source: draft-ietf-httpbis/04/draft-ietf-httpbis-p1-messaging-04.xml @ 2082

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fix mime types

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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<!DOCTYPE rfc
17  PUBLIC "" "rfc2629.dtd">
18<rfc obsoletes="2616" category="std" ipr="full3978" docName="draft-ietf-httpbis-p1-messaging-04">
19<front>
20
21  <title abbrev="HTTP/1.1, Part 1">HTTP/1.1, part 1: URIs, Connections, and Message Parsing</title>
22
23  <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
24    <organization abbrev="Day Software">Day Software</organization>
25    <address>
26      <postal>
27        <street>23 Corporate Plaza DR, Suite 280</street>
28        <city>Newport Beach</city>
29        <region>CA</region>
30        <code>92660</code>
31        <country>USA</country>
32      </postal>
33      <phone>+1-949-706-5300</phone>
34      <facsimile>+1-949-706-5305</facsimile>
35      <email>fielding@gbiv.com</email>
36      <uri>http://roy.gbiv.com/</uri>
37    </address>
38  </author>
39
40  <author initials="J." surname="Gettys" fullname="Jim Gettys">
41    <organization>One Laptop per Child</organization>
42    <address>
43      <postal>
44        <street>21 Oak Knoll Road</street>
45        <city>Carlisle</city>
46        <region>MA</region>
47        <code>01741</code>
48        <country>USA</country>
49      </postal>
50      <email>jg@laptop.org</email>
51      <uri>http://www.laptop.org/</uri>
52    </address>
53  </author>
54 
55  <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
56    <organization abbrev="HP">Hewlett-Packard Company</organization>
57    <address>
58      <postal>
59        <street>HP Labs, Large Scale Systems Group</street>
60        <street>1501 Page Mill Road, MS 1177</street>
61        <city>Palo Alto</city>
62        <region>CA</region>
63        <code>94304</code>
64        <country>USA</country>
65      </postal>
66      <email>JeffMogul@acm.org</email>
67    </address>
68  </author>
69
70  <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
71    <organization abbrev="Microsoft">Microsoft Corporation</organization>
72    <address>
73      <postal>
74        <street>1 Microsoft Way</street>
75        <city>Redmond</city>
76        <region>WA</region>
77        <code>98052</code>
78        <country>USA</country>
79      </postal>
80      <email>henrikn@microsoft.com</email>
81    </address>
82  </author>
83
84  <author initials="L." surname="Masinter" fullname="Larry Masinter">
85    <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
86    <address>
87      <postal>
88        <street>345 Park Ave</street>
89        <city>San Jose</city>
90        <region>CA</region>
91        <code>95110</code>
92        <country>USA</country>
93      </postal>
94      <email>LMM@acm.org</email>
95      <uri>http://larry.masinter.net/</uri>
96    </address>
97  </author>
98 
99  <author initials="P." surname="Leach" fullname="Paul J. Leach">
100    <organization abbrev="Microsoft">Microsoft Corporation</organization>
101    <address>
102      <postal>
103        <street>1 Microsoft Way</street>
104        <city>Redmond</city>
105        <region>WA</region>
106        <code>98052</code>
107      </postal>
108      <email>paulle@microsoft.com</email>
109    </address>
110  </author>
111   
112  <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
113    <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
114    <address>
115      <postal>
116        <street>MIT Computer Science and Artificial Intelligence Laboratory</street>
117        <street>The Stata Center, Building 32</street>
118        <street>32 Vassar Street</street>
119        <city>Cambridge</city>
120        <region>MA</region>
121        <code>02139</code>
122        <country>USA</country>
123      </postal>
124      <email>timbl@w3.org</email>
125      <uri>http://www.w3.org/People/Berners-Lee/</uri>
126    </address>
127  </author>
128
129  <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
130    <organization abbrev="W3C">World Wide Web Consortium</organization>
131    <address>
132      <postal>
133        <street>W3C / ERCIM</street>
134        <street>2004, rte des Lucioles</street>
135        <city>Sophia-Antipolis</city>
136        <region>AM</region>
137        <code>06902</code>
138        <country>France</country>
139      </postal>
140      <email>ylafon@w3.org</email>
141      <uri>http://www.raubacapeu.net/people/yves/</uri>
142    </address>
143  </author>
144
145  <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
146    <organization abbrev="greenbytes">greenbytes GmbH</organization>
147    <address>
148      <postal>
149        <street>Hafenweg 16</street>
150        <city>Muenster</city><region>NW</region><code>48155</code>
151        <country>Germany</country>
152      </postal>
153      <phone>+49 251 2807760</phone>   
154      <facsimile>+49 251 2807761</facsimile>   
155      <email>julian.reschke@greenbytes.de</email>       
156      <uri>http://greenbytes.de/tech/webdav/</uri>     
157    </address>
158  </author>
159
160  <date month="August" year="2008" day="29"/>
161
162<abstract>
163<t>
164   The Hypertext Transfer Protocol (HTTP) is an application-level
165   protocol for distributed, collaborative, hypermedia information
166   systems. HTTP has been in use by the World Wide Web global information
167   initiative since 1990. This document is Part 1 of the seven-part specification
168   that defines the protocol referred to as "HTTP/1.1" and, taken together,
169   obsoletes RFC 2616.  Part 1 provides an overview of HTTP and
170   its associated terminology, defines the "http" and "https" Uniform
171   Resource Identifier (URI) schemes, defines the generic message syntax
172   and parsing requirements for HTTP message frames, and describes
173   general security concerns for implementations.
174</t>
175</abstract>
176
177<note title="Editorial Note (To be removed by RFC Editor)">
178  <t>
179    Discussion of this draft should take place on the HTTPBIS working group
180    mailing list (ietf-http-wg@w3.org). The current issues list is
181    at <eref target="http://www.tools.ietf.org/wg/httpbis/trac/report/11"/>
182    and related documents (including fancy diffs) can be found at
183    <eref target="http://www.tools.ietf.org/wg/httpbis/"/>.
184  </t>
185  <t>
186    The changes in this draft are summarized in <xref target="changes.since.02"/>.
187  </t>
188</note>
189</front>
190<middle>
191<section title="Introduction" anchor="introduction">
192<t>
193   The Hypertext Transfer Protocol (HTTP) is an application-level
194   protocol for distributed, collaborative, hypermedia information
195   systems. HTTP has been in use by the World-Wide Web global
196   information initiative since 1990. The first version of HTTP, commonly
197   referred to as HTTP/0.9, was a simple protocol for raw data transfer
198   across the Internet with only a single method and no metadata.
199   HTTP/1.0, as defined by <xref target="RFC1945"/>, improved
200   the protocol by allowing messages to be in the format of MIME-like
201   messages, containing metadata about the data transferred and
202   modifiers on the request/response semantics. However, HTTP/1.0 did
203   not sufficiently take into consideration the effects of hierarchical
204   proxies, caching, the need for persistent connections, or name-based
205   virtual hosts. In addition, the proliferation of incompletely-implemented
206   applications calling themselves "HTTP/1.0" necessitated a
207   protocol version change in order for two communicating applications
208   to determine each other's true capabilities.
209</t>
210<t>
211   This document is Part 1 of the seven-part specification that defines
212   the protocol referred to as "HTTP/1.1", obsoleting <xref target="RFC2616"/>.
213   HTTP/1.1 remains compatible with HTTP/1.0 by including more stringent
214   requirements that enable reliable implementations and adding only
215   those new features that will either be safely ignored by an HTTP/1.0
216   recipient or only sent when communicating with a party advertising
217   compliance with HTTP/1.1.
218   Part 1 defines those aspects of HTTP/1.1 related to overall network
219   operation, message framing, interaction with transport protocols, and
220   URI schemes.
221</t>
222<t>
223   This document is currently disorganized in order to minimize the changes
224   between drafts and enable reviewers to see the smaller errata changes.
225   The next draft will reorganize the sections to better reflect the content.
226   In particular, the sections will be organized according to the typical
227   process of deciding when to use HTTP (URI schemes), overall network operation,
228   connection management, message framing, and generic message parsing.
229   The current mess reflects how widely dispersed these topics and associated
230   requirements had become in <xref target="RFC2616"/>.
231</t>
232
233<section title="Purpose" anchor="intro.purpose">
234<t>
235   Practical information systems require more functionality than simple
236   retrieval, including search, front-end update, and annotation. HTTP
237   allows an open-ended set of methods and headers that indicate the
238   purpose of a request <xref target="RFC2324"/>. It builds on the discipline of reference
239   provided by the Uniform Resource Identifier (URI) <xref target="RFC1630"/>, as a location
240   (URL) <xref target="RFC1738"/> or name (URN) <xref target="RFC1737"/>, for indicating the resource to which a
241   method is to be applied. Messages are passed in a format similar to
242   that used by Internet mail <xref target="RFC2822"/> as defined by the Multipurpose
243   Internet Mail Extensions (MIME) <xref target="RFC2045"/>.
244</t>
245<t>
246   HTTP is also used as a generic protocol for communication between
247   user agents and proxies/gateways to other Internet systems, including
248   those supported by the SMTP <xref target="RFC2821"/>, NNTP <xref target="RFC3977"/>, FTP <xref target="RFC959"/>, Gopher <xref target="RFC1436"/>,
249   and WAIS <xref target="WAIS"/> protocols. In this way, HTTP allows basic hypermedia
250   access to resources available from diverse applications.
251</t>
252</section>
253
254<section title="Requirements" anchor="intro.requirements">
255<t>
256   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
257   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
258   document are to be interpreted as described in <xref target="RFC2119"/>.
259</t>
260<t>
261   An implementation is not compliant if it fails to satisfy one or more
262   of the MUST or REQUIRED level requirements for the protocols it
263   implements. An implementation that satisfies all the MUST or REQUIRED
264   level and all the SHOULD level requirements for its protocols is said
265   to be "unconditionally compliant"; one that satisfies all the MUST
266   level requirements but not all the SHOULD level requirements for its
267   protocols is said to be "conditionally compliant."
268</t>
269</section>
270
271<section title="Terminology" anchor="intro.terminology">
272<t>
273   This specification uses a number of terms to refer to the roles
274   played by participants in, and objects of, the HTTP communication.
275</t>
276<t>
277  <iref item="connection"/>
278  connection
279  <list>
280    <t>
281      A transport layer virtual circuit established between two programs
282      for the purpose of communication.
283    </t>
284  </list>
285</t>
286<t>
287  <iref item="message"/>
288  message
289  <list>
290    <t>
291      The basic unit of HTTP communication, consisting of a structured
292      sequence of octets matching the syntax defined in <xref target="http.message"/> and
293      transmitted via the connection.
294    </t>
295  </list>
296</t>
297<t>
298  <iref item="request"/>
299  request
300  <list>
301    <t>
302      An HTTP request message, as defined in <xref target="request"/>.
303    </t>
304  </list>
305</t>
306<t>
307  <iref item="response"/>
308  response
309  <list>
310    <t>
311      An HTTP response message, as defined in <xref target="response"/>.
312    </t>
313  </list>
314</t>
315<t>
316  <iref item="resource"/>
317  resource
318  <list>
319    <t>
320      A network data object or service that can be identified by a URI,
321      as defined in <xref target="uri"/>. Resources may be available in multiple
322      representations (e.g. multiple languages, data formats, size, and
323      resolutions) or vary in other ways.
324    </t>
325  </list>
326</t>
327<t>
328  <iref item="entity"/>
329  entity
330  <list>
331    <t>
332      The information transferred as the payload of a request or
333      response. An entity consists of metainformation in the form of
334      entity-header fields and content in the form of an entity-body, as
335      described in Section 4 of <xref target="Part3"/>.
336    </t>
337  </list>
338</t>
339<t>
340  <iref item="representation"/>
341  representation
342  <list>
343    <t>
344      An entity included with a response that is subject to content
345      negotiation, as described in Section 5 of <xref target="Part3"/>. There may exist multiple
346      representations associated with a particular response status.
347    </t>
348  </list>
349</t>
350<t>
351  <iref item="content negotiation"/>
352  content negotiation
353  <list>
354    <t>
355      The mechanism for selecting the appropriate representation when
356      servicing a request, as described in Section 5 of <xref target="Part3"/>. The
357      representation of entities in any response can be negotiated
358      (including error responses).
359    </t>
360  </list>
361</t>
362<t>
363  <iref item="variant"/>
364  variant
365  <list>
366    <t>
367      A resource may have one, or more than one, representation(s)
368      associated with it at any given instant. Each of these
369      representations is termed a `variant'.  Use of the term `variant'
370      does not necessarily imply that the resource is subject to content
371      negotiation.
372    </t>
373  </list>
374</t>
375<t>
376  <iref item="client"/>
377  client
378  <list>
379    <t>
380      A program that establishes connections for the purpose of sending
381      requests.
382    </t>
383  </list>
384</t>
385<t>
386  <iref item="user agent"/>
387  user agent
388  <list>
389    <t>
390      The client which initiates a request. These are often browsers,
391      editors, spiders (web-traversing robots), or other end user tools.
392    </t>
393  </list>
394</t>
395<t>
396  <iref item="server"/>
397  server
398  <list>
399    <t>
400      An application program that accepts connections in order to
401      service requests by sending back responses. Any given program may
402      be capable of being both a client and a server; our use of these
403      terms refers only to the role being performed by the program for a
404      particular connection, rather than to the program's capabilities
405      in general. Likewise, any server may act as an origin server,
406      proxy, gateway, or tunnel, switching behavior based on the nature
407      of each request.
408    </t>
409  </list>
410</t>
411<t>
412  <iref item="origin server"/>
413  origin server
414  <list>
415    <t>
416      The server on which a given resource resides or is to be created.
417    </t>
418  </list>
419</t>
420<t>
421  <iref item="proxy"/>
422  proxy
423  <list>
424    <t>
425      An intermediary program which acts as both a server and a client
426      for the purpose of making requests on behalf of other clients.
427      Requests are serviced internally or by passing them on, with
428      possible translation, to other servers. A proxy MUST implement
429      both the client and server requirements of this specification. A
430      "transparent proxy" is a proxy that does not modify the request or
431      response beyond what is required for proxy authentication and
432      identification. A "non-transparent proxy" is a proxy that modifies
433      the request or response in order to provide some added service to
434      the user agent, such as group annotation services, media type
435      transformation, protocol reduction, or anonymity filtering. Except
436      where either transparent or non-transparent behavior is explicitly
437      stated, the HTTP proxy requirements apply to both types of
438      proxies.
439    </t>
440  </list>
441</t>
442<t>
443  <iref item="gateway"/>
444  gateway
445  <list>
446    <t>
447      A server which acts as an intermediary for some other server.
448      Unlike a proxy, a gateway receives requests as if it were the
449      origin server for the requested resource; the requesting client
450      may not be aware that it is communicating with a gateway.
451    </t>
452  </list>
453</t>
454<t>
455  <iref item="tunnel"/>
456  tunnel
457  <list>
458    <t>
459      An intermediary program which is acting as a blind relay between
460      two connections. Once active, a tunnel is not considered a party
461      to the HTTP communication, though the tunnel may have been
462      initiated by an HTTP request. The tunnel ceases to exist when both
463      ends of the relayed connections are closed.
464    </t>
465  </list>
466</t>
467<t>
468  <iref item="cache"/>
469  cache
470  <list>
471    <t>
472      A program's local store of response messages and the subsystem
473      that controls its message storage, retrieval, and deletion. A
474      cache stores cacheable responses in order to reduce the response
475      time and network bandwidth consumption on future, equivalent
476      requests. Any client or server may include a cache, though a cache
477      cannot be used by a server that is acting as a tunnel.
478    </t>
479  </list>
480</t>
481<t>
482  <iref item="cacheable"/>
483  cacheable
484  <list>
485    <t>
486      A response is cacheable if a cache is allowed to store a copy of
487      the response message for use in answering subsequent requests. The
488      rules for determining the cacheability of HTTP responses are
489      defined in Section 1 of <xref target="Part6"/>. Even if a resource is cacheable, there may
490      be additional constraints on whether a cache can use the cached
491      copy for a particular request.
492    </t>
493  </list>
494</t>
495<t>
496  <iref item="upstream"/>
497  <iref item="downstream"/>
498  upstream/downstream
499  <list>
500    <t>
501      Upstream and downstream describe the flow of a message: all
502      messages flow from upstream to downstream.
503    </t>
504  </list>
505</t>
506<t>
507  <iref item="inbound"/>
508  <iref item="outbound"/>
509  inbound/outbound
510  <list>
511    <t>
512      Inbound and outbound refer to the request and response paths for
513      messages: "inbound" means "traveling toward the origin server",
514      and "outbound" means "traveling toward the user agent"
515    </t>
516  </list>
517</t>
518</section>
519
520<section title="Overall Operation" anchor="intro.overall.operation">
521<t>
522   HTTP is a request/response protocol. A client sends a
523   request to the server in the form of a request method, URI, and
524   protocol version, followed by a MIME-like message containing request
525   modifiers, client information, and possible body content over a
526   connection with a server. The server responds with a status line,
527   including the message's protocol version and a success or error code,
528   followed by a MIME-like message containing server information, entity
529   metainformation, and possible entity-body content. The relationship
530   between HTTP and MIME is described in Appendix A of <xref target="Part3"/>.
531</t>
532<t>
533   Most HTTP communication is initiated by a user agent and consists of
534   a request to be applied to a resource on some origin server. In the
535   simplest case, this may be accomplished via a single connection (v)
536   between the user agent (UA) and the origin server (O).
537</t>
538<figure><artwork type="drawing"><![CDATA[
539       request chain ------------------------>
540    UA -------------------v------------------- O
541       <----------------------- response chain
542]]></artwork></figure>
543<t>
544   A more complicated situation occurs when one or more intermediaries
545   are present in the request/response chain. There are three common
546   forms of intermediary: proxy, gateway, and tunnel. A proxy is a
547   forwarding agent, receiving requests for a URI in its absolute form,
548   rewriting all or part of the message, and forwarding the reformatted
549   request toward the server identified by the URI. A gateway is a
550   receiving agent, acting as a layer above some other server(s) and, if
551   necessary, translating the requests to the underlying server's
552   protocol. A tunnel acts as a relay point between two connections
553   without changing the messages; tunnels are used when the
554   communication needs to pass through an intermediary (such as a
555   firewall) even when the intermediary cannot understand the contents
556   of the messages.
557</t>
558<figure><artwork type="drawing"><![CDATA[
559       request chain -------------------------------------->
560    UA -----v----- A -----v----- B -----v----- C -----v----- O
561       <------------------------------------- response chain
562]]></artwork></figure>
563<t>
564   The figure above shows three intermediaries (A, B, and C) between the
565   user agent and origin server. A request or response message that
566   travels the whole chain will pass through four separate connections.
567   This distinction is important because some HTTP communication options
568   may apply only to the connection with the nearest, non-tunnel
569   neighbor, only to the end-points of the chain, or to all connections
570   along the chain. Although the diagram is linear, each participant may
571   be engaged in multiple, simultaneous communications. For example, B
572   may be receiving requests from many clients other than A, and/or
573   forwarding requests to servers other than C, at the same time that it
574   is handling A's request.
575</t>
576<t>
577   Any party to the communication which is not acting as a tunnel may
578   employ an internal cache for handling requests. The effect of a cache
579   is that the request/response chain is shortened if one of the
580   participants along the chain has a cached response applicable to that
581   request. The following illustrates the resulting chain if B has a
582   cached copy of an earlier response from O (via C) for a request which
583   has not been cached by UA or A.
584</t>
585<figure><artwork type="drawing"><![CDATA[
586          request chain ---------->
587       UA -----v----- A -----v----- B - - - - - - C - - - - - - O
588          <--------- response chain
589]]></artwork></figure>
590<t>
591   Not all responses are usefully cacheable, and some requests may
592   contain modifiers which place special requirements on cache behavior.
593   HTTP requirements for cache behavior and cacheable responses are
594   defined in Section 1 of <xref target="Part6"/>.
595</t>
596<t>
597   In fact, there are a wide variety of architectures and configurations
598   of caches and proxies currently being experimented with or deployed
599   across the World Wide Web. These systems include national hierarchies
600   of proxy caches to save transoceanic bandwidth, systems that
601   broadcast or multicast cache entries, organizations that distribute
602   subsets of cached data via CD-ROM, and so on. HTTP systems are used
603   in corporate intranets over high-bandwidth links, and for access via
604   PDAs with low-power radio links and intermittent connectivity. The
605   goal of HTTP/1.1 is to support the wide diversity of configurations
606   already deployed while introducing protocol constructs that meet the
607   needs of those who build web applications that require high
608   reliability and, failing that, at least reliable indications of
609   failure.
610</t>
611<t>
612   HTTP communication usually takes place over TCP/IP connections. The
613   default port is TCP 80 (<eref target="http://www.iana.org/assignments/port-numbers"/>), but other ports can be used. This does
614   not preclude HTTP from being implemented on top of any other protocol
615   on the Internet, or on other networks. HTTP only presumes a reliable
616   transport; any protocol that provides such guarantees can be used;
617   the mapping of the HTTP/1.1 request and response structures onto the
618   transport data units of the protocol in question is outside the scope
619   of this specification.
620</t>
621<t>
622   In HTTP/1.0, most implementations used a new connection for each
623   request/response exchange. In HTTP/1.1, a connection may be used for
624   one or more request/response exchanges, although connections may be
625   closed for a variety of reasons (see <xref target="persistent.connections"/>).
626</t>
627</section>
628</section>
629
630<section title="Notational Conventions and Generic Grammar" anchor="notation">
631
632<section title="Augmented BNF" anchor="notation.abnf">
633<t>
634   All of the mechanisms specified in this document are described in
635   both prose and an augmented Backus-Naur Form (BNF) similar to that
636   used by <xref target="RFC822ABNF"/>. Implementors will need to be familiar with the
637   notation in order to understand this specification. The augmented BNF
638   includes the following constructs:
639</t>
640<t>
641   name = definition
642  <list>
643    <t>
644      The name of a rule is simply the name itself (without any
645      enclosing "&lt;" and "&gt;") and is separated from its definition by the
646      equal "=" character. White space is only significant in that
647      indentation of continuation lines is used to indicate a rule
648      definition that spans more than one line. Certain basic rules are
649      in uppercase, such as SP, LWS, HTAB, CRLF, DIGIT, ALPHA, etc. Angle
650      brackets are used within definitions whenever their presence will
651      facilitate discerning the use of rule names.
652    </t>
653  </list>
654</t>
655<t>
656   "literal"
657  <list>
658    <t>
659      Quotation marks surround literal text. Unless stated otherwise,
660      the text is case-insensitive.
661    </t>
662  </list>
663</t>
664<t>
665   rule1 | rule2
666  <list>
667    <t>
668      Elements separated by a bar ("|") are alternatives, e.g., "yes |
669      no" will accept yes or no.
670    </t>
671  </list>
672</t>
673<t>
674   (rule1 rule2)
675  <list>
676    <t>
677      Elements enclosed in parentheses are treated as a single element.
678      Thus, "(elem (foo | bar) elem)" allows the token sequences "elem
679      foo elem" and "elem bar elem".
