source: draft-ietf-httpbis/13/draft-ietf-httpbis-p1-messaging-13.xml

Last change on this file was 1500, checked in by julian.reschke@…, 9 years ago

fix mime types

  • Property svn:eol-style set to native
  • Property svn:mime-type set to text/xml
File size: 233.3 KB
Line 
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-13">
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="March" year="2011" day="14"/>
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). The current issues list is
181    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/>
182    and related documents (including fancy diffs) can be found at
183    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
184  </t>
185  <t>
186    The changes in this draft are summarized in <xref target="changes.since.12"/>.
187  </t>
188</note>
189</front>
190<middle>
191<section title="Introduction" anchor="introduction">
192<t>
193   The Hypertext Transfer Protocol (HTTP) is an application-level
194   request/response protocol that uses extensible semantics and MIME-like
195   message payloads for flexible interaction with network-based hypertext
196   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
197   standard <xref target="RFC3986"/> to indicate the target resource and
198   relationships between resources.
199   Messages are passed in a format similar to that used by Internet mail
200   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
201   (MIME) <xref target="RFC2045"/> (see Appendix A of <xref target="Part3"/> for the differences
202   between HTTP and MIME messages).
203</t>
204<t>
205   HTTP is a generic interface protocol for information systems. It is
206   designed to hide the details of how a service is implemented by presenting
207   a uniform interface to clients that is independent of the types of
208   resources provided. Likewise, servers do not need to be aware of each
209   client's purpose: an HTTP request can be considered in isolation rather
210   than being associated with a specific type of client or a predetermined
211   sequence of application steps. The result is a protocol that can be used
212   effectively in many different contexts and for which implementations can
213   evolve independently over time.
214</t>
215<t>
216   HTTP is also designed for use as an intermediation protocol for translating
217   communication to and from non-HTTP information systems.
218   HTTP proxies and gateways can provide access to alternative information
219   services by translating their diverse protocols into a hypertext
220   format that can be viewed and manipulated by clients in the same way
221   as HTTP services.
222</t>
223<t>
224   One consequence of HTTP flexibility is that the protocol cannot be
225   defined in terms of what occurs behind the interface. Instead, we
226   are limited to defining the syntax of communication, the intent
227   of received communication, and the expected behavior of recipients.
228   If the communication is considered in isolation, then successful
229   actions ought to be reflected in corresponding changes to the
230   observable interface provided by servers. However, since multiple
231   clients might act in parallel and perhaps at cross-purposes, we
232   cannot require that such changes be observable beyond the scope
233   of a single response.
234</t>
235<t>
236   This document is Part 1 of the seven-part specification of HTTP,
237   defining the protocol referred to as "HTTP/1.1", obsoleting
238   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
239   Part 1 describes the architectural elements that are used or
240   referred to in HTTP, defines the "http" and "https" URI schemes,
241   describes overall network operation and connection management,
242   and defines HTTP message framing and forwarding requirements.
243   Our goal is to define all of the mechanisms necessary for HTTP message
244   handling that are independent of message semantics, thereby defining the
245   complete set of requirements for message parsers and
246   message-forwarding intermediaries.
247</t>
248
249<section title="Requirements" anchor="intro.requirements">
250<t>
251   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
252   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
253   document are to be interpreted as described in <xref target="RFC2119"/>.
254</t>
255<t>
256   An implementation is not compliant if it fails to satisfy one or more
257   of the "MUST" or "REQUIRED" level requirements for the protocols it
258   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
259   level and all the "SHOULD" level requirements for its protocols is said
260   to be "unconditionally compliant"; one that satisfies all the "MUST"
261   level requirements but not all the "SHOULD" level requirements for its
262   protocols is said to be "conditionally compliant".
263</t>
264</section>
265
266<section title="Syntax Notation" anchor="notation">
267<iref primary="true" item="Grammar" subitem="ALPHA"/>
268<iref primary="true" item="Grammar" subitem="CR"/>
269<iref primary="true" item="Grammar" subitem="CRLF"/>
270<iref primary="true" item="Grammar" subitem="CTL"/>
271<iref primary="true" item="Grammar" subitem="DIGIT"/>
272<iref primary="true" item="Grammar" subitem="DQUOTE"/>
273<iref primary="true" item="Grammar" subitem="HEXDIG"/>
274<iref primary="true" item="Grammar" subitem="LF"/>
275<iref primary="true" item="Grammar" subitem="OCTET"/>
276<iref primary="true" item="Grammar" subitem="SP"/>
277<iref primary="true" item="Grammar" subitem="VCHAR"/>
278<iref primary="true" item="Grammar" subitem="WSP"/>
279<t>
280   This specification uses the Augmented Backus-Naur Form (ABNF) notation
281   of <xref target="RFC5234"/>.
282</t>
283<t anchor="core.rules">
284 
285 
286 
287 
288 
289 
290 
291 
292 
293 
294 
295 
296   The following core rules are included by
297   reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
298   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
299   DIGIT (decimal 0-9), DQUOTE (double quote),
300   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
301   OCTET (any 8-bit sequence of data), SP (space),
302   VCHAR (any visible <xref target="USASCII"/> character),
303   and WSP (whitespace).
304</t>
305<t>
306   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
307   "obsolete" grammar rules that appear for historical reasons.
308</t>
309
310<section title="ABNF Extension: #rule" anchor="notation.abnf">
311<t>
312  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
313  improve readability.
314</t>
315<t>
316  A construct "#" is defined, similar to "*", for defining comma-delimited
317  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
318  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
319  comma (",") and optional whitespace (OWS,
320  <xref target="basic.rules"/>).   
321</t>
322<figure><preamble>
323  Thus,
324</preamble><artwork type="example"><![CDATA[
325  1#element => element *( OWS "," OWS element )
326]]></artwork></figure>
327<figure><preamble>
328  and:
329</preamble><artwork type="example"><![CDATA[
330  #element => [ 1#element ]
331]]></artwork></figure>
332<figure><preamble>
333  and for n &gt;= 1 and m &gt; 1:
334</preamble><artwork type="example"><![CDATA[
335  <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
336]]></artwork></figure>
337<t>
338  For compatibility with legacy list rules, recipients SHOULD accept empty
339  list elements. In other words, consumers would follow the list productions:
340</t>
341<figure><artwork type="example"><![CDATA[
342  #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
343 
344  1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
345]]></artwork></figure>
346<t>
347  Note that empty elements do not contribute to the count of elements present,
348  though.
349</t>
350<t>
351  For example, given these ABNF productions:
352</t>
353<figure><artwork type="example"><![CDATA[
354  example-list      = 1#example-list-elmt
355  example-list-elmt = token ; see Section 1.2.2
356]]></artwork></figure>
357<t>
358  Then these are valid values for example-list (not including the double
359  quotes, which are present for delimitation only):
360</t>
361<figure><artwork type="example"><![CDATA[
362  "foo,bar"
363  " foo ,bar,"
364  "  foo , ,bar,charlie   "
365  "foo ,bar,   charlie "
366]]></artwork></figure>
367<t>
368  But these values would be invalid, as at least one non-empty element is
369  required:
370</t>
371<figure><artwork type="example"><![CDATA[
372  ""
373  ","
374  ",   ,"
375]]></artwork></figure>
376<t>
377  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
378  expanded as explained above.
379</t>
380</section>
381
382<section title="Basic Rules" anchor="basic.rules">
383<t anchor="rule.CRLF">
384 
385   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
386   protocol elements other than the message-body
387   (see <xref target="tolerant.applications"/> for tolerant applications).
388</t>
389<t anchor="rule.LWS">
390   This specification uses three rules to denote the use of linear
391   whitespace: OWS (optional whitespace), RWS (required whitespace), and
392   BWS ("bad" whitespace).
393</t>
394<t>
395   The OWS rule is used where zero or more linear whitespace octets might
396   appear. OWS SHOULD either not be produced or be produced as a single
397   SP. Multiple OWS octets that occur within field-content SHOULD
398   be replaced with a single SP before interpreting the field value or
399   forwarding the message downstream.
400</t>
401<t>
402   RWS is used when at least one linear whitespace octet is required to
403   separate field tokens. RWS SHOULD be produced as a single SP.
404   Multiple RWS octets that occur within field-content SHOULD be
405   replaced with a single SP before interpreting the field value or
406   forwarding the message downstream.
407</t>
408<t>
409   BWS is used where the grammar allows optional whitespace for historical
410   reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
411   recipients MUST accept such bad optional whitespace and remove it before
412   interpreting the field value or forwarding the message downstream.
413</t>
414<t anchor="rule.whitespace">
415 
416 
417 
418 
419</t>
420<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[
421  OWS            = *( [ obs-fold ] WSP )
422                 ; "optional" whitespace
423  RWS            = 1*( [ obs-fold ] WSP )
424                 ; "required" whitespace
425  BWS            = OWS
426                 ; "bad" whitespace
427  obs-fold       = CRLF
428                 ; see Section 3.2
429]]></artwork></figure>
430<t anchor="rule.token.separators">
431 
432 
433 
434 
435   Many HTTP/1.1 header field values consist of words (token or quoted-string)
436   separated by whitespace or special characters. These special characters
437   MUST be in a quoted string to be used within a parameter value (as defined
438   in <xref target="transfer.codings"/>).
439</t>
440<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[
441  word           = token / quoted-string
442
443  token          = 1*tchar
444
445  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
446                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
447                 / DIGIT / ALPHA
448                 ; any VCHAR, except special
449
450  special        = "(" / ")" / "<" / ">" / "@" / ","
451                 / ";" / ":" / "\" / DQUOTE / "/" / "["
452                 / "]" / "?" / "=" / "{" / "}"
453]]></artwork></figure>
454<t anchor="rule.quoted-string">
455 
456 
457 
458   A string of text is parsed as a single word if it is quoted using
459   double-quote marks.
460</t>
461<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[
462  quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
463  qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
464                 ; OWS / <VCHAR except DQUOTE and "\"> / obs-text
465  obs-text       = %x80-FF
466]]></artwork></figure>
467<t anchor="rule.quoted-pair">
468 
469   The backslash octet ("\") can be used as a single-octet
470   quoting mechanism within quoted-string constructs:
471</t>
472<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
473  quoted-pair    = "\" ( WSP / VCHAR / obs-text )
474]]></artwork></figure>
475<t>
476   Senders SHOULD NOT escape octets that do not require escaping
477   (i.e., other than DQUOTE and the backslash octet).
478</t>
479</section>
480
481</section>
482</section>
483
484<section title="HTTP-related architecture" anchor="architecture">
485<t>
486   HTTP was created for the World Wide Web architecture
487   and has evolved over time to support the scalability needs of a worldwide
488   hypertext system. Much of that architecture is reflected in the terminology
489   and syntax productions used to define HTTP.
490</t>
491
492<section title="Client/Server Messaging" anchor="operation">
493<iref primary="true" item="client"/>
494<iref primary="true" item="server"/>
495<iref primary="true" item="connection"/>
496<t>
497   HTTP is a stateless request/response protocol that operates by exchanging
498   messages across a reliable transport or session-layer connection. An HTTP
499   "client" is a program that establishes a connection to a server for the
500   purpose of sending one or more HTTP requests.  An HTTP "server" is a
501   program that accepts connections in order to service HTTP requests by
502   sending HTTP responses.
503</t>
504<iref primary="true" item="user agent"/>
505<iref primary="true" item="origin server"/>
506<iref primary="true" item="browser"/>
507<iref primary="true" item="spider"/>
508<t>
509   Note that the terms client and server refer only to the roles that
510   these programs perform for a particular connection.  The same program
511   might act as a client on some connections and a server on others.  We use
512   the term "user agent" to refer to the program that initiates a request,
513   such as a WWW browser, editor, or spider (web-traversing robot), and
514   the term "origin server" to refer to the program that can originate
515   authoritative responses to a request.  For general requirements, we use
516   the term "sender" to refer to whichever component sent a given message
517   and the term "recipient" to refer to any component that receives the
518   message.
519</t>
520<t>
521   Most HTTP communication consists of a retrieval request (GET) for
522   a representation of some resource identified by a URI.  In the
523   simplest case, this might be accomplished via a single bidirectional
524   connection (===) between the user agent (UA) and the origin server (O).
525</t>
526<figure><artwork type="drawing"><![CDATA[
527         request   >
528    UA ======================================= O
529                                <   response
530]]></artwork></figure>
531<iref primary="true" item="message"/>
532<iref primary="true" item="request"/>
533<iref primary="true" item="response"/>
534<t>
535   A client sends an HTTP request to the server in the form of a request
536   message (<xref target="request"/>), beginning with a method, URI, and
537   protocol version, followed by MIME-like header fields containing
538   request modifiers, client information, and payload metadata, an empty
539   line to indicate the end of the header section, and finally the payload
540   body (if any).
541</t>
542<t>
543   A server responds to the client's request by sending an HTTP response
544   message (<xref target="response"/>), beginning with a status line that
545   includes the protocol version, a success or error code, and textual
546   reason phrase, followed by MIME-like header fields containing server
547   information, resource metadata, and payload metadata, an empty line to
548   indicate the end of the header section, and finally the payload body (if any).
549</t>
550<t>
551   The following example illustrates a typical message exchange for a
552   GET request on the URI "http://www.example.com/hello.txt":
553</t>
554<figure><preamble>
555client request:
556</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
557  GET /hello.txt HTTP/1.1
558  User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
559  Host: www.example.com
560  Accept: */*
561 
562  ]]></artwork></figure>
563<figure><preamble>
564server response:
565</preamble><artwork type="message/http; msgtype=&#34;response&#34;"><![CDATA[
566  HTTP/1.1 200 OK
567  Date: Mon, 27 Jul 2009 12:28:53 GMT
568  Server: Apache
569  Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
570  ETag: "34aa387-d-1568eb00"
571  Accept-Ranges: bytes
572  Content-Length: 14
573  Vary: Accept-Encoding
574  Content-Type: text/plain
575 
576  Hello World!
577  ]]></artwork></figure>
578</section>
579
580<section title="Connections and Transport Independence" anchor="transport-independence">
581<t>
582   HTTP messaging is independent of the underlying transport or
583   session-layer connection protocol(s).  HTTP only presumes a reliable
584   transport with in-order delivery of requests and the corresponding
585   in-order delivery of responses.  The mapping of HTTP request and
586   response structures onto the data units of the underlying transport
587   protocol is outside the scope of this specification.
588</t>
589<t>
590   The specific connection protocols to be used for an interaction
591   are determined by client configuration and the target resource's URI.
592   For example, the "http" URI scheme
593   (<xref target="http.uri"/>) indicates a default connection of TCP
594   over IP, with a default TCP port of 80, but the client might be
595   configured to use a proxy via some other connection port or protocol
596   instead of using the defaults.
597</t>
598<t>
599   A connection might be used for multiple HTTP request/response exchanges,
600   as defined in <xref target="persistent.connections"/>.
601</t>
602</section>
603
604<section title="Intermediaries" anchor="intermediaries">
605<iref primary="true" item="intermediary"/>
606<t>
607   HTTP enables the use of intermediaries to satisfy requests through
608   a chain of connections.  There are three common forms of HTTP
609   intermediary: proxy, gateway, and tunnel.  In some cases,
610   a single intermediary might act as an origin server, proxy, gateway,
611   or tunnel, switching behavior based on the nature of each request.
612</t>
613<figure><artwork type="drawing"><![CDATA[
614         >             >             >             >
615    UA =========== A =========== B =========== C =========== O
616               <             <             <             <
617]]></artwork></figure>
618<t>
619   The figure above shows three intermediaries (A, B, and C) between the
620   user agent and origin server. A request or response message that
621   travels the whole chain will pass through four separate connections.
622   Some HTTP communication options
623   might apply only to the connection with the nearest, non-tunnel
624   neighbor, only to the end-points of the chain, or to all connections
625   along the chain. Although the diagram is linear, each participant might
626   be engaged in multiple, simultaneous communications. For example, B
627   might be receiving requests from many clients other than A, and/or
628   forwarding requests to servers other than C, at the same time that it
629   is handling A's request.
630</t>
631<t>
632<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
633<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
634   We use the terms "upstream" and "downstream" to describe various
635   requirements in relation to the directional flow of a message:
636   all messages flow from upstream to downstream.
637   Likewise, we use the terms "inbound" and "outbound" to refer to
638   directions in relation to the request path: "inbound" means toward
639   the origin server and "outbound" means toward the user agent.
640</t>
641<t><iref primary="true" item="proxy"/>
642   A "proxy" is a message forwarding agent that is selected by the
643   client, usually via local configuration rules, to receive requests
644   for some type(s) of absolute URI and attempt to satisfy those
645   requests via translation through the HTTP interface.  Some translations
646   are minimal, such as for proxy requests for "http" URIs, whereas
647   other requests might require translation to and from entirely different
648   application-layer protocols. Proxies are often used to group an
649   organization's HTTP requests through a common intermediary for the
650   sake of security, annotation services, or shared caching.
651</t>
652<t>
653<iref primary="true" item="transforming proxy"/>
654<iref primary="true" item="non-transforming proxy"/>
655   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
656   or configured to modify request or response messages in a semantically
657   meaningful way (i.e., modifications, beyond those required by normal
658   HTTP processing, that change the message in a way that would be
659   significant to the original sender or potentially significant to
660   downstream recipients).  For example, a transforming proxy might be
661   acting as a shared annotation server (modifying responses to include
662   references to a local annotation database), a malware filter, a
663   format transcoder, or an intranet-to-Internet privacy filter.  Such
664   transformations are presumed to be desired by the client (or client
665   organization) that selected the proxy and are beyond the scope of
666   this specification.  However, when a proxy is not intended to transform
667   a given message, we use the term "non-transforming proxy" to target
668   requirements that preserve HTTP message semantics.
669</t>
670<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
671<iref primary="true" item="accelerator"/>
672   A "gateway" (a.k.a., "reverse proxy") is a receiving agent that acts
673   as a layer above some other server(s) and translates the received
674   requests to the underlying server's protocol.  Gateways are often
675   used to encapsulate legacy or untrusted information services, to
676   improve server performance through "accelerator" caching, and to
677   enable partitioning or load-balancing of HTTP services across
678   multiple machines.
679</t>
680<t>
681   A gateway behaves as an origin server on its outbound connection and
682   as a user agent on its inbound connection.
683   All HTTP requirements applicable to an origin server
684   also apply to the outbound communication of a gateway.
685   A gateway communicates with inbound servers using any protocol that
686   it desires, including private extensions to HTTP that are outside
687   the scope of this specification.  However, an HTTP-to-HTTP gateway
688   that wishes to interoperate with third-party HTTP servers MUST
689   comply with HTTP user agent requirements on the gateway's inbound
690   connection and MUST implement the Connection
691   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
692   header fields for both connections.
693</t>
694<t><iref primary="true" item="tunnel"/>
695   A "tunnel" acts as a blind relay between two connections
696   without changing the messages. Once active, a tunnel is not
697   considered a party to the HTTP communication, though the tunnel might
698   have been initiated by an HTTP request. A tunnel ceases to exist when
699   both ends of the relayed connection are closed. Tunnels are used to
700   extend a virtual connection through an intermediary, such as when
701   transport-layer security is used to establish private communication
702   through a shared firewall proxy.
703</t>
704<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
705<iref primary="true" item="captive portal"/>
706   In addition, there may exist network intermediaries that are not
707   considered part of the HTTP communication but nevertheless act as
708   filters or redirecting agents (usually violating HTTP semantics,
709   causing security problems, and otherwise making a mess of things).
710   Such a network intermediary, often referred to as an "interception proxy"
711   <xref target="RFC3040"/>, "transparent proxy" <xref target="RFC1919"/>,
712   or "captive portal",
713   differs from an HTTP proxy because it has not been selected by the client.
714   Instead, the network intermediary redirects outgoing TCP port 80 packets
715   (and occasionally other common port traffic) to an internal HTTP server.
716   Interception proxies are commonly found on public network access points,
717   as a means of enforcing account subscription prior to allowing use of
718   non-local Internet services, and within corporate firewalls to enforce
719   network usage policies.
720   They are indistinguishable from a man-in-the-middle attack.
721</t>
722</section>
723
724<section title="Caches" anchor="caches">
725<iref primary="true" item="cache"/>
726<t>
727   A "cache" is a local store of previous response messages and the
728   subsystem that controls its message storage, retrieval, and deletion.
729   A cache stores cacheable responses in order to reduce the response
730   time and network bandwidth consumption on future, equivalent
731   requests. Any client or server MAY employ a cache, though a cache
732   cannot be used by a server while it is acting as a tunnel.
733</t>
734<t>
735   The effect of a cache is that the request/response chain is shortened
736   if one of the participants along the chain has a cached response
737   applicable to that request. The following illustrates the resulting
738   chain if B has a cached copy of an earlier response from O (via C)
739   for a request which has not been cached by UA or A.
740</t>
741<figure><artwork type="drawing"><![CDATA[
742            >             >
743       UA =========== A =========== B - - - - - - C - - - - - - O
744                  <             <
745]]></artwork></figure>
746<t><iref primary="true" item="cacheable"/>
747   A response is "cacheable" if a cache is allowed to store a copy of
748   the response message for use in answering subsequent requests.
749   Even when a response is cacheable, there might be additional
750   constraints placed by the client or by the origin server on when
751   that cached response can be used for a particular request. HTTP
752   requirements for cache behavior and cacheable responses are
753   defined in Section 2 of <xref target="Part6"/>. 
754</t>
755<t>
756   There are a wide variety of architectures and configurations
757   of caches and proxies deployed across the World Wide Web and
758   inside large organizations. These systems include national hierarchies
759   of proxy caches to save transoceanic bandwidth, systems that
760   broadcast or multicast cache entries, organizations that distribute
761   subsets of cached data via optical media, and so on.
762</t>
763</section>
764
765<section title="Protocol Versioning" anchor="http.version">
766 
767 
768<t>
769   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
770   versions of the protocol. This specification defines version "1.1".
771   The protocol version as a whole indicates the sender's compliance
772   with the set of requirements laid out in that version's corresponding
773   specification of HTTP.
774</t>
775<t>
776   The version of an HTTP message is indicated by an HTTP-Version field
777   in the first line of the message. HTTP-Version is case-sensitive.
778</t>
779<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
780  HTTP-Version   = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
781  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
782]]></artwork></figure>
783<t>
784   The HTTP version number consists of two non-negative decimal integers
785   separated by a "." (period or decimal point).  The first
786   number ("major version") indicates the HTTP messaging syntax, whereas
787   the second number ("minor version") indicates the highest minor
788   version to which the sender is at least conditionally compliant and
789   able to understand for future communication.  The minor version
790   advertises the sender's communication capabilities even when the
791   sender is only using a backwards-compatible subset of the protocol,
792   thereby letting the recipient know that more advanced features can
793   be used in response (by servers) or in future requests (by clients).
794</t>
795<t>
796   When comparing HTTP versions, the numbers MUST be compared
797   numerically rather than lexically.  For example, HTTP/2.4 is a lower
798   version than HTTP/2.13, which in turn is lower than HTTP/12.3.
799   Leading zeros MUST be ignored by recipients and MUST NOT be sent.
800</t>
801<t>
802   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
803   <xref target="RFC1945"/> or a recipient whose version is unknown,
804   the HTTP/1.1 message is constructed such that it can be interpreted
805   as a valid HTTP/1.0 message if all of the newer features are ignored.
806   This specification places recipient-version requirements on some
807   new features so that a compliant sender will only use compatible
808   features until it has determined, through configuration or the
809   receipt of a message, that the recipient supports HTTP/1.1.
810</t>
811<t>
812   The interpretation of an HTTP header field does not change
813   between minor versions of the same major version, though the default
814   behavior of a recipient in the absence of such a field can change.
815   Unless specified otherwise, header fields defined in HTTP/1.1 are
816   defined for all versions of HTTP/1.x.  In particular, the Host and
817   Connection header fields ought to be implemented by all HTTP/1.x
818   implementations whether or not they advertise compliance with HTTP/1.1.
819</t>
820<t>
821   New header fields can be defined such that, when they are
822   understood by a recipient, they might override or enhance the
823   interpretation of previously defined header fields.  When an
824   implementation receives an unrecognized header field, the recipient
825   MUST ignore that header field for local processing regardless of
826   the message's HTTP version.  An unrecognized header field received
827   by a proxy MUST be forwarded downstream unless the header field's
828   field-name is listed in the message's Connection header-field
829   (see <xref target="header.connection"/>).
