source: draft-ietf-httpbis/09/draft-ietf-httpbis-p1-messaging-09.xml @ 847

Last change on this file since 847 was 772, checked in by julian.reschke@…, 10 years ago

Prepare publication of -09 drafts on March 08

File size: 217.0 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-09">
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 month="March" year="2010" day="8"/>
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.08"/>.
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<t>
307   As a syntactical convention, ABNF rule names prefixed with "obs-" denote
308   "obsolete" grammar rules that appear for historical reasons.
309</t>
310
311<section title="ABNF Extension: #rule" anchor="notation.abnf">
312<t>
313  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
314  improve readability.
315</t>
316<t>
317  A construct "#" is defined, similar to "*", for defining comma-delimited
318  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
319  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
320  comma (",") and optional whitespace (OWS,
321  <xref target="basic.rules"/>).   
322</t>
323<figure><preamble>
324  Thus,
325</preamble><artwork type="example"><![CDATA[
326  1#element => element *( OWS "," OWS element )
327]]></artwork></figure>
328<figure><preamble>
329  and:
330</preamble><artwork type="example"><![CDATA[
331  #element => [ 1#element ]
332]]></artwork></figure>
333<figure><preamble>
334  and for n &gt;= 1 and m &gt; 1:
335</preamble><artwork type="example"><![CDATA[
336  <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
337]]></artwork></figure>
338<t>
339  For compatibility with legacy list rules, recipients SHOULD accept empty
340  list elements. In other words, consumers would follow the list productions:
341</t>
342<figure><artwork type="example"><![CDATA[
343  #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
344 
345  1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
346]]></artwork></figure>
347<t>
348  Note that empty elements do not contribute to the count of elements present,
349  though.
350</t>
351<t>
352  For example, given these ABNF productions:
353</t>
354<figure><artwork type="example"><![CDATA[
355  example-list      = 1#example-list-elmt
356  example-list-elmt = token ; see Section 1.2.2
357]]></artwork></figure>
358<t>
359  Then these are valid values for example-list (not including the double
360  quotes, which are present for delimitation only):
361</t>
362<figure><artwork type="example"><![CDATA[
363  "foo,bar"
364  " foo ,bar,"
365  "  foo , ,bar,charlie   "
366  "foo ,bar,   charlie "
367]]></artwork></figure>
368<t>
369  But these values would be invalid, as at least one non-empty element is
370  required:
371</t>
372<figure><artwork type="example"><![CDATA[
373  ""
374  ","
375  ",   ,"
376]]></artwork></figure>
377<t>
378  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
379  expanded as explained above.
380</t>
381</section>
382
383<section title="Basic Rules" anchor="basic.rules">
384<t anchor="rule.CRLF">
385 
386   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
387   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
388   tolerant applications). The end-of-line marker within an entity-body
389   is defined by its associated media type, as described in Section 2.3 of <xref target="Part3"/>.
390</t>
391<t anchor="rule.LWS">
392   This specification uses three rules to denote the use of linear
393   whitespace: OWS (optional whitespace), RWS (required whitespace), and
394   BWS ("bad" whitespace).
395</t>
396<t>
397   The OWS rule is used where zero or more linear whitespace characters may
398   appear. OWS SHOULD either not be produced or be produced as a single SP
399   character. Multiple OWS characters that occur within field-content SHOULD
400   be replaced with a single SP before interpreting the field value or
401   forwarding the message downstream.
402</t>
403<t>
404   RWS is used when at least one linear whitespace character is required to
405   separate field tokens. RWS SHOULD be produced as a single SP character.
406   Multiple RWS characters that occur within field-content SHOULD be
407   replaced with a single SP before interpreting the field value or
408   forwarding the message downstream.
409</t>
410<t>
411   BWS is used where the grammar allows optional whitespace for historical
412   reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
413   recipients MUST accept such bad optional whitespace and remove it before
414   interpreting the field value or forwarding the message downstream.
415</t>
416<t anchor="rule.whitespace">
417 
418 
419 
420 
421</t>
422<figure><iref primary="true" item="Grammar" subitem="OWS"/><iref primary="true" item="Grammar" subitem="RWS"/><iref primary="true" item="Grammar" subitem="BWS"/><artwork type="abnf2616"><![CDATA[
423  OWS            = *( [ obs-fold ] WSP )
424                 ; "optional" whitespace
425  RWS            = 1*( [ obs-fold ] WSP )
426                 ; "required" whitespace
427  BWS            = OWS
428                 ; "bad" whitespace
429  obs-fold       = CRLF
430                 ; see Section 3.2
431]]></artwork></figure>
432<t anchor="rule.token.separators">
433 
434 
435 
436   Many HTTP/1.1 header field values consist of words (token or quoted-string)
437   separated by whitespace or special characters. These special characters
438   MUST be in a quoted string to be used within a parameter value (as defined
439   in <xref target="transfer.codings"/>).
440</t>
441<figure><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/><artwork type="abnf2616"><![CDATA[
442  token          = 1*tchar
443
444  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
445                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
446                 / DIGIT / ALPHA
447                 ; any VCHAR, except special
448
449  special        = "(" / ")" / "<" / ">" / "@" / ","
450                 / ";" / ":" / "\" / DQUOTE / "/" / "["
451                 / "]" / "?" / "=" / "{" / "}"
452]]></artwork></figure>
453<t anchor="rule.quoted-string">
454 
455 
456 
457   A string of text is parsed as a single word if it is quoted using
458   double-quote marks.
459</t>
460<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[
461  quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
462  qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
463                 ; OWS / <VCHAR except DQUOTE and "\"> / obs-text
464  obs-text       = %x80-FF
465]]></artwork></figure>
466<t anchor="rule.quoted-pair">
467 
468   The backslash character ("\") can be used as a single-character
469   quoting mechanism within quoted-string constructs:
470</t>
471<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
472  quoted-pair    = "\" ( WSP / VCHAR / obs-text )
473]]></artwork></figure>
474<t>
475   Producers SHOULD NOT escape characters that do not require escaping
476   (i.e., other than DQUOTE and the backslash character).
477</t>
478</section>
479
480<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
481 
482 
483 
484 
485 
486 
487 
488<t>
489  The ABNF rules below are defined in other parts:
490</t>
491<figure><artwork type="abnf2616"><![CDATA[
492  request-header  = <request-header, defined in [Part2], Section 3>
493  response-header = <response-header, defined in [Part2], Section 5>
494]]></artwork></figure>
495<figure><artwork type="abnf2616"><![CDATA[
496  entity-body     = <entity-body, defined in [Part3], Section 3.2>
497  entity-header   = <entity-header, defined in [Part3], Section 3.1>
498]]></artwork></figure>
499<figure><artwork type="abnf2616"><![CDATA[
500  Cache-Control   = <Cache-Control, defined in [Part6], Section 3.4>
501  Pragma          = <Pragma, defined in [Part6], Section 3.4>
502  Warning         = <Warning, defined in [Part6], Section 3.6>
503]]></artwork></figure>
504</section>
505
506</section>
507</section>
508
509<section title="HTTP architecture" anchor="architecture">
510<t>
511   HTTP was created for the World Wide Web architecture
512   and has evolved over time to support the scalability needs of a worldwide
513   hypertext system. Much of that architecture is reflected in the terminology
514   and syntax productions used to define HTTP.
515</t>
516
517<section title="Client/Server Operation" anchor="operation">
518<iref item="client"/>
519<iref item="server"/>
520<iref item="connection"/>
521<t>
522   HTTP is a request/response protocol that operates by exchanging messages
523   across a reliable transport or session-layer connection. An HTTP client
524   is a program that establishes a connection to a server for the purpose
525   of sending one or more HTTP requests.  An HTTP server is a program that
526   accepts connections in order to service HTTP requests by sending HTTP
527   responses.
528</t>
529<iref item="user agent"/>
530<iref item="origin server"/>
531<t>
532   Note that the terms "client" and "server" refer only to the roles that
533   these programs perform for a particular connection.  The same program
534   may act as a client on some connections and a server on others.  We use
535   the term "user agent" to refer to the program that initiates a request,
536   such as a WWW browser, editor, or spider (web-traversing robot), and
537   the term "origin server" to refer to the program that can originate
538   authoritative responses to a request.
539</t>
540<t>
541   Most HTTP communication consists of a retrieval request (GET) for
542   a representation of some resource identified by a URI.  In the
543   simplest case, this may be accomplished via a single connection (v)
544   between the user agent (UA) and the origin server (O).
545</t>
546<figure><artwork type="drawing"><![CDATA[
547       request chain ------------------------>
548    UA -------------------v------------------- O
549       <----------------------- response chain
550]]></artwork></figure>
551<iref item="message"/>
552<iref item="request"/>
553<iref item="response"/>
554<t>
555   A client sends an HTTP request to the server in the form of a request
556   message (<xref target="request"/>), beginning with a method, URI, and
557   protocol version, followed by MIME-like header fields containing
558   request modifiers, client information, and payload metadata, an empty
559   line to indicate the end of the header section, and finally the payload
560   body (if any).
561</t>
562<t>
563   A server responds to the client's request by sending an HTTP response
564   message (<xref target="response"/>), beginning with a status line that
565   includes the protocol version, a success or error code, and textual
566   reason phrase, followed by MIME-like header fields containing server
567   information, resource metadata, and payload metadata, an empty line to
568   indicate the end of the header section, and finally the payload body (if any).
569</t>
570<t>
571   The following example illustrates a typical message exchange for a
572   GET request on the URI "http://www.example.com/hello.txt":
573</t>
574<figure><preamble>
575client request:
576</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
577  GET /hello.txt HTTP/1.1
578  User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
579  Host: www.example.com
580  Accept: */*
581 
582  ]]></artwork></figure>
583<figure><preamble>
584server response:
585</preamble><artwork type="message/http; msgtype=&#34;response&#34;"><![CDATA[
586  HTTP/1.1 200 OK
587  Date: Mon, 27 Jul 2009 12:28:53 GMT
588  Server: Apache
589  Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
590  ETag: "34aa387-d-1568eb00"
591  Accept-Ranges: bytes
592  Content-Length: 14
593  Vary: Accept-Encoding
594  Content-Type: text/plain
595 
596  Hello World!
597  ]]></artwork></figure>
598</section>
599
600<section title="Intermediaries" anchor="intermediaries">
601<t>
602   A more complicated situation occurs when one or more intermediaries
603   are present in the request/response chain. There are three common
604   forms of intermediary: proxy, gateway, and tunnel.  In some cases,
605   a single intermediary may act as an origin server, proxy, gateway,
606   or tunnel, switching behavior based on the nature of each request.
607</t>
608<figure><artwork type="drawing"><![CDATA[
609       request chain -------------------------------------->
610    UA -----v----- A -----v----- B -----v----- C -----v----- O
611       <------------------------------------- response chain
612]]></artwork></figure>
613<t>
614   The figure above shows three intermediaries (A, B, and C) between the
615   user agent and origin server. A request or response message that
616   travels the whole chain will pass through four separate connections.
617   Some HTTP communication options
618   may apply only to the connection with the nearest, non-tunnel
619   neighbor, only to the end-points of the chain, or to all connections
620   along the chain. Although the diagram is linear, each participant may
621   be engaged in multiple, simultaneous communications. For example, B
622   may be receiving requests from many clients other than A, and/or
623   forwarding requests to servers other than C, at the same time that it
624   is handling A's request.
625</t>
626<t>
627<iref item="upstream"/><iref item="downstream"/>
628<iref item="inbound"/><iref item="outbound"/>
629   We use the terms "upstream" and "downstream" to describe various
630   requirements in relation to the directional flow of a message:
631   all messages flow from upstream to downstream.
632   Likewise, we use the terms "inbound" and "outbound" to refer to
633   directions in relation to the request path: "inbound" means toward
634   the origin server and "outbound" means toward the user agent.
635</t>
636<t><iref item="proxy"/>
637   A proxy is a message forwarding agent that is selected by the
638   client, usually via local configuration rules, to receive requests
639   for some type(s) of absolute URI and attempt to satisfy those
640   requests via translation through the HTTP interface.  Some translations
641   are minimal, such as for proxy requests for "http" URIs, whereas
642   other requests may require translation to and from entirely different
643   application-layer protocols. Proxies are often used to group an
644   organization's HTTP requests through a common intermediary for the
645   sake of security, annotation services, or shared caching.
646</t>
647<t><iref item="gateway"/><iref item="reverse proxy"/>
648   A gateway (a.k.a., reverse proxy) is a receiving agent that acts
649   as a layer above some other server(s) and translates the received
650   requests to the underlying server's protocol.  Gateways are often
651   used for load balancing or partitioning HTTP services across
652   multiple machines.
653   Unlike a proxy, a gateway receives requests as if it were the
654   origin server for the requested resource; the requesting client
655   will not be aware that it is communicating with a gateway.
656   A gateway communicates with the client as if the gateway is the
657   origin server and thus is subject to all of the requirements on
658   origin servers for that connection.  A gateway communicates
659   with inbound servers using any protocol it desires, including
660   private extensions to HTTP that are outside the scope of this
661   specification.
662</t>
663<t><iref item="tunnel"/>
664   A tunnel acts as a blind relay between two connections
665   without changing the messages. Once active, a tunnel is not
666   considered a party to the HTTP communication, though the tunnel may
667   have been initiated by an HTTP request. A tunnel ceases to exist when
668   both ends of the relayed connection are closed. Tunnels are used to
669   extend a virtual connection through an intermediary, such as when
670   transport-layer security is used to establish private communication
671   through a shared firewall proxy.
672</t>
673</section>
674
675<section title="Caches" anchor="caches">
676<iref item="cache"/>
677<t>
678   Any party to HTTP communication that is not acting as a tunnel may
679   employ an internal cache for handling requests.
680   A cache is a local store of previous response messages and the
681   subsystem that controls its message storage, retrieval, and deletion.
682   A cache stores cacheable responses in order to reduce the response
683   time and network bandwidth consumption on future, equivalent
684   requests. Any client or server may include a cache, though a cache
685   cannot be used by a server while it is acting as a tunnel.
686</t>
687<t>
688   The effect of a cache is that the request/response chain is shortened
689   if one of the participants along the chain has a cached response
690   applicable to that request. The following illustrates the resulting
691   chain if B has a cached copy of an earlier response from O (via C)
692   for a request which has not been cached by UA or A.
693</t>
694<figure><artwork type="drawing"><![CDATA[
695          request chain ---------->
696       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
697          <--------- response chain
698]]></artwork></figure>
699<t><iref item="cacheable"/>
700   A response is cacheable if a cache is allowed to store a copy of
701   the response message for use in answering subsequent requests.
702   Even when a response is cacheable, there may be additional
703   constraints placed by the client or by the origin server on when
704   that cached response can be used for a particular request. HTTP
705   requirements for cache behavior and cacheable responses are
706   defined in Section 2 of <xref target="Part6"/>
707</t>
708<t>
709   There are a wide variety of architectures and configurations
710   of caches and proxies deployed across the World Wide Web and
711   inside large organizations. These systems include national hierarchies
712   of proxy caches to save transoceanic bandwidth, systems that
713   broadcast or multicast cache entries, organizations that distribute
714   subsets of cached data via optical media, and so on.
715</t>
716</section>
717
718<section title="Transport Independence" anchor="transport-independence">
719<t>
720  HTTP systems are used in a wide variety of environments, from
721  corporate intranets with high-bandwidth links to long-distance
722  communication over low-power radio links and intermittent connectivity.
723</t>
724<t>
725   HTTP communication usually takes place over TCP/IP connections. The
726   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
727   not preclude HTTP from being implemented on top of any other protocol
728   on the Internet, or on other networks. HTTP only presumes a reliable
729   transport; any protocol that provides such guarantees can be used;
730   the mapping of the HTTP/1.1 request and response structures onto the
731   transport data units of the protocol in question is outside the scope
732   of this specification.
733</t>
734<t>
735   In HTTP/1.0, most implementations used a new connection for each
736   request/response exchange. In HTTP/1.1, a connection may be used for
737   one or more request/response exchanges, although connections may be
738   closed for a variety of reasons (see <xref target="persistent.connections"/>).
739</t>
740</section>
741
742<section title="HTTP Version" anchor="http.version">
743 
744 
745<t>
746   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
747   of the protocol. The protocol versioning policy is intended to allow
748   the sender to indicate the format of a message and its capacity for
749   understanding further HTTP communication, rather than the features
750   obtained via that communication. No change is made to the version
751   number for the addition of message components which do not affect
752   communication behavior or which only add to extensible field values.
753   The &lt;minor&gt; number is incremented when the changes made to the
754   protocol add features which do not change the general message parsing
755   algorithm, but which may add to the message semantics and imply
756   additional capabilities of the sender. The &lt;major&gt; number is
757   incremented when the format of a message within the protocol is
758   changed. See <xref target="RFC2145"/> for a fuller explanation.
759</t>
760<t>
761   The version of an HTTP message is indicated by an HTTP-Version field
762   in the first line of the message. HTTP-Version is case-sensitive.
763</t>
764<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
765  HTTP-Version   = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
766  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
767]]></artwork></figure>
768<t>
769   Note that the major and minor numbers MUST be treated as separate
770   integers and that each MAY be incremented higher than a single digit.
771   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
772   lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and
773   MUST NOT be sent.
774</t>
775<t>
776   An application that sends a request or response message that includes
777   HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
778   with this specification. Applications that are at least conditionally
779   compliant with this specification SHOULD use an HTTP-Version of
780   "HTTP/1.1" in their messages, and MUST do so for any message that is
781   not compatible with HTTP/1.0. For more details on when to send
782   specific HTTP-Version values, see <xref target="RFC2145"/>.
783</t>
784<t>
785   The HTTP version of an application is the highest HTTP version for
786   which the application is at least conditionally compliant.
787</t>
788<t>
789   Proxy and gateway applications need to be careful when forwarding
790   messages in protocol versions different from that of the application.
791   Since the protocol version indicates the protocol capability of the
792   sender, a proxy/gateway MUST NOT send a message with a version
793   indicator which is greater than its actual version. If a higher
794   version request is received, the proxy/gateway MUST either downgrade
795   the request version, or respond with an error, or switch to tunnel
796   behavior.
797</t>
798<t>
799   Due to interoperability problems with HTTP/1.0 proxies discovered
800   since the publication of <xref target="RFC2068"/>, caching proxies MUST, gateways
801   MAY, and tunnels MUST NOT upgrade the request to the highest version
802   they support. The proxy/gateway's response to that request MUST be in
803   the same major version as the request.
804</t>
805<t><list>
806  <t>
807    Note: Converting between versions of HTTP may involve modification
808    of header fields required or forbidden by the versions involved.
809  </t>
810</list></t>
811</section>
812
813<section title="Uniform Resource Identifiers" anchor="uri">
814<iref primary="true" item="resource"/>
815<t>
816   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
817   throughout HTTP as the means for identifying resources. URI references
818   are used to target requests, indicate redirects, and define relationships.
819   HTTP does not limit what a resource may be; it merely defines an interface
820   that can be used to interact with a resource via HTTP. More information on
821   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
822</t>
823 
824 
825 
826 
827 
828 
829 
830 
831 
832 
833 
834<t>
835   This specification adopts the definitions of "URI-reference",
836   "absolute-URI", "relative-part", "port", "host",
837   "path-abempty", "path-absolute", "query", and "authority" from
838   <xref target="RFC3986"/>. In addition, we define a partial-URI rule for
839   protocol elements that allow a relative URI without a fragment.
840</t>
841<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[
842  URI           = <URI, defined in [RFC3986], Section 3>
843  URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
844  absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
845  relative-part = <relative-part, defined in [RFC3986], Section 4.2>
846  authority     = <authority, defined in [RFC3986], Section 3.2>
847  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
848  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
849  port          = <port, defined in [RFC3986], Section 3.2.3>
850  query         = <query, defined in [RFC3986], Section 3.4>
851  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
852 
853  partial-URI   = relative-part [ "?" query ]
854]]></artwork></figure>
855<t>
856   Each protocol element in HTTP that allows a URI reference will indicate in
857   its ABNF production whether the element allows only a URI in absolute form
858   (absolute-URI), any relative reference (relative-ref), or some other subset
859   of the URI-reference grammar. Unless otherwise indicated, URI references
860   are parsed relative to the request target (the default base URI for both
861   the request and its corresponding response).
862</t>
863
864<section title="http URI scheme" anchor="http.uri">
865 
866  <iref item="http URI scheme" primary="true"/>
867  <iref item="URI scheme" subitem="http" primary="true"/>
868<t>
869   The "http" URI scheme is hereby defined for the purpose of minting
870   identifiers according to their association with the hierarchical
871   namespace governed by a potential HTTP origin server listening for
872   TCP connections on a given port.
873   The HTTP server is identified via the generic syntax's
874   <xref target="uri" format="none">authority</xref> component, which includes a host
875   identifier and optional TCP port, and the remainder of the URI is
876   considered to be identifying data corresponding to a resource for
877   which that server might provide an HTTP interface.
878</t>
879<figure><iref primary="true" item="Grammar" subitem="http-URI"/><artwork type="abnf2616"><![CDATA[
880  http-URI = "http:" "//" authority path-abempty [ "?" query ]
881]]></artwork></figure>
882<t>
883   The host identifier within an <xref target="uri" format="none">authority</xref> component is
884   defined in <xref target="RFC3986"/>, Section 3.2.2.  If host is
885   provided as an IP literal or IPv4 address, then the HTTP server is any
886   listener on the indicated TCP port at that IP address. If host is a
887   registered name, then that name is considered an indirect identifier
888   and the recipient might use a name resolution service, such as DNS,
889   to find the address of a listener for that host.
890   The host MUST NOT be empty; if an "http" URI is received with an
891   empty host, then it MUST be rejected as invalid.
892   If the port subcomponent is empty or not given, then TCP port 80 is
893   assumed (the default reserved port for WWW services).
894</t>
895<t>
896   Regardless of the form of host identifier, access to that host is not
897   implied by the mere presence of its name or address. The host may or may
898   not exist and, even when it does exist, may or may not be running an
899   HTTP server or listening to the indicated port. The "http" URI scheme
900   makes use of the delegated nature of Internet names and addresses to
901   establish a naming authority (whatever entity has the ability to place
902   an HTTP server at that Internet name or address) and allows that
903   authority to determine which names are valid and how they might be used.
