source: draft-ietf-httpbis/18/draft-ietf-httpbis-p1-messaging-18.xml @ 1499

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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-18">
20
21<front>
22
23  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
24
25  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
26    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
27    <address>
28      <postal>
29        <street>345 Park Ave</street>
30        <city>San Jose</city>
31        <region>CA</region>
32        <code>95110</code>
33        <country>USA</country>
34      </postal>
35      <email>fielding@gbiv.com</email>
36      <uri>http://roy.gbiv.com/</uri>
37    </address>
38  </author>
39
40  <author initials="J." surname="Gettys" fullname="Jim Gettys">
41    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
42    <address>
43      <postal>
44        <street>21 Oak Knoll Road</street>
45        <city>Carlisle</city>
46        <region>MA</region>
47        <code>01741</code>
48        <country>USA</country>
49      </postal>
50      <email>jg@freedesktop.org</email>
51      <uri>http://gettys.wordpress.com/</uri>
52    </address>
53  </author>
54 
55  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
56    <organization abbrev="HP">Hewlett-Packard Company</organization>
57    <address>
58      <postal>
59        <street>HP Labs, Large Scale Systems Group</street>
60        <street>1501 Page Mill Road, MS 1177</street>
61        <city>Palo Alto</city>
62        <region>CA</region>
63        <code>94304</code>
64        <country>USA</country>
65      </postal>
66      <email>JeffMogul@acm.org</email>
67    </address>
68  </author>
69
70  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
71    <organization abbrev="Microsoft">Microsoft Corporation</organization>
72    <address>
73      <postal>
74        <street>1 Microsoft Way</street>
75        <city>Redmond</city>
76        <region>WA</region>
77        <code>98052</code>
78        <country>USA</country>
79      </postal>
80      <email>henrikn@microsoft.com</email>
81    </address>
82  </author>
83
84  <author initials="L." surname="Masinter" fullname="Larry Masinter">
85    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
86    <address>
87      <postal>
88        <street>345 Park Ave</street>
89        <city>San Jose</city>
90        <region>CA</region>
91        <code>95110</code>
92        <country>USA</country>
93      </postal>
94      <email>LMM@acm.org</email>
95      <uri>http://larry.masinter.net/</uri>
96    </address>
97  </author>
98 
99  <author initials="P." surname="Leach" fullname="Paul J. Leach">
100    <organization abbrev="Microsoft">Microsoft Corporation</organization>
101    <address>
102      <postal>
103        <street>1 Microsoft Way</street>
104        <city>Redmond</city>
105        <region>WA</region>
106        <code>98052</code>
107      </postal>
108      <email>paulle@microsoft.com</email>
109    </address>
110  </author>
111   
112  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
113    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
114    <address>
115      <postal>
116        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
117        <street>The Stata Center, Building 32</street>
118        <street>32 Vassar Street</street>
119        <city>Cambridge</city>
120        <region>MA</region>
121        <code>02139</code>
122        <country>USA</country>
123      </postal>
124      <email>timbl@w3.org</email>
125      <uri>http://www.w3.org/People/Berners-Lee/</uri>
126    </address>
127  </author>
128
129  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
130    <organization abbrev="W3C">World Wide Web Consortium</organization>
131    <address>
132      <postal>
133        <street>W3C / ERCIM</street>
134        <street>2004, rte des Lucioles</street>
135        <city>Sophia-Antipolis</city>
136        <region>AM</region>
137        <code>06902</code>
138        <country>France</country>
139      </postal>
140      <email>ylafon@w3.org</email>
141      <uri>http://www.raubacapeu.net/people/yves/</uri>
142    </address>
143  </author>
144
145  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
146    <organization abbrev="greenbytes">greenbytes GmbH</organization>
147    <address>
148      <postal>
149        <street>Hafenweg 16</street>
150        <city>Muenster</city><region>NW</region><code>48155</code>
151        <country>Germany</country>
152      </postal>
153      <phone>+49 251 2807760</phone>
154      <facsimile>+49 251 2807761</facsimile>
155      <email>julian.reschke@greenbytes.de</email>
156      <uri>http://greenbytes.de/tech/webdav/</uri>
157    </address>
158  </author>
159
160  <date month="January" year="2012" day="4"/>
161  <workgroup>HTTPbis Working Group</workgroup>
162
163<abstract>
164<t>
165   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
166   distributed, collaborative, hypertext information systems. HTTP has been in
167   use by the World Wide Web global information initiative since 1990. This
168   document is Part 1 of the seven-part specification that defines the protocol
169   referred to as "HTTP/1.1" and, taken together, obsoletes
170   RFC 2616 and moves it to historic
171   status, along with its predecessor RFC
172   2068.
173</t>
174<t>
175   Part 1 provides an overview of HTTP and its associated terminology, defines
176   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
177   the generic message syntax and parsing requirements for HTTP message frames,
178   and describes general security concerns for implementations.
179</t>
180<t>
181   This part also obsoletes RFCs 2145
182   (on HTTP version numbers) and 2817
183   (on using CONNECT for TLS upgrades) and moves them to historic status.
184</t>
185</abstract>
186
187<note title="Editorial Note (To be removed by RFC Editor)">
188  <t>
189    Discussion of this draft should take place on the HTTPBIS working group
190    mailing list (ietf-http-wg@w3.org), which is archived at
191    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
192  </t>
193  <t>
194    The current issues list is at
195    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
196    documents (including fancy diffs) can be found at
197    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
198  </t>
199  <t>
200    The changes in this draft are summarized in <xref target="changes.since.17"/>.
201  </t>
202</note>
203</front>
204<middle>
205<section title="Introduction" anchor="introduction">
206<t>
207   The Hypertext Transfer Protocol (HTTP) is an application-level
208   request/response protocol that uses extensible semantics and MIME-like
209   message payloads for flexible interaction with network-based hypertext
210   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
211   standard <xref target="RFC3986"/> to indicate the target resource and
212   relationships between resources.
213   Messages are passed in a format similar to that used by Internet mail
214   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
215   (MIME) <xref target="RFC2045"/> (see Appendix A of <xref target="Part3"/> for the differences
216   between HTTP and MIME messages).
217</t>
218<t>
219   HTTP is a generic interface protocol for information systems. It is
220   designed to hide the details of how a service is implemented by presenting
221   a uniform interface to clients that is independent of the types of
222   resources provided. Likewise, servers do not need to be aware of each
223   client's purpose: an HTTP request can be considered in isolation rather
224   than being associated with a specific type of client or a predetermined
225   sequence of application steps. The result is a protocol that can be used
226   effectively in many different contexts and for which implementations can
227   evolve independently over time.
228</t>
229<t>
230   HTTP is also designed for use as an intermediation protocol for translating
231   communication to and from non-HTTP information systems.
232   HTTP proxies and gateways can provide access to alternative information
233   services by translating their diverse protocols into a hypertext
234   format that can be viewed and manipulated by clients in the same way
235   as HTTP services.
236</t>
237<t>
238   One consequence of HTTP flexibility is that the protocol cannot be
239   defined in terms of what occurs behind the interface. Instead, we
240   are limited to defining the syntax of communication, the intent
241   of received communication, and the expected behavior of recipients.
242   If the communication is considered in isolation, then successful
243   actions ought to be reflected in corresponding changes to the
244   observable interface provided by servers. However, since multiple
245   clients might act in parallel and perhaps at cross-purposes, we
246   cannot require that such changes be observable beyond the scope
247   of a single response.
248</t>
249<t>
250   This document is Part 1 of the seven-part specification of HTTP,
251   defining the protocol referred to as "HTTP/1.1", obsoleting
252   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
253   Part 1 describes the architectural elements that are used or
254   referred to in HTTP, defines the "http" and "https" URI schemes,
255   describes overall network operation and connection management,
256   and defines HTTP message framing and forwarding requirements.
257   Our goal is to define all of the mechanisms necessary for HTTP message
258   handling that are independent of message semantics, thereby defining the
259   complete set of requirements for message parsers and
260   message-forwarding intermediaries.
261</t>
262
263<section title="Conformance and Error Handling" anchor="intro.conformance.and.error.handling">
264<t>
265   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
266   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
267   document are to be interpreted as described in <xref target="RFC2119"/>.
268</t>
269<t>
270   This document defines conformance criteria for several roles in HTTP
271   communication, including Senders, Recipients, Clients, Servers, User-Agents,
272   Origin Servers, Intermediaries, Proxies and Gateways. See <xref target="architecture"/>
273   for definitions of these terms.
274</t>
275<t>
276   An implementation is considered conformant if it complies with all of the
277   requirements associated with its role(s). Note that SHOULD-level requirements
278   are relevant here, unless one of the documented exceptions is applicable.
279</t>
280<t>
281   This document also uses ABNF to define valid protocol elements
282   (<xref target="notation"/>). In addition to the prose requirements placed
283   upon them, Senders MUST NOT generate protocol elements that are invalid.
284</t>
285<t>
286   Unless noted otherwise, Recipients MAY take steps to recover a usable
287   protocol element from an invalid construct. However, HTTP does not define
288   specific error handling mechanisms, except in cases where it has direct
289   impact on security. This is because different uses of the protocol require
290   different error handling strategies; for example, a Web browser may wish to
291   transparently recover from a response where the Location header field
292   doesn't parse according to the ABNF, whereby in a systems control protocol
293   using HTTP, this type of error recovery could lead to dangerous consequences.
294</t>
295</section>
296
297<section title="Syntax Notation" anchor="notation">
298<iref primary="true" item="Grammar" subitem="ALPHA"/>
299<iref primary="true" item="Grammar" subitem="CR"/>
300<iref primary="true" item="Grammar" subitem="CRLF"/>
301<iref primary="true" item="Grammar" subitem="CTL"/>
302<iref primary="true" item="Grammar" subitem="DIGIT"/>
303<iref primary="true" item="Grammar" subitem="DQUOTE"/>
304<iref primary="true" item="Grammar" subitem="HEXDIG"/>
305<iref primary="true" item="Grammar" subitem="HTAB"/>
306<iref primary="true" item="Grammar" subitem="LF"/>
307<iref primary="true" item="Grammar" subitem="OCTET"/>
308<iref primary="true" item="Grammar" subitem="SP"/>
309<iref primary="true" item="Grammar" subitem="VCHAR"/>
310<t>
311   This specification uses the Augmented Backus-Naur Form (ABNF) notation
312   of <xref target="RFC5234"/>.
313</t>
314<t anchor="core.rules">
315 
316 
317 
318 
319 
320 
321 
322 
323 
324 
325 
326 
327   The following core rules are included by
328   reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
329   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
330   DIGIT (decimal 0-9), DQUOTE (double quote),
331   HEXDIG (hexadecimal 0-9/A-F/a-f), HTAB (horizontal tab), LF (line feed),
332   OCTET (any 8-bit sequence of data), SP (space), and
333   VCHAR (any visible <xref target="USASCII"/> character).
334</t>
335<t>
336   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
337   "obsolete" grammar rules that appear for historical reasons.
338</t>
339
340<section title="ABNF Extension: #rule" anchor="notation.abnf">
341<t>
342  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
343  improve readability.
344</t>
345<t>
346  A construct "#" is defined, similar to "*", for defining comma-delimited
347  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
348  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
349  comma (",") and optional whitespace (OWS, <xref target="basic.rules"/>).   
350</t>
351<figure><preamble>
352  Thus,
353</preamble><artwork type="example"><![CDATA[
354  1#element => element *( OWS "," OWS element )
355]]></artwork></figure>
356<figure><preamble>
357  and:
358</preamble><artwork type="example"><![CDATA[
359  #element => [ 1#element ]
360]]></artwork></figure>
361<figure><preamble>
362  and for n &gt;= 1 and m &gt; 1:
363</preamble><artwork type="example"><![CDATA[
364  <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
365]]></artwork></figure>
366<t>
367  For compatibility with legacy list rules, recipients SHOULD accept empty
368  list elements. In other words, consumers would follow the list productions:
369</t>
370<figure><artwork type="example"><![CDATA[
371  #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
372 
373  1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
374]]></artwork></figure>
375<t>
376  Note that empty elements do not contribute to the count of elements present,
377  though.
378</t>
379<t>
380  For example, given these ABNF productions:
381</t>
382<figure><artwork type="example"><![CDATA[
383  example-list      = 1#example-list-elmt
384  example-list-elmt = token ; see Section 3.2.3
385]]></artwork></figure>
386<t>
387  Then these are valid values for example-list (not including the double
388  quotes, which are present for delimitation only):
389</t>
390<figure><artwork type="example"><![CDATA[
391  "foo,bar"
392  "foo ,bar,"
393  "foo , ,bar,charlie   "
394]]></artwork></figure>
395<t>
396  But these values would be invalid, as at least one non-empty element is
397  required:
398</t>
399<figure><artwork type="example"><![CDATA[
400  ""
401  ","
402  ",   ,"
403]]></artwork></figure>
404<t>
405  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
406  expanded as explained above.
407</t>
408</section>
409
410<section title="Basic Rules" anchor="basic.rules">
411<t anchor="rule.LWS">
412   This specification uses three rules to denote the use of linear
413   whitespace: OWS (optional whitespace), RWS (required whitespace), and
414   BWS ("bad" whitespace).
415</t>
416<t anchor="rule.OWS">
417   The OWS rule is used where zero or more linear whitespace octets might
418   appear. OWS SHOULD either not be produced or be produced as a single
419   SP. Multiple OWS octets that occur within field-content SHOULD either
420   be replaced with a single SP or transformed to all SP octets (each
421   octet other than SP replaced with SP) before interpreting the field value
422   or forwarding the message downstream.
423</t>
424<t anchor="rule.RWS">
425   RWS is used when at least one linear whitespace octet is required to
426   separate field tokens. RWS SHOULD be produced as a single SP.
427   Multiple RWS octets that occur within field-content SHOULD either
428   be replaced with a single SP or transformed to all SP octets before
429   interpreting the field value or forwarding the message downstream.
430</t>
431<t anchor="rule.BWS">
432   BWS is used where the grammar allows optional whitespace for historical
433   reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
434   recipients MUST accept such bad optional whitespace and remove it before
435   interpreting the field value or forwarding the message downstream.
436</t>
437<t anchor="rule.whitespace">
438 
439 
440 
441 
442</t>
443<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[
444  OWS            = *( SP / HTAB / obs-fold )
445                 ; "optional" whitespace
446  RWS            = 1*( SP / HTAB / obs-fold )
447                 ; "required" whitespace
448  BWS            = OWS
449                 ; "bad" whitespace
450  obs-fold       = CRLF ( SP / HTAB )
451                 ; obsolete line folding
452                 ; see Section 3.2.1
453]]></artwork></figure>
454</section>
455</section>
456</section>
457
458<section title="Architecture" anchor="architecture">
459<t>
460   HTTP was created for the World Wide Web architecture
461   and has evolved over time to support the scalability needs of a worldwide
462   hypertext system. Much of that architecture is reflected in the terminology
463   and syntax productions used to define HTTP.
464</t>
465
466<section title="Client/Server Messaging" anchor="operation">
467<iref primary="true" item="client"/>
468<iref primary="true" item="server"/>
469<iref primary="true" item="connection"/>
470<t>
471   HTTP is a stateless request/response protocol that operates by exchanging
472   messages (<xref target="http.message"/>) across a reliable
473   transport or session-layer
474   "connection". An HTTP "client" is a
475   program that establishes a connection to a server for the purpose of
476   sending one or more HTTP requests.  An HTTP "server" is a
477   program that accepts connections in order to service HTTP requests by
478   sending HTTP responses.
479</t>
480<iref primary="true" item="user agent"/>
481<iref primary="true" item="origin server"/>
482<iref primary="true" item="browser"/>
483<iref primary="true" item="spider"/>
484<iref primary="true" item="sender"/>
485<iref primary="true" item="recipient"/>
486<t>
487   Note that the terms client and server refer only to the roles that
488   these programs perform for a particular connection.  The same program
489   might act as a client on some connections and a server on others.  We use
490   the term "user agent" to refer to the program that initiates a request,
491   such as a WWW browser, editor, or spider (web-traversing robot), and
492   the term "origin server" to refer to the program that can originate
493   authoritative responses to a request.  For general requirements, we use
494   the term "sender" to refer to whichever component sent a given message
495   and the term "recipient" to refer to any component that receives the
496   message.
497</t>
498<t><list>
499  <t>
500    Note: The term 'user agent' covers both those situations where
501    there is a user (human) interacting with the software agent (and for which
502    user interface or interactive suggestions might be made, e.g., warning the
503    user or given the user an option in the case of security or privacy
504    options) and also those where the software agent may act autonomously.
505  </t>
506</list></t>
507<t>
508   Most HTTP communication consists of a retrieval request (GET) for
509   a representation of some resource identified by a URI.  In the
510   simplest case, this might be accomplished via a single bidirectional
511   connection (===) between the user agent (UA) and the origin server (O).
512</t>
513<figure><artwork type="drawing"><![CDATA[
514         request   >
515    UA ======================================= O
516                                <   response
517]]></artwork></figure>
518<iref primary="true" item="message"/>
519<iref primary="true" item="request"/>
520<iref primary="true" item="response"/>
521<t>
522   A client sends an HTTP request to the server in the form of a request
523   message, beginning with a request-line that includes a method, URI, and
524   protocol version (<xref target="request.line"/>),
525   followed by MIME-like header fields containing
526   request modifiers, client information, and payload metadata
527   (<xref target="header.fields"/>),
528   an empty line to indicate the end of the header section, and finally
529   a message body containing the payload body (if any,
530   <xref target="message.body"/>).
531</t>
532<t>
533   A server responds to the client's request by sending an HTTP response
534   message, beginning with a status line that
535   includes the protocol version, a success or error code, and textual
536   reason phrase (<xref target="status.line"/>),
537   followed by MIME-like header fields containing server
538   information, resource metadata, and payload metadata
539   (<xref target="header.fields"/>),
540   an empty line to indicate the end of the header section, and finally
541   a message body containing the payload body (if any,
542   <xref target="message.body"/>).
543</t>
544<t>
545   Note that 1xx responses (Section 7.1 of <xref target="Part2"/>) are not final; therefore, a server
546   can send zero or more 1xx responses, followed by exactly one final response
547   (with any other status code).
548</t>
549<t>
550   The following example illustrates a typical message exchange for a
551   GET request on the URI "http://www.example.com/hello.txt":
552</t>
553<figure><preamble>
554client request:
555</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
556  GET /hello.txt HTTP/1.1
557  User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
558  Host: www.example.com
559  Accept: */*
560 
561  ]]></artwork></figure>
562<figure><preamble>
563server response:
564</preamble><artwork type="message/http; msgtype=&#34;response&#34;"><![CDATA[
565  HTTP/1.1 200 OK
566  Date: Mon, 27 Jul 2009 12:28:53 GMT
567  Server: Apache
568  Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
569  ETag: "34aa387-d-1568eb00"
570  Accept-Ranges: bytes
571  Content-Length: 14
572  Vary: Accept-Encoding
573  Content-Type: text/plain
574 
575  Hello World!
576  ]]></artwork></figure>
577</section>
578
579<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
580<t>
581   Fundamentally, HTTP is a message-based protocol. Although message bodies can
582   be chunked (<xref target="chunked.encoding"/>) and implementations often
583   make parts of a message available progressively, this is not required, and
584   some widely-used implementations only make a message available when it is
585   complete. Furthermore, while most proxies will progressively stream messages,
586   some amount of buffering will take place, and some proxies might buffer
587   messages to perform transformations, check content or provide other services.
588</t>
589<t>
590   Therefore, extensions to and uses of HTTP cannot rely on the availability of
591   a partial message, or assume that messages will not be buffered. There are
592   strategies that can be used to test for buffering in a given connection, but
593   it should be understood that behaviors can differ across connections, and
594   between requests and responses.
595</t>
596<t>
597   Recipients MUST consider every message in a connection in isolation;
598   because HTTP is a stateless protocol, it cannot be assumed that two requests
599   on the same connection are from the same client or share any other common
600   attributes. In particular, intermediaries might mix requests from different
601   clients into a single server connection. Note that some existing HTTP
602   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
603   potentially causing interoperability and security problems.
604</t>
605</section>
606
607<section title="Connections and Transport Independence" anchor="transport-independence">
608<t>
609   HTTP messaging is independent of the underlying transport or
610   session-layer connection protocol(s).  HTTP only presumes a reliable
611   transport with in-order delivery of requests and the corresponding
612   in-order delivery of responses.  The mapping of HTTP request and
613   response structures onto the data units of the underlying transport
614   protocol is outside the scope of this specification.
615</t>
616<t>
617   The specific connection protocols to be used for an interaction
618   are determined by client configuration and the target resource's URI.
619   For example, the "http" URI scheme
620   (<xref target="http.uri"/>) indicates a default connection of TCP
621   over IP, with a default TCP port of 80, but the client might be
622   configured to use a proxy via some other connection port or protocol
623   instead of using the defaults.
624</t>
625<t>
626   A connection might be used for multiple HTTP request/response exchanges,
627   as defined in <xref target="persistent.connections"/>.
628</t>
629</section>
630
631<section title="Intermediaries" anchor="intermediaries">
632<iref primary="true" item="intermediary"/>
633<t>
634   HTTP enables the use of intermediaries to satisfy requests through
635   a chain of connections.  There are three common forms of HTTP
636   intermediary: proxy, gateway, and tunnel.  In some cases,
637   a single intermediary might act as an origin server, proxy, gateway,
638   or tunnel, switching behavior based on the nature of each request.
639</t>
640<figure><artwork type="drawing"><![CDATA[
641         >             >             >             >
642    UA =========== A =========== B =========== C =========== O
643               <             <             <             <
644]]></artwork></figure>
645<t>
646   The figure above shows three intermediaries (A, B, and C) between the
647   user agent and origin server. A request or response message that
648   travels the whole chain will pass through four separate connections.
649   Some HTTP communication options
650   might apply only to the connection with the nearest, non-tunnel
651   neighbor, only to the end-points of the chain, or to all connections
652   along the chain. Although the diagram is linear, each participant might
653   be engaged in multiple, simultaneous communications. For example, B
654   might be receiving requests from many clients other than A, and/or
655   forwarding requests to servers other than C, at the same time that it
656   is handling A's request.
657</t>
658<t>
659<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
660<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
661   We use the terms "upstream" and "downstream"
662   to describe various requirements in relation to the directional flow of a
663   message: all messages flow from upstream to downstream.
664   Likewise, we use the terms inbound and outbound to refer to
665   directions in relation to the request path:
666   "inbound" means toward the origin server and
667   "outbound" means toward the user agent.
668</t>
669<t><iref primary="true" item="proxy"/>
670   A "proxy" is a message forwarding agent that is selected by the
671   client, usually via local configuration rules, to receive requests
672   for some type(s) of absolute URI and attempt to satisfy those
673   requests via translation through the HTTP interface.  Some translations
674   are minimal, such as for proxy requests for "http" URIs, whereas
675   other requests might require translation to and from entirely different
676   application-layer protocols. Proxies are often used to group an
677   organization's HTTP requests through a common intermediary for the
678   sake of security, annotation services, or shared caching.
679</t>
680<t>
681<iref primary="true" item="transforming proxy"/>
682<iref primary="true" item="non-transforming proxy"/>
683   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
684   or configured to modify request or response messages in a semantically
685   meaningful way (i.e., modifications, beyond those required by normal
686   HTTP processing, that change the message in a way that would be
687   significant to the original sender or potentially significant to
688   downstream recipients).  For example, a transforming proxy might be
689   acting as a shared annotation server (modifying responses to include
690   references to a local annotation database), a malware filter, a
691   format transcoder, or an intranet-to-Internet privacy filter.  Such
692   transformations are presumed to be desired by the client (or client
693   organization) that selected the proxy and are beyond the scope of
694   this specification.  However, when a proxy is not intended to transform
695   a given message, we use the term "non-transforming proxy" to target
696   requirements that preserve HTTP message semantics. See Section 7.2.4 of <xref target="Part2"/> and
697   Section 3.6 of <xref target="Part6"/> for status and warning codes related to transformations.
698</t>
699<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
700<iref primary="true" item="accelerator"/>
701   A "gateway" (a.k.a., "reverse proxy")
702   is a receiving agent that acts
703   as a layer above some other server(s) and translates the received
704   requests to the underlying server's protocol.  Gateways are often
705   used to encapsulate legacy or untrusted information services, to
706   improve server performance through "accelerator" caching, and to
707   enable partitioning or load-balancing of HTTP services across
708   multiple machines.
709</t>
710<t>
711   A gateway behaves as an origin server on its outbound connection and
712   as a user agent on its inbound connection.
713   All HTTP requirements applicable to an origin server
714   also apply to the outbound communication of a gateway.
715   A gateway communicates with inbound servers using any protocol that
716   it desires, including private extensions to HTTP that are outside
717   the scope of this specification.  However, an HTTP-to-HTTP gateway
718   that wishes to interoperate with third-party HTTP servers MUST
719   comply with HTTP user agent requirements on the gateway's inbound
720   connection and MUST implement the Connection
721   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
722   header fields for both connections.
