source: draft-ietf-httpbis/16/draft-ietf-httpbis-p1-messaging-16.xml @ 1860

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fix mime types

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  • Property svn:mime-type set to text/xml
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1<?xml version="1.0" encoding="UTF-8"?>
2<!--
3    This XML document is the output of clean-for-DTD.xslt; a tool that strips
4    extensions to RFC2629(bis) from documents for processing with xml2rfc.
5-->
6<?xml-stylesheet type='text/xsl' href='../myxml2rfc.xslt'?>
7<?rfc toc="yes" ?>
8<?rfc symrefs="yes" ?>
9<?rfc sortrefs="yes" ?>
10<?rfc compact="yes"?>
11<?rfc subcompact="no" ?>
12<?rfc linkmailto="no" ?>
13<?rfc editing="no" ?>
14<?rfc comments="yes"?>
15<?rfc inline="yes"?>
16<?rfc rfcedstyle="yes"?>
17<!DOCTYPE rfc
18  PUBLIC "" "rfc2629.dtd">
19<rfc obsoletes="2145,2616" updates="2817" category="std" ipr="pre5378Trust200902" docName="draft-ietf-httpbis-p1-messaging-16">
20<front>
21
22  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
23
24  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
25    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
26    <address>
27      <postal>
28        <street>345 Park Ave</street>
29        <city>San Jose</city>
30        <region>CA</region>
31        <code>95110</code>
32        <country>USA</country>
33      </postal>
34      <email>fielding@gbiv.com</email>
35      <uri>http://roy.gbiv.com/</uri>
36    </address>
37  </author>
38
39  <author initials="J." surname="Gettys" fullname="Jim Gettys">
40    <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
41    <address>
42      <postal>
43        <street>21 Oak Knoll Road</street>
44        <city>Carlisle</city>
45        <region>MA</region>
46        <code>01741</code>
47        <country>USA</country>
48      </postal>
49      <email>jg@freedesktop.org</email>
50      <uri>http://gettys.wordpress.com/</uri>
51    </address>
52  </author>
53 
54  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
55    <organization abbrev="HP">Hewlett-Packard Company</organization>
56    <address>
57      <postal>
58        <street>HP Labs, Large Scale Systems Group</street>
59        <street>1501 Page Mill Road, MS 1177</street>
60        <city>Palo Alto</city>
61        <region>CA</region>
62        <code>94304</code>
63        <country>USA</country>
64      </postal>
65      <email>JeffMogul@acm.org</email>
66    </address>
67  </author>
68
69  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
70    <organization abbrev="Microsoft">Microsoft Corporation</organization>
71    <address>
72      <postal>
73        <street>1 Microsoft Way</street>
74        <city>Redmond</city>
75        <region>WA</region>
76        <code>98052</code>
77        <country>USA</country>
78      </postal>
79      <email>henrikn@microsoft.com</email>
80    </address>
81  </author>
82
83  <author initials="L." surname="Masinter" fullname="Larry Masinter">
84    <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
85    <address>
86      <postal>
87        <street>345 Park Ave</street>
88        <city>San Jose</city>
89        <region>CA</region>
90        <code>95110</code>
91        <country>USA</country>
92      </postal>
93      <email>LMM@acm.org</email>
94      <uri>http://larry.masinter.net/</uri>
95    </address>
96  </author>
97 
98  <author initials="P." surname="Leach" fullname="Paul J. Leach">
99    <organization abbrev="Microsoft">Microsoft Corporation</organization>
100    <address>
101      <postal>
102        <street>1 Microsoft Way</street>
103        <city>Redmond</city>
104        <region>WA</region>
105        <code>98052</code>
106      </postal>
107      <email>paulle@microsoft.com</email>
108    </address>
109  </author>
110   
111  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
112    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
113    <address>
114      <postal>
115        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
116        <street>The Stata Center, Building 32</street>
117        <street>32 Vassar Street</street>
118        <city>Cambridge</city>
119        <region>MA</region>
120        <code>02139</code>
121        <country>USA</country>
122      </postal>
123      <email>timbl@w3.org</email>
124      <uri>http://www.w3.org/People/Berners-Lee/</uri>
125    </address>
126  </author>
127
128  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
129    <organization abbrev="W3C">World Wide Web Consortium</organization>
130    <address>
131      <postal>
132        <street>W3C / ERCIM</street>
133        <street>2004, rte des Lucioles</street>
134        <city>Sophia-Antipolis</city>
135        <region>AM</region>
136        <code>06902</code>
137        <country>France</country>
138      </postal>
139      <email>ylafon@w3.org</email>
140      <uri>http://www.raubacapeu.net/people/yves/</uri>
141    </address>
142  </author>
143
144  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
145    <organization abbrev="greenbytes">greenbytes GmbH</organization>
146    <address>
147      <postal>
148        <street>Hafenweg 16</street>
149        <city>Muenster</city><region>NW</region><code>48155</code>
150        <country>Germany</country>
151      </postal>
152      <phone>+49 251 2807760</phone>
153      <facsimile>+49 251 2807761</facsimile>
154      <email>julian.reschke@greenbytes.de</email>
155      <uri>http://greenbytes.de/tech/webdav/</uri>
156    </address>
157  </author>
158
159  <date month="August" year="2011" day="24"/>
160  <workgroup>HTTPbis Working Group</workgroup>
161
162<abstract>
163<t>
164   The Hypertext Transfer Protocol (HTTP) is an application-level protocol for
165   distributed, collaborative, hypertext information systems. HTTP has been in
166   use by the World Wide Web global information initiative since 1990. This
167   document is Part 1 of the seven-part specification that defines the protocol
168   referred to as "HTTP/1.1" and, taken together, obsoletes
169   RFC 2616 and moves it to historic
170   status, along with its predecessor RFC
171   2068.
172</t>
173<t>
174   Part 1 provides an overview of HTTP and its associated terminology, defines
175   the "http" and "https" Uniform Resource Identifier (URI) schemes, defines
176   the generic message syntax and parsing requirements for HTTP message frames,
177   and describes general security concerns for implementations.
178</t>
179<t>
180   This part also obsoletes RFCs 2145
181   (on HTTP version numbers) and 2817
182   (on using CONNECT for TLS upgrades) and moves them to historic status.
183</t>
184</abstract>
185
186<note title="Editorial Note (To be removed by RFC Editor)">
187  <t>
188    Discussion of this draft should take place on the HTTPBIS working group
189    mailing list (ietf-http-wg@w3.org), which is archived at
190    <eref target="http://lists.w3.org/Archives/Public/ietf-http-wg/"/>.
191  </t>
192  <t>
193    The current issues list is at
194    <eref target="http://tools.ietf.org/wg/httpbis/trac/report/3"/> and related
195    documents (including fancy diffs) can be found at
196    <eref target="http://tools.ietf.org/wg/httpbis/"/>.
197  </t>
198  <t>
199    The changes in this draft are summarized in <xref target="changes.since.15"/>.
200  </t>
201</note>
202</front>
203<middle>
204<section title="Introduction" anchor="introduction">
205<t>
206   The Hypertext Transfer Protocol (HTTP) is an application-level
207   request/response protocol that uses extensible semantics and MIME-like
208   message payloads for flexible interaction with network-based hypertext
209   information systems. HTTP relies upon the Uniform Resource Identifier (URI)
210   standard <xref target="RFC3986"/> to indicate the target resource and
211   relationships between resources.
212   Messages are passed in a format similar to that used by Internet mail
213   <xref target="RFC5322"/> and the Multipurpose Internet Mail Extensions
214   (MIME) <xref target="RFC2045"/> (see Appendix A of <xref target="Part3"/> for the differences
215   between HTTP and MIME messages).
216</t>
217<t>
218   HTTP is a generic interface protocol for information systems. It is
219   designed to hide the details of how a service is implemented by presenting
220   a uniform interface to clients that is independent of the types of
221   resources provided. Likewise, servers do not need to be aware of each
222   client's purpose: an HTTP request can be considered in isolation rather
223   than being associated with a specific type of client or a predetermined
224   sequence of application steps. The result is a protocol that can be used
225   effectively in many different contexts and for which implementations can
226   evolve independently over time.
227</t>
228<t>
229   HTTP is also designed for use as an intermediation protocol for translating
230   communication to and from non-HTTP information systems.
231   HTTP proxies and gateways can provide access to alternative information
232   services by translating their diverse protocols into a hypertext
233   format that can be viewed and manipulated by clients in the same way
234   as HTTP services.
235</t>
236<t>
237   One consequence of HTTP flexibility is that the protocol cannot be
238   defined in terms of what occurs behind the interface. Instead, we
239   are limited to defining the syntax of communication, the intent
240   of received communication, and the expected behavior of recipients.
241   If the communication is considered in isolation, then successful
242   actions ought to be reflected in corresponding changes to the
243   observable interface provided by servers. However, since multiple
244   clients might act in parallel and perhaps at cross-purposes, we
245   cannot require that such changes be observable beyond the scope
246   of a single response.
247</t>
248<t>
249   This document is Part 1 of the seven-part specification of HTTP,
250   defining the protocol referred to as "HTTP/1.1", obsoleting
251   <xref target="RFC2616"/> and <xref target="RFC2145"/>.
252   Part 1 describes the architectural elements that are used or
253   referred to in HTTP, defines the "http" and "https" URI schemes,
254   describes overall network operation and connection management,
255   and defines HTTP message framing and forwarding requirements.
256   Our goal is to define all of the mechanisms necessary for HTTP message
257   handling that are independent of message semantics, thereby defining the
258   complete set of requirements for message parsers and
259   message-forwarding intermediaries.
260</t>
261
262<section title="Requirements" anchor="intro.requirements">
263<t>
264   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
265   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
266   document are to be interpreted as described in <xref target="RFC2119"/>.
267</t>
268<t>
269   An implementation is not compliant if it fails to satisfy one or more
270   of the "MUST" or "REQUIRED" level requirements for the protocols it
271   implements. An implementation that satisfies all the "MUST" or "REQUIRED"
272   level and all the "SHOULD" level requirements for its protocols is said
273   to be "unconditionally compliant"; one that satisfies all the "MUST"
274   level requirements but not all the "SHOULD" level requirements for its
275   protocols is said to be "conditionally compliant".
276</t>
277</section>
278
279<section title="Syntax Notation" anchor="notation">
280<iref primary="true" item="Grammar" subitem="ALPHA"/>
281<iref primary="true" item="Grammar" subitem="CR"/>
282<iref primary="true" item="Grammar" subitem="CRLF"/>
283<iref primary="true" item="Grammar" subitem="CTL"/>
284<iref primary="true" item="Grammar" subitem="DIGIT"/>
285<iref primary="true" item="Grammar" subitem="DQUOTE"/>
286<iref primary="true" item="Grammar" subitem="HEXDIG"/>
287<iref primary="true" item="Grammar" subitem="LF"/>
288<iref primary="true" item="Grammar" subitem="OCTET"/>
289<iref primary="true" item="Grammar" subitem="SP"/>
290<iref primary="true" item="Grammar" subitem="VCHAR"/>
291<iref primary="true" item="Grammar" subitem="WSP"/>
292<t>
293   This specification uses the Augmented Backus-Naur Form (ABNF) notation
294   of <xref target="RFC5234"/>.
295</t>
296<t anchor="core.rules">
297 
298 
299 
300 
301 
302 
303 
304 
305 
306 
307 
308 
309   The following core rules are included by
310   reference, as defined in <xref target="RFC5234"/>, Appendix B.1:
311   ALPHA (letters), CR (carriage return), CRLF (CR LF), CTL (controls),
312   DIGIT (decimal 0-9), DQUOTE (double quote),
313   HEXDIG (hexadecimal 0-9/A-F/a-f), LF (line feed),
314   OCTET (any 8-bit sequence of data), SP (space),
315   VCHAR (any visible <xref target="USASCII"/> character),
316   and WSP (whitespace).
317</t>
318<t>
319   As a syntactic convention, ABNF rule names prefixed with "obs-" denote
320   "obsolete" grammar rules that appear for historical reasons.
321</t>
322
323<section title="ABNF Extension: #rule" anchor="notation.abnf">
324<t>
325  The #rule extension to the ABNF rules of <xref target="RFC5234"/> is used to
326  improve readability.
327</t>
328<t>
329  A construct "#" is defined, similar to "*", for defining comma-delimited
330  lists of elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating
331  at least &lt;n&gt; and at most &lt;m&gt; elements, each separated by a single
332  comma (",") and optional whitespace (OWS, <xref target="basic.rules"/>).   
333</t>
334<figure><preamble>
335  Thus,
336</preamble><artwork type="example"><![CDATA[
337  1#element => element *( OWS "," OWS element )
338]]></artwork></figure>
339<figure><preamble>
340  and:
341</preamble><artwork type="example"><![CDATA[
342  #element => [ 1#element ]
343]]></artwork></figure>
344<figure><preamble>
345  and for n &gt;= 1 and m &gt; 1:
346</preamble><artwork type="example"><![CDATA[
347  <n>#<m>element => element <n-1>*<m-1>( OWS "," OWS element )
348]]></artwork></figure>
349<t>
350  For compatibility with legacy list rules, recipients SHOULD accept empty
351  list elements. In other words, consumers would follow the list productions:
352</t>
353<figure><artwork type="example"><![CDATA[
354  #element => [ ( "," / element ) *( OWS "," [ OWS element ] ) ]
355 
356  1#element => *( "," OWS ) element *( OWS "," [ OWS element ] )
357]]></artwork></figure>
358<t>
359  Note that empty elements do not contribute to the count of elements present,
360  though.
361</t>
362<t>
363  For example, given these ABNF productions:
364</t>
365<figure><artwork type="example"><![CDATA[
366  example-list      = 1#example-list-elmt
367  example-list-elmt = token ; see Section 3.2.3
368]]></artwork></figure>
369<t>
370  Then these are valid values for example-list (not including the double
371  quotes, which are present for delimitation only):
372</t>
373<figure><artwork type="example"><![CDATA[
374  "foo,bar"
375  " foo ,bar,"
376  "  foo , ,bar,charlie   "
377  "foo ,bar,   charlie "
378]]></artwork></figure>
379<t>
380  But these values would be invalid, as at least one non-empty element is
381  required:
382</t>
383<figure><artwork type="example"><![CDATA[
384  ""
385  ","
386  ",   ,"
387]]></artwork></figure>
388<t>
389  <xref target="collected.abnf"/> shows the collected ABNF, with the list rules
390  expanded as explained above.
391</t>
392</section>
393
394<section title="Basic Rules" anchor="basic.rules">
395<t anchor="rule.LWS">
396   This specification uses three rules to denote the use of linear
397   whitespace: OWS (optional whitespace), RWS (required whitespace), and
398   BWS ("bad" whitespace).
399</t>
400<t anchor="rule.OWS">
401   The OWS rule is used where zero or more linear whitespace octets might
402   appear. OWS SHOULD either not be produced or be produced as a single
403   SP. Multiple OWS octets that occur within field-content SHOULD either
404   be replaced with a single SP or transformed to all SP octets (each WSP
405   octet other than SP replaced with SP) before interpreting the field value
406   or forwarding the message downstream.
407</t>
408<t anchor="rule.RWS">
409   RWS is used when at least one linear whitespace octet is required to
410   separate field tokens. RWS SHOULD be produced as a single SP.
411   Multiple RWS octets octets that occur within field-content SHOULD either
412   be replaced with a single SP or transformed to all SP octets (each WSP
413   octet other than SP replaced with SP) before interpreting the field value
414   or forwarding the message downstream.
415</t>
416<t anchor="rule.BWS">
417   BWS is used where the grammar allows optional whitespace for historical
418   reasons but senders SHOULD NOT produce it in messages. HTTP/1.1
419   recipients MUST accept such bad optional whitespace and remove it before
420   interpreting the field value or forwarding the message downstream.
421</t>
422<t anchor="rule.whitespace">
423 
424 
425 
426 
427</t>
428<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[
429  OWS            = *( [ obs-fold ] WSP )
430                 ; "optional" whitespace
431  RWS            = 1*( [ obs-fold ] WSP )
432                 ; "required" whitespace
433  BWS            = OWS
434                 ; "bad" whitespace
435  obs-fold       = CRLF
436                 ; see Section 3.2
437]]></artwork></figure>
438</section>
439</section>
440</section>
441
442<section title="HTTP-related architecture" anchor="architecture">
443<t>
444   HTTP was created for the World Wide Web architecture
445   and has evolved over time to support the scalability needs of a worldwide
446   hypertext system. Much of that architecture is reflected in the terminology
447   and syntax productions used to define HTTP.
448</t>
449
450<section title="Client/Server Messaging" anchor="operation">
451<iref primary="true" item="client"/>
452<iref primary="true" item="server"/>
453<iref primary="true" item="connection"/>
454<t>
455   HTTP is a stateless request/response protocol that operates by exchanging
456   messages across a reliable transport or session-layer
457   "connection". An HTTP "client" is a
458   program that establishes a connection to a server for the purpose of
459   sending one or more HTTP requests.  An HTTP "server" is a
460   program that accepts connections in order to service HTTP requests by
461   sending HTTP responses.
462</t>
463<iref primary="true" item="user agent"/>
464<iref primary="true" item="origin server"/>
465<iref primary="true" item="browser"/>
466<iref primary="true" item="spider"/>
467<iref primary="true" item="sender"/>
468<iref primary="true" item="recipient"/>
469<t>
470   Note that the terms client and server refer only to the roles that
471   these programs perform for a particular connection.  The same program
472   might act as a client on some connections and a server on others.  We use
473   the term "user agent" to refer to the program that initiates a request,
474   such as a WWW browser, editor, or spider (web-traversing robot), and
475   the term "origin server" to refer to the program that can originate
476   authoritative responses to a request.  For general requirements, we use
477   the term "sender" to refer to whichever component sent a given message
478   and the term "recipient" to refer to any component that receives the
479   message.
480</t>
481<t>
482   Most HTTP communication consists of a retrieval request (GET) for
483   a representation of some resource identified by a URI.  In the
484   simplest case, this might be accomplished via a single bidirectional
485   connection (===) between the user agent (UA) and the origin server (O).
486</t>
487<figure><artwork type="drawing"><![CDATA[
488         request   >
489    UA ======================================= O
490                                <   response
491]]></artwork></figure>
492<iref primary="true" item="message"/>
493<iref primary="true" item="request"/>
494<iref primary="true" item="response"/>
495<t>
496   A client sends an HTTP request to the server in the form of a request
497   message (<xref target="request"/>), beginning with a method, URI, and
498   protocol version, followed by MIME-like header fields containing
499   request modifiers, client information, and payload metadata, an empty
500   line to indicate the end of the header section, and finally the payload
501   body (if any).
502</t>
503<t>
504   A server responds to the client's request by sending an HTTP response
505   message (<xref target="response"/>), beginning with a status line that
506   includes the protocol version, a success or error code, and textual
507   reason phrase, followed by MIME-like header fields containing server
508   information, resource metadata, and payload metadata, an empty line to
509   indicate the end of the header section, and finally the payload body (if any).
510</t>
511<t>
512   The following example illustrates a typical message exchange for a
513   GET request on the URI "http://www.example.com/hello.txt":
514</t>
515<figure><preamble>
516client request:
517</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
518  GET /hello.txt HTTP/1.1
519  User-Agent: curl/7.16.3 libcurl/7.16.3 OpenSSL/0.9.7l zlib/1.2.3
520  Host: www.example.com
521  Accept: */*
522 
523  ]]></artwork></figure>
524<figure><preamble>
525server response:
526</preamble><artwork type="message/http; msgtype=&#34;response&#34;"><![CDATA[
527  HTTP/1.1 200 OK
528  Date: Mon, 27 Jul 2009 12:28:53 GMT
529  Server: Apache
530  Last-Modified: Wed, 22 Jul 2009 19:15:56 GMT
531  ETag: "34aa387-d-1568eb00"
532  Accept-Ranges: bytes
533  Content-Length: 14
534  Vary: Accept-Encoding
535  Content-Type: text/plain
536 
537  Hello World!
538  ]]></artwork></figure>
539</section>
540
541<section title="Message Orientation and Buffering" anchor="message-orientation-and-buffering">
542<t>
543   Fundamentally, HTTP is a message-based protocol. Although message bodies can
544   be chunked (<xref target="chunked.encoding"/>) and implementations often
545   make parts of a message available progressively, this is not required, and
546   some widely-used implementations only make a message available when it is
547   complete. Furthermore, while most proxies will progressively stream messages,
548   some amount of buffering will take place, and some proxies might buffer
549   messages to perform transformations, check content or provide other services.
550</t>
551<t>
552   Therefore, extensions to and uses of HTTP cannot rely on the availability of
553   a partial message, or assume that messages will not be buffered. There are
554   strategies that can be used to test for buffering in a given connection, but
555   it should be understood that behaviors can differ across connections, and
556   between requests and responses.
557</t>
558<t>
559   Recipients MUST consider every message in a connection in isolation;
560   because HTTP is a stateless protocol, it cannot be assumed that two requests
561   on the same connection are from the same client or share any other common
562   attributes. In particular, intermediaries might mix requests from different
563   clients into a single server connection. Note that some existing HTTP
564   extensions (e.g., <xref target="RFC4559"/>) violate this requirement, thereby
565   potentially causing interoperability and security problems.
566</t>
567</section>
568
569<section title="Connections and Transport Independence" anchor="transport-independence">
570<t>
571   HTTP messaging is independent of the underlying transport or
572   session-layer connection protocol(s).  HTTP only presumes a reliable
573   transport with in-order delivery of requests and the corresponding
574   in-order delivery of responses.  The mapping of HTTP request and
575   response structures onto the data units of the underlying transport
576   protocol is outside the scope of this specification.
577</t>
578<t>
579   The specific connection protocols to be used for an interaction
580   are determined by client configuration and the target resource's URI.
581   For example, the "http" URI scheme
582   (<xref target="http.uri"/>) indicates a default connection of TCP
583   over IP, with a default TCP port of 80, but the client might be
584   configured to use a proxy via some other connection port or protocol
585   instead of using the defaults.
586</t>
587<t>
588   A connection might be used for multiple HTTP request/response exchanges,
589   as defined in <xref target="persistent.connections"/>.
590</t>
591</section>
592
593<section title="Intermediaries" anchor="intermediaries">
594<iref primary="true" item="intermediary"/>
595<t>
596   HTTP enables the use of intermediaries to satisfy requests through
597   a chain of connections.  There are three common forms of HTTP
598   intermediary: proxy, gateway, and tunnel.  In some cases,
599   a single intermediary might act as an origin server, proxy, gateway,
600   or tunnel, switching behavior based on the nature of each request.
601</t>
602<figure><artwork type="drawing"><![CDATA[
603         >             >             >             >
604    UA =========== A =========== B =========== C =========== O
605               <             <             <             <
606]]></artwork></figure>
607<t>
608   The figure above shows three intermediaries (A, B, and C) between the
609   user agent and origin server. A request or response message that
610   travels the whole chain will pass through four separate connections.
611   Some HTTP communication options
612   might apply only to the connection with the nearest, non-tunnel
613   neighbor, only to the end-points of the chain, or to all connections
614   along the chain. Although the diagram is linear, each participant might
615   be engaged in multiple, simultaneous communications. For example, B
616   might be receiving requests from many clients other than A, and/or
617   forwarding requests to servers other than C, at the same time that it
618   is handling A's request.
619</t>
620<t>
621<iref primary="true" item="upstream"/><iref primary="true" item="downstream"/>
622<iref primary="true" item="inbound"/><iref primary="true" item="outbound"/>
623   We use the terms "upstream" and "downstream"
624   to describe various requirements in relation to the directional flow of a
625   message: all messages flow from upstream to downstream.
626   Likewise, we use the terms inbound and outbound to refer to
627   directions in relation to the request path:
628   "inbound" means toward the origin server and
629   "outbound" means toward the user agent.
630</t>
631<t><iref primary="true" item="proxy"/>
632   A "proxy" is a message forwarding agent that is selected by the
633   client, usually via local configuration rules, to receive requests
634   for some type(s) of absolute URI and attempt to satisfy those
635   requests via translation through the HTTP interface.  Some translations
636   are minimal, such as for proxy requests for "http" URIs, whereas
637   other requests might require translation to and from entirely different
638   application-layer protocols. Proxies are often used to group an
639   organization's HTTP requests through a common intermediary for the
640   sake of security, annotation services, or shared caching.
641</t>
642<t>
643<iref primary="true" item="transforming proxy"/>
644<iref primary="true" item="non-transforming proxy"/>
645   An HTTP-to-HTTP proxy is called a "transforming proxy" if it is designed
646   or configured to modify request or response messages in a semantically
647   meaningful way (i.e., modifications, beyond those required by normal
648   HTTP processing, that change the message in a way that would be
649   significant to the original sender or potentially significant to
650   downstream recipients).  For example, a transforming proxy might be
651   acting as a shared annotation server (modifying responses to include
652   references to a local annotation database), a malware filter, a
653   format transcoder, or an intranet-to-Internet privacy filter.  Such
654   transformations are presumed to be desired by the client (or client
655   organization) that selected the proxy and are beyond the scope of
656   this specification.  However, when a proxy is not intended to transform
657   a given message, we use the term "non-transforming proxy" to target
658   requirements that preserve HTTP message semantics. See Section 8.2.4 of <xref target="Part2"/> and
659   Section 3.6 of <xref target="Part6"/> for status and warning codes related to transformations.
660</t>
661<t><iref primary="true" item="gateway"/><iref primary="true" item="reverse proxy"/>
662<iref primary="true" item="accelerator"/>
663   A "gateway" (a.k.a., "reverse proxy")
664   is a receiving agent that acts
665   as a layer above some other server(s) and translates the received
666   requests to the underlying server's protocol.  Gateways are often
667   used to encapsulate legacy or untrusted information services, to
668   improve server performance through "accelerator" caching, and to
669   enable partitioning or load-balancing of HTTP services across
670   multiple machines.
671</t>
672<t>
673   A gateway behaves as an origin server on its outbound connection and
674   as a user agent on its inbound connection.
675   All HTTP requirements applicable to an origin server
676   also apply to the outbound communication of a gateway.
677   A gateway communicates with inbound servers using any protocol that
678   it desires, including private extensions to HTTP that are outside
679   the scope of this specification.  However, an HTTP-to-HTTP gateway
680   that wishes to interoperate with third-party HTTP servers MUST
681   comply with HTTP user agent requirements on the gateway's inbound
682   connection and MUST implement the Connection
683   (<xref target="header.connection"/>) and Via (<xref target="header.via"/>)
684   header fields for both connections.
685</t>
686<t><iref primary="true" item="tunnel"/>
687   A "tunnel" acts as a blind relay between two connections
688   without changing the messages. Once active, a tunnel is not
689   considered a party to the HTTP communication, though the tunnel might
690   have been initiated by an HTTP request. A tunnel ceases to exist when
691   both ends of the relayed connection are closed. Tunnels are used to
692   extend a virtual connection through an intermediary, such as when
693   transport-layer security is used to establish private communication
694   through a shared firewall proxy.
695</t>
696<t><iref primary="true" item="interception proxy"/><iref primary="true" item="transparent proxy"/>
697<iref primary="true" item="captive portal"/>
698   In addition, there may exist network intermediaries that are not
699   considered part of the HTTP communication but nevertheless act as
700   filters or redirecting agents (usually violating HTTP semantics,
701   causing security problems, and otherwise making a mess of things).
702   Such a network intermediary, often referred to as an "interception proxy"
703   <xref target="RFC3040"/>, "transparent proxy" <xref target="RFC1919"/>,
704   or "captive portal",
705   differs from an HTTP proxy because it has not been selected by the client.