904</t>
905<t>
906   When an "http" URI is used within a context that calls for access to the
907   indicated resource, a client MAY attempt access by resolving
908   the host to an IP address, establishing a TCP connection to that address
909   on the indicated port, and sending an HTTP request message to the server
910   containing the URI's identifying data as described in <xref target="request"/>.
911   If the server responds to that request with a non-interim HTTP response
912   message, as described in <xref target="response"/>, then that response
913   is considered an authoritative answer to the client's request.
914</t>
915<t>
916   Although HTTP is independent of the transport protocol, the "http"
917   scheme is specific to TCP-based services because the name delegation
918   process depends on TCP for establishing authority.
919   An HTTP service based on some other underlying connection protocol
920   would presumably be identified using a different URI scheme, just as
921   the "https" scheme (below) is used for servers that require an SSL/TLS
922   transport layer on a connection. Other protocols may also be used to
923   provide access to "http" identified resources --- it is only the
924   authoritative interface used for mapping the namespace that is
925   specific to TCP.
926</t>
927</section>
928
929<section title="https URI scheme" anchor="https.uri">
930   
931   <iref item="https URI scheme"/>
932   <iref item="URI scheme" subitem="https"/>
933<t>
934   The "https" URI scheme is hereby defined for the purpose of minting
935   identifiers according to their association with the hierarchical
936   namespace governed by a potential HTTP origin server listening for
937   SSL/TLS-secured connections on a given TCP port.
938   The host and port are determined in the same way
939   as for the "http" scheme, except that a default TCP port of 443
940   is assumed if the port subcomponent is empty or not given.
941</t>
942<figure><iref primary="true" item="Grammar" subitem="https-URI"/><artwork type="abnf2616"><![CDATA[
943  https-URI = "https:" "//" authority path-abempty [ "?" query ]
944]]></artwork></figure>
945<t>
946   The primary difference between the "http" and "https" schemes is
947   that interaction with the latter is required to be secured for
948   privacy through the use of strong encryption. The URI cannot be
949   sent in a request until the connection is secure. Likewise, the
950   default for caching is that each response that would be considered
951   "public" under the "http" scheme is instead treated as "private"
952   and thus not eligible for shared caching.
953</t>
954<t>
955   The process for authoritative access to an "https" identified
956   resource is defined in <xref target="RFC2818"/>.
957</t>
958</section>
959
960<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
961<t>
962   Since the "http" and "https" schemes conform to the URI generic syntax,
963   such URIs are normalized and compared according to the algorithm defined
964   in <xref target="RFC3986"/>, Section 6, using the defaults
965   described above for each scheme.
966</t>
967<t>
968   If the port is equal to the default port for a scheme, the normal
969   form is to elide the port subcomponent. Likewise, an empty path
970   component is equivalent to an absolute path of "/", so the normal
971   form is to provide a path of "/" instead. The scheme and host
972   are case-insensitive and normally provided in lowercase; all
973   other components are compared in a case-sensitive manner.
974   Characters other than those in the "reserved" set are equivalent
975   to their percent-encoded octets (see <xref target="RFC3986"/>, Section 2.1): the normal form is to not encode them.
976</t>
977<t>
978   For example, the following three URIs are equivalent:
979</t>
980<figure><artwork type="example"><![CDATA[
981   http://example.com:80/~smith/home.html
982   http://EXAMPLE.com/%7Esmith/home.html
983   http://EXAMPLE.com:/%7esmith/home.html
984]]></artwork></figure>
985<t>
986   <cref anchor="TODO-not-here" source="roy">This paragraph does not belong here.</cref>
987   If path-abempty is the empty string (i.e., there is no slash "/"
988   path separator following the authority), then the "http" URI
989   MUST be given as "/" when
990   used as a request-target (<xref target="request-target"/>). If a proxy
991   receives a host name which is not a fully qualified domain name, it
992   MAY add its domain to the host name it received. If a proxy receives
993   a fully qualified domain name, the proxy MUST NOT change the host
994   name.
995</t>
996</section>
997</section>
998</section>
999
1000<section title="HTTP Message" anchor="http.message">
1001
1002
1003
1004
1005<iref item="header section"/>
1006<iref item="headers"/>
1007<iref item="header field"/>
1008<t>
1009   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1010   characters in a format similar to the Internet Message Format
1011   <xref target="RFC5322"/>: zero or more header fields (collectively
1012   referred to as the "headers" or the "header section"), an empty line
1013   indicating the end of the header section, and an optional message-body.
1014</t>
1015<t>
1016   An HTTP message can either be a request from client to server or a
1017   response from server to client.  Syntactically, the two types of message
1018   differ only in the start-line, which is either a Request-Line (for requests)
1019   or a Status-Line (for responses), and in the algorithm for determining
1020   the length of the message-body (<xref target="message.length"/>).
1021   In theory, a client could receive requests and a server could receive
1022   responses, distinguishing them by their different start-line formats,
1023   but in practice servers are implemented to only expect a request
1024   (a response is interpreted as an unknown or invalid request method)
1025   and clients are implemented to only expect a response.
1026</t>
1027<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1028  HTTP-message    = start-line
1029                    *( header-field CRLF )
1030                    CRLF
1031                    [ message-body ]
1032  start-line      = Request-Line / Status-Line
1033]]></artwork></figure>
1034<t>
1035   Whitespace (WSP) MUST NOT be sent between the start-line and the first
1036   header field. The presence of whitespace might be an attempt to trick a
1037   noncompliant implementation of HTTP into ignoring that field or processing
1038   the next line as a new request, either of which may result in security
1039   issues when implementations within the request chain interpret the
1040   same message differently. HTTP/1.1 servers MUST reject such a message
1041   with a 400 (Bad Request) response.
1042</t>
1043
1044<section title="Message Parsing Robustness" anchor="message.robustness">
1045<t>
1046   In the interest of robustness, servers SHOULD ignore at least one
1047   empty line received where a Request-Line is expected. In other words, if
1048   the server is reading the protocol stream at the beginning of a
1049   message and receives a CRLF first, it should ignore the CRLF.
1050</t>
1051<t>
1052   Some old HTTP/1.0 client implementations generate an extra CRLF
1053   after a POST request as a lame workaround for some early server
1054   applications that failed to read message-body content that was
1055   not terminated by a line-ending. An HTTP/1.1 client MUST NOT
1056   preface or follow a request with an extra CRLF.  If terminating
1057   the request message-body with a line-ending is desired, then the
1058   client MUST include the terminating CRLF octets as part of the
1059   message-body length.
1060</t>
1061<t>
1062   The normal procedure for parsing an HTTP message is to read the
1063   start-line into a structure, read each header field into a hash
1064   table by field name until the empty line, and then use the parsed
1065   data to determine if a message-body is expected.  If a message-body
1066   has been indicated, then it is read as a stream until an amount
1067   of OCTETs equal to the message-length is read or the connection
1068   is closed.  Care must be taken to parse an HTTP message as a sequence
1069   of OCTETs in an encoding that is a superset of US-ASCII.  Attempting
1070   to parse HTTP as a stream of Unicode characters in a character encoding
1071   like UTF-16 may introduce security flaws due to the differing ways
1072   that such parsers interpret invalid characters.
1073</t>
1074</section>
1075
1076<section title="Header Fields" anchor="header.fields">
1077 
1078 
1079 
1080 
1081 
1082<t>
1083   Each HTTP header field consists of a case-insensitive field name
1084   followed by a colon (":"), optional whitespace, and the field value.
1085</t>
1086<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[
1087  header-field   = field-name ":" OWS [ field-value ] OWS
1088  field-name     = token
1089  field-value    = *( field-content / OWS )
1090  field-content  = *( WSP / VCHAR / obs-text )
1091]]></artwork></figure>
1092<t>
1093   No whitespace is allowed between the header field name and colon. For
1094   security reasons, any request message received containing such whitespace
1095   MUST be rejected with a response code of 400 (Bad Request). A proxy
1096   MUST remove any such whitespace from a response message before
1097   forwarding the message downstream.
1098</t>
1099<t>
1100   A field value MAY be preceded by optional whitespace (OWS); a single SP is
1101   preferred. The field value does not include any leading or trailing white
1102   space: OWS occurring before the first non-whitespace character of the
1103   field value or after the last non-whitespace character of the field value
1104   is ignored and SHOULD be removed before further processing (as this does
1105   not change the meaning of the header field).
1106</t>
1107<t>
1108   The order in which header fields with differing field names are
1109   received is not significant. However, it is "good practice" to send
1110   header fields that contain control data first, such as Host on
1111   requests and Date on responses, so that implementations can decide
1112   when not to handle a message as early as possible.  A server MUST
1113   wait until the entire header section is received before interpreting
1114   a request message, since later header fields might include conditionals,
1115   authentication credentials, or deliberately misleading duplicate
1116   header fields that would impact request processing.
1117</t>
1118<t>
1119   Multiple header fields with the same field name MUST NOT be
1120   sent in a message unless the entire field value for that
1121   header field is defined as a comma-separated list [i.e., #(values)].
1122   Multiple header fields with the same field name can be combined into
1123   one "field-name: field-value" pair, without changing the semantics of the
1124   message, by appending each subsequent field value to the combined
1125   field value in order, separated by a comma. The order in which
1126   header fields with the same field name are received is therefore
1127   significant to the interpretation of the combined field value;
1128   a proxy MUST NOT change the order of these field values when
1129   forwarding a message.
1130</t>
1131<t><list>
1132  <t>
1133   Note: The "Set-Cookie" header as implemented in
1134   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1135   can occur multiple times, but does not use the list syntax, and thus cannot
1136   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1137   for details.) Also note that the Set-Cookie2 header specified in
1138   <xref target="RFC2965"/> does not share this problem.
1139  </t>
1140</list></t>
1141<t>
1142   Historically, HTTP header field values could be extended over multiple
1143   lines by preceding each extra line with at least one space or horizontal
1144   tab character (line folding). This specification deprecates such line
1145   folding except within the message/http media type
1146   (<xref target="internet.media.type.message.http"/>).
1147   HTTP/1.1 senders MUST NOT produce messages that include line folding
1148   (i.e., that contain any field-content that matches the obs-fold rule) unless
1149   the message is intended for packaging within the message/http media type.
1150   HTTP/1.1 recipients SHOULD accept line folding and replace any embedded
1151   obs-fold whitespace with a single SP prior to interpreting the field value
1152   or forwarding the message downstream.
1153</t>
1154<t>
1155   Historically, HTTP has allowed field content with text in the ISO-8859-1
1156   <xref target="ISO-8859-1"/> character encoding and supported other
1157   character sets only through use of <xref target="RFC2047"/> encoding.
1158   In practice, most HTTP header field values use only a subset of the
1159   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1160   header fields SHOULD limit their field values to US-ASCII characters.
1161   Recipients SHOULD treat other (obs-text) octets in field content as
1162   opaque data.
1163</t>
1164<t anchor="rule.comment">
1165 
1166 
1167   Comments can be included in some HTTP header fields by surrounding
1168   the comment text with parentheses. Comments are only allowed in
1169   fields containing "comment" as part of their field value definition.
1170</t>
1171<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
1172  comment        = "(" *( ctext / quoted-cpair / comment ) ")"
1173  ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
1174                 ; OWS / <VCHAR except "(", ")", and "\"> / obs-text
1175]]></artwork></figure>
1176<t anchor="rule.quoted-cpair">
1177 
1178   The backslash character ("\") can be used as a single-character
1179   quoting mechanism within comment constructs:
1180</t>
1181<figure><iref primary="true" item="Grammar" subitem="quoted-cpair"/><artwork type="abnf2616"><![CDATA[
1182  quoted-cpair    = "\" ( WSP / VCHAR / obs-text )
1183]]></artwork></figure>
1184<t>
1185   Producers SHOULD NOT escape characters that do not require escaping
1186   (i.e., other than the backslash character "\" and the parentheses "(" and
1187   ")").
1188</t>
1189</section>
1190
1191<section title="Message Body" anchor="message.body">
1192 
1193<t>
1194   The message-body (if any) of an HTTP message is used to carry the
1195   entity-body associated with the request or response. The message-body
1196   differs from the entity-body only when a transfer-coding has been
1197   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1198</t>
1199<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1200  message-body = entity-body
1201               / <entity-body encoded as per Transfer-Encoding>
1202]]></artwork></figure>
1203<t>
1204   Transfer-Encoding MUST be used to indicate any transfer-codings
1205   applied by an application to ensure safe and proper transfer of the
1206   message. Transfer-Encoding is a property of the message, not of the
1207   entity, and thus MAY be added or removed by any application along the
1208   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1209   when certain transfer-codings may be used.)
1210</t>
1211<t>
1212   The rules for when a message-body is allowed in a message differ for
1213   requests and responses.
1214</t>
1215<t>
1216   The presence of a message-body in a request is signaled by the
1217   inclusion of a Content-Length or Transfer-Encoding header field in
1218   the request's header fields.
1219   When a request message contains both a message-body of non-zero
1220   length and a method that does not define any semantics for that
1221   request message-body, then an origin server SHOULD either ignore
1222   the message-body or respond with an appropriate error message
1223   (e.g., 413).  A proxy or gateway, when presented the same request,
1224   SHOULD either forward the request inbound with the message-body or
1225   ignore the message-body when determining a response.
1226</t>
1227<t>
1228   For response messages, whether or not a message-body is included with
1229   a message is dependent on both the request method and the response
1230   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1231   MUST NOT include a message-body, even though the presence of entity-header
1232   fields might lead one to believe they do. All 1xx
1233   (Informational), 204 (No Content), and 304 (Not Modified) responses
1234   MUST NOT include a message-body. All other responses do include a
1235   message-body, although it MAY be of zero length.
1236</t>
1237</section>
1238
1239<section title="Message Length" anchor="message.length">
1240<t>
1241   The transfer-length of a message is the length of the message-body as
1242   it appears in the message; that is, after any transfer-codings have
1243   been applied. When a message-body is included with a message, the
1244   transfer-length of that body is determined by one of the following
1245   (in order of precedence):
1246</t>
1247<t>
1248  <list style="numbers">
1249    <t>
1250     Any response message which "MUST NOT" include a message-body (such
1251     as the 1xx, 204, and 304 responses and any response to a HEAD
1252     request) is always terminated by the first empty line after the
1253     header fields, regardless of the entity-header fields present in
1254     the message.
1255    </t>
1256    <t>
1257     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1258     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1259     is used, the transfer-length is defined by the use of this transfer-coding.
1260     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1261     is not present, the transfer-length is defined by the sender closing the connection.
1262    </t>
1263    <t>
1264     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1265     value in OCTETs represents both the entity-length and the
1266     transfer-length. The Content-Length header field MUST NOT be sent
1267     if these two lengths are different (i.e., if a Transfer-Encoding
1268     header field is present). If a message is received with both a
1269     Transfer-Encoding header field and a Content-Length header field,
1270     the latter MUST be ignored.
1271    </t>
1272    <t>
1273     If the message uses the media type "multipart/byteranges", and the
1274     transfer-length is not otherwise specified, then this self-delimiting
1275     media type defines the transfer-length. This media type
1276     MUST NOT be used unless the sender knows that the recipient can parse
1277     it; the presence in a request of a Range header with multiple byte-range
1278     specifiers from a HTTP/1.1 client implies that the client can parse
1279     multipart/byteranges responses.
1280    <list style="empty"><t>
1281       A range header might be forwarded by a HTTP/1.0 proxy that does not
1282       understand multipart/byteranges; in this case the server MUST
1283       delimit the message using methods defined in items 1, 3 or 5 of
1284       this section.
1285    </t></list>
1286    </t>
1287    <t>
1288     By the server closing the connection. (Closing the connection
1289     cannot be used to indicate the end of a request body, since that
1290     would leave no possibility for the server to send back a response.)
1291    </t>
1292  </list>
1293</t>
1294<t>
1295   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1296   containing a message-body MUST include a valid Content-Length header
1297   field unless the server is known to be HTTP/1.1 compliant. If a
1298   request contains a message-body and a Content-Length is not given,
1299   the server SHOULD respond with 400 (Bad Request) if it cannot
1300   determine the length of the message, or with 411 (Length Required) if
1301   it wishes to insist on receiving a valid Content-Length.
1302</t>
1303<t>
1304   All HTTP/1.1 applications that receive entities MUST accept the
1305   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1306   to be used for messages when the message length cannot be determined
1307   in advance.
1308</t>
1309<t>
1310   Messages MUST NOT include both a Content-Length header field and a
1311   transfer-coding. If the message does include a
1312   transfer-coding, the Content-Length MUST be ignored.
1313</t>
1314<t>
1315   When a Content-Length is given in a message where a message-body is
1316   allowed, its field value MUST exactly match the number of OCTETs in
1317   the message-body. HTTP/1.1 user agents MUST notify the user when an
1318   invalid length is received and detected.
1319</t>
1320</section>
1321
1322<section title="General Header Fields" anchor="general.header.fields">
1323 
1324<t>
1325   There are a few header fields which have general applicability for
1326   both request and response messages, but which do not apply to the
1327   entity being transferred. These header fields apply only to the
1328   message being transmitted.
1329</t>
1330<figure><iref primary="true" item="Grammar" subitem="general-header"/><artwork type="abnf2616"><![CDATA[
1331  general-header = Cache-Control            ; [Part6], Section 3.2
1332                 / Connection               ; Section 9.1
1333                 / Date                     ; Section 9.3
1334                 / Pragma                   ; [Part6], Section 3.4
1335                 / Trailer                  ; Section 9.6
1336                 / Transfer-Encoding        ; Section 9.7
1337                 / Upgrade                  ; Section 9.8
1338                 / Via                      ; Section 9.9
1339                 / Warning                  ; [Part6], Section 3.6
1340]]></artwork></figure>
1341<t>
1342   General-header field names can be extended reliably only in
1343   combination with a change in the protocol version. However, new or
1344   experimental header fields may be given the semantics of general
1345   header fields if all parties in the communication recognize them to
1346   be general-header fields. Unrecognized header fields are treated as
1347   entity-header fields.
1348</t>
1349</section>
1350</section>
1351
1352<section title="Request" anchor="request">
1353 
1354<t>
1355   A request message from a client to a server includes, within the
1356   first line of that message, the method to be applied to the resource,
1357   the identifier of the resource, and the protocol version in use.
1358</t>
1359<!--                 Host                      ; should be moved here eventually -->
1360<figure><iref primary="true" item="Grammar" subitem="Request"/><artwork type="abnf2616"><![CDATA[
1361  Request       = Request-Line              ; Section 4.1
1362                  *(( general-header        ; Section 3.5
1363                   / request-header         ; [Part2], Section 3
1364                   / entity-header ) CRLF ) ; [Part3], Section 3.1
1365                  CRLF
1366                  [ message-body ]          ; Section 3.3
1367]]></artwork></figure>
1368
1369<section title="Request-Line" anchor="request-line">
1370 
1371<t>
1372   The Request-Line begins with a method token, followed by the
1373   request-target and the protocol version, and ending with CRLF. The
1374   elements are separated by SP characters. No CR or LF is allowed
1375   except in the final CRLF sequence.
1376</t>
1377<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1378  Request-Line   = Method SP request-target SP HTTP-Version CRLF
1379]]></artwork></figure>
1380
1381<section title="Method" anchor="method">
1382 
1383<t>
1384   The Method  token indicates the method to be performed on the
1385   resource identified by the request-target. The method is case-sensitive.
1386</t>
1387<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
1388  Method         = token
1389]]></artwork></figure>
1390</section>
1391
1392<section title="request-target" anchor="request-target">
1393 
1394<t>
1395   The request-target
1396   identifies the resource upon which to apply the request.
1397</t>
1398<figure><iref primary="true" item="Grammar" subitem="request-target"/><artwork type="abnf2616"><![CDATA[
1399  request-target = "*"
1400                 / absolute-URI
1401                 / ( path-absolute [ "?" query ] )
1402                 / authority
1403]]></artwork></figure>
1404<t>
1405   The four options for request-target are dependent on the nature of the
1406   request. The asterisk "*" means that the request does not apply to a
1407   particular resource, but to the server itself, and is only allowed
1408   when the method used does not necessarily apply to a resource. One
1409   example would be
1410</t>
1411<figure><artwork type="example"><![CDATA[
1412  OPTIONS * HTTP/1.1
1413]]></artwork></figure>
1414<t>
1415   The absolute-URI form is REQUIRED when the request is being made to a
1416   proxy. The proxy is requested to forward the request or service it
1417   from a valid cache, and return the response. Note that the proxy MAY
1418   forward the request on to another proxy or directly to the server
1419   specified by the absolute-URI. In order to avoid request loops, a
1420   proxy MUST be able to recognize all of its server names, including
1421   any aliases, local variations, and the numeric IP address. An example
1422   Request-Line would be:
1423</t>
1424<figure><artwork type="example"><![CDATA[
1425  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1426]]></artwork></figure>
1427<t>
1428   To allow for transition to absolute-URIs in all requests in future
1429   versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
1430   form in requests, even though HTTP/1.1 clients will only generate
1431   them in requests to proxies.
1432</t>
1433<t>
1434   The authority form is only used by the CONNECT method (Section 7.9 of <xref target="Part2"/>).
1435</t>
1436<t>
1437   The most common form of request-target is that used to identify a
1438   resource on an origin server or gateway. In this case the absolute
1439   path of the URI MUST be transmitted (see <xref target="http.uri"/>, path-absolute) as
1440   the request-target, and the network location of the URI (authority) MUST
1441   be transmitted in a Host header field. For example, a client wishing
1442   to retrieve the resource above directly from the origin server would
1443   create a TCP connection to port 80 of the host "www.example.org" and send
1444   the lines:
1445</t>
1446<figure><artwork type="example"><![CDATA[
1447  GET /pub/WWW/TheProject.html HTTP/1.1
1448  Host: www.example.org
1449]]></artwork></figure>
1450<t>
1451   followed by the remainder of the Request. Note that the absolute path
1452   cannot be empty; if none is present in the original URI, it MUST be
1453   given as "/" (the server root).
1454</t>
1455<t>
1456   If a proxy receives a request without any path in the request-target and
1457   the method specified is capable of supporting the asterisk form of
1458   request-target, then the last proxy on the request chain MUST forward the
1459   request with "*" as the final request-target.
