source: draft-ietf-httpbis/17/draft-ietf-httpbis-p1-messaging-17.xml @ 1529

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fix mime types

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  • Property svn:mime-type set to text/xml
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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<?rfc rfcedstyle="yes"?>
17<!DOCTYPE rfc
18  PUBLIC "" "rfc2629.dtd">
19<rfc obsoletes="2145,2616" updates="2817" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-17">
20<front>
21
22  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
23
24  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
25    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
26    <address>
27      <postal>
28        <street>345 Park Ave</street>
29        <city>San Jose</city>
30        <region>CA</region>
31        <code>95110</code>
32        <country>USA</country>
33      </postal>
34      <email>fielding@gbiv.com</email>
35      <uri>http://roy.gbiv.com/</uri>
36    </address>
37  </author>
38
39  <author initials="J." surname="Gettys" fullname="Jim Gettys">
40    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
41    <address>
42      <postal>
43        <street>21 Oak Knoll Road</street>
44        <city>Carlisle</city>
45        <region>MA</region>
46        <code>01741</code>
47        <country>USA</country>
48      </postal>
49      <email>jg@freedesktop.org</email>
50      <uri>http://gettys.wordpress.com/</uri>
51    </address>
52  </author>
53 
54  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
55    <organization abbrev="HP">Hewlett-Packard Company</organization>
56    <address>
57      <postal>
58        <street>HP Labs, Large Scale Systems Group</street>
59        <street>1501 Page Mill Road, MS 1177</street>
60        <city>Palo Alto</city>
61        <region>CA</region>
62        <code>94304</code>
63        <country>USA</country>
64      </postal>
65      <email>JeffMogul@acm.org</email>
66    </address>
67  </author>
68
69  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
70    <organization abbrev="Microsoft">Microsoft Corporation</organization>
71    <address>
72      <postal>
73        <street>1 Microsoft Way</street>
74        <city>Redmond</city>
75        <region>WA</region>
76        <code>98052</code>
77        <country>USA</country>
78      </postal>
79      <email>henrikn@microsoft.com</email>
80    </address>
81  </author>
82
83  <author initials="L." surname="Masinter" fullname="Larry Masinter">
84    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
85    <address>
86      <postal>
87        <street>345 Park Ave</street>
88        <city>San Jose</city>
89        <region>CA</region>
90        <code>95110</code>
91        <country>USA</country>
92      </postal>
93      <email>LMM@acm.org</email>
94      <uri>http://larry.masinter.net/</uri>
95    </address>
96  </author>
97 
98  <author initials="P." surname="Leach" fullname="Paul J. Leach">
99    <organization abbrev="Microsoft">Microsoft Corporation</organization>
100    <address>
101      <postal>
102        <street>1 Microsoft Way</street>
103        <city>Redmond</city>
104        <region>WA</region>
105        <code>98052</code>
106      </postal>
107      <email>paulle@microsoft.com</email>
108    </address>
109  </author>
110   
111  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
112    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
113    <address>
114      <postal>
115        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
116        <street>The Stata Center, Building 32</street>
117        <street>32 Vassar Street</street>
118        <city>Cambridge</city>
119        <region>MA</region>
120        <code>02139</code>
121        <country>USA</country>
122      </postal>
123      <email>timbl@w3.org</email>
124      <uri>http://www.w3.org/People/Berners-Lee/</uri>
125    </address>
126  </author>
127
128  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
129    <organization abbrev="W3C">World Wide Web Consortium</organization>
130    <address>
131      <postal>
132        <street>W3C / ERCIM</street>
133        <street>2004, rte des Lucioles</street>
134        <city>Sophia-Antipolis</city>
135        <region>AM</region>
136        <code>06902</code>
137        <country>France</country>
138      </postal>
139      <email>ylafon@w3.org</email>
140      <uri>http://www.raubacapeu.net/people/yves/</uri>
141    </address>
142  </author>
143
144  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
145    <organization abbrev="greenbytes">greenbytes GmbH</organization>
146    <address>
147      <postal>
148        <street>Hafenweg 16</street>
149        <city>Muenster</city><region>NW</region><code>48155</code>
150        <country>Germany</country>
151      </postal>
152      <phone>+49 251 2807760</phone>
153      <facsimile>+49 251 2807761</facsimile>
154      <email>julian.reschke@greenbytes.de</email>
155      <uri>http://greenbytes.de/tech/webdav/</uri>
156    </address>
157  </author>
158
159  <date month="October" year="2011" day="31"/>
160  <workgroup>HTTPbis Working Group</workgroup>
161
162<abstract>
163<t>
164   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
165   distributed, collaborative, hypertext information systems. HTTP has been in
166   use by the World Wide Web global information initiative since 1990. This
167   document is Part 1 of the seven-part specification that defines the protocol
168   referred to as "HTTP/1.1" and, taken together, obsoletes
169   RFC 2616 and moves it to historic
170   status, along with its predecessor RFC
171   2068.
172</t>
173<t>
174   Part 1 provides an overview of HTTP and its associated terminology, defines
175   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
176   the generic message syntax and parsing requirements for HTTP message frames,
177   and describes general security concerns for implementations.
178</t>
179<t>
180   This part also obsoletes RFCs 2145
181   (on HTTP version numbers) and 2817
182   (on using CONNECT for TLS upgrades) and moves them to historic status.
183</t>
184</abstract>
185
186<note title="Editorial Note (To be removed by RFC Editor)">
187  <t>
188    Discussion of this draft should take place on the HTTPBIS working group
189    mailing list (ietf-http-wg@w3.org), which is archived at
190    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
191  </t>
192  <t>
193    The current issues list is at
194    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
195    documents (including fancy diffs) can be found at
196    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
197  </t>
198  <t>
199    The changes in this draft are summarized in <xref target="changes.since.16"/>.
200  </t>
201</note>
202</front>
203<middle>
204<section title="Introduction" anchor="introduction">
205<t>
206   The Hypertext Transfer Protocol (HTTP) is an application-level
207   request/response protocol that uses extensible semantics and MIME-like
208   message payloads for flexible interaction with network-based hypertext
209   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
210   standard <xref target="RFC3986"/> to indicate the target resource and
211   relationships between resources.
212   Messages are passed in a format similar to that used by Internet mail
213   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
214   (MIME) <xref target="RFC2045"/> (see Appendix A of <xref target="Part3"/> for the differences
215   between HTTP and MIME messages).
216</t>
217<t>
218   HTTP is a generic interface protocol for information systems. It is
219   designed to hide the details of how a service is implemented by presenting
220   a uniform interface to clients that is independent of the types of
221   resources provided. Likewise, servers do not need to be aware of each
222   client's purpose: an HTTP request can be considered in isolation rather
223   than being associated with a specific type of client or a predetermined
224   sequence of application steps. The result is a protocol that can be used
225   effectively in many different contexts and for which implementations can
226   evolve independently over time.
227</t>
228<t>
229   HTTP is also designed for use as an intermediation protocol for translating
230   communication to and from non-HTTP information systems.
231   HTTP proxies and gateways can provide access to alternative information
232   services by translating their diverse protocols into a hypertext
233   format that can be viewed and manipulated by clients in the same way
234   as HTTP services.
235</t>
236<t>
237   One consequence of HTTP flexibility is that the protocol cannot be
238   defined in terms of what occurs behind the interface. Instead, we
239   are limited to defining the syntax of communication, the intent
240   of received communication, and the expected behavior of recipients.
241   If the communication is considered in isolation, then successful
242   actions ought to be reflected in corresponding changes to the
243   observable interface provided by servers. However, since multiple
244   clients might act in parallel and perhaps at cross-purposes, we
245   cannot require that such changes be observable beyond the scope
246   of a single response.
247</t>
248<t>
249   This document is Part 1 of the seven-part specification of HTTP,
250   defining the protocol referred to as "HTTP/1.1", obsoleting
251   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
252   Part 1 describes the architectural elements that are used or
253   referred to in HTTP, defines the "http" and "https" URI schemes,
254   describes overall network operation and connection management,
255   and defines HTTP message framing and forwarding requirements.
256   Our goal is to define all of the mechanisms necessary for HTTP message
257   handling that are independent of message semantics, thereby defining the
258   complete set of requirements for message parsers and
259   message-forwarding intermediaries.
260</t>
261
262<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
263<t>
264   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
265   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
266   document are to be interpreted as described in <xref target="RFC2119"/>.
267</t>
268<t>
269   This document defines conformance criteria for several roles in HTTP
270   communication, including Senders, Recipients, Clients, Servers, User-Agents,
271   Origin Servers, Intermediaries, Proxies and Gateways. See <xref target="architecture"/>
272   for definitions of these terms.
273</t>
274<t>
275   An implementation is considered conformant if it complies with all of the
276   requirements associated with its role(s). Note that SHOULD-level requirements
277   are relevant here, unless one of the documented exceptions is applicable.
278</t>
279<t>
280   This document also uses ABNF to define valid protocol elements
281   (<xref target="notation"/>). In addition to the prose requirements placed
282   upon them, Senders MUST NOT generate protocol elements that are invalid.
283</t>
284<t>
285   Unless noted otherwise, Recipients MAY take steps to recover a usable
286   protocol element from an invalid construct. However, HTTP does not define
287   specific error handling mechanisms, except in cases where it has direct
288   impact on security. This is because different uses of the protocol require
289   different error handling strategies; for example, a Web browser may wish to
290   transparently recover from a response where the Location header field
291   doesn't parse according to the ABNF, whereby in a systems control protocol
292   using HTTP, this type of error recovery could lead to dangerous consequences.
293</t>
294</section>
295
296<section title="Syntax Notation" anchor="notation">
297<iref primary="true" item="Grammar" subitem="ALPHA"/>
298<iref primary="true" item="Grammar" subitem="CR"/>
299<iref primary="true" item="Grammar" subitem="CRLF"/>
300<iref primary="true" item="Grammar" subitem="CTL"/>
301<iref primary="true" item="Grammar" subitem="DIGIT"/>
302<iref primary="true" item="Grammar" subitem="DQUOTE"/>
303<iref primary="true" item="Grammar" subitem="HEXDIG"/>
304<iref primary="true" item="Grammar" subitem="HTAB"/>
305<iref primary="true" item="Grammar" subitem="LF"/>
306<iref primary="true" item="Grammar" subitem="OCTET"/>
307<iref primary="true" item="Grammar" subitem="SP"/>
308<iref primary="true" item="Grammar" subitem="VCHAR"/>
309<t>
310   This specification uses the Augmented Backus-Naur Form (ABNF) notation
311   of <xref target="RFC5234"/>.
312</t>
313<t anchor="core.rules">
314 
315 
316 
317 
318 
319 
320 
321 
322 
323 
324 
325 
326   The following core rules are included by
327   reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
328   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
329   DIGIT (decimal 0-9), DQUOTE (double quote),
330   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
331   OCTET (any 8-bit sequence of data), SP (space), and
332   VCHAR (any visible <xref target="USASCII"/> character).
333</t>
334<t>
335   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
336   "obsolete" grammar rules that appear for historical reasons.
337</t>
338
339<section title="ABNF Extension: #rule" anchor="notation.abnf">
340<t>
341  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
342  improve readability.
343</t>
344<t>
345  A construct "#" is defined, similar to "*", for defining comma-delimited
346  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
347  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
348  comma (",") and optional whitespace (OWS, <xref target="basic.rules"/>).   
349</t>
350<figure><preamble>
351  Thus,
352</preamble><artwork type="example"><![CDATA[
353  1#element => element *( OWS "," OWS element )
354]]></artwork></figure>
355<figure><preamble>
356  and:
357</preamble><artwork type="example"><![CDATA[
358  #element => [ 1#element ]
359]]></artwork></figure>
360<figure><preamble>
361  and for n &gt;= 1 and m &gt; 1:
362</preamble><artwork type="example"><![CDATA[
363  <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
364]]></artwork></figure>
365<t>
366  For compatibility with legacy list rules, recipients SHOULD accept empty
367  list elements. In other words, consumers would follow the list productions:
368</t>
369<figure><artwork type="example"><![CDATA[
370  #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
371 
372  1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
373]]></artwork></figure>
374<t>
375  Note that empty elements do not contribute to the count of elements present,
376  though.
377</t>
378<t>
379  For example, given these ABNF productions:
380</t>
381<figure><artwork type="example"><![CDATA[
382  example-list      = 1#example-list-elmt
383  example-list-elmt = token ; see Section 3.2.3
384]]></artwork></figure>
385<t>
386  Then these are valid values for example-list (not including the double
387  quotes, which are present for delimitation only):
388</t>
389<figure><artwork type="example"><![CDATA[
390  "foo,bar"
391  "foo ,bar,"
392  "foo , ,bar,charlie   "
393]]></artwork></figure>
394<t>
395  But these values would be invalid, as at least one non-empty element is
396  required:
397</t>
398<figure><artwork type="example"><![CDATA[
399  ""
400  ","
401  ",   ,"
402]]></artwork></figure>
403<t>
404  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
405  expanded as explained above.
406</t>
407</section>
408
409<section title="Basic Rules" anchor="basic.rules">
410<t anchor="rule.LWS">
411   This specification uses three rules to denote the use of linear
412   whitespace: OWS (optional whitespace), RWS (required whitespace), and
413   BWS ("bad" whitespace).
414</t>
415<t anchor="rule.OWS">
416   The OWS rule is used where zero or more linear whitespace octets might
417   appear. OWS SHOULD either not be produced or be produced as a single
418   SP. Multiple OWS octets that occur within field-content SHOULD either
419   be replaced with a single SP or transformed to all SP octets (each
420   octet other than SP replaced with SP) before interpreting the field value
421   or forwarding the message downstream.
422</t>
423<t anchor="rule.RWS">
424   RWS is used when at least one linear whitespace octet is required to
425   separate field tokens. RWS SHOULD be produced as a single SP.
426   Multiple RWS octets that occur within field-content SHOULD either
427   be replaced with a single SP or transformed to all SP octets before
428   interpreting the field value or forwarding the message downstream.
429</t>
430<t anchor="rule.BWS">
431   BWS is used where the grammar allows optional whitespace for historical
432   reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
433   recipients MUST accept such bad optional whitespace and remove it before
434   interpreting the field value or forwarding the message downstream.
435</t>
436<t anchor="rule.whitespace">
437 
438 
439 
440 
441</t>
442<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[
443  OWS            = *( SP / HTAB / obs-fold )
444                 ; "optional" whitespace
445  RWS            = 1*( SP / HTAB / obs-fold )
446                 ; "required" whitespace
447  BWS            = OWS
448                 ; "bad" whitespace
449  obs-fold       = CRLF ( SP / HTAB )
450                 ; obsolete line folding
451                 ; see Section 3.2.1
452]]></artwork></figure>
453</section>
454</section>
455</section>
456
457<section title="Architecture" anchor="architecture">
458<t>
459   HTTP was created for the World Wide Web architecture
460   and has evolved over time to support the scalability needs of a worldwide
461   hypertext system. Much of that architecture is reflected in the terminology
462   and syntax productions used to define HTTP.
463</t>
464
465<section title="Client/Server Messaging" anchor="operation">
466<iref primary="true" item="client"/>
467<iref primary="true" item="server"/>
468<iref primary="true" item="connection"/>
469<t>
470   HTTP is a stateless request/response protocol that operates by exchanging
471   messages (<xref target="http.message"/>) across a reliable
472   transport or session-layer
473   "connection". An HTTP "client" is a
474   program that establishes a connection to a server for the purpose of
475   sending one or more HTTP requests.  An HTTP "server" is a
476   program that accepts connections in order to service HTTP requests by
477   sending HTTP responses.
478</t>
479<iref primary="true" item="user agent"/>
480<iref primary="true" item="origin server"/>
481<iref primary="true" item="browser"/>
482<iref primary="true" item="spider"/>
483<iref primary="true" item="sender"/>
484<iref primary="true" item="recipient"/>
485<t>
486   Note that the terms client and server refer only to the roles that
487   these programs perform for a particular connection.  The same program
488   might act as a client on some connections and a server on others.  We use
489   the term "user agent" to refer to the program that initiates a request,
490   such as a WWW browser, editor, or spider (web-traversing robot), and
491   the term "origin server" to refer to the program that can originate
492   authoritative responses to a request.  For general requirements, we use
493   the term "sender" to refer to whichever component sent a given message
494   and the term "recipient" to refer to any component that receives the
495   message.
496</t>
497<t>
498   Most HTTP communication consists of a retrieval request (GET) for
499   a representation of some resource identified by a URI.  In the
500   simplest case, this might be accomplished via a single bidirectional
501   connection (===) between the user agent (UA) and the origin server (O).
502</t>
503<figure><artwork type="drawing"><![CDATA[
504         request   >
505    UA ======================================= O
506                                <   response
507]]></artwork></figure>
508<iref primary="true" item="message"/>
509<iref primary="true" item="request"/>
510<iref primary="true" item="response"/>
511<t>
512   A client sends an HTTP request to the server in the form of a request
513   message, beginning with a request-line that includes a method, URI, and
514   protocol version (<xref target="request.line"/>),
515   followed by MIME-like header fields containing
516   request modifiers, client information, and payload metadata
517   (<xref target="header.fields"/>),
518   an empty line to indicate the end of the header section, and finally
519   a message body containing the payload body (if any,
520   <xref target="message.body"/>).
521</t>
522<t>
523   A server responds to the client's request by sending an HTTP response
524   message, beginning with a status line that
525   includes the protocol version, a success or error code, and textual
526   reason phrase (<xref target="status.line"/>),
527   followed by MIME-like header fields containing server
528   information, resource metadata, and payload metadata
529   (<xref target="header.fields"/>),
530   an empty line to indicate the end of the header section, and finally
531   a message body containing the payload body (if any,
532   <xref target="message.body"/>).
533</t>
534<t>
535   The following example illustrates a typical message exchange for a
536   GET request on the URI "http://www.example.com/hello.txt":
537</t>
538<figure><preamble>
539client request:
540</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
541  GET /hello.txt HTTP/1.1
542  User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
543  Host: www.example.com
544  Accept: */*
545 
546  ]]></artwork></figure>
547<figure><preamble>
548server response:
549</preamble><artwork type="message/http; msgtype=&#34;response&#34;"><![CDATA[
550  HTTP/1.1 200 OK
551  Date: Mon, 27 Jul 2009 12:28:53 GMT
552  Server: Apache
553  Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
554  ETag: "34aa387-d-1568eb00"
555  Accept-Ranges: bytes
556  Content-Length: 14
557  Vary: Accept-Encoding
558  Content-Type: text/plain
559 
560  Hello World!
561  ]]></artwork></figure>
562</section>
563
564<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
565<t>
566   Fundamentally, HTTP is a message-based protocol. Although message bodies can
567   be chunked (<xref target="chunked.encoding"/>) and implementations often
568   make parts of a message available progressively, this is not required, and
569   some widely-used implementations only make a message available when it is
570   complete. Furthermore, while most proxies will progressively stream messages,
571   some amount of buffering will take place, and some proxies might buffer
572   messages to perform transformations, check content or provide other services.
573</t>
574<t>
575   Therefore, extensions to and uses of HTTP cannot rely on the availability of
576   a partial message, or assume that messages will not be buffered. There are
577   strategies that can be used to test for buffering in a given connection, but
578   it should be understood that behaviors can differ across connections, and
579   between requests and responses.
580</t>
581<t>
582   Recipients MUST consider every message in a connection in isolation;
583   because HTTP is a stateless protocol, it cannot be assumed that two requests
584   on the same connection are from the same client or share any other common
585   attributes. In particular, intermediaries might mix requests from different
586   clients into a single server connection. Note that some existing HTTP
587   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
588   potentially causing interoperability and security problems.
589</t>
590</section>
591
592<section title="Connections and Transport Independence" anchor="transport-independence">
593<t>
594   HTTP messaging is independent of the underlying transport or
595   session-layer connection protocol(s).  HTTP only presumes a reliable
596   transport with in-order delivery of requests and the corresponding
597   in-order delivery of responses.  The mapping of HTTP request and
598   response structures onto the data units of the underlying transport
599   protocol is outside the scope of this specification.
600</t>
601<t>
602   The specific connection protocols to be used for an interaction
603   are determined by client configuration and the target resource's URI.
604   For example, the "http" URI scheme
605   (<xref target="http.uri"/>) indicates a default connection of TCP
606   over IP, with a default TCP port of 80, but the client might be
607   configured to use a proxy via some other connection port or protocol
608   instead of using the defaults.
609</t>
610<t>
611   A connection might be used for multiple HTTP request/response exchanges,
612   as defined in <xref target="persistent.connections"/>.
613</t>
614</section>
615
616<section title="Intermediaries" anchor="intermediaries">
617<iref primary="true" item="intermediary"/>
618<t>
619   HTTP enables the use of intermediaries to satisfy requests through
620   a chain of connections.  There are three common forms of HTTP
621   intermediary: proxy, gateway, and tunnel.  In some cases,
622   a single intermediary might act as an origin server, proxy, gateway,
623   or tunnel, switching behavior based on the nature of each request.
624</t>
625<figure><artwork type="drawing"><![CDATA[
626         >             >             >             >
627    UA =========== A =========== B =========== C =========== O
628               <             <             <             <
629]]></artwork></figure>
630<t>
631   The figure above shows three intermediaries (A, B, and C) between the
632   user agent and origin server. A request or response message that
633   travels the whole chain will pass through four separate connections.
634   Some HTTP communication options
635   might apply only to the connection with the nearest, non-tunnel
636   neighbor, only to the end-points of the chain, or to all connections
637   along the chain. Although the diagram is linear, each participant might
638   be engaged in multiple, simultaneous communications. For example, B
639   might be receiving requests from many clients other than A, and/or
640   forwarding requests to servers other than C, at the same time that it
641   is handling A's request.
642</t>
643<t>
644<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
645<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
646   We use the terms "upstream" and "downstream"
647   to describe various requirements in relation to the directional flow of a
648   message: all messages flow from upstream to downstream.
649   Likewise, we use the terms inbound and outbound to refer to
650   directions in relation to the request path:
651   "inbound" means toward the origin server and
652   "outbound" means toward the user agent.
653</t>
654<t><iref primary="true" item="proxy"/>
655   A "proxy" is a message forwarding agent that is selected by the
656   client, usually via local configuration rules, to receive requests
657   for some type(s) of absolute URI and attempt to satisfy those
658   requests via translation through the HTTP interface.  Some translations
659   are minimal, such as for proxy requests for "http" URIs, whereas
660   other requests might require translation to and from entirely different
661   application-layer protocols. Proxies are often used to group an
662   organization's HTTP requests through a common intermediary for the
663   sake of security, annotation services, or shared caching.
664</t>
665<t>
666<iref primary="true" item="transforming proxy"/>
667<iref primary="true" item="non-transforming proxy"/>
668   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
669   or configured to modify request or response messages in a semantically
670   meaningful way (i.e., modifications, beyond those required by normal
671   HTTP processing, that change the message in a way that would be
672   significant to the original sender or potentially significant to
673   downstream recipients).  For example, a transforming proxy might be
674   acting as a shared annotation server (modifying responses to include
675   references to a local annotation database), a malware filter, a
676   format transcoder, or an intranet-to-Internet privacy filter.  Such
677   transformations are presumed to be desired by the client (or client
678   organization) that selected the proxy and are beyond the scope of
679   this specification.  However, when a proxy is not intended to transform
680   a given message, we use the term "non-transforming proxy" to target
681   requirements that preserve HTTP message semantics. See Section 7.2.4 of <xref target="Part2"/> and
682   Section 3.6 of <xref target="Part6"/> for status and warning codes related to transformations.
683</t>
684<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
685<iref primary="true" item="accelerator"/>
686   A "gateway" (a.k.a., "reverse proxy")
687   is a receiving agent that acts
688   as a layer above some other server(s) and translates the received
689   requests to the underlying server's protocol.  Gateways are often
690   used to encapsulate legacy or untrusted information services, to
691   improve server performance through "accelerator" caching, and to
692   enable partitioning or load-balancing of HTTP services across
693   multiple machines.
694</t>
695<t>
696   A gateway behaves as an origin server on its outbound connection and
697   as a user agent on its inbound connection.
698   All HTTP requirements applicable to an origin server
699   also apply to the outbound communication of a gateway.
700   A gateway communicates with inbound servers using any protocol that
701   it desires, including private extensions to HTTP that are outside
702   the scope of this specification.  However, an HTTP-to-HTTP gateway
703   that wishes to interoperate with third-party HTTP servers MUST
704   comply with HTTP user agent requirements on the gateway's inbound
705   connection and MUST implement the Connection
706   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
707   header fields for both connections.