706   Instead, the network intermediary redirects outgoing TCP port 80 packets
707   (and occasionally other common port traffic) to an internal HTTP server.
708   Interception proxies are commonly found on public network access points,
709   as a means of enforcing account subscription prior to allowing use of
710   non-local Internet services, and within corporate firewalls to enforce
711   network usage policies.
712   They are indistinguishable from a man-in-the-middle attack.
713</t>
714</section>
715
716<section title="Caches" anchor="caches">
717<iref primary="true" item="cache"/>
718<t>
719   A "cache" is a local store of previous response messages and the
720   subsystem that controls its message storage, retrieval, and deletion.
721   A cache stores cacheable responses in order to reduce the response
722   time and network bandwidth consumption on future, equivalent
723   requests. Any client or server MAY employ a cache, though a cache
724   cannot be used by a server while it is acting as a tunnel.
725</t>
726<t>
727   The effect of a cache is that the request/response chain is shortened
728   if one of the participants along the chain has a cached response
729   applicable to that request. The following illustrates the resulting
730   chain if B has a cached copy of an earlier response from O (via C)
731   for a request which has not been cached by UA or A.
732</t>
733<figure><artwork type="drawing"><![CDATA[
734            >             >
735       UA =========== A =========== B - - - - - - C - - - - - - O
736                  <             <
737]]></artwork></figure>
738<t><iref primary="true" item="cacheable"/>
739   A response is "cacheable" if a cache is allowed to store a copy of
740   the response message for use in answering subsequent requests.
741   Even when a response is cacheable, there might be additional
742   constraints placed by the client or by the origin server on when
743   that cached response can be used for a particular request. HTTP
744   requirements for cache behavior and cacheable responses are
745   defined in Section 2 of <xref target="Part6"/>
746</t>
747<t>
748   There are a wide variety of architectures and configurations
749   of caches and proxies deployed across the World Wide Web and
750   inside large organizations. These systems include national hierarchies
751   of proxy caches to save transoceanic bandwidth, systems that
752   broadcast or multicast cache entries, organizations that distribute
753   subsets of cached data via optical media, and so on.
754</t>
755</section>
756
757<section title="Protocol Versioning" anchor="http.version">
758 
759 
760<t>
761   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate
762   versions of the protocol. This specification defines version "1.1".
763   The protocol version as a whole indicates the sender's compliance
764   with the set of requirements laid out in that version's corresponding
765   specification of HTTP.
766</t>
767<t>
768   The version of an HTTP message is indicated by an HTTP-Version field
769   in the first line of the message. HTTP-Version is case-sensitive.
770</t>
771<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
772  HTTP-Version   = HTTP-Prot-Name "/" DIGIT "." DIGIT
773  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
774]]></artwork></figure>
775<t>
776   The HTTP version number consists of two decimal digits separated by a "."
777   (period or decimal point).  The first digit ("major version") indicates the
778   HTTP messaging syntax, whereas the second digit ("minor version") indicates
779   the highest minor version to which the sender is at least conditionally
780   compliant and able to understand for future communication.  The minor
781   version advertises the sender's communication capabilities even when the
782   sender is only using a backwards-compatible subset of the protocol,
783   thereby letting the recipient know that more advanced features can
784   be used in response (by servers) or in future requests (by clients).
785</t>
786<t>
787   When an HTTP/1.1 message is sent to an HTTP/1.0 recipient
788   <xref target="RFC1945"/> or a recipient whose version is unknown,
789   the HTTP/1.1 message is constructed such that it can be interpreted
790   as a valid HTTP/1.0 message if all of the newer features are ignored.
791   This specification places recipient-version requirements on some
792   new features so that a compliant sender will only use compatible
793   features until it has determined, through configuration or the
794   receipt of a message, that the recipient supports HTTP/1.1.
795</t>
796<t>
797   The interpretation of an HTTP header field does not change
798   between minor versions of the same major version, though the default
799   behavior of a recipient in the absence of such a field can change.
800   Unless specified otherwise, header fields defined in HTTP/1.1 are
801   defined for all versions of HTTP/1.x.  In particular, the Host and
802   Connection header fields ought to be implemented by all HTTP/1.x
803   implementations whether or not they advertise compliance with HTTP/1.1.
804</t>
805<t>
806   New header fields can be defined such that, when they are
807   understood by a recipient, they might override or enhance the
808   interpretation of previously defined header fields.  When an
809   implementation receives an unrecognized header field, the recipient
810   MUST ignore that header field for local processing regardless of
811   the message's HTTP version.  An unrecognized header field received
812   by a proxy MUST be forwarded downstream unless the header field's
813   field-name is listed in the message's Connection header-field
814   (see <xref target="header.connection"/>).
815   These requirements allow HTTP's functionality to be enhanced without
816   requiring prior update of all compliant intermediaries.
817</t>
818<t>
819   Intermediaries that process HTTP messages (i.e., all intermediaries
820   other than those acting as a tunnel) MUST send their own HTTP-Version
821   in forwarded messages.  In other words, they MUST NOT blindly
822   forward the first line of an HTTP message without ensuring that the
823   protocol version matches what the intermediary understands, and
824   is at least conditionally compliant to, for both the receiving and
825   sending of messages.  Forwarding an HTTP message without rewriting
826   the HTTP-Version might result in communication errors when downstream
827   recipients use the message sender's version to determine what features
828   are safe to use for later communication with that sender.
829</t>
830<t>
831   An HTTP client SHOULD send a request version equal to the highest
832   version for which the client is at least conditionally compliant and
833   whose major version is no higher than the highest version supported
834   by the server, if this is known.  An HTTP client MUST NOT send a
835   version for which it is not at least conditionally compliant.
836</t>
837<t>
838   An HTTP client MAY send a lower request version if it is known that
839   the server incorrectly implements the HTTP specification, but only
840   after the client has attempted at least one normal request and determined
841   from the response status or header fields (e.g., Server) that the
842   server improperly handles higher request versions.
843</t>
844<t>
845   An HTTP server SHOULD send a response version equal to the highest
846   version for which the server is at least conditionally compliant and
847   whose major version is less than or equal to the one received in the
848   request.  An HTTP server MUST NOT send a version for which it is not
849   at least conditionally compliant.  A server MAY send a 505 (HTTP
850   Version Not Supported) response if it cannot send a response using the
851   major version used in the client's request.
852</t>
853<t>
854   An HTTP server MAY send an HTTP/1.0 response to an HTTP/1.0 request
855   if it is known or suspected that the client incorrectly implements the
856   HTTP specification and is incapable of correctly processing later
857   version responses, such as when a client fails to parse the version
858   number correctly or when an intermediary is known to blindly forward
859   the HTTP-Version even when it doesn't comply with the given minor
860   version of the protocol. Such protocol downgrades SHOULD NOT be
861   performed unless triggered by specific client attributes, such as when
862   one or more of the request header fields (e.g., User-Agent) uniquely
863   match the values sent by a client known to be in error.
864</t>
865<t>
866   The intention of HTTP's versioning design is that the major number
867   will only be incremented if an incompatible message syntax is
868   introduced, and that the minor number will only be incremented when
869   changes made to the protocol have the effect of adding to the message
870   semantics or implying additional capabilities of the sender.  However,
871   the minor version was not incremented for the changes introduced between
872   <xref target="RFC2068"/> and <xref target="RFC2616"/>, and this revision
873   is specifically avoiding any such changes to the protocol.
874</t>
875</section>
876
877<section title="Uniform Resource Identifiers" anchor="uri">
878<iref primary="true" item="resource"/>
879<t>
880   Uniform Resource Identifiers (URIs) <xref target="RFC3986"/> are used
881   throughout HTTP as the means for identifying resources. URI references
882   are used to target requests, indicate redirects, and define relationships.
883   HTTP does not limit what a resource might be; it merely defines an interface
884   that can be used to interact with a resource via HTTP. More information on
885   the scope of URIs and resources can be found in <xref target="RFC3986"/>.
886</t>
887 
888 
889 
890 
891 
892 
893 
894 
895 
896 
897<t>
898   This specification adopts the definitions of "URI-reference",
899   "absolute-URI", "relative-part", "port", "host",
900   "path-abempty", "path-absolute", "query", and "authority" from the
901   URI generic syntax <xref target="RFC3986"/>.
902   In addition, we define a partial-URI rule for protocol elements
903   that allow a relative URI but not a fragment.
904</t>
905<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[
906  URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
907  absolute-URI  = <absolute-URI, defined in [RFC3986], Section 4.3>
908  relative-part = <relative-part, defined in [RFC3986], Section 4.2>
909  authority     = <authority, defined in [RFC3986], Section 3.2>
910  path-abempty  = <path-abempty, defined in [RFC3986], Section 3.3>
911  path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
912  port          = <port, defined in [RFC3986], Section 3.2.3>
913  query         = <query, defined in [RFC3986], Section 3.4>
914  uri-host      = <host, defined in [RFC3986], Section 3.2.2>
915 
916  partial-URI   = relative-part [ "?" query ]
917]]></artwork></figure>
918<t>
919   Each protocol element in HTTP that allows a URI reference will indicate
920   in its ABNF production whether the element allows any form of reference
921   (URI-reference), only a URI in absolute form (absolute-URI), only the
922   path and optional query components, or some combination of the above.
923   Unless otherwise indicated, URI references are parsed relative to the
924   effective request URI, which defines the default base URI for references
925   in both the request and its corresponding response.
926</t>
927
928<section title="http URI scheme" anchor="http.uri">
929 
930  <iref item="http URI scheme" primary="true"/>
931  <iref item="URI scheme" subitem="http" primary="true"/>
932<t>
933   The "http" URI scheme is hereby defined for the purpose of minting
934   identifiers according to their association with the hierarchical
935   namespace governed by a potential HTTP origin server listening for
936   TCP connections on a given port.
937</t>
938<figure><iref primary="true" item="Grammar" subitem="http-URI"/><artwork type="abnf2616"><![CDATA[
939  http-URI = "http:" "//" authority path-abempty [ "?" query ]
940]]></artwork></figure>
941<t>
942   The HTTP origin server is identified by the generic syntax's
943   <xref target="uri" format="none">authority</xref> component, which includes a host identifier
944   and optional TCP port (<xref target="RFC3986"/>, Section 3.2.2).
945   The remainder of the URI, consisting of both the hierarchical path
946   component and optional query component, serves as an identifier for
947   a potential resource within that origin server's name space.
948</t>
949<t>
950   If the host identifier is provided as an IP literal or IPv4 address,
951   then the origin server is any listener on the indicated TCP port at
952   that IP address. If host is a registered name, then that name is
953   considered an indirect identifier and the recipient might use a name
954   resolution service, such as DNS, to find the address of a listener
955   for that host.
956   The host MUST NOT be empty; if an "http" URI is received with an
957   empty host, then it MUST be rejected as invalid.
958   If the port subcomponent is empty or not given, then TCP port 80 is
959   assumed (the default reserved port for WWW services).
960</t>
961<t>
962   Regardless of the form of host identifier, access to that host is not
963   implied by the mere presence of its name or address. The host might or might
964   not exist and, even when it does exist, might or might not be running an
965   HTTP server or listening to the indicated port. The "http" URI scheme
966   makes use of the delegated nature of Internet names and addresses to
967   establish a naming authority (whatever entity has the ability to place
968   an HTTP server at that Internet name or address) and allows that
969   authority to determine which names are valid and how they might be used.
970</t>
971<t>
972   When an "http" URI is used within a context that calls for access to the
973   indicated resource, a client MAY attempt access by resolving
974   the host to an IP address, establishing a TCP connection to that address
975   on the indicated port, and sending an HTTP request message to the server
976   containing the URI's identifying data as described in <xref target="request"/>.
977   If the server responds to that request with a non-interim HTTP response
978   message, as described in <xref target="response"/>, then that response
979   is considered an authoritative answer to the client's request.
980</t>
981<t>
982   Although HTTP is independent of the transport protocol, the "http"
983   scheme is specific to TCP-based services because the name delegation
984   process depends on TCP for establishing authority.
985   An HTTP service based on some other underlying connection protocol
986   would presumably be identified using a different URI scheme, just as
987   the "https" scheme (below) is used for servers that require an SSL/TLS
988   transport layer on a connection. Other protocols might also be used to
989   provide access to "http" identified resources — it is only the
990   authoritative interface used for mapping the namespace that is
991   specific to TCP.
992</t>
993<t>
994   The URI generic syntax for authority also includes a deprecated
995   userinfo subcomponent (<xref target="RFC3986"/>, Section 3.2.1)
996   for including user authentication information in the URI.  Some
997   implementations make use of the userinfo component for internal
998   configuration of authentication information, such as within command
999   invocation options, configuration files, or bookmark lists, even
1000   though such usage might expose a user identifier or password.
1001   Senders MUST NOT include a userinfo subcomponent (and its "@"
1002   delimiter) when transmitting an "http" URI in a message.  Recipients
1003   of HTTP messages that contain a URI reference SHOULD parse for the
1004   existence of userinfo and treat its presence as an error, likely
1005   indicating that the deprecated subcomponent is being used to obscure
1006   the authority for the sake of phishing attacks.
1007</t>
1008</section>
1009
1010<section title="https URI scheme" anchor="https.uri">
1011   
1012   <iref item="https URI scheme"/>
1013   <iref item="URI scheme" subitem="https"/>
1014<t>
1015   The "https" URI scheme is hereby defined for the purpose of minting
1016   identifiers according to their association with the hierarchical
1017   namespace governed by a potential HTTP origin server listening for
1018   SSL/TLS-secured connections on a given TCP port.
1019</t>
1020<t>
1021   All of the requirements listed above for the "http" scheme are also
1022   requirements for the "https" scheme, except that a default TCP port
1023   of 443 is assumed if the port subcomponent is empty or not given,
1024   and the TCP connection MUST be secured for privacy through the
1025   use of strong encryption prior to sending the first HTTP request.
1026</t>
1027<figure><iref primary="true" item="Grammar" subitem="https-URI"/><artwork type="abnf2616"><![CDATA[
1028  https-URI = "https:" "//" authority path-abempty [ "?" query ]
1029]]></artwork></figure>
1030<t>
1031   Unlike the "http" scheme, responses to "https" identified requests
1032   are never "public" and thus MUST NOT be reused for shared caching.
1033   They can, however, be reused in a private cache if the message is
1034   cacheable by default in HTTP or specifically indicated as such by
1035   the Cache-Control header field (Section 3.2 of <xref target="Part6"/>).
1036</t>
1037<t>
1038   Resources made available via the "https" scheme have no shared
1039   identity with the "http" scheme even if their resource identifiers
1040   indicate the same authority (the same host listening to the same
1041   TCP port).  They are distinct name spaces and are considered to be
1042   distinct origin servers.  However, an extension to HTTP that is
1043   defined to apply to entire host domains, such as the Cookie protocol
1044   <xref target="RFC6265"/>, can allow information
1045   set by one service to impact communication with other services
1046   within a matching group of host domains.
1047</t>
1048<t>
1049   The process for authoritative access to an "https" identified
1050   resource is defined in <xref target="RFC2818"/>.
1051</t>
1052</section>
1053
1054<section title="http and https URI Normalization and Comparison" anchor="uri.comparison">
1055<t>
1056   Since the "http" and "https" schemes conform to the URI generic syntax,
1057   such URIs are normalized and compared according to the algorithm defined
1058   in <xref target="RFC3986"/>, Section 6, using the defaults
1059   described above for each scheme.
1060</t>
1061<t>
1062   If the port is equal to the default port for a scheme, the normal
1063   form is to elide the port subcomponent. Likewise, an empty path
1064   component is equivalent to an absolute path of "/", so the normal
1065   form is to provide a path of "/" instead. The scheme and host
1066   are case-insensitive and normally provided in lowercase; all
1067   other components are compared in a case-sensitive manner.
1068   Characters other than those in the "reserved" set are equivalent
1069   to their percent-encoded octets (see <xref target="RFC3986"/>, Section 2.1): the normal form is to not encode them.
1070</t>
1071<t>
1072   For example, the following three URIs are equivalent:
1073</t>
1074<figure><artwork type="example"><![CDATA[
1075   http://example.com:80/~smith/home.html
1076   http://EXAMPLE.com/%7Esmith/home.html
1077   http://EXAMPLE.com:/%7esmith/home.html
1078]]></artwork></figure>
1079</section>
1080</section>
1081</section>
1082
1083<section title="Message Format" anchor="http.message">
1084
1085
1086
1087
1088<iref item="header section"/>
1089<iref item="headers"/>
1090<iref item="header field"/>
1091<t>
1092   All HTTP/1.1 messages consist of a start-line followed by a sequence of
1093   octets in a format similar to the Internet Message Format
1094   <xref target="RFC5322"/>: zero or more header fields (collectively
1095   referred to as the "headers" or the "header section"), an empty line
1096   indicating the end of the header section, and an optional message-body.
1097</t>
1098<t>
1099   An HTTP message can either be a request from client to server or a
1100   response from server to client.  Syntactically, the two types of message
1101   differ only in the start-line, which is either a Request-Line (for requests)
1102   or a Status-Line (for responses), and in the algorithm for determining
1103   the length of the message-body (<xref target="message.body"/>).
1104   In theory, a client could receive requests and a server could receive
1105   responses, distinguishing them by their different start-line formats,
1106   but in practice servers are implemented to only expect a request
1107   (a response is interpreted as an unknown or invalid request method)
1108   and clients are implemented to only expect a response.
1109</t>
1110<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1111  HTTP-message    = start-line
1112                    *( header-field CRLF )
1113                    CRLF
1114                    [ message-body ]
1115  start-line      = Request-Line / Status-Line
1116]]></artwork></figure>
1117<t>
1118   Implementations MUST NOT send whitespace between the start-line and
1119   the first header field. The presence of such whitespace in a request
1120   might be an attempt to trick a server into ignoring that field or
1121   processing the line after it as a new request, either of which might
1122   result in a security vulnerability if other implementations within
1123   the request chain interpret the same message differently.
1124   Likewise, the presence of such whitespace in a response might be
1125   ignored by some clients or cause others to cease parsing.
1126</t>
1127
1128<section title="Message Parsing and Robustness" anchor="message.robustness">
1129<t>
1130   The normal procedure for parsing an HTTP message is to read the
1131   start-line into a structure, read each header field into a hash
1132   table by field name until the empty line, and then use the parsed
1133   data to determine if a message-body is expected.  If a message-body
1134   has been indicated, then it is read as a stream until an amount
1135   of octets equal to the message-body length is read or the connection
1136   is closed.
1137</t>
1138<t>
1139   Care must be taken to parse an HTTP message as a sequence
1140   of octets in an encoding that is a superset of US-ASCII.  Attempting
1141   to parse HTTP as a stream of Unicode characters in a character encoding
1142   like UTF-16 might introduce security flaws due to the differing ways
1143   that such parsers interpret invalid characters.
1144</t>
1145<t>
1146   Older HTTP/1.0 client implementations might send an extra CRLF
1147   after a POST request as a lame workaround for some early server
1148   applications that failed to read message-body content that was
1149   not terminated by a line-ending. An HTTP/1.1 client MUST NOT
1150   preface or follow a request with an extra CRLF.  If terminating
1151   the request message-body with a line-ending is desired, then the
1152   client MUST include the terminating CRLF octets as part of the
1153   message-body length.
1154</t>
1155<t>
1156   In the interest of robustness, servers SHOULD ignore at least one
1157   empty line received where a Request-Line is expected. In other words, if
1158   the server is reading the protocol stream at the beginning of a
1159   message and receives a CRLF first, it SHOULD ignore the CRLF.
1160   Likewise, although the line terminator for the start-line and header
1161   fields is the sequence CRLF, we recommend that recipients recognize a
1162   single LF as a line terminator and ignore any CR.
1163</t>
1164<t>
1165   When a server listening only for HTTP request messages, or processing
1166   what appears from the start-line to be an HTTP request message,
1167   receives a sequence of octets that does not match the HTTP-message
1168   grammar aside from the robustness exceptions listed above, the
1169   server MUST respond with an HTTP/1.1 400 (Bad Request) response. 
1170</t>
1171</section>
1172
1173<section title="Header Fields" anchor="header.fields">
1174 
1175 
1176 
1177 
1178 
1179<t>
1180   Each HTTP header field consists of a case-insensitive field name
1181   followed by a colon (":"), optional whitespace, and the field value.
1182</t>
1183<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[
1184  header-field   = field-name ":" OWS [ field-value ] OWS
1185  field-name     = token
1186  field-value    = *( field-content / OWS )
1187  field-content  = *( WSP / VCHAR / obs-text )
1188]]></artwork></figure>
1189<t>
1190   The field-name token labels the corresponding field-value as having the
1191   semantics defined by that header field.  For example, the Date header field
1192   is defined in <xref target="header.date"/> as containing the origination
1193   timestamp for the message in which it appears.
1194</t>
1195<t>
1196   HTTP header fields are fully extensible: there is no limit on the
1197   introduction of new field names, each presumably defining new semantics,
1198   or on the number of header fields used in a given message.  Existing
1199   fields are defined in each part of this specification and in many other
1200   specifications outside the standards process.
1201   New header fields can be introduced without changing the protocol version
1202   if their defined semantics allow them to be safely ignored by recipients
1203   that do not recognize them.
1204</t>
1205<t>
1206   New HTTP header fields SHOULD be registered with IANA according
1207   to the procedures in <xref target="header.field.registration"/>.
1208   Unrecognized header fields MUST be forwarded by a proxy unless the
1209   field-name is listed in the Connection header field
1210   (<xref target="header.connection"/>) or the proxy is specifically
1211   configured to block or otherwise transform such fields.
1212   Unrecognized header fields SHOULD be ignored by other recipients.
1213</t>
1214<t>
1215   The order in which header fields with differing field names are
1216   received is not significant. However, it is "good practice" to send
1217   header fields that contain control data first, such as Host on
1218   requests and Date on responses, so that implementations can decide
1219   when not to handle a message as early as possible.  A server MUST
1220   wait until the entire header section is received before interpreting
1221   a request message, since later header fields might include conditionals,
1222   authentication credentials, or deliberately misleading duplicate
1223   header fields that would impact request processing.
1224</t>
1225<t>
1226   Multiple header fields with the same field name MUST NOT be
1227   sent in a message unless the entire field value for that
1228   header field is defined as a comma-separated list [i.e., #(values)].
1229   Multiple header fields with the same field name can be combined into
1230   one "field-name: field-value" pair, without changing the semantics of the
1231   message, by appending each subsequent field value to the combined
1232   field value in order, separated by a comma. The order in which
1233   header fields with the same field name are received is therefore
1234   significant to the interpretation of the combined field value;
1235   a proxy MUST NOT change the order of these field values when
1236   forwarding a message.
1237</t>
1238<t><list>
1239  <t>
1240   Note: The "Set-Cookie" header field as implemented in
1241   practice can occur multiple times, but does not use the list syntax, and
1242   thus cannot be combined into a single line (<xref target="RFC6265"/>). (See Appendix A.2.3 of <xref target="Kri2001"/>
1243   for details.) Also note that the Set-Cookie2 header field specified in
1244   <xref target="RFC2965"/> does not share this problem.
1245  </t>
1246</list></t>
1247
1248<section title="Field Parsing" anchor="field.parsing">
1249<t>
1250   No whitespace is allowed between the header field-name and colon.
1251   In the past, differences in the handling of such whitespace have led to
1252   security vulnerabilities in request routing and response handling.
1253   Any received request message that contains whitespace between a header
1254   field-name and colon MUST be rejected with a response code of 400
1255   (Bad Request).  A proxy MUST remove any such whitespace from a response
1256   message before forwarding the message downstream.
1257</t>
1258<t>
1259   A field value MAY be preceded by optional whitespace (OWS); a single SP is
1260   preferred. The field value does not include any leading or trailing white
1261   space: OWS occurring before the first non-whitespace octet of the
1262   field value or after the last non-whitespace octet of the field value
1263   is ignored and SHOULD be removed before further processing (as this does
1264   not change the meaning of the header field).
1265</t>
1266<t>
1267   Historically, HTTP header field values could be extended over multiple
1268   lines by preceding each extra line with at least one space or horizontal
1269   tab octet (line folding). This specification deprecates such line
1270   folding except within the message/http media type
1271   (<xref target="internet.media.type.message.http"/>).
1272   HTTP senders MUST NOT produce messages that include line folding
1273   (i.e., that contain any field-content that matches the obs-fold rule) unless
1274   the message is intended for packaging within the message/http media type.
1275   HTTP recipients SHOULD accept line folding and replace any embedded
1276   obs-fold whitespace with either a single SP or a matching number of SP
1277   octets (to avoid buffer copying) prior to interpreting the field value or
1278   forwarding the message downstream.
1279</t>
1280<t>
1281   Historically, HTTP has allowed field content with text in the ISO-8859-1
1282   <xref target="ISO-8859-1"/> character encoding and supported other
1283   character sets only through use of <xref target="RFC2047"/> encoding.
1284   In practice, most HTTP header field values use only a subset of the
1285   US-ASCII character encoding <xref target="USASCII"/>. Newly defined
1286   header fields SHOULD limit their field values to US-ASCII octets.
1287   Recipients SHOULD treat other (obs-text) octets in field content as
1288   opaque data.
1289</t>
1290</section>
1291
1292<section title="Field Length" anchor="field.length">
1293<t>
1294   HTTP does not place a pre-defined limit on the length of header fields,
1295   either in isolation or as a set. A server MUST be prepared to receive
1296   request header fields of unbounded length and respond with a 4xx status
1297   code if the received header field(s) would be longer than the server wishes
1298   to handle.
1299</t>
1300<t>
1301   A client that receives response headers that are longer than it wishes to
1302   handle can only treat it as a server error.
1303</t>
1304<t>
1305   Various ad-hoc limitations on header length are found in practice. It is
1306   RECOMMENDED that all HTTP senders and recipients support messages whose
1307   combined header fields have 4000 or more octets.
1308</t>
1309</section>
1310
1311<section title="Common Field ABNF Rules" anchor="field.rules">
1312<t anchor="rule.token.separators">
1313 
1314 
1315 
1316 
1317   Many HTTP/1.1 header field values consist of words (token or quoted-string)
1318   separated by whitespace or special characters. These special characters
1319   MUST be in a quoted string to be used within a parameter value (as defined
1320   in <xref target="transfer.codings"/>).
1321</t>
1322<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[
1323  word           = token / quoted-string
1324
1325  token          = 1*tchar
1326
1327  tchar          = "!" / "#" / "$" / "%" / "&" / "'" / "*"
1328                 / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
1329                 / DIGIT / ALPHA
1330                 ; any VCHAR, except special
1331
1332  special        = "(" / ")" / "<" / ">" / "@" / ","
1333                 / ";" / ":" / "\" / DQUOTE / "/" / "["
1334                 / "]" / "?" / "=" / "{" / "}"
1335]]></artwork></figure>
1336<t anchor="rule.quoted-string">
1337 
1338 
1339 
1340   A string of text is parsed as a single word if it is quoted using
1341   double-quote marks.
1342</t>
1343<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[
1344  quoted-string  = DQUOTE *( qdtext / quoted-pair ) DQUOTE
1345  qdtext         = OWS / %x21 / %x23-5B / %x5D-7E / obs-text
1346  obs-text       = %x80-FF
1347]]></artwork></figure>
1348<t anchor="rule.quoted-pair">
1349 
1350   The backslash octet ("\") can be used as a single-octet
1351   quoting mechanism within quoted-string constructs:
1352</t>
1353<figure><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
1354  quoted-pair    = "\" ( WSP / VCHAR / obs-text )
1355]]></artwork></figure>
1356<t>
1357   Recipients that process the value of the quoted-string MUST handle a
1358   quoted-pair as if it were replaced by the octet following the backslash.
