source: draft-ietf-httpbis/08/draft-ietf-httpbis-p1-messaging-08.xml @ 2462

Last change on this file since 2462 was 1500, checked in by julian.reschke@…, 9 years ago

fix mime types

  • Property svn:executable set to *
  • Property svn:mime-type set to text/xml
File size: 211.2 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<!DOCTYPE rfc
17  PUBLIC "" "rfc2629.dtd">
18<rfc obsoletes="2616" updates="2817" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-08">
19<front>
20
21  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
22
23  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
24    <organization abbrev="Day Software">Day Software</organization>
25    <address>
26      <postal>
27        <street>23 Corporate Plaza DR, Suite 280</street>
28        <city>Newport Beach</city>
29        <region>CA</region>
30        <code>92660</code>
31        <country>USA</country>
32      </postal>
33      <phone>+1-949-706-5300</phone>
34      <facsimile>+1-949-706-5305</facsimile>
35      <email>fielding@gbiv.com</email>
36      <uri>http://roy.gbiv.com/</uri>
37    </address>
38  </author>
39
40  <author initials="J." surname="Gettys" fullname="Jim Gettys">
41    <organization>One Laptop per Child</organization>
42    <address>
43      <postal>
44        <street>21 Oak Knoll Road</street>
45        <city>Carlisle</city>
46        <region>MA</region>
47        <code>01741</code>
48        <country>USA</country>
49      </postal>
50      <email>jg@laptop.org</email>
51      <uri>http://www.laptop.org/</uri>
52    </address>
53  </author>
54 
55  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
56    <organization abbrev="HP">Hewlett-Packard Company</organization>
57    <address>
58      <postal>
59        <street>HP Labs, Large Scale Systems Group</street>
60        <street>1501 Page Mill Road, MS 1177</street>
61        <city>Palo Alto</city>
62        <region>CA</region>
63        <code>94304</code>
64        <country>USA</country>
65      </postal>
66      <email>JeffMogul@acm.org</email>
67    </address>
68  </author>
69
70  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
71    <organization abbrev="Microsoft">Microsoft Corporation</organization>
72    <address>
73      <postal>
74        <street>1 Microsoft Way</street>
75        <city>Redmond</city>
76        <region>WA</region>
77        <code>98052</code>
78        <country>USA</country>
79      </postal>
80      <email>henrikn@microsoft.com</email>
81    </address>
82  </author>
83
84  <author initials="L." surname="Masinter" fullname="Larry Masinter">
85    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
86    <address>
87      <postal>
88        <street>345 Park Ave</street>
89        <city>San Jose</city>
90        <region>CA</region>
91        <code>95110</code>
92        <country>USA</country>
93      </postal>
94      <email>LMM@acm.org</email>
95      <uri>http://larry.masinter.net/</uri>
96    </address>
97  </author>
98 
99  <author initials="P." surname="Leach" fullname="Paul J. Leach">
100    <organization abbrev="Microsoft">Microsoft Corporation</organization>
101    <address>
102      <postal>
103        <street>1 Microsoft Way</street>
104        <city>Redmond</city>
105        <region>WA</region>
106        <code>98052</code>
107      </postal>
108      <email>paulle@microsoft.com</email>
109    </address>
110  </author>
111   
112  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
113    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
114    <address>
115      <postal>
116        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
117        <street>The Stata Center, Building 32</street>
118        <street>32 Vassar Street</street>
119        <city>Cambridge</city>
120        <region>MA</region>
121        <code>02139</code>
122        <country>USA</country>
123      </postal>
124      <email>timbl@w3.org</email>
125      <uri>http://www.w3.org/People/Berners-Lee/</uri>
126    </address>
127  </author>
128
129  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
130    <organization abbrev="W3C">World Wide Web Consortium</organization>
131    <address>
132      <postal>
133        <street>W3C / ERCIM</street>
134        <street>2004, rte des Lucioles</street>
135        <city>Sophia-Antipolis</city>
136        <region>AM</region>
137        <code>06902</code>
138        <country>France</country>
139      </postal>
140      <email>ylafon@w3.org</email>
141      <uri>http://www.raubacapeu.net/people/yves/</uri>
142    </address>
143  </author>
144
145  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
146    <organization abbrev="greenbytes">greenbytes GmbH</organization>
147    <address>
148      <postal>
149        <street>Hafenweg 16</street>
150        <city>Muenster</city><region>NW</region><code>48155</code>
151        <country>Germany</country>
152      </postal>
153      <phone>+49 251 2807760</phone>
154      <facsimile>+49 251 2807761</facsimile>
155      <email>julian.reschke@greenbytes.de</email>
156      <uri>http://greenbytes.de/tech/webdav/</uri>
157    </address>
158  </author>
159
160  <date day="26" month="October" year="2009"/>
161  <workgroup>HTTPbis Working Group</workgroup>
162
163<abstract>
164<t>
165   The Hypertext Transfer Protocol (HTTP) is an application-level
166   protocol for distributed, collaborative, hypertext information
167   systems. HTTP has been in use by the World Wide Web global information
168   initiative since 1990. This document is Part 1 of the seven-part specification
169   that defines the protocol referred to as "HTTP/1.1" and, taken together,
170   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
171   its associated terminology, defines the "http" and "https" Uniform
172   Resource Identifier (URI) schemes, defines the generic message syntax
173   and parsing requirements for HTTP message frames, and describes
174   general security concerns for implementations.
175</t>
176</abstract>
177
178<note title="Editorial Note (To be removed by RFC Editor)">
179  <t>
180    Discussion of this draft should take place on the HTTPBIS working group
181    mailing list (ietf-http-wg@w3.org). The current issues list is
182    at <eref target="http://tools.ietf.org/wg/httpbis/trac/report/11"/>
183    and related documents (including fancy diffs) can be found at
184    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
185  </t>
186  <t>
187    The changes in this draft are summarized in <xref target="changes.since.07"/>.
188  </t>
189</note>
190</front>
191<middle>
192<section title="Introduction" anchor="introduction">
193<t>
194   The Hypertext Transfer Protocol (HTTP) is an application-level
195   request/response protocol that uses extensible semantics and MIME-like
196   message payloads for flexible interaction with network-based hypertext
197   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
198   standard <xref target="RFC3986"/> to indicate request targets and
199   relationships between resources.
200   Messages are passed in a format similar to that used by Internet mail
201   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
202   (MIME) <xref target="RFC2045"/> (see Appendix A of <xref target="Part3"/> for the differences
203   between HTTP and MIME messages).
204</t>
205<t>
206   HTTP is a generic interface protocol for information systems. It is
207   designed to hide the details of how a service is implemented by presenting
208   a uniform interface to clients that is independent of the types of
209   resources provided. Likewise, servers do not need to be aware of each
210   client's purpose: an HTTP request can be considered in isolation rather
211   than being associated with a specific type of client or a predetermined
212   sequence of application steps. The result is a protocol that can be used
213   effectively in many different contexts and for which implementations can
214   evolve independently over time.
215</t>
216<t>
217   HTTP is also designed for use as a generic protocol for translating
218   communication to and from other Internet information systems.
219   HTTP proxies and gateways provide access to alternative information
220   services by translating their diverse protocols into a hypertext
221   format that can be viewed and manipulated by clients in the same way
222   as HTTP services.
223</t>
224<t>
225   One consequence of HTTP flexibility is that the protocol cannot be
226   defined in terms of what occurs behind the interface. Instead, we
227   are limited to defining the syntax of communication, the intent
228   of received communication, and the expected behavior of recipients.
229   If the communication is considered in isolation, then successful
230   actions should be reflected in corresponding changes to the
231   observable interface provided by servers. However, since multiple
232   clients may act in parallel and perhaps at cross-purposes, we
233   cannot require that such changes be observable beyond the scope
234   of a single response.
235</t>
236<t>
237   This document is Part 1 of the seven-part specification of HTTP,
238   defining the protocol referred to as "HTTP/1.1" and obsoleting
239   <xref target="RFC2616"/>.
240   Part 1 describes the architectural elements that are used or
241   referred to in HTTP, defines the "http" and "https" URI schemes,
242   describes overall network operation and connection management,
243   and defines HTTP message framing and forwarding requirements.
244   Our goal is to define all of the mechanisms necessary for HTTP message
245   handling that are independent of message semantics, thereby defining the
246   complete set of requirements for message parsers and
247   message-forwarding intermediaries.
248</t>
249
250<section title="Requirements" anchor="intro.requirements">
251<t>
252   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
253   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
254   document are to be interpreted as described in <xref target="RFC2119"/>.
255</t>
256<t>
257   An implementation is not compliant if it fails to satisfy one or more
258   of the MUST or REQUIRED level requirements for the protocols it
259   implements. An implementation that satisfies all the MUST or REQUIRED
260   level and all the SHOULD level requirements for its protocols is said
261   to be "unconditionally compliant"; one that satisfies all the MUST
262   level requirements but not all the SHOULD level requirements for its
263   protocols is said to be "conditionally compliant."
264</t>
265</section>
266
267<section title="Syntax Notation" anchor="notation">
268<iref primary="true" item="Grammar" subitem="ALPHA"/>
269<iref primary="true" item="Grammar" subitem="CR"/>
270<iref primary="true" item="Grammar" subitem="CRLF"/>
271<iref primary="true" item="Grammar" subitem="CTL"/>
272<iref primary="true" item="Grammar" subitem="DIGIT"/>
273<iref primary="true" item="Grammar" subitem="DQUOTE"/>
274<iref primary="true" item="Grammar" subitem="HEXDIG"/>
275<iref primary="true" item="Grammar" subitem="LF"/>
276<iref primary="true" item="Grammar" subitem="OCTET"/>
277<iref primary="true" item="Grammar" subitem="SP"/>
278<iref primary="true" item="Grammar" subitem="VCHAR"/>
279<iref primary="true" item="Grammar" subitem="WSP"/>
280<t>
281   This specification uses the Augmented Backus-Naur Form (ABNF) notation
282   of <xref target="RFC5234"/>.
283</t>
284<t anchor="core.rules">
285 
286 
287 
288 
289 
290 
291 
292 
293 
294 
295 
296 
297   The following core rules are included by
298   reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
299   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
300   DIGIT (decimal 0-9), DQUOTE (double quote),
301   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
302   OCTET (any 8-bit sequence of data), SP (space),
303   VCHAR (any visible <xref target="USASCII"/> character),
304   and WSP (whitespace).
305</t>
306
307<section title="ABNF Extension: #rule" anchor="notation.abnf">
308  <t>
309    One extension to the ABNF rules of <xref target="RFC5234"/> is used to
310    improve readability.
311  </t>
312  <t>
313    A construct "#" is defined, similar to "*", for defining lists of
314    elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
315    &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single comma
316    (",") and optional whitespace (OWS).   
317  </t>
318  <figure><preamble>
319    Thus,
320</preamble><artwork type="example"><![CDATA[
321  1#element => element *( OWS "," OWS element )
322]]></artwork></figure>
323  <figure><preamble>
324    and:
325</preamble><artwork type="example"><![CDATA[
326  #element => [ 1#element ]
327]]></artwork></figure>
328  <figure><preamble>
329    and for n &gt;= 1 and m &gt; 1:
330</preamble><artwork type="example"><![CDATA[
331  <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
332]]></artwork></figure>
333  <t>
334    For compatibility with legacy list rules, recipients SHOULD accept empty
335    list elements. In other words, consumers would follow the list productions:
336  </t>
337<figure><artwork type="example"><![CDATA[
338  #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
339 
340  1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
341]]></artwork></figure> 
342<t>
343  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
344  expanded as explained above.
345</t>
346</section>
347
348<section title="Basic Rules" anchor="basic.rules">
349<t anchor="rule.CRLF">
350 
351   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
352   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
353   tolerant applications). The end-of-line marker within an entity-body
354   is defined by its associated media type, as described in Section 2.3 of <xref target="Part3"/>.
355</t>
356<t anchor="rule.LWS">
357   This specification uses three rules to denote the use of linear
358   whitespace: OWS (optional whitespace), RWS (required whitespace), and
359   BWS ("bad" whitespace).
360</t>
361<t>
362   The OWS rule is used where zero or more linear whitespace characters may
363   appear. OWS SHOULD either not be produced or be produced as a single SP
364   character. Multiple OWS characters that occur within field-content SHOULD
365   be replaced with a single SP before interpreting the field value or
366   forwarding the message downstream.
367</t>
368<t>
369   RWS is used when at least one linear whitespace character is required to
370   separate field tokens. RWS SHOULD be produced as a single SP character.
371   Multiple RWS characters that occur within field-content SHOULD be
372   replaced with a single SP before interpreting the field value or
373   forwarding the message downstream.
374</t>
375<t>
376   BWS is used where the grammar allows optional whitespace for historical
377   reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
378   recipients MUST accept such bad optional whitespace and remove it before
379   interpreting the field value or forwarding the message downstream.
380</t>
381<t anchor="rule.whitespace">
382 
383 
384 
385 
386</t>
387<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[
388  OWS            = *( [ obs-fold ] WSP )
389                 ; "optional" whitespace
390  RWS            = 1*( [ obs-fold ] WSP )
391                 ; "required" whitespace
392  BWS            = OWS
393                 ; "bad" whitespace
394  obs-fold       = CRLF
395                 ; see Section 3.2
396]]></artwork></figure>
397<t anchor="rule.token.separators">
398 
399 
400   Many HTTP/1.1 header field values consist of words separated by whitespace
401   or special characters. These special characters MUST be in a quoted
402   string to be used within a parameter value (as defined in
403   <xref target="transfer.codings"/>).
404</t>
405<figure><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><artwork type="abnf2616"><![CDATA[
406  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
407                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
408                 / DIGIT / ALPHA
409                 
410  token          = 1*tchar
411]]></artwork></figure>
412<t anchor="rule.quoted-string">
413 
414 
415 
416   A string of text is parsed as a single word if it is quoted using
417   double-quote marks.
418</t>
419<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[
420  quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
421  qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
422                 ; OWS / <VCHAR except DQUOTE and "\"> / obs-text
423  obs-text       = %x80-FF
424]]></artwork></figure>
425<t anchor="rule.quoted-pair">
426 
427   The backslash character ("\") can be used as a single-character
428   quoting mechanism within quoted-string constructs:
429</t>
430<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
431  quoted-pair    = "\" ( WSP / VCHAR / obs-text )
432]]></artwork></figure>
433<t>
434   Producers SHOULD NOT escape characters that do not require escaping
435   (i.e., other than DQUOTE and the backslash character).
436</t>
437</section>
438
439<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
440 
441 
442 
443 
444 
445 
446 
447<t>
448  The ABNF rules below are defined in other parts:
449</t>
450<figure><artwork type="abnf2616"><![CDATA[
451  request-header  = <request-header, defined in [Part2], Section 3>
452  response-header = <response-header, defined in [Part2], Section 5>
453]]></artwork></figure>
454<figure><artwork type="abnf2616"><![CDATA[
455  entity-body     = <entity-body, defined in [Part3], Section 3.2>
456  entity-header   = <entity-header, defined in [Part3], Section 3.1>
457]]></artwork></figure>
458<figure><artwork type="abnf2616"><![CDATA[
459  Cache-Control   = <Cache-Control, defined in [Part6], Section 3.4>
460  Pragma          = <Pragma, defined in [Part6], Section 3.4>
461  Warning         = <Warning, defined in [Part6], Section 3.6>
462]]></artwork></figure>
463</section>
464
465</section>
466</section>
467
468<section title="HTTP architecture" anchor="architecture">
469<t>
470   HTTP was created for the World Wide Web architecture
471   and has evolved over time to support the scalability needs of a worldwide
472   hypertext system. Much of that architecture is reflected in the terminology
473   and syntax productions used to define HTTP.
474</t>
475
476<section title="Client/Server Operation" anchor="operation">
477<iref item="client"/>
478<iref item="server"/>
479<iref item="connection"/>
480<t>
481   HTTP is a request/response protocol that operates by exchanging messages
482   across a reliable transport or session-layer connection. An HTTP client
483   is a program that establishes a connection to a server for the purpose
484   of sending one or more HTTP requests.  An HTTP server is a program that
485   accepts connections in order to service HTTP requests by sending HTTP
486   responses.
487</t>
488<iref item="user agent"/>
489<iref item="origin server"/>
490<t>
491   Note that the terms "client" and "server" refer only to the roles that
492   these programs perform for a particular connection.  The same program
493   may act as a client on some connections and a server on others.  We use
494   the term "user agent" to refer to the program that initiates a request,
495   such as a WWW browser, editor, or spider (web-traversing robot), and
496   the term "origin server" to refer to the program that can originate
497   authoritative responses to a request.
498</t>
499<t>
500   Most HTTP communication consists of a retrieval request (GET) for
501   a representation of some resource identified by a URI.  In the
502   simplest case, this may be accomplished via a single connection (v)
503   between the user agent (UA) and the origin server (O).
504</t>
505<figure><artwork type="drawing"><![CDATA[
506       request chain ------------------------>
507    UA -------------------v------------------- O
508       <----------------------- response chain
509]]></artwork></figure>
510<iref item="message"/>
511<iref item="request"/>
512<iref item="response"/>
513<t>
514   A client sends an HTTP request to the server in the form of a request
515   message (<xref target="request"/>), beginning with a method, URI, and
516   protocol version, followed by MIME-like header fields containing
517   request modifiers, client information, and payload metadata, an empty
518   line to indicate the end of the header section, and finally the payload
519   body (if any).
520</t>
521<t>
522   A server responds to the client's request by sending an HTTP response
523   message (<xref target="response"/>), beginning with a status line that
524   includes the protocol version, a success or error code, and textual
525   reason phrase, followed by MIME-like header fields containing server
526   information, resource metadata, and payload metadata, an empty line to
527   indicate the end of the header section, and finally the payload body (if any).
528</t>
529<t>
530   The following example illustrates a typical message exchange for a
531   GET request on the URI "http://www.example.com/hello.txt":
532</t>
533<figure><preamble>
534client request:
535</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
536  GET /hello.txt HTTP/1.1
537  User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
538  Host: www.example.com
539  Accept: */*
540 
541  ]]></artwork></figure>
542<figure><preamble>
543server response:
544</preamble><artwork type="message/http; msgtype=&#34;response&#34;"><![CDATA[
545  HTTP/1.1 200 OK
546  Date: Mon, 27 Jul 2009 12:28:53 GMT
547  Server: Apache
548  Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
549  ETag: "34aa387-d-1568eb00"
550  Accept-Ranges: bytes
551  Content-Length: 14
552  Vary: Accept-Encoding
553  Content-Type: text/plain
554 
555  Hello World!
556  ]]></artwork></figure>
557</section>
558
559<section title="Intermediaries" anchor="intermediaries">
560<t>
561   A more complicated situation occurs when one or more intermediaries
562   are present in the request/response chain. There are three common
563   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
564   a single intermediary may act as an origin server, proxy, gateway,
565   or tunnel, switching behavior based on the nature of each request.
566</t>
567<figure><artwork type="drawing"><![CDATA[
568       request chain -------------------------------------->
569    UA -----v----- A -----v----- B -----v----- C -----v----- O
570       <------------------------------------- response chain
571]]></artwork></figure>
572<t>
573   The figure above shows three intermediaries (A, B, and C) between the
574   user agent and origin server. A request or response message that
575   travels the whole chain will pass through four separate connections.
576   Some HTTP communication options
577   may apply only to the connection with the nearest, non-tunnel
578   neighbor, only to the end-points of the chain, or to all connections
579   along the chain. Although the diagram is linear, each participant may
580   be engaged in multiple, simultaneous communications. For example, B
581   may be receiving requests from many clients other than A, and/or
582   forwarding requests to servers other than C, at the same time that it
583   is handling A's request.
584</t>
585<t>
586<iref item="upstream"/><iref item="downstream"/>
587<iref item="inbound"/><iref item="outbound"/>
588   We use the terms "upstream" and "downstream" to describe various
589   requirements in relation to the directional flow of a message:
590   all messages flow from upstream to downstream.
591   Likewise, we use the terms "inbound" and "outbound" to refer to
592   directions in relation to the request path: "inbound" means toward
593   the origin server and "outbound" means toward the user agent.
594</t>
595<t><iref item="proxy"/>
596   A proxy is a message forwarding agent that is selected by the
597   client, usually via local configuration rules, to receive requests
598   for some type(s) of absolute URI and attempt to satisfy those
599   requests via translation through the HTTP interface.  Some translations
600   are minimal, such as for proxy requests for "http" URIs, whereas
601   other requests may require translation to and from entirely different
602   application-layer protocols. Proxies are often used to group an
603   organization's HTTP requests through a common intermediary for the
604   sake of security, annotation services, or shared caching.
605</t>
606<t><iref item="gateway"/><iref item="reverse proxy"/>
607   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
608   as a layer above some other server(s) and translates the received
609   requests to the underlying server's protocol.  Gateways are often
610   used for load balancing or partitioning HTTP services across
611   multiple machines.
612   Unlike a proxy, a gateway receives requests as if it were the
613   origin server for the requested resource; the requesting client
614   will not be aware that it is communicating with a gateway.
615   A gateway communicates with the client as if the gateway is the
616   origin server and thus is subject to all of the requirements on
617   origin servers for that connection.  A gateway communicates
618   with inbound servers using any protocol it desires, including
619   private extensions to HTTP that are outside the scope of this
620   specification.
621</t>
622<t><iref item="tunnel"/>
623   A tunnel acts as a blind relay between two connections
624   without changing the messages. Once active, a tunnel is not
625   considered a party to the HTTP communication, though the tunnel may
626   have been initiated by an HTTP request. A tunnel ceases to exist when
627   both ends of the relayed connection are closed. Tunnels are used to
628   extend a virtual connection through an intermediary, such as when
629   transport-layer security is used to establish private communication
630   through a shared firewall proxy.
631</t>
632</section>
633
634<section title="Caches" anchor="caches">
635<iref item="cache"/>
636<t>
637   Any party to HTTP communication that is not acting as a tunnel may
638   employ an internal cache for handling requests.
639   A cache is a local store of previous response messages and the
640   subsystem that controls its message storage, retrieval, and deletion.
641   A cache stores cacheable responses in order to reduce the response
642   time and network bandwidth consumption on future, equivalent
643   requests. Any client or server may include a cache, though a cache
644   cannot be used by a server while it is acting as a tunnel.
645</t>
646<t>
647   The effect of a cache is that the request/response chain is shortened
648   if one of the participants along the chain has a cached response
649   applicable to that request. The following illustrates the resulting
650   chain if B has a cached copy of an earlier response from O (via C)
651   for a request which has not been cached by UA or A.
