source: draft-ietf-httpbis/14/draft-ietf-httpbis-p1-messaging-14.xml @ 1837

Last change on this file since 1837 was 1500, checked in by julian.reschke@…, 8 years ago

fix mime types

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  • Property svn:mime-type set to text/xml
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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<?rfc rfcedstyle="yes"?>
17<!DOCTYPE rfc
18  PUBLIC "" "rfc2629.dtd">
19<rfc obsoletes="2145,2616" updates="2817" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-14">
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="Adobe">Adobe Systems Incorporated</organization>
26    <address>
27      <postal>
28        <street>345 Park Ave</street>
29        <city>San Jose</city>
30        <region>CA</region>
31        <code>95110</code>
32        <country>USA</country>
33      </postal>
34      <email>fielding@gbiv.com</email>
35      <uri>http://roy.gbiv.com/</uri>
36    </address>
37  </author>
38
39  <author initials="J." surname="Gettys" fullname="Jim Gettys">
40    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
41    <address>
42      <postal>
43        <street>21 Oak Knoll Road</street>
44        <city>Carlisle</city>
45        <region>MA</region>
46        <code>01741</code>
47        <country>USA</country>
48      </postal>
49      <email>jg@freedesktop.org</email>
50      <uri>http://gettys.wordpress.com/</uri>
51    </address>
52  </author>
53 
54  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
55    <organization abbrev="HP">Hewlett-Packard Company</organization>
56    <address>
57      <postal>
58        <street>HP Labs, Large Scale Systems Group</street>
59        <street>1501 Page Mill Road, MS 1177</street>
60        <city>Palo Alto</city>
61        <region>CA</region>
62        <code>94304</code>
63        <country>USA</country>
64      </postal>
65      <email>JeffMogul@acm.org</email>
66    </address>
67  </author>
68
69  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
70    <organization abbrev="Microsoft">Microsoft Corporation</organization>
71    <address>
72      <postal>
73        <street>1 Microsoft Way</street>
74        <city>Redmond</city>
75        <region>WA</region>
76        <code>98052</code>
77        <country>USA</country>
78      </postal>
79      <email>henrikn@microsoft.com</email>
80    </address>
81  </author>
82
83  <author initials="L." surname="Masinter" fullname="Larry Masinter">
84    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
85    <address>
86      <postal>
87        <street>345 Park Ave</street>
88        <city>San Jose</city>
89        <region>CA</region>
90        <code>95110</code>
91        <country>USA</country>
92      </postal>
93      <email>LMM@acm.org</email>
94      <uri>http://larry.masinter.net/</uri>
95    </address>
96  </author>
97 
98  <author initials="P." surname="Leach" fullname="Paul J. Leach">
99    <organization abbrev="Microsoft">Microsoft Corporation</organization>
100    <address>
101      <postal>
102        <street>1 Microsoft Way</street>
103        <city>Redmond</city>
104        <region>WA</region>
105        <code>98052</code>
106      </postal>
107      <email>paulle@microsoft.com</email>
108    </address>
109  </author>
110   
111  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
112    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
113    <address>
114      <postal>
115        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
116        <street>The Stata Center, Building 32</street>
117        <street>32 Vassar Street</street>
118        <city>Cambridge</city>
119        <region>MA</region>
120        <code>02139</code>
121        <country>USA</country>
122      </postal>
123      <email>timbl@w3.org</email>
124      <uri>http://www.w3.org/People/Berners-Lee/</uri>
125    </address>
126  </author>
127
128  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
129    <organization abbrev="W3C">World Wide Web Consortium</organization>
130    <address>
131      <postal>
132        <street>W3C / ERCIM</street>
133        <street>2004, rte des Lucioles</street>
134        <city>Sophia-Antipolis</city>
135        <region>AM</region>
136        <code>06902</code>
137        <country>France</country>
138      </postal>
139      <email>ylafon@w3.org</email>
140      <uri>http://www.raubacapeu.net/people/yves/</uri>
141    </address>
142  </author>
143
144  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
145    <organization abbrev="greenbytes">greenbytes GmbH</organization>
146    <address>
147      <postal>
148        <street>Hafenweg 16</street>
149        <city>Muenster</city><region>NW</region><code>48155</code>
150        <country>Germany</country>
151      </postal>
152      <phone>+49 251 2807760</phone>
153      <facsimile>+49 251 2807761</facsimile>
154      <email>julian.reschke@greenbytes.de</email>
155      <uri>http://greenbytes.de/tech/webdav/</uri>
156    </address>
157  </author>
158
159  <date month="April" year="2011" day="18"/>
160  <workgroup>HTTPbis Working Group</workgroup>
161
162<abstract>
163<t>
164   The Hypertext Transfer Protocol (HTTP) is an application-level
165   protocol for distributed, collaborative, hypertext information
166   systems. HTTP has been in use by the World Wide Web global information
167   initiative since 1990. This document is Part 1 of the seven-part specification
168   that defines the protocol referred to as "HTTP/1.1" and, taken together,
169   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
170   its associated terminology, defines the "http" and "https" Uniform
171   Resource Identifier (URI) schemes, defines the generic message syntax
172   and parsing requirements for HTTP message frames, and describes
173   general security concerns for implementations.
174</t>
175</abstract>
176
177<note title="Editorial Note (To be removed by RFC Editor)">
178  <t>
179    Discussion of this draft should take place on the HTTPBIS working group
180    mailing list (ietf-http-wg@w3.org), which is archived at
181    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
182  </t>
183  <t>
184    The current issues list is at
185    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
186    documents (including fancy diffs) can be found at
187    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
188  </t>
189  <t>
190    The changes in this draft are summarized in <xref target="changes.since.13"/>.
191  </t>
192</note>
193</front>
194<middle>
195<section title="Introduction" anchor="introduction">
196<t>
197   The Hypertext Transfer Protocol (HTTP) is an application-level
198   request/response protocol that uses extensible semantics and MIME-like
199   message payloads for flexible interaction with network-based hypertext
200   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
201   standard <xref target="RFC3986"/> to indicate the target resource and
202   relationships between resources.
203   Messages are passed in a format similar to that used by Internet mail
204   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
205   (MIME) <xref target="RFC2045"/> (see Appendix A of <xref target="Part3"/> for the differences
206   between HTTP and MIME messages).
207</t>
208<t>
209   HTTP is a generic interface protocol for information systems. It is
210   designed to hide the details of how a service is implemented by presenting
211   a uniform interface to clients that is independent of the types of
212   resources provided. Likewise, servers do not need to be aware of each
213   client's purpose: an HTTP request can be considered in isolation rather
214   than being associated with a specific type of client or a predetermined
215   sequence of application steps. The result is a protocol that can be used
216   effectively in many different contexts and for which implementations can
217   evolve independently over time.
218</t>
219<t>
220   HTTP is also designed for use as an intermediation protocol for translating
221   communication to and from non-HTTP information systems.
222   HTTP proxies and gateways can provide access to alternative information
223   services by translating their diverse protocols into a hypertext
224   format that can be viewed and manipulated by clients in the same way
225   as HTTP services.
226</t>
227<t>
228   One consequence of HTTP flexibility is that the protocol cannot be
229   defined in terms of what occurs behind the interface. Instead, we
230   are limited to defining the syntax of communication, the intent
231   of received communication, and the expected behavior of recipients.
232   If the communication is considered in isolation, then successful
233   actions ought to be reflected in corresponding changes to the
234   observable interface provided by servers. However, since multiple
235   clients might act in parallel and perhaps at cross-purposes, we
236   cannot require that such changes be observable beyond the scope
237   of a single response.
238</t>
239<t>
240   This document is Part 1 of the seven-part specification of HTTP,
241   defining the protocol referred to as "HTTP/1.1", obsoleting
242   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
243   Part 1 describes the architectural elements that are used or
244   referred to in HTTP, defines the "http" and "https" URI schemes,
245   describes overall network operation and connection management,
246   and defines HTTP message framing and forwarding requirements.
247   Our goal is to define all of the mechanisms necessary for HTTP message
248   handling that are independent of message semantics, thereby defining the
249   complete set of requirements for message parsers and
250   message-forwarding intermediaries.
251</t>
252
253<section title="Requirements" anchor="intro.requirements">
254<t>
255   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
256   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
257   document are to be interpreted as described in <xref target="RFC2119"/>.
258</t>
259<t>
260   An implementation is not compliant if it fails to satisfy one or more
261   of the "MUST" or "REQUIRED" level requirements for the protocols it
262   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
263   level and all the "SHOULD" level requirements for its protocols is said
264   to be "unconditionally compliant"; one that satisfies all the "MUST"
265   level requirements but not all the "SHOULD" level requirements for its
266   protocols is said to be "conditionally compliant".
267</t>
268</section>
269
270<section title="Syntax Notation" anchor="notation">
271<iref primary="true" item="Grammar" subitem="ALPHA"/>
272<iref primary="true" item="Grammar" subitem="CR"/>
273<iref primary="true" item="Grammar" subitem="CRLF"/>
274<iref primary="true" item="Grammar" subitem="CTL"/>
275<iref primary="true" item="Grammar" subitem="DIGIT"/>
276<iref primary="true" item="Grammar" subitem="DQUOTE"/>
277<iref primary="true" item="Grammar" subitem="HEXDIG"/>
278<iref primary="true" item="Grammar" subitem="LF"/>
279<iref primary="true" item="Grammar" subitem="OCTET"/>
280<iref primary="true" item="Grammar" subitem="SP"/>
281<iref primary="true" item="Grammar" subitem="VCHAR"/>
282<iref primary="true" item="Grammar" subitem="WSP"/>
283<t>
284   This specification uses the Augmented Backus-Naur Form (ABNF) notation
285   of <xref target="RFC5234"/>.
286</t>
287<t anchor="core.rules">
288 
289 
290 
291 
292 
293 
294 
295 
296 
297 
298 
299 
300   The following core rules are included by
301   reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
302   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
303   DIGIT (decimal 0-9), DQUOTE (double quote),
304   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
305   OCTET (any 8-bit sequence of data), SP (space),
306   VCHAR (any visible <xref target="USASCII"/> character),
307   and WSP (whitespace).
308</t>
309<t>
310   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
311   "obsolete" grammar rules that appear for historical reasons.
312</t>
313
314<section title="ABNF Extension: #rule" anchor="notation.abnf">
315<t>
316  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
317  improve readability.
318</t>
319<t>
320  A construct "#" is defined, similar to "*", for defining comma-delimited
321  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
322  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
323  comma (",") and optional whitespace (OWS,
324  <xref target="basic.rules"/>).   
325</t>
326<figure><preamble>
327  Thus,
328</preamble><artwork type="example"><![CDATA[
329  1#element => element *( OWS "," OWS element )
330]]></artwork></figure>
331<figure><preamble>
332  and:
333</preamble><artwork type="example"><![CDATA[
334  #element => [ 1#element ]
335]]></artwork></figure>
336<figure><preamble>
337  and for n &gt;= 1 and m &gt; 1:
338</preamble><artwork type="example"><![CDATA[
339  <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
340]]></artwork></figure>
341<t>
342  For compatibility with legacy list rules, recipients SHOULD accept empty
343  list elements. In other words, consumers would follow the list productions:
344</t>
345<figure><artwork type="example"><![CDATA[
346  #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
347 
348  1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
349]]></artwork></figure>
350<t>
351  Note that empty elements do not contribute to the count of elements present,
352  though.
353</t>
354<t>
355  For example, given these ABNF productions:
356</t>
357<figure><artwork type="example"><![CDATA[
358  example-list      = 1#example-list-elmt
359  example-list-elmt = token ; see Section 1.2.2
360]]></artwork></figure>
361<t>
362  Then these are valid values for example-list (not including the double
363  quotes, which are present for delimitation only):
364</t>
365<figure><artwork type="example"><![CDATA[
366  "foo,bar"
367  " foo ,bar,"
368  "  foo , ,bar,charlie   "
369  "foo ,bar,   charlie "
370]]></artwork></figure>
371<t>
372  But these values would be invalid, as at least one non-empty element is
373  required:
374</t>
375<figure><artwork type="example"><![CDATA[
376  ""
377  ","
378  ",   ,"
379]]></artwork></figure>
380<t>
381  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
382  expanded as explained above.
383</t>
384</section>
385
386<section title="Basic Rules" anchor="basic.rules">
387<t anchor="rule.CRLF">
388 
389   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
390   protocol elements other than the message-body
391   (see <xref target="tolerant.applications"/> for tolerant applications).
392</t>
393<t anchor="rule.LWS">
394   This specification uses three rules to denote the use of linear
395   whitespace: OWS (optional whitespace), RWS (required whitespace), and
396   BWS ("bad" whitespace).
397</t>
398<t>
399   The OWS rule is used where zero or more linear whitespace octets might
400   appear. OWS SHOULD either not be produced or be produced as a single
401   SP. Multiple OWS octets that occur within field-content SHOULD
402   be replaced with a single SP before interpreting the field value or
403   forwarding the message downstream.
404</t>
405<t>
406   RWS is used when at least one linear whitespace octet is required to
407   separate field tokens. RWS SHOULD be produced as a single SP.
408   Multiple RWS octets that occur within field-content SHOULD be
409   replaced with a single SP before interpreting the field value or
410   forwarding the message downstream.
411</t>
412<t>
413   BWS is used where the grammar allows optional whitespace for historical
414   reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
415   recipients MUST accept such bad optional whitespace and remove it before
416   interpreting the field value or forwarding the message downstream.
417</t>
418<t anchor="rule.whitespace">
419 
420 
421 
422 
423</t>
424<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[
425  OWS            = *( [ obs-fold ] WSP )
426                 ; "optional" whitespace
427  RWS            = 1*( [ obs-fold ] WSP )
428                 ; "required" whitespace
429  BWS            = OWS
430                 ; "bad" whitespace
431  obs-fold       = CRLF
432                 ; see Section 3.2
433]]></artwork></figure>
434<t anchor="rule.token.separators">
435 
436 
437 
438 
439   Many HTTP/1.1 header field values consist of words (token or quoted-string)
440   separated by whitespace or special characters. These special characters
441   MUST be in a quoted string to be used within a parameter value (as defined
442   in <xref target="transfer.codings"/>).
443</t>
444<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[
445  word           = token / quoted-string
446
447  token          = 1*tchar
448
449  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
450                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
451                 / DIGIT / ALPHA
452                 ; any VCHAR, except special
453
454  special        = "(" / ")" / "<" / ">" / "@" / ","
455                 / ";" / ":" / "\" / DQUOTE / "/" / "["
456                 / "]" / "?" / "=" / "{" / "}"
457]]></artwork></figure>
458<t anchor="rule.quoted-string">
459 
460 
461 
462   A string of text is parsed as a single word if it is quoted using
463   double-quote marks.
464</t>
465<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[
466  quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
467  qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
468                 ; OWS / <VCHAR except DQUOTE and "\"> / obs-text
469  obs-text       = %x80-FF
470]]></artwork></figure>
471<t anchor="rule.quoted-pair">
472 
473   The backslash octet ("\") can be used as a single-octet
474   quoting mechanism within quoted-string constructs:
475</t>
476<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
477  quoted-pair    = "\" ( WSP / VCHAR / obs-text )
478]]></artwork></figure>
479<t>
480   Senders SHOULD NOT escape octets that do not require escaping
481   (i.e., other than DQUOTE and the backslash octet).
482</t>
483</section>
484
485</section>
486</section>
487
488<section title="HTTP-related architecture" anchor="architecture">
489<t>
490   HTTP was created for the World Wide Web architecture
491   and has evolved over time to support the scalability needs of a worldwide
492   hypertext system. Much of that architecture is reflected in the terminology
493   and syntax productions used to define HTTP.
494</t>
495
496<section title="Client/Server Messaging" anchor="operation">
497<iref primary="true" item="client"/>
498<iref primary="true" item="server"/>
499<iref primary="true" item="connection"/>
500<t>
501   HTTP is a stateless request/response protocol that operates by exchanging
502   messages across a reliable transport or session-layer
503   "connection". An HTTP "client" is a
504   program that establishes a connection to a server for the purpose of
505   sending one or more HTTP requests.  An HTTP "server" is a
506   program that accepts connections in order to service HTTP requests by
507   sending HTTP responses.
508</t>
509<iref primary="true" item="user agent"/>
510<iref primary="true" item="origin server"/>
511<iref primary="true" item="browser"/>
512<iref primary="true" item="spider"/>
513<iref primary="true" item="sender"/>
514<iref primary="true" item="recipient"/>
515<t>
516   Note that the terms client and server refer only to the roles that
517   these programs perform for a particular connection.  The same program
518   might act as a client on some connections and a server on others.  We use
519   the term "user agent" to refer to the program that initiates a request,
520   such as a WWW browser, editor, or spider (web-traversing robot), and
521   the term "origin server" to refer to the program that can originate
522   authoritative responses to a request.  For general requirements, we use
523   the term "sender" to refer to whichever component sent a given message
524   and the term "recipient" to refer to any component that receives the
525   message.
526</t>
527<t>
528   Most HTTP communication consists of a retrieval request (GET) for
529   a representation of some resource identified by a URI.  In the
530   simplest case, this might be accomplished via a single bidirectional
531   connection (===) between the user agent (UA) and the origin server (O).
532</t>
533<figure><artwork type="drawing"><![CDATA[
534         request   >
535    UA ======================================= O
536                                <   response
537]]></artwork></figure>
538<iref primary="true" item="message"/>
539<iref primary="true" item="request"/>
540<iref primary="true" item="response"/>
541<t>
542   A client sends an HTTP request to the server in the form of a request
543   message (<xref target="request"/>), beginning with a method, URI, and
544   protocol version, followed by MIME-like header fields containing
545   request modifiers, client information, and payload metadata, an empty
546   line to indicate the end of the header section, and finally the payload
547   body (if any).
548</t>
549<t>
550   A server responds to the client's request by sending an HTTP response
551   message (<xref target="response"/>), beginning with a status line that
552   includes the protocol version, a success or error code, and textual
553   reason phrase, followed by MIME-like header fields containing server
554   information, resource metadata, and payload metadata, an empty line to
555   indicate the end of the header section, and finally the payload body (if any).
556</t>
557<t>
558   The following example illustrates a typical message exchange for a
559   GET request on the URI "http://www.example.com/hello.txt":
560</t>
561<figure><preamble>
562client request:
563</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
564  GET /hello.txt HTTP/1.1
565  User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
566  Host: www.example.com
567  Accept: */*
568 
569  ]]></artwork></figure>
570<figure><preamble>
571server response:
572</preamble><artwork type="message/http; msgtype=&#34;response&#34;"><![CDATA[
573  HTTP/1.1 200 OK
574  Date: Mon, 27 Jul 2009 12:28:53 GMT
575  Server: Apache
576  Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
577  ETag: "34aa387-d-1568eb00"
578  Accept-Ranges: bytes
579  Content-Length: 14
580  Vary: Accept-Encoding
581  Content-Type: text/plain
582 
583  Hello World!
584  ]]></artwork></figure>
585</section>
586
587<section title="Connections and Transport Independence" anchor="transport-independence">
588<t>
589   HTTP messaging is independent of the underlying transport or
590   session-layer connection protocol(s).  HTTP only presumes a reliable
591   transport with in-order delivery of requests and the corresponding
592   in-order delivery of responses.  The mapping of HTTP request and
593   response structures onto the data units of the underlying transport
594   protocol is outside the scope of this specification.
595</t>
596<t>
597   The specific connection protocols to be used for an interaction
598   are determined by client configuration and the target resource's URI.
599   For example, the "http" URI scheme
600   (<xref target="http.uri"/>) indicates a default connection of TCP
601   over IP, with a default TCP port of 80, but the client might be
602   configured to use a proxy via some other connection port or protocol
603   instead of using the defaults.
604</t>
605<t>
606   A connection might be used for multiple HTTP request/response exchanges,
607   as defined in <xref target="persistent.connections"/>.
608</t>
609</section>
610
611<section title="Intermediaries" anchor="intermediaries">
612<iref primary="true" item="intermediary"/>
613<t>
614   HTTP enables the use of intermediaries to satisfy requests through
615   a chain of connections.  There are three common forms of HTTP
616   intermediary: proxy, gateway, and tunnel.  In some cases,
617   a single intermediary might act as an origin server, proxy, gateway,
618   or tunnel, switching behavior based on the nature of each request.
619</t>
620<figure><artwork type="drawing"><![CDATA[
621         >             >             >             >
622    UA =========== A =========== B =========== C =========== O
623               <             <             <             <
624]]></artwork></figure>
625<t>
626   The figure above shows three intermediaries (A, B, and C) between the
627   user agent and origin server. A request or response message that
628   travels the whole chain will pass through four separate connections.
629   Some HTTP communication options
630   might apply only to the connection with the nearest, non-tunnel
631   neighbor, only to the end-points of the chain, or to all connections
632   along the chain. Although the diagram is linear, each participant might
633   be engaged in multiple, simultaneous communications. For example, B
634   might be receiving requests from many clients other than A, and/or
635   forwarding requests to servers other than C, at the same time that it
636   is handling A's request.
637</t>
638<t>
639<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
640<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
641   We use the terms "upstream" and "downstream"
642   to describe various requirements in relation to the directional flow of a
643   message: all messages flow from upstream to downstream.
644   Likewise, we use the terms inbound and outbound to refer to
645   directions in relation to the request path:
646   "inbound" means toward the origin server and
647   "outbound" means toward the user agent.
648</t>
649<t><iref primary="true" item="proxy"/>
650   A "proxy" is a message forwarding agent that is selected by the
651   client, usually via local configuration rules, to receive requests
652   for some type(s) of absolute URI and attempt to satisfy those
653   requests via translation through the HTTP interface.  Some translations
654   are minimal, such as for proxy requests for "http" URIs, whereas
655   other requests might require translation to and from entirely different
656   application-layer protocols. Proxies are often used to group an
657   organization's HTTP requests through a common intermediary for the
658   sake of security, annotation services, or shared caching.
659</t>
660<t>
661<iref primary="true" item="transforming proxy"/>
662<iref primary="true" item="non-transforming proxy"/>
663   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
664   or configured to modify request or response messages in a semantically
665   meaningful way (i.e., modifications, beyond those required by normal
666   HTTP processing, that change the message in a way that would be
667   significant to the original sender or potentially significant to
668   downstream recipients).  For example, a transforming proxy might be
669   acting as a shared annotation server (modifying responses to include
670   references to a local annotation database), a malware filter, a
671   format transcoder, or an intranet-to-Internet privacy filter.  Such
672   transformations are presumed to be desired by the client (or client
673   organization) that selected the proxy and are beyond the scope of
674   this specification.  However, when a proxy is not intended to transform
675   a given message, we use the term "non-transforming proxy" to target
676   requirements that preserve HTTP message semantics.
677</t>
678<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
679<iref primary="true" item="accelerator"/>
680   A "gateway" (a.k.a., "reverse proxy")
681   is a receiving agent that acts
682   as a layer above some other server(s) and translates the received
683   requests to the underlying server's protocol.  Gateways are often
684   used to encapsulate legacy or untrusted information services, to
685   improve server performance through "accelerator" caching, and to
686   enable partitioning or load-balancing of HTTP services across
687   multiple machines.
688</t>
689<t>
690   A gateway behaves as an origin server on its outbound connection and
691   as a user agent on its inbound connection.
692   All HTTP requirements applicable to an origin server
693   also apply to the outbound communication of a gateway.
694   A gateway communicates with inbound servers using any protocol that
695   it desires, including private extensions to HTTP that are outside
696   the scope of this specification.  However, an HTTP-to-HTTP gateway
697   that wishes to interoperate with third-party HTTP servers MUST
698   comply with HTTP user agent requirements on the gateway's inbound
699   connection and MUST implement the Connection
700   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
701   header fields for both connections.
702</t>
703<t><iref primary="true" item="tunnel"/>
704   A "tunnel" acts as a blind relay between two connections
705   without changing the messages. Once active, a tunnel is not
706   considered a party to the HTTP communication, though the tunnel might
707   have been initiated by an HTTP request. A tunnel ceases to exist when
708   both ends of the relayed connection are closed. Tunnels are used to
709   extend a virtual connection through an intermediary, such as when
710   transport-layer security is used to establish private communication
711   through a shared firewall proxy.
712</t>
713<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
714<iref primary="true" item="captive portal"/>
715   In addition, there may exist network intermediaries that are not
716   considered part of the HTTP communication but nevertheless act as
717   filters or redirecting agents (usually violating HTTP semantics,
718   causing security problems, and otherwise making a mess of things).
719   Such a network intermediary, often referred to as an "interception proxy"
720   <xref target="RFC3040"/>, "transparent proxy" <xref target="RFC1919"/>,
721   or "captive portal",
722   differs from an HTTP proxy because it has not been selected by the client.
723   Instead, the network intermediary redirects outgoing TCP port 80 packets
724   (and occasionally other common port traffic) to an internal HTTP server.
725   Interception proxies are commonly found on public network access points,
726   as a means of enforcing account subscription prior to allowing use of
727   non-local Internet services, and within corporate firewalls to enforce
728   network usage policies.