708</t>
709<t><iref primary="true" item="tunnel"/>
710   A "tunnel" acts as a blind relay between two connections
711   without changing the messages. Once active, a tunnel is not
712   considered a party to the HTTP communication, though the tunnel might
713   have been initiated by an HTTP request. A tunnel ceases to exist when
714   both ends of the relayed connection are closed. Tunnels are used to
715   extend a virtual connection through an intermediary, such as when
716   transport-layer security is used to establish private communication
717   through a shared firewall proxy.
718</t>
719<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
720<iref primary="true" item="captive portal"/>
721   In addition, there may exist network intermediaries that are not
722   considered part of the HTTP communication but nevertheless act as
723   filters or redirecting agents (usually violating HTTP semantics,
724   causing security problems, and otherwise making a mess of things).
725   Such a network intermediary, often referred to as an "interception proxy"
726   <xref target="RFC3040"/>, "transparent proxy" <xref target="RFC1919"/>,
727   or "captive portal",
728   differs from an HTTP proxy because it has not been selected by the client.
729   Instead, the network intermediary redirects outgoing TCP port 80 packets
730   (and occasionally other common port traffic) to an internal HTTP server.
731   Interception proxies are commonly found on public network access points,
732   as a means of enforcing account subscription prior to allowing use of
733   non-local Internet services, and within corporate firewalls to enforce
734   network usage policies.
735   They are indistinguishable from a man-in-the-middle attack.
736</t>
737</section>
738
739<section title="Caches" anchor="caches">
740<iref primary="true" item="cache"/>
741<t>
742   A "cache" is a local store of previous response messages and the
743   subsystem that controls its message storage, retrieval, and deletion.
744   A cache stores cacheable responses in order to reduce the response
745   time and network bandwidth consumption on future, equivalent
746   requests. Any client or server MAY employ a cache, though a cache
747   cannot be used by a server while it is acting as a tunnel.
748</t>
749<t>
750   The effect of a cache is that the request/response chain is shortened
751   if one of the participants along the chain has a cached response
752   applicable to that request. The following illustrates the resulting
753   chain if B has a cached copy of an earlier response from O (via C)
754   for a request which has not been cached by UA or A.
755</t>
756<figure><artwork type="drawing"><![CDATA[
757            >             >
758       UA =========== A =========== B - - - - - - C - - - - - - O
759                  <             <
760]]></artwork></figure>
761<t><iref primary="true" item="cacheable"/>
762   A response is "cacheable" if a cache is allowed to store a copy of
763   the response message for use in answering subsequent requests.
764   Even when a response is cacheable, there might be additional
765   constraints placed by the client or by the origin server on when
766   that cached response can be used for a particular request. HTTP
767   requirements for cache behavior and cacheable responses are
768   defined in Section 2 of <xref target="Part6"/>
769</t>
770<t>
771   There are a wide variety of architectures and configurations
772   of caches and proxies deployed across the World Wide Web and
773   inside large organizations. These systems include national hierarchies
774   of proxy caches to save transoceanic bandwidth, systems that
775   broadcast or multicast cache entries, organizations that distribute
776   subsets of cached data via optical media, and so on.
777</t>
778</section>
779
780<section title="Protocol Versioning" anchor="http.version">
781 
782 
783<t>
784   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
785   versions of the protocol. This specification defines version "1.1".
786   The protocol version as a whole indicates the sender's compliance
787   with the set of requirements laid out in that version's corresponding
788   specification of HTTP.
789</t>
790<t>
791   The version of an HTTP message is indicated by an HTTP-Version field
792   in the first line of the message. HTTP-Version is case-sensitive.
793</t>
794<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
795  HTTP-Version   = HTTP-Prot-Name "/" DIGIT "." DIGIT
796  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
797]]></artwork></figure>
798<t>
799   The HTTP version number consists of two decimal digits separated by a "."
800   (period or decimal point).  The first digit ("major version") indicates the
801   HTTP messaging syntax, whereas the second digit ("minor version") indicates
802   the highest minor version to which the sender is at least conditionally
803   compliant and able to understand for future communication.  The minor
804   version advertises the sender's communication capabilities even when the
805   sender is only using a backwards-compatible subset of the protocol,
806   thereby letting the recipient know that more advanced features can
807   be used in response (by servers) or in future requests (by clients).
808</t>
809<t>
810   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
811   <xref target="RFC1945"/> or a recipient whose version is unknown,
812   the HTTP/1.1 message is constructed such that it can be interpreted
813   as a valid HTTP/1.0 message if all of the newer features are ignored.
814   This specification places recipient-version requirements on some
815   new features so that a compliant sender will only use compatible
816   features until it has determined, through configuration or the
817   receipt of a message, that the recipient supports HTTP/1.1.
818</t>
819<t>
820   The interpretation of an HTTP header field does not change
821   between minor versions of the same major version, though the default
822   behavior of a recipient in the absence of such a field can change.
823   Unless specified otherwise, header fields defined in HTTP/1.1 are
824   defined for all versions of HTTP/1.x.  In particular, the Host and
825   Connection header fields ought to be implemented by all HTTP/1.x
826   implementations whether or not they advertise compliance with HTTP/1.1.
827</t>
828<t>
829   New header fields can be defined such that, when they are
830   understood by a recipient, they might override or enhance the
831   interpretation of previously defined header fields.  When an
832   implementation receives an unrecognized header field, the recipient
833   MUST ignore that header field for local processing regardless of
834   the message's HTTP version.  An unrecognized header field received
835   by a proxy MUST be forwarded downstream unless the header field's
836   field-name is listed in the message's Connection header-field
837   (see <xref target="header.connection"/>).
838   These requirements allow HTTP's functionality to be enhanced without
839   requiring prior update of all compliant intermediaries.
840</t>
841<t>
842   Intermediaries that process HTTP messages (i.e., all intermediaries
843   other than those acting as a tunnel) MUST send their own HTTP-Version
844   in forwarded messages.  In other words, they MUST NOT blindly
845   forward the first line of an HTTP message without ensuring that the
846   protocol version matches what the intermediary understands, and
847   is at least conditionally compliant to, for both the receiving and
848   sending of messages.  Forwarding an HTTP message without rewriting
849   the HTTP-Version might result in communication errors when downstream
850   recipients use the message sender's version to determine what features
851   are safe to use for later communication with that sender.
852</t>
853<t>
854   An HTTP client SHOULD send a request version equal to the highest
855   version for which the client is at least conditionally compliant and
856   whose major version is no higher than the highest version supported
857   by the server, if this is known.  An HTTP client MUST NOT send a
858   version for which it is not at least conditionally compliant.
859</t>
860<t>
861   An HTTP client MAY send a lower request version if it is known that
862   the server incorrectly implements the HTTP specification, but only
863   after the client has attempted at least one normal request and determined
864   from the response status or header fields (e.g., Server) that the
865   server improperly handles higher request versions.
866</t>
867<t>
868   An HTTP server SHOULD send a response version equal to the highest
869   version for which the server is at least conditionally compliant and
870   whose major version is less than or equal to the one received in the
871   request.  An HTTP server MUST NOT send a version for which it is not
872   at least conditionally compliant.  A server MAY send a 505 (HTTP
873   Version Not Supported) response if it cannot send a response using the
874   major version used in the client's request.
875</t>
876<t>
877   An HTTP server MAY send an HTTP/1.0 response to an HTTP/1.0 request
878   if it is known or suspected that the client incorrectly implements the
879   HTTP specification and is incapable of correctly processing later
880   version responses, such as when a client fails to parse the version
881   number correctly or when an intermediary is known to blindly forward
882   the HTTP-Version even when it doesn't comply with the given minor
883   version of the protocol. Such protocol downgrades SHOULD NOT be
884   performed unless triggered by specific client attributes, such as when
885   one or more of the request header fields (e.g., User-Agent) uniquely
886   match the values sent by a client known to be in error.
887</t>
888<t>
889   The intention of HTTP's versioning design is that the major number
890   will only be incremented if an incompatible message syntax is
891   introduced, and that the minor number will only be incremented when
892   changes made to the protocol have the effect of adding to the message
893   semantics or implying additional capabilities of the sender.  However,
894   the minor version was not incremented for the changes introduced between
895   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
896   is specifically avoiding any such changes to the protocol.
897</t>
898</section>
899
900<section title="Uniform Resource Identifiers" anchor="uri">
901<iref primary="true" item="resource"/>
902<t>
903   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
904   throughout HTTP as the means for identifying resources. URI references
905   are used to target requests, indicate redirects, and define relationships.
906   HTTP does not limit what a resource might be; it merely defines an interface
907   that can be used to interact with a resource via HTTP. More information on
908   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
909</t>
910 
911 
912 
913 
914 
915 
916 
917 
918 
919 
920<t>
921   This specification adopts the definitions of "URI-reference",
922   "absolute-URI", "relative-part", "port", "host",
923   "path-abempty", "path-absolute", "query", and "authority" from the
924   URI generic syntax <xref target="RFC3986"/>.
925   In addition, we define a partial-URI rule for protocol elements
926   that allow a relative URI but not a fragment.
927</t>
928<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[
929  URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
930  absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
931  relative-part = <relative-part, defined in [RFC3986], Section 4.2>
932  authority     = <authority, defined in [RFC3986], Section 3.2>
933  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
934  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
935  port          = <port, defined in [RFC3986], Section 3.2.3>
936  query         = <query, defined in [RFC3986], Section 3.4>
937  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
938 
939  partial-URI   = relative-part [ "?" query ]
940]]></artwork></figure>
941<t>
942   Each protocol element in HTTP that allows a URI reference will indicate
943   in its ABNF production whether the element allows any form of reference
944   (URI-reference), only a URI in absolute form (absolute-URI), only the
945   path and optional query components, or some combination of the above.
946   Unless otherwise indicated, URI references are parsed relative to the
947   effective request URI, which defines the default base URI for references
948   in both the request and its corresponding response.
949</t>
950
951<section title="http URI scheme" anchor="http.uri">
952 
953  <iref item="http URI scheme" primary="true"/>
954  <iref item="URI scheme" subitem="http" primary="true"/>
955<t>
956   The "http" URI scheme is hereby defined for the purpose of minting
957   identifiers according to their association with the hierarchical
958   namespace governed by a potential HTTP origin server listening for
959   TCP connections on a given port.
960</t>
961<figure><iref primary="true" item="Grammar" subitem="http-URI"/><artwork type="abnf2616"><![CDATA[
962  http-URI = "http:" "//" authority path-abempty [ "?" query ]
963]]></artwork></figure>
964<t>
965   The HTTP origin server is identified by the generic syntax's
966   <xref target="uri" format="none">authority</xref> component, which includes a host identifier
967   and optional TCP port (<xref target="RFC3986"/>, Section 3.2.2).
968   The remainder of the URI, consisting of both the hierarchical path
969   component and optional query component, serves as an identifier for
970   a potential resource within that origin server's name space.
971</t>
972<t>
973   If the host identifier is provided as an IP literal or IPv4 address,
974   then the origin server is any listener on the indicated TCP port at
975   that IP address. If host is a registered name, then that name is
976   considered an indirect identifier and the recipient might use a name
977   resolution service, such as DNS, to find the address of a listener
978   for that host.
979   The host MUST NOT be empty; if an "http" URI is received with an
980   empty host, then it MUST be rejected as invalid.
981   If the port subcomponent is empty or not given, then TCP port 80 is
982   assumed (the default reserved port for WWW services).
983</t>
984<t>
985   Regardless of the form of host identifier, access to that host is not
986   implied by the mere presence of its name or address. The host might or might
987   not exist and, even when it does exist, might or might not be running an
988   HTTP server or listening to the indicated port. The "http" URI scheme
989   makes use of the delegated nature of Internet names and addresses to
990   establish a naming authority (whatever entity has the ability to place
991   an HTTP server at that Internet name or address) and allows that
992   authority to determine which names are valid and how they might be used.
993</t>
994<t>
995   When an "http" URI is used within a context that calls for access to the
996   indicated resource, a client MAY attempt access by resolving
997   the host to an IP address, establishing a TCP connection to that address
998   on the indicated port, and sending an HTTP request message
999   (<xref target="http.message"/>) containing the URI's identifying data
1000   (<xref target="message.routing"/>) to the server.
1001   If the server responds to that request with a non-interim HTTP response
1002   message, as described in Section 4 of <xref target="Part2"/>, then that response
1003   is considered an authoritative answer to the client's request.
1004</t>
1005<t>
1006   Although HTTP is independent of the transport protocol, the "http"
1007   scheme is specific to TCP-based services because the name delegation
1008   process depends on TCP for establishing authority.
1009   An HTTP service based on some other underlying connection protocol
1010   would presumably be identified using a different URI scheme, just as
1011   the "https" scheme (below) is used for servers that require an SSL/TLS
1012   transport layer on a connection. Other protocols might also be used to
1013   provide access to "http" identified resources — it is only the
1014   authoritative interface used for mapping the namespace that is
1015   specific to TCP.
1016</t>
1017<t>
1018   The URI generic syntax for authority also includes a deprecated
1019   userinfo subcomponent (<xref target="RFC3986"/>, Section 3.2.1)
1020   for including user authentication information in the URI.  Some
1021   implementations make use of the userinfo component for internal
1022   configuration of authentication information, such as within command
1023   invocation options, configuration files, or bookmark lists, even
1024   though such usage might expose a user identifier or password.
1025   Senders MUST NOT include a userinfo subcomponent (and its "@"
1026   delimiter) when transmitting an "http" URI in a message.  Recipients
1027   of HTTP messages that contain a URI reference SHOULD parse for the
1028   existence of userinfo and treat its presence as an error, likely
1029   indicating that the deprecated subcomponent is being used to obscure
1030   the authority for the sake of phishing attacks.
1031</t>
1032</section>
1033
1034<section title="https URI scheme" anchor="https.uri">
1035   
1036   <iref item="https URI scheme"/>
1037   <iref item="URI scheme" subitem="https"/>
1038<t>
1039   The "https" URI scheme is hereby defined for the purpose of minting
1040   identifiers according to their association with the hierarchical
1041   namespace governed by a potential HTTP origin server listening for
1042   SSL/TLS-secured connections on a given TCP port.
1043</t>
1044<t>
1045   All of the requirements listed above for the "http" scheme are also
1046   requirements for the "https" scheme, except that a default TCP port
1047   of 443 is assumed if the port subcomponent is empty or not given,
1048   and the TCP connection MUST be secured for privacy through the
1049   use of strong encryption prior to sending the first HTTP request.
1050</t>
1051<figure><iref primary="true" item="Grammar" subitem="https-URI"/><artwork type="abnf2616"><![CDATA[
1052  https-URI = "https:" "//" authority path-abempty [ "?" query ]
1053]]></artwork></figure>
1054<t>
1055   Unlike the "http" scheme, responses to "https" identified requests
1056   are never "public" and thus MUST NOT be reused for shared caching.
1057   They can, however, be reused in a private cache if the message is
1058   cacheable by default in HTTP or specifically indicated as such by
1059   the Cache-Control header field (Section 3.2 of <xref target="Part6"/>).
1060</t>
1061<t>
1062   Resources made available via the "https" scheme have no shared
1063   identity with the "http" scheme even if their resource identifiers
1064   indicate the same authority (the same host listening to the same
1065   TCP port).  They are distinct name spaces and are considered to be
1066   distinct origin servers.  However, an extension to HTTP that is
1067   defined to apply to entire host domains, such as the Cookie protocol
1068   <xref target="RFC6265"/>, can allow information
1069   set by one service to impact communication with other services
1070   within a matching group of host domains.
1071</t>
1072<t>
1073   The process for authoritative access to an "https" identified
1074   resource is defined in <xref target="RFC2818"/>.
1075</t>
1076</section>
1077
1078<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1079<t>
1080   Since the "http" and "https" schemes conform to the URI generic syntax,
1081   such URIs are normalized and compared according to the algorithm defined
1082   in <xref target="RFC3986"/>, Section 6, using the defaults
1083   described above for each scheme.
1084</t>
1085<t>
1086   If the port is equal to the default port for a scheme, the normal
1087   form is to elide the port subcomponent. Likewise, an empty path
1088   component is equivalent to an absolute path of "/", so the normal
1089   form is to provide a path of "/" instead. The scheme and host
1090   are case-insensitive and normally provided in lowercase; all
1091   other components are compared in a case-sensitive manner.
1092   Characters other than those in the "reserved" set are equivalent
1093   to their percent-encoded octets (see <xref target="RFC3986"/>, Section 2.1): the normal form is to not encode them.
1094</t>
1095<t>
1096   For example, the following three URIs are equivalent:
1097</t>
1098<figure><artwork type="example"><![CDATA[
1099   http://example.com:80/~smith/home.html
1100   http://EXAMPLE.com/%7Esmith/home.html
1101   http://EXAMPLE.com:/%7esmith/home.html
1102]]></artwork></figure>
1103</section>
1104</section>
1105</section>
1106
1107<section title="Message Format" anchor="http.message">
1108
1109
1110
1111
1112<iref item="header section"/>
1113<iref item="headers"/>
1114<iref item="header field"/>
1115<t>
1116   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1117   octets in a format similar to the Internet Message Format
1118   <xref target="RFC5322"/>: zero or more header fields (collectively
1119   referred to as the "headers" or the "header section"), an empty line
1120   indicating the end of the header section, and an optional message-body.
1121</t>
1122<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1123  HTTP-message    = start-line
1124                    *( header-field CRLF )
1125                    CRLF
1126                    [ message-body ]
1127]]></artwork></figure>
1128<t>
1129   The normal procedure for parsing an HTTP message is to read the
1130   start-line into a structure, read each header field into a hash
1131   table by field name until the empty line, and then use the parsed
1132   data to determine if a message-body is expected.  If a message-body
1133   has been indicated, then it is read as a stream until an amount
1134   of octets equal to the message-body length is read or the connection
1135   is closed.
1136</t>
1137<t>
1138   Recipients MUST parse an HTTP message as a sequence of octets in an
1139   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1140   Parsing an HTTP message as a stream of Unicode characters, without regard
1141   for the specific encoding, creates security vulnerabilities due to the
1142   varying ways that string processing libraries handle invalid multibyte
1143   character sequences that contain the octet LF (%x0A).  String-based
1144   parsers can only be safely used within protocol elements after the element
1145   has been extracted from the message, such as within a header field-value
1146   after message parsing has delineated the individual fields.
1147</t>
1148
1149<section title="Start Line" anchor="start.line">
1150 
1151<t>
1152   An HTTP message can either be a request from client to server or a
1153   response from server to client.  Syntactically, the two types of message
1154   differ only in the start-line, which is either a Request-Line (for requests)
1155   or a Status-Line (for responses), and in the algorithm for determining
1156   the length of the message-body (<xref target="message.body"/>).
1157   In theory, a client could receive requests and a server could receive
1158   responses, distinguishing them by their different start-line formats,
1159   but in practice servers are implemented to only expect a request
1160   (a response is interpreted as an unknown or invalid request method)
1161   and clients are implemented to only expect a response.
1162</t>
1163<figure><iref primary="true" item="Grammar" subitem="start-line"/><artwork type="abnf2616"><![CDATA[
1164  start-line      = Request-Line / Status-Line
1165]]></artwork></figure>
1166<t>
1167</t>
1168<t>
1169   Implementations MUST NOT send whitespace between the start-line and
1170   the first header field. The presence of such whitespace in a request
1171   might be an attempt to trick a server into ignoring that field or
1172   processing the line after it as a new request, either of which might
1173   result in a security vulnerability if other implementations within
1174   the request chain interpret the same message differently.
1175   Likewise, the presence of such whitespace in a response might be
1176   ignored by some clients or cause others to cease parsing.
1177</t>
1178
1179<section title="Request-Line" anchor="request.line">
1180 
1181 
1182<t>
1183   The Request-Line begins with a method token, followed by a single
1184   space (SP), the request-target, another single space (SP), the
1185   protocol version, and ending with CRLF.
1186</t>
1187<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1188  Request-Line   = Method SP request-target SP HTTP-Version CRLF
1189]]></artwork></figure>
1190
1191<section title="Method" anchor="method">
1192 
1193<t>
1194   The Method token indicates the request method to be performed on the
1195   target resource. The request method is case-sensitive.
1196</t>
1197<figure><iref primary="true" item="Grammar" subitem="Method"/><artwork type="abnf2616"><![CDATA[
1198  Method         = token
1199]]></artwork></figure>
1200<t>
1201   See Section 2 of <xref target="Part2"/> for further information, such as the list of methods defined
1202   by this specification, the IANA registry, and considerations for new methods.
1203</t>
1204</section>
1205
1206<section title="request-target" anchor="request-target">
1207 
1208<t>
1209   The request-target identifies the target resource upon which to apply
1210   the request.  The four options for request-target are described in
1211   <xref target="request-target-types"/>.
1212</t>
1213<figure><iref primary="true" item="Grammar" subitem="request-target"/><artwork type="abnf2616"><![CDATA[
1214  request-target = "*"
1215                 / absolute-URI
1216                 / ( path-absolute [ "?" query ] )
1217                 / authority
1218]]></artwork></figure>
1219<t>
1220   HTTP does not place a pre-defined limit on the length of a request-target.
1221   A server MUST be prepared to receive URIs of unbounded length and
1222   respond with the 414 (URI Too Long) status code if the received
1223   request-target would be longer than the server wishes to handle
1224   (see Section 7.4.15 of <xref target="Part2"/>).
1225</t>
1226<t>
1227   Various ad-hoc limitations on request-target length are found in practice.
1228   It is RECOMMENDED that all HTTP senders and recipients support
1229   request-target lengths of 8000 or more octets.
1230</t>
1231<t><list>
1232  <t>
1233    Note: Fragments (<xref target="RFC3986"/>, Section 3.5)
1234    are not part of the request-target and thus will not be transmitted
1235    in an HTTP request.
1236  </t>
1237</list></t>
1238</section>
1239</section>
1240
1241<section title="Response Status-Line" anchor="status.line">
1242 
1243 
1244<t>
1245   The first line of a Response message is the Status-Line, consisting
1246   of the protocol version, a space (SP), the status code, another space,
1247   a possibly-empty textual phrase describing the status code, and
1248   ending with CRLF.
1249</t>
1250<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1251  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1252]]></artwork></figure>
1253
1254<section title="Status Code" anchor="status.code">
1255 
1256<t>
1257   The Status-Code element is a 3-digit integer result code of the attempt to
1258   understand and satisfy the request. See Section 4 of <xref target="Part2"/> for
1259   further information, such as the list of status codes defined by this
1260   specification, the IANA registry, and considerations for new status codes.
1261</t>
1262<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><artwork type="abnf2616"><![CDATA[
1263  Status-Code    = 3DIGIT
1264]]></artwork></figure>
1265</section>
1266
1267<section title="Reason Phrase" anchor="reason.phrase">
1268 
1269<t>   
1270   The Reason Phrase exists for the sole purpose of providing a textual
1271   description associated with the numeric status code, out of deference to
1272   earlier Internet application protocols that were more frequently used with
1273   interactive text clients. A client SHOULD ignore the content of the Reason
1274   Phrase.
1275</t>
1276<figure><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
1277  Reason-Phrase  = *( HTAB / SP / VCHAR / obs-text )
1278]]></artwork></figure>
1279</section>
1280</section>
1281
1282</section>
1283
1284<section title="Header Fields" anchor="header.fields">
1285 
1286 
1287 
1288 
1289 
1290<t>
1291   Each HTTP header field consists of a case-insensitive field name
1292   followed by a colon (":"), optional whitespace, and the field value.
1293</t>
1294<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[
1295  header-field   = field-name ":" OWS field-value BWS
1296  field-name     = token
1297  field-value    = *( field-content / obs-fold )
1298  field-content  = *( HTAB / SP / VCHAR / obs-text )
1299]]></artwork></figure>
1300<t>
1301   The field-name token labels the corresponding field-value as having the
1302   semantics defined by that header field.  For example, the Date header field
1303   is defined in Section 9.2 of <xref target="Part2"/> as containing the origination
1304   timestamp for the message in which it appears.
1305</t>
1306<t>
1307   HTTP header fields are fully extensible: there is no limit on the
1308   introduction of new field names, each presumably defining new semantics,
1309   or on the number of header fields used in a given message.  Existing
1310   fields are defined in each part of this specification and in many other
1311   specifications outside the standards process.
1312   New header fields can be introduced without changing the protocol version
1313   if their defined semantics allow them to be safely ignored by recipients
1314   that do not recognize them.
1315</t>
1316<t>
1317   New HTTP header fields SHOULD be registered with IANA according
1318   to the procedures in Section 3.1 of <xref target="Part2"/>.
1319   Unrecognized header fields MUST be forwarded by a proxy unless the
1320   field-name is listed in the Connection header field
1321   (<xref target="header.connection"/>) or the proxy is specifically
1322   configured to block or otherwise transform such fields.
