespace between certain grammar productions
4845  have been removed; now it's only allowed when specifically pointed out
4846  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4847  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4848  Non-ASCII content in header fields and reason phrase has been obsoleted and
4849  made opaque (the TEXT rule was removed)
4850  (<xref target="basic.rules"/>)
4851</t>
4852<t>
4853  Clarify that HTTP-Version is case sensitive.
4854  (<xref target="http.version"/>)
4855</t>
4856<t>
4857  Remove reference to non-existent identity transfer-coding value tokens.
4858  (Sections <xref format="counter" target="transfer.codings"/> and
4859  <xref format="counter" target="message.length"/>)
4860</t>
4861<t>
4862  Require that invalid whitespace around field-names be rejected.
4863  (<xref target="header.fields"/>)
4864</t>
4865<t>
4866  Update use of abs_path production from RFC1808 to the path-absolute + query
4867  components of RFC3986.
4868  (<xref target="request-target"/>)
4869</t>
4870<t>
4871  Clarification that the chunk length does not include the count of the octets
4872  in the chunk header and trailer. Furthermore disallowed line folding
4873  in chunk extensions.
4874  (<xref target="chunked.encoding"/>)
4875</t>
4876<t>
4877  Remove hard limit of two connections per server.
4878  (<xref target="persistent.practical"/>)
4879</t>
4880<t>
4881  Clarify exactly when close connection options must be sent.
4882  (<xref target="header.connection"/>)
4883</t>
4884</section>
4885</section>
4886
4887
4888<section title="Collected ABNF" anchor="collected.abnf">
4889<figure>
4890<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
4891BWS = OWS
4892
4893Cache-Control = <Cache-Control, defined in [Part6], Section 3.4>
4894Chunked-Body = *chunk last-chunk trailer-part CRLF
4895Connection = "Connection:" OWS Connection-v
4896Connection-v = *( "," OWS ) connection-token *( OWS "," [ OWS
4897 connection-token ] )
4898Content-Length = "Content-Length:" OWS 1*Content-Length-v
4899Content-Length-v = 1*DIGIT
4900
4901Date = "Date:" OWS Date-v
4902Date-v = HTTP-date
4903
4904GMT = %x47.4D.54 ; GMT
4905
4906HTTP-Prot-Name = %x48.54.54.50 ; HTTP
4907HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4908HTTP-date = rfc1123-date / obs-date
4909HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
4910 ]
4911Host = "Host:" OWS Host-v
4912Host-v = uri-host [ ":" port ]
4913
4914Method = token
4915
4916OWS = *( [ obs-fold ] WSP )
4917
4918Pragma = <Pragma, defined in [Part6], Section 3.4>
4919
4920RWS = 1*( [ obs-fold ] WSP )
4921Reason-Phrase = *( WSP / VCHAR / obs-text )
4922Request = Request-Line *( ( general-header / request-header /
4923 entity-header ) CRLF ) CRLF [ message-body ]
4924Request-Line = Method SP request-target SP HTTP-Version CRLF
4925Response = Status-Line *( ( general-header / response-header /
4926 entity-header ) CRLF ) CRLF [ message-body ]
4927
4928Status-Code = 3DIGIT
4929Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4930
4931TE = "TE:" OWS TE-v
4932TE-v = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4933Trailer = "Trailer:" OWS Trailer-v
4934Trailer-v = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4935Transfer-Encoding = "Transfer-Encoding:" OWS Transfer-Encoding-v
4936Transfer-Encoding-v = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4937 transfer-coding ] )
4938
4939URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
4940Upgrade = "Upgrade:" OWS Upgrade-v
4941Upgrade-v = *( "," OWS ) product *( OWS "," [ OWS product ] )
4942
4943Via = "Via:" OWS Via-v
4944Via-v = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4945 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4946 ] )
4947
4948Warning = <Warning, defined in [Part6], Section 3.6>
4949
4950absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
4951asctime-date = day-name SP date3 SP time-of-day SP year
4952attribute = token
4953authority = <authority, defined in [RFC3986], Section 3.2>
4954
4955chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4956chunk-data = 1*OCTET
4957chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4958chunk-ext-name = token
4959chunk-ext-val = token / quoted-str-nf
4960chunk-size = 1*HEXDIG
4961comment = "(" *( ctext / quoted-cpair / comment ) ")"
4962connection-token = token
4963ctext = OWS / %x21-27 ; '!'-'''
4964 / %x2A-5B ; '*'-'['
4965 / %x5D-7E ; ']'-'~'
4966 / obs-text
4967
4968date1 = day SP month SP year
4969date2 = day "-" month "-" 2DIGIT