723</t>
724<t><iref primary="true" item="tunnel"/>
725   A "tunnel" acts as a blind relay between two connections
726   without changing the messages. Once active, a tunnel is not
727   considered a party to the HTTP communication, though the tunnel might
728   have been initiated by an HTTP request. A tunnel ceases to exist when
729   both ends of the relayed connection are closed. Tunnels are used to
730   extend a virtual connection through an intermediary, such as when
731   transport-layer security is used to establish private communication
732   through a shared firewall proxy.
733</t>
734<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
735<iref primary="true" item="captive portal"/>
736   In addition, there may exist network intermediaries that are not
737   considered part of the HTTP communication but nevertheless act as
738   filters or redirecting agents (usually violating HTTP semantics,
739   causing security problems, and otherwise making a mess of things).
740   Such a network intermediary, often referred to as an "interception proxy"
741   <xref target="RFC3040"/>, "transparent proxy" <xref target="RFC1919"/>,
742   or "captive portal",
743   differs from an HTTP proxy because it has not been selected by the client.
744   Instead, the network intermediary redirects outgoing TCP port 80 packets
745   (and occasionally other common port traffic) to an internal HTTP server.
746   Interception proxies are commonly found on public network access points,
747   as a means of enforcing account subscription prior to allowing use of
748   non-local Internet services, and within corporate firewalls to enforce
749   network usage policies.
750   They are indistinguishable from a man-in-the-middle attack.
751</t>
752</section>
753
754<section title="Caches" anchor="caches">
755<iref primary="true" item="cache"/>
756<t>
757   A "cache" is a local store of previous response messages and the
758   subsystem that controls its message storage, retrieval, and deletion.
759   A cache stores cacheable responses in order to reduce the response
760   time and network bandwidth consumption on future, equivalent
761   requests. Any client or server MAY employ a cache, though a cache
762   cannot be used by a server while it is acting as a tunnel.
763</t>
764<t>
765   The effect of a cache is that the request/response chain is shortened
766   if one of the participants along the chain has a cached response
767   applicable to that request. The following illustrates the resulting
768   chain if B has a cached copy of an earlier response from O (via C)
769   for a request which has not been cached by UA or A.
770</t>
771<figure><artwork type="drawing"><![CDATA[
772            >             >
773       UA =========== A =========== B - - - - - - C - - - - - - O
774                  <             <
775]]></artwork></figure>
776<t><iref primary="true" item="cacheable"/>
777   A response is "cacheable" if a cache is allowed to store a copy of
778   the response message for use in answering subsequent requests.
779   Even when a response is cacheable, there might be additional
780   constraints placed by the client or by the origin server on when
781   that cached response can be used for a particular request. HTTP
782   requirements for cache behavior and cacheable responses are
783   defined in Section 2 of <xref target="Part6"/>
784</t>
785<t>
786   There are a wide variety of architectures and configurations
787   of caches and proxies deployed across the World Wide Web and
788   inside large organizations. These systems include national hierarchies
789   of proxy caches to save transoceanic bandwidth, systems that
790   broadcast or multicast cache entries, organizations that distribute
791   subsets of cached data via optical media, and so on.
792</t>
793</section>
794
795<section title="Protocol Versioning" anchor="http.version">
796 
797 
798<t>
799   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
800   versions of the protocol. This specification defines version "1.1".
801   The protocol version as a whole indicates the sender's compliance
802   with the set of requirements laid out in that version's corresponding
803   specification of HTTP.
804</t>
805<t>
806   The version of an HTTP message is indicated by an HTTP-Version field
807   in the first line of the message. HTTP-Version is case-sensitive.
808</t>
809<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
810  HTTP-Version   = HTTP-Prot-Name "/" DIGIT "." DIGIT
811  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
812]]></artwork></figure>
813<t>
814   The HTTP version number consists of two decimal digits separated by a "."
815   (period or decimal point).  The first digit ("major version") indicates the
816   HTTP messaging syntax, whereas the second digit ("minor version") indicates
817   the highest minor version to which the sender is at least conditionally
818   compliant and able to understand for future communication.  The minor
819   version advertises the sender's communication capabilities even when the
820   sender is only using a backwards-compatible subset of the protocol,
821   thereby letting the recipient know that more advanced features can
822   be used in response (by servers) or in future requests (by clients).
823</t>
824<t>
825   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
826   <xref target="RFC1945"/> or a recipient whose version is unknown,
827   the HTTP/1.1 message is constructed such that it can be interpreted
828   as a valid HTTP/1.0 message if all of the newer features are ignored.
829   This specification places recipient-version requirements on some
830   new features so that a compliant sender will only use compatible
831   features until it has determined, through configuration or the
832   receipt of a message, that the recipient supports HTTP/1.1.
833</t>
834<t>
835   The interpretation of an HTTP header field does not change
836   between minor versions of the same major version, though the default
837   behavior of a recipient in the absence of such a field can change.
838   Unless specified otherwise, header fields defined in HTTP/1.1 are
839   defined for all versions of HTTP/1.x.  In particular, the Host and
840   Connection header fields ought to be implemented by all HTTP/1.x
841   implementations whether or not they advertise compliance with HTTP/1.1.
842</t>
843<t>
844   New header fields can be defined such that, when they are
845   understood by a recipient, they might override or enhance the
846   interpretation of previously defined header fields.  When an
847   implementation receives an unrecognized header field, the recipient
848   MUST ignore that header field for local processing regardless of
849   the message's HTTP version.  An unrecognized header field received
850   by a proxy MUST be forwarded downstream unless the header field's
851   field-name is listed in the message's Connection header-field
852   (see <xref target="header.connection"/>).
853   These requirements allow HTTP's functionality to be enhanced without
854   requiring prior update of all compliant intermediaries.
855</t>
856<t>
857   Intermediaries that process HTTP messages (i.e., all intermediaries
858   other than those acting as a tunnel) MUST send their own HTTP-Version
859   in forwarded messages.  In other words, they MUST NOT blindly
860   forward the first line of an HTTP message without ensuring that the
861   protocol version matches what the intermediary understands, and
862   is at least conditionally compliant to, for both the receiving and
863   sending of messages.  Forwarding an HTTP message without rewriting
864   the HTTP-Version might result in communication errors when downstream
865   recipients use the message sender's version to determine what features
866   are safe to use for later communication with that sender.
867</t>
868<t>
869   An HTTP client SHOULD send a request version equal to the highest
870   version for which the client is at least conditionally compliant and
871   whose major version is no higher than the highest version supported
872   by the server, if this is known.  An HTTP client MUST NOT send a
873   version for which it is not at least conditionally compliant.
874</t>
875<t>
876   An HTTP client MAY send a lower request version if it is known that
877   the server incorrectly implements the HTTP specification, but only
878   after the client has attempted at least one normal request and determined
879   from the response status or header fields (e.g., Server) that the
880   server improperly handles higher request versions.
881</t>
882<t>
883   An HTTP server SHOULD send a response version equal to the highest
884   version for which the server is at least conditionally compliant and
885   whose major version is less than or equal to the one received in the
886   request.  An HTTP server MUST NOT send a version for which it is not
887   at least conditionally compliant.  A server MAY send a 505 (HTTP
888   Version Not Supported) response if it cannot send a response using the
889   major version used in the client's request.
890</t>
891<t>
892   An HTTP server MAY send an HTTP/1.0 response to an HTTP/1.0 request
893   if it is known or suspected that the client incorrectly implements the
894   HTTP specification and is incapable of correctly processing later
895   version responses, such as when a client fails to parse the version
896   number correctly or when an intermediary is known to blindly forward
897   the HTTP-Version even when it doesn't comply with the given minor
898   version of the protocol. Such protocol downgrades SHOULD NOT be
899   performed unless triggered by specific client attributes, such as when
900   one or more of the request header fields (e.g., User-Agent) uniquely
901   match the values sent by a client known to be in error.
902</t>
903<t>
904   The intention of HTTP's versioning design is that the major number
905   will only be incremented if an incompatible message syntax is
906   introduced, and that the minor number will only be incremented when
907   changes made to the protocol have the effect of adding to the message
908   semantics or implying additional capabilities of the sender.  However,
909   the minor version was not incremented for the changes introduced between
910   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
911   is specifically avoiding any such changes to the protocol.
912</t>
913</section>
914
915<section title="Uniform Resource Identifiers" anchor="uri">
916<iref primary="true" item="resource"/>
917<t>
918   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
919   throughout HTTP as the means for identifying resources. URI references
920   are used to target requests, indicate redirects, and define relationships.
921   HTTP does not limit what a resource might be; it merely defines an interface
922   that can be used to interact with a resource via HTTP. More information on
923   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
924</t>
925 
926 
927 
928 
929 
930 
931 
932 
933 
934 
935<t>
936   This specification adopts the definitions of "URI-reference",
937   "absolute-URI", "relative-part", "port", "host",
938   "path-abempty", "path-absolute", "query", and "authority" from the
939   URI generic syntax <xref target="RFC3986"/>.
940   In addition, we define a partial-URI rule for protocol elements
941   that allow a relative URI but not a fragment.
942</t>
943<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[
944  URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
945  absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
946  relative-part = <relative-part, defined in [RFC3986], Section 4.2>
947  authority     = <authority, defined in [RFC3986], Section 3.2>
948  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
949  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
950  port          = <port, defined in [RFC3986], Section 3.2.3>
951  query         = <query, defined in [RFC3986], Section 3.4>
952  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
953 
954  partial-URI   = relative-part [ "?" query ]
955]]></artwork></figure>
956<t>
957   Each protocol element in HTTP that allows a URI reference will indicate
958   in its ABNF production whether the element allows any form of reference
959   (URI-reference), only a URI in absolute form (absolute-URI), only the
960   path and optional query components, or some combination of the above.
961   Unless otherwise indicated, URI references are parsed relative to the
962   effective request URI, which defines the default base URI for references
963   in both the request and its corresponding response.
964</t>
965
966<section title="http URI scheme" anchor="http.uri">
967 
968  <iref item="http URI scheme" primary="true"/>
969  <iref item="URI scheme" subitem="http" primary="true"/>
970<t>
971   The "http" URI scheme is hereby defined for the purpose of minting
972   identifiers according to their association with the hierarchical
973   namespace governed by a potential HTTP origin server listening for
974   TCP connections on a given port.
975</t>
976<figure><iref primary="true" item="Grammar" subitem="http-URI"/><artwork type="abnf2616"><![CDATA[
977  http-URI = "http:" "//" authority path-abempty [ "?" query ]
978]]></artwork></figure>
979<t>
980   The HTTP origin server is identified by the generic syntax's
981   <xref target="uri" format="none">authority</xref> component, which includes a host identifier
982   and optional TCP port (<xref target="RFC3986"/>, Section 3.2.2).
983   The remainder of the URI, consisting of both the hierarchical path
984   component and optional query component, serves as an identifier for
985   a potential resource within that origin server's name space.
986</t>
987<t>
988   If the host identifier is provided as an IP literal or IPv4 address,
989   then the origin server is any listener on the indicated TCP port at
990   that IP address. If host is a registered name, then that name is
991   considered an indirect identifier and the recipient might use a name
992   resolution service, such as DNS, to find the address of a listener
993   for that host.
994   The host MUST NOT be empty; if an "http" URI is received with an
995   empty host, then it MUST be rejected as invalid.
996   If the port subcomponent is empty or not given, then TCP port 80 is
997   assumed (the default reserved port for WWW services).
998</t>
999<t>
1000   Regardless of the form of host identifier, access to that host is not
1001   implied by the mere presence of its name or address. The host might or might
1002   not exist and, even when it does exist, might or might not be running an
1003   HTTP server or listening to the indicated port. The "http" URI scheme
1004   makes use of the delegated nature of Internet names and addresses to
1005   establish a naming authority (whatever entity has the ability to place
1006   an HTTP server at that Internet name or address) and allows that
1007   authority to determine which names are valid and how they might be used.
1008</t>
1009<t>
1010   When an "http" URI is used within a context that calls for access to the
1011   indicated resource, a client MAY attempt access by resolving
1012   the host to an IP address, establishing a TCP connection to that address
1013   on the indicated port, and sending an HTTP request message
1014   (<xref target="http.message"/>) containing the URI's identifying data
1015   (<xref target="message.routing"/>) to the server.
1016   If the server responds to that request with a non-interim HTTP response
1017   message, as described in Section 4 of <xref target="Part2"/>, then that response
1018   is considered an authoritative answer to the client's request.
1019</t>
1020<t>
1021   Although HTTP is independent of the transport protocol, the "http"
1022   scheme is specific to TCP-based services because the name delegation
1023   process depends on TCP for establishing authority.
1024   An HTTP service based on some other underlying connection protocol
1025   would presumably be identified using a different URI scheme, just as
1026   the "https" scheme (below) is used for servers that require an SSL/TLS
1027   transport layer on a connection. Other protocols might also be used to
1028   provide access to "http" identified resources — it is only the
1029   authoritative interface used for mapping the namespace that is
1030   specific to TCP.
1031</t>
1032<t>
1033   The URI generic syntax for authority also includes a deprecated
1034   userinfo subcomponent (<xref target="RFC3986"/>, Section 3.2.1)
1035   for including user authentication information in the URI.  Some
1036   implementations make use of the userinfo component for internal
1037   configuration of authentication information, such as within command
1038   invocation options, configuration files, or bookmark lists, even
1039   though such usage might expose a user identifier or password.
1040   Senders MUST NOT include a userinfo subcomponent (and its "@"
1041   delimiter) when transmitting an "http" URI in a message.  Recipients
1042   of HTTP messages that contain a URI reference SHOULD parse for the
1043   existence of userinfo and treat its presence as an error, likely
1044   indicating that the deprecated subcomponent is being used to obscure
1045   the authority for the sake of phishing attacks.
1046</t>
1047</section>
1048
1049<section title="https URI scheme" anchor="https.uri">
1050   
1051   <iref item="https URI scheme"/>
1052   <iref item="URI scheme" subitem="https"/>
1053<t>
1054   The "https" URI scheme is hereby defined for the purpose of minting
1055   identifiers according to their association with the hierarchical
1056   namespace governed by a potential HTTP origin server listening for
1057   SSL/TLS-secured connections on a given TCP port.
1058</t>
1059<t>
1060   All of the requirements listed above for the "http" scheme are also
1061   requirements for the "https" scheme, except that a default TCP port
1062   of 443 is assumed if the port subcomponent is empty or not given,
1063   and the TCP connection MUST be secured for privacy through the
1064   use of strong encryption prior to sending the first HTTP request.
1065</t>
1066<figure><iref primary="true" item="Grammar" subitem="https-URI"/><artwork type="abnf2616"><![CDATA[
1067  https-URI = "https:" "//" authority path-abempty [ "?" query ]
1068]]></artwork></figure>
1069<t>
1070   Unlike the "http" scheme, responses to "https" identified requests
1071   are never "public" and thus MUST NOT be reused for shared caching.
1072   They can, however, be reused in a private cache if the message is
1073   cacheable by default in HTTP or specifically indicated as such by
1074   the Cache-Control header field (Section 3.2 of <xref target="Part6"/>).
1075</t>
1076<t>
1077   Resources made available via the "https" scheme have no shared
1078   identity with the "http" scheme even if their resource identifiers
1079   indicate the same authority (the same host listening to the same
1080   TCP port).  They are distinct name spaces and are considered to be
1081   distinct origin servers.  However, an extension to HTTP that is
1082   defined to apply to entire host domains, such as the Cookie protocol
1083   <xref target="RFC6265"/>, can allow information
1084   set by one service to impact communication with other services
1085   within a matching group of host domains.
1086</t>
1087<t>
1088   The process for authoritative access to an "https" identified
1089   resource is defined in <xref target="RFC2818"/>.
1090</t>
1091</section>
1092
1093<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1094<t>
1095   Since the "http" and "https" schemes conform to the URI generic syntax,
1096   such URIs are normalized and compared according to the algorithm defined
1097   in <xref target="RFC3986"/>, Section 6, using the defaults
1098   described above for each scheme.
1099</t>
1100<t>
1101   If the port is equal to the default port for a scheme, the normal
1102   form is to elide the port subcomponent. Likewise, an empty path
1103   component is equivalent to an absolute path of "/", so the normal
1104   form is to provide a path of "/" instead. The scheme and host
1105   are case-insensitive and normally provided in lowercase; all
1106   other components are compared in a case-sensitive manner.
1107   Characters other than those in the "reserved" set are equivalent
1108   to their percent-encoded octets (see <xref target="RFC3986"/>, Section 2.1): the normal form is to not encode them.
1109</t>
1110<t>
1111   For example, the following three URIs are equivalent:
1112</t>
1113<figure><artwork type="example"><![CDATA[
1114   http://example.com:80/~smith/home.html
1115   http://EXAMPLE.com/%7Esmith/home.html
1116   http://EXAMPLE.com:/%7esmith/home.html
1117]]></artwork></figure>
1118</section>
1119</section>
1120</section>
1121
1122<section title="Message Format" anchor="http.message">
1123
1124
1125
1126
1127<iref item="header section"/>
1128<iref item="headers"/>
1129<iref item="header field"/>
1130<t>
1131   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1132   octets in a format similar to the Internet Message Format
1133   <xref target="RFC5322"/>: zero or more header fields (collectively
1134   referred to as the "headers" or the "header section"), an empty line
1135   indicating the end of the header section, and an optional message-body.
1136</t>
1137<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1138  HTTP-message    = start-line
1139                    *( header-field CRLF )
1140                    CRLF
1141                    [ message-body ]
1142]]></artwork></figure>
1143<t>
1144   The normal procedure for parsing an HTTP message is to read the
1145   start-line into a structure, read each header field into a hash
1146   table by field name until the empty line, and then use the parsed
1147   data to determine if a message-body is expected.  If a message-body
1148   has been indicated, then it is read as a stream until an amount
1149   of octets equal to the message-body length is read or the connection
1150   is closed.
1151</t>
1152<t>
1153   Recipients MUST parse an HTTP message as a sequence of octets in an
1154   encoding that is a superset of US-ASCII <xref target="USASCII"/>.
1155   Parsing an HTTP message as a stream of Unicode characters, without regard
1156   for the specific encoding, creates security vulnerabilities due to the
1157   varying ways that string processing libraries handle invalid multibyte
1158   character sequences that contain the octet LF (%x0A).  String-based
1159   parsers can only be safely used within protocol elements after the element
1160   has been extracted from the message, such as within a header field-value
1161   after message parsing has delineated the individual fields.
1162</t>
1163
1164<section title="Start Line" anchor="start.line">
1165 
1166<t>
1167   An HTTP message can either be a request from client to server or a
1168   response from server to client.  Syntactically, the two types of message
1169   differ only in the start-line, which is either a Request-Line (for requests)
1170   or a Status-Line (for responses), and in the algorithm for determining
1171   the length of the message-body (<xref target="message.body"/>).
1172   In theory, a client could receive requests and a server could receive
1173   responses, distinguishing them by their different start-line formats,
1174   but in practice servers are implemented to only expect a request
1175   (a response is interpreted as an unknown or invalid request method)
1176   and clients are implemented to only expect a response.
1177</t>
1178<figure><iref primary="true" item="Grammar" subitem="start-line"/><artwork type="abnf2616"><![CDATA[
1179  start-line      = Request-Line / Status-Line
1180]]></artwork></figure>
1181<t>
1182</t>
1183<t>
1184   Implementations MUST NOT send whitespace between the start-line and
1185   the first header field. The presence of such whitespace in a request
1186   might be an attempt to trick a server into ignoring that field or
1187   processing the line after it as a new request, either of which might
1188   result in a security vulnerability if other implementations within
1189   the request chain interpret the same message differently.
1190   Likewise, the presence of such whitespace in a response might be
1191   ignored by some clients or cause others to cease parsing.
1192</t>
1193
1194<section title="Request-Line" anchor="request.line">
1195 
1196 
1197<t>
1198   The Request-Line begins with a method token, followed by a single
1199   space (SP), the request-target, another single space (SP), the
1200   protocol version, and ending with CRLF.
1201</t>
1202<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1203  Request-Line   = Method SP request-target SP HTTP-Version CRLF
1204]]></artwork></figure>
1205
1206<section title="Method" anchor="method">
1207 
1208<t>
1209   The Method token indicates the request method to be performed on the
1210   target resource. The request method is case-sensitive.
1211</t>
1212<figure><iref primary="true" item="Grammar" subitem="Method"/><artwork type="abnf2616"><![CDATA[
1213  Method         = token
1214]]></artwork></figure>
1215<t>
1216   See Section 2 of <xref target="Part2"/> for further information, such as the list of methods defined
1217   by this specification, the IANA registry, and considerations for new methods.
1218</t>
1219</section>
1220
1221<section title="request-target" anchor="request-target">
1222 
1223<t>
1224   The request-target identifies the target resource upon which to apply
1225   the request.  The four options for request-target are described in
1226   <xref target="request-target-types"/>.
1227</t>
1228<figure><iref primary="true" item="Grammar" subitem="request-target"/><artwork type="abnf2616"><![CDATA[
1229  request-target = "*"
1230                 / absolute-URI
1231                 / ( path-absolute [ "?" query ] )
1232                 / authority
1233]]></artwork></figure>
1234<t>
1235   HTTP does not place a pre-defined limit on the length of a request-target.
1236   A server MUST be prepared to receive URIs of unbounded length and
1237   respond with the 414 (URI Too Long) status code if the received
1238   request-target would be longer than the server wishes to handle
1239   (see Section 7.4.15 of <xref target="Part2"/>).
1240</t>
1241<t>
1242   Various ad-hoc limitations on request-target length are found in practice.
1243   It is RECOMMENDED that all HTTP senders and recipients support
1244   request-target lengths of 8000 or more octets.
1245</t>
1246<t><list>
1247  <t>
1248    Note: Fragments (<xref target="RFC3986"/>, Section 3.5)
1249    are not part of the request-target and thus will not be transmitted
1250    in an HTTP request.
1251  </t>
1252</list></t>
1253</section>
1254</section>
1255
1256<section title="Response Status-Line" anchor="status.line">
1257 
1258 
1259<t>
1260   The first line of a Response message is the Status-Line, consisting
1261   of the protocol version, a space (SP), the status code, another space,
1262   a possibly-empty textual phrase describing the status code, and
1263   ending with CRLF.
1264</t>
1265<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1266  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1267]]></artwork></figure>
1268
1269<section title="Status Code" anchor="status.code">
1270 
1271<t>
1272   The Status-Code element is a 3-digit integer result code of the attempt to
1273   understand and satisfy the request. See Section 4 of <xref target="Part2"/> for
1274   further information, such as the list of status codes defined by this
1275   specification, the IANA registry, and considerations for new status codes.
1276</t>
1277<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><artwork type="abnf2616"><![CDATA[
1278  Status-Code    = 3DIGIT
1279]]></artwork></figure>
1280</section>
1281
1282<section title="Reason Phrase" anchor="reason.phrase">
1283 
1284<t>   
1285   The Reason Phrase exists for the sole purpose of providing a textual
1286   description associated with the numeric status code, out of deference to
1287   earlier Internet application protocols that were more frequently used with
1288   interactive text clients. A client SHOULD ignore the content of the Reason
1289   Phrase.
1290</t>
1291<figure><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
1292  Reason-Phrase  = *( HTAB / SP / VCHAR / obs-text )
1293]]></artwork></figure>
1294</section>
1295</section>
1296
1297</section>
1298
1299<section title="Header Fields" anchor="header.fields">
1300 
1301 
1302 
1303 
1304 
1305<t>
1306   Each HTTP header field consists of a case-insensitive field name
1307   followed by a colon (":"), optional whitespace, and the field value.
1308</t>
1309<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[
1310  header-field   = field-name ":" OWS field-value BWS
1311  field-name     = token
1312  field-value    = *( field-content / obs-fold )
1313  field-content  = *( HTAB / SP / VCHAR / obs-text )
1314]]></artwork></figure>
1315<t>
1316   The field-name token labels the corresponding field-value as having the
1317   semantics defined by that header field.  For example, the Date header field
1318   is defined in Section 9.2 of <xref target="Part2"/> as containing the origination
1319   timestamp for the message in which it appears.
1320</t>
1321<t>
1322   HTTP header fields are fully extensible: there is no limit on the
1323   introduction of new field names, each presumably defining new semantics,
1324   or on the number of header fields used in a given message.  Existing
1325   fields are defined in each part of this specification and in many other
1326   specifications outside the standards process.
1327   New header fields can be introduced without changing the protocol version
1328   if their defined semantics allow them to be safely ignored by recipients
1329   that do not recognize them.
1330</t>
1331<t>
1332   New HTTP header fields SHOULD be registered with IANA according
1333   to the procedures in Section 3.1 of <xref target="Part2"/>.