652</t>
653<figure><artwork type="drawing"><![CDATA[
654          request chain ---------->
655       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
656          <--------- response chain
657]]></artwork></figure>
658<t><iref item="cacheable"/>
659   A response is cacheable if a cache is allowed to store a copy of
660   the response message for use in answering subsequent requests.
661   Even when a response is cacheable, there may be additional
662   constraints placed by the client or by the origin server on when
663   that cached response can be used for a particular request. HTTP
664   requirements for cache behavior and cacheable responses are
665   defined in Section 2 of <xref target="Part6"/>. 
666</t>
667<t>
668   There are a wide variety of architectures and configurations
669   of caches and proxies deployed across the World Wide Web and
670   inside large organizations. These systems include national hierarchies
671   of proxy caches to save transoceanic bandwidth, systems that
672   broadcast or multicast cache entries, organizations that distribute
673   subsets of cached data via optical media, and so on.
674</t>
675</section>
676
677<section title="Transport Independence" anchor="transport-independence">
678<t>
679  HTTP systems are used in a wide variety of environments, from
680  corporate intranets with high-bandwidth links to long-distance
681  communication over low-power radio links and intermittent connectivity.
682</t>
683<t>
684   HTTP communication usually takes place over TCP/IP connections. The
685   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
686   not preclude HTTP from being implemented on top of any other protocol
687   on the Internet, or on other networks. HTTP only presumes a reliable
688   transport; any protocol that provides such guarantees can be used;
689   the mapping of the HTTP/1.1 request and response structures onto the
690   transport data units of the protocol in question is outside the scope
691   of this specification.
692</t>
693<t>
694   In HTTP/1.0, most implementations used a new connection for each
695   request/response exchange. In HTTP/1.1, a connection may be used for
696   one or more request/response exchanges, although connections may be
697   closed for a variety of reasons (see <xref target="persistent.connections"/>).
698</t>
699</section>
700
701<section title="HTTP Version" anchor="http.version">
702 
703 
704<t>
705   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
706   of the protocol. The protocol versioning policy is intended to allow
707   the sender to indicate the format of a message and its capacity for
708   understanding further HTTP communication, rather than the features
709   obtained via that communication. No change is made to the version
710   number for the addition of message components which do not affect
711   communication behavior or which only add to extensible field values.
712   The &lt;minor&gt; number is incremented when the changes made to the
713   protocol add features which do not change the general message parsing
714   algorithm, but which may add to the message semantics and imply
715   additional capabilities of the sender. The &lt;major&gt; number is
716   incremented when the format of a message within the protocol is
717   changed. See <xref target="RFC2145"/> for a fuller explanation.
718</t>
719<t>
720   The version of an HTTP message is indicated by an HTTP-Version field
721   in the first line of the message. HTTP-Version is case-sensitive.
722</t>
723<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
724  HTTP-Version   = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
725  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
726]]></artwork></figure>
727<t>
728   Note that the major and minor numbers MUST be treated as separate
729   integers and that each MAY be incremented higher than a single digit.
730   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
731   lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and
732   MUST NOT be sent.
733</t>
734<t>
735   An application that sends a request or response message that includes
736   HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
737   with this specification. Applications that are at least conditionally
738   compliant with this specification SHOULD use an HTTP-Version of
739   "HTTP/1.1" in their messages, and MUST do so for any message that is
740   not compatible with HTTP/1.0. For more details on when to send
741   specific HTTP-Version values, see <xref target="RFC2145"/>.
742</t>
743<t>
744   The HTTP version of an application is the highest HTTP version for
745   which the application is at least conditionally compliant.
746</t>
747<t>
748   Proxy and gateway applications need to be careful when forwarding
749   messages in protocol versions different from that of the application.
750   Since the protocol version indicates the protocol capability of the
751   sender, a proxy/gateway MUST NOT send a message with a version
752   indicator which is greater than its actual version. If a higher
753   version request is received, the proxy/gateway MUST either downgrade
754   the request version, or respond with an error, or switch to tunnel
755   behavior.
756</t>
757<t>
758   Due to interoperability problems with HTTP/1.0 proxies discovered
759   since the publication of <xref target="RFC2068"/>, caching proxies MUST, gateways
760   MAY, and tunnels MUST NOT upgrade the request to the highest version
761   they support. The proxy/gateway's response to that request MUST be in
762   the same major version as the request.
763</t>
764<t><list>
765  <t>
766    Note: Converting between versions of HTTP may involve modification
767    of header fields required or forbidden by the versions involved.
768  </t>
769</list></t>
770</section>
771
772<section title="Uniform Resource Identifiers" anchor="uri">
773<iref primary="true" item="resource"/>
774<t>
775   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
776   throughout HTTP as the means for identifying resources. URI references
777   are used to target requests, indicate redirects, and define relationships.
778   HTTP does not limit what a resource may be; it merely defines an interface
779   that can be used to interact with a resource via HTTP. More information on
780   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
781</t>
782 
783 
784 
785 
786 
787 
788 
789 
790 
791 
792 
793<t>
794   This specification adopts the definitions of "URI-reference",
795   "absolute-URI", "relative-part", "port", "host",
796   "path-abempty", "path-absolute", "query", and "authority" from
797   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
798   protocol elements that allow a relative URI without a fragment.
799</t>
800<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[
801  URI           = <URI, defined in [RFC3986], Section 3>
802  URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
803  absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
804  relative-part = <relative-part, defined in [RFC3986], Section 4.2>
805  authority     = <authority, defined in [RFC3986], Section 3.2>
806  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
807  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
808  port          = <port, defined in [RFC3986], Section 3.2.3>
809  query         = <query, defined in [RFC3986], Section 3.4>
810  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
811 
812  partial-URI   = relative-part [ "?" query ]
813]]></artwork></figure>
814<t>
815   Each protocol element in HTTP that allows a URI reference will indicate in
816   its ABNF production whether the element allows only a URI in absolute form
817   (absolute-URI), any relative reference (relative-ref), or some other subset
818   of the URI-reference grammar. Unless otherwise indicated, URI references
819   are parsed relative to the request target (the default base URI for both
820   the request and its corresponding response).
821</t>
822
823<section title="http URI scheme" anchor="http.uri">
824 
825  <iref item="http URI scheme" primary="true"/>
826  <iref item="URI scheme" subitem="http" primary="true"/>
827<t>
828   The "http" URI scheme is hereby defined for the purpose of minting
829   identifiers according to their association with the hierarchical
830   namespace governed by a potential HTTP origin server listening for
831   TCP connections on a given port.
832   The HTTP server is identified via the generic syntax's
833   <xref target="uri" format="none">authority</xref> component, which includes a host
834   identifier and optional TCP port, and the remainder of the URI is
835   considered to be identifying data corresponding to a resource for
836   which that server might provide an HTTP interface.
837</t>
838<figure><iref primary="true" item="Grammar" subitem="http-URI"/><artwork type="abnf2616"><![CDATA[
839  http-URI = "http:" "//" authority path-abempty [ "?" query ]
840]]></artwork></figure>
841<t>
842   The host identifier within an <xref target="uri" format="none">authority</xref> component is
843   defined in <xref target="RFC3986"/>, Section 3.2.2.  If host is
844   provided as an IP literal or IPv4 address, then the HTTP server is any
845   listener on the indicated TCP port at that IP address. If host is a
846   registered name, then that name is considered an indirect identifier
847   and the recipient might use a name resolution service, such as DNS,
848   to find the address of a listener for that host.
849   The host MUST NOT be empty; if an "http" URI is received with an
850   empty host, then it MUST be rejected as invalid.
851   If the port subcomponent is empty or not given, then TCP port 80 is
852   assumed (the default reserved port for WWW services).
853</t>
854<t>
855   Regardless of the form of host identifier, access to that host is not
856   implied by the mere presence of its name or address. The host may or may
857   not exist and, even when it does exist, may or may not be running an
858   HTTP server or listening to the indicated port. The "http" URI scheme
859   makes use of the delegated nature of Internet names and addresses to
860   establish a naming authority (whatever entity has the ability to place
861   an HTTP server at that Internet name or address) and allows that
862   authority to determine which names are valid and how they might be used.
863</t>
864<t>
865   When an "http" URI is used within a context that calls for access to the
866   indicated resource, a client MAY attempt access by resolving
867   the host to an IP address, establishing a TCP connection to that address
868   on the indicated port, and sending an HTTP request message to the server
869   containing the URI's identifying data as described in <xref target="request"/>.
870   If the server responds to that request with a non-interim HTTP response
871   message, as described in <xref target="response"/>, then that response
872   is considered an authoritative answer to the client's request.
873</t>
874<t>
875   Although HTTP is independent of the transport protocol, the "http"
876   scheme is specific to TCP-based services because the name delegation
877   process depends on TCP for establishing authority.
878   An HTTP service based on some other underlying connection protocol
879   would presumably be identified using a different URI scheme, just as
880   the "https" scheme (below) is used for servers that require an SSL/TLS
881   transport layer on a connection. Other protocols may also be used to
882   provide access to "http" identified resources --- it is only the
883   authoritative interface used for mapping the namespace that is
884   specific to TCP.
885</t>
886</section>
887
888<section title="https URI scheme" anchor="https.uri">
889   
890   <iref item="https URI scheme"/>
891   <iref item="URI scheme" subitem="https"/>
892<t>
893   The "https" URI scheme is hereby defined for the purpose of minting
894   identifiers according to their association with the hierarchical
895   namespace governed by a potential HTTP origin server listening for
896   SSL/TLS-secured connections on a given TCP port.
897   The host and port are determined in the same way
898   as for the "http" scheme, except that a default TCP port of 443
899   is assumed if the port subcomponent is empty or not given.
900</t>
901<figure><iref primary="true" item="Grammar" subitem="https-URI"/><artwork type="abnf2616"><![CDATA[
902  https-URI = "https:" "//" authority path-abempty [ "?" query ]
903]]></artwork></figure>
904<t>
905   The primary difference between the "http" and "https" schemes is
906   that interaction with the latter is required to be secured for
907   privacy through the use of strong encryption. The URI cannot be
908   sent in a request until the connection is secure. Likewise, the
909   default for caching is that each response that would be considered
910   "public" under the "http" scheme is instead treated as "private"
911   and thus not eligible for shared caching.
912</t>
913<t>
914   The process for authoritative access to an "https" identified
915   resource is defined in <xref target="RFC2818"/>.
916</t>
917</section>
918
919<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
920<t>
921   Since the "http" and "https" schemes conform to the URI generic syntax,
922   such URIs are normalized and compared according to the algorithm defined
923   in <xref target="RFC3986"/>, Section 6, using the defaults
924   described above for each scheme.
925</t>
926<t>
927   If the port is equal to the default port for a scheme, the normal
928   form is to elide the port subcomponent. Likewise, an empty path
929   component is equivalent to an absolute path of "/", so the normal
930   form is to provide a path of "/" instead. The scheme and host
931   are case-insensitive and normally provided in lowercase; all
932   other components are compared in a case-sensitive manner.
933   Characters other than those in the "reserved" set are equivalent
934   to their percent-encoded octets (see <xref target="RFC3986"/>, Section 2.1): the normal form is to not encode them.
935</t>
936<t>
937   For example, the following three URIs are equivalent:
938</t>
939<figure><artwork type="example"><![CDATA[
940   http://example.com:80/~smith/home.html
941   http://EXAMPLE.com/%7Esmith/home.html
942   http://EXAMPLE.com:/%7esmith/home.html
943]]></artwork></figure>
944<t>
945   <cref>[[This paragraph does not belong here. --Roy]]</cref>
946   If path-abempty is the empty string (i.e., there is no slash "/"
947   path separator following the authority), then the "http" URI
948   MUST be given as "/" when
949   used as a request-target (<xref target="request-target"/>). If a proxy
950   receives a host name which is not a fully qualified domain name, it
951   MAY add its domain to the host name it received. If a proxy receives
952   a fully qualified domain name, the proxy MUST NOT change the host
953   name.
954</t>
955</section>
956</section>
957</section>
958
959<section title="HTTP Message" anchor="http.message">
960
961
962
963
964<iref item="header section"/>
965<iref item="headers"/>
966<iref item="header field"/>
967<t>
968   All HTTP/1.1 messages consist of a start-line followed by a sequence of
969   characters in a format similar to the Internet Message Format
970   <xref target="RFC5322"/>: zero or more header fields (collectively
971   referred to as the "headers" or the "header section"), an empty line
972   indicating the end of the header section, and an optional message-body.
973</t>
974<t>
975   An HTTP message can either be a request from client to server or a
976   response from server to client.  Syntactically, the two types of message
977   differ only in the start-line, which is either a Request-Line (for requests)
978   or a Status-Line (for responses), and in the algorithm for determining
979   the length of the message-body (<xref target="message.length"/>).
980   In theory, a client could receive requests and a server could receive
981   responses, distinguishing them by their different start-line formats,
982   but in practice servers are implemented to only expect a request
983   (a response is interpreted as an unknown or invalid request method)
984   and clients are implemented to only expect a response.
985</t>
986<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
987  HTTP-message    = start-line
988                    *( header-field CRLF )
989                    CRLF
990                    [ message-body ]
991  start-line      = Request-Line / Status-Line
992]]></artwork></figure>
993<t>
994   Whitespace (WSP) MUST NOT be sent between the start-line and the first
995   header field. The presence of whitespace might be an attempt to trick a
996   noncompliant implementation of HTTP into ignoring that field or processing
997   the next line as a new request, either of which may result in security
998   issues when implementations within the request chain interpret the
999   same message differently. HTTP/1.1 servers MUST reject such a message
1000   with a 400 (Bad Request) response.
1001</t>
1002
1003<section title="Message Parsing Robustness" anchor="message.robustness">
1004<t>
1005   In the interest of robustness, servers SHOULD ignore at least one
1006   empty line received where a Request-Line is expected. In other words, if
1007   the server is reading the protocol stream at the beginning of a
1008   message and receives a CRLF first, it should ignore the CRLF.
1009</t>
1010<t>
1011   Some old HTTP/1.0 client implementations generate an extra CRLF
1012   after a POST request as a lame workaround for some early server
1013   applications that failed to read message-body content that was
1014   not terminated by a line-ending. An HTTP/1.1 client MUST NOT
1015   preface or follow a request with an extra CRLF.  If terminating
1016   the request message-body with a line-ending is desired, then the
1017   client MUST include the terminating CRLF octets as part of the
1018   message-body length.
1019</t>
1020<t>
1021   The normal procedure for parsing an HTTP message is to read the
1022   start-line into a structure, read each header field into a hash
1023   table by field name until the empty line, and then use the parsed
1024   data to determine if a message-body is expected.  If a message-body
1025   has been indicated, then it is read as a stream until an amount
1026   of OCTETs equal to the message-length is read or the connection
1027   is closed.  Care must be taken to parse an HTTP message as a sequence
1028   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1029   to parse HTTP as a stream of Unicode characters in a character encoding
1030   like UTF-16 may introduce security flaws due to the differing ways
1031   that such parsers interpret invalid characters.
1032</t>
1033</section>
1034
1035<section title="Header Fields" anchor="header.fields">
1036 
1037 
1038 
1039 
1040 
1041<t>
1042   Each HTTP header field consists of a case-insensitive field name
1043   followed by a colon (":"), optional whitespace, and the field value.
1044</t>
1045<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[
1046  header-field   = field-name ":" OWS [ field-value ] OWS
1047  field-name     = token
1048  field-value    = *( field-content / OWS )
1049  field-content  = *( WSP / VCHAR / obs-text )
1050]]></artwork></figure>
1051<t>
1052   No whitespace is allowed between the header field name and colon. For
1053   security reasons, any request message received containing such whitespace
1054   MUST be rejected with a response code of 400 (Bad Request). A proxy
1055   MUST remove any such whitespace from a response message before
1056   forwarding the message downstream.
1057</t>
1058<t>
1059   A field value MAY be preceded by optional whitespace (OWS); a single SP is
1060   preferred. The field value does not include any leading or trailing white
1061   space: OWS occurring before the first non-whitespace character of the
1062   field value or after the last non-whitespace character of the field value
1063   is ignored and SHOULD be removed without changing the meaning of the header
1064   field.
1065</t>
1066<t>
1067   The order in which header fields with differing field names are
1068   received is not significant. However, it is "good practice" to send
1069   header fields that contain control data first, such as Host on
1070   requests and Date on responses, so that implementations can decide
1071   when not to handle a message as early as possible.  A server MUST
1072   wait until the entire header section is received before interpreting
1073   a request message, since later header fields might include conditionals,
1074   authentication credentials, or deliberately misleading duplicate
1075   header fields that would impact request processing.
1076</t>
1077<t>
1078   Multiple header fields with the same field name MUST NOT be
1079   sent in a message unless the entire field value for that
1080   header field is defined as a comma-separated list [i.e., #(values)].
1081   Multiple header fields with the same field name can be combined into
1082   one "field-name: field-value" pair, without changing the semantics of the
1083   message, by appending each subsequent field value to the combined
1084   field value in order, separated by a comma. The order in which
1085   header fields with the same field name are received is therefore
1086   significant to the interpretation of the combined field value;
1087   a proxy MUST NOT change the order of these field values when
1088   forwarding a message.
1089</t>
1090<t><list>
1091  <t>
1092   Note: the "Set-Cookie" header as implemented in
1093   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1094   can occur multiple times, but does not use the list syntax, and thus cannot
1095   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1096   for details.) Also note that the Set-Cookie2 header specified in
1097   <xref target="RFC2965"/> does not share this problem.
1098  </t>
1099</list></t>
1100<t>
1101   Historically, HTTP header field values could be extended over multiple
1102   lines by preceding each extra line with at least one space or horizontal
1103   tab character (line folding). This specification deprecates such line
1104   folding except within the message/http media type
1105   (<xref target="internet.media.type.message.http"/>).
1106   HTTP/1.1 senders MUST NOT produce messages that include line folding
1107   (i.e., that contain any field-content that matches the obs-fold rule) unless
1108   the message is intended for packaging within the message/http media type.
1109   HTTP/1.1 recipients SHOULD accept line folding and replace any embedded
1110   obs-fold whitespace with a single SP prior to interpreting the field value
1111   or forwarding the message downstream.
1112</t>
1113<t>
1114   Historically, HTTP has allowed field content with text in the ISO-8859-1
1115   <xref target="ISO-8859-1"/> character encoding and supported other
1116   character sets only through use of <xref target="RFC2047"/> encoding.
1117   In practice, most HTTP header field values use only a subset of the
1118   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1119   header fields SHOULD limit their field values to US-ASCII characters.
1120   Recipients SHOULD treat other (obs-text) octets in field content as
1121   opaque data.
1122</t>
1123<t anchor="rule.comment">
1124 
1125 
1126   Comments can be included in some HTTP header fields by surrounding
1127   the comment text with parentheses. Comments are only allowed in
1128   fields containing "comment" as part of their field value definition.
1129</t>
1130<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
1131  comment        = "(" *( ctext / quoted-cpair / comment ) ")"
1132  ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
1133                 ; OWS / <VCHAR except "(", ")", and "\"> / obs-text
1134]]></artwork></figure>
1135<t anchor="rule.quoted-cpair">
1136 
1137   The backslash character ("\") can be used as a single-character
1138   quoting mechanism within comment constructs:
1139</t>
1140<figure><iref primary="true" item="Grammar" subitem="quoted-cpair"/><artwork type="abnf2616"><![CDATA[
1141  quoted-cpair    = "\" ( WSP / VCHAR / obs-text )
1142]]></artwork></figure>
1143<t>
1144   Producers SHOULD NOT escape characters that do not require escaping
1145   (i.e., other than the backslash character "\" and the parentheses "(" and
1146   ")").
1147</t>
1148</section>
1149
1150<section title="Message Body" anchor="message.body">
1151 
1152<t>
1153   The message-body (if any) of an HTTP message is used to carry the
1154   entity-body associated with the request or response. The message-body
1155   differs from the entity-body only when a transfer-coding has been
1156   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1157</t>
1158<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1159  message-body = entity-body
1160               / <entity-body encoded as per Transfer-Encoding>
1161]]></artwork></figure>
1162<t>
1163   Transfer-Encoding MUST be used to indicate any transfer-codings
1164   applied by an application to ensure safe and proper transfer of the
1165   message. Transfer-Encoding is a property of the message, not of the
1166   entity, and thus MAY be added or removed by any application along the
1167   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1168   when certain transfer-codings may be used.)
1169</t>
1170<t>
1171   The rules for when a message-body is allowed in a message differ for
1172   requests and responses.
1173</t>
1174<t>
1175   The presence of a message-body in a request is signaled by the
1176   inclusion of a Content-Length or Transfer-Encoding header field in
1177   the request's header fields.
1178   When a request message contains both a message-body of non-zero
1179   length and a method that does not define any semantics for that
1180   request message-body, then an origin server SHOULD either ignore
1181   the message-body or respond with an appropriate error message
1182   (e.g., 413).  A proxy or gateway, when presented the same request,
1183   SHOULD either forward the request inbound with the message-body or
1184   ignore the message-body when determining a response.
1185</t>
1186<t>
1187   For response messages, whether or not a message-body is included with
1188   a message is dependent on both the request method and the response
1189   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1190   MUST NOT include a message-body, even though the presence of entity-header
1191   fields might lead one to believe they do. All 1xx
1192   (informational), 204 (No Content), and 304 (Not Modified) responses
1193   MUST NOT include a message-body. All other responses do include a
1194   message-body, although it MAY be of zero length.
1195</t>
1196</section>
1197
1198<section title="Message Length" anchor="message.length">
1199<t>
1200   The transfer-length of a message is the length of the message-body as
1201   it appears in the message; that is, after any transfer-codings have
1202   been applied. When a message-body is included with a message, the
1203   transfer-length of that body is determined by one of the following
1204   (in order of precedence):
1205</t>
1206<t>
1207  <list style="numbers">
1208    <t>
1209     Any response message which "MUST NOT" include a message-body (such
1210     as the 1xx, 204, and 304 responses and any response to a HEAD
1211     request) is always terminated by the first empty line after the
1212     header fields, regardless of the entity-header fields present in
1213     the message.
1214    </t>
1215    <t>
1216     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1217     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1218     is used, the transfer-length is defined by the use of this transfer-coding.
1219     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1220     is not present, the transfer-length is defined by the sender closing the connection.
1221    </t>
1222    <t>
1223     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1224     value in OCTETs represents both the entity-length and the
1225     transfer-length. The Content-Length header field MUST NOT be sent
1226     if these two lengths are different (i.e., if a Transfer-Encoding
1227     header field is present). If a message is received with both a
1228     Transfer-Encoding header field and a Content-Length header field,
1229     the latter MUST be ignored.