729   They are indistinguishable from a man-in-the-middle attack.
730</t>
731</section>
732
733<section title="Caches" anchor="caches">
734<iref primary="true" item="cache"/>
735<t>
736   A "cache" is a local store of previous response messages and the
737   subsystem that controls its message storage, retrieval, and deletion.
738   A cache stores cacheable responses in order to reduce the response
739   time and network bandwidth consumption on future, equivalent
740   requests. Any client or server MAY employ a cache, though a cache
741   cannot be used by a server while it is acting as a tunnel.
742</t>
743<t>
744   The effect of a cache is that the request/response chain is shortened
745   if one of the participants along the chain has a cached response
746   applicable to that request. The following illustrates the resulting
747   chain if B has a cached copy of an earlier response from O (via C)
748   for a request which has not been cached by UA or A.
749</t>
750<figure><artwork type="drawing"><![CDATA[
751            >             >
752       UA =========== A =========== B - - - - - - C - - - - - - O
753                  <             <
754]]></artwork></figure>
755<t><iref primary="true" item="cacheable"/>
756   A response is "cacheable" if a cache is allowed to store a copy of
757   the response message for use in answering subsequent requests.
758   Even when a response is cacheable, there might be additional
759   constraints placed by the client or by the origin server on when
760   that cached response can be used for a particular request. HTTP
761   requirements for cache behavior and cacheable responses are
762   defined in Section 2 of <xref target="Part6"/>. 
763</t>
764<t>
765   There are a wide variety of architectures and configurations
766   of caches and proxies deployed across the World Wide Web and
767   inside large organizations. These systems include national hierarchies
768   of proxy caches to save transoceanic bandwidth, systems that
769   broadcast or multicast cache entries, organizations that distribute
770   subsets of cached data via optical media, and so on.
771</t>
772</section>
773
774<section title="Protocol Versioning" anchor="http.version">
775 
776 
777<t>
778   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
779   versions of the protocol. This specification defines version "1.1".
780   The protocol version as a whole indicates the sender's compliance
781   with the set of requirements laid out in that version's corresponding
782   specification of HTTP.
783</t>
784<t>
785   The version of an HTTP message is indicated by an HTTP-Version field
786   in the first line of the message. HTTP-Version is case-sensitive.
787</t>
788<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
789  HTTP-Version   = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
790  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
791]]></artwork></figure>
792<t>
793   The HTTP version number consists of two non-negative decimal integers
794   separated by a "." (period or decimal point).  The first
795   number ("major version") indicates the HTTP messaging syntax, whereas
796   the second number ("minor version") indicates the highest minor
797   version to which the sender is at least conditionally compliant and
798   able to understand for future communication.  The minor version
799   advertises the sender's communication capabilities even when the
800   sender is only using a backwards-compatible subset of the protocol,
801   thereby letting the recipient know that more advanced features can
802   be used in response (by servers) or in future requests (by clients).
803</t>
804<t>
805   When comparing HTTP versions, the numbers MUST be compared
806   numerically rather than lexically.  For example, HTTP/2.4 is a lower
807   version than HTTP/2.13, which in turn is lower than HTTP/12.3.
808   Leading zeros MUST be ignored by recipients and MUST NOT be sent.
809</t>
810<t>
811   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
812   <xref target="RFC1945"/> or a recipient whose version is unknown,
813   the HTTP/1.1 message is constructed such that it can be interpreted
814   as a valid HTTP/1.0 message if all of the newer features are ignored.
815   This specification places recipient-version requirements on some
816   new features so that a compliant sender will only use compatible
817   features until it has determined, through configuration or the
818   receipt of a message, that the recipient supports HTTP/1.1.
819</t>
820<t>
821   The interpretation of an HTTP header field does not change
822   between minor versions of the same major version, though the default
823   behavior of a recipient in the absence of such a field can change.
824   Unless specified otherwise, header fields defined in HTTP/1.1 are
825   defined for all versions of HTTP/1.x.  In particular, the Host and
826   Connection header fields ought to be implemented by all HTTP/1.x
827   implementations whether or not they advertise compliance with HTTP/1.1.
828</t>
829<t>
830   New header fields can be defined such that, when they are
831   understood by a recipient, they might override or enhance the
832   interpretation of previously defined header fields.  When an
833   implementation receives an unrecognized header field, the recipient
834   MUST ignore that header field for local processing regardless of
835   the message's HTTP version.  An unrecognized header field received
836   by a proxy MUST be forwarded downstream unless the header field's
837   field-name is listed in the message's Connection header-field
838   (see <xref target="header.connection"/>).
839   These requirements allow HTTP's functionality to be enhanced without
840   requiring prior update of all compliant intermediaries.
841</t>
842<t>
843   Intermediaries that process HTTP messages (i.e., all intermediaries
844   other than those acting as a tunnel) MUST send their own HTTP-Version
845   in forwarded messages.  In other words, they MUST NOT blindly
846   forward the first line of an HTTP message without ensuring that the
847   protocol version matches what the intermediary understands, and
848   is at least conditionally compliant to, for both the receiving and
849   sending of messages.  Forwarding an HTTP message without rewriting
850   the HTTP-Version might result in communication errors when downstream
851   recipients use the message sender's version to determine what features
852   are safe to use for later communication with that sender.
853</t>
854<t>
855   An HTTP client SHOULD send a request version equal to the highest
856   version for which the client is at least conditionally compliant and
857   whose major version is no higher than the highest version supported
858   by the server, if this is known.  An HTTP client MUST NOT send a
859   version for which it is not at least conditionally compliant.
860</t>
861<t>
862   An HTTP client MAY send a lower request version if it is known that
863   the server incorrectly implements the HTTP specification, but only
864   after the client has attempted at least one normal request and determined
865   from the response status or header fields (e.g., Server) that the
866   server improperly handles higher request versions.
867</t>
868<t>
869   An HTTP server SHOULD send a response version equal to the highest
870   version for which the server is at least conditionally compliant and
871   whose major version is less than or equal to the one received in the
872   request.  An HTTP server MUST NOT send a version for which it is not
873   at least conditionally compliant.  A server MAY send a 505 (HTTP
874   Version Not Supported) response if it cannot send a response using the
875   major version used in the client's request.
876</t>
877<t>
878   An HTTP server MAY send an HTTP/1.0 response to an HTTP/1.0 request
879   if it is known or suspected that the client incorrectly implements the
880   HTTP specification and is incapable of correctly processing later
881   version responses, such as when a client fails to parse the version
882   number correctly or when an intermediary is known to blindly forward
883   the HTTP-Version even when it doesn't comply with the given minor
884   version of the protocol. Such protocol downgrades SHOULD NOT be
885   performed unless triggered by specific client attributes, such as when
886   one or more of the request header fields (e.g., User-Agent) uniquely
887   match the values sent by a client known to be in error.
888</t>
889<t>
890   The intention of HTTP's versioning design is that the major number
891   will only be incremented if an incompatible message syntax is
892   introduced, and that the minor number will only be incremented when
893   changes made to the protocol have the effect of adding to the message
894   semantics or implying additional capabilities of the sender.  However,
895   the minor version was not incremented for the changes introduced between
896   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
897   is specifically avoiding any such changes to the protocol.
898</t>
899</section>
900
901<section title="Uniform Resource Identifiers" anchor="uri">
902<iref primary="true" item="resource"/>
903<t>
904   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
905   throughout HTTP as the means for identifying resources. URI references
906   are used to target requests, indicate redirects, and define relationships.
907   HTTP does not limit what a resource might be; it merely defines an interface
908   that can be used to interact with a resource via HTTP. More information on
909   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
910</t>
911 
912 
913 
914 
915 
916 
917 
918 
919 
920 
921<t>
922   This specification adopts the definitions of "URI-reference",
923   "absolute-URI", "relative-part", "port", "host",
924   "path-abempty", "path-absolute", "query", and "authority" from the
925   URI generic syntax <xref target="RFC3986"/>.
926   In addition, we define a partial-URI rule for protocol elements
927   that allow a relative URI but not a fragment.
928</t>
929<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[
930  URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
931  absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
932  relative-part = <relative-part, defined in [RFC3986], Section 4.2>
933  authority     = <authority, defined in [RFC3986], Section 3.2>
934  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
935  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
936  port          = <port, defined in [RFC3986], Section 3.2.3>
937  query         = <query, defined in [RFC3986], Section 3.4>
938  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
939 
940  partial-URI   = relative-part [ "?" query ]
941]]></artwork></figure>
942<t>
943   Each protocol element in HTTP that allows a URI reference will indicate
944   in its ABNF production whether the element allows any form of reference
945   (URI-reference), only a URI in absolute form (absolute-URI), only the
946   path and optional query components, or some combination of the above.
947   Unless otherwise indicated, URI references are parsed relative to the
948   effective request URI, which defines the default base URI for references
949   in both the request and its corresponding response.
950</t>
951
952<section title="http URI scheme" anchor="http.uri">
953 
954  <iref item="http URI scheme" primary="true"/>
955  <iref item="URI scheme" subitem="http" primary="true"/>
956<t>
957   The "http" URI scheme is hereby defined for the purpose of minting
958   identifiers according to their association with the hierarchical
959   namespace governed by a potential HTTP origin server listening for
960   TCP connections on a given port.
961</t>
962<figure><iref primary="true" item="Grammar" subitem="http-URI"/><artwork type="abnf2616"><![CDATA[
963  http-URI = "http:" "//" authority path-abempty [ "?" query ]
964]]></artwork></figure>
965<t>
966   The HTTP origin server is identified by the generic syntax's
967   <xref target="uri" format="none">authority</xref> component, which includes a host identifier
968   and optional TCP port (<xref target="RFC3986"/>, Section 3.2.2).
969   The remainder of the URI, consisting of both the hierarchical path
970   component and optional query component, serves as an identifier for
971   a potential resource within that origin server's name space.
972</t>
973<t>
974   If the host identifier is provided as an IP literal or IPv4 address,
975   then the origin server is any listener on the indicated TCP port at
976   that IP address. If host is a registered name, then that name is
977   considered an indirect identifier and the recipient might use a name
978   resolution service, such as DNS, to find the address of a listener
979   for that host.
980   The host MUST NOT be empty; if an "http" URI is received with an
981   empty host, then it MUST be rejected as invalid.
982   If the port subcomponent is empty or not given, then TCP port 80 is
983   assumed (the default reserved port for WWW services).
984</t>
985<t>
986   Regardless of the form of host identifier, access to that host is not
987   implied by the mere presence of its name or address. The host might or might
988   not exist and, even when it does exist, might or might not be running an
989   HTTP server or listening to the indicated port. The "http" URI scheme
990   makes use of the delegated nature of Internet names and addresses to
991   establish a naming authority (whatever entity has the ability to place
992   an HTTP server at that Internet name or address) and allows that
993   authority to determine which names are valid and how they might be used.
994</t>
995<t>
996   When an "http" URI is used within a context that calls for access to the
997   indicated resource, a client MAY attempt access by resolving
998   the host to an IP address, establishing a TCP connection to that address
999   on the indicated port, and sending an HTTP request message to the server
1000   containing the URI's identifying data as described in <xref target="request"/>.
1001   If the server responds to that request with a non-interim HTTP response
1002   message, as described in <xref target="response"/>, then that response
1003   is considered an authoritative answer to the client's request.
1004</t>
1005<t>
1006   Although HTTP is independent of the transport protocol, the "http"
1007   scheme is specific to TCP-based services because the name delegation
1008   process depends on TCP for establishing authority.
1009   An HTTP service based on some other underlying connection protocol
1010   would presumably be identified using a different URI scheme, just as
1011   the "https" scheme (below) is used for servers that require an SSL/TLS
1012   transport layer on a connection. Other protocols might also be used to
1013   provide access to "http" identified resources — it is only the
1014   authoritative interface used for mapping the namespace that is
1015   specific to TCP.
1016</t>
1017<t>
1018   The URI generic syntax for authority also includes a deprecated
1019   userinfo subcomponent (<xref target="RFC3986"/>, Section 3.2.1)
1020   for including user authentication information in the URI.  Some
1021   implementations make use of the userinfo component for internal
1022   configuration of authentication information, such as within command
1023   invocation options, configuration files, or bookmark lists, even
1024   though such usage might expose a user identifier or password.
1025   Senders MUST NOT include a userinfo subcomponent (and its "@"
1026   delimiter) when transmitting an "http" URI in a message.  Recipients
1027   of HTTP messages that contain a URI reference SHOULD parse for the
1028   existence of userinfo and treat its presence as an error, likely
1029   indicating that the deprecated subcomponent is being used to obscure
1030   the authority for the sake of phishing attacks.
1031</t>
1032</section>
1033
1034<section title="https URI scheme" anchor="https.uri">
1035   
1036   <iref item="https URI scheme"/>
1037   <iref item="URI scheme" subitem="https"/>
1038<t>
1039   The "https" URI scheme is hereby defined for the purpose of minting
1040   identifiers according to their association with the hierarchical
1041   namespace governed by a potential HTTP origin server listening for
1042   SSL/TLS-secured connections on a given TCP port.
1043</t>
1044<t>
1045   All of the requirements listed above for the "http" scheme are also
1046   requirements for the "https" scheme, except that a default TCP port
1047   of 443 is assumed if the port subcomponent is empty or not given,
1048   and the TCP connection MUST be secured for privacy through the
1049   use of strong encryption prior to sending the first HTTP request.
1050</t>
1051<figure><iref primary="true" item="Grammar" subitem="https-URI"/><artwork type="abnf2616"><![CDATA[
1052  https-URI = "https:" "//" authority path-abempty [ "?" query ]
1053]]></artwork></figure>
1054<t>
1055   Unlike the "http" scheme, responses to "https" identified requests
1056   are never "public" and thus MUST NOT be reused for shared caching.
1057   They can, however, be reused in a private cache if the message is
1058   cacheable by default in HTTP or specifically indicated as such by
1059   the Cache-Control header field (Section 3.2 of <xref target="Part6"/>).
1060</t>
1061<t>
1062   Resources made available via the "https" scheme have no shared
1063   identity with the "http" scheme even if their resource identifiers
1064   indicate the same authority (the same host listening to the same
1065   TCP port).  They are distinct name spaces and are considered to be
1066   distinct origin servers.  However, an extension to HTTP that is
1067   defined to apply to entire host domains, such as the Cookie protocol
1068   <xref target="draft-ietf-httpstate-cookie"/>, can allow information
1069   set by one service to impact communication with other services
1070   within a matching group of host domains.
1071</t>
1072<t>
1073   The process for authoritative access to an "https" identified
1074   resource is defined in <xref target="RFC2818"/>.
1075</t>
1076</section>
1077
1078<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1079<t>
1080   Since the "http" and "https" schemes conform to the URI generic syntax,
1081   such URIs are normalized and compared according to the algorithm defined
1082   in <xref target="RFC3986"/>, Section 6, using the defaults
1083   described above for each scheme.
1084</t>
1085<t>
1086   If the port is equal to the default port for a scheme, the normal
1087   form is to elide the port subcomponent. Likewise, an empty path
1088   component is equivalent to an absolute path of "/", so the normal
1089   form is to provide a path of "/" instead. The scheme and host
1090   are case-insensitive and normally provided in lowercase; all
1091   other components are compared in a case-sensitive manner.
1092   Characters other than those in the "reserved" set are equivalent
1093   to their percent-encoded octets (see <xref target="RFC3986"/>, Section 2.1): the normal form is to not encode them.
1094</t>
1095<t>
1096   For example, the following three URIs are equivalent:
1097</t>
1098<figure><artwork type="example"><![CDATA[
1099   http://example.com:80/~smith/home.html
1100   http://EXAMPLE.com/%7Esmith/home.html
1101   http://EXAMPLE.com:/%7esmith/home.html
1102]]></artwork></figure>
1103</section>
1104</section>
1105</section>
1106
1107<section title="Message Format" anchor="http.message">
1108
1109
1110
1111
1112<iref item="header section"/>
1113<iref item="headers"/>
1114<iref item="header field"/>
1115<t>
1116   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1117   octets in a format similar to the Internet Message Format
1118   <xref target="RFC5322"/>: zero or more header fields (collectively
1119   referred to as the "headers" or the "header section"), an empty line
1120   indicating the end of the header section, and an optional message-body.
1121</t>
1122<t>
1123   An HTTP message can either be a request from client to server or a
1124   response from server to client.  Syntactically, the two types of message
1125   differ only in the start-line, which is either a Request-Line (for requests)
1126   or a Status-Line (for responses), and in the algorithm for determining
1127   the length of the message-body (<xref target="message.body"/>).
1128   In theory, a client could receive requests and a server could receive
1129   responses, distinguishing them by their different start-line formats,
1130   but in practice servers are implemented to only expect a request
1131   (a response is interpreted as an unknown or invalid request method)
1132   and clients are implemented to only expect a response.
1133</t>
1134<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1135  HTTP-message    = start-line
1136                    *( header-field CRLF )
1137                    CRLF
1138                    [ message-body ]
1139  start-line      = Request-Line / Status-Line
1140]]></artwork></figure>
1141<t>
1142   Implementations MUST NOT send whitespace between the start-line and
1143   the first header field. The presence of such whitespace in a request
1144   might be an attempt to trick a server into ignoring that field or
1145   processing the line after it as a new request, either of which might
1146   result in a security vulnerability if other implementations within
1147   the request chain interpret the same message differently.
1148   Likewise, the presence of such whitespace in a response might be
1149   ignored by some clients or cause others to cease parsing.
1150</t>
1151
1152<section title="Message Parsing Robustness" anchor="message.robustness">
1153<t>
1154   In the interest of robustness, servers SHOULD ignore at least one
1155   empty line received where a Request-Line is expected. In other words, if
1156   the server is reading the protocol stream at the beginning of a
1157   message and receives a CRLF first, it SHOULD ignore the CRLF.
1158</t>
1159<t>
1160   Some old HTTP/1.0 client implementations send an extra CRLF
1161   after a POST request as a lame workaround for some early server
1162   applications that failed to read message-body content that was
1163   not terminated by a line-ending. An HTTP/1.1 client MUST NOT
1164   preface or follow a request with an extra CRLF.  If terminating
1165   the request message-body with a line-ending is desired, then the
1166   client MUST include the terminating CRLF octets as part of the
1167   message-body length.
1168</t>
1169<t>
1170   When a server listening only for HTTP request messages, or processing
1171   what appears from the start-line to be an HTTP request message,
1172   receives a sequence of octets that does not match the HTTP-message
1173   grammar aside from the robustness exceptions listed above, the
1174   server MUST respond with an HTTP/1.1 400 (Bad Request) response. 
1175</t>
1176<t>
1177   The normal procedure for parsing an HTTP message is to read the
1178   start-line into a structure, read each header field into a hash
1179   table by field name until the empty line, and then use the parsed
1180   data to determine if a message-body is expected.  If a message-body
1181   has been indicated, then it is read as a stream until an amount
1182   of octets equal to the message-body length is read or the connection
1183   is closed.  Care must be taken to parse an HTTP message as a sequence
1184   of octets in an encoding that is a superset of US-ASCII.  Attempting
1185   to parse HTTP as a stream of Unicode characters in a character encoding
1186   like UTF-16 might introduce security flaws due to the differing ways
1187   that such parsers interpret invalid characters.
1188</t>
1189<t>
1190   HTTP allows the set of defined header fields to be extended without
1191   changing the protocol version (see <xref target="header.field.registration"/>).
1192   Unrecognized header fields MUST be forwarded by a proxy unless the
1193   proxy is specifically configured to block or otherwise transform such
1194   fields.  Unrecognized header fields SHOULD be ignored by other recipients.
1195</t>
1196</section>
1197
1198<section title="Header Fields" anchor="header.fields">
1199 
1200 
1201 
1202 
1203 
1204<t>
1205   Each HTTP header field consists of a case-insensitive field name
1206   followed by a colon (":"), optional whitespace, and the field value.
1207</t>
1208<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[
1209  header-field   = field-name ":" OWS [ field-value ] OWS
1210  field-name     = token
1211  field-value    = *( field-content / OWS )
1212  field-content  = *( WSP / VCHAR / obs-text )
1213]]></artwork></figure>
1214<t>
1215   No whitespace is allowed between the header field name and colon. For
1216   security reasons, any request message received containing such whitespace
1217   MUST be rejected with a response code of 400 (Bad Request). A proxy
1218   MUST remove any such whitespace from a response message before
1219   forwarding the message downstream.
1220</t>
1221<t>
1222   A field value MAY be preceded by optional whitespace (OWS); a single SP is
1223   preferred. The field value does not include any leading or trailing white
1224   space: OWS occurring before the first non-whitespace octet of the
1225   field value or after the last non-whitespace octet of the field value
1226   is ignored and SHOULD be removed before further processing (as this does
1227   not change the meaning of the header field).
1228</t>
1229<t>
1230   The order in which header fields with differing field names are
1231   received is not significant. However, it is "good practice" to send
1232   header fields that contain control data first, such as Host on
1233   requests and Date on responses, so that implementations can decide
1234   when not to handle a message as early as possible.  A server MUST
1235   wait until the entire header section is received before interpreting
1236   a request message, since later header fields might include conditionals,
1237   authentication credentials, or deliberately misleading duplicate
1238   header fields that would impact request processing.
1239</t>
1240<t>
1241   Multiple header fields with the same field name MUST NOT be
1242   sent in a message unless the entire field value for that
1243   header field is defined as a comma-separated list [i.e., #(values)].
1244   Multiple header fields with the same field name can be combined into
1245   one "field-name: field-value" pair, without changing the semantics of the
1246   message, by appending each subsequent field value to the combined
1247   field value in order, separated by a comma. The order in which
1248   header fields with the same field name are received is therefore
1249   significant to the interpretation of the combined field value;
1250   a proxy MUST NOT change the order of these field values when
1251   forwarding a message.
1252</t>
1253<t><list>
1254  <t>
1255   Note: The "Set-Cookie" header field as implemented in
1256   practice can occur multiple times, but does not use the list syntax, and
1257   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1258   for details.) Also note that the Set-Cookie2 header field specified in
1259   <xref target="RFC2965"/> does not share this problem.
1260  </t>
1261</list></t>
1262<t>
1263   Historically, HTTP header field values could be extended over multiple
1264   lines by preceding each extra line with at least one space or horizontal
1265   tab octet (line folding). This specification deprecates such line
1266   folding except within the message/http media type
1267   (<xref target="internet.media.type.message.http"/>).
1268   HTTP/1.1 senders MUST NOT produce messages that include line folding
1269   (i.e., that contain any field-content that matches the obs-fold rule) unless
1270   the message is intended for packaging within the message/http media type.
1271   HTTP/1.1 recipients SHOULD accept line folding and replace any embedded
1272   obs-fold whitespace with a single SP prior to interpreting the field value
1273   or forwarding the message downstream.
1274</t>
1275<t>
1276   Historically, HTTP has allowed field content with text in the ISO-8859-1
1277   <xref target="ISO-8859-1"/> character encoding and supported other
1278   character sets only through use of <xref target="RFC2047"/> encoding.
1279   In practice, most HTTP header field values use only a subset of the
1280   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1281   header fields SHOULD limit their field values to US-ASCII octets.
1282   Recipients SHOULD treat other (obs-text) octets in field content as
1283   opaque data.
1284</t>
1285<t anchor="rule.comment">
1286 
1287 
1288   Comments can be included in some HTTP header fields by surrounding
1289   the comment text with parentheses. Comments are only allowed in
1290   fields containing "comment" as part of their field value definition.
1291</t>
1292<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
1293  comment        = "(" *( ctext / quoted-cpair / comment ) ")"
1294  ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
1295                 ; OWS / <VCHAR except "(", ")", and "\"> / obs-text
1296]]></artwork></figure>
1297<t anchor="rule.quoted-cpair">
1298 
1299   The backslash octet ("\") can be used as a single-octet
1300   quoting mechanism within comment constructs:
1301</t>
1302<figure><iref primary="true" item="Grammar" subitem="quoted-cpair"/><artwork type="abnf2616"><![CDATA[
1303  quoted-cpair    = "\" ( WSP / VCHAR / obs-text )
1304]]></artwork></figure>
1305<t>
1306   Senders SHOULD NOT escape octets that do not require escaping
1307   (i.e., other than the backslash octet "\" and the parentheses "(" and
1308   ")").
1309</t>
1310</section>
1311
1312<section title="Message Body" anchor="message.body">
1313 
1314<t>
1315   The message-body (if any) of an HTTP message is used to carry the
1316   payload body associated with the request or response.
1317</t>
1318<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1319  message-body = *OCTET
1320]]></artwork></figure>
1321<t>
1322   The message-body differs from the payload body only when a transfer-coding
1323   has been applied, as indicated by the Transfer-Encoding header field
1324   (<xref target="header.transfer-encoding"/>).  If more than one
1325   Transfer-Encoding header field is present in a message, the multiple
1326   field-values MUST be combined into one field-value, according to the
1327   algorithm defined in <xref target="header.fields"/>, before determining
1328   the message-body length.