1359</t>
1360<t>
1361   Senders SHOULD NOT escape octets in quoted-strings that do not require
1362   escaping (i.e., other than DQUOTE and the backslash octet).
1363</t>
1364<t anchor="rule.comment">
1365 
1366 
1367   Comments can be included in some HTTP header fields by surrounding
1368   the comment text with parentheses. Comments are only allowed in
1369   fields containing "comment" as part of their field value definition.
1370</t>
1371<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
1372  comment        = "(" *( ctext / quoted-cpair / comment ) ")"
1373  ctext          = OWS / %x21-27 / %x2A-5B / %x5D-7E / obs-text
1374]]></artwork></figure>
1375<t anchor="rule.quoted-cpair">
1376 
1377   The backslash octet ("\") can be used as a single-octet
1378   quoting mechanism within comment constructs:
1379</t>
1380<figure><iref primary="true" item="Grammar" subitem="quoted-cpair"/><artwork type="abnf2616"><![CDATA[
1381  quoted-cpair    = "\" ( WSP / VCHAR / obs-text )
1382]]></artwork></figure>
1383<t>
1384   Senders SHOULD NOT escape octets in comments that do not require escaping
1385   (i.e., other than the backslash octet "\" and the parentheses "(" and ")").
1386</t>
1387</section>
1388</section>
1389
1390<section title="Message Body" anchor="message.body">
1391 
1392<t>
1393   The message-body (if any) of an HTTP message is used to carry the
1394   payload body associated with the request or response.
1395</t>
1396<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1397  message-body = *OCTET
1398]]></artwork></figure>
1399<t>
1400   The message-body differs from the payload body only when a transfer-coding
1401   has been applied, as indicated by the Transfer-Encoding header field
1402   (<xref target="header.transfer-encoding"/>).  If more than one
1403   Transfer-Encoding header field is present in a message, the multiple
1404   field-values MUST be combined into one field-value, according to the
1405   algorithm defined in <xref target="header.fields"/>, before determining
1406   the message-body length.
1407</t>
1408<t>
1409   When one or more transfer-codings are applied to a payload in order to
1410   form the message-body, the Transfer-Encoding header field MUST contain
1411   the list of transfer-codings applied. Transfer-Encoding is a property of
1412   the message, not of the payload, and thus MAY be added or removed by
1413   any implementation along the request/response chain under the constraints
1414   found in <xref target="transfer.codings"/>.
1415</t>
1416<t>
1417   If a message is received that has multiple Content-Length header fields
1418   (<xref target="header.content-length"/>) with field-values consisting
1419   of the same decimal value, or a single Content-Length header field with
1420   a field value containing a list of identical decimal values (e.g.,
1421   "Content-Length: 42, 42"), indicating that duplicate Content-Length
1422   header fields have been generated or combined by an upstream message
1423   processor, then the recipient MUST either reject the message as invalid
1424   or replace the duplicated field-values with a single valid Content-Length
1425   field containing that decimal value prior to determining the message-body
1426   length.
1427</t>
1428<t>
1429   The rules for when a message-body is allowed in a message differ for
1430   requests and responses.
1431</t>
1432<t>
1433   The presence of a message-body in a request is signaled by the
1434   inclusion of a Content-Length or Transfer-Encoding header field in
1435   the request's header fields, even if the request method does not
1436   define any use for a message-body.  This allows the request
1437   message framing algorithm to be independent of method semantics.
1438</t>
1439<t>
1440   For response messages, whether or not a message-body is included with
1441   a message is dependent on both the request method and the response
1442   status code (<xref target="status.code.and.reason.phrase"/>).
1443   Responses to the HEAD request method never include a message-body
1444   because the associated response header fields (e.g., Transfer-Encoding,
1445   Content-Length, etc.) only indicate what their values would have been
1446   if the request method had been GET.  All 1xx (Informational), 204 (No Content),
1447   and 304 (Not Modified) responses MUST NOT include a message-body.
1448   All other responses do include a message-body, although the body
1449   MAY be of zero length.
1450</t>
1451<t>
1452   The length of the message-body is determined by one of the following
1453   (in order of precedence):
1454</t>
1455<t>
1456  <list style="numbers">
1457    <t>
1458     Any response to a HEAD request and any response with a status
1459     code of 100-199, 204, or 304 is always terminated by the first
1460     empty line after the header fields, regardless of the header
1461     fields present in the message, and thus cannot contain a message-body.
1462    </t>
1463    <t>
1464     If a Transfer-Encoding header field is present
1465     and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1466     is the final encoding, the message-body length is determined by reading
1467     and decoding the chunked data until the transfer-coding indicates the
1468     data is complete.
1469    <vspace blankLines="1"/>
1470     If a Transfer-Encoding header field is present in a response and the
1471     "chunked" transfer-coding is not the final encoding, the message-body
1472     length is determined by reading the connection until it is closed by
1473     the server.
1474     If a Transfer-Encoding header field is present in a request and the
1475     "chunked" transfer-coding is not the final encoding, the message-body
1476     length cannot be determined reliably; the server MUST respond with
1477     the 400 (Bad Request) status code and then close the connection.
1478    <vspace blankLines="1"/>
1479     If a message is received with both a Transfer-Encoding header field
1480     and a Content-Length header field, the Transfer-Encoding overrides
1481     the Content-Length.
1482     Such a message might indicate an attempt to perform request or response
1483     smuggling (bypass of security-related checks on message routing or content)
1484     and thus ought to be handled as an error.  The provided Content-Length MUST
1485     be removed, prior to forwarding the message downstream, or replaced with
1486     the real message-body length after the transfer-coding is decoded.
1487    </t>
1488    <t>
1489     If a message is received without Transfer-Encoding and with either
1490     multiple Content-Length header fields having differing field-values or
1491     a single Content-Length header field having an invalid value, then the
1492     message framing is invalid and MUST be treated as an error to
1493     prevent request or response smuggling.
1494     If this is a request message, the server MUST respond with
1495     a 400 (Bad Request) status code and then close the connection.
1496     If this is a response message received by a proxy, the proxy
1497     MUST discard the received response, send a 502 (Bad Gateway)
1498     status code as its downstream response, and then close the connection.
1499     If this is a response message received by a user-agent, it MUST be
1500     treated as an error by discarding the message and closing the connection.
1501    </t>
1502    <t>
1503     If a valid Content-Length header field
1504     is present without Transfer-Encoding, its decimal value defines the
1505     message-body length in octets.  If the actual number of octets sent in
1506     the message is less than the indicated Content-Length, the recipient
1507     MUST consider the message to be incomplete and treat the connection
1508     as no longer usable.
1509     If the actual number of octets sent in the message is more than the indicated
1510     Content-Length, the recipient MUST only process the message-body up to the
1511     field value's number of octets; the remainder of the message MUST either
1512     be discarded or treated as the next message in a pipeline.  For the sake of
1513     robustness, a user-agent MAY attempt to detect and correct such an error
1514     in message framing if it is parsing the response to the last request on
1515     a connection and the connection has been closed by the server.
1516    </t>
1517    <t>
1518     If this is a request message and none of the above are true, then the
1519     message-body length is zero (no message-body is present).
1520    </t>
1521    <t>
1522     Otherwise, this is a response message without a declared message-body
1523     length, so the message-body length is determined by the number of octets
1524     received prior to the server closing the connection.
1525    </t>
1526  </list>
1527</t>
1528<t>
1529   Since there is no way to distinguish a successfully completed,
1530   close-delimited message from a partially-received message interrupted
1531   by network failure, implementations SHOULD use encoding or
1532   length-delimited messages whenever possible.  The close-delimiting
1533   feature exists primarily for backwards compatibility with HTTP/1.0.
1534</t>
1535<t>
1536   A server MAY reject a request that contains a message-body but
1537   not a Content-Length by responding with 411 (Length Required).
1538</t>
1539<t>
1540   Unless a transfer-coding other than "chunked" has been applied,
1541   a client that sends a request containing a message-body SHOULD
1542   use a valid Content-Length header field if the message-body length
1543   is known in advance, rather than the "chunked" encoding, since some
1544   existing services respond to "chunked" with a 411 (Length Required)
1545   status code even though they understand the chunked encoding.  This
1546   is typically because such services are implemented via a gateway that
1547   requires a content-length in advance of being called and the server
1548   is unable or unwilling to buffer the entire request before processing.
1549</t>
1550<t>
1551   A client that sends a request containing a message-body MUST include a
1552   valid Content-Length header field if it does not know the server will
1553   handle HTTP/1.1 (or later) requests; such knowledge can be in the form
1554   of specific user configuration or by remembering the version of a prior
1555   received response.
1556</t>
1557</section>
1558
1559<section anchor="incomplete.messages" title="Incomplete Messages">
1560<t>
1561   Request messages that are prematurely terminated, possibly due to a
1562   cancelled connection or a server-imposed time-out exception, MUST
1563   result in closure of the connection; sending an HTTP/1.1 error response
1564   prior to closing the connection is OPTIONAL.
1565</t>
1566<t>
1567   Response messages that are prematurely terminated, usually by closure
1568   of the connection prior to receiving the expected number of octets or by
1569   failure to decode a transfer-encoded message-body, MUST be recorded
1570   as incomplete.  A response that terminates in the middle of the header
1571   block (before the empty line is received) cannot be assumed to convey the
1572   full semantics of the response and MUST be treated as an error.
1573</t>
1574<t>
1575   A message-body that uses the chunked transfer encoding is
1576   incomplete if the zero-sized chunk that terminates the encoding has not
1577   been received.  A message that uses a valid Content-Length is incomplete
1578   if the size of the message-body received (in octets) is less than the
1579   value given by Content-Length.  A response that has neither chunked
1580   transfer encoding nor Content-Length is terminated by closure of the
1581   connection, and thus is considered complete regardless of the number of
1582   message-body octets received, provided that the header block was received
1583   intact.
1584</t>
1585<t>
1586   A user agent MUST NOT render an incomplete response message-body as if
1587   it were complete (i.e., some indication must be given to the user that an
1588   error occurred).  Cache requirements for incomplete responses are defined
1589   in Section 2.1 of <xref target="Part6"/>.
1590</t>
1591<t>
1592   A server MUST read the entire request message-body or close
1593   the connection after sending its response, since otherwise the
1594   remaining data on a persistent connection would be misinterpreted
1595   as the next request.  Likewise,
1596   a client MUST read the entire response message-body if it intends
1597   to reuse the same connection for a subsequent request.  Pipelining
1598   multiple requests on a connection is described in <xref target="pipelining"/>.
1599</t>
1600</section>
1601
1602<section title="General Header Fields" anchor="general.header.fields">
1603 
1604<t>
1605   There are a few header fields which have general applicability for
1606   both request and response messages, but which do not apply to the
1607   payload being transferred. These header fields apply only to the
1608   message being transmitted.
1609</t>
1610<texttable align="left">
1611  <ttcol>Header Field Name</ttcol>
1612  <ttcol>Defined in...</ttcol>
1613 
1614  <c>Connection</c> <c><xref target="header.connection"/></c>
1615  <c>Date</c> <c><xref target="header.date"/></c>
1616  <c>Trailer</c> <c><xref target="header.trailer"/></c>
1617  <c>Transfer-Encoding</c> <c><xref target="header.transfer-encoding"/></c>
1618  <c>Upgrade</c> <c><xref target="header.upgrade"/></c>
1619  <c>Via</c> <c><xref target="header.via"/></c>
1620</texttable>
1621</section>
1622</section>
1623
1624<section title="Request" anchor="request">
1625 
1626<t>
1627   A request message from a client to a server begins with a
1628   Request-Line, followed by zero or more header fields, an empty
1629   line signifying the end of the header block, and an optional
1630   message body.
1631</t>
1632<!--                 Host                      ; should be moved here eventually -->
1633<figure><iref primary="true" item="Grammar" subitem="Request"/><artwork type="abnf2616"><![CDATA[
1634  Request       = Request-Line              ; Section 4.1
1635                  *( header-field CRLF )    ; Section 3.2
1636                  CRLF
1637                  [ message-body ]          ; Section 3.3
1638]]></artwork></figure>
1639
1640<section title="Request-Line" anchor="request-line">
1641 
1642<t>
1643   The Request-Line begins with a method token, followed by a single
1644   space (SP), the request-target, another single space (SP), the
1645   protocol version, and ending with CRLF.
1646</t>
1647<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1648  Request-Line   = Method SP request-target SP HTTP-Version CRLF
1649]]></artwork></figure>
1650
1651<section title="Method" anchor="method">
1652 
1653<t>
1654   The Method token indicates the request method to be performed on the
1655   target resource. The request method is case-sensitive.
1656</t>
1657<figure><iref primary="true" item="Grammar" subitem="Method"/><artwork type="abnf2616"><![CDATA[
1658  Method         = token
1659]]></artwork></figure>
1660</section>
1661
1662<section title="request-target" anchor="request-target">
1663 
1664<t>
1665   The request-target identifies the target resource upon which to apply
1666   the request.  In most cases, the user agent is provided a URI reference
1667   from which it determines an absolute URI for identifying the target
1668   resource.  When a request to the resource is initiated, all or part
1669   of that URI is used to construct the HTTP request-target.
1670</t>
1671<figure><iref primary="true" item="Grammar" subitem="request-target"/><artwork type="abnf2616"><![CDATA[
1672  request-target = "*"
1673                 / absolute-URI
1674                 / ( path-absolute [ "?" query ] )
1675                 / authority
1676]]></artwork></figure>
1677<t>
1678   The four options for request-target are dependent on the nature of the
1679   request.
1680</t>   
1681<t><iref item="asterisk form (of request-target)"/>
1682   The asterisk "*" form of request-target, which MUST NOT be used
1683   with any request method other than OPTIONS, means that the request
1684   applies to the server as a whole (the listening process) rather than
1685   to a specific named resource at that server.  For example,
1686</t>
1687<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1688  OPTIONS * HTTP/1.1
1689  ]]></artwork></figure>
1690<t><iref item="absolute-URI form (of request-target)"/>
1691   The "absolute-URI" form is REQUIRED when the request is being made to a
1692   proxy. The proxy is requested to either forward the request or service it
1693   from a valid cache, and then return the response. Note that the proxy MAY
1694   forward the request on to another proxy or directly to the server
1695   specified by the absolute-URI. In order to avoid request loops, a
1696   proxy that forwards requests to other proxies MUST be able to
1697   recognize and exclude all of its own server names, including
1698   any aliases, local variations, and the numeric IP address. An example
1699   Request-Line would be:
1700</t>
1701<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1702  GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1703  ]]></artwork></figure>
1704<t>
1705   To allow for transition to absolute-URIs in all requests in future
1706   versions of HTTP, all HTTP/1.1 servers MUST accept the absolute-URI
1707   form in requests, even though HTTP/1.1 clients will only generate
1708   them in requests to proxies.
1709</t>
1710<t>
1711   If a proxy receives a host name that is not a fully qualified domain
1712   name, it MAY add its domain to the host name it received. If a proxy
1713   receives a fully qualified domain name, the proxy MUST NOT change
1714   the host name.
1715</t>
1716<t><iref item="authority form (of request-target)"/>
1717   The "authority form" is only used by the CONNECT request method (Section 7.9 of <xref target="Part2"/>).
1718</t>
1719<t><iref item="origin form (of request-target)"/>
1720   The most common form of request-target is that used when making
1721   a request to an origin server ("origin form").
1722   In this case, the absolute path and query components of the URI
1723   MUST be transmitted as the request-target, and the authority component
1724   MUST be transmitted in a Host header field. For example, a client wishing
1725   to retrieve a representation of the resource, as identified above,
1726   directly from the origin server would open (or reuse) a TCP connection
1727   to port 80 of the host "www.example.org" and send the lines:
1728</t>
1729<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1730  GET /pub/WWW/TheProject.html HTTP/1.1
1731  Host: www.example.org
1732  ]]></artwork></figure>
1733<t>
1734   followed by the remainder of the Request. Note that the origin form
1735   of request-target always starts with an absolute path; if the target
1736   resource's URI path is empty, then an absolute path of "/" MUST be
1737   provided in the request-target.
1738</t>
1739<t>
1740   If a proxy receives an OPTIONS request with an absolute-URI form of
1741   request-target in which the URI has an empty path and no query component,
1742   then the last proxy on the request chain MUST use a request-target
1743   of "*" when it forwards the request to the indicated origin server.
1744</t>
1745<figure><preamble>   
1746   For example, the request
1747</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1748  OPTIONS http://www.example.org:8001 HTTP/1.1
1749  ]]></artwork></figure>
1750<figure><preamble>   
1751  would be forwarded by the final proxy as
1752</preamble><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
1753  OPTIONS * HTTP/1.1
1754  Host: www.example.org:8001
1755  ]]></artwork>
1756<postamble>
1757   after connecting to port 8001 of host "www.example.org".
1758</postamble>
1759</figure>
1760<t>
1761   The request-target is transmitted in the format specified in
1762   <xref target="http.uri"/>. If the request-target is percent-encoded
1763   (<xref target="RFC3986"/>, Section 2.1), the origin server
1764   MUST decode the request-target in order to
1765   properly interpret the request. Servers SHOULD respond to invalid
1766   request-targets with an appropriate status code.
1767</t>
1768<t>
1769   A non-transforming proxy MUST NOT rewrite the "path-absolute" part of the
1770   received request-target when forwarding it to the next inbound server,
1771   except as noted above to replace a null path-absolute with "/" or "*".
1772</t>
1773<t><list>
1774  <t>
1775    Note: The "no rewrite" rule prevents the proxy from changing the
1776    meaning of the request when the origin server is improperly using
1777    a non-reserved URI character for a reserved purpose.  Implementors
1778    need to be aware that some pre-HTTP/1.1 proxies have been known to
1779    rewrite the request-target.
1780  </t>
1781</list></t>
1782<t>
1783   HTTP does not place a pre-defined limit on the length of a request-target.
1784   A server MUST be prepared to receive URIs of unbounded length and
1785   respond with the 414 (URI Too Long) status code if the received
1786   request-target would be longer than the server wishes to handle
1787   (see Section 8.4.15 of <xref target="Part2"/>).
1788</t>
1789<t>
1790   Various ad-hoc limitations on request-target length are found in practice.
1791   It is RECOMMENDED that all HTTP senders and recipients support
1792   request-target lengths of 8000 or more octets.
1793</t>
1794<t><list>
1795  <t>
1796    Note: Fragments (<xref target="RFC3986"/>, Section 3.5)
1797    are not part of the request-target and thus will not be transmitted
1798    in an HTTP request.
1799  </t>
1800</list></t>
1801</section>
1802</section>
1803
1804<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1805<t>
1806   The exact resource identified by an Internet request is determined by
1807   examining both the request-target and the Host header field.
1808</t>
1809<t>
1810   An origin server that does not allow resources to differ by the
1811   requested host MAY ignore the Host header field value when
1812   determining the resource identified by an HTTP/1.1 request. (But see
1813   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1814   for other requirements on Host support in HTTP/1.1.)
1815</t>
1816<t>
1817   An origin server that does differentiate resources based on the host
1818   requested (sometimes referred to as virtual hosts or vanity host
1819   names) MUST use the following rules for determining the requested
1820   resource on an HTTP/1.1 request:
1821  <list style="numbers">
1822    <t>If request-target is an absolute-URI, the host is part of the
1823     request-target. Any Host header field value in the request MUST be
1824     ignored.</t>
1825    <t>If the request-target is not an absolute-URI, and the request includes
1826     a Host header field, the host is determined by the Host header
1827     field value.</t>
1828    <t>If the host as determined by rule 1 or 2 is not a valid host on
1829     the server, the response MUST be a 400 (Bad Request) error message.</t>
1830  </list>
1831</t>
1832<t>
1833   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1834   attempt to use heuristics (e.g., examination of the URI path for
1835   something unique to a particular host) in order to determine what
1836   exact resource is being requested.
1837</t>
1838</section>
1839
1840<section title="Effective Request URI" anchor="effective.request.uri">
1841  <iref primary="true" item="effective request URI"/>
1842  <iref primary="true" item="target resource"/>
1843<t>
1844   HTTP requests often do not carry the absolute URI (<xref target="RFC3986"/>, Section 4.3)
1845   for the target resource; instead, the URI needs to be inferred from the
1846   request-target, Host header field, and connection context. The result of
1847   this process is called the "effective request URI".  The "target resource"
1848   is the resource identified by the effective request URI.
1849</t>
1850<t>
1851   If the request-target is an absolute-URI, then the effective request URI is
1852   the request-target.
1853</t>
1854<t>
1855   If the request-target uses the path-absolute form or the asterisk form,
1856   and the Host header field is present, then the effective request URI is
1857   constructed by concatenating
1858</t>
1859<t>
1860  <list style="symbols">
1861    <t>
1862      the scheme name: "http" if the request was received over an insecure
1863      TCP connection, or "https" when received over a SSL/TLS-secured TCP
1864      connection,
1865    </t>
1866    <t>
1867      the octet sequence "://",
1868    </t>
1869    <t>
1870      the authority component, as specified in the Host header field
1871      (<xref target="header.host"/>), and
1872    </t>
1873    <t>
1874      the request-target obtained from the Request-Line, unless the
1875      request-target is just the asterisk "*".
1876    </t>
1877  </list>
1878</t>
1879<t>
1880   If the request-target uses the path-absolute form or the asterisk form,
1881   and the Host header field is not present, then the effective request URI is
1882   undefined.
1883</t>
1884<t>
1885   Otherwise, when request-target uses the authority form, the effective
1886   request URI is undefined.
1887</t>
1888<figure>
1889<preamble>
1890   Example 1: the effective request URI for the message
1891</preamble> 
1892<artwork type="example"><![CDATA[
1893  GET /pub/WWW/TheProject.html HTTP/1.1
1894  Host: www.example.org:8080
1895  ]]></artwork>
1896<postamble>
1897  (received over an insecure TCP connection) is "http", plus "://", plus the
1898  authority component "www.example.org:8080", plus the request-target
1899  "/pub/WWW/TheProject.html", thus
1900  "http://www.example.org:8080/pub/WWW/TheProject.html".
1901</postamble>
1902</figure>
1903<figure>
1904<preamble>
1905   Example 2: the effective request URI for the message
1906</preamble> 
1907<artwork type="example"><![CDATA[
1908  OPTIONS * HTTP/1.1
1909  Host: www.example.org
1910  ]]></artwork>
1911<postamble>
1912  (received over an SSL/TLS secured TCP connection) is "https", plus "://", plus the
1913  authority component "www.example.org", thus "https://www.example.org".
1914</postamble>
1915</figure>
1916<t>
1917   Effective request URIs are compared using the rules described in
1918   <xref target="uri.comparison"/>, except that empty path components MUST NOT
1919   be treated as equivalent to an absolute path of "/".
1920</t> 
1921</section>
1922
1923</section>
1924
1925
1926<section title="Response" anchor="response">
1927 
1928<t>
1929   After receiving and interpreting a request message, a server responds
1930   with an HTTP response message.
1931</t>
1932<figure><iref primary="true" item="Grammar" subitem="Response"/><artwork type="abnf2616"><![CDATA[
1933  Response      = Status-Line               ; Section 5.1
1934                  *( header-field CRLF )    ; Section 3.2
1935                  CRLF
1936                  [ message-body ]          ; Section 3.3
1937]]></artwork></figure>
1938
1939<section title="Status-Line" anchor="status-line">
1940 
1941<t>
1942   The first line of a Response message is the Status-Line, consisting
1943   of the protocol version, a space (SP), the status code, another space,
1944   a possibly-empty textual phrase describing the status code, and
1945   ending with CRLF.
1946</t>
1947<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1948  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1949]]></artwork></figure>
1950
1951<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1952 
1953 
1954<t>
1955   The Status-Code element is a 3-digit integer result code of the
1956   attempt to understand and satisfy the request. These codes are fully
1957   defined in Section 8 of <xref target="Part2"/>.  The Reason Phrase exists for the sole
1958   purpose of providing a textual description associated with the numeric
1959   status code, out of deference to earlier Internet application protocols
1960   that were more frequently used with interactive text clients.
1961   A client SHOULD ignore the content of the Reason Phrase.
1962</t>
1963<t>
1964   The first digit of the Status-Code defines the class of response. The
1965   last two digits do not have any categorization role. There are 5
1966   values for the first digit:
1967  <list style="symbols">
1968    <t>
1969      1xx: Informational - Request received, continuing process
1970    </t>
1971    <t>
1972      2xx: Success - The action was successfully received,
1973        understood, and accepted
1974    </t>
1975    <t>
1976      3xx: Redirection - Further action must be taken in order to
1977        complete the request
1978    </t>
1979    <t>
1980      4xx: Client Error - The request contains bad syntax or cannot
1981        be fulfilled
1982    </t>
1983    <t>
1984      5xx: Server Error - The server failed to fulfill an apparently
1985        valid request
1986    </t>
1987  </list>
1988</t>
1989<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
1990  Status-Code    = 3DIGIT
1991  Reason-Phrase  = *( WSP / VCHAR / obs-text )
1992]]></artwork></figure>
1993</section>
1994</section>
1995
1996</section>
1997
1998
1999<section title="Protocol Parameters" anchor="protocol.parameters">
2000
2001<section title="Date/Time Formats: Full Date" anchor="date.time.formats.full.date">
2002 
2003<t>
2004   HTTP applications have historically allowed three different formats
2005   for date/time stamps. However, the preferred format is a fixed-length subset
2006   of that defined by <xref target="RFC1123"/>:
2007</t>
2008<figure><artwork type="example"><![CDATA[
2009  Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 1123
2010  ]]></artwork></figure>
2011<t>
2012   The other formats are described here only for compatibility with obsolete
2013   implementations.
2014</t>
2015<figure><artwork type="example"><![CDATA[
2016  Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
2017  Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
2018  ]]></artwork></figure>
2019<t>
2020   HTTP/1.1 clients and servers that parse a date value MUST accept
2021   all three formats (for compatibility with HTTP/1.0), though they MUST
2022   only generate the RFC 1123 format for representing HTTP-date values
2023   in header fields.
2024</t>
2025<t>
2026   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
2027   (GMT), without exception. For the purposes of HTTP, GMT is exactly
2028   equal to UTC (Coordinated Universal Time). This is indicated in the
2029   first two formats by the inclusion of "GMT" as the three-letter
2030   abbreviation for time zone, and MUST be assumed when reading the
2031   asctime format. HTTP-date is case sensitive and MUST NOT include
2032   additional whitespace beyond that specifically included as SP in the
2033   grammar.