1460</t>
1461<figure><preamble>   
1462   For example, the request
1463</preamble><artwork type="example"><![CDATA[
1464  OPTIONS http://www.example.org:8001 HTTP/1.1
1465]]></artwork></figure>
1466<figure><preamble>   
1467  would be forwarded by the proxy as
1468</preamble><artwork type="example"><![CDATA[
1469  OPTIONS * HTTP/1.1
1470  Host: www.example.org:8001
1471]]></artwork>
1472<postamble>
1473   after connecting to port 8001 of host "www.example.org".
1474</postamble>
1475</figure>
1476<t>
1477   The request-target is transmitted in the format specified in
1478   <xref target="http.uri"/>. If the request-target is percent-encoded
1479   (<xref target="RFC3986"/>, Section 2.1), the origin server
1480   MUST decode the request-target in order to
1481   properly interpret the request. Servers SHOULD respond to invalid
1482   request-targets with an appropriate status code.
1483</t>
1484<t>
1485   A transparent proxy MUST NOT rewrite the "path-absolute" part of the
1486   received request-target when forwarding it to the next inbound server,
1487   except as noted above to replace a null path-absolute with "/".
1488</t>
1489<t><list>
1490  <t>
1491    Note: The "no rewrite" rule prevents the proxy from changing the
1492    meaning of the request when the origin server is improperly using
1493    a non-reserved URI character for a reserved purpose.  Implementors
1494    should be aware that some pre-HTTP/1.1 proxies have been known to
1495    rewrite the request-target.
1496  </t>
1497</list></t>
1498<t>
1499   HTTP does not place a pre-defined limit on the length of a request-target.
1500   A server MUST be prepared to receive URIs of unbounded length and
1501   respond with the 414 (URI Too Long) status if the received
1502   request-target would be longer than the server wishes to handle
1503   (see Section 8.4.15 of <xref target="Part2"/>).
1504</t>
1505<t>
1506   Various ad-hoc limitations on request-target length are found in practice.
1507   It is RECOMMENDED that all HTTP senders and recipients support
1508   request-target lengths of 8000 or more OCTETs.
1509</t>
1510</section>
1511</section>
1512
1513<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1514<t>
1515   The exact resource identified by an Internet request is determined by
1516   examining both the request-target and the Host header field.
1517</t>
1518<t>
1519   An origin server that does not allow resources to differ by the
1520   requested host MAY ignore the Host header field value when
1521   determining the resource identified by an HTTP/1.1 request. (But see
1522   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1523   for other requirements on Host support in HTTP/1.1.)
1524</t>
1525<t>
1526   An origin server that does differentiate resources based on the host
1527   requested (sometimes referred to as virtual hosts or vanity host
1528   names) MUST use the following rules for determining the requested
1529   resource on an HTTP/1.1 request:
1530  <list style="numbers">
1531    <t>If request-target is an absolute-URI, the host is part of the
1532     request-target. Any Host header field value in the request MUST be
1533     ignored.</t>
1534    <t>If the request-target is not an absolute-URI, and the request includes
1535     a Host header field, the host is determined by the Host header
1536     field value.</t>
1537    <t>If the host as determined by rule 1 or 2 is not a valid host on
1538     the server, the response MUST be a 400 (Bad Request) error message.</t>
1539  </list>
1540</t>
1541<t>
1542   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1543   attempt to use heuristics (e.g., examination of the URI path for
1544   something unique to a particular host) in order to determine what
1545   exact resource is being requested.
1546</t>
1547</section>
1548
1549</section>
1550
1551
1552<section title="Response" anchor="response">
1553 
1554<t>
1555   After receiving and interpreting a request message, a server responds
1556   with an HTTP response message.
1557</t>
1558<figure><iref primary="true" item="Grammar" subitem="Response"/><artwork type="abnf2616"><![CDATA[
1559  Response      = Status-Line               ; Section 5.1
1560                  *(( general-header        ; Section 3.5
1561                   / response-header        ; [Part2], Section 5
1562                   / entity-header ) CRLF ) ; [Part3], Section 3.1
1563                  CRLF
1564                  [ message-body ]          ; Section 3.3
1565]]></artwork></figure>
1566
1567<section title="Status-Line" anchor="status-line">
1568 
1569<t>
1570   The first line of a Response message is the Status-Line, consisting
1571   of the protocol version followed by a numeric status code and its
1572   associated textual phrase, with each element separated by SP
1573   characters. No CR or LF is allowed except in the final CRLF sequence.
1574</t>
1575<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1576  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1577]]></artwork></figure>
1578
1579<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1580 
1581 
1582<t>
1583   The Status-Code element is a 3-digit integer result code of the
1584   attempt to understand and satisfy the request. These codes are fully
1585   defined in Section 8 of <xref target="Part2"/>.  The Reason Phrase exists for the sole
1586   purpose of providing a textual description associated with the numeric
1587   status code, out of deference to earlier Internet application protocols
1588   that were more frequently used with interactive text clients.
1589   A client SHOULD ignore the content of the Reason Phrase.
1590</t>
1591<t>
1592   The first digit of the Status-Code defines the class of response. The
1593   last two digits do not have any categorization role. There are 5
1594   values for the first digit:
1595  <list style="symbols">
1596    <t>
1597      1xx: Informational - Request received, continuing process
1598    </t>
1599    <t>
1600      2xx: Success - The action was successfully received,
1601        understood, and accepted
1602    </t>
1603    <t>
1604      3xx: Redirection - Further action must be taken in order to
1605        complete the request
1606    </t>
1607    <t>
1608      4xx: Client Error - The request contains bad syntax or cannot
1609        be fulfilled
1610    </t>
1611    <t>
1612      5xx: Server Error - The server failed to fulfill an apparently
1613        valid request
1614    </t>
1615  </list>
1616</t>
1617<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[
1618  Status-Code    = 3DIGIT
1619  Reason-Phrase  = *( WSP / VCHAR / obs-text )
1620]]></artwork></figure>
1621</section>
1622</section>
1623
1624</section>
1625
1626
1627<section title="Protocol Parameters" anchor="protocol.parameters">
1628
1629<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
1630 
1631<t>
1632   HTTP applications have historically allowed three different formats
1633   for the representation of date/time stamps:
1634</t>
1635<figure><artwork type="example"><![CDATA[
1636  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
1637  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1638  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1639]]></artwork></figure>
1640<t>
1641   The first format is preferred as an Internet standard and represents
1642   a fixed-length subset of that defined by <xref target="RFC1123"/>. The
1643   other formats are described here only for
1644   compatibility with obsolete implementations.
1645   HTTP/1.1 clients and servers that parse the date value MUST accept
1646   all three formats (for compatibility with HTTP/1.0), though they MUST
1647   only generate the RFC 1123 format for representing HTTP-date values
1648   in header fields. See <xref target="tolerant.applications"/> for further information.
1649</t>
1650<t>
1651   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
1652   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1653   equal to UTC (Coordinated Universal Time). This is indicated in the
1654   first two formats by the inclusion of "GMT" as the three-letter
1655   abbreviation for time zone, and MUST be assumed when reading the
1656   asctime format. HTTP-date is case sensitive and MUST NOT include
1657   additional whitespace beyond that specifically included as SP in the
1658   grammar.
1659</t>
1660<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><artwork type="abnf2616"><![CDATA[
1661  HTTP-date    = rfc1123-date / obs-date
1662]]></artwork></figure>
1663<t anchor="preferred.date.format">
1664 
1665 
1666 
1667 
1668 
1669 
1670 
1671 
1672 
1673 
1674  Preferred format:
1675</t>
1676<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[
1677  rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
1678
1679  day-name     = %x4D.6F.6E ; "Mon", case-sensitive
1680               / %x54.75.65 ; "Tue", case-sensitive
1681               / %x57.65.64 ; "Wed", case-sensitive
1682               / %x54.68.75 ; "Thu", case-sensitive
1683               / %x46.72.69 ; "Fri", case-sensitive
1684               / %x53.61.74 ; "Sat", case-sensitive
1685               / %x53.75.6E ; "Sun", case-sensitive
1686               
1687  date1        = day SP month SP year
1688               ; e.g., 02 Jun 1982
1689
1690  day          = 2DIGIT
1691  month        = %x4A.61.6E ; "Jan", case-sensitive
1692               / %x46.65.62 ; "Feb", case-sensitive
1693               / %x4D.61.72 ; "Mar", case-sensitive
1694               / %x41.70.72 ; "Apr", case-sensitive
1695               / %x4D.61.79 ; "May", case-sensitive
1696               / %x4A.75.6E ; "Jun", case-sensitive
1697               / %x4A.75.6C ; "Jul", case-sensitive
1698               / %x41.75.67 ; "Aug", case-sensitive
1699               / %x53.65.70 ; "Sep", case-sensitive
1700               / %x4F.63.74 ; "Oct", case-sensitive
1701               / %x4E.6F.76 ; "Nov", case-sensitive
1702               / %x44.65.63 ; "Dec", case-sensitive
1703  year         = 4DIGIT
1704
1705  GMT   = %x47.4D.54 ; "GMT", case-sensitive
1706
1707  time-of-day  = hour ":" minute ":" second
1708                 ; 00:00:00 - 23:59:59
1709                 
1710  hour         = 2DIGIT               
1711  minute       = 2DIGIT               
1712  second       = 2DIGIT               
1713]]></artwork></figure>
1714<t>
1715  The semantics of <xref target="preferred.date.format" format="none">day-name</xref>, <xref target="preferred.date.format" format="none">day</xref>,
1716  <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
1717  same as those defined for the RFC 5322 constructs
1718  with the corresponding name (<xref target="RFC5322"/>, Section 3.3).
1719</t>
1720<t anchor="obsolete.date.formats">
1721 
1722 
1723 
1724 
1725 
1726 
1727 
1728 
1729  Obsolete formats:
1730</t>
1731<figure><iref primary="true" item="Grammar" subitem="obs-date"/><artwork type="abnf2616"><![CDATA[
1732  obs-date     = rfc850-date / asctime-date
1733]]></artwork></figure>
1734<figure><iref primary="true" item="Grammar" subitem="rfc850-date"/><artwork type="abnf2616"><![CDATA[
1735  rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
1736  date2        = day "-" month "-" 2DIGIT
1737                 ; day-month-year (e.g., 02-Jun-82)
1738
1739  day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
1740         / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
1741         / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
1742         / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
1743         / %x46.72.69.64.61.79 ; "Friday", case-sensitive
1744         / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
1745         / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
1746]]></artwork></figure>
1747<figure><iref primary="true" item="Grammar" subitem="asctime-date"/><artwork type="abnf2616"><![CDATA[
1748  asctime-date = day-name SP date3 SP time-of-day SP year
1749  date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
1750                 ; month day (e.g., Jun  2)
1751]]></artwork></figure>
1752<t><list>
1753  <t>
1754    Note: Recipients of date values are encouraged to be robust in
1755    accepting date values that may have been sent by non-HTTP
1756    applications, as is sometimes the case when retrieving or posting
1757    messages via proxies/gateways to SMTP or NNTP.
1758  </t>
1759</list></t>
1760<t><list>
1761  <t>
1762    Note: HTTP requirements for the date/time stamp format apply only
1763    to their usage within the protocol stream. Clients and servers are
1764    not required to use these formats for user presentation, request
1765    logging, etc.
1766  </t>
1767</list></t>
1768</section>
1769
1770<section title="Transfer Codings" anchor="transfer.codings">
1771 
1772 
1773<t>
1774   Transfer-coding values are used to indicate an encoding
1775   transformation that has been, can be, or may need to be applied to an
1776   entity-body in order to ensure "safe transport" through the network.
1777   This differs from a content coding in that the transfer-coding is a
1778   property of the message, not of the original entity.
1779</t>
1780<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
1781  transfer-coding         = "chunked" ; Section 6.2.1
1782                          / "compress" ; Section 6.2.2.1
1783                          / "deflate" ; Section 6.2.2.2
1784                          / "gzip" ; Section 6.2.2.3
1785                          / transfer-extension
1786  transfer-extension      = token *( OWS ";" OWS transfer-parameter )
1787]]></artwork></figure>
1788<t anchor="rule.parameter">
1789 
1790 
1791 
1792   Parameters are in  the form of attribute/value pairs.
1793</t>
1794<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[
1795  transfer-parameter      = attribute BWS "=" BWS value
1796  attribute               = token
1797  value                   = token / quoted-string
1798]]></artwork></figure>
1799<t>
1800   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1801   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1802   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1803</t>
1804<t>
1805   Whenever a transfer-coding is applied to a message-body, the set of
1806   transfer-codings MUST include "chunked", unless the message indicates it
1807   is terminated by closing the connection. When the "chunked" transfer-coding
1808   is used, it MUST be the last transfer-coding applied to the
1809   message-body. The "chunked" transfer-coding MUST NOT be applied more
1810   than once to a message-body. These rules allow the recipient to
1811   determine the transfer-length of the message (<xref target="message.length"/>).
1812</t>
1813<t>
1814   Transfer-codings are analogous to the Content-Transfer-Encoding values of
1815   MIME, which were designed to enable safe transport of binary data over a
1816   7-bit transport service (<xref target="RFC2045"/>, Section 6).
1817   However, safe transport
1818   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1819   the only unsafe characteristic of message-bodies is the difficulty in
1820   determining the exact body length (<xref target="message.length"/>), or the desire to
1821   encrypt data over a shared transport.
1822</t>
1823<t>
1824   A server which receives an entity-body with a transfer-coding it does
1825   not understand SHOULD return 501 (Not Implemented), and close the
1826   connection. A server MUST NOT send transfer-codings to an HTTP/1.0
1827   client.
1828</t>
1829
1830<section title="Chunked Transfer Coding" anchor="chunked.encoding">
1831  <iref item="chunked (Coding Format)"/>
1832  <iref item="Coding Format" subitem="chunked"/>
1833 
1834 
1835 
1836 
1837 
1838 
1839 
1840 
1841 
1842 
1843 
1844<t>
1845   The chunked encoding modifies the body of a message in order to
1846   transfer it as a series of chunks, each with its own size indicator,
1847   followed by an OPTIONAL trailer containing entity-header fields. This
1848   allows dynamically produced content to be transferred along with the
1849   information necessary for the recipient to verify that it has
1850   received the full message.
1851</t>
1852<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[
1853  Chunked-Body   = *chunk
1854                   last-chunk
1855                   trailer-part
1856                   CRLF
1857 
1858  chunk          = chunk-size *WSP [ chunk-ext ] CRLF
1859                   chunk-data CRLF
1860  chunk-size     = 1*HEXDIG
1861  last-chunk     = 1*("0") *WSP [ chunk-ext ] CRLF
1862 
1863  chunk-ext      = *( ";" *WSP chunk-ext-name
1864                      [ "=" chunk-ext-val ] *WSP )
1865  chunk-ext-name = token
1866  chunk-ext-val  = token / quoted-str-nf
1867  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
1868  trailer-part   = *( entity-header CRLF )
1869 
1870  quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
1871                 ; like quoted-string, but disallowing line folding
1872  qdtext-nf      = WSP / %x21 / %x23-5B / %x5D-7E / obs-text
1873                 ; WSP / <VCHAR except DQUOTE and "\"> / obs-text
1874]]></artwork></figure>
1875<t>
1876   The chunk-size field is a string of hex digits indicating the size of
1877   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1878   zero, followed by the trailer, which is terminated by an empty line.
1879</t>
1880<t>
1881   The trailer allows the sender to include additional HTTP header
1882   fields at the end of the message. The Trailer header field can be
1883   used to indicate which header fields are included in a trailer (see
1884   <xref target="header.trailer"/>).
1885</t>
1886<t>
1887   A server using chunked transfer-coding in a response MUST NOT use the
1888   trailer for any header fields unless at least one of the following is
1889   true:
1890  <list style="numbers">
1891    <t>the request included a TE header field that indicates "trailers" is
1892     acceptable in the transfer-coding of the  response, as described in
1893     <xref target="header.te"/>; or,</t>
1894
1895    <t>the server is the origin server for the response, the trailer
1896     fields consist entirely of optional metadata, and the recipient
1897     could use the message (in a manner acceptable to the origin server)
1898     without receiving this metadata.  In other words, the origin server
1899     is willing to accept the possibility that the trailer fields might
1900     be silently discarded along the path to the client.</t>
1901  </list>
1902</t>
1903<t>
1904   This requirement prevents an interoperability failure when the
1905   message is being received by an HTTP/1.1 (or later) proxy and
1906   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1907   compliance with the protocol would have necessitated a possibly
1908   infinite buffer on the proxy.
1909</t>
1910<t>
1911   A process for decoding the "chunked" transfer-coding
1912   can be represented in pseudo-code as:
1913</t>
1914<figure><artwork type="code"><![CDATA[
1915  length := 0
1916  read chunk-size, chunk-ext (if any) and CRLF
1917  while (chunk-size > 0) {
1918     read chunk-data and CRLF
1919     append chunk-data to entity-body
1920     length := length + chunk-size
1921     read chunk-size and CRLF
1922  }
1923  read entity-header
1924  while (entity-header not empty) {
1925     append entity-header to existing header fields
1926     read entity-header
1927  }
1928  Content-Length := length
1929  Remove "chunked" from Transfer-Encoding
1930]]></artwork></figure>
1931<t>
1932   All HTTP/1.1 applications MUST be able to receive and decode the
1933   "chunked" transfer-coding, and MUST ignore chunk-ext extensions
1934   they do not understand.
1935</t>
1936</section>
1937
1938<section title="Compression Codings" anchor="compression.codings">
1939<t>
1940   The codings defined below can be used to compress the payload of a
1941   message.
1942</t>
1943<t><list><t>
1944   Note: Use of program names for the identification of encoding formats
1945   is not desirable and is discouraged for future encodings. Their
1946   use here is representative of historical practice, not good
1947   design.
1948</t></list></t>
1949<t><list><t>
1950   Note: For compatibility with previous implementations of HTTP,
1951   applications SHOULD consider "x-gzip" and "x-compress" to be
1952   equivalent to "gzip" and "compress" respectively.
1953</t></list></t>
1954
1955<section title="Compress Coding" anchor="compress.coding">
1956<iref item="compress (Coding Format)"/>
1957<iref item="Coding Format" subitem="compress"/>
1958<t>
1959   The "compress" format is produced by the common UNIX file compression
1960   program "compress". This format is an adaptive Lempel-Ziv-Welch
1961   coding (LZW).
1962</t>
1963</section>
1964
1965<section title="Deflate Coding" anchor="deflate.coding">
1966<iref item="deflate (Coding Format)"/>
1967<iref item="Coding Format" subitem="deflate"/>
1968<t>
1969   The "zlib" format is defined in <xref target="RFC1950"/> in combination with
1970   the "deflate" compression mechanism described in <xref target="RFC1951"/>.
1971</t>
1972</section>
1973
1974<section title="Gzip Coding" anchor="gzip.coding">
1975<iref item="gzip (Coding Format)"/>
1976<iref item="Coding Format" subitem="gzip"/>
1977<t>
1978   The "gzip" format is produced by the file compression program
1979   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
1980   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
1981</t>
1982</section>
1983
1984</section>
1985
1986<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
1987<t>
1988   The HTTP Transfer Coding Registry defines the name space for the transfer
1989   coding names.
1990</t>
1991<t>
1992   Registrations MUST include the following fields:
1993   <list style="symbols">
1994     <t>Name</t>
1995     <t>Description</t>
1996     <t>Pointer to specification text</t>
1997   </list>
1998</t>
1999<t>
2000   Values to be added to this name space require expert review and a specification
2001   (see "Expert Review" and "Specification Required" in
2002   Section 4.1 of <xref target="RFC5226"/>), and MUST
2003   conform to the purpose of transfer coding defined in this section.
2004</t>
2005<t>
2006   The registry itself is maintained at
2007   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2008</t>
2009</section>
2010</section>
2011
2012<section title="Product Tokens" anchor="product.tokens">
2013 
2014 
2015<t>
2016   Product tokens are used to allow communicating applications to
2017   identify themselves by software name and version. Most fields using
2018   product tokens also allow sub-products which form a significant part
2019   of the application to be listed, separated by whitespace. By
2020   convention, the products are listed in order of their significance
2021   for identifying the application.
2022</t>
2023<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
2024  product         = token ["/" product-version]
2025  product-version = token
2026]]></artwork></figure>
2027<t>
2028   Examples:
2029</t>
2030<figure><artwork type="example"><![CDATA[
2031  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2032  Server: Apache/0.8.4
2033]]></artwork></figure>
2034<t>
2035   Product tokens SHOULD be short and to the point. They MUST NOT be
2036   used for advertising or other non-essential information. Although any
2037   token character MAY appear in a product-version, this token SHOULD
2038   only be used for a version identifier (i.e., successive versions of
2039   the same product SHOULD only differ in the product-version portion of
2040   the product value).
2041</t>
2042</section>
2043
2044<section title="Quality Values" anchor="quality.values">
2045 
2046<t>
2047   Both transfer codings (TE request header, <xref target="header.te"/>)
2048   and content negotiation (Section 4 of <xref target="Part3"/>) use short "floating point"
2049   numbers to indicate the relative importance ("weight") of various
2050   negotiable parameters.  A weight is normalized to a real number in
2051   the range 0 through 1, where 0 is the minimum and 1 the maximum
2052   value. If a parameter has a quality value of 0, then content with
2053   this parameter is "not acceptable" for the client. HTTP/1.1
2054   applications MUST NOT generate more than three digits after the
2055   decimal point. User configuration of these values SHOULD also be
2056   limited in this fashion.
2057</t>
2058<figure><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
2059  qvalue         = ( "0" [ "." 0*3DIGIT ] )
2060                 / ( "1" [ "." 0*3("0") ] )
2061]]></artwork></figure>
2062<t><list>
2063  <t>
2064     Note: "Quality values" is a misnomer, since these values merely represent
2065     relative degradation in desired quality.
2066  </t>
2067</list></t>
2068</section>
2069
2070</section>
2071
2072<section title="Connections" anchor="connections">
2073
2074<section title="Persistent Connections" anchor="persistent.connections">
2075
2076<section title="Purpose" anchor="persistent.purpose">
2077<t>
2078   Prior to persistent connections, a separate TCP connection was
2079   established to fetch each URL, increasing the load on HTTP servers
2080   and causing congestion on the Internet. The use of inline images and
2081   other associated data often requires a client to make multiple
2082   requests of the same server in a short amount of time. Analysis of
2083   these performance problems and results from a prototype
2084   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2085   measurements of actual HTTP/1.1 implementations show good
2086   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2087   T/TCP <xref target="Tou1998"/>.