4970date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
4971day = 2DIGIT
4972day-name = %x4D.6F.6E ; Mon
4973 / %x54.75.65 ; Tue
4974 / %x57.65.64 ; Wed
4975 / %x54.68.75 ; Thu
4976 / %x46.72.69 ; Fri
4977 / %x53.61.74 ; Sat
4978 / %x53.75.6E ; Sun
4979day-name-l = %x4D.6F.6E.64.61.79 ; Monday
4980 / %x54.75.65.73.64.61.79 ; Tuesday
4981 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4982 / %x54.68.75.72.73.64.61.79 ; Thursday
4983 / %x46.72.69.64.61.79 ; Friday
4984 / %x53.61.74.75.72.64.61.79 ; Saturday
4985 / %x53.75.6E.64.61.79 ; Sunday
4986
4987entity-body = <entity-body, defined in [Part3], Section 3.2>
4988entity-header = <entity-header, defined in [Part3], Section 3.1>
4989
4990field-content = *( WSP / VCHAR / obs-text )
4991field-name = token
4992field-value = *( field-content / OWS )
4993
4994general-header = Cache-Control / Connection / Date / Pragma / Trailer
4995 / Transfer-Encoding / Upgrade / Via / Warning
4996
4997header-field = field-name ":" OWS [ field-value ] OWS
4998hour = 2DIGIT
4999http-URI = "http://" authority path-abempty [ "?" query ]
5000https-URI = "https://" authority path-abempty [ "?" query ]
5001
5002last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF
5003
5004message-body = entity-body /
5005 <entity-body encoded as per Transfer-Encoding>
5006minute = 2DIGIT
5007month = %x4A.61.6E ; Jan
5008 / %x46.65.62 ; Feb
5009 / %x4D.61.72 ; Mar
5010 / %x41.70.72 ; Apr
5011 / %x4D.61.79 ; May
5012 / %x4A.75.6E ; Jun
5013 / %x4A.75.6C ; Jul
5014 / %x41.75.67 ; Aug
5015 / %x53.65.70 ; Sep
5016 / %x4F.63.74 ; Oct
5017 / %x4E.6F.76 ; Nov
5018 / %x44.65.63 ; Dec
5019
5020obs-date = rfc850-date / asctime-date
5021obs-fold = CRLF
5022obs-text = %x80-FF
5023
5024partial-URI = relative-part [ "?" query ]
5025path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
5026path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
5027port = <port, defined in [RFC3986], Section 3.2.3>
5028product = token [ "/" product-version ]
5029product-version = token
5030protocol-name = token
5031protocol-version = token
5032pseudonym = token
5033
5034qdtext = OWS / "!" / %x23-5B ; '#'-'['
5035 / %x5D-7E ; ']'-'~'
5036 / obs-text
5037qdtext-nf = WSP / "!" / %x23-5B ; '#'-'['
5038 / %x5D-7E ; ']'-'~'
5039 / obs-text
5040query = <query, defined in [RFC3986], Section 3.4>
5041quoted-cpair = "\" ( WSP / VCHAR / obs-text )
5042quoted-pair = "\" ( WSP / VCHAR / obs-text )
5043quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5044quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5045qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5046
5047received-by = ( uri-host [ ":" port ] ) / pseudonym
5048received-protocol = [ protocol-name "/" ] protocol-version
5049relative-part = <relative-part, defined in [RFC3986], Section 4.2>
5050request-header = <request-header, defined in [Part2], Section 3>
5051request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5052 / authority
5053response-header = <response-header, defined in [Part2], Section 5>
5054rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
5055rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
5056
5057second = 2DIGIT
5058special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
5059 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5060start-line = Request-Line / Status-Line
5061
5062t-codings = "trailers" / ( transfer-extension [ te-params ] )
5063tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
5064 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5065te-ext = OWS ";" OWS token [ "=" word ]
5066te-params = OWS ";" OWS "q=" qvalue *te-ext
5067time-of-day = hour ":" minute ":" second
5068token = 1*tchar
5069trailer-part = *( entity-header CRLF )
5070transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
5071 transfer-extension
5072transfer-extension = token *( OWS ";" OWS transfer-parameter )
5073transfer-parameter = attribute BWS "=" BWS value
5074
5075uri-host = <host, defined in [RFC3986], Section 3.2.2>
5076
5077value = word
5078
5079word = token / quoted-string
5080
5081year = 4DIGIT
5082]]></artwork>
5083</figure>
5084<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
5085; Chunked-Body defined but not used
5086; Content-Length defined but not used
5087; HTTP-message defined but not used
5088; Host defined but not used
5089; Request defined but not used
5090; Response defined but not used
5091; TE defined but not used
5092; URI-reference defined but not used
5093; http-URI defined but not used
5094; https-URI defined but not used
5095; partial-URI defined but not used