830   These requirements allow HTTP's functionality to be enhanced without
831   requiring prior update of all compliant intermediaries.
832</t>
833<t>
834   Intermediaries that process HTTP messages (i.e., all intermediaries
835   other than those acting as a tunnel) MUST send their own HTTP-Version
836   in forwarded messages.  In other words, they MUST NOT blindly
837   forward the first line of an HTTP message without ensuring that the
838   protocol version matches what the intermediary understands, and
839   is at least conditionally compliant to, for both the receiving and
840   sending of messages.  Forwarding an HTTP message without rewriting
841   the HTTP-Version might result in communication errors when downstream
842   recipients use the message sender's version to determine what features
843   are safe to use for later communication with that sender.
844</t>
845<t>
846   An HTTP client SHOULD send a request version equal to the highest
847   version for which the client is at least conditionally compliant and
848   whose major version is no higher than the highest version supported
849   by the server, if this is known.  An HTTP client MUST NOT send a
850   version for which it is not at least conditionally compliant.
851</t>
852<t>
853   An HTTP client MAY send a lower request version if it is known that
854   the server incorrectly implements the HTTP specification, but only
855   after the client has attempted at least one normal request and determined
856   from the response status or header fields (e.g., Server) that the
857   server improperly handles higher request versions.
858</t>
859<t>
860   An HTTP server SHOULD send a response version equal to the highest
861   version for which the server is at least conditionally compliant and
862   whose major version is less than or equal to the one received in the
863   request.  An HTTP server MUST NOT send a version for which it is not
864   at least conditionally compliant.  A server MAY send a 505 (HTTP
865   Version Not Supported) response if it cannot send a response using the
866   major version used in the client's request.
867</t>
868<t>
869   An HTTP server MAY send an HTTP/1.0 response to an HTTP/1.0 request
870   if it is known or suspected that the client incorrectly implements the
871   HTTP specification and is incapable of correctly processing later
872   version responses, such as when a client fails to parse the version
873   number correctly or when an intermediary is known to blindly forward
874   the HTTP-Version even when it doesn't comply with the given minor
875   version of the protocol. Such protocol downgrades SHOULD NOT be
876   performed unless triggered by specific client attributes, such as when
877   one or more of the request header fields (e.g., User-Agent) uniquely
878   match the values sent by a client known to be in error.
879</t>
880<t>
881   The intention of HTTP's versioning design is that the major number
882   will only be incremented if an incompatible message syntax is
883   introduced, and that the minor number will only be incremented when
884   changes made to the protocol have the effect of adding to the message
885   semantics or implying additional capabilities of the sender.  However,
886   the minor version was not incremented for the changes introduced between
887   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
888   is specifically avoiding any such changes to the protocol.
889</t>
890</section>
891
892<section title="Uniform Resource Identifiers" anchor="uri">
893<iref primary="true" item="resource"/>
894<t>
895   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
896   throughout HTTP as the means for identifying resources. URI references
897   are used to target requests, indicate redirects, and define relationships.
898   HTTP does not limit what a resource might be; it merely defines an interface
899   that can be used to interact with a resource via HTTP. More information on
900   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
901</t>
902 
903 
904 
905 
906 
907 
908 
909 
910 
911 
912<t>
913   This specification adopts the definitions of "URI-reference",
914   "absolute-URI", "relative-part", "port", "host",
915   "path-abempty", "path-absolute", "query", and "authority" from the
916   URI generic syntax <xref target="RFC3986"/>.
917   In addition, we define a partial-URI rule for protocol elements
918   that allow a relative URI but not a fragment.
919</t>
920<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[
921  URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
922  absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
923  relative-part = <relative-part, defined in [RFC3986], Section 4.2>
924  authority     = <authority, defined in [RFC3986], Section 3.2>
925  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
926  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
927  port          = <port, defined in [RFC3986], Section 3.2.3>
928  query         = <query, defined in [RFC3986], Section 3.4>
929  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
930 
931  partial-URI   = relative-part [ "?" query ]
932]]></artwork></figure>
933<t>
934   Each protocol element in HTTP that allows a URI reference will indicate
935   in its ABNF production whether the element allows any form of reference
936   (URI-reference), only a URI in absolute form (absolute-URI), only the
937   path and optional query components, or some combination of the above.
938   Unless otherwise indicated, URI references are parsed relative to the
939   effective request URI, which defines the default base URI for references
940   in both the request and its corresponding response.
941</t>
942
943<section title="http URI scheme" anchor="http.uri">
944 
945  <iref item="http URI scheme" primary="true"/>
946  <iref item="URI scheme" subitem="http" primary="true"/>
947<t>
948   The "http" URI scheme is hereby defined for the purpose of minting
949   identifiers according to their association with the hierarchical
950   namespace governed by a potential HTTP origin server listening for
951   TCP connections on a given port.
952</t>
953<figure><iref primary="true" item="Grammar" subitem="http-URI"/><artwork type="abnf2616"><![CDATA[
954  http-URI = "http:" "//" authority path-abempty [ "?" query ]
955]]></artwork></figure>
956<t>
957   The HTTP origin server is identified by the generic syntax's
958   <xref target="uri" format="none">authority</xref> component, which includes a host identifier
959   and optional TCP port (<xref target="RFC3986"/>, Section 3.2.2).
960   The remainder of the URI, consisting of both the hierarchical path
961   component and optional query component, serves as an identifier for
962   a potential resource within that origin server's name space.
963</t>
964<t>
965   If the host identifier is provided as an IP literal or IPv4 address,
966   then the origin server is any listener on the indicated TCP port at
967   that IP address. If host is a registered name, then that name is
968   considered an indirect identifier and the recipient might use a name
969   resolution service, such as DNS, to find the address of a listener
970   for that host.
971   The host MUST NOT be empty; if an "http" URI is received with an
972   empty host, then it MUST be rejected as invalid.
973   If the port subcomponent is empty or not given, then TCP port 80 is
974   assumed (the default reserved port for WWW services).
975</t>
976<t>
977   Regardless of the form of host identifier, access to that host is not
978   implied by the mere presence of its name or address. The host might or might
979   not exist and, even when it does exist, might or might not be running an
980   HTTP server or listening to the indicated port. The "http" URI scheme
981   makes use of the delegated nature of Internet names and addresses to
982   establish a naming authority (whatever entity has the ability to place
983   an HTTP server at that Internet name or address) and allows that
984   authority to determine which names are valid and how they might be used.
985</t>
986<t>
987   When an "http" URI is used within a context that calls for access to the
988   indicated resource, a client MAY attempt access by resolving
989   the host to an IP address, establishing a TCP connection to that address
990   on the indicated port, and sending an HTTP request message to the server
991   containing the URI's identifying data as described in <xref target="request"/>.
992   If the server responds to that request with a non-interim HTTP response
993   message, as described in <xref target="response"/>, then that response
994   is considered an authoritative answer to the client's request.
995</t>
996<t>
997   Although HTTP is independent of the transport protocol, the "http"
998   scheme is specific to TCP-based services because the name delegation
999   process depends on TCP for establishing authority.
1000   An HTTP service based on some other underlying connection protocol
1001   would presumably be identified using a different URI scheme, just as
1002   the "https" scheme (below) is used for servers that require an SSL/TLS
1003   transport layer on a connection. Other protocols might also be used to
1004   provide access to "http" identified resources — it is only the
1005   authoritative interface used for mapping the namespace that is
1006   specific to TCP.
1007</t>
1008<t>
1009   The URI generic syntax for authority also includes a deprecated
1010   userinfo subcomponent (<xref target="RFC3986"/>, Section 3.2.1)
1011   for including user authentication information in the URI.  Some
1012   implementations make use of the userinfo component for internal
1013   configuration of authentication information, such as within command
1014   invocation options, configuration files, or bookmark lists, even
1015   though such usage might expose a user identifier or password.
1016   Senders MUST NOT include a userinfo subcomponent (and its "@"
1017   delimiter) when transmitting an "http" URI in a message.  Recipients
1018   of HTTP messages that contain a URI reference SHOULD parse for the
1019   existence of userinfo and treat its presence as an error, likely
1020   indicating that the deprecated subcomponent is being used to obscure
1021   the authority for the sake of phishing attacks.
1022</t>
1023</section>
1024
1025<section title="https URI scheme" anchor="https.uri">
1026   
1027   <iref item="https URI scheme"/>
1028   <iref item="URI scheme" subitem="https"/>
1029<t>
1030   The "https" URI scheme is hereby defined for the purpose of minting
1031   identifiers according to their association with the hierarchical
1032   namespace governed by a potential HTTP origin server listening for
1033   SSL/TLS-secured connections on a given TCP port.
1034</t>
1035<t>
1036   All of the requirements listed above for the "http" scheme are also
1037   requirements for the "https" scheme, except that a default TCP port
1038   of 443 is assumed if the port subcomponent is empty or not given,
1039   and the TCP connection MUST be secured for privacy through the
1040   use of strong encryption prior to sending the first HTTP request.
1041</t>
1042<figure><iref primary="true" item="Grammar" subitem="https-URI"/><artwork type="abnf2616"><![CDATA[
1043  https-URI = "https:" "//" authority path-abempty [ "?" query ]
1044]]></artwork></figure>
1045<t>
1046   Unlike the "http" scheme, responses to "https" identified requests
1047   are never "public" and thus MUST NOT be reused for shared caching.
1048   They can, however, be reused in a private cache if the message is
1049   cacheable by default in HTTP or specifically indicated as such by
1050   the Cache-Control header field (Section 3.2 of <xref target="Part6"/>).
1051</t>
1052<t>
1053   Resources made available via the "https" scheme have no shared
1054   identity with the "http" scheme even if their resource identifiers
1055   indicate the same authority (the same host listening to the same
1056   TCP port).  They are distinct name spaces and are considered to be
1057   distinct origin servers.  However, an extension to HTTP that is
1058   defined to apply to entire host domains, such as the Cookie protocol
1059   <xref target="draft-ietf-httpstate-cookie"/>, can allow information
1060   set by one service to impact communication with other services
1061   within a matching group of host domains.
1062</t>
1063<t>
1064   The process for authoritative access to an "https" identified
1065   resource is defined in <xref target="RFC2818"/>.
1066</t>
1067</section>
1068
1069<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1070<t>
1071   Since the "http" and "https" schemes conform to the URI generic syntax,
1072   such URIs are normalized and compared according to the algorithm defined
1073   in <xref target="RFC3986"/>, Section 6, using the defaults
1074   described above for each scheme.
1075</t>
1076<t>
1077   If the port is equal to the default port for a scheme, the normal
1078   form is to elide the port subcomponent. Likewise, an empty path
1079   component is equivalent to an absolute path of "/", so the normal
1080   form is to provide a path of "/" instead. The scheme and host
1081   are case-insensitive and normally provided in lowercase; all
1082   other components are compared in a case-sensitive manner.
1083   Characters other than those in the "reserved" set are equivalent
1084   to their percent-encoded octets (see <xref target="RFC3986"/>, Section 2.1): the normal form is to not encode them.
1085</t>
1086<t>
1087   For example, the following three URIs are equivalent:
1088</t>
1089<figure><artwork type="example"><![CDATA[
1090   http://example.com:80/~smith/home.html
1091   http://EXAMPLE.com/%7Esmith/home.html
1092   http://EXAMPLE.com:/%7esmith/home.html
1093]]></artwork></figure>
1094</section>
1095</section>
1096</section>
1097
1098<section title="Message Format" anchor="http.message">
1099
1100
1101
1102
1103<iref item="header section"/>
1104<iref item="headers"/>
1105<iref item="header field"/>
1106<t>
1107   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1108   octets in a format similar to the Internet Message Format
1109   <xref target="RFC5322"/>: zero or more header fields (collectively
1110   referred to as the "headers" or the "header section"), an empty line
1111   indicating the end of the header section, and an optional message-body.
1112</t>
1113<t>
1114   An HTTP message can either be a request from client to server or a
1115   response from server to client.  Syntactically, the two types of message
1116   differ only in the start-line, which is either a Request-Line (for requests)
1117   or a Status-Line (for responses), and in the algorithm for determining
1118   the length of the message-body (<xref target="message.body"/>).
1119   In theory, a client could receive requests and a server could receive
1120   responses, distinguishing them by their different start-line formats,
1121   but in practice servers are implemented to only expect a request
1122   (a response is interpreted as an unknown or invalid request method)
1123   and clients are implemented to only expect a response.
1124</t>
1125<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1126  HTTP-message    = start-line
1127                    *( header-field CRLF )
1128                    CRLF
1129                    [ message-body ]
1130  start-line      = Request-Line / Status-Line
1131]]></artwork></figure>
1132<t>
1133   Implementations MUST NOT send whitespace between the start-line and
1134   the first header field. The presence of such whitespace in a request
1135   might be an attempt to trick a server into ignoring that field or
1136   processing the line after it as a new request, either of which might
1137   result in a security vulnerability if other implementations within
1138   the request chain interpret the same message differently.
1139   Likewise, the presence of such whitespace in a response might be
1140   ignored by some clients or cause others to cease parsing.
1141</t>
1142
1143<section title="Message Parsing Robustness" anchor="message.robustness">
1144<t>
1145   In the interest of robustness, servers SHOULD ignore at least one
1146   empty line received where a Request-Line is expected. In other words, if
1147   the server is reading the protocol stream at the beginning of a
1148   message and receives a CRLF first, it SHOULD ignore the CRLF.
1149</t>
1150<t>
1151   Some old HTTP/1.0 client implementations send an extra CRLF
1152   after a POST request as a lame workaround for some early server
1153   applications that failed to read message-body content that was
1154   not terminated by a line-ending. An HTTP/1.1 client MUST NOT
1155   preface or follow a request with an extra CRLF.  If terminating
1156   the request message-body with a line-ending is desired, then the
1157   client MUST include the terminating CRLF octets as part of the
1158   message-body length.
1159</t>
1160<t>
1161   When a server listening only for HTTP request messages, or processing
1162   what appears from the start-line to be an HTTP request message,
1163   receives a sequence of octets that does not match the HTTP-message
1164   grammar aside from the robustness exceptions listed above, the
1165   server MUST respond with an HTTP/1.1 400 (Bad Request) response. 
1166</t>
1167<t>
1168   The normal procedure for parsing an HTTP message is to read the
1169   start-line into a structure, read each header field into a hash
1170   table by field name until the empty line, and then use the parsed
1171   data to determine if a message-body is expected.  If a message-body
1172   has been indicated, then it is read as a stream until an amount
1173   of octets equal to the message-body length is read or the connection
1174   is closed.  Care must be taken to parse an HTTP message as a sequence
1175   of octets in an encoding that is a superset of US-ASCII.  Attempting
1176   to parse HTTP as a stream of Unicode characters in a character encoding
1177   like UTF-16 might introduce security flaws due to the differing ways
1178   that such parsers interpret invalid characters.
1179</t>
1180<t>
1181   HTTP allows the set of defined header fields to be extended without
1182   changing the protocol version (see <xref target="header.field.registration"/>).
1183   Unrecognized header fields MUST be forwarded by a proxy unless the
1184   proxy is specifically configured to block or otherwise transform such
1185   fields.  Unrecognized header fields SHOULD be ignored by other recipients.
1186</t>
1187</section>
1188
1189<section title="Header Fields" anchor="header.fields">
1190 
1191 
1192 
1193 
1194 
1195<t>
1196   Each HTTP header field consists of a case-insensitive field name
1197   followed by a colon (":"), optional whitespace, and the field value.
1198</t>
1199<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[
1200  header-field   = field-name ":" OWS [ field-value ] OWS
1201  field-name     = token
1202  field-value    = *( field-content / OWS )
1203  field-content  = *( WSP / VCHAR / obs-text )
1204]]></artwork></figure>
1205<t>
1206   No whitespace is allowed between the header field name and colon. For
1207   security reasons, any request message received containing such whitespace
1208   MUST be rejected with a response code of 400 (Bad Request). A proxy
1209   MUST remove any such whitespace from a response message before
1210   forwarding the message downstream.
1211</t>
1212<t>
1213   A field value MAY be preceded by optional whitespace (OWS); a single SP is
1214   preferred. The field value does not include any leading or trailing white
1215   space: OWS occurring before the first non-whitespace octet of the
1216   field value or after the last non-whitespace octet of the field value
1217   is ignored and SHOULD be removed before further processing (as this does
1218   not change the meaning of the header field).
1219</t>
1220<t>
1221   The order in which header fields with differing field names are
1222   received is not significant. However, it is "good practice" to send
1223   header fields that contain control data first, such as Host on
1224   requests and Date on responses, so that implementations can decide
1225   when not to handle a message as early as possible.  A server MUST
1226   wait until the entire header section is received before interpreting
1227   a request message, since later header fields might include conditionals,
1228   authentication credentials, or deliberately misleading duplicate
1229   header fields that would impact request processing.
1230</t>
1231<t>
1232   Multiple header fields with the same field name MUST NOT be
1233   sent in a message unless the entire field value for that
1234   header field is defined as a comma-separated list [i.e., #(values)].
1235   Multiple header fields with the same field name can be combined into
1236   one "field-name: field-value" pair, without changing the semantics of the
1237   message, by appending each subsequent field value to the combined
1238   field value in order, separated by a comma. The order in which
1239   header fields with the same field name are received is therefore
1240   significant to the interpretation of the combined field value;
1241   a proxy MUST NOT change the order of these field values when
1242   forwarding a message.
1243</t>
1244<t><list>
1245  <t>
1246   Note: The "Set-Cookie" header field as implemented in
1247   practice can occur multiple times, but does not use the list syntax, and
1248   thus cannot be combined into a single line (<xref target="draft-ietf-httpstate-cookie"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1249   for details.) Also note that the Set-Cookie2 header field specified in
1250   <xref target="RFC2965"/> does not share this problem.
1251  </t>
1252</list></t>
1253<t>
1254   Historically, HTTP header field values could be extended over multiple
1255   lines by preceding each extra line with at least one space or horizontal
1256   tab octet (line folding). This specification deprecates such line
1257   folding except within the message/http media type
1258   (<xref target="internet.media.type.message.http"/>).
1259   HTTP/1.1 senders MUST NOT produce messages that include line folding
1260   (i.e., that contain any field-content that matches the obs-fold rule) unless
1261   the message is intended for packaging within the message/http media type.
1262   HTTP/1.1 recipients SHOULD accept line folding and replace any embedded
1263   obs-fold whitespace with a single SP prior to interpreting the field value
1264   or forwarding the message downstream.
1265</t>
1266<t>
1267   Historically, HTTP has allowed field content with text in the ISO-8859-1
1268   <xref target="ISO-8859-1"/> character encoding and supported other
1269   character sets only through use of <xref target="RFC2047"/> encoding.
1270   In practice, most HTTP header field values use only a subset of the
1271   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1272   header fields SHOULD limit their field values to US-ASCII octets.
1273   Recipients SHOULD treat other (obs-text) octets in field content as
1274   opaque data.
1275</t>
1276<t anchor="rule.comment">
1277 
1278 
1279   Comments can be included in some HTTP header fields by surrounding
1280   the comment text with parentheses. Comments are only allowed in
1281   fields containing "comment" as part of their field value definition.
1282</t>
1283<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
1284  comment        = "(" *( ctext / quoted-cpair / comment ) ")"
1285  ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
1286                 ; OWS / <VCHAR except "(", ")", and "\"> / obs-text
1287]]></artwork></figure>
1288<t anchor="rule.quoted-cpair">
1289 
1290   The backslash octet ("\") can be used as a single-octet
1291   quoting mechanism within comment constructs:
1292</t>
1293<figure><iref primary="true" item="Grammar" subitem="quoted-cpair"/><artwork type="abnf2616"><![CDATA[
1294  quoted-cpair    = "\" ( WSP / VCHAR / obs-text )
1295]]></artwork></figure>
1296<t>
1297   Senders SHOULD NOT escape octets that do not require escaping
1298   (i.e., other than the backslash octet "\" and the parentheses "(" and
1299   ")").
1300</t>
1301</section>
1302
1303<section title="Message Body" anchor="message.body">
1304 
1305<t>
1306   The message-body (if any) of an HTTP message is used to carry the
1307   payload body associated with the request or response.
1308</t>
1309<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1310  message-body = *OCTET
1311]]></artwork></figure>
1312<t>
1313   The message-body differs from the payload body only when a transfer-coding
1314   has been applied, as indicated by the Transfer-Encoding header field
1315   (<xref target="header.transfer-encoding"/>).  If more than one
1316   Transfer-Encoding header field is present in a message, the multiple
1317   field-values MUST be combined into one field-value, according to the
1318   algorithm defined in <xref target="header.fields"/>, before determining
1319   the message-body length.
1320</t>
1321<t>
1322   When one or more transfer-codings are applied to a payload in order to
1323   form the message-body, the Transfer-Encoding header field MUST contain
1324   the list of transfer-codings applied. Transfer-Encoding is a property of
1325   the message, not of the payload, and thus MAY be added or removed by
1326   any implementation along the request/response chain under the constraints
1327   found in <xref target="transfer.codings"/>.
1328</t>
1329<t>
1330   If a message is received that has multiple Content-Length header fields
1331   (<xref target="header.content-length"/>) with field-values consisting
1332   of the same decimal value, or a single Content-Length header field with
1333   a field value containing a list of identical decimal values (e.g.,
1334   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1335   header fields have been generated or combined by an upstream message
1336   processor, then the recipient MUST replace the duplicated fields or
1337   field-values with a single valid Content-Length field containing that
1338   decimal value prior to determining the message-body length.
1339</t>
1340<t>
1341   The rules for when a message-body is allowed in a message differ for
1342   requests and responses.
1343</t>
1344<t>
1345   The presence of a message-body in a request is signaled by the
1346   inclusion of a Content-Length or Transfer-Encoding header field in
1347   the request's header fields, even if the request method does not
1348   define any use for a message-body.  This allows the request
1349   message framing algorithm to be independent of method semantics.
1350</t>
1351<t>
1352   For response messages, whether or not a message-body is included with
1353   a message is dependent on both the request method and the response
1354   status code (<xref target="status.code.and.reason.phrase"/>).
1355   Responses to the HEAD request method never include a message-body
1356   because the associated response header fields (e.g., Transfer-Encoding,
1357   Content-Length, etc.) only indicate what their values would have been
1358   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1359   and 304 (Not Modified) responses MUST NOT include a message-body.
1360   All other responses do include a message-body, although the body
1361   MAY be of zero length.
1362</t>
1363<t>
1364   The length of the message-body is determined by one of the following
1365   (in order of precedence):
1366</t>
1367<t>
1368  <list style="numbers">
1369    <t>
1370     Any response to a HEAD request and any response with a status
1371     code of 100-199, 204, or 304 is always terminated by the first
1372     empty line after the header fields, regardless of the header
1373     fields present in the message, and thus cannot contain a message-body.
1374    </t>
1375    <t>
1376     If a Transfer-Encoding header field is present
1377     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1378     is the final encoding, the message-body length is determined by reading
1379     and decoding the chunked data until the transfer-coding indicates the
1380     data is complete.
1381    <vspace blankLines="1"/>
1382     If a Transfer-Encoding header field is present in a response and the
1383     "chunked" transfer-coding is not the final encoding, the message-body
1384     length is determined by reading the connection until it is closed by
1385     the server.
1386     If a Transfer-Encoding header field is present in a request and the
1387     "chunked" transfer-coding is not the final encoding, the message-body
1388     length cannot be determined reliably; the server MUST respond with
1389     the 400 (Bad Request) status code and then close the connection.
1390    <vspace blankLines="1"/>
1391     If a message is received with both a Transfer-Encoding header field
1392     and a Content-Length header field, the Transfer-Encoding overrides
1393     the Content-Length.
1394     Such a message might indicate an attempt to perform request or response
1395     smuggling (bypass of security-related checks on message routing or content)
1396     and thus ought to be handled as an error.  The provided Content-Length MUST
1397     be removed, prior to forwarding the message downstream, or replaced with
1398     the real message-body length after the transfer-coding is decoded.
1399    </t>
1400    <t>
1401     If a message is received without Transfer-Encoding and with either
1402     multiple Content-Length header fields having differing field-values or
1403     a single Content-Length header field having an invalid value, then the
1404     message framing is invalid and MUST be treated as an error to
1405     prevent request or response smuggling.
1406     If this is a request message, the server MUST respond with
1407     a 400 (Bad Request) status code and then close the connection.