1323   Unrecognized header fields SHOULD be ignored by other recipients.
1324</t>
1325<t>
1326   The order in which header fields with differing field names are
1327   received is not significant. However, it is "good practice" to send
1328   header fields that contain control data first, such as Host on
1329   requests and Date on responses, so that implementations can decide
1330   when not to handle a message as early as possible.  A server MUST
1331   wait until the entire header section is received before interpreting
1332   a request message, since later header fields might include conditionals,
1333   authentication credentials, or deliberately misleading duplicate
1334   header fields that would impact request processing.
1335</t>
1336<t>
1337   Multiple header fields with the same field name MUST NOT be
1338   sent in a message unless the entire field value for that
1339   header field is defined as a comma-separated list [i.e., #(values)].
1340   Multiple header fields with the same field name can be combined into
1341   one "field-name: field-value" pair, without changing the semantics of the
1342   message, by appending each subsequent field value to the combined
1343   field value in order, separated by a comma. The order in which
1344   header fields with the same field name are received is therefore
1345   significant to the interpretation of the combined field value;
1346   a proxy MUST NOT change the order of these field values when
1347   forwarding a message.
1348</t>
1349<t><list>
1350  <t>
1351   Note: The "Set-Cookie" header field as implemented in
1352   practice can occur multiple times, but does not use the list syntax, and
1353   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1354   for details.) Also note that the Set-Cookie2 header field specified in
1355   <xref target="RFC2965"/> does not share this problem.
1356  </t>
1357</list></t>
1358
1359<section title="Field Parsing" anchor="field.parsing">
1360<t>
1361   No whitespace is allowed between the header field-name and colon.
1362   In the past, differences in the handling of such whitespace have led to
1363   security vulnerabilities in request routing and response handling.
1364   Any received request message that contains whitespace between a header
1365   field-name and colon MUST be rejected with a response code of 400
1366   (Bad Request).  A proxy MUST remove any such whitespace from a response
1367   message before forwarding the message downstream.
1368</t>
1369<t>
1370   A field value MAY be preceded by optional whitespace (OWS); a single SP is
1371   preferred. The field value does not include any leading or trailing white
1372   space: OWS occurring before the first non-whitespace octet of the
1373   field value or after the last non-whitespace octet of the field value
1374   is ignored and SHOULD be removed before further processing (as this does
1375   not change the meaning of the header field).
1376</t>
1377<t>
1378   Historically, HTTP header field values could be extended over multiple
1379   lines by preceding each extra line with at least one space or horizontal
1380   tab (obs-fold). This specification deprecates such line
1381   folding except within the message/http media type
1382   (<xref target="internet.media.type.message.http"/>).
1383   HTTP senders MUST NOT produce messages that include line folding
1384   (i.e., that contain any field-content that matches the obs-fold rule) unless
1385   the message is intended for packaging within the message/http media type.
1386   HTTP recipients SHOULD accept line folding and replace any embedded
1387   obs-fold whitespace with either a single SP or a matching number of SP
1388   octets (to avoid buffer copying) prior to interpreting the field value or
1389   forwarding the message downstream.
1390</t>
1391<t>
1392   Historically, HTTP has allowed field content with text in the ISO-8859-1
1393   <xref target="ISO-8859-1"/> character encoding and supported other
1394   character sets only through use of <xref target="RFC2047"/> encoding.
1395   In practice, most HTTP header field values use only a subset of the
1396   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1397   header fields SHOULD limit their field values to US-ASCII octets.
1398   Recipients SHOULD treat other (obs-text) octets in field content as
1399   opaque data.
1400</t>
1401</section>
1402
1403<section title="Field Length" anchor="field.length">
1404<t>
1405   HTTP does not place a pre-defined limit on the length of header fields,
1406   either in isolation or as a set. A server MUST be prepared to receive
1407   request header fields of unbounded length and respond with a 4xx status
1408   code if the received header field(s) would be longer than the server wishes
1409   to handle.
1410</t>
1411<t>
1412   A client that receives response headers that are longer than it wishes to
1413   handle can only treat it as a server error.
1414</t>
1415<t>
1416   Various ad-hoc limitations on header length are found in practice. It is
1417   RECOMMENDED that all HTTP senders and recipients support messages whose
1418   combined header fields have 4000 or more octets.
1419</t>
1420</section>
1421
1422<section title="Common Field ABNF Rules" anchor="field.rules">
1423<t anchor="rule.token.separators">
1424 
1425 
1426 
1427 
1428   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1429   separated by whitespace or special characters. These special characters
1430   MUST be in a quoted string to be used within a parameter value (as defined
1431   in <xref target="transfer.codings"/>).
1432</t>
1433<figure><iref primary="true" item="Grammar" subitem="word"/><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="special"/><artwork type="abnf2616"><![CDATA[
1434  word           = token / quoted-string
1435
1436  token          = 1*tchar
1437
1438  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
1439                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1440                 / DIGIT / ALPHA
1441                 ; any VCHAR, except special
1442
1443  special        = "(" / ")" / "<" / ">" / "@" / ","
1444                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1445                 / "]" / "?" / "=" / "{" / "}"
1446]]></artwork></figure>
1447<t anchor="rule.quoted-string">
1448 
1449 
1450 
1451   A string of text is parsed as a single word if it is quoted using
1452   double-quote marks.
1453</t>
1454<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[
1455  quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
1456  qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
1457  obs-text       = %x80-FF
1458]]></artwork></figure>
1459<t anchor="rule.quoted-pair">
1460 
1461   The backslash octet ("\") can be used as a single-octet
1462   quoting mechanism within quoted-string constructs:
1463</t>
1464<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
1465  quoted-pair    = "\" ( HTAB / SP / VCHAR / obs-text )
1466]]></artwork></figure>
1467<t>
1468   Recipients that process the value of the quoted-string MUST handle a
1469   quoted-pair as if it were replaced by the octet following the backslash.
1470</t>
1471<t>
1472   Senders SHOULD NOT escape octets in quoted-strings that do not require
1473   escaping (i.e., other than DQUOTE and the backslash octet).
1474</t>
1475<t anchor="rule.comment">
1476 
1477 
1478   Comments can be included in some HTTP header fields by surrounding
1479   the comment text with parentheses. Comments are only allowed in
1480   fields containing "comment" as part of their field value definition.
1481</t>
1482<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
1483  comment        = "(" *( ctext / quoted-cpair / comment ) ")"
1484  ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
1485]]></artwork></figure>
1486<t anchor="rule.quoted-cpair">
1487 
1488   The backslash octet ("\") can be used as a single-octet
1489   quoting mechanism within comment constructs:
1490</t>
1491<figure><iref primary="true" item="Grammar" subitem="quoted-cpair"/><artwork type="abnf2616"><![CDATA[
1492  quoted-cpair    = "\" ( HTAB / SP / VCHAR / obs-text )
1493]]></artwork></figure>
1494<t>
1495   Senders SHOULD NOT escape octets in comments that do not require escaping
1496   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1497</t>
1498</section>
1499</section>
1500
1501<section title="Message Body" anchor="message.body">
1502 
1503<t>
1504   The message-body (if any) of an HTTP message is used to carry the
1505   payload body associated with the request or response.
1506</t>
1507<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1508  message-body = *OCTET
1509]]></artwork></figure>
1510<t>
1511   The message-body differs from the payload body only when a transfer-coding
1512   has been applied, as indicated by the Transfer-Encoding header field
1513   (<xref target="header.transfer-encoding"/>).  If more than one
1514   Transfer-Encoding header field is present in a message, the multiple
1515   field-values MUST be combined into one field-value, according to the
1516   algorithm defined in <xref target="header.fields"/>, before determining
1517   the message-body length.
1518</t>
1519<t>
1520   When one or more transfer-codings are applied to a payload in order to
1521   form the message-body, the Transfer-Encoding header field MUST contain
1522   the list of transfer-codings applied. Transfer-Encoding is a property of
1523   the message, not of the payload, and thus MAY be added or removed by
1524   any implementation along the request/response chain under the constraints
1525   found in <xref target="transfer.codings"/>.
1526</t>
1527<t>
1528   If a message is received that has multiple Content-Length header fields
1529   (<xref target="header.content-length"/>) with field-values consisting
1530   of the same decimal value, or a single Content-Length header field with
1531   a field value containing a list of identical decimal values (e.g.,
1532   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1533   header fields have been generated or combined by an upstream message
1534   processor, then the recipient MUST either reject the message as invalid
1535   or replace the duplicated field-values with a single valid Content-Length
1536   field containing that decimal value prior to determining the message-body
1537   length.
1538</t>
1539<t>
1540   The rules for when a message-body is allowed in a message differ for
1541   requests and responses.
1542</t>
1543<t>
1544   The presence of a message-body in a request is signaled by the
1545   inclusion of a Content-Length or Transfer-Encoding header field in
1546   the request's header fields, even if the request method does not
1547   define any use for a message-body.  This allows the request
1548   message framing algorithm to be independent of method semantics.
1549</t>
1550<t>
1551   For response messages, whether or not a message-body is included with
1552   a message is dependent on both the request method and the response
1553   status code (<xref target="status.code"/>).
1554   Responses to the HEAD request method never include a message-body
1555   because the associated response header fields (e.g., Transfer-Encoding,
1556   Content-Length, etc.) only indicate what their values would have been
1557   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1558   and 304 (Not Modified) responses MUST NOT include a message-body.
1559   All other responses do include a message-body, although the body
1560   MAY be of zero length.
1561</t>
1562<t>
1563   The length of the message-body is determined by one of the following
1564   (in order of precedence):
1565</t>
1566<t>
1567  <list style="numbers">
1568    <t>
1569     Any response to a HEAD request and any response with a status
1570     code of 100-199, 204, or 304 is always terminated by the first
1571     empty line after the header fields, regardless of the header
1572     fields present in the message, and thus cannot contain a message-body.
1573    </t>
1574    <t>
1575     If a Transfer-Encoding header field is present
1576     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1577     is the final encoding, the message-body length is determined by reading
1578     and decoding the chunked data until the transfer-coding indicates the
1579     data is complete.
1580    <vspace blankLines="1"/>
1581     If a Transfer-Encoding header field is present in a response and the
1582     "chunked" transfer-coding is not the final encoding, the message-body
1583     length is determined by reading the connection until it is closed by
1584     the server.
1585     If a Transfer-Encoding header field is present in a request and the
1586     "chunked" transfer-coding is not the final encoding, the message-body
1587     length cannot be determined reliably; the server MUST respond with
1588     the 400 (Bad Request) status code and then close the connection.
1589    <vspace blankLines="1"/>
1590     If a message is received with both a Transfer-Encoding header field
1591     and a Content-Length header field, the Transfer-Encoding overrides
1592     the Content-Length.
1593     Such a message might indicate an attempt to perform request or response
1594     smuggling (bypass of security-related checks on message routing or content)
1595     and thus ought to be handled as an error.  The provided Content-Length MUST
1596     be removed, prior to forwarding the message downstream, or replaced with
1597     the real message-body length after the transfer-coding is decoded.
1598    </t>
1599    <t>
1600     If a message is received without Transfer-Encoding and with either
1601     multiple Content-Length header fields having differing field-values or
1602     a single Content-Length header field having an invalid value, then the
1603     message framing is invalid and MUST be treated as an error to
1604     prevent request or response smuggling.
1605     If this is a request message, the server MUST respond with
1606     a 400 (Bad Request) status code and then close the connection.
1607     If this is a response message received by a proxy, the proxy
1608     MUST discard the received response, send a 502 (Bad Gateway)
1609     status code as its downstream response, and then close the connection.
1610     If this is a response message received by a user-agent, it MUST be
1611     treated as an error by discarding the message and closing the connection.
1612    </t>
1613    <t>
1614     If a valid Content-Length header field
1615     is present without Transfer-Encoding, its decimal value defines the
1616     message-body length in octets.  If the actual number of octets sent in
1617     the message is less than the indicated Content-Length, the recipient
1618     MUST consider the message to be incomplete and treat the connection
1619     as no longer usable.
1620     If the actual number of octets sent in the message is more than the indicated
1621     Content-Length, the recipient MUST only process the message-body up to the
1622     field value's number of octets; the remainder of the message MUST either
1623     be discarded or treated as the next message in a pipeline.  For the sake of
1624     robustness, a user-agent MAY attempt to detect and correct such an error
1625     in message framing if it is parsing the response to the last request on
1626     a connection and the connection has been closed by the server.
1627    </t>
1628    <t>
1629     If this is a request message and none of the above are true, then the
1630     message-body length is zero (no message-body is present).
1631    </t>
1632    <t>
1633     Otherwise, this is a response message without a declared message-body
1634     length, so the message-body length is determined by the number of octets
1635     received prior to the server closing the connection.
1636    </t>
1637  </list>
1638</t>
1639<t>
1640   Since there is no way to distinguish a successfully completed,
1641   close-delimited message from a partially-received message interrupted
1642   by network failure, implementations SHOULD use encoding or
1643   length-delimited messages whenever possible.  The close-delimiting
1644   feature exists primarily for backwards compatibility with HTTP/1.0.
1645</t>
1646<t>
1647   A server MAY reject a request that contains a message-body but
1648   not a Content-Length by responding with 411 (Length Required).
1649</t>
1650<t>
1651   Unless a transfer-coding other than "chunked" has been applied,
1652   a client that sends a request containing a message-body SHOULD
1653   use a valid Content-Length header field if the message-body length
1654   is known in advance, rather than the "chunked" encoding, since some
1655   existing services respond to "chunked" with a 411 (Length Required)
1656   status code even though they understand the chunked encoding.  This
1657   is typically because such services are implemented via a gateway that
1658   requires a content-length in advance of being called and the server
1659   is unable or unwilling to buffer the entire request before processing.
1660</t>
1661<t>
1662   A client that sends a request containing a message-body MUST include a
1663   valid Content-Length header field if it does not know the server will
1664   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1665   of specific user configuration or by remembering the version of a prior
1666   received response.
1667</t>
1668</section>
1669
1670<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1671<t>
1672   Request messages that are prematurely terminated, possibly due to a
1673   cancelled connection or a server-imposed time-out exception, MUST
1674   result in closure of the connection; sending an HTTP/1.1 error response
1675   prior to closing the connection is OPTIONAL.
1676</t>
1677<t>
1678   Response messages that are prematurely terminated, usually by closure
1679   of the connection prior to receiving the expected number of octets or by
1680   failure to decode a transfer-encoded message-body, MUST be recorded
1681   as incomplete.  A response that terminates in the middle of the header
1682   block (before the empty line is received) cannot be assumed to convey the
1683   full semantics of the response and MUST be treated as an error.
1684</t>
1685<t>
1686   A message-body that uses the chunked transfer encoding is
1687   incomplete if the zero-sized chunk that terminates the encoding has not
1688   been received.  A message that uses a valid Content-Length is incomplete
1689   if the size of the message-body received (in octets) is less than the
1690   value given by Content-Length.  A response that has neither chunked
1691   transfer encoding nor Content-Length is terminated by closure of the
1692   connection, and thus is considered complete regardless of the number of
1693   message-body octets received, provided that the header block was received
1694   intact.
1695</t>
1696<t>
1697   A user agent MUST NOT render an incomplete response message-body as if
1698   it were complete (i.e., some indication must be given to the user that an
1699   error occurred).  Cache requirements for incomplete responses are defined
1700   in Section 2.1 of <xref target="Part6"/>.
1701</t>
1702<t>
1703   A server MUST read the entire request message-body or close
1704   the connection after sending its response, since otherwise the
1705   remaining data on a persistent connection would be misinterpreted
1706   as the next request.  Likewise,
1707   a client MUST read the entire response message-body if it intends
1708   to reuse the same connection for a subsequent request.  Pipelining
1709   multiple requests on a connection is described in <xref target="pipelining"/>.
1710</t>
1711</section>
1712
1713<section title="Message Parsing Robustness" anchor="message.robustness">
1714<t>
1715   Older HTTP/1.0 client implementations might send an extra CRLF
1716   after a POST request as a lame workaround for some early server
1717   applications that failed to read message-body content that was
1718   not terminated by a line-ending. An HTTP/1.1 client MUST NOT
1719   preface or follow a request with an extra CRLF.  If terminating
1720   the request message-body with a line-ending is desired, then the
1721   client MUST include the terminating CRLF octets as part of the
1722   message-body length.
1723</t>
1724<t>
1725   In the interest of robustness, servers SHOULD ignore at least one
1726   empty line received where a Request-Line is expected. In other words, if
1727   the server is reading the protocol stream at the beginning of a
1728   message and receives a CRLF first, it SHOULD ignore the CRLF.
1729   Likewise, although the line terminator for the start-line and header
1730   fields is the sequence CRLF, we recommend that recipients recognize a
1731   single LF as a line terminator and ignore any CR.
1732</t>
1733<t>
1734   When a server listening only for HTTP request messages, or processing
1735   what appears from the start-line to be an HTTP request message,
1736   receives a sequence of octets that does not match the HTTP-message
1737   grammar aside from the robustness exceptions listed above, the
1738   server MUST respond with an HTTP/1.1 400 (Bad Request) response. 
1739</t>
1740</section>
1741</section>
1742
1743<section title="Message Routing" anchor="message.routing">
1744<t>
1745   In most cases, the user agent is provided a URI reference
1746   from which it determines an absolute URI for identifying the target
1747   resource.  When a request to the resource is initiated, all or part
1748   of that URI is used to construct the HTTP request-target.
1749</t>
1750
1751<section title="Types of Request Target" anchor="request-target-types">
1752<t>
1753   The four options for request-target are dependent on the nature of the
1754   request.
1755</t>   
1756<t><iref item="asterisk form (of request-target)"/>
1757   The asterisk "*" form of request-target, which MUST NOT be used
1758   with any request method other than OPTIONS, means that the request
1759   applies to the server as a whole (the listening process) rather than
1760   to a specific named resource at that server.  For example,
1761</t>
1762<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1763  OPTIONS * HTTP/1.1
1764  ]]></artwork></figure>
1765<t><iref item="absolute-URI form (of request-target)"/>
1766   The "absolute-URI" form is REQUIRED when the request is being made to a
1767   proxy. The proxy is requested to either forward the request or service it
1768   from a valid cache, and then return the response. Note that the proxy MAY
1769   forward the request on to another proxy or directly to the server
1770   specified by the absolute-URI. In order to avoid request loops, a
1771   proxy that forwards requests to other proxies MUST be able to
1772   recognize and exclude all of its own server names, including
1773   any aliases, local variations, and the numeric IP address. An example
1774   Request-Line would be:
1775</t>
1776<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1777  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1778  ]]></artwork></figure>
1779<t>
1780   To allow for transition to absolute-URIs in all requests in future
1781   versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
1782   form in requests, even though HTTP/1.1 clients will only generate
1783   them in requests to proxies.
1784</t>
1785<t>
1786   If a proxy receives a host name that is not a fully qualified domain
1787   name, it MAY add its domain to the host name it received. If a proxy
1788   receives a fully qualified domain name, the proxy MUST NOT change
1789   the host name.
1790</t>
1791<t><iref item="authority form (of request-target)"/>
1792   The "authority form" is only used by the CONNECT request method (Section 6.9 of <xref target="Part2"/>).
1793</t>
1794<t><iref item="origin form (of request-target)"/>
1795   The most common form of request-target is that used when making
1796   a request to an origin server ("origin form").
1797   In this case, the absolute path and query components of the URI
1798   MUST be transmitted as the request-target, and the authority component
1799   MUST be transmitted in a Host header field. For example, a client wishing
1800   to retrieve a representation of the resource, as identified above,
1801   directly from the origin server would open (or reuse) a TCP connection
1802   to port 80 of the host "www.example.org" and send the lines:
1803</t>
1804<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1805  GET /pub/WWW/TheProject.html HTTP/1.1
1806  Host: www.example.org
1807  ]]></artwork></figure>
1808<t>
1809   followed by the remainder of the Request. Note that the origin form
1810   of request-target always starts with an absolute path; if the target
1811   resource's URI path is empty, then an absolute path of "/" MUST be
1812   provided in the request-target.
1813</t>
1814<t>
1815   If a proxy receives an OPTIONS request with an absolute-URI form of
1816   request-target in which the URI has an empty path and no query component,
1817   then the last proxy on the request chain MUST use a request-target
1818   of "*" when it forwards the request to the indicated origin server.
1819</t>
1820<figure><preamble>   
1821   For example, the request
1822</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1823  OPTIONS http://www.example.org:8001 HTTP/1.1
1824  ]]></artwork></figure>
1825<figure><preamble>   
1826  would be forwarded by the final proxy as
1827</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1828  OPTIONS * HTTP/1.1
1829  Host: www.example.org:8001
1830  ]]></artwork>
1831<postamble>
1832   after connecting to port 8001 of host "www.example.org".
1833</postamble>
1834</figure>
1835<t>
1836   The request-target is transmitted in the format specified in
1837   <xref target="http.uri"/>. If the request-target is percent-encoded
1838   (<xref target="RFC3986"/>, Section 2.1), the origin server
1839   MUST decode the request-target in order to
1840   properly interpret the request. Servers SHOULD respond to invalid
1841   request-targets with an appropriate status code.
1842</t>
1843<t>
1844   A non-transforming proxy MUST NOT rewrite the "path-absolute" part of the
1845   received request-target when forwarding it to the next inbound server,
1846   except as noted above to replace a null path-absolute with "/" or "*".
1847</t>
1848<t><list>
1849  <t>
1850    Note: The "no rewrite" rule prevents the proxy from changing the
1851    meaning of the request when the origin server is improperly using
1852    a non-reserved URI character for a reserved purpose.  Implementors
1853    need to be aware that some pre-HTTP/1.1 proxies have been known to
1854    rewrite the request-target.
1855  </t>
1856</list></t>
1857</section>
1858
1859<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1860<t>
1861   The exact resource identified by an Internet request is determined by
1862   examining both the request-target and the Host header field.
1863</t>
1864<t>
1865   An origin server that does not allow resources to differ by the
1866   requested host MAY ignore the Host header field value when
1867   determining the resource identified by an HTTP/1.1 request. (But see
1868   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1869   for other requirements on Host support in HTTP/1.1.)
1870</t>
1871<t>
1872   An origin server that does differentiate resources based on the host
1873   requested (sometimes referred to as virtual hosts or vanity host
1874   names) MUST use the following rules for determining the requested
1875   resource on an HTTP/1.1 request:
1876  <list style="numbers">
1877    <t>If request-target is an absolute-URI, the host is part of the
1878     request-target. Any Host header field value in the request MUST be
1879     ignored.</t>
1880    <t>If the request-target is not an absolute-URI, and the request includes
1881     a Host header field, the host is determined by the Host header
1882     field value.</t>
1883    <t>If the host as determined by rule 1 or 2 is not a valid host on
1884     the server, the response MUST be a 400 (Bad Request) error message.</t>
1885  </list>
1886</t>
1887<t>
1888   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1889   attempt to use heuristics (e.g., examination of the URI path for
1890   something unique to a particular host) in order to determine what
1891   exact resource is being requested.
1892</t>
1893</section>
1894
1895<section title="Effective Request URI" anchor="effective.request.uri">
1896  <iref primary="true" item="effective request URI"/>
1897  <iref primary="true" item="target resource"/>
1898<t>
1899   HTTP requests often do not carry the absolute URI (<xref target="RFC3986"/>, Section 4.3)
1900   for the target resource; instead, the URI needs to be inferred from the
1901   request-target, Host header field, and connection context. The result of
1902   this process is called the "effective request URI".  The "target resource"
1903   is the resource identified by the effective request URI.
1904</t>
1905<t>
1906   If the request-target is an absolute-URI, then the effective request URI is
1907   the request-target.
1908</t>
1909<t>
1910   If the request-target uses the path-absolute form or the asterisk form,
1911   and the Host header field is present, then the effective request URI is
1912   constructed by concatenating
1913</t>
1914<t>
1915  <list style="symbols">
1916    <t>
1917      the scheme name: "http" if the request was received over an insecure
1918      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1919      connection,
1920    </t>
1921    <t>
1922      the octet sequence "://",
1923    </t>
1924    <t>
1925      the authority component, as specified in the Host header field
1926      (<xref target="header.host"/>), and
1927    </t>
1928    <t>
1929      the request-target obtained from the Request-Line, unless the
1930      request-target is just the asterisk "*".
1931    </t>
1932  </list>
1933</t>
1934<t>
1935   If the request-target uses the path-absolute form or the asterisk form,
1936   and the Host header field is not present, then the effective request URI is
1937   undefined.
1938</t>
1939<t>
1940   Otherwise, when request-target uses the authority form, the effective
1941   request URI is undefined.