1329</t>
1330<t>
1331   When one or more transfer-codings are applied to a payload in order to
1332   form the message-body, the Transfer-Encoding header field MUST contain
1333   the list of transfer-codings applied. Transfer-Encoding is a property of
1334   the message, not of the payload, and thus MAY be added or removed by
1335   any implementation along the request/response chain under the constraints
1336   found in <xref target="transfer.codings"/>.
1337</t>
1338<t>
1339   If a message is received that has multiple Content-Length header fields
1340   (<xref target="header.content-length"/>) with field-values consisting
1341   of the same decimal value, or a single Content-Length header field with
1342   a field value containing a list of identical decimal values (e.g.,
1343   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1344   header fields have been generated or combined by an upstream message
1345   processor, then the recipient MUST either reject the message as invalid
1346   or replace the duplicated field-values with a single valid Content-Length
1347   field containing that decimal value prior to determining the message-body
1348   length.
1349</t>
1350<t>
1351   The rules for when a message-body is allowed in a message differ for
1352   requests and responses.
1353</t>
1354<t>
1355   The presence of a message-body in a request is signaled by the
1356   inclusion of a Content-Length or Transfer-Encoding header field in
1357   the request's header fields, even if the request method does not
1358   define any use for a message-body.  This allows the request
1359   message framing algorithm to be independent of method semantics.
1360</t>
1361<t>
1362   For response messages, whether or not a message-body is included with
1363   a message is dependent on both the request method and the response
1364   status code (<xref target="status.code.and.reason.phrase"/>).
1365   Responses to the HEAD request method never include a message-body
1366   because the associated response header fields (e.g., Transfer-Encoding,
1367   Content-Length, etc.) only indicate what their values would have been
1368   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1369   and 304 (Not Modified) responses MUST NOT include a message-body.
1370   All other responses do include a message-body, although the body
1371   MAY be of zero length.
1372</t>
1373<t>
1374   The length of the message-body is determined by one of the following
1375   (in order of precedence):
1376</t>
1377<t>
1378  <list style="numbers">
1379    <t>
1380     Any response to a HEAD request and any response with a status
1381     code of 100-199, 204, or 304 is always terminated by the first
1382     empty line after the header fields, regardless of the header
1383     fields present in the message, and thus cannot contain a message-body.
1384    </t>
1385    <t>
1386     If a Transfer-Encoding header field is present
1387     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1388     is the final encoding, the message-body length is determined by reading
1389     and decoding the chunked data until the transfer-coding indicates the
1390     data is complete.
1391    <vspace blankLines="1"/>
1392     If a Transfer-Encoding header field is present in a response and the
1393     "chunked" transfer-coding is not the final encoding, the message-body
1394     length is determined by reading the connection until it is closed by
1395     the server.
1396     If a Transfer-Encoding header field is present in a request and the
1397     "chunked" transfer-coding is not the final encoding, the message-body
1398     length cannot be determined reliably; the server MUST respond with
1399     the 400 (Bad Request) status code and then close the connection.
1400    <vspace blankLines="1"/>
1401     If a message is received with both a Transfer-Encoding header field
1402     and a Content-Length header field, the Transfer-Encoding overrides
1403     the Content-Length.
1404     Such a message might indicate an attempt to perform request or response
1405     smuggling (bypass of security-related checks on message routing or content)
1406     and thus ought to be handled as an error.  The provided Content-Length MUST
1407     be removed, prior to forwarding the message downstream, or replaced with
1408     the real message-body length after the transfer-coding is decoded.
1409    </t>
1410    <t>
1411     If a message is received without Transfer-Encoding and with either
1412     multiple Content-Length header fields having differing field-values or
1413     a single Content-Length header field having an invalid value, then the
1414     message framing is invalid and MUST be treated as an error to
1415     prevent request or response smuggling.
1416     If this is a request message, the server MUST respond with
1417     a 400 (Bad Request) status code and then close the connection.
1418     If this is a response message received by a proxy, the proxy
1419     MUST discard the received response, send a 502 (Bad Gateway)
1420     status code as its downstream response, and then close the connection.
1421     If this is a response message received by a user-agent, it MUST be
1422     treated as an error by discarding the message and closing the connection.
1423    </t>
1424    <t>
1425     If a valid Content-Length header field
1426     is present without Transfer-Encoding, its decimal value defines the
1427     message-body length in octets.  If the actual number of octets sent in
1428     the message is less than the indicated Content-Length, the recipient
1429     MUST consider the message to be incomplete and treat the connection
1430     as no longer usable.
1431     If the actual number of octets sent in the message is more than the indicated
1432     Content-Length, the recipient MUST only process the message-body up to the
1433     field value's number of octets; the remainder of the message MUST either
1434     be discarded or treated as the next message in a pipeline.  For the sake of
1435     robustness, a user-agent MAY attempt to detect and correct such an error
1436     in message framing if it is parsing the response to the last request on
1437     on a connection and the connection has been closed by the server.
1438    </t>
1439    <t>
1440     If this is a request message and none of the above are true, then the
1441     message-body length is zero (no message-body is present).
1442    </t>
1443    <t>
1444     Otherwise, this is a response message without a declared message-body
1445     length, so the message-body length is determined by the number of octets
1446     received prior to the server closing the connection.
1447    </t>
1448  </list>
1449</t>
1450<t>
1451   Since there is no way to distinguish a successfully completed,
1452   close-delimited message from a partially-received message interrupted
1453   by network failure, implementations SHOULD use encoding or
1454   length-delimited messages whenever possible.  The close-delimiting
1455   feature exists primarily for backwards compatibility with HTTP/1.0.
1456</t>
1457<t>
1458   A server MAY reject a request that contains a message-body but
1459   not a Content-Length by responding with 411 (Length Required).
1460</t>
1461<t>
1462   Unless a transfer-coding other than "chunked" has been applied,
1463   a client that sends a request containing a message-body SHOULD
1464   use a valid Content-Length header field if the message-body length
1465   is known in advance, rather than the "chunked" encoding, since some
1466   existing services respond to "chunked" with a 411 (Length Required)
1467   status code even though they understand the chunked encoding.  This
1468   is typically because such services are implemented via a gateway that
1469   requires a content-length in advance of being called and the server
1470   is unable or unwilling to buffer the entire request before processing.
1471</t>
1472<t>
1473   A client that sends a request containing a message-body MUST include a
1474   valid Content-Length header field if it does not know the server will
1475   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1476   of specific user configuration or by remembering the version of a prior
1477   received response.
1478</t>
1479<t>
1480   Request messages that are prematurely terminated, possibly due to a
1481   cancelled connection or a server-imposed time-out exception, MUST
1482   result in closure of the connection; sending an HTTP/1.1 error response
1483   prior to closing the connection is OPTIONAL.
1484   Response messages that are prematurely terminated, usually by closure
1485   of the connection prior to receiving the expected number of octets or by
1486   failure to decode a transfer-encoded message-body, MUST be recorded
1487   as incomplete.  A user agent MUST NOT render an incomplete response
1488   message-body as if it were complete (i.e., some indication must be given
1489   to the user that an error occurred).  Cache requirements for incomplete
1490   responses are defined in Section 2.1.1 of <xref target="Part6"/>.
1491</t>
1492<t>
1493   A server MUST read the entire request message-body or close
1494   the connection after sending its response, since otherwise the
1495   remaining data on a persistent connection would be misinterpreted
1496   as the next request.  Likewise,
1497   a client MUST read the entire response message-body if it intends
1498   to reuse the same connection for a subsequent request.  Pipelining
1499   multiple requests on a connection is described in <xref target="pipelining"/>.
1500</t>
1501</section>
1502
1503<section title="General Header Fields" anchor="general.header.fields">
1504 
1505<t>
1506   There are a few header fields which have general applicability for
1507   both request and response messages, but which do not apply to the
1508   payload being transferred. These header fields apply only to the
1509   message being transmitted.
1510</t>
1511<texttable align="left">
1512  <ttcol>Header Field Name</ttcol>
1513  <ttcol>Defined in...</ttcol>
1514 
1515  <c>Connection</c> <c><xref target="header.connection"/></c>
1516  <c>Date</c> <c><xref target="header.date"/></c>
1517  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1518  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1519  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1520  <c>Via</c> <c><xref target="header.via"/></c>
1521</texttable>
1522</section>
1523</section>
1524
1525<section title="Request" anchor="request">
1526 
1527<t>
1528   A request message from a client to a server begins with a
1529   Request-Line, followed by zero or more header fields, an empty
1530   line signifying the end of the header block, and an optional
1531   message body.
1532</t>
1533<!--                 Host                      ; should be moved here eventually -->
1534<figure><iref primary="true" item="Grammar" subitem="Request"/><artwork type="abnf2616"><![CDATA[
1535  Request       = Request-Line              ; Section 4.1
1536                  *( header-field CRLF )    ; Section 3.2
1537                  CRLF
1538                  [ message-body ]          ; Section 3.3
1539]]></artwork></figure>
1540
1541<section title="Request-Line" anchor="request-line">
1542 
1543<t>
1544   The Request-Line begins with a method token, followed by a single
1545   space (SP), the request-target, another single space (SP), the
1546   protocol version, and ending with CRLF.
1547</t>
1548<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1549  Request-Line   = Method SP request-target SP HTTP-Version CRLF
1550]]></artwork></figure>
1551
1552<section title="Method" anchor="method">
1553 
1554<t>
1555   The Method token indicates the request method to be performed on the
1556   target resource. The request method is case-sensitive.
1557</t>
1558<figure><iref primary="true" item="Grammar" subitem="Method"/><artwork type="abnf2616"><![CDATA[
1559  Method         = token
1560]]></artwork></figure>
1561</section>
1562
1563<section title="request-target" anchor="request-target">
1564 
1565<t>
1566   The request-target identifies the target resource upon which to apply
1567   the request.  In most cases, the user agent is provided a URI reference
1568   from which it determines an absolute URI for identifying the target
1569   resource.  When a request to the resource is initiated, all or part
1570   of that URI is used to construct the HTTP request-target.
1571</t>
1572<figure><iref primary="true" item="Grammar" subitem="request-target"/><artwork type="abnf2616"><![CDATA[
1573  request-target = "*"
1574                 / absolute-URI
1575                 / ( path-absolute [ "?" query ] )
1576                 / authority
1577]]></artwork></figure>
1578<t>
1579   The four options for request-target are dependent on the nature of the
1580   request.
1581</t>   
1582<t><iref item="asterisk form (of request-target)"/>
1583   The asterisk "*" form of request-target, which MUST NOT be used
1584   with any request method other than OPTIONS, means that the request
1585   applies to the server as a whole (the listening process) rather than
1586   to a specific named resource at that server.  For example,
1587</t>
1588<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1589  OPTIONS * HTTP/1.1
1590  ]]></artwork></figure>
1591<t><iref item="absolute-URI form (of request-target)"/>
1592   The "absolute-URI" form is REQUIRED when the request is being made to a
1593   proxy. The proxy is requested to either forward the request or service it
1594   from a valid cache, and then return the response. Note that the proxy MAY
1595   forward the request on to another proxy or directly to the server
1596   specified by the absolute-URI. In order to avoid request loops, a
1597   proxy that forwards requests to other proxies MUST be able to
1598   recognize and exclude all of its own server names, including
1599   any aliases, local variations, and the numeric IP address. An example
1600   Request-Line would be:
1601</t>
1602<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1603  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1604  ]]></artwork></figure>
1605<t>
1606   To allow for transition to absolute-URIs in all requests in future
1607   versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
1608   form in requests, even though HTTP/1.1 clients will only generate
1609   them in requests to proxies.
1610</t>
1611<t>
1612   If a proxy receives a host name that is not a fully qualified domain
1613   name, it MAY add its domain to the host name it received. If a proxy
1614   receives a fully qualified domain name, the proxy MUST NOT change
1615   the host name.
1616</t>
1617<t><iref item="authority form (of request-target)"/>
1618   The "authority form" is only used by the CONNECT request method (Section 7.9 of <xref target="Part2"/>).
1619</t>
1620<t><iref item="origin form (of request-target)"/>
1621   The most common form of request-target is that used when making
1622   a request to an origin server ("origin form").
1623   In this case, the absolute path and query components of the URI
1624   MUST be transmitted as the request-target, and the authority component
1625   MUST be transmitted in a Host header field. For example, a client wishing
1626   to retrieve a representation of the resource, as identified above,
1627   directly from the origin server would open (or reuse) a TCP connection
1628   to port 80 of the host "www.example.org" and send the lines:
1629</t>
1630<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1631  GET /pub/WWW/TheProject.html HTTP/1.1
1632  Host: www.example.org
1633  ]]></artwork></figure>
1634<t>
1635   followed by the remainder of the Request. Note that the origin form
1636   of request-target always starts with an absolute path; if the target
1637   resource's URI path is empty, then an absolute path of "/" MUST be
1638   provided in the request-target.
1639</t>
1640<t>
1641   If a proxy receives an OPTIONS request with an absolute-URI form of
1642   request-target in which the URI has an empty path and no query component,
1643   then the last proxy on the request chain MUST use a request-target
1644   of "*" when it forwards the request to the indicated origin server.
1645</t>
1646<figure><preamble>  
1647   For example, the request
1648</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1649  OPTIONS http://www.example.org:8001 HTTP/1.1
1650  ]]></artwork></figure>
1651<figure><preamble>  
1652  would be forwarded by the final proxy as
1653</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1654  OPTIONS * HTTP/1.1
1655  Host: www.example.org:8001
1656  ]]></artwork>
1657<postamble>
1658   after connecting to port 8001 of host "www.example.org".
1659</postamble>
1660</figure>
1661<t>
1662   The request-target is transmitted in the format specified in
1663   <xref target="http.uri"/>. If the request-target is percent-encoded
1664   (<xref target="RFC3986"/>, Section 2.1), the origin server
1665   MUST decode the request-target in order to
1666   properly interpret the request. Servers SHOULD respond to invalid
1667   request-targets with an appropriate status code.
1668</t>
1669<t>
1670   A non-transforming proxy MUST NOT rewrite the "path-absolute" part of the
1671   received request-target when forwarding it to the next inbound server,
1672   except as noted above to replace a null path-absolute with "/" or "*".
1673</t>
1674<t><list>
1675  <t>
1676    Note: The "no rewrite" rule prevents the proxy from changing the
1677    meaning of the request when the origin server is improperly using
1678    a non-reserved URI character for a reserved purpose.  Implementors
1679    need to be aware that some pre-HTTP/1.1 proxies have been known to
1680    rewrite the request-target.
1681  </t>
1682</list></t>
1683<t>
1684   HTTP does not place a pre-defined limit on the length of a request-target.
1685   A server MUST be prepared to receive URIs of unbounded length and
1686   respond with the 414 (URI Too Long) status code if the received
1687   request-target would be longer than the server wishes to handle
1688   (see Section 8.4.15 of <xref target="Part2"/>).
1689</t>
1690<t>
1691   Various ad-hoc limitations on request-target length are found in practice.
1692   It is RECOMMENDED that all HTTP senders and recipients support
1693   request-target lengths of 8000 or more octets.
1694</t>
1695<t><list>
1696  <t>
1697    Note: Fragments (<xref target="RFC3986"/>, Section 3.5)
1698    are not part of the request-target and thus will not be transmitted
1699    in an HTTP request.
1700  </t>
1701</list></t>
1702</section>
1703</section>
1704
1705<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1706<t>
1707   The exact resource identified by an Internet request is determined by
1708   examining both the request-target and the Host header field.
1709</t>
1710<t>
1711   An origin server that does not allow resources to differ by the
1712   requested host MAY ignore the Host header field value when
1713   determining the resource identified by an HTTP/1.1 request. (But see
1714   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1715   for other requirements on Host support in HTTP/1.1.)
1716</t>
1717<t>
1718   An origin server that does differentiate resources based on the host
1719   requested (sometimes referred to as virtual hosts or vanity host
1720   names) MUST use the following rules for determining the requested
1721   resource on an HTTP/1.1 request:
1722  <list style="numbers">
1723    <t>If request-target is an absolute-URI, the host is part of the
1724     request-target. Any Host header field value in the request MUST be
1725     ignored.</t>
1726    <t>If the request-target is not an absolute-URI, and the request includes
1727     a Host header field, the host is determined by the Host header
1728     field value.</t>
1729    <t>If the host as determined by rule 1 or 2 is not a valid host on
1730     the server, the response MUST be a 400 (Bad Request) error message.</t>
1731  </list>
1732</t>
1733<t>
1734   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1735   attempt to use heuristics (e.g., examination of the URI path for
1736   something unique to a particular host) in order to determine what
1737   exact resource is being requested.
1738</t>
1739</section>
1740
1741<section title="Effective Request URI" anchor="effective.request.uri">
1742  <iref primary="true" item="effective request URI"/>
1743  <iref primary="true" item="target resource"/>
1744<t>
1745   HTTP requests often do not carry the absolute URI (<xref target="RFC3986"/>, Section 4.3)
1746   for the target resource; instead, the URI needs to be inferred from the
1747   request-target, Host header field, and connection context. The result of
1748   this process is called the "effective request URI".  The "target resource"
1749   is the resource identified by the effective request URI.
1750</t>
1751<t>
1752   If the request-target is an absolute-URI, then the effective request URI is
1753   the request-target.
1754</t>
1755<t>
1756   If the request-target uses the path-absolute form or the asterisk form,
1757   and the Host header field is present, then the effective request URI is
1758   constructed by concatenating
1759</t>
1760<t>
1761  <list style="symbols">
1762    <t>
1763      the scheme name: "http" if the request was received over an insecure
1764      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1765      connection,
1766    </t>
1767    <t>
1768      the octet sequence "://",
1769    </t>
1770    <t>
1771      the authority component, as specified in the Host header field
1772      (<xref target="header.host"/>), and
1773    </t>
1774    <t>
1775      the request-target obtained from the Request-Line, unless the
1776      request-target is just the asterisk "*".
1777    </t>
1778  </list>
1779</t>
1780<t>
1781   If the request-target uses the path-absolute form or the asterisk form,
1782   and the Host header field is not present, then the effective request URI is
1783   undefined.
1784</t>
1785<t>
1786   Otherwise, when request-target uses the authority form, the effective
1787   request URI is undefined.
1788</t>
1789<figure>
1790<preamble>
1791   Example 1: the effective request URI for the message
1792</preamble>
1793<artwork type="example"><![CDATA[
1794  GET /pub/WWW/TheProject.html HTTP/1.1
1795  Host: www.example.org:8080
1796  ]]></artwork>
1797<postamble>
1798  (received over an insecure TCP connection) is "http", plus "://", plus the
1799  authority component "www.example.org:8080", plus the request-target
1800  "/pub/WWW/TheProject.html", thus
1801  "http://www.example.org:8080/pub/WWW/TheProject.html".
1802</postamble>
1803</figure>
1804<figure>
1805<preamble>
1806   Example 2: the effective request URI for the message
1807</preamble>
1808<artwork type="example"><![CDATA[
1809  GET * HTTP/1.1
1810  Host: www.example.org
1811  ]]></artwork>
1812<postamble>
1813  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1814  authority component "www.example.org", thus "https://www.example.org".
1815</postamble>
1816</figure>
1817<t>
1818   Effective request URIs are compared using the rules described in
1819   <xref target="uri.comparison"/>, except that empty path components MUST NOT
1820   be treated as equivalent to an absolute path of "/".
1821</t> 
1822</section>
1823
1824</section>
1825
1826
1827<section title="Response" anchor="response">
1828 
1829<t>
1830   After receiving and interpreting a request message, a server responds
1831   with an HTTP response message.
1832</t>
1833<figure><iref primary="true" item="Grammar" subitem="Response"/><artwork type="abnf2616"><![CDATA[
1834  Response      = Status-Line               ; Section 5.1
1835                  *( header-field CRLF )    ; Section 3.2
1836                  CRLF
1837                  [ message-body ]          ; Section 3.3
1838]]></artwork></figure>
1839
1840<section title="Status-Line" anchor="status-line">
1841 
1842<t>
1843   The first line of a Response message is the Status-Line, consisting
1844   of the protocol version, a space (SP), the status code, another space,
1845   a possibly-empty textual phrase describing the status code, and
1846   ending with CRLF.
1847</t>
1848<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1849  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1850]]></artwork></figure>
1851
1852<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1853 
1854 
1855<t>
1856   The Status-Code element is a 3-digit integer result code of the
1857   attempt to understand and satisfy the request. These codes are fully
1858   defined in Section 8 of <xref target="Part2"/>.  The Reason Phrase exists for the sole
1859   purpose of providing a textual description associated with the numeric
1860   status code, out of deference to earlier Internet application protocols
1861   that were more frequently used with interactive text clients.
1862   A client SHOULD ignore the content of the Reason Phrase.
1863</t>
1864<t>
1865   The first digit of the Status-Code defines the class of response. The
1866   last two digits do not have any categorization role. There are 5
1867   values for the first digit:
1868  <list style="symbols">
1869    <t>
1870      1xx: Informational - Request received, continuing process
1871    </t>
1872    <t>
1873      2xx: Success - The action was successfully received,
1874        understood, and accepted
1875    </t>
1876    <t>
1877      3xx: Redirection - Further action must be taken in order to
1878        complete the request
1879    </t>
1880    <t>
1881      4xx: Client Error - The request contains bad syntax or cannot
1882        be fulfilled
1883    </t>
1884    <t>
1885      5xx: Server Error - The server failed to fulfill an apparently
1886        valid request
1887    </t>
1888  </list>
1889</t>
1890<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
1891  Status-Code    = 3DIGIT
1892  Reason-Phrase  = *( WSP / VCHAR / obs-text )
1893]]></artwork></figure>
1894</section>
1895</section>
1896
1897</section>
1898
1899
1900<section title="Protocol Parameters" anchor="protocol.parameters">
1901
1902<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1903 
1904<t>
1905   HTTP applications have historically allowed three different formats
1906   for date/time stamps. However, the preferred format is a fixed-length subset
1907   of that defined by <xref target="RFC1123"/>:
1908</t>
1909<figure><artwork type="example"><![CDATA[
1910  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1911  ]]></artwork></figure>
1912<t>
1913   The other formats are described here only for compatibility with obsolete
1914   implementations.
1915</t>
1916<figure><artwork type="example"><![CDATA[
1917  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1918  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1919  ]]></artwork></figure>
1920<t>
1921   HTTP/1.1 clients and servers that parse a date value MUST accept
1922   all three formats (for compatibility with HTTP/1.0), though they MUST
1923   only generate the RFC 1123 format for representing HTTP-date values
1924   in header fields. See <xref target="tolerant.applications"/> for further information.
1925</t>
1926<t>
1927   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
1928   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1929   equal to UTC (Coordinated Universal Time). This is indicated in the
1930   first two formats by the inclusion of "GMT" as the three-letter
1931   abbreviation for time zone, and MUST be assumed when reading the
1932   asctime format. HTTP-date is case sensitive and MUST NOT include
1933   additional whitespace beyond that specifically included as SP in the
1934   grammar.
1935</t>
1936<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><artwork type="abnf2616"><![CDATA[
1937  HTTP-date    = rfc1123-date / obs-date
1938]]></artwork></figure>
1939<t anchor="preferred.date.format">
1940 
1941 
1942 
1943 
1944 
1945 
1946 
1947 
1948 
1949 
1950  Preferred format:
1951</t>
1952<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[
1953  rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
1954  ; fixed length subset of the format defined in
1955  ; Section 5.2.14 of [RFC1123]
1956 
1957  day-name     = %x4D.6F.6E ; "Mon", case-sensitive
1958               / %x54.75.65 ; "Tue", case-sensitive
1959               / %x57.65.64 ; "Wed", case-sensitive
1960               / %x54.68.75 ; "Thu", case-sensitive
1961               / %x46.72.69 ; "Fri", case-sensitive
1962               / %x53.61.74 ; "Sat", case-sensitive
1963               / %x53.75.6E ; "Sun", case-sensitive
1964               
1965  date1        = day SP month SP year
1966               ; e.g., 02 Jun 1982
1967
1968  day          = 2DIGIT
1969  month        = %x4A.61.6E ; "Jan", case-sensitive
1970               / %x46.65.62 ; "Feb", case-sensitive
1971               / %x4D.61.72 ; "Mar", case-sensitive
1972               / %x41.70.72 ; "Apr", case-sensitive
1973               / %x4D.61.79 ; "May", case-sensitive
1974               / %x4A.75.6E ; "Jun", case-sensitive
1975               / %x4A.75.6C ; "Jul", case-sensitive
1976               / %x41.75.67 ; "Aug", case-sensitive
1977               / %x53.65.70 ; "Sep", case-sensitive
1978               / %x4F.63.74 ; "Oct", case-sensitive
1979               / %x4E.6F.76 ; "Nov", case-sensitive
1980               / %x44.65.63 ; "Dec", case-sensitive
1981  year         = 4DIGIT
1982
1983  GMT   = %x47.4D.54 ; "GMT", case-sensitive
1984
1985  time-of-day  = hour ":" minute ":" second
1986                 ; 00:00:00 - 23:59:59
1987                 
1988  hour         = 2DIGIT               
1989  minute       = 2DIGIT               
1990  second       = 2DIGIT               
1991]]></artwork></figure>
1992<t>
1993  The semantics of <xref target="preferred.date.format" format="none">day-name</xref>, <xref target="preferred.date.format" format="none">day</xref>,
1994  <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
1995  same as those defined for the RFC 5322 constructs
1996  with the corresponding name (<xref target="RFC5322"/>, Section 3.3).