2034</t>
2035<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><artwork type="abnf2616"><![CDATA[
2036  HTTP-date    = rfc1123-date / obs-date
2037]]></artwork></figure>
2038<t anchor="preferred.date.format">
2039 
2040 
2041 
2042 
2043 
2044 
2045 
2046 
2047 
2048 
2049  Preferred format:
2050</t>
2051<figure><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="time-of-day"/><iref primary="true" item="Grammar" subitem="hour"/><iref primary="true" item="Grammar" subitem="minute"/><iref primary="true" item="Grammar" subitem="second"/><iref primary="true" item="Grammar" subitem="day-name"/><iref primary="true" item="Grammar" subitem="day-name-l"/><iref primary="true" item="Grammar" subitem="day"/><iref primary="true" item="Grammar" subitem="month"/><iref primary="true" item="Grammar" subitem="year"/><iref primary="true" item="Grammar" subitem="GMT"/><artwork type="abnf2616"><![CDATA[
2052  rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
2053  ; fixed length subset of the format defined in
2054  ; Section 5.2.14 of [RFC1123]
2055 
2056  day-name     = %x4D.6F.6E ; "Mon", case-sensitive
2057               / %x54.75.65 ; "Tue", case-sensitive
2058               / %x57.65.64 ; "Wed", case-sensitive
2059               / %x54.68.75 ; "Thu", case-sensitive
2060               / %x46.72.69 ; "Fri", case-sensitive
2061               / %x53.61.74 ; "Sat", case-sensitive
2062               / %x53.75.6E ; "Sun", case-sensitive
2063               
2064  date1        = day SP month SP year
2065               ; e.g., 02 Jun 1982
2066
2067  day          = 2DIGIT
2068  month        = %x4A.61.6E ; "Jan", case-sensitive
2069               / %x46.65.62 ; "Feb", case-sensitive
2070               / %x4D.61.72 ; "Mar", case-sensitive
2071               / %x41.70.72 ; "Apr", case-sensitive
2072               / %x4D.61.79 ; "May", case-sensitive
2073               / %x4A.75.6E ; "Jun", case-sensitive
2074               / %x4A.75.6C ; "Jul", case-sensitive
2075               / %x41.75.67 ; "Aug", case-sensitive
2076               / %x53.65.70 ; "Sep", case-sensitive
2077               / %x4F.63.74 ; "Oct", case-sensitive
2078               / %x4E.6F.76 ; "Nov", case-sensitive
2079               / %x44.65.63 ; "Dec", case-sensitive
2080  year         = 4DIGIT
2081
2082  GMT   = %x47.4D.54 ; "GMT", case-sensitive
2083
2084  time-of-day  = hour ":" minute ":" second
2085                 ; 00:00:00 - 23:59:59
2086                 
2087  hour         = 2DIGIT               
2088  minute       = 2DIGIT               
2089  second       = 2DIGIT               
2090]]></artwork></figure>
2091<t>
2092  The semantics of <xref target="preferred.date.format" format="none">day-name</xref>, <xref target="preferred.date.format" format="none">day</xref>,
2093  <xref target="preferred.date.format" format="none">month</xref>, <xref target="preferred.date.format" format="none">year</xref>, and <xref target="preferred.date.format" format="none">time-of-day</xref> are the
2094  same as those defined for the RFC 5322 constructs
2095  with the corresponding name (<xref target="RFC5322"/>, Section 3.3).
2096</t>
2097<t anchor="obsolete.date.formats">
2098 
2099 
2100 
2101 
2102 
2103 
2104 
2105 
2106  Obsolete formats:
2107</t>
2108<figure><iref primary="true" item="Grammar" subitem="obs-date"/><artwork type="abnf2616"><![CDATA[
2109  obs-date     = rfc850-date / asctime-date
2110]]></artwork></figure>
2111<figure><iref primary="true" item="Grammar" subitem="rfc850-date"/><artwork type="abnf2616"><![CDATA[
2112  rfc850-date  = day-name-l "," SP date2 SP time-of-day SP GMT
2113  date2        = day "-" month "-" 2DIGIT
2114                 ; day-month-year (e.g., 02-Jun-82)
2115
2116  day-name-l   = %x4D.6F.6E.64.61.79 ; "Monday", case-sensitive
2117         / %x54.75.65.73.64.61.79 ; "Tuesday", case-sensitive
2118         / %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
2119         / %x54.68.75.72.73.64.61.79 ; "Thursday", case-sensitive
2120         / %x46.72.69.64.61.79 ; "Friday", case-sensitive
2121         / %x53.61.74.75.72.64.61.79 ; "Saturday", case-sensitive
2122         / %x53.75.6E.64.61.79 ; "Sunday", case-sensitive
2123]]></artwork></figure>
2124<figure><iref primary="true" item="Grammar" subitem="asctime-date"/><artwork type="abnf2616"><![CDATA[
2125  asctime-date = day-name SP date3 SP time-of-day SP year
2126  date3        = month SP ( 2DIGIT / ( SP 1DIGIT ))
2127                 ; month day (e.g., Jun  2)
2128]]></artwork></figure>
2129<t><list>
2130  <t>
2131    Note: Recipients of date values are encouraged to be robust in
2132    accepting date values that might have been sent by non-HTTP
2133    applications, as is sometimes the case when retrieving or posting
2134    messages via proxies/gateways to SMTP or NNTP.
2135  </t>
2136</list></t>
2137<t><list>
2138  <t>
2139    Note: HTTP requirements for the date/time stamp format apply only
2140    to their usage within the protocol stream. Clients and servers are
2141    not required to use these formats for user presentation, request
2142    logging, etc.
2143  </t>
2144</list></t>
2145</section>
2146
2147<section title="Transfer Codings" anchor="transfer.codings">
2148 
2149 
2150<t>
2151   Transfer-coding values are used to indicate an encoding
2152   transformation that has been, can be, or might need to be applied to a
2153   payload body in order to ensure "safe transport" through the network.
2154   This differs from a content coding in that the transfer-coding is a
2155   property of the message rather than a property of the representation
2156   that is being transferred.
2157</t>
2158<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
2159  transfer-coding         = "chunked" ; Section 6.2.1
2160                          / "compress" ; Section 6.2.2.1
2161                          / "deflate" ; Section 6.2.2.2
2162                          / "gzip" ; Section 6.2.2.3
2163                          / transfer-extension
2164  transfer-extension      = token *( OWS ";" OWS transfer-parameter )
2165]]></artwork></figure>
2166<t anchor="rule.parameter">
2167 
2168 
2169 
2170   Parameters are in the form of attribute/value pairs.
2171</t>
2172<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[
2173  transfer-parameter      = attribute BWS "=" BWS value
2174  attribute               = token
2175  value                   = word
2176]]></artwork></figure>
2177<t>
2178   All transfer-coding values are case-insensitive. HTTP/1.1 uses
2179   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
2180   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
2181</t>
2182<t>
2183   Transfer-codings are analogous to the Content-Transfer-Encoding values of
2184   MIME, which were designed to enable safe transport of binary data over a
2185   7-bit transport service (<xref target="RFC2045"/>, Section 6).
2186   However, safe transport
2187   has a different focus for an 8bit-clean transfer protocol. In HTTP,
2188   the only unsafe characteristic of message-bodies is the difficulty in
2189   determining the exact message body length (<xref target="message.body"/>),
2190   or the desire to encrypt data over a shared transport.
2191</t>
2192<t>
2193   A server that receives a request message with a transfer-coding it does
2194   not understand SHOULD respond with 501 (Not Implemented) and then
2195   close the connection. A server MUST NOT send transfer-codings to an HTTP/1.0
2196   client.
2197</t>
2198
2199<section title="Chunked Transfer Coding" anchor="chunked.encoding">
2200  <iref item="chunked (Coding Format)"/>
2201  <iref item="Coding Format" subitem="chunked"/>
2202 
2203 
2204 
2205 
2206 
2207 
2208 
2209 
2210 
2211 
2212 
2213<t>
2214   The chunked encoding modifies the body of a message in order to
2215   transfer it as a series of chunks, each with its own size indicator,
2216   followed by an OPTIONAL trailer containing header fields. This
2217   allows dynamically produced content to be transferred along with the
2218   information necessary for the recipient to verify that it has
2219   received the full message.
2220</t>
2221<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[
2222  Chunked-Body   = *chunk
2223                   last-chunk
2224                   trailer-part
2225                   CRLF
2226 
2227  chunk          = chunk-size *WSP [ chunk-ext ] CRLF
2228                   chunk-data CRLF
2229  chunk-size     = 1*HEXDIG
2230  last-chunk     = 1*("0") *WSP [ chunk-ext ] CRLF
2231 
2232  chunk-ext      = *( ";" *WSP chunk-ext-name
2233                      [ "=" chunk-ext-val ] *WSP )
2234  chunk-ext-name = token
2235  chunk-ext-val  = token / quoted-str-nf
2236  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
2237  trailer-part   = *( header-field CRLF )
2238 
2239  quoted-str-nf  = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
2240                 ; like quoted-string, but disallowing line folding
2241  qdtext-nf      = WSP / %x21 / %x23-5B / %x5D-7E / obs-text
2242                 ; WSP / <VCHAR except DQUOTE and "\"> / obs-text
2243]]></artwork></figure>
2244<t>
2245   The chunk-size field is a string of hex digits indicating the size of
2246   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
2247   zero, followed by the trailer, which is terminated by an empty line.
2248</t>
2249<t>
2250   The trailer allows the sender to include additional HTTP header
2251   fields at the end of the message. The Trailer header field can be
2252   used to indicate which header fields are included in a trailer (see
2253   <xref target="header.trailer"/>).
2254</t>
2255<t>
2256   A server using chunked transfer-coding in a response MUST NOT use the
2257   trailer for any header fields unless at least one of the following is
2258   true:
2259  <list style="numbers">
2260    <t>the request included a TE header field that indicates "trailers" is
2261     acceptable in the transfer-coding of the  response, as described in
2262     <xref target="header.te"/>; or,</t>
2263     
2264    <t>the trailer fields consist entirely of optional metadata, and the
2265    recipient could use the message (in a manner acceptable to the server where
2266    the field originated) without receiving it. In other words, the server that
2267    generated the header (often but not always the origin server) is willing to
2268    accept the possibility that the trailer fields might be silently discarded
2269    along the path to the client.</t>
2270  </list>
2271</t>
2272<t>
2273   This requirement prevents an interoperability failure when the
2274   message is being received by an HTTP/1.1 (or later) proxy and
2275   forwarded to an HTTP/1.0 recipient. It avoids a situation where
2276   compliance with the protocol would have necessitated a possibly
2277   infinite buffer on the proxy.
2278</t>
2279<t>
2280   A process for decoding the "chunked" transfer-coding
2281   can be represented in pseudo-code as:
2282</t>
2283<figure><artwork type="code"><![CDATA[
2284  length := 0
2285  read chunk-size, chunk-ext (if any) and CRLF
2286  while (chunk-size > 0) {
2287     read chunk-data and CRLF
2288     append chunk-data to decoded-body
2289     length := length + chunk-size
2290     read chunk-size and CRLF
2291  }
2292  read header-field
2293  while (header-field not empty) {
2294     append header-field to existing header fields
2295     read header-field
2296  }
2297  Content-Length := length
2298  Remove "chunked" from Transfer-Encoding
2299]]></artwork></figure>
2300<t>
2301   All HTTP/1.1 applications MUST be able to receive and decode the
2302   "chunked" transfer-coding and MUST ignore chunk-ext extensions
2303   they do not understand.
2304</t>
2305<t>
2306   Since "chunked" is the only transfer-coding required to be understood
2307   by HTTP/1.1 recipients, it plays a crucial role in delimiting messages
2308   on a persistent connection.  Whenever a transfer-coding is applied to
2309   a payload body in a request, the final transfer-coding applied MUST
2310   be "chunked".  If a transfer-coding is applied to a response payload
2311   body, then either the final transfer-coding applied MUST be "chunked"
2312   or the message MUST be terminated by closing the connection. When the
2313   "chunked" transfer-coding is used, it MUST be the last transfer-coding
2314   applied to form the message-body. The "chunked" transfer-coding MUST NOT
2315   be applied more than once in a message-body.
2316</t>
2317</section>
2318
2319<section title="Compression Codings" anchor="compression.codings">
2320<t>
2321   The codings defined below can be used to compress the payload of a
2322   message.
2323</t>
2324<t><list><t>
2325   Note: Use of program names for the identification of encoding formats
2326   is not desirable and is discouraged for future encodings. Their
2327   use here is representative of historical practice, not good
2328   design.
2329</t></list></t>
2330<t><list><t>
2331   Note: For compatibility with previous implementations of HTTP,
2332   applications SHOULD consider "x-gzip" and "x-compress" to be
2333   equivalent to "gzip" and "compress" respectively.
2334</t></list></t>
2335
2336<section title="Compress Coding" anchor="compress.coding">
2337<iref item="compress (Coding Format)"/>
2338<iref item="Coding Format" subitem="compress"/>
2339<t>
2340   The "compress" format is produced by the common UNIX file compression
2341   program "compress". This format is an adaptive Lempel-Ziv-Welch
2342   coding (LZW).
2343</t>
2344</section>
2345
2346<section title="Deflate Coding" anchor="deflate.coding">
2347<iref item="deflate (Coding Format)"/>
2348<iref item="Coding Format" subitem="deflate"/>
2349<t>
2350   The "deflate" format is defined as the "deflate" compression mechanism
2351   (described in <xref target="RFC1951"/>) used inside the "zlib"
2352   data format (<xref target="RFC1950"/>).
2353</t>
2354<t><list>
2355  <t>
2356    Note: Some incorrect implementations send the "deflate"
2357    compressed data without the zlib wrapper.
2358   </t>
2359</list></t>
2360</section>
2361
2362<section title="Gzip Coding" anchor="gzip.coding">
2363<iref item="gzip (Coding Format)"/>
2364<iref item="Coding Format" subitem="gzip"/>
2365<t>
2366   The "gzip" format is produced by the file compression program
2367   "gzip" (GNU zip), as described in <xref target="RFC1952"/>. This format is a
2368   Lempel-Ziv coding (LZ77) with a 32 bit CRC.
2369</t>
2370</section>
2371
2372</section>
2373
2374<section title="Transfer Coding Registry" anchor="transfer.coding.registry">
2375<t>
2376   The HTTP Transfer Coding Registry defines the name space for the transfer
2377   coding names.
2378</t>
2379<t>
2380   Registrations MUST include the following fields:
2381   <list style="symbols">
2382     <t>Name</t>
2383     <t>Description</t>
2384     <t>Pointer to specification text</t>
2385   </list>
2386</t>
2387<t>
2388   Names of transfer codings MUST NOT overlap with names of content codings
2389   (Section 2.2 of <xref target="Part3"/>), unless the encoding transformation is identical (as it
2390   is the case for the compression codings defined in
2391   <xref target="compression.codings"/>).
2392</t>
2393<t>
2394   Values to be added to this name space require a specification
2395   (see "Specification Required" in Section 4.1 of <xref target="RFC5226"/>), and MUST
2396   conform to the purpose of transfer coding defined in this section.
2397</t>
2398<t>
2399   The registry itself is maintained at
2400   <eref target="http://www.iana.org/assignments/http-parameters"/>.
2401</t>
2402</section>
2403</section>
2404
2405<section title="Product Tokens" anchor="product.tokens">
2406 
2407 
2408<t>
2409   Product tokens are used to allow communicating applications to
2410   identify themselves by software name and version. Most fields using
2411   product tokens also allow sub-products which form a significant part
2412   of the application to be listed, separated by whitespace. By
2413   convention, the products are listed in order of their significance
2414   for identifying the application.
2415</t>
2416<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
2417  product         = token ["/" product-version]
2418  product-version = token
2419]]></artwork></figure>
2420<t>
2421   Examples:
2422</t>
2423<figure><artwork type="example"><![CDATA[
2424  User-Agent: CERN-LineMode/2.15 libwww/2.17b3
2425  Server: Apache/0.8.4
2426]]></artwork></figure>
2427<t>
2428   Product tokens SHOULD be short and to the point. They MUST NOT be
2429   used for advertising or other non-essential information. Although any
2430   token octet MAY appear in a product-version, this token SHOULD
2431   only be used for a version identifier (i.e., successive versions of
2432   the same product SHOULD only differ in the product-version portion of
2433   the product value).
2434</t>
2435</section>
2436
2437<section title="Quality Values" anchor="quality.values">
2438 
2439<t>
2440   Both transfer codings (TE request header field, <xref target="header.te"/>)
2441   and content negotiation (Section 5 of <xref target="Part3"/>) use short "floating point"
2442   numbers to indicate the relative importance ("weight") of various
2443   negotiable parameters.  A weight is normalized to a real number in
2444   the range 0 through 1, where 0 is the minimum and 1 the maximum
2445   value. If a parameter has a quality value of 0, then content with
2446   this parameter is "not acceptable" for the client. HTTP/1.1
2447   applications MUST NOT generate more than three digits after the
2448   decimal point. User configuration of these values SHOULD also be
2449   limited in this fashion.
2450</t>
2451<figure><iref primary="true" item="Grammar" subitem="qvalue"/><artwork type="abnf2616"><![CDATA[
2452  qvalue         = ( "0" [ "." 0*3DIGIT ] )
2453                 / ( "1" [ "." 0*3("0") ] )
2454]]></artwork></figure>
2455<t><list>
2456  <t>
2457     Note: "Quality values" is a misnomer, since these values merely represent
2458     relative degradation in desired quality.
2459  </t>
2460</list></t>
2461</section>
2462
2463</section>
2464
2465<section title="Connections" anchor="connections">
2466
2467<section title="Persistent Connections" anchor="persistent.connections">
2468
2469<section title="Purpose" anchor="persistent.purpose">
2470<t>
2471   Prior to persistent connections, a separate TCP connection was
2472   established for each request, increasing the load on HTTP servers
2473   and causing congestion on the Internet. The use of inline images and
2474   other associated data often requires a client to make multiple
2475   requests of the same server in a short amount of time. Analysis of
2476   these performance problems and results from a prototype
2477   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
2478   measurements of actual HTTP/1.1 implementations show good
2479   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
2480   T/TCP <xref target="Tou1998"/>.
2481</t>
2482<t>
2483   Persistent HTTP connections have a number of advantages:
2484  <list style="symbols">
2485      <t>
2486        By opening and closing fewer TCP connections, CPU time is saved
2487        in routers and hosts (clients, servers, proxies, gateways,
2488        tunnels, or caches), and memory used for TCP protocol control
2489        blocks can be saved in hosts.
2490      </t>
2491      <t>
2492        HTTP requests and responses can be pipelined on a connection.
2493        Pipelining allows a client to make multiple requests without
2494        waiting for each response, allowing a single TCP connection to
2495        be used much more efficiently, with much lower elapsed time.
2496      </t>
2497      <t>
2498        Network congestion is reduced by reducing the number of packets
2499        caused by TCP opens, and by allowing TCP sufficient time to
2500        determine the congestion state of the network.
2501      </t>
2502      <t>
2503        Latency on subsequent requests is reduced since there is no time
2504        spent in TCP's connection opening handshake.
2505      </t>
2506      <t>
2507        HTTP can evolve more gracefully, since errors can be reported
2508        without the penalty of closing the TCP connection. Clients using
2509        future versions of HTTP might optimistically try a new feature,
2510        but if communicating with an older server, retry with old
2511        semantics after an error is reported.
2512      </t>
2513    </list>
2514</t>
2515<t>
2516   HTTP implementations SHOULD implement persistent connections.
2517</t>
2518</section>
2519
2520<section title="Overall Operation" anchor="persistent.overall">
2521<t>
2522   A significant difference between HTTP/1.1 and earlier versions of
2523   HTTP is that persistent connections are the default behavior of any
2524   HTTP connection. That is, unless otherwise indicated, the client
2525   SHOULD assume that the server will maintain a persistent connection,
2526   even after error responses from the server.
2527</t>
2528<t>
2529   Persistent connections provide a mechanism by which a client and a
2530   server can signal the close of a TCP connection. This signaling takes
2531   place using the Connection header field (<xref target="header.connection"/>). Once a close
2532   has been signaled, the client MUST NOT send any more requests on that
2533   connection.
2534</t>
2535
2536<section title="Negotiation" anchor="persistent.negotiation">
2537<t>
2538   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
2539   maintain a persistent connection unless a Connection header field including
2540   the connection-token "close" was sent in the request. If the server
2541   chooses to close the connection immediately after sending the
2542   response, it SHOULD send a Connection header field including the
2543   connection-token "close".
2544</t>
2545<t>
2546   An HTTP/1.1 client MAY expect a connection to remain open, but would
2547   decide to keep it open based on whether the response from a server
2548   contains a Connection header field with the connection-token close. In case
2549   the client does not want to maintain a connection for more than that
2550   request, it SHOULD send a Connection header field including the
2551   connection-token close.
2552</t>
2553<t>
2554   If either the client or the server sends the close token in the
2555   Connection header field, that request becomes the last one for the
2556   connection.
2557</t>
2558<t>
2559   Clients and servers SHOULD NOT  assume that a persistent connection is
2560   maintained for HTTP versions less than 1.1 unless it is explicitly
2561   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2562   compatibility with HTTP/1.0 clients.
2563</t>
2564<t>
2565   In order to remain persistent, all messages on the connection MUST
2566   have a self-defined message length (i.e., one not defined by closure
2567   of the connection), as described in <xref target="message.body"/>.
2568</t>
2569</section>
2570
2571<section title="Pipelining" anchor="pipelining">
2572<t>
2573   A client that supports persistent connections MAY "pipeline" its
2574   requests (i.e., send multiple requests without waiting for each
2575   response). A server MUST send its responses to those requests in the
2576   same order that the requests were received.
2577</t>
2578<t>
2579   Clients which assume persistent connections and pipeline immediately
2580   after connection establishment SHOULD be prepared to retry their
2581   connection if the first pipelined attempt fails. If a client does
2582   such a retry, it MUST NOT pipeline before it knows the connection is
2583   persistent. Clients MUST also be prepared to resend their requests if
2584   the server closes the connection before sending all of the
2585   corresponding responses.
2586</t>
2587<t>
2588   Clients SHOULD NOT pipeline requests using non-idempotent request methods or
2589   non-idempotent sequences of request methods (see Section 7.1.2 of <xref target="Part2"/>). Otherwise, a
2590   premature termination of the transport connection could lead to
2591   indeterminate results. A client wishing to send a non-idempotent
2592   request SHOULD wait to send that request until it has received the
2593   response status line for the previous request.
2594</t>
2595</section>
2596</section>
2597
2598<section title="Proxy Servers" anchor="persistent.proxy">
2599<t>
2600   It is especially important that proxies correctly implement the
2601   properties of the Connection header field as specified in <xref target="header.connection"/>.
2602</t>
2603<t>
2604   The proxy server MUST signal persistent connections separately with
2605   its clients and the origin servers (or other proxy servers) that it
2606   connects to. Each persistent connection applies to only one transport
2607   link.
2608</t>
2609<t>
2610   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
2611   with an HTTP/1.0 client (but see Section 19.7.1 of <xref target="RFC2068"/>
2612   for information and discussion of the problems with the Keep-Alive header field
2613   implemented by many HTTP/1.0 clients).
2614</t>
2615
2616<section title="End-to-end and Hop-by-hop Header Fields" anchor="end-to-end.and.hop-by-hop.header-fields">
2617<!--<t>
2618  <cref anchor="TODO-end-to-end" source="jre">
2619    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.1"/>.
2620    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2621  </cref>
2622</t>-->
2623<t>
2624   For the purpose of defining the behavior of caches and non-caching
2625   proxies, we divide HTTP header fields into two categories:
2626  <list style="symbols">
2627      <t>End-to-end header fields, which are  transmitted to the ultimate
2628        recipient of a request or response. End-to-end header fields in
2629        responses MUST be stored as part of a cache entry and MUST be
2630        transmitted in any response formed from a cache entry.</t>
2631
2632      <t>Hop-by-hop header fields, which are meaningful only for a single
2633        transport-level connection, and are not stored by caches or
2634        forwarded by proxies.</t>
2635  </list>
2636</t>
2637<t>
2638   The following HTTP/1.1 header fields are hop-by-hop header fields:
2639  <list style="symbols">
2640      <t>Connection</t>
2641      <t>Keep-Alive</t>
2642      <t>Proxy-Authenticate</t>
2643      <t>Proxy-Authorization</t>
2644      <t>TE</t>
2645      <t>Trailer</t>
2646      <t>Transfer-Encoding</t>
2647      <t>Upgrade</t>
2648  </list>
2649</t>
2650<t>
2651   All other header fields defined by HTTP/1.1 are end-to-end header fields.
2652</t>
2653<t>
2654   Other hop-by-hop header fields MUST be listed in a Connection header field
2655   (<xref target="header.connection"/>).
2656</t>
2657</section>
2658
2659<section title="Non-modifiable Header Fields" anchor="non-modifiable.header-fields">
2660<!--<t>
2661  <cref anchor="TODO-non-mod-headers" source="jre">
2662    Restored from <eref target="http://tools.ietf.org/html/draft-ietf-httpbis-p6-cache-05#section-7.2"/>.
2663    See also <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>.
2664  </cref>
2665</t>-->
2666<t>
2667   Some features of HTTP/1.1, such as Digest Authentication, depend on the
2668   value of certain end-to-end header fields. A non-transforming proxy SHOULD NOT
2669   modify an end-to-end header field unless the definition of that header field requires
2670   or specifically allows that.
2671</t>
2672<t>
2673   A non-transforming proxy MUST NOT modify any of the following fields in a
2674   request or response, and it MUST NOT add any of these fields if not
2675   already present:
2676  <list style="symbols">
2677    <t>Allow</t>
2678    <t>Content-Location</t>
2679    <t>Content-MD5</t>
2680    <t>ETag</t>
2681    <t>Last-Modified</t>
2682    <t>Server</t>
2683  </list>
2684</t>
2685<t>
2686   A non-transforming proxy MUST NOT modify any of the following fields in a
2687   response:
2688  <list style="symbols">
2689    <t>Expires</t>
2690  </list>
2691</t>
2692<t>
2693   but it MAY add any of these fields if not already present. If an
2694   Expires header field is added, it MUST be given a field-value identical to
2695   that of the Date header field in that response.
2696</t>
2697<t>
2698   A proxy MUST NOT modify or add any of the following fields in a
2699   message that contains the no-transform cache-control directive, or in
2700   any request:
2701  <list style="symbols">
2702    <t>Content-Encoding</t>
2703    <t>Content-Range</t>
2704    <t>Content-Type</t>
2705  </list>
2706</t>
2707<t>
2708   A transforming proxy MAY modify or add these fields to a message
2709   that does not include no-transform, but if it does so, it MUST add a
2710   Warning 214 (Transformation applied) if one does not already appear
2711   in the message (see Section 3.6 of <xref target="Part6"/>).
2712</t>
2713<t><list>
2714  <t>
2715    Warning: Unnecessary modification of end-to-end header fields might
2716    cause authentication failures if stronger authentication
2717    mechanisms are introduced in later versions of HTTP. Such
2718    authentication mechanisms MAY rely on the values of header fields
2719    not listed here.
2720  </t>
2721</list></t>
2722<t>
2723   A non-transforming proxy MUST preserve the message payload (<xref target="Part3"/>),
2724   though it MAY change the message-body through application or removal
2725   of a transfer-coding (<xref target="transfer.codings"/>).
2726</t>
2727</section>
2728
2729</section>
2730
2731<section title="Practical Considerations" anchor="persistent.practical">
2732<t>
2733   Servers will usually have some time-out value beyond which they will
2734   no longer maintain an inactive connection. Proxy servers might make
2735   this a higher value since it is likely that the client will be making
2736   more connections through the same server. The use of persistent
2737   connections places no requirements on the length (or existence) of
2738   this time-out for either the client or the server.
2739</t>
2740<t>
2741   When a client or server wishes to time-out it SHOULD issue a graceful
2742   close on the transport connection. Clients and servers SHOULD both
2743   constantly watch for the other side of the transport close, and
2744   respond to it as appropriate. If a client or server does not detect
2745   the other side's close promptly it could cause unnecessary resource
2746   drain on the network.
2747</t>
2748<t>
2749   A client, server, or proxy MAY close the transport connection at any
2750   time. For example, a client might have started to send a new request
2751   at the same time that the server has decided to close the "idle"
2752   connection. From the server's point of view, the connection is being
2753   closed while it was idle, but from the client's point of view, a
2754   request is in progress.