5096; special defined but not used
5097]]></artwork></figure></section>
5098
5099
5100<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5101
5102<section title="Since RFC2616">
5103<t>
5104  Extracted relevant partitions from <xref target="RFC2616"/>.
5105</t>
5106</section>
5107
5108<section title="Since draft-ietf-httpbis-p1-messaging-00">
5109<t>
5110  Closed issues:
5111  <list style="symbols"> 
5112    <t>
5113      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5114      "HTTP Version should be case sensitive"
5115      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5116    </t>
5117    <t>
5118      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5119      "'unsafe' characters"
5120      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5121    </t>
5122    <t>
5123      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5124      "Chunk Size Definition"
5125      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5126    </t>
5127    <t>
5128      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5129      "Message Length"
5130      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5131    </t>
5132    <t>
5133      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5134      "Media Type Registrations"
5135      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5136    </t>
5137    <t>
5138      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5139      "URI includes query"
5140      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5141    </t>
5142    <t>
5143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5144      "No close on 1xx responses"
5145      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5146    </t>
5147    <t>
5148      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5149      "Remove 'identity' token references"
5150      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5151    </t>
5152    <t>
5153      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5154      "Import query BNF"
5155    </t>
5156    <t>
5157      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5158      "qdtext BNF"
5159    </t>
5160    <t>
5161      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5162      "Normative and Informative references"
5163    </t>
5164    <t>
5165      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5166      "RFC2606 Compliance"
5167    </t>
5168    <t>
5169      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5170      "RFC977 reference"
5171    </t>
5172    <t>
5173      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5174      "RFC1700 references"
5175    </t>
5176    <t>
5177      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5178      "inconsistency in date format explanation"
5179    </t>
5180    <t>
5181      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5182      "Date reference typo"
5183    </t>
5184    <t>
5185      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5186      "Informative references"
5187    </t>
5188    <t>
5189      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5190      "ISO-8859-1 Reference"
5191    </t>
5192    <t>
5193      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5194      "Normative up-to-date references"
5195    </t>
5196  </list>
5197</t>
5198<t>
5199  Other changes:
5200  <list style="symbols"> 
5201    <t>
5202      Update media type registrations to use RFC4288 template.
5203    </t>
5204    <t>
5205      Use names of RFC4234 core rules DQUOTE and WSP,
5206      fix broken ABNF for chunk-data
5207      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5208    </t>
5209  </list>
5210</t>
5211</section>
5212
5213<section title="Since draft-ietf-httpbis-p1-messaging-01">
5214<t>
5215  Closed issues:
5216  <list style="symbols"> 
5217    <t>
5218      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5219      "Bodies on GET (and other) requests"
5220    </t>
5221    <t>
5222      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5223      "Updating to RFC4288"
5224    </t>
5225    <t>
5226      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5227      "Status Code and Reason Phrase"
5228    </t>
5229    <t>
5230      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5231      "rel_path not used"
5232    </t>
5233  </list>
5234</t>
5235<t>
5236  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5237  <list style="symbols"> 
5238    <t>
5239      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
5240      "trailer-part").