1942</t>
1943<figure>
1944<preamble>
1945   Example 1: the effective request URI for the message
1946</preamble> 
1947<artwork type="example"><![CDATA[
1948  GET /pub/WWW/TheProject.html HTTP/1.1
1949  Host: www.example.org:8080
1950  ]]></artwork>
1951<postamble>
1952  (received over an insecure TCP connection) is "http", plus "://", plus the
1953  authority component "www.example.org:8080", plus the request-target
1954  "/pub/WWW/TheProject.html", thus
1955  "http://www.example.org:8080/pub/WWW/TheProject.html".
1956</postamble>
1957</figure>
1958<figure>
1959<preamble>
1960   Example 2: the effective request URI for the message
1961</preamble> 
1962<artwork type="example"><![CDATA[
1963  OPTIONS * HTTP/1.1
1964  Host: www.example.org
1965  ]]></artwork>
1966<postamble>
1967  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1968  authority component "www.example.org", thus "https://www.example.org".
1969</postamble>
1970</figure>
1971<t>
1972   Effective request URIs are compared using the rules described in
1973   <xref target="uri.comparison"/>, except that empty path components MUST NOT
1974   be treated as equivalent to an absolute path of "/".
1975</t> 
1976</section>
1977</section>
1978
1979
1980<section title="Protocol Parameters" anchor="protocol.parameters">
1981
1982<section title="Transfer Codings" anchor="transfer.codings">
1983 
1984 
1985<t>
1986   Transfer-coding values are used to indicate an encoding
1987   transformation that has been, can be, or might need to be applied to a
1988   payload body in order to ensure "safe transport" through the network.
1989   This differs from a content coding in that the transfer-coding is a
1990   property of the message rather than a property of the representation
1991   that is being transferred.
1992</t>
1993<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
1994  transfer-coding         = "chunked" ; Section 5.1.1
1995                          / "compress" ; Section 5.1.2.1
1996                          / "deflate" ; Section 5.1.2.2
1997                          / "gzip" ; Section 5.1.2.3
1998                          / transfer-extension
1999  transfer-extension      = token *( OWS ";" OWS transfer-parameter )
2000]]></artwork></figure>
2001<t anchor="rule.parameter">
2002 
2003 
2004 
2005   Parameters are in the form of attribute/value pairs.
2006</t>
2007<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[
2008  transfer-parameter      = attribute BWS "=" BWS value
2009  attribute               = token
2010  value                   = word
2011]]></artwork></figure>
2012<t>
2013   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2014   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2015   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2016</t>
2017<t>
2018   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2019   MIME, which were designed to enable safe transport of binary data over a
2020   7-bit transport service (<xref target="RFC2045"/>, Section 6).
2021   However, safe transport
2022   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2023   the only unsafe characteristic of message-bodies is the difficulty in
2024   determining the exact message body length (<xref target="message.body"/>),
2025   or the desire to encrypt data over a shared transport.
2026</t>
2027<t>
2028   A server that receives a request message with a transfer-coding it does
2029   not understand SHOULD respond with 501 (Not Implemented) and then
2030   close the connection. A server MUST NOT send transfer-codings to an HTTP/1.0
2031   client.
2032</t>
2033
2034<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2035  <iref item="chunked (Coding Format)"/>
2036  <iref item="Coding Format" subitem="chunked"/>
2037 
2038 
2039 
2040 
2041 
2042 
2043 
2044 
2045 
2046 
2047 
2048<t>
2049   The chunked encoding modifies the body of a message in order to
2050   transfer it as a series of chunks, each with its own size indicator,
2051   followed by an OPTIONAL trailer containing header fields. This
2052   allows dynamically produced content to be transferred along with the
2053   information necessary for the recipient to verify that it has
2054   received the full message.
2055</t>
2056<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[
2057  Chunked-Body   = *chunk
2058                   last-chunk
2059                   trailer-part
2060                   CRLF
2061 
2062  chunk          = chunk-size [ chunk-ext ] CRLF
2063                   chunk-data CRLF
2064  chunk-size     = 1*HEXDIG
2065  last-chunk     = 1*("0") [ chunk-ext ] CRLF
2066 
2067  chunk-ext      = *( ";" chunk-ext-name
2068                      [ "=" chunk-ext-val ] )
2069  chunk-ext-name = token
2070  chunk-ext-val  = token / quoted-str-nf
2071  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
2072  trailer-part   = *( header-field CRLF )
2073 
2074  quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
2075                 ; like quoted-string, but disallowing line folding
2076  qdtext-nf      = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text
2077]]></artwork></figure>
2078<t>
2079   The chunk-size field is a string of hex digits indicating the size of
2080   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2081   zero, followed by the trailer, which is terminated by an empty line.
2082</t>
2083<t>
2084   The trailer allows the sender to include additional HTTP header
2085   fields at the end of the message. The Trailer header field can be
2086   used to indicate which header fields are included in a trailer (see
2087   <xref target="header.trailer"/>).
2088</t>
2089<t>
2090   A server using chunked transfer-coding in a response MUST NOT use the
2091   trailer for any header fields unless at least one of the following is
2092   true:
2093  <list style="numbers">
2094    <t>the request included a TE header field that indicates "trailers" is
2095     acceptable in the transfer-coding of the  response, as described in
2096     <xref target="header.te"/>; or,</t>
2097     
2098    <t>the trailer fields consist entirely of optional metadata, and the
2099    recipient could use the message (in a manner acceptable to the server where
2100    the field originated) without receiving it. In other words, the server that
2101    generated the header (often but not always the origin server) is willing to
2102    accept the possibility that the trailer fields might be silently discarded
2103    along the path to the client.</t>
2104  </list>
2105</t>
2106<t>
2107   This requirement prevents an interoperability failure when the
2108   message is being received by an HTTP/1.1 (or later) proxy and
2109   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2110   compliance with the protocol would have necessitated a possibly
2111   infinite buffer on the proxy.
2112</t>
2113<t>
2114   A process for decoding the "chunked" transfer-coding
2115   can be represented in pseudo-code as:
2116</t>
2117<figure><artwork type="code"><![CDATA[
2118  length := 0
2119  read chunk-size, chunk-ext (if any) and CRLF
2120  while (chunk-size > 0) {
2121     read chunk-data and CRLF
2122     append chunk-data to decoded-body
2123     length := length + chunk-size
2124     read chunk-size and CRLF
2125  }
2126  read header-field
2127  while (header-field not empty) {
2128     append header-field to existing header fields
2129     read header-field
2130  }
2131  Content-Length := length
2132  Remove "chunked" from Transfer-Encoding
2133]]></artwork></figure>
2134<t>
2135   All HTTP/1.1 applications MUST be able to receive and decode the
2136   "chunked" transfer-coding and MUST ignore chunk-ext extensions
2137   they do not understand.
2138</t>
2139<t>
2140   Since "chunked" is the only transfer-coding required to be understood
2141   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2142   on a persistent connection.  Whenever a transfer-coding is applied to
2143   a payload body in a request, the final transfer-coding applied MUST
2144   be "chunked".  If a transfer-coding is applied to a response payload
2145   body, then either the final transfer-coding applied MUST be "chunked"
2146   or the message MUST be terminated by closing the connection. When the
2147   "chunked" transfer-coding is used, it MUST be the last transfer-coding
2148   applied to form the message-body. The "chunked" transfer-coding MUST NOT
2149   be applied more than once in a message-body.
2150</t>
2151</section>
2152
2153<section title="Compression Codings" anchor="compression.codings">
2154<t>
2155   The codings defined below can be used to compress the payload of a
2156   message.
2157</t>
2158<t><list><t>
2159   Note: Use of program names for the identification of encoding formats
2160   is not desirable and is discouraged for future encodings. Their
2161   use here is representative of historical practice, not good
2162   design.
2163</t></list></t>
2164<t><list><t>
2165   Note: For compatibility with previous implementations of HTTP,
2166   applications SHOULD consider "x-gzip" and "x-compress" to be
2167   equivalent to "gzip" and "compress" respectively.
2168</t></list></t>
2169
2170<section title="Compress Coding" anchor="compress.coding">
2171<iref item="compress (Coding Format)"/>
2172<iref item="Coding Format" subitem="compress"/>
2173<t>
2174   The "compress" format is produced by the common UNIX file compression
2175   program "compress". This format is an adaptive Lempel-Ziv-Welch
2176   coding (LZW).
2177</t>
2178</section>
2179
2180<section title="Deflate Coding" anchor="deflate.coding">
2181<iref item="deflate (Coding Format)"/>
2182<iref item="Coding Format" subitem="deflate"/>
2183<t>
2184   The "deflate" format is defined as the "deflate" compression mechanism
2185   (described in <xref target="RFC1951"/>) used inside the "zlib"
2186   data format (<xref target="RFC1950"/>).
2187</t>
2188<t><list>
2189  <t>
2190    Note: Some incorrect implementations send the "deflate"
2191    compressed data without the zlib wrapper.
2192   </t>
2193</list></t>
2194</section>
2195
2196<section title="Gzip Coding" anchor="gzip.coding">
2197<iref item="gzip (Coding Format)"/>
2198<iref item="Coding Format" subitem="gzip"/>
2199<t>
2200   The "gzip" format is produced by the file compression program
2201   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2202   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2203</t>
2204</section>
2205
2206</section>
2207
2208<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2209<t>
2210   The HTTP Transfer Coding Registry defines the name space for the transfer
2211   coding names.
2212</t>
2213<t>
2214   Registrations MUST include the following fields:
2215   <list style="symbols">
2216     <t>Name</t>
2217     <t>Description</t>
2218     <t>Pointer to specification text</t>
2219   </list>
2220</t>
2221<t>
2222   Names of transfer codings MUST NOT overlap with names of content codings
2223   (Section 2.2 of <xref target="Part3"/>), unless the encoding transformation is identical (as it
2224   is the case for the compression codings defined in
2225   <xref target="compression.codings"/>).
2226</t>
2227<t>
2228   Values to be added to this name space require a specification
2229   (see "Specification Required" in Section 4.1 of <xref target="RFC5226"/>), and MUST
2230   conform to the purpose of transfer coding defined in this section.
2231</t>
2232<t>
2233   The registry itself is maintained at
2234   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2235</t>
2236</section>
2237</section>
2238
2239<section title="Product Tokens" anchor="product.tokens">
2240 
2241 
2242<t>
2243   Product tokens are used to allow communicating applications to
2244   identify themselves by software name and version. Most fields using
2245   product tokens also allow sub-products which form a significant part
2246   of the application to be listed, separated by whitespace. By
2247   convention, the products are listed in order of their significance
2248   for identifying the application.
2249</t>
2250<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
2251  product         = token ["/" product-version]
2252  product-version = token
2253]]></artwork></figure>
2254<t>
2255   Examples:
2256</t>
2257<figure><artwork type="example"><![CDATA[
2258  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2259  Server: Apache/0.8.4
2260]]></artwork></figure>
2261<t>
2262   Product tokens SHOULD be short and to the point. They MUST NOT be
2263   used for advertising or other non-essential information. Although any
2264   token octet MAY appear in a product-version, this token SHOULD
2265   only be used for a version identifier (i.e., successive versions of
2266   the same product SHOULD only differ in the product-version portion of
2267   the product value).
2268</t>
2269</section>
2270
2271<section title="Quality Values" anchor="quality.values">
2272 
2273<t>
2274   Both transfer codings (TE request header field, <xref target="header.te"/>)
2275   and content negotiation (Section 5 of <xref target="Part3"/>) use short "floating point"
2276   numbers to indicate the relative importance ("weight") of various
2277   negotiable parameters.  A weight is normalized to a real number in
2278   the range 0 through 1, where 0 is the minimum and 1 the maximum
2279   value. If a parameter has a quality value of 0, then content with
2280   this parameter is "not acceptable" for the client. HTTP/1.1
2281   applications MUST NOT generate more than three digits after the
2282   decimal point. User configuration of these values SHOULD also be
2283   limited in this fashion.
2284</t>
2285<figure><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
2286  qvalue         = ( "0" [ "." 0*3DIGIT ] )
2287                 / ( "1" [ "." 0*3("0") ] )
2288]]></artwork></figure>
2289<t><list>
2290  <t>
2291     Note: "Quality values" is a misnomer, since these values merely represent
2292     relative degradation in desired quality.
2293  </t>
2294</list></t>
2295</section>
2296
2297</section>
2298
2299<section title="Connections" anchor="connections">
2300
2301<section title="Persistent Connections" anchor="persistent.connections">
2302
2303<section title="Purpose" anchor="persistent.purpose">
2304<t>
2305   Prior to persistent connections, a separate TCP connection was
2306   established for each request, increasing the load on HTTP servers
2307   and causing congestion on the Internet. The use of inline images and
2308   other associated data often requires a client to make multiple
2309   requests of the same server in a short amount of time. Analysis of
2310   these performance problems and results from a prototype
2311   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2312   measurements of actual HTTP/1.1 implementations show good
2313   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2314   T/TCP <xref target="Tou1998"/>.
2315</t>
2316<t>
2317   Persistent HTTP connections have a number of advantages:
2318  <list style="symbols">
2319      <t>
2320        By opening and closing fewer TCP connections, CPU time is saved
2321        in routers and hosts (clients, servers, proxies, gateways,
2322        tunnels, or caches), and memory used for TCP protocol control
2323        blocks can be saved in hosts.
2324      </t>
2325      <t>
2326        HTTP requests and responses can be pipelined on a connection.
2327        Pipelining allows a client to make multiple requests without
2328        waiting for each response, allowing a single TCP connection to
2329        be used much more efficiently, with much lower elapsed time.
2330      </t>
2331      <t>
2332        Network congestion is reduced by reducing the number of packets
2333        caused by TCP opens, and by allowing TCP sufficient time to
2334        determine the congestion state of the network.
2335      </t>
2336      <t>
2337        Latency on subsequent requests is reduced since there is no time
2338        spent in TCP's connection opening handshake.
2339      </t>
2340      <t>
2341        HTTP can evolve more gracefully, since errors can be reported
2342        without the penalty of closing the TCP connection. Clients using
2343        future versions of HTTP might optimistically try a new feature,
2344        but if communicating with an older server, retry with old
2345        semantics after an error is reported.
2346      </t>
2347    </list>
2348</t>
2349<t>
2350   HTTP implementations SHOULD implement persistent connections.
2351</t>
2352</section>
2353
2354<section title="Overall Operation" anchor="persistent.overall">
2355<t>
2356   A significant difference between HTTP/1.1 and earlier versions of
2357   HTTP is that persistent connections are the default behavior of any
2358   HTTP connection. That is, unless otherwise indicated, the client
2359   SHOULD assume that the server will maintain a persistent connection,
2360   even after error responses from the server.
2361</t>
2362<t>
2363   Persistent connections provide a mechanism by which a client and a
2364   server can signal the close of a TCP connection. This signaling takes
2365   place using the Connection header field (<xref target="header.connection"/>). Once a close
2366   has been signaled, the client MUST NOT send any more requests on that
2367   connection.
2368</t>
2369
2370<section title="Negotiation" anchor="persistent.negotiation">
2371<t>
2372   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
2373   maintain a persistent connection unless a Connection header field including
2374   the connection-token "close" was sent in the request. If the server
2375   chooses to close the connection immediately after sending the
2376   response, it SHOULD send a Connection header field including the
2377   connection-token "close".
2378</t>
2379<t>
2380   An HTTP/1.1 client MAY expect a connection to remain open, but would
2381   decide to keep it open based on whether the response from a server
2382   contains a Connection header field with the connection-token close. In case
2383   the client does not want to maintain a connection for more than that
2384   request, it SHOULD send a Connection header field including the
2385   connection-token close.
2386</t>
2387<t>
2388   If either the client or the server sends the close token in the
2389   Connection header field, that request becomes the last one for the
2390   connection.
2391</t>
2392<t>
2393   Clients and servers SHOULD NOT  assume that a persistent connection is
2394   maintained for HTTP versions less than 1.1 unless it is explicitly
2395   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2396   compatibility with HTTP/1.0 clients.
2397</t>
2398<t>
2399   In order to remain persistent, all messages on the connection MUST
2400   have a self-defined message length (i.e., one not defined by closure
2401   of the connection), as described in <xref target="message.body"/>.
2402</t>
2403</section>
2404
2405<section title="Pipelining" anchor="pipelining">
2406<t>
2407   A client that supports persistent connections MAY "pipeline" its
2408   requests (i.e., send multiple requests without waiting for each
2409   response). A server MUST send its responses to those requests in the
2410   same order that the requests were received.
2411</t>
2412<t>
2413   Clients which assume persistent connections and pipeline immediately
2414   after connection establishment SHOULD be prepared to retry their
2415   connection if the first pipelined attempt fails. If a client does
2416   such a retry, it MUST NOT pipeline before it knows the connection is
2417   persistent. Clients MUST also be prepared to resend their requests if
2418   the server closes the connection before sending all of the
2419   corresponding responses.
2420</t>
2421<t>
2422   Clients SHOULD NOT pipeline requests using non-idempotent request methods or
2423   non-idempotent sequences of request methods (see Section 6.1.2 of <xref target="Part2"/>). Otherwise, a
2424   premature termination of the transport connection could lead to
2425   indeterminate results. A client wishing to send a non-idempotent
2426   request SHOULD wait to send that request until it has received the
2427   response status line for the previous request.
2428</t>
2429</section>
2430</section>
2431
2432<section title="Proxy Servers" anchor="persistent.proxy">
2433<t>
2434   It is especially important that proxies correctly implement the
2435   properties of the Connection header field as specified in <xref target="header.connection"/>.
2436</t>
2437<t>
2438   The proxy server MUST signal persistent connections separately with
2439   its clients and the origin servers (or other proxy servers) that it
2440   connects to. Each persistent connection applies to only one transport
2441   link.
2442</t>
2443<t>
2444   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
2445   with an HTTP/1.0 client (but see Section 19.7.1 of <xref target="RFC2068"/>
2446   for information and discussion of the problems with the Keep-Alive header field
2447   implemented by many HTTP/1.0 clients).
2448</t>
2449
2450<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2451<!--<t>
2452  <cref anchor="TODO-end-to-end" source="jre">
2453    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2454    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2455  </cref>
2456</t>-->
2457<t>
2458   For the purpose of defining the behavior of caches and non-caching
2459   proxies, we divide HTTP header fields into two categories:
2460  <list style="symbols">
2461      <t>End-to-end header fields, which are  transmitted to the ultimate
2462        recipient of a request or response. End-to-end header fields in
2463        responses MUST be stored as part of a cache entry and MUST be
2464        transmitted in any response formed from a cache entry.</t>
2465
2466      <t>Hop-by-hop header fields, which are meaningful only for a single
2467        transport-level connection, and are not stored by caches or
2468        forwarded by proxies.</t>
2469  </list>
2470</t>
2471<t>
2472   The following HTTP/1.1 header fields are hop-by-hop header fields:
2473  <list style="symbols">
2474      <t>Connection</t>
2475      <t>Keep-Alive</t>
2476      <t>Proxy-Authenticate</t>
2477      <t>Proxy-Authorization</t>
2478      <t>TE</t>
2479      <t>Trailer</t>
2480      <t>Transfer-Encoding</t>
2481      <t>Upgrade</t>
2482  </list>
2483</t>
2484<t>
2485   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2486</t>
2487<t>
2488   Other hop-by-hop header fields MUST be listed in a Connection header field
2489   (<xref target="header.connection"/>).
2490</t>
2491</section>
2492
2493<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2494<!--<t>
2495  <cref anchor="TODO-non-mod-headers" source="jre">
2496    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2497    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2498  </cref>
2499</t>-->
2500<t>
2501   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2502   value of certain end-to-end header fields. A non-transforming proxy SHOULD NOT
2503   modify an end-to-end header field unless the definition of that header field requires
2504   or specifically allows that.
2505</t>
2506<t>
2507   A non-transforming proxy MUST NOT modify any of the following fields in a
2508   request or response, and it MUST NOT add any of these fields if not
2509   already present:
2510  <list style="symbols">
2511    <t>Allow</t>
2512    <t>Content-Location</t>
2513    <t>Content-MD5</t>
2514    <t>ETag</t>
2515    <t>Last-Modified</t>
2516    <t>Server</t>
2517  </list>
2518</t>
2519<t>
2520   A non-transforming proxy MUST NOT modify any of the following fields in a
2521   response:
2522  <list style="symbols">
2523    <t>Expires</t>
2524  </list>
2525</t>
2526<t>
2527   but it MAY add any of these fields if not already present. If an
2528   Expires header field is added, it MUST be given a field-value identical to
2529   that of the Date header field in that response.
2530</t>
2531<t>
2532   A proxy MUST NOT modify or add any of the following fields in a
2533   message that contains the no-transform cache-control directive, or in
2534   any request:
2535  <list style="symbols">
2536    <t>Content-Encoding</t>
2537    <t>Content-Range</t>
2538    <t>Content-Type</t>
2539  </list>
2540</t>
2541<t>
2542   A transforming proxy MAY modify or add these fields to a message
2543   that does not include no-transform, but if it does so, it MUST add a
2544   Warning 214 (Transformation applied) if one does not already appear
2545   in the message (see Section 3.6 of <xref target="Part6"/>).
2546</t>
2547<t><list>
2548  <t>
2549    Warning: Unnecessary modification of end-to-end header fields might
2550    cause authentication failures if stronger authentication
2551    mechanisms are introduced in later versions of HTTP. Such
2552    authentication mechanisms MAY rely on the values of header fields
2553    not listed here.
2554  </t>
2555</list></t>
2556<t>
2557   A non-transforming proxy MUST preserve the message payload (<xref target="Part3"/>),
2558   though it MAY change the message-body through application or removal
2559   of a transfer-coding (<xref target="transfer.codings"/>).
2560</t>
2561</section>
2562
2563</section>
2564
2565<section title="Practical Considerations" anchor="persistent.practical">
2566<t>
2567   Servers will usually have some time-out value beyond which they will
2568   no longer maintain an inactive connection. Proxy servers might make
2569   this a higher value since it is likely that the client will be making
2570   more connections through the same server. The use of persistent
2571   connections places no requirements on the length (or existence) of
2572   this time-out for either the client or the server.
2573</t>
2574<t>
2575   When a client or server wishes to time-out it SHOULD issue a graceful
2576   close on the transport connection. Clients and servers SHOULD both
2577   constantly watch for the other side of the transport close, and
2578   respond to it as appropriate. If a client or server does not detect
2579   the other side's close promptly it could cause unnecessary resource
2580   drain on the network.
2581</t>
2582<t>
2583   A client, server, or proxy MAY close the transport connection at any
2584   time. For example, a client might have started to send a new request
2585   at the same time that the server has decided to close the "idle"
2586   connection. From the server's point of view, the connection is being
2587   closed while it was idle, but from the client's point of view, a
2588   request is in progress.
2589</t>
2590<t>
2591   Clients (including proxies) SHOULD limit the number of simultaneous
2592   connections that they maintain to a given server (including proxies).
2593</t>
2594<t>
2595   Previous revisions of HTTP gave a specific number of connections as a
2596   ceiling, but this was found to be impractical for many applications. As a
2597   result, this specification does not mandate a particular maximum number of
2598   connections, but instead encourages clients to be conservative when opening
2599   multiple connections.
2600</t>
2601<t>
2602   In particular, while using multiple connections avoids the "head-of-line
2603   blocking" problem (whereby a request that takes significant server-side
2604   processing and/or has a large payload can block subsequent requests on the
2605   same connection), each connection used consumes server resources (sometimes
2606   significantly), and furthermore using multiple connections can cause
2607   undesirable side effects in congested networks.
2608</t>
2609<t>
2610   Note that servers might reject traffic that they deem abusive, including an
2611   excessive number of connections from a client.
2612</t>
2613</section>
2614
2615<section title="Retrying Requests" anchor="persistent.retrying.requests">
2616<t>
2617   Senders can close the transport connection at any time. Therefore,
2618   clients, servers, and proxies MUST be able to recover
2619   from asynchronous close events. Client software MAY reopen the
2620   transport connection and retransmit the aborted sequence of requests
2621   without user interaction so long as the request sequence is
2622   idempotent (see Section 6.1.2 of <xref target="Part2"/>). Non-idempotent request methods or sequences
2623   MUST NOT be automatically retried, although user agents MAY offer a
2624   human operator the choice of retrying the request(s). Confirmation by
2625   user-agent software with semantic understanding of the application
2626   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2627   be repeated if the second sequence of requests fails.
2628</t>
2629</section>
2630
2631</section>
2632
2633<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2634
2635<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2636<t>
2637   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2638   flow control mechanisms to resolve temporary overloads, rather than
2639   terminating connections with the expectation that clients will retry.