2755</t>
2756<t>
2757   This means that clients, servers, and proxies MUST be able to recover
2758   from asynchronous close events. Client software SHOULD reopen the
2759   transport connection and retransmit the aborted sequence of requests
2760   without user interaction so long as the request sequence is
2761   idempotent (see Section 7.1.2 of <xref target="Part2"/>). Non-idempotent request methods or sequences
2762   MUST NOT be automatically retried, although user agents MAY offer a
2763   human operator the choice of retrying the request(s). Confirmation by
2764   user-agent software with semantic understanding of the application
2765   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2766   be repeated if the second sequence of requests fails.
2767</t>
2768<t>
2769   Servers SHOULD always respond to at least one request per connection,
2770   if at all possible. Servers SHOULD NOT  close a connection in the
2771   middle of transmitting a response, unless a network or client failure
2772   is suspected.
2773</t>
2774<t>
2775   Clients (including proxies) SHOULD limit the number of simultaneous
2776   connections that they maintain to a given server (including proxies).
2777</t>
2778<t>
2779   Previous revisions of HTTP gave a specific number of connections as a
2780   ceiling, but this was found to be impractical for many applications. As a
2781   result, this specification does not mandate a particular maximum number of
2782   connections, but instead encourages clients to be conservative when opening
2783   multiple connections.
2784</t>
2785<t>
2786   In particular, while using multiple connections avoids the "head-of-line
2787   blocking" problem (whereby a request that takes significant server-side
2788   processing and/or has a large payload can block subsequent requests on the
2789   same connection), each connection used consumes server resources (sometimes
2790   significantly), and furthermore using multiple connections can cause
2791   undesirable side effects in congested networks.
2792</t>
2793<t>
2794   Note that servers might reject traffic that they deem abusive, including an
2795   excessive number of connections from a client.
2796</t>
2797</section>
2798</section>
2799
2800<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2801
2802<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2803<t>
2804   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2805   flow control mechanisms to resolve temporary overloads, rather than
2806   terminating connections with the expectation that clients will retry.
2807   The latter technique can exacerbate network congestion.
2808</t>
2809</section>
2810
2811<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2812<t>
2813   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2814   the network connection for an error status code while it is transmitting
2815   the request. If the client sees an error status code, it SHOULD
2816   immediately cease transmitting the body. If the body is being sent
2817   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2818   empty trailer MAY be used to prematurely mark the end of the message.
2819   If the body was preceded by a Content-Length header field, the client MUST
2820   close the connection.
2821</t>
2822</section>
2823
2824<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2825<t>
2826   The purpose of the 100 (Continue) status code (see Section 8.1.1 of <xref target="Part2"/>) is to
2827   allow a client that is sending a request message with a request body
2828   to determine if the origin server is willing to accept the request
2829   (based on the request header fields) before the client sends the request
2830   body. In some cases, it might either be inappropriate or highly
2831   inefficient for the client to send the body if the server will reject
2832   the message without looking at the body.
2833</t>
2834<t>
2835   Requirements for HTTP/1.1 clients:
2836  <list style="symbols">
2837    <t>
2838        If a client will wait for a 100 (Continue) response before
2839        sending the request body, it MUST send an Expect header
2840        field (Section 9.2 of <xref target="Part2"/>) with the "100-continue" expectation.
2841    </t>
2842    <t>
2843        A client MUST NOT send an Expect header field (Section 9.2 of <xref target="Part2"/>)
2844        with the "100-continue" expectation if it does not intend
2845        to send a request body.
2846    </t>
2847  </list>
2848</t>
2849<t>
2850   Because of the presence of older implementations, the protocol allows
2851   ambiguous situations in which a client might send "Expect: 100-continue"
2852   without receiving either a 417 (Expectation Failed)
2853   or a 100 (Continue) status code. Therefore, when a client sends this
2854   header field to an origin server (possibly via a proxy) from which it
2855   has never seen a 100 (Continue) status code, the client SHOULD NOT 
2856   wait for an indefinite period before sending the request body.
2857</t>
2858<t>
2859   Requirements for HTTP/1.1 origin servers:
2860  <list style="symbols">
2861    <t> Upon receiving a request which includes an Expect header
2862        field with the "100-continue" expectation, an origin server MUST
2863        either respond with 100 (Continue) status code and continue to read
2864        from the input stream, or respond with a final status code. The
2865        origin server MUST NOT wait for the request body before sending
2866        the 100 (Continue) response. If it responds with a final status
2867        code, it MAY close the transport connection or it MAY continue
2868        to read and discard the rest of the request.  It MUST NOT
2869        perform the request method if it returns a final status code.
2870    </t>
2871    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2872        the request message does not include an Expect header
2873        field with the "100-continue" expectation, and MUST NOT send a
2874        100 (Continue) response if such a request comes from an HTTP/1.0
2875        (or earlier) client. There is an exception to this rule: for
2876        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2877        status code in response to an HTTP/1.1 PUT or POST request that does
2878        not include an Expect header field with the "100-continue"
2879        expectation. This exception, the purpose of which is
2880        to minimize any client processing delays associated with an
2881        undeclared wait for 100 (Continue) status code, applies only to
2882        HTTP/1.1 requests, and not to requests with any other HTTP-version
2883        value.
2884    </t>
2885    <t> An origin server MAY omit a 100 (Continue) response if it has
2886        already received some or all of the request body for the
2887        corresponding request.
2888    </t>
2889    <t> An origin server that sends a 100 (Continue) response MUST
2890    ultimately send a final status code, once the request body is
2891        received and processed, unless it terminates the transport
2892        connection prematurely.
2893    </t>
2894    <t> If an origin server receives a request that does not include an
2895        Expect header field with the "100-continue" expectation,
2896        the request includes a request body, and the server responds
2897        with a final status code before reading the entire request body
2898        from the transport connection, then the server SHOULD NOT  close
2899        the transport connection until it has read the entire request,
2900        or until the client closes the connection. Otherwise, the client
2901        might not reliably receive the response message. However, this
2902        requirement is not be construed as preventing a server from
2903        defending itself against denial-of-service attacks, or from
2904        badly broken client implementations.
2905      </t>
2906    </list>
2907</t>
2908<t>
2909   Requirements for HTTP/1.1 proxies:
2910  <list style="symbols">
2911    <t> If a proxy receives a request that includes an Expect header
2912        field with the "100-continue" expectation, and the proxy
2913        either knows that the next-hop server complies with HTTP/1.1 or
2914        higher, or does not know the HTTP version of the next-hop
2915        server, it MUST forward the request, including the Expect header
2916        field.
2917    </t>
2918    <t> If the proxy knows that the version of the next-hop server is
2919        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2920        respond with a 417 (Expectation Failed) status code.
2921    </t>
2922    <t> Proxies SHOULD maintain a record of the HTTP version
2923        numbers received from recently-referenced next-hop servers.
2924    </t>
2925    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2926        request message was received from an HTTP/1.0 (or earlier)
2927        client and did not include an Expect header field with
2928        the "100-continue" expectation. This requirement overrides the
2929        general rule for forwarding of 1xx responses (see Section 8.1 of <xref target="Part2"/>).
2930    </t>
2931  </list>
2932</t>
2933</section>
2934
2935<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2936<t>
2937   If an HTTP/1.1 client sends a request which includes a request body,
2938   but which does not include an Expect header field with the
2939   "100-continue" expectation, and if the client is not directly
2940   connected to an HTTP/1.1 origin server, and if the client sees the
2941   connection close before receiving a status line from the server, the
2942   client SHOULD retry the request.  If the client does retry this
2943   request, it MAY use the following "binary exponential backoff"
2944   algorithm to be assured of obtaining a reliable response:
2945  <list style="numbers">
2946    <t>
2947      Initiate a new connection to the server
2948    </t>
2949    <t>
2950      Transmit the request-line, header fields, and the CRLF that
2951      indicates the end of header fields.
2952    </t>
2953    <t>
2954      Initialize a variable R to the estimated round-trip time to the
2955         server (e.g., based on the time it took to establish the
2956         connection), or to a constant value of 5 seconds if the round-trip
2957         time is not available.
2958    </t>
2959    <t>
2960       Compute T = R * (2**N), where N is the number of previous
2961         retries of this request.
2962    </t>
2963    <t>
2964       Wait either for an error response from the server, or for T
2965         seconds (whichever comes first)
2966    </t>
2967    <t>
2968       If no error response is received, after T seconds transmit the
2969         body of the request.
2970    </t>
2971    <t>
2972       If client sees that the connection is closed prematurely,
2973         repeat from step 1 until the request is accepted, an error
2974         response is received, or the user becomes impatient and
2975         terminates the retry process.
2976    </t>
2977  </list>
2978</t>
2979<t>
2980   If at any point an error status code is received, the client
2981  <list style="symbols">
2982      <t>SHOULD NOT  continue and</t>
2983
2984      <t>SHOULD close the connection if it has not completed sending the
2985        request message.</t>
2986    </list>
2987</t>
2988</section>
2989</section>
2990</section>
2991
2992
2993<section title="Miscellaneous notes that might disappear" anchor="misc">
2994<section title="Scheme aliases considered harmful" anchor="scheme.aliases">
2995<t>
2996   <cref anchor="TBD-aliases-harmful">describe why aliases like webcal are harmful.</cref>
2997</t>
2998</section>
2999
3000<section title="Use of HTTP for proxy communication" anchor="http.proxy">
3001<t>
3002   <cref anchor="TBD-proxy-other">Configured to use HTTP to proxy HTTP or other protocols.</cref>
3003</t>
3004</section>
3005
3006<section title="Interception of HTTP for access control" anchor="http.intercept">
3007<t>
3008   <cref anchor="TBD-intercept">Interception of HTTP traffic for initiating access control.</cref>
3009</t>
3010</section>
3011
3012<section title="Use of HTTP by other protocols" anchor="http.others">
3013<t>
3014   <cref anchor="TBD-profiles">Profiles of HTTP defined by other protocol.
3015   Extensions of HTTP like WebDAV.</cref>
3016</t>
3017
3018</section>
3019<section title="Use of HTTP by media type specification" anchor="http.media">
3020<t>
3021   <cref anchor="TBD-hypertext">Instructions on composing HTTP requests via hypertext formats.</cref>
3022</t>
3023</section>
3024</section>
3025
3026<section title="Header Field Definitions" anchor="header.field.definitions">
3027<t>
3028   This section defines the syntax and semantics of HTTP header fields
3029   related to message framing and transport protocols.
3030</t>
3031
3032<section title="Connection" anchor="header.connection">
3033  <iref primary="true" item="Connection header field"/>
3034  <iref primary="true" item="Header Fields" subitem="Connection"/>
3035 
3036 
3037<t>
3038   The "Connection" header field allows the sender to specify
3039   options that are desired only for that particular connection.
3040   Such connection options MUST be removed or replaced before the
3041   message can be forwarded downstream by a proxy or gateway.
3042   This mechanism also allows the sender to indicate which HTTP
3043   header fields used in the message are only intended for the
3044   immediate recipient ("hop-by-hop"), as opposed to all recipients
3045   on the chain ("end-to-end"), enabling the message to be
3046   self-descriptive and allowing future connection-specific extensions
3047   to be deployed in HTTP without fear that they will be blindly
3048   forwarded by previously deployed intermediaries.
3049</t>
3050<t>
3051   The Connection header field's value has the following grammar:
3052</t>
3053<figure><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/><artwork type="abnf2616"><![CDATA[
3054  Connection       = 1#connection-token
3055  connection-token = token
3056]]></artwork></figure>
3057<t>
3058   A proxy or gateway MUST parse a received Connection
3059   header field before a message is forwarded and, for each
3060   connection-token in this field, remove any header field(s) from
3061   the message with the same name as the connection-token, and then
3062   remove the Connection header field itself or replace it with the
3063   sender's own connection options for the forwarded message.
3064</t>
3065<t>
3066   A sender MUST NOT include field-names in the Connection header
3067   field-value for fields that are defined as expressing constraints
3068   for all recipients in the request or response chain, such as the
3069   Cache-Control header field (Section 3.2 of <xref target="Part6"/>).
3070</t>
3071<t>
3072   The connection options do not have to correspond to a header field
3073   present in the message, since a connection-specific header field
3074   might not be needed if there are no parameters associated with that
3075   connection option.  Recipients that trigger certain connection
3076   behavior based on the presence of connection options MUST do so
3077   based on the presence of the connection-token rather than only the
3078   presence of the optional header field.  In other words, if the
3079   connection option is received as a header field but not indicated
3080   within the Connection field-value, then the recipient MUST ignore
3081   the connection-specific header field because it has likely been
3082   forwarded by an intermediary that is only partially compliant.
3083</t>
3084<t>
3085   When defining new connection options, specifications ought to
3086   carefully consider existing deployed header fields and ensure
3087   that the new connection-token does not share the same name as
3088   an unrelated header field that might already be deployed.
3089   Defining a new connection-token essentially reserves that potential
3090   field-name for carrying additional information related to the
3091   connection option, since it would be unwise for senders to use
3092   that field-name for anything else.
3093</t>
3094<t>
3095   HTTP/1.1 defines the "close" connection option for the sender to
3096   signal that the connection will be closed after completion of the
3097   response. For example,
3098</t>
3099<figure><artwork type="example"><![CDATA[
3100  Connection: close
3101]]></artwork></figure>
3102<t>
3103   in either the request or the response header fields indicates that
3104   the connection SHOULD NOT  be considered "persistent" (<xref target="persistent.connections"/>)
3105   after the current request/response is complete.
3106</t>
3107<t>
3108   An HTTP/1.1 client that does not support persistent connections MUST
3109   include the "close" connection option in every request message.
3110</t>
3111<t>
3112   An HTTP/1.1 server that does not support persistent connections MUST
3113   include the "close" connection option in every response message that
3114   does not have a 1xx (Informational) status code.
3115</t>
3116</section>
3117
3118<section title="Content-Length" anchor="header.content-length">
3119  <iref primary="true" item="Content-Length header field"/>
3120  <iref primary="true" item="Header Fields" subitem="Content-Length"/>
3121 
3122<t>
3123   The "Content-Length" header field indicates the size of the
3124   message-body, in decimal number of octets, for any message other than
3125   a response to a HEAD request or a response with a status code of 304.
3126   In the case of a response to a HEAD request, Content-Length indicates
3127   the size of the payload body (not including any potential transfer-coding)
3128   that would have been sent had the request been a GET.
3129   In the case of a 304 (Not Modified) response to a GET request,
3130   Content-Length indicates the size of the payload body (not including
3131   any potential transfer-coding) that would have been sent in a 200 (OK)
3132   response.
3133</t>
3134<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><artwork type="abnf2616"><![CDATA[
3135  Content-Length = 1*DIGIT
3136]]></artwork></figure>
3137<t>
3138   An example is
3139</t>
3140<figure><artwork type="example"><![CDATA[
3141  Content-Length: 3495
3142]]></artwork></figure>
3143<t>
3144   Implementations SHOULD use this field to indicate the message-body
3145   length when no transfer-coding is being applied and the
3146   payload's body length can be determined prior to being transferred.
3147   <xref target="message.body"/> describes how recipients determine the length
3148   of a message-body.
3149</t>
3150<t>
3151   Any Content-Length greater than or equal to zero is a valid value.
3152</t>
3153<t>
3154   Note that the use of this field in HTTP is significantly different from
3155   the corresponding definition in MIME, where it is an optional field
3156   used within the "message/external-body" content-type.
3157</t>
3158</section>
3159
3160<section title="Date" anchor="header.date">
3161  <iref primary="true" item="Date header field"/>
3162  <iref primary="true" item="Header Fields" subitem="Date"/>
3163 
3164<t>
3165   The "Date" header field represents the date and time at which
3166   the message was originated, having the same semantics as the Origination
3167   Date Field (orig-date) defined in Section 3.6.1 of <xref target="RFC5322"/>.
3168   The field value is an HTTP-date, as described in <xref target="date.time.formats.full.date"/>;
3169   it MUST be sent in rfc1123-date format.
3170</t>
3171<figure><iref primary="true" item="Grammar" subitem="Date"/><artwork type="abnf2616"><![CDATA[
3172  Date = HTTP-date
3173]]></artwork></figure>
3174<t>
3175   An example is
3176</t>
3177<figure><artwork type="example"><![CDATA[
3178  Date: Tue, 15 Nov 1994 08:12:31 GMT
3179]]></artwork></figure>
3180<t>
3181   Origin servers MUST include a Date header field in all responses,
3182   except in these cases:
3183  <list style="numbers">
3184      <t>If the response status code is 100 (Continue) or 101 (Switching
3185         Protocols), the response MAY include a Date header field, at
3186         the server's option.</t>
3187
3188      <t>If the response status code conveys a server error, e.g., 500
3189         (Internal Server Error) or 503 (Service Unavailable), and it is
3190         inconvenient or impossible to generate a valid Date.</t>
3191
3192      <t>If the server does not have a clock that can provide a
3193         reasonable approximation of the current time, its responses
3194         MUST NOT include a Date header field. In this case, the rules
3195         in <xref target="clockless.origin.server.operation"/> MUST be followed.</t>
3196  </list>
3197</t>
3198<t>
3199   A received message that does not have a Date header field MUST be
3200   assigned one by the recipient if the message will be cached by that
3201   recipient.
3202</t>
3203<t>
3204   Clients can use the Date header field as well; in order to keep request
3205   messages small, they are advised not to include it when it doesn't convey
3206   any useful information (as it is usually the case for requests that do not
3207   contain a payload).
3208</t>
3209<t>
3210   The HTTP-date sent in a Date header field SHOULD NOT  represent a date and
3211   time subsequent to the generation of the message. It SHOULD represent
3212   the best available approximation of the date and time of message
3213   generation, unless the implementation has no means of generating a
3214   reasonably accurate date and time. In theory, the date ought to
3215   represent the moment just before the payload is generated. In
3216   practice, the date can be generated at any time during the message
3217   origination without affecting its semantic value.
3218</t>
3219
3220<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
3221<t>
3222   Some origin server implementations might not have a clock available.
3223   An origin server without a clock MUST NOT assign Expires or Last-Modified
3224   values to a response, unless these values were associated
3225   with the resource by a system or user with a reliable clock. It MAY
3226   assign an Expires value that is known, at or before server
3227   configuration time, to be in the past (this allows "pre-expiration"
3228   of responses without storing separate Expires values for each
3229   resource).
3230</t>
3231</section>
3232</section>
3233
3234<section title="Host" anchor="header.host">
3235  <iref primary="true" item="Host header field"/>
3236  <iref primary="true" item="Header Fields" subitem="Host"/>
3237 
3238<t>
3239   The "Host" header field in a request provides the host and port
3240   information from the target resource's URI, enabling the origin
3241   server to distinguish between resources while servicing requests
3242   for multiple host names on a single IP address.  Since the Host
3243   field-value is critical information for handling a request, it
3244   SHOULD be sent as the first header field following the Request-Line.
3245</t>
3246<figure><iref primary="true" item="Grammar" subitem="Host"/><artwork type="abnf2616"><![CDATA[
3247  Host = uri-host [ ":" port ] ; Section 2.7.1
3248]]></artwork></figure>
3249<t>
3250   A client MUST send a Host header field in all HTTP/1.1 request
3251   messages.  If the target resource's URI includes an authority
3252   component, then the Host field-value MUST be identical to that
3253   authority component after excluding any userinfo (<xref target="http.uri"/>).
3254   If the authority component is missing or undefined for the target
3255   resource's URI, then the Host header field MUST be sent with an
3256   empty field-value.
3257</t>
3258<t>
3259   For example, a GET request to the origin server for
3260   &lt;http://www.example.org/pub/WWW/&gt; would begin with:
3261</t>
3262<figure><artwork type="message/http; msgtype=&#34;request&#34;"><![CDATA[
3263  GET /pub/WWW/ HTTP/1.1
3264  Host: www.example.org
3265  ]]></artwork></figure>
3266<t>
3267   The Host header field MUST be sent in an HTTP/1.1 request even
3268   if the request-target is in the form of an absolute-URI, since this
3269   allows the Host information to be forwarded through ancient HTTP/1.0
3270   proxies that might not have implemented Host.
3271</t>
3272<t>
3273   When an HTTP/1.1 proxy receives a request with a request-target in
3274   the form of an absolute-URI, the proxy MUST ignore the received
3275   Host header field (if any) and instead replace it with the host
3276   information of the request-target.  When a proxy forwards a request,
3277   it MUST generate the Host header field based on the received
3278   absolute-URI rather than the received Host.
3279</t>
3280<t>
3281   Since the Host header field acts as an application-level routing
3282   mechanism, it is a frequent target for malware seeking to poison
3283   a shared cache or redirect a request to an unintended server.
3284   An interception proxy is particularly vulnerable if it relies on
3285   the Host header field value for redirecting requests to internal
3286   servers, or for use as a cache key in a shared cache, without
3287   first verifying that the intercepted connection is targeting a
3288   valid IP address for that host.
3289</t>
3290<t>
3291   A server MUST respond with a 400 (Bad Request) status code to
3292   any HTTP/1.1 request message that lacks a Host header field and
3293   to any request message that contains more than one Host header field
3294   or a Host header field with an invalid field-value.
3295</t>
3296<t>
3297   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
3298   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
3299   for other requirements relating to Host.
3300</t>
3301</section>
3302
3303<section title="TE" anchor="header.te">
3304  <iref primary="true" item="TE header field"/>
3305  <iref primary="true" item="Header Fields" subitem="TE"/>
3306 
3307 
3308 
3309 
3310<t>
3311   The "TE" header field indicates what extension transfer-codings
3312   it is willing to accept in the response, and whether or not it is
3313   willing to accept trailer fields in a chunked transfer-coding.
3314</t>
3315<t>
3316   Its value consists of the keyword "trailers" and/or a comma-separated
3317   list of extension transfer-coding names with optional accept
3318   parameters (as described in <xref target="transfer.codings"/>).
3319</t>
3320<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[
3321  TE        = #t-codings
3322  t-codings = "trailers" / ( transfer-extension [ te-params ] )
3323  te-params = OWS ";" OWS "q=" qvalue *( te-ext )
3324  te-ext    = OWS ";" OWS token [ "=" word ]
3325]]></artwork></figure>
3326<t>
3327   The presence of the keyword "trailers" indicates that the client is
3328   willing to accept trailer fields in a chunked transfer-coding, as
3329   defined in <xref target="chunked.encoding"/>. This keyword is reserved for use with
3330   transfer-coding values even though it does not itself represent a
3331   transfer-coding.
3332</t>
3333<t>
3334   Examples of its use are:
3335</t>
3336<figure><artwork type="example"><![CDATA[
3337  TE: deflate
3338  TE:
3339  TE: trailers, deflate;q=0.5
3340]]></artwork></figure>
3341<t>
3342   The TE header field only applies to the immediate connection.
3343   Therefore, the keyword MUST be supplied within a Connection header
3344   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
3345</t>
3346<t>
3347   A server tests whether a transfer-coding is acceptable, according to
3348   a TE field, using these rules:
3349  <list style="numbers">
3350    <t>The "chunked" transfer-coding is always acceptable. If the
3351         keyword "trailers" is listed, the client indicates that it is
3352         willing to accept trailer fields in the chunked response on
3353         behalf of itself and any downstream clients. The implication is
3354         that, if given, the client is stating that either all
3355         downstream clients are willing to accept trailer fields in the
3356         forwarded response, or that it will attempt to buffer the
3357         response on behalf of downstream recipients.
3358      <vspace blankLines="1"/>
3359         Note: HTTP/1.1 does not define any means to limit the size of a
3360         chunked response such that a client can be assured of buffering
3361         the entire response.</t>
3362    <t>If the transfer-coding being tested is one of the transfer-codings
3363         listed in the TE field, then it is acceptable unless it
3364         is accompanied by a qvalue of 0. (As defined in <xref target="quality.values"/>, a
3365         qvalue of 0 means "not acceptable".)</t>
3366    <t>If multiple transfer-codings are acceptable, then the
3367         acceptable transfer-coding with the highest non-zero qvalue is
3368         preferred.  The "chunked" transfer-coding always has a qvalue
3369         of 1.</t>
3370  </list>
3371</t>
3372<t>
3373   If the TE field-value is empty or if no TE field is present, the only
3374   transfer-coding is "chunked". A message with no transfer-coding is
3375   always acceptable.
3376</t>
3377</section>
3378
3379<section title="Trailer" anchor="header.trailer">
3380  <iref primary="true" item="Trailer header field"/>
3381  <iref primary="true" item="Header Fields" subitem="Trailer"/>
3382 
3383<t>
3384   The "Trailer" header field indicates that the given set of
3385   header fields is present in the trailer of a message encoded with
3386   chunked transfer-coding.
3387</t>
3388<figure><iref primary="true" item="Grammar" subitem="Trailer"/><artwork type="abnf2616"><![CDATA[
3389  Trailer = 1#field-name
3390]]></artwork></figure>
3391<t>
3392   An HTTP/1.1 message SHOULD include a Trailer header field in a
3393   message using chunked transfer-coding with a non-empty trailer. Doing
3394   so allows the recipient to know which header fields to expect in the
3395   trailer.
3396</t>
3397<t>
3398   If no Trailer header field is present, the trailer SHOULD NOT  include
3399   any header fields. See <xref target="chunked.encoding"/> for restrictions on the use of
3400   trailer fields in a "chunked" transfer-coding.
3401</t>
3402<t>
3403   Message header fields listed in the Trailer header field MUST NOT
3404   include the following header fields:
3405  <list style="symbols">
3406    <t>Transfer-Encoding</t>
3407    <t>Content-Length</t>
3408    <t>Trailer</t>
3409  </list>
3410</t>
3411</section>
3412
3413<section title="Transfer-Encoding" anchor="header.transfer-encoding">
3414  <iref primary="true" item="Transfer-Encoding header field"/>
3415  <iref primary="true" item="Header Fields" subitem="Transfer-Encoding"/>
3416 
3417<t>
3418   The "Transfer-Encoding" header field indicates what transfer-codings
3419   (if any) have been applied to the message body. It differs from
3420   Content-Encoding (Section 2.2 of <xref target="Part3"/>) in that transfer-codings are a property
3421   of the message (and therefore are removed by intermediaries), whereas
3422   content-codings are not.
3423</t>
3424<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><artwork type="abnf2616"><![CDATA[
3425  Transfer-Encoding = 1#transfer-coding
3426]]></artwork></figure>
3427<t>
3428   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
3429</t>
3430<figure><artwork type="example"><![CDATA[
3431  Transfer-Encoding: chunked
3432]]></artwork></figure>
3433<t>
3434   If multiple encodings have been applied to a representation, the transfer-codings
3435   MUST be listed in the order in which they were applied.
3436   Additional information about the encoding parameters MAY be provided
3437   by other header fields not defined by this specification.
3438</t>
3439<t>
3440   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
3441   header field.
3442</t>
3443</section>
3444
3445<section title="Upgrade" anchor="header.upgrade">
3446  <iref primary="true" item="Upgrade header field"/>
3447  <iref primary="true" item="Header Fields" subitem="Upgrade"/>
3448 
3449<t>
3450   The "Upgrade" header field allows the client to specify what
3451   additional communication protocols it would like to use, if the server
3452   chooses to switch protocols. Servers can use it to indicate what protocols
3453   they are willing to switch to.
3454</t>
3455<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><artwork type="abnf2616"><![CDATA[
3456  Upgrade = 1#product
3457]]></artwork></figure>
3458<t>
3459   For example,
3460</t>
3461<figure><artwork type="example"><![CDATA[
3462  Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
3463]]></artwork></figure>
3464<t>
3465   The Upgrade header field is intended to provide a simple mechanism
3466   for transition from HTTP/1.1 to some other, incompatible protocol. It
3467   does so by allowing the client to advertise its desire to use another
3468   protocol, such as a later version of HTTP with a higher major version
3469   number, even though the current request has been made using HTTP/1.1.