1997</t>
1998<t anchor="obsolete.date.formats">
1999 
2000 
2001 
2002 
2003 
2004 
2005 
2006 
2007  Obsolete formats:
2008</t>
2009<figure><iref primary="true" item="Grammar" subitem="obs-date"/><artwork type="abnf2616"><![CDATA[
2010  obs-date     = rfc850-date / asctime-date
2011]]></artwork></figure>
2012<figure><iref primary="true" item="Grammar" subitem="rfc850-date"/><artwork type="abnf2616"><![CDATA[
2013  rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
2014  date2        = day "-" month "-" 2DIGIT
2015                 ; day-month-year (e.g., 02-Jun-82)
2016
2017  day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
2018         / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
2019         / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
2020         / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
2021         / %x46.72.69.64.61.79 ; "Friday", case-sensitive
2022         / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
2023         / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
2024]]></artwork></figure>
2025<figure><iref primary="true" item="Grammar" subitem="asctime-date"/><artwork type="abnf2616"><![CDATA[
2026  asctime-date = day-name SP date3 SP time-of-day SP year
2027  date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
2028                 ; month day (e.g., Jun  2)
2029]]></artwork></figure>
2030<t><list>
2031  <t>
2032    Note: Recipients of date values are encouraged to be robust in
2033    accepting date values that might have been sent by non-HTTP
2034    applications, as is sometimes the case when retrieving or posting
2035    messages via proxies/gateways to SMTP or NNTP.
2036  </t>
2037</list></t>
2038<t><list>
2039  <t>
2040    Note: HTTP requirements for the date/time stamp format apply only
2041    to their usage within the protocol stream. Clients and servers are
2042    not required to use these formats for user presentation, request
2043    logging, etc.
2044  </t>
2045</list></t>
2046</section>
2047
2048<section title="Transfer Codings" anchor="transfer.codings">
2049 
2050 
2051<t>
2052   Transfer-coding values are used to indicate an encoding
2053   transformation that has been, can be, or might need to be applied to a
2054   payload body in order to ensure "safe transport" through the network.
2055   This differs from a content coding in that the transfer-coding is a
2056   property of the message rather than a property of the representation
2057   that is being transferred.
2058</t>
2059<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
2060  transfer-coding         = "chunked" ; Section 6.2.1
2061                          / "compress" ; Section 6.2.2.1
2062                          / "deflate" ; Section 6.2.2.2
2063                          / "gzip" ; Section 6.2.2.3
2064                          / transfer-extension
2065  transfer-extension      = token *( OWS ";" OWS transfer-parameter )
2066]]></artwork></figure>
2067<t anchor="rule.parameter">
2068 
2069 
2070 
2071   Parameters are in the form of attribute/value pairs.
2072</t>
2073<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[
2074  transfer-parameter      = attribute BWS "=" BWS value
2075  attribute               = token
2076  value                   = word
2077]]></artwork></figure>
2078<t>
2079   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2080   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2081   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2082</t>
2083<t>
2084   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2085   MIME, which were designed to enable safe transport of binary data over a
2086   7-bit transport service (<xref target="RFC2045"/>, Section 6).
2087   However, safe transport
2088   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2089   the only unsafe characteristic of message-bodies is the difficulty in
2090   determining the exact message body length (<xref target="message.body"/>),
2091   or the desire to encrypt data over a shared transport.
2092</t>
2093<t>
2094   A server that receives a request message with a transfer-coding it does
2095   not understand SHOULD respond with 501 (Not Implemented) and then
2096   close the connection. A server MUST NOT send transfer-codings to an HTTP/1.0
2097   client.
2098</t>
2099
2100<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2101  <iref item="chunked (Coding Format)"/>
2102  <iref item="Coding Format" subitem="chunked"/>
2103 
2104 
2105 
2106 
2107 
2108 
2109 
2110 
2111 
2112 
2113 
2114<t>
2115   The chunked encoding modifies the body of a message in order to
2116   transfer it as a series of chunks, each with its own size indicator,
2117   followed by an OPTIONAL trailer containing header fields. This
2118   allows dynamically produced content to be transferred along with the
2119   information necessary for the recipient to verify that it has
2120   received the full message.
2121</t>
2122<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[
2123  Chunked-Body   = *chunk
2124                   last-chunk
2125                   trailer-part
2126                   CRLF
2127 
2128  chunk          = chunk-size *WSP [ chunk-ext ] CRLF
2129                   chunk-data CRLF
2130  chunk-size     = 1*HEXDIG
2131  last-chunk     = 1*("0") *WSP [ chunk-ext ] CRLF
2132 
2133  chunk-ext      = *( ";" *WSP chunk-ext-name
2134                      [ "=" chunk-ext-val ] *WSP )
2135  chunk-ext-name = token
2136  chunk-ext-val  = token / quoted-str-nf
2137  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
2138  trailer-part   = *( header-field CRLF )
2139 
2140  quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
2141                 ; like quoted-string, but disallowing line folding
2142  qdtext-nf      = WSP / %x21 / %x23-5B / %x5D-7E / obs-text
2143                 ; WSP / <VCHAR except DQUOTE and "\"> / obs-text
2144]]></artwork></figure>
2145<t>
2146   The chunk-size field is a string of hex digits indicating the size of
2147   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2148   zero, followed by the trailer, which is terminated by an empty line.
2149</t>
2150<t>
2151   The trailer allows the sender to include additional HTTP header
2152   fields at the end of the message. The Trailer header field can be
2153   used to indicate which header fields are included in a trailer (see
2154   <xref target="header.trailer"/>).
2155</t>
2156<t>
2157   A server using chunked transfer-coding in a response MUST NOT use the
2158   trailer for any header fields unless at least one of the following is
2159   true:
2160  <list style="numbers">
2161    <t>the request included a TE header field that indicates "trailers" is
2162     acceptable in the transfer-coding of the  response, as described in
2163     <xref target="header.te"/>; or,</t>
2164     
2165    <t>the trailer fields consist entirely of optional metadata, and the
2166    recipient could use the message (in a manner acceptable to the server where
2167    the field originated) without receiving it. In other words, the server that
2168    generated the header (often but not always the origin server) is willing to
2169    accept the possibility that the trailer fields might be silently discarded
2170    along the path to the client.</t>
2171  </list>
2172</t>
2173<t>
2174   This requirement prevents an interoperability failure when the
2175   message is being received by an HTTP/1.1 (or later) proxy and
2176   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2177   compliance with the protocol would have necessitated a possibly
2178   infinite buffer on the proxy.
2179</t>
2180<t>
2181   A process for decoding the "chunked" transfer-coding
2182   can be represented in pseudo-code as:
2183</t>
2184<figure><artwork type="code"><![CDATA[
2185  length := 0
2186  read chunk-size, chunk-ext (if any) and CRLF
2187  while (chunk-size > 0) {
2188     read chunk-data and CRLF
2189     append chunk-data to decoded-body
2190     length := length + chunk-size
2191     read chunk-size and CRLF
2192  }
2193  read header-field
2194  while (header-field not empty) {
2195     append header-field to existing header fields
2196     read header-field
2197  }
2198  Content-Length := length
2199  Remove "chunked" from Transfer-Encoding
2200]]></artwork></figure>
2201<t>
2202   All HTTP/1.1 applications MUST be able to receive and decode the
2203   "chunked" transfer-coding and MUST ignore chunk-ext extensions
2204   they do not understand.
2205</t>
2206<t>
2207   Since "chunked" is the only transfer-coding required to be understood
2208   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2209   on a persistent connection.  Whenever a transfer-coding is applied to
2210   a payload body in a request, the final transfer-coding applied MUST
2211   be "chunked".  If a transfer-coding is applied to a response payload
2212   body, then either the final transfer-coding applied MUST be "chunked"
2213   or the message MUST be terminated by closing the connection. When the
2214   "chunked" transfer-coding is used, it MUST be the last transfer-coding
2215   applied to form the message-body. The "chunked" transfer-coding MUST NOT
2216   be applied more than once in a message-body.
2217</t>
2218</section>
2219
2220<section title="Compression Codings" anchor="compression.codings">
2221<t>
2222   The codings defined below can be used to compress the payload of a
2223   message.
2224</t>
2225<t><list><t>
2226   Note: Use of program names for the identification of encoding formats
2227   is not desirable and is discouraged for future encodings. Their
2228   use here is representative of historical practice, not good
2229   design.
2230</t></list></t>
2231<t><list><t>
2232   Note: For compatibility with previous implementations of HTTP,
2233   applications SHOULD consider "x-gzip" and "x-compress" to be
2234   equivalent to "gzip" and "compress" respectively.
2235</t></list></t>
2236
2237<section title="Compress Coding" anchor="compress.coding">
2238<iref item="compress (Coding Format)"/>
2239<iref item="Coding Format" subitem="compress"/>
2240<t>
2241   The "compress" format is produced by the common UNIX file compression
2242   program "compress". This format is an adaptive Lempel-Ziv-Welch
2243   coding (LZW).
2244</t>
2245</section>
2246
2247<section title="Deflate Coding" anchor="deflate.coding">
2248<iref item="deflate (Coding Format)"/>
2249<iref item="Coding Format" subitem="deflate"/>
2250<t>
2251   The "deflate" format is defined as the "deflate" compression mechanism
2252   (described in <xref target="RFC1951"/>) used inside the "zlib"
2253   data format (<xref target="RFC1950"/>).
2254</t>
2255<t><list>
2256  <t>
2257    Note: Some incorrect implementations send the "deflate"
2258    compressed data without the zlib wrapper.
2259   </t>
2260</list></t>
2261</section>
2262
2263<section title="Gzip Coding" anchor="gzip.coding">
2264<iref item="gzip (Coding Format)"/>
2265<iref item="Coding Format" subitem="gzip"/>
2266<t>
2267   The "gzip" format is produced by the file compression program
2268   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2269   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2270</t>
2271</section>
2272
2273</section>
2274
2275<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2276<t>
2277   The HTTP Transfer Coding Registry defines the name space for the transfer
2278   coding names.
2279</t>
2280<t>
2281   Registrations MUST include the following fields:
2282   <list style="symbols">
2283     <t>Name</t>
2284     <t>Description</t>
2285     <t>Pointer to specification text</t>
2286   </list>
2287</t>
2288<t>
2289   Names of transfer codings MUST NOT overlap with names of content codings
2290   (Section 2.2 of <xref target="Part3"/>), unless the encoding transformation is identical (as it
2291   is the case for the compression codings defined in
2292   <xref target="compression.codings"/>).
2293</t>
2294<t>
2295   Values to be added to this name space require a specification
2296   (see "Specification Required" in Section 4.1 of <xref target="RFC5226"/>), and MUST
2297   conform to the purpose of transfer coding defined in this section.
2298</t>
2299<t>
2300   The registry itself is maintained at
2301   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2302</t>
2303</section>
2304</section>
2305
2306<section title="Product Tokens" anchor="product.tokens">
2307 
2308 
2309<t>
2310   Product tokens are used to allow communicating applications to
2311   identify themselves by software name and version. Most fields using
2312   product tokens also allow sub-products which form a significant part
2313   of the application to be listed, separated by whitespace. By
2314   convention, the products are listed in order of their significance
2315   for identifying the application.
2316</t>
2317<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
2318  product         = token ["/" product-version]
2319  product-version = token
2320]]></artwork></figure>
2321<t>
2322   Examples:
2323</t>
2324<figure><artwork type="example"><![CDATA[
2325  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2326  Server: Apache/0.8.4
2327]]></artwork></figure>
2328<t>
2329   Product tokens SHOULD be short and to the point. They MUST NOT be
2330   used for advertising or other non-essential information. Although any
2331   token octet MAY appear in a product-version, this token SHOULD
2332   only be used for a version identifier (i.e., successive versions of
2333   the same product SHOULD only differ in the product-version portion of
2334   the product value).
2335</t>
2336</section>
2337
2338<section title="Quality Values" anchor="quality.values">
2339 
2340<t>
2341   Both transfer codings (TE request header field, <xref target="header.te"/>)
2342   and content negotiation (Section 5 of <xref target="Part3"/>) use short "floating point"
2343   numbers to indicate the relative importance ("weight") of various
2344   negotiable parameters.  A weight is normalized to a real number in
2345   the range 0 through 1, where 0 is the minimum and 1 the maximum
2346   value. If a parameter has a quality value of 0, then content with
2347   this parameter is "not acceptable" for the client. HTTP/1.1
2348   applications MUST NOT generate more than three digits after the
2349   decimal point. User configuration of these values SHOULD also be
2350   limited in this fashion.
2351</t>
2352<figure><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
2353  qvalue         = ( "0" [ "." 0*3DIGIT ] )
2354                 / ( "1" [ "." 0*3("0") ] )
2355]]></artwork></figure>
2356<t><list>
2357  <t>
2358     Note: "Quality values" is a misnomer, since these values merely represent
2359     relative degradation in desired quality.
2360  </t>
2361</list></t>
2362</section>
2363
2364</section>
2365
2366<section title="Connections" anchor="connections">
2367
2368<section title="Persistent Connections" anchor="persistent.connections">
2369
2370<section title="Purpose" anchor="persistent.purpose">
2371<t>
2372   Prior to persistent connections, a separate TCP connection was
2373   established for each request, increasing the load on HTTP servers
2374   and causing congestion on the Internet. The use of inline images and
2375   other associated data often requires a client to make multiple
2376   requests of the same server in a short amount of time. Analysis of
2377   these performance problems and results from a prototype
2378   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2379   measurements of actual HTTP/1.1 implementations show good
2380   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2381   T/TCP <xref target="Tou1998"/>.
2382</t>
2383<t>
2384   Persistent HTTP connections have a number of advantages:
2385  <list style="symbols">
2386      <t>
2387        By opening and closing fewer TCP connections, CPU time is saved
2388        in routers and hosts (clients, servers, proxies, gateways,
2389        tunnels, or caches), and memory used for TCP protocol control
2390        blocks can be saved in hosts.
2391      </t>
2392      <t>
2393        HTTP requests and responses can be pipelined on a connection.
2394        Pipelining allows a client to make multiple requests without
2395        waiting for each response, allowing a single TCP connection to
2396        be used much more efficiently, with much lower elapsed time.
2397      </t>
2398      <t>
2399        Network congestion is reduced by reducing the number of packets
2400        caused by TCP opens, and by allowing TCP sufficient time to
2401        determine the congestion state of the network.
2402      </t>
2403      <t>
2404        Latency on subsequent requests is reduced since there is no time
2405        spent in TCP's connection opening handshake.
2406      </t>
2407      <t>
2408        HTTP can evolve more gracefully, since errors can be reported
2409        without the penalty of closing the TCP connection. Clients using
2410        future versions of HTTP might optimistically try a new feature,
2411        but if communicating with an older server, retry with old
2412        semantics after an error is reported.
2413      </t>
2414    </list>
2415</t>
2416<t>
2417   HTTP implementations SHOULD implement persistent connections.
2418</t>
2419</section>
2420
2421<section title="Overall Operation" anchor="persistent.overall">
2422<t>
2423   A significant difference between HTTP/1.1 and earlier versions of
2424   HTTP is that persistent connections are the default behavior of any
2425   HTTP connection. That is, unless otherwise indicated, the client
2426   SHOULD assume that the server will maintain a persistent connection,
2427   even after error responses from the server.
2428</t>
2429<t>
2430   Persistent connections provide a mechanism by which a client and a
2431   server can signal the close of a TCP connection. This signaling takes
2432   place using the Connection header field (<xref target="header.connection"/>). Once a close
2433   has been signaled, the client MUST NOT send any more requests on that
2434   connection.
2435</t>
2436
2437<section title="Negotiation" anchor="persistent.negotiation">
2438<t>
2439   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
2440   maintain a persistent connection unless a Connection header field including
2441   the connection-token "close" was sent in the request. If the server
2442   chooses to close the connection immediately after sending the
2443   response, it SHOULD send a Connection header field including the
2444   connection-token "close".
2445</t>
2446<t>
2447   An HTTP/1.1 client MAY expect a connection to remain open, but would
2448   decide to keep it open based on whether the response from a server
2449   contains a Connection header field with the connection-token close. In case
2450   the client does not want to maintain a connection for more than that
2451   request, it SHOULD send a Connection header field including the
2452   connection-token close.
2453</t>
2454<t>
2455   If either the client or the server sends the close token in the
2456   Connection header field, that request becomes the last one for the
2457   connection.
2458</t>
2459<t>
2460   Clients and servers SHOULD NOT  assume that a persistent connection is
2461   maintained for HTTP versions less than 1.1 unless it is explicitly
2462   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2463   compatibility with HTTP/1.0 clients.
2464</t>
2465<t>
2466   In order to remain persistent, all messages on the connection MUST
2467   have a self-defined message length (i.e., one not defined by closure
2468   of the connection), as described in <xref target="message.body"/>.
2469</t>
2470</section>
2471
2472<section title="Pipelining" anchor="pipelining">
2473<t>
2474   A client that supports persistent connections MAY "pipeline" its
2475   requests (i.e., send multiple requests without waiting for each
2476   response). A server MUST send its responses to those requests in the
2477   same order that the requests were received.
2478</t>
2479<t>
2480   Clients which assume persistent connections and pipeline immediately
2481   after connection establishment SHOULD be prepared to retry their
2482   connection if the first pipelined attempt fails. If a client does
2483   such a retry, it MUST NOT pipeline before it knows the connection is
2484   persistent. Clients MUST also be prepared to resend their requests if
2485   the server closes the connection before sending all of the
2486   corresponding responses.
2487</t>
2488<t>
2489   Clients SHOULD NOT pipeline requests using non-idempotent request methods or
2490   non-idempotent sequences of request methods (see Section 7.1.2 of <xref target="Part2"/>). Otherwise, a
2491   premature termination of the transport connection could lead to
2492   indeterminate results. A client wishing to send a non-idempotent
2493   request SHOULD wait to send that request until it has received the
2494   response status line for the previous request.
2495</t>
2496</section>
2497</section>
2498
2499<section title="Proxy Servers" anchor="persistent.proxy">
2500<t>
2501   It is especially important that proxies correctly implement the
2502   properties of the Connection header field as specified in <xref target="header.connection"/>.
2503</t>
2504<t>
2505   The proxy server MUST signal persistent connections separately with
2506   its clients and the origin servers (or other proxy servers) that it
2507   connects to. Each persistent connection applies to only one transport
2508   link.
2509</t>
2510<t>
2511   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
2512   with an HTTP/1.0 client (but see Section 19.7.1 of <xref target="RFC2068"/>
2513   for information and discussion of the problems with the Keep-Alive header field
2514   implemented by many HTTP/1.0 clients).
2515</t>
2516
2517<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2518<!--<t>
2519  <cref anchor="TODO-end-to-end" source="jre">
2520    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2521    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2522  </cref>
2523</t>-->
2524<t>
2525   For the purpose of defining the behavior of caches and non-caching
2526   proxies, we divide HTTP header fields into two categories:
2527  <list style="symbols">
2528      <t>End-to-end header fields, which are  transmitted to the ultimate
2529        recipient of a request or response. End-to-end header fields in
2530        responses MUST be stored as part of a cache entry and MUST be
2531        transmitted in any response formed from a cache entry.</t>
2532
2533      <t>Hop-by-hop header fields, which are meaningful only for a single
2534        transport-level connection, and are not stored by caches or
2535        forwarded by proxies.</t>
2536  </list>
2537</t>
2538<t>
2539   The following HTTP/1.1 header fields are hop-by-hop header fields:
2540  <list style="symbols">
2541      <t>Connection</t>
2542      <t>Keep-Alive</t>
2543      <t>Proxy-Authenticate</t>
2544      <t>Proxy-Authorization</t>
2545      <t>TE</t>
2546      <t>Trailer</t>
2547      <t>Transfer-Encoding</t>
2548      <t>Upgrade</t>
2549  </list>
2550</t>
2551<t>
2552   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2553</t>
2554<t>
2555   Other hop-by-hop header fields MUST be listed in a Connection header field
2556   (<xref target="header.connection"/>).
2557</t>
2558</section>
2559
2560<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2561<!--<t>
2562  <cref anchor="TODO-non-mod-headers" source="jre">
2563    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2564    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2565  </cref>
2566</t>-->
2567<t>
2568   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2569   value of certain end-to-end header fields. A non-transforming proxy SHOULD NOT
2570   modify an end-to-end header field unless the definition of that header field requires
2571   or specifically allows that.
2572</t>
2573<t>
2574   A non-transforming proxy MUST NOT modify any of the following fields in a
2575   request or response, and it MUST NOT add any of these fields if not
2576   already present:
2577  <list style="symbols">
2578    <t>Allow</t>
2579    <t>Content-Location</t>
2580    <t>Content-MD5</t>
2581    <t>ETag</t>
2582    <t>Last-Modified</t>
2583    <t>Server</t>
2584  </list>
2585</t>
2586<t>
2587   A non-transforming proxy MUST NOT modify any of the following fields in a
2588   response:
2589  <list style="symbols">
2590    <t>Expires</t>
2591  </list>
2592</t>
2593<t>
2594   but it MAY add any of these fields if not already present. If an
2595   Expires header field is added, it MUST be given a field-value identical to
2596   that of the Date header field in that response.
2597</t>
2598<t>
2599   A proxy MUST NOT modify or add any of the following fields in a
2600   message that contains the no-transform cache-control directive, or in
2601   any request:
2602  <list style="symbols">
2603    <t>Content-Encoding</t>
2604    <t>Content-Range</t>
2605    <t>Content-Type</t>
2606  </list>
2607</t>
2608<t>
2609   A transforming proxy MAY modify or add these fields to a message
2610   that does not include no-transform, but if it does so, it MUST add a
2611   Warning 214 (Transformation applied) if one does not already appear
2612   in the message (see Section 3.6 of <xref target="Part6"/>).
2613</t>
2614<t><list>
2615  <t>
2616    Warning: Unnecessary modification of end-to-end header fields might
2617    cause authentication failures if stronger authentication
2618    mechanisms are introduced in later versions of HTTP. Such
2619    authentication mechanisms MAY rely on the values of header fields
2620    not listed here.
2621  </t>
2622</list></t>
2623<t>
2624   A non-transforming proxy MUST preserve the message payload (<xref target="Part3"/>),
2625   though it MAY change the message-body through application or removal
2626   of a transfer-coding (<xref target="transfer.codings"/>).
2627</t>
2628</section>
2629
2630</section>
2631
2632<section title="Practical Considerations" anchor="persistent.practical">
2633<t>
2634   Servers will usually have some time-out value beyond which they will
2635   no longer maintain an inactive connection. Proxy servers might make
2636   this a higher value since it is likely that the client will be making
2637   more connections through the same server. The use of persistent
2638   connections places no requirements on the length (or existence) of
2639   this time-out for either the client or the server.
2640</t>
2641<t>
2642   When a client or server wishes to time-out it SHOULD issue a graceful
2643   close on the transport connection. Clients and servers SHOULD both
2644   constantly watch for the other side of the transport close, and
2645   respond to it as appropriate. If a client or server does not detect
2646   the other side's close promptly it could cause unnecessary resource
2647   drain on the network.
2648</t>
2649<t>
2650   A client, server, or proxy MAY close the transport connection at any
2651   time. For example, a client might have started to send a new request
2652   at the same time that the server has decided to close the "idle"
2653   connection. From the server's point of view, the connection is being
2654   closed while it was idle, but from the client's point of view, a
2655   request is in progress.
2656</t>
2657<t>
2658   This means that clients, servers, and proxies MUST be able to recover
2659   from asynchronous close events. Client software SHOULD reopen the
2660   transport connection and retransmit the aborted sequence of requests
2661   without user interaction so long as the request sequence is
2662   idempotent (see Section 7.1.2 of <xref target="Part2"/>). Non-idempotent request methods or sequences
2663   MUST NOT be automatically retried, although user agents MAY offer a
2664   human operator the choice of retrying the request(s). Confirmation by
2665   user-agent software with semantic understanding of the application
2666   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2667   be repeated if the second sequence of requests fails.
2668</t>
2669<t>
2670   Servers SHOULD always respond to at least one request per connection,
2671   if at all possible. Servers SHOULD NOT  close a connection in the
2672   middle of transmitting a response, unless a network or client failure
2673   is suspected.
2674</t>
2675<t>
2676   Clients (including proxies) SHOULD limit the number of simultaneous
2677   connections that they maintain to a given server (including proxies).