1334   Unrecognized header fields MUST be forwarded by a proxy unless the
1335   field-name is listed in the Connection header field
1336   (<xref target="header.connection"/>) or the proxy is specifically
1337   configured to block or otherwise transform such fields.
1338   Unrecognized header fields SHOULD be ignored by other recipients.
1339</t>
1340<t>
1341   The order in which header fields with differing field names are
1342   received is not significant. However, it is "good practice" to send
1343   header fields that contain control data first, such as Host on
1344   requests and Date on responses, so that implementations can decide
1345   when not to handle a message as early as possible.  A server MUST
1346   wait until the entire header section is received before interpreting
1347   a request message, since later header fields might include conditionals,
1348   authentication credentials, or deliberately misleading duplicate
1349   header fields that would impact request processing.
1350</t>
1351<t>
1352   Multiple header fields with the same field name MUST NOT be
1353   sent in a message unless the entire field value for that
1354   header field is defined as a comma-separated list [i.e., #(values)].
1355   Multiple header fields with the same field name can be combined into
1356   one "field-name: field-value" pair, without changing the semantics of the
1357   message, by appending each subsequent field value to the combined
1358   field value in order, separated by a comma. The order in which
1359   header fields with the same field name are received is therefore
1360   significant to the interpretation of the combined field value;
1361   a proxy MUST NOT change the order of these field values when
1362   forwarding a message.
1363</t>
1364<t><list>
1365  <t>
1366   Note: The "Set-Cookie" header field as implemented in
1367   practice can occur multiple times, but does not use the list syntax, and
1368   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1369   for details.) Also note that the Set-Cookie2 header field specified in
1370   <xref target="RFC2965"/> does not share this problem.
1371  </t>
1372</list></t>
1373
1374<section title="Field Parsing" anchor="field.parsing">
1375<t>
1376   No whitespace is allowed between the header field-name and colon.
1377   In the past, differences in the handling of such whitespace have led to
1378   security vulnerabilities in request routing and response handling.
1379   Any received request message that contains whitespace between a header
1380   field-name and colon MUST be rejected with a response code of 400
1381   (Bad Request).  A proxy MUST remove any such whitespace from a response
1382   message before forwarding the message downstream.
1383</t>
1384<t>
1385   A field value MAY be preceded by optional whitespace (OWS); a single SP is
1386   preferred. The field value does not include any leading or trailing white
1387   space: OWS occurring before the first non-whitespace octet of the
1388   field value or after the last non-whitespace octet of the field value
1389   is ignored and SHOULD be removed before further processing (as this does
1390   not change the meaning of the header field).
1391</t>
1392<t>
1393   Historically, HTTP header field values could be extended over multiple
1394   lines by preceding each extra line with at least one space or horizontal
1395   tab (obs-fold). This specification deprecates such line
1396   folding except within the message/http media type
1397   (<xref target="internet.media.type.message.http"/>).
1398   HTTP senders MUST NOT produce messages that include line folding
1399   (i.e., that contain any field-content that matches the obs-fold rule) unless
1400   the message is intended for packaging within the message/http media type.
1401   HTTP recipients SHOULD accept line folding and replace any embedded
1402   obs-fold whitespace with either a single SP or a matching number of SP
1403   octets (to avoid buffer copying) prior to interpreting the field value or
1404   forwarding the message downstream.
1405</t>
1406<t>
1407   Historically, HTTP has allowed field content with text in the ISO-8859-1
1408   <xref target="ISO-8859-1"/> character encoding and supported other
1409   character sets only through use of <xref target="RFC2047"/> encoding.
1410   In practice, most HTTP header field values use only a subset of the
1411   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1412   header fields SHOULD limit their field values to US-ASCII octets.
1413   Recipients SHOULD treat other (obs-text) octets in field content as
1414   opaque data.
1415</t>
1416</section>
1417
1418<section title="Field Length" anchor="field.length">
1419<t>
1420   HTTP does not place a pre-defined limit on the length of header fields,
1421   either in isolation or as a set. A server MUST be prepared to receive
1422   request header fields of unbounded length and respond with a 4xx status
1423   code if the received header field(s) would be longer than the server wishes
1424   to handle.
1425</t>
1426<t>
1427   A client that receives response headers that are longer than it wishes to
1428   handle can only treat it as a server error.
1429</t>
1430<t>
1431   Various ad-hoc limitations on header length are found in practice. It is
1432   RECOMMENDED that all HTTP senders and recipients support messages whose
1433   combined header fields have 4000 or more octets.
1434</t>
1435</section>
1436
1437<section title="Common Field ABNF Rules" anchor="field.rules">
1438<t anchor="rule.token.separators">
1439 
1440 
1441 
1442 
1443   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1444   separated by whitespace or special characters. These special characters
1445   MUST be in a quoted string to be used within a parameter value (as defined
1446   in <xref target="transfer.codings"/>).
1447</t>
1448<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[
1449  word           = token / quoted-string
1450
1451  token          = 1*tchar
1452
1453  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
1454                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1455                 / DIGIT / ALPHA
1456                 ; any VCHAR, except special
1457
1458  special        = "(" / ")" / "<" / ">" / "@" / ","
1459                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1460                 / "]" / "?" / "=" / "{" / "}"
1461]]></artwork></figure>
1462<t anchor="rule.quoted-string">
1463 
1464 
1465 
1466   A string of text is parsed as a single word if it is quoted using
1467   double-quote marks.
1468</t>
1469<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[
1470  quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
1471  qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
1472  obs-text       = %x80-FF
1473]]></artwork></figure>
1474<t anchor="rule.quoted-pair">
1475 
1476   The backslash octet ("\") can be used as a single-octet
1477   quoting mechanism within quoted-string constructs:
1478</t>
1479<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
1480  quoted-pair    = "\" ( HTAB / SP / VCHAR / obs-text )
1481]]></artwork></figure>
1482<t>
1483   Recipients that process the value of the quoted-string MUST handle a
1484   quoted-pair as if it were replaced by the octet following the backslash.
1485</t>
1486<t>
1487   Senders SHOULD NOT escape octets in quoted-strings that do not require
1488   escaping (i.e., other than DQUOTE and the backslash octet).
1489</t>
1490<t anchor="rule.comment">
1491 
1492 
1493   Comments can be included in some HTTP header fields by surrounding
1494   the comment text with parentheses. Comments are only allowed in
1495   fields containing "comment" as part of their field value definition.
1496</t>
1497<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
1498  comment        = "(" *( ctext / quoted-cpair / comment ) ")"
1499  ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
1500]]></artwork></figure>
1501<t anchor="rule.quoted-cpair">
1502 
1503   The backslash octet ("\") can be used as a single-octet
1504   quoting mechanism within comment constructs:
1505</t>
1506<figure><iref primary="true" item="Grammar" subitem="quoted-cpair"/><artwork type="abnf2616"><![CDATA[
1507  quoted-cpair    = "\" ( HTAB / SP / VCHAR / obs-text )
1508]]></artwork></figure>
1509<t>
1510   Senders SHOULD NOT escape octets in comments that do not require escaping
1511   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1512</t>
1513</section>
1514</section>
1515
1516<section title="Message Body" anchor="message.body">
1517 
1518<t>
1519   The message-body (if any) of an HTTP message is used to carry the
1520   payload body associated with the request or response.
1521</t>
1522<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1523  message-body = *OCTET
1524]]></artwork></figure>
1525<t>
1526   The message-body differs from the payload body only when a transfer-coding
1527   has been applied, as indicated by the Transfer-Encoding header field
1528   (<xref target="header.transfer-encoding"/>).  If more than one
1529   Transfer-Encoding header field is present in a message, the multiple
1530   field-values MUST be combined into one field-value, according to the
1531   algorithm defined in <xref target="header.fields"/>, before determining
1532   the message-body length.
1533</t>
1534<t>
1535   When one or more transfer-codings are applied to a payload in order to
1536   form the message-body, the Transfer-Encoding header field MUST contain
1537   the list of transfer-codings applied. Transfer-Encoding is a property of
1538   the message, not of the payload, and thus MAY be added or removed by
1539   any implementation along the request/response chain under the constraints
1540   found in <xref target="transfer.codings"/>.
1541</t>
1542<t>
1543   If a message is received that has multiple Content-Length header fields
1544   (<xref target="header.content-length"/>) with field-values consisting
1545   of the same decimal value, or a single Content-Length header field with
1546   a field value containing a list of identical decimal values (e.g.,
1547   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1548   header fields have been generated or combined by an upstream message
1549   processor, then the recipient MUST either reject the message as invalid
1550   or replace the duplicated field-values with a single valid Content-Length
1551   field containing that decimal value prior to determining the message-body
1552   length.
1553</t>
1554<t>
1555   The rules for when a message-body is allowed in a message differ for
1556   requests and responses.
1557</t>
1558<t>
1559   The presence of a message-body in a request is signaled by the
1560   inclusion of a Content-Length or Transfer-Encoding header field in
1561   the request's header fields, even if the request method does not
1562   define any use for a message-body.  This allows the request
1563   message framing algorithm to be independent of method semantics.
1564</t>
1565<t>
1566   For response messages, whether or not a message-body is included with
1567   a message is dependent on both the request method and the response
1568   status code (<xref target="status.code"/>).
1569   Responses to the HEAD request method never include a message-body
1570   because the associated response header fields (e.g., Transfer-Encoding,
1571   Content-Length, etc.) only indicate what their values would have been
1572   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1573   and 304 (Not Modified) responses MUST NOT include a message-body.
1574   All other responses do include a message-body, although the body
1575   MAY be of zero length.
1576</t>
1577<t>
1578   The length of the message-body is determined by one of the following
1579   (in order of precedence):
1580</t>
1581<t>
1582  <list style="numbers">
1583    <t>
1584     Any response to a HEAD request and any response with a status
1585     code of 100-199, 204, or 304 is always terminated by the first
1586     empty line after the header fields, regardless of the header
1587     fields present in the message, and thus cannot contain a message-body.
1588    </t>
1589    <t>
1590     If a Transfer-Encoding header field is present
1591     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1592     is the final encoding, the message-body length is determined by reading
1593     and decoding the chunked data until the transfer-coding indicates the
1594     data is complete.
1595    <vspace blankLines="1"/>
1596     If a Transfer-Encoding header field is present in a response and the
1597     "chunked" transfer-coding is not the final encoding, the message-body
1598     length is determined by reading the connection until it is closed by
1599     the server.
1600     If a Transfer-Encoding header field is present in a request and the
1601     "chunked" transfer-coding is not the final encoding, the message-body
1602     length cannot be determined reliably; the server MUST respond with
1603     the 400 (Bad Request) status code and then close the connection.
1604    <vspace blankLines="1"/>
1605     If a message is received with both a Transfer-Encoding header field
1606     and a Content-Length header field, the Transfer-Encoding overrides
1607     the Content-Length.
1608     Such a message might indicate an attempt to perform request or response
1609     smuggling (bypass of security-related checks on message routing or content)
1610     and thus ought to be handled as an error.  The provided Content-Length MUST
1611     be removed, prior to forwarding the message downstream, or replaced with
1612     the real message-body length after the transfer-coding is decoded.
1613    </t>
1614    <t>
1615     If a message is received without Transfer-Encoding and with either
1616     multiple Content-Length header fields having differing field-values or
1617     a single Content-Length header field having an invalid value, then the
1618     message framing is invalid and MUST be treated as an error to
1619     prevent request or response smuggling.
1620     If this is a request message, the server MUST respond with
1621     a 400 (Bad Request) status code and then close the connection.
1622     If this is a response message received by a proxy, the proxy
1623     MUST discard the received response, send a 502 (Bad Gateway)
1624     status code as its downstream response, and then close the connection.
1625     If this is a response message received by a user-agent, it MUST be
1626     treated as an error by discarding the message and closing the connection.
1627    </t>
1628    <t>
1629     If a valid Content-Length header field
1630     is present without Transfer-Encoding, its decimal value defines the
1631     message-body length in octets.  If the actual number of octets sent in
1632     the message is less than the indicated Content-Length, the recipient
1633     MUST consider the message to be incomplete and treat the connection
1634     as no longer usable.
1635     If the actual number of octets sent in the message is more than the indicated
1636     Content-Length, the recipient MUST only process the message-body up to the
1637     field value's number of octets; the remainder of the message MUST either
1638     be discarded or treated as the next message in a pipeline.  For the sake of
1639     robustness, a user-agent MAY attempt to detect and correct such an error
1640     in message framing if it is parsing the response to the last request on
1641     a connection and the connection has been closed by the server.
1642    </t>
1643    <t>
1644     If this is a request message and none of the above are true, then the
1645     message-body length is zero (no message-body is present).
1646    </t>
1647    <t>
1648     Otherwise, this is a response message without a declared message-body
1649     length, so the message-body length is determined by the number of octets
1650     received prior to the server closing the connection.
1651    </t>
1652  </list>
1653</t>
1654<t>
1655   Since there is no way to distinguish a successfully completed,
1656   close-delimited message from a partially-received message interrupted
1657   by network failure, implementations SHOULD use encoding or
1658   length-delimited messages whenever possible.  The close-delimiting
1659   feature exists primarily for backwards compatibility with HTTP/1.0.
1660</t>
1661<t>
1662   A server MAY reject a request that contains a message-body but
1663   not a Content-Length by responding with 411 (Length Required).
1664</t>
1665<t>
1666   Unless a transfer-coding other than "chunked" has been applied,
1667   a client that sends a request containing a message-body SHOULD
1668   use a valid Content-Length header field if the message-body length
1669   is known in advance, rather than the "chunked" encoding, since some
1670   existing services respond to "chunked" with a 411 (Length Required)
1671   status code even though they understand the chunked encoding.  This
1672   is typically because such services are implemented via a gateway that
1673   requires a content-length in advance of being called and the server
1674   is unable or unwilling to buffer the entire request before processing.
1675</t>
1676<t>
1677   A client that sends a request containing a message-body MUST include a
1678   valid Content-Length header field if it does not know the server will
1679   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1680   of specific user configuration or by remembering the version of a prior
1681   received response.
1682</t>
1683</section>
1684
1685<section anchor="incomplete.messages" title="Handling Incomplete Messages">
1686<t>
1687   Request messages that are prematurely terminated, possibly due to a
1688   cancelled connection or a server-imposed time-out exception, MUST
1689   result in closure of the connection; sending an HTTP/1.1 error response
1690   prior to closing the connection is OPTIONAL.
1691</t>
1692<t>
1693   Response messages that are prematurely terminated, usually by closure
1694   of the connection prior to receiving the expected number of octets or by
1695   failure to decode a transfer-encoded message-body, MUST be recorded
1696   as incomplete.  A response that terminates in the middle of the header
1697   block (before the empty line is received) cannot be assumed to convey the
1698   full semantics of the response and MUST be treated as an error.
1699</t>
1700<t>
1701   A message-body that uses the chunked transfer encoding is
1702   incomplete if the zero-sized chunk that terminates the encoding has not
1703   been received.  A message that uses a valid Content-Length is incomplete
1704   if the size of the message-body received (in octets) is less than the
1705   value given by Content-Length.  A response that has neither chunked
1706   transfer encoding nor Content-Length is terminated by closure of the
1707   connection, and thus is considered complete regardless of the number of
1708   message-body octets received, provided that the header block was received
1709   intact.
1710</t>
1711<t>
1712   A user agent MUST NOT render an incomplete response message-body as if
1713   it were complete (i.e., some indication must be given to the user that an
1714   error occurred).  Cache requirements for incomplete responses are defined
1715   in Section 2.1 of <xref target="Part6"/>.
1716</t>
1717<t>
1718   A server MUST read the entire request message-body or close
1719   the connection after sending its response, since otherwise the
1720   remaining data on a persistent connection would be misinterpreted
1721   as the next request.  Likewise,
1722   a client MUST read the entire response message-body if it intends
1723   to reuse the same connection for a subsequent request.  Pipelining
1724   multiple requests on a connection is described in <xref target="pipelining"/>.
1725</t>
1726</section>
1727
1728<section title="Message Parsing Robustness" anchor="message.robustness">
1729<t>
1730   Older HTTP/1.0 client implementations might send an extra CRLF
1731   after a POST request as a lame workaround for some early server
1732   applications that failed to read message-body content that was
1733   not terminated by a line-ending. An HTTP/1.1 client MUST NOT
1734   preface or follow a request with an extra CRLF.  If terminating
1735   the request message-body with a line-ending is desired, then the
1736   client MUST include the terminating CRLF octets as part of the
1737   message-body length.
1738</t>
1739<t>
1740   In the interest of robustness, servers SHOULD ignore at least one
1741   empty line received where a Request-Line is expected. In other words, if
1742   the server is reading the protocol stream at the beginning of a
1743   message and receives a CRLF first, it SHOULD ignore the CRLF.
1744   Likewise, although the line terminator for the start-line and header
1745   fields is the sequence CRLF, we recommend that recipients recognize a
1746   single LF as a line terminator and ignore any CR.
1747</t>
1748<t>
1749   When a server listening only for HTTP request messages, or processing
1750   what appears from the start-line to be an HTTP request message,
1751   receives a sequence of octets that does not match the HTTP-message
1752   grammar aside from the robustness exceptions listed above, the
1753   server MUST respond with an HTTP/1.1 400 (Bad Request) response. 
1754</t>
1755</section>
1756</section>
1757
1758<section title="Message Routing" anchor="message.routing">
1759<t>
1760   In most cases, the user agent is provided a URI reference
1761   from which it determines an absolute URI for identifying the target
1762   resource.  When a request to the resource is initiated, all or part
1763   of that URI is used to construct the HTTP request-target.
1764</t>
1765
1766<section title="Types of Request Target" anchor="request-target-types">
1767<t>
1768   The four options for request-target are dependent on the nature of the
1769   request.
1770</t>   
1771<t anchor="asterix-form"><iref item="asterisk form (of request-target)"/>
1772   The asterisk "*" form of request-target, which MUST NOT be used
1773   with any request method other than OPTIONS, means that the request
1774   applies to the server as a whole (the listening process) rather than
1775   to a specific named resource at that server.  For example,
1776</t>
1777<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1778  OPTIONS * HTTP/1.1
1779  ]]></artwork></figure>
1780<t anchor="absolute-URI-form"><iref item="absolute-URI form (of request-target)"/>
1781   The "absolute-URI" form is REQUIRED when the request is being made to a
1782   proxy. The proxy is requested to either forward the request or service it
1783   from a valid cache, and then return the response. Note that the proxy MAY
1784   forward the request on to another proxy or directly to the server
1785   specified by the absolute-URI. In order to avoid request loops, a
1786   proxy that forwards requests to other proxies MUST be able to
1787   recognize and exclude all of its own server names, including
1788   any aliases, local variations, and the numeric IP address. An example
1789   Request-Line would be:
1790</t>
1791<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1792  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1793  ]]></artwork></figure>
1794<t>
1795   To allow for transition to absolute-URIs in all requests in future
1796   versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
1797   form in requests, even though HTTP/1.1 clients will only generate
1798   them in requests to proxies.
1799</t>
1800<t>
1801   If a proxy receives a host name that is not a fully qualified domain
1802   name, it MAY add its domain to the host name it received. If a proxy
1803   receives a fully qualified domain name, the proxy MUST NOT change
1804   the host name.
1805</t>
1806<t anchor="authority-form"><iref item="authority form (of request-target)"/>
1807   The "authority form" is only used by the CONNECT request method (Section 6.9 of <xref target="Part2"/>).
1808</t>
1809<t anchor="origin-form"><iref item="origin form (of request-target)"/>
1810   The most common form of request-target is that used when making
1811   a request to an origin server ("origin form").
1812   In this case, the absolute path and query components of the URI
1813   MUST be transmitted as the request-target, and the authority component
1814   MUST be transmitted in a Host header field. For example, a client wishing
1815   to retrieve a representation of the resource, as identified above,
1816   directly from the origin server would open (or reuse) a TCP connection
1817   to port 80 of the host "www.example.org" and send the lines:
1818</t>
1819<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1820  GET /pub/WWW/TheProject.html HTTP/1.1
1821  Host: www.example.org
1822  ]]></artwork></figure>
1823<t>
1824   followed by the remainder of the Request. Note that the origin form
1825   of request-target always starts with an absolute path; if the target
1826   resource's URI path is empty, then an absolute path of "/" MUST be
1827   provided in the request-target.
1828</t>
1829<t>
1830   If a proxy receives an OPTIONS request with an absolute-URI form of
1831   request-target in which the URI has an empty path and no query component,
1832   then the last proxy on the request chain MUST use a request-target
1833   of "*" when it forwards the request to the indicated origin server.
1834</t>
1835<figure><preamble>   
1836   For example, the request
1837</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1838  OPTIONS http://www.example.org:8001 HTTP/1.1
1839  ]]></artwork></figure>
1840<figure><preamble>   
1841  would be forwarded by the final proxy as
1842</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1843  OPTIONS * HTTP/1.1
1844  Host: www.example.org:8001
1845  ]]></artwork>
1846<postamble>
1847   after connecting to port 8001 of host "www.example.org".
1848</postamble>
1849</figure>
1850<t>
1851   The request-target is transmitted in the format specified in
1852   <xref target="http.uri"/>. If the request-target is percent-encoded
1853   (<xref target="RFC3986"/>, Section 2.1), the origin server
1854   MUST decode the request-target in order to
1855   properly interpret the request. Servers SHOULD respond to invalid
1856   request-targets with an appropriate status code.
1857</t>
1858<t>
1859   A non-transforming proxy MUST NOT rewrite the "path-absolute" and "query"
1860   parts of the received request-target when forwarding it to the next inbound
1861   server, except as noted above to replace a null path-absolute with "/" or
1862   "*".
1863</t>
1864<t><list>
1865  <t>
1866    Note: The "no rewrite" rule prevents the proxy from changing the
1867    meaning of the request when the origin server is improperly using
1868    a non-reserved URI character for a reserved purpose.  Implementors
1869    need to be aware that some pre-HTTP/1.1 proxies have been known to
1870    rewrite the request-target.
1871  </t>
1872</list></t>
1873</section>
1874
1875<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1876<t>
1877   The exact resource identified by an Internet request is determined by
1878   examining both the request-target and the Host header field.
1879</t>
1880<t>
1881   An origin server that does not allow resources to differ by the
1882   requested host MAY ignore the Host header field value when
1883   determining the resource identified by an HTTP/1.1 request. (But see
1884   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1885   for other requirements on Host support in HTTP/1.1.)
1886</t>
1887<t>
1888   An origin server that does differentiate resources based on the host
1889   requested (sometimes referred to as virtual hosts or vanity host
1890   names) MUST use the following rules for determining the requested
1891   resource on an HTTP/1.1 request:
1892  <list style="numbers">
1893    <t>If request-target is an absolute-URI, the host is part of the
1894     request-target. Any Host header field value in the request MUST be
1895     ignored.</t>
1896    <t>If the request-target is not an absolute-URI, and the request includes
1897     a Host header field, the host is determined by the Host header
1898     field value.</t>
1899    <t>If the host as determined by rule 1 or 2 is not a valid host on
1900     the server, the response MUST be a 400 (Bad Request) error message.</t>
1901  </list>
1902</t>
1903<t>
1904   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1905   attempt to use heuristics (e.g., examination of the URI path for
1906   something unique to a particular host) in order to determine what
1907   exact resource is being requested.
1908</t>
1909</section>
1910
1911<section title="Effective Request URI" anchor="effective.request.uri">
1912  <iref primary="true" item="effective request URI"/>
1913  <iref primary="true" item="target resource"/>
1914<t>
1915   HTTP requests often do not carry the absolute URI (<xref target="RFC3986"/>, Section 4.3)
1916   for the target resource; instead, the URI needs to be inferred from the
1917   request-target, Host header field, and connection context. The result of
1918   this process is called the "effective request URI".  The "target resource"
1919   is the resource identified by the effective request URI.
1920</t>
1921<t>
1922   If the request-target is an absolute-URI, then the effective request URI is
1923   the request-target.
1924</t>
1925<t>
1926   If the request-target uses the origin form or the asterisk form,
1927   and the Host header field is present, then the effective request URI is
1928   constructed by concatenating
1929</t>
1930<t>
1931  <list style="symbols">
1932    <t>
1933      the scheme name: "http" if the request was received over an insecure
1934      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1935      connection,
1936    </t>
1937    <t>
1938      the octet sequence "://",
1939    </t>
1940    <t>
1941      the authority component, as specified in the Host header field
1942      (<xref target="header.host"/>), and
1943    </t>
1944    <t>
1945      the request-target obtained from the Request-Line, unless the
1946      request-target is just the asterisk "*".
1947    </t>
1948  </list>
1949</t>
1950<t>
1951   If the request-target uses the origin form or the asterisk form,
1952   and the Host header field is not present, then the effective request URI is
1953   undefined.
1954</t>
1955<t>
1956   Otherwise, when request-target uses the authority form, the effective
1957   request URI is undefined.