1230    </t>
1231    <t>
1232     If the message uses the media type "multipart/byteranges", and the
1233     transfer-length is not otherwise specified, then this self-delimiting
1234     media type defines the transfer-length. This media type
1235     MUST NOT be used unless the sender knows that the recipient can parse
1236     it; the presence in a request of a Range header with multiple byte-range
1237     specifiers from a 1.1 client implies that the client can parse
1238     multipart/byteranges responses.
1239    <list style="empty"><t>
1240       A range header might be forwarded by a 1.0 proxy that does not
1241       understand multipart/byteranges; in this case the server MUST
1242       delimit the message using methods defined in items 1, 3 or 5 of
1243       this section.
1244    </t></list>
1245    </t>
1246    <t>
1247     By the server closing the connection. (Closing the connection
1248     cannot be used to indicate the end of a request body, since that
1249     would leave no possibility for the server to send back a response.)
1250    </t>
1251  </list>
1252</t>
1253<t>
1254   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1255   containing a message-body MUST include a valid Content-Length header
1256   field unless the server is known to be HTTP/1.1 compliant. If a
1257   request contains a message-body and a Content-Length is not given,
1258   the server SHOULD respond with 400 (Bad Request) if it cannot
1259   determine the length of the message, or with 411 (Length Required) if
1260   it wishes to insist on receiving a valid Content-Length.
1261</t>
1262<t>
1263   All HTTP/1.1 applications that receive entities MUST accept the
1264   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1265   to be used for messages when the message length cannot be determined
1266   in advance.
1267</t>
1268<t>
1269   Messages MUST NOT include both a Content-Length header field and a
1270   transfer-coding. If the message does include a
1271   transfer-coding, the Content-Length MUST be ignored.
1272</t>
1273<t>
1274   When a Content-Length is given in a message where a message-body is
1275   allowed, its field value MUST exactly match the number of OCTETs in
1276   the message-body. HTTP/1.1 user agents MUST notify the user when an
1277   invalid length is received and detected.
1278</t>
1279</section>
1280
1281<section title="General Header Fields" anchor="general.header.fields">
1282 
1283<t>
1284   There are a few header fields which have general applicability for
1285   both request and response messages, but which do not apply to the
1286   entity being transferred. These header fields apply only to the
1287   message being transmitted.
1288</t>
1289<figure><iref primary="true" item="Grammar" subitem="general-header"/><artwork type="abnf2616"><![CDATA[
1290  general-header = Cache-Control            ; [Part6], Section 3.2
1291                 / Connection               ; Section 9.1
1292                 / Date                     ; Section 9.3
1293                 / Pragma                   ; [Part6], Section 3.4
1294                 / Trailer                  ; Section 9.6
1295                 / Transfer-Encoding        ; Section 9.7
1296                 / Upgrade                  ; Section 9.8
1297                 / Via                      ; Section 9.9
1298                 / Warning                  ; [Part6], Section 3.6
1299]]></artwork></figure>
1300<t>
1301   General-header field names can be extended reliably only in
1302   combination with a change in the protocol version. However, new or
1303   experimental header fields may be given the semantics of general
1304   header fields if all parties in the communication recognize them to
1305   be general-header fields. Unrecognized header fields are treated as
1306   entity-header fields.
1307</t>
1308</section>
1309</section>
1310
1311<section title="Request" anchor="request">
1312 
1313<t>
1314   A request message from a client to a server includes, within the
1315   first line of that message, the method to be applied to the resource,
1316   the identifier of the resource, and the protocol version in use.
1317</t>
1318<!--                 Host                      ; should be moved here eventually -->
1319<figure><iref primary="true" item="Grammar" subitem="Request"/><artwork type="abnf2616"><![CDATA[
1320  Request       = Request-Line              ; Section 4.1
1321                  *(( general-header        ; Section 3.5
1322                   / request-header         ; [Part2], Section 3
1323                   / entity-header ) CRLF ) ; [Part3], Section 3.1
1324                  CRLF
1325                  [ message-body ]          ; Section 3.3
1326]]></artwork></figure>
1327
1328<section title="Request-Line" anchor="request-line">
1329 
1330<t>
1331   The Request-Line begins with a method token, followed by the
1332   request-target and the protocol version, and ending with CRLF. The
1333   elements are separated by SP characters. No CR or LF is allowed
1334   except in the final CRLF sequence.
1335</t>
1336<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1337  Request-Line   = Method SP request-target SP HTTP-Version CRLF
1338]]></artwork></figure>
1339
1340<section title="Method" anchor="method">
1341 
1342<t>
1343   The Method  token indicates the method to be performed on the
1344   resource identified by the request-target. The method is case-sensitive.
1345</t>
1346<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
1347  Method         = token
1348]]></artwork></figure>
1349</section>
1350
1351<section title="request-target" anchor="request-target">
1352 
1353<t>
1354   The request-target
1355   identifies the resource upon which to apply the request.
1356</t>
1357<figure><iref primary="true" item="Grammar" subitem="request-target"/><artwork type="abnf2616"><![CDATA[
1358  request-target = "*"
1359                 / absolute-URI
1360                 / ( path-absolute [ "?" query ] )
1361                 / authority
1362]]></artwork></figure>
1363<t>
1364   The four options for request-target are dependent on the nature of the
1365   request. The asterisk "*" means that the request does not apply to a
1366   particular resource, but to the server itself, and is only allowed
1367   when the method used does not necessarily apply to a resource. One
1368   example would be
1369</t>
1370<figure><artwork type="example"><![CDATA[
1371  OPTIONS * HTTP/1.1
1372]]></artwork></figure>
1373<t>
1374   The absolute-URI form is REQUIRED when the request is being made to a
1375   proxy. The proxy is requested to forward the request or service it
1376   from a valid cache, and return the response. Note that the proxy MAY
1377   forward the request on to another proxy or directly to the server
1378   specified by the absolute-URI. In order to avoid request loops, a
1379   proxy MUST be able to recognize all of its server names, including
1380   any aliases, local variations, and the numeric IP address. An example
1381   Request-Line would be:
1382</t>
1383<figure><artwork type="example"><![CDATA[
1384  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1385]]></artwork></figure>
1386<t>
1387   To allow for transition to absolute-URIs in all requests in future
1388   versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
1389   form in requests, even though HTTP/1.1 clients will only generate
1390   them in requests to proxies.
1391</t>
1392<t>
1393   The authority form is only used by the CONNECT method (Section 7.9 of <xref target="Part2"/>).
1394</t>
1395<t>
1396   The most common form of request-target is that used to identify a
1397   resource on an origin server or gateway. In this case the absolute
1398   path of the URI MUST be transmitted (see <xref target="http.uri"/>, path-absolute) as
1399   the request-target, and the network location of the URI (authority) MUST
1400   be transmitted in a Host header field. For example, a client wishing
1401   to retrieve the resource above directly from the origin server would
1402   create a TCP connection to port 80 of the host "www.example.org" and send
1403   the lines:
1404</t>
1405<figure><artwork type="example"><![CDATA[
1406  GET /pub/WWW/TheProject.html HTTP/1.1
1407  Host: www.example.org
1408]]></artwork></figure>
1409<t>
1410   followed by the remainder of the Request. Note that the absolute path
1411   cannot be empty; if none is present in the original URI, it MUST be
1412   given as "/" (the server root).
1413</t>
1414<t>
1415   If a proxy receives a request without any path in the request-target and
1416   the method specified is capable of supporting the asterisk form of
1417   request-target, then the last proxy on the request chain MUST forward the
1418   request with "*" as the final request-target.
1419</t>
1420<figure><preamble>  
1421   For example, the request
1422</preamble><artwork type="example"><![CDATA[
1423  OPTIONS http://www.example.org:8001 HTTP/1.1
1424]]></artwork></figure>
1425<figure><preamble>  
1426  would be forwarded by the proxy as
1427</preamble><artwork type="example"><![CDATA[
1428  OPTIONS * HTTP/1.1
1429  Host: www.example.org:8001
1430]]></artwork>
1431<postamble>
1432   after connecting to port 8001 of host "www.example.org".
1433</postamble>
1434</figure>
1435<t>
1436   The request-target is transmitted in the format specified in
1437   <xref target="http.uri"/>. If the request-target is percent-encoded
1438   (<xref target="RFC3986"/>, Section 2.1), the origin server
1439   MUST decode the request-target in order to
1440   properly interpret the request. Servers SHOULD respond to invalid
1441   request-targets with an appropriate status code.
1442</t>
1443<t>
1444   A transparent proxy MUST NOT rewrite the "path-absolute" part of the
1445   received request-target when forwarding it to the next inbound server,
1446   except as noted above to replace a null path-absolute with "/".
1447</t>
1448<t><list>
1449  <t>
1450    Note: The "no rewrite" rule prevents the proxy from changing the
1451    meaning of the request when the origin server is improperly using
1452    a non-reserved URI character for a reserved purpose.  Implementors
1453    should be aware that some pre-HTTP/1.1 proxies have been known to
1454    rewrite the request-target.
1455  </t>
1456</list></t>
1457<t>
1458   HTTP does not place a pre-defined limit on the length of a request-target.
1459   A server MUST be prepared to receive URIs of unbounded length and
1460   respond with the 414 (URI Too Long) status if the received
1461   request-target would be longer than the server wishes to handle
1462   (see Section 8.4.15 of <xref target="Part2"/>).
1463</t>
1464<t>
1465   Various ad-hoc limitations on request-target length are found in practice.
1466   It is RECOMMENDED that all HTTP senders and recipients support
1467   request-target lengths of 8000 or more OCTETs.
1468</t>
1469</section>
1470</section>
1471
1472<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1473<t>
1474   The exact resource identified by an Internet request is determined by
1475   examining both the request-target and the Host header field.
1476</t>
1477<t>
1478   An origin server that does not allow resources to differ by the
1479   requested host MAY ignore the Host header field value when
1480   determining the resource identified by an HTTP/1.1 request. (But see
1481   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1482   for other requirements on Host support in HTTP/1.1.)
1483</t>
1484<t>
1485   An origin server that does differentiate resources based on the host
1486   requested (sometimes referred to as virtual hosts or vanity host
1487   names) MUST use the following rules for determining the requested
1488   resource on an HTTP/1.1 request:
1489  <list style="numbers">
1490    <t>If request-target is an absolute-URI, the host is part of the
1491     request-target. Any Host header field value in the request MUST be
1492     ignored.</t>
1493    <t>If the request-target is not an absolute-URI, and the request includes
1494     a Host header field, the host is determined by the Host header
1495     field value.</t>
1496    <t>If the host as determined by rule 1 or 2 is not a valid host on
1497     the server, the response MUST be a 400 (Bad Request) error message.</t>
1498  </list>
1499</t>
1500<t>
1501   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1502   attempt to use heuristics (e.g., examination of the URI path for
1503   something unique to a particular host) in order to determine what
1504   exact resource is being requested.
1505</t>
1506</section>
1507
1508</section>
1509
1510
1511<section title="Response" anchor="response">
1512 
1513<t>
1514   After receiving and interpreting a request message, a server responds
1515   with an HTTP response message.
1516</t>
1517<figure><iref primary="true" item="Grammar" subitem="Response"/><artwork type="abnf2616"><![CDATA[
1518  Response      = Status-Line               ; Section 5.1
1519                  *(( general-header        ; Section 3.5
1520                   / response-header        ; [Part2], Section 5
1521                   / entity-header ) CRLF ) ; [Part3], Section 3.1
1522                  CRLF
1523                  [ message-body ]          ; Section 3.3
1524]]></artwork></figure>
1525
1526<section title="Status-Line" anchor="status-line">
1527 
1528<t>
1529   The first line of a Response message is the Status-Line, consisting
1530   of the protocol version followed by a numeric status code and its
1531   associated textual phrase, with each element separated by SP
1532   characters. No CR or LF is allowed except in the final CRLF sequence.
1533</t>
1534<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1535  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1536]]></artwork></figure>
1537
1538<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1539 
1540 
1541<t>
1542   The Status-Code element is a 3-digit integer result code of the
1543   attempt to understand and satisfy the request. These codes are fully
1544   defined in Section 8 of <xref target="Part2"/>.  The Reason Phrase exists for the sole
1545   purpose of providing a textual description associated with the numeric
1546   status code, out of deference to earlier Internet application protocols
1547   that were more frequently used with interactive text clients.
1548   A client SHOULD ignore the content of the Reason Phrase.
1549</t>
1550<t>
1551   The first digit of the Status-Code defines the class of response. The
1552   last two digits do not have any categorization role. There are 5
1553   values for the first digit:
1554  <list style="symbols">
1555    <t>
1556      1xx: Informational - Request received, continuing process
1557    </t>
1558    <t>
1559      2xx: Success - The action was successfully received,
1560        understood, and accepted
1561    </t>
1562    <t>
1563      3xx: Redirection - Further action must be taken in order to
1564        complete the request
1565    </t>
1566    <t>
1567      4xx: Client Error - The request contains bad syntax or cannot
1568        be fulfilled
1569    </t>
1570    <t>
1571      5xx: Server Error - The server failed to fulfill an apparently
1572        valid request
1573    </t>
1574  </list>
1575</t>
1576<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
1577  Status-Code    = 3DIGIT
1578  Reason-Phrase  = *( WSP / VCHAR / obs-text )
1579]]></artwork></figure>
1580</section>
1581</section>
1582
1583</section>
1584
1585
1586<section title="Protocol Parameters" anchor="protocol.parameters">
1587
1588<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1589 
1590<t>
1591   HTTP applications have historically allowed three different formats
1592   for the representation of date/time stamps:
1593</t>
1594<figure><artwork type="example"><![CDATA[
1595  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1596  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1597  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1598]]></artwork></figure>
1599<t>
1600   The first format is preferred as an Internet standard and represents
1601   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
1602   other formats are described here only for
1603   compatibility with obsolete implementations.
1604   HTTP/1.1 clients and servers that parse the date value MUST accept
1605   all three formats (for compatibility with HTTP/1.0), though they MUST
1606   only generate the RFC 1123 format for representing HTTP-date values
1607   in header fields. See <xref target="tolerant.applications"/> for further information.
1608</t>
1609<t>
1610   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
1611   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1612   equal to UTC (Coordinated Universal Time). This is indicated in the
1613   first two formats by the inclusion of "GMT" as the three-letter
1614   abbreviation for time zone, and MUST be assumed when reading the
1615   asctime format. HTTP-date is case sensitive and MUST NOT include
1616   additional whitespace beyond that specifically included as SP in the
1617   grammar.
1618</t>
1619<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><artwork type="abnf2616"><![CDATA[
1620  HTTP-date    = rfc1123-date / obs-date
1621]]></artwork></figure>
1622<t anchor="preferred.date.format">
1623 
1624 
1625 
1626 
1627 
1628 
1629 
1630 
1631 
1632 
1633  Preferred format:
1634</t>
1635<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[
1636  rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
1637
1638  day-name     = %x4D.6F.6E ; "Mon", case-sensitive
1639               / %x54.75.65 ; "Tue", case-sensitive
1640               / %x57.65.64 ; "Wed", case-sensitive
1641               / %x54.68.75 ; "Thu", case-sensitive
1642               / %x46.72.69 ; "Fri", case-sensitive
1643               / %x53.61.74 ; "Sat", case-sensitive
1644               / %x53.75.6E ; "Sun", case-sensitive
1645               
1646  date1        = day SP month SP year
1647               ; e.g., 02 Jun 1982
1648
1649  day          = 2DIGIT
1650  month        = %x4A.61.6E ; "Jan", case-sensitive
1651               / %x46.65.62 ; "Feb", case-sensitive
1652               / %x4D.61.72 ; "Mar", case-sensitive
1653               / %x41.70.72 ; "Apr", case-sensitive
1654               / %x4D.61.79 ; "May", case-sensitive
1655               / %x4A.75.6E ; "Jun", case-sensitive
1656               / %x4A.75.6C ; "Jul", case-sensitive
1657               / %x41.75.67 ; "Aug", case-sensitive
1658               / %x53.65.70 ; "Sep", case-sensitive
1659               / %x4F.63.74 ; "Oct", case-sensitive
1660               / %x4E.6F.76 ; "Nov", case-sensitive
1661               / %x44.65.63 ; "Dec", case-sensitive
1662  year         = 4DIGIT
1663
1664  GMT   = %x47.4D.54 ; "GMT", case-sensitive
1665
1666  time-of-day  = hour ":" minute ":" second
1667                 ; 00:00:00 - 23:59:59
1668                 
1669  hour         = 2DIGIT               
1670  minute       = 2DIGIT               
1671  second       = 2DIGIT               
1672]]></artwork></figure>
1673<t>
1674  The semantics of <xref target="preferred.date.format" format="none">day-name</xref>, <xref target="preferred.date.format" format="none">day</xref>,
1675  <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
1676  same as those defined for the RFC 5322 constructs
1677  with the corresponding name (<xref target="RFC5322"/>, Section 3.3).
1678</t>
1679<t anchor="obsolete.date.formats">
1680 
1681 
1682 
1683 
1684 
1685 
1686 
1687 
1688  Obsolete formats:
1689</t>
1690<figure><iref primary="true" item="Grammar" subitem="obs-date"/><artwork type="abnf2616"><![CDATA[
1691  obs-date     = rfc850-date / asctime-date
1692]]></artwork></figure>
1693<figure><iref primary="true" item="Grammar" subitem="rfc850-date"/><artwork type="abnf2616"><![CDATA[
1694  rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
1695  date2        = day "-" month "-" 2DIGIT
1696                 ; day-month-year (e.g., 02-Jun-82)
1697
1698  day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
1699         / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
1700         / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
1701         / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
1702         / %x46.72.69.64.61.79 ; "Friday", case-sensitive
1703         / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
1704         / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
1705]]></artwork></figure>
1706<figure><iref primary="true" item="Grammar" subitem="asctime-date"/><artwork type="abnf2616"><![CDATA[
1707  asctime-date = day-name SP date3 SP time-of-day SP year
1708  date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
1709                 ; month day (e.g., Jun  2)
1710]]></artwork></figure>
1711<t><list>
1712  <t>
1713    Note: Recipients of date values are encouraged to be robust in
1714    accepting date values that may have been sent by non-HTTP
1715    applications, as is sometimes the case when retrieving or posting
1716    messages via proxies/gateways to SMTP or NNTP.
1717  </t>
1718</list></t>
1719<t><list>
1720  <t>
1721    Note: HTTP requirements for the date/time stamp format apply only
1722    to their usage within the protocol stream. Clients and servers are
1723    not required to use these formats for user presentation, request
1724    logging, etc.
1725  </t>
1726</list></t>
1727</section>
1728
1729<section title="Transfer Codings" anchor="transfer.codings">
1730 
1731 
1732<t>
1733   Transfer-coding values are used to indicate an encoding
1734   transformation that has been, can be, or may need to be applied to an
1735   entity-body in order to ensure "safe transport" through the network.
1736   This differs from a content coding in that the transfer-coding is a
1737   property of the message, not of the original entity.
1738</t>
1739<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
1740  transfer-coding         = "chunked" ; Section 6.2.1
1741                          / "compress" ; Section 6.2.2.1
1742                          / "deflate" ; Section 6.2.2.2
1743                          / "gzip" ; Section 6.2.2.3
1744                          / transfer-extension
1745  transfer-extension      = token *( OWS ";" OWS transfer-parameter )
1746]]></artwork></figure>
1747<t anchor="rule.parameter">
1748 
1749 
1750 
1751   Parameters are in  the form of attribute/value pairs.
1752</t>
1753<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[
1754  transfer-parameter      = attribute BWS "=" BWS value
1755  attribute               = token
1756  value                   = token / quoted-string
1757]]></artwork></figure>
1758<t>
1759   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1760   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1761   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1762</t>
1763<t>
1764   Whenever a transfer-coding is applied to a message-body, the set of
1765   transfer-codings MUST include "chunked", unless the message indicates it
1766   is terminated by closing the connection. When the "chunked" transfer-coding
1767   is used, it MUST be the last transfer-coding applied to the
1768   message-body. The "chunked" transfer-coding MUST NOT be applied more
1769   than once to a message-body. These rules allow the recipient to
1770   determine the transfer-length of the message (<xref target="message.length"/>).
1771</t>
1772<t>
1773   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1774   MIME, which were designed to enable safe transport of binary data over a
1775   7-bit transport service (<xref target="RFC2045"/>, Section 6).
1776   However, safe transport
1777   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1778   the only unsafe characteristic of message-bodies is the difficulty in
1779   determining the exact body length (<xref target="message.length"/>), or the desire to
1780   encrypt data over a shared transport.
1781</t>
1782<t>
1783   A server which receives an entity-body with a transfer-coding it does
1784   not understand SHOULD return 501 (Not Implemented), and close the
1785   connection. A server MUST NOT send transfer-codings to an HTTP/1.0
1786   client.
1787</t>
1788
1789<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1790  <iref item="chunked (Coding Format)"/>
1791  <iref item="Coding Format" subitem="chunked"/>
1792 
1793 
1794 
1795 
1796 
1797 
1798 
1799 
1800 
1801 
1802 
1803<t>
1804   The chunked encoding modifies the body of a message in order to
1805   transfer it as a series of chunks, each with its own size indicator,
1806   followed by an OPTIONAL trailer containing entity-header fields. This
1807   allows dynamically produced content to be transferred along with the
1808   information necessary for the recipient to verify that it has
1809   received the full message.
1810</t>
1811<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[
1812  Chunked-Body   = *chunk
1813                   last-chunk
1814                   trailer-part
1815                   CRLF
1816 
1817  chunk          = chunk-size *WSP [ chunk-ext ] CRLF
1818                   chunk-data CRLF
1819  chunk-size     = 1*HEXDIG
1820  last-chunk     = 1*("0") *WSP [ chunk-ext ] CRLF
1821 
1822  chunk-ext      = *( ";" *WSP chunk-ext-name
1823                      [ "=" chunk-ext-val ] *WSP )
1824  chunk-ext-name = token
1825  chunk-ext-val  = token / quoted-str-nf
1826  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
1827  trailer-part   = *( entity-header CRLF )
1828 
1829  quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
1830                 ; like quoted-string, but disallowing line folding
1831  qdtext-nf      = WSP / %x21 / %x23-5B / %x5D-7E / obs-text
1832                 ; WSP / <VCHAR except DQUOTE and "\"> / obs-text
1833]]></artwork></figure>
1834<t>
1835   The chunk-size field is a string of hex digits indicating the size of
1836   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1837   zero, followed by the trailer, which is terminated by an empty line.
1838</t>
1839<t>
1840   The trailer allows the sender to include additional HTTP header
1841   fields at the end of the message. The Trailer header field can be
1842   used to indicate which header fields are included in a trailer (see
1843   <xref target="header.trailer"/>).