5241    </t>
5242    <t>
5243      Avoid underscore character in rule names ("http_URL" -&gt;
5244      "http-URL", "abs_path" -&gt; "path-absolute").
5245    </t>
5246    <t>
5247      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5248      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5249      have to be updated when switching over to RFC3986.
5250    </t>
5251    <t>
5252      Synchronize core rules with RFC5234.
5253    </t>
5254    <t>
5255      Get rid of prose rules that span multiple lines.
5256    </t>
5257    <t>
5258      Get rid of unused rules LOALPHA and UPALPHA.
5259    </t>
5260    <t>
5261      Move "Product Tokens" section (back) into Part 1, as "token" is used
5262      in the definition of the Upgrade header.
5263    </t>
5264    <t>
5265      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5266    </t>
5267    <t>
5268      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5269    </t>
5270  </list>
5271</t>
5272</section>
5273
5274<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5275<t>
5276  Closed issues:
5277  <list style="symbols"> 
5278    <t>
5279      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5280      "HTTP-date vs. rfc1123-date"
5281    </t>
5282    <t>
5283      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5284      "WS in quoted-pair"
5285    </t>
5286  </list>
5287</t>
5288<t>
5289  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5290  <list style="symbols"> 
5291    <t>
5292      Reference RFC 3984, and update header registrations for headers defined
5293      in this document.
5294    </t>
5295  </list>
5296</t>
5297<t>
5298  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5299  <list style="symbols"> 
5300    <t>
5301      Replace string literals when the string really is case-sensitive (HTTP-Version).
5302    </t>
5303  </list>
5304</t>
5305</section>
5306
5307<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5308<t>
5309  Closed issues:
5310  <list style="symbols"> 
5311    <t>
5312      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5313      "Connection closing"
5314    </t>
5315    <t>
5316      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5317      "Move registrations and registry information to IANA Considerations"
5318    </t>
5319    <t>
5320      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5321      "need new URL for PAD1995 reference"
5322    </t>
5323    <t>
5324      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5325      "IANA Considerations: update HTTP URI scheme registration"
5326    </t>
5327    <t>
5328      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5329      "Cite HTTPS URI scheme definition"
5330    </t>
5331    <t>
5332      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5333      "List-type headers vs Set-Cookie"
5334    </t>
5335  </list>
5336</t>
5337<t>
5338  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5339  <list style="symbols"> 
5340    <t>
5341      Replace string literals when the string really is case-sensitive (HTTP-Date).
5342    </t>
5343    <t>
5344      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5345    </t>
5346  </list>
5347</t>
5348</section>
5349
5350<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5351<t>
5352  Closed issues:
5353  <list style="symbols"> 
5354    <t>
5355      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5356      "Out-of-date reference for URIs"
5357    </t>
5358    <t>
5359      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5360      "RFC 2822 is updated by RFC 5322"
5361    </t>
5362  </list>
5363</t>
5364<t>
5365  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5366  <list style="symbols"> 
5367    <t>
5368      Use "/" instead of "|" for alternatives.
5369    </t>
5370    <t>
5371      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5372    </t>
5373    <t>
5374      Only reference RFC 5234's core rules.
5375    </t>
5376    <t>
5377      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5378      whitespace ("OWS") and required whitespace ("RWS").
5379    </t>
5380    <t>
5381      Rewrite ABNFs to spell out whitespace rules, factor out
5382      header value format definitions.
5383    </t>
5384  </list>
5385</t>
5386</section>
5387
5388<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5389<t>
5390  Closed issues:
5391  <list style="symbols"> 
5392    <t>
5393      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5394      "Header LWS"
5395    </t>
5396    <t>
5397      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5398      "Sort 1.3 Terminology"
5399    </t>
5400    <t>
5401      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5402      "RFC2047 encoded words"
5403    </t>
5404    <t>
5405      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5406      "Character Encodings in TEXT"
5407    </t>
5408    <t>
5409      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5410      "Line Folding"
5411    </t>
5412    <t>
5413      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5414      "OPTIONS * and proxies"
5415    </t>
5416    <t>
5417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5418      "Reason-Phrase BNF"
5419    </t>
5420    <t>
5421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5422      "Use of TEXT"
5423    </t>
5424    <t>
5425      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5426      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5427    </t>
5428    <t>
5429      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5430      "RFC822 reference left in discussion of date formats"
5431    </t>
5432  </list>
5433</t>
5434<t>
5435  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5436  <list style="symbols"> 