1958</t>
1959<figure>
1960<preamble>
1961   Example 1: the effective request URI for the message
1962</preamble> 
1963<artwork type="example"><![CDATA[
1964  GET /pub/WWW/TheProject.html HTTP/1.1
1965  Host: www.example.org:8080
1966  ]]></artwork>
1967<postamble>
1968  (received over an insecure TCP connection) is "http", plus "://", plus the
1969  authority component "www.example.org:8080", plus the request-target
1970  "/pub/WWW/TheProject.html", thus
1971  "http://www.example.org:8080/pub/WWW/TheProject.html".
1972</postamble>
1973</figure>
1974<figure>
1975<preamble>
1976   Example 2: the effective request URI for the message
1977</preamble> 
1978<artwork type="example"><![CDATA[
1979  OPTIONS * HTTP/1.1
1980  Host: www.example.org
1981  ]]></artwork>
1982<postamble>
1983  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1984  authority component "www.example.org", thus "https://www.example.org".
1985</postamble>
1986</figure>
1987<t>
1988   Effective request URIs are compared using the rules described in
1989   <xref target="uri.comparison"/>, except that empty path components MUST NOT
1990   be treated as equivalent to an absolute path of "/".
1991</t> 
1992</section>
1993</section>
1994
1995
1996<section title="Protocol Parameters" anchor="protocol.parameters">
1997
1998<section title="Transfer Codings" anchor="transfer.codings">
1999 
2000 
2001<t>
2002   Transfer-coding values are used to indicate an encoding
2003   transformation that has been, can be, or might need to be applied to a
2004   payload body in order to ensure "safe transport" through the network.
2005   This differs from a content coding in that the transfer-coding is a
2006   property of the message rather than a property of the representation
2007   that is being transferred.
2008</t>
2009<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
2010  transfer-coding         = "chunked" ; Section 5.1.1
2011                          / "compress" ; Section 5.1.2.1
2012                          / "deflate" ; Section 5.1.2.2
2013                          / "gzip" ; Section 5.1.2.3
2014                          / transfer-extension
2015  transfer-extension      = token *( OWS ";" OWS transfer-parameter )
2016]]></artwork></figure>
2017<t anchor="rule.parameter">
2018 
2019 
2020 
2021   Parameters are in the form of attribute/value pairs.
2022</t>
2023<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[
2024  transfer-parameter      = attribute BWS "=" BWS value
2025  attribute               = token
2026  value                   = word
2027]]></artwork></figure>
2028<t>
2029   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2030   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2031   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2032</t>
2033<t>
2034   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2035   MIME, which were designed to enable safe transport of binary data over a
2036   7-bit transport service (<xref target="RFC2045"/>, Section 6).
2037   However, safe transport
2038   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2039   the only unsafe characteristic of message-bodies is the difficulty in
2040   determining the exact message body length (<xref target="message.body"/>),
2041   or the desire to encrypt data over a shared transport.
2042</t>
2043<t>
2044   A server that receives a request message with a transfer-coding it does
2045   not understand SHOULD respond with 501 (Not Implemented) and then
2046   close the connection. A server MUST NOT send transfer-codings to an HTTP/1.0
2047   client.
2048</t>
2049
2050<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2051  <iref item="chunked (Coding Format)"/>
2052  <iref item="Coding Format" subitem="chunked"/>
2053 
2054 
2055 
2056 
2057 
2058 
2059 
2060 
2061 
2062 
2063 
2064<t>
2065   The chunked encoding modifies the body of a message in order to
2066   transfer it as a series of chunks, each with its own size indicator,
2067   followed by an OPTIONAL trailer containing header fields. This
2068   allows dynamically produced content to be transferred along with the
2069   information necessary for the recipient to verify that it has
2070   received the full message.
2071</t>
2072<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[
2073  Chunked-Body   = *chunk
2074                   last-chunk
2075                   trailer-part
2076                   CRLF
2077 
2078  chunk          = chunk-size [ chunk-ext ] CRLF
2079                   chunk-data CRLF
2080  chunk-size     = 1*HEXDIG
2081  last-chunk     = 1*("0") [ chunk-ext ] CRLF
2082 
2083  chunk-ext      = *( ";" chunk-ext-name
2084                      [ "=" chunk-ext-val ] )
2085  chunk-ext-name = token
2086  chunk-ext-val  = token / quoted-str-nf
2087  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
2088  trailer-part   = *( header-field CRLF )
2089 
2090  quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
2091                 ; like quoted-string, but disallowing line folding
2092  qdtext-nf      = HTAB / SP / %x21 / %x23-5B / %x5D-7E / obs-text
2093]]></artwork></figure>
2094<t>
2095   The chunk-size field is a string of hex digits indicating the size of
2096   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2097   zero, followed by the trailer, which is terminated by an empty line.
2098</t>
2099<t>
2100   The trailer allows the sender to include additional HTTP header
2101   fields at the end of the message. The Trailer header field can be
2102   used to indicate which header fields are included in a trailer (see
2103   <xref target="header.trailer"/>).
2104</t>
2105<t>
2106   A server using chunked transfer-coding in a response MUST NOT use the
2107   trailer for any header fields unless at least one of the following is
2108   true:
2109  <list style="numbers">
2110    <t>the request included a TE header field that indicates "trailers" is
2111     acceptable in the transfer-coding of the  response, as described in
2112     <xref target="header.te"/>; or,</t>
2113     
2114    <t>the trailer fields consist entirely of optional metadata, and the
2115    recipient could use the message (in a manner acceptable to the server where
2116    the field originated) without receiving it. In other words, the server that
2117    generated the header (often but not always the origin server) is willing to
2118    accept the possibility that the trailer fields might be silently discarded
2119    along the path to the client.</t>
2120  </list>
2121</t>
2122<t>
2123   This requirement prevents an interoperability failure when the
2124   message is being received by an HTTP/1.1 (or later) proxy and
2125   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2126   compliance with the protocol would have necessitated a possibly
2127   infinite buffer on the proxy.
2128</t>
2129<t>
2130   A process for decoding the "chunked" transfer-coding
2131   can be represented in pseudo-code as:
2132</t>
2133<figure><artwork type="code"><![CDATA[
2134  length := 0
2135  read chunk-size, chunk-ext (if any) and CRLF
2136  while (chunk-size > 0) {
2137     read chunk-data and CRLF
2138     append chunk-data to decoded-body
2139     length := length + chunk-size
2140     read chunk-size and CRLF
2141  }
2142  read header-field
2143  while (header-field not empty) {
2144     append header-field to existing header fields
2145     read header-field
2146  }
2147  Content-Length := length
2148  Remove "chunked" from Transfer-Encoding
2149]]></artwork></figure>
2150<t>
2151   All HTTP/1.1 applications MUST be able to receive and decode the
2152   "chunked" transfer-coding and MUST ignore chunk-ext extensions
2153   they do not understand.
2154</t>
2155<t>
2156   Since "chunked" is the only transfer-coding required to be understood
2157   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2158   on a persistent connection.  Whenever a transfer-coding is applied to
2159   a payload body in a request, the final transfer-coding applied MUST
2160   be "chunked".  If a transfer-coding is applied to a response payload
2161   body, then either the final transfer-coding applied MUST be "chunked"
2162   or the message MUST be terminated by closing the connection. When the
2163   "chunked" transfer-coding is used, it MUST be the last transfer-coding
2164   applied to form the message-body. The "chunked" transfer-coding MUST NOT
2165   be applied more than once in a message-body.
2166</t>
2167</section>
2168
2169<section title="Compression Codings" anchor="compression.codings">
2170<t>
2171   The codings defined below can be used to compress the payload of a
2172   message.
2173</t>
2174<t><list><t>
2175   Note: Use of program names for the identification of encoding formats
2176   is not desirable and is discouraged for future encodings. Their
2177   use here is representative of historical practice, not good
2178   design.
2179</t></list></t>
2180<t><list><t>
2181   Note: For compatibility with previous implementations of HTTP,
2182   applications SHOULD consider "x-gzip" and "x-compress" to be
2183   equivalent to "gzip" and "compress" respectively.
2184</t></list></t>
2185
2186<section title="Compress Coding" anchor="compress.coding">
2187<iref item="compress (Coding Format)"/>
2188<iref item="Coding Format" subitem="compress"/>
2189<t>
2190   The "compress" format is produced by the common UNIX file compression
2191   program "compress". This format is an adaptive Lempel-Ziv-Welch
2192   coding (LZW).
2193</t>
2194</section>
2195
2196<section title="Deflate Coding" anchor="deflate.coding">
2197<iref item="deflate (Coding Format)"/>
2198<iref item="Coding Format" subitem="deflate"/>
2199<t>
2200   The "deflate" format is defined as the "deflate" compression mechanism
2201   (described in <xref target="RFC1951"/>) used inside the "zlib"
2202   data format (<xref target="RFC1950"/>).
2203</t>
2204<t><list>
2205  <t>
2206    Note: Some incorrect implementations send the "deflate"
2207    compressed data without the zlib wrapper.
2208   </t>
2209</list></t>
2210</section>
2211
2212<section title="Gzip Coding" anchor="gzip.coding">
2213<iref item="gzip (Coding Format)"/>
2214<iref item="Coding Format" subitem="gzip"/>
2215<t>
2216   The "gzip" format is produced by the file compression program
2217   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2218   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2219</t>
2220</section>
2221
2222</section>
2223
2224<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2225<t>
2226   The HTTP Transfer Coding Registry defines the name space for the transfer
2227   coding names.
2228</t>
2229<t>
2230   Registrations MUST include the following fields:
2231   <list style="symbols">
2232     <t>Name</t>
2233     <t>Description</t>
2234     <t>Pointer to specification text</t>
2235   </list>
2236</t>
2237<t>
2238   Names of transfer codings MUST NOT overlap with names of content codings
2239   (Section 2.2 of <xref target="Part3"/>), unless the encoding transformation is identical (as it
2240   is the case for the compression codings defined in
2241   <xref target="compression.codings"/>).
2242</t>
2243<t>
2244   Values to be added to this name space require a specification
2245   (see "Specification Required" in Section 4.1 of <xref target="RFC5226"/>), and MUST
2246   conform to the purpose of transfer coding defined in this section.
2247</t>
2248<t>
2249   The registry itself is maintained at
2250   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2251</t>
2252</section>
2253</section>
2254
2255<section title="Product Tokens" anchor="product.tokens">
2256 
2257 
2258<t>
2259   Product tokens are used to allow communicating applications to
2260   identify themselves by software name and version. Most fields using
2261   product tokens also allow sub-products which form a significant part
2262   of the application to be listed, separated by whitespace. By
2263   convention, the products are listed in order of their significance
2264   for identifying the application.
2265</t>
2266<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
2267  product         = token ["/" product-version]
2268  product-version = token
2269]]></artwork></figure>
2270<t>
2271   Examples:
2272</t>
2273<figure><artwork type="example"><![CDATA[
2274  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2275  Server: Apache/0.8.4
2276]]></artwork></figure>
2277<t>
2278   Product tokens SHOULD be short and to the point. They MUST NOT be
2279   used for advertising or other non-essential information. Although any
2280   token octet MAY appear in a product-version, this token SHOULD
2281   only be used for a version identifier (i.e., successive versions of
2282   the same product SHOULD only differ in the product-version portion of
2283   the product value).
2284</t>
2285</section>
2286
2287<section title="Quality Values" anchor="quality.values">
2288 
2289<t>
2290   Both transfer codings (TE request header field, <xref target="header.te"/>)
2291   and content negotiation (Section 5 of <xref target="Part3"/>) use short "floating point"
2292   numbers to indicate the relative importance ("weight") of various
2293   negotiable parameters.  A weight is normalized to a real number in
2294   the range 0 through 1, where 0 is the minimum and 1 the maximum
2295   value. If a parameter has a quality value of 0, then content with
2296   this parameter is "not acceptable" for the client. HTTP/1.1
2297   applications MUST NOT generate more than three digits after the
2298   decimal point. User configuration of these values SHOULD also be
2299   limited in this fashion.
2300</t>
2301<figure><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
2302  qvalue         = ( "0" [ "." 0*3DIGIT ] )
2303                 / ( "1" [ "." 0*3("0") ] )
2304]]></artwork></figure>
2305<t><list>
2306  <t>
2307     Note: "Quality values" is a misnomer, since these values merely represent
2308     relative degradation in desired quality.
2309  </t>
2310</list></t>
2311</section>
2312
2313</section>
2314
2315<section title="Connections" anchor="connections">
2316
2317<section title="Persistent Connections" anchor="persistent.connections">
2318
2319<section title="Purpose" anchor="persistent.purpose">
2320<t>
2321   Prior to persistent connections, a separate TCP connection was
2322   established for each request, increasing the load on HTTP servers
2323   and causing congestion on the Internet. The use of inline images and
2324   other associated data often requires a client to make multiple
2325   requests of the same server in a short amount of time. Analysis of
2326   these performance problems and results from a prototype
2327   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2328   measurements of actual HTTP/1.1 implementations show good
2329   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2330   T/TCP <xref target="Tou1998"/>.
2331</t>
2332<t>
2333   Persistent HTTP connections have a number of advantages:
2334  <list style="symbols">
2335      <t>
2336        By opening and closing fewer TCP connections, CPU time is saved
2337        in routers and hosts (clients, servers, proxies, gateways,
2338        tunnels, or caches), and memory used for TCP protocol control
2339        blocks can be saved in hosts.
2340      </t>
2341      <t>
2342        HTTP requests and responses can be pipelined on a connection.
2343        Pipelining allows a client to make multiple requests without
2344        waiting for each response, allowing a single TCP connection to
2345        be used much more efficiently, with much lower elapsed time.
2346      </t>
2347      <t>
2348        Network congestion is reduced by reducing the number of packets
2349        caused by TCP opens, and by allowing TCP sufficient time to
2350        determine the congestion state of the network.
2351      </t>
2352      <t>
2353        Latency on subsequent requests is reduced since there is no time
2354        spent in TCP's connection opening handshake.
2355      </t>
2356      <t>
2357        HTTP can evolve more gracefully, since errors can be reported
2358        without the penalty of closing the TCP connection. Clients using
2359        future versions of HTTP might optimistically try a new feature,
2360        but if communicating with an older server, retry with old
2361        semantics after an error is reported.
2362      </t>
2363    </list>
2364</t>
2365<t>
2366   HTTP implementations SHOULD implement persistent connections.
2367</t>
2368</section>
2369
2370<section title="Overall Operation" anchor="persistent.overall">
2371<t>
2372   A significant difference between HTTP/1.1 and earlier versions of
2373   HTTP is that persistent connections are the default behavior of any
2374   HTTP connection. That is, unless otherwise indicated, the client
2375   SHOULD assume that the server will maintain a persistent connection,
2376   even after error responses from the server.
2377</t>
2378<t>
2379   Persistent connections provide a mechanism by which a client and a
2380   server can signal the close of a TCP connection. This signaling takes
2381   place using the Connection header field (<xref target="header.connection"/>). Once a close
2382   has been signaled, the client MUST NOT send any more requests on that
2383   connection.
2384</t>
2385
2386<section title="Negotiation" anchor="persistent.negotiation">
2387<t>
2388   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
2389   maintain a persistent connection unless a Connection header field including
2390   the connection-token "close" was sent in the request. If the server
2391   chooses to close the connection immediately after sending the
2392   response, it SHOULD send a Connection header field including the
2393   connection-token "close".
2394</t>
2395<t>
2396   An HTTP/1.1 client MAY expect a connection to remain open, but would
2397   decide to keep it open based on whether the response from a server
2398   contains a Connection header field with the connection-token close. In case
2399   the client does not want to maintain a connection for more than that
2400   request, it SHOULD send a Connection header field including the
2401   connection-token close.
2402</t>
2403<t>
2404   If either the client or the server sends the close token in the
2405   Connection header field, that request becomes the last one for the
2406   connection.
2407</t>
2408<t>
2409   Clients and servers SHOULD NOT  assume that a persistent connection is
2410   maintained for HTTP versions less than 1.1 unless it is explicitly
2411   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2412   compatibility with HTTP/1.0 clients.
2413</t>
2414<t>
2415   In order to remain persistent, all messages on the connection MUST
2416   have a self-defined message length (i.e., one not defined by closure
2417   of the connection), as described in <xref target="message.body"/>.
2418</t>
2419</section>
2420
2421<section title="Pipelining" anchor="pipelining">
2422<t>
2423   A client that supports persistent connections MAY "pipeline" its
2424   requests (i.e., send multiple requests without waiting for each
2425   response). A server MUST send its responses to those requests in the
2426   same order that the requests were received.
2427</t>
2428<t>
2429   Clients which assume persistent connections and pipeline immediately
2430   after connection establishment SHOULD be prepared to retry their
2431   connection if the first pipelined attempt fails. If a client does
2432   such a retry, it MUST NOT pipeline before it knows the connection is
2433   persistent. Clients MUST also be prepared to resend their requests if
2434   the server closes the connection before sending all of the
2435   corresponding responses.
2436</t>
2437<t>
2438   Clients SHOULD NOT pipeline requests using non-idempotent request methods or
2439   non-idempotent sequences of request methods (see Section 6.1.2 of <xref target="Part2"/>). Otherwise, a
2440   premature termination of the transport connection could lead to
2441   indeterminate results. A client wishing to send a non-idempotent
2442   request SHOULD wait to send that request until it has received the
2443   response status line for the previous request.
2444</t>
2445</section>
2446</section>
2447
2448<section title="Proxy Servers" anchor="persistent.proxy">
2449<t>
2450   It is especially important that proxies correctly implement the
2451   properties of the Connection header field as specified in <xref target="header.connection"/>.
2452</t>
2453<t>
2454   The proxy server MUST signal persistent connections separately with
2455   its clients and the origin servers (or other proxy servers) that it
2456   connects to. Each persistent connection applies to only one transport
2457   link.
2458</t>
2459<t>
2460   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
2461   with an HTTP/1.0 client (but see Section 19.7.1 of <xref target="RFC2068"/>
2462   for information and discussion of the problems with the Keep-Alive header field
2463   implemented by many HTTP/1.0 clients).
2464</t>
2465
2466<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2467<!--<t>
2468  <cref anchor="TODO-end-to-end" source="jre">
2469    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2470    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2471  </cref>
2472</t>-->
2473<t>
2474   For the purpose of defining the behavior of caches and non-caching
2475   proxies, we divide HTTP header fields into two categories:
2476  <list style="symbols">
2477      <t>End-to-end header fields, which are  transmitted to the ultimate
2478        recipient of a request or response. End-to-end header fields in
2479        responses MUST be stored as part of a cache entry and MUST be
2480        transmitted in any response formed from a cache entry.</t>
2481
2482      <t>Hop-by-hop header fields, which are meaningful only for a single
2483        transport-level connection, and are not stored by caches or
2484        forwarded by proxies.</t>
2485  </list>
2486</t>
2487<t>
2488   The following HTTP/1.1 header fields are hop-by-hop header fields:
2489  <list style="symbols">
2490      <t>Connection</t>
2491      <t>Keep-Alive</t>
2492      <t>Proxy-Authenticate</t>
2493      <t>Proxy-Authorization</t>
2494      <t>TE</t>
2495      <t>Trailer</t>
2496      <t>Transfer-Encoding</t>
2497      <t>Upgrade</t>
2498  </list>
2499</t>
2500<t>
2501   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2502</t>
2503<t>
2504   Other hop-by-hop header fields MUST be listed in a Connection header field
2505   (<xref target="header.connection"/>).
2506</t>
2507</section>
2508
2509<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2510<!--<t>
2511  <cref anchor="TODO-non-mod-headers" source="jre">
2512    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2513    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2514  </cref>
2515</t>-->
2516<t>
2517   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2518   value of certain end-to-end header fields. A non-transforming proxy SHOULD NOT
2519   modify an end-to-end header field unless the definition of that header field requires
2520   or specifically allows that.
2521</t>
2522<t>
2523   A non-transforming proxy MUST NOT modify any of the following fields in a
2524   request or response, and it MUST NOT add any of these fields if not
2525   already present:
2526  <list style="symbols">
2527    <t>Allow</t>
2528    <t>Content-Location</t>
2529    <t>Content-MD5</t>
2530    <t>ETag</t>
2531    <t>Last-Modified</t>
2532    <t>Server</t>
2533  </list>
2534</t>
2535<t>
2536   A non-transforming proxy MUST NOT modify any of the following fields in a
2537   response:
2538  <list style="symbols">
2539    <t>Expires</t>
2540  </list>
2541</t>
2542<t>
2543   but it MAY add any of these fields if not already present. If an
2544   Expires header field is added, it MUST be given a field-value identical to
2545   that of the Date header field in that response.
2546</t>
2547<t>
2548   A proxy MUST NOT modify or add any of the following fields in a
2549   message that contains the no-transform cache-control directive, or in
2550   any request:
2551  <list style="symbols">
2552    <t>Content-Encoding</t>
2553    <t>Content-Range</t>
2554    <t>Content-Type</t>
2555  </list>
2556</t>
2557<t>
2558   A transforming proxy MAY modify or add these fields to a message
2559   that does not include no-transform, but if it does so, it MUST add a
2560   Warning 214 (Transformation applied) if one does not already appear
2561   in the message (see Section 3.6 of <xref target="Part6"/>).
2562</t>
2563<t><list>
2564  <t>
2565    Warning: Unnecessary modification of end-to-end header fields might
2566    cause authentication failures if stronger authentication
2567    mechanisms are introduced in later versions of HTTP. Such
2568    authentication mechanisms MAY rely on the values of header fields
2569    not listed here.
2570  </t>
2571</list></t>
2572<t>
2573   A non-transforming proxy MUST preserve the message payload (<xref target="Part3"/>),
2574   though it MAY change the message-body through application or removal
2575   of a transfer-coding (<xref target="transfer.codings"/>).
2576</t>
2577</section>
2578
2579</section>
2580
2581<section title="Practical Considerations" anchor="persistent.practical">
2582<t>
2583   Servers will usually have some time-out value beyond which they will
2584   no longer maintain an inactive connection. Proxy servers might make
2585   this a higher value since it is likely that the client will be making
2586   more connections through the same server. The use of persistent
2587   connections places no requirements on the length (or existence) of
2588   this time-out for either the client or the server.
2589</t>
2590<t>
2591   When a client or server wishes to time-out it SHOULD issue a graceful
2592   close on the transport connection. Clients and servers SHOULD both
2593   constantly watch for the other side of the transport close, and
2594   respond to it as appropriate. If a client or server does not detect
2595   the other side's close promptly it could cause unnecessary resource
2596   drain on the network.
2597</t>
2598<t>
2599   A client, server, or proxy MAY close the transport connection at any
2600   time. For example, a client might have started to send a new request
2601   at the same time that the server has decided to close the "idle"
2602   connection. From the server's point of view, the connection is being
2603   closed while it was idle, but from the client's point of view, a
2604   request is in progress.
2605</t>
2606<t>
2607   Clients (including proxies) SHOULD limit the number of simultaneous
2608   connections that they maintain to a given server (including proxies).
2609</t>
2610<t>
2611   Previous revisions of HTTP gave a specific number of connections as a
2612   ceiling, but this was found to be impractical for many applications. As a
2613   result, this specification does not mandate a particular maximum number of
2614   connections, but instead encourages clients to be conservative when opening
2615   multiple connections.
2616</t>
2617<t>
2618   In particular, while using multiple connections avoids the "head-of-line
2619   blocking" problem (whereby a request that takes significant server-side
2620   processing and/or has a large payload can block subsequent requests on the
2621   same connection), each connection used consumes server resources (sometimes
2622   significantly), and furthermore using multiple connections can cause
2623   undesirable side effects in congested networks.
2624</t>
2625<t>
2626   Note that servers might reject traffic that they deem abusive, including an
2627   excessive number of connections from a client.
2628</t>
2629</section>
2630
2631<section title="Retrying Requests" anchor="persistent.retrying.requests">
2632<t>
2633   Senders can close the transport connection at any time. Therefore,
2634   clients, servers, and proxies MUST be able to recover
2635   from asynchronous close events. Client software MAY reopen the
2636   transport connection and retransmit the aborted sequence of requests
2637   without user interaction so long as the request sequence is
2638   idempotent (see Section 6.1.2 of <xref target="Part2"/>). Non-idempotent request methods or sequences
2639   MUST NOT be automatically retried, although user agents MAY offer a
2640   human operator the choice of retrying the request(s). Confirmation by
2641   user-agent software with semantic understanding of the application
2642   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2643   be repeated if the second sequence of requests fails.
2644</t>
2645</section>
2646
2647</section>
2648
2649<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2650
2651<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2652<t>
2653   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2654   flow control mechanisms to resolve temporary overloads, rather than
2655   terminating connections with the expectation that clients will retry.