1844</t>
1845<t>
1846   A server using chunked transfer-coding in a response MUST NOT use the
1847   trailer for any header fields unless at least one of the following is
1848   true:
1849  <list style="numbers">
1850    <t>the request included a TE header field that indicates "trailers" is
1851     acceptable in the transfer-coding of the  response, as described in
1852     <xref target="header.te"/>; or,</t>
1853
1854    <t>the server is the origin server for the response, the trailer
1855     fields consist entirely of optional metadata, and the recipient
1856     could use the message (in a manner acceptable to the origin server)
1857     without receiving this metadata.  In other words, the origin server
1858     is willing to accept the possibility that the trailer fields might
1859     be silently discarded along the path to the client.</t>
1860  </list>
1861</t>
1862<t>
1863   This requirement prevents an interoperability failure when the
1864   message is being received by an HTTP/1.1 (or later) proxy and
1865   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1866   compliance with the protocol would have necessitated a possibly
1867   infinite buffer on the proxy.
1868</t>
1869<t>
1870   A process for decoding the "chunked" transfer-coding
1871   can be represented in pseudo-code as:
1872</t>
1873<figure><artwork type="code"><![CDATA[
1874  length := 0
1875  read chunk-size, chunk-ext (if any) and CRLF
1876  while (chunk-size > 0) {
1877     read chunk-data and CRLF
1878     append chunk-data to entity-body
1879     length := length + chunk-size
1880     read chunk-size and CRLF
1881  }
1882  read entity-header
1883  while (entity-header not empty) {
1884     append entity-header to existing header fields
1885     read entity-header
1886  }
1887  Content-Length := length
1888  Remove "chunked" from Transfer-Encoding
1889]]></artwork></figure>
1890<t>
1891   All HTTP/1.1 applications MUST be able to receive and decode the
1892   "chunked" transfer-coding, and MUST ignore chunk-ext extensions
1893   they do not understand.
1894</t>
1895</section>
1896
1897<section title="Compression Codings" anchor="compression.codings">
1898<t>
1899   The codings defined below can be used to compress the payload of a
1900   message.
1901</t>
1902<t><list><t>
1903   Note: Use of program names for the identification of encoding formats
1904   is not desirable and is discouraged for future encodings. Their
1905   use here is representative of historical practice, not good
1906   design.
1907</t></list></t>
1908<t><list><t>
1909   Note: For compatibility with previous implementations of HTTP,
1910   applications SHOULD consider "x-gzip" and "x-compress" to be
1911   equivalent to "gzip" and "compress" respectively.
1912</t></list></t>
1913
1914<section title="Compress Coding" anchor="compress.coding">
1915<iref item="compress (Coding Format)"/>
1916<iref item="Coding Format" subitem="compress"/>
1917<t>
1918   The "compress" format is produced by the common UNIX file compression
1919   program "compress". This format is an adaptive Lempel-Ziv-Welch
1920   coding (LZW).
1921</t>
1922</section>
1923
1924<section title="Deflate Coding" anchor="deflate.coding">
1925<iref item="deflate (Coding Format)"/>
1926<iref item="Coding Format" subitem="deflate"/>
1927<t>
1928   The "zlib" format is defined in <xref target="RFC1950"/> in combination with
1929   the "deflate" compression mechanism described in <xref target="RFC1951"/>.
1930</t>
1931</section>
1932
1933<section title="Gzip Coding" anchor="gzip.coding">
1934<iref item="gzip (Coding Format)"/>
1935<iref item="Coding Format" subitem="gzip"/>
1936<t>
1937   The "gzip" format is produced by the file compression program
1938   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
1939   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
1940</t>
1941</section>
1942
1943</section>
1944
1945<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
1946<t>
1947   The HTTP Transfer Coding Registry defines the name space for the transfer
1948   coding names.
1949</t>
1950<t>
1951   Registrations MUST include the following fields:
1952   <list style="symbols">
1953     <t>Name</t>
1954     <t>Description</t>
1955     <t>Pointer to specification text</t>
1956   </list>
1957</t>
1958<t>
1959   Values to be added to this name space require expert review and a specification
1960   (see "Expert Review" and "Specification Required" in
1961   Section 4.1 of <xref target="RFC5226"/>), and MUST
1962   conform to the purpose of transfer coding defined in this section.
1963</t>
1964<t>
1965   The registry itself is maintained at
1966   <eref target="http://www.iana.org/assignments/http-parameters"/>.
1967</t>
1968</section>
1969</section>
1970
1971<section title="Product Tokens" anchor="product.tokens">
1972 
1973 
1974<t>
1975   Product tokens are used to allow communicating applications to
1976   identify themselves by software name and version. Most fields using
1977   product tokens also allow sub-products which form a significant part
1978   of the application to be listed, separated by whitespace. By
1979   convention, the products are listed in order of their significance
1980   for identifying the application.
1981</t>
1982<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
1983  product         = token ["/" product-version]
1984  product-version = token
1985]]></artwork></figure>
1986<t>
1987   Examples:
1988</t>
1989<figure><artwork type="example"><![CDATA[
1990  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1991  Server: Apache/0.8.4
1992]]></artwork></figure>
1993<t>
1994   Product tokens SHOULD be short and to the point. They MUST NOT be
1995   used for advertising or other non-essential information. Although any
1996   token character MAY appear in a product-version, this token SHOULD
1997   only be used for a version identifier (i.e., successive versions of
1998   the same product SHOULD only differ in the product-version portion of
1999   the product value).
2000</t>
2001</section>
2002
2003<section title="Quality Values" anchor="quality.values">
2004 
2005<t>
2006   Both transfer codings (TE request header, <xref target="header.te"/>)
2007   and content negotiation (Section 4 of <xref target="Part3"/>) use short "floating point"
2008   numbers to indicate the relative importance ("weight") of various
2009   negotiable parameters.  A weight is normalized to a real number in
2010   the range 0 through 1, where 0 is the minimum and 1 the maximum
2011   value. If a parameter has a quality value of 0, then content with
2012   this parameter is `not acceptable' for the client. HTTP/1.1
2013   applications MUST NOT generate more than three digits after the
2014   decimal point. User configuration of these values SHOULD also be
2015   limited in this fashion.
2016</t>
2017<figure><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
2018  qvalue         = ( "0" [ "." 0*3DIGIT ] )
2019                 / ( "1" [ "." 0*3("0") ] )
2020]]></artwork></figure>
2021<t><list>
2022  <t>
2023     Note: "Quality values" is a misnomer, since these values merely represent
2024     relative degradation in desired quality.
2025  </t>
2026</list></t>
2027</section>
2028
2029</section>
2030
2031<section title="Connections" anchor="connections">
2032
2033<section title="Persistent Connections" anchor="persistent.connections">
2034
2035<section title="Purpose" anchor="persistent.purpose">
2036<t>
2037   Prior to persistent connections, a separate TCP connection was
2038   established to fetch each URL, increasing the load on HTTP servers
2039   and causing congestion on the Internet. The use of inline images and
2040   other associated data often require a client to make multiple
2041   requests of the same server in a short amount of time. Analysis of
2042   these performance problems and results from a prototype
2043   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2044   measurements of actual HTTP/1.1 implementations show good
2045   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2046   T/TCP <xref target="Tou1998"/>.
2047</t>
2048<t>
2049   Persistent HTTP connections have a number of advantages:
2050  <list style="symbols">
2051      <t>
2052        By opening and closing fewer TCP connections, CPU time is saved
2053        in routers and hosts (clients, servers, proxies, gateways,
2054        tunnels, or caches), and memory used for TCP protocol control
2055        blocks can be saved in hosts.
2056      </t>
2057      <t>
2058        HTTP requests and responses can be pipelined on a connection.
2059        Pipelining allows a client to make multiple requests without
2060        waiting for each response, allowing a single TCP connection to
2061        be used much more efficiently, with much lower elapsed time.
2062      </t>
2063      <t>
2064        Network congestion is reduced by reducing the number of packets
2065        caused by TCP opens, and by allowing TCP sufficient time to
2066        determine the congestion state of the network.
2067      </t>
2068      <t>
2069        Latency on subsequent requests is reduced since there is no time
2070        spent in TCP's connection opening handshake.
2071      </t>
2072      <t>
2073        HTTP can evolve more gracefully, since errors can be reported
2074        without the penalty of closing the TCP connection. Clients using
2075        future versions of HTTP might optimistically try a new feature,
2076        but if communicating with an older server, retry with old
2077        semantics after an error is reported.
2078      </t>
2079    </list>
2080</t>
2081<t>
2082   HTTP implementations SHOULD implement persistent connections.
2083</t>
2084</section>
2085
2086<section title="Overall Operation" anchor="persistent.overall">
2087<t>
2088   A significant difference between HTTP/1.1 and earlier versions of
2089   HTTP is that persistent connections are the default behavior of any
2090   HTTP connection. That is, unless otherwise indicated, the client
2091   SHOULD assume that the server will maintain a persistent connection,
2092   even after error responses from the server.
2093</t>
2094<t>
2095   Persistent connections provide a mechanism by which a client and a
2096   server can signal the close of a TCP connection. This signaling takes
2097   place using the Connection header field (<xref target="header.connection"/>). Once a close
2098   has been signaled, the client MUST NOT send any more requests on that
2099   connection.
2100</t>
2101
2102<section title="Negotiation" anchor="persistent.negotiation">
2103<t>
2104   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
2105   maintain a persistent connection unless a Connection header including
2106   the connection-token "close" was sent in the request. If the server
2107   chooses to close the connection immediately after sending the
2108   response, it SHOULD send a Connection header including the
2109   connection-token close.
2110</t>
2111<t>
2112   An HTTP/1.1 client MAY expect a connection to remain open, but would
2113   decide to keep it open based on whether the response from a server
2114   contains a Connection header with the connection-token close. In case
2115   the client does not want to maintain a connection for more than that
2116   request, it SHOULD send a Connection header including the
2117   connection-token close.
2118</t>
2119<t>
2120   If either the client or the server sends the close token in the
2121   Connection header, that request becomes the last one for the
2122   connection.
2123</t>
2124<t>
2125   Clients and servers SHOULD NOT  assume that a persistent connection is
2126   maintained for HTTP versions less than 1.1 unless it is explicitly
2127   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2128   compatibility with HTTP/1.0 clients.
2129</t>
2130<t>
2131   In order to remain persistent, all messages on the connection MUST
2132   have a self-defined message length (i.e., one not defined by closure
2133   of the connection), as described in <xref target="message.length"/>.
2134</t>
2135</section>
2136
2137<section title="Pipelining" anchor="pipelining">
2138<t>
2139   A client that supports persistent connections MAY "pipeline" its
2140   requests (i.e., send multiple requests without waiting for each
2141   response). A server MUST send its responses to those requests in the
2142   same order that the requests were received.
2143</t>
2144<t>
2145   Clients which assume persistent connections and pipeline immediately
2146   after connection establishment SHOULD be prepared to retry their
2147   connection if the first pipelined attempt fails. If a client does
2148   such a retry, it MUST NOT pipeline before it knows the connection is
2149   persistent. Clients MUST also be prepared to resend their requests if
2150   the server closes the connection before sending all of the
2151   corresponding responses.
2152</t>
2153<t>
2154   Clients SHOULD NOT  pipeline requests using non-idempotent methods or
2155   non-idempotent sequences of methods (see Section 7.1.2 of <xref target="Part2"/>). Otherwise, a
2156   premature termination of the transport connection could lead to
2157   indeterminate results. A client wishing to send a non-idempotent
2158   request SHOULD wait to send that request until it has received the
2159   response status for the previous request.
2160</t>
2161</section>
2162</section>
2163
2164<section title="Proxy Servers" anchor="persistent.proxy">
2165<t>
2166   It is especially important that proxies correctly implement the
2167   properties of the Connection header field as specified in <xref target="header.connection"/>.
2168</t>
2169<t>
2170   The proxy server MUST signal persistent connections separately with
2171   its clients and the origin servers (or other proxy servers) that it
2172   connects to. Each persistent connection applies to only one transport
2173   link.
2174</t>
2175<t>
2176   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
2177   with an HTTP/1.0 client (but see Section 19.7.1 of <xref target="RFC2068"/>
2178   for information and discussion of the problems with the Keep-Alive header
2179   implemented by many HTTP/1.0 clients).
2180</t>
2181</section>
2182
2183<section title="Practical Considerations" anchor="persistent.practical">
2184<t>
2185   Servers will usually have some time-out value beyond which they will
2186   no longer maintain an inactive connection. Proxy servers might make
2187   this a higher value since it is likely that the client will be making
2188   more connections through the same server. The use of persistent
2189   connections places no requirements on the length (or existence) of
2190   this time-out for either the client or the server.
2191</t>
2192<t>
2193   When a client or server wishes to time-out it SHOULD issue a graceful
2194   close on the transport connection. Clients and servers SHOULD both
2195   constantly watch for the other side of the transport close, and
2196   respond to it as appropriate. If a client or server does not detect
2197   the other side's close promptly it could cause unnecessary resource
2198   drain on the network.
2199</t>
2200<t>
2201   A client, server, or proxy MAY close the transport connection at any
2202   time. For example, a client might have started to send a new request
2203   at the same time that the server has decided to close the "idle"
2204   connection. From the server's point of view, the connection is being
2205   closed while it was idle, but from the client's point of view, a
2206   request is in progress.
2207</t>
2208<t>
2209   This means that clients, servers, and proxies MUST be able to recover
2210   from asynchronous close events. Client software SHOULD reopen the
2211   transport connection and retransmit the aborted sequence of requests
2212   without user interaction so long as the request sequence is
2213   idempotent (see Section 7.1.2 of <xref target="Part2"/>). Non-idempotent methods or sequences
2214   MUST NOT be automatically retried, although user agents MAY offer a
2215   human operator the choice of retrying the request(s). Confirmation by
2216   user-agent software with semantic understanding of the application
2217   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2218   be repeated if the second sequence of requests fails.
2219</t>
2220<t>
2221   Servers SHOULD always respond to at least one request per connection,
2222   if at all possible. Servers SHOULD NOT  close a connection in the
2223   middle of transmitting a response, unless a network or client failure
2224   is suspected.
2225</t>
2226<t>
2227   Clients (including proxies) SHOULD limit the number of simultaneous
2228   connections that they maintain to a given server (including proxies).
2229</t>
2230<t>
2231   Previous revisions of HTTP gave a specific number of connections as a
2232   ceiling, but this was found to be impractical for many applications. As a
2233   result, this specification does not mandate a particular maximum number of
2234   connections, but instead encourages clients to be conservative when opening
2235   multiple connections.
2236</t>
2237<t>
2238   In particular, while using multiple connections avoids the "head-of-line
2239   blocking" problem (whereby a request that takes significant server-side
2240   processing and/or has a large payload can block subsequent requests on the
2241   same connection), each connection used consumes server resources (sometimes
2242   significantly), and furthermore using multiple connections can cause
2243   undesirable side effects in congested networks.
2244</t>
2245<t>
2246   Note that servers might reject traffic that they deem abusive, including an
2247   excessive number of connections from a client.
2248</t>
2249</section>
2250</section>
2251
2252<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2253
2254<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2255<t>
2256   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2257   flow control mechanisms to resolve temporary overloads, rather than
2258   terminating connections with the expectation that clients will retry.
2259   The latter technique can exacerbate network congestion.
2260</t>
2261</section>
2262
2263<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2264<t>
2265   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2266   the network connection for an error status while it is transmitting
2267   the request. If the client sees an error status, it SHOULD
2268   immediately cease transmitting the body. If the body is being sent
2269   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2270   empty trailer MAY be used to prematurely mark the end of the message.
2271   If the body was preceded by a Content-Length header, the client MUST
2272   close the connection.
2273</t>
2274</section>
2275
2276<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2277<t>
2278   The purpose of the 100 (Continue) status (see Section 8.1.1 of <xref target="Part2"/>) is to
2279   allow a client that is sending a request message with a request body
2280   to determine if the origin server is willing to accept the request
2281   (based on the request headers) before the client sends the request
2282   body. In some cases, it might either be inappropriate or highly
2283   inefficient for the client to send the body if the server will reject
2284   the message without looking at the body.
2285</t>
2286<t>
2287   Requirements for HTTP/1.1 clients:
2288  <list style="symbols">
2289    <t>
2290        If a client will wait for a 100 (Continue) response before
2291        sending the request body, it MUST send an Expect request-header
2292        field (Section 9.2 of <xref target="Part2"/>) with the "100-continue" expectation.
2293    </t>
2294    <t>
2295        A client MUST NOT send an Expect request-header field (Section 9.2 of <xref target="Part2"/>)
2296        with the "100-continue" expectation if it does not intend
2297        to send a request body.
2298    </t>
2299  </list>
2300</t>
2301<t>
2302   Because of the presence of older implementations, the protocol allows
2303   ambiguous situations in which a client may send "Expect: 100-continue"
2304   without receiving either a 417 (Expectation Failed) status
2305   or a 100 (Continue) status. Therefore, when a client sends this
2306   header field to an origin server (possibly via a proxy) from which it
2307   has never seen a 100 (Continue) status, the client SHOULD NOT  wait
2308   for an indefinite period before sending the request body.
2309</t>
2310<t>
2311   Requirements for HTTP/1.1 origin servers:
2312  <list style="symbols">
2313    <t> Upon receiving a request which includes an Expect request-header
2314        field with the "100-continue" expectation, an origin server MUST
2315        either respond with 100 (Continue) status and continue to read
2316        from the input stream, or respond with a final status code. The
2317        origin server MUST NOT wait for the request body before sending
2318        the 100 (Continue) response. If it responds with a final status
2319        code, it MAY close the transport connection or it MAY continue
2320        to read and discard the rest of the request.  It MUST NOT
2321        perform the requested method if it returns a final status code.
2322    </t>
2323    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2324        the request message does not include an Expect request-header
2325        field with the "100-continue" expectation, and MUST NOT send a
2326        100 (Continue) response if such a request comes from an HTTP/1.0
2327        (or earlier) client. There is an exception to this rule: for
2328        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2329        status in response to an HTTP/1.1 PUT or POST request that does
2330        not include an Expect request-header field with the "100-continue"
2331        expectation. This exception, the purpose of which is
2332        to minimize any client processing delays associated with an
2333        undeclared wait for 100 (Continue) status, applies only to
2334        HTTP/1.1 requests, and not to requests with any other HTTP-version
2335        value.
2336    </t>
2337    <t> An origin server MAY omit a 100 (Continue) response if it has
2338        already received some or all of the request body for the
2339        corresponding request.
2340    </t>
2341    <t> An origin server that sends a 100 (Continue) response MUST
2342    ultimately send a final status code, once the request body is
2343        received and processed, unless it terminates the transport
2344        connection prematurely.
2345    </t>
2346    <t> If an origin server receives a request that does not include an
2347        Expect request-header field with the "100-continue" expectation,
2348        the request includes a request body, and the server responds
2349        with a final status code before reading the entire request body
2350        from the transport connection, then the server SHOULD NOT  close
2351        the transport connection until it has read the entire request,
2352        or until the client closes the connection. Otherwise, the client
2353        might not reliably receive the response message. However, this
2354        requirement is not be construed as preventing a server from
2355        defending itself against denial-of-service attacks, or from
2356        badly broken client implementations.
2357      </t>
2358    </list>
2359</t>
2360<t>
2361   Requirements for HTTP/1.1 proxies:
2362  <list style="symbols">
2363    <t> If a proxy receives a request that includes an Expect request-header
2364        field with the "100-continue" expectation, and the proxy
2365        either knows that the next-hop server complies with HTTP/1.1 or
2366        higher, or does not know the HTTP version of the next-hop
2367        server, it MUST forward the request, including the Expect header
2368        field.
2369    </t>
2370    <t> If the proxy knows that the version of the next-hop server is
2371        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2372        respond with a 417 (Expectation Failed) status.
2373    </t>
2374    <t> Proxies SHOULD maintain a cache recording the HTTP version
2375        numbers received from recently-referenced next-hop servers.
2376    </t>
2377    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2378        request message was received from an HTTP/1.0 (or earlier)
2379        client and did not include an Expect request-header field with
2380        the "100-continue" expectation. This requirement overrides the
2381        general rule for forwarding of 1xx responses (see Section 8.1 of <xref target="Part2"/>).
2382    </t>
2383  </list>
2384</t>
2385</section>
2386
2387<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2388<t>
2389   If an HTTP/1.1 client sends a request which includes a request body,
2390   but which does not include an Expect request-header field with the
2391   "100-continue" expectation, and if the client is not directly
2392   connected to an HTTP/1.1 origin server, and if the client sees the
2393   connection close before receiving any status from the server, the
2394   client SHOULD retry the request.  If the client does retry this
2395   request, it MAY use the following "binary exponential backoff"
2396   algorithm to be assured of obtaining a reliable response:
2397  <list style="numbers">
2398    <t>
2399      Initiate a new connection to the server
2400    </t>
2401    <t>
2402      Transmit the request-headers
2403    </t>
2404    <t>
2405      Initialize a variable R to the estimated round-trip time to the
2406         server (e.g., based on the time it took to establish the
2407         connection), or to a constant value of 5 seconds if the round-trip
2408         time is not available.
2409    </t>
2410    <t>
2411       Compute T = R * (2**N), where N is the number of previous
2412         retries of this request.
2413    </t>
2414    <t>
2415       Wait either for an error response from the server, or for T
2416         seconds (whichever comes first)
2417    </t>
2418    <t>
2419       If no error response is received, after T seconds transmit the
2420         body of the request.
2421    </t>
2422    <t>
2423       If client sees that the connection is closed prematurely,
2424         repeat from step 1 until the request is accepted, an error
2425         response is received, or the user becomes impatient and
2426         terminates the retry process.
2427    </t>
2428  </list>
2429</t>
2430<t>
2431   If at any point an error status is received, the client
2432  <list style="symbols">
2433      <t>SHOULD NOT  continue and</t>
2434
2435      <t>SHOULD close the connection if it has not completed sending the
2436        request message.</t>
2437    </list>
2438</t>
2439</section>
2440</section>
2441</section>
2442
2443
2444<section title="Miscellaneous notes that may disappear" anchor="misc">
2445<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2446<t>
2447   <cref>TBS: describe why aliases like webcal are harmful.</cref>
2448</t>
2449</section>
2450
2451<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2452<t>
2453   <cref>TBD: Configured to use HTTP to proxy HTTP or other protocols.</cref>
2454</t>
2455</section>
2456
2457<section title="Interception of HTTP for access control" anchor="http.intercept">
2458<t>
2459   <cref>TBD: Interception of HTTP traffic for initiating access control.</cref>
2460</t>
2461</section>
2462
2463<section title="Use of HTTP by other protocols" anchor="http.others">
2464<t>
2465   <cref>TBD: Profiles of HTTP defined by other protocol.