5437    <t>
5438      Rewrite definition of list rules, deprecate empty list elements.
5439    </t>
5440    <t>
5441      Add appendix containing collected and expanded ABNF.
5442    </t>
5443  </list>
5444</t>
5445<t>
5446  Other changes:
5447  <list style="symbols"> 
5448    <t>
5449      Rewrite introduction; add mostly new Architecture Section.
5450    </t>
5451    <t>
5452      Move definition of quality values from Part 3 into Part 1;
5453      make TE request header grammar independent of accept-params (defined in Part 3).
5454    </t>
5455  </list>
5456</t>
5457</section>
5458
5459<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5460<t>
5461  Closed issues:
5462  <list style="symbols"> 
5463    <t>
5464      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5465      "base for numeric protocol elements"
5466    </t>
5467    <t>
5468      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5469      "comment ABNF"
5470    </t>
5471  </list>
5472</t>
5473<t>
5474  Partly resolved issues:
5475  <list style="symbols"> 
5476    <t>
5477      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5478      "205 Bodies" (took out language that implied that there may be
5479      methods for which a request body MUST NOT be included)
5480    </t>
5481    <t>
5482      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5483      "editorial improvements around HTTP-date"
5484    </t>
5485  </list>
5486</t>
5487</section>
5488
5489<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5490<t>
5491  Closed issues:
5492  <list style="symbols"> 
5493    <t>
5494      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5495      "Repeating single-value headers"
5496    </t>
5497    <t>
5498      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5499      "increase connection limit"
5500    </t>
5501    <t>
5502      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5503      "IP addresses in URLs"
5504    </t>
5505    <t>
5506      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5507      "take over HTTP Upgrade Token Registry"
5508    </t>
5509    <t>
5510      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5511      "CR and LF in chunk extension values"
5512    </t>
5513    <t>
5514      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5515      "HTTP/0.9 support"
5516    </t>
5517    <t>
5518      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5519      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5520    </t>
5521    <t>
5522      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5523      "move definitions of gzip/deflate/compress to part 1"
5524    </t>
5525    <t>
5526      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5527      "disallow control characters in quoted-pair"
5528    </t>
5529  </list>
5530</t>
5531<t>
5532  Partly resolved issues:
5533  <list style="symbols"> 
5534    <t>
5535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5536      "update IANA requirements wrt Transfer-Coding values" (add the
5537      IANA Considerations subsection)
5538    </t>
5539  </list>
5540</t>
5541</section>
5542
5543<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5544<t>
5545  Closed issues:
5546  <list style="symbols"> 
5547    <t>
5548      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5549      "header parsing, treatment of leading and trailing OWS"
5550    </t>
5551  </list>
5552</t>
5553<t>
5554  Partly resolved issues:
5555  <list style="symbols"> 
5556    <t>
5557      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5558      "Placement of 13.5.1 and 13.5.2"
5559    </t>
5560    <t>
5561      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5562      "use of term "word" when talking about header structure"
5563    </t>
5564  </list>
5565</t>
5566</section>
5567
5568<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5569<t>
5570  Closed issues:
5571  <list style="symbols"> 
5572    <t>
5573      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5574      "Clarification of the term 'deflate'"
5575    </t>
5576    <t>
5577      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5578      "OPTIONS * and proxies"
5579    </t>
5580    <t>
5581      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5582      "IANA registry for content/transfer encodings"
5583    </t>
5584    <t>
5585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5586      "Case-sensitivity of HTTP-date"
5587    </t>
5588    <t>
5589      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5590      "use of term "word" when talking about header structure"
5591    </t>
5592  </list>
5593</t>
5594<t>
5595  Partly resolved issues:
5596  <list style="symbols"> 
5597    <t>
5598      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5599      "Term for the requested resource's URI"
5600    </t>
5601  </list>
5602</t>
5603</section>
5604
5605</section>
5606
5607</back>
5608</rfc>
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