2640   The latter technique can exacerbate network congestion.
2641</t>
2642</section>
2643
2644<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2645<t>
2646   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2647   the network connection for an error status code while it is transmitting
2648   the request. If the client sees an error status code, it SHOULD
2649   immediately cease transmitting the body. If the body is being sent
2650   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2651   empty trailer MAY be used to prematurely mark the end of the message.
2652   If the body was preceded by a Content-Length header field, the client MUST
2653   close the connection.
2654</t>
2655</section>
2656
2657<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2658<t>
2659   The purpose of the 100 (Continue) status code (see Section 7.1.1 of <xref target="Part2"/>) is to
2660   allow a client that is sending a request message with a request body
2661   to determine if the origin server is willing to accept the request
2662   (based on the request header fields) before the client sends the request
2663   body. In some cases, it might either be inappropriate or highly
2664   inefficient for the client to send the body if the server will reject
2665   the message without looking at the body.
2666</t>
2667<t>
2668   Requirements for HTTP/1.1 clients:
2669  <list style="symbols">
2670    <t>
2671        If a client will wait for a 100 (Continue) response before
2672        sending the request body, it MUST send an Expect header
2673        field (Section 9.3 of <xref target="Part2"/>) with the "100-continue" expectation.
2674    </t>
2675    <t>
2676        A client MUST NOT send an Expect header field (Section 9.3 of <xref target="Part2"/>)
2677        with the "100-continue" expectation if it does not intend
2678        to send a request body.
2679    </t>
2680  </list>
2681</t>
2682<t>
2683   Because of the presence of older implementations, the protocol allows
2684   ambiguous situations in which a client might send "Expect: 100-continue"
2685   without receiving either a 417 (Expectation Failed)
2686   or a 100 (Continue) status code. Therefore, when a client sends this
2687   header field to an origin server (possibly via a proxy) from which it
2688   has never seen a 100 (Continue) status code, the client SHOULD NOT 
2689   wait for an indefinite period before sending the request body.
2690</t>
2691<t>
2692   Requirements for HTTP/1.1 origin servers:
2693  <list style="symbols">
2694    <t> Upon receiving a request which includes an Expect header
2695        field with the "100-continue" expectation, an origin server MUST
2696        either respond with 100 (Continue) status code and continue to read
2697        from the input stream, or respond with a final status code. The
2698        origin server MUST NOT wait for the request body before sending
2699        the 100 (Continue) response. If it responds with a final status
2700        code, it MAY close the transport connection or it MAY continue
2701        to read and discard the rest of the request.  It MUST NOT
2702        perform the request method if it returns a final status code.
2703    </t>
2704    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2705        the request message does not include an Expect header
2706        field with the "100-continue" expectation, and MUST NOT send a
2707        100 (Continue) response if such a request comes from an HTTP/1.0
2708        (or earlier) client. There is an exception to this rule: for
2709        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2710        status code in response to an HTTP/1.1 PUT or POST request that does
2711        not include an Expect header field with the "100-continue"
2712        expectation. This exception, the purpose of which is
2713        to minimize any client processing delays associated with an
2714        undeclared wait for 100 (Continue) status code, applies only to
2715        HTTP/1.1 requests, and not to requests with any other HTTP-version
2716        value.
2717    </t>
2718    <t> An origin server MAY omit a 100 (Continue) response if it has
2719        already received some or all of the request body for the
2720        corresponding request.
2721    </t>
2722    <t> An origin server that sends a 100 (Continue) response MUST
2723    ultimately send a final status code, once the request body is
2724        received and processed, unless it terminates the transport
2725        connection prematurely.
2726    </t>
2727    <t> If an origin server receives a request that does not include an
2728        Expect header field with the "100-continue" expectation,
2729        the request includes a request body, and the server responds
2730        with a final status code before reading the entire request body
2731        from the transport connection, then the server SHOULD NOT  close
2732        the transport connection until it has read the entire request,
2733        or until the client closes the connection. Otherwise, the client
2734        might not reliably receive the response message. However, this
2735        requirement is not be construed as preventing a server from
2736        defending itself against denial-of-service attacks, or from
2737        badly broken client implementations.
2738      </t>
2739    </list>
2740</t>
2741<t>
2742   Requirements for HTTP/1.1 proxies:
2743  <list style="symbols">
2744    <t> If a proxy receives a request that includes an Expect header
2745        field with the "100-continue" expectation, and the proxy
2746        either knows that the next-hop server complies with HTTP/1.1 or
2747        higher, or does not know the HTTP version of the next-hop
2748        server, it MUST forward the request, including the Expect header
2749        field.
2750    </t>
2751    <t> If the proxy knows that the version of the next-hop server is
2752        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2753        respond with a 417 (Expectation Failed) status code.
2754    </t>
2755    <t> Proxies SHOULD maintain a record of the HTTP version
2756        numbers received from recently-referenced next-hop servers.
2757    </t>
2758    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2759        request message was received from an HTTP/1.0 (or earlier)
2760        client and did not include an Expect header field with
2761        the "100-continue" expectation. This requirement overrides the
2762        general rule for forwarding of 1xx responses (see Section 7.1 of <xref target="Part2"/>).
2763    </t>
2764  </list>
2765</t>
2766</section>
2767
2768</section>
2769</section>
2770
2771
2772<section title="Miscellaneous notes that might disappear" anchor="misc">
2773<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2774<t>
2775   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2776</t>
2777</section>
2778
2779<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2780<t>
2781   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2782</t>
2783</section>
2784
2785<section title="Interception of HTTP for access control" anchor="http.intercept">
2786<t>
2787   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2788</t>
2789</section>
2790
2791<section title="Use of HTTP by other protocols" anchor="http.others">
2792<t>
2793   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2794   Extensions of HTTP like WebDAV.</cref>
2795</t>
2796
2797</section>
2798<section title="Use of HTTP by media type specification" anchor="http.media">
2799<t>
2800   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2801</t>
2802</section>
2803</section>
2804
2805<section title="Header Field Definitions" anchor="header.field.definitions">
2806<t>
2807   This section defines the syntax and semantics of HTTP header fields
2808   related to message origination, framing, and routing.
2809</t>
2810<texttable align="left">
2811  <ttcol>Header Field Name</ttcol>
2812  <ttcol>Defined in...</ttcol>
2813 
2814  <c>Connection</c> <c><xref target="header.connection"/></c>
2815  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
2816  <c>Host</c> <c><xref target="header.host"/></c>
2817  <c>TE</c> <c><xref target="header.te"/></c>
2818  <c>Trailer</c> <c><xref target="header.trailer"/></c>
2819  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
2820  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
2821  <c>Via</c> <c><xref target="header.via"/></c>
2822</texttable>
2823
2824<section title="Connection" anchor="header.connection">
2825  <iref primary="true" item="Connection header field"/>
2826  <iref primary="true" item="Header Fields" subitem="Connection"/>
2827 
2828 
2829<t>
2830   The "Connection" header field allows the sender to specify
2831   options that are desired only for that particular connection.
2832   Such connection options MUST be removed or replaced before the
2833   message can be forwarded downstream by a proxy or gateway.
2834   This mechanism also allows the sender to indicate which HTTP
2835   header fields used in the message are only intended for the
2836   immediate recipient ("hop-by-hop"), as opposed to all recipients
2837   on the chain ("end-to-end"), enabling the message to be
2838   self-descriptive and allowing future connection-specific extensions
2839   to be deployed in HTTP without fear that they will be blindly
2840   forwarded by previously deployed intermediaries.
2841</t>
2842<t>
2843   The Connection header field's value has the following grammar:
2844</t>
2845<figure><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/><artwork type="abnf2616"><![CDATA[
2846  Connection       = 1#connection-token
2847  connection-token = token
2848]]></artwork></figure>
2849<t>
2850   A proxy or gateway MUST parse a received Connection
2851   header field before a message is forwarded and, for each
2852   connection-token in this field, remove any header field(s) from
2853   the message with the same name as the connection-token, and then
2854   remove the Connection header field itself or replace it with the
2855   sender's own connection options for the forwarded message.
2856</t>
2857<t>
2858   A sender MUST NOT include field-names in the Connection header
2859   field-value for fields that are defined as expressing constraints
2860   for all recipients in the request or response chain, such as the
2861   Cache-Control header field (Section 3.2 of <xref target="Part6"/>).
2862</t>
2863<t>
2864   The connection options do not have to correspond to a header field
2865   present in the message, since a connection-specific header field
2866   might not be needed if there are no parameters associated with that
2867   connection option.  Recipients that trigger certain connection
2868   behavior based on the presence of connection options MUST do so
2869   based on the presence of the connection-token rather than only the
2870   presence of the optional header field.  In other words, if the
2871   connection option is received as a header field but not indicated
2872   within the Connection field-value, then the recipient MUST ignore
2873   the connection-specific header field because it has likely been
2874   forwarded by an intermediary that is only partially compliant.
2875</t>
2876<t>
2877   When defining new connection options, specifications ought to
2878   carefully consider existing deployed header fields and ensure
2879   that the new connection-token does not share the same name as
2880   an unrelated header field that might already be deployed.
2881   Defining a new connection-token essentially reserves that potential
2882   field-name for carrying additional information related to the
2883   connection option, since it would be unwise for senders to use
2884   that field-name for anything else.
2885</t>
2886<t>
2887   HTTP/1.1 defines the "close" connection option for the sender to
2888   signal that the connection will be closed after completion of the
2889   response. For example,
2890</t>
2891<figure><artwork type="example"><![CDATA[
2892  Connection: close
2893]]></artwork></figure>
2894<t>
2895   in either the request or the response header fields indicates that
2896   the connection SHOULD NOT  be considered "persistent" (<xref target="persistent.connections"/>)
2897   after the current request/response is complete.
2898</t>
2899<t>
2900   An HTTP/1.1 client that does not support persistent connections MUST
2901   include the "close" connection option in every request message.
2902</t>
2903<t>
2904   An HTTP/1.1 server that does not support persistent connections MUST
2905   include the "close" connection option in every response message that
2906   does not have a 1xx (Informational) status code.
2907</t>
2908</section>
2909
2910<section title="Content-Length" anchor="header.content-length">
2911  <iref primary="true" item="Content-Length header field"/>
2912  <iref primary="true" item="Header Fields" subitem="Content-Length"/>
2913 
2914<t>
2915   The "Content-Length" header field indicates the size of the
2916   message-body, in decimal number of octets, for any message other than
2917   a response to a HEAD request or a response with a status code of 304.
2918   In the case of a response to a HEAD request, Content-Length indicates
2919   the size of the payload body (not including any potential transfer-coding)
2920   that would have been sent had the request been a GET.
2921   In the case of a 304 (Not Modified) response to a GET request,
2922   Content-Length indicates the size of the payload body (not including
2923   any potential transfer-coding) that would have been sent in a 200 (OK)
2924   response.
2925</t>
2926<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><artwork type="abnf2616"><![CDATA[
2927  Content-Length = 1*DIGIT
2928]]></artwork></figure>
2929<t>
2930   An example is
2931</t>
2932<figure><artwork type="example"><![CDATA[
2933  Content-Length: 3495
2934]]></artwork></figure>
2935<t>
2936   Implementations SHOULD use this field to indicate the message-body
2937   length when no transfer-coding is being applied and the
2938   payload's body length can be determined prior to being transferred.
2939   <xref target="message.body"/> describes how recipients determine the length
2940   of a message-body.
2941</t>
2942<t>
2943   Any Content-Length greater than or equal to zero is a valid value.
2944</t>
2945<t>
2946   Note that the use of this field in HTTP is significantly different from
2947   the corresponding definition in MIME, where it is an optional field
2948   used within the "message/external-body" content-type.
2949</t>
2950</section>
2951
2952<section title="Host" anchor="header.host">
2953  <iref primary="true" item="Host header field"/>
2954  <iref primary="true" item="Header Fields" subitem="Host"/>
2955 
2956<t>
2957   The "Host" header field in a request provides the host and port
2958   information from the target resource's URI, enabling the origin
2959   server to distinguish between resources while servicing requests
2960   for multiple host names on a single IP address.  Since the Host
2961   field-value is critical information for handling a request, it
2962   SHOULD be sent as the first header field following the Request-Line.
2963</t>
2964<figure><iref primary="true" item="Grammar" subitem="Host"/><artwork type="abnf2616"><![CDATA[
2965  Host = uri-host [ ":" port ] ; Section 2.7.1
2966]]></artwork></figure>
2967<t>
2968   A client MUST send a Host header field in all HTTP/1.1 request
2969   messages.  If the target resource's URI includes an authority
2970   component, then the Host field-value MUST be identical to that
2971   authority component after excluding any userinfo (<xref target="http.uri"/>).
2972   If the authority component is missing or undefined for the target
2973   resource's URI, then the Host header field MUST be sent with an
2974   empty field-value.
2975</t>
2976<t>
2977   For example, a GET request to the origin server for
2978   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2979</t>
2980<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
2981  GET /pub/WWW/ HTTP/1.1
2982  Host: www.example.org
2983  ]]></artwork></figure>
2984<t>
2985   The Host header field MUST be sent in an HTTP/1.1 request even
2986   if the request-target is in the form of an absolute-URI, since this
2987   allows the Host information to be forwarded through ancient HTTP/1.0
2988   proxies that might not have implemented Host.
2989</t>
2990<t>
2991   When an HTTP/1.1 proxy receives a request with a request-target in
2992   the form of an absolute-URI, the proxy MUST ignore the received
2993   Host header field (if any) and instead replace it with the host
2994   information of the request-target.  When a proxy forwards a request,
2995   it MUST generate the Host header field based on the received
2996   absolute-URI rather than the received Host.
2997</t>
2998<t>
2999   Since the Host header field acts as an application-level routing
3000   mechanism, it is a frequent target for malware seeking to poison
3001   a shared cache or redirect a request to an unintended server.
3002   An interception proxy is particularly vulnerable if it relies on
3003   the Host header field value for redirecting requests to internal
3004   servers, or for use as a cache key in a shared cache, without
3005   first verifying that the intercepted connection is targeting a
3006   valid IP address for that host.
3007</t>
3008<t>
3009   A server MUST respond with a 400 (Bad Request) status code to
3010   any HTTP/1.1 request message that lacks a Host header field and
3011   to any request message that contains more than one Host header field
3012   or a Host header field with an invalid field-value.
3013</t>
3014<t>
3015   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3016   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3017   for other requirements relating to Host.
3018</t>
3019</section>
3020
3021<section title="TE" anchor="header.te">
3022  <iref primary="true" item="TE header field"/>
3023  <iref primary="true" item="Header Fields" subitem="TE"/>
3024 
3025 
3026 
3027 
3028<t>
3029   The "TE" header field indicates what extension transfer-codings
3030   it is willing to accept in the response, and whether or not it is
3031   willing to accept trailer fields in a chunked transfer-coding.
3032</t>
3033<t>
3034   Its value consists of the keyword "trailers" and/or a comma-separated
3035   list of extension transfer-coding names with optional accept
3036   parameters (as described in <xref target="transfer.codings"/>).
3037</t>
3038<figure><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><iref primary="true" item="Grammar" subitem="te-params"/><iref primary="true" item="Grammar" subitem="te-ext"/><artwork type="abnf2616"><![CDATA[
3039  TE        = #t-codings
3040  t-codings = "trailers" / ( transfer-extension [ te-params ] )
3041  te-params = OWS ";" OWS "q=" qvalue *( te-ext )
3042  te-ext    = OWS ";" OWS token [ "=" word ]
3043]]></artwork></figure>
3044<t>
3045   The presence of the keyword "trailers" indicates that the client is
3046   willing to accept trailer fields in a chunked transfer-coding, as
3047   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3048   transfer-coding values even though it does not itself represent a
3049   transfer-coding.
3050</t>
3051<t>
3052   Examples of its use are:
3053</t>
3054<figure><artwork type="example"><![CDATA[
3055  TE: deflate
3056  TE:
3057  TE: trailers, deflate;q=0.5
3058]]></artwork></figure>
3059<t>
3060   The TE header field only applies to the immediate connection.
3061   Therefore, the keyword MUST be supplied within a Connection header
3062   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3063</t>
3064<t>
3065   A server tests whether a transfer-coding is acceptable, according to
3066   a TE field, using these rules:
3067  <list style="numbers">
3068    <t>The "chunked" transfer-coding is always acceptable. If the
3069         keyword "trailers" is listed, the client indicates that it is
3070         willing to accept trailer fields in the chunked response on
3071         behalf of itself and any downstream clients. The implication is
3072         that, if given, the client is stating that either all
3073         downstream clients are willing to accept trailer fields in the
3074         forwarded response, or that it will attempt to buffer the
3075         response on behalf of downstream recipients.
3076      <vspace blankLines="1"/>
3077         Note: HTTP/1.1 does not define any means to limit the size of a
3078         chunked response such that a client can be assured of buffering
3079         the entire response.</t>
3080    <t>If the transfer-coding being tested is one of the transfer-codings
3081         listed in the TE field, then it is acceptable unless it
3082         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3083         qvalue of 0 means "not acceptable".)</t>
3084    <t>If multiple transfer-codings are acceptable, then the
3085         acceptable transfer-coding with the highest non-zero qvalue is
3086         preferred.  The "chunked" transfer-coding always has a qvalue
3087         of 1.</t>
3088  </list>
3089</t>
3090<t>
3091   If the TE field-value is empty or if no TE field is present, the only
3092   transfer-coding is "chunked". A message with no transfer-coding is
3093   always acceptable.
3094</t>
3095</section>
3096
3097<section title="Trailer" anchor="header.trailer">
3098  <iref primary="true" item="Trailer header field"/>
3099  <iref primary="true" item="Header Fields" subitem="Trailer"/>
3100 
3101<t>
3102   The "Trailer" header field indicates that the given set of
3103   header fields is present in the trailer of a message encoded with
3104   chunked transfer-coding.
3105</t>
3106<figure><iref primary="true" item="Grammar" subitem="Trailer"/><artwork type="abnf2616"><![CDATA[
3107  Trailer = 1#field-name
3108]]></artwork></figure>
3109<t>
3110   An HTTP/1.1 message SHOULD include a Trailer header field in a
3111   message using chunked transfer-coding with a non-empty trailer. Doing
3112   so allows the recipient to know which header fields to expect in the
3113   trailer.
3114</t>
3115<t>
3116   If no Trailer header field is present, the trailer SHOULD NOT  include
3117   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3118   trailer fields in a "chunked" transfer-coding.
3119</t>
3120<t>
3121   Message header fields listed in the Trailer header field MUST NOT
3122   include the following header fields:
3123  <list style="symbols">
3124    <t>Transfer-Encoding</t>
3125    <t>Content-Length</t>
3126    <t>Trailer</t>
3127  </list>
3128</t>
3129</section>
3130
3131<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3132  <iref primary="true" item="Transfer-Encoding header field"/>
3133  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding"/>
3134 
3135<t>
3136   The "Transfer-Encoding" header field indicates what transfer-codings
3137   (if any) have been applied to the message body. It differs from
3138   Content-Encoding (Section 2.2 of <xref target="Part3"/>) in that transfer-codings are a property
3139   of the message (and therefore are removed by intermediaries), whereas
3140   content-codings are not.
3141</t>
3142<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><artwork type="abnf2616"><![CDATA[
3143  Transfer-Encoding = 1#transfer-coding
3144]]></artwork></figure>
3145<t>
3146   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3147</t>
3148<figure><artwork type="example"><![CDATA[
3149  Transfer-Encoding: chunked
3150]]></artwork></figure>
3151<t>
3152   If multiple encodings have been applied to a representation, the transfer-codings
3153   MUST be listed in the order in which they were applied.
3154   Additional information about the encoding parameters MAY be provided
3155   by other header fields not defined by this specification.
3156</t>
3157<t>
3158   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3159   header field.
3160</t>
3161</section>
3162
3163<section title="Upgrade" anchor="header.upgrade">
3164  <iref primary="true" item="Upgrade header field"/>
3165  <iref primary="true" item="Header Fields" subitem="Upgrade"/>
3166 
3167<t>
3168   The "Upgrade" header field allows the client to specify what
3169   additional communication protocols it would like to use, if the server
3170   chooses to switch protocols. Servers can use it to indicate what protocols
3171   they are willing to switch to.
3172</t>
3173<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><artwork type="abnf2616"><![CDATA[
3174  Upgrade = 1#product
3175]]></artwork></figure>
3176<t>
3177   For example,
3178</t>
3179<figure><artwork type="example"><![CDATA[
3180  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3181]]></artwork></figure>
3182<t>
3183   The Upgrade header field is intended to provide a simple mechanism
3184   for transition from HTTP/1.1 to some other, incompatible protocol. It
3185   does so by allowing the client to advertise its desire to use another
3186   protocol, such as a later version of HTTP with a higher major version
3187   number, even though the current request has been made using HTTP/1.1.
3188   This eases the difficult transition between incompatible protocols by
3189   allowing the client to initiate a request in the more commonly
3190   supported protocol while indicating to the server that it would like
3191   to use a "better" protocol if available (where "better" is determined
3192   by the server, possibly according to the nature of the request method
3193   or target resource).
3194</t>
3195<t>
3196   The Upgrade header field only applies to switching application-layer
3197   protocols upon the existing transport-layer connection. Upgrade
3198   cannot be used to insist on a protocol change; its acceptance and use
3199   by the server is optional. The capabilities and nature of the
3200   application-layer communication after the protocol change is entirely
3201   dependent upon the new protocol chosen, although the first action
3202   after changing the protocol MUST be a response to the initial HTTP
3203   request containing the Upgrade header field.
3204</t>
3205<t>
3206   The Upgrade header field only applies to the immediate connection.
3207   Therefore, the upgrade keyword MUST be supplied within a Connection
3208   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3209   HTTP/1.1 message.
3210</t>
3211<t>
3212   The Upgrade header field cannot be used to indicate a switch to a
3213   protocol on a different connection. For that purpose, it is more
3214   appropriate to use a 3xx redirection response (Section 7.3 of <xref target="Part2"/>).
3215</t>
3216<t>
3217   Servers MUST include the "Upgrade" header field in 101 (Switching
3218   Protocols) responses to indicate which protocol(s) are being switched to,
3219   and MUST include it in 426 (Upgrade Required) responses to indicate
3220   acceptable protocols to upgrade to. Servers MAY include it in any other
3221   response to indicate that they are willing to upgrade to one of the
3222   specified protocols.
3223</t>
3224<t>
3225   This specification only defines the protocol name "HTTP" for use by
3226   the family of Hypertext Transfer Protocols, as defined by the HTTP
3227   version rules of <xref target="http.version"/> and future updates to this
3228   specification. Additional tokens can be registered with IANA using the
3229   registration procedure defined below. 
3230</t>
3231
3232<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3233<t>
3234   The HTTP Upgrade Token Registry defines the name space for product
3235   tokens used to identify protocols in the Upgrade header field.
3236   Each registered token is associated with contact information and
3237   an optional set of specifications that details how the connection
3238   will be processed after it has been upgraded.
3239</t>
3240<t>
3241   Registrations are allowed on a First Come First Served basis as
3242   described in Section 4.1 of <xref target="RFC5226"/>. The
3243   specifications need not be IETF documents or be subject to IESG review.
3244   Registrations are subject to the following rules:
3245  <list style="numbers">
3246    <t>A token, once registered, stays registered forever.</t>
3247    <t>The registration MUST name a responsible party for the
3248       registration.</t>
3249    <t>The registration MUST name a point of contact.</t>
3250    <t>The registration MAY name a set of specifications associated with that
3251       token. Such specifications need not be publicly available.</t>
3252    <t>The responsible party MAY change the registration at any time.
3253       The IANA will keep a record of all such changes, and make them
3254       available upon request.</t>
3255    <t>The responsible party for the first registration of a "product"
3256       token MUST approve later registrations of a "version" token
3257       together with that "product" token before they can be registered.</t>
3258    <t>If absolutely required, the IESG MAY reassign the responsibility
3259       for a token. This will normally only be used in the case when a
3260       responsible party cannot be contacted.</t>
3261  </list>
3262</t>
3263</section>
3264
3265
3266</section>
3267
3268<section title="Via" anchor="header.via">
3269  <iref primary="true" item="Via header field"/>
3270  <iref primary="true" item="Header Fields" subitem="Via"/>
3271 
3272 
3273 
3274 
3275 
3276 
3277<t>
3278   The "Via" header field MUST be sent by a proxy or gateway to
3279   indicate the intermediate protocols and recipients between the user
3280   agent and the server on requests, and between the origin server and
3281   the client on responses. It is analogous to the "Received" field
3282   used by email systems (Section 3.6.7 of <xref target="RFC5322"/>)
3283   and is intended to be used for tracking message forwards,
3284   avoiding request loops, and identifying the protocol capabilities of
3285   all senders along the request/response chain.