2466   Extensions of HTTP like WebDAV.</cref>
2467</t>
2468
2469</section>
2470<section title="Use of HTTP by media type specification" anchor="http.media">
2471<t>
2472   <cref>TBD: Instructions on composing HTTP requests via hypertext formats.</cref>
2473</t>
2474</section>
2475</section>
2476
2477<section title="Header Field Definitions" anchor="header.field.definitions">
2478<t>
2479   This section defines the syntax and semantics of HTTP/1.1 header fields
2480   related to message framing and transport protocols.
2481</t>
2482<t>
2483   For entity-header fields, both sender and recipient refer to either the
2484   client or the server, depending on who sends and who receives the entity.
2485</t>
2486
2487<section title="Connection" anchor="header.connection">
2488  <iref primary="true" item="Connection header"/>
2489  <iref primary="true" item="Headers" subitem="Connection"/>
2490 
2491 
2492 
2493<t>
2494   The "Connection" general-header field allows the sender to specify
2495   options that are desired for that particular connection and MUST NOT
2496   be communicated by proxies over further connections.
2497</t>
2498<t>
2499   The Connection header's value has the following grammar:
2500</t>
2501<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[
2502  Connection       = "Connection" ":" OWS Connection-v
2503  Connection-v     = 1#connection-token
2504  connection-token = token
2505]]></artwork></figure>
2506<t>
2507   HTTP/1.1 proxies MUST parse the Connection header field before a
2508   message is forwarded and, for each connection-token in this field,
2509   remove any header field(s) from the message with the same name as the
2510   connection-token. Connection options are signaled by the presence of
2511   a connection-token in the Connection header field, not by any
2512   corresponding additional header field(s), since the additional header
2513   field may not be sent if there are no parameters associated with that
2514   connection option.
2515</t>
2516<t>
2517   Message headers listed in the Connection header MUST NOT include
2518   end-to-end headers, such as Cache-Control.
2519</t>
2520<t>
2521   HTTP/1.1 defines the "close" connection option for the sender to
2522   signal that the connection will be closed after completion of the
2523   response. For example,
2524</t>
2525<figure><artwork type="example"><![CDATA[
2526  Connection: close
2527]]></artwork></figure>
2528<t>
2529   in either the request or the response header fields indicates that
2530   the connection SHOULD NOT  be considered `persistent' (<xref target="persistent.connections"/>)
2531   after the current request/response is complete.
2532</t>
2533<t>
2534   An HTTP/1.1 client that does not support persistent connections MUST
2535   include the "close" connection option in every request message.
2536</t>
2537<t>
2538   An HTTP/1.1 server that does not support persistent connections MUST
2539   include the "close" connection option in every response message that
2540   does not have a 1xx (informational) status code.
2541</t>
2542<t>
2543   A system receiving an HTTP/1.0 (or lower-version) message that
2544   includes a Connection header MUST, for each connection-token in this
2545   field, remove and ignore any header field(s) from the message with
2546   the same name as the connection-token. This protects against mistaken
2547   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2548</t>
2549</section>
2550
2551<section title="Content-Length" anchor="header.content-length">
2552  <iref primary="true" item="Content-Length header"/>
2553  <iref primary="true" item="Headers" subitem="Content-Length"/>
2554 
2555 
2556<t>
2557   The "Content-Length" entity-header field indicates the size of the
2558   entity-body, in number of OCTETs. In the case of responses to the HEAD
2559   method, it indicates the size of the entity-body that would have been sent
2560   had the request been a GET.
2561</t>
2562<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/><artwork type="abnf2616"><![CDATA[
2563  Content-Length   = "Content-Length" ":" OWS 1*Content-Length-v
2564  Content-Length-v = 1*DIGIT
2565]]></artwork></figure>
2566<t>
2567   An example is
2568</t>
2569<figure><artwork type="example"><![CDATA[
2570  Content-Length: 3495
2571]]></artwork></figure>
2572<t>
2573   Applications SHOULD use this field to indicate the transfer-length of
2574   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2575</t>
2576<t>
2577   Any Content-Length greater than or equal to zero is a valid value.
2578   <xref target="message.length"/> describes how to determine the length of a message-body
2579   if a Content-Length is not given.
2580</t>
2581<t>
2582   Note that the meaning of this field is significantly different from
2583   the corresponding definition in MIME, where it is an optional field
2584   used within the "message/external-body" content-type. In HTTP, it
2585   SHOULD be sent whenever the message's length can be determined prior
2586   to being transferred, unless this is prohibited by the rules in
2587   <xref target="message.length"/>.
2588</t>
2589</section>
2590
2591<section title="Date" anchor="header.date">
2592  <iref primary="true" item="Date header"/>
2593  <iref primary="true" item="Headers" subitem="Date"/>
2594 
2595 
2596<t>
2597   The "Date" general-header field represents the date and time at which
2598   the message was originated, having the same semantics as orig-date in
2599   Section 3.6.1 of <xref target="RFC5322"/>. The field value is an
2600   HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2601   it MUST be sent in rfc1123-date format.
2602</t>
2603<figure><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/><artwork type="abnf2616"><![CDATA[
2604  Date   = "Date" ":" OWS Date-v
2605  Date-v = HTTP-date
2606]]></artwork></figure>
2607<t>
2608   An example is
2609</t>
2610<figure><artwork type="example"><![CDATA[
2611  Date: Tue, 15 Nov 1994 08:12:31 GMT
2612]]></artwork></figure>
2613<t>
2614   Origin servers MUST include a Date header field in all responses,
2615   except in these cases:
2616  <list style="numbers">
2617      <t>If the response status code is 100 (Continue) or 101 (Switching
2618         Protocols), the response MAY include a Date header field, at
2619         the server's option.</t>
2620
2621      <t>If the response status code conveys a server error, e.g. 500
2622         (Internal Server Error) or 503 (Service Unavailable), and it is
2623         inconvenient or impossible to generate a valid Date.</t>
2624
2625      <t>If the server does not have a clock that can provide a
2626         reasonable approximation of the current time, its responses
2627         MUST NOT include a Date header field. In this case, the rules
2628         in <xref target="clockless.origin.server.operation"/> MUST be followed.</t>
2629  </list>
2630</t>
2631<t>
2632   A received message that does not have a Date header field MUST be
2633   assigned one by the recipient if the message will be cached by that
2634   recipient or gatewayed via a protocol which requires a Date. An HTTP
2635   implementation without a clock MUST NOT cache responses without
2636   revalidating them on every use. An HTTP cache, especially a shared
2637   cache, SHOULD use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2638   clock with a reliable external standard.
2639</t>
2640<t>
2641   Clients SHOULD only send a Date header field in messages that include
2642   an entity-body, as in the case of the PUT and POST requests, and even
2643   then it is optional. A client without a clock MUST NOT send a Date
2644   header field in a request.
2645</t>
2646<t>
2647   The HTTP-date sent in a Date header SHOULD NOT  represent a date and
2648   time subsequent to the generation of the message. It SHOULD represent
2649   the best available approximation of the date and time of message
2650   generation, unless the implementation has no means of generating a
2651   reasonably accurate date and time. In theory, the date ought to
2652   represent the moment just before the entity is generated. In
2653   practice, the date can be generated at any time during the message
2654   origination without affecting its semantic value.
2655</t>
2656
2657<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2658<t>
2659   Some origin server implementations might not have a clock available.
2660   An origin server without a clock MUST NOT assign Expires or Last-Modified
2661   values to a response, unless these values were associated
2662   with the resource by a system or user with a reliable clock. It MAY
2663   assign an Expires value that is known, at or before server
2664   configuration time, to be in the past (this allows "pre-expiration"
2665   of responses without storing separate Expires values for each
2666   resource).
2667</t>
2668</section>
2669</section>
2670
2671<section title="Host" anchor="header.host">
2672  <iref primary="true" item="Host header"/>
2673  <iref primary="true" item="Headers" subitem="Host"/>
2674 
2675 
2676<t>
2677   The "Host" request-header field specifies the Internet host and port
2678   number of the resource being requested, allowing the origin server or
2679   gateway to differentiate between internally-ambiguous URLs, such as the root
2680   "/" URL of a server for multiple host names on a single IP address.
2681</t>
2682<t>    
2683   The Host field value MUST represent the naming authority of the origin
2684   server or gateway given by the original URL obtained from the user or
2685   referring resource (generally an http URI, as described in
2686   <xref target="http.uri"/>).
2687</t>
2688<figure><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/><artwork type="abnf2616"><![CDATA[
2689  Host   = "Host" ":" OWS Host-v
2690  Host-v = uri-host [ ":" port ] ; Section 2.6.1
2691]]></artwork></figure>
2692<t>
2693   A "host" without any trailing port information implies the default
2694   port for the service requested (e.g., "80" for an HTTP URL). For
2695   example, a request on the origin server for
2696   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2697</t>
2698<figure><artwork type="example"><![CDATA[
2699  GET /pub/WWW/ HTTP/1.1
2700  Host: www.example.org
2701]]></artwork></figure>
2702<t>
2703   A client MUST include a Host header field in all HTTP/1.1 request
2704   messages. If the requested URI does not include an Internet host
2705   name for the service being requested, then the Host header field MUST
2706   be given with an empty value. An HTTP/1.1 proxy MUST ensure that any
2707   request message it forwards does contain an appropriate Host header
2708   field that identifies the service being requested by the proxy. All
2709   Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
2710   status code to any HTTP/1.1 request message which lacks a Host header
2711   field.
2712</t>
2713<t>
2714   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2715   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2716   for other requirements relating to Host.
2717</t>
2718</section>
2719
2720<section title="TE" anchor="header.te">
2721  <iref primary="true" item="TE header"/>
2722  <iref primary="true" item="Headers" subitem="TE"/>
2723 
2724 
2725 
2726 
2727 
2728<t>
2729   The "TE" request-header field indicates what extension transfer-codings
2730   it is willing to accept in the response, and whether or not it is
2731   willing to accept trailer fields in a chunked transfer-coding.
2732</t>
2733<t>
2734   Its value may consist of the keyword "trailers" and/or a comma-separated
2735   list of extension transfer-coding names with optional accept
2736   parameters (as described in <xref target="transfer.codings"/>).
2737</t>
2738<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[
2739  TE        = "TE" ":" OWS TE-v
2740  TE-v      = #t-codings
2741  t-codings = "trailers" / ( transfer-extension [ te-params ] )
2742  te-params = OWS ";" OWS "q=" qvalue *( te-ext )
2743  te-ext    = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2744]]></artwork></figure>
2745<t>
2746   The presence of the keyword "trailers" indicates that the client is
2747   willing to accept trailer fields in a chunked transfer-coding, as
2748   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2749   transfer-coding values even though it does not itself represent a
2750   transfer-coding.
2751</t>
2752<t>
2753   Examples of its use are:
2754</t>
2755<figure><artwork type="example"><![CDATA[
2756  TE: deflate
2757  TE:
2758  TE: trailers, deflate;q=0.5
2759]]></artwork></figure>
2760<t>
2761   The TE header field only applies to the immediate connection.
2762   Therefore, the keyword MUST be supplied within a Connection header
2763   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2764</t>
2765<t>
2766   A server tests whether a transfer-coding is acceptable, according to
2767   a TE field, using these rules:
2768  <list style="numbers">
2769    <t>The "chunked" transfer-coding is always acceptable. If the
2770         keyword "trailers" is listed, the client indicates that it is
2771         willing to accept trailer fields in the chunked response on
2772         behalf of itself and any downstream clients. The implication is
2773         that, if given, the client is stating that either all
2774         downstream clients are willing to accept trailer fields in the
2775         forwarded response, or that it will attempt to buffer the
2776         response on behalf of downstream recipients.
2777      <vspace blankLines="1"/>
2778         Note: HTTP/1.1 does not define any means to limit the size of a
2779         chunked response such that a client can be assured of buffering
2780         the entire response.</t>
2781    <t>If the transfer-coding being tested is one of the transfer-codings
2782         listed in the TE field, then it is acceptable unless it
2783         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2784         qvalue of 0 means "not acceptable.")</t>
2785    <t>If multiple transfer-codings are acceptable, then the
2786         acceptable transfer-coding with the highest non-zero qvalue is
2787         preferred.  The "chunked" transfer-coding always has a qvalue
2788         of 1.</t>
2789  </list>
2790</t>
2791<t>
2792   If the TE field-value is empty or if no TE field is present, the only
2793   transfer-coding is "chunked". A message with no transfer-coding is
2794   always acceptable.
2795</t>
2796</section>
2797
2798<section title="Trailer" anchor="header.trailer">
2799  <iref primary="true" item="Trailer header"/>
2800  <iref primary="true" item="Headers" subitem="Trailer"/>
2801 
2802 
2803<t>
2804   The "Trailer" general-header field indicates that the given set of
2805   header fields is present in the trailer of a message encoded with
2806   chunked transfer-coding.
2807</t>
2808<figure><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/><artwork type="abnf2616"><![CDATA[
2809  Trailer   = "Trailer" ":" OWS Trailer-v
2810  Trailer-v = 1#field-name
2811]]></artwork></figure>
2812<t>
2813   An HTTP/1.1 message SHOULD include a Trailer header field in a
2814   message using chunked transfer-coding with a non-empty trailer. Doing
2815   so allows the recipient to know which header fields to expect in the
2816   trailer.
2817</t>
2818<t>
2819   If no Trailer header field is present, the trailer SHOULD NOT  include
2820   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2821   trailer fields in a "chunked" transfer-coding.
2822</t>
2823<t>
2824   Message header fields listed in the Trailer header field MUST NOT
2825   include the following header fields:
2826  <list style="symbols">
2827    <t>Transfer-Encoding</t>
2828    <t>Content-Length</t>
2829    <t>Trailer</t>
2830  </list>
2831</t>
2832</section>
2833
2834<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2835  <iref primary="true" item="Transfer-Encoding header"/>
2836  <iref primary="true" item="Headers" subitem="Transfer-Encoding"/>
2837 
2838 
2839<t>
2840   The "Transfer-Encoding" general-header field indicates what transfer-codings
2841   (if any) have been applied to the message body. It differs from
2842   Content-Encoding (Section 2.2 of <xref target="Part3"/>) in that transfer-codings are a property
2843   of the message (and therefore are removed by intermediaries), whereas
2844   content-codings are not.
2845</t>
2846<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/><artwork type="abnf2616"><![CDATA[
2847  Transfer-Encoding   = "Transfer-Encoding" ":" OWS
2848                        Transfer-Encoding-v
2849  Transfer-Encoding-v = 1#transfer-coding
2850]]></artwork></figure>
2851<t>
2852   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2853</t>
2854<figure><artwork type="example"><![CDATA[
2855  Transfer-Encoding: chunked
2856]]></artwork></figure>
2857<t>
2858   If multiple encodings have been applied to an entity, the transfer-codings
2859   MUST be listed in the order in which they were applied.
2860   Additional information about the encoding parameters MAY be provided
2861   by other entity-header fields not defined by this specification.
2862</t>
2863<t>
2864   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2865   header.
2866</t>
2867</section>
2868
2869<section title="Upgrade" anchor="header.upgrade">
2870  <iref primary="true" item="Upgrade header"/>
2871  <iref primary="true" item="Headers" subitem="Upgrade"/>
2872 
2873 
2874<t>
2875   The "Upgrade" general-header field allows the client to specify what
2876   additional communication protocols it would like to use, if the server
2877   chooses to switch protocols. Additionally, the server MUST use the Upgrade
2878   header field within a 101 (Switching Protocols) response to indicate which
2879   protocol(s) are being switched to.
2880</t>
2881<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/><artwork type="abnf2616"><![CDATA[
2882  Upgrade   = "Upgrade" ":" OWS Upgrade-v
2883  Upgrade-v = 1#product
2884]]></artwork></figure>
2885<t>
2886   For example,
2887</t>
2888<figure><artwork type="example"><![CDATA[
2889  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2890]]></artwork></figure>
2891<t>
2892   The Upgrade header field is intended to provide a simple mechanism
2893   for transition from HTTP/1.1 to some other, incompatible protocol. It
2894   does so by allowing the client to advertise its desire to use another
2895   protocol, such as a later version of HTTP with a higher major version
2896   number, even though the current request has been made using HTTP/1.1.
2897   This eases the difficult transition between incompatible protocols by
2898   allowing the client to initiate a request in the more commonly
2899   supported protocol while indicating to the server that it would like
2900   to use a "better" protocol if available (where "better" is determined
2901   by the server, possibly according to the nature of the method and/or
2902   resource being requested).
2903</t>
2904<t>
2905   The Upgrade header field only applies to switching application-layer
2906   protocols upon the existing transport-layer connection. Upgrade
2907   cannot be used to insist on a protocol change; its acceptance and use
2908   by the server is optional. The capabilities and nature of the
2909   application-layer communication after the protocol change is entirely
2910   dependent upon the new protocol chosen, although the first action
2911   after changing the protocol MUST be a response to the initial HTTP
2912   request containing the Upgrade header field.
2913</t>
2914<t>
2915   The Upgrade header field only applies to the immediate connection.
2916   Therefore, the upgrade keyword MUST be supplied within a Connection
2917   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2918   HTTP/1.1 message.
2919</t>
2920<t>
2921   The Upgrade header field cannot be used to indicate a switch to a
2922   protocol on a different connection. For that purpose, it is more
2923   appropriate to use a 301, 302, 303, or 305 redirection response.
2924</t>
2925<t>
2926   This specification only defines the protocol name "HTTP" for use by
2927   the family of Hypertext Transfer Protocols, as defined by the HTTP
2928   version rules of <xref target="http.version"/> and future updates to this
2929   specification. Additional tokens can be registered with IANA using the
2930   registration procedure defined below. 
2931</t>
2932
2933<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
2934<t>
2935   The HTTP Upgrade Token Registry defines the name space for product
2936   tokens used to identify protocols in the Upgrade header field.
2937   Each registered token should be associated with one or a set of
2938   specifications, and with contact information.
2939</t>
2940<t>
2941   Registrations should be allowed on a First Come First Served basis as
2942   described in Section 4.1 of <xref target="RFC5226"/>. These
2943   specifications need not be IETF documents or be subject to IESG review, but
2944   should obey the following rules:
2945  <list style="numbers">
2946    <t>A token, once registered, stays registered forever.</t>
2947    <t>The registration MUST name a responsible party for the
2948       registration.</t>
2949    <t>The registration MUST name a point of contact.</t>
2950    <t>The registration MAY name the documentation required for the
2951       token.</t>
2952    <t>The responsible party MAY change the registration at any time.
2953       The IANA will keep a record of all such changes, and make them
2954       available upon request.</t>
2955    <t>The responsible party for the first registration of a "product"
2956       token MUST approve later registrations of a "version" token
2957       together with that "product" token before they can be registered.</t>
2958    <t>If absolutely required, the IESG MAY reassign the responsibility
2959       for a token. This will normally only be used in the case when a
2960       responsible party cannot be contacted.</t>
2961  </list>
2962</t>
2963<t>
2964   It is not required that specifications for upgrade tokens be made
2965   publicly available, but the contact information for the registration
2966   should be.
2967</t>
2968</section>
2969
2970
2971</section>
2972
2973<section title="Via" anchor="header.via">
2974  <iref primary="true" item="Via header"/>
2975  <iref primary="true" item="Headers" subitem="Via"/>
2976 
2977 
2978 
2979 
2980 
2981 
2982 
2983<t>
2984   The "Via" general-header field MUST be used by gateways and proxies to
2985   indicate the intermediate protocols and recipients between the user
2986   agent and the server on requests, and between the origin server and
2987   the client on responses. It is analogous to the "Received" field defined in
2988   Section 3.6.7 of <xref target="RFC5322"/> and is intended to be used for tracking message forwards,
2989   avoiding request loops, and identifying the protocol capabilities of
2990   all senders along the request/response chain.
2991</t>
2992<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[
2993  Via               = "Via" ":" OWS Via-v
2994  Via-v             = 1#( received-protocol RWS received-by
2995                          [ RWS comment ] )
2996  received-protocol = [ protocol-name "/" ] protocol-version
2997  protocol-name     = token
2998  protocol-version  = token
2999  received-by       = ( uri-host [ ":" port ] ) / pseudonym
3000  pseudonym         = token
3001]]></artwork></figure>
3002<t>
3003   The received-protocol indicates the protocol version of the message
3004   received by the server or client along each segment of the
3005   request/response chain. The received-protocol version is appended to
3006   the Via field value when the message is forwarded so that information
3007   about the protocol capabilities of upstream applications remains
3008   visible to all recipients.
3009</t>
3010<t>
3011   The protocol-name is optional if and only if it would be "HTTP". The
3012   received-by field is normally the host and optional port number of a
3013   recipient server or client that subsequently forwarded the message.
3014   However, if the real host is considered to be sensitive information,
3015   it MAY be replaced by a pseudonym. If the port is not given, it MAY
3016   be assumed to be the default port of the received-protocol.
3017</t>
3018<t>
3019   Multiple Via field values represents each proxy or gateway that has
3020   forwarded the message. Each recipient MUST append its information
3021   such that the end result is ordered according to the sequence of
3022   forwarding applications.
3023</t>
3024<t>
3025   Comments MAY be used in the Via header field to identify the software
3026   of the recipient proxy or gateway, analogous to the User-Agent and
3027   Server header fields. However, all comments in the Via field are
3028   optional and MAY be removed by any recipient prior to forwarding the
3029   message.
3030</t>
3031<t>
3032   For example, a request message could be sent from an HTTP/1.0 user
3033   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3034   forward the request to a public proxy at p.example.net, which completes
3035   the request by forwarding it to the origin server at www.example.com.
3036   The request received by www.example.com would then have the following
3037   Via header field:
3038</t>
3039<figure><artwork type="example"><![CDATA[
3040  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3041]]></artwork></figure>
3042<t>
3043   Proxies and gateways used as a portal through a network firewall
3044   SHOULD NOT, by default, forward the names and ports of hosts within
3045   the firewall region. This information SHOULD only be propagated if
3046   explicitly enabled. If not enabled, the received-by host of any host
3047   behind the firewall SHOULD be replaced by an appropriate pseudonym
3048   for that host.