3470   This eases the difficult transition between incompatible protocols by
3471   allowing the client to initiate a request in the more commonly
3472   supported protocol while indicating to the server that it would like
3473   to use a "better" protocol if available (where "better" is determined
3474   by the server, possibly according to the nature of the request method
3475   or target resource).
3476</t>
3477<t>
3478   The Upgrade header field only applies to switching application-layer
3479   protocols upon the existing transport-layer connection. Upgrade
3480   cannot be used to insist on a protocol change; its acceptance and use
3481   by the server is optional. The capabilities and nature of the
3482   application-layer communication after the protocol change is entirely
3483   dependent upon the new protocol chosen, although the first action
3484   after changing the protocol MUST be a response to the initial HTTP
3485   request containing the Upgrade header field.
3486</t>
3487<t>
3488   The Upgrade header field only applies to the immediate connection.
3489   Therefore, the upgrade keyword MUST be supplied within a Connection
3490   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
3491   HTTP/1.1 message.
3492</t>
3493<t>
3494   The Upgrade header field cannot be used to indicate a switch to a
3495   protocol on a different connection. For that purpose, it is more
3496   appropriate to use a 3xx redirection response (Section 8.3 of <xref target="Part2"/>).
3497</t>
3498<t>
3499   Servers MUST include the "Upgrade" header field in 101 (Switching
3500   Protocols) responses to indicate which protocol(s) are being switched to,
3501   and MUST include it in 426 (Upgrade Required) responses to indicate
3502   acceptable protocols to upgrade to. Servers MAY include it in any other
3503   response to indicate that they are willing to upgrade to one of the
3504   specified protocols.
3505</t>
3506<t>
3507   This specification only defines the protocol name "HTTP" for use by
3508   the family of Hypertext Transfer Protocols, as defined by the HTTP
3509   version rules of <xref target="http.version"/> and future updates to this
3510   specification. Additional tokens can be registered with IANA using the
3511   registration procedure defined below. 
3512</t>
3513
3514<section title="Upgrade Token Registry" anchor="upgrade.token.registry">
3515<t>
3516   The HTTP Upgrade Token Registry defines the name space for product
3517   tokens used to identify protocols in the Upgrade header field.
3518   Each registered token is associated with contact information and
3519   an optional set of specifications that details how the connection
3520   will be processed after it has been upgraded.
3521</t>
3522<t>
3523   Registrations are allowed on a First Come First Served basis as
3524   described in Section 4.1 of <xref target="RFC5226"/>. The
3525   specifications need not be IETF documents or be subject to IESG review.
3526   Registrations are subject to the following rules:
3527  <list style="numbers">
3528    <t>A token, once registered, stays registered forever.</t>
3529    <t>The registration MUST name a responsible party for the
3530       registration.</t>
3531    <t>The registration MUST name a point of contact.</t>
3532    <t>The registration MAY name a set of specifications associated with that
3533       token. Such specifications need not be publicly available.</t>
3534    <t>The responsible party MAY change the registration at any time.
3535       The IANA will keep a record of all such changes, and make them
3536       available upon request.</t>
3537    <t>The responsible party for the first registration of a "product"
3538       token MUST approve later registrations of a "version" token
3539       together with that "product" token before they can be registered.</t>
3540    <t>If absolutely required, the IESG MAY reassign the responsibility
3541       for a token. This will normally only be used in the case when a
3542       responsible party cannot be contacted.</t>
3543  </list>
3544</t>
3545</section>
3546
3547
3548</section>
3549
3550<section title="Via" anchor="header.via">
3551  <iref primary="true" item="Via header field"/>
3552  <iref primary="true" item="Header Fields" subitem="Via"/>
3553 
3554 
3555 
3556 
3557 
3558 
3559<t>
3560   The "Via" header field MUST be sent by a proxy or gateway to
3561   indicate the intermediate protocols and recipients between the user
3562   agent and the server on requests, and between the origin server and
3563   the client on responses. It is analogous to the "Received" field
3564   used by email systems (Section 3.6.7 of <xref target="RFC5322"/>)
3565   and is intended to be used for tracking message forwards,
3566   avoiding request loops, and identifying the protocol capabilities of
3567   all senders along the request/response chain.
3568</t>
3569<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[
3570  Via               = 1#( received-protocol RWS received-by
3571                          [ RWS comment ] )
3572  received-protocol = [ protocol-name "/" ] protocol-version
3573  protocol-name     = token
3574  protocol-version  = token
3575  received-by       = ( uri-host [ ":" port ] ) / pseudonym
3576  pseudonym         = token
3577]]></artwork></figure>
3578<t>
3579   The received-protocol indicates the protocol version of the message
3580   received by the server or client along each segment of the
3581   request/response chain. The received-protocol version is appended to
3582   the Via field value when the message is forwarded so that information
3583   about the protocol capabilities of upstream applications remains
3584   visible to all recipients.
3585</t>
3586<t>
3587   The protocol-name is excluded if and only if it would be "HTTP". The
3588   received-by field is normally the host and optional port number of a
3589   recipient server or client that subsequently forwarded the message.
3590   However, if the real host is considered to be sensitive information,
3591   it MAY be replaced by a pseudonym. If the port is not given, it MAY
3592   be assumed to be the default port of the received-protocol.
3593</t>
3594<t>
3595   Multiple Via field values represent each proxy or gateway that has
3596   forwarded the message. Each recipient MUST append its information
3597   such that the end result is ordered according to the sequence of
3598   forwarding applications.
3599</t>
3600<t>
3601   Comments MAY be used in the Via header field to identify the software
3602   of each recipient, analogous to the User-Agent and Server header fields.
3603   However, all comments in the Via field are optional and MAY be removed
3604   by any recipient prior to forwarding the message.
3605</t>
3606<t>
3607   For example, a request message could be sent from an HTTP/1.0 user
3608   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
3609   forward the request to a public proxy at p.example.net, which completes
3610   the request by forwarding it to the origin server at www.example.com.
3611   The request received by www.example.com would then have the following
3612   Via header field:
3613</t>
3614<figure><artwork type="example"><![CDATA[
3615  Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
3616]]></artwork></figure>
3617<t>
3618   A proxy or gateway used as a portal through a network firewall
3619   SHOULD NOT forward the names and ports of hosts within the firewall
3620   region unless it is explicitly enabled to do so. If not enabled, the
3621   received-by host of any host behind the firewall SHOULD be replaced
3622   by an appropriate pseudonym for that host.
3623</t>
3624<t>
3625   For organizations that have strong privacy requirements for hiding
3626   internal structures, a proxy or gateway MAY combine an ordered
3627   subsequence of Via header field entries with identical received-protocol
3628   values into a single such entry. For example,
3629</t>
3630<figure><artwork type="example"><![CDATA[
3631  Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
3632]]></artwork></figure>
3633<t>
3634  could be collapsed to
3635</t>
3636<figure><artwork type="example"><![CDATA[
3637  Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
3638]]></artwork></figure>
3639<t>
3640   Senders SHOULD NOT combine multiple entries unless they are all
3641   under the same organizational control and the hosts have already been
3642   replaced by pseudonyms. Senders MUST NOT combine entries which
3643   have different received-protocol values.
3644</t>
3645</section>
3646
3647</section>
3648
3649<section title="IANA Considerations" anchor="IANA.considerations">
3650
3651<section title="Header Field Registration" anchor="header.field.registration">
3652<t>
3653   The Message Header Field Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> shall be updated
3654   with the permanent registrations below (see <xref target="RFC3864"/>):
3655</t>
3656
3657<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
3658<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
3659   <ttcol>Header Field Name</ttcol>
3660   <ttcol>Protocol</ttcol>
3661   <ttcol>Status</ttcol>
3662   <ttcol>Reference</ttcol>
3663
3664   <c>Connection</c>
3665   <c>http</c>
3666   <c>standard</c>
3667   <c>
3668      <xref target="header.connection"/>
3669   </c>
3670   <c>Content-Length</c>
3671   <c>http</c>
3672   <c>standard</c>
3673   <c>
3674      <xref target="header.content-length"/>
3675   </c>
3676   <c>Date</c>
3677   <c>http</c>
3678   <c>standard</c>
3679   <c>
3680      <xref target="header.date"/>
3681   </c>
3682   <c>Host</c>
3683   <c>http</c>
3684   <c>standard</c>
3685   <c>
3686      <xref target="header.host"/>
3687   </c>
3688   <c>TE</c>
3689   <c>http</c>
3690   <c>standard</c>
3691   <c>
3692      <xref target="header.te"/>
3693   </c>
3694   <c>Trailer</c>
3695   <c>http</c>
3696   <c>standard</c>
3697   <c>
3698      <xref target="header.trailer"/>
3699   </c>
3700   <c>Transfer-Encoding</c>
3701   <c>http</c>
3702   <c>standard</c>
3703   <c>
3704      <xref target="header.transfer-encoding"/>
3705   </c>
3706   <c>Upgrade</c>
3707   <c>http</c>
3708   <c>standard</c>
3709   <c>
3710      <xref target="header.upgrade"/>
3711   </c>
3712   <c>Via</c>
3713   <c>http</c>
3714   <c>standard</c>
3715   <c>
3716      <xref target="header.via"/>
3717   </c>
3718</texttable>
3719<!--(END)-->
3720
3721<t>
3722   Furthermore, the header field name "Close" shall be registered as "reserved", as its use as
3723   HTTP header field would be in conflict with the use of the "close" connection
3724   option for the "Connection" header field (<xref target="header.connection"/>).
3725</t>
3726<texttable align="left" suppress-title="true">
3727   <ttcol>Header Field Name</ttcol>
3728   <ttcol>Protocol</ttcol>
3729   <ttcol>Status</ttcol>
3730   <ttcol>Reference</ttcol>
3731
3732   <c>Close</c>
3733   <c>http</c>
3734   <c>reserved</c>
3735   <c>
3736      <xref target="header.field.registration"/>
3737   </c>
3738</texttable>
3739<t>
3740   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
3741</t>
3742</section>
3743
3744<section title="URI Scheme Registration" anchor="uri.scheme.registration">
3745<t>
3746   The entries for the "http" and "https" URI Schemes in the registry located at
3747   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
3748   shall be updated to point to Sections <xref target="http.uri" format="counter"/>
3749   and <xref target="https.uri" format="counter"/> of this document
3750   (see <xref target="RFC4395"/>).
3751</t>
3752</section>
3753
3754<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
3755<t>
3756   This document serves as the specification for the Internet media types
3757   "message/http" and "application/http". The following is to be registered with
3758   IANA (see <xref target="RFC4288"/>).
3759</t>
3760<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
3761<iref item="Media Type" subitem="message/http" primary="true"/>
3762<iref item="message/http Media Type" primary="true"/>
3763<t>
3764   The message/http type can be used to enclose a single HTTP request or
3765   response message, provided that it obeys the MIME restrictions for all
3766   "message" types regarding line length and encodings.
3767</t>
3768<t>
3769  <list style="hanging">
3770    <t hangText="Type name:">
3771      message
3772    </t>
3773    <t hangText="Subtype name:">
3774      http
3775    </t>
3776    <t hangText="Required parameters:">
3777      none
3778    </t>
3779    <t hangText="Optional parameters:">
3780      version, msgtype
3781      <list style="hanging">
3782        <t hangText="version:">
3783          The HTTP-Version number of the enclosed message
3784          (e.g., "1.1"). If not present, the version can be
3785          determined from the first line of the body.
3786        </t>
3787        <t hangText="msgtype:">
3788          The message type — "request" or "response". If not
3789          present, the type can be determined from the first
3790          line of the body.
3791        </t>
3792      </list>
3793    </t>
3794    <t hangText="Encoding considerations:">
3795      only "7bit", "8bit", or "binary" are permitted
3796    </t>
3797    <t hangText="Security considerations:">
3798      none
3799    </t>
3800    <t hangText="Interoperability considerations:">
3801      none
3802    </t>
3803    <t hangText="Published specification:">
3804      This specification (see <xref target="internet.media.type.message.http"/>).
3805    </t>
3806    <t hangText="Applications that use this media type:">
3807    </t>
3808    <t hangText="Additional information:">
3809      <list style="hanging">
3810        <t hangText="Magic number(s):">none</t>
3811        <t hangText="File extension(s):">none</t>
3812        <t hangText="Macintosh file type code(s):">none</t>
3813      </list>
3814    </t>
3815    <t hangText="Person and email address to contact for further information:">
3816      See Authors Section.
3817    </t>
3818    <t hangText="Intended usage:">
3819      COMMON
3820    </t>
3821    <t hangText="Restrictions on usage:">
3822      none
3823    </t>
3824    <t hangText="Author/Change controller:">
3825      IESG
3826    </t>
3827  </list>
3828</t>
3829</section>
3830<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3831<iref item="Media Type" subitem="application/http" primary="true"/>
3832<iref item="application/http Media Type" primary="true"/>
3833<t>
3834   The application/http type can be used to enclose a pipeline of one or more
3835   HTTP request or response messages (not intermixed).
3836</t>
3837<t>
3838  <list style="hanging">
3839    <t hangText="Type name:">
3840      application
3841    </t>
3842    <t hangText="Subtype name:">
3843      http
3844    </t>
3845    <t hangText="Required parameters:">
3846      none
3847    </t>
3848    <t hangText="Optional parameters:">
3849      version, msgtype
3850      <list style="hanging">
3851        <t hangText="version:">
3852          The HTTP-Version number of the enclosed messages
3853          (e.g., "1.1"). If not present, the version can be
3854          determined from the first line of the body.
3855        </t>
3856        <t hangText="msgtype:">
3857          The message type — "request" or "response". If not
3858          present, the type can be determined from the first
3859          line of the body.
3860        </t>
3861      </list>
3862    </t>
3863    <t hangText="Encoding considerations:">
3864      HTTP messages enclosed by this type
3865      are in "binary" format; use of an appropriate
3866      Content-Transfer-Encoding is required when
3867      transmitted via E-mail.
3868    </t>
3869    <t hangText="Security considerations:">
3870      none
3871    </t>
3872    <t hangText="Interoperability considerations:">
3873      none
3874    </t>
3875    <t hangText="Published specification:">
3876      This specification (see <xref target="internet.media.type.application.http"/>).
3877    </t>
3878    <t hangText="Applications that use this media type:">
3879    </t>
3880    <t hangText="Additional information:">
3881      <list style="hanging">
3882        <t hangText="Magic number(s):">none</t>
3883        <t hangText="File extension(s):">none</t>
3884        <t hangText="Macintosh file type code(s):">none</t>
3885      </list>
3886    </t>
3887    <t hangText="Person and email address to contact for further information:">
3888      See Authors Section.
3889    </t>
3890    <t hangText="Intended usage:">
3891      COMMON
3892    </t>
3893    <t hangText="Restrictions on usage:">
3894      none
3895    </t>
3896    <t hangText="Author/Change controller:">
3897      IESG
3898    </t>
3899  </list>
3900</t>
3901</section>
3902</section>
3903
3904<section title="Transfer Coding Registry" anchor="transfer.coding.registration">
3905<t>
3906   The registration procedure for HTTP Transfer Codings is now defined by
3907   <xref target="transfer.coding.registry"/> of this document.
3908</t>
3909<t>
3910   The HTTP Transfer Codings Registry located at <eref target="http://www.iana.org/assignments/http-parameters"/>
3911   shall be updated with the registrations below:
3912</t>
3913<texttable align="left" suppress-title="true" anchor="iana.transfer.coding.registration.table">
3914   <ttcol>Name</ttcol>
3915   <ttcol>Description</ttcol>
3916   <ttcol>Reference</ttcol>
3917   <c>chunked</c>
3918   <c>Transfer in a series of chunks</c>
3919   <c>
3920      <xref target="chunked.encoding"/>
3921   </c>
3922   <c>compress</c>
3923   <c>UNIX "compress" program method</c>
3924   <c>
3925      <xref target="compress.coding"/>
3926   </c>
3927   <c>deflate</c>
3928   <c>"deflate" compression mechanism (<xref target="RFC1951"/>) used inside
3929   the "zlib" data format (<xref target="RFC1950"/>)
3930   </c>
3931   <c>
3932      <xref target="deflate.coding"/>
3933   </c>
3934   <c>gzip</c>
3935   <c>Same as GNU zip <xref target="RFC1952"/></c>
3936   <c>
3937      <xref target="gzip.coding"/>
3938   </c>
3939</texttable>
3940</section>
3941
3942<section title="Upgrade Token Registration" anchor="upgrade.token.registration">
3943<t>
3944   The registration procedure for HTTP Upgrade Tokens — previously defined
3945   in Section 7.2 of <xref target="RFC2817"/> — is now defined
3946   by <xref target="upgrade.token.registry"/> of this document.
3947</t>
3948<t>
3949   The HTTP Status Code Registry located at <eref target="http://www.iana.org/assignments/http-upgrade-tokens/"/>
3950   shall be updated with the registration below:
3951</t>
3952<texttable align="left" suppress-title="true">
3953   <ttcol>Value</ttcol>
3954   <ttcol>Description</ttcol>
3955   <ttcol>Reference</ttcol>
3956
3957   <c>HTTP</c>
3958   <c>Hypertext Transfer Protocol</c> 
3959   <c><xref target="http.version"/> of this specification</c>
3960
3961</texttable>
3962</section>
3963
3964</section>
3965
3966<section title="Security Considerations" anchor="security.considerations">
3967<t>
3968   This section is meant to inform application developers, information
3969   providers, and users of the security limitations in HTTP/1.1 as
3970   described by this document. The discussion does not include
3971   definitive solutions to the problems revealed, though it does make
3972   some suggestions for reducing security risks.
3973</t>
3974
3975<section title="Personal Information" anchor="personal.information">
3976<t>
3977   HTTP clients are often privy to large amounts of personal information
3978   (e.g., the user's name, location, mail address, passwords, encryption
3979   keys, etc.), and SHOULD be very careful to prevent unintentional
3980   leakage of this information.
3981   We very strongly recommend that a convenient interface be provided
3982   for the user to control dissemination of such information, and that
3983   designers and implementors be particularly careful in this area.
3984   History shows that errors in this area often create serious security
3985   and/or privacy problems and generate highly adverse publicity for the
3986   implementor's company.
3987</t>
3988</section>
3989
3990<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3991<t>
3992   A server is in the position to save personal data about a user's
3993   requests which might identify their reading patterns or subjects of
3994   interest. This information is clearly confidential in nature and its
3995   handling can be constrained by law in certain countries. People using
3996   HTTP to provide data are responsible for ensuring that
3997   such material is not distributed without the permission of any
3998   individuals that are identifiable by the published results.
3999</t>
4000</section>
4001
4002<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
4003<t>
4004   Implementations of HTTP origin servers SHOULD be careful to restrict
4005   the documents returned by HTTP requests to be only those that were
4006   intended by the server administrators. If an HTTP server translates
4007   HTTP URIs directly into file system calls, the server MUST take
4008   special care not to serve files that were not intended to be
4009   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
4010   other operating systems use ".." as a path component to indicate a
4011   directory level above the current one. On such a system, an HTTP
4012   server MUST disallow any such construct in the request-target if it
4013   would otherwise allow access to a resource outside those intended to
4014   be accessible via the HTTP server. Similarly, files intended for
4015   reference only internally to the server (such as access control
4016   files, configuration files, and script code) MUST be protected from
4017   inappropriate retrieval, since they might contain sensitive
4018   information. Experience has shown that minor bugs in such HTTP server
4019   implementations have turned into security risks.
4020</t>
4021</section>
4022
4023<section title="DNS-related Attacks" anchor="dns.related.attacks">
4024<t>
4025   HTTP clients rely heavily on the Domain Name Service (DNS), and are thus
4026   generally prone to security attacks based on the deliberate misassociation
4027   of IP addresses and DNS names not protected by DNSSec. Clients need to be
4028   cautious in assuming the validity of an IP number/DNS name association unless
4029   the response is protected by DNSSec (<xref target="RFC4033"/>).
4030</t>
4031</section>
4032
4033<section title="Proxies and Caching" anchor="attack.proxies">
4034<t>
4035   By their very nature, HTTP proxies are men-in-the-middle, and
4036   represent an opportunity for man-in-the-middle attacks. Compromise of
4037   the systems on which the proxies run can result in serious security
4038   and privacy problems. Proxies have access to security-related
4039   information, personal information about individual users and
4040   organizations, and proprietary information belonging to users and
4041   content providers. A compromised proxy, or a proxy implemented or
4042   configured without regard to security and privacy considerations,
4043   might be used in the commission of a wide range of potential attacks.
4044</t>
4045<t>
4046   Proxy operators need to protect the systems on which proxies run as
4047   they would protect any system that contains or transports sensitive
4048   information. In particular, log information gathered at proxies often
4049   contains highly sensitive personal information, and/or information
4050   about organizations. Log information needs to be carefully guarded, and
4051   appropriate guidelines for use need to be developed and followed.
4052   (<xref target="abuse.of.server.log.information"/>).
4053</t>
4054<t>
4055   Proxy implementors need to consider the privacy and security
4056   implications of their design and coding decisions, and of the
4057   configuration options they provide to proxy operators (especially the
4058   default configuration).
4059</t>
4060<t>
4061   Users of a proxy need to be aware that proxies are no trustworthier than
4062   the people who run them; HTTP itself cannot solve this problem.
4063</t>
4064<t>
4065   The judicious use of cryptography, when appropriate, might suffice to
4066   protect against a broad range of security and privacy attacks. Such
4067   cryptography is beyond the scope of the HTTP/1.1 specification.
4068</t>
4069</section>
4070
4071<section title="Protocol Element Size Overflows" anchor="attack.protocol.element.size.overflows">
4072<t>
4073   Because HTTP uses mostly textual, character-delimited fields, attackers can
4074   overflow buffers in implementations, and/or perform a Denial of Service
4075   against implementations that accept fields with unlimited lengths.
4076</t>
4077<t>
4078   To promote interoperability, this specification makes specific
4079   recommendations for size limits on request-targets (<xref target="request-target"/>)
4080   and blocks of header fields (<xref target="header.fields"/>). These are
4081   minimum recommendations, chosen to be supportable even by implementations
4082   with limited resources; it is expected that most implementations will choose
4083   substantially higher limits.
4084</t>
4085<t>
4086   This specification also provides a way for servers to reject messages that
4087   have request-targets that are too long (Section 8.4.15 of <xref target="Part2"/>) or request entities
4088   that are too large (Section 8.4 of <xref target="Part2"/>).
4089</t>
4090<t>
4091   Other fields (including but not limited to request methods, response status
4092   phrases, header field-names, and body chunks) SHOULD be limited by
4093   implementations carefully, so as to not impede interoperability.
4094</t>
4095</section>
4096
4097<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
4098<t>
4099   They exist. They are hard to defend against. Research continues.
4100   Beware.
4101</t>
4102</section>
4103</section>
4104
4105<section title="Acknowledgments" anchor="acks">
4106<t>
4107   This document revision builds on the work that went into
4108   <xref target="RFC2616" format="none">RFC 2616</xref> and its predecessors.
4109   See Section 16 of <xref target="RFC2616"/> for detailed
4110   acknowledgements.
4111</t>
4112<t>
4113  <cref anchor="todoacks">Insert HTTPbis-specific acknowledgements here.</cref>
4114</t>
4115<!--
4116
4117Acknowledgements TODO list
4118
4119- Jeff Hodges ("effective request URI")
4120
4121-->
4122</section>
4123
4124</middle>
4125<back>
4126
4127<references title="Normative References">
4128
4129<reference anchor="ISO-8859-1">
4130  <front>
4131    <title>
4132     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
4133    </title>
4134    <author>
4135      <organization>International Organization for Standardization</organization>
4136    </author>
4137    <date year="1998"/>
4138  </front>
4139  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
4140</reference>
4141
4142<reference anchor="Part2">
4143  <front>
4144    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
4145    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4146      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4147      <address><email>fielding@gbiv.com</email></address>
4148    </author>
4149    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4150      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4151      <address><email>jg@freedesktop.org</email></address>
4152    </author>
4153    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4154      <organization abbrev="HP">Hewlett-Packard Company</organization>
4155      <address><email>JeffMogul@acm.org</email></address>
4156    </author>
4157    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4158      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4159      <address><email>henrikn@microsoft.com</email></address>
4160    </author>
4161    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4162      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4163      <address><email>LMM@acm.org</email></address>
4164    </author>
4165    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4166      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4167      <address><email>paulle@microsoft.com</email></address>
4168    </author>
4169    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4170      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4171      <address><email>timbl@w3.org</email></address>
4172    </author>
4173    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4174      <organization abbrev="W3C">World Wide Web Consortium</organization>
4175      <address><email>ylafon@w3.org</email></address>
4176    </author>
4177    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4178      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4179      <address><email>julian.reschke@greenbytes.de</email></address>
4180    </author>
4181    <date month="August" year="2011"/>
4182  </front>
4183  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-16"/>
4184 
4185</reference>
4186
4187<reference anchor="Part3">
4188  <front>
4189    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
4190    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4191      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4192      <address><email>fielding@gbiv.com</email></address>
4193    </author>
4194    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4195      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4196      <address><email>jg@freedesktop.org</email></address>
4197    </author>
4198    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4199      <organization abbrev="HP">Hewlett-Packard Company</organization>
4200      <address><email>JeffMogul@acm.org</email></address>
4201    </author>
4202    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4203      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4204      <address><email>henrikn@microsoft.com</email></address>
4205    </author>
4206    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4207      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4208      <address><email>LMM@acm.org</email></address>
4209    </author>
4210    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4211      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4212      <address><email>paulle@microsoft.com</email></address>
4213    </author>
4214    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4215      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4216      <address><email>timbl@w3.org</email></address>
4217    </author>
4218    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4219      <organization abbrev="W3C">World Wide Web Consortium</organization>
4220      <address><email>ylafon@w3.org</email></address>
4221    </author>
4222    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4223      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4224      <address><email>julian.reschke@greenbytes.de</email></address>
4225    </author>
4226    <date month="August" year="2011"/>
4227  </front>
4228  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-16"/>
4229 
4230</reference>
4231
4232<reference anchor="Part6">
4233  <front>
4234    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
4235    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
4236      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4237      <address><email>fielding@gbiv.com</email></address>
4238    </author>
4239    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4240      <organization abbrev="Alcatel-Lucent">Alcatel-Lucent Bell Labs</organization>
4241      <address><email>jg@freedesktop.org</email></address>
4242    </author>
4243    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4244      <organization abbrev="HP">Hewlett-Packard Company</organization>
4245      <address><email>JeffMogul@acm.org</email></address>
4246    </author>
4247    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
4248      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4249      <address><email>henrikn@microsoft.com</email></address>
4250    </author>
4251    <author initials="L." surname="Masinter" fullname="Larry Masinter">
4252      <organization abbrev="Adobe">Adobe Systems Incorporated</organization>
4253      <address><email>LMM@acm.org</email></address>
4254    </author>
4255    <author initials="P." surname="Leach" fullname="Paul J. Leach">
4256      <organization abbrev="Microsoft">Microsoft Corporation</organization>
4257      <address><email>paulle@microsoft.com</email></address>
4258    </author>
4259    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4260      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4261      <address><email>timbl@w3.org</email></address>
4262    </author>
4263    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
4264      <organization abbrev="W3C">World Wide Web Consortium</organization>
4265      <address><email>ylafon@w3.org</email></address>
4266    </author>
4267    <author initials="M." surname="Nottingham" fullname="Mark Nottingham" role="editor">
4268      <address><email>mnot@mnot.net</email></address>
4269    </author>
4270    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
4271      <organization abbrev="greenbytes">greenbytes GmbH</organization>
4272      <address><email>julian.reschke@greenbytes.de</email></address>
4273    </author>
4274    <date month="August" year="2011"/>
4275  </front>
4276  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-16"/>
4277 
4278</reference>
4279
4280<reference anchor="RFC5234">
4281  <front>
4282    <title abbrev="ABNF for Syntax Specifications">Augmented BNF for Syntax Specifications: ABNF</title>
4283    <author initials="D." surname="Crocker" fullname="Dave Crocker" role="editor">
4284      <organization>Brandenburg InternetWorking</organization>
4285      <address>
4286        <email>dcrocker@bbiw.net</email>
4287      </address> 
4288    </author>
4289    <author initials="P." surname="Overell" fullname="Paul Overell">
4290      <organization>THUS plc.</organization>
4291      <address>
4292        <email>paul.overell@thus.net</email>
4293      </address>
4294    </author>
4295    <date month="January" year="2008"/>
4296  </front>
4297  <seriesInfo name="STD" value="68"/>
4298  <seriesInfo name="RFC" value="5234"/>
4299</reference>
4300
4301<reference anchor="RFC2119">
4302  <front>
4303    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
4304    <author initials="S." surname="Bradner" fullname="Scott Bradner">
4305      <organization>Harvard University</organization>
4306      <address><email>sob@harvard.edu</email></address>
4307    </author>
4308    <date month="March" year="1997"/>
4309  </front>
4310  <seriesInfo name="BCP" value="14"/>
4311  <seriesInfo name="RFC" value="2119"/>
4312</reference>
4313
4314<reference anchor="RFC3986">
4315 <front>
4316  <title abbrev="URI Generic Syntax">Uniform Resource Identifier (URI): Generic Syntax</title>
4317  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4318    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
4319    <address>
4320       <email>timbl@w3.org</email>
4321       <uri>http://www.w3.org/People/Berners-Lee/</uri>
4322    </address>
4323  </author>
4324  <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4325    <organization abbrev="Day Software">Day Software</organization>
4326    <address>
4327      <email>fielding@gbiv.com</email>
4328      <uri>http://roy.gbiv.com/</uri>
4329    </address>
4330  </author>
4331  <author initials="L." surname="Masinter" fullname="Larry Masinter">
4332    <organization abbrev="Adobe Systems">Adobe Systems Incorporated</organization>
4333    <address>
4334      <email>LMM@acm.org</email>
4335      <uri>http://larry.masinter.net/</uri>
4336    </address>
4337  </author>
4338  <date month="January" year="2005"/>
4339 </front>
4340 <seriesInfo name="STD" value="66"/>
4341 <seriesInfo name="RFC" value="3986"/>
4342</reference>
4343
4344<reference anchor="USASCII">
4345  <front>
4346    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
4347    <author>
4348      <organization>American National Standards Institute</organization>
4349    </author>
4350    <date year="1986"/>
4351  </front>
4352  <seriesInfo name="ANSI" value="X3.4"/>
4353</reference>
4354
4355<reference anchor="RFC1950">
4356  <front>
4357    <title>ZLIB Compressed Data Format Specification version 3.3</title>
4358    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4359      <organization>Aladdin Enterprises</organization>
4360      <address><email>ghost@aladdin.com</email></address>
4361    </author>
4362    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly"/>
4363    <date month="May" year="1996"/>
4364  </front>
4365  <seriesInfo name="RFC" value="1950"/>
4366  <annotation>
4367    RFC 1950 is an Informational RFC, thus it might be less stable than
4368    this specification. On the other hand, this downward reference was
4369    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4370    therefore it is unlikely to cause problems in practice. See also
4371    <xref target="BCP97"/>.