2088</t>
2089<t>
2090   Persistent HTTP connections have a number of advantages:
2091  <list style="symbols">
2092      <t>
2093        By opening and closing fewer TCP connections, CPU time is saved
2094        in routers and hosts (clients, servers, proxies, gateways,
2095        tunnels, or caches), and memory used for TCP protocol control
2096        blocks can be saved in hosts.
2097      </t>
2098      <t>
2099        HTTP requests and responses can be pipelined on a connection.
2100        Pipelining allows a client to make multiple requests without
2101        waiting for each response, allowing a single TCP connection to
2102        be used much more efficiently, with much lower elapsed time.
2103      </t>
2104      <t>
2105        Network congestion is reduced by reducing the number of packets
2106        caused by TCP opens, and by allowing TCP sufficient time to
2107        determine the congestion state of the network.
2108      </t>
2109      <t>
2110        Latency on subsequent requests is reduced since there is no time
2111        spent in TCP's connection opening handshake.
2112      </t>
2113      <t>
2114        HTTP can evolve more gracefully, since errors can be reported
2115        without the penalty of closing the TCP connection. Clients using
2116        future versions of HTTP might optimistically try a new feature,
2117        but if communicating with an older server, retry with old
2118        semantics after an error is reported.
2119      </t>
2120    </list>
2121</t>
2122<t>
2123   HTTP implementations SHOULD implement persistent connections.
2124</t>
2125</section>
2126
2127<section title="Overall Operation" anchor="persistent.overall">
2128<t>
2129   A significant difference between HTTP/1.1 and earlier versions of
2130   HTTP is that persistent connections are the default behavior of any
2131   HTTP connection. That is, unless otherwise indicated, the client
2132   SHOULD assume that the server will maintain a persistent connection,
2133   even after error responses from the server.
2134</t>
2135<t>
2136   Persistent connections provide a mechanism by which a client and a
2137   server can signal the close of a TCP connection. This signaling takes
2138   place using the Connection header field (<xref target="header.connection"/>). Once a close
2139   has been signaled, the client MUST NOT send any more requests on that
2140   connection.
2141</t>
2142
2143<section title="Negotiation" anchor="persistent.negotiation">
2144<t>
2145   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
2146   maintain a persistent connection unless a Connection header including
2147   the connection-token "close" was sent in the request. If the server
2148   chooses to close the connection immediately after sending the
2149   response, it SHOULD send a Connection header including the
2150   connection-token "close".
2151</t>
2152<t>
2153   An HTTP/1.1 client MAY expect a connection to remain open, but would
2154   decide to keep it open based on whether the response from a server
2155   contains a Connection header with the connection-token close. In case
2156   the client does not want to maintain a connection for more than that
2157   request, it SHOULD send a Connection header including the
2158   connection-token close.
2159</t>
2160<t>
2161   If either the client or the server sends the close token in the
2162   Connection header, that request becomes the last one for the
2163   connection.
2164</t>
2165<t>
2166   Clients and servers SHOULD NOT  assume that a persistent connection is
2167   maintained for HTTP versions less than 1.1 unless it is explicitly
2168   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2169   compatibility with HTTP/1.0 clients.
2170</t>
2171<t>
2172   In order to remain persistent, all messages on the connection MUST
2173   have a self-defined message length (i.e., one not defined by closure
2174   of the connection), as described in <xref target="message.length"/>.
2175</t>
2176</section>
2177
2178<section title="Pipelining" anchor="pipelining">
2179<t>
2180   A client that supports persistent connections MAY "pipeline" its
2181   requests (i.e., send multiple requests without waiting for each
2182   response). A server MUST send its responses to those requests in the
2183   same order that the requests were received.
2184</t>
2185<t>
2186   Clients which assume persistent connections and pipeline immediately
2187   after connection establishment SHOULD be prepared to retry their
2188   connection if the first pipelined attempt fails. If a client does
2189   such a retry, it MUST NOT pipeline before it knows the connection is
2190   persistent. Clients MUST also be prepared to resend their requests if
2191   the server closes the connection before sending all of the
2192   corresponding responses.
2193</t>
2194<t>
2195   Clients SHOULD NOT  pipeline requests using non-idempotent methods or
2196   non-idempotent sequences of methods (see Section 7.1.2 of <xref target="Part2"/>). Otherwise, a
2197   premature termination of the transport connection could lead to
2198   indeterminate results. A client wishing to send a non-idempotent
2199   request SHOULD wait to send that request until it has received the
2200   response status for the previous request.
2201</t>
2202</section>
2203</section>
2204
2205<section title="Proxy Servers" anchor="persistent.proxy">
2206<t>
2207   It is especially important that proxies correctly implement the
2208   properties of the Connection header field as specified in <xref target="header.connection"/>.
2209</t>
2210<t>
2211   The proxy server MUST signal persistent connections separately with
2212   its clients and the origin servers (or other proxy servers) that it
2213   connects to. Each persistent connection applies to only one transport
2214   link.
2215</t>
2216<t>
2217   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
2218   with an HTTP/1.0 client (but see Section 19.7.1 of <xref target="RFC2068"/>
2219   for information and discussion of the problems with the Keep-Alive header
2220   implemented by many HTTP/1.0 clients).
2221</t>
2222
2223<section title="End-to-end and Hop-by-hop Headers" anchor="end-to-end.and.hop-by-hop.headers">
2224<t>
2225  <cref anchor="TODO-end-to-end" source="jre">
2226    Restored from &lt;http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1&gt;.
2227    See also &lt;http://trac.tools.ietf.org/wg/httpbis/trac/ticket/60&gt;.
2228  </cref>
2229</t>
2230<t>
2231   For the purpose of defining the behavior of caches and non-caching
2232   proxies, we divide HTTP headers into two categories:
2233  <list style="symbols">
2234      <t>End-to-end headers, which are  transmitted to the ultimate
2235        recipient of a request or response. End-to-end headers in
2236        responses MUST be stored as part of a cache entry and MUST be
2237        transmitted in any response formed from a cache entry.</t>
2238
2239      <t>Hop-by-hop headers, which are meaningful only for a single
2240        transport-level connection, and are not stored by caches or
2241        forwarded by proxies.</t>
2242  </list>
2243</t>
2244<t>
2245   The following HTTP/1.1 headers are hop-by-hop headers:
2246  <list style="symbols">
2247      <t>Connection</t>
2248      <t>Keep-Alive</t>
2249      <t>Proxy-Authenticate</t>
2250      <t>Proxy-Authorization</t>
2251      <t>TE</t>
2252      <t>Trailer</t>
2253      <t>Transfer-Encoding</t>
2254      <t>Upgrade</t>
2255  </list>
2256</t>
2257<t>
2258   All other headers defined by HTTP/1.1 are end-to-end headers.
2259</t>
2260<t>
2261   Other hop-by-hop headers MUST be listed in a Connection header
2262   (<xref target="header.connection"/>).
2263</t>
2264</section>
2265
2266<section title="Non-modifiable Headers" anchor="non-modifiable.headers">
2267<t>
2268  <cref anchor="TODO-non-mod-headers" source="jre">
2269    Restored from &lt;http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2&gt;.
2270    See also &lt;http://trac.tools.ietf.org/wg/httpbis/trac/ticket/60&gt;.
2271  </cref>
2272</t>
2273<t>
2274   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2275   value of certain end-to-end headers. A transparent proxy SHOULD NOT
2276   modify an end-to-end header unless the definition of that header requires
2277   or specifically allows that.
2278</t>
2279<t>
2280   A transparent proxy MUST NOT modify any of the following fields in a
2281   request or response, and it MUST NOT add any of these fields if not
2282   already present:
2283  <list style="symbols">
2284      <t>Content-Location</t>
2285      <t>Content-MD5</t>
2286      <t>ETag</t>
2287      <t>Last-Modified</t>
2288  </list>
2289</t>
2290<t>
2291   A transparent proxy MUST NOT modify any of the following fields in a
2292   response:
2293  <list style="symbols">
2294    <t>Expires</t>
2295  </list>
2296</t>
2297<t>
2298   but it MAY add any of these fields if not already present. If an
2299   Expires header is added, it MUST be given a field-value identical to
2300   that of the Date header in that response.
2301</t>
2302<t>
2303   A proxy MUST NOT modify or add any of the following fields in a
2304   message that contains the no-transform cache-control directive, or in
2305   any request:
2306  <list style="symbols">
2307    <t>Content-Encoding</t>
2308    <t>Content-Range</t>
2309    <t>Content-Type</t>
2310  </list>
2311</t>
2312<t>
2313   A non-transparent proxy MAY modify or add these fields to a message
2314   that does not include no-transform, but if it does so, it MUST add a
2315   Warning 214 (Transformation applied) if one does not already appear
2316   in the message (see Section 3.6 of <xref target="Part6"/>).
2317</t>
2318<t><list>
2319  <t>
2320    Warning: Unnecessary modification of end-to-end headers might
2321    cause authentication failures if stronger authentication
2322    mechanisms are introduced in later versions of HTTP. Such
2323    authentication mechanisms MAY rely on the values of header fields
2324    not listed here.
2325  </t>
2326</list></t>
2327<t>
2328   The Content-Length field of a request or response is added or deleted
2329   according to the rules in <xref target="message.length"/>. A transparent proxy MUST
2330   preserve the entity-length (Section 3.2.2 of <xref target="Part3"/>) of the entity-body,
2331   although it MAY change the transfer-length (<xref target="message.length"/>).
2332</t>
2333</section>
2334
2335</section>
2336
2337<section title="Practical Considerations" anchor="persistent.practical">
2338<t>
2339   Servers will usually have some time-out value beyond which they will
2340   no longer maintain an inactive connection. Proxy servers might make
2341   this a higher value since it is likely that the client will be making
2342   more connections through the same server. The use of persistent
2343   connections places no requirements on the length (or existence) of
2344   this time-out for either the client or the server.
2345</t>
2346<t>
2347   When a client or server wishes to time-out it SHOULD issue a graceful
2348   close on the transport connection. Clients and servers SHOULD both
2349   constantly watch for the other side of the transport close, and
2350   respond to it as appropriate. If a client or server does not detect
2351   the other side's close promptly it could cause unnecessary resource
2352   drain on the network.
2353</t>
2354<t>
2355   A client, server, or proxy MAY close the transport connection at any
2356   time. For example, a client might have started to send a new request
2357   at the same time that the server has decided to close the "idle"
2358   connection. From the server's point of view, the connection is being
2359   closed while it was idle, but from the client's point of view, a
2360   request is in progress.
2361</t>
2362<t>
2363   This means that clients, servers, and proxies MUST be able to recover
2364   from asynchronous close events. Client software SHOULD reopen the
2365   transport connection and retransmit the aborted sequence of requests
2366   without user interaction so long as the request sequence is
2367   idempotent (see Section 7.1.2 of <xref target="Part2"/>). Non-idempotent methods or sequences
2368   MUST NOT be automatically retried, although user agents MAY offer a
2369   human operator the choice of retrying the request(s). Confirmation by
2370   user-agent software with semantic understanding of the application
2371   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2372   be repeated if the second sequence of requests fails.
2373</t>
2374<t>
2375   Servers SHOULD always respond to at least one request per connection,
2376   if at all possible. Servers SHOULD NOT  close a connection in the
2377   middle of transmitting a response, unless a network or client failure
2378   is suspected.
2379</t>
2380<t>
2381   Clients (including proxies) SHOULD limit the number of simultaneous
2382   connections that they maintain to a given server (including proxies).
2383</t>
2384<t>
2385   Previous revisions of HTTP gave a specific number of connections as a
2386   ceiling, but this was found to be impractical for many applications. As a
2387   result, this specification does not mandate a particular maximum number of
2388   connections, but instead encourages clients to be conservative when opening
2389   multiple connections.
2390</t>
2391<t>
2392   In particular, while using multiple connections avoids the "head-of-line
2393   blocking" problem (whereby a request that takes significant server-side
2394   processing and/or has a large payload can block subsequent requests on the
2395   same connection), each connection used consumes server resources (sometimes
2396   significantly), and furthermore using multiple connections can cause
2397   undesirable side effects in congested networks.
2398</t>
2399<t>
2400   Note that servers might reject traffic that they deem abusive, including an
2401   excessive number of connections from a client.
2402</t>
2403</section>
2404</section>
2405
2406<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2407
2408<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2409<t>
2410   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2411   flow control mechanisms to resolve temporary overloads, rather than
2412   terminating connections with the expectation that clients will retry.
2413   The latter technique can exacerbate network congestion.
2414</t>
2415</section>
2416
2417<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2418<t>
2419   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2420   the network connection for an error status while it is transmitting
2421   the request. If the client sees an error status, it SHOULD
2422   immediately cease transmitting the body. If the body is being sent
2423   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2424   empty trailer MAY be used to prematurely mark the end of the message.
2425   If the body was preceded by a Content-Length header, the client MUST
2426   close the connection.
2427</t>
2428</section>
2429
2430<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2431<t>
2432   The purpose of the 100 (Continue) status (see Section 8.1.1 of <xref target="Part2"/>) is to
2433   allow a client that is sending a request message with a request body
2434   to determine if the origin server is willing to accept the request
2435   (based on the request headers) before the client sends the request
2436   body. In some cases, it might either be inappropriate or highly
2437   inefficient for the client to send the body if the server will reject
2438   the message without looking at the body.
2439</t>
2440<t>
2441   Requirements for HTTP/1.1 clients:
2442  <list style="symbols">
2443    <t>
2444        If a client will wait for a 100 (Continue) response before
2445        sending the request body, it MUST send an Expect request-header
2446        field (Section 9.2 of <xref target="Part2"/>) with the "100-continue" expectation.
2447    </t>
2448    <t>
2449        A client MUST NOT send an Expect request-header field (Section 9.2 of <xref target="Part2"/>)
2450        with the "100-continue" expectation if it does not intend
2451        to send a request body.
2452    </t>
2453  </list>
2454</t>
2455<t>
2456   Because of the presence of older implementations, the protocol allows
2457   ambiguous situations in which a client may send "Expect: 100-continue"
2458   without receiving either a 417 (Expectation Failed) status
2459   or a 100 (Continue) status. Therefore, when a client sends this
2460   header field to an origin server (possibly via a proxy) from which it
2461   has never seen a 100 (Continue) status, the client SHOULD NOT  wait
2462   for an indefinite period before sending the request body.
2463</t>
2464<t>
2465   Requirements for HTTP/1.1 origin servers:
2466  <list style="symbols">
2467    <t> Upon receiving a request which includes an Expect request-header
2468        field with the "100-continue" expectation, an origin server MUST
2469        either respond with 100 (Continue) status and continue to read
2470        from the input stream, or respond with a final status code. The
2471        origin server MUST NOT wait for the request body before sending
2472        the 100 (Continue) response. If it responds with a final status
2473        code, it MAY close the transport connection or it MAY continue
2474        to read and discard the rest of the request.  It MUST NOT
2475        perform the requested method if it returns a final status code.
2476    </t>
2477    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2478        the request message does not include an Expect request-header
2479        field with the "100-continue" expectation, and MUST NOT send a
2480        100 (Continue) response if such a request comes from an HTTP/1.0
2481        (or earlier) client. There is an exception to this rule: for
2482        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2483        status in response to an HTTP/1.1 PUT or POST request that does
2484        not include an Expect request-header field with the "100-continue"
2485        expectation. This exception, the purpose of which is
2486        to minimize any client processing delays associated with an
2487        undeclared wait for 100 (Continue) status, applies only to
2488        HTTP/1.1 requests, and not to requests with any other HTTP-version
2489        value.
2490    </t>
2491    <t> An origin server MAY omit a 100 (Continue) response if it has
2492        already received some or all of the request body for the
2493        corresponding request.
2494    </t>
2495    <t> An origin server that sends a 100 (Continue) response MUST
2496    ultimately send a final status code, once the request body is
2497        received and processed, unless it terminates the transport
2498        connection prematurely.
2499    </t>
2500    <t> If an origin server receives a request that does not include an
2501        Expect request-header field with the "100-continue" expectation,
2502        the request includes a request body, and the server responds
2503        with a final status code before reading the entire request body
2504        from the transport connection, then the server SHOULD NOT  close
2505        the transport connection until it has read the entire request,
2506        or until the client closes the connection. Otherwise, the client
2507        might not reliably receive the response message. However, this
2508        requirement is not be construed as preventing a server from
2509        defending itself against denial-of-service attacks, or from
2510        badly broken client implementations.
2511      </t>
2512    </list>
2513</t>
2514<t>
2515   Requirements for HTTP/1.1 proxies:
2516  <list style="symbols">
2517    <t> If a proxy receives a request that includes an Expect request-header
2518        field with the "100-continue" expectation, and the proxy
2519        either knows that the next-hop server complies with HTTP/1.1 or
2520        higher, or does not know the HTTP version of the next-hop
2521        server, it MUST forward the request, including the Expect header
2522        field.
2523    </t>
2524    <t> If the proxy knows that the version of the next-hop server is
2525        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2526        respond with a 417 (Expectation Failed) status.
2527    </t>
2528    <t> Proxies SHOULD maintain a cache recording the HTTP version
2529        numbers received from recently-referenced next-hop servers.
2530    </t>
2531    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2532        request message was received from an HTTP/1.0 (or earlier)
2533        client and did not include an Expect request-header field with
2534        the "100-continue" expectation. This requirement overrides the
2535        general rule for forwarding of 1xx responses (see Section 8.1 of <xref target="Part2"/>).
2536    </t>
2537  </list>
2538</t>
2539</section>
2540
2541<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2542<t>
2543   If an HTTP/1.1 client sends a request which includes a request body,
2544   but which does not include an Expect request-header field with the
2545   "100-continue" expectation, and if the client is not directly
2546   connected to an HTTP/1.1 origin server, and if the client sees the
2547   connection close before receiving any status from the server, the
2548   client SHOULD retry the request.  If the client does retry this
2549   request, it MAY use the following "binary exponential backoff"
2550   algorithm to be assured of obtaining a reliable response:
2551  <list style="numbers">
2552    <t>
2553      Initiate a new connection to the server
2554    </t>
2555    <t>
2556      Transmit the request-headers
2557    </t>
2558    <t>
2559      Initialize a variable R to the estimated round-trip time to the
2560         server (e.g., based on the time it took to establish the
2561         connection), or to a constant value of 5 seconds if the round-trip
2562         time is not available.
2563    </t>
2564    <t>
2565       Compute T = R * (2**N), where N is the number of previous
2566         retries of this request.
2567    </t>
2568    <t>
2569       Wait either for an error response from the server, or for T
2570         seconds (whichever comes first)
2571    </t>
2572    <t>
2573       If no error response is received, after T seconds transmit the
2574         body of the request.
2575    </t>
2576    <t>
2577       If client sees that the connection is closed prematurely,
2578         repeat from step 1 until the request is accepted, an error
2579         response is received, or the user becomes impatient and
2580         terminates the retry process.
2581    </t>
2582  </list>
2583</t>
2584<t>
2585   If at any point an error status is received, the client
2586  <list style="symbols">
2587      <t>SHOULD NOT  continue and</t>
2588
2589      <t>SHOULD close the connection if it has not completed sending the
2590        request message.</t>
2591    </list>
2592</t>
2593</section>
2594</section>
2595</section>
2596
2597
2598<section title="Miscellaneous notes that may disappear" anchor="misc">
2599<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2600<t>
2601   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2602</t>
2603</section>
2604
2605<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2606<t>
2607   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2608</t>
2609</section>
2610
2611<section title="Interception of HTTP for access control" anchor="http.intercept">
2612<t>
2613   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2614</t>
2615</section>
2616
2617<section title="Use of HTTP by other protocols" anchor="http.others">
2618<t>
2619   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2620   Extensions of HTTP like WebDAV.</cref>
2621</t>
2622
2623</section>
2624<section title="Use of HTTP by media type specification" anchor="http.media">
2625<t>
2626   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2627</t>
2628</section>
2629</section>
2630
2631<section title="Header Field Definitions" anchor="header.field.definitions">
2632<t>
2633   This section defines the syntax and semantics of HTTP/1.1 header fields
2634   related to message framing and transport protocols.
2635</t>
2636<t>
2637   For entity-header fields, both sender and recipient refer to either the
2638   client or the server, depending on who sends and who receives the entity.
2639</t>
2640
2641<section title="Connection" anchor="header.connection">
2642  <iref primary="true" item="Connection header"/>
2643  <iref primary="true" item="Headers" subitem="Connection"/>
2644 
2645 
2646 
2647<t>
2648   The "Connection" general-header field allows the sender to specify
2649   options that are desired for that particular connection and MUST NOT
2650   be communicated by proxies over further connections.
2651</t>
2652<t>
2653   The Connection header's value has the following grammar:
2654</t>
2655<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[
2656  Connection       = "Connection" ":" OWS Connection-v
2657  Connection-v     = 1#connection-token
2658  connection-token = token
2659]]></artwork></figure>
2660<t>
2661   HTTP/1.1 proxies MUST parse the Connection header field before a
2662   message is forwarded and, for each connection-token in this field,
2663   remove any header field(s) from the message with the same name as the
2664   connection-token. Connection options are signaled by the presence of
2665   a connection-token in the Connection header field, not by any
2666   corresponding additional header field(s), since the additional header
2667   field may not be sent if there are no parameters associated with that
2668   connection option.
2669</t>
2670<t>
2671   Message headers listed in the Connection header MUST NOT include
2672   end-to-end headers, such as Cache-Control.
2673</t>
2674<t>
2675   HTTP/1.1 defines the "close" connection option for the sender to
2676   signal that the connection will be closed after completion of the
2677   response. For example,
2678</t>
2679<figure><artwork type="example"><![CDATA[
2680  Connection: close
2681]]></artwork></figure>
2682<t>
2683   in either the request or the response header fields indicates that
2684   the connection SHOULD NOT  be considered "persistent" (<xref target="persistent.connections"/>)
2685   after the current request/response is complete.
2686</t>
2687<t>
2688   An HTTP/1.1 client that does not support persistent connections MUST
2689   include the "close" connection option in every request message.
2690</t>
2691<t>
2692   An HTTP/1.1 server that does not support persistent connections MUST
2693   include the "close" connection option in every response message that
2694   does not have a 1xx (Informational) status code.