2678</t>
2679<t>
2680   Previous revisions of HTTP gave a specific number of connections as a
2681   ceiling, but this was found to be impractical for many applications. As a
2682   result, this specification does not mandate a particular maximum number of
2683   connections, but instead encourages clients to be conservative when opening
2684   multiple connections.
2685</t>
2686<t>
2687   In particular, while using multiple connections avoids the "head-of-line
2688   blocking" problem (whereby a request that takes significant server-side
2689   processing and/or has a large payload can block subsequent requests on the
2690   same connection), each connection used consumes server resources (sometimes
2691   significantly), and furthermore using multiple connections can cause
2692   undesirable side effects in congested networks.
2693</t>
2694<t>
2695   Note that servers might reject traffic that they deem abusive, including an
2696   excessive number of connections from a client.
2697</t>
2698</section>
2699</section>
2700
2701<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2702
2703<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2704<t>
2705   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2706   flow control mechanisms to resolve temporary overloads, rather than
2707   terminating connections with the expectation that clients will retry.
2708   The latter technique can exacerbate network congestion.
2709</t>
2710</section>
2711
2712<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2713<t>
2714   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2715   the network connection for an error status code while it is transmitting
2716   the request. If the client sees an error status code, it SHOULD
2717   immediately cease transmitting the body. If the body is being sent
2718   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2719   empty trailer MAY be used to prematurely mark the end of the message.
2720   If the body was preceded by a Content-Length header field, the client MUST
2721   close the connection.
2722</t>
2723</section>
2724
2725<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2726<t>
2727   The purpose of the 100 (Continue) status code (see Section 8.1.1 of <xref target="Part2"/>) is to
2728   allow a client that is sending a request message with a request body
2729   to determine if the origin server is willing to accept the request
2730   (based on the request header fields) before the client sends the request
2731   body. In some cases, it might either be inappropriate or highly
2732   inefficient for the client to send the body if the server will reject
2733   the message without looking at the body.
2734</t>
2735<t>
2736   Requirements for HTTP/1.1 clients:
2737  <list style="symbols">
2738    <t>
2739        If a client will wait for a 100 (Continue) response before
2740        sending the request body, it MUST send an Expect header
2741        field (Section 9.2 of <xref target="Part2"/>) with the "100-continue" expectation.
2742    </t>
2743    <t>
2744        A client MUST NOT send an Expect header field (Section 9.2 of <xref target="Part2"/>)
2745        with the "100-continue" expectation if it does not intend
2746        to send a request body.
2747    </t>
2748  </list>
2749</t>
2750<t>
2751   Because of the presence of older implementations, the protocol allows
2752   ambiguous situations in which a client might send "Expect: 100-continue"
2753   without receiving either a 417 (Expectation Failed)
2754   or a 100 (Continue) status code. Therefore, when a client sends this
2755   header field to an origin server (possibly via a proxy) from which it
2756   has never seen a 100 (Continue) status code, the client SHOULD NOT 
2757   wait for an indefinite period before sending the request body.
2758</t>
2759<t>
2760   Requirements for HTTP/1.1 origin servers:
2761  <list style="symbols">
2762    <t> Upon receiving a request which includes an Expect header
2763        field with the "100-continue" expectation, an origin server MUST
2764        either respond with 100 (Continue) status code and continue to read
2765        from the input stream, or respond with a final status code. The
2766        origin server MUST NOT wait for the request body before sending
2767        the 100 (Continue) response. If it responds with a final status
2768        code, it MAY close the transport connection or it MAY continue
2769        to read and discard the rest of the request.  It MUST NOT
2770        perform the request method if it returns a final status code.
2771    </t>
2772    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2773        the request message does not include an Expect header
2774        field with the "100-continue" expectation, and MUST NOT send a
2775        100 (Continue) response if such a request comes from an HTTP/1.0
2776        (or earlier) client. There is an exception to this rule: for
2777        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2778        status code in response to an HTTP/1.1 PUT or POST request that does
2779        not include an Expect header field with the "100-continue"
2780        expectation. This exception, the purpose of which is
2781        to minimize any client processing delays associated with an
2782        undeclared wait for 100 (Continue) status code, applies only to
2783        HTTP/1.1 requests, and not to requests with any other HTTP-version
2784        value.
2785    </t>
2786    <t> An origin server MAY omit a 100 (Continue) response if it has
2787        already received some or all of the request body for the
2788        corresponding request.
2789    </t>
2790    <t> An origin server that sends a 100 (Continue) response MUST
2791    ultimately send a final status code, once the request body is
2792        received and processed, unless it terminates the transport
2793        connection prematurely.
2794    </t>
2795    <t> If an origin server receives a request that does not include an
2796        Expect header field with the "100-continue" expectation,
2797        the request includes a request body, and the server responds
2798        with a final status code before reading the entire request body
2799        from the transport connection, then the server SHOULD NOT  close
2800        the transport connection until it has read the entire request,
2801        or until the client closes the connection. Otherwise, the client
2802        might not reliably receive the response message. However, this
2803        requirement is not be construed as preventing a server from
2804        defending itself against denial-of-service attacks, or from
2805        badly broken client implementations.
2806      </t>
2807    </list>
2808</t>
2809<t>
2810   Requirements for HTTP/1.1 proxies:
2811  <list style="symbols">
2812    <t> If a proxy receives a request that includes an Expect header
2813        field with the "100-continue" expectation, and the proxy
2814        either knows that the next-hop server complies with HTTP/1.1 or
2815        higher, or does not know the HTTP version of the next-hop
2816        server, it MUST forward the request, including the Expect header
2817        field.
2818    </t>
2819    <t> If the proxy knows that the version of the next-hop server is
2820        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2821        respond with a 417 (Expectation Failed) status code.
2822    </t>
2823    <t> Proxies SHOULD maintain a cache recording the HTTP version
2824        numbers received from recently-referenced next-hop servers.
2825    </t>
2826    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2827        request message was received from an HTTP/1.0 (or earlier)
2828        client and did not include an Expect header field with
2829        the "100-continue" expectation. This requirement overrides the
2830        general rule for forwarding of 1xx responses (see Section 8.1 of <xref target="Part2"/>).
2831    </t>
2832  </list>
2833</t>
2834</section>
2835
2836<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2837<t>
2838   If an HTTP/1.1 client sends a request which includes a request body,
2839   but which does not include an Expect header field with the
2840   "100-continue" expectation, and if the client is not directly
2841   connected to an HTTP/1.1 origin server, and if the client sees the
2842   connection close before receiving a status line from the server, the
2843   client SHOULD retry the request.  If the client does retry this
2844   request, it MAY use the following "binary exponential backoff"
2845   algorithm to be assured of obtaining a reliable response:
2846  <list style="numbers">
2847    <t>
2848      Initiate a new connection to the server
2849    </t>
2850    <t>
2851      Transmit the request-line, header fields, and the CRLF that
2852      indicates the end of header fields.
2853    </t>
2854    <t>
2855      Initialize a variable R to the estimated round-trip time to the
2856         server (e.g., based on the time it took to establish the
2857         connection), or to a constant value of 5 seconds if the round-trip
2858         time is not available.
2859    </t>
2860    <t>
2861       Compute T = R * (2**N), where N is the number of previous
2862         retries of this request.
2863    </t>
2864    <t>
2865       Wait either for an error response from the server, or for T
2866         seconds (whichever comes first)
2867    </t>
2868    <t>
2869       If no error response is received, after T seconds transmit the
2870         body of the request.
2871    </t>
2872    <t>
2873       If client sees that the connection is closed prematurely,
2874         repeat from step 1 until the request is accepted, an error
2875         response is received, or the user becomes impatient and
2876         terminates the retry process.
2877    </t>
2878  </list>
2879</t>
2880<t>
2881   If at any point an error status code is received, the client
2882  <list style="symbols">
2883      <t>SHOULD NOT  continue and</t>
2884
2885      <t>SHOULD close the connection if it has not completed sending the
2886        request message.</t>
2887    </list>
2888</t>
2889</section>
2890</section>
2891</section>
2892
2893
2894<section title="Miscellaneous notes that might disappear" anchor="misc">
2895<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2896<t>
2897   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2898</t>
2899</section>
2900
2901<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2902<t>
2903   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2904</t>
2905</section>
2906
2907<section title="Interception of HTTP for access control" anchor="http.intercept">
2908<t>
2909   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2910</t>
2911</section>
2912
2913<section title="Use of HTTP by other protocols" anchor="http.others">
2914<t>
2915   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2916   Extensions of HTTP like WebDAV.</cref>
2917</t>
2918
2919</section>
2920<section title="Use of HTTP by media type specification" anchor="http.media">
2921<t>
2922   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2923</t>
2924</section>
2925</section>
2926
2927<section title="Header Field Definitions" anchor="header.field.definitions">
2928<t>
2929   This section defines the syntax and semantics of HTTP header fields
2930   related to message framing and transport protocols.
2931</t>
2932
2933<section title="Connection" anchor="header.connection">
2934  <iref primary="true" item="Connection header field"/>
2935  <iref primary="true" item="Header Fields" subitem="Connection"/>
2936 
2937 
2938<t>
2939   The "Connection" header field allows the sender to specify
2940   options that are desired only for that particular connection.
2941   Such connection options MUST be removed or replaced before the
2942   message can be forwarded downstream by a proxy or gateway.
2943   This mechanism also allows the sender to indicate which HTTP
2944   header fields used in the message are only intended for the
2945   immediate recipient ("hop-by-hop"), as opposed to all recipients
2946   on the chain ("end-to-end"), enabling the message to be
2947   self-descriptive and allowing future connection-specific extensions
2948   to be deployed in HTTP without fear that they will be blindly
2949   forwarded by previously deployed intermediaries.
2950</t>
2951<t>
2952   The Connection header field's value has the following grammar:
2953</t>
2954<figure><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/><artwork type="abnf2616"><![CDATA[
2955  Connection       = 1#connection-token
2956  connection-token = token
2957]]></artwork></figure>
2958<t>
2959   A proxy or gateway MUST parse a received Connection
2960   header field before a message is forwarded and, for each
2961   connection-token in this field, remove any header field(s) from
2962   the message with the same name as the connection-token, and then
2963   remove the Connection header field itself or replace it with the
2964   sender's own connection options for the forwarded message.
2965</t>
2966<t>
2967   A sender MUST NOT include field-names in the Connection header
2968   field-value for fields that are defined as expressing constraints
2969   for all recipients in the request or response chain, such as the
2970   Cache-Control header field (Section 3.2 of <xref target="Part6"/>).
2971</t>
2972<t>
2973   The connection options do not have to correspond to a header field
2974   present in the message, since a connection-specific header field
2975   might not be needed if there are no parameters associated with that
2976   connection option.  Recipients that trigger certain connection
2977   behavior based on the presence of connection options MUST do so
2978   based on the presence of the connection-token rather than only the
2979   presence of the optional header field.  In other words, if the
2980   connection option is received as a header field but not indicated
2981   within the Connection field-value, then the recipient MUST ignore
2982   the connection-specific header field because it has likely been
2983   forwarded by an intermediary that is only partially compliant.
2984</t>
2985<t>
2986   When defining new connection options, specifications ought to
2987   carefully consider existing deployed header fields and ensure
2988   that the new connection-token does not share the same name as
2989   an unrelated header field that might already be deployed.
2990   Defining a new connection-token essentially reserves that potential
2991   field-name for carrying additional information related to the
2992   connection option, since it would be unwise for senders to use
2993   that field-name for anything else.
2994</t>
2995<t>
2996   HTTP/1.1 defines the "close" connection option for the sender to
2997   signal that the connection will be closed after completion of the
2998   response. For example,
2999</t>
3000<figure><artwork type="example"><![CDATA[
3001  Connection: close
3002]]></artwork></figure>
3003<t>
3004   in either the request or the response header fields indicates that
3005   the connection SHOULD NOT  be considered "persistent" (<xref target="persistent.connections"/>)
3006   after the current request/response is complete.
3007</t>
3008<t>
3009   An HTTP/1.1 client that does not support persistent connections MUST
3010   include the "close" connection option in every request message.
3011</t>
3012<t>
3013   An HTTP/1.1 server that does not support persistent connections MUST
3014   include the "close" connection option in every response message that
3015   does not have a 1xx (Informational) status code.
3016</t>
3017</section>
3018
3019<section title="Content-Length" anchor="header.content-length">
3020  <iref primary="true" item="Content-Length header field"/>
3021  <iref primary="true" item="Header Fields" subitem="Content-Length"/>
3022 
3023<t>
3024   The "Content-Length" header field indicates the size of the
3025   message-body, in decimal number of octets, for any message other than
3026   a response to a HEAD request or a response with a status code of 304.
3027   In the case of a response to a HEAD request, Content-Length indicates
3028   the size of the payload body (not including any potential transfer-coding)
3029   that would have been sent had the request been a GET.
3030   In the case of a 304 (Not Modified) response to a GET request,
3031   Content-Length indicates the size of the payload body (not including
3032   any potential transfer-coding) that would have been sent in a 200 (OK)
3033   response.
3034</t>
3035<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><artwork type="abnf2616"><![CDATA[
3036  Content-Length = 1*DIGIT
3037]]></artwork></figure>
3038<t>
3039   An example is
3040</t>
3041<figure><artwork type="example"><![CDATA[
3042  Content-Length: 3495
3043]]></artwork></figure>
3044<t>
3045   Implementations SHOULD use this field to indicate the message-body
3046   length when no transfer-coding is being applied and the
3047   payload's body length can be determined prior to being transferred.
3048   <xref target="message.body"/> describes how recipients determine the length
3049   of a message-body.
3050</t>
3051<t>
3052   Any Content-Length greater than or equal to zero is a valid value.
3053</t>
3054<t>
3055   Note that the use of this field in HTTP is significantly different from
3056   the corresponding definition in MIME, where it is an optional field
3057   used within the "message/external-body" content-type.
3058</t>
3059</section>
3060
3061<section title="Date" anchor="header.date">
3062  <iref primary="true" item="Date header field"/>
3063  <iref primary="true" item="Header Fields" subitem="Date"/>
3064 
3065<t>
3066   The "Date" header field represents the date and time at which
3067   the message was originated, having the same semantics as the Origination
3068   Date Field (orig-date) defined in Section 3.6.1 of <xref target="RFC5322"/>.
3069   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
3070   it MUST be sent in rfc1123-date format.
3071</t>
3072<figure><iref primary="true" item="Grammar" subitem="Date"/><artwork type="abnf2616"><![CDATA[
3073  Date = HTTP-date
3074]]></artwork></figure>
3075<t>
3076   An example is
3077</t>
3078<figure><artwork type="example"><![CDATA[
3079  Date: Tue, 15 Nov 1994 08:12:31 GMT
3080]]></artwork></figure>
3081<t>
3082   Origin servers MUST include a Date header field in all responses,
3083   except in these cases:
3084  <list style="numbers">
3085      <t>If the response status code is 100 (Continue) or 101 (Switching
3086         Protocols), the response MAY include a Date header field, at
3087         the server's option.</t>
3088
3089      <t>If the response status code conveys a server error, e.g., 500
3090         (Internal Server Error) or 503 (Service Unavailable), and it is
3091         inconvenient or impossible to generate a valid Date.</t>
3092
3093      <t>If the server does not have a clock that can provide a
3094         reasonable approximation of the current time, its responses
3095         MUST NOT include a Date header field. In this case, the rules
3096         in <xref target="clockless.origin.server.operation"/> MUST be followed.</t>
3097  </list>
3098</t>
3099<t>
3100   A received message that does not have a Date header field MUST be
3101   assigned one by the recipient if the message will be cached by that
3102   recipient.
3103</t>
3104<t>
3105   Clients can use the Date header field as well; in order to keep request
3106   messages small, they are advised not to include it when it doesn't convey
3107   any useful information (as it is usually the case for requests that do not
3108   contain a payload).
3109</t>
3110<t>
3111   The HTTP-date sent in a Date header field SHOULD NOT  represent a date and
3112   time subsequent to the generation of the message. It SHOULD represent
3113   the best available approximation of the date and time of message
3114   generation, unless the implementation has no means of generating a
3115   reasonably accurate date and time. In theory, the date ought to
3116   represent the moment just before the payload is generated. In
3117   practice, the date can be generated at any time during the message
3118   origination without affecting its semantic value.
3119</t>
3120
3121<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3122<t>
3123   Some origin server implementations might not have a clock available.
3124   An origin server without a clock MUST NOT assign Expires or Last-Modified
3125   values to a response, unless these values were associated
3126   with the resource by a system or user with a reliable clock. It MAY
3127   assign an Expires value that is known, at or before server
3128   configuration time, to be in the past (this allows "pre-expiration"
3129   of responses without storing separate Expires values for each
3130   resource).
3131</t>
3132</section>
3133</section>
3134
3135<section title="Host" anchor="header.host">
3136  <iref primary="true" item="Host header field"/>
3137  <iref primary="true" item="Header Fields" subitem="Host"/>
3138 
3139<t>
3140   The "Host" header field in a request provides the host and port
3141   information from the target resource's URI, enabling the origin
3142   server to distinguish between resources while servicing requests
3143   for multiple host names on a single IP address.  Since the Host
3144   field-value is critical information for handling a request, it
3145   SHOULD be sent as the first header field following the Request-Line.
3146</t>
3147<figure><iref primary="true" item="Grammar" subitem="Host"/><artwork type="abnf2616"><![CDATA[
3148  Host = uri-host [ ":" port ] ; Section 2.6.1
3149]]></artwork></figure>
3150<t>
3151   A client MUST send a Host header field in all HTTP/1.1 request
3152   messages.  If the target resource's URI includes an authority
3153   component, then the Host field-value MUST be identical to that
3154   authority component after excluding any userinfo (<xref target="http.uri"/>).
3155   If the authority component is missing or undefined for the target
3156   resource's URI, then the Host header field MUST be sent with an
3157   empty field-value.
3158</t>
3159<t>
3160   For example, a GET request to the origin server for
3161   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3162</t>
3163<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
3164  GET /pub/WWW/ HTTP/1.1
3165  Host: www.example.org
3166  ]]></artwork></figure>
3167<t>
3168   The Host header field MUST be sent in an HTTP/1.1 request even
3169   if the request-target is in the form of an absolute-URI, since this
3170   allows the Host information to be forwarded through ancient HTTP/1.0
3171   proxies that might not have implemented Host.
3172</t>
3173<t>
3174   When an HTTP/1.1 proxy receives a request with a request-target in
3175   the form of an absolute-URI, the proxy MUST ignore the received
3176   Host header field (if any) and instead replace it with the host
3177   information of the request-target.  When a proxy forwards a request,
3178   it MUST generate the Host header field based on the received
3179   absolute-URI rather than the received Host.
3180</t>
3181<t>
3182   Since the Host header field acts as an application-level routing
3183   mechanism, it is a frequent target for malware seeking to poison
3184   a shared cache or redirect a request to an unintended server.
3185   An interception proxy is particularly vulnerable if it relies on
3186   the Host header field value for redirecting requests to internal
3187   servers, or for use as a cache key in a shared cache, without
3188   first verifying that the intercepted connection is targeting a
3189   valid IP address for that host.
3190</t>
3191<t>
3192   A server MUST respond with a 400 (Bad Request) status code to
3193   any HTTP/1.1 request message that lacks a Host header field and
3194   to any request message that contains more than one Host header field
3195   or a Host header field with an invalid field-value.
3196</t>
3197<t>
3198   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3199   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3200   for other requirements relating to Host.
3201</t>
3202</section>
3203
3204<section title="TE" anchor="header.te">
3205  <iref primary="true" item="TE header field"/>
3206  <iref primary="true" item="Header Fields" subitem="TE"/>
3207 
3208 
3209 
3210 
3211<t>
3212   The "TE" header field indicates what extension transfer-codings
3213   it is willing to accept in the response, and whether or not it is
3214   willing to accept trailer fields in a chunked transfer-coding.
3215</t>
3216<t>
3217   Its value consists of the keyword "trailers" and/or a comma-separated
3218   list of extension transfer-coding names with optional accept
3219   parameters (as described in <xref target="transfer.codings"/>).
3220</t>
3221<figure><iref primary="true" item="Grammar" subitem="TE"/><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[
3222  TE        = #t-codings
3223  t-codings = "trailers" / ( transfer-extension [ te-params ] )
3224  te-params = OWS ";" OWS "q=" qvalue *( te-ext )
3225  te-ext    = OWS ";" OWS token [ "=" word ]
3226]]></artwork></figure>
3227<t>
3228   The presence of the keyword "trailers" indicates that the client is
3229   willing to accept trailer fields in a chunked transfer-coding, as
3230   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3231   transfer-coding values even though it does not itself represent a
3232   transfer-coding.
3233</t>
3234<t>
3235   Examples of its use are:
3236</t>
3237<figure><artwork type="example"><![CDATA[
3238  TE: deflate
3239  TE:
3240  TE: trailers, deflate;q=0.5
3241]]></artwork></figure>
3242<t>
3243   The TE header field only applies to the immediate connection.
3244   Therefore, the keyword MUST be supplied within a Connection header
3245   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3246</t>
3247<t>
3248   A server tests whether a transfer-coding is acceptable, according to
3249   a TE field, using these rules:
3250  <list style="numbers">
3251    <t>The "chunked" transfer-coding is always acceptable. If the
3252         keyword "trailers" is listed, the client indicates that it is
3253         willing to accept trailer fields in the chunked response on
3254         behalf of itself and any downstream clients. The implication is
3255         that, if given, the client is stating that either all
3256         downstream clients are willing to accept trailer fields in the
3257         forwarded response, or that it will attempt to buffer the
3258         response on behalf of downstream recipients.
3259      <vspace blankLines="1"/>
3260         Note: HTTP/1.1 does not define any means to limit the size of a
3261         chunked response such that a client can be assured of buffering
3262         the entire response.</t>
3263    <t>If the transfer-coding being tested is one of the transfer-codings
3264         listed in the TE field, then it is acceptable unless it
3265         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3266         qvalue of 0 means "not acceptable".)</t>
3267    <t>If multiple transfer-codings are acceptable, then the
3268         acceptable transfer-coding with the highest non-zero qvalue is
3269         preferred.  The "chunked" transfer-coding always has a qvalue
3270         of 1.</t>
3271  </list>
3272</t>
3273<t>
3274   If the TE field-value is empty or if no TE field is present, the only
3275   transfer-coding is "chunked". A message with no transfer-coding is
3276   always acceptable.
3277</t>
3278</section>
3279
3280<section title="Trailer" anchor="header.trailer">
3281  <iref primary="true" item="Trailer header field"/>
3282  <iref primary="true" item="Header Fields" subitem="Trailer"/>
3283 
3284<t>
3285   The "Trailer" header field indicates that the given set of
3286   header fields is present in the trailer of a message encoded with
3287   chunked transfer-coding.
3288</t>
3289<figure><iref primary="true" item="Grammar" subitem="Trailer"/><artwork type="abnf2616"><![CDATA[
3290  Trailer = 1#field-name
3291]]></artwork></figure>
3292<t>
3293   An HTTP/1.1 message SHOULD include a Trailer header field in a
3294   message using chunked transfer-coding with a non-empty trailer. Doing
3295   so allows the recipient to know which header fields to expect in the
3296   trailer.
3297</t>
3298<t>
3299   If no Trailer header field is present, the trailer SHOULD NOT  include
3300   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3301   trailer fields in a "chunked" transfer-coding.
3302</t>
3303<t>
3304   Message header fields listed in the Trailer header field MUST NOT
3305   include the following header fields:
3306  <list style="symbols">
3307    <t>Transfer-Encoding</t>
3308    <t>Content-Length</t>
3309    <t>Trailer</t>
3310  </list>
3311</t>
3312</section>
3313
3314<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3315  <iref primary="true" item="Transfer-Encoding header field"/>
3316  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding"/>
3317 
3318<t>
3319   The "Transfer-Encoding" header field indicates what transfer-codings
3320   (if any) have been applied to the message body. It differs from
3321   Content-Encoding (Section 2.2 of <xref target="Part3"/>) in that transfer-codings are a property
3322   of the message (and therefore are removed by intermediaries), whereas
3323   content-codings are not.
3324</t>
3325<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><artwork type="abnf2616"><![CDATA[
3326  Transfer-Encoding = 1#transfer-coding
3327]]></artwork></figure>
3328<t>
3329   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3330</t>
3331<figure><artwork type="example"><![CDATA[
3332  Transfer-Encoding: chunked
3333]]></artwork></figure>
3334<t>
3335   If multiple encodings have been applied to a representation, the transfer-codings
3336   MUST be listed in the order in which they were applied.
3337   Additional information about the encoding parameters MAY be provided
3338   by other header fields not defined by this specification.
3339</t>
3340<t>
3341   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3342   header field.
3343</t>
3344</section>
3345
3346<section title="Upgrade" anchor="header.upgrade">
3347  <iref primary="true" item="Upgrade header field"/>
3348  <iref primary="true" item="Header Fields" subitem="Upgrade"/>
3349 
3350<t>
3351   The "Upgrade" header field allows the client to specify what
3352   additional communication protocols it would like to use, if the server
3353   chooses to switch protocols. Servers can use it to indicate what protocols
3354   they are willing to switch to.