680    </t>
681  </list>
682</t>
683<t>
684   *rule
685  <list>
686    <t>
687      The character "*" preceding an element indicates repetition. The
688      full form is "&lt;n&gt;*&lt;m&gt;element" indicating at least &lt;n&gt; and at most
689      &lt;m&gt; occurrences of element. Default values are 0 and infinity so
690      that "*(element)" allows any number, including zero; "1*element"
691      requires at least one; and "1*2element" allows one or two.
692    </t>
693  </list>
694</t>
695<t>
696   [rule]
697  <list>
698    <t>
699      Square brackets enclose optional elements; "[foo bar]" is
700      equivalent to "*1(foo bar)".
701    </t>
702  </list>
703</t>
704<t>
705   N rule
706  <list>
707    <t>
708      Specific repetition: "&lt;n&gt;(element)" is equivalent to
709      "&lt;n&gt;*&lt;n&gt;(element)"; that is, exactly &lt;n&gt; occurrences of (element).
710      Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three
711      alphabetic characters.
712    </t>
713  </list>
714</t>
715<t>
716   #rule
717  <list>
718    <t>
719      A construct "#" is defined, similar to "*", for defining lists of
720      elements. The full form is "&lt;n&gt;#&lt;m&gt;element" indicating at least
721      &lt;n&gt; and at most &lt;m&gt; elements, each separated by one or more commas
722      (",") and OPTIONAL linear white space (LWS). This makes the usual
723      form of lists very easy; a rule such as
724      <figure><artwork type="example"><![CDATA[
725   ( *LWS element *( *LWS "," *LWS element ))]]></artwork></figure>
726    </t>
727    <t>
728      can be shown as
729      <figure><artwork type="example"><![CDATA[
730   1#element]]></artwork></figure>
731    </t>
732    <t>
733      Wherever this construct is used, null elements are allowed, but do
734      not contribute to the count of elements present. That is,
735      "(element), , (element) " is permitted, but counts as only two
736      elements. Therefore, where at least one element is required, at
737      least one non-null element MUST be present. Default values are 0
738      and infinity so that "#element" allows any number, including zero;
739      "1#element" requires at least one; and "1#2element" allows one or
740      two.
741    </t>
742  </list>
743</t>
744<t>
745   ; comment
746  <list>
747    <t>
748      A semi-colon, set off some distance to the right of rule text,
749      starts a comment that continues to the end of line. This is a
750      simple way of including useful notes in parallel with the
751      specifications.
752    </t>
753  </list>
754</t>
755<t anchor="implied.LWS">
756  <iref item="implied *LWS" primary="true"/>
757   implied *LWS
758  <list>
759    <t>
760      The grammar described by this specification is word-based. Except
761      where noted otherwise, linear white space (LWS) can be included
762      between any two adjacent words (token or quoted-string), and
763      between adjacent words and separators, without changing the
764      interpretation of a field. At least one delimiter (LWS and/or
765      separators) MUST exist between any two tokens (for the definition
766      of "token" below), since they would otherwise be interpreted as a
767      single token.
768    </t>
769  </list>
770</t>
771</section>
772
773<section title="Basic Rules" anchor="basic.rules">
774<t anchor="core.rules">
775 
776 
777 
778 
779 
780 
781 
782 
783 
784 
785   The following rules are used throughout this specification to
786   describe basic parsing constructs. The US-ASCII coded character set
787   is defined by ANSI X3.4-1986 <xref target="USASCII"/>.
788</t>
789<figure><iref primary="true" item="Grammar" subitem="OCTET"/><iref primary="true" item="Grammar" subitem="CHAR"/><iref primary="true" item="Grammar" subitem="ALPHA"/><iref primary="true" item="Grammar" subitem="DIGIT"/><iref primary="true" item="Grammar" subitem="CTL"/><iref primary="true" item="Grammar" subitem="CR"/><iref primary="true" item="Grammar" subitem="LF"/><iref primary="true" item="Grammar" subitem="SP"/><iref primary="true" item="Grammar" subitem="HTAB"/><iref primary="true" item="Grammar" subitem="DQUOTE"/><artwork type="abnf2616"><![CDATA[
790  OCTET          = %x00-FF
791                   ; any 8-bit sequence of data
792  CHAR           = %x01-7F
793                   ; any US-ASCII character, excluding NUL
794  ALPHA          = %x41-5A | %x61-7A
795                   ; A-Z | a-z
796  DIGIT          = %x30-39
797                   ; any US-ASCII digit "0".."9"
798  CTL            = %x00-1F | %x7F
799                   ; (octets 0 - 31) and DEL (127)
800  CR             = %x0D
801                   ; US-ASCII CR, carriage return (13)
802  LF             = %x0A
803                   ; US-ASCII LF, linefeed (10)
804  SP             = %x20
805                   ; US-ASCII SP, space (32)
806  HTAB           = %x09
807                   ; US-ASCII HT, horizontal-tab (9)
808  DQUOTE         = %x22
809                   ; US-ASCII double-quote mark (34)
810]]></artwork></figure>
811<t anchor="rule.CRLF">
812 
813   HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
814   protocol elements except the entity-body (see <xref target="tolerant.applications"/> for
815   tolerant applications). The end-of-line marker within an entity-body
816   is defined by its associated media type, as described in Section 3.3 of <xref target="Part3"/>.
817</t>
818<figure><iref primary="true" item="Grammar" subitem="CRLF"/><artwork type="abnf2616"><![CDATA[
819  CRLF           = CR LF
820]]></artwork></figure>
821<t anchor="rule.LWS">
822 
823   HTTP/1.1 header field values can be folded onto multiple lines if the
824   continuation line begins with a space or horizontal tab. All linear
825   white space, including folding, has the same semantics as SP. A
826   recipient MAY replace any linear white space with a single SP before
827   interpreting the field value or forwarding the message downstream.
828</t>
829<figure><iref primary="true" item="Grammar" subitem="LWS"/><artwork type="abnf2616"><![CDATA[
830  LWS            = [CRLF] 1*( SP | HTAB )
831]]></artwork></figure>
832<t anchor="rule.TEXT">
833 
834   The TEXT rule is only used for descriptive field contents and values
835   that are not intended to be interpreted by the message parser. Words
836   of *TEXT MAY contain characters from character sets other than ISO-8859-1
837   <xref target="ISO-8859-1"/> only when encoded according to the rules of
838   <xref target="RFC2047"/>.
839</t>
840<figure><iref primary="true" item="Grammar" subitem="TEXT"/><artwork type="abnf2616"><![CDATA[
841  TEXT           = %x20-7E | %x80-FF | LWS
842                 ; any OCTET except CTLs, but including LWS
843]]></artwork></figure>
844<t>
845   A CRLF is allowed in the definition of TEXT only as part of a header
846   field continuation. It is expected that the folding LWS will be
847   replaced with a single SP before interpretation of the TEXT value.
848</t>
849<t anchor="rule.HEXDIG">
850 
851   Hexadecimal numeric characters are used in several protocol elements.
852</t>
853<figure><iref primary="true" item="Grammar" subitem="HEXDIG"/><artwork type="abnf2616"><![CDATA[
854  HEXDIG         = "A" | "B" | "C" | "D" | "E" | "F"
855                 | "a" | "b" | "c" | "d" | "e" | "f" | DIGIT
856]]></artwork></figure>
857<t anchor="rule.token.separators">
858 
859 
860 
861   Many HTTP/1.1 header field values consist of words separated by LWS
862   or special characters. These special characters MUST be in a quoted
863   string to be used within a parameter value (as defined in
864   <xref target="transfer.codings"/>).
865</t>
866<figure><iref primary="true" item="Grammar" subitem="token"/><iref primary="true" item="Grammar" subitem="tchar"/><iref primary="true" item="Grammar" subitem="separators"/><artwork type="abnf2616"><![CDATA[
867  separators     = "(" | ")" | "<" | ">" | "@"
868                 | "," | ";" | ":" | "\" | DQUOTE
869                 | "/" | "[" | "]" | "?" | "="
870                 | "{" | "}" | SP | HTAB
871                 
872  tchar          = "!" | "#" | "$" | "%" | "&" | "'" | "*"
873                 | "+" | "-" | "." | "^" | "_" | "`" | "|" | "~"
874                 | DIGIT | ALPHA
875                 ; any CHAR except CTLs or separators
876                 
877  token          = 1*tchar
878]]></artwork></figure>
879<t anchor="rule.comment">
880 
881 
882   Comments can be included in some HTTP header fields by surrounding
883   the comment text with parentheses. Comments are only allowed in
884   fields containing "comment" as part of their field value definition.
885   In all other fields, parentheses are considered part of the field
886   value.
887</t>
888<figure><iref primary="true" item="Grammar" subitem="comment"/><iref primary="true" item="Grammar" subitem="ctext"/><artwork type="abnf2616"><![CDATA[
889  comment        = "(" *( ctext | quoted-pair | comment ) ")"
890  ctext          = <any TEXT excluding "(" and ")">
891]]></artwork></figure>
892<t anchor="rule.quoted-string">
893 
894 
895   A string of text is parsed as a single word if it is quoted using
896   double-quote marks.
897</t>
898<figure><iref primary="true" item="Grammar" subitem="quoted-string"/><iref primary="true" item="Grammar" subitem="qdtext"/><artwork type="abnf2616"><![CDATA[
899  quoted-string  = ( DQUOTE *(qdtext | quoted-pair ) DQUOTE )
900  qdtext         = <any TEXT excluding DQUOTE and "\">
901]]></artwork></figure>
902<t anchor="rule.quoted-pair">
903 
904 
905   The backslash character ("\") MAY be used as a single-character
906   quoting mechanism only within quoted-string and comment constructs.
907</t>
908<figure><iref primary="true" item="Grammar" subitem="quoted-text"/><iref primary="true" item="Grammar" subitem="quoted-pair"/><artwork type="abnf2616"><![CDATA[
909  quoted-text    = %x01-09 |
910                   %x0B-0C |
911                   %x0E-FF ; Characters excluding NUL, CR and LF
912  quoted-pair    = "\" quoted-text
913]]></artwork></figure>
914</section>
915
916<section title="ABNF Rules defined in other Parts of the Specification" anchor="abnf.dependencies">
917 
918 
919 
920 
921 
922 
923 
924 
925<t>
926  The ABNF rules below are defined in other parts:
927</t>
928<figure><!-- Part2--><artwork type="abnf2616"><![CDATA[
929  request-header  = <request-header, defined in [Part2], Section 4>
930  response-header = <response-header, defined in [Part2], Section 6>
931]]></artwork></figure>
932<figure><!-- Part3--><artwork type="abnf2616"><![CDATA[
933  accept-params   = <accept-params, defined in [Part3], Section 6.1>
934  entity-body     = <entity-body, defined in [Part3], Section 4.2>
935  entity-header   = <entity-header, defined in [Part3], Section 4.1>
936]]></artwork></figure>
937<figure><!-- Part6--><artwork type="abnf2616"><![CDATA[
938  Cache-Control   = <Cache-Control, defined in [Part6], Section 16.4>
939  Pragma          = <Pragma, defined in [Part6], Section 16.4>
940  Warning         = <Warning, defined in [Part6], Section 16.6>
941]]></artwork></figure>
942</section>
943
944</section>
945
946<section title="Protocol Parameters" anchor="protocol.parameters">
947
948<section title="HTTP Version" anchor="http.version">
949 
950 
951<t>
952   HTTP uses a "&lt;major&gt;.&lt;minor&gt;" numbering scheme to indicate versions
953   of the protocol. The protocol versioning policy is intended to allow
954   the sender to indicate the format of a message and its capacity for
955   understanding further HTTP communication, rather than the features
956   obtained via that communication. No change is made to the version
957   number for the addition of message components which do not affect
958   communication behavior or which only add to extensible field values.
959   The &lt;minor&gt; number is incremented when the changes made to the
960   protocol add features which do not change the general message parsing
961   algorithm, but which may add to the message semantics and imply
962   additional capabilities of the sender. The &lt;major&gt; number is
963   incremented when the format of a message within the protocol is
964   changed. See <xref target="RFC2145"/> for a fuller explanation.
965</t>
966<t>
967   The version of an HTTP message is indicated by an HTTP-Version field
968   in the first line of the message. HTTP-Version is case-sensitive.
969</t>
970<figure><iref primary="true" item="Grammar" subitem="HTTP-Version"/><iref primary="true" item="Grammar" subitem="HTTP-Prot-Name"/><artwork type="abnf2616"><![CDATA[
971  HTTP-Version   = HTTP-Prot-Name "/" 1*DIGIT "." 1*DIGIT
972  HTTP-Prot-Name = %x48.54.54.50 ; "HTTP", case-sensitive
973]]></artwork></figure>
974<t>
975   Note that the major and minor numbers MUST be treated as separate
976   integers and that each MAY be incremented higher than a single digit.
977   Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
978   lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and
979   MUST NOT be sent.
980</t>
981<t>
982   An application that sends a request or response message that includes
983   HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
984   with this specification. Applications that are at least conditionally
985   compliant with this specification SHOULD use an HTTP-Version of
986   "HTTP/1.1" in their messages, and MUST do so for any message that is
987   not compatible with HTTP/1.0. For more details on when to send
988   specific HTTP-Version values, see <xref target="RFC2145"/>.
989</t>
990<t>
991   The HTTP version of an application is the highest HTTP version for
992   which the application is at least conditionally compliant.
993</t>
994<t>
995   Proxy and gateway applications need to be careful when forwarding
996   messages in protocol versions different from that of the application.
997   Since the protocol version indicates the protocol capability of the
998   sender, a proxy/gateway MUST NOT send a message with a version
999   indicator which is greater than its actual version. If a higher
1000   version request is received, the proxy/gateway MUST either downgrade
1001   the request version, or respond with an error, or switch to tunnel
1002   behavior.
1003</t>
1004<t>
1005   Due to interoperability problems with HTTP/1.0 proxies discovered
1006   since the publication of <xref target="RFC2068"/>, caching proxies MUST, gateways
1007   MAY, and tunnels MUST NOT upgrade the request to the highest version
1008   they support. The proxy/gateway's response to that request MUST be in
1009   the same major version as the request.
1010</t>
1011<t>
1012  <list>
1013    <t>
1014      Note: Converting between versions of HTTP may involve modification
1015      of header fields required or forbidden by the versions involved.
1016    </t>
1017  </list>
1018</t>
1019</section>
1020
1021<section title="Uniform Resource Identifiers" anchor="uri">
1022<t>
1023   URIs have been known by many names: WWW addresses, Universal Document
1024   Identifiers, Universal Resource Identifiers <xref target="RFC1630"/>, and finally the
1025   combination of Uniform Resource Locators (URL) <xref target="RFC1738"/> and Names (URN)
1026   <xref target="RFC1737"/>. As far as HTTP is concerned, Uniform Resource Identifiers are
1027   simply formatted strings which identify--via name, location, or any
1028   other characteristic--a resource.
1029</t>
1030
1031<section title="General Syntax" anchor="general.syntax">
1032 
1033 
1034 
1035 
1036 
1037 
1038 
1039 
1040<t>
1041   URIs in HTTP can be represented in absolute form or relative to some
1042   known base URI <xref target="RFC1808"/>, depending upon the context of their use. The two
1043   forms are differentiated by the fact that absolute URIs always begin
1044   with a scheme name followed by a colon. For definitive information on
1045   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
1046   Generic Syntax and Semantics," <xref target="RFC2396"/> (which replaces <xref target="RFC1738"/>
1047   and <xref target="RFC1808"/>). This specification adopts the
1048   definitions of "URI-reference", "absoluteURI", "fragment", "relativeURI", "port",
1049   "host", "abs_path", "query", and "authority" from that specification:
1050</t>
1051<figure><iref primary="true" item="Grammar" subitem="absoluteURI"/><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="relativeURI"/><iref primary="true" item="Grammar" subitem="uri-host"/><artwork type="abnf2616"><![CDATA[
1052  absoluteURI   = <absoluteURI, defined in [RFC2396], Section 3>
1053  authority     = <authority, defined in [RFC2396], Section 3.2>
1054  fragment      = <fragment, defined in [RFC2396], Section 4.1>
1055  path-absolute = <abs_path, defined in [RFC2396], Section 3>
1056  port          = <port, defined in [RFC2396], Section 3.2.2>
1057  query         = <query, defined in [RFC2396], Section 3.4>
1058  relativeURI   = <relativeURI, defined in [RFC2396], Section 5>
1059  uri-host      = <host, defined in [RFC2396], Section 3.2.2>
1060]]></artwork></figure>
1061<t>
1062   HTTP does not place any a priori limit on the length of
1063   a URI. Servers MUST be able to handle the URI of any resource they
1064   serve, and SHOULD be able to handle URIs of unbounded length if they
1065   provide GET-based forms that could generate such URIs. A server
1066   SHOULD return 414 (Request-URI Too Long) status if a URI is longer
1067   than the server can handle (see Section 9.4.15 of <xref target="Part2"/>).
1068</t>
1069<t>
1070  <list>
1071    <t>
1072      Note: Servers ought to be cautious about depending on URI lengths
1073      above 255 bytes, because some older client or proxy
1074      implementations might not properly support these lengths.
1075    </t>
1076  </list>
1077</t>
1078</section>
1079
1080<section title="http URL" anchor="http.url">
1081 
1082  <iref item="http URI scheme" primary="true"/>
1083  <iref item="URI scheme" subitem="http" primary="true"/>
1084<t>
1085   The "http" scheme is used to locate network resources via the HTTP
1086   protocol. This section defines the scheme-specific syntax and
1087   semantics for http URLs.
1088</t>
1089<figure><iref primary="true" item="Grammar" subitem="http-URL"/><artwork type="abnf2616"><![CDATA[
1090  http-URL = "http:" "//" uri-host [ ":" port ]
1091             [ path-absolute [ "?" query ]]
1092]]></artwork></figure>
1093<t>
1094   If the port is empty or not given, port 80 is assumed. The semantics
1095   are that the identified resource is located at the server listening
1096   for TCP connections on that port of that host, and the Request-URI
1097   for the resource is path-absolute (<xref target="request-uri"/>). The use of IP addresses
1098   in URLs SHOULD be avoided whenever possible (see <xref target="RFC1900"/>). If
1099   the path-absolute is not present in the URL, it MUST be given as "/" when
1100   used as a Request-URI for a resource (<xref target="request-uri"/>). If a proxy
1101   receives a host name which is not a fully qualified domain name, it
1102   MAY add its domain to the host name it received. If a proxy receives
1103   a fully qualified domain name, the proxy MUST NOT change the host
1104   name.
1105</t>
1106<t><list><t>
1107  <iref item="https URI scheme"/>
1108  <iref item="URI scheme" subitem="https"/>
1109  Note: the "https" scheme is defined in <xref target="RFC2818"/>.
1110</t></list></t>
1111</section>
1112
1113<section title="URI Comparison" anchor="uri.comparison">
1114<t>
1115   When comparing two URIs to decide if they match or not, a client
1116   SHOULD use a case-sensitive octet-by-octet comparison of the entire
1117   URIs, with these exceptions:
1118  <list style="symbols">
1119    <t>A port that is empty or not given is equivalent to the default
1120        port for that URI-reference;</t>
1121    <t>Comparisons of host names MUST be case-insensitive;</t>
1122    <t>Comparisons of scheme names MUST be case-insensitive;</t>
1123    <t>An empty path-absolute is equivalent to an path-absolute of "/".</t>
1124  </list>
1125</t>
1126<t>
1127   Characters other than those in the "reserved" set (see
1128   <xref target="RFC2396"/>, Section 2.2) are equivalent to their
1129   ""%" <xref target="rule.HEXDIG" format="none">HEXDIG</xref> <xref target="rule.HEXDIG" format="none">HEXDIG</xref>" encoding.
1130</t>
1131<t>
1132   For example, the following three URIs are equivalent:
1133</t>
1134<figure><artwork type="example"><![CDATA[
1135   http://example.com:80/~smith/home.html
1136   http://EXAMPLE.com/%7Esmith/home.html
1137   http://EXAMPLE.com:/%7esmith/home.html
1138]]></artwork></figure>
1139</section>
1140</section>
1141
1142<section title="Date/Time Formats" anchor="date.time.formats">
1143<section title="Full Date" anchor="full.date">
1144 
1145 
1146 
1147 
1148 
1149 
1150 
1151 
1152 
1153 
1154 
1155 
1156 
1157<t>
1158   HTTP applications have historically allowed three different formats
1159   for the representation of date/time stamps:
1160</t>
1161<figure><artwork type="example"><![CDATA[
1162   Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
1163   Sunday, 06-Nov-94 08:49:37 GMT ; obsolete RFC 850 format
1164   Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
1165]]></artwork></figure>
1166<t>
1167   The first format is preferred as an Internet standard and represents
1168   a fixed-length subset of that defined by <xref target="RFC1123"/> (an update to
1169   <xref target="RFC822"/>). The other formats are described here only for
1170   compatibility with obsolete implementations.
1171   HTTP/1.1 clients and servers that parse the date value MUST accept
1172   all three formats (for compatibility with HTTP/1.0), though they MUST
1173   only generate the RFC 1123 format for representing HTTP-date values
1174   in header fields. See <xref target="tolerant.applications"/> for further information.
1175</t>
1176<t><list><t>
1177      Note: Recipients of date values are encouraged to be robust in
1178      accepting date values that may have been sent by non-HTTP
1179      applications, as is sometimes the case when retrieving or posting
1180      messages via proxies/gateways to SMTP or NNTP.
1181</t></list></t>
1182<t>
1183   All HTTP date/time stamps MUST be represented in Greenwich Mean Time
1184   (GMT), without exception. For the purposes of HTTP, GMT is exactly
1185   equal to UTC (Coordinated Universal Time). This is indicated in the
1186   first two formats by the inclusion of "GMT" as the three-letter
1187   abbreviation for time zone, and MUST be assumed when reading the
1188   asctime format. HTTP-date is case sensitive and MUST NOT include
1189   additional LWS beyond that specifically included as SP in the
1190   grammar.