3286</t>
3287<figure><iref primary="true" item="Grammar" subitem="Via"/><iref primary="true" item="Grammar" subitem="received-protocol"/><iref primary="true" item="Grammar" subitem="protocol-name"/><iref primary="true" item="Grammar" subitem="protocol-version"/><iref primary="true" item="Grammar" subitem="received-by"/><iref primary="true" item="Grammar" subitem="pseudonym"/><artwork type="abnf2616"><![CDATA[
3288  Via               = 1#( received-protocol RWS received-by
3289                          [ RWS comment ] )
3290  received-protocol = [ protocol-name "/" ] protocol-version
3291  protocol-name     = token
3292  protocol-version  = token
3293  received-by       = ( uri-host [ ":" port ] ) / pseudonym
3294  pseudonym         = token
3295]]></artwork></figure>
3296<t>
3297   The received-protocol indicates the protocol version of the message
3298   received by the server or client along each segment of the
3299   request/response chain. The received-protocol version is appended to
3300   the Via field value when the message is forwarded so that information
3301   about the protocol capabilities of upstream applications remains
3302   visible to all recipients.
3303</t>
3304<t>
3305   The protocol-name is excluded if and only if it would be "HTTP". The
3306   received-by field is normally the host and optional port number of a
3307   recipient server or client that subsequently forwarded the message.
3308   However, if the real host is considered to be sensitive information,
3309   it MAY be replaced by a pseudonym. If the port is not given, it MAY
3310   be assumed to be the default port of the received-protocol.
3311</t>
3312<t>
3313   Multiple Via field values represent each proxy or gateway that has
3314   forwarded the message. Each recipient MUST append its information
3315   such that the end result is ordered according to the sequence of
3316   forwarding applications.
3317</t>
3318<t>
3319   Comments MAY be used in the Via header field to identify the software
3320   of each recipient, analogous to the User-Agent and Server header fields.
3321   However, all comments in the Via field are optional and MAY be removed
3322   by any recipient prior to forwarding the message.
3323</t>
3324<t>
3325   For example, a request message could be sent from an HTTP/1.0 user
3326   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3327   forward the request to a public proxy at p.example.net, which completes
3328   the request by forwarding it to the origin server at www.example.com.
3329   The request received by www.example.com would then have the following
3330   Via header field:
3331</t>
3332<figure><artwork type="example"><![CDATA[
3333  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3334]]></artwork></figure>
3335<t>
3336   A proxy or gateway used as a portal through a network firewall
3337   SHOULD NOT forward the names and ports of hosts within the firewall
3338   region unless it is explicitly enabled to do so. If not enabled, the
3339   received-by host of any host behind the firewall SHOULD be replaced
3340   by an appropriate pseudonym for that host.
3341</t>
3342<t>
3343   For organizations that have strong privacy requirements for hiding
3344   internal structures, a proxy or gateway MAY combine an ordered
3345   subsequence of Via header field entries with identical received-protocol
3346   values into a single such entry. For example,
3347</t>
3348<figure><artwork type="example"><![CDATA[
3349  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3350]]></artwork></figure>
3351<t>
3352  could be collapsed to
3353</t>
3354<figure><artwork type="example"><![CDATA[
3355  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3356]]></artwork></figure>
3357<t>
3358   Senders SHOULD NOT combine multiple entries unless they are all
3359   under the same organizational control and the hosts have already been
3360   replaced by pseudonyms. Senders MUST NOT combine entries which
3361   have different received-protocol values.
3362</t>
3363</section>
3364
3365</section>
3366
3367<section title="IANA Considerations" anchor="IANA.considerations">
3368
3369<section title="Header Field Registration" anchor="header.field.registration">
3370<t>
3371   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3372   with the permanent registrations below (see <xref target="RFC3864"/>):
3373</t>
3374
3375<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3376<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3377   <ttcol>Header Field Name</ttcol>
3378   <ttcol>Protocol</ttcol>
3379   <ttcol>Status</ttcol>
3380   <ttcol>Reference</ttcol>
3381
3382   <c>Connection</c>
3383   <c>http</c>
3384   <c>standard</c>
3385   <c>
3386      <xref target="header.connection"/>
3387   </c>
3388   <c>Content-Length</c>
3389   <c>http</c>
3390   <c>standard</c>
3391   <c>
3392      <xref target="header.content-length"/>
3393   </c>
3394   <c>Host</c>
3395   <c>http</c>
3396   <c>standard</c>
3397   <c>
3398      <xref target="header.host"/>
3399   </c>
3400   <c>TE</c>
3401   <c>http</c>
3402   <c>standard</c>
3403   <c>
3404      <xref target="header.te"/>
3405   </c>
3406   <c>Trailer</c>
3407   <c>http</c>
3408   <c>standard</c>
3409   <c>
3410      <xref target="header.trailer"/>
3411   </c>
3412   <c>Transfer-Encoding</c>
3413   <c>http</c>
3414   <c>standard</c>
3415   <c>
3416      <xref target="header.transfer-encoding"/>
3417   </c>
3418   <c>Upgrade</c>
3419   <c>http</c>
3420   <c>standard</c>
3421   <c>
3422      <xref target="header.upgrade"/>
3423   </c>
3424   <c>Via</c>
3425   <c>http</c>
3426   <c>standard</c>
3427   <c>
3428      <xref target="header.via"/>
3429   </c>
3430</texttable>
3431<!--(END)-->
3432
3433<t>
3434   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3435   HTTP header field would be in conflict with the use of the "close" connection
3436   option for the "Connection" header field (<xref target="header.connection"/>).
3437</t>
3438<texttable align="left" suppress-title="true">
3439   <ttcol>Header Field Name</ttcol>
3440   <ttcol>Protocol</ttcol>
3441   <ttcol>Status</ttcol>
3442   <ttcol>Reference</ttcol>
3443
3444   <c>Close</c>
3445   <c>http</c>
3446   <c>reserved</c>
3447   <c>
3448      <xref target="header.field.registration"/>
3449   </c>
3450</texttable>
3451<t>
3452   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3453</t>
3454</section>
3455
3456<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3457<t>
3458   The entries for the "http" and "https" URI Schemes in the registry located at
3459   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3460   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3461   and <xref target="https.uri" format="counter"/> of this document
3462   (see <xref target="RFC4395"/>).
3463</t>
3464</section>
3465
3466<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3467<t>
3468   This document serves as the specification for the Internet media types
3469   "message/http" and "application/http". The following is to be registered with
3470   IANA (see <xref target="RFC4288"/>).
3471</t>
3472<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3473<iref item="Media Type" subitem="message/http" primary="true"/>
3474<iref item="message/http Media Type" primary="true"/>
3475<t>
3476   The message/http type can be used to enclose a single HTTP request or
3477   response message, provided that it obeys the MIME restrictions for all
3478   "message" types regarding line length and encodings.
3479</t>
3480<t>
3481  <list style="hanging">
3482    <t hangText="Type name:">
3483      message
3484    </t>
3485    <t hangText="Subtype name:">
3486      http
3487    </t>
3488    <t hangText="Required parameters:">
3489      none
3490    </t>
3491    <t hangText="Optional parameters:">
3492      version, msgtype
3493      <list style="hanging">
3494        <t hangText="version:">
3495          The HTTP-Version number of the enclosed message
3496          (e.g., "1.1"). If not present, the version can be
3497          determined from the first line of the body.
3498        </t>
3499        <t hangText="msgtype:">
3500          The message type — "request" or "response". If not
3501          present, the type can be determined from the first
3502          line of the body.
3503        </t>
3504      </list>
3505    </t>
3506    <t hangText="Encoding considerations:">
3507      only "7bit", "8bit", or "binary" are permitted
3508    </t>
3509    <t hangText="Security considerations:">
3510      none
3511    </t>
3512    <t hangText="Interoperability considerations:">
3513      none
3514    </t>
3515    <t hangText="Published specification:">
3516      This specification (see <xref target="internet.media.type.message.http"/>).
3517    </t>
3518    <t hangText="Applications that use this media type:">
3519    </t>
3520    <t hangText="Additional information:">
3521      <list style="hanging">
3522        <t hangText="Magic number(s):">none</t>
3523        <t hangText="File extension(s):">none</t>
3524        <t hangText="Macintosh file type code(s):">none</t>
3525      </list>
3526    </t>
3527    <t hangText="Person and email address to contact for further information:">
3528      See Authors Section.
3529    </t>
3530    <t hangText="Intended usage:">
3531      COMMON
3532    </t>
3533    <t hangText="Restrictions on usage:">
3534      none
3535    </t>
3536    <t hangText="Author/Change controller:">
3537      IESG
3538    </t>
3539  </list>
3540</t>
3541</section>
3542<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3543<iref item="Media Type" subitem="application/http" primary="true"/>
3544<iref item="application/http Media Type" primary="true"/>
3545<t>
3546   The application/http type can be used to enclose a pipeline of one or more
3547   HTTP request or response messages (not intermixed).
3548</t>
3549<t>
3550  <list style="hanging">
3551    <t hangText="Type name:">
3552      application
3553    </t>
3554    <t hangText="Subtype name:">
3555      http
3556    </t>
3557    <t hangText="Required parameters:">
3558      none
3559    </t>
3560    <t hangText="Optional parameters:">
3561      version, msgtype
3562      <list style="hanging">
3563        <t hangText="version:">
3564          The HTTP-Version number of the enclosed messages
3565          (e.g., "1.1"). If not present, the version can be
3566          determined from the first line of the body.
3567        </t>
3568        <t hangText="msgtype:">
3569          The message type — "request" or "response". If not
3570          present, the type can be determined from the first
3571          line of the body.
3572        </t>
3573      </list>
3574    </t>
3575    <t hangText="Encoding considerations:">
3576      HTTP messages enclosed by this type
3577      are in "binary" format; use of an appropriate
3578      Content-Transfer-Encoding is required when
3579      transmitted via E-mail.
3580    </t>
3581    <t hangText="Security considerations:">
3582      none
3583    </t>
3584    <t hangText="Interoperability considerations:">
3585      none
3586    </t>
3587    <t hangText="Published specification:">
3588      This specification (see <xref target="internet.media.type.application.http"/>).
3589    </t>
3590    <t hangText="Applications that use this media type:">
3591    </t>
3592    <t hangText="Additional information:">
3593      <list style="hanging">
3594        <t hangText="Magic number(s):">none</t>
3595        <t hangText="File extension(s):">none</t>
3596        <t hangText="Macintosh file type code(s):">none</t>
3597      </list>
3598    </t>
3599    <t hangText="Person and email address to contact for further information:">
3600      See Authors Section.
3601    </t>
3602    <t hangText="Intended usage:">
3603      COMMON
3604    </t>
3605    <t hangText="Restrictions on usage:">
3606      none
3607    </t>
3608    <t hangText="Author/Change controller:">
3609      IESG
3610    </t>
3611  </list>
3612</t>
3613</section>
3614</section>
3615
3616<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3617<t>
3618   The registration procedure for HTTP Transfer Codings is now defined by
3619   <xref target="transfer.coding.registry"/> of this document.
3620</t>
3621<t>
3622   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3623   shall be updated with the registrations below:
3624</t>
3625<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3626   <ttcol>Name</ttcol>
3627   <ttcol>Description</ttcol>
3628   <ttcol>Reference</ttcol>
3629   <c>chunked</c>
3630   <c>Transfer in a series of chunks</c>
3631   <c>
3632      <xref target="chunked.encoding"/>
3633   </c>
3634   <c>compress</c>
3635   <c>UNIX "compress" program method</c>
3636   <c>
3637      <xref target="compress.coding"/>
3638   </c>
3639   <c>deflate</c>
3640   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3641   the "zlib" data format (<xref target="RFC1950"/>)
3642   </c>
3643   <c>
3644      <xref target="deflate.coding"/>
3645   </c>
3646   <c>gzip</c>
3647   <c>Same as GNU zip <xref target="RFC1952"/></c>
3648   <c>
3649      <xref target="gzip.coding"/>
3650   </c>
3651</texttable>
3652</section>
3653
3654<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3655<t>
3656   The registration procedure for HTTP Upgrade Tokens — previously defined
3657   in Section 7.2 of <xref target="RFC2817"/> — is now defined
3658   by <xref target="upgrade.token.registry"/> of this document.
3659</t>
3660<t>
3661   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3662   shall be updated with the registration below:
3663</t>
3664<texttable align="left" suppress-title="true">
3665   <ttcol>Value</ttcol>
3666   <ttcol>Description</ttcol>
3667   <ttcol>Reference</ttcol>
3668
3669   <c>HTTP</c>
3670   <c>Hypertext Transfer Protocol</c> 
3671   <c><xref target="http.version"/> of this specification</c>
3672
3673</texttable>
3674</section>
3675
3676</section>
3677
3678<section title="Security Considerations" anchor="security.considerations">
3679<t>
3680   This section is meant to inform application developers, information
3681   providers, and users of the security limitations in HTTP/1.1 as
3682   described by this document. The discussion does not include
3683   definitive solutions to the problems revealed, though it does make
3684   some suggestions for reducing security risks.
3685</t>
3686
3687<section title="Personal Information" anchor="personal.information">
3688<t>
3689   HTTP clients are often privy to large amounts of personal information
3690   (e.g., the user's name, location, mail address, passwords, encryption
3691   keys, etc.), and SHOULD be very careful to prevent unintentional
3692   leakage of this information.
3693   We very strongly recommend that a convenient interface be provided
3694   for the user to control dissemination of such information, and that
3695   designers and implementors be particularly careful in this area.
3696   History shows that errors in this area often create serious security
3697   and/or privacy problems and generate highly adverse publicity for the
3698   implementor's company.
3699</t>
3700</section>
3701
3702<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3703<t>
3704   A server is in the position to save personal data about a user's
3705   requests which might identify their reading patterns or subjects of
3706   interest. This information is clearly confidential in nature and its
3707   handling can be constrained by law in certain countries. People using
3708   HTTP to provide data are responsible for ensuring that
3709   such material is not distributed without the permission of any
3710   individuals that are identifiable by the published results.
3711</t>
3712</section>
3713
3714<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3715<t>
3716   Implementations of HTTP origin servers SHOULD be careful to restrict
3717   the documents returned by HTTP requests to be only those that were
3718   intended by the server administrators. If an HTTP server translates
3719   HTTP URIs directly into file system calls, the server MUST take
3720   special care not to serve files that were not intended to be
3721   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3722   other operating systems use ".." as a path component to indicate a
3723   directory level above the current one. On such a system, an HTTP
3724   server MUST disallow any such construct in the request-target if it
3725   would otherwise allow access to a resource outside those intended to
3726   be accessible via the HTTP server. Similarly, files intended for
3727   reference only internally to the server (such as access control
3728   files, configuration files, and script code) MUST be protected from
3729   inappropriate retrieval, since they might contain sensitive
3730   information. Experience has shown that minor bugs in such HTTP server
3731   implementations have turned into security risks.
3732</t>
3733</section>
3734
3735<section title="DNS-related Attacks" anchor="dns.related.attacks">
3736<t>
3737   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3738   generally prone to security attacks based on the deliberate misassociation
3739   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3740   cautious in assuming the validity of an IP number/DNS name association unless
3741   the response is protected by DNSSec (<xref target="RFC4033"/>).
3742</t>
3743</section>
3744
3745<section title="Proxies and Caching" anchor="attack.proxies">
3746<t>
3747   By their very nature, HTTP proxies are men-in-the-middle, and
3748   represent an opportunity for man-in-the-middle attacks. Compromise of
3749   the systems on which the proxies run can result in serious security
3750   and privacy problems. Proxies have access to security-related
3751   information, personal information about individual users and
3752   organizations, and proprietary information belonging to users and
3753   content providers. A compromised proxy, or a proxy implemented or
3754   configured without regard to security and privacy considerations,
3755   might be used in the commission of a wide range of potential attacks.
3756</t>
3757<t>
3758   Proxy operators need to protect the systems on which proxies run as
3759   they would protect any system that contains or transports sensitive
3760   information. In particular, log information gathered at proxies often
3761   contains highly sensitive personal information, and/or information
3762   about organizations. Log information needs to be carefully guarded, and
3763   appropriate guidelines for use need to be developed and followed.
3764   (<xref target="abuse.of.server.log.information"/>).
3765</t>
3766<t>
3767   Proxy implementors need to consider the privacy and security
3768   implications of their design and coding decisions, and of the
3769   configuration options they provide to proxy operators (especially the
3770   default configuration).
3771</t>
3772<t>
3773   Users of a proxy need to be aware that proxies are no trustworthier than
3774   the people who run them; HTTP itself cannot solve this problem.
3775</t>
3776<t>
3777   The judicious use of cryptography, when appropriate, might suffice to
3778   protect against a broad range of security and privacy attacks. Such
3779   cryptography is beyond the scope of the HTTP/1.1 specification.
3780</t>
3781</section>
3782
3783<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3784<t>
3785   Because HTTP uses mostly textual, character-delimited fields, attackers can
3786   overflow buffers in implementations, and/or perform a Denial of Service
3787   against implementations that accept fields with unlimited lengths.
3788</t>
3789<t>
3790   To promote interoperability, this specification makes specific
3791   recommendations for size limits on request-targets (<xref target="request-target"/>)
3792   and blocks of header fields (<xref target="header.fields"/>). These are
3793   minimum recommendations, chosen to be supportable even by implementations
3794   with limited resources; it is expected that most implementations will choose
3795   substantially higher limits.
3796</t>
3797<t>
3798   This specification also provides a way for servers to reject messages that
3799   have request-targets that are too long (Section 7.4.15 of <xref target="Part2"/>) or request entities
3800   that are too large (Section 7.4 of <xref target="Part2"/>).
3801</t>
3802<t>
3803   Other fields (including but not limited to request methods, response status
3804   phrases, header field-names, and body chunks) SHOULD be limited by
3805   implementations carefully, so as to not impede interoperability.
3806</t>
3807</section>
3808
3809<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3810<t>
3811   They exist. They are hard to defend against. Research continues.
3812   Beware.
3813</t>
3814</section>
3815</section>
3816
3817<section title="Acknowledgments" anchor="acks">
3818<t>
3819   This document revision builds on the work that went into
3820   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3821   See Section 16 of <xref target="RFC2616"/> for detailed
3822   acknowledgements.
3823</t>
3824<t>
3825   Since 1999, many contributors have helped by reporting bugs, asking
3826   smart questions, drafting and reviewing text, and discussing open issues:
3827</t>
3828
3829<t>Adam Barth,
3830Adam Roach,
3831Addison Phillips,
3832Adrian Chadd,
3833Adrien de Croy,
3834Alan Ford,
3835Alan Ruttenberg,
3836Albert Lunde,
3837Alex Rousskov,
3838Alexey Melnikov,
3839Alisha Smith,
3840Amichai Rothman,
3841Amit Klein,
3842Amos Jeffries,
3843Andreas Maier,
3844Andreas Petersson,
3845Anne van Kesteren,
3846Anthony Bryan,
3847Asbjorn Ulsberg,
3848Balachander Krishnamurthy,
3849Barry Leiba,
3850Ben Laurie,
3851Benjamin Niven-Jenkins,
3852Bil Corry,
3853Bill Burke,
3854Bjoern Hoehrmann,
3855Bob Scheifler,
3856Boris Zbarsky,
3857Brett Slatkin,
3858Brian Kell,
3859Brian McBarron,
3860Brian Pane,
3861Brian Smith,
3862Bryce Nesbitt,
3863Carl Kugler,
3864Charles Fry,
3865Chris Newman,
3866Cyrus Daboo,
3867Dale Robert Anderson,
3868Dan Winship,
3869Daniel Stenberg,
3870Dave Cridland,
3871Dave Crocker,
3872Dave Kristol,
3873David Booth,
3874David Singer,
3875David W. Morris,
3876Diwakar Shetty,
3877Drummond Reed,
3878Duane Wessels,
3879Edward Lee,
3880Eliot Lear,
3881Eran Hammer-Lahav,
3882Eric D. Williams,
3883Eric J. Bowman,
3884Eric Lawrence,
3885Erik Aronesty,
3886Florian Weimer,
3887Frank Ellermann,
3888Fred Bohle,
3889Geoffrey Sneddon,
3890Gervase Markham,
3891Greg Wilkins,
3892Harald Tveit Alvestrand,
3893Harry Halpin,
3894Helge Hess,
3895Henrik Nordstrom,
3896Henry S. Thompson,
3897Henry Story,
3898Howard Melman,
3899Hugo Haas,
3900Ian Hickson,
3901Ingo Struck,
3902J. Ross Nicoll,
3903James H. Manger,
3904James Lacey,
3905James M. Snell,
3906Jamie Lokier,
3907Jan Algermissen,
3908Jeff Hodges (for coming up with the term 'effective Request-URI'),
3909Jeff Walden,
3910Jim Luther,
3911Joe D. Williams,
3912Joe Gregorio,
3913Joe Orton,
3914John C. Klensin,
3915John C. Mallery,
3916John Cowan,
3917John Kemp,
3918John Panzer,
3919John Schneider,
3920John Stracke,
3921Jonas Sicking,
3922Jonathan Moore,
3923Jonathan Rees,
3924Jordi Ros,
3925Joris Dobbelsteen,
3926Josh Cohen,
3927Julien Pierre,
3928Jungshik Shin,
3929Justin Chapweske,
3930Justin Erenkrantz,
3931Justin James,
3932Kalvinder Singh,
3933Karl Dubost,
3934Keith Hoffman,
3935Keith Moore,
3936Koen Holtman,
3937Konstantin Voronkov,
3938Kris Zyp,
3939Lisa Dusseault,
3940Maciej Stachowiak,
3941Marc Schneider,
3942Marc Slemko,
3943Mark Baker,
3944Mark Nottingham (Working Group chair),
3945Mark Pauley,
3946Martin J. Duerst,
3947Martin Thomson,
3948Matt Lynch,
3949Matthew Cox,
3950Max Clark,
3951Michael Burrows,
3952Michael Hausenblas,
3953Mike Amundsen,
3954Mike Kelly,
3955Mike Schinkel,
3956Miles Sabin,
3957Mykyta Yevstifeyev,
3958Nathan Rixham,
3959Nicholas Shanks,
3960Nico Williams,
3961Nicolas Alvarez,
3962Noah Slater,
3963Pablo Castro,
3964Pat Hayes,
3965Patrick R. McManus,
3966Paul E. Jones,
3967Paul Hoffman,
3968Paul Marquess,
3969Peter Saint-Andre,
3970Peter Watkins,
3971Phil Archer,
3972Phillip Hallam-Baker,
3973Poul-Henning Kamp,
3974Preethi Natarajan,
3975Reto Bachmann-Gmuer,
3976Richard Cyganiak,
3977Robert Brewer,
3978Robert Collins,
3979Robert O'Callahan,
3980Robert Olofsson,
3981Robert Sayre,
3982Robert Siemer,
3983Robert de Wilde,
3984Roberto Javier Godoy,
3985Ronny Widjaja,
3986S. Mike Dierken,
3987Salvatore Loreto,
3988Sam Johnston,
3989Sam Ruby,
3990Scott Lawrence (for maintaining the original issues list),
3991Sean B. Palmer,
3992Shane McCarron,
3993Stefan Eissing,
3994Stefan Tilkov,
3995Stefanos Harhalakis,
3996Stephane Bortzmeyer,
3997Stuart Williams,
3998Subbu Allamaraju,
3999Sylvain Hellegouarch,
4000Tapan Divekar,
4001Thomas Broyer,
4002Thomas Nordin,
4003Thomas Roessler,
4004Tim Morgan,
4005Tim Olsen,
4006Travis Snoozy,
4007Tyler Close,
4008Vincent Murphy,
4009Wenbo Zhu,
4010Werner Baumann,
4011Wilbur Streett,
4012Wilfredo Sanchez Vega,
4013William A. Rowe Jr.,
4014William Chan,
4015Willy Tarreau,
4016Xiaoshu Wang,
4017Yaron Goland,
4018Yngve Nysaeter Pettersen,
4019Yogesh Bang,
4020Yutaka Oiwa, and
4021Zed A. Shaw.