2656   The latter technique can exacerbate network congestion.
2657</t>
2658</section>
2659
2660<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2661<t>
2662   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2663   the network connection for an error status code while it is transmitting
2664   the request. If the client sees an error status code, it SHOULD
2665   immediately cease transmitting the body. If the body is being sent
2666   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2667   empty trailer MAY be used to prematurely mark the end of the message.
2668   If the body was preceded by a Content-Length header field, the client MUST
2669   close the connection.
2670</t>
2671</section>
2672
2673<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2674<t>
2675   The purpose of the 100 (Continue) status code (see Section 7.1.1 of <xref target="Part2"/>) is to
2676   allow a client that is sending a request message with a request body
2677   to determine if the origin server is willing to accept the request
2678   (based on the request header fields) before the client sends the request
2679   body. In some cases, it might either be inappropriate or highly
2680   inefficient for the client to send the body if the server will reject
2681   the message without looking at the body.
2682</t>
2683<t>
2684   Requirements for HTTP/1.1 clients:
2685  <list style="symbols">
2686    <t>
2687        If a client will wait for a 100 (Continue) response before
2688        sending the request body, it MUST send an Expect header
2689        field (Section 9.3 of <xref target="Part2"/>) with the "100-continue" expectation.
2690    </t>
2691    <t>
2692        A client MUST NOT send an Expect header field (Section 9.3 of <xref target="Part2"/>)
2693        with the "100-continue" expectation if it does not intend
2694        to send a request body.
2695    </t>
2696  </list>
2697</t>
2698<t>
2699   Because of the presence of older implementations, the protocol allows
2700   ambiguous situations in which a client might send "Expect: 100-continue"
2701   without receiving either a 417 (Expectation Failed)
2702   or a 100 (Continue) status code. Therefore, when a client sends this
2703   header field to an origin server (possibly via a proxy) from which it
2704   has never seen a 100 (Continue) status code, the client SHOULD NOT 
2705   wait for an indefinite period before sending the request body.
2706</t>
2707<t>
2708   Requirements for HTTP/1.1 origin servers:
2709  <list style="symbols">
2710    <t> Upon receiving a request which includes an Expect header
2711        field with the "100-continue" expectation, an origin server MUST
2712        either respond with 100 (Continue) status code and continue to read
2713        from the input stream, or respond with a final status code. The
2714        origin server MUST NOT wait for the request body before sending
2715        the 100 (Continue) response. If it responds with a final status
2716        code, it MAY close the transport connection or it MAY continue
2717        to read and discard the rest of the request.  It MUST NOT
2718        perform the request method if it returns a final status code.
2719    </t>
2720    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2721        the request message does not include an Expect header
2722        field with the "100-continue" expectation, and MUST NOT send a
2723        100 (Continue) response if such a request comes from an HTTP/1.0
2724        (or earlier) client. There is an exception to this rule: for
2725        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2726        status code in response to an HTTP/1.1 PUT or POST request that does
2727        not include an Expect header field with the "100-continue"
2728        expectation. This exception, the purpose of which is
2729        to minimize any client processing delays associated with an
2730        undeclared wait for 100 (Continue) status code, applies only to
2731        HTTP/1.1 requests, and not to requests with any other HTTP-version
2732        value.
2733    </t>
2734    <t> An origin server MAY omit a 100 (Continue) response if it has
2735        already received some or all of the request body for the
2736        corresponding request.
2737    </t>
2738    <t> An origin server that sends a 100 (Continue) response MUST
2739    ultimately send a final status code, once the request body is
2740        received and processed, unless it terminates the transport
2741        connection prematurely.
2742    </t>
2743    <t> If an origin server receives a request that does not include an
2744        Expect header field with the "100-continue" expectation,
2745        the request includes a request body, and the server responds
2746        with a final status code before reading the entire request body
2747        from the transport connection, then the server SHOULD NOT  close
2748        the transport connection until it has read the entire request,
2749        or until the client closes the connection. Otherwise, the client
2750        might not reliably receive the response message. However, this
2751        requirement is not be construed as preventing a server from
2752        defending itself against denial-of-service attacks, or from
2753        badly broken client implementations.
2754      </t>
2755    </list>
2756</t>
2757<t>
2758   Requirements for HTTP/1.1 proxies:
2759  <list style="symbols">
2760    <t> If a proxy receives a request that includes an Expect header
2761        field with the "100-continue" expectation, and the proxy
2762        either knows that the next-hop server complies with HTTP/1.1 or
2763        higher, or does not know the HTTP version of the next-hop
2764        server, it MUST forward the request, including the Expect header
2765        field.
2766    </t>
2767    <t> If the proxy knows that the version of the next-hop server is
2768        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2769        respond with a 417 (Expectation Failed) status code.
2770    </t>
2771    <t> Proxies SHOULD maintain a record of the HTTP version
2772        numbers received from recently-referenced next-hop servers.
2773    </t>
2774    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2775        request message was received from an HTTP/1.0 (or earlier)
2776        client and did not include an Expect header field with
2777        the "100-continue" expectation. This requirement overrides the
2778        general rule for forwarding of 1xx responses (see Section 7.1 of <xref target="Part2"/>).
2779    </t>
2780  </list>
2781</t>
2782</section>
2783
2784</section>
2785</section>
2786
2787
2788<section title="Miscellaneous notes that might disappear" anchor="misc">
2789<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2790<t>
2791   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2792</t>
2793</section>
2794
2795<section title="Use of HTTP for proxy communication" anchor="http.proxy">
2796<t>
2797   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
2798</t>
2799</section>
2800
2801<section title="Interception of HTTP for access control" anchor="http.intercept">
2802<t>
2803   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
2804</t>
2805</section>
2806
2807<section title="Use of HTTP by other protocols" anchor="http.others">
2808<t>
2809   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
2810   Extensions of HTTP like WebDAV.</cref>
2811</t>
2812
2813</section>
2814<section title="Use of HTTP by media type specification" anchor="http.media">
2815<t>
2816   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
2817</t>
2818</section>
2819</section>
2820
2821<section title="Header Field Definitions" anchor="header.field.definitions">
2822<t>
2823   This section defines the syntax and semantics of HTTP header fields
2824   related to message origination, framing, and routing.
2825</t>
2826<texttable align="left">
2827  <ttcol>Header Field Name</ttcol>
2828  <ttcol>Defined in...</ttcol>
2829 
2830  <c>Connection</c> <c><xref target="header.connection"/></c>
2831  <c>Content-Length</c> <c><xref target="header.content-length"/></c>
2832  <c>Host</c> <c><xref target="header.host"/></c>
2833  <c>TE</c> <c><xref target="header.te"/></c>
2834  <c>Trailer</c> <c><xref target="header.trailer"/></c>
2835  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
2836  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
2837  <c>Via</c> <c><xref target="header.via"/></c>
2838</texttable>
2839
2840<section title="Connection" anchor="header.connection">
2841  <iref primary="true" item="Connection header field"/>
2842  <iref primary="true" item="Header Fields" subitem="Connection"/>
2843 
2844 
2845<t>
2846   The "Connection" header field allows the sender to specify
2847   options that are desired only for that particular connection.
2848   Such connection options MUST be removed or replaced before the
2849   message can be forwarded downstream by a proxy or gateway.
2850   This mechanism also allows the sender to indicate which HTTP
2851   header fields used in the message are only intended for the
2852   immediate recipient ("hop-by-hop"), as opposed to all recipients
2853   on the chain ("end-to-end"), enabling the message to be
2854   self-descriptive and allowing future connection-specific extensions
2855   to be deployed in HTTP without fear that they will be blindly
2856   forwarded by previously deployed intermediaries.
2857</t>
2858<t>
2859   The Connection header field's value has the following grammar:
2860</t>
2861<figure><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/><artwork type="abnf2616"><![CDATA[
2862  Connection       = 1#connection-token
2863  connection-token = token
2864]]></artwork></figure>
2865<t>
2866   A proxy or gateway MUST parse a received Connection
2867   header field before a message is forwarded and, for each
2868   connection-token in this field, remove any header field(s) from
2869   the message with the same name as the connection-token, and then
2870   remove the Connection header field itself or replace it with the
2871   sender's own connection options for the forwarded message.
2872</t>
2873<t>
2874   A sender MUST NOT include field-names in the Connection header
2875   field-value for fields that are defined as expressing constraints
2876   for all recipients in the request or response chain, such as the
2877   Cache-Control header field (Section 3.2 of <xref target="Part6"/>).
2878</t>
2879<t>
2880   The connection options do not have to correspond to a header field
2881   present in the message, since a connection-specific header field
2882   might not be needed if there are no parameters associated with that
2883   connection option.  Recipients that trigger certain connection
2884   behavior based on the presence of connection options MUST do so
2885   based on the presence of the connection-token rather than only the
2886   presence of the optional header field.  In other words, if the
2887   connection option is received as a header field but not indicated
2888   within the Connection field-value, then the recipient MUST ignore
2889   the connection-specific header field because it has likely been
2890   forwarded by an intermediary that is only partially compliant.
2891</t>
2892<t>
2893   When defining new connection options, specifications ought to
2894   carefully consider existing deployed header fields and ensure
2895   that the new connection-token does not share the same name as
2896   an unrelated header field that might already be deployed.
2897   Defining a new connection-token essentially reserves that potential
2898   field-name for carrying additional information related to the
2899   connection option, since it would be unwise for senders to use
2900   that field-name for anything else.
2901</t>
2902<t>
2903   HTTP/1.1 defines the "close" connection option for the sender to
2904   signal that the connection will be closed after completion of the
2905   response. For example,
2906</t>
2907<figure><artwork type="example"><![CDATA[
2908  Connection: close
2909]]></artwork></figure>
2910<t>
2911   in either the request or the response header fields indicates that
2912   the connection SHOULD NOT  be considered "persistent" (<xref target="persistent.connections"/>)
2913   after the current request/response is complete.
2914</t>
2915<t>
2916   An HTTP/1.1 client that does not support persistent connections MUST
2917   include the "close" connection option in every request message.
2918</t>
2919<t>
2920   An HTTP/1.1 server that does not support persistent connections MUST
2921   include the "close" connection option in every response message that
2922   does not have a 1xx (Informational) status code.
2923</t>
2924</section>
2925
2926<section title="Content-Length" anchor="header.content-length">
2927  <iref primary="true" item="Content-Length header field"/>
2928  <iref primary="true" item="Header Fields" subitem="Content-Length"/>
2929 
2930<t>
2931   The "Content-Length" header field indicates the size of the
2932   message-body, in decimal number of octets, for any message other than
2933   a response to a HEAD request or a response with a status code of 304.
2934   In the case of a response to a HEAD request, Content-Length indicates
2935   the size of the payload body (not including any potential transfer-coding)
2936   that would have been sent had the request been a GET.
2937   In the case of a 304 (Not Modified) response to a GET request,
2938   Content-Length indicates the size of the payload body (not including
2939   any potential transfer-coding) that would have been sent in a 200 (OK)
2940   response.
2941</t>
2942<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><artwork type="abnf2616"><![CDATA[
2943  Content-Length = 1*DIGIT
2944]]></artwork></figure>
2945<t>
2946   An example is
2947</t>
2948<figure><artwork type="example"><![CDATA[
2949  Content-Length: 3495
2950]]></artwork></figure>
2951<t>
2952   Implementations SHOULD use this field to indicate the message-body
2953   length when no transfer-coding is being applied and the
2954   payload's body length can be determined prior to being transferred.
2955   <xref target="message.body"/> describes how recipients determine the length
2956   of a message-body.
2957</t>
2958<t>
2959   Any Content-Length greater than or equal to zero is a valid value.
2960</t>
2961<t>
2962   Note that the use of this field in HTTP is significantly different from
2963   the corresponding definition in MIME, where it is an optional field
2964   used within the "message/external-body" content-type.
2965</t>
2966</section>
2967
2968<section title="Host" anchor="header.host">
2969  <iref primary="true" item="Host header field"/>
2970  <iref primary="true" item="Header Fields" subitem="Host"/>
2971 
2972<t>
2973   The "Host" header field in a request provides the host and port
2974   information from the target resource's URI, enabling the origin
2975   server to distinguish between resources while servicing requests
2976   for multiple host names on a single IP address.  Since the Host
2977   field-value is critical information for handling a request, it
2978   SHOULD be sent as the first header field following the Request-Line.
2979</t>
2980<figure><iref primary="true" item="Grammar" subitem="Host"/><artwork type="abnf2616"><![CDATA[
2981  Host = uri-host [ ":" port ] ; Section 2.7.1
2982]]></artwork></figure>
2983<t>
2984   A client MUST send a Host header field in all HTTP/1.1 request
2985   messages.  If the target resource's URI includes an authority
2986   component, then the Host field-value MUST be identical to that
2987   authority component after excluding any userinfo (<xref target="http.uri"/>).
2988   If the authority component is missing or undefined for the target
2989   resource's URI, then the Host header field MUST be sent with an
2990   empty field-value.
2991</t>
2992<t>
2993   For example, a GET request to the origin server for
2994   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
2995</t>
2996<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
2997  GET /pub/WWW/ HTTP/1.1
2998  Host: www.example.org
2999  ]]></artwork></figure>
3000<t>
3001   The Host header field MUST be sent in an HTTP/1.1 request even
3002   if the request-target is in the form of an absolute-URI, since this
3003   allows the Host information to be forwarded through ancient HTTP/1.0
3004   proxies that might not have implemented Host.
3005</t>
3006<t>
3007   When an HTTP/1.1 proxy receives a request with a request-target in
3008   the form of an absolute-URI, the proxy MUST ignore the received
3009   Host header field (if any) and instead replace it with the host
3010   information of the request-target.  When a proxy forwards a request,
3011   it MUST generate the Host header field based on the received
3012   absolute-URI rather than the received Host.
3013</t>
3014<t>
3015   Since the Host header field acts as an application-level routing
3016   mechanism, it is a frequent target for malware seeking to poison
3017   a shared cache or redirect a request to an unintended server.
3018   An interception proxy is particularly vulnerable if it relies on
3019   the Host header field value for redirecting requests to internal
3020   servers, or for use as a cache key in a shared cache, without
3021   first verifying that the intercepted connection is targeting a
3022   valid IP address for that host.
3023</t>
3024<t>
3025   A server MUST respond with a 400 (Bad Request) status code to
3026   any HTTP/1.1 request message that lacks a Host header field and
3027   to any request message that contains more than one Host header field
3028   or a Host header field with an invalid field-value.
3029</t>
3030<t>
3031   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3032   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3033   for other requirements relating to Host.
3034</t>
3035</section>
3036
3037<section title="TE" anchor="header.te">
3038  <iref primary="true" item="TE header field"/>
3039  <iref primary="true" item="Header Fields" subitem="TE"/>
3040 
3041 
3042 
3043 
3044<t>
3045   The "TE" header field indicates what extension transfer-codings
3046   it is willing to accept in the response, and whether or not it is
3047   willing to accept trailer fields in a chunked transfer-coding.
3048</t>
3049<t>
3050   Its value consists of the keyword "trailers" and/or a comma-separated
3051   list of extension transfer-coding names with optional accept
3052   parameters (as described in <xref target="transfer.codings"/>).
3053</t>
3054<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[
3055  TE        = #t-codings
3056  t-codings = "trailers" / ( transfer-extension [ te-params ] )
3057  te-params = OWS ";" OWS "q=" qvalue *( te-ext )
3058  te-ext    = OWS ";" OWS token [ "=" word ]
3059]]></artwork></figure>
3060<t>
3061   The presence of the keyword "trailers" indicates that the client is
3062   willing to accept trailer fields in a chunked transfer-coding, as
3063   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3064   transfer-coding values even though it does not itself represent a
3065   transfer-coding.
3066</t>
3067<t>
3068   Examples of its use are:
3069</t>
3070<figure><artwork type="example"><![CDATA[
3071  TE: deflate
3072  TE:
3073  TE: trailers, deflate;q=0.5
3074]]></artwork></figure>
3075<t>
3076   The TE header field only applies to the immediate connection.
3077   Therefore, the keyword MUST be supplied within a Connection header
3078   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3079</t>
3080<t>
3081   A server tests whether a transfer-coding is acceptable, according to
3082   a TE field, using these rules:
3083  <list style="numbers">
3084    <t>The "chunked" transfer-coding is always acceptable. If the
3085         keyword "trailers" is listed, the client indicates that it is
3086         willing to accept trailer fields in the chunked response on
3087         behalf of itself and any downstream clients. The implication is
3088         that, if given, the client is stating that either all
3089         downstream clients are willing to accept trailer fields in the
3090         forwarded response, or that it will attempt to buffer the
3091         response on behalf of downstream recipients.
3092      <vspace blankLines="1"/>
3093         Note: HTTP/1.1 does not define any means to limit the size of a
3094         chunked response such that a client can be assured of buffering
3095         the entire response.</t>
3096    <t>If the transfer-coding being tested is one of the transfer-codings
3097         listed in the TE field, then it is acceptable unless it
3098         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3099         qvalue of 0 means "not acceptable".)</t>
3100    <t>If multiple transfer-codings are acceptable, then the
3101         acceptable transfer-coding with the highest non-zero qvalue is
3102         preferred.  The "chunked" transfer-coding always has a qvalue
3103         of 1.</t>
3104  </list>
3105</t>
3106<t>
3107   If the TE field-value is empty or if no TE field is present, the only
3108   transfer-coding is "chunked". A message with no transfer-coding is
3109   always acceptable.
3110</t>
3111</section>
3112
3113<section title="Trailer" anchor="header.trailer">
3114  <iref primary="true" item="Trailer header field"/>
3115  <iref primary="true" item="Header Fields" subitem="Trailer"/>
3116 
3117<t>
3118   The "Trailer" header field indicates that the given set of
3119   header fields is present in the trailer of a message encoded with
3120   chunked transfer-coding.
3121</t>
3122<figure><iref primary="true" item="Grammar" subitem="Trailer"/><artwork type="abnf2616"><![CDATA[
3123  Trailer = 1#field-name
3124]]></artwork></figure>
3125<t>
3126   An HTTP/1.1 message SHOULD include a Trailer header field in a
3127   message using chunked transfer-coding with a non-empty trailer. Doing
3128   so allows the recipient to know which header fields to expect in the
3129   trailer.
3130</t>
3131<t>
3132   If no Trailer header field is present, the trailer SHOULD NOT  include
3133   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3134   trailer fields in a "chunked" transfer-coding.
3135</t>
3136<t>
3137   Message header fields listed in the Trailer header field MUST NOT
3138   include the following header fields:
3139  <list style="symbols">
3140    <t>Transfer-Encoding</t>
3141    <t>Content-Length</t>
3142    <t>Trailer</t>
3143  </list>
3144</t>
3145</section>
3146
3147<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3148  <iref primary="true" item="Transfer-Encoding header field"/>
3149  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding"/>
3150 
3151<t>
3152   The "Transfer-Encoding" header field indicates what transfer-codings
3153   (if any) have been applied to the message body. It differs from
3154   Content-Encoding (Section 2.2 of <xref target="Part3"/>) in that transfer-codings are a property
3155   of the message (and therefore are removed by intermediaries), whereas
3156   content-codings are not.
3157</t>
3158<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><artwork type="abnf2616"><![CDATA[
3159  Transfer-Encoding = 1#transfer-coding
3160]]></artwork></figure>
3161<t>
3162   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3163</t>
3164<figure><artwork type="example"><![CDATA[
3165  Transfer-Encoding: chunked
3166]]></artwork></figure>
3167<t>
3168   If multiple encodings have been applied to a representation, the transfer-codings
3169   MUST be listed in the order in which they were applied.
3170   Additional information about the encoding parameters MAY be provided
3171   by other header fields not defined by this specification.
3172</t>
3173<t>
3174   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3175   header field.
3176</t>
3177</section>
3178
3179<section title="Upgrade" anchor="header.upgrade">
3180  <iref primary="true" item="Upgrade header field"/>
3181  <iref primary="true" item="Header Fields" subitem="Upgrade"/>
3182 
3183<t>
3184   The "Upgrade" header field allows the client to specify what
3185   additional communication protocols it would like to use, if the server
3186   chooses to switch protocols. Servers can use it to indicate what protocols
3187   they are willing to switch to.
3188</t>
3189<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><artwork type="abnf2616"><![CDATA[
3190  Upgrade = 1#product
3191]]></artwork></figure>
3192<t>
3193   For example,
3194</t>
3195<figure><artwork type="example"><![CDATA[
3196  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3197]]></artwork></figure>
3198<t>
3199   The Upgrade header field is intended to provide a simple mechanism
3200   for transition from HTTP/1.1 to some other, incompatible protocol. It
3201   does so by allowing the client to advertise its desire to use another
3202   protocol, such as a later version of HTTP with a higher major version
3203   number, even though the current request has been made using HTTP/1.1.
3204   This eases the difficult transition between incompatible protocols by
3205   allowing the client to initiate a request in the more commonly
3206   supported protocol while indicating to the server that it would like
3207   to use a "better" protocol if available (where "better" is determined
3208   by the server, possibly according to the nature of the request method
3209   or target resource).
3210</t>
3211<t>
3212   The Upgrade header field only applies to switching application-layer
3213   protocols upon the existing transport-layer connection. Upgrade
3214   cannot be used to insist on a protocol change; its acceptance and use
3215   by the server is optional. The capabilities and nature of the
3216   application-layer communication after the protocol change is entirely
3217   dependent upon the new protocol chosen, although the first action
3218   after changing the protocol MUST be a response to the initial HTTP
3219   request containing the Upgrade header field.
3220</t>
3221<t>
3222   The Upgrade header field only applies to the immediate connection.
3223   Therefore, the upgrade keyword MUST be supplied within a Connection
3224   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3225   HTTP/1.1 message.
3226</t>
3227<t>
3228   The Upgrade header field cannot be used to indicate a switch to a
3229   protocol on a different connection. For that purpose, it is more
3230   appropriate to use a 3xx redirection response (Section 7.3 of <xref target="Part2"/>).
3231</t>
3232<t>
3233   Servers MUST include the "Upgrade" header field in 101 (Switching
3234   Protocols) responses to indicate which protocol(s) are being switched to,
3235   and MUST include it in 426 (Upgrade Required) responses to indicate
3236   acceptable protocols to upgrade to. Servers MAY include it in any other
3237   response to indicate that they are willing to upgrade to one of the
3238   specified protocols.
3239</t>
3240<t>
3241   This specification only defines the protocol name "HTTP" for use by
3242   the family of Hypertext Transfer Protocols, as defined by the HTTP
3243   version rules of <xref target="http.version"/> and future updates to this
3244   specification. Additional tokens can be registered with IANA using the
3245   registration procedure defined below. 
3246</t>
3247
3248<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3249<t>
3250   The HTTP Upgrade Token Registry defines the name space for product
3251   tokens used to identify protocols in the Upgrade header field.
3252   Each registered token is associated with contact information and
3253   an optional set of specifications that details how the connection
3254   will be processed after it has been upgraded.
3255</t>
3256<t>
3257   Registrations are allowed on a First Come First Served basis as
3258   described in Section 4.1 of <xref target="RFC5226"/>. The
3259   specifications need not be IETF documents or be subject to IESG review.
3260   Registrations are subject to the following rules:
3261  <list style="numbers">
3262    <t>A token, once registered, stays registered forever.</t>
3263    <t>The registration MUST name a responsible party for the
3264       registration.</t>
3265    <t>The registration MUST name a point of contact.</t>
3266    <t>The registration MAY name a set of specifications associated with that
3267       token. Such specifications need not be publicly available.</t>
3268    <t>The responsible party MAY change the registration at any time.
3269       The IANA will keep a record of all such changes, and make them
3270       available upon request.</t>
3271    <t>The responsible party for the first registration of a "product"
3272       token MUST approve later registrations of a "version" token
3273       together with that "product" token before they can be registered.</t>
3274    <t>If absolutely required, the IESG MAY reassign the responsibility
3275       for a token. This will normally only be used in the case when a
3276       responsible party cannot be contacted.</t>
3277  </list>
3278</t>
3279</section>
3280
3281
3282</section>
3283
3284<section title="Via" anchor="header.via">
3285  <iref primary="true" item="Via header field"/>
3286  <iref primary="true" item="Header Fields" subitem="Via"/>
3287 
3288 
3289 
3290 
3291 
3292 
3293<t>
3294   The "Via" header field MUST be sent by a proxy or gateway to
3295   indicate the intermediate protocols and recipients between the user
3296   agent and the server on requests, and between the origin server and
3297   the client on responses. It is analogous to the "Received" field
3298   used by email systems (Section 3.6.7 of <xref target="RFC5322"/>)
3299   and is intended to be used for tracking message forwards,
3300   avoiding request loops, and identifying the protocol capabilities of
3301   all senders along the request/response chain.