1191</t>
1192<figure><iref primary="true" item="Grammar" subitem="HTTP-date"/><iref primary="true" item="Grammar" subitem="rfc1123-date"/><iref primary="true" item="Grammar" subitem="obsolete-date"/><iref primary="true" item="Grammar" subitem="rfc850-date"/><iref primary="true" item="Grammar" subitem="asctime-date"/><iref primary="true" item="Grammar" subitem="date1"/><iref primary="true" item="Grammar" subitem="date2"/><iref primary="true" item="Grammar" subitem="date3"/><iref primary="true" item="Grammar" subitem="time"/><iref primary="true" item="Grammar" subitem="wkday"/><iref primary="true" item="Grammar" subitem="weekday"/><iref primary="true" item="Grammar" subitem="month"/><artwork type="abnf2616"><![CDATA[
1193  HTTP-date    = rfc1123-date | obsolete-date
1194  obsolete-date = rfc850-date | asctime-date
1195  rfc1123-date = wkday "," SP date1 SP time SP GMT
1196  rfc850-date  = weekday "," SP date2 SP time SP GMT
1197  asctime-date = wkday SP date3 SP time SP 4DIGIT
1198  date1        = 2DIGIT SP month SP 4DIGIT
1199                 ; day month year (e.g., 02 Jun 1982)
1200  date2        = 2DIGIT "-" month "-" 2DIGIT
1201                 ; day-month-year (e.g., 02-Jun-82)
1202  date3        = month SP ( 2DIGIT | ( SP 1DIGIT ))
1203                 ; month day (e.g., Jun  2)
1204  time         = 2DIGIT ":" 2DIGIT ":" 2DIGIT
1205                 ; 00:00:00 - 23:59:59
1206  wkday        = s-Mon | s-Tue | s-Wed
1207               | s-Thu | s-Fri | s-Sat | s-Sun
1208  weekday      = l-Mon | l-Tue | l-Wed
1209               | l-Thu | l-Fri | l-Sat | l-Sun
1210  month        = s-Jan | s-Feb | s-Mar | s-Apr
1211               | s-May | s-Jun | s-Jul | s-Aug
1212               | s-Sep | s-Oct | s-Nov | s-Dec
1213               
1214  GMT   = %x47.4D.54 ; "GMT", case-sensitive
1215
1216  s-Mon = %x4D.6F.6E ; "Mon", case-sensitive
1217  s-Tue = %x54.75.65 ; "Tue", case-sensitive
1218  s-Wed = %x57.65.64 ; "Wed", case-sensitive
1219  s-Thu = %x54.68.75 ; "Thu", case-sensitive
1220  s-Fri = %x46.72.69 ; "Fri", case-sensitive
1221  s-Sat = %x53.61.74 ; "Sat", case-sensitive
1222  s-Sun = %x53.75.6E ; "Sun", case-sensitive
1223
1224  l-Mon = %x4D.6F.6E.64.61.79          ; "Monday", case-sensitive
1225  l-Tue = %x54.75.65.73.64.61.79       ; "Tuesday", case-sensitive
1226  l-Wed = %x57.65.64.6E.65.73.64.61.79 ; "Wednesday", case-sensitive
1227  l-Thu = %x54.68.75.72.73.64.61.79    ; "Thursday", case-sensitive
1228  l-Fri = %x46.72.69.64.61.79          ; "Friday", case-sensitive
1229  l-Sat = %x53.61.74.75.72.64.61.79    ; "Saturday", case-sensitive
1230  l-Sun = %x53.75.6E.64.61.79          ; "Sunday", case-sensitive
1231
1232  s-Jan = %x4A.61.6E ; "Jan", case-sensitive
1233  s-Feb = %x46.65.62 ; "Feb", case-sensitive
1234  s-Mar = %x4D.61.72 ; "Mar", case-sensitive
1235  s-Apr = %x41.70.72 ; "Apr", case-sensitive
1236  s-May = %x4D.61.79 ; "May", case-sensitive
1237  s-Jun = %x4A.75.6E ; "Jun", case-sensitive
1238  s-Jul = %x4A.75.6C ; "Jul", case-sensitive
1239  s-Aug = %x41.75.67 ; "Aug", case-sensitive
1240  s-Sep = %x53.65.70 ; "Sep", case-sensitive
1241  s-Oct = %x4F.63.74 ; "Oct", case-sensitive
1242  s-Nov = %x4E.6F.76 ; "Nov", case-sensitive
1243  s-Dec = %x44.65.63 ; "Dec", case-sensitive
1244]]></artwork></figure>
1245<t>
1246      Note: HTTP requirements for the date/time stamp format apply only
1247      to their usage within the protocol stream. Clients and servers are
1248      not required to use these formats for user presentation, request
1249      logging, etc.
1250</t>
1251</section>
1252</section>
1253
1254<section title="Transfer Codings" anchor="transfer.codings">
1255 
1256 
1257 
1258<t>
1259   Transfer-coding values are used to indicate an encoding
1260   transformation that has been, can be, or may need to be applied to an
1261   entity-body in order to ensure "safe transport" through the network.
1262   This differs from a content coding in that the transfer-coding is a
1263   property of the message, not of the original entity.
1264</t>
1265<figure><iref primary="true" item="Grammar" subitem="transfer-coding"/><iref primary="true" item="Grammar" subitem="transfer-extension"/><artwork type="abnf2616"><![CDATA[
1266  transfer-coding         = "chunked" | transfer-extension
1267  transfer-extension      = token *( ";" parameter )
1268]]></artwork></figure>
1269<t anchor="rule.parameter">
1270 
1271 
1272 
1273   Parameters are in  the form of attribute/value pairs.
1274</t>
1275<figure><iref primary="true" item="Grammar" subitem="parameter"/><iref primary="true" item="Grammar" subitem="attribute"/><iref primary="true" item="Grammar" subitem="value"/><artwork type="abnf2616"><![CDATA[
1276  parameter               = attribute "=" value
1277  attribute               = token
1278  value                   = token | quoted-string
1279]]></artwork></figure>
1280<t>
1281   All transfer-coding values are case-insensitive. HTTP/1.1 uses
1282   transfer-coding values in the TE header field (<xref target="header.te"/>) and in
1283   the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1284</t>
1285<t>
1286   Whenever a transfer-coding is applied to a message-body, the set of
1287   transfer-codings MUST include "chunked", unless the message indicates it
1288   is terminated by closing the connection. When the "chunked" transfer-coding
1289   is used, it MUST be the last transfer-coding applied to the
1290   message-body. The "chunked" transfer-coding MUST NOT be applied more
1291   than once to a message-body. These rules allow the recipient to
1292   determine the transfer-length of the message (<xref target="message.length"/>).
1293</t>
1294<t>
1295   Transfer-codings are analogous to the Content-Transfer-Encoding
1296   values of MIME <xref target="RFC2045"/>, which were designed to enable safe transport of
1297   binary data over a 7-bit transport service. However, safe transport
1298   has a different focus for an 8bit-clean transfer protocol. In HTTP,
1299   the only unsafe characteristic of message-bodies is the difficulty in
1300   determining the exact body length (<xref target="message.length"/>), or the desire to
1301   encrypt data over a shared transport.
1302</t>
1303<t>
1304   The Internet Assigned Numbers Authority (IANA) acts as a registry for
1305   transfer-coding value tokens. Initially, the registry contains the
1306   following tokens: "chunked" (<xref target="chunked.transfer.encoding"/>),
1307   "gzip", "compress", and "deflate" (Section 3.2 of <xref target="Part3"/>).
1308</t>
1309<t>
1310   New transfer-coding value tokens SHOULD be registered in the same way
1311   as new content-coding value tokens (Section 3.2 of <xref target="Part3"/>).
1312</t>
1313<t>
1314   A server which receives an entity-body with a transfer-coding it does
1315   not understand SHOULD return 501 (Not Implemented), and close the
1316   connection. A server MUST NOT send transfer-codings to an HTTP/1.0
1317   client.
1318</t>
1319
1320<section title="Chunked Transfer Coding" anchor="chunked.transfer.encoding">
1321 
1322 
1323 
1324 
1325 
1326 
1327 
1328 
1329 
1330<t>
1331   The chunked encoding modifies the body of a message in order to
1332   transfer it as a series of chunks, each with its own size indicator,
1333   followed by an OPTIONAL trailer containing entity-header fields. This
1334   allows dynamically produced content to be transferred along with the
1335   information necessary for the recipient to verify that it has
1336   received the full message.
1337</t>
1338<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-extension"/><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"/><artwork type="abnf2616"><![CDATA[
1339  Chunked-Body   = *chunk
1340                   last-chunk
1341                   trailer-part
1342                   CRLF
1343 
1344  chunk          = chunk-size [ chunk-extension ] CRLF
1345                   chunk-data CRLF
1346  chunk-size     = 1*HEXDIG
1347  last-chunk     = 1*("0") [ chunk-extension ] CRLF
1348 
1349  chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
1350  chunk-ext-name = token
1351  chunk-ext-val  = token | quoted-string
1352  chunk-data     = 1*OCTET ; a sequence of chunk-size octets
1353  trailer-part   = *(entity-header CRLF)
1354]]></artwork></figure>
1355<t>
1356   The chunk-size field is a string of hex digits indicating the size of
1357   the chunk-data in octets. The chunked encoding is ended by any chunk whose size is
1358   zero, followed by the trailer, which is terminated by an empty line.
1359</t>
1360<t>
1361   The trailer allows the sender to include additional HTTP header
1362   fields at the end of the message. The Trailer header field can be
1363   used to indicate which header fields are included in a trailer (see
1364   <xref target="header.trailer"/>).
1365</t>
1366<t>
1367   A server using chunked transfer-coding in a response MUST NOT use the
1368   trailer for any header fields unless at least one of the following is
1369   true:
1370  <list style="numbers">
1371    <t>the request included a TE header field that indicates "trailers" is
1372     acceptable in the transfer-coding of the  response, as described in
1373     <xref target="header.te"/>; or,</t>
1374
1375    <t>the server is the origin server for the response, the trailer
1376     fields consist entirely of optional metadata, and the recipient
1377     could use the message (in a manner acceptable to the origin server)
1378     without receiving this metadata.  In other words, the origin server
1379     is willing to accept the possibility that the trailer fields might
1380     be silently discarded along the path to the client.</t>
1381  </list>
1382</t>
1383<t>
1384   This requirement prevents an interoperability failure when the
1385   message is being received by an HTTP/1.1 (or later) proxy and
1386   forwarded to an HTTP/1.0 recipient. It avoids a situation where
1387   compliance with the protocol would have necessitated a possibly
1388   infinite buffer on the proxy.
1389</t>
1390<t>
1391   A process for decoding the "chunked" transfer-coding
1392   can be represented in pseudo-code as:
1393</t>
1394<figure><artwork type="code"><![CDATA[
1395    length := 0
1396    read chunk-size, chunk-extension (if any) and CRLF
1397    while (chunk-size > 0) {
1398       read chunk-data and CRLF
1399       append chunk-data to entity-body
1400       length := length + chunk-size
1401       read chunk-size and CRLF
1402    }
1403    read entity-header
1404    while (entity-header not empty) {
1405       append entity-header to existing header fields
1406       read entity-header
1407    }
1408    Content-Length := length
1409    Remove "chunked" from Transfer-Encoding
1410]]></artwork></figure>
1411<t>
1412   All HTTP/1.1 applications MUST be able to receive and decode the
1413   "chunked" transfer-coding, and MUST ignore chunk-extension extensions
1414   they do not understand.
1415</t>
1416</section>
1417</section>
1418
1419<section title="Product Tokens" anchor="product.tokens">
1420 
1421 
1422<t>
1423   Product tokens are used to allow communicating applications to
1424   identify themselves by software name and version. Most fields using
1425   product tokens also allow sub-products which form a significant part
1426   of the application to be listed, separated by white space. By
1427   convention, the products are listed in order of their significance
1428   for identifying the application.
1429</t>
1430<figure><iref primary="true" item="Grammar" subitem="product"/><iref primary="true" item="Grammar" subitem="product-version"/><artwork type="abnf2616"><![CDATA[
1431  product         = token ["/" product-version]
1432  product-version = token
1433]]></artwork></figure>
1434<t>
1435   Examples:
1436</t>
1437<figure><artwork type="example"><![CDATA[
1438    User-Agent: CERN-LineMode/2.15 libwww/2.17b3
1439    Server: Apache/0.8.4
1440]]></artwork></figure>
1441<t>
1442   Product tokens SHOULD be short and to the point. They MUST NOT be
1443   used for advertising or other non-essential information. Although any
1444   token character MAY appear in a product-version, this token SHOULD
1445   only be used for a version identifier (i.e., successive versions of
1446   the same product SHOULD only differ in the product-version portion of
1447   the product value).
1448</t>
1449</section>
1450
1451</section>
1452
1453<section title="HTTP Message" anchor="http.message">
1454
1455<section title="Message Types" anchor="message.types">
1456 
1457 
1458 
1459<t>
1460   HTTP messages consist of requests from client to server and responses
1461   from server to client.
1462</t>
1463<figure><iref primary="true" item="Grammar" subitem="HTTP-message"/><artwork type="abnf2616"><![CDATA[
1464  HTTP-message   = Request | Response     ; HTTP/1.1 messages
1465]]></artwork></figure>
1466<t>
1467   Request (<xref target="request"/>) and Response (<xref target="response"/>) messages use the generic
1468   message format of <xref target="RFC2822"/> for transferring entities (the payload
1469   of the message). Both types of message consist of a start-line, zero
1470   or more header fields (also known as "headers"), an empty line (i.e.,
1471   a line with nothing preceding the CRLF) indicating the end of the
1472   header fields, and possibly a message-body.
1473</t>
1474<figure><iref primary="true" item="Grammar" subitem="generic-message"/><iref primary="true" item="Grammar" subitem="start-line"/><artwork type="abnf2616"><![CDATA[
1475  generic-message = start-line
1476                    *(message-header CRLF)
1477                    CRLF
1478                    [ message-body ]
1479  start-line      = Request-Line | Status-Line
1480]]></artwork></figure>
1481<t>
1482   In the interest of robustness, servers SHOULD ignore any empty
1483   line(s) received where a Request-Line is expected. In other words, if
1484   the server is reading the protocol stream at the beginning of a
1485   message and receives a CRLF first, it should ignore the CRLF.
1486</t>
1487<t>
1488   Certain buggy HTTP/1.0 client implementations generate extra CRLF's
1489   after a POST request. To restate what is explicitly forbidden by the
1490   BNF, an HTTP/1.1 client MUST NOT preface or follow a request with an
1491   extra CRLF.
1492</t>
1493</section>
1494
1495<section title="Message Headers" anchor="message.headers">
1496 
1497 
1498 
1499 
1500<t>
1501   HTTP header fields, which include general-header (<xref target="general.header.fields"/>),
1502   request-header (Section 4 of <xref target="Part2"/>), response-header (Section 6 of <xref target="Part2"/>), and
1503   entity-header (Section 4.1 of <xref target="Part3"/>) fields, follow the same generic format as
1504   that given in Section 2.1 of <xref target="RFC2822"/>. Each header field consists
1505   of a name followed by a colon (":") and the field value. Field names
1506   are case-insensitive. The field value MAY be preceded by any amount
1507   of LWS, though a single SP is preferred. Header fields can be
1508   extended over multiple lines by preceding each extra line with at
1509   least one SP or HTAB. Applications ought to follow "common form", where
1510   one is known or indicated, when generating HTTP constructs, since
1511   there might exist some implementations that fail to accept anything
1512   beyond the common forms.
1513</t>
1514<figure><iref primary="true" item="Grammar" subitem="message-header"/><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[
1515  message-header = field-name ":" [ field-value ]
1516  field-name     = token
1517  field-value    = *( field-content | LWS )
1518  field-content  = <field content>
1519                   ; the OCTETs making up the field-value
1520                   ; and consisting of either *TEXT or combinations
1521                   ; of token, separators, and quoted-string
1522]]></artwork></figure>
1523<t>
1524   The field-content does not include any leading or trailing LWS:
1525   linear white space occurring before the first non-whitespace
1526   character of the field-value or after the last non-whitespace
1527   character of the field-value. Such leading or trailing LWS MAY be
1528   removed without changing the semantics of the field value. Any LWS
1529   that occurs between field-content MAY be replaced with a single SP
1530   before interpreting the field value or forwarding the message
1531   downstream.
1532</t>
1533<t>
1534   The order in which header fields with differing field names are
1535   received is not significant. However, it is "good practice" to send
1536   general-header fields first, followed by request-header or response-header
1537   fields, and ending with the entity-header fields.
1538</t>
1539<t>
1540   Multiple message-header fields with the same field-name MAY be
1541   present in a message if and only if the entire field-value for that
1542   header field is defined as a comma-separated list [i.e., #(values)].
1543   It MUST be possible to combine the multiple header fields into one
1544   "field-name: field-value" pair, without changing the semantics of the
1545   message, by appending each subsequent field-value to the first, each
1546   separated by a comma. The order in which header fields with the same
1547   field-name are received is therefore significant to the
1548   interpretation of the combined field value, and thus a proxy MUST NOT
1549   change the order of these field values when a message is forwarded.
1550</t>
1551<t>
1552  <list><t>
1553   Note: the "Set-Cookie" header as implemented in
1554   practice (as opposed to how it is specified in <xref target="RFC2109"/>)
1555   can occur multiple times, but does not use the list syntax, and thus cannot
1556   be combined into a single line. (See Appendix A.2.3 of <xref target="Kri2001"/>
1557   for details.) Also note that the Set-Cookie2 header specified in
1558   <xref target="RFC2965"/> does not share this problem.
1559  </t></list>
1560</t>
1561 
1562</section>
1563
1564<section title="Message Body" anchor="message.body">
1565 
1566<t>
1567   The message-body (if any) of an HTTP message is used to carry the
1568   entity-body associated with the request or response. The message-body
1569   differs from the entity-body only when a transfer-coding has been
1570   applied, as indicated by the Transfer-Encoding header field (<xref target="header.transfer-encoding"/>).
1571</t>
1572<figure><iref primary="true" item="Grammar" subitem="message-body"/><artwork type="abnf2616"><![CDATA[
1573  message-body = entity-body
1574               | <entity-body encoded as per Transfer-Encoding>
1575]]></artwork></figure>
1576<t>
1577   Transfer-Encoding MUST be used to indicate any transfer-codings
1578   applied by an application to ensure safe and proper transfer of the
1579   message. Transfer-Encoding is a property of the message, not of the
1580   entity, and thus MAY be added or removed by any application along the
1581   request/response chain. (However, <xref target="transfer.codings"/> places restrictions on
1582   when certain transfer-codings may be used.)
1583</t>
1584<t>
1585   The rules for when a message-body is allowed in a message differ for
1586   requests and responses.
1587</t>
1588<t>
1589   The presence of a message-body in a request is signaled by the
1590   inclusion of a Content-Length or Transfer-Encoding header field in
1591   the request's message-headers. A message-body MUST NOT be included in
1592   a request if the specification of the request method (Section 3 of <xref target="Part2"/>)
1593   explicitly disallows an entity-body in requests.
1594   When a request message contains both a message-body of non-zero
1595   length and a method that does not define any semantics for that
1596   request message-body, then an origin server SHOULD either ignore
1597   the message-body or respond with an appropriate error message
1598   (e.g., 413).  A proxy or gateway, when presented the same request,
1599   SHOULD either forward the request inbound with the message-body or
1600   ignore the message-body when determining a response.
1601</t>
1602<t>
1603   For response messages, whether or not a message-body is included with
1604   a message is dependent on both the request method and the response
1605   status code (<xref target="status.code.and.reason.phrase"/>). All responses to the HEAD request method
1606   MUST NOT include a message-body, even though the presence of entity-header
1607   fields might lead one to believe they do. All 1xx
1608   (informational), 204 (No Content), and 304 (Not Modified) responses
1609   MUST NOT include a message-body. All other responses do include a
1610   message-body, although it MAY be of zero length.
1611</t>
1612</section>
1613
1614<section title="Message Length" anchor="message.length">
1615<t>
1616   The transfer-length of a message is the length of the message-body as
1617   it appears in the message; that is, after any transfer-codings have
1618   been applied. When a message-body is included with a message, the
1619   transfer-length of that body is determined by one of the following
1620   (in order of precedence):
1621</t>
1622<t>
1623  <list style="numbers">
1624    <t>
1625     Any response message which "MUST NOT" include a message-body (such
1626     as the 1xx, 204, and 304 responses and any response to a HEAD
1627     request) is always terminated by the first empty line after the
1628     header fields, regardless of the entity-header fields present in
1629     the message.
1630    </t>
1631    <t>
1632     If a Transfer-Encoding header field (<xref target="header.transfer-encoding"/>)
1633     is present and the "chunked" transfer-coding (<xref target="transfer.codings"/>)
1634     is used, the transfer-length is defined by the use of this transfer-coding.
1635     If a Transfer-Encoding header field is present and the "chunked" transfer-coding
1636     is not present, the transfer-length is defined by the sender closing the connection.
1637    </t>
1638    <t>
1639     If a Content-Length header field (<xref target="header.content-length"/>) is present, its
1640     decimal value in OCTETs represents both the entity-length and the
1641     transfer-length. The Content-Length header field MUST NOT be sent
1642     if these two lengths are different (i.e., if a Transfer-Encoding
1643     header field is present). If a message is received with both a
1644     Transfer-Encoding header field and a Content-Length header field,
1645     the latter MUST be ignored.
1646    </t>
1647    <t>
1648     If the message uses the media type "multipart/byteranges", and the
1649     transfer-length is not otherwise specified, then this self-delimiting
1650     media type defines the transfer-length. This media type
1651     MUST NOT be used unless the sender knows that the recipient can parse
1652     it; the presence in a request of a Range header with multiple byte-range
1653     specifiers from a 1.1 client implies that the client can parse
1654     multipart/byteranges responses.
1655    <list style="empty"><t>
1656       A range header might be forwarded by a 1.0 proxy that does not
1657       understand multipart/byteranges; in this case the server MUST
1658       delimit the message using methods defined in items 1, 3 or 5 of
1659       this section.
1660    </t></list>
1661    </t>
1662    <t>
1663     By the server closing the connection. (Closing the connection
1664     cannot be used to indicate the end of a request body, since that
1665     would leave no possibility for the server to send back a response.)
1666    </t>
1667  </list>
1668</t>
1669<t>
1670   For compatibility with HTTP/1.0 applications, HTTP/1.1 requests
1671   containing a message-body MUST include a valid Content-Length header
1672   field unless the server is known to be HTTP/1.1 compliant. If a
1673   request contains a message-body and a Content-Length is not given,
1674   the server SHOULD respond with 400 (Bad Request) if it cannot
1675   determine the length of the message, or with 411 (Length Required) if
1676   it wishes to insist on receiving a valid Content-Length.
1677</t>
1678<t>
1679   All HTTP/1.1 applications that receive entities MUST accept the
1680   "chunked" transfer-coding (<xref target="transfer.codings"/>), thus allowing this mechanism
1681   to be used for messages when the message length cannot be determined
1682   in advance.
1683</t>
1684<t>
1685   Messages MUST NOT include both a Content-Length header field and a
1686   transfer-coding. If the message does include a
1687   transfer-coding, the Content-Length MUST be ignored.
1688</t>
1689<t>
1690   When a Content-Length is given in a message where a message-body is
1691   allowed, its field value MUST exactly match the number of OCTETs in
1692   the message-body. HTTP/1.1 user agents MUST notify the user when an
1693   invalid length is received and detected.
1694</t>
1695</section>
1696
1697<section title="General Header Fields" anchor="general.header.fields">
1698 
1699<t>
1700   There are a few header fields which have general applicability for
1701   both request and response messages, but which do not apply to the
1702   entity being transferred. These header fields apply only to the
1703   message being transmitted.
1704</t>
1705<figure><iref primary="true" item="Grammar" subitem="general-header"/><artwork type="abnf2616"><![CDATA[
1706  general-header = Cache-Control            ; [Part6], Section 16.2
1707                 | Connection               ; Section 8.1
1708                 | Date                     ; Section 8.3
1709                 | Pragma                   ; [Part6], Section 16.4
1710                 | Trailer                  ; Section 8.6
1711                 | Transfer-Encoding        ; Section 8.7
1712                 | Upgrade                  ; Section 8.8
1713                 | Via                      ; Section 8.9
1714                 | Warning                  ; [Part6], Section 16.6
1715]]></artwork></figure>
1716<t>
1717   General-header field names can be extended reliably only in
1718   combination with a change in the protocol version. However, new or
1719   experimental header fields may be given the semantics of general
1720   header fields if all parties in the communication recognize them to
1721   be general-header fields. Unrecognized header fields are treated as
1722   entity-header fields.