2695</t>
2696<t>
2697   A system receiving an HTTP/1.0 (or lower-version) message that
2698   includes a Connection header MUST, for each connection-token in this
2699   field, remove and ignore any header field(s) from the message with
2700   the same name as the connection-token. This protects against mistaken
2701   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2702</t>
2703</section>
2704
2705<section title="Content-Length" anchor="header.content-length">
2706  <iref primary="true" item="Content-Length header"/>
2707  <iref primary="true" item="Headers" subitem="Content-Length"/>
2708 
2709 
2710<t>
2711   The "Content-Length" entity-header field indicates the size of the
2712   entity-body, in number of OCTETs. In the case of responses to the HEAD
2713   method, it indicates the size of the entity-body that would have been sent
2714   had the request been a GET.
2715</t>
2716<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><iref primary="true" item="Grammar" subitem="Content-Length-v"/><artwork type="abnf2616"><![CDATA[
2717  Content-Length   = "Content-Length" ":" OWS 1*Content-Length-v
2718  Content-Length-v = 1*DIGIT
2719]]></artwork></figure>
2720<t>
2721   An example is
2722</t>
2723<figure><artwork type="example"><![CDATA[
2724  Content-Length: 3495
2725]]></artwork></figure>
2726<t>
2727   Applications SHOULD use this field to indicate the transfer-length of
2728   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2729</t>
2730<t>
2731   Any Content-Length greater than or equal to zero is a valid value.
2732   <xref target="message.length"/> describes how to determine the length of a message-body
2733   if a Content-Length is not given.
2734</t>
2735<t>
2736   Note that the meaning of this field is significantly different from
2737   the corresponding definition in MIME, where it is an optional field
2738   used within the "message/external-body" content-type. In HTTP, it
2739   SHOULD be sent whenever the message's length can be determined prior
2740   to being transferred, unless this is prohibited by the rules in
2741   <xref target="message.length"/>.
2742</t>
2743</section>
2744
2745<section title="Date" anchor="header.date">
2746  <iref primary="true" item="Date header"/>
2747  <iref primary="true" item="Headers" subitem="Date"/>
2748 
2749 
2750<t>
2751   The "Date" general-header field represents the date and time at which
2752   the message was originated, having the same semantics as the Origination
2753   Date Field (orig-date) defined in Section 3.6.1 of <xref target="RFC5322"/>.
2754   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
2755   it MUST be sent in rfc1123-date format.
2756</t>
2757<figure><iref primary="true" item="Grammar" subitem="Date"/><iref primary="true" item="Grammar" subitem="Date-v"/><artwork type="abnf2616"><![CDATA[
2758  Date   = "Date" ":" OWS Date-v
2759  Date-v = HTTP-date
2760]]></artwork></figure>
2761<t>
2762   An example is
2763</t>
2764<figure><artwork type="example"><![CDATA[
2765  Date: Tue, 15 Nov 1994 08:12:31 GMT
2766]]></artwork></figure>
2767<t>
2768   Origin servers MUST include a Date header field in all responses,
2769   except in these cases:
2770  <list style="numbers">
2771      <t>If the response status code is 100 (Continue) or 101 (Switching
2772         Protocols), the response MAY include a Date header field, at
2773         the server's option.</t>
2774
2775      <t>If the response status code conveys a server error, e.g., 500
2776         (Internal Server Error) or 503 (Service Unavailable), and it is
2777         inconvenient or impossible to generate a valid Date.</t>
2778
2779      <t>If the server does not have a clock that can provide a
2780         reasonable approximation of the current time, its responses
2781         MUST NOT include a Date header field. In this case, the rules
2782         in <xref target="clockless.origin.server.operation"/> MUST be followed.</t>
2783  </list>
2784</t>
2785<t>
2786   A received message that does not have a Date header field MUST be
2787   assigned one by the recipient if the message will be cached by that
2788   recipient or gatewayed via a protocol which requires a Date. An HTTP
2789   implementation without a clock MUST NOT cache responses without
2790   revalidating them on every use. An HTTP cache, especially a shared
2791   cache, SHOULD use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2792   clock with a reliable external standard.
2793</t>
2794<t>
2795   Clients SHOULD only send a Date header field in messages that include
2796   an entity-body, as in the case of the PUT and POST requests, and even
2797   then it is optional. A client without a clock MUST NOT send a Date
2798   header field in a request.
2799</t>
2800<t>
2801   The HTTP-date sent in a Date header SHOULD NOT  represent a date and
2802   time subsequent to the generation of the message. It SHOULD represent
2803   the best available approximation of the date and time of message
2804   generation, unless the implementation has no means of generating a
2805   reasonably accurate date and time. In theory, the date ought to
2806   represent the moment just before the entity is generated. In
2807   practice, the date can be generated at any time during the message
2808   origination without affecting its semantic value.
2809</t>
2810
2811<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2812<t>
2813   Some origin server implementations might not have a clock available.
2814   An origin server without a clock MUST NOT assign Expires or Last-Modified
2815   values to a response, unless these values were associated
2816   with the resource by a system or user with a reliable clock. It MAY
2817   assign an Expires value that is known, at or before server
2818   configuration time, to be in the past (this allows "pre-expiration"
2819   of responses without storing separate Expires values for each
2820   resource).
2821</t>
2822</section>
2823</section>
2824
2825<section title="Host" anchor="header.host">
2826  <iref primary="true" item="Host header"/>
2827  <iref primary="true" item="Headers" subitem="Host"/>
2828 
2829 
2830<t>
2831   The "Host" request-header field specifies the Internet host and port
2832   number of the resource being requested, allowing the origin server or
2833   gateway to differentiate between internally-ambiguous URLs, such as the root
2834   "/" URL of a server for multiple host names on a single IP address.
2835</t>
2836<t>   
2837   The Host field value MUST represent the naming authority of the origin
2838   server or gateway given by the original URL obtained from the user or
2839   referring resource (generally an http URI, as described in
2840   <xref target="http.uri"/>).
2841</t>
2842<figure><iref primary="true" item="Grammar" subitem="Host"/><iref primary="true" item="Grammar" subitem="Host-v"/><artwork type="abnf2616"><![CDATA[
2843  Host   = "Host" ":" OWS Host-v
2844  Host-v = uri-host [ ":" port ] ; Section 2.6.1
2845]]></artwork></figure>
2846<t>
2847   A "host" without any trailing port information implies the default
2848   port for the service requested (e.g., "80" for an HTTP URL). For
2849   example, a request on the origin server for
2850   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2851</t>
2852<figure><artwork type="example"><![CDATA[
2853  GET /pub/WWW/ HTTP/1.1
2854  Host: www.example.org
2855]]></artwork></figure>
2856<t>
2857   A client MUST include a Host header field in all HTTP/1.1 request
2858   messages. If the requested URI does not include an Internet host
2859   name for the service being requested, then the Host header field MUST
2860   be given with an empty value. An HTTP/1.1 proxy MUST ensure that any
2861   request message it forwards does contain an appropriate Host header
2862   field that identifies the service being requested by the proxy. All
2863   Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
2864   status code to any HTTP/1.1 request message which lacks a Host header
2865   field.
2866</t>
2867<t>
2868   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2869   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2870   for other requirements relating to Host.
2871</t>
2872</section>
2873
2874<section title="TE" anchor="header.te">
2875  <iref primary="true" item="TE header"/>
2876  <iref primary="true" item="Headers" subitem="TE"/>
2877 
2878 
2879 
2880 
2881 
2882<t>
2883   The "TE" request-header field indicates what extension transfer-codings
2884   it is willing to accept in the response, and whether or not it is
2885   willing to accept trailer fields in a chunked transfer-coding.
2886</t>
2887<t>
2888   Its value may consist of the keyword "trailers" and/or a comma-separated
2889   list of extension transfer-coding names with optional accept
2890   parameters (as described in <xref target="transfer.codings"/>).
2891</t>
2892<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[
2893  TE        = "TE" ":" OWS TE-v
2894  TE-v      = #t-codings
2895  t-codings = "trailers" / ( transfer-extension [ te-params ] )
2896  te-params = OWS ";" OWS "q=" qvalue *( te-ext )
2897  te-ext    = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
2898]]></artwork></figure>
2899<t>
2900   The presence of the keyword "trailers" indicates that the client is
2901   willing to accept trailer fields in a chunked transfer-coding, as
2902   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
2903   transfer-coding values even though it does not itself represent a
2904   transfer-coding.
2905</t>
2906<t>
2907   Examples of its use are:
2908</t>
2909<figure><artwork type="example"><![CDATA[
2910  TE: deflate
2911  TE:
2912  TE: trailers, deflate;q=0.5
2913]]></artwork></figure>
2914<t>
2915   The TE header field only applies to the immediate connection.
2916   Therefore, the keyword MUST be supplied within a Connection header
2917   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2918</t>
2919<t>
2920   A server tests whether a transfer-coding is acceptable, according to
2921   a TE field, using these rules:
2922  <list style="numbers">
2923    <t>The "chunked" transfer-coding is always acceptable. If the
2924         keyword "trailers" is listed, the client indicates that it is
2925         willing to accept trailer fields in the chunked response on
2926         behalf of itself and any downstream clients. The implication is
2927         that, if given, the client is stating that either all
2928         downstream clients are willing to accept trailer fields in the
2929         forwarded response, or that it will attempt to buffer the
2930         response on behalf of downstream recipients.
2931      <vspace blankLines="1"/>
2932         Note: HTTP/1.1 does not define any means to limit the size of a
2933         chunked response such that a client can be assured of buffering
2934         the entire response.</t>
2935    <t>If the transfer-coding being tested is one of the transfer-codings
2936         listed in the TE field, then it is acceptable unless it
2937         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
2938         qvalue of 0 means "not acceptable.")</t>
2939    <t>If multiple transfer-codings are acceptable, then the
2940         acceptable transfer-coding with the highest non-zero qvalue is
2941         preferred.  The "chunked" transfer-coding always has a qvalue
2942         of 1.</t>
2943  </list>
2944</t>
2945<t>
2946   If the TE field-value is empty or if no TE field is present, the only
2947   transfer-coding is "chunked". A message with no transfer-coding is
2948   always acceptable.
2949</t>
2950</section>
2951
2952<section title="Trailer" anchor="header.trailer">
2953  <iref primary="true" item="Trailer header"/>
2954  <iref primary="true" item="Headers" subitem="Trailer"/>
2955 
2956 
2957<t>
2958   The "Trailer" general-header field indicates that the given set of
2959   header fields is present in the trailer of a message encoded with
2960   chunked transfer-coding.
2961</t>
2962<figure><iref primary="true" item="Grammar" subitem="Trailer"/><iref primary="true" item="Grammar" subitem="Trailer-v"/><artwork type="abnf2616"><![CDATA[
2963  Trailer   = "Trailer" ":" OWS Trailer-v
2964  Trailer-v = 1#field-name
2965]]></artwork></figure>
2966<t>
2967   An HTTP/1.1 message SHOULD include a Trailer header field in a
2968   message using chunked transfer-coding with a non-empty trailer. Doing
2969   so allows the recipient to know which header fields to expect in the
2970   trailer.
2971</t>
2972<t>
2973   If no Trailer header field is present, the trailer SHOULD NOT  include
2974   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
2975   trailer fields in a "chunked" transfer-coding.
2976</t>
2977<t>
2978   Message header fields listed in the Trailer header field MUST NOT
2979   include the following header fields:
2980  <list style="symbols">
2981    <t>Transfer-Encoding</t>
2982    <t>Content-Length</t>
2983    <t>Trailer</t>
2984  </list>
2985</t>
2986</section>
2987
2988<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2989  <iref primary="true" item="Transfer-Encoding header"/>
2990  <iref primary="true" item="Headers" subitem="Transfer-Encoding"/>
2991 
2992 
2993<t>
2994   The "Transfer-Encoding" general-header field indicates what transfer-codings
2995   (if any) have been applied to the message body. It differs from
2996   Content-Encoding (Section 2.2 of <xref target="Part3"/>) in that transfer-codings are a property
2997   of the message (and therefore are removed by intermediaries), whereas
2998   content-codings are not.
2999</t>
3000<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><iref primary="true" item="Grammar" subitem="Transfer-Encoding-v"/><artwork type="abnf2616"><![CDATA[
3001  Transfer-Encoding   = "Transfer-Encoding" ":" OWS
3002                        Transfer-Encoding-v
3003  Transfer-Encoding-v = 1#transfer-coding
3004]]></artwork></figure>
3005<t>
3006   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3007</t>
3008<figure><artwork type="example"><![CDATA[
3009  Transfer-Encoding: chunked
3010]]></artwork></figure>
3011<t>
3012   If multiple encodings have been applied to an entity, the transfer-codings
3013   MUST be listed in the order in which they were applied.
3014   Additional information about the encoding parameters MAY be provided
3015   by other entity-header fields not defined by this specification.
3016</t>
3017<t>
3018   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3019   header.
3020</t>
3021</section>
3022
3023<section title="Upgrade" anchor="header.upgrade">
3024  <iref primary="true" item="Upgrade header"/>
3025  <iref primary="true" item="Headers" subitem="Upgrade"/>
3026 
3027 
3028<t>
3029   The "Upgrade" general-header field allows the client to specify what
3030   additional communication protocols it would like to use, if the server
3031   chooses to switch protocols. Additionally, the server MUST use the Upgrade
3032   header field within a 101 (Switching Protocols) response to indicate which
3033   protocol(s) are being switched to.
3034</t>
3035<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><iref primary="true" item="Grammar" subitem="Upgrade-v"/><artwork type="abnf2616"><![CDATA[
3036  Upgrade   = "Upgrade" ":" OWS Upgrade-v
3037  Upgrade-v = 1#product
3038]]></artwork></figure>
3039<t>
3040   For example,
3041</t>
3042<figure><artwork type="example"><![CDATA[
3043  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3044]]></artwork></figure>
3045<t>
3046   The Upgrade header field is intended to provide a simple mechanism
3047   for transition from HTTP/1.1 to some other, incompatible protocol. It
3048   does so by allowing the client to advertise its desire to use another
3049   protocol, such as a later version of HTTP with a higher major version
3050   number, even though the current request has been made using HTTP/1.1.
3051   This eases the difficult transition between incompatible protocols by
3052   allowing the client to initiate a request in the more commonly
3053   supported protocol while indicating to the server that it would like
3054   to use a "better" protocol if available (where "better" is determined
3055   by the server, possibly according to the nature of the method and/or
3056   resource being requested).
3057</t>
3058<t>
3059   The Upgrade header field only applies to switching application-layer
3060   protocols upon the existing transport-layer connection. Upgrade
3061   cannot be used to insist on a protocol change; its acceptance and use
3062   by the server is optional. The capabilities and nature of the
3063   application-layer communication after the protocol change is entirely
3064   dependent upon the new protocol chosen, although the first action
3065   after changing the protocol MUST be a response to the initial HTTP
3066   request containing the Upgrade header field.
3067</t>
3068<t>
3069   The Upgrade header field only applies to the immediate connection.
3070   Therefore, the upgrade keyword MUST be supplied within a Connection
3071   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3072   HTTP/1.1 message.
3073</t>
3074<t>
3075   The Upgrade header field cannot be used to indicate a switch to a
3076   protocol on a different connection. For that purpose, it is more
3077   appropriate to use a 301, 302, 303, or 305 redirection response.
3078</t>
3079<t>
3080   This specification only defines the protocol name "HTTP" for use by
3081   the family of Hypertext Transfer Protocols, as defined by the HTTP
3082   version rules of <xref target="http.version"/> and future updates to this
3083   specification. Additional tokens can be registered with IANA using the
3084   registration procedure defined below. 
3085</t>
3086
3087<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3088<t>
3089   The HTTP Upgrade Token Registry defines the name space for product
3090   tokens used to identify protocols in the Upgrade header field.
3091   Each registered token should be associated with one or a set of
3092   specifications, and with contact information.
3093</t>
3094<t>
3095   Registrations should be allowed on a First Come First Served basis as
3096   described in Section 4.1 of <xref target="RFC5226"/>. These
3097   specifications need not be IETF documents or be subject to IESG review, but
3098   should obey the following rules:
3099  <list style="numbers">
3100    <t>A token, once registered, stays registered forever.</t>
3101    <t>The registration MUST name a responsible party for the
3102       registration.</t>
3103    <t>The registration MUST name a point of contact.</t>
3104    <t>The registration MAY name the documentation required for the
3105       token.</t>
3106    <t>The responsible party MAY change the registration at any time.
3107       The IANA will keep a record of all such changes, and make them
3108       available upon request.</t>
3109    <t>The responsible party for the first registration of a "product"
3110       token MUST approve later registrations of a "version" token
3111       together with that "product" token before they can be registered.</t>
3112    <t>If absolutely required, the IESG MAY reassign the responsibility
3113       for a token. This will normally only be used in the case when a
3114       responsible party cannot be contacted.</t>
3115  </list>
3116</t>
3117<t>
3118   It is not required that specifications for upgrade tokens be made
3119   publicly available, but the contact information for the registration
3120   should be.
3121</t>
3122</section>
3123
3124
3125</section>
3126
3127<section title="Via" anchor="header.via">
3128  <iref primary="true" item="Via header"/>
3129  <iref primary="true" item="Headers" subitem="Via"/>
3130 
3131 
3132 
3133 
3134 
3135 
3136 
3137<t>
3138   The "Via" general-header field MUST be used by gateways and proxies to
3139   indicate the intermediate protocols and recipients between the user
3140   agent and the server on requests, and between the origin server and
3141   the client on responses. It is analogous to the "Received" field defined in
3142   Section 3.6.7 of <xref target="RFC5322"/> and is intended to be used for tracking message forwards,
3143   avoiding request loops, and identifying the protocol capabilities of
3144   all senders along the request/response chain.
3145</t>
3146<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[
3147  Via               = "Via" ":" OWS Via-v
3148  Via-v             = 1#( received-protocol RWS received-by
3149                          [ RWS comment ] )
3150  received-protocol = [ protocol-name "/" ] protocol-version
3151  protocol-name     = token
3152  protocol-version  = token
3153  received-by       = ( uri-host [ ":" port ] ) / pseudonym
3154  pseudonym         = token
3155]]></artwork></figure>
3156<t>
3157   The received-protocol indicates the protocol version of the message
3158   received by the server or client along each segment of the
3159   request/response chain. The received-protocol version is appended to
3160   the Via field value when the message is forwarded so that information
3161   about the protocol capabilities of upstream applications remains
3162   visible to all recipients.
3163</t>
3164<t>
3165   The protocol-name is optional if and only if it would be "HTTP". The
3166   received-by field is normally the host and optional port number of a
3167   recipient server or client that subsequently forwarded the message.
3168   However, if the real host is considered to be sensitive information,
3169   it MAY be replaced by a pseudonym. If the port is not given, it MAY
3170   be assumed to be the default port of the received-protocol.
3171</t>
3172<t>
3173   Multiple Via field values represent each proxy or gateway that has
3174   forwarded the message. Each recipient MUST append its information
3175   such that the end result is ordered according to the sequence of
3176   forwarding applications.
3177</t>
3178<t>
3179   Comments MAY be used in the Via header field to identify the software
3180   of the recipient proxy or gateway, analogous to the User-Agent and
3181   Server header fields. However, all comments in the Via field are
3182   optional and MAY be removed by any recipient prior to forwarding the
3183   message.
3184</t>
3185<t>
3186   For example, a request message could be sent from an HTTP/1.0 user
3187   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3188   forward the request to a public proxy at p.example.net, which completes
3189   the request by forwarding it to the origin server at www.example.com.
3190   The request received by www.example.com would then have the following
3191   Via header field:
3192</t>
3193<figure><artwork type="example"><![CDATA[
3194  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3195]]></artwork></figure>
3196<t>
3197   Proxies and gateways used as a portal through a network firewall
3198   SHOULD NOT, by default, forward the names and ports of hosts within
3199   the firewall region. This information SHOULD only be propagated if
3200   explicitly enabled. If not enabled, the received-by host of any host
3201   behind the firewall SHOULD be replaced by an appropriate pseudonym
3202   for that host.
3203</t>
3204<t>
3205   For organizations that have strong privacy requirements for hiding
3206   internal structures, a proxy MAY combine an ordered subsequence of
3207   Via header field entries with identical received-protocol values into
3208   a single such entry. For example,
3209</t>
3210<figure><artwork type="example"><![CDATA[
3211  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3212]]></artwork></figure>
3213<t>
3214        could be collapsed to
3215</t>
3216<figure><artwork type="example"><![CDATA[
3217  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3218]]></artwork></figure>
3219<t>
3220   Applications SHOULD NOT  combine multiple entries unless they are all
3221   under the same organizational control and the hosts have already been
3222   replaced by pseudonyms. Applications MUST NOT combine entries which
3223   have different received-protocol values.
3224</t>
3225</section>
3226
3227</section>
3228
3229<section title="IANA Considerations" anchor="IANA.considerations">
3230
3231<section title="Message Header Registration" anchor="message.header.registration">
3232<t>
3233   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
3234   with the permanent registrations below (see <xref target="RFC3864"/>):
3235</t>
3236
3237<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3238<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3239   <ttcol>Header Field Name</ttcol>
3240   <ttcol>Protocol</ttcol>
3241   <ttcol>Status</ttcol>
3242   <ttcol>Reference</ttcol>
3243
3244   <c>Connection</c>
3245   <c>http</c>
3246   <c>standard</c>
3247   <c>
3248      <xref target="header.connection"/>
3249   </c>
3250   <c>Content-Length</c>
3251   <c>http</c>
3252   <c>standard</c>
3253   <c>
3254      <xref target="header.content-length"/>
3255   </c>
3256   <c>Date</c>
3257   <c>http</c>
3258   <c>standard</c>
3259   <c>
3260      <xref target="header.date"/>
3261   </c>
3262   <c>Host</c>
3263   <c>http</c>
3264   <c>standard</c>
3265   <c>
3266      <xref target="header.host"/>
3267   </c>
3268   <c>TE</c>
3269   <c>http</c>
3270   <c>standard</c>
3271   <c>
3272      <xref target="header.te"/>
3273   </c>
3274   <c>Trailer</c>
3275   <c>http</c>
3276   <c>standard</c>
3277   <c>
3278      <xref target="header.trailer"/>
3279   </c>
3280   <c>Transfer-Encoding</c>
3281   <c>http</c>
3282   <c>standard</c>
3283   <c>
3284      <xref target="header.transfer-encoding"/>
3285   </c>
3286   <c>Upgrade</c>
3287   <c>http</c>
3288   <c>standard</c>
3289   <c>
3290      <xref target="header.upgrade"/>
3291   </c>
3292   <c>Via</c>
3293   <c>http</c>
3294   <c>standard</c>
3295   <c>
3296      <xref target="header.via"/>
3297   </c>
3298</texttable>
3299<!--(END)-->
3300
3301<t>
3302   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3303</t>
3304</section>
3305
3306<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3307<t>
3308   The entries for the "http" and "https" URI Schemes in the registry located at
3309   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3310   should be updated to point to Sections <xref target="http.uri" format="counter"/>
3311   and <xref target="https.uri" format="counter"/> of this document
3312   (see <xref target="RFC4395"/>).