1408     If this is a response message received by a proxy, the proxy
1409     MUST discard the received response, send a 502 (Bad Gateway)
1410     status code as its downstream response, and then close the connection.
1411     If this is a response message received by a user-agent, it MUST be
1412     treated as an error by discarding the message and closing the connection.
1413    </t>
1414    <t>
1415     If a valid Content-Length header field
1416     is present without Transfer-Encoding, its decimal value defines the
1417     message-body length in octets.  If the actual number of octets sent in
1418     the message is less than the indicated Content-Length, the recipient
1419     MUST consider the message to be incomplete and treat the connection
1420     as no longer usable.
1421     If the actual number of octets sent in the message is more than the indicated
1422     Content-Length, the recipient MUST only process the message-body up to the
1423     field value's number of octets; the remainder of the message MUST either
1424     be discarded or treated as the next message in a pipeline.  For the sake of
1425     robustness, a user-agent MAY attempt to detect and correct such an error
1426     in message framing if it is parsing the response to the last request on
1427     on a connection and the connection has been closed by the server.
1428    </t>
1429    <t>
1430     If this is a request message and none of the above are true, then the
1431     message-body length is zero (no message-body is present).
1432    </t>
1433    <t>
1434     Otherwise, this is a response message without a declared message-body
1435     length, so the message-body length is determined by the number of octets
1436     received prior to the server closing the connection.
1437    </t>
1438  </list>
1439</t>
1440<t>
1441   Since there is no way to distinguish a successfully completed,
1442   close-delimited message from a partially-received message interrupted
1443   by network failure, implementations SHOULD use encoding or
1444   length-delimited messages whenever possible.  The close-delimiting
1445   feature exists primarily for backwards compatibility with HTTP/1.0.
1446</t>
1447<t>
1448   A server MAY reject a request that contains a message-body but
1449   not a Content-Length by responding with 411 (Length Required).
1450</t>
1451<t>
1452   Unless a transfer-coding other than "chunked" has been applied,
1453   a client that sends a request containing a message-body SHOULD
1454   use a valid Content-Length header field if the message-body length
1455   is known in advance, rather than the "chunked" encoding, since some
1456   existing services respond to "chunked" with a 411 (Length Required)
1457   status code even though they understand the chunked encoding.  This
1458   is typically because such services are implemented via a gateway that
1459   requires a content-length in advance of being called and the server
1460   is unable or unwilling to buffer the entire request before processing.
1461</t>
1462<t>
1463   A client that sends a request containing a message-body MUST include a
1464   valid Content-Length header field if it does not know the server will
1465   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1466   of specific user configuration or by remembering the version of a prior
1467   received response.
1468</t>
1469<t>
1470   Request messages that are prematurely terminated, possibly due to a
1471   cancelled connection or a server-imposed time-out exception, MUST
1472   result in closure of the connection; sending an HTTP/1.1 error response
1473   prior to closing the connection is OPTIONAL.
1474   Response messages that are prematurely terminated, usually by closure
1475   of the connection prior to receiving the expected number of octets or by
1476   failure to decode a transfer-encoded message-body, MUST be recorded
1477   as incomplete.  A user agent MUST NOT render an incomplete response
1478   message-body as if it were complete (i.e., some indication must be given
1479   to the user that an error occurred).  Cache requirements for incomplete
1480   responses are defined in Section 2.1.1 of <xref target="Part6"/>.
1481</t>
1482<t>
1483   A server MUST read the entire request message-body or close
1484   the connection after sending its response, since otherwise the
1485   remaining data on a persistent connection would be misinterpreted
1486   as the next request.  Likewise,
1487   a client MUST read the entire response message-body if it intends
1488   to reuse the same connection for a subsequent request.  Pipelining
1489   multiple requests on a connection is described in <xref target="pipelining"/>.
1490</t>
1491</section>
1492
1493<section title="General Header Fields" anchor="general.header.fields">
1494 
1495<t>
1496   There are a few header fields which have general applicability for
1497   both request and response messages, but which do not apply to the
1498   payload being transferred. These header fields apply only to the
1499   message being transmitted.
1500</t>
1501<texttable align="left">
1502  <ttcol>Header Field Name</ttcol>
1503  <ttcol>Defined in...</ttcol>
1504 
1505  <c>Connection</c> <c><xref target="header.connection"/></c>
1506  <c>Date</c> <c><xref target="header.date"/></c>
1507  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1508  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1509  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1510  <c>Via</c> <c><xref target="header.via"/></c>
1511</texttable>
1512</section>
1513</section>
1514
1515<section title="Request" anchor="request">
1516 
1517<t>
1518   A request message from a client to a server begins with a
1519   Request-Line, followed by zero or more header fields, an empty
1520   line signifying the end of the header block, and an optional
1521   message body.
1522</t>
1523<!--                 Host                      ; should be moved here eventually -->
1524<figure><iref primary="true" item="Grammar" subitem="Request"/><artwork type="abnf2616"><![CDATA[
1525  Request       = Request-Line              ; Section 4.1
1526                  *( header-field CRLF )    ; Section 3.2
1527                  CRLF
1528                  [ message-body ]          ; Section 3.3
1529]]></artwork></figure>
1530
1531<section title="Request-Line" anchor="request-line">
1532 
1533<t>
1534   The Request-Line begins with a method token, followed by a single
1535   space (SP), the request-target, another single space (SP), the
1536   protocol version, and ending with CRLF.
1537</t>
1538<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1539  Request-Line   = Method SP request-target SP HTTP-Version CRLF
1540]]></artwork></figure>
1541
1542<section title="Method" anchor="method">
1543 
1544<t>
1545   The Method token indicates the request method to be performed on the
1546   target resource. The request method is case-sensitive.
1547</t>
1548<figure><iref primary="true" item="Grammar" subitem="Method"/><artwork type="abnf2616"><![CDATA[
1549  Method         = token
1550]]></artwork></figure>
1551</section>
1552
1553<section title="request-target" anchor="request-target">
1554 
1555<t>
1556   The request-target identifies the target resource upon which to apply
1557   the request.  In most cases, the user agent is provided a URI reference
1558   from which it determines an absolute URI for identifying the target
1559   resource.  When a request to the resource is initiated, all or part
1560   of that URI is used to construct the HTTP request-target.
1561</t>
1562<figure><iref primary="true" item="Grammar" subitem="request-target"/><artwork type="abnf2616"><![CDATA[
1563  request-target = "*"
1564                 / absolute-URI
1565                 / ( path-absolute [ "?" query ] )
1566                 / authority
1567]]></artwork></figure>
1568<t>
1569   The four options for request-target are dependent on the nature of the
1570   request.
1571</t>   
1572<t><iref item="asterisk form (of request-target)"/>
1573   The asterisk "*" form of request-target, which MUST NOT be used
1574   with any request method other than OPTIONS, means that the request
1575   applies to the server as a whole (the listening process) rather than
1576   to a specific named resource at that server.  For example,
1577</t>
1578<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1579  OPTIONS * HTTP/1.1
1580  ]]></artwork></figure>
1581<t><iref item="absolute-URI form (of request-target)"/>
1582   The "absolute-URI" form is REQUIRED when the request is being made to a
1583   proxy. The proxy is requested to either forward the request or service it
1584   from a valid cache, and then return the response. Note that the proxy MAY
1585   forward the request on to another proxy or directly to the server
1586   specified by the absolute-URI. In order to avoid request loops, a
1587   proxy that forwards requests to other proxies MUST be able to
1588   recognize and exclude all of its own server names, including
1589   any aliases, local variations, and the numeric IP address. An example
1590   Request-Line would be:
1591</t>
1592<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1593  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1594  ]]></artwork></figure>
1595<t>
1596   To allow for transition to absolute-URIs in all requests in future
1597   versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
1598   form in requests, even though HTTP/1.1 clients will only generate
1599   them in requests to proxies.
1600</t>
1601<t>
1602   If a proxy receives a host name that is not a fully qualified domain
1603   name, it MAY add its domain to the host name it received. If a proxy
1604   receives a fully qualified domain name, the proxy MUST NOT change
1605   the host name.
1606</t>
1607<t><iref item="authority form (of request-target)"/>
1608   The "authority form" is only used by the CONNECT request method (Section 7.9 of <xref target="Part2"/>).
1609</t>
1610<t><iref item="origin form (of request-target)"/>
1611   The most common form of request-target is that used when making
1612   a request to an origin server ("origin form").
1613   In this case, the absolute path and query components of the URI
1614   MUST be transmitted as the request-target, and the authority component
1615   MUST be transmitted in a Host header field. For example, a client wishing
1616   to retrieve a representation of the resource, as identified above,
1617   directly from the origin server would open (or reuse) a TCP connection
1618   to port 80 of the host "www.example.org" and send the lines:
1619</t>
1620<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1621  GET /pub/WWW/TheProject.html HTTP/1.1
1622  Host: www.example.org
1623  ]]></artwork></figure>
1624<t>
1625   followed by the remainder of the Request. Note that the origin form
1626   of request-target always starts with an absolute path; if the target
1627   resource's URI path is empty, then an absolute path of "/" MUST be
1628   provided in the request-target.
1629</t>
1630<t>
1631   If a proxy receives an OPTIONS request with an absolute-URI form of
1632   request-target in which the URI has an empty path and no query component,
1633   then the last proxy on the request chain MUST use a request-target
1634   of "*" when it forwards the request to the indicated origin server.
1635</t>
1636<figure><preamble>  
1637   For example, the request
1638</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1639  OPTIONS http://www.example.org:8001 HTTP/1.1
1640  ]]></artwork></figure>
1641<figure><preamble>  
1642  would be forwarded by the final proxy as
1643</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1644  OPTIONS * HTTP/1.1
1645  Host: www.example.org:8001
1646  ]]></artwork>
1647<postamble>
1648   after connecting to port 8001 of host "www.example.org".
1649</postamble>
1650</figure>
1651<t>
1652   The request-target is transmitted in the format specified in
1653   <xref target="http.uri"/>. If the request-target is percent-encoded
1654   (<xref target="RFC3986"/>, Section 2.1), the origin server
1655   MUST decode the request-target in order to
1656   properly interpret the request. Servers SHOULD respond to invalid
1657   request-targets with an appropriate status code.
1658</t>
1659<t>
1660   A non-transforming proxy MUST NOT rewrite the "path-absolute" part of the
1661   received request-target when forwarding it to the next inbound server,
1662   except as noted above to replace a null path-absolute with "/" or "*".
1663</t>
1664<t><list>
1665  <t>
1666    Note: The "no rewrite" rule prevents the proxy from changing the
1667    meaning of the request when the origin server is improperly using
1668    a non-reserved URI character for a reserved purpose.  Implementors
1669    need to be aware that some pre-HTTP/1.1 proxies have been known to
1670    rewrite the request-target.
1671  </t>
1672</list></t>
1673<t>
1674   HTTP does not place a pre-defined limit on the length of a request-target.
1675   A server MUST be prepared to receive URIs of unbounded length and
1676   respond with the 414 (URI Too Long) status code if the received
1677   request-target would be longer than the server wishes to handle
1678   (see Section 8.4.15 of <xref target="Part2"/>).
1679</t>
1680<t>
1681   Various ad-hoc limitations on request-target length are found in practice.
1682   It is RECOMMENDED that all HTTP senders and recipients support
1683   request-target lengths of 8000 or more octets.
1684</t>
1685<t><list>
1686  <t>
1687    Note: Fragments (<xref target="RFC3986"/>, Section 3.5)
1688    are not part of the request-target and thus will not be transmitted
1689    in an HTTP request.
1690  </t>
1691</list></t>
1692</section>
1693</section>
1694
1695<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1696<t>
1697   The exact resource identified by an Internet request is determined by
1698   examining both the request-target and the Host header field.
1699</t>
1700<t>
1701   An origin server that does not allow resources to differ by the
1702   requested host MAY ignore the Host header field value when
1703   determining the resource identified by an HTTP/1.1 request. (But see
1704   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1705   for other requirements on Host support in HTTP/1.1.)
1706</t>
1707<t>
1708   An origin server that does differentiate resources based on the host
1709   requested (sometimes referred to as virtual hosts or vanity host
1710   names) MUST use the following rules for determining the requested
1711   resource on an HTTP/1.1 request:
1712  <list style="numbers">
1713    <t>If request-target is an absolute-URI, the host is part of the
1714     request-target. Any Host header field value in the request MUST be
1715     ignored.</t>
1716    <t>If the request-target is not an absolute-URI, and the request includes
1717     a Host header field, the host is determined by the Host header
1718     field value.</t>
1719    <t>If the host as determined by rule 1 or 2 is not a valid host on
1720     the server, the response MUST be a 400 (Bad Request) error message.</t>
1721  </list>
1722</t>
1723<t>
1724   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1725   attempt to use heuristics (e.g., examination of the URI path for
1726   something unique to a particular host) in order to determine what
1727   exact resource is being requested.
1728</t>
1729</section>
1730
1731<section title="Effective Request URI" anchor="effective.request.uri">
1732  <iref primary="true" item="effective request URI"/>
1733  <iref primary="true" item="target resource"/>
1734<t>
1735   HTTP requests often do not carry the absolute URI (<xref target="RFC3986"/>, Section 4.3)
1736   for the target resource; instead, the URI needs to be inferred from the
1737   request-target, Host header field, and connection context. The result of
1738   this process is called the "effective request URI".  The "target resource"
1739   is the resource identified by the effective request URI.
1740</t>
1741<t>
1742   If the request-target is an absolute-URI, then the effective request URI is
1743   the request-target.
1744</t>
1745<t>
1746   If the request-target uses the path-absolute form or the asterisk form,
1747   and the Host header field is present, then the effective request URI is
1748   constructed by concatenating
1749</t>
1750<t>
1751  <list style="symbols">
1752    <t>
1753      the scheme name: "http" if the request was received over an insecure
1754      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1755      connection,
1756    </t>
1757    <t>
1758      the octet sequence "://",
1759    </t>
1760    <t>
1761      the authority component, as specified in the Host header field
1762      (<xref target="header.host"/>), and
1763    </t>
1764    <t>
1765      the request-target obtained from the Request-Line, unless the
1766      request-target is just the asterisk "*".
1767    </t>
1768  </list>
1769</t>
1770<t>
1771   If the request-target uses the path-absolute form or the asterisk form,
1772   and the Host header field is not present, then the effective request URI is
1773   undefined.
1774</t>
1775<t>
1776   Otherwise, when request-target uses the authority form, the effective
1777   request URI is undefined.
1778</t>
1779<figure>
1780<preamble>
1781   Example 1: the effective request URI for the message
1782</preamble>
1783<artwork type="example"><![CDATA[
1784  GET /pub/WWW/TheProject.html HTTP/1.1
1785  Host: www.example.org:8080
1786  ]]></artwork>
1787<postamble>
1788  (received over an insecure TCP connection) is "http", plus "://", plus the
1789  authority component "www.example.org:8080", plus the request-target
1790  "/pub/WWW/TheProject.html", thus
1791  "http://www.example.org:8080/pub/WWW/TheProject.html".
1792</postamble>
1793</figure>
1794<figure>
1795<preamble>
1796   Example 2: the effective request URI for the message
1797</preamble>
1798<artwork type="example"><![CDATA[
1799  GET * HTTP/1.1
1800  Host: www.example.org
1801  ]]></artwork>
1802<postamble>
1803  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1804  authority component "www.example.org", thus "https://www.example.org".
1805</postamble>
1806</figure>
1807<t>
1808   Effective request URIs are compared using the rules described in
1809   <xref target="uri.comparison"/>, except that empty path components MUST NOT
1810   be treated as equivalent to an absolute path of "/".
1811</t> 
1812</section>
1813
1814</section>
1815
1816
1817<section title="Response" anchor="response">
1818 
1819<t>
1820   After receiving and interpreting a request message, a server responds
1821   with an HTTP response message.
1822</t>
1823<figure><iref primary="true" item="Grammar" subitem="Response"/><artwork type="abnf2616"><![CDATA[
1824  Response      = Status-Line               ; Section 5.1
1825                  *( header-field CRLF )    ; Section 3.2
1826                  CRLF
1827                  [ message-body ]          ; Section 3.3
1828]]></artwork></figure>
1829
1830<section title="Status-Line" anchor="status-line">
1831 
1832<t>
1833   The first line of a Response message is the Status-Line, consisting
1834   of the protocol version, a space (SP), the status code, another space,
1835   a possibly-empty textual phrase describing the status code, and
1836   ending with CRLF.
1837</t>
1838<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1839  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1840]]></artwork></figure>
1841
1842<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1843 
1844 
1845<t>
1846   The Status-Code element is a 3-digit integer result code of the
1847   attempt to understand and satisfy the request. These codes are fully
1848   defined in Section 8 of <xref target="Part2"/>.  The Reason Phrase exists for the sole
1849   purpose of providing a textual description associated with the numeric
1850   status code, out of deference to earlier Internet application protocols
1851   that were more frequently used with interactive text clients.
1852   A client SHOULD ignore the content of the Reason Phrase.
1853</t>
1854<t>
1855   The first digit of the Status-Code defines the class of response. The
1856   last two digits do not have any categorization role. There are 5
1857   values for the first digit:
1858  <list style="symbols">
1859    <t>
1860      1xx: Informational - Request received, continuing process
1861    </t>
1862    <t>
1863      2xx: Success - The action was successfully received,
1864        understood, and accepted
1865    </t>
1866    <t>
1867      3xx: Redirection - Further action must be taken in order to
1868        complete the request
1869    </t>
1870    <t>
1871      4xx: Client Error - The request contains bad syntax or cannot
1872        be fulfilled
1873    </t>
1874    <t>
1875      5xx: Server Error - The server failed to fulfill an apparently
1876        valid request
1877    </t>
1878  </list>
1879</t>
1880<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
1881  Status-Code    = 3DIGIT
1882  Reason-Phrase  = *( WSP / VCHAR / obs-text )
1883]]></artwork></figure>
1884</section>
1885</section>
1886
1887</section>
1888
1889
1890<section title="Protocol Parameters" anchor="protocol.parameters">
1891
1892<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1893 
1894<t>
1895   HTTP applications have historically allowed three different formats
1896   for date/time stamps. However, the preferred format is a fixed-length subset
1897   of that defined by <xref target="RFC1123"/>:
1898</t>
1899<figure><artwork type="example"><![CDATA[
1900  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1901  ]]></artwork></figure>
1902<t>
1903   The other formats are described here only for compatibility with obsolete
1904   implementations.
1905</t>
1906<figure><artwork type="example"><![CDATA[
1907  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1908  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1909  ]]></artwork></figure>
1910<t>
1911   HTTP/1.1 clients and servers that parse a date value MUST accept
1912   all three formats (for compatibility with HTTP/1.0), though they MUST
1913   only generate the RFC 1123 format for representing HTTP-date values
1914   in header fields. See <xref target="tolerant.applications"/> for further information.
1915</t>
1916<t>
1917   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
1918   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1919   equal to UTC (Coordinated Universal Time). This is indicated in the
1920   first two formats by the inclusion of "GMT" as the three-letter
1921   abbreviation for time zone, and MUST be assumed when reading the
1922   asctime format. HTTP-date is case sensitive and MUST NOT include
1923   additional whitespace beyond that specifically included as SP in the
1924   grammar.
1925</t>
1926<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><artwork type="abnf2616"><![CDATA[
1927  HTTP-date    = rfc1123-date / obs-date
1928]]></artwork></figure>
1929<t anchor="preferred.date.format">
1930 
1931 
1932 
1933 
1934 
1935 
1936 
1937 
1938 
1939 
1940  Preferred format:
1941</t>
1942<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[
1943  rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
1944  ; fixed length subset of the format defined in
1945  ; Section 5.2.14 of [RFC1123]
1946 
1947  day-name     = %x4D.6F.6E ; "Mon", case-sensitive
1948               / %x54.75.65 ; "Tue", case-sensitive
1949               / %x57.65.64 ; "Wed", case-sensitive
1950               / %x54.68.75 ; "Thu", case-sensitive
1951               / %x46.72.69 ; "Fri", case-sensitive
1952               / %x53.61.74 ; "Sat", case-sensitive
1953               / %x53.75.6E ; "Sun", case-sensitive
1954               
1955  date1        = day SP month SP year
1956               ; e.g., 02 Jun 1982
1957
1958  day          = 2DIGIT
1959  month        = %x4A.61.6E ; "Jan", case-sensitive
1960               / %x46.65.62 ; "Feb", case-sensitive
1961               / %x4D.61.72 ; "Mar", case-sensitive
1962               / %x41.70.72 ; "Apr", case-sensitive
1963               / %x4D.61.79 ; "May", case-sensitive
1964               / %x4A.75.6E ; "Jun", case-sensitive
1965               / %x4A.75.6C ; "Jul", case-sensitive
1966               / %x41.75.67 ; "Aug", case-sensitive
1967               / %x53.65.70 ; "Sep", case-sensitive
1968               / %x4F.63.74 ; "Oct", case-sensitive
1969               / %x4E.6F.76 ; "Nov", case-sensitive
1970               / %x44.65.63 ; "Dec", case-sensitive
1971  year         = 4DIGIT
1972
1973  GMT   = %x47.4D.54 ; "GMT", case-sensitive
1974
1975  time-of-day  = hour ":" minute ":" second
1976                 ; 00:00:00 - 23:59:59
1977                 
1978  hour         = 2DIGIT               
1979  minute       = 2DIGIT               
1980  second       = 2DIGIT               
1981]]></artwork></figure>
1982<t>
1983  The semantics of <xref target="preferred.date.format" format="none">day-name</xref>, <xref target="preferred.date.format" format="none">day</xref>,
1984  <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
1985  same as those defined for the RFC 5322 constructs
1986  with the corresponding name (<xref target="RFC5322"/>, Section 3.3).
1987</t>
1988<t anchor="obsolete.date.formats">
1989 
1990 
1991 
1992 
1993 
1994 
1995 
1996 
1997  Obsolete formats:
1998</t>
1999<figure><iref primary="true" item="Grammar" subitem="obs-date"/><artwork type="abnf2616"><![CDATA[
2000  obs-date     = rfc850-date / asctime-date
2001]]></artwork></figure>
2002<figure><iref primary="true" item="Grammar" subitem="rfc850-date"/><artwork type="abnf2616"><![CDATA[
2003  rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
2004  date2        = day "-" month "-" 2DIGIT
2005                 ; day-month-year (e.g., 02-Jun-82)
2006
2007  day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
2008         / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
2009         / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
2010         / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
2011         / %x46.72.69.64.61.79 ; "Friday", case-sensitive
2012         / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
2013         / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
2014]]></artwork></figure>
2015<figure><iref primary="true" item="Grammar" subitem="asctime-date"/><artwork type="abnf2616"><![CDATA[
2016  asctime-date = day-name SP date3 SP time-of-day SP year
2017  date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
2018                 ; month day (e.g., Jun  2)
2019]]></artwork></figure>
2020<t><list>
2021  <t>
2022    Note: Recipients of date values are encouraged to be robust in
2023    accepting date values that might have been sent by non-HTTP
2024    applications, as is sometimes the case when retrieving or posting
2025    messages via proxies/gateways to SMTP or NNTP.
2026  </t>
2027</list></t>
2028<t><list>
2029  <t>
2030    Note: HTTP requirements for the date/time stamp format apply only
2031    to their usage within the protocol stream. Clients and servers are
2032    not required to use these formats for user presentation, request
2033    logging, etc.
2034  </t>
2035</list></t>
2036</section>
2037
2038<section title="Transfer Codings" anchor="transfer.codings">
2039 
2040 
2041<t>
2042   Transfer-coding values are used to indicate an encoding
2043   transformation that has been, can be, or might need to be applied to a
2044   payload body in order to ensure "safe transport" through the network.
2045   This differs from a content coding in that the transfer-coding is a
2046   property of the message rather than a property of the representation
2047   that is being transferred.
2048</t>
2049<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
2050  transfer-coding         = "chunked" ; Section 6.2.1
2051                          / "compress" ; Section 6.2.2.1
2052                          / "deflate" ; Section 6.2.2.2
2053                          / "gzip" ; Section 6.2.2.3
2054                          / transfer-extension
2055  transfer-extension      = token *( OWS ";" OWS transfer-parameter )
2056]]></artwork></figure>
2057<t anchor="rule.parameter">
2058 
2059 
2060 
2061   Parameters are in the form of attribute/value pairs.
2062</t>
2063<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[
2064  transfer-parameter      = attribute BWS "=" BWS value
2065  attribute               = token
2066  value                   = word
2067]]></artwork></figure>
2068<t>
2069   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2070   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2071   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2072</t>
2073<t>
2074   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2075   MIME, which were designed to enable safe transport of binary data over a
2076   7-bit transport service (<xref target="RFC2045"/>, Section 6).