4022</t>
4023
4024</section>
4025
4026</middle>
4027<back>
4028
4029<references title="Normative References">
4030
4031<reference anchor="ISO-8859-1">
4032  <front>
4033    <title>
4034     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4035    </title>
4036    <author>
4037      <organization>International Organization for Standardization</organization>
4038    </author>
4039    <date year="1998"/>
4040  </front>
4041  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4042</reference>
4043
4044<reference anchor="Part2">
4045  <front>
4046    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4047    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4048      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4049      <address><email>fielding@gbiv.com</email></address>
4050    </author>
4051    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4052      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4053      <address><email>jg@freedesktop.org</email></address>
4054    </author>
4055    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4056      <organization abbrev="HP">Hewlett-Packard Company</organization>
4057      <address><email>JeffMogul@acm.org</email></address>
4058    </author>
4059    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4060      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4061      <address><email>henrikn@microsoft.com</email></address>
4062    </author>
4063    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4064      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4065      <address><email>LMM@acm.org</email></address>
4066    </author>
4067    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4068      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4069      <address><email>paulle@microsoft.com</email></address>
4070    </author>
4071    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4072      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4073      <address><email>timbl@w3.org</email></address>
4074    </author>
4075    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4076      <organization abbrev="W3C">World Wide Web Consortium</organization>
4077      <address><email>ylafon@w3.org</email></address>
4078    </author>
4079    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4080      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4081      <address><email>julian.reschke@greenbytes.de</email></address>
4082    </author>
4083    <date month="October" year="2011"/>
4084  </front>
4085  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-17"/>
4086 
4087</reference>
4088
4089<reference anchor="Part3">
4090  <front>
4091    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4092    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4093      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4094      <address><email>fielding@gbiv.com</email></address>
4095    </author>
4096    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4097      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4098      <address><email>jg@freedesktop.org</email></address>
4099    </author>
4100    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4101      <organization abbrev="HP">Hewlett-Packard Company</organization>
4102      <address><email>JeffMogul@acm.org</email></address>
4103    </author>
4104    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4105      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4106      <address><email>henrikn@microsoft.com</email></address>
4107    </author>
4108    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4109      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4110      <address><email>LMM@acm.org</email></address>
4111    </author>
4112    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4113      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4114      <address><email>paulle@microsoft.com</email></address>
4115    </author>
4116    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4117      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4118      <address><email>timbl@w3.org</email></address>
4119    </author>
4120    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4121      <organization abbrev="W3C">World Wide Web Consortium</organization>
4122      <address><email>ylafon@w3.org</email></address>
4123    </author>
4124    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4125      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4126      <address><email>julian.reschke@greenbytes.de</email></address>
4127    </author>
4128    <date month="October" year="2011"/>
4129  </front>
4130  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-17"/>
4131 
4132</reference>
4133
4134<reference anchor="Part6">
4135  <front>
4136    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4137    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4138      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4139      <address><email>fielding@gbiv.com</email></address>
4140    </author>
4141    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4142      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4143      <address><email>jg@freedesktop.org</email></address>
4144    </author>
4145    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4146      <organization abbrev="HP">Hewlett-Packard Company</organization>
4147      <address><email>JeffMogul@acm.org</email></address>
4148    </author>
4149    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4150      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4151      <address><email>henrikn@microsoft.com</email></address>
4152    </author>
4153    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4154      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4155      <address><email>LMM@acm.org</email></address>
4156    </author>
4157    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4158      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4159      <address><email>paulle@microsoft.com</email></address>
4160    </author>
4161    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4162      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4163      <address><email>timbl@w3.org</email></address>
4164    </author>
4165    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4166      <organization abbrev="W3C">World Wide Web Consortium</organization>
4167      <address><email>ylafon@w3.org</email></address>
4168    </author>
4169    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4170      <organization>Rackspace</organization>
4171      <address><email>mnot@mnot.net</email></address>
4172    </author>
4173    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4174      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4175      <address><email>julian.reschke@greenbytes.de</email></address>
4176    </author>
4177    <date month="October" year="2011"/>
4178  </front>
4179  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-17"/>
4180 
4181</reference>
4182
4183<reference anchor="RFC5234">
4184  <front>
4185    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4186    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4187      <organization>Brandenburg InternetWorking</organization>
4188      <address>
4189        <email>dcrocker@bbiw.net</email>
4190      </address> 
4191    </author>
4192    <author initials="P." surname="Overell" fullname="Paul Overell">
4193      <organization>THUS plc.</organization>
4194      <address>
4195        <email>paul.overell@thus.net</email>
4196      </address>
4197    </author>
4198    <date month="January" year="2008"/>
4199  </front>
4200  <seriesInfo name="STD" value="68"/>
4201  <seriesInfo name="RFC" value="5234"/>
4202</reference>
4203
4204<reference anchor="RFC2119">
4205  <front>
4206    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4207    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4208      <organization>Harvard University</organization>
4209      <address><email>sob@harvard.edu</email></address>
4210    </author>
4211    <date month="March" year="1997"/>
4212  </front>
4213  <seriesInfo name="BCP" value="14"/>
4214  <seriesInfo name="RFC" value="2119"/>
4215</reference>
4216
4217<reference anchor="RFC3986">
4218 <front>
4219  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
4220  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4221    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4222    <address>
4223       <email>timbl@w3.org</email>
4224       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4225    </address>
4226  </author>
4227  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4228    <organization abbrev="Day Software">Day Software</organization>
4229    <address>
4230      <email>fielding@gbiv.com</email>
4231      <uri>http://roy.gbiv.com/</uri>
4232    </address>
4233  </author>
4234  <author initials="L." surname="Masinter" fullname="Larry Masinter">
4235    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4236    <address>
4237      <email>LMM@acm.org</email>
4238      <uri>http://larry.masinter.net/</uri>
4239    </address>
4240  </author>
4241  <date month="January" year="2005"/>
4242 </front>
4243 <seriesInfo name="STD" value="66"/>
4244 <seriesInfo name="RFC" value="3986"/>
4245</reference>
4246
4247<reference anchor="USASCII">
4248  <front>
4249    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4250    <author>
4251      <organization>American National Standards Institute</organization>
4252    </author>
4253    <date year="1986"/>
4254  </front>
4255  <seriesInfo name="ANSI" value="X3.4"/>
4256</reference>
4257
4258<reference anchor="RFC1950">
4259  <front>
4260    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4261    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4262      <organization>Aladdin Enterprises</organization>
4263      <address><email>ghost@aladdin.com</email></address>
4264    </author>
4265    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4266    <date month="May" year="1996"/>
4267  </front>
4268  <seriesInfo name="RFC" value="1950"/>
4269  <annotation>
4270    RFC 1950 is an Informational RFC, thus it might be less stable than
4271    this specification. On the other hand, this downward reference was
4272    present since the publication of RFC 2068 in 1997,
4273    therefore it is unlikely to cause problems in practice. See also
4274    <xref target="BCP97"/>.
4275  </annotation>
4276</reference>
4277
4278<reference anchor="RFC1951">
4279  <front>
4280    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4281    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4282      <organization>Aladdin Enterprises</organization>
4283      <address><email>ghost@aladdin.com</email></address>
4284    </author>
4285    <date month="May" year="1996"/>
4286  </front>
4287  <seriesInfo name="RFC" value="1951"/>
4288  <annotation>
4289    RFC 1951 is an Informational RFC, thus it might be less stable than
4290    this specification. On the other hand, this downward reference was
4291    present since the publication of RFC 2068 in 1997,
4292    therefore it is unlikely to cause problems in practice. See also
4293    <xref target="BCP97"/>.
4294  </annotation>
4295</reference>
4296
4297<reference anchor="RFC1952">
4298  <front>
4299    <title>GZIP file format specification version 4.3</title>
4300    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4301      <organization>Aladdin Enterprises</organization>
4302      <address><email>ghost@aladdin.com</email></address>
4303    </author>
4304    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4305      <address><email>gzip@prep.ai.mit.edu</email></address>
4306    </author>
4307    <author initials="M." surname="Adler" fullname="Mark Adler">
4308      <address><email>madler@alumni.caltech.edu</email></address>
4309    </author>
4310    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4311      <address><email>ghost@aladdin.com</email></address>
4312    </author>
4313    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4314      <address><email>randeg@alumni.rpi.edu</email></address>
4315    </author>
4316    <date month="May" year="1996"/>
4317  </front>
4318  <seriesInfo name="RFC" value="1952"/>
4319  <annotation>
4320    RFC 1952 is an Informational RFC, thus it might be less stable than
4321    this specification. On the other hand, this downward reference was
4322    present since the publication of RFC 2068 in 1997,
4323    therefore it is unlikely to cause problems in practice. See also
4324    <xref target="BCP97"/>.
4325  </annotation>
4326</reference>
4327
4328</references>
4329
4330<references title="Informative References">
4331
4332<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4333  <front>
4334    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4335    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4336    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4337    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4338    <author initials="H." surname="Lie" fullname="H. Lie"/>
4339    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4340    <date year="1997" month="September"/>
4341  </front>
4342  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4343</reference>
4344
4345<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4346  <front>
4347    <title>Improving HTTP Latency</title>
4348    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4349    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4350    <date year="1995" month="December"/>
4351  </front>
4352  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4353</reference>
4354
4355<reference anchor="RFC1919">
4356  <front>
4357    <title>Classical versus Transparent IP Proxies</title>
4358    <author initials="M." surname="Chatel" fullname="Marc Chatel">
4359      <address><email>mchatel@pax.eunet.ch</email></address>
4360    </author>
4361    <date year="1996" month="March"/>
4362  </front>
4363  <seriesInfo name="RFC" value="1919"/>
4364</reference>
4365
4366<reference anchor="RFC1945">
4367  <front>
4368    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4369    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4370      <organization>MIT, Laboratory for Computer Science</organization>
4371      <address><email>timbl@w3.org</email></address>
4372    </author>
4373    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4374      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4375      <address><email>fielding@ics.uci.edu</email></address>
4376    </author>
4377    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4378      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4379      <address><email>frystyk@w3.org</email></address>
4380    </author>
4381    <date month="May" year="1996"/>
4382  </front>
4383  <seriesInfo name="RFC" value="1945"/>
4384</reference>
4385
4386<reference anchor="RFC2045">
4387  <front>
4388    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4389    <author initials="N." surname="Freed" fullname="Ned Freed">
4390      <organization>Innosoft International, Inc.</organization>
4391      <address><email>ned@innosoft.com</email></address>
4392    </author>
4393    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4394      <organization>First Virtual Holdings</organization>
4395      <address><email>nsb@nsb.fv.com</email></address>
4396    </author>
4397    <date month="November" year="1996"/>
4398  </front>
4399  <seriesInfo name="RFC" value="2045"/>
4400</reference>
4401
4402<reference anchor="RFC2047">
4403  <front>
4404    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4405    <author initials="K." surname="Moore" fullname="Keith Moore">
4406      <organization>University of Tennessee</organization>
4407      <address><email>moore@cs.utk.edu</email></address>
4408    </author>
4409    <date month="November" year="1996"/>
4410  </front>
4411  <seriesInfo name="RFC" value="2047"/>
4412</reference>
4413
4414<reference anchor="RFC2068">
4415  <front>
4416    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4417    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4418      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4419      <address><email>fielding@ics.uci.edu</email></address>
4420    </author>
4421    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4422      <organization>MIT Laboratory for Computer Science</organization>
4423      <address><email>jg@w3.org</email></address>
4424    </author>
4425    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4426      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4427      <address><email>mogul@wrl.dec.com</email></address>
4428    </author>
4429    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4430      <organization>MIT Laboratory for Computer Science</organization>
4431      <address><email>frystyk@w3.org</email></address>
4432    </author>
4433    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4434      <organization>MIT Laboratory for Computer Science</organization>
4435      <address><email>timbl@w3.org</email></address>
4436    </author>
4437    <date month="January" year="1997"/>
4438  </front>
4439  <seriesInfo name="RFC" value="2068"/>
4440</reference>
4441
4442<reference anchor="RFC2145">
4443  <front>
4444    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4445    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4446      <organization>Western Research Laboratory</organization>
4447      <address><email>mogul@wrl.dec.com</email></address>
4448    </author>
4449    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4450      <organization>Department of Information and Computer Science</organization>
4451      <address><email>fielding@ics.uci.edu</email></address>
4452    </author>
4453    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4454      <organization>MIT Laboratory for Computer Science</organization>
4455      <address><email>jg@w3.org</email></address>
4456    </author>
4457    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4458      <organization>W3 Consortium</organization>
4459      <address><email>frystyk@w3.org</email></address>
4460    </author>
4461    <date month="May" year="1997"/>
4462  </front>
4463  <seriesInfo name="RFC" value="2145"/>
4464</reference>
4465
4466<reference anchor="RFC2616">
4467  <front>
4468    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4469    <author initials="R." surname="Fielding" fullname="R. Fielding">
4470      <organization>University of California, Irvine</organization>
4471      <address><email>fielding@ics.uci.edu</email></address>
4472    </author>
4473    <author initials="J." surname="Gettys" fullname="J. Gettys">
4474      <organization>W3C</organization>
4475      <address><email>jg@w3.org</email></address>
4476    </author>
4477    <author initials="J." surname="Mogul" fullname="J. Mogul">
4478      <organization>Compaq Computer Corporation</organization>
4479      <address><email>mogul@wrl.dec.com</email></address>
4480    </author>
4481    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4482      <organization>MIT Laboratory for Computer Science</organization>
4483      <address><email>frystyk@w3.org</email></address>
4484    </author>
4485    <author initials="L." surname="Masinter" fullname="L. Masinter">
4486      <organization>Xerox Corporation</organization>
4487      <address><email>masinter@parc.xerox.com</email></address>
4488    </author>
4489    <author initials="P." surname="Leach" fullname="P. Leach">
4490      <organization>Microsoft Corporation</organization>
4491      <address><email>paulle@microsoft.com</email></address>
4492    </author>
4493    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4494      <organization>W3C</organization>
4495      <address><email>timbl@w3.org</email></address>
4496    </author>
4497    <date month="June" year="1999"/>
4498  </front>
4499  <seriesInfo name="RFC" value="2616"/>
4500</reference>
4501
4502<reference anchor="RFC2817">
4503  <front>
4504    <title>Upgrading to TLS Within HTTP/1.1</title>
4505    <author initials="R." surname="Khare" fullname="R. Khare">
4506      <organization>4K Associates / UC Irvine</organization>
4507      <address><email>rohit@4K-associates.com</email></address>
4508    </author>
4509    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
4510      <organization>Agranat Systems, Inc.</organization>
4511      <address><email>lawrence@agranat.com</email></address>
4512    </author>
4513    <date year="2000" month="May"/>
4514  </front>
4515  <seriesInfo name="RFC" value="2817"/>
4516</reference>
4517
4518<reference anchor="RFC2818">
4519  <front>
4520    <title>HTTP Over TLS</title>
4521    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
4522      <organization>RTFM, Inc.</organization>
4523      <address><email>ekr@rtfm.com</email></address>
4524    </author>
4525    <date year="2000" month="May"/>
4526  </front>
4527  <seriesInfo name="RFC" value="2818"/>
4528</reference>
4529
4530<reference anchor="RFC2965">
4531  <front>
4532    <title>HTTP State Management Mechanism</title>
4533    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
4534      <organization>Bell Laboratories, Lucent Technologies</organization>
4535      <address><email>dmk@bell-labs.com</email></address>
4536    </author>
4537    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4538      <organization>Epinions.com, Inc.</organization>
4539      <address><email>lou@montulli.org</email></address>
4540    </author>
4541    <date year="2000" month="October"/>
4542  </front>
4543  <seriesInfo name="RFC" value="2965"/>
4544</reference>
4545
4546<reference anchor="RFC3040">
4547  <front>
4548    <title>Internet Web Replication and Caching Taxonomy</title>
4549    <author initials="I." surname="Cooper" fullname="I. Cooper">
4550      <organization>Equinix, Inc.</organization>
4551    </author>
4552    <author initials="I." surname="Melve" fullname="I. Melve">
4553      <organization>UNINETT</organization>
4554    </author>
4555    <author initials="G." surname="Tomlinson" fullname="G. Tomlinson">
4556      <organization>CacheFlow Inc.</organization>
4557    </author>
4558    <date year="2001" month="January"/>
4559  </front>
4560  <seriesInfo name="RFC" value="3040"/>
4561</reference>
4562
4563<reference anchor="RFC3864">
4564  <front>
4565    <title>Registration Procedures for Message Header Fields</title>
4566    <author initials="G." surname="Klyne" fullname="G. Klyne">
4567      <organization>Nine by Nine</organization>
4568      <address><email>GK-IETF@ninebynine.org</email></address>
4569    </author>
4570    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
4571      <organization>BEA Systems</organization>
4572      <address><email>mnot@pobox.com</email></address>
4573    </author>
4574    <author initials="J." surname="Mogul" fullname="J. Mogul">
4575      <organization>HP Labs</organization>
4576      <address><email>JeffMogul@acm.org</email></address>
4577    </author>
4578    <date year="2004" month="September"/>
4579  </front>
4580  <seriesInfo name="BCP" value="90"/>
4581  <seriesInfo name="RFC" value="3864"/>
4582</reference>
4583
4584<reference anchor="RFC4033">
4585  <front>
4586    <title>DNS Security Introduction and Requirements</title>
4587    <author initials="R." surname="Arends" fullname="R. Arends"/>
4588    <author initials="R." surname="Austein" fullname="R. Austein"/>
4589    <author initials="M." surname="Larson" fullname="M. Larson"/>
4590    <author initials="D." surname="Massey" fullname="D. Massey"/>
4591    <author initials="S." surname="Rose" fullname="S. Rose"/>
4592    <date year="2005" month="March"/>
4593  </front>
4594  <seriesInfo name="RFC" value="4033"/>
4595</reference>
4596
4597<reference anchor="RFC4288">
4598  <front>
4599    <title>Media Type Specifications and Registration Procedures</title>
4600    <author initials="N." surname="Freed" fullname="N. Freed">
4601      <organization>Sun Microsystems</organization>
4602      <address>
4603        <email>ned.freed@mrochek.com</email>
4604      </address>
4605    </author>
4606    <author initials="J." surname="Klensin" fullname="J. Klensin">
4607      <address>
4608        <email>klensin+ietf@jck.com</email>
4609      </address>
4610    </author>
4611    <date year="2005" month="December"/>
4612  </front>
4613  <seriesInfo name="BCP" value="13"/>
4614  <seriesInfo name="RFC" value="4288"/>
4615</reference>
4616
4617<reference anchor="RFC4395">
4618  <front>
4619    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4620    <author initials="T." surname="Hansen" fullname="T. Hansen">
4621      <organization>AT&amp;T Laboratories</organization>
4622      <address>
4623        <email>tony+urireg@maillennium.att.com</email>
4624      </address>
4625    </author>
4626    <author initials="T." surname="Hardie" fullname="T. Hardie">
4627      <organization>Qualcomm, Inc.</organization>
4628      <address>
4629        <email>hardie@qualcomm.com</email>
4630      </address>
4631    </author>
4632    <author initials="L." surname="Masinter" fullname="L. Masinter">
4633      <organization>Adobe Systems</organization>
4634      <address>
4635        <email>LMM@acm.org</email>
4636      </address>
4637    </author>
4638    <date year="2006" month="February"/>
4639  </front>
4640  <seriesInfo name="BCP" value="115"/>
4641  <seriesInfo name="RFC" value="4395"/>
4642</reference>
4643
4644<reference anchor="RFC4559">
4645  <front>
4646    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4647    <author initials="K." surname="Jaganathan" fullname="K. Jaganathan"/>
4648    <author initials="L." surname="Zhu" fullname="L. Zhu"/>
4649    <author initials="J." surname="Brezak" fullname="J. Brezak"/>
4650    <date year="2006" month="June"/>
4651  </front>
4652  <seriesInfo name="RFC" value="4559"/>
4653</reference>
4654
4655<reference anchor="RFC5226">
4656  <front>
4657    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4658    <author initials="T." surname="Narten" fullname="T. Narten">
4659      <organization>IBM</organization>
4660      <address><email>narten@us.ibm.com</email></address>
4661    </author>
4662    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
4663      <organization>Google</organization>
4664      <address><email>Harald@Alvestrand.no</email></address>
4665    </author>
4666    <date year="2008" month="May"/>
4667  </front>
4668  <seriesInfo name="BCP" value="26"/>
4669  <seriesInfo name="RFC" value="5226"/>
4670</reference>
4671
4672<reference anchor="RFC5322">
4673  <front>
4674    <title>Internet Message Format</title>
4675    <author initials="P." surname="Resnick" fullname="P. Resnick">
4676      <organization>Qualcomm Incorporated</organization>
4677    </author>
4678    <date year="2008" month="October"/>
4679  </front> 
4680  <seriesInfo name="RFC" value="5322"/>
4681</reference>
4682
4683<reference anchor="RFC6265">
4684  <front>
4685    <title>HTTP State Management Mechanism</title>
4686    <author initials="A." surname="Barth" fullname="Adam Barth">
4687      <organization abbrev="U.C. Berkeley">
4688        University of California, Berkeley
4689      </organization>
4690      <address><email>abarth@eecs.berkeley.edu</email></address>
4691    </author>
4692    <date year="2011" month="April"/>
4693  </front>
4694  <seriesInfo name="RFC" value="6265"/>
4695</reference>
4696
4697<reference anchor="BCP97">
4698  <front>
4699    <title>Handling Normative References to Standards-Track Documents</title>
4700    <author initials="J." surname="Klensin" fullname="J. Klensin">
4701      <address>
4702        <email>klensin+ietf@jck.com</email>
4703      </address>
4704    </author>
4705    <author initials="S." surname="Hartman" fullname="S. Hartman">
4706      <organization>MIT</organization>
4707      <address>
4708        <email>hartmans-ietf@mit.edu</email>
4709      </address>
4710    </author>
4711    <date year="2007" month="June"/>
4712  </front>
4713  <seriesInfo name="BCP" value="97"/>
4714  <seriesInfo name="RFC" value="4897"/>
4715</reference>
4716
4717<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4718  <front>
4719    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4720    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4721    <date year="2001" month="November"/>
4722  </front>
4723  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4724</reference>
4725
4726<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4727  <front>
4728    <title>Analysis of HTTP Performance Problems</title>
4729    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4730    <date/>
4731  </front>
4732</reference>
4733
4734<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4735  <front>
4736  <title>Analysis of HTTP Performance</title>
4737  <author initials="J." surname="Touch" fullname="Joe Touch">
4738    <organization>USC/Information Sciences Institute</organization>
4739    <address><email>touch@isi.edu</email></address>
4740  </author>
4741  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4742    <organization>USC/Information Sciences Institute</organization>
4743    <address><email>johnh@isi.edu</email></address>
4744  </author>
4745  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4746    <organization>USC/Information Sciences Institute</organization>
4747    <address><email>katia@isi.edu</email></address>
4748  </author>
4749  <date year="1998" month="Aug"/>
4750  </front>
4751  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4752  <annotation>(original report dated Aug. 1996)</annotation>
4753</reference>
4754
4755</references>
4756
4757
4758<section title="HTTP Version History" anchor="compatibility">
4759<t>
4760   HTTP has been in use by the World-Wide Web global information initiative
4761   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4762   was a simple protocol for hypertext data transfer across the Internet
4763   with only a single request method (GET) and no metadata.
4764   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4765   methods and MIME-like messaging that could include metadata about the data
4766   transferred and modifiers on the request/response semantics. However,
4767   HTTP/1.0 did not sufficiently take into consideration the effects of
4768   hierarchical proxies, caching, the need for persistent connections, or
4769   name-based virtual hosts. The proliferation of incompletely-implemented
4770   applications calling themselves "HTTP/1.0" further necessitated a
4771   protocol version change in order for two communicating applications
4772   to determine each other's true capabilities.
4773</t>
4774<t>
4775   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4776   requirements that enable reliable implementations, adding only
4777   those new features that will either be safely ignored by an HTTP/1.0
4778   recipient or only sent when communicating with a party advertising
4779   compliance with HTTP/1.1.
4780</t>
4781<t>
4782   It is beyond the scope of a protocol specification to mandate
4783   compliance with previous versions. HTTP/1.1 was deliberately
4784   designed, however, to make supporting previous versions easy.
4785   We would expect a general-purpose HTTP/1.1 server to understand
4786   any valid request in the format of HTTP/1.0 and respond appropriately
4787   with an HTTP/1.1 message that only uses features understood (or
4788   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4789   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4790</t>
4791<t>
4792   Since HTTP/0.9 did not support header fields in a request,
4793   there is no mechanism for it to support name-based virtual
4794   hosts (selection of resource by inspection of the Host header
4795   field).  Any server that implements name-based virtual hosts
4796   ought to disable support for HTTP/0.9.  Most requests that
4797   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4798   requests wherein a buggy client failed to properly encode
4799   linear whitespace found in a URI reference and placed in
4800   the request-target.
4801</t>
4802
4803<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4804<t>
4805   This section summarizes major differences between versions HTTP/1.0
4806   and HTTP/1.1.
4807</t>
4808
4809<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4810<t>
4811   The requirements that clients and servers support the Host header
4812   field (<xref target="header.host"/>), report an error if it is
4813   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4814   are among the most important changes defined by HTTP/1.1.