3313</t>
3314</section>
3315
3316<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3317<t>
3318   This document serves as the specification for the Internet media types
3319   "message/http" and "application/http". The following is to be registered with
3320   IANA (see <xref target="RFC4288"/>).
3321</t>
3322<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3323<iref item="Media Type" subitem="message/http" primary="true"/>
3324<iref item="message/http Media Type" primary="true"/>
3325<t>
3326   The message/http type can be used to enclose a single HTTP request or
3327   response message, provided that it obeys the MIME restrictions for all
3328   "message" types regarding line length and encodings.
3329</t>
3330<t>
3331  <list style="hanging">
3332    <t hangText="Type name:">
3333      message
3334    </t>
3335    <t hangText="Subtype name:">
3336      http
3337    </t>
3338    <t hangText="Required parameters:">
3339      none
3340    </t>
3341    <t hangText="Optional parameters:">
3342      version, msgtype
3343      <list style="hanging">
3344        <t hangText="version:">
3345          The HTTP-Version number of the enclosed message
3346          (e.g., "1.1"). If not present, the version can be
3347          determined from the first line of the body.
3348        </t>
3349        <t hangText="msgtype:">
3350          The message type -- "request" or "response". If not
3351          present, the type can be determined from the first
3352          line of the body.
3353        </t>
3354      </list>
3355    </t>
3356    <t hangText="Encoding considerations:">
3357      only "7bit", "8bit", or "binary" are permitted
3358    </t>
3359    <t hangText="Security considerations:">
3360      none
3361    </t>
3362    <t hangText="Interoperability considerations:">
3363      none
3364    </t>
3365    <t hangText="Published specification:">
3366      This specification (see <xref target="internet.media.type.message.http"/>).
3367    </t>
3368    <t hangText="Applications that use this media type:">
3369    </t>
3370    <t hangText="Additional information:">
3371      <list style="hanging">
3372        <t hangText="Magic number(s):">none</t>
3373        <t hangText="File extension(s):">none</t>
3374        <t hangText="Macintosh file type code(s):">none</t>
3375      </list>
3376    </t>
3377    <t hangText="Person and email address to contact for further information:">
3378      See Authors Section.
3379    </t>
3380    <t hangText="Intended usage:">
3381      COMMON
3382    </t>
3383    <t hangText="Restrictions on usage:">
3384      none
3385    </t>
3386    <t hangText="Author/Change controller:">
3387      IESG
3388    </t>
3389  </list>
3390</t>
3391</section>
3392<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3393<iref item="Media Type" subitem="application/http" primary="true"/>
3394<iref item="application/http Media Type" primary="true"/>
3395<t>
3396   The application/http type can be used to enclose a pipeline of one or more
3397   HTTP request or response messages (not intermixed).
3398</t>
3399<t>
3400  <list style="hanging">
3401    <t hangText="Type name:">
3402      application
3403    </t>
3404    <t hangText="Subtype name:">
3405      http
3406    </t>
3407    <t hangText="Required parameters:">
3408      none
3409    </t>
3410    <t hangText="Optional parameters:">
3411      version, msgtype
3412      <list style="hanging">
3413        <t hangText="version:">
3414          The HTTP-Version number of the enclosed messages
3415          (e.g., "1.1"). If not present, the version can be
3416          determined from the first line of the body.
3417        </t>
3418        <t hangText="msgtype:">
3419          The message type -- "request" or "response". If not
3420          present, the type can be determined from the first
3421          line of the body.
3422        </t>
3423      </list>
3424    </t>
3425    <t hangText="Encoding considerations:">
3426      HTTP messages enclosed by this type
3427      are in "binary" format; use of an appropriate
3428      Content-Transfer-Encoding is required when
3429      transmitted via E-mail.
3430    </t>
3431    <t hangText="Security considerations:">
3432      none
3433    </t>
3434    <t hangText="Interoperability considerations:">
3435      none
3436    </t>
3437    <t hangText="Published specification:">
3438      This specification (see <xref target="internet.media.type.application.http"/>).
3439    </t>
3440    <t hangText="Applications that use this media type:">
3441    </t>
3442    <t hangText="Additional information:">
3443      <list style="hanging">
3444        <t hangText="Magic number(s):">none</t>
3445        <t hangText="File extension(s):">none</t>
3446        <t hangText="Macintosh file type code(s):">none</t>
3447      </list>
3448    </t>
3449    <t hangText="Person and email address to contact for further information:">
3450      See Authors Section.
3451    </t>
3452    <t hangText="Intended usage:">
3453      COMMON
3454    </t>
3455    <t hangText="Restrictions on usage:">
3456      none
3457    </t>
3458    <t hangText="Author/Change controller:">
3459      IESG
3460    </t>
3461  </list>
3462</t>
3463</section>
3464</section>
3465
3466<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3467<t>
3468   The registration procedure for HTTP Transfer Codings is now defined by
3469   <xref target="transfer.coding.registry"/> of this document.
3470</t>
3471<t>
3472   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3473   should be updated with the registrations below:
3474</t>
3475<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3476   <ttcol>Name</ttcol>
3477   <ttcol>Description</ttcol>
3478   <ttcol>Reference</ttcol>
3479   <c>chunked</c>
3480   <c>Transfer in a series of chunks</c>
3481   <c>
3482      <xref target="chunked.encoding"/>
3483   </c>
3484   <c>compress</c>
3485   <c>UNIX "compress" program method</c>
3486   <c>
3487      <xref target="compress.coding"/>
3488   </c>
3489   <c>deflate</c>
3490   <c>"zlib" format <xref target="RFC1950"/> with "deflate" compression</c>
3491   <c>
3492      <xref target="deflate.coding"/>
3493   </c>
3494   <c>gzip</c>
3495   <c>Same as GNU zip <xref target="RFC1952"/></c>
3496   <c>
3497      <xref target="gzip.coding"/>
3498   </c>
3499</texttable>
3500</section>
3501
3502<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3503<t>
3504   The registration procedure for HTTP Upgrade Tokens -- previously defined
3505   in Section 7.2 of <xref target="RFC2817"/> -- is now defined
3506   by <xref target="upgrade.token.registry"/> of this document.
3507</t>
3508<t>
3509   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3510   should be updated with the registration below:
3511</t>
3512<texttable align="left" suppress-title="true">
3513   <ttcol>Value</ttcol>
3514   <ttcol>Description</ttcol>
3515   <ttcol>Reference</ttcol>
3516
3517   <c>HTTP</c>
3518   <c>Hypertext Transfer Protocol</c> 
3519   <c><xref target="http.version"/> of this specification</c>
3520<!-- IANA should add this without our instructions; emailed on June 05, 2009
3521   <c>TLS/1.0</c>
3522   <c>Transport Layer Security</c>
3523   <c><xref target="RFC2817"/></c> -->
3524
3525</texttable>
3526</section>
3527
3528</section>
3529
3530<section title="Security Considerations" anchor="security.considerations">
3531<t>
3532   This section is meant to inform application developers, information
3533   providers, and users of the security limitations in HTTP/1.1 as
3534   described by this document. The discussion does not include
3535   definitive solutions to the problems revealed, though it does make
3536   some suggestions for reducing security risks.
3537</t>
3538
3539<section title="Personal Information" anchor="personal.information">
3540<t>
3541   HTTP clients are often privy to large amounts of personal information
3542   (e.g., the user's name, location, mail address, passwords, encryption
3543   keys, etc.), and SHOULD be very careful to prevent unintentional
3544   leakage of this information.
3545   We very strongly recommend that a convenient interface be provided
3546   for the user to control dissemination of such information, and that
3547   designers and implementors be particularly careful in this area.
3548   History shows that errors in this area often create serious security
3549   and/or privacy problems and generate highly adverse publicity for the
3550   implementor's company.
3551</t>
3552</section>
3553
3554<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3555<t>
3556   A server is in the position to save personal data about a user's
3557   requests which might identify their reading patterns or subjects of
3558   interest. This information is clearly confidential in nature and its
3559   handling can be constrained by law in certain countries. People using
3560   HTTP to provide data are responsible for ensuring that
3561   such material is not distributed without the permission of any
3562   individuals that are identifiable by the published results.
3563</t>
3564</section>
3565
3566<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3567<t>
3568   Implementations of HTTP origin servers SHOULD be careful to restrict
3569   the documents returned by HTTP requests to be only those that were
3570   intended by the server administrators. If an HTTP server translates
3571   HTTP URIs directly into file system calls, the server MUST take
3572   special care not to serve files that were not intended to be
3573   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3574   other operating systems use ".." as a path component to indicate a
3575   directory level above the current one. On such a system, an HTTP
3576   server MUST disallow any such construct in the request-target if it
3577   would otherwise allow access to a resource outside those intended to
3578   be accessible via the HTTP server. Similarly, files intended for
3579   reference only internally to the server (such as access control
3580   files, configuration files, and script code) MUST be protected from
3581   inappropriate retrieval, since they might contain sensitive
3582   information. Experience has shown that minor bugs in such HTTP server
3583   implementations have turned into security risks.
3584</t>
3585</section>
3586
3587<section title="DNS Spoofing" anchor="dns.spoofing">
3588<t>
3589   Clients using HTTP rely heavily on the Domain Name Service, and are
3590   thus generally prone to security attacks based on the deliberate
3591   mis-association of IP addresses and DNS names. Clients need to be
3592   cautious in assuming the continuing validity of an IP number/DNS name
3593   association.
3594</t>
3595<t>
3596   In particular, HTTP clients SHOULD rely on their name resolver for
3597   confirmation of an IP number/DNS name association, rather than
3598   caching the result of previous host name lookups. Many platforms
3599   already can cache host name lookups locally when appropriate, and
3600   they SHOULD be configured to do so. It is proper for these lookups to
3601   be cached, however, only when the TTL (Time To Live) information
3602   reported by the name server makes it likely that the cached
3603   information will remain useful.
3604</t>
3605<t>
3606   If HTTP clients cache the results of host name lookups in order to
3607   achieve a performance improvement, they MUST observe the TTL
3608   information reported by DNS.
3609</t>
3610<t>
3611   If HTTP clients do not observe this rule, they could be spoofed when
3612   a previously-accessed server's IP address changes. As network
3613   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3614   possibility of this form of attack will grow. Observing this
3615   requirement thus reduces this potential security vulnerability.
3616</t>
3617<t>
3618   This requirement also improves the load-balancing behavior of clients
3619   for replicated servers using the same DNS name and reduces the
3620   likelihood of a user's experiencing failure in accessing sites which
3621   use that strategy.
3622</t>
3623</section>
3624
3625<section title="Proxies and Caching" anchor="attack.proxies">
3626<t>
3627   By their very nature, HTTP proxies are men-in-the-middle, and
3628   represent an opportunity for man-in-the-middle attacks. Compromise of
3629   the systems on which the proxies run can result in serious security
3630   and privacy problems. Proxies have access to security-related
3631   information, personal information about individual users and
3632   organizations, and proprietary information belonging to users and
3633   content providers. A compromised proxy, or a proxy implemented or
3634   configured without regard to security and privacy considerations,
3635   might be used in the commission of a wide range of potential attacks.
3636</t>
3637<t>
3638   Proxy operators should protect the systems on which proxies run as
3639   they would protect any system that contains or transports sensitive
3640   information. In particular, log information gathered at proxies often
3641   contains highly sensitive personal information, and/or information
3642   about organizations. Log information should be carefully guarded, and
3643   appropriate guidelines for use should be developed and followed.
3644   (<xref target="abuse.of.server.log.information"/>).
3645</t>
3646<t>
3647   Proxy implementors should consider the privacy and security
3648   implications of their design and coding decisions, and of the
3649   configuration options they provide to proxy operators (especially the
3650   default configuration).
3651</t>
3652<t>
3653   Users of a proxy need to be aware that proxies are no trustworthier than
3654   the people who run them; HTTP itself cannot solve this problem.
3655</t>
3656<t>
3657   The judicious use of cryptography, when appropriate, may suffice to
3658   protect against a broad range of security and privacy attacks. Such
3659   cryptography is beyond the scope of the HTTP/1.1 specification.
3660</t>
3661</section>
3662
3663<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3664<t>
3665   They exist. They are hard to defend against. Research continues.
3666   Beware.
3667</t>
3668</section>
3669</section>
3670
3671<section title="Acknowledgments" anchor="ack">
3672<t>
3673   HTTP has evolved considerably over the years. It has
3674   benefited from a large and active developer community--the many
3675   people who have participated on the www-talk mailing list--and it is
3676   that community which has been most responsible for the success of
3677   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3678   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3679   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3680   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3681   VanHeyningen deserve special recognition for their efforts in
3682   defining early aspects of the protocol.
3683</t>
3684<t>
3685   This document has benefited greatly from the comments of all those
3686   participating in the HTTP-WG. In addition to those already mentioned,
3687   the following individuals have contributed to this specification:
3688</t>
3689<t>
3690   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3691   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3692   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3693   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3694   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3695   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3696   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3697   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3698   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3699   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3700   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3701   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3702   Josh Cohen.
3703</t>
3704<t>
3705   Thanks to the "cave men" of Palo Alto. You know who you are.
3706</t>
3707<t>
3708   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3709   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3710   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3711   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3712   Larry Masinter for their help. And thanks go particularly to Jeff
3713   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3714</t>
3715<t>
3716   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3717   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3718   discovery of many of the problems that this document attempts to
3719   rectify.
3720</t>
3721<t>
3722   This specification makes heavy use of the augmented BNF and generic
3723   constructs defined by David H. Crocker for <xref target="RFC5234"/>. Similarly, it
3724   reuses many of the definitions provided by Nathaniel Borenstein and
3725   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3726   specification will help reduce past confusion over the relationship
3727   between HTTP and Internet mail message formats.
3728</t>
3729</section>
3730
3731</middle>
3732<back>
3733
3734<references title="Normative References">
3735
3736<reference anchor="ISO-8859-1">
3737  <front>
3738    <title>
3739     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3740    </title>
3741    <author>
3742      <organization>International Organization for Standardization</organization>
3743    </author>
3744    <date year="1998"/>
3745  </front>
3746  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3747</reference>
3748
3749<reference anchor="Part2">
3750  <front>
3751    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3752    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3753      <organization abbrev="Day Software">Day Software</organization>
3754      <address><email>fielding@gbiv.com</email></address>
3755    </author>
3756    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3757      <organization>One Laptop per Child</organization>
3758      <address><email>jg@laptop.org</email></address>
3759    </author>
3760    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3761      <organization abbrev="HP">Hewlett-Packard Company</organization>
3762      <address><email>JeffMogul@acm.org</email></address>
3763    </author>
3764    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3765      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3766      <address><email>henrikn@microsoft.com</email></address>
3767    </author>
3768    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3769      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3770      <address><email>LMM@acm.org</email></address>
3771    </author>
3772    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3773      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3774      <address><email>paulle@microsoft.com</email></address>
3775    </author>
3776    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3777      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3778      <address><email>timbl@w3.org</email></address>
3779    </author>
3780    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3781      <organization abbrev="W3C">World Wide Web Consortium</organization>
3782      <address><email>ylafon@w3.org</email></address>
3783    </author>
3784    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3785      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3786      <address><email>julian.reschke@greenbytes.de</email></address>
3787    </author>
3788    <date month="March" year="2010"/>
3789  </front>
3790  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-09"/>
3791 
3792</reference>
3793
3794<reference anchor="Part3">
3795  <front>
3796    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3797    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3798      <organization abbrev="Day Software">Day Software</organization>
3799      <address><email>fielding@gbiv.com</email></address>
3800    </author>
3801    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3802      <organization>One Laptop per Child</organization>
3803      <address><email>jg@laptop.org</email></address>
3804    </author>
3805    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3806      <organization abbrev="HP">Hewlett-Packard Company</organization>
3807      <address><email>JeffMogul@acm.org</email></address>
3808    </author>
3809    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3810      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3811      <address><email>henrikn@microsoft.com</email></address>
3812    </author>
3813    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3814      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3815      <address><email>LMM@acm.org</email></address>
3816    </author>
3817    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3818      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3819      <address><email>paulle@microsoft.com</email></address>
3820    </author>
3821    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3822      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3823      <address><email>timbl@w3.org</email></address>
3824    </author>
3825    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3826      <organization abbrev="W3C">World Wide Web Consortium</organization>
3827      <address><email>ylafon@w3.org</email></address>
3828    </author>
3829    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3830      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3831      <address><email>julian.reschke@greenbytes.de</email></address>
3832    </author>
3833    <date month="March" year="2010"/>
3834  </front>
3835  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-09"/>
3836 
3837</reference>
3838
3839<reference anchor="Part5">
3840  <front>
3841    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3842    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3843      <organization abbrev="Day Software">Day Software</organization>
3844      <address><email>fielding@gbiv.com</email></address>
3845    </author>
3846    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3847      <organization>One Laptop per Child</organization>
3848      <address><email>jg@laptop.org</email></address>
3849    </author>
3850    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3851      <organization abbrev="HP">Hewlett-Packard Company</organization>
3852      <address><email>JeffMogul@acm.org</email></address>
3853    </author>
3854    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3855      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3856      <address><email>henrikn@microsoft.com</email></address>
3857    </author>
3858    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3859      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3860      <address><email>LMM@acm.org</email></address>
3861    </author>
3862    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3863      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3864      <address><email>paulle@microsoft.com</email></address>
3865    </author>
3866    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3867      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3868      <address><email>timbl@w3.org</email></address>
3869    </author>
3870    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3871      <organization abbrev="W3C">World Wide Web Consortium</organization>
3872      <address><email>ylafon@w3.org</email></address>
3873    </author>
3874    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3875      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3876      <address><email>julian.reschke@greenbytes.de</email></address>
3877    </author>
3878    <date month="March" year="2010"/>
3879  </front>
3880  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-09"/>
3881 
3882</reference>
3883
3884<reference anchor="Part6">
3885  <front>
3886    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3887    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3888      <organization abbrev="Day Software">Day Software</organization>
3889      <address><email>fielding@gbiv.com</email></address>
3890    </author>
3891    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3892      <organization>One Laptop per Child</organization>
3893      <address><email>jg@laptop.org</email></address>
3894    </author>
3895    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3896      <organization abbrev="HP">Hewlett-Packard Company</organization>
3897      <address><email>JeffMogul@acm.org</email></address>
3898    </author>
3899    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3900      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3901      <address><email>henrikn@microsoft.com</email></address>
3902    </author>
3903    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3904      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3905      <address><email>LMM@acm.org</email></address>
3906    </author>
3907    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3908      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3909      <address><email>paulle@microsoft.com</email></address>
3910    </author>
3911    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3912      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3913      <address><email>timbl@w3.org</email></address>
3914    </author>
3915    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3916      <organization abbrev="W3C">World Wide Web Consortium</organization>
3917      <address><email>ylafon@w3.org</email></address>
3918    </author>
3919    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
3920      <address><email>mnot@mnot.net</email></address>
3921    </author>
3922    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3923      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3924      <address><email>julian.reschke@greenbytes.de</email></address>
3925    </author>
3926    <date month="March" year="2010"/>
3927  </front>
3928  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-09"/>
3929 
3930</reference>
3931
3932<reference anchor="RFC5234">
3933  <front>
3934    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
3935    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
3936      <organization>Brandenburg InternetWorking</organization>
3937      <address>
3938        <email>dcrocker@bbiw.net</email>
3939      </address> 
3940    </author>
3941    <author initials="P." surname="Overell" fullname="Paul Overell">
3942      <organization>THUS plc.</organization>
3943      <address>
3944        <email>paul.overell@thus.net</email>
3945      </address>
3946    </author>
3947    <date month="January" year="2008"/>
3948  </front>
3949  <seriesInfo name="STD" value="68"/>
3950  <seriesInfo name="RFC" value="5234"/>
3951</reference>
3952
3953<reference anchor="RFC2119">
3954  <front>
3955    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3956    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3957      <organization>Harvard University</organization>
3958      <address><email>sob@harvard.edu</email></address>
3959    </author>
3960    <date month="March" year="1997"/>
3961  </front>
3962  <seriesInfo name="BCP" value="14"/>
3963  <seriesInfo name="RFC" value="2119"/>
3964</reference>
3965
3966<reference anchor="RFC3986">
3967 <front>
3968  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
3969  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3970    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3971    <address>
3972       <email>timbl@w3.org</email>
3973       <uri>http://www.w3.org/People/Berners-Lee/</uri>
3974    </address>
3975  </author>
3976  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3977    <organization abbrev="Day Software">Day Software</organization>
3978    <address>
3979      <email>fielding@gbiv.com</email>
3980      <uri>http://roy.gbiv.com/</uri>
3981    </address>
3982  </author>
3983  <author initials="L." surname="Masinter" fullname="Larry Masinter">
3984    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
3985    <address>
3986      <email>LMM@acm.org</email>
3987      <uri>http://larry.masinter.net/</uri>
3988    </address>
3989  </author>
3990  <date month="January" year="2005"/>
3991 </front>
3992 <seriesInfo name="RFC" value="3986"/>
3993 <seriesInfo name="STD" value="66"/>
3994</reference>
3995
3996<reference anchor="USASCII">
3997  <front>
3998    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3999    <author>
4000      <organization>American National Standards Institute</organization>
4001    </author>
4002    <date year="1986"/>
4003  </front>
4004  <seriesInfo name="ANSI" value="X3.4"/>
4005</reference>
4006
4007<reference anchor="RFC1950">
4008  <front>
4009    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4010    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4011      <organization>Aladdin Enterprises</organization>
4012      <address><email>ghost@aladdin.com</email></address>
4013    </author>
4014    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4015    <date month="May" year="1996"/>
4016  </front>
4017  <seriesInfo name="RFC" value="1950"/>
4018  <annotation>
4019    RFC 1950 is an Informational RFC, thus it may be less stable than
4020    this specification. On the other hand, this downward reference was
4021    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4022    therefore it is unlikely to cause problems in practice. See also
4023    <xref target="BCP97"/>.