2077   However, safe transport
2078   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2079   the only unsafe characteristic of message-bodies is the difficulty in
2080   determining the exact message body length (<xref target="message.body"/>),
2081   or the desire to encrypt data over a shared transport.
2082</t>
2083<t>
2084   A server that receives a request message with a transfer-coding it does
2085   not understand SHOULD respond with 501 (Not Implemented) and then
2086   close the connection. A server MUST NOT send transfer-codings to an HTTP/1.0
2087   client.
2088</t>
2089
2090<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2091  <iref item="chunked (Coding Format)"/>
2092  <iref item="Coding Format" subitem="chunked"/>
2093 
2094 
2095 
2096 
2097 
2098 
2099 
2100 
2101 
2102 
2103 
2104<t>
2105   The chunked encoding modifies the body of a message in order to
2106   transfer it as a series of chunks, each with its own size indicator,
2107   followed by an OPTIONAL trailer containing header fields. This
2108   allows dynamically produced content to be transferred along with the
2109   information necessary for the recipient to verify that it has
2110   received the full message.
2111</t>
2112<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[
2113  Chunked-Body   = *chunk
2114                   last-chunk
2115                   trailer-part
2116                   CRLF
2117 
2118  chunk          = chunk-size *WSP [ chunk-ext ] CRLF
2119                   chunk-data CRLF
2120  chunk-size     = 1*HEXDIG
2121  last-chunk     = 1*("0") *WSP [ chunk-ext ] CRLF
2122 
2123  chunk-ext      = *( ";" *WSP chunk-ext-name
2124                      [ "=" chunk-ext-val ] *WSP )
2125  chunk-ext-name = token
2126  chunk-ext-val  = token / quoted-str-nf
2127  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
2128  trailer-part   = *( header-field CRLF )
2129 
2130  quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
2131                 ; like quoted-string, but disallowing line folding
2132  qdtext-nf      = WSP / %x21 / %x23-5B / %x5D-7E / obs-text
2133                 ; WSP / <VCHAR except DQUOTE and "\"> / obs-text
2134]]></artwork></figure>
2135<t>
2136   The chunk-size field is a string of hex digits indicating the size of
2137   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2138   zero, followed by the trailer, which is terminated by an empty line.
2139</t>
2140<t>
2141   The trailer allows the sender to include additional HTTP header
2142   fields at the end of the message. The Trailer header field can be
2143   used to indicate which header fields are included in a trailer (see
2144   <xref target="header.trailer"/>).
2145</t>
2146<t>
2147   A server using chunked transfer-coding in a response MUST NOT use the
2148   trailer for any header fields unless at least one of the following is
2149   true:
2150  <list style="numbers">
2151    <t>the request included a TE header field that indicates "trailers" is
2152     acceptable in the transfer-coding of the  response, as described in
2153     <xref target="header.te"/>; or,</t>
2154     
2155    <t>the trailer fields consist entirely of optional metadata, and the
2156    recipient could use the message (in a manner acceptable to the server where
2157    the field originated) without receiving it. In other words, the server that
2158    generated the header (often but not always the origin server) is willing to
2159    accept the possibility that the trailer fields might be silently discarded
2160    along the path to the client.</t>
2161  </list>
2162</t>
2163<t>
2164   This requirement prevents an interoperability failure when the
2165   message is being received by an HTTP/1.1 (or later) proxy and
2166   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2167   compliance with the protocol would have necessitated a possibly
2168   infinite buffer on the proxy.
2169</t>
2170<t>
2171   A process for decoding the "chunked" transfer-coding
2172   can be represented in pseudo-code as:
2173</t>
2174<figure><artwork type="code"><![CDATA[
2175  length := 0
2176  read chunk-size, chunk-ext (if any) and CRLF
2177  while (chunk-size > 0) {
2178     read chunk-data and CRLF
2179     append chunk-data to decoded-body
2180     length := length + chunk-size
2181     read chunk-size and CRLF
2182  }
2183  read header-field
2184  while (header-field not empty) {
2185     append header-field to existing header fields
2186     read header-field
2187  }
2188  Content-Length := length
2189  Remove "chunked" from Transfer-Encoding
2190]]></artwork></figure>
2191<t>
2192   All HTTP/1.1 applications MUST be able to receive and decode the
2193   "chunked" transfer-coding and MUST ignore chunk-ext extensions
2194   they do not understand.
2195</t>
2196<t>
2197   Since "chunked" is the only transfer-coding required to be understood
2198   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2199   on a persistent connection.  Whenever a transfer-coding is applied to
2200   a payload body in a request, the final transfer-coding applied MUST
2201   be "chunked".  If a transfer-coding is applied to a response payload
2202   body, then either the final transfer-coding applied MUST be "chunked"
2203   or the message MUST be terminated by closing the connection. When the
2204   "chunked" transfer-coding is used, it MUST be the last transfer-coding
2205   applied to form the message-body. The "chunked" transfer-coding MUST NOT
2206   be applied more than once in a message-body.
2207</t>
2208</section>
2209
2210<section title="Compression Codings" anchor="compression.codings">
2211<t>
2212   The codings defined below can be used to compress the payload of a
2213   message.
2214</t>
2215<t><list><t>
2216   Note: Use of program names for the identification of encoding formats
2217   is not desirable and is discouraged for future encodings. Their
2218   use here is representative of historical practice, not good
2219   design.
2220</t></list></t>
2221<t><list><t>
2222   Note: For compatibility with previous implementations of HTTP,
2223   applications SHOULD consider "x-gzip" and "x-compress" to be
2224   equivalent to "gzip" and "compress" respectively.
2225</t></list></t>
2226
2227<section title="Compress Coding" anchor="compress.coding">
2228<iref item="compress (Coding Format)"/>
2229<iref item="Coding Format" subitem="compress"/>
2230<t>
2231   The "compress" format is produced by the common UNIX file compression
2232   program "compress". This format is an adaptive Lempel-Ziv-Welch
2233   coding (LZW).
2234</t>
2235</section>
2236
2237<section title="Deflate Coding" anchor="deflate.coding">
2238<iref item="deflate (Coding Format)"/>
2239<iref item="Coding Format" subitem="deflate"/>
2240<t>
2241   The "deflate" format is defined as the "deflate" compression mechanism
2242   (described in <xref target="RFC1951"/>) used inside the "zlib"
2243   data format (<xref target="RFC1950"/>).
2244</t>
2245<t><list>
2246  <t>
2247    Note: Some incorrect implementations send the "deflate"
2248    compressed data without the zlib wrapper.
2249   </t>
2250</list></t>
2251</section>
2252
2253<section title="Gzip Coding" anchor="gzip.coding">
2254<iref item="gzip (Coding Format)"/>
2255<iref item="Coding Format" subitem="gzip"/>
2256<t>
2257   The "gzip" format is produced by the file compression program
2258   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2259   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2260</t>
2261</section>
2262
2263</section>
2264
2265<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2266<t>
2267   The HTTP Transfer Coding Registry defines the name space for the transfer
2268   coding names.
2269</t>
2270<t>
2271   Registrations MUST include the following fields:
2272   <list style="symbols">
2273     <t>Name</t>
2274     <t>Description</t>
2275     <t>Pointer to specification text</t>
2276   </list>
2277</t>
2278<t>
2279   Names of transfer codings MUST NOT overlap with names of content codings
2280   (Section 2.2 of <xref target="Part3"/>), unless the encoding transformation is identical (as it
2281   is the case for the compression codings defined in
2282   <xref target="compression.codings"/>).
2283</t>
2284<t>
2285   Values to be added to this name space require a specification
2286   (see "Specification Required" in Section 4.1 of <xref target="RFC5226"/>), and MUST
2287   conform to the purpose of transfer coding defined in this section.
2288</t>
2289<t>
2290   The registry itself is maintained at
2291   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2292</t>
2293</section>
2294</section>
2295
2296<section title="Product Tokens" anchor="product.tokens">
2297 
2298 
2299<t>
2300   Product tokens are used to allow communicating applications to
2301   identify themselves by software name and version. Most fields using
2302   product tokens also allow sub-products which form a significant part
2303   of the application to be listed, separated by whitespace. By
2304   convention, the products are listed in order of their significance
2305   for identifying the application.
2306</t>
2307<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
2308  product         = token ["/" product-version]
2309  product-version = token
2310]]></artwork></figure>
2311<t>
2312   Examples:
2313</t>
2314<figure><artwork type="example"><![CDATA[
2315  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2316  Server: Apache/0.8.4
2317]]></artwork></figure>
2318<t>
2319   Product tokens SHOULD be short and to the point. They MUST NOT be
2320   used for advertising or other non-essential information. Although any
2321   token octet MAY appear in a product-version, this token SHOULD
2322   only be used for a version identifier (i.e., successive versions of
2323   the same product SHOULD only differ in the product-version portion of
2324   the product value).
2325</t>
2326</section>
2327
2328<section title="Quality Values" anchor="quality.values">
2329 
2330<t>
2331   Both transfer codings (TE request header field, <xref target="header.te"/>)
2332   and content negotiation (Section 5 of <xref target="Part3"/>) use short "floating point"
2333   numbers to indicate the relative importance ("weight") of various
2334   negotiable parameters.  A weight is normalized to a real number in
2335   the range 0 through 1, where 0 is the minimum and 1 the maximum
2336   value. If a parameter has a quality value of 0, then content with
2337   this parameter is "not acceptable" for the client. HTTP/1.1
2338   applications MUST NOT generate more than three digits after the
2339   decimal point. User configuration of these values SHOULD also be
2340   limited in this fashion.
2341</t>
2342<figure><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
2343  qvalue         = ( "0" [ "." 0*3DIGIT ] )
2344                 / ( "1" [ "." 0*3("0") ] )
2345]]></artwork></figure>
2346<t><list>
2347  <t>
2348     Note: "Quality values" is a misnomer, since these values merely represent
2349     relative degradation in desired quality.
2350  </t>
2351</list></t>
2352</section>
2353
2354</section>
2355
2356<section title="Connections" anchor="connections">
2357
2358<section title="Persistent Connections" anchor="persistent.connections">
2359
2360<section title="Purpose" anchor="persistent.purpose">
2361<t>
2362   Prior to persistent connections, a separate TCP connection was
2363   established for each request, increasing the load on HTTP servers
2364   and causing congestion on the Internet. The use of inline images and
2365   other associated data often requires a client to make multiple
2366   requests of the same server in a short amount of time. Analysis of
2367   these performance problems and results from a prototype
2368   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2369   measurements of actual HTTP/1.1 implementations show good
2370   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2371   T/TCP <xref target="Tou1998"/>.
2372</t>
2373<t>
2374   Persistent HTTP connections have a number of advantages:
2375  <list style="symbols">
2376      <t>
2377        By opening and closing fewer TCP connections, CPU time is saved
2378        in routers and hosts (clients, servers, proxies, gateways,
2379        tunnels, or caches), and memory used for TCP protocol control
2380        blocks can be saved in hosts.
2381      </t>
2382      <t>
2383        HTTP requests and responses can be pipelined on a connection.
2384        Pipelining allows a client to make multiple requests without
2385        waiting for each response, allowing a single TCP connection to
2386        be used much more efficiently, with much lower elapsed time.
2387      </t>
2388      <t>
2389        Network congestion is reduced by reducing the number of packets
2390        caused by TCP opens, and by allowing TCP sufficient time to
2391        determine the congestion state of the network.
2392      </t>
2393      <t>
2394        Latency on subsequent requests is reduced since there is no time
2395        spent in TCP's connection opening handshake.
2396      </t>
2397      <t>
2398        HTTP can evolve more gracefully, since errors can be reported
2399        without the penalty of closing the TCP connection. Clients using
2400        future versions of HTTP might optimistically try a new feature,
2401        but if communicating with an older server, retry with old
2402        semantics after an error is reported.
2403      </t>
2404    </list>
2405</t>
2406<t>
2407   HTTP implementations SHOULD implement persistent connections.
2408</t>
2409</section>
2410
2411<section title="Overall Operation" anchor="persistent.overall">
2412<t>
2413   A significant difference between HTTP/1.1 and earlier versions of
2414   HTTP is that persistent connections are the default behavior of any
2415   HTTP connection. That is, unless otherwise indicated, the client
2416   SHOULD assume that the server will maintain a persistent connection,
2417   even after error responses from the server.
2418</t>
2419<t>
2420   Persistent connections provide a mechanism by which a client and a
2421   server can signal the close of a TCP connection. This signaling takes
2422   place using the Connection header field (<xref target="header.connection"/>). Once a close
2423   has been signaled, the client MUST NOT send any more requests on that
2424   connection.
2425</t>
2426
2427<section title="Negotiation" anchor="persistent.negotiation">
2428<t>
2429   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
2430   maintain a persistent connection unless a Connection header field including
2431   the connection-token "close" was sent in the request. If the server
2432   chooses to close the connection immediately after sending the
2433   response, it SHOULD send a Connection header field including the
2434   connection-token "close".
2435</t>
2436<t>
2437   An HTTP/1.1 client MAY expect a connection to remain open, but would
2438   decide to keep it open based on whether the response from a server
2439   contains a Connection header field with the connection-token close. In case
2440   the client does not want to maintain a connection for more than that
2441   request, it SHOULD send a Connection header field including the
2442   connection-token close.
2443</t>
2444<t>
2445   If either the client or the server sends the close token in the
2446   Connection header field, that request becomes the last one for the
2447   connection.
2448</t>
2449<t>
2450   Clients and servers SHOULD NOT  assume that a persistent connection is
2451   maintained for HTTP versions less than 1.1 unless it is explicitly
2452   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2453   compatibility with HTTP/1.0 clients.
2454</t>
2455<t>
2456   In order to remain persistent, all messages on the connection MUST
2457   have a self-defined message length (i.e., one not defined by closure
2458   of the connection), as described in <xref target="message.body"/>.
2459</t>
2460</section>
2461
2462<section title="Pipelining" anchor="pipelining">
2463<t>
2464   A client that supports persistent connections MAY "pipeline" its
2465   requests (i.e., send multiple requests without waiting for each
2466   response). A server MUST send its responses to those requests in the
2467   same order that the requests were received.
2468</t>
2469<t>
2470   Clients which assume persistent connections and pipeline immediately
2471   after connection establishment SHOULD be prepared to retry their
2472   connection if the first pipelined attempt fails. If a client does
2473   such a retry, it MUST NOT pipeline before it knows the connection is
2474   persistent. Clients MUST also be prepared to resend their requests if
2475   the server closes the connection before sending all of the
2476   corresponding responses.
2477</t>
2478<t>
2479   Clients SHOULD NOT pipeline requests using non-idempotent request methods or
2480   non-idempotent sequences of request methods (see Section 7.1.2 of <xref target="Part2"/>). Otherwise, a
2481   premature termination of the transport connection could lead to
2482   indeterminate results. A client wishing to send a non-idempotent
2483   request SHOULD wait to send that request until it has received the
2484   response status line for the previous request.
2485</t>
2486</section>
2487</section>
2488
2489<section title="Proxy Servers" anchor="persistent.proxy">
2490<t>
2491   It is especially important that proxies correctly implement the
2492   properties of the Connection header field as specified in <xref target="header.connection"/>.
2493</t>
2494<t>
2495   The proxy server MUST signal persistent connections separately with
2496   its clients and the origin servers (or other proxy servers) that it
2497   connects to. Each persistent connection applies to only one transport
2498   link.
2499</t>
2500<t>
2501   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
2502   with an HTTP/1.0 client (but see Section 19.7.1 of <xref target="RFC2068"/>
2503   for information and discussion of the problems with the Keep-Alive header field
2504   implemented by many HTTP/1.0 clients).
2505</t>
2506
2507<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2508<!--<t>
2509  <cref anchor="TODO-end-to-end" source="jre">
2510    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2511    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2512  </cref>
2513</t>-->
2514<t>
2515   For the purpose of defining the behavior of caches and non-caching
2516   proxies, we divide HTTP header fields into two categories:
2517  <list style="symbols">
2518      <t>End-to-end header fields, which are  transmitted to the ultimate
2519        recipient of a request or response. End-to-end header fields in
2520        responses MUST be stored as part of a cache entry and MUST be
2521        transmitted in any response formed from a cache entry.</t>
2522
2523      <t>Hop-by-hop header fields, which are meaningful only for a single
2524        transport-level connection, and are not stored by caches or
2525        forwarded by proxies.</t>
2526  </list>
2527</t>
2528<t>
2529   The following HTTP/1.1 header fields are hop-by-hop header fields:
2530  <list style="symbols">
2531      <t>Connection</t>
2532      <t>Keep-Alive</t>
2533      <t>Proxy-Authenticate</t>
2534      <t>Proxy-Authorization</t>
2535      <t>TE</t>
2536      <t>Trailer</t>
2537      <t>Transfer-Encoding</t>
2538      <t>Upgrade</t>
2539  </list>
2540</t>
2541<t>
2542   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2543</t>
2544<t>
2545   Other hop-by-hop header fields MUST be listed in a Connection header field
2546   (<xref target="header.connection"/>).
2547</t>
2548</section>
2549
2550<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2551<!--<t>
2552  <cref anchor="TODO-non-mod-headers" source="jre">
2553    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2554    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2555  </cref>
2556</t>-->
2557<t>
2558   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2559   value of certain end-to-end header fields. A non-transforming proxy SHOULD NOT
2560   modify an end-to-end header field unless the definition of that header field requires
2561   or specifically allows that.
2562</t>
2563<t>
2564   A non-transforming proxy MUST NOT modify any of the following fields in a
2565   request or response, and it MUST NOT add any of these fields if not
2566   already present:
2567  <list style="symbols">
2568      <t>Content-Location</t>
2569      <t>Content-MD5</t>
2570      <t>ETag</t>
2571      <t>Last-Modified</t>
2572  </list>
2573</t>
2574<t>
2575   A non-transforming proxy MUST NOT modify any of the following fields in a
2576   response:
2577  <list style="symbols">
2578    <t>Expires</t>
2579  </list>
2580</t>
2581<t>
2582   but it MAY add any of these fields if not already present. If an
2583   Expires header field is added, it MUST be given a field-value identical to
2584   that of the Date header field in that response.
2585</t>
2586<t>
2587   A proxy MUST NOT modify or add any of the following fields in a
2588   message that contains the no-transform cache-control directive, or in
2589   any request:
2590  <list style="symbols">
2591    <t>Content-Encoding</t>
2592    <t>Content-Range</t>
2593    <t>Content-Type</t>
2594  </list>
2595</t>
2596<t>
2597   A transforming proxy MAY modify or add these fields to a message
2598   that does not include no-transform, but if it does so, it MUST add a
2599   Warning 214 (Transformation applied) if one does not already appear
2600   in the message (see Section 3.6 of <xref target="Part6"/>).
2601</t>
2602<t><list>
2603  <t>
2604    Warning: Unnecessary modification of end-to-end header fields might
2605    cause authentication failures if stronger authentication
2606    mechanisms are introduced in later versions of HTTP. Such
2607    authentication mechanisms MAY rely on the values of header fields
2608    not listed here.
2609  </t>
2610</list></t>
2611<t>
2612   A non-transforming proxy MUST preserve the message payload (<xref target="Part3"/>),
2613   though it MAY change the message-body through application or removal
2614   of a transfer-coding (<xref target="transfer.codings"/>).
2615</t>
2616</section>
2617
2618</section>
2619
2620<section title="Practical Considerations" anchor="persistent.practical">
2621<t>
2622   Servers will usually have some time-out value beyond which they will
2623   no longer maintain an inactive connection. Proxy servers might make
2624   this a higher value since it is likely that the client will be making
2625   more connections through the same server. The use of persistent
2626   connections places no requirements on the length (or existence) of
2627   this time-out for either the client or the server.
2628</t>
2629<t>
2630   When a client or server wishes to time-out it SHOULD issue a graceful
2631   close on the transport connection. Clients and servers SHOULD both
2632   constantly watch for the other side of the transport close, and
2633   respond to it as appropriate. If a client or server does not detect
2634   the other side's close promptly it could cause unnecessary resource
2635   drain on the network.
2636</t>
2637<t>
2638   A client, server, or proxy MAY close the transport connection at any
2639   time. For example, a client might have started to send a new request
2640   at the same time that the server has decided to close the "idle"
2641   connection. From the server's point of view, the connection is being
2642   closed while it was idle, but from the client's point of view, a
2643   request is in progress.
2644</t>
2645<t>
2646   This means that clients, servers, and proxies MUST be able to recover
2647   from asynchronous close events. Client software SHOULD reopen the
2648   transport connection and retransmit the aborted sequence of requests
2649   without user interaction so long as the request sequence is
2650   idempotent (see Section 7.1.2 of <xref target="Part2"/>). Non-idempotent request methods or sequences
2651   MUST NOT be automatically retried, although user agents MAY offer a
2652   human operator the choice of retrying the request(s). Confirmation by
2653   user-agent software with semantic understanding of the application
2654   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2655   be repeated if the second sequence of requests fails.
2656</t>
2657<t>
2658   Servers SHOULD always respond to at least one request per connection,
2659   if at all possible. Servers SHOULD NOT  close a connection in the
2660   middle of transmitting a response, unless a network or client failure
2661   is suspected.
2662</t>
2663<t>
2664   Clients (including proxies) SHOULD limit the number of simultaneous
2665   connections that they maintain to a given server (including proxies).
2666</t>
2667<t>
2668   Previous revisions of HTTP gave a specific number of connections as a
2669   ceiling, but this was found to be impractical for many applications. As a
2670   result, this specification does not mandate a particular maximum number of
2671   connections, but instead encourages clients to be conservative when opening
2672   multiple connections.
2673</t>
2674<t>
2675   In particular, while using multiple connections avoids the "head-of-line
2676   blocking" problem (whereby a request that takes significant server-side
2677   processing and/or has a large payload can block subsequent requests on the
2678   same connection), each connection used consumes server resources (sometimes
2679   significantly), and furthermore using multiple connections can cause
2680   undesirable side effects in congested networks.
2681</t>
2682<t>
2683   Note that servers might reject traffic that they deem abusive, including an
2684   excessive number of connections from a client.
2685</t>
2686</section>
2687</section>
2688
2689<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2690
2691<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2692<t>
2693   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2694   flow control mechanisms to resolve temporary overloads, rather than
2695   terminating connections with the expectation that clients will retry.
2696   The latter technique can exacerbate network congestion.
2697</t>
2698</section>
2699
2700<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2701<t>
2702   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2703   the network connection for an error status code while it is transmitting
2704   the request. If the client sees an error status code, it SHOULD
2705   immediately cease transmitting the body. If the body is being sent
2706   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2707   empty trailer MAY be used to prematurely mark the end of the message.
2708   If the body was preceded by a Content-Length header field, the client MUST
2709   close the connection.
2710</t>
2711</section>
2712
2713<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2714<t>
2715   The purpose of the 100 (Continue) status code (see Section 8.1.1 of <xref target="Part2"/>) is to
2716   allow a client that is sending a request message with a request body
2717   to determine if the origin server is willing to accept the request
2718   (based on the request header fields) before the client sends the request
2719   body. In some cases, it might either be inappropriate or highly
2720   inefficient for the client to send the body if the server will reject
2721   the message without looking at the body.
2722</t>
2723<t>
2724   Requirements for HTTP/1.1 clients:
2725  <list style="symbols">
2726    <t>
2727        If a client will wait for a 100 (Continue) response before
2728        sending the request body, it MUST send an Expect header
2729        field (Section 9.2 of <xref target="Part2"/>) with the "100-continue" expectation.
2730    </t>
2731    <t>
2732        A client MUST NOT send an Expect header field (Section 9.2 of <xref target="Part2"/>)
2733        with the "100-continue" expectation if it does not intend
2734        to send a request body.
2735    </t>
2736  </list>
2737</t>
2738<t>
2739   Because of the presence of older implementations, the protocol allows
2740   ambiguous situations in which a client might send "Expect: 100-continue"
2741   without receiving either a 417 (Expectation Failed)
2742   or a 100 (Continue) status code. Therefore, when a client sends this
2743   header field to an origin server (possibly via a proxy) from which it
2744   has never seen a 100 (Continue) status code, the client SHOULD NOT 
2745   wait for an indefinite period before sending the request body.