3355</t>
3356<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><artwork type="abnf2616"><![CDATA[
3357  Upgrade = 1#product
3358]]></artwork></figure>
3359<t>
3360   For example,
3361</t>
3362<figure><artwork type="example"><![CDATA[
3363  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3364]]></artwork></figure>
3365<t>
3366   The Upgrade header field is intended to provide a simple mechanism
3367   for transition from HTTP/1.1 to some other, incompatible protocol. It
3368   does so by allowing the client to advertise its desire to use another
3369   protocol, such as a later version of HTTP with a higher major version
3370   number, even though the current request has been made using HTTP/1.1.
3371   This eases the difficult transition between incompatible protocols by
3372   allowing the client to initiate a request in the more commonly
3373   supported protocol while indicating to the server that it would like
3374   to use a "better" protocol if available (where "better" is determined
3375   by the server, possibly according to the nature of the request method
3376   or target resource).
3377</t>
3378<t>
3379   The Upgrade header field only applies to switching application-layer
3380   protocols upon the existing transport-layer connection. Upgrade
3381   cannot be used to insist on a protocol change; its acceptance and use
3382   by the server is optional. The capabilities and nature of the
3383   application-layer communication after the protocol change is entirely
3384   dependent upon the new protocol chosen, although the first action
3385   after changing the protocol MUST be a response to the initial HTTP
3386   request containing the Upgrade header field.
3387</t>
3388<t>
3389   The Upgrade header field only applies to the immediate connection.
3390   Therefore, the upgrade keyword MUST be supplied within a Connection
3391   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3392   HTTP/1.1 message.
3393</t>
3394<t>
3395   The Upgrade header field cannot be used to indicate a switch to a
3396   protocol on a different connection. For that purpose, it is more
3397   appropriate to use a 3xx redirection response (Section 8.3 of <xref target="Part2"/>).
3398</t>
3399<t>
3400   Servers MUST include the "Upgrade" header field in 101 (Switching
3401   Protocols) responses to indicate which protocol(s) are being switched to,
3402   and MUST include it in 426 (Upgrade Required) responses to indicate
3403   acceptable protocols to upgrade to. Servers MAY include it in any other
3404   response to indicate that they are willing to upgrade to one of the
3405   specified protocols.
3406</t>
3407<t>
3408   This specification only defines the protocol name "HTTP" for use by
3409   the family of Hypertext Transfer Protocols, as defined by the HTTP
3410   version rules of <xref target="http.version"/> and future updates to this
3411   specification. Additional tokens can be registered with IANA using the
3412   registration procedure defined below. 
3413</t>
3414
3415<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3416<t>
3417   The HTTP Upgrade Token Registry defines the name space for product
3418   tokens used to identify protocols in the Upgrade header field.
3419   Each registered token is associated with contact information and
3420   an optional set of specifications that details how the connection
3421   will be processed after it has been upgraded.
3422</t>
3423<t>
3424   Registrations are allowed on a First Come First Served basis as
3425   described in Section 4.1 of <xref target="RFC5226"/>. The
3426   specifications need not be IETF documents or be subject to IESG review.
3427   Registrations are subject to the following rules:
3428  <list style="numbers">
3429    <t>A token, once registered, stays registered forever.</t>
3430    <t>The registration MUST name a responsible party for the
3431       registration.</t>
3432    <t>The registration MUST name a point of contact.</t>
3433    <t>The registration MAY name a set of specifications associated with that
3434       token. Such specifications need not be publicly available.</t>
3435    <t>The responsible party MAY change the registration at any time.
3436       The IANA will keep a record of all such changes, and make them
3437       available upon request.</t>
3438    <t>The responsible party for the first registration of a "product"
3439       token MUST approve later registrations of a "version" token
3440       together with that "product" token before they can be registered.</t>
3441    <t>If absolutely required, the IESG MAY reassign the responsibility
3442       for a token. This will normally only be used in the case when a
3443       responsible party cannot be contacted.</t>
3444  </list>
3445</t>
3446</section>
3447
3448
3449</section>
3450
3451<section title="Via" anchor="header.via">
3452  <iref primary="true" item="Via header field"/>
3453  <iref primary="true" item="Header Fields" subitem="Via"/>
3454 
3455 
3456 
3457 
3458 
3459 
3460<t>
3461   The "Via" header field MUST be sent by a proxy or gateway to
3462   indicate the intermediate protocols and recipients between the user
3463   agent and the server on requests, and between the origin server and
3464   the client on responses. It is analogous to the "Received" field
3465   used by email systems (Section 3.6.7 of <xref target="RFC5322"/>)
3466   and is intended to be used for tracking message forwards,
3467   avoiding request loops, and identifying the protocol capabilities of
3468   all senders along the request/response chain.
3469</t>
3470<figure><iref primary="true" item="Grammar" subitem="Via"/><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[
3471  Via               = 1#( received-protocol RWS received-by
3472                          [ RWS comment ] )
3473  received-protocol = [ protocol-name "/" ] protocol-version
3474  protocol-name     = token
3475  protocol-version  = token
3476  received-by       = ( uri-host [ ":" port ] ) / pseudonym
3477  pseudonym         = token
3478]]></artwork></figure>
3479<t>
3480   The received-protocol indicates the protocol version of the message
3481   received by the server or client along each segment of the
3482   request/response chain. The received-protocol version is appended to
3483   the Via field value when the message is forwarded so that information
3484   about the protocol capabilities of upstream applications remains
3485   visible to all recipients.
3486</t>
3487<t>
3488   The protocol-name is excluded if and only if it would be "HTTP". The
3489   received-by field is normally the host and optional port number of a
3490   recipient server or client that subsequently forwarded the message.
3491   However, if the real host is considered to be sensitive information,
3492   it MAY be replaced by a pseudonym. If the port is not given, it MAY
3493   be assumed to be the default port of the received-protocol.
3494</t>
3495<t>
3496   Multiple Via field values represent each proxy or gateway that has
3497   forwarded the message. Each recipient MUST append its information
3498   such that the end result is ordered according to the sequence of
3499   forwarding applications.
3500</t>
3501<t>
3502   Comments MAY be used in the Via header field to identify the software
3503   of each recipient, analogous to the User-Agent and Server header fields.
3504   However, all comments in the Via field are optional and MAY be removed
3505   by any recipient prior to forwarding the message.
3506</t>
3507<t>
3508   For example, a request message could be sent from an HTTP/1.0 user
3509   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3510   forward the request to a public proxy at p.example.net, which completes
3511   the request by forwarding it to the origin server at www.example.com.
3512   The request received by www.example.com would then have the following
3513   Via header field:
3514</t>
3515<figure><artwork type="example"><![CDATA[
3516  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3517]]></artwork></figure>
3518<t>
3519   A proxy or gateway used as a portal through a network firewall
3520   SHOULD NOT forward the names and ports of hosts within the firewall
3521   region unless it is explicitly enabled to do so. If not enabled, the
3522   received-by host of any host behind the firewall SHOULD be replaced
3523   by an appropriate pseudonym for that host.
3524</t>
3525<t>
3526   For organizations that have strong privacy requirements for hiding
3527   internal structures, a proxy or gateway MAY combine an ordered
3528   subsequence of Via header field entries with identical received-protocol
3529   values into a single such entry. For example,
3530</t>
3531<figure><artwork type="example"><![CDATA[
3532  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3533]]></artwork></figure>
3534<t>
3535  could be collapsed to
3536</t>
3537<figure><artwork type="example"><![CDATA[
3538  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3539]]></artwork></figure>
3540<t>
3541   Senders SHOULD NOT combine multiple entries unless they are all
3542   under the same organizational control and the hosts have already been
3543   replaced by pseudonyms. Senders MUST NOT combine entries which
3544   have different received-protocol values.
3545</t>
3546</section>
3547
3548</section>
3549
3550<section title="IANA Considerations" anchor="IANA.considerations">
3551
3552<section title="Header Field Registration" anchor="header.field.registration">
3553<t>
3554   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3555   with the permanent registrations below (see <xref target="RFC3864"/>):
3556</t>
3557
3558<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3559<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3560   <ttcol>Header Field Name</ttcol>
3561   <ttcol>Protocol</ttcol>
3562   <ttcol>Status</ttcol>
3563   <ttcol>Reference</ttcol>
3564
3565   <c>Connection</c>
3566   <c>http</c>
3567   <c>standard</c>
3568   <c>
3569      <xref target="header.connection"/>
3570   </c>
3571   <c>Content-Length</c>
3572   <c>http</c>
3573   <c>standard</c>
3574   <c>
3575      <xref target="header.content-length"/>
3576   </c>
3577   <c>Date</c>
3578   <c>http</c>
3579   <c>standard</c>
3580   <c>
3581      <xref target="header.date"/>
3582   </c>
3583   <c>Host</c>
3584   <c>http</c>
3585   <c>standard</c>
3586   <c>
3587      <xref target="header.host"/>
3588   </c>
3589   <c>TE</c>
3590   <c>http</c>
3591   <c>standard</c>
3592   <c>
3593      <xref target="header.te"/>
3594   </c>
3595   <c>Trailer</c>
3596   <c>http</c>
3597   <c>standard</c>
3598   <c>
3599      <xref target="header.trailer"/>
3600   </c>
3601   <c>Transfer-Encoding</c>
3602   <c>http</c>
3603   <c>standard</c>
3604   <c>
3605      <xref target="header.transfer-encoding"/>
3606   </c>
3607   <c>Upgrade</c>
3608   <c>http</c>
3609   <c>standard</c>
3610   <c>
3611      <xref target="header.upgrade"/>
3612   </c>
3613   <c>Via</c>
3614   <c>http</c>
3615   <c>standard</c>
3616   <c>
3617      <xref target="header.via"/>
3618   </c>
3619</texttable>
3620<!--(END)-->
3621
3622<t>
3623   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3624</t>
3625</section>
3626
3627<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3628<t>
3629   The entries for the "http" and "https" URI Schemes in the registry located at
3630   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3631   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3632   and <xref target="https.uri" format="counter"/> of this document
3633   (see <xref target="RFC4395"/>).
3634</t>
3635</section>
3636
3637<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3638<t>
3639   This document serves as the specification for the Internet media types
3640   "message/http" and "application/http". The following is to be registered with
3641   IANA (see <xref target="RFC4288"/>).
3642</t>
3643<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3644<iref item="Media Type" subitem="message/http" primary="true"/>
3645<iref item="message/http Media Type" primary="true"/>
3646<t>
3647   The message/http type can be used to enclose a single HTTP request or
3648   response message, provided that it obeys the MIME restrictions for all
3649   "message" types regarding line length and encodings.
3650</t>
3651<t>
3652  <list style="hanging">
3653    <t hangText="Type name:">
3654      message
3655    </t>
3656    <t hangText="Subtype name:">
3657      http
3658    </t>
3659    <t hangText="Required parameters:">
3660      none
3661    </t>
3662    <t hangText="Optional parameters:">
3663      version, msgtype
3664      <list style="hanging">
3665        <t hangText="version:">
3666          The HTTP-Version number of the enclosed message
3667          (e.g., "1.1"). If not present, the version can be
3668          determined from the first line of the body.
3669        </t>
3670        <t hangText="msgtype:">
3671          The message type — "request" or "response". If not
3672          present, the type can be determined from the first
3673          line of the body.
3674        </t>
3675      </list>
3676    </t>
3677    <t hangText="Encoding considerations:">
3678      only "7bit", "8bit", or "binary" are permitted
3679    </t>
3680    <t hangText="Security considerations:">
3681      none
3682    </t>
3683    <t hangText="Interoperability considerations:">
3684      none
3685    </t>
3686    <t hangText="Published specification:">
3687      This specification (see <xref target="internet.media.type.message.http"/>).
3688    </t>
3689    <t hangText="Applications that use this media type:">
3690    </t>
3691    <t hangText="Additional information:">
3692      <list style="hanging">
3693        <t hangText="Magic number(s):">none</t>
3694        <t hangText="File extension(s):">none</t>
3695        <t hangText="Macintosh file type code(s):">none</t>
3696      </list>
3697    </t>
3698    <t hangText="Person and email address to contact for further information:">
3699      See Authors Section.
3700    </t>
3701    <t hangText="Intended usage:">
3702      COMMON
3703    </t>
3704    <t hangText="Restrictions on usage:">
3705      none
3706    </t>
3707    <t hangText="Author/Change controller:">
3708      IESG
3709    </t>
3710  </list>
3711</t>
3712</section>
3713<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3714<iref item="Media Type" subitem="application/http" primary="true"/>
3715<iref item="application/http Media Type" primary="true"/>
3716<t>
3717   The application/http type can be used to enclose a pipeline of one or more
3718   HTTP request or response messages (not intermixed).
3719</t>
3720<t>
3721  <list style="hanging">
3722    <t hangText="Type name:">
3723      application
3724    </t>
3725    <t hangText="Subtype name:">
3726      http
3727    </t>
3728    <t hangText="Required parameters:">
3729      none
3730    </t>
3731    <t hangText="Optional parameters:">
3732      version, msgtype
3733      <list style="hanging">
3734        <t hangText="version:">
3735          The HTTP-Version number of the enclosed messages
3736          (e.g., "1.1"). If not present, the version can be
3737          determined from the first line of the body.
3738        </t>
3739        <t hangText="msgtype:">
3740          The message type — "request" or "response". If not
3741          present, the type can be determined from the first
3742          line of the body.
3743        </t>
3744      </list>
3745    </t>
3746    <t hangText="Encoding considerations:">
3747      HTTP messages enclosed by this type
3748      are in "binary" format; use of an appropriate
3749      Content-Transfer-Encoding is required when
3750      transmitted via E-mail.
3751    </t>
3752    <t hangText="Security considerations:">
3753      none
3754    </t>
3755    <t hangText="Interoperability considerations:">
3756      none
3757    </t>
3758    <t hangText="Published specification:">
3759      This specification (see <xref target="internet.media.type.application.http"/>).
3760    </t>
3761    <t hangText="Applications that use this media type:">
3762    </t>
3763    <t hangText="Additional information:">
3764      <list style="hanging">
3765        <t hangText="Magic number(s):">none</t>
3766        <t hangText="File extension(s):">none</t>
3767        <t hangText="Macintosh file type code(s):">none</t>
3768      </list>
3769    </t>
3770    <t hangText="Person and email address to contact for further information:">
3771      See Authors Section.
3772    </t>
3773    <t hangText="Intended usage:">
3774      COMMON
3775    </t>
3776    <t hangText="Restrictions on usage:">
3777      none
3778    </t>
3779    <t hangText="Author/Change controller:">
3780      IESG
3781    </t>
3782  </list>
3783</t>
3784</section>
3785</section>
3786
3787<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3788<t>
3789   The registration procedure for HTTP Transfer Codings is now defined by
3790   <xref target="transfer.coding.registry"/> of this document.
3791</t>
3792<t>
3793   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3794   shall be updated with the registrations below:
3795</t>
3796<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3797   <ttcol>Name</ttcol>
3798   <ttcol>Description</ttcol>
3799   <ttcol>Reference</ttcol>
3800   <c>chunked</c>
3801   <c>Transfer in a series of chunks</c>
3802   <c>
3803      <xref target="chunked.encoding"/>
3804   </c>
3805   <c>compress</c>
3806   <c>UNIX "compress" program method</c>
3807   <c>
3808      <xref target="compress.coding"/>
3809   </c>
3810   <c>deflate</c>
3811   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3812   the "zlib" data format (<xref target="RFC1950"/>)
3813   </c>
3814   <c>
3815      <xref target="deflate.coding"/>
3816   </c>
3817   <c>gzip</c>
3818   <c>Same as GNU zip <xref target="RFC1952"/></c>
3819   <c>
3820      <xref target="gzip.coding"/>
3821   </c>
3822</texttable>
3823</section>
3824
3825<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3826<t>
3827   The registration procedure for HTTP Upgrade Tokens — previously defined
3828   in Section 7.2 of <xref target="RFC2817"/> — is now defined
3829   by <xref target="upgrade.token.registry"/> of this document.
3830</t>
3831<t>
3832   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3833   shall be updated with the registration below:
3834</t>
3835<texttable align="left" suppress-title="true">
3836   <ttcol>Value</ttcol>
3837   <ttcol>Description</ttcol>
3838   <ttcol>Reference</ttcol>
3839
3840   <c>HTTP</c>
3841   <c>Hypertext Transfer Protocol</c>
3842   <c><xref target="http.version"/> of this specification</c>
3843<!-- IANA should add this without our instructions; emailed on June 05, 2009
3844   <c>TLS/1.0</c>
3845   <c>Transport Layer Security</c>
3846   <c><xref target="RFC2817"/></c> -->
3847
3848</texttable>
3849</section>
3850
3851</section>
3852
3853<section title="Security Considerations" anchor="security.considerations">
3854<t>
3855   This section is meant to inform application developers, information
3856   providers, and users of the security limitations in HTTP/1.1 as
3857   described by this document. The discussion does not include
3858   definitive solutions to the problems revealed, though it does make
3859   some suggestions for reducing security risks.
3860</t>
3861
3862<section title="Personal Information" anchor="personal.information">
3863<t>
3864   HTTP clients are often privy to large amounts of personal information
3865   (e.g., the user's name, location, mail address, passwords, encryption
3866   keys, etc.), and SHOULD be very careful to prevent unintentional
3867   leakage of this information.
3868   We very strongly recommend that a convenient interface be provided
3869   for the user to control dissemination of such information, and that
3870   designers and implementors be particularly careful in this area.
3871   History shows that errors in this area often create serious security
3872   and/or privacy problems and generate highly adverse publicity for the
3873   implementor's company.
3874</t>
3875</section>
3876
3877<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3878<t>
3879   A server is in the position to save personal data about a user's
3880   requests which might identify their reading patterns or subjects of
3881   interest. This information is clearly confidential in nature and its
3882   handling can be constrained by law in certain countries. People using
3883   HTTP to provide data are responsible for ensuring that
3884   such material is not distributed without the permission of any
3885   individuals that are identifiable by the published results.
3886</t>
3887</section>
3888
3889<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3890<t>
3891   Implementations of HTTP origin servers SHOULD be careful to restrict
3892   the documents returned by HTTP requests to be only those that were
3893   intended by the server administrators. If an HTTP server translates
3894   HTTP URIs directly into file system calls, the server MUST take
3895   special care not to serve files that were not intended to be
3896   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3897   other operating systems use ".." as a path component to indicate a
3898   directory level above the current one. On such a system, an HTTP
3899   server MUST disallow any such construct in the request-target if it
3900   would otherwise allow access to a resource outside those intended to
3901   be accessible via the HTTP server. Similarly, files intended for
3902   reference only internally to the server (such as access control
3903   files, configuration files, and script code) MUST be protected from
3904   inappropriate retrieval, since they might contain sensitive
3905   information. Experience has shown that minor bugs in such HTTP server
3906   implementations have turned into security risks.
3907</t>
3908</section>
3909
3910<section title="DNS Spoofing" anchor="dns.spoofing">
3911<t>
3912   Clients using HTTP rely heavily on the Domain Name Service, and are
3913   thus generally prone to security attacks based on the deliberate
3914   mis-association of IP addresses and DNS names. Clients need to be
3915   cautious in assuming the continuing validity of an IP number/DNS name
3916   association.
3917</t>
3918<t>
3919   In particular, HTTP clients SHOULD rely on their name resolver for
3920   confirmation of an IP number/DNS name association, rather than
3921   caching the result of previous host name lookups. Many platforms
3922   already can cache host name lookups locally when appropriate, and
3923   they SHOULD be configured to do so. It is proper for these lookups to
3924   be cached, however, only when the TTL (Time To Live) information
3925   reported by the name server makes it likely that the cached
3926   information will remain useful.
3927</t>
3928<t>
3929   If HTTP clients cache the results of host name lookups in order to
3930   achieve a performance improvement, they MUST observe the TTL
3931   information reported by DNS.
3932</t>
3933<t>
3934   If HTTP clients do not observe this rule, they could be spoofed when
3935   a previously-accessed server's IP address changes. As network
3936   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3937   possibility of this form of attack will grow. Observing this
3938   requirement thus reduces this potential security vulnerability.
3939</t>
3940<t>
3941   This requirement also improves the load-balancing behavior of clients
3942   for replicated servers using the same DNS name and reduces the
3943   likelihood of a user's experiencing failure in accessing sites which
3944   use that strategy.
3945</t>
3946</section>
3947
3948<section title="Proxies and Caching" anchor="attack.proxies">
3949<t>
3950   By their very nature, HTTP proxies are men-in-the-middle, and
3951   represent an opportunity for man-in-the-middle attacks. Compromise of
3952   the systems on which the proxies run can result in serious security
3953   and privacy problems. Proxies have access to security-related
3954   information, personal information about individual users and
3955   organizations, and proprietary information belonging to users and
3956   content providers. A compromised proxy, or a proxy implemented or
3957   configured without regard to security and privacy considerations,
3958   might be used in the commission of a wide range of potential attacks.
3959</t>
3960<t>
3961   Proxy operators need to protect the systems on which proxies run as
3962   they would protect any system that contains or transports sensitive
3963   information. In particular, log information gathered at proxies often
3964   contains highly sensitive personal information, and/or information
3965   about organizations. Log information needs to be carefully guarded, and
3966   appropriate guidelines for use need to be developed and followed.
3967   (<xref target="abuse.of.server.log.information"/>).
3968</t>
3969<t>
3970   Proxy implementors need to consider the privacy and security
3971   implications of their design and coding decisions, and of the
3972   configuration options they provide to proxy operators (especially the
3973   default configuration).
3974</t>
3975<t>
3976   Users of a proxy need to be aware that proxies are no trustworthier than
3977   the people who run them; HTTP itself cannot solve this problem.
3978</t>
3979<t>
3980   The judicious use of cryptography, when appropriate, might suffice to
3981   protect against a broad range of security and privacy attacks. Such
3982   cryptography is beyond the scope of the HTTP/1.1 specification.
3983</t>
3984</section>
3985
3986<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3987<t>
3988   They exist. They are hard to defend against. Research continues.
3989   Beware.
3990</t>
3991</section>
3992</section>
3993
3994<section title="Acknowledgments" anchor="ack">
3995<t>
3996   HTTP has evolved considerably over the years. It has
3997   benefited from a large and active developer community — the many
3998   people who have participated on the www-talk mailing list — and it is
3999   that community which has been most responsible for the success of
4000   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4001   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4002   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4003   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4004   VanHeyningen deserve special recognition for their efforts in
4005   defining early aspects of the protocol.
4006</t>
4007<t>
4008   This document has benefited greatly from the comments of all those
4009   participating in the HTTP-WG. In addition to those already mentioned,
4010   the following individuals have contributed to this specification:
4011</t>
4012<t>
4013   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4014   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4015   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4016   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4017   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4018   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4019   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4020   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4021   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4022   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4023   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4024   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4025</t>
4026<t>
4027   Thanks to the "cave men" of Palo Alto. You know who you are.
4028</t>
4029<t>
4030   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4031   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4032   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4033   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4034   Larry Masinter for their help. And thanks go particularly to Jeff
4035   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4036</t>
4037<t>
4038   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4039   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4040   discovery of many of the problems that this document attempts to
4041   rectify.
4042</t>
4043<t>
4044   This specification makes heavy use of the augmented BNF and generic
4045   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4046   reuses many of the definitions provided by Nathaniel Borenstein and
4047   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4048   specification will help reduce past confusion over the relationship
4049   between HTTP and Internet mail message formats.