1723</t>
1724</section>
1725</section>
1726
1727<section title="Request" anchor="request">
1728 
1729<t>
1730   A request message from a client to a server includes, within the
1731   first line of that message, the method to be applied to the resource,
1732   the identifier of the resource, and the protocol version in use.
1733</t>
1734<!--                 Host                      ; should be moved here eventually -->
1735<figure><iref primary="true" item="Grammar" subitem="Request"/><artwork type="abnf2616"><![CDATA[
1736  Request       = Request-Line              ; Section 5.1
1737                  *(( general-header        ; Section 4.5
1738                   | request-header         ; [Part2], Section 4
1739                   | entity-header ) CRLF)  ; [Part3], Section 4.1
1740                  CRLF
1741                  [ message-body ]          ; Section 4.3
1742]]></artwork></figure>
1743
1744<section title="Request-Line" anchor="request-line">
1745 
1746<t>
1747   The Request-Line begins with a method token, followed by the
1748   Request-URI and the protocol version, and ending with CRLF. The
1749   elements are separated by SP characters. No CR or LF is allowed
1750   except in the final CRLF sequence.
1751</t>
1752<figure><iref primary="true" item="Grammar" subitem="Request-Line"/><artwork type="abnf2616"><![CDATA[
1753  Request-Line   = Method SP Request-URI SP HTTP-Version CRLF
1754]]></artwork></figure>
1755
1756<section title="Method" anchor="method">
1757 
1758<t>
1759   The Method  token indicates the method to be performed on the
1760   resource identified by the Request-URI. The method is case-sensitive.
1761</t>
1762<figure><iref primary="true" item="Grammar" subitem="Method"/><iref primary="true" item="Grammar" subitem="extension-method"/><artwork type="abnf2616"><![CDATA[
1763  Method         = token
1764]]></artwork></figure>
1765</section>
1766
1767<section title="Request-URI" anchor="request-uri">
1768 
1769<t>
1770   The Request-URI is a Uniform Resource Identifier (<xref target="uri"/>) and
1771   identifies the resource upon which to apply the request.
1772</t>
1773<figure><iref primary="true" item="Grammar" subitem="Request-URI"/><artwork type="abnf2616"><![CDATA[
1774  Request-URI    = "*"
1775                 | absoluteURI
1776                 | ( path-absolute [ "?" query ] )
1777                 | authority
1778]]></artwork></figure>
1779<t>
1780   The four options for Request-URI are dependent on the nature of the
1781   request. The asterisk "*" means that the request does not apply to a
1782   particular resource, but to the server itself, and is only allowed
1783   when the method used does not necessarily apply to a resource. One
1784   example would be
1785</t>
1786<figure><artwork type="example"><![CDATA[
1787    OPTIONS * HTTP/1.1
1788]]></artwork></figure>
1789<t>
1790   The absoluteURI form is REQUIRED when the request is being made to a
1791   proxy. The proxy is requested to forward the request or service it
1792   from a valid cache, and return the response. Note that the proxy MAY
1793   forward the request on to another proxy or directly to the server
1794   specified by the absoluteURI. In order to avoid request loops, a
1795   proxy MUST be able to recognize all of its server names, including
1796   any aliases, local variations, and the numeric IP address. An example
1797   Request-Line would be:
1798</t>
1799<figure><artwork type="example"><![CDATA[
1800    GET http://www.example.org/pub/WWW/TheProject.html HTTP/1.1
1801]]></artwork></figure>
1802<t>
1803   To allow for transition to absoluteURIs in all requests in future
1804   versions of HTTP, all HTTP/1.1 servers MUST accept the absoluteURI
1805   form in requests, even though HTTP/1.1 clients will only generate
1806   them in requests to proxies.
1807</t>
1808<t>
1809   The authority form is only used by the CONNECT method (Section 8.9 of <xref target="Part2"/>).
1810</t>
1811<t>
1812   The most common form of Request-URI is that used to identify a
1813   resource on an origin server or gateway. In this case the absolute
1814   path of the URI MUST be transmitted (see <xref target="general.syntax"/>, path-absolute) as
1815   the Request-URI, and the network location of the URI (authority) MUST
1816   be transmitted in a Host header field. For example, a client wishing
1817   to retrieve the resource above directly from the origin server would
1818   create a TCP connection to port 80 of the host "www.example.org" and send
1819   the lines:
1820</t>
1821<figure><artwork type="example"><![CDATA[
1822    GET /pub/WWW/TheProject.html HTTP/1.1
1823    Host: www.example.org
1824]]></artwork></figure>
1825<t>
1826   followed by the remainder of the Request. Note that the absolute path
1827   cannot be empty; if none is present in the original URI, it MUST be
1828   given as "/" (the server root).
1829</t>
1830<t>
1831   The Request-URI is transmitted in the format specified in
1832   <xref target="general.syntax"/>. If the Request-URI is encoded using the
1833   "% <xref target="rule.HEXDIG" format="none">HEXDIG</xref> <xref target="rule.HEXDIG" format="none">HEXDIG</xref>" encoding
1834   (<xref target="RFC2396"/>, Section 2.4.1), the origin server
1835   MUST decode the Request-URI in order to
1836   properly interpret the request. Servers SHOULD respond to invalid
1837   Request-URIs with an appropriate status code.
1838</t>
1839<t>
1840   A transparent proxy MUST NOT rewrite the "path-absolute" part of the
1841   received Request-URI when forwarding it to the next inbound server,
1842   except as noted above to replace a null path-absolute with "/".
1843</t>
1844<t>
1845  <list><t>
1846      Note: The "no rewrite" rule prevents the proxy from changing the
1847      meaning of the request when the origin server is improperly using
1848      a non-reserved URI character for a reserved purpose.  Implementors
1849      should be aware that some pre-HTTP/1.1 proxies have been known to
1850      rewrite the Request-URI.
1851  </t></list>
1852</t>
1853</section>
1854</section>
1855
1856<section title="The Resource Identified by a Request" anchor="the.resource.identified.by.a.request">
1857<t>
1858   The exact resource identified by an Internet request is determined by
1859   examining both the Request-URI and the Host header field.
1860</t>
1861<t>
1862   An origin server that does not allow resources to differ by the
1863   requested host MAY ignore the Host header field value when
1864   determining the resource identified by an HTTP/1.1 request. (But see
1865   <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses"/>
1866   for other requirements on Host support in HTTP/1.1.)
1867</t>
1868<t>
1869   An origin server that does differentiate resources based on the host
1870   requested (sometimes referred to as virtual hosts or vanity host
1871   names) MUST use the following rules for determining the requested
1872   resource on an HTTP/1.1 request:
1873  <list style="numbers">
1874    <t>If Request-URI is an absoluteURI, the host is part of the
1875     Request-URI. Any Host header field value in the request MUST be
1876     ignored.</t>
1877    <t>If the Request-URI is not an absoluteURI, and the request includes
1878     a Host header field, the host is determined by the Host header
1879     field value.</t>
1880    <t>If the host as determined by rule 1 or 2 is not a valid host on
1881     the server, the response MUST be a 400 (Bad Request) error message.</t>
1882  </list>
1883</t>
1884<t>
1885   Recipients of an HTTP/1.0 request that lacks a Host header field MAY
1886   attempt to use heuristics (e.g., examination of the URI path for
1887   something unique to a particular host) in order to determine what
1888   exact resource is being requested.
1889</t>
1890</section>
1891
1892</section>
1893
1894
1895<section title="Response" anchor="response">
1896 
1897<t>
1898   After receiving and interpreting a request message, a server responds
1899   with an HTTP response message.
1900</t>
1901<figure><iref primary="true" item="Grammar" subitem="Response"/><artwork type="abnf2616"><![CDATA[
1902  Response      = Status-Line               ; Section 6.1
1903                  *(( general-header        ; Section 4.5
1904                   | response-header        ; [Part2], Section 6
1905                   | entity-header ) CRLF)  ; [Part3], Section 4.1
1906                  CRLF
1907                  [ message-body ]          ; Section 4.3
1908]]></artwork></figure>
1909
1910<section title="Status-Line" anchor="status-line">
1911 
1912<t>
1913   The first line of a Response message is the Status-Line, consisting
1914   of the protocol version followed by a numeric status code and its
1915   associated textual phrase, with each element separated by SP
1916   characters. No CR or LF is allowed except in the final CRLF sequence.
1917</t>
1918<figure><iref primary="true" item="Grammar" subitem="Status-Line"/><artwork type="abnf2616"><![CDATA[
1919  Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
1920]]></artwork></figure>
1921
1922<section title="Status Code and Reason Phrase" anchor="status.code.and.reason.phrase">
1923 
1924 
1925<t>
1926   The Status-Code element is a 3-digit integer result code of the
1927   attempt to understand and satisfy the request. These codes are fully
1928   defined in Section 9 of <xref target="Part2"/>.  The Reason Phrase exists for the sole
1929   purpose of providing a textual description associated with the numeric
1930   status code, out of deference to earlier Internet application protocols
1931   that were more frequently used with interactive text clients.
1932   A client SHOULD ignore the content of the Reason Phrase.
1933</t>
1934<t>
1935   The first digit of the Status-Code defines the class of response. The
1936   last two digits do not have any categorization role. There are 5
1937   values for the first digit:
1938  <list style="symbols">
1939    <t>
1940      1xx: Informational - Request received, continuing process
1941    </t>
1942    <t>
1943      2xx: Success - The action was successfully received,
1944        understood, and accepted
1945    </t>
1946    <t>
1947      3xx: Redirection - Further action must be taken in order to
1948        complete the request
1949    </t>
1950    <t>
1951      4xx: Client Error - The request contains bad syntax or cannot
1952        be fulfilled
1953    </t>
1954    <t>
1955      5xx: Server Error - The server failed to fulfill an apparently
1956        valid request
1957    </t>
1958  </list>
1959</t>
1960<figure><iref primary="true" item="Grammar" subitem="Status-Code"/><iref primary="true" item="Grammar" subitem="extension-code"/><iref primary="true" item="Grammar" subitem="Reason-Phrase"/><artwork type="abnf2616"><![CDATA[
1961  Status-Code    = 3DIGIT
1962  Reason-Phrase  = *<TEXT, excluding CR, LF>
1963]]></artwork></figure>
1964</section>
1965</section>
1966
1967</section>
1968
1969
1970<section title="Connections" anchor="connections">
1971
1972<section title="Persistent Connections" anchor="persistent.connections">
1973
1974<section title="Purpose" anchor="persistent.purpose">
1975<t>
1976   Prior to persistent connections, a separate TCP connection was
1977   established to fetch each URL, increasing the load on HTTP servers
1978   and causing congestion on the Internet. The use of inline images and
1979   other associated data often require a client to make multiple
1980   requests of the same server in a short amount of time. Analysis of
1981   these performance problems and results from a prototype
1982   implementation are available <xref target="Pad1995"/> <xref target="Spe"/>. Implementation experience and
1983   measurements of actual HTTP/1.1 (RFC 2068) implementations show good
1984   results <xref target="Nie1997"/>. Alternatives have also been explored, for example,
1985   T/TCP <xref target="Tou1998"/>.
1986</t>
1987<t>
1988   Persistent HTTP connections have a number of advantages:
1989  <list style="symbols">
1990      <t>
1991        By opening and closing fewer TCP connections, CPU time is saved
1992        in routers and hosts (clients, servers, proxies, gateways,
1993        tunnels, or caches), and memory used for TCP protocol control
1994        blocks can be saved in hosts.
1995      </t>
1996      <t>
1997        HTTP requests and responses can be pipelined on a connection.
1998        Pipelining allows a client to make multiple requests without
1999        waiting for each response, allowing a single TCP connection to
2000        be used much more efficiently, with much lower elapsed time.
2001      </t>
2002      <t>
2003        Network congestion is reduced by reducing the number of packets
2004        caused by TCP opens, and by allowing TCP sufficient time to
2005        determine the congestion state of the network.
2006      </t>
2007      <t>
2008        Latency on subsequent requests is reduced since there is no time
2009        spent in TCP's connection opening handshake.
2010      </t>
2011      <t>
2012        HTTP can evolve more gracefully, since errors can be reported
2013        without the penalty of closing the TCP connection. Clients using
2014        future versions of HTTP might optimistically try a new feature,
2015        but if communicating with an older server, retry with old
2016        semantics after an error is reported.
2017      </t>
2018    </list>
2019</t>
2020<t>
2021   HTTP implementations SHOULD implement persistent connections.
2022</t>
2023</section>
2024
2025<section title="Overall Operation" anchor="persistent.overall">
2026<t>
2027   A significant difference between HTTP/1.1 and earlier versions of
2028   HTTP is that persistent connections are the default behavior of any
2029   HTTP connection. That is, unless otherwise indicated, the client
2030   SHOULD assume that the server will maintain a persistent connection,
2031   even after error responses from the server.
2032</t>
2033<t>
2034   Persistent connections provide a mechanism by which a client and a
2035   server can signal the close of a TCP connection. This signaling takes
2036   place using the Connection header field (<xref target="header.connection"/>). Once a close
2037   has been signaled, the client MUST NOT send any more requests on that
2038   connection.
2039</t>
2040
2041<section title="Negotiation" anchor="persistent.negotiation">
2042<t>
2043   An HTTP/1.1 server MAY assume that a HTTP/1.1 client intends to
2044   maintain a persistent connection unless a Connection header including
2045   the connection-token "close" was sent in the request. If the server
2046   chooses to close the connection immediately after sending the
2047   response, it SHOULD send a Connection header including the
2048   connection-token close.
2049</t>
2050<t>
2051   An HTTP/1.1 client MAY expect a connection to remain open, but would
2052   decide to keep it open based on whether the response from a server
2053   contains a Connection header with the connection-token close. In case
2054   the client does not want to maintain a connection for more than that
2055   request, it SHOULD send a Connection header including the
2056   connection-token close.
2057</t>
2058<t>
2059   If either the client or the server sends the close token in the
2060   Connection header, that request becomes the last one for the
2061   connection.
2062</t>
2063<t>
2064   Clients and servers SHOULD NOT  assume that a persistent connection is
2065   maintained for HTTP versions less than 1.1 unless it is explicitly
2066   signaled. See <xref target="compatibility.with.http.1.0.persistent.connections"/> for more information on backward
2067   compatibility with HTTP/1.0 clients.
2068</t>
2069<t>
2070   In order to remain persistent, all messages on the connection MUST
2071   have a self-defined message length (i.e., one not defined by closure
2072   of the connection), as described in <xref target="message.length"/>.
2073</t>
2074</section>
2075
2076<section title="Pipelining" anchor="pipelining">
2077<t>
2078   A client that supports persistent connections MAY "pipeline" its
2079   requests (i.e., send multiple requests without waiting for each
2080   response). A server MUST send its responses to those requests in the
2081   same order that the requests were received.
2082</t>
2083<t>
2084   Clients which assume persistent connections and pipeline immediately
2085   after connection establishment SHOULD be prepared to retry their
2086   connection if the first pipelined attempt fails. If a client does
2087   such a retry, it MUST NOT pipeline before it knows the connection is
2088   persistent. Clients MUST also be prepared to resend their requests if
2089   the server closes the connection before sending all of the
2090   corresponding responses.
2091</t>
2092<t>
2093   Clients SHOULD NOT  pipeline requests using non-idempotent methods or
2094   non-idempotent sequences of methods (see Section 8.1.2 of <xref target="Part2"/>). Otherwise, a
2095   premature termination of the transport connection could lead to
2096   indeterminate results. A client wishing to send a non-idempotent
2097   request SHOULD wait to send that request until it has received the
2098   response status for the previous request.
2099</t>
2100</section>
2101</section>
2102
2103<section title="Proxy Servers" anchor="persistent.proxy">
2104<t>
2105   It is especially important that proxies correctly implement the
2106   properties of the Connection header field as specified in <xref target="header.connection"/>.
2107</t>
2108<t>
2109   The proxy server MUST signal persistent connections separately with
2110   its clients and the origin servers (or other proxy servers) that it
2111   connects to. Each persistent connection applies to only one transport
2112   link.
2113</t>
2114<t>
2115   A proxy server MUST NOT establish a HTTP/1.1 persistent connection
2116   with an HTTP/1.0 client (but see <xref target="RFC2068"/> for information and
2117   discussion of the problems with the Keep-Alive header implemented by
2118   many HTTP/1.0 clients).
2119</t>
2120</section>
2121
2122<section title="Practical Considerations" anchor="persistent.practical">
2123<t>
2124   Servers will usually have some time-out value beyond which they will
2125   no longer maintain an inactive connection. Proxy servers might make
2126   this a higher value since it is likely that the client will be making
2127   more connections through the same server. The use of persistent
2128   connections places no requirements on the length (or existence) of
2129   this time-out for either the client or the server.
2130</t>
2131<t>
2132   When a client or server wishes to time-out it SHOULD issue a graceful
2133   close on the transport connection. Clients and servers SHOULD both
2134   constantly watch for the other side of the transport close, and
2135   respond to it as appropriate. If a client or server does not detect
2136   the other side's close promptly it could cause unnecessary resource
2137   drain on the network.
2138</t>
2139<t>
2140   A client, server, or proxy MAY close the transport connection at any
2141   time. For example, a client might have started to send a new request
2142   at the same time that the server has decided to close the "idle"
2143   connection. From the server's point of view, the connection is being
2144   closed while it was idle, but from the client's point of view, a
2145   request is in progress.
2146</t>
2147<t>
2148   This means that clients, servers, and proxies MUST be able to recover
2149   from asynchronous close events. Client software SHOULD reopen the
2150   transport connection and retransmit the aborted sequence of requests
2151   without user interaction so long as the request sequence is
2152   idempotent (see Section 8.1.2 of <xref target="Part2"/>). Non-idempotent methods or sequences
2153   MUST NOT be automatically retried, although user agents MAY offer a
2154   human operator the choice of retrying the request(s). Confirmation by
2155   user-agent software with semantic understanding of the application
2156   MAY substitute for user confirmation. The automatic retry SHOULD NOT
2157   be repeated if the second sequence of requests fails.
2158</t>
2159<t>
2160   Servers SHOULD always respond to at least one request per connection,
2161   if at all possible. Servers SHOULD NOT  close a connection in the
2162   middle of transmitting a response, unless a network or client failure
2163   is suspected.
2164</t>
2165<t>
2166   Clients that use persistent connections SHOULD limit the number of
2167   simultaneous connections that they maintain to a given server. A
2168   single-user client SHOULD NOT maintain more than 2 connections with
2169   any server or proxy. A proxy SHOULD use up to 2*N connections to
2170   another server or proxy, where N is the number of simultaneously
2171   active users. These guidelines are intended to improve HTTP response
2172   times and avoid congestion.
2173</t>
2174</section>
2175</section>
2176
2177<section title="Message Transmission Requirements" anchor="message.transmission.requirements">
2178
2179<section title="Persistent Connections and Flow Control" anchor="persistent.flow">
2180<t>
2181   HTTP/1.1 servers SHOULD maintain persistent connections and use TCP's
2182   flow control mechanisms to resolve temporary overloads, rather than
2183   terminating connections with the expectation that clients will retry.
2184   The latter technique can exacerbate network congestion.
2185</t>
2186</section>
2187
2188<section title="Monitoring Connections for Error Status Messages" anchor="persistent.monitor">
2189<t>
2190   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
2191   the network connection for an error status while it is transmitting
2192   the request. If the client sees an error status, it SHOULD
2193   immediately cease transmitting the body. If the body is being sent
2194   using a "chunked" encoding (<xref target="transfer.codings"/>), a zero length chunk and
2195   empty trailer MAY be used to prematurely mark the end of the message.
2196   If the body was preceded by a Content-Length header, the client MUST
2197   close the connection.
2198</t>
2199</section>
2200
2201<section title="Use of the 100 (Continue) Status" anchor="use.of.the.100.status">
2202<t>
2203   The purpose of the 100 (Continue) status (see Section 9.1.1 of <xref target="Part2"/>) is to
2204   allow a client that is sending a request message with a request body
2205   to determine if the origin server is willing to accept the request
2206   (based on the request headers) before the client sends the request
2207   body. In some cases, it might either be inappropriate or highly
2208   inefficient for the client to send the body if the server will reject
2209   the message without looking at the body.
2210</t>
2211<t>
2212   Requirements for HTTP/1.1 clients:
2213  <list style="symbols">
2214    <t>
2215        If a client will wait for a 100 (Continue) response before
2216        sending the request body, it MUST send an Expect request-header
2217        field (Section 10.2 of <xref target="Part2"/>) with the "100-continue" expectation.
2218    </t>
2219    <t>
2220        A client MUST NOT send an Expect request-header field (Section 10.2 of <xref target="Part2"/>)
2221        with the "100-continue" expectation if it does not intend
2222        to send a request body.
2223    </t>
2224  </list>
2225</t>
2226<t>
2227   Because of the presence of older implementations, the protocol allows
2228   ambiguous situations in which a client may send "Expect: 100-continue"
2229   without receiving either a 417 (Expectation Failed) status
2230   or a 100 (Continue) status. Therefore, when a client sends this
2231   header field to an origin server (possibly via a proxy) from which it
2232   has never seen a 100 (Continue) status, the client SHOULD NOT  wait
2233   for an indefinite period before sending the request body.
2234</t>
2235<t>
2236   Requirements for HTTP/1.1 origin servers:
2237  <list style="symbols">
2238    <t> Upon receiving a request which includes an Expect request-header
2239        field with the "100-continue" expectation, an origin server MUST
2240        either respond with 100 (Continue) status and continue to read
2241        from the input stream, or respond with a final status code. The
2242        origin server MUST NOT wait for the request body before sending
2243        the 100 (Continue) response. If it responds with a final status
2244        code, it MAY close the transport connection or it MAY continue
2245        to read and discard the rest of the request.  It MUST NOT
2246        perform the requested method if it returns a final status code.
2247    </t>
2248    <t> An origin server SHOULD NOT  send a 100 (Continue) response if
2249        the request message does not include an Expect request-header
2250        field with the "100-continue" expectation, and MUST NOT send a
2251        100 (Continue) response if such a request comes from an HTTP/1.0
2252        (or earlier) client. There is an exception to this rule: for
2253        compatibility with <xref target="RFC2068"/>, a server MAY send a 100 (Continue)
2254        status in response to an HTTP/1.1 PUT or POST request that does
2255        not include an Expect request-header field with the "100-continue"
2256        expectation. This exception, the purpose of which is
2257        to minimize any client processing delays associated with an
2258        undeclared wait for 100 (Continue) status, applies only to
2259        HTTP/1.1 requests, and not to requests with any other HTTP-version
2260        value.
2261    </t>
2262    <t> An origin server MAY omit a 100 (Continue) response if it has
2263        already received some or all of the request body for the
2264        corresponding request.
2265    </t>
2266    <t> An origin server that sends a 100 (Continue) response MUST
2267    ultimately send a final status code, once the request body is
2268        received and processed, unless it terminates the transport
2269        connection prematurely.
2270    </t>
2271    <t> If an origin server receives a request that does not include an
2272        Expect request-header field with the "100-continue" expectation,
2273        the request includes a request body, and the server responds
2274        with a final status code before reading the entire request body
2275        from the transport connection, then the server SHOULD NOT  close
2276        the transport connection until it has read the entire request,
2277        or until the client closes the connection. Otherwise, the client
2278        might not reliably receive the response message. However, this
2279        requirement is not be construed as preventing a server from
2280        defending itself against denial-of-service attacks, or from
2281        badly broken client implementations.