2746</t>
2747<t>
2748   Requirements for HTTP/1.1 origin servers:
2749  <list style="symbols">
2750    <t> Upon receiving a request which includes an Expect header
2751        field with the "100-continue" expectation, an origin server MUST
2752        either respond with 100 (Continue) status code and continue to read
2753        from the input stream, or respond with a final status code. The
2754        origin server MUST NOT wait for the request body before sending
2755        the 100 (Continue) response. If it responds with a final status
2756        code, it MAY close the transport connection or it MAY continue
2757        to read and discard the rest of the request.  It MUST NOT
2758        perform the request method if it returns a final status code.
2759    </t>
2760    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2761        the request message does not include an Expect header
2762        field with the "100-continue" expectation, and MUST NOT send a
2763        100 (Continue) response if such a request comes from an HTTP/1.0
2764        (or earlier) client. There is an exception to this rule: for
2765        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2766        status code in response to an HTTP/1.1 PUT or POST request that does
2767        not include an Expect header field with the "100-continue"
2768        expectation. This exception, the purpose of which is
2769        to minimize any client processing delays associated with an
2770        undeclared wait for 100 (Continue) status code, applies only to
2771        HTTP/1.1 requests, and not to requests with any other HTTP-version
2772        value.
2773    </t>
2774    <t> An origin server MAY omit a 100 (Continue) response if it has
2775        already received some or all of the request body for the
2776        corresponding request.
2777    </t>
2778    <t> An origin server that sends a 100 (Continue) response MUST
2779    ultimately send a final status code, once the request body is
2780        received and processed, unless it terminates the transport
2781        connection prematurely.
2782    </t>
2783    <t> If an origin server receives a request that does not include an
2784        Expect header field with the "100-continue" expectation,
2785        the request includes a request body, and the server responds
2786        with a final status code before reading the entire request body
2787        from the transport connection, then the server SHOULD NOT  close
2788        the transport connection until it has read the entire request,
2789        or until the client closes the connection. Otherwise, the client
2790        might not reliably receive the response message. However, this
2791        requirement is not be construed as preventing a server from
2792        defending itself against denial-of-service attacks, or from
2793        badly broken client implementations.
2794      </t>
2795    </list>
2796</t>
2797<t>
2798   Requirements for HTTP/1.1 proxies:
2799  <list style="symbols">
2800    <t> If a proxy receives a request that includes an Expect header
2801        field with the "100-continue" expectation, and the proxy
2802        either knows that the next-hop server complies with HTTP/1.1 or
2803        higher, or does not know the HTTP version of the next-hop
2804        server, it MUST forward the request, including the Expect header
2805        field.
2806    </t>
2807    <t> If the proxy knows that the version of the next-hop server is
2808        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2809        respond with a 417 (Expectation Failed) status code.
2810    </t>
2811    <t> Proxies SHOULD maintain a cache recording the HTTP version
2812        numbers received from recently-referenced next-hop servers.
2813    </t>
2814    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2815        request message was received from an HTTP/1.0 (or earlier)
2816        client and did not include an Expect header field with
2817        the "100-continue" expectation. This requirement overrides the
2818        general rule for forwarding of 1xx responses (see Section 8.1 of <xref target="Part2"/>).
2819    </t>
2820  </list>
2821</t>
2822</section>
2823
2824<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2825<t>
2826   If an HTTP/1.1 client sends a request which includes a request body,
2827   but which does not include an Expect header field with the
2828   "100-continue" expectation, and if the client is not directly
2829   connected to an HTTP/1.1 origin server, and if the client sees the
2830   connection close before receiving a status line from the server, the
2831   client SHOULD retry the request.  If the client does retry this
2832   request, it MAY use the following "binary exponential backoff"
2833   algorithm to be assured of obtaining a reliable response:
2834  <list style="numbers">
2835    <t>
2836      Initiate a new connection to the server
2837    </t>
2838    <t>
2839      Transmit the request-line, header fields, and the CRLF that
2840      indicates the end of header fields.
2841    </t>
2842    <t>
2843      Initialize a variable R to the estimated round-trip time to the
2844         server (e.g., based on the time it took to establish the
2845         connection), or to a constant value of 5 seconds if the round-trip
2846         time is not available.
2847    </t>
2848    <t>
2849       Compute T = R * (2**N), where N is the number of previous
2850         retries of this request.
2851    </t>
2852    <t>
2853       Wait either for an error response from the server, or for T
2854         seconds (whichever comes first)
2855    </t>
2856    <t>
2857       If no error response is received, after T seconds transmit the
2858         body of the request.
2859    </t>
2860    <t>
2861       If client sees that the connection is closed prematurely,
2862         repeat from step 1 until the request is accepted, an error
2863         response is received, or the user becomes impatient and
2864         terminates the retry process.
2865    </t>
2866  </list>
2867</t>
2868<t>
2869   If at any point an error status code is received, the client
2870  <list style="symbols">
2871      <t>SHOULD NOT  continue and</t>
2872
2873      <t>SHOULD close the connection if it has not completed sending the
2874        request message.</t>
2875    </list>
2876</t>
2877</section>
2878</section>
2879</section>
2880
2881
2882<section title="Miscellaneous notes that might disappear" anchor="misc">
2883<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2884<t>
2885   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2886</t>
2887</section>
2888
2889<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2890<t>
2891   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2892</t>
2893</section>
2894
2895<section title="Interception of HTTP for access control" anchor="http.intercept">
2896<t>
2897   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2898</t>
2899</section>
2900
2901<section title="Use of HTTP by other protocols" anchor="http.others">
2902<t>
2903   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2904   Extensions of HTTP like WebDAV.</cref>
2905</t>
2906
2907</section>
2908<section title="Use of HTTP by media type specification" anchor="http.media">
2909<t>
2910   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2911</t>
2912</section>
2913</section>
2914
2915<section title="Header Field Definitions" anchor="header.field.definitions">
2916<t>
2917   This section defines the syntax and semantics of HTTP header fields
2918   related to message framing and transport protocols.
2919</t>
2920
2921<section title="Connection" anchor="header.connection">
2922  <iref primary="true" item="Connection header field"/>
2923  <iref primary="true" item="Header Fields" subitem="Connection"/>
2924 
2925 
2926 
2927<t>
2928   The "Connection" header field allows the sender to specify
2929   options that are desired only for that particular connection.
2930   Such connection options MUST be removed or replaced before the
2931   message can be forwarded downstream by a proxy or gateway.
2932   This mechanism also allows the sender to indicate which HTTP
2933   header fields used in the message are only intended for the
2934   immediate recipient ("hop-by-hop"), as opposed to all recipients
2935   on the chain ("end-to-end"), enabling the message to be
2936   self-descriptive and allowing future connection-specific extensions
2937   to be deployed in HTTP without fear that they will be blindly
2938   forwarded by previously deployed intermediaries.
2939</t>
2940<t>
2941   The Connection header field's value has the following grammar:
2942</t>
2943<figure><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="Connection-v"/><iref primary="true" item="Grammar" subitem="connection-token"/><artwork type="abnf2616"><![CDATA[
2944  Connection       = "Connection" ":" OWS Connection-v
2945  Connection-v     = 1#connection-token
2946  connection-token = token
2947]]></artwork></figure>
2948<t>
2949   A proxy or gateway MUST parse a received Connection
2950   header field before a message is forwarded and, for each
2951   connection-token in this field, remove any header field(s) from
2952   the message with the same name as the connection-token, and then
2953   remove the Connection header field itself or replace it with the
2954   sender's own connection options for the forwarded message.
2955</t>
2956<t>
2957   A sender MUST NOT include field-names in the Connection header
2958   field-value for fields that are defined as expressing constraints
2959   for all recipients in the request or response chain, such as the
2960   Cache-Control header field (Section 3.2 of <xref target="Part6"/>).
2961</t>
2962<t>
2963   The connection options do not have to correspond to a header field
2964   present in the message, since a connection-specific header field
2965   might not be needed if there are no parameters associated with that
2966   connection option.  Recipients that trigger certain connection
2967   behavior based on the presence of connection options MUST do so
2968   based on the presence of the connection-token rather than only the
2969   presence of the optional header field.  In other words, if the
2970   connection option is received as a header field but not indicated
2971   within the Connection field-value, then the recipient MUST ignore
2972   the connection-specific header field because it has likely been
2973   forwarded by an intermediary that is only partially compliant.
2974</t>
2975<t>
2976   When defining new connection options, specifications ought to
2977   carefully consider existing deployed header fields and ensure
2978   that the new connection-token does not share the same name as
2979   an unrelated header field that might already be deployed.
2980   Defining a new connection-token essentially reserves that potential
2981   field-name for carrying additional information related to the
2982   connection option, since it would be unwise for senders to use
2983   that field-name for anything else.
2984</t>
2985<t>
2986   HTTP/1.1 defines the "close" connection option for the sender to
2987   signal that the connection will be closed after completion of the
2988   response. For example,
2989</t>
2990<figure><artwork type="example"><![CDATA[
2991  Connection: close
2992]]></artwork></figure>
2993<t>
2994   in either the request or the response header fields indicates that
2995   the connection SHOULD NOT  be considered "persistent" (<xref target="persistent.connections"/>)
2996   after the current request/response is complete.
2997</t>
2998<t>
2999   An HTTP/1.1 client that does not support persistent connections MUST
3000   include the "close" connection option in every request message.
3001</t>
3002<t>
3003   An HTTP/1.1 server that does not support persistent connections MUST
3004   include the "close" connection option in every response message that
3005   does not have a 1xx (Informational) status code.
3006</t>
3007</section>
3008
3009<section title="Content-Length" anchor="header.content-length">
3010  <iref primary="true" item="Content-Length header field"/>
3011  <iref primary="true" item="Header Fields" subitem="Content-Length"/>
3012 
3013 
3014<t>
3015   The "Content-Length" header field indicates the size of the
3016   message-body, in decimal number of octets, for any message other than
3017   a response to a HEAD request or a response with a status code of 304.
3018   In the case of a response to a HEAD request, Content-Length indicates
3019   the size of the payload body (not including any potential transfer-coding)
3020   that would have been sent had the request been a GET.
3021   In the case of a 304 (Not Modified) response to a GET request,
3022   Content-Length indicates the size of the payload body (not including
3023   any potential transfer-coding) that would have been sent in a 200 (OK)
3024   response.
3025</t>
3026<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/><artwork type="abnf2616"><![CDATA[
3027  Content-Length   = "Content-Length" ":" OWS 1*Content-Length-v
3028  Content-Length-v = 1*DIGIT
3029]]></artwork></figure>
3030<t>
3031   An example is
3032</t>
3033<figure><artwork type="example"><![CDATA[
3034  Content-Length: 3495
3035]]></artwork></figure>
3036<t>
3037   Implementations SHOULD use this field to indicate the message-body
3038   length when no transfer-coding is being applied and the
3039   payload's body length can be determined prior to being transferred.
3040   <xref target="message.body"/> describes how recipients determine the length
3041   of a message-body.
3042</t>
3043<t>
3044   Any Content-Length greater than or equal to zero is a valid value.
3045</t>
3046<t>
3047   Note that the use of this field in HTTP is significantly different from
3048   the corresponding definition in MIME, where it is an optional field
3049   used within the "message/external-body" content-type.
3050</t>
3051</section>
3052
3053<section title="Date" anchor="header.date">
3054  <iref primary="true" item="Date header field"/>
3055  <iref primary="true" item="Header Fields" subitem="Date"/>
3056 
3057 
3058<t>
3059   The "Date" header field represents the date and time at which
3060   the message was originated, having the same semantics as the Origination
3061   Date Field (orig-date) defined in Section 3.6.1 of <xref target="RFC5322"/>.
3062   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
3063   it MUST be sent in rfc1123-date format.
3064</t>
3065<figure><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/><artwork type="abnf2616"><![CDATA[
3066  Date   = "Date" ":" OWS Date-v
3067  Date-v = HTTP-date
3068]]></artwork></figure>
3069<t>
3070   An example is
3071</t>
3072<figure><artwork type="example"><![CDATA[
3073  Date: Tue, 15 Nov 1994 08:12:31 GMT
3074]]></artwork></figure>
3075<t>
3076   Origin servers MUST include a Date header field in all responses,
3077   except in these cases:
3078  <list style="numbers">
3079      <t>If the response status code is 100 (Continue) or 101 (Switching
3080         Protocols), the response MAY include a Date header field, at
3081         the server's option.</t>
3082
3083      <t>If the response status code conveys a server error, e.g., 500
3084         (Internal Server Error) or 503 (Service Unavailable), and it is
3085         inconvenient or impossible to generate a valid Date.</t>
3086
3087      <t>If the server does not have a clock that can provide a
3088         reasonable approximation of the current time, its responses
3089         MUST NOT include a Date header field. In this case, the rules
3090         in <xref target="clockless.origin.server.operation"/> MUST be followed.</t>
3091  </list>
3092</t>
3093<t>
3094   A received message that does not have a Date header field MUST be
3095   assigned one by the recipient if the message will be cached by that
3096   recipient.
3097</t>
3098<t>
3099   Clients can use the Date header field as well; in order to keep request
3100   messages small, they are advised not to include it when it doesn't convey
3101   any useful information (as it is usually the case for requests that do not
3102   contain a payload).
3103</t>
3104<t>
3105   The HTTP-date sent in a Date header field SHOULD NOT  represent a date and
3106   time subsequent to the generation of the message. It SHOULD represent
3107   the best available approximation of the date and time of message
3108   generation, unless the implementation has no means of generating a
3109   reasonably accurate date and time. In theory, the date ought to
3110   represent the moment just before the payload is generated. In
3111   practice, the date can be generated at any time during the message
3112   origination without affecting its semantic value.
3113</t>
3114
3115<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3116<t>
3117   Some origin server implementations might not have a clock available.
3118   An origin server without a clock MUST NOT assign Expires or Last-Modified
3119   values to a response, unless these values were associated
3120   with the resource by a system or user with a reliable clock. It MAY
3121   assign an Expires value that is known, at or before server
3122   configuration time, to be in the past (this allows "pre-expiration"
3123   of responses without storing separate Expires values for each
3124   resource).
3125</t>
3126</section>
3127</section>
3128
3129<section title="Host" anchor="header.host">
3130  <iref primary="true" item="Host header field"/>
3131  <iref primary="true" item="Header Fields" subitem="Host"/>
3132 
3133 
3134<t>
3135   The "Host" header field in a request provides the host and port
3136   information from the target resource's URI, enabling the origin
3137   server to distinguish between resources while servicing requests
3138   for multiple host names on a single IP address.  Since the Host
3139   field-value is critical information for handling a request, it
3140   SHOULD be sent as the first header field following the Request-Line.
3141</t>
3142<figure><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/><artwork type="abnf2616"><![CDATA[
3143  Host   = "Host" ":" OWS Host-v
3144  Host-v = uri-host [ ":" port ] ; Section 2.6.1
3145]]></artwork></figure>
3146<t>
3147   A client MUST send a Host header field in all HTTP/1.1 request
3148   messages.  If the target resource's URI includes an authority
3149   component, then the Host field-value MUST be identical to that
3150   authority component after excluding any userinfo (<xref target="http.uri"/>).
3151   If the authority component is missing or undefined for the target
3152   resource's URI, then the Host header field MUST be sent with an
3153   empty field-value.
3154</t>
3155<t>
3156   For example, a GET request to the origin server for
3157   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3158</t>
3159<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
3160  GET /pub/WWW/ HTTP/1.1
3161  Host: www.example.org
3162  ]]></artwork></figure>
3163<t>
3164   The Host header field MUST be sent in an HTTP/1.1 request even
3165   if the request-target is in the form of an absolute-URI, since this
3166   allows the Host information to be forwarded through ancient HTTP/1.0
3167   proxies that might not have implemented Host.
3168</t>
3169<t>
3170   When an HTTP/1.1 proxy receives a request with a request-target in
3171   the form of an absolute-URI, the proxy MUST ignore the received
3172   Host header field (if any) and instead replace it with the host
3173   information of the request-target.  When a proxy forwards a request,
3174   it MUST generate the Host header field based on the received
3175   absolute-URI rather than the received Host.
3176</t>
3177<t>
3178   Since the Host header field acts as an application-level routing
3179   mechanism, it is a frequent target for malware seeking to poison
3180   a shared cache or redirect a request to an unintended server.
3181   An interception proxy is particularly vulnerable if it relies on
3182   the Host header field value for redirecting requests to internal
3183   servers, or for use as a cache key in a shared cache, without
3184   first verifying that the intercepted connection is targeting a
3185   valid IP address for that host.
3186</t>
3187<t>
3188   A server MUST respond with a 400 (Bad Request) status code to
3189   any HTTP/1.1 request message that lacks a Host header field and
3190   to any request message that contains more than one Host header field
3191   or a Host header field with an invalid field-value.
3192</t>
3193<t>
3194   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3195   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3196   for other requirements relating to Host.
3197</t>
3198</section>
3199
3200<section title="TE" anchor="header.te">
3201  <iref primary="true" item="TE header field"/>
3202  <iref primary="true" item="Header Fields" subitem="TE"/>
3203 
3204 
3205 
3206 
3207 
3208<t>
3209   The "TE" header field indicates what extension transfer-codings
3210   it is willing to accept in the response, and whether or not it is
3211   willing to accept trailer fields in a chunked transfer-coding.
3212</t>
3213<t>
3214   Its value consists of the keyword "trailers" and/or a comma-separated
3215   list of extension transfer-coding names with optional accept
3216   parameters (as described in <xref target="transfer.codings"/>).
3217</t>
3218<figure><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="TE-v"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/><artwork type="abnf2616"><![CDATA[
3219  TE        = "TE" ":" OWS TE-v
3220  TE-v      = #t-codings
3221  t-codings = "trailers" / ( transfer-extension [ te-params ] )
3222  te-params = OWS ";" OWS "q=" qvalue *( te-ext )
3223  te-ext    = OWS ";" OWS token [ "=" word ]
3224]]></artwork></figure>
3225<t>
3226   The presence of the keyword "trailers" indicates that the client is
3227   willing to accept trailer fields in a chunked transfer-coding, as
3228   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3229   transfer-coding values even though it does not itself represent a
3230   transfer-coding.
3231</t>
3232<t>
3233   Examples of its use are:
3234</t>
3235<figure><artwork type="example"><![CDATA[
3236  TE: deflate
3237  TE:
3238  TE: trailers, deflate;q=0.5
3239]]></artwork></figure>
3240<t>
3241   The TE header field only applies to the immediate connection.
3242   Therefore, the keyword MUST be supplied within a Connection header
3243   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3244</t>
3245<t>
3246   A server tests whether a transfer-coding is acceptable, according to
3247   a TE field, using these rules:
3248  <list style="numbers">
3249    <t>The "chunked" transfer-coding is always acceptable. If the
3250         keyword "trailers" is listed, the client indicates that it is
3251         willing to accept trailer fields in the chunked response on
3252         behalf of itself and any downstream clients. The implication is
3253         that, if given, the client is stating that either all
3254         downstream clients are willing to accept trailer fields in the
3255         forwarded response, or that it will attempt to buffer the
3256         response on behalf of downstream recipients.
3257      <vspace blankLines="1"/>
3258         Note: HTTP/1.1 does not define any means to limit the size of a
3259         chunked response such that a client can be assured of buffering
3260         the entire response.</t>
3261    <t>If the transfer-coding being tested is one of the transfer-codings
3262         listed in the TE field, then it is acceptable unless it
3263         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3264         qvalue of 0 means "not acceptable".)</t>
3265    <t>If multiple transfer-codings are acceptable, then the
3266         acceptable transfer-coding with the highest non-zero qvalue is
3267         preferred.  The "chunked" transfer-coding always has a qvalue
3268         of 1.</t>
3269  </list>
3270</t>
3271<t>
3272   If the TE field-value is empty or if no TE field is present, the only
3273   transfer-coding is "chunked". A message with no transfer-coding is
3274   always acceptable.
3275</t>
3276</section>
3277
3278<section title="Trailer" anchor="header.trailer">
3279  <iref primary="true" item="Trailer header field"/>
3280  <iref primary="true" item="Header Fields" subitem="Trailer"/>
3281 
3282 
3283<t>
3284   The "Trailer" header field indicates that the given set of
3285   header fields is present in the trailer of a message encoded with
3286   chunked transfer-coding.
3287</t>
3288<figure><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/><artwork type="abnf2616"><![CDATA[
3289  Trailer   = "Trailer" ":" OWS Trailer-v
3290  Trailer-v = 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 
3319<t>
3320   The "Transfer-Encoding" header field indicates what transfer-codings
3321   (if any) have been applied to the message body. It differs from
3322   Content-Encoding (Section 2.2 of <xref target="Part3"/>) in that transfer-codings are a property
3323   of the message (and therefore are removed by intermediaries), whereas
3324   content-codings are not.
3325</t>
3326<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/><artwork type="abnf2616"><![CDATA[
3327  Transfer-Encoding   = "Transfer-Encoding" ":" OWS
3328                        Transfer-Encoding-v
3329  Transfer-Encoding-v = 1#transfer-coding
3330]]></artwork></figure>
3331<t>
3332   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3333</t>
3334<figure><artwork type="example"><![CDATA[
3335  Transfer-Encoding: chunked
3336]]></artwork></figure>
3337<t>
3338   If multiple encodings have been applied to a representation, the transfer-codings
3339   MUST be listed in the order in which they were applied.
3340   Additional information about the encoding parameters MAY be provided
3341   by other header fields not defined by this specification.
3342</t>
3343<t>
3344   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3345   header field.
3346</t>
3347</section>
3348
3349<section title="Upgrade" anchor="header.upgrade">
3350  <iref primary="true" item="Upgrade header field"/>
3351  <iref primary="true" item="Header Fields" subitem="Upgrade"/>
3352 
3353 
3354<t>
3355   The "Upgrade" header field allows the client to specify what
3356   additional communication protocols it would like to use, if the server
3357   chooses to switch protocols. Servers can use it to indicate what protocols
3358   they are willing to switch to.
3359</t>
3360<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/><artwork type="abnf2616"><![CDATA[
3361  Upgrade   = "Upgrade" ":" OWS Upgrade-v
3362  Upgrade-v = 1#product
3363]]></artwork></figure>
3364<t>
3365   For example,
3366</t>
3367<figure><artwork type="example"><![CDATA[
3368  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3369]]></artwork></figure>
3370<t>
3371   The Upgrade header field is intended to provide a simple mechanism
3372   for transition from HTTP/1.1 to some other, incompatible protocol. It
3373   does so by allowing the client to advertise its desire to use another
3374   protocol, such as a later version of HTTP with a higher major version
3375   number, even though the current request has been made using HTTP/1.1.
3376   This eases the difficult transition between incompatible protocols by
3377   allowing the client to initiate a request in the more commonly
3378   supported protocol while indicating to the server that it would like
3379   to use a "better" protocol if available (where "better" is determined
3380   by the server, possibly according to the nature of the request method
3381   or target resource).
3382</t>
3383<t>
3384   The Upgrade header field only applies to switching application-layer
3385   protocols upon the existing transport-layer connection. Upgrade
3386   cannot be used to insist on a protocol change; its acceptance and use
3387   by the server is optional. The capabilities and nature of the
3388   application-layer communication after the protocol change is entirely
3389   dependent upon the new protocol chosen, although the first action
3390   after changing the protocol MUST be a response to the initial HTTP
3391   request containing the Upgrade header field.
3392</t>
3393<t>
3394   The Upgrade header field only applies to the immediate connection.
3395   Therefore, the upgrade keyword MUST be supplied within a Connection
3396   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3397   HTTP/1.1 message.
3398</t>
3399<t>
3400   The Upgrade header field cannot be used to indicate a switch to a
3401   protocol on a different connection. For that purpose, it is more
3402   appropriate to use a 3xx redirection response (Section 8.3 of <xref target="Part2"/>).
3403</t>
3404<t>
3405   Servers MUST include the "Upgrade" header field in 101 (Switching
3406   Protocols) responses to indicate which protocol(s) are being switched to,
3407   and MUST include it in 426 (Upgrade Required) responses to indicate
3408   acceptable protocols to upgrade to. Servers MAY include it in any other
3409   response to indicate that they are willing to upgrade to one of the
3410   specified protocols.