3049</t>
3050<t>
3051   For organizations that have strong privacy requirements for hiding
3052   internal structures, a proxy MAY combine an ordered subsequence of
3053   Via header field entries with identical received-protocol values into
3054   a single such entry. For example,
3055</t>
3056<figure><artwork type="example"><![CDATA[
3057  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3058]]></artwork></figure>
3059<t>
3060        could be collapsed to
3061</t>
3062<figure><artwork type="example"><![CDATA[
3063  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3064]]></artwork></figure>
3065<t>
3066   Applications SHOULD NOT  combine multiple entries unless they are all
3067   under the same organizational control and the hosts have already been
3068   replaced by pseudonyms. Applications MUST NOT combine entries which
3069   have different received-protocol values.
3070</t>
3071</section>
3072
3073</section>
3074
3075<section title="IANA Considerations" anchor="IANA.considerations">
3076
3077<section title="Message Header Registration" anchor="message.header.registration">
3078<t>
3079   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3080   with the permanent registrations below (see <xref target="RFC3864"/>):
3081</t>
3082
3083<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3084<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3085   <ttcol>Header Field Name</ttcol>
3086   <ttcol>Protocol</ttcol>
3087   <ttcol>Status</ttcol>
3088   <ttcol>Reference</ttcol>
3089
3090   <c>Connection</c>
3091   <c>http</c>
3092   <c>standard</c>
3093   <c>
3094      <xref target="header.connection"/>
3095   </c>
3096   <c>Content-Length</c>
3097   <c>http</c>
3098   <c>standard</c>
3099   <c>
3100      <xref target="header.content-length"/>
3101   </c>
3102   <c>Date</c>
3103   <c>http</c>
3104   <c>standard</c>
3105   <c>
3106      <xref target="header.date"/>
3107   </c>
3108   <c>Host</c>
3109   <c>http</c>
3110   <c>standard</c>
3111   <c>
3112      <xref target="header.host"/>
3113   </c>
3114   <c>TE</c>
3115   <c>http</c>
3116   <c>standard</c>
3117   <c>
3118      <xref target="header.te"/>
3119   </c>
3120   <c>Trailer</c>
3121   <c>http</c>
3122   <c>standard</c>
3123   <c>
3124      <xref target="header.trailer"/>
3125   </c>
3126   <c>Transfer-Encoding</c>
3127   <c>http</c>
3128   <c>standard</c>
3129   <c>
3130      <xref target="header.transfer-encoding"/>
3131   </c>
3132   <c>Upgrade</c>
3133   <c>http</c>
3134   <c>standard</c>
3135   <c>
3136      <xref target="header.upgrade"/>
3137   </c>
3138   <c>Via</c>
3139   <c>http</c>
3140   <c>standard</c>
3141   <c>
3142      <xref target="header.via"/>
3143   </c>
3144</texttable>
3145<!--(END)-->
3146
3147<t>
3148   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3149</t>
3150</section>
3151
3152<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3153<t>
3154   The entries for the "http" and "https" URI Schemes in the registry located at
3155   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3156   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3157   and <xref target="https.uri" format="counter"/> of this document
3158   (see <xref target="RFC4395"/>).
3159</t>
3160</section>
3161
3162<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3163<t>
3164   This document serves as the specification for the Internet media types
3165   "message/http" and "application/http". The following is to be registered with
3166   IANA (see <xref target="RFC4288"/>).
3167</t>
3168<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3169<iref item="Media Type" subitem="message/http" primary="true"/>
3170<iref item="message/http Media Type" primary="true"/>
3171<t>
3172   The message/http type can be used to enclose a single HTTP request or
3173   response message, provided that it obeys the MIME restrictions for all
3174   "message" types regarding line length and encodings.
3175</t>
3176<t>
3177  <list style="hanging">
3178    <t hangText="Type name:">
3179      message
3180    </t>
3181    <t hangText="Subtype name:">
3182      http
3183    </t>
3184    <t hangText="Required parameters:">
3185      none
3186    </t>
3187    <t hangText="Optional parameters:">
3188      version, msgtype
3189      <list style="hanging">
3190        <t hangText="version:">
3191          The HTTP-Version number of the enclosed message
3192          (e.g., "1.1"). If not present, the version can be
3193          determined from the first line of the body.
3194        </t>
3195        <t hangText="msgtype:">
3196          The message type -- "request" or "response". If not
3197          present, the type can be determined from the first
3198          line of the body.
3199        </t>
3200      </list>
3201    </t>
3202    <t hangText="Encoding considerations:">
3203      only "7bit", "8bit", or "binary" are permitted
3204    </t>
3205    <t hangText="Security considerations:">
3206      none
3207    </t>
3208    <t hangText="Interoperability considerations:">
3209      none
3210    </t>
3211    <t hangText="Published specification:">
3212      This specification (see <xref target="internet.media.type.message.http"/>).
3213    </t>
3214    <t hangText="Applications that use this media type:">
3215    </t>
3216    <t hangText="Additional information:">
3217      <list style="hanging">
3218        <t hangText="Magic number(s):">none</t>
3219        <t hangText="File extension(s):">none</t>
3220        <t hangText="Macintosh file type code(s):">none</t>
3221      </list>
3222    </t>
3223    <t hangText="Person and email address to contact for further information:">
3224      See Authors Section.
3225    </t>
3226    <t hangText="Intended usage:">
3227      COMMON
3228    </t>
3229    <t hangText="Restrictions on usage:">
3230      none
3231    </t>
3232    <t hangText="Author/Change controller:">
3233      IESG
3234    </t>
3235  </list>
3236</t>
3237</section>
3238<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3239<iref item="Media Type" subitem="application/http" primary="true"/>
3240<iref item="application/http Media Type" primary="true"/>
3241<t>
3242   The application/http type can be used to enclose a pipeline of one or more
3243   HTTP request or response messages (not intermixed).
3244</t>
3245<t>
3246  <list style="hanging">
3247    <t hangText="Type name:">
3248      application
3249    </t>
3250    <t hangText="Subtype name:">
3251      http
3252    </t>
3253    <t hangText="Required parameters:">
3254      none
3255    </t>
3256    <t hangText="Optional parameters:">
3257      version, msgtype
3258      <list style="hanging">
3259        <t hangText="version:">
3260          The HTTP-Version number of the enclosed messages
3261          (e.g., "1.1"). If not present, the version can be
3262          determined from the first line of the body.
3263        </t>
3264        <t hangText="msgtype:">
3265          The message type -- "request" or "response". If not
3266          present, the type can be determined from the first
3267          line of the body.
3268        </t>
3269      </list>
3270    </t>
3271    <t hangText="Encoding considerations:">
3272      HTTP messages enclosed by this type
3273      are in "binary" format; use of an appropriate
3274      Content-Transfer-Encoding is required when
3275      transmitted via E-mail.
3276    </t>
3277    <t hangText="Security considerations:">
3278      none
3279    </t>
3280    <t hangText="Interoperability considerations:">
3281      none
3282    </t>
3283    <t hangText="Published specification:">
3284      This specification (see <xref target="internet.media.type.application.http"/>).
3285    </t>
3286    <t hangText="Applications that use this media type:">
3287    </t>
3288    <t hangText="Additional information:">
3289      <list style="hanging">
3290        <t hangText="Magic number(s):">none</t>
3291        <t hangText="File extension(s):">none</t>
3292        <t hangText="Macintosh file type code(s):">none</t>
3293      </list>
3294    </t>
3295    <t hangText="Person and email address to contact for further information:">
3296      See Authors Section.
3297    </t>
3298    <t hangText="Intended usage:">
3299      COMMON
3300    </t>
3301    <t hangText="Restrictions on usage:">
3302      none
3303    </t>
3304    <t hangText="Author/Change controller:">
3305      IESG
3306    </t>
3307  </list>
3308</t>
3309</section>
3310</section>
3311
3312<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3313<t>
3314   The registration procedure for HTTP Transfer Codings is now defined by
3315   <xref target="transfer.coding.registry"/> of this document.
3316</t>
3317<t>
3318   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3319   should be updated with the registrations below:
3320</t>
3321<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3322   <ttcol>Name</ttcol>
3323   <ttcol>Description</ttcol>
3324   <ttcol>Reference</ttcol>
3325   <c>chunked</c>
3326   <c>Transfer in a series of chunks</c>
3327   <c>
3328      <xref target="chunked.encoding"/>
3329   </c>
3330   <c>compress</c>
3331   <c>UNIX "compress" program method</c>
3332   <c>
3333      <xref target="compress.coding"/>
3334   </c>
3335   <c>deflate</c>
3336   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
3337   <c>
3338      <xref target="deflate.coding"/>
3339   </c>
3340   <c>gzip</c>
3341   <c>Same as GNU zip <xref target="RFC1952"/></c>
3342   <c>
3343      <xref target="gzip.coding"/>
3344   </c>
3345</texttable>
3346</section>
3347
3348<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3349<t>
3350   The registration procedure for HTTP Upgrade Tokens -- previously defined
3351   in Section 7.2 of <xref target="RFC2817"/> -- is now defined
3352   by <xref target="upgrade.token.registry"/> of this document.
3353</t>
3354<t>
3355   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3356   should be updated with the registration below:
3357</t>
3358<texttable align="left" suppress-title="true">
3359   <ttcol>Value</ttcol>
3360   <ttcol>Description</ttcol>
3361   <ttcol>Reference</ttcol>
3362
3363   <c>HTTP</c>
3364   <c>Hypertext Transfer Protocol</c>
3365   <c><xref target="http.version"/> of this specification</c>
3366<!-- IANA should add this without our instructions; emailed on June 05, 2009
3367   <c>TLS/1.0</c>
3368   <c>Transport Layer Security</c>
3369   <c><xref target="RFC2817"/></c> -->
3370
3371</texttable>
3372</section>
3373
3374</section>
3375
3376<section title="Security Considerations" anchor="security.considerations">
3377<t>
3378   This section is meant to inform application developers, information
3379   providers, and users of the security limitations in HTTP/1.1 as
3380   described by this document. The discussion does not include
3381   definitive solutions to the problems revealed, though it does make
3382   some suggestions for reducing security risks.
3383</t>
3384
3385<section title="Personal Information" anchor="personal.information">
3386<t>
3387   HTTP clients are often privy to large amounts of personal information
3388   (e.g. the user's name, location, mail address, passwords, encryption
3389   keys, etc.), and SHOULD be very careful to prevent unintentional
3390   leakage of this information.
3391   We very strongly recommend that a convenient interface be provided
3392   for the user to control dissemination of such information, and that
3393   designers and implementors be particularly careful in this area.
3394   History shows that errors in this area often create serious security
3395   and/or privacy problems and generate highly adverse publicity for the
3396   implementor's company.
3397</t>
3398</section>
3399
3400<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3401<t>
3402   A server is in the position to save personal data about a user's
3403   requests which might identify their reading patterns or subjects of
3404   interest. This information is clearly confidential in nature and its
3405   handling can be constrained by law in certain countries. People using
3406   HTTP to provide data are responsible for ensuring that
3407   such material is not distributed without the permission of any
3408   individuals that are identifiable by the published results.
3409</t>
3410</section>
3411
3412<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3413<t>
3414   Implementations of HTTP origin servers SHOULD be careful to restrict
3415   the documents returned by HTTP requests to be only those that were
3416   intended by the server administrators. If an HTTP server translates
3417   HTTP URIs directly into file system calls, the server MUST take
3418   special care not to serve files that were not intended to be
3419   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3420   other operating systems use ".." as a path component to indicate a
3421   directory level above the current one. On such a system, an HTTP
3422   server MUST disallow any such construct in the request-target if it
3423   would otherwise allow access to a resource outside those intended to
3424   be accessible via the HTTP server. Similarly, files intended for
3425   reference only internally to the server (such as access control
3426   files, configuration files, and script code) MUST be protected from
3427   inappropriate retrieval, since they might contain sensitive
3428   information. Experience has shown that minor bugs in such HTTP server
3429   implementations have turned into security risks.
3430</t>
3431</section>
3432
3433<section title="DNS Spoofing" anchor="dns.spoofing">
3434<t>
3435   Clients using HTTP rely heavily on the Domain Name Service, and are
3436   thus generally prone to security attacks based on the deliberate
3437   mis-association of IP addresses and DNS names. Clients need to be
3438   cautious in assuming the continuing validity of an IP number/DNS name
3439   association.
3440</t>
3441<t>
3442   In particular, HTTP clients SHOULD rely on their name resolver for
3443   confirmation of an IP number/DNS name association, rather than
3444   caching the result of previous host name lookups. Many platforms
3445   already can cache host name lookups locally when appropriate, and
3446   they SHOULD be configured to do so. It is proper for these lookups to
3447   be cached, however, only when the TTL (Time To Live) information
3448   reported by the name server makes it likely that the cached
3449   information will remain useful.
3450</t>
3451<t>
3452   If HTTP clients cache the results of host name lookups in order to
3453   achieve a performance improvement, they MUST observe the TTL
3454   information reported by DNS.
3455</t>
3456<t>
3457   If HTTP clients do not observe this rule, they could be spoofed when
3458   a previously-accessed server's IP address changes. As network
3459   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3460   possibility of this form of attack will grow. Observing this
3461   requirement thus reduces this potential security vulnerability.
3462</t>
3463<t>
3464   This requirement also improves the load-balancing behavior of clients
3465   for replicated servers using the same DNS name and reduces the
3466   likelihood of a user's experiencing failure in accessing sites which
3467   use that strategy.
3468</t>
3469</section>
3470
3471<section title="Proxies and Caching" anchor="attack.proxies">
3472<t>
3473   By their very nature, HTTP proxies are men-in-the-middle, and
3474   represent an opportunity for man-in-the-middle attacks. Compromise of
3475   the systems on which the proxies run can result in serious security
3476   and privacy problems. Proxies have access to security-related
3477   information, personal information about individual users and
3478   organizations, and proprietary information belonging to users and
3479   content providers. A compromised proxy, or a proxy implemented or
3480   configured without regard to security and privacy considerations,
3481   might be used in the commission of a wide range of potential attacks.
3482</t>
3483<t>
3484   Proxy operators should protect the systems on which proxies run as
3485   they would protect any system that contains or transports sensitive
3486   information. In particular, log information gathered at proxies often
3487   contains highly sensitive personal information, and/or information
3488   about organizations. Log information should be carefully guarded, and
3489   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3490</t>
3491<t>
3492   Proxy implementors should consider the privacy and security
3493   implications of their design and coding decisions, and of the
3494   configuration options they provide to proxy operators (especially the
3495   default configuration).
3496</t>
3497<t>
3498   Users of a proxy need to be aware that they are no trustworthier than
3499   the people who run the proxy; HTTP itself cannot solve this problem.
3500</t>
3501<t>
3502   The judicious use of cryptography, when appropriate, may suffice to
3503   protect against a broad range of security and privacy attacks. Such
3504   cryptography is beyond the scope of the HTTP/1.1 specification.
3505</t>
3506</section>
3507
3508<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3509<t>
3510   They exist. They are hard to defend against. Research continues.
3511   Beware.
3512</t>
3513</section>
3514</section>
3515
3516<section title="Acknowledgments" anchor="ack">
3517<t>
3518   HTTP has evolved considerably over the years. It has
3519   benefited from a large and active developer community--the many
3520   people who have participated on the www-talk mailing list--and it is
3521   that community which has been most responsible for the success of
3522   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3523   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3524   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3525   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3526   VanHeyningen deserve special recognition for their efforts in
3527   defining early aspects of the protocol.
3528</t>
3529<t>
3530   This document has benefited greatly from the comments of all those
3531   participating in the HTTP-WG. In addition to those already mentioned,
3532   the following individuals have contributed to this specification:
3533</t>
3534<t>
3535   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3536   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3537   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3538   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3539   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3540   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3541   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3542   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3543   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3544   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3545   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3546   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3547   Josh Cohen.
3548</t>
3549<t>
3550   Thanks to the "cave men" of Palo Alto. You know who you are.
3551</t>
3552<t>
3553   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3554   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3555   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3556   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3557   Larry Masinter for their help. And thanks go particularly to Jeff
3558   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3559</t>
3560<t>
3561   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3562   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3563   discovery of many of the problems that this document attempts to
3564   rectify.
3565</t>
3566<t>
3567   This specification makes heavy use of the augmented BNF and generic
3568   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3569   reuses many of the definitions provided by Nathaniel Borenstein and
3570   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3571   specification will help reduce past confusion over the relationship
3572   between HTTP and Internet mail message formats.
3573</t>
3574</section>
3575
3576</middle>
3577<back>
3578
3579<references title="Normative References">
3580
3581<reference anchor="ISO-8859-1">
3582  <front>
3583    <title>
3584     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3585    </title>
3586    <author>
3587      <organization>International Organization for Standardization</organization>
3588    </author>
3589    <date year="1998"/>
3590  </front>
3591  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3592</reference>
3593
3594<reference anchor="Part2">
3595  <front>
3596    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3597    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3598      <organization abbrev="Day Software">Day Software</organization>
3599      <address><email>fielding@gbiv.com</email></address>
3600    </author>
3601    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3602      <organization>One Laptop per Child</organization>
3603      <address><email>jg@laptop.org</email></address>
3604    </author>
3605    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3606      <organization abbrev="HP">Hewlett-Packard Company</organization>
3607      <address><email>JeffMogul@acm.org</email></address>
3608    </author>
3609    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3610      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3611      <address><email>henrikn@microsoft.com</email></address>
3612    </author>
3613    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3614      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3615      <address><email>LMM@acm.org</email></address>
3616    </author>
3617    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3618      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3619      <address><email>paulle@microsoft.com</email></address>
3620    </author>
3621    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3622      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3623      <address><email>timbl@w3.org</email></address>
3624    </author>
3625    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3626      <organization abbrev="W3C">World Wide Web Consortium</organization>
3627      <address><email>ylafon@w3.org</email></address>
3628    </author>
3629    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3630      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3631      <address><email>julian.reschke@greenbytes.de</email></address>
3632    </author>
3633    <date month="October" year="2009"/>
3634  </front>
3635  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-08"/>
3636 
3637</reference>
3638
3639<reference anchor="Part3">
3640  <front>
3641    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3642    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3643      <organization abbrev="Day Software">Day Software</organization>
3644      <address><email>fielding@gbiv.com</email></address>
3645    </author>
3646    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3647      <organization>One Laptop per Child</organization>
3648      <address><email>jg@laptop.org</email></address>
3649    </author>
3650    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3651      <organization abbrev="HP">Hewlett-Packard Company</organization>
3652      <address><email>JeffMogul@acm.org</email></address>
3653    </author>
3654    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3655      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3656      <address><email>henrikn@microsoft.com</email></address>
3657    </author>
3658    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3659      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3660      <address><email>LMM@acm.org</email></address>
3661    </author>
3662    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3663      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3664      <address><email>paulle@microsoft.com</email></address>
3665    </author>
3666    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3667      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3668      <address><email>timbl@w3.org</email></address>
3669    </author>
3670    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3671      <organization abbrev="W3C">World Wide Web Consortium</organization>
3672      <address><email>ylafon@w3.org</email></address>
3673    </author>
3674    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3675      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3676      <address><email>julian.reschke@greenbytes.de</email></address>
3677    </author>
3678    <date month="October" year="2009"/>
3679  </front>
3680  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-08"/>
3681 
3682</reference>
3683
3684<reference anchor="Part5">
3685  <front>
3686    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3687    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3688      <organization abbrev="Day Software">Day Software</organization>
3689      <address><email>fielding@gbiv.com</email></address>
3690    </author>
3691    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3692      <organization>One Laptop per Child</organization>
3693      <address><email>jg@laptop.org</email></address>
3694    </author>
3695    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3696      <organization abbrev="HP">Hewlett-Packard Company</organization>
3697      <address><email>JeffMogul@acm.org</email></address>
3698    </author>
3699    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3700      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3701      <address><email>henrikn@microsoft.com</email></address>
3702    </author>
3703    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3704      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3705      <address><email>LMM@acm.org</email></address>
3706    </author>
3707    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3708      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3709      <address><email>paulle@microsoft.com</email></address>
3710    </author>
3711    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3712      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3713      <address><email>timbl@w3.org</email></address>
3714    </author>
3715    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3716      <organization abbrev="W3C">World Wide Web Consortium</organization>
3717      <address><email>ylafon@w3.org</email></address>
3718    </author>
3719    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3720      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3721      <address><email>julian.reschke@greenbytes.de</email></address>
3722    </author>
3723    <date month="October" year="2009"/>
3724  </front>
3725  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-08"/>
3726 
3727</reference>
3728
3729<reference anchor="Part6">
3730  <front>
3731    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3732    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3733      <organization abbrev="Day Software">Day Software</organization>
3734      <address><email>fielding@gbiv.com</email></address>
3735    </author>
3736    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3737      <organization>One Laptop per Child</organization>
3738      <address><email>jg@laptop.org</email></address>
3739    </author>
3740    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3741      <organization abbrev="HP">Hewlett-Packard Company</organization>
3742      <address><email>JeffMogul@acm.org</email></address>
3743    </author>
3744    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3745      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3746      <address><email>henrikn@microsoft.com</email></address>
3747    </author>
3748    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3749      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3750      <address><email>LMM@acm.org</email></address>
3751    </author>
3752    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3753      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3754      <address><email>paulle@microsoft.com</email></address>
3755    </author>
3756    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3757      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3758      <address><email>timbl@w3.org</email></address>
3759    </author>
3760    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3761      <organization abbrev="W3C">World Wide Web Consortium</organization>
3762      <address><email>ylafon@w3.org</email></address>
3763    </author>
3764    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3765      <address><email>mnot@mnot.net</email></address>
3766    </author>
3767    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3768      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3769      <address><email>julian.reschke@greenbytes.de</email></address>
3770    </author>
3771    <date month="October" year="2009"/>
3772  </front>
3773  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-08"/>
3774 
3775</reference>
3776
3777<reference anchor="RFC5234">
3778  <front>
3779    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3780    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3781      <organization>Brandenburg InternetWorking</organization>
3782      <address>
3783      <postal>
3784      <street>675 Spruce Dr.</street>
3785      <city>Sunnyvale</city>
3786      <region>CA</region>
3787      <code>94086</code>
3788      <country>US</country></postal>
3789      <phone>+1.408.246.8253</phone>
3790      <email>dcrocker@bbiw.net</email></address> 
3791    </author>
3792    <author initials="P." surname="Overell" fullname="Paul Overell">
3793      <organization>THUS plc.</organization>
3794      <address>
3795      <postal>
3796      <street>1/2 Berkeley Square</street>
3797      <street>99 Berkely Street</street>
3798      <city>Glasgow</city>
3799      <code>G3 7HR</code>
3800      <country>UK</country></postal>
3801      <email>paul.overell@thus.net</email></address>
3802    </author>
3803    <date month="January" year="2008"/>
3804  </front>
3805  <seriesInfo name="STD" value="68"/>
3806  <seriesInfo name="RFC" value="5234"/>
3807</reference>
3808
3809<reference anchor="RFC2119">
3810  <front>
3811    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3812    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3813      <organization>Harvard University</organization>
3814      <address><email>sob@harvard.edu</email></address>
3815    </author>
3816    <date month="March" year="1997"/>
3817  </front>
3818  <seriesInfo name="BCP" value="14"/>
3819  <seriesInfo name="RFC" value="2119"/>
3820</reference>
3821
3822<reference anchor="RFC3986">
3823 <front>
3824  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
3825  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3826    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3827    <address>
3828       <email>timbl@w3.org</email>
3829       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3830    </address>
3831  </author>
3832  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3833    <organization abbrev="Day Software">Day Software</organization>
3834    <address>
3835      <email>fielding@gbiv.com</email>
3836      <uri>http://roy.gbiv.com/</uri>
3837    </address>
3838  </author>
3839  <author initials="L." surname="Masinter" fullname="Larry Masinter">
3840    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3841    <address>
3842      <email>LMM@acm.org</email>
3843      <uri>http://larry.masinter.net/</uri>
3844    </address>
3845  </author>
3846  <date month="January" year="2005"/>
3847 </front>
3848 <seriesInfo name="RFC" value="3986"/>
3849 <seriesInfo name="STD" value="66"/>
3850</reference>
3851
3852<reference anchor="USASCII">
3853  <front>
3854    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3855    <author>
3856      <organization>American National Standards Institute</organization>
3857    </author>
3858    <date year="1986"/>
3859  </front>
3860  <seriesInfo name="ANSI" value="X3.4"/>
3861</reference>
3862
3863<reference anchor="RFC1950">
3864  <front>
3865    <title>ZLIB Compressed Data Format Specification version 3.3</title>
3866    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3867      <organization>Aladdin Enterprises</organization>
3868      <address><email>ghost@aladdin.com</email></address>
3869    </author>
3870    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
3871    <date month="May" year="1996"/>
3872  </front>
3873  <seriesInfo name="RFC" value="1950"/>
3874  <annotation>
3875    RFC 1950 is an Informational RFC, thus it may be less stable than
3876    this specification. On the other hand, this downward reference was
3877    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3878    therefore it is unlikely to cause problems in practice. See also
3879    <xref target="BCP97"/>.