2282      </t>
2283    </list>
2284</t>
2285<t>
2286   Requirements for HTTP/1.1 proxies:
2287  <list style="symbols">
2288    <t> If a proxy receives a request that includes an Expect request-header
2289        field with the "100-continue" expectation, and the proxy
2290        either knows that the next-hop server complies with HTTP/1.1 or
2291        higher, or does not know the HTTP version of the next-hop
2292        server, it MUST forward the request, including the Expect header
2293        field.
2294    </t>
2295    <t> If the proxy knows that the version of the next-hop server is
2296        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
2297        respond with a 417 (Expectation Failed) status.
2298    </t>
2299    <t> Proxies SHOULD maintain a cache recording the HTTP version
2300        numbers received from recently-referenced next-hop servers.
2301    </t>
2302    <t> A proxy MUST NOT forward a 100 (Continue) response if the
2303        request message was received from an HTTP/1.0 (or earlier)
2304        client and did not include an Expect request-header field with
2305        the "100-continue" expectation. This requirement overrides the
2306        general rule for forwarding of 1xx responses (see Section 9.1 of <xref target="Part2"/>).
2307    </t>
2308  </list>
2309</t>
2310</section>
2311
2312<section title="Client Behavior if Server Prematurely Closes Connection" anchor="connection.premature">
2313<t>
2314   If an HTTP/1.1 client sends a request which includes a request body,
2315   but which does not include an Expect request-header field with the
2316   "100-continue" expectation, and if the client is not directly
2317   connected to an HTTP/1.1 origin server, and if the client sees the
2318   connection close before receiving any status from the server, the
2319   client SHOULD retry the request.  If the client does retry this
2320   request, it MAY use the following "binary exponential backoff"
2321   algorithm to be assured of obtaining a reliable response:
2322  <list style="numbers">
2323    <t>
2324      Initiate a new connection to the server
2325    </t>
2326    <t>
2327      Transmit the request-headers
2328    </t>
2329    <t>
2330      Initialize a variable R to the estimated round-trip time to the
2331         server (e.g., based on the time it took to establish the
2332         connection), or to a constant value of 5 seconds if the round-trip
2333         time is not available.
2334    </t>
2335    <t>
2336       Compute T = R * (2**N), where N is the number of previous
2337         retries of this request.
2338    </t>
2339    <t>
2340       Wait either for an error response from the server, or for T
2341         seconds (whichever comes first)
2342    </t>
2343    <t>
2344       If no error response is received, after T seconds transmit the
2345         body of the request.
2346    </t>
2347    <t>
2348       If client sees that the connection is closed prematurely,
2349         repeat from step 1 until the request is accepted, an error
2350         response is received, or the user becomes impatient and
2351         terminates the retry process.
2352    </t>
2353  </list>
2354</t>
2355<t>
2356   If at any point an error status is received, the client
2357  <list style="symbols">
2358      <t>SHOULD NOT  continue and</t>
2359
2360      <t>SHOULD close the connection if it has not completed sending the
2361        request message.</t>
2362    </list>
2363</t>
2364</section>
2365</section>
2366</section>
2367
2368
2369<section title="Header Field Definitions" anchor="header.fields">
2370<t>
2371   This section defines the syntax and semantics of HTTP/1.1 header fields
2372   related to message framing and transport protocols.
2373</t>
2374<t>
2375   For entity-header fields, both sender and recipient refer to either the
2376   client or the server, depending on who sends and who receives the entity.
2377</t>
2378
2379<section title="Connection" anchor="header.connection">
2380  <iref primary="true" item="Connection header"/>
2381  <iref primary="true" item="Headers" subitem="Connection"/>
2382 
2383 
2384<t>
2385   The Connection general-header field allows the sender to specify
2386   options that are desired for that particular connection and MUST NOT
2387   be communicated by proxies over further connections.
2388</t>
2389<t>
2390   The Connection header has the following grammar:
2391</t>
2392<figure><iref primary="true" item="Grammar" subitem="Connection"/><iref primary="true" item="Grammar" subitem="connection-token"/><artwork type="abnf2616"><![CDATA[
2393  Connection = "Connection" ":" 1#(connection-token)
2394  connection-token  = token
2395]]></artwork></figure>
2396<t>
2397   HTTP/1.1 proxies MUST parse the Connection header field before a
2398   message is forwarded and, for each connection-token in this field,
2399   remove any header field(s) from the message with the same name as the
2400   connection-token. Connection options are signaled by the presence of
2401   a connection-token in the Connection header field, not by any
2402   corresponding additional header field(s), since the additional header
2403   field may not be sent if there are no parameters associated with that
2404   connection option.
2405</t>
2406<t>
2407   Message headers listed in the Connection header MUST NOT include
2408   end-to-end headers, such as Cache-Control.
2409</t>
2410<t>
2411   HTTP/1.1 defines the "close" connection option for the sender to
2412   signal that the connection will be closed after completion of the
2413   response. For example,
2414</t>
2415<figure><artwork type="example"><![CDATA[
2416    Connection: close
2417]]></artwork></figure>
2418<t>
2419   in either the request or the response header fields indicates that
2420   the connection SHOULD NOT  be considered `persistent' (<xref target="persistent.connections"/>)
2421   after the current request/response is complete.
2422</t>
2423<t>
2424   An HTTP/1.1 client that does not support persistent connections MUST
2425   include the "close" connection option in every request message.
2426</t>
2427<t>
2428   An HTTP/1.1 server that does not support persistent connections MUST
2429   include the "close" connection option in every response message that
2430   does not have a 1xx (informational) status code.
2431</t>
2432<t>
2433   A system receiving an HTTP/1.0 (or lower-version) message that
2434   includes a Connection header MUST, for each connection-token in this
2435   field, remove and ignore any header field(s) from the message with
2436   the same name as the connection-token. This protects against mistaken
2437   forwarding of such header fields by pre-HTTP/1.1 proxies. See <xref target="compatibility.with.http.1.0.persistent.connections"/>.
2438</t>
2439</section>
2440
2441<section title="Content-Length" anchor="header.content-length">
2442  <iref primary="true" item="Content-Length header"/>
2443  <iref primary="true" item="Headers" subitem="Content-Length"/>
2444 
2445<t>
2446   The Content-Length entity-header field indicates the size of the
2447   entity-body, in decimal number of OCTETs, sent to the recipient or,
2448   in the case of the HEAD method, the size of the entity-body that
2449   would have been sent had the request been a GET.
2450</t>
2451<figure><iref primary="true" item="Grammar" subitem="Content-Length"/><artwork type="abnf2616"><![CDATA[
2452  Content-Length    = "Content-Length" ":" 1*DIGIT
2453]]></artwork></figure>
2454<t>
2455   An example is
2456</t>
2457<figure><artwork type="example"><![CDATA[
2458    Content-Length: 3495
2459]]></artwork></figure>
2460<t>
2461   Applications SHOULD use this field to indicate the transfer-length of
2462   the message-body, unless this is prohibited by the rules in <xref target="message.length"/>.
2463</t>
2464<t>
2465   Any Content-Length greater than or equal to zero is a valid value.
2466   <xref target="message.length"/> describes how to determine the length of a message-body
2467   if a Content-Length is not given.
2468</t>
2469<t>
2470   Note that the meaning of this field is significantly different from
2471   the corresponding definition in MIME, where it is an optional field
2472   used within the "message/external-body" content-type. In HTTP, it
2473   SHOULD be sent whenever the message's length can be determined prior
2474   to being transferred, unless this is prohibited by the rules in
2475   <xref target="message.length"/>.
2476</t>
2477</section>
2478
2479<section title="Date" anchor="header.date">
2480  <iref primary="true" item="Date header"/>
2481  <iref primary="true" item="Headers" subitem="Date"/>
2482 
2483<t>
2484   The Date general-header field represents the date and time at which
2485   the message was originated, having the same semantics as orig-date in
2486   Section 3.6.1 of <xref target="RFC2822"/>. The field value is an HTTP-date, as described in <xref target="full.date"/>;
2487   it MUST be sent in rfc1123-date format.
2488</t>
2489<figure><iref primary="true" item="Grammar" subitem="Date"/><artwork type="abnf2616"><![CDATA[
2490  Date  = "Date" ":" HTTP-date
2491]]></artwork></figure>
2492<t>
2493   An example is
2494</t>
2495<figure><artwork type="example"><![CDATA[
2496    Date: Tue, 15 Nov 1994 08:12:31 GMT
2497]]></artwork></figure>
2498<t>
2499   Origin servers MUST include a Date header field in all responses,
2500   except in these cases:
2501  <list style="numbers">
2502      <t>If the response status code is 100 (Continue) or 101 (Switching
2503         Protocols), the response MAY include a Date header field, at
2504         the server's option.</t>
2505
2506      <t>If the response status code conveys a server error, e.g. 500
2507         (Internal Server Error) or 503 (Service Unavailable), and it is
2508         inconvenient or impossible to generate a valid Date.</t>
2509
2510      <t>If the server does not have a clock that can provide a
2511         reasonable approximation of the current time, its responses
2512         MUST NOT include a Date header field. In this case, the rules
2513         in <xref target="clockless.origin.server.operation"/> MUST be followed.</t>
2514  </list>
2515</t>
2516<t>
2517   A received message that does not have a Date header field MUST be
2518   assigned one by the recipient if the message will be cached by that
2519   recipient or gatewayed via a protocol which requires a Date. An HTTP
2520   implementation without a clock MUST NOT cache responses without
2521   revalidating them on every use. An HTTP cache, especially a shared
2522   cache, SHOULD use a mechanism, such as NTP <xref target="RFC1305"/>, to synchronize its
2523   clock with a reliable external standard.
2524</t>
2525<t>
2526   Clients SHOULD only send a Date header field in messages that include
2527   an entity-body, as in the case of the PUT and POST requests, and even
2528   then it is optional. A client without a clock MUST NOT send a Date
2529   header field in a request.
2530</t>
2531<t>
2532   The HTTP-date sent in a Date header SHOULD NOT  represent a date and
2533   time subsequent to the generation of the message. It SHOULD represent
2534   the best available approximation of the date and time of message
2535   generation, unless the implementation has no means of generating a
2536   reasonably accurate date and time. In theory, the date ought to
2537   represent the moment just before the entity is generated. In
2538   practice, the date can be generated at any time during the message
2539   origination without affecting its semantic value.
2540</t>
2541
2542<section title="Clockless Origin Server Operation" anchor="clockless.origin.server.operation">
2543<t>
2544   Some origin server implementations might not have a clock available.
2545   An origin server without a clock MUST NOT assign Expires or Last-Modified
2546   values to a response, unless these values were associated
2547   with the resource by a system or user with a reliable clock. It MAY
2548   assign an Expires value that is known, at or before server
2549   configuration time, to be in the past (this allows "pre-expiration"
2550   of responses without storing separate Expires values for each
2551   resource).
2552</t>
2553</section>
2554</section>
2555
2556<section title="Host" anchor="header.host">
2557  <iref primary="true" item="Host header"/>
2558  <iref primary="true" item="Headers" subitem="Host"/>
2559 
2560<t>
2561   The Host request-header field specifies the Internet host and port
2562   number of the resource being requested, as obtained from the original
2563   URI given by the user or referring resource (generally an HTTP URL,
2564   as described in <xref target="http.url"/>). The Host field value MUST represent
2565   the naming authority of the origin server or gateway given by the
2566   original URL. This allows the origin server or gateway to
2567   differentiate between internally-ambiguous URLs, such as the root "/"
2568   URL of a server for multiple host names on a single IP address.
2569</t>
2570<figure><iref primary="true" item="Grammar" subitem="Host"/><artwork type="abnf2616"><![CDATA[
2571  Host = "Host" ":" uri-host [ ":" port ] ; Section 3.2.2
2572]]></artwork></figure>
2573<t>
2574   A "host" without any trailing port information implies the default
2575   port for the service requested (e.g., "80" for an HTTP URL). For
2576   example, a request on the origin server for
2577   &lt;http://www.example.org/pub/WWW/&gt; would properly include:
2578</t>
2579<figure><artwork type="example"><![CDATA[
2580    GET /pub/WWW/ HTTP/1.1
2581    Host: www.example.org
2582]]></artwork></figure>
2583<t>
2584   A client MUST include a Host header field in all HTTP/1.1 request
2585   messages. If the requested URI does not include an Internet host
2586   name for the service being requested, then the Host header field MUST
2587   be given with an empty value. An HTTP/1.1 proxy MUST ensure that any
2588   request message it forwards does contain an appropriate Host header
2589   field that identifies the service being requested by the proxy. All
2590   Internet-based HTTP/1.1 servers MUST respond with a 400 (Bad Request)
2591   status code to any HTTP/1.1 request message which lacks a Host header
2592   field.
2593</t>
2594<t>
2595   See Sections <xref target="the.resource.identified.by.a.request" format="counter"/>
2596   and <xref target="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses" format="counter"/>
2597   for other requirements relating to Host.
2598</t>
2599</section>
2600
2601<section title="TE" anchor="header.te">
2602  <iref primary="true" item="TE header"/>
2603  <iref primary="true" item="Headers" subitem="TE"/>
2604 
2605 
2606<t>
2607   The TE request-header field indicates what extension transfer-codings
2608   it is willing to accept in the response and whether or not it is
2609   willing to accept trailer fields in a chunked transfer-coding. Its
2610   value may consist of the keyword "trailers" and/or a comma-separated
2611   list of extension transfer-coding names with optional accept
2612   parameters (as described in <xref target="transfer.codings"/>).
2613</t>
2614<figure><iref primary="true" item="Grammar" subitem="TE"/><iref primary="true" item="Grammar" subitem="t-codings"/><artwork type="abnf2616"><![CDATA[
2615  TE        = "TE" ":" #( t-codings )
2616  t-codings = "trailers" | ( transfer-extension [ accept-params ] )
2617]]></artwork></figure>
2618<t>
2619   The presence of the keyword "trailers" indicates that the client is
2620   willing to accept trailer fields in a chunked transfer-coding, as
2621   defined in <xref target="chunked.transfer.encoding"/>. This keyword is reserved for use with
2622   transfer-coding values even though it does not itself represent a
2623   transfer-coding.
2624</t>
2625<t>
2626   Examples of its use are:
2627</t>
2628<figure><artwork type="example"><![CDATA[
2629    TE: deflate
2630    TE:
2631    TE: trailers, deflate;q=0.5
2632]]></artwork></figure>
2633<t>
2634   The TE header field only applies to the immediate connection.
2635   Therefore, the keyword MUST be supplied within a Connection header
2636   field (<xref target="header.connection"/>) whenever TE is present in an HTTP/1.1 message.
2637</t>
2638<t>
2639   A server tests whether a transfer-coding is acceptable, according to
2640   a TE field, using these rules:
2641  <list style="numbers">
2642    <t>The "chunked" transfer-coding is always acceptable. If the
2643         keyword "trailers" is listed, the client indicates that it is
2644         willing to accept trailer fields in the chunked response on
2645         behalf of itself and any downstream clients. The implication is
2646         that, if given, the client is stating that either all
2647         downstream clients are willing to accept trailer fields in the
2648         forwarded response, or that it will attempt to buffer the
2649         response on behalf of downstream recipients.
2650      <vspace blankLines="1"/>
2651         Note: HTTP/1.1 does not define any means to limit the size of a
2652         chunked response such that a client can be assured of buffering
2653         the entire response.</t>
2654    <t>If the transfer-coding being tested is one of the transfer-codings
2655         listed in the TE field, then it is acceptable unless it
2656         is accompanied by a qvalue of 0. (As defined in Section 3.4 of <xref target="Part3"/>, a
2657         qvalue of 0 means "not acceptable.")</t>
2658    <t>If multiple transfer-codings are acceptable, then the
2659         acceptable transfer-coding with the highest non-zero qvalue is
2660         preferred.  The "chunked" transfer-coding always has a qvalue
2661         of 1.</t>
2662  </list>
2663</t>
2664<t>
2665   If the TE field-value is empty or if no TE field is present, the only
2666   transfer-coding  is "chunked". A message with no transfer-coding is
2667   always acceptable.
2668</t>
2669</section>
2670
2671<section title="Trailer" anchor="header.trailer">
2672  <iref primary="true" item="Trailer header"/>
2673  <iref primary="true" item="Headers" subitem="Trailer"/>
2674 
2675<t>
2676   The Trailer general field value indicates that the given set of
2677   header fields is present in the trailer of a message encoded with
2678   chunked transfer-coding.
2679</t>
2680<figure><iref primary="true" item="Grammar" subitem="Trailer"/><artwork type="abnf2616"><![CDATA[
2681  Trailer  = "Trailer" ":" 1#field-name
2682]]></artwork></figure>
2683<t>
2684   An HTTP/1.1 message SHOULD include a Trailer header field in a
2685   message using chunked transfer-coding with a non-empty trailer. Doing
2686   so allows the recipient to know which header fields to expect in the
2687   trailer.
2688</t>
2689<t>
2690   If no Trailer header field is present, the trailer SHOULD NOT  include
2691   any header fields. See <xref target="chunked.transfer.encoding"/> for restrictions on the use of
2692   trailer fields in a "chunked" transfer-coding.
2693</t>
2694<t>
2695   Message header fields listed in the Trailer header field MUST NOT
2696   include the following header fields:
2697  <list style="symbols">
2698    <t>Transfer-Encoding</t>
2699    <t>Content-Length</t>
2700    <t>Trailer</t>
2701  </list>
2702</t>
2703</section>
2704
2705<section title="Transfer-Encoding" anchor="header.transfer-encoding">
2706  <iref primary="true" item="Transfer-Encoding header"/>
2707  <iref primary="true" item="Headers" subitem="Transfer-Encoding"/>
2708 
2709<t>
2710   The Transfer-Encoding general-header field indicates what (if any)
2711   type of transformation has been applied to the message body in order
2712   to safely transfer it between the sender and the recipient. This
2713   differs from the content-coding in that the transfer-coding is a
2714   property of the message, not of the entity.
2715</t>
2716<figure><iref primary="true" item="Grammar" subitem="Transfer-Encoding"/><artwork type="abnf2616"><![CDATA[
2717  Transfer-Encoding       = "Transfer-Encoding" ":" 1#transfer-coding
2718]]></artwork></figure>
2719<t>
2720   Transfer-codings are defined in <xref target="transfer.codings"/>. An example is:
2721</t>
2722<figure><artwork type="example"><![CDATA[
2723  Transfer-Encoding: chunked
2724]]></artwork></figure>
2725<t>
2726   If multiple encodings have been applied to an entity, the transfer-codings
2727   MUST be listed in the order in which they were applied.
2728   Additional information about the encoding parameters MAY be provided
2729   by other entity-header fields not defined by this specification.
2730</t>
2731<t>
2732   Many older HTTP/1.0 applications do not understand the Transfer-Encoding
2733   header.
2734</t>
2735</section>
2736
2737<section title="Upgrade" anchor="header.upgrade">
2738  <iref primary="true" item="Upgrade header"/>
2739  <iref primary="true" item="Headers" subitem="Upgrade"/>
2740 
2741<t>
2742   The Upgrade general-header allows the client to specify what
2743   additional communication protocols it supports and would like to use
2744   if the server finds it appropriate to switch protocols. The server
2745   MUST use the Upgrade header field within a 101 (Switching Protocols)
2746   response to indicate which protocol(s) are being switched.
2747</t>
2748<figure><iref primary="true" item="Grammar" subitem="Upgrade"/><artwork type="abnf2616"><![CDATA[
2749  Upgrade        = "Upgrade" ":" 1#product
2750]]></artwork></figure>
2751<t>
2752   For example,
2753</t>
2754<figure><artwork type="example"><![CDATA[
2755    Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
2756]]></artwork></figure>
2757<t>
2758   The Upgrade header field is intended to provide a simple mechanism
2759   for transition from HTTP/1.1 to some other, incompatible protocol. It
2760   does so by allowing the client to advertise its desire to use another
2761   protocol, such as a later version of HTTP with a higher major version
2762   number, even though the current request has been made using HTTP/1.1.
2763   This eases the difficult transition between incompatible protocols by
2764   allowing the client to initiate a request in the more commonly
2765   supported protocol while indicating to the server that it would like
2766   to use a "better" protocol if available (where "better" is determined
2767   by the server, possibly according to the nature of the method and/or
2768   resource being requested).
2769</t>
2770<t>
2771   The Upgrade header field only applies to switching application-layer
2772   protocols upon the existing transport-layer connection. Upgrade
2773   cannot be used to insist on a protocol change; its acceptance and use
2774   by the server is optional. The capabilities and nature of the
2775   application-layer communication after the protocol change is entirely
2776   dependent upon the new protocol chosen, although the first action
2777   after changing the protocol MUST be a response to the initial HTTP
2778   request containing the Upgrade header field.
2779</t>
2780<t>
2781   The Upgrade header field only applies to the immediate connection.
2782   Therefore, the upgrade keyword MUST be supplied within a Connection
2783   header field (<xref target="header.connection"/>) whenever Upgrade is present in an
2784   HTTP/1.1 message.
2785</t>
2786<t>
2787   The Upgrade header field cannot be used to indicate a switch to a
2788   protocol on a different connection. For that purpose, it is more
2789   appropriate to use a 301, 302, 303, or 305 redirection response.
2790</t>
2791<t>
2792   This specification only defines the protocol name "HTTP" for use by
2793   the family of Hypertext Transfer Protocols, as defined by the HTTP
2794   version rules of <xref target="http.version"/> and future updates to this
2795   specification. Any token can be used as a protocol name; however, it
2796   will only be useful if both the client and server associate the name
2797   with the same protocol.
2798</t>
2799</section>
2800
2801<section title="Via" anchor="header.via">
2802  <iref primary="true" item="Via header"/>
2803  <iref primary="true" item="Headers" subitem="Via"/>
2804 
2805 
2806 
2807 
2808 
2809 
2810<t>
2811   The Via general-header field MUST be used by gateways and proxies to
2812   indicate the intermediate protocols and recipients between the user
2813   agent and the server on requests, and between the origin server and
2814   the client on responses. It is analogous to the "Received" field defined in
2815   Section 3.6.7 of <xref target="RFC2822"/> and is intended to be used for tracking message forwards,
2816   avoiding request loops, and identifying the protocol capabilities of
2817   all senders along the request/response chain.
2818</t>
2819<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[
2820  Via =  "Via" ":" 1#( received-protocol received-by [ comment ] )
2821  received-protocol = [ protocol-name "/" ] protocol-version
2822  protocol-name     = token
2823  protocol-version  = token
2824  received-by       = ( uri-host [ ":" port ] ) | pseudonym
2825  pseudonym         = token
2826]]></artwork></figure>
2827<t>
2828   The received-protocol indicates the protocol version of the message
2829   received by the server or client along each segment of the
2830   request/response chain. The received-protocol version is appended to
2831   the Via field value when the message is forwarded so that information
2832   about the protocol capabilities of upstream applications remains
2833   visible to all recipients.
2834</t>
2835<t>
2836   The protocol-name is optional if and only if it would be "HTTP". The
2837   received-by field is normally the host and optional port number of a
2838   recipient server or client that subsequently forwarded the message.