3302</t>
3303<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[
3304  Via               = 1#( received-protocol RWS received-by
3305                          [ RWS comment ] )
3306  received-protocol = [ protocol-name "/" ] protocol-version
3307  protocol-name     = token
3308  protocol-version  = token
3309  received-by       = ( uri-host [ ":" port ] ) / pseudonym
3310  pseudonym         = token
3311]]></artwork></figure>
3312<t>
3313   The received-protocol indicates the protocol version of the message
3314   received by the server or client along each segment of the
3315   request/response chain. The received-protocol version is appended to
3316   the Via field value when the message is forwarded so that information
3317   about the protocol capabilities of upstream applications remains
3318   visible to all recipients.
3319</t>
3320<t>
3321   The protocol-name is excluded if and only if it would be "HTTP". The
3322   received-by field is normally the host and optional port number of a
3323   recipient server or client that subsequently forwarded the message.
3324   However, if the real host is considered to be sensitive information,
3325   it MAY be replaced by a pseudonym. If the port is not given, it MAY
3326   be assumed to be the default port of the received-protocol.
3327</t>
3328<t>
3329   Multiple Via field values represent each proxy or gateway that has
3330   forwarded the message. Each recipient MUST append its information
3331   such that the end result is ordered according to the sequence of
3332   forwarding applications.
3333</t>
3334<t>
3335   Comments MAY be used in the Via header field to identify the software
3336   of each recipient, analogous to the User-Agent and Server header fields.
3337   However, all comments in the Via field are optional and MAY be removed
3338   by any recipient prior to forwarding the message.
3339</t>
3340<t>
3341   For example, a request message could be sent from an HTTP/1.0 user
3342   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3343   forward the request to a public proxy at p.example.net, which completes
3344   the request by forwarding it to the origin server at www.example.com.
3345   The request received by www.example.com would then have the following
3346   Via header field:
3347</t>
3348<figure><artwork type="example"><![CDATA[
3349  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3350]]></artwork></figure>
3351<t>
3352   A proxy or gateway used as a portal through a network firewall
3353   SHOULD NOT forward the names and ports of hosts within the firewall
3354   region unless it is explicitly enabled to do so. If not enabled, the
3355   received-by host of any host behind the firewall SHOULD be replaced
3356   by an appropriate pseudonym for that host.
3357</t>
3358<t>
3359   For organizations that have strong privacy requirements for hiding
3360   internal structures, a proxy or gateway MAY combine an ordered
3361   subsequence of Via header field entries with identical received-protocol
3362   values into a single such entry. For example,
3363</t>
3364<figure><artwork type="example"><![CDATA[
3365  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3366]]></artwork></figure>
3367<t>
3368  could be collapsed to
3369</t>
3370<figure><artwork type="example"><![CDATA[
3371  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3372]]></artwork></figure>
3373<t>
3374   Senders SHOULD NOT combine multiple entries unless they are all
3375   under the same organizational control and the hosts have already been
3376   replaced by pseudonyms. Senders MUST NOT combine entries which
3377   have different received-protocol values.
3378</t>
3379</section>
3380
3381</section>
3382
3383<section title="IANA Considerations" anchor="IANA.considerations">
3384
3385<section title="Header Field Registration" anchor="header.field.registration">
3386<t>
3387   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3388   with the permanent registrations below (see <xref target="RFC3864"/>):
3389</t>
3390
3391<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3392<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3393   <ttcol>Header Field Name</ttcol>
3394   <ttcol>Protocol</ttcol>
3395   <ttcol>Status</ttcol>
3396   <ttcol>Reference</ttcol>
3397
3398   <c>Connection</c>
3399   <c>http</c>
3400   <c>standard</c>
3401   <c>
3402      <xref target="header.connection"/>
3403   </c>
3404   <c>Content-Length</c>
3405   <c>http</c>
3406   <c>standard</c>
3407   <c>
3408      <xref target="header.content-length"/>
3409   </c>
3410   <c>Host</c>
3411   <c>http</c>
3412   <c>standard</c>
3413   <c>
3414      <xref target="header.host"/>
3415   </c>
3416   <c>TE</c>
3417   <c>http</c>
3418   <c>standard</c>
3419   <c>
3420      <xref target="header.te"/>
3421   </c>
3422   <c>Trailer</c>
3423   <c>http</c>
3424   <c>standard</c>
3425   <c>
3426      <xref target="header.trailer"/>
3427   </c>
3428   <c>Transfer-Encoding</c>
3429   <c>http</c>
3430   <c>standard</c>
3431   <c>
3432      <xref target="header.transfer-encoding"/>
3433   </c>
3434   <c>Upgrade</c>
3435   <c>http</c>
3436   <c>standard</c>
3437   <c>
3438      <xref target="header.upgrade"/>
3439   </c>
3440   <c>Via</c>
3441   <c>http</c>
3442   <c>standard</c>
3443   <c>
3444      <xref target="header.via"/>
3445   </c>
3446</texttable>
3447<!--(END)-->
3448
3449<t>
3450   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3451   HTTP header field would be in conflict with the use of the "close" connection
3452   option for the "Connection" header field (<xref target="header.connection"/>).
3453</t>
3454<texttable align="left" suppress-title="true">
3455   <ttcol>Header Field Name</ttcol>
3456   <ttcol>Protocol</ttcol>
3457   <ttcol>Status</ttcol>
3458   <ttcol>Reference</ttcol>
3459
3460   <c>Close</c>
3461   <c>http</c>
3462   <c>reserved</c>
3463   <c>
3464      <xref target="header.field.registration"/>
3465   </c>
3466</texttable>
3467<t>
3468   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3469</t>
3470</section>
3471
3472<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3473<t>
3474   The entries for the "http" and "https" URI Schemes in the registry located at
3475   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3476   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3477   and <xref target="https.uri" format="counter"/> of this document
3478   (see <xref target="RFC4395"/>).
3479</t>
3480</section>
3481
3482<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3483<t>
3484   This document serves as the specification for the Internet media types
3485   "message/http" and "application/http". The following is to be registered with
3486   IANA (see <xref target="RFC4288"/>).
3487</t>
3488<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3489<iref item="Media Type" subitem="message/http" primary="true"/>
3490<iref item="message/http Media Type" primary="true"/>
3491<t>
3492   The message/http type can be used to enclose a single HTTP request or
3493   response message, provided that it obeys the MIME restrictions for all
3494   "message" types regarding line length and encodings.
3495</t>
3496<t>
3497  <list style="hanging">
3498    <t hangText="Type name:">
3499      message
3500    </t>
3501    <t hangText="Subtype name:">
3502      http
3503    </t>
3504    <t hangText="Required parameters:">
3505      none
3506    </t>
3507    <t hangText="Optional parameters:">
3508      version, msgtype
3509      <list style="hanging">
3510        <t hangText="version:">
3511          The HTTP-Version number of the enclosed message
3512          (e.g., "1.1"). If not present, the version can be
3513          determined from the first line of the body.
3514        </t>
3515        <t hangText="msgtype:">
3516          The message type — "request" or "response". If not
3517          present, the type can be determined from the first
3518          line of the body.
3519        </t>
3520      </list>
3521    </t>
3522    <t hangText="Encoding considerations:">
3523      only "7bit", "8bit", or "binary" are permitted
3524    </t>
3525    <t hangText="Security considerations:">
3526      none
3527    </t>
3528    <t hangText="Interoperability considerations:">
3529      none
3530    </t>
3531    <t hangText="Published specification:">
3532      This specification (see <xref target="internet.media.type.message.http"/>).
3533    </t>
3534    <t hangText="Applications that use this media type:">
3535    </t>
3536    <t hangText="Additional information:">
3537      <list style="hanging">
3538        <t hangText="Magic number(s):">none</t>
3539        <t hangText="File extension(s):">none</t>
3540        <t hangText="Macintosh file type code(s):">none</t>
3541      </list>
3542    </t>
3543    <t hangText="Person and email address to contact for further information:">
3544      See Authors Section.
3545    </t>
3546    <t hangText="Intended usage:">
3547      COMMON
3548    </t>
3549    <t hangText="Restrictions on usage:">
3550      none
3551    </t>
3552    <t hangText="Author/Change controller:">
3553      IESG
3554    </t>
3555  </list>
3556</t>
3557</section>
3558<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3559<iref item="Media Type" subitem="application/http" primary="true"/>
3560<iref item="application/http Media Type" primary="true"/>
3561<t>
3562   The application/http type can be used to enclose a pipeline of one or more
3563   HTTP request or response messages (not intermixed).
3564</t>
3565<t>
3566  <list style="hanging">
3567    <t hangText="Type name:">
3568      application
3569    </t>
3570    <t hangText="Subtype name:">
3571      http
3572    </t>
3573    <t hangText="Required parameters:">
3574      none
3575    </t>
3576    <t hangText="Optional parameters:">
3577      version, msgtype
3578      <list style="hanging">
3579        <t hangText="version:">
3580          The HTTP-Version number of the enclosed messages
3581          (e.g., "1.1"). If not present, the version can be
3582          determined from the first line of the body.
3583        </t>
3584        <t hangText="msgtype:">
3585          The message type — "request" or "response". If not
3586          present, the type can be determined from the first
3587          line of the body.
3588        </t>
3589      </list>
3590    </t>
3591    <t hangText="Encoding considerations:">
3592      HTTP messages enclosed by this type
3593      are in "binary" format; use of an appropriate
3594      Content-Transfer-Encoding is required when
3595      transmitted via E-mail.
3596    </t>
3597    <t hangText="Security considerations:">
3598      none
3599    </t>
3600    <t hangText="Interoperability considerations:">
3601      none
3602    </t>
3603    <t hangText="Published specification:">
3604      This specification (see <xref target="internet.media.type.application.http"/>).
3605    </t>
3606    <t hangText="Applications that use this media type:">
3607    </t>
3608    <t hangText="Additional information:">
3609      <list style="hanging">
3610        <t hangText="Magic number(s):">none</t>
3611        <t hangText="File extension(s):">none</t>
3612        <t hangText="Macintosh file type code(s):">none</t>
3613      </list>
3614    </t>
3615    <t hangText="Person and email address to contact for further information:">
3616      See Authors Section.
3617    </t>
3618    <t hangText="Intended usage:">
3619      COMMON
3620    </t>
3621    <t hangText="Restrictions on usage:">
3622      none
3623    </t>
3624    <t hangText="Author/Change controller:">
3625      IESG
3626    </t>
3627  </list>
3628</t>
3629</section>
3630</section>
3631
3632<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3633<t>
3634   The registration procedure for HTTP Transfer Codings is now defined by
3635   <xref target="transfer.coding.registry"/> of this document.
3636</t>
3637<t>
3638   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3639   shall be updated with the registrations below:
3640</t>
3641<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3642   <ttcol>Name</ttcol>
3643   <ttcol>Description</ttcol>
3644   <ttcol>Reference</ttcol>
3645   <c>chunked</c>
3646   <c>Transfer in a series of chunks</c>
3647   <c>
3648      <xref target="chunked.encoding"/>
3649   </c>
3650   <c>compress</c>
3651   <c>UNIX "compress" program method</c>
3652   <c>
3653      <xref target="compress.coding"/>
3654   </c>
3655   <c>deflate</c>
3656   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3657   the "zlib" data format (<xref target="RFC1950"/>)
3658   </c>
3659   <c>
3660      <xref target="deflate.coding"/>
3661   </c>
3662   <c>gzip</c>
3663   <c>Same as GNU zip <xref target="RFC1952"/></c>
3664   <c>
3665      <xref target="gzip.coding"/>
3666   </c>
3667</texttable>
3668</section>
3669
3670<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3671<t>
3672   The registration procedure for HTTP Upgrade Tokens — previously defined
3673   in Section 7.2 of <xref target="RFC2817"/> — is now defined
3674   by <xref target="upgrade.token.registry"/> of this document.
3675</t>
3676<t>
3677   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3678   shall be updated with the registration below:
3679</t>
3680<texttable align="left" suppress-title="true">
3681   <ttcol>Value</ttcol>
3682   <ttcol>Description</ttcol>
3683   <ttcol>Reference</ttcol>
3684
3685   <c>HTTP</c>
3686   <c>Hypertext Transfer Protocol</c> 
3687   <c><xref target="http.version"/> of this specification</c>
3688
3689</texttable>
3690</section>
3691
3692</section>
3693
3694<section title="Security Considerations" anchor="security.considerations">
3695<t>
3696   This section is meant to inform application developers, information
3697   providers, and users of the security limitations in HTTP/1.1 as
3698   described by this document. The discussion does not include
3699   definitive solutions to the problems revealed, though it does make
3700   some suggestions for reducing security risks.
3701</t>
3702
3703<section title="Personal Information" anchor="personal.information">
3704<t>
3705   HTTP clients are often privy to large amounts of personal information
3706   (e.g., the user's name, location, mail address, passwords, encryption
3707   keys, etc.), and SHOULD be very careful to prevent unintentional
3708   leakage of this information.
3709   We very strongly recommend that a convenient interface be provided
3710   for the user to control dissemination of such information, and that
3711   designers and implementors be particularly careful in this area.
3712   History shows that errors in this area often create serious security
3713   and/or privacy problems and generate highly adverse publicity for the
3714   implementor's company.
3715</t>
3716</section>
3717
3718<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3719<t>
3720   A server is in the position to save personal data about a user's
3721   requests which might identify their reading patterns or subjects of
3722   interest. This information is clearly confidential in nature and its
3723   handling can be constrained by law in certain countries. People using
3724   HTTP to provide data are responsible for ensuring that
3725   such material is not distributed without the permission of any
3726   individuals that are identifiable by the published results.
3727</t>
3728</section>
3729
3730<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3731<t>
3732   Implementations of HTTP origin servers SHOULD be careful to restrict
3733   the documents returned by HTTP requests to be only those that were
3734   intended by the server administrators. If an HTTP server translates
3735   HTTP URIs directly into file system calls, the server MUST take
3736   special care not to serve files that were not intended to be
3737   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3738   other operating systems use ".." as a path component to indicate a
3739   directory level above the current one. On such a system, an HTTP
3740   server MUST disallow any such construct in the request-target if it
3741   would otherwise allow access to a resource outside those intended to
3742   be accessible via the HTTP server. Similarly, files intended for
3743   reference only internally to the server (such as access control
3744   files, configuration files, and script code) MUST be protected from
3745   inappropriate retrieval, since they might contain sensitive
3746   information. Experience has shown that minor bugs in such HTTP server
3747   implementations have turned into security risks.
3748</t>
3749</section>
3750
3751<section title="DNS-related Attacks" anchor="dns.related.attacks">
3752<t>
3753   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
3754   generally prone to security attacks based on the deliberate misassociation
3755   of IP addresses and DNS names not protected by DNSSec. Clients need to be
3756   cautious in assuming the validity of an IP number/DNS name association unless
3757   the response is protected by DNSSec (<xref target="RFC4033"/>).
3758</t>
3759</section>
3760
3761<section title="Proxies and Caching" anchor="attack.proxies">
3762<t>
3763   By their very nature, HTTP proxies are men-in-the-middle, and
3764   represent an opportunity for man-in-the-middle attacks. Compromise of
3765   the systems on which the proxies run can result in serious security
3766   and privacy problems. Proxies have access to security-related
3767   information, personal information about individual users and
3768   organizations, and proprietary information belonging to users and
3769   content providers. A compromised proxy, or a proxy implemented or
3770   configured without regard to security and privacy considerations,
3771   might be used in the commission of a wide range of potential attacks.
3772</t>
3773<t>
3774   Proxy operators need to protect the systems on which proxies run as
3775   they would protect any system that contains or transports sensitive
3776   information. In particular, log information gathered at proxies often
3777   contains highly sensitive personal information, and/or information
3778   about organizations. Log information needs to be carefully guarded, and
3779   appropriate guidelines for use need to be developed and followed.
3780   (<xref target="abuse.of.server.log.information"/>).
3781</t>
3782<t>
3783   Proxy implementors need to consider the privacy and security
3784   implications of their design and coding decisions, and of the
3785   configuration options they provide to proxy operators (especially the
3786   default configuration).
3787</t>
3788<t>
3789   Users of a proxy need to be aware that proxies are no trustworthier than
3790   the people who run them; HTTP itself cannot solve this problem.
3791</t>
3792<t>
3793   The judicious use of cryptography, when appropriate, might suffice to
3794   protect against a broad range of security and privacy attacks. Such
3795   cryptography is beyond the scope of the HTTP/1.1 specification.
3796</t>
3797</section>
3798
3799<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
3800<t>
3801   Because HTTP uses mostly textual, character-delimited fields, attackers can
3802   overflow buffers in implementations, and/or perform a Denial of Service
3803   against implementations that accept fields with unlimited lengths.
3804</t>
3805<t>
3806   To promote interoperability, this specification makes specific
3807   recommendations for size limits on request-targets (<xref target="request-target"/>)
3808   and blocks of header fields (<xref target="header.fields"/>). These are
3809   minimum recommendations, chosen to be supportable even by implementations
3810   with limited resources; it is expected that most implementations will choose
3811   substantially higher limits.
3812</t>
3813<t>
3814   This specification also provides a way for servers to reject messages that
3815   have request-targets that are too long (Section 7.4.15 of <xref target="Part2"/>) or request entities
3816   that are too large (Section 7.4 of <xref target="Part2"/>).
3817</t>
3818<t>
3819   Other fields (including but not limited to request methods, response status
3820   phrases, header field-names, and body chunks) SHOULD be limited by
3821   implementations carefully, so as to not impede interoperability.
3822</t>
3823</section>
3824
3825<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3826<t>
3827   They exist. They are hard to defend against. Research continues.
3828   Beware.
3829</t>
3830</section>
3831</section>
3832
3833<section title="Acknowledgments" anchor="acks">
3834<t>
3835   This document revision builds on the work that went into
3836   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
3837   See Section 16 of <xref target="RFC2616"/> for detailed
3838   acknowledgements.
3839</t>
3840<t>
3841   Since 1999, many contributors have helped by reporting bugs, asking
3842   smart questions, drafting and reviewing text, and discussing open issues:
3843</t>
3844
3845<t>Adam Barth,
3846Adam Roach,
3847Addison Phillips,
3848Adrian Chadd,
3849Adrien de Croy,
3850Alan Ford,
3851Alan Ruttenberg,
3852Albert Lunde,
3853Alex Rousskov,
3854Alexey Melnikov,
3855Alisha Smith,
3856Amichai Rothman,
3857Amit Klein,
3858Amos Jeffries,
3859Andreas Maier,
3860Andreas Petersson,
3861Anne van Kesteren,
3862Anthony Bryan,
3863Asbjorn Ulsberg,
3864Balachander Krishnamurthy,
3865Barry Leiba,
3866Ben Laurie,
3867Benjamin Niven-Jenkins,
3868Bil Corry,
3869Bill Burke,
3870Bjoern Hoehrmann,
3871Bob Scheifler,
3872Boris Zbarsky,
3873Brett Slatkin,
3874Brian Kell,
3875Brian McBarron,
3876Brian Pane,
3877Brian Smith,
3878Bryce Nesbitt,
3879Cameron Heavon-Jones,
3880Carl Kugler,
3881Charles Fry,
3882Chris Newman,
3883Cyrus Daboo,
3884Dale Robert Anderson,
3885Dan Winship,
3886Daniel Stenberg,
3887Dave Cridland,
3888Dave Crocker,
3889Dave Kristol,
3890David Booth,
3891David Singer,
3892David W. Morris,
3893Diwakar Shetty,
3894Dmitry Kurochkin,
3895Drummond Reed,
3896Duane Wessels,
3897Edward Lee,
3898Eliot Lear,
3899Eran Hammer-Lahav,
3900Eric D. Williams,
3901Eric J. Bowman,
3902Eric Lawrence,
3903Erik Aronesty,
3904Florian Weimer,
3905Frank Ellermann,
3906Fred Bohle,
3907Geoffrey Sneddon,
3908Gervase Markham,
3909Greg Wilkins,
3910Harald Tveit Alvestrand,
3911Harry Halpin,
3912Helge Hess,
3913Henrik Nordstrom,
3914Henry S. Thompson,
3915Henry Story,
3916Herbert van de Sompel,
3917Howard Melman,
3918Hugo Haas,
3919Ian Hickson,
3920Ingo Struck,
3921J. Ross Nicoll,
3922James H. Manger,
3923James Lacey,
3924James M. Snell,
3925Jamie Lokier,
3926Jan Algermissen,
3927Jeff Hodges (for coming up with the term 'effective Request-URI'),
3928Jeff Walden,
3929Jim Luther,
3930Joe D. Williams,
3931Joe Gregorio,
3932Joe Orton,
3933John C. Klensin,
3934John C. Mallery,
3935John Cowan,
3936John Kemp,
3937John Panzer,
3938John Schneider,
3939John Stracke,
3940Jonas Sicking,
3941Jonathan Moore,
3942Jonathan Rees,
3943Jordi Ros,
3944Joris Dobbelsteen,
3945Josh Cohen,
3946Julien Pierre,
3947Jungshik Shin,
3948Justin Chapweske,
3949Justin Erenkrantz,
3950Justin James,
3951Kalvinder Singh,
3952Karl Dubost,
3953Keith Hoffman,
3954Keith Moore,
3955Koen Holtman,
3956Konstantin Voronkov,
3957Kris Zyp,
3958Lisa Dusseault,
3959Maciej Stachowiak,
3960Marc Schneider,
3961Marc Slemko,
3962Mark Baker,
3963Mark Nottingham (Working Group chair),
3964Mark Pauley,
3965Martin J. Duerst,
3966Martin Thomson,
3967Matt Lynch,
3968Matthew Cox,
3969Max Clark,
3970Michael Burrows,
3971Michael Hausenblas,
3972Mike Amundsen,
3973Mike Kelly,
3974Mike Schinkel,
3975Miles Sabin,
3976Mykyta Yevstifeyev,
3977Nathan Rixham,
3978Nicholas Shanks,
3979Nico Williams,
3980Nicolas Alvarez,
3981Noah Slater,
3982Pablo Castro,
3983Pat Hayes,
3984Patrick R. McManus,
3985Paul E. Jones,
3986Paul Hoffman,
3987Paul Marquess,
3988Peter Saint-Andre,
3989Peter Watkins,
3990Phil Archer,
3991Phillip Hallam-Baker,
3992Poul-Henning Kamp,
3993Preethi Natarajan,
3994Reto Bachmann-Gmuer,
3995Richard Cyganiak,
3996Robert Brewer,
3997Robert Collins,
3998Robert O'Callahan,
3999Robert Olofsson,
4000Robert Sayre,
4001Robert Siemer,
4002Robert de Wilde,
4003Roberto Javier Godoy,
4004Ronny Widjaja,
4005S. Mike Dierken,
4006Salvatore Loreto,
4007Sam Johnston,
4008Sam Ruby,
4009Scott Lawrence (for maintaining the original issues list),
4010Sean B. Palmer,
4011Shane McCarron,
4012Stefan Eissing,
4013Stefan Tilkov,
4014Stefanos Harhalakis,
4015Stephane Bortzmeyer,
4016Stuart Williams,
4017Subbu Allamaraju,
4018Sylvain Hellegouarch,
4019Tapan Divekar,
4020Thomas Broyer,
4021Thomas Nordin,
4022Thomas Roessler,
4023Tim Morgan,
4024Tim Olsen,
4025Travis Snoozy,
4026Tyler Close,
4027Vincent Murphy,
4028Wenbo Zhu,
4029Werner Baumann,
4030Wilbur Streett,
4031Wilfredo Sanchez Vega,
4032William A. Rowe Jr.,
4033William Chan,
4034Willy Tarreau,
4035Xiaoshu Wang,
4036Yaron Goland,
4037Yngve Nysaeter Pettersen,
4038Yogesh Bang,
4039Yutaka Oiwa, and
4040Zed A. Shaw.