3880  </annotation>
3881</reference>
3882
3883<reference anchor="RFC1951">
3884  <front>
3885    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
3886    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3887      <organization>Aladdin Enterprises</organization>
3888      <address><email>ghost@aladdin.com</email></address>
3889    </author>
3890    <date month="May" year="1996"/>
3891  </front>
3892  <seriesInfo name="RFC" value="1951"/>
3893  <annotation>
3894    RFC 1951 is an Informational RFC, thus it may be less stable than
3895    this specification. On the other hand, this downward reference was
3896    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3897    therefore it is unlikely to cause problems in practice. See also
3898    <xref target="BCP97"/>.
3899  </annotation>
3900</reference>
3901
3902<reference anchor="RFC1952">
3903  <front>
3904    <title>GZIP file format specification version 4.3</title>
3905    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
3906      <organization>Aladdin Enterprises</organization>
3907      <address><email>ghost@aladdin.com</email></address>
3908    </author>
3909    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
3910      <address><email>gzip@prep.ai.mit.edu</email></address>
3911    </author>
3912    <author initials="M." surname="Adler" fullname="Mark Adler">
3913      <address><email>madler@alumni.caltech.edu</email></address>
3914    </author>
3915    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
3916      <address><email>ghost@aladdin.com</email></address>
3917    </author>
3918    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
3919      <address><email>randeg@alumni.rpi.edu</email></address>
3920    </author>
3921    <date month="May" year="1996"/>
3922  </front>
3923  <seriesInfo name="RFC" value="1952"/>
3924  <annotation>
3925    RFC 1952 is an Informational RFC, thus it may be less stable than
3926    this specification. On the other hand, this downward reference was
3927    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
3928    therefore it is unlikely to cause problems in practice. See also
3929    <xref target="BCP97"/>.
3930  </annotation>
3931</reference>
3932
3933</references>
3934
3935<references title="Informative References">
3936
3937<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3938  <front>
3939    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3940    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen"/>
3941    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
3942    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
3943    <author initials="H." surname="Lie" fullname="H. Lie"/>
3944    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
3945    <date year="1997" month="September"/>
3946  </front>
3947  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3948</reference>
3949
3950<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3951  <front>
3952    <title>Improving HTTP Latency</title>
3953    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
3954    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
3955    <date year="1995" month="December"/>
3956  </front>
3957  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3958</reference>
3959
3960<reference anchor="RFC1123">
3961  <front>
3962    <title>Requirements for Internet Hosts - Application and Support</title>
3963    <author initials="R." surname="Braden" fullname="Robert Braden">
3964      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3965      <address><email>Braden@ISI.EDU</email></address>
3966    </author>
3967    <date month="October" year="1989"/>
3968  </front>
3969  <seriesInfo name="STD" value="3"/>
3970  <seriesInfo name="RFC" value="1123"/>
3971</reference>
3972
3973<reference anchor="RFC1305">
3974  <front>
3975    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3976    <author initials="D." surname="Mills" fullname="David L. Mills">
3977      <organization>University of Delaware, Electrical Engineering Department</organization>
3978      <address><email>mills@udel.edu</email></address>
3979    </author>
3980    <date month="March" year="1992"/>
3981  </front>
3982  <seriesInfo name="RFC" value="1305"/>
3983</reference>
3984
3985<reference anchor="RFC1900">
3986  <front>
3987    <title>Renumbering Needs Work</title>
3988    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3989      <organization>CERN, Computing and Networks Division</organization>
3990      <address><email>brian@dxcoms.cern.ch</email></address>
3991    </author>
3992    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3993      <organization>cisco Systems</organization>
3994      <address><email>yakov@cisco.com</email></address>
3995    </author>
3996    <date month="February" year="1996"/>
3997  </front>
3998  <seriesInfo name="RFC" value="1900"/>
3999</reference>
4000
4001<reference anchor="RFC1945">
4002  <front>
4003    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4004    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4005      <organization>MIT, Laboratory for Computer Science</organization>
4006      <address><email>timbl@w3.org</email></address>
4007    </author>
4008    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4009      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4010      <address><email>fielding@ics.uci.edu</email></address>
4011    </author>
4012    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4013      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4014      <address><email>frystyk@w3.org</email></address>
4015    </author>
4016    <date month="May" year="1996"/>
4017  </front>
4018  <seriesInfo name="RFC" value="1945"/>
4019</reference>
4020
4021<reference anchor="RFC2045">
4022  <front>
4023    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4024    <author initials="N." surname="Freed" fullname="Ned Freed">
4025      <organization>Innosoft International, Inc.</organization>
4026      <address><email>ned@innosoft.com</email></address>
4027    </author>
4028    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4029      <organization>First Virtual Holdings</organization>
4030      <address><email>nsb@nsb.fv.com</email></address>
4031    </author>
4032    <date month="November" year="1996"/>
4033  </front>
4034  <seriesInfo name="RFC" value="2045"/>
4035</reference>
4036
4037<reference anchor="RFC2047">
4038  <front>
4039    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4040    <author initials="K." surname="Moore" fullname="Keith Moore">
4041      <organization>University of Tennessee</organization>
4042      <address><email>moore@cs.utk.edu</email></address>
4043    </author>
4044    <date month="November" year="1996"/>
4045  </front>
4046  <seriesInfo name="RFC" value="2047"/>
4047</reference>
4048
4049<reference anchor="RFC2068">
4050  <front>
4051    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4052    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4053      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4054      <address><email>fielding@ics.uci.edu</email></address>
4055    </author>
4056    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4057      <organization>MIT Laboratory for Computer Science</organization>
4058      <address><email>jg@w3.org</email></address>
4059    </author>
4060    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4061      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4062      <address><email>mogul@wrl.dec.com</email></address>
4063    </author>
4064    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4065      <organization>MIT Laboratory for Computer Science</organization>
4066      <address><email>frystyk@w3.org</email></address>
4067    </author>
4068    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4069      <organization>MIT Laboratory for Computer Science</organization>
4070      <address><email>timbl@w3.org</email></address>
4071    </author>
4072    <date month="January" year="1997"/>
4073  </front>
4074  <seriesInfo name="RFC" value="2068"/>
4075</reference>
4076
4077<reference anchor="RFC2109">
4078  <front>
4079    <title>HTTP State Management Mechanism</title>
4080    <author initials="D.M." surname="Kristol" fullname="David M. Kristol">
4081      <organization>Bell Laboratories, Lucent Technologies</organization>
4082      <address><email>dmk@bell-labs.com</email></address>
4083    </author>
4084    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4085      <organization>Netscape Communications Corp.</organization>
4086      <address><email>montulli@netscape.com</email></address>
4087    </author>
4088    <date year="1997" month="February"/>
4089  </front>
4090  <seriesInfo name="RFC" value="2109"/>
4091</reference>
4092
4093<reference anchor="RFC2145">
4094  <front>
4095    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4096    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4097      <organization>Western Research Laboratory</organization>
4098      <address><email>mogul@wrl.dec.com</email></address>
4099    </author>
4100    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4101      <organization>Department of Information and Computer Science</organization>
4102      <address><email>fielding@ics.uci.edu</email></address>
4103    </author>
4104    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4105      <organization>MIT Laboratory for Computer Science</organization>
4106      <address><email>jg@w3.org</email></address>
4107    </author>
4108    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4109      <organization>W3 Consortium</organization>
4110      <address><email>frystyk@w3.org</email></address>
4111    </author>
4112    <date month="May" year="1997"/>
4113  </front>
4114  <seriesInfo name="RFC" value="2145"/>
4115</reference>
4116
4117<reference anchor="RFC2616">
4118  <front>
4119    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4120    <author initials="R." surname="Fielding" fullname="R. Fielding">
4121      <organization>University of California, Irvine</organization>
4122      <address><email>fielding@ics.uci.edu</email></address>
4123    </author>
4124    <author initials="J." surname="Gettys" fullname="J. Gettys">
4125      <organization>W3C</organization>
4126      <address><email>jg@w3.org</email></address>
4127    </author>
4128    <author initials="J." surname="Mogul" fullname="J. Mogul">
4129      <organization>Compaq Computer Corporation</organization>
4130      <address><email>mogul@wrl.dec.com</email></address>
4131    </author>
4132    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4133      <organization>MIT Laboratory for Computer Science</organization>
4134      <address><email>frystyk@w3.org</email></address>
4135    </author>
4136    <author initials="L." surname="Masinter" fullname="L. Masinter">
4137      <organization>Xerox Corporation</organization>
4138      <address><email>masinter@parc.xerox.com</email></address>
4139    </author>
4140    <author initials="P." surname="Leach" fullname="P. Leach">
4141      <organization>Microsoft Corporation</organization>
4142      <address><email>paulle@microsoft.com</email></address>
4143    </author>
4144    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4145      <organization>W3C</organization>
4146      <address><email>timbl@w3.org</email></address>
4147    </author>
4148    <date month="June" year="1999"/>
4149  </front>
4150  <seriesInfo name="RFC" value="2616"/>
4151</reference>
4152
4153<reference anchor="RFC2817">
4154  <front>
4155    <title>Upgrading to TLS Within HTTP/1.1</title>
4156    <author initials="R." surname="Khare" fullname="R. Khare">
4157      <organization>4K Associates / UC Irvine</organization>
4158      <address><email>rohit@4K-associates.com</email></address>
4159    </author>
4160    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
4161      <organization>Agranat Systems, Inc.</organization>
4162      <address><email>lawrence@agranat.com</email></address>
4163    </author>
4164    <date year="2000" month="May"/>
4165  </front>
4166  <seriesInfo name="RFC" value="2817"/>
4167</reference>
4168
4169<reference anchor="RFC2818">
4170  <front>
4171    <title>HTTP Over TLS</title>
4172    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
4173      <organization>RTFM, Inc.</organization>
4174      <address><email>ekr@rtfm.com</email></address>
4175    </author>
4176    <date year="2000" month="May"/>
4177  </front>
4178  <seriesInfo name="RFC" value="2818"/>
4179</reference>
4180
4181<reference anchor="RFC2965">
4182  <front>
4183    <title>HTTP State Management Mechanism</title>
4184    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
4185      <organization>Bell Laboratories, Lucent Technologies</organization>
4186      <address><email>dmk@bell-labs.com</email></address>
4187    </author>
4188    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4189      <organization>Epinions.com, Inc.</organization>
4190      <address><email>lou@montulli.org</email></address>
4191    </author>
4192    <date year="2000" month="October"/>
4193  </front>
4194  <seriesInfo name="RFC" value="2965"/>
4195</reference>
4196
4197<reference anchor="RFC3864">
4198  <front>
4199    <title>Registration Procedures for Message Header Fields</title>
4200    <author initials="G." surname="Klyne" fullname="G. Klyne">
4201      <organization>Nine by Nine</organization>
4202      <address><email>GK-IETF@ninebynine.org</email></address>
4203    </author>
4204    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
4205      <organization>BEA Systems</organization>
4206      <address><email>mnot@pobox.com</email></address>
4207    </author>
4208    <author initials="J." surname="Mogul" fullname="J. Mogul">
4209      <organization>HP Labs</organization>
4210      <address><email>JeffMogul@acm.org</email></address>
4211    </author>
4212    <date year="2004" month="September"/>
4213  </front>
4214  <seriesInfo name="BCP" value="90"/>
4215  <seriesInfo name="RFC" value="3864"/>
4216</reference>
4217
4218<reference anchor="RFC4288">
4219  <front>
4220    <title>Media Type Specifications and Registration Procedures</title>
4221    <author initials="N." surname="Freed" fullname="N. Freed">
4222      <organization>Sun Microsystems</organization>
4223      <address>
4224        <email>ned.freed@mrochek.com</email>
4225      </address>
4226    </author>
4227    <author initials="J." surname="Klensin" fullname="J. Klensin">
4228      <address>
4229        <email>klensin+ietf@jck.com</email>
4230      </address>
4231    </author>
4232    <date year="2005" month="December"/>
4233  </front>
4234  <seriesInfo name="BCP" value="13"/>
4235  <seriesInfo name="RFC" value="4288"/>
4236</reference>
4237
4238<reference anchor="RFC4395">
4239  <front>
4240    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4241    <author initials="T." surname="Hansen" fullname="T. Hansen">
4242      <organization>AT&amp;T Laboratories</organization>
4243      <address>
4244        <email>tony+urireg@maillennium.att.com</email>
4245      </address>
4246    </author>
4247    <author initials="T." surname="Hardie" fullname="T. Hardie">
4248      <organization>Qualcomm, Inc.</organization>
4249      <address>
4250        <email>hardie@qualcomm.com</email>
4251      </address>
4252    </author>
4253    <author initials="L." surname="Masinter" fullname="L. Masinter">
4254      <organization>Adobe Systems</organization>
4255      <address>
4256        <email>LMM@acm.org</email>
4257      </address>
4258    </author>
4259    <date year="2006" month="February"/>
4260  </front>
4261  <seriesInfo name="BCP" value="115"/>
4262  <seriesInfo name="RFC" value="4395"/>
4263</reference>
4264
4265<reference anchor="RFC5226">
4266  <front>
4267    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4268    <author initials="T." surname="Narten" fullname="T. Narten">
4269      <organization>IBM</organization>
4270      <address><email>narten@us.ibm.com</email></address>
4271    </author>
4272    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
4273      <organization>Google</organization>
4274      <address><email>Harald@Alvestrand.no</email></address>
4275    </author>
4276    <date year="2008" month="May"/>
4277  </front>
4278  <seriesInfo name="BCP" value="26"/>
4279  <seriesInfo name="RFC" value="5226"/>
4280</reference>
4281
4282<reference anchor="RFC5322">
4283  <front>
4284    <title>Internet Message Format</title>
4285    <author initials="P." surname="Resnick" fullname="P. Resnick">
4286      <organization>Qualcomm Incorporated</organization>
4287    </author>
4288    <date year="2008" month="October"/>
4289  </front>
4290  <seriesInfo name="RFC" value="5322"/>
4291</reference>
4292
4293<reference anchor="BCP97">
4294  <front>
4295    <title>Handling Normative References to Standards-Track Documents</title>
4296    <author initials="J." surname="Klensin" fullname="J. Klensin">
4297      <address>
4298        <email>klensin+ietf@jck.com</email>
4299      </address>
4300    </author>
4301    <author initials="S." surname="Hartman" fullname="S. Hartman">
4302      <organization>MIT</organization>
4303      <address>
4304        <email>hartmans-ietf@mit.edu</email>
4305      </address>
4306    </author>
4307    <date year="2007" month="June"/>
4308  </front>
4309  <seriesInfo name="BCP" value="97"/>
4310  <seriesInfo name="RFC" value="4897"/>
4311</reference>
4312
4313<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4314  <front>
4315    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4316    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4317    <date year="2001" month="November"/>
4318  </front>
4319  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4320</reference>
4321
4322<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4323  <front>
4324    <title>Analysis of HTTP Performance Problems</title>
4325    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4326    <date/>
4327  </front>
4328</reference>
4329
4330<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4331  <front>
4332  <title>Analysis of HTTP Performance</title>
4333  <author initials="J." surname="Touch" fullname="Joe Touch">
4334    <organization>USC/Information Sciences Institute</organization>
4335    <address><email>touch@isi.edu</email></address>
4336  </author>
4337  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4338    <organization>USC/Information Sciences Institute</organization>
4339    <address><email>johnh@isi.edu</email></address>
4340  </author>
4341  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4342    <organization>USC/Information Sciences Institute</organization>
4343    <address><email>katia@isi.edu</email></address>
4344  </author>
4345  <date year="1998" month="Aug"/>
4346  </front>
4347  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4348  <annotation>(original report dated Aug. 1996)</annotation>
4349</reference>
4350
4351</references>
4352
4353
4354<section title="Tolerant Applications" anchor="tolerant.applications">
4355<t>
4356   Although this document specifies the requirements for the generation
4357   of HTTP/1.1 messages, not all applications will be correct in their
4358   implementation. We therefore recommend that operational applications
4359   be tolerant of deviations whenever those deviations can be
4360   interpreted unambiguously.
4361</t>
4362<t>
4363   Clients SHOULD be tolerant in parsing the Status-Line and servers
4364   tolerant when parsing the Request-Line. In particular, they SHOULD
4365   accept any amount of WSP characters between fields, even though
4366   only a single SP is required.
4367</t>
4368<t>
4369   The line terminator for header fields is the sequence CRLF.
4370   However, we recommend that applications, when parsing such headers,
4371   recognize a single LF as a line terminator and ignore the leading CR.
4372</t>
4373<t>
4374   The character set of an entity-body SHOULD be labeled as the lowest
4375   common denominator of the character codes used within that body, with
4376   the exception that not labeling the entity is preferred over labeling
4377   the entity with the labels US-ASCII or ISO-8859-1. See <xref target="Part3"/>.
4378</t>
4379<t>
4380   Additional rules for requirements on parsing and encoding of dates
4381   and other potential problems with date encodings include:
4382</t>
4383<t>
4384  <list style="symbols">
4385     <t>HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
4386        which appears to be more than 50 years in the future is in fact
4387        in the past (this helps solve the "year 2000" problem).</t>
4388
4389     <t>An HTTP/1.1 implementation MAY internally represent a parsed
4390        Expires date as earlier than the proper value, but MUST NOT
4391        internally represent a parsed Expires date as later than the
4392        proper value.</t>
4393
4394     <t>All expiration-related calculations MUST be done in GMT. The
4395        local time zone MUST NOT influence the calculation or comparison
4396        of an age or expiration time.</t>
4397
4398     <t>If an HTTP header incorrectly carries a date value with a time
4399        zone other than GMT, it MUST be converted into GMT using the
4400        most conservative possible conversion.</t>
4401  </list>
4402</t>
4403</section>
4404
4405<section title="Compatibility with Previous Versions" anchor="compatibility">
4406<t>
4407   HTTP has been in use by the World-Wide Web global information initiative
4408   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4409   was a simple protocol for hypertext data transfer across the Internet
4410   with only a single method and no metadata.
4411   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4412   methods and MIME-like messaging that could include metadata about the data
4413   transferred and modifiers on the request/response semantics. However,
4414   HTTP/1.0 did not sufficiently take into consideration the effects of
4415   hierarchical proxies, caching, the need for persistent connections, or
4416   name-based virtual hosts. The proliferation of incompletely-implemented
4417   applications calling themselves "HTTP/1.0" further necessitated a
4418   protocol version change in order for two communicating applications
4419   to determine each other's true capabilities.
4420</t>
4421<t>
4422   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4423   requirements that enable reliable implementations, adding only
4424   those new features that will either be safely ignored by an HTTP/1.0
4425   recipient or only sent when communicating with a party advertising
4426   compliance with HTTP/1.1.
4427</t>
4428<t>
4429   It is beyond the scope of a protocol specification to mandate
4430   compliance with previous versions. HTTP/1.1 was deliberately
4431   designed, however, to make supporting previous versions easy. It is
4432   worth noting that, at the time of composing this specification, we would
4433   expect general-purpose HTTP/1.1 servers to:
4434  <list style="symbols">
4435     <t>understand any valid request in the format of HTTP/1.0 and
4436        1.1;</t>
4437
4438     <t>respond appropriately with a message in the same major version
4439        used by the client.</t>
4440  </list>
4441</t>
4442<t>
4443   And we would expect HTTP/1.1 clients to:
4444  <list style="symbols">
4445     <t>understand any valid response in the format of HTTP/1.0 or
4446        1.1.</t>
4447  </list>
4448</t>
4449<t>
4450   For most implementations of HTTP/1.0, each connection is established
4451   by the client prior to the request and closed by the server after
4452   sending the response. Some implementations implement the Keep-Alive
4453   version of persistent connections described in Section 19.7.1 of <xref target="RFC2068"/>.
4454</t>
4455
4456<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4457<t>
4458   This section summarizes major differences between versions HTTP/1.0
4459   and HTTP/1.1.
4460</t>
4461
4462<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4463<t>
4464   The requirements that clients and servers support the Host request-header,
4465   report an error if the Host request-header (<xref target="header.host"/>) is
4466   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4467   are among the most important changes defined by this
4468   specification.