2839   However, if the real host is considered to be sensitive information,
2840   it MAY be replaced by a pseudonym. If the port is not given, it MAY
2841   be assumed to be the default port of the received-protocol.
2842</t>
2843<t>
2844   Multiple Via field values represents each proxy or gateway that has
2845   forwarded the message. Each recipient MUST append its information
2846   such that the end result is ordered according to the sequence of
2847   forwarding applications.
2848</t>
2849<t>
2850   Comments MAY be used in the Via header field to identify the software
2851   of the recipient proxy or gateway, analogous to the User-Agent and
2852   Server header fields. However, all comments in the Via field are
2853   optional and MAY be removed by any recipient prior to forwarding the
2854   message.
2855</t>
2856<t>
2857   For example, a request message could be sent from an HTTP/1.0 user
2858   agent to an internal proxy code-named "fred", which uses HTTP/1.1 to
2859   forward the request to a public proxy at p.example.net, which completes
2860   the request by forwarding it to the origin server at www.example.com.
2861   The request received by www.example.com would then have the following
2862   Via header field:
2863</t>
2864<figure><artwork type="example"><![CDATA[
2865    Via: 1.0 fred, 1.1 p.example.net (Apache/1.1)
2866]]></artwork></figure>
2867<t>
2868   Proxies and gateways used as a portal through a network firewall
2869   SHOULD NOT, by default, forward the names and ports of hosts within
2870   the firewall region. This information SHOULD only be propagated if
2871   explicitly enabled. If not enabled, the received-by host of any host
2872   behind the firewall SHOULD be replaced by an appropriate pseudonym
2873   for that host.
2874</t>
2875<t>
2876   For organizations that have strong privacy requirements for hiding
2877   internal structures, a proxy MAY combine an ordered subsequence of
2878   Via header field entries with identical received-protocol values into
2879   a single such entry. For example,
2880</t>
2881<figure><artwork type="example"><![CDATA[
2882    Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
2883]]></artwork></figure>
2884<t>
2885        could be collapsed to
2886</t>
2887<figure><artwork type="example"><![CDATA[
2888    Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
2889]]></artwork></figure>
2890<t>
2891   Applications SHOULD NOT  combine multiple entries unless they are all
2892   under the same organizational control and the hosts have already been
2893   replaced by pseudonyms. Applications MUST NOT combine entries which
2894   have different received-protocol values.
2895</t>
2896</section>
2897
2898</section>
2899
2900<section title="IANA Considerations" anchor="IANA.considerations">
2901<section title="Message Header Registration" anchor="message.header.registration">
2902<t>
2903   The Message Header Registry located at <eref target="http://www.iana.org/assignments/message-headers/message-header-index.html"/> should be updated
2904   with the permanent registrations below (see <xref target="RFC3864"/>):
2905</t>
2906<!--AUTOGENERATED FROM extract-header-defs.xslt, do not edit manually-->
2907<texttable align="left" suppress-title="true" anchor="iana.header.registration.table">
2908   <ttcol>Header Field Name</ttcol>
2909   <ttcol>Protocol</ttcol>
2910   <ttcol>Status</ttcol>
2911   <ttcol>Reference</ttcol>
2912
2913   <c>Connection</c>
2914   <c>http</c>
2915   <c>standard</c>
2916   <c>
2917      <xref target="header.connection"/>
2918   </c>
2919   <c>Content-Length</c>
2920   <c>http</c>
2921   <c>standard</c>
2922   <c>
2923      <xref target="header.content-length"/>
2924   </c>
2925   <c>Date</c>
2926   <c>http</c>
2927   <c>standard</c>
2928   <c>
2929      <xref target="header.date"/>
2930   </c>
2931   <c>Host</c>
2932   <c>http</c>
2933   <c>standard</c>
2934   <c>
2935      <xref target="header.host"/>
2936   </c>
2937   <c>TE</c>
2938   <c>http</c>
2939   <c>standard</c>
2940   <c>
2941      <xref target="header.te"/>
2942   </c>
2943   <c>Trailer</c>
2944   <c>http</c>
2945   <c>standard</c>
2946   <c>
2947      <xref target="header.trailer"/>
2948   </c>
2949   <c>Transfer-Encoding</c>
2950   <c>http</c>
2951   <c>standard</c>
2952   <c>
2953      <xref target="header.transfer-encoding"/>
2954   </c>
2955   <c>Upgrade</c>
2956   <c>http</c>
2957   <c>standard</c>
2958   <c>
2959      <xref target="header.upgrade"/>
2960   </c>
2961   <c>Via</c>
2962   <c>http</c>
2963   <c>standard</c>
2964   <c>
2965      <xref target="header.via"/>
2966   </c>
2967</texttable>
2968<!--(END)-->
2969<t>
2970   The change controller is: "IETF (iesg@ietf.org) - Internet Engineering Task Force".
2971</t>
2972</section>
2973
2974<section title="URI Scheme Registration" anchor="uri.scheme.registration">
2975<t>
2976   The entry for the "http" URI Scheme in the registry located at
2977   <eref target="http://www.iana.org/assignments/uri-schemes.html"/>
2978   should be updated to point to <xref target="http.url"/> of this document
2979   (see <xref target="RFC4395"/>).
2980</t>
2981</section>
2982
2983<section title="Internet Media Type Registrations" anchor="internet.media.type.http">
2984<t>
2985   This document serves as the specification for the Internet media types
2986   "message/http" and "application/http". The following is to be registered with
2987   IANA (see <xref target="RFC4288"/>).
2988</t>
2989<section title="Internet Media Type message/http" anchor="internet.media.type.message.http">
2990<iref item="Media Type" subitem="message/http" primary="true"/>
2991<iref item="message/http Media Type" primary="true"/>
2992<t>
2993   The message/http type can be used to enclose a single HTTP request or
2994   response message, provided that it obeys the MIME restrictions for all
2995   "message" types regarding line length and encodings.
2996</t>
2997<t>
2998  <list style="hanging">
2999    <t hangText="Type name:">
3000      message
3001    </t>
3002    <t hangText="Subtype name:">
3003      http
3004    </t>
3005    <t hangText="Required parameters:">
3006      none
3007    </t>
3008    <t hangText="Optional parameters:">
3009      version, msgtype
3010      <list style="hanging">
3011        <t hangText="version:">
3012          The HTTP-Version number of the enclosed message
3013          (e.g., "1.1"). If not present, the version can be
3014          determined from the first line of the body.
3015        </t>
3016        <t hangText="msgtype:">
3017          The message type -- "request" or "response". If not
3018          present, the type can be determined from the first
3019          line of the body.
3020        </t>
3021      </list>
3022    </t>
3023    <t hangText="Encoding considerations:">
3024      only "7bit", "8bit", or "binary" are permitted
3025    </t>
3026    <t hangText="Security considerations:">
3027      none
3028    </t>
3029    <t hangText="Interoperability considerations:">
3030      none
3031    </t>
3032    <t hangText="Published specification:">
3033      This specification (see <xref target="internet.media.type.message.http"/>).
3034    </t>
3035    <t hangText="Applications that use this media type:">
3036    </t>
3037    <t hangText="Additional information:">
3038      <list style="hanging">
3039        <t hangText="Magic number(s):">none</t>
3040        <t hangText="File extension(s):">none</t>
3041        <t hangText="Macintosh file type code(s):">none</t>
3042      </list>
3043    </t>
3044    <t hangText="Person and email address to contact for further information:">
3045      See Authors Section.
3046    </t>
3047                <t hangText="Intended usage:">
3048                  COMMON
3049    </t>
3050                <t hangText="Restrictions on usage:">
3051                  none
3052    </t>
3053    <t hangText="Author/Change controller:">
3054      IESG
3055    </t>
3056  </list>
3057</t>
3058</section>
3059<section title="Internet Media Type application/http" anchor="internet.media.type.application.http">
3060<iref item="Media Type" subitem="application/http" primary="true"/>
3061<iref item="application/http Media Type" primary="true"/>
3062<t>
3063   The application/http type can be used to enclose a pipeline of one or more
3064   HTTP request or response messages (not intermixed).
3065</t>
3066<t>
3067  <list style="hanging">
3068    <t hangText="Type name:">
3069      application
3070    </t>
3071    <t hangText="Subtype name:">
3072      http
3073    </t>
3074    <t hangText="Required parameters:">
3075      none
3076    </t>
3077    <t hangText="Optional parameters:">
3078      version, msgtype
3079      <list style="hanging">
3080        <t hangText="version:">
3081          The HTTP-Version number of the enclosed messages
3082          (e.g., "1.1"). If not present, the version can be
3083          determined from the first line of the body.
3084        </t>
3085        <t hangText="msgtype:">
3086          The message type -- "request" or "response". If not
3087          present, the type can be determined from the first
3088          line of the body.
3089        </t>
3090      </list>
3091    </t>
3092    <t hangText="Encoding considerations:">
3093      HTTP messages enclosed by this type
3094      are in "binary" format; use of an appropriate
3095      Content-Transfer-Encoding is required when
3096      transmitted via E-mail.
3097    </t>
3098    <t hangText="Security considerations:">
3099      none
3100    </t>
3101    <t hangText="Interoperability considerations:">
3102      none
3103    </t>
3104    <t hangText="Published specification:">
3105      This specification (see <xref target="internet.media.type.application.http"/>).
3106    </t>
3107    <t hangText="Applications that use this media type:">
3108    </t>
3109    <t hangText="Additional information:">
3110      <list style="hanging">
3111        <t hangText="Magic number(s):">none</t>
3112        <t hangText="File extension(s):">none</t>
3113        <t hangText="Macintosh file type code(s):">none</t>
3114      </list>
3115    </t>
3116    <t hangText="Person and email address to contact for further information:">
3117      See Authors Section.
3118    </t>
3119                <t hangText="Intended usage:">
3120                  COMMON
3121    </t>
3122                <t hangText="Restrictions on usage:">
3123                  none
3124    </t>
3125    <t hangText="Author/Change controller:">
3126      IESG
3127    </t>
3128  </list>
3129</t>
3130</section>
3131</section>
3132
3133</section>
3134
3135<section title="Security Considerations" anchor="security.considerations">
3136<t>
3137   This section is meant to inform application developers, information
3138   providers, and users of the security limitations in HTTP/1.1 as
3139   described by this document. The discussion does not include
3140   definitive solutions to the problems revealed, though it does make
3141   some suggestions for reducing security risks.
3142</t>
3143
3144<section title="Personal Information" anchor="personal.information">
3145<t>
3146   HTTP clients are often privy to large amounts of personal information
3147   (e.g. the user's name, location, mail address, passwords, encryption
3148   keys, etc.), and SHOULD be very careful to prevent unintentional
3149   leakage of this information.
3150   We very strongly recommend that a convenient interface be provided
3151   for the user to control dissemination of such information, and that
3152   designers and implementors be particularly careful in this area.
3153   History shows that errors in this area often create serious security
3154   and/or privacy problems and generate highly adverse publicity for the
3155   implementor's company.
3156</t>
3157</section>
3158
3159<section title="Abuse of Server Log Information" anchor="abuse.of.server.log.information">
3160<t>
3161   A server is in the position to save personal data about a user's
3162   requests which might identify their reading patterns or subjects of
3163   interest. This information is clearly confidential in nature and its
3164   handling can be constrained by law in certain countries. People using
3165   HTTP to provide data are responsible for ensuring that
3166   such material is not distributed without the permission of any
3167   individuals that are identifiable by the published results.
3168</t>
3169</section>
3170
3171<section title="Attacks Based On File and Path Names" anchor="attack.pathname">
3172<t>
3173   Implementations of HTTP origin servers SHOULD be careful to restrict
3174   the documents returned by HTTP requests to be only those that were
3175   intended by the server administrators. If an HTTP server translates
3176   HTTP URIs directly into file system calls, the server MUST take
3177   special care not to serve files that were not intended to be
3178   delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
3179   other operating systems use ".." as a path component to indicate a
3180   directory level above the current one. On such a system, an HTTP
3181   server MUST disallow any such construct in the Request-URI if it
3182   would otherwise allow access to a resource outside those intended to
3183   be accessible via the HTTP server. Similarly, files intended for
3184   reference only internally to the server (such as access control
3185   files, configuration files, and script code) MUST be protected from
3186   inappropriate retrieval, since they might contain sensitive
3187   information. Experience has shown that minor bugs in such HTTP server
3188   implementations have turned into security risks.
3189</t>
3190</section>
3191
3192<section title="DNS Spoofing" anchor="dns.spoofing">
3193<t>
3194   Clients using HTTP rely heavily on the Domain Name Service, and are
3195   thus generally prone to security attacks based on the deliberate
3196   mis-association of IP addresses and DNS names. Clients need to be
3197   cautious in assuming the continuing validity of an IP number/DNS name
3198   association.
3199</t>
3200<t>
3201   In particular, HTTP clients SHOULD rely on their name resolver for
3202   confirmation of an IP number/DNS name association, rather than
3203   caching the result of previous host name lookups. Many platforms
3204   already can cache host name lookups locally when appropriate, and
3205   they SHOULD be configured to do so. It is proper for these lookups to
3206   be cached, however, only when the TTL (Time To Live) information
3207   reported by the name server makes it likely that the cached
3208   information will remain useful.
3209</t>
3210<t>
3211   If HTTP clients cache the results of host name lookups in order to
3212   achieve a performance improvement, they MUST observe the TTL
3213   information reported by DNS.
3214</t>
3215<t>
3216   If HTTP clients do not observe this rule, they could be spoofed when
3217   a previously-accessed server's IP address changes. As network
3218   renumbering is expected to become increasingly common <xref target="RFC1900"/>, the
3219   possibility of this form of attack will grow. Observing this
3220   requirement thus reduces this potential security vulnerability.
3221</t>
3222<t>
3223   This requirement also improves the load-balancing behavior of clients
3224   for replicated servers using the same DNS name and reduces the
3225   likelihood of a user's experiencing failure in accessing sites which
3226   use that strategy.
3227</t>
3228</section>
3229
3230<section title="Proxies and Caching" anchor="attack.proxies">
3231<t>
3232   By their very nature, HTTP proxies are men-in-the-middle, and
3233   represent an opportunity for man-in-the-middle attacks. Compromise of
3234   the systems on which the proxies run can result in serious security
3235   and privacy problems. Proxies have access to security-related
3236   information, personal information about individual users and
3237   organizations, and proprietary information belonging to users and
3238   content providers. A compromised proxy, or a proxy implemented or
3239   configured without regard to security and privacy considerations,
3240   might be used in the commission of a wide range of potential attacks.
3241</t>
3242<t>
3243   Proxy operators should protect the systems on which proxies run as
3244   they would protect any system that contains or transports sensitive
3245   information. In particular, log information gathered at proxies often
3246   contains highly sensitive personal information, and/or information
3247   about organizations. Log information should be carefully guarded, and
3248   appropriate guidelines for use developed and followed. (<xref target="abuse.of.server.log.information"/>).
3249</t>
3250<t>
3251   Proxy implementors should consider the privacy and security
3252   implications of their design and coding decisions, and of the
3253   configuration options they provide to proxy operators (especially the
3254   default configuration).
3255</t>
3256<t>
3257   Users of a proxy need to be aware that they are no trustworthier than
3258   the people who run the proxy; HTTP itself cannot solve this problem.
3259</t>
3260<t>
3261   The judicious use of cryptography, when appropriate, may suffice to
3262   protect against a broad range of security and privacy attacks. Such
3263   cryptography is beyond the scope of the HTTP/1.1 specification.
3264</t>
3265</section>
3266
3267<section title="Denial of Service Attacks on Proxies" anchor="attack.DoS">
3268<t>
3269   They exist. They are hard to defend against. Research continues.
3270   Beware.
3271</t>
3272</section>
3273</section>
3274
3275<section title="Acknowledgments" anchor="ack">
3276<t>
3277   This specification makes heavy use of the augmented BNF and generic
3278   constructs defined by David H. Crocker for <xref target="RFC822ABNF"/>. Similarly, it
3279   reuses many of the definitions provided by Nathaniel Borenstein and
3280   Ned Freed for MIME <xref target="RFC2045"/>. We hope that their inclusion in this
3281   specification will help reduce past confusion over the relationship
3282   between HTTP and Internet mail message formats.
3283</t>
3284<t>
3285   HTTP has evolved considerably over the years. It has
3286   benefited from a large and active developer community--the many
3287   people who have participated on the www-talk mailing list--and it is
3288   that community which has been most responsible for the success of
3289   HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
3290   Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
3291   Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
3292   McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
3293   VanHeyningen deserve special recognition for their efforts in
3294   defining early aspects of the protocol.
3295</t>
3296<t>
3297   This document has benefited greatly from the comments of all those
3298   participating in the HTTP-WG. In addition to those already mentioned,
3299   the following individuals have contributed to this specification:
3300</t>
3301<t>
3302   Gary Adams, Harald Tveit Alvestrand, Keith Ball, Brian Behlendorf,
3303   Paul Burchard, Maurizio Codogno, Mike Cowlishaw, Roman Czyborra,
3304   Michael A. Dolan, Daniel DuBois, David J. Fiander, Alan Freier, Marc Hedlund, Greg Herlihy,
3305   Koen Holtman, Alex Hopmann, Bob Jernigan, Shel Kaphan, Rohit Khare,
3306   John Klensin, Martijn Koster, Alexei Kosut, David M. Kristol,
3307   Daniel LaLiberte, Ben Laurie, Paul J. Leach, Albert Lunde,
3308   John C. Mallery, Jean-Philippe Martin-Flatin, Mitra, David Morris,
3309   Gavin Nicol, Ross Patterson, Bill Perry, Jeffrey Perry, Scott Powers, Owen Rees,
3310   Luigi Rizzo, David Robinson, Marc Salomon, Rich Salz,
3311   Allan M. Schiffman, Jim Seidman, Chuck Shotton, Eric W. Sink,
3312   Simon E. Spero, Richard N. Taylor, Robert S. Thau,
3313   Bill (BearHeart) Weinman, Francois Yergeau, Mary Ellen Zurko,
3314   Josh Cohen.
3315</t>
3316<t>
3317   Thanks to the "cave men" of Palo Alto. You know who you are.
3318</t>
3319<t>
3320   Jim Gettys (the editor of <xref target="RFC2616"/>) wishes particularly
3321   to thank Roy Fielding, the editor of <xref target="RFC2068"/>, along
3322   with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
3323   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
3324   Larry Masinter for their help. And thanks go particularly to Jeff
3325   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
3326</t>
3327<t>
3328   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
3329   Frystyk implemented RFC 2068 early, and we wish to thank them for the
3330   discovery of many of the problems that this document attempts to
3331   rectify.