4372  </annotation>
4373</reference>
4374
4375<reference anchor="RFC1951">
4376  <front>
4377    <title>DEFLATE Compressed Data Format Specification version 1.3</title>
4378    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4379      <organization>Aladdin Enterprises</organization>
4380      <address><email>ghost@aladdin.com</email></address>
4381    </author>
4382    <date month="May" year="1996"/>
4383  </front>
4384  <seriesInfo name="RFC" value="1951"/>
4385  <annotation>
4386    RFC 1951 is an Informational RFC, thus it might be less stable than
4387    this specification. On the other hand, this downward reference was
4388    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4389    therefore it is unlikely to cause problems in practice. See also
4390    <xref target="BCP97"/>.
4391  </annotation>
4392</reference>
4393
4394<reference anchor="RFC1952">
4395  <front>
4396    <title>GZIP file format specification version 4.3</title>
4397    <author initials="P." surname="Deutsch" fullname="L. Peter Deutsch">
4398      <organization>Aladdin Enterprises</organization>
4399      <address><email>ghost@aladdin.com</email></address>
4400    </author>
4401    <author initials="J-L." surname="Gailly" fullname="Jean-Loup Gailly">
4402      <address><email>gzip@prep.ai.mit.edu</email></address>
4403    </author>
4404    <author initials="M." surname="Adler" fullname="Mark Adler">
4405      <address><email>madler@alumni.caltech.edu</email></address>
4406    </author>
4407    <author initials="L.P." surname="Deutsch" fullname="L. Peter Deutsch">
4408      <address><email>ghost@aladdin.com</email></address>
4409    </author>
4410    <author initials="G." surname="Randers-Pehrson" fullname="Glenn Randers-Pehrson">
4411      <address><email>randeg@alumni.rpi.edu</email></address>
4412    </author>
4413    <date month="May" year="1996"/>
4414  </front>
4415  <seriesInfo name="RFC" value="1952"/>
4416  <annotation>
4417    RFC 1952 is an Informational RFC, thus it might be less stable than
4418    this specification. On the other hand, this downward reference was
4419    present since the publication of RFC 2068 in 1997 (<xref target="RFC2068"/>),
4420    therefore it is unlikely to cause problems in practice. See also
4421    <xref target="BCP97"/>.
4422  </annotation>
4423</reference>
4424
4425</references>
4426
4427<references title="Informative References">
4428
4429<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
4430  <front>
4431    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
4432    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen"/>
4433    <author initials="J." surname="Gettys" fullname="J. Gettys"/>
4434    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux"/>
4435    <author initials="H." surname="Lie" fullname="H. Lie"/>
4436    <author initials="C." surname="Lilley" fullname="C. Lilley"/>
4437    <date year="1997" month="September"/>
4438  </front>
4439  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
4440</reference>
4441
4442<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
4443  <front>
4444    <title>Improving HTTP Latency</title>
4445    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan"/>
4446    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul"/>
4447    <date year="1995" month="December"/>
4448  </front>
4449  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
4450</reference>
4451
4452<reference anchor="RFC1123">
4453  <front>
4454    <title>Requirements for Internet Hosts - Application and Support</title>
4455    <author initials="R." surname="Braden" fullname="Robert Braden">
4456      <organization>University of Southern California (USC), Information Sciences Institute</organization>
4457      <address><email>Braden@ISI.EDU</email></address>
4458    </author>
4459    <date month="October" year="1989"/>
4460  </front>
4461  <seriesInfo name="STD" value="3"/>
4462  <seriesInfo name="RFC" value="1123"/>
4463</reference>
4464
4465<reference anchor="RFC1919">
4466  <front>
4467    <title>Classical versus Transparent IP Proxies</title>
4468    <author initials="M." surname="Chatel" fullname="Marc Chatel">
4469      <address><email>mchatel@pax.eunet.ch</email></address>
4470    </author>
4471    <date year="1996" month="March"/>
4472  </front>
4473  <seriesInfo name="RFC" value="1919"/>
4474</reference>
4475
4476<reference anchor="RFC1945">
4477  <front>
4478    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
4479    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4480      <organization>MIT, Laboratory for Computer Science</organization>
4481      <address><email>timbl@w3.org</email></address>
4482    </author>
4483    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4484      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4485      <address><email>fielding@ics.uci.edu</email></address>
4486    </author>
4487    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4488      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
4489      <address><email>frystyk@w3.org</email></address>
4490    </author>
4491    <date month="May" year="1996"/>
4492  </front>
4493  <seriesInfo name="RFC" value="1945"/>
4494</reference>
4495
4496<reference anchor="RFC2045">
4497  <front>
4498    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
4499    <author initials="N." surname="Freed" fullname="Ned Freed">
4500      <organization>Innosoft International, Inc.</organization>
4501      <address><email>ned@innosoft.com</email></address>
4502    </author>
4503    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
4504      <organization>First Virtual Holdings</organization>
4505      <address><email>nsb@nsb.fv.com</email></address>
4506    </author>
4507    <date month="November" year="1996"/>
4508  </front>
4509  <seriesInfo name="RFC" value="2045"/>
4510</reference>
4511
4512<reference anchor="RFC2047">
4513  <front>
4514    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
4515    <author initials="K." surname="Moore" fullname="Keith Moore">
4516      <organization>University of Tennessee</organization>
4517      <address><email>moore@cs.utk.edu</email></address>
4518    </author>
4519    <date month="November" year="1996"/>
4520  </front>
4521  <seriesInfo name="RFC" value="2047"/>
4522</reference>
4523
4524<reference anchor="RFC2068">
4525  <front>
4526    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
4527    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
4528      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
4529      <address><email>fielding@ics.uci.edu</email></address>
4530    </author>
4531    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4532      <organization>MIT Laboratory for Computer Science</organization>
4533      <address><email>jg@w3.org</email></address>
4534    </author>
4535    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
4536      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
4537      <address><email>mogul@wrl.dec.com</email></address>
4538    </author>
4539    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4540      <organization>MIT Laboratory for Computer Science</organization>
4541      <address><email>frystyk@w3.org</email></address>
4542    </author>
4543    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
4544      <organization>MIT Laboratory for Computer Science</organization>
4545      <address><email>timbl@w3.org</email></address>
4546    </author>
4547    <date month="January" year="1997"/>
4548  </front>
4549  <seriesInfo name="RFC" value="2068"/>
4550</reference>
4551
4552<reference anchor="RFC2145">
4553  <front>
4554    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
4555    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
4556      <organization>Western Research Laboratory</organization>
4557      <address><email>mogul@wrl.dec.com</email></address>
4558    </author>
4559    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
4560      <organization>Department of Information and Computer Science</organization>
4561      <address><email>fielding@ics.uci.edu</email></address>
4562    </author>
4563    <author initials="J." surname="Gettys" fullname="Jim Gettys">
4564      <organization>MIT Laboratory for Computer Science</organization>
4565      <address><email>jg@w3.org</email></address>
4566    </author>
4567    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
4568      <organization>W3 Consortium</organization>
4569      <address><email>frystyk@w3.org</email></address>
4570    </author>
4571    <date month="May" year="1997"/>
4572  </front>
4573  <seriesInfo name="RFC" value="2145"/>
4574</reference>
4575
4576<reference anchor="RFC2616">
4577  <front>
4578    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
4579    <author initials="R." surname="Fielding" fullname="R. Fielding">
4580      <organization>University of California, Irvine</organization>
4581      <address><email>fielding@ics.uci.edu</email></address>
4582    </author>
4583    <author initials="J." surname="Gettys" fullname="J. Gettys">
4584      <organization>W3C</organization>
4585      <address><email>jg@w3.org</email></address>
4586    </author>
4587    <author initials="J." surname="Mogul" fullname="J. Mogul">
4588      <organization>Compaq Computer Corporation</organization>
4589      <address><email>mogul@wrl.dec.com</email></address>
4590    </author>
4591    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
4592      <organization>MIT Laboratory for Computer Science</organization>
4593      <address><email>frystyk@w3.org</email></address>
4594    </author>
4595    <author initials="L." surname="Masinter" fullname="L. Masinter">
4596      <organization>Xerox Corporation</organization>
4597      <address><email>masinter@parc.xerox.com</email></address>
4598    </author>
4599    <author initials="P." surname="Leach" fullname="P. Leach">
4600      <organization>Microsoft Corporation</organization>
4601      <address><email>paulle@microsoft.com</email></address>
4602    </author>
4603    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
4604      <organization>W3C</organization>
4605      <address><email>timbl@w3.org</email></address>
4606    </author>
4607    <date month="June" year="1999"/>
4608  </front>
4609  <seriesInfo name="RFC" value="2616"/>
4610</reference>
4611
4612<reference anchor="RFC2817">
4613  <front>
4614    <title>Upgrading to TLS Within HTTP/1.1</title>
4615    <author initials="R." surname="Khare" fullname="R. Khare">
4616      <organization>4K Associates / UC Irvine</organization>
4617      <address><email>rohit@4K-associates.com</email></address>
4618    </author>
4619    <author initials="S." surname="Lawrence" fullname="S. Lawrence">
4620      <organization>Agranat Systems, Inc.</organization>
4621      <address><email>lawrence@agranat.com</email></address>
4622    </author>
4623    <date year="2000" month="May"/>
4624  </front>
4625  <seriesInfo name="RFC" value="2817"/>
4626</reference>
4627
4628<reference anchor="RFC2818">
4629  <front>
4630    <title>HTTP Over TLS</title>
4631    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
4632      <organization>RTFM, Inc.</organization>
4633      <address><email>ekr@rtfm.com</email></address>
4634    </author>
4635    <date year="2000" month="May"/>
4636  </front>
4637  <seriesInfo name="RFC" value="2818"/>
4638</reference>
4639
4640<reference anchor="RFC2965">
4641  <front>
4642    <title>HTTP State Management Mechanism</title>
4643    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
4644      <organization>Bell Laboratories, Lucent Technologies</organization>
4645      <address><email>dmk@bell-labs.com</email></address>
4646    </author>
4647    <author initials="L." surname="Montulli" fullname="Lou Montulli">
4648      <organization>Epinions.com, Inc.</organization>
4649      <address><email>lou@montulli.org</email></address>
4650    </author>
4651    <date year="2000" month="October"/>
4652  </front>
4653  <seriesInfo name="RFC" value="2965"/>
4654</reference>
4655
4656<reference anchor="RFC3040">
4657  <front>
4658    <title>Internet Web Replication and Caching Taxonomy</title>
4659    <author initials="I." surname="Cooper" fullname="I. Cooper">
4660      <organization>Equinix, Inc.</organization>
4661    </author>
4662    <author initials="I." surname="Melve" fullname="I. Melve">
4663      <organization>UNINETT</organization>
4664    </author>
4665    <author initials="G." surname="Tomlinson" fullname="G. Tomlinson">
4666      <organization>CacheFlow Inc.</organization>
4667    </author>
4668    <date year="2001" month="January"/>
4669  </front>
4670  <seriesInfo name="RFC" value="3040"/>
4671</reference>
4672
4673<reference anchor="RFC3864">
4674  <front>
4675    <title>Registration Procedures for Message Header Fields</title>
4676    <author initials="G." surname="Klyne" fullname="G. Klyne">
4677      <organization>Nine by Nine</organization>
4678      <address><email>GK-IETF@ninebynine.org</email></address>
4679    </author>
4680    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
4681      <organization>BEA Systems</organization>
4682      <address><email>mnot@pobox.com</email></address>
4683    </author>
4684    <author initials="J." surname="Mogul" fullname="J. Mogul">
4685      <organization>HP Labs</organization>
4686      <address><email>JeffMogul@acm.org</email></address>
4687    </author>
4688    <date year="2004" month="September"/>
4689  </front>
4690  <seriesInfo name="BCP" value="90"/>
4691  <seriesInfo name="RFC" value="3864"/>
4692</reference>
4693
4694<reference anchor="RFC4033">
4695  <front>
4696    <title>DNS Security Introduction and Requirements</title>
4697    <author initials="R." surname="Arends" fullname="R. Arends"/>
4698    <author initials="R." surname="Austein" fullname="R. Austein"/>
4699    <author initials="M." surname="Larson" fullname="M. Larson"/>
4700    <author initials="D." surname="Massey" fullname="D. Massey"/>
4701    <author initials="S." surname="Rose" fullname="S. Rose"/>
4702    <date year="2005" month="March"/>
4703  </front>
4704  <seriesInfo name="RFC" value="4033"/>
4705</reference>
4706
4707<reference anchor="RFC4288">
4708  <front>
4709    <title>Media Type Specifications and Registration Procedures</title>
4710    <author initials="N." surname="Freed" fullname="N. Freed">
4711      <organization>Sun Microsystems</organization>
4712      <address>
4713        <email>ned.freed@mrochek.com</email>
4714      </address>
4715    </author>
4716    <author initials="J." surname="Klensin" fullname="J. Klensin">
4717      <address>
4718        <email>klensin+ietf@jck.com</email>
4719      </address>
4720    </author>
4721    <date year="2005" month="December"/>
4722  </front>
4723  <seriesInfo name="BCP" value="13"/>
4724  <seriesInfo name="RFC" value="4288"/>
4725</reference>
4726
4727<reference anchor="RFC4395">
4728  <front>
4729    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4730    <author initials="T." surname="Hansen" fullname="T. Hansen">
4731      <organization>AT&amp;T Laboratories</organization>
4732      <address>
4733        <email>tony+urireg@maillennium.att.com</email>
4734      </address>
4735    </author>
4736    <author initials="T." surname="Hardie" fullname="T. Hardie">
4737      <organization>Qualcomm, Inc.</organization>
4738      <address>
4739        <email>hardie@qualcomm.com</email>
4740      </address>
4741    </author>
4742    <author initials="L." surname="Masinter" fullname="L. Masinter">
4743      <organization>Adobe Systems</organization>
4744      <address>
4745        <email>LMM@acm.org</email>
4746      </address>
4747    </author>
4748    <date year="2006" month="February"/>
4749  </front>
4750  <seriesInfo name="BCP" value="115"/>
4751  <seriesInfo name="RFC" value="4395"/>
4752</reference>
4753
4754<reference anchor="RFC4559">
4755  <front>
4756    <title>SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows</title>
4757    <author initials="K." surname="Jaganathan" fullname="K. Jaganathan"/>
4758    <author initials="L." surname="Zhu" fullname="L. Zhu"/>
4759    <author initials="J." surname="Brezak" fullname="J. Brezak"/>
4760    <date year="2006" month="June"/>
4761  </front>
4762  <seriesInfo name="RFC" value="4559"/>
4763</reference>
4764
4765<reference anchor="RFC5226">
4766  <front>
4767    <title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
4768    <author initials="T." surname="Narten" fullname="T. Narten">
4769      <organization>IBM</organization>
4770      <address><email>narten@us.ibm.com</email></address>
4771    </author>
4772    <author initials="H." surname="Alvestrand" fullname="H. Alvestrand">
4773      <organization>Google</organization>
4774      <address><email>Harald@Alvestrand.no</email></address>
4775    </author>
4776    <date year="2008" month="May"/>
4777  </front>
4778  <seriesInfo name="BCP" value="26"/>
4779  <seriesInfo name="RFC" value="5226"/>
4780</reference>
4781
4782<reference anchor="RFC5322">
4783  <front>
4784    <title>Internet Message Format</title>
4785    <author initials="P." surname="Resnick" fullname="P. Resnick">
4786      <organization>Qualcomm Incorporated</organization>
4787    </author>
4788    <date year="2008" month="October"/>
4789  </front> 
4790  <seriesInfo name="RFC" value="5322"/>
4791</reference>
4792
4793<reference anchor="RFC6265">
4794  <front>
4795    <title>HTTP State Management Mechanism</title>
4796    <author initials="A." surname="Barth" fullname="Adam Barth">
4797      <organization abbrev="U.C. Berkeley">
4798        University of California, Berkeley
4799      </organization>
4800      <address><email>abarth@eecs.berkeley.edu</email></address>
4801    </author>
4802    <date year="2011" month="April"/>
4803  </front>
4804  <seriesInfo name="RFC" value="6265"/>
4805</reference>
4806
4807<reference anchor="BCP97">
4808  <front>
4809    <title>Handling Normative References to Standards-Track Documents</title>
4810    <author initials="J." surname="Klensin" fullname="J. Klensin">
4811      <address>
4812        <email>klensin+ietf@jck.com</email>
4813      </address>
4814    </author>
4815    <author initials="S." surname="Hartman" fullname="S. Hartman">
4816      <organization>MIT</organization>
4817      <address>
4818        <email>hartmans-ietf@mit.edu</email>
4819      </address>
4820    </author>
4821    <date year="2007" month="June"/>
4822  </front>
4823  <seriesInfo name="BCP" value="97"/>
4824  <seriesInfo name="RFC" value="4897"/>
4825</reference>
4826
4827<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4828  <front>
4829    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4830    <author initials="D." surname="Kristol" fullname="David M. Kristol"/>
4831    <date year="2001" month="November"/>
4832  </front>
4833  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4834</reference>
4835
4836<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4837  <front>
4838    <title>Analysis of HTTP Performance Problems</title>
4839    <author initials="S." surname="Spero" fullname="Simon E. Spero"/>
4840    <date/>
4841  </front>
4842</reference>
4843
4844<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4845  <front>
4846  <title>Analysis of HTTP Performance</title>
4847  <author initials="J." surname="Touch" fullname="Joe Touch">
4848    <organization>USC/Information Sciences Institute</organization>
4849    <address><email>touch@isi.edu</email></address>
4850  </author>
4851  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4852    <organization>USC/Information Sciences Institute</organization>
4853    <address><email>johnh@isi.edu</email></address>
4854  </author>
4855  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4856    <organization>USC/Information Sciences Institute</organization>
4857    <address><email>katia@isi.edu</email></address>
4858  </author>
4859  <date year="1998" month="Aug"/>
4860  </front>
4861  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4862  <annotation>(original report dated Aug. 1996)</annotation>
4863</reference>
4864
4865</references>
4866
4867
4868<section title="HTTP Version History" anchor="compatibility">
4869<t>
4870   HTTP has been in use by the World-Wide Web global information initiative
4871   since 1990. The first version of HTTP, later referred to as HTTP/0.9,
4872   was a simple protocol for hypertext data transfer across the Internet
4873   with only a single request method (GET) and no metadata.
4874   HTTP/1.0, as defined by <xref target="RFC1945"/>, added a range of request
4875   methods and MIME-like messaging that could include metadata about the data
4876   transferred and modifiers on the request/response semantics. However,
4877   HTTP/1.0 did not sufficiently take into consideration the effects of
4878   hierarchical proxies, caching, the need for persistent connections, or
4879   name-based virtual hosts. The proliferation of incompletely-implemented
4880   applications calling themselves "HTTP/1.0" further necessitated a
4881   protocol version change in order for two communicating applications
4882   to determine each other's true capabilities.
4883</t>
4884<t>
4885   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
4886   requirements that enable reliable implementations, adding only
4887   those new features that will either be safely ignored by an HTTP/1.0
4888   recipient or only sent when communicating with a party advertising
4889   compliance with HTTP/1.1.
4890</t>
4891<t>
4892   It is beyond the scope of a protocol specification to mandate
4893   compliance with previous versions. HTTP/1.1 was deliberately
4894   designed, however, to make supporting previous versions easy.
4895   We would expect a general-purpose HTTP/1.1 server to understand
4896   any valid request in the format of HTTP/1.0 and respond appropriately
4897   with an HTTP/1.1 message that only uses features understood (or
4898   safely ignored) by HTTP/1.0 clients.  Likewise, would expect
4899   an HTTP/1.1 client to understand any valid HTTP/1.0 response.
4900</t>
4901<t>
4902   Since HTTP/0.9 did not support header fields in a request,
4903   there is no mechanism for it to support name-based virtual
4904   hosts (selection of resource by inspection of the Host header
4905   field).  Any server that implements name-based virtual hosts
4906   ought to disable support for HTTP/0.9.  Most requests that
4907   appear to be HTTP/0.9 are, in fact, badly constructed HTTP/1.x
4908   requests wherein a buggy client failed to properly encode
4909   linear whitespace found in a URI reference and placed in
4910   the request-target.
4911</t>
4912
4913<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4914<t>
4915   This section summarizes major differences between versions HTTP/1.0
4916   and HTTP/1.1.
4917</t>
4918
4919<section title="Multi-homed Web Servers" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4920<t>
4921   The requirements that clients and servers support the Host header
4922   field (<xref target="header.host"/>), report an error if it is
4923   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-target"/>)
4924   are among the most important changes defined by HTTP/1.1.
4925</t>
4926<t>
4927   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4928   addresses and servers; there was no other established mechanism for
4929   distinguishing the intended server of a request than the IP address
4930   to which that request was directed. The Host header field was
4931   introduced during the development of HTTP/1.1 and, though it was
4932   quickly implemented by most HTTP/1.0 browsers, additional requirements
4933   were placed on all HTTP/1.1 requests in order to ensure complete
4934   adoption.  At the time of this writing, most HTTP-based services
4935   are dependent upon the Host header field for targeting requests.
4936</t>
4937</section>
4938
4939<section title="Keep-Alive Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4940<t>
4941   For most implementations of HTTP/1.0, each connection is established
4942   by the client prior to the request and closed by the server after
4943   sending the response. However, some implementations implement the
4944   Keep-Alive version of persistent connections described in
4945   Section 19.7.1 of <xref target="RFC2068"/>.
4946</t>
4947<t>
4948   Some clients and servers might wish to be compatible with some
4949   previous implementations of persistent connections in HTTP/1.0
4950   clients and servers. Persistent connections in HTTP/1.0 are
4951   explicitly negotiated as they are not the default behavior. HTTP/1.0
4952   experimental implementations of persistent connections are faulty,
4953   and the new facilities in HTTP/1.1 are designed to rectify these
4954   problems. The problem was that some existing HTTP/1.0 clients might
4955   send Keep-Alive to a proxy server that doesn't understand
4956   Connection, which would then erroneously forward it to the next
4957   inbound server, which would establish the Keep-Alive connection and
4958   result in a hung HTTP/1.0 proxy waiting for the close on the
4959   response. The result is that HTTP/1.0 clients must be prevented from
4960   using Keep-Alive when talking to proxies.
4961</t>
4962<t>
4963   However, talking to proxies is the most important use of persistent
4964   connections, so that prohibition is clearly unacceptable. Therefore,
4965   we need some other mechanism for indicating a persistent connection
4966   is desired, which is safe to use even when talking to an old proxy
4967   that ignores Connection. Persistent connections are the default for
4968   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4969   declaring non-persistence. See <xref target="header.connection"/>.
4970</t>
4971</section>
4972</section>
4973
4974<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4975<t>
4976  Empty list elements in list productions have been deprecated.
4977  (<xref target="notation.abnf"/>)
4978</t>
4979<t>
4980  Rules about implicit linear whitespace between certain grammar productions
4981  have been removed; now it's only allowed when specifically pointed out
4982  in the ABNF.
4983  (<xref target="basic.rules"/>)
4984</t>
4985<t>
4986  Clarify that the string "HTTP" in the HTTP-Version ABFN production is case
4987  sensitive. Restrict the version numbers to be single digits due to the fact
4988  that implementations are known to handle multi-digit version numbers
4989  incorrectly.
4990  (<xref target="http.version"/>)
4991</t>
4992<t>
4993  Require that invalid whitespace around field-names be rejected.
4994  (<xref target="header.fields"/>)
4995</t>
4996<t> 
4997  The NUL octet is no longer allowed in comment and quoted-string
4998  text. The quoted-pair rule no longer allows escaping control characters other than HTAB.
4999  Non-ASCII content in header fields and reason phrase has been obsoleted and
5000  made opaque (the TEXT rule was removed).
5001  (<xref target="field.rules"/>)
5002</t>
5003<t>
5004  Require recipients to handle bogus Content-Length header fields as errors.
5005  (<xref target="message.body"/>)
5006</t>
5007<t>
5008  Remove reference to non-existent identity transfer-coding value tokens.
5009  (Sections <xref format="counter" target="message.body"/> and
5010  <xref format="counter" target="transfer.codings"/>)
5011</t>
5012<t>
5013  Update use of abs_path production from RFC 1808 to the path-absolute + query
5014  components of RFC 3986. State that the asterisk form is allowed for the OPTIONS
5015  request method only.