4469</t>
4470<t>
4471   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4472   addresses and servers; there was no other established mechanism for
4473   distinguishing the intended server of a request than the IP address
4474   to which that request was directed. The changes outlined above will
4475   allow the Internet, once older HTTP clients are no longer common, to
4476   support multiple Web sites from a single IP address, greatly
4477   simplifying large operational Web servers, where allocation of many
4478   IP addresses to a single host has created serious problems. The
4479   Internet will also be able to recover the IP addresses that have been
4480   allocated for the sole purpose of allowing special-purpose domain
4481   names to be used in root-level HTTP URLs. Given the rate of growth of
4482   the Web, and the number of servers already deployed, it is extremely
4483   important that all implementations of HTTP (including updates to
4484   existing HTTP/1.0 applications) correctly implement these
4485   requirements:
4486  <list style="symbols">
4487     <t>Both clients and servers MUST support the Host request-header.</t>
4488
4489     <t>A client that sends an HTTP/1.1 request MUST send a Host header.</t>
4490
4491     <t>Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
4492        request does not include a Host request-header.</t>
4493
4494     <t>Servers MUST accept absolute URIs.</t>
4495  </list>
4496</t>
4497</section>
4498</section>
4499
4500<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4501<t>
4502   Some clients and servers might wish to be compatible with some
4503   previous implementations of persistent connections in HTTP/1.0
4504   clients and servers. Persistent connections in HTTP/1.0 are
4505   explicitly negotiated as they are not the default behavior. HTTP/1.0
4506   experimental implementations of persistent connections are faulty,
4507   and the new facilities in HTTP/1.1 are designed to rectify these
4508   problems. The problem was that some existing 1.0 clients may be
4509   sending Keep-Alive to a proxy server that doesn't understand
4510   Connection, which would then erroneously forward it to the next
4511   inbound server, which would establish the Keep-Alive connection and
4512   result in a hung HTTP/1.0 proxy waiting for the close on the
4513   response. The result is that HTTP/1.0 clients must be prevented from
4514   using Keep-Alive when talking to proxies.
4515</t>
4516<t>
4517   However, talking to proxies is the most important use of persistent
4518   connections, so that prohibition is clearly unacceptable. Therefore,
4519   we need some other mechanism for indicating a persistent connection
4520   is desired, which is safe to use even when talking to an old proxy
4521   that ignores Connection. Persistent connections are the default for
4522   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4523   declaring non-persistence. See <xref target="header.connection"/>.
4524</t>
4525<t>
4526   The original HTTP/1.0 form of persistent connections (the Connection:
4527   Keep-Alive and Keep-Alive header) is documented in Section 19.7.1 of <xref target="RFC2068"/>.
4528</t>
4529</section>
4530
4531<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4532<t>
4533   This specification has been carefully audited to correct and
4534   disambiguate key word usage; RFC 2068 had many problems in respect to
4535   the conventions laid out in <xref target="RFC2119"/>.
4536</t>
4537<t>
4538   Transfer-coding and message lengths all interact in ways that
4539   required fixing exactly when chunked encoding is used (to allow for
4540   transfer encoding that may not be self delimiting); it was important
4541   to straighten out exactly how message lengths are computed. (Sections
4542   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4543   <xref target="header.content-length" format="counter"/>,
4544   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4545</t>
4546<t>
4547   The use and interpretation of HTTP version numbers has been clarified
4548   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4549   version they support to deal with problems discovered in HTTP/1.0
4550   implementations (<xref target="http.version"/>)
4551</t>
4552<t>
4553   Quality Values of zero should indicate that "I don't want something"
4554   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4555</t>
4556<t>
4557   Transfer-coding had significant problems, particularly with
4558   interactions with chunked encoding. The solution is that transfer-codings
4559   become as full fledged as content-codings. This involves
4560   adding an IANA registry for transfer-codings (separate from content
4561   codings), a new header field (TE) and enabling trailer headers in the
4562   future. Transfer encoding is a major performance benefit, so it was
4563   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4564   interoperability problem that could have occurred due to interactions
4565   between authentication trailers, chunked encoding and HTTP/1.0
4566   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.encoding" format="counter"/>,
4567   and <xref target="header.te" format="counter"/>)
4568</t>
4569</section>
4570
4571<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4572<t>
4573  Empty list elements in list productions have been deprecated.
4574  (<xref target="notation.abnf"/>)
4575</t>
4576<t>
4577  Rules about implicit linear whitespace between certain grammar productions
4578  have been removed; now it's only allowed when specifically pointed out
4579  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4580  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4581  Non-ASCII content in header fields and reason phrase has been obsoleted and
4582  made opaque (the TEXT rule was removed)
4583  (<xref target="basic.rules"/>)
4584</t>
4585<t>
4586  Clarify that HTTP-Version is case sensitive.
4587  (<xref target="http.version"/>)
4588</t>
4589<t>
4590  Remove reference to non-existant identity transfer-coding value tokens.
4591  (Sections <xref format="counter" target="transfer.codings"/> and
4592  <xref format="counter" target="message.length"/>)
4593</t>
4594<t>
4595  Require that invalid whitespace around field-names be rejected.
4596  (<xref target="header.fields"/>)
4597</t>
4598<t>
4599  Update use of abs_path production from RFC1808 to the path-absolute + query
4600  components of RFC3986.
4601  (<xref target="request-target"/>)
4602</t>
4603<t>
4604  Clarification that the chunk length does not include the count of the octets
4605  in the chunk header and trailer. Furthermore disallowed line folding
4606  in chunk extensions.
4607  (<xref target="chunked.encoding"/>)
4608</t>
4609<t>
4610  Remove hard limit of two connections per server.
4611  (<xref target="persistent.practical"/>)
4612</t>
4613<t>
4614  Clarify exactly when close connection options must be sent.
4615  (<xref target="header.connection"/>)
4616</t>
4617</section>
4618</section>
4619
4620
4621<section title="Collected ABNF" anchor="collected.abnf">
4622<figure>
4623<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
4624BWS = OWS
4625
4626Cache-Control = <Cache-Control, defined in [Part6], Section 3.4>
4627Chunked-Body = *chunk last-chunk trailer-part CRLF
4628Connection = "Connection:" OWS Connection-v
4629Connection-v = *( "," OWS ) connection-token *( OWS "," [ OWS
4630 connection-token ] )
4631Content-Length = "Content-Length:" OWS 1*Content-Length-v
4632Content-Length-v = 1*DIGIT
4633
4634Date = "Date:" OWS Date-v
4635Date-v = HTTP-date
4636
4637GMT = %x47.4D.54 ; GMT
4638
4639HTTP-Prot-Name = %x48.54.54.50 ; HTTP
4640HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4641HTTP-date = rfc1123-date / obs-date
4642HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
4643 ]
4644Host = "Host:" OWS Host-v
4645Host-v = uri-host [ ":" port ]
4646
4647Method = token
4648
4649OWS = *( [ obs-fold ] WSP )
4650
4651Pragma = <Pragma, defined in [Part6], Section 3.4>
4652
4653RWS = 1*( [ obs-fold ] WSP )
4654Reason-Phrase = *( WSP / VCHAR / obs-text )
4655Request = Request-Line *( ( general-header / request-header /
4656 entity-header ) CRLF ) CRLF [ message-body ]
4657Request-Line = Method SP request-target SP HTTP-Version CRLF
4658Response = Status-Line *( ( general-header / response-header /
4659 entity-header ) CRLF ) CRLF [ message-body ]
4660
4661Status-Code = 3DIGIT
4662Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4663
4664TE = "TE:" OWS TE-v
4665TE-v = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4666Trailer = "Trailer:" OWS Trailer-v
4667Trailer-v = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4668Transfer-Encoding = "Transfer-Encoding:" OWS Transfer-Encoding-v
4669Transfer-Encoding-v = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4670 transfer-coding ] )
4671
4672URI = <URI, defined in [RFC3986], Section 3>
4673URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
4674Upgrade = "Upgrade:" OWS Upgrade-v
4675Upgrade-v = *( "," OWS ) product *( OWS "," [ OWS product ] )
4676
4677Via = "Via:" OWS Via-v
4678Via-v = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4679 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4680 ] )
4681
4682Warning = <Warning, defined in [Part6], Section 3.6>
4683
4684absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
4685asctime-date = day-name SP date3 SP time-of-day SP year
4686attribute = token
4687authority = <authority, defined in [RFC3986], Section 3.2>
4688
4689chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4690chunk-data = 1*OCTET
4691chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4692chunk-ext-name = token
4693chunk-ext-val = token / quoted-str-nf
4694chunk-size = 1*HEXDIG
4695comment = "(" *( ctext / quoted-cpair / comment ) ")"
4696connection-token = token
4697ctext = OWS / %x21-27 ; '!'-'''
4698 / %x2A-5B ; '*'-'['
4699 / %x5D-7E ; ']'-'~'
4700 / obs-text
4701
4702date1 = day SP month SP year
4703date2 = day "-" month "-" 2DIGIT
4704date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
4705day = 2DIGIT
4706day-name = %x4D.6F.6E ; Mon
4707 / %x54.75.65 ; Tue
4708 / %x57.65.64 ; Wed
4709 / %x54.68.75 ; Thu
4710 / %x46.72.69 ; Fri
4711 / %x53.61.74 ; Sat
4712 / %x53.75.6E ; Sun
4713day-name-l = %x4D.6F.6E.64.61.79 ; Monday
4714 / %x54.75.65.73.64.61.79 ; Tuesday
4715 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4716 / %x54.68.75.72.73.64.61.79 ; Thursday
4717 / %x46.72.69.64.61.79 ; Friday
4718 / %x53.61.74.75.72.64.61.79 ; Saturday
4719 / %x53.75.6E.64.61.79 ; Sunday
4720
4721entity-body = <entity-body, defined in [Part3], Section 3.2>
4722entity-header = <entity-header, defined in [Part3], Section 3.1>
4723
4724field-content = *( WSP / VCHAR / obs-text )
4725field-name = token
4726field-value = *( field-content / OWS )
4727
4728general-header = Cache-Control / Connection / Date / Pragma / Trailer
4729 / Transfer-Encoding / Upgrade / Via / Warning
4730
4731header-field = field-name ":" OWS [ field-value ] OWS
4732hour = 2DIGIT
4733http-URI = "http://" authority path-abempty [ "?" query ]
4734https-URI = "https://" authority path-abempty [ "?" query ]
4735
4736last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF
4737
4738message-body = entity-body /
4739 <entity-body encoded as per Transfer-Encoding>
4740minute = 2DIGIT
4741month = %x4A.61.6E ; Jan
4742 / %x46.65.62 ; Feb
4743 / %x4D.61.72 ; Mar
4744 / %x41.70.72 ; Apr
4745 / %x4D.61.79 ; May
4746 / %x4A.75.6E ; Jun
4747 / %x4A.75.6C ; Jul
4748 / %x41.75.67 ; Aug
4749 / %x53.65.70 ; Sep
4750 / %x4F.63.74 ; Oct
4751 / %x4E.6F.76 ; Nov
4752 / %x44.65.63 ; Dec
4753
4754obs-date = rfc850-date / asctime-date
4755obs-fold = CRLF
4756obs-text = %x80-FF
4757
4758partial-URI = relative-part [ "?" query ]
4759path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
4760path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
4761port = <port, defined in [RFC3986], Section 3.2.3>
4762product = token [ "/" product-version ]
4763product-version = token
4764protocol-name = token
4765protocol-version = token
4766pseudonym = token
4767
4768qdtext = OWS / "!" / %x23-5B ; '#'-'['
4769 / %x5D-7E ; ']'-'~'
4770 / obs-text
4771qdtext-nf = WSP / "!" / %x23-5B ; '#'-'['
4772 / %x5D-7E ; ']'-'~'
4773 / obs-text
4774query = <query, defined in [RFC3986], Section 3.4>
4775quoted-cpair = "\" ( WSP / VCHAR / obs-text )
4776quoted-pair = "\" ( WSP / VCHAR / obs-text )
4777quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4778quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4779qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4780
4781received-by = ( uri-host [ ":" port ] ) / pseudonym
4782received-protocol = [ protocol-name "/" ] protocol-version
4783relative-part = <relative-part, defined in [RFC3986], Section 4.2>
4784request-header = <request-header, defined in [Part2], Section 3>
4785request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4786 / authority
4787response-header = <response-header, defined in [Part2], Section 5>
4788rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
4789rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
4790
4791second = 2DIGIT
4792start-line = Request-Line / Status-Line
4793
4794t-codings = "trailers" / ( transfer-extension [ te-params ] )
4795tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
4796 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4797te-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4798te-params = OWS ";" OWS "q=" qvalue *te-ext
4799time-of-day = hour ":" minute ":" second
4800token = 1*tchar
4801trailer-part = *( entity-header CRLF )
4802transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
4803 transfer-extension
4804transfer-extension = token *( OWS ";" OWS transfer-parameter )
4805transfer-parameter = attribute BWS "=" BWS value
4806
4807uri-host = <host, defined in [RFC3986], Section 3.2.2>
4808
4809value = token / quoted-string
4810
4811year = 4DIGIT
4812]]></artwork>
4813</figure>
4814<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
4815; Chunked-Body defined but not used
4816; Content-Length defined but not used
4817; HTTP-message defined but not used
4818; Host defined but not used
4819; Request defined but not used
4820; Response defined but not used
4821; TE defined but not used
4822; URI defined but not used
4823; URI-reference defined but not used
4824; http-URI defined but not used
4825; https-URI defined but not used
4826; partial-URI defined but not used
4827]]></artwork></figure></section>
4828
4829
4830<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4831
4832<section title="Since RFC2616">
4833<t>
4834  Extracted relevant partitions from <xref target="RFC2616"/>.
4835</t>
4836</section>
4837
4838<section title="Since draft-ietf-httpbis-p1-messaging-00">
4839<t>
4840  Closed issues:
4841  <list style="symbols">
4842    <t>
4843      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4844      "HTTP Version should be case sensitive"
4845      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4846    </t>
4847    <t>
4848      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4849      "'unsafe' characters"
4850      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4851    </t>
4852    <t>
4853      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4854      "Chunk Size Definition"
4855      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4856    </t>
4857    <t>
4858      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4859      "Message Length"
4860      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4861    </t>
4862    <t>
4863      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4864      "Media Type Registrations"
4865      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4866    </t>
4867    <t>
4868      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4869      "URI includes query"
4870      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4871    </t>
4872    <t>
4873      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4874      "No close on 1xx responses"
4875      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4876    </t>
4877    <t>
4878      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4879      "Remove 'identity' token references"
4880      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4881    </t>
4882    <t>
4883      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4884      "Import query BNF"
4885    </t>
4886    <t>
4887      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4888      "qdtext BNF"
4889    </t>
4890    <t>
4891      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4892      "Normative and Informative references"
4893    </t>
4894    <t>
4895      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4896      "RFC2606 Compliance"
4897    </t>
4898    <t>
4899      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4900      "RFC977 reference"
4901    </t>
4902    <t>
4903      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4904      "RFC1700 references"
4905    </t>
4906    <t>
4907      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4908      "inconsistency in date format explanation"
4909    </t>
4910    <t>
4911      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4912      "Date reference typo"
4913    </t>
4914    <t>
4915      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4916      "Informative references"
4917    </t>
4918    <t>
4919      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4920      "ISO-8859-1 Reference"
4921    </t>
4922    <t>
4923      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4924      "Normative up-to-date references"
4925    </t>
4926  </list>
4927</t>
4928<t>
4929  Other changes:
4930  <list style="symbols">
4931    <t>
4932      Update media type registrations to use RFC4288 template.
4933    </t>
4934    <t>
4935      Use names of RFC4234 core rules DQUOTE and WSP,
4936      fix broken ABNF for chunk-data
4937      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4938    </t>
4939  </list>
4940</t>
4941</section>
4942
4943<section title="Since draft-ietf-httpbis-p1-messaging-01">
4944<t>
4945  Closed issues:
4946  <list style="symbols">
4947    <t>
4948      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4949      "Bodies on GET (and other) requests"
4950    </t>
4951    <t>
4952      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4953      "Updating to RFC4288"
4954    </t>
4955    <t>
4956      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4957      "Status Code and Reason Phrase"
4958    </t>
4959    <t>
4960      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4961      "rel_path not used"
4962    </t>
4963  </list>
4964</t>
4965<t>
4966  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4967  <list style="symbols">
4968    <t>
4969      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
4970      "trailer-part").
4971    </t>
4972    <t>
4973      Avoid underscore character in rule names ("http_URL" -&gt;
4974      "http-URL", "abs_path" -&gt; "path-absolute").
4975    </t>
4976    <t>
4977      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4978      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4979      have to be updated when switching over to RFC3986.
4980    </t>
4981    <t>
4982      Synchronize core rules with RFC5234.
4983    </t>
4984    <t>
4985      Get rid of prose rules that span multiple lines.
4986    </t>
4987    <t>
4988      Get rid of unused rules LOALPHA and UPALPHA.
4989    </t>
4990    <t>
4991      Move "Product Tokens" section (back) into Part 1, as "token" is used
4992      in the definition of the Upgrade header.
4993    </t>
4994    <t>
4995      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4996    </t>
4997    <t>
4998      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4999    </t>
5000  </list>
5001</t>
5002</section>
5003
5004<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5005<t>
5006  Closed issues:
5007  <list style="symbols">
5008    <t>
5009      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5010      "HTTP-date vs. rfc1123-date"
5011    </t>
5012    <t>
5013      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5014      "WS in quoted-pair"
5015    </t>
5016  </list>
5017</t>
5018<t>
5019  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5020  <list style="symbols">
5021    <t>
5022      Reference RFC 3984, and update header registrations for headers defined
5023      in this document.
5024    </t>
5025  </list>
5026</t>
5027<t>
5028  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5029  <list style="symbols">
5030    <t>
5031      Replace string literals when the string really is case-sensitive (HTTP-Version).
5032    </t>
5033  </list>
5034</t>
5035</section>
5036
5037<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5038<t>
5039  Closed issues:
5040  <list style="symbols">
5041    <t>
5042      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5043      "Connection closing"
5044    </t>
5045    <t>
5046      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5047      "Move registrations and registry information to IANA Considerations"
5048    </t>
5049    <t>
5050      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5051      "need new URL for PAD1995 reference"
5052    </t>
5053    <t>
5054      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5055      "IANA Considerations: update HTTP URI scheme registration"
5056    </t>
5057    <t>
5058      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5059      "Cite HTTPS URI scheme definition"
5060    </t>
5061    <t>
5062      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5063      "List-type headers vs Set-Cookie"
5064    </t>
5065  </list>
5066</t>
5067<t>
5068  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5069  <list style="symbols">
5070    <t>
5071      Replace string literals when the string really is case-sensitive (HTTP-Date).
5072    </t>
5073    <t>
5074      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5075    </t>
5076  </list>
5077</t>
5078</section>
5079
5080<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5081<t>
5082  Closed issues:
5083  <list style="symbols">
5084    <t>
5085      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5086      "Out-of-date reference for URIs"
5087    </t>
5088    <t>
5089      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5090      "RFC 2822 is updated by RFC 5322"
5091    </t>
5092  </list>
5093</t>
5094<t>
5095  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5096  <list style="symbols">
5097    <t>
5098      Use "/" instead of "|" for alternatives.
5099    </t>
5100    <t>
5101      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5102    </t>
5103    <t>
5104      Only reference RFC 5234's core rules.
5105    </t>
5106    <t>
5107      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5108      whitespace ("OWS") and required whitespace ("RWS").
5109    </t>
5110    <t>
5111      Rewrite ABNFs to spell out whitespace rules, factor out
5112      header value format definitions.
5113    </t>
5114  </list>
5115</t>
5116</section>
5117
5118<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5119<t>
5120  Closed issues:
5121  <list style="symbols">
5122    <t>
5123      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5124      "Header LWS"
5125    </t>
5126    <t>
5127      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5128      "Sort 1.3 Terminology"
5129    </t>
5130    <t>
5131      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5132      "RFC2047 encoded words"
5133    </t>
5134    <t>
5135      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5136      "Character Encodings in TEXT"
5137    </t>
5138    <t>
5139      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5140      "Line Folding"
5141    </t>
5142    <t>
5143      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5144      "OPTIONS * and proxies"
5145    </t>
5146    <t>
5147      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5148      "Reason-Phrase BNF"
5149    </t>
5150    <t>
5151      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5152      "Use of TEXT"
5153    </t>
5154    <t>
5155      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5156      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5157    </t>
5158    <t>
5159      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5160      "RFC822 reference left in discussion of date formats"
5161    </t>
5162  </list>
5163</t>
5164<t>
5165  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5166  <list style="symbols">
5167    <t>
5168      Rewrite definition of list rules, deprecate empty list elements.
5169    </t>
5170    <t>
5171      Add appendix containing collected and expanded ABNF.
5172    </t>
5173  </list>
5174</t>
5175<t>
5176  Other changes:
5177  <list style="symbols">
5178    <t>
5179      Rewrite introduction; add mostly new Architecture Section.
5180    </t>
5181    <t>
5182      Move definition of quality values from Part 3 into Part 1;
5183      make TE request header grammar independent of accept-params (defined in Part 3).
5184    </t>
5185  </list>
5186</t>
5187</section>
5188
5189<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5190<t>
5191  Closed issues:
5192  <list style="symbols">
5193    <t>
5194      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5195      "base for numeric protocol elements"
5196    </t>
5197    <t>
5198      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5199      "comment ABNF"
5200    </t>
5201  </list>
5202</t>
5203<t>
5204  Partly resolved issues:
5205  <list style="symbols">
5206    <t>
5207      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5208      "205 Bodies" (took out language that implied that there may be
5209      methods for which a request body MUST NOT be included)
5210    </t>
5211    <t>
5212      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5213      "editorial improvements around HTTP-date"
5214    </t>
5215  </list>
5216</t>
5217</section>
5218
5219<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5220<t>
5221  Closed issues:
5222  <list style="symbols">
5223    <t>
5224      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5225      "Repeating single-value headers"
5226    </t>
5227    <t>
5228      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5229      "increase connection limit"
5230    </t>
5231    <t>
5232      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5233      "IP addresses in URLs"
5234    </t>
5235    <t>
5236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5237      "take over HTTP Upgrade Token Registry"
5238    </t>
5239    <t>
5240      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5241      "CR and LF in chunk extension values"
5242    </t>
5243    <t>
5244      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5245      "HTTP/0.9 support"
5246    </t>
5247    <t>
5248      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5249      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5250    </t>
5251    <t>
5252      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5253      "move definitions of gzip/deflate/compress to part 1"
5254    </t>
5255    <t>
5256      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5257      "disallow control characters in quoted-pair"
5258    </t>
5259  </list>
5260</t>
5261<t>
5262  Partly resolved issues:
5263  <list style="symbols">
5264    <t>
5265      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5266      "update IANA requirements wrt Transfer-Coding values" (add the
5267      IANA Considerations subsection)
5268    </t>
5269  </list>
5270</t>
5271
5272</section>
5273
5274</section>
5275
5276</back>
5277</rfc>
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