4024  </annotation>
4025</reference>
4026
4027<reference anchor="RFC1951">
4028  <front>
4029    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4030    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4031      <organization>Aladdin Enterprises</organization>
4032      <address><email>ghost@aladdin.com</email></address>
4033    </author>
4034    <date month="May" year="1996"/>
4035  </front>
4036  <seriesInfo name="RFC" value="1951"/>
4037  <annotation>
4038    RFC 1951 is an Informational RFC, thus it may be less stable than
4039    this specification. On the other hand, this downward reference was
4040    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4041    therefore it is unlikely to cause problems in practice. See also
4042    <xref target="BCP97"/>.
4043  </annotation>
4044</reference>
4045
4046<reference anchor="RFC1952">
4047  <front>
4048    <title>GZIP file format specification version 4.3</title>
4049    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4050      <organization>Aladdin Enterprises</organization>
4051      <address><email>ghost@aladdin.com</email></address>
4052    </author>
4053    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4054      <address><email>gzip@prep.ai.mit.edu</email></address>
4055    </author>
4056    <author initials="M." surname="Adler" fullname="Mark Adler">
4057      <address><email>madler@alumni.caltech.edu</email></address>
4058    </author>
4059    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4060      <address><email>ghost@aladdin.com</email></address>
4061    </author>
4062    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4063      <address><email>randeg@alumni.rpi.edu</email></address>
4064    </author>
4065    <date month="May" year="1996"/>
4066  </front>
4067  <seriesInfo name="RFC" value="1952"/>
4068  <annotation>
4069    RFC 1952 is an Informational RFC, thus it may be less stable than
4070    this specification. On the other hand, this downward reference was
4071    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4072    therefore it is unlikely to cause problems in practice. See also
4073    <xref target="BCP97"/>.
4074  </annotation>
4075</reference>
4076
4077</references>
4078
4079<references title="Informative References">
4080
4081<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4082  <front>
4083    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4084    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen"/>
4085    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4086    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4087    <author initials="H." surname="Lie" fullname="H. Lie"/>
4088    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4089    <date year="1997" month="September"/>
4090  </front>
4091  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4092</reference>
4093
4094<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4095  <front>
4096    <title>Improving HTTP Latency</title>
4097    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4098    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4099    <date year="1995" month="December"/>
4100  </front>
4101  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4102</reference>
4103
4104<reference anchor="RFC1123">
4105  <front>
4106    <title>Requirements for Internet Hosts - Application and Support</title>
4107    <author initials="R." surname="Braden" fullname="Robert Braden">
4108      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4109      <address><email>Braden@ISI.EDU</email></address>
4110    </author>
4111    <date month="October" year="1989"/>
4112  </front>
4113  <seriesInfo name="STD" value="3"/>
4114  <seriesInfo name="RFC" value="1123"/>
4115</reference>
4116
4117<reference anchor="RFC1305">
4118  <front>
4119    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
4120    <author initials="D." surname="Mills" fullname="David L. Mills">
4121      <organization>University of Delaware, Electrical Engineering Department</organization>
4122      <address><email>mills@udel.edu</email></address>
4123    </author>
4124    <date month="March" year="1992"/>
4125  </front>
4126  <seriesInfo name="RFC" value="1305"/>
4127</reference>
4128
4129<reference anchor="RFC1900">
4130  <front>
4131    <title>Renumbering Needs Work</title>
4132    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
4133      <organization>CERN, Computing and Networks Division</organization>
4134      <address><email>brian@dxcoms.cern.ch</email></address>
4135    </author>
4136    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
4137      <organization>cisco Systems</organization>
4138      <address><email>yakov@cisco.com</email></address>
4139    </author>
4140    <date month="February" year="1996"/>
4141  </front>
4142  <seriesInfo name="RFC" value="1900"/>
4143</reference>
4144
4145<reference anchor="RFC1945">
4146  <front>
4147    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4148    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4149      <organization>MIT, Laboratory for Computer Science</organization>
4150      <address><email>timbl@w3.org</email></address>
4151    </author>
4152    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4153      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4154      <address><email>fielding@ics.uci.edu</email></address>
4155    </author>
4156    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4157      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4158      <address><email>frystyk@w3.org</email></address>
4159    </author>
4160    <date month="May" year="1996"/>
4161  </front>
4162  <seriesInfo name="RFC" value="1945"/>
4163</reference>
4164
4165<reference anchor="RFC2045">
4166  <front>
4167    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4168    <author initials="N." surname="Freed" fullname="Ned Freed">
4169      <organization>Innosoft International, Inc.</organization>
4170      <address><email>ned@innosoft.com</email></address>
4171    </author>
4172    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4173      <organization>First Virtual Holdings</organization>
4174      <address><email>nsb@nsb.fv.com</email></address>
4175    </author>
4176    <date month="November" year="1996"/>
4177  </front>
4178  <seriesInfo name="RFC" value="2045"/>
4179</reference>
4180
4181<reference anchor="RFC2047">
4182  <front>
4183    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4184    <author initials="K." surname="Moore" fullname="Keith Moore">
4185      <organization>University of Tennessee</organization>
4186      <address><email>moore@cs.utk.edu</email></address>
4187    </author>
4188    <date month="November" year="1996"/>
4189  </front>
4190  <seriesInfo name="RFC" value="2047"/>
4191</reference>
4192
4193<reference anchor="RFC2068">
4194  <front>
4195    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4196    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4197      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4198      <address><email>fielding@ics.uci.edu</email></address>
4199    </author>
4200    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4201      <organization>MIT Laboratory for Computer Science</organization>
4202      <address><email>jg@w3.org</email></address>
4203    </author>
4204    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4205      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4206      <address><email>mogul@wrl.dec.com</email></address>
4207    </author>
4208    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4209      <organization>MIT Laboratory for Computer Science</organization>
4210      <address><email>frystyk@w3.org</email></address>
4211    </author>
4212    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4213      <organization>MIT Laboratory for Computer Science</organization>
4214      <address><email>timbl@w3.org</email></address>
4215    </author>
4216    <date month="January" year="1997"/>
4217  </front>
4218  <seriesInfo name="RFC" value="2068"/>
4219</reference>
4220
4221<reference anchor="RFC2109">
4222  <front>
4223    <title>HTTP State Management Mechanism</title>
4224    <author initials="D.M." surname="Kristol" fullname="David M. Kristol">
4225      <organization>Bell Laboratories, Lucent Technologies</organization>
4226      <address><email>dmk@bell-labs.com</email></address>
4227    </author>
4228    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4229      <organization>Netscape Communications Corp.</organization>
4230      <address><email>montulli@netscape.com</email></address>
4231    </author>
4232    <date year="1997" month="February"/>
4233  </front>
4234  <seriesInfo name="RFC" value="2109"/>
4235</reference>
4236
4237<reference anchor="RFC2145">
4238  <front>
4239    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4240    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4241      <organization>Western Research Laboratory</organization>
4242      <address><email>mogul@wrl.dec.com</email></address>
4243    </author>
4244    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4245      <organization>Department of Information and Computer Science</organization>
4246      <address><email>fielding@ics.uci.edu</email></address>
4247    </author>
4248    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4249      <organization>MIT Laboratory for Computer Science</organization>
4250      <address><email>jg@w3.org</email></address>
4251    </author>
4252    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4253      <organization>W3 Consortium</organization>
4254      <address><email>frystyk@w3.org</email></address>
4255    </author>
4256    <date month="May" year="1997"/>
4257  </front>
4258  <seriesInfo name="RFC" value="2145"/>
4259</reference>
4260
4261<reference anchor="RFC2616">
4262  <front>
4263    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4264    <author initials="R." surname="Fielding" fullname="R. Fielding">
4265      <organization>University of California, Irvine</organization>
4266      <address><email>fielding@ics.uci.edu</email></address>
4267    </author>
4268    <author initials="J." surname="Gettys" fullname="J. Gettys">
4269      <organization>W3C</organization>
4270      <address><email>jg@w3.org</email></address>
4271    </author>
4272    <author initials="J." surname="Mogul" fullname="J. Mogul">
4273      <organization>Compaq Computer Corporation</organization>
4274      <address><email>mogul@wrl.dec.com</email></address>
4275    </author>
4276    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4277      <organization>MIT Laboratory for Computer Science</organization>
4278      <address><email>frystyk@w3.org</email></address>
4279    </author>
4280    <author initials="L." surname="Masinter" fullname="L. Masinter">
4281      <organization>Xerox Corporation</organization>
4282      <address><email>masinter@parc.xerox.com</email></address>
4283    </author>
4284    <author initials="P." surname="Leach" fullname="P. Leach">
4285      <organization>Microsoft Corporation</organization>
4286      <address><email>paulle@microsoft.com</email></address>
4287    </author>
4288    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4289      <organization>W3C</organization>
4290      <address><email>timbl@w3.org</email></address>
4291    </author>
4292    <date month="June" year="1999"/>
4293  </front>
4294  <seriesInfo name="RFC" value="2616"/>
4295</reference>
4296
4297<reference anchor="RFC2817">
4298  <front>
4299    <title>Upgrading to TLS Within HTTP/1.1</title>
4300    <author initials="R." surname="Khare" fullname="R. Khare">
4301      <organization>4K Associates / UC Irvine</organization>
4302      <address><email>rohit@4K-associates.com</email></address>
4303    </author>
4304    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
4305      <organization>Agranat Systems, Inc.</organization>
4306      <address><email>lawrence@agranat.com</email></address>
4307    </author>
4308    <date year="2000" month="May"/>
4309  </front>
4310  <seriesInfo name="RFC" value="2817"/>
4311</reference>
4312
4313<reference anchor="RFC2818">
4314  <front>
4315    <title>HTTP Over TLS</title>
4316    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
4317      <organization>RTFM, Inc.</organization>
4318      <address><email>ekr@rtfm.com</email></address>
4319    </author>
4320    <date year="2000" month="May"/>
4321  </front>
4322  <seriesInfo name="RFC" value="2818"/>
4323</reference>
4324
4325<reference anchor="RFC2965">
4326  <front>
4327    <title>HTTP State Management Mechanism</title>
4328    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
4329      <organization>Bell Laboratories, Lucent Technologies</organization>
4330      <address><email>dmk@bell-labs.com</email></address>
4331    </author>
4332    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4333      <organization>Epinions.com, Inc.</organization>
4334      <address><email>lou@montulli.org</email></address>
4335    </author>
4336    <date year="2000" month="October"/>
4337  </front>
4338  <seriesInfo name="RFC" value="2965"/>
4339</reference>
4340
4341<reference anchor="RFC3864">
4342  <front>
4343    <title>Registration Procedures for Message Header Fields</title>
4344    <author initials="G." surname="Klyne" fullname="G. Klyne">
4345      <organization>Nine by Nine</organization>
4346      <address><email>GK-IETF@ninebynine.org</email></address>
4347    </author>
4348    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
4349      <organization>BEA Systems</organization>
4350      <address><email>mnot@pobox.com</email></address>
4351    </author>
4352    <author initials="J." surname="Mogul" fullname="J. Mogul">
4353      <organization>HP Labs</organization>
4354      <address><email>JeffMogul@acm.org</email></address>
4355    </author>
4356    <date year="2004" month="September"/>
4357  </front>
4358  <seriesInfo name="BCP" value="90"/>
4359  <seriesInfo name="RFC" value="3864"/>
4360</reference>
4361
4362<reference anchor="RFC4288">
4363  <front>
4364    <title>Media Type Specifications and Registration Procedures</title>
4365    <author initials="N." surname="Freed" fullname="N. Freed">
4366      <organization>Sun Microsystems</organization>
4367      <address>
4368        <email>ned.freed@mrochek.com</email>
4369      </address>
4370    </author>
4371    <author initials="J." surname="Klensin" fullname="J. Klensin">
4372      <address>
4373        <email>klensin+ietf@jck.com</email>
4374      </address>
4375    </author>
4376    <date year="2005" month="December"/>
4377  </front>
4378  <seriesInfo name="BCP" value="13"/>
4379  <seriesInfo name="RFC" value="4288"/>
4380</reference>
4381
4382<reference anchor="RFC4395">
4383  <front>
4384    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4385    <author initials="T." surname="Hansen" fullname="T. Hansen">
4386      <organization>AT&amp;T Laboratories</organization>
4387      <address>
4388        <email>tony+urireg@maillennium.att.com</email>
4389      </address>
4390    </author>
4391    <author initials="T." surname="Hardie" fullname="T. Hardie">
4392      <organization>Qualcomm, Inc.</organization>
4393      <address>
4394        <email>hardie@qualcomm.com</email>
4395      </address>
4396    </author>
4397    <author initials="L." surname="Masinter" fullname="L. Masinter">
4398      <organization>Adobe Systems</organization>
4399      <address>
4400        <email>LMM@acm.org</email>
4401      </address>
4402    </author>
4403    <date year="2006" month="February"/>
4404  </front>
4405  <seriesInfo name="BCP" value="115"/>
4406  <seriesInfo name="RFC" value="4395"/>
4407</reference>
4408
4409<reference anchor="RFC5226">
4410  <front>
4411    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4412    <author initials="T." surname="Narten" fullname="T. Narten">
4413      <organization>IBM</organization>
4414      <address><email>narten@us.ibm.com</email></address>
4415    </author>
4416    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
4417      <organization>Google</organization>
4418      <address><email>Harald@Alvestrand.no</email></address>
4419    </author>
4420    <date year="2008" month="May"/>
4421  </front>
4422  <seriesInfo name="BCP" value="26"/>
4423  <seriesInfo name="RFC" value="5226"/>
4424</reference>
4425
4426<reference anchor="RFC5322">
4427  <front>
4428    <title>Internet Message Format</title>
4429    <author initials="P." surname="Resnick" fullname="P. Resnick">
4430      <organization>Qualcomm Incorporated</organization>
4431    </author>
4432    <date year="2008" month="October"/>
4433  </front> 
4434  <seriesInfo name="RFC" value="5322"/>
4435</reference>
4436
4437<reference anchor="BCP97">
4438  <front>
4439    <title>Handling Normative References to Standards-Track Documents</title>
4440    <author initials="J." surname="Klensin" fullname="J. Klensin">
4441      <address>
4442        <email>klensin+ietf@jck.com</email>
4443      </address>
4444    </author>
4445    <author initials="S." surname="Hartman" fullname="S. Hartman">
4446      <organization>MIT</organization>
4447      <address>
4448        <email>hartmans-ietf@mit.edu</email>
4449      </address>
4450    </author>
4451    <date year="2007" month="June"/>
4452  </front>
4453  <seriesInfo name="BCP" value="97"/>
4454  <seriesInfo name="RFC" value="4897"/>
4455</reference>
4456
4457<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4458  <front>
4459    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4460    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4461    <date year="2001" month="November"/>
4462  </front>
4463  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4464</reference>
4465
4466<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4467  <front>
4468    <title>Analysis of HTTP Performance Problems</title>
4469    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4470    <date/>
4471  </front>
4472</reference>
4473
4474<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4475  <front>
4476  <title>Analysis of HTTP Performance</title>
4477  <author initials="J." surname="Touch" fullname="Joe Touch">
4478    <organization>USC/Information Sciences Institute</organization>
4479    <address><email>touch@isi.edu</email></address>
4480  </author>
4481  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4482    <organization>USC/Information Sciences Institute</organization>
4483    <address><email>johnh@isi.edu</email></address>
4484  </author>
4485  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4486    <organization>USC/Information Sciences Institute</organization>
4487    <address><email>katia@isi.edu</email></address>
4488  </author>
4489  <date year="1998" month="Aug"/>
4490  </front>
4491  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4492  <annotation>(original report dated Aug. 1996)</annotation>
4493</reference>
4494
4495</references>
4496
4497
4498<section title="Tolerant Applications" anchor="tolerant.applications">
4499<t>
4500   Although this document specifies the requirements for the generation
4501   of HTTP/1.1 messages, not all applications will be correct in their
4502   implementation. We therefore recommend that operational applications
4503   be tolerant of deviations whenever those deviations can be
4504   interpreted unambiguously.
4505</t>
4506<t>
4507   Clients SHOULD be tolerant in parsing the Status-Line and servers
4508   SHOULD be tolerant when parsing the Request-Line. In particular, they
4509   SHOULD accept any amount of WSP characters between fields, even though
4510   only a single SP is required.
4511</t>
4512<t>
4513   The line terminator for header fields is the sequence CRLF.
4514   However, we recommend that applications, when parsing such headers,
4515   recognize a single LF as a line terminator and ignore the leading CR.
4516</t>
4517<t>
4518   The character set of an entity-body SHOULD be labeled as the lowest
4519   common denominator of the character codes used within that body, with
4520   the exception that not labeling the entity is preferred over labeling
4521   the entity with the labels US-ASCII or ISO-8859-1. See <xref target="Part3"/>.
4522</t>
4523<t>
4524   Additional rules for requirements on parsing and encoding of dates
4525   and other potential problems with date encodings include:
4526</t>
4527<t>
4528  <list style="symbols">
4529     <t>HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
4530        which appears to be more than 50 years in the future is in fact
4531        in the past (this helps solve the "year 2000" problem).</t>
4532
4533     <t>An HTTP/1.1 implementation MAY internally represent a parsed
4534        Expires date as earlier than the proper value, but MUST NOT
4535        internally represent a parsed Expires date as later than the
4536        proper value.</t>
4537
4538     <t>All expiration-related calculations MUST be done in GMT. The
4539        local time zone MUST NOT influence the calculation or comparison
4540        of an age or expiration time.</t>
4541
4542     <t>If an HTTP header incorrectly carries a date value with a time
4543        zone other than GMT, it MUST be converted into GMT using the
4544        most conservative possible conversion.</t>
4545  </list>
4546</t>
4547</section>
4548
4549<section title="Compatibility with Previous Versions" anchor="compatibility">
4550<t>
4551   HTTP has been in use by the World-Wide Web global information initiative
4552   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4553   was a simple protocol for hypertext data transfer across the Internet
4554   with only a single method and no metadata.
4555   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4556   methods and MIME-like messaging that could include metadata about the data
4557   transferred and modifiers on the request/response semantics. However,
4558   HTTP/1.0 did not sufficiently take into consideration the effects of
4559   hierarchical proxies, caching, the need for persistent connections, or
4560   name-based virtual hosts. The proliferation of incompletely-implemented
4561   applications calling themselves "HTTP/1.0" further necessitated a
4562   protocol version change in order for two communicating applications
4563   to determine each other's true capabilities.
4564</t>
4565<t>
4566   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4567   requirements that enable reliable implementations, adding only
4568   those new features that will either be safely ignored by an HTTP/1.0
4569   recipient or only sent when communicating with a party advertising
4570   compliance with HTTP/1.1.
4571</t>
4572<t>
4573   It is beyond the scope of a protocol specification to mandate
4574   compliance with previous versions. HTTP/1.1 was deliberately
4575   designed, however, to make supporting previous versions easy. It is
4576   worth noting that, at the time of composing this specification, we would
4577   expect general-purpose HTTP/1.1 servers to:
4578  <list style="symbols">
4579     <t>understand any valid request in the format of HTTP/1.0 and
4580        1.1;</t>
4581
4582     <t>respond appropriately with a message in the same major version
4583        used by the client.</t>
4584  </list>
4585</t>
4586<t>
4587   And we would expect HTTP/1.1 clients to:
4588  <list style="symbols">
4589     <t>understand any valid response in the format of HTTP/1.0 or
4590        1.1.</t>
4591  </list>
4592</t>
4593<t>
4594   For most implementations of HTTP/1.0, each connection is established
4595   by the client prior to the request and closed by the server after
4596   sending the response. Some implementations implement the Keep-Alive
4597   version of persistent connections described in Section 19.7.1 of <xref target="RFC2068"/>.
4598</t>
4599
4600<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4601<t>
4602   This section summarizes major differences between versions HTTP/1.0
4603   and HTTP/1.1.
4604</t>
4605
4606<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">
4607<t>
4608   The requirements that clients and servers support the Host request-header,
4609   report an error if the Host request-header (<xref target="header.host"/>) is
4610   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4611   are among the most important changes defined by this
4612   specification.
4613</t>
4614<t>
4615   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4616   addresses and servers; there was no other established mechanism for
4617   distinguishing the intended server of a request than the IP address
4618   to which that request was directed. The changes outlined above will
4619   allow the Internet, once older HTTP clients are no longer common, to
4620   support multiple Web sites from a single IP address, greatly
4621   simplifying large operational Web servers, where allocation of many
4622   IP addresses to a single host has created serious problems. The
4623   Internet will also be able to recover the IP addresses that have been
4624   allocated for the sole purpose of allowing special-purpose domain
4625   names to be used in root-level HTTP URLs. Given the rate of growth of
4626   the Web, and the number of servers already deployed, it is extremely
4627   important that all implementations of HTTP (including updates to
4628   existing HTTP/1.0 applications) correctly implement these
4629   requirements:
4630  <list style="symbols">
4631     <t>Both clients and servers MUST support the Host request-header.</t>
4632
4633     <t>A client that sends an HTTP/1.1 request MUST send a Host header.</t>
4634
4635     <t>Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
4636        request does not include a Host request-header.</t>
4637
4638     <t>Servers MUST accept absolute URIs.</t>
4639  </list>
4640</t>
4641</section>
4642</section>
4643
4644<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4645<t>
4646   Some clients and servers might wish to be compatible with some
4647   previous implementations of persistent connections in HTTP/1.0
4648   clients and servers. Persistent connections in HTTP/1.0 are
4649   explicitly negotiated as they are not the default behavior. HTTP/1.0
4650   experimental implementations of persistent connections are faulty,
4651   and the new facilities in HTTP/1.1 are designed to rectify these
4652   problems. The problem was that some existing HTTP/1.0 clients may be
4653   sending Keep-Alive to a proxy server that doesn't understand
4654   Connection, which would then erroneously forward it to the next
4655   inbound server, which would establish the Keep-Alive connection and
4656   result in a hung HTTP/1.0 proxy waiting for the close on the
4657   response. The result is that HTTP/1.0 clients must be prevented from
4658   using Keep-Alive when talking to proxies.