4050</t>
4051<!--
4052
4053Acknowledgements TODO list
4054
4055- Jeff Hodges ("effective request URI")
4056
4057-->
4058</section>
4059
4060</middle>
4061<back>
4062
4063<references title="Normative References">
4064
4065<reference anchor="ISO-8859-1">
4066  <front>
4067    <title>
4068     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4069    </title>
4070    <author>
4071      <organization>International Organization for Standardization</organization>
4072    </author>
4073    <date year="1998"/>
4074  </front>
4075  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4076</reference>
4077
4078<reference anchor="Part2">
4079  <front>
4080    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4081    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4082      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4083      <address><email>fielding@gbiv.com</email></address>
4084    </author>
4085    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4086      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4087      <address><email>jg@freedesktop.org</email></address>
4088    </author>
4089    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4090      <organization abbrev="HP">Hewlett-Packard Company</organization>
4091      <address><email>JeffMogul@acm.org</email></address>
4092    </author>
4093    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4094      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4095      <address><email>henrikn@microsoft.com</email></address>
4096    </author>
4097    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4098      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4099      <address><email>LMM@acm.org</email></address>
4100    </author>
4101    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4102      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4103      <address><email>paulle@microsoft.com</email></address>
4104    </author>
4105    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4106      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4107      <address><email>timbl@w3.org</email></address>
4108    </author>
4109    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4110      <organization abbrev="W3C">World Wide Web Consortium</organization>
4111      <address><email>ylafon@w3.org</email></address>
4112    </author>
4113    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4114      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4115      <address><email>julian.reschke@greenbytes.de</email></address>
4116    </author>
4117    <date month="April" year="2011"/>
4118  </front>
4119  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-14"/>
4120 
4121</reference>
4122
4123<reference anchor="Part3">
4124  <front>
4125    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4126    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4127      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4128      <address><email>fielding@gbiv.com</email></address>
4129    </author>
4130    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4131      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4132      <address><email>jg@freedesktop.org</email></address>
4133    </author>
4134    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4135      <organization abbrev="HP">Hewlett-Packard Company</organization>
4136      <address><email>JeffMogul@acm.org</email></address>
4137    </author>
4138    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4139      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4140      <address><email>henrikn@microsoft.com</email></address>
4141    </author>
4142    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4143      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4144      <address><email>LMM@acm.org</email></address>
4145    </author>
4146    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4147      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4148      <address><email>paulle@microsoft.com</email></address>
4149    </author>
4150    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4151      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4152      <address><email>timbl@w3.org</email></address>
4153    </author>
4154    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4155      <organization abbrev="W3C">World Wide Web Consortium</organization>
4156      <address><email>ylafon@w3.org</email></address>
4157    </author>
4158    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4159      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4160      <address><email>julian.reschke@greenbytes.de</email></address>
4161    </author>
4162    <date month="April" year="2011"/>
4163  </front>
4164  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-14"/>
4165 
4166</reference>
4167
4168<reference anchor="Part6">
4169  <front>
4170    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4171    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4172      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4173      <address><email>fielding@gbiv.com</email></address>
4174    </author>
4175    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4176      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4177      <address><email>jg@freedesktop.org</email></address>
4178    </author>
4179    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4180      <organization abbrev="HP">Hewlett-Packard Company</organization>
4181      <address><email>JeffMogul@acm.org</email></address>
4182    </author>
4183    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4184      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4185      <address><email>henrikn@microsoft.com</email></address>
4186    </author>
4187    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4188      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4189      <address><email>LMM@acm.org</email></address>
4190    </author>
4191    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4192      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4193      <address><email>paulle@microsoft.com</email></address>
4194    </author>
4195    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4196      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4197      <address><email>timbl@w3.org</email></address>
4198    </author>
4199    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4200      <organization abbrev="W3C">World Wide Web Consortium</organization>
4201      <address><email>ylafon@w3.org</email></address>
4202    </author>
4203    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4204      <address><email>mnot@mnot.net</email></address>
4205    </author>
4206    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4207      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4208      <address><email>julian.reschke@greenbytes.de</email></address>
4209    </author>
4210    <date month="April" year="2011"/>
4211  </front>
4212  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-14"/>
4213 
4214</reference>
4215
4216<reference anchor="RFC5234">
4217  <front>
4218    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4219    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4220      <organization>Brandenburg InternetWorking</organization>
4221      <address>
4222        <email>dcrocker@bbiw.net</email>
4223      </address> 
4224    </author>
4225    <author initials="P." surname="Overell" fullname="Paul Overell">
4226      <organization>THUS plc.</organization>
4227      <address>
4228        <email>paul.overell@thus.net</email>
4229      </address>
4230    </author>
4231    <date month="January" year="2008"/>
4232  </front>
4233  <seriesInfo name="STD" value="68"/>
4234  <seriesInfo name="RFC" value="5234"/>
4235</reference>
4236
4237<reference anchor="RFC2119">
4238  <front>
4239    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4240    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4241      <organization>Harvard University</organization>
4242      <address><email>sob@harvard.edu</email></address>
4243    </author>
4244    <date month="March" year="1997"/>
4245  </front>
4246  <seriesInfo name="BCP" value="14"/>
4247  <seriesInfo name="RFC" value="2119"/>
4248</reference>
4249
4250<reference anchor="RFC3986">
4251 <front>
4252  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
4253  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4254    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4255    <address>
4256       <email>timbl@w3.org</email>
4257       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4258    </address>
4259  </author>
4260  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4261    <organization abbrev="Day Software">Day Software</organization>
4262    <address>
4263      <email>fielding@gbiv.com</email>
4264      <uri>http://roy.gbiv.com/</uri>
4265    </address>
4266  </author>
4267  <author initials="L." surname="Masinter" fullname="Larry Masinter">
4268    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4269    <address>
4270      <email>LMM@acm.org</email>
4271      <uri>http://larry.masinter.net/</uri>
4272    </address>
4273  </author>
4274  <date month="January" year="2005"/>
4275 </front>
4276 <seriesInfo name="STD" value="66"/>
4277 <seriesInfo name="RFC" value="3986"/>
4278</reference>
4279
4280<reference anchor="USASCII">
4281  <front>
4282    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4283    <author>
4284      <organization>American National Standards Institute</organization>
4285    </author>
4286    <date year="1986"/>
4287  </front>
4288  <seriesInfo name="ANSI" value="X3.4"/>
4289</reference>
4290
4291<reference anchor="RFC1950">
4292  <front>
4293    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4294    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4295      <organization>Aladdin Enterprises</organization>
4296      <address><email>ghost@aladdin.com</email></address>
4297    </author>
4298    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4299    <date month="May" year="1996"/>
4300  </front>
4301  <seriesInfo name="RFC" value="1950"/>
4302  <annotation>
4303    RFC 1950 is an Informational RFC, thus it might be less stable than
4304    this specification. On the other hand, this downward reference was
4305    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4306    therefore it is unlikely to cause problems in practice. See also
4307    <xref target="BCP97"/>.
4308  </annotation>
4309</reference>
4310
4311<reference anchor="RFC1951">
4312  <front>
4313    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4314    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4315      <organization>Aladdin Enterprises</organization>
4316      <address><email>ghost@aladdin.com</email></address>
4317    </author>
4318    <date month="May" year="1996"/>
4319  </front>
4320  <seriesInfo name="RFC" value="1951"/>
4321  <annotation>
4322    RFC 1951 is an Informational RFC, thus it might be less stable than
4323    this specification. On the other hand, this downward reference was
4324    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4325    therefore it is unlikely to cause problems in practice. See also
4326    <xref target="BCP97"/>.
4327  </annotation>
4328</reference>
4329
4330<reference anchor="RFC1952">
4331  <front>
4332    <title>GZIP file format specification version 4.3</title>
4333    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4334      <organization>Aladdin Enterprises</organization>
4335      <address><email>ghost@aladdin.com</email></address>
4336    </author>
4337    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4338      <address><email>gzip@prep.ai.mit.edu</email></address>
4339    </author>
4340    <author initials="M." surname="Adler" fullname="Mark Adler">
4341      <address><email>madler@alumni.caltech.edu</email></address>
4342    </author>
4343    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4344      <address><email>ghost@aladdin.com</email></address>
4345    </author>
4346    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4347      <address><email>randeg@alumni.rpi.edu</email></address>
4348    </author>
4349    <date month="May" year="1996"/>
4350  </front>
4351  <seriesInfo name="RFC" value="1952"/>
4352  <annotation>
4353    RFC 1952 is an Informational RFC, thus it might be less stable than
4354    this specification. On the other hand, this downward reference was
4355    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4356    therefore it is unlikely to cause problems in practice. See also
4357    <xref target="BCP97"/>.
4358  </annotation>
4359</reference>
4360
4361</references>
4362
4363<references title="Informative References">
4364
4365<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4366  <front>
4367    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4368    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4369    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4370    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4371    <author initials="H." surname="Lie" fullname="H. Lie"/>
4372    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4373    <date year="1997" month="September"/>
4374  </front>
4375  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4376</reference>
4377
4378<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4379  <front>
4380    <title>Improving HTTP Latency</title>
4381    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4382    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4383    <date year="1995" month="December"/>
4384  </front>
4385  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4386</reference>
4387
4388<reference anchor="RFC1123">
4389  <front>
4390    <title>Requirements for Internet Hosts - Application and Support</title>
4391    <author initials="R." surname="Braden" fullname="Robert Braden">
4392      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4393      <address><email>Braden@ISI.EDU</email></address>
4394    </author>
4395    <date month="October" year="1989"/>
4396  </front>
4397  <seriesInfo name="STD" value="3"/>
4398  <seriesInfo name="RFC" value="1123"/>
4399</reference>
4400
4401<reference anchor="RFC1900">
4402  <front>
4403    <title>Renumbering Needs Work</title>
4404    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4405      <organization>CERN, Computing and Networks Division</organization>
4406      <address><email>brian@dxcoms.cern.ch</email></address>
4407    </author>
4408    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4409      <organization>cisco Systems</organization>
4410      <address><email>yakov@cisco.com</email></address>
4411    </author>
4412    <date month="February" year="1996"/>
4413  </front>
4414  <seriesInfo name="RFC" value="1900"/>
4415</reference>
4416
4417<reference anchor="RFC1919">
4418  <front>
4419    <title>Classical versus Transparent IP Proxies</title>
4420    <author initials="M." surname="Chatel" fullname="Marc Chatel">
4421      <address><email>mchatel@pax.eunet.ch</email></address>
4422    </author>
4423    <date year="1996" month="March"/>
4424  </front>
4425  <seriesInfo name="RFC" value="1919"/>
4426</reference>
4427
4428<reference anchor="RFC1945">
4429  <front>
4430    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4431    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4432      <organization>MIT, Laboratory for Computer Science</organization>
4433      <address><email>timbl@w3.org</email></address>
4434    </author>
4435    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4436      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4437      <address><email>fielding@ics.uci.edu</email></address>
4438    </author>
4439    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4440      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4441      <address><email>frystyk@w3.org</email></address>
4442    </author>
4443    <date month="May" year="1996"/>
4444  </front>
4445  <seriesInfo name="RFC" value="1945"/>
4446</reference>
4447
4448<reference anchor="RFC2045">
4449  <front>
4450    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4451    <author initials="N." surname="Freed" fullname="Ned Freed">
4452      <organization>Innosoft International, Inc.</organization>
4453      <address><email>ned@innosoft.com</email></address>
4454    </author>
4455    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4456      <organization>First Virtual Holdings</organization>
4457      <address><email>nsb@nsb.fv.com</email></address>
4458    </author>
4459    <date month="November" year="1996"/>
4460  </front>
4461  <seriesInfo name="RFC" value="2045"/>
4462</reference>
4463
4464<reference anchor="RFC2047">
4465  <front>
4466    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4467    <author initials="K." surname="Moore" fullname="Keith Moore">
4468      <organization>University of Tennessee</organization>
4469      <address><email>moore@cs.utk.edu</email></address>
4470    </author>
4471    <date month="November" year="1996"/>
4472  </front>
4473  <seriesInfo name="RFC" value="2047"/>
4474</reference>
4475
4476<reference anchor="RFC2068">
4477  <front>
4478    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4479    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4480      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4481      <address><email>fielding@ics.uci.edu</email></address>
4482    </author>
4483    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4484      <organization>MIT Laboratory for Computer Science</organization>
4485      <address><email>jg@w3.org</email></address>
4486    </author>
4487    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4488      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4489      <address><email>mogul@wrl.dec.com</email></address>
4490    </author>
4491    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4492      <organization>MIT Laboratory for Computer Science</organization>
4493      <address><email>frystyk@w3.org</email></address>
4494    </author>
4495    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4496      <organization>MIT Laboratory for Computer Science</organization>
4497      <address><email>timbl@w3.org</email></address>
4498    </author>
4499    <date month="January" year="1997"/>
4500  </front>
4501  <seriesInfo name="RFC" value="2068"/>
4502</reference>
4503
4504<reference anchor="RFC2145">
4505  <front>
4506    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4507    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4508      <organization>Western Research Laboratory</organization>
4509      <address><email>mogul@wrl.dec.com</email></address>
4510    </author>
4511    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4512      <organization>Department of Information and Computer Science</organization>
4513      <address><email>fielding@ics.uci.edu</email></address>
4514    </author>
4515    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4516      <organization>MIT Laboratory for Computer Science</organization>
4517      <address><email>jg@w3.org</email></address>
4518    </author>
4519    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4520      <organization>W3 Consortium</organization>
4521      <address><email>frystyk@w3.org</email></address>
4522    </author>
4523    <date month="May" year="1997"/>
4524  </front>
4525  <seriesInfo name="RFC" value="2145"/>
4526</reference>
4527
4528<reference anchor="RFC2616">
4529  <front>
4530    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4531    <author initials="R." surname="Fielding" fullname="R. Fielding">
4532      <organization>University of California, Irvine</organization>
4533      <address><email>fielding@ics.uci.edu</email></address>
4534    </author>
4535    <author initials="J." surname="Gettys" fullname="J. Gettys">
4536      <organization>W3C</organization>
4537      <address><email>jg@w3.org</email></address>
4538    </author>
4539    <author initials="J." surname="Mogul" fullname="J. Mogul">
4540      <organization>Compaq Computer Corporation</organization>
4541      <address><email>mogul@wrl.dec.com</email></address>
4542    </author>
4543    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4544      <organization>MIT Laboratory for Computer Science</organization>
4545      <address><email>frystyk@w3.org</email></address>
4546    </author>
4547    <author initials="L." surname="Masinter" fullname="L. Masinter">
4548      <organization>Xerox Corporation</organization>
4549      <address><email>masinter@parc.xerox.com</email></address>
4550    </author>
4551    <author initials="P." surname="Leach" fullname="P. Leach">
4552      <organization>Microsoft Corporation</organization>
4553      <address><email>paulle@microsoft.com</email></address>
4554    </author>
4555    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4556      <organization>W3C</organization>
4557      <address><email>timbl@w3.org</email></address>
4558    </author>
4559    <date month="June" year="1999"/>
4560  </front>
4561  <seriesInfo name="RFC" value="2616"/>
4562</reference>
4563
4564<reference anchor="RFC2817">
4565  <front>
4566    <title>Upgrading to TLS Within HTTP/1.1</title>
4567    <author initials="R." surname="Khare" fullname="R. Khare">
4568      <organization>4K Associates / UC Irvine</organization>
4569      <address><email>rohit@4K-associates.com</email></address>
4570    </author>
4571    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
4572      <organization>Agranat Systems, Inc.</organization>
4573      <address><email>lawrence@agranat.com</email></address>
4574    </author>
4575    <date year="2000" month="May"/>
4576  </front>
4577  <seriesInfo name="RFC" value="2817"/>
4578</reference>
4579
4580<reference anchor="RFC2818">
4581  <front>
4582    <title>HTTP Over TLS</title>
4583    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
4584      <organization>RTFM, Inc.</organization>
4585      <address><email>ekr@rtfm.com</email></address>
4586    </author>
4587    <date year="2000" month="May"/>
4588  </front>
4589  <seriesInfo name="RFC" value="2818"/>
4590</reference>
4591
4592<reference anchor="RFC2965">
4593  <front>
4594    <title>HTTP State Management Mechanism</title>
4595    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
4596      <organization>Bell Laboratories, Lucent Technologies</organization>
4597      <address><email>dmk@bell-labs.com</email></address>
4598    </author>
4599    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4600      <organization>Epinions.com, Inc.</organization>
4601      <address><email>lou@montulli.org</email></address>
4602    </author>
4603    <date year="2000" month="October"/>
4604  </front>
4605  <seriesInfo name="RFC" value="2965"/>
4606</reference>
4607
4608<reference anchor="RFC3040">
4609  <front>
4610    <title>Internet Web Replication and Caching Taxonomy</title>
4611    <author initials="I." surname="Cooper" fullname="I. Cooper">
4612      <organization>Equinix, Inc.</organization>
4613    </author>
4614    <author initials="I." surname="Melve" fullname="I. Melve">
4615      <organization>UNINETT</organization>
4616    </author>
4617    <author initials="G." surname="Tomlinson" fullname="G. Tomlinson">
4618      <organization>CacheFlow Inc.</organization>
4619    </author>
4620    <date year="2001" month="January"/>
4621  </front>
4622  <seriesInfo name="RFC" value="3040"/>
4623</reference>
4624
4625<reference anchor="RFC3864">
4626  <front>
4627    <title>Registration Procedures for Message Header Fields</title>
4628    <author initials="G." surname="Klyne" fullname="G. Klyne">
4629      <organization>Nine by Nine</organization>
4630      <address><email>GK-IETF@ninebynine.org</email></address>
4631    </author>
4632    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
4633      <organization>BEA Systems</organization>
4634      <address><email>mnot@pobox.com</email></address>
4635    </author>
4636    <author initials="J." surname="Mogul" fullname="J. Mogul">
4637      <organization>HP Labs</organization>
4638      <address><email>JeffMogul@acm.org</email></address>
4639    </author>
4640    <date year="2004" month="September"/>
4641  </front>
4642  <seriesInfo name="BCP" value="90"/>
4643  <seriesInfo name="RFC" value="3864"/>
4644</reference>
4645
4646<reference anchor="RFC4288">
4647  <front>
4648    <title>Media Type Specifications and Registration Procedures</title>
4649    <author initials="N." surname="Freed" fullname="N. Freed">
4650      <organization>Sun Microsystems</organization>
4651      <address>
4652        <email>ned.freed@mrochek.com</email>
4653      </address>
4654    </author>
4655    <author initials="J." surname="Klensin" fullname="J. Klensin">
4656      <address>
4657        <email>klensin+ietf@jck.com</email>
4658      </address>
4659    </author>
4660    <date year="2005" month="December"/>
4661  </front>
4662  <seriesInfo name="BCP" value="13"/>
4663  <seriesInfo name="RFC" value="4288"/>
4664</reference>
4665
4666<reference anchor="RFC4395">
4667  <front>
4668    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4669    <author initials="T." surname="Hansen" fullname="T. Hansen">
4670      <organization>AT&amp;T Laboratories</organization>
4671      <address>
4672        <email>tony+urireg@maillennium.att.com</email>
4673      </address>
4674    </author>
4675    <author initials="T." surname="Hardie" fullname="T. Hardie">
4676      <organization>Qualcomm, Inc.</organization>
4677      <address>
4678        <email>hardie@qualcomm.com</email>
4679      </address>
4680    </author>
4681    <author initials="L." surname="Masinter" fullname="L. Masinter">
4682      <organization>Adobe Systems</organization>
4683      <address>
4684        <email>LMM@acm.org</email>
4685      </address>
4686    </author>
4687    <date year="2006" month="February"/>
4688  </front>
4689  <seriesInfo name="BCP" value="115"/>
4690  <seriesInfo name="RFC" value="4395"/>
4691</reference>
4692
4693<reference anchor="RFC5226">
4694  <front>
4695    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4696    <author initials="T." surname="Narten" fullname="T. Narten">
4697      <organization>IBM</organization>
4698      <address><email>narten@us.ibm.com</email></address>
4699    </author>
4700    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
4701      <organization>Google</organization>
4702      <address><email>Harald@Alvestrand.no</email></address>
4703    </author>
4704    <date year="2008" month="May"/>
4705  </front>
4706  <seriesInfo name="BCP" value="26"/>
4707  <seriesInfo name="RFC" value="5226"/>
4708</reference>
4709
4710<reference anchor="RFC5322">
4711  <front>
4712    <title>Internet Message Format</title>
4713    <author initials="P." surname="Resnick" fullname="P. Resnick">
4714      <organization>Qualcomm Incorporated</organization>
4715    </author>
4716    <date year="2008" month="October"/>
4717  </front>
4718  <seriesInfo name="RFC" value="5322"/>
4719</reference>
4720
4721<reference anchor="draft-ietf-httpstate-cookie">
4722  <front>
4723    <title>HTTP State Management Mechanism</title>
4724    <author initials="A." surname="Barth" fullname="Adam Barth">
4725      <organization abbrev="U.C. Berkeley">
4726        University of California, Berkeley
4727      </organization>
4728      <address><email>abarth@eecs.berkeley.edu</email></address>
4729    </author>
4730    <date year="2011" month="March"/>
4731  </front>
4732  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4733</reference>
4734
4735<reference anchor="BCP97">
4736  <front>
4737    <title>Handling Normative References to Standards-Track Documents</title>
4738    <author initials="J." surname="Klensin" fullname="J. Klensin">
4739      <address>
4740        <email>klensin+ietf@jck.com</email>
4741      </address>
4742    </author>
4743    <author initials="S." surname="Hartman" fullname="S. Hartman">
4744      <organization>MIT</organization>
4745      <address>
4746        <email>hartmans-ietf@mit.edu</email>
4747      </address>
4748    </author>
4749    <date year="2007" month="June"/>
4750  </front>
4751  <seriesInfo name="BCP" value="97"/>
4752  <seriesInfo name="RFC" value="4897"/>
4753</reference>
4754
4755<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4756  <front>
4757    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4758    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4759    <date year="2001" month="November"/>
4760  </front>
4761  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4762</reference>
4763
4764<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4765  <front>
4766    <title>Analysis of HTTP Performance Problems</title>
4767    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4768    <date/>
4769  </front>
4770</reference>
4771
4772<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4773  <front>
4774  <title>Analysis of HTTP Performance</title>
4775  <author initials="J." surname="Touch" fullname="Joe Touch">
4776    <organization>USC/Information Sciences Institute</organization>
4777    <address><email>touch@isi.edu</email></address>
4778  </author>
4779  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4780    <organization>USC/Information Sciences Institute</organization>
4781    <address><email>johnh@isi.edu</email></address>
4782  </author>
4783  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4784    <organization>USC/Information Sciences Institute</organization>
4785    <address><email>katia@isi.edu</email></address>
4786  </author>
4787  <date year="1998" month="Aug"/>
4788  </front>
4789  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4790  <annotation>(original report dated Aug. 1996)</annotation>
4791</reference>
4792
4793</references>
4794
4795
4796<section title="Tolerant Applications" anchor="tolerant.applications">
4797<t>
4798   Although this document specifies the requirements for the generation
4799   of HTTP/1.1 messages, not all applications will be correct in their
4800   implementation. We therefore recommend that operational applications
4801   be tolerant of deviations whenever those deviations can be
4802   interpreted unambiguously.
4803</t>
4804<t>
4805   The line terminator for header fields is the sequence CRLF.
4806   However, we recommend that applications, when parsing such headers fields,
4807   recognize a single LF as a line terminator and ignore the leading CR.
4808</t>
4809<t>
4810   The character encoding of a representation SHOULD be labeled as the lowest
4811   common denominator of the character codes used within that representation, with
4812   the exception that not labeling the representation is preferred over labeling
4813   the representation with the labels US-ASCII or ISO-8859-1. See <xref target="Part3"/>.
4814</t>
4815<t>
4816   Additional rules for requirements on parsing and encoding of dates
4817   and other potential problems with date encodings include:
4818</t>
4819<t>
4820  <list style="symbols">
4821     <t>HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
4822        which appears to be more than 50 years in the future is in fact
4823        in the past (this helps solve the "year 2000" problem).</t>
4824
4825     <t>Although all date formats are specified to be case-sensitive,
4826        recipients SHOULD match day, week and timezone names
4827        case-insensitively.</t>
4828             
4829     <t>An HTTP/1.1 implementation MAY internally represent a parsed
4830        Expires date as earlier than the proper value, but MUST NOT
4831        internally represent a parsed Expires date as later than the
4832        proper value.</t>
4833
4834     <t>All expiration-related calculations MUST be done in GMT. The
4835        local time zone MUST NOT influence the calculation or comparison
4836        of an age or expiration time.</t>
4837
4838     <t>If an HTTP header field incorrectly carries a date value with a time
4839        zone other than GMT, it MUST be converted into GMT using the
4840        most conservative possible conversion.</t>
4841  </list>
4842</t>
4843</section>
4844
4845<section title="HTTP Version History" anchor="compatibility">
4846<t>
4847   HTTP has been in use by the World-Wide Web global information initiative
4848   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4849   was a simple protocol for hypertext data transfer across the Internet
4850   with only a single request method (GET) and no metadata.
4851   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4852   methods and MIME-like messaging that could include metadata about the data
4853   transferred and modifiers on the request/response semantics. However,
4854   HTTP/1.0 did not sufficiently take into consideration the effects of
4855   hierarchical proxies, caching, the need for persistent connections, or
4856   name-based virtual hosts. The proliferation of incompletely-implemented
4857   applications calling themselves "HTTP/1.0" further necessitated a
4858   protocol version change in order for two communicating applications
4859   to determine each other's true capabilities.
4860</t>
4861<t>
4862   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4863   requirements that enable reliable implementations, adding only
4864   those new features that will either be safely ignored by an HTTP/1.0
4865   recipient or only sent when communicating with a party advertising
4866   compliance with HTTP/1.1.
4867</t>
4868<t>
4869   It is beyond the scope of a protocol specification to mandate
4870   compliance with previous versions. HTTP/1.1 was deliberately
4871   designed, however, to make supporting previous versions easy.
4872   We would expect a general-purpose HTTP/1.1 server to understand
4873   any valid request in the format of HTTP/1.0 and respond appropriately
4874   with an HTTP/1.1 message that only uses features understood (or
4875   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4876   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4877</t>
4878<t>
4879   Since HTTP/0.9 did not support header fields in a request,
4880   there is no mechanism for it to support name-based virtual
4881   hosts (selection of resource by inspection of the Host header
4882   field).  Any server that implements name-based virtual hosts
4883   ought to disable support for HTTP/0.9.  Most requests that
4884   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4885   requests wherein a buggy client failed to properly encode
4886   linear whitespace found in a URI reference and placed in
4887   the request-target.