3411</t>
3412<t>
3413   This specification only defines the protocol name "HTTP" for use by
3414   the family of Hypertext Transfer Protocols, as defined by the HTTP
3415   version rules of <xref target="http.version"/> and future updates to this
3416   specification. Additional tokens can be registered with IANA using the
3417   registration procedure defined below. 
3418</t>
3419
3420<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3421<t>
3422   The HTTP Upgrade Token Registry defines the name space for product
3423   tokens used to identify protocols in the Upgrade header field.
3424   Each registered token is associated with contact information and
3425   an optional set of specifications that details how the connection
3426   will be processed after it has been upgraded.
3427</t>
3428<t>
3429   Registrations are allowed on a First Come First Served basis as
3430   described in Section 4.1 of <xref target="RFC5226"/>. The
3431   specifications need not be IETF documents or be subject to IESG review.
3432   Registrations are subject to the following rules:
3433  <list style="numbers">
3434    <t>A token, once registered, stays registered forever.</t>
3435    <t>The registration MUST name a responsible party for the
3436       registration.</t>
3437    <t>The registration MUST name a point of contact.</t>
3438    <t>The registration MAY name a set of specifications associated with that
3439       token. Such specifications need not be publicly available.</t>
3440    <t>The responsible party MAY change the registration at any time.
3441       The IANA will keep a record of all such changes, and make them
3442       available upon request.</t>
3443    <t>The responsible party for the first registration of a "product"
3444       token MUST approve later registrations of a "version" token
3445       together with that "product" token before they can be registered.</t>
3446    <t>If absolutely required, the IESG MAY reassign the responsibility
3447       for a token. This will normally only be used in the case when a
3448       responsible party cannot be contacted.</t>
3449  </list>
3450</t>
3451</section>
3452
3453
3454</section>
3455
3456<section title="Via" anchor="header.via">
3457  <iref primary="true" item="Via header field"/>
3458  <iref primary="true" item="Header Fields" subitem="Via"/>
3459 
3460 
3461 
3462 
3463 
3464 
3465 
3466<t>
3467   The "Via" header field MUST be sent by a proxy or gateway to
3468   indicate the intermediate protocols and recipients between the user
3469   agent and the server on requests, and between the origin server and
3470   the client on responses. It is analogous to the "Received" field
3471   used by email systems (Section 3.6.7 of <xref target="RFC5322"/>)
3472   and is intended to be used for tracking message forwards,
3473   avoiding request loops, and identifying the protocol capabilities of
3474   all senders along the request/response chain.
3475</t>
3476<figure><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="Via-v"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/><artwork type="abnf2616"><![CDATA[
3477  Via               = "Via" ":" OWS Via-v
3478  Via-v             = 1#( received-protocol RWS received-by
3479                          [ RWS comment ] )
3480  received-protocol = [ protocol-name "/" ] protocol-version
3481  protocol-name     = token
3482  protocol-version  = token
3483  received-by       = ( uri-host [ ":" port ] ) / pseudonym
3484  pseudonym         = token
3485]]></artwork></figure>
3486<t>
3487   The received-protocol indicates the protocol version of the message
3488   received by the server or client along each segment of the
3489   request/response chain. The received-protocol version is appended to
3490   the Via field value when the message is forwarded so that information
3491   about the protocol capabilities of upstream applications remains
3492   visible to all recipients.
3493</t>
3494<t>
3495   The protocol-name is excluded if and only if it would be "HTTP". The
3496   received-by field is normally the host and optional port number of a
3497   recipient server or client that subsequently forwarded the message.
3498   However, if the real host is considered to be sensitive information,
3499   it MAY be replaced by a pseudonym. If the port is not given, it MAY
3500   be assumed to be the default port of the received-protocol.
3501</t>
3502<t>
3503   Multiple Via field values represent each proxy or gateway that has
3504   forwarded the message. Each recipient MUST append its information
3505   such that the end result is ordered according to the sequence of
3506   forwarding applications.
3507</t>
3508<t>
3509   Comments MAY be used in the Via header field to identify the software
3510   of each recipient, analogous to the User-Agent and Server header fields.
3511   However, all comments in the Via field are optional and MAY be removed
3512   by any recipient prior to forwarding the message.
3513</t>
3514<t>
3515   For example, a request message could be sent from an HTTP/1.0 user
3516   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3517   forward the request to a public proxy at p.example.net, which completes
3518   the request by forwarding it to the origin server at www.example.com.
3519   The request received by www.example.com would then have the following
3520   Via header field:
3521</t>
3522<figure><artwork type="example"><![CDATA[
3523  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3524]]></artwork></figure>
3525<t>
3526   A proxy or gateway used as a portal through a network firewall
3527   SHOULD NOT forward the names and ports of hosts within the firewall
3528   region unless it is explicitly enabled to do so. If not enabled, the
3529   received-by host of any host behind the firewall SHOULD be replaced
3530   by an appropriate pseudonym for that host.
3531</t>
3532<t>
3533   For organizations that have strong privacy requirements for hiding
3534   internal structures, a proxy or gateway MAY combine an ordered
3535   subsequence of Via header field entries with identical received-protocol
3536   values into a single such entry. For example,
3537</t>
3538<figure><artwork type="example"><![CDATA[
3539  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3540]]></artwork></figure>
3541<t>
3542  could be collapsed to
3543</t>
3544<figure><artwork type="example"><![CDATA[
3545  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3546]]></artwork></figure>
3547<t>
3548   Senders SHOULD NOT combine multiple entries unless they are all
3549   under the same organizational control and the hosts have already been
3550   replaced by pseudonyms. Senders MUST NOT combine entries which
3551   have different received-protocol values.
3552</t>
3553</section>
3554
3555</section>
3556
3557<section title="IANA Considerations" anchor="IANA.considerations">
3558
3559<section title="Header Field Registration" anchor="header.field.registration">
3560<t>
3561   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3562   with the permanent registrations below (see <xref target="RFC3864"/>):
3563</t>
3564
3565<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3566<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3567   <ttcol>Header Field Name</ttcol>
3568   <ttcol>Protocol</ttcol>
3569   <ttcol>Status</ttcol>
3570   <ttcol>Reference</ttcol>
3571
3572   <c>Connection</c>
3573   <c>http</c>
3574   <c>standard</c>
3575   <c>
3576      <xref target="header.connection"/>
3577   </c>
3578   <c>Content-Length</c>
3579   <c>http</c>
3580   <c>standard</c>
3581   <c>
3582      <xref target="header.content-length"/>
3583   </c>
3584   <c>Date</c>
3585   <c>http</c>
3586   <c>standard</c>
3587   <c>
3588      <xref target="header.date"/>
3589   </c>
3590   <c>Host</c>
3591   <c>http</c>
3592   <c>standard</c>
3593   <c>
3594      <xref target="header.host"/>
3595   </c>
3596   <c>TE</c>
3597   <c>http</c>
3598   <c>standard</c>
3599   <c>
3600      <xref target="header.te"/>
3601   </c>
3602   <c>Trailer</c>
3603   <c>http</c>
3604   <c>standard</c>
3605   <c>
3606      <xref target="header.trailer"/>
3607   </c>
3608   <c>Transfer-Encoding</c>
3609   <c>http</c>
3610   <c>standard</c>
3611   <c>
3612      <xref target="header.transfer-encoding"/>
3613   </c>
3614   <c>Upgrade</c>
3615   <c>http</c>
3616   <c>standard</c>
3617   <c>
3618      <xref target="header.upgrade"/>
3619   </c>
3620   <c>Via</c>
3621   <c>http</c>
3622   <c>standard</c>
3623   <c>
3624      <xref target="header.via"/>
3625   </c>
3626</texttable>
3627<!--(END)-->
3628
3629<t>
3630   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3631</t>
3632</section>
3633
3634<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3635<t>
3636   The entries for the "http" and "https" URI Schemes in the registry located at
3637   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3638   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3639   and <xref target="https.uri" format="counter"/> of this document
3640   (see <xref target="RFC4395"/>).
3641</t>
3642</section>
3643
3644<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3645<t>
3646   This document serves as the specification for the Internet media types
3647   "message/http" and "application/http". The following is to be registered with
3648   IANA (see <xref target="RFC4288"/>).
3649</t>
3650<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3651<iref item="Media Type" subitem="message/http" primary="true"/>
3652<iref item="message/http Media Type" primary="true"/>
3653<t>
3654   The message/http type can be used to enclose a single HTTP request or
3655   response message, provided that it obeys the MIME restrictions for all
3656   "message" types regarding line length and encodings.
3657</t>
3658<t>
3659  <list style="hanging">
3660    <t hangText="Type name:">
3661      message
3662    </t>
3663    <t hangText="Subtype name:">
3664      http
3665    </t>
3666    <t hangText="Required parameters:">
3667      none
3668    </t>
3669    <t hangText="Optional parameters:">
3670      version, msgtype
3671      <list style="hanging">
3672        <t hangText="version:">
3673          The HTTP-Version number of the enclosed message
3674          (e.g., "1.1"). If not present, the version can be
3675          determined from the first line of the body.
3676        </t>
3677        <t hangText="msgtype:">
3678          The message type — "request" or "response". If not
3679          present, the type can be determined from the first
3680          line of the body.
3681        </t>
3682      </list>
3683    </t>
3684    <t hangText="Encoding considerations:">
3685      only "7bit", "8bit", or "binary" are permitted
3686    </t>
3687    <t hangText="Security considerations:">
3688      none
3689    </t>
3690    <t hangText="Interoperability considerations:">
3691      none
3692    </t>
3693    <t hangText="Published specification:">
3694      This specification (see <xref target="internet.media.type.message.http"/>).
3695    </t>
3696    <t hangText="Applications that use this media type:">
3697    </t>
3698    <t hangText="Additional information:">
3699      <list style="hanging">
3700        <t hangText="Magic number(s):">none</t>
3701        <t hangText="File extension(s):">none</t>
3702        <t hangText="Macintosh file type code(s):">none</t>
3703      </list>
3704    </t>
3705    <t hangText="Person and email address to contact for further information:">
3706      See Authors Section.
3707    </t>
3708    <t hangText="Intended usage:">
3709      COMMON
3710    </t>
3711    <t hangText="Restrictions on usage:">
3712      none
3713    </t>
3714    <t hangText="Author/Change controller:">
3715      IESG
3716    </t>
3717  </list>
3718</t>
3719</section>
3720<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3721<iref item="Media Type" subitem="application/http" primary="true"/>
3722<iref item="application/http Media Type" primary="true"/>
3723<t>
3724   The application/http type can be used to enclose a pipeline of one or more
3725   HTTP request or response messages (not intermixed).
3726</t>
3727<t>
3728  <list style="hanging">
3729    <t hangText="Type name:">
3730      application
3731    </t>
3732    <t hangText="Subtype name:">
3733      http
3734    </t>
3735    <t hangText="Required parameters:">
3736      none
3737    </t>
3738    <t hangText="Optional parameters:">
3739      version, msgtype
3740      <list style="hanging">
3741        <t hangText="version:">
3742          The HTTP-Version number of the enclosed messages
3743          (e.g., "1.1"). If not present, the version can be
3744          determined from the first line of the body.
3745        </t>
3746        <t hangText="msgtype:">
3747          The message type — "request" or "response". If not
3748          present, the type can be determined from the first
3749          line of the body.
3750        </t>
3751      </list>
3752    </t>
3753    <t hangText="Encoding considerations:">
3754      HTTP messages enclosed by this type
3755      are in "binary" format; use of an appropriate
3756      Content-Transfer-Encoding is required when
3757      transmitted via E-mail.
3758    </t>
3759    <t hangText="Security considerations:">
3760      none
3761    </t>
3762    <t hangText="Interoperability considerations:">
3763      none
3764    </t>
3765    <t hangText="Published specification:">
3766      This specification (see <xref target="internet.media.type.application.http"/>).
3767    </t>
3768    <t hangText="Applications that use this media type:">
3769    </t>
3770    <t hangText="Additional information:">
3771      <list style="hanging">
3772        <t hangText="Magic number(s):">none</t>
3773        <t hangText="File extension(s):">none</t>
3774        <t hangText="Macintosh file type code(s):">none</t>
3775      </list>
3776    </t>
3777    <t hangText="Person and email address to contact for further information:">
3778      See Authors Section.
3779    </t>
3780    <t hangText="Intended usage:">
3781      COMMON
3782    </t>
3783    <t hangText="Restrictions on usage:">
3784      none
3785    </t>
3786    <t hangText="Author/Change controller:">
3787      IESG
3788    </t>
3789  </list>
3790</t>
3791</section>
3792</section>
3793
3794<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3795<t>
3796   The registration procedure for HTTP Transfer Codings is now defined by
3797   <xref target="transfer.coding.registry"/> of this document.
3798</t>
3799<t>
3800   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3801   shall be updated with the registrations below:
3802</t>
3803<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3804   <ttcol>Name</ttcol>
3805   <ttcol>Description</ttcol>
3806   <ttcol>Reference</ttcol>
3807   <c>chunked</c>
3808   <c>Transfer in a series of chunks</c>
3809   <c>
3810      <xref target="chunked.encoding"/>
3811   </c>
3812   <c>compress</c>
3813   <c>UNIX "compress" program method</c>
3814   <c>
3815      <xref target="compress.coding"/>
3816   </c>
3817   <c>deflate</c>
3818   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3819   the "zlib" data format (<xref target="RFC1950"/>)
3820   </c>
3821   <c>
3822      <xref target="deflate.coding"/>
3823   </c>
3824   <c>gzip</c>
3825   <c>Same as GNU zip <xref target="RFC1952"/></c>
3826   <c>
3827      <xref target="gzip.coding"/>
3828   </c>
3829</texttable>
3830</section>
3831
3832<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3833<t>
3834   The registration procedure for HTTP Upgrade Tokens — previously defined
3835   in Section 7.2 of <xref target="RFC2817"/> — is now defined
3836   by <xref target="upgrade.token.registry"/> of this document.
3837</t>
3838<t>
3839   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3840   shall be updated with the registration below:
3841</t>
3842<texttable align="left" suppress-title="true">
3843   <ttcol>Value</ttcol>
3844   <ttcol>Description</ttcol>
3845   <ttcol>Reference</ttcol>
3846
3847   <c>HTTP</c>
3848   <c>Hypertext Transfer Protocol</c>
3849   <c><xref target="http.version"/> of this specification</c>
3850<!-- IANA should add this without our instructions; emailed on June 05, 2009
3851   <c>TLS/1.0</c>
3852   <c>Transport Layer Security</c>
3853   <c><xref target="RFC2817"/></c> -->
3854
3855</texttable>
3856</section>
3857
3858</section>
3859
3860<section title="Security Considerations" anchor="security.considerations">
3861<t>
3862   This section is meant to inform application developers, information
3863   providers, and users of the security limitations in HTTP/1.1 as
3864   described by this document. The discussion does not include
3865   definitive solutions to the problems revealed, though it does make
3866   some suggestions for reducing security risks.
3867</t>
3868
3869<section title="Personal Information" anchor="personal.information">
3870<t>
3871   HTTP clients are often privy to large amounts of personal information
3872   (e.g., the user's name, location, mail address, passwords, encryption
3873   keys, etc.), and SHOULD be very careful to prevent unintentional
3874   leakage of this information.
3875   We very strongly recommend that a convenient interface be provided
3876   for the user to control dissemination of such information, and that
3877   designers and implementors be particularly careful in this area.
3878   History shows that errors in this area often create serious security
3879   and/or privacy problems and generate highly adverse publicity for the
3880   implementor's company.
3881</t>
3882</section>
3883
3884<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3885<t>
3886   A server is in the position to save personal data about a user's
3887   requests which might identify their reading patterns or subjects of
3888   interest. This information is clearly confidential in nature and its
3889   handling can be constrained by law in certain countries. People using
3890   HTTP to provide data are responsible for ensuring that
3891   such material is not distributed without the permission of any
3892   individuals that are identifiable by the published results.
3893</t>
3894</section>
3895
3896<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3897<t>
3898   Implementations of HTTP origin servers SHOULD be careful to restrict
3899   the documents returned by HTTP requests to be only those that were
3900   intended by the server administrators. If an HTTP server translates
3901   HTTP URIs directly into file system calls, the server MUST take
3902   special care not to serve files that were not intended to be
3903   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3904   other operating systems use ".." as a path component to indicate a
3905   directory level above the current one. On such a system, an HTTP
3906   server MUST disallow any such construct in the request-target if it
3907   would otherwise allow access to a resource outside those intended to
3908   be accessible via the HTTP server. Similarly, files intended for
3909   reference only internally to the server (such as access control
3910   files, configuration files, and script code) MUST be protected from
3911   inappropriate retrieval, since they might contain sensitive
3912   information. Experience has shown that minor bugs in such HTTP server
3913   implementations have turned into security risks.
3914</t>
3915</section>
3916
3917<section title="DNS Spoofing" anchor="dns.spoofing">
3918<t>
3919   Clients using HTTP rely heavily on the Domain Name Service, and are
3920   thus generally prone to security attacks based on the deliberate
3921   mis-association of IP addresses and DNS names. Clients need to be
3922   cautious in assuming the continuing validity of an IP number/DNS name
3923   association.
3924</t>
3925<t>
3926   In particular, HTTP clients SHOULD rely on their name resolver for
3927   confirmation of an IP number/DNS name association, rather than
3928   caching the result of previous host name lookups. Many platforms
3929   already can cache host name lookups locally when appropriate, and
3930   they SHOULD be configured to do so. It is proper for these lookups to
3931   be cached, however, only when the TTL (Time To Live) information
3932   reported by the name server makes it likely that the cached
3933   information will remain useful.
3934</t>
3935<t>
3936   If HTTP clients cache the results of host name lookups in order to
3937   achieve a performance improvement, they MUST observe the TTL
3938   information reported by DNS.
3939</t>
3940<t>
3941   If HTTP clients do not observe this rule, they could be spoofed when
3942   a previously-accessed server's IP address changes. As network
3943   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3944   possibility of this form of attack will grow. Observing this
3945   requirement thus reduces this potential security vulnerability.
3946</t>
3947<t>
3948   This requirement also improves the load-balancing behavior of clients
3949   for replicated servers using the same DNS name and reduces the
3950   likelihood of a user's experiencing failure in accessing sites which
3951   use that strategy.
3952</t>
3953</section>
3954
3955<section title="Proxies and Caching" anchor="attack.proxies">
3956<t>
3957   By their very nature, HTTP proxies are men-in-the-middle, and
3958   represent an opportunity for man-in-the-middle attacks. Compromise of
3959   the systems on which the proxies run can result in serious security
3960   and privacy problems. Proxies have access to security-related
3961   information, personal information about individual users and
3962   organizations, and proprietary information belonging to users and
3963   content providers. A compromised proxy, or a proxy implemented or
3964   configured without regard to security and privacy considerations,
3965   might be used in the commission of a wide range of potential attacks.
3966</t>
3967<t>
3968   Proxy operators need to protect the systems on which proxies run as
3969   they would protect any system that contains or transports sensitive
3970   information. In particular, log information gathered at proxies often
3971   contains highly sensitive personal information, and/or information
3972   about organizations. Log information needs to be carefully guarded, and
3973   appropriate guidelines for use need to be developed and followed.
3974   (<xref target="abuse.of.server.log.information"/>).
3975</t>
3976<t>
3977   Proxy implementors need to consider the privacy and security
3978   implications of their design and coding decisions, and of the
3979   configuration options they provide to proxy operators (especially the
3980   default configuration).
3981</t>
3982<t>
3983   Users of a proxy need to be aware that proxies are no trustworthier than
3984   the people who run them; HTTP itself cannot solve this problem.
3985</t>
3986<t>
3987   The judicious use of cryptography, when appropriate, might suffice to
3988   protect against a broad range of security and privacy attacks. Such
3989   cryptography is beyond the scope of the HTTP/1.1 specification.
3990</t>
3991</section>
3992
3993<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3994<t>
3995   They exist. They are hard to defend against. Research continues.
3996   Beware.
3997</t>
3998</section>
3999</section>
4000
4001<section title="Acknowledgments" anchor="ack">
4002<t>
4003   HTTP has evolved considerably over the years. It has
4004   benefited from a large and active developer community — the many
4005   people who have participated on the www-talk mailing list — and it is
4006   that community which has been most responsible for the success of
4007   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
4008   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
4009   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
4010   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
4011   VanHeyningen deserve special recognition for their efforts in
4012   defining early aspects of the protocol.
4013</t>
4014<t>
4015   This document has benefited greatly from the comments of all those
4016   participating in the HTTP-WG. In addition to those already mentioned,
4017   the following individuals have contributed to this specification:
4018</t>
4019<t>
4020   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
4021   Paul Burchard, Maurizio Codogno, Josh Cohen, Mike Cowlishaw, Roman Czyborra,
4022   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
4023   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
4024   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
4025   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
4026   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
4027   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
4028   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
4029   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
4030   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
4031   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko.
4032</t>
4033<t>
4034   Thanks to the "cave men" of Palo Alto. You know who you are.
4035</t>
4036<t>
4037   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
4038   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
4039   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
4040   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
4041   Larry Masinter for their help. And thanks go particularly to Jeff
4042   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
4043</t>
4044<t>
4045   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
4046   Frystyk implemented RFC 2068 early, and we wish to thank them for the
4047   discovery of many of the problems that this document attempts to
4048   rectify.
4049</t>
4050<t>
4051   This specification makes heavy use of the augmented BNF and generic
4052   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
4053   reuses many of the definitions provided by Nathaniel Borenstein and
4054   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
4055   specification will help reduce past confusion over the relationship
4056   between HTTP and Internet mail message formats.