4815</t>
4816<t>
4817   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4818   addresses and servers; there was no other established mechanism for
4819   distinguishing the intended server of a request than the IP address
4820   to which that request was directed. The Host header field was
4821   introduced during the development of HTTP/1.1 and, though it was
4822   quickly implemented by most HTTP/1.0 browsers, additional requirements
4823   were placed on all HTTP/1.1 requests in order to ensure complete
4824   adoption.  At the time of this writing, most HTTP-based services
4825   are dependent upon the Host header field for targeting requests.
4826</t>
4827</section>
4828
4829<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4830<t>
4831   For most implementations of HTTP/1.0, each connection is established
4832   by the client prior to the request and closed by the server after
4833   sending the response. However, some implementations implement the
4834   Keep-Alive version of persistent connections described in
4835   Section 19.7.1 of <xref target="RFC2068"/>.
4836</t>
4837<t>
4838   Some clients and servers might wish to be compatible with some
4839   previous implementations of persistent connections in HTTP/1.0
4840   clients and servers. Persistent connections in HTTP/1.0 are
4841   explicitly negotiated as they are not the default behavior. HTTP/1.0
4842   experimental implementations of persistent connections are faulty,
4843   and the new facilities in HTTP/1.1 are designed to rectify these
4844   problems. The problem was that some existing HTTP/1.0 clients might
4845   send Keep-Alive to a proxy server that doesn't understand
4846   Connection, which would then erroneously forward it to the next
4847   inbound server, which would establish the Keep-Alive connection and
4848   result in a hung HTTP/1.0 proxy waiting for the close on the
4849   response. The result is that HTTP/1.0 clients must be prevented from
4850   using Keep-Alive when talking to proxies.
4851</t>
4852<t>
4853   However, talking to proxies is the most important use of persistent
4854   connections, so that prohibition is clearly unacceptable. Therefore,
4855   we need some other mechanism for indicating a persistent connection
4856   is desired, which is safe to use even when talking to an old proxy
4857   that ignores Connection. Persistent connections are the default for
4858   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4859   declaring non-persistence. See <xref target="header.connection"/>.
4860</t>
4861</section>
4862</section>
4863
4864<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4865<t>
4866  Empty list elements in list productions have been deprecated.
4867  (<xref target="notation.abnf"/>)
4868</t>
4869<t>
4870  Rules about implicit linear whitespace between certain grammar productions
4871  have been removed; now it's only allowed when specifically pointed out
4872  in the ABNF.
4873  (<xref target="basic.rules"/>)
4874</t>
4875<t>
4876  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4877  sensitive. Restrict the version numbers to be single digits due to the fact
4878  that implementations are known to handle multi-digit version numbers
4879  incorrectly.
4880  (<xref target="http.version"/>)
4881</t>
4882<t>
4883  Require that invalid whitespace around field-names be rejected.
4884  (<xref target="header.fields"/>)
4885</t>
4886<t> 
4887  The NUL octet is no longer allowed in comment and quoted-string
4888  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4889  Non-ASCII content in header fields and reason phrase has been obsoleted and
4890  made opaque (the TEXT rule was removed).
4891  (<xref target="field.rules"/>)
4892</t>
4893<t>
4894  Require recipients to handle bogus Content-Length header fields as errors.
4895  (<xref target="message.body"/>)
4896</t>
4897<t>
4898  Remove reference to non-existent identity transfer-coding value tokens.
4899  (Sections <xref format="counter" target="message.body"/> and
4900  <xref format="counter" target="transfer.codings"/>)
4901</t>
4902<t>
4903  Update use of abs_path production from RFC 1808 to the path-absolute + query
4904  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4905  request method only.
4906  (<xref target="request-target"/>)
4907</t>
4908<t>
4909  Clarification that the chunk length does not include the count of the octets
4910  in the chunk header and trailer. Furthermore disallowed line folding
4911  in chunk extensions.
4912  (<xref target="chunked.encoding"/>)
4913</t>
4914<t>
4915  Remove hard limit of two connections per server.
4916  Remove requirement to retry a sequence of requests as long it was idempotent.
4917  Remove requirements about when servers are allowed to close connections
4918  prematurely.
4919  (<xref target="persistent.practical"/>)
4920</t>
4921<t>
4922  Remove requirement to retry requests under certain cirumstances when the
4923  server prematurely closes the connection.
4924  (<xref target="message.transmission.requirements"/>)
4925</t>
4926<t>
4927  Change ABNF productions for header fields to only define the field value.
4928  (<xref target="header.field.definitions"/>)
4929</t>
4930<t>
4931  Clarify exactly when close connection options must be sent.
4932  (<xref target="header.connection"/>)
4933</t>
4934<t>
4935  Define the semantics of the "Upgrade" header field in responses other than
4936  101 (this was incorporated from <xref target="RFC2817"/>).
4937  (<xref target="header.upgrade"/>)
4938</t>
4939</section>
4940</section>
4941
4942
4943<section title="Collected ABNF" anchor="collected.abnf">
4944<figure>
4945<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
4946BWS = OWS
4947
4948Chunked-Body = *chunk last-chunk trailer-part CRLF
4949Connection = *( "," OWS ) connection-token *( OWS "," [ OWS
4950 connection-token ] )
4951Content-Length = 1*DIGIT
4952
4953HTTP-Prot-Name = %x48.54.54.50 ; HTTP
4954HTTP-Version = HTTP-Prot-Name "/" DIGIT "." DIGIT
4955HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
4956 ]
4957Host = uri-host [ ":" port ]
4958
4959Method = token
4960
4961OWS = *( SP / HTAB / obs-fold )
4962
4963RWS = 1*( SP / HTAB / obs-fold )
4964Reason-Phrase = *( HTAB / SP / VCHAR / obs-text )
4965Request-Line = Method SP request-target SP HTTP-Version CRLF
4966
4967Status-Code = 3DIGIT
4968Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4969
4970TE = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4971Trailer = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4972Transfer-Encoding = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4973 transfer-coding ] )
4974
4975URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
4976Upgrade = *( "," OWS ) product *( OWS "," [ OWS product ] )
4977
4978Via = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
4979 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
4980 )
4981
4982absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
4983attribute = token
4984authority = <authority, defined in [RFC3986], Section 3.2>
4985
4986chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
4987chunk-data = 1*OCTET
4988chunk-ext = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
4989chunk-ext-name = token
4990chunk-ext-val = token / quoted-str-nf
4991chunk-size = 1*HEXDIG
4992comment = "(" *( ctext / quoted-cpair / comment ) ")"
4993connection-token = token
4994ctext = OWS / %x21-27 ; '!'-'''
4995 / %x2A-5B ; '*'-'['
4996 / %x5D-7E ; ']'-'~'
4997 / obs-text
4998
4999field-content = *( HTAB / SP / VCHAR / obs-text )
5000field-name = token
5001field-value = *( field-content / obs-fold )
5002
5003header-field = field-name ":" OWS field-value BWS
5004http-URI = "http://" authority path-abempty [ "?" query ]
5005https-URI = "https://" authority path-abempty [ "?" query ]
5006
5007last-chunk = 1*"0" [ chunk-ext ] CRLF
5008
5009message-body = *OCTET
5010
5011obs-fold = CRLF ( SP / HTAB )
5012obs-text = %x80-FF
5013
5014partial-URI = relative-part [ "?" query ]
5015path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
5016path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
5017port = <port, defined in [RFC3986], Section 3.2.3>
5018product = token [ "/" product-version ]
5019product-version = token
5020protocol-name = token
5021protocol-version = token
5022pseudonym = token
5023
5024qdtext = OWS / "!" / %x23-5B ; '#'-'['
5025 / %x5D-7E ; ']'-'~'
5026 / obs-text
5027qdtext-nf = HTAB / SP / "!" / %x23-5B ; '#'-'['
5028 / %x5D-7E ; ']'-'~'
5029 / obs-text
5030query = <query, defined in [RFC3986], Section 3.4>
5031quoted-cpair = "\" ( HTAB / SP / VCHAR / obs-text )
5032quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
5033quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5034quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5035qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5036
5037received-by = ( uri-host [ ":" port ] ) / pseudonym
5038received-protocol = [ protocol-name "/" ] protocol-version
5039relative-part = <relative-part, defined in [RFC3986], Section 4.2>
5040request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5041 / authority
5042
5043special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
5044 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5045start-line = Request-Line / Status-Line
5046
5047t-codings = "trailers" / ( transfer-extension [ te-params ] )
5048tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
5049 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5050te-ext = OWS ";" OWS token [ "=" word ]
5051te-params = OWS ";" OWS "q=" qvalue *te-ext
5052token = 1*tchar
5053trailer-part = *( header-field CRLF )
5054transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
5055 transfer-extension
5056transfer-extension = token *( OWS ";" OWS transfer-parameter )
5057transfer-parameter = attribute BWS "=" BWS value
5058
5059uri-host = <host, defined in [RFC3986], Section 3.2.2>
5060
5061value = word
5062
5063word = token / quoted-string
5064]]></artwork>
5065</figure>
5066<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
5067; Chunked-Body defined but not used
5068; Connection defined but not used
5069; Content-Length defined but not used
5070; HTTP-message defined but not used
5071; Host defined but not used
5072; TE defined but not used
5073; Trailer defined but not used
5074; Transfer-Encoding defined but not used
5075; URI-reference defined but not used
5076; Upgrade defined but not used
5077; Via defined but not used
5078; http-URI defined but not used
5079; https-URI defined but not used
5080; partial-URI defined but not used
5081; special defined but not used
5082]]></artwork></figure></section>
5083
5084
5085<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5086
5087<section title="Since RFC 2616">
5088<t>
5089  Extracted relevant partitions from <xref target="RFC2616"/>.
5090</t>
5091</section>
5092
5093<section title="Since draft-ietf-httpbis-p1-messaging-00">
5094<t>
5095  Closed issues:
5096  <list style="symbols"> 
5097    <t>
5098      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5099      "HTTP Version should be case sensitive"
5100      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5101    </t>
5102    <t>
5103      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5104      "'unsafe' characters"
5105      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5106    </t>
5107    <t>
5108      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5109      "Chunk Size Definition"
5110      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5111    </t>
5112    <t>
5113      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5114      "Message Length"
5115      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5116    </t>
5117    <t>
5118      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5119      "Media Type Registrations"
5120      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5121    </t>
5122    <t>
5123      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5124      "URI includes query"
5125      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5126    </t>
5127    <t>
5128      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5129      "No close on 1xx responses"
5130      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5131    </t>
5132    <t>
5133      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5134      "Remove 'identity' token references"
5135      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5136    </t>
5137    <t>
5138      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5139      "Import query BNF"
5140    </t>
5141    <t>
5142      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5143      "qdtext BNF"
5144    </t>
5145    <t>
5146      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5147      "Normative and Informative references"
5148    </t>
5149    <t>
5150      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5151      "RFC2606 Compliance"
5152    </t>
5153    <t>
5154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5155      "RFC977 reference"
5156    </t>
5157    <t>
5158      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5159      "RFC1700 references"
5160    </t>
5161    <t>
5162      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5163      "inconsistency in date format explanation"
5164    </t>
5165    <t>
5166      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5167      "Date reference typo"
5168    </t>
5169    <t>
5170      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5171      "Informative references"
5172    </t>
5173    <t>
5174      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5175      "ISO-8859-1 Reference"
5176    </t>
5177    <t>
5178      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5179      "Normative up-to-date references"
5180    </t>
5181  </list>
5182</t>
5183<t>
5184  Other changes:
5185  <list style="symbols"> 
5186    <t>
5187      Update media type registrations to use RFC4288 template.
5188    </t>
5189    <t>
5190      Use names of RFC4234 core rules DQUOTE and HTAB,
5191      fix broken ABNF for chunk-data
5192      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5193    </t>
5194  </list>
5195</t>
5196</section>
5197
5198<section title="Since draft-ietf-httpbis-p1-messaging-01">
5199<t>
5200  Closed issues:
5201  <list style="symbols"> 
5202    <t>
5203      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5204      "Bodies on GET (and other) requests"
5205    </t>
5206    <t>
5207      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5208      "Updating to RFC4288"
5209    </t>
5210    <t>
5211      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5212      "Status Code and Reason Phrase"
5213    </t>
5214    <t>
5215      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5216      "rel_path not used"
5217    </t>
5218  </list>
5219</t>
5220<t>
5221  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5222  <list style="symbols"> 
5223    <t>
5224      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
5225      "trailer-part").
5226    </t>
5227    <t>
5228      Avoid underscore character in rule names ("http_URL" -&gt;
5229      "http-URL", "abs_path" -&gt; "path-absolute").
5230    </t>
5231    <t>
5232      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5233      "path-absolute", "port", "query", "relativeURI", "host) — these will
5234      have to be updated when switching over to RFC3986.
5235    </t>
5236    <t>
5237      Synchronize core rules with RFC5234.
5238    </t>
5239    <t>
5240      Get rid of prose rules that span multiple lines.
5241    </t>
5242    <t>
5243      Get rid of unused rules LOALPHA and UPALPHA.
5244    </t>
5245    <t>
5246      Move "Product Tokens" section (back) into Part 1, as "token" is used
5247      in the definition of the Upgrade header field.
5248    </t>
5249    <t>
5250      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5251    </t>
5252    <t>
5253      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5254    </t>
5255  </list>
5256</t>
5257</section>
5258
5259<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5260<t>
5261  Closed issues:
5262  <list style="symbols"> 
5263    <t>
5264      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5265      "HTTP-date vs. rfc1123-date"
5266    </t>
5267    <t>
5268      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5269      "WS in quoted-pair"
5270    </t>
5271  </list>
5272</t>
5273<t>
5274  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5275  <list style="symbols"> 
5276    <t>
5277      Reference RFC 3984, and update header field registrations for headers defined
5278      in this document.
5279    </t>
5280  </list>
5281</t>
5282<t>
5283  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5284  <list style="symbols"> 
5285    <t>
5286      Replace string literals when the string really is case-sensitive (HTTP-Version).
5287    </t>
5288  </list>
5289</t>
5290</section>
5291
5292<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5293<t>
5294  Closed issues:
5295  <list style="symbols"> 
5296    <t>
5297      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5298      "Connection closing"
5299    </t>
5300    <t>
5301      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5302      "Move registrations and registry information to IANA Considerations"
5303    </t>
5304    <t>
5305      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5306      "need new URL for PAD1995 reference"
5307    </t>
5308    <t>
5309      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5310      "IANA Considerations: update HTTP URI scheme registration"
5311    </t>
5312    <t>
5313      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5314      "Cite HTTPS URI scheme definition"
5315    </t>
5316    <t>
5317      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5318      "List-type headers vs Set-Cookie"
5319    </t>
5320  </list>
5321</t>
5322<t>
5323  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5324  <list style="symbols"> 
5325    <t>
5326      Replace string literals when the string really is case-sensitive (HTTP-Date).
5327    </t>
5328    <t>
5329      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5330    </t>
5331  </list>
5332</t>
5333</section>
5334
5335<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5336<t>
5337  Closed issues:
5338  <list style="symbols"> 
5339    <t>
5340      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5341      "Out-of-date reference for URIs"
5342    </t>
5343    <t>
5344      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5345      "RFC 2822 is updated by RFC 5322"
5346    </t>
5347  </list>
5348</t>
5349<t>
5350  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5351  <list style="symbols"> 
5352    <t>
5353      Use "/" instead of "|" for alternatives.
5354    </t>
5355    <t>
5356      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5357    </t>
5358    <t>
5359      Only reference RFC 5234's core rules.
5360    </t>
5361    <t>
5362      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5363      whitespace ("OWS") and required whitespace ("RWS").
5364    </t>
5365    <t>
5366      Rewrite ABNFs to spell out whitespace rules, factor out
5367      header field value format definitions.
5368    </t>
5369  </list>
5370</t>
5371</section>
5372
5373<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5374<t>
5375  Closed issues:
5376  <list style="symbols"> 
5377    <t>
5378      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5379      "Header LWS"
5380    </t>
5381    <t>
5382      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5383      "Sort 1.3 Terminology"
5384    </t>
5385    <t>
5386      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5387      "RFC2047 encoded words"
5388    </t>
5389    <t>
5390      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5391      "Character Encodings in TEXT"
5392    </t>
5393    <t>
5394      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5395      "Line Folding"
5396    </t>
5397    <t>
5398      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5399      "OPTIONS * and proxies"
5400    </t>
5401    <t>
5402      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5403      "Reason-Phrase BNF"
5404    </t>
5405    <t>
5406      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5407      "Use of TEXT"
5408    </t>
5409    <t>
5410      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5411      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5412    </t>
5413    <t>
5414      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5415      "RFC822 reference left in discussion of date formats"
5416    </t>
5417  </list>
5418</t>
5419<t>
5420  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5421  <list style="symbols"> 
5422    <t>
5423      Rewrite definition of list rules, deprecate empty list elements.
5424    </t>
5425    <t>
5426      Add appendix containing collected and expanded ABNF.
5427    </t>
5428  </list>
5429</t>
5430<t>
5431  Other changes:
5432  <list style="symbols"> 
5433    <t>
5434      Rewrite introduction; add mostly new Architecture Section.
5435    </t>
5436    <t>
5437      Move definition of quality values from Part 3 into Part 1;
5438      make TE request header field grammar independent of accept-params (defined in Part 3).
5439    </t>
5440  </list>
5441</t>
5442</section>
5443
5444<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5445<t>
5446  Closed issues:
5447  <list style="symbols"> 
5448    <t>
5449      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5450      "base for numeric protocol elements"
5451    </t>
5452    <t>
5453      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5454      "comment ABNF"
5455    </t>
5456  </list>
5457</t>
5458<t>
5459  Partly resolved issues:
5460  <list style="symbols"> 
5461    <t>
5462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5463      "205 Bodies" (took out language that implied that there might be
5464      methods for which a request body MUST NOT be included)
5465    </t>
5466    <t>
5467      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5468      "editorial improvements around HTTP-date"
5469    </t>
5470  </list>
5471</t>
5472</section>
5473
5474<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5475<t>
5476  Closed issues:
5477  <list style="symbols"> 
5478    <t>
5479      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5480      "Repeating single-value headers"
5481    </t>
5482    <t>
5483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5484      "increase connection limit"
5485    </t>
5486    <t>
5487      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5488      "IP addresses in URLs"
5489    </t>
5490    <t>
5491      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5492      "take over HTTP Upgrade Token Registry"
5493    </t>
5494    <t>
5495      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5496      "CR and LF in chunk extension values"
5497    </t>
5498    <t>
5499      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5500      "HTTP/0.9 support"
5501    </t>
5502    <t>
5503      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5504      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5505    </t>
5506    <t>
5507      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5508      "move definitions of gzip/deflate/compress to part 1"
5509    </t>
5510    <t>
5511      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5512      "disallow control characters in quoted-pair"
5513    </t>
5514  </list>
5515</t>
5516<t>
5517  Partly resolved issues:
5518  <list style="symbols"> 
5519    <t>
5520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5521      "update IANA requirements wrt Transfer-Coding values" (add the
5522      IANA Considerations subsection)
5523    </t>
5524  </list>
5525</t>
5526</section>
5527
5528<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5529<t>
5530  Closed issues:
5531  <list style="symbols"> 
5532    <t>
5533      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5534      "header parsing, treatment of leading and trailing OWS"
5535    </t>
5536  </list>
5537</t>
5538<t>
5539  Partly resolved issues:
5540  <list style="symbols"> 
5541    <t>
5542      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5543      "Placement of 13.5.1 and 13.5.2"
5544    </t>
5545    <t>
5546      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5547      "use of term "word" when talking about header structure"
5548    </t>
5549  </list>
5550</t>
5551</section>
5552
5553<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5554<t>
5555  Closed issues:
5556  <list style="symbols"> 
5557    <t>
5558      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5559      "Clarification of the term 'deflate'"
5560    </t>
5561    <t>
5562      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5563      "OPTIONS * and proxies"
5564    </t>
5565    <t>
5566      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5567      "MIME-Version not listed in P1, general header fields"
5568    </t>
5569    <t>
5570      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5571      "IANA registry for content/transfer encodings"
5572    </t>
5573    <t>
5574      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5575      "Case-sensitivity of HTTP-date"
5576    </t>
5577    <t>
5578      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5579      "use of term "word" when talking about header structure"
5580    </t>
5581  </list>
5582</t>
5583<t>
5584  Partly resolved issues:
5585  <list style="symbols"> 
5586    <t>
5587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5588      "Term for the requested resource's URI"
5589    </t>
5590  </list>
5591</t>
5592</section>
5593
5594<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5595<t>
5596  Closed issues:
5597  <list style="symbols">
5598    <t>
5599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5600      "Connection Closing"
5601    </t>
5602    <t>
5603      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5604      "Delimiting messages with multipart/byteranges"
5605    </t>
5606    <t>
5607      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5608      "Handling multiple Content-Length headers"
5609    </t>
5610    <t>
5611      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5612      "Clarify entity / representation / variant terminology"
5613    </t>
5614    <t>
5615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5616      "consider removing the 'changes from 2068' sections"
5617    </t>
5618  </list>
5619</t>
5620<t>
5621  Partly resolved issues:
5622  <list style="symbols"> 
5623    <t>
5624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5625      "HTTP(s) URI scheme definitions"
5626    </t>
5627  </list>
5628</t>
5629</section>
5630
5631<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5632<t>
5633  Closed issues:
5634  <list style="symbols">
5635    <t>
5636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5637      "Trailer requirements"
5638    </t>
5639    <t>
5640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5641      "Text about clock requirement for caches belongs in p6"
5642    </t>
5643    <t>
5644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5645      "effective request URI: handling of missing host in HTTP/1.0"
5646    </t>
5647    <t>
5648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5649      "confusing Date requirements for clients"
5650    </t>
5651  </list>
5652</t>
5653<t>
5654  Partly resolved issues:
5655  <list style="symbols"> 
5656    <t>
5657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5658      "Handling multiple Content-Length headers"
5659    </t>
5660  </list>
5661</t>
5662</section>
5663
5664<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5665<t>
5666  Closed issues:
5667  <list style="symbols">
5668    <t>
5669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5670      "RFC2145 Normative"
5671    </t>
5672    <t>
5673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5674      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5675    </t>
5676    <t>
5677      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5678      "define 'transparent' proxy"
5679    </t>
5680    <t>
5681      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5682      "Header Classification"
5683    </t>
5684    <t>
5685      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5686      "Is * usable as a request-uri for new methods?"
5687    </t>
5688    <t>
5689      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5690      "Migrate Upgrade details from RFC2817"
5691    </t>
5692    <t>
5693      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5694      "untangle ABNFs for header fields"
5695    </t>
5696    <t>
5697      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5698      "update RFC 2109 reference"
5699    </t>
5700  </list>
5701</t>
5702</section>
5703
5704<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5705<t>
5706  Closed issues:
5707  <list style="symbols">
5708    <t>
5709      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5710      "Allow is not in 13.5.2"
5711    </t>
5712    <t>
5713      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5714      "Handling multiple Content-Length headers"
5715    </t>
5716    <t>
5717      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5718      "untangle ABNFs for header fields"
5719    </t>
5720    <t>
5721      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5722      "Content-Length ABNF broken"
5723    </t>
5724  </list>
5725</t>
5726</section>
5727
5728<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5729<t>
5730  Closed issues:
5731  <list style="symbols">
5732    <t>
5733      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5734      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5735    </t>
5736    <t>
5737      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5738      "Recommend minimum sizes for protocol elements"
5739    </t>
5740    <t>
5741      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5742      "Set expectations around buffering"
5743    </t>
5744    <t>
5745      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5746      "Considering messages in isolation"
5747    </t>
5748  </list>
5749</t>
5750</section>
5751
5752<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5753<t>
5754  Closed issues:
5755  <list style="symbols">
5756    <t>
5757      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5758      "DNS Spoofing / DNS Binding advice"
5759    </t>
5760    <t>
5761      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5762      "move RFCs 2145, 2616, 2817 to Historic status"
5763    </t>
5764    <t>
5765      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5766      "\-escaping in quoted strings"
5767    </t>
5768    <t>
5769      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5770      "'Close' should be reserved in the HTTP header field registry"
5771    </t>
5772  </list>
5773</t>
5774</section>
5775
5776<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5777<t>
5778  Closed issues:
5779  <list style="symbols">
5780    <t>
5781      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5782      "Document HTTP's error-handling philosophy"
5783    </t>
5784    <t>
5785      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5786      "Explain header registration"
5787    </t>
5788    <t>
5789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5790      "Revise Acknowledgements Sections"
5791    </t>
5792    <t>
5793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5794      "Retrying Requests"
5795    </t>
5796    <t>
5797      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5798      "Closing the connection on server error"
5799    </t>
5800  </list>
5801</t>
5802</section>
5803
5804</section>
5805
5806</back>
5807</rfc>
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