3332</t>
3333</section>
3334
3335</middle>
3336<back>
3337
3338<references title="Normative References">
3339
3340<reference anchor="ISO-8859-1">
3341  <front>
3342    <title>
3343     Information technology -- 8-bit single-byte coded graphic character sets -- Part 1: Latin alphabet No. 1
3344    </title>
3345    <author>
3346      <organization>International Organization for Standardization</organization>
3347    </author>
3348    <date year="1998"/>
3349  </front>
3350  <seriesInfo name="ISO/IEC" value="8859-1:1998"/>
3351</reference>
3352
3353<reference anchor="Part2">
3354  <front>
3355    <title abbrev="HTTP/1.1">HTTP/1.1, part 2: Message Semantics</title>
3356    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3357      <organization abbrev="Day Software">Day Software</organization>
3358      <address><email>fielding@gbiv.com</email></address>
3359    </author>
3360    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3361      <organization>One Laptop per Child</organization>
3362      <address><email>jg@laptop.org</email></address>
3363    </author>
3364    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3365      <organization abbrev="HP">Hewlett-Packard Company</organization>
3366      <address><email>JeffMogul@acm.org</email></address>
3367    </author>
3368    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3369      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3370      <address><email>henrikn@microsoft.com</email></address>
3371    </author>
3372    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3373      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3374      <address><email>LMM@acm.org</email></address>
3375    </author>
3376    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3377      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3378      <address><email>paulle@microsoft.com</email></address>
3379    </author>
3380    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3381      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3382      <address><email>timbl@w3.org</email></address>
3383    </author>
3384    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3385      <organization abbrev="W3C">World Wide Web Consortium</organization>
3386      <address><email>ylafon@w3.org</email></address>
3387    </author>
3388    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3389      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3390      <address><email>julian.reschke@greenbytes.de</email></address>
3391    </author>
3392    <date month="August" year="2008"/>
3393  </front>
3394  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p2-semantics-04"/>
3395 
3396</reference>
3397
3398<reference anchor="Part3">
3399  <front>
3400    <title abbrev="HTTP/1.1">HTTP/1.1, part 3: Message Payload and Content Negotiation</title>
3401    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3402      <organization abbrev="Day Software">Day Software</organization>
3403      <address><email>fielding@gbiv.com</email></address>
3404    </author>
3405    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3406      <organization>One Laptop per Child</organization>
3407      <address><email>jg@laptop.org</email></address>
3408    </author>
3409    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3410      <organization abbrev="HP">Hewlett-Packard Company</organization>
3411      <address><email>JeffMogul@acm.org</email></address>
3412    </author>
3413    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3414      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3415      <address><email>henrikn@microsoft.com</email></address>
3416    </author>
3417    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3418      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3419      <address><email>LMM@acm.org</email></address>
3420    </author>
3421    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3422      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3423      <address><email>paulle@microsoft.com</email></address>
3424    </author>
3425    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3426      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3427      <address><email>timbl@w3.org</email></address>
3428    </author>
3429    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3430      <organization abbrev="W3C">World Wide Web Consortium</organization>
3431      <address><email>ylafon@w3.org</email></address>
3432    </author>
3433    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3434      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3435      <address><email>julian.reschke@greenbytes.de</email></address>
3436    </author>
3437    <date month="August" year="2008"/>
3438  </front>
3439  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p3-payload-04"/>
3440 
3441</reference>
3442
3443<reference anchor="Part5">
3444  <front>
3445    <title abbrev="HTTP/1.1">HTTP/1.1, part 5: Range Requests and Partial Responses</title>
3446    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3447      <organization abbrev="Day Software">Day Software</organization>
3448      <address><email>fielding@gbiv.com</email></address>
3449    </author>
3450    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3451      <organization>One Laptop per Child</organization>
3452      <address><email>jg@laptop.org</email></address>
3453    </author>
3454    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3455      <organization abbrev="HP">Hewlett-Packard Company</organization>
3456      <address><email>JeffMogul@acm.org</email></address>
3457    </author>
3458    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3459      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3460      <address><email>henrikn@microsoft.com</email></address>
3461    </author>
3462    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3463      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3464      <address><email>LMM@acm.org</email></address>
3465    </author>
3466    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3467      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3468      <address><email>paulle@microsoft.com</email></address>
3469    </author>
3470    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3471      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3472      <address><email>timbl@w3.org</email></address>
3473    </author>
3474    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3475      <organization abbrev="W3C">World Wide Web Consortium</organization>
3476      <address><email>ylafon@w3.org</email></address>
3477    </author>
3478    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3479      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3480      <address><email>julian.reschke@greenbytes.de</email></address>
3481    </author>
3482    <date month="August" year="2008"/>
3483  </front>
3484  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p5-range-04"/>
3485 
3486</reference>
3487
3488<reference anchor="Part6">
3489  <front>
3490    <title abbrev="HTTP/1.1">HTTP/1.1, part 6: Caching</title>
3491    <author initials="R." surname="Fielding" fullname="Roy T. Fielding" role="editor">
3492      <organization abbrev="Day Software">Day Software</organization>
3493      <address><email>fielding@gbiv.com</email></address>
3494    </author>
3495    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3496      <organization>One Laptop per Child</organization>
3497      <address><email>jg@laptop.org</email></address>
3498    </author>
3499    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3500      <organization abbrev="HP">Hewlett-Packard Company</organization>
3501      <address><email>JeffMogul@acm.org</email></address>
3502    </author>
3503    <author initials="H." surname="Frystyk" fullname="Henrik Frystyk Nielsen">
3504      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3505      <address><email>henrikn@microsoft.com</email></address>
3506    </author>
3507    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3508      <organization abbrev="Adobe Systems">Adobe Systems, Incorporated</organization>
3509      <address><email>LMM@acm.org</email></address>
3510    </author>
3511    <author initials="P." surname="Leach" fullname="Paul J. Leach">
3512      <organization abbrev="Microsoft">Microsoft Corporation</organization>
3513      <address><email>paulle@microsoft.com</email></address>
3514    </author>
3515    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3516      <organization abbrev="W3C/MIT">World Wide Web Consortium</organization>
3517      <address><email>timbl@w3.org</email></address>
3518    </author>
3519    <author initials="Y." surname="Lafon" fullname="Yves Lafon" role="editor">
3520      <organization abbrev="W3C">World Wide Web Consortium</organization>
3521      <address><email>ylafon@w3.org</email></address>
3522    </author>
3523    <author initials="J. F." surname="Reschke" fullname="Julian F. Reschke" role="editor">
3524      <organization abbrev="greenbytes">greenbytes GmbH</organization>
3525      <address><email>julian.reschke@greenbytes.de</email></address>
3526    </author>
3527    <date month="August" year="2008"/>
3528  </front>
3529  <seriesInfo name="Internet-Draft" value="draft-ietf-httpbis-p6-cache-04"/>
3530 
3531</reference>
3532
3533<reference anchor="RFC822ABNF">
3534  <front>
3535    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3536    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3537      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3538      <address><email>DCrocker@UDel-Relay</email></address>
3539    </author>
3540    <date month="August" day="13" year="1982"/>
3541  </front>
3542  <seriesInfo name="STD" value="11"/>
3543  <seriesInfo name="RFC" value="822"/>
3544</reference>
3545
3546<reference anchor="RFC2045">
3547  <front>
3548    <title abbrev="Internet Message Bodies">Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</title>
3549    <author initials="N." surname="Freed" fullname="Ned Freed">
3550      <organization>Innosoft International, Inc.</organization>
3551      <address><email>ned@innosoft.com</email></address>
3552    </author>
3553    <author initials="N.S." surname="Borenstein" fullname="Nathaniel S. Borenstein">
3554      <organization>First Virtual Holdings</organization>
3555      <address><email>nsb@nsb.fv.com</email></address>
3556    </author>
3557    <date month="November" year="1996"/>
3558  </front>
3559  <seriesInfo name="RFC" value="2045"/>
3560</reference>
3561
3562<reference anchor="RFC2047">
3563  <front>
3564    <title abbrev="Message Header Extensions">MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text</title>
3565    <author initials="K." surname="Moore" fullname="Keith Moore">
3566      <organization>University of Tennessee</organization>
3567      <address><email>moore@cs.utk.edu</email></address>
3568    </author>
3569    <date month="November" year="1996"/>
3570  </front>
3571  <seriesInfo name="RFC" value="2047"/>
3572</reference>
3573
3574<reference anchor="RFC2119">
3575  <front>
3576    <title>Key words for use in RFCs to Indicate Requirement Levels</title>
3577    <author initials="S." surname="Bradner" fullname="Scott Bradner">
3578      <organization>Harvard University</organization>
3579      <address><email>sob@harvard.edu</email></address>
3580    </author>
3581    <date month="March" year="1997"/>
3582  </front>
3583  <seriesInfo name="BCP" value="14"/>
3584  <seriesInfo name="RFC" value="2119"/>
3585</reference>
3586
3587<reference anchor="RFC2396">
3588  <front>
3589    <title abbrev="URI Generic Syntax">Uniform Resource Identifiers (URI): Generic Syntax</title>
3590    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3591      <organization abbrev="MIT/LCS">World Wide Web Consortium</organization>
3592      <address><email>timbl@w3.org</email></address>
3593    </author>
3594    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3595      <organization abbrev="U.C. Irvine">Department of Information and Computer Science</organization>
3596      <address><email>fielding@ics.uci.edu</email></address>
3597    </author>
3598    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3599      <organization abbrev="Xerox Corporation">Xerox PARC</organization>
3600      <address><email>masinter@parc.xerox.com</email></address>
3601    </author>
3602    <date month="August" year="1998"/>
3603  </front>
3604  <seriesInfo name="RFC" value="2396"/>
3605</reference>
3606
3607<reference anchor="USASCII">
3608  <front>
3609    <title>Coded Character Set -- 7-bit American Standard Code for Information Interchange</title>
3610    <author>
3611      <organization>American National Standards Institute</organization>
3612    </author>
3613    <date year="1986"/>
3614  </front>
3615  <seriesInfo name="ANSI" value="X3.4"/>
3616</reference>
3617
3618</references>
3619
3620<references title="Informative References">
3621
3622<reference anchor="Nie1997" target="http://doi.acm.org/10.1145/263105.263157">
3623  <front>
3624    <title>Network Performance Effects of HTTP/1.1, CSS1, and PNG</title>
3625    <author initials="H.F.." surname="Nielsen" fullname="H.F. Nielsen">
3626      <organization/>
3627    </author>
3628    <author initials="J." surname="Gettys" fullname="J. Gettys">
3629      <organization/>
3630    </author>
3631    <author initials="E." surname="Prud'hommeaux" fullname="E. Prud'hommeaux">
3632      <organization/>
3633    </author>
3634    <author initials="H." surname="Lie" fullname="H. Lie">
3635      <organization/>
3636    </author>
3637    <author initials="C." surname="Lilley" fullname="C. Lilley">
3638      <organization/>
3639    </author>
3640    <date year="1997" month="September"/>
3641  </front>
3642  <seriesInfo name="ACM" value="Proceedings of the ACM SIGCOMM '97 conference on Applications, technologies, architectures, and protocols for computer communication SIGCOMM '97"/>
3643</reference>
3644
3645<reference anchor="Pad1995" target="http://portal.acm.org/citation.cfm?id=219094">
3646  <front>
3647    <title>Improving HTTP Latency</title>
3648    <author initials="V.N." surname="Padmanabhan" fullname="Venkata N. Padmanabhan">
3649      <organization/>
3650    </author>
3651    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3652      <organization/>
3653    </author>
3654    <date year="1995" month="December"/>
3655  </front>
3656  <seriesInfo name="Computer Networks and ISDN Systems" value="v. 28, pp. 25-35"/>
3657</reference>
3658
3659<reference anchor="RFC822">
3660  <front>
3661    <title abbrev="Standard for ARPA Internet Text Messages">Standard for the format of ARPA Internet text messages</title>
3662    <author initials="D.H." surname="Crocker" fullname="David H. Crocker">
3663      <organization>University of Delaware, Dept. of Electrical Engineering</organization>
3664      <address><email>DCrocker@UDel-Relay</email></address>
3665    </author>
3666    <date month="August" day="13" year="1982"/>
3667  </front>
3668  <seriesInfo name="STD" value="11"/>
3669  <seriesInfo name="RFC" value="822"/>
3670</reference>
3671
3672<reference anchor="RFC959">
3673  <front>
3674    <title abbrev="File Transfer Protocol">File Transfer Protocol</title>
3675    <author initials="J." surname="Postel" fullname="J. Postel">
3676      <organization>Information Sciences Institute (ISI)</organization>
3677    </author>
3678    <author initials="J." surname="Reynolds" fullname="J. Reynolds">
3679      <organization/>
3680    </author>
3681    <date month="October" year="1985"/>
3682  </front>
3683  <seriesInfo name="STD" value="9"/>
3684  <seriesInfo name="RFC" value="959"/>
3685</reference>
3686
3687<reference anchor="RFC1123">
3688  <front>
3689    <title>Requirements for Internet Hosts - Application and Support</title>
3690    <author initials="R." surname="Braden" fullname="Robert Braden">
3691      <organization>University of Southern California (USC), Information Sciences Institute</organization>
3692      <address><email>Braden@ISI.EDU</email></address>
3693    </author>
3694    <date month="October" year="1989"/>
3695  </front>
3696  <seriesInfo name="STD" value="3"/>
3697  <seriesInfo name="RFC" value="1123"/>
3698</reference>
3699
3700<reference anchor="RFC1305">
3701  <front>
3702    <title>Network Time Protocol (Version 3) Specification, Implementation</title>
3703    <author initials="D." surname="Mills" fullname="David L. Mills">
3704      <organization>University of Delaware, Electrical Engineering Department</organization>
3705      <address><email>mills@udel.edu</email></address>
3706    </author>
3707    <date month="March" year="1992"/>
3708  </front>
3709  <seriesInfo name="RFC" value="1305"/>
3710</reference>
3711
3712<reference anchor="RFC1436">
3713  <front>
3714    <title abbrev="Gopher">The Internet Gopher Protocol (a distributed document search and retrieval protocol)</title>
3715    <author initials="F." surname="Anklesaria" fullname="Farhad Anklesaria">
3716      <organization>University of Minnesota, Computer and Information Services</organization>
3717      <address><email>fxa@boombox.micro.umn.edu</email></address>
3718    </author>
3719    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3720      <organization>University of Minnesota, Computer and Information Services</organization>
3721      <address><email>mpm@boombox.micro.umn.edu</email></address>
3722    </author>
3723    <author initials="P." surname="Lindner" fullname="Paul Lindner">
3724      <organization>University of Minnesota, Computer and Information Services</organization>
3725      <address><email>lindner@boombox.micro.umn.edu</email></address>
3726    </author>
3727    <author initials="D." surname="Johnson" fullname="David Johnson">
3728      <organization>University of Minnesota, Computer and Information Services</organization>
3729      <address><email>dmj@boombox.micro.umn.edu</email></address>
3730    </author>
3731    <author initials="D." surname="Torrey" fullname="Daniel Torrey">
3732      <organization>University of Minnesota, Computer and Information Services</organization>
3733      <address><email>daniel@boombox.micro.umn.edu</email></address>
3734    </author>
3735    <author initials="B." surname="Alberti" fullname="Bob Alberti">
3736      <organization>University of Minnesota, Computer and Information Services</organization>
3737      <address><email>alberti@boombox.micro.umn.edu</email></address>
3738    </author>
3739    <date month="March" year="1993"/>
3740  </front>
3741  <seriesInfo name="RFC" value="1436"/>
3742</reference>
3743
3744<reference anchor="RFC1630">
3745  <front>
3746    <title abbrev="URIs in WWW">Universal Resource Identifiers in WWW: A Unifying Syntax for the Expression of Names and Addresses of Objects on the Network as used in the World-Wide Web</title>
3747    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3748      <organization>CERN, World-Wide Web project</organization>
3749      <address><email>timbl@info.cern.ch</email></address>
3750    </author>
3751    <date month="June" year="1994"/>
3752  </front>
3753  <seriesInfo name="RFC" value="1630"/>
3754</reference>
3755
3756<reference anchor="RFC1737">
3757  <front>
3758    <title abbrev="Requirements for Uniform Resource Names">Functional Requirements for Uniform Resource Names</title>
3759    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3760      <organization>Xerox Palo Alto Research Center</organization>
3761      <address><email>masinter@parc.xerox.com</email></address>
3762    </author>
3763    <author initials="K." surname="Sollins" fullname="Karen Sollins">
3764      <organization>MIT Laboratory for Computer Science</organization>
3765      <address><email>sollins@lcs.mit.edu</email></address>
3766    </author>
3767    <date month="December" year="1994"/>
3768  </front>
3769  <seriesInfo name="RFC" value="1737"/>
3770</reference>
3771
3772<reference anchor="RFC1738">
3773  <front>
3774    <title>Uniform Resource Locators (URL)</title>
3775    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3776      <organization>CERN, World-Wide Web project</organization>
3777      <address><email>timbl@info.cern.ch</email></address>
3778    </author>
3779    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3780      <organization>Xerox PARC</organization>
3781      <address><email>masinter@parc.xerox.com</email></address>
3782    </author>
3783    <author initials="M." surname="McCahill" fullname="Mark McCahill">
3784      <organization>University of Minnesota, Computer and Information Services</organization>
3785      <address><email>mpm@boombox.micro.umn.edu</email></address>
3786    </author>
3787    <date month="December" year="1994"/>
3788  </front>
3789  <seriesInfo name="RFC" value="1738"/>
3790</reference>
3791
3792<reference anchor="RFC1808">
3793  <front>
3794    <title>Relative Uniform Resource Locators</title>
3795    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3796      <organization>University of California Irvine, Department of Information and Computer Science</organization>
3797      <address><email>fielding@ics.uci.edu</email></address>
3798    </author>
3799    <date month="June" year="1995"/>
3800  </front>
3801  <seriesInfo name="RFC" value="1808"/>
3802</reference>
3803
3804<reference anchor="RFC1900">
3805  <front>
3806    <title>Renumbering Needs Work</title>
3807    <author initials="B." surname="Carpenter" fullname="Brian E. Carpenter">
3808      <organization>CERN, Computing and Networks Division</organization>
3809      <address><email>brian@dxcoms.cern.ch</email></address>
3810    </author>
3811    <author initials="Y." surname="Rekhter" fullname="Yakov Rekhter">
3812      <organization>cisco Systems</organization>
3813      <address><email>yakov@cisco.com</email></address>
3814    </author>
3815    <date month="February" year="1996"/>
3816  </front>
3817  <seriesInfo name="RFC" value="1900"/>
3818</reference>
3819
3820<reference anchor="RFC1945">
3821  <front>
3822    <title abbrev="HTTP/1.0">Hypertext Transfer Protocol -- HTTP/1.0</title>
3823    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3824      <organization>MIT, Laboratory for Computer Science</organization>
3825      <address><email>timbl@w3.org</email></address>
3826    </author>
3827    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3828      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3829      <address><email>fielding@ics.uci.edu</email></address>
3830    </author>
3831    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3832      <organization>W3 Consortium, MIT Laboratory for Computer Science</organization>
3833      <address><email>frystyk@w3.org</email></address>
3834    </author>
3835    <date month="May" year="1996"/>
3836  </front>
3837  <seriesInfo name="RFC" value="1945"/>
3838</reference>
3839
3840<reference anchor="RFC2068">
3841  <front>
3842    <title abbrev="HTTP/1.1">Hypertext Transfer Protocol -- HTTP/1.1</title>
3843    <author initials="R." surname="Fielding" fullname="Roy T. Fielding">
3844      <organization>University of California, Irvine, Department of Information and Computer Science</organization>
3845      <address><email>fielding@ics.uci.edu</email></address>
3846    </author>
3847    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3848      <organization>MIT Laboratory for Computer Science</organization>
3849      <address><email>jg@w3.org</email></address>
3850    </author>
3851    <author initials="J." surname="Mogul" fullname="Jeffrey C. Mogul">
3852      <organization>Digital Equipment Corporation, Western Research Laboratory</organization>
3853      <address><email>mogul@wrl.dec.com</email></address>
3854    </author>
3855    <author initials="H." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3856      <organization>MIT Laboratory for Computer Science</organization>
3857      <address><email>frystyk@w3.org</email></address>
3858    </author>
3859    <author initials="T." surname="Berners-Lee" fullname="Tim Berners-Lee">
3860      <organization>MIT Laboratory for Computer Science</organization>
3861      <address><email>timbl@w3.org</email></address>
3862    </author>
3863    <date month="January" year="1997"/>
3864  </front>
3865  <seriesInfo name="RFC" value="2068"/>
3866</reference>
3867
3868<reference anchor="RFC2109">
3869  <front>
3870    <title>HTTP State Management Mechanism</title>
3871    <author initials="D.M." surname="Kristol" fullname="David M. Kristol">
3872      <organization>Bell Laboratories, Lucent Technologies</organization>
3873      <address><email>dmk@bell-labs.com</email></address>
3874    </author>
3875    <author initials="L." surname="Montulli" fullname="Lou Montulli">
3876      <organization>Netscape Communications Corp.</organization>
3877      <address><email>montulli@netscape.com</email></address>
3878    </author>
3879    <date year="1997" month="February"/>
3880  </front>
3881  <seriesInfo name="RFC" value="2109"/>
3882</reference>
3883
3884<reference anchor="RFC2145">
3885  <front>
3886    <title abbrev="HTTP Version Numbers">Use and Interpretation of HTTP Version Numbers</title>
3887    <author initials="J.C." surname="Mogul" fullname="Jeffrey C. Mogul">
3888      <organization>Western Research Laboratory</organization>
3889      <address><email>mogul@wrl.dec.com</email></address>
3890    </author>
3891    <author initials="R.T." surname="Fielding" fullname="Roy T. Fielding">
3892      <organization>Department of Information and Computer Science</organization>
3893      <address><email>fielding@ics.uci.edu</email></address>
3894    </author>
3895    <author initials="J." surname="Gettys" fullname="Jim Gettys">
3896      <organization>MIT Laboratory for Computer Science</organization>
3897      <address><email>jg@w3.org</email></address>
3898    </author>
3899    <author initials="H.F." surname="Nielsen" fullname="Henrik Frystyk Nielsen">
3900      <organization>W3 Consortium</organization>
3901      <address><email>frystyk@w3.org</email></address>
3902    </author>
3903    <date month="May" year="1997"/>
3904  </front>
3905  <seriesInfo name="RFC" value="2145"/>
3906</reference>
3907
3908<reference anchor="RFC2324">
3909  <front>
3910    <title abbrev="HTCPCP/1.0">Hyper Text Coffee Pot Control Protocol (HTCPCP/1.0)</title>
3911    <author initials="L." surname="Masinter" fullname="Larry Masinter">
3912      <organization>Xerox Palo Alto Research Center</organization>
3913      <address><email>masinter@parc.xerox.com</email></address>
3914    </author>
3915    <date month="April" day="1" year="1998"/>
3916  </front>
3917  <seriesInfo name="RFC" value="2324"/>
3918</reference>
3919
3920<reference anchor="RFC2616">
3921  <front>
3922    <title>Hypertext Transfer Protocol -- HTTP/1.1</title>
3923    <author initials="R." surname="Fielding" fullname="R. Fielding">
3924      <organization>University of California, Irvine</organization>
3925      <address><email>fielding@ics.uci.edu</email></address>
3926    </author>
3927    <author initials="J." surname="Gettys" fullname="J. Gettys">
3928      <organization>W3C</organization>
3929      <address><email>jg@w3.org</email></address>
3930    </author>
3931    <author initials="J." surname="Mogul" fullname="J. Mogul">
3932      <organization>Compaq Computer Corporation</organization>
3933      <address><email>mogul@wrl.dec.com</email></address>
3934    </author>
3935    <author initials="H." surname="Frystyk" fullname="H. Frystyk">
3936      <organization>MIT Laboratory for Computer Science</organization>
3937      <address><email>frystyk@w3.org</email></address>
3938    </author>
3939    <author initials="L." surname="Masinter" fullname="L. Masinter">
3940      <organization>Xerox Corporation</organization>
3941      <address><email>masinter@parc.xerox.com</email></address>
3942    </author>
3943    <author initials="P." surname="Leach" fullname="P. Leach">
3944      <organization>Microsoft Corporation</organization>
3945      <address><email>paulle@microsoft.com</email></address>
3946    </author>
3947    <author initials="T." surname="Berners-Lee" fullname="T. Berners-Lee">
3948      <organization>W3C</organization>
3949      <address><email>timbl@w3.org</email></address>
3950    </author>
3951    <date month="June" year="1999"/>
3952  </front>
3953  <seriesInfo name="RFC" value="2616"/>
3954</reference>
3955
3956<reference anchor="RFC2818">
3957  <front>
3958    <title>HTTP Over TLS</title>
3959    <author initials="E." surname="Rescorla" fullname="Eric Rescorla">
3960      <organization>RTFM, Inc.</organization>
3961      <address><email>ekr@rtfm.com</email></address>
3962    </author>
3963    <date year="2000" month="May"/>
3964  </front>
3965  <seriesInfo name="RFC" value="2818"/>
3966</reference>
3967
3968<reference anchor="RFC2821">
3969  <front>
3970    <title>Simple Mail Transfer Protocol</title>
3971    <author initials="J." surname="Klensin" fullname="J. Klensin">
3972      <organization>AT&amp;T Laboratories</organization>
3973      <address><email>klensin@research.att.com</email></address>
3974    </author>
3975    <date year="2001" month="April"/>
3976  </front>
3977  <seriesInfo name="RFC" value="2821"/>
3978</reference>
3979
3980<reference anchor="RFC2822">
3981  <front>
3982    <title>Internet Message Format</title>
3983    <author initials="P." surname="Resnick" fullname="P. Resnick">
3984      <organization>QUALCOMM Incorporated</organization>
3985    </author>
3986    <date year="2001" month="April"/>
3987  </front> 
3988  <seriesInfo name="RFC" value="2822"/>
3989</reference>
3990
3991<reference anchor="RFC2965">
3992  <front>
3993    <title>HTTP State Management Mechanism</title>
3994    <author initials="D. M." surname="Kristol" fullname="David M. Kristol">
3995      <organization>Bell Laboratories, Lucent Technologies</organization>
3996      <address><email>dmk@bell-labs.com</email></address>
3997    </author>
3998    <author initials="L." surname="Montulli" fullname="Lou Montulli">
3999      <organization>Epinions.com, Inc.</organization>
4000      <address><email>lou@montulli.org</email></address>
4001    </author>
4002    <date year="2000" month="October"/>
4003  </front>
4004  <seriesInfo name="RFC" value="2965"/>
4005</reference>
4006
4007<reference anchor="RFC3864">
4008  <front>
4009    <title>Registration Procedures for Message Header Fields</title>
4010    <author initials="G." surname="Klyne" fullname="G. Klyne">
4011      <organization>Nine by Nine</organization>
4012      <address><email>GK-IETF@ninebynine.org</email></address>
4013    </author>
4014    <author initials="M." surname="Nottingham" fullname="M. Nottingham">
4015      <organization>BEA Systems</organization>
4016      <address><email>mnot@pobox.com</email></address>
4017    </author>
4018    <author initials="J." surname="Mogul" fullname="J. Mogul">
4019      <organization>HP Labs</organization>
4020      <address><email>JeffMogul@acm.org</email></address>
4021    </author>
4022    <date year="2004" month="September"/>
4023  </front>
4024  <seriesInfo name="BCP" value="90"/>
4025  <seriesInfo name="RFC" value="3864"/>
4026</reference>
4027
4028<reference anchor="RFC3977">
4029  <front>
4030    <title>Network News Transfer Protocol (NNTP)</title>
4031    <author initials="C." surname="Feather" fullname="C. Feather">
4032      <organization>THUS plc</organization>
4033      <address><email>clive@demon.net</email></address>
4034    </author>
4035    <date year="2006" month="October"/>
4036  </front>
4037  <seriesInfo name="RFC" value="3977"/>
4038</reference>
4039
4040<reference anchor="RFC4288">
4041  <front>
4042    <title>Media Type Specifications and Registration Procedures</title>
4043    <author initials="N." surname="Freed" fullname="N. Freed">
4044      <organization>Sun Microsystems</organization>
4045      <address>
4046        <email>ned.freed@mrochek.com</email>
4047      </address>
4048    </author>
4049    <author initials="J." surname="Klensin" fullname="J. Klensin">
4050      <organization/>
4051      <address>
4052        <email>klensin+ietf@jck.com</email>
4053      </address>
4054    </author>
4055    <date year="2005" month="December"/>
4056  </front>
4057  <seriesInfo name="BCP" value="13"/>
4058  <seriesInfo name="RFC" value="4288"/>
4059</reference>
4060
4061<reference anchor="RFC4395">
4062  <front>
4063    <title>Guidelines and Registration Procedures for New URI Schemes</title>
4064    <author initials="T." surname="Hansen" fullname="T. Hansen">
4065      <organization>AT&amp;T Laboratories</organization>
4066      <address>
4067        <email>tony+urireg@maillennium.att.com</email>
4068      </address>
4069    </author>
4070    <author initials="T." surname="Hardie" fullname="T. Hardie">
4071      <organization>Qualcomm, Inc.</organization>
4072      <address>
4073        <email>hardie@qualcomm.com</email>
4074      </address>
4075    </author>
4076    <author initials="L." surname="Masinter" fullname="L. Masinter">
4077      <organization>Adobe Systems</organization>
4078      <address>
4079        <email>LMM@acm.org</email>
4080      </address>
4081    </author>
4082    <date year="2006" month="February"/>
4083  </front>
4084  <seriesInfo name="BCP" value="115"/>
4085  <seriesInfo name="RFC" value="4395"/>
4086</reference>
4087
4088<reference anchor="Kri2001" target="http://arxiv.org/abs/cs.SE/0105018">
4089  <front>
4090    <title>HTTP Cookies: Standards, Privacy, and Politics</title>
4091    <author initials="D." surname="Kristol" fullname="David M. Kristol">
4092      <organization/>
4093    </author>
4094    <date year="2001" month="November"/>
4095  </front>
4096  <seriesInfo name="ACM Transactions on Internet Technology" value="Vol. 1, #2"/>
4097</reference>
4098
4099<reference anchor="Spe" target="http://sunsite.unc.edu/mdma-release/http-prob.html">
4100  <front>
4101  <title>Analysis of HTTP Performance Problems</title>
4102  <author initials="S." surname="Spero" fullname="Simon E. Spero">
4103    <organization/>
4104  </author>
4105  <date/>
4106  </front>
4107</reference>
4108
4109<reference anchor="Tou1998" target="http://www.isi.edu/touch/pubs/http-perf96/">
4110  <front>
4111  <title>Analysis of HTTP Performance</title>
4112  <author initials="J." surname="Touch" fullname="Joe Touch">
4113    <organization>USC/Information Sciences Institute</organization>
4114    <address><email>touch@isi.edu</email></address>
4115  </author>
4116  <author initials="J." surname="Heidemann" fullname="John Heidemann">
4117    <organization>USC/Information Sciences Institute</organization>
4118    <address><email>johnh@isi.edu</email></address>
4119  </author>
4120  <author initials="K." surname="Obraczka" fullname="Katia Obraczka">
4121    <organization>USC/Information Sciences Institute</organization>
4122    <address><email>katia@isi.edu</email></address>
4123  </author>
4124  <date year="1998" month="Aug"/>
4125  </front>
4126  <seriesInfo name="ISI Research Report" value="ISI/RR-98-463"/>
4127  <annotation>(original report dated Aug. 1996)</annotation>
4128</reference>
4129
4130<reference anchor="WAIS">
4131  <front>
4132    <title>WAIS Interface Protocol Prototype Functional Specification (v1.5)</title>
4133    <author initials="F." surname="Davis" fullname="F. Davis">
4134      <organization>Thinking Machines Corporation</organization>
4135    </author>
4136    <author initials="B." surname="Kahle" fullname="B. Kahle">
4137      <organization>Thinking Machines Corporation</organization>
4138    </author>
4139    <author initials="H." surname="Morris" fullname="H. Morris">
4140      <organization>Thinking Machines Corporation</organization>
4141    </author>
4142    <author initials="J." surname="Salem" fullname="J. Salem">
4143      <organization>Thinking Machines Corporation</organization>
4144    </author>
4145    <author initials="T." surname="Shen" fullname="T. Shen">
4146      <organization>Thinking Machines Corporation</organization>
4147    </author>
4148    <author initials="R." surname="Wang" fullname="R. Wang">
4149      <organization>Thinking Machines Corporation</organization>
4150    </author>
4151    <author initials="J." surname="Sui" fullname="J. Sui">
4152      <organization>Thinking Machines Corporation</organization>
4153    </author>
4154    <author initials="M." surname="Grinbaum" fullname="M. Grinbaum">
4155      <organization>Thinking Machines Corporation</organization>
4156    </author>
4157    <date month="April" year="1990"/>
4158  </front>
4159  <seriesInfo name="Thinking Machines Corporation" value=""/>
4160</reference>
4161
4162</references>
4163
4164
4165<section title="Tolerant Applications" anchor="tolerant.applications">
4166<t>
4167   Although this document specifies the requirements for the generation
4168   of HTTP/1.1 messages, not all applications will be correct in their
4169   implementation. We therefore recommend that operational applications
4170   be tolerant of deviations whenever those deviations can be
4171   interpreted unambiguously.