4041</t>
4042
4043</section>
4044
4045</middle>
4046<back>
4047
4048<references title="Normative References">
4049
4050<reference anchor="ISO-8859-1">
4051  <front>
4052    <title>
4053     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4054    </title>
4055    <author>
4056      <organization>International Organization for Standardization</organization>
4057    </author>
4058    <date year="1998"/>
4059  </front>
4060  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4061</reference>
4062
4063<reference anchor="Part2">
4064  <front>
4065    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4066    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4067      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4068      <address><email>fielding@gbiv.com</email></address>
4069    </author>
4070    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4071      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4072      <address><email>jg@freedesktop.org</email></address>
4073    </author>
4074    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4075      <organization abbrev="HP">Hewlett-Packard Company</organization>
4076      <address><email>JeffMogul@acm.org</email></address>
4077    </author>
4078    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4079      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4080      <address><email>henrikn@microsoft.com</email></address>
4081    </author>
4082    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4083      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4084      <address><email>LMM@acm.org</email></address>
4085    </author>
4086    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4087      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4088      <address><email>paulle@microsoft.com</email></address>
4089    </author>
4090    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4091      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4092      <address><email>timbl@w3.org</email></address>
4093    </author>
4094    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4095      <organization abbrev="W3C">World Wide Web Consortium</organization>
4096      <address><email>ylafon@w3.org</email></address>
4097    </author>
4098    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4099      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4100      <address><email>julian.reschke@greenbytes.de</email></address>
4101    </author>
4102    <date month="January" year="2012"/>
4103  </front>
4104  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-18"/>
4105 
4106</reference>
4107
4108<reference anchor="Part3">
4109  <front>
4110    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4111    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4112      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4113      <address><email>fielding@gbiv.com</email></address>
4114    </author>
4115    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4116      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4117      <address><email>jg@freedesktop.org</email></address>
4118    </author>
4119    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4120      <organization abbrev="HP">Hewlett-Packard Company</organization>
4121      <address><email>JeffMogul@acm.org</email></address>
4122    </author>
4123    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4124      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4125      <address><email>henrikn@microsoft.com</email></address>
4126    </author>
4127    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4128      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4129      <address><email>LMM@acm.org</email></address>
4130    </author>
4131    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4132      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4133      <address><email>paulle@microsoft.com</email></address>
4134    </author>
4135    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4136      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4137      <address><email>timbl@w3.org</email></address>
4138    </author>
4139    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4140      <organization abbrev="W3C">World Wide Web Consortium</organization>
4141      <address><email>ylafon@w3.org</email></address>
4142    </author>
4143    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4144      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4145      <address><email>julian.reschke@greenbytes.de</email></address>
4146    </author>
4147    <date month="January" year="2012"/>
4148  </front>
4149  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-18"/>
4150 
4151</reference>
4152
4153<reference anchor="Part6">
4154  <front>
4155    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4156    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4157      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4158      <address><email>fielding@gbiv.com</email></address>
4159    </author>
4160    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4161      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4162      <address><email>jg@freedesktop.org</email></address>
4163    </author>
4164    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4165      <organization abbrev="HP">Hewlett-Packard Company</organization>
4166      <address><email>JeffMogul@acm.org</email></address>
4167    </author>
4168    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4169      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4170      <address><email>henrikn@microsoft.com</email></address>
4171    </author>
4172    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4173      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4174      <address><email>LMM@acm.org</email></address>
4175    </author>
4176    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4177      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4178      <address><email>paulle@microsoft.com</email></address>
4179    </author>
4180    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4181      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4182      <address><email>timbl@w3.org</email></address>
4183    </author>
4184    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4185      <organization abbrev="W3C">World Wide Web Consortium</organization>
4186      <address><email>ylafon@w3.org</email></address>
4187    </author>
4188    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4189      <organization>Rackspace</organization>
4190      <address><email>mnot@mnot.net</email></address>
4191    </author>
4192    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4193      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4194      <address><email>julian.reschke@greenbytes.de</email></address>
4195    </author>
4196    <date month="January" year="2012"/>
4197  </front>
4198  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-18"/>
4199 
4200</reference>
4201
4202<reference anchor="RFC5234">
4203  <front>
4204    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4205    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4206      <organization>Brandenburg InternetWorking</organization>
4207      <address>
4208        <email>dcrocker@bbiw.net</email>
4209      </address> 
4210    </author>
4211    <author initials="P." surname="Overell" fullname="Paul Overell">
4212      <organization>THUS plc.</organization>
4213      <address>
4214        <email>paul.overell@thus.net</email>
4215      </address>
4216    </author>
4217    <date month="January" year="2008"/>
4218  </front>
4219  <seriesInfo name="STD" value="68"/>
4220  <seriesInfo name="RFC" value="5234"/>
4221</reference>
4222
4223<reference anchor="RFC2119">
4224  <front>
4225    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4226    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4227      <organization>Harvard University</organization>
4228      <address><email>sob@harvard.edu</email></address>
4229    </author>
4230    <date month="March" year="1997"/>
4231  </front>
4232  <seriesInfo name="BCP" value="14"/>
4233  <seriesInfo name="RFC" value="2119"/>
4234</reference>
4235
4236<reference anchor="RFC3986">
4237 <front>
4238  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
4239  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4240    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4241    <address>
4242       <email>timbl@w3.org</email>
4243       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4244    </address>
4245  </author>
4246  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4247    <organization abbrev="Day Software">Day Software</organization>
4248    <address>
4249      <email>fielding@gbiv.com</email>
4250      <uri>http://roy.gbiv.com/</uri>
4251    </address>
4252  </author>
4253  <author initials="L." surname="Masinter" fullname="Larry Masinter">
4254    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4255    <address>
4256      <email>LMM@acm.org</email>
4257      <uri>http://larry.masinter.net/</uri>
4258    </address>
4259  </author>
4260  <date month="January" year="2005"/>
4261 </front>
4262 <seriesInfo name="STD" value="66"/>
4263 <seriesInfo name="RFC" value="3986"/>
4264</reference>
4265
4266<reference anchor="USASCII">
4267  <front>
4268    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4269    <author>
4270      <organization>American National Standards Institute</organization>
4271    </author>
4272    <date year="1986"/>
4273  </front>
4274  <seriesInfo name="ANSI" value="X3.4"/>
4275</reference>
4276
4277<reference anchor="RFC1950">
4278  <front>
4279    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4280    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4281      <organization>Aladdin Enterprises</organization>
4282      <address><email>ghost@aladdin.com</email></address>
4283    </author>
4284    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4285    <date month="May" year="1996"/>
4286  </front>
4287  <seriesInfo name="RFC" value="1950"/>
4288  <!--<annotation>
4289    RFC 1950 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 <xref target="RFC2068" x:fmt="none">RFC 2068</xref> 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="RFC1951">
4298  <front>
4299    <title>DEFLATE Compressed Data Format Specification version 1.3</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    <date month="May" year="1996"/>
4305  </front>
4306  <seriesInfo name="RFC" value="1951"/>
4307  <!--<annotation>
4308    RFC 1951 is an Informational RFC, thus it might be less stable than
4309    this specification. On the other hand, this downward reference was
4310    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4311    therefore it is unlikely to cause problems in practice. See also
4312    <xref target="BCP97"/>.
4313  </annotation>-->
4314</reference>
4315
4316<reference anchor="RFC1952">
4317  <front>
4318    <title>GZIP file format specification version 4.3</title>
4319    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4320      <organization>Aladdin Enterprises</organization>
4321      <address><email>ghost@aladdin.com</email></address>
4322    </author>
4323    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4324      <address><email>gzip@prep.ai.mit.edu</email></address>
4325    </author>
4326    <author initials="M." surname="Adler" fullname="Mark Adler">
4327      <address><email>madler@alumni.caltech.edu</email></address>
4328    </author>
4329    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4330      <address><email>ghost@aladdin.com</email></address>
4331    </author>
4332    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4333      <address><email>randeg@alumni.rpi.edu</email></address>
4334    </author>
4335    <date month="May" year="1996"/>
4336  </front>
4337  <seriesInfo name="RFC" value="1952"/>
4338  <!--<annotation>
4339    RFC 1952 is an Informational RFC, thus it might be less stable than
4340    this specification. On the other hand, this downward reference was
4341    present since the publication of <xref target="RFC2068" x:fmt="none">RFC 2068</xref> in 1997,
4342    therefore it is unlikely to cause problems in practice. See also
4343    <xref target="BCP97"/>.
4344  </annotation>-->
4345</reference>
4346
4347</references>
4348
4349<references title="Informative References">
4350
4351<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4352  <front>
4353    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4354    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4355    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4356    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4357    <author initials="H." surname="Lie" fullname="H. Lie"/>
4358    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4359    <date year="1997" month="September"/>
4360  </front>
4361  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4362</reference>
4363
4364<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4365  <front>
4366    <title>Improving HTTP Latency</title>
4367    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4368    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4369    <date year="1995" month="December"/>
4370  </front>
4371  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4372</reference>
4373
4374<reference anchor="RFC1919">
4375  <front>
4376    <title>Classical versus Transparent IP Proxies</title>
4377    <author initials="M." surname="Chatel" fullname="Marc Chatel">
4378      <address><email>mchatel@pax.eunet.ch</email></address>
4379    </author>
4380    <date year="1996" month="March"/>
4381  </front>
4382  <seriesInfo name="RFC" value="1919"/>
4383</reference>
4384
4385<reference anchor="RFC1945">
4386  <front>
4387    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4388    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4389      <organization>MIT, Laboratory for Computer Science</organization>
4390      <address><email>timbl@w3.org</email></address>
4391    </author>
4392    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4393      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4394      <address><email>fielding@ics.uci.edu</email></address>
4395    </author>
4396    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4397      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4398      <address><email>frystyk@w3.org</email></address>
4399    </author>
4400    <date month="May" year="1996"/>
4401  </front>
4402  <seriesInfo name="RFC" value="1945"/>
4403</reference>
4404
4405<reference anchor="RFC2045">
4406  <front>
4407    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4408    <author initials="N." surname="Freed" fullname="Ned Freed">
4409      <organization>Innosoft International, Inc.</organization>
4410      <address><email>ned@innosoft.com</email></address>
4411    </author>
4412    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4413      <organization>First Virtual Holdings</organization>
4414      <address><email>nsb@nsb.fv.com</email></address>
4415    </author>
4416    <date month="November" year="1996"/>
4417  </front>
4418  <seriesInfo name="RFC" value="2045"/>
4419</reference>
4420
4421<reference anchor="RFC2047">
4422  <front>
4423    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4424    <author initials="K." surname="Moore" fullname="Keith Moore">
4425      <organization>University of Tennessee</organization>
4426      <address><email>moore@cs.utk.edu</email></address>
4427    </author>
4428    <date month="November" year="1996"/>
4429  </front>
4430  <seriesInfo name="RFC" value="2047"/>
4431</reference>
4432
4433<reference anchor="RFC2068">
4434  <front>
4435    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4436    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4437      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4438      <address><email>fielding@ics.uci.edu</email></address>
4439    </author>
4440    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4441      <organization>MIT Laboratory for Computer Science</organization>
4442      <address><email>jg@w3.org</email></address>
4443    </author>
4444    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4445      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4446      <address><email>mogul@wrl.dec.com</email></address>
4447    </author>
4448    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4449      <organization>MIT Laboratory for Computer Science</organization>
4450      <address><email>frystyk@w3.org</email></address>
4451    </author>
4452    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4453      <organization>MIT Laboratory for Computer Science</organization>
4454      <address><email>timbl@w3.org</email></address>
4455    </author>
4456    <date month="January" year="1997"/>
4457  </front>
4458  <seriesInfo name="RFC" value="2068"/>
4459</reference>
4460
4461<reference anchor="RFC2145">
4462  <front>
4463    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4464    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4465      <organization>Western Research Laboratory</organization>
4466      <address><email>mogul@wrl.dec.com</email></address>
4467    </author>
4468    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4469      <organization>Department of Information and Computer Science</organization>
4470      <address><email>fielding@ics.uci.edu</email></address>
4471    </author>
4472    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4473      <organization>MIT Laboratory for Computer Science</organization>
4474      <address><email>jg@w3.org</email></address>
4475    </author>
4476    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4477      <organization>W3 Consortium</organization>
4478      <address><email>frystyk@w3.org</email></address>
4479    </author>
4480    <date month="May" year="1997"/>
4481  </front>
4482  <seriesInfo name="RFC" value="2145"/>
4483</reference>
4484
4485<reference anchor="RFC2616">
4486  <front>
4487    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4488    <author initials="R." surname="Fielding" fullname="R. Fielding">
4489      <organization>University of California, Irvine</organization>
4490      <address><email>fielding@ics.uci.edu</email></address>
4491    </author>
4492    <author initials="J." surname="Gettys" fullname="J. Gettys">
4493      <organization>W3C</organization>
4494      <address><email>jg@w3.org</email></address>
4495    </author>
4496    <author initials="J." surname="Mogul" fullname="J. Mogul">
4497      <organization>Compaq Computer Corporation</organization>
4498      <address><email>mogul@wrl.dec.com</email></address>
4499    </author>
4500    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4501      <organization>MIT Laboratory for Computer Science</organization>
4502      <address><email>frystyk@w3.org</email></address>
4503    </author>
4504    <author initials="L." surname="Masinter" fullname="L. Masinter">
4505      <organization>Xerox Corporation</organization>
4506      <address><email>masinter@parc.xerox.com</email></address>
4507    </author>
4508    <author initials="P." surname="Leach" fullname="P. Leach">
4509      <organization>Microsoft Corporation</organization>
4510      <address><email>paulle@microsoft.com</email></address>
4511    </author>
4512    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4513      <organization>W3C</organization>
4514      <address><email>timbl@w3.org</email></address>
4515    </author>
4516    <date month="June" year="1999"/>
4517  </front>
4518  <seriesInfo name="RFC" value="2616"/>
4519</reference>
4520
4521<reference anchor="RFC2817">
4522  <front>
4523    <title>Upgrading to TLS Within HTTP/1.1</title>
4524    <author initials="R." surname="Khare" fullname="R. Khare">
4525      <organization>4K Associates / UC Irvine</organization>
4526      <address><email>rohit@4K-associates.com</email></address>
4527    </author>
4528    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
4529      <organization>Agranat Systems, Inc.</organization>
4530      <address><email>lawrence@agranat.com</email></address>
4531    </author>
4532    <date year="2000" month="May"/>
4533  </front>
4534  <seriesInfo name="RFC" value="2817"/>
4535</reference>
4536
4537<reference anchor="RFC2818">
4538  <front>
4539    <title>HTTP Over TLS</title>
4540    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
4541      <organization>RTFM, Inc.</organization>
4542      <address><email>ekr@rtfm.com</email></address>
4543    </author>
4544    <date year="2000" month="May"/>
4545  </front>
4546  <seriesInfo name="RFC" value="2818"/>
4547</reference>
4548
4549<reference anchor="RFC2965">
4550  <front>
4551    <title>HTTP State Management Mechanism</title>
4552    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
4553      <organization>Bell Laboratories, Lucent Technologies</organization>
4554      <address><email>dmk@bell-labs.com</email></address>
4555    </author>
4556    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4557      <organization>Epinions.com, Inc.</organization>
4558      <address><email>lou@montulli.org</email></address>
4559    </author>
4560    <date year="2000" month="October"/>
4561  </front>
4562  <seriesInfo name="RFC" value="2965"/>
4563</reference>
4564
4565<reference anchor="RFC3040">
4566  <front>
4567    <title>Internet Web Replication and Caching Taxonomy</title>
4568    <author initials="I." surname="Cooper" fullname="I. Cooper">
4569      <organization>Equinix, Inc.</organization>
4570    </author>
4571    <author initials="I." surname="Melve" fullname="I. Melve">
4572      <organization>UNINETT</organization>
4573    </author>
4574    <author initials="G." surname="Tomlinson" fullname="G. Tomlinson">
4575      <organization>CacheFlow Inc.</organization>
4576    </author>
4577    <date year="2001" month="January"/>
4578  </front>
4579  <seriesInfo name="RFC" value="3040"/>
4580</reference>
4581
4582<reference anchor="RFC3864">
4583  <front>
4584    <title>Registration Procedures for Message Header Fields</title>
4585    <author initials="G." surname="Klyne" fullname="G. Klyne">
4586      <organization>Nine by Nine</organization>
4587      <address><email>GK-IETF@ninebynine.org</email></address>
4588    </author>
4589    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
4590      <organization>BEA Systems</organization>
4591      <address><email>mnot@pobox.com</email></address>
4592    </author>
4593    <author initials="J." surname="Mogul" fullname="J. Mogul">
4594      <organization>HP Labs</organization>
4595      <address><email>JeffMogul@acm.org</email></address>
4596    </author>
4597    <date year="2004" month="September"/>
4598  </front>
4599  <seriesInfo name="BCP" value="90"/>
4600  <seriesInfo name="RFC" value="3864"/>
4601</reference>
4602
4603<reference anchor="RFC4033">
4604  <front>
4605    <title>DNS Security Introduction and Requirements</title>
4606    <author initials="R." surname="Arends" fullname="R. Arends"/>
4607    <author initials="R." surname="Austein" fullname="R. Austein"/>
4608    <author initials="M." surname="Larson" fullname="M. Larson"/>
4609    <author initials="D." surname="Massey" fullname="D. Massey"/>
4610    <author initials="S." surname="Rose" fullname="S. Rose"/>
4611    <date year="2005" month="March"/>
4612  </front>
4613  <seriesInfo name="RFC" value="4033"/>
4614</reference>
4615
4616<reference anchor="RFC4288">
4617  <front>
4618    <title>Media Type Specifications and Registration Procedures</title>
4619    <author initials="N." surname="Freed" fullname="N. Freed">
4620      <organization>Sun Microsystems</organization>
4621      <address>
4622        <email>ned.freed@mrochek.com</email>
4623      </address>
4624    </author>
4625    <author initials="J." surname="Klensin" fullname="J. Klensin">
4626      <address>
4627        <email>klensin+ietf@jck.com</email>
4628      </address>
4629    </author>
4630    <date year="2005" month="December"/>
4631  </front>
4632  <seriesInfo name="BCP" value="13"/>
4633  <seriesInfo name="RFC" value="4288"/>
4634</reference>
4635
4636<reference anchor="RFC4395">
4637  <front>
4638    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4639    <author initials="T." surname="Hansen" fullname="T. Hansen">
4640      <organization>AT&amp;T Laboratories</organization>
4641      <address>
4642        <email>tony+urireg@maillennium.att.com</email>
4643      </address>
4644    </author>
4645    <author initials="T." surname="Hardie" fullname="T. Hardie">
4646      <organization>Qualcomm, Inc.</organization>
4647      <address>
4648        <email>hardie@qualcomm.com</email>
4649      </address>
4650    </author>
4651    <author initials="L." surname="Masinter" fullname="L. Masinter">
4652      <organization>Adobe Systems</organization>
4653      <address>
4654        <email>LMM@acm.org</email>
4655      </address>
4656    </author>
4657    <date year="2006" month="February"/>
4658  </front>
4659  <seriesInfo name="BCP" value="115"/>
4660  <seriesInfo name="RFC" value="4395"/>
4661</reference>
4662
4663<reference anchor="RFC4559">
4664  <front>
4665    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4666    <author initials="K." surname="Jaganathan" fullname="K. Jaganathan"/>
4667    <author initials="L." surname="Zhu" fullname="L. Zhu"/>
4668    <author initials="J." surname="Brezak" fullname="J. Brezak"/>
4669    <date year="2006" month="June"/>
4670  </front>
4671  <seriesInfo name="RFC" value="4559"/>
4672</reference>
4673
4674<reference anchor="RFC5226">
4675  <front>
4676    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4677    <author initials="T." surname="Narten" fullname="T. Narten">
4678      <organization>IBM</organization>
4679      <address><email>narten@us.ibm.com</email></address>
4680    </author>
4681    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
4682      <organization>Google</organization>
4683      <address><email>Harald@Alvestrand.no</email></address>
4684    </author>
4685    <date year="2008" month="May"/>
4686  </front>
4687  <seriesInfo name="BCP" value="26"/>
4688  <seriesInfo name="RFC" value="5226"/>
4689</reference>
4690
4691<reference anchor="RFC5322">
4692  <front>
4693    <title>Internet Message Format</title>
4694    <author initials="P." surname="Resnick" fullname="P. Resnick">
4695      <organization>Qualcomm Incorporated</organization>
4696    </author>
4697    <date year="2008" month="October"/>
4698  </front> 
4699  <seriesInfo name="RFC" value="5322"/>
4700</reference>
4701
4702<reference anchor="RFC6265">
4703  <front>
4704    <title>HTTP State Management Mechanism</title>
4705    <author initials="A." surname="Barth" fullname="Adam Barth">
4706      <organization abbrev="U.C. Berkeley">
4707        University of California, Berkeley
4708      </organization>
4709      <address><email>abarth@eecs.berkeley.edu</email></address>
4710    </author>
4711    <date year="2011" month="April"/>
4712  </front>
4713  <seriesInfo name="RFC" value="6265"/>
4714</reference>
4715
4716<!--<reference anchor='BCP97'>
4717  <front>
4718    <title>Handling Normative References to Standards-Track Documents</title>
4719    <author initials='J.' surname='Klensin' fullname='J. Klensin'>
4720      <address>
4721        <email>klensin+ietf@jck.com</email>
4722      </address>
4723    </author>
4724    <author initials='S.' surname='Hartman' fullname='S. Hartman'>
4725      <organization>MIT</organization>
4726      <address>
4727        <email>hartmans-ietf@mit.edu</email>
4728      </address>
4729    </author>
4730    <date year='2007' month='June' />
4731  </front>
4732  <seriesInfo name='BCP' value='97' />
4733  <seriesInfo name='RFC' value='4897' />
4734</reference>-->
4735
4736<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4737  <front>
4738    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4739    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4740    <date year="2001" month="November"/>
4741  </front>
4742  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4743</reference>
4744
4745<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4746  <front>
4747    <title>Analysis of HTTP Performance Problems</title>
4748    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4749    <date/>
4750  </front>
4751</reference>
4752
4753<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4754  <front>
4755  <title>Analysis of HTTP Performance</title>
4756  <author initials="J." surname="Touch" fullname="Joe Touch">
4757    <organization>USC/Information Sciences Institute</organization>
4758    <address><email>touch@isi.edu</email></address>
4759  </author>
4760  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4761    <organization>USC/Information Sciences Institute</organization>
4762    <address><email>johnh@isi.edu</email></address>
4763  </author>
4764  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4765    <organization>USC/Information Sciences Institute</organization>
4766    <address><email>katia@isi.edu</email></address>
4767  </author>
4768  <date year="1998" month="Aug"/>
4769  </front>
4770  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4771  <annotation>(original report dated Aug. 1996)</annotation>
4772</reference>
4773
4774</references>
4775
4776
4777<section title="HTTP Version History" anchor="compatibility">
4778<t>
4779   HTTP has been in use by the World-Wide Web global information initiative
4780   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4781   was a simple protocol for hypertext data transfer across the Internet
4782   with only a single request method (GET) and no metadata.
4783   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4784   methods and MIME-like messaging that could include metadata about the data
4785   transferred and modifiers on the request/response semantics. However,
4786   HTTP/1.0 did not sufficiently take into consideration the effects of
4787   hierarchical proxies, caching, the need for persistent connections, or
4788   name-based virtual hosts. The proliferation of incompletely-implemented
4789   applications calling themselves "HTTP/1.0" further necessitated a
4790   protocol version change in order for two communicating applications
4791   to determine each other's true capabilities.
4792</t>
4793<t>
4794   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4795   requirements that enable reliable implementations, adding only
4796   those new features that will either be safely ignored by an HTTP/1.0
4797   recipient or only sent when communicating with a party advertising
4798   compliance with HTTP/1.1.
4799</t>
4800<t>
4801   It is beyond the scope of a protocol specification to mandate
4802   compliance with previous versions. HTTP/1.1 was deliberately
4803   designed, however, to make supporting previous versions easy.
4804   We would expect a general-purpose HTTP/1.1 server to understand
4805   any valid request in the format of HTTP/1.0 and respond appropriately
4806   with an HTTP/1.1 message that only uses features understood (or
4807   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4808   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4809</t>
4810<t>
4811   Since HTTP/0.9 did not support header fields in a request,
4812   there is no mechanism for it to support name-based virtual
4813   hosts (selection of resource by inspection of the Host header
4814   field).  Any server that implements name-based virtual hosts
4815   ought to disable support for HTTP/0.9.  Most requests that
4816   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4817   requests wherein a buggy client failed to properly encode
4818   linear whitespace found in a URI reference and placed in
4819   the request-target.
4820</t>
4821
4822<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4823<t>
4824   This section summarizes major differences between versions HTTP/1.0
4825   and HTTP/1.1.
4826</t>
4827
4828<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4829<t>
4830   The requirements that clients and servers support the Host header
4831   field (<xref target="header.host"/>), report an error if it is
4832   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4833   are among the most important changes defined by HTTP/1.1.
4834</t>
4835<t>
4836   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4837   addresses and servers; there was no other established mechanism for
4838   distinguishing the intended server of a request than the IP address
4839   to which that request was directed. The Host header field was
4840   introduced during the development of HTTP/1.1 and, though it was
4841   quickly implemented by most HTTP/1.0 browsers, additional requirements
4842   were placed on all HTTP/1.1 requests in order to ensure complete
4843   adoption.  At the time of this writing, most HTTP-based services
4844   are dependent upon the Host header field for targeting requests.
4845</t>
4846</section>
4847
4848<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4849<t>
4850   In HTTP/1.0, each connection is established by the client prior to the
4851   request and closed by the server after sending the response. However, some
4852   implementations implement the explicitly negotiated ("Keep-Alive") version
4853   of persistent connections described in Section 19.7.1 of <xref target="RFC2068"/>.
4854</t>
4855<t>
4856   Some clients and servers might wish to be compatible with these previous
4857   approaches to persistent connections, by explicitly negotiating for them
4858   with a "Connection: keep-alive" request header field. However, some
4859   experimental implementations of HTTP/1.0 persistent connections are faulty;
4860   for example, if a HTTP/1.0 proxy server doesn't understand Connection, it
4861   will erroneously forward that header to the next inbound server, which
4862   would result in a hung connection.