4057</t>
4058<!--
4059
4060Acknowledgements TODO list
4061
4062- Jeff Hodges ("effective request URI")
4063
4064-->
4065</section>
4066
4067</middle>
4068<back>
4069
4070<references title="Normative References">
4071
4072<reference anchor="ISO-8859-1">
4073  <front>
4074    <title>
4075     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4076    </title>
4077    <author>
4078      <organization>International Organization for Standardization</organization>
4079    </author>
4080    <date year="1998"/>
4081  </front>
4082  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4083</reference>
4084
4085<reference anchor="Part2">
4086  <front>
4087    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4088    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4089      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4090      <address><email>fielding@gbiv.com</email></address>
4091    </author>
4092    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4093      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4094      <address><email>jg@freedesktop.org</email></address>
4095    </author>
4096    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4097      <organization abbrev="HP">Hewlett-Packard Company</organization>
4098      <address><email>JeffMogul@acm.org</email></address>
4099    </author>
4100    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4101      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4102      <address><email>henrikn@microsoft.com</email></address>
4103    </author>
4104    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4105      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4106      <address><email>LMM@acm.org</email></address>
4107    </author>
4108    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4109      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4110      <address><email>paulle@microsoft.com</email></address>
4111    </author>
4112    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4113      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4114      <address><email>timbl@w3.org</email></address>
4115    </author>
4116    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4117      <organization abbrev="W3C">World Wide Web Consortium</organization>
4118      <address><email>ylafon@w3.org</email></address>
4119    </author>
4120    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4121      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4122      <address><email>julian.reschke@greenbytes.de</email></address>
4123    </author>
4124    <date month="March" year="2011"/>
4125  </front>
4126  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-13"/>
4127 
4128</reference>
4129
4130<reference anchor="Part3">
4131  <front>
4132    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4133    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4134      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4135      <address><email>fielding@gbiv.com</email></address>
4136    </author>
4137    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4138      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4139      <address><email>jg@freedesktop.org</email></address>
4140    </author>
4141    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4142      <organization abbrev="HP">Hewlett-Packard Company</organization>
4143      <address><email>JeffMogul@acm.org</email></address>
4144    </author>
4145    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4146      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4147      <address><email>henrikn@microsoft.com</email></address>
4148    </author>
4149    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4150      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4151      <address><email>LMM@acm.org</email></address>
4152    </author>
4153    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4154      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4155      <address><email>paulle@microsoft.com</email></address>
4156    </author>
4157    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4158      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4159      <address><email>timbl@w3.org</email></address>
4160    </author>
4161    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4162      <organization abbrev="W3C">World Wide Web Consortium</organization>
4163      <address><email>ylafon@w3.org</email></address>
4164    </author>
4165    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4166      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4167      <address><email>julian.reschke@greenbytes.de</email></address>
4168    </author>
4169    <date month="March" year="2011"/>
4170  </front>
4171  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-13"/>
4172 
4173</reference>
4174
4175<reference anchor="Part6">
4176  <front>
4177    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4178    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4179      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4180      <address><email>fielding@gbiv.com</email></address>
4181    </author>
4182    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4183      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4184      <address><email>jg@freedesktop.org</email></address>
4185    </author>
4186    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4187      <organization abbrev="HP">Hewlett-Packard Company</organization>
4188      <address><email>JeffMogul@acm.org</email></address>
4189    </author>
4190    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4191      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4192      <address><email>henrikn@microsoft.com</email></address>
4193    </author>
4194    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4195      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4196      <address><email>LMM@acm.org</email></address>
4197    </author>
4198    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4199      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4200      <address><email>paulle@microsoft.com</email></address>
4201    </author>
4202    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4203      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4204      <address><email>timbl@w3.org</email></address>
4205    </author>
4206    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4207      <organization abbrev="W3C">World Wide Web Consortium</organization>
4208      <address><email>ylafon@w3.org</email></address>
4209    </author>
4210    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4211      <address><email>mnot@mnot.net</email></address>
4212    </author>
4213    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4214      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4215      <address><email>julian.reschke@greenbytes.de</email></address>
4216    </author>
4217    <date month="March" year="2011"/>
4218  </front>
4219  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-13"/>
4220 
4221</reference>
4222
4223<reference anchor="RFC5234">
4224  <front>
4225    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4226    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4227      <organization>Brandenburg InternetWorking</organization>
4228      <address>
4229        <email>dcrocker@bbiw.net</email>
4230      </address> 
4231    </author>
4232    <author initials="P." surname="Overell" fullname="Paul Overell">
4233      <organization>THUS plc.</organization>
4234      <address>
4235        <email>paul.overell@thus.net</email>
4236      </address>
4237    </author>
4238    <date month="January" year="2008"/>
4239  </front>
4240  <seriesInfo name="STD" value="68"/>
4241  <seriesInfo name="RFC" value="5234"/>
4242</reference>
4243
4244<reference anchor="RFC2119">
4245  <front>
4246    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4247    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4248      <organization>Harvard University</organization>
4249      <address><email>sob@harvard.edu</email></address>
4250    </author>
4251    <date month="March" year="1997"/>
4252  </front>
4253  <seriesInfo name="BCP" value="14"/>
4254  <seriesInfo name="RFC" value="2119"/>
4255</reference>
4256
4257<reference anchor="RFC3986">
4258 <front>
4259  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
4260  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4261    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4262    <address>
4263       <email>timbl@w3.org</email>
4264       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4265    </address>
4266  </author>
4267  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4268    <organization abbrev="Day Software">Day Software</organization>
4269    <address>
4270      <email>fielding@gbiv.com</email>
4271      <uri>http://roy.gbiv.com/</uri>
4272    </address>
4273  </author>
4274  <author initials="L." surname="Masinter" fullname="Larry Masinter">
4275    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4276    <address>
4277      <email>LMM@acm.org</email>
4278      <uri>http://larry.masinter.net/</uri>
4279    </address>
4280  </author>
4281  <date month="January" year="2005"/>
4282 </front>
4283 <seriesInfo name="STD" value="66"/>
4284 <seriesInfo name="RFC" value="3986"/>
4285</reference>
4286
4287<reference anchor="USASCII">
4288  <front>
4289    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4290    <author>
4291      <organization>American National Standards Institute</organization>
4292    </author>
4293    <date year="1986"/>
4294  </front>
4295  <seriesInfo name="ANSI" value="X3.4"/>
4296</reference>
4297
4298<reference anchor="RFC1950">
4299  <front>
4300    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4301    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4302      <organization>Aladdin Enterprises</organization>
4303      <address><email>ghost@aladdin.com</email></address>
4304    </author>
4305    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4306    <date month="May" year="1996"/>
4307  </front>
4308  <seriesInfo name="RFC" value="1950"/>
4309  <annotation>
4310    RFC 1950 is an Informational RFC, thus it might be less stable than
4311    this specification. On the other hand, this downward reference was
4312    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4313    therefore it is unlikely to cause problems in practice. See also
4314    <xref target="BCP97"/>.
4315  </annotation>
4316</reference>
4317
4318<reference anchor="RFC1951">
4319  <front>
4320    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4321    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4322      <organization>Aladdin Enterprises</organization>
4323      <address><email>ghost@aladdin.com</email></address>
4324    </author>
4325    <date month="May" year="1996"/>
4326  </front>
4327  <seriesInfo name="RFC" value="1951"/>
4328  <annotation>
4329    RFC 1951 is an Informational RFC, thus it might be less stable than
4330    this specification. On the other hand, this downward reference was
4331    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4332    therefore it is unlikely to cause problems in practice. See also
4333    <xref target="BCP97"/>.
4334  </annotation>
4335</reference>
4336
4337<reference anchor="RFC1952">
4338  <front>
4339    <title>GZIP file format specification version 4.3</title>
4340    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4341      <organization>Aladdin Enterprises</organization>
4342      <address><email>ghost@aladdin.com</email></address>
4343    </author>
4344    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4345      <address><email>gzip@prep.ai.mit.edu</email></address>
4346    </author>
4347    <author initials="M." surname="Adler" fullname="Mark Adler">
4348      <address><email>madler@alumni.caltech.edu</email></address>
4349    </author>
4350    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4351      <address><email>ghost@aladdin.com</email></address>
4352    </author>
4353    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4354      <address><email>randeg@alumni.rpi.edu</email></address>
4355    </author>
4356    <date month="May" year="1996"/>
4357  </front>
4358  <seriesInfo name="RFC" value="1952"/>
4359  <annotation>
4360    RFC 1952 is an Informational RFC, thus it might be less stable than
4361    this specification. On the other hand, this downward reference was
4362    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4363    therefore it is unlikely to cause problems in practice. See also
4364    <xref target="BCP97"/>.
4365  </annotation>
4366</reference>
4367
4368</references>
4369
4370<references title="Informative References">
4371
4372<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4373  <front>
4374    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4375    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4376    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4377    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4378    <author initials="H." surname="Lie" fullname="H. Lie"/>
4379    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4380    <date year="1997" month="September"/>
4381  </front>
4382  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4383</reference>
4384
4385<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4386  <front>
4387    <title>Improving HTTP Latency</title>
4388    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4389    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4390    <date year="1995" month="December"/>
4391  </front>
4392  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4393</reference>
4394
4395<reference anchor="RFC1123">
4396  <front>
4397    <title>Requirements for Internet Hosts - Application and Support</title>
4398    <author initials="R." surname="Braden" fullname="Robert Braden">
4399      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4400      <address><email>Braden@ISI.EDU</email></address>
4401    </author>
4402    <date month="October" year="1989"/>
4403  </front>
4404  <seriesInfo name="STD" value="3"/>
4405  <seriesInfo name="RFC" value="1123"/>
4406</reference>
4407
4408<reference anchor="RFC1900">
4409  <front>
4410    <title>Renumbering Needs Work</title>
4411    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4412      <organization>CERN, Computing and Networks Division</organization>
4413      <address><email>brian@dxcoms.cern.ch</email></address>
4414    </author>
4415    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4416      <organization>cisco Systems</organization>
4417      <address><email>yakov@cisco.com</email></address>
4418    </author>
4419    <date month="February" year="1996"/>
4420  </front>
4421  <seriesInfo name="RFC" value="1900"/>
4422</reference>
4423
4424<reference anchor="RFC1919">
4425  <front>
4426    <title>Classical versus Transparent IP Proxies</title>
4427    <author initials="M." surname="Chatel" fullname="Marc Chatel">
4428      <address><email>mchatel@pax.eunet.ch</email></address>
4429    </author>
4430    <date year="1996" month="March"/>
4431  </front>
4432  <seriesInfo name="RFC" value="1919"/>
4433</reference>
4434
4435<reference anchor="RFC1945">
4436  <front>
4437    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4438    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4439      <organization>MIT, Laboratory for Computer Science</organization>
4440      <address><email>timbl@w3.org</email></address>
4441    </author>
4442    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4443      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4444      <address><email>fielding@ics.uci.edu</email></address>
4445    </author>
4446    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4447      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4448      <address><email>frystyk@w3.org</email></address>
4449    </author>
4450    <date month="May" year="1996"/>
4451  </front>
4452  <seriesInfo name="RFC" value="1945"/>
4453</reference>
4454
4455<reference anchor="RFC2045">
4456  <front>
4457    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4458    <author initials="N." surname="Freed" fullname="Ned Freed">
4459      <organization>Innosoft International, Inc.</organization>
4460      <address><email>ned@innosoft.com</email></address>
4461    </author>
4462    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4463      <organization>First Virtual Holdings</organization>
4464      <address><email>nsb@nsb.fv.com</email></address>
4465    </author>
4466    <date month="November" year="1996"/>
4467  </front>
4468  <seriesInfo name="RFC" value="2045"/>
4469</reference>
4470
4471<reference anchor="RFC2047">
4472  <front>
4473    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4474    <author initials="K." surname="Moore" fullname="Keith Moore">
4475      <organization>University of Tennessee</organization>
4476      <address><email>moore@cs.utk.edu</email></address>
4477    </author>
4478    <date month="November" year="1996"/>
4479  </front>
4480  <seriesInfo name="RFC" value="2047"/>
4481</reference>
4482
4483<reference anchor="RFC2068">
4484  <front>
4485    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4486    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4487      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4488      <address><email>fielding@ics.uci.edu</email></address>
4489    </author>
4490    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4491      <organization>MIT Laboratory for Computer Science</organization>
4492      <address><email>jg@w3.org</email></address>
4493    </author>
4494    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4495      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4496      <address><email>mogul@wrl.dec.com</email></address>
4497    </author>
4498    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4499      <organization>MIT Laboratory for Computer Science</organization>
4500      <address><email>frystyk@w3.org</email></address>
4501    </author>
4502    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4503      <organization>MIT Laboratory for Computer Science</organization>
4504      <address><email>timbl@w3.org</email></address>
4505    </author>
4506    <date month="January" year="1997"/>
4507  </front>
4508  <seriesInfo name="RFC" value="2068"/>
4509</reference>
4510
4511<reference anchor="RFC2145">
4512  <front>
4513    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4514    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4515      <organization>Western Research Laboratory</organization>
4516      <address><email>mogul@wrl.dec.com</email></address>
4517    </author>
4518    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4519      <organization>Department of Information and Computer Science</organization>
4520      <address><email>fielding@ics.uci.edu</email></address>
4521    </author>
4522    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4523      <organization>MIT Laboratory for Computer Science</organization>
4524      <address><email>jg@w3.org</email></address>
4525    </author>
4526    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4527      <organization>W3 Consortium</organization>
4528      <address><email>frystyk@w3.org</email></address>
4529    </author>
4530    <date month="May" year="1997"/>
4531  </front>
4532  <seriesInfo name="RFC" value="2145"/>
4533</reference>
4534
4535<reference anchor="RFC2616">
4536  <front>
4537    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4538    <author initials="R." surname="Fielding" fullname="R. Fielding">
4539      <organization>University of California, Irvine</organization>
4540      <address><email>fielding@ics.uci.edu</email></address>
4541    </author>
4542    <author initials="J." surname="Gettys" fullname="J. Gettys">
4543      <organization>W3C</organization>
4544      <address><email>jg@w3.org</email></address>
4545    </author>
4546    <author initials="J." surname="Mogul" fullname="J. Mogul">
4547      <organization>Compaq Computer Corporation</organization>
4548      <address><email>mogul@wrl.dec.com</email></address>
4549    </author>
4550    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4551      <organization>MIT Laboratory for Computer Science</organization>
4552      <address><email>frystyk@w3.org</email></address>
4553    </author>
4554    <author initials="L." surname="Masinter" fullname="L. Masinter">
4555      <organization>Xerox Corporation</organization>
4556      <address><email>masinter@parc.xerox.com</email></address>
4557    </author>
4558    <author initials="P." surname="Leach" fullname="P. Leach">
4559      <organization>Microsoft Corporation</organization>
4560      <address><email>paulle@microsoft.com</email></address>
4561    </author>
4562    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4563      <organization>W3C</organization>
4564      <address><email>timbl@w3.org</email></address>
4565    </author>
4566    <date month="June" year="1999"/>
4567  </front>
4568  <seriesInfo name="RFC" value="2616"/>
4569</reference>
4570
4571<reference anchor="RFC2817">
4572  <front>
4573    <title>Upgrading to TLS Within HTTP/1.1</title>
4574    <author initials="R." surname="Khare" fullname="R. Khare">
4575      <organization>4K Associates / UC Irvine</organization>
4576      <address><email>rohit@4K-associates.com</email></address>
4577    </author>
4578    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
4579      <organization>Agranat Systems, Inc.</organization>
4580      <address><email>lawrence@agranat.com</email></address>
4581    </author>
4582    <date year="2000" month="May"/>
4583  </front>
4584  <seriesInfo name="RFC" value="2817"/>
4585</reference>
4586
4587<reference anchor="RFC2818">
4588  <front>
4589    <title>HTTP Over TLS</title>
4590    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
4591      <organization>RTFM, Inc.</organization>
4592      <address><email>ekr@rtfm.com</email></address>
4593    </author>
4594    <date year="2000" month="May"/>
4595  </front>
4596  <seriesInfo name="RFC" value="2818"/>
4597</reference>
4598
4599<reference anchor="RFC2965">
4600  <front>
4601    <title>HTTP State Management Mechanism</title>
4602    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
4603      <organization>Bell Laboratories, Lucent Technologies</organization>
4604      <address><email>dmk@bell-labs.com</email></address>
4605    </author>
4606    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4607      <organization>Epinions.com, Inc.</organization>
4608      <address><email>lou@montulli.org</email></address>
4609    </author>
4610    <date year="2000" month="October"/>
4611  </front>
4612  <seriesInfo name="RFC" value="2965"/>
4613</reference>
4614
4615<reference anchor="RFC3040">
4616  <front>
4617    <title>Internet Web Replication and Caching Taxonomy</title>
4618    <author initials="I." surname="Cooper" fullname="I. Cooper">
4619      <organization>Equinix, Inc.</organization>
4620    </author>
4621    <author initials="I." surname="Melve" fullname="I. Melve">
4622      <organization>UNINETT</organization>
4623    </author>
4624    <author initials="G." surname="Tomlinson" fullname="G. Tomlinson">
4625      <organization>CacheFlow Inc.</organization>
4626    </author>
4627    <date year="2001" month="January"/>
4628  </front>
4629  <seriesInfo name="RFC" value="3040"/>
4630</reference>
4631
4632<reference anchor="RFC3864">
4633  <front>
4634    <title>Registration Procedures for Message Header Fields</title>
4635    <author initials="G." surname="Klyne" fullname="G. Klyne">
4636      <organization>Nine by Nine</organization>
4637      <address><email>GK-IETF@ninebynine.org</email></address>
4638    </author>
4639    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
4640      <organization>BEA Systems</organization>
4641      <address><email>mnot@pobox.com</email></address>
4642    </author>
4643    <author initials="J." surname="Mogul" fullname="J. Mogul">
4644      <organization>HP Labs</organization>
4645      <address><email>JeffMogul@acm.org</email></address>
4646    </author>
4647    <date year="2004" month="September"/>
4648  </front>
4649  <seriesInfo name="BCP" value="90"/>
4650  <seriesInfo name="RFC" value="3864"/>
4651</reference>
4652
4653<reference anchor="RFC4288">
4654  <front>
4655    <title>Media Type Specifications and Registration Procedures</title>
4656    <author initials="N." surname="Freed" fullname="N. Freed">
4657      <organization>Sun Microsystems</organization>
4658      <address>
4659        <email>ned.freed@mrochek.com</email>
4660      </address>
4661    </author>
4662    <author initials="J." surname="Klensin" fullname="J. Klensin">
4663      <address>
4664        <email>klensin+ietf@jck.com</email>
4665      </address>
4666    </author>
4667    <date year="2005" month="December"/>
4668  </front>
4669  <seriesInfo name="BCP" value="13"/>
4670  <seriesInfo name="RFC" value="4288"/>
4671</reference>
4672
4673<reference anchor="RFC4395">
4674  <front>
4675    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4676    <author initials="T." surname="Hansen" fullname="T. Hansen">
4677      <organization>AT&amp;T Laboratories</organization>
4678      <address>
4679        <email>tony+urireg@maillennium.att.com</email>
4680      </address>
4681    </author>
4682    <author initials="T." surname="Hardie" fullname="T. Hardie">
4683      <organization>Qualcomm, Inc.</organization>
4684      <address>
4685        <email>hardie@qualcomm.com</email>
4686      </address>
4687    </author>
4688    <author initials="L." surname="Masinter" fullname="L. Masinter">
4689      <organization>Adobe Systems</organization>
4690      <address>
4691        <email>LMM@acm.org</email>
4692      </address>
4693    </author>
4694    <date year="2006" month="February"/>
4695  </front>
4696  <seriesInfo name="BCP" value="115"/>
4697  <seriesInfo name="RFC" value="4395"/>
4698</reference>
4699
4700<reference anchor="RFC5226">
4701  <front>
4702    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4703    <author initials="T." surname="Narten" fullname="T. Narten">
4704      <organization>IBM</organization>
4705      <address><email>narten@us.ibm.com</email></address>
4706    </author>
4707    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
4708      <organization>Google</organization>
4709      <address><email>Harald@Alvestrand.no</email></address>
4710    </author>
4711    <date year="2008" month="May"/>
4712  </front>
4713  <seriesInfo name="BCP" value="26"/>
4714  <seriesInfo name="RFC" value="5226"/>
4715</reference>
4716
4717<reference anchor="RFC5322">
4718  <front>
4719    <title>Internet Message Format</title>
4720    <author initials="P." surname="Resnick" fullname="P. Resnick">
4721      <organization>Qualcomm Incorporated</organization>
4722    </author>
4723    <date year="2008" month="October"/>
4724  </front>
4725  <seriesInfo name="RFC" value="5322"/>
4726</reference>
4727
4728<reference anchor="draft-ietf-httpstate-cookie">
4729  <front>
4730    <title>HTTP State Management Mechanism</title>
4731    <author initials="A." surname="Barth" fullname="Adam Barth">
4732      <organization abbrev="U.C. Berkeley">
4733        University of California, Berkeley
4734      </organization>
4735      <address><email>abarth@eecs.berkeley.edu</email></address>
4736    </author>
4737    <date year="2011" month="March"/>
4738  </front>
4739  <seriesInfo name="Internet-Draft" value="draft-ietf-httpstate-cookie-23"/>
4740</reference>
4741
4742<reference anchor="BCP97">
4743  <front>
4744    <title>Handling Normative References to Standards-Track Documents</title>
4745    <author initials="J." surname="Klensin" fullname="J. Klensin">
4746      <address>
4747        <email>klensin+ietf@jck.com</email>
4748      </address>
4749    </author>
4750    <author initials="S." surname="Hartman" fullname="S. Hartman">
4751      <organization>MIT</organization>
4752      <address>
4753        <email>hartmans-ietf@mit.edu</email>
4754      </address>
4755    </author>
4756    <date year="2007" month="June"/>
4757  </front>
4758  <seriesInfo name="BCP" value="97"/>
4759  <seriesInfo name="RFC" value="4897"/>
4760</reference>
4761
4762<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4763  <front>
4764    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4765    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4766    <date year="2001" month="November"/>
4767  </front>
4768  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4769</reference>
4770
4771<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4772  <front>
4773    <title>Analysis of HTTP Performance Problems</title>
4774    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4775    <date/>
4776  </front>
4777</reference>
4778
4779<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4780  <front>
4781  <title>Analysis of HTTP Performance</title>
4782  <author initials="J." surname="Touch" fullname="Joe Touch">
4783    <organization>USC/Information Sciences Institute</organization>
4784    <address><email>touch@isi.edu</email></address>
4785  </author>
4786  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4787    <organization>USC/Information Sciences Institute</organization>
4788    <address><email>johnh@isi.edu</email></address>
4789  </author>
4790  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4791    <organization>USC/Information Sciences Institute</organization>
4792    <address><email>katia@isi.edu</email></address>
4793  </author>
4794  <date year="1998" month="Aug"/>
4795  </front>
4796  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4797  <annotation>(original report dated Aug. 1996)</annotation>
4798</reference>
4799
4800</references>
4801
4802
4803<section title="Tolerant Applications" anchor="tolerant.applications">
4804<t>
4805   Although this document specifies the requirements for the generation
4806   of HTTP/1.1 messages, not all applications will be correct in their
4807   implementation. We therefore recommend that operational applications
4808   be tolerant of deviations whenever those deviations can be
4809   interpreted unambiguously.
4810</t>
4811<t>
4812   The line terminator for header fields is the sequence CRLF.
4813   However, we recommend that applications, when parsing such headers fields,
4814   recognize a single LF as a line terminator and ignore the leading CR.
4815</t>
4816<t>
4817   The character encoding of a representation SHOULD be labeled as the lowest
4818   common denominator of the character codes used within that representation, with
4819   the exception that not labeling the representation is preferred over labeling
4820   the representation with the labels US-ASCII or ISO-8859-1. See <xref target="Part3"/>.
4821</t>
4822<t>
4823   Additional rules for requirements on parsing and encoding of dates
4824   and other potential problems with date encodings include:
4825</t>
4826<t>
4827  <list style="symbols">
4828     <t>HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
4829        which appears to be more than 50 years in the future is in fact
4830        in the past (this helps solve the "year 2000" problem).</t>
4831
4832     <t>Although all date formats are specified to be case-sensitive,
4833        recipients SHOULD match day, week and timezone names
4834        case-insensitively.</t>
4835             
4836     <t>An HTTP/1.1 implementation MAY internally represent a parsed
4837        Expires date as earlier than the proper value, but MUST NOT
4838        internally represent a parsed Expires date as later than the
4839        proper value.</t>
4840
4841     <t>All expiration-related calculations MUST be done in GMT. The
4842        local time zone MUST NOT influence the calculation or comparison
4843        of an age or expiration time.</t>
4844
4845     <t>If an HTTP header field incorrectly carries a date value with a time
4846        zone other than GMT, it MUST be converted into GMT using the
4847        most conservative possible conversion.</t>
4848  </list>
4849</t>
4850</section>
4851
4852<section title="HTTP Version History" anchor="compatibility">
4853<t>
4854   HTTP has been in use by the World-Wide Web global information initiative
4855   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4856   was a simple protocol for hypertext data transfer across the Internet
4857   with only a single request method (GET) and no metadata.
4858   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4859   methods and MIME-like messaging that could include metadata about the data
4860   transferred and modifiers on the request/response semantics. However,
4861   HTTP/1.0 did not sufficiently take into consideration the effects of
4862   hierarchical proxies, caching, the need for persistent connections, or
4863   name-based virtual hosts. The proliferation of incompletely-implemented
4864   applications calling themselves "HTTP/1.0" further necessitated a
4865   protocol version change in order for two communicating applications
4866   to determine each other's true capabilities.
4867</t>
4868<t>
4869   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4870   requirements that enable reliable implementations, adding only
4871   those new features that will either be safely ignored by an HTTP/1.0
4872   recipient or only sent when communicating with a party advertising
4873   compliance with HTTP/1.1.
4874</t>
4875<t>
4876   It is beyond the scope of a protocol specification to mandate
4877   compliance with previous versions. HTTP/1.1 was deliberately
4878   designed, however, to make supporting previous versions easy.
4879   We would expect a general-purpose HTTP/1.1 server to understand
4880   any valid request in the format of HTTP/1.0 and respond appropriately
4881   with an HTTP/1.1 message that only uses features understood (or
4882   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4883   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4884</t>
4885<t>
4886   Since HTTP/0.9 did not support header fields in a request,
4887   there is no mechanism for it to support name-based virtual
4888   hosts (selection of resource by inspection of the Host header
4889   field).  Any server that implements name-based virtual hosts
4890   ought to disable support for HTTP/0.9.  Most requests that
4891   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4892   requests wherein a buggy client failed to properly encode
4893   linear whitespace found in a URI reference and placed in
4894   the request-target.
4895</t>
4896
4897<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4898<t>
4899   This section summarizes major differences between versions HTTP/1.0
4900   and HTTP/1.1.
4901</t>
4902
4903<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4904<t>
4905   The requirements that clients and servers support the Host header
4906   field (<xref target="header.host"/>), report an error if it is
4907   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4908   are among the most important changes defined by HTTP/1.1.