5016  (<xref target="request-target"/>)
5017</t>
5018<t>
5019  Clarification that the chunk length does not include the count of the octets
5020  in the chunk header and trailer. Furthermore disallowed line folding
5021  in chunk extensions.
5022  (<xref target="chunked.encoding"/>)
5023</t>
5024<t>
5025  Remove hard limit of two connections per server.
5026  (<xref target="persistent.practical"/>)
5027</t>
5028<t>
5029  Change ABNF productions for header fields to only define the field value.
5030  (<xref target="header.field.definitions"/>)
5031</t>
5032<t>
5033  Clarify exactly when close connection options must be sent.
5034  (<xref target="header.connection"/>)
5035</t>
5036<t>
5037  Define the semantics of the "Upgrade" header field in responses other than
5038  101 (this was incorporated from <xref target="RFC2817"/>).
5039  (<xref target="header.upgrade"/>)
5040</t>
5041</section>
5042</section>
5043
5044
5045<section title="Collected ABNF" anchor="collected.abnf">
5046<figure>
5047<artwork type="abnf" name="p1-messaging.parsed-abnf"><![CDATA[
5048BWS = OWS
5049
5050Chunked-Body = *chunk last-chunk trailer-part CRLF
5051Connection = *( "," OWS ) connection-token *( OWS "," [ OWS
5052 connection-token ] )
5053Content-Length = 1*DIGIT
5054
5055Date = HTTP-date
5056
5057GMT = %x47.4D.54 ; GMT
5058
5059HTTP-Prot-Name = %x48.54.54.50 ; HTTP
5060HTTP-Version = HTTP-Prot-Name "/" DIGIT "." DIGIT
5061HTTP-date = rfc1123-date / obs-date
5062HTTP-message = start-line *( header-field CRLF ) CRLF [ message-body
5063 ]
5064Host = uri-host [ ":" port ]
5065
5066Method = token
5067
5068OWS = *( [ obs-fold ] WSP )
5069
5070RWS = 1*( [ obs-fold ] WSP )
5071Reason-Phrase = *( WSP / VCHAR / obs-text )
5072Request = Request-Line *( header-field CRLF ) CRLF [ message-body ]
5073Request-Line = Method SP request-target SP HTTP-Version CRLF
5074Response = Status-Line *( header-field CRLF ) CRLF [ message-body ]
5075
5076Status-Code = 3DIGIT
5077Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
5078
5079TE = [ ( "," / t-codings ) *( OWS "," [ OWS t-codings ] ) ]
5080Trailer = *( "," OWS ) field-name *( OWS "," [ OWS field-name ] )
5081Transfer-Encoding = *( "," OWS ) transfer-coding *( OWS "," [ OWS
5082 transfer-coding ] )
5083
5084URI-reference = <URI-reference, defined in [RFC3986], Section 4.1>
5085Upgrade = *( "," OWS ) product *( OWS "," [ OWS product ] )
5086
5087Via = *( "," OWS ) received-protocol RWS received-by [ RWS comment ]
5088 *( OWS "," [ OWS received-protocol RWS received-by [ RWS comment ] ]
5089 )
5090
5091absolute-URI = <absolute-URI, defined in [RFC3986], Section 4.3>
5092asctime-date = day-name SP date3 SP time-of-day SP year
5093attribute = token
5094authority = <authority, defined in [RFC3986], Section 3.2>
5095
5096chunk = chunk-size *WSP [ chunk-ext ] CRLF chunk-data CRLF
5097chunk-data = 1*OCTET
5098chunk-ext = *( ";" *WSP chunk-ext-name [ "=" chunk-ext-val ] *WSP )
5099chunk-ext-name = token
5100chunk-ext-val = token / quoted-str-nf
5101chunk-size = 1*HEXDIG
5102comment = "(" *( ctext / quoted-cpair / comment ) ")"
5103connection-token = token
5104ctext = OWS / %x21-27 ; '!'-'''
5105 / %x2A-5B ; '*'-'['
5106 / %x5D-7E ; ']'-'~'
5107 / obs-text
5108
5109date1 = day SP month SP year
5110date2 = day "-" month "-" 2DIGIT
5111date3 = month SP ( 2DIGIT / ( SP DIGIT ) )
5112day = 2DIGIT
5113day-name = %x4D.6F.6E ; Mon
5114 / %x54.75.65 ; Tue
5115 / %x57.65.64 ; Wed
5116 / %x54.68.75 ; Thu
5117 / %x46.72.69 ; Fri
5118 / %x53.61.74 ; Sat
5119 / %x53.75.6E ; Sun
5120day-name-l = %x4D.6F.6E.64.61.79 ; Monday
5121 / %x54.75.65.73.64.61.79 ; Tuesday
5122 / %x57.65.64.6E.65.73.64.61.79 ; Wednesday
5123 / %x54.68.75.72.73.64.61.79 ; Thursday
5124 / %x46.72.69.64.61.79 ; Friday
5125 / %x53.61.74.75.72.64.61.79 ; Saturday
5126 / %x53.75.6E.64.61.79 ; Sunday
5127
5128field-content = *( WSP / VCHAR / obs-text )
5129field-name = token
5130field-value = *( field-content / OWS )
5131
5132header-field = field-name ":" OWS [ field-value ] OWS
5133hour = 2DIGIT
5134http-URI = "http://" authority path-abempty [ "?" query ]
5135https-URI = "https://" authority path-abempty [ "?" query ]
5136
5137last-chunk = 1*"0" *WSP [ chunk-ext ] CRLF
5138
5139message-body = *OCTET
5140minute = 2DIGIT
5141month = %x4A.61.6E ; Jan
5142 / %x46.65.62 ; Feb
5143 / %x4D.61.72 ; Mar
5144 / %x41.70.72 ; Apr
5145 / %x4D.61.79 ; May
5146 / %x4A.75.6E ; Jun
5147 / %x4A.75.6C ; Jul
5148 / %x41.75.67 ; Aug
5149 / %x53.65.70 ; Sep
5150 / %x4F.63.74 ; Oct
5151 / %x4E.6F.76 ; Nov
5152 / %x44.65.63 ; Dec
5153
5154obs-date = rfc850-date / asctime-date
5155obs-fold = CRLF
5156obs-text = %x80-FF
5157
5158partial-URI = relative-part [ "?" query ]
5159path-abempty = <path-abempty, defined in [RFC3986], Section 3.3>
5160path-absolute = <path-absolute, defined in [RFC3986], Section 3.3>
5161port = <port, defined in [RFC3986], Section 3.2.3>
5162product = token [ "/" product-version ]
5163product-version = token
5164protocol-name = token
5165protocol-version = token
5166pseudonym = token
5167
5168qdtext = OWS / "!" / %x23-5B ; '#'-'['
5169 / %x5D-7E ; ']'-'~'
5170 / obs-text
5171qdtext-nf = WSP / "!" / %x23-5B ; '#'-'['
5172 / %x5D-7E ; ']'-'~'
5173 / obs-text
5174query = <query, defined in [RFC3986], Section 3.4>
5175quoted-cpair = "\" ( WSP / VCHAR / obs-text )
5176quoted-pair = "\" ( WSP / VCHAR / obs-text )
5177quoted-str-nf = DQUOTE *( qdtext-nf / quoted-pair ) DQUOTE
5178quoted-string = DQUOTE *( qdtext / quoted-pair ) DQUOTE
5179qvalue = ( "0" [ "." *3DIGIT ] ) / ( "1" [ "." *3"0" ] )
5180
5181received-by = ( uri-host [ ":" port ] ) / pseudonym
5182received-protocol = [ protocol-name "/" ] protocol-version
5183relative-part = <relative-part, defined in [RFC3986], Section 4.2>
5184request-target = "*" / absolute-URI / ( path-absolute [ "?" query ] )
5185 / authority
5186rfc1123-date = day-name "," SP date1 SP time-of-day SP GMT
5187rfc850-date = day-name-l "," SP date2 SP time-of-day SP GMT
5188
5189second = 2DIGIT
5190special = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "\" /
5191 DQUOTE / "/" / "[" / "]" / "?" / "=" / "{" / "}"
5192start-line = Request-Line / Status-Line
5193
5194t-codings = "trailers" / ( transfer-extension [ te-params ] )
5195tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "." /
5196 "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA
5197te-ext = OWS ";" OWS token [ "=" word ]
5198te-params = OWS ";" OWS "q=" qvalue *te-ext
5199time-of-day = hour ":" minute ":" second
5200token = 1*tchar
5201trailer-part = *( header-field CRLF )
5202transfer-coding = "chunked" / "compress" / "deflate" / "gzip" /
5203 transfer-extension
5204transfer-extension = token *( OWS ";" OWS transfer-parameter )
5205transfer-parameter = attribute BWS "=" BWS value
5206
5207uri-host = <host, defined in [RFC3986], Section 3.2.2>
5208
5209value = word
5210
5211word = token / quoted-string
5212
5213year = 4DIGIT
5214]]></artwork>
5215</figure>
5216<figure><preamble>ABNF diagnostics:</preamble><artwork type="inline"><![CDATA[
5217; Chunked-Body defined but not used
5218; Connection defined but not used
5219; Content-Length defined but not used
5220; Date defined but not used
5221; HTTP-message defined but not used
5222; Host defined but not used
5223; Request defined but not used
5224; Response defined but not used
5225; TE defined but not used
5226; Trailer defined but not used
5227; Transfer-Encoding defined but not used
5228; URI-reference defined but not used
5229; Upgrade defined but not used
5230; Via defined but not used
5231; http-URI defined but not used
5232; https-URI defined but not used
5233; partial-URI defined but not used
5234; special defined but not used
5235]]></artwork></figure></section>
5236
5237
5238<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
5239
5240<section title="Since RFC 2616">
5241<t>
5242  Extracted relevant partitions from <xref target="RFC2616"/>.
5243</t>
5244</section>
5245
5246<section title="Since draft-ietf-httpbis-p1-messaging-00">
5247<t>
5248  Closed issues:
5249  <list style="symbols"> 
5250    <t>
5251      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
5252      "HTTP Version should be case sensitive"
5253      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
5254    </t>
5255    <t>
5256      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
5257      "'unsafe' characters"
5258      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
5259    </t>
5260    <t>
5261      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
5262      "Chunk Size Definition"
5263      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
5264    </t>
5265    <t>
5266      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
5267      "Message Length"
5268      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
5269    </t>
5270    <t>
5271      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
5272      "Media Type Registrations"
5273      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
5274    </t>
5275    <t>
5276      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
5277      "URI includes query"
5278      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
5279    </t>
5280    <t>
5281      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
5282      "No close on 1xx responses"
5283      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
5284    </t>
5285    <t>
5286      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
5287      "Remove 'identity' token references"
5288      (<eref target="http://purl.org/NET/http-errata#identity"/>)
5289    </t>
5290    <t>
5291      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
5292      "Import query BNF"
5293    </t>
5294    <t>
5295      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
5296      "qdtext BNF"
5297    </t>
5298    <t>
5299      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
5300      "Normative and Informative references"
5301    </t>
5302    <t>
5303      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
5304      "RFC2606 Compliance"
5305    </t>
5306    <t>
5307      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
5308      "RFC977 reference"
5309    </t>
5310    <t>
5311      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
5312      "RFC1700 references"
5313    </t>
5314    <t>
5315      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
5316      "inconsistency in date format explanation"
5317    </t>
5318    <t>
5319      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
5320      "Date reference typo"
5321    </t>
5322    <t>
5323      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
5324      "Informative references"
5325    </t>
5326    <t>
5327      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
5328      "ISO-8859-1 Reference"
5329    </t>
5330    <t>
5331      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
5332      "Normative up-to-date references"
5333    </t>
5334  </list>
5335</t>
5336<t>
5337  Other changes:
5338  <list style="symbols"> 
5339    <t>
5340      Update media type registrations to use RFC4288 template.
5341    </t>
5342    <t>
5343      Use names of RFC4234 core rules DQUOTE and WSP,
5344      fix broken ABNF for chunk-data
5345      (work in progress on <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
5346    </t>
5347  </list>
5348</t>
5349</section>
5350
5351<section title="Since draft-ietf-httpbis-p1-messaging-01">
5352<t>
5353  Closed issues:
5354  <list style="symbols"> 
5355    <t>
5356      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
5357      "Bodies on GET (and other) requests"
5358    </t>
5359    <t>
5360      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
5361      "Updating to RFC4288"
5362    </t>
5363    <t>
5364      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
5365      "Status Code and Reason Phrase"
5366    </t>
5367    <t>
5368      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
5369      "rel_path not used"
5370    </t>
5371  </list>
5372</t>
5373<t>
5374  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5375  <list style="symbols"> 
5376    <t>
5377      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
5378      "trailer-part").
5379    </t>
5380    <t>
5381      Avoid underscore character in rule names ("http_URL" -&gt;
5382      "http-URL", "abs_path" -&gt; "path-absolute").
5383    </t>
5384    <t>
5385      Add rules for terms imported from URI spec ("absoluteURI", "authority",
5386      "path-absolute", "port", "query", "relativeURI", "host) — these will
5387      have to be updated when switching over to RFC3986.
5388    </t>
5389    <t>
5390      Synchronize core rules with RFC5234.
5391    </t>
5392    <t>
5393      Get rid of prose rules that span multiple lines.
5394    </t>
5395    <t>
5396      Get rid of unused rules LOALPHA and UPALPHA.
5397    </t>
5398    <t>
5399      Move "Product Tokens" section (back) into Part 1, as "token" is used
5400      in the definition of the Upgrade header field.
5401    </t>
5402    <t>
5403      Add explicit references to BNF syntax and rules imported from other parts of the specification.
5404    </t>
5405    <t>
5406      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
5407    </t>
5408  </list>
5409</t>
5410</section>
5411
5412<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
5413<t>
5414  Closed issues:
5415  <list style="symbols"> 
5416    <t>
5417      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
5418      "HTTP-date vs. rfc1123-date"
5419    </t>
5420    <t>
5421      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
5422      "WS in quoted-pair"
5423    </t>
5424  </list>
5425</t>
5426<t>
5427  Ongoing work on IANA Message Header Field Registration (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
5428  <list style="symbols"> 
5429    <t>
5430      Reference RFC 3984, and update header field registrations for headers defined
5431      in this document.
5432    </t>
5433  </list>
5434</t>
5435<t>
5436  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5437  <list style="symbols"> 
5438    <t>
5439      Replace string literals when the string really is case-sensitive (HTTP-Version).
5440    </t>
5441  </list>
5442</t>
5443</section>
5444
5445<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
5446<t>
5447  Closed issues:
5448  <list style="symbols"> 
5449    <t>
5450      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5451      "Connection closing"
5452    </t>
5453    <t>
5454      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
5455      "Move registrations and registry information to IANA Considerations"
5456    </t>
5457    <t>
5458      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
5459      "need new URL for PAD1995 reference"
5460    </t>
5461    <t>
5462      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
5463      "IANA Considerations: update HTTP URI scheme registration"
5464    </t>
5465    <t>
5466      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
5467      "Cite HTTPS URI scheme definition"
5468    </t>
5469    <t>
5470      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
5471      "List-type headers vs Set-Cookie"
5472    </t>
5473  </list>
5474</t>
5475<t>
5476  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5477  <list style="symbols"> 
5478    <t>
5479      Replace string literals when the string really is case-sensitive (HTTP-Date).
5480    </t>
5481    <t>
5482      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
5483    </t>
5484  </list>
5485</t>
5486</section>
5487
5488<section title="Since draft-ietf-httpbis-p1-messaging-04" anchor="changes.since.04">
5489<t>
5490  Closed issues:
5491  <list style="symbols"> 
5492    <t>
5493      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/34"/>:
5494      "Out-of-date reference for URIs"
5495    </t>
5496    <t>
5497      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/132"/>:
5498      "RFC 2822 is updated by RFC 5322"
5499    </t>
5500  </list>
5501</t>
5502<t>
5503  Ongoing work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5504  <list style="symbols"> 
5505    <t>
5506      Use "/" instead of "|" for alternatives.
5507    </t>
5508    <t>
5509      Get rid of RFC822 dependency; use RFC5234 plus extensions instead.
5510    </t>
5511    <t>
5512      Only reference RFC 5234's core rules.
5513    </t>
5514    <t>
5515      Introduce new ABNF rules for "bad" whitespace ("BWS"), optional
5516      whitespace ("OWS") and required whitespace ("RWS").
5517    </t>
5518    <t>
5519      Rewrite ABNFs to spell out whitespace rules, factor out
5520      header field value format definitions.
5521    </t>
5522  </list>
5523</t>
5524</section>
5525
5526<section title="Since draft-ietf-httpbis-p1-messaging-05" anchor="changes.since.05">
5527<t>
5528  Closed issues:
5529  <list style="symbols"> 
5530    <t>
5531      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/30"/>:
5532      "Header LWS"
5533    </t>
5534    <t>
5535      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/52"/>:
5536      "Sort 1.3 Terminology"
5537    </t>
5538    <t>
5539      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/63"/>:
5540      "RFC2047 encoded words"
5541    </t>
5542    <t>
5543      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/74"/>:
5544      "Character Encodings in TEXT"
5545    </t>
5546    <t>
5547      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/77"/>:
5548      "Line Folding"
5549    </t>
5550    <t>
5551      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5552      "OPTIONS * and proxies"
5553    </t>
5554    <t>
5555      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/94"/>:
5556      "Reason-Phrase BNF"
5557    </t>
5558    <t>
5559      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/111"/>:
5560      "Use of TEXT"
5561    </t>
5562    <t>
5563      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/118"/>:
5564      "Join "Differences Between HTTP Entities and RFC 2045 Entities"?"
5565    </t>
5566    <t>
5567      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/134"/>:
5568      "RFC822 reference left in discussion of date formats"
5569    </t>
5570  </list>
5571</t>
5572<t>
5573  Final work on ABNF conversion (<eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
5574  <list style="symbols"> 
5575    <t>
5576      Rewrite definition of list rules, deprecate empty list elements.
5577    </t>
5578    <t>
5579      Add appendix containing collected and expanded ABNF.
5580    </t>
5581  </list>
5582</t>
5583<t>
5584  Other changes:
5585  <list style="symbols"> 
5586    <t>
5587      Rewrite introduction; add mostly new Architecture Section.
5588    </t>
5589    <t>
5590      Move definition of quality values from Part 3 into Part 1;
5591      make TE request header field grammar independent of accept-params (defined in Part 3).
5592    </t>
5593  </list>
5594</t>
5595</section>
5596
5597<section title="Since draft-ietf-httpbis-p1-messaging-06" anchor="changes.since.06">
5598<t>
5599  Closed issues:
5600  <list style="symbols"> 
5601    <t>
5602      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/161"/>:
5603      "base for numeric protocol elements"
5604    </t>
5605    <t>
5606      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/162"/>:
5607      "comment ABNF"
5608    </t>
5609  </list>
5610</t>
5611<t>
5612  Partly resolved issues:
5613  <list style="symbols"> 
5614    <t>
5615      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/88"/>:
5616      "205 Bodies" (took out language that implied that there might be
5617      methods for which a request body MUST NOT be included)
5618    </t>
5619    <t>
5620      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/163"/>:
5621      "editorial improvements around HTTP-date"
5622    </t>
5623  </list>
5624</t>
5625</section>
5626
5627<section title="Since draft-ietf-httpbis-p1-messaging-07" anchor="changes.since.07">
5628<t>
5629  Closed issues:
5630  <list style="symbols"> 
5631    <t>
5632      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/93"/>:
5633      "Repeating single-value headers"
5634    </t>
5635    <t>
5636      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/131"/>:
5637      "increase connection limit"
5638    </t>
5639    <t>
5640      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/157"/>:
5641      "IP addresses in URLs"
5642    </t>
5643    <t>
5644      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/172"/>:
5645      "take over HTTP Upgrade Token Registry"
5646    </t>
5647    <t>
5648      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/173"/>:
5649      "CR and LF in chunk extension values"
5650    </t>
5651    <t>
5652      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/184"/>:
5653      "HTTP/0.9 support"
5654    </t>
5655    <t>
5656      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/188"/>:
5657      "pick IANA policy (RFC5226) for Transfer Coding / Content Coding"
5658    </t>
5659    <t>
5660      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/189"/>:
5661      "move definitions of gzip/deflate/compress to part 1"
5662    </t>
5663    <t>
5664      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/194"/>:
5665      "disallow control characters in quoted-pair"
5666    </t>
5667  </list>
5668</t>
5669<t>
5670  Partly resolved issues:
5671  <list style="symbols"> 
5672    <t>
5673      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/148"/>:
5674      "update IANA requirements wrt Transfer-Coding values" (add the
5675      IANA Considerations subsection)
5676    </t>
5677  </list>
5678</t>
5679</section>
5680
5681<section title="Since draft-ietf-httpbis-p1-messaging-08" anchor="changes.since.08">
5682<t>
5683  Closed issues:
5684  <list style="symbols"> 
5685    <t>
5686      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/201"/>:
5687      "header parsing, treatment of leading and trailing OWS"
5688    </t>
5689  </list>
5690</t>
5691<t>
5692  Partly resolved issues:
5693  <list style="symbols"> 
5694    <t>
5695      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/60"/>:
5696      "Placement of 13.5.1 and 13.5.2"
5697    </t>
5698    <t>
5699      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5700      "use of term "word" when talking about header structure"
5701    </t>
5702  </list>
5703</t>
5704</section>
5705
5706<section title="Since draft-ietf-httpbis-p1-messaging-09" anchor="changes.since.09">
5707<t>
5708  Closed issues:
5709  <list style="symbols"> 
5710    <t>
5711      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/73"/>:
5712      "Clarification of the term 'deflate'"
5713    </t>
5714    <t>
5715      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/83"/>:
5716      "OPTIONS * and proxies"
5717    </t>
5718    <t>
5719      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/122"/>:
5720      "MIME-Version not listed in P1, general header fields"
5721    </t>
5722    <t>
5723      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/143"/>:
5724      "IANA registry for content/transfer encodings"
5725    </t>
5726    <t>
5727      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/165"/>:
5728      "Case-sensitivity of HTTP-date"
5729    </t>
5730    <t>
5731      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/200"/>:
5732      "use of term "word" when talking about header structure"
5733    </t>
5734  </list>
5735</t>
5736<t>
5737  Partly resolved issues:
5738  <list style="symbols"> 
5739    <t>
5740      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/196"/>:
5741      "Term for the requested resource's URI"
5742    </t>
5743  </list>
5744</t>
5745</section>
5746
5747<section title="Since draft-ietf-httpbis-p1-messaging-10" anchor="changes.since.10">
5748<t>
5749  Closed issues:
5750  <list style="symbols">
5751    <t>
5752      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
5753      "Connection Closing"
5754    </t>
5755    <t>
5756      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/90"/>:
5757      "Delimiting messages with multipart/byteranges"
5758    </t>
5759    <t>
5760      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5761      "Handling multiple Content-Length headers"
5762    </t>
5763    <t>
5764      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/109"/>:
5765      "Clarify entity / representation / variant terminology"
5766    </t>
5767    <t>
5768      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/220"/>:
5769      "consider removing the 'changes from 2068' sections"
5770    </t>
5771  </list>
5772</t>
5773<t>
5774  Partly resolved issues:
5775  <list style="symbols"> 
5776    <t>
5777      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5778      "HTTP(s) URI scheme definitions"
5779    </t>
5780  </list>
5781</t>
5782</section>
5783
5784<section title="Since draft-ietf-httpbis-p1-messaging-11" anchor="changes.since.11">
5785<t>
5786  Closed issues:
5787  <list style="symbols">
5788    <t>
5789      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/193"/>:
5790      "Trailer requirements"
5791    </t>
5792    <t>
5793      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/204"/>:
5794      "Text about clock requirement for caches belongs in p6"
5795    </t>
5796    <t>
5797      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/221"/>:
5798      "effective request URI: handling of missing host in HTTP/1.0"
5799    </t>
5800    <t>
5801      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/248"/>:
5802      "confusing Date requirements for clients"
5803    </t>
5804  </list>
5805</t>
5806<t>
5807  Partly resolved issues:
5808  <list style="symbols"> 
5809    <t>
5810      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5811      "Handling multiple Content-Length headers"
5812    </t>
5813  </list>
5814</t>
5815</section>
5816
5817<section title="Since draft-ietf-httpbis-p1-messaging-12" anchor="changes.since.12">
5818<t>
5819  Closed issues:
5820  <list style="symbols">
5821    <t>
5822      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/75"/>:
5823      "RFC2145 Normative"
5824    </t>
5825    <t>
5826      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/159"/>:
5827      "HTTP(s) URI scheme definitions" (tune the requirements on userinfo)
5828    </t>
5829    <t>
5830      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/210"/>:
5831      "define 'transparent' proxy"
5832    </t>
5833    <t>
5834      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/224"/>:
5835      "Header Classification"
5836    </t>
5837    <t>
5838      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/233"/>:
5839      "Is * usable as a request-uri for new methods?"
5840    </t>
5841    <t>
5842      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/240"/>:
5843      "Migrate Upgrade details from RFC2817"
5844    </t>
5845    <t>
5846      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5847      "untangle ABNFs for header fields"
5848    </t>
5849    <t>
5850      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/279"/>:
5851      "update RFC 2109 reference"
5852    </t>
5853  </list>
5854</t>
5855</section>
5856
5857<section title="Since draft-ietf-httpbis-p1-messaging-13" anchor="changes.since.13">
5858<t>
5859  Closed issues:
5860  <list style="symbols">
5861    <t>
5862      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/53"/>:
5863      "Allow is not in 13.5.2"
5864    </t>
5865    <t>
5866      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/95"/>:
5867      "Handling multiple Content-Length headers"
5868    </t>
5869    <t>
5870      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/276"/>:
5871      "untangle ABNFs for header fields"
5872    </t>
5873    <t>
5874      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/286"/>:
5875      "Content-Length ABNF broken"
5876    </t>
5877  </list>
5878</t>
5879</section>
5880
5881<section title="Since draft-ietf-httpbis-p1-messaging-14" anchor="changes.since.14">
5882<t>
5883  Closed issues:
5884  <list style="symbols">
5885    <t>
5886      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/273"/>:
5887      "HTTP-Version should be redefined as fixed length pair of DIGIT . DIGIT"
5888    </t>
5889    <t>
5890      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/282"/>:
5891      "Recommend minimum sizes for protocol elements"
5892    </t>
5893    <t>
5894      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/283"/>:
5895      "Set expectations around buffering"
5896    </t>
5897    <t>
5898      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/288"/>:
5899      "Considering messages in isolation"
5900    </t>
5901  </list>
5902</t>
5903</section>
5904
5905<section title="Since draft-ietf-httpbis-p1-messaging-15" anchor="changes.since.15">
5906<t>
5907  Closed issues:
5908  <list style="symbols">
5909    <t>
5910      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/100"/>:
5911      "DNS Spoofing / DNS Binding advice"
5912    </t>
5913    <t>
5914      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/254"/>:
5915      "move RFCs 2145, 2616, 2817 to Historic status"
5916    </t>
5917    <t>
5918      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/270"/>:
5919      "\-escaping in quoted strings"
5920    </t>
5921    <t>
5922      <eref target="http://tools.ietf.org/wg/httpbis/trac/ticket/305"/>:
5923      "'Close' should be reserved in the HTTP header field registry"
5924    </t>
5925  </list>
5926</t>
5927</section>
5928
5929</section>
5930
5931</back>
5932</rfc>
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