4659</t>
4660<t>
4661   However, talking to proxies is the most important use of persistent
4662   connections, so that prohibition is clearly unacceptable. Therefore,
4663   we need some other mechanism for indicating a persistent connection
4664   is desired, which is safe to use even when talking to an old proxy
4665   that ignores Connection. Persistent connections are the default for
4666   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4667   declaring non-persistence. See <xref target="header.connection"/>.
4668</t>
4669<t>
4670   The original HTTP/1.0 form of persistent connections (the Connection:
4671   Keep-Alive and Keep-Alive header) is documented in Section 19.7.1 of <xref target="RFC2068"/>.
4672</t>
4673</section>
4674
4675<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4676<t>
4677   This specification has been carefully audited to correct and
4678   disambiguate key word usage; RFC 2068 had many problems in respect to
4679   the conventions laid out in <xref target="RFC2119"/>.
4680</t>
4681<t>
4682   Transfer-coding and message lengths all interact in ways that
4683   required fixing exactly when chunked encoding is used (to allow for
4684   transfer encoding that may not be self delimiting); it was important
4685   to straighten out exactly how message lengths are computed. (Sections
4686   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4687   <xref target="header.content-length" format="counter"/>,
4688   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4689</t>
4690<t>
4691   The use and interpretation of HTTP version numbers has been clarified
4692   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4693   version they support to deal with problems discovered in HTTP/1.0
4694   implementations (<xref target="http.version"/>)
4695</t>
4696<t>
4697   Quality Values of zero should indicate that "I don't want something"
4698   to allow clients to refuse a representation. (<xref target="quality.values"/>)
4699</t>
4700<t>
4701   Transfer-coding had significant problems, particularly with
4702   interactions with chunked encoding. The solution is that transfer-codings
4703   become as full fledged as content-codings. This involves
4704   adding an IANA registry for transfer-codings (separate from content
4705   codings), a new header field (TE) and enabling trailer headers in the
4706   future. Transfer encoding is a major performance benefit, so it was
4707   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4708   interoperability problem that could have occurred due to interactions
4709   between authentication trailers, chunked encoding and HTTP/1.0
4710   clients.(Section
4711   <xref target="transfer.codings" format="counter"/>,
4712   <xref target="chunked.encoding" format="counter"/>,
4713   <xref target="non-modifiable.headers" format="counter"/>,
4714   and <xref target="header.te" format="counter"/>)
4715</t>
4716<t>
4717  Proxies should be able to add Content-Length when appropriate.
4718  (<xref target="non-modifiable.headers"/>)
4719</t>
4720</section>
4721
4722<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4723<t>
4724  Empty list elements in list productions have been deprecated.
4725  (<xref target="notation.abnf"/>)
4726</t>
4727<t>
4728  Rules about implicit linear whitespace between certain grammar productions
4729  have been removed; now it's only allowed when specifically pointed out
4730  in the ABNF. The NUL character is no longer allowed in comment and quoted-string
4731  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4732  Non-ASCII content in header fields and reason phrase has been obsoleted and
4733  made opaque (the TEXT rule was removed)
4734  (<xref target="basic.rules"/>)
4735</t>
4736<t>
4737  Clarify that HTTP-Version is case sensitive.
4738  (<xref target="http.version"/>)
4739</t>
4740<t>
4741  Remove reference to non-existent identity transfer-coding value tokens.
4742  (Sections <xref format="counter" target="transfer.codings"/> and
4743  <xref format="counter" target="message.length"/>)
4744</t>
4745<t>
4746  Require that invalid whitespace around field-names be rejected.
4747  (<xref target="header.fields"/>)
4748</t>
4749<t>
4750  Update use of abs_path production from RFC1808 to the path-absolute + query
4751  components of RFC3986.
4752  (<xref target="request-target"/>)
4753</t>
4754<t>
4755  Clarification that the chunk length does not include the count of the octets
4756  in the chunk header and trailer. Furthermore disallowed line folding
4757  in chunk extensions.
4758  (<xref target="chunked.encoding"/>)
4759</t>
4760<t>
4761  Remove hard limit of two connections per server.
4762  (<xref target="persistent.practical"/>)
4763</t>
4764<t>
4765  Clarify exactly when close connection options must be sent.
4766  (<xref target="header.connection"/>)
4767</t>
4768</section>
4769</section>
4770
4771
4772<section title="Collected ABNF" anchor="collected.abnf">
4773<figure>
4774<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
4775BWS = OWS
4776
4777Cache-Control = <Cache-Control, defined in [Part6], Section 3.4>
4778Chunked-Body = *chunk last-chunk trailer-part CRLF
4779Connection = "Connection:" OWS Connection-v
4780Connection-v = *( "," OWS ) connection-token *( OWS "," [ OWS
4781 connection-token ] )
4782Content-Length = "Content-Length:" OWS 1*Content-Length-v
4783Content-Length-v = 1*DIGIT
4784
4785Date = "Date:" OWS Date-v
4786Date-v = HTTP-date
4787
4788GMT = %x47.4D.54 ; GMT
4789
4790HTTP-Prot-Name = %x48.54.54.50 ; HTTP
4791HTTP-Version = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
4792HTTP-date = rfc1123-date / obs-date
4793HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
4794 ]
4795Host = "Host:" OWS Host-v
4796Host-v = uri-host [ ":" port ]
4797
4798Method = token
4799
4800OWS = *( [ obs-fold ] WSP )
4801
4802Pragma = <Pragma, defined in [Part6], Section 3.4>
4803
4804RWS = 1*( [ obs-fold ] WSP )
4805Reason-Phrase = *( WSP / VCHAR / obs-text )
4806Request = Request-Line *( ( general-header / request-header /
4807 entity-header ) CRLF ) CRLF [ message-body ]
4808Request-Line = Method SP request-target SP HTTP-Version CRLF
4809Response = Status-Line *( ( general-header / response-header /
4810 entity-header ) CRLF ) CRLF [ message-body ]
4811
4812Status-Code = 3DIGIT
4813Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4814
4815TE = "TE:" OWS TE-v
4816TE-v = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4817Trailer = "Trailer:" OWS Trailer-v
4818Trailer-v = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4819Transfer-Encoding = "Transfer-Encoding:" OWS Transfer-Encoding-v
4820Transfer-Encoding-v = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4821 transfer-coding ] )
4822
4823URI = <URI, defined in [RFC3986], Section 3>
4824URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
4825Upgrade = "Upgrade:" OWS Upgrade-v
4826Upgrade-v = *( "," OWS ) product *( OWS "," [ OWS product ] )
4827
4828Via = "Via:" OWS Via-v
4829Via-v = *( "," OWS ) received-protocol RWS received-by [ RWS comment
4830 ] *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ]
4831 ] )
4832
4833Warning = <Warning, defined in [Part6], Section 3.6>
4834
4835absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
4836asctime-date = day-name SP date3 SP time-of-day SP year
4837attribute = token
4838authority = <authority, defined in [RFC3986], Section 3.2>
4839
4840chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
4841chunk-data = 1*OCTET
4842chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
4843chunk-ext-name = token
4844chunk-ext-val = token / quoted-str-nf
4845chunk-size = 1*HEXDIG
4846comment = "(" *( ctext / quoted-cpair / comment ) ")"
4847connection-token = token
4848ctext = OWS / %x21-27 ; '!'-'''
4849 / %x2A-5B ; '*'-'['
4850 / %x5D-7E ; ']'-'~'
4851 / obs-text
4852
4853date1 = day SP month SP year
4854date2 = day "-" month "-" 2DIGIT
4855date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
4856day = 2DIGIT
4857day-name = %x4D.6F.6E ; Mon
4858 / %x54.75.65 ; Tue
4859 / %x57.65.64 ; Wed
4860 / %x54.68.75 ; Thu
4861 / %x46.72.69 ; Fri
4862 / %x53.61.74 ; Sat
4863 / %x53.75.6E ; Sun
4864day-name-l = %x4D.6F.6E.64.61.79 ; Monday
4865 / %x54.75.65.73.64.61.79 ; Tuesday
4866 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
4867 / %x54.68.75.72.73.64.61.79 ; Thursday
4868 / %x46.72.69.64.61.79 ; Friday
4869 / %x53.61.74.75.72.64.61.79 ; Saturday
4870 / %x53.75.6E.64.61.79 ; Sunday
4871
4872entity-body = <entity-body, defined in [Part3], Section 3.2>
4873entity-header = <entity-header, defined in [Part3], Section 3.1>
4874
4875field-content = *( WSP / VCHAR / obs-text )
4876field-name = token
4877field-value = *( field-content / OWS )
4878
4879general-header = Cache-Control / Connection / Date / Pragma / Trailer
4880 / Transfer-Encoding / Upgrade / Via / Warning
4881
4882header-field = field-name ":" OWS [ field-value ] OWS
4883hour = 2DIGIT
4884http-URI = "http://" authority path-abempty [ "?" query ]
4885https-URI = "https://" authority path-abempty [ "?" query ]
4886
4887last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF
4888
4889message-body = entity-body /
4890 <entity-body encoded as per Transfer-Encoding>
4891minute = 2DIGIT
4892month = %x4A.61.6E ; Jan
4893 / %x46.65.62 ; Feb
4894 / %x4D.61.72 ; Mar
4895 / %x41.70.72 ; Apr
4896 / %x4D.61.79 ; May
4897 / %x4A.75.6E ; Jun
4898 / %x4A.75.6C ; Jul
4899 / %x41.75.67 ; Aug
4900 / %x53.65.70 ; Sep
4901 / %x4F.63.74 ; Oct
4902 / %x4E.6F.76 ; Nov
4903 / %x44.65.63 ; Dec
4904
4905obs-date = rfc850-date / asctime-date
4906obs-fold = CRLF
4907obs-text = %x80-FF
4908
4909partial-URI = relative-part [ "?" query ]
4910path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
4911path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
4912port = <port, defined in [RFC3986], Section 3.2.3>
4913product = token [ "/" product-version ]
4914product-version = token
4915protocol-name = token
4916protocol-version = token
4917pseudonym = token
4918
4919qdtext = OWS / "!" / %x23-5B ; '#'-'['
4920 / %x5D-7E ; ']'-'~'
4921 / obs-text
4922qdtext-nf = WSP / "!" / %x23-5B ; '#'-'['
4923 / %x5D-7E ; ']'-'~'
4924 / obs-text
4925query = <query, defined in [RFC3986], Section 3.4>
4926quoted-cpair = "\" ( WSP / VCHAR / obs-text )
4927quoted-pair = "\" ( WSP / VCHAR / obs-text )
4928quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
4929quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
4930qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
4931
4932received-by = ( uri-host [ ":" port ] ) / pseudonym
4933received-protocol = [ protocol-name "/" ] protocol-version
4934relative-part = <relative-part, defined in [RFC3986], Section 4.2>
4935request-header = <request-header, defined in [Part2], Section 3>
4936request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
4937 / authority
4938response-header = <response-header, defined in [Part2], Section 5>
4939rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
4940rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
4941
4942second = 2DIGIT
4943special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
4944 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
4945start-line = Request-Line / Status-Line
4946
4947t-codings = "trailers" / ( transfer-extension [ te-params ] )
4948tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
4949 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
4950te-ext = OWS ";" OWS token [ "=" ( token / quoted-string ) ]
4951te-params = OWS ";" OWS "q=" qvalue *te-ext
4952time-of-day = hour ":" minute ":" second
4953token = 1*tchar
4954trailer-part = *( entity-header CRLF )
4955transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
4956 transfer-extension
4957transfer-extension = token *( OWS ";" OWS transfer-parameter )
4958transfer-parameter = attribute BWS "=" BWS value
4959
4960uri-host = <host, defined in [RFC3986], Section 3.2.2>
4961
4962value = token / quoted-string
4963
4964year = 4DIGIT
4965]]></artwork>
4966</figure>
4967<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
4968; Chunked-Body defined but not used
4969; Content-Length defined but not used
4970; HTTP-message defined but not used
4971; Host defined but not used
4972; Request defined but not used
4973; Response defined but not used
4974; TE defined but not used
4975; URI defined but not used
4976; URI-reference defined but not used
4977; http-URI defined but not used
4978; https-URI defined but not used
4979; partial-URI defined but not used
4980; special defined but not used
4981]]></artwork></figure></section>
4982
4983
4984<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4985
4986<section title="Since RFC2616">
4987<t>
4988  Extracted relevant partitions from <xref target="RFC2616"/>.
4989</t>
4990</section>
4991
4992<section title="Since draft-ietf-httpbis-p1-messaging-00">
4993<t>
4994  Closed issues:
4995  <list style="symbols"> 
4996    <t>
4997      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4998      "HTTP Version should be case sensitive"
4999      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5000    </t>
5001    <t>
5002      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5003      "'unsafe' characters"
5004      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5005    </t>
5006    <t>
5007      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5008      "Chunk Size Definition"
5009      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5010    </t>
5011    <t>
5012      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5013      "Message Length"
5014      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5015    </t>
5016    <t>
5017      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5018      "Media Type Registrations"
5019      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5020    </t>
5021    <t>
5022      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5023      "URI includes query"
5024      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5025    </t>
5026    <t>
5027      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5028      "No close on 1xx responses"
5029      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5030    </t>
5031    <t>
5032      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5033      "Remove 'identity' token references"
5034      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5035    </t>
5036    <t>
5037      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5038      "Import query BNF"
5039    </t>
5040    <t>
5041      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5042      "qdtext BNF"
5043    </t>
5044    <t>
5045      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5046      "Normative and Informative references"
5047    </t>
5048    <t>
5049      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5050      "RFC2606 Compliance"
5051    </t>
5052    <t>
5053      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5054      "RFC977 reference"
5055    </t>
5056    <t>
5057      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5058      "RFC1700 references"
5059    </t>
5060    <t>
5061      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5062      "inconsistency in date format explanation"
5063    </t>
5064    <t>
5065      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5066      "Date reference typo"
5067    </t>
5068    <t>
5069      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5070      "Informative references"
5071    </t>
5072    <t>
5073      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5074      "ISO-8859-1 Reference"
5075    </t>
5076    <t>
5077      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5078      "Normative up-to-date references"
5079    </t>
5080  </list>
5081</t>
5082<t>
5083  Other changes:
5084  <list style="symbols"> 
5085    <t>
5086      Update media type registrations to use RFC4288 template.
5087    </t>
5088    <t>
5089      Use names of RFC4234 core rules DQUOTE and WSP,
5090      fix broken ABNF for chunk-data
5091      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5092    </t>
5093  </list>
5094</t>
5095</section>
5096
5097<section title="Since draft-ietf-httpbis-p1-messaging-01">
5098<t>
5099  Closed issues:
5100  <list style="symbols"> 
5101    <t>
5102      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5103      "Bodies on GET (and other) requests"
5104    </t>
5105    <t>
5106      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5107      "Updating to RFC4288"
5108    </t>
5109    <t>
5110      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5111      "Status Code and Reason Phrase"
5112    </t>
5113    <t>
5114      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5115      "rel_path not used"
5116    </t>
5117  </list>
5118</t>
5119<t>
5120  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5121  <list style="symbols"> 
5122    <t>
5123      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
5124      "trailer-part").
5125    </t>
5126    <t>
5127      Avoid underscore character in rule names ("http_URL" -&gt;
5128      "http-URL", "abs_path" -&gt; "path-absolute").
5129    </t>
5130    <t>
5131      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5132      "path-absolute", "port", "query", "relativeURI", "host) -- these will
5133      have to be updated when switching over to RFC3986.
5134    </t>
5135    <t>
5136      Synchronize core rules with RFC5234.
5137    </t>
5138    <t>
5139      Get rid of prose rules that span multiple lines.
5140    </t>
5141    <t>
5142      Get rid of unused rules LOALPHA and UPALPHA.
5143    </t>
5144    <t>
5145      Move "Product Tokens" section (back) into Part 1, as "token" is used
5146      in the definition of the Upgrade header.
5147    </t>
5148    <t>
5149      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5150    </t>
5151    <t>
5152      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5153    </t>
5154  </list>
5155</t>
5156</section>
5157
5158<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5159<t>
5160  Closed issues:
5161  <list style="symbols"> 
5162    <t>
5163      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5164      "HTTP-date vs. rfc1123-date"
5165    </t>
5166    <t>
5167      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5168      "WS in quoted-pair"
5169    </t>
5170  </list>
5171</t>
5172<t>
5173  Ongoing work on IANA Message Header Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5174  <list style="symbols"> 
5175    <t>
5176      Reference RFC 3984, and update header registrations for headers defined
5177      in this document.
5178    </t>
5179  </list>
5180</t>
5181<t>
5182  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5183  <list style="symbols"> 
5184    <t>
5185      Replace string literals when the string really is case-sensitive (HTTP-Version).
5186    </t>
5187  </list>
5188</t>
5189</section>
5190
5191<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5192<t>
5193  Closed issues:
5194  <list style="symbols"> 
5195    <t>
5196      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5197      "Connection closing"
5198    </t>
5199    <t>
5200      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5201      "Move registrations and registry information to IANA Considerations"
5202    </t>
5203    <t>
5204      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5205      "need new URL for PAD1995 reference"
5206    </t>
5207    <t>
5208      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5209      "IANA Considerations: update HTTP URI scheme registration"
5210    </t>
5211    <t>
5212      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5213      "Cite HTTPS URI scheme definition"
5214    </t>
5215    <t>
5216      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5217      "List-type headers vs Set-Cookie"
5218    </t>
5219  </list>
5220</t>
5221<t>
5222  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5223  <list style="symbols"> 
5224    <t>
5225      Replace string literals when the string really is case-sensitive (HTTP-Date).
5226    </t>
5227    <t>
5228      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5229    </t>
5230  </list>
5231</t>
5232</section>
5233
5234<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5235<t>
5236  Closed issues:
5237  <list style="symbols"> 
5238    <t>
5239      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5240      "Out-of-date reference for URIs"
5241    </t>
5242    <t>
5243      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5244      "RFC 2822 is updated by RFC 5322"
5245    </t>
5246  </list>
5247</t>
5248<t>
5249  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5250  <list style="symbols"> 
5251    <t>
5252      Use "/" instead of "|" for alternatives.
5253    </t>
5254    <t>
5255      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5256    </t>
5257    <t>
5258      Only reference RFC 5234's core rules.
5259    </t>
5260    <t>
5261      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5262      whitespace ("OWS") and required whitespace ("RWS").
5263    </t>
5264    <t>
5265      Rewrite ABNFs to spell out whitespace rules, factor out
5266      header value format definitions.
5267    </t>
5268  </list>
5269</t>
5270</section>
5271
5272<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5273<t>
5274  Closed issues:
5275  <list style="symbols"> 
5276    <t>
5277      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5278      "Header LWS"
5279    </t>
5280    <t>
5281      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5282      "Sort 1.3 Terminology"
5283    </t>
5284    <t>
5285      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5286      "RFC2047 encoded words"
5287    </t>
5288    <t>
5289      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5290      "Character Encodings in TEXT"
5291    </t>
5292    <t>
5293      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5294      "Line Folding"
5295    </t>
5296    <t>
5297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5298      "OPTIONS * and proxies"
5299    </t>
5300    <t>
5301      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5302      "Reason-Phrase BNF"
5303    </t>
5304    <t>
5305      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5306      "Use of TEXT"
5307    </t>
5308    <t>
5309      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5310      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5311    </t>
5312    <t>
5313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5314      "RFC822 reference left in discussion of date formats"
5315    </t>
5316  </list>
5317</t>
5318<t>
5319  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5320  <list style="symbols"> 
5321    <t>
5322      Rewrite definition of list rules, deprecate empty list elements.
5323    </t>
5324    <t>
5325      Add appendix containing collected and expanded ABNF.
5326    </t>
5327  </list>
5328</t>
5329<t>
5330  Other changes:
5331  <list style="symbols"> 
5332    <t>
5333      Rewrite introduction; add mostly new Architecture Section.
5334    </t>
5335    <t>
5336      Move definition of quality values from Part 3 into Part 1;
5337      make TE request header grammar independent of accept-params (defined in Part 3).
5338    </t>
5339  </list>
5340</t>
5341</section>
5342
5343<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5344<t>
5345  Closed issues:
5346  <list style="symbols"> 
5347    <t>
5348      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5349      "base for numeric protocol elements"
5350    </t>
5351    <t>
5352      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5353      "comment ABNF"
5354    </t>
5355  </list>
5356</t>
5357<t>
5358  Partly resolved issues:
5359  <list style="symbols"> 
5360    <t>
5361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5362      "205 Bodies" (took out language that implied that there may be
5363      methods for which a request body MUST NOT be included)
5364    </t>
5365    <t>
5366      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5367      "editorial improvements around HTTP-date"
5368    </t>
5369  </list>
5370</t>
5371</section>
5372
5373<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5374<t>
5375  Closed issues:
5376  <list style="symbols"> 
5377    <t>
5378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5379      "Repeating single-value headers"
5380    </t>
5381    <t>
5382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5383      "increase connection limit"
5384    </t>
5385    <t>
5386      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5387      "IP addresses in URLs"
5388    </t>
5389    <t>
5390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5391      "take over HTTP Upgrade Token Registry"
5392    </t>
5393    <t>
5394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5395      "CR and LF in chunk extension values"
5396    </t>
5397    <t>
5398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5399      "HTTP/0.9 support"
5400    </t>
5401    <t>
5402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5403      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5404    </t>
5405    <t>
5406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5407      "move definitions of gzip/deflate/compress to part 1"
5408    </t>
5409    <t>
5410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5411      "disallow control characters in quoted-pair"
5412    </t>
5413  </list>
5414</t>
5415<t>
5416  Partly resolved issues:
5417  <list style="symbols"> 
5418    <t>
5419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5420      "update IANA requirements wrt Transfer-Coding values" (add the
5421      IANA Considerations subsection)
5422    </t>
5423  </list>
5424</t>
5425</section>
5426
5427<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5428<t>
5429  Closed issues:
5430  <list style="symbols"> 
5431    <t>
5432      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5433      "header parsing, treatment of leading and trailing OWS"
5434    </t>
5435  </list>
5436</t>
5437<t>
5438  Partly resolved issues:
5439  <list style="symbols"> 
5440    <t>
5441      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5442      "Placement of 13.5.1 and 13.5.2"
5443    </t>
5444    <t>
5445      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5446      "use of term "word" when talking about header structure"
5447    </t>
5448  </list>
5449</t>
5450</section>
5451
5452</section>
5453
5454</back>
5455</rfc>
Note: See TracBrowser for help on using the repository browser.