4172</t>
4173<t>
4174   Clients SHOULD be tolerant in parsing the Status-Line and servers
4175   tolerant when parsing the Request-Line. In particular, they SHOULD
4176   accept any amount of SP or HTAB characters between fields, even though
4177   only a single SP is required.
4178</t>
4179<t>
4180   The line terminator for message-header fields is the sequence CRLF.
4181   However, we recommend that applications, when parsing such headers,
4182   recognize a single LF as a line terminator and ignore the leading CR.
4183</t>
4184<t>
4185   The character set of an entity-body SHOULD be labeled as the lowest
4186   common denominator of the character codes used within that body, with
4187   the exception that not labeling the entity is preferred over labeling
4188   the entity with the labels US-ASCII or ISO-8859-1. See <xref target="Part3"/>.
4189</t>
4190<t>
4191   Additional rules for requirements on parsing and encoding of dates
4192   and other potential problems with date encodings include:
4193</t>
4194<t>
4195  <list style="symbols">
4196     <t>HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
4197        which appears to be more than 50 years in the future is in fact
4198        in the past (this helps solve the "year 2000" problem).</t>
4199
4200     <t>An HTTP/1.1 implementation MAY internally represent a parsed
4201        Expires date as earlier than the proper value, but MUST NOT
4202        internally represent a parsed Expires date as later than the
4203        proper value.</t>
4204
4205     <t>All expiration-related calculations MUST be done in GMT. The
4206        local time zone MUST NOT influence the calculation or comparison
4207        of an age or expiration time.</t>
4208
4209     <t>If an HTTP header incorrectly carries a date value with a time
4210        zone other than GMT, it MUST be converted into GMT using the
4211        most conservative possible conversion.</t>
4212  </list>
4213</t>
4214</section>
4215
4216<section title="Conversion of Date Formats" anchor="conversion.of.date.formats">
4217<t>
4218   HTTP/1.1 uses a restricted set of date formats (<xref target="full.date"/>) to
4219   simplify the process of date comparison. Proxies and gateways from
4220   other protocols SHOULD ensure that any Date header field present in a
4221   message conforms to one of the HTTP/1.1 formats and rewrite the date
4222   if necessary.
4223</t>
4224</section>
4225
4226<section title="Compatibility with Previous Versions" anchor="compatibility">
4227<t>
4228   It is beyond the scope of a protocol specification to mandate
4229   compliance with previous versions. HTTP/1.1 was deliberately
4230   designed, however, to make supporting previous versions easy. It is
4231   worth noting that, at the time of composing this specification
4232   (1996), we would expect commercial HTTP/1.1 servers to:
4233  <list style="symbols">
4234     <t>recognize the format of the Request-Line for HTTP/0.9, 1.0, and
4235        1.1 requests;</t>
4236
4237     <t>understand any valid request in the format of HTTP/0.9, 1.0, or
4238        1.1;</t>
4239
4240     <t>respond appropriately with a message in the same major version
4241        used by the client.</t>
4242  </list>
4243</t>
4244<t>
4245   And we would expect HTTP/1.1 clients to:
4246  <list style="symbols">
4247     <t>recognize the format of the Status-Line for HTTP/1.0 and 1.1
4248        responses;</t>
4249
4250     <t>understand any valid response in the format of HTTP/0.9, 1.0, or
4251        1.1.</t>
4252  </list>
4253</t>
4254<t>
4255   For most implementations of HTTP/1.0, each connection is established
4256   by the client prior to the request and closed by the server after
4257   sending the response. Some implementations implement the Keep-Alive
4258   version of persistent connections described in Section 19.7.1 of <xref target="RFC2068"/>.
4259</t>
4260
4261<section title="Changes from HTTP/1.0" anchor="changes.from.1.0">
4262<t>
4263   This section summarizes major differences between versions HTTP/1.0
4264   and HTTP/1.1.
4265</t>
4266
4267<section title="Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses" anchor="changes.to.simplify.multi-homed.web.servers.and.conserve.ip.addresses">
4268<t>
4269   The requirements that clients and servers support the Host request-header,
4270   report an error if the Host request-header (<xref target="header.host"/>) is
4271   missing from an HTTP/1.1 request, and accept absolute URIs (<xref target="request-uri"/>)
4272   are among the most important changes defined by this
4273   specification.
4274</t>
4275<t>
4276   Older HTTP/1.0 clients assumed a one-to-one relationship of IP
4277   addresses and servers; there was no other established mechanism for
4278   distinguishing the intended server of a request than the IP address
4279   to which that request was directed. The changes outlined above will
4280   allow the Internet, once older HTTP clients are no longer common, to
4281   support multiple Web sites from a single IP address, greatly
4282   simplifying large operational Web servers, where allocation of many
4283   IP addresses to a single host has created serious problems. The
4284   Internet will also be able to recover the IP addresses that have been
4285   allocated for the sole purpose of allowing special-purpose domain
4286   names to be used in root-level HTTP URLs. Given the rate of growth of
4287   the Web, and the number of servers already deployed, it is extremely
4288   important that all implementations of HTTP (including updates to
4289   existing HTTP/1.0 applications) correctly implement these
4290   requirements:
4291  <list style="symbols">
4292     <t>Both clients and servers MUST support the Host request-header.</t>
4293
4294     <t>A client that sends an HTTP/1.1 request MUST send a Host header.</t>
4295
4296     <t>Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
4297        request does not include a Host request-header.</t>
4298
4299     <t>Servers MUST accept absolute URIs.</t>
4300  </list>
4301</t>
4302</section>
4303</section>
4304
4305<section title="Compatibility with HTTP/1.0 Persistent Connections" anchor="compatibility.with.http.1.0.persistent.connections">
4306<t>
4307   Some clients and servers might wish to be compatible with some
4308   previous implementations of persistent connections in HTTP/1.0
4309   clients and servers. Persistent connections in HTTP/1.0 are
4310   explicitly negotiated as they are not the default behavior. HTTP/1.0
4311   experimental implementations of persistent connections are faulty,
4312   and the new facilities in HTTP/1.1 are designed to rectify these
4313   problems. The problem was that some existing 1.0 clients may be
4314   sending Keep-Alive to a proxy server that doesn't understand
4315   Connection, which would then erroneously forward it to the next
4316   inbound server, which would establish the Keep-Alive connection and
4317   result in a hung HTTP/1.0 proxy waiting for the close on the
4318   response. The result is that HTTP/1.0 clients must be prevented from
4319   using Keep-Alive when talking to proxies.
4320</t>
4321<t>
4322   However, talking to proxies is the most important use of persistent
4323   connections, so that prohibition is clearly unacceptable. Therefore,
4324   we need some other mechanism for indicating a persistent connection
4325   is desired, which is safe to use even when talking to an old proxy
4326   that ignores Connection. Persistent connections are the default for
4327   HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
4328   declaring non-persistence. See <xref target="header.connection"/>.
4329</t>
4330<t>
4331   The original HTTP/1.0 form of persistent connections (the Connection:
4332   Keep-Alive and Keep-Alive header) is documented in <xref target="RFC2068"/>.
4333</t>
4334</section>
4335
4336<section title="Changes from RFC 2068" anchor="changes.from.rfc.2068">
4337<t>
4338   This specification has been carefully audited to correct and
4339   disambiguate key word usage; RFC 2068 had many problems in respect to
4340   the conventions laid out in <xref target="RFC2119"/>.
4341</t>
4342<t>
4343   Transfer-coding and message lengths all interact in ways that
4344   required fixing exactly when chunked encoding is used (to allow for
4345   transfer encoding that may not be self delimiting); it was important
4346   to straighten out exactly how message lengths are computed. (Sections
4347   <xref target="transfer.codings" format="counter"/>, <xref target="message.length" format="counter"/>,
4348   <xref target="header.content-length" format="counter"/>,
4349   see also <xref target="Part3"/>, <xref target="Part5"/> and <xref target="Part6"/>)
4350</t>
4351<t>
4352   The use and interpretation of HTTP version numbers has been clarified
4353   by <xref target="RFC2145"/>. Require proxies to upgrade requests to highest protocol
4354   version they support to deal with problems discovered in HTTP/1.0
4355   implementations (<xref target="http.version"/>)
4356</t>
4357<t>
4358   Transfer-coding had significant problems, particularly with
4359   interactions with chunked encoding. The solution is that transfer-codings
4360   become as full fledged as content-codings. This involves
4361   adding an IANA registry for transfer-codings (separate from content
4362   codings), a new header field (TE) and enabling trailer headers in the
4363   future. Transfer encoding is a major performance benefit, so it was
4364   worth fixing <xref target="Nie1997"/>. TE also solves another, obscure, downward
4365   interoperability problem that could have occurred due to interactions
4366   between authentication trailers, chunked encoding and HTTP/1.0
4367   clients.(Section <xref target="transfer.codings" format="counter"/>, <xref target="chunked.transfer.encoding" format="counter"/>,
4368   and <xref target="header.te" format="counter"/>)
4369</t>
4370</section>
4371
4372<section title="Changes from RFC 2616" anchor="changes.from.rfc.2616">
4373<t>
4374  The CHAR rule does not allow the NUL character anymore (this affects
4375  the comment and quoted-string rules).  Furthermore, the quoted-pair
4376  rule does not allow escaping NUL, CR or LF anymore.
4377  (<xref target="basic.rules"/>)
4378</t>
4379<t>
4380  Clarify that HTTP-Version is case sensitive.
4381  (<xref target="http.version"/>)
4382</t>
4383<t>
4384  Remove reference to non-existant identity transfer-coding value tokens.
4385  (Sections <xref format="counter" target="transfer.codings"/> and
4386  <xref format="counter" target="message.length"/>)
4387</t>
4388<t>
4389  Clarification that the chunk length does not include
4390  the count of the octets in the chunk header and trailer.
4391  (<xref target="chunked.transfer.encoding"/>)
4392</t>
4393<t>
4394  Fix BNF to add query, as the abs_path production in
4395  Section 3 of <xref target="RFC2396"/> doesn't define it.
4396  (<xref target="request-uri"/>)
4397</t>
4398<t>
4399  Clarify exactly when close connection options must be sent.
4400  (<xref target="header.connection"/>)
4401</t>
4402</section>
4403</section>
4404
4405<section title="Change Log (to be removed by RFC Editor before publication)" anchor="change.log">
4406
4407<section title="Since RFC2616">
4408<t>
4409  Extracted relevant partitions from <xref target="RFC2616"/>.
4410</t>
4411</section>
4412
4413<section title="Since draft-ietf-httpbis-p1-messaging-00">
4414<t>
4415  Closed issues:
4416  <list style="symbols"> 
4417    <t>
4418      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/1"/>:
4419      "HTTP Version should be case sensitive"
4420      (<eref target="http://purl.org/NET/http-errata#verscase"/>)
4421    </t>
4422    <t>
4423      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/2"/>:
4424      "'unsafe' characters"
4425      (<eref target="http://purl.org/NET/http-errata#unsafe-uri"/>)
4426    </t>
4427    <t>
4428      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/3"/>:
4429      "Chunk Size Definition"
4430      (<eref target="http://purl.org/NET/http-errata#chunk-size"/>)
4431    </t>
4432    <t>
4433      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/4"/>:
4434      "Message Length"
4435      (<eref target="http://purl.org/NET/http-errata#msg-len-chars"/>)
4436    </t>
4437    <t>
4438      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/8"/>:
4439      "Media Type Registrations"
4440      (<eref target="http://purl.org/NET/http-errata#media-reg"/>)
4441    </t>
4442    <t>
4443      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/11"/>:
4444      "URI includes query"
4445      (<eref target="http://purl.org/NET/http-errata#uriquery"/>)
4446    </t>
4447    <t>
4448      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/15"/>:
4449      "No close on 1xx responses"
4450      (<eref target="http://purl.org/NET/http-errata#noclose1xx"/>)
4451    </t>
4452    <t>
4453      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/16"/>:
4454      "Remove 'identity' token references"
4455      (<eref target="http://purl.org/NET/http-errata#identity"/>)
4456    </t>
4457    <t>
4458      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/26"/>:
4459      "Import query BNF"
4460    </t>
4461    <t>
4462      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/31"/>:
4463      "qdtext BNF"
4464    </t>
4465    <t>
4466      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/35"/>:
4467      "Normative and Informative references"
4468    </t>
4469    <t>
4470      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/42"/>:
4471      "RFC2606 Compliance"
4472    </t>
4473    <t>
4474      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/45"/>:
4475      "RFC977 reference"
4476    </t>
4477    <t>
4478      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/46"/>:
4479      "RFC1700 references"
4480    </t>
4481    <t>
4482      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/47"/>:
4483      "inconsistency in date format explanation"
4484    </t>
4485    <t>
4486      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/48"/>:
4487      "Date reference typo"
4488    </t>
4489    <t>
4490      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/65"/>:
4491      "Informative references"
4492    </t>
4493    <t>
4494      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/66"/>:
4495      "ISO-8859-1 Reference"
4496    </t>
4497    <t>
4498      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/86"/>:
4499      "Normative up-to-date references"
4500    </t>
4501  </list>
4502</t>
4503<t>
4504  Other changes:
4505  <list style="symbols"> 
4506    <t>
4507      Update media type registrations to use RFC4288 template.
4508    </t>
4509    <t>
4510      Use names of RFC4234 core rules DQUOTE and HTAB,
4511      fix broken ABNF for chunk-data
4512      (work in progress on <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>)
4513    </t>
4514  </list>
4515</t>
4516</section>
4517
4518<section title="Since draft-ietf-httpbis-p1-messaging-01">
4519<t>
4520  Closed issues:
4521  <list style="symbols"> 
4522    <t>
4523      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/19"/>:
4524      "Bodies on GET (and other) requests"
4525    </t>
4526    <t>
4527      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/55"/>:
4528      "Updating to RFC4288"
4529    </t>
4530    <t>
4531      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/57"/>:
4532      "Status Code and Reason Phrase"
4533    </t>
4534    <t>
4535      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/82"/>:
4536      "rel_path not used"
4537    </t>
4538  </list>
4539</t>
4540<t>
4541  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4542  <list style="symbols"> 
4543    <t>
4544      Get rid of duplicate BNF rule names ("host" -&gt; "uri-host", "trailer" -&gt;
4545      "trailer-part").
4546    </t>
4547    <t>
4548      Avoid underscore character in rule names ("http_URL" -&gt;
4549      "http-URL", "abs_path" -&gt; "path-absolute").
4550    </t>
4551    <t>
4552      Add rules for terms imported from URI spec ("absoluteURI", "authority",
4553      "path-absolute", "port", "query", "relativeURI", "host) -- these will
4554      have to be updated when switching over to RFC3986.
4555    </t>
4556    <t>
4557      Synchronize core rules with RFC5234 (this includes a change to CHAR
4558      which now excludes NUL).
4559    </t>
4560    <t>
4561      Get rid of prose rules that span multiple lines.
4562    </t>
4563    <t>
4564      Get rid of unused rules LOALPHA and UPALPHA.
4565    </t>
4566    <t>
4567      Move "Product Tokens" section (back) into Part 1, as "token" is used
4568      in the definition of the Upgrade header.
4569    </t>
4570    <t>
4571      Add explicit references to BNF syntax and rules imported from other parts of the specification.
4572    </t>
4573    <t>
4574      Rewrite prose rule "token" in terms of "tchar", rewrite prose rule "TEXT".
4575    </t>
4576  </list>
4577</t>
4578</section>
4579
4580<section title="Since draft-ietf-httpbis-p1-messaging-02" anchor="changes.since.02">
4581<t>
4582  Closed issues:
4583  <list style="symbols"> 
4584    <t>
4585      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/51"/>:
4586      "HTTP-date vs. rfc1123-date"
4587    </t>
4588    <t>
4589      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/64"/>:
4590      "WS in quoted-pair"
4591    </t>
4592  </list>
4593</t>
4594<t>
4595  Ongoing work on IANA Message Header Registration (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/40"/>):
4596  <list style="symbols"> 
4597    <t>
4598      Reference RFC 3984, and update header registrations for headers defined
4599      in this document.
4600    </t>
4601  </list>
4602</t>
4603<t>
4604  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4605  <list style="symbols"> 
4606    <t>
4607      Replace string literals when the string really is case-sensitive (HTTP-Version).
4608    </t>
4609  </list>
4610</t>
4611</section>
4612
4613<section title="Since draft-ietf-httpbis-p1-messaging-03" anchor="changes.since.03">
4614<t>
4615  Closed issues:
4616  <list style="symbols"> 
4617    <t>
4618      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/28"/>:
4619      "Connection closing"
4620    </t>
4621    <t>
4622      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/97"/>:
4623      "Move registrations and registry information to IANA Considerations"
4624    </t>
4625    <t>
4626      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/120"/>:
4627      "need new URL for PAD1995 reference"
4628    </t>
4629    <t>
4630      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/127"/>:
4631      "IANA Considerations: update HTTP URI scheme registration"
4632    </t>
4633    <t>
4634      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/128"/>:
4635      "Cite HTTPS URI scheme definition"
4636    </t>
4637    <t>
4638      <eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/129"/>:
4639      "List-type headers vs Set-Cookie"
4640    </t>
4641  </list>
4642</t>
4643<t>
4644  Ongoing work on ABNF conversion (<eref target="http://www3.tools.ietf.org/wg/httpbis/trac/ticket/36"/>):
4645  <list style="symbols"> 
4646    <t>
4647      Replace string literals when the string really is case-sensitive (HTTP-Date).
4648    </t>
4649    <t>
4650      Replace HEX by HEXDIG for future consistence with RFC 5234's core rules.
4651    </t>
4652  </list>
4653</t>
4654</section>
4655
4656</section>
4657
4658</back>
4659</rfc>
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