4909</t>
4910<t>
4911   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4912   addresses and servers; there was no other established mechanism for
4913   distinguishing the intended server of a request than the IP address
4914   to which that request was directed. The Host header field was
4915   introduced during the development of HTTP/1.1 and, though it was
4916   quickly implemented by most HTTP/1.0 browsers, additional requirements
4917   were placed on all HTTP/1.1 requests in order to ensure complete
4918   adoption.  At the time of this writing, most HTTP-based services
4919   are dependent upon the Host header field for targeting requests.
4920</t>
4921</section>
4922
4923<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4924<t>
4925   For most implementations of HTTP/1.0, each connection is established
4926   by the client prior to the request and closed by the server after
4927   sending the response. However, some implementations implement the
4928   Keep-Alive version of persistent connections described in
4929   Section 19.7.1 of <xref target="RFC2068"/>.
4930</t>
4931<t>
4932   Some clients and servers might wish to be compatible with some
4933   previous implementations of persistent connections in HTTP/1.0
4934   clients and servers. Persistent connections in HTTP/1.0 are
4935   explicitly negotiated as they are not the default behavior. HTTP/1.0
4936   experimental implementations of persistent connections are faulty,
4937   and the new facilities in HTTP/1.1 are designed to rectify these
4938   problems. The problem was that some existing HTTP/1.0 clients might
4939   send Keep-Alive to a proxy server that doesn't understand
4940   Connection, which would then erroneously forward it to the next
4941   inbound server, which would establish the Keep-Alive connection and
4942   result in a hung HTTP/1.0 proxy waiting for the close on the
4943   response. The result is that HTTP/1.0 clients must be prevented from
4944   using Keep-Alive when talking to proxies.
4945</t>
4946<t>
4947   However, talking to proxies is the most important use of persistent
4948   connections, so that prohibition is clearly unacceptable. Therefore,
4949   we need some other mechanism for indicating a persistent connection
4950   is desired, which is safe to use even when talking to an old proxy
4951   that ignores Connection. Persistent connections are the default for
4952   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4953   declaring non-persistence. See <xref target="header.connection"/>.
4954</t>
4955</section>
4956</section>
4957
4958<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4959<t>
4960  Empty list elements in list productions have been deprecated.
4961  (<xref target="notation.abnf"/>)
4962</t>
4963<t>
4964  Rules about implicit linear whitespace between certain grammar productions
4965  have been removed; now it's only allowed when specifically pointed out
4966  in the ABNF. The NUL octet is no longer allowed in comment and quoted-string
4967  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4968  Non-ASCII content in header fields and reason phrase has been obsoleted and
4969  made opaque (the TEXT rule was removed)
4970  (<xref target="basic.rules"/>)
4971</t>
4972<t>
4973  Clarify that HTTP-Version is case sensitive.
4974  (<xref target="http.version"/>)
4975</t>
4976<t>
4977  Require that invalid whitespace around field-names be rejected.
4978  (<xref target="header.fields"/>)
4979</t>
4980<t>
4981  Require recipients to handle bogus Content-Length header fields as errors.
4982  (<xref target="message.body"/>)
4983</t>
4984<t>
4985  Remove reference to non-existent identity transfer-coding value tokens.
4986  (Sections <xref format="counter" target="message.body"/> and
4987  <xref format="counter" target="transfer.codings"/>)
4988</t>
4989<t>
4990  Update use of abs_path production from RFC 1808 to the path-absolute + query
4991  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4992  request method only.
4993  (<xref target="request-target"/>)
4994</t>
4995<t>
4996  Clarification that the chunk length does not include the count of the octets
4997  in the chunk header and trailer. Furthermore disallowed line folding
4998  in chunk extensions.
4999  (<xref target="chunked.encoding"/>)
5000</t>
5001<t>
5002  Remove hard limit of two connections per server.
5003  (<xref target="persistent.practical"/>)
5004</t>
5005<t>
5006  Clarify exactly when close connection options must be sent.
5007  (<xref target="header.connection"/>)
5008</t>
5009<t>
5010  Define the semantics of the "Upgrade" header field in responses other than
5011  101 (this was incorporated from <xref target="RFC2817"/>).
5012  (<xref target="header.upgrade"/>)
5013</t>
5014</section>
5015</section>
5016
5017
5018<section title="Collected ABNF" anchor="collected.abnf">
5019<figure>
5020<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
5021BWS = OWS
5022
5023Chunked-Body = *chunk last-chunk trailer-part CRLF
5024Connection = "Connection:" OWS Connection-v
5025Connection-v = *( "," OWS ) connection-token *( OWS "," [ OWS
5026 connection-token ] )
5027Content-Length = "Content-Length:" OWS 1*Content-Length-v
5028Content-Length-v = 1*DIGIT
5029
5030Date = "Date:" OWS Date-v
5031Date-v = HTTP-date
5032
5033GMT = %x47.4D.54 ; GMT
5034
5035HTTP-Prot-Name = %x48.54.54.50 ; HTTP
5036HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
5037HTTP-date = rfc1123-date / obs-date
5038HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
5039 ]
5040Host = "Host:" OWS Host-v
5041Host-v = uri-host [ ":" port ]
5042
5043Method = token
5044
5045OWS = *( [ obs-fold ] WSP )
5046
5047RWS = 1*( [ obs-fold ] WSP )
5048Reason-Phrase = *( WSP / VCHAR / obs-text )
5049Request = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5050Request-Line = Method SP request-target SP HTTP-Version CRLF
5051Response = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5052
5053Status-Code = 3DIGIT
5054Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5055
5056TE = "TE:" OWS TE-v
5057TE-v = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5058Trailer = "Trailer:" OWS Trailer-v
5059Trailer-v = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5060Transfer-Encoding = "Transfer-Encoding:" OWS Transfer-Encoding-v
5061Transfer-Encoding-v = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5062 transfer-coding ] )
5063
5064URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
5065Upgrade = "Upgrade:" OWS Upgrade-v
5066Upgrade-v = *( "," OWS ) product *( OWS "," [ OWS product ] )
5067
5068Via = "Via:" OWS Via-v
5069Via-v = *( "," OWS ) received-protocol RWS received-by [ RWS comment
5070 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
5071 ] )
5072
5073absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
5074asctime-date = day-name SP date3 SP time-of-day SP year
5075attribute = token
5076authority = <authority, defined in [RFC3986], Section 3.2>
5077
5078chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5079chunk-data = 1*OCTET
5080chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5081chunk-ext-name = token
5082chunk-ext-val = token / quoted-str-nf
5083chunk-size = 1*HEXDIG
5084comment = "(" *( ctext / quoted-cpair / comment ) ")"
5085connection-token = token
5086ctext = OWS / %x21-27 ; '!'-'''
5087 / %x2A-5B ; '*'-'['
5088 / %x5D-7E ; ']'-'~'
5089 / obs-text
5090
5091date1 = day SP month SP year
5092date2 = day "-" month "-" 2DIGIT
5093date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
5094day = 2DIGIT
5095day-name = %x4D.6F.6E ; Mon
5096 / %x54.75.65 ; Tue
5097 / %x57.65.64 ; Wed
5098 / %x54.68.75 ; Thu
5099 / %x46.72.69 ; Fri
5100 / %x53.61.74 ; Sat
5101 / %x53.75.6E ; Sun
5102day-name-l = %x4D.6F.6E.64.61.79 ; Monday
5103 / %x54.75.65.73.64.61.79 ; Tuesday
5104 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
5105 / %x54.68.75.72.73.64.61.79 ; Thursday
5106 / %x46.72.69.64.61.79 ; Friday
5107 / %x53.61.74.75.72.64.61.79 ; Saturday
5108 / %x53.75.6E.64.61.79 ; Sunday
5109
5110field-content = *( WSP / VCHAR / obs-text )
5111field-name = token
5112field-value = *( field-content / OWS )
5113
5114header-field = field-name ":" OWS [ field-value ] OWS
5115hour = 2DIGIT
5116http-URI = "http://" authority path-abempty [ "?" query ]
5117https-URI = "https://" authority path-abempty [ "?" query ]
5118
5119last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF
5120
5121message-body = *OCTET
5122minute = 2DIGIT
5123month = %x4A.61.6E ; Jan
5124 / %x46.65.62 ; Feb
5125 / %x4D.61.72 ; Mar
5126 / %x41.70.72 ; Apr
5127 / %x4D.61.79 ; May
5128 / %x4A.75.6E ; Jun
5129 / %x4A.75.6C ; Jul
5130 / %x41.75.67 ; Aug
5131 / %x53.65.70 ; Sep
5132 / %x4F.63.74 ; Oct
5133 / %x4E.6F.76 ; Nov
5134 / %x44.65.63 ; Dec
5135
5136obs-date = rfc850-date / asctime-date
5137obs-fold = CRLF
5138obs-text = %x80-FF
5139
5140partial-URI = relative-part [ "?" query ]
5141path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
5142path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
5143port = <port, defined in [RFC3986], Section 3.2.3>
5144product = token [ "/" product-version ]
5145product-version = token
5146protocol-name = token
5147protocol-version = token
5148pseudonym = token
5149
5150qdtext = OWS / "!" / %x23-5B ; '#'-'['
5151 / %x5D-7E ; ']'-'~'
5152 / obs-text
5153qdtext-nf = WSP / "!" / %x23-5B ; '#'-'['
5154 / %x5D-7E ; ']'-'~'
5155 / obs-text
5156query = <query, defined in [RFC3986], Section 3.4>
5157quoted-cpair = "\" ( WSP / VCHAR / obs-text )
5158quoted-pair = "\" ( WSP / VCHAR / obs-text )
5159quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5160quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5161qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5162
5163received-by = ( uri-host [ ":" port ] ) / pseudonym
5164received-protocol = [ protocol-name "/" ] protocol-version
5165relative-part = <relative-part, defined in [RFC3986], Section 4.2>
5166request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5167 / authority
5168rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
5169rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
5170
5171second = 2DIGIT
5172special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
5173 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5174start-line = Request-Line / Status-Line
5175
5176t-codings = "trailers" / ( transfer-extension [ te-params ] )
5177tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
5178 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5179te-ext = OWS ";" OWS token [ "=" word ]
5180te-params = OWS ";" OWS "q=" qvalue *te-ext
5181time-of-day = hour ":" minute ":" second
5182token = 1*tchar
5183trailer-part = *( header-field CRLF )
5184transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
5185 transfer-extension
5186transfer-extension = token *( OWS ";" OWS transfer-parameter )
5187transfer-parameter = attribute BWS "=" BWS value
5188
5189uri-host = <host, defined in [RFC3986], Section 3.2.2>
5190
5191value = word
5192
5193word = token / quoted-string
5194
5195year = 4DIGIT
5196]]></artwork>
5197</figure>
5198<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
5199; Chunked-Body defined but not used
5200; Connection defined but not used
5201; Content-Length defined but not used
5202; Date defined but not used
5203; HTTP-message defined but not used
5204; Host defined but not used
5205; Request defined but not used
5206; Response defined but not used
5207; TE defined but not used
5208; Trailer defined but not used
5209; Transfer-Encoding defined but not used
5210; URI-reference defined but not used
5211; Upgrade defined but not used
5212; Via defined but not used
5213; http-URI defined but not used
5214; https-URI defined but not used
5215; partial-URI defined but not used
5216; special defined but not used
5217]]></artwork></figure></section>
5218
5219
5220<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5221
5222<section title="Since RFC 2616">
5223<t>
5224  Extracted relevant partitions from <xref target="RFC2616"/>.
5225</t>
5226</section>
5227
5228<section title="Since draft-ietf-httpbis-p1-messaging-00">
5229<t>
5230  Closed issues:
5231  <list style="symbols">
5232    <t>
5233      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5234      "HTTP Version should be case sensitive"
5235      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5236    </t>
5237    <t>
5238      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5239      "'unsafe' characters"
5240      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5241    </t>
5242    <t>
5243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5244      "Chunk Size Definition"
5245      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5246    </t>
5247    <t>
5248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5249      "Message Length"
5250      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5251    </t>
5252    <t>
5253      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5254      "Media Type Registrations"
5255      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5256    </t>
5257    <t>
5258      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5259      "URI includes query"
5260      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5261    </t>
5262    <t>
5263      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5264      "No close on 1xx responses"
5265      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5266    </t>
5267    <t>
5268      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5269      "Remove 'identity' token references"
5270      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5271    </t>
5272    <t>
5273      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5274      "Import query BNF"
5275    </t>
5276    <t>
5277      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5278      "qdtext BNF"
5279    </t>
5280    <t>
5281      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5282      "Normative and Informative references"
5283    </t>
5284    <t>
5285      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5286      "RFC2606 Compliance"
5287    </t>
5288    <t>
5289      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5290      "RFC977 reference"
5291    </t>
5292    <t>
5293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5294      "RFC1700 references"
5295    </t>
5296    <t>
5297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5298      "inconsistency in date format explanation"
5299    </t>
5300    <t>
5301      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5302      "Date reference typo"
5303    </t>
5304    <t>
5305      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5306      "Informative references"
5307    </t>
5308    <t>
5309      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5310      "ISO-8859-1 Reference"
5311    </t>
5312    <t>
5313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5314      "Normative up-to-date references"
5315    </t>
5316  </list>
5317</t>
5318<t>
5319  Other changes:
5320  <list style="symbols">
5321    <t>
5322      Update media type registrations to use RFC4288 template.
5323    </t>
5324    <t>
5325      Use names of RFC4234 core rules DQUOTE and WSP,
5326      fix broken ABNF for chunk-data
5327      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5328    </t>
5329  </list>
5330</t>
5331</section>
5332
5333<section title="Since draft-ietf-httpbis-p1-messaging-01">
5334<t>
5335  Closed issues:
5336  <list style="symbols">
5337    <t>
5338      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5339      "Bodies on GET (and other) requests"
5340    </t>
5341    <t>
5342      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5343      "Updating to RFC4288"
5344    </t>
5345    <t>
5346      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5347      "Status Code and Reason Phrase"
5348    </t>
5349    <t>
5350      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5351      "rel_path not used"
5352    </t>
5353  </list>
5354</t>
5355<t>
5356  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5357  <list style="symbols">
5358    <t>
5359      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
5360      "trailer-part").
5361    </t>
5362    <t>
5363      Avoid underscore character in rule names ("http_URL" -&gt;
5364      "http-URL", "abs_path" -&gt; "path-absolute").
5365    </t>
5366    <t>
5367      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5368      "path-absolute", "port", "query", "relativeURI", "host) — these will
5369      have to be updated when switching over to RFC3986.
5370    </t>
5371    <t>
5372      Synchronize core rules with RFC5234.
5373    </t>
5374    <t>
5375      Get rid of prose rules that span multiple lines.
5376    </t>
5377    <t>
5378      Get rid of unused rules LOALPHA and UPALPHA.
5379    </t>
5380    <t>
5381      Move "Product Tokens" section (back) into Part 1, as "token" is used
5382      in the definition of the Upgrade header field.
5383    </t>
5384    <t>
5385      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5386    </t>
5387    <t>
5388      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5389    </t>
5390  </list>
5391</t>
5392</section>
5393
5394<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5395<t>
5396  Closed issues:
5397  <list style="symbols">
5398    <t>
5399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5400      "HTTP-date vs. rfc1123-date"
5401    </t>
5402    <t>
5403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5404      "WS in quoted-pair"
5405    </t>
5406  </list>
5407</t>
5408<t>
5409  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5410  <list style="symbols">
5411    <t>
5412      Reference RFC 3984, and update header field registrations for headers defined
5413      in this document.
5414    </t>
5415  </list>
5416</t>
5417<t>
5418  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5419  <list style="symbols">
5420    <t>
5421      Replace string literals when the string really is case-sensitive (HTTP-Version).
5422    </t>
5423  </list>
5424</t>
5425</section>
5426
5427<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5428<t>
5429  Closed issues:
5430  <list style="symbols">
5431    <t>
5432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5433      "Connection closing"
5434    </t>
5435    <t>
5436      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5437      "Move registrations and registry information to IANA Considerations"
5438    </t>
5439    <t>
5440      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5441      "need new URL for PAD1995 reference"
5442    </t>
5443    <t>
5444      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5445      "IANA Considerations: update HTTP URI scheme registration"
5446    </t>
5447    <t>
5448      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5449      "Cite HTTPS URI scheme definition"
5450    </t>
5451    <t>
5452      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5453      "List-type headers vs Set-Cookie"
5454    </t>
5455  </list>
5456</t>
5457<t>
5458  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5459  <list style="symbols">
5460    <t>
5461      Replace string literals when the string really is case-sensitive (HTTP-Date).
5462    </t>
5463    <t>
5464      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5465    </t>
5466  </list>
5467</t>
5468</section>
5469
5470<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5471<t>
5472  Closed issues:
5473  <list style="symbols">
5474    <t>
5475      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5476      "Out-of-date reference for URIs"
5477    </t>
5478    <t>
5479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5480      "RFC 2822 is updated by RFC 5322"
5481    </t>
5482  </list>
5483</t>
5484<t>
5485  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5486  <list style="symbols">
5487    <t>
5488      Use "/" instead of "|" for alternatives.
5489    </t>
5490    <t>
5491      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5492    </t>
5493    <t>
5494      Only reference RFC 5234's core rules.
5495    </t>
5496    <t>
5497      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5498      whitespace ("OWS") and required whitespace ("RWS").
5499    </t>
5500    <t>
5501      Rewrite ABNFs to spell out whitespace rules, factor out
5502      header field value format definitions.
5503    </t>
5504  </list>
5505</t>
5506</section>
5507
5508<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5509<t>
5510  Closed issues:
5511  <list style="symbols">
5512    <t>
5513      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5514      "Header LWS"
5515    </t>
5516    <t>
5517      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5518      "Sort 1.3 Terminology"
5519    </t>
5520    <t>
5521      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5522      "RFC2047 encoded words"
5523    </t>
5524    <t>
5525      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5526      "Character Encodings in TEXT"
5527    </t>
5528    <t>
5529      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5530      "Line Folding"
5531    </t>
5532    <t>
5533      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5534      "OPTIONS * and proxies"
5535    </t>
5536    <t>
5537      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5538      "Reason-Phrase BNF"
5539    </t>
5540    <t>
5541      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5542      "Use of TEXT"
5543    </t>
5544    <t>
5545      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5546      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5547    </t>
5548    <t>
5549      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5550      "RFC822 reference left in discussion of date formats"
5551    </t>
5552  </list>
5553</t>
5554<t>
5555  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5556  <list style="symbols">
5557    <t>
5558      Rewrite definition of list rules, deprecate empty list elements.
5559    </t>
5560    <t>
5561      Add appendix containing collected and expanded ABNF.
5562    </t>
5563  </list>
5564</t>
5565<t>
5566  Other changes:
5567  <list style="symbols">
5568    <t>
5569      Rewrite introduction; add mostly new Architecture Section.
5570    </t>
5571    <t>
5572      Move definition of quality values from Part 3 into Part 1;
5573      make TE request header field grammar independent of accept-params (defined in Part 3).
5574    </t>
5575  </list>
5576</t>
5577</section>
5578
5579<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5580<t>
5581  Closed issues:
5582  <list style="symbols">
5583    <t>
5584      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5585      "base for numeric protocol elements"
5586    </t>
5587    <t>
5588      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5589      "comment ABNF"
5590    </t>
5591  </list>
5592</t>
5593<t>
5594  Partly resolved issues:
5595  <list style="symbols">
5596    <t>
5597      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5598      "205 Bodies" (took out language that implied that there might be
5599      methods for which a request body MUST NOT be included)
5600    </t>
5601    <t>
5602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5603      "editorial improvements around HTTP-date"
5604    </t>
5605  </list>
5606</t>
5607</section>
5608
5609<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5610<t>
5611  Closed issues:
5612  <list style="symbols">
5613    <t>
5614      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5615      "Repeating single-value headers"
5616    </t>
5617    <t>
5618      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5619      "increase connection limit"
5620    </t>
5621    <t>
5622      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5623      "IP addresses in URLs"
5624    </t>
5625    <t>
5626      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5627      "take over HTTP Upgrade Token Registry"
5628    </t>
5629    <t>
5630      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5631      "CR and LF in chunk extension values"
5632    </t>
5633    <t>
5634      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5635      "HTTP/0.9 support"
5636    </t>
5637    <t>
5638      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5639      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5640    </t>
5641    <t>
5642      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5643      "move definitions of gzip/deflate/compress to part 1"
5644    </t>
5645    <t>
5646      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5647      "disallow control characters in quoted-pair"
5648    </t>
5649  </list>
5650</t>
5651<t>
5652  Partly resolved issues:
5653  <list style="symbols">
5654    <t>
5655      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5656      "update IANA requirements wrt Transfer-Coding values" (add the
5657      IANA Considerations subsection)
5658    </t>
5659  </list>
5660</t>
5661</section>
5662
5663<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5664<t>
5665  Closed issues:
5666  <list style="symbols">
5667    <t>
5668      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5669      "header parsing, treatment of leading and trailing OWS"
5670    </t>
5671  </list>
5672</t>
5673<t>
5674  Partly resolved issues:
5675  <list style="symbols">
5676    <t>
5677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5678      "Placement of 13.5.1 and 13.5.2"
5679    </t>
5680    <t>
5681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5682      "use of term "word" when talking about header structure"
5683    </t>
5684  </list>
5685</t>
5686</section>
5687
5688<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5689<t>
5690  Closed issues:
5691  <list style="symbols">
5692    <t>
5693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5694      "Clarification of the term 'deflate'"
5695    </t>
5696    <t>
5697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5698      "OPTIONS * and proxies"
5699    </t>
5700    <t>
5701      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5702      "MIME-Version not listed in P1, general header fields"
5703    </t>
5704    <t>
5705      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5706      "IANA registry for content/transfer encodings"
5707    </t>
5708    <t>
5709      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5710      "Case-sensitivity of HTTP-date"
5711    </t>
5712    <t>
5713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5714      "use of term "word" when talking about header structure"
5715    </t>
5716  </list>
5717</t>
5718<t>
5719  Partly resolved issues:
5720  <list style="symbols">
5721    <t>
5722      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5723      "Term for the requested resource's URI"
5724    </t>
5725  </list>
5726</t>
5727</section>
5728
5729<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5730<t>
5731  Closed issues:
5732  <list style="symbols">
5733    <t>
5734      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5735      "Connection Closing"
5736    </t>
5737    <t>
5738      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5739      "Delimiting messages with multipart/byteranges"
5740    </t>
5741    <t>
5742      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5743      "Handling multiple Content-Length headers"
5744    </t>
5745    <t>
5746      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5747      "Clarify entity / representation / variant terminology"
5748    </t>
5749    <t>
5750      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5751      "consider removing the 'changes from 2068' sections"
5752    </t>
5753  </list>
5754</t>
5755<t>
5756  Partly resolved issues:
5757  <list style="symbols">
5758    <t>
5759      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5760      "HTTP(s) URI scheme definitions"
5761    </t>
5762  </list>
5763</t>
5764</section>
5765
5766<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5767<t>
5768  Closed issues:
5769  <list style="symbols">
5770    <t>
5771      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5772      "Trailer requirements"
5773    </t>
5774    <t>
5775      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5776      "Text about clock requirement for caches belongs in p6"
5777    </t>
5778    <t>
5779      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5780      "effective request URI: handling of missing host in HTTP/1.0"
5781    </t>
5782    <t>
5783      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5784      "confusing Date requirements for clients"
5785    </t>
5786  </list>
5787</t>
5788<t>
5789  Partly resolved issues:
5790  <list style="symbols">
5791    <t>
5792      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5793      "Handling multiple Content-Length headers"
5794    </t>
5795  </list>
5796</t>
5797</section>
5798
5799<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5800<t>
5801  Closed issues:
5802  <list style="symbols">
5803    <t>
5804      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5805      "RFC2145 Normative"
5806    </t>
5807    <t>
5808      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5809      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5810    </t>
5811    <t>
5812      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5813      "define 'transparent' proxy"
5814    </t>
5815    <t>
5816      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5817      "Header Classification"
5818    </t>
5819    <t>
5820      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5821      "Is * usable as a request-uri for new methods?"
5822    </t>
5823    <t>
5824      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5825      "Migrate Upgrade details from RFC2817"
5826    </t>
5827    <t>
5828      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5829      "untangle ABNFs for header fields"
5830    </t>
5831    <t>
5832      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5833      "update RFC 2109 reference"
5834    </t>
5835  </list>
5836</t>
5837</section>
5838
5839</section>
5840
5841</back>
5842</rfc>
Note: See TracBrowser for help on using the repository browser.