4888</t>
4889
4890<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4891<t>
4892   This section summarizes major differences between versions HTTP/1.0
4893   and HTTP/1.1.
4894</t>
4895
4896<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4897<t>
4898   The requirements that clients and servers support the Host header
4899   field (<xref target="header.host"/>), report an error if it is
4900   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4901   are among the most important changes defined by HTTP/1.1.
4902</t>
4903<t>
4904   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4905   addresses and servers; there was no other established mechanism for
4906   distinguishing the intended server of a request than the IP address
4907   to which that request was directed. The Host header field was
4908   introduced during the development of HTTP/1.1 and, though it was
4909   quickly implemented by most HTTP/1.0 browsers, additional requirements
4910   were placed on all HTTP/1.1 requests in order to ensure complete
4911   adoption.  At the time of this writing, most HTTP-based services
4912   are dependent upon the Host header field for targeting requests.
4913</t>
4914</section>
4915
4916<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4917<t>
4918   For most implementations of HTTP/1.0, each connection is established
4919   by the client prior to the request and closed by the server after
4920   sending the response. However, some implementations implement the
4921   Keep-Alive version of persistent connections described in
4922   Section 19.7.1 of <xref target="RFC2068"/>.
4923</t>
4924<t>
4925   Some clients and servers might wish to be compatible with some
4926   previous implementations of persistent connections in HTTP/1.0
4927   clients and servers. Persistent connections in HTTP/1.0 are
4928   explicitly negotiated as they are not the default behavior. HTTP/1.0
4929   experimental implementations of persistent connections are faulty,
4930   and the new facilities in HTTP/1.1 are designed to rectify these
4931   problems. The problem was that some existing HTTP/1.0 clients might
4932   send Keep-Alive to a proxy server that doesn't understand
4933   Connection, which would then erroneously forward it to the next
4934   inbound server, which would establish the Keep-Alive connection and
4935   result in a hung HTTP/1.0 proxy waiting for the close on the
4936   response. The result is that HTTP/1.0 clients must be prevented from
4937   using Keep-Alive when talking to proxies.
4938</t>
4939<t>
4940   However, talking to proxies is the most important use of persistent
4941   connections, so that prohibition is clearly unacceptable. Therefore,
4942   we need some other mechanism for indicating a persistent connection
4943   is desired, which is safe to use even when talking to an old proxy
4944   that ignores Connection. Persistent connections are the default for
4945   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4946   declaring non-persistence. See <xref target="header.connection"/>.
4947</t>
4948</section>
4949</section>
4950
4951<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4952<t>
4953  Empty list elements in list productions have been deprecated.
4954  (<xref target="notation.abnf"/>)
4955</t>
4956<t>
4957  Rules about implicit linear whitespace between certain grammar productions
4958  have been removed; now it's only allowed when specifically pointed out
4959  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
4960  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4961  Non-ASCII content in header fields and reason phrase has been obsoleted and
4962  made opaque (the TEXT rule was removed)
4963  (<xref target="basic.rules"/>)
4964</t>
4965<t>
4966  Clarify that HTTP-Version is case sensitive.
4967  (<xref target="http.version"/>)
4968</t>
4969<t>
4970  Require that invalid whitespace around field-names be rejected.
4971  (<xref target="header.fields"/>)
4972</t>
4973<t>
4974  Require recipients to handle bogus Content-Length header fields as errors.
4975  (<xref target="message.body"/>)
4976</t>
4977<t>
4978  Remove reference to non-existent identity transfer-coding value tokens.
4979  (Sections <xref format="counter" target="message.body"/> and
4980  <xref format="counter" target="transfer.codings"/>)
4981</t>
4982<t>
4983  Update use of abs_path production from RFC 1808 to the path-absolute + query
4984  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4985  request method only.
4986  (<xref target="request-target"/>)
4987</t>
4988<t>
4989  Clarification that the chunk length does not include the count of the octets
4990  in the chunk header and trailer. Furthermore disallowed line folding
4991  in chunk extensions.
4992  (<xref target="chunked.encoding"/>)
4993</t>
4994<t>
4995  Remove hard limit of two connections per server.
4996  (<xref target="persistent.practical"/>)
4997</t>
4998<t>
4999  Change ABNF productions for header fields to only define the field value.
5000  (<xref target="header.field.definitions"/>)
5001</t>
5002<t>
5003  Clarify exactly when close connection options must be sent.
5004  (<xref target="header.connection"/>)
5005</t>
5006<t>
5007  Define the semantics of the "Upgrade" header field in responses other than
5008  101 (this was incorporated from <xref target="RFC2817"/>).
5009  (<xref target="header.upgrade"/>)
5010</t>
5011</section>
5012</section>
5013
5014
5015<section title="Collected ABNF" anchor="collected.abnf">
5016<figure>
5017<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
5018BWS = OWS
5019
5020Chunked-Body = *chunk last-chunk trailer-part CRLF
5021Connection = *( "," OWS ) connection-token *( OWS "," [ OWS
5022 connection-token ] )
5023Content-Length = 1*DIGIT
5024
5025Date = HTTP-date
5026
5027GMT = %x47.4D.54 ; GMT
5028
5029HTTP-Prot-Name = %x48.54.54.50 ; HTTP
5030HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5031HTTP-date = rfc1123-date / obs-date
5032HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
5033 ]
5034Host = uri-host [ ":" port ]
5035
5036Method = token
5037
5038OWS = *( [ obs-fold ] WSP )
5039
5040RWS = 1*( [ obs-fold ] WSP )
5041Reason-Phrase = *( WSP / VCHAR / obs-text )
5042Request = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5043Request-Line = Method SP request-target SP HTTP-Version CRLF
5044Response = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5045
5046Status-Code = 3DIGIT
5047Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5048
5049TE = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5050Trailer = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5051Transfer-Encoding = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5052 transfer-coding ] )
5053
5054URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
5055Upgrade = *( "," OWS ) product *( OWS "," [ OWS product ] )
5056
5057Via = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5058 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5059 )
5060
5061absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
5062asctime-date = day-name SP date3 SP time-of-day SP year
5063attribute = token
5064authority = <authority, defined in [RFC3986], Section 3.2>
5065
5066chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5067chunk-data = 1*OCTET
5068chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5069chunk-ext-name = token
5070chunk-ext-val = token / quoted-str-nf
5071chunk-size = 1*HEXDIG
5072comment = "(" *( ctext / quoted-cpair / comment ) ")"
5073connection-token = token
5074ctext = OWS / %x21-27 ; '!'-'''
5075 / %x2A-5B ; '*'-'['
5076 / %x5D-7E ; ']'-'~'
5077 / obs-text
5078
5079date1 = day SP month SP year
5080date2 = day "-" month "-" 2DIGIT
5081date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
5082day = 2DIGIT
5083day-name = %x4D.6F.6E ; Mon
5084 / %x54.75.65 ; Tue
5085 / %x57.65.64 ; Wed
5086 / %x54.68.75 ; Thu
5087 / %x46.72.69 ; Fri
5088 / %x53.61.74 ; Sat
5089 / %x53.75.6E ; Sun
5090day-name-l = %x4D.6F.6E.64.61.79 ; Monday
5091 / %x54.75.65.73.64.61.79 ; Tuesday
5092 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
5093 / %x54.68.75.72.73.64.61.79 ; Thursday
5094 / %x46.72.69.64.61.79 ; Friday
5095 / %x53.61.74.75.72.64.61.79 ; Saturday
5096 / %x53.75.6E.64.61.79 ; Sunday
5097
5098field-content = *( WSP / VCHAR / obs-text )
5099field-name = token
5100field-value = *( field-content / OWS )
5101
5102header-field = field-name ":" OWS [ field-value ] OWS
5103hour = 2DIGIT
5104http-URI = "http://" authority path-abempty [ "?" query ]
5105https-URI = "https://" authority path-abempty [ "?" query ]
5106
5107last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF
5108
5109message-body = *OCTET
5110minute = 2DIGIT
5111month = %x4A.61.6E ; Jan
5112 / %x46.65.62 ; Feb
5113 / %x4D.61.72 ; Mar
5114 / %x41.70.72 ; Apr
5115 / %x4D.61.79 ; May
5116 / %x4A.75.6E ; Jun
5117 / %x4A.75.6C ; Jul
5118 / %x41.75.67 ; Aug
5119 / %x53.65.70 ; Sep
5120 / %x4F.63.74 ; Oct
5121 / %x4E.6F.76 ; Nov
5122 / %x44.65.63 ; Dec
5123
5124obs-date = rfc850-date / asctime-date
5125obs-fold = CRLF
5126obs-text = %x80-FF
5127
5128partial-URI = relative-part [ "?" query ]
5129path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
5130path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
5131port = <port, defined in [RFC3986], Section 3.2.3>
5132product = token [ "/" product-version ]
5133product-version = token
5134protocol-name = token
5135protocol-version = token
5136pseudonym = token
5137
5138qdtext = OWS / "!" / %x23-5B ; '#'-'['
5139 / %x5D-7E ; ']'-'~'
5140 / obs-text
5141qdtext-nf = WSP / "!" / %x23-5B ; '#'-'['
5142 / %x5D-7E ; ']'-'~'
5143 / obs-text
5144query = <query, defined in [RFC3986], Section 3.4>
5145quoted-cpair = "\" ( WSP / VCHAR / obs-text )
5146quoted-pair = "\" ( WSP / VCHAR / obs-text )
5147quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5148quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5149qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5150
5151received-by = ( uri-host [ ":" port ] ) / pseudonym
5152received-protocol = [ protocol-name "/" ] protocol-version
5153relative-part = <relative-part, defined in [RFC3986], Section 4.2>
5154request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5155 / authority
5156rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
5157rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
5158
5159second = 2DIGIT
5160special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
5161 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5162start-line = Request-Line / Status-Line
5163
5164t-codings = "trailers" / ( transfer-extension [ te-params ] )
5165tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
5166 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5167te-ext = OWS ";" OWS token [ "=" word ]
5168te-params = OWS ";" OWS "q=" qvalue *te-ext
5169time-of-day = hour ":" minute ":" second
5170token = 1*tchar
5171trailer-part = *( header-field CRLF )
5172transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
5173 transfer-extension
5174transfer-extension = token *( OWS ";" OWS transfer-parameter )
5175transfer-parameter = attribute BWS "=" BWS value
5176
5177uri-host = <host, defined in [RFC3986], Section 3.2.2>
5178
5179value = word
5180
5181word = token / quoted-string
5182
5183year = 4DIGIT
5184]]></artwork>
5185</figure>
5186<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
5187; Chunked-Body defined but not used
5188; Connection defined but not used
5189; Content-Length defined but not used
5190; Date defined but not used
5191; HTTP-message defined but not used
5192; Host defined but not used
5193; Request defined but not used
5194; Response defined but not used
5195; TE defined but not used
5196; Trailer defined but not used
5197; Transfer-Encoding defined but not used
5198; URI-reference defined but not used
5199; Upgrade defined but not used
5200; Via defined but not used
5201; http-URI defined but not used
5202; https-URI defined but not used
5203; partial-URI defined but not used
5204; special defined but not used
5205]]></artwork></figure></section>
5206
5207
5208<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5209
5210<section title="Since RFC 2616">
5211<t>
5212  Extracted relevant partitions from <xref target="RFC2616"/>.
5213</t>
5214</section>
5215
5216<section title="Since draft-ietf-httpbis-p1-messaging-00">
5217<t>
5218  Closed issues:
5219  <list style="symbols">
5220    <t>
5221      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5222      "HTTP Version should be case sensitive"
5223      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5224    </t>
5225    <t>
5226      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5227      "'unsafe' characters"
5228      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5229    </t>
5230    <t>
5231      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5232      "Chunk Size Definition"
5233      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5234    </t>
5235    <t>
5236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5237      "Message Length"
5238      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5239    </t>
5240    <t>
5241      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5242      "Media Type Registrations"
5243      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5244    </t>
5245    <t>
5246      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5247      "URI includes query"
5248      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5249    </t>
5250    <t>
5251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5252      "No close on 1xx responses"
5253      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5254    </t>
5255    <t>
5256      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5257      "Remove 'identity' token references"
5258      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5259    </t>
5260    <t>
5261      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5262      "Import query BNF"
5263    </t>
5264    <t>
5265      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5266      "qdtext BNF"
5267    </t>
5268    <t>
5269      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5270      "Normative and Informative references"
5271    </t>
5272    <t>
5273      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5274      "RFC2606 Compliance"
5275    </t>
5276    <t>
5277      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5278      "RFC977 reference"
5279    </t>
5280    <t>
5281      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5282      "RFC1700 references"
5283    </t>
5284    <t>
5285      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5286      "inconsistency in date format explanation"
5287    </t>
5288    <t>
5289      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5290      "Date reference typo"
5291    </t>
5292    <t>
5293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5294      "Informative references"
5295    </t>
5296    <t>
5297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5298      "ISO-8859-1 Reference"
5299    </t>
5300    <t>
5301      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5302      "Normative up-to-date references"
5303    </t>
5304  </list>
5305</t>
5306<t>
5307  Other changes:
5308  <list style="symbols">
5309    <t>
5310      Update media type registrations to use RFC4288 template.
5311    </t>
5312    <t>
5313      Use names of RFC4234 core rules DQUOTE and WSP,
5314      fix broken ABNF for chunk-data
5315      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5316    </t>
5317  </list>
5318</t>
5319</section>
5320
5321<section title="Since draft-ietf-httpbis-p1-messaging-01">
5322<t>
5323  Closed issues:
5324  <list style="symbols">
5325    <t>
5326      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5327      "Bodies on GET (and other) requests"
5328    </t>
5329    <t>
5330      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5331      "Updating to RFC4288"
5332    </t>
5333    <t>
5334      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5335      "Status Code and Reason Phrase"
5336    </t>
5337    <t>
5338      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5339      "rel_path not used"
5340    </t>
5341  </list>
5342</t>
5343<t>
5344  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5345  <list style="symbols">
5346    <t>
5347      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
5348      "trailer-part").
5349    </t>
5350    <t>
5351      Avoid underscore character in rule names ("http_URL" -&gt;
5352      "http-URL", "abs_path" -&gt; "path-absolute").
5353    </t>
5354    <t>
5355      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5356      "path-absolute", "port", "query", "relativeURI", "host) — these will
5357      have to be updated when switching over to RFC3986.
5358    </t>
5359    <t>
5360      Synchronize core rules with RFC5234.
5361    </t>
5362    <t>
5363      Get rid of prose rules that span multiple lines.
5364    </t>
5365    <t>
5366      Get rid of unused rules LOALPHA and UPALPHA.
5367    </t>
5368    <t>
5369      Move "Product Tokens" section (back) into Part 1, as "token" is used
5370      in the definition of the Upgrade header field.
5371    </t>
5372    <t>
5373      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5374    </t>
5375    <t>
5376      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5377    </t>
5378  </list>
5379</t>
5380</section>
5381
5382<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5383<t>
5384  Closed issues:
5385  <list style="symbols">
5386    <t>
5387      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5388      "HTTP-date vs. rfc1123-date"
5389    </t>
5390    <t>
5391      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5392      "WS in quoted-pair"
5393    </t>
5394  </list>
5395</t>
5396<t>
5397  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5398  <list style="symbols">
5399    <t>
5400      Reference RFC 3984, and update header field registrations for headers defined
5401      in this document.
5402    </t>
5403  </list>
5404</t>
5405<t>
5406  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5407  <list style="symbols">
5408    <t>
5409      Replace string literals when the string really is case-sensitive (HTTP-Version).
5410    </t>
5411  </list>
5412</t>
5413</section>
5414
5415<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5416<t>
5417  Closed issues:
5418  <list style="symbols">
5419    <t>
5420      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5421      "Connection closing"
5422    </t>
5423    <t>
5424      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5425      "Move registrations and registry information to IANA Considerations"
5426    </t>
5427    <t>
5428      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5429      "need new URL for PAD1995 reference"
5430    </t>
5431    <t>
5432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5433      "IANA Considerations: update HTTP URI scheme registration"
5434    </t>
5435    <t>
5436      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5437      "Cite HTTPS URI scheme definition"
5438    </t>
5439    <t>
5440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5441      "List-type headers vs Set-Cookie"
5442    </t>
5443  </list>
5444</t>
5445<t>
5446  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5447  <list style="symbols">
5448    <t>
5449      Replace string literals when the string really is case-sensitive (HTTP-Date).
5450    </t>
5451    <t>
5452      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5453    </t>
5454  </list>
5455</t>
5456</section>
5457
5458<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5459<t>
5460  Closed issues:
5461  <list style="symbols">
5462    <t>
5463      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5464      "Out-of-date reference for URIs"
5465    </t>
5466    <t>
5467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5468      "RFC 2822 is updated by RFC 5322"
5469    </t>
5470  </list>
5471</t>
5472<t>
5473  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5474  <list style="symbols">
5475    <t>
5476      Use "/" instead of "|" for alternatives.
5477    </t>
5478    <t>
5479      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5480    </t>
5481    <t>
5482      Only reference RFC 5234's core rules.
5483    </t>
5484    <t>
5485      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5486      whitespace ("OWS") and required whitespace ("RWS").
5487    </t>
5488    <t>
5489      Rewrite ABNFs to spell out whitespace rules, factor out
5490      header field value format definitions.
5491    </t>
5492  </list>
5493</t>
5494</section>
5495
5496<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5497<t>
5498  Closed issues:
5499  <list style="symbols">
5500    <t>
5501      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5502      "Header LWS"
5503    </t>
5504    <t>
5505      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5506      "Sort 1.3 Terminology"
5507    </t>
5508    <t>
5509      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5510      "RFC2047 encoded words"
5511    </t>
5512    <t>
5513      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5514      "Character Encodings in TEXT"
5515    </t>
5516    <t>
5517      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5518      "Line Folding"
5519    </t>
5520    <t>
5521      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5522      "OPTIONS * and proxies"
5523    </t>
5524    <t>
5525      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5526      "Reason-Phrase BNF"
5527    </t>
5528    <t>
5529      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5530      "Use of TEXT"
5531    </t>
5532    <t>
5533      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5534      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5535    </t>
5536    <t>
5537      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5538      "RFC822 reference left in discussion of date formats"
5539    </t>
5540  </list>
5541</t>
5542<t>
5543  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5544  <list style="symbols">
5545    <t>
5546      Rewrite definition of list rules, deprecate empty list elements.
5547    </t>
5548    <t>
5549      Add appendix containing collected and expanded ABNF.
5550    </t>
5551  </list>
5552</t>
5553<t>
5554  Other changes:
5555  <list style="symbols">
5556    <t>
5557      Rewrite introduction; add mostly new Architecture Section.
5558    </t>
5559    <t>
5560      Move definition of quality values from Part 3 into Part 1;
5561      make TE request header field grammar independent of accept-params (defined in Part 3).
5562    </t>
5563  </list>
5564</t>
5565</section>
5566
5567<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5568<t>
5569  Closed issues:
5570  <list style="symbols">
5571    <t>
5572      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5573      "base for numeric protocol elements"
5574    </t>
5575    <t>
5576      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5577      "comment ABNF"
5578    </t>
5579  </list>
5580</t>
5581<t>
5582  Partly resolved issues:
5583  <list style="symbols">
5584    <t>
5585      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5586      "205 Bodies" (took out language that implied that there might be
5587      methods for which a request body MUST NOT be included)
5588    </t>
5589    <t>
5590      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5591      "editorial improvements around HTTP-date"
5592    </t>
5593  </list>
5594</t>
5595</section>
5596
5597<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5598<t>
5599  Closed issues:
5600  <list style="symbols">
5601    <t>
5602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5603      "Repeating single-value headers"
5604    </t>
5605    <t>
5606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5607      "increase connection limit"
5608    </t>
5609    <t>
5610      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5611      "IP addresses in URLs"
5612    </t>
5613    <t>
5614      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5615      "take over HTTP Upgrade Token Registry"
5616    </t>
5617    <t>
5618      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5619      "CR and LF in chunk extension values"
5620    </t>
5621    <t>
5622      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5623      "HTTP/0.9 support"
5624    </t>
5625    <t>
5626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5627      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5628    </t>
5629    <t>
5630      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5631      "move definitions of gzip/deflate/compress to part 1"
5632    </t>
5633    <t>
5634      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5635      "disallow control characters in quoted-pair"
5636    </t>
5637  </list>
5638</t>
5639<t>
5640  Partly resolved issues:
5641  <list style="symbols">
5642    <t>
5643      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5644      "update IANA requirements wrt Transfer-Coding values" (add the
5645      IANA Considerations subsection)
5646    </t>
5647  </list>
5648</t>
5649</section>
5650
5651<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5652<t>
5653  Closed issues:
5654  <list style="symbols">
5655    <t>
5656      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5657      "header parsing, treatment of leading and trailing OWS"
5658    </t>
5659  </list>
5660</t>
5661<t>
5662  Partly resolved issues:
5663  <list style="symbols">
5664    <t>
5665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5666      "Placement of 13.5.1 and 13.5.2"
5667    </t>
5668    <t>
5669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5670      "use of term "word" when talking about header structure"
5671    </t>
5672  </list>
5673</t>
5674</section>
5675
5676<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5677<t>
5678  Closed issues:
5679  <list style="symbols">
5680    <t>
5681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5682      "Clarification of the term 'deflate'"
5683    </t>
5684    <t>
5685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5686      "OPTIONS * and proxies"
5687    </t>
5688    <t>
5689      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5690      "MIME-Version not listed in P1, general header fields"
5691    </t>
5692    <t>
5693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5694      "IANA registry for content/transfer encodings"
5695    </t>
5696    <t>
5697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5698      "Case-sensitivity of HTTP-date"
5699    </t>
5700    <t>
5701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5702      "use of term "word" when talking about header structure"
5703    </t>
5704  </list>
5705</t>
5706<t>
5707  Partly resolved issues:
5708  <list style="symbols">
5709    <t>
5710      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5711      "Term for the requested resource's URI"
5712    </t>
5713  </list>
5714</t>
5715</section>
5716
5717<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5718<t>
5719  Closed issues:
5720  <list style="symbols">
5721    <t>
5722      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5723      "Connection Closing"
5724    </t>
5725    <t>
5726      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5727      "Delimiting messages with multipart/byteranges"
5728    </t>
5729    <t>
5730      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5731      "Handling multiple Content-Length headers"
5732    </t>
5733    <t>
5734      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5735      "Clarify entity / representation / variant terminology"
5736    </t>
5737    <t>
5738      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5739      "consider removing the 'changes from 2068' sections"
5740    </t>
5741  </list>
5742</t>
5743<t>
5744  Partly resolved issues:
5745  <list style="symbols">
5746    <t>
5747      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5748      "HTTP(s) URI scheme definitions"
5749    </t>
5750  </list>
5751</t>
5752</section>
5753
5754<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5755<t>
5756  Closed issues:
5757  <list style="symbols">
5758    <t>
5759      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5760      "Trailer requirements"
5761    </t>
5762    <t>
5763      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5764      "Text about clock requirement for caches belongs in p6"
5765    </t>
5766    <t>
5767      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5768      "effective request URI: handling of missing host in HTTP/1.0"
5769    </t>
5770    <t>
5771      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5772      "confusing Date requirements for clients"
5773    </t>
5774  </list>
5775</t>
5776<t>
5777  Partly resolved issues:
5778  <list style="symbols">
5779    <t>
5780      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5781      "Handling multiple Content-Length headers"
5782    </t>
5783  </list>
5784</t>
5785</section>
5786
5787<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5788<t>
5789  Closed issues:
5790  <list style="symbols">
5791    <t>
5792      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5793      "RFC2145 Normative"
5794    </t>
5795    <t>
5796      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5797      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5798    </t>
5799    <t>
5800      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5801      "define 'transparent' proxy"
5802    </t>
5803    <t>
5804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5805      "Header Classification"
5806    </t>
5807    <t>
5808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5809      "Is * usable as a request-uri for new methods?"
5810    </t>
5811    <t>
5812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5813      "Migrate Upgrade details from RFC2817"
5814    </t>
5815    <t>
5816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5817      "untangle ABNFs for header fields"
5818    </t>
5819    <t>
5820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5821      "update RFC 2109 reference"
5822    </t>
5823  </list>
5824</t>
5825</section>
5826
5827<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5828<t>
5829  Closed issues:
5830  <list style="symbols">
5831    <t>
5832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5833      "Allow is not in 13.5.2"
5834    </t>
5835    <t>
5836      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5837      "untangle ABNFs for header fields"
5838    </t>
5839    <t>
5840      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5841      "Content-Length ABNF broken"
5842    </t>
5843  </list>
5844</t>
5845</section>
5846
5847</section>
5848
5849</back>
5850</rfc>
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