4863</t>
4864<t>
4865   One attempted solution was the introduction of a Proxy-Connection header,
4866   targeted specifically at proxies. In practice, this was also unworkable,
4867   because proxies are often deployed in multiple layers, bringing about the
4868   same problem discussed above.
4869</t>
4870<t>
4871   As a result, clients are encouraged not to send the Proxy-Connection header
4872   in any requests.
4873</t>
4874<t>
4875   Clients are also encouraged to consider the use of Connection: keep-alive
4876   in requests carefully; while they can enable persistent connections with
4877   HTTP/1.0 servers, clients using them need will need to monitor the
4878   connection for "hung" requests (which indicate that the client ought stop
4879   sending the header), and this mechanism ought not be used by clients at all
4880   when a proxy is being used.
4881</t>
4882</section>
4883</section>
4884
4885<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4886<t>
4887  Empty list elements in list productions have been deprecated.
4888  (<xref target="notation.abnf"/>)
4889</t>
4890<t>
4891  Rules about implicit linear whitespace between certain grammar productions
4892  have been removed; now it's only allowed when specifically pointed out
4893  in the ABNF.
4894  (<xref target="basic.rules"/>)
4895</t>
4896<t>
4897  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4898  sensitive. Restrict the version numbers to be single digits due to the fact
4899  that implementations are known to handle multi-digit version numbers
4900  incorrectly.
4901  (<xref target="http.version"/>)
4902</t>
4903<t>
4904  Require that invalid whitespace around field-names be rejected.
4905  (<xref target="header.fields"/>)
4906</t>
4907<t> 
4908  The NUL octet is no longer allowed in comment and quoted-string
4909  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4910  Non-ASCII content in header fields and reason phrase has been obsoleted and
4911  made opaque (the TEXT rule was removed).
4912  (<xref target="field.rules"/>)
4913</t>
4914<t>
4915  Require recipients to handle bogus Content-Length header fields as errors.
4916  (<xref target="message.body"/>)
4917</t>
4918<t>
4919  Remove reference to non-existent identity transfer-coding value tokens.
4920  (Sections <xref format="counter" target="message.body"/> and
4921  <xref format="counter" target="transfer.codings"/>)
4922</t>
4923<t>
4924  Update use of abs_path production from RFC 1808 to the path-absolute + query
4925  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
4926  request method only.
4927  (<xref target="request-target"/>)
4928</t>
4929<t>
4930  Clarification that the chunk length does not include the count of the octets
4931  in the chunk header and trailer. Furthermore disallowed line folding
4932  in chunk extensions.
4933  (<xref target="chunked.encoding"/>)
4934</t>
4935<t>
4936  Remove hard limit of two connections per server.
4937  Remove requirement to retry a sequence of requests as long it was idempotent.
4938  Remove requirements about when servers are allowed to close connections
4939  prematurely.
4940  (<xref target="persistent.practical"/>)
4941</t>
4942<t>
4943  Remove requirement to retry requests under certain cirumstances when the
4944  server prematurely closes the connection.
4945  (<xref target="message.transmission.requirements"/>)
4946</t>
4947<t>
4948  Change ABNF productions for header fields to only define the field value.
4949  (<xref target="header.field.definitions"/>)
4950</t>
4951<t>
4952  Clarify exactly when close connection options must be sent.
4953  (<xref target="header.connection"/>)
4954</t>
4955<t>
4956  Define the semantics of the "Upgrade" header field in responses other than
4957  101 (this was incorporated from <xref target="RFC2817"/>).
4958  (<xref target="header.upgrade"/>)
4959</t>
4960</section>
4961</section>
4962
4963
4964<section title="Collected ABNF" anchor="collected.abnf">
4965<figure>
4966<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
4967BWS = OWS
4968
4969Chunked-Body = *chunk last-chunk trailer-part CRLF
4970Connection = *( "," OWS ) connection-token *( OWS "," [ OWS
4971 connection-token ] )
4972Content-Length = 1*DIGIT
4973
4974HTTP-Prot-Name = %x48.54.54.50 ; HTTP
4975HTTP-Version = HTTP-Prot-Name "/" DIGIT "." DIGIT
4976HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
4977 ]
4978Host = uri-host [ ":" port ]
4979
4980Method = token
4981
4982OWS = *( SP / HTAB / obs-fold )
4983
4984RWS = 1*( SP / HTAB / obs-fold )
4985Reason-Phrase = *( HTAB / SP / VCHAR / obs-text )
4986Request-Line = Method SP request-target SP HTTP-Version CRLF
4987
4988Status-Code = 3DIGIT
4989Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
4990
4991TE = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
4992Trailer = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
4993Transfer-Encoding = *( "," OWS ) transfer-coding *( OWS "," [ OWS
4994 transfer-coding ] )
4995
4996URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
4997Upgrade = *( "," OWS ) product *( OWS "," [ OWS product ] )
4998
4999Via = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5000 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5001 )
5002
5003absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
5004attribute = token
5005authority = <authority, defined in [RFC3986], Section 3.2>
5006
5007chunk = chunk-size [ chunk-ext ] CRLF chunk-data CRLF
5008chunk-data = 1*OCTET
5009chunk-ext = *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
5010chunk-ext-name = token
5011chunk-ext-val = token / quoted-str-nf
5012chunk-size = 1*HEXDIG
5013comment = "(" *( ctext / quoted-cpair / comment ) ")"
5014connection-token = token
5015ctext = OWS / %x21-27 ; '!'-'''
5016 / %x2A-5B ; '*'-'['
5017 / %x5D-7E ; ']'-'~'
5018 / obs-text
5019
5020field-content = *( HTAB / SP / VCHAR / obs-text )
5021field-name = token
5022field-value = *( field-content / obs-fold )
5023
5024header-field = field-name ":" OWS field-value BWS
5025http-URI = "http://" authority path-abempty [ "?" query ]
5026https-URI = "https://" authority path-abempty [ "?" query ]
5027
5028last-chunk = 1*"0" [ chunk-ext ] CRLF
5029
5030message-body = *OCTET
5031
5032obs-fold = CRLF ( SP / HTAB )
5033obs-text = %x80-FF
5034
5035partial-URI = relative-part [ "?" query ]
5036path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
5037path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
5038port = <port, defined in [RFC3986], Section 3.2.3>
5039product = token [ "/" product-version ]
5040product-version = token
5041protocol-name = token
5042protocol-version = token
5043pseudonym = token
5044
5045qdtext = OWS / "!" / %x23-5B ; '#'-'['
5046 / %x5D-7E ; ']'-'~'
5047 / obs-text
5048qdtext-nf = HTAB / SP / "!" / %x23-5B ; '#'-'['
5049 / %x5D-7E ; ']'-'~'
5050 / obs-text
5051query = <query, defined in [RFC3986], Section 3.4>
5052quoted-cpair = "\" ( HTAB / SP / VCHAR / obs-text )
5053quoted-pair = "\" ( HTAB / SP / VCHAR / obs-text )
5054quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5055quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5056qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5057
5058received-by = ( uri-host [ ":" port ] ) / pseudonym
5059received-protocol = [ protocol-name "/" ] protocol-version
5060relative-part = <relative-part, defined in [RFC3986], Section 4.2>
5061request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5062 / authority
5063
5064special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
5065 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5066start-line = Request-Line / Status-Line
5067
5068t-codings = "trailers" / ( transfer-extension [ te-params ] )
5069tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
5070 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5071te-ext = OWS ";" OWS token [ "=" word ]
5072te-params = OWS ";" OWS "q=" qvalue *te-ext
5073token = 1*tchar
5074trailer-part = *( header-field CRLF )
5075transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
5076 transfer-extension
5077transfer-extension = token *( OWS ";" OWS transfer-parameter )
5078transfer-parameter = attribute BWS "=" BWS value
5079
5080uri-host = <host, defined in [RFC3986], Section 3.2.2>
5081
5082value = word
5083
5084word = token / quoted-string
5085]]></artwork>
5086</figure>
5087<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
5088; Chunked-Body defined but not used
5089; Connection defined but not used
5090; Content-Length defined but not used
5091; HTTP-message defined but not used
5092; Host defined but not used
5093; TE defined but not used
5094; Trailer defined but not used
5095; Transfer-Encoding defined but not used
5096; URI-reference defined but not used
5097; Upgrade defined but not used
5098; Via defined but not used
5099; http-URI defined but not used
5100; https-URI defined but not used
5101; partial-URI defined but not used
5102; special defined but not used
5103]]></artwork></figure></section>
5104
5105
5106<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5107
5108<section title="Since RFC 2616">
5109<t>
5110  Extracted relevant partitions from <xref target="RFC2616"/>.
5111</t>
5112</section>
5113
5114<section title="Since draft-ietf-httpbis-p1-messaging-00">
5115<t>
5116  Closed issues:
5117  <list style="symbols"> 
5118    <t>
5119      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5120      "HTTP Version should be case sensitive"
5121      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5122    </t>
5123    <t>
5124      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5125      "'unsafe' characters"
5126      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5127    </t>
5128    <t>
5129      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5130      "Chunk Size Definition"
5131      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5132    </t>
5133    <t>
5134      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5135      "Message Length"
5136      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5137    </t>
5138    <t>
5139      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5140      "Media Type Registrations"
5141      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5142    </t>
5143    <t>
5144      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5145      "URI includes query"
5146      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5147    </t>
5148    <t>
5149      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5150      "No close on 1xx responses"
5151      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5152    </t>
5153    <t>
5154      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5155      "Remove 'identity' token references"
5156      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5157    </t>
5158    <t>
5159      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5160      "Import query BNF"
5161    </t>
5162    <t>
5163      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5164      "qdtext BNF"
5165    </t>
5166    <t>
5167      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5168      "Normative and Informative references"
5169    </t>
5170    <t>
5171      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5172      "RFC2606 Compliance"
5173    </t>
5174    <t>
5175      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5176      "RFC977 reference"
5177    </t>
5178    <t>
5179      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5180      "RFC1700 references"
5181    </t>
5182    <t>
5183      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5184      "inconsistency in date format explanation"
5185    </t>
5186    <t>
5187      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5188      "Date reference typo"
5189    </t>
5190    <t>
5191      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5192      "Informative references"
5193    </t>
5194    <t>
5195      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5196      "ISO-8859-1 Reference"
5197    </t>
5198    <t>
5199      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5200      "Normative up-to-date references"
5201    </t>
5202  </list>
5203</t>
5204<t>
5205  Other changes:
5206  <list style="symbols"> 
5207    <t>
5208      Update media type registrations to use RFC4288 template.
5209    </t>
5210    <t>
5211      Use names of RFC4234 core rules DQUOTE and HTAB,
5212      fix broken ABNF for chunk-data
5213      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5214    </t>
5215  </list>
5216</t>
5217</section>
5218
5219<section title="Since draft-ietf-httpbis-p1-messaging-01">
5220<t>
5221  Closed issues:
5222  <list style="symbols"> 
5223    <t>
5224      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5225      "Bodies on GET (and other) requests"
5226    </t>
5227    <t>
5228      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5229      "Updating to RFC4288"
5230    </t>
5231    <t>
5232      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5233      "Status Code and Reason Phrase"
5234    </t>
5235    <t>
5236      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5237      "rel_path not used"
5238    </t>
5239  </list>
5240</t>
5241<t>
5242  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5243  <list style="symbols"> 
5244    <t>
5245      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
5246      "trailer-part").
5247    </t>
5248    <t>
5249      Avoid underscore character in rule names ("http_URL" -&gt;
5250      "http-URL", "abs_path" -&gt; "path-absolute").
5251    </t>
5252    <t>
5253      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5254      "path-absolute", "port", "query", "relativeURI", "host) — these will
5255      have to be updated when switching over to RFC3986.
5256    </t>
5257    <t>
5258      Synchronize core rules with RFC5234.
5259    </t>
5260    <t>
5261      Get rid of prose rules that span multiple lines.
5262    </t>
5263    <t>
5264      Get rid of unused rules LOALPHA and UPALPHA.
5265    </t>
5266    <t>
5267      Move "Product Tokens" section (back) into Part 1, as "token" is used
5268      in the definition of the Upgrade header field.
5269    </t>
5270    <t>
5271      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5272    </t>
5273    <t>
5274      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5275    </t>
5276  </list>
5277</t>
5278</section>
5279
5280<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5281<t>
5282  Closed issues:
5283  <list style="symbols"> 
5284    <t>
5285      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5286      "HTTP-date vs. rfc1123-date"
5287    </t>
5288    <t>
5289      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5290      "WS in quoted-pair"
5291    </t>
5292  </list>
5293</t>
5294<t>
5295  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5296  <list style="symbols"> 
5297    <t>
5298      Reference RFC 3984, and update header field registrations for headers defined
5299      in this document.
5300    </t>
5301  </list>
5302</t>
5303<t>
5304  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5305  <list style="symbols"> 
5306    <t>
5307      Replace string literals when the string really is case-sensitive (HTTP-Version).
5308    </t>
5309  </list>
5310</t>
5311</section>
5312
5313<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5314<t>
5315  Closed issues:
5316  <list style="symbols"> 
5317    <t>
5318      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5319      "Connection closing"
5320    </t>
5321    <t>
5322      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5323      "Move registrations and registry information to IANA Considerations"
5324    </t>
5325    <t>
5326      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5327      "need new URL for PAD1995 reference"
5328    </t>
5329    <t>
5330      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5331      "IANA Considerations: update HTTP URI scheme registration"
5332    </t>
5333    <t>
5334      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5335      "Cite HTTPS URI scheme definition"
5336    </t>
5337    <t>
5338      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5339      "List-type headers vs Set-Cookie"
5340    </t>
5341  </list>
5342</t>
5343<t>
5344  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5345  <list style="symbols"> 
5346    <t>
5347      Replace string literals when the string really is case-sensitive (HTTP-Date).
5348    </t>
5349    <t>
5350      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5351    </t>
5352  </list>
5353</t>
5354</section>
5355
5356<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5357<t>
5358  Closed issues:
5359  <list style="symbols"> 
5360    <t>
5361      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5362      "Out-of-date reference for URIs"
5363    </t>
5364    <t>
5365      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5366      "RFC 2822 is updated by RFC 5322"
5367    </t>
5368  </list>
5369</t>
5370<t>
5371  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5372  <list style="symbols"> 
5373    <t>
5374      Use "/" instead of "|" for alternatives.
5375    </t>
5376    <t>
5377      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5378    </t>
5379    <t>
5380      Only reference RFC 5234's core rules.
5381    </t>
5382    <t>
5383      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5384      whitespace ("OWS") and required whitespace ("RWS").
5385    </t>
5386    <t>
5387      Rewrite ABNFs to spell out whitespace rules, factor out
5388      header field value format definitions.
5389    </t>
5390  </list>
5391</t>
5392</section>
5393
5394<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5395<t>
5396  Closed issues:
5397  <list style="symbols"> 
5398    <t>
5399      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5400      "Header LWS"
5401    </t>
5402    <t>
5403      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5404      "Sort 1.3 Terminology"
5405    </t>
5406    <t>
5407      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5408      "RFC2047 encoded words"
5409    </t>
5410    <t>
5411      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5412      "Character Encodings in TEXT"
5413    </t>
5414    <t>
5415      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5416      "Line Folding"
5417    </t>
5418    <t>
5419      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5420      "OPTIONS * and proxies"
5421    </t>
5422    <t>
5423      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5424      "Reason-Phrase BNF"
5425    </t>
5426    <t>
5427      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5428      "Use of TEXT"
5429    </t>
5430    <t>
5431      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5432      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5433    </t>
5434    <t>
5435      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5436      "RFC822 reference left in discussion of date formats"
5437    </t>
5438  </list>
5439</t>
5440<t>
5441  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5442  <list style="symbols"> 
5443    <t>
5444      Rewrite definition of list rules, deprecate empty list elements.
5445    </t>
5446    <t>
5447      Add appendix containing collected and expanded ABNF.
5448    </t>
5449  </list>
5450</t>
5451<t>
5452  Other changes:
5453  <list style="symbols"> 
5454    <t>
5455      Rewrite introduction; add mostly new Architecture Section.
5456    </t>
5457    <t>
5458      Move definition of quality values from Part 3 into Part 1;
5459      make TE request header field grammar independent of accept-params (defined in Part 3).
5460    </t>
5461  </list>
5462</t>
5463</section>
5464
5465<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5466<t>
5467  Closed issues:
5468  <list style="symbols"> 
5469    <t>
5470      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5471      "base for numeric protocol elements"
5472    </t>
5473    <t>
5474      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5475      "comment ABNF"
5476    </t>
5477  </list>
5478</t>
5479<t>
5480  Partly resolved issues:
5481  <list style="symbols"> 
5482    <t>
5483      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5484      "205 Bodies" (took out language that implied that there might be
5485      methods for which a request body MUST NOT be included)
5486    </t>
5487    <t>
5488      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5489      "editorial improvements around HTTP-date"
5490    </t>
5491  </list>
5492</t>
5493</section>
5494
5495<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5496<t>
5497  Closed issues:
5498  <list style="symbols"> 
5499    <t>
5500      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5501      "Repeating single-value headers"
5502    </t>
5503    <t>
5504      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5505      "increase connection limit"
5506    </t>
5507    <t>
5508      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5509      "IP addresses in URLs"
5510    </t>
5511    <t>
5512      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5513      "take over HTTP Upgrade Token Registry"
5514    </t>
5515    <t>
5516      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5517      "CR and LF in chunk extension values"
5518    </t>
5519    <t>
5520      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5521      "HTTP/0.9 support"
5522    </t>
5523    <t>
5524      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5525      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5526    </t>
5527    <t>
5528      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5529      "move definitions of gzip/deflate/compress to part 1"
5530    </t>
5531    <t>
5532      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5533      "disallow control characters in quoted-pair"
5534    </t>
5535  </list>
5536</t>
5537<t>
5538  Partly resolved issues:
5539  <list style="symbols"> 
5540    <t>
5541      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5542      "update IANA requirements wrt Transfer-Coding values" (add the
5543      IANA Considerations subsection)
5544    </t>
5545  </list>
5546</t>
5547</section>
5548
5549<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5550<t>
5551  Closed issues:
5552  <list style="symbols"> 
5553    <t>
5554      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5555      "header parsing, treatment of leading and trailing OWS"
5556    </t>
5557  </list>
5558</t>
5559<t>
5560  Partly resolved issues:
5561  <list style="symbols"> 
5562    <t>
5563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5564      "Placement of 13.5.1 and 13.5.2"
5565    </t>
5566    <t>
5567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5568      "use of term "word" when talking about header structure"
5569    </t>
5570  </list>
5571</t>
5572</section>
5573
5574<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5575<t>
5576  Closed issues:
5577  <list style="symbols"> 
5578    <t>
5579      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5580      "Clarification of the term 'deflate'"
5581    </t>
5582    <t>
5583      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5584      "OPTIONS * and proxies"
5585    </t>
5586    <t>
5587      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5588      "MIME-Version not listed in P1, general header fields"
5589    </t>
5590    <t>
5591      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5592      "IANA registry for content/transfer encodings"
5593    </t>
5594    <t>
5595      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5596      "Case-sensitivity of HTTP-date"
5597    </t>
5598    <t>
5599      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5600      "use of term "word" when talking about header structure"
5601    </t>
5602  </list>
5603</t>
5604<t>
5605  Partly resolved issues:
5606  <list style="symbols"> 
5607    <t>
5608      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5609      "Term for the requested resource's URI"
5610    </t>
5611  </list>
5612</t>
5613</section>
5614
5615<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5616<t>
5617  Closed issues:
5618  <list style="symbols">
5619    <t>
5620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5621      "Connection Closing"
5622    </t>
5623    <t>
5624      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5625      "Delimiting messages with multipart/byteranges"
5626    </t>
5627    <t>
5628      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5629      "Handling multiple Content-Length headers"
5630    </t>
5631    <t>
5632      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5633      "Clarify entity / representation / variant terminology"
5634    </t>
5635    <t>
5636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5637      "consider removing the 'changes from 2068' sections"
5638    </t>
5639  </list>
5640</t>
5641<t>
5642  Partly resolved issues:
5643  <list style="symbols"> 
5644    <t>
5645      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5646      "HTTP(s) URI scheme definitions"
5647    </t>
5648  </list>
5649</t>
5650</section>
5651
5652<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5653<t>
5654  Closed issues:
5655  <list style="symbols">
5656    <t>
5657      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5658      "Trailer requirements"
5659    </t>
5660    <t>
5661      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5662      "Text about clock requirement for caches belongs in p6"
5663    </t>
5664    <t>
5665      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5666      "effective request URI: handling of missing host in HTTP/1.0"
5667    </t>
5668    <t>
5669      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5670      "confusing Date requirements for clients"
5671    </t>
5672  </list>
5673</t>
5674<t>
5675  Partly resolved issues:
5676  <list style="symbols"> 
5677    <t>
5678      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5679      "Handling multiple Content-Length headers"
5680    </t>
5681  </list>
5682</t>
5683</section>
5684
5685<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5686<t>
5687  Closed issues:
5688  <list style="symbols">
5689    <t>
5690      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5691      "RFC2145 Normative"
5692    </t>
5693    <t>
5694      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5695      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5696    </t>
5697    <t>
5698      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5699      "define 'transparent' proxy"
5700    </t>
5701    <t>
5702      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5703      "Header Classification"
5704    </t>
5705    <t>
5706      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5707      "Is * usable as a request-uri for new methods?"
5708    </t>
5709    <t>
5710      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5711      "Migrate Upgrade details from RFC2817"
5712    </t>
5713    <t>
5714      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5715      "untangle ABNFs for header fields"
5716    </t>
5717    <t>
5718      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5719      "update RFC 2109 reference"
5720    </t>
5721  </list>
5722</t>
5723</section>
5724
5725<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5726<t>
5727  Closed issues:
5728  <list style="symbols">
5729    <t>
5730      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5731      "Allow is not in 13.5.2"
5732    </t>
5733    <t>
5734      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5735      "Handling multiple Content-Length headers"
5736    </t>
5737    <t>
5738      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5739      "untangle ABNFs for header fields"
5740    </t>
5741    <t>
5742      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5743      "Content-Length ABNF broken"
5744    </t>
5745  </list>
5746</t>
5747</section>
5748
5749<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5750<t>
5751  Closed issues:
5752  <list style="symbols">
5753    <t>
5754      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5755      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5756    </t>
5757    <t>
5758      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5759      "Recommend minimum sizes for protocol elements"
5760    </t>
5761    <t>
5762      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5763      "Set expectations around buffering"
5764    </t>
5765    <t>
5766      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5767      "Considering messages in isolation"
5768    </t>
5769  </list>
5770</t>
5771</section>
5772
5773<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5774<t>
5775  Closed issues:
5776  <list style="symbols">
5777    <t>
5778      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5779      "DNS Spoofing / DNS Binding advice"
5780    </t>
5781    <t>
5782      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5783      "move RFCs 2145, 2616, 2817 to Historic status"
5784    </t>
5785    <t>
5786      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5787      "\-escaping in quoted strings"
5788    </t>
5789    <t>
5790      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5791      "'Close' should be reserved in the HTTP header field registry"
5792    </t>
5793  </list>
5794</t>
5795</section>
5796
5797<section title="Since draft-ietf-httpbis-p1-messaging-16" anchor="changes.since.16">
5798<t>
5799  Closed issues:
5800  <list style="symbols">
5801    <t>
5802      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/186"/>:
5803      "Document HTTP's error-handling philosophy"
5804    </t>
5805    <t>
5806      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/215"/>:
5807      "Explain header registration"
5808    </t>
5809    <t>
5810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/219"/>:
5811      "Revise Acknowledgements Sections"
5812    </t>
5813    <t>
5814      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/297"/>:
5815      "Retrying Requests"
5816    </t>
5817    <t>
5818      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/318"/>:
5819      "Closing the connection on server error"
5820    </t>
5821  </list>
5822</t>
5823</section>
5824
5825<section title="Since draft-ietf-httpbis-p1-messaging-17" anchor="changes.since.17">
5826<t>
5827  Closed issues:
5828  <list style="symbols">
5829    <t>
5830      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/166"/>:
5831      "Clarify 'User Agent'"
5832    </t>
5833    <t>
5834      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/300"/>:
5835      "Define non-final responses"
5836    </t>
5837    <t>
5838      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/323"/>:
5839      "intended maturity level vs normative references"
5840    </t>
5841    <t>
5842      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/324"/>:
5843      "Intermediary rewriting of queries"
5844    </t>
5845    <t>
5846      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/158"/>:
5847      "Proxy-Connection and Keep-Alive"
5848    </t>
5849  </list>
5850</t>
5851</section>
5852
5853</section>
5854
5855</back>
5